Selection of Friction Materials Used in Compact, High Performance Inverter Controlled Rotary Compressors

T. IIZUKA and K. IKEDA Tochigi Works Hitachi, Ltd. Shimotsuga-gun, Tochigi-ken, Japan, 329-44 Since applications of rotary compressors driven by inverter motors have become more widespread, l~bricating problems with the sliding parts have been appearing. The sliding parts require sufficient antiseizure and wear-resistant properties under the boundary lubricating conditions. The authors have developed a new oxynitriding plus steam-treatment process. The surface of the material formed by the new process has an uppermost porous layer, which has a superior oil retaining property. Consequently, lubricating oil which penetrates and is held in the porous layer by capillary action, improves the lubricating ability in case of oil film breakdown. Wear tests were made using a Suzuki-type abrasion testing machine with chloro fluoro carbon (CFC)-diluted refrigerating oil. Combinations of the new· surface treated sliding members provided high reliability along with high antiseizure, and wear-resistant properties. INTRODUCTION Among the compressors that are used for air-conditioners, refrigerators and the like, there are several types including rotary, reciprocating, scroll, and screwtypes. The number of rotary compressors being used in air-conditioners and refrigerators has been rapidly increasing due to their higher efficiency, compacter size and lighter weight (Ref. 1). Compactness and high-output compressors of the variable speed control type are able to satisfy present trends for these appliances to have sophisticated functions. Since applications of rolling-piston-type rotary compressors driven by inverter motors have become more widespread (Ref. 2), lubricating problems with their sliding parts have arisen. The rotation rates of inverter motors are quickly changed between 700-10,000 rpm, so their rotation modes are quite different from those of conventional rotary compressors. When the rotation rate is low and the pressure between the slides of the compressors is high, adhesive wear of the sliding members tends to occur because of breakdown of the oil film between the metal/metal bo~daries. These are known as the bo~ndary lubricating conditions. Fig. 1 shows a sectional view of a typical rotary compressor. A rotary compressor is comprised of a rotatable crankshaft supported by an upper bearing and a lower bearing, a rotatable roller mounted on a crank pin of the crankshaft, a cylinder to accommodate the roller, and a slidable vane located within the vane slot formed in the cylinder. The distal end portion of the vane has a slide on the outer peripheral surface of the roller. In partic~lar, consideration must be given to the distal end portion of the vane and the outer peripheral s~rface of the roller, the vane sides and the vane slot formed in the cylinder, and the shaft and bearings all of which receive the severest wear conditions. In general, making the sliding members, e.g. crankshafts and vanes, of softnitrided or manganese-iron phosphated iron-based materials, is impractical at high speeds, because these materials lack sufficient antiseizure and wear-resistant properties. Therefore, in order to improve those characteristics under the boundary l~bricating conditions, new combinations of materials are required. In this paper, suitable combinations of materials to prevent abrasion through metal contact under the conditions with chloro fluoro carbon (CFC) dissolved in the lubricant oil are described.