It should be distinguished:
- slow braking - at the beginning of the braking process, the driver does not apply enough force to press the pedal and increases it slowly;
- insufficient braking - during the entire braking process, the driver does not press the brake pedal hard enough.
Brake Assist was developed to optimize the braking process (emergency braking system).
Purpose
Brake Assist System (BAS, emergency braking system) is an active safety system that is activated when the driver presses the brake pedal hard in an emergency. The system determines the presence of an emergency braking situation based on the speed at which the driver presses the pedal. In this case, the solenoid valve in the brake booster opens - and the booster applies full force to brake.
When the driver releases the brake pedal, the system detects a decrease in the degree of pressure on the pedal and closes the solenoid valve again.
VN 9.063
VN 9.064 A. Insufficient braking; b. slow braking; With. Braking in BAS mode
Advantages
- Thanks to optimal deceleration, it reduces the risk of accidents in emergency situations and thus provides significant support in driving.
- Maintains the ABS system, providing the maximum possible braking force.
- When the BAS system is activated, the operation of the ABS is not affected.
- Significantly reduces the braking distance during slow or insufficient braking.
Normal BAS Mode: Functional Description
Braking process in normal mode (without the participation of the BAS system)
Brake booster BAS (A7/7) through the vacuum line is constantly provided with vacuum from the intake manifold or (on a diesel engine) from the vacuum pump. When the brake pedal is not depressed, the same vacuum is created on both sides of the membranes. The pressure spring holds the diaphragm plate in its original position.
During braking, external air is supplied through the channel to the rear side of the membranes. Between the front and rear chambers of the booster, a pressure difference arises, which increases during braking, which acts in the direction of the brake master cylinder and thereby increases the pedal force.
VN 9.065 Illustration: slowdown; A7/7. Brake booster BAS; s1. Disconnect switch BAS; y1. BAS solenoid valve (control valve); A. Atmosphere pressure; b. Reduced vacuum; With. Underpressure
Pressurizing mode (BAS): functional description
Pressurization (BAS)
When the conditions for activation of the braking mode BAS are met, the solenoid valve B AS (y1) open. On the reverse side of the stem seal is atmospheric pressure. As a result of the pressure difference between the front and rear walls of the membrane, the maximum increase in braking pressure occurs.
VN 9.066 Illustration: slowdown; A7/7. Brake booster BAS; s1. Disconnect switch BAS; y1. BAS solenoid valve (control valve); A. Atmosphere pressure; With. Underpressure
Pressure Relief Mode (BAS functional description)
Disconnect switch BAS (s1) switches to the passive state. Solenoid valve (y1) turns off and creates a brake pressure corresponding to the position of the brake pedal.
VN 9.067 Illustration: slowdown; A7/7. Brake booster BAS; s1. Disconnect switch BAS; y1. BAS solenoid valve (control valve); A. Atmosphere pressure; With. Underpressure