BMW X5: Fuel Supply System - System Functions

> E65, E66

The fuel supply system on the BMW 7-Series is requirement-orientated and thus depends on consumption.

The DME calculates the amount of fuel required on the basis of various operating variables.

In turn, the engine's current fuel requirement is calculated from this value. The DME requests this value as a volumetric flow with the unit "liters per hour".

The DME sends this request on the following path: DME (digital engine electronics -> PT-CAN -> SGM (safety and gateway module) -> byteflight -> SBSR (B-pillar satellite, right) -> EKP (regulated fuel pump).

The B-pillar satellite, right converts the amount of fuel requested into a nominal speed for the fuel pump.

The pump speed is regulated via the cycle ratio of a pulse-width-modulated signal. This rectangular signal gives the effective supply voltage for the fuel pump: The longer the pause between the edges of the rectangular signal, the lower the supply voltage for the fuel pump. The fuel pump delivery volume is correspondingly lower. The fuel pump speed is sent back to the B-pillar satellite, right as an input variable.

This method has the following benefits compared to the conventional way of actuating the fuel pump (fuel-pump relay):

• Lower current draw from fuel pump
• Reduced heating up of fuel
• Longer service life for fuel pump
• No fuel-pump relay needed

The flow of fuel is interrupted in the event of a crash of sufficient impact. This prevents the fuel from escaping or igniting (emergency fuel cutoff).

The fuel pump can be reactivated by switching the ignition off and on again.

If the request signal from the DME or the pulse-width-modulated signal from the SBSR is not received: The fuel pump will operate a maximum delivery capacity. This guarantees sufficient fuel supply for all operating conditions (emergency operation).

> E60, E61, E63, E64 and E70

The DME switches the fuel pump on using the fuel-pump relay.

Fuel injection

During fully sequential fuel injection, each injector is controlled by means of its own final stage.

Fully sequential fuel injection has the following advantages:

• Improved fuel preparation for each individual cylinder
• Adaptation of the fuel injection timing to suit the engine's operating condition (engine speed, load, engine temperature)
• Cylinder-selective correction of injected fuel quantity for varying load (during a cycle, the fuel injection timing can be corrected by extending or shortening it)
• Cylinder-selective cutoff (e.g. when an ignition coil is defective)
• Diagnosis for each individual injector possible

The control of each injector by means of its own individual final stage achieves a fuel build-up which is the same in all cylinders. This ensures a uniformly-effective fuel preparation throughout.

The fuel build-up time is variable and depends on the load, engine speed and engine temperature.

As it is only injected once per camshaft rotation, the spread of fuel due to tolerances in the components is reduced.

In addition, the idle-running performance is improved as the response and dropout times at the injectors are reduced.

Moreover, a marginal reduction in fuel consumption is also achieved.

When the vehicle is in motion and there is a sudden acceleration or the throttle is closed, the fuel injection period can be adjusted. If the injectors are still open, the mixture at every valve can be adjusted by extending or shortening the fuel injection period. This achieves an improved engine response.

Ignition-circuit monitoring

The current in the primary coil for the ignition coil is used to monitor the ignition circuit. When the engine is switched on, the current must stay within specific values during certain time thresholds.

The ignition diagnosis monitors the:

• Primary power circuit for the ignition coil
• Ignition wiring harness
• Secondary power circuit for the ignition coil with the spark plug

The ignition-circuit monitoring can detect the following faults:

• Short circuit at the primary end of the ignition coil
• Short circuit at the secondary end of the ignition coil
• Defective spark plug
• Break in wire to actuator
• Defective ignition output stage

The following are not detected:

• Intermittent faults such as loose contacts in the wire to the actuator
• Spark-over in high-tension circuit parallel to spark gab where a short-circuit in the coil does not develop

Alternator actuation (bit-serial data interface)

The following functions have been implemented in the DME control unit for the alternator with bit-serial data interface (BSD):

• Switching the alternator on and off using defined parameters
• Specification of the alternator's maximum permissible power consumption
• Calculation of the input torque for the alternator based on the power consumption
• Control of the alternator's response when higher electrical loads are connected (load-response function)
• Diagnosis for the data line between the alternator and DME control unit
• Storage of faults which develop in the alternator in the fault memory of the DME control unit
• Actuation of the charge-current indicator light in the instrument cluster via bus connection
• Introduction of intelligent alternator regulation:
  > from 03/2007 in the E60, E61
  > from 09/2007 in the E63, E64, E70

The principal function of the alternator is also guaranteed when communication between the alternator and DME control unit is interrupted.

The following fault causes can be distinguished in fault memory entries:

• Overheating protection:
  The alternator is overloaded. For safety reasons, the alternator voltage is reduced until the alternator has cooled down (charge telltale light does not light up).
• Mechanical fault:
  There is a mechanical block in the alternator. or: The belt drive is defective.
• Electrical fault:
  Excitation diode defective, excitation coil has been interrupted, overvoltage due to defective governor.
• Communication failure:
  Line between DME control unit and alternator defective.

An interruption or short circuit in the alternator coils will not be detected.

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