Bicycle power transmission system

Abstract

This suppresses wear on the first and second plates. [Solution] The coil spring is placed in the first window of the first plate, the second window of the second plate, and the housing hole of the first rotating body. The first plate has a first contact surface and a first notch. The first contact surface contacts the end face of the coil spring. The first notch is formed on the first contact surface. The second plate has a second contact surface and a second notch. The second contact surface contacts the end face of the coil spring. The second notch is formed on the second contact surface.

Description

Technical Field

[0001] The present invention relates to a power transmission device for a bicycle.

Background Art

[0002] A power transmission device for a bicycle has a first rotating body, a first plate, and a second plate (for example, Patent Document 1). The first and second plates are configured to rotate integrally with each other. The first rotating body, the first plate, and the second plate are elastically connected by a coil spring. Specifically, the coil spring is disposed within a housing hole of the first rotating body, within a window portion of the first plate, and within a window portion of the second plate.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the power transmission device for a bicycle is in use, the coil spring rotates within each window portion, and there is a risk that the first and second plates will wear. Therefore, an object of the present invention is to suppress wear of the first and second plates.

Means for Solving the Problems

[0005] A bicycle power transmission device according to the first embodiment comprises a first rotating body, a first plate, a second plate, and a coil spring. The first rotating body has a housing hole. The first plate has a first window. The first plate is arranged to be rotatable relative to the first rotating body. The second plate has a second window. The second plate is configured to rotate integrally with the first plate. The second plate is arranged to sandwich the first rotating body axially between itself and the first plate. The coil spring is arranged in the first window, the second window, and the housing hole. The coil spring elastically connects the first rotating body to the first and second plates. The first plate has a first contact surface and a first notch. The first contact surface contacts the end face of the coil spring. The first notch is formed on the first contact surface. The second plate has a second contact surface and a second notch. The second contact surface contacts the end face of the coil spring. The second notch is formed on the second contact surface.

[0006] With this configuration, since a first notch is formed on the first contact surface, the radially outer portion and the radially inner portion relative to the first notch become more easily deformed in accordance with the rotation of the coil spring. As a result, relative rotation of the coil spring with respect to the first contact surface is suppressed, and wear of the first plate can be suppressed. Similarly, since a second notch is formed on the second contact surface, wear of the second plate can be suppressed.

[0007] A bicycle power transmission device according to the second embodiment is configured as follows in the bicycle power transmission device according to the first embodiment: The first plate has a first offset portion. The first offset portion is positioned radially inward with respect to the first notch. The first offset portion is offset toward the first rotating body.

[0008] The bicycle power transmission device according to the third embodiment is configured as follows in the bicycle power transmission device according to the second embodiment: The second plate has a second offset portion. The second offset portion is positioned radially inward with respect to the second notch. The second offset portion is offset toward the first rotating body.

[0009] The bicycle power transmission device according to the fourth embodiment is configured as follows in the bicycle power transmission device according to the second or third embodiment: The coil spring is not in contact with the first offset portion.

[0010] The fifth embodiment of the bicycle power transmission device is configured as follows in the bicycle power transmission device according to any of the first to fourth embodiments: The first rotating body has a third contact surface. The third contact surface contacts a coil spring. The first rotating body does not have a notch on the third contact surface. [Effects of the Invention]

[0011] According to the present invention, wear of the first and second plates can be suppressed. [Brief explanation of the drawing]

[0012] [Figure 1] Cross-sectional view of a bicycle power transmission system. [Figure 2] Front view of a bicycle power transmission system. [Figure 3] Front view of the first rotating body. [Figure 4] Front view of the first plate. [Figure 5] Figure 4 shows a cross-sectional view along the VV line. [Figure 6] Front view of the second plate. [Figure 7] Figure 6 shows a cross-sectional view along line VII-VII. [Figure 8] Side view of the stopper component. [Modes for carrying out the invention]

[0013] The following description of the bicycle power transmission device 100 (hereinafter also simply referred to as the power transmission device 100) according to this embodiment will be made with reference to the drawings. In the following description, the axial direction refers to the direction in which the rotation axis O of the power transmission device 100 extends. The circumferential direction refers to the circumferential direction of a circle centered on the rotation axis O, and the radial direction refers to the radial direction of a circle centered on the rotation axis O. The first axial side refers to the left side of Figure 1, and the second axial side refers to the right side of Figure 1. The rotation direction R refers to the direction in which the power transmission device 100 rotates when the bicycle on which the power transmission device 100 is mounted is in motion. The rotation direction R is the clockwise direction in Figure 2.

[0014] Figure 1 is a cross-sectional view of the power transmission device 100. As shown in Figure 1, the power transmission device 100 includes a first rotating body 2, a second rotating body 3, a plurality of coil springs 4, a plurality of stopper members 5, a sprocket 6, a crank arm 7, a plurality of first nuts 8, and a plurality of second nuts 9. The power transmission device 100 is rotatably arranged around the rotation axis O.

[0015] The power transmission device 100 is mounted on a bicycle. The power transmission device 100 is mounted on a bicycle that does not have an electric motor, for example, that is, a bicycle that is driven only by human power. However, the power transmission device 100 may also be mounted on a bicycle that has an electric motor. In this case, for example, the bicycle may have an electric mode driven only by the electric motor and a human-powered mode driven only by human power. The bicycle may also have an assist mode driven by both the electric motor and human power, or it may not have an assist mode. The power transmission device 100 is configured to transmit torque input to a pedal (not shown) attached to the tip of the crank arm 7 to a drive wheel (not shown).

[0016] Figure 2 is a front view of the power transmission device 100 with several coil springs 4, crank arms 7, and the second plate 32 of the second rotating body 3 (described later) removed. As shown in Figure 2, the power transmission device 100 is configured to rotate in the rotational direction R (clockwise in Figure 2).

[0017] <First rotating body> Figure 3 is a front view of the first rotating body 2. As shown in Figure 3, the first rotating body 2 has a plurality of accommodation holes 21. In this embodiment, the first rotating body 2 has three accommodation holes 21. Each accommodation hole 21 penetrates in the axial direction. Each accommodation hole 21 is arranged at intervals in the circumferential direction. Each accommodation hole 21 is arranged at equal intervals.

[0018] The first rotating body 2 has a plurality of third abutting surfaces 27. The third abutting surface 27 is a surface that abuts against the coil spring 4. Specifically, the third abutting surface 27 is a surface that abuts against the end surface of the coil spring 4 among the surfaces that define the accommodation hole 21. That is, the first rotating body 2 has a pair of third abutting surfaces 27 for each accommodation hole 21. The pair of third abutting surfaces 27 face the circumferential direction and are opposed to each other. No notch is formed on the third abutting surface 27. That is, in the axial view, the third abutting surface 27 extends linearly.

[0019] The first rotating body 2 is arranged to be rotatable in the rotation direction R. Torque is input to the first rotating body 2 from the crank arm 7. The first rotating body 2 is configured to rotate integrally with the crank arm 7.

[0020] As shown in FIGS. 1 to 3, the first rotating body 2 has a hub portion 22, an outer flange portion 23, and an inner flange portion 24. The hub portion 22 is cylindrical and extends in the axial direction. In a state where the power transmission device 100 is mounted on a bicycle, a crankshaft (not shown) extends through the hub portion 22.

[0021] The outer flange portion 23 extends radially outward from the hub portion 22. The accommodation hole 21 is formed in the outer flange portion 23. The accommodation hole 21 penetrates the outer flange portion 23 in the axial direction. The outer flange portion 23 is formed at the axial center of the hub portion 22.

[0022] The inner flange portion 24 extends radially inward from the hub portion 22. The inner flange portion 24 has spline holes 241 on its inner circumferential surface. The inner flange portion 24 is formed at the axial end of the hub portion 22. Specifically, the inner flange portion 24 is formed at the second axial end of the hub portion 22. The position where the inner flange portion 24 is located differs in the axial direction from the position where the outer flange portion 23 is located. That is, in a radial view, the inner flange portion 24 does not overlap with the outer flange portion 23.

[0023] The first rotating body 2 has a plurality of stopper surfaces 25. More specifically, the first rotating body 2 has a plurality of notches 26. Each notch 26 is spaced apart in the circumferential direction. The notches 26 are located between a pair of housing holes 21 in the circumferential direction. Each notch 26 opens radially outward. Of the inner wall surfaces defining the notches 26, the surface facing the rotation direction R becomes the stopper surface 25.

[0024] The stopper surface 25 is oriented in the circumferential direction. More specifically, the stopper surface 25 is oriented in the rotational direction R. The stopper surface 25 is positioned opposite the stopper portion 51 in the circumferential direction, with a gap between them.

[0025] The first rotating body 2 can be made of, for example, iron, stainless steel, or carbon fiber reinforced plastic (CFRP).

[0026] <Second Rotating Body> The second rotating body 3 is arranged to be rotatable in the rotational direction R. The second rotating body 3 is arranged to be rotatable relative to the first rotating body 2. The second rotating body 3 has a first plate 31 and a second plate 32.

[0027] The first plate 31 and the second plate 32 are spaced apart from each other in the axial direction. The first rotating body 2 is positioned between the first plate 31 and the second plate 32. That is, the first plate 31 and the second plate 32 are positioned to sandwich the first rotating body 2 in the axial direction. In detail, the outer flange portion 23 of the first rotating body 2 is positioned between the first plate 31 and the second plate 32 in the axial direction. The first plate 31 is positioned on the first axial side with respect to the outer flange portion 23. The second plate 32 is positioned on the second axial side with respect to the outer flange portion 23.

[0028] Figure 4 is a plan view of the first plate 31, and Figure 5 is a cross-sectional view of Figure 4 along line VV. As shown in Figures 4 and 5, the first plate 31 is disc-shaped and has an opening in its center. The hub portion 22 of the first rotating body 2 extends axially through this opening in the first plate 31.

[0029] The first plate 31 has a plurality of first window portions 311. In this embodiment, the first plate 31 has three first window portions 311. The first window portions 311 penetrate the first plate 31 in the axial direction. Each first window portion 311 is spaced apart from the others in the circumferential direction.

[0030] The first plate 31 has a plurality of first through holes 312. Each first through hole 312 is spaced apart from the others in the circumferential direction. In the circumferential direction, each first window portion 311 and each first through hole 312 are arranged alternately.

[0031] The first plate 31 has a plurality of first contact surfaces 313, a plurality of first notches 314, and a first offset portion 315. The first contact surfaces 313 are surfaces that contact the end faces of the coil springs 4. More specifically, the first contact surfaces 313 are surfaces that define the first window portion 311 and contact the end faces of the coil springs 4. That is, the first plate 31 has a pair of first contact surfaces 313 for each first window portion 311. This pair of first contact surfaces 313 are oriented in the circumferential direction and face each other. The coil springs 4 are positioned between this pair of first contact surfaces 313.

[0032] The first notch 314 is formed in the first contact surface 313. The first notch 314 may be formed after the first window 311 is formed, or it may be formed together with the first window 311.

[0033] The first notch 314 is formed to be recessed circumferentially from the first contact surface 313. The first notch 314 does not contact the coil spring 4. The coil spring 4 contacts the first contact surface 313 on the radially outer side of the first notch 314 and also contacts the first contact surface 313 on the radially inner side of the first notch 314. The first contact surface 313 is divided into an outer portion 313a and an inner portion 313b, with the first notch 314 as the boundary. The coil spring 4 then contacts both the outer portion 313a and the inner portion 313b of the first contact surface 313.

[0034] The first offset portion 315 is a portion of the first contact surface 313 that is offset in the axial direction. The first offset portion 315 is offset toward the outer flange portion 23. That is, the first offset portion 315 is offset toward the second axial direction. The first offset portion 315 is positioned radially inward with respect to the first notch portion 314. That is, the first offset portion 315 is formed in the inner portion 313b of the first contact surface 313. Note that the first offset portion 315 is not in contact with the coil spring 4. The coil spring 4 is in contact with the first contact surface 313 radially inward with respect to the first offset portion 315.

[0035] Figure 6 is a plan view of the second plate 32, and Figure 7 is a cross-sectional view taken along line VII-VII in Figure 6. As shown in Figures 6 and 7, the second plate 32 is disc-shaped and has an opening in its center. The hub portion 22 of the first rotating body 2 extends axially through this opening in the second plate 32. The second plate 32 is configured to rotate integrally with the first plate 31. In detail, the first plate 31 and the second plate 32 are fastened to each other by a plurality of stopper members 5.

[0036] The second plate 32 has a plurality of second window portions 321. In this embodiment, the second plate 32 has three second window portions 321. The second window portions 321 penetrate the second plate 32 in the axial direction. Each second window portion 321 is spaced apart from each other in the circumferential direction. Each second window portion 321 overlaps with the corresponding first window portion 311 in an axial view.

[0037] The second plate 32 has a plurality of second through holes 322. Each second through hole 322 is spaced apart from the others in the circumferential direction. In the circumferential direction, each second window portion 321 and each second through hole 322 are arranged alternately. Each second through hole 322 overlaps with the corresponding first through hole 312 in an axial view.

[0038] The second plate 32 has a plurality of second contact surfaces 323, a plurality of second notches 324, and a second offset portion 325. The second contact surfaces 323 are surfaces that contact the end faces of the coil springs 4. More specifically, the second contact surfaces 323 are surfaces that define the second window portion 321 and contact the end faces of the coil springs 4. That is, the second plate 32 has a pair of second contact surfaces 323 for each second window portion 321. This pair of second contact surfaces 323 are oriented in the circumferential direction and face each other. The coil springs 4 are positioned between this pair of second contact surfaces 323.

[0039] The second notch 324 is formed in the second contact surface 323. The second notch 324 may be formed after the second window 321 is formed, or it may be formed together with the second window 321.

[0040] The second notch 324 is formed to be recessed circumferentially from the second contact surface 323. The second notch 324 does not contact the coil spring 4. The coil spring 4 contacts the second contact surface 323 on the radially outer side of the second notch 324 and on the radially inner side of the second notch 324. The second contact surface 323 is divided into an outer portion 323a and an inner portion 323b, with the second notch 324 as the boundary. The coil spring 4 then contacts both the outer portion 323a and the inner portion 323b of the second contact surface 323.

[0041] The second offset portion 325 is a portion of the second contact surface 323 that is offset in the axial direction. The second offset portion 325 is offset toward the outer flange portion 23. That is, the first offset portion 315 is offset toward the first axial direction. The second offset portion 325 is positioned radially inward with respect to the second notch portion 324. That is, the second offset portion 325 is formed in the inner portion 323b of the second contact surface 323. Note that the second offset portion 325 is not in contact with the coil spring 4. The coil spring 4 is in contact with the second contact surface 323 radially inward with respect to the second offset portion 325.

[0042] The first plate 31 and the second plate 32 can be made of, for example, iron, stainless steel, or carbon fiber reinforced plastic (CFRP).

[0043] <Coil spring> The coil spring 4 is housed within the housing hole 21, the first window 311, and the second window 321. The coil spring 4 elastically connects the first rotating body 2 and the first plate 31 and the second plate 32 in the rotational direction R. That is, torque from the first rotating body 2 is transmitted to the first plate 31 and the second plate 32 via the coil spring 4. The coil spring 4 also rotates together with the first rotating body 2, the first plate 31, and the second plate 32. When torque is transmitted, the coil spring 4 contracts, causing the first rotating body 2 and the second rotating body 3 to twist relative to each other. When the coil spring 4 is not contracted, the first rotating body 2 and the second rotating body 3 do not twist, and the twist angle is 0 degrees.

[0044] Within the first window portion 311, one end face of the coil spring 4 contacts the first contact surface 313 of the pair of first contact surfaces 313 that faces the rotational direction R. Also within the first window portion 311, the other end face of the coil spring 4 contacts the first contact surface 313 of the pair of first contact surfaces 313 that faces the direction opposite to the rotational direction R.

[0045] Within the second window portion 321, one end face of the coil spring 4 contacts the second contact surface 323 of the pair of second contact surfaces 323 that faces the rotational direction R. Also within the second window portion 321, the other end face of the coil spring 4 contacts the second contact surface 323 of the pair of second contact surfaces 323 that faces the direction opposite to the rotational direction R.

[0046] Within the housing hole 21, one end face of the coil spring 4 contacts the third contact surface 27 of the pair of third contact surfaces 27 that faces the rotational direction R. Also within the housing hole 21, the other end face of the coil spring 4 contacts the third contact surface 27 of the pair of third contact surfaces 27 that faces the direction opposite to the rotational direction R.

[0047] <Sprocket> As shown in Figure 1, the sprocket 6 is attached to the first plate 31. The sprocket 6 is attached to the first plate 31 by a stopper member 5, a first nut 8, and a second nut 9. The sprocket 6 rotates integrally with the first plate 31 and the second plate 32. The sprocket 6 has multiple teeth on its outer circumference. A chain (not shown) is attached to the sprocket 6, and torque is transmitted from the sprocket 6 to the drive wheel (not shown) via the chain or the like.

[0048] The sprocket 6 has a plurality of engagement holes 61. Each engagement hole 61 is spaced apart from each other in the circumferential direction. Each engagement hole 61 overlaps with the corresponding first through holes 312 and second through holes 322 in an axial view.

[0049] <Stopper component> Figure 8 is a side view of the stopper member 5. As shown in Figures 1 and 8, the stopper member 5 works in cooperation with the first nut 8 and the second nut 9 to removably fasten the first plate 31 and the second plate 32. The sprocket 6 is fastened to the first plate 31 by the stopper member 5 and the first nut 8. The stopper member 5 is attached to the second rotating body 3. The stopper member 5 is configured to rotate integrally with the second rotating body 3.

[0050] The stopper member 5 has a stopper portion 51, a first threaded portion 52, a first intermediate portion 53, a second threaded portion 54, and a second intermediate portion 55. The stopper portion 51, the first threaded portion 52, the first intermediate portion 53, the second threaded portion 54, and the second intermediate portion 55 are integrally formed from each other. In detail, the stopper portion 51, the first threaded portion 52, the first intermediate portion 53, the second threaded portion 54, and the second intermediate portion 55 are integrally formed from a single member. The stopper member 5 is solid and does not have a cavity inside.

[0051] The stopper portion 51 is cylindrical. The stopper portion 51 extends in the axial direction. The stopper portion 51 faces the stopper surface 25 in the circumferential direction. The stopper portion 51 is positioned between the first plate 31 and the second plate 32 in the axial direction. The stopper portion 51 is sandwiched between the first plate 31 and the second plate 32. The stopper portion 51 is positioned within the notch 26 of the first rotating body 2.

[0052] The first threaded portion 52 is integrally formed with the stopper portion 51. The first threaded portion 52 extends in the axial direction. Threads are formed on the outer circumferential surface of the first threaded portion 52. The outer diameter of the first threaded portion 52 is smaller than that of the stopper portion 51.

[0053] The first threaded portion 52 is positioned on the first axial side relative to the stopper portion 51. The first threaded portion 52 is positioned on the first axial side relative to the first plate 31. Furthermore, the first threaded portion 52 is positioned on the first axial side relative to the sprocket 6.

[0054] The first intermediate portion 53 is positioned axially between the stopper portion 51 and the first threaded portion 52. Specifically, the first intermediate portion 53 extends from the stopper portion 51 toward the first axial direction. The first threaded portion 52 extends from the first intermediate portion 53 toward the first axial direction.

[0055] The first intermediate section 53 is cylindrical. The first intermediate section 53 extends in the axial direction. The length of the first intermediate section 53 is less than the sum of the thickness of the first plate 31 and the thickness of the sprocket 6. Also, the length of the first intermediate section 53 is greater than the thickness of the first plate 31. Note that the length of each part of the stopper member 5 refers to the axial dimension.

[0056] The first intermediate portion 53 has a smaller outer diameter than the stopper portion 51 and a larger outer diameter than the first threaded portion 52. The first intermediate portion 53 is positioned within the first through hole 312 and the engagement hole 61. The first intermediate portion 53 does not protrude axially in the first direction from within the first through hole 312 and the engagement hole 61.

[0057] The second threaded portion 54 is integrally formed with the stopper portion 51. The second threaded portion 54 extends in the axial direction. Threads are formed on the outer surface of the second threaded portion 54. The second threaded portion 54 has a smaller outer diameter than the stopper portion 51. The second threaded portion 54 has approximately the same outer diameter as the first threaded portion 52.

[0058] The second screw portion 54 is positioned on the second axial side relative to the stopper portion 51. The second screw portion 54 is positioned on the second axial side relative to the second plate 32.

[0059] The second intermediate portion 55 is positioned in the axial direction between the stopper portion 51 and the second threaded portion 54. Specifically, the second intermediate portion 55 extends from the stopper portion 51 to the second axial direction. The second threaded portion 54 extends from the second intermediate portion 55 to the second axial direction.

[0060] The second intermediate section 55 is cylindrical. The second intermediate section 55 extends in the axial direction. The length of the second intermediate section 55 is shorter than the length of the first intermediate section 53. The length of the second intermediate section 55 is less than the thickness of the second plate 32.

[0061] The second intermediate portion 55 has a smaller outer diameter than the stopper portion 51 and a larger outer diameter than the second threaded portion 54. The second intermediate portion 55 has approximately the same outer diameter as the first intermediate portion 53. The second intermediate portion 55 is located within the second through hole 322. The second intermediate portion 55 does not protrude from within the second through hole 322 toward the second axial direction.

[0062] <First and second nuts> The first nut 8 is screwed onto the first threaded portion 52. The first nut 8 works in cooperation with the stopper portion 51 to clamp the sprocket 6 and the first plate 31. The first nut 8 is a flange nut.

[0063] The second nut 9 is screwed onto the second threaded portion 54. The second nut 9 works in cooperation with the stopper portion 51 to clamp the second plate 32. The second nut 9 is a flange nut.

[0064] <crank arm> The crank arm 7 is configured to rotate integrally with the first rotating body 2. That is, the crank arm 7 is rotatably positioned around the rotation axis O. The crank arm 7 is attached to the inner flange portion 24 of the first rotating body 2. More specifically, the crank arm 7 is configured to spline-fit to the inner flange portion 24.

[0065] The crank arm 7 has an arm body portion 71 and a mounting portion 72. The arm body portion 71 extends radially. The mounting portion 72 extends axially from one of the ends of the arm body portion 71. A pedal (not shown) is attached to the other end of the arm body portion 71.

[0066] The tip portion 721 of the mounting portion 72 has a smaller outer diameter than the rest of the mounting portion 72. This tip portion 721 spline-fits to the inner flange portion 24. The tip portion 721 also penetrates the inner flange portion 24 in the axial direction. The tip portion 721 is then crimped and fixed to the inner flange portion 24. In detail, by crimping the tip portion 721, the tip portion 721 and the inner flange portion 24 become tightly fitted together. In addition, the outer diameter of the portion of the tip portion 721 that protrudes from the inner flange portion 24 in the first axial direction becomes larger due to the crimping process, and becomes larger than the inner diameter of the inner flange portion 24. As a result, the tip portion 721 cannot be removed from the inner flange portion 24, and it is possible to prevent the crank arm 7 and the first rotating body 2 from moving away from each other in the axial direction.

[0067] The mounting portion 72 has a mounting hole 722. This mounting hole 722 is rectangular in shape when viewed in the axial direction. A crankshaft (not shown) is fitted into this mounting hole 722, and the crank arm 7 rotates integrally with the crankshaft.

[0068] <Operation> The operation of the power transmission device 100 configured as described above will now be explained. First, when torque is input to the first rotating body 2 via the crank arm 7 by the user pedaling, the first rotating body 2 rotates in the rotational direction R. Then, torque is transmitted from the first rotating body 2 to the second rotating body 3 via the coil spring 4. As a result, the second rotating body 3 rotates in the rotational direction R, and torque is transmitted to the drive wheels.

[0069] Here, when the coil spring 4 is compressed and the torsional angle between the first rotating body 2 and the second rotating body 3 reaches a predetermined angle, the stopper surface 25 comes into contact with the stopper portion 51. By the stopper portion 51 coming into contact with the stopper surface 25 in this way, the first rotating body 2 is prevented from rotating further relative to the second rotating body 3. That is, the first rotating body 2 rotates relative to the second rotating body 3 until the stopper member 5 comes into contact with the stopper surface 25. After the stopper portion 51 comes into contact with the stopper surface 25, the first rotating body 2 rotates integrally with the second rotating body 3. The torsional angle between the first rotating body 2 and the second rotating body 3 when the stopper surface 25 comes into contact with the stopper portion 51 is called the maximum torsional angle. Note that when no torque is input to the power transmission device 100, the torsional angle between the first rotating body 2 and the second rotating body 3 is 0 degrees.

[0070] [Differentiation] Although embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications are possible without departing from the spirit of the invention. Furthermore, the following modifications can basically be applied simultaneously.

[0071] (a) In the above embodiment, the crank arm 7 was attached to the first rotating body 2 and the sprocket 6 was attached to the second rotating body 3, but the configuration of the power transmission device 100 is not limited to this. For example, the crank arm 7 may be attached to the first plate 31 or the second plate 32 of the second rotating body 3, and the sprocket 6 may be attached to the first rotating body 2.

[0072] (b) In the above embodiment, a pair of first notches 314 are formed in all first window portions 311, but the configuration of the first plate 31 is not limited thereto. For example, only one first notch 314 may be formed in each first window portion 311, or the first notch 314 may be formed in only one of the multiple first window portions 311. The same applies to the second plate 32. [Explanation of Symbols]

[0073] 2: First rotational body 21: Containment hole 27: Third contact surface 4: Coil spring 31: First Plate 311: First Window Section 313: First contact surface 314: 1st notch 315: First offset section 32: Second Plate 321: Second Window Section 323: Second contact surface 324:Second notch 325: Second offset section 100: Bicycle power transmission device

Claims

1. A first rotating body having a housing hole, A first plate having a first window and arranged to be rotatable relative to the first rotating body, The second plate has a second window portion and is configured to rotate integrally with the first plate, and is positioned to sandwich the first rotating body in the axial direction between itself and the first plate, A coil spring is disposed within the first window portion, the second window portion, and the housing hole, and elastically connects the first rotating body and the first and second plates. Equipped with, The first plate has a first contact surface that contacts the end face of the coil spring, and a first notch formed on the first contact surface. The second plate has a second contact surface that contacts the end face of the coil spring, and a second notch formed on the second contact surface. A power transmission device for bicycles.

2. The first plate has a first offset portion that is positioned radially inward with respect to the first notch and offset toward the first rotating body. The bicycle power transmission device according to claim 1.

3. The second plate has a second offset portion that is positioned radially inward with respect to the second notch and offset toward the first rotating body. The bicycle power transmission device according to claim 2.

4. The coil spring is not in contact with the first offset portion. The bicycle power transmission device according to claim 2.

5. The first rotating body has a third contact surface that contacts the coil spring, and the third contact surface does not have a notch. The bicycle power transmission device according to claim 1.

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