Simulation Study On Frictional Noise Of Rotary Air Conditioning Compressors Caused By Friction Self-excited Vibration

Noise source of air conditioning compressors can be divided into aerodynamic noise,electromagnetic noise and mechanical noise.Mechanical noise is mainly caused by friction and uneven force transmission between components.Frictional noise is more common in engineering applications and mainly occurs when the relative sliding speed of sliding contact components is low,such as the squeal of automobile brakes,the flutter of hinge rotation,and so on.In this thesis,the force analysis and speed analysis of the crankshaft-flange assembly are carried out.The friction coefficient of each friction pair of the compressor is measured,and the measured friction coefficient is imposed on the crankshaft-flange system model and the whole model in the form of negative slope of friction relative sliding speed to explore the location and trend of frictional noise.Extracting the characteristic frequency of the measured noise signal,using the friction self-excited vibration theory to explain the generation mechanism of the compressor noise.The conclusions can be drawn as follows:（1）According to the test,the sliding friction coefficient of each friction pair of the rotary compressor about 0.1 was obtained,and the dry friction coefficient of generally stable at about 0.2.When wear occurred,it could reach a higher value according to different wear conditions.In addition,through the analysis of the vibration acceleration signal of the rotary compressor,it was concluded that the vibration was coupled in different directions,and the characteristic frequencies extracted from the acceleration signal and the sound pressure signal are very close to each other.（2）In the crankshaft flange system,f=1085Hz is the dominant frequency of the unstable mode.The friction self-excited vibration of the contact friction pair between the crankshaft thrust surface and the lower flange will cause the low-frequency noise.Reducing the sliding friction coefficient and static friction coefficient can eliminate the unstable mode:f=3918Hz is the non-dominant frequency of the unstable mode.At this frequency,the main noise source was radiated by crankshaft thrust surface and the lower flange.Reducing the static friction coefficient or increasing the sliding friction coefficient can suppress the squeal noise at this frequency.When the sliding friction coefficient is less than 0.2,the unstable mode disappears.The surface concentric groove on the flange has little effect on the complex eigenvalues of the friction system,but has an effect on the equivalent damping ratio.（3）Under good lubrication conditions,the simulation results show that the compressor model has no unstable mode.But only when the static friction coefficient of the roller-sliding vane against the roller-cylinder wall reaches 0.35,unstable mode appears,the unstable modal frequency is 10292Hz,10047Hz and 7200Hz respectively.（4）As the difference l-_sk between sliding friction coefficient and static friction coefficient increases,the instability of the system increases in the whole machine model.When l-_sk>0.07,the increase of l-_sk will generate the unstable modes whose frequencies are 7524Hz,7249Hz and 10294Hz,unstable modes are more complicated.when the frictional attenuation coefficient d is between 10-2 and 10-3,the instability of the friction system easily occurs,too fast or too slow exponential decay is helpful to suppress unstable modes.The transient dynamic response analysis shows that the frequencies of 6 special location points of the rotary compressor are in good agreement with the frequencies of the actual measurement frequencies of the rotary compressor and the frequencies predicted by the complex eigenvalue method.