Orbiting fluid displacement apparatus with counterweight attachment

A scroll type fluid displacement apparatus, in particular, a compressor of an orbiting piston type is disclosed. The compressor includes a housing with a fluid inlet port and a fluid outlet port. A fixed scroll member with first end plate and first spiral element is fixed relative to the housing. An orbiting scroll member with second end plate and second spiral element is disposed for orbiting motion in the housing. The first and second spiral elements interfit with one another at an angular and radial offset to make a plurality of line contacts to define at least one pair of sealed off fluid pockets. A drive pin is eccentrically disposed at an inner end of the drive shaft. The orbiting scroll member has a boss which rotatably supports a bushing. An eccentric hole is formed in the bushing and the drive pin is received within this hole. The center of drive pin is located on an opposite side to the center of the drive shaft with regard to a straight line, which passes through the center of the bushing and is perpendicular to a connecting line passing through the center of the drive shaft and the center of the bushing. The center of the drive pin is also beyond the connecting line in the direction of rotation of the drive shaft. A separate balance weight is attached to the bushing at its end surface by a fastener which can limit the amount of swing angle of bushing. The balance weight cancels a centrifugal force which arises because of the orbital motion of the scroll and the bushing.