Fuel Supply, Function - GF07.10-P-1003MRS
Engine 264.9 in Model 205, 253
Function requirements, general
- Circuit 15 (ignition ON)
Electronic ignition lock control unit (N73) transmits the circuit status via the suspension FlexRay (Flex E), powertrain control unit (N127) and drive CAN (CAN C1) to the ME-SFI [ME] control unit (N3/10).
Fuel supply, general points
The fuel supply system supplies the fuel high-pressure pump with a sufficient quantity of filtered fuel from the fuel tank at sufficient pressure under all operating conditions.
The fuel supply system is subdivided into the following points:
- Low-pressure fuel circuit
- High-pressure fuel circuit
- Safety fuel shutoff
Low-pressure fuel circuit
The low-pressure fuel circuit ensures the fuel supply of the fuel high-pressure pump.
The ME-SFI [ME] control unit transmits the "Fuel pump ON (M3)" request via a direct line and redundantly via the drive CAN to the fuel system control unit (N118). The ME-SFI [ME] control unit also transmits the specified fuel pressure via the drive CAN to the fuel system control unit. The ME-SFI [ME] control unit calculates the specified fuel pressure (fuel requirement) from the current fuel pressure and the load requirement of the Engine. Depending on the fuel requirements, a fuel delivery rate of 0 to 130 l/h is regulated for a fuel pressure of approx. 4 to 6.7 bar.
The fuel system control unit accordingly actuates the fuel pump, evaluates the fuel pressure and transmits this via the drive CAN to the ME-SFI [ME] control unit. The fuel pressure is recorded by the fuel pressure sensor (B4/7). The fuel system control unit reads in the signals of the fuel pressure sensor directly.
The fuel pump intakes fuel from the fuel delivery module and pumps it through the fuel filter to the fuel high-pressure pump (single-line system, without return line). The overflow valve in the fuel filter opens at a fuel pressure of approx. 7 to 9bar. A check valve is located in the fuel filter feed line that prevents a decrease in the fuel pressure (to below 4.5 bar) where the fuel pump is OFF.
The fuel pressure sensor also records the fuel temperature.
High-pressure fuel circuit
In the high-pressure fuel circuit, the high fuel pressure of approx. 200 bar required for the spray-guided direct injection is generated, regulated and stored in the rail.
The quantity control valve (Y94) is located on the fuel high-pressure pump. The quantity control valve regulates the fuel quantity that is supplied to the pump element in the fuel high-pressure pump in a demand- and map-dependent manner. The ME-SFI [ME] control unit evaluates the signals of the fuel pressure and temperature sensor (B4/25) for this purpose.
The ME-SFI [ME] control unit accordingly actuates the quantity control valve. The fuel pressure and temperature sensor is installed on the rail.
The fuel high-pressure pump supplies the fuel via the high-pressure line and rail to the following components of the fuel injection system that are then accordingly actuated by the ME-SFI [ME] control unit:
- Cylinder 1 fuel injector (Y76/1)
- Cylinder 2 fuel injector (Y76/2)
- Cylinder 3 fuel injector (Y76/3)
- Cylinder 4 fuel injector (Y76/4)
In Engine idle and for selector lever position "N" or "P", the pressure is reduced to approx. 130 bar to reduce the noise emission of the fuel high-pressure pump.
When a hot Engine is stopped, the fuel pressure can increase to as much as 250 bar (+17 bar). In this case, the quantity control valve at the fuel high-pressure pump is opened and the pressure is reduced.
A differentiation is made between the following operating states during the regulation of the high-pressure fuel circuit:
- Start
- Normal mode
- Low-pressure limp-home mode (fuel high pressure is not reached)
- Stop
Start
The quantity control valve is energized and is thus closed. The fuel high-pressure pump delivers at max. capacity. The pressure in the rail is quickly built up. The fuel pump pressure is 4.5 to6.7 bar at the low-pressure side.
Normal mode
The ME-SFI [ME] control unit actuates the quantity control valve in a pulse width modulated manner and thus regulates the required fuel quantity. The fuel pump pressure is 4.5 to6.7 bar at the low-pressure side (depending on the Engine speed and fuel temperature).
Low-pressure limp-home mode (fuel high pressure is not reached)
The quantity control valve is not energized and is thus opened. The fuel pump pressure is 4.5 to6.7 bar. Fuel flows via the open quantity control valve into the rail. The fuel injectors are actuated for longer. In low-pressure limp-home mode, the Engine is operated in an output reduced manner. The maximum speed is 70 km/h.
Stop
The quantity control valve is not energized and is thus opened. The fuel pressure in the rail in reduced. The fuel pump is no longer actuated.
Fuel high-pressure system
Safety shutoff
In the event of an accident, the ME-SFI [ME] control unit switches the Engine off and stops the fuel supply.
The Supplemental Restraint System control unit (N2/10) transmits the crash signal via a direct line (analog) and also via the user interface CAN (CAN HMI), electronic ignition lock control unit, suspension FlexRay, powertrain control unit and Engine CAN (CAN C) to the ME-SFI [ME] control unit. The ME-SFI [ME] control unit then ends the actuation of the fuel injectors, quantity control valve and fuel pump.
The Engine is switched off, and the ME-SFI [ME] control unit reads in the crankshaft Hall sensor (B70) signals directly. The fuel pressure in the high-pressure fuel circuit is reduced. There is less risk of fire after an accident.
| Electrical function schematic for safety fuel shutoff | PE07.10-P-2733-97FBI | ||
| Electrical function schematic for fuel supply | PE07.10-P-2703-97FBI | ||
| Overview of system components for gasoline injection and ignition system with direct injection | GF07.70-P-9998MRS |