Power Brake Assist: Description and Operation

GF42.31-P-2000SK BAS Braking Assistant - Operation

Braking behavior
Studies when driving normally on the driving simulator and on the test track have shown that most drivers in emergency braking situations, above all in the initial phase of brake application, in fact press the brake pedal quickly but not hard enough.

A distinction is made between:
^ Hesistant braking, e.g. in the initial phase the driver applies too little pedal force and increases it too slowly.
^ Inadequate braking, e.g. the driver applies too little pedal force throughout the entire braking application.

Brake Assist (BAS) has been developed to improve this situation.

Advantages:
^ The BAS system reduces the accident risk in dangerous situations by optimum braking deceleration.
^ The BAS system significantly reduces the brake distance during hesitant or inadequate braking.

Task
The BAS system is part of the active safety system. It becomes active when the driver brakes very quickly in an emergency situation. The system detects whether an emergency braking situation exists on the basis of the speed at which the brake pedal is depressed.

Function
A brake application with BAS functions exactly as with a normal brake application, only the pressure is built up more quickly corresponding to the pedal speed. BAS is completely integrated in the Electronic Stability Program (Electronic Stability Program) (ESP). The electronics are located in the ESP and BAS control unit (N47-5). The pressure reservoir in the traction systems hydraulic unit is used for pressure generation (A7/3). After the engine is started, a vehicle identification and self-check of the system takes place.

From the operating speed of the brake pedal and the vehicle speed the ESP and BAS control unit (N47-5) detects that the conditions for a BAS cut-in exist. Using the rate of pressure increase in the pre-pressure sensor and the signal of the pedal value sensor the ESP and BAS control unit (N47-5) calculates the operating speed of the brake pedal.

The operating speed of the brake pedal and vehicle speed is detected in the ESP and BAS control unit (N47-5). If the pedal speed is greater than the threshold value specified for the respective vehicle speed, the high-pressure charging pump in the traction system hydraulic unit (A7/3) is actuated in the ESP and BAS control unit (N47-5) and thus the full brake force is achieved. The BAS system cuts in when the following conditions apply:
^ The speed is > 10 km/h.
^ The brake pedal is operated.
^ No current fault is detected.
^ The system is released after a self-test.
^ The pedal speed threshold is exceeded.

The BAS system is switched off when one of the following conditions applies:
^ The brake pedal pressure is reduced by the driver to such an extent that emergency braking is no longer required.
^ The speed is < 3 km/h.
^ A fault is detected which leads to the actuation of the upper multifunction display (A1p13) in the instrument cluster (A1).

The BAS system is not used in the event of a defect; this is shown by the upper multifunction display(A1p13) in the instrument cluster (A1). The normal function of the brake is not affected by this.