Starter-Alternator Control Unit Component Description - GF54.21-P-4191FR

Model 257, 290 with engine 256 up to model year 2021 with code B01 (48V technology) 

Shown on engine 256.9 

Location 

The starter-alternator control unit is located at the side of the engine.

Tasks 

The starter-alternator control unit is equipped with a power electronics unit, which sets up the connection between the three-phase A/C system of the integrated starter alternator (A79) and the D/C system of the 48 V on-board electrical system. It uses the power electronics to set the operating mode of the integrated starter alternator, thereby defining how much electrical energy is generated or consumed by the integrated starter alternator.

The starter-alternator control unit is cooled with water.

The interface between the starter-alternator control unit and the integrated starter alternator is protected by an interlock signal. The interlock signal is interrupted when the assembly cover is opened or when the connector coupling between the starter-alternator control unit and the integrated starter-alternator is interrupted. In this instance, the starter-alternator control unit detects the missing interlock signal and switches off the energy supply to the integrated starter alternator so that it can no longer develop any drive torque.

The starter-alternator control unit is also responsible for the following tasks:

• Reading in of sensors and signals 
• Evaluation of input factors 
• Sending signals 

Reading in of sensors and signals 

The input factors are read in via the following connections:

• Direct line 
• Hybrid CAN (CAN L) 

Direct line 

The signals from the following components are read via direct lines:

• Circuit 30c (crash signal)
• Terminal 87c (Wake-up signal)
• CAM Sync
• Temperature sensor 1 in integrated starter alternator
• Temperature sensor 2 in integrated starter alternator
• Resolver sine in integrated starter alternator
• Resolver cosine in integrated starter alternator

Hybrid CAN 

The starter-alternator control unit also reads in the following signals over the hybrid CAN:

• Permissible current and voltage limits
• Mode

Evaluation of input factors 

The integrated microprocessor evaluates the input factors read in.

Sending signals 

The starter-alternator control unit also sends the following signals over the hybrid CAN:

• Alternator utilization

The functions that use these signals are described in the individual function descriptions (see the appropriate block diagram or function schematic).

Wiring diagram for integrated starter alternator control unit

PE54.21-P-2155-97XBA