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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.

Traditional IC engine powered vehicles readily mask the lower amplitude transients like hiss, clicks and slight tones. However, due to the popularity and expected increase in number of hybrid and electrically driven automobiles all around the world, all the OEMs are concerned about the vehicle interior quietness and sound quality. Refrigerant system induced hiss/gurgle is quite normal phenomenon but its excessive levels and frequent occurrences can be objectionable to demanding customers. Introduction of new environmentally friendly refrigerants (HFO-1234yf), A/C compressors with built-in oil separation (reduced damping in evaporator), and use of IHX with coupled suction and liquid lines, may lead to increased refrigerant system induced hiss and gurgle. Operation of typical A/C system generates steady-state and transient noises that consist of audible tones and high frequency hiss.

Audible tones in vehicle interiors are undesirable because of their impact on customer satisfaction and quality metrics. Most of the loudest tonal noise sources located in the engine compartment are isolated from the vehicle interior by the dash-wall. A majority of the automotive blower/s are located in the vehicle interior in the close proximity of the driver and passengers. Hence, the blower induced tones (if present) become audible and airborne, they readily propagate to the vehicle occupants. The severity of these audible tones is going to be most annoying in future especially in vehicles equipped with hybrid, electric and start/stop at idle technologies, for improved fuel economy mandates in future. Due to increased demands for quieter vehicle interiors with higher airflow for achieving quick thermal comfort, the HVAC systems are designed with lower pressure drop which helps reduced low frequency broad-band noise but does not mask the BPF tone and its harmonics.