Alternator Interface Function - GF07.10-D-1009TSC

Engine 642.8 in model 907 

Block diagram 

Function requirements for the alternator interface, general points 

• Circuit 87 (engine timing ON)
• Engine running.

Alternator interface, general points 

Using the alternator interface, messages are exchanged via the drive LIN (LIN C1) between the alternator (G2) and the CDI control unit (N3/28) and the control response of the alternator is controlled. To do this, the CDI control unit reads in information from the following signals:

• Crankshaft position sensor (B70/1), engine speed
• On-board electrical system battery voltage (G1) through circuit 30
• Alternator, status

Function sequence for alternator interface 

The CDI control unit controls the alternator control response, e.g. to reduce the charging voltage 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 CDI control unit controls the following functions:

• Switching on of the alternator depending on the condition of the onboard electrical system and the requirements from the engine
• Regulation of the alternator based on characteristics maps stored in the CDI control unit. To do this, the charging voltage is prescribed by the CDI control unit.
• Protecting the alternator against overheating.
• Adapting the charging voltage with a delay in the event of frequent load changes at the alternator in idle to stabilize the idling speed.
• Report recognized errors to the instrument cluster (A1) to actuate the respective symbols and display messages.
• Keep the charging voltage at a low value.
• Charge battery more intensely in overrun mode (fuel saving).
• Generate the circuit 61 CAN signal (alternator in operation).

The alternator constantly performs a self-diagnosis and sends the results when requested to the CDI 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 alternator faults based on this.

The following faults are identified:

• Line (drive LIN) of the alternator interface has an open circuit or interface driver in CDI control unit defective (the alternator regulates to 14.3 V in this case)
• Electrical and mechanical fault on 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

To check the charging voltage, the on-board electrical system battery must be loaded with a battery tester since the charging voltage can be significantly reduced when the on-board electrical system battery is fully charged and under no load.

From the information that the CDI control unit receives via the alternator interface, the circuit 61 signal is simulated in the CDI control unit and issued via the CAN network (e.g. for the instrument cluster).

Electrical function schematic for alternator interface	PE07.10-D-2709-97TSC
Overview of system components for common rail diesel injection (CDI)	GF07.16-D-9997TSC