Abstract:
The invention provides a compressor with a shut off valve disposed between the crank case and the suction cavity. The valve is moveable between an open and closed position in response to the pressure in the discharge cavity of the compressor. The valve is an on/off valve and is operable rapidly depressurize the interior of the crank case when the compressor transitions from a minimum stroke. The valve can define first and second fluid pathways. The first fluid pathway can be larger than the second fluid pathway and be selectively opened and closed. The second fluid pathway can be permanently open and act as a bleed between the crank case and the suction cavity.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of the provisional patent application 60/471,876 for a CRANK CASE SHUT OFF VALVE, filed on May 20, 2003, which is hereby incorporated by reference in its entirety. This claim is made under 35 U.S.C. §119(e); 37 C.F.R. § 1.78; and 65 Fed. Reg. 50093. 

   TECHNICAL FIELD 
   The invention provides a compressor for the climate control system of a vehicle and, more specifically, the invention provides a valve for controlling the flow of refrigerant between a crank case of the compressor and a suction cavity of the compressor, or discharge and crank case cavity to rapidly depressurize or re-pressurize the crank case. 
   BACKGROUND OF THE INVENTION 
   Variable displacement compressors have been applied to climate control systems for vehicles and were introduced with pneumatic or mechanical control hardware. With the advancement of electronic technologies, solenoids have commonly been used to increase the compressor control range. With the refinement of electronic control valves, compressor clutches are being eliminated. This type of compressor is commonly called a clutchless compressor and is usually an electronically controlled, variable displacement compressor. 
   The clutchless compressor cannot disengage or re-engage the clutch, hence the compressor is operational whenever the vehicle engine is running. When the climate control system is turned off, the compressor is placed at a minimum displacement. Ideally, the minimum displacement would be zero, but current compressor technology does not allow for such a device. Instead, the compressor must displace some refrigerant at minimum stroke. 
   Mainstream clutchless compressor technology utilizes a three-port electronic control valve in conjunction with a fixed orifice bleed to determine compressor displacement. In one known method, the electronic control valve regulates the flow of discharge gas to the compressor crank case and the fixed orifice bleed flows refrigerant from the crank case to the suction cavity in a rear head of the compressor. In a second method, the electronic control valve regulates the flow of refrigerant from the compressor crank case to the suction cavity and a fixed orifice bleed defines a pathway for refrigerant to flow from the discharge cavity in the rear head of the compressor to the crank case. 
   SUMMARY OF THE INVENTION 
   The present invention provides a climate control system having a compressor with a fluid pathway extending between a cavity defined by a crank case and a suction cavity and a valve operable to open and close the fluid pathway in response to pressure in a discharge cavity. The valve can include a housing, a piston moveably positioned in the housing between open and closed positions, and a spring to bias the piston to a closed position. The piston can define a surface in communication with the discharge cavity. Fluid in the discharge cavity can direct pressure against the surface defined by the piston and move the piston from the closed position to the open position. The housing and the piston can define a portion of the fluid pathway extending between the crank case and the suction cavity. The housing can also define a second fluid pathway between the crank case and the suction cavity that is permanently open. The valve of the present invention can also control flow from the discharge cavity to the cavity defined by the crank case. 
   Other applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein: 
       FIG. 1  is a cross-sectional view of the compressor according to the exemplary embodiment of the invention; 
       FIG. 2  is a perspective view showing the valve positioned in a rear head of the compressor shown in  FIG. 1 ; 
       FIG. 3  is an exploded view of the valve shown in  FIGS. 1 and 2 ; 
       FIG. 4  is a cross-sectional view of the valve shown in  FIGS. 1-3  in the open position; 
       FIG. 5  is a cross-sectional view of the valve shown in  FIGS. 1-4  in the closed position; and 
       FIG. 6  is a graph illustrating the operation of the valve as a difference in pressure between the discharge cavity and the suction cavity increases. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to  FIG. 1 , the present invention provides a compressor  10  for a climate control system of a vehicle. The compressor  10  includes a crank case  12 , suction cavity  14 , and a discharge cavity  16 . The invention also includes a first fluid pathway  18  extending between the crank case  12  and the suction cavity  14 . A valve  20  is positioned along the first fluid pathway  18  and is operable to open and close the first fluid pathway  18  in response to a fluid pressure in the discharge cavity  16 . 
   In the exemplary embodiment of the invention, the crank case  12  includes a first portion  22  and a second portion  24  operably associated with one another to define a crank case interior  25 . As used herein, the crank case  12  and the crank case interior  25  are generally redundant, both terms referring to essentially the same structure and having the same purpose. The crank case  12  houses at least one piston  26  moveable in a cylinder  28 . The cylinder  28  communicates with the suction cavity  14  and the discharge cavity  16 . In particular, fluid such as refrigerant is drawn into the cylinder  28  from the suction cavity  14  during an upstroke of the piston  26 . Fluid is discharged into the discharge cavity  16  from the cylinder  28  during a downward stroke of the piston  26 . The pressure of the fluid is increased during movement from the suction cavity  14  to the discharge cavity  16  through the cylinder  28 . 
   A rear head  30  can be connected to the crank case  12  and a valve plate  32  can be positioned between the rear head  30  and the crank case  12 . The rear head can define the suction cavity  14  and the discharge cavity  16 . The valve  20  can be disposed in an aperture  34  defined by the rear head  30 . 
   Refeffing now to  FIGS. 2 and 3 , the valve  20  can include a housing  36  and a piston  38  moveably positioned in the housing  36 . The housing  36  can be received in the aperture  34  of the rear head  30 . The housing  36  can define one or more projections, such as tabs  40 ,  42 , that cooperate with surfaces  44 ,  46 , respectively, defined by the rear head  30  to orient the housing  36  as desired. The housing  36  can be positioned between the valve plate  32  and a bottom surface  70  of the aperture  34  such that the housing  36  is maintained longitudinally in a desired position. The bottom surface  70  of the aperture  34  is thus part of the discharge cavity  16 . 
   The interior of the crank case  12  (shown in  FIG. 1 ) can communicate with a well  48  defined by the rear head  30 . The well  48  communicates with the aperture  34 . The suction cavity  14  (shown in  FIG. 1 ) can communicate with an opening  50  defined by the rear head  30 . The valve  20  is positioned between the well  48  and the opening  50 . 
   Refeffing now to  FIGS. 2-4 , the piston  38  is moveably positioned within the housing  36  between an open position, shown in  FIG. 4 , and a closed position, shown in  FIG. 5 . The piston  38  and housing  36  cooperate to open and close the fluid pathway  18 . The housing  36  defines first and second apertures  52 ,  54 , respectively. The apertures  52 ,  54  extend transverse to the housing  36  and define a portion of the fluid line  18 . As shown in the perspective view of  FIG. 3 , the apertures  52 ,  54  extend partially annularly around the housing body  36 . In the exemplary embodiment of the invention, the first fluid pathway  18  extends between the crank case  12  and the suction cavity  14  and is defined by the well  48 , first aperture  52 , the second aperture  54 , and the opening  50 . 
   The piston  38  includes a first head  58  defining an outer surface  64 , a second head  60  defining an outer surface  72 , and a neck  62  disposed between the first head  58  and the second head  60 . When the piston  38  is in the closed position, the second head  60  closes the apertures  52 ,  54 . When the piston  38  is in the open position, the fluid pathway is also defined, in part by an inner surface  78  of the first head  58 , an inner surface  80  of the second head  60  and the neck  62 , fluid moving around the neck  62  between the apertures  52 ,  54 . 
   The housing  36  also defines a third aperture  56  communicating with the discharge cavity  16 . The third aperture  56  is transverse to the first and second apertures  52 ,  54 . A surface  66  of the piston  38  is open to the discharge cavity  16 ; fluid in the discharge cavity  16  can apply a pressure to the surface  66 . The surface  64  of the first head  58  slidably cooperates with the aperture  56 . The surface  72  of second head  60  slidably cooperates with the a reduced portion  74  of the aperture  56 . A projection  68  extends from the surface  66  to engage the surface  70  when the piston  38  is in the closed position. The cooperation between the projection  68  and the surface  70  ensures that a space or gap is defined between the surface  66  and the surface  70  for pressurized fluid to enter the aperture  56  and act on the surface. 
   In the exemplary embodiment of the invention, a spring  76  is positioned between the housing and the piston  38  to bias the piston  38  to the closed position. The housing  36  and the piston  38  cooperate to define a spring chamber  82  in which the spring  76  is positioned. The neck  62  defines an aperture  84  communicating with the spring chamber  82 . When the piston  38  is in the open or closed position, the aperture  84  communicates fluid from the fluid pathway  18  to the spring chamber  82 . As a result, the pressure in the spring chamber  82  is the pressure in the suction cavity  14  and is less than the pressure in the discharge cavity  16 . Also, the spring  76  and surfaces defining the spring chamber  82  can be lubricated by the fluid flowing along the pathway ( 18 ). The spring rate of the spring  76  is minimal; the valve  20  opens substantially as soon as the stroke of the piston  26  increases from a minimum stroke. 
   When the pressure in the discharge cavity  16  increases, corresponding to a stroke of the piston  26  greater than minimum stroke, the piston  38  moves to the open position. Also, the inner surface  78  of the first head  58  engages and seals against a shoulder  86  defined by the housing  36 , sealing the fluid pathway  18  from the discharge cavity  16 . The open fluid pathway  18  allows for rapid depressurization of the crank  12 . As can be seen by  FIGS. 4 and 5 , the aperture  54  is oriented relative to the suction cavity  14  such that any force resulting from vacuum will act on the piston  38  in direction that is not the direction of movement of the piston  38 . In other words, a suction force originating in the suction cavity  14  will act on the side of the piston  38  and will not urge the piston  38  to move away from the aperture  54  and thereby unblock the aperture  54 . 
   The valve  20  also defines a second fluid pathway  88  extending between the crank case  12  and the suction cavity  14 . The pathway  88  extends between a surface  90  of the housing  36  and the valve plate  32  and further bounded by a gasket disposed between the valve plate  32  and the rear head  30 . The gasket is not shown to enhance the clarity of the drawings. A projection  92  can extend from the surface  90  and engage the valve plate  32 . The cooperation between the projection  92  and the valve plate  32  ensures that a space or gap is defined between the surface  90  and the valve plate  32  for fluid to move between the crank case  12  and the suction cavity  14 . The projection  92  can be sized such that the second fluid pathway  88  communicates less fluid between the crank case  12  and the suction cavity  14  than a 1.6 millimeter bleed valve that has been previously used in compressors. 
   The graph in  FIG. 6  illustrates volumetric flow of fluid from the crank case  12  to the suction cavity along the y-axis and the difference in pressure between the discharge cavity  16  and the suction cavity  14  along the x-axis. The dashed line represents flow through a 1.6 millimeter bleed valve, previously used in compressors. A line portion  94  extends parallel to the x-axis from the y-axis to a point  96 . The line  94  represents fluid flow between the crank case  12  and the suction cavity  14  through the second fluid pathway  88  while the piston  38  is in the closed position. The fluid flow represented by line  94  is less than the flow through a conventional 1.6 millimeter bleed. At point  96 , the pressure in the discharge cavity  16  urges the piston  38  to the open position and volumetric flow between the crank case  12  and the suction cavity  14  increases to a second line portion  98  and the crank case  12  is quickly depressurized. Thus, in operation, the valve opens when a pressure differential between the discharge cavity and the suction cavity is at a first level and closes when the pressure differential between the discharge cavity and the suction cavity is at a second level less than the first level. 
   As the compressor  10  is position to a minimum stoke, the difference in pressure between the discharge cavity  16  and the suction cavity  14  decreases and the operation of the compressor  10  is represented by point  100  along the line portion  98 . At point  100 , the piston  38  moves to the closed position and volumetric flow between the crank case  12  and the suction cavity  14  decreases to line portion  94 . 
   In operation, the compressor  10  according to the present invention provides numerous benefits and advantages over prior compressors. When the piston  38  is in the closed position, volumetric flow between the crank case  12  and the suction cavity  14  is reduced since the second fluid pathway  88  is smaller than a convention 1.6 millimeter bleed. As a result, the pressure in the crank case  12  will increase faster and the minimum displacement of the piston  36  will decrease. Furthermore, the reduced minimum displacement of the piston  36  will result in reduced power consumption, less wear, reduced torque fluctuations, and reduced likelihood of evaporator freeze. When the piston  38  is in the open position, volumetric flow between the crank case  12  and the suction cavity  14  is increased since the first and second fluid pathways  18 ,  88  are collectively larger than a convention 1.6 millimeter bleed. As a result, the transition from minimum piston stroke will be enhanced under all operating conditions. 
   While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.