Charging System: Description and Operation
CHARGING SYSTEMThe charging system consists of:
- Generator
- Decoupler Pulley (If equipped)
- Electronic Voltage Regulator (EVR) circuitry within the Powertrain Control Module (PCM)
- Ignition switch (refer to the Ignition System for information)
- Battery (refer to the Battery for information)
- Battery temperature sensor
- Voltmeter (refer to the Instrument Cluster for information)
- Wiring harness and connections (refer to the Wiring for information)
- Accessory drive belt (refer to the Cooling for more information)
The charging system is turned ON and OFF with the ignition switch. The system is ON when the engine is running and the ASD relay is energized. When the ASD relay is ON, voltage is supplied to the ASD relay sense circuit at the PCM. This voltage is connected, in some cases, through the PCM and supplied to one of the generator field terminals (Gen Source +). On all others, the Gen field is connected directly to the ASD output voltage. The amount of current produced by the generator is controlled by the Electronic Voltage Regulator (EVR) circuitry in the PCM. This temperature, along with sensed line voltage, is used by the PCM to vary the battery charging rate. This is done by cycling the ground path to the other generator field terminal (Gen field driver). Battery temperature is determined from Inlet Air Temperature Sensor.
The generator is driven by the engine through a serpentine belt and pulley or decoupler pulley arrangement.
The amount of DC current produced by the generator is controlled by the EVR (field control) circuitry contained within the PCM. This circuitry is connected in series with the second rotor field terminal and ground.
A battery temperature sensor is used to sense battery temperature. This temperature data, along with data from monitored line voltage, is used by the PCM to vary the battery charging rate. This is done by cycling the ground path to control the strength of the rotor magnetic field. The PCM then compensates and regulates generator current output accordingly to maintain system voltage at the targeted system voltage based on battery temperature.
All vehicles are equipped with On-Board Diagnostics (OBD). All OBD-sensed systems, including EVR (field control) circuitry, are monitored by the PCM. Each monitored circuit is assigned a Diagnostic Trouble Code (DTC). The PCM will store a DTC in electronic memory for certain failures it detects. Refer to On-Board Diagnostics in the Electronic Control Modules(Refer to ELECTRICAL/ELECTRONIC CONTROL MODULES/POWERTRAIN CONTROL MODULE - DESCRIPTION) for more DTC information.
The Check Gauges Lamp (if equipped) monitors: charging system voltage, engine coolant temperature and engine oil pressure. If an extreme condition is indicated, the lamp will be illuminated. This is done as reminder to check the three gauges. The signal to activate the lamp is sent via the PCI bus circuits. The lamp is located on the instrument panel. Refer to the Instrument Cluster for additional information.
Fig.1 Inlet Air Temperature Sensor:
BATTERY TEMPERATURE SENSOR
The IAT sensor attaches to the intake air duct (Fig. 1).
The IAT Sensor is a Negative Temperature Coefficient (NTC) Sensor that provides information to the PCM regarding the temperature of the air entering the intake manifold. The PCM sends 5 volts to the sensor and is grounded through the sensor return line. As temperature increases, resistance in the sensor decreases.
Inlet/Intake Air Temperature
The inlet air temperature sensor replaces the intake air temperature sensor and the battery temperature sensor. The PCM uses the information from the inlet air temperature sensor along with other stored parameters to determine values to use as an intake air temperature and a battery temperature. The IAT sensor value is used by the PCM to determine air density.
The PCM uses this information to calculate:
- Injector pulse width
- Adjustment of ignition timing (to prevent spark knock at high intake air temperatures)
Battery Temperature
The battery temperature information along with data from monitored line voltage (B+), is used by the PCM to vary the battery charging rate. System voltage will be higher at colder temperatures and is gradually reduced at warmer temperatures.
The battery temperature information is also used for OBD II diagnostics. Certain faults and OBD II monitors are either enabled or disabled depending upon the battery temperature sensor input (example: disable purge, enable LDP). Most OBD II monitors are disabled below 20 °F.
GENERATOR
The generator is belt-driven by the engine. It is serviced only as a complete assembly. If the generator fails for any reason, the entire assembly must be replaced. The generator produces DC voltage.
As the energized rotor begins to rotate within the generator, the spinning magnetic field induces a current into the windings of the stator coil. Once the generator begins producing sufficient current, it also provides the current needed to energize the rotor.
The Y type stator winding connections deliver the induced AC current to 3 positive and 3 negative diodes for rectification. From the diodes, rectified DC current is delivered to the vehicles electrical system through the generator, battery, and ground terminals.
Noise emitting from the generator may be caused by:
- Worn, loose or defective bearings
- Loose or defective drive pulley
- Incorrect, worn, damaged or misadjusted drive belt
- Loose mounting bolts
- Misaligned drive pulley
- Defective stator or diode
- Damaged internal fins
VOLTAGE REGULATOR
The Electronic Voltage Regulator (EVR) is not a separate component. It is actually a voltage regulating circuit located within the Powertrain Control Module (PCM). The EVR is not serviced separately. If replacement is necessary the PCM must be replaced.
The amount of DC current produced by the generator is controlled by EVR circuitry contained within the PCM. This circuitry is connected in series with the generators second rotor field terminal and its ground.
Voltage is regulated by cycling the ground path to control the strength of the rotor magnetic field. The EVR circuitry monitors system line voltage (B+) and battery temperature or inlet air temperature sensor (refer to Battery Temperature Sensor or Inlet Air Temperature Sensor for more information). It then determines a target charging voltage. If sensed battery voltage is 325 mv or lower than the target voltage, the PCM grounds the field winding until sensed battery voltage is 325 mv above target voltage. A circuit in the PCM cycles the ground side of the generator field up to 250 times per second (250Hz), but has the capability to ground the field control wire 100% of the time (full field) to achieve the target voltage. If the charging rate cannot be monitored (limp-in), a duty cycle of 25% is used by the PCM in order to have some generator output. Also refer to Charging System Operation for additional information.