Influence of Air Conditioning Characteristics on Vehicle Interior Noise

Reduction of Heating, Ventilation and Air Conditioning (HVAC) systems and other components such as engine and exhaust system has resulted the study on the vehicle noise as an increasingly important aspect for the automotive industry in meeting the passenger comfort requirements. In this paper, the influence of vehicle air conditioning characteristics such as the fan speed, engine speed and air conditioning positions (i.e., ON or OFF) on the vehicle interior Sound Pressure Level (SPL) is presented. The generation of noise and its transmission mechanisms are studied. The major contributors to the HVAC system airborne noise are the aerodynamic, mechanical and hydraulic noises from the compressor and handling units. Since the HVAC's fan is driven directly by the vehicle battery that is separated from the HVAC, the noise generation due to the fan speeds or positions can be directly obtained by turning the compressor to OFF and the fan to ON positions. Meanwhile, the mechanical and hydraulic noises can be obtained by extracting the airborne noise by turning the compressor to OFF and the fan to ON positions from those obtained by turning both the compressor and fan to ON position. The experimental results indicate that the principal source of vehicle noise is related to the aerodynamic noise and the noise level has shown considerable increase when both the fan and compressor units are turned to ON positions. For a specific fan speed, an increase in the noise due to the mechanical and hydraulic sources is observed for an increase in the engine speed.