ISIS electronic control of the fuel pump

The fuel delivery rate and the fuel cutoff are controlled in the ISIS (Intelligent Safety Integration System).

Brief description of components

EKP electrical fuel pump

The fuel pump is a 2-stage internal gear pump.

• The pre-delivery stage reduces formation of bubbles in the fuel.
  
• The delivery stage delivers the required volume of fuel depending on consumption.
  

The fuel pump is driven via a collector. The speed of the collector is fed back to the processor of the SBSR (satellite, B-pillar, right) as an input variable.

Supply:

• The SBSR is supplied by the SIM (Safety Information Module). This also buffers the SBSR with a reserve power supply provided by the SIM in the case of failure of the vehicle voltage in the short term.
  
• The fuel pump is supplied with voltage via terminal 30.
  

control modules

The following control modules are involved in the message transmission for electronic control of the fuel pump:

• DME (Digital Engine Electronics): The fuel requirement of the engine is calculated in the DME. The fuel requirement is calculated from the required injection quantity and the additional fuel volume for the suction spray pump in the fuel tank. (The suction spray pump conveys the fuel from one tank chamber into the other.)
  
• ZGM (Central Gateway Module)
  
• SIM (Safety Information Module)
  
• SBSR (satellite, B-pillar, right)
  

Main functions

Consumption-dependent supply of fuel

Fuel is supplied depending on consumption. The DME (digital engine electronics) determines a fuel requirement in liters per hour.

The DME sends that fuel volume request via the PT-CAN bus (powertrain CAN bus) -> ZGM (central gateway module) -> BYTEFLIGHT bus -> SIM (safety information module) -> BYTEFLIGHT-Bus -> to the SBSR (satellite, B-pillar right) control module.

The required volume of fuel is converted into a nominal speed for the fuel pump.

The pump speed is controlled by the pulse duty factor of a pulse-width modulated square-wave signal. This square-wave signal provides the voltage supply at the motor of the fuel pump: the longer the pause between the vertical flanks of the square-wave signal, the lower the voltage supply at the fuel pump. The delivery rate of the fuel pump is correspondingly lower.

If the DME fails to issue the fuel requirement signal, the fuel pump is activated with the adjustable maximum speed.

Fuel cutoff in an emergency

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.

Emergency running properties in the event of failure of the bus line

The pump is operated on an adjustable maximum supply rate if, with terminal R ON,

• the DME fails to issue the fuel rate requirement signal
  
• the pulse-width modulated signal from SBSR to the power supply of the pump fails (satellite, B-pillar, right).
  

This ensures that the full supply rate remains available. The fuel cutoff in an emergency is unaffected by this.

Note on safety

In all cases, only perform work on the fuel pump with the ignition off.