Finite Element Study Of The Mechanism Of Frictional Noise In Rotor Compressors For Air Conditioners

The noise generated during the operation of air conditioners not only greatly aggravates their work qualities,but also cause great harm to people’s physical and mental health.Therefore,the noise of air conditioners has always been a hot topic attracting many scholars’ concern.In the literature,the studies of air conditioners’ noise mainly focus on the suppression measures to reduce the noise sources in air conditioners to achieve the purpose of controlling vibration and noise.As compressors are one of the main noise sources in air conditioners,it is of great significance to study their noise problems.Based on the mode coupling mechanism of friction systems,this thesis developed a finite element model to study the friction squeal of a rotary compressor.The model can truthfully simulate the compressor’s working conditions,and can more accurately predict the unstable vibrations of the compressor.The main research work and conclusions are presented as follows:(1)The friction coefficients of several key friction pairs in the rotary compressor were measured using a pin-on-disk testing machine.The torque sensor in the testing machine was calibrated before the measurement,and the relationship between the output voltage of the sensor and the input torque was determined.The test results show that the friction coefficients of the friction pairs in the dry friction will be significantly higher than those in the oil lubrication.When the internal lubrication environment of the compressor becomes very poor due to the lack of necessary cleaning and maintenance,the friction at the friction pairs will become larger,which is easier to stimulate the unstable vibrations and squeal of the compressor.(2)Since the boundary conditions in the finite element model have a very important influence on the prediction results of the model,the author also made a dynamic analysis of the moving parts in the compressor,determined the force and movement of these parts,which were added to the finite element model as boundary conditions.Since the dynamic analysis of the compressor needs to solve the differential equations of the system,the author used the Matlab language to write the relevant program files.Running the program files can obtain the relevant boundary conditions as inputs of the finite element model.(3)The finite element model of the compressor friction system was established with ABAQUS software.The influences of the friction coefficient between the crankshaft and the flange,the stiffness of the flange and the damping ring parameters on the frictional squeal were studied respectively.The model prediction results show that as the friction coefficient increases,the energy inputted by the friction to the friction system gradually increases,when the friction coefficient reaches a critical value,the friction system becomes unstable;Appropriately reducing the stiffness of the flange will greatly reduce the friction between the flange and the crankshaft,when the energy inputted by the friction to the friction system is not enough to stimulate the unsteady vibrations of the system,the system will remain stable;The introduction of the damping ring can obviously suppress the unstable vibrations of the friction system and make the system’s original negative equivalent damping ratio become positive;When the friction system is unstable,the frequencies of the tangential vibration and normal vibration of the system are the same,which indicates that the tangential vibration and normal vibration of the system are coupled,and mode coupling is an important cause of the unstable vibrations and squeal of the system.(4)The transient dynamics analysis model of the compressor friction system was established using ABAQUS software.The transient dynamics analysis can introduce many nonlinear factors into the finite element model,and the analysis results are more in line with the actual condition.Although there are certain errors between the system’s dynamic response in the time domain and the measured data,these errors will not have a great impact on the results of the transient dynamics analysis,and the results of the transient dynamics analysis show that when the system is unstable,the tangential vibration and normal vibration of the lower flange are coupled,which is consistent with the conclusion drawn by the complex eigenvalue analysis of the system.In this paper,for the first time,the transient analysis results of the compressor friction system had been made short-time Fourier transform,and when compared with the time-frequency analysis results of the measured signals,the results show that the unstable vibrations of the friction system usually occurs in the first half of the system operating cycle,which is consistent with the actual operation of the compressor.