Brake Assist (BAS) Function
Flow Chart
Tests with normal drivers in a driving simulator and on a test track have shown that in emergency braking situations most drivers press the brake pedal quickly but not hard enough, especially in the initial phase of braking.
Legend
a Inadequate Braking
b Hesitant Braking
c BAS Braking
A distinction is made between:
Hesitant braking - the driver applies too little pedal force in the initial phase and increases it too slowly
Inadequate braking - the driver applies too little pedal force throughout the entire braking.
Brake Assist has been developed to improve these situations.
Purpose
"Brake Assist" BAS is an active safety system. It is active when the driver brakes very quickly in an emergency situation. According to the speed with which the brake pedal is operated, the system recognizes whether an emergency braking situation exists. If this is the case, a solenoid valve in the brake booster is opened, thereby activating the full booster power.
If the driver releases the brake, this is recognized and the solenoid valve is closed again.
Benefits
Reduces the risk of accident in dangerous situations through optimum brake deceleration and thereby assists the driver considerably
Supports ABS through the highest possible brake boost
ABS maintains complete steerability even during BAS intervention.
Reduces the stopping distance considerably in the case of hesitant or inadequate braking.
Functional survey
The normal brake booster increases the force applied by the driver's foot proportionally. If the vehicle is not braked, vacuum which is produced by the engine or a vacuum pump prevails in both chambers. When braking, air under atmospheric pressure flows into the rear chamber through a mechanical control valve in the brake booster which is operated by the force applied by the drivers foot The resultant difference in pressure between the two chambers and consequently the boost power produced are proportional to the force applied by the driver's foot. The force applied by drivers foot is boosted up to the point at which full atmospheric pressure prevails in the rear chamber.
With the BAS brake booster the basic version is extended by the following parts:
BAS diaphragm travel sensor for measuring the brake pedal travel.
BAS solenoid valve for activation of brake boost
BAS release switch for recognizing the end of the braking operation.
BAS control module for recording the values and for actuating
BAS brake intervention.
The BAS function is integrated into the ESP control module on vehicles with engine 111, 112, 113, 605, 606, 611, 612, 613 and ESP.
The BAS function is integrated into the ESP control module on models 163, 168, 203, 215 and 220.
A vehicle identification and system self-check takes place after the engine is started.
BAS is ready to operate if no fault exists and the vehicle exceeds a speed of 8 km/h after starting off. The BAS can be switched on down to a speed of 3 km/h.
The speed at which the brake pedal is operated and vehicle speed is recorded in the BAS control module (N48) or ESP control module (N47-5). If the speed at which the brake pedal is operated is higher than the threshold value specified for the respective vehicle speed, a solenoid valve in the brake booster is actuated so that the full booster power is reached.
BAS does not come on in the event of a defect (display by malfunction indicator lamp or multifunction display in the instrument cluster). The normal function of the brake booster is not thereby impaired.
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