Patent Publication Number: US-6042344-A

Title: Control of scroll compressor at shutdown to prevent unpowered reverse rotation

Description:
BACKGROUND OF THE INVENTION 
     This application relates to a unique method of controlling an unloader valve in a scroll compressor at shutdown to prevent unpowered reverse rotation. 
     Scroll compressors are becoming widely utilized in air conditioning and refrigerant applications. However, there are still design challenges facing scroll compressor designers. One persistent challenge with scroll compressor operation is unpowered reverse rotation at shutdown. 
     As known, scroll compressors consist of two interfitting and generally spiral wraps. The interfitting wraps define compression pressure pockets. One of the wraps usually orbits relative to the other and the size of the compression pockets change to compress an entrapped fluid. The orbiting scroll is driven by an electric motor via a shaft. On shutdown, when the power is turned off, there is no torque applied by the motor and the orbiting scroll can start rotating in reverse, as the high pressure fluid from the discharge line and compressor discharge muffler is expanded back through the compression elements into the compressor suction. After the pressure is equalized, or nearly equalized, the reverse rotation is stopped. Similarly, unpowered reverse rotation can occur if the fluid is expanded from an economizer line into the compressor suction through compression elements. This reverse rotation can create unwanted noise, and further can create other operational problems. 
     Thus, the prior art has attempted to reduce or eliminate the occurrence of unpowered reverse rotation. For the most part, the solutions to the unpowered reverse rotation problem have included the application of additional elements into the scroll compressor. One of the prior solutions was to use an internal compressor check valve which would close when high pressure fluid from the discharge line would rush back into the compressor after shutdown. The check valve blocked the high pressure fluid from entering the wraps and thus minimized the duration, or eliminated, unpowered reverse rotation. However, for compressors with an economizer circuit, the high pressure fluid can enter the compressor upstream of the check valve and still cause reverse rotation. Thus even the inclusion of additional costly internal elements as often used in the past would have not prevented unpowered reverse rotation of a scroll compressor with an economizer circuit. 
     Thus, it would be desirable to find a solution to the problem of unpowered reverse rotation that does not require any additional components to be added into the scroll compressor. 
     SUMMARY OF THE INVENTION 
     In a disclosed embodiment of this invention, a scroll compressor is operated by opening an unloader by-pass valve shortly before, or at, shutdown of the scroll compressor. By opening the unloader by-pass valve, the entrapped fluid at high pressure is short circuited directly to the suction line by-passing the compression elements. Unpowered reverse rotation is thus reduced or eliminated. In one preferred embodiment of this invention, the unloader valve is in communication with an economizer line and a suction inlet line. Economizer circuits are known compressor features wherein a supplemental inlet fluid is injected into the compression chambers at an intermediate compression point. An economizer line directs fluid at a pressure which significantly exceeds the suction pressure into the compression chamber. Thus, due to the significant volume of the economizer line and its associated components, the high pressure vapor from the economizer line expanding through scroll compressor elements can drive the orbiting scroll in reverse on shutdown. 
     By opening an unloader valve between the economizer line and the suction line, on or shortly before shutdown the high pressure fluid is directed into the suction line, thus, bypassing scroll compressor wraps. Thus, any unpowered reverse rotation which would have been caused by high pressure vapor in the economizer line is eliminated. It should be noted that this invention can be utilized on its own, or in addition to other ways of reducing or eliminating unpowered reverse rotation. 
     It should also be noted that the placement of an unloader valve between the economizer line and the suction inlet line is itself inventive as it provides capacity modulation of scroll compressor and the subject of a co-pending patent application entitled &#34;Unloader Valve Between Economizer and Suction Line&#34; which was filed on even date herewith, assigned Ser. No. 09/114,395, and owned by the assignee of this application. Another application of interest is Ser. No. 08/986,447 filed May 12, 1997 and entitled &#34;Pulsed Flow for Capacity Control&#34;. 
     In other features of this invention, the system is provided with a control for both the electric motor for the scroll compressor and the unloader valve. The unloader valve is opened at a time approximately five seconds before shutdown of the motor. In this way, the problem of unpowered reverse rotation is reduced or eliminated. 
     These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The sole FIGURE is a schematic view of a scroll compressor system incorporating the present invention. 
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
     A scroll compressor system 20 is illustrated in FIG. 1 incorporating a pump unit 22, a motor 24 driving an orbiting scroll 26, and a non-orbiting scroll 28. As known, the two scroll members include wraps which interfit to define compression pockets. The compression pockets trap and compress a refrigerant. At shutdown, the high pressure refrigerant in the economizer or discharge line can drive the orbiting scroll in a reverse direction from the direction through which it is typically driven. This reverse rotation can be noisy and undesirable. 
     The scroll compressor 20 includes a suction line 30 for supplying refrigerant to pump unit 22 for compression, and a discharge line 32 directing refrigerant to downstream elements in a refrigerant system. An economizer line 34 supplies an economizer fluid to the scroll compressor. As known, an economizer line directs fluid to an intermediate point in the compression cycle. An economizer portion of heat exchanger 36 is shown schematically. An economizer circuit is utilized to increase the overall efficiency and capacity of the refrigerant system. 
     However, at shutdown, the presence of the economizer inlet line 34 can create further problems with regard to unpowered reverse rotation. The pressure in the economizer line 34 significantly exceeds the pressure in the suction line 30, and thus reverse rotation may occur as vapor at high pressure at the economizer line 34 expands through the compression elements, if unloader valve 40 is closed. 
     Thus, according to this invention, an unloader valve 40 and associated communication passage 38, which directly communicates the economizer line 34 to the suction inlet line 30 can be opened at, or shortly before, shutdown. Unloader valves for capacity modulation are known in scroll compressor application. As known, an unloader valve typically communicates a compressed fluid back to suction when capacity modulation is desired. The unloader valve is selectively open to achieve capacity modulation when the motor is operating normally. The present invention uses this unloader valve to also address reverse rotation. However, the positioning of an unloader valve to communicate the economizer line to the suction line is novel. This novel placement of an unloader valve is detailed in a co-pending patent application Ser. No. 09/114,395, filed on even date herewith, and entitled &#34;Unloader Valve Between Economizer and Suction Line.&#34; 
     As to this application, it is the unique method of operating an unloader valve shortly after, at, or just before shutdown to prevent unpowered reverse rotation which is inventive. 
     Control 42 for the unloader valve 40 communicates with a control 44 for the overall system. Control 44 communicates with motor 24. In a preferred embodiment, the control 44 opens unloader valve 40 to communicate the economizer line 34 to suction line 30 just before shutdown of the motor 24. Preferably, the unloader valve is opened less than five seconds before shutdown of the scroll compressor. Most preferably, the time period may be one or two seconds. Also, the opening can occur within a few seconds after shutdown. As an example, less than one second after shutdown. 
     It is also possible to open the unloader valve at the same time the motor is shut down. It is also possible to have a built-in delay in the motor shutdown. In these cases the use of controllers 42 and/or 44 can be eliminated. 
     When the control 44 determines that the motor 24 will be shut down, it opens the unloader valve 40, and then shuts down the motor 24. By opening the unloader valve 40, the pressure in the economizer line 34 and the suction line 30 will be equalized. Thus, vapor from the economizer line will not expand into the scroll compressor wraps and unpowered reverse rotation will be eliminated. 
     In addition, any high pressure vapor from the discharge line and high pressure vapor trapped in the scroll compressor wraps, and between the scroll compressor wraps and the discharge line will also be by-passed into the economizer line and then directly into suction line. This further minimizes the possibility of unpowered reverse rotation. 
     It should be noted that the method of this invention will be utilized even when the economizer system 36 is not functioning or not present at all and only bypass operation is desired. The economizer cycle is typically utilized only when high capacity operation is desired. Even so, it is preferred that the unloader valve 40 be opened whether the economizer cycle is operating or not, as the pressure in line 34 exceeds the pressure in the suction line 30 even when the economizer circuit 36 is not operating. 
     It is also preferred that the unloader value 40 is open even if no economizer circuit is present at all. In this case high pressure fluid inside the scroll compression element and line 34 is directed into compressor suction, by-passing a portion of the scroll compression elements. Thus, also minimizing possibility of unpowered reverse rotation. 
     Preferred embodiments of this invention have been disclosed; however, a worker of ordinary skill in the art would recognize that certain modifications come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.