SAAB WIS ONLINE

Brake Assist System Description and Operation

Brake Assist System Description and Operation

System Component Description

The brake assist system consists of the following:

Brake Pedal

Multiplies the braking effort applied by the driver.

Brake Pedal Pushrod

Transfers multiplied input force received from the brake pedal to the vacuum brake booster.

Power Vacuum Brake Booster

Uses source vacuum to decrease effort required by the driver when applying the brakes.

Vacuum Brake Booster Control Valve

Regulates the vacuum/atmospheric pressure within the vacuum brake booster. The calibration of the control valve gives more powerful vacuum assistance during low brake pedal pressure.

Vacuum Source

The source vacuum is either derived from the intake manifold or delivered from a pump, mechanically or electrically driven. For further information refer to Brake Booster Vacuum Assist Description and Operation .

Vacuum Source Delivery System

Enables delivery and retention of source vacuum for vacuum brake booster.

System Operation

Brake system input force from the driver is multiplied by the brake pedal and transferred by the pedal pushrod to the hydraulic brake master cylinder. Effort required to apply the brake system is reduced by the operation of the vacuum brake booster.

At rest, source vacuum is applied to both sides of each of the diaphragms in the dual booster. Return springs maintain the booster in a rest position.

When brake system force is applied, vacuum to the rear of the diaphragms is cut off, and air at atmospheric pressure is admitted in its place. The vacuum acts to pull the diaphragms forward, while the atmospheric pressure acts to push from behind. As a result, the amount of effort required by the driver is reduced. When input force is removed, vacuum again replaces atmospheric pressure within the vacuum power brake booster to help return the booster to rest. Return springs maintain the system in a rest position.