RVC Systems Feature Many Benefits Traditional charging systems use an internal temperature sensor inside the generator to establish generator voltage set points. When the generator is cold, it raises the voltage output set point. When the generator is hot, it lowers the voltage output set point. This type of system tends to overcharge the battery on long trips at highway speeds and under- charge the battery on short trips with low vehicle speeds. Regulated Voltage Control (RVC) is a new dynamic control of the vehicle’s system voltage. It regulates the genera- tor’s output voltage, based mainly on estimated battery temperature and bat- tery state-of-charge. The main benefits of this system are: * improved fuel economy, ¢ extended battery life, * extended lamp life, * extended switch life. GM is using three different genera- tions of RVC systems on a number of new models, including Cadillac CTS, SRX and STS, Chevrolet and GMC full-size trucks and SUVs, Chevrolet Cobalt and Uplander, Buick LaCrosse and Terazza, and Pontiac Grand Prix and Montana SV6. Since the RVC system allows changes to vehicle voltage, up or down, under various scenarios—the battery state of charge and the vehicle’s present electrical needs are two conditions taken into account—the voltmeter may fluc- tuate. Conventional systems usually maintain a consistent reading of 14 volts. The fluctuation of the RVC sys- tem may range between 12 and 24 volts. This is normal system operation. Two RVC Systems There are two types of RVC systems used today— integrated RVC and stand- alone RVC (SARVC). Integrated systems use a battery cur- rent sensor to provide a body control module (BCM) the amount the battery is charging or discharging. Accurate voltage measurements are taken through the battery positive voltage and ignition 1-voltage circuits. The BCM then com- municates information over serial data circuits for the ECM/PCM to directly control the generator. SARVC systems do not use the BCM for operation. They have a generator battery control module mounted to the negative battery cable, to interpret bat- tery current, and voltage and battery temperature inputs. The battery current sensor is internal to the module. This module also directly controls the gener- ator L-terminal duty cycle instead of the ECM/PCM. Both types of system have two types of corrective actions to ensure the bat- tery stays at an 80 percent state of charge. These include up to three levels of load shed and up to three levels of idle boost operation. System Operation The basic operation of the RVC sys- tem is covered here, but not all systems will enter all modes of operation; refer to the applicable service manual infor- mation for more details. The purpose of the RVC system is to maintain the battery state-of-charge at 80 percent or above and support vehicle loads. The six modes of operation include charge mode; fuel economy mode; volt- age reduction mode; start up mode; windshield de-ice mode; and battery sulfation mode. The PCM/ECM (generator battery control module on full-size trucks) con- trols the generator through the generator L-terminal control circuit. It monitors the generator performance through the gen- erator field duty cycle signal circuit. The signal is a 5 volt Pulse Width Modulated (PWM) signal of 128 Hz with a duty cycle of 0 to 100 percent. Normal duty cycle is between 5 and 95 percent. The ranges between 0 to 5 percent and 95 to 100 percent are for diagnostic purposes. Commanded duty cycle and output volt- age of the generator are shown below. Duty Cycle Generator Voltage Set Point 10 % 11.0V 20 % 11.56V 30 % 12.12V 40 % 12.68V 50 % 13.25V 60 % 13.81V 70 % 14.37V 80 % 14.94V 90 % 15.5V The generator provides a feedback signal of the generator load through the generator field duty cycle signal circuit to the control module. The signal is a 5 volt PWM signal of 128 Hz, with a duty cycle of 0 to 100 percent. Normal duty cycle is between 5 and 99 percent. The ranges between 0 and 5 percent and 100 percent are for diagnostic purposes. Charge Mode—The control module enters charge mode whenever one of the following conditions is met: ¢ Under WOT conditions and when the fuel rate (sent by the ECM/ PCM) 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 eight seconds. ¢ The electric cooling fans are on high speed. ¢ The rear defogger is on. ¢ The battery state of charge is less than 80 percent. When one of these conditions is met, the control module ramps up the voltage slowly to a level between 13.4 to 15.5 volts (depending upon the mode of operation the system is presently in) at a rate of 8 mV to 50 mV per second. Fuel Economy Mode—The control module enters fuel economy mode when the following conditions are met: ¢ The calculated ambient air temper- ature is above 0 degrees C (32 degrees F). ¢The calculated battery current is less than 15 amperes and greater than -8