Abstract:
A variable capacity swash plate type compressor  10  incorporates a pressure relief valve  43  in fluid communication with a suction chamber  20  and a crank chamber  40 . The pressure relief valve  43  prevents over pressurization in the crank chamber  40  to minimize friction and forces acting on the components of the compressor  10.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a variable capacity swash plate type compressor adapted for use in an air conditioning system for a vehicle, and more particularly to a swash plate type compressor having a valve for controlling the pressure differential between the crank chamber and the suction chamber to facilitate improved pressure regulation in the crank chamber. 
     BACKGROUND OF THE INVENTION 
     Variable capacity 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 rotatably supported drive shaft, and a swash plate. The swash plate is adapted to be rotated by the drive shaft. The rotation of the swash plate is effective to reciprocatively drive the pistons. The length of the stroke of the piston is varied by an inclination angle of the swash plate. The inclination angle of the swash plate is varied by controlling the pressure differential between a suction chamber and a crank chamber using a control valve means. 
     The control of the crank chamber pressure is critical to the performance and durability of the compressor. If the pressure differential between the suction chamber and the crank chamber is too high, certain components in the compressor will be susceptible to failure due to overrates. The pressure differential can also negatively affect the optimum operation of the compressor. 
     In the prior art, an electronic control valve has been used to control the flow from the crank chamber to the suction plenum. To protect the crank chamber from being over pressurized, the electronic control valve sensed inputs of the crank chamber pressure and suction chamber pressure. Over pressurization can have several undesirable consequences. The components of the compressor are designed to endure forces in a given direction. If the pressure within the crank chamber increases substantially, the forces acting on the various compressor components will reverse causing undesirable effects on the durability of parts such as the pistons and bearings. In addition, the compressor can remain fixed in the minimum capacity condition if the pressure differential is not controlled. Increased friction and decreased durability could also result if the compressor is operated continuously at high crank chamber pressures. 
     An object of the invention is to produce a swash plate type compressor wherein the pressure in the crank chamber is monitored. 
     Another object of the invention is to produce a swash plate type compressor wherein the pressure in the crank chamber is controlled to minimize friction and component stresses on the components of the compressor. 
     Another object of the invention is to produce a swash plate type compressor wherein the pressure in the crank chamber is controlled to result in increased durability and duty cycle of the compressor. 
     Still another object of the invention is to produce a swash plate type compressor wherein the pressure in the crank chamber is regulated to result in smoother operation of the compressor. 
     SUMMARY OF THE INVENTION 
     This invention includes a variable capacity swash plate type compressor. The compressor includes a cylinder block, a cylinder head attached to the cylinder block and cooperating with the cylinder block to form an airtight seal, the head having a suction chamber and a discharge chamber formed therein, a crankcase attached to the cylinder block and cooperating with the cylinder block to define an airtight sealed crank chamber, a pressure control valve in fluid communication with the suction chamber of the head and the crank chamber for adjustably controlling a pressure differential between the suction chamber of the head and the crank chamber, and a pressure relief valve for decreasing a pressure differential between the suction chamber of the head and the crank chamber. 
     Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of a swash plate type compressor incorporating the features of the invention wherein a pressure relief valve is shown for decreasing a pressure differential between the suction chamber the crank chamber and showing the swash plate at a minimum inclination angle. 
     FIG. 2 is a sectional view of the swash plate type compressor illustrated in FIG. 1 showing the swash plate at a maximum inclination angle. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A variable capacity swash plate type compressor according to this invention is indicated generally at  10  in FIGS. 1 and 2. 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 head  16 . 
     The head  16  includes a suction chamber  20  and a discharge chamber  22 . The suction chamber  20  has an inlet port  24  and the discharge chamber  22  has an outlet port  26 . The suction chamber  20  communicates with each of the cylinders  14  through a suction port  28  disposed in the valve plate  18 . Each of the suction ports  28  is opened and closed by a suction valve  30 . Each of the cylinders  14  communicate with the discharge chamber  22  through a discharge port  32  disposed in the valve plate  18 . Each of the discharge ports  32  is opened and closed by a discharge valve  34 . The opening of the discharge valve  34  is restricted by a retainer  36 . 
     A crankcase  38  is sealingly disposed at the other end of the cylinder block  12 . The crankcase  38  and cylinder block  12  cooperate to form an airtight crank chamber  40 . A control valve  42  is provided with the compressor  10  for adjusting a pressure level in the crank chamber  40 . A pressure relief valve  43  is disposed between the suction chamber  20  and the crank chamber  40  in a parallel relation to the control valve  42 . In the preferred embodiment, the pressure relief valve  43  includes a helical spring  44  and a ball  45 . An orifice tube  46  fluidly connects the discharge chamber  22  and the crank chamber  40 . 
     A drive shaft  47  is centrally disposed in and arranged to extend through the crankcase  38  to the cylinder block  12 . The drive shaft  47  is rotatably supported by a bearing  48  mounted in the crankcase  38  and a bearing  50  mounted in the cylinder block  12 . Longitudinal movement of the drive shaft  47  is restricted by a thrust bearing  52  mounted in the cylinder block  12 . 
     A rotor  54  is fixedly mounted on an outer surface of the drive shaft  47  adjacent one end of the crankcase  38  within the crank chamber  40 . A thrust bearing  56  is mounted on an inner wall of the crankcase  38  in the crank chamber  40  disposed between the crankcase  38  and the rotor  54  and provides a bearing surface for the rotor  54 . An arm  58  extends laterally from a surface of the rotor  54  opposite the surface of the rotor  54  that contacts the thrust bearing  56 . A rectangular slot  60  is formed in the distal end of the arm  58 . A pin  62  has one end slidingly disposed in the slot  60  of the arm  58  of the rotor  54 . 
     A swash plate assembly includes a hub  64  and an annular plate  66 . The hub  64  includes arm  68  that extends upwardly and laterally from the surface of the hub  64 . The distal end of the arm  68  includes a hole  70 . The pin  62 , with one end slidingly disposed in the slot  60  of the arm  58  of the rotor  54 , has the other end fixedly disposed in the hole  70  of the arm  68 . 
     A hollow annular extension  72  depends from the opposite surface of the hub  64  as the arm  68 . Two pins  74 ,  76  are disposed in the hub  64  with a portion of the outer surface of the pins  74 ,  76  exposed in the aperture of the annular extension  72  of the hub  64 . 
     The annular plate  66  has a centrally disposed aperture. The annular extension  72  of the hub  64  extends through the aperture of the annular plate  66 . The drive shaft  47  is inserted in the aperture formed by the hub  64  of the swash plate assembly. 
     A spring  78  is disposed to extend around the outer surface of the drive shaft  47 . One end of the spring  78  abuts the rotor  54 . The opposite end of the spring  78  abuts the hub  64  of the swash plate assembly. 
     A plurality of pistons  80  are slidably disposed in the cylinders  14  in the cylinder block  12 . The pistons  80  each include a head  82 , a dependent skirt portion  84 , and a bridge portion  86 . The skirt portion  84  terminates in the bridge portion  86 . A pair of concave shoe pockets  88  are formed in the bridge portion  86  of each piston  80  for rotatably supporting a pair of semi-spherical shoes  90 . The spherical surfaces of the shoes  90  are disposed in the shoe pockets  88  with a flat bearing surface disposed opposite the spherical face for slidable engagement with opposite surfaces of the annular plate  66  of the swash plate assembly. 
     The operation of the compressor  10  is accomplished by rotation of the drive shaft  47  by an auxiliary drive means (not shown), which may typically be the internal combustion engine of a vehicle. Rotation of the drive shaft  47  causes the rotor  54  to correspondingly rotate with the drive shaft  47 . The swash plate assembly is connected to the rotor  54  by a hinge mechanism formed by the pin  62  slidingly disposed in the slot  60  of the arm  58  of the rotor  54  and fixedly disposed in the hole  70  of the arm  68  of the hub  64 . As the rotor  54  rotates, the connection made by the pin  62  between the swash plate assembly and the rotor  54  causes the swash plate assembly to rotate. During rotation, the swash plate assembly is disposed at an inclination angle. The sliding engagement between the annular plate  66  and the shoes  90  causes a reciprocation of the pistons  80  due to the inclination angle of the swash plate assembly. The reciprocation of the pistons  80  causes refrigerant gas to be introduced from the suction chamber  20  of the head  16  into the respective cylinders  14  in which the refrigerant gas is compressed by the reciprocating motion of the pistons  80 . The compressed refrigerant gas is discharged from the respective cylinders  14  into the discharge chamber  22 . 
     The capacity of the compressor  10  can be changed by changing the inclination angle of the swash plate assembly and thereby changing the length of the stroke for the pistons  80 . The capacity of the compressor  10  is controlled by the control valve  42 , which adjustably changes the pressure differential between the crank chamber  40  and the suction chamber  20 . Specifically, when the pressure level in the suction chamber  20  is raised with an increase in the thermal load, the control valve  42  cuts off the refrigerant gas travelling between the suction chamber  20  and the crank chamber  40 . Therefore, the pressure differential between the crank chamber  40  and the suction chamber  20  is increased and the backpressure acting on the respective pistons  80  in the crank chamber  40  is decreased. As a result, the pin  62  is moved slidably and downwardly within the slot  60 , the swash plate assembly is moved against the force of the spring  78 , and the inclination angle of the swash plate assembly and the capacity of the compressor are increased, as illustrated in FIG.  2 . 
     Conversely, when the pressure in the suction chamber  20  is lowered with a decrease in thermal load, the control valve  42  permits flow of refrigerant gas between the suction chamber  20  and the crank chamber  40 . Therefore, the pressure differential between the crank chamber  40  and the suction chamber  20  is decreased and the backpressure acting on the respective pistons  80  in the crank chamber  40  is increased. As a result, the pin  62  is moved slidably and upwardly within the slot  60 , the swash plate assembly yields to the force of the spring  78 , and the angle of inclination of the swash plate assembly and the capacity of the compressor are decreased, as illustrated in FIG.  1 . 
     The pressure relief valve  43  operates to relieve an over pressurization in the crank chamber  40 . The over pressurization may be caused by malfunction of the control valve  42  or inability of the control valve  42  to accurately control the pressure in the crank chamber  40  at minimum flow conditions. If the pressure differential between the crank chamber  40  and the suction chamber  20  exceeds a set point of the pressure relief valve  43 , the ball  45  of the pressure relief valve  43  is urged against the spring  44  and away from the orifice, thereby decreasing the pressure differential by passing refrigerant gas from the crank chamber  40  to the suction chamber  20 . 
     Since the parts of the compressor  10  are designed to endure forces in a given direction and the compressor  10  can be caused to stop in the minimum capacity condition if the pressure differential between the suction chamber  20  and the crank chamber  40  is too great, the pressure relief valve  43  minimizes undesirable wear and potential damage to the compressor  10 . The use of the pressure relief valve  43  provides for improved durability of the compressor  10 . 
     From the foregoing description, one ordinarily skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications to the invention to adapt it to various usages and conditions.