Electrically assisted drive unit and bicycle

Abstract

To provide a power-assisted drive unit which enables easy assembly of components during manufacturing and easily achieves reduction of the size and the weight.SOLUTION: A power-assisted drive unit 1 includes a crankshaft 10, a casing 20, a motor 40, and a speed reducer 50. The casing is supported through a first bearing 81 in a radial direction by the crankshaft. The motor and the speed reducer are disposed in a space between the crankshaft and the casing. The motor has a stator 41 and a rotor 43. The stator is fixed to the casing. The rotor is supported through a second bearing 82 in the radial direction by the crankshaft. The rotor rotates in response to a load exerted on the crankshaft. The speed reducer reduces a speed of rotation of the rotor to output the rotation to the crankshaft.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an electrically assisted drive unit and a bicycle. [Background technology]

[0002] Conventionally, bicycles equipped with an electric assist drive unit having a motor and a reduction gear are known. The electric assist drive unit drives the motor to assist the rotation of the pedals when the user's load is large, such as when the bicycle starts moving or travels uphill. A conventional electric assist drive unit is described, for example, in Japanese Patent No. 6637997. [Patent Document 1] Patent No. 6637997 specification Summary of the Invention [Problem to be solved by the invention]

[0003] An electric power-assisted drive unit has a structure in which a motor and a reduction gear are housed in the space between a crankshaft connected to the pedals of a bicycle and a casing of the electric power-assisted drive unit. However, in conventional electric power-assisted drive unit structures, the motor rotor is supported by the casing. This makes the assembly structure of the motor and reduction gear to the crankshaft and casing complicated. In addition, the bearings that support the rotor by the casing have a large diameter, making it difficult to make the electric power-assisted drive unit smaller and lighter.

[0004] An object of the present invention is to provide an electrically assisted drive unit that is easy to assemble during manufacture and that can be easily made small and lightweight. [Means for solving the problem]

[0005] The first invention of the present application isAn electrically assisted drive unit that assists rotation by human power with the driving force of a motor includes a crankshaft that rotates around a central axis by human power, a casing that is supported by the crankshaft via a first bearing in the radial direction, and a motor and a reducer that are arranged in the space between the crankshaft and the casing. The motor has a stator fixed to the casing, a circuit board that supplies a drive current to the stator in accordance with the load on the crankshaft, and a rotor that rotates around the central axis by a rotating magnetic field generated from the stator by the drive current. The reducer reduces the rotation of the rotor and outputs it to the crankshaft, and the rotor is supported by the crankshaft via a second bearing in the radial direction, The reducer has an intermediate rotating body fixed to the rotor, a fixed member fixed to the casing, and an output rotating body that rotates at a reduced rotational speed around the central axis, and as the intermediate rotating body rotates, the output rotating body rotates relative to the fixed member at a lower rotational speed than the intermediate rotating body, and the fixed member is a fixed internal gear that is annular about the central axis, and the reducer has a movable internal gear that is annular about the central axis and rotates together with the output rotating body, the number of teeth of the fixed internal gear is different from the number of teeth of the movable internal gear, and the reducer further has a planetary gear that meshes with the fixed internal gear and the movable internal gear and revolves around the central axis as the intermediate rotating body rotates. A second invention of the present application is an electric assist drive unit that assists rotation by human power with the driving force of a motor, comprising: a crankshaft that rotates about a central axis by human power, a casing supported by the crankshaft via a first bearing in the radial direction, and a motor and a reducer disposed in a space between the crankshaft and the casing. The motor has a stator fixed to the casing, a circuit board that supplies a drive current to the stator in response to a load on the crankshaft, and a rotor that rotates about the central axis by a rotating magnetic field generated from the stator by the drive current. The reducer reduces the rotation of the rotor and outputs it to the crankshaft, the rotor being supported on the crankshaft radially via a second bearing, the reducer has an intermediate rotor fixed to the rotor, a fixed member fixed to the casing, and an output rotor rotating at a reduced rotation speed around the central axis, and as the intermediate rotor rotates, the output rotor rotates at a lower rotation speed relative to the fixed member than the intermediate rotor, and the fixed member is an annular non-rotating ring centered on the central axis, the reducer has a rotatable ring centered on the central axis and is annular, and rotates together with the output rotor, an inner diameter of the rotatable ring is different from an inner diameter of the non-rotating ring, and the reducer further has a planetary roller that contacts the non-rotating ring and the rotatable ring and revolves around the central axis as the intermediate rotor rotates. The third invention of the present application is an electric assist drive unit that assists rotation by human power with the driving force of a motor, comprising: a crankshaft that rotates about a central axis by human power, a casing supported by the crankshaft via a first bearing in the radial direction, and a motor and a reducer disposed in a space between the crankshaft and the casing. The motor has a stator fixed to the casing, a circuit board that supplies a drive current to the stator in response to a load on the crankshaft, and a rotor that rotates about the central axis by a rotating magnetic field generated from the stator by the drive current. The reducer reduces the rotation speed of the rotor and outputs the reduced rotation speed to the crankshaft, the rotor being supported by the crankshaft via a second bearing in the radial direction, the reducer having an intermediate rotor fixed to the rotor, a fixed member fixed to the casing, and an output rotor rotating at a reduced rotation speed around the central axis, and as the intermediate rotor rotates, the output rotor rotates at a lower rotation speed relative to the fixed member than the intermediate rotor, and the fixed member is fixed to the central axis. the reduction gear has a fixed internal gear in a circular ring shape centered on an axis, the reduction gear has a movable internal gear in a circular ring shape centered on the central axis and rotates together with the output rotor, the number of teeth of the fixed internal gear is different from the number of teeth of the movable internal gear, the intermediate rotor includes a non-circular cam whose outer diameter varies depending on the circumferential position, and the reduction gear further has an annular external gear that flexes and deforms when pressed against the outer circumferential surface of the cam and meshes with the fixed internal gear and the movable internal gear at a portion of the circumferential direction. A fourth invention of the present application is an electric assist drive unit that assists rotation by human power with the driving force of a motor, comprising: a crankshaft that rotates about a central axis by human power, a casing supported by the crankshaft via a first bearing in the radial direction, and a motor and a reducer that are arranged in a space between the crankshaft and the casing. The motor has a stator fixed to the casing, a circuit board that supplies a drive current to the stator in response to a load on the crankshaft, and a rotor that rotates about the central axis by a rotating magnetic field generated from the stator by the drive current. The reducer reduces the rotation of the rotor and outputs it to the crankshaft, the rotor being supported on the crankshaft radially via a second bearing, and the reducer has an intermediate rotor fixed to the rotor and including a non-circular cam whose outer diameter varies depending on the circumferential position, an annular internal gear centered on the central axis, an external gear that is pressed against the outer circumferential surface of the cam and flexes and deforms, and meshes with the internal gear at a part of the circumferential direction, and an output rotor that rotates around the central axis at a reduced rotation speed, and one of the internal gear and the external gear is fixed to the casing, and the other of the internal gear and the external gear rotates around the central axis together with the output rotor at a rotation speed lower than that of the intermediate rotor. A fifth invention of the present application is an electric assist drive unit that assists rotation by human power with the driving force of a motor, comprising: a crankshaft that rotates about a central axis by human power, a casing supported by the crankshaft via a first bearing in the radial direction, and a motor and a reducer that are arranged in a space between the crankshaft and the casing. The motor has a stator fixed to the casing, a circuit board that supplies a drive current to the stator in response to a load on the crankshaft, and a rotor that rotates about the central axis by a rotating magnetic field generated from the stator by the drive current. The reducer reduces the rotation of the rotor and outputs it to the crankshaft, the rotor is supported on the crankshaft radially via a second bearing, and further includes a one-way clutch between the output rotor and the crankshaft that transmits only rotation in one direction around the central axis, the output rotor has a cylindrical sleeve that protrudes axially toward the motor, and the one-way clutch is located radially between the sleeve and the crankshaft. The sixth invention of the present application is an electric assist drive unit that assists rotation by human power with the driving force of a motor, comprising: a crankshaft that rotates around a central axis by human power; a casing that is supported by the crankshaft via a first bearing in the radial direction; and a motor and a reducer that are arranged in a space between the crankshaft and the casing. The motor has a stator fixed to the casing, a circuit board that supplies a drive current to the stator in response to a load on the crankshaft, and a rotor that rotates around the central axis by a rotating magnetic field generated from the stator by the drive current. The reducer reduces the rotation of the rotor and outputs it to the crankshaft, the rotor is supported by the crankshaft via a second bearing in the radial direction, the crankshaft is rotatably supported with respect to a frame, the casing has a rotation stopper that contacts the frame, and the rotation stopper contacts the frame to stop the rotation of the casing around the central axis. Effect of the Invention

[0006] According to the present invention, the rotation of the crankshaft by human power can be assisted by the driving force generated by the motor. The casing is supported on the crankshaft via a first bearing. The rotor of the motor is also supported on the crankshaft via a second bearing. This allows parts to be assembled around the crankshaft. This makes it easy to manufacture the electric assist drive unit. Also, the second bearing can be made smaller than when the rotor is supported by the casing. This makes it easy to make the electric assist drive unit smaller and lighter. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram of a bicycle equipped with an electrically assisted drive unit. [Diagram 2]FIG. 2 is a side view of the electric assist drive unit. [Diagram 3] FIG. 3 is a vertical cross-sectional view of the electric assist drive unit. [Figure 4] FIG. 4 is a cross-sectional view of the electric assist drive unit as seen from the position AA in FIG. [Diagram 5] FIG. 5 is a vertical cross-sectional view of an electric assist drive unit according to a first modified example. [Figure 6] FIG. 6 is a vertical cross-sectional view of an electric assist drive unit according to a second modified example. [Figure 7] FIG. 7 is a vertical cross-sectional view of an electric assist drive unit according to a third modified example. [Figure 8] FIG. 8 is a cross-sectional view of the electric assist drive unit as seen from the position BB in FIG. [Figure 9] FIG. 9 is a vertical cross-sectional view of an electric assist drive unit according to a fourth modified example. [Figure 10] FIG. 10 is a vertical cross-sectional view of an electric assist drive unit according to a fifth modified example. [Figure 11] FIG. 11 is a cross-sectional view of an electric assist drive unit according to a sixth modified example. [Figure 12] FIG. 12 is a side view of an electric assist drive unit according to a seventh modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings.

[0009] <1. About bicycles> FIG. 1 is a schematic diagram of a bicycle 100 equipped with an electric assist drive unit 1 according to an embodiment of the present invention. As shown in FIG. 1, the bicycle 100 includes a front wheel 110, a rear wheel 120, pedals 130, and a roller chain 140. The pedals 130 are disposed on each of both sides of the bicycle 100. Hereinafter, one of the directions in which the pedals 130 rotate is referred to as the "forward direction." When a user pedals the pedals 130 in the forward direction, the rotational motion of the pedals 130 is transmitted to the rear wheel 120 via the roller chain 140. This causes the rear wheel 120 to rotate, and the rotation of the rear wheel 120 and the front wheel 110 causes the bicycle 100 to move forward.

[0010] The bicycle 100 also includes an electric assist drive unit 1. The electric assist drive unit 1 is disposed between the pedals 130 disposed on both sides of the bicycle 100. The electric assist drive unit 1 is also disposed inside a chain cover 141 that covers a roller chain 140. When the load on the pedals 130 is large, such as when starting off or riding uphill, the electric assist drive unit 1 supplies a rotational drive force in the forward direction to the pedals 130. This reduces the force with which the user pedals the pedals 130. As a result, the user can ride the bicycle 100 with ease.

[0011] <2. Electrically assisted drive unit> Next, the structure of the electric assist drive unit 1 will be described.

[0012] Fig. 2 is a side view of the electric assist drive unit 1. Fig. 3 is a vertical cross-sectional view of the electric assist drive unit 1. This electric assist drive unit 1 is a device that assists the rotational motion of a pedal 130 caused by human power with the driving force of a motor 40. As shown in Figs. 2 and 3, the electric assist drive unit 1 includes a crankshaft 10, a casing 20, a torque sensor 30, a motor 40, a reducer 50, a one-way clutch 60, and a sprocket 70.

[0013] In the following description, the direction parallel to the central axis of the crankshaft 10 is referred to as the "axial direction," the direction perpendicular to the central axis is referred to as the "radial direction," and the direction along the arc centered on the central axis is referred to as the "circumferential direction." However, the above "parallel direction" also includes a direction that is approximately parallel. Furthermore, the above "orthogonal direction" also includes a direction that is approximately orthogonal.

[0014] Crankshaft 10 is a cylindrical member extending along central axis 9. Both axial ends of crankshaft 10 protrude outside casing 20. As shown in FIG. 2, crankshaft 10 is rotatably supported by frame 150 of bicycle 100 via a pair of bearings 80. Pedals 130 are fixed to both axial ends of crankshaft 10, respectively. When a user of bicycle 100 pedals pedal 130, the pedal force (human power) causes pedal 130 and crankshaft 10 to rotate about central axis 9.

[0015] The casing 20 is a housing that houses the motor 40 and the reducer 50 therein. As shown in Figures 2 and 3, the casing 20 has a motor casing 21, a reducer casing 22, and an end cover 23. The end cover 23 is located on one axial side of the motor casing 21. The reducer casing 22 is located on the other axial side of the motor casing 21. The motor casing 21, the reducer casing 22, and the end cover 23 are fixed to each other by bolts 24.

[0016] Moreover, the casing 20 of this embodiment has a partition plate portion 27. The partition plate portion 27 expands radially inward from the inner circumferential surface of the casing 20. The partition plate portion 27 is plate-shaped and annular. The motor 40 is located on one axial side of the partition plate portion 27. The reducer 50 is located on the other axial side of the partition plate portion 27.

[0017] A pair of first bearings 81 are disposed radially between the crankshaft 10 and the casing 20. The casing 20 is supported by the crankshaft 10 via the first bearings 81. Therefore, the casing 20 and the crankshaft 10 are capable of relative rotation. As shown in FIG. 2, the casing 20 has a rotation prevention portion 25. The rotation prevention portion 25 protrudes radially outward from the outer circumferential surface of the casing 20. When the bicycle 100 is traveling, the rotation prevention portion 25 comes into contact with the frame 150 in the circumferential direction. This stops the rotation of the casing 20 around the central axis 9.

[0018] Thus, in the structure of this embodiment, the crankshaft 10 is supported directly by the frame 150 without the casing 20. Therefore, the casing 20 does not need to have the strength to support the crankshaft 10. Therefore, a material with low strength can be used for the casing 20. For example, the casing 20 may be made of resin to reduce the weight of the casing 20. However, the material of the casing 20 may also be a metal such as aluminum.

[0019] The torque sensor 30 is a sensor that detects the load applied to the crankshaft 10. The torque sensor 30 is provided at the radially inner end of the motor casing 21. The torque sensor 30 detects the distortion of the crankshaft 10 in a non-contact manner and converts the amount of distortion into a torque value. The torque sensor 30 inputs a detection signal indicating the torque value of the crankshaft 10 to a circuit board 42 described later.

[0020] The motor 40 is a power source that generates a driving force for assisting human power. The motor 40 is disposed in the space between the crankshaft 10 and the casing 20. The motor 40 is located on one axial side of the reducer 50. As shown in FIG. 3, the motor 40 has a stator 41, a circuit board 42, and a rotor 43.

[0021] The stator 41 is a stator of the motor 40. The stator 41 is fixed to the motor casing 21. The stator 41 has a stator core 411 and a plurality of coils 412. The stator core 411 is formed of a magnetic material such as laminated steel plates. The stator core 411 has a plurality of teeth that protrude radially outward. The plurality of teeth are arranged at equal intervals in the circumferential direction. The coils 412 are formed of conductive wires wound around the teeth.

[0022] The circuit board 42 is a board on which an electric circuit for supplying a driving current to the coil 412 of the stator 41 is mounted. The circuit board 42 is electrically connected to the coil 412, the torque sensor 30, and a battery (not shown). The circuit board 42 acquires a detection signal indicating the torque of the crankshaft 10 from the torque sensor 30. In addition, a preset torque threshold value is stored in a memory mounted on the circuit board 42.

[0023] When the torque value indicated by the detection signal obtained from the torque sensor 30 is less than the threshold value, the circuit board 42 does not supply a drive current to the coil 412. When the torque value indicated by the detection signal obtained from the torque sensor 30 is equal to or greater than the threshold value, the circuit board 42 generates a drive current according to the torque value using power supplied from the battery and supplies the drive current to the coil 412.

[0024] The rotor 43 is a rotor of the motor 40. A second bearing 82 is disposed radially between the crankshaft 10 and the rotor 43. The rotor 43 is supported by the crankshaft 10 via the second bearing 82. Therefore, the rotor 43 can rotate about the central axis 9 at a rotation speed different from that of the crankshaft 10.

[0025] The rotor 43 has a rotor yoke 431 and a plurality of magnets 432 fixed to the rotor yoke 431. The rotor yoke 431 is formed of a magnetic material such as iron. The plurality of magnets 432 are permanent magnets. The plurality of magnets 432 are located radially outside the stator 41. In other words, the motor 40 of this embodiment is an outer rotor type motor. The plurality of magnets 432 are arranged in an annular shape such that the N poles and the S poles are arranged alternately in the circumferential direction. The radially outer end faces of the teeth and the radially inner surface of the magnets 432 face each other with a small radial gap therebetween.

[0026] When the motor 40 is driven, a driving current is supplied from the circuit board 42 to the coil 412 of the stator 41. This generates a rotating magnetic field in the stator core 411. Then, a circumferential torque is generated between the stator 41 and the rotor 43 due to the magnetic attraction and magnetic repulsion between the stator core 411 and the multiple magnets 432. As a result, the rotor 43 rotates about the central axis 9.

[0027] The reducer 50 is a mechanism that reduces the speed of the rotational motion of the rotor 43 and outputs it to the crankshaft 10. FIG. 4 is a cross-sectional view of the electric assist drive unit 1 seen from the position AA in FIG. 3. To avoid complicating the drawing, hatching indicating the cross section and illustration of the teeth of each gear are omitted in FIG. 4. The reducer 50 is disposed in the space between the crankshaft 10 and the casing 20. As shown in FIGS. 3 and 4, the reducer 50 has an intermediate rotor 51, a plurality of planetary gears 52, a fixed internal gear 53, a movable internal gear 54, and an output rotor 55.

[0028] The intermediate rotor 51 is an annular member centered on the central axis 9. The intermediate rotor 51 is located on the other axial side of the rotor 43. A third bearing 83 is disposed radially between the crankshaft 10 and the intermediate rotor 51. The intermediate rotor 51 is supported by the crankshaft 10 via the third bearing 83. Therefore, the intermediate rotor 51 is rotatable about the central axis 9 at a rotation speed different from that of the crankshaft 10.

[0029] Moreover, the motor-equipped reducer 1 of this embodiment has an oil seal 28. The oil seal 28 is located between the radially inner end of the partition plate portion 27 and the outer circumferential surface of the intermediate rotor 51. This makes it possible to prevent the lubricating oil used in the reducer 50 from entering the motor 40 side.

[0030] Furthermore, the rotor 43 and the intermediate rotor 51 are fixed to each other by bolts 56. Therefore, when the motor 40 is driven, the intermediate rotor 51 rotates together with the rotor 43 about the central axis 9. The second bearing 82 and the third bearing 83 described above are disposed with a gap therebetween in the axial direction. This stabilizes the rotational attitude of the rotor 43 and the intermediate rotor 51 relative to the crankshaft 10.

[0031] The planetary gears 52 are arranged at equal intervals in the circumferential direction on the radially outer side of the crankshaft 10. As shown in FIG. 4, the speed reducer 50 of this embodiment has eight planetary gears 52 arranged around the crankshaft 10. However, the number of planetary gears 52 of the speed reducer 50 is not limited to eight. Each planetary gear 52 is supported by a planetary shaft 511 fixed to the intermediate rotor 51. The planetary shaft 511 extends in the axial direction. A fourth bearing 84 is interposed between the planetary shaft 511 and the planetary gears 52. Therefore, the planetary gears 52 can rotate about the planetary shaft 511. The planetary gears 52 revolve around the central axis 9 as the intermediate rotor 51 rotates.

[0032] The planetary gear 52 has a plurality of first external teeth 521 and a plurality of second external teeth 522 on its outer circumferential surface. The plurality of first external teeth 521 are located on one axial side of the plurality of second external teeth 522. The diameter of the first external teeth 521 is larger than the diameter of the second external teeth 522. The number of the first external teeth 521 owned by the planetary gear 52 is different from the number of the second external teeth 522 owned by the planetary gear 52.

[0033] The fixed internal gear 53 is an annular gear centered on the central axis 9. The fixed internal gear 53 is an example of a "fixed member". The fixed internal gear 53 is fixed to the inner circumferential surface of the casing 20 via a key 532. Therefore, the fixed internal gear 53 cannot rotate relative to the casing 20. The fixed internal gear 53 has a plurality of first internal teeth 531 on its inner circumferential surface. The first external teeth 521 of the planetary gear 52 mesh with the first internal teeth 531 of the fixed internal gear 53.

[0034] The movable internal gear 54 is an annular gear centered on the central axis 9. The movable internal gear 54 is located on the other axial side of the fixed internal gear 53. The inner diameter of the movable internal gear 54 is smaller than the inner diameter of the fixed internal gear 53. The movable internal gear 54 has a plurality of second internal teeth 541 on its inner circumferential surface. The second external teeth 522 of the planetary gear 52 mesh with the second internal teeth 541 of the movable internal gear 54. The number (number of teeth) of the first internal teeth 531 of the fixed internal gear 53 is different from the number (number of teeth) of the second internal teeth 541 of the movable internal gear 54.

[0035] When the motor 40 is driven, the rotor 43 and the intermediate rotor 51 rotate around the central axis 9 at a first rotation speed before deceleration. Accordingly, the multiple planetary gears 52 revolve around the central axis 9 in the circumferential direction. At this time, the first external teeth 521 of each planetary gear 52 mesh with the first internal teeth 531 of the fixed internal gear 53, so that the planetary gears 52 rotate around the planetary shaft 511. In addition, the second external teeth 522 of each planetary gear 52 mesh with the second internal teeth 541 of the movable internal gear 54, so that the movable internal gear 54 rotates around the central axis 9 relative to the fixed internal gear 53 due to the difference between the number of teeth of the first external teeth 521 and the first internal teeth 531 and the number of teeth of the second external teeth 522 and the second internal teeth 541. The rotation speed of this movable internal gear 54 becomes a second rotation speed lower than the above-mentioned first rotation speed.

[0036] The output rotor 55 is an annular member centered on the central axis 9. The output rotor 55 has a flange 551 and a sleeve 552. The flange 551 spreads in a disk shape on the other axial side of the multiple planetary gears 52. The sleeve 552 protrudes axially from the radially inner end of the flange 551 toward the motor 40. The sleeve 552 is cylindrical and centered on the central axis 9. The sleeve 552 is located radially inside the multiple planetary gears 52. The radially outer end of the flange 551 and the movable internal gear 54 are fixed to each other by a bolt 57. Therefore, the output rotor 55 rotates together with the movable internal gear 54 around the central axis 9 at the second rotation speed after deceleration. The movable internal gear 54 and the output rotor 55 may be a single member.

[0037] The one-way clutch 60 is a mechanism that allows the relative rotation of the output rotor 55 with respect to the crankshaft 10 in only one direction. The one-way clutch 60 is located radially between the sleeve 552 of the output rotor 55 and the crankshaft 10. That is, in the structure of this embodiment, the one-way clutch 60 is provided radially inside the sleeve 552 of the output rotor 55 that is folded back toward the motor 40. This allows the electric assist drive unit 1 to be made smaller in the axial direction.

[0038] When the forward rotation speed of the crankshaft 10 is greater than the forward rotation speed of the output rotor 55, the one-way clutch 60 permits such rotation. Thus, when the motor 40 is not driven, the user of the bicycle 100 can rotate the crankshaft 10 via the pedals 130 without experiencing resistance from the motor 40.

[0039] However, one-way clutch 60 prohibits the forward rotational speed of output rotor 55 from becoming greater than the forward rotational speed of crankshaft 10. Therefore, when motor 40 is driven and the forward rotational speed of output rotor 55 catches up with the forward rotational speed of crankshaft 10, crankshaft 10 rotates in the forward direction at the same rotational speed as output rotor 55. In this way, one-way clutch 60 transmits only unidirectional rotational motion about central axis 9 from output rotor 55 to crankshaft 10.

[0040] The sprocket 70 is a component for transmitting the rotation of the crankshaft 10 to the roller chain 140. The sprocket 70 is disk-shaped and centered on the central axis 9. The sprocket 70 is located outside the casing 20. The sprocket 70 is fixed to the crankshaft 10. The sprocket 70 has a plurality of external teeth 71 on its outer periphery. The sprocket 70 engages with the roller chain 140 of the bicycle 100 by means of these external teeth 71. When the crankshaft 10 rotates due to the pedaling force from the pedal 130 or the driving force from the motor 40, the sprocket 70 also rotates about the central axis 9. This causes the roller chain 140 to rotate between the sprocket 70 and the rear wheel 120.

[0041] As described above, when the load on the crankshaft 10 is large, the electrically assisted drive unit 1 drives the motor 40 to supply driving force to the crankshaft 10. At that time, the reducer 50 decelerates the rotational motion output from the motor 40, thereby increasing the torque and transmitting it to the crankshaft 10. This makes it possible to assist the rotation of the crankshaft 10 by human power.

[0042] Particularly, in the structure of this embodiment, the casing 20 is supported by the crankshaft 10 via a first bearing 81. The rotor 43 of the motor 40 is also supported by the crankshaft 10 via a second bearing 82. This allows each component to be assembled with the crankshaft 10 at the center. This allows the electric assist drive unit 1 to be easily manufactured.

[0043] Furthermore, in the structure of this embodiment, the rotor 43 is supported by the crankshaft 10, not by the casing 20, via the second bearing 82. In this way, a smaller diameter second bearing 82 can be used compared to when the rotor 43 is supported by the casing 20 via a bearing. This makes it easier to make the electric assist drive unit 1 smaller and lighter.

[0044] Furthermore, in the structure of this embodiment, the intermediate rotor 51 is also supported by the crankshaft 10, not by the casing 20, via the third bearing 83. In this way, a smaller diameter third bearing 83 can be used compared to when the intermediate rotor 51 is supported by the casing 20 via a bearing. This makes it easier to make the electric assist drive unit 1 smaller and lighter.

[0045] Moreover, the electric assist drive unit 1 of this embodiment has a one-way clutch 60 between the output rotor 55 and the crankshaft 10. Therefore, when the load on the crankshaft 10 is less than a threshold, the crankshaft 10 can be rotated by human power alone without resistance from the motor 40. Moreover, the circuit board 42 drives the motor 40 only when the load on the crankshaft 10 is equal to or greater than a threshold. Therefore, when assistance is not required, the motor 40 can be stopped to reduce battery consumption.

[0046] <3. Modifications> Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment. Various modified examples will be described below. The following description will focus on differences from the above embodiment. Duplicate descriptions of parts equivalent to the above embodiment will be omitted.

[0047] <3-1. First modified example> Fig. 5 is a vertical cross-sectional view of an electric power assist drive unit 1 according to a first modified example. The electric power assist drive unit 1 in Fig. 5 differs from the above-described embodiment in the structure of the motor 40.

[0048] In the structure of FIG. 5, a stator core 411 of a motor 40 has a plurality of teeth protruding radially inward. The plurality of teeth are arranged at equal intervals in the circumferential direction. A coil 412 is formed of a conductive wire wound around the teeth. A plurality of magnets 432 are fixed to the outer peripheral surface of a rotor yoke 431. The plurality of magnets 432 are located on the radially inner side of the stator 41. The plurality of magnets 432 are arranged in an annular shape such that the north poles and south poles are arranged alternately in the circumferential direction. The radially inner end faces of the teeth and the radially outer surface of the magnets 432 face each other with a small radial gap therebetween.

[0049] In this way, the motor 40 of the electric assist drive unit 1 may be an inner rotor type motor in which the magnet 432 of the rotor 43 is located radially inside the stator 41.

[0050] <3-2. Second modified example> Fig. 6 is a vertical cross-sectional view of an electric power assist drive unit 1 according to a second modified example. The electric power assist drive unit 1 in Fig. 6 differs from the above embodiment in the structures of the motor 40 and the reducer 50.

[0051] In the structure of FIG. 6, the stator 41 of the motor 40 is substantially disk-shaped and centered on the central axis 9. The stator 41 has a plurality of coils (not shown) arranged in the circumferential direction. The magnetic core of each coil faces the axial direction. The rotor 43 has a first rotor yoke 431a, a second rotor yoke 431b, a first magnet 432a, and a second magnet 432b. The first rotor yoke 431a extends in a disk shape centered on the central axis 9 on one axial side of the stator 41. The second rotor yoke 431b extends in a disk shape centered on the central axis 9 on the other axial side of the stator 41.

[0052] The first magnet 432a is fixed to a surface on the other axial side of the first rotor yoke 431a. The second magnet 432b is fixed to a surface on one axial side of the second rotor yoke 431b. The first magnet 432a and the second magnet 432b are each annular about the central axis 9. The surface of the first magnet 432a faces the surface on one axial side of the stator 41 in the axial direction with a small gap therebetween. The surface of the second magnet 432b faces the surface on the other axial side of the stator 41 in the axial direction with a small gap therebetween. The surfaces of the first magnet 432a and the second magnet 432b are magnetized with N poles and S poles alternately in the circumferential direction.

[0053] In this way, the motor 40 of the electric assist drive unit 1 may be an axial gap type motor in which the stator 41 and the magnets 432a, 432b of the rotor 43 face each other in the axial direction. By making the motor 40 an axial gap type, the axial dimension of the motor 40 can be reduced compared to when an outer rotor type or inner rotor type motor with equivalent performance is used.

[0054] In particular, the motor 40 of this embodiment has two magnets 432a and 432b arranged on either side of the stator 41. This makes it possible to increase the torque output from the motor 40 compared to a case in which magnets are arranged on only one side of the stator 41.

[0055] The reducer 50 of the electric assist drive unit 1 in FIG. 6 has an intermediate rotor 51, a plurality of planetary rollers 52, a non-rotating ring 53, a rotatable ring 54, and an output rotor 55.

[0056] The planetary rollers 52 are arranged at equal intervals in the circumferential direction on the radially outer side of the crankshaft 10. Each planetary roller 52 is supported by a planetary shaft 511 fixed to the intermediate rotor 51. The planetary shaft 511 extends in the axial direction. Each planetary roller 52 can rotate about the planetary shaft 511. Furthermore, the planetary rollers 52 revolve around the central axis 9 as the intermediate rotor 51 rotates.

[0057] The planetary roller 52 has a first inclined surface 521 and a second inclined surface 522 on its outer circumferential surface. The first inclined surface 521 is located on one axial side of the second inclined surface 522. The first inclined surface 521 is an inclined surface whose diameter decreases toward one axial side. The second inclined surface 522 is an inclined surface whose diameter decreases toward the other axial side.

[0058] Non-rotating ring 53 is an annular member centered on central axis 9. Non-rotating ring 53 is an example of a "fixed member." Non-rotating ring 53 is disposed along the inner circumferential surface of casing 20. Non-rotating ring 53 is unable to rotate relative to casing 20. The inner circumferential surface of non-rotating ring 53 includes third inclined surface 531. Third inclined surface 531 is an inclined surface whose diameter decreases toward one axial side.

[0059] The reducer 50 has a pressing mechanism 58 on one axial side of the non-rotating ring 53. The pressing mechanism 58 presses the non-rotating ring 53 in the axial direction toward the rotatable ring 54. In the structure of FIG. 6, the pressing mechanism 58 is composed of a spring that can expand and contract in the axial direction and a pressure adjustment cam that applies a pressing force proportional to the load torque. However, either the spring or the pressure adjustment cam may be omitted. Also, an elastic member other than a spring may be used as the pressing mechanism 58. The pressing force of the pressing mechanism 58 causes the third inclined surface 531 of the non-rotating ring 53 to come into contact with the first inclined surface 521 of the planetary roller 52.

[0060] A thrust bearing 59 is disposed in the axial gap between the flange 551 of the output rotor 55 and the reducer casing 22. The thrust bearing 59 supports the axial pressing force and reaction force of the pressing mechanism 58 in the casing 20. For this reason, the pressing force of the pressing mechanism 58 does not affect parts other than the inclined surface described above.

[0061] The rotatable ring 54 is an annular member centered on the central axis 9. The rotatable ring 54 is located on the other axial side of the non-rotatable ring 53. The inner peripheral surface of the rotatable ring 54 includes a fourth inclined surface 541. The fourth inclined surface 541 is an inclined surface that decreases in diameter toward the other axial side. The second inclined surface 522 of the planetary roller 52 contacts the fourth inclined surface 541 of the rotatable ring 54. The inner diameter of the non-rotatable ring 53 and the inner diameter of the rotatable ring 54 are slightly different.

[0062] When the motor 40 is driven, the rotor 43 and the intermediate rotor 51 rotate around the central axis 9 at a first rotation speed before deceleration. Accordingly, the planetary rollers 52 revolve in the circumferential direction around the central axis 9. At this time, the first inclined surface 521 of each planetary roller 52 contacts the third inclined surface 5 of the non-rotating ring 53, so that the planetary rollers 52 rotate around the planetary axis 511. In addition, the second inclined surface 522 of each planetary roller 52 contacts the fourth inclined surface 541 of the rotatable ring 54, so that the rotatable ring 54 rotates around the central axis 9 relative to the non-rotating ring 53 due to the diameter difference between the contact portion between the first inclined surface 521 and the third inclined surface 531 and the contact portion between the second inclined surface 522 and the fourth inclined surface 541. The rotation speed of the rotatable ring 54 becomes a second rotation speed lower than the above-mentioned first rotation speed.

[0063] In addition, the rotatable ring 54 and the output rotor 55 are fixed to each other. Therefore, the output rotor 55 rotates together with the rotatable ring 54 around the central axis 9 at the second rotation speed after deceleration. Note that the rotatable ring 54 and the output rotor 55 may be a single member.

[0064] 6, the first inclined surface 521 of the planetary roller 52 and the third inclined surface 531 of the non-rotating ring 53 are in contact with each other. However, the structure is not limited to such a structure in which the inclined surfaces are in contact with each other, and a structure in which the inclined surface is in contact with a protrusion may also be used. That is, at the contact portion between the planetary roller 52 and the non-rotating ring 53, it is sufficient that at least one of the surfaces of the planetary roller 52 and the non-rotating ring 53 is an inclined surface whose diameter decreases as it moves away from the rotatable ring 54.

[0065] 6, the second inclined surface 522 of the planetary roller 52 and the fourth inclined surface 541 of the rotatable ring 54 are in contact with each other. However, the structure is not limited to such a structure in which the inclined surfaces are in contact with each other, and a structure in which the inclined surface is in contact with a protrusion may also be used. That is, it is sufficient that at least one of the surfaces of the planetary roller 52 and the rotatable ring 54 at the contact portion between the planetary roller 52 and the rotatable ring 54 is an inclined surface whose diameter decreases as it moves away from the non-rotatable ring 53.

[0066] <3-3.Third modified example> Fig. 7 is a longitudinal sectional view of the electric assist drive unit 1 according to the third modified example. Fig. 8 is a transverse sectional view of the electric assist drive unit 1 as seen from position BB in Fig. 7. To avoid complicating the drawing, hatching indicating a cross section is omitted in Fig. 8. The electric assist drive unit 1 in Figs. 7 and 8 differs from the above embodiment in the structures of the motor 40 and the reducer 50. However, the structure of the motor 40 is the same as that of the second modified example, and therefore a duplicated description will be omitted.

[0067] The reducer 50 of the electric assist drive unit 1 in FIGS. 7 and 8 has an intermediate rotor 51, a flexible external gear 52, a fixed internal gear 53, a movable internal gear 54, and an output rotor 55.

[0068] Intermediate rotor 51 of this modified example includes cam 512. In Fig. 8, the shape of the outer peripheral surface of cam 512 when viewed in the axial direction is elliptical. However, the shape of the outer peripheral surface of cam 512 is not necessarily limited to elliptical. Cam 512 may have a non-circular outer peripheral surface whose outer diameter (distance from central axis 9) varies depending on the circumferential position.

[0069] The flexible external gear 52 is a thin-walled gear that can flexibly deform. The flexible external gear 52 is annular, and is located radially outside the cam 512. The flexible external gear 52 has a plurality of external teeth 523 on its outer circumferential surface. In addition, a flexible bearing 85 is interposed between the outer circumferential surface of the cam 512 and the flexible external gear 52. The flexible bearing 85 is a bearing that can flexibly deform. Therefore, the rotation of the cam 512 causes the flexible external gear 52 to flex radially via the flexible bearing 85.

[0070] The fixed internal gear 53 is an annular gear centered on the central axis 9. The fixed internal gear 53 is an example of a "fixed member". The fixed internal gear 53 is fixed to the inner circumferential surface of the casing 20. Therefore, the fixed internal gear 53 cannot rotate relative to the casing 20. The fixed internal gear 53 has a plurality of first internal teeth 531 on its inner circumferential surface.

[0071] The movable internal gear 54 is an annular gear centered on the central axis 9. The movable internal gear 54 is located on the other axial side of the fixed internal gear 53. The movable internal gear 54 has a plurality of second internal teeth 541 on its inner circumferential surface. The number of first internal teeth 531 (the number of teeth) of the fixed internal gear 53 and the number of second internal teeth 541 (the number of teeth) of the movable internal gear 54 are different.

[0072] The inner ring of the flexible bearing 85 mentioned above contacts the outer peripheral surface of the cam 512. The outer ring of the flexible bearing 85 contacts the inner peripheral surface of the flexible external gear 52. The flexible bearing 85 deforms into an elliptical shape along the outer peripheral surface of the cam 512. Therefore, the flexible external gear 52 also deforms into an elliptical shape along the outer peripheral surface of the cam 512. As a result, at two points corresponding to both ends of the major axis of the ellipse, some of the external teeth 523 of the flexible external gear 52 are pressed against the outer peripheral surface of the cam 512 via the flexible bearing 85, thereby meshing with the first internal teeth 531 of the fixed internal gear 53 and the second internal teeth 541 of the movable internal gear 54. At other positions in the circumferential direction, the external teeth 523 do not mesh with the first internal teeth 531 and the second internal teeth 541.

[0073] When the motor 40 is driven, the rotor 43 and the intermediate rotor 51 rotate around the central axis 9 at the first rotation speed before deceleration. Accordingly, the cam 512 also rotates around the central axis 9 at the first rotation speed. Then, the major axis of the ellipse of the flexible external gear 52 also rotates at the first rotation speed. Therefore, the meshing position between the external teeth 523 of the flexible external gear 52 and the first internal teeth 531 of the fixed internal gear 53 also moves in the circumferential direction at the first rotation speed. In addition, the external teeth 523 of the flexible external gear 52 also mesh with the second internal teeth 541 of the movable internal gear 54, so that the difference in the number of teeth between the first internal teeth 531 and the second internal teeth 541 causes the movable internal gear 54 to rotate around the central axis 9 relative to the fixed internal gear 53. The rotation speed of this movable internal gear 54 becomes a second rotation speed lower than the above-mentioned first rotation speed.

[0074] The movable internal gear 54 and the output rotor 55 are fixed to each other by bolts 57. Therefore, the output rotor 55 rotates together with the movable internal gear 54 about the central axis 9 at the second rotation speed after deceleration. Note that the movable internal gear 54 and the output rotor 55 may be a single member.

[0075] <3-4. Fourth modified example> Fig. 9 is a vertical cross-sectional view of an electric assist drive unit 1 according to a fourth modified example. The electric assist drive unit 1 in Fig. 9 differs from the above embodiment in the structures of the motor 40 and the reducer 50. However, the structure of the motor 40 is the same as that of the first modified example, so a duplicated description will be omitted.

[0076] The reducer 50 of the electric assist drive unit 1 in FIG. 9 has an intermediate rotor 51, a flexible external gear 52, an internal gear 53, and an output rotor 55.

[0077] Intermediate rotor 51 of this modified example includes cam 512. The shape of the outer peripheral surface of cam 512 when viewed in the axial direction is elliptical. However, the shape of the outer peripheral surface of cam 512 is not necessarily limited to elliptical. Cam 512 may have a noncircular outer peripheral surface whose outer diameter (distance from central axis 9) varies depending on the circumferential position.

[0078] The flexible external gear 52 is a thin-walled gear that is flexibly deformable. The flexible external gear 52 has a generally cup-shaped outer shape. That is, the flexible external gear 52 has a cylindrical portion 524 and a disk portion 525. The cylindrical portion 524 is located radially outside the cam 512. The disk portion 525 expands radially inward from the other axial end of the cylindrical portion 524.

[0079] The cylindrical portion 524 has a plurality of external teeth 523 on its outer circumferential surface. A flexible bearing 85 is interposed between the outer circumferential surface of the cam 512 and the inner circumferential surface of the cylindrical portion 524. The flexible bearing 85 is a bearing that can flexibly deform. Therefore, the rotation of the cam 512 causes the cylindrical portion 524 of the flexible external gear 52 to flex in the radial direction via the flexible bearing 85.

[0080] The internal gear 53 is an annular gear centered on the central axis 9. The internal gear 53 is fixed to the inner circumferential surface of the casing 20. Therefore, the internal gear 53 is unable to rotate relative to the casing 20. The internal gear 53 has a plurality of internal teeth 531 on its inner circumferential surface. The number of external teeth 523 (the number of teeth) of the flexible external gear 52 is different from the number of internal teeth 531 (the number of teeth) of the internal gear 53.

[0081] The inner ring of the flexible bearing 85 described above contacts the outer peripheral surface of the cam 512. The outer ring of the flexible bearing 85 contacts the inner peripheral surface of the cylindrical portion 524 of the flexible external gear 52. The flexible bearing 85 deforms into an elliptical shape along the outer peripheral surface of the cam 512. Therefore, the cylindrical portion 524 of the flexible external gear 52 also deforms into an elliptical shape along the outer peripheral surface of the cam 512. As a result, at two points corresponding to both ends of the major axis of the ellipse, some of the external teeth 523 of the flexible external gear 52 are pressed against the outer peripheral surface of the cam 512 via the flexible bearing 85, thereby meshing with the internal teeth 531 of the internal gear 53. At other positions in the circumferential direction, the external teeth 523 do not mesh with the internal teeth 531.

[0082] When the motor 40 is driven, the rotor 43 and the intermediate rotor 51 rotate around the central axis 9 at the first rotation speed before deceleration. Accordingly, the cam 512 also rotates around the central axis 9 at the first rotation speed. Then, the major axis of the ellipse of the cylindrical portion 524 of the flexible external gear 52 also rotates at the first rotation speed. Therefore, the meshing position between the external teeth 523 of the flexible external gear 52 and the internal teeth 531 of the internal gear 53 also moves circumferentially at the first rotation speed. In addition, the number of the external teeth 523 of the flexible external gear 52 is different from the number of the internal teeth 531 of the internal gear 53. Therefore, due to the difference in the number of teeth, the flexible external gear 52 rotates around the central axis 9 relative to the internal gear 53. The rotation speed of the flexible external gear 52 becomes a second rotation speed lower than the above-mentioned first rotation speed.

[0083] The flexible external gear 52 and the output rotor 55 are fixed to each other by bolts 57. Therefore, the output rotor 55 rotates together with the flexible external gear 52 around the central axis 9 at the second rotation speed after deceleration. The flexible external gear 52 and the output rotor 55 may be a single member.

[0084] <3-5. Fifth Modification> Fig. 10 is a vertical cross-sectional view of an electric assist drive unit 1 according to a fifth modified example. The electric assist drive unit 1 in Fig. 10 differs from the above-described embodiment in the structure of the reducer 50.

[0085] The reducer 50 of the electric assist drive unit 1 in FIG. 10 has an intermediate rotor 51, a flexible external gear 52, an internal gear 53, and an output rotor 55.

[0086] Intermediate rotor 51 of this modified example includes cam 512. The shape of the outer peripheral surface of cam 512 when viewed in the axial direction is elliptical. However, the shape of the outer peripheral surface of cam 512 is not necessarily limited to elliptical. Cam 512 may have a noncircular outer peripheral surface whose outer diameter (distance from central axis 9) varies depending on the circumferential position.

[0087] The flexible external gear 52 is a thin-walled gear that can flexibly deform. The flexible external gear 52 has a generally top hat-shaped outer shape. That is, the flexible external gear 52 has a cylindrical portion 524 and a disk portion 525. The cylindrical portion 524 is located radially outside the cam 512. The disk portion 525 expands radially outward from one axial end of the cylindrical portion 524. The radially outer end of the disk portion 525 is fixed to the casing 20.

[0088] The cylindrical portion 524 has a plurality of external teeth 523 on its outer circumferential surface. A flexible bearing 85 is interposed between the outer circumferential surface of the cam 512 and the inner circumferential surface of the cylindrical portion 524. The flexible bearing 85 is a bearing that can flexibly deform. Therefore, the rotation of the cam 512 causes the cylindrical portion 524 of the flexible external gear 52 to flex in the radial direction via the flexible bearing 85.

[0089] The internal gear 53 is an annular gear centered on the central axis 9. A cross roller bearing 86 is disposed radially between the casing 20 and the internal gear 53. The internal gear 53 is supported by the casing 20 via this cross roller bearing 86. Therefore, the internal gear 53 is rotatable around the central axis 9. The internal gear 53 has a plurality of internal teeth 531 on its inner circumferential surface. The number of external teeth 523 (the number of teeth) of the flexible external gear 52 is different from the number of internal teeth 531 (the number of teeth) of the internal gear 53.

[0090] The inner ring of the flexible bearing 85 described above contacts the outer peripheral surface of the cam 512. The outer ring of the flexible bearing 85 contacts the inner peripheral surface of the cylindrical portion 524 of the flexible external gear 52. The flexible bearing 85 deforms into an elliptical shape along the outer peripheral surface of the cam 512. Therefore, the cylindrical portion 524 of the flexible external gear 52 also deforms into an elliptical shape along the outer peripheral surface of the cam 512. As a result, at two points corresponding to both ends of the major axis of the ellipse, some of the external teeth 523 of the flexible external gear 52 are pressed against the outer peripheral surface of the cam 512 via the flexible bearing 85, thereby meshing with the internal teeth 531 of the internal gear 53. At other positions in the circumferential direction, the external teeth 523 do not mesh with the internal teeth 531.

[0091] When the motor 40 is driven, the rotor 43 and the intermediate rotor 51 rotate around the central axis 9 at the first rotation speed before deceleration. Accordingly, the cam 512 also rotates around the central axis 9 at the first rotation speed. Then, the major axis of the ellipse of the cylindrical portion 524 of the flexible external gear 52 also rotates at the first rotation speed. Therefore, the meshing position between the external teeth 523 of the flexible external gear 52 and the internal teeth 531 of the internal gear 53 also moves circumferentially at the first rotation speed. In addition, the number of the external teeth 523 of the flexible external gear 52 is different from the number of the internal teeth 531 of the internal gear 53. Therefore, due to the difference in the number of teeth, the internal gear 53 rotates around the central axis 9 relative to the flexible external gear 52. The rotation speed of this internal gear 53 becomes a second rotation speed lower than the above-mentioned first rotation speed.

[0092] The internal gear 53 and the output rotor 55 are fixed to each other by bolts 57. Therefore, the output rotor 55 rotates together with the internal gear 53 around the central axis 9 at the second rotation speed after reduction. Note that the flexible external gear 52 and the output rotor 55 may be a single member.

[0093] In the above-mentioned fourth modified example, the internal gear 53 is fixed to the casing 20, and the flexible external gear 52 is rotated relative to the internal gear 53 at the second rotation speed after deceleration. In contrast, in the fifth modified example, the flexible external gear 52 is fixed to the casing 20, and the internal gear 53 is rotated relative to the flexible external gear 52 at the second rotation speed after deceleration. In this way, when the flexible external gear 52 is used in the reducer 50, it is sufficient that either the flexible external gear 52 or the internal gear 53 is fixed to the casing 20. Then, it is sufficient that the other of the flexible external gear 52 and the internal gear 53 rotates together with the output rotor 55 at the second rotation speed.

[0094] <3-6. Sixth Variation> Fig. 11 is a cross-sectional view of an electric assist drive unit 1 according to a sixth modified example. The electric assist drive unit 1 of Fig. 11 differs from the above-described embodiment in the structures of the motor 40 and the reducer 50. However, the structure of the motor 40 is equivalent to that of the above-described second modified example. Furthermore, the structure of the reducer 50 is equivalent to that of the above-described fifth modified example. In this way, the type of motor 40 and the type of reducer 50 can be combined in any way.

[0095] <3-7. Seventh Variation> Fig. 12 is a side view of an electric power assist drive unit 1 according to a seventh modified example. The electric power assist drive unit 1 in Fig. 12 differs from the above-described embodiments in the support structure for the frame 150 of the bicycle 100.

[0096] In the example of FIG. 12, the casing 20 is fixed to the frame 150 of the bicycle 100 with bolts 26. This allows the casing 20 to be supported by the frame 150. Similar to the above embodiment, a first bearing 81 (see FIG. 3) is disposed radially between the crankshaft 10 and the casing 20. The crankshaft 10 is supported by the casing 20 via this first bearing 81. In the structure of this modification, the casing 20 supports the crankshaft 10, so the casing 20 needs to be stronger than in the above embodiment. However, by adopting the structure of this modification, the bearing 80 of the above embodiment can be omitted. Therefore, the structure of the electric assist drive unit 1 can be simplified.

[0097] <3-8. Other variations> In the above embodiment and modified example, the electric assist drive unit 1 mounted on the bicycle 100 has been described. However, the electric assist drive unit 1 of the present invention may be mounted on equipment other than a bicycle. For example, the electric assist drive unit of the present invention may be mounted on an assist suit, a fishing rod reel, or the like to assist human power.

[0098] In addition, the detailed shape of the electric power assist drive unit may be different from the shapes shown in the drawings of the present application. Furthermore, the elements appearing in the above-mentioned embodiment or modified example may be appropriately combined to the extent that no contradiction occurs. [Industrial Applicability]

[0099] The present invention can be used in an electrically assisted drive unit and a bicycle. [Explanation of symbols]

[0100] 1 Electrically assisted drive unit 9 Center axis 10. Crankshaft 20 Casing 25 Anti-rotation part 30 Torque Sensor 40 Motor 41 Stator 42 Circuit Board 43 Rotor 50 reducer 51 Intermediate Rotor 52 Planetary gears, planetary rollers, flexible external gears 53 Internal gear, non-rotating ring, fixed internal gear 54 Rotatable ring, movable internal gear 55 Output Rotor 58 Pressing mechanism 60 One-way clutch 70 Sprocket 81 No. 1 bearing 82 No. 2 bearing 83 3rd bearing 84 4th bearing 85 Flexible Bearings 86 Cross roller bearing 100 Bicycles 130 Pedals 150 frames 551 Flange 552 Sleeve

Claims

1. An electric assist drive unit that assists rotation by human power with the driving force of a motor, A crankshaft that rotates around a central axis by human power; a casing supported by the crankshaft via a first bearing in the radial direction; a motor and a reducer disposed in a space between the crankshaft and the casing; Equipped with The motor is a stator fixed to the casing; a circuit board that supplies a drive current to the stator in response to a load applied to the crankshaft; a rotor that rotates about the central axis by a rotating magnetic field generated from the stator by the driving current; having the reducer reduces the rotation speed of the rotor and outputs the reduced rotation speed to the crankshaft; The rotor is supported by the crankshaft via a second bearing in the radial direction, The reducer includes: an intermediate rotor fixed to the rotor; A fixing member fixed to the casing; an output rotor that rotates around the central axis at a reduced rotation speed; having With the rotation of the intermediate rotor, the output rotor rotates relative to the fixed member at a rotation speed lower than that of the intermediate rotor, the fixed member is an annular fixed internal gear centered on the central axis, the reduction gear has an annular shape centered on the central axis and includes a movable internal gear that rotates together with the output rotor, The number of teeth of the fixed internal gear is different from the number of teeth of the movable internal gear, The reducer includes: The rotor further includes a planetary gear that meshes with the fixed internal gear and the movable internal gear and revolves around the central axis as the intermediate rotor rotates. Electrically assisted drive unit.

2. An electric assist drive unit that assists rotation by human power with the driving force of a motor, A crankshaft that rotates around a central axis by human power; a casing supported by the crankshaft via a first bearing in the radial direction; a motor and a reducer disposed in a space between the crankshaft and the casing; Equipped with The motor is a stator fixed to the casing; a circuit board that supplies a drive current to the stator in response to a load applied to the crankshaft; a rotor that rotates about the central axis by a rotating magnetic field generated from the stator by the driving current; having the reducer reduces the rotation speed of the rotor and outputs the reduced rotation speed to the crankshaft; the rotor is supported by the crankshaft via a second bearing in the radial direction; The reducer includes: an intermediate rotor fixed to the rotor; A fixing member fixed to the casing; an output rotor that rotates around the central axis at a reduced rotation speed; having With the rotation of the intermediate rotor, the output rotor rotates relative to the fixed member at a rotation speed lower than that of the intermediate rotor, the fixed member is an annular non-rotating ring centered on the central axis, the reducer has a rotatable ring that is annular about the central axis and rotates together with the output rotor, The inner diameter of the rotatable ring is different from the inner diameter of the non-rotatable ring, The reducer includes: The intermediate rotor contacts the non-rotating ring and the rotatable ring, and as the intermediate rotor rotates, The electrically assisted drive unit further includes a planetary roller that revolves around the central axis.

3. An electric assist drive unit as described in claim 2, At a contact portion between the non-rotating ring and the planetary roller, at least one of the surfaces of the non-rotating ring and the planetary roller is an inclined surface whose diameter decreases as it moves away from the rotatable ring, An electric assist drive unit, wherein at a contact portion between the rotatable ring and the planetary roller, at least one of the surfaces of the rotatable ring and the planetary roller is an inclined surface whose diameter decreases as it moves away from the non-rotatable ring.

4. An electric assist drive unit as described in claim 3, The reducer includes: The electrically assisted drive unit further includes a pressing mechanism that presses the non-rotating ring in the axial direction toward the rotatable ring.

5. An electric assist drive unit that assists rotation by human power with the driving force of a motor, A crankshaft that rotates around a central axis by human power; a casing supported by the crankshaft via a first bearing in the radial direction; a motor and a reducer disposed in a space between the crankshaft and the casing; Equipped with The motor is a stator fixed to the casing; a circuit board that supplies a drive current to the stator in response to a load applied to the crankshaft; a rotor that rotates about the central axis by a rotating magnetic field generated from the stator by the driving current; having the reducer reduces the rotation speed of the rotor and outputs the reduced rotation speed to the crankshaft; The rotor is supported by the crankshaft via a second bearing in the radial direction, The reducer includes: an intermediate rotor fixed to the rotor; A fixing member fixed to the casing; an output rotor that rotates around the central axis at a reduced rotation speed; having With the rotation of the intermediate rotor, the output rotor rotates relative to the fixed member at a rotation speed lower than that of the intermediate rotor, the fixed member is an annular fixed internal gear centered on the central axis, the reduction gear has an annular shape centered on the central axis and includes a movable internal gear that rotates together with the output rotor, The number of teeth of the fixed internal gear is different from the number of teeth of the movable internal gear, the intermediate rotor includes a non-circular cam having a different outer diameter depending on a circumferential position, The reducer includes: The electrically assisted drive unit further includes an annular external gear that is pressed against an outer peripheral surface of the cam and flexibly deforms, and that meshes with the fixed internal gear and the movable internal gear at a portion in the circumferential direction.

6. An electric assist drive unit that assists rotation by human power with the driving force of a motor, A crankshaft that rotates around a central axis by human power; a casing supported by the crankshaft via a first bearing in the radial direction; a motor and a reducer disposed in a space between the crankshaft and the casing; Equipped with The motor is a stator fixed to the casing; a circuit board that supplies a drive current to the stator in response to a load applied to the crankshaft; a rotor that rotates about the central axis by a rotating magnetic field generated from the stator by the driving current; having the reducer reduces the rotation speed of the rotor and outputs the reduced rotation speed to the crankshaft; The rotor is supported by the crankshaft via a second bearing in the radial direction, The reducer includes: an intermediate rotor including a non-circular cam fixed to the rotor and having an outer diameter that varies depending on a circumferential position; An annular internal gear centered on the central axis; an external gear that is pressed against an outer peripheral surface of the cam and deforms to mesh with the internal gear at a portion in the circumferential direction; an output rotor that rotates around the central axis at a reduced rotation speed; having One of the internal gear and the external gear is fixed to the casing, An electrically assisted drive unit, in which the other of the internal gear and the external gear rotates together with the output rotor about the central axis at a rotation speed lower than that of the intermediate rotor.

7. An electric assist drive unit as described in claim 6, The internal gear is fixed to the casing, The external gear is a cylindrical portion having a plurality of external teeth; a disk portion extending radially inward from an axial end of the cylindrical portion; having The output rotor rotates together with the external gear.

8. An electric assist drive unit as described in claim 6, The external gear is a cylindrical portion having a plurality of external teeth; a disk portion extending radially outward from an axial end of the cylindrical portion; having The disk portion is fixed to the casing, The output rotor rotates together with the internal gear.

9. An electric assist drive unit as described in claim 8, The internal gear is supported by the casing via a cross roller bearing.

10. An electric assist drive unit according to any one of claims 1 to 9, The motor is an axial gap type motor in which the stator and the magnet of the rotor face each other in the axial direction.

11. An electric assist drive unit as described in claim 10, The motor is an outer rotor type motor in which a magnet of the rotor is located radially outside the stator.

12. An electric assist drive unit according to any one of claims 1 to 11, The motor is an inner rotor type motor in which a magnet of the rotor is located radially inside the stator.

13. An electric assist drive unit according to any one of claims 1 to 11, The casing is supported by a frame; The casing was secured to the frame.

14. An electric assist drive unit according to any one of claims 1 to 11, The casing is made of resin.

15. An electric assist drive unit according to any one of claims 1 to 14, a torque sensor that detects the torque of the crankshaft and inputs a detection signal to the circuit board; The circuit board supplies the drive current to the stator when the torque indicated by the detection signal is equal to or greater than a preset threshold value.

16. An electric assist drive unit according to any one of claims 1 to 14, It is mounted on a bicycle having pedals, The crankshaft rotates due to the pedal force.

17. An electric assist drive unit as described in claim 16, a sprocket adapted to engage a chain of the bicycle; The sprocket is fixed to the crankshaft.

18. An electric assist drive unit according to any one of claims 1 to 17, a torque sensor that detects the torque of the crankshaft and inputs a detection signal to the circuit board; When the torque indicated by the detection signal is equal to or greater than a preset threshold value, The drive current is supplied to the stator.

19. An electric assist drive unit according to any one of claims 1 to 18, It is mounted on a bicycle having pedals, The crankshaft rotates due to the pedal force.

20. An electric assist drive unit as claimed in claim 19, a sprocket adapted to engage a chain of the bicycle; The sprocket is fixed to the crankshaft.

21. A bicycle equipped with an electric assist drive unit as described in claim 19 or claim 20.

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