Alternator Interface Function - GF07.10-D-1009TSB
Engine 274 in model 907
Block diagram
Function requirements for the alternator interface, general points
- Circuit 87M (Engine management ON)
- Engine running.
Alternator interface, general points
With the alternator interface, messages (e. g. the "dynamo field monitor signal") are exchanged via the drive LIN (LIN C1) between the alternator (G2) and the ME-SFI [ME] control unit (N3/36) and the alternator control response is regulated. 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 max. data transfer rate between the ME-SFI [ME] control unit and the LIN control of the alternator is 19.2 kbit/s. The ME-SFI [ME] control unit reads in the following signals:
- Crankshaft Hall sensor (B70/2), engine RPM
- On-board electrical system battery (G1), on-board electrical system voltage via "circuit 30"
- Alternator, status via the drive LIN
Function sequence for alternator interface
The ME-SFI [ME] control unit regulates the alternator control response to, for example, reduce the charging voltage in idle where the on-board electrical system battery is sufficiently charged.
This reduces the engine load, thus also reducing fuel consumption and reduces exhaust emissions.
The ME-SFI [ME] control unit controls the following functions:
- Switching on of the alternator dependent on the condition of the on-board 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 circuit 61 signal (alternator operational).
- Communication of detected faults for the actuation of the corresponding symbols and display messages to the instrument cluster (A1) via the drive CAN (CAN C), powertrain control unit (N127), suspension FlexRay (Flex E), EZS control unit (N73/8) and user interface CAN (CAN HMI).
- Keep the charging voltage at a low level and charge the battery more strongly in the deceleration mode (fuel saving).
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 alternator faults based on this.
The following faults are identified:
- Line of alternator interface (drive LIN) has an open circuit or interface driver in ME-SFI [ME] control unit defective (alternator 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
Based on the information that the ME-SFI [ME] control unit receives via the alternator interface, the "circuit 61 signal" in 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-D-2709-97TSB |
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