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

Engine 651 in model 907 

Block diagram 

Function requirements for fuel supply, general points 

• Circuit 15 ON (ignition ON)
• Circuit 87M ON (Engine management 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 

Switching on the fuel pump with fill level sensor takes place if a "fuel pump ON" signal is received by the fuel pump control unit. This signal is sent redundantly by the CDI control unit as a CAN signal via the drive CAN and as a ground signal.

• Fuel pump with fill level sensor
• Fuel lines
• Fuel filter
• Quantity control valve
• High-pressure pump, low-pressure side
• Fuel temperature sensor
• Pressure regulating valve, low-pressure side
• Fuel injectors

The fuel system control unit detects the current fuel pressure by means of a voltage signal from the fuel pressure sensor and transmits this information via the drive train CAN to the CDI control unit.

The fuel pump control unit evaluates the current fuel pressure, compares it with the fuel specified pressure, and actuates the fuel pump with fill level sensor accordingly with a pulse width modulated signal in such a way that the actual value corresponds to the specified value.

Upon actuation, the fuel pump with fill level sensor suctions the fuel out of the fuel delivery module and pumps it through the fuel filter to the high-pressure pump.

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 tank

Depending on the fuel requirement, the fuel pressure is variably regulated to approx. 4.0 bar via the pressure limiting valve integrated in the high-pressure pump.

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

The maximum feed volume at 12 V supply voltage and loaded fuel filter is 155 l/h.

Fuel preheating system

To ensure the flowability of the fuel at low outside temperatures, a fuel filter heater with a condensation sensor is installed for water level monitoring. The heating element is energized by the glow output stage and warms the fuel in the fuel filter.

Condensation level monitoring in the fuel filter takes place via the fuel filter heater with condensation sensor. The condensation level is read in by the glow output stage and forwarded to the CDI control unit via the drive LIN. From a condensation level of approx. 100 ml, the CDI control unit sends a message to the instrument cluster, which is displayed as a warning message in the multifunction display.

View of fuel system 

Function sequence for fuel system high-pressure circuit 

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

• High pressure pump
• Rail
• High-pressure lines
• Rail pressure sensor
• Pressure regulator valve
• Fuel injectors

The high-pressure pump pumps the fuel into the rail depending on the signal of the accelerator pedal sensor in the accelerator pedal module and the engine speed. From the rail, the fuel flows through the high-pressure lines to the fuel injectors. The fuel injectors inject finely atomized fuel selectively into each cylinder.

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 depends on the fuel pressure in the rail and the actuation time of the fuel injectors.

The fuel pressure in the rail is controlled by the pressure regulating valve and quantity control valve. The actual fuel pressure actually present in the rail is measured by the rail pressure sensor and continuously transmitted to the CDI control unit.

The fuel temperature is measured by the fuel temperature sensor and transmitted continuously 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 signals:

• Rpm sensor, engine speed
• Supplemental Restraint System control unit (SRS), direct crash signal

The safety fuel shutoff is activated by the CDI control unit for 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 from the Supplemental Restraint System (SRS) control unit, it switches off the following component parts:

• Fuel pump with fill level sensor
• Fuel injectors
• Pressure regulator valve
• Quantity control valve

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