An anti-lock braking system abbreviated as ABS is a braking system or security system which prevents the wheels on an automobile from locking up while braking. The wheels revolving on the road let the driver to maintain steering control under heavy braking by preventing a skid and allowing the wheel to continue interacting tractively with the road surface as directed by driver steering inputs. The ABS offers better vehicle control, and may reduce ending distances on dry and especially slippery surfaces. It can also boost braking distance on loose surfaces such as snow and gravel.

Since initial widespread of anti-lock braking system use in production cars have evolved significantly. New versions not only prevent wheel lock under braking, but also electronically control the front-to-rear brake bias. This function, depending on its specific capabilities and implementation, is known as electronic brakeforce distribution (EBD or EBFD) or electronic brakeforce limitation (EBL), traction control system, emergency brake assist, or electronic stability control.

Operation of Anti-lock Brake System

The Anti-lock Brake System is composed of a central electronic control unit (ECU), four wheel speed sensors one for each wheel and two or more hydraulic valves inside the brake hydraulics. The ECU continuously observes the revolving speed of every wheel, and when it senses a wheel rotating significantly slower than the other wheels a condition indicative of approaching wheel lock it trigger the valves to decrease hydraulic pressure to the brake at the affected wheel, thus dropping the braking power on that wheel. Then the wheel turns quicker when the ECU senses it is rotating significantly faster than the others, brake hydraulic pressure to the wheel is improved so the braking force is reapplied and the wheel slows. This process is repeated always, and it is perceived by the driver via brake pedal pulsation. A typical anti-lock system can apply and discharge braking pressure up to 20 times a second.

The ECU is programmed to ignore differences in wheel revolving speed below a critical threshold. When the automobile is turning, the two wheels towards the center of the curve turn slower than the outer two. For this similar reason, a gap is used virtually in all automobiles or vehicles.

If a fault happens in any part of the ABS, a warning light will glow on the vehicle instrument panel, and the ABS will be disabled until the fault is repaired. The anti-lock brake controller is also known as the Controller Anti-lock Brake which is abbreviated as CAB.

Recently the Electronic Stability Control systems are development of ABS model. Two extra sensors are added to assist the system work a steering wheel angle sensor and a gyroscopic sensor. The function of this sensor is easy, when the gyroscopic sensor senses that the direction of the automobile not matches with the steering wheel sensor it informs the ESC software to brake the essential individual wheel(s), so that the vehicle runs as determined by the driver. The steering wheel sensor also assist in the operation of Cornering Brake Control (CBC), since this will inform the ABS that wheels within the curve should brake more than wheels on outside, and by how much.

The ABS is also used to implement traction control system (TCS) on acceleration of the vehicle. When accelerating, if the tire loses traction, the ABS controller senses the situation and takes proper action so that traction is recovered. Producers offer this as an individually valued option even though the infrastructure is mostly shared with ABS. More stylish versions also control throttle levels and brakes concurrently.

Antilock Brake System FAQ

See also

Air Brake
Disc Brake
Drum Brake
Hydraulic Brake System