Noise Sources Characterization of Automotive HVAC Systems

Abstract

<p>The noise sources and mechanisms of the front and rear HVAC systems of an automotive are characterized experimentally. The front system has three main outlet ducts equipped with louvers and operates in two modes of bypass and recirculation. The inlet and outlet sides of the rear system are both located in the cabin; hence, it always works only on the recirculation mode. The outlet duct of the rear system is covered by a ten-hole curved plate which is found to be a strong source of noise. Both systems are tested at the highest possible flow rate, as it is the most annoying condition of noise generation. The noise coming out of each duct of the front and rear systems and their fan units are measured separately. Since the fan is an important part of the systems, it is studied at different speeds with more details. In order to compare the effect of the noise generated by the fan section with the noise produced by the complete system, the impeller is replaced with a speaker generating an overall sound level similar to the fan noise. Under this condition, the flow noise due to the evaporator core, distributive ducts and louvers are cancelled. It is concluded that at low frequencies the duct flow-noise is dominant. At high frequencies, the effects of both duct flow-noise and fan noise are impor1ant. To find out how the combination of the outgoing sound from the vents and fans inlet affect on the driver and passengers, some measurements are carried out inside the cabin of the automobile.</p>