Abstract:
A variable-displacement inclined plate compressor includes a drive shaft, a rotor provided on the drive shaft, and an inclined plate provided around the drive shaft and rotated synchronously with the drive shaft via the rotor. The compressor comprises a cam mechanism provided between the rotor and the inclined plate for controlling an inclination angle of the inclined plate relative to an axis of the drive shaft. The cam mechanism comprises a ball located between the rotor and the inclined plate. The cam mechanism prevents improper assembly and facilitates the efficient management of the assembly. Further, the cam mechanism facilitates the processing of parts and the decrease in the number of parts, thereby reducing the manufacturing cost.

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 for a cam mechanism provided between a rotor and an inclined plate in the compressor. 
     2. Description of Related Art 
     Variable-displacement inclined plate compressors are known in the art. Variable-displacement inclined plate compressors are used, for example, in a refrigerating cycle of an air conditioner for vehicles. A known structure of a variable-displacement inclined plate compressor is constructed as depicted in FIG.  22 . In FIG. 22, variable-displacement inclined plate compressor  100  has cylinder block  103  forming an outline of compressor housing  102 , and front housing  105  closing one end of cylinder block  103 . Cylinder block  103  includes a plurality of cylinder bores  101 . The space enclosed by cylinder block  103  and front housing  105  forms crank chamber  104 . Cylinder head  107  is attached to the other end of cylinder block  103  via valve plate  106 . 
     Drive shaft  110  is provided to extend from the outside of front housing  105  to the inside of cylinder block  103  through boss portion  105   a  of front housing  105  and crank chamber  104 . One end portion of drive shaft  110  is rotatably supported by bearing  108 , which is provided in boss portion  105   a  of front housing  105 . The other end portion of drive shaft  110  is rotatably supported by bearing  109 , which is provided in through hole  103   a  defined in the central portion of cylinder block  103  to extend in the same direction as the axis of drive shaft  110 . Seal member  147  is provided between boss portion  105   a  of front housing  105  and drive shaft  110 . 
     Inclined plate  112  is provided around drive shaft  110  in crank chamber  104 . Inclined plate  112  is slidably provided on drive shaft  110  via cylindrical sleeve  111 , and rotatably attached to sleeve  111  via pin  111   b  and opening  111   a  (FIG.  23 ). Inclined plate  112  is rotated synchronously with drive shaft  110  via rotor  116  attached to drive shaft  110 . Inclined plate  112  is variable in its inclination angle. Wobble plate  113  is provided around inclined plate  112 . Wobble plate  113  is supported by inclined plate  112  via bearings  141  and  142  so that inclined plate  112  can rotate relative to wobble plate  113 . The rotation of wobble plate  113  is prevented by rotation preventing mechanism  150 . Rotation preventing mechanism  150  comprises guide member  144  extending along the axis direction of drive shaft  110  in crank chamber  104 , and engaging member  143  provided on the outer surface of wobble plate  113  for slidably engaging guide member  144 . Spring  146  is provided around drive shaft  110  between inclined plate  112  and cylinder block  103 . The rotational motion of drive shaft  110  is changed to the wobble motion of wobble plate  113  via rotor  116  and inclined plate  112 . 
     Piston  114  is inserted into each cylinder bore  101 . Piston  114  is connected to wobble plate  113  via piston rod  115 . One spherical end portion  115   a  of piston rod  115  is contained in spherical hollow portion  114   a  formed in piston  114 . The other spherical end portion  115   b  of piston rod  115  is contained in spherical hollow portion  113   a  formed on the side surface of wobble plate  113 . 
     Rotor  116  has arm  116   a  extending in a radially outward direction within a plane which includes the axis of drive shaft  110 , and pivot pin  116   b  extending in a direction across the extending direction of arm  116   a . Rotor  116  is rotatably supported on inner wall surface  105   b  of front housing  105  via thrust bearing  145 . Inclined plate  112  has sleeve portion  112   a  projecting toward the side of rotor  116 . Slot  112   b  engaging pivot pin  116   b  is defined in sleeve portion  112   a.    
     Electromagnetic clutch  120  is provided around boss portion  105   a  for transmitting/interrupting a driving force from an external drive source to drive shaft  110 . Electromagnetic clutch  120  comprises electric magnet  123  disposed in pulley  122 , which is provided on boss portion  105   a  via bearing  121 , clutch plate  125  provided to face one end surface of pulley  122 , and fastener  126  for fixing clutch plate  125  to the end of drive shaft  110 . 
     Discharge chamber  132  and suction chamber  133  are defined in cylinder head  107 , respectively, by separating the inside of cylinder head  107 , closed by valve plate  106 , by outer wall  131   a , bottom wall  131   b  and inner wall  131   c . Discharge chamber  132  communicates with discharge port  134 , which is formed on the wall of cylinder head  107 , and discharge port  106   a , which is formed on valve plate  106 . Suction chamber  133  communicates with suction port  135 , which is formed on the wall of cylinder head  107 , and suction port  106   b , which is formed on valve plate  106 . A suction valve (not shown) is provided on suction port  106   b  to cover suction port  106   b . A discharge valve (not shown) and retainer  106   c  are provided on discharge port  106   a  in discharge chamber  132  to cover discharge port  106   a . Control valve  117  is provided between crank chamber  104  and discharge chamber  132 . Pressure control valve  117  adjusts the inclination angle of inclined plate  112  by adjusting the pressure in crank chamber  104 , thereby controlling the stroke of piston  114 . Thus, the displacement of the compressor is controlled by control valve  117 . 
     In such a variable-displacement inclined plate compressor  100 , when drive shaft  110  rotates, rotor  116  rotates. By the rotation of rotor  116 , inclined plate  112  rotates around drive shaft  110 , including wobble movement in a plane containing the axis of drive shaft  110 . The rotational motion including the wobble movement of inclined plate  112  is transformed into the wobble movement of wobble plate  113  in the plane containing the axis of drive shaft  110 . The wobble movement of wobble plate  113  is transformed into the reciprocal movement of piston  114  in a direction along the axis of drive shaft  110  via piston rod  115 . When piston  114  moves from the position depicted in FIG. 22 to a position of the crank chamber side (left side), the fluid is drawn from suction port  135  into cylinder bore  101  through suction chamber  133  and suction port  106   b . Thereafter, when piston  114  moves toward the cylinder head side (right side), the fluid in cylinder bore  101  is compressed. The compressed fluid is discharged from cylinder bore  101  to the outside of the compressor through discharge port  106   a , discharge chamber  132  and discharge port  134 . 
     FIG. 23 depicts an exploded view of the cam mechanism including rotor  116  and inclined plate  112  in compressor  100 . FIG. 24 is a plan view of the assembled cam mechanism depicted in FIG. 23, and FIGS. 25 and 26 are sectional views of the cam mechanism showing the respective operational conditions. 
     As depicted in FIG. 23, rotor  116  is fixed to drive shaft  110 . Pins  111   b  are inserted from the inside of sleeve  111  in the directions opposite to each other as shown by arrows, and inserted into respective holes  112   d , which are defined on the inner surface of through hole  112   c  formed in the central portion of inclined plate  112 . After sleeve  111  is fixed in through hole  112   c  of inclined plate  112 , drive shaft  110  is inserted into sleeve  111 . 
     As depicted in FIGS. 23 and 24, sleeve portion  112   a  of inclined plate  112  is inserted between arm portions  116   a  of rotor  116 . Washers  112   e  are interposed between sleeve portion  112   a  and both arm portions  116   a . Pivot pin  116   b  is inserted through a series of holes, which are formed by holes  116   c  in arm portions  116   a , the holes of washers  112   e  and slot  112   b  in sleeve portion  112   a . Snap rings  116   d  are provided on both end portions of pivot pin  116   b  that project through holes  116   c.    
     In cam mechanism  140  for a variable-displacement inclined plate compressor, inclined plate  112  and rotor  116  are connected by inserting pivot pin  116   b  into slot  112   b  formed in inclined plate  112  and holes  116   c  formed in rotor  116 . Pivot pin  116   b  may be press fitted into the holes for preventing movement, or may be fixed by using snap rings  116   d  after insertion. 
     On the other hand, a cam mechanism, having a reversed positional relationship between the slot and the hole, is also known. In this type of a cam mechanism, a hole is provided in the inclined plate side, and a slot is provided in the rotor side. 
     FIG. 25 depicts a condition of minimum cam angle θ min of cam mechanism  140  depicted in FIG. 24, namely, a condition of a minimum angle between an axis perpendicular to the axis of drive shaft  110  and inclined plate  112 . In this condition, the displacement for compression of variable-displacement inclined plate compressor  100  is minimized. FIG. 26 depicts a condition of maximum cam angle θ max of cam mechanism  140  depicted in FIG. 24, namely, a condition of a maximum angle between an axis perpendicular to the axis of drive shaft  110  and inclined plate  112 . In this condition, the displacement for compression of variable-displacement inclined plate compressor  100  is maximized. 
     Thus, in known cam mechanism  140  for variable-displacement inclined plate compressor  100 , the rotational force is received by the surface contact between arm portions  116   a  of rotor  116  and sleeve portion  112   a  of inclined plate  112 . The reactive force of compression is received by the line contact between the inner surface of slot  112   b  of sleeve portion  112   a  and the outer surface of pivot pin  116   b.    
     In such a known cam mechanism  140 , however, the number of parts, such as the structure for press fitting pivot pin  116   b  or snap rings  116   d , is great, the assembly may be complicated. Therefore, improper assembly may happen. Moreover, efficient management of the parts and the assembly is difficult. 
     Further, a tracer control for machining slot  112   b  is required, and its processing is not simple. Moreover,because of a large number of parts, the cost for processing is expensive. 
     Further, because noise may be created during compression operation resulting from a clearance of the cam in cam mechanism  140 , a shim or an increase in the processing grade of parts is required to prevent such noise. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide an improved structure for a cam mechanism in a variable-displacement inclined plate compressor that prevents improper assembly and facilitates the efficient management of the assembly of the cam mechanism. 
     It is another object of the present invention to provide an improved structure for a cam mechanism in a variable-displacement inclined plate compressor that may facilitate the processing of parts and decrease the number of parts for the cam mechanism, thereby reducing the manufacturing cost. 
     It is a further object of the present invention to provide an improved structure for a cam mechanism in a variable-displacement inclined plate compressor that may absorb a clearance of a cam by a structure without applying a shim or increasing the processing grade of parts, thereby easily reducing a noise generated during compression operation. 
     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 drive shaft, a rotor provided on the drive shaft, and an inclined plate provided around the drive shaft and rotated synchronously with the drive shaft via the rotor. The compressor comprises a cam mechanism provided between the rotor and the inclined plate for controlling an inclination angle of the inclined plate relative to an axis of the drive shaft. The cam mechanism comprises a ball which connects between the rotor and the inclined plate. 
     In the variable-displacement inclined plate compressor, a hole may be defined in one of the rotor and the inclined plate. A groove may be defined in the other of the rotor and the inclined plate. The ball may be contained in the hole and moved along the groove. 
     In the cam mechanism having such hole and groove, the hole may be formed as a semi-spherical hole, and the groove may be formed in a semi-circular cross section. In this structure, a diameter of the semi-circular cross section of the groove is preferred to be slightly larger than a diameter of the ball. Alternatively, the hole may be formed as a cylindrical hole, and the groove may be formed in a rectangular cross section. Further alternatively, the hole may be formed as a conical hole, and the groove may be formed in a triangular cross section. 
     In these cam mechanisms, a lubricating oil hole may be provided in at least one of the hole and the groove. Further, the shapes of the holes and grooves may be combined arbitrarily among the above-described shapes. 
     In the cam mechanism for the variable-displacement inclined plate compressor according to the present invention, the transmission of the driving force and the compression reactive force between the rotor and the inclined plate and the control of the inclination angle of the inclined plate are performed by the cam mechanism formed by the ball, the hole containing the ball, and the groove along which the ball moves. Because it is not necessary to use a pivot pin as in the known cam mechanism, the assembly of the cam mechanism according to the present invention is simpler. Therefore, improper assembly may be prevented. Moreover, the management of the assembly may be efficiently facilitated. 
     Moreover, because the number of parts in the cam mechanism is reduced as compared with that of the known mechanism, processing of the parts may be easily facilitated, and the manufacturing cost is reduced. 
     Further, in the cam mechanism according to the present invention, because the clearance of the cam may be automatically absorbed by the structure and the movement of the ball along the groove, any noise created during compression operation may be reduced. Further, because the ball performs a rolling motion during changing the angle of the cam (i.e., the inclination angle of the inclined plate), resistance may be very small, and the displacement of the compressor is smoothly controlled. 
     Further objects, features, and advantages of the present 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 
     Embodiments of the invention are now described with reference to the accompanying figures, which are given by way of example only, and are not intended to limit the present invention. 
     FIG. 1 is an exploded perspective view of a cam mechanism of a variable-displacement inclined plate compressor according to a first embodiment of the present invention. 
     FIG. 2 is a vertical sectional view of the cam mechanism depicted in FIG. 1, showing an assembling method for the cam mechanism. 
     FIG. 3 is a plan view of the cam mechanism depicted in FIG. 1, showing its assembled state. 
     FIG. 4 is a vertical sectional view of the cam mechanism depicted in FIG. 1, showing an operation of the mechanism. 
     FIG. 5 is a vertical sectional view of the cam mechanism depicted in FIG. 1, showing another operation of the mechanism. 
     FIG. 6 is a sectional view of a part of the cam mechanism depicted in FIG. 1, showing a ball engaging a hole and a groove in an unloaded condition. 
     FIG. 7 is a sectional view of a part of the cam mechanism depicted in FIG. 1, showing a ball engaging a hole and a groove in a loaded condition. 
     FIG. 8 is an exploded plan view of a cam mechanism of a variable-displacement inclined plate compressor according to a second embodiment of the present invention. 
     FIG. 9 is a plan view of the cam mechanism depicted in FIG. 8, showing its assembled state. 
     FIG. 10 is a vertical sectional view of the cam mechanism depicted in FIG. 8, showing an operation of the mechanism. 
     FIG. 11 is a vertical sectional view of the cam mechanism depicted in FIG. 8, showing another operation of the mechanism. 
     FIG. 12 is an exploded plan view of a cam mechanism of a variable-displacement inclined plate compressor according to a third embodiment of the present invention. 
     FIG. 13 is an exploded plan view of a cam mechanism of a variable-displacement inclined plate compressor according to a fourth embodiment of the present invention. 
     FIG. 14 is an exploded plan view of a cam mechanism of a variable-displacement inclined plate compressor according to a fifth embodiment of the present invention. 
     FIG. 15 is a plan view of the cam mechanism depicted in FIG. 14, showing its assembled state. 
     FIG. 16 is an exploded plan view of a cam mechanism of a variable-displacement inclined plate compressor according to a sixth embodiment of the present invention. 
     FIG. 17 is a plan view of the cam mechanism depicted in FIG.  16 , showing its assembled state. 
     FIG. 18 is a vertical sectional view of a cam mechanism according to the present invention, showing the same condition as that depicted in FIG.  10 . 
     FIGS. 19A-19D are cross-sectional views of rotor sides of various cam mechanisms according to the present invention, as viewed along line B—B of FIG.  18 . 
     FIGS. 20A-20D are cross-sectional views of inclined plate sides of various cam mechanisms according to the present invention, as viewed along line B—B of FIG.  18 . 
     FIG. 21 is a cross-sectional view of a cam mechanism of a variable-displacement inclined plate compressor according to a seventh embodiment of the present invention. 
     FIG. 22 is a vertical sectional view of a known variable-displacement inclined plate compressor. 
     FIG. 23 is an exploded perspective view of a cam mechanism of the variable-displacement inclined plate compressor depicted in FIG.  22 . 
     FIG. 24 is a plan view of the cam mechanism depicted in FIG.  23 . 
     FIG. 25 is a vertical sectional view of the cam mechanism depicted in FIG. 24, showing an operation of the mechanism. 
     FIG. 26 is a vertical sectional view of the cam mechanism depicted in FIG. 24, showing another operation of the mechanism. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A variable-displacement inclined plate compressor according to the present invention has a similar structure as that of the known compressor depicted in FIG. 22 except for an improved cam mechanism. Therefore, embodiments of the present invention described below will be explained only as to their respective cam mechanisms. 
     Referring to FIGS. 1-7, a variable-displacement inclined plate compressor according to a first embodiment of the present invention is provided. In FIG. 1, cam mechanism  10  according to a first embodiment of the present invention includes rotor  1  fixed to drive shaft  110 , and inclined plate  2  provided on drive shaft  110  at a position near to rotor  1 . Two arm portions  3  are provided in rotor  1  to extend in the same direction, that is directed at a predetermined angle relative to the axis of drive shaft  110 . Semispherical hole  4  is defined on the outer side surface of the tip portion of each arm portion  3 . A pair of projecting portions  5  are provided on one side surface of inclined plate  2  to extend in the same direction, that is directed at a predetermined angle relative to the axis of drive shaft  110 . A pair of grooves  6 , each having a semicircular cross section, are defined on the inner side surfaces of the respective projecting portions  5 , which face each other. Both grooves  6  extend in the same direction. 
     Referring to FIG. 2, ball  7  is disposed in each hole  4  of each arm portion  3  of rotor  1 . In a state in that drive shaft  110  is inserted into through hole  8  of inclined plate  2 , the portion of each ball  7  protruded from each hole  4  is inserted into each groove  6  from the end of groove  6 . As depicted in FIG. 3, each arm portion  3  and each projecting portion  5  engage each other via each ball  7  disposed in hole  4  and groove  6 . Consequently, rotor  1  and inclined plate  2  engage each other in a direction of the axis of drive shaft  110 . Thus, the assembly of cam mechanism  10  is completed. 
     The operation of cam mechanism  10  will be explained. As depicted in FIG. 4, a snap ring  9  is attached to drive shaft  110  at a state of a minimum cam angle, and snap ring  9  is brought into contact with the side surface of inclined plate  2  opposite to the side surface provided with projecting portions  5 . By this, inclined plate  2  is set at a minimum cam angle θ min by snap ring  9 , and each ball  7  is held in each groove  6  at that position. 
     As depicted in FIG. 5, when the cam angle is at a maximum cam angle θ max, the peripheral surface of drive shaft  110  comes into contact with the inner surface of a part of through hole  8  of inclined plate  2 , thereby regulating the maximum cam angle θ max. Also in this condition, each ball  7  is held in each respective groove  6  at its position near drive shaft  110 . 
     Although inclined plate  2  is supported on drive shaft  110  via through hole  8  having a saddle shape in this first embodiment, a supporting mechanism using a sleeve as depicted in FIG. 22 may be employed. 
     As depicted in FIG. 5, when inclined plate  2  is inclined, ball  7  moves along groove  6  having a semicircular cross section. Therefore, inclined plate  2  is inclined while a cam motion, whose top dead center is determined at a constant position by the position of groove  6  and the supporting of the center portion, is performed. If the diameter of groove  6  having a semicircular cross section and the diameter of hole  4  are set to be slightly larger than the diameter of ball  7 , ball  7  can slightly move even in the fitting condition. Therefore, when cam mechanism  10  receives a rotation force or a compression reactive force, ball  7  may come into close contact with both of inclined plate  2  and rotor  1 . Consequently, a clearance between these members may be well absorbed, and a noise caused by any vibration may be reduced. Thus, the force transmission between rotor  1  and inclined plate  2  may be smoothly performed by the engaging mechanism for inserting ball  7  into both of hole  4  and groove  6 . 
     FIGS. 6 and 7 depict the states of connection between semispherical hole  4  of rotor  1  and semicircular cross-section groove  6  of inclined plate  2 . FIG. 6 depicts an unloaded state, and FIG. 7 depicts a loaded state. 
     Referring to FIG. 6, radius R of semispherical hole  4  and semicircular cross-section groove  6  is set to be slightly larger than radius “r” of ball  7  (R&gt;r). When inclined plate  2  and rotor  1  are connected, a clearance  19  is generated between the inner surfaces of hole  4  and groove  6  and the surface of ball  7 . In this condition, because ball  7  is independent from the respective inner surfaces of hole  4  and groove  6 , ball  7  may freely move in the space formed by hole  4  and groove  6 . 
     Referring to FIG. 7, rotation force Ft shown by arrow  17   a  is applied from the upper side in the figure, and compression reactive force Fp shown by arrow  17   b  is applied from the right side in the Figure. When these two forces Ft and Fp are received, and because ball  7  can move as described above, ball  7  comes into contact with both the hole  4  and groove  6  at portions A shown in the figure. In such a condition, the above-described clearance  19  becomes zero, and at the same time, the resistance decreases. 
     FIGS. 8-11 depict a cam mechanism of a variable-displacement inclined plate compressor according to a second embodiment of the present invention. As depicted in FIG. 8, in this embodiment, although rotor  11  and inclined plate  12  are provided in cam mechanism  20 , the positional relationship between the hole and the groove formed on them is reversed relative to that in the first embodiment. A pair of projecting portions  13  are provided on rotor  11  to extend in the same direction, and grooves  14  are defined on the inner surfaces of projecting portions  13  facing each other. A pair of arm portions  15  are provided on inclined plate  12 , and semispherical holes  16  are defined on the outer side surfaces of respective arm portions  15 . Ball  7  is inserted into each hole  16 . The portion of ball  7  protruded from hole  16  is inserted into groove  14 . Thus, rotor  11  and inclined plate  12  engage each other via balls  7  inserted into respective holes  16  and grooves  14 . FIG. 9 depicts the completed assembly condition. 
     FIG. 10 depicts a condition of minimum cam angle of cam mechanism  20 . In this condition, ball  7  is present at a position near drive shaft  110  in groove  14 . In the central portion of inclined plate  12 , through hole  18  is provided to extend along the axis of drive shaft  110 . Through hole  18  has a first inner surface  18   a , and a second inner surface  18   b  inclined at an acute angle relative to first inner surface  18   a . In the condition depicted in FIG. 10, the minimum cam angle may be regulated by bringing snap ring  19   b  into contact with one side surface of inclined plate  12 . The first inner surface  18   a  is slightly inclined relative to the peripheral surface of drive shaft  110 , because it may be necessary to set the angle of the first inner surface  18   a  smaller than the minimum cam angle for the assembly of rotor  11  and inclined plate  12 . Therefore, this first inner surface  18   a  is not used for the regulation of the cam angle. 
     FIG. 11 depicts a condition of maximum cam angle of cam mechanism  20 . In this condition, ball  7  is present at the farthermost position away from drive shaft  110 . 
     FIG. 12 depicts a cam mechanism of a variable-displacement inclined plate compressor according to a third embodiment of the present invention. In FIG. 12, a single arm portion  23  is provided on rotor  21  of cam mechanism  30 . Grooves  24  each having a semicircular cross section are defined symmetrically on the respective outer side surfaces of portion  23 . A pair of projecting portions  25  are provided on inclined plate  22 . Holes  26 , each having a semispherical shape, are defined symmetrically on the respective inner side surfaces of projecting portions  25 . When cam mechanism  30  is assembled, after balls  7  are inserted into respective holes  26 , the portions of balls  7  that protrude from holes  26  are inserted into respective grooves  24 . Balls  7  engage both of holes  26  and grooves  24 , thereby engaging rotor  21  and inclined plate  22  in the direction of the axis of the drive shaft. In this embodiment, although arm portion  23  of rotor  21  is formed as a single arm portion, the operation may be substantially the same as compared with that in a mechanism having a plurality of arm portions. Therefore, in cam mechanism  30  according to this third embodiment, substantially the same advantages as those in the first and second embodiments may be obtained. 
     FIG. 13 depicts a cam mechanism of a variable-displacement inclined plate compressor according to a fourth embodiment of the present invention. In FIG. 13, cam mechanism  40  includes rotor  31  and inclined plate  32 . A pair of arm portions  33  are provided on rotor  31  to extend in the same direction. Semispherical holes  34  are defined on the inner side surfaces of respective arm portions  33 , which face each other. A single projecting portion  35  is provided on inclined plate  32 . Grooves  36  each having a semicircular cross section are defined on the respective outer side surfaces of projecting portion  35 . When cam mechanism  40  is assembled, after balls  7  are inserted into respective holes  34 , the portions of balls  7  that protrude from holes  34  are inserted into respective grooves  36 . Balls  7  engage both of holes  34  and grooves  36 , thereby engaging rotor  31  and inclined plate  32  in the direction of the axis of the drive shaft. In this embodiment, although projecting portion  35  is formed as a single projecting portion, a plurality of projecting portions may be provided on inclined plate  32 . In cam mechanism  40  according to this fourth embodiment, substantially the same advantages as those in the first through third embodiments may be obtained. 
     FIGS. 14 and 15 depict a cam mechanism of a variable-displacement inclined plate compressor according to a fifth embodiment of the present invention. In FIG. 14, cam mechanism  50  includes rotor  41  and inclined plate  42 . A single arm portion  43  is provided on rotor  41 . Groove  44  having a semicircular cross section is defined on a side surface of arm portion  43 , which is the surface farthest from center axis  47  of rotor  41 . A pair of projecting portions  45  are provided on inclined plate  42  to extend along center axis  47 . Spherical hole  46  is defined on the inner side surface of one of projecting portions  45 . When cam mechanism  50  is assembled, after ball  7  is inserted into hole  46  defined on one of projecting portions  45 , arm portion  43  is inserted between the pair of projecting portions  45  so that the portion of ball  7  protruded from hole  46  is inserted into groove  44 . Ball  7  engages both hole  46  and groove  44 , thereby engaging rotor  41  and inclined plate  42  in the direction of the axis of the drive shaft. Thus, the assembly of cam mechanism  50  is completed as depicted in FIG.  15 . Although arm portion  43  is provided at a position eccentric from center axis  47  and respective projecting portions  45  are provided at nonsymmetric positions relative to center axis  47 , arm portion  43  may be provided at a position of center axis  47  and respective projecting portions  45  may be provided at symmetric positions relative to center axis  47 . In cam mechanism  50  according to this fifth embodiment, substantially the same advantages as those in the first through fourth embodiments may be obtained. 
     FIGS. 16 and 17 depict a cam mechanism of a variable-displacement inclined plate compressor according to a sixth embodiment of the present invention. In FIG. 16, cam mechanism  60  includes rotor  51  and inclined plate  52 . A pair of arm portions  53  are provided on rotor  51 . Through holes  54  are defined on respective arm portions  53  to extend in the same direction at the corresponding positions. Three projecting portions  55  are provided on inclined plate  52 . Grooves  56  each having a semicircular cross section are defined on respective side surfaces of respective projecting portions  55 , which face each other. When cam mechanism  60  is assembled, after balls  7  are inserted into respective through holes  54  defined on respective arm portions  53 , respective projecting portions  55  are moved between arm portions  53  and toward the outside positions of arm portions  53  so that the portions of balls  7  protruded from holes  54  are inserted into grooves  56 . Balls  7  engage both holes  54  and grooves  56 , thereby engaging rotor  51  and inclined plate  52  in the direction of the axis of the drive shaft. Thus, the assembly of cam mechanism  60  is completed as depicted in FIG.  17 . In cam mechanism  60  according to this sixth embodiment, substantially the same advantages as those in the first through fifth embodiments may be obtained. 
     In the above-described embodiments, various shapes for a hole containing a ball and a groove engaging the ball may be employed. FIG. 18 depicts a cam mechanism according to the present invention, and shows the same condition as that depicted in FIG.  10 . FIGS. 19A-19D and FIGS. 20A-20D are cross-sectional views as viewed along line B—B of FIG. 18; FIGS. 19A-19D depict various shapes of a rotor side; and FIGS. 20A-20D depict various shapes of an inclined plate side. 
     FIG. 19A depicts groove  14 , having a semicircular cross section, which is formed on arm portion  13  of rotor  11  in the second embodiment. FIG. 20A depicts spherical hole  16  formed on projecting portion  15  of inclined plate  12  in the second embodiment. FIG.  19 B and FIG. 20B show a first modification of the cam mechanism depicted in FIGS. 19A and 20A. In FIG. 19B, groove  61  formed on arm portion  13  of rotor  11  has a rectangular cross section. In FIG. 20B, hole  65  formed on projecting portion  15  of inclined plate  12  has a cylindrical shape. FIG.  19 C and FIG. 20C show a second modification of the cam mechanism depicted in FIGS. 19A and 20A. In FIG. 19C, groove  62  formed on arm portion  13  of rotor  11  has a triangular cross section. In FIG. 20C, hole  66  formed on projecting portion  15  of inclined plate  12  has a conical shape. FIG.  19 D and FIG. 20D show a third modification of the cam mechanism depicted in FIGS. 19A and 20A. In FIG. 19C, lubricating oil hole  63  is defined in arm portion  13  of rotor  11  to communicate triangular groove  62 . In FIG. 20D, lubricating oil hole  67  is defined on the bottom portion of conical hole  66  to communicate conical hole  66 . Thus, various modifications may be employed. 
     Although the above-described modifications have been explained as modifications of the second embodiment, such modifications may be applied to other embodiments including a seventh embodiment described later. Further, in the present invention, the shapes of the groove and the hole are not limited to the above-described shapes of circular, spherical, rectangular, triangular and conical shapes. Other shapes such as polygonal and oval shapes, that can hold or engage a ball, may be employed. 
     FIG. 21 depicts a cam mechanism of a variable-displacement inclined plate compressor according to a seventh embodiment of the present invention. In FIG. 21, cam mechanism  70  includes rotor  71  and inclined plate  72 . A single arm portion  73  is provided on rotor  71  at the central portion of rotor  71 . Through hole  74  is defined in arm portion  73  to extend in a direction perpendicular to the direction in that arm portion  73  projects. A pair of projecting portions  75  are provided on inclined plate  72 . Grooves  76  each having an arc cross section are defined on the respective inner side surfaces of projecting portion  75 , which face each other. When cam mechanism  70  is assembled, after ball  7  is inserted into through holes  74  of rotor  71 , both the upper and lower portions of ball  7  that protrude from hole  74  are inserted into respective grooves  76 . Ball  7  engages both of hole  74  and grooves  76 , thereby engaging rotor  71  and inclined plate  72  in the direction of the axis of the drive shaft. In cam mechanism  70  according to this seventh embodiment, substantially the same advantages as those in the first through sixth embodiments may be obtained. 
     Although the above-described embodiments have been explained with respect to a variable-displacement inclined plate compressor having an inclined plate and a wobble plate, the present invention may be applied to a variable-displacement inclined plate compressor which does not have a wobble plate. In such a compressor, the force from an inclined plate may be transmitted to piston rods and pistons, for example, via a shoe mechanism. For example, a shoe may be provided on an end of each piston rod, and the shoe may slidably engage the rotating inclined plate. The cam mechanism between a rotor and an inclined plate according to the present invention may be applied to this type of compressor, and also similarly to the above-described embodiments. 
     Although several embodiments of the present invention have 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 embodiments disclosed herein are 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.