Refrigeration system's having scroll compressor's should be designed to deal with overheating of discharge gas, backflow during shutdown, and reverse rotation due to improperly connecting the motor's electrical leads.
Current systems protect against overheating by employing a temperature sensor attached to a discharge line leading from the compressor's hermetic shell. The compressor motor is de-energized in response to sensing a predetermined temperature limit. This method of protection, however, is inadequate in refrigeration systems which often experience high temperatures during low flow rate conditions. The flow rate can become so low in scroll compressors that the refrigerant at the discharge opening of the stationary scroll plate can exceed the safe operating temperature well before an externally mounted sensor can detect the problem. Nevertheless, such methods of protection are still being used.
Protection against backflow during shutdown is currently accomplished by simply installing a check valve directly over the stationary scroll plate's discharge opening. At shutdown, the check valve prevents high pressure discharge gas from re-entering the scroll plates, which could otherwise rapidly reverse the compressor's direction of rotation and drive the orbiting scroll plate in reverse at extremely high speeds. The rapid reversal jars a scroll compressor's swinglink (drive coupling between the motor and the orbiting scroll plate) and exerts a severe bending moment on the compressor's "Oldham" coupling (anti-rotation coupling). A swing link (Item 13, FIG. 1) and an Oldham coupling (Item 15, FIG. 1), as well as other details of a scroll compressor, are disclosed in U.S. Pat. Nos. 4,655,696 and 4,666,381 which are specifically incorporated by reference herein.
To be effective, the check valve must be positioned inside the compressor's shell, directly over the scroll plate's discharge opening to minimize the volume between the valve and the opening. However, the pressure of the small volume at the discharge opening fluctuates due to the normal operating characteristics of a scroll compressor. This causes the check valve to flutter, resulting in unnecessary noise and valve wear. Attempts have been made to locate the valve on a discharge line outside the shell. Such a location, however, leaves enough pressurized refrigerant between the valve and the discharge opening to briefly drive the compressor in reverse at thousands of RPM upon de-energizing the compressor motor.
The same check valve, used for protection against backflow, presents another problem should the compressor motor ever be improperly wired to rotate in reverse. This is a common problem with 3-phase motors whose rotational direction is simply reversed by switching two of its three motor leads. In reverse rotation, the check valve prevents gas from passing through the compressor which causes an extremely low pressure to develop between the scroll plates. The low pressure forces the scroll plates together with damages the tips of their scroll wraps.
Although it may be possible to address each of the above problems individually, it is an object of the invention to solve all of the above problems by employing a single solenoid valve mounted inside a hermetic shell of a scroll compressor.
Another object of the invention is to provide a method of sensing the temperature of the refrigerant just as its leaving a discharge opening through a stationary scroll plate.
Another object of the invention is to use the coil of a solenoid valve to sense the temperature of discharge refrigerant inside the hermetic shell of a scroll compressor.
Yet another object is to avoid the higher flow resistance associated with many conventional solenoid valves by using the back side of a stationary scroll plate as a valve seat.
A further object is to penetrate a scroll compressor's hermetic shell with only two electrically feedthroughes that are connected to actuate a solenoid valve disposed inside the shell and connected to a means for sensing the temperature of the refrigerant inside the shell.
A still further object is to avoid valve flutter by providing a scroll compressor with a solenoid valve disposed inside the compressor's hermetic shell, and magnetically holding the valve fully open whenever the compressor's motor is energized.
Another object of the invention is to allow refrigerant, whenever the compressor motor is energized, to flow in either direction through a discharge opening in the compressor's stationary scroll plate, regardless of the compressor's rotational direction, and when the compressor motor is de-energized, allow refrigerant to flow in only one direction.
These and other objects of the invention will be apparent from the attached drawings and the description of the preferred embodiment which follows hereinbelow.