Mild hybrid technique using the automotive air-conditioning system

Abstract

Among all the ancillary loads of a vehicle, the air-conditioning system accounts for the majority of fuel consumption, and its performance significantly affects the fuel economy of the vehicle. Topological similarities between the electrical system and the air-conditioning system can be utilized to formulate a new mild hybrid technique in which the compressor is treated as an energy conversion device and the evaporator as an energy storage device. Thus, the free kinetic energy during vehicle deceleration is harvestable by the air-conditioning system, provided that the on–off sequence of the clutch command is synchronized to the occurrence times of deceleration events. Motivated by this conceptualization, we are interested in three problems: first, the way in which the specific energy and the specific power of the evaporator can be measured; second, the types of new feature that the formulated optimization problem has; third, the method that is an appropriate mathematical tool for solving the problem. In order to solve these problems, energy-based models developed for air-conditioning systems with conventional evaporators and storage evaporators using a phase-change material are utilized, because they are physics based and have been validated against experimental data in previous work. A framework similar to that used in the energy management of a hybrid electric vehicle is established, and its unique characteristics are identified. The low-cost method using the air-conditioning system as an energy buffer, which is a very promising mild hybrid technique that has been demonstrated in conventional vehicles, is also applicable to hybrid electric vehicles.