Anti-lock Braking System

Presentation Outline 

What is an Anti-Lock Braking System (ABS) ?

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Motivation for ABS Development History of ABS Principles for ABS Operation ABS Component Overview ABS Components How Does ABS Works ? ABS Configuration Design Challenges Limitations Summary

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1. What is ABS ?  An

anti-lock braking system is a safety system that allows the wheels on a motor vehicle to continue interacting tractively with the road surface as directed by driver steering inputs while braking, preventing the wheels from locking up (that is, ceasing rotation) and therefore avoid skidding.

2. Motivation for ABS 

Under hard braking, an ideal braking system should:

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provide the shortest stopping distances on all surfaces

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maintain vehicle stability and steer ability

Anti-lock braking systems were developed to best meet these needs.

3. History of ABS

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1936: German company Bosch is awarded a patent for an “Apparatus for preventing lock-braking of wheels in a motor vehicle”. 1936-: Bosch and Mercedes-Benz partner - R&D into ABS. 1972: WABCO partners with Mercedes-Benz developing first ABS for trucks. 1978: First production-line installation of ABS into Mercedes and BMW vehicles. 1981: 100,000 Bosch ABS installed.

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1985: First ABS installed on US vehicles.

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1986: 1M Bosch ABS installed. 1987: Traction control - in conjunction with ABS - used on passenger vehicles. 1989: ABS hydraulic unit combined with standard hydraulic brake unit 1992: 10M Bosch ABS installed. 1995: Electronic Stability - in conjunction with ABS and TCS - for passenger cars. 1999: 50M Bosch ABS installed. 2000: 6 of 10 new cars on the road are ABS equipped. 2003: 100M Bosch ABS installed.

4. Principles of ABS Operations  Design Goals:  Attain minimum stopping distance

 Maintain stability and steer ability  Design Solution: Develop a system that rapidly modulates the braking force under hard braking conditions to:

It maximize braking force Permit the vehicle to be steered with stability maintained by

preventing skidding

5. ABS Components Overview •

Typical ABS Components:

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Wheel Speed Sensors (up to 4)

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Valves

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Pump

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Electronic Control Unit (ECU)

ABS Components 

A). Wheel Speed Sensor (WSS)

The ABS needs some way of knowing when a wheel is about to lock up. The speed sensors, which are located at each wheel provides this information.

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B). Valves

There is a valve in a 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. 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.

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C). Pump Since the Valve is able to release some 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. ABS „pumps‟ the brakes much faster than any driver could.

Anti-lock brake pump and valves

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D). Electronic Control Unit It‟s a computer in the car. The ECU receives information from each individual wheel speed sensor , in turn if a wheel loses traction the signal is sent to the controller , the controller will then limit the brake force and activate the ABS modulator which actuates the valves on and off.

6. How Does ABS works ? There are many different variations and algorithm for ABS system. We will discuss how one of the simpler system works. Basically, there are sensor at each of the four wheels. These sensors watch the rotation of the wheel. When any one of the wheel stop rotating due to too much brake application, the sensors tell the car‟s computer, which then releases some of the brake line pressure you‟ve applied – allowing the wheel to turn again. Then, just as fast as it released the pressure, the computer allows the pressure to be applied again – which stops the rotation of the wheel again. Then it releases it again. And so on. With most ABS, this releasing and re-application - or pulsing – of brake pressure happens 20 or more times per second. Practically speaking this keeps the wheel just at the limit before locking up and skidding. ABS prevents you from ever locking up the brakes and skidding.ABS prevents you from ever locking up and skidding – no matter how hard you apply the brakes. Obviously, this is going to mean much more steering control.

With ABS, all you have to do in an emergency is quickly squeeze the brake pedal as hard as you can and hold it there. Let the system do the finesse work for you.

Anti-lock brake components

7. ABS Configuration

Depending on the ABS application, there are several typical layouts.

8. Design Challenges Because of the safety related nature of the ABS application, special emphasis is placed on functions design to detect system faults and ensure that fail-safe state occurs during faults. These functions may be implemented with techniques such as dual processors and specialized self test and watchdog modules. ABS system typically include eight electronic solenoid valves and other electrical loads, such as relays and pump motors, that requires considerable drive currents. Electronic drive circuitry is often required to sense any failure of these components during operation.

9. Limitations Two points should be obvious, but don't appear to when looking at the type of crashes some drivers have with ABS-equipped vehicles. Contrary to popular belief, ABS : does not allow you to drive faster; and  does not allow you to corner faster.  less effective under some limited circumstances (Snow, Gravel).

10. Summary  An ABS typically consists of:

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 Up to 4 wheel speed sensors  An ABS ECU  Pumps and Valves  The vehicle‟s physical brakes An ABS is designed to modulate braking pressure to attain the peak coefficient of kinetic friction between the tire and the road, and to avoid total wheel lockup. An ABS, under hard braking conditions, is designed to reduce stopping distances under most conditions, while maintaining vehicle stability and steer ability.

SOURCE….  HowStuffWorks.com  Wikipedia.org

 Bosch-escential.com

Presented By :-

Rajat Srivastava ME – 3rd Yr ( 5th Sem) 0916340081