Research And Optimization Of NVH Performance Of HVAC Assembly In Automotive Air-conditioning System

In recent years,with the increasing requirement for comfortable driving environment,the problem of improving the NVH performance(noise,vibration and harshness)of the car has begun to attract the attention of various research teams in the industry.The performance of the NVH of the car affects the psychological and physical health of the driver and passengers on the one hand,and is directly linked to the core competitiveness of the vehicle brand on the other hand.Therefore,it is very practical to study and optimize the NVH performance of automobiles.There are many sources of noise and vibration during driving.With the reduction of major noise sources such as engine and road noise,and the improvement of the passenger compartment sealing effect,the NVH problem of the air conditioning system has become increasingly prominent.The HVAC assembly is an important component and also the main source of noise in the air conditioning system.Therefore,this paper carries out research work on the HVAC assembly of automotive air conditioners,including the aerodynamic noise,structural vibration and refrigerant flow noise of HVAC assembly.The main research contents and results are as follows:1.The generation mechanism and influencing factors of aerodynamic noise,structural noise and refrigerant flow noise of HVAC assembly are expounded,which lays a theoretical foundation for the follow-up work.2.The aerodynamic noise performance of the HVAC assembly was optimized.The flow field simulation model was established to identify the noise source.The blower volute,air-conditioning case and position of defroster damper were improved.The aerodynamic noise of the optimized HVAC assembly was significantly reduced.3.The vibration characteristic of the HVAC assembly structure was tested experimentally.The test program was designed to test and analyze the two important characteristics,the modal natural frequency and dynamic stiffness.The test results show that the natural frequency of the HVAC assembly is up to standard(>=40Hz)and the dynamic stiffness is insufficient.The shell is optimized by adding the rib reinforcement,and the dynamic stiffness of the improved HVAC assembly meets the performance requirement(>=20 N/mm).4.A test method including objective test and subjective evaluation was proposed to analyze the high frequency abnormal noise of the refrigerant flow after the compressor starts,and an air conditioning system test bench was built to reproduce the abnormal noise and verify the optimization plan.A small-hole muffler was designed for noise optimization.The test results show that,changing the internal structure and infusing method of TXV,and using the self-designed small-hole muffler and expansion chamber muffler,can all achieve the weakening of the refrigerant flow noise.