HVAC NVH Refinement in Electric Vehicle

Customers expect much 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 mass. This paper focuses on reducing the tactile vibration in electric vehicle when AC is switched on. Vibration levels were high and modulating in nature in 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 1st order vibration of compressor was dominant on tactile locations at all the compressor speeds. Vibration levels were improved by 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 to reduce the effect of pulsation. With the above modifications, steering wheel vibration levels 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 ~ 10 dB . 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.