ELECTRO-HYDRAULIC BRAKE.doc.docx ... · Web viewpresent invention relates to an electro-hydraulic brake system for motor vehicles which is controllable in a brake-by-wire operating

ELECTRO-HYDRAULIC BRAKE Seminar report’10

CARMEL POLYTECHNIC COLLEGE

ALAPPUZHA

DEPARTMENT OF AUTOMOBILE ENGINEERING

SEMINAR REPORTON

ELECTRO-HYDRAULIC BRAKE Submitted by: SHAN SHOUKATHRegister No :88050045

FIFTH SEMESTER AUTOMOBILE ENGINEERING (2010-2011)

CARMEL POLYTECHNIC COLLEGE

1

21


ALAPPUZHA

CERTIFICATEThis 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

1

21


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

1

21


CONTENTS● INTRODUCTION 2

● ABOUT EHB

● WORKING 5

● SYSTEM OVER VIEW

● COMPARISON

● ADVANTAGES 18

● DISADVANTAGES

● APPLICATIONS 21

● CONCLUSION

REFERENCE

1

21


INTRODUCTION

The next brake concept. This system is a system which senses the driver's will of braking through the pedal simulator 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 (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 1

21


“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 of electronics and hydraulics to create a more versatile brake system. The electronics provide control flexibility, while the hydraulics supply the power.

Electrohydraulic braking offers many 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 the 1

21


brakes, reducing plumbing costs. Remote operations are easily handled without having to duplicate the valving. Vehicle controls can be improved by implementing a variety of control schemes such as electrohydraulicbrake systems, anti-lock brake systems (ABS), and traction control systems (TCS). These systems are a result of hydraulics and electronics combining to create brake systems that provide value added features for the machine operator.

These systems provide flexible control while complying with requirements of primary and secondary braking standards. Dual pedal angle sensors send signals to redundant input valve drivers that control the brakevalves.

WORKING

First, the driver’s input is normally interpreted by up to three different devices: a brake switch, a travel sensor, and a pressure sensor while an emulator provides the normal pedal “feel”. To prevent unwanted brake applications, two of the three inputs must be detected to initiate base brake pressure. The backup master cylinder is subsequently locked out 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 by pressurizing brake fluid from the reservoir with an electrohydraulic pump into a suitable pre-charged vessel. The accumulator pressure is regulated by a separate pressure sensor or other device. The “by-wire” characteristics now come into play as the driver’s braking intent signals are sent to the ECU. Here an algorithm 1

21


translates the dynamically changing voltage input signals into the corresponding solenoid valve driver output current waveforms.As the apply and release valves open and close, a pressure sensor at each wheel continuously “closes the loop” by feeding back information to the ECU so the next series of current commands can be given to the solenoid valves to assure fast and accurate pressure response.

It is obvious the EHB system is significantly more complex in nature. To address this concern, numerous steps have been taken to eliminate the possibility of boost failure due to electronic or mechanical faults. In the ECU design, component redundancy is used throughout. This includes multiple wire feeds, multiple processors and internal circuit isolation for critical valve drivers. The extra components and the resulting software to control them, does add a small level of additional complexity in itself. Thermal robustness must also carefully be designed into the unit, as duty cycles for valves and 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. Special consideration must be given to the ECU cover heat transfer properties, which could include the addition of cooling fins. On the mechanical side there is redundancy in valves and wheel brake sensors in that the vehicle may still be braked with two or three boosted channels. In regards to the E-H pump andaccumulator, backup components are not typically considered practical from a size, mass, and cost viewpoint. However, these few components are extremely robust in nature and thoroughly tested to exceed durability requirements.

MASTER CYLINDER 1

21


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 the other end of the hydraulic system, such as one or more slave cylinders. As piston(s) move along the bore of the master cylinder, this movement is transferred through the hydraulic fluid, to result in a movement of the slave cylinder(s). The hydraulic pressure created by moving a piston (inside the bore of the master cylinder) toward the slave cylinder(s) compresses the fluid evenly, but by varying the comparative surface-area of the master cylinder and/or each slave cylinder, one will vary the amount of force and displacement applied to each slave cylinder

E C U

1

21


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

PRESSURE SENSOR

Pressure sensors are used for control and monitoring in thousands of everyday applications. Pressure sensors can also be used to indirectly measure other variables such

as fluid/gas flow, speed, water level, and altitude. Pressure sensors can alternatively be called pressure transducers, pressure transmitters, pressure senders, pressure indicators and piezometers, manometers, among other 1

21


names.

TRAVEL SENSORS

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

COMPARISON OF EHB AND CONVENTIONAL BRAKE Analogous to a vacuum boosted system in base brake mode, EHB supplies a braking force proportional 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 to manual brakes where brake input energy is supplied in full 1

21


by the driver. As would be expected, the pedal forces vs. vehicle deceleration characteristics are significantly affected. This is shown by the input pedal force vs. Brake line pressure output in Figure 1 of a typical vacuum boosted vehicle.

Looking at a comparison using the failsafe pedal force input limit of 500 N, the difference between the resulting brake line pressure is 2.5 MPa unboosted vs. 8.5 MPa boosted. This correlates to an approximately proportional difference in vehicle deceleration. In this example there approximately correlates to 0.3 g’s decel. Unboosted, and 0.9 g’s boosted. With EHB systems, there is room to improve this performance, but only at the expense of pedal travel, which becomes a hydraulic lever arm of sorts. For example, to achieve 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 to perhaps 150 mm,which is about the practical limit for brake pedal travel. Thus, due to the

consequences of boost failure, careful attention must be paid to component system design irrespective of the type of mechanism employed.A comparison between the conventional vacuum boosted system and an EHB system is shown in Figure 2.

The conventional system utilizes a largely mechanical link all 1

21


the way from the brake pedal through the vacuum booster and into the master cylinder piston. Proportional assist is provided by an air valve acting in conjunction with the booster diaphragm to tilize the stored vacuum energy. The piston and seal trap brake fluid and transmitthe hydraulic energy to the wheel brake.

ADVANTAGES An electrohydraulic braking or "brake-by-wire" system is a braking system that replaces the control elements of the traditional braking system such as pumps, cylinders, hoses, belts and braking fluids, with electronic components activated by an electronic control device. Such systems are increasingly being used in aircraft as well as the automotive industry due to several advantages they offer over traditional braking systems. When designers want to remove the brake valve from the cab, electrohydraulic brake systems should be considered

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 1

21


the actuator force increases. Since, in conventional hydraulic 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 Brake system is commonly used in industrial applications .Because these was Fail safe brakes when power fails the brake will be applied. 1 . Cranes 2 . Transfer Cars 3 . Rotating Machines 4 . N.C.Machines 5 . C.N.C.Machines

1

21


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 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.

1

21


REFERANCE http\www.Car Craft magazine. Htm http/www.google.com http/www.torqecars. co. uk http/www.wikipedia.com http/www.git.com

1

21

Documents

ELECTRO-HYDRAULIC BRAKE.doc.docx ... · Web viewpresent invention relates to an electro-hydraulic brake system for motor vehicles which is controllable in a brake-by-wire operating