Antilock Brake System (ABS)

One of the major advantages of ABS is that the car can still be steered when the brakes are applied, with the result that in an emergency the driver has a better chance of driving around obstructions or guiding the car through gaps.

The basic principle of ABS is quite simple. As soon as braking pressure builds up and a wheel threatens to lock, the automatic control system reduces the pressure until the wheel is just able to rotate. As a result, there is no risk of locking the wheels even if full pedal effort is applied.

The ABS consists basically of the electronic control unit and the hydraulic pressure control unit, integrated into the standard brake system. Each front and rear wheel has its own speed sensor, which measures the number of wheel revolutions and transmits a corresponding signal to the electronic control unit. This converts them into wheel speed and circumferential rate of acceleration, compares this data with fixed, programmed constant values and transmits commands to the hydraulic unit if necessary. This in turn consists of 4 electromagnetic valves, one for each wheel brake, and an electrically driven returnflow pump. The hydraulic unit regulates braking pressure individually at each front wheel and for both rear wheels together.

The regulating cycle takes only a few fractions of a second, and the driver is warned that it is in action by slight pulsation at the brake pedal. A telltale light on the instrument panel comes on if the ABS is not operational.