GF07.10-P-1003MAF Fuel Supply, Function

GF07.10-P-1003MAF Fuel Supply, Function

Function requirements for fuel supply, general points
^ Circuit 15 ON (ignition ON)

Fuel supply, general points
Under all operating conditions, the fuel supply supplies filtered fuel to the injection valves (Y62) from the fuel tank, in sufficient quantity and at sufficient pressure (injection pressure).

Fuel supply, function sequence
The function sequence for the fuel supply is described in the following points:
^ Fuel pump control function sequence
^ Fuel delivery function sequence
^ Function sequence for safety fuel shutoff

Fuel pump control function sequence
The fuel supply is controlled and monitored by the ME-SFI [ME] control unit (N3/10) and the fuel pump control unit (N118).
The fuel pump (M3) is switched on when the "fuel pump ON" direct ground signal is received by the fuel system control unit from the ME-SFI [ME] control unit.

The ME-SFI [ME] control unit determines the current fuel pressure via the fuel pressure sensor (B4/15). To control the fuel pump, the ME-SFI control unit evaluates the fuel pressure and load requirement and sends the "specified fuel pressure" PWM signal (pulse width modulated signal) to the fuel pump control units (with a duty cycle of 10 to 90 %). The latter evaluates the PWM signal and actuates the corresponding fuel pump with three phase-offset alternating current signals.

The fuel system control unit actuates the fuel pump as required so that the actual value of the fuel pressure matches the specified value.
Depending on the fuel requirement, fuel pressure is varied between 3.0 and 4.5 bar.

Fuel feed
The fuel pump sucks the fuel out of the fuel feed module through the fuel strainer (fuel prefiler) and out of the right fuel tank chamber with the suction jet pump in the fuel feed module. Then the fuel pump pumps the suctioned fuel via the check valve and the fuel filter to the fuel manifold (single line system, without return line).
In doing so, the fuel pressure is limited by the pressure limiting valve to approx. 6.0 bar.

There is a check valve at the feed point of the fuel filter which prevents reduction of the fuel pressure when the fuel pump is switched off.

The LH suction jet pump is supplied with fuel from the fuel return of the pressure limiting valve, and part of the fuel feed from the fuel pumps. This suction jet pump pumps the fuel out of the left fuel tank chamber into the fuel feed module.

A junction of the fuel pump actuates the right fuel jet pump with fuel. This suction jet pump pumps the fuel out of the right fuel tank chamber into the fuel feed module.

Component Identification:

Function sequence for safety fuel shutoff
To ensure traffic and passenger safety, safety fuel shutoff is applied. The ME-SFI [ME] control unit controls the safety fuel shutoff on the basis of the following sensors and signals:
- Crankshaft Hall sensor (B70), engine speed
- Front and rear throttle valve actuator (M16/3, M16/4), throttle valve positions
- Supplemental restraint system control unit (N2/10), direct crash signal
- Supplemental restraint system control unit, indirect crash signal via the chassis CAN (CAN E)

The safety fuel shutoff is activated by the ME-SFI [ME] control unit in the following conditions:
^ Mechanical error in front and rear throttle valve actuator
^ Absence of the engine speed signal
^ Crash signal

Mechanical error in front and rear throttle valve actuator
If the ME-SFI control unit detects a mechanical fault in t he front or rear throttle valve positioner by evaluating the throttle valve positions, both throttle valve positioners are switched off. When the injection valves are shut off, the engine speed is limited to approx. 1400 rpm when idling and approx. 1800 rpm when driving.

Absence of the engine speed signal
If the engine speed signal generated by the ME-SFI [ME] control unit is missing, the fuel pump is shut off via the fuel pump control unit.

Crash signal
If the ME-SFI control unit receives a crash signal directly or indirectly from the restraint systems control unit over the chassis CAN, it switches off the fuel pump through the fuel pump control unit and briefly actuates the fuel injection valves in order to depressurize the fuel system.