Patent Publication Number: US-7713610-B2

Title: Sliding member

Description:
FIELD OF THE INVENTION 
   The present invention relates to a sliding surface of a sliding member such as a semispherical shoe and, more particularly, to a sliding surface of a sliding member in which the seizure resistance is increased by improving the sliding surface thereof. 
   BACKGROUND OF THE INVENTION 
   Conventionally, various types of sliding members have been known, and a semispherical shoe used for a swash plate compressor has been known as a sliding member used under severe conditions. 
   The semispherical shoe has a semispherical surface having a semispherical shape and a smooth end surface. The semispherical surface comes into a slidable contact with a semispherical concave portion of a piston forming the swash plate compressor, and the end surface comes into a slidable contact with a swash plate provided on a rotating shaft. Thus, the semispherical shoe is configured so that the semispherical surface serves as the sliding surface with respect to the piston, and the end surface serves as the sliding surface with respect to the swash plate. 
   The sliding surface of the semispherical shoe is usually manufactured so as to be smooth with a roughness not higher than the required value disclosed in Japanese Patent Laid-Open No. 2001-153039. 
   SUMMARY OF THE INVENTION 
   The semispherical shoe is required to have high seizure resistance in order to supply a sufficient amount of lubricating oil to the end surface that comes into a slidable contact with the swash plate. It is not easy to supply the sufficient lubricating oil to the end surface because the lubricating oil is supplied while it is contained in a refrigerant, making the fluctuations in a pressing force to the swash plate caused by the reciprocating motion of a piston more serious. Moreover, the end surface is momentarily brought into a contact with the swash plate under a considerably high pressure. 
   An object of the present invention is to provide the sliding surface of the sliding member, so that the seizure resistance of the sliding surface of the sliding member such as a semispherical shoe that needs to have high seizure resistance is further improved. 
   The sliding member includes convex portions formed by directly quenching the sliding surface of the sliding member in a line shape or a dot shape, and concave portions formed in indirectly quenched portions adjacent to the directly quenched portions. An irregular surface is formed on the sliding surface by the directly quenched portions and the indirectly quenched portions. 
   Since the irregular surface is formed on the sliding surface of the sliding member by the directly quenched portions and the indirectly quenched portions, high seizure resistance can be ensured as compared with the conventional sliding surface of the sliding member having no irregular surface. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a front view showing a first embodiment of the present invention; 
       FIG. 2  is a bottom view of  FIG. 1 ; 
       FIG. 3  is an enlarged sectional view of an essential portion, showing in an exaggerated way; 
       FIG. 4  is a graph showing the experimental result of seizure resistance; 
       FIG. 5  is a bottom view showing a second embodiment of the present invention; 
       FIG. 6  is a bottom view showing a third embodiment of the present invention; 
       FIG. 7  is a bottom view showing a fourth embodiment of the present invention; and 
       FIG. 8  is a bottom view showing a fifth embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   The present invention will be explained with reference to embodiments shown in the accompanying drawings. 
   In  FIG. 1 , a semispherical shoe  1  serving as a sliding member is used for a conventionally well-known swash plate compressor, and is interposed between a swash plate provided tiltingly on a rotating shaft and a semispherical concave portion provided in a piston so that the piston can be reciprocatingly driven with the rotation of the swash plate. 
   The semispherical shoe  1  has a semispherical surface  2  having a semispherical shape and a smooth end surface  3 , and is configured so that the semispherical surface  2  is in a slidable contact with the semispherical concave portion in the piston, and the end surface  3  is in a slidable contact with the swash plate. Also, in the central portion of the end surface  3 , an oil reservoir  4  consisting of a concave portion is formed. 
   In an example shown in  FIG. 2 , lattice-shaped convex portions  3   a  are formed on the end surface  3 , and portions other than the convex portions  3   a  relatively become concave portions  3   b , by which an irregular surface is formed on the end surface  3 . 
   The convex portions  3   a  are formed by directly quenching the end surface  3  after the irradiation of a laser. Specifically, as shown in  FIG. 3 , in the portions irradiated with the laser, a base material surface  3   c  originally forming the surface of the end surface  3  becomes in a directly quenched state and expands from the base material surface, by which the convex portions  3   a  are formed. 
   Although the portions irradiated with the laser become in a directly quenched state, the concave portions  3   b  that are located adjacent to the portions irradiated with the laser and are not irradiated with the laser are not quenched directly, and become indirectly quenched portions. These indirectly quenched portions are recessed relative to the convex portions  3   a , and therefore the concave portions  3   b  are formed. 
   However, this does not mean that the concave portions  3   b , which are the indirectly quenched portions, are not quenched completely. Specifically, since the range quenched by the laser irradiation has a semicircular shape in the cross section with the laser irradiation position being the center, for example, as indicated by an imaginary line  5  in  FIG. 3 , by narrowing the adjacent laser irradiation intervals, the concave portions  3   b , which are the indirectly quenched portions at intermediate positions of the intervals, can also be quenched. Whether the concave portions  3   b , which are the indirectly quenched portions, are quenched or not can be determined by the setting of the laser irradiation intervals. If the concave portions  3   b , which are the indirectly quenched portions, are quenched, those portions expand from the base material surface  3   c  though not expanding so much as the convex portions  3   a  expand. 
   The experimental result of the seizure resistance will be explained. 
   In this experiment, a YAG laser is applied to the end surface  3  of the semispherical shoe  1  manufactured of SUJ2 straightly and in parallel at intervals of 0.2 mm, and then is applied in the perpendicular direction in parallel at intervals of 0.2 mm. As a whole, the YAG laser is applied in the lattice form. The interval is preferably in the range of 0.1 to 0.3 mm. 
   The output of the YAG laser is 50 W, and the condenser lens is adjusted so that the YAG laser is in focus at a position of 2 mm depth with respect to the surface of the end surface  3 . Therefore, the YAG laser is applied to the surface of the end surface  3  in a defocused state. 
   The surface of the convex portion  3   a , which is the directly quenched portion irradiated with the laser, has a hardness about Hv100 higher than the hardness of the base material, which is Hv750, and also the surface of the concave portion  3   b  has a hardness increased by about Hv50. On the other hand, a portion  6  (refer to  FIG. 3 ) slightly deeper than the directly quenched portion is quenched so that the hardness thereof is about Hv100 lower than the hardness of the base material. Also, an intersection of the two convex portions  3   a , which are directly quenched portions, namely, a portion in which the laser irradiation portions intersect, is also quenched so that the hardness thereof is likewise about Hv100 lower than the hardness of the base material. However, since the quenching with the laser involves rapid cooling, the decrease in the hardness of the base material is not recognized at a position still deeper than the slightly deep portion  6 . 
   After being irradiated with the laser as described above, the end surface  3  of the semispherical shoe  1  is completed by being subjected to lapping and buffing in succession. The height of the convex portion  3   a  with respect to the concave portion  3   b  is about 0.1 to 10 μm immediately after the laser treatment, and the height thereof of the completed product after the lapping and buffing is preferably in the range of 0.1 to 1 μm. 
   The wear resistance is measured under the following test conditions on the invented product manufactured as described above and the reference product subjected to lapping and buffing under the same conditions without being irradiated with the laser. For the reference product, the whole semispherical shoe is quenched, and the hardness thereof is Hv750. 
   Rotational speed of the swash plate: increased in nine steps every one minute by 1000 rpm: the maximum rotational speed 9000 rpm (circumferential speed 38 m/s) 
   Surface pressure: increased every one minute by 2.7 MPa from a preload of 2.7 MPa: up to seizure 
   Quantity of oil mist: 0.05 to 0.25 g/min nozzle position fixed 
   Oil: refrigerating machine oil 
   Seizure condition: shaft torque 4.0 N·m over 
   The rotational speed of the swash plate is increased under the above-described condition in the state in which the end surface of the invented product is brought into a contact with the swash plate under pressure. On the other hand, the surface pressure at the time when the invented product is brought into a contact with the swash plate under pressure is increased under the above-described condition. When the shaft torque applied to the swash plate exceeds 4.0 N·m, it is determined that the seizure occurs. The same test is also conducted on the reference product. 
   As seen from the experimental result shown in  FIG. 4 , the invented product provides significantly high seizure resistance as compared with the reference product. 
     FIGS. 5 to 8  show other embodiments of the present invention. In  FIG. 5 , the convex portions  3   a  are formed by forming the directly quenched portions in a parallel straight line shape, and the concave portions  3   b  are formed in the indirectly quenched portions adjacent to the directly quenched portions, by which the irregular surface is formed on the sliding surface by the directly quenched portions and the indirectly quenched portions. 
   Also, in  FIG. 6 , the convex portions  3   a  are formed in a concentric circle shape. In  FIG. 7 , the convex portions  3   a  are formed in a spiral shape. Further, in  FIG. 8 , dot-shaped convex portions  3   a  are formed on the sliding surface by applying the laser to the intersection of a lattice shape. 
   In the above-described examples, the semispherical shoe  1  is used as the sliding member. However, the sliding member is not limited to the above-described examples, and needless to say, the present invention can be applied to various sliding surfaces. 
   Also, in the above-described examples, the convex portions are formed by directly quenching the sliding surface by the laser. However, the quenching method is not limited to the laser, and a plasma beam or other methods can be used.