Chain sprocket

Abstract

To provide a chain sprocket that can contribute to weight reduction while reducing stress concentration in an outer edge of a lightening hole.SOLUTION: A chain sprocket transmits a drive force of a drive source (12) for driving a vehicle (10), to a wheel (15). The chain sprocket is provided with a lightening hole (74 or 474) comprising an outer edge (81 or 481), an inner edge (82) shorter than the outer edge (81 or 481), and two side edges (83 and 483) connecting ends of the outer edge (81 or 481) and ends of the inner edge (82). The outer edge (81 or 481) is formed of arcs (81A, 81B, or 481B) having a plurality of curvature radii (R1, R2, or R401), or formed of a pair of arcs (81A, 81B, or 481B) having at least one curvature radius (R1, R2, or R401), and a line (481A) connecting the pair of arcs (81A, 81B, or 481B).SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a chain sprocket. [Background technology]

[0002] Conventionally, there is known a technique for reducing the weight of a chain sprocket (see, for example, Patent Document 1). In Patent Document 1, a camshaft sprocket has a plurality of lightening holes formed in the circumferential direction, and the back side of each tooth is lightened approximately along the tooth shape to reduce the weight. In the camshaft sprocket in Patent Document 1, the outer edge of the lightening holes is recognized to be formed by a circular arc with a single radius of curvature. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Utility Model Application Publication No. 1-58856 Summary of the Invention [Problem to be solved by the invention]

[0004] However, Patent Document 1 leaves room for improvement in terms of stress concentration. The present invention has been made in consideration of the above-mentioned circumstances, and has an object to provide a chain sprocket that can reduce stress concentration on the outer edges of lightening holes while also contributing to weight reduction. [Means for solving the problem]

[0005] A chain sprocket transmits the driving force of a drive source that drives a vehicle to a wheel, and is characterized in that the chain sprocket has a lightening hole consisting of an outer edge, an inner edge that is shorter than the outer edge, and two side edges connecting the ends of the outer edge and the inner edge, and the outer edge is formed by arcs with multiple radii of curvature, or is formed by a pair of arcs with at least one radius of curvature and a line connecting the pair of arcs. Effect of the Invention

[0006] It is possible to provide a chain sprocket that can reduce stress concentration on the outer edges of the lightening holes while also contributing to weight reduction. [Brief description of the drawings]

[0007] [Figure 1] 1 is a side view of a saddle-ride type vehicle according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a perspective view of the swing arm as viewed from the left rear side. [Diagram 3] FIG. 1 is a diagram showing a driven sprocket according to a first embodiment. [Figure 4] FIG. 1 is a diagram showing a driven sprocket having a conventional shape. [Diagram 5] FIG. 4 is a diagram showing an analysis result regarding the stress distribution of the driven sprocket according to the first embodiment. [Figure 6] FIG. 6 is a diagram showing an analysis result regarding the stress distribution of the driven sprocket according to the first comparative example. [Figure 7] FIG. 11 is a diagram showing an analysis result regarding the stress distribution of a driven sprocket according to a second comparative example. [Figure 8] FIG. 11 is a diagram showing a driven sprocket according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the description, directions such as front, rear, left, right, up and down are the same as directions relative to the vehicle body unless otherwise specified. In addition, the symbol FR in each drawing indicates the front of the vehicle body, the symbol UP indicates the upper side of the vehicle body, and the symbol LH indicates the left side of the vehicle body.

[0009] [Embodiment Mode] FIG. 1 is a side view of a saddle-ride type vehicle 10 according to an embodiment of the present invention. The saddle-type vehicle 10 is a vehicle that includes a body frame 11, a power unit 12 supported by the body frame 11, a front fork 14 that supports a front wheel 13 so as to be steerable, a swing arm 16 that supports a rear wheel 15, and a seat 17 for a passenger. The saddle-ride type vehicle 10 is a vehicle in which a rider sits astride a seat 17. The seat 17 is provided above the rear part of the body frame 11.

[0010] The body frame 11 includes a head pipe 18 provided at the front end of the body frame 11, a front frame 19 located rearward of the head pipe 18, and a rear frame 20 located rearward of the front frame 19. The front end of the front frame 19 is connected to the head pipe 18. The seat 17 is supported by a rear frame 20 .

[0011] The front fork 14 is supported by a head pipe 18 so as to be steerable left and right. The front wheel 13 is supported by an axle 13a provided at the lower end of the front fork 14. A steering handle 21 that is held by a rider is attached to the upper end of the front fork 14.

[0012] The swing arm 16 is supported by a pivot shaft 22 that is supported by the body frame 11. The pivot shaft 22 is a shaft that extends horizontally in the vehicle width direction. The pivot shaft 22 is inserted into the front end of the swing arm 16. The swing arm 16 swings up and down about the pivot shaft 22. The rear wheel 15 is supported by an axle 15 a provided at the rear end of a swing arm 16 .

[0013] The power unit 12 is disposed between the front wheels 13 and the rear wheels 15 and is supported by the body frame 11. The power unit 12 is an internal combustion engine. The power unit 12 includes a crankcase 23 and a cylinder portion 24 that houses a reciprocating piston. An exhaust device 25 is connected to an exhaust port of the cylinder portion 24. The output of the power unit 12 is transmitted to the rear wheels 15 by a driving force transmission member that connects the power unit 12 and the rear wheels 15 .

[0014] The saddle-ride type vehicle 10 also includes a front fender 26 that covers the front wheel 13 from above, a rear fender 27 that covers the rear wheel 15 from above, a step 28 on which a rider places his or her feet, and a fuel tank 29 that stores fuel used by the power unit 12. The front fender 26 is attached to the front fork 14. The rear fender 27 and the step 28 are provided below the seat 17. The fuel tank 29 is supported by the body frame 11.

[0015] A drive sprocket 31 is fixed to the output shaft of the power unit 12. An endless drive chain 32 is wound around the drive sprocket 31. The drive chain 32 extends toward the rear wheel 15 and is wound around a driven sprocket 33 provided on the rear wheel 15. When the drive sprocket 31 is rotated by the power unit 12, the driven sprocket 33 rotates via the drive chain 32, and a rotational force is transmitted to the rear wheel 15 as a driving force. The rear wheel 15 includes a wheel 35 rotatably supported on the axle 15a, and a tire 36 supported on the wheel 35. A driven sprocket 33 is supported on the wheel 35.

[0016] The saddle-ride type vehicle 10 includes a rear cushion 38. The rear cushion 38 extends in the vertical direction. An upper end of the rear cushion 38 is connected to the vehicle body frame 11. A lower end of the rear cushion 38 is connected to the swing arm 16 via a link mechanism 39. The link mechanism 39 is supported on a lower rear end of the front frame 19 so as to be able to swing.

[0017] FIG. 2 is a perspective view of the swing arm 16 as viewed from the rear left side. The swing arm 16 includes a cylindrical pivot portion 41 extending in the vehicle width direction. The pivot shaft 22 (see FIG. 1) is inserted through the pivot portion 41. A left arm portion 42 extending rearward is formed on a left portion (one side in the vehicle width direction) of the pivot portion 41. A right arm portion 43 extending rearward facing the left arm portion 42 is formed on a right portion (the other side in the vehicle width direction) of the pivot portion 41. A cross member portion 44 is formed between the left arm portion 42 and the right arm portion 43 to connect the arm portions 42, 43 in the vehicle width direction.

[0018] The pivot portion 41, the left and right arm portions 42, 43, and the cross member portion 44 form an open cushion insertion portion 16A that penetrates in the vertical direction. The rear cushion 38 is disposed in a state of being inserted in the vertical direction through the cushion insertion portion 16A. A cushion receiving portion 44A is formed at the lower portion of the cross member portion 44. The lower end of the rear cushion 38 is connected to the cushion receiving portion 44A via the link mechanism 39. The pivot portion 41, the arm portions 42, 43 and the cross member portion 44 are integral with each other.

[0019] The arm portions 42, 43 are formed hollow. The end pieces 60L, 60R are attached to the rear ends of the arm portions 42, 43 from the rear and fixed thereto. The end pieces 60L, 60R are formed with long holes extending in the front-rear direction (not shown in FIG. 2). The axle 15a of the rear wheel 15 is inserted into the long hole. The end pieces 60L, 60R have a mounting portion 45 whose outer surface in the vehicle width direction is recessed inward in the vehicle width direction. The mounting portion 45 has an adjuster mechanism 50 that adjusts the tension of the drive chain 32. The adjuster mechanism 50 has an adjuster plate 51 through which the axle 15a is inserted, an adjustment bolt 52 that positions the adjuster plate 51, and a lock nut 53 fastened to the adjustment bolt 52.

[0020] A bolt hole 98 extending in the front-rear direction is formed in the front of the arrangement portion 45. An adjustment bolt 52 is fastened to the bolt hole 98 with a lock nut 53 fastened thereto. The front-rear position of the adjustment bolt 52 is adjusted by the amount that the adjustment bolt 52 is fastened to the bolt hole 98. Thus, the front-rear position of the adjuster plate 51 that abuts against the adjustment bolt 52 is adjusted, and the position of the driven sprocket 33 supported by the axle 15a is adjusted. This adjusts the distance between the drive sprocket 31 and the driven sprocket 33, and adjusts the tension of the drive chain 32.

[0021] The rear wheel 15 (see FIG. 1) is rotatably supported on the axle 15a. A hub damper 34 is supported on the left side (one side in the vehicle width direction) of a wheel 35 of the rear wheel 15 in the axial direction of the axle 15a. The hub damper 34 has a generally cylindrical appearance. The hub damper 34 is inserted into the axle 15a and configured to be rotatable relative to the axle 15a. The hub damper 34 has multiple dampers 34A and a casing 34B that houses the multiple dampers 34A. The hub damper 34 is connected to the wheel 35 via the damper 34A. The hub damper 34 can rotate integrally with the wheel 35 by the damper 34A.

[0022] A driven sprocket 33 is fixed to a casing 34B of the hub damper 34. Therefore, when the drive sprocket 31 is rotated by the power unit 12, the rotational force is transmitted to the driven sprocket 33 via the drive chain 32, and the rotational force is transmitted to the wheel 35 of the rear wheel 15 via the hub damper 34. At this time, the driven sprocket 33 is connected to the wheel 35 via the damper 34A, so torque shocks associated with acceleration and deceleration are easily reduced.

[0023] A rear wheel braking device 55 is provided on the opposite side of the rear wheel 15 from the driven sprocket 33. The rear wheel braking device 55 in this embodiment is a disc brake. The rear wheel braking device 55 has a disk-shaped brake disc 56, a brake caliper 57 that holds and brakes the brake disc 56, and a caliper stay 58 that supports the brake caliper 57.

[0024] The brake disc 56 is fixed to the right side surface (the other side surface in the vehicle width direction) of the wheel 35 by a plurality of bolts 56A. Therefore, the brake disc 56 rotates integrally with the rear wheel 15. On the other hand, the brake caliper 57 is fixed to the swing arm 16 via a caliper stay 58.

[0025] The caliper stay 58 has a cylindrical spacer portion 58A through which the axle 15a is inserted. The spacer portion 58A determines the axial positioning of the caliper stay 58 relative to the axle 15a. The spacer portion 58A is formed with a support portion 58B extending radially forward. The brake caliper 57 is supported by the support portion 58B. The support portion 58B is connected to a brake anti-rotation portion 43A protruding from the inner surface of the right arm portion 43. The brake anti-rotation portion 43A prevents the brake caliper 57 from following the rotation of the brake disc 56 when the brake caliper 57 clamps the brake disc 56.

[0026] The axle 15a is bolt-shaped. A nut portion 59 is fastened to one end of the axle 15a. When the nut portion 59 is fastened and the arm portions 42, 43 are tightened, the hub damper 34 on the axle 15a, the wheel 35 of the rear wheel 15, the caliper stay 58 of the rear wheel braking device 55, and the like are positioned in the axial direction.

[0027] FIG. 3 is a diagram showing the driven sprocket 33 according to the first embodiment. The driven sprocket (chain sprocket) 33 has a disk-shaped disk portion 71 centered at position P0, and a toothed portion 72 provided on the outer periphery of the disk portion 71. The toothed portion 72 is formed in an annular shape. The toothed portion 72 is formed to have a greater thickness (size in the axial direction) than the disk portion 71. In other words, the toothed portion 72 is formed so as to protrude on both sides in the axial direction from the disk portion 71. The toothed portion 72 has a plurality of sprocket teeth 72A formed in the circumferential direction. The drive chain 32 meshes with the sprocket teeth 72A.

[0028] A central hole 73 is formed in the disc portion 71, penetrating the disc portion 71 in the thickness direction. The central hole 73 is a circular hole concentric with the center position P0 of the disc portion 71. A lightening hole 74 is formed radially outward of the central hole 73. The lightening hole 74 has an outer edge 81, an inner edge 82 formed opposite the outer edge 81, and a pair of side edges 83 connecting the ends of the outer edge 81 and the inner edge 82 on both sides. The outer edge 81 is longer than the inner edge 82. The side edges 83 have straight portions. The lightening hole 74 is formed by the surrounding shape of the outer edge 81, the inner edge 82, and the pair of side edges 83. The lightening hole 74 in this embodiment has a fan-shaped shape. Here, the term "fan-shaped" for the lightening hole 74 refers to a shape in which, when the lightening hole 74 is composed of an outer edge 81, an inner edge 82, and a side edge 83, the side edge 83 has a straight portion, and the same radial positions of the pair of side edges 83 are spaced apart from each other as they move radially outward.

[0029] The lightening holes 74 are formed at equal intervals in the circumferential direction. In this embodiment, five lightening holes 74 are formed. Between adjacent lightening holes 74, bolt holes (second holes) 75 are provided that penetrate the disk portion 71 in the thickness direction. The bolt holes 75 are circular holes. The bolt holes 75 are formed radially inward from the outer edge 81. The bolt holes 75 are provided between all adjacent lightening holes 74. The bolt holes 75 are provided on the position P0 side of the center of the disk portion 71. The bolt holes 75 overlap with the lightening holes 74 in the radial direction. More specifically, the position occupied by the center of the bolt holes 75 in the radial direction overlaps with the position occupied by the lightening holes 74 in the radial direction. In other words, when a virtual circle C1 passing through the center of the bolt holes 75 is assumed, the virtual circle C1 passes through the lightening holes 74. Therefore, an inner edge 82 of the lightening hole 74 is located inside the imaginary circle C1. The lightening hole 74 is a hole large enough that the inner edge 82 is located inside the imaginary circle C1.

[0030] The outer shape of the disk portion 71 is determined by the shape cut out by the center hole 73, the lightening holes 74, and the bolt holes 75. In other words, the disk portion 71 has an annular base portion 76 in which the center hole 73 is formed, a plurality of extension portions 77 extending radially outward from the base portion 76, and an annular outer peripheral portion 78 supported by the radial outer ends of the extension portions 77. The circumferential width of the extension portions 77 narrows as they move radially outward. Teeth 72 are formed on the outer peripheral surface of the outer peripheral portion 78. Bolt holes 75 are formed on the base 76 side of the extension portions 77.

[0031] In this embodiment, the lightening holes 74 are formed symmetrically with respect to a predetermined line L1 extending in the radial direction. Here, the outer edge 81 of the lightening hole 74 has a first arc portion (arc) 81A and a second arc portion (arc) 81B extending from both ends of the first arc portion 81A. The first arc portion 81A is an arc with a predetermined radius of curvature R1 centered at the central position P0. The second arc portion 81B is an arc with a predetermined radius of curvature R2 centered at a position P1 on the inner edge 82. The radius of curvature R2 of the second arc portion 81B is smaller than the radius of curvature R1 of the first arc portion 81A. In this embodiment, the radius of curvature R2 is smaller than 1 / 2 of the radius of curvature R1. That is, the radius of curvature R2 is smaller than half of the radius of curvature R1.

[0032] The inner edge 82 is a circular arc having a predetermined radius of curvature R3 centered at the central position P0.

[0033] The side edge 83 is composed of a straight portion 83A extending linearly, an outer arc portion 83B extending from the radial outer end of the straight portion 83A and connected to the outer edge 81, and an inner arc portion 83C extending from the radial inner end of the straight portion 83A and connected to the inner edge 82. The outer arc portion 83B extends smoothly from the straight portion 83A and is smoothly connected to the second arc portion 81B of the outer edge 81. The outer arc portion 83B is formed by an arc having a predetermined radius of curvature R4. The inner arc portion 83C extends smoothly from the straight portion 83A and is smoothly connected to the inner edge 82. The inner arc portion 83C is formed by an arc having a predetermined radius of curvature R5. Therefore, the side edge 83 does not include three or more arc portions.

[0034] The connection (transition) portions of the outer edge 81, the inner edge 82, and the side edges 83 are positions where the radii of curvature R2, R3, R4, and R5 change.

[0035] FIG. 4 is a diagram showing a driven sprocket 133 having a conventional shape. In the conventional driven sprocket 133, the parts corresponding to the driven sprocket 33 are shown by adding 100 to the numerals in the reference numerals of the driven sprocket 33. For example, the driven sprocket 133 has a lightening hole 174 formed therein corresponding to the lightening hole 74.

[0036] In the conventional driven sprocket 133, the outer edge 181 of the lightening hole 174 is formed as a single circular arc. That is, the outer edge 181 is a circular arc having a predetermined radius of curvature R101 centered at the position P100 of the base 171. In addition, when imaginary circle C101 passing through the center of the bolt hole 175 is assumed, the imaginary circle C101 does not pass through the lightening hole 174. That is, the lightening hole 174 is small enough that the imaginary circle C101 does not pass through it.

[0037] Fig. 5 is a diagram showing an analysis result regarding stress distribution of the driven sprocket 33 according to the first embodiment. Fig. 6 is a diagram showing an analysis result regarding stress distribution of the driven sprocket 233 according to the first comparative example. Fig. 7 is a diagram showing an analysis result regarding stress distribution of the driven sprocket 333 according to the second comparative example. 5 to 7, the stress generated in each part of the driven sprocket 33, 233, 333 was obtained when maximum tension was applied to the tooth portion 72, 272, 372 via the drive chain 32. In Figures 5 to 7, the denser the points are, the greater the stress.

[0038] 5, in the driven sprocket 33 according to the first embodiment, it is confirmed that stress concentration occurs near the side edge 83 on the downstream side in the rotation direction A. In addition, stress concentration is confirmed near the connection between the outer edge 81 and the side edge 83 of the lightening hole 74 on the upstream side in the rotation direction A. On the other hand, no significant stress concentration is confirmed at the inner edge 82.

[0039] In FIG. 6, in the driven sprocket 233 according to the first comparative example, the outer edge 81 of the lightening hole 274 is formed by a single circular arc. In the driven sprocket 233 of the first comparative example, the stress distribution is observed to be substantially the same as that in FIG. 5. However, the outer periphery 278 and the base 276 are larger in the radial direction than the driven sprocket 33 of the first embodiment. In other words, it is understood that it is difficult to reduce the weight with the configuration of the first comparative example. Note that in FIG. 6, the parts of the driven sprocket 233 that correspond to the driven sprocket 33 are indicated by adding 200 to the numerals of the reference numerals of the parts of the driven sprocket 33.

[0040] In FIG. 7, in the driven sprocket 333 according to the second comparative example, the outer edge 381 of the lightening hole 374 is formed by a single arc, and the outer periphery 378 and the base 376 are smaller in the radial direction than those of the first comparative example. That is, the lightening hole 374 is larger than the lightening hole 274 of the first comparative example. In the driven sprocket 333 according to the second comparative example, it is confirmed that a larger stress concentration occurs near the side edge 83 on the downstream side in the rotation direction A than in the first comparative example, and a larger stress concentration is confirmed near the connection between the outer edge 81 and the side edge 83 of the lightening hole 74 on the upstream side in the rotation direction A than in the first comparative example. That is, it is understood that when the lightening hole 374 is large, stress concentration is likely to occur at the outer edge 381 of a single arc. In FIG. 7, the parts of the driven sprocket 33 that correspond to the driven sprocket 33 are indicated by adding 300 to the numerals of the parts of the driven sprocket 33.

[0041] As shown in Figures 6 and 7, when the outer edge 281, 381 is formed by a single arc, it is understood that the lightening holes 274, 374 cannot be made large in size in order to suppress the concentration of stress, which tends to increase the weight. In contrast, as shown in Figure 5, in the driven sprocket 133 according to this embodiment, it is easy to provide multiple shape change points in the outer edge 81 up to the connection between the outer edge 81 and the side edge 83, which tends to reduce the concentration of stress. Therefore, it is easy to move the outer edge 81 of the lightening hole 74 closer to the tooth portion 72 of the driven sprocket 33 while reducing the concentration of stress. Therefore, it is easy to make the lightening hole 74 large, which also contributes to weight reduction.

[0042] As described above, according to the first embodiment to which the present invention is applied, in the driven sprocket 33 that transmits the driving force of the power unit (driving source) 12 that drives the saddle-ride type vehicle (vehicle) 10 to the rear wheel 15, the chain sprocket 33 is provided with a lightening hole 74 consisting of an outer edge 81, an inner edge 82 that is shorter than the outer edge 81, and two side edges 83 connecting the end of the outer edge 81 and the end of the inner edge 82, and the outer edge 81 is formed by multiple arc portions 81A, 81B having radii of curvature R1, R2. According to this configuration, multiple shape change points are provided between the outer edge 81 and the transition between the side edge 83, so that the degree of change in local shape change points at the outer edge 81 of the lightening hole 74 can be reduced. This makes it possible to bring the outer edge 81 closer to the outer periphery of the driven sprocket 33 while reducing stress concentration at the outer edge 81 of the lightening hole 74, thereby contributing to weight reduction.

[0043] In this embodiment, when the outer edge 81 is formed by arc portions 81A, 81B having two radii of curvature R1, R2, the smaller of the two radii of curvature R1, R2 is smaller than 1 / 2 of the larger radius of curvature R1. According to this configuration, the connection portion between the outer edge 81 and the side edge 83 can be prevented from changing drastically, and stress concentration can be further reduced.

[0044] In addition, in this embodiment, the driven sprocket 33 is provided with a bolt hole 75 different from the lightening hole 74, the bolt hole 75 is provided radially inward from the outer edge 81, and the position occupied by the center of the bolt hole 75 in the radial direction overlaps with the position occupied by the lightening hole 74 in the radial direction. With this configuration, stress is less likely to concentrate when force is applied to the outer edge 81 of the chain sprocket because the inner edge 82 is separated from the drive chain 32. By providing another bolt hole 75 at a position radially overlapping with the inner edge 82, it is possible to reduce the weight while reducing the stress concentration.

[0045] [Second embodiment] A second embodiment to which the present invention is applied will be described below. In this second embodiment, parts configured similarly to the first embodiment are given the same reference numerals and descriptions thereof will be omitted.

[0046] FIG. 8 is a diagram showing a driven sprocket 433 according to the second embodiment. In the driven sprocket 433 according to the second embodiment, the shape of the lightening hole 474 is different from that of the lightening hole 74 of the driven sprocket 33 according to the first embodiment. That is, the outer edge 481 and the side edge 483 of the lightening hole 474 are different from the outer edge 81 and the side edge 83 of the first embodiment.

[0047] In the second embodiment, the outer edge 481 of the lightening hole 474 has a line portion 481A extending in the circumferential direction and arc portions 481B extending from both ends of the line portion 481A. In the present embodiment, the line portion 481A is a straight line. The arc portion 481B is an arc having a predetermined radius of curvature R402. The arc portion 481B is an arc having a predetermined position P401 as its center. The predetermined position P402 may or may not be on the inner edge 82.

[0048] In this embodiment as well, it is easy to provide a shape change point in outer edge 481 toward the connection portion between outer edge 481 and inner edge 482. This makes it easy to alleviate stress concentration at the connection portion between outer edge 481 and inner edge 482. In addition, it is easy to bring outer edge 481 close to tooth portion 72, which is preferable for weight reduction.

[0049] As described above, according to the second embodiment to which the present invention is applied, in the driven sprocket 433 that transmits rotational power to the rear wheel 15 by receiving the rotation of the drive chain 32 that rotates in response to the driving force of the power unit 12 that drives the saddle-ride type vehicle 10, the driven sprocket 433 is provided with a lightening hole 474 consisting of an outer edge 481, an inner edge 82 that is shorter than the outer edge 481, and two side edges 483 connecting the end of the outer edge 481 and the end of the inner edge 82, and the outer edge 481 is formed from at least one pair of arc portions 481B having a radius of curvature R401 and a line portion 481A connecting the pair of arc portions 481B. According to this configuration, multiple shape change points are provided between the transition from the outer edge 481 to the side edge 483, so that the degree of local change in shape at the outer edge 481 of the lightening hole 474 can be reduced, and the outer edge 481 can be brought closer to the outer periphery of the driven sprocket 433 while reducing stress concentration at the outer edge 481 of the lightening hole 474, thereby contributing to weight reduction.

[0050] [Other embodiments] The above-described embodiment merely shows one aspect of the present invention, and any modification and application can be made without departing from the spirit and scope of the present invention.

[0051] In the above-described first embodiment, the outer edge 81 is formed by a first arc portion 81A and a second arc portion 81B having two radii of curvature R1 and R2, and the smaller radius of curvature R2 of the two radii of curvature R1 and R2 is smaller than 1 / 2 of the larger radius of curvature R1. However, the magnitude relationship between the two radii of curvature R1 and R2 is not limited to this. That is, when outer edge 81 is formed by arc portions 81A, 81B with two radii of curvature R1, R2, the smaller of the two radii of curvature R1, R2 may be greater than half the larger radius of curvature R1. With this configuration, the shape change point is closer to the outer periphery of driven sprocket 33 than the connection portion between outer edge 81 and side edge 83, making it easier to enlarge the shape of lightening hole 74 and reducing weight.

[0052] In the above-described first embodiment, the outer edge 81 is formed by a first arc portion 81A and a second arc portion 81B having two radii of curvature R1 and R2, and the smaller radius of curvature R2 of the two radii of curvature R1 and R2 is smaller than 1 / 2 of the larger radius of curvature R1. However, the magnitude relationship between the two radii of curvature R1 and R2 is not limited to this. That is, when outer edge 81 is formed by arc portions 81A, 81B with two radii of curvature R1, R2, the smaller radius of curvature R2 of the two radii of curvature R1, R2 may be 1 / 2 the larger radius of curvature R1. With this configuration, extreme changes in the connection between outer edge 81 and side edge 83 can be prevented, further reducing stress concentration, and since the shape change point of the connection is closer to the outer periphery of driven sprocket 33, it is easier to enlarge the shape of lightening hole 74, resulting in weight reduction.

[0053] In the above second embodiment, the line portion 481A is described as being linear, but the line portion 481A may be a single arc instead of a straight line. In this case, the single arc may be an arc that is convex radially inward instead of an arc that is convex radially outward. Furthermore, the line portion 481A may be a plurality of arcs. When the line portion 481A is composed of a plurality of arcs, the radius of curvature of the arc becomes smaller as it approaches the side edge 483.

[0054] In the above first and second embodiments, bolt holes 75, 475 are given as an example of the second hole, but the second hole may be a lightening hole instead of bolt holes 75, 475. When the second hole is a lightening hole, it may be a hole of any shape, such as a square hole or an equilateral hole. Here, the center of the second hole corresponds to the position of the center of gravity of a flat plate when a flat plate corresponding to the shape of the second hole is assumed.

[0055] In the above embodiment, the saddle-ride type vehicle 10 having the power unit 12 as an internal combustion engine has been exemplified as the saddle-ride type vehicle 10, but is not limited thereto. For example, the saddle-ride type vehicle 10 may be a vehicle that does not have the power unit 12 as an internal combustion engine, that is, an electric vehicle. Thus, in the above embodiment, the power unit 12 has been exemplified as the power unit that drives the vehicle body, but the power unit may be a power unit equipped with an electric motor for driving.

[0056] In the above first and second embodiments, the rear wheels 15 are exemplified as the wheels to which the driving force of the power unit 12 that drives the saddle riding type vehicle 10 is transmitted, but the wheels may be the front wheels 13. In other words, the configuration of the present invention may be applied to a configuration in which the driving force of the power unit 12 is transmitted to the front wheels 13.

[0057] In the above first and second embodiments, the driven sprockets 33 and 433 are exemplified as the chain sprocket, but the drive sprocket 31 may also be used as the chain sprocket. In other words, the chain sprocket may be a drive-side chain sprocket as long as it transmits the driving force of the driving source that drives the vehicle to the wheels.

[0058] In the above embodiment, a motorcycle having a front wheel 13 and a rear wheel 15 has been used as an example of saddle-ride vehicle 10, but the present invention is not limited to this, and the present invention can be applied to a three-wheel saddle-ride vehicle having two front or two rear wheels, or a saddle-ride vehicle having four or more wheels.

[0059] [Configuration supported by the above embodiment] The above embodiment supports the following configurations.

[0060] (Configuration 1) A chain sprocket that transmits the driving force of a driving source that drives a vehicle to a wheel, the chain sprocket having a lightening hole consisting of an outer edge, an inner edge that is shorter than the outer edge, and two side edges connecting the end of the outer edge and the end of the inner edge, the outer edge being formed by arcs with multiple radii of curvature, or being formed by a pair of arcs with at least one radius of curvature and a line connecting the pair of arcs. With this configuration, multiple shape change points are provided between the outer edge and the transition between the side edges, so that the degree of local change in shape at the outer edge of the lightening hole can be reduced.This reduces stress concentration at the outer edge of the lightening hole while bringing the outer edge closer to the outer periphery of the chain sprocket, thereby contributing to weight reduction.

[0061] (Configuration 2) A chain sprocket as described in configuration 1, characterized in that when the outer edge is formed by an arc of two radii of curvature, the smaller of the two radii of curvature is smaller than 1 / 2 of the larger radius of curvature. According to this configuration, the connection between the outer edge and the side edge can be prevented from changing drastically, and stress concentration can be further reduced.

[0062] (Configuration 3) A chain sprocket as described in configuration 1, characterized in that when the outer edge is formed by an arc of two radii of curvature, the smaller of the two radii of curvature is greater than 1 / 2 of the larger radius of curvature. With this configuration, the point of change in shape is closer to the outer periphery of the chain sprocket than the connection between the outer edge and the side edge, so that the shape of the lightening hole can be made larger easily, resulting in weight reduction.

[0063] (Configuration 4) A chain sprocket as described in configuration 1, characterized in that when the outer edge is formed by an arc of two radii of curvature, the smaller of the two radii of curvature is 1 / 2 of the larger of the two radii of curvature. With this configuration, extreme changes in the connection between the outer edge and the side edge can be prevented, further reducing stress concentration, and since the shape change point is closer to the outer periphery of the chain sprocket than the connection, it is easier to enlarge the shape of the lightening hole, resulting in weight reduction.

[0064] (Configuration 5) A chain sprocket according to any one of configurations 1 to 4, characterized in that the chain sprocket has a second hole different from the lightening hole, the second hole is located radially inward from the outer edge, and the radial position of the center of the second hole overlaps with the radial position of the lightening hole. With this configuration, since the inner edge is separated from the chain, stress is less likely to concentrate when force is applied to the outer edge of the chain sprocket. By providing a second hole at a position that overlaps the inner edge in the radial direction, stress concentration can be reduced while also reducing weight. [Explanation of symbols]

[0065] 10 Saddle-type vehicle (vehicle) 12 Power unit (drive source) 15 Rear wheel (wheel) 33 Driven sprocket (chain sprocket) 74 Hole 75 Bolt hole (second hole) 81 Outer Edge 81A First arc section (arc) 81B Second arc section (arc) 82 Common-law marriage 83 Side edge 433 Driven sprocket (chain sprocket) 474 Hole 475 Bolt hole (second hole) 481 Outer edge 481A Line part (line) 481B Arc section (arc) 483 Side edge R1 radius of curvature R2 radius of curvature R401 radius of curvature

Claims

1. A chain sprocket for transmitting a driving force of a driving source (12) for driving a vehicle (10) to wheels (15), The chain sprocket is provided with a lightening hole (74, 474) including an outer edge (81, 481), an inner edge (82) shorter than the outer edge (81, 481), and two side edges (83, 483) connecting an end of the outer edge (81, 481) and an end of the inner edge (82), The outer edge (81, 481) is formed by arcs (81A, 81B, 481B) having a plurality of radii of curvature (R1, R2, R401), or is formed by a pair of arcs (81A, 81B, 481B) having at least one radius of curvature (R1, R2, R401) and a line (481A) connecting the pair of arcs (81A, 81B, 481B). A chain sprocket characterized by:

2. When the outer edge (81) is formed by arcs (81A, 81B) having two radii of curvature (R1, R2), the smaller radius of curvature (R2) of the two radii of curvature (R1, R2) is smaller than 1 / 2 of the larger radius of curvature (R1).

2. A chain sprocket according to claim 1.

3. When the outer edge (81) is formed by arcs (81A, 81B) having two radii of curvature (R1, R2), the smaller radius of curvature (R2) of the two radii of curvature (R1, R2) is greater than 1 / 2 of the larger radius of curvature (R1).

2. A chain sprocket according to claim 1.

4. When the outer edge (81) is formed by arcs (81A, 81B) having two radii of curvature (R1, R2), the smaller radius of curvature (R2) of the two radii of curvature (R1, R2) is 1 / 2 of the larger radius of curvature (R1).

2. A chain sprocket according to claim 1.

5. The chain sprocket is provided with a second hole (75) different from the lightening hole (74, 474), The second hole (75) is provided radially inward from the outer edge (81, 481), The position where the center of the second hole (75) occupies in the radial direction overlaps with the position where the lightening hole (74, 474) occupies in the radial direction. A chain sprocket according to any one of claims 1 to 4.

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