Fuel Supply, Function - GF07.10-P-1003OLF
ENGINE 651.9 in MODEL 166 as of model year 2016
Function requirements for fuel supply, general points
- Circuit 15 (ignition ON)
- Circuit 87M (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
To switch on the fuel pump (M3) the CDI control unit (N3/9) sends the "Fuel pump ON" signal to the fuel system control unit (N118). This signal is sent redundantly from the CDI control unit as a CAN signal via the drive train 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 tank
- Fuel pump (FP)
- Fuel lines
- Fuel filter
- Quantity control valve (Y94)
- High-pressure pump, low-pressure side
- Fuel temperature sensor (B50)
- Pressure regulating valve (Y74), low-pressure side
The fuel system control unit detects the current fuel pressure by means of a voltage signal from the fuel pressure sensor (B4/7) and sends this information via drive train CAN to the CDI control unit.
The fuel system control unit evaluates the current fuel pressure, compares it with the fuel specified pressure and actuates the fuel pump accordingly by means of a pulse width modulated signal in such a way that the actual value corresponds to the specified value.
During actuation the fuel pump suctions the fuel out of the fuel feed module and pumps it through the fuel filter to the high-pressure pump.
Depending on the fuel requirement, the fuel pressure is regulated to about 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.
Fuel preheating system
In order to achieve flowability of the fuel at low outside temperatures, a fuel filter condensation sensor with heating element (B76/1) for water level monitoring is installed. The heating element is energized by the glow output stage (N14/3) 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. As of a condensation level of approx. 100 ml, the CDI control unit sends a message via chassis CAN 1 (CAN E1), electronic ignition lock control unit (N73) and chassis CAN 2 (CAN E2) to the instrument cluster (A1) that is shown as a warning message in the multifunction display (A1p13).
Shown on fuel low-pressure circuit
Function sequence for fuel system high-pressure circuit
The fuel high-pressure circuit consists of the following component:
- High-pressure pump
- Rail
- High-pressure lines
- Fuel pressure sensor
- Fuel temperature sensor
- Pressure regulating valve
- Fuel injectors
- Quantity control valve
The high-pressure pump delivers the fuel into the rail in accordance with the signal from the accelerator pedal sensor (B37), the engine speed and the fuel temperature. From the rail, the fuel flows through 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 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 applied fuel pressure in the rail 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 passenger safety.
The CDI control unit controls the safety fuel shutoff on the basis of the following sensors and signals:
- Crankshaft Hall sensor (B70), engine rpm
- Supplemental restraint system control unit (N2/10), direct crash signal
- Supplemental restraint system control unit, indirect crash signal via chassis CAN 1
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 will be switched off.
Crash signal
If the CDI control unit receives a crash signal indirectly via chassis CAN 1 or directly from the supplemental restraint system control unit, it switches off the fuel pump, 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-P-2703-97NBF | ||
| Electrical function schematic for safety fuel shutoff | PE07.10-P-2733-97NBF | ||
| Overview of system components for common rail diesel injection (CDI) | GF07.16-P-9997OLF |