Abstract:
The invention provides a compressor swash plate which is lead-free and is able to demonstrate a superior durability. A compressor swash plate in the invention includes a base member and a sliding layer being formed on the surface of the base member and constituting at least a sliding surface for allowing a shoe to slide thereon. The sliding layer is formed by thermal spraying Cu-based-MnS by HVOF thermal spraying method. A method of manufacturing the compressor swash plate according to the invention includes a step of thermal spraying powder formed of Cu-based-MnS onto the base member by the HVOF thermal spraying method to form the sliding layer which constitutes at least the sliding surface which allows the shoe to slide thereon on the base member. More specifically, the Cu-based-MnS is Cu-Ni-MnS.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of priority to Japanese Patent Application No. 2007-115567, filed on Apr. 25, 2007, the contents of which are hereby incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a compressor swash plate and a method of manufacturing the same. 
         [0003]    Compressor swash plates in the related art are disclosed in JP-A-11-193780and JP-A-2001-234859. These compressor swash plates each include a base member and a sliding layer which is formed on the surface of the base member and constitutes a sliding surface for allowing a shoe to slide thereon. 
         [0004]    JP-A-11-193780 discloses the compressor swash plate in which the base member is formed of iron-based material such as Nodular graphite cast iron (FCD) or bearing steel (SUJ2), and the sliding layer is formed by thermal spraying Cu-Sn-Pb is disclosed. The sliding layer is formed with a lubricating layer formed of MoS 2  and polyamide-imide thereon. 
         [0005]    JP-A-2001-234859 discloses the compressor swash plate in which the base member is formed of iron-based material, and the sliding layer is formed of Al-Si deposited by frictional heat. This compressor swash plate is formed with two such sliding layers. 
         [0006]    The compressor swash plate as described above is used for the swash-plate-type compressor. The swash-plate-type compressor includes housings formed in the interior thereof with cylinder bores, a crank chamber, an suction chamber and a discharge chamber; pistons stored in the cylinder bores so as to be capable of reciprocating and defining compression chambers in the cylinder bores; a drive shaft driven by an external drive source and rotatably supported by the housings; and a swash plate provided in the crank chamber for transforming the rotational movement of the drive shaft to the reciprocating movement of the pistons via pairs of shoes which come into contact with the front and rear surfaces of its own. The general swash plate is a single unit, and is capable of rotating with the drive shaft in a state in which the front and rear surfaces of its own are inclined with respect to the drive shaft. On the other hand, the each shoe is formed into a substantially semispherical shape, and substantially flat surfaces of the shoes come into contact with the front and rear surfaces of the swash plate. 
         [0007]    In the swash-plate-type compressor configured as described above, when the drive shaft rotates by the external drive source, the swash plate also rotates, and the pistons reciprocate in the cylinder bores, respectively via the shoes. Accordingly, the swash-plate-type compressor sucks refrigerant gas from the suction chamber to the compression chambers, compresses the refrigerant gas in the compression chambers, and discharges into the discharge chamber. 
         [0008]    The swash-plate-type compressor as described above is used with an evaporator, an expansion valve, a condenser and a piping to constitute a refrigerating circuit for vehicles, so that a cabin or the like is air-conditioned. 
         [0009]    In recent years, reduction of usage of lead is requested in the field of manufacturing mechanical parts from the reasons of environment. Therefore, as regards the swash-plate-type compressors in various types, a change from above described Cu-Sn-Pb which contains lead to a lead-free material as a material to form the sliding layer is desired. 
         [0010]    However, although the above-described Al-Si does not contain lead and demonstrates a certain level of slidability, when there is little or no lubrication oil, the slidability is lower than Cu-Sn-Pb. According to the inspection by the inventors, it is the same with Cu-Sn-Al-Si. Therefore, when the sliding layer is formed on the base member using such alloy as a material, portions between the swash plate and the shoes are liable to burn, so that the durability of the swash-plate-type compressor may be deteriorated. 
       BRIEF SUMMARY OF THE INVENTION 
       [0011]    In view of such circumstances, it is an object of the invention to provide a compressor swash plate which is lead-free and is able to demonstrate a superior durability. 
         [0012]    The inventors have devoted ourselves to study for finding a material which is lead-free and demonstrates a desirable slidability as a material of sliding layers. Consequently, the inventors found that the siding layer formed by thermal spraying Cu-based-MnS by HVOF (High Velocity Oxygen Fuel) thermal spraying method is able to achieve the above-described object. 
         [0013]    In other words, the compressor swash plate according to the invention is characterized by having a base member and a sliding layer being formed on the surface of the base member and constituting at least a sliding surface for allowing a shoe to slide thereon, wherein the sliding layer is formed by thermal spraying Cu-based-MnS by the HVOF thermal spraying method. 
         [0014]    A method of manufacturing a compressor swash plate according to the invention is characterized by including a step of thermal spraying powder formed of Cu-based-MnS onto a base member by the HVOF thermal spraying method to form a sliding layer which constitutes at least a sliding surface which allows a shoe to slide thereon on the base member. 
         [0015]    Other aspects and advantages of the invention will be apparent from embodiments disclosed in the attached drawings, illustrations exemplified therein, and the concept of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0016]    The invention will be described in more detail along with the concept and advantages thereof by referring to the attached drawings and the detailed description of the preferred embodiments below. 
           [0017]      FIG. 1  is a vertical cross-section of a swash-plate-type compressor according to Embodiment 1; 
           [0018]      FIG. 2  is an enlarged vertical cross-sectional view showing a principal portion of the swash-plate-type compressor according to Embodiment 1; 
           [0019]      FIG. 3  is a cross-sectional view showing a method of manufacturing the compressor swash plate according to Embodiment 1; and 
           [0020]      FIG. 4  is a schematic pattern diagram showing a method of measuring a burning load between a swash plate sample and a shoe. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     Embodiment 1  
       [0021]    First of all, a variable capacity swash-plate-type compressor in which a compressor swash plate according to Embodiment 1 is employed will be described. As shown in  FIG. 1 , in the compressor, a front housing  2  is joined to the front end of a cylinder block  1 , and a rear housing  4  is joined to the rear end of the cylinder block  1  via a valve unit  3 . The cylinder block  1  and the front housing  2  are formed with shaft holes  1   a ,  2   a  extending therethrough in the axial direction, and a drive shaft  5  is rotatably supported by the shaft holes  1   a ,  2   a  via bearing devices or the like, respectively. The left side in  FIG. 1  corresponds to the front side, and the right side corresponds to the rear side. 
         [0022]    The interior of the front housing  2  functions as a crank chamber  6 . In the crank chamber  6 , a lug plate  7  is fixed to the drive shaft  5  via the bearing device with respect to the front housing  2 . A swash plate  8  is provided behind the lug plate  7  in the crank chamber  6 . The swash plate  8  is penetrated by the drive shaft  5  therethrough and, in this state, the angle of inclination changes by a link mechanism  9  provided between the lug plate  7  and the swash plate  8 . 
         [0023]    The cylinder block  1  is formed with a plurality of cylinder bores  1   b  extending concentrically therethrough in the axial direction. A single headed piston  10  is stored in each cylinder bore  1   b  so as to be capable of reciprocating therein. The each piston  10  has a neck portion on the crank chamber  6  side, and the neck portion of the each piston  10  is formed with receiving seats  10   a  each depressed with a spherical surface so as to oppose to each other. 
         [0024]    A pair of front and rear shoes  21  are provided between the swash plate  8  and the respective pistons  10 . As shown in  FIG. 2 , the swash plate  8  includes a base member  81 , and sliding layers  82  and  82  formed on the peripheral edges of the front and rear surfaces of the base member  81 . The base member  81  is formed of iron-based material such as FCD, SUJ2. The sliding layer  82  is formed by thermal spraying Cu-31Ni-6.4MnS by HVOF thermal spraying method. 
         [0025]    The surfaces of the sliding layers  82  and  82  include flat sliding surfaces  8   a  and  8   a  which allow the shoes  21  to slide thereon, respectively. It is also possible to form a lubricating layer formed of MoS 2  and polyamide-imide on the sliding layer  82 . In this case, the sliding layer  82  and the lubricating layer constitute the sliding surfaces  8   a  and  8   a . The shoes  21  are each formed into a substantially semispherical shape, and the semispherical surfaces of the shoes  21  come into contact with the receiving seats  10   a  of the piston  10 , and the substantially flat surfaces thereof come into contact with the sliding surfaces  8   a  and  8   a  of the swash plate  8 . 
         [0026]    As shown in  FIG. 1 , an suction chamber  4   a  and a discharge chamber  4   b  is formed in the rear housing  4 . The cylinder bores  1   b  are able to communicate with the suction chamber  4   a  via an suction valve mechanism of a valve unit  3 , and are able to communicate with the discharge chamber  4   b  via a discharge valve mechanism of the valve unit  3 . 
         [0027]    A capacity control valve  11  is stored in the rear housing  4 . The capacity control valve  11  communicates with the suction chamber  4   a  via a detection path  4   c , and communicates the discharge chamber  4   b  and the crank chamber  6  by a gas-supply path  4   d . The capacity control valve  11  changes the opening of the gas-supply path  4   d  by detecting the pressure of the suction chamber  4   a , and changes the discharge capacity of the compressor. The crank chamber  6  and the suction chamber  4   a  are communicated by a gas-extraction path  4   e . A condenser  13 , an expansion valve  14  and an evaporator  15  are connected to the discharge chamber  4   b  via a piping  12 , and the evaporator  15  is connected to the suction chamber  4   a  via the piping  12 . 
         [0028]    A pulley  16  is provided at the front end of the front housing  2  so as to rotatable with the bearing device, and the pulley  16  is fixed to the drive shaft  5 . A belt  18 , which is rotated by an engine  17  is wound around the pulley  16 . 
         [0029]    The swash plate  8  is manufactured as follows. As shown in  FIG. 3A , the base member  81  formed of the iron-based material such as FCD or SUJ2 is prepared by casting or machining. Then, as shown in  FIG. 3B , the peripheral edges  81   a  on the front and rear surfaces of the base member  81  is roughened by sand blast or the like to achieve an average roughness of 20 to 40 μm. 
         [0030]    On the other hand, powder formed of Cu-31Ni-6.4Mns is prepared. Then the powder and DJ-type HVOF thermal spraying system manufactured by Sulzer Metco are used to spray the peripheral edges  81   a  of the base member  81  by the HVOF thermal spraying method. The conditions of the HVOF thermal spraying method are as follows. 
         [0031]    Oxygen supply pressure: 150 psi 
         [0032]    Fuel (Kerosene) supply pressure: 80 psi 
         [0033]    Carrier gas (Nitrogen) supply pressure: 150 psi 
         [0034]    Air supply pressure: 75 psi 
         [0035]    In this manner, a thermal spraying layer is formed as shown in  FIG. 3C . Since the thermal spraying layer after sprayed thermally has roughness of about 8 μm Ra on the surface thereof, the surface is polished until the roughness is reduced to about 0.05 μm Ra. The sliding layer  82  is formed in this manner. As shown in  FIG. 3D , a lubricating layer  82   a  formed of MoS 2  and polyamide-imide is formed on the sliding layer  82  as needed. 
         [0036]    In the compressor configured as described above, the swash plate  8  rotates synchronously with the rotation of the drive shaft  5  shown in  FIG. 1 , and the pistons  10  reciprocate in the cylinder bores  1   b  via the shoes  21 . Accordingly, the capacity of a compression chamber formed on the head side of the piston  10  is changed. Consequently, the refrigerant gas gas in the suction chamber  4   a  is taken into the compression chamber and is compressed therein, and then discharged into the discharge chamber  4   b . In this manner, refrigerating action is carried out in a refrigerating circuit composed of the compressor, the condenser  13 , the expansion valve  14  and the evaporator  15 . During this period, the substantially flat surfaces of the shoes  21  come into sliding contact with the sliding surfaces  8   a  of the swash plate  8 , and the semispherical surfaces thereof come into sliding contact with the receiving seats  10   a  of the piston  10 . 
         [0037]    In order to evaluate the durability of the compressor in Embodiment 1, an experiment was conducted as follows. As shown in  FIG. 4 , a swash plate sample  88  which is an imitation of the swash plate  8  and shoes  25  were prepared. The swash plate sample  88  was obtained by forming a sliding layer  88   b  on the upper surface of a base member  88   a  which was the same type as the swash plate  8 . The surface of the sliding layer  88   b  constitutes a flat sliding surface  88   c  for allowing the each shoe  25  slide. The shoes  25  were placed so that the substantially flat surfaces thereof come into contact with the sliding layer  88   b  of the swash plate sample  88 . Then, the shoes  25  are pressed against the swash plate sample  88  at a predetermined load by a pressing jig  99  on which shoe seats  38   a  in the form of depressions corresponding to the semispherical surfaces of the shoes  25  are formed thereon. In this manner, the swash plate sample  88  was rotated at about a rotational speed of 1000 rpm in a state in which the swash plate sample  88  and the shoe  25  were in contact and the approximate load value which causes the burning was evaluated. 
         [0038]    The sliding layer  88   b  of the swash plate sample  88  in Embodiment 1 is formed by thermal spraying Cu-31Ni-6.4Mns by HVOF thermal spraying method. The sliding layer  88   b  of the swash plate sample  88  in Comparative Embodiment 1 is formed by thermal spraying Cu-15Sn-30Al-20Si by a general thermal spraying method. The sliding layer  88   b  of the swash plate sample  88  in Comparative Example 2 is formed of Al-40Si sprayed in the same manner. The sliding layer  88   b  of the swash plate sample  88  in Comparative Example 3 is formed by thermal spraying Cu-10Sn-10Pb in a general thermal splaying method. A lubricating layer of MoS 2  and polyamide-imide is formed on the each sliding layer  88   b  in Embodiment 1 and Comparative Examples 1 to 3. 
         [0039]    The evaluations are made for the case in which the shoe  25  formed of SUJ2 is used and for the case in which a plated layer formed of Ni is applied on the base member of the shoe formed of aluminum-based material. The lubricating condition is “No lubrication”. The results are shown in Table 1. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
                 Sliding movement 
                 Sliding movement 
               
               
                   
                   
                 with respect to 
                 with respect to 
               
               
                   
                   
                 iron—based shoe 
                 aluminum—based 
               
               
                   
                 Composition 
                 (kgf) 
                 shoe (kgf) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Embodiment 1 
                 Cu—Ni—MnS 
                 100 
                 120 
               
               
                 Comparative 
                 Cu—Sn—Al—Si 
                 60 
                 70 
               
               
                 Example 1 
               
               
                 Comparative 
                 Al—Si 
                 60 
                 60 
               
               
                 Example 2 
               
               
                 Comparative 
                 Cu—Sn—Pb 
                 80 
                 100 
               
               
                 Example 3 
               
               
                   
               
             
          
         
       
     
         [0040]    As shown in Table 1, it was found that the swash plate sample  88  in Embodiment 1 demonstrates a higher burning resistant load with respect to the iron-based and aluminum-based shoes  25  in comparison with the swash plate sample  88  in Comparative Examples 1 to 3. 
         [0041]    Therefore, the swash plate  8 , which is the same as the swash plate sample  88  in Embodiment 1, is lead-free, and demonstrates a superior durability. Therefore, it was found that the swash-plate-type compressor in Embodiment 1 demonstrates a superior environmental performance and a long life. 
         [0042]    The invention has been described in conjunction with Embodiment 1, it is needless to say that the invention is not limited to Embodiment 1 shown above, and modifications may be made without departing the scope of the invention as needed. 
         [0043]    According to the results of experiments conducted by the inventors, the compressor swash plate in the invention demonstrates a high burning-resistant load with respect to the shoe formed of iron-based materials or aluminum-based materials. The swash plate in the invention demonstrates a higher burning-resistant load than not only the swash plate having the sliding layer formed of Al-Si in the related art, but also the swash plate having the sliding layer formed of Cu-Sn-Pb in the related art. A lubricating layer formed of MoS 2  and polyamide-imide maybe formed on the sliding layer. 
         [0044]    For example, JP-A-57-198245 and JP-A-2005-133130 describe that Cu-based-MnS is a material superior in slidability and abrasion resistance. However, there is no description saying that Cu-based-MnS is able to be used for the compressor swash plate and no disclosure of thermal spraying the material by the HVOF thermal spraying method. 
         [0045]    The inventors consider the reason why the sliding layer formed by thermal spraying Cu-based-MnS by the HVOF thermal spraying method demonstrates slidability suitable for the compressor swash plate as follows. In the process of the HVOF thermal spraying method, a high-pressure oxygen and fuel mixture is burned in a combustion chamber and ejected out to the atmosphere while squeezing the burning flame by a nozzle. Accordingly, the flame is subjected to an abrupt gas expansion at a moment when it is ejected out to the atmosphere and be a supersonic jet flame. When the powder formed of Cu-based-MnS is used in the HVOF thermal spraying method, the power accelerated by a high accelerating energy is considered to keep the superior slidability and abrasion resistance in terms of components with little oxidation or fatigue while being kept in a semi-fused state with moderately solid portion contained therein so that a high-density and precise sliding layer under a high adhesiveness is formed. 
         [0046]    Therefore, the compressor swash plate in the invention is lead-free and demonstrates superior durability. Therefore, the swash-plate-type compressor employing this swash plate demonstrates a superior environmental performance and realizes a long life. 
         [0047]    The base member may be formed of iron-based materials such as FCD or SUJ2. The surface of the base member is preferably roughened. According to the understanding of the inventors, the average roughness of the surface of the base member is preferably 20 to 40 μm. 
         [0048]    The sliding layer is formed on the surface of the base member, and constitutes the sliding surface on which the shoe slides. The sliding layer may configure a portion other than the sliding surface, that is, other portions of the swash plate. According to the understanding of the inventors, the thickness of the sliding layer is preferably 30 to 200 μm. According to the results of experiments conducted by the inventors, the sliding layer according to the invention is Hv150 to 350. 
         [0049]    The shoe, which is the counterpart of the swash plate, may be formed of the iron-based material such as SUJ2 or the aluminum-based material. According to the results of experiments conducted by the inventors, the swash plate in the invention demonstrates a significant effect when the shoe is formed of the iron-based material such as SUJ2. The shoe formed of the aluminum-based material may have a plated layer formed of Ni on the surface thereof. 
         [0050]    The swash-plate-type compressor may use CO 2  refrigerant gas as well as general refrigerant gas such as R134a. In particular, when CO 2 is used as the refrigerant gas, the effect of the invention is remarkably enjoyed. It is because CO 2  as the refrigerant gas achieves a very high pressure on the order of 15 MPa at time of compression and a compression reaction force applied from the piston to the swash plate via the shoes is also very high. CO 2  as the refrigerant gas has a very low in lubricating capability in comparison with other general refrigerant gas even though the lubricating component is added. 
         [0051]    The compressor swash plate in the invention may be employed in various swash-plate-type compressors using the swash plate. For example, the compressor swash plate in the invention may be employed not only in general swash-plate-type compressors having a single swash plate, but also in the swash-plate-type compressors employing a first swash plate rotatable with the drive shaft and a second swash plate supported so as to be capable of rotating relatively with respect to the first swash plate. In the case of the swash-plate-type compressor having the single swash plate, the compressor swash plate in the invention may be applied to a swash plate which changes in angle of inclination with respect to the drive shaft, and may be employed to a swash plate which does not change in angle of inclination with respect to the drive shaft. In the case of the swash-plate-type compressor having the swash plate including the first swash plate and the second swash plate, the compressor swash plate in the invention may be employed as the second swash plate. 
         [0052]    Cu-based-MnS is an alloy containing MnS in Cu as a base component. The inventors confirmed the effect of the invention when Cu-based-MnS is Cu-Ni-MnS. According to the understanding of the inventors, Cu-Ni-MnS preferably composed of by 40 to 70% Cu, 20 to 40% Ni, and 1 to 10% MnS in mass. When it contains less than40% Cu in mass, Cu alloy phase is reduced, which results in fragility, and when it contains more than 70% Cu in mass, the strength is lowered. When it contains less than 20% Ni in mass, the amount of dissolution of MnS is lowered, and when it contains more than 40% Ni in mass, the Cu alloy phase is reduced, which results in fragility. When it contains less than 1% MnS in mass, it is dissolved by Cu alloy, which results in decrease in deposited amount, so that the effect of improvement of sliding property is lowered. It contains more than 10% MnS in mass, the size of sludge of MnS increases, which results in segregation and poor distribution, so that fragility increases. 
         [0053]    The invention is available for the swash-plate-type compressor.