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VVT iVariable Valve Timed intelligent systemVVT iVariable Valve Timed intelligent system

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Abstract:Modern Trends in IC Engines & Automobiles VVT-i:

As we know the current global scenario, there is only a little amount of crude oil left onthe earth. This crude oil can hold things together just for another 30 years. So, it is the need ofthe hour to devise a bail-out for the human race from this blow of energy crisis.The introduction starts by acknowledging Rudolf Diesel and Karl Benz for the inventionof the internal combustion engine, which made some of man s most cherished dreams,

becomereality; the aircraft, the motor car, the submarine, the tank and many other inventions before theycould be born in their practical form. However now, the internal combustion engine (ICE) is onthe way out and electric motors are on the way in, but ICEs have been around for

so long that weshould be careful about announcing their demise. They're going to stick around a

while longer,and so it's very important to make them as efficient and clean as possible.

Since we have to manage with the ICE for much more time, it would be wise to make itcleaner & powerful. In other words, engines must be made more efficient. From the day ICEswere invented, the work of improvisation started. Various researches were conducted. Finally,the best method to improve it, was a lot on the chemistry part, i.e., on the fuel. Among the othermethods, include cylinder de-activation, turbo-charging etc.; the best method which can be veryefficiently used and is being used is the variable valve timing intelligent (VVT-i) system.Variable valve timing and lift allows the valves to open and close to allow air

and fuel toenter cylinders and for the products of combustion to exit. Different valve timings produce differentresults (more power, better fuel economy). This allows a smaller displacement engine toproduce more peak power, so it allows for downsizing and fuel savings.

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Chapter 1:

Introduction

1.1. Defining the VVT i:Variable valve timing and lift allows the valves to open and close to allow airand fuel toenter cylinders and for the products of combustion to exit. Different valve timings produce differentresults (more power, better fuel economy). This allows a smaller displacement engine toproduce more peak power, so it allows for downsizing and fuel savings.1.2. The growth of IC engine:Petroleum fuels are very widely used in many engines. From automobile engines to

therocket, power is provided by the fossil fuels. The most common prime mover powered by fuel isthe internal combustion engine. The internal combustion engine has been with usfor a long time-since about 1885. Familiar layouts soon appeared with, for example, six cylinders seen as earlyas 1902. Multiple valves per cylinder, double overhead cam-shafts, super-chargers, turbochargers,

and fuel injection are all well and truly before the World War 2 period. Thoughtheywere convincing in the design level, only on paper, still they gathered no heat.

After that, itmight be said that there was no very novel and lasting engine concept until theoil crisis andstricter anti-pollution laws started a movement towards greater engine efficiency.1.3. The search for improvement:In the quest for better & improved ICEs, researchers, inventors, scientists have

stumbledupon different types of ICEs. However, they still work basically on the same principle as they

ever did. But the old 4-cylinder engines which produced about 20 horsepower, have evolved intoones which can generate up to 250 hp while being cleaner and burning less fuel.So, the top fiveor the best five improvements that could have ever happened in the field of automotive enginetechnology are the following:

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6. Clean Fuel:The best method of cutting on emissions and obtaining good power is by using fuel of thebest quality. Various advances such as the availability of ultra low sulfur diesel fuel, better catalystsand particulate matter traps, better control over combustion are making diesel enginescleaner, have made it possible. Diesel engines are certainly far from perfect, but they have inherentlybetter thermal efficiency than gasoline engines, and they are usually more durable. Anotherbenefit is that they can run on biodiesel.. Direct injection:Before direct injection, the fuel was mixed with air in the car's intake manifold. Now,with direct injection, the fuel is mixed with air inside the cylinder, allowingfor better controlover the amount of fuel used, and variations depending on demand (acceleration vs. cruising).This makes the engine more fuel efficient.. Cylinder deactivation:The name says it all. ICEs with this feature can simply deactivate some cylinder

s whenless power is required, temporarily reducing the total volume of the engine cylinders and soburning less fuel. This feature is found on V6 and V8 engines.. Turbochargers:Turbochargers increase the pressure inside cylinders, cramming more air and allowingcombustion to generate more power. This doesn't make the engine more economicalin itself, butsince a smaller displacement engine can generate more peak power, you can more easily downsizeand save there.The 5th best method is the incorporation of a Variable Valve Timed (VVT) system,

whichis explained further in the report.

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Chapter 2:

Variable valve timing

2.1. Introduction:Variable valve timing, or VVT, is a generic term for an automobile piston engine

technology.VVT allows the lift / duration / timing of the intake or exhaust valves (or both) to bechanged while the engine is in operation. Two-stroke engines use a Power valve system to getsimilar results to VVT.Fig 2.1: The VVT system found in the Honda K20Z3Piston engines normally use poppet valves for intake and exhaust. These are driven bycams on a camshaft. The cams open the valves for a certain amount of time during

each intakeand exhaust cycle. The timing of the valve opening and closing is also important. The camshaft isdriven by the crankshaft through timing belts, gears or chains. The profile, orposition and shapeof the cam lobes on the shaft, is optimized for a certain engine RPM, and this trade off normally

limits low-end torque or high-end power. VVT allows the cam profile to change, which results ingreater efficiency and power. At high engine speeds, it provides the engine with

large amounts ofair, which is the major advantage. The peer pressure to meet environmental goals

and fuel efficiencystandards is forcing car manufacturers to turn to VVT as a solution.

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2.2. History:The earliest variable valve timing systems came into existence in the 19th century onsteam engines. Stephenson valve gear, as used on early steam locomotives supported variablecutoff. Admission and exhaust cutoff were decoupled with the development of theCorliss valve.These were widely used in constant speed variable load stationary engines. As poppet valvescame into use, simplified valve gear using a camshaft came into use.

s first passenger car diesel engine that features a variable valve timing system.

With such engines, variable cutoff could be achieved with variable profile camsthat wereshifted along the camshaft by the governor. The earliest Variable valve timing systems on inter-nal combustion engines were on the Lycoming R-7755 hyper engine, which had cam profilesthat were selectable by the pilot. This allowed the pilot to choose full take off and pursuit poweror economical cruising speed, depending on what was needed.

Fiat was the first auto manufacturer to patent a functional automotive variablevalve tim-ing system which included variable lift. Developed by Giovanni Torazza in the late 1960s, thesystem used hydraulic pressure to vary the fulcrum of the cam followers (US Patent 3,641,988).In September 1975, General Motors (GM) patented a system intended to vary valvelift. AlfaRomeo was the first manufacturer to use a variable valve timing system in production cars (USPatent 4,231,330). Honda's REV motorcycle employed on the Japanese market-only HondaCBR400F in 1983 provided a technology base for VTEC. The 2008 Dodge Viper uses M

echa-dyne's concentric camshaft assembly to help boost power. In 2009 Porsche introduced an en-hanced version of VarioCam Plus on its 911 GT3 including the previous variable valve timingand two stage valve lift on the intake valves but with additional variable timing of the exhaustvalve. In 2010, Mitsubishi developed and started mass production of its 4N13 1.8

L DOHC I4world'2.3. VARIABLE VALVE TIMING INTELLIGENT (VVT-i) SYSTEM:VVT-i system is a computer controlled mechanism that continually varies the timing for

opening and closing the intake valves in accordance with the vehicle's operatingconditions. TheVVT-i system is designed to control the intake camshaft within a range of 50 (ofcrankshaft

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Angle) to provide valve timing optimally suited to the engine condition .This improves the torquein all the speed ranges as well as fuel economy and reducing exhaust emissions.This systemcontrols the intake camshaft valve timing so as to obtain balance between the engine output, fuelconsumption & emission control performance.

2.3.1. VVT-I control system:Fig: 2.2 VVT-I control system

The Variable Valve Timing (VVT) system includes the Electronic Control Module(ECM), Oil Control Valve (OCV) and VVT controller. The ECM sends a target duty-cycle con-trol signal to the OCV. This control signal regulates the oil pressure suppliedto theVVT controller. Camshaft timing control is performed according to engine operatingconditions such as the intake air volume, throttle valve position and engine coolant temperature.The ECM controls the OCV, based on the signals transmitted by several sensors. TheVVT controller regulates the intake camshaft angle using oil pressure through th

e OCV. As aresult, the relative positions of the camshaft and crankshaft are optimized, theengine torque and

fuel economy improve, and the exhaust emissions decrease under overall driving condi-tions. The ECM detects the actual intake valve timing using signals from the camshaft andcrankshaft position sensors, and performs feedback control.

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10Fig 2.3 Electronic Control Module (ECM):The ECM optimizes the valve timing using the VVT system to control the intake camshaft.The VVT system includes the ECM, the OCV and the VVT controller. The ECM sends a target duty-cycle control signal to the OCV. This control signal regulates the oil pressure suppliedto the VVT controller. The VVT controller can advance or retard the intake camshaft.After the ECM sends the target duty-cycle signal to the OCV, the ECM monitorsthe OCV current to establish an actual duty-cycle. The ECM determines the existenceof a malfunction and sets the DTC when the actual duty- cycle ratio varies fromthe target dutycycleratio.3.3.2. Important parts. VVT-i Controller:This controller consists of the housing driven from the timing chain and the vane coupledwith the intake camshaft. The oil pressure sent from the advance or retard sidepath at the intakecamshaft causes rotation in the VVT-i controller vane circumferential direction

to vary the intakevalve timing continuously. When the engine is stopped, the intake camshaft willbe in the mostretarded state to ensure start-ability. When hydraulic pressure is not applied to the VVT-i con

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11troller immediately after the engine has been started, the lock pin locks the movement of theVVT-i controller to prevent a knocking noise.Fig 2.5 Different parts of VVT i. Camshaft Timing Oil Control Valve:This camshaft timing oil control valve controls the spool valve position in accordancewith the duty-cycle control from the ECM. This allows hydraulic pressure to be applied to theVVT-i controller advance or retard side. When the engine is stopped, the camshaft timing oilcontrol valve is in the most retarded state.Fig 2.6 Camshaft Timing Oil Control Valve

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123.4. Operation:The camshaft timing oil control valve selects the path according to the advance,

retard orhold signal from the ECM. The VVT-i controller rotates the intake camshaft in the timing advanceor retard position or holds it according to the position where the oil pressureis applied.. ADVANCE:When the camshaft timing oil control valve is positioned as illustrated below by

the advancesignals from the ECM, the resultant oil pressure is applied to the vane chamberof advanceside to rotate the camshaft in the timing advance direction.. RETARD:When the camshaft timing oil control valve is positioned as illustrated below by

the retardsignals from the ECM, the resultant oil pressure is applied to the vane chamberof retard sideto rotate the camshaft in the timing retard direction.Fig 2.7 Camshaft Timing Oil Control Valve inFig 2.8 Camshaft Timing Oil Control Valve in retard position

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Chapter 3

Valve Timing

3.1. Valve Timing:Since the entire issue is in improvising the engine based on its valve positioning, the followingvalve positions can be obtained thru the VVT-i system. Based on the power requirement,load, speed, the ECM varies the valve position. It also provides a good overlapto generateenough power.14

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Chapter 4

Research

4.1. Research practicality test:An experiment was undertaken on Toyota 1JZ-GTE engine. Using the existing engine

asa base, a continuously variable valve timing mechanism (VVT-i) was adopted for the intakecamshaft. Also, because of the increase of the compression ratio, a further improvement of fueleconomy was possible. Lastly, an electronically controlled throttle was adoptedthat achievessafe and smooth operation of the throttle.

Engine Toyota 1JZ -GTE New PreviousDisplacement (cc) 2491 sameConfiguration In-line 6 cylinder sameValve Mechanism DOHC 4-valve sameFuel System Electronic Fuel Injection sameFuel Requirement Unleaded Premium sameCompression Ratio 9.0 8.5Bore x Stroke 86 x 71.5 same

Maximum Power (kW @ RPM) / [PS@ RPM](206 @ 6200) / [280 @6200] sameMaximum Torque (Nm @ RPM) /[kgm @ RPM] / {lb-ft @ RPM}(378 @ 2400) / [38.5 @2400] / {278 @ 2400}(363 @ 4800) / [37.0 @4800] / {268 @ 4800}Fuel Consumption Rate (g/kWh @RPM) 278 @ 2000 285 @ 20004.2 Result:

i) We can see from the table that the VVT-i engine produces a torque of 378 Nm,whichis obtained at a speed of 2400 RPM, whereas a lower torque (363 Nm) is obtainedfrom a regularengine at double the same speed.

ii) Also, the fuel efficiency is increased with a lower fuel consumption rate of278 g/kWh is

achieved, rather than 285 g/kWh at the same speed.

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Chapter 5:

Conclusion

The report started with the elaboration of the need of an efficient engine, in the purviewof energy crisis. It was made clear that internal combustion engines (ICE) cannot be directly disused,but has to be improved to serve the purpose. The trend followed in the evolution

of ICEwas also briefly traced. Out of the best five techniques for a good engine, variable valve timing(VVT) system was selected for the research.

The further chapters explained in detail the working of VVT-i system. In brief,Variablevalve timing allows the relationship between the separate inlet and exhaust camshafts to vary thevalve timing overlap. In doing so it overcomes the side effects described aboveby using a computerto continuously vary the intake valve timing and overlap. The valve timing and overlap areadjusted through a series of simple mechanisms to ensure the optimum conditions

apply acrossall the working rev range. The advantages are lower fuel consumption, lower exhaust emissionsand higher power output. Since the system is continuously variable, an i for intelligent hasbeen added to the abbreviation.

Lastly, excerpts of an experiment conducted by Toyota on VVT-i system was consideredin the report. From the observation table, it can be seen that a higher torque is achieved at lowerrpm & even the fuel consumption is also decreased. Hence the purpose of adopting

a VVT-i engine

is achieved. So, it would be a wise decision to opt for a VVT-i engine rather than a conventionalengine.

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