Patent Publication Number: US-6705841-B2

Title: Variable displacement compressor with stepped shaft

Description:
BACKGROUND OF INVENTION 
     1. Technical Field of the Invention 
     The present invention generally relates to a variable displacement compressor having a swash-ring construction. More specifically, the present invention relates to a variable displacement swash-ring compressor having a stepped shaft. 
     2. Description of the Prior Art 
     In an automotive vehicle equipped with air conditioning, a compressor is used to pump coolant through the air conditioning system to cool the vehicle. Most often, the compressor is driven by a serpentine belt of the vehicle and, hence, the speed of the compressor is controlled by the speed of the vehicle. In order to provide consistent operation of the air conditioning system, variable displacement compressors have been developed to allow the compressor to provide constant performance at all vehicle speeds. In a variable displacement compressor, higher displacement is necessary when the vehicle is idling or running at low speeds. When the vehicle is running at high speeds, the compressor is cycling much more rapidly, and therefore can provide equivalent performance at a lower displacement. 
     The typical automotive air conditioning compressor uses multiple pistons to pump the coolant through the system. The pistons are driven back and forth within the compressor by a plate or ring that is attached to a rotating shaft. The plate or ring is mounted at an angle relative to the shaft and engages each of the pistons. Due to the angle of the ring, radial positions around a periphery of the ring have varying axial positions within the compressor. The pistons are fixed radially within the compressor housing, so that as the shaft and ring rotate the pistons slide along the periphery of the ring and are thereby moved axially back and forth with rotations of the shaft and ring. Variable displacement is achieved by limiting the stroke of the pistons. Variable displacement compressors are available in three basic types: 1) wobble plate compressors, 2) swash-plate compressors, or 3) swash-ring compressors. The present invention is related to a swash-ring compressor. 
     In a swash-ring compressor, the pistons within the compressor are driven by a swash-ring. Variable displacement, by limiting the stoke of the pistons, is achieved by varying the angle of the swash-ring relative to the rotating shaft. U.S. Pat. No. 6,164,252 describes the construction of a variable displacement swash-ring compressor and is hereby incorporated by reference into the present application. 
     In the &#39;252 patent, a sleeve is slidably mounted for limited axial movement along the compressor&#39;s shaft and a swash-ring is pivotally mounted onto the sleeve. A pin, rigidly mounted within and extending from the shaft, engages the swash-ring at an axial distance from the pivotal connection between the swash-ring and the sleeve. As the sleeve slides along the shaft, the swash-ring moves axially with the sleeve at the pivotal connection, but cannot move axially at the point where the pin engages the swash-ring. This causes the swash-ring to pivot about the point where the pin engages the swash-ring, thereby changing the angle of the swash-ring relative to the shaft. 
     As a result of the pin transferring rotation to the swash-ring, the pin undergoes very high stresses that require the diameter of the shaft to be large enough to provide sufficient strength to support the pin. Specifically, the shaft is provided with a constant diameter over the entire length along which the sleeve slides. This makes the shaft very heavy and forces other components within the compressor to be designed around the large diameter of the shaft. 
     As seen from the above, there is a need to improve the design of a shaft for a compressor so that the compressor can be made lighter and more compact. 
     It is therefore an object of the present invention to provide an improved variable displacement compressor of lighter weight and more compact construction. 
     A further object of the present invention is to provide a variable displacement compressor having a stepped shaft which will reduce the size and weight of the shaft, as well as allowing other compressor components to be designed smaller and lighter. 
     SUMMARY OF THE INVENTION 
     The disadvantages of the prior art are overcome by providing a variable displacement swash-ring compressor with a stepped shaft. Use of the stepped shaft reduces the size and weight of the shaft, and therefore the compressor itself, as well as allowing other compressor components to be designed smaller and lighter. 
     In one aspect, the present invention is a compressor that includes a shaft rotatably mounted within the compressor. A sleeve is slidably supported on the shaft and includes collar portions, at opposite ends thereof, that support the sleeve on the shaft. A swash-ring is pivotally mounted onto the sleeve such that the swash-ring is angularly adjustable with respect to the shaft. A pin is fixedly mounted to and extends from the shaft and a distal end of the pin pivotally engages the swash-ring. The connection between the swash-ring and the pin forces the swash-ring to rotate with the shaft, while allowing the swash-ring to be angularly adjusted relative to the shaft. 
     The shaft includes a step adjacent the pin, defining a reduced diameter portion on the shaft and end thereof. By way of this step and reduced diameter portion, an annular gap is formed between the shaft and the inner diameter of the sleeve where the sleeve overlies the reduced diameter portion of the shaft. The annular gap therefore extends along a portion of the sleeve between the first and second collar portions. The sleeve is further biased along the shaft by a spring whose position may be varied. 
     In another aspect of the present invention, the shaft includes a pair of steps, with each of the steps being located on opposing sides of the pin. 
     Further variations on the invention include various locations for the spring and for a positive stop for the sleeve. The positive stop can be defined by the step within the shaft, or, the shaft may include a snap ring groove with a snap ring engaged therein to define a positive stop for the sleeve. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of a prior art swash-ring compressor; 
     FIG. 2 is a perspective view of the shaft, swash-ring and sleeve of the compressor of FIG. 1; 
     FIG. 3 is a sectional view of a first preferred embodiment of the present invention wherein the shaft includes a single step; 
     FIG. 4 is a sectional view of a variation of the first preferred embodiment seen in FIG. 3, wherein a spring is positioned within a gap formed between the sleeve and the shaft adjacent the step; 
     FIG. 5 is a sectional view of another preferred embodiment including a single step; 
     FIG. 6 is a sectional view of a variation of the preferred embodiment seen in FIG. 5 wherein a spring is positioned within a gap formed adjacent the step, between the sleeve and the shaft; 
     FIG. 7 is a sectional view of yet another preferred embodiment of the present invention wherein the shaft includes a pair of steps; 
     FIG. 8 is a sectional view of a variation of the preferred embodiment seen in FIG. 7 wherein a spring is positioned within a gap formed adjacent the step between the sleeve and the shaft, and the shaft includes a snap ring and a spring washer to provide a positive stop for the sleeve; 
     FIG. 9 is a sectional view of another variation, similar to FIG. 8, wherein a spring is positioned within a gap formed adjacent the step, between the sleeve and the shaft and a positive stop is defined by one of the steps; 
     FIG. 10 is a sectional view of a preferred embodiment having a shortened shafts; 
     FIG. 11 is a perspective view of a shaft and swash-ring of the present invention; and 
     FIG. 12 is a sectional view taken along line  12 — 12  of FIG.  11 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1 and 2, a prior art variable displacement piston compressor is shown therein and generally designated at  10 . The variable displacement compressor  10  is a swash-ring type compressor having a rotating driven shaft  12  with a swash-ring  14  supported thereon. A sleeve  15  is slidable along the shaft  12  and is pivotally connected to the swash-ring  14 . By sliding the sleeve  15  along the shaft  12 , the angle of the swash-ring  14  is varied. A complete description of the variable displacement swash-ring compressor is found in U.S. Pat. No. 6,164,252 which has been incorporated by reference into the present application. 
     Referring now to FIG. 3, a variable displacement piston compressor of the present invention is shown generally at  16 . Just as the compressor  10  shown in FIG. 1, the compressor  16  of the present invention includes a driven shaft  18  having a first end  20  and a second end  22 . The first and second ends  20 ,  22  of the shaft  18  are supported within a compressor housing  21  by bearing elements  23 . The shaft  18  is adapted for rotational movement within the compressor housing  21 . Typically, the shaft  18  will have a pulley (not shown) mounted to one of the ends  20 ,  22 . The pulley engages a serpentine belt of an automotive vehicle, although, the concepts of the present invention would work on a compressor where the shaft  18  is driven by other means. 
     A sleeve  30  is slidably supported on the shaft  18  and includes a first collar portion  32  and a second collar portion  34  at opposing ends thereof. The first and second collar portions  32 ,  34  support the sleeve on the shaft  18 . The shaft  18  further includes a stepped profile defining a reduced diameter portion  35 . Where the sleeve  30  overlies the reduced diameter portion  35 , an annular gap  38  is formed between an inner diameter of the sleeve  30  and the shaft  18 . A spring  36  is mounted on the shaft  18  to bias the sleeve  30  along the shaft  18  for adjustment purposes of a swash-ring  24  further discussed below. The spring  36  can be positioned between one of the collar portions  32 ,  34  of the sleeve  30  and a structural portion of the compressor  16 , or the spring  36  can be positioned within the gap  38 . 
     The swash-ring  24  is pivotally mounted onto the sleeve  30 . The swash-ring  24  is supported on the sleeve  30  by a pair of bearing pins  31 . The bearing pins  31  are axially aligned with one another and extend radially outward from diametrically opposed sides of the sleeve  30 . The bearing pins  31  pivotally engage the swash-ring  24  wherein the swash-ring  24  is pivotable about an axis  33  running longitudinally through the bearing pins  31  and through the shaft  18 . The pivotal connection between the swash-ring  24  and the sleeve  30  allows the angle of the swash-ring  24  relative to the shaft  18  to be adjusted. 
     A pin  26  is mounted within and extends from the shaft  18 . The swash-ring includes a radially inwardly open pocket  37 . A distal end  28  of the pin  26  pivotally engages the radially inwardly open pocket  37  such that the swash-ring  24  is allowed to pivot about the distal end  28  of the pin  26 . However, the connection between the distal end  28  of the pin  26  and the swash-ring  24  forces the swash-ring  24  to rotate with the shaft  18 . 
     In one embodiment, the shaft  18  includes a step  40  adjacent to the pin  26  and toward one of the first and second ends  20 ,  22  of the shaft  18 . The step  40  formed within the shaft  18  allows the diameter of the shaft  18  to remain large enough at and near the pin  26  to provide sufficient strength to support the pin  26 . The diameter of portions  35  of the shaft  18  not immediately adjacent the pin  26  is reduced, thereby reducing the weight of the shaft  18  and allowing other components, which are designed around the shaft  18 , to be made smaller. The advantages of the present invention include lightening the compressor  16  as well as allowing a reduction of the overall size of the compressor  16 . 
     In the first preferred embodiment, seen in FIG. 3, the shaft  18  includes a single step  40  that is adjacent the pin  26  toward the first end  20  of the shaft  18 . A spring  36  is positioned about the shaft  18  between the sleeve  30  and a structural component  41  of the compressor  16 . Preferably, the shaft  18  includes a stop  42  to provide a positive stop for the sleeve  30 . For the stop  42 , the shaft  18  can include a snap ring groove  44  having a snap ring  46  disposed therein defining the stop  42 . The stop  42  can be defined by the step  40  within the shaft  18 . Alternatively, in either case, a spring washer  48  is positioned against the stop  42  to buffer contact between the sleeve  30  and the stop  42 . 
     In FIG. 3, the snap ring  46  mounted onto the shaft  18  toward the second end  22  of the shaft  18  defines the stop  42 . Additionally, the first collar portion  32  of the sleeve  30  is larger than the second collar portion  34  of the sleeve  30  due to the smaller diameter of the shaft  18  toward the first end  20 . This allows the sleeve  30  to slide evenly along the shaft  18  with the step  40  located between the first and second collar portions  32 ,  34 . Referring to FIG. 4, the spring  36  is seen located in an alternate position, within the gap  38  between the first collar portion  32  and the step  40 . 
     A second preferred embodiment includes a single step  40  which is adjacent the pin  26  and toward the second end  22  of the shaft  18 . Referring to FIG. 5, the spring  36  is positioned between the sleeve  30  and a structural component  41  of the compressor  16  and the stop  42  is provided by a snap ring  46  mounted to the shaft  18  in the reduced diameter portion  35  of the shaft  18 . In this construction, the second collar portion  34  of the sleeve  30  is larger than the first collar portion  32  of the sleeve  30  due to the smaller diameter of the shaft  18  toward the second end  20 . This allows the sleeve  30  to slide evenly along the shaft  18  with the step  40  located between the first and second collar portions  32 ,  34 . 
     As seen in FIG. 6, the spring  36  is alternatively mounted within the gap  38  between the second collar portion  34  of the sleeve  30  and the step  40 . 
     In another embodiment, the shaft  18  can include a pair of steps  40   a ,  40   b  with one of the steps  40   a ,  40   b  being positioned adjacent the pin  26  and toward each of the first and second ends  20 ,  22  of the shaft  18 . An embodiment of this variety is shown in FIG.  7 . The spring  36  is positioned between the sleeve  30  and a structural component  41  of the compressor  16 , just as the first preferred embodiment shown in FIG.  3 . The stop  42  of this embodiment, however, is defined by the step  40   a  within the shaft  18  and the spring washer  48  rests against the face of the step  40   a . The length of sleeve  30  is formed such that the second collar portion  34  of the sleeve  30  will not extend beyond the step  40   b  when the sleeve  30  moved. As in prior embodiments first collar portion  32  is larger than the second collar portion  34 . 
     In a first variation of the embodiment seen in FIG. 7, the second collar portion  34  does extend beyond the step  40   b , therefore the second collar portion  34  also has a size to allow the sleeve  30  to slide along the smaller diameter shaft  18 , as shown in FIG.  8 . The spring  36  in this variation is placed within the gap  38  between the step  40   b  and the second collar portion  34 . The stop  42  is defined by a snap ring  46  with a spring washer  48  adjacent thereto. The stop  42  could also be defined by the step  40   a  toward the first end  20  as shown in FIG.  9 . 
     FIG. 10 illustrates a further embodiment wherein the bearings  50  which support the shaft  18  within the compressor  16  are moved toward the pin  26  such that the overall length of the shaft  18  can be reduced. This configuration having a shortened shaft  18  could be utilized with any of the previously discussed preferred embodiments. 
     The foregoing discussion discloses and describes three preferred embodiments, and variations thereof, of the present invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that changes and modifications can be made to the invention without departing from the true spirit and fair scope of the invention as defined in the following claims. The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation.