GF42.31-D-0001H Braking Assistant (BAS) - Operation

GF42.31-D-0001H Braking Assistant (BAS) - Operation


The Brake Assist System helps to shorten the brake distance during panic braking. The brake assistant is based on the knowledge that in critical situations car drivers depress the brake pedal quickly but not hard enough. If by means of the speed of brake actuation the ESP control unit (N30/4) detects an emergency stop, within fractions of a second the full braking pressure is built up in the braking system via the pump integrated in the traction system hydraulic unit. During emergency braking the wheels do not lock as the antilock brake system (ABS) modulates the brake force at the slip limit. The vehicle is braked to the maximum extent and remains steerable in the process. The Brake Assist System is only deactivated again when the driver reduces the pedal pressure.

By means of the following information the ESP control unit detects that an emergency case braking exists:

^ Pressure rise characteristics of the brake pressure, via the brake pressure switch in the traction system hydraulic unit
^ Driver brakes via the stop lamp switch (S9/1)
^ Brake pressure level, via the brake pressure switch in the traction system hydraulic unit
^ Vehicle speed, via the left front rpm sensor (L6/1), right front rpm sensor (L6/2), left rear rpm sensor (L6/3) and right rear rpm sensor (L6/4)

The BAS system cuts in when the following conditions apply:

^ The BAS system is enabled once the engine has started "circuit 61 ON" and once self-diagnosis has taken place if no fault is present.
^ The speed of the vehicle after starting off is > 8 km/h.
^ When the brake pedal is operated the pedal speed is greater than the specified threshold value for the associated vehicle speed.

The BAS system is switched off when one of the following conditions applies:

^ The vehicle speed is < 3 km/h.
^ The duty cycle of the BAS system is more than t = 20 s.
^ The signal from the stop lamp switch remains deactivated
^ There is a BAS system malfunction.
^ The brake pedal pressure is reduced by the driver to such an extent that emergency braking is no longer required.