Abstract:
A roller chain with a simple structure is provided, which can mitigate impact load on rollers due to collision with sprockets and can lengthen roller life, as well as minimize interference between the sprockets and inner plates. A roller chain includes rollers that are formed in a cylindrical shape tubularly connected continuously in axial and circumferential directions of the rollers. Each of the rollers is curved such that an inner diameter at both ends thereof differs from that of a middle part, and that their outer diameter at both ends differs from that of the middle part, so that the rollers deform elastically when contacting sprockets S as the rollers are sandwiched between bushings and the sprockets.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
       [0001]    The present invention relates to a roller chain formed by a plurality of inner links and outer links coupled together in an endless manner. 
       2. Description of the Related Art 
       [0002]    Roller chains formed by a plurality of inner links, a plurality of outer links, and rollers are conventionally known. The inner links are each configured by coupling a pair of front and rear bushings to a pair of left and right inner plates. The outer links are each configured by coupling a pair of front and rear connecting pins to a pair of left and right outer plates. The rollers are fitted on the bushings. The inner links and outer links are alternately and pivotably coupled together in a longitudinal direction of the chain by inserting the connecting pins in the bushings. 
         [0003]    In such a roller chain, it is known that, when the chain runs, the rollers generate noise as they collide sprockets. It has been proposed, therefore, to fit rollers  180  formed by coiled spring wires in the shape of a coil spring on the bushings  140  as shown in  FIGS. 9A and 98  for the purpose of reducing this noise (see, for example, Japanese Patent Application Laid-open No. H9-287637 and US Pat. No. 2,909,938). 
         [0004]    When colliding with sprockets S, each of the ring-like parts  180   a  that form the rollers  180  elastically deform in a radial direction, so as to mitigate the impact load due to the collision with the sprockets S, and thereby reduce the noise generated when they mate with the sprockets S. 
       SUMMARY OF THE INVENTION 
       [0005]    However, each of the ring-like parts  180   a  that form the coil spring-like rollers  180  does not necessarily deform elastically in a uniform manner when the rollers  180  collide with the sprockets S. Elastic deformation occurs disproportionately and localizes in the large-diameter ring-like parts  180   a  that make contact with the sprockets S more frequently as shown in  FIGS. 9A and 9B . Thus the large-diameter ring-like parts  180   a  are more susceptible to plastic deformation and damage, as a result of which life of the rollers  180  could be shortened. 
         [0006]    When the large-diameter ring-like parts  180   a  undergo plastic deformation into an oval shape or the like, the rollers  180  can no longer rotate smoothly relative to the bushings  140 . As this deteriorates the original function of the rollers, which is to reduce resistance between bushings and sprockets S, the rollers  180  will be even more susceptible to local damage or the like. 
         [0007]    In modern car engine applications, demands are growing for more lightweight designs for timing chains and the like used in the engine for the purpose of, for example, improving fuel economy of the engine. The rollers  180 , too, are therefore desired to be lighter. To meet with the demands, for example the coil spring-like rollers  180  need to be formed from thinner spring wires, which only results in lowered strength of the ring-like parts  180   a  and exacerbates the problems described above. 
         [0008]    An object of the present invention is to solve these problems and to provide a roller chain with a simple structure that can mitigate impact load on rollers due to collision with sprockets and can lengthen roller life, as well as minimize interference between the sprockets and inner plates. 
         [0009]    The present invention solve the problems above by providing a roller chain including a plurality of inner links each configured by coupling a pair of front and rear bushings to a pair of left and right inner plates, a plurality of outer links each configured by coupling a pair of front and rear connecting pins to a pair of left and right outer plates, and rollers fitted on the brushings, the inner links and the outer links being alternately and pivotably coupled together in a longitudinal direction of the chain by inserting the connecting pins in the bushings, the rollers being formed in a cylindrical shape tabularly connected continuously in axial and circumferential directions of the rollers, and each of the rollers being curved such that an inner diameter at both ends thereof differs from that of a middle part thereof, and an outer diameter at both ends thereof differs from that of the middle part, so that the rollers deform elastically when contacting sprockets as the rollers are sandwiched between the bushings and the sprockets. 
         [0010]    According to one aspect of the present invention, the rollers are curved so that they deform elastically when contacting sprockets as they are sandwiched between the sprockets and the bushings. This way, the rollers provide springiness by undergoing elastic deformation to mitigate impact load due to collision with sprockets, and can thus reduce noise generated when they mate with the sprockets. 
         [0011]    The rollers are formed in a cylindrical shape tabularly connected continuously in axial and circumferential directions of the rollers, so that they can absorb the impact from the sprockets by the elastic deformation in their entirety, unlike conventional rollers in the form of a coil spring, where the impact from the sprockets localizes in large-diameter ring-like parts. This way, local plastic deformation and damage of roller are minimized and roller life can be lengthened. 
         [0012]    According to another aspect of the present invention, the rollers are curved such that the inner diameter at both ends of the rollers is larger than that of the middle part, and the outer diameter at both ends thereof is larger than that of the middle part. This way, lubricating oil can readily enter between the rollers and the bushings from both ends of the rollers, so that the lubricating oil itself between the rollers and the bushings can provide a function of mitigating and damping impacts, and thus the impact load due to collision with so can be further reduced. 
         [0013]    Also, the rollers are formed in a cylindrical shape tubularly connected continuously in the axial and circumferential directions of the rollers, and curved such that the outer diameter at both ends thereof is larger then that of the middle part of the rollers. This way, when contacting the sprockets, the rollers can smoothly guide the sprockets axially inward by the outer circumferential surface thereof that is facially continuous in the axial direction, and thereby minimize interference between the sprockets and the inner plates, which prevents generation of noise. 
         [0014]    According to another aspect of the present invention, the rollers are curved such that the inner diameter at both ends thereof is smaller than that of the middle part, and the outer diameter at both ends thereof is smaller than that of the middle part. This way, lubricating oil can be readily kept between the rollers and the bushings, so that the lubricating oil itself between the rollers and the bushings can provide a function of mitigating and damping impacts, and thus the impact load due to collision with sprockets can be further reduced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a cross-sectional perspective view illustrating an inner link of a roller chain according to a first embodiment; 
           [0016]      FIG. 2  is a cross-sectional view illustrating the roller chain according to the first embodiment; 
           [0017]      FIG. 3  is an illustrative diagram showing how a sprocket and a roller make contact with each other in the first embodiment; 
           [0018]      FIG. 4  is an illustrative diagram showing an example of a forming method of the roller of the first embodiment; 
           [0019]      FIG. 5  is a cross-sectional perspective view illustrating an inner link of a roller chain according to a second embodiment; 
           [0020]      FIG. 6  is a cross-sectional view illustrating the roller chain according to the second embodiment; 
           [0021]      FIG. 7  is an illustrative diagram showing how a sprocket and a roller make contact with each other in the second embodiment; 
           [0022]      FIG. 8  is an illustrative diagram showing an example of a forming method of the roller of the second embodiment; and 
           [0023]      FIGS. 9A and 9B  are illustrative diagrams showing how a sprocket and a roller make contact with each other in a conventional roller chain. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]    Hereinafter, a roller chain  10  according to a first embodiment of the present invention will be described with reference to  FIGS. 1 to 4 . 
         [0025]    The roller chain  10  of the first embodiment is configured as a timing chain used in a car engine and includes, as shown in  FIGS. 1 and 2 , a plurality of inner links  20  each made up of a pair of front and rear cylindrical bushings  40  connected to a pair of left and right inner plates  30 , a plurality of outer links  50  each made up of pair of front and rear connecting pins  70  connected to a pair of left and right outer plates  60 , and metal rollers  80  fitted on the bushings  40 . These plurality of inner links  20  and outer links  50  are alternately and pivotably connected to each other along the longitudinal direction of the chain by inserting the connecting pins  70  in the bushings  40 . 
         [0026]    Each roller  80  is formed in a cylindrical shape tubularly connected continuously in axial and circumferential directions of the roller as shown in  FIGS. 1 to 3 . 
         [0027]    Each roller  80  is curved to flare out at both ends, so that the inner diameter at both ends of the roller is larger than the inner diameter of a middle part of the roller, as well as the outer diameter at both ends of the roller is larger than the outer diameter of the middle part of the roller. 
         [0028]    The outer circumferential surface of the roller  80  is concavely curved such that the roller diameter reduces smoothly from both axial ends of the roller toward the center of the roller. 
         [0029]    The inner circumferential surface of the roller  80  is convexly curved such that the roller diameter reduces smoothly from both axial ends of the roller toward the center of the roller. 
         [0030]    The thickness of the roller  80  is substantially uniform over the entire surface. 
         [0031]    In this embodiment, the roller  80  is formed as shown in  FIG. 4 , wherein, after forming a sheet material into a cylindrical shape, jigs T 1  are inserted from both ends of the roller to fit into the inner circumference of the roller  80 . 
         [0032]    Specific methods of forming the roller  80  are not limited to the one described above and may include any means or processes. 
         [0033]    In the roller chain  10  of the first embodiment thus obtained, when the roller contacts the sprocket S, the outer circumferential surface of the roller  80  makes contact with the sprocket S at two sprocket contact portions  81  near both ends of the roller, while the inner circumferential surface of the roller  80  makes contact with the bushing  40  at one bushing contact portion  82  near the center of the roller, as shown in  FIG. 3 . 
         [0034]    The roller thus makes contact with the sprocket S and bushing  40  at two sprocket contact portions  81  and one bushing contact portion  82 , respectively, which are axially offset, and is sandwiched between the bushing  40  and the sprocket S, so that, when contacting the sprocket S, the roller  80  undergoes elastic deformation substantially entirely, so as to mitigate the impact load due to collision with the sprocket S. 
         [0035]    Specific shapes of the roller  80  are not limited to the one described above and may include any features as long as the roller  80  is curved such that its inner diameter is larger at both ends than in the middle and its outer diameter is larger at both ends than in the middle so that the roller deforms elastically when making contact with the sprocket S as it is sandwiched between the bushing  40  and the sprocket S. 
         [0036]    For example, while the roller  80  described above is curved entirely along its axial direction, the roller may be curved only at both ends to increase in diameter outward in the axial direction, and not curved in the middle. In this case, the middle part of the roller is kept cylindrical, so that the inner circumferential surface of the roller  80  makes contact with the outer circumferential surface of the bushing  40  over a predetermined distance along the axial direction of the roller in the middle of the roller (bushing contact portion  82 ), which will minimize tilting of the roller  80  relative to the bushing  40 . 
         [0037]    Next, a roller chain  10  according to a second embodiment of the present invention will be described with reference to  FIGS. 5 to 8 . The second embodiment is exactly the same as the previously described first embodiment other than the roller  80 , and therefore the configurations other than the roller  80  will not be described again. 
         [0038]    The roller  80  in the roller chain  10  of the second embodiment is formed in a cylindrical shape tubularly connected continuously in the axial and circumferential directions of the roller as shown in  FIGS. 5 to 7 . 
         [0039]    Each roller  80  is curved in a barrel-like shape such as to bulge in the middle, so that the inner diameter at both ends of the roller is smaller than the inner diameter in the middle part of the roller, as well as the outer diameter at both ends of the roller is smaller than the outer diameter in the middle part of the roller. 
         [0040]    The outer circumferential surface of the roller  80  is convexly curved such what the roller diameter increases smoothly from both axial ends of the roller toward the center of the roller. 
         [0041]    The inner circumferential surface of the roller  80  is concavely curved such that the roller diameter increases smoothly from both axial ends of the roller toward the center of the roller. 
         [0042]    The thickness of the roller  80  is substantially uniform over the entire surface. 
         [0043]    In this embodiment, the roller  80  is formed as shown in  FIG. 8 , wherein, after forming a sheet material into a cylindrical shape, two jigs T 2  on both ends of the roller opposite each other are brought closer to apply forces to the roller such as to reduce the diameter at both ends of the roller  80 . 
         [0044]    T 3  in  FIG. 8  represents another jig for positioning the two jigs T 2 . 
         [0045]    Specific methods of forming the roller  80  are not limited to the one described above and may include any means or processes. 
         [0046]    In the roller chain  10  of the second embodiment thus obtained, when the roller contacts the sprocket S, the outer circumferential surface of the roller  80  makes contact with the sprocket S at one sprocket contact portion  81  in the middle of the roller, while the inner circumferential surface of the roller  80  makes contact with the bushing  40  at two bushing contact portions  82  near both ends of the roller, as shown in  FIG. 7 . 
         [0047]    The roller thus makes contact with the sprocket S and bushing  40  at one sprocket contact portion  81  and two bushing contact portions  82 , respectively, which are axially offset, and is sandwiched between the bushing  40  and the sprocket S, so that, when contacting the sprocket S, the roller  80  undergoes elastic deformation substantially entirely, so as to mitigate the impact load due to collision with the sprocket S. 
         [0048]    Specific shapes of the roller  80  are not limited to the one described above and may include any features as long as the roller  80  is curved such that its inner diameter is smaller at both ends than in the middle and its outer diameter is smaller at both ends than in the middle, so that the roller deforms elastically when making contact with the sprocket S as it is sandwiched between the bushing  40  and the sprocket S. 
         [0049]    For example, while the roller  80  described above is curved entirely along its axial direction, the roller may be curved only at both ends to reduce in diameter outward in the axial direction, and not curved in the middle. In this case, the middle part of the roller is kept cylindrical, so that the outer circumferential surface of the roller  80  makes contact with the sprocket S over a predetermined distance along the axial direction of the roller in the middle of the roller (sprocket contact portion  81 ), which will minimize tilting of the roller  80  relative to the sprocket S. 
         [0050]    While embodiments of the present invention have been described in detail, the present invention is not limited to the above-described embodiments and may be carried out with various design changes without departing from the scope of the present invention set forth in the claims. 
         [0051]    For example, while the roller chain was described as a timing chain of a car engine in the embodiments above, the purpose of use of the roller chain of the present invention is not limited to this application, and may be used as a transmission chain or a conveyor chain. 
         [0052]    While the chains in the embodiments above have one inner link in the chain width direction, they may have a plurality of inner links arranged in the chain width direction. 
         [0053]    While the bushings are cylindrical in the embodiments described above, specific shapes of the bushings are not limited to the one described. The bushing may have any other shapes, e.g., curved such as to bulge in the middle in the axial direction thereof, in a barrel-like shape. 
         [0054]    The rollers may be formed by rolling a sheet material into a tube, or may be formed seamlessly.