Abstract:
A sliding bearing apparatus having a superior resistance to fretting comprising: a sliding bearing provided with a back metal layer having an inner face and a rear face, and a bearing alloy layer provided on an inner face of said back metal layer; and a housing having an inner face on which said sliding bearing is mounted, the rear face of said back metal layer and/or the inner face of said housing being provided with a coating made of a ceramic.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a sliding bearing apparatus having an excellent resistance to fretting. 
     In recent years, for the purpose of weight-saving or the like, a housing to which a sliding bearing is mounted is designed to have a thin thickness or to be made of an aluminum alloy, so that the rigidity thereof is reduced. Thus, in the housing, small, repetitive strains are apt to occur easily in correspondence with dynamic loads applied thereto. For example, in the bearing housing such as a large end portion of a connecting rod and a main bearing portion in an engine for a motor car, since the weight saving design explained above is adopted, relative micro-collisions and/or micro-slips occur between the inner, peripheral surface of the bearing housing and the rear face of the sliding bearing mounted on the inner face of the bearing housing in correspondence with the repetitive strains of the bearing housing, so that there occurs such a state as a damage due to the fretting abrasion is apt to be caused. 
     Conventionally, as a countermeasure to address the problem of the fretting, there has been known a technique of coating a resin material having an excellent lubricity such as, for example, a polytetrafluoroethylene (PTFE) on the rear face of the sliding bearing, or applying a metal plating such as a copper, a nickel or the like thereto. 
     SUMMARY OF THE INVENTION 
     In the sliding bearing apparatus in which the PTFE is coated, there can be obtained an effect of preventing the fretting from occurring at an early stage under the operation of the sliding bearing. However, the PTFE is apt to be worn away, so that there is a problem that it lacks the reliability insofar as the long-term resistance to fretting is concerned. Further, in the sliding bearing apparatus in which the plating layer of a metal such as copper, nickel or the like is applied, an adhesion phenomenon is apt to occur between the metal plating layer and the housing, so that there is another problem that the satisfactory resistance to fretting can not be obtained. 
     The present invention is achieved by taking the matters explained above into consideration, and an object of the invention is to provide a sliding bearing apparatus in which a layer provided for the purpose of preventing a fretting from occurring hardly causes the abrasion or the adhesion and in which an excellent resistance to fretting can be maintained for a long period of time. 
     According to the first aspect of the invention, there is provided a sliding bearing apparatus comprising: a sliding bearing having a back metal layer provided with an inner face and a rear face, and a bearing alloy layer bonded to the inner face of the back metal layer; a housing having an inner face onto which the sliding bearing is fitted, the rear face of the back metal layer and/or the inner face of the housing being provided with the layer of a ceramic material bonded thereto. Since, in general, ceramics has low coefficient of friction and are hardly adhered, they have superior resistance to fretting. Further, they are hard in hardness and are hardly worn, it is possible to maintain an excellent resistance to fretting for a long period of time. 
     According to the second aspect of the invention, there is provided a sliding bearing apparatus as set forth in the first aspect in which apparatus the ceramic material is selected from the group consisting of a nitride, a carbide, an oxide, a boride, a sulfide and a fluoride. 
     In this case, the ceramics is inferior in thermal conductivity. Thus, in a case where the layer of the ceramic interposed between the sliding bearing and the housing is thick in thickness, the heat dissipation from the sliding bearing to the housing is suppressed, so that the temperature of the sliding bearing is raised unfavorably. However, when the thickness of the layer of the ceramic is in the range of 0.05 to 5 μm, the effect thereof for dissipating the heat can be obtained. 
     That is, according to the third aspect of the invention, there is provided a sliding bearing apparatus as set forth in the first aspect in which apparatus the thickness of the ceramic layer is in the range of 0.05 to 5 μm. 
     In prior arts, the thickness of the PTFE layer inferior, similarly to the ceramic materials, in thermal conductivity is 30 μm, and the thickness of the metal plating layer such as the copper, the nickel or the like is about 5 μm. In comparison with these cases of the prior arts, the thickness of the ceramic layer is thin in thickness, so that it is possible to enhance the heat dissipation of the sliding bearing and to thereby improve the bearing properties of the sliding layer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross sectional view of a part of a sliding bearing apparatus embodying the invention; and 
     FIG. 2 is a front elevational view of a connecting rod in which the sliding bearing apparatus is mounted. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of the invention is described below in which a sliding bearing apparatus is used regarding a crank pin of an engine, while referring the drawings. 
     A connecting rod of an engine for a motor car is shown in FIG.  2 . In both end portions of the connecting rod, as is well known, a side connected to a piston pin is called a small end portion and another side connected to the crank pin is called a large end portion. The connecting rod  1  shown in FIG. 2 is provided with a cap  4  fixed to one wide end portion  3  of a rod main body  2  by bolts  5 . 
     Each of both of the large end portion  6  constituted by one end portion  3  of the rod main body  2  and by the cap  4  and the small end portion  7  corresponding to another end portion of the rod main body  2  acts as a bearing housing. In the large end portion  6  is arranged a bearing  8  for the crank pin, and a bearing  9  for the piston pin is arranged in the small end portion  7 . The crank pin bearing  8  relating to the invention is constructed by vertically abutted, two sliding bearing portions  10  (hereinafter, refer to as half bearings) each formed to have a semi-cylindrical shape. 
     The half bearing  10  is provided with, as shown in FIG. 1, a back metal layer  11  having an inner face and a rear face, a bearing alloy layer bonded onto the inner face of the back metal which bearing alloy layer is made of a Cu-based alloy or an Al-based alloy, an overlay  13  bonded onto the bearing alloy layer  12 , and a ceramic layer  14  made of a ceramic which ceramic layer is bonded onto the rear face of the back metal layer. The ceramic used to form the ceramic layer  14  is selected from the group consisting of: a nitride such as AlN, Si 3 N 4 , TiN, CrN, BN, TiAlN, TiCrN, AlCrN, ZrN, NbN, TaN, or HfN etc.; a carbide such as SiC, TiC, WC, B 4 C, NbC, TaC, or Cr 3 C etc.; an oxide such as Al 2 O 3 , SiO 2 , TiO 2 , ZnO, WO 3 , In 2 O 3 , SnO 2 , Ta 2 O 5 , Fe 3 O 4 , Co—Al 2 O 3 , Ti 2 —ZnO 2 , PbO—TiO 2 , CoO—Al 2 O 2 —Cr 2 O 3 , Cr 2 O 3 —Sb 2 O 3 —TiO 2 , or CoO—Cr 2 O 3 —MnO 2 —Fe 2 O 3  etc.; a boride such as TiB 2 , ZrB 2 , or LaB 6  etc.; a sulfide such as MoS 2 , CdS, CuS, PbS, or ZnS etc.; a fluoride such as CaF 2  or BaF 2  etc.; and a combined ceramic such as TiCN etc. 
     Next, a method of manufacturing the half bearing  10  is described below. At first, a bimetal is formed by bonding the bearing alloy layer  12  onto a steel sheet constituting the back metal  11  by use of a sintering or pressure-bonding or the like. Next, the bimetal is cut into rectangular pieces, each of which pieces is then formed into a semi-cylindrical shape, and thereafter, the overlay layer  13  is formed on the surface of the bearing alloy layer  12  of the semi-cylindrically formed product. Then, a masking treatment is performed regarding the semi-cylindrically formed product with the exception of the rear face of the back metal  11 , and thereafter the product is received within a dry type plating apparatus such as a sputtering apparatus or the like, and the ceramic coating  14  is provided on the rear face of the back metal  11 . In this case, a temperature of the coating (, that is, a temperature within the sputtering apparatus) is between 150 and 500° C. Further, a period of time during which the ceramic is coated is controlled so that the ceramic coating  14  may have a thickness ranging from 0.05 to 5 μm, whereby the half bearing  10  is manufactured. 
     The ceramic coating has a low coefficient of friction. Since the half bearing  10  of this embodiment is provided on the rear face of the back metal thereof with the ceramic coating of a low friction, it is possible to obtain an excellent resistance to fretting. Further, the ceramic is hardly adhered to the metal, so that the fretting due to the adhesion hardly occurs. In addition, since the ceramic is very hard in hardness in comparison with the steel as shown in the following Table 1, it is hardly worn, so that it is possible to keep the excellent resistance to fretting for a long time. 
     
       
         
               
               
             
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 HARDNESS (Hv) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 TiN 
                 2200 
               
               
                   
                 CrN 
                 2200 
               
               
                   
                 TiCrN 
                 3300 
               
               
                   
                 TiAlN 
                 2400 
               
               
                   
                 STEEL 
                 1000 
               
               
                   
                   
               
             
          
         
       
     
     In the side of the inner face of the half bearing  10 , a friction heat occurs between the inner face and the crank pin. The heat occurring in the inner face side is dissipated by a lubricating oil and by being transferred to the side of the large end portion  6  through the bearing alloy  12  and the back metal  11 , whereby the half bearing  10  is cooled. 
     In this case, the thermal conductivity of the ceramic is low. Thus, in a case where the ceramic coating  14  is thick in thickness, the thermal conduction from the back metal  11  to the side of the connecting rod  1  is deteriorated, so that the heat-dissipation property of the half bearing  10  is lowered. However, since the ceramic coating  14  is hardly worn, it is possible to make the thickness thereof very thin. For example, it is sufficient that the thickness of the coating  14  ranges from 0.05 to 5 μm as described above, so that even in the case of the low thermal conductivity of the ceramic coating  14 , there occurs no fear that the thermal conduction from the back metal  11  to the side of the connecting rod  1  is deteriorated, so that there is no fear of deteriorating the heat dissipation property of the half bearing  10 . 
     According to the embodiment, the coating  14  made of the ceramic is provided on the rear face of the back metal  11 , so that it is possible to obtain an improved resistance to fretting for a long period of time, and at the same time to obtain such an excellent effect as the thermal conduction from the back metal  11  to the side of the connecting rod  1  is not suppressed with the result that the heat dissipation of the half sliding bearing is not deteriorated although the ceramic low in thermal conductivity is used as the material of the coating  14 . 
     The invention is not limited to the embodiment described above and shown in the drawings, and an expansion or a modification explained below may be employed. 
     The coating  14  may be provided not only on the rear face of the back metal  11  but also on the inner face of the large end portion  6  corresponding to the bearing housing. 
     The ceramic of the coating  14  may be one kind or may be a mixture of a plurality of kinds. Further, the overlay layer  13  may be provided on the surface of the bearing alloy layer  12  after providing the coating  14  on the rear face of the back metal  11 . 
     The dry type plating for providing the ceramic coating on the rear face of the back metal  11  is not limited to the sputtering, and other means such as an ion plating, or an ion implantation, or a flame spray etc. may be used. 
     The present invention is described regarding the bearing apparatus for receiving the crank pin, however, the technical idea of the invention can be adopted to apparatus etc. other than the bearing apparatus.