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ELECTRO-HYDRAULIC BRAKE Seminar report’10

CARMEL POLYTECHNIC

COLLEGEALAPPUZHA

DEPARTMENT OF AUTOMOBILE ENGINEERING

SEMINAR REPORTON

ELECTRO-HYDRAULIC BRAKESubmitted by

: SHAN SHOUKATH

Register No :88050045

FIFTH SEMESTER AUTOMOBILE ENGINEERING (2010-2011)

CARMEL POLYTECHNIC

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COLLEGE

ALAPPUZHA

CERTIFICATE

This is to certify that the seminar entitile

‘‘ ELECTRO-HYDRAULIC BRAKE ’’ the bonafide

report of work done by Mr. SHAN SHOUKATH of fifth

semester Automobile engineering at Carmel polytechnic college punnapra, Alappuzha towards the fullfilment of diploma in

Automobile engineering under the board of technical education during

the year 2010 – 2011.

Lecture in charge Head of section

Internal Examiner External Examiner

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ACKNOWLEDGEMENT

I here by gladly present this seminar on

“ELECTRO- HYDRAULIC

BRAKE ” towards the fulfillment of the award Engineering.

At the submission of the report I use this opportunity to express my sincere

gratitude to our Head of Department Sri.A.S RADHAKRISHNA PILLAI,

Automobile engg: for permitting me to do this seminar.

I also express my profound gratitude to our seminar co-ordinators

Sri. S.R., RAJENDRANATHAN NAIR, Mr. JONU JOSEPH , Mr. BINU.

N. KUNJUMON, Mr. KRISHNANUNNI.M, Mr. ARUN GEORGE and

for their inspiring assistance, encouragement and useful guidance.

I am also indebted to all the teachers of the department of Automobile engg:

for their co-operation and suggestion spirit behind this report. I also wish to

express my heartful thanks to all my friends for their good will and constructive ideas which helped me a lot in bringing out this report.

Above all I humbly express my thanks to GOD ALMIGHTY for his

blessing and helps to overcome all the difficulties on the way of my seminar.

SHAN SHOUKATH

Automobile Engineering

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CONTENTS

● INTRODUCTION 2

● ABOUT EHB

● WORKING 5

● SYSTEM OVER VIEW

● COMPARISON

● ADVANTAGES 18

● DISADVANTAGES

● APPLICATIONS 21

● CONCLUSION

REFERENCE

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INTRODUCTION

The next brake concept. This system is a system whichsenses the driver's will of braking through the pedalsimulator and controls the braking ressures to each wheels.

The system is also a hydraulic Brake by Wire system.

Many of the vehicle sub-systems in today’s modern vehicles are being converted into“by-wire” type systems. This normally implies a function, which in the past was activated directly through a purely mechanical device, is now implemented through electro-mechanical means by way of signal transfer to and from an Electronic Control Unit. Optionally, the ECU may

apply additional “intelligence” based upon input from other sensors outside of the driver’s influence. Electro-Hydraulic Brake is not a true “by-wire” system with the thought process that the physical wires do not extend all the way to the wheel brakes. However, in the true sense of the definition, any EHB vehicle may be braked with an electrical “joystick” completely independent of the traditional brake pedal. It just so happens that hydraulic fluid is used to transmit energy from the actuator to the wheel brakes. This configuration offers the distinct advantage that the current production wheel brakes may be maintained while an integral, manually applied, hydraulic

failsafe backup system may be directly incorporated in the EHB system. The cost and complexity of this approach typically compares favorably to an Electro-Mechanical Brake

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(EMB) system, which requires significant investment in vehicle electrical failsafe architecture, with some needing a 42 volt power source. Therefore, EHB may be classified a “stepping stone” technology to full Electro-Mechanical

Brakes.

present invention relates to an electro-hydraulic brake system for motor vehicles which is controllable in a brake-by-wire operating mode by the vehicle operator as well as independently of the vehicle operator, and which can be operated in a back-up operational mode where only operation by the vehicle operator is possible. The brake system includes an emergency pressure generator or master brake cylinder which has at least one pressure chamber and is operable by way of a brake pedal, and a hydraulic auxiliary pressure source whose pressure is used to act upon wheel brakes that are connectable to the master brake cylinder by way of at least one hydraulic connection closable by a separating valve, as well as an electronic control and regulating unit. In order to achieve a very rapid change-over of the separating valves into the closing position, the present invention arranges for an additional electric circuit that actuates the separating valve independently of the

electronic control and regulating unit as the driver's deceleration demand occurs

ELECTRO-HYDRAULIC BRAKE

Electrohydraulic brake systems are the combination ofelectronics and hydraulics to create a more versatile brakesystem. The electronics provide control flexibility, while thehydraulics supply the power.

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Electrohydraulic braking offersmany advantages over raditional hydraulic braking systems.These advantages can be exploited to provide improved

system performance and greater comfort for the operator.Valves can be moved away from the cab and closer to thebrakes, reducing plumbing costs. Remote operations areeasily handled without having to duplicate the valving.Vehicle controls can be improved by implementing a varietyof control schemes such as electrohydraulicbrake systems, anti-lock brake systems (ABS), and tractioncontrol systems (TCS). These systems are a result ofhydraulics and electronics combining to create brakesystems that provide value added features for the machineoperator.

These systems provide flexible control whilecomplying with requirements of primary and secondarybraking standards. Dual pedal angle sensors send signals toredundant input valve drivers that control the brakevalves.

WORKING

First, the driver’s input is normally interpreted by up to threedifferent devices: a brake switch, a travel sensor, and apressure sensor while an emulator provides the normalpedal “feel”. To prevent unwanted brake applications, two ofthe three inputs must be detected to initiate base brake

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pressure. The backup master cylinder is subsequently lockedout of the main wheel circuit using isolation solenoid valves,

so all wheel brake pressure must come from a high-pressure

accumulator source. This stored energy is created bypressurizing brake fluid from the reservoir with anelectrohydraulic pump into a suitable pre-charged vessel.The accumulator pressure is regulated by a separatepressure sensor or other device. The “by-wire”characteristics now come into play as the driver’s brakingintent signals are sent to the ECU. Here an algorithmtranslates the dynamically changing voltage input signalsinto the corresponding solenoid valve driver output currentwaveforms.As the apply and release valves open and close,a pressure sensor at each wheel continuously “closes theloop” by feeding back information to the ECU so the nextseries of current commands can be given to the solenoidvalves to assure fast and accurate pressure response.

It is obvious the EHBsystem is significantly more complex in nature. To addressthis concern, numerous steps have been taken to eliminatethe possibility of boost failure due to electronic or

mechanical faults. In the ECU design, componentredundancy is used throughout. This includes multiple wirefeeds, multiple processors and internal circuit isolation forcritical valve drivers. The extra components and theresulting software to control them, does add a small level ofadditional complexity in itself. Thermal robustness must alsocarefully be designed into the unit, as duty cycles for valvesand motors will be higher than in add-on type system. Thus,careful attention must be given to heat sinking,

materials, circuit designs, and component selection. Specialconsideration must be given to the ECU cover heat transferproperties, which could include the addition of cooling fins.On the mechanical side there is redundancy in valves andwheel brake sensors in that the vehicle may still be brakedwith two or three boosted channels. In regards to the E-H

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pump andaccumulator, backup components are not typicallyconsidered practical from a size, mass, and cost viewpoint.However, these few components are extremely robust in

nature and thoroughly tested to exceed durabilityrequirements.

MASTER CYLINDER

The master cylinder is a control device that converts

non-hydraulic pressure (commonly from a driver's foot) into hydraulic

pressure

, in order to move other device(s) which are located at theother end of the hydraulic system, such as one or more slavecylinders . As piston (s) move along the bore of the master cylinder,this movement is transferred through the hydraulic fluid, to result in amovement of the slave cylinder(s). The hydraulic pressure created bymoving a piston (inside the bore of the master cylinder) toward theslave cylinder(s) compresses the fluid evenly, but by varying thecomparative surface-area of the master cylinder and/or each slavecylinder, one will vary the amount of force and displacement applied toeach slave cylinder

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http://force/

http://bore/

http://piston/

http://hydraulic/

http://pressure/

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E C U

ECU is the heart of EHB It is located

under the centre of the instrument pannel, and is

the controll centre for the entire brake system. It

constantly look at the informations from the BPP

sensor and controls the system. It also recoganize

the problems within the system and alert the driver

through a "check engine" light on the dash board.It

can also store informations about the problem to

aid the technicion in making repaires. There are no

serviceable parts in the ECM

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PRESSURE SENSOR

Pressure sensors are used

for control and monitoring in thousands of everydayapplications. Pressure sensors can also be used to indirectlymeasure other variables such

as fluid/gas flow, speed, water level, and altitude. Pressuresensors can alternatively be called pressure transducers,

pressure transmitters, pressure senders, pressureindicators and piezometers, manometers, among othernames.

TRAVEL SENSORS

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Travel sensor is a device used to measure thevehicle to be travelled and angle position on the theperfomance of vehicle

COMPARISON OF EHB AND CONVENTIONALBRAKE

Analogous to a vacuum boostedsystem in base brake mode, EHB supplies a braking forceproportional to driver input, which reduces braking effort.The boost characteristics also contribute to the pedal “feel”of the vehicle. If the boost source fails, the system resorts tomanual brakes where brake input energy is supplied in fullby the driver. As would be expected, the pedal forces vs.vehicle deceleration characteristics are significantly affected.

This is shown by the input pedal forcevs. Brake line pressure output in Figure 1 of a typicalvacuum boosted vehicle.

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Looking at a comparison using the failsafe pedal force inputlimit of 500 N, the difference between the resulting brakeline pressure is 2.5 MPa unboosted vs. 8.5 MPa boosted.This correlates to an approximately proportional difference invehicle deceleration. In this example there approximatelycorrelates to 0.3 g’s decel. Unboosted, and 0.9 g’s boosted.With EHB systems, there is room to improve thisperformance, but only at the expense of pedal travel, whichbecomes a hydraulic lever arm of sorts. For example, toachieve a higher decel from 0.3 g to 0.5 g in failed system,the pedal travel may have to increase from 50 - 75 mm toperhaps 150 mm,which is about the practical limit for brake pedal travel.Thus, due to the

consequences of boost failure, careful attention must be paidto component system design irrespective of the type of

mechanism employed.A comparison between the conventional vacuum boostedsystem and an EHB system is shown in Figure 2.

The conventional system utilizes a largely mechanical link allthe way from the brake pedal through the vacuum boosterand into the master cylinder piston. Proportional assist isprovided by an air valve acting in conjunction with thebooster diaphragm to tilize the stored vacuum energy. Thepiston and seal trap brake fluid and transmitthe hydraulic

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energy to the wheel brake.

ADVANTAGES

An electrohydraulic braking or "brake-by-wire" system isa braking system that replaces the control elements of thetraditional braking system such as pumps, cylinders, hoses,belts and braking fluids, with electronic componentsactivated by an electronic control device. Such systems areincreasingly being used in aircraft as well as the automotiveindustry due to several advantages they offer overtraditional braking systems. When designers want to remove

the brake valve from the cab, electrohydraulic brakesystems should beconsidered

DISADVANTAGES

self-energizing brakes are known from the prior art, in particular from the field of drum brakes for motor vehicles. Self-energizing brakes have, however, the disadvantage that their coefficient of friction increases disproportionately as the actuator force increases. Since, in conventional hydraulic

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brake systems, the distribution of the brake force at the individual wheel brake cylinders is determined by the pressure in the brake lines and the area of the hydraulic pistons, the different coefficients of friction which are

present in reality between the friction linings of the brake and the brake disc or brake drum to be braked inevitably lead, when self-energizing brakes are used, to great differences in the braking forces at the individual wheels of a vehicle. The driver of the vehicle becomes aware of this

because his vehicle pulls into a skewed alignment during braking, i.e. it changes its direction of travel in an undesired way. In particular on a slippery road surface this can lead to the respective vehicle skidding. Because of these disadvantages which are associated with them, self-energizing brakes have therefore no longer been used as a service brake in the field of motor vehicles for some time

APPLICATIONS

The Electro Hydraulic Brakesystem is commonly used in industrial applications .Becausethese wasFail safe brakes when power fails the brake will be applied.

1 . Cranes2 . Transfer Cars3 . Rotating Machines4 . N.C.Machines5 . C.N.C.Machines

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CONCLUSION

Similar to the days of early ABS introduction, multiple EMB design configurations have emerged. From the mid 80’s through the latter part of the 1990’s numerous ABS configurations ranging from mechanically operated systems, to four valve flow control designs, to modulators based upon ball screws and electric motors came to market before the 8-valve, closed recirculation system became the de facto standard. As with

any new technology, there are concerns and tradeoffs to be dealt with. In the case of the electro-hydraulic brake they center around increased electrical and mechanical complexity, failsafe braking performance, accumulator safety, and 2-wheel versus 4-wheel backup modes. Each of these concerns has been answered by prudent designs and incorporation of new component technologies. The configuration adopted in Delphi’s EMB development has included use of four-wheel failsafe with individual isolation

pistons and utilization of mechanical pedal feel lockout. This particular design allows system flexibility, inherent accumulator precharge isolation, and the ability to tune for optimum failed system stopping performance for all vehicle classes. Ultimately, no matter which final configuration is selected for a specific vehicle platform, it will have to undergo the rigors of full brake system validation. A

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carefully de-signed and implemented EMB system holds the promise of enabling the new brake-by-wire features while still reliably performing the everyday task of stopping the vehicle.

REFERANCE

http\www.Car Craft magazine. Htm

http/www.google.comhttp/www.torqecars. co. ukhttp/www.wikipedia.comhttp/www.git.com

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