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

Engine 264.9 in Model 205 

except code B01 (48V Technology) 

Function requirements, general 

• Engine runs

The ME-SFI [ME] control unit (N3/10) detects the Engine running via the evaluation of the crankshaft Hall sensor signals (B70). The ME-SFI [ME] control unit directly reads in the signals of the crankshaft Hall sensor.

Alternator interface, general points 

The alternator interface facilitates the communication of the ME-SFI [ME] control unit with the alternator (G2) via the drive LIN (LIN C1).

The control response of the alternator is controlled via the alternator interface.

The ME-SFI [ME] control unit controls the control response of the alternator to reduce, for example, the charging voltage in idle in the case of a sufficiently charged on-board electrical system battery (G1).

Via the thus reduced Engine load, the fuel consumption is reduced and the exhaust gas emissions improved.

The ME-SFI [ME] control unit reads in the following signals:

• Engine speed

  Crankshaft Hall sensor

• On-board electrical system utilization

  The front SAM control unit (N10/6) transmits information on the on board electrical system utilization via the interior CAN (CAN B), electronic ignition lock control unit (N73), suspension FlexRay (Flex E), powertrain control unit (N127) and Engine CAN (CAN C) to the ME-SFI [ME] control unit.

• Alternator, status
• On-board electrical system battery, status

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 transmits this information via the Engine CAN, powertrain control unit, suspension FlexRay, electronic ignition lock control unit and interior CAN to the front SAM control unit.

The front SAM control unit calculates the required specified alternator voltage. It then transmits these values via the interior CAN, electronic ignition lock control unit, suspension FlexRay, powertrain control unit, and Engine CAN to the ME-SFI [ME] control unit. The ME-SFI [ME] control unit evaluates these values taking into account additional input factors (e. g. air conditioning system ON) and calculates the optimal specified alternator voltage. 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-SFI [ME] control unit also checks the input factors for plausibility in order to rule out any overcharging or faulty charging of the on-board electrical system battery.

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 onboard electrical system voltage is not high enough, the power management is gradually reduced. The alternator can then make its full output available.

The performance management in the ME-SFI [ME] control unit takes over the specified alternator voltage values of the front SAM control unit solely as reference values, as certain vehicle statuses (e. g. Engine comfort, idle stability, Engine start, irregular Engine running) must also be taken into account. The actual specified alternator voltage thus arises from the specified alternator voltages transmitted by the front SAM control unit, superimposed by the corrections of the power management.

The ME-SFI [ME] control unit also generates the circuit 61 signal (alternator in operation). Detected faults are transmitted via the Engine CAN, powertrain control unit, suspension FlexRay, electronic ignition lock control unit and user interface CAN (CAN HMI) to the instrument cluster (A1). The instrument cluster actuates the corresponding warning lamps and outputs the display messages.

The alternator performs continuous self-diagnosis and transmits the results when requested to the ME-SFI [ME] control unit. This compares the results with additional signals (e. g. Engine speed, on-board electrical system battery voltage, time after Engine start) and detects from this any faults in the alternator.

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 activated in advance in the vehicle (e. g. rear window heater, seat heating, high beam, low beam etc.) to load the on-board electrical system battery, as the charging voltage can be significantly reduced for a full loaded and unloaded on-board electrical system battery.

Circuit 61 signal:

From the information that the ME-SFI [ME] control unit receives via the alternator interface, the circuit 61 signal is simulated in the ME-SFI [ME] control unit and output via the CAN network (e. g. for the instrument cluster).

	Electrical function schematic for alternator interface		PE07.10-P-2709-97FBI
	Overview of system components for gasoline injection and ignition system with direct injection		GF07.70-P-9998MRS