Abstract:
A shaft antiseizing type sprocket in which seizing liable to occur in the contact portion between the sprocket and the sprocket shaft is completely avoided for a long period of use. Effecting replacement is possible without use of a special-purpose removing tool or a fixing tool with a rotating body. The shaft antiseizing type sprocket has a boss portion which is integrally molded with a sprocket tooth portion. The boss has a shaft bore, the inner circumferential surface of which is adapted to be fixed to a sprocket shaft. A solid lubricant is embedded in the boss portion, and is disposed in a partially exposed state toward the shaft bore inner circumferential surface of the boss portion.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a divisional of U.S. application Ser. No. 11/947,128 filed Nov. 29, 2007 which claims priority to Japanese Application No. 2007-022433 filed Jan. 13, 2007, the foregoing applications being incorporated herein by reference. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention relates to a sprocket, which is incorporated and fixed to a sprocket shaft in a power transmission mechanism, and more specifically it relates to a shaft antiseizing type sprocket, in which seizing with a sprocket shaft is prevented and installation replacement is possible. 
       BACKGROUND OF THE INVENTION 
       [0003]    When damage such as wear or the like is generated in a sprocket tooth portion, a sprocket, which is installed and fixed to a sprocket shaft in a power transmission mechanism or the like, is replaced. Since heavy seizing is generated at a contact portion with the sprocket shaft with the sprocket depending on a use load and use time of the sprocket to be replaced, the sprocket is impossible to remove from the sprocket shaft. 
         [0004]    Thus, when a sprocket had damage such as wear or the like, a sprocket tooth portion is removed from the sprocket shaft, the sprocket. a sprocket is forcibly removed from the sprocket shaft through a special-purpose removing tool called a gear puller or the like (see for example Japanese Laid-Open Patent Publication No. 2002-361571 (page 1, FIG. 1)) or a sprocket of a special shape in which only a tooth portion damaged by wear or the like can be replaced is used (see for example Japanese Examined Patent Publication No. Sho. 61-28862 (page 1, FIG. 1)), and a sprocket is removably mounted to the sprocket shaft using a mounting having a rotating body, which fastens the sprocket by tapered surfaces of an inner ring and an outer ring (see for example Japanese Laid-Open Patent Publication No. Hei. 10-37971 (page 1, FIG. 1)). 
       PROBLEMS TO BE SOLVED BY THE INVENTION 
       [0005]    However, the removing special-purpose tool disclosed in Japanese Laid-Open Patent Publication No. 2002-361571 (page 1, FIG. 1) needs not only large working labor at the removal but also a sprocket damaged by wear or the like in a sprocket tooth portion is needed only in a case where the sprocket is removed from the sprocket shaft. Thus there was a troublesome problem that the removing special-purpose tool must be stored separately until the time when it is desired to use it. 
         [0006]    In a sprocket of a special shape disclosed in Japanese Examined Patent Publication No. Sho. 61-28862 (page 1, FIG. 1) in which only a tooth portion can be replaced, there was a problem that a shape structure of the sprocket is complicated and the handling of the sprocket is troublesome, and additionally the sprocket becomes expensive. 
         [0007]    Further, there was a problem that a fixing tool of a rotating body, which fastens the sprocket by tapered surfaces of an inner ring and an outer ring disclosed in Japanese Laid-Open Patent Publication No. Hei. 10-37971 (page 1, FIG. 1) needs a number of parts for attaching the sprocket and additionally the sprocket becomes expensive. 
         [0008]    Therefore, since any solutions disclosed in these patent references are post-measures when seizing was generated at a contact portion between the sprocket and the sprocket shaft, various solutions to positively avoid such seizing have been labored and studied. 
         [0009]    Namely, application of a lubricant such as oil or grease to the sprocket and the sprocket shaft has been tried. However, since the clearance gap between the sprocket and the sprocket shaft designed according to JIS-B-0401 is narrow, there was a problem that a transient application of the lubricant cannot maintain an oil film during heat generation, such as by kinetic energy and the like, and complete avoidance of seizing cannot be attained. 
         [0010]    Thus, while paying attention to the heat generation, such as by kinetic energy and the like liable to occur in a sprocket, the present invention has solved the above-mentioned conventional problems. 
         [0011]    Namely, the object of the present invention is to provide a shaft antiseizing type sprocket in which seizing liable to occur in the contact portion between the sprocket and the sprocket shaft is completely avoided in a simple sprocket structure for a long period of time and installation replacement is possible without use of a special-purpose removal tool or a mounting having a rotating body. 
       SUMMARY OF THE INVENTION 
       [0012]    The invention solves the above-mentioned problems by a shaft antiseizing type sprocket in which the inner circumferential surface of the shaft bore in the boss portion is integrally molded with the sprocket teeth portion and is installed on a sprocket shaft. The invention is characterized in that a solid lubricant is disposed in said boss portion in a state where it is partially exposed to the inner circumferential surface of the shaft bore in the boss portion. 
         [0013]    The shaft antiseizing type sprocket further solves the above-mentioned problems by that in addition, said solid lubricant is solidified in polyethylene with the lubricant being dispersedly held. 
         [0014]    According to the present invention, when a shaft bore inner circumferential surface of a boss portion integrally molded with a sprocket teeth portion is installed and fixed to a sprocket shaft, a special fixing tool on a rotating body is not needed and the following effects can be obtained by the claimed sprocket structure. 
         [0015]    Namely, a solid lubricant embedded in the boss portion is disposed in a partially exposed state toward the inner circumferential surface of the shaft bore in the boss portion, a solid lubricant, which is gradually softened by heat generated such as by kinetic energy or the like occurring in the sprocket. The lubricant forms an oil film in the gap between the inner circumferential surface of the sprocket shaft bore and the sprocket shaft by swelling and capillary attraction. Thus, seizing liable to occur in the contact portion between the sprocket and the sprocket shaft is avoided by this simple sprocket structure so that an easy installation and replacement can be attained. 
         [0016]    According to the shaft antiseizing type sprocket of the invention, since the solid lubricant is solidified in polyethylene with lubricant dispersedly held, in addition to the above-mentioned effects obtained by the invention, polyethylene and the solid lubricant is gradually softened by heat generation such as kinetic energy, which occurs in the sprocket during power transmission, and the lubricating oil dispersed and held in polyethylene is gradually diffused. Therefore, lubricating oil enough to form an oil film within a gap between the inner circumferential surface of the sprocket shaft bore and the sprocket shaft can be continuously supplied for a long period of time. 
         [0017]    If in a shaft antiseizing type sprocket in which the inner circumferential surface of the shaft bore in a boss portion integrally molded with a sprocket teeth portion is installed and fixed to a sprocket shaft, a solid lubricant confined in said boss portion is disposed in a partially exposed state toward the shaft bore inner circumferential surface of said boss portion, seizing liable to occur in the contact portion between a sprocket and the sprocket shaft is completely avoided by a simple structure for a long period of time and installation of a replacement sprocket is possible without use of special-purpose tool or mounting tool having a rotating body. Any concrete embodiment of the present invention may be used. 
         [0018]    For example, according to the invention, sprockets which may be power transmitting components are attached to a transmitting shaft or the like and are removed. For example, the term “sprockets” includes not only sprockets in a narrow sense but also gears and chain wheels. 
         [0019]    Further, the basic shapes of sprockets of the present invention may be formed by casting and forging or machining such as sintering, cutting and the like, or any one of these fabricating methods. 
         [0020]    Any arrangement formed of a solid lubricant confined in the sprocket of the present invention may be used in which the solid lubricant is directed toward an inner circumferential surface of a shaft bore of a boss portion in a partially exposed state. For example, one may use a form in which a solid lubricant is radially arranged from an inner circumferential surface of a shaft bore of the boss portion toward the inside of the boss portion, or a form in which a solid lubricant is dispersedly arranged along the inner circumferential surface of the shaft bore of the boss portion. 
         [0021]    It is noted that the solid lubricants used in the present invention are either embedded in a boss portion in a state where lubricating oil is mixed into polyethylene or are attached to the inside of a boss portion in an expanded resin or a porous body holding the lubricating oil in a dispersedly held state. The lubricating oil sinks into the expanded resin or a porous body capable of containing the lubricating oil. Any appropriate embodiment of the solid lubricant may be used. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    Examples of shaft antiseizing type sprockets according to the present invention will be described with reference to drawings, wherein 
           [0023]      FIG. 1  is a plan view of a shaft antiseizing type sprocket, which is a first example of the present invention; 
           [0024]      FIG. 2  is a perspective view, cutout through an angled line A-A, of the shaft antiseizing type sprocket shown in  FIG. 1 ; 
           [0025]      FIG. 3  is a plan view of a shaft antiseizing type sprocket, which is a second example of the present invention; 
           [0026]      FIG. 4  is a perspective view cutout through an angled line A-A, of the shaft antiseizing type sprocket shown in  FIG. 3 ; 
           [0027]      FIG. 5  is a plan view of a shaft antiseizing type sprocket, which is a third example of the present invention; 
           [0028]      FIG. 6  is a perspective view, cutout through an angled line A-A, of the shaft antiseizing type sprocket shown in  FIG. 5 ; 
           [0029]      FIG. 7  is a plan view of a shaft antiseizing type sprocket, which is a fourth example of the present invention; 
           [0030]      FIG. 8  is a perspective view, cutout through an angled line A-A, of the shaft antiseizing type sprocket shown in  FIG. 7 ; and 
           [0031]      FIG. 9  is a perspective view of a shaft illustrating a means for fixing the sprockets to the shaft. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0032]    With reference to  FIGS. 1 and 2 , a shaft antiseizing type sprocket  100 , which is a first example of the present invention, includes sprocket tooth portions  110  and a boss portion  120  integrally molded to the sprocket tooth portions  110 , and is formed so that a keyway  130  is formed in an inner circumferential surface  121  of a shaft bore of the boss portion  120 . The sprocket  100  is incorporated and fixed to a sprocket shaft S ( FIG. 9 ) in a power transmitting mechanism or the like through a key K which engages a keyway  130 . The sprocket  100  can be replaced when wear loss is generated in a sprocket tooth portion  110 , or when the number of sprocket teeth is changed or the like. 
         [0033]    A solid lubricant  140  in the form of an annular ring is embodied in the boss portion  120  for avoiding seizing which is liable to occur in the contact portion between the inner circumferential surface  121  of the shaft bore of the sprocket  100  and the sprocket shaft S. The solid lubricant  140  is disposed toward the central region of the inner circumferential surface  121  of the shaft bore in the boss portion  120  in a partially exposed state. 
         [0034]    Further, the solid lubricant  140  is in the form of an annular ring embedded in the boss portion  120  in a state where lubricating oil is dispersedly held in polyethylene 
         [0035]    It is noted that in a case of the first example the lubricating oil is embedded in the boss portion  120  in a state where lubricating oil is mixed into polyethylene in a dispersedly held state. 
         [0036]    According to the first example, since the solid lubricant  140  embedded in a boss portion  120  is disposed in a partially exposed state toward the inner circumferential surface  121  of the shaft bore of the boss portion  120 , the solid lubricant  140  is gradually softened by heat generated by kinetic energy or the like during power transmission and is swelled and by a capillary attraction, forms an oil film in the clearance gap between the shaft bore inner circumferential surface  121  and the sprocket shaft S. Accordingly, seizing which normally occurs in the contact portion between the sprocket and the sprocket shaft S is avoided and an easy bodily replacement can be achieved in the simple sprocket structure of the present invention. 
         [0037]    Since the solid lubricant  140  used in the first example is solidified in polyethylene with lubricant dispersedly held, polyethylene and the solid lubricant  140  is gradually softened by heat generation, in the sprocket  100  which occurs during power transmission such as by kinetic energy, and lubricating oil dispersed and held in the polyethylene is gradually diffused. Therefore, lubricating oil enough to form an oil film in the clearance gap between the inner circumferential surface  121  of the sprocket shaft bore and the sprocket shaft S can be continuously supplied for a long period of time. When the temperature of the portion of the boss  120  in contact with the sprocket shaft S is excessively increased, the molecular movement of polyethylene is activated so that a mutual separating action is accelerated. Thus, an amount of dispersed lubricating oil is increased so that seizing is avoided. 
         [0038]    A second example of the present invention is shown in  FIG. 3  and  FIG. 4 . 
         [0039]    A shaft antiseizing type sprocket  200  includes sprocket tooth portions  210  and a boss portion  220  integrally molded to this sprocket tooth portions  210  as in the first example, and is formed so that a keyway  230  is formed the inner circumferential surface  221  of the shaft bore of the boss portion  220 . The sprocket  200  is fixed to a sprocket shaft S in a power transmitting mechanism or the like through a key K and the keyway  230 . The sprocket  200  may be replaced when wear loss is generated in a sprocket tooth portion  210 , or when the number of sprocket teeth is changed or the like. 
         [0040]    A solid lubricant  240  is disposed in the boss portion  220  for avoiding seizing liable to occur in a contact portion between the inner circumferential surface  221  of the shaft bore of the boss portion  220  of the sprocket  200  and the sprocket shaft S. The lubricant  240  is disposed toward opening portions on both ends of the inner circumferential surface  221  of the shaft bore in the boss portion  220  in a partially exposed state. 
         [0041]    Further, the solid lubricant  240  is embedded in the boss portion  220  in a state where lubricating oil is dispersedly held in polyethylene 
         [0042]    In the second example, the lubricating oil comprises a pair of annular rings embedded in the boss portion  220  in a state where lubricating oil is mixed into polyethylene in a dispersedly held state. 
         [0043]    According to the shaft antiseizing type sprocket  200  of the second example, a solid lubricant  240  embedded in the boss portion  220  is disposed in a partially exposed state toward the inner circumferential surface  221  of the shaft bore of the boss portion  220 , the solid lubricant  240  gradually softened by heat generated by kinetic energy or the like during power transmission, and a capillary attraction forms an oil film at the clearance gap between the shaft bore inner circumferential surface  221  and the sprocket shaft S. Accordingly, seizing liable to occur at a contact portion between the sprocket and the sprocket shaft S is avoided and an easy replacement can be attained by the simple sprocket structure of the present invention. 
         [0044]    The solid lubricant  240  comprises annular rings concentrically disposed with the shaft bore inner circumferential surface  221  of the boss portion  220 . The solid lubricant  240  is disposed toward open portions on both ends of the inner circumferential surface  221  of the shaft bore of the boss portion  220  in a partially exposed state. Even if the solid lubricant  240  is used with a vertically disposed sprocket shaft S, an oil film is formed over the entire region of contact of the shaft with the inner circumferential surface  221  of the shaft bore of the boss portion  220 . Therefore, partial seizing of the contact portion with the inner circumferential surface  221  of the shaft bore of the boss portion  220  can be avoided. 
         [0045]    Since the solid lubricant  240  used in the second example is solidified in polyethylene with lubricant dispersedly held, the polyethylene of the solid lubricant  240  is gradually softened by heat generated by kinetic energy, which occurs in the sprocket  200  during power transmission. Lubricating oil dispersed and held in polyethylene is therefore gradually diffused, and lubricating oil enough to form an oil film in the clearance gap between the inner circumferential surface  221  of the sprocket shaft bore and the sprocket shaft S can be continuously supplied for a long period of time. When the temperature of the contact portion with the sprocket shaft S is excessively increased, the molecular movement of polyethylene is activated so that a mutual separating action is accelerated. Thus an amount of dispersed lubricating oil is increased so that seizing is avoided. 
         [0046]    A third example of the present invention is shown in  FIG. 5  and  FIG. 6 . 
         [0047]    A shaft antiseizing type sprocket  300  includes a sprocket tooth portions  310  and a boss portion  320  integrally molded to this sprocket tooth portions  310  as in the first example, and is formed so that a keyway  330  formed in a shaft bore inner circumferential surface  321  of the boss portion  320  is incorporated and fixed to a sprocket shaft S in a power transmitting mechanism or the like through a key K. The sprocket  300  can be replaced when wear loss is generated in a sprocket tooth portion  310 , or when the number of sprocket teeth is changed or the like. 
         [0048]    A solid lubricant  340  is dispersedly disposed for avoiding seizing liable to occur in the contact portion between the sprocket  300  and the sprocket shaft S. The solid lubricant  340  is embedded in axial grooves at three positions other than the keyway  330  along the shaft bore inner circumferential surface  321  of the boss portion  320  in a partially exposed state. 
         [0049]    Further, the solid lubricant  340  is embedded in the boss portion  320  in a state where lubricating oil is dispersedly held in polyethylene. 
         [0050]    It is noted that in a case of the third example the lubricating oil is a plurality of axially-extending bars embedded in a boss portion  320  in a state where lubricating oil is mixed into polyethylene in a dispersedly held state of lubricating oil. 
         [0051]    According to the shaft antiseizing type sprocket  300  of the third example, since the solid lubricant  340  in the boss portion  320  is disposed in a partially exposed state toward the inner circumferential surface  221  of the shaft bore of the boss portion  320 , the solid lubricant  340  is gradually softened by heat generated by kinetic energy or the like generated during power transmission and is swelled by a capillary phenomenon to form an oil film at a gap between the inner circumferential surface  321  and the sprocket shaft S. Accordingly, seizing liable to occur in the contact portion between the sprocket  300  and the sprocket shaft S is avoided and an easy replacement can be achieved in a simple sprocket structure. 
         [0052]    Since the solid lubricant  340  is dispersedly disposed at three positions other than the keyway  330  along the inner circumferential surface  321  in a partially exposed state, an oil film is formed over the entire region of a contact portion with the inner circumferential surface  321  of the shaft bore of the boss portion  320  other than the keyway  330 . Thus, the key K is not dislodged inadvertently and seizing of the contact portion with the shaft bore inner circumferential surface  321  of the boss portion  320  can be completely avoided. 
         [0053]    The solid lubricant  340  used in the third example is solidified in polyethylene with lubricant dispersedly held, and the polyethylene of the solid lubricant  340  is gradually softened by heat generated by kinetic energy, which occurs in the sprocket  300  during power transmission and, as a result, lubricating oil dispersed and held in polyethylene is gradually diffused. Therefore, lubricating oil enough to form an oil film in the clearance gap between the inner circumferential surface  321  of the sprocket shaft bore and the sprocket shaft S can be continuously supplied for a long period of time. When the temperature in the contact portion with the sprocket shaft S is excessively increased, the molecular movement of polyethylene is activated so that a mutual separating action of the lubricant  340  is accelerated. Thus, an amount of dispersed lubricating oil is increased so that seizing is avoided. Therefore, the advantageous effects of the example are very large. 
         [0054]    A fourth example of the present invention is shown in  FIG. 7  and  FIG. 8 . 
         [0055]    In these figures, a shaft antiseizing type sprocket  400  includes a sprocket tooth portions  410  and a boss portion  420  integrally molded to the sprocket tooth portions  410  as in the first example, and is formed so that a keyway  430  is formed in the shaft bore inner circumferential surface  421  of the shaft bore of the boss portion  420 . The sprocket  400  is fixed to a sprocket shaft S in a power transmitting mechanism or the like through a key K. The sprocket can be bodily replaced when wear loss is generated in a sprocket tooth portion  410 , or when the number of sprocket teeth is changed or the like. 
         [0056]    Radially-extending plugs of a solid lubricant  440  are dispersedly disposed in the boss portion  420  for avoiding seizing liable to occur in the contact portion between a sprocket  400  and the sprocket shaft S. The plugs are disposed at four positions other than the keyway  430  and extend radially inward toward the inner circumferential surface  421  of the shaft bore of the boss portion  420  in a partially exposed state. In this embodiment, the plugs of lubricant  440  are embedded in a plurality of radial bores extending from the circumferential surface  421  outwardly to an exterior surface of the boss portion  420 . 
         [0057]    Further, the solid lubricant  440  is embedded in the boss portion  420  in a state where lubricating oil is dispersedly held in polyethylene 
         [0058]    It is noted that in a case of the fourth example, the lubricating oil is embedded in a boss portion  420  in a state where lubricating oil is mixed into polyethylene in a dispersedly held state of lubricating oil. 
         [0059]    According to the shaft antiseizing type sprocket  400  of the fourth example, since a solid lubricant  440  possessed in a boss portion  420  is disposed in a partially exposed state toward the shaft bore inner circumferential surface  421  of the boss portion  420 , the solid lubricant  440  is gradually softened by heat generated by kinetic energy or the like generated during power transmission and is affected by a capillary attraction to form an oil film in the clearance gap between the shaft bore inner circumferential surface  421  and the sprocket shaft S. Accordingly, seizing liable to occur at a contact portion between the sprocket and the sprocket shaft S is avoided and an easy bodily replacement can be achieved with the simple sprocket structure. 
         [0060]    Each solid lubricant  440  plug is dispersedly embedded at four positions other than the keyway  430  and extends radially from the shaft bore inner circumferential surface  421  toward the boss portion  420  a in a partially exposed state, an oil film is formed over the entire region of the contact portion of the sprocket  400  with the inner circumferential surface  421  of the shaft bore of the boss portion  420  other than the keyway  430 . Thus, the key K is not dislodged inadvertently and seizing in the contact portion between the sprocket and the inner circumferential surface  421  of the shaft bore of the boss portion  420  can be completely avoided, and containment of the solid lubricant  440  can be more ensured. 
         [0061]    The solid lubricant  440  used in the fourth example is solidified in polyethylene with lubricant dispersedly held, and polyethylene of the solid lubricant  440  is gradually softened by heat generated by kinetic energy, which occurs in the sprocket  400  during power transmission. Lubricating oil dispersed and held in polyethylene is gradually diffused. Therefore, lubricating oil enough to form an oil film in the clearance gap between the inner circumferential surface  421  of the sprocket shaft bore and the sprocket shaft S can be continuously supplied for a long period of time. When the temperature of a contact portion with the sprocket shaft S is excessively increased, the molecular movement of polyethylene is activated so that a mutual separating action is accelerated. Thus an amount of dispersed lubricating oil is increased so that seizing is prevented