Patent Publication Number: US-6217302-B1

Title: Floating seal bias for reverse fun protection in scroll compressor

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a scroll compressor having a floating seal which has a protection device which is actuated upon reverse rotation. 
     Scroll compressors are becoming increasingly popular for refrigerant compression applications. In a scroll compressor a first scroll member has a base and a generally spiral wrap extending from the base. 
     A second scroll member also has a base and a generally spiral wrap extending from its base. The wraps of the first and second scroll member interfit to define compression chambers. The second scroll member is caused to orbit relative to the first scroll member, and as the wraps orbit relative to each other, a refrigerant to be compressed is entrapped and moved toward a discharge port. 
     As the refrigerant is compressed, a force is created tending to separate the first and second scroll member. One technique utilized to address this separating force is a back pressure chamber. A back pressure chamber is defined by tapping a compressed fluid to a chamber defined by seals behind one of the first or second scroll members. The fluid in the chamber creates a force in opposition to the separating force. In one known type of scroll compressor, the first scroll member, known as the non-orbiting scroll, is axially moveable relative to the second scroll member. A seal is placed in the base of the non-orbiting scroll and defines the back pressure chamber. This seal also separates an inlet zone from a discharge pressure zone. 
     During normal operation the seal is biased into contact with another component in the scroll compressor. Typically, the seal is biased against a separator plate which defines a discharge pressure chamber above the non-orbiting scroll. The seal is moveable away from the separator plate wall to allow the discharge and suction pressure zones to communicate. 
     Scroll compressors are sometimes prone to operation in a reverse direction. When the scroll compressor is operated in a reverse direction, the refrigerant is drawn through the discharge port, into the compression chambers, and then outwardly through the suction port. Operation in reverse rotation is undesirable, and potentially detrimental to the scroll compressor. 
     In the prior art mentioned above, operation in the reverse rotation will typically draw the seal away from the separator plate wall, allowing the discharge and suction pressure zones to communicate. This is true since the fluid which is tapped to the back pressure chamber will be at a very low pressure during reverse rotation. The seal will thus be drawn away from the plate, allowing communication between the discharge and suction pressure zone. This is somewhat undesirable, as oil is allowed to enter the discharge port from the suction pressure zone. The oil is then pumped through the scrolls and out of the compressor through a suction tube. This can lead to a loss of oil within the scroll compressor. 
     It would be desirable to have a scroll compressor seal which is structured to prevent the communication of the suction and discharge pressure zones during reverse rotation. 
     SUMMARY OF THE INVENTION 
     In the disclosed embodiment of this invention, a seal is mounted in the base of the non-orbiting scroll. The seal is biased into contact with the separator plate to define a back pressure chamber. An intermediate pressure fluid is tapped to the back pressure chamber to create a back pressure force resisting a separating force. During normal operation, the seal is maintained in contact with the separator plate. At this position the seal also separates a discharge pressure zone radially inwardly of the seal from a suction pressure zone, which is radially outward of the seal. 
     Upon reverse rotation, the pressure at the intermediate pressure zone will drop dramatically. This low pressure will draw the seal downwardly away from the separator plate. In the prior art, when this occurred, the discharge pressure zone communicates with the suction pressure zone. Oil in the suction pressure zone enters the discharge pressure zone, and is then pumped out the compressor through a suction tube. As mentioned above, this is undesirable. 
     The present invention addresses this concern by providing a check valve working with the seal. The check valve prevents flow from the back pressure chamber through the seal in a direction towards the separator plate. However, during reverse rotation, the relatively high pressure in the suction zone will pass into the tap, moving through the check valve and into the back pressure chamber. In this way, the relatively high pressure fluid in the suction zone will move into the back pressure chamber, preventing movement of the seal downwardly away from the separator plate. The flow of a large amount of oil from the suction pressure zone into the discharge pressure zone is prevented. In embodiments, the check valve could be in the seal or in the non-orbiting scroll. 
     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 DRAWINGS 
     FIG. 1 shows a scroll compressor incorporating the present invention in a first position. 
     FIG. 2 shows a valve as part of the invention of FIG. 1 in a second position. 
     FIG. 3 is a top view of the inventive seal. 
     FIG. 4 shows an alternative embodiment. 
     FIG. 5 shows another embodiment. 
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
     A scroll compressor  20  illustrated in FIG. 1 incorporates a casing  22  having an internal separator plate  24 . A discharge opening  26  is formed adjacent a central area in the separator plate  24 . A seal  28  seals against plate  24 , and is spring biased at  30  away from the base of a non-orbiting scroll  32 . The non-orbiting scroll is axially moveable, and a intermediate compressed fluid is tapped through tap  34  into a back pressure chamber  35  defined forwardly of seal  28 . A scroll wrap  36  is formed on the non-orbiting scroll  32  and an orbiting scroll  38  includes its own wrap  40  which interfits with the wrap  36 , as known. A central discharge port  42  communicates with a discharge pressure zone  44 . Seal  28  separates discharge pressure zone  44  from a suction pressure zone  46 . 
     A check valve  48  is typically seated against seat  52 , isolating tap  50  extending through the seal  28 . As shown in FIG. 1, during normal operation, the pressure in tap  34  is high and valve  48  is held against valve seat  52 . The spring  30  holds seal  28  against the separator plate  24  in combination with the pressure from tap  34 . The zones  44  and  46  are maintained separate by the seal  28 . 
     As shown in FIG. 2, when reverse rotation occurs, as may occur during shutdown of a scroll compressor, or if the motor is improperly wired, the pressure at the chamber  47  communicating with tap  34  drops dramatically. The low pressure from the compression chamber being communicated through tap  34  to chamber  35 , will draw seal  28  downwardly away from the separator plate  24 . This allows chambers  44  and  46  to communicate, which is described above as somewhat undesirable. 
     However, at the same time, the valve  48  moves away from the valve seat  52 . The relatively high pressure in the zone  46  will move through the tap  50 , and into the chamber  35 . This relatively high pressure fluid will move back downwardly through the tap  34 , but will also maintain the chamber  35  at a relatively high pressure, such that the force of the spring  30  will continue to hold seal  28  against the separator plate  24 . In this way, the seal  28  will not move away from the separator plate to fully communicate chambers  44  and  46  during reverse running conditions. There might be some slight communication, however, in general, the two zones will be maintained separate. The oil will not flow between the chambers as was the case in the prior art. 
     FIG. 3 is a top view of the seal  28  and tap  50 . 
     FIG. 4 shows another embodiment  100 , wherein a seal  130  is positioned above a chamber  135  communicating with the tap  134  to a compression chamber. The embodiment  100  is similar in operation to the earlier embodiment including the use of a spring and a check valve  148  moveable against a stop  152  to isolate a tap  150 . However, the tap  150  in this embodiment extends radially outwardly of the seal, and the seal does have an upper wall  154  in contact with a separator plate  155 . The tap  150  communicates with a suction pressure chamber  156 . The seal also seals between the suction pressure chamber  156  and a discharge pressure chamber  158 . 
     FIG. 5 shows another embodiment  200 , wherein the check valve  248  is associated with a tap  250  in the base of the non-orbiting scroll  252 . This embodiment will control flow of suction pressure fluid into the back pressure chamber  35  similar to the earlier embodiments. For purposes of this application, all three embodiments include check valves which are associated with the back pressure seal to control flow. The first two embodiments have the check valves mounted within the seal, and this third embodiment has its check valve mounted within the non-orbiting scroll. 
     Although a preferred embodiment of this invention has been disclosed, a worker in this 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.