Charging System Description and Operation
Electrical Power Management Overview
The electrical power management system is designed to monitor and control the charging system and send diagnostic messagesto alert the driver of possible problems with the battery and generator. This electrical power management system primarilyutilizes existing on-board computer capability to maximize the effectiveness of the generator, to manage the load, improvebattery state-of-charge and life, and minimize the system's impact onfuel economy. The electrical power management system performs 3 functions:
•Monitor the battery voltage and estimate the battery condition
•Take corrective actions by boosting idle speeds, and adjusting the regulated voltage
•Perform diagnostics and driver notification
The battery condition is estimated during ignition/vehicle off and during ignition/vehicle on. During ignition/vehicle offthe state-of-charge of the battery is determined by measuring the open-circuit voltage. The state-of-charge is a functionof the acid concentration and the internal resistance of the battery, and is estimated by reading the battery open circuitvoltage when the battery has been at rest for several hours.
Any time the ignition/vehicle is on, the vehicle algorithm continuously estimates battery state-of-charge based on adjustednet amp hours, battery capacity, initial state-of-charge, and calculated temperature.
While the engine is running, the battery degree of discharge is primarily determined by the integrated battery current sensor,to obtain net amp hours.
In addition, the electrical power management function is designed to perform regulated voltage control to improve batterystate-of-charge, battery life, and fuel economy. This is accomplished by using knowledge of the battery state-of-charge andtemperature to set the charging voltage to an optimum battery voltage level for recharging without detriment to battery life.
Charging System Components
Generator
The engine drive belt drives the generator. When the rotor is spun, it induces an alternating current (AC) into the statorwindings. The AC voltage is then sent through a series of diodes for rectification. The rectified voltage has been convertedinto a direct current (DC) for use by the vehicles electrical system to maintain electrical loads and the battery charge.The voltage regulator integral to the generator controls the outputof the generator; It is not serviceable. The voltage regulator controls the amount of current provided to the rotor. If thegenerator has field control circuit fault, the generator defaults to an output voltage of 13.8 V.
The generator is serviced as a complete assembly. If there is a diagnosed fault in the generator, it must be replaced as anassembly.
Generator Pulley
The pulley drives the Generator via the engine drive belt. There are 2 types of pulleys:
1. Conventional solid Pulley which is bolted to the Generator stator shaft. This Pulley can be serviced separately.
2. One Way Clutch Pulley or Overrunning Alternator Decoupler Pulley allows the Generator to spin freely when the engine rapidlyslows down on sudden deceleration. This part is not serviceable and the Generator needs to be replaced as an assembly.
Body Control Module (BCM)
The BCM communicates with the Engine Control Module (ECM) and the instrument cluster for electrical power management operation.The BCM determines the output of the generator and sends the information to the ECM for control of the generator turn on signalcircuit. It monitors the generator field duty cycle signal circuit information sent from the ECM for control of the generator.It monitors the battery current sensor, the battery positivevoltage circuit, and estimates battery temperature to determine battery state of charge. The BCM also performs idle boost.
Battery Current Sensor (if applicable)
The Battery Current Sensor is a serviceable component that is connected to the negative battery cable at the battery. Thebattery current sensor is a 3-wire hall effect current sensor. The battery current sensor monitors the battery current. Itdirectly inputs to the BCM. It creates a 5 volt Pulse Width Modulation (PWM) signal of 128 Hz with a duty cycle of 0–100%.Normal duty cycle is between 5–95%. Between 0–5% and 95–100% arefor diagnostic purposes.
Battery Sensor Module (if applicable)
The BCM monitors the Battery Sensor Module for battery state of current, state of health, and battery charge via serial data.If the battery is determined to be in poor state of health or having a low state of charge, the BCM will not allow the ECMto perform an auto-stop.
Engine Control Module (ECM)
When the engine is running, the generator turn-on signal is sent to the generator from the ECM, turning on the regulator.The generator's voltage regulator controls current to the rotor, thereby controlling the output voltage. The rotor currentis proportional to the electrical pulse width supplied by the regulator. When the engine is started, the regulator sensesgenerator rotation by detecting AC voltage at the stator through an internalwire. Once the engine is running, the regulator varies the field current by controlling the pulse width. This regulates thegenerator output voltage for proper battery charging and electrical system operation. The generator field duty terminal isconnected internally to the voltage regulator and externally to the ECM. When the voltage regulator detects a charging systemproblem, it grounds this circuit to signal the ECM that a problem exists.The ECM monitors the generator field duty cycle signal circuit, and receives control decisions based on information from theBCM.
Instrument Cluster
As a means of displaying the charging system functions, some vehicles may be equipped with a voltmeter gauge on the instrumentcluster and/or a system voltage display in the driver information center. These will indicate the current vehicle system voltage.
The instrument cluster also provides customer notification if there is a concern with the charging system. There are two meansof notification: a charge indicator on the instrument cluster and/or a service system message displayed on the Driver InformationCenter (DIC) if equipped.
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Charging System Operation
The purpose of the charging system is to maintain the battery charge and vehicle loads. There are 6 modes of operation andthey include:
•Battery Sulfation Mode
•Charge Mode
•Fuel Economy Mode
•Head lamp Mode
•Start Up Mode
•Voltage Reduction Mode
The ECM Controls the Generator through the generator turn–on signal circuit, also known as the Generator L-terminal. The ECMmonitors the generator performance though the Generator field duty cycle signal circuit, also known as the generator F-terminal.
The Generator turn–on signal (Generator L-terminal) is a Pulse Width Modulation (PWM) signal of 128 Hz with a duty cycle of0–100%. Normal duty cycle is between 5–95%. 0–5% and 95–100% are for diagnostic purposes, with 0–5% monitoring for an opencircuit and 95–100% monitoring for a short to ground at a fixed 13.8 V. The following table shows the commanded duty cycleand output voltage of the Generator:
Commanded Duty Cycle
Generator Output Voltage (+/- .25 V)
0–5%
13.8 V
10%
11 V
20%
11.56 V
30%
12.13 V
40%
12.69 V
50%
13.25 V
60%
13.81 V
70%
14.38 V
80%
14.94 V
90%
15.5 V
