Patent Publication Number: US-6341945-B1

Title: Scroll compressor with reduced capacity at high operating temperatures

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a scroll compressor in which the capacity of the compressor is reduced when the temperature of the refrigerant becomes high. High temperature is indicative of a low charge, loss of charge or reverse rotation, and the reduction of the capacity provides a protective function. 
     Scroll compressors are becoming widely utilized in refrigerant compression applications. In a scroll compressor, a pair of scroll members each having a base and a spiral wrap extending from the base are placed facing each other. The spiral wraps of the two scroll members interfit to define compression chambers. One of the two scroll members is caused to orbit relative to the other, and the spiral wraps define decreasing volume compression chambers as the one scroll member orbits relative to the other. 
     Scroll compressors raise many design challenges. One challenge relates to operation of the scroll compressor when the charge of refrigerant becomes low. In such so-called “loss of charge” operation, the temperature of the refrigerant becomes undesirably high. The temperature also can be high during reverse rotation, low suction pressure operation or other abnormal conditions. Damage can result to the components of the scroll compressor from the high temperatures. 
     Thus, it would be desirable to have a mechanism for protecting the scroll compressor in a loss of charge situation. 
     Reduced capacity systems are known for scroll compressors. However, the reduced capacity systems have generally been used to achieve a reduced capacity when a variable outside of the compressor indicates a need for a reduced charge. Thus, if a control decides that the cooling capacity, as an example, is low, then the capacity of the compressor may be reduced. 
     Similar problems are encountered during low suction pressure operation, reverse running operation, or other conditions which could result in an elevated temperature. 
     SUMMARY OF THE INVENTION 
     In a disclosed embodiment of this invention, an internal condition in the scroll compressor is sensed, and the capacity of the compressor is reduced in response to that sensed condition. Preferably the orbit radius of the orbiting scroll is reduced upon the condition being sensed. 
     In several embodiments, a bi-metal or shape memory alloy metal component does not actuate the orbit reduction until a predetermined temperature is reached. If the predetermined temperature is reached, then a component is actuated which reduces the orbit radius. As one example, a pin is fixed in the orbiting scroll, and extends upwardly into a chamber in the non-orbiting scroll. A cap which has a ramped inner surface is biased away from the pin, and received in the chamber. Discharge pressure refrigerant is selectively tapped to the reverse side of the cap. A bi-metal valve prevents flow of the discharge pressure to the chamber under normal operating conditions. However, if the temperature becomes high, then the bi-metal valve allows flow of discharge pressure to the chamber, and the cap is biased downwardly such that it prevents the full orbiting movement of the pin. When the pin&#39;s orbiting movement is restricted, the orbit movement of the orbiting scroll is also restricted. 
     In a second embodiment, the pin is offset relative to the axis of the chamber. The cap includes an eccentric passage which selectively receives the pin. Normally, the cap is biased away from the pin. However, when the discharge pressure is directed into the chamber, the cap is biased downwardly to contact the pin. At this time, the orbiting radius of the orbiting scroll is reduced. 
     In another embodiment, a suction pressure is tapped to one side of a pin-piston. A spring also biases the pin-piston upwardly into a groove in the rear face of the orbiting scroll. The pin-piston is movable within the back pressure chamber of the scroll. The back pressure chamber is typically at an intermediate compressed pressure. Thus, the intermediate pressure is normally sufficiently high such that the pin-piston is biased downwardly and is not moved into the groove. 
     In a low charge, low suction pressure, and reverse running situations, the suction pressure approaches the intermediate compressed pressure. In these conditions, the spring will bias the pin-piston upwardly into the groove. Thus, the orbiting radius of the orbiting scroll is reduced. 
     A similar embodiment, rather than utilizing suction pressure versus intermediate pressure, a bi-metal element is utilized which selectively biases the pin upwardly when the refrigerant reaches an elevated temperature. 
     In another embodiment of this invention, a pin-piston is received in a groove in a base of the orbiting scroll. A first torsion spring twists the pin in a first direction. A second shape memory alloy tends to bias the pin in a second direction. Under normal “relaxed” conditions, the torsion spring overcomes the force from the shape memory alloy, and the pin is biased to a position at which it does not affect the orbit of the orbiting scroll. However, upon an elevated temperature being encountered in the refrigerant, the shape memory alloy increases its force on the pin, and the pin is moved to a position at which it reduces the orbiting radius of the orbiting scroll. 
     In another embodiment, a fluid-filled bellows forces a shim outwardly against a pin received in the orbiting scroll. The fluid filled bellows is normally retracted under normal operating temperatures. However, upon the occurrence of an elevated temperature, the bellows expands forcing the shim against the orbiting pin. This would then reduce the orbiting radius of the orbiting scroll. 
     In yet another embodiment, a shape memory alloy actuator selectively forces a pin radially outwardly to contact the Oldham coupling. Thus, upon the occurrence of an elevated temperature, the pin is forced outwardly to contact the Oldham coupling. This limits the reciprocating movement of the Oldham coupling, and consequently limits the orbit radius of the orbiting scroll. 
     In general, the present invention discloses a number of embodiments wherein the orbit radius of the orbiting scroll is limited by elements which are actuated upon a sensed condition within the 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. 1A is a cross-sectional view of a first embodiment scroll compressor. 
     FIG. 1B is an enlarged view of the first embodiment. 
     FIG. 2A shows a second embodiment. 
     FIG. 2B is a top view of the second embodiment. 
     FIG. 3 shows a third embodiment. 
     FIG. 4 shows a fourth embodiment. 
     FIG. 5A shows a fifth embodiment. 
     FIG. 5B is a top view of the fifth embodiment. 
     FIG. 6A shows a sixth embodiment. 
     FIG. 6B is a top view of the sixth embodiment. 
     FIG. 7 shows a seventh embodiment. 
     FIG. 8A shows one detail of the seventh embodiment. 
     FIG. 8B shows a seventh embodiment in an actuated position. 
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
     FIG. 1A shows a scroll compressor  20  incorporating a non-orbiting scroll  22  and an orbiting scroll  24 . A shaft  25  drives the orbiting scroll  24  to orbit relative to the non-orbiting scroll  22 . Interfitting wraps  26  and  28  define compression chambers which decrease in volume as the orbiting scroll  24  orbits. An Oldhain coupling  30 , shown schematically, causes the orbiting scroll to orbit when it is driven by the rotating shaft  25 . 
     A discharge pressure port  31  extends through the base of the non-orbiting scroll  22  and communicates to a tap  32 . Tap  32  extends through a pipe  34 . An intermediate valve chamber  36  receives a bi-metal or shape memory valve  38 . Under normal operating conditions of the scroll compressor, the valve  38  closes communication between tap  32  and pipe  34 . 
     A chamber  40  communicates with the pipe  34 . A cap  42  has an inner ramp surface  44 . An end shoulder  45  provides a bias surface for a spring  48 , tending to bias the cap  42  upwardly towards the top of the chamber  40 . A pin  46  is received in the orbiting scroll  24 . 
     As can be appreciated from FIG. 1B, the ramp surface  44  can cam off of the ramped top of the pin  46 . This will limit the orbiting movement of the pin  46 , and thus the orbiting movement of the orbiting scroll  24 . 
     Under periods of normal operation, the valve  38  is closed and discharge pressure cannot communicate to the chamber  40 . Spring  48  biases cap  42  upwardly, and the cap  42  does not restrict orbiting movement of pin  46 . Orbiting scroll  24  can thus orbit through its entire normal orbit radius. 
     However, if an elevated temperature is seen in the scroll compressor chamber, the valve  38  moves to its actuated position. Valves formed of a bi-temperature metal, or a shape memory alloy having the ability to move to an actuated position once a predetermined elevated temperature is reached are known. The valve structure itself forms no portion of this invention. When the valve moves to the actuated position, discharge pressure communicates to the chamber  40 , and the cap  42  is driven downwardly. In this position, such as shown in FIG. 1B, the orbiting radius of the pin  46 , and thus the orbiting scroll  24  is limited. In this way, the capacity of the compressor is limited. Since the elevated temperature is indicative of some problem in the overall operation of the scroll compressor, limiting the capacity serves to protect the scroll compressor. 
     FIG. 2A shows another embodiment  50 . In embodiment  50 , the cap  52  has a bore  54  which is eccentric relative to the center of the chamber  55 . The pin  56  is received off-center within the bore  54 . As shown in phantum normally, the bore  54  does not contact or restrict movement of the pin  56 . 
     However, as can be appreciated from FIG. 2B, when the pin  56  moves through its normal orbiting path, it moves beyond the inner periphery of the bore  54 . This is allowed under normal operating circumstances since the cap  54  will be biased upwardly towards the top of chamber  55 , and the bore  54  would not restrict orbiting movement of the pin  56 . 
     However, when the valve  38  is actuated and discharge pressure reaches the chamber  55 , the cap  52  is forced downwardly. In this position, the orbiting movement of the pin  56  is limited. This is shown in dotted line in FIG.  2 B. 
     FIG. 3 shows another embodiment  60 . In embodiment  60  the crankcase  63  has a tap  64  tapping suction pressure through the crankcase  63 . A pin-piston  66  has an upper pin finger  70  selectively moved into a channel  68  in the rear of the base of the orbiting scroll  62 . A spring  72  biases the pin-piston  66  upwardly towards the channel  68 . When the pin finger  70  is received in channel  68 , it restricts the free orbiting movement of the orbiting scroll  62 , as with the above embodiments. A seal  74  is shown on the outer periphery of the pin-piston  66 . As can be appreciated, the pin-piston  66  is received within the back pressure chamber  76  of the scroll  60 . 
     During normal operating conditions, the pressure in the chamber  76  greatly exceeds the suction pressure at tap  64 . Thus, the pin-piston  66  is biased downwardly, and the pin finger  70  is removed from the groove  68 . However, during low charge, reverse operation, or low suction pressure operation, the pressure in the chamber  76  will begin to approach the pressure at tap  64 . The spring  72  now becomes the greatest factor in controlling movement of the pin-piston  66 . The pin-piston  66  is then forced upwardly towards the groove  68 , and finger  70  restricts orbiting movement of the orbiting scroll  62 . 
     FIG. 4 shows a similar embodiment  80  wherein the orbiting scroll  82  is positioned adjacent the crankcase  84 . The groove  86  selectively receives the pin-piston  88 . The back pressure chamber  90  communicates to contact a bi-metal element  96 , such that when the gas in the chamber  90  reaches an elevated temperature, it will actuate the bi-element  96 . In the actuated position, the pin-piston  88  is forced upwardly against the force of spring  92  and into the groove  86 . Once in the groove  86 , the pin-piston  94  limits the orbiting movement of the orbiting scroll  82 . 
     FIG. 5A shows yet another embodiment  100  wherein the orbiting scroll  102  has a groove  104 . A chamber  106  is formed in the crankcase. A piston finger  108  is formed on a piston  109 . A holder  110  receives a torsion spring  112  and a shape memory alloy spring  114 . 
     As can be appreciated from FIG. 5B, the torsion spring twists the pin finger  108  to a position where it does not contact the groove  104  during the full orbiting movement of the orbiting scroll  102 . However, if an elevated temperature is reached, the shape memory alloy spring  104  increases its torque and twists the pin  108  to a position at which it does contact the inner surface of the groove  104 . Thus, the full orbiting movement of the orbiting scroll  102  is restricted. 
     FIG. 6A shows another embodiment  120  wherein the orbiting scroll  122  has a pin extending into crankcase  124 . Pin  126  extends downwardly from the base of the orbiting scroll  122  into groove  128  formed in the crankcase  124 . A shim  130  is positioned outwardly of a fluid-filled bellows  132  received in a bore  134 . The fluid filled bellows  132  is normally retracted at normal operating temperatures. Thus, the shim  130  is not biased against the pin  126 , and the orbiting scroll  122  is allowed to move through its full orbiting radius. 
     However, if the temperature in the compressor increases, the fluid-filled bellows  132  will expand as shown in FIG.  6 B. The shim  134  is forced outwardly, and does contact the orbiting pin  126 , reducing the orbiting radius of the orbiting scroll  122 . 
     FIG. 7 shows yet another embodiment  139 . In embodiment  139 , the Oldham coupling key  140  is positioned just outwardly of an outer seal groove  142 , which defines the back pressure chamber  141  with a second inner seal  144 . An opening  146  communicates gas from the back pressure chamber  141  into a chamber receiving a shaped memory alloy spring  148 . Shape memory alloy spring  148  selectively biases the pin  152  radially outwardly through a bore  150 . 
     As shown in FIG. 8A, in a non-actuated position the pin  152  does not contact the key  140 . In this position, the Oldham coupling key, and hence the orbiting scroll, are both allowed to move through a full orbiting radius. 
     However, as shown in FIG. 8B, the pin  152  has been forced outwardly by actuation of the shape memory alloy spring  148 . In this position, the Oldham coupling key  140  is restricted in its movement, and thus the radius of the orbiting scroll will be reduced. 
     In general, the present invention discloses a number of scroll compressor embodiments wherein the orbit radius of the orbiting scroll is reduced in response to an internal condition. This will prevent damage to the scroll compressor, and thus better protect the scroll compressor. 
     Although preferred embodiments have been disclosed, a worker in this art would recognize that certain modifications would 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.