Description And Operation: Operation: Notes
Smart Generator equipped vehicles operate under a strategy named the Smart Alternator Management (SAM). The SAM control strategy depends on the vehicle driving conditions and the battery status and is used to improve the vehicles fuel economy. The smart generator is a Local Interface Network (LIN) generator.
The main strategy is:
- the smart generator set point voltage is regulated to the highest possible value in order to store part of the kinetic energy into the battery when the vehicle is decelerating
- the smart generator set point voltage is regulated to the lowest possible value in order to decrease the generators passive torque when high torque is requested during the acceleration and deceleration phases. The voltage set point is regulated in order to reach an optimal State of Charge (SOC).
- the smart generator voltage maximum limit and minimum limit are calculated based on the battery status and the vehicle electrical load activations.
The SAM strategy used will depend on the trip profile of vehicle:
- Strong acceleration with high increase of requested torque (Passive Boost phase)
- Braking, cut-off condition (Regenerative Braking phase)
- Vehicle state different from Passive Boost or Regenerative Braking (Steady State phase)
- Engine cranking phase (Optimized engine crank)
- Engine shut-off phase (Engine shutdown dynamic control).
During these phases the smart generators voltage is regulated dynamically. The maximum voltage and the minimum voltage limit depends on the vehicle system (battery SOC, temperature, various vehicle system electrical loads)
STANDARD GENERATOR SYSTEM OPERATION
The Electronic Voltage Regulation (EVR) system maintains the system voltage at a desired level by turning the Pulse Width Modulated (PWM) generator field control circuit (A) on and off. When the generator field is turned on, the system voltage increases. When the generator 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) can be maintained only when the generator field is switched on and off at a duty cycle that very accurately emulates the existing electrical loads given the existing ambient under hood temperature and engine speed.
During normal operation, the voltage reading at the generator output stud will be very close to the target charging voltage viewed on the scan tool. This is the system voltage and is sensed by the PCM through the fused B+ circuit (B). With the generator connector plugged in, the voltage reading on the generator sense circuit will be approximately 3.5 volts less than the voltage at the generator output stud due the resistor inside the generator. This is the generator sense (E) input to the PCM. These two voltage sense inputs are used and compared during the different diagnostics performed on the EVR System by the PCM.
In diagnostic mode, when the PCM detects that the output voltage is too high or too low, the PCM runs a series of diagnostics to determine the cause. When the diagnostic is initiated, the PCM will change the field control circuit and look for a change in the output voltage. If no reaction is detected, the PCM rationalizes that it has lost control of the generator field control (A) due to an open or shorted condition. If the generator field control is active, and the engine speed is above a calibrated threshold, the PCM will run a series of tests that turn the generator field control off and on for a brief period of time and monitors the system voltage (B) for a calibrated amount of change in the voltage, to determine a failure of the generator. This diagnostic test requires repeated failures to insure that an erroneous fault is not set.