Abstract:
In a swash-plate compressor for compressing a fluid, the compressor includes a cylinder block having a cylinder bore and a piston having a first end portion reciprocally movable in the cylinder bore and a second end portion opposite to the first end portion. The second end portion has a pair of engaging portions faced to each other with a space left therebetween and a side wall portion connecting the engaging portions to each other. The compressor further includes a swash plate having a part inserted between the engaging portions and driven to rotate and a pair of sliding members interposed between the engaging portions and the swash plate, respectively. Each of the sliding members has a flat portion slidably contacted with the swash plate and a spherical portion opposite to the flat portion. Each of the engaging portions has a contact surface slidably contacted with the spherical portion. Each of the contact surfaces extends to the side wall portion.

Description:
[0001]    This application claims priority to prior Japanese application JP 2002-2360766, the disclosure of which is incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    This invention relates to a swash-plate compressor for use in, for example, a refrigerating circuit of an automotive air conditioner.  
           [0003]    A swash-plate compressor of the type comprises a compressor body or a cylinder block having a plurality of cylinder bores spaced from one another in a circumferential direction, a plurality of pistons reciprocally movable in the cylinder bores, respectively, a swash plate slidably engaged with one ends of the pistons, and a drive shaft for rotating the swash plate. The drive shaft has one end to which a pulley is attached. By transmitting an external drive force to the pulley, the drive shaft is rotated.  
           [0004]    Each piston has one end provided with a pair of engaging portions faced to each other with the swash plate interposed therebetween, and a side wall portion connecting the engaging portions to each other. Between the engaging portions and the swash plate, a pair of semispherical shoes which serve as sliding members slidably contacted with the swash plate are interposed, respectively. Each of the engaging portions is provided with a contact surface to be slidably contacted with a spherical surface portion of the shoe. The side wall portion of the piston is provided with a recessed portion receiving a peripheral portion of the shoe in a non-contact manner.  
           [0005]    In an automotive air conditioner, a carbon dioxide refrigerant is increasingly used in a refrigerating circuit instead of a chlorofluorocarbon refrigerant in view of environment protection. A compressor adapted to be used with the carbon dioxide refrigerant is disclosed, for example, in Japanese Patent Application Publication No. 2002-31047 (JP-A).  
           [0006]    As compared with the case where the chlorofluorocarbon refrigerant is used, the discharge volume of the compressor is reduced down to ⅙ to ⅛ when the carbon dioxide refrigerant is used. Therefore, the piston having a small outer diameter is used. On the other hand, the working pressure is increased to about 10 times and the load imposed upon the swash plate by the piston is increased by about 20-30%. Therefore, the shoe having a large outer diameter must be used so as to accommodate such a large load from the piston.  
           [0007]    However, use of the shoe large in outer diameter generally requires the side wall portion of the piston to be enlarged outward, resulting in an increase in size of the compressor. Alternatively, the above-mentioned recessed portion may be reduced in thickness and increased in depth without enlarging the side wall portion. In this event, however, the strength of the piston is decreased.  
           [0008]    When the tilting angle of the swash plate is increased with the piston reaching a top dead center or a bottom dead center, the displacement of each shoe is also increased in a radial direction of the piston in the manner known in the art. Sometimes, a part of the spherical portion of each shoe may move out of the contact surface of the engaging portion. In this event, the contact area between the spherical portion of the shoe and the contact surface of the engaging portion is reduced. Such reduction in contact area results in an abnormal sliding condition of the shoe. For example, smooth sliding movement between the shoe and the engaging portion is interfered or inhibited. Sometimes, the shoe may be released and dropped from its position between the swash plate and the engaging portion.  
         SUMMARY OF THE INVENTION  
         [0009]    It is therefore an object of the present invention to provide a swash-plate compressor which is capable of increasing an outer diameter of a sliding member without causing an increase in size of the compressor and a decrease in strength of a piston and which is capable of reliably preventing the sliding member from sliding in an abnormal sliding condition or from being released.  
           [0010]    Other objects of the present invention will become clear as the description proceeds.  
           [0011]    According to an aspect of the present invention, there is provided a swash-plate compressor for compressing a fluid. The compressor comprises a cylinder block having a cylinder bore, a piston having a first end portion reciprocally movable in the cylinder bore and a second end portion opposite to the first end portion, the second end portion having a pair of engaging portions faced to each other with a space left therebetween and a side wall portion connecting the engaging portions to each other, a swash plate having a part inserted between the engaging portions and driven to rotate, and a pair of sliding members interposed between the engaging portions and the swash plate, respectively. Each of the sliding members having a flat portion slidably contacted with the swash plate and a spherical portion opposite to the flat portion. Each of the engaging portions having a contact surface slidably contacted with the spherical portion. Each of the contact surfaces extending to the side wall portion. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0012]    [0012]FIG. 1 is a vertical sectional view of a swash-plate compressor according to one embodiment of the present invention;  
         [0013]    [0013]FIG. 2 is a front view of a piston used in the swash-plate compressor illustrated in FIG. 1;  
         [0014]    [0014]FIG. 3 is a side view of the piston illustrated in FIG. 2;  
         [0015]    [0015]FIG. 4 is a sectional view showing the relationship between the piston and shoes;  
         [0016]    [0016]FIG. 5 is a sectional view for describing the force acting between the piston and the shoes illustrated in FIG. 4;  
         [0017]    [0017]FIG. 6 is a sectional view of a piston as a comparative example;  
         [0018]    [0018]FIG. 7 is a sectional view for describing the force acting between the piston and shoes illustrated in FIG. 6;  
         [0019]    [0019]FIG. 8 is a front view of a modification of the piston according to this invention; and  
         [0020]    [0020]FIG. 9 is a front view of another modification of the piston according to this invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    Referring to FIGS. 1 through 4, description will be made of a swash-plate compressor according to an embodiment of the present invention.  
         [0022]    The swash-plate compressor illustrated in FIG. 1 is used, for example, in a refrigerating circuit of an automotive air conditioner and is adapted to compress a carbon dioxide refrigerant. The swash-plate compressor is of a so-called single-head piston type and includes a compressor body  1  having a cylinder block. The compressor body  1  has one end provided with a plurality of cylinder bores  2  spaced from one another in a circumferential direction. Each of the cylinder bores  2  receives one end of a piston  10  inserted therein to be reciprocally movable. The piston  10  has a small outer diameter and intended to be used with the carbon dioxide refrigerant.  
         [0023]    As well known, a cylinder head  4  is attached to one end face of the compressor body  1  through a valve assembly  3 . The cylinder head  4  has a discharge chamber  4   a  formed at its center and a suction chamber  4   b  formed around the discharge chamber  4   a . Each of the discharge chamber  4   a  and the suction chamber  4   b  is communicable with the cylinder bores  2  through valves contained in the valve assembly  3 . Furthermore, the discharge chamber  4   a  and the suction  4   b  are connected to opposite ends of the refrigerating circuit (not shown), respectively.  
         [0024]    The swash-plate compressor illustrated in the figure further comprises a rotatable drive shaft  5 . The drive shaft  5  has one end to which a pulley  6  is mounted. In order to engage and disengage the pulley  6  and the drive shaft  5 , an electromagnetic clutch  8  is provided. By supplying the pulley  6  with an external drive force and exciting the electromagnetic clutch  8 , the drive shaft  5  is rotated.  
         [0025]    In a crank chamber  1  a formed inside the compressor body  1 , a swash plate  11  is connected through a hinge  7   a  to a rotor  7  rotating integrally with the drive shaft  5 . As a consequence, the swash plate  11  is tiltable with respect to the drive shaft  5  and rotatable together with the drive shaft  5 . The swash plate  11  is urged towards each piston  10  by a coil spring  7   b  wound around the drive shaft  5 .  
         [0026]    The piston  10  has the other end with which a peripheral portion of the swash plate  11  is slidably engaged in a structure which will presently be described. Each piston  10  has one end provided with a pair of engaging portions  10   a  and  10   b  faced to each other with the swash plate  11  interposed therebetween, and a side wall portion  10   c  extending from one side end of one engaging portion  10   a  to one side end of the other engaging portion  10   b . The engaging portions  10   a  and  10   b  and the side wall portion  10   c  are integrally formed. Between the engaging portions  10   a  and  10   b  and the swash plate  11 , a pair of shoes  12  are interposed, respectively. The shoes  12  serve as sliding members slidably contacted with the swash plate  11 . Each of the shoes  12  has a spherical portion  12   a  and a flat portion  12   b  opposite to the spherical portion  12   a  and slidably contacted with the swash plate  11 .  
         [0027]    The piston  10  has a contact surface  14  extending over the engaging portions  10   a  and  10   b  and the side wall portion  10   c  to be slidably contacted with the spherical portions  12   a  of the shoes  12 . In other words, the contact surface  14  is continuously formed from the one engaging portion  10   a  through the side wall portion  10   c  to the other engaging portion  10   b . It may be understood that the contact surface  14  is extensively formed on each of the engaging portions  10   a  and  10   b  and the side wall portion  10   c  and that these contact surfaces  14  are connected to one another. The contact surface  14  is formed along a spherical surface having a curvature equal to that of the spherical portion  12   a  of each shoe  12 . The swash plate  11  is adapted to accommodate a large load owing to the use of the carbon dioxide refrigerant. For example, the swash plate  11  has a sufficiently large thickness.  
         [0028]    When the drive shaft  5  is rotated by the drive force supplied to the pulley  6 , the swash plate  11  is rotated together with the drive shaft  5 . Owing to the inclination of the swash plate  11 , each piston  10  reciprocally moves in an axial direction. When the piston  10  reciprocally moves, the carbon dioxide refrigerant circulates through a refrigerating circuit. Specifically, the carbon dioxide refrigerant is sucked from the refrigerating circuit through the suction chamber  4   b  into the cylinder bores  2  and is discharged through the discharge chamber  4   a  to the refrigerating circuit. Due to a pressure difference between the suction chamber  4   b  and the crank chamber la, each piston  10  is applied with a pressure on its rear side (on the side of the crank chamber  1   a ). Depending upon the above-mentioned pressure, the tilting angle of the swash plate  11  is changed so that the discharge volume by the piston  10  is varied. The cylinder head  4  is provided with a pressure adjusting mechanism  15  for adjusting the pressure difference between the suction chamber  4   b  and the crank chamber  1   a.    
         [0029]    When the piston  10  is driven, the swash plate  11  slides along the flat portion  12   b  of each shoe  12  in contact therewith. Simultaneously, each shoe  12  slides along the contact surface  14  with the spherical portion  12   a  kept in contact with the contact surface  14 . If the tilting angle of the swash plate  11  is increased, for example, when the piston  10  reaches a top dead center or a bottom dead center, the displacement of each shoe  12  is increased. However, since the contact surface  14  is continuously formed over the engaging portions  10   a  and  10   b  and the side wall portion  10   c , the spherical portion  12   a  slides along the contact surface  14  continuously in contact therewith even if the shoe  12  is displaced towards the side wall portion  10   c  as illustrated in FIG. 4. Therefore, even if a shoe  12 ′ greater in outer diameter is used as depicted by a dash-and-dot line in the figure, an increase in diameter of the shoe  12 ′ results in an increase in contact area between the spherical portion  12   a  and the contact surface  14  and does not require any modification in shape and size of the contact surface  14 .  
         [0030]    Referring to FIG. 5, when the shoe  12  is displaced towards the side wall portion  10   c , the contact area between the spherical portion  12   a  of the shoe  12  and the contact surface  14  is not reduced. Therefore, as depicted by arrows in the figure, reactive force applied from the contact surface  14  upon the shoe  12  is uniformly distributed throughout a whole of the spherical portion  12   a.    
         [0031]    Next referring to FIG. 6, a piston  13  in a comparative example has engaging portions  13   a  and  13   b  and a side wall portion  13   c  between the engaging portions  13   a  and  13   b . Each of the engaging portions  13   a  and  13   b  is provided with a contact surface  13   d . On the other hand, the side wall portion  13   c  is provided with a recessed portion  13   e  receiving a lateral side of the shoe  12  in a non-contact manner. In case where the shoe  12 ′ having a greater diameter is used as depicted by a dash-and-dot line in the figure, the recessed portion  13   e  will interfere with the lateral side of the shoe  12 ′ unless the depth of the recessed portion  13   e  is increased. In order to avoid such interference, the depth of the recessed portion  13   e  must be increased. For this purpose, the side wall portion  13   c  is enlarged outward in a lateral direction of the piston  13 . Disadvantageously, this results in an increase in size of the compressor body  1 . Alternatively, the depth of the recessed portion  13   e  can be increased by reducing the thickness of the side wall portion  13   c  without enlarging the side wall portion  13   c  outward in the lateral direction of the piston  13 . In this event, however, the strength of the piston  13  is decreased.  
         [0032]    Referring to FIG. 7, consideration will be made about the force acting between the shoe  12  and the contact surface  13   d  in case where the side wall portion  13   c  is provided with the recessed portion  13   e  receiving the lateral side of the shoe  12 . In this case, a part of the spherical portion  12   a  of the shoe  12  displaced towards the side wall portion  13   c  moves out of the contact surface  13   d  of each of the engaging portions  13   a  and  13   b . Therefore, the contact area between the spherical portion  12   a  of the shoe  12  and the contact surface  13   d  is reduced. As a consequence, reactive force applied from the contact surface  13   d  upon the shoe  12  is concentrated to a part of the spherical portion  12   a  as depicted by arrows in the figure. This may result in an abnormal sliding condition of the shoe  12  or a release of the shoe  12  from the piston  13 .  
         [0033]    As compared with the comparative example mentioned above, the swash-plate compressor illustrated in FIG. 1 has a structure in which the contact surface  14  is continuously formed over the engaging portions  10   a  and  10   b  and the side wall portion  10   c . With this structure, even if the shoe  12  is displaced towards the side wall portion  10   c , the spherical portion  12   a  of the shoe  12  is continuously kept in contact with the contact surface  14 . Therefore, even if the shoe  12 ′ having a greater outer diameter is used, it is unnecessary to modify the shape or the size of the contact surface  14 . In addition, it is unnecessary to enlarge the side wall portion  10   c  outward in the lateral direction of the piston  10  and to reduce the thickness of the side wall portion  10   c . Thus, it is possible to avoid an increase in size of the compressor body  1  and a decrease in strength of the piston  10 .  
         [0034]    Even if the shoe  12  is displaced towards the side wall portion  10   c , the reactive force from the contact surface  14  can uniformly be received by a whole of the spherical portion  12   a . Therefore, even if the tilting angle of the swash plate  11  is large, the shoe  12  can continuously smoothly slide along the contact surface  14 . Accordingly, it is possible to reliably prevent an abnormal sliding condition and a release of the shoe  12  from the piston  10  and to distribute the reactive force from the contact surface  14  so that occurrence of local wear is avoided. Thus, the above-mentioned structure of this invention is advantageous also in view of improvement of the durability.  
         [0035]    Furthermore, the contact surface  14  is continuously formed over the engaging portions  10   a  and  10   b  and the side wall portion  10   c . Therefore, it is possible to accommodate not only an increase in diameter of each shoe  12  but also an increase in sliding range of each shoe  12 . Thus, the versatility can be improved. In this case, since the contact surface  14  is formed on the side wall portion  10   c  by cutting, the piston  10  can be reduced in weight. This structure is advantageous if it is desired to reduce the inertial force. Because the contact surface  14  is continuously formed between the engaging portions  10   a  and  10   b , a lubricating oil  15  can be retained on the contact surface  14  between the shoes  12  as illustrated in FIG. 5. Thus, it is possible to reliably supply the lubricating oil  15  to each shoe  12 . As a consequence, each shoe  12  can very effectively be prevented from seizure.  
         [0036]    Furthermore, it is possible to easily produce the contact surface  14  continuously formed. In this case, the contact surface  14  is formed along a spherical surface having a curvature equal to that of the spherical portion  12   a  of each shoe  12 . Therefore, the contact surface  14  can be easily formed by cutting or the like so that the productivity is improved.  
         [0037]    Furthermore, the durability can be improved without causing an increase in size of the compressor body  1  and a decrease in strength of the piston  10  as described above. Therefore, it is possible to use the carbon dioxide refrigerant high in working pressure. Thus, by the use of the carbon dioxide refrigerant, it is possible to achieve the refrigerating circuit advantageous in environment protection. Particularly when the compressor is used in the automotive air conditioner, the structure of this invention is very effective.  
         [0038]    As illustrated in FIG. 8, the contact surface  14  may be formed continuously from each of the engaging portions  10   a  and  10   b  to a part of the side wall portion  10   c.    
         [0039]    As illustrated in FIG. 9, the contact surface  14  may be divided by a groove  10   e.    
         [0040]    By forming an integral member corresponding to a combination of the swash plate  11  and the rotor  7 , it is possible to provide a fixed-volume or fixed- displacement compressor comprising a swash plate having a predetermined fixed tilting angle with respect to the drive shaft  5 . In such a compressor, this invention can similarly be embodied to achieve the similar effect.  
         [0041]    Although the present invention has been shown and described in conjunction with a few preferred embodiments thereof, it should be understood by those skilled in the art that the present invention is not limited to the foregoing description but may be changed and modified in various other manners without departing from the spirit and scope of the present invention as set forth in the appended claims. For example, the present invention is not limited to a compressor of a single-head piston type but is applicable to a swash-plate compressor using a double-head piston.