Vacuum Pump: Description and Operation

Vacuum Pump

To secure the supply of vacuum in the brake servo unit under varying operating conditions, there is a vacuum pump fitted in the car. This pump supplies the brake servo unit with negative pressure when the engine is not able to provide a sufficient vacuum.

Brake Vacuum Circuit:

In a situation with an idling engine and a stationary car, the brake pedal may feel "soft" and sink somewhat lower than normal when applied. This is completely normal and will not affect braking force in a negative manner.

Cars equipped with HFV6 are fitted with an electric vacuum pump and two connections to the intake manifold. One of them has a venturi for amplifying the brake vacuum.

The electric pump is powered by +30 voltage via a relay. The relay in turn is governed by a pressure sensor located on the hose between the vacuum pump and the brake servo. This sensor comprises a diaphragm, spring, switch and check valve. The switch closes to start the pump at a pressure of 49 ±3 KPa. When the pressure reaches 42 ±3 Kpa, the switch will open and the pump will stop.

On the vacuum pipe between the electric vacuum pump and the brake servo unit is a T-coupling. From this T-coupling, the pipe returns to the intake manifold where it divides to two connections. On one of the pipes, connected directly to the intake manifold, there is also a check valve.






Index:
1. Venturi
2. Camshaft cover connection
3. Brake servo connection
4. Intake manifold connection
5. Check valves
6. Chamber
7. Jet

The venturi (1) has three connections. One of the venturi connections is held by barbs and is sealed with an O-ring. This is connected directly to the camshaft cover (2) on the rear cylinder bank. On the vacuum hose (4) that is connected to the intake manifold there is a check valve. The difference in pressure between the two connections provides an airflow through the jet (7).

As the inlet in the jet is tapered, the speed of the passing air will be increased to create an ejector effect that increases the negative pressure in the hose connected to the brake servo (3). To prevent air flowing in the wrong direction through the chambers (6) to the brake servo, the venturi is equipped with check valves (5).