Brake Torque Control Circuit

Wheel Spin Threshold:

The Brake Torque Control Circuit is based on the electronic and hydraulic components of the service brakes with ABS.

ELECTRONIC
The ABS/ASR control unit contains all of the circuitry for both ABS and ASR. Compared to the standard ABS control unit there are additional input signals as well as 2 ASR microcomputers for the ASR functions and its additional outputs.

HYDRAULICS
Based on the standard ABS control unit, a one piece hydraulic unit was developed for ASR. The ABS/ASR hydraulic unit contains, alongside the components familiar from ABS, a switchover valve for the change from braking range to ASR control range, pressure limiting valves as hydraulic safety equipment and one solenoid valve each for the rear wheel brakes. The brake pressure necessary for ASR control comes from the pressure reservoir, filled by the ASR charging pump together with the ASR return/pressure pump.


The ABS/ASR control unit constantly processes the wheel speed signals from the wheel speed sensors for the following values:

^ Drive wheel spin,
^ Acceleration,
^ Vehicle speed (front wheel speed),
^ Turn identification.

If the monitored values exceed specific values, the output signals of the ABS/ASR control unit initiate control of the three pressure phases (pressure increase, pressure retention, pressure release) in the ABS/ASR hydraulic unit (braking actuation).

Depending on the vehicle speed, the brake torque control starts as soon as the speed difference between front and rear wheels increases above the spin threshold of the brake torque control. Thus pressure increase, retention or release control the braking of the corresponding rear wheel. If the speed difference falls below the threshold again for a predetermined period of time, the system switches to pressure release.