Patent Publication Number: US-6217295-B1

Title: Swash plate type compressor

Description:
TECHNICAL FIELD 
     The present invention relates to a swash plate type compressor and, more particularly, to a swash plate type compressor provided with a swash plate and pistons which are finished by improved surface treatment to exercise enhanced performance, and capable of functioning with improved reliability. 
     BACKGROUND ART 
     A double-headed swash plate type compressor applied to an automobile air conditioning system, for example, has a drive shaft, a pair of cylinder blocks supporting the drive shaft for rotation, and a swash plate fixedly supported on the drive shaft for rotation together with the drive shaft in a swash plate chamber formed in a region including the boundary between the pair of cylinder blocks. A plurality of cylinder bores are formed so as to extend in both the cylinder blocks and are arranged around the drive shaft. Double-headed pistons are fitted for axial movement in the cylinder bores, respectively. Each piston is operatively engaged with the swash plate by shoes. The rotary motion of the swash plate is converted into the linear motion of the pistons for the suction, compression and discharge of a refrigerant gas. 
     A single-headed swash plate type compressor has a cylinder block and a housing closing the inner end of the cylinder block and having a swash plate chamber or a crank chamber. A swash plate is mounted on a drive shaft in the swash plate chamber and is linked to pistons by shoes. In a variable-displacement swash plate compressor, a swash plate is linked to single-headed pistons fitted in a plurality of cylinder bores by shoes, and is mounted on a drive shaft so as to wobble on a supporting point. The inclination of the swash plate is changed according to pressure in the crank chamber so that gas pressures acting on the opposite ends of the single-headed piston balance each other. Consequently, the stroke of the single-headed piston is adjusted to control the displacement of the compressor. 
     A significant demand for weight reduction in those swash plate type compressors has progressively increased in order to apply the swash plate type compressors to automobile air conditioning systems, and most of the swash plates and the pistons, as well as the cylinder blocks, of those swash plate type compressors are made of aluminum alloys in lightweight constructions. Therefore, abrasion-resistant and seizing-preventive measures have been examined for protecting surfaces exposed to severe, high-speed abrasive action for a long time, such as the surfaces of the swash plate in sliding contact with the shoes, and the sliding contact surface of the piston in sliding contact with the surface of the bore. Such measures include the formation of a fluorocarbon resin film on the sliding contact surface of the piston and the formation of a film of a solid lubricant on the sliding contact surface of the swash plate. 
     However, the double-headed piston is provided with a recess extending across the periphery of the swash plate, and interfering surfaces formed in the recess to restrain the piston from rotation come into impulsive contact with the outer circumference of the swash plate to restrain the piston from rotation by a rotation moment acting on the piston. The single-headed piston is provided with a rotation-preventive interfering surface in its base end part, and the interfering surface comes into impulsive contact with the inner surface of the housing to restrain the piston from rotation. Accordingly, it is possible, under a substantially nonlubricated state which occurs at the start of the compressor, that seizing occurs at the interfering surface of the piston and the outer circumference of the swash plate, and attempts have been made to form a lubricating film over the interfering surface of the piston and the outer circumference of the swash plate. Nevertheless, the yield of a coating material used in, for example, a spray coating process for coating the pistons and the swash plate with a lubricating film is extremely low. Furthermore, the spherical surfaces of the pistons must be masked in the spray coating process and the spray coating process is hardly satisfactory in working efficiency. 
     DISCLOSURE OF THE INVENTION 
     It is an object of the present invention to provide an improved swash plate type compressor capable of providing improved functional reliability attained by employing, in combination, an improved swash plate and improved pistons provided with an excellent lubricating film capable of being manufactured with a high productivity. 
     Another object of the present invention is to provide a long-life swash plate type compressor capable of properly functioning for an extended period of use when applied to an automobile air conditioning system and driven by the engine of a vehicle to compress a refrigerant. 
     In accordance with the present invention, there is provided a swash plate type compressor which comprises: a cylinder block provided with a plurality of cylinder bores; pistons fitted in the cylinder bores; a drive shaft supported for rotation about its axis of rotation; and a swash plate supported for rotation together with the drive shaft, having at least sliding contact surfaces to be in sliding contact with shoes and linked to the pistons by the shoes; 
     wherein the pistons are made of an aluminum alloy as a base material, each piston has an interfering surface which is interfered with by another member to restrain the piston from rotation, and the interference surfaces of the pistons are coated with a film of at least one solid lubricant selected from molybdenum disulfide, tungsten disulfide and graphite. 
     In the described swash plate type compressor, the excellent lubricating performance of the film of the solid lubricant formed on the interfering surface for retraining the piston from rotation effectively prevents the seizing of the interfering surface, and the outer circumference of the swash plate, i.e., another member, or the inner surface of a crank chamber with which the interfering surface comes into nonlubricated contact, enhances the functional reliability of the swash plate compressor, and extends the life of the swash plate compressor. 
     The seizing preventing effect of a film of a solid lubricant containing molybdenum disulfide as an essential component is particularly remarkable. 
     If the sliding contact surface of the piston in sliding contact with a surface defining the cylinder bore is coated with a film of a material containing a fluorocarbon resin as a principal component or a film of a solid lubricant, the abrasion resistance and the seizing preventing capability of the piston sliding in the bore can be improved. 
     When a transfer method is employed in forming the lubricating films on the sliding contact surfaces of the pistons in sliding contact with surfaces defining the cylinder bores, and the rotation-preventive interfering surfaces of the pistons, the coating material is not wasted, masking work is unnecessary when forming the film, and it is very advantageous in quality assurance, such as film thickness control. 
     In a swash plate type compressor in which the rotation-preventive interfering surfaces of pistons come into impulsive contact with the outer circumference of a swash plate to prevent the pistons from rotation, it is preferable to plate the outer circumference of the swash plate with a metal containing tin as a principal component or to form a lubricating film of a solid lubricant on the outer circumference of the swash plate. In the swash plate compressor, the cooperative effect of the outer circumference of the swash plate and the interfering surfaces of the pistons further effectively prevents the seizing of the pistons and the swash plate. 
     A metal layer of a material containing tin as a principal component formed by plating so as to underlie the film of the solid lubricant formed on the outer circumference of the swash plate will further enhance the durability of the film. 
     Obviously, the film of the solid lubricant can quite simply be formed on the outer circumference of the swash plate by a transfer method. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become apparent from the ensuing description, taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a longitudinal sectional view of a double-headed swash plate type compressor in a preferred embodiment according to the present invention; 
     FIG. 2A is a perspective view of a double-headed piston employed in the compressor of FIG. 1; 
     FIG. 2B is a longitudinal sectional view taken on line  2 B— 2 B in FIG. 2A, showing the positions of interference surfaces; 
     FIG. 3 is a longitudinal sectional view of a single-headed swash plate type compressor in another embodiment according to the present invention; 
     FIG. 4A is a front view of a single-headed piston employed in the compressor of FIG. 3; 
     FIG. 4B is a rear end view showing a rotation-preventive interfering surface formed in the single-headed piston; 
     FIG. 5A is a typical view of a transfer apparatus for forming a film of a solid lubricant on the sliding contact surfaces of a piston by a transfer method; 
     FIG. 5B is a typical development showing the relation between a workpiece for making a piston and a roller arrangement included in the transfer apparatus; 
     FIG. 6A is a typical view of a transfer apparatus for forming a film of a solid lubricant on the rotation-preventive interfering surfaces of a double-headed piston; 
     FIG. 6B is a typical development schematically showing the relation between a workpiece for making a piston held on a transfer apparatus and a roller arrangement included in the transfer apparatus; 
     FIG. 7 is a typical view of a transfer apparatus for forming a film of a solid lubricant on the rotation-preventive interfering surfaces of a single-headed piston by a transfer method; and 
     FIG. 8 is a typical view of a transfer apparatus for forming a film of a solid lubricant on the outer circumference of a swash plate by a transfer method. 
    
    
     BEST MODE OF CARRYING OUT THE INVENTION 
     Referring to FIGS. 1,  2 A and  2 B, a double-headed swash plate type compressor has a front cylinder block  1 A and a rear cylinder block  1 B, and a drive shaft  2  is supported for rotation about an axis of rotation on the cylinder blocks  1 A and  1 B. A swash plate chamber  4  is formed in a region around the joint of the cylinder blocks  1 A and  1 B in the cylinder blocks  1 A and  1 B. A swash plate  3  is contained in the swash plate chamber  4  and is combined with the drive shaft  2  for rotation together with the drive shaft  2 . Bores of a predetermined diameter are formed in the cylinder blocks  1 A and  1 B, and the cylinder blocks  1 A and  1 B are joined together with the respective axes of the corresponding bores aligned with each other so as to form a plurality of axial cylinder bores (hereinafter referred to simply as “bores”)  5  arranged around the drive shaft  2 . Opposite end parts of double-headed pistons  6  are fitted in the bores  5 , respectively, for axial sliding movement. Each piston  6  is linked to the sliding contact surfaces  3   a  of the swash plate  3  by shoes  7 . A rotary motion of the swash plate  3  is converted into a linear motion of the piston  6  for the suction, compression and discharge of a refrigerant gas. 
     In this embodiment, the shoes  7  are made of a ferrous metal, the cylinder blocks  1   a  and  1 B and the swash plate  3  and the double-headed pistons  6  are made of an aluminum alloy, such as a hypereutectic aluminum-silicon alloy. 
     As best shown in FIGS. 2A and 2B, the double-headed piston  6  has cylindrical sliding contact surfaces  6   a  of a predetermined length formed in the opposite end parts thereof and capable of being slidably fitted in the bores  5 , and a recess  6   b  formed in a middle part thereof between the opposite end parts provided with the sliding contact surfaces  6   a  so as to extend across the outer circumference of the swash plate  3 . Semispherical seats  6   c  on which the shoes  7  are seated, respectively, are formed axially opposite to each other in the recess  6   b . Interfering surfaces  6   d  for restraining the piston  6  from rotation are formed axisymmetrically in the middle part. The interfering surfaces  6   d  come into impulsive contact with the outer circumference  3   b  of the swash plate  3  to inhibit the rotation of the piston  6  about its axis due to a rotation moment exerted by the shoes  7  on the piston  6 . 
     Referring to FIGS. 3,  4 A and  4 B, a variable-displacement swash plate type compressor in another embodiment according to the present invention has a cylinder block  10  having opposite end surfaces, a front housing  11  joined to the cylinder block  10  so as to cover the front end of the cylinder block  10 , a valve plate  12  placed on the rear end surface of the cylinder block  10 , and a rear housing  13  joined to the cylinder block  10  so as to cover the rear end of the cylinder block  10 . The cylinder block  10 , the front housing  11  and the rear housing  13  are firmly fastened together with through bolts so that the joints thereof are sealed. In the compressor, the cylinder block  10  and the front housing  11  define a crank chamber  14 , and a drive shaft  15  is extended axially in the crank chamber  14  and is supported for rotation in a pair of radial bearings held respectively on the cylinder block  10  and the front housing  11 . 
     A plurality of cylinder bores (hereinafter referred to simply as “bores”)  16  are formed around the drive shaft  15  in the cylinder block  10 , and single-headed pistons  17  are fitted for reciprocation in the bores  16 , respectively. 
     In the crank chamber, a rotor  20  is fixedly mounted on the drive shaft  15  for rotation together with the drive shaft  15 . An axial load exerted on the rotor  20  is sustained through a thrust bearing by the front housing  11 . A swash plate  18  is mounted on the drive shaft  15  at a position behind the rotor  20 . The swash plate  18  is always biased backward by the resilience of a compression spring interposed between the swash plate  18  and the rotor  20 . 
     The swash plate  18  has a shape generally resembling a plate and is provided with flat sliding contact surfaces  18   a  formed on the opposite sides of a peripheral part thereof. Semispherical shoes  19  are put in contact with the sliding contact surfaces  18   a , respectively. The shoes  19  are in sliding contact with semispherical seats  17   c  formed in the piston  17 . A hinge mechanism K is formed between the swash plate  18  and the rotor  20  to allow the swash plate  18  to move pivotally relative to the rotor  20 . 
     The swash plate  18  is provided with a bent central hole  18   b  formed through a central part thereof. The drive shaft  15  is extended through the central hole  18   b  to support the swash plate  18  thereon. The inclination of the swash plate  18  is variable without varying the top dead center of each single-headed piston  17  relative to the corresponding bore  16 . When the swash plate  18  is inclined to a maximum inclination position, a projecting surface  10   a , projecting from the swash plate  18  abuts against a projection  12   e  on rotor  20  which restricts further movement of the swash plate  18  from the maximum inclination position. 
     In this embodiment, the cylinder block  10 , the swash plate  18  and the piston  17  are made of an aluminum alloy, such as a hypereutectic aluminum-silicon alloy. Each piston  17  is provided in its head part with a sliding contact surface  17   a  of a predetermined length fitting the bore  16 , in its tail end part with a recess  17   b  (FIG. 4A) extending across the swash plate  18 , and on the back side of a part thereof forming the recess  17   b  with a curved interfering surface  17   d  of a large radius of curvature capable of coming into impulsive contact with the inner surface  14   a  defining the crank chamber  14  to prevent the piston  17  from rotating. 
     The surface treatment of the piston, which is one of the features of the present invention, will be described with reference to FIGS. 5A to  7 . 
     Although the double-headed piston  6  and the single-headed piston  17  included respectively in the swash plate type compressors in the foregoing embodiments differ from each other in shape, the double-headed piston  6  has rotation-preventive interfering surfaces  6   d  which come into impulsive contact with the swash plate  3  to restrain the piston  6  from rotation about its axis, and the single-headed piston  17  has the rotation-preventive interfering surface  17   d  which comes into impulsive contact with the inner wall surface  14   a  defining the crank chamber  14  to prevent or restrain the piston  17  from rotating about its axis. The interfering surfaces  6   d  and  17   d  are coated with films formed by coating the interfering surfaces  6   d  and  17   d  with films of a lubricating material prepared by mixing molybdenum disulfide and graphite chosen as solid lubricants, and a polyamidimide resin (bonding agent), and heating and hardening the films of the lubricating material. The sliding contact surfaces  6   a  and  17   a  of the parts of the pistons  6  and  17  fitted in the bores  5  and  16 , respectively, are coated with a film of a generally used fluorocarbon resin (polytetrafluoroethylene). 
     The pistons  6  and  17  in those embodiments are provided with the rotation-preventive interfering surfaces  6   d  and  17   d , which are subject to seizing, coated with the lubricating films of a solid lubricant, such as molybdenum disulfide. Therefore, the seizing resistance of the pistons  6  and  17  is far higher than that of pistons substantially entirely coated with a fluorocarbon resin. 
     Since the lubricating films formed on the sliding contact surfaces  6   a  and  17   a  and the interfering surfaces  6   d  and  17   d  of the pistons  6  and  17  are formed by a transfer method regardless of the materials, the lubricating films can very easily be formed without entailing substantial increase in work even if the lubricating films are formed of different materials. Further, strength of connection of the lubricating films to the above-mentioned sliding contact surfaces and to the above-mentioned sliding contact surfaces can be increased. 
     A transfer method (roller transfer method) of forming fluorocarbon resin films on the sliding contact surfaces  6   a ,  6   a  formed on a workpiece  6 W for making the piston will be described. 
     FIG. 5A is a typical view of a transfer apparatus and FIG. 5B is a development showing the workpiece for making eh piston, and rollers. 
     Referring to FIGS. 5A and 5B, a transfer apparatus  50  has a tank  52  containing a coating material “C” containing a lubricant, such as polytetrafluoroethylene, a binder resin, a solvent, such as N-methyl-pyrrolidone, and a filler, a metal roller  53  partly dipped in the coating material C contained in the tank  52 , a comma roller  54  disposed near the metal roller  53  with a predetermined gap therebetween, a transfer roller  55  of a synthetic rubber having coating parts  55   a  of an increased diameter with which the sliding contact surfaces  6   a  of the workpiece  6 W can be brought into contact, and disposed with the coating parts  55   a  in contact with the metal roller  53 , a work holder  56  for rotatably holding the workpiece  6 W, and a driving mechanism  51  for driving the rollers  53  and  55  for rotation in the directions of the arrows. 
     When the rollers  53  and  55  are rotationally driven by the driving mechanism  51 , the coating material C adheres to the circumference of the metal roller  53 , the thickness of a layer of the coating material C on the metal roller  53  is adjusted by the comma roller  54 , and the layer of the coating material C is transferred from the metal roller  53  to the coating parts  55   a  of the transfer roller  55 . When the rotating workpiece  6 W is brought into contact with the transfer roller  55  by the work holder  56 , the coating material C is applied (transferred) to the sliding contact surfaces  6   a  of the workpiece  6 W from the transfer roller  55 . 
     Then the workpiece  6 W is separated from the transfer roller  55  and is removed from the work holder  56 . The workpiece  6 W is subjected to a drying process to remove the solvent from the coating material C and is subjected to a baking process to form films firmly adhering to the sliding contact surfaces  6   a.    
     A transfer method (roller transfer method) of forming films of a solid lubricant on the interfering surfaces  6   d  of the workpiece  6 W for making the piston will be described hereinbelow. 
     Referring to FIGS. 6A and 6B, a transfer apparatus  60  has a tank  62  containing a coating material C′ containing a solid lubricant, such as a mixture of molybdenum disulfide and graphite, and a unhardened thermosetting resin, such as a polyamidimide resin, a metal roller  63  partly dipped in the coating material C′ contained in the tank  62 , a comma roller  64  disposed near the metal roller  63  with a predetermined gap therebetween, a transfer roller  65  of a synthetic rubber having coating parts  65   a  of an increased diameter having a width corresponding to that of the interfering surfaces  6   d  of the workpiece  6 W and capable of being inserted in the recess  6   b , and a driving mechanism  61  for driving the rollers  63  and  65  for rotation in the directions of the arrows. A robot arm  66  for supporting the workpiece  6 W is capable of turning on its pivot shaft  66   a , and of being turned through a predetermined angle about the axis of the workpiece  6 W by a means, not shown. 
     When the rollers  63  and  65  are rotated by the driving mechanism  61 , the coating material C′ adheres to the circumference of the metal roller  63 , the thickness of a layer of the coating material C′ on the metal roller  63  is adjusted by the comma roller  64 , and the layer of the coating material C′ is transferred from the metal roller  63  to the coating part  65   a  of the transfer roller  65 . When one of the interfering surfaces  6   d  of the workpiece  6 W supported on the robot arm  66  is brought into contact with the transfer roller  65  by turning the workpiece  6 W clockwise, as viewed in FIG. 6A, about its axis through a predetermined angle, the coating material C′ is transferred to the interfering surface  6   d  to coat the same. Subsequently, the workpiece  6 W is moved to the right to separate the workpiece  6 W from the transfer roller  65 , the workpiece  6 W is reversed on the pivotal shaft  66   a  of the robot art  66 , and then the workpiece  6 W is moved to the left to bring the other interfering surface  6   d  into contact with the transfer roller  65 . Consequently, the other interfering surface  6   d  is coated with the coating material C′. Subsequently, the workpiece  6 W is subjected to a drying process and a baking process to form films firmly adhering to the interfering surfaces  6   d.    
     FIG. 7 shows a transfer apparatus for forming a film of a solid lubricant on the interfering surface  17   d  of a workpiece  17 W for making a piston. The transfer apparatus  70  is provided with rollers  73  and  75  and a driving mechanism  71  similar to those of the transfer apparatus  50  shown in FIGS. 5A and 5B. 
     Accordingly, a transfer method to be carried out by the transfer apparatus  70  is basically the same as that to be carried out by the transfer apparatus  50 . Since the center of curvature of the interfering surface  17   d  is at a considerable distance from the center of turning of the workpiece  17 W, a work holder  76  is provided with a mechanism for permitting a displacement of the center of rotation of the workpiece  17 W, not shown. 
     Description of the surface treatment of the outer circumference  3   b  of the swash plate  3  with which the rotation-preventive interfering surface  6   d  of the piston  6  comes into impulsive contact will be provided hereinbelow. 
     The outer circumference  3   b  of the swash plate  3  is covered with a plated metal layer of a metal containing tin as a principal component and, if necessary, a film of a solid lubricant is formed on the plated metal layer. 
     FIG. 8 shows a transfer apparatus for forming a film of a solid lubricant on the outer circumference  3   b  of a workpiece  3 W for making the swash plate. Since the transfer apparatus has rollers  83 ,  84  and  85  and work holder  86  whose functions are similar to those of the transfer apparatus shown in FIGS. 5A and 5B, and carries out substantially the same transfer method as those in the foregoing embodiments, the specific description thereof will be omitted. 
     As is apparent from the foregoing description, according to the present invention, the rotation-preventive interfering surfaces of the pistons of the swash plate type compressor or both the sliding contact surfaces of parts of the pistons fitted in the bores and the interfering surfaces of the pistons are coated with the lubricating films, whereby the seizing of the interfering surface, and the outer circumference of the swash plate or the inner surface of the housing with which the interfering surface comes into nonlubricated contact can be effectively prevented. 
     When the lubricating films are formed on the interference surfaces and the sliding contact surfaces by a transfer method, the coating material is not wasted, masking work is unnecessary and the productivity can be improved. Further, strength of connection of the lubricating films to the sliding contact surfaces and to the sliding contact surfaces can be increased. 
     When the outer circumference of the swash plate with which the rotation-preventive interfering surfaces of the pistons come into impulsive contact is coated with the plated metal layer of a metal containing tin as a principal component and the lubricating film of a solid lubricant, and the swash plate is used in combination with the foregoing pistons, the seizing of the swash plate and the pistons can further effectively be prevented, and the plated metal layer of a metal containing tin as a principal component formed on the outer circumference of the swash plate and underlying the film of the solid lubricant further enhances the durability. 
     The film of the solid lubricant can very simply be formed on the outer circumference of the swash plate by a transfer mode. 
     LIST OF REFERENCE CHARACTERS 
       1 A Cylinder block 
       1 B Cylinder block 
       2  Drive shaft 
       3  Swash plate 
       3 A Sliding contact surface 
       3 B Outer circumference 
       4  Swash plate chamber 
       5  Cylinder bore 
       6  Double-headed piston 
       6 A Sliding contact surface 
       6 B Recess 
       6 D Interfering surface 
       7  Shoe 
       10  Cylinder block 
       11  Front housing 
       12  Valve plate 
       13  Rear housing 
       14  Crank chamber 
       14 A Inner wall surface 
       15  Drive shaft 
       16  Cylinder bore 
       17  Single-headed piston 
       17 A Sliding contact surface 
       17 D Interfering surface 
       18  Swash plate 
       18 A Sliding contact surface 
       19  Shoe 
       50  Transfer apparatus 
       60  Transfer apparatus 
       70  Transfer apparatus