Patent Publication Number: US-2004055456-A1

Title: Variable displacement compressor

Description:
BACKGROUND OF THE INVENTION  
       [0001] The present invention relates to a variable displacement piston type compressor for use in a vehicle air conditioner.  
       [0002] Unexamined Japanese Patent Publication No. 9-203377 discloses a variable displacement compressor of such type. FIG. 14 illustrates a partially longitudinal cross-sectional view of a variable displacement compressor according to a prior art. A housing  101  of the compressor defines a cylinder bore  101   a  that accommodates a piston  102 . A drive shaft  103  is rotatably supported by the housing  101 . A rotor  104  is connected to the drive shaft  103  so as to rotate integrally therewith. A swash plate  105  is supported by the drive shaft  103  so that it slides and inclines relative to the drive shaft  103 . The piston  102  engages the periphery of the swash plate  105  through a pair of shoes  107 . A hinge mechanism  108  is interposed between the rotor  104  and the swash plate  105 .  
       [0003] Accordingly, the rotation of the drive shaft  103  is converted to the reciprocation of the piston  102  through the rotor  104 , the hinge mechanism  108  and the swash plate  105 , while the swash plate  105  is guided by the hinge mechanism  108  to slide on the drive shaft  103  in accordance with the inclination of the swash plate  105 . Thus, the displacement volume of the compressor is varied.  
       [0004] The hinge mechanism  108  includes a pair of first protrusions  108   a  (only one is shown in FIG. 14), a second protrusion  108   b  and a cam surface  108   c . The first protrusions  108   a  extend from the rotor  104  toward the swash plate  105 . The second protrusion  108   b  extends from the swash plate  105  toward the rotor  104 . The distal end of the second protrusion  108   b  is inserted between the first protrusions  108   a . The cam surface  108   c  is formed at the proximal portion of the first protrusions  108   a . The first protrusions  108   a  and the second protrusion  108   b  contact with a certain amount of area to engage each other so that the rotation of the rotor  104  is transmitted to the swash plate  105  through the hinge mechanism  108 . The distal end of the second protrusion  108   b  slidably contacts the cam surface  108   c  so that axial load that acts on the swash plate  105  due to compression reactive force is received by the cam surface  108   c  through the second protrusion  108   b.    
       [0005] In the hinge mechanism  108 , the first protrusions  108   a  and the second protrusion  108   b  are integrally formed with the rotor  104  and the swash plate  105 , respectively. An unwanted feature is that as the swash plate  105  inclines to twist the second protrusion  108   b  by the pair of first protrusions  108   b  due to offset axial load based upon the compression reactive force, sliding resistances increase between the side surfaces of the first protrusions  108   a  and the second protrusion  108   b  and between the distal end of the second protrusion  108   b  and the cam surface  108   c  due to the contact of the edge. This leads to early abrasion of each sliding surface. In other words, durability of the hinge mechanism  108  is deteriorated, and unsmooth operation of the hinge mechanism  108  leads to deteriorated controllability for the displacement volume of the compressor. Therefore, there is a need for a variable displacement compressor that improves durability of a hinge mechanism and that ensures smooth operation of the hinge mechanism.  
       SUMMARY OF THE INVENTION  
       [0006] In accordance with the present invention, a variable displacement compressor has a housing, a piston, a drive shaft, a rotor, a cam plate and a hinge mechanism. The housing defines a cylinder bore. The piston is accommodated in the cylinder bore. The drive shaft is rotatably supported by the housing. The rotor is connected to the drive shaft so as to rotate integrally with. The cam plate is supported by the drive shaft so as to slide and incline relative to the drive shaft and is operatively connected to the piston. The hinge mechanism is interposed between the rotor and the cam plate and guides the cam plate to incline and slide relative to the drive shaft. Thus, the displacement volume of the compressor is varied. The rotation of the drive shaft is converted to the reciprocation of the piston through the rotor, the hinge mechanism and the cam plate. The hinge mechanism includes a first hinge element and a second hinge element. The first hinge element is provided on the rotor. The second hinge element is provided on the cam plate and is engaged with the first hinge element. At least one of the first and second hinge elements has a degree of freedom for motion against the rotor and/or the cam plate to which the hinge element having the degree of freedom for motion belongs.  
       [0007] Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0008] The features of the present invention that are believed to be novel are set forth with particularity in the appended claims. The invention together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:  
     [0009]FIG. 1 is a longitudinal cross-sectional view of a variable displacement compressor according to a first preferred embodiment of the present invention;  
     [0010]FIG. 2 is a side view of a hinge mechanism according to the first preferred embodiment of the present invention;  
     [0011]FIG. 3 is a plan view of the hinge mechanism according to the first preferred embodiment of the present invention;  
     [0012]FIG. 4 is a hinge element of a swash plate according to the first preferred embodiment of the present invention;  
     [0013]FIG. 5 is an enlarged longitudinal cross-sectional view of a hinge mechanism according to a second preferred embodiment of the present invention;  
     [0014]FIG. 6 is a plan view of a hinge mechanism according to a third preferred embodiment of the present invention;  
     [0015]FIG. 7 is an enlarged side view of a hinge mechanism according to a fourth preferred embodiment of the present invention;  
     [0016]FIG. 8 is an enlarged longitudinal cross-sectional view of a hinge mechanism according to a fifth preferred embodiment of the present invention;  
     [0017]FIG. 9 is a plan view of a hinge mechanism according to a sixth preferred embodiment of the present invention;  
     [0018]FIG. 10 is an enlarged longitudinal cross-sectional view of a hinge mechanism according to a seventh preferred embodiment of the present invention;  
     [0019]FIG. 11 is an enlarged perspective view of the hinge mechanism according to the seventh preferred embodiment of the present invention;  
     [0020]FIG. 12 is a longitudinal cross-sectional view of a hinge mechanism according to an eighth preferred embodiment of the present invention;  
     [0021]FIG. 13 is a plan view of the hinge mechanism according to the eighth preferred embodiment of the present invention; and  
     [0022]FIG. 14 is a partially longitudinal cross-sectional view of a variable displacement compressor according to a prior art.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0023] A first preferred embodiment of the present invention will now be described with reference to FIGS. 1 through 4. The present invention is applied to a variable displacement compressor for a refrigerant circuit of a vehicle air conditioner in the first preferred embodiment. The left side and the right side respectively correspond to the front side and the rear side of the compressor in FIG. 1.  
     [0024]FIG. 1 illustrates a longitudinal cross-sectional view of the variable displacement compressor according to the first preferred embodiment of the present invention. A housing of the compressor includes a cylinder block  11 , a front housing  12  and a rear housing  14 . The front housing  12  is fixedly connected to the front end of the cylinder block  11 . The rear housing  14  is fixedly connected to the rear end of the cylinder block  11  through a valve plate assembly  13 .  
     [0025] A crank chamber  15  is defined between the cylinder block  11  and the front housing  12 . A drive shaft  16  is rotatably supported by the housing and extends through the crank chamber  15  from the front housing  12  to the cylinder block  11 . The drive shaft  16  is rotated by the power transmitted from an engine (not shown) for traveling a vehicle.  
     [0026] In the crank chamber  15 , a rotor  17  made of cast iron is fixedly connected to the drive shaft  16  so as to rotate integrally therewith. The front end surface of the rotor  17  and the facing inner wall surface of the front housing  12  interpose a thrust bearing  35 . The crank chamber  15  accommodates a swash plate or a cam plate  18 . The swash plate  18  is made of iron series metal, such as iron and iron alloy. The swash plate  18  is formed by forging.  
     [0027] A through hole  20  is formed at the center of the swash plate  18 . The drive shaft  16  extends through the through hole  20 . The swash plate  18  is supported by the drive shaft  16  through an inner surface  20   a  of the through hole  20  in such a manner that the swash plate  18  inclines and slides relative to the drive shaft  16 . A circular clip  32  is fitted on the drive shaft  16  on the rear side to the swash plate  18 . A coil spring  33  for increasing inclination angle of the swash plate  18  is arranged between the circular clip  32  and the swash plate  18  so as to urge the middle portion of the swash plate  18  forward.  
     [0028] A hinge mechanism  19  is interposed between the rotor  17  and the swash plate  18 . The hinge mechanism  19  includes a first hinge element  52  provided on the rotor  17  and a second hinge element  51  provided on the swash plate  18 . The swash plate  18  is coupled to the rotor  17  through the hinge mechanism  19  and is supported by the drive shaft  16  through the inner surface  20   a  of the though hole  20 . Accordingly, the swash plate  18  is integrally rotatable with the rotor  17  and the drive shaft  16 , while it is inclinable relative to the drive shaft  16  in accordance with sliding movement in the direction of the axis L of the drive shaft  16 .  
     [0029] Incidentally, with respect to the swash plate  18 , the inner surface  20   a  of the through hole  20  is treated by induction hardening for improving sliding performance against the drive shaft  16  and for improving abrasion resistance.  
     [0030] A plurality of cylinder bores  22  (one of them shown in FIG. 1) extends through the cylinder block  11  and is arranged around the axis L of the drive shaft  16  at equiangular positions. Each of the cylinder bores  22  accommodates a single-headed piston  23  so as to be reciprocated therein. The front and rear openings of each cylinder bore  22  are respectively closed by the top end surface of the piston  23  and the front end surface of the valve port assembly  13 . Thus, a compression chamber  24  is defined in each of the cylinder bores  22  and varies its volume in accordance with the reciprocation of the respective piston  23 . Each of the pistons  23  engages the outer periphery of the swash plate  18  through a pair of semispherical shoes  25 . Accordingly, the rotation of the swash plate  18  in accordance with the rotation of the drive shaft  16  is converted to the reciprocation of the piston  23  through the shoes  25 .  
     [0031] Incidentally, with respect to the swash plate  18 , sliding surfaces  18 b against the respective shoes  25  are treated by induction hardening for improving sliding performance against the shoes  25  and for improving abrasion resistance.  
     [0032] A suction chamber  26  and a discharge chamber  27  are defined between the valve plate assembly  13  and the rear housing  14 . The refrigerant gas in the suction chamber  26  is introduced into the compression chamber  24  through a suction port  28  and a suction valve  29  as each piston  23  moves from its top dead center to its bottom dead center. The suction port  28  and the suction valve  29  are formed in the valve plate assembly  13 . The refrigerant gas in the compression chamber  24  is compressed to a predetermined pressure value as the piston  23  moves from the bottom dead center to the top dead center. The compressed refrigerant gas is discharged to the discharge chamber  27  through a discharge port  30  and a discharge valve  31 , which are formed in the valve plate assembly  13 .  
     [0033] The compressor optionally varies its displacement volume and regulates its displacement volume in such a manner that a control valve  21  adjusts pressure in the crank chamber  15 . In other words, pressure differential between the crank chamber  15  and the compression chambers  24  is varied by the control valve  21  in response to variation of the pressure in the crank chamber  15 . As a result, the inclination angle of the swash plate  18  is varied, and the stroke of the piston  23  is adjusted.  
     [0034] As the pressure in the crank chamber  15  decreases, the swash plate  18  is pushed by the coil spring  33  to increase its inclination angle. Thus, the strokes of the pistons  23  increase, and the displacement volume of the compressor increases. The front end surface of the swash plate  18  has a portion  18   a  for regulating maximum inclination angle. The portion  18   a  also serves as a balance weight. The maximum inclination angle of the swash plate  18  is regulated in such a manner that the portion  18   a  contacts the rear end surface of the rotor  17 , as shown in FIG. 1.  
     [0035] On the other hand, as the pressure in the crank chamber  15  increases, the swash plate  18  resists against the coil spring  33  to decrease its inclination angle. Thus, the strokes of the pistons  23  decrease, and the displacement volume of the compressor decreases. The minimum inclination angle of the swash plate  18  is regulated by the circular clip  32  and the coil spring  33 .  
     [0036]FIG. 2 illustrates a side view of the hinge mechanism  19  according to the first preferred embodiment of the present invention. FIG. 3 illustrates a plan view of the hinge mechanism  19  according to the first preferred embodiment of the present invention. Now referring to FIGS. 1 through 3, an engaging recess  41  is formed at the rear end of the rotor  17  and faces a point TDC of the swash plate  18 . The point TDC is a center of the hypothetical spherical surface of the shoes  25  when the piston  23  is positioned at a top dead center. The engaging recess  41  is defined by a pair of first protrusions  43  that extend toward the swash plate  18 . The first protrusions  43  are respectively disposed at the rear end on a preceding side and on a following side in the rotational direction of the rotor  17 .  
     [0037] A pair of second protrusions  44  extends toward the rotor  17  and is arranged at the front end of the swash plate  18  so as to face the engaging recess  41 . The second protrusions  44  are respectively disposed on a preceding side and on a following side in the rotational direction of the drive shaft  16  so as to interpose a hypothetical plane including the axis L and the point TDC. Each of the distal ends of the second protrusions  44  fits into the engaging recess  41 . Each of the second protrusions  44  includes a side surface  44   a  that faces away from each other. Each of the side surfaces  44   a  contacts a side surface  43   a  of the first protrusion  43  with a certain amount of area. The side surfaces  43   a  partially form the inner surface of the engaging recess  41 . Accordingly, the rotational power of the rotor  17  is transmitted to the swash plate  18  through one of the first protrusions  43  (the side surfaces  43   a ) and one of the second protrusions  44  (the side surfaces  44   a ).  
     [0038] Incidentally, to improve general-purpose property, with respect to the compressor of the first preferred embodiment, the hinge mechanism  19  is symmetrically formed relative to the the hypothetical plane including TDC and the axis L along the rotational direction of the drive shaft  16  so as to appropriately respond either rotational direction of the drive shaft  16 , even if a mounted engine rotates in either direction.  
     [0039] A cam portion  45  for receiving axial load is formed on the proximal portion of each first protrusion  43  in the engaging recess  41 . The cam portions  45  and the first protrusions  43  constitute the first hinge element  52  on the side of the rotor  17 . The rear end surface of each cam portion  45  facing the swash plate  18  forms a cam surface  45   a  that protrudes toward the rear side as it approaches the drive shaft  16 . Each of the second protrusions  44  forms a convex circular arc surface  44   b  and slidably contacts the cam surface  45   a  of the corresponding cam portion  45  by the circular arc surface  44   b . Accordingly, the axial load that acts on the swash plate  18  due to the compression reactive force is received by the cam surfaces  45   a  of the cam portions  45  through the circular arc surfaces  44   b  of the second protrusions  44 , respectively.  
     [0040] With respect to the prior art shown in FIG. 14, the hinge mechanism  108  includes the single and relatively large-scaled second protrusion  108   b . However, in the first preferred embodiment, the second protrusion  108   b  of the prior art is divided into the two second protrusions  44 . The above structure ensures the same width for receiving axial load as that of the second protrusion  108   b  of the prior art and lightens the swash plate assembly  18 ,  51  by changing the structure of the second protrusion  108   b  of the prior art to a hollow structure.  
     [0041] As the compressor increases its displacement volume, the distal ends of the second protrusions  44  rotate around a central axis S of the circular arc surfaces  44   b  in the clockwise direction in FIG. 1, while they move on the cam surfaces  45   a  of the respective cam portions  45  away from the drive shaft  16 . Thus, the hinge mechanism  19  guides to increase the inclination angle of the swash plate  18 . On the contrary, when the compressor reduces its displacement volume, the distal ends of the second protrusions  44  rotate around the central axis S of the circular arc surfaces  44   b  in the counterclockwise direction in FIG. 1, while they move on the cam surfaces  45   a  of the cam portions  45  to approach the drive shaft  16 . Thus, the hinge mechanism  19  guides to reduce the inclination angle of the swash plate  18 .  
     [0042] Incidentally, the first hinge element  52  and the second hinge element  51  slide on each other at sliding surfaces, such as the side surfaces  43   a ,  44   a  of the respective first and second protrusions  43 ,  44 , the circular arc surfaces  44   b  of the respective second protrusions  44 , and the cam surfaces  45   a  of the respective cam portions  45 . The above sliding surfaces are treated by induction hardening for improving their sliding performance and abrasion resistance.  
     [0043] In the second hinge element  51 , the induction hardening may exclusively be treated at a portion including the side surfaces  44   a  and the circular arc surfaces  44   b  or may entirely be treated. Particularly, the former treatment restrains the distortion and crack of the second hinge element  51  of the swash plate  18  due to heat affection of the hardening. Incidentally, the induction hardening may be treated only at portions including the side surfaces  43   a  and the cam surfaces  45   a  or may be treated at the entire first hinge element  52 . Particularly, the former treatment restrains the distortion and crack of the first hinge element  52  due to heat affection of the hardening.  
     [0044] As shown in FIGS. 1 through 3, the second hinge element  51  is separately formed from the swash plate  18 . The second hinge element  51  includes a base plate or a base  47  and a pair of second protrusions  44  that extend from the front end surface of the base plate  47 . The swash plate  18  is made of iron series metal and is formed by forging. On the other hand, the second hinge element  51  is made of aluminum series metal, such as aluminum and aluminum alloy. That is, the second hinge element  51  is made of different material from that of the swash plate  18 , and the second protrusions  44  and the base plate  47  are integrally formed by forging or by molding. With respect to the swash plate  18 , the sliding surfaces  18   b  against the shoes  25  and the inner surface  20   a  of the through hole  20  are polished and treated by induction hardening before the second hinge element  51  is assembled to the swash plate  18 .  
     [0045] In the second hinge element  51 , a shaft  48  is integrally formed at the center of the rear end surface of the base plate  47  and extends vertically relative to the base plate  47 . In the swash plate  18 , a shaft hole  18   c  is recessed inwardly from the sliding surfaces  18   b  against the shoes  25  and extends in thickness of the swash plate  18 . The second hinge element  51  is loosely fitted into the shaft hole  18   c  of the swash plate  18  by the shaft  48 .  
     [0046] Accordingly, referring to FIG. 4, the diagram illustrates the second hinge element  51  according to the first preferred embodiment of the present invention. The second hinge element  51  is rotatable on the swash plate  18  relative to an axis M of the shaft  48  (or the shaft hole  18   c ). Namely, the second hinge element  51  has the degree of freedom for rotation against the swash plate  18  to which the second hinge element  51  belongs. The rotation of the second hinge element  51  is regulated in a predetermined angular range in such a manner that an end surface  47   a  of the base plate  47  near the drive shaft  16  contacts the wall surface of a step or a regulating means  18   d  formed on the front end surface of the swash plate  18 .  
     [0047] Incidentally, referring back to FIGS. 1 and 2, a lightening recess  48   a  is formed at the distal end of the shaft  48  on the side near the drive shaft  16  so that the swash plate  18  avoids interfering with the coil spring  33  when positioned at the maximum inclination angle.  
     [0048] The following advantageous effects are obtained from the first preferred embodiment.  
     [0049] (1) The second hinge element  51  has the degree of freedom for motion against the swash plate  18 . Accordingly, even if offset axial load due to the compression reactive force acts on the inclined swash plate  18  to twist the second protrusions  44  in the engaging recess  41 , stress due to the inclined swash plate  18  moves the second hinge element  51  so that the second protrusions  44  avoid twisting in the engaging recess  41 . As a result, the side surfaces  44   a  of the respective second protrusions  44  and the side surfaces  43   a  of the respective first protrusions  43  contact each other with a certain amount of area, while the circular arc surfaces  44   b  of the respective second protrusions  44  and the cam surfaces  45   a  of the respective cam portions  45  contact each other with a line. Thus, no edge abuts at each sliding surface. Accordingly, the hinge mechanism  19  smoothly moves, and the displacement volume of the compressor smoothly varies.  
     [0050] (2) The second hinge element  51  on the swash plate  18  has the degree of freedom for rotation. In comparison to a hinge mechanism that has a degree of freedom for sliding, the second hinge element  51  effectively avoids the second protrusions  44  from twisting in the engaging recess  41 .  
     [0051] (3) The rotation of the second hinge element  51  is regulated in a predetermined angular range in such a manner that the second hinge element  51  contacts the step  18   d  formed on the swash plate  18 . Accordingly, the second hinge element  51  is prevented from excessively rotating on the swash plate  18  so that noise due to collision between the second protrusions  44  and the first protrusions  43  is reduced. The structure for regulating the rotation of the second hinge element  51  helps to assemble the swash plate assembly  18 ,  51  to the compressor, that is, the structure helps to easily insert the second protrusions  44  into the engaging recess  41 . Namely, for example, without the structure for regulating the rotation of the second hinge element  51 , the rotation of the second hinge element  51  must be temporarily regulated to fit the second protrusions  44  into the engaging recess  41 . Accordingly, a jig for regulating the rotation of the second hinge element  51  is required so that assembling becomes complicated.  
     [0052] (4) Since the second hinge element  51  has the degree of freedom for motion against the swash plate  18 , that is, since the second hinge element  51  is separately formed from the swash plate  18 , the shape of the swash plate  18  becomes simple. Accordingly, the swash plate  18  employs forging as a manufacturing procedure because forging provides better yield and easy after-machining in comparison to molding. Even if the second hinge element  51  needs to be separately formed and assembled to the swash plate  18 , costs are reduced for manufacturing the compressor. Incidentally, the swash plate  18  formed by forging has relatively high hardenability in comparison to the one formed by molding.  
     [0053] The separately formed swash plate  18  and the second hinge element  51  permit appropriate selection for their respective material. Accordingly, in the first preferred embodiment, the swash plate  18  is made of iron series metal that has relatively high relative density for ensuring its strength and for ensuring moment for stable variation of the displacement volume. Additionally, the second hinge element  51  that is arranged at an offset position on the swash plate  18  is made of aluminum series metal that has relatively low relative density for balancing around the axis L of the swash plate assembly  18 ,  51 . The second hinge element  51  made of light aluminum series metal helps the balance weight  18   a  for balancing around the axis L of the second hinge element  51  to be compact. This leads to the lightened swash plate assembly  18 ,  51  and to the lightened compressor.  
     [0054] Furthermore, the second hinge element  51  made of aluminum series metal that is different from that of the first hinge element  52  made of cast iron effectively prevents a same-metal phenomenon due to slide between the first hinge elements  52 . The same-metal phenomenon means that mutually same metals lead to inconveniences such as an increase in coefficient of friction.  
     [0055] (5) In the first and second hinge elements  51 ,  52  for the hinge mechanism  19 , the second hinge element  51  is separately formed from the swash plate  18 . Accordingly, a depth for fitting the shaft  48  into the shaft hole  18   c  may be relatively long in the direction of the axis M so that the swash plate  18  supports the second hinge element  51  in stable. As a result, for example, the second hinge element  51  may be rotated in stable relative to the swash plate  18  so as to avoid twisting of the second protrusions  44  in the engaging recess  41 . This leads to smooth operation of the hinge mechanism  19  and to smooth variation of the displacement volume of the compressor.  
     [0056] Namely, for example, according to a second preferred embodiment of FIG. 5 which will be described later, when the first hinge element  52  is separately formed from the rotor  17 , the distal end of the shaft  55  needs consideration for not protruding the distal end of the shaft  55  from the shaft hole  17   a  including dimensional tolerance so as to avoid interference between the shaft  55  and the thrust bearing  35  (See FIG. 1) that is arranged on the front end surface of the rotor  17 . Accordingly, the depth for fitting between the shaft  55  and the shaft hole  17   a  tends to become small in the direction of the axis M so that the rotor  17  supports the first hinge element  52  in unstable.  
     [0057] (6) When the swash plate  18  is separately formed from the second hinge element  51 , the second hinge element  51  does not interfere with the approach of a grind stone to the sliding surface  18   b  in a polishing process of the sliding surfaces  18   b  that slide on the shoes  25  before the second hinge element  51  is assembled to the swash plate  18 . Therefore, workability of the swash plate  18  becomes better. In other words, the second hinge element  51  does not need to consider the interference when the sliding surfaces  18   b  are polished and permits free determination of its shape and also permits ideal shape for transmitting power and for guiding inclination of the swash plate  18 .  
     [0058] (7) The second hinge element  51  includes a pair of the second protrusions  44  that are integrated with each other and is rotatable on the swash plate  18 . In comparison to a plurality of the second protrusions  44  that are individually rotatable on the swash plate  18 , the structure of the second hinge element  51  for rotation, that Is, the structure for increasing the degree of freedom, may be simple in the first preferred embodiment. Additionally, a plurality of the integrated second protrusions  44  leads to easy setting in high accuracy the width between the side surfaces  44   a  of the respective second protrusions  44 . The width largely affects the smooth operation of the hinge mechanism  19 .  
     [0059] (8) The swash plate  18  that is separately formed from the second hinge element  51  is treated by hardening at sliding surfaces  18   b  against the shoes  25  and the inner surface  20   a  of the through hole  20  that slides on the drive shaft  16  before the second hinge element  51  is assembled to the swash plate  18 . Accordingly, the second hinge element  51  does not receive heat affection due to hardening and avoids distortion due to the heat affection. No modification for distortion of the second hinge element  51  is required, but the hinge mechanism  19  smoothly operates so that costs are reduced for manufacturing the compressor.  
     [0060] A second preferred embodiment of the present invention will now be described with reference to FIG. 5. The components that are different from those of the first preferred embodiment are only described. The same reference numerals denote the substantially identical components to those of the first preferred embodiment, and the description is omitted.  
     [0061]FIG. 5 illustrates an enlarged longitudinal cross-sectional view of the hinge mechanism  19  according to the second preferred embodiment of the present invention. In the second preferred embodiment, the second hinge element  51  is integrally formed with the swash plate  18 , while the first hinge element  52  is separately formed from the rotor  17 . The first hinge element  52  integrally forms a base plate  56 , a pair of the first protrusions  43  and a pair of the cam portions  45 . The first protrusions  43  extend from the rear end surface of the base plate  56 . The cam portions  45  are formed on the proximal portions of the respective first protrusions  43 . The rotor  17  that is separately formed from the first hinge element  52  is simple and may apply forging as a manufacturing procedure.  
     [0062] The first hinge element  52  is loosely fitted into a shaft hole  17   a  at a shaft  55  thereof. The shaft  55  extends from the front end surface of the base plate  56 . The shaft hole  17   a  is formed through the rotor  17 . Accordingly, the first hinge element  52  is rotatable on the rotor  17  around the axis M of the shaft  55  (or the shaft hole  17   a ) that is parallel with the axis L of the drive shaft  16 . Namely, the first hinge element  52  has the degree of freedom for rotation against the rotor  17 . The rotation of the first hinge element  52  is regulated in a predetermined angular range on the rotor  17  in such a manner that an end surface  56   a  facing the drive shaft  16  contacts the wall surface of the step  17   b  that is formed on the rotor  17 .  
     [0063] In the second preferred embodiment, the first hinge element  52  is rotatable on the rotor  17 . Accordingly, even if the swash plate  18  inclines to twist the second protrusions  44  in the engaging recess  41  by the axial load due to the compression reactive force, stress due to the inclination rotates the first hinge element  52  around the axis M on the rotor  17  so as to prevent the swash plate  18  from twisting the second protrusions  44 .  
     [0064] A third preferred embodiment of the present invention will now be described with reference to FIG. 6. The components that are different from those of the first preferred embodiment are only described. The same reference numerals denote the substantially identical components to those of the first preferred embodiment, and the description is omitted.  
     [0065]FIG. 6 illustrates a plan view of the hinge mechanism  19  according to the third preferred embodiment of the present invention. In the third preferred embodiment, the engaging recess  41  is formed between a pair of the second protrusions  44  in the second hinge element  51 . The rotor  17  includes the single first protrusion  43  at its rear end surface facing the engaging recess  41 . The first protrusion  43  extends toward the swash plate  18 . The distal end of the first protrusion  43  is inserted in the engaging recess  41 . The first protrusion  43  has a pair of side surfaces  43   b , while each of the second protrusions  44  has a side surface  44   c  that is a part of the inner surface of the engaging recess  41 . The side surfaces  43   b  of the first protrusion  43  contact the side surfaces  44   c  with a certain amount of area. Accordingly, the rotational power of the rotor  17  is transmitted to the swash plate  18  through one of the side surfaces  43   b  of the first protrusion  43  and one of the side surfaces  44   c  of the respective second protrusions  44 .  
     [0066] The second hinge element  51  includes the cam portion  45  at the proximal portions of the second protrusions  44  in the engaging recess  41 . The distal end of the first protrusion  43  forms a convex circular arc surface  43   d  and slidably contacts a cam surface  45   c  of the cam portion  45 . Accordingly, the axial load that acts on the swash plate  18  due to the compression reactive force is received by the cam surface  45   c  of the cam portion  45 .  
     [0067] A fourth preferred embodiment of the present invention will now be described with reference to FIG. 7. The components that are different from those of the first preferred embodiment are only described. The same reference numerals denote the substantially identical components to those of the first preferred embodiment, and the description is omitted.  
     [0068]FIG. 7 illustrates an enlarged side view of the hinge mechanism  19  according to the fourth preferred embodiment of the present invention. In the fourth preferred embodiment, the side surface  43   a  of the first protrusion  43  includes a guide groove  43   c  that extends along the direction of the cam surface  45   a  of the cam portion  45 . The side surface  44   a  of the second protrusion  44  includes a guide protrusion  44   d  on the central axis S of the circular arc surface  44   b , and the guide protrusion  44   d  is engagedly inserted in the guide groove  43   c  for guiding the swash plate  18  to incline and slide relative to the drive shaft  16 .  
     [0069] Even if the compression reactive force that acts on the swash plate  18  disappears due to the stop of the compressor, or even if the compression reactive force that acts on the swash plate  18  decreases due to the operation of the compressor in a minimum displacement volume, the swash plate assembly  18 ,  51  engages the rotor  17  by the engagement between the guide groove  43   c  and the guide protrusion  44   d . As a result, the swash plate assembly  18 ,  51  is prevented from rattling due to vibration of a vehicle, with a consequence of preventing noise generated on the compressor.  
     [0070] A fifth preferred embodiment of the present invention will now be described with reference to FIG. 8. The components that are different from those of the first preferred embodiment are only described. The same reference numerals denote the substantially identical components to those of the first preferred embodiment, and the description is omitted.  
     [0071]FIG. 8 illustrates an enlarged longitudinal cross-sectional view of the hinge mechanism  19  according to the fifth preferred embodiment of the present invention. In the fifth preferred embodiment, a slider  57  is interposed between the circular arc surface  44   b  of the second protrusion  44  and the cam surface  45   a  of the cam portion  45 . Namely, the second protrusion  44  (the circular arc surface  44   b ) and the cam portion  45  (the cam surface  45   a ) slidably contact each other through the slider  57 .  
     [0072] The slider  57  includes a concave circular arc surface  57   a  and a planar surface  57   b . The concave circular arc surface  57   a  slides on the circular arc surface  44   b  of the second protrusion  44 . The planar surface  57   b  slides on the cam surface  45   a . Accordingly, the cam portion  45  and the slider  57  contact each other with a certain amount of area, and the second protrusion  44  and the slider  57  contact each other with a certain amount of area. The areal contacts reduce abrasion of the cam surface  45   a  and the circular arc surface  44   b . That is, the areal contacts contribute to improved durability of the hinge mechanism  19 .  
     [0073] A sixth preferred embodiment of the present invention will now be described with reference to FIG. 9. The components that are different from those of the first preferred embodiment are only described. The same reference numerals denote the substantially identical components to those of the first preferred embodiment, and the description is omitted.  
     [0074]FIG. 9 illustrates a plan view of the hinge mechanism  19  according to the sixth preferred embodiment of the present invention. In the sixth preferred embodiment, the drive shaft  16  rotates in the direction of an arrow R, and the hinge mechanism  19  is particularly configured to appropriately handle a state when the drive shaft  16  rotates in the direction of the arrow R.  
     [0075] Namely, with respect to the hinge mechanism  19 , a cam portion  45 A and a second protrusion  44 A shown in the lower side of FIG. 9 in a compression cycle mainly receive the axial load that acts on the swash plate  18  based upon the compression reactive force, while the first protrusion  43  and another second protrusion  44 B shown in the upper side of FIG. 9 in a suction cycle transmit power from the rotor  17  to the swash plate  18 . Then, with respect to the second protrusions  44 A,  44 B, when absolute amount of load, variation of the load and its variation rate are considered, the second protrusion  44 A for receiving the axial load is hard in strength than the second protrusion  44 B for power transmission.  
     [0076] Then, in the sixth preferred embodiment, the cam surface  45   a  of the cam portion  45 A for receiving the axial load is widened than the cam surface  45   a  of the cam portion  45 B for power transmission, while the second protrusion  44 A for receiving the axial load is thicker than the second protrusion  44 B for power transmission. Thus, the width of the circular arc surface  44   b  of the second protrusion  44 A is predetermined to be wide. Accordingly, the strength of the second protrusion  44 A for receiving the axial load is improved. In comparison to the thickened second protrusions  44 A,  44 B, an increase in weight is relatively small, while durability of the hinge mechanism  19  is ensured at equivalent level in the sixth preferred embodiment.  
     [0077] A seventh preferred embodiment of the present invention will now be described with reference to FIGS. 10 and 11. The components that are different from those of the first preferred embodiment are only described. The same reference numerals denote the substantially identical components to those of the first preferred embodiment, and the description is omitted.  
     [0078]FIG. 10 illustrates an enlarged longitudinal cross-sectional view of the hinge mechanism  19  according to the seventh preferred embodiment of the present invention. FIG. 11 illustrates an enlarged perspective view of the hinge mechanism  19  according to the seventh preferred embodiment of the present invention. In the seventh preferred embodiment, a slider  60  is supported by the drive shaft  16  so as to slide in the direction of the axis L. A fulcrum shaft  60   a  is formed with the slider  60  and inclinably supports the swash plate  18 .  
     [0079] With respect to the hinge mechanism  19 , the cam portion  45  is omitted from the first hinge element  52 , and the first and second hinge elements  52 ,  51  engage each other through link arms  61 .  
     [0080] Namely, the second hinge element  51  includes the single second protrusion  44 . An insertion hole  44   e  is formed through the distal end of the second protrusion  44  in the direction perpendicular to the axis L of the drive shaft  16 . The first hinge element  52  includes the single first protrusion  43  that radially extends from the outer periphery of the rotor  17 . An insertion hole  43   e  is formed through the distal end of the first protrusion  43  in the direction perpendicular to the axis L of the drive shaft  16 .  
     [0081] A pair of the link arms  61  is arranged on each side of the distal ends of the first and second protrusions  43 ,  44  and each of the link arms  61  has through holes  61   a ,  61   b  at both ends. One end of each link arm  61  is pivotally supported through the through hole  61  a by a pin  62  that is inserted into the through hole  43   e  of the first protrusion  43 . The other end of each link arm  61  is pivotally supported through the through hole  61  b by another pin  63  that is inserted through the through hole  44   e  of the second protrusion  44 . Accordingly, the swash plate  18  inclines around the pins  62 ,  63  in accordance with slide on the drive shaft  16 .  
     [0082] According to the seventh preferred embodiment, the second hinge element  51  is rotatable on the swash plate  18 . Accordingly, even if the swash plate  18  inclines to twist the second protrusion  44  between the link arms  61  by the axial load due to the compression reactive force, stress due to the inclination rotates the second hinge element  51  around the axis M on the swash plate  18  so as to prevent the second protrusion  44  from twisting between the link arms  61 .  
     [0083] An eighth preferred embodiment of the present invention will now be described with reference to FIGS. 12 and 13. The components that are different from those of the first preferred embodiment are only described. The same reference numerals denote the substantially identical components to those of the first preferred embodiment, and the description is omitted.  
     [0084]FIG. 12 illustrates a longitudinal cross-sectional view of the hinge mechanism  19  according to the eighth preferred embodiment of the present invention. FIG. 13 illustrates a plan view of the hinge mechanism  19  according to the eighth preferred embodiment of the present invention. In the eighth preferred embodiment, the second hinge element  51  includes the single second protrusion  44 . A through hole  44   f  is formed through the distal end of the second protrusion  44 . A pin  65  is fixedly inserted into the through hole  44   f  in the direction perpendicular to the axis L of the drive shaft  16 . With respect to the first hinge element  52 , a cam groove  43   f  is formed in each of the first protrusions  43 . The second protrusion  44  is inserted in between the first protrusions  43  so as to permit power transmission from the rotor  17  to the swash plate  18  by contacting the side surfaces  43   a ,  44   a  through a washer  67  and to slidably contact the inner surface of the cam groove  43   f  by a cylindrical surface  65   a  of both sides of the pin  65  that is inserted into the cam groove  43   f.    
     [0085] Accordingly, the axial load that acts on the swash plate  18  due to the compression reactive force and the like is received by the inner surface of the cam groove  43   f  of the first protrusion  43  through the pin  65  of the second hinge element  51 . When the swash plate  18  varies its inclination angle, the hinge mechanism  19  guides to increase the inclination angle of the swash plate  18  in such a manner that the pin  65  (the cylindrical surface  65   a ) moves away from the drive shaft  16  along the inner surface of the cam groove  43   f  on the side of the rotor  17 , while the distal end of the second protrusion  44  rotates around a central axis of the pin  65 .  
     [0086] According to the eighth preferred embodiment, the second hinge element  51  is rotatable on the swash plate  18 . Accordingly, even if the swash plate  18  inclines to twist the second protrusion  44  between the first protrusions  43  and also inclines to twist the pin  65  in the cam groove  43   f  by the axial load due to the compression reactive force, stress due to the inclination rotates the second hinge element  51  around the axis M on the swash plate  18  so as to avoid their twisting.  
     [0087] The present invention is not limited to the embodiments described above but may be modified into the following alternative embodiments.  
     [0088] In alternative embodiments to those of the above first and third through eighth preferred embodiments, the second hinge element  51  is made of iron series sintered metal. In alternative embodiments to those of the above second preferred embodiment, the first hinge element  52  is made of iron series sintered metal. Accordingly, the sintered metal effectively holds lubricating oil so that sliding performance and seizure resistance improve between the first and second hinge elements  52 ,  51 . Incidentally, the lubricating oil is supplied to the crank chamber  15  with its mist contained in the refrigerant gas.  
     [0089] In alternative embodiments to those of the above preferred embodiments, the second hinge element  51  is rotatable on the swash plate  18 , while the first hinge element  52  is rotatable on the rotor  17 .  
     [0090] In alternative embodiments to those of the above second preferred embodiment, the first protrusion  43  is only rotatable on the rotor  17  in the components  43 ,  45  of the first hinge element  52 , while the cam portion  45  is fixed to the rotor  17 . Similarly, in alternative embodiments to those of the above third preferred embodiment, the second protrusion  44  is only rotatable on the swash plate  18  in the components  44 ,  45  of the second hinge element  51 , while the cam portion  45  is fixed to the swash plate  18 .  
     [0091] In alternative embodiments to those of the above first and third through eighth preferred embodiments, a plurality of the second protrusions  44  is separately formed, and each of the second protrusions  44  is individually rotatable on the swash plate  18 .  
     [0092] In alternative embodiments to those of the above preferred embodiments, a plane bearing or a rolling bearing is interposed between the shaft portion  48  or  55  and the shaft hole  18   c  or  17   a , respectively. Also, solid lubricant such as fluororesin and molybdenum disulfide is applied on at least one of the outer circumferential surface of the shaft portion  48  or  55  and the inner circumferential surface of the shaft hole  18   c  or  17   a , respectively. Accordingly, the second hinge element  51  smoothly rotates on the swash plate  18  according to the first and third through eighth preferred embodiments or the first hinge element  52  smoothly rotates on the rotor  17  according to the second preferred embodiment. As a result, the swash plate  18  smoothly varies its inclination angle. That is, the compressor smoothly varies its displacement volume.  
     [0093] In alternative embodiments to those of the above preferred embodiments, at least one of the first and second hinge elements  52 ,  51  includes a shaft hole, while the rotor  17  or the swash plate  18  on which the hinge element is arranged includes a shaft portion. Also, a pair of the first hinge element  52  and the rotor  17  or a pair of the second hinge element  51  and the swash plate  18  respectively includes shaft holes, and a shaft member is interposed between the shaft holes by inserting the shaft member into the shaft holes.  
     [0094] In alternative embodiments to those of the above preferred embodiments, the first hinge element  52  or the second hinge element  51  has the degree of freedom for slide relative to the rotor  17  or the swash plate  18 , respectively.  
     [0095] In alternative embodiments to those of the above preferred embodiments, at least one of the first and second hinge elements  52 ,  51  has two dimensional degree of freedom for motion against the rotor  17  or the swash plate  18  on which the hinge element is arranged. For example, one of the first and second hinge elements  52 ,  51  has the degree of freedom for rotation and for slide relative to the rotor  17  or the swash plate  18 , respectively.  
     [0096] In alternative embodiments to those of the above preferred embodiments, an engaging groove is recessed in a merely disc-shaped rotor (for example, the shape from which the first and second hinge elements  52 ,  51  are omitted in the above preferred embodiments) or a disc of a swash plate.  
     [0097] In alternative embodiments to those of the above preferred embodiments, the compressor is a variable displacement compressor that has a double-headed piston.  
     [0098] In alternative embodiments to those of the above preferred embodiments, the compressor is a wobble type variable displacement compressor that has a wobble plate or a cam plate.  
     [0099] Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein but may be modified within the scope of the appended claims.