HVAC NVH Refinement in Electric Vehicle

Customers expect more advanced features and comfort in electric vehicles. It is challenging for NVH engineers to reduce the vibration levels to a great extent in the vehicle without adding cost and weight.

This paper focuses on reducing the tactile vibration in electric vehicle when AC is switched ON. Vibration levels were not acceptable and modulating in nature on the test vehicle. Electric compressor is used for cabin cooling and battery cooling in the vehicle. Compressor is connected to body with the help of isolators. Depending upon cooling load, the compressor operates between 1000 rpm and 8000 rpm. The 1^st order vibration of compressor was dominant on tactile locations at all the compressor speeds. Vibration levels on steering wheel were improved by 10 dB on reducing the dynamic stiffness of isolators. To reduce the transfer of compressor vibration further, isolators are provided on HVAC line connection on body and mufflers are provided in suction and discharge line. With the above modifications, steering wheel vibration levels were reduced by ~ 2 dB. It is identified that radiator fan Pulse Width Modulation (PWM) frequency is also contributing to higher tactile vibration. Shifting PWM frequency to high frequency and stiffness increase on the fan motor casing has reduced the vibration levels by ~ 16 dB and cabin noise by ~ 2 dB (A). Alternative solutions like reducing of fan isolator stiffness is also explored. Blower vibrations contributing to steering wheel vibrations were reduced by controlling the unbalance on the blower. With all the modifications, tactile vibration levels are reduced considerably by ~ 20 dB. Modal criteria during design of compressor bushes and the NVH requirements during selection of fan PWM frequency to avoid higher levels of vibration during AC ON condition are explained.