5 Series E34 525td (M51) TOUR
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Electric vacuum pump
On some engines, an electric vacuum pump is fitted for additional vacuum supply.
In certain temporary operating situations, the vacuum in the inlet pipe may be too low. In such cases, the inlet
pipe vacuum cannot be adequately boosted by the suction-jet pump. In these situations, the electric vacuum
pump ensures that sufficient vacuum is available.
Reason: After a cold start, an operating situation occurs in which there is very little inlet pipe vacuum due to the
higher load. The electric vacuum pump is actuated for a certain time. This ensures that the brake is sufficiently
boosted when manoeuvring.
After a cold start, the DME will actuate the electric vacuum pump once only for max. 60 seconds.
The electric vacuum pump is actuated in the following situations:
•
Engine-running signal from DME
•
Coolant temperature below 60
°
C
The electric vacuum pump is a vane-cell pump.
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Throttle valve
The throttle valve changes the cross-sectional area of the inlet pipe. This creates an inlet pipe vacuum behind
the throttle valve, especially in overrun mode.
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DME or DDE: Digital engine electronics or digital diesel electronics
The DME or DDE actuates the components needed for system functions (e.g. solenoid valves, electric
switching valves, electropneumatic pressure converters).
System functions
The system functions of the vacuum system are described using the following examples:
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Power assist for brakes
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Actuation of exhaust flaps
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Adjustment of variable turbine geometry
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Actuation of controlled damping mounts
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Exhaust gas recirculation
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Drawing off of blow-by gases from crankcase
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Blowing out activated charcoal filter
Power assist for brakes
The brake booster amplifies the force excerpted at the brake pedal. To do this, the brake booster stores part of
the vacuum generated by the engine. The vacuum then amplifies the force generated by pressure on the brake
pedal.
Actuation of exhaust flap
A controlled electropneumatic exhaust flap is fitted in the exhaust system. The exhaust flap enhances active
sound-damping. The exhaust flap is closed by vacuum.
Adjustment of variable turbine geometry
The variable turbine geometry controls the boost pressure via adjustable guide vanes. The guide vanes are
actuated by vacuum.
Actuation of controlled damping mounts
In the basic setting, there is no vacuum at the control component od the mount. The bypass in the mount is
SBT Vacuum supply All models
BMW AG - TIS
23.01.2013 11:39
Issue status (12/2007) Valid only until next DVD is issued
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