Power Brake Assist: Description and Operation

GF42.31-P-4004RC BAS brake booster, component description

Component Identification:

Location
The brake booster is located on the left of the engine compartment.

Task
The brake booster boosts the pedal force applied by the driver during braking. In the event of an emergency stop, the Brake Assist (BAS) function is also activated.

Design
The BAS brake booster contains the following electrical components:

- BAS diaphragm travel sensor
- BAS release switch
- ESP brake pressure sensor 1
- BAS solenoid valve (A7/7y1)

Function
The brake booster is constantly supplied with vacuum via a vacuum line. If the brake is not actuated, equal vacuum exists on both sides of the diaphragm. A push spring holds the diaphragm plate in its starting position.

During the brake application outside air is lead to the back of the diaphragm via a port. Between the front and rear chamber of the brake booster, a pressure difference occurs which acts in the direction of the master brake cylinder and thus boosts the pedal force applied by the driver. In the event of an emergency stop, the ESP and BAS control unit (N47-5) actuates the brake booster via the BAS solenoid valve.

The signals from the electrical components of the brake booster are read in and processed by the ESP and BAS control unit.