GF42.31-P-0001RT Braking Assistant (BAS), Function
GF42.31-P-0001RT Braking Assistant (BAS), function
On model 251, the BAS function is integrated in the ESP control unit (N47-5).
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:
^ Hesitant brake application - the driver applies too little pedal force in the initial phase and increases it too slowly.
^ Insufficient brake application - the driver applies too little pedal force during the entire brake application.
To improve these situations, Brake Assist has been developed.
"Brake Assist" BAS is an 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 driver presses the brake pedal.
If this is the case, a solenoid valve opens in the brake booster and activates the full servo power. If the driver releases the brake, this is detected and the solenoid valve closes again.
Advantages
^ Optimum braking deceleration reduces the risk of an accident in danger situations and thus provides vital support to the driver.
^ Supports the ABS by providing the greatest possible brake servo assistance.
^ ABS maintains full steerability even during BAS intervention.
^ Considerably reduces the braking distance in the case of hesitant or insufficient brake application.
Component Identification:
Function overview
The normal brake booster amplifies the force of the driver's foot proportionally. If braking is not taking place, a vacuum created by the engine exists in both chambers. A mechanical control valve in the brake booster operated by the force of the driver's foot allows air at atmospheric pressure to flow into the rear chamber when braking. The pressure difference existing between the two chambers and the amplification force created is therefore proportional to the force applied by the driver's foot. Amplification of the force of the foot takes place up to the point at which full atmospheric pressure exists in the rear chamber.
With the BAS brake booster, the basic version is expanded with the following parts:
^ BAS diaphragm travel sensor for measuring brake pedal travel
^ BAS solenoid valve for active implementation of brake servo assistance
^ BAS release switch for detecting end of brake application
^ ESP control unit for measuring values and controlling BAS braking intervention
After the driver starts the engine, a vehicle identification and self-check of the system takes place. The BAS is ready to function if no fault is present and the vehicle has exceeded a speed of 8 km/h after driving off. Following this, BAS can be activated down to a speed of 3 km/h.
The speed at which the brake pedal is depressed and the speed of the vehicle are detected in the ESP control unit.
If the pedal speed is greater than the threshold value specified for the particular vehicle speed, the BAS solenoid valve in the brake booster is activated and full servo force is achieved.
If there is a fault, the BAS is not used (this is indicated by the ESP warning lamp (A1e41) in the instrument cluster (A1)). The normal function of the brake booster is not affected by this.