The alternator control system consists of an alternator, electric load current sensor and engine control module (ECM). The ECM controls the generated electricity by adjusting the voltage of the regulator so that the voltage is suitable for the engine and electrical load conditions. To prevent a drop in idling speed that would result from quick increase in electric load and a consequent increase in engine load, the ECM performs a control so that the alternator output increases gradually. In the case of a temporary increase in electrical generation demand while driving, the ECM performs a control to limit the operation of the alternator and thus limit the increase in load on the engine to maintain the engine performance whenever necessary.
The ECM optimally controls the alternator output voltage by changing the duty ratio of the signal to the alternator control terminal, based on the following information:
- Engine condition (engine coolant temperature, vehicle speed, engine speed, throttle position, etc.)
- Battery voltage (ECM power voltage)
- Electric load condition (blower motor, rear end door window defogger, headlights, radiator fan, A/C, etc.)
- FR terminal output to indicate the operation rate of the field coil.
The duty cycle signal to the alternator control terminal adjusts the regulating voltage of the regulator, which in turn controls the duty ratio of the field coil and thus the output voltage of the alternator (battery terminal).
The generating condition of the alternator is controlled to the optimum level using the load current sensor, which detects the current consumption linearly even when a sudden electrical load variation occurs and the engine load is changed.
System Block Diagram
- 1. Alternator
- 2. Regulator
- 3. Field coil
- 4. ECM
- 5. Ignition switch
- 6. Load current sensor
- 7. Battery
- 8. Engine condition
- 9. Battery voltage
- 10. Electric load condition
- 11. Body control module (BCM)
- 12. Instrument housing
- 13. CAN driver
- 14. Battery terminal (alternator output)
- 15. Ignition terminal
- 16. Light terminal
- 17. FR terminal
- 18. Alternator control terminal
- 19. Earth