Abstract:
A variable displacement swash plate type compressor which incorporates a conduit formed in the cylinder block to provide fluid communication between a crank chamber and one or more cylinders to eliminate the need for an orifice tube in fluid communication between a discharge chamber and the crank chamber and to increase the flow of refrigerant gas and lubricating oil to the crank chamber under all operating conditions and to increase the internal fluid pressure in the crank chamber.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a variable displacement swash plate type compressor adapted for use in an air conditioning system for a vehicle, and more particularly to a compressor conduit means for pressurizing a crankcase to control the displacement of the swash plate of the compressor, and for facilitating lubrication of compressor components. 
     BACKGROUND OF THE INVENTION 
     Variable displacement swash plate type compressors typically include a cylinder block provided with a number of cylinders, a piston disposed in each of the cylinders of the cylinder block, a crankcase sealingly disposed on one end of the cylinder block, a rotatably supported drive shaft, and a swash plate. The swash plate is adapted to be rotated by the drive shaft. Rotation of the swash plate is effective to reciprocatively drive the pistons. The length of the stroke of the pistons is varied by the inclination of the swash plate. Inclination of the swash plate is varied by controlling the pressure differential between a suction chamber and a crank chamber. The pressure differential is typically controlled using a control valve and an orifice tube which facilitates fluid communication between a discharge chamber and the crank chamber to convey compressed gases from the discharge chamber to the crank chamber based on pressure in a suction chamber. 
     The compressor arrangement in the prior art described above has several disadvantages. First, due to the introduction of refrigerant gas through the orifice tube into the crank chamber, the pressure within the crank chamber cannot be accurately controlled. Second, when the compressor is operating at maximum capacity, the control valve closes, thereby eliminating flow through the orifice tube. Therefore, ineffective lubrication of the close tolerance moving parts within the crank chamber occurs due to the lack of consistent flow of refrigerant gas from the discharge chamber to the crank chamber. Finally, the tight tolerances required in the orifice tube are difficult to achieve in manufacturing due to the small diameter of the orifice tube. 
     An object of the present invention is to produce a swash plate type compressor wherein the pressure within the crankcase is increased and efficiently controlled. 
     Another object of the present invention is to produce a swash plate type compressor wherein oil flow to the crankcase during both minimum and maximum operating conditions is facilitated to result in improved lubrication of the compressor components. 
     SUMMARY OF THE INVENTION 
     The above, as well as other objects of the invention, may be readily achieved by a variable displacement swash plate type compressor comprising: a cylinder block having a plurality of cylinders arranged radially therein; a piston reciprocatively disposed in each of the cylinders of the cylinder block; a cylinder head attached to the cylinder block; a crankcase cooperating with the cylinder block to define a crank chamber; a drive shaft rotatably supported by the crankcase and the cylinder block; a swash plate adapted to be driven by the drive shaft, the swash plate having a central aperture for receiving the drive shaft, radially outwardly extending side walls, and a peripheral edge; and conduit means providing fluid communication between the crank chamber and at least one of the cylinders of the cylinder block. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above, as well as other objects, features, and advantages of the present invention will be understood from the detailed description of the preferred embodiment of the present invention with reference to the accompanying drawings, in which: 
     FIG. 1 is a cross sectional elevational view of a variable displacement swash plate type compressor incorporating the features of the invention, showing a conduit in fluid communication with the crank chamber and one cylinder; 
     FIG. 2 is a perspective view of the cylinder block of the compressor illustrated in FIG. 1 showing the features of the invention, the bore portion of the conduit is illustrated by a phantom line; 
     FIG. 3 is a graph illustrating the relationship between the pressure in the crank chamber, discharge chamber, suction chamber, and cylinder during one revolution of the compressor; 
     FIG. 4 is a graph illustrating the relationship between the net flow of refrigerant gas from a cylinder into the crank chamber for a prior art compressor having an orifice tube, and the net flow of refrigerant gas from a cylinder into the crank chamber for a compressor incorporating the conduit of the present invention; 
     FIG. 5 is a graph illustrating the relationship between flow rate of refrigerant gas for a prior art compressor having an orifice tube, and the flow rate of refrigerant gas for a compressor incorporating the conduit of the present invention; 
     FIG. 6 is a perspective view of an alternate embodiment of the invention of FIG. 1 schematically showing a ball type valve in the conduit of the cylinder block; and 
     FIG. 7 is a partial cross sectional elevational view of the embodiment illustrated in FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, and particularly FIG. 1, there is shown generally at  10  a variable displacement swash plate type compressor incorporating the features of the invention. The compressor  10  includes a cylinder block  12  having a plurality of cylinders  14 . A cylinder head  16  is disposed adjacent one end of the cylinder block  12  and sealingly closes the end of the cylinder block  12 . A valve plate  18  is disposed between the cylinder block  12  and the cylinder head  16 . A crankcase  20  is sealingly disposed at the other end of the cylinder block  12 . The crankcase  20  and cylinder block  12  cooperate to form an airtight crank chamber  22 . 
     The cylinder head  16  includes a suction chamber  24  and a discharge chamber  26 . An inlet port  28  and associated inlet conduit  30  provide fluid communication between the evaporator (not shown) of the cooling portion of the air conditioning system for a vehicle and the suction chamber  24 . An outlet port  32  and associated outlet conduit  34  provide fluid communication between the discharge chamber  26  and the cooling portion of the air conditioning system for a vehicle. Suction ports  36  provide fluid communication between the suction chamber  24  and each cylinder  14 . Each suction port  36  is opened and closed by a suction valve  37 . Discharge ports  38  provide fluid communication between each cylinder  14  and the discharge chamber  26 . Each discharge port  38  is opened and closed by a discharge valve  39 . A retainer  40  restricts the opening of the discharge valve  39 . 
     A drive shaft  41  is centrally disposed in and arranged to extend through the crankcase  20  to the cylinder block  12 . The drive shaft  41  is rotatably supported in the crankcase  20 . 
     A rotor  42  is fixedly mounted on an outer surface of the drive shaft  41  adjacent one end of the crankcase  20  within the crank chamber  22 . An arm  44  extends outwardly from a surface of the rotor  42  opposite the surface of the rotor  42  that is adjacent the end of the crankcase  20 . A slot  46  is formed in the distal end of the arm  44 . A pin  48  has one end slidingly disposed in the slot  46  of the arm  44  of the rotor  42 . 
     A swash plate  50  is formed to include a hub  52  and an annular plate  54  with a peripheral marginal edge  56 . The hub  52  includes an annular main body  58  with a centrally disposed aperture  60  formed therein and an arm  62  that extends outwardly and perpendicularly from the surface of the hub  52 . An aperture  64  is formed in the distal end of the arm  62  of the hub  52 . One end of the pin  48  is slidingly disposed in the slot  46  of the arm  44  of the rotor  42 , while the other end is fixedly disposed in the aperture  64  of the arm  62 . 
     A hollow annular extension  66  extends from the opposite surface of the hub  52  as the arm  62 . Two holes  68 ,  70  are formed in the annular extension  66  of the hub  52 . Two pins  72 ,  74  are disposed in the holes  68 ,  70 , respectively. A portion of the outer surface of the pins  72 ,  74  extend inwardly within the hollow annular extension  66  of the hub  52 . 
     The annular plate  54  has a centrally disposed aperture  76  formed therein to receive the annular extension  66  of the hub  52 . The annular extension  66  is press fit in the aperture  76  of the annular plate  54 . The drive shaft  41  is adapted to extend through the hollow annular extension  66 . 
     A helical spring  78  is disposed to extend around the outer surface of the drive shaft  41 . One end of the spring  78  abuts the rotor  42 , while the opposite end abuts the hub  52  of the swash plate  50 . 
     A piston  80  is slidably disposed in each of the cylinders  14  in the cylinder block  12 . Each piston  80  includes a head  82 , a middle portion  84 , and a bridge portion  86 . A compression chamber  87  is formed between the head  82  of piston  80  and the valve plate  18 . A circumferential groove  88  is formed in an outer cylindrical wall of the head  82  to receive piston rings (not shown). The middle portion  84  terminates in the bridge portion  86  defining an interior space  90  for receiving the peripheral marginal edge  56  of the annular plate  54 . Spaced apart concave pockets  92  are formed in the interior space  90  of the bridge portion  86  for rotatably containing a pair of semi-spherical shoes  94 . The spherical surfaces of the shoes  94  are disposed in the shoe pockets  92  with a flat bearing surface disposed opposite the spherical surface for slidable engagement with the opposing sides of the annular plate  54 . 
     A channel or conduit  96 , illustrated in FIGS. 1 and 2, is disposed between the crank chamber  22  and one of the cylinders  14 . The conduit  96  is formed by a bore portion  98  and a slot portion  100 . The bore portion  98  extends longitudinally through the cylinder block  12  adjacent and substantially parallel to one of the cylinders  14 . The slot portion  100  is formed in the surface of the cylinder block  12  adjacent to the valve plate  18 , and extends laterally from one of the cylinders  14  to the bore portion  98 . The conduit  96  provides direct fluid communication between the crank chamber  22  and the compression chamber  87  of one of the cylinders  14 . In FIG. 2, only one cylinder is illustrated by a phantom line, however it is understood that the embodiment cylinder block illustrated includes six cylinders. 
     In an alternate embodiment, a control valve  102 ′ may be disposed in the conduit  96 ′ for controlling the flow of refrigerant gas from the cylinder  14 ′ to the crank chamber  22 , as illustrated in FIGS. 6 and 7. It should be noted that the conduit  96 ′ is rotated from the location of FIG. 2 in order to accommodate the control valve  102 ′. The control valve  102 ′ may be of any conventional type such as, for example, a ball type valve. The control valve  102 ′ may be adapted to receive a signal from a remote source to vary the flow of the refrigerant gas therethrough. Either a mechanical or electronic type control valve may be used. The mechanical type control valve can be arranged to receive either a temperature or pressure control signal from an evaporator in the air conditioning system of a vehicle. Alternatively, the electronic type control valve is arranged to receive an electrical signal from a microprocessor. The microprocessor for the electronic type control valve monitors the discharge pressure of the compressor, the RPM of the vehicle engine, and the like, to control the flow of refrigerant gas from the one of the cylinders  14 ′, through the conduit  96 ′, and to the crank chamber  22 . 
     The operation of the compressor  10  is accomplished by rotation of the drive shaft  41  by an auxiliary drive means (not shown), which may typically be the internal combustion engine of a vehicle. Rotation of the drive shaft  41  causes the rotor  42  to correspondingly rotate with the drive shaft  41 . The swash plate  50  is connected to the rotor  42  by a hinge mechanism formed by the pin  48  slidingly disposed in the slot  46  of the arm  44  of the rotor  42  and fixedly disposed in the aperture  64  of the arm  62  of the hub  52 . As the rotor  42  rotates, the connection made by the pin  48  between the swash plate  50  and the rotor  42  causes the swash plate  50  to rotate. During rotation, the swash plate  50  is disposed at an inclination. The rotation of the swash plate  50  is effective to reciprocatively drive the pistons  80 . The rotation of the swash plate  50  further causes a sliding engagement between the opposing sides of the annular plate  54  and the cooperating spaced apart shoes  94 . The reciprocation of the pistons  80  causes refrigerant gas to be introduced from the suction chamber  22  into the respective cylinders  14  of the cylinder head  16 . The reciprocating motion of the pistons  80  then compresses the refrigerant gas within each cylinder  14 . When the pressure within each cylinder  14  exceeds the pressure within the discharge chamber  26 , the compressed refrigerant gas is discharged into the discharge chamber  26 . 
     The capacity of the compressor  10  can be changed by changing the inclination of the swash plate  50  and thereby changing the length of the stroke for the pistons  80 . The inclination of the swash plate  50  is changed by controlling the pressure differential between the crank chamber  22  and the suction chamber  24 . The pressure differential is controlled by controlling the net flow of refrigerant gas from the at least one cylinder  14  to the crank chamber  22  through the conduit  96 . 
     Specifically, as the piston  80  is caused to move toward a bottom dead center position, the pressure within the cylinder  14  is less than the pressure within the suction chamber  24 . The suction valve  37  is caused to open causing refrigerant gas to flow into the cylinder  14  through the suction port  36 . As illustrated in FIG. 3, the pressure within the crank chamber  22  remains at a level between the pressure within the suction chamber  24  and the pressure within the discharge chamber  26  during rotation of the drive shaft  41 . 
     Conversely, as the piston  80  is caused to move toward a top dead center position, the refrigerant gas within the cylinder  14  is compressed until the pressure within the cylinder  14  is caused to exceed the pressure within the discharge chamber  26 . The discharge valve  39  is caused to open and refrigerant gas is caused to flow through the discharge port  38  to the discharge chamber  26 . 
     Further, as the piston  80  is caused to move toward a bottom dead center position within the at least one cylinder  14 , the pressure within the cylinder  14  is less than the pressure within the crank chamber  22 , causing refrigerant gas to flow through the conduit  96  to the cylinder  14 . As the piston  80  is caused to move toward a top dead center position, the refrigerant gas within the cylinder  14  is compressed causing the pressure within the cylinder  14  to increase and exceed the pressure within the crank chamber  22 . When the pressure within the cylinder  14  exceeds the pressure within the crank chamber  22 , refrigerant gas is caused to flow through the conduit  96  to the crank chamber  22 . Additionally, as the refrigerant gas within the cylinder  14  is compressed, the net flow and the rate of flow of refrigerant gas from the cylinder  14  to the crank chamber  22  are increased and become positive, as illustrated in FIGS. 4 and 5. 
     By introducing the refrigerant gas from the cylinder  14  into the crank chamber  22  through the conduit  96 , instead of introducing the refrigerant gas from the discharge chamber  26  into the crank chamber  22  through an orifice tube, several benefits are apparent. The capacity and efficiency of the compressor  10  have been maximized. The orifice tube of prior art compressors bypasses compressed refrigerant gas from the discharge chamber  26  to the crank chamber  22 , thereby preventing the compressed gas from being used in the cooling portion of the air conditioning system for a vehicle. By creating a conduit communicating the crank chamber  22  and the one of the cylinders  14 , the flow of refrigerant gas from the cylinder  14  into the crank chamber  22  is efficiently controlled. Rather than bleeding highly pressurized refrigerant gas from the discharge chamber  26  into the crank chamber  22 , the net flow of refrigerant gas is from the one of the cylinders  14  into the crank chamber  22 . Because refrigerant gas flows from the cylinder  14  to the crank chamber  22  before the pressure of the refrigerant gas reaches the higher pressure within the discharge chamber  26 , the net flow of refrigerant gas into the crank chamber  22  occurs at a lower pressure than with a prior art orifice tube. 
     An additional benefit of the present invention is that oil present in the refrigerant gas provides lubrication to the close tolerance moving components of the compressor  10 . The lubrication maximizes the durability of the compressor  10 . 
     Finally, by introducing the refrigerant gas to the crank chamber  22  through the conduit  96 , the orifice tube of prior art is eliminated. 
     Use of the control valve  102  of the alternate embodiment controls the flow of refrigerant gas between the cylinder  14  and the crank chamber  22 . Only unidirectional flow is permitted from the cylinder  14  to the crank chamber  22 .