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

Engine 274.9 in model 172.4 

as of model year 2017 

Engine 276.8 in model 172.4 

Function requirements for the alternator interface, general points 

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

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 transmission rate between the ME-SFI [ME] control unit and the LIN control for the alternator is 19.2 kbit/s. The LIN control has no direct outputs. The ME-SFI [ME] control unit reads in the following signals:

• Crankshaft Hall sensor (B70), engine RPM
• On-board electrical system battery voltage (G1) over "circuit 30"
• Alternator, status via the drive LIN

Function sequence for alternator interface 

The ME-SFI [ME] control unit regulates the control response of the alternator, for example in order to reduce the charging voltage when idling if the on-board electrical system battery is sufficiently charged. This reduces the engine load, thus also reducing fuel consumption and improving exhaust emissions.

The ME-SFI [ME] control unit controls the following functions:

• Switching on of the ALT dependent on the condition of the onboard electrical system and the requirements from the engine.
• Regulation of the alternator according to characteristics maps stored in the ME-SFI [ME] control unit. To do this the charging voltage is determined by the ME-SFI [ME] control unit.
• Adapting the charging voltage with a delay in the event of frequent load changes at the alternator in idle to stabilize the idling speed.
• Protecting the alternator against overheating.
• Generation of a "circuit 61 signal" (alternator in operation).
• Report recognized faults via the chassis CAN 1 (CAN E1), front SAM control unit with fuse and relay module (N10/1) and chassis CAN 2 (CAN E2) to the IC (A1) for actuation of the respective warning lamps and display messages.
• Keeps charging voltage at a low value and charges the on-board electrical system battery more strongly in the deceleration phases (fuel saving).

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 RPM, on-board electrical system battery voltage, time since engine start) and thus detects any alternator faults.

The following faults are identified:

• Line for the alternator interface (drive train LIN) has an open circuit or the interface driver in the ME-SFI [ME] control unit is defective (the ALT regulates in this case at 14.3 V).
• Electrical and mechanical fault at the alternator:
  • Control or diodes defective
  • Stator interruption or short circuit
  • Excitation interruption
  • Charging voltage and charging current not achieved.
  • Charging voltage too high
  • A cracked or loose poly-V belt

Diagnosis

In order check the charging voltage the on-board electrical system battery is loaded using a battery test device since for a completely charged and under no load on-board electrical system battery, the charging voltage is significantly reduced.

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 IC).

	Electrical function schematic for alternator interface		PE07.10-P-2709-97TAI
	Overview of system components for gasoline injection and ignition system with direct injection	Engine 276.8 in model 172.4	GF07.70-P-9998MNC
		Engine 274.9 in model 172.4 as of model year 2017	GF07.70-P-9998MRE