TWM673032U - Mid-mounted motor drive for electric-assisted bicycles - Google Patents

Abstract

A mid-mounted motor drive for an electric-assisted bicycle has a crankshaft forming a transmission portion in the middle, a harmonic reducer coaxially disposed around the crankshaft, an input end having a motor input shaft, and an output end being a connecting ring disposed at the bottom of a cup-shaped flexible gear. A central through-hole for the crankshaft to pass through is formed on the inner side of the connecting ring; a driving ring is respectively coupled to the connecting ring and the transmission portion, and the two driving rings are located within the flexible gear. Each is connected to a large-disc output shaft via a one-way drive structure. The large-disc output shaft has a through-hole in the middle and a large-disc seat at the right end. This invention fully utilizes the space within the flexible gear by accommodating the two drive rings, the one-way drive structure, and part of the large-disc output shaft. This effectively reduces the space that the transmission device would otherwise occupy axially, thus solving the problem of insufficient space at the installation site.

Description

Mid-mounted motor drive for electric-assisted bicycles

This work relates to electric-assisted bicycles; in particular, to a mid-mounted motor drive system for electric-assisted bicycles.

The applicant in this case previously applied for and received Taiwan Patent No. TWI821957B for the "Flexible Gear Connection Structure" invention. The harmonic reducer in this invention is threaded with a mating component via a flexible gear connection seat. This significantly reduces the size and weight of the harmonic reducer while maintaining the same rated torque. This makes the structure suitable for installation in limited spaces and meets requirements for lightweight design and threading holes.

When the harmonic speed reducer of the aforementioned invention is used in a mid-mounted motor drive system on an electric power-assisted bicycle, it is installed within the bottom bracket shell of the electric power-assisted bicycle along with a transmission structure such as a crankshaft. After reducing the motor's rotational output speed, the power is transmitted to the large plate output shaft. Although the harmonic speed reducer invented by the aforementioned applicant is smaller than conventional harmonic speed reducers, because the large plate output shaft, which serves as a counter-acting component, is located outside the flexible gear, it still cannot effectively reduce the space occupied by the transmission system in the axial direction, and thus cannot further solve the problem of insufficient space at the device installation site.

In light of this, the present invention aims to provide a transmission device using a harmonic reduction gear as a deceleration mechanism, which can be installed at the bottom bracket of an electric power-assisted bicycle. By fully utilizing the space within the flexible gear to accommodate the structure that would otherwise protrude axially from the flexible gear, the space occupied by the transmission device in the axial direction is effectively reduced, thereby solving the problem of insufficient space at the device installation site.

To achieve the above objectives, this invention provides a mid-mounted motor drive for an electric-assisted bicycle, comprising a crankshaft, a harmonic speed reducer, a first drive ring, a second drive ring, and a large plate output shaft. The crankshaft has a shaft, with crank couplings formed at each end, and a drive unit formed in the middle of the crankshaft. The harmonic reducer is coaxially arranged around the shaft with the crankshaft and includes a rigid gear, a flexible gear, a motor input shaft, and a flexible bearing; the inner circumference of the rigid gear has a plurality of rigid gear teeth; the flexible gear is cup-shaped and includes a flexible peripheral wall, and a plurality of flexible gear teeth are formed on the outer circumference of one side of the flexible peripheral wall. The flexible gear teeth are engaged with the rigid gear. The gear is connected to an inwardly extending ring at the end edge of the other side of the flexible peripheral wall. The inner periphery of the ring is connected to a connecting ring. The inner side of the connecting ring forms a through-hole, and the shaft passes through the center of the through-hole. The motor input shaft system tube has an elliptical cam formed at one end. The flexible bearing is sleeved on the elliptical cam and abuts against the inner periphery of the flexible peripheral wall with its outer periphery.

The first drive ring is coaxially arranged around the shaft and located in the flexible gear, and the first drive ring is coupled to the connecting ring. The second drive ring is coaxially arranged around the shaft and located in the flexible gear, and one side of the second drive ring is coupled to the transmission part. The large disc output shaft is a tubular body that rotatably fits around the shaft. The large disc output shaft includes a straight tube, a large disc seat, and an annular wall connected between the straight tube and the large disc seat. The straight tube passes through the through hole and extends into the flexible gear. A drive portion is formed on the straight tube. A first one-way drive structure is provided between the drive portion and the first drive ring, and a second one-way drive structure is provided between the drive portion and the second drive ring. A large disc coupling portion is formed on the side of the large disc seat facing away from the harmonic reducer.

The effect of this invention is that when the mid-mounted motor drive device of the electric-assisted bicycle is installed on the bottom bracket of the electric-assisted bicycle, the crankshaft can be rotated by human power, and the crankshaft drives the large plate output shaft to rotate through the second drive ring and the second one-way drive structure, thereby driving the electric-assisted bicycle forward. Alternatively, the electric-assisted bicycle can be driven forward by a motor directly connected to the motor input shaft, which is decelerated by the harmonic reducer and drives the large plate output shaft to rotate through the first drive ring and the first one-way drive structure.

This invention benefits from the small size and light weight of the harmonic reducer. Furthermore, the first drive ring, first one-way drive structure, second drive ring, second one-way drive structure, and part of the large plate output shaft are housed within the flexible gear. This fully utilizes the space within the flexible gear and accommodates structures that would otherwise protrude axially from the flexible gear in the structural design. This further reduces the axial volume of the invention, solving the problem of insufficient space within the bottom bracket shell and leaving more room around the crankshaft for the motor or other electronic components.

To more clearly illustrate this invention, a preferred embodiment is provided below with detailed descriptions along with accompanying drawings. Referring to Figures 1 to 3A and Figures 5 and 6, a mid-mounted motor transmission device 100 for an electric-assisted bicycle, a preferred embodiment of this invention, is shown. The device comprises a crankshaft 10, a harmonic speed reducer 20, a first drive ring 30, a second drive ring 40, a large plate output shaft 50, a first one-way drive structure 60, and a second one-way drive structure 70, wherein:

Referring to Figures 1 through 3A , the center of the crankshaft 10 defines a rotational axis L, which extends in a left-right direction. The crankshaft 10 includes a shaft 12, with crank couplings 14 formed at the left and right ends of the shaft 12. In the preferred embodiment, the two crank couplings 14 are splines formed on the outer circumference of each end of the shaft 12. In other preferred embodiments, the crank couplings 14 may be square or octagonal heads formed on each end of the shaft 12. A transmission portion 16 is formed in the center of the crankshaft 10. In the preferred embodiment, the transmission portion 16 is a gear integrally connected to the outer circumference of the shaft 12. The transmission portion 16 divides the left and right sides of the shaft 12 into a left section 121 and a right section 122 .

The harmonic reducer 20 is coaxially disposed around the shaft 12, with its axis coinciding with the rotation axis L. Specifically, the harmonic reducer 20 is disposed around the right section 122. The harmonic reducer 20 includes a rigid gear 22, a flexible gear 24, a motor input shaft 26, and a flexible bearing 28. The rigid gear 22 has a plurality of locking holes 222 arranged in a circumferential and evenly spaced arrangement, and a plurality of rigid gear teeth 221 are formed on the inner circumference of the rigid gear 22. The flexible gear 24 is a cup-shaped structure and includes a flexible peripheral wall 241, a plurality of flexible gear teeth 242, a ring 243, and a connecting ring 244. The flexible gear teeth 242 are formed on the outer circumference of one side of the flexible peripheral wall 241 and engage with the steel gear 221. The ring 243 is connected to the end edge of the other side of the flexible peripheral wall 241. Specifically, the ring 243 is an annular plate with an outer circumference connected to the end edge of the flexible peripheral wall 241 and an inner circumference extending inward toward the rotation axis L.

The connecting ring 244 is connected to the inner periphery of the ring plate 243. In the preferred embodiment, the connecting ring 244 extends from the inner periphery of the ring plate 243 into the flexible gear 24. The outer peripheral surface of the connecting ring 244 has an external connecting thread 245. The inner side of the connecting ring 244 forms a through hole 246. The diameter of the through hole 246 is larger than the outer diameter of the shaft 12. The shaft 12 passes through the center of the through hole 246. The motor input shaft 26 is a tubular structure, and an elliptical cam 261 is formed on one end of the motor input shaft 26 facing the connecting ring 244. The inner circumference of the flexible bearing 28 is fitted on the outer circumference of the elliptical cam 261, and the outer circumference of the flexible bearing 28 abuts against the inner circumference of the flexible peripheral wall 241.

Referring to Figures 3 to 7 , the first drive ring 30 is coaxially and rotatably disposed around the shaft 12 , with the axis of the first drive ring 30 coinciding with the rotation axis L. The first drive ring 30 is positioned within the flexible gear 24 . An inner connecting thread 32 is formed on the inner circumference of one side of the first drive ring 30 . A stop surface 34 is formed on the portion of the first drive ring 30 adjacent to the inner connecting thread 32 . The first drive ring 30 is threadedly engaged with the outer connecting thread 245 via the inner connecting thread 32, and the stop surface 34 abuts against the end of the connecting ring 244, thereby coaxially coupling the first drive ring 30 to the connecting ring 244. A first one-way structural seat 36 is formed on the side of the first drive ring 30 facing away from the connecting ring 244. A plurality of first ratchet grooves 361 are formed in a circumferential and spaced arrangement on the first one-way structural seat 36, each opening toward the rotation axis L. Each first ratchet groove 361 has a first pivot portion 362 and a first spring portion 363 formed on either side of the first ratchet groove 361 in the direction of rotation about the rotation axis L.

The second drive ring 40 is coaxially and rotatably disposed around the shaft 12. In the preferred embodiment, the second drive ring 40 is located within the flexible gear 24. The side of the second drive ring 40 facing away from the connecting ring 244 engages with the transmission portion 16 of the crankshaft 10. Specifically, the side of the second drive ring 40 facing away from the connecting ring 244 forms a connecting gear 42. The connecting gear 42 engages with the gear-type transmission portion 16 to achieve power transmission from the crankshaft 10. A second one-way structural seat 44 is formed on the other side of the second drive ring 40. A plurality of second ratchet grooves 441 are formed on the second one-way structural seat 44 in a circumferential and spaced arrangement, each opening facing the direction of the rotation axis L. Each second ratchet groove 441 has a second pivot portion 442 and a second elastic portion 443 formed on both sides of the second ratchet groove 441 corresponding to the rotation direction centered on the rotation axis L.

The large disc output shaft 50 is a tubular structure that rotatably fits around the shaft 12. Specifically, the large disc output shaft 50 rotatably fits around the right section 122. The large disc output shaft 50 comprises a straight tube 52, a large disc seat 54, and an annular wall 53. The inner periphery of the annular wall 53 is connected to the straight tube 52, and the outer periphery of the annular wall 53 is connected to the large disc seat 54. The straight tube 52 passes through the through hole 246 of the connecting ring 244 and extends into the flexible gear 24. A driving portion 521 is formed at the portion of the straight tube 52 located inside the flexible gear 24. In the preferred embodiment, the driving portion 521 is a plurality of ratchets formed around the outer circumference of the straight tube 52.

The large disc seat 54 is located adjacent to the crank coupling 14 on the right side along the rotation axis L. The outer diameter of the large disc seat 54 is larger than the outer diameter of the straight tube 52, and the inner diameter of the large disc seat 54 is larger than the inner diameter of the straight tube 52. A large disc coupling portion 541 is formed on the side of the large disc seat 54 facing away from the harmonic reducer 20. In the preferred embodiment, the large disc coupling portion 541 is a plurality of ratchets formed around the outer circumference of the large disc seat 54. An inner bearing 56 is disposed between the inner circumference of the large disc seat 54, which is adjacent to the harmonic reducer 20, and the outer circumference of the shaft 12. The outer circumference of the inner bearing 56 abuts against the inner circumference of the large disc seat 54, and the inner circumference of the inner bearing 56 abuts against the outer circumference of the shaft 12. In this way, the inner bearing 56 supports the large disc output shaft 50 for rotation around the shaft 12. An outer bearing 58 is sleeved onto the outer circumference of the large disc seat 54, which is adjacent to the harmonic reducer 20. The inner bearing 56 and the outer bearing 58 are opposed to each other on the inside and outside.

A first one-way driving structure 60 is provided between the side of the driving portion 521 close to the connecting ring 244 and the first one-way structural seat 36 of the first driving ring 30. The first one-way driving structure 60 includes a plurality of first ratchet blocks 62 and a plurality of first springs 64. The inner end of each first ratchet block 62 is pivotally connected to each first pivot portion. 362, the outer end of each first ratchet block 62 engages with a side of the drive portion 521 near the connecting ring 244; the inner end of each first spring plate 64 is embedded in each first spring plate portion 363, and the outer end of each first spring plate 64 abuts against each first ratchet block 62, so that each first ratchet block 62 unidirectionally engages with the drive portion 521. Thus, when the electric motor rotor is connected to the motor input shaft 26, the speed reduction energy of the harmonic reducer 20 drives the first drive ring 30 to unidirectionally rotate the large plate output shaft 50.

A second one-way driving structure 70 is provided between the other side of the driving portion 521 away from the connecting ring 244 and the second one-way structural seat 44 of the second driving ring 40. The second one-way driving structure 70 includes a plurality of second ratchet blocks 72 and a plurality of second springs 74. The inner end of each second ratchet block 72 is pivotally connected to each second spring. The outer ends of the second ratchet blocks 72 of the second pivot portion 442 engage with the other side of the drive portion 521 facing away from the connecting ring 244. The inner ends of the second springs 74 are embedded in the second spring portions 443, with their outer ends abutting against the second ratchet blocks 72, allowing the second ratchet blocks 72 to unidirectionally engage with the drive portion 521. Consequently, when the crankshaft 10 rotates about the rotation axis L, it drives the second drive ring 40 to unidirectionally rotate the large plate output shaft 50. In addition, when the crankshaft 10 and the harmonic reducer 20 simultaneously drive the first one-way drive structure 60 and the second one-way drive structure 70 to drive the large plate output shaft 50 to rotate, the one with a faster rotation speed can drive the large plate output shaft 50 to rotate together.

In addition to the preferred embodiment described above, the present invention further provides that the first one-way drive structure 60 and the second one-way drive structure 70 are configured to have a first ratchet block 62 or a second ratchet block 72, which can respectively unidirectionally engage with the drive portion 521 of the large plate output shaft 50. Alternatively, the first one-way drive structure 60 and the second one-way drive structure 70 can be modified into one-way bearings, which are respectively coupled between the drive portion 521 and the first one-way structure seat 36, and between the drive portion 521 and the second one-way structure seat 44, thereby similarly achieving the function of unidirectionally driving the large plate output shaft 50 to rotate via the first drive ring 30 or the second drive ring 40.

When the preferred embodiment of the invention is used, as shown in FIG1, FIG3 and FIG3A, since there is space for the motor to be installed around the left section 121, when the mid-mounted motor transmission device 100 of the electric-assisted bicycle is installed on the bottom bracket of the electric-assisted bicycle (not shown), the harmonic reducer 20 can be screwed to the inner wall of the bottom bracket through the locking holes 222 of the rigid gear 22. The stem 10 passes through the center of the bottom bracket and is coupled to a crank and pedal (not shown) at each crank coupling 14. The top plate of an electric bicycle (not shown) is then fitted onto the top plate coupling 541 of the top plate base 54. A motor (not shown) is mounted within the bottom bracket at a position corresponding to the periphery of the left section 121. The motor's rotor is directly connected to the motor input shaft 26 of the harmonic reducer 20.

Thus, by utilizing the characteristics of the harmonic reducer 20 being small in size, high in speed reduction ratio, and light in weight, and by combining the design that the connecting ring 244 of the harmonic reducer 20 is screwed with the first drive ring 30, and the design that the first drive ring 30, the second drive ring 40, the first one-way drive structure 60, the second one-way drive structure 70, and a portion of the large plate output shaft 50 are all housed in the flexible gear 24, the cost-effective harmonic reducer 20 and the first drive ring 30, the second drive ring 40, the first one-way drive structure 60, the second one-way drive structure 70, and a portion of the large plate output shaft 50 are all housed in the flexible gear 24, can be created. The volume occupied by the dynamic structure 60, the second one-way drive structure 70, and the large crank output shaft 50 along the direction of the rotation axis L increases the space available for the motor or other electronic components, thereby solving the problem of insufficient space in the bottom bracket shell. Furthermore, the crankshaft 10 can input the power of the user's pedaling to the large crank output shaft 50 for output to drive the electric-assisted bicycle forward, and the motor input shaft can input the power output of the motor to the large crank output shaft 50 for output to drive the electric-assisted bicycle forward.

The above description is merely an example of the best possible implementation of this invention. Any equivalent variations made by applying the description of this invention and the scope of patent application should be included in the patent scope of this invention.

100: Mid-Motor Drive for an Electric-Assisted Bicycle 10: Crankshaft 12: Shaft 121: Left Section 122: Right Section 14: Crank Joint 16: Drive 20: Harmonic Reducer 22: Rigid Gear 221: Rigid Gear 222: Locking Hole 24: Flexible Gear 241: Flexible Peripheral Wall 242: Flexible Pulley Gear 243: Ring 244: Connecting Ring 245: External Connecting Thread 246: Through Hole 26: Motor Input Shaft 261: Elliptical Cam 28: Flexible Bearing 30: First Drive Ring 32: Internal Connecting Thread 34: Stop Surface 36: First One-Way Structural Seat 3 61: First ratchet groove 362: First pivot portion 363: First spring portion 40: Second drive ring 42: Connecting gear 44: Second one-way structure seat 441: Second ratchet groove 442: Second pivot portion 443: Second spring portion 50: Large disc output shaft 52: Straight tube 521: Drive portion 53: Annular wall 54: Large disc seat 541: Large disc coupling portion 56: Inner bearing 58: Outer bearing 60: First one-way drive structure 62: First ratchet block 64: First spring 70: Second one-way drive structure 72: Second ratchet block 74: Second spring L: Rotating shaft

Figure 1 is a perspective view of a preferred embodiment of this invention. Figure 2 is a side view of the preferred embodiment of this invention. Figure 3 is a cross-sectional view taken along line 3-3 of Figure 2. Figure 3A is an enlarged view of the area marked 3A in Figure 3. Figure 4 is a side view of the preferred embodiment of this invention. Figure 5 is a cross-sectional view taken along line 5-5 of Figure 4. Figure 6 is a cross-sectional view taken along line 6-6 of Figure 4. Figure 7 is a cross-sectional view taken along line 7-7 of Figure 4.

100: Mid-mounted motor drive for electric-assisted bicycles

10: Crankshaft

12: Shaft

121: Left Section

14: Crank joint

16: Transmission

20: Harmonic reducer

22: Rigid gear

222: Keyhole

24: Flexible gear

26: Motor input shaft

50: Large plate output shaft

541: Plate junction

58: External bearing

L: Rotation axis

Claims (9)

A mid-mounted motor transmission device for an electric-assisted bicycle comprises: a crankshaft having a shaft, wherein the two ends of the shaft respectively form a crank coupling portion, and a transmission portion is formed in the middle of the crankshaft; a harmonic reducer is coaxially arranged around the shaft with the crankshaft and comprises a rigid gear, a flexible gear, a motor input shaft, and a flexible bearing; the inner circumference of the rigid gear is provided with a plurality of rigid gear teeth; the flexible gear The wheel is cup-shaped and includes a flexible peripheral wall. A plurality of flexible gears are formed on the outer peripheral surface of one side of the flexible peripheral wall. These flexible gears are engaged with the steel gears. An inwardly extending ring is connected to the end edge of the other side of the flexible peripheral wall. The inner periphery of the ring is connected to a connecting ring. A through-hole is formed on the inner side of the connecting ring. The shaft passes through the center of the through-hole. The motor input shaft system tube has an elliptical cam formed on one end. The flexible bearing is sleeved on the elliptical ring. The circular cam is abutted against the inner circumference of the flexible peripheral wall with its outer circumference; a first drive ring is coaxially arranged around the shaft and located in the flexible gear, the first drive ring is coupled to the connecting ring; a second drive ring is coaxially arranged around the shaft and located in the flexible gear, one side of the second drive ring is coupled to the transmission part; and a large plate output shaft is a tubular body and is rotatably fitted around the shaft, the large plate output shaft is a cylindrical body and is rotatably fitted around the shaft, the large plate output shaft is a cylindrical body and is rotatably fitted around the shaft, the large plate output shaft is a cylindrical body and is rotatably fitted around the shaft, the large plate output shaft is a cylindrical body and is rotatably fitted around the shaft, the large plate output shaft is a cylindrical body and is rotatably fitted around the shaft, the large plate output shaft is a cylindrical body and is rotatably fitted around the shaft, the large plate output shaft is a cylindrical body and is rotatably fitted around the shaft, the large plate output shaft is a cylindrical body and is rotatably fitted around the shaft, the large plate output shaft is a cylindrical body and is rotatably fitted around the shaft, the large plate output shaft is a cylindrical body and is rotatably fitted around the shaft, the large plate output shaft is a cylindrical body and is rotatably fitted around the shaft, the large plate output shaft is a cylindrical body and is The disc output shaft includes a straight tube, a large disc seat, and an annular wall connected between the straight tube and the large disc seat. The straight tube passes through the through hole and extends into the flexible gear. A drive portion is formed on the straight tube. A first one-way drive structure is provided between the drive portion and the first drive ring, and a second one-way drive structure is provided between the drive portion and the second drive ring. A large disc coupling portion is formed on the side of the large disc seat facing away from the harmonic reducer. A mid-mounted motor transmission device for an electric-assisted bicycle as described in claim 1, wherein the connecting ring extends into the flexible gear and has an outer connecting thread on the outer periphery of the connecting ring; an inner connecting thread is formed on the inner periphery of one side of the first drive ring, and a stop surface is formed on the portion of the first drive ring adjacent to the inner connecting thread, the inner connecting thread is threaded into the outer connecting thread, the stop surface abuts against the connecting ring, and a first one-way structural seat is formed on the other side of the first drive ring; the first one-way drive structure is arranged between the drive portion and the first one-way structural seat of the first drive ring. A mid-mounted motor transmission device for an electric-assisted bicycle as described in claim 2, wherein one side of the second drive ring is coupled to the transmission portion, and the other side of the second drive ring forms a second one-way structural seat; the second one-way drive structure is disposed between the drive portion and the second one-way structural seat of the second drive ring. The mid-mounted motor transmission device for an electric-assisted bicycle as described in claim 3, wherein the transmission portion of the crankshaft is a gear; a connecting gear is formed on one side of the second drive ring, and the connecting gear is engaged with the transmission portion. A mid-mounted motor transmission device for an electric-assisted bicycle as described in claim 2, wherein the driving portion is formed as a plurality of ratchets on the outer circumferential surface of the straight tube; a plurality of first ratchet grooves are formed in a circumferential and spaced arrangement on the first one-way structural seat, and a first pivot portion and a first elastic portion are formed on both sides of each first ratchet groove; the first one-way driving structure includes a plurality of first ratchet blocks and a plurality of first elastic plates, the inner end of each first ratchet block is pivoted to each first pivot portion, and the outer end of each first ratchet block is engaged with the driving portion; the inner end of each first elastic plate is embedded in each first elastic plate portion, and the outer end of each elastic plate abuts against each first ratchet block. As described in claim 3, the mid-mounted motor transmission device of the electric-assisted bicycle, wherein the driving portion is formed with multiple ratchets on the outer peripheral surface of the straight tube; a plurality of second ratchet grooves are formed in a circumferential and spaced arrangement on the second one-way structural seat, and a second pivot portion and a second elastic portion are formed on both sides of each second ratchet groove; the second one-way driving structure includes a plurality of second ratchet blocks and a plurality of second elastic plates, the inner end of each second ratchet block is pivoted to each second pivot portion, and the outer end of each second ratchet block is engaged with the driving portion; the inner end of each second elastic plate is embedded in each second elastic plate portion, and the outer end of each elastic plate abuts against each second ratchet block. As described in claim 1, the mid-mounted motor transmission device of the electric-assisted bicycle, wherein the outer diameter of the large disc seat is larger than the outer diameter of the straight tube, the inner diameter of the large disc seat is larger than the inner diameter of the straight tube, an inner support bearing is provided between the inner circumference of the large disc seat and the outer circumference of the shaft, and an outer support bearing is sleeved on the outer circumference of the large disc seat; the two crank couplings are respectively formed at the left and right end portions of the shaft, and the large disc coupling is adjacent to the crank coupling on the right side. A mid-mounted motor transmission device for an electric-assisted bicycle as described in claim 1, wherein the transmission portion divides the left and right sides of the shaft into a left section and a right section; the harmonic reducer is coaxially arranged around the right section of the shaft with the crankshaft; the large plate output shaft is a tubular body and is rotatably fitted around the right section of the shaft, and the large plate seat is adjacent to the crank coupling on the right side. In the mid-mounted motor transmission device of the electric-assisted bicycle as described in claim 1, each crank coupling portion is a spline; and the large plate coupling portion is a plurality of ratchets formed around the outer peripheral surface of the large plate base.