Patent Publication Number: US-2013243617-A1

Title: Swash plate type compressor

Description:
FIELD OF THE INVENTION 
     The present invention relates to a swash plate type compressor, and relates to a swash plate type compressor arranged with a swash plate which rotates around a shaft, a piston which moves back and forth with the rotation of the swash plate, and a shoe formed with a flat part which slides against the swash plate and a spherical surface part which slides in a spherical groove part formed on the piston. 
     BACKGROUND OF THE INVENTION 
     Conventionally, a swash plate type compressor is known arranged with a swash plate which rotates around a shaft, a piston which moves back and forth with the rotation of the swash plate, and a shoe formed with a flat part which slides against the swash plate and a spherical surface part which slides in a spherical groove part formed on the piston (patent documents 1, 2). 
     A coating layer comprised from a resin is formed on the surface of the swash plate, and spiral or concentric shaped grooves formed with the center of the swash plate at the center on the surface of the coating layer in the swash plate type compressor in patent document 1 in order to improve lubrication between the shoe and swash plate. 
     In addition, the conventional swash plate type compressor described in patent document 1 etc generally has a flat part with a diameter of about 11-12 mm. 
     PRIOR ART 
     Patent Documents 
     
         
         Patent Document 1: International Published Patent WO2002-075172 
       
    
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     Here, because the shoe is pressed against the swash plate by the reciprocating movement of the piston, the larger the diameter of the flat part of the shoe, the greater is the friction between the shoe and the swash plate which causes problems to the fuel consumption capacity of an engine which runs a swash plate type compressor. 
     Thus, reducing the friction between the shoe and swash plate and improving fuel consumption of an engine which runs a swash plate type compressor can be expected in order to tackle this type of problem by reducing the diameter of the flat part of the shoe. 
     However, if the diameter of the flat part of the shoe is reduced, a load is concentrated on the sections which contact with the flat part where the concentrics protrude causing the concentric protrusions to elastically deform and when the shoe slides against the swash plate, a shear resistance generated between the shoe and concentric protrusions causes wear to the coating layer and when the concentric protrusions disappear, the affinity between the shoe and swash plate or lubrication retention worsens. 
     Thus in order to solve these problems, the present invention provides a swash plate type compressor which can reduce friction with the swash plate and reduce wear of a coating layer by reducing the diameter of the flat part of a shoe. 
     Means for Solving the Problems 
     That is, a swash plate type compressor of claim  1  is arranged with a swash plate which rotates around a shaft, a piston formed with a spherical indent part and which moves back and forth with the rotation of the swash plate, and a shoe formed with a flat part which slides against the swash plate and a spherical surface part which slides in the spherical indent part formed on the piston, wherein a coating layer comprised from a resin is formed on the surface of the swash plate, and spiral or concentric shaped grooves are formed with the center of the swash plate at the center on the surface of the coating layer, a diameter of the flat part is set at less than 10.5 mm and the pitch of a concentric protrusion formed between the concentric shaped grooves is set to satisfy the following conditions: 
     
       
         
           
             
               
                 
                   
                     
                       ∑ 
                       
                         k 
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                         1 
                       
                       N 
                     
                      
                     
                       L 
                       k 
                     
                   
                   &gt; 
                   
                     300 
                      
                     
                       ( 
                       mm 
                       ) 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Formula 
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         L=length (mm) of the concentric protrusion which contact the flat part of the shoe, 
         N=number of concentric protrusions which contact the flat part of the shoe. 
       
    
     Effects of the Invention 
     According to the structure described above, even if friction between the shoe and swash plate is reduced by reducing the diameter of the flat part of the shoe compared to a conventional shoe, by increasing the length of a concentric protrusion which contacts with the flat part of a shoe using the formula described above, it is possible to disperse surface pressure on the flat part across multiple concentric protrusions, reduce elastic deformation of the concentric protrusions, reduce shear resistance between the shoe and concentric protrusions, and reduce wear of the coating layer. 
    
    
     
       BRIEF EXPLANATION OF THE DRAWINGS 
         FIG. 1  is a cross sectional diagram of a swash plate type compressor. 
         FIG. 2  is an expanded view diagram of a shoe and a swash plate. 
         FIG. 3  shows the state of a concentric protrusion which contacts with a flat part of the shoe. 
         FIG. 4  shows the state of the shoe and the swash plate which satisfy the conditions of formula 1. 
         FIG. 5  is a graph showing experiment results. 
         FIG. 6  is a graph showing experiment results. 
         FIG. 7  is a graph showing experiment results. 
         FIG. 8  is a cross sectional diagram of a shoe including other shapes. 
     
    
    
     EMBODIMENTS FOR REALIZING THE INVENTION 
     Explaining the embodiments illustrated below,  FIG. 1  shows the internal structure of a swash plate type compressor  1 , a shaft  2  supported by a housing which is not shown, a swash plate  3  attached to the shaft  2 , a plurality of pistons  4  which move back and forth within a cylinder not shown in the housing, and a plurality of shoes  5  arranged so as to face the interior of each piston  4  and which fasten the swash plate  3 . 
     The swash plate  3  is either fixed diagonally with respect to the shaft  2  or the inclination of the swash plate  3  can be changed and is fastened by two shoes  5  for each piston  4 . 
     The pistons  4  are formed with a spherical indent part  4   a  so that each mutually faces each other and the rotation of the swash plate  3  is converted to back and forth movement of the piston  4  while the shoe  5  slides against the indent part  4   a.    
     Furthermore, the swash plate type compressor  1  having this type of structure is a conventionally known compressor and thus further explanation is omitted. 
     The shoe  5  of the present embodiment is manufactured a sintered material or resin material etc in addition to a steel, copper, aluminum material and a forged or rolled SUJ2 manufactured shoe  4  is preferred. 
       FIG. 2  shows an expanded view diagram of the vicinity of the shoe  5 . The shoe  5  is formed from a flat part  5   a  which slides against the swash plate  3 , a spherical surface part  5   b  which slides against the indent part  4   a  of the piston  4 , a recess part  5   c  comprised from a curved surface formed to surround the spherical surface part  5   b,  and a flat taper part  5   d  formed to surround the flat part  5   a.  Furthermore,  FIG. 2  is an exemplary diagram and exaggerates the scale of a part of the actual shape of the shoe  5 . 
     The flat part  5   a  and the taper part  5   d  are connected by a smooth surface, the flat part  5   a  is formed from a roughly flat surface which does not include the smooth curved surface described above and includes a circle shape which has a diameter set to d&lt;10.5 mm. This diameter d is preferred to be set to 3.5 mm≦d≦9.5 mm, and more preferably 5.5 mm≦d≦8.5 mm. 
     That is, the flat part  5   a  of the present embodiment has a smaller diameter than a flat part of a conventionally known shoe of 11-12 mm. 
     Here, the diameter d of the flat part, that is, the boundary between the flat part  5   a  and the smooth curved surface can be recognized by measuring the flat part  5   a  using a scale where vertical magnification (magnification in the height direction of the shoe) is  100  larger than horizontal magnification (magnification is a radial direction of the shoe). 
     The spherical surface part  5   b  and recess part  5   c  are each formed by a curved surface and the taper part  5   d  formed between the recess part  5   c  and flat part  5   a  inclines in a direction offset from the swash plate  3  with respect to the flat part  5   a.    
     Furthermore, a dimple may be formed at the center of the flat part  5   a  of the shoe  5  or other parts and the flat part  5   a  may have a raised center shape. 
     Next, the swash plate  3  of the present embodiment is formed from a base  3   a  formed in a disc shape, and a coating layer  3   b  formed on the surface of the base  3   a.  A spiral shaped concentric groove  3   c  is formed on the surface of the coating layer  3   b  so as to surround the shaft  22 . 
     The base  3  is manufactured by a steel, copper or aluminum material and in the case where an intermediate later is arranged between the base  3   a  and coating layer  3   b,  it is possible to form the base using a method such as steel sinteconcentric, copper spraying, aluminum spraying, or copper aluminum spraying etc. 
     The coating layer  3   b  is formed by adding a solid lubricant to a thermoset resin binder and a polyimide group resin (PI), polyamide-imide group resin (PAI), epoxy resin, phenol resin etc, or polyamide (nylon), elastomer may be used as the thermoset resin binder. 
     Molybdenum disulfide (MoS 2 ), polytetrafluoroethylene (PTFE), tungsten disulfide (WS 2 ), hexagonal boron nitride (h-BN), graphite fluoride (CF), or fluoride resin can be used as the solid lubricant and the particle diameter is preferred to be 15 μm or less and more preferably 0.2˜10 μm with a contained ratio of 5˜8% by weight. 
     Furthermore, hard particles may be added to the coating layer  3   b.  An oxide such as alumina or silica, a nitride such as silicon nitride (SiN), a carbide such as silicon carbon (SIC) or a sulfide such as zinc sulfide (ZnS) are examples of the hard particle with a preferred particle diameter of 0.01˜μm and a contained ratio of 0.2˜7% by weight. 
     The concentric groove  3   c  is formed by mechanical processing after forming the coating layer  3   b  on the surface of the substrate  3   a  and can be formed into a concentric shape as well as a spiral shape. 
     With this type of structure, the concentric projection  3   d  formed between adjacent concentric grooves  3   c  contacts the flat part  5   a  of the shoe shown in  FIG. 3  in a stripe shape. Furthermore,  FIG. 3  is also an exemplary diagram which describes a different scale to the actual scale of the concentric protrusion  3   d.    
     In addition, in the swash plate type compressor  1  of the present embodiment, the pitch of the concentric protrusion  3   d  with respect to the small diameter shoe  5  described above is set so as to satisfy the following relationship. 
     
       
         
           
             
               
                 
                   
                     
                       ∑ 
                       
                         k 
                         = 
                         1 
                       
                       N 
                     
                      
                     
                       L 
                       k 
                     
                   
                   &gt; 
                   
                     300 
                      
                     
                       ( 
                       mm 
                       ) 
                     
                   
                 
               
               
                 
                   [ 
                   
                     formula 
                      
                     
                         
                     
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         (L: length of the concentric protrusion  3   d  which contacts the flat part  5   a,  N: number of concentric protrusions which contact with the flat part  5   a ) 
       
    
     On the left side of formula 1 the length of the concentric protrusion  3   d  which contacts on the left side of the flat part  5   a  shown in  FIG. 3  is L 1  and the length of the adjacent concentric protrusion  3   d  is L 2 , and in the case where the length of the concentric protrusion  3   d  positioned on the right end of the diagram is Ln, it is possible to describe the right side of formula 1 as L 1 +L 2  . . . ; Ln. 
     That is, formula 1 expresses the fact that the sum of the lengths of the concentric protrusions which contact the flat part  5   a  equals 300 mm or more and if the diameter of the flat part  5   a  of the shoe  5  is set at 5.5 mm,  69  concentric protrusions  3   d  contact with the flat part  5   a  and the pitch of the concentric protrusions  3   d  is set at 0.079 mm or less. 
     In addition, in the swash plate type compressor  1  arranged with the small diameter shoe  5  described above, it is possible to obtain the following effects when the conditions in formula 1 are satisfied. 
     First, when the swash plate type compressor  1  is operated, the indent part  4   a  of the piston  4  sways while the shoe  5  arranged to sandwich the swash plate  3  slides against the swash plate  3  when the swash plate  3  rotates which causes the piston  4  to move back and forth. 
     The shoe  5  is applied with pressure by the surface of the swash plate  3  with the back and forth movement of the piston  4 , and the diameter of the flat part  5   a  of the shoe  5  is set at less than 10.5 mm which is smaller than a conventional shoe  5 . 
     As a result, friction between the shoe  5  and the swash plate  3  is reduced and because it is possible to run the swash plate  3  with a small amount of power, it is possible to improve fuel consumption of an engine which runs the swash plate type compressor  1 . 
     When the coating layer  3   b  of the swash plate  3  is applied with pressure by the back and forth movement of the piston  4 , the concentric protrusion  3   d  is elastically modified by the surface pressure of the flat part  5   a  of the shoe  5  and the shoe  5  sinks by a depth amount H of the elastic modification with respect to the swash plate  3 . 
     Here, because the swash plate type compressor  1  of the present embodiment satisfies the conditions of formula 1 described above, the sum of the lengths of the concentric protrusions  3   d  which contact with the flat part  5   a  equal 300 mm or more and in the case where the diameter of the flat part  5   a  is set at 5.5 mm, 69 concentric protrusions  3   d  or more contact the flat part  3   a.    
     Consequently, the surface pressure of the flat part  5   a  is dispersed among a plurality of concentric protrusions  3   d  which contact the flat part  5   a  and it is possible to make the depth H of the elastic modification described above more shallow by increasing the sum of the length of the concentric protrusions  3   d  which contact in the present embodiment. 
     If the elastic modification depth H is shallow, it is possible to reduce the shear resistance which occurs when the concentric protrusion  3   d  of the shoes  5  is elastically modified when the shoe  5  slides in a circular direction with respect to the swash plat  3 , and it is possible to reduce wear of the coating layer  3   b  (see  FIG. 4 ). 
     Although arranged with the same shoe  5  as the shoe  5  described above,  FIG. 4  shows a cross sectional view of the shoe  5  and swash plate  3  of the swash plate type compressor  1  which does not satisfy the conditions of formula  1 ,  FIG. 4(   a ) shows a cross sectional view in a radial direction of the swash plate  3  and  FIG. 4(   b ) shows a cross sectional view along a circumferential direction of the swash plate  3 . In addition,  FIG. 4  describes a scale different to the actual scale. 
     The sum of the lengths of the concentric protrusions  3   d  which contact the flat part  5   a  of the swash plate type compressor  1  shown in  FIG. 4  is less than 300 mm. 
     Consequently, because the surface pressure which is dispersed over each concentric protrusion  3   d  is large and because the concentric protrusion  3   d  is greatly elastically modified and the depth H of elastic modification increases, when the shoe  5  slides in a circumferential direction with respect to the swash plate  3  as is shown in  FIG. 4(   b ), shoe shear resistance generated when the concentric protrusion  3   d  elastically modifies increases and the amount of wear of the coating layer  3   b  increases. 
       FIG. 5  shows a graph which shows experiment results with regards to the swash plate type compressor  1  related to the present embodiment. In the graph, the left side of the formula 1 on the horizontal axis, that is, the sum of the lengths of the concentric protrusions  3   d  which contact with the flat part  5   a  is shown, and the seizure load of the swash plate  3  and wear depth of the coating layer  3   b  on the swash plate  3  are shown on the vertical axis. Furthermore, the number of concentric protrusions  3   d  which contact with the flat part  5   a  of the shoe  5  is also displayed on the horizontal axis for reference. 
     A shoe  5  with a flat part  5   a  having a diameter of 5.5 mm is used in each of the experiments, the coating layer  3   b  on the swash plate  3  has a mixed ratio with a thermoset resin of 45% and solid lubrication of 55% and thickness set at 25 μm. 
     Furthermore, 3 types of swash plate  3  are prepared in which the sum of the lengths of the concentric protrusions  3   d  which contact with the flat part  5   a  of the shoe  5  equal 160 mm, 240 mm and 320 mm respectively, and the pitch of each concentric protrusion  3   d  is 0.15 mm, 0.10 mm and 0.075 mm. 
     In addition, the experiment was performed by applying a gradually increasing load of 519˜1735N to the shoe  5  while rotating the swash plate  3  at 9500 rpm in a refrigerant/refrigerant oil mixed compressor intake atmosphere. Furthermore the experiment conditions were also applied to the experiment in  FIG. 6  and  FIG. 7 . 
     First, the experiment results related to the relationship between the sum of the lengths of the concentric protrusions  3   d  which contact the flat part  5   a  and a seizure load are explained. In the case where the sum of the lengths of the concentric protrusions  3   d  which contact the flat part  5   a  is 300 mm or more, no seizure occurred even after applying a load of 1700N or more, however, seizure occurred with a load of about 700N when the sum was 240 mm. 
     Next, the experiment results related to the relationship between the sum of the lengths of the concentric protrusions  3   d  which contact with the flat part  5   a  and the depth of wear of the coating layer  3   b  on the swash plate  3  are explained. In the case where the sum of the lengths of the concentric protrusions  3   d  which contact the flat part  5   a  is 300 mm or more, although wear depth was reduced to about 3 μm, wear depth was about 6 μm when the sum was 160 mm. 
       FIG. 6  shows experiment results in the case where the same experiment as in  FIG. 5  is performed with respect to the shoe  5  with a flat part  5   a  having a diameter of 9.5 mm. 
     3 types of swash plate  3  used in this experiment are prepared in which the sum of the lengths of the concentric protrusions  3   d  which contact with the flat part  5   a  of the shoe  5  equal 280 mm, 470 mm and 710 mm respectively, and the pitch of each concentric protrusion  3   d  is 0.10 mm, 0.15 mm and 0.25 mm. 
     First, the experiment results related to the relationship between the sum of the lengths of the concentric protrusions  3   d  which contact the flat part  5   a  and a seizure load are explained. In 2 swash plates  3  where the sum of the lengths of the concentric protrusions  3   d  which contact the flat part  5   a  exceeds 300 mm, no seizure occurred even after applying a load of 1700N or more, however, seizure occurred with a load of about 1400N when the sum was 280 mm. 
     Next, the experiment results related to the relationship between the sum of the lengths of the concentric protrusions  3   d  which contact with the flat part  5   a  and the depth of wear of the coating layer  3   b  on the swash plate  3  are explained. In 2 swash plates  3  where the sum of the lengths of the concentric protrusions  3   d  which contact the flat part  5   a  exceeds 300 m, although wear depth was reduced to about 2 μm, wear depth was about 4 μm when the sum was 280 mm. 
       FIG. 7  shows the experiment results related to the relationship between the diameter of the flat part  5   a  of the shoe  5  and a friction coefficient. In this graph, the diameter of the flat part of the shoe  5  is shown in the horizontal axis and the friction coefficient which occurs between swash plates  3  is shown on the vertical axis. 
     The pitch of the concentric protrusions  3   d  of the swash plate  3  used in the present experiment is 0.15 mm and a shoe  5  with flat parts  5   a  having a diameter of 5.5 mm. 7.5 mm, 9.5 mm and 11.5 mm was used. Among these shoes  5 , shoes  5  with a flat part  5   a  having a diameter of 5.5 mm, 7.5 mm and 9.5 mm respectively are equivalent to the present invention which satisfies the requirements of formula 1 described above and the shoe  5  with a flat part  5   a  diameter of 11.5 mm is equivalent to a conventional shoe with a general size. 
     According to the experiments, it can be seen that the friction coefficient decreases as the diameter of the flat part  5   a  decreases. 
     Furthermore, the shape of the shoe  5  described above may be any shape other than that described in the present embodiment. 
     For example, as is shown in  FIG. 8 , the shoe  5  may have a column shape part  5   e  formed between the spherical surface part  5   b  and the flat part  5   a  and a flange  5   f  arranged on the spherical surface part side which forms the spherical surface part  5   b  on a boundary part between the column part  5   e  and the spherical part  5   b  and which protrudes outwards in a radial direction. 
     By adopting this type of structure it is possible to reduce only the diameter of the flat part while maintaining the spherical surface part at the same conventional size and reduce the weight of the shoe  5 . 
     EXPLANATION OF THE SYMBOLS 
     
         
           1  Swash Plate Type Compressor 
           3  Swash Plate 
           3   b  Coating Layer 
           3   c  Concentric Groove 
           3   d  Concentric Protrusion 
           4  Piston 
           5  Shoe 
           5   a  Flat part