The electronic demand-based fuel pump control function is integrated in the ISIS system (Intelligent Safety Integration System).
The fuel pump is a 2-stage internal gear pump:
The pump is driven by an electric motor.
Supply:
The following control units are involved in the process of electronic demand-based control of the fuel pump:
The DME/DDE calculates the required injection volume on the basis of various operating variables. And from that figure it calculates the current fuel requirement for the engine as a whole. The DME/DDE requests that value as the volumetric fuel flow rate in ”litres per hour”.
The DME/DDE sends this request across the following path:
PT CAN bus (POWERTRAIN CAN bus) -> ZGM (Central Gateway Module) -> BYTEFLIGHT-bus -> SIM (Safety Information Module) -> BYTEFLIGHT-bus -> SBSR (right B-pillar satellite).
The SBSR control unit converts the requested fuel flow rate into a required speed for the fuel pump and adjusts the pump to that speed.
The pump speed is controlled by the pulse duty factor of a pulse-width modulated square-wave signal. This square-wave signal indicates the effective power supply voltage for the fuel-pump motor: the longer the pause between the edges of the square-wave signal, the lower is the voltage of the power supply to the fuel pump. The delivery rate of the fuel pump is correspondingly lower. The speed of the fuel pump is fed back to the processor of the SBSR (satellite, B-pillar, right) as an input variable.
This system offers the following advantages over conventional methods of controlling the fuel pump:
If the ISIS system detects a crash of sufficient severity, the flow of fuel is interrupted. This prevents the fuel from leaking out and igniting.
The fuel pump can be reactivated by switching the ignition off and on.
If the fuel quantity requirement signal from the DME/DDE or the pulse-width modulated signal from the SBSR is lost, the fuel pump continues to run at maximum delivery rate. This ensures that sufficient fuel is delivered for all operating conditions.
Fuel cut-off in an emergency is not affected by this.
Diagnosis of the demand-controlled fuel pump is provided by the SBSR (satellite, right B-pillar) control unit. In the event of faults, the following fault codes may be recorded in the SBSR fault memory:
The DME/DDE fault memory does not record any faults relating to the fuel pump. Inadequate supply of fuel may under certain circumstances show itself in the form of lack of power, poor accelerator response, misfiring or difficulties with starting.
Always make sure the ignition is switched off before carrying out any work on the fuel pump.