Patent Publication Number: US-6990889-B2

Title: Swash plate drive system

Description:
TECHNICAL FIELD 
   This invention relates to swash plate drive apparatus. The invention is applicable, for example, for use in compressors. However, the invention can be utilized in and with equipment other than compressors. 
   BACKGROUND OF THE INVENTION 
   The use of swash plates in compressors and other types of equipment is well known. Swash plates convert rotary motion into reciprocating motion imparted to pistons or other members. 
   In conventional swash plate arrangements, it is standard practice to provide structure preventing rotation of the swash plate and provide mechanical linkages, such as connector rods, between the non-rotating swash plate and pistons or other reciprocating members actuated thereby. Such arrangements produce wear and metal fatigue in the swash plate and associated structure. 
   DISCLOSURE OF INVENTION 
   The present invention relates to a unique approach for converting rotary motion into reciprocating motion. The arrangement eliminates the need for an anti-rotation means for the swash plate, allowing different locations on the contact surface of the swash plate to be engaged during operation. This greatly reduces wear and metal fatigue at the contact points. Also, the apparatus of the present invention eliminates the need for a connecting rod or other interconnecting structure between the swash plate and reciprocating members at fixed locations thereon. 
   The invention relates to a combination of structural elements including a housing defining a housing interior. 
   A swash plate drive shaft is disposed within the housing interior and rotatably mounted relative to the housing about an axis of rotation. 
   A swash plate is mounted on the swash plate drive shaft and angularly disposed relative to the axis of rotation, the swash plate being located in the housing interior. The swash plate has an outer swash plate portion surrounding the swash plate drive shaft and generally freely rotatably moveable about and relative to the swash plate drive shaft. The outer swash plate portion has a contact surface. 
   The apparatus also includes a plurality of spaced reciprocating members mounted for reciprocatable axial movement relative to the housing and engaging the contact surface of the outer swash plate portion. The locations of contact between the contact surface and the reciprocating members changes when the outer swash plate portion rotates about the swash plate drive shaft. 
   The swash plate comprises a ball bearing assembly, the outer swash plate portion comprising an outer race of the ball bearing assembly. 
   Other features, advantages and objects of the present invention will become apparent with reference to the following description and accompanying drawings. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a perspective view of an air compressor incorporating the present invention; 
       FIG. 2  is an exploded, perspective view illustrating selected components of the compressor, including a housing, a swash plate drive shaft, a swash plate and one reciprocating member to be actuated by the swash plate; 
       FIGS. 3A and 3B  are sectional views taken along the line  3 — 3  in  FIG. 1  and illustrating selected components of the invention in alternative relative positions assumed thereby during operation of the compressor; and 
       FIG. 4  is a greatly enlarged, cross-sectional view illustrating an upper portion of the compressor housing, a swash plate drive shaft, a swash plate constructed in accordance with the teachings of the present invention mounted on the swash plate drive shaft and reciprocating members mounted for axial reciprocatable movement relative to the housing and engaged by the swash plate. 
   

   BEST MODE FOR CARRYING OUT THE INVENTION 
   Referring now to the drawings, an air compressor  10  incorporating the present invention is illustrated, the compressor having a housing  12  defining a housing interior  14 . 
   A swash plate drive shaft  20  is disposed in the housing interior and rotatably mounted relative to the housing by a motor of the compressor about an axis of rotation A (see  FIG. 4 ). A portion  22  of the drive shaft is canted, i.e. angularly oriented relative to axis of rotation A. Bearings such as ball bearing  24  are disposed about the drive shaft to rotatably support the drive shaft relative to the compressor housing. 
   A swash plate  30  in the form of a ball bearing assembly is mounted on the swash plate drive shaft and angularly disposed relative to axis of rotation A, the swash plate being located in housing interior  14 . 
   The outer swash plate portion of the ball bearing assembly comprising the swash plate is in the form of an outer ball bearing assembly race  32 . The ball bearing assembly further includes an inner race  36  and ball bearings  40  disposed between the inner race and the outer race. The inner race is fixedly secured to drive shaft portion  22  and the outer race  32  is freely rotatably moveable about and relative to the swash plate drive shaft  20 . 
   The outer race or swash plate portion  32  has two substantially planar contact surfaces  42 ,  44  which are substantially parallel to one another. 
   The outer race  32  also has a convexly curved outer peripheral wall  50  adjacent to and extending between contact surfaces  42 ,  44 . The convexly curved outer peripheral wall  50  comprises a segment of an imaginary sphere. 
   The illustrated compressor also includes spaced reciprocating members. Two such members  52 ,  54  are illustrated. The reciprocating members are in the form of pistons, the topmost portions thereof (as viewed in the drawings) being of different diameters. In swash plate compressors per se, the feature of pistons having different diameters is commonplace and conventional, the pistons slidably positioned for reciprocatable movement in bores of corresponding size formed in the compressor housing. Typically, there are three or more such pistons. 
   Typically, pistons or other reciprocating members associated with a conventional swash plate are attached to the swash plate by connector rods or other mechanical linkages and the swash plate is fixed against rotatable movement. As will now be seen, the arrangement of the present invention is substantially different and does not have the drawbacks and disadvantages discussed above found in conventional arrangements. 
   In the present invention, the reciprocating members have cavities  70 ,  72  receiving the outer race. These cavities are respectively defined by concavely curved cavity walls  74 ,  76  of the reciprocating members or pistons. The concavely curved cavity walls  74 ,  76  and the convexly curved outer peripheral wall  50  of the outer race conform in shape. The peripheral wall  50  engages the cavity walls  74 ,  76  during all stages of the operation of the apparatus. The outer race  32  has a central diametric axis and the axis of rotation A of the swash plate drive shaft is intersected by the central diametric axis of the outer race substantially at the center of the imaginary sphere of which the convexly curved outer peripheral wall of the outer race comprises a segment. 
   In the arrangement illustrated, the substantially parallel, substantially planar contact surfaces  42 ,  44  are engaged by ball bearings  80  of the reciprocating members projecting into cavities  70 ,  72  and engaging the two substantially planar contact surfaces. 
   As is the case with conventional swash plate arrangements, rotation of the swash plate drive shaft will cause the swash plate to wobble, as illustrated, for example, in  FIGS. 3A ,  3 B. This movement will be translated into reciprocatable axial movement of the pistons relative to the housing. 
   As compared to prior art arrangements, however, the outer race or outer portion of the ball bearing assembly  30  is free to rotate and in fact does so, continuously placing different locations on the contact surfaces of the swash plate into engagement with ball bearings  80 , greatly reducing wear and metal fatigue at the contact points. Furthermore, the unique interconnection between the swash plate and the reciprocating members eliminates the need for a connecting rod between the swash plate and reciprocating members at fixed locations thereon and the associated connector rod bearings.