On-board electrical system power supply, function (Engine 642) - GF15.40-P-0001C

ENGINE 272 in MODEL 164, 171, 203, 209, 211, 219, 221, 230, 251 only valid with engine control unit variant ME 9.7 

ENGINE 629 in MODEL 164, 211, 221 only valid with engine control unit variant CDI 5 

ENGINE 642 in MODEL 164, 203, 209, 211, 219, 221, 251 only valid with engine control unit variant CDI 4 

Shown on model 211 with engine 272 

Networking 

Fig 1: On-Board Electrical System Power Supply Function Diagram - Shown On Model 211 With Engine 272

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Shown on model 211 with engine 642 

Networking 

Fig 2: On-Board Electrical System Power Supply Function Diagram - Shown On Model 211 With Engine 642

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

General 

When the engine is running, the alternator supplies the on-board electrical system with electrical energy and charges the battery. For this purpose, the alternator generates three-phase current which is rectified. A local interconnect network is used as the alternator interface between the engine control unit and the alternator.

The LIN bus is a bidirectional single-wire interface with a maximum transfer rate of 20 kbit/s.

Function and task 

Messages between the engine control unit and the alternator are exchanged via the alternator interface. This follows the master-slave principle. The engine control unit is the master and the alternator acts as the slave. The alternator only sends when it is requested to do so by the master. The following tasks are performed:

• Switching on of the alternator after the engine has been started, and regulation of the alternator according to the information stored in the engine control unit. To do this, the control voltage is preset by the engine control unit.
• Delayed adaptation of the regulation voltage in the case of a major change in alternator load.
• Protects the generator against overheating.
• Protects the generator against overheating.
• Generation of terminal 61 (information "alternator is turning") in the engine control unit.

The alternator constantly performs self-diagnosis and sends the results when requested to the engine control unit. The engine control unit compares them with other signals (e.g. engine speed, battery voltage and time after engine start) and detects the following faults:

• Electrical and mechanical faults at the alternator (regulator or diodes defective, stator interruption or short circuit, exciter interruption, regulation voltage and charging current may not be achieved, regulation voltage too high, cracked or loose poly-V belt).
• Line for the alternator interface interrupted between engine control unit and alternator. With this fault, the alternator operates using its fixed parameters. A regulation voltage of approx. 14.3 V is predefined.
• Short circuit or open circuit at output terminal 61 of engine control unit.

Networking 

The engine control unit uses the alternator interface to control the control response of the alternator in order to reduce, in idle, the generator torque which is produced at a high power output. As a result of the reduced engine load, less fuel is injected and the exhaust characteristics are optimized.

Terminal 61 in the engine control unit is simulated using information which the engine control unit receives via the alternator interface. This information is supplied to the driver-side SAM control unit with fuse and relay module via Controller Area Network bus class C or via a signal line.

The driver-side SAM control unit with fuse and relay module conditions the signal and makes it available to the instrument cluster via Controller Area Network bus class B.

The upper limit value of the regulation voltage can be up to approx. 15 V.

Engine speed 

Pulses from the Hall sensor or position sensor to the crankshaft are read in by the engine control unit.

The engine control unit delivers the message engine speed (in RPM) to the Controller Area Network bus Class C.

Diagnosis 

The following faults are detected after "ignition ON" and may be stored as a fault entry in the engine control unit:

• Alternator interface defective.
• Line interruption (tml. 30)

The following faults are detected after "Engine start" and may be stored as a fault entry in the engine control unit:

• Electrical fault at alternator
• Mechanical fault at alternator
• Line interruption (tml. 30)
• Undervoltage and defective alternator interface

The "battery symbol" and the "Visit workshop" message also appear in the multifunction display in the instrument cluster.

This fault message in the multifunction display in the instrument cluster can also be triggered by information from the following control units:

• Battery control unit
• EIS [EZS] control unit

Test prerequisites for the alternator test are listed in the diagnosis assistance system (DAS) and must always be observed. The test itself is a test routine and is menu-assisted.

Emergency running 

If communication between the alternator and engine control unit is interrupted, the alternator continues to run at its fixed default parameters during normal engine operation.

Emergency start 

The alternator has an emergency start function. If the communication between the alternator and engine control unit is interrupted, the alternator can build up a voltage via the residual magnetism depending on the rotational speed. If, on the basis of the voltage and frequency, the regulator detects that the alternator is rotating, it automatically begins energizing of the field and enters regulation mode.

Limitations:

• The command "Regulation Off" from the engine control unit interrupts this limp-home.
• Precise specification of the starting speed for the emergency start function is not possible.