Generator/Battery Control Module

CHARGING SYSTEM DESCRIPTION AND OPERATION (GENERATOR/BATTERY CONTROL MODULE)

ELECTRICAL POWER MANAGEMENT (EPM) OVERVIEW
The electrical power management (EPM) system is designed to monitor and control the charging system and send diagnostic messages to alert the driver of possible problems with the battery and generator. This EPM system primarily utilizes existing on-board computer capability to maximize the effectiveness of the generator, to manage the load, improve battery state-of-charge (SOC) and life, and minimize the system's impact on fuel economy. The EPM system performs 3 functions:
- It monitors the battery voltage and estimates the battery condition.
- It takes corrective actions by adjusting the regulated voltage.
- It performs diagnostics and driver notification.

The battery condition is estimated during key-off and during key-on. During key-off the SOC of the battery is determined by measuring the open-circuit voltage. The SOC is a function of the acid concentration and the internal resistance of the battery, and is estimated by reading the battery open-circuit-voltage when the battery has been at rest for several hours.

The SOC can be used as a diagnostic tool to tell the customer or the dealer the condition of the battery. Throughout key-on the algorithm continuously estimates SOC based on adjusted net amp hours, battery capacity, initial SOC, and temperature.

While running, the battery degree of discharge is primarily determined by a battery current sensor, which is integrated to obtain net amp hours.

In addition, the EPM function is designed to perform regulated voltage control (RVC) to improve battery SOC, battery life, and fuel economy. This is accomplished by using knowledge of the battery's SOC and temperature to set the charging voltage to an optimum battery voltage level for recharging without detriment to battery life.

The Charging System Description and Operation is divided into 3 sections. The first section describes the charging system components and their integration into the EPM. The second section describes charging system operation. The third section describes the instrument panel cluster operation of the charge indicator, driver information center messages and voltmeter operation.

CHARGING SYSTEM COMPONENTS

Generator
The generator is a serviceable component. If there is a diagnosed failure of the generator it must be replaced as an assembly. The engine drive belt drives the generator. When the rotor is spun it induces an alternating current (AC) into the stator windings. The AC voltage is then sent through a series of diodes for rectification. The rectified voltage has been converted into 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 output of the generator. It is not serviceable. The voltage regulator controls the amount of current provided to the rotor. If the generator has field control circuit failure, the generator defaults to an output voltage of 13.8 volts.

Generator Battery Control Module
The generator battery control module is a class 2 device. It communicates with the powertrain control module (PCM), instrument panel cluster and the body control module for electrical power management (EPM) operation. It is a serviceable component that is connected to the negative battery cable at the battery. It directly controls the generator field control circuit input to the generator. It monitors the generator field duty cycle signal circuit, its internal battery current sensor, the battery positive voltage circuit, and estimated battery temperature to determine battery state of charge (SOC). If the generator battery control module losses communication with other modules that provides input to it the default voltage will be set to XX volts.

Powertrain Control Module (PCM)
The PCM provides information over the class 2 serial data circuit to the generator battery control module. The generator battery control module monitors the following data parameters provided by the PCM:
- Intake air temperature
- Fuel grams per second
- Throttle position
- Cooling System fan speed
- Engine coolant temperature

The generator battery control module uses these data parameters for different charging system modes depending on the required voltage needed.

Instrument Panel Cluster (IPC)
The instrument panel cluster (IPC) provides a means of customer notification in case of a failure and a voltmeter. There is two means of notification, a charge indicator and a driver information center message of SERVICE CHARGING SYSTEM and CHARGING SYSTEM FAULT.

CHARGING SYSTEM OPERATION
The purpose of the charging system is to maintain the battery charge and vehicle loads. There are 6 modes of operation and they include:
- Charge Mode
- Fuel Economy Mode
- Voltage Reduction Mode
- Start Up Mode
- Windshield Deice Mode
- Battery Sulfation Mode




The generator battery control module controls the generator through the generator field control circuit. It monitors the generator performance though the generator field duty cycle signal circuit and the battery positive voltage circuit. The generator battery control module controls the generator through the generator field control circuit. The signal is a 5-volt pulse width modulation (PWM) signal of 128 Hz with a duty cycle of 0-100 percent. Normal duty cycle is between 5-95 percent. Between 0-5 percent and 95-100 percent are for diagnostic purposes. The table shows the commanded duty cycle and output voltage of the generator:

The generator provides a feedback signal of the generator voltage output through the generator field duty cycle signal circuit to the generator battery control module. The signal is a 5-volt PWM signal of 128 Hz with a duty cycle of 0-100 percent. Normal duty cycle is between 5-99 percent. Between 0-5 percent and 100 percent are for diagnostic purposes.

Charge Mode
The generator battery control module will enter Charge Mode when ever one of the following conditions are met:
- The interpreted fuel rate is greater than 21 g/s and the throttle position is greater than 90 percent.
- The headlamps are ON low or high beam.
- The wipers are ON for more than 8 seconds.
- The electric cooling fans are on high speed.
- The rear defogger is ON.

Once one of these conditions are met the generator battery control module will set the targeted generator output voltage to 13.4 volts and then ramp that voltage up to 14.5 volts at a rate of 50 mV per second.

Fuel Economy Mode
The generator battery control module will enter Fuel Economy Mode when the calculated ambient air temperature is above 0°C (32°F), the calculated battery current is less than 15 amperes and greater than -8 amperes, and the battery state of charge is greater than 80 percent. Its targeted generator output voltage is 13 volts. The generator battery control module will exit this mode once the criteria are met for Charge Mode.

Voltage Reduction Mode
The generator battery control module will enter Voltage Reduction Mode when the calculated ambient air temperature is above 0°C (32°F); the calculated battery current is less than 2 amperes and greater than -7 amperes, and the generator field duty cycle is less than 99 percent. Its targeted generator output voltage is 12.9 volts. The generator battery control module will exit this mode once the criteria are met for Charge Mode.

Start Up Mode
After the engine has started the generator battery control module sets a targeted generator output voltage of 14.5 volts for 20 seconds.

Windshield Deice Mode
After the engine has run for more than 10 seconds, the generator battery control module sets a targeted generator output voltage of 13.8 volts if the calculated ambient air temperature is less that 0°C (32°F). The generator battery control module will stay in this mode until the engine coolant temperature reaches 75°C (167°F) for 10 minutes.

Battery Sulfation Mode
The generator battery control module will enter this mode when the interpreted generator output voltage is less than 13.2 volts for 45 minutes. Once in this mode the generator battery control module will set a targeted output voltage of 13.8 volts for 5 minutes. The generator battery control module will then determine which mode to enter depending on voltage requirements.

INSTRUMENT PANEL CLUSTER (IPC) OPERATION

Charge Indicator Operation
The instrument panel cluster (IPC) illuminates the charge indicator in the message center when the one or more of the following occurs:
- The powertrain control module (PCM) detects that the generator output is less than 11 volts or greater than 16 volts. The IPC receives a class 2 message from the generator battery control module requesting illumination.
- The IPC determines that the system voltage is less than 11 volts or greater than 16 volts. The IPC receives a class 2 message from the body control module (BCM) indicating there is a system voltage range concern.
- The IPC performs the displays test at the start of each ignition cycle. The indicator illuminates for approximately 3 seconds.
- The ignition is ON, with the engine OFF.

Charging System Failure
The generator battery control module will send a class 2 message to the IPC for the CHARGING SYSTEM FAILURE message to be displayed. It is commanded ON when DTC B1487 sets. The message is turned off when the conditions for clearing the DTC have been met.

Service Charging System
The generator battery control module will send a class 2 message to the IPC for the SERVICE CHARGING SYSTEM message to be displayed. It is commanded ON when DTC B1390, B1488, B1492, B1493 or B1516 sets. The message is turned off when the conditions for clearing the DTC have been met.

Voltmeter Operation
The IPC displays the system voltage as detected at the ignition 1 input of the IPC. When the engine is ON, the gage should be between 10-16 volts. The voltmeter will be noticeably different than previous model year vehicle as far as voltage fluctuations. If there is a concern with gage operation ensure to compare to a known good like vehicle.