Resolution of HEV Battery Cooling System Inlet Noise Issue by Optimizing Duct Design and Fan Speed Control Strategy

The power battery cooling system of a hybrid electric vehicle is composed of a fan and duct assembly with its inlet positioned inside the vehicle cabin. For the prototype vehicle considered in this work, the air inlet is positioned on the package tray due to limited feasible choices. When the battery temperature is over rated limit, the cooling fan starts to operate to cool the battery system. Propelled by the fan in the cooling system, the air in the passenger compartment enters the duct inlet, and rushes through the air duct to reach the battery pack to fulfill the intended cooling function. In this case, the rear seat occupants could clearly perceive the existence of an annoying whirring noise. In this paper, the characteristics of the battery air cooling system and its working principles are briefly described. The air inlet noise generation mechanism and its frequency characteristics are then analyzed. It is found that the fan noise is the prominent contributor to the inlet noise perceived by the occupants. To resolve the issue, the directionality of the inlet noise is modified by implementing a cap structure over the inlet opening, and the reduction of the inlet noise is achieved by placing sound-absorbing material in the duct. In addition, since the background noise inside the passenger cabin increases with the increase of the vehicle speed, based on the sound masking principle, the fan speed is controlled optimally such that the fan operates at its maximum allowable speed subject to the condition that the fan noise is being masked. Finally, the on-road subjective evaluations show that the inlet noise from the battery cooling system could hardly be perceived by rear seat occupants under all normal vehicle operating conditions.