Abstract:
A variable displacement swash plate type compressor which incorporates a swash plate slidably mounted on a drive shaft, the swash plate having side walls that taper toward one another for constant point contact with a ball bearing of an associated piston which results in a smaller required diameter for the swash plate and smoother operation of the compressor over prior art structures.

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 tapered swash plate which effectively causes constant bearing contact between the swash plate and the associated pistons during any changes in the inclination of the swash plate. 
     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. The 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. 
     In the prior art, a variety of structures have been disclosed for operatively connecting the swash plate and the pistons. Typically, a pair of semi-spherical shoes is disposed in a bridge portion of the pistons and slidingly engages a swash plate of uniform thickness. Specifically, the flat bearing surface of a semi-spherical shoe slidably engages the swash plate, with the spherical surface typically disposed in a concave shoe pocket in the bridge portion of each piston. As the swash plate is caused to slide along the flat bearing surface of the semi-spherical shoes of the pistons, friction is created causing undesirable heat and wear. 
     Prior art structures typically include a swash plate having machined surfaces adapted to engage the entire flat bearing surfaces of the semi-spherical shoes. A disadvantage of the prior art is that the swash plate must be of a specified diameter and weight to support the surface area of the semi-spherical shoes of the pistons. The flat bearing surfaces of the shoes must be polished, adding expense. In addition, the polished surfaces may also require surface hardening adding even more expense. 
     An object of the present invention is to produce a swash plate type compressor wherein the contacting surface area between the swash plate and each shoe is minimized thereby minimizing friction, heat, and wear. 
     SUMMARY OF THE INVENTION 
     The above, as well as other objects of the present 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 plurality of pistons, each of the pistons reciprocatively disposed in each of the cylinders of the cylinder block; a cylinder head attached to the cylinder block and cooperating with the cylinder block to define an airtight seal; a crankcase attached to the cylinder block and cooperating with the cylinder block to define an airtight sealed crank chamber; a drive shaft rotatably supported by the crankcase and the cylinder block in the crank chamber; bearing means disposed in a bridge portion of the pistons; and a swash plate adapted to be driven by the drive shaft, the swash plate having a central aperture, opposing sides, and a peripheral edge, the drive shaft extending through the aperture of the swash plate the opposing sides of the swash plate having tapered surfaces intermediate the central aperture and. the peripheral edge, the tapered surfaces causing the swash plate to remain in constant bearing contact with the bearing means as the inclination of the swash plate changes. 
    
    
     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 embodiments 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 and showing the swash plate at a maximum inclination; and 
     FIG. 2 is a partial cross sectional view of the swash plate type compressor illustrated in FIG. 1 showing the ball bearings, the swash plate at a minimum inclination, the radially outwardly extending tapered side walls, and phantom lines illustrating the swash plate at a maximum inclination when the piston is at a top dead center position and at a bottom dead center position. 
    
    
     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 heat exchanger (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 In 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 a tapered annular plate  54 . The annular plate  54  has side walls or opposing sides  55 , and a peripheral marginal edge  56 , the opposing sides  55  being tapered at tapered portions  57  intermediate the hub  52  and the 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, with a portion of the outer surface of the pins  72 ,  74  extending 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 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 ball bearings  94 , as clearly illustrated in FIGS. 1 and 2. It will be understood that other embodiments of the present invention may include a bearing element of another shape such as, for example, semi-spherical, cylindrical, or elliptical. 
     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 rolling engagement between the opposing sides  55  of the annular plate  54  and the cooperating spaced apart ball bearings  94 . 
     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 . 
     A control valve (not shown) is arranged to monitor the suction and discharge pressures of the compressor  10 , and control the flow of refrigerant gas from the discharge chamber  26  to the crank chamber  22  through a conduit (not shown). Specifically, when an increase in thermal load occurs, the control valve is caused to close, thereby stopping the flow of refrigerant gas through the control valve to the crank chamber  22 . The pressure differential between the crank chamber  22  and the suction chamber  24  is then equalized by bleeding refrigerant gas through an orifice (not shown) to the suction chamber  24 . As a result of the decreased backpressure acting on the pistons  80  in the crank chamber  22 , the pin  48  connecting the rotor  42  and the swash plate  50  is caused to move slidably and outwardly within the slot  46 . The swash plate  50  is moved against the force of the spring  78 , the inclination of the swash plate  50  is increased, and as a result, the length of the stroke of each piston  80  is increased. 
     Conversely, when a decrease in thermal load occurs, the control valve is caused to open, thereby bleeding refrigerant gas from the discharge chamber  26  to the crank chamber  22  through the conduit. Because the flow of pressurized refrigerant gas to the crank chamber  22  from the discharge  26  is larger than the flow of refrigerant gas from the crank chamber  22 , to the suction chamber  24 , through the orifice, the backpressure acting on the pistons  80  in the crank chamber  22  is increased. As a result of the increased backpressure in the crank chamber  22 , the pin  48  is moved slidably and inwardly within the slot  46 . The swash plate  50  yields to the force of the spring  78 , the inclination of the swash plate  50  is decreased, and as a result, the length of the stroke of each piston  80  is reduced. 
     During rotation of the swash plate  50 , each piston  80  is caused to move from a top dead center position to a bottom dead center position in respect of each cooperating cylinder  14 . FIG. 2 illustrates the annular plate  54  at a minimum inclination; the annular plate  54 ′ at a maximum inclination when the piston  80  is at a bottom dead center position; and the annular plate  54 ″ at a maximum inclination when the piston  80  is at a top dead center position. 
     As further illustrated in FIG. 2, the opposing sides  55  of the annular plate  54  are tapered at tapered portions  57  such that the opposing sides  55  are in constant rolling contact with the adjacent ball bearings  94  at all swash plate  50  inclinations. For example, at a minimum inclination, the annular plate  54  contacts the ball bearings  94  at engagement points a and b. When the swash plate  50  is at a maximum inclination and the piston  80  is at a bottom dead center position, the annular plate  54 ′ contacts the ball bearings  94  at engagement points a′ and b′. Additionally, when the swash plate  50  is at a maximum inclination and the piston  80  is at a top dead center position, the annular plate  54 ″ contacts the ball bearings  94  at engagement points a″ and b″. Therefore, as the swash plate  50  rotates, each piston  80  is caused to move from a top dead center position to a bottom dead center position, and the inclination of the swash plate  50  relative to each piston  80  changes. The opposing sides  55  of the annular plate  54  therefore allow the annular plate  54  to travel freely between the ball bearings  94  while remaining in constant contact with the ball bearings  94  as the swash plate  50  rotates. 
     Further, because the opposing sides  55  of the annular plate  54  remain in constant contact with the bearings  94  as the inclination of the swash plate  50  changes, the bearings  94  are caused to remain rotatably contained in the pockets  92 , thus minimizing vibration and wear of the bearings  94  and the associated pockets  92 . 
     Additionally, the use of ball bearings  94  as the bearing means minimizes the contacting surface area between the opposing sides  55  of the annular plate  54  and the ball bearings  94 . The reduced contacting surface area minimizes frictional engagement, thereby minimizing the resultant heat and wear of the annular plate  54  and the associated bearings  94 . Further, the tapered shape of the tapered portions  57  of the annular plate  54  reduces the amount of material required to manufacture the annular plate  54 , thereby minimizing material costs and the overall weight 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.