System Components

System components
The brake servo unit boosts the pressure on the brake pedal exerted by the driver when the brakes are applied. The extra power supplied by the servo unit is obtained from the difference between the vacuum in the engine intake manifold or the vacuum pump and atmospheric pressure. In order to achieve this servo assistance in a compact design, the servo unit has dual operating chambers.

The brake servo unit includes the Mechanical Brake Assist (MBA) function which provides more powerful vacuum assistance during lower pedal pressure than previously available. This has been accomplished with modified control valve calibration for regulating vacuum/atmospheric pressure in the brake servo unit. At pedal pressures of 500 N. an output force of approx. 4200 N is achieved compared with a normal force of 3000 N.

The servo unit is attached to the intake manifold and vacuum pump by means of a hose. The servo unit consists of a metal casing, valve unit and dual diaphragms mounted between the brake pedal and master cylinder and is connected to them by pushrods. If the supply of vacuum to the servo unit is lost, the two pushrods act as a single pushrod. The brakes will then work conventionally without servo assistance but much greater pedal force will be required.

The master brake cylinder, which is mounted on the brake servo unit, contains a secondary and primary piston. The brake fluid reservoir is fitted on the master cylinder with separate chambers for the primary and secondary circuits.

In cars with a manual gearbox, the brake fluid reservoir serves as the reservoir for brake fluid used in clutch system. A brake fluid level switch is mounted on the brake fluid reservoir. The Level switch contains a float magnet which affects a reed element that closes an electric circuit and warns the driver regarding the condition.