Functions
Fuel supply system
The fuel pressure sensor sends a voltage signal, corresponding to the system pressure
applied between the fuel pump and the high pressure pump, to the engine control unit
(DME/ECM). The system pressure (fuel pressure) is determined with the fuel
pressure sensor upstream of the high pressure pump. The target pressure is constantly
compared to the actual pressure in the DME.
If the target pressure deviates from the actual pressure, the engine control unit increases
or decreases the voltage for the electric fuel pump. This voltage is sent in the form of a
message via the PT-CAN to the EKP control unit.
The electric fuel pump (EKP) control unit converts the message into an output voltage
for the electric fuel pump, thus regulating the required delivery pressure for the engine
(or high pressure pump). The electric fuel pump is pilot-controlled in the event of signal
failure (fuel pressure sensor). Should the CAN bus fail the EKP control unit operates the
electric fuel pump with the applied system voltage. The fuel flows via the high pressure
line to the fuel rail. The fuel is buffered in the fuel rail and distributed to the fuel injectors.
Fuel quantity control
The rail pressure sensor measures the current fuel pressure in the rail. The excess fuel is
returned to the inlet of the high pressure pump when the quantity control valve in the
high pressure pump opens. Vehicle operation is restricted in the event of the high pres-
sure pump failing.
The quantity control valve controls the fuel pressure in the rail. The engine management
actuates the quantity control valve with a pulse width-modulated signal. Depending on
the pulse width, a variable throttle cross section is released, thus providing the quantity of
fuel required for the current load status of the engine. It is also possible to reduce the
pressure in the rail.
Boost pressure control
The engine management controls the boost pressure with the wastegate valve at the
turbocharger. An electropneumatic pressure converter (vacuum solenoid) receives the
signals from the engine management and supplies vacuum to open the wastegate valve
when the specified maximum boost pressure is reached.
90
N55 Engine
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