FIELD

The present application generally relates to vehicle charging control systems and, more particularly, to techniques to regulate charging with an alternator and a battery to minimize vehicle fuel consumption.

BACKGROUND

An alternator is a device that is mechanically-driven by a crankshaft of an engine to generate electrical energy that is used to power vehicle accessory loads and/or to recharge a battery. The additional fuel that is consumed by the engine to drive the alternator can vary greatly depending on the operating zone of the engine. Similar to the engine, the alternator itself has operating regions of higher and lower efficiency. As a result, the vehicle could consume excessive fuel to generate electrical energy via the alternator when the engine is operating in inefficient operating zones. Conventional solutions to this situation include “smart charging” systems, such as regenerative braking or high load charging reduction. These conventional solutions, however, are not fully optimized (e.g., they may only operate during deceleration conditions). Accordingly, while these conventional systems do work for their intended purpose, there remains a need for improvement in the relevant art.

SUMMARY

According to one example aspect of the invention, a charging control system for a vehicle is presented. In one exemplary implementation, the system comprises: 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.

In some implementations, 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. In some implementations, the optimal duty cycle corresponds to a minimum cost-to-charge metric across the range of alternator duty cycles.

In some implementations, 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.

In some implementations, 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. In some implementations, the controller is further configured to command a maximum duty cycle of the alternator during vehicle deceleration periods.

In some implementations, the set of operating parameters of the engine comprise air charge, engine speed, spark advance, fuel/air ratio, temperature, and accessory loads. In some implementations, the alternator energy output is determined using experimentally determined maps of alternator input torque and alternator efficiency.

According to another example aspect of the invention, a charging control method for a vehicle including an engine that drives an alternator configured to charge a battery of the vehicle is presented. In one exemplary implementation, the method comprises: 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.

In some implementations, 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. In some implementations, the optimal duty cycle corresponds to a minimum cost-to-charge metric across the range of alternator duty cycles.

In some implementations, 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.

In some implementations, the method further comprises 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. In some implementations, the method further comprises commanding, by the controller, a maximum duty cycle of the alternator during vehicle deceleration periods.

In some implementations, the set of operating parameters of the engine comprise air charge, engine speed, spark advance, fuel/air ratio, temperature, and accessory loads. In some implementations, the alternator energy output is determined using experimentally determined maps of alternator input torque and alternator efficiency.

Further areas of applicability of the teachings of the present disclosure will become apparent from the detailed description, claims and the drawings provided hereinafter, wherein like reference numerals refer to like features throughout the several views of the drawings. It should be understood that the detailed description, including disclosed embodiments and drawings referenced therein, are merely exemplary in nature intended for purposes of illustration only and are not intended to limit the scope of the present disclosure, its application or uses. Thus, variations that do not depart from the gist of the present disclosure are intended to be within the scope of the present disclosure.

