antilock braking system (ABS)


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ANTI-LOCK BRAKING SYSTEM (ABS) Department of Automobile Engineering Sardar Patel Institute of Technology Piludara


INTRODUCTION ANTILOCK BRAKING SYSTEM, which is commonly known as ABS is used as an antiskid device in a vehicle. It used to prevent skidding of wheels while braking when we want to stop the vehicle or suddenly reduce its speed at any time. It provides better stability and control over vehicle while braking at high speed.


TYPES OF ANTI-BRAKES Four-channel, four sensor ABS Three-channel , three sensor ABS One-channel, one sensor ABS


CONSTRUCTION Speed Sensors Valves Pumps Electronic Brake Control Module Hydraulic Control Unit


SPEED SENSOR The anti-lock braking system needs some way of knowing when a wheel is about to lock up this work is done by speed sensors. The speed sensors, which are located at each wheel. 1 2 3 4 5 6 1 Electric cable 2 Permanent magnet 3 Housing 4 Winding 5 Pole pin 6 Sensor ring


VALVES There is a valve in the brake line of each brake controlled by the ABS. On some systems, the valve has three positions: In position one, the valve is open; pressure from the master cylinder is passed right through to the brake. In position two, the valve blocks the line, isolating that brake from the master cylinder.

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This prevents the pressure from rising further should the driver push the brake pedal harder. In position three, the valve releases some of the pressure from the brake.


PUMP Since the valve is able to release pressure from the brakes, there has to be some way to put that pressure back. That is what the pump does; when a valve reduces the pressure in a line, the pump is there to get the pressure back up.


ELECTRONIC BRAKE CONTROL MODULE (EBCM) The system monitors the speed of the wheels during braking. The Electronic Brake Control Module (EBCM) processes these values to produce command controls to prevent the wheels from locking. The EBCM mounted on a bracket next to the master cylinder, contains a microprocessor and software for system operation.


HYDRAULIC CONTROL UNIT It is a central unit which controls the flow of hydraulic fluid to each valves located near to the wheels. This unit is to regulate the pressure for each wheel independently.



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When the brakes are applied, fluid is forced from the brake master cylinder outlet ports to the HCU inlet ports. This pressure is transmitted through four normally open solenoid valves contained inside the HCU, then through the outlet ports of the HCU to each wheel. The primary (rear) circuit of the brake master cylinder feeds the front brakes. The secondary (front) circuit of the brake master cylinder feeds the rear brakes.

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If the EBCM senses a wheel is about to lock, based on speed sensor data, it closes the normally open solenoid valve for that circuit. This prevents any more fluid from entering that circuit. The EBCM operates the anti lock pressure valve to keep the wheels from locking up to do this the EBCM uses a three-step cycle: Pressure Decrease Pressure Increase Pressure Maintain

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The EBCM then looks at the speed sensor signal from the affected wheel again. If that wheel is still decelerating, it opens the solenoid valve for that circuit. Once the affected wheel comes back up to speed, the EBCM returns the solenoid valves to their normal condition allowing fluid flow to the affected brake. Loss of hydraulic fluid in the brake master cylinder will disable the anti-lock system.

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The 4-wheel anti-lock brake system is self-monitoring. When the ignition switch is turned to the RUN position, the anti-lock brake control module will perform a preliminary self-check on the anti-lock electrical system indicated by a three second illumination of the yellow ABS wanting indicator. Each time the vehicle is driven, as soon as vehicle speed reaches approximately 20 km/h, the anti-lock brake control module turns on the pump motor for approximately one-half second. At this time, a mechanical noise may be heard.

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This is a normal function of the self-check by the anti-lock brake control module. When the vehicle speed goes below 20 km/h, the ABS turns off. WITH ABS & WITHOUT ABS


ADVANTAGES It helps in avoiding potential accidents. ABS provides greater vehicle stability and control during hard braking (lockup) to the driver . ABS helps in shorting the stopping distance.


DISADVANTAGES It does not increase or decrease ultimate stopping power . Poor brake maintenance. Loss of hydraulic fluid in brakes master cylinder will disable the anti-lock system.



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