JP2019034686A - Crank arm - Google Patents

Abstract

To provide a crank arm which is light-weight and has required strength.SOLUTION: A crank arm includes: a first member; a second member which is connected to the first member so as to form an internal space; a first mounting hole which is provided in at least the first member so as to attach a crank shaft; and a second mounting hole which is provided in at least the second member so as to attach a pedal shaft. The first member includes a first side wall which is disposed at the bicycle frame side relative to the internal space in a first direction along a center axis of the crank shaft. The second member includes a second side wall which is disposed at the opposite side of the first side wall relative to the internal space in the first direction. The second side wall includes a first area and a second area disposed between the first mounting hole and the second mounting hole in a second direction along a longitudinal direction of the crank arm. A thickness of a thickest part of the first area which is thickest in the first direction is larger than a thickness of the second area and is 3.0 mm or thinner.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a bicycle crank arm.

  A crank arm that can be attached to a bicycle frame via a crankshaft is known. The crank arm includes a first member and a second member connected to the first member so as to form an internal space. The first member is disposed on the bicycle frame side with respect to the internal space in a direction along the center axis of the crankshaft. The second member is disposed on the opposite side to the first member with respect to the internal space in the direction along the center axis of the crankshaft. Patent Document 1 discloses an example of a conventional crank arm.

JP 2015-227152 A

Conventionally, the entire first member is manufactured with a predetermined thickness in order to increase the strength of the crank arm. For this reason, the weight of a crank arm becomes large.
An object of the present invention is to provide a crank arm that is lightweight and has the required strength.

The crank arm according to the first aspect of the present invention is a crank arm that can be attached to a bicycle frame via a crankshaft, and is connected to the first member and the first member so as to form an internal space. A first mounting hole provided in at least the first member so that the crankshaft can be attached, and a second mounting hole provided in at least the second member so that a pedal shaft can be attached. The member includes a first side wall disposed on the bicycle frame side with respect to the internal space in a first direction along a center axis of the crankshaft, and the second member is the internal space in the first direction. The second side wall is disposed on the opposite side of the first side wall, and the second side wall extends in the second direction along the longitudinal direction of the crank arm. Including a first region and a second region disposed between the mounting hole and a thickness of the thickest thickest portion in the first direction of the first region being larger than a thickness of the second region; 0.0 mm or less.
Since the thickness of the portion of the second side wall of the second member that requires strength is set to be partially increased, a crank arm having a light weight and necessary strength can be provided.

In the crank arm on the second side according to the first side, the first region is provided in at least a portion of the second side wall on the second attachment hole side in the second direction.
For this reason, it is possible to reinforce the portion of the crank arm on the pedal shaft side where stress is most concentrated during pedaling.

In the crank arm of the third side surface according to the second side surface, the first region extends in the first direction and the second direction from the first mounting hole side toward the second mounting hole side in the second direction. The width in the third direction orthogonal to is widened.
For this reason, the stress which acts on the whole crank arm at the time of pedaling can be approached uniformly.

In the crank arm on the fourth side according to the second or third side, the second member further includes an outer peripheral wall extending from the outer peripheral portion of the second side wall toward the first side wall.
For this reason, a crank arm having high strength can be provided.

In the crank arm on the fifth side according to the fourth side, the outer peripheral wall includes a first portion and a second portion extending in the second direction, and the first portion and the second portion are in the first direction and It faces through the internal space in a third direction orthogonal to the second direction.
For this reason, a crank arm having high strength can be provided.

In the crank arm on the sixth side according to the fifth side, the thickness of the first region increases from the first part toward the second part in the third direction.
For this reason, the stress which acts on the whole crank arm at the time of pedaling can be approached uniformly.

In the crank arm on the seventh side according to the sixth side, the first portion is provided on the outer peripheral portion of the second side wall on the downstream side in the drive rotation direction of the sprocket that rotates about the crankshaft. The portion is provided on the upstream side in the drive rotation direction of the sprocket at the outer peripheral portion of the second side wall.
For this reason, the pedal shaft side portion of the crank arm where stress is most concentrated during pedaling can be further reinforced, and the stress acting on the entire crank arm during pedaling can be made more uniform.

In the crank arm of the eighth side according to the sixth or seventh side, the second side wall is an inner surface facing the first member in the first direction, and opposite to the first member in the first direction. And further including an outer surface provided on a side, wherein the inner surface of the first region is inclined with respect to the outer surface of the first region.
Since the inclination of the first region does not appear outside, the appearance of the crank arm can be maintained in a good state.

In the crank arm on the ninth side according to any one of the fourth to eighth sides, the second member is an outer surface of the second side wall provided on the side opposite to the first member in the first direction, And it further includes a recess recessed from the outer surface side toward the inner space, and the recess extends in the second direction.
Since the volume of the crank arm is reduced by the recess, a lightweight crank arm can be provided.

In the crank arm on the tenth side according to the ninth side, the recess is provided at a portion where the second side wall and the outer peripheral wall are connected.
For this reason, the external appearance of a crank arm can be maintained in a favorable state.

In the crank arm on the eleventh side according to the ninth or tenth side, the recess includes a first end and a second end in the second direction, and the second member includes the first end and the A first thick portion is provided at at least one of the second ends, and the thickness of the first thick portion is greater than the thickness of the central portion of the recess in the second direction.
It is possible to reinforce the end of the recess where stress is concentrated during pedaling.

In the crank arm of the twelfth side according to any one of the fourth to eleventh sides, the second side wall further includes an inner surface facing the first member in the first direction, and the first region has the first region. The inner surface is provided on the side opposite to the first member with respect to the end surface of the outer peripheral wall in the first direction.
For this reason, a lightweight crank arm can be provided.

In the crank arm on the thirteenth side according to any one of the first to twelfth sides, the first region is formed so that the thickness continuously changes.
For this reason, the stress which acts on the whole crank arm at the time of pedaling can be approached uniformly.

In the crank arm on the fourteenth side according to any one of the first to thirteenth side, the thickness of the second region is uniform.
For this reason, the stress which acts on the whole crank arm at the time of pedaling can be approached uniformly.

In the crank arm on the fifteenth side according to the fourteenth side, the second region is provided in at least a portion of the second side wall on the first mounting hole side in the second direction.
For this reason, the stress which acts on the whole crank arm at the time of pedaling can be approached uniformly.

In the sixteenth side crank arm according to the fifteenth side, the first region is formed to be continuous with the second region.
For this reason, the stress which acts on the whole crank arm at the time of pedaling can be approached uniformly.

In the crank arm of the seventeenth side according to any one of the first to sixteenth sides, the thickness of the thinnest portion in the first direction of the first region is equal to or greater than the thickness of the second region. is there.
For this reason, the stress which acts on the whole crank arm at the time of pedaling can be approached uniformly.

In the crank arm on the eighteenth side according to any one of the first to seventeenth side surfaces, the first member further includes a sprocket mounting portion to which a sprocket rotating around the crankshaft can be mounted.
For this reason, the crank arm which has light weight and required intensity | strength can be provided.

In the nineteenth side crank arm according to the eighteenth side, the sprocket mounting portion includes a boss extending from the first side wall toward the center side of the crankshaft in the first direction.
Therefore, it is possible to provide a direct mount type crank arm having a light weight and a necessary strength.

In the crank arm on the twentieth side according to the nineteenth side, the boss portion includes a plurality of splines.
Therefore, it is possible to provide a direct mount type crank arm having a light weight and a necessary strength.

In the crank arm on the twenty-first side according to any one of the first to twentieth side surfaces, the first side wall is disposed between the first mounting hole and the second mounting hole in the second direction, A third region having a uniform thickness in the first direction is further included, and the thickness of the third region is equal to or less than the thickness of the thickest portion of the first region.
For this reason, a lightweight crank arm can be provided.

In the crank arm on the twenty-second side according to the twenty-first side, the thickness of the third region is equal to or less than the thickness of the thinnest portion in the first direction of the first region.
For this reason, a lighter crank arm can be provided.

In the crank arm on the twenty-third side according to the twenty-first or twenty-second side, the dimension of the third region in the second direction is larger than the dimension of the first region in the second direction.
Since the third region having a small thickness is large, a lightweight crank arm can be provided.

In the crank arm of the 24th side according to any one of the 1st to 23rd sides, the first member is provided on an outer peripheral portion of the first side wall so as to extend in the second direction, and the first direction And a pair of ribs facing each other through the internal space in a third direction orthogonal to the second direction, wherein at least one of the ribs is provided at an intermediate portion in the second direction, A second thick portion protruding toward the rib.
For this reason, when adhering the first member and the second member with an adhesive, the bonding allowance between the first member and the second member can be increased.

The crank arm on the 25th side according to any one of the first to 24th sides further includes an adhesive for bonding the first member and the second member.
For this reason, a lightweight crank arm can be provided.

In the crank arm on the 26th side according to any one of the first to 25th sides, the second member is manufactured by forging.
For this reason, the 2nd member containing the 1st field can be manufactured easily.

In the crank arm on the 27th side according to any one of the first to 26th sides, the first member is manufactured by forging.
For this reason, when manufacturing the 1st member containing the field where the thickness in the 1st direction is not uniform, the 1st member can be manufactured easily.

  The crank arm of the present invention is lightweight and has the required strength.

The side view of the bicycle containing the crank arm of an embodiment. The perspective view which shows the crank arm and crankshaft of FIG. The disassembled perspective view which shows the state which decomposed | disassembled the crank arm of FIG. FIG. 3 is a cross-sectional perspective view showing the adjustment mechanism of FIG. 2 and its periphery. The perspective view which shows the inner surface of the 2nd member of FIG. Sectional drawing which follows the D6-D6 line | wire of FIG. Sectional drawing which follows the D7-D7 line | wire of FIG. Sectional drawing which follows the D8-D8 line | wire of FIG. Sectional drawing which follows the D9-D9 line | wire of FIG. The perspective view which shows the inner surface of the 1st member of FIG. Sectional drawing which follows the D11-D11 line | wire of FIG.

(Embodiment)
A bicycle 10 including a crank arm 30 will be described with reference to FIG.
The bicycle 10 includes a pair of crank arms 30. The type of bicycle 10 shown is a mountain bike. In one example, the bicycle 10 further includes a bicycle frame 12 (hereinafter “frame 12”), a front wheel WF, a rear wheel WR, and a drive train 14.

  The drive train 14 includes a crank assembly 16, a sprocket 24, and a chain 26. The crank assembly 16 includes a crankshaft 18, a pair of crank arms 30, and a pair of pedals 20. The crankshaft 18 is rotatably supported by the frame 12 via a bottom bracket (not shown). The crank arm 30 is attached to the frame 12 via the crankshaft 18. The pedal 20 is rotatably attached to the tip end of the crank arm 30 via the pedal shaft 22.

  The sprocket 24 includes one or more front sprockets 24A and one or more rear sprockets 24B. In the example shown in FIG. 1, the sprocket 24 includes only one front sprocket 24A and a plurality of rear sprockets 24B. The front sprocket 24A is provided in the crank assembly 16 so as to rotate integrally with the crankshaft 18 around the crankshaft 18, for example. The plurality of rear sprockets 24B are provided on the hub axle AH of the rear wheel WR. The chain 26 engages with any one of the front sprocket 24A and the rear sprocket 24B among the plurality of rear sprockets 24B. The gear ratio of the bicycle 10 is changed by switching the combination of the front sprocket 24A and the rear sprocket 24B with which the chain 26 is engaged. The driving force applied to the pedal 20 is transmitted to the rear wheel WR via the crank assembly 16, the front sprocket 24A, the chain 26, and the rear sprocket 24B.

The configuration of the crank arm 30 will be described with reference to FIGS.
As shown in FIGS. 2 and 3, the pair of crank arms 30 includes a first crank arm 32 and a second crank arm 34. The first crank arm 32 is the right crank arm 30 on which the front sprocket 24A is disposed. The second crank arm 34 is the left crank arm 30 opposite to the first crank arm 32. In the first crank arm 32 and the second crank arm 34, the components that are common to each other will be described with the same reference numerals given mainly to the crank arm 30.

  The crank arm 30 includes a first member 40 and a second member 60 connected to the first member 40 so as to form an internal space S. The first member 40 includes a first side wall 42 disposed on the frame 12 side with respect to the internal space S in the first direction D1 along the center axis C of the crankshaft 18. The first side wall 42 includes an inner surface 42A (see FIG. 10) that faces the second member 60 in the first direction D1, and an outer surface 42B that is provided on the opposite side of the second member 60 in the first direction D1. An example of the material constituting the first member 40 is an aluminum alloy. The first member 40 is manufactured by forging. The first member 40 may be manufactured by sheet metal, for example.

  The second member 60 includes a second side wall 62 disposed on the side opposite to the first side wall 42 with respect to the internal space S in the first direction D1. The second side wall 62 includes an inner surface 62A that faces the first member 40 in the first direction D1, and an outer surface 62B that is provided on the opposite side of the first member 40 in the first direction D1. An example of the material constituting the second member 60 is an aluminum alloy. The second member 60 is manufactured by forging.

  The crank arm 30 includes a first attachment hole 80 provided in at least the first member 40 so that the crankshaft 18 can be attached, and a second attachment hole 82 provided in at least the second member 60 so that the pedal shaft 22 can be attached. . The first mounting hole 80 is provided at one end 30 </ b> A of the crank arm 30 in the second direction D <b> 2 along the longitudinal direction of the crank arm 30. The second mounting hole 82 is provided at the other end 30B of the crank arm 30 in the second direction D2. The second direction D2 is a direction parallel to a straight line passing through the central axes of the first mounting hole 80 and the second mounting hole 82, for example, when viewed from a direction parallel to the central axis of the first mounting hole 80. is there. In one example, the first attachment hole 80 and the second attachment hole 82 penetrate the first member 40 and the second member 60 in the first direction D1.

  The first member 40 of the first crank arm 32 further includes a sprocket attachment portion 50 to which the front sprocket 24A can be attached. The sprocket mounting portion 50 is provided at a portion corresponding to the first mounting hole 80 on the outer surface 42 </ b> B of the first side wall 42 of the first crank arm 32. The sprocket mounting portion 50 includes a boss portion 52 that extends from the first side wall 42 toward the center of the crankshaft 18 in the first direction D1. That is, the first crank arm 32 is a direct mount type crank arm. In one example, the front sprocket 24 </ b> A has a boss portion of the sprocket mounting portion 50 in a state where movement of the first direction D <b> 1 with respect to the crankshaft 18 is restricted by fitting a lock ring (not shown) from the center side of the crankshaft 18. 52 is attached. Boss portion 52 includes a plurality of splines 52A. The plurality of splines 52A engage with a plurality of splines (not shown) provided on the inner peripheral side of the front sprocket 24A.

  The second crank arm 34 further includes an adjustment mechanism 54 that can adjust the distance between the second crank arm 34 and the bottom bracket in the first direction D1. The adjustment mechanism 54 is provided in a portion corresponding to the first mounting hole 80 on the outer surface 42 </ b> B of the first side wall 42 of the second crank arm 34.

  As shown in FIG. 4, the second crank arm 34 further includes an adjustment mechanism attachment portion 56 to which the adjustment mechanism 54 can be attached. The adjustment mechanism attachment portion 56 is formed in a portion corresponding to the first attachment hole 80 on the outer surface 42 </ b> B of the first side wall 42 of the second crank arm 34. A male screw 56 </ b> A is formed on the outer peripheral surface of the adjustment mechanism attachment portion 56. The adjustment mechanism 54 is disposed between an adjustment nut 54A that can be attached to the adjustment mechanism attachment portion 56, a washer 54C that is disposed between the adjustment nut 54A and the adjustment mechanism attachment portion 56, and between the adjustment nut 54A and the bottom bracket. The elastic member 54D is included. The adjustment nut 54A is formed with a female screw 54B that can be engaged with the male screw 56A of the adjustment mechanism mounting portion 56. An example of the washer 54C is a wave washer that presses the adjustment nut 54A toward the bottom bracket side in the first direction D1. An example of the elastic member 54D is an O-ring that improves waterproofness and dustproofness.

  The distance between the second crank arm 34 and the bottom bracket in the first direction D1 is adjusted by the state in which the adjustment nut 54A is attached to the adjustment mechanism attachment portion 56. Specifically, the adjustment nut 54A can be moved in the first direction D1 until the adjustment nut 54A comes into contact with the bottom bracket, so that the rattling of the second crank arm 34 with respect to the bottom bracket can be adjusted. . Further, since the washer 54C is provided between the adjustment nut 54A and the adjustment mechanism attachment portion 56, the state where the adjustment nut 54A is properly attached to the adjustment mechanism attachment portion 56 can be maintained. In addition, since the direction in which the female screw 54B of the adjustment nut 54A is loosened corresponds to the direction in which the adjustment nut 54A is directed toward the bottom bracket, it is possible to maintain a state in which rattling is difficult. The adjustment mechanism 54 may omit the elastic member 54D.

  As shown in FIG. 5, the second member 60 further includes an outer peripheral wall 64 that extends from the outer peripheral portion of the second side wall 62 toward the first side wall 42. The outer peripheral wall 64 includes a first portion 64A and a second portion 64B extending in the second direction D2. The first portion 64A and the second portion 64B oppose each other via the internal space S in a third direction D3 orthogonal to the first direction D1 and the second direction D2. The first portion 64A is provided on the outer peripheral portion of the second side wall 62 on the downstream side in the driving rotation direction of the front sprocket 24A. The driving rotation direction of the front sprocket 24A is the rotation direction of the front sprocket 24A when the driving force applied to the pedal 20 is transmitted to the rear wheel WR. The second portion 64B is provided on the upstream side in the drive rotation direction of the front sprocket 24A on the outer peripheral portion of the second side wall 62.

  The outer peripheral wall 64 further includes a third portion 64C and a fourth portion 64D that connect the first portion 64A and the second portion 64B in the third direction D3. The third portion 64C and the fourth portion 64D are opposed to each other through the internal space S in the second direction D2. The third portion 64 </ b> C is provided on the first mounting hole 80 side in the outer peripheral portion of the second side wall 62. The fourth portion 64 </ b> D is provided on the second mounting hole 82 side in the outer peripheral portion of the second side wall 62. The third portion 64C and the fourth portion 64D have, for example, a curved shape.

  The second side wall 62 further includes a first region 66 and a second region 68 disposed between the first mounting hole 80 and the second mounting hole 82 in the second direction D2. The thickness of the first region 66 is not uniform (see FIG. 6). The thickness of the first region 66 is defined by the distance between the inner surface 62A and the outer surface 62B of the second side wall 62 in the first direction D1. The first region 66 is provided in at least a portion of the second side wall 62 on the second attachment hole 82 side in the second direction D2. In one example, the first region 66 is mainly a portion on the second mounting hole 82 side with respect to an intermediate portion between the first mounting hole 80 and the second mounting hole 82 in the second side wall 62 in the second direction D2. Is provided. The thickness of the second region 68 is uniform (see FIG. 8). The thickness of the second region 68 is defined by the distance between the inner surface 62A and the outer surface 62B of the second side wall 62 in the first direction D1. The second region 68 is provided in at least a portion of the second side wall 62 on the first attachment hole 80 side in the second direction D2. In one example, the second region 68 is mainly a portion on the first mounting hole 80 side with respect to an intermediate portion between the first mounting hole 80 and the second mounting hole 82 in the second side wall 62 in the second direction D2. Is provided. A two-dot chain line shown in FIG. 5 indicates a boundary between the first region 66 and the second region 68.

  The first region 66 has a width in the third direction D3 that increases from the first mounting hole 80 side toward the second mounting hole 82 side in the second direction D2. In one example, the edge 67 of the first region 66 that constitutes the boundary between the first region 66 and the second region 68 is changed from the first mounting hole 80 side toward the second mounting hole 82 side in the second direction D2. In the three directions D3, the outer peripheral wall 64 extends from the second portion 64B toward the first portion 64A. The second region 68 has a width in the third direction D3 that increases in the second direction D2 from the second mounting hole 82 side toward the first mounting hole 80 side. In one example, the edge 69 of the second region 68 that constitutes the boundary between the first region 66 and the second region 68 is changed from the second mounting hole 82 side toward the first mounting hole 80 side in the second direction D2. In the three directions D3, the outer peripheral wall 64 extends from the first portion 64A toward the second portion 64B.

  As shown in FIGS. 6 and 7, the inner surface 62A of the first region 66 is provided on the side opposite to the first member 40 with respect to the end surface 64E of the outer peripheral wall 64 in the first direction D1. In other words, the end surface 64E is disposed closer to the first member 40 than the inner surface 62A of the first region 66. In one example, the distance between the inner surface 62A of the first region 66 and the end surface 64E of the outer peripheral wall 64 in the first direction D1 is greater than the thickness of the first region 66. The first region 66 is formed so that the thickness continuously changes. The first region 66 is formed so as to be continuous with the second region 68.

  The thickness of the first region 66 increases from the first portion 64A to the second portion 64B of the outer peripheral wall 64 in the third direction D3. In one example, the inner surface 62A of the first region 66 is inclined with respect to the outer surface 62B of the first region 66. The first region 66 includes a thickest portion 66A that is the thickest in the first direction D1, and a thinnest portion 66B that is the thinnest in the first direction D1. In the example shown in FIG. 6, the thickest portion 66A is provided at the portion closest to the second portion 64B in the first region 66 in the third direction D3, and the first portion 64A in the first region 66 in the third direction D3. The thinnest portion 66B is provided at the close portion. The thickest portion 66A may be disposed at an intermediate portion between the first portion 64A and the second portion 64B in the first region 66 in the third direction D3.

  As shown in FIG. 7, the outer surface 62B of the second side wall 62 includes a planar portion 62C and a pair of inclined portions 62D. The inclined portion 62D is a portion inclined with respect to the planar portion 62C. One inclined portion 62D is provided on the first portion 64A side of the outer surface 62B of the second side wall 62 in the third direction D3. The other inclined portion 62D is provided on the second portion 64B side of the outer surface 62B of the second side wall 62 in the third direction D3. In the example shown in FIG. 7, the thickest portion 66A is provided in the portion closest to the second portion 64B in the portion corresponding to the planar portion 62C in the first region 66 in the third direction D3, and in the third direction D3. The thinnest portion 66B is provided in the portion of the first region 66 closest to the first portion 64A. The outer surface 62B of the second side wall 62 may omit at least one inclined portion 62D.

  The thickness of the thickest portion 66A of the first region 66 (hereinafter, “thickest portion thickness TA1”) is larger than the thickness of the second region 68 (hereinafter, “second region thickness TB”). The thickest part thickness TA1 is 3.0 mm or less. In a preferred example, the thickest part thickness TA1 is 2.5 mm or less. In one example, the thickest part thickness TA1 is 2.4 mm. The thickness of the thinnest portion 66B of the first region 66 (hereinafter, “thinnest portion thickness TA2”) is equal to or greater than the second region thickness TB. The thinnest part thickness TA2 is 1.0 mm or more. In a preferred example, the thinnest part thickness TA2 is 1.5 mm or more. In one example, the thinnest part thickness TA2 is 1.7 mm. The ratio of the thinnest part thickness TA2 to the thickest part thickness TA1 (hereinafter, “thickness ratio TR”) is preferably 0.5 or more. An example of the thickness ratio TR is around 0.7. An example of the second region thickness TB is 1.7 mm.

  As shown in FIG. 8, the second member 60 further includes a pair of recesses 70 that are recessed from the outer surface 62B side to the inner space S side. The recess 70 extends in the second direction D2 (see FIG. 2). The recess 70 is provided in a portion where the second side wall 62 and the outer peripheral wall 64 are connected. One recess 70 is provided, for example, in a portion where the second side wall 62 and the first portion 64A are connected. The other recess 70 is provided, for example, at a portion where the second side wall 62 and the second portion 64B are connected. In other words, one recess 70 is provided on the downstream side in the drive rotation direction of the front sprocket 24A, and the other recess 70 is provided on the upstream side in the drive rotation direction of the front sprocket 24A.

  As shown in FIG. 2, the recess 70 includes a first end 70A and a second end 70B in the second direction D2. For example, the first end portion 70A is provided on the first attachment hole 80 side in the second direction D2. For example, the second end portion 70B is provided on the second mounting hole 82 side in the second direction D2. As shown in FIG. 5, the second member 60 includes a first thick portion 72 provided on at least one of the first end portion 70A and the second end portion 70B. In one example, the first thick portion 72 is provided in the second end portion 70B in one recess 70, and is provided in each of the first end portion 70A and the second end portion 70B in the other recess portion 70. The dots shown in FIG. 5 indicate the arrangement of the first thick portions 72.

  As shown in FIG. 9, the thickness of the first thick portion 72 (hereinafter referred to as “thick portion thickness TW”) is the thickness of the central portion 70C of the concave portion 70 in the second direction D2 (hereinafter referred to as “center”). Greater than the partial thickness TM "). The thick part thickness TW is defined by the thickest part of the first thick part 72 in the first direction D1. The thickness part thickness TW is 5.0 mm or less. In a preferred example, the thick part thickness TW is 4.5 mm or less. In one example, the thickness TW on the first end portion 70A side is 4.0 mm, and the thickness TW on the second end portion 70B side is 3.6 mm. An example of the central part thickness TM is 2.0 mm. The second member 60 may omit at least one recess 70.

  As shown in FIG. 10, the first side wall 42 of the first member 40 is disposed between the first mounting hole 80 and the second mounting hole 82 in the second direction D2, and has a thickness in the first direction D1. A uniform third region 44 is further included. The dimension L1 of the third region 44 in the second direction D2 is larger than the dimension L2 (see FIG. 5) of the first region 66 in the second direction D2. The dimension L1 of the third region 44 is defined by the largest dimension L1 of the third region 44 in the second direction D2. The dimension L2 of the first region 66 is defined by the dimension L2 of the first region 66 that is the largest in the second direction D2.

  The first member 40 further includes a pair of ribs 48 provided on the outer peripheral portion 46 of the first side wall 42 so as to extend in the second direction D2 and facing each other through the internal space S in the third direction D3. At least one of the ribs 48 includes a second thick portion 48A that is provided in an intermediate portion 46A of the outer peripheral portion 46 in the second direction D2 and protrudes from the outer peripheral portion 46 toward the other rib 48. In one example, the second thick part 48 </ b> A is provided on each of the pair of ribs 48.

  The crank arm 30 further includes an adhesive 84 that bonds the first member 40 and the second member 60 together. For example, the adhesive 84 is applied to the entire portion of the first member 40 that contacts the second member 60. In one example, the adhesive 84 is applied to a portion of the inner surface 42 </ b> A of the first side wall 42 excluding the third region 44, the outer peripheral surface 42 </ b> C of the first side wall 42, and the surface 48 </ b> B of the rib 48. By attaching the second member 60 to the first member 40 to which the adhesive 84 is applied, the first member 40 and the second member 60 are connected so as to form the internal space S. The dots shown in FIG. 10 indicate the arrangement of the adhesive 84.

  As shown in FIG. 11, the thickness of the third region 44 (hereinafter, “third region thickness TC”) is defined by the distance between the inner surface 42A and the outer surface 42B of the first side wall 42 in the first direction D1. The The third region thickness TC is equal to or less than the thickest portion thickness TA1 of the first region 66 (see FIG. 6). The third region thickness TC is equal to or less than the thinnest portion thickness TA2 (see FIG. 6) of the first region 66. The third region thickness TC is 1.0 mm or more. In a preferred example, the third region thickness TC is 1.2 mm or more. In one example, the third region thickness TC is 1.7 mm.

(Modification)
The description related to the above embodiment is an example of the form that the crank arm according to the present invention can take, and is not intended to limit the form. In addition to the above-described embodiment, the crank arm according to the present invention may take a form in which, for example, the following modified example of the above-described embodiment and at least two modified examples that do not contradict each other are combined. In the following modified examples, the same reference numerals as those in the embodiment are given to portions common to the embodiment, and the description thereof is omitted.

  -The connection method of the 1st member 40 and the 2nd member 60 can be changed arbitrarily. In the first example, the first member 40 and the second member 60 are connected by diffusion bonding. In the second example, the first member 40 and the second member 60 are connected by welding. In the third example, the first member 40 and the second member 60 are connected by welding.

  -The structure of the rib 48 can be changed arbitrarily. In the first example, at least one rib 48 is provided on the first attachment hole 80 side with respect to the intermediate portion 46A of the outer peripheral portion 46 in the second direction D2. In the second example, at least one rib 48 is provided on the second attachment hole 82 side with respect to the intermediate portion 46A of the outer peripheral portion 46 in the second direction D2. The first member 40 may omit at least one of the pair of ribs 48.

  The relationship between the dimension L1 of the third region 44 and the dimension L2 of the first region 66 can be arbitrarily changed. In the first example, the dimension L1 of the third region 44 is substantially the same as the dimension L2 of the first region 66. In the second example, the dimension L1 of the third region 44 is smaller than the dimension L2 of the first region 66.

The relationship between the thinnest part thickness TA2 and the second region thickness TB can be arbitrarily changed. In one example, the thinnest portion thickness TA2 is smaller than the second region thickness TB.
The relationship between the third region thickness TC and the thickness of the first region 66 can be arbitrarily changed. In the first example, the third region thickness TC is larger than the thinnest part thickness TA2 and equal to or less than the thickest part thickness TA1. In the second example, the third region thickness TC is larger than the thickest part thickness TA1.

  -The structure of the sprocket mounting part 50 can be changed arbitrarily. In one example, the sprocket mounting portion 50 includes spiders (not shown) extending radially from the crankshaft 18. According to this example, the sprocket mounting portion 50 is not included in the elements constituting the crank arm 30.

  The relationship between the first area 66 and the second area 68 can be arbitrarily changed. In the first example, another region is formed between the first region 66 and the second region 68. An example of another region is a region including a rib extending from the second side wall 62 toward the first side wall 42. In the second example, the first region 66 is connected to the second region 68 by adhesion, welding, welding, or the like. According to the first example and the second example, the first region 66 is formed so as not to be continuous with the second region 68. In the third example, the first region 66 is provided in a portion of the second side wall 62 on the first mounting hole 80 side in the second direction D2, and the second region 68 is formed in the second side wall 62 in the second direction D2. Of the second mounting hole 82 side.

  The configuration of the second area 68 can be arbitrarily changed. In one example, the second region 68 includes a thickest part that is thickest in the first direction D1 and a thinnest part that is thinnest in the first direction D1. The thickness of the thickest part of the second region 68 is larger than the thickness of the thinnest part of the second region 68. According to this example, the thickness of the second region 68 is not uniform.

  The configuration of the first area 66 can be arbitrarily changed. In the first example, the thickest part thickness TA1 is substantially the same as the thinnest part thickness TA2. According to this example, the thickness of the first region 66 is uniform. In the second example, the first region 66 is formed so that the thickness changes stepwise. In the third example, the thickness of the first region 66 decreases from the first portion 64A toward the second portion 64B in the third direction D3. In the fourth example, the first region 66 becomes narrower in the third direction D3 as it goes from the first mounting hole 80 side to the second mounting hole 82 side in the second direction D2. In the fifth example, the first region 66 has a constant width in the third direction D3.

DESCRIPTION OF SYMBOLS 12 ... Frame (bicycle frame), 18 ... Crank shaft, 22 ... Pedal shaft, 24 ... Sprocket, 24A ... Front sprocket (sprocket), 30 ... Crank arm, 32 ... First crank arm (crank arm), 34 ... Second Crank arm (crank arm), 40 ... first member, 42 ... first side wall, 44 ... third region, 46 ... outer peripheral part, 46A ... intermediate part, 48 ... rib, 48A ... second thick part, 50 ... sprocket Mounting portion 52 ... Boss portion 52A ... Spline 60 ... Second member 62 ... Second side wall 62A ... Inner surface 62B ... Outer surface 64 ... Outer peripheral wall 64A ... First portion 64B ... Second portion 64E ... end face, 66 ... first region, 66A ... thickest part, 66B ... thinnest part, 68 ... second region, 70 ... concave part, 70A ... first end, 70B ... second end, 70C ... central part 72 ... 1st thick part, 80 ... 1st attachment hole, 82 ... 2nd attachment hole, 84 ... Adhesive agent, C ... Center axis, D1 ... 1st direction, D2 ... 2nd direction, D3 ... 3rd Direction, L1 ... dimension, L2 ... dimension, S ... internal space.

Claims (27)

A crank arm that can be attached to a bicycle frame via a crankshaft,
A first member;
A second member coupled to the first member to form an internal space;
A first mounting hole provided in at least the first member so that the crankshaft can be mounted;
A second mounting hole provided in at least the second member so that a pedal shaft can be mounted;
The first member includes a first side wall disposed on the bicycle frame side with respect to the internal space in a first direction along a center axis of the crankshaft,
The second member includes a second side wall disposed on a side opposite to the first side wall with respect to the internal space in the first direction,
The second side wall includes a first region and a second region disposed between the first mounting hole and the second mounting hole in a second direction along a longitudinal direction of the crank arm,
The crank arm, wherein a thickness of a thickest portion of the first region that is thickest in the first direction is greater than a thickness of the second region and is 3.0 mm or less.   2. The crank arm according to claim 1, wherein the first region is provided in at least a portion of the second side wall on the second mounting hole side in the second direction.   The first region has a width in a third direction that is orthogonal to the first direction and the second direction as it goes from the first mounting hole side to the second mounting hole side in the second direction. Item 3. The crank arm according to item 2.   The crank arm according to claim 2 or 3, wherein the second member further includes an outer peripheral wall extending from an outer peripheral portion of the second side wall to the first side wall. The outer peripheral wall includes a first portion and a second portion extending in the second direction,
5. The crank arm according to claim 4, wherein the first portion and the second portion are opposed to each other through the internal space in a third direction orthogonal to the first direction and the second direction.   The crank arm according to claim 5, wherein a thickness of the first region increases from the first portion toward the second portion in the third direction. The first portion is provided on the outer peripheral portion of the second side wall on the downstream side in the drive rotation direction of the sprocket rotating around the crankshaft,
The crank arm according to claim 6, wherein the second portion is provided on the upstream side in the drive rotation direction of the sprocket at the outer peripheral portion of the second side wall. The second side wall further includes an inner surface facing the first member in the first direction, and an outer surface provided on the opposite side of the first member in the first direction,
The crank arm according to claim 6 or 7, wherein the inner surface of the first region is inclined with respect to the outer surface of the first region. The second member further includes an outer surface of the second side wall provided on the opposite side of the first member in the first direction, and a recess recessed from the outer surface side to the inner space side,
The crank arm according to any one of claims 4 to 8, wherein the recess extends in the second direction.   The crank arm according to claim 9, wherein the recess is provided in a portion where the second side wall and the outer peripheral wall are connected. The recess includes a first end and a second end in the second direction,
The second member includes a first thick portion provided on at least one of the first end and the second end,
The crank arm according to claim 9 or 10, wherein a thickness of the first thick portion is larger than a thickness of a central portion of the concave portion in the second direction. The second side wall further includes an inner surface facing the first member in the first direction,
The crank arm according to any one of claims 4 to 11, wherein the inner surface of the first region is provided on a side opposite to the first member with respect to an end surface of the outer peripheral wall in the first direction.   The crank arm according to any one of claims 1 to 12, wherein the first region is formed so as to continuously change in thickness.   The crank arm according to any one of claims 1 to 13, wherein the thickness of the second region is uniform.   The crank arm according to claim 14, wherein the second region is provided in at least a portion of the second side wall on the first mounting hole side in the second direction.   The crank arm according to claim 15, wherein the first region is formed to be continuous with the second region.   The crank arm according to any one of claims 1 to 16, wherein a thickness of a thinnest portion of the first region that is thinnest in the first direction is equal to or greater than a thickness of the second region.   The crank arm according to any one of claims 1 to 17, wherein the first member further includes a sprocket attachment portion to which a sprocket rotating around the crankshaft can be attached.   The crank arm according to claim 18, wherein the sprocket mounting portion includes a boss portion extending from the first side wall toward the center side of the crankshaft in the first direction.   The crank arm according to claim 19, wherein the boss portion includes a plurality of splines. The first side wall further includes a third region disposed between the first mounting hole and the second mounting hole in the second direction and having a uniform thickness in the first direction,
The crank arm according to any one of claims 1 to 20, wherein a thickness of the third region is equal to or less than a thickness of the thickest portion of the first region.   The crank arm according to claim 21, wherein a thickness of the third region is equal to or less than a thickness of a thinnest portion of the first region that is thinnest in the first direction.   The crank arm according to claim 21 or 22, wherein a dimension of the third region in the second direction is larger than a dimension of the first region in the second direction. The first member is provided on an outer peripheral portion of the first side wall so as to extend in the second direction, and is opposed to the first direction and a third direction orthogonal to the second direction through the internal space. Further including ribs,
The at least one rib includes a second thick portion provided at an intermediate portion in the second direction and protruding from the outer peripheral portion toward the other rib. Crank arm as described.   The crank arm according to any one of claims 1 to 24, further comprising an adhesive that bonds the first member and the second member.   The crank arm according to any one of claims 1 to 25, wherein the second member is manufactured by forging. The crank arm according to any one of claims 1 to 26, wherein the first member is manufactured by forging.