PCM-Controlled Charging System
Overview
The PCM-Controlled charging system (Figure 142) provides many additional benefits over the current Integral Generator Regulator system. The first benefit is improved battery life. In an integral generator regulator system, the regulator set point is established by a temperature sensor in the regulator which estimates battery temperature. Field data has shown this approach lacks accuracy. With a PCM-controlled generator, the regulator voltage set point is determined by the PCM and communicated to the regulator via the generator communication line. The PCM will use a calibratable algorithm to estimate battery temperature. Improving battery temperature estimates will reduce battery damage caused by over- and undercharging.
The second benefit is improved engine performance. Whenever the PCM senses a wide-open throttle (WOT) condition, the PCM will momentarily lower the regulator voltage set point. This reduces the torque load of the generator on the engine and improves acceleration. The PCM has a calibratable time limit on this reduced voltage feature. This is to prevent the generator output from being cut back for an extended WOT period, which could cause battery discharge.
The third benefit is improved idle stability. In response to the PCM's generator communication signal, the regulator uses a generator monitor signal to provide feedback to the PCM. The generator monitor signal provides the PCM with charging system information. Specifically, it lets the PCM know when the charging system receives a transient electrical load which would normally affect idle stability. Because the PCM can anticipate additional loads, actions can be taken to minimize idle sag. The PCM can choose to either reduce the regulator set point or increase engine idle speed, both of which are calibratable features. In order to establish whether the regulator is accurately maintaining the desired voltage set point, the regulator uses a charging system voltage line to sense battery voltage at the rear power distribution box.
The fourth benefit is reduced cranking efforts. The PCM can reduce the mechanical load on the starter by initially commanding a low voltage set point. This may improve start times.
If the PCM detects a charging system error, it will broadcast a low voltage telltale (ON) command which tells the cluster to light the charge indicator. The charge indicator will be illuminated if the PCM fails to see a signal on the generator monitor line for a time period greater than 500 milliseconds. This telltale command will also be used to indicate over-voltage conditions detected by the PCM controlled generator.
Each time the ignition switch is cycled to the run position, the cluster will initiate a bulb check by illuminating the charge indicator. It is the PCM's responsibility to issue a low voltage telltale (OFF) command if the charging system is functioning properly. This message should be sent during Network Initialization in the voluntary phase (250 milliseconds to 450 milliseconds after the ignition switch is cycled to the run position). If a low voltage telltale (OFF) command is not received by the cluster, the cluster will continue to light the charge light indefinitely.