Estimation, of the Starting Torque, of Refrigerant Rotary Compressors

Estimation of starting torque is very important for motor design and for improvement in compressor efficiency. Especially, when compressors are restarted after a period of inoperation, motors sometimes meet large starting torque. The assumed reasons are as follow . The compressors temperature is sometimes lower than any other parts of the refrigerant cycle. In this case, the refrigerant tends to collect in the compressor and is condensed there(l). So, the oil between the lubricated surface is dissolved in the refrigerant and removed by this refrigerant liquid. Furthermore, the unbalanced magneti8 pull force in induction motors make the starting torque larger. An experimental model has been developed for measuring torque. Using this apparatus, torque was measured at various pull forces, various oil conditions, and with variously treated shafts. A mathematical model was made for analyzing the starting torque. Based on this analysis, it is possible to predict individual torques under various conditions, using the value of friction coefficients obtained from experimental data, and the value of pull force. The theoretical analysis, based on the mathematical model for starting torque, agrees fairly well with experimental data obtained from using actual compressors. The influences of compressor dimension, shaft surface treatment, mechanical air gap in the motor, compressors blade spring on starting torque are found qualitatively and quantitatively by this study.