Design of Phase-Angled Balance Weights for an Inverter Driven Scroll Compressor

This paper presents a new design method of balance weights with phase angles for scroll compressors. Based on force and moment balances on crankshaft and compressor frame, mathematical formulation of shaft bearing loads, unbalanced force and moment acting on the frame has been made in terms of balance weight design parameters such as masses and phase angles of the upper and lower balance weights. Any two of crankshaft main bearing load, sub bearing load, unbalanced body force, and overturning moment can be controlled by the balance weight design parameters. NOMENCLATURE F 3, F 4 Reactions between oldham ring keys and frame Fa, Frg, Ftg Gas forces in axial, radial, and tangential directions, respectively. Fsody Unbalanced body force or resultant force acting on the frame Fcp Total resultant force acting on crank pin F cpc, F esc, Fore, F osc, F sbc Centrifugal forces of crank pin, crankshaft, oldham ring, orbiting scroll, and slider bush, respectively Fdw, Fuw Centrifugal forces of lower and upper balance weight, respectively. Fmi, Fsi Main and sub bearing loads at crankshaft, respectively. Frs Radial sealing force between wraps of fixed and orbiting scroll members lcp, lcs, ldw, lh, lsi. luw Lengths defined in Fig. 2 and Fig. 3 Msody Overturning moment or resultant moment acting on the frame mdw, muw Masses of lower and upper balance weights, respectively rd, ru Radii of mass center of lower and upper balance weights, respectively rep, rs Eccentricity of crank pin, and orbiting radius, respectively rx, ry Radial and tangential reaction positions at thrust surface 131, 13 2 Phase angles of upper and lower balance weights m , B Angula velocity of crankshaft and crank angle, respectively Subscripts c, n r, t Conventional and new, respectively Radial and tangential components, respectively. INTRODUCTION Conventional balance weight design for scroll compressors typically employs two balance weights: upper one is circumferentially positioned 180 deg. from the crank pin and lower one on