This invention relates to a compressor, and more particularly, to a scroll type compressor for an automobile air conditioning system which includes a mechanism for adjusting the displacement of the compressor.
Scroll type fluid displacement devices are well known in the prior art. For example, U.S. Pat. No. 801,182 issued to Creux discloses such a device which includes two scrolls, each having a circular end plate and a spiroidal or involute spiral element. The scrolls are maintained angularly and radially offset so that both spiral elements interfit to form a plurality of line contacts between their spiral curved surfaces to thereby seal off and define at least one pair of fluid pockets. The relative orbital motion of the two scrolls shifts the line contacts along the spiral curved surfaces and, as a result, the volume of the fluid pockets increases or decreases, dependent on the direction of the orbital motion. Thus, a scroll type fluid displacement device may be used to compress, expand or pump fluids.
Scroll type fluid displacement devices are suitable for use as refrigerant compressors in air conditioners. In such air conditioners, thermal control in the room or control of the air conditioner is generally accomplished by intermittent operation of the compressor. Once the temperature in the room has been cooled to a desired level, the refrigerant capacity of the air conditioner required for maintaining the room at the desired temperature is usually not very large. Because air conditioners known in the prior art do not have a capacity control mechanism, the room is maintained at the desired temperature by intermittent operation of the compressor. Thus, the relatively large load which is required to drive the compressor is intermittently applied by the driving source. Operation of the compressor in this manner wastefully consumes large amounts of energy.
When prior art scroll type compressors are used in automobile air conditioners, they are usually driven by the automobile engine through an electromagnetic clutch. Once the passenger compartment is cooled to the desired temperature, control of the output of the compressor is accomplished by intermittent operation of the compressor through the electromagnetic clutch. Thus, the relatively large load which is required to drive the compressor is intermittently applied by the automobile engine. Accordingly, scroll type compressors known in the prior art which are used in automobile air conditioners also wastefully consume large amounts of energy in maintaining the desired temperature in the passenger compartment.
It is desirable to provide a scroll type compressor which includes a displacement or volume adjusting mechanism which controls the compression ratio as occasion demands. In a scroll type compressor, control of the compression ratio can be easily accomplished by controlling the volume of the sealed off fluid pockets. A displacement adjusting mechanism is disclosed in copending application Ser. No. 356,648 filed on Mar. 9, 1982. This application discloses a mechanism which includes a pair of holes formed through one of the end plates of the scrolls. The pair of holes directly connect the intermediate fluid pockets to the suction chamber. The opening and closing of the holes is usually controlled by an electrically operated valve plate which is displaced in the suction chamber.
While the displacement adjusting mechanism disclosed in application Ser. No. 356,648 significantly improves the operation of scroll type compressors known in the prior art, the mechanism is deficient in several areas. For example, in scroll type compressors, the pressure in the suction chamber is usually lower than the pressure in the sealed off fluid pockets. Thus, when the valve plates are operated to open the holes in the scroll end plate, fluid from the fluid pockets may be inadvertently drawn into the suction chamber. Furthermore, the valve plates must be operated by one or more magnetic coils which adds additional complexity to the system.