Thermal Analysis of Cooling System in Hybrid Electric Vehicles

Increased cooling demands in Hybrid Electric Vehicles (HEVs), compactness of engine compartment, and the additional hardware under the hood make it challenging to provide an effective cooling system that has least impact on fuel economy, cabin comfort and cost. Typically HEVs tend to have a dedicated cooling system for the hybrid components due to the different coolant temperatures and coolant flow rates. The additional cooling system doubles the hardware, maintenance, cost, weight and affects vehicle fuel economy. In addition to the cooling hardware, there are several harnesses and electronics that need air cooling under the hood. This additional hardware causes airflow restriction affecting the convective heat transfer under the hood. It also affects the radiation heat transfer due to the proximity of hardware close to the major heat sources like the exhaust pipe. KULI, a commercial software, was used to analyze the underhood thermal behavior and to study the effects of the additional hardware on the performance of the cooling system of a HEV. As a result of this analysis, modification to the hardware, pipe and harnesses routing were made under the hood. This paper also investigates a single cooling system for the engine and HEV components to overcome some of the listed issues and presents results of the cooling analysis of the single cooling system.