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Int. J. Mech. Eng. & Rob. Res. 2014 Sahil Jitesh, 2014

ISSN 2278 – 0149 www.ijmerr.com

Vol. 3, No. 4, October, 2014

© 2014 IJMERR. All Rights Reserved

Research Paper

ANTILOCK BRAKING SYSTEM (ABS)

Sahil Jitesh1*

*Corresponding Author: Sahil Jitesh � sahiljitesh@hotmail.com

Antilock Breaking System (ABS) is used in advanced automobiles to prevent slip and locking ofwheel after brakes applied. It is automobile safety system, the controller is provided to controlthe necessary torque to maintain optimum slip ration. The slip ration denote in terms of vehiclespeed and wheel rotation. It’s an automated system that run on principles of threshold brakingand cadence braking which were practiced by skillful drivers with previous generation brakingsystem. It response time is very faster so that makes easy steering for the driver. ABS generallyoffer advanced vehicle control and minimize the stopping distance in slippery and dry surface,conversely on loose surface like gravel or snow covered pavement, ABS can significantly increasebraking distance, although still improving vehicle control.

Keywords: ABS, Antilock Brakes, Antilock Breaking system, Safety, Slip Factor, AdvanceBraking System, Vehicle Stability Control, Electrical Control Unit (ECU)

1 Department of Mechanical Engineer, G.K. Bharad Institute of Engineering, Gujarat Technological University, India.

INTRODUCTION

Antilock braking system (ABS) preventbrakes from locking during braking. In normalbraking situation the driver control the brakes,however during severs braking or on slipperyroadways when driver the wheels toapproach lockup, the antilock takes overhere. The ABS modulates the brake linepressure independent of the pedal force tobring the wheel speed back to the slip levelrange that necessary to the optimal brakingperformance. The ABS does not allow fullwheel lock under braking.

In simple terms, during emergency ofbraking, the wheel does not get locked even

if you push a full auto brake pedal and hencethe skidding does not takes place. It alloweddriver to control the car easier, even on roadswith low adhesion, such a rain, snow andmuddy road. The brain of antilock brakingsystem consist Electronic Control Unit (ECU),wheel speed sensor and hydraulic modulator.ABS is a closed circuit, hence it used thefeedback control system that modulates thebrake pressure in response to the wheeldeceleration and wheel angular velocity toprevent the controlled wheel from locking.

SUBSYSTEM OF ANTILOCKBRAKING SYSTEM (ABS)

Wheel-Speed Sensors

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Figure 1: ABS in BMW Bike

Figure 2: Car Dashboard Indicating ABS

Each of the ABS wheel speed sensorsdetects the speed of the correspondingwheel. The sensor consists of a permanentmagnet, coil and tone wheel. The magneticflux produced by the permanent magnetchanges as each tooth of the tone wheel(which rotates together with the wheel)passes in front of the magnet’s pole piece.The changing magnetic flux induces voltagesat a frequency corresponding to the wheelspeed.

Electronic Control Unit (ECU)

The work of ECU is to receive, amplifies andfilter the sensor signals for calculating thespeed rotation and acceleration of thevehicle. ECU also uses the speeds of twodiagonally opposite wheels to calculate an

Figure 3: Electronic Control Unit (ECU)

estimate for the speed of the vehicle. Theslip of each wheel is obtain by comparing thereference speed with the individual wheel.During wheel slip or wheel accelerationcondition signal server to alert the ECU. Themicrocomputer alert by sending the triggerthe pressure control valve of the solenoidsof the pressure modulator to modulate thebrake pressure in the individual wheel brakecylinders.

The ECU reacts to a recognized defect orerror by switching off the malfunctioning partof the system or shutting down the entireABS.

Figure 4: 4S/4M Configuration

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Hydraulic Pressure Modulator/

Hydraulic Control Unit

The Hydraulic pressure modulator is anelectro-hydraulic device for reducing, restor-ing and holding the pressure of the wheel bymanipulating the solenoid valve in the hydrau-lic brake system. ABS hydraulic modulatorunit contain the valve, solenoid and piston.Under hard braking condition, this assemblycontrol the holding and release of the differ-ent hydraulic brake circuit. During the nor-mal condition the standard braking systemused.

Whenever hard braking situation occur, thesystem sense the change in the rotation ofthe speed sensor and decide whether to holdor release pressure to a brake circuit. A tirehas its best traction just before it begin toskid, once it begins to skid a portion of trac-tion and steering will be lost.

Figure 5: Hydraulic Control Unit

ANTI-LOCK BRAKE TYPE

Different schemes of anti-lock braking systemuses depending upon the types of brakesuse. Depending upon the channel (valve) andnumber of speed sensors the antilock brakeare classified.

Four Channel, Four Sensor ABS

It is a more preferable type, the speed sensoron all the four wheels and contain separatevalve for all four wheels. By using this setup,the controller monitors each wheelindividually to make sure it is achievingmaximum braking force.

Three Channel, Three Sensor ABS

This type of system is can be foundcommonly in the pickup trucks with four wheelABS, on each of the front wheels there is avalve and a speed sensor, and one valve andone sensor for both rear wheels. The speedsensor for rear wheels is located in the rearaxle.

To achieve the maximum braking force,this system provides individual control to thefront wheels. The rear wheels, however, arecontrolled together; they are both have to startto lock up before the ABS will active on therear. With the help of this system, it's possiblethat one if the rear wheels will lock during astop, reducing brake effectiveness.

One Channel, One Sensor ABS

This Arrangement can be seen in a pickuptrucks and heavy trucks with rear wheel ABS.It consist one valve, which operate both rearwheel, and one speed sensor located in therear axle. This is quite similar as the rear endof a three channel system. The rear wheelare monitored together and they both haveto lockup before ABS starts its action. In thissystem there is also probability that one ofthe rear wheels will lock, results reducing inbrake effectiveness. This system is easy toidentify, usually there will be one brake linegoing through a T-fitting to both rear wheels.

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FUNCTION OF SENSORS AND

ACTUATORS

Figure 6: Sensors and Actuators

(1) ABS control module and hydrauliccontrol unit (ABSCM & H/U)

(2) Two-way connector(3) Diagnosis connector(4) ABS warning light(5) Data link connector (for SUBARU

select monitor)(6) Transmission control module (AT

models only)(7) Tone wheels(8) ABS wheel speed sensor(9) Wheel cylinder(10) G sensor(11) Stop light switch(12) Master cylinder(13) Brake & EBD warning light(14) Lateral G sensor (STi)

Table 1: Function of Sensors Andactuators

ABS control module and hydrauliccontrol unit (ABSCM & H/U)

Name Function

ABSCM section

H/U section

Valve relay section

Motor relay section

ABS wheel speed sensors

• It determines the conditions of the wheels and the vehiclebody from the wheel speed data and controls the hydraulicunit depending on the result.

• When the ABS is active, the ABSCM provides theautomatic transmission control module with control signalswhich are used by the module for cooperative control ofthe vehicle with the ABSCM.

• Whenever the ignition switch is placed at ON, the moduleperforms a self-diagnosis sequence. If anything wrong isdetected, the module cuts off the system.

• It communicates with the SUBARU select monitor.

• When the ABS is active, the H/U changes fluid passagesto the wheel cylinders in response to commands from theABSCM.

• It constitutes the brake fluid passage from the mastercylinder to the wheel cylinders together with the piping.

• It serves as a power switch for the solenoid valves andmotor relay coil. It operates in response to a commandfrom the ABSCM.

• It serves as a power switch for the pump motor. It operatesin response to a command from the ABSCM

These sensors detect the wheel speed in terms of a changein the density of the magnetic flux passing through them and

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convert it into an electrical signal. The electrical signal is sentto the ABSCM.

They give a change in the magnetic flux density by the teetharound themselves to let the ABS wheel speed sensorsgenerate electrical signals.

It detects a change in acceleration in the longitudinal directionof the vehicle and outputs it to the ABSCM as a voltage signal.

Converts the variation in lateral G on the vehicle into a changein capacity of the sensor condenser, and outputs a varyingvoltage to the ABS ECU.

It provides information on whether the brake pedal isdepressed or not to the ABSCM. The ABSCM uses it todetermine ABS operation.

It alerts the driver to an ABS fault. When the diagnosisconnector and diagnosis terminal are connected, the lightflashes to indicate a diagnostic trouble code stored in theABSCM.

It provides gear controls (fixing the speed at 3rd or changingpower transmission to front and rear wheels) in response tocontrol signals from the ABSCM.

It alerts the driver to an EBD fault. This warning light is alsoused for parking brake warning and brake fluid level warning.

Tone wheels

G sensor

Lateral G sensor (STi)

Stop light signal

ABS warning light

Automatic transmission control module

Brake warning light

IMPORTANTCE OF ABS

Stopping Distance

The Stopping distance is a one of theimportant factor when it comes for braking.Stopping distance is the function of vehiclemass, its initial velocity and the braking force.Stopping distance can be minimize byincreasing in braking force (keeping all otherfactors constant). In all types of road surfacethere is always exists a peak in friction

Figure 7: Effect of ABS

coefficient. An antilock system can attainmaximum fictional force and results minimumstopping distance. This objective of antilocksystems however, is tempered by the needfor vehicle stability and steerability.

Stability

The fundamental purpose of braking systemis to decelerating and stopping of vehicle,maximum friction force may not be describedin some cases like asphalt and ice (p-split)surface, such that significantly more brakingforce is obtainable on one side of the vehiclethan on the other side. So when applying fullbrake on both the sides will result yaw orskidding moment that will tend to pull thevehicle to the high friction side and resultsvehicle instability. Here comes the conceptof antilock system that maintain the slip bothrear wheels at the same level and minimizetwo friction coefficient peaks, then lateral

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force is reasonably high thought notmaximized. This contributes to stability andis an objective of antilock systems.

Figure 8: Stability by Using ABS

Steerability

Good peak frictional force control isnecessary in order to achieve satisfactorylateral forces and, therefore, satisfactorysteerability. Steerability while braking isimportant not only for minor coursecorrections but also for the possibility ofsteering around an obstacle. Tirecharacteristics play an important role in thebraking and steering response of a vehicle.For ABS-equipped vehicles the tireperformance is of critical significance. Allbraking and steering forces must begenerated within the small tire contact patchbetween the vehicle and the road. Tiretraction forces as well as side forces can onlybe produced when a difference existsbetween the speed of the tire circumferenceand the speed of the vehicle relative to theroad surface. This difference is denoted asslip. It is common to relate the tire brakingforce to the tire braking slip.

After the peak value has been reached,increased tire slip causes reduction of tire-road friction coefficient. ABS has to limit theslip to values below the peak value to preventwheel from locking. Tires with a high peakfriction point achieve maximum friction at 10to 20% slip. The optimum slip valuedecreases as tire-road friction decreases.

CONCLUSION

With development in a technology inautomobiles the braking system is gettingmore and more advanced. Antilock brakeshelp drivers to have better control of a vehiclein some road conditions where hard brakingmay be necessary. In vehicles withoutantilock brake systems, drivers whoencounter slippery conditions have to pumptheir brakes to make sure they do not spinout of control because of locked up wheels.Antilock braking system coordinates wheelactivity with a sensor on each wheel thatregulate brake pressure as necessary, so thatall wheels are operating in a similar speedrange.

ACKNOWLEDGMENT

I would like to express my greatest gratitudeto the people who have helped & supportedme. I am grateful to my teacher for continuoussupport for the project, from initial advice &contacts in the early stages of conceptualinception & through ongoing advice &encouragement to this day. A special thanksto Jasmin G. Kotak who helped me incompleting this research & she exchangedher interesting ideas, thoughts & made thiseasy and accurate. I wish to thank my parentsfor their undivided support and interest whoinspired me and encouraged me to go my

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own way, at last but not the least I want tothank my friends who appreciated me for mywork and motivated me.

REFERENCES

1. A B Sharkawy (2010), “Genetic FuzzySelf-tuning PID Controllers for AntilockBraking Systems” EngineeringApplications of Artificial Intelligence, Vol.23, pp. 1041-1052.

2. A Poursamad (2009), “AdaptiveFeedback Linearization Control ofAntilock Bracking System Using NeuralNetworks”, Mechatronics, Vol. 19, pp.767-773.

3. David W Gilbert (2001), “Magneto-Resistive Wheel Speed Sensors”, “New“Active” Wheel Speed Sensors ChangingABS Diagnostic Procedures”, http://www.asashop.org/autoinc/aug2001/mech.cfm

4. H Mirzaeinejad and M Mirzaei (2010), “ANovel Method for Non-linear Control ofWheel Slip in Anti-lock Braking Systems’,Control Engineering Practice, Vol. 18, pp.918-926.

5. Y Onit, E Kayacan and O Kaynak (2009),“A Dynamic Method to Forecast WheelSlip for ABS & its ExperimentalEvaluation”, IEEE Trans. Systems, Man& Cybernetics, Part B: cybernetics, Vol.39, pp. 551-560.