Glossary: ABS - anti-lock braking system

Derived from the German word ‘anti blockier system‘, an anti-lock braking system (ABS) is a system which prevents the wheels from locking during braking. The main aim of this system is to allow the driver to maintain steering control under heavy braking. In some cases, ABS helps to shorten braking distances.

The ABS consists of an electronic controller unit, speed sensors (either one for each wheel or one common sensor for both wheels on the same axle), hydraulic valves and a pump on the brake circuit. The controller unit monitors the rotational speeds of the individual wheels and when it senses a lock up in a particular wheel(when any of the wheels is rotating significantly slower than the others) it reduces the hydraulic pressure in the brake line of that wheel alone by the use of the valve. Thus the flow of brake fluid being delivered to the brake calipers of the locked up wheel is regulated. Now, the brakes rapidly alternate (at a rate of 15 to 30 times per second) from full pressure to full release (rapid pumping) controlled completely by the electronic controller unit and hence the driver is able to steer and keep the vehicle under control even when the brakes are fully applied.

Anti-lock braking systems were first developed for use in aircrafts and the first car they appeared on was the Ford Zodiac.