Alternator: Description and Operation
Generator
COMPONENT LOCATION
NOTE:
Installation on supercharged engine shown, installation on naturally aspirated engine similar.
OVERVIEW
The generator is a self exciting type manufactured by Denso and is capable of producing an output current of 150 Amps. The generator is located at the front RH (right-hand) side of the engine, and is secured to an engine mounted bracket with a top pivot bolt and 2 lower bolts. The generator mountings provide the electrical ground connection for the generator.
The generator pulley is driven by the engine crankshaft pulley via the accessory drive belt. For additional information, refer to Accessory Drive
The generator comprises the following major components:
- Stator
- Rotor
- Rectifier pack
- Regulator.
Stator
The stator contains 3 sets of coils manufactured from copper wire with the ends formed into a 'star' connection. Rotation of the rotor within the stator produces an AC (alternating current) in the coils.
Rotor
The rotor comprises a field winding, wound around an iron core and mounted on a common shaft. The ends of the common shaft form the magnetic north and south poles. The rotor is housed within the stator and mounted on bearings to provide smooth running and support, due to the side loading applied by the accessory drive belt tension.
During engine cranking when generator speed is low, the ignition switch supply provides an excitation current to the rotor via brushes and contact slip rings at the end of the common shaft. As the generator speed increases the generator becomes self exciting.
Rectifier
The rectifier converts the AC (alternating current) current produced in the stator coils into DC (direct current) that is required by the vehicle electrical system. The rectifier also prevents current flow from the battery to the generator when the generator output voltage is less than the battery voltage.
The rectifier comprises 12 semi-conductor diodes, 6 mounted on the positive heat sink and 6 on the negative. The heat sink dissipates the resultant heat created in the electrical conversion process.
Regulator
The regulator provides a controllable variable voltage output from the generator and feedback of various parameters including fault information. A threaded copper post connection on the generator outer casing supplies the rectified and regulated DC (direct current) current from the generator, via a large diameter cable to the battery positive terminal. A single pin electrical connector located on the rear outer casing provides a LIN (local interconnect network) interface for generator monitoring and control by the ECM (engine control module).
The Battery Monitoring system (BMS) monitors battery temperature and calculates the optimal charging voltage setpoint. This is sent via LIN (local interconnect network) to the CJB (central junction box) which in turn sends it to the ECM (engine control module) via the CAN (controller area network). The ECM (engine control module) then sends this voltage setpoint to the alternator via LIN (local interconnect network). The entire system operates on a closed loop principle to maintain optimal battery terminal voltage.
The ECM (engine control module) monitors the generator for mechanical or electrical failure. If a fault is detected, DTC (diagnostic trouble code)'s are stored in the ECM (engine control module) memory and a message is communicated on the high speed CAN (controller area network) bus to the instrument cluster to illuminate the charge warning indicator lamp. For additional information, refer to Instrument Cluster
During engine starting, the charge warning indicator lamp is illuminated in the instrument cluster when the ignition is energized, and is extinguished when the engine starts and there are no faults present on the charging system.
If the generator is close to being overloaded then an increased idle speed set point will be set which will optimize the amount of power available to operate vehicle features.
LOAD MANAGEMENT SYSTEM
The load management system comprises software resident in the ECM (engine control module) module.
The purpose of load management is to protect the battery during abnormal usage of the vehicle. With the engine not running the system will request the systems on the Media Orientated System Transport (MOST) ring and the air suspension system to enter 'power save' mode. , A 'WARNING - LOW BATTERY' message will be displayed in the message center. For additional information, refer to Information and Message Center Description and Operation
With the engine running the system will modulate features such as seat and screen heating to prevent the battery voltage becoming critically low to the point where the vehicle becomes un-operational.
CONTROL DIAGRAM
NOTE:
A = Hardwired; D = High speed CAN (controller area network); N = Medium speed CAN (controller area network); O = LIN (local interconnect network) bus
PRINCIPLES OF OPERATION
The output voltage required from the generator is calculated by the battery monitoring system. For additional information, refer to Battery, Mounting and Cables (414-01 Battery, Mounting and Cables, Description and Operation).
The battery monitoring system signals the required voltage to the ECM (engine control module) via the CJB (central junction box) and the instrument cluster. The ECM (engine control module) then transmits the required voltage on the LIN (local interconnect network) bus connection with the voltage regulator in the generator. The output from the generator is supplied to the battery through the main battery positive cable.
The ECM (engine control module) will over-ride the voltage value requested by the battery monitoring system if it detects a fault in the generator. The ECM (engine control module) also signals the instrument cluster to display a warning message if it detects a fault with the generator.