Anti-Lock Braking Systems(For Safe Braking)

Presented By :-Name DIPAK KUMAR.

PRESENTATION OUTLINE What is an Anti-Lock Braking System (ABS)? Motivation for ABS Development History of ABS Overview Principles for ABS Operation ABS Components overview ABS Components How does ABS work? System Diagram ABS Configurations Differences between ABS and Rear Anti-lock Brakes. Video on Without ABS Car and With ABS Car (Difference) Limitations Summary Query Session

1. WHAT IS ABS?

“An anti-lock brake system is a feedback control system that modulates brake pressure in response to measured wheel deceleration, preventing the controlled wheels from becoming fully locked.”

2. MOTIVATION FOR ABS

Under hard braking, an ideal braking system should:

provide the shortest stopping distances on all surfaces

maintain vehicle stability and steerability

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

3. HISTORY OF ABS

1936: German company Bosch is awarded a patent for an “Apparatus for preventing lock-braking of wheels in a motor vehicle”.

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.

1985: First ABS installed on US vehicles. 1986: 1M Bosch ABS installed. 1992: 10M Bosch ABS installed. 1999: 50M Bosch ABS installed. 2000: 6 out of 10 new cars on the road are ABS equipped. 2003: 100M Bosch ABS installed.

4. OVERVIEW

Anti-Lock Braking Systems (ABS) are designed to maintain driver control and stability of the car during emergency braking. Locked wheels will slow a car down but will not provide steering ability. ABS allows maximum braking to be applied while retaining the ability to 'steer out of trouble‘ . The operation of ABS can slightly reduce stopping distance in some cases like on wet road surfaces, but it can increase the stopping distance in others, as may be the case in deep snow or gravel.

An ABS system monitors four wheel speed sensors to evaluate wheel slippage. Slip can be determined by calculating the ratio of wheel speed to vehicle speed, which is continuously calculated from the four individual wheel speeds. During a braking event, the function of the control system is to maintain maximum possible wheel grip on the road - without the wheel locking - by adjusting the hydraulic fluid pressure to each brake by way of electronically controlled solenoid valves.

For passenger car applications, the majority of ABS components are often housed together in a single, under-hood mounted module.

5. PRINCIPLES FOR ABS OPERATION

Design Goals:

• attain minimum stopping distance

• maintain stability and steerability

Design Solution:

Develop a system that rapidly modulates the braking force under hard braking conditions to:

• maintain the ideal tire slip percentage to maximize braking force (≈ 15%), recalling that Fbrake = µBN

• permit the vehicle to be steered with stability maintained by preventing skidding

6. ABS COMPONENTS OVERVIEW

Typical ABS Components: Wheel Speed Sensors (up to 4) Electronic Control Unit (ECU)

Brake Master Cylinder, Hydraulic Modulator Unit with Pump and Valves

Vehicle’s Physical Brakes

ABS COMPONENTS

Teeth on the sensor ring rotate past the magnetic sensor, causing a reversal of the magnetic field polarity, resulting in a signal with frequency related to the angular velocity of the axle.

a) Wheel Speed Sensor (WSS)

Valves and Brakes

The valves modulate the brake pressure up to 20 times per second, effectively realizing the ideal tire slip percentage.

ABS ‘pumps’ the brakes much faster than any driver could.

7. HOW DOES ABS WORK?

Basically, there are sensors at each of the four wheels (or in the case of the less sophisticated three-channel system, one on each of the fronts and only one for the pair of rears). These sensors watch the rotation of the wheels. When any one of the wheels stops rotating due to too much brake application, the sensors tell the car's computer, which then releases some of the brake line pressure that 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 the brake pressure happens 20 or more times per second.

Practically speaking, this keeps the wheel just at the limit - the threshold - before locking up and skidding. ABS prevents you from ever locking up the brakes 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. And when I say hard, I mean HARD. Let the system do the finesse work for you. This may not be as easy as it sounds. After years of being told (and practising) not to press too hard on the brake pedal, this may not feel very natural.

8. SYSTEM DIAGRAM

9. ABS CONFIGURATIONS

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

10. DIFFERENCES BETWEEN ABS AND REAR ANTI-LOCK BRAKES.

Finally, there is a great difference between ABS and Rear Anti-lock Brakes. ABS is on all four wheels. Rear Anti-lock Brakes, as the name suggests, are only on the rear wheels. This system is often used on pick-up trucks and vans, and is a less-expensive compromise. It is used because the weight load on the rear of a truck or van can vary so much. The brakes needed to handle a heavily loaded vehicle are too effective for when it is lightly loaded. Therefore, the rear brakes are much more susceptible to locking-up.

11. VIDEO ON WITHOUT ABS CAR AND WITH ABS CAR (DIFFERENCE

12. LIMITATIONS

Three 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; • does not allow you to brake later; and • does not allow you to corner faster.

13. SUMMARY

An ABS typically consists of: Up to 4 wheel speed sensors An ABS ECU A Brake Master Cylinder, with accompanying

Hydraulic Modulator Unit and Solenoid 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 steerability.

QUESTIONS ?

Thanks