Motion of Rolling Piston in Rotary Compressor

This paper describes the behavior of a rolling piston in a rolling piston type rotary compressor under various operating conditions. Kinematic behavior of the rolling piston is discussed with attention to the friction forces acting on the rolling piston and the vane. Emphasis is on the following simulation approach. (1) The equation of motion of the rolling piston is solved in conjunction with the equilibrium equations of forces acting on the vane. (2) The following three cases of contact between the vane tip and the rolling piston are examined by comparing the ratio of the tractive force to the contacting force with the coefficient of friction. A. Sliding Contact~ the rolling pistou rubs the vane tip in the same direction as the eccentric shaft rotates. B. Rolling Contact: no sliding between the vane tip and the rolling piston. C. Sliding Contact: the direction of sliding is opposite to that in the state A. The analysis for a typical refrigerating compressor leads the following results. ~1) The trajectory of a point on the side surface of the rolling piston looks like a trochoid. It suggests that the rolling piston rotates slowly in the same direction as the eccentric shaft rotates and that the revolution rate of the rolling piston is not constant but varies periodically. (2) The friction force at the tip of the vane fluctuates continuously or sometimes its direction abruptly changes. This affects the angular velocity of the rolling piston. Using this analysis, the kinematic behavior of the rolling piston can be easily predicted under various kinds of dimeusions and operating conditious. 17& and Kimio KUYAMA, Manager Shizuoka Works Mitsubishi Electric Corp. Shizuoka, Shizuoka, Japan INTRODUCTION The rolling piston in a rolling piston type compressor plays a part of partition between the vane and the rotor. In the design of actual compressor, there is requirement that the wear of the vane tip should be decreased to the minimum. The wear of the vane tip should be affected by the behavior of the rolling piston. ·However, the behavior of the rolling piston may be very complicated because it is not decided geometrically but ruled by the fluctuating frictional forces acting on the rolling piston. The behavior of the rolling piston has been interested in by many investigators [l-4]. The authors attempted to analyse the behavior of the rolling piston [1]. The two frictional forces were considered to rule the behavior of the rolling piston. One of them is the Coulomb's frictional force acting on the contacting point between the vane tip and the rolling piston. Another frictional force is the fluid film friction generated within the thin oil film between the rolling piston and the eccentric. The angular velocity of the rolling piston was calculated by solving the equation of motion in conjunction with the two frictional forces. T. Shimizu also analyzed the behavior of a rolling piston with attention to another frictional force; the viscouse dragging force between the rolling piston and the cylinder head [2]. These studies were both made with computer aided analyses because of those complexities. P. Pandeya and W. Soedel analyzed kinematics of a rolling piston type rotary compressor with more simple and practical formulae [3]. All the three analys~s above mentioned were not confirmed by any experiments. J. Tanizaki, T. Shimizu and T. Shiga performed an experiment to confirm the behavior of the rolling piston [4]. Referring to this experimental results, it is noticed that the rolling piston rotates slowly to the same direction as the eccentric rotate·s and the angular velocity of the rolling piston is not comstant but varies periodically. The similar behavior was already predicted in the reference [1]. It is now considered that the analytical way of study such as th~ reference [1] may be available to predict the behavior of the rolling piston. This pap-er describes the b~havior of rolling piston under various operating conditions and different dimensions.