Brake Assist System (BAS): Functional Description (Mercedes-Benz Vito W639)

Simulator studies with regular drivers and on a test track have shown that most drivers, in the event of emergency braking, first of all, at the beginning of the braking process press the pedal quickly, but not hard enough.

It is necessary to distinguish:

• slow braking - at the beginning of the braking process, the driver applies insufficient force to press the pedal and increases it slowly;
• insufficient braking - throughout the entire braking process, the driver does not press the brake pedal hard enough.

To optimize the braking process, the Brake Assist system was developed (emergency braking system).

Purpose

Brake Assist System (BAS, Brake Assistance System) is an active safety system. It is activated when, in an emergency situation, the driver suddenly presses the brake pedal. Based on the speed at which the driver presses the pedal, the system determines whether an emergency braking situation exists. In this case, the electromagnetic valve in the brake booster opens - and the booster applies full force for braking.

When the driver releases the brake pedal, the system detects a decrease in the degree of pressure on the pedal and closes the electromagnetic valve again.

Advantages

- Thanks to optimal deceleration, it reduces the risk of accidents in emergency situations and thus provides significant support in driving.

- Supports the operation of the ABS system, providing the maximum possible braking force.

- When the BAS system is turned on, the ABS operation is not affected.

- Significantly reduces the braking distance during slow or insufficient braking.

BAS Normal Mode: Functional Description

The braking process in normal mode (without the participation of the BAS system)

The brake booster BAS (A7/7) is constantly supplied with vacuum from the intake manifold via a vacuum line or (on a diesel engine) from the vacuum pump. When the brake pedal is not pressed, the same vacuum is created on both sides of the membranes. The pressure spring holds the membrane plate in its original position.

During braking, outside air is supplied through a channel to the rear side of the membranes. Between the front and rear chambers of the booster, a pressure difference arises that increases during braking, which acts in the direction of the main brake cylinder and thereby increases the pedal pressure.

Boosting Pressure Mode (BAS): Functional Description

Pressure Boosting (BAS)

When the conditions for activating the BAS braking mode are met, the BAS electromagnetic valve (y1) is open. Atmospheric pressure is on the back side of the rod seal. As a result of the pressure difference between the front and rear walls of the membrane, the maximum increase in braking pressure occurs.

Pressure relief mode (BAS functional description)

The disconnecting switch BAS (s1) switches to the passive state. The solenoid valve (y1) is switched off and creates brake pressure corresponding to the position of the brake pedal.