D. Overall function

The ABS is operational when the ignition is switched on and a speed of 5-7 km/h has been attained. All braking operations in the locking range are controlled starting at the so-called control speed of 8 km/h (from 12 km/h on 1st version up to 02/84).

The following describes the control cycle on one wheel. The control sequence on the other wheels is the same. The wheel speed measured by the wheel speed sensor provides the wheel deceleration and the wheel acceleration signals for the electronic control unit. Linking of the individual wheel speeds provides the so-called reference speed, which is the approximate vehicle speed. A comparison of the wheel speed with the reference speed supplies the slip signals.

If, as a result of excessive brake fluid pressure in a brake caliper the wheel shows a tendency toward locking, a condition which is recognized by means of the wheel speed sequence (wheel slip), the fluid pressure will be held constant, that is an additional pressure increase is not possible.