COMBINATION OF A SPROCKET AND A CHAIN

Abstract: A sprocket permitting the use of existing chains and having a reduced weight. Specifically, a sprocket (2) comprising a sprocket body (4) and teeth (6) provided around the periphery of the sprocket body (4), wherein the teeth (6) are made thicker than the sprocket body (4).

Description: The present invention relates to a combination of a sprocket and a chain as described in the preamble of claim 1. TECHNICAL BACKGROUND A known sprocket includes a generally annular body, and a plurality of integral teeth arranged on the peripheral edge of the body at equal intervals. Typically, such a sprocket is mounted on the drive or driven wheel of a motorcycle and is operatively associated with a chain. To improve fuel economy, there is a need in the motorcycle industry to reduce the weight of a motorcycle. An attempt has been made to simply reduce the thickness of the overall sprocket. However, a reduction in the axial thickness of the teeth (or the face width of the teeth) requires a corresponding reduction in the width of the chain and prevents the use of an existing chain. This results in an increase in the production costs of the mechanism. Also, a narrow chain lacks durability as compared with the existing chain. Reference should also be made to US-A-4,555,240, FR-A-2,404,780, which comprises the features mentioned in the preamble of claim 1, and EP-A-0,764,482 which describe proposals for annular discs such as sprockets, gears and the like which are to be driven by, for example, a chain. Accordingly, it is an object of the present invention to provide a sprocket which has a reduced weight and which enables the use of the existing chain. DISCLOSURE OF THE INVENTION To achieve this object, the present invention provides a combination of a sprocket and a chain as described in claim 1. As the thickness of the teeth is greater than that of the body which occupies a substantial part of the sprocket, the sprocket can be reduced in weight and production costs. The teeth are thick enough to readily correspond with the width of the existing chain. In other words, the teeth are sufficiently thick to accept the existing chain. The present invention thus enables the use of the existing chain and enjoys the strength of the existing chain. The present invention provides a combination of sprocket and a chain, the sprocket comprising a body, and teeth formed on the peripheral edge of the body, wherein the body has a thickness less than that of the teeth. As the thickness of the body is less than that of the teeth, and the body occupies a substantial part of the sprocket, the sprocket can be reduced in weight and production costs. The axial thickness of the teeth can be maintained and the teeth can be thick enough to readily correspond with the width of the existing chain. The present invention thus enables the use of the existing chain and enjoys the strength of the existing chain. The present invention also provides a combination of a sprocket and a chain, the sprocket comprising a substantially annular body having a first side, an opposite, second side, a peripheral edge, and a central axis extending through the substantially central points of the first and second sides and in a direction perpendicular to the sides, and a plurality of teeth arranged on the peripheral edge of the body, wherein each of the teeth include a first step extending radially outwardly from the first side of the body, a first side connected to the first step and extending substantially parallel to the first side of the body, a second step extending radially outwardly from the second side of the body, a second side connected to the second step and extending substantially parallel to the second side of the body, a peripheral wall extending along the peripheral edge of the body and between the first side and the second side of the teeth, and a recess formed in the peripheral wall of each of the teeth. As the axial thickness of the teeth is greater than that of the body which occupies a substantial part of the sprocket, the sprocket can be reduced in weight and production costs. The teeth are thick enough to readily correspond with the width of the existing chain. The present invention thus enables the use of the existing chain and enjoys the strength of the existing chain. Further, with the recesses in the peripheral walls of the teeth, the teeth have a larger area to dissipate more heat. Heat is generated by friction when the teeth of the sprocket are drivingly engaged with a chain. Such heat is dissipated through the recesses. The chain is substantially free from thermal expansion or elongation. This results in an increase in the durability of the chain. Advantageously, the recesses provide a path along which dirt or mud is removed from the chain and helps prevent dirt from adhering to the teeth. This results in a decrease in the amount of friction between the chain and the sprocket and thus, in an increase in the service life of the chain and sprocket. The present invention additionally provides a combination of a sprocket and a chain, the sprocket comprising a body having a peripheral edge, and teeth formed on the peripheral edge of the body and including respective recesses formed in the peripheral walls of the teeth. With recesses in the peripheral walls of the teeth, the teeth have a larger area to dissipate more heat. Heat is generated by friction when the teeth of the sprocket are drivingly engaged with a chain. Such heat is dissipated through the recesses. The chain is substantially free from thermal expansion or elongation. This results in an increase in the durability of the chain. Advantageously, the recesses provide a path along which dirt or mud is removed from the chain and helps prevent dirt from adhering to the teeth. This results in a decrease in the amount friction between the chain and the sprocket and thus, in an increase in the service life of the chain and sprocket. As the body which occupies a substantial part of the sprocket is thin, the sprocket can be reduced in weight and production costs. The teeth are thick enough to readily correspond with the width of the existing chain. The present invention thus enables the use of the existing chain and enjoys the strength of the existing chain. Moreover, the teeth are made thicker than the rest of the workpiece during formation of the teeth. This results in a decrease in the number of production steps and costs of the sprocket. Before one embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its application to the details of the construction and the arrangements of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Other features and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a front view of a sprocket according to a first embodiment of the present invention; Fig. 2 is a sectional view taken on the line II-II in Fig, 1; Fig. 3 is a sectional view, on an enlarged scale, of part of the sprocket shown in Fig. 2; Fig. 4 is a plan view of one tooth of the sprocket shown in Fig. 3; Fig. 5 is a sectional view of a sprocket according to a second embodiment of the present invention; Fig. 6 is a sectional view, on an enlarged scale, of part of the sprocket shown in Fig. 5; Fig. 7 is a flow chart showing a method for manufacturing the sprocket; Fig. 8 is a plan view of a tool for use in the method shown in Fig. 7; Fig. 9 is a side view, partly in section, of part of a workpiece with the tool being forced into the workpiece; Fig. 10 is a flow chart showing another method for manufacturing the sprocket; Fig. 11 is a plan view of a tooth forming tool used to manufacture the sprocket shown in Fig. 10; Fig. 12 is a perspective view of the tooth forming tool shown in Fig. 11; Fig. 13 is a side view of the tooth forming tool shown in Fig. 11; Fig. 14(a) is a perspective view showing the manner in which a tool is moved toward a workpiece; Fig. 14(b) is a perspective view similar to that of Fig. 14(a), but showing the manner in which the tool is pressed against the workpiece; Fig. 14(c) is a perspective view of the sprocket in its final form; Figs. 15(a) to 15(c) are schematic side views showing a sequence of operation of a rotary press machine; Fig. 16 is a front view of a sprocket according to a third embodiment of the present invention; Fig. 17 is a sectional view of the sprocket shown in Fig. 16, taken along the line 17 - 17; Fig. 18 is a sectional view, on an enlarged scale, of part of the sprocket shown in Fig. 17; Fig. 19 is a fragmentary enlarged sectional view of the sprocket shown in Fig. 16, taken along the line 19 - 19; Fig. 20 is a sectional view of a sprocket according to a fourth embodiment of the present invention; and Fig. 21 is a sectional view, on an enlarged scale, of part of the sprocket shown in Fig. 20. BEST MODE FOR CARRYING OUT THE INVENTION A sprocket according to one embodiment of the present invention will now be described with reference to the accompanying drawings. Illustratively, a sprocket 2 includes a generally annular body 4, and a plurality of integral teeth 6 arranged on the periphery of the body 4. The body 4 has a central axis 8 extending in a direction perpendicular to the surfaces of the body 4, a peripheral edge 10 extending about the central axis, and a pair of opposite sides, that is, a first side 12 and a second side 14. The central axis 8 extends centrally through the first side 12 and the second side 14 of the body 4. The teeth 6 are arranged on the peripheral edge 10 of the body 4 at equal intervals. A plurality of arcuate recesses 11 are formed between adjacent teeth 6. As shown in Fig. 3, the teeth 6 have a face width M or a thickness M in the direction of the axis 8. The body 4 has a thickness N in the direction of the axis 8. The thickness M of the teeth 6 is greater than the thickness N of the body 4. In other words, the body 4 is thinner than the teeth 6. A reduction in the thickness of the body 4 results in a corresponding reduction in the weight and the production costs of the overall sprocket. For example, the thickness of the body 4 can be substantially half of that of the body of a conventional sprocket. Thus, only the thickness N of the body 4 can be decreased to make the axial thickness M of the teeth 6 thicker than that of the body so that the teeth 6 are identical in thickness to those of a conventional sprocket (typically, 5.8 mm, 7.2 mm or 8.7 mm). This design enables the use of a conventional chain, the width of which is typically, 6.35 mm, 7.94 mm or 9.53 mm. Thus, the present invention eliminates the need for a new chain, thus reducing production costs and enjoys the strength of the existing chain. The sprocket 2 may be mounted to the drive or driven wheel of a motorcycle. As the sprocket is reduced in weight, such a motorcycle provides better fuel economy. Each of the teeth 6 includes a first step 16 extending radially outwardly from the first side 12 of the body 4, a first side 18 extending radially outwardly from the first step 16 in parallel relation to the first side 12 of the body 4, a second step 20 extending radially outwardly from the second side 14 of the body 4, a second side 22 extending radially outwardly from the second step 20 in parallel relation to the second side 14 of the body 4, a peripheral wall 24 provided radially outwardly of and extending along the peripheral edge 10 of the body 4, and a recess or groove 13 formed in the peripheral wall 24 each of the teeth. The first and second steps 16 and 20 are formed to extend away from the first and second sides 12 and 14, respectively. The grooves 13 are defined in and extend radially inwardly from the peripheral walls 24 of the teeth. Preferably, each of the grooves 13 is located in the substantially central part of the peripheral wall 24 of each of the teeth in the direction of the face width M or the thickness M of the teeth 6 (or in the direction of the central axis 8). Also, the grooves 13 preferably extend through the teeth 6 along the circumference of the body 4 and circumferentially about the central axis 8 as shown by the arrow X in Figs. 1 and 4 to make a single peripheral groove. The grooves 13 are formed, for example, by pressing the substantially central parts of the peripheral walls 24 of the teeth 6 in the axial direction. As a result, the first side 18 and the second side 22 of the teeth 6 are axially outwardly urged and extended beyond the first side 12 and the second side 14 of the body 4 so that the thickness M of the teeth 6 is greater than the thickness N of the body 4. With the grooves 13, the teeth 6 have a larger area to dissipate more heat. Typically, heat is generated by friction when the teeth 6 are drivingly engaged with an associated chain. Advantageously, such heat is dissipated through the grooves 13. Thus, the chain is substantially free from thermal expansion or elongation. This results in an increase in the durability life of the chain as well as the sprocket. Also, each of the grooves 13 serves as a flow path for allowing dirt or mud adhering to the chain to move through the grooves, thereby substantially preventing dirt from adhering to the teeth. This brings about a reduction in the amount of friction between the chain and the sprocket and thus, increases the service life of the chain and sprocket. The grooves 13 extend through the teeth 6 and cooperate together to provide the entire sprocket with a path along which dirt can be removed. With the sprocket according to the first embodiment of the present invention, the first step 16 enables the first side 12 of the body 4 to be offset from the first side 18 of the teeth 6. Similarly, the second step 20 enables the second side 14 of the body to be offset from the second side 22 of the teeth 6. As shown in Fig. 3, a spacer 25 may be attached to the second side 14 of the body 4. The spacer 25 is in the form of a thin plate and has an outer surface 25a. The spacer 25 may have a thickness so that the outer surface 25a of the spacer 25 becomes flush with the second side 22 of the teeth 6 when the spacer 25 is attached to the second side 14 of the body 4. The spacer 25 may be secured to a sprocket mount 30 with the outer surface 25a held in contact with the sprocket mount 30 (as shown by a broken line in Fig. 3) before the sprocket 2 is attached to the sprocket mount 30. This arrangement readily enables the teeth 6 to be positioned relative to the sprocket mount 30 as in conventional. In other words, the distance between the sprocket mount 30 and the center line P of a chain 26 as shown by a broken line in Fig. 3 (or the center line of the teeth 6) is identical to that of a conventional sprocket. Thus, there is no need to use a special chain instead of an existing chain. Also, the sprocket can be mounted to the sprocket mount 30 in a known manner. A sprocket according to a second embodiment of the present invention will next be described with reference to Figs. 5 and 6. Like parts are given like reference numerals and will not be described in detail. A sprocket includes a body 4. The body 4 has a first side 12 and a second side 14. Each tooth 6 has a pair of opposite sides, that is, a first side 18 and a second side 28. The second side 28 of the tooth 6 is flush with a second side 14 of the body 4. The body 4 is attached to a sprocket mount 30 with the second side 28 held in contact with the sprocket mount 30. With this arrangement, the distance between the sprocket mount 30 and the center line P of the chain 26 (or the center line of the tooth 6) can be made identical to that of a conventional sprocket without the need for the spacer 25 used in the first embodiment. Reference will now be made to a method and machine for manufacturing the sprockets. Referring to Fig. 7, a method for manufacturing the sprocket comprises a first step 100 of forming a sprocket wherein the thickness of the body 4 is identical to that of the teeth 6 arranged on the periphery of the body 4, and a second step 102 of increasing the thickness M of the teeth 6 so that the teeth 6 are thicker than the body 4. The first step 100 may be performed by casting, forging, rolling or other known processes. The second step 102 comprises the steps of pressing substantially the center of the peripheral walls 24 of the teeth 6 in the axial direction so as to form the recesses or grooves 13 in the teeth 6, and outwardly extending the first side 18 and the second side 22 of the teeth beyond the body 4 so that the thickness of the teeth 6 is greater than the thickness of the body 4. Referring specifically to Figs. 8 and 9, a forming hand tool 32 is used in the second step 102 to form the teeth 6 so that the teeth 6 are thicker than the body 4. The tool 32 has a body 34 of a substantially rectangular shape as viewed in plan, and a tip 36 tapered from the body 34. The tip 36 is pressed against the peripheral walls 24 of the teeth 6 so that the teeth 6 are thicker than the body 4. The second step can be performed manually. However, the tool 32 may be mounted to a press machine to automatically perform the second step. Reference will next be made to another method and machine for manufacturing the sprockets. Referring to Fig. 10, another method comprises a first step 104 of preparing an annular workpiece or ring 70 having a predetermined thickness, and a second step 106 of forming a plurality of teeth on the peripheral edge of the annular workpiece 70 at equal intervals so that the teeth have a thickness (or a face width) greater than that of the annular workpiece 70. The annular workpiece 70 can be made by pressing, casting, forging or other known processes. As shown in Figs. 14(a) and 15(a), the annular workpiece 70 has a central axis 71, and a peripheral edge 72 extending about the central axis 71. The second step 106 may be performed by a rotary pressing process using a rotary press machine 40 shown in Fig. 15. The rotary press machine 40 includes a tooth forming tool 42, a motor 80 for drivingly rotate the tooth forming tool 42, and a transfer unit 90 for gradually and reciprocatingly moving the tooth forming machine 42 and the motor 80 in a horizontal direction to the workpiece and from the sprocket formed from the workpiece (see Fig. 15). The motor 80 includes an output shaft 81. The tooth forming tool 42 is detachably mounted to the free end of the output shaft 81. The motor 80 is energized to rotate the output shaft 81 whereby the tooth forming tool 42 is rotated about a central axis 58. The components of the machine are only schematically shown in Fig. 15 for ease of illustration. Similarly, some of the components are omitted from Fig. 14. Referring to Figs. 11 to 13, the tooth forming tool 42 includes a press member 44 adapted to directly press substantially centrally the peripheral walls 24 of the teeth 6 along the circumference of the teeth 6, and a tooth forming member 50 adapted to hold the press member 44 and to form the teeth 6 on the peripheral edge 72 of the workpiece 70 at equal intervals. The tooth forming member 50 includes an annular body 52, and a plurality of integral projections 54 arranged on the periphery of the body 52 at regular intervals. The body 52 has a vertical central axis 58 extending in a direction perpendicular relative to the body 52 and a peripheral edge 60 extending about the central axis 58. As described earlier, the projections 54 are integrally formed on the peripheral edge 60 of the body 52 and arranged at regular intervals to define recesses 55 between adjacent projections 54. Each of the recesses 55 is defined by a pair of inclined sides 54b, 54b of the adjacent projections 54 and a bottom or root 54c between the adjacent projections 54. The recesses 55 has a shape complimentary to that of the teeth 6. As described later the tooth forming member 50 is pressed against the workpiece 70 while the tool forming tool 42 is being rotated by the motor. As a result, the teeth 6 are gradually formed on the workpiece 70 by such rolling. Each of the projections 54 has a tip 54a. At the last stage of this process, the tip 54a of each of the projections 54 is positioned in the bottom of the teeth 6. The press member 44 is generally in the form of a ring. The press member 44 extends along the circumference of the tooth forming member 50 and is located centrally (as viewed in a direction of the central axis 58) in the peripheral edge 60 of the tooth forming member 50. The press member 44 includes a body 46 extending radially outwardly from the center of the peripheral edge 60, and an edge 48 extending radially outwardly from the body 46. The press body 46 extends horizontally from the peripheral edge 60 and is then tapered toward the tips 54a of the projections 54. The edge 48 is also tapered by a predetermined length from the body 46 to form a cutting edge. As the press body 46 and the edge 48 are taped, the edge 48 can be sharply formed. With this arrangement, the press member 44 is pressed against the peripheral edge 72 of the workpiece 70 while it is being rotated. Then, the grooves 13 are gradually formed in the entire peripheral edge 72 of the workpiece 70. Therefore, the teeth 6 are formed while the teeth 6 are axially outwardly extended beyond the body 4. In this embodiment, the depth of the grooves 13 of the teeth 6 is substantially equal to a distance X (see Fig. 11) between the peripheral edge 60 and the edge 48. The use of the rotary press machine 40 will be described with reference to Figs. 14 and 15. A holder 73 (see Fig. 15) is placed adjacent to the rotary press machine 40. The holder 73 is of a known structure and only schematically shown in Fig. 15. First, the annular workpiece 70 is rotatably mounted to the holder 73 as shown in Fig. 14(a) and 15(a). At this time, the workpiece 70 is positioned so that the edge 48 faces against the center of the peripheral edge 72 of the workpiece 70 in the axial direction thereof. Next, the motor 80 is energized to rotate the tooth forming tool 42. The transfer unit 90 is then operated to move the motor 80 together with the tool 42 gradually toward the workpiece 70. The tool 42 is pressed against the workpiece 70 with the tool 42 being rotated. The workpiece 70 and the tool 42 are rotated in opposite directions. A substantial pressure is applied from the tool 42 to the workpiece 70 whereby the shape of the tool 42 is transferred to the workpiece 70 as shown in Figs. 14(b) and 15(b). The tool 42 is rotated by the motor 80 and is brought into contact with the workpiece 70 so that the workpiece 70 is rotated about its own axis 71. At this time, the press member 44 and the projections 54 are brought into local contact with the peripheral edge 72 of the workpiece 70 so that the surface layer of the peripheral edge 72 is repeatedly plastically deformed to thereby gradually form the sprocket 2. More specifically, the press member 44 is first pressed against the peripheral edge 72 of the workpiece 70 and the projections 54 are then pressed against the peripheral edge 72 of the workpiece 70. Pressing the projections 54 against the peripheral edge 72 causes the convex shape of the projections to be transferred to the workpiece 70 as the concave shape, thereby gradually forming the teeth 6 on the peripheral edge of the workpiece 70. The taper edge 48 of the press member 44 is then urged into the peripheral edge 72 of the workpiece 70. The taper body 46 of the press member 44 is then forced into the peripheral edge 72 of the workpiece 70 whereby the grooves 13 are formed in the teeth 6 while the teeth 6 are formed. The grooved teeth 6 are outwardly split by the taper edge 48 and the taper body 46 until the first side 18 and the second side 22 of the teeth 6 are extended outwardly beyond the sprocket body 4 so that the thickness of the teeth 6 becomes greater than the thickness of the sprocket body 4. As described earlier, the teeth 6 are made thicker than the workpiece 70 while they are formed on the peripheral edge of the workpiece 70 as shown in 14(c) and 15(c). This method is thus capable of reducing the number of production steps with a high throughput and effectively manufacturing the sprockets on a commercial basis. In the illustrated embodiment, the projections 54 are integral with the tool body 52. Alternatively, a plurality of cylindrical rollers (not shown) may be rotatably mounted to the peripheral edge of the tool body 52. In such a case, the press member 44 may have openings to loosely receive the rollers. The rollers are adapted to guide the teeth and resist deformation of each tooth toward the tooth adjacent thereto when the teeth are split outwards. In the illustrated embodiment, the rotary press machine 40 is moved to and from the workpiece 70. However, the invention is not limited thereto. For example, the workpiece 70 may be moved to and from the rotary press machine 40. The method may include an additional step of finishing the workpiece so that the teeth 6 have a required thickness after the teeth 6 become thicker than the body 4. In the illustrated embodiment, the grooved teeth are split outwards so that the teeth are thicker than the body. However, the invention is not limited thereto. The body may be machined so that the teeth are thicker than the body. A lathe or similar cutting tools may be used to cut the body until the body is thinner than the teeth. The sprocket is preferably mounted to a motorcycle and more particularly, to the rear wheel of a motorcycle. The invention is not limited thereto. The sprocket may be used with a conveyor chain, a bicycle, a chain saw or any other means which require the use of a chain to transmit rotary motion. The sprocket may further comprise noise reduction means for reducing noise generated by contact between the sprocket and a chain. Such a sprocket will be described below. Like parts are given like reference numerals and will not be described in detail. First, a sprocket according to a third embodiment of the present invention will next be described with reference to Figs. 16, 17 and 18. With the sprocket according to the third embodiment of the present invention, as shown in Figs. 16, 17 and 18, a flexible and elastic rubber annular cushioning material 120 is provided as noise reduction means along the entire circumference of the sprocket 2 shown in Figs. 1, 2 and 3. The annular cushioning material 120 is located along the recesses 11 formed between adjacent teeth 6 and the grooves 13 formed in the peripheral walls 24 of the teeth 6. Thus, with this arrangement, rollers (not shown) of the chain 26 are brought into contact with the cushioning material 120 in the recesses 11 upon engagement between the chain 26 and the sprocket 2, so that noise generated by contact between the sprocket and the chain can be suppressed. More specifically, since the sprocket 2 according to the third embodiment is provided by the method as shown in Figs. 11 to 15, an annular concave portion 124 is formed on the entire circumference of the sprocket 2. In other words, the annular concave portion 124 is provided along a bottom 126 of the recesses 11 and the bottom of the grooves 13. As shown in Fig. 19, the recess 11 has the bottom 126 partially defining the recess 11. The concave portion 124 is formed on the bottom 126 of the recess. The cushioning material 120 is fixedly mounted on the annular concave portion 124 so that the upper surface of the cushioning material 120 is substantially flush with the bottom 126. Thus the cushioning material 120 does not substantially project over the bottom 126, thereby allowing an amount of deformation of the cushioning material 120 caused by contact between the sprocket rollers and the cushioning material 120 to be decreased to prevent the cushioning material 120 from being subject to damage for a long time. In the third embodiment of the present invention, the cushioning material 120 is provided along the entire circumference of the sprocket. However, in the present invention, the cushioning material need not be provided along the entire circumference of the sprocket. Separately formed cushioning materials may be provided in the annular concave portion 124 at each of the recesses 11. The cushioning material can be fixed, by an adhesive, to the annular concave portion 124. The cushioning material may be fixed to the annular concave portion 124 by curing or vulcanization. Fixing of the cushioning material to the annular concave portion 124 enables the cushioning material 120 to be prevented from being scattered, even if the cushioning material 120 is damaged and degraded by deposition of sand and dust to the cushioning material 120 to wear the cushioning material 120 by the deposited sand and dust. Next, a sprocket according to a fourth embodiment of the present invention will next be described with reference to Figs. 20 and 21. With the sprocket according to the fourth embodiment of the present invention, as in the case of the third embodiment, a flexible and elastic rubber annular cushioning material 122 is provided as noise reduction means along the entire circumference of the sprocket. Therefore, noise generated by contact between the sprocket and the chain upon engagement between the chain and the sprocket can be suppressed. In this embodiment, the cushioning material 122 need not be provided along the entire circumference of the sprocket. The cushioning material may be provided in each of the recesses between the teeth. Various features of the present invention are described in the appended claims. INDUSTRIAL APPLICABILITY According to the invention of claim 1, as the thickness of the teeth is greater than that of the body which occupies a substantial part of the sprocket, the sprocket can be reduced in weight and production costs. The teeth are thick enough to readily correspond with the width of the existing chain. In other words, the teeth are sufficiently thick to accept the existing chain. The present invention thus enables the use of the existing chain and enjoys the strength of the existing chain. As the thickness of the body is less than that of the teeth, and the body occupies a substantial part of the sprocket, the sprocket can be reduced in weight and production costs. The thickness of the teeth can be maintained and the teeth can be thick enough to readily correspond with the width of the existing chain. The present invention thus enables the use of the existing chain and enjoys the strength of the existing chain. As the thickness of the teeth is greater than that of the body which occupies a substantial body of the sprocket, the sprocket can be reduced in weight and production costs. The teeth are thick enough to readily correspond with the width of the existing chain. The present invention thus enables the use of the existing chain and enjoys the strength of the existing chain. Further, with the recesses in the peripheral walls of the teeth, the teeth have a larger area to dissipate more heat. Heat is generated by friction when the teeth of the sprocket are drivingly engaged with a chain. Such heat is dissipated through the recesses. The chain is substantially free from thermal expansion or elongation. This results in an increase in the durability of the chain. Advantageously, the recesses provide a path along which dirt or mud is removed from the chain and helps prevent dirt from adhering to the teeth. This results in a decrease in the amount of friction between the chain and the sprocket and thus, in an increase in the service life of the chain and sprocket. With the recesses in the peripheral walls of the teeth, the teeth have a larger area to dissipate more heat. Heat is generated by friction when the teeth of the sprocket are drivingly engaged with a chain. Such heat is dissipated through the recesses. The chain is substantially free from thermal expansion or elongation. This results in an increase in the durability of the chain. Advantageously, the recesses provide a path along which dirt or mud is removed from the chain and helps prevent dirt from adhering to the teeth. This results in a decrease in the amount of friction between the chain and the sprocket and thus, in an increase in the service life of the chain and sprocket. As the body which occupies a substantial part of the sprocket is thin, the sprocket can be reduced in weight and production costs. The teeth are thick enough to readily correspond with the width of the existing chain. The present invention thus enables the use of the existing chain and enjoys the strength of the existing chain. As the body which occupies a substantial part of the sprocket is thin, the sprocket can be reduced in weight and production costs. The teeth are thick enough to readily correspond with the width of the existing chain. The present invention thus enables the use of the existing chain and enjoys the strength of the existing chain. Moreover, the teeth are made thicker than the rest of the workpiece during formation of the teeth. This results in a decrease in the number of production steps and costs of the sprocket. As the body which occupies a substantial part of the sprocket is made thin, the sprocket can be reduced in weight and production costs. The teeth are thick enough to readily correspond with the width of the existing chain. The present invention thus enables the use of the existing chain and enjoys the strength of the existing chain. As the thickness of the teeth is greater than that of the body which occupies a substantial part of the circular toothed disk, the circular toothed disk can be reduced in weight and production costs. Further, with the recesses in the peripheral walls of the teeth, the teeth have a larger area to dissipate more heat. The recesses provide a path along which dirt or mud is removed from the chain and helps prevent dirt from adhering to the teeth. As the thickness of the body is less than that of the teeth, and the body occupies a substantial part of the circular toothed disk, the circular toothed disk can be reduced in weight and production costs. Further, with the recesses in the peripheral walls of the teeth, the teeth have a larger area to dissipate more heat. The recesses provide a path along which dirt or mud is removed from the chain and helps prevent dirt from adhering to the teeth. The teeth are formed in the peripheral edge of the workpiece at given intervals while at the same time, the teeth are made thicker than the rest of the workpiece. The present invention is thus capable of reducing the number of production steps and the production costs of the sprocket.

Claims: A combination of a sprocket (2) and a chain, said sprocket comprising: a body (4) having an axis (8) and a peripheral edge (10); a plurality of circumferentially spaced teeth (6) extending outwardly from said peripheral edge (10) and defining therebetween a plurality of circumferentially spaced first recesses (11), each recess including a respective bottom (126) partially defining said first recess (11), and said teeth having respective peripheral walls (24); said teeth having a thickness greater than a thickness of said body; a second recess (13) located centrally inside each tooth (6) in a direction axially of said sprocket extending inwardly from said peripheral walls (24) of each said tooth and said second recesses (13) being aligned and extending circumferentially; and said chain comprising a plurality of barrels with links therebetween; said bottom (126) of each of said first recesses (11) has therein a groove (124) which extends circumferentially and which is located substantially centrally of said bottom (126) in said direction axially of said sprocket, said groove (124) of each of said bottoms (126) of said first recesses (11) and bottom portions (124) of said second recesses (13) are substantially aligned circumferentially and define an annular groove (124) extending entirely circumferentially of said sprocket characterised in that each barrel of said chain is disposed over said annular groove (124). A combination of a sprocket and a chain as claimed in Claim 1, wherein said body (4) and said teeth (6) comprise a unitary one-piece member. A combination of a sprocket and a chain as claimed in Claim 1, wherein said second recesses (13) have a construction resulting from inward deformation of material of said body (4) from said peripheral edge (10) thereof, resulting in deformation of said material in opposite directions axially of said body (4), to thereby result in said teeth (6) of greater thickness than said body (4). A combination of a sprocket and a chain as claimed in Claim 1, wherein said sprocket (2) is adapted to be mounted on a motorcycle. A combination of a sprocket and a chain as claimed in Claim 4, wherein the motorcycle includes a front wheel and a rear wheel, and said sprocket (2) is adapted to be mounted on the rear wheel. A combination of a sprocket and a chain as claimed in Claim 1, wherein said body (4) has opposite first and second sides, said teeth have opposite first and second sides, and said first side (12) of said body (4) is offset in said direction axially of said body, relative to said first side (18) of said teeth corresponding to said first side (12) of said body (4). A combination of a sprocket and a chain as claimed in Claim 6, further comprising a spacer (25) adapted to be attached to said second side (14) of said body (4) said spacer (25) comprising a thin plate having a thickness such that said spacer (25), when attached to said second side of said body (4), is in alignment with said second side (22) of said teeth. A combination of a sprocket and a chain as claimed in Claim 1, wherein said body (4) has opposite first and second sides, said teeth have opposite first and second sides, and said second side (14) of said body is aligned with said second side (28)of said teeth. A combination of a sprocket and a chain as claimed in Claim 1, wherein said thickness of said body (4) is adapted to be substantially half a thickness of a body of an existing sprocket. A combination of a sprocket and a chain as claimed in Claim 9, wherein said thickness of said teeth (6) is adapted to be equal to a thickness of teeth of the existing sprocket. A combination of a sprocket and a chain as claimed in Claim 10, wherein said thickness of said teeth (6) is one of 5.8mm, 7.2mm and 8.7mm. A motorcycle having mounted thereto a combination of a sprocket and a chain as claimed in Claim 1. A motorcycle as claimed in Claim 12, including a front wheel and a rear wheel, said sprocket (2) being mounted to said rear wheel. A combination of a sprocket and a chain as claimed in Claim 1, wherein said body (4) is annular. A combination of a sprocket and a chain as claimed in Claim 1, wherein said body (4) is substantially annular having a first side (12), an opposite second side (14), and said central axis (8) extends centrally through said first and second sides, said plurality of teeth (6) include: first steps (16) extending axially outwardly from said first side (12) of said body (4); first sides (18) connected to said first steps and extending substantially parallel to said first side (12) of said body (4); second steps (20) extending axially outwardly from said second side (14) of said body (4); second sides (22) connected to said second steps (20) and extending substantially parallel to said second side (14) of said body (4); and said peripheral walls (24) extending circumferentially of said body (4) and axially between respective said first sides (18) and said second sides (22) of said teeth. A combination of a sprocket and a chain as claimed in Claim 15, wherein said body (4) and said teeth (6) comprise a unitary one-piece member.

Inventors: TAKAMORI NORIHIKO, TAKAMORI, NORIHIKO, TAKAMORI, Norihiko Kinugasa Green Haitsu 618
Applicants: UNI SUNSTAR BV, UNI-SUNSTAR B.V.
Application year: 1998
Main classification: F16H55
IPC codes: B21H5, F16H55, B62M9, B21D53, B21H1