Fuel Supply, Function - GF07.10-P-1003MNF
Engine 176.9 in model 463
as of model year 2016 up to model year 2019
Function requirements for fuel supply, general points
- Circuit 15 (Ignition ON)
- Circuit 87M (Engine management ON)
Circuit relay 87M (F58kN) is activated for 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
The ME-SFI [ME] control unit (N3/10) transmits the "fuel pump ON" signal via the drive CAN (CAN C) to the fuel system control unit (N118). At the same time, the ME-SFI [ME] control unit actuates the fuel system control unit via a direct line (circuit 31).
In addition, the ME-SFI [ME] control unit transmits the "fuel specified pressure" signal via Drivetrain CAN to the FSCU. The fuel system control unit detects the current fuel pressure based on the 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 specified fuel pressure and actuates the fuel pump (M3) with a pulse width modulated signal so 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. Depending on the fuel requirements, the fuel delivery rate is regulated variably from 0 to 130 l/h at a fuel pressure of approx 4.5 bar to approx. 6.7 bar.
The fuel pump suctions the fuel from the fuel feed module and pumps it through the fuel filter to the fuel system high pressure pumps (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.
For vehicles with code ZU8 (USA national version), the low-pressure fuel pressure sensor also detects the fuel temperature. The fuel system control unit directly reads in the signals of the low-pressure fuel pressure sensor and transmits the information via the drive CAN to the ME-SFI [ME] control unit.
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 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 for cylinders 1 to 8 (Y76/1 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 to 6.7 bar, fuel flows via the opened 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 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 CAN 1 (CAN 1), powertrain control unit (N127) and drive CAN to the ME-SFI [ME] control unit
The ME-SFI [ME] control unit activates the safety fuel shutoff under the following conditions:
- Mechanical fault in throttle valve actuator
- Absence of the engine speed signal
- Crash signal
Mechanical fault in throttle valve actuator
If the ME-SFI [ME] control unit detects a mechanical fault in the left and right throttle valve actuators due to the evaluation of the throttle valve position, the engine speed is limited to approx. 1400 rpm in idle and approx. 1800 rpm during vehicle operation due to the deactivation of the fuel injectors for cylinders 1 to 8.
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 suspension CAN 1, powertrain control unit and drive 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 left and right quantity control valves to depressurize the fuel system.
| Electrical function schematic for fuel supply | PE07.10-P-2703-97ZGD | ||
| Overview of system components for gasoline injection and ignition system with direct injection | GF07.70-P-9998MNF |