Techniques to regulate charging with an alternator and a battery to minimize vehicle fuel consumption
Charging control techniques for a vehicle including an engine that drives an alternator configured to charge a battery of the vehicle comprise modeling a fuel consumption of the alternator for each load level across a range of alternator loads using an engine torque model and a set of operating parameters of the engine, determining an energy output from the alternator for each load level across the range of alternator loads, calculating a cost-to-charge metric based on the modeled alternator fuel consumption and the determined alternator energy output for each duty cycle across a range of duty cycles of the alternator, determining an optimal cost-to-charge from the calculated cost-to-charge metrics, determining a target cost-to-charge metric based on a state of charge of the battery, and operating the alternator accordingly at an optimal duty cycle based on the metrics and current engine operating conditions.
1. A charging control system for a vehicle, the system comprising:
an alternator driven by an engine of the vehicle and configured to charge a battery of the vehicle; and
a controller configured to:
model a fuel consumption of the alternator for each load level across a range of alternator loads using an engine torque model and a set of operating parameters of the engine;
determine an energy output from the alternator for each load level across the range of alternator loads;
calculate a cost-to-charge metric based on the modeled alternator fuel consumption and the determined alternator energy output for each duty cycle across a range of duty cycles of the alternator;
determine an optimal cost-to-charge from the calculated cost-to-charge metrics;
determine a target cost-to-charge based on a state of charge of the battery; and
operate the alternator at an optimal duty cycle corresponding to the optimal cost to charge, a target duty cycle corresponding to the target cost to charge, or zero duty cycle based on whether current engine operating conditions are indicative of a higher efficiency optimal cost zone for the engine or a lower efficiency target cost zone for the engine.
2. The system of claim 1 , wherein the controller is configured to calculate the cost-to-charge metric for each duty cycle of the alternator as a ratio of (i) the alternator fuel consumption to (ii) the alternator energy output.
3. The system of claim 1 , wherein the optimal duty cycle corresponds to a minimum cost-to-charge metric across the range of alternator duty cycles.
4. The system of claim 1 , wherein:
when the engine operating conditions are indicative of the optimal operating zone, the controller is configured to (i) operate the alternator at the optimal duty cycle when the optimal cost-to-charge is less than the target cost-to-charge and operate the alternator at zero duty cycle when the optimal cost-to-charge is not less than the target cost-to-charge; and
when the engine operating conditions are indicative of the target operating zone, the controller is configured to (i) operate the alternator at the target duty cycle when the one of the optimal cost-to-charge metrics is less than or equal to the target cost-to-charge and (ii) operate the alternator at zero duty cycle when none of the optimal cost-to-charge metrics is less than or equal to the target cost-to-charge.
5. The system of claim 1 , wherein the controller is further configured to calculate the target cost-to-charge metric using a calibrated function where the target cost-to-charge metric increases as the battery state of charge decreases.
6. The system of claim 1 , wherein the controller is further configured to command a maximum duty cycle of the alternator during vehicle deceleration periods.
7. The system of claim 1 , wherein the set of operating parameters of the engine comprise air charge, engine speed, spark advance, fuel/air ratio, temperature, and accessory loads.
8. The system of claim 1 , wherein the alternator energy output is determined using experimentally determined maps of alternator input torque and alternator efficiency.
9. A charging control method for a vehicle including an engine that drives an alternator configured to charge a battery of the vehicle, the method comprising:
modeling, by a controller of the vehicle, a fuel consumption of the alternator for each load level across a range of alternator loads using an engine torque model and a set of operating parameters of the engine;
determining, by the controller, an energy output from the alternator for each load level across the range of alternator loads;
calculating, by the controller, a cost-to-charge metric based on the modeled alternator fuel consumption and the determined alternator energy output for each duty cycle across a range of duty cycles of the alternator;
determining, by the controller, an optimal cost-to-charge from the calculated cost-to-charge metrics;
determining, by the controller, a target cost-to-charge metric based on a state of charge of the battery; and
operating, by the controller, the alternator at an optimal duty cycle corresponding to the optimal cost to charge, a target duty cycle corresponding to the target cost to charge, or zero duty cycle based on whether current engine operating conditions are indicative of a higher efficiency optimal cost zone for the engine or a lower efficiency target cost zone for the engine.
10. The method of claim 9 , wherein the cost-to-charge metric is calculated for each duty cycle of the alternator as a ratio of (i) the alternator fuel consumption to (ii) the alternator energy output.
11. The method of claim 9 , wherein the optimal duty cycle corresponds to a minimum cost-to-charge metric across the range of alternator duty cycles.
12. The method of claim 9 , wherein:
when the engine operating conditions are indicative of the optimal operating zone, the controller (i) operates the alternator at the optimal duty cycle when the optimal cost-to-charge is less than the target cost-to-charge and operates the alternator at zero duty cycle when the optimal cost-to-charge is not less than the target cost-to-charge; and
when the engine operating conditions are indicative of the target operating zone, the controller (i) operates the alternator at the target duty cycle when the one of the optimal cost-to-charge metrics is less than or equal to the target cost-to-charge and (ii) operates the alternator at zero duty cycle when none of the optimal cost-to-charge metrics is less than or equal to the target cost-to-charge.
13. The method of claim 9 , further comprising calculating, by the controller, the target cost-to-charge metric using a calibrated function where the target cost-to-charge metric increases as the battery state of charge decreases.
14. The method of claim 9 , further comprising commanding, by the controller, a maximum duty cycle of the alternator during vehicle deceleration periods.
15. The method of claim 9 , wherein the set of operating parameters of the engine comprise air charge, engine speed, spark advance, fuel/air ratio, temperature, and accessory loads.
16. The method of claim 9 , wherein the alternator energy output is determined using experimentally determined maps of alternator input torque and alternator efficiency.