Patent Publication Number: US-6210124-B1

Title: Variable swash plate compressor

Description:
TECHNICAL FIELD 
     The present invention relates generally to a swash plate compressor and more particularly to improvements to such a compressor so that the size, energy consumption, and vibrational characteristics are minimized. 
     BACKGROUND ART 
     Conventional swash plate compressors utilize a rotating swash plate, driven by a drive shaft, to drive a piston. The piston is used to transfer fluid from the low pressure side of an air conditioning system or other device to the high pressure side. Conventional swash plate compressors utilize an elbow to transfer the rotational drive of the drive shaft to the swash plate. The utilization of an elbow, or similar mechanism, to transfer the rotational drive of the drive shaft has several undesirable characteristics. This conventional design transfers undesirable stresses to the swash plate requiring the swash plate to be designed for a higher strength. This adds to the size, weight, and cost of the swash plate compressor. The presence alone of the elbow or similar mechanism adds to the size, weight, complexity and manufacturing cost of the conventional swash plate compressor. In addition, the elbow, as it rotates with the drive shaft, limits the potential travel distance of the piston. 
     It is known that varying the angle of the swash plate relative to the drive shaft allows the swash plate compressor to produce variable fluid transfer rates. One known design utilizes a biasing spring and the crankcase pressure within the compressor to vary the angle of the swash plate. This crankcase pressure can lead to undesirable stresses on the swash plate and can have a negative effect on the vibrational characteristics of the swash plate compressor. 
     Finally, the piston driving mechanisms in known variable swash plate compressors utilize multiple pivot locations. The swash plate itself typically slides and/or rotates axially on the drive shaft, the elbow joint slides and/or rotates about a pin in the elbow, and the piston joint rotates about its connection with the swash plate. The position and rotation of the swash plate, the elbow, and the piston in relation to each pivot location controls the path of the piston. These multiple pivot locations often result in a variable Top-Dead-Center (“TDC”) of the piston. The TDC of the piston is the distance between the piston face and the piston chamber outlet face at the top of the piston cycle. Variations in the piston TDC result in undesirable variations in the variable swash plate compressor&#39;s output. 
     Therefore, there is a need for a variable swash plate compressor design that reduces the stresses in the swash plate, allows for greater piston travel without increasing the compressor size, reduces undesirable vibrational characteristics, reduces variation in piston TDC, and reduces the size, weight, and manufacturing cost of known variable swash plate compressor designs. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a variable swash plate compressor that reduces the stress in the swash plate, reduces vibrations in the compressor, and reduces the variation in piston TDC. It is a further object of the present invention to provide a variable swash plate compressor that reduces the size, weight, and manufacturing costs associated with conventional swash plate compressor design. 
     In accordance with the objects of this invention, a variable swash plate compressor is provided. The variable swash plate compressor includes a housing, a drive shaft and a control surface element. The control surface element is attached to and receives a rotational drive force from the drive shaft. The control surface element has a pinnacle element attached thereto. 
     The variable swash plate compressor also includes a swash plate with a bore located in its center. The control surface element sits within the bore of the swash plate. The swash plate also includes a pocket in which the pinnacle element is seated. The drive shaft transmits a rotational drive force to the swash plate through the control surface element seated in the bore of the swash plate and the pinnacle element seated in the swash plate pocket. 
     The variable swash plate compressor also includes a compression piston positioned within a piston chamber formed in the housing. As the compression piston moves within the piston chamber it alternates between drawing fluid into the piston chamber through an inlet and forcing fluid within the piston chamber out of an outlet. The compression piston is moved in this cyclical fashion by remaining in contact with the rotating swash plate such that only axial forces are transmitted between the swash plate and the compression piston. As the angle between the swash plate and the drive shaft is increased, the travel path of the compression piston is increased resulting in an increase in the output of the variable swash plate compressor. 
     The variable swash plate compressor also includes a fulcrum piston assemby for controlling the angle of the swash plate relative to the drive shaft. As the angle of the swash plate relative to the drive shaft is increased, the output of the variable swash plate compressor is increased. The fulcrum piston assembly changes the angle of the swash plate by exerting a force on the swash plate causing it to pivot about the tip of the pinnacle element. The tip of the pinnacle element orbits the axial center of the drive shaft at a distance equal to the distance from the center of the drive shaft to the axial center of the compression piston. By pivoting the swash plate about a point that orbits over the axial center of the compression piston, variation in the TDC of the compression piston is reduced. 
     Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a perspective view of a preferred embodiment of a variable swash plate compressor in accordance with the present invention; 
     FIG. 2 is a cross-sectional view of the variable swash plate compressor illustrated in FIG. 1, the cross-section being taken along the line  2 — 2  in FIG.  1  and in the direction of the arrows, the cross-section illustrating the variable swash plate compressor in its nonidle position; 
     FIG. 3A is a side view of the drive shaft illustrated in FIG. 2; 
     FIG. 3B is a top view of the drive shaft illustrated in FIG. 2; 
     FIG. 4A is a top view of the swash plate illustrated in FIG. 2; 
     FIG. 4B is a cross-sectional view of the swash plate illustrated in FIG. 4A, the cross-section being taken along the line  4 B— 4 B in FIG.  4 A and in the direction of the arrows; 
     FIG. 5 is a cross-sectional view of the variable swash plate compressor illustrated in FIG. 1, the cross-section being taken along the line  2 — 2  in FIG.  1  and in the direction of the arrows, the cross-section illustrating the variable swash plate compressor in its idle position; and 
     FIG. 6 is an illustration of the drive shaft, swash plate, control surface element and pinnacle element illustrated in FIG.  2 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     Referring now to FIG. 1, which is a schematic view of a variable swash plate compressor  10  in accordance with the present invention. The disclosed variable swash plate compressor  10  is preferably for use in automotive air conditioning applications. However, the disclosed variable swash plate compressor  10  may be used in a variety of applications, including non-automotive applications. 
     Referring now to FIG. 2, which is a cross-sectional view of the variable swash plate compressor  10  in accordance with the present invention. The variable swash plate compressor  10  includes a housing  12 . In the embodiment shown in FIG. 2, the housing  12  is comprised of a top housing section  12 A, a middle housing section  12 B, and a bottom housing section  12 C. A top inlet  14 A is located within the top housing  12 A and is in fluid connection with a bottom inlet  14 B located within the bottom housing  12 C to allows fluid to be conveyed into a pumping chamber  16  located within the middle housing  12 B. The bottom inlet  14 B is in fluid communication with a source of fluid outside the compressor  10 . A compression piston  18  situated within the pumping chamber  16  draws fluid from the top inlet  14 A into the pumping chamber  16  and is used to force the fluid within the pumping chamber  16  out through a top outlet  20 A. The top outlet  20 A is in fluid connection with a bottom outlet  20 B to allow fluid from the top outlet  20 A and the bottom outlet  20 B to exit the bottom housing section  12 C of the compressor  10 . Although the embodiment is described in terms of inlets and outlets located on both the top and bottom of the compressor, it should be understood that in other embodiments the inlets and outlets may be located on only the top or the bottom of the compressor. 
     The compression piston  18  is activated through the use of a drive shaft  22  located with the housing  12 . In one preferred embodiment, the drive shaft  22  is imparted with a rotational drive force from a source outside the variable swash plate compressor  10 . Alternatively, the drive shaft  22  may be imparted with a rotational drive force from a source within the variable swash plate compressor  10 . A control surface element  24  is affixed to the drive shaft  22  and rotates in unison with the drive shaft  22 . A pivot element  26  is affixed to the control surface element  24  and travels in a path radially around the axis of the drive shaft  22 . FIGS. 3A and 3B illustrate the assembly of the drive shaft  22 , the control surface  24  and the pivot element  26 . Alternatively, the drive shaft  22 , the control surface element  24 , and the pivot element  26  may all be formed as a single element. 
     As the drive shaft  22  rotates, it imparts a drive force through the control surface  24  and the pivot element  26  to a swash plate  28 . The swash plate  28  is formed with a bore  30  in which the control surface element  24  sits. The swash plate  28  is additionally formed with a pocket  32  in which the pivot element  26  sits. FIGS. 4A and 4B illustrate the swash plate  28 , the bore  30  and the pocket  32 . Through the bore  30  and the pocket  32 , the rotational drive of the drive shaft  22  is imparted to the swash plate  28 . The pocket  32  is preferably formed in the center plane of the swash plate  28  such that the drive imparted to the swash plate  28  is primarily rotational and such that stresses within the swash plate  28  are minimized. 
     The swash plate  28  is connected to the compression piston  18  through the use of a ball joint  36  located within a generally c-shaped opening  38  in the compression piston  18 . The ball joint  36  prevents the majority of the rotational drive force of the swash plate  28  from being transmitted to the compression piston  18 . When the swash plate  28  is positioned at an angle β from a position perpendicular to the drive shaft  22 , it moves the compression piston  18  axially within the pumping chamber  16  as the swash plate  28  rotates with the drive shaft  22 . As the angle β is increased the travel path of the compression piston  18  is increased and the pumping capacity of the variable swash plate compressor  10  is increased. As the angle β approaches zero and the swash plate  28  becomes approximately perpendicular to the drive shaft  22 , the output of the variable swash plate compressor  10  is minimized (see FIG.  5 ). 
     The angle β of the swash plate  28  is increased by pivoting the swash plate  28  about the pivot element  26  (see FIG.  6 ). The pocket  32  located within the swash plate  28  and the pivot element  26  are shaped such that the swash plate  28  pivots about the pivot element tip  39 . The pivot element tip  39  is positioned at a distance from the axial center of the drive shaft  22  approximately equal to the distance from the axial center of the compression piston  18  to the axial center of the drive shaft  22 . The allows variations in the top-dead-center (“TDC”) of the compression piston  18  to be minimized at all angles β of the swash plate  28 . Minimization of TDC variations allows for greater control of the variable swash plate compressor  10  output. 
     The angle β of the swash plate  28  is varied through the use of a fulcrum piston assembly  40 . The fulcrum piston assembly is comprised of a fulcrum element  41  and a control piston  42 . The fulcrum element  41  is connected to the control piston  42  through the use of thrust bearings  44  to allow the fulcrum element  41  to rotate with the drive shaft  22 . Fluid pressure in the output chamber  46  controls the position of the fulcrum piston assembly  40  and subsequently the angle β. The output chamber  46  remains in fluid communication with the bottom outlet  20 B. A control valve  48 , through a connection  49  with the output chamber  46 , increases the pressure in the output chamber  46  during periods where increased compressor capacity is required. During periods where it is desirable for the compressor to remain idle, the control valve  48  allows the fluid pressure in the output chamber  46  to drop and the fulcrum piston assembly  40  drops allowing the swash plate  28  to position itself nearly perpendicular to the drive shaft  22 . The advantage of using this pressure controlled system for adjusting the angle β of the swash plate  28 , as opposed to using known spring biased or crackcase pressure designs, is that the fulcrum piston assembly  40  acts as a damper to minimize vibrations in the rotating swash plate  28 . In another embodiment, the control valve  48  may also be used to allow a bleed line, with a bleed input  50  and a bleed output  52 , to allow portions of fluid from either the top inlet  14 A or the bottom inlet  14 B to be in fluid communication with the crankcase  54 . This allows moving parts within the crankcase  54  to be cooled and lubricated. 
     Although the present embodiment was described with a single compression piston  18 , multiple compression pistons may be used in the variable swash plate compressor  10 . One embodiment makes use of five compression pistons. 
     While particular embodiments of the invention have been shown and described, numerous variations and alternate embodiments will occur to those skilled in the art. Accordingly, it is intended that the invention be limited only in terms of the appended claims.