General
NOTE: For model name/model number cross reference refer to Model Designation Table. Application and ID
Functional Diagram
General
Tests with normal drivers in the driving simulator and on the test track have shown that in emergency braking situations most drivers, primarily in the initial phase of braking press the brake pedal quickly but not hard enough.
A distinction is made between:
- Hesitant braking - the driver does not apply enough force on the pedal in the initial phase and increases it too slowly.
- insufficient braking - the driver does not apply enough force on the pedal throughout the entire braking process.
Brake Assist (BAS) has been developed to improve these situations.
Task
"Brake Assist" BAS is an active safety system. It is active when the driver brakes very quickly in an emergency situation. By the speed with which the brake pedal is operated the system recognizes whether there is an emergency braking situation. If this is the case a solenoid valve in the brake booster is opened, activating the full booster power.
If the driver releases the brake, this is recognized and the solenoid valve is closed again.
Advantages
- Reduces the accident risk in dangerous situations by optimum brake retardation and therefore assists the driver considerably
- Assists ABS through the greatest possible brake force assistance
- ABS maintains full steerability even during BAS intervention
- Reduces the stopping distance considerably during hesitant or insufficient braking
Function Overview
The normal brake booster boosts the driver's pedal effort proportionally. if the vehicle is not braked, vacuum which is generated by the engine or a vacuum pump prevails in both chambers. By means of a mechanical control valve in the brake booster which is operated by the pedal effort, air at atmospheric pressure flows into the rear chamber when braking. The resultant difference in pressure between both chambers and therefore also the boost power produced are proportional to the driver's pedal effort. The pedal effort is boosted up to the point where full atmospheric pressure prevails in the rear chamber.
With the BAS brake booster the basic version is expanded by the components below:
- BAS diaphragm travel sensor for measuring the brake pedal travel.
- BAS solenoid valve for actively carrying out brake force assistance.
- BAS release switch for recognizing the end of the braking process.
- BAS control module for recording the values and actuating the BAS brake intervention.
On vehicles with engine 112 or 113 and ESP, the BAS function is integrated in the Electronic Stability Program (ESP) control module On models 263, 168 and 220 the BAS function is integrated in the ESP control module.
Once the engine has started a vehicle identification takes place and a system self -check. BAS is ready for operation when there is no fault present and the vehicle exceeds a speed of 8 km/h after starting off. BAS can be switched on down to a speed of 3 km/h.
The operating speed of the brake pedal and vehicle speed is recorded in the BAS control module (N48) or ESP control module (N47-5). if the pedal speed is greater than the threshold value specified for the respective vehicle speed, a solenoid valve in the brake booster is actuated and therefore the full booster power achieved.
If there is a defect, BAS is not used (display by indicator lamp or multifunction display in the instrument cluster). The normal function of the brake booster is not impaired by this.