Patent Publication Number: US-6212995-B1

Title: Variable-displacement inclined plate compressor

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a variable-displacement inclined plate compressor, and, more specifically, to a variable-displacement inclined plate compressor with an improved structure of cylinder bores of a cylinder block suitable, for use in a refrigerating cycle of an air conditioner for vehicles. 
     2. Description of Related Art 
     Variable-displacement inclined plate compressors are known in the art. A known structure of a variable-displacement inclined plate compressor is constructed as depicted in FIG. 4, and such a compressor structure is disclosed, for example, in JP-A-7-91366. In FIG. 4, front housing  2  is connected to the front side of cylinder block  1 , and rear housing  3  is connected to the rear side of cylinder block  1  via valve plate  4 . A crank chamber  5  is defined by cylinder block  1  and front housing  2 . A drive shaft  6 , extending in its axial direction X, is disposed in crank chamber  5 . Drive shaft  6  is rotatably supported by bearings  7   a  and  7   b . Cylinder bores  8  are defined in cylinder block  1  around a central bore  41 , into which one end of drive shaft  6  is inserted. Pistons  9  are slidably inserted into the respective cylinder bores  8 . 
     Rotor  10  is fixed onto drive shaft  6  in crank chamber  5 . Rotor  10  rotates synchronously with the rotation of drive shaft  6 . Rotor  10  is rotatably supported by bearing  7   c  relative to front housing  2 . Inclined plate  11  is provided around drive shaft  6  at a rear side of rotor  10  in crank chamber  5 . Drive shaft  6  is inserted into a through hole  20  defined at the center of inclined plate  11 . Supporting portion  20   a  is formed in through hole  20 . Inclined plate  11  is supported on drive shaft  6  via supporting portion  20   a , so that inclined plate  11  may be slid along axial direction X of drive shaft  6  and rotated synchronously with the rotation of drive shaft  6 . Spring  12  is interposed between rotor  10  and inclined plate  11 . Spring  12  urges inclined plate  11  in the direction toward rear housing  3 . 
     Semi-spherical shoe  14  is provided between the radially outer portion of inclined plate  11  and each piston  9 . Shoe  14  connects inclined plate  11  and each piston  9  by the slidable engagement of shoe  14  with the side surfaces of inclined plate  11  and the spherical inner surface of each piston  9 . Thus, respective pistons  9 , slidably engaged with inclined plate  11  via respective shoes  14 , may be reciprocally moved in respective cylinder bores  8 . Hinge mechanism K is provided on the front side of inclined plate  11 . Hinge mechanism K has a pair of brackets  15  positioned at both sides of top dead center position T of inclined plate  11 . A first end of guide pin  16  is fixed to each bracket  15 , and a second end of guide pin  16  is formed as a spherical portion  16   a.    
     A pair of supporting arms  17  are provided on rotor  10 , so that each supporting arm  17  slidably engages corresponding guide pin  16 . These supporting arms  17  form the remaining part of hinge mechanism K. Guide hole  17   a  is defined on the tip portion of each supporting arm  17 . Guide hole  17   a  extends in parallel to a plane defined by axis X of drive shaft  6  and top dead center position T of inclined plate  11 , and extends straight in a direction approaching from radially outside of axis X of drive shaft  6 . The axial directions of respective guide holes  17   a  are set, so that top dead center position T of piston  9  does not vary significantly in the front/rear direction despite the inclination of inclined plate  11 . Respective spherical portions  16   a  of respective guide pins  16  are inserted rotatably and slidably into respective guide holes  17   a.    
     When spring  12  is at its maximum extension, rear end recess  11   b  of inclined plate  11 , which is formed at the rear end of through hole  20 , comes into contact with C-clip  13  engaged on drive shaft  6 . By this contact, inclined plate  11  is restricted from further movement in an inclination angle decreasing direction. When spring  12  is fully contracted, front end surface  11   a  of inclined plate  11 , which is formed at the lower front side surface of inclined plate  11  as an inclined surface, comes into contact with rear end surface  10   a  of rotor  10 . By this contact, inclined plate  11  is restricted from further movement in an inclination angle increasing direction. 
     The interior of rear housing  3  is divided into suction chamber  30  and discharge chamber  31 . Suction port  32  and discharge port  33  are opened on valve plate  4  in correspondence with each cylinder bore  8 . A compression chamber, formed between valve plate  4  and piston  9 , may communicate with suction chamber  30  and discharge chamber  31  via suction port  32  and discharge port  33 . A control valve (not shown) is provided on each suction port  32  to control the opening and closing of suction port  32 . A control valve (not shown) is provided also on each discharge port  33  to control the opening and closing of discharge port  33 . The opening operation of the control valve for discharge port  33  is restricted by retainer  34 . Further, a pressure control valve (not shown) is provided between suction chamber  30  and crank chamber  5  to control the pressure in crank chamber  5 . 
     In such a variable-displacement inclined plate compressor, when inclined plate  11  rotates in accompaniment with the rotation of drive shaft  6 , the driving force is transmitted to each piston  9  via each shoe  14 , and each piston  9  reciprocally moves in each cylinder bore  8 . By the reciprocal motion of each piston  9 , gas, for example, refrigerant gas, is sucked from suction chamber  30  into a compression chamber through suction port  32 . The gas is compressed in the compression chamber. The compressed gas is discharged into discharge chamber  31  through discharge port  33 . During this operation, the volume of the compressed gas discharged into discharge chamber  31  is controlled by the controlling pressure in crank chamber  5  due to the pressure control valve. 
     When the above-described compressor is assembled, in order to facilitate the insertion of piston  9  and piston rings attached thereon into cylinder bore  8  of cylinder block  1 , generally front edge  1   b  of cylinder bore  8  may be chamfered as a straight-line tapered, chamfered portion. However, in such a straight-line tapered, chamfered portion, the end of the tapered, chamfered portion and a connecting portion of a cylinder liner may be formed as a relatively sharp corner portion. If such a corner portion exists, the sliding resistance of piston  9  against a radial pressing force, generated particularly when piston  9  moves from the bottom dead center position toward the top dead center position, may increase. Such an increase of the sliding resistance of piston  9  may result in the generation of scratches on the surface of the coating of piston  9 . Further, an excessive load caused by the sliding resistance of piston  9  may adversely affect the control of the inclination of inclined plate  11 , thereby reducing the durability of inclined plate  11 . 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide an improved structure for a variable-displacement inclined plate compressor that may decrease the sliding resistance of a piston, generated in accompaniment with the reciprocating motion of the piston, and may prevent the piston coating from being scratched, thereby smoothly controlling the inclination angle of an inclined plate by a reduced load. 
     To achieve the foregoing and other objects, a variable-displacement inclined plate compressor according to the present invention is herein provided. The variable-displacement inclined plate compressor includes a crank chamber defined by a cylinder block and a front housing connected to the cylinder block. The cylinder block has a central bore, into which a drive shaft is inserted, and a plurality of cylinder bores defined around the central bore and opening toward the crank chamber. The compressor further comprises an edge formed on each cylinder bore and extending circumferentially around the cylinder bore at a crank chamber-side axial end of the cylinder bore. The edge is formed as a rounded surface. Particularly, the edge may be formed as a convex surface in its cross section. 
     The rounded edge may be formed on a circumferential portion of the cylinder bore, preferably except at the connecting portion of the cylinder block with the front housing. Further, the rounded edge preferably has a predetermined radius of curvature. Desired relationships between the radius of curvature, an radial width, and an axial length of the rounded edge will be described later. 
     In the variable-displacement inclined plate compressor, because the edge of each cylinder bore at the crank chamber-side axial end of the cylinder bore is formed as a rounded surface, i.e., a rounded corner, the sliding resistance of the piston against a radial pressing force, which is generated when the piston moves from the bottom dead center position toward the top dead center position, may decrease. By reducing the sliding resistance, scratching the piston coating may be avoided. Moreover, the decreased sliding resistance may reduce the load on the compressor. The reduced load may achieve a smooth control of the inclination angle of the inclined plate. Consequently, the heating value and the consumed power of the compressor may decrease, and the durability of the compressor may increase. Further, the ease of assembly of the pistons into the cylinder bores also may be ensured by the improved structure of the rounded surface edges. 
     Further objects, features, and advantages of the present invention will be understood from the following detailed description of a preferred embodiment of the present invention with reference to the accompanying figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An embodiment of the invention is now described with reference to the accompanying figures, which is given by way of example only, and is not intended to limit the present invention. 
     FIG. 1 is a vertical, cross-sectional view of a variable-displacement inclined plate compressor according to an embodiment of the present invention. 
     FIG. 2A is a partial, elevational view of a cylinder block and a front housing of the compressor depicted in FIG. 1, as viewed along line C—C of FIG. 1 with the pistons removed. 
     FIG. 2B is a partial, cross-sectional view of the cylinder block and the front housing of the compressor depicted in FIG. 2A, as viewed along line A—A of FIG.  2 A. 
     FIG. 2C is a partial, cross-sectional view of the cylinder block and the front housing of the compressor depicted in FIG. 2A, as viewed along line B—B of FIG.  2 A. 
     FIG. 3 is a comparison view showing schematic plan views of a cylinder bore according to the present invention (FIG. 3-3) and known cylinder bores (FIGS. 3-1 and  3 - 2 ). 
     FIG. 4 is a vertical, cross-sectional view of a known variable-displacement inclined plate compressor. 
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
     Referring to FIGS. 1 and 2, a variable-displacement inclined plate compressor according to an embodiment of the present invention is provided. In FIG. 1, the structure of cylinder bore  8   b  having crank chamber-side edge la defined in cylinder block  1  is different from that of cylinder bore  8  having crank chamber-side edge  1   b  depicted in FIG.  4 . The structures of the other portions basically are the same as those of the known compressor depicted in FIG.  4 . Therefore, the explanation of the other portions is omitted by providing the same labels to the other portions of FIG. 1, as those depicted in FIG.  4 . 
     In this compressor, a plurality of cylinder bores  8   b  are defined in cylinder block  1  around central bore  41 . One end portion of drive shaft  6  is inserted into central bore  41 . Crank chamber  5  is defined by cylinder block  1  and front housing  2 . Edge  1   a  of each cylinder bore  8   b  extends circumferentially around the cylinder bore  8   b  at a crank chamber-side axial end of the cylinder bore  8   b . Edge  1   a  of each cylinder bore  8   b  is adjacent to crank chamber  5 . Each edge  1   a  is formed as a rounded surface forming a rounded corner. 
     FIGS. 2A-2C depict the configuration of cylinder bore  8   b  and rounded edge  1   a . As depicted in FIGS. 2B and 2C, edge  1   a  is formed as a rounded surface on a circumferential portion of edge  1   a  except a connecting portion  1   c  of cylinder block  1  with front housing  2 . In other words, edge  1   a  formed as a rounded surface extends in a circumferential direction almost over its entire length, except for connecting portion  1   c.    
     FIG. 3 depicts the configuration of cylinder bore  8   b  as compared to the configurations of known cylinder bores  8  and  8   a . In known cylinder bore  8  depicted in FIG. 3-1, crank chamber-side edge  1   b  of cylinder bore  8  is formed as a straight-line tapered, chamfered portion. The straight-line tapered, chamfered portion has a radial width “a” to facilitate insertion of piston  9  into cylinder bore  8  during assembly of the compressor. In this structure, however, the end of the tapered, chamfered portion and a connecting portion of a cylinder liner (substantially the same portion) is formed as a relatively sharp corner portion. If such a corner portion exists, the sliding resistance of piston  9  against a radial pressing force, generated particularly when piston  9  moves from the bottom dead center position toward the top dead center position, may increase. 
     In known cylinder bore  8   a  depicted in FIG. 3-2, crank chamber-side edge  1   d  of cylinder bore  8   a  is formed as a straight-line tapered, chamfered portion, so that the axial length of the taper chamfered portion is lengthened by Δx as compared with edge  1   b . In this structure, however, the axial length of cylinder bore  8   a  for supporting piston  9  decreases by Δx. Therefore, although the problems originating from the above-described relatively sharp corner portion may be reduced, by the decrease of the supporting length of cylinder bore  8   a  for supporting piston  9 , the inclination of piston  9  within cylinder bore  8   a  may increase. Such a condition may adversely effect control of compression. 
     In the improved structure according to the present invention depicted in FIG. 3-3, crank chamber-side edge  1   a  of cylinder bore  8   b  is formed as a rounded surface convex toward the interior of cylinder bore  8   b  having a predetermined desired radius of curvature “r”. This rounded edge  1   a  is formed within the radial width “a” to facilitate insertion of piston  9  into cylinder bore  8   b  in the assembly of the compressor. The predetermined radius of curvature “r” and the radial width “a” of rounded edge  1   a  preferably satisfy an equation of r≧a. Further, the radial width “a” of rounded edge  1   a  and an axial length “c” of rounded edge  1   a  preferably satisfy an equation of c≧a. Preferably, the radius of curvature “r” is determined such that c≧a is achieved. Thus, in this improved structure, a sharp corner portion is not formed. Because a sharp corner portion is not formed on crank chamber-side edge  1   a  of cylinder bore  8   b , the sliding resistance of piston  9  against a radial pressing force, which is generated when piston  9  moves from the bottom dead center position toward the top dead center position, may decrease. In addition, the reduced sliding resistance may prevent the piston coating from being scratched. Moreover, the decreased sliding resistance may reduce the load on the compressor. The reduced load may achieve a smooth control of the inclination angle of inclined plate  11 . Consequently, the heating value and the consumed power of the compressor may decrease, and the durability of the compressor may increase. 
     Further, because rounded edge  1   a  is formed within the desired radial width “a” without an accompanying decrease in the supporting length for piston  9 , excessive inclination of piston  9  in cylinder bore  8   b  may be avoided, and a desired control of compression may be accomplished. Of course, the ease of assembly of pistons  9  into cylinder bores  8   b  also may be ensured by providing rounded edges  1   a  to respective cylinder bores  8   b.    
     Although only one embodiment of the present invention has been described in detail herein, the scope of the invention is not limited thereto. It will be appreciated by those skilled in the art that various modifications may be made without departing from the scope of the invention. Accordingly, the embodiment disclosed herein is only exemplary. It is to be understood that the scope of the invention is not to be limited thereby, but is to be determined by the claims which follow.