Abstract:
A self-modulating scroll compressor includes a pair of valves. A first valve moves to a low capacity position when the pressure differential is below a predetermined amount. A second valve moves to a low capacity position when the suction pressure is above a predetermined amount. Low capacity operation will only occur when both valves are open. The present invention thus provides a scroll compressor design with the ability to self-modulate and control the conditions under which low capacity operation occurs based upon two criteria.

Description:
This is a continuation of application Ser. No. 10/607,282, file Jun. 26, 2003. 

   BACKGROUND OF THE INVENTION 
   This invention relates to a scroll compressor which self-modulates between high and low capacity based upon two distinct criteria. 
   Scroll compressors are becoming widely utilized in 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 is held in a non-orbiting fashion relative to the first scroll member and has a wrap that interfits with a wrap from the first scroll member. The first scroll member is driven to orbit relative to the second, and the interfitting wraps define compression chambers for compressing an entrapped refrigerant. 
   It is a goal in modern compressor design to be able to provide at least two capacity levels. In some instances, such as when the cooling load on a refrigerant cycle is not particularly high, a lower capacity may be desirable. Less energy is used to compress a lesser amount of refrigerant in low capacity operations. Thus, various modulation schemes have been developed in the prior art. 
   In one modulation scheme, the compressor moves to low capacity operation when the pressure differential is low. The pressure differential is the delta (difference) of the discharge pressure to the suction pressure. When this quantity is low, there is some indication that lower capacity operation may be in order. 
   This prior art compressor performs adequately to provide low capacity operation when the compressor is utilized in an air conditioning cycle. However, it is also desirable to use such compressors as part of a heat pump system. In a compressor that is utilized for both air conditioning and heat pump operation, there are times when a relatively low pressure differential is not indicative of a need for low capacity. In particular, if the suction pressure is also low, the compressor may be operating in heat pump mode, and high capacity operation would still be desirable. The prior art will still provide low capacity operation under those circumstances. 
   SUMMARY OF THE INVENTION 
   In a disclosed embodiment of this invention, two distinct criteria are considered by the self-modulating capacity control. A first valve is operative to move between an open and closed position based upon the suction pressure. If the suction pressure is low, then the valve is maintained in the closed position, and high capacity operation occurs. A second valve is maintained in a closed position when the pressure differential is high. As long as either of these two conditions (low suction pressure or high pressure differential) are maintained, then high capacity operation occurs. However, if neither condition occurs, then both valves move to the open position and the compressor self-modulates to low capacity operation. 
   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 capacity envelope. 
       FIG. 2  is a cross-sectional view through a scroll compressor embodying the present invention. 
       FIG. 3A  shows a compressor control under conditions resulting in low capacity. 
       FIG. 3B  shows one condition wherein high capacity would still be maintained. 
       FIG. 3C  shows another high capacity condition. 
       FIG. 3D  shows yet another high capacity condition. 
       FIG. 4  is a graph showing the conditions that will result in the four valve positions of  FIGS. 3A–3D . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  shows a desired capacity envelope for a scroll compressor which could be utilized in both heat pump and air conditioning applications. As mentioned previously, the prior art does not have the low capacity condition confined only to the right side of the overall envelope. Instead, the top line t of the low capacity envelope, extended to the left as shown in dotted line with the prior art compressor. As mentioned above, the area to the left of the low capacity envelope shown in  FIG. 1  would desirably be maintained at high capacity operation at least during heat pump operation. 
   The compressor shown in  FIG. 2  achieves the envelope shown in  FIG. 1 . The compressor  20  incorporates an orbiting scroll  22  orbiting relative to a non-orbiting scroll  24 . An intermediate pressure dump  26  and a intermediate pressure tap  28  deliver refrigerant into a valve chamber associated with a valve  29 . Valve  29  is responsive to overall suction pressure. Suction pressure, as is known, is related by a multiplier to the intermediate pressure. A spring  32  drives the valve body  40  away from a valve stop  31  having a pin  34 . As shown in  FIG. 2 , suction pressure  36  leads to a tap  38  on a side of the valve body  40  that also includes the spring  32 . Thus, suction pressure and the spring force drives the valve  40  to the right against the intermediate pressure force. As can be seen in  FIG. 2 , the intermediate pressure passing through dump  26  moves into a passage  42 . Thus, this intermediate pressure is delivered intermediate to enlarged portions  41  of the valve body  40 . Since this intermediate pressure “sees” both portions  41 , it does not effect the position of the valve body  40 . However, as is also clear, the intermediate pressure through tap  28  passes into a chamber on the right side of the valve body  40 , and its rightmost enlarged portion  41 , and drives the valve body  40  to the left. As the suction pressure increases, the difference between the intermediate pressure and the suction pressure also increases, and eventually the position of the valve body  40  moves to that shown in  FIG. 2 . As shown, the valve  40  includes a necked-down intermediate portion between the two enlarged portions  41 . 
   A valve stop is identified by element  30 , which stops the valve body  40  as it is driven to the right. As a worker of ordinary skill in the art would appreciate, the valve stop  30  is configured such that fluid can pass from the tap  28  into the chamber to the left of the valve stop  30 , and against the rightmost of the enlarged portions  41 . 
   A second valve  44  includes a piston  46  in a housing  54  that sees discharge pressure on the left hand side from a discharge pressure chamber  47 . A suction pressure tap  49  and an intermediate pressure tap  51  deliver refrigerant pressure into a chamber to the right hand side of the piston  46 . A stop  50  and  48  will stop piston  46  when it is driven to the right from the illustrated position. This pressure fluid along with the spring force  52  tends to hold the piston  46  at the illustrated position against a piston stop  60 . In  FIG. 2 , both the valves  29  and  44  are shown in the open position such that refrigerant can flow from the dump  26 , into lines  42 ,  51 ,  49  and  38  back to suction  36 . Thus, with the valves  29  and  44  in the position illustrated in  FIG. 2 , low capacity operation is achieved. As can be appreciated from  FIG. 2 , the refrigerant tap through line  42  is simply the refrigerant to be dumped under low capacity operation.  FIG. 3A  shows this same low capacity operation. This is a condition wherein the suction pressure is above a particular amount and the pressure differential is below a particular amount. This is zone  1  of  FIG. 4 . Under these conditions, low capacity operation is desirable. 
   As shown in  FIG. 3A , the pressure differential is now increased such that the discharge pressure to the left side of the piston  46  has overcome the force on the right side of the piston  46 . Under these conditions, the piston  46  blocks the tap  49  and refrigerant is no longer bypassed. Thus, high capacity operation occurs. As shown in  FIG. 3B , the suction pressure is also low such that the valve body  40  has moved to the right blocking line  42 . For this separate reason, high capacity operation will occur. As shown in  FIG. 4 , this would be zone  2 . 
   As shown in  FIG. 3C , the pressure differential is lower. However, the suction pressure is still sufficiently low that the valve  40  remains in a position blocking line  42 . High capacity operation will still occur. This is zone  3  from  FIG. 4 . 
     FIG. 3D  shows the condition wherein the pressure differential is sufficiently high to drive the piston  46  to the right, while the suction pressure is also sufficiently high such that the valve body  40  moves to the open position. Even so, since the piston  46  blocks flow through the line  49 , high capacity operation still occurs. This is zone  4  from  FIG. 4 . 
   In sum, the present invention discloses a simple system which requires two distinct conditions to occur before the compressor self-modulates to low capacity operation. Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill 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.