A Study on the Reduction of Torque Variation in Scroll Compressors

This paper introduces a way of reducing the torque variation in scroll compressors. In a scroll compressor where radial compliance device such as the slider bush is used for the flank sealing, the orbiting scroll member is given the freedom of movement in the radial direction. When such an orbiting scroll member orbits around the nonorbiting scroll member whose center is offset from that of the crankshaft, the distance from the crankshaft center to the point of loading is subject to variation. while constant orbiting radius can be maintained. If the variation of this loading distance is made opposite to that of the loading, then the amplitude of the torque variation can be made reduced. Illustrative calculation on a typical scroll compressor has been made to demonstrate this concept of reduc1ion in the torque variation of a scroll compressor. NOMENCLATURE b : oldham ring key height c : distance to orbiting scroll e.g d : torque arm F1.F2,F3,F.: reaction forces at oldham ring Fa, F,9 , Fr9 : gas forces in the axial, tangen1ial, and radial directions Fbr : driving force of crank pin Fe. Fcbr : centrifugal forces of orbiting scroll & slider bush Fst>t,Fsbr : components of drive bearing force in tangential and radial directions fs : radial sealing force h : wrap height I : orbiting scroll hub length 1noc : oldham ring moss 01 : crankshaft center 02 : fiXed scroll center 03 : orbiting scroll and bush center o.. : crank pin center P : point of loading on the slider bush ra : orbiting radius re : offset distance of fixed scroll rp : crank pin eccentricity Rax.Rav : radii of oldham ring in x & y axes rsb : radius of the slider bush Yr : oldham ring displacement in y axis WbJ : distance from crank pin center to sliding surface a 1 : offset angle of fixed scroll r : sliding surface inclination o : orbiting scroll end plate thickness B c : crank angle p : friction coefficient INTRODUCTION One of the sources for the refrigerant compressor vibra1ion is the crankshaft load fluctuation. It has been known that the crankshaft load fluctua1ion of a scroll compressor is far Jess than those of other types of compressors[l]. This dis1inctive characteristic of the scroll compressor results from smooth varia1ion of the gas loading. In scroll compressors, several compression chambers are simultaneously involved in the gas compression process so that the gas compression rate is not so rapid as in other types of compressors. In this study, we present a way of achieving further reduction in the crankshaft torque fluctuation for scroll compressors. For conventional scroll compressors, the fluctuation pattern of the crankshaft torque resembles that of the gas loading. Hence, if the crank arm can be made variable in the opposite sense to the variation of the gas loading, the torque fluctuation could be managed to be reduced. One way of generating variable crank arm is to displace the center of the fixed scroll from the axis of the crankshaft