Fuel Supply, Function - GF07.10-D-1003TSC

Engine 642.8 in model 907 

Function requirements for fuel supply, general points 

• Circuit 87M (engine timing ON)
• Circuit 15 ON (ignition ON)

Fuel supply, general points 

The fuel supply supplies filtered fuel out of the fuel tank in adequate amounts under all operating conditions at an adequate pressure to the fuel injectors (Y76).

Function sequence for fuel supply 

The function sequence for fuel supply is described in the following steps:

• Function sequence for fuel pump actuation
• Function sequence for fuel low-pressure circuit
• Function sequence for fuel system high-pressure circuit
• Function sequence for safety fuel shutoff

Function sequence for fuel pump actuation 

The fuel pump with fill level sensor (M3/6) is switched on if the signal "fuel pump ON" is received by the fuel system control unit (N118/9).

This signal is sent redundantly from the CDI control unit (N3/28) via the drive CAN (CAN C) and as a ground signal. The fuel system control unit also receives the CAN signal "Fuel specified pressure" from the CDI control unit.

Function sequence for fuel low-pressure circuit 

The fuel low-pressure circuit consists of the following components:

• Fuel pump with fill level sensor (M3/6)
• Fuel lines
• Fuel filter
• Fuel pressure sensor (B4/17)
• Quantity control valve (Y94/4)
• Fuel system high pressure pump, low-pressure side
• Fuel temperature sensor (B50/6)
• Pressure regulating valve (Y74/6), low-pressure side

The fuel pressure sensor sends a voltage signal to the CDI control unit.

The CDI control unit evaluates the current fuel pressure, comparing it to the specified fuel pressure. The CDI control unit actuates the fuel pump along with the fill level sensor accordingly using a pulse width modulated signal so that the actual value matches the specified value.

When actuated, the fuel pump along with the fill level sensor sucks the fuel out of the fuel delivery module and pumps it through the fuel filter to the fuel high-pressure pump.

Depending on the fuel requirements, the fuel pressure is regulated to about 4.0 bar through the pressure limiting valve integrated into the fuel high-pressure pump.

The quantity control valve also regulates the supply of fuel to the fuel high-pressure pump (feed quantity) depending on the engine operating point in order to keep the fuel temperature low.

Fuel preheating system

• Fuel tank

A fuel filter heater with condensation sensor (R53/4) is installed to ensure flowability of the fuel at low outside temperatures. The heating element is energized by the glow output stage (N14/8) and heats the fuel in the fuel filter. Condensation level monitoring in the fuel filter is by means of the condensation sensor.

The condensation level is read in by the glow output stage and passed on via the drive train LIN (LIN C1) to the CDI control unit. Beginning with a condensation level of approx. 100 ml, the CDI control unit sends a message over the drive CAN (CAN C), powertrain control unit (N127), suspension FlexRay (Flex E), EZS control unit (N738) and over the user interface CAN (CAN HMI) to the instrument cluster (A1), where it is displayed as a warning message.

Shown on fuel low-pressure circuit 

Function sequence for fuel system high-pressure circuit 

The fuel high-pressure circuit consists of the following assembly parts:

• Fuel system high pressure pump
• Left rail
• Right rail
• High-pressure lines
• Fuel pressure sensor
• High pressure fuel temperature sensor
• Pressure regulator valve
• Quantity control valve
• Fuel injectors

Dependent on the signal received from the accelerator pedal module (A68), the engine speed, and the fuel temperature, the fuel high-pressure pump delivers fuel to the left rail and from there simultaneously to the right rail.

The fuel passes from the respective rail via the high-pressure lines to the fuel injectors. The fuel injectors spray fuel in a fine atomized form. The CDI control unit calculates the injection quantity selectively for each cylinder based on a characteristics map for the respective operating condition. The injection quantity is dependent upon the fuel pressure in the rail and the actuation duration of fuel injectors.

The fuel pressure in the rail is controlled by the pressure regulating valve and quantity control valve. The actual applied fuel pressure in the rails is detected by the high pressure fuel pressure sensor and is limited by the pressure regulating valve to a maximum of 1800 bar.

The fuel temperature is detected over the fuel temperature sensor. Both pieces of information are passed on permanently to the CDI control unit.

Shown: fuel high-pressure circuit 

Function sequence for safety fuel shutoff 

The safety fuel shutoff system is designed to ensure traffic and occupant safety.

The CDI control unit controls the safety fuel shutoff on the basis of the following sensors and signals:

• Crankshaft position sensor (B70/1), engine speed
• Supplemental Restraint System control unit (SRS) (N2/5), direct crash signal
• SRS control unit, indirect crash signal via the user interface CAN, EZS control unit, suspension FlexRay, powertrain control unit, and engine CAN

The safety fuel shutoff is activated by the CDI control unit in the following conditions:

• Absence of the engine speed signal
• Crash signal

Absence of the engine speed signal 

If the engine speed signal generated by the CDI control unit is missing the fuel pump with fill level sensor will be switched off.

Crash signal 

If the CDI control unit receives a crash signal indirectly or directly from the SRS control unit, it switches off the fuel pump with the fill level sensor, the quantity control valve, and the pressure regulating valve and briefly actuates the fuel injectors to depressurize the fuel system.

Electrical function schematic for fuel supply	PE07.10-D-2703-97TSC
Overview of system components for common rail diesel injection (CDI)	GF07.16-D-9997TSC