PRE-RELEASE
Brake Booster Vacuum Assist Description and Operation
| Brake Booster Vacuum Assist Description and Operation |
The vehicle may be equipped with a vacuum pump to ensure a vacuum is available for the Power Vacuum Brake Booster, either as supplementary to the normal vacuum formed in the intake manifold or a stand-alone component. The pump delivers a negative pressure when the engine is not able to provide sufficient vacuum, eg when cold starting, during rapid acceleration at high altitudes and at low turbo pressure.
| Mechanical |
The mechanical vacuum pump is driven by a camshaft. The pump delivers maximum vacuum irrespective of the engine speed. This means that in certain situations, the pump will deliver more vacuum than the system requires.
| Electrical |
A low vacuum switch controls the 12 V to the relay coil in the brake vacuum assist pump. When more vacuum is needed the vacuum switch closes. The relay coil closes the relay contact and connects the electric motor to ground. The electric motor is fed with 12 V. When sufficient vacuum is reached the switch opens and the pump stops.
A venturi is connected between the intake manifold and the vacuum brake booster, amplifying the vacuum. This reduces the on-time for the pump. To prevent air flowing in the wrong direction check valves are used.
