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Dieseldistributor fuel-injection pumps

Diesel-engine management

Technical Instruction

Published by:

© Robert Bosch GmbH, 1999Postfach 3002 20,D-70442 Stuttgart.Automotive Equipment Business Sector,Department for Automotive Services,Technical Publications (KH/PDI2).

Editor-in-Chief:Dipl.-Ing. (FH) Horst Bauer.

Editors:Dipl.-Ing. Karl-Heinz Dietsche,Dipl.-Ing. (BA) Jürgen Crepin,Dipl.-Holzw. Folkhart Dinkler,Dipl.-Ing. (FH) Anton Beer.

Author:Dr.-Ing. Helmut Tschöke, assisted by theresponsible technical departments of Robert Bosch GmbH.

Presentation:Dipl.-Ing. (FH) Ulrich Adler,Berthold Gauder, Leinfelden-Echterdingen.

Translation:Peter Girling.

Photographs:Audi AG, Ingolstadt andVolkswagen AG, Wolfsburg.

Technical graphics:Bauer & Partner, Stuttgart.

Unless otherwise specified, the above persons areemployees of Robert Bosch GmbH, Stuttgart.

Reproduction, copying, or translation of thispublication, wholly or in part, only with our previous written permission and with source credit.Illustrations, descriptions, schematic drawings, andother particulars only serve to explain and illustratethe text. They are not to be used as the basis fordesign, installation, or delivery conditions. Weassume no responsibility for agreement of thecontents with local laws and regulations.Robert Bosch GmbH is exempt from liability,and reserves the right to makechanges at any time.

Printed in Germany.Imprimé en Allemagne.

4th Edition, April 1999.English translation of the German edition dated:November 1998.

Combustion in the diesel engineThe diesel engine 2

Diesel fuel-injection systems: An overviewFields of application 4Technical requirements 4Injection-pump designs 6

Mechanically-controlled (governed)axial-piston distributor fuel-injectionpumps VEFuel-injection systems 8Fuel-injection techniques 9Fuel supply and delivery 12Mechanical engine-speed control (governing) 22Injection timing 29Add-on modules and shutoff devices 32Testing and calibration 45Nozzles and nozzle holders 46

Electronically-controlled axial-piston distributor fuel-injectionpumps VE-EDC 54

Solenoid-valve-controlled axial-piston distributor fuel-injectionpumps VE-MV 60

Start-assist systems 62

Dieseldistributor fuel-injection pumps VE

The reasons behind the diesel-poweredvehicle’s continuing success can bereduced to one common denominator:Diesels use considerably less fuel thantheir gasoline-powered counterparts.And in the meantime the diesel haspractically caught up with the gasolineengine when it comes to starting andrunning refinement. Regarding exhaust-gas emissions, the diesel engine is justas good as a gasoline engine withcatalytic converter. In some cases, it iseven better. The diesel engine’s emis-sions of CO2, which is responsible forthe “green-house effect”, are also lowerthan for the gasoline engine, althoughthis is a direct result of the dieselengine’s better fuel economy. It was also possible during the past few yearsto considerably lower the particulateemissions which are typical for thediesel engine. The popularity of the high-speed dieselengine in the passenger car though,would have been impossible without the diesel fuel-injection systems fromBosch. The very high level of precisioninherent in the distributor pump meansthat it is possible to precisely meterextremely small injection quantities tothe engine. And thanks to the specialgovernor installed with the VE-pump inpassenger-car applications, the engineresponds immediately to even the finestchange in accelerator-pedal setting. Allpoints which contribute to the sophisti-cated handling qualities of a modern-day automobile.The Electronic Diesel Control (EDC)also plays a decisive role in the overallimprovement of the diesel-enginedpassenger car.The following pages will deal with thedesign and construction of the VE distri-butor pump, and how it adapts injectedfuel quantity, start-of-injection, andduration of injection to the differentengine operating conditions.

The diesel engine

Diesel combustion principleThe diesel engine is a compression-ignition (CI) engine which draws in air and compresses it to a very high level.With its overall efficiency figure, the dieselengine rates as the most efficient com-bustion engine (CE). Large, slow-runningmodels can have efficiency figures of asmuch as 50% or even more. The resulting low fuel consumption,coupled with the low level of pollutants inthe exhaust gas, all serve to underlinethe diesel engine’s significance. The diesel engine can utilise either the 4- or 2-stroke principle. In automotiveapplications though, diesels are practi-cally always of the 4-stroke type (Figs. 1and 2).

Working cycle (4-stroke)In the case of 4-stroke diesel engines,gas-exchange valves are used to controlthe gas exchange process by openingand closing the inlet and exhaust ports.

Induction strokeDuring the first stroke, the downwardmovement of the piston draws in un-throttled air through the open intake valve.

Compression strokeDuring the second stroke, the so-calledcompression stroke, the air trapped in thecylinder is compressed by the pistonwhich is now moving upwards. Com-pression ratios are between 14:1 and24:1. In the process, the air heats up totemperatures around 900°C. At the endof the compression stroke the nozzle in-jects fuel into the heated air at pressuresof up to 2,000 bar.

Power strokeFollowing the ignition delay, at the begin-ning of the third stroke the finely atom-ized fuel ignites as a result of auto-igni-tion and burns almost completely. Thecylinder charge heats up even furtherand the cylinder pressure increasesagain. The energy released by the igni-tion is applied to the piston.The piston is forced downwards and thecombustion energy is transformed intomechanical energy.

Exhaust strokeIn the fourth stroke, the piston moves upagain and drives out the burnt gasesthrough the open exhaust valve. A fresh charge of air is then drawn inagain and the working cycle repeated.

Combustion chambers,turbocharging and superchargingBoth divided and undivided combustionchambers are used in diesel engines

Combustion in the diesel

engine

2

Combustion in the dieselengine

Principle of the reciprocating piston engine

TDC Top Dead Center, BDC Bottom Dead Center.Vh Stroke volume, VC Compression volume,s Piston stroke.

Fig. 1

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(prechamber engines and direct-injec-tion engines respectively).

Direct-injection (DI) engines are more ef-ficient and more economical than theirprechamber counterparts. For this rea-son, DI engines are used in all commer-cial-vehicles and trucks. On the otherhand, due to their lower noise level,prechamber engines are fitted in passen-ger cars where comfort plays a more im-portant role than it does in the commer-cial-vehicle sector. In addition, theprechamber diesel engine features con-siderably lower toxic emissions (HC andNOX), and is less costly to produce thanthe DI engine. The fact though that theprechamber engine uses slightly morefuel than the DI engine (10...15%) isleading to the DI engine coming moreand more to the forefront. Compared tothe gasoline engine, both diesel versionsare more economical especially in thepart-load range.

Diesel engines are particularly suitablefor use with exhaust-gas turbochargersor mechanical superchargers. Using anexhaust-gas turbocharger with the dieselengine increases not only the poweryield, and with it the efficiency, but alsoreduces the combustion noise and thetoxic content of the exhaust gas.

Diesel-engine exhaustemissionsA variety of different combustion depositsare formed when diesel fuel is burnt.These reaction products are dependentupon engine design, engine power out-put, and working load.The complete combustion of the fuelleads to major reductions in the forma-tion of toxic substances. Complete com-bustion is supported by the carefulmatching of the air-fuel mixture, abso-lute precision in the injection process,and optimum air-fuel mixture turbulence.In the first place, water (H2O) and carbondioxide (CO2) are generated. And in rela-tively low concentrations, the followingsubstances are also produced:

– Carbon monoxide (CO),– Unburnt hydrocarbons (HC),– Nitrogen oxides (NOX),– Sulphur dioxide (SO2) and sulphuric

acid (H2SO4), as well as– Soot particles.

When the engine is cold, the exhaust-gasconstituents which are immediatelynoticeable are the non-oxidized or onlypartly oxidized hydrocarbons which aredirectly visible in the form of white or bluesmoke, and the strongly smelling alde-hydes.

The dieselengine

3

4-stroke diesel engine

1 Induction stroke, 2 Compression stroke, 3 Power stroke, 4 Exhaust stroke.

1 2 3 4

Fig. 2

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Fields of applicationDiesel engines are characterized by theirhigh levels of economic efficiency. This isof particular importance in commercialapplications. Diesel engines are em-ployed in a wide range of different ver-sions (Fig. 1 and Table 1), for example as: – The drive for mobile electric generators

(up to approx. 10 kW/cylinder),– High-speed engines for passenger

cars and light commercial vehicles (upto approx. 50 kW/cylinder),

– Engines for construction, agricultural,and forestry machinery (up to approx.50 kW/cylinder),

– Engines for heavy trucks, buses, andtractors (up to approx. 80 kW/cylinder),

– Stationary engines, for instance asused in emergency generating sets (upto approx. 160 kW/cylinder),

– Engines for locomotives and ships (upto approx. 1,000 kW/cylinder).

Technical requirements

More and more demands are being madeon the diesel engine’s injection system asa result of the severe regulations govern-ing exhaust and noise emissions, and the demand for lower fuel-consumption.Basically speaking, depending on theparticular diesel combustion process(direct or indirect injection), in order toensure efficient air/fuel mixture formation,the injection system must inject the fuelinto the combustion chamber at a pres-sure between 350 and 2,050 bar, and theinjected fuel quantity must be meteredwith extreme accuracy. With the dieselengine, load and speed control must takeplace using the injected fuel quantity with-out intake-air throttling taking place. The mechanical (flyweight) governingprinciple for diesel injection systems is in-

Diesel fuel-injection

systems:An overview

4

Diesel fuel-injection systems:An overview

Overview of the Bosch diesel fuel-injection systems

M, MW, A, P, ZWM, CW in-line injection pumps in order of increasing size; PF single-plunger injection pumps; VE axial-piston distributor injection pumps; VR radial-piston distributor injection pumps; UPS unitpump system; UIS unit injector system; CR Common Rail system.

VE

VR

M

MW

CR

UIS

PF VE

MW

A

P

VE

MW

A

P

ZWM

CW

PF

CR

UPS

ZWM

CW

PF

CR

UPS

VE

VR

MW

P

CR

UPS

UIS

Fig. 1

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creasingly being superseded by the Elec-tronic Diesel Control (EDC). In the pas-senger-car and commercial-vehicle sec-tor, new diesel fuel-injection systems areall EDC-controlled.

According to the latest state-of-the-art, it is mainly the high-pressure injection systems listed below which are used formotor-vehicle diesel engines.

Fields ofapplication, Technicalrequirements

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Fuel-injection Injection Engine-related datasystemType

mm3 bar min–1 kW

In-line injection pumpsM 111,60 1,550 m, e IDI – 4…6 5,000 1,120A 11,120 1,750 m DI / IDI – 2…12 2,800 1,127MW 11,150 1,100 m DI – 4…8 2,600 1,136P 3000 11,250 1,950 m, e DI – 4…12 2,600 1,145P 7100 11,250 1,200 m, e DI – 4…12 2,500 1,155P 8000 11,250 1,300 m, e DI – 6…12 2,500 1,155P 8500 11,250 1,300 m, e DI – 4…12 2,500 1,155H 1 11,240 1,300 e DI – 6…8 2,400 1,155H 1000 11,250 1,350 e DI – 5…8 2,200 1,170

Axial-piston distributor injection pumpsVE 11,120 1,200/350 m DI / IDI – 4…6 4,500 1,125VE…EDC 1) 11,170 1,200/350 e, em DI / IDI – 3…6 4,200 1,125VE…MV 11,170 1,400/350 e, MV DI / IDI – 3…6 4,500 1,125

Radial-piston distributor injection pumpVR…MV 1,1135 1,700 e, MV DI – 4.6 4,500 1,150

Single-plunger injection pumpsPF(R)… 150… 800… m, em DI / IDI – arbitrary 300… 75…

18,000 1,500 2,000 1,000UIS 30 2) 11,160 1,600 e, MV DI VE 8 3a) 3,000 1,145UIS 31 2) 11,300 1,600 e, MV DI VE 8 3a) 3,000 1,175UIS 32 2) 11,400 1,800 e, MV DI VE 8 3a) 3,000 1,180UIS-P1 3) 111,62 2,050 e, MV DI VE 6 3a) 5,000 1,125UPS 12 4) 11,150 1,600 e, MV DI VE 8 3a) 2,600 1,135UPS 20 4) 11,400 1,800 e, MV DI VE 8 3a) 2,600 1,180UPS (PF[R]) 13,000 1,400 e, MV DI – 6…20 1,500 1,500

Common Rail accumulator injection systemCR 5) 1,100 1,350 e, MV DI VE 5a)/NE 3…8 5,000 5b) 30CR 6) 1,400 1,400 e, MV DI VE 6a)/NE 6…16 2,800 200

Table 1Diesel fuel-injection systems: Properties and characteristic data

1) EDC Electronic Diesel Control; 2) UIS unit injector system for comm. vehs. 3) UIS unit injector system for pass. cars; 3a) With two ECU’s large numbers of cylinders are possible; 4) UPS unit pump system for comm. vehs. and buses; 5) CR 1st generation for pass. cars and light comm. vehs.; 5a) Up to 90˚ crankshaft BTDC, freely selectable; 5b) Up to 5,500 min–1 during overrun; 6) CR for comm. vehs., buses, and diesel-powered locomotives; 6a) Up to 30˚ crankshaft BTDC.

Injection-pump designs

In-line fuel-injection pumps

All in-line fuel-injection pumps have aplunger-and-barrel assembly for eachcylinder. As the name implies, this com-prises the pump barrel and the corre-sponding plunger. The pump camshaftintegrated in the pump and driven by theengine, forces the pump plunger in the delivery direction. The plunger is re-turned by its spring. The plunger-and-barrel assemblies arearranged in-line, and plunger lift cannotbe varied. In order to permit changes inthe delivery quantity, slots have beenmachined into the plunger, the diagonaledges of which are known as helixes.When the plunger is rotated by the mov-able control rack, the helixes permit theselection of the required effective stroke.Depending upon the fuel-injection con-ditions, delivery valves are installed be-tween the pump’s pressure chamber andthe fuel-injection lines. These not onlyprecisely terminate the injection processand prevent secondary injection (dribble)at the nozzle, but also ensure a family of uniform pump characteristic curves(pump map).

PE standard in-line fuel-injection pumpStart of fuel delivery is defined by an inletport which is closed by the plunger’s topedge. The delivery quantity is determinedby the second inlet port being opened bythe helix which is diagonally machinedinto the plunger.The control rack’s setting is determinedby a mechanical (flyweight) governor orby an electric actuator (EDC).

Control-sleeve in-line fuel-injectionpumpThe control-sleeve in-line fuel-injectionpump differs from a conventional in-lineinjection pump by having a “controlsleeve” which slides up and down thepump plunger. By way of an actuator shaft,this can vary the plunger lift to port closing,

and with it the start of delivery and the startof injection. The control sleeve’s positionis varied as a function of a variety of dif-ferent influencing variables. Compared to the standard PE in-line injection pumptherefore, the control-sleeve version fea-tures an additional degree of freedom.

Distributor fuel-injectionpumpsDistributor pumps have a mechanical(flyweight) governor, or an electroniccontrol with integrated timing device. Thedistributor pump has only one plunger-and-barrel asembly for all the engine’scylinders.

Axial-piston distributor pumpIn the case of the axial-piston distributorpump, fuel is supplied by a vane-typepump. Pressure generation, and distribu-tion to the individual engine cylinders, isthe job of a central piston which runs ona cam plate. For one revolution of thedriveshaft, the piston performs as manystrokes as there are engine cylinders.The rotating-reciprocating movement isimparted to the plunger by the cams onthe underside of the cam plate which rideon the rollers of the roller ring. On the conventional VE axial-piston dis-tributor pump with mechanical (flyweight)governor, or electronically controlledactuator, a control collar defines theeffective stroke and with it the injectedfuel quantity. The pump’s start of deliverycan be adjusted by the roller ring (timingdevice). On the conventional solenoid-valve-controlled axial-piston distributorpump, instead of a control collar an electronically controlled high-pressuresolenoid valve controls the injected fuelquantity. The open and closed-loop con-trol signals are processed in two ECU’s.Speed is controlled by appropriate trig-gering of the actuator.

Radial-piston distributor pumpIn the case of the radial-piston distributorpump, fuel is supplied by a vane-typepump. A radial-piston pump with cam ringand two to four radial pistons is responsible

Diesel fuel-injection

systems:An overview

6

for generation of the high pressure and forfuel delivery. The injected fuel quantity ismetered by a high-pressure solenoidvalve. The timing device rotates the camring in order to adjust the start of delivery.As is the case with the solenoid-valve-controlled axial-piston pump, all open andclosed-loop control signals are processedin two ECU’s. Speed is controlled byappropriate triggering of the actuator.

Single-plunger fuel-injectionpumpsPF single-plunger pumpsPF single-plunger injection pumps areused for small engines, diesel locomo-tives, marine engines, and constructionmachinery. They have no camshaft oftheir own, although they correspond tothe PE in-line injection pumps regardingtheir method of operation. In the case oflarge engines, the mechanical-hydraulicgovernor or electronic controller is at-tached directly to the engine block. Thefuel-quantity adjustment as defined bythe governor (or controller) is transferredby a rack integrated in the engine. The actuating cams for the individual PFsingle-plunger pumps are located on theengine camshaft. This means that injec-tion timing cannot be implemented byrotating the camshaft. Here, by adjustingan intermediate element (for instance, arocker between camshaft and roller tap-pet) an advance angle of several angulardegrees can be obtained.Single-plunger injection pumps are alsosuitable for operation with viscous heavyoils.

Unit-injector system (UIS)With the unit-injector system, injectionpump and injection nozzle form a unit.One of these units is installed in the en-gine’s cylinder head for each engine cyl-inder, and driven directly by a tappet orindirectly from the engine’s camshaftthrough a valve lifter.

Compared with in-line and distributor in-jection pumps, considerably higher injec-tion pressures (up to 2050 bar) have be-

come possible due to the omission of thehigh-pressure lines. Such high injectionpressures coupled with the electronicmap-based control of duration of injection(or injected fuel quantity), mean that aconsiderable reduction of the diesel en-gine’s toxic emissions has become possi-ble together with good shaping of therate-of-discharge curve. Electronic control concepts permit a va-riety of additional functions.

Unit-pump system (UPS)The principle of the UPS unit-pump sys-tem is the same as that of the UIS unit injector. It is a modular high-pressure in-jection system. Similar to the UIS, theUPS system features one UPS single-plunger injection pump for each enginecylinder. Each UP pump is driven by theengine’s camshaft. Connection to the no-zzle-and-holder assembly is through ashort high-pressure delivery line preci-sely matched to the pump-system com-ponents.Electronic map-based control of the startof injection and injection duration (inother words, of injected fuel quantity)leads to a pronounced reduction in thediesel engine’s toxic emissions. The useof a high-speed electronically triggeredsolenoid valve enables the character-istic of the individual injection process,the so-called rate-of-discharge curve, tobe precisely defined.

Accumulator injectionsystemCommon-Rail system (CR)Pressure generation and the actual injec-tion process have been decoupled fromeach other in the Common Rail accumu-lator injection system. The injection pres-sure is generated independent of enginespeed and injected fuel quantity, and isstored, ready for each injection process,in the rail (fuel accumulator). The start ofinjection and the injected fuel quantityare calculated in the ECU and, via the in-jection unit, implemented at each cylin-der through a triggered solenoid valve.

Injection-pumpdesigns

7

Fuel-injectionsystemsAssignments

The fuel-injection system is responsiblefor supplying the diesel engine with fuel.To do so, the injection pump generatesthe pressure required for fuel injection.The fuel under pressure is forced throughthe high-pressure fuel-injection tubing tothe injection nozzle which then injects itinto the combustion chamber.The fuel-injection system (Fig. 1) in-cludes the following components andassemblies: The fuel tank, the fuel filter,the fuel-supply pump, the injectionnozzles, the high-pressure injection

tubing, the governor, and the timingdevice (if required). The combustion processes in the diesel engine depend to a large degree uponthe quantity of fuel which is injected andupon the method of introducing this fuelto the combustion chamber. The most important criteria in this re-spect are the fuel-injection timing and theduration of injection, the fuel’s distributionin the combustion chamber, the momentin time when combustion starts, theamount of fuel metered to the engine perdegree crankshaft, and the total injectedfuel quantity in accordance with theengine loading. The optimum interplay ofall these parameters is decisive for thefaultless functioning of the diesel engineand of the fuel-injection system.

Axial-pistondistributor

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Mechanically-controlled(governed) axial-piston distributorfuel-Injection pumps VE

Fuel-injection system with mechanically-controlled (governed) distributor injection pump

1 Fuel tank, 2 Fuel filter, 3 Distributor fuel-injection pump, 4 Nozzle holder with nozzle, 5 Fuel return line, 6 Sheathed-element glow plug (GSK) 7 Battery, 8 Glow-plug and starter switch, 9 Glow control unit (GZS).

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Types

The increasing demands placed uponthe diesel fuel-injection system made itnecessary to continually develop andimprove the fuel-injection pump.Following systems comply with thepresent state-of-the-art:– In-line fuel-injection pump (PE) with

mechanical (flyweight) governor orElectronic Diesel Control (EDC) and, ifrequired, attached timing device,

– Control-sleeve in-line fuel-injectionpump (PE), with Electronic DieselControl (EDC) and infinitely variablestart of delivery (without attachedtiming device),

– Single-plunger fuel-injection pump (PF),– Distributor fuel-injection pump (VE)

with mechanical (flyweight) governoror Electronic Diesel Control (EDC).With integral timing device,

– Radial-piston distributor injectionpump (VR),

– Common Rail accumulator injectionsystem (CRS),

– Unit-injector system (UIS),– Unit-pump system (UPS).

Fuel-injectiontechniques

Fields of applicationSmall high-speed diesel enginesdemand a lightweight and compact fuel-injection installation. The VE distributorfuel-injection pump (Fig. 2) fulfills thesestipulations by combining – Fuel-supply pump, – High-pressure pump, – Governor, and – Timing device,in a small, compact unit. The dieselengine’s rated speed, its power output,and its configuration determine theparameters for the particular distributorpump.Distributor pumps are used in passengercars, commercial vehicles, agriculturaltractors and stationary engines.


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Fig. 2: VE distributor pump fitted to a 4-cylinderdiesel engine

Subassemblies

In contrast to the in-line injection pump,the VE distributor pump has only onepump cylinder and one plunger, even formulti-cylinder engines. The fuel deliv-ered by the pump plunger is apportionedby a distributor groove to the outlet portsas determined by the engine’s number ofcylinders. The distributor pump’s closedhousing contains the following functionalgroups:

– High-pressure pump with distributor,– Mechanical (flyweight) governor,– Hydraulic timing device, – Vane-type fuel-supply pump, – Shutoff device, and – Engine-specific add-on modules.

Fig. 3 shows the functional groups andtheir assignments. The add-on modules

facilitate adaptation to the specificrequirements of the diesel engine inquestion.

Design and constructionThe distributor pump’s drive shaft runs in bearings in the pump housing and drives the vane-type fuel-supply pump.The roller ring is located inside the pump at the end of the drive shaft al-though it is not connected to it. A rotat-ing-reciprocating movement is impartedto the distributor plunger by way of thecam plate which is driven by the inputshaft and rides on the rollers of the roller ring. The plunger moves inside the distributor head which is bolted to thepump housing. Installed in the dis-tributor head are the electrical fuel shutoff device, the screw plug with ventscrew, and the delivery valves with their


pumps

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The subassemblies and their functions

1 Vane-type fuel-supply pump with pressure regulating valve: Draws in fuel and generates pressure inside the pump.

2 High-pressure pump with distributor: Generates injection pressure, delivers and distributes fuel. 3 Mechanical (flyweight) governor: Controls the pump speed and varies the delivery quantity within

the control range. 4 Electromagnetic fuel shutoff valve: Interrupts the fuel supply. 5 Timing device: Adjusts the start of delivery (port closing) as a function of the pump speed and

in part as a function of the load.

1

5 2

4

3

Fig. 3

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holders. If the distributor pump is alsoequipped with a mechanical fuel shutoffdevice this is mounted in the governorcover.The governor assembly comprising theflyweights and the control sleeve is driven by the drive shaft (gear with rubber damper) via a gear pair. The governor linkage mechanism whichconsists of the control, starting, andtensioning levers, can pivot in thehousing.The governor shifts the position of thecontrol collar on the pump plunger. Onthe governor mechanism’s top side is the governor spring which engages with the external control lever through the control-lever shaft which is held in bearings in the governor cover.The control lever is used to control pump function. The governor coverforms the top of the distributor pump, and

also contains the full-load adjustingscrew, the overflow restriction or theoverflow valve, and the engine-speedadjusting screw. The hydraulic injectiontiming device is located at the bottom ofthe pump at right angles to the pump’slongitudinal axis. Its operation is in-fluenced by the pump’s internal pressurewhich in turn is defined by the vane-typefuel-supply pump and by the pres-sure-regulating valve. The timing deviceis closed off by a cover on each side of the pump (Fig. 4).


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The subassemblies and their configuration

1 Pressure-control valve, 2 Governor assembly, 3 Overflow restriction, 4 Distributor head with high-pressure pump, 5 Vane-type fuel-supply pump, 6 Timing device, 7 Cam plate, 8 Electromagnetic shutoff valve.

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Pump drive

The distributor injection pump is drivenby the diesel engine through a specialdrive unit. For 4-stroke engines, thepump is driven at exactly half the enginecrankshaft speed, in other words at camshaft speed. The VE pump mustbe positively driven so that it’s drive shaft is synchronized to the engine’s piston movement. This positive drive is implemented bymeans of either toothed belts, pinion,gear wheel or chain. Distributor pumpsare available for clockwise and for counter-clockwise rotation, whereby theinjection sequence differs dependingupon the direction of rotation. The fuel outlets though are always supplied with fuel in their geometric sequence, and are identified with the letters A, B, C etc. to avoid confusionwith the engine-cylinder numbering. Distributor pumps are suitable for en-gines with up to max. 6 cylinders.

Fuel supply anddeliveryConsidering an injection system withdistributor injection pump, fuel supplyand delivery is divided into low-pressureand high-pressure delivery (Fig. 1).

Low-pressure stageLow-pressure deliveryThe low-pressure stage of a distributor-pump fuel-injection installation com-prises the fuel tank, fuel lines, fuel filter,vane-type fuel-supply pump, pressure-control valve, and overflow restriction.The vane-type fuel-supply pump drawsfuel from the fuel tank. It delivers avirtually constant flow of fuel perrevolution to the interior of the injectionpump. A pressure-control valve is fittedto ensure that a defined injection-pumpinterior pressure is maintained as afunction of supply-pump speed. Usingthis valve, it is possible to set a definedpressure for a given speed. The pump’s


pumps

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Fuel supply and delivery in a distributor-pump fuel-injection system

1 Fuel tank, 2 Fuel line (suction pressure), 3 Fuel filter, 4 Distributor injection pump, 5 High-pressure fuel-injection line, 6 Injection nozzle, 7 Fuel-return line (pressureless), 8 Sheathed-element glow plug.

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interior pressure then increases inproportion to the speed (in other words,the higher the pump speed the higher the pump interior pressure). Some of thefuel flows through the pressure-regulating valve and returns to thesuction side. Some fuel also flowsthrough the overflow restriction and back to the fuel tank in order to pro-vide cooling and self-venting for theinjection pump (Fig. 2). An overflow valvecan be fitted instead of the overflowrestriction.

Fuel-line configurationFor the injection pump to function ef-ficiently it is necessary that its high-pressure stage is continually providedwith pressurized fuel which is free of vapor bubbles. Normally, in the case ofpassenger cars and light commercial vehicles, the difference in height betweenthe fuel tank and the fuel-injection equipment is negligible. Furthermore, thefuel lines are not too long and they haveadequate internal diameters. As a result,the vane-type supply pump in the

injection pump is powerful enough to drawthe fuel out of the fuel tank and to build upsufficient pressure in the interior of the in-jection pump.In those cases in which the difference in height between fuel tank and injectionpump is excessive and (or) the fuel linebetween tank and pump is too long, apre-supply pump must be installed. Thisovercomes the resistances in the fuel line and the fuel filter. Gravity-feed tanks are mainly used on stationaryengines.

Fuel tankThe fuel tank must be of noncorrodingmaterial, and must remain free of leaks at double the operating pressure and inany case at 0.3 bar. Suitable openings orsafety valves must be provided, or similar measures taken, in order topermit excess pressure to escape of its own accord. Fuel must not leak pastthe filler cap or through pressure-compensation devices. This applieswhen the vehicle is subjected to minormechanical shocks, as well as when


13

Interaction of the fuel-supply pump, pressure-control valve, and overflow restriction

1 Drive shaft, 2 Pressure-control valve, 3 Eccentric ring, 4 Support ring, 5 Governor drive, 6 Drive-shaft dogs, 7 Overflow restriction, 8 Pump housing.

1 2 3 4 5 6 7 8

Fig. 2

UM

K03

21Y

cornering, and when standing or drivingon an incline. The fuel tank and theengine must be so far apart from eachother that in case of an accident there isno danger of fire. In addition, specialregulations concerning the height of thefuel tank and its protective shieldingapply to vehicles with open cabins, aswell as to tractors and buses

Fuel linesAs an alternative to steel pipes, flame-inhibiting, steel-braid-armored flexiblefuel lines can be used for the low-pressure stage. These must be routed toensure that they cannot be damagedmechanically, and fuel which has drippedor evaporated must not be able toaccumulate nor must it be able to ignite.

Fuel filterThe injection pump’s high-pressurestage and the injection nozzle aremanufactured with accuracies of severalthousandths of a millimeter. As a result,


pumps

14

Vane-type fuel-supply pump for low-pressure delivery

1 Inlet, 2 Outlet.

1

2

UM

K03

20Y

Fig. 4

UM

K03

24Y

Fig. 3: Vane-type fuel-supply pump with impelleron the drive shaft

contaminants in the fuel can lead tomalfunctions, and inefficient filtering cancause damage to the pump com-ponents, delivery valves, and injector nozzles. This means that a fuel filter specifically aligned to the requirementsof the fuel-injection system is absolutelyimperative if trouble-free operation and a long service life are to be achieved.Fuel can contain water in bound form(emulsion) or unbound form (e.g.,condensation due to temperaturechanges). If this water gets into theinjection pump, corrosion damage can bethe result. Distributor pumps musttherefore be equipped with a fuel filterincorporating a water accumulator fromwhich the water must be drained off atregular intervals. The increasingpopularity of the diesel engine in thepassenger car has led to thedevelopment of an automatic water-warning device which indicates by means of a warning lamp when watermust be drained.

Vane-type fuel supply pumpThe vane-type pump (Figs. 3 and 4) islocated around the injection pump’s driveshaft. Its impeller is concentric with theshaft and connected to it with a Woodruffkey and runs inside an eccentric ringmounted in the pump housing.When the drive shaft rotates, centrifugal

force pushes the impeller’s four vanesoutward against the inside of theeccentric ring. The fuel between thevanes’ undersides and the impellerserves to support the outward movementof the vanes.The fuel enters through theinlet passage and a kidney-shapedrecess in the pump’s housing, and fillsthe space formed by the impeller, thevane, and the inside of the eccentric ring.The rotary motion causes the fuelbetween adjacent vanes to be forced intothe upper (outlet) kidney-shaped recessand through a passage into the interior ofthe pump. At the same time, some of thefuel flows through a second passage tothe pressure-control valve.

Pressure-control valveThe pressure-control valve (Fig. 5) isconnected through a passage to the upper (outlet) kidney-shaped recess, andis mounted in the immediate vicinity ofthe fuel-supply pump. It is a spring-loaded spool-type valve with which thepump’s internal pressure can be variedas a function of the quantity of fuel beingdelivered. If fuel pressure increasesbeyond a given value, the valve spoolopens the return passage so that the fuelcan flow back to the supply pump’ssuction side. If the fuel pressure is toolow, the return passage is closed by thespring.


15

Pressure-control valve Overflow restriction

Fig. 5

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K03

22Y

Fig. 6

UM

K03

23Y

The spring’s initial tension can beadjusted to set the valve openingpressure.

Overflow restrictionThe overflow restriction (Figure 6) is screwed into the injection pump’s governor cover and connected to thepump’s interior. It permits a variable amount of fuel to return to the fuel tankthrough a narrow passage. For this fuel, the restriction represents a flow resistance that assists in maintaining the pressure inside the injection pump.Being as inside the pump a precisely defined pressure is required as a functionof pump speed, the overflow restrictionand the flow-control valve are pre-cisely matched to each other.

High-pressure stage

The fuel pressure needed for fuel injection is generated in the injectionpump’s high-pressure stage. Thepressurized fuel then travels to theinjection nozzles through the deliveryvalves and the fuel-injection tubing.

Distributor-plunger driveThe rotary movement of the drive shaft is transferred to the distributor plungervia a coupling unit (Fig. 7), whereby thedogs on cam plate and drive shaftengage with the recesses in the yoke,which is located between the end of thedrive shaft and the cam plate. The camplate is forced against the roller ring by a spring, and when it rotates the cam lobes riding on the ring’s rollers convertthe purely rotational movement of thedrive shaft into a rotating-reciprocatingmovement of the cam plate. The distributor plunger is held in the camplate by its cylindrical fitting piece and islocked into position relative to the cam


pumps

16

Pump assembly for generation and delivery of high pressure in the distributor-pump interior

Fig. 7

UM

K03

26Y

plate by a pin. The distributor plunger is forced upwards to its TDC position by the cams on the cam plate, and thetwo symmetrically arranged plunger-return springs force it back down again toits BDC position. The plunger-return springs abut at oneend against the distributor head and atthe other their force is directed to theplunger through a link element. Thesesprings also prevent the cam platejumping off the rollers during harshacceleration. The lengths of the returnsprings are carefully matched to eachother so that the plunger is not displacedfrom its centered position (Fig. 8).

Cam plates and cam contoursThe cam plate and its cam contour in-fluence the fuel-injection pressure and the injection duration, whereby camstroke and plunger-lift velocity are thedecisive criteria. Considering the differentcombustion-chamber configurations andcombustion systems used in the variousengine types, it becomes imperative thatthe fuel-injection factors are individuallytailored to each other. For this reason, aspecial cam-plate surface is generated foreach engine type and machined into thecam-plate face. This defined cam plate isthen assembled in the correspondingdistributor pump. Since the cam-platesurface is specific to a given engine type,the cam plates are not interchangeablebetween the different VE-pump variants.


17

Pump assembly with distributor head

Generates the high pressure and distributes the fuel to the respective fuel injector.1 Yoke, 2 Roller ring, 3 Cam plate, 4 Distributor-plunger foot, 5 Distributor plunger, 6 Link element,7 Control collar, 8 Distributor-head flange, 9 Delivery-valve holder, 10 Plunger-return spring,4...8 Distributor head.

4 5 6 7 10 8 9

1 2 3

Fig. 8

UM

K03

27Y

Distributor headThe distributor plunger, the distributor-head bushing and the control collar areso precisely fitted (lapped) into the distributor head (Fig. 8), that they sealeven at very high pressures. Smallleakage losses are nevertheless un-avoidable, as well as being desirable forplunger lubrication. For this reason, thedistributor head is only to be replaced as a complete assembly, and never theplunger, control collar, or distributorflange alone.

Fuel meteringThe fuel delivery from a fuel-injectionpump is a dynamic process comprisingseveral stroke phases (Fig. 9). Thepressure required for the actual fuel injection is generated by the high-pres-sure pump. The distributor plunger’sstroke and delivery phases (Fig. 10) show the metering of fuel to an enginecylinder. For a 4-cylinder engine thedistributor plunger rotates through 90°for a stroke from BDC to TDC and backagain. In the case of a 6-cylinder en-gine, the plunger must have completed

these movements within 60° of plungerrotation.As the distributor plunger moves fromTDC to BDC, fuel flows through the openinlet passage and into the high-pressurechamber above the plunger. At BDC, theplunger’s rotating movement then closesthe inlet passage and opens the distribu-tor slot for a given outlet port (Fig. 10a).The plunger now reverses its direction of movement and moves upwards, theworking stroke begins. The pressure that builds up in the high-pressurechamber above the plunger and in theoutlet-port passage suffices to open thedelivery valve in question and the fuel is forced through the high-pressure line to the injector nozzle (Fig. 10b). Theworking stroke is completed as soon asthe plunger’s transverse cutoff borereaches the control edge of the controlcollar and pressure collapses. From this point on, no more fuel is delivered to the injector and the delivery valvecloses the high-pressure line.


pumps

18 UM

K03

28Y

Fig. 9: The cam plate rotates against the roller ring,whereby its cam track follows the rollers causingit to lift (for TDC) and drop back again (for BDC)


19

Distributor plunger with stroke and delivery phases

a Inlet passagecloses.At BDC, the metering slot (1) closes the inlet passage, and the distributor slot (2) opens the outlet port.

b Fuel delivery.During the plunger stroke towards TDC (working stroke), the plunger pressurizes the fuel in the high-pressure chamber (3). The fuel travels through the outlet-port passage (4) to the injection nozzle.

c End of delivery. Fuel delivery ceases as soon as the control collar (5) opens the transverse cutoff bore (6).

d Entry of fuel. Shortly before TDC, the inlet passage is opened. During the plunger’s return stroke to BDC, the high-pressure chamber is filled with fuel and the transverse cutoff bore is closed again. The outlet-portpassage is alsoclosed at this point.

5 6

1

2

324

UT OT

OT = TDCUT = BDC

UT OT

UT

UT

Fig. 10

UM

K03

29Y

During the plunger’s continued move-ment to TDC, fuel returns through thecutoff bore to the pump interior. Duringthis phase, the inlet passage is openedagain for the plunger’s next working cycle(Fig. 10c).During the plunger’s return stroke, itstransverse cutoff bore is closed by theplunger’s rotating stroke movement, and the high-pressure chamber above theplunger is again filled with fuel through the open inlet passage (Fig. 10d).

Delivery valveThe delivery valve closes off the high-pressure line from the pump. It has the job of relieving the pressure in the line by removing a defined volume of fuel upon completion of the delivery phase.This ensures precise closing of the in-jection nozzle at the end of the injectionprocess. At the same time, stablepressure conditions between injectionpulses are created in the high-pressurelines, regardless of the quantity of fuelbeing injected at a particular time.

The delivery valve is a plunger-typevalve. It is opened by the injection pres-sure and closed by its return spring.Between the plunger’s individual deliverystrokes for a given cylinder, the delivery valve in question remains closed. This separates the high-pres-sure line and the distributor head’s outlet-port passage. During delivery, the pressure generated in the high-pressure chamber above the plungercauses the delivery valve to open. Fuelthen flows via longitudinal slots, into aring-shaped groove and through the delivery-valve holder, the high-pressureline and the nozzle holder to the injectionnozzle. As soon as delivery ceases (transversecutoff bore opened), the pressure in the high-pressure chamber above theplunger and in the highpressure linesdrops to that of the pump interior, and thedelivery-valve spring together with thestatic pressure in the line force the de-livery-valve plunger back onto its seat again (Fig. 11).


pumps

20

Distributor head with high-pressure chamber

1 Control collar, 2 Distributor head, 3 Distributor plunger, 4 Delivery-valve holder, 5 Delivery-valve.

1

2

3

45

Fig. 11

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K03

35Y

Delivery valve with return-flow restrictionPrecise pressure relief in the lines is necessary at the end of injection. Thisthough generates pressure waves which are reflected at the delivery valve. These cause the delivery valve to open again, or cause vacuum phasesin the high-pressure line. These pro-cesses result in post-injection of fuel withattendant increases in exhaust emis-sions or cavitation and wear in the injec-tion line or at the nozzle. To prevent suchharmful reflections, the delivery valve isprovided with a restriction bore which isonly effective in the direction of returnflow. This return-flow restriction com-prises a valve plate and a pressurespring so arranged that the restriction is ineffective in the delivery direction,whereas in the return direction dampingcomes into effect (Fig. 12).

Constant-pressure valveWith high-speed direct-injection (Dl) engines, it is often the case that the

“retraction volume” resulting from the retraction piston on the delivery-valveplunger does not suffice to reliably prevent cavitation, secondary injection,and combustion-gas blowback into the nozzle-and-holder assembly. Here, constant-pressure valves are fitted which relieve the high-pressure system (injection line and nozzle-and-holder assembly) by means of a single-actingnon-return valve which can be set to agiven pressure, e.g., 60 bar (Fig. 13).

High-pressure linesThe pressure lines installed in the fuel-injection system have been matchedprecisely to the rate-of-discharge curveand must not be tampered with duringservice and repair work. The high-pres-sure lines connect the injection pump to the injection nozzles and are routed so that they have no sharp bends. Inautomotive applications, the high-pressure lines are normally secured withspecial clamps at specific intervals, andare made of seamless steel tubing.


21

Delivery valve with return-flow restriction

1 Delivery-valve holder, 2 Return-flow restriction, 3 Delivery-valve spring, 4 Valve holder, 5 Piston shaft, 6 Retraction piston.

Constant-pressure valve

1 Delivery-valve holder, 2 Filler piece with springlocator, 3 Delivery-valve spring, 4 Delivery-valveplunger, 5 Constant-pressure valve, 6 Spring seat, 7 Valve spring (constant-pressure valve), 8 Setting sleeve, 9 Valve holder, 10 Shims.

1

2

3

4

5

6

1

2

3

4

5

6

7

8

9

10

Fig. 12

UM

K11

83Y

Fig. 13

UM

K11

84Y

Mechanical engine-speed control(governing)

ApplicationThe driveability of a diesel-powered vehicle can be said to be satisfactorywhen its engine immediately responds to driver inputs from the accelerator pedal. Apart from this, upon driving offthe engine must not tend to stall. Theengine must respond to accelerator-pedal changes by accelerating or decel-erating smoothly and without hesitation.On the flat, or on a constant gradient,with the accelerator pedal held in a givenposition, the vehicle speed should also remain constant. When the pedal is released the engine must brake thevehicle. On the diesel engine, it is theinjection pump’s governor that ensuresthat these stipulations are complied with.The governor assembly comprises the

mechanical (flyweight) governor and thelever assembly. It is a sensitive controldevice which determines the position of the control collar, thereby defining the delivery stroke and with it the injectedfuel quantity. It is possible to adapt the governor’s response to setpoint changes by varying the design of the lever assembly (Fig. 1).

Governor functionsThe basic function of all governors is the limitation of the engine’s maximumspeed. Depending upon type, the gov-ernor is also responsible for keepingcertain engine speeds constant, such as idle speed, or the minimum andmaximum engine speeds of a stipulatedengine-speed range, or of the completespeed range, between idle and maxi-mum speed. The different governor types are a direct result of the variety ofgovernor assignments (Fig. 2):– Low-idle-speed governing: The dieselengine’s low-idle speed is controlled bythe injection-pump governor.


pumps

22

Distributor injection pump with governor assembly, comprising flyweight governor and leverassembly

Fig. 1

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43Y

– Maximum-speed governing: With theaccelerator pedal fully depressed, themaximum full-load speed must notincrease to more than high idle speed(maximum speed) when the load isremoved. Here, the governor respondsby shifting the control collar back towardsthe “Stop” position, and the supply of fuelto the engine is reduced.– Intermediate-speed governing: Vari-able-speed governors incorporate in-termediate-speed governing. Within certain limits, these governors can alsomaintain the engine speeds between idle and maximum constant. This means that depending upon load, theengine speed n varies inside the en-gine’s power range only between nVT

(a given speed on the full-load curve) and nLT (with no load on the engine).Other control functions are performed by the governor in addition to its gov-erning responsibilities:– Releasing or blocking of the extra fuelrequired for starting,– Changing the full-load delivery as a

function of engine speed (torque control).In some cases, add-on modules arenecessary for these extra assignments.

Speed-control (governing) accuracyThe parameter used as the measure forthe governor’s accuracy in controllingengine speed when load is removed isthe so-called speed droop (P-degree).This is the engine-speed increase,expressed as a percentage, that occurswhen the diesel engine’s load is re-moved with the control-lever (accelera-tor) position unchanged. Within thespeed-control range, the increase in engine speed is not to exceed a given figure. This is stipulated as the high idlespeed. This is the engine speed whichresults when the diesel engine, startingat its maximum speed under full load, isrelieved of all load. The speed increase isproportional to the change in load, and increases along with it.

δ = nlo – nvonvo

or expressed in %:

δ = nlo – nvo .100%nvo

whereδ = Speed droopnlo = High idle (maximum) speednvo = Maximum full-load speed

The required speed droop depends onengine application. For instance, on anengine used to power an electrical gen-erator set, a small speed droop is re-quired so that load changes result in only minor speed changes and there-fore minimal frequency changes. On theother hand, for automotive applicationslarge speed droops are preferablebecause these result in more stablecontrol in case of only slight loadchanges (acceleration or deceleration)and lead to better driveability. A low-valuespeed droop would lead to rough, jerking operation when the load changes.

Mechanicalgoverning

23

Governor characteristics

a Minimum-maximum-speed governor, b Variable-speed governor.1 Start quantity, 2 Full-load delivery, 3 Torque control (positive), 4 Full-load speed regulation, 5 Idle.

2 3 4

1

5

2 3 4

1

5

a

b

0 Engine speed min–1

mm

Con

trol

-col

lar

trav

el

mm

Con

trol

-col

lar

trav

el

Fig. 2

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44E

Variable-speed governor

The variable-speed governor controls all engine speeds between start and high idle (maximum). The variable-speedgovernor also controls the idle speed andthe maximum full-load speed, as well asthe engine-speed range in between.Here, any engine speed can be selectedby the accelerator pedal and, dependingupon the speed droop, maintainedpractically constant (Fig. 4).This is necessary for instance when ancillary units (winches, fire-fightingpumps, cranes etc.) are mounted on thevehicle. The variable-speed governor is also often fitted in commercial andagricultural vehicles (tractors andcombine harvesters).

Design and constructionThe governor assembly is driven by thedrive shaft and comprises the flyweighthousing complete with flyweights.The governor assembly is attached to the governor shaft which is fixed in the

governor housing, and is free to rotatearound it. When the flyweights rotate they pivot outwards due to centrifugalforce and their radial movement isconverted to an axial movement of the sliding sleeve. The sliding-sleeve traveland the force developed by the sleeveinfluence the governor lever assembly.This comprises the starting lever, ten-sioning lever, and adjusting lever (notshown). The interaction of spring forcesand sliding-sleeve force defines the setting of the governor lever assembly,variations of which are transferred to the control collar and result in adjust-ments to the injected fuel quantity.

StartingWith the engine at standstill, the fly-weights and the sliding sleeve are in theirinitial position (Fig. 3a). The start-ing lever has been pushed to the startposition by the starting spring and haspivoted around its fulcrum M2. At thesame time the control collar on the dis-tributor plunger has been shifted to its


pumps

24

Variable-speed governor. Start and idle positions

a Start position, b Idle position.1 Flyweights, 2 Sliding sleeve, 3 Tensioning lever, 4 Starting lever, 5 Starting spring, 6 Control collar,7 Distributor-plunger cutoff port, 8 Distributor plunger, 9 Idle-speed adjusting screw, 10 Engine-speed control lever, 11 Control lever, 12 Control-lever shaft, 13 Governor spring, 14 Retaining pin, 15 Idle spring. a Starting-spring travel, c Idle-spring travel, h1 max. working stroke (start); h2 min. working stroke (idle):M2 fulcrum for 4 and 5.

1

12

3

4

5

M2

6

7

8 h1 h2

12

13 14 c

15

M2

10

11

9

a b

a

Fig. 3

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46Y

start-quantity position by the ball pin onthe starting lever. This means that when the engine is cranked thedistributor plunger must travel through acomplete working stroke (= maximumdelivery quantity) before the cutoff bore is opened and delivery ceases. Thus the start quantity (= maximum deliveryquantity) is automatically made availablewhen the engine is cranked.The adjusting lever is held in the pumphousing so that it can rotate. It can beshifted by the fuel-delivery adjustingscrew (not shown in Figure 3). Similarly,the start lever and tensioning lever arealso able to rotate in the adjusting lever.A ball pin which engages in the controlcollar is attached to the underside of the start lever, and the start spring to its upper section. The idle spring is attached to a retaining pin at the top end of the tensioning lever. Also attached to this pin is the governorspring. The connection to the engine-speed control lever is through a lever andthe control-lever shaft.It only needs a very low speed for the sliding sleeve to shift against the softstart spring by the amount a. In the process, the start lever pivots aroundfulcrum M2 and the start quantity is auto-matically reduced to the idle quantity.

Low-idle-speed controlWith the engine running, and theaccelerator pedal released, the engine-speed control lever shifts to the idle position (Figure 3b) up against the idle-speed adjusting screw. The idle speed is selected so that the engine still runsreliably and smoothly when unloaded oronly slightly loaded. The actual control is by means of the idle spring on the retaining pin which counteracts the forcegenerated by the flyweights.This balance of forces determines thesliding-sleeve’s position relative to thedistributor plunger’s cutoff bore, and with it the working stroke. At speedsabove idle, the spring has beencompressed by the amount c and is no longer effective. Using the special idlespring attached to the governor housing,

this means that idle speed can beadjusted independent of the accelerator-pedal setting, and can be increased ordecreased as a function of temperatureor load.

Operation under loadDuring actual operation, depending upon the required engine speed orvehicle speed, the engine-speed controllever is in a given position within its pivot range. This is stipulated by the driver through a given setting of the accelerator pedal. At engine speeds above idle, start spring and idle springhave been compressed completely andhave no further effect on governoraction. This is taken over by thegovernor spring.

Mechanicalgoverning

25

Characteristic curves of the variable-speed governor

A: Start position of the control collar,S: Engine starts with start quantity,S–L: Start quantity reduces to idle quantity,L: Idle speed nLN following engine start-up (no-load),L–B: Engine acceleration phase after shifting theengine-speed control lever from idle to a given required speed nc,B–B': The control collar remains briefly in the full-load position and causes a rapid increase in engine speed,B'–C: Control collar moves back (less injected fuel quantity, higher engine speed). In accordancewith the speed droop, the vehicle maintains the required speed or speed nc in the part-loadrange,E: Engine speed nLT, after removal of load from the engine with the position of the engine-speed control-lever remaining unchanged.

S

B B' Full load

L E No-load

0 500 1,000 1,500 2,000 min–1

Engine speed n

mm

Con

trol

-col

lar

trav

el s

nA nC nLT nVHnLO

A

C

Fig. 4

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48E

Example (Fig. 5):Using the accelerator pedal, the driversets the engine-speed control lever to aspecific position corresponding to a desired (higher) speed. As a result of this adjustment of the control-lever position, the governor spring is ten-sioned by a given amount, with the result that the governor-spring force exceeds the centrifugal force of the flyweights and causes the start lever andthe tensioning lever to pivot around fulcrum M2. Due to the mechanical transmission ratio designed into the system, the control collar shifts in the“Full-load” direction. As a result, the delivery quantity is increased and theengine speed rises. This causes theflyweights to generate more force which,through the sliding sleeve, opposes thegovernor-spring force.The control collar remains in the “Full-load” position until a torque balance occurs. If the engine speed continues to increase, the flyweights separate evenfurther, the sliding-sleeve force prevails,

and as a result the start and tensioninglevers pivot around M2 and push thecontrol collar in the “Stop” direction sothat the control port is opened sooner. It is possible to reduce the deliveryquantity to “zero” which ensures that engine-speed limitation takes place. Thismeans that during operation, and as longas the engine is not overloaded, everyposition of the engine-speed control leveris allocated to a specific speed rangebetween full-load and zero. The result is that within the limits set by itsspeed droop, the governor maintains thedesired speed (Fig. 4).If the load increases to such an extent(for instance on a gradient) that eventhough the control collar is in the full-load position the engine speed con-tinues to drop, this indicates that it is impossible to increase fuel delivery anyfurther. This means that the engine isoverloaded and the driver must changedown to a lower gear.


pumps

26

Fig. 5: Variable-speed governor, operation under load

a Governor function with increasing engine speed, b with falling engine speed. 1 Flyweights, 2 Engine-speed control lever, 3 Idle-speed adjusting screw, 4 Governor spring, 5 Idle spring, 6 Start lever, 7 Tensioning lever, 8 Tensioning-lever stop, 9 Starting spring, 10 Control collar, 11 Adjusting screw for high idle (maximum) speed, 12 Sliding sleeve, 13 Distributor-plunger cutoff bore, 14 Distributor plunger.h1 Working stroke, idle, h2 Working stroke, full-load, M2 fulcrum for 6 and 7.

1

1

67

9

M2

10

4

h1 h2

M2

a b

2

35

812

14

13

11

Fig. 5

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49Y

Overrun (engine braking)During downhill operation the engine is“driven” by the vehicle, and enginespeed tends to increase. This causesthe flyweights to move outwards so thatthe sliding sleeve presses against thetensioning and start levers. Both leverschange their position and push thecontrol collar in the direction of less fuel delivery until a reduced fuel-delivery figure is reached which corresponds tothe new loading level. At the extreme,the delivery figure is zero. Basically, with the variable-speed governor, thisprocess applies for all settings of theengine-speed control lever, when the engine load or engine speed changes to such an extent that the control collar shifts to either its full-load or stopposition.

Minimum-maximum-speedgovernorThe minimum-maximum-speed gover-nor controls (governs) only the idle (minimum) speed and the maximumspeed. The speed range between thesepoints is directly controlled by the ac-celerator pedal (Fig. 6).

Design and constructionThe governor assembly with flyweights,and the lever configuration, are com-parable with those of the variable-speed governor already dealt with. The maindifference lies in the governor spring andits installation. It is in the form of a compression spring and is held in aguide element. Tensioning lever and governor spring are connected by aretaining pin.

StartingWith the engine at standstill, the fly-weights are also stationary and the sliding sleeve is in its initial position. Thisenables the starting spring to push theflyweights to their inner position throughthe starting lever and the sliding sleeve.On the distributor plunger, the controlcollar is in the start-quantity position.

Idle controlOnce the engine is running and theaccelerator pedal has been released, theengine-speed control lever is pulled backto the idle position by its return spring.The centrifugal force generated by theflyweights increases along with enginespeed (Fig. 7a) and the inner flyweightlegs push the sliding sleeve up againstthe start lever. The idle spring on thetensioning lever is responsible for thecontrolling action. The control collar isshifted in the direction of “less delivery”by the pivoting action of the start lever, itsposition being determined by interactionbetween centrifugal force and springforce.

Mechanicalgoverning

27

Characteristic curves of the minimum-maximum-speed governor with idle spring and intermediate spring

a Starting-spring range,b Range of starting and idle spring,d Intermediate-spring range,f Governor-spring range.

Engine speed n min–1

mm

Con

trol

-col

lar

trav

el s

a b d Uncontrolled f

Full load

No-load

Fig. 6

UM

K03

51E

Operation under loadIf the driver depresses the acceleratorpedal, the engine-speed control lever is pivoted through a given angle. Thestarting and idle springs are no longereffective and the intermediate spring comes into effect. The intermediatespring on the minimum-maximum-speedgovernor provides a “soft” transition tothe uncontrolled range. If the engine-speed control lever is pressed even further in the full-load direction, the intermediate spring is compressed untilthe tensioning lever abuts against theretaining pin (Fig. 7b). The intermediatespring is now ineffective and theuncontrolled range has been entered.This uncontrolled range is a function ofthe governor-spring pretension, and inthis range the spring can be regarded as a solid element. The accelerator-pedalposition (engine-speed control lever) isnow transferred directly through the governor lever mechanism to the controlcollar, which means that the injected

fuel quantity is directly determined by theaccelerator pedal. To accelerate, or climba hill, the driver must “give gas”, or easeoff on the accelerator if less enginepower is needed.If engine load is now reduced, with the engine-speed control lever position unchanged, engine speed increaseswithout an increase in fuel delivery. Theflyweights’ centrifugal force also in-creases and pushes the sliding sleeveeven harder against the start andtensioning levers. Full-load speed controldoes not set in, at or near the engine’srated speed, until the governor-springpre-tension has been overcome by theeffect of the sliding-sleeve force.If the engine is relieved of all load, speed increases to the high idle speed, and theengine is thus protected against over-revving.Passenger cars are usually equippedwith a combination of variable-speed governor and minimum-maximum-speedgovernor.


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28

Minimum-maximum-speed governor

a Idle setting, b Full-load setting.1 Flyweights, 2 Engine-speed control lever, 3 Idle-speed adjusting screw, 4 Governor spring, 5 Intermediate spring, 6 Retaining pin, 7 Idle spring, 8 Start lever, 9 Tensioning lever, 10 Tensioning-leverstop, 11 Starting spring, 12 Control collar, 13 Full-load speed control, 14 Sliding sleeve, 15 Distributorplunger cutoff bore, 16 Distributor plunger.a Start and idle-spring travel, b Intermediate-spring travel, h1 Idle working stroke, h2 Full-load workingstroke, M2 fulcrum for 8 and 9.

1

1

M2

12

4

h1

a b

2

35

14

7

9

1110

13

h2

b

a6

8

1516

M2

Fig. 7

UM

K03

52Y

Injection timingIn order to compensate for the injectionlag and the ignition lag, as engine speed increases the timing device advances the distributor pump’s start of delivery referred to the engine’scrankshaft. Example (Fig. 1):Start of delivery (FB) takes place afterthe inlet port is closed. The high pres-sure then builds up in the pump which, as soon as the nozzle-opening pres-sure has been reached leads to the start of injection (SB). The periodbetween FB and SB is referred to as the injection lag (SV). The increasingcompression of the air-fuel mixture in thecombustion chamber then initiates theignition (VB). The period between SBand VB is the ignition lag (ZV). As soonas the cutoff port is opened again thepump pressure collapses (end of pumpdelivery), and the nozzle needle closesagain (end of injection, SE). This is followed by the end of combustion (VE).

AssignmentDuring the fuel-delivery process, theinjection nozzle is opened by a pressurewave which propagates in the high-pressure line at the speed of sound. Basically speaking, the time required forthis process is independent of enginespeed, although with increasing enginespeed the crankshaft angle betweenstart of delivery and start of injection also increases. This must becompensated for by advancing the start of delivery. The pressure wave’spropagation time is determined by thelength of the high-pressure line and the speed of sound which is approx. 1,500 m/s in diesel fuel. The intervalrepresented by this propagation time istermed the injection lag. In other words,the start of injection lags behind the startof delivery. This phenomena is thereason for the injector opening later(referred to the engine’s piston position)at higher engine speeds than at lowengine speeds. Following injection, theinjected fuel needs a certain time in

Injectiontiming

29

Curve of a working stroke at full load and at low speed (not drawn to scale).

FB Start of delivery, SB Start of injection,SV Injection lag, VB Start of combustion,ZV Ignition lag, SE End of injection,VE End of combustion.1 Combustion pressure, 2 Compression pressure,UT BDC,OT TDC.

BDC TDC BDC

TDC2 84 12 16-4-2-16 -12 -8

SV

0

100

200

300

400

bar

TDC

TDC

ZV

SV

FBSB

SEVE

Pum

p hi

gh p

ress

ure

pN

ozzl

e-ne

edle

lift

n DR

ate

of in

ject

ion

Q

0

0.1

0.2

0.3

mm

0

2

4

6

mm3

°cms

°cms ATDC°cms BTDCDegrees camshaft

Com

bust

ion-

cham

ber

pres

sure

bar

1

2

VB

FB SB SE

Plunger position h

Fig. 1

UM

K03

57E

order to atomize and mix with the air toform an ignitable mixture.This is termed the air-fuel mixturepreparation time and is independent of engine speed. In a diesel engine, thetime required between start of injectionand start of combustion is termed the ignition lag.The ignition lag is influenced by the diesel fuel’s ignition quality (defined bythe Cetane Number), the compressionratio, the intake-air temperature, and the quality of fuel atomization. As a rule, the ignition lag is in the order of 1 millisecond. This means that pre-suming a constant start of injection, thecrankshaft angle between start ofinjection and start of combustionincreases along with increasing enginespeed. The result is that combustion canno longer start at the correct point(referred to the engine-piston position).Being as the diesel engine’s mostefficient combustion and power can only be developed at a given crankshaft or

piston position, this means that the in-jection pump’s start of delivery must beadvanced along with increasing enginespeed in order to compensate for theoverall delay caused by ignition lag and injection lag. This start-of-deliveryadvance is carried out by the engine-speed-dependent timing device.

Timing device

Design and constructionThe hydraulically controlled timing de-vice is located in the bottom of thedistributor pump’s housing, at rightangles to the pump’s longitudinal axis(Fig. 2), whereby its piston is free to move in the pump housing. The housingis closed with a cover on each side.There is a passage in one end of thetiming device plunger through which thefuel can enter, while at the other end theplunger is held by a compression spring.The piston is connected to the roller ring


pumps

30

Distributor injection pump with timing device

1 Roller ring, 2 Roller-ring rollers, 3 Sliding block, 4 Pin, 5 Timing-device piston, 6 Cam plate, 7 Distributor plunger.

1 2 3 4 5 6 7

Fig. 2

UM

K03

54Y

through a sliding block and a pin so thatpiston movement can be converted torotational movement of the roller ring.

Method of operationThe timing-device piston is held in its initial position by the timing-device spring(Fig. 3a). During operation, the pressure-control valve regulates the fuel pressureinside the pump so that it is proportionalto engine speed. As a result, the engine-speed-dependent fuel pressure is ap-plied to the end of the timing-devicepiston opposite to the spring.As from about 300 min–1, the fuelpressure inside the pump overcomes thespring preload and shifts the timing-device piston to the left and with it thesliding block and the pin which engagesin the roller ring (Fig. 3b). The roller ringis rotated by movement of the pin, andthe relative position of the roller ring tothe cam plate changes with the resultthat the rollers lift the rotating cam plateat an earlier moment in time. In otherwords, the roller ring has been rotatedthrough a defined angle with respect to the cam plate and the distributor plunger. Normally, the maximum angle is 12 degrees camshaft (24 degreescrankshaft).

Injectiontiming

31

Timing device, method of operation

a Initial position, b Operating position. 1 Pump housing, 2 Roller ring, 3 Roller-ring rollers, 4 Pin, 5 Passage in timing-device piston, 6 Cover, 7 Timing-device piston, 8 Sliding block, 9 Timing-device spring.

1

2

3

4

5

6

789

a

b

Fig. 3

UM

K03

55Y

Add-on modulesand shutoff devices

Application

The distributor injection pump is built according to modular constructionprinciples, and can be equipped with a variety of supplementary (add-on) units (Fig. 1). These enable the implemen-tation of a wide range of adaptation possibilities with regard to optimization of engine torque, power output, fuel economy, and exhaust-gas composition.The overview provides a summary of

the add-on modules and their effectsupon the diesel engine. The schematic(Fig. 2) shows the interaction of the basic distributor pump and the variousadd-on modules.

Torque controlTorque control is defined as varying fuel delivery as a function of enginespeed in order to match it to the engine’s fuel-requirement characteristic.If there are special stipulations with regard to the full-load characteristic (optimization of exhaust-gas compo-sition, of torque characteristic curve, andof fuel economy), it may be necessary


pumps

32

Distributor injection pump with add-on modules

1 Cold-start accelerator,2 Manifold-pressure compensator.

1 2

Fig. 1

UM

K03

58Y

Add-onmodulesand shutoffdevices

33

Schematic of the VE distributor pump with mechanical/hydraulic full-load torque control

LDA Manifold-pressure compensator.Controls the delivery quantity as a function of the charge-air pressure.

HBA Hydraulically controlled torque control.Controls the delivery quantity as a function of the engine speed (not for pressure-charged engines with LDA).

LFB Load-dependent start of delivery.Adaptation of pump delivery to load. For reduction of noise and exhaust-gas emissions.

ADA Altitude-pressure compensator.Controls the delivery quantity as a function of atmospheric pressure.

KSB Cold-start accelerator.Improves cold-start behavior by changing the start of delivery.

GST Graded (or variable) start quantity.Prevents excessive start quantity during warm start.

TLA Temperature-controlled idle-speed increase.Improves engine warm-up and smooth running when the engine is cold.

ELAB Electrical shutoff device.

A Cutoff port, nactual Actual engine speed (controlled variable), nsetpoint Desired engine speed (reference variable), QF Delivery quantity, tM Engine temperature, tLU Ambient-air temperature, pL Charge-air pressure, pA Atmospheric pressure, pi Pump interior pressure.

1 Full-load torque control with governor lever assembly, 2 Hydraulic full-load torque control.

TLA GST

Control of injectedfuel quantity

Engine-speed control

LDAADA

ELAB HBA

High-pressurepump with distributor

Vane-type fuel-supply pump

Delivery-valveassembly

Timing device

LFB

1 2

A

KSB

tLU /tM nsetpoint Uon /Uoff pL /pA

ppi

nactualDrive

Fuel

Injectionnozzles QF

Add-on moduleBasic pump

tM

Fig. 2

UM

K03

59E

to install torque control. In other words,the engine should receive precisely theamount of fuel it needs. The engine’s fuel requirement first of all climbs as a function of engine speed and then levelsoff somewhat at higher speeds. The fuel-delivery curve of an injection pumpwithout torque control is shown in Fig. 3.As can be seen, with the same setting ofthe control collar on the distributorplunger, the injection pump deliversslightly more fuel at high speeds than itdoes at lower speeds. This is due to thethrottling effect at the distributor plunger’scutoff port. This means that if theinjection pump’s delivery quantity isspecified so that maximum-possibletorque is developed at low enginespeeds, this would lead to the enginebeing unable to completely combust theexcess fuel injected at higher speeds and smoke would be the result togetherwith engine overheat. On the other hand, if the maximum delivery quantity is specified so that it corresponds to the engine’s requirements at maximumspeed and full-load, the engine will not beable to develop full power at low enginespeeds due to the delivery quantitydropping along with reductions in enginespeed. Performance would be belowoptimum. The injected fuel quantity musttherefore be adjusted to the engine’s

actual fuel requirements. This is knownas “torque control”, and in the case of the distributor injection pump can beimplemented using the delivery valve, thecutoff port, or an extended governor-lever assembly, or the hydraulicallycontrolled torque control (HBA). Full-loadtorque control using the governor leverassembly is applied in those cases inwhich the positive full-load torque controlwith the delivery valve no longer suffices,or a negative full-load torque control hasbecome necessary.

Positive torque controlPositive torque control is required onthose injection pumps which deliver toomuch fuel at higher engine revs. The delivery quantity must be reduced as engine speed increases.

Positive torque control using the delivery valveWithin certain limits, positive torque control can be achieved by means of thedelivery valve, for instance by fitting asofter delivery-valve spring.

Positive torque control using the cutoff portOptimization of the cutoff port’s dimen-sions and shape permit its throttling effectto be utilized for reducing the deliveryquantity at higher engine speeds.

Positive torque control using thegovernor lever assembly (Fig. 4a) The decisive engine speed for start oftorque control is set by preloading thetorque-control springs. When this speedis reached, the sliding-sleeve force (FM)and the spring preload must be in equilibrium, whereby the torque-controllever (6) abuts against the stop lug (5) of the tensioning lever (4). The free endof the torque-control lever (6) abutsagainst the torque-control pin (7).If engine speed now increases, the sliding-sleeve force acting against thestarting lever (1) increases and the common pivot point (M4) of starting lever and torque-control lever (6) changes its position. At the same time,


pumps

34

Fuel-delivery characteristics, with andwithout torque control

a Negative, b Positive torque control.1 Excess injected fuel,2 Engine fuel requirement, 3 Full-load delivery with torque control,Shaded area:Full-load delivery without torque control.

Engine speed n

Del

iver

y qu

antit

y Q

F

min–1

mm3

stroke

ab

1 2 3

Fig. 3

UM

K03

60E

the torque-control lever tilts around thestop pin (5) and forces the torque-control pin (7) in the direction of the stop, while the starting lever (1) swivelsaround the pivot point (M2) and forces thecontrol collar (8) in the direction of re-duced fuel delivery. Torque control ceasesas soon as the torque-control-pin collar(10) abuts against the starting lever (1).

Negative torque controlNegative torque control may be necessary in the case of engines whichhave black-smoke problems in the lower speed range, or which must generate specific torque characteristics.Similarly, turbocharged engines alsoneed negative torque control when themanifold-pressure compensator (LDA)has ceased to be effective. In this case,the fuel delivery is increased along withengine speed (Fig. 3).

Negative torque control using thegovernor lever assembly (Fig. 4b)Once the starting spring (9) has beencompressed, the torque-control lever (6) applies pressure to the tensioning lever (4) through the stop lug (5). Thetorque-control pin (7) also abuts againstthe tensioning lever (4). If the sliding-sleeve force (FM) increases due to risingengine speed, the torque-control lever

presses against the preloaded torque-control spring. As soon as the slid-ing-sleeve force exceeds the torque-control spring force, the torque-control lever (6) is forced in the direction of thetorque-control-pin collar. As a result, thecommon pivot point (M4) of the startinglever and torque-control lever changes itsposition. At the same time the startinglever swivels around its pivot point (M2) and pushes the control collar (8) in the direction of increased delivery.Torque control ceases as soon as thetorque-control lever abuts against the pincollar.

Negative torque control using hydrauli-cally controlled torque control HBAIn the case of naturally aspirated dieselengines, in order to give a special shapeto the full-load delivery characteristic as a function of engine speed, a form of torque control can be applied which is similar to the LDA (manifold-pressurecompensator).Here, the shift force developed by thehydraulic piston is generated by thepressure in the pump interior, which inturn depends upon pump speed. In contrast to spring-type torque control,within limits the shape of the full-loadcharacteristic can be determined by acam on a sliding pin.


35

Torque control using the governor-lever assembly

a Positive torque control, b Negative torque control. 1 Starting lever, 2 Torque-control spring, 3 Governor spring, 4 Tensioning lever, 5 Stop lug, 6 Torque-control lever, 7 Torque-control pin, 8 Control collar, 9 Starting spring, 10 Pin collar, 11 Stop point, M2 Pivot point for 1 and 4, M4 Pivot point for 1 and 6, FM Sliding-sleeve force, ∆ s Control-collar travel.

4

M4

26

7

b

3 4

2

59

1110

1M2

8

FM

1

M45

67M2

8

a

FM

∆ s ∆ s

Fig. 4

UM

K03

62Y

Manifold-pressurecompensationExhaust-gas turbochargingBecause it increases the mass of air inducted by the engine, exhaust turbo-charging boosts a diesel engine’s poweroutput considerably over that of a nat-urally aspirated diesel engine, with littleincrease in dimensions and enginespeeds. This means that the brake horsepower can be increased corre-sponding to the increase in air mass (Figure 6). In addition, it is often possible to also reduce the specific fuel con-sumption. An exhaust-gas turbochargeris used to pressure-charge the dieselengine (Fig. 5).

With an exhaust turbocharger, theengine’s exhaust gas, instead of simplybeing discharged into the atmosphere, is used to drive the turbocharger’s turbine at speeds which can exceed100,000 min–1. Turbine and turbochargercompressor are connected through ashaft. The compressor draws in air,compresses it, and supplies it to the engine’s combustion chambers underpressure, whereby not only the air pressure rises but also the airtemperature. If temperatures becomeexcessive, some form of air cooling(intercooling) is needed between theturbocharger and the engine intake.


pumps

36 UM

K03

65Y

Fig. 5: Diesel engine with exhaust-gas turbo-charger

Manifold-pressure compensator(LDA)The manifold-pressure compensator(LDA) reacts to the charge-air pressuregenerated by the exhaust-gas turbo-charger, or the (mechanical) super-charger, and adapts the full-load deliv-ery to the charge-air pressure (Figs. 6and 7).

AssignmentThe manifold-pressure compensator(LDA) is used on pressure-charged diesel engines. On these engines the injected fuel quantity is adapted to the engine’s increased air charge (due topressure-charging). If the pressure-charged diesel engine operates with areduced cylinder air charge, the in-


37

Power and torque comparison, naturally aspi-rated and pressure-charged engines

kW

min–1

Nm

Pe

Md

Engine speed n

Tor

que

Md

Pow

er P

e

Naturally aspirated enginePressure-charged engine

Distributor injection pump with manifold-pressure compensator (LDA)

1 Governor spring, 2 Governor cover, 3 Reverse lever, 4 Guide pin, 5 Adjusting nut, 6 Diaphragm, 7 Compression spring, 8 Sliding pin, 9 Control cone, 10 Full-load adjusting screw, 11 Adjusting lever, 12 Tensioning lever, 13 Starting lever, 14 Connection for the charge-air, 15 Vent bore. M1 pivot for 3.

6

8

7

9

10

14

15

111213

5

4

M1

123

Fig. 6Fig. 7

UM

K03

67E

UM

K03

64Y

jected fuel quantity must be adapted to the lower air mass. This is performedby the manifold-pressure compensatorwhich, below a given (selectable)charge-air pressure, reduces the full-loadquantity.

Design and constructionThe LDA is mounted on the top of thedistributor pump (Fig. 7). In turn, the topof the LDA incorporates the connectionfor the charge-air and the vent bore. The interior of the LDA is divided into two separate airtight chambers by a dia-phragm to which pressure is applied by a spring. At its opposite end, the spring is held by an adjusting nut with which the spring’s preload is set. This serves to match the LDA’s response point to the charge pressure of the exhaustturbocharger. The diaphragm is con-nected to the LDA’s sliding pin which has a taper in the form of a control cone.This is contacted by a guide pin whichtransfers the sliding-pin movements tothe reverse lever which in turn changesthe setting of the full-load stop. The initialsetting of the diaphragm and the slidingpin is set by the adjusting screw in the topof the LDA.

Method of operationIn the lower engine-speed range thecharge-air pressure generated by theexhaust turbocharger and applied to thediaphragm is insufficient to overcome thepressure of the spring. The diaphragmremains in its initial position. As soon asthe charge-air pressure applied to thediaphragm becomes effective, the dia-phragm, and with it the sliding pin andcontrol cone, shift against the force of thespring. The guide pin changes itsposition as a result of the control cone’svertical movement and causes thereverse lever to swivel around its pivotpoint M1 (Fig. 7). Due to the force exertedby the governor spring, there is a non-positive connection between tensioninglever, reverse lever, guide pin, andsliding-pin control cone. As a result, thetensioning lever follows the reverselever’s swivelling movement, causing the

starting lever and tensioning lever toswivel around their common pivot pointthus shifting the control collar in thedirection of increased fuel delivery. Fueldelivery is adapted in response to theincreased air mass in the combustionchamber (Fig. 8). On the other hand,when the charge-air pressure drops, the spring underneath the diaphragmpushes the diaphragm upwards, and withit the sliding pin. The compensationaction of the governor lever mechanismnow takes place in the reverse directionand the injected fuel quantity is adaptedto the change in charge pressure. Shouldthe turbocharger fail, the LDA reverts toits initial position and the engine operatesnormally without developing smoke. Thefull-load delivery with charge-air pressureis adjusted by the full-load stop screwfitted in the governor cover.


pumps

38

Charge-air pressure: Operative range

a Turbocharger operation, b Normally aspirated operation.p1 Lower charge-air pressure,p2 Upper charge-air pressure.

Charge-air pressure p

p1 p2 mbar

a

b

mm3/stroke LDA operative

range

Inje

cted

fuel

qu

antit

y Q

e

Fig. 8

UM

K03

68E

Load-dependentcompensationDepending upon the diesel engine’s load,the injection timing (start of delivery)must be adjusted either in the “advance”or “retard” direction.

Load-dependent start of delivery(LFB)

AssignmentLoad-dependent start of delivery is de-signed so that with decreasing load (e.g., change from full-load to part-load), with the control-lever position un-changed, the start of delivery is shifted in the “retard” direction. And when en-gine load increases, the start of delivery(or start of injection) is shifted in the“advance” direction. These adjustmentslead to “softer” engine operation, andcleaner exhaust gas at part- and full-load.

Design and constructionFor load-dependent injection timing,modifications must be made to the gov-ernor shaft, sliding sleeve, and pumphousing. The sliding sleeve is providedwith an additional cutoff port, and the governor shaft with a ring-shapedgroove, a longitudinal passage and twotransverse passages (Fig. 9). The pumphousing is provided with a bore so that a connection is established from theinterior of the pump to the suction side ofthe vane-type supply pump.

Method of operationAs a result of the rise in the supply-pump pressure when the engine speedincreases, the timing device adjusts thestart of delivery in the “advance” direc-tion. On the other hand, with the drop inthe pump’s interior pressure caused bythe LFB it is possible to implement a (relative) shift in the “retard” direction.This is controlled by the ring-shapedgroove in the governor shaft and the sliding-sleeve’s control port. The control


39

Design and construction of the governor assembly with load-dependent start of delivery (LFB)

1 Governor spring, 2 Sliding sleeve, 3 Tensioning lever, 4 Start lever, 5 Control collar,6 Distributor plunger, 7 Governor shaft, 8 Flyweights.M2 Pivot point for 3 and 4.

3

4

M2

5

1 2

6

87

Fig. 9

UM

K03

69Y

lever is used to input a given full-loadspeed. If this speed is reached and theload is less than full load, the speed increases even further, because with arise in speed the flyweights swiveloutwards and shift the sliding sleeve. Onthe one hand, this reduces the deliveryquantity in line with the conventional governing process. On the other, the sliding sleeve’s control port is opened bythe control edge of the governor-shaftgroove. The result is that a portion of thefuel now flows to the suction side throughthe governor shaft’s longitudinal andtransverse passages and causes apressure drop in the pump’s interior.This pressure drop results in the timing-device piston moving to a new position.This leads to the roller ring being turnedin the direction of pump rotation so thatstart of delivery is shifted in the “retard”direction. If the position of the controllever remains unchanged and the loadincreases again, the engine speed drops.The flyweights move inwards and thesliding sleeve is shifted so that its control

port is closed again. The fuel in the pumpinterior can now no longer flow throughthe governor shaft to the suction side,and the pump interior pressure increasesagain. The timing-device piston shiftsagainst the force of the timing-device spring and adjusts the roller ringso that start of delivery is shifted in the“advance” direction (Fig. 10).

Atmospheric-pressurecompensation

At high altitudes, the lower air density reduces the mass of the inducted air, and the injected full-load fuel quantitycannot burn completely. Smoke resultsand engine temperature rises. To pre-vent this, an altitude-pressure compen-sator is used to adjust the full-load quantity as a function of atmosphericpressure.

Altitude-pressure compensator(ADA)

Design and constructionThe construction of the ADA is identicalto that of the LDA. The only differencebeing that the ADA is equipped with ananeroid capsule which is connected to a vacuum system somewhere in the vehicle (e.g., the power-assisted brakesystem). The aneroid provides a con-stant reference pressure of 700mbar(absolute).

Method of operationAtmospheric pressure is applied to theupper side of the ADA diaphragm. Thereference pressure (held constant by the aneroid capsule) is applied to thediaphragm’s underside. If the atmo-spheric pressure drops (for instance when the vehicle is driven in the mountains), the sliding bolt shifts verti-cally away from the lower stop and, similar to the LDA, the reverse levercauses the injected fuel quantity to bereduced.


pumps

40

Sliding-sleeve positions in the load-dependent injection timing (LFB)

a Start position (initial position),b Full-load position shortly before the control port is opened,c Control port opened, pressure reduction in pump interior.1 Longitudinal bore in the governor shaft,2 Governor shaft, 3 Sliding-sleeve control port,4 Sliding-sleeve, 5 Governor-shaft transverse passage, 6 Control edge of the groove in the governor shaft, 7 Governor-shaft transversepassage.

5 76

4321

a

b

c

Fig. 10

UM

K03

70Y

Cold-start compensation

The diesel engine’s cold-start charac-teristics are improved by fitting a cold-start compensation module which shiftsthe start of injection in the “advance”direction. Operation is triggered either by the driver using a bowden cable in the cab, or automatically by means of a temperature-sensitive advance mech-anism (Fig. 11).

Mechanical cold-start accelerator(KSB) on the roller ring

Design and constructionThe KSB is attached to the pump housing, the stop lever being connectedthrough a shaft to the inner lever on which a ball pin is eccentrically mounted. The ball pin’s head extendsinto the roller ring (a version is availablein which the advance mechanism en-gages in the timing-device piston). Thestop lever’s initial position is defined by the stop itself and by the helical coiled spring. Attached to the top of the stop lever is a bowden cable whichserves as the connection to the manualor to the automatic advance mechanism.The automatic advance mechanism ismounted on the distributor pump, where-as the manual operating mechanism is in the driver’s cab (Fig. 12).

Method of operationAutomatically and manually operatedcold-start accelerators (KSB) differ onlywith regard to their external advancemechanisms. The method of operation isidentical. With the bowden cable notpulled, the coil spring pushes the stoplever up against the stop. Ball pin androller ring are in their initial position. Theforce applied by the bowden cable


41

Mechanical cold-start accelerator (KSB), advance mechanism with automatic operation (cold-start position)

1 Clamp,2 Bowden cable,3 Stop lever,4 Coil spring,5 KSB advance lever,6 Control device

sensitive to the temperature of the coolant and the surroundings.

Mechanical cold-start accelerator (KSB)engaging in roller ring (cold-start position)

1 Lever, 2 Access window, 3 Ball pin,4 Longitudinal slot, 5 Pump housing, 6 Roller ring,7 Roller in the roller ring, 8 Timing-device piston, 9 Torque-control pin, 10 Sliding block. 11 Timing-device spring, 12 Shaft, 13 Coil spring.

1 2

3 4 5 6

1

5

6

7

8

2 3 4

91011

1213

Fig. 11

Fig. 12

UM

K03

73Y

UM

K03

72Y

causes the stop lever, the shaft, the innerlever and the ball pin, to swivel andchange the roller ring’s setting so that thestart of delivery is advanced. The ball pinengages in a slot in the roller ring, whichmeans that the timing-device pistoncannot rotate the roller ring any further inthe “advance” direction until a givenengine speed has been exceeded.In those cases in which the KSB is triggered by the driver from the cab (timing-device KSB), independent of theadvance defined by the timing device (a),an advance of approx. 2.5° camshaft ismaintained (b), as shown in Fig. 13. Withthe automatically operated KSB, thisadvance depends upon the enginetemperature or ambient temperature.The automatic advance mechanism usesa control device in which a temperature-sensitive expansion element converts theengine temperature into a stroke move-ment. The advantage of this method isthat for a given temperature, the optimumstart of delivery (or start of injection) isalways selected.There are a number of different leverconfigurations and operating mecha-nisms in use depending upon thedirection of rotation, and on which sidethe KSB is mounted.

Temperature-controlled idle-speed increase (TLA)The TLA is also operated by the controldevice and is combined with the KSB.Here, when the engine is cold, the ballpin at the end of the elongated KSB advance lever presses against the en-gine-speed control lever and lifts it awayfrom the idle-speed stop screw. The idlespeed increases as a result, and roughrunning is avoided. When the engine haswarmed up, the KSB advance lever abutsagainst its stop and, as a result, theengine-speed control lever is also upagainst its stop and the TLA is no longereffective (Fig. 14).

Hydraulic cold-start acceleratorAdvancing the start of injection by shifting the timing-device piston has only limited applications. In the case ofthe hydraulic start-of-injection advance,the speed-dependent pump interior pressure is applied to the timing-device piston. In order to implement a start-of-injection advance, referred to theconventional timing-device curve, thepump interior pressure is increasedautomatically. To do so, the automaticcontrol of pump interior pressure ismodified through a bypass in thepressure-holding valve.


pumps

42

Mechanical cold-start accelerator (automatically controlled) with temperature-dependent idle-speed increase

1 Engine-speed control lever, 2 Ball pin, 3 KSB advance lever, 4 Stop.

Effect of the mechanical cold-start accelerator (KSB)

a Timing-device advance,b Minimum advance (approx. 2.5° camshaft).

00

Pump speed p

2.5°

a

b

Inje

ctio

n-tim

ing

adva

nce

°cms

min–1

12

34

Fig. 13

UM

K03

74E

Fig. 14

UM

K03

77Y

Design and constructionThe hydraulic cold-start acceleratorcomprises a modified pressure-controlvalve, a KSB ball valve, a KSB controlvalve, and an electrically heated ex-pansion element.

Method of operationThe fuel delivered by the fuel-supplypump is applied to one of the timing device piston’s end faces via the injectionpump’s interior. In accordance with theinjection pump’s interior pressure, thepiston is shifted against the force of its spring and changes the start-of-injection timing. Pump interiorpressure is determined by a pressure-control valve which increases pumpinterior pressure along with increasingpump speed and the resulting rise inpump delivery (Fig. 15).There is a restriction passage in thepressure-control valve’s plunger in orderto achieve the pressure increase needed for the KSB function, and the resulting advance curve shown as a dotted line in Fig. 16. This ensures thatthe same pressure is effective at thespring side of the pressure-control valve. The KSB ball-type valve has acorrespondingly higher pressure leveland is used in conjunction with thethermo-element both for switching-onand switching-off the KSB function, aswell as for safety switchoff. Using an

adjusting screw in the integrated KSBcontrol valve, the KSB function can beset to a given engine speed. The fuelsupply pump pressure shifts the KSBcontrol valve’s plunger against the force of a spring. A damping restriction isused to reduce the pressure fluctu-ations at the control plunger. The KSBpressure characteristic is controlled by its plunger’s control edge and the sectionat the valve holder. The KSB function is adapted by correct selection of theKSB control valve’s spring rate and itscontrol section. When the warm engine is started, the expansion element hasalready opened the ball valve due to theprevailing temperature.


43

Effect of the hydraulic cold-start accelerator (KSB)

1 Injection-timing advance.

Hydraulic cold-start accelerator (KSB)

11 Pressure-control valve, 12 Valve plunger, 13 Restriction passage, 14 Internal pressure, 15 Fuel-supply pump, 16 Electrically heated

expansion element,17 KSB ball valve,18 Pressureless fuel return, 19 KSB control valve,

adjustable, 10 Timing device.

��

1

2

67

8

910

34

5

1

Pump speed p

Inje

ctio

n-tim

ing

adva

nce

°cms

min–1

Fig. 15

UM

K11

95Y

Fig. 16

UM

K03

79E

Engine shutoff

AssignmentThe principle of auto-ignition as appliedto the diesel engine means that the engine can only be switched off byinterrupting its supply of fuel.Normally, the mechanically governeddistributor pump is switched off by a solenoid-operated shutoff (ELAB). Onlyin special cases is it equipped with a mechanical shutoff device.

Electrical shutoff device (ELAB)The electrical shutoff (Fig. 17) using thevehicle’s key-operated starting switch iscoming more and more to the forefrontdue to its convenience for the driver.On the distributor pump, the solenoidvalve for interrupting the fuel supply isinstalled in the top of the distributor head. When the engine is running, thesolenoid is energized and the valvekeeps the passage into the injectionpump’s high-pressure chamber open(armature with sealing cone has pulledin). When the driving switch is turned to “OFF”, the current to the solenoid winding is also cut, the magnetic fieldcollapses, and the spring forces the armature and sealing cone back onto the valve seat again. This closes the inlet passage to the high-pressure chamber, the distributor-pump plungerceases to deliver fuel, and the enginestops. From the circuitry point of view,there are a variety of different possi-bilities for implementing the electricalshutoff (pull or push solenoid).

Mechanical shutoff deviceOn the injection pump, the mechanicalshutoff device is in the form of a lever assembly (Fig. 18). This is located in the governor cover and comprises anouter and an inner stop lever. The outerlever is operated by the driver from insidethe vehicle (for instance by means ofbowden cable). When the cable is pulled, both levers swivel around theircommon pivot point, whereby the inner

stop lever pushes against the start leverof the governor-lever mechanism. Thisswivels around its pivot point M2 andshifts the control collar to the shutoff position. The distributor plunger’s cutoffport remains open and the plunger delivers no fuel.


pumps

44

Mechanical shutoff device

1 Outer stop lever, 2 Start lever, 3 Control collar, 4 Distributor plunger, 5 Inner stop lever, 6 Tensioning lever, 7 Cutoff port. M2 Pivot point for 2 and 6.

Electrical shutoff device (pull solenoid)

1 Inlet passage, 2 Distributor plunger, 3 Distributor head, 4 Push or pull solenoid, 5 High-pressure chamber.

1

3

4

5

2

5

6

M2

7

4

3

1

2

Fig. 17

Fig. 18

UM

K03

82Y

UM

K03

80Y

Testing and calibration

Injection-pump test benchesPrecisely tested and calibrated injectionpumps and governors are the prerequisitefor achieving the optimum fuel-con-sumption/performance ratio and compli-ance with the increasingly stringentexhaust-gas legislation. And it is at thispoint that the injection-pump test benchbecomes imperative. The most importantframework conditions for the test benchand for the testing itself are defined in ISO-Standards which, in particular, placevery high demands upon the rigidity anduniformity of the pump drive.The injection pump under test is clamped to the test-bench bed and con-nected at its drive end to the test-benchcoupling. Drive is through an electricmotor (via hydrostatic or manually-switched transmission to flywheel and

coupling, or with direct frequency control).The pump is connected to the bench’scalibrating-oil supply via oil inlet andoutlet, and to its delivery measuringdevice via high-pressure lines. Themeasuring device comprises calibratingnozzles with precisely set openingpressures which inject into the bench’smeasuring system via spray dampers. Oiltemperature and pressure is adjusted inaccordance with test specifications.There are two methods for fuel-deliverymeasurement. One is the so-calledcontinuous method. Here, a precisiongear pump delivers per cylinder and unit oftime, the same quantity of calibrating-oilas the quantity of injected fuel. The gearpump’s delivery is therefore a measure ofdelivery quantity per unit of time. A com-puter then evaluates the measurementresults and displays them as a bar charton the screen. This measuring method is very accurate, and features goodreproducibility (Fig. 1).The other method for fuel-delivery mea-surement uses glass measuring gradu-ates. The fuel to be measured is at first directed past the graduates and back tothe tank with a slide. When the specifiednumber of strokes has been set on thestroke-counting mechanism the mea-surement starts, and the slide opens andthe graduates fill with oil. When the setnumber of strokes has been com-pleted, the slider cuts off the flow of oilagain. The injected quantity can be readoff directly from the graduates.

Engine tester for diesel enginesThe diesel-engine tester is necessary for the precise timing of the injectionpump to the engine. Without opening thehigh-pressure lines, this tester measuresthe start of pump delivery, injection timing, and engine speeds. A sensor is clamped over the high-pressure line to cylinder 1, and with the stroboscopic timing light or the TDC sensor for detect-ing crankshaft position, the testercalculates start of delivery and injection timing.

Testing andcalibration

45

Continuous injected-fuel-quantity measuring system

1 Calibrating-oil tank, 2 Injection pump, 3 Calibrating nozzle, 4 Measuring cell, 5 Pulse counter, 6 Display monitor.

��

M

1

4

5

2

3

6

Fig. 18

UW

T00

59Y

Nozzles and nozzle holdersThe injection nozzles and their respec-tive nozzle holders are vitally importantcomponents situated between the in-lineinjection pump and the diesel engine. Their assignments are as follows:– Metering the injection of fuel,– Management of the fuel,– Defining the rate-of-discharge curve,– Sealing-off against the combustion

chamber.Considering the wide variety of com-bustion processes and the different formsof combustion chamber, it is necessarythat the shape, “penetration force”, andatomization of the fuel spray injected bythe nozzle are adapted to the prevailingconditions. This also applies to the injec-tion time, and the injected fuel quantityper degree camshaft.Since the design of the nozzle-holdercombination makes maximum use ofstandardized components and assem-blies, this means that the required flexi-bility can be achieved with a minimum ofcomponents. The following nozzles andnozzle holders are used with in-line injec-tion pumps:– Pintle nozzles (DN..) for indirect-injec-

tion (IDI) engines, and – Hole-type nozzles (DLL../DLSA..) for

direct-injection (DI) engines,– Standard nozzle holders (single-

spring nozzle holders), with and with-out needle-motion sensor, and

– Two-spring nozzle holders, with andwithout needle-motion sensor.

Pintle nozzles

ApplicationPintle nozzles are used with in-line in-jection pumps on indirect-injection en-gines (pre-chamber and whirl-chamberengines).In this type of diesel engine, the air/fuelmixture is for the most part formed by theair’s vortex work. The injected fuel sprayserves to support this mixture-formationprocess.

The following types of pintle nozzle areavailable:– Standard pintle nozzles (Fig. 1),– Throttling pintle nozzles, and– Flat-cut pintle nozzles (Fig. 2).

Design and constructionAll pintle nozzles are of practically identi-cal design, the only difference being inthe pintle’s geometry:

Standard pintle nozzleOn the standard pintle nozzle, the nozzleneedle is provided with a pintle whichextends into the injection orifice of thenozzle body in which it is free to movewith a minimum of play. The injectionspray can be matched to the engine’srequirements by appropriate choice ofdimensions and pintle designs.


pumps

46

Standard pintle nozzle

1 Lift stop surface, 2 Ring groove, 3 Needle guide,4 Nozzle-body shaft, 5 Pressure chamber, 6 Pressure shoulder, 7 Seat lead-in, 8 Inlet port, 9 Nozzle-body shoulder, 10 Nozzle-body collar, 11 Sealing surface, 12 Pressure shaft, 13 Pressure-pin contact surface.

1

2

4

5

6

8

9

10

11

12

13

7

3

Fig. 1

UM

K13

90Y

Throttling pintle nozzleThe throttling pintle nozzle is a pintlenozzle with special pintle dimensions.The special pintle design serves to definethe shape of the rate-of-discharge curve.When the nozzle needle lifts it first of allopens a small annular gap so that only asmall amount of fuel is injected (throttlingeffect). As needle lift increases (due to pressurerise), the spray orifice is opened increas-ingly until the major portion of the injec-tion (main injection) takes place towardsthe end of needle lift. Since the pressurein the combustion chamber rises lesssharply, this shaping of the rate-of-injec-tion curve leads to “softer” combustion.This results in quieter combustion in thepart-load range. In other words, it ispossible to shape the required rate-of-discharge curve by means of the pintleshape, the characteristic of the nozzleneedle’s spring, and the throttling gap.

Flat-cut pintle nozzleThis nozzle’s pintle has a ground surfacewhich opens a flow cross-section in addi-tion to the annular gap when the pintleopens (only slight needle lift). The result-ing increased flow volume prevents de-posits forming in this flow channel. This isthe reason why flat-cut pintle nozzlescoke-up far less, and any coking whichdoes take place is more uniform. Theannular gap between spray orifice andthrottling pintle is very small (less than 10 µm). Very often, the flat-cut pintle sur-face is parallel to the nozzle-needle axis.Referring to Fig. 3, with an additionalinclined cut on the pintle, the gradient ofthe injected-fuel-quantity curve’s flat por-tion can be increased so that the tran-sition to full nozzle opening is lessabrupt. Specially shaped pintles, such asthe “radius” or “profile surface” types, canbe applied to match the flow curve toengine-specific requirements. Part-loadnoise and vehicle driveability are bothimproved as a result.

Nozzles and nozzleholders

47

Flat-cut pintle nozzle

a Side view, b Front view.1 Needle seat, 2 Nozzle-body floor, 3 Throttling pintle, 4 Flat cut, 5 Injection orifice, 6 Profiled pintle, 7 Total overlap, 8 Cylindrical overlap, 9 Nozzle-body seat.

1

a

b

2

6

9

7

8

345

Flow quantity as a function of needle lift andnozzle version

1 Throttling pintle nozzle,2 Throttling pintle nozzle with inclined cut on

pintle (flat-cut pintle nozzle)

l /h

300

200

100

0

Flo

w q

uant

ity

0 0.2

2 1

0.4Needle lift

0.6 0.8 mm

Fig. 2

UM

K13

91Y

Fig. 3

UM

K13

97E

Hole-type nozzles

ApplicationHole-type nozzles are used with in-lineinjection pumps on direct-injection en-gines. One differentiates between:– Sac-hole, and – Seat-hole nozzles.

The hole-type nozzles also vary accord-ing to their size:– Type P with 4 mm needle diameter,

and– Type S with 5 and 6 mm needle dia-

meters.

Design and constructionThe spray holes are located on the en-velope of a spray cone (Fig. 4). The num-ber of spray holes and their diameter de-pend upon:– The injected fuel quantity,– The combustion-chamber shape, and– The air swirl in the combustion cham-

ber.

The input edges of the spray holes canbe rounded by hydro-erosive (HE) ma-chining.

At those points where high flow ratesoccur (spray-hole entrance), the abrasiveparticles in the hydro-erosive (HE) me-dium cause material loss. This so-called HE-rounding process canbe applied to both sac-hole and seat-holenozzles, whereby the target is:– Prevent in advance the edge wear

caused by abrasive particles in the fueland/or

– Reduce the flow tolerance.

For low hydrocarbon emissions, it ishighly important that the volume filledwith fuel (residual volume) below theedge of the nozzle-needle seat is kept toa minimum. Seat-hole nozzles are there-fore used.

Designs

Sac-hole nozzleThe spray holes of the sac-hole nozzle(Fig. 5) are arranged in the sac hole. In the case of a round nozzle tip (Fig. 6a),depending upon design the spray holesare drilled mechanically or by means ofelectrochemical machining (e.c.m.).Sac-hole nozzles with conical tip (Figs.6b and 6c) are always drilled using e.c.m.Sac-hole nozzles are available – With cylindrical, and – Conical sac holesin a variety of different dimensions.

Sac-hole nozzle with cylindrical sac holeand round tip (Fig. 6a):This nozzle’s sac hole has a cylindricaland a semispherical portion, and permitsa high level of design freedom withrespect to – Number of spray holes, – Spray-hole length, and – Injection angle.

The nozzle tip is semispherical, andtogether with the shape of the sac hole,ensures that the spray holes are ofidentical length.


pumps

48

Spray cone

γ Spray-cone offset angle, d Spray cone.

γ

δ

Fig. 4

UM

K14

02Y

Sac-hole nozzle with cylindrical sac holeand conical tip (6b):This type of nozzle is used exclusivelywith spray-hole lengths of 0.6 mm. Thetip’s conical shape enables the wallthickness to be increased between thethroat radius and the nozzle-body seatwith an attending improvement of nozzle-tip strength.

Sac-hole nozzle with conical sac holeand conical tip (Fig. 6c):Due to the conical shape of this nozzle’ssac hole, its volume is less than that of anozzle with cylindrical sac hole. Thevolume is between that for a seat-holenozzle and a sac-hole nozzle with cylin-drical sac hole. In order to achieve uni-form tip-wall thickness, the tip’s conicaldesign corresponds to that of the sachole.


49

Sac-hole nozzle

1 Pressure shaft, 2 Needle-lift stop face,3 Inlet passage, 4 Pressure shoulder,5 Needle shaft, 6 Nozzle tip,7 Nozzle-body shaft, 8 Nozzle-body shoulder,9 Pressure chamber, 10 Needle guide,11 Nozzle-body collar, 12 Locating hole,13 Sealing surface, 14 Pressure-pin contact surface.

Sac-hole shapes

a Cylindrical sac hole with round tip,b Cylindrical sac hole with conical tip,c Conical sac hole with conical tip.1 Shoulder, 2 Seat entrance, 3 Needle seat, 4 Needle tip, 5 Injection orifice, 6 Injection-orifice entrance, 7 Sac hole, 8 Throat radius, 9 Nozzle-tip cone, 10 Nozzle-body seat, 11 Damping cone.

567891011

4

23

1

a

b

c

Fig. 5U

MK

1403

YFig. 6

UM

K16

50Y

Seat-hole nozzleIn order to minimise the residual volume– and therefore the HC emissions – thestart of the spray hole is located in theseat taper, and with the nozzle closed it iscovered almost completely by the nozzleneedle. This means that there is no directconnection between the sac hole and thecombustion chamber (Figs. 7 and 8). Thesac-hole volume here is much lower thanthat of the sac-hole nozzle. Compared tosac-hole nozzles, seat-hole nozzles havea much lower loading limit and are there-fore only manufactured as Size P with aspray-hole length of 1 mm.For reasons of strength, the nozzle tip isconically shaped. The spray holes arealways formed using e.c.m. methods.

Standard nozzle holders

Assignments and designsNozzle holders with hole-type nozzles incombination with a radial-piston distrib-utor injection pump are used on DIengines. With regard to the nozzle holders, onedifferentiates between – Standard nozzle holders (single-

spring nozzle holders) with and with-out needle-motion sensor, and

– Two-spring nozzle holders, with andwithout needle-motion sensor.

ApplicationThe nozzle holders described here havethe following characteristics:– Cylindrical external shape with diame-

ters between 17 and 21 mm,– Bottom-mounted springs (leads to low

moving masses),– Pin-located nozzles for direct-injection

engines, and – Standardised components (springs,

pressure pin, nozzle-retaining nut)make combinations an easy matter.

DesignThe nozzle-and-holder assembly is com-posed of the injection nozzle and thenozzle holder.The nozzle holder comprises the follow-ing components (Fig. 9):– Nozzle-holder body,– Intermediate element,– Nozzle-retaining nut,– Pressure pin,– Spring,– Shim, and – Locating pins.

The nozzle is centered in the nozzle bodyand fastened using the nozzle-retainingnut. When nozzle body and retaining nutare screwed together, the intermediateelement is forced up against the sealingsurfaces of nozzle body and retainingnut. The intermediate element serves asthe needle-lift stop and with its locatingpins centers the nozzle in the nozzle-holder body.


pumps

50

Seat-hole nozzle

Seat-hole nozzle: Tip shape

Fig. 7

UM

K14

08Y

UM

K14

07Y

Fig. 8

The nozzle-holder body contains the– Pressure pin,– Spring, and – Shim.

The spring is centered in position by thepressure pin, whereby the pressure pin isguided by the nozzle-needle’s pressureshaft.The nozzle is connected to the injectionpump’s high-pressure line via the nozzle-holder feed passage, the intermediateelement, and the nozzle-body feed pas-sage. If required, an edge-type filter canbe installed in the nozzle holder.

Method of operationThe nozzle-holder spring applies pres-sure to the nozzle needle through thepressure pin. The spring’s initial tensiondefines the nozzle’s opening pressurewhich can be adjusted using a shim. On its way to the nozzle seat, the fuel pas-ses through the nozzle-holder inlet pas-sage, the intermediate element, and thenozzle nody. When injection takes place,the nozzle needle is lifted by the injectionpressure and fuel is injected through theinjection orifices into the combustionchamber. Injection terminates as soon asthe injection pressure drops far enough forthe nozzle spring to force the nozzleneedle back onto its seat.

Two-spring nozzle holders

ApplicationThe two-spring nozzle holder is a fur-ther development of the standard nozzleholder, and serves to reduce combustionnoise particularly in the idle and part-loadranges.

DesignThe two-spring nozzle holder featurestwo springs located one behind the other.At first, only one of these springs has aninfluence on the nozzle needle and assuch defines the initial opening pressure.The second spring is in contact with astop sleeve which limits the needle’sinitial stroke.


51

Standard nozzle holder

1 Edge-type filter, 2 Inlet passage,3 Pressure pin, 4 Intermediate element,5 Nozzle-retaining nut, 6 Wall thickness,7 Nozzle, 8 Locating pins, 9 Spring,10 Shim, 11 Leak-fuel passage,12 Leak-fuel connection thread,13 Nozzle-holder body, 14 Connection thread,15 Sealing cone.

1

2

3

4

5

6

7

8

9

10

11

12

14

13

15

Fig. 9

UM

K14

13Y

When strokes take place in excess of theinitial stroke, the stop sleeve lifts and bothsprings have an effect upon the nozzleneedle (Fig. 10).

Method of operationDuring the actual injection process, thenozzle needle first of all opens an initialamount so that only a small volume offuel is injected into the combustionchamber. Along with increasing injection pressurein the nozzle holder though, the nozzleneedle opens completely and the mainquantity is injected (Fig. 11). This 2-stagerate-of-discharge curve leads to “softer”combustion and to a reduction in noise.

Nozzle holders with needle-motion sensor

ApplicationThe start-of-injection point is an impor-tant parameter for optimum diesel-engineoperation. For instance, its evaluationpermits load and speed-dependent injec-tion timing, and/or control of the exhaust-gas recirculation (EGR) rate.


pumps

52

Two-spring nozzle holder for direct-injection(DI) engines

1 Nozzle-holder body, 2 Shim,3 Spring 1, 4 Pressure pin,5 Guide element, 6 Spring 2,7 Pressure pin, 8 Spring seat,9 Shim, 10 Intermediate element,

11 Stop sleeve, 12 Nozzle needle,13 Nozzle-retaining nut, 14 Nozzle body.

h1 Initial stroke,h2 Main stroke.

1

2

3

4

5

6

7

891011

12

13

14

h2

h1

Comparison of needle-lift curves

a Standard nozzle holder (single-spring nozzleholder),b Two-spring nozzle holder.h1 Initial stroke, h2 Main stroke.

0.4

mm

0.2

0

0 1Time

Noz

zle-

need

le li

ft

2 ms

0.4

mmb

a

0.2

0

h 2h 1

UM

K14

23-1

Y

Fig. 10

UM

K14

22E

Fig. 11

This necessitates a nozzle holder withneedle-motion sensor (Fig. 13) whichoutputs a signal as soon as the nozzleneedle opens.

DesignWhen it moves, the extended pressurepin enters the current coil. The degree to which it enters the coil(overlap length “X” in Fig. 14) determinesthe strength of the magnetic flux.

Method of operationThe magnetic flux in the coil changes asa result of nozzle-needle movement andinduces a signal voltage which is propor-tional to the needle’s speed of movementbut not to the distance it has travelled.This signal is processed directly in anevaluation circuit (Fig. 12). When a given threshold voltage is ex-ceeded, this serves as the signal to the evaluation circuit for the start of injection.


53

Needle-motion sensor in a two-spring nozzleholder for direct-injection (DI) engines

1 Adjusting pin, 2 Terminal,3 Current coil, 4 Pressure pin,5 Spring seat.X Overlap length.

2

1

X 3

45

Two-spring nozzle holder with needle-motionsensor for direct-injection (DI) engines

1 Nozzle-holder body, 2 Needle-motion sensor,3 Spring 1, 4 Guide element, 5 Spring 2,6 Pressure pin, 7 Nozzle-retaining nut.

1

2

3

4

5

6

7

UM

K15

88D

Comparison between a needle-lift curve andthe corresponding signal-voltage curve of theneedle-motion sensor

aNeedle-lift-sensor signal

Needle-motion-sensor signal

Start-of-injectionsignal

Thesholdvoltage

Nee

dle

lift

Sig

nal v

olta

ge

b

°cks

Fig. 12

UM

K14

27E

Fig. 14U

MK

1529

YFig. 13

UM

K15

88Y

Mechanical diesel-engine speed control(mechanical governing) registers a widevariety of different operating statuses and permits high-quality A/F mixtureformation. The Electronic Diesel Control (EDC)takes additional requirements into ac-count. By applying electronic measure-ment, highly-flexible electronic data pro-cessing, and closed control loops withelectric actuators, it is able to processmechanical influencing variables which itwas impossible to take into account withthe previous purely mechanical control(governing) system. The EDC permits data to be exchangedwith other electronic systems in the

vehicle (for instance, traction controlsystem (TCS), and electronic transmis-sion-shift control). In other words, it canbe integrated completely into the overallvehicle system.

System blocksThe electronic control is divided intothree system blocks (Fig. 1):1. Sensors for registering operatingconditions. A wide variety of physicalquantities are converted into electricalsignals.

2. Electronic control unit (ECU) withmicroprocessors which processes the in-


pumps,VE-EDC

54

Electronic Diesel Control (EDC): System blocks

Needle-motion sensor

Temperature sensors(water, air, fuel)

Sensor forcontrol-collar position

Air-flow sensor

Engine-speed sensor

Vehicle-speed sensor

Sensors

Setpoint generators

Glow control unit

Transducer withEGR valve

Fuel-injection pump

ActuatorsECU

Micro-pro-cessor

Maps

Start ofinjection

Startingcontrol

EGR

Engineshutoff

Injectedfuel quantity

Atmospheric-pressuresensor

Diagnosis

Diagnosis displayAccelerator-pedal sensor

Speed-selection lever

Electronically-controlledaxial-piston distributor fuel-injection pumps VE-EDC

Fig. 1

UM

K04

67E

formation in accordance with specificcontrol algorithms, and outputs corre-sponding electrical signals.3. Actuators which convert the ECU’s electrical output signals into mechanicalquantities.

ComponentsSensorsThe positions of the accelerator and thecontrol collar in the injection pump areregistered by the angle sensors. Theseuse contacting and non-contactingmethods respectively. Engine speed andTDC are registered by inductive sensors.Sensors with high measuring accuracyand long-term stability are used for pres-sure and temperature measurements.The start of injection is registered by asensor which is directly integrated in the nozzle holder and which detects the startof injection by sensing the needle move-ment (Figs. 2 and 3).

Electronic control unit (ECU)The ECU employs digital technology. Themicroprocessors with their input andoutput interface circuits form the heart of the ECU. The circuitry is completed by the memory units and devices for the conversion of the sensor signals into computer-compatible quantities. TheECU is installed in the passenger com-partment to protect it from external in-fluences.There are a number of different mapsstored in the ECU, and these come intoeffect as a function of such parametersas: Load, engine speed, coolant tem-perature, air quantity etc. Exacting de-mands are made upon interference immunity. Inputs and outputs are short-circuit-proof and protected against spu-rious pulses from the vehicle electricalsystem. Protective circuitry and me-chanical shielding provide a high level of EMC (Electro-Magnetic Compatibility)against outside interference.

Electroniccontrol fordistributorpumps

55

Sensor signals

1 Untreated signal from the needle-motion sensor(NBF),

2 Signal derived from the NBF signal, 3 Untreated signal from the engine-speed signal,4 Signal derived from untreated engine-speed

signal,5 Evaluated start-of-injection signal.

Nozzle-and-holder assembly withneedle-motion sensor (NBF)

1 Setting pin, 2 Sensor winding, 3 Pressure pin,4 Cable, 5 Plug.

1

2

3

4

5

3

1

2

4

5

Fig. 2 Fig. 3

UM

K04

66Y

UM

K04

68Y

Solenoid actuator for injectedfuel quantity controlThe solenoid actuator (rotary actuator)engages with the control collar through a shaft (Fig. 4). Similar to the mechani-cally governed fuel-injection pump, thecutoff ports are opened or closed de-pending upon the control collar’s posi-tion. The injected fuel quantity can beinfinitely varied between zero and maximum (e.g., for cold starting). Usingan angle sensor (e.g., potentiometer),the rotary actuator’s angle of rotation,and thus the position of the control col-lar, are reported back to the ECU andused to determine the injected fuelquantity as a function of engine speed.When no voltage is applied to the ac-tuator, its return springs reduce the in-jected fuel quantity to zero.

Solenoid valve for start-of-injection control The pump interior pressure is depen-dent upon pump speed. Similar to themechanical timing device, this pressureis applied to the timing-device piston (Fig. 4). This pressure on the timing-device pressure side is modulated by aclocked solenoid valve.With the solenoid valve permanentlyopened (pressure reduction), start of injection is retarded, and with it fully closed (pressure increase), start of in-jection is advanced. In the intermediaterange, the on/off ratio (the ratio of solenoid valve open to solenoid valveclosed) can be infinitely varied by theECU.


pumps,VE-EDC

56

1

2

3

4

56

Distributor injection pump for electronic diesel control

1 Control-collar position sensor, 2 Solenoid actuator for the injected fuel quantity, 3 Electromagnetic shutoff valve, 4 Delivery plunger, 5 Solenoid valve for start-of-injection timing, 6 Control collar.

Fig. 4

UM

K04

64Y

Closed control loops (Fig. 5)

Injected fuel quantityThe injected fuel quantity has a decisiveinfluence upon the vehicle’s starting, idling, power output and driveability characteristics, as well as upon its par-ticulate emissions. For this reason, thecorresponding maps for start quantity,idle, full load, accelerator-pedal charac-teristic, smoke limitation, and pump characteristic, are programmed into theECU. The driver inputs his or her re-quirements regarding torque or enginespeed through the accelerator sensor.Taking into account the stored map data, and the actual input values from the sensors, a setpoint is calculated forthe setting of the rotary actuator in thepump. This rotary actuator is equipped

with a check-back signalling unit and ensures that the control collar is cor-rectly set.

Start of injectionThe start of injection has a decisive in-fluence upon starting, noise, fuel con-sumption, and exhaust emissions. Start-of-injection maps programmed into theECU take these interdependencies intoaccount. A closed control loop is used to guarantee the high accuracy of thestart-of-injection point. A needle-motionsensor (NBF) registers the actual start ofinjection directly at the nozzle andcompares it with the programmed start of injection (Figs. 2 and 3). Deviationsresult in a change to the on/off ratio of the timing-device solenoid valve, whichcontinues until deviation reaches zero.


57

Closed control loop of the electronic diesel control (EDC)

Q Air-flow quantity, nact Engine speed (actual), pA Atmospheric pressure, sset Control-collar signal (setpoint), sact Control-collar position (actual), sv set Timing-device signal (setpoint), tK Fuel temperature, tL Intake-air temperature, tM Engine temperature, ti act Start of injection (actual).

n actualt

Fuel

ELABOn/Off Cruise

control

Acceleratorpedal

EGRcontrol

Injected-fuel-quan-tity control

Start-of-injectioncontrol

Injectionnozzle

Start-quantitycontrol

ECU

Engine and vehicle

Operator’spanel

Air

Exhaustemissions

EGR valveM

t i actual

pA

t L

Ql

sv setpoint

sactual

t K

ssetpoint

VE-pump

Vehiclespeedsensor

UM

K04

65E

Fig. 5

This clocked solenoid valve is used tomodulate the positioning pressure at thetiming-device piston, and this results inthe dynamic behavior being comparableto that obtained with the mechanicalstart-of-injection timing.Because during engine overrun (with injection suppressed) and engine start-ing there are either no start-of-injectionsignals available, or they are inadequate,the controller is switched off and anopen-loop-control mode is selected. Theon/off ratio for controlling the solenoidvalve is then taken from a control map inthe ECU.

Exhaust-gas recirculation (EGR)EGR is applied to reduce the engine’stoxic emissions. A defined portion of theexhaust gas is tapped-off and mixed with the fresh intake air. The engine’s intake-air quantity (which is proportionalto the EGR rate) is measured by an air-flow sensor and compared in the ECUwith the programmed value for the EGRmap, whereby additional engine and injection data for every operating pointare taken into account.In case of deviation, the ECU modifiesthe triggering signal applied to an electropneumatic transducer. This thenadjusts the EGR valve to the correct EGR rate.

Cruise controlAn evaluated vehicle-speed signal iscompared with the setpoint signal input-ted by the driver at the cruise-control panel. The injected fuel quantity is thenadjusted to maintain the speed selectedby the driver.

Supplementary functionsThe electronic diesel control (EDC) provides for supplementary functionswhich considerably improve the ve-hicle’s driveability compared to themechanically governed injection pump.

Active anti-buck dampingWith the active anti-buck damping (ARD) facility, the vehicle’s unpleasantlongitudinal oscillations can be avoided.

Idle-speed controlThe idle-speed control avoids engine“shake” at idle by metering the appro-priate amount of fuel to each individualcylinder.

Safety measures

Self-monitoringThe safety concept comprises the ECU’s monitoring of sensors, actuators,and microprocessors, as well as of thelimp-home and emergency functions provided in case a component fails. Ifmalfunctions occur on important com-ponents, the diagnostic system not onlywarns the driver by means of a lamp inthe instrument panel but also provides afacility for detailed trouble-shooting in the workshop.

Limp-home and emergency functionsThere are a large number of sophisti-cated limp-home and emergency func-tions integrated in the system. For in-stance if the engine-speed sensor fails, a substitute engine-speed signal is generated using the interval between the start-of-injection signals from theneedle-motion sensor (NBF). And if theinjected-fuel quantity actuator fails, aseparate electrical shutoff device (ELAB) switches off the engine. Thewarning lamp only lights up if importantsensors fail. The Table below shows theECU’s reaction should certain faults occur.

Diagnostic outputA diagnostic output can be made by means of diagnostic equipment, whichcan be used on all Bosch electronic automotive systems. By applying a special test sequence, it is possible tosystematically check all the sensors and their connectors, as well as thecorrect functioning of the ECU’s.


pumps,VE-EDC

58

Advantages

– Flexible adaptation enables optimi-zation of engine behavior and emissioncontrol.– Clear-cut delineation of individual func-tions: The curve of full-load injected fuelquantity is independent of governorcharacteristic and hydraulic configuration.– Processing of parameters which pre-viously could not be performed me-chanically (e.g., temperature-correctionof the injected fuel quantity characteris-tic, load-independent idle control).– High degree of accuracy throughoutcomplete service life due to closed con-trol loops which reduce the effects of tolerances.– Improved driveability: Map storageenables ideal control characteristics andcontrol parameters to be established independent of hydraulic effects. Theseare then precisely adjusted during theoptimisation of the complete engine/vehicle system. Bucking and idle shakeno longer occur.– Interlinking with other electronic sys-tems in the vehicle leads the way towards making the vehicle safer, morecomfortable, and more economical, aswell as increasing its level of environ-mental compatibility (e.g., glow systemsor electronic transmission-shift control). The fact that mechanical add-on units nolonger need to be accomodated, leads to marked reductions in the amount ofspace required for the fuel-injectionpump.

Engine shutoff

As already stated on Page 40, the prin-ciple of auto-ignition as applied to thediesel engine means that the engine can only be switched off by interruptingits supply of fuel.When equipped with Electronic DieselControl (EDC), the engine is switched off by the injected-fuel quantity actuator(Input from the ECU: Injected fuel quantity = Zero). As already dealt with,the separate electrical engine shutoffdevice serves as a standby shutoff incase the actuator should fail.

Electrical shutoff deviceThe electrical shutoff device is operatedwith the “ignition key” and is above allused to provide the driver with a higherlevel of sophistication and comfort. On the distributor fuel-injection pump, the solenoid valve for interrupting thesupply of fuel is fitted in the top of thedistributor head. With the diesel enginerunning, the inlet opening to the high-pressure chamber is held open by the en-ergized solenoid valve (the armature withsealing cone is pulled in). When the “igni-tion switch” is turned to “Off”, the powersupply to the solenoid is interrupted andthe solenoid de-energized. The springcan now push the armature with sealingcone onto the valve seat and close off theinlet opening to the high-pressure cham-ber so that the distributor plunger can nolonger deliver fuel.


59

Failure Monitoring Reaction Warning Diagnosticof lamp output

Correction Signal range Reduce injected●sensors fuel quantity

System- Signal range Limp-home sensors or emergency ● ●

function (graded)Computer Program runtime Limp-home

(self-test) or emergency ● ●function

Fuel-quantity Permanent Engine shutoff ● ●actuator deviation

Table 1. ECU reactions

Prospects

On the electronically-controlled distrib-utor pumps of the future, the electricalactuator mechanism with control collarfor fuel metering will be superseded by ahigh-pressure solenoid valve. This willpermit an even higher degree of flexibilityin the fuel metering and in the variabilityof the start of injection.

Design and constructionThis pump is of modular design. The field-proven distributor injection pump can thusbe combined with a new electronicallycontrolled fuel-metering system (Fig. 1).Basically speaking, the solenoid-valve-controlled distributor pump’s dimensions,installation conditions, and drivetrain in-cluding the pump’s cam drive, are identi-cal to those of the conventional distributorpump. The most important new compo-nents are:– Angle-of-rotation sensor (in the form

of an incremental angle/time system[IWZ]) which is located in the injectionpump on the driveshaft between thevane-type supply pump and the rollerring,

– Electronic pump ECU, which is mount-ed as a compact unit on the top side ofthe pump and connected to the engineECU,

– High-pressure solenoid valve, installedin the center of the distributor head.

With regard to its installation and hydrau-lic control, the timing device with pulsevalve is identical to the one in the pre-vious electronically-controlled distributorpump.

Components

Angle-of-rotation sensorAngle-of-rotation detection uses thefollowing components: Sensor, sensorretaining ring on the driveshaft, and thetrigger wheel with a given tooth pitch.Detection is based upon the signalsgenerated by the sensor. The pulses generated by the sensor areinputted to the ECU where they are pro-cessed by an evaluation circuit. The factthat the sensor is coupled to the pump’sroller ring ensures the correct assign-ment of the angular increment to theposition of the cam when the roller ring isrotated by the timing device.

Pump ECUThe pump ECU is mounted on the upperside of the pump and uses hybrid tech-niques. In addition to the mechanicalloading with which it is confronted in the vehicle's under-hood environment,the pump must also fulfill the followingassignments:– Data exchange with the separately

mounted engine ECU via the serialbus system,

– Evaluation of the signal from theangle-of-rotation sensor (IWZ),

– Triggering of the high-pressure sol-enoid valve,

– Triggering of the timing device.

Maps are stored in the pump ECU whichnot only take into account the settingpoints for the particular vehicle applica-tion and certain engine characteristics,but also permit the plausibility of the re-ceived signals to be checked. In addition,they form the basis for defining a numberof different computational values.


pumps,VE-MV

60

Solenoid-valve-controlledaxial-piston distributor fuel-injection pumps VE-MV

High-pressure solenoid valveThe high-pressure solenoid valve mustfulfill the following assignments:– Large valve cross-section for efficient

filling of the high-pressure chamber,even at very high rotational speeds,

– Low weight (low moving masses), tokeep the loading of the parts to a mini-mum,

– Short switching times to guaranteehigh-precision fuel metering, and

– Magnetic forces which are powerfulenough to cope with the high pressures.

The high-pressure solenoid valve is com-prised of:– The valve body,– The valve needle, and– The electromagnet with electrical

connection to the pump ECU.The magnetic circuit is concentric to thevalve. This fact permits a compact as-sembly comprising high-pressure sol-enoid valve and distributor head.

Method of operation

PrinciplePressure generation in the solenoid-valve-controlled distributor injectionpump is based on the same principle asthat in the conventional electronically-controlled VE pump.

Fuel supply and deliveryVia the distributor head and the openedhigh-pressure solenoid valve, the vane-type supply pump delivers fuel to thehigh-pressure chamber at a pressure ofapprox. 12 bar.No fuel is delivered when the high-pres-sure solenoid valve is de-energized(open). The valve’s instant of closingdefines the injection pump’s start ofdelivery. This can be located at thebottom dead center (BDC) of the cam oron the rise portion of the cam slope.Similarly, the valve’s instant of openingdefines the pump’s end of delivery. Thelength of time the valve is closed deter-mines the injected fuel quantity.The high pressure generated in the high-pressure chamber (the fuel from thesupply pump is compressed by the axialpiston when this is forced up by the camplate riding over the rollers of the rollerring) opens the delivery valve and thefuel is forced through the pressure line to the injection nozzle in the nozzleholder. Injection pressure at the nozzle is 1400 bar. Excess fuel is directed backto the tank through return lines. Since there are no additional intake portsavailable, if the high-pressure solenoidvalve should fail, fuel injection stops. This prevents uncontrolled “racing” of theengine.


61

Solenoid-valve-controlled axial-piston distributor fuel-injection pump (section)

Fig. 1

UM

K12

05Y

Since leakage and heat losses reduce thepressure and the temperature of the A/Fmixture at the end of the compressionstroke, the cold diesel engine is more diffi-cult to start and the mixture more difficult toignite than it is when hot. These facts make it particularly important that start-assistsystems are used. The minimum startingtemperature depends upon the enginetype. Pre-chamber and swirl-chamberengines are equipped with a sheathed-element glow plug (GSK) in the auxiliarycombustion chamber which functions as a“hot spot”. On small direct-injection (DI)engines, this “hot spot” is located on thecombustion chamber’s periphery. Large DItruck engines on the other hand have thealternative of using air preheating in theintake manifold (flame start) or special,easily ignitable fuel (Start Pilot) which issprayed into the intake air. Today, the start-assist systems use sheathed-elementglow plugs practically without exception.

Sheathed-element glow plugThe sheathed-element glow plug’s tubularheating element is so firmly pressed intothe glow-plug shell that a gas-tight seal is

formed. The element is a metal tube whichis resistant to both corrosion and hot gases,and which contains a heater (glow) elementembedded in magnesium-oxide powder(Fig. 1). This heater element comprisestwo series-connected resistors: the heaterfilament in the glow-tube tip, and the con-trol filament. Whereas the heater filamentmaintains virtually constant electrical resistance regardless of temperature, thecontrol filament is made of material with apositive temperature coefficient (PTC). Onnewer-generation glow plugs (GSK2), itsresistance increases even more rapidlywith rising temperature than was the casewith the conventional S-RSK glow plug.This means that the newer GSK2 glowplugs are characterized by reaching thetemperature needed for ignition far morequickly (850°C in 4s). They also feature alower steady-state temperature (Fig. 2)which means that the glow plug’s tem-perature is limited to a non-critical level.The result is that the GSK2 glow plug can remain on for up to 3 minutes following engine start. This post-glow feature improves both the warm-up andrun-up phases with considerable im-provements in noise and exhaust-gasemissions.

Start-assist systems

62

Sheathed-element glow plug GSK2

1 Electrical connector terminal, 2 Insulating washer, 3 Double gasket, 4 Terminal pin, 5 Glow-plug shell, 6 Heater seal, 7 Heater and control filament, 8 Glow tube, 9 Filling powder.

987542 31 6

UM

S06

85-1

Y

Start-assist systems

Fig. 1

Flame glow plug

The flame glow plug burns fuel to heatthe intake air. Normally, the injection system’s supply pump delivers fuel to theflame plug through a solenoid valve. Theflame plug’s connection fitting is pro-vided with a filter, and a metering devicewhich permits passage of precisely the correct amount of fuel appropriate to the particular engine. This fuel thenevaporates in an evaporator tube sur-rounding the tubular heating element and mixes with the intake air. The resultingmixture ignites on the 1,000°C heatingelement at the flame-plug tip.

Glow control unit

For triggering the glow plugs, the glowcontrol unit (GZS) is provided with a power relay and a number of electronicswitching blocks. These, for instance,control the glow duration of the glowplugs, or have safety and monitoring functions. Using their diagnosis func-tions, more sophisticated glow controlunits are also able to recognise the failure of individual glow plugs and inform the driver accordingly. Multipleplugs are used as the control inputs to the ECU. In order to avoid voltagedrops, the power supply to the glowplugs is through suitable threaded pinsor plugs.

Functional sequence

The diesel engine’s glow plug and starterswitch, which controls the preheat and starting sequence, functions in a similar manner to the ignition and starting switch on the spark-ignition (SI)engine. Switching to the “Ignition on”position starts the preheating processand the glow-plug indicator lamp lightsup. This extinguishes to indicate that the glow plugs are hot enough for theengine to start, and cranking can begin.In the following starting phase, the drop-lets of injected fuel ignite in the hot, com-pressed air. The heat released as a resultleads to the initiation of the combustionprocess (Fig. 3).In the warm-up phase following a suc-cessful start, post-heating contributes to faultless engine running (no misfiring)and therefore to practically smokelessengine run-up and idle. At the sametime, when the engine is cold, pre-heating reduces combustion noise. Aglow-plug safety switchoff prevents battery discharge in case the enginecannot be started.The glow-control unit can be coupled to the ECU of the Electronic Diesel Control (EDC) so that information available in the EDC control unit can beapplied for optimum control of the glowplugs in accordance with the particularoperating conditions. This is yet anotherpossibility for reducing the levels of bluesmoke and noise.

Sheathed-element glow plugs,Flame glow plugs

63

Sheathed-element glow plugs:Temperature-time diagram

1 S-RSK, 2 GSK2.

Typical preheating sequence

1 Glow-plug and starter switch, 2 Starter, 3 Glow-plug indicator lamp, 4 Load switch, 5 Glow plugs, 6 Self-sustained engine operation, tv Pre-heating time, tS Ready to start, tN Post-heating time.

tV tS tN

1

2

3

4

56 Time t

0 10 20 30 40 50650

750

850

950

1,050

1,150

s

°C

1

2

Time t

Tem

pera

ture

Fig. 2

UM

S06

88E

Fig. 3

UM

S06

67-1

E

(4.0)

1 987 722 164

KH/PDI-04.99-En

The Program Order NumberGasoline-engine management

Emission Control (for Gasoline Engines) 1 987 722 102Gasoline Fuel-Injection System K-Jetronic 1 987 722 159Gasoline Fuel-Injection System KE-Jetronic 1 987 722 101Gasoline Fuel-Injection System L-Jetronic 1 987 722 160Gasoline Fuel-Injection System Mono-Jetronic 1 987 722 105Ignition 1 987 722 154Spark Plugs 1 987 722 155M-Motronic Engine Management 1 987 722 161ME-Motronic Engine Management 1 987 722 178Diesel-engine managementDiesel Fuel-Injection: An Overview 1 987 722 104Diesel Accumulator Fuel-Injection SystemCommon Rail CR 1 987 722 175Diesel Fuel-Injection SystemsUnit Injector System / Unit Pump System 1 987 722 179Radial-Piston Distributor Fuel-InjectionPumps Type VR 1 987 722 174Diesel Distributor Fuel-Injection Pumps VE 1 987 722 164Diesel In-Line Fuel-Injection Pumps PE 1 987 722 162Governors for Diesel In-Line Fuel-Injection Pumps 1 987 722 163Automotive electrics/Automotive electronicsAlternators 1 987 722 156Batteries 1 987 722 153Starting Systems 1 987 722 170Electrical Symbols and Circuit Diagrams 1 987 722 169Lighting Technology 1 987 722 176Safety, Comfort and Convenience Systems 1 987 722 150Driving and road-safety systemsCompressed-Air Systems for CommercialVehicles (1): Systems and Schematic Diagrams 1 987 722 165Compressed-Air Systems for CommercialVehicles (2): Equipment 1 987 722 166Brake Systems for Passenger Cars 1 987 722 103ESP Electronic Stability Program 1 987 722 177

Automotive electric/electronic systems

Safety, Comfort and

Convenience Systems


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Automotive Electric/Electronic Systems

Lighting Technology


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Æ

Vehicle safety systems for passenger cars

ESP Electronic Stability Program


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Æ

Engine management for diesel engines

Radial-Piston Distributor

Fuel-injection Pumps Type VR


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Electronic engine management for diesel engines

Diesel Acumulator Fuel-Injection

System Common Rail


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Engine management for spark-ignition engines

Emission Control


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Gasoline-engine managementME-Motronic

Engine Management


æ

ÆEngine management for spark-ignition engines

Spark Plugs


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Æ

Brake systems for passenger cars

Brake Systems


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Download - Diesel distributor fuel-injection pumps

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