Component description for the alternator

P15.40-2359-08

Shown on engine 135

G2 Alternator

A Connection for signal lines

B+ Battery positive

1 FR-Terminal

2 L-Terminal

3 S-Terminal

4 G-Terminal

Location

For engine 134 and 135 the alternator is located at the right front in the engine compartment.

For engine 122 the alternator is located at the right on the engine, in the area of the front axle carrier.

Assignment connection for signal lines

 Drive control terminal:
Signal for alternator operating rate to motor electronics control unit (N3/10)

 L-terminal:
Preexcitation of the alternator, control of the alternator charge indicator/warning lamp (A1e5)

 S-terminal
Sensor line for alternator directly to circuit 30

 G-terminal:
Charging voltage request from motor electronics control unit

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Task

The alternator supplies sufficient energy to the on-board electrical system for all occurring rotational speeds during driving and thus guarantees the on-board electrical supply and charging of batteries (G1).

Design

The alternator is designed as an alternator with integrated regulation.

Functional principle

Voltage generation in the alternator is based on the principle of induction. If a magnetic field changes in a conducting loop (coil or winding) an electrical voltage is induced in the conducting loop. If a coil has a rotating magnetic field running through it with a north and south pole then a sinusoidal AC voltage is generated.

The AC voltage is rectified using diodes.

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In the case of an alternator one differentiates between the electrical circuits:

pre-excitation electrical circuit

The pre-excitation electrical circuit builds up a magnetic field in the excitation winding after switching on the ignition
(terminal 15). After starting the engine the alternator provides the excitation function itself.

When the excitation current is flowing the alternator charge indicator/warning lamp goes out.

 In the case of a defect alternator charge indicator/warning lamp or line interruption no preexcitation takes place since the pre-excitation electrical circuit is interrupted.

Excitation current circuit

The excitation current builds up the magnetic field in the excitation current of the rotor.

Charge current circuit

The charge current circuit supplies the on-board electrical system with electrical energy.

Control

Regulation of the alternator takes place by means of the integral electronics depending on the rotational speed, on-board power supply voltage and request from the motor electronics control unit.

The on-board power supply voltage is directly detected by the alternator electronics and evaluated.

The motor electronics control unit transmits its requirements in the form of a voltage signal to the alternator.

Voltage > 5 V: regulating voltage 14.2 V

Voltage < 5 V: regulating voltage 12.8 V

 If there is a problem (e.g. line interruption) the alternator cannot deliver its full output.

Operating rate feedback

The signal operating rate feedback it readable using an oscilloscope. It is, however, not possible to make any statement about the current operating rate since no fixed pulse width exists.