Fuel Supply, Function - GF07.10-P-1003MNL
Engine 176.9, 177.9 in model 217
Engine 176.9, 177.9 in model 222
Engine 177.9 in model 290
up to model year 2021
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 system high pressure pumps.
Function sequence for fuel supply
The function sequence for fuel supply is described in the following steps:
- 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 low-pressure circuit
Switching on of the fuel pump (M3) takes place when the signal "fuel pump ON" is received by the fuel system control unit (N118). This signal is sent redundantly from the ME-SFI [ME] control unit (N3/10) as a CAN signal over the drive train CAN (CAN C1) and as a ground signal.
The fuel system control unit also receives the CAN signal "specified pressure of the fuel" from the ME-SFI [ME] control unit. The fuel system control unit detects the current fuel pressure by means of a voltage signal from the fuel pressure sensor (B4/7) and transmits this information via the drive CAN to the ME-SFI [ME] control unit.
The fuel system control unit evaluates the current fuel pressure, compares it with the fuel specified pressure and actuates the fuel pump in such a way that the actual pressure corresponds to the specified pressure.
In order to determine the fuel specified pressure (fuel requirements), the ME-SFI [ME] control unit evaluates the fuel pressure and load requirements. The fuel delivery volume is in this way regulated variably from 0 to 130 l/h, at a fuel pressure of about 4.5 to 6.7 bar, depending on fuel requirements.
For actuation the fuel pump suctions the fuel from the fuel feed module and pumps it through the fuel filter to the fuel system 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 9 bar.
There is a check valve in the feed line to the fuel filter which prevents dropping of the fuel pressure (down to below approx. 4.5 bar) for a switched-off fuel pump.
Function sequence for fuel system high-pressure circuit
In the fuel high-pressure circuit, the fuel high pressure of about 200 bar required for spray guided direct injection is generated, regulated and stored in the rails. The ME-SFI [ME] control unit reads in the signals from the following sensors to regulate the high fuel pressure in the rails:
- Right fuel pressure and temperature sensor (B42/1)
- Left fuel pressure and temperature sensor (B42/2)
The fuel high-pressure pumps deliver the fuel at a pressure of up to 200 bar (depending on operating status) and directs it via the high-pressure lines and the rails to the fuel injectors of cylinders 1 to 8 (Y76/1 to Y76/8).
At the left and right fuel high-pressure pump, there is a quantity control valve on the left or right (Y94/1, Y94/2) that regulates the amount of fuel fed to the pump element in the fuel high-pressure pump depending on the requirements and characteristics map. Actuation of the respective quantity control valve takes place by means of a pulse width modulated signal from the ME-SFI [ME] control unit.
The fuel pressure and temperature sensors sense the current high fuel pressure as well as the temperature of the fuel in the rail.
The operating pressure is approx. 200 bar. It is solely when the vehicle is stationary and the selector lever position is "N" or "P" that the pressure is reduced to 130 bar to reduce the noise emissions of the fuel high-pressure pump.
If a vehicle is switched off with a hot engine, the fuel pressure may rise up to approx 250 bar (+17 bar) in the high-pressure fuel circuit. Upon reaching this threshold a valve opens in the respective fuel high-pressure pump and the pressure is reduced. Upon starting the engine the pressure falls rapidly to the normal operating pressure of about 200 bar.
During regulation of the fuel high-pressure circuit one differentiates between the following operating conditions:
- Start
- Normal mode
- Low-pressure limp-home mode (fuel high pressure is not reached)
- Stop
Start
- Quantity control valves are energized and closed so there is full delivery of the fuel high-pressure pumps and pressure builds up rapidly.
- Fuel pump pressure is approx. 4.5 up to 6.7 bar.
Normal mode
- The quantity control valves regulate the supplied and the required fuel quantity over the duty cycle.
- Fuel pump pressure is regulated to match the fuel temperature between approx. 3 and 5.5 bar.
- The fuel predelivery pressure is varied depending on the engine speed and fuel temperature between 4.5 and 6.7 bar (absolute).
Low-pressure limp-home mode (fuel high pressure is not reached)
- Quantity control valves are deenergized and thus open.
- Fuel pump pressure is approx. 4.5 up to 6.7 bar, fuel flows via the open quantity control valves into the rails.
- Actuation of fuel injectors is extended.
- Power output limitation, max. speed approx. 70 km/h
Stop
- Quantity control valves are deenergized and open.
- Fuel pump is not actuated.
Assembly operations
The high pressure fuel lines made out of stainless steel can be reused after checking.
Fuel high-pressure system
Function sequence for safety fuel shutoff
The safety fuel shutoff system is designed to ensure traffic and occupant safety.
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
- Left throttle valve actuator (M16/60) and right throttle valve actuator (M16/61), throttle valve position
- Supplemental restraint system control unit (N2/10), direct crash signal to the ME-SFI [ME] control unit
- Supplemental restraint system control unit, indirect crash signal via the suspension FlexRay (Flex E), powertrain control unit (N127) and drive CAN to the ME-SFI [ME] control unit
The safety fuel shutoff is activated by the ME-SFI [ME] control unit for the following conditions:
- Mechanical faults in the throttle valve actuators
- Absence of the engine speed signal
- Crash signal
Mechanical faults in the throttle valve actuators
When evaluating the throttle valve position, if the ME-SFI [ME] control unit detects a mechanical fault in the throttle valve actuators, engine speed is limited to approx. 1400 rpm at idle and approx. 1800 rpm in driving mode by shutting off the fuel injectors.
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 system control unit.
Crash signal
If the ME-SFI control unit receives a crash signal indirectly via the user interface CAN (CAN HMI), electronic ignition lock control unit (N73), suspension FlexRay, powertrain control unit, and engine CAN (CAN C), or directly from the Supplemental Restraint System control unit, it deactivates the fuel pump via the fuel system control unit (directly and via the drive CAN) and quantity control valves to depressurize the fuel system.
| Electrical function schematic for fuel supply | Engine 177.9 in model 290 up to model year 2021 | PE07.10-P-2703-97XBA | |
| Engine 176.9, 177.9 in model 217 Engine 176.9, 177.9 in model 222 | PE07.10-P-2703-97SEL | ||
| Electrical function schematic for safety fuel shutoff | Engine 177.9 in model 290 up to model year 2021 | PE07.10-P-2733-97XBA | |
| Engine 176.9, 177.9 in model 217 Engine 176.9, 177.9 in model 222 | PE07.10-P-2733-97SEL | ||
| Overview of system components for gasoline injection and ignition system with direct injection | GF07.70-P-9998MNL |