Design

Design

Exploded view of the generator




The main components of the generator consist of:
1. Stator
2. Rotor with slip rings
3. Integrated cooling fans
4. Rectifier bridge
5. Charge regulator
6. Carbon brushes
7. Pulley with freewheel.
Alternator 150 A has double stator windings and diodes.

Generator terminals





Generator (GEN) terminals, 5 cylinder engine:
1. Screw terminal #1. B+ to the battery via the starter motor
2. Upper terminal #1. Not used
3. Center terminal #2. To the engine control module (ECM)
4. Lower terminal #3. Not used.

Generator (GEN) terminals, 4 cylinder engine:
1. Screw terminal #1. B+ to the battery via the starter motor
2. Upper terminal #1. To the engine control module (ECM)
3. Center terminal #2. To the engine control module (ECM)
4. Lower terminal #3. Reference voltage from the battery.

Stator




The stator is fixed and consists of grooved plates which are insulated internally and pressed together onto a fixed plate unit. Stator winding coils are positioned in the grooves. They are delta connected at 120° and provide a three phase alternating current to the rectifier bridge.
The 150 A generator (GEN) has double stator windings in one unit to maintain a constant high current.

Rotor with slip rings




The rotor consists of two halves (claw-poles) which interlock. The halves are pressed on the rotor shaft. There are 16 claws on the rotor, i.e. 16 poles. One half has 8 north poles and the other half 8 south poles. The excitation winding is secured on the rotor shaft between the claw-pole halves. The excitation winding (also known as rotor winding) consists of a circular coil surrounded by the claw-poles and connected to the slip rings. The charge regulator supplies a magnetic current through carbon brushes positioned against the slip rings. The higher the current in the rotor the stronger the magnet field of the rotor, and therefore the higher the current generated in the windings of the stator.

Cooling fans




The heat generated in the generator is, in principle, proportional to the current generated and must be directed away to prevent damage to the insulation and diodes. The generator is therefore air cooled and two integrated cooling fans are positioned on the rotor shaft.

Rectifier




Alternating current (AC) is created in the generator stator windings. This must be converted to direct current (DC) before it can be used in the electrical system of the car.
This conversion is made using a rectifier bridge which consists of six diodes, two diodes per phase winding.
Alternator 150 A with its double stator windings has twice the number of diodes, that is, 12 diodes. The diodes are pressed into a diode holder.

Charge regulator with carbon brushes

General




At the trailing edge, the alternator has an integrated welded-on charging regulator. For 5-cylinder engine, the charging regulator is also called Alternator control module (ACM). It is possible to change the regulator. On the regulator, bolted against the rotor's slip rings, there are brushes (carbon). The brushes can be changed separate from the regulator.

Charge voltage
At room temperature a fully charged battery cell produces 2.12 V. A 12 V battery has 6 cells and therefore produces 12.72 V when the battery is fully charged.
The battery has an internal resistance which must be exceeded before charging can take place. At room temperature 0.2 V is required per cell, or 1.2 V for the entire battery. Therefore to charge a battery at room temperature, 13.92 V (12.72 V+1.2 V) is required.
In cold conditions, the chemical reactions take place at a slower rate and the internal resistance increases. This requires a higher voltage during charging to exceed the internal resistance.
The charge regulator, depending on how it is controlled by the engine control module (ECM)/central electronic module (CEM), regulates the output voltage so that the battery receives optimal charge.

Charge regulator, 5 cylinder engines




For 5-cylinder engines the charging regulator (also called Alternator control module (ACM)) is connected to Engine control module (ECM) and communicates via LIN-communication. Engine control module (ECM) then communicates with Central electronic module (CEM) via the CAN-net when it comes to control of the alternator.
The central electronic module (CEM) has internal functions to regulate the voltage level and the power consumption in the vehicle. The central electronic module (CEM) controls the charge regulator via the engine control module (ECM) and therefore the current/voltage generated by the generator (GEN).
The generator does not initially charge when the engine is started. The charge increases successively when the engine has been started, controlled by Engine control module (ECM). When there is an increase in load at the generator, the increase from 0 - 100% takes place over the course of a few seconds (this time varies slightly depending on the operating mode the engine management system is in). This is to gradually increase the load on the engine during the start-up phase and to ensure the engine starts.
If the engine speed (RPM) exceeds idle speed (the exact engine speed varies depending on the mode the engine management system is in) during this delay, or if the progressive increase is interrupted, full charge is obtained immediately.
If there is no communication with the charge regulator, the charge regulator will not start charging on start-up. The charge regulator can however self magnetize the rotor and start charging. This occurs at engine speeds greater than approximately 2100 rpm. There is no charge engagement by stages with self magnetization, the generator operates at full charge immediately.
When self magnetizing has begun, the generator (GEN) also charges at engine speeds below 2100 rpm.

Charge regulator, 4 cylinder engines




On 4 cylinder engines the charge regulator is connected to both the engine control module (ECM) and the battery. The engine control module (ECM) then communicates with the central electronic module (CEM) via the controller area network (CAN) to regulate the generator (GEN).

Note! For vehicles with the function Regeneration of brake energy, alternator control is different. See Design and Function, Regenerating brake energy.

The central electronic module (CEM) has internal functions to regulate the voltage level and the power consumption in the vehicle. The central electronic module (CEM) controls the charge regulator via the engine control module (ECM) and therefore the current/voltage generated by the generator (GEN).
The communication between the charge regulator and the engine control module (ECM) occurs across two cables using pulse width modulated (PWM) signals.
One cable is used to transmit information about the requested voltage (desired value) to the regulator from the central electronic module (CEM) via the engine control module (ECM).
The second cable is used to transmit information about the generator (GEN) load from the regulator to the central electronic module (CEM) via the engine control module (ECM). This cable is also used to transmit any fault information.
A direct connection to the battery measures the drop in voltage between the generator (GEN) and battery so that any such drop can be compensated for.
If the generated voltage exceeds or is below the pre-determined desired value, the regulator controls the current to the rotor so that its magnetic field increases or is reduced, thus raising or lowering the voltage from the stator windings as necessary. This process is repeated continually.
The alternator does not initially charge when the engine is started. The charge increases successively when the engine has been started, controlled by Engine control module (ECM). When there is an increase in load at the alternator, the increase from 0 - 100% takes place over the course of a few seconds (this time varies slightly depending on the operating mode the engine management system is in). This is to gradually increase the load on the engine during the start-up phase and to ensure the engine starts. If the engine rpm passes over idle rpm (exact rpm varies slightly depending on which engine management system the vehicle has) during the delay or the successive increase, the increase is cancelled and full charging is obtained immediately.
If the communication with the charge regulator is missing, the regulator will not start charging on start-up. The charge regulator can however self magnetize the rotor and start charging. This begins however at engine speeds above approximately 2000 rpm (the exact engine speed varies slightly depending on the engine management system in the vehicle). There is no charge engagement by stages with self magnetization, the generator operates at full charge immediately.

Freewheel




Certain generators are equipped with a freewheel between the rotor shaft and the pulley. The freewheel on the pulley can be seen on the internal hexagonal section of the center of the pulley. Using the freewheel, the generator rotor shaft can only rotate freely in one direction. This minimizes any jerking in the belt transmission.