GF07.10-P-1003MAW Fuel Supply, Function
GF07.10-P-1003MAW Fuel Supply, Function
ENGINES 156.9 in MODEL 204.0 /2 /3
Function requirements for fuel supply, general points
^ Circuit 15 (ignition ON)
Fuel supply, general points
Under all operating conditions, the fuel supply supplies filtered fuel to the injection valves (Y62) from the fuel tank, in sufficient quantity and at sufficient pressure (injection pressure).
Function sequence for fuel supply
The function sequence for fuel supply is described in the following
Operation steps:
^ Function sequence for fuel pump control
^ Function sequence for fuel delivery
^ Function sequence for safety fuel shutoff
Function sequence for fuel pump control
The fuel supply is controlled and monitored by the ME-SFI control unit (N3/10) and the LH and RH fuel system control units (N118/3, N118/4).
The fuel pumps are switched on when the LH and RH fuel system control units (M3/2, M3) receive the "fuel pump ON" ground signal from the ME-SFI control unit.
The ME-SFI [ME] control unit determines the current fuel pressure via the fuel pressure sensor (B4/15). To control the fuel pumps, the ME-SFI control unit evaluates the fuel pressure and load requirement and transmits the "specified fuel pressure" PWM signal (pulse width modulated signal) to the fuel system control units (with a duty cycle of 10 to 90%). These evaluate the pulse width modulation signal and actuate the fuel pumps in single- phase appropriately using a pulse width modulation signal.
The left fuel system control unit actuates the left fuel pump and the right fuel system control unit actuates the right fuel pump as required so that the actual value of the fuel pressure corresponds the specified value.
The fuel pumps are actuated independently of each other.
Fuel pressure is varied between 3.0 and 4.8 bar dependent on the fuel specified pressure.
Fuel feed
The fuel pumps draw fuel through the fuel strainers (fuel prefilters) from the fuel feed module and through the RH suction jet pumps from the RH fuel tank chamber. Then the fuel pump pumps the suctioned fuel via the check valve and the fuel filter to the fuel manifold (single line system, without return line).
In doing so, the fuel pressure is limited by the pressure limiting valve to about 5.0 bar.
A check valve is placed on the feed to the fuel filter, to prevent the fuel pressure falling when the fuel pumps are switched off.
The LH suction jet pump is driven with fuel from the fuel return of the pressure limiting valve, and part of the fuel feed from the fuel pumps. This suction jet pump delivers fuel from the LH fuel tank chamber to the fuel feed module located in the RH fuel tank chamber.
Fuel supply hydraulic diagram
17 Fuel distribution rail
55 Fuel feed module
55a Right suction jet pump
55/2a Fuel filter
55/2b Pressure limiting valve
55/2c Check valve
56 Left suction jet pump
75 Fuel tank
B4/15 Fuel pressure sensor
M3 Right fuel pump
M3/2 Left fuel pump
Y62 Injection valves
A Fuel feed to fuel filter
B Fuel return from pressure limiting valve
C Fuel to fuel distribution rail
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
- Front and rear throttle valve actuator (M16/3, M16/4), throttle valve positions
- Supplemental restraint system control unit (N2/10), direct crash signal via the chassis CAN (CAN E)
The safety fuel shutoff is activated by the ME-SFI [ME] control unit in the following conditions:
D Mechanical error in front and rear throttle valve actuator
D Absence of the engine speed signal
D Crash signal
Mechanical error in front and rear throttle valve actuator
If the ME-SFI control unit detects a mechanical fault in the front or rear throttle valve actuator by evaluating the throttle valve positions, both throttle valve actuators are switched off. When the injection valves are cut out, the engine speed is limited to approx. 1400 rpm when idling and approx. 1800 rpm when driving.
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 directly or indirectly from the supplemental restraint systems control unit over the chassis CAN, it switches off the fuel pump through the fuel system control unit and briefly actuates the fuel injection valves in order to depressurize the fuel system.
