Alternator Interface Function - GF07.10-P-1009MNH

Engine 176.9, 177.9 in model 463 

as of model year 2019 

Function requirements for the alternator interface, general points 

• Circuit 87M (Engine management ON)
• Engine runs

The circuit relay 87M (K40/8kN) is switched on for circuit 15 ON.

Alternator interface, general points 

With the alternator interface, messages (for example the "Dynamo Field Monitor Signal") are exchanged via the drive LIN (LIN C1) between the alternator (G2) and the ME-SFI [ME] control unit (N3/10) and the control response of the alternator is controlled.

To do this there is delayed adaptation of the charging voltage for a larger change in load of the alternator. The current operating rate of the alternator is transmitted by the dynamo field monitor signal.

The maximum data rate between the ME-SFI control unit and the LIN control for the alternator is 19.2 kbit/s. The LIN control is not fitted with any direct outlets. The ME-SFI [ME] control unit reads in the following signals:

• Crankshaft Hall sensor (B70), engine speed
• N73 On-board electrical system voltage, requested specified voltage from front SAM control unit (N10/6) via drive CAN (CAN C1), powertrain control unit, suspension FlexRay (Flex E), and electronic ignition lock control unit (N127)
• Alternator, status via the drive LIN

Function sequence for alternator interface 

The alternator management in the ME control unit controls the power output of the alternator. The ME control unit assesses the operating rate of the alternator based on the data sent. It then sends this information to the front SAM control unit via the drive CAN, powertrain control unit, suspension FlexRay, electronic ignition lock control unit, and interior CAN.

The front SAM control unit calculates the required specified voltage of the alternator. It then sends these values over the known path to the ME control unit. The ME control unit evaluates these values, taking additional input factors (such as air conditioning system ON) into consideration, and calculates the optimum specified voltage for the alternator. The ME control unit then sends the calculated specified alternator voltage over the drive LIN to the alternator; the alternator then sets this voltage. The ME control unit also checks the input factors for plausibility in order to rule out any overcharging or undercharging of the on-board electrical system battery (G1).

The ME control unit compares the optimum values for the specified alternator voltage with the actual alternator voltage in order to get a picture of the on-board electrical system. A continuous comparison of these two values and the corresponding corrections are designated as energy management. As soon as it becomes apparent that the on-board electrical system voltage is not high enough, the power management is gradually reduced. The alternator can then make its full output available.

The power management function in the ME control unit adopts the specified alternator voltage values for the front SAM control unit only as guideline values only, because certain vehicle conditions (e.g. engine comfort, idle stability, engine start, and irregular engine running) need to be taken into consideration. The actual specified alternator voltage is therefore obtained by overlaying the corrections of the energy management with the specified alternator voltages sent by the front SAM control unit.

The ME control unit also controls the following functions:

• Generation of a "circuit 61 signal" (alternator in operation).
• Communication of detected faults via the drive CAN, powertrain control unit, suspension FlexRay, electronic ignition lock control unit and user interface CAN (CAN HMI) to the instrument cluster (A1) for the actuation of the corresponding warning lamps and display message.

The alternator performs continuous self-diagnosis and transmits the results when requested to the ME-SFI [ME] control unit. The control unit compares the results with other signals (for example, engine speed, on-board electrical system battery voltage, time since engine start) and thus detects any alternator faults.

The following faults are identified:

• Line of the alternator interface (drive LIN) interrupted
• Interface driver in ME control unit defective (in this case, the alternator sets the voltage to 14.3)
• Electrical and mechanical fault at the alternator:
  • Control or diodes defective
  • Stator interruption or short circuit
  • Excitation interruption
  • Charging voltage not reached.
  • Charging voltage too high
  • A cracked or loose poly-V-belt

Diagnosis

Test the alternator in the workshop to check the charging voltage. Alternatively, measure the charging voltage using a multimeter. For this purpose, a variety of electrical consumers must be first activated in the vehicle (such as rear window heater, seat heating, long beam, low beam, etc.) in order to load the on-board electrical system battery, since the charging voltage can be significantly reduced when the on-board electrical system battery is fully charged and under no load.

Circuit 61 signal

Using information received by the ME-SFI [ME] control unit over the alternator interface, the "circuit 61 signal" is simulated in the ME-SFI [ME] control unit and issued over the CAN network (e.g. for the instrument cluster).

	Electrical function schematic for alternator interface		PE07.10-P-2709-97ZGF
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