Automotive Refrigerant System Induced Phenomena – Bench to Vehicle Correlation

With the advent of EVs/HEVs and implementation of Idle-Stop-Start (ISS) technologies on internal combustion engine (ICE) driven cars/trucks to improve fuel economy and reduce pollution, refrigerant sub-system (RSS) induced noise phenomena like, hissing, gurgling and tones become readily audible and can result in customer complaints and concerns. One of the key components that induce these noise phenomena is the Thermostatic Expansion Valve (TXV). The TXV throttles compressed liquid refrigerant through the evaporator that results in air-conditioning (A/C) or thermal system comfort for occupants and dehumidification for safety, when needed. Under certain operating conditions, the flow of gas and/or liquid/gas refrigerant at high pressure and velocity excites audible acoustical and structural modes inherent in the tubing/evaporator/HVAC case. These modes may often get masked and sometimes enhanced by the engine harmonics and blower noise. Due to the seasonal demands on A/C compressors, cycling ON/OFF on fixed displacement and during de-stroking of variable displacement compressors, these noises being transient can be easily perceived in the vehicle interior. This paper presents a case study with a systematic approach to excite and quantify these noises induced by the Refrigerant Sub-System (RSS) at the bench-level in a laboratory environment with simulated vehicle operating conditions at a variety of thermal loads. This capability facilitates development of cost-effective and robust counter-measures that can be validated at the bench and implemented later at the vehicle level, if needed. Based on the sound quality analysis and listening studies of bench and vehicle level measurements, some sound quality metrics were investigated for their suitability. Reliable and objective targets for hiss and gurgle phenomena can be developed at an early stage of vehicle development.