System Operation - Smart Charging System
Most current vehicles utilize the Smart Charging control strategy. This strategy helps to improve vehicle performance, reduce CO2 emissions and increase fuel efficiency. The control strategy takes into account battery state of charge and electrical loads on the battery, as well as engine load. Vehicles that utilize the Smart Charging control strategy are equipped with an Intelligent Battery Sensor (IBS). The IBS is an important component of the Smart Charging control strategy.
There are three general modes of operation:
- Idle and acceleration: Charging is typically suspended during idle and acceleration conditions. Due to this strategy it can be common for the alternator output to be equal to, or close to typical battery voltage at idle and during engine acceleration.
- Steady state speeds: During steady state speeds the charge rate is typically low, just enough to maintain battery voltage.
- Deceleration (regenerative braking): The charge rate is typically very high during deceleration.
The Smart Charging strategy can be used with any combination of the following vehicle configurations:
- Single Battery System
- Dual Battery System
- Electronic Voltage Regulation (EVR) Charging systems which use a standard alternator directly controlled by the PCM
- Charging systems using a smart alternator communicating with the PCM via LIN Bus
On vehicles equipped with a standard alternator and Electronic Voltage Regulation (EVR) system, the Powertrain Control Module (PCM) directly controls the charge rate through the Pulse Width Modulated (PCM) alternator field control circuit.
ALTERNATOR CONTROL AND DIAGNOSTICS
The generic graphic below shows a single battery system. This graphic is used for the purpose of demonstrating the fundamental operation of the Electronic Voltage Regulation (EVR) system. A dual battery system is wired slightly different but basic charging system control, sense and operation is the same for both.
The Electronic Voltage Regulation (EVR) charging system maintains the system voltage at a desired level by toggling the Pulse Width Modulated (PWM) alternator field control circuit (A) on and off. When the alternator field is turned on, the system voltage increases. When the alternator field is turned off, the system voltage slowly drops. The rate at which this happens is dependent upon the existing electrical loads, ambient under hood temperature, and the engine speed. A constant system voltage (B, C, D) is maintained when the alternator field is switched on and off at a duty cycle to match the voltage set point based on the existing electrical loads, ambient under hood temperature and engine speed.
When operating normally the voltage reading at the alternator output stud will be very close to the target charging voltage viewed on the scan tool. This is the system voltage and it is sensed by the Powertrain Control Module (PCM) through the Fused B(+) circuit (B) . With the alternator connector plugged in, and back probing the alternator sense circuit (E) , the voltage reading will read approximately 3.5 volts less than the voltage at the alternator output stud due the resistor inside the alternator. This is the alternator sense input to the PCM and is normal. These two voltage sense inputs are used and compared during the different diagnostics performed on the EVR System by the PCM.