GF42.31-P-0001GZ Braking Assistant (BAS) - Operation
GF42.31-P-0001GZ Braking Assistant (BAS) - Operation
On model 164 the BAS function is integrated in the ESP control unit.
Studies with normal drivers in the driving simulator and on the test track have shown that in emergency braking situations most drivers press the brake pedal quickly but not hard enough, above all in the initial phase of the brake application.
A distinction is made between:
^ Hesitant brake application - in the initial phase the driver applies too little pedal force and increases it too slowly
^ Inadequate braking - the driver applies too little brake force throughout 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 brake pedal is depressed.
If this is the case, a solenoid valve opens in the brake servo and activates the full servo power. If the driver releases the brake, this is detected and the solenoid valve closes again.
Advantages
^ Reduces the accident risk in hazardous situations through optimal brake deceleration and thus assists the driver considerably
^ Supports the ABS by providing the greatest possible servo action.
^ ABS retains the full steerability also during intervention by the BAS
^ Reduces the brake distance considerably during hesitant or inadequate brake application
Component Identification:
Function overview
The normal brake booster amplifies the force of the driver's foot proportionally. If the vehicle is not braked the vacuum which is produced by the engine prevails in both chambers. A mechanical control valve in the brake servo 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 BAS (A7/7) the basic version is expanded by the following parts:
^ Diaphragm travel sensor BAS (A7/7b1) for measuring the brake pedal travel
^ BAS solenoid valve (A7/7y1) for actively carrying out brake force assist
^ BAS release switch (A7/7s1) for detecting the end of the brake application
^ ESP (N47-5) for recording the values and for actuating the BAS brake intervention
A vehicle identification and self-check of the system takes place once the engine has started. 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 operating speed of the brake pedal and the vehicle speed is recorded in the ESP control unit.
If the pedal speed is greater than the threshold value specified for the respective vehicle speed, the BAS solenoid valve in the brake booster is actuated and thus the full booster force is reached.
BAS is not used in the event of a defect (display by ESP warning lamp (A1e41) (in the instrument cluster). The normal function of the brake booster is not affected by this.
