Conference Year
2018
Keywords
vibrations, acoustics, unbalancing, dynamics
Abstract
In this Paper a detailed study of dynamics of the hermetic compressor is shown. The key point of this study is the well-known issue of compressor reciprocating kinematic unbalancing which is the main cause of modern refrigerator structural vibrations and consequently acoustical performance. In this frame-work the main target of this work is the reduction and redistribution of compressor accelerations along “privileged” axes to reduce the aforementioned phenomena. Starting from the general treatment of Professor Sōdel, specific studies on reciprocating kinematic balancing, discharge pipe, suspension springs and crankcase dynamics are performed. In particular, a detailed model is developed to calculate kinematic forcing terms applying Newton’s second law on each component of the reciprocating mechanism. In this model, crankcase reaction forces are equal to kit shaking ones, transmitted to the shell thanks to the suspension springs and the discharge pipe. These shaking forces are minimized and redistributed modifying crankshaft mass distribution. Parallelly, numerical investigations on spring and discharge pipe are performed to optimize their transmissibility curves together with studies on crankcase dynamics to optimize its mass distribution. To validate the analytical/numerical models, several vibration and acoustics tests are carried out on variable-speed compressors working both at an un-constrained configuration test and in a load stand at Ashrae standard conditions. In the first case, cylinder head accelerations are detected in terms of both time series signals and averaged data values, while in the last case, vibrations and acoustic emission are measured on the shell surface and particularly near to suction and delivery ducts. Different test ensembles are completed modifying single kit components in the frame of the DOE approach. Experimental results match with theoretical predictions in terms of both vibration reduction and redistribution along reference axes for all the tested displacements, with beneficial effects on compressor acoustics too. Furthermore, the developed software reveals to be a useful research tool for product update, simplification and innovation.