Fuel Supply, Function - GF07.10-P-1003MNH
Engine 176.9, 177.9 in model 463
as of model year 2019
Function requirements for fuel supply, general points
- Circuit 15 (ignition ON)
- Circuit 87M (Engine management ON)
Circuit relay 87M (K40/8kN) is activated where circuit 15 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 Drivetrain 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 via a voltage signal from the low-pressure 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.
Illustration of the principle of the hydraulic scheme for the fuel low-pressure circuit
Function sequence for fuel system high-pressure circuit
In the fuel high-pressure circuit, the fuel high pressure of about 200 bar that is required for spray-guided direct injection is generated, regulated and stored in the rails. The ME-SFI [ME] control unit reads signals from the following sensors for regulation of the fuel high pressure:
- Right fuel pressure and temperature sensor (B42/1)
- Left fuel pressure and temperature sensor (B42/2)
The fuel high-pressure pumps compress the fuel (depending on the operating status) up to approx. 200 bar and route it via the high-pressure lines and rails to the fuel injectors of cylinders 1 to 8 (Y76/1 up to Y76/8).
The left quantity control valve (Y94/1) and right quantity control valve (Y94/2) that regulate the fuel quantity supplied to the pump elements in the fuel high-pressure pumps in a demand- and characteristics map-dependent manner are located on the fuel high-pressure pumps. The ME-SFI [ME] control unit actuates the left and right quantity control valves over pulse width modulated signals.
The fuel pressure and temperature sensors detect the current fuel high pressure (pressure in the rails) as well as the temperature of the fuel in the rails. 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 in order to reduce the noise emission of the fuel high-pressure pumps.
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, valves open in the fuel system 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
- Quantity control valves regulate the supplied and required fuel quantity.
- Fuel pump pressure is regulated to match the fuel temperature between approx. 3.0 and 5.5 bar.
- Fuel predelivery pressure is regulated between 4.5 and 6.7 bar (absolute) depending on the engine speed and fuel temperature.
Low-pressure limp-home mode (fuel high pressure is not reached)
- Quantity control valves are de-energized 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 de-energized and open.
- Fuel pump is not actuated.
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 ME-SFI [ME] control unit controls the safety fuel shutoff on the basis of the following sensors and signals:
- Crankshaft Hall sensor (B70), engine rpm
- 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 [ME] 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 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 the quantity control valves in order to depressurize the fuel system.
| Electrical function schematic for fuel supply | PE07.10-P-2703-97ZGF | ||
| Electrical function schematic for safety fuel shutoff | PE07.10-P-2733-97ZGF | ||
| Overview of system components for gasoline injection and ignition system with direct injection | GF07.70-P-9998MNH |