JP6342789B2 - Drive unit, battery-assisted bicycle, and sprocket mounting mechanism - Google Patents

Description

  The present invention relates to a drive unit used for a battery-assisted bicycle. Specifically, the present invention relates to a drive unit in which a sprocket is attached to a drive shaft.

  In motorcycles and battery-assisted bicycles, a drive unit including a motor is provided. The drive unit has a drive shaft that is rotated by the drive force of the motor. A sprocket is attached to the drive shaft. In this drive unit, the sprocket of the drive shaft is rotated by the drive force of the motor, and the drive force is transmitted to the wheels via a chain wound around the sprocket. Thereby, the vehicle moves forward.

  In the battery-assisted bicycle, the driving force of the motor assists the driver's pedaling force (hereinafter referred to as pedaling force). The drive unit of the battery-assisted bicycle includes a crank shaft that rotates by a pedaling force and a drive shaft that rotates by a driving force of a motor. A sprocket is attached to each of the crankshaft and the drive shaft. A chain is wound around each sprocket. That is, the chain rotates both by the pedal force and the driving force of the motor. The chain is also wound around a driven sprocket attached to the axle of the rear wheel (for example, Patent Document 1).

  In a battery-assisted bicycle, a circlip is used in a sprocket attachment mechanism that attaches a sprocket to one end of a drive shaft. FIG. 10 is an exploded perspective view of a conventional sprocket mounting mechanism. One end of the drive shaft 1081 includes a sprocket mounting portion 1081B for mounting the sprocket 1043 and a circlip groove 1081C for mounting the circlip 1142.

  The sprocket mounting portion 1081B has a spline 1081Ba. The sprocket 1043 has a spline 1043a on the inner peripheral surface. Then, the sprocket 1043 is mounted on the sprocket mounting portion 1081B so that the spline 1081Ba of the sprocket mounting portion 1081B and the spline 1043a of the sprocket 1043 mesh with each other. Since the spline 1081Ba and the spline 1043a are engaged with each other, the relative rotational motion of the sprocket 1043 with respect to the drive shaft 1081 around the axis L is restricted.

  FIG. 11 is a cross-sectional view of a conventional sprocket mounting mechanism 1140. As shown in FIG. 11, the sprocket mounting portion 1081B of the drive shaft 1081 has a smaller diameter than the portion 1081A in the direction opposite to the circlip groove 1081C of the sprocket mounting portion 1081B. Therefore, a step 1081D is formed between the portion 1081A and the sprocket mounting portion 1081B. The sprocket 1043 is restricted from moving toward the portion 1081A of the drive shaft 1081 by the step 1081D.

  The circlip 1142 is fitted into the circlip groove 1081C of the drive shaft 1081. As shown in FIG. 11, the circlip 1142 restricts the sprocket 1043 from moving toward the circlip groove 1081 </ b> C.

JP 2011-168180 A

  By the way, this inventor repeated examination about the abnormal noise which generate | occur | produces during driving | running | working of a battery-assisted bicycle. As a result, the present inventor has obtained knowledge that abnormal noise generated during the traveling of the battery-assisted bicycle is generated from the periphery of the drive shaft. As a result of more detailed examination, the present inventor has found that the abnormal noise is caused by a method of fixing the sprocket to the drive shaft.

  An object of this invention is to provide the drive unit which can suppress generation | occurrence | production of the noise resulting from the fixing method of a sprocket.

  Another object of the present invention is to provide a battery-assisted bicycle including the drive unit.

  Furthermore, an object of the present invention is to provide a sprocket mounting mechanism that can suppress the generation of abnormal noise caused by the sprocket fixing method.

Means for Solving the Problems and Effects of the Invention

  The drive unit according to the first aspect of the present invention includes a motor, a drive shaft that is rotated by the driving force of the motor, a first member that is fixed to the outer peripheral surface of the drive shaft and rotates integrally with the drive shaft, and a drive shaft And a sprocket for transmitting the driving force of the motor to the wound chain, and an annular damper mounted on the drive shaft and positioned between the sprocket and the first member. . Of the surface of the damper, the first surface facing one end of the drive shaft in the axial direction of the drive shaft is in contact with the sprocket. Of the surface of the damper, the second surface facing the other end of the drive shaft in the axial direction of the drive shaft is in contact with the first member.

  According to the drive unit of the above aspect, the annular damper is fitted to the drive shaft. The first surface of the damper surface facing the one end of the drive shaft in the axial direction of the drive shaft contacts the sprocket, and the other surface of the damper faces the other end of the drive shaft in the axial direction of the drive shaft. The second surface is in contact with the first member. Therefore, when the chain is wound around the sprocket and the chain is rotated, the damper restricts the movement of the sprocket in the axial direction of the drive shaft. Therefore, it is possible to suppress the generation of abnormal noise caused by the movement of the sprocket in the axial direction. That is, it is possible to suppress the generation of abnormal noise caused by the sprocket fixing method.

FIG. 1 is a right side view showing a battery-assisted bicycle according to the present embodiment. FIG. 2 is a right side view of the drive unit and the driven sprocket of the battery-assisted bicycle according to the present embodiment. FIG. 3 is a cross-sectional view taken along line III-III in FIG. FIG. 4 is an enlarged perspective view of one end of the output shaft. FIG. 5 is a right side view of the drive unit in a state where the chain is wound around the drive unit. FIG. 6 is a cross-sectional view of the drive unit in a state where a chain is wound around the drive unit. FIG. 7A is a sectional view of the damper, and FIG. 7B is a side view of the damper. FIG. 8 is an exploded perspective view of the sprocket mounting mechanism. FIG. 9 is an enlarged perspective view of one end of an output shaft according to another embodiment. FIG. 10 is an exploded perspective view of a conventional sprocket mounting mechanism. FIG. 11 is a cross-sectional view including a sprocket mounting mechanism of a drive unit according to a conventional configuration.

  A drive unit provided in a motorcycle or a battery-assisted bicycle has a drive shaft that is rotated by the drive force of a motor. In this drive unit, the sprocket attached to the drive shaft is rotated by the drive force of the motor, and the drive force is transmitted to the wheels via a chain wound around the sprocket. Thereby, the vehicle moves forward.

  The present inventor has repeatedly studied the abnormal noise generated during the traveling of the battery-assisted bicycle. As a result, the present inventor has obtained knowledge that abnormal noise generated during the traveling of the battery-assisted bicycle is generated from the periphery of the drive shaft. As a result of more detailed examination, the present inventor has found that the abnormal noise is caused by a method of fixing the sprocket to the drive shaft. Furthermore, the present inventor has clarified that one of the specific causes of the occurrence of abnormal noise is the rattling of the drive shaft in the axial direction.

  With reference to FIG. 11, the rattling of the sprocket 1043 found by the present inventor will be described. The sprocket 1043 is fixed by engaging the spline 1081Ba and the spline 1043a with the drive shaft 1081. As a result, the rotational movement of the sprocket 1043 with respect to the drive shaft 1081 around the axis L is restricted, and rattling due to the rotational movement of the sprocket 1043 is suppressed. On the other hand, since the movement of the drive shaft 1081 in the axial direction of the sprocket 1043 is restricted only by being sandwiched between the step 1081D and the circlip 1142, it is difficult to completely suppress the movement in the axial direction. Therefore, the sprocket 1043 rattles along the axial direction of the drive shaft 1081.

  The present inventor has repeatedly studied a method for suppressing the generation of abnormal noise caused by the above-described sprocket mounting method. As a result, the inventor has paid attention to a configuration in which a damper is interposed between the first member rotating integrally with the drive shaft and the sprocket. And the knowledge of suppressing generation | occurrence | production of the said abnormal noise by making a damper contact both a 1st part goods and a sprocket was discovered.

[Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the dimension of the structural member in each figure does not represent the dimension of an actual structural member, the dimension ratio of each structural member, etc. faithfully.

  In the following description, front, rear, left, and right mean front, rear, left, and right as viewed from a user who is seated on the seat 24 of the battery-assisted bicycle 1 while grasping the handle 23.

[Embodiment 1]
[Overall configuration of battery-assisted bicycle]
FIG. 1 is a right side view showing the battery-assisted bicycle 1 according to the first embodiment. FIG. 2 is a right side view showing the drive unit 40 and the driven sprocket 45 of the battery-assisted bicycle 1 according to the first embodiment.

  As shown in FIG. 1, the battery-assisted bicycle 1 has a body frame 11. The body frame 11 extends in the front-rear direction. The vehicle body frame 11 includes a head pipe 12, a down frame 13, a seat frame 14, a pair of chain stays 16, and a pair of seat stays 17. The head pipe 12 is disposed at the front portion of the battery-assisted bicycle 1. The front end of the down frame 13 is connected to the head pipe 12. The down frame 13 extends in the front-rear direction. The down frame 13 extends obliquely downward from a connection portion with the head pipe 12. The seat frame 14 is connected to the rear end of the down frame 13. The seat frame 14 extends upward and obliquely rearward from the rear end of the down frame 13.

  As shown in FIG. 2, a bracket 15 is attached to the rear end of the down frame 13. A pair of chain stays 16 are connected to the rear end of the bracket 15. As shown in FIG. 1, the pair of chain stays 16 are arranged so as to sandwich the rear wheel 22 from the left and right. As shown in FIG. 2, one end of a seat stay 17 is connected to the rear end of each chain stay 16. As shown in FIG. 1, the pair of seat stays 17 are arranged so as to sandwich the rear wheel 22 from the left and right. As shown in FIG. 1, the other end of each seat stay 17 is connected to the upper portion of the seat frame 14.

  A handle stem 25 is rotatably inserted into the head pipe 12 as shown in FIG. A handle 23 is fixed to the upper end of the handle stem 25. A front fork 26 is fixed to the lower end of the handle stem 25. A front wheel 21 is rotatably supported on the lower end of the front fork 26 by an axle 27.

  Grips 73 are attached to the left and right ends of the handle 23, respectively. A left brake lever 74 is attached to the left part of the handle 23, and a right brake lever 75 is attached to the right part of the handle 23. The left brake lever 74 is a lever for operating a brake (not shown) of the rear wheel 22. The right brake lever 75 is a lever for operating a brake (not shown) of the front wheel 21.

  As shown in FIG. 1, a seat pipe 28 is inserted into the cylindrical seat frame 14. A seat 24 is provided at the upper end of the seat pipe 28.

  A rear wheel 22 is rotatably supported by an axle 29 at the rear ends of the pair of chain stays 16. A driven sprocket 45 coaxial with the axle 29 is provided on the right side of the rear wheel 22. The driven sprocket 45 is connected to the rear wheel 22 via a one-way clutch (not shown).

  A chain cover 47 is attached to the body frame 11. The chain cover 47 has a main cover 48 and a sub cover 49. The main cover 48 extends in the front-rear direction. The main cover 48 covers the right front portion of the drive unit 40 and the chain 46. The sub cover 49 covers the right rear portion of the drive unit 40.

  As shown in FIG. 1, a battery unit 35 is disposed behind the seat frame 14. The battery unit 35 supplies power to the electric motor 61 (see FIG. 2) of the drive unit 40. The battery unit 35 includes a battery and a battery control unit (not shown). The battery is a chargeable / dischargeable rechargeable battery. The battery control unit controls the charging / discharging of the battery, and monitors the output current and remaining capacity of the battery.

  As shown in FIG. 2, the drive unit 40 includes a main body 51, a crankshaft 41, a drive force generator 60, and a chain tensioner 86. FIG. 3 is a cross-sectional view of the drive unit 40 of FIG. 2 taken along line III-III.

  As shown in FIG. 3, the main body 51 has a housing lid 52 and a housing main body 53. The housing lid body 52 and the housing main body 53 are combined with each other from the left and right, and are fixed to each other by a plurality of fasteners 54. The main body 51 is attached to the bracket 15 by a fastening bracket 30. As shown in FIG. 3, the housing main body 53 includes a first housing portion 53 </ b> R that forms the right portion of the drive unit 40 and a second housing portion 53 </ b> L that forms the left portion of the drive unit 40. The first housing portion 53R is formed larger than the second housing portion 53L. The first housing portion 53R and the second housing portion 53L are divided by a wall surface 53P. The housing lid body 52 is fixed to the housing main body 53 so as to close the first housing portion 53R of the housing main body 53.

  A shaft hole 53 a through which the crankshaft 41 passes is formed in the front portion of the housing body 53. Further, a shaft hole 52 a through which the crankshaft 41 passes is formed in the front portion of the housing lid body 52. The crankshaft 41 passes through the drive unit 40 by passing through the shaft holes 53a and 52a. The crankshaft 41 is rotatably supported by the housing main body 53 and the housing lid 53 through the rolling bearings 44A and 44B.

  As shown in FIG. 1, crank arms 31 and 32 are attached to both ends of the crankshaft 41. Pedals 33 and 34 are attached to the tips of the crank arms 31 and 32, respectively. When the user steps on the pedals 33 and 34, the crankshaft 41 rotates. A chain 46 is wound around the first sprocket 42 and a driven sprocket 45.

  As shown in FIG. 3, the rotating member 56, the one-way clutch 55, and the first sprocket 42 are disposed on the crankshaft 41 coaxially with the crankshaft 41. The rotating member 56 and the one-way clutch 55 are accommodated in the first accommodating portion 53 </ b> R of the housing body 53. The rotating member 56 is disposed slightly to the left in the center in the left-right direction of the crankshaft 41. The rotating member 56 is substantially cylindrical. The right end of the rotating member 56 is supported by the crankshaft 41 via a cylindrical slide bearing 71. The central part and the left part of the rotating member 56 are connected to the crankshaft 41. The center part and the left part of the rotation member 56 and the crankshaft 41 are connected by, for example, a spline structure. Thereby, the rotating member 56 rotates integrally with the crankshaft 41.

  The one-way clutch 55 is disposed on the right part of the crankshaft 41. The one-way clutch 55 includes an inner member 55a and an outer member 55b.

  The inner member 55 a is disposed on the right side of the rotating member 56. The inner member 55a has a substantially cylindrical shape and is rotatable with respect to the crankshaft 41. A first sprocket 42 is attached and fixed to the outer peripheral surface at the right end of the inner member 55a. Thereby, the inner member 55a and the 1st sprocket 42 rotate integrally. The first sprocket 42 is disposed on the right side of the housing lid 52.

  The outer member 55b is disposed so as to cover the right part of the rotating member 56 and the left part of the inner member 55a. The outer member 55b is substantially cylindrical. The outer member 55b and the rotating member 56 are connected. The outer member 55b and the rotation member 56 are connected by, for example, a spline structure. Thereby, the outer member 55b and the rotation member 56 rotate integrally.

  The outer member 55b and the inner member 55a are forwardly rotated from the outer member 55b to the inner member 55a (referred to as a clockwise direction when the battery-assisted bicycle 1 is viewed from the right side as shown in FIG. 1, the same applies hereinafter). It is connected to transmit only the rotational force. The outer member 55b and the inner member 55a are connected by, for example, a ratchet structure. The rotational force in the backward rotation direction (referred to as a counterclockwise direction when the battery-assisted bicycle 1 is viewed from the right side as shown in FIG. 1; hereinafter the same) is not transmitted from the outer member 55b to the inner member 55a.

  The crankshaft 41, the first sprocket 42, the one-way clutch 55, and the rotating member 56 are configured as described above. As a result, when the user steps on the pedals 33 and 34 to advance the battery-assisted bicycle 1 and rotates the crankshaft 41 in the forward rotation direction, the pedaling force of the user is transferred from the crankshaft 41 to the rotating member 56. And the outer member 55b. The rotation of the outer member 55b in the forward rotation direction is transmitted to the inner member 55a. For this reason, the first sprocket 42 attached to the inner member 55a rotates in the forward rotation direction. On the other hand, when the user rotates the crankshaft 41 in the backward rotation direction, the rotation in the backward rotation direction is not transmitted from the outer member 55b to the inner member 55a due to the ratchet structure. Therefore, the inner member 55a and the first sprocket 42 do not rotate in the backward rotation direction.

  As shown in FIG. 3, the drive unit 40 is provided with a torque detector 57 near the outer periphery of the rotating member 56. The torque detector 57 is accommodated in the first accommodating portion 53 </ b> R of the housing body 53. The torque detector 57 detects the torque generated in the crankshaft 41 by the pedal effort. The torque detector 57 is, for example, a magnetostrictive torque sensor. In addition to the torque detector 57, the drive unit 40 may be provided with a crank rotation detector (not shown), for example.

  The torque detector 57 is not limited to a magnetostrictive torque sensor as long as the pedal depression force can be detected. The torque detector 57 may be configured to detect the torque of the crankshaft 41 from the tension generated in the chain 46 without directly detecting the torque of the crankshaft 41.

  As shown in FIG. 3, a driving force generation unit 60 is disposed in the center of the main body 51 in the front-rear direction. The driving force generator 60 includes an electric motor 61, an output shaft 81, and a gear 82.

  The electric motor 61 is accommodated in the second accommodating portion 53 </ b> L of the housing body 53. A motor cover 65 that covers the left side of the electric motor 61 is attached to the housing body 53. The motor cover 65 is fixed to the housing main body 53 by a plurality of fasteners 68. The electric motor 61 generates an auxiliary driving force for assisting the travel of the battery-assisted bicycle 1 by the pedal effort based on a control signal output from an assist control unit (not shown) of the control board 38.

  As shown in FIG. 3, the electric motor 61 has a stator 62, a rotor 63, and a motor shaft 64. The stator 62 is fixed to the housing body 53. A shaft hole 53c through which the motor shaft 64 passes is formed in the wall surface 53P of the housing body 53. A motor shaft support portion 65 c that supports the motor shaft 64 is formed on the right side surface of the motor cover 65. The motor shaft 64 passes through the shaft hole 53c and is supported by the motor shaft support portion 65c, thereby being positioned from the second housing portion 53L to the first housing portion 53R. The motor shaft 64 is rotatably supported by the housing body 53 and the motor cover 65 via rolling bearings 66 and 67. A rotor 63 is fixed to the motor shaft 64. A gear groove 64a is formed on the outer periphery of the motor shaft 64 from the right end toward the center. In addition, the electric motor 61 may include, for example, a motor rotation detection unit (not shown).

  A shaft hole 52 b through which the output shaft 81 passes is formed in the rear portion of the housing lid portion 52. An output shaft support portion 53 b that supports the output shaft 81 is formed on the rear and right side of the housing body 53. The output shaft 81 penetrates the shaft hole 52b and is supported by the output shaft support portion 53b, so that the output shaft 81 is positioned so as to protrude rightward from the first housing portion 53R.

  The output shaft 81 is rotatably supported by the housing lid 52 and the housing main body 53 via rolling bearings 83 and 84. The rolling bearing 83 includes an inner race 83A, an outer race 83B, rolling elements 83C, a cage (not shown), and oil seals 83D and 83E with reference to FIG. 6 described later. With reference to FIG. 3, the rolling bearing 84 includes an inner race 84A, an outer race 84B, a rolling element 84C, a cage (not shown), and an oil seal (not shown). Inner races 83 </ b> A and 84 </ b> A of the rolling bearings 83 and 84 are fixed to the output shaft 81. On the other hand, the outer race 83 </ b> B of the rolling bearing 83 is fixed to the housing lid 52. The outer race 84 </ b> B of the rolling bearing 84 is fixed to the housing body 53. As a result, the output shaft 81 can rotate about the shaft L as the center of rotation independently of the housing body 53 and the housing lid 52.

  FIG. 4 is an enlarged perspective view showing one end of the output shaft 81. The end portion of the output shaft 81 from the portion where the inner race 83A is fixed includes the first portion 81A, the second portion 81B that is the end portion from the first portion 81A, and the third portion that is the end portion from the second portion 81B. . A damper 141 described later is attached to the first portion 81A. A second sprocket 43 to be described later is attached to the second portion 81B. A circlip 142 described later is attached to the third portion 81C. The diameter of the second part 81B is smaller than the diameter of the first part 81A, thereby forming a step 81D between the first part 81A and the second part 81B. A spline 81Ba is formed on the surface of the second portion 81B.

  A gear 82 is attached to the output shaft 81 via a one-way clutch 85. The gear 82 is disposed coaxially with the output shaft 81 between the rolling bearing 83 and the rolling bearing 84. The gear 82 meshes with a gear groove 64 a formed on the motor shaft 64 of the electric motor 61. The gear groove 64a and the gear 82 formed in the motor shaft 64 constitute a reduction gear. In the present embodiment, when the electric motor 61 operates, the motor shaft 64 rotates in the forward rotation direction. For this reason, the gear 82 rotates in the backward rotation direction by the rotation of the motor shaft 64 in the forward rotation direction.

  The one-way clutch 85 is configured to transmit only the rotation in the backward rotation direction generated in the gear 82 or the output shaft 81. For this reason, when the electric motor 61 operates and the gear 82 rotates in the backward rotation direction, the rotation is transmitted to the output shaft 81 and the output shaft 81 rotates in the backward rotation direction. On the other hand, even if rotation in the forward direction occurs on the output shaft 81, rotation in the forward direction is not transmitted to the gear 82.

  As shown in FIG. 3, a resin cover 59 that covers the gear 82 and the right side of the motor shaft 64 is attached to the housing main body 53. The control board 38 is disposed on the right side of the resin cover 59 and is fixed to the resin cover 59 and the housing main body 53 by a fastening bracket 39.

  A second sprocket 43 is attached by a sprocket attachment mechanism 140 to one end of the output shaft 81, that is, to the right end of the output shaft 81 and to the right of the resin cover 59. The second sprocket 43 and the output shaft 81 are connected by, for example, a spline structure. The second sprocket 43 rotates integrally with the output shaft 81. Thereby, when the electric motor 61 is operated, the rotation of the motor shaft 64 of the electric motor 61 is transmitted to the second sprocket 43 via the gear 82, the one-way clutch 85, and the output shaft 81. That is, the auxiliary driving force generated by the driving force generator 60 is transmitted from the output shaft 81 to the second sprocket 43, and the second sprocket 43 rotates in the backward rotation direction. Details of the sprocket mounting mechanism 140 will be described later.

  As shown in FIG. 2, a chain tensioner 86 is disposed at the rear part of the main body 51. A tension sprocket 90 is rotatably attached to the chain tensioner 86 by a support bolt 89. As shown in FIG. 2, one end of the chain tensioner 86 is rotatably connected to the housing lid 52 by a support bolt 88. The other end of the chain tensioner 86 is connected to the housing lid 52 via a tension spring 87. A chain 46 is wound around the tension sprocket 90 so as to push the tension sprocket 90 rearward and upward. The chain tensioner 86 applies an appropriate tension to the chain 46 by the elastic force of the tension spring 87.

  As shown in FIG. 2, in the battery-assisted bicycle 1 of the present embodiment, the first sprocket 42 and the second sprocket 43 transmit driving force to the rear wheel 22 via a chain 46. Specifically, the pedal depression force generated when the user depresses the pedals 33 and 34 rotates the first sprocket 42 in the forward rotation direction and drives the rear wheel 22 in the forward rotation direction via the chain 46. Transmitted as power. The rotational force generated by the operation of the electric motor 61 is transmitted as an auxiliary driving force that rotates the second sprocket 43 in the backward rotation direction and rotates the rear wheel 22 in the forward rotation direction via the chain 46. . Thereby, the pedal depression force generated by the user depressing the pedals 33 and 34 is assisted by the driving force output from the electric motor 61.

  FIG. 5 is a right side view of the drive unit 40 when the chain 46 is wound around the first sprocket 42, the second sprocket 43, the tension sprocket 90, and the driven sprocket 45. In FIG. 5, the state in which the chain 46 is wound around the first sprocket 42 and the second sprocket 43 is shown in detail, and the illustration of the configuration of the tension sprocket 90 and the like is omitted. In the first sprocket 42, the chain 46 is wound so that the inner peripheral surface 46 </ b> A of the chain 46 faces the rotation center of the first sprocket 42. In the second sprocket 43, the chain 46 is wound so that the outer peripheral surface 46 </ b> B of the chain 46 faces the rotation center of the second sprocket 43. The chain 46 is bent toward the inner periphery of the chain 46 at a portion wound from the first sprocket 42 to the second sprocket 43. Due to the presence of the second sprocket 43, the chain 46 is bent inward as compared with the case where only the first sprocket 42 and the driven sprocket 45 are wound.

  FIG. 6 is a cross-sectional view showing the sprocket attachment mechanism 140 in which the second sprocket 43 is attached to the output shaft 81. In the sprocket attachment mechanism 140, the damper 141, the second sprocket 43, and the circlip 142 are attached to the output shaft 81. Specifically, as shown in FIG. 4, the damper 141 is attached to the first portion 81 </ b> A of the output shaft 81. The second sprocket 43 is attached to the second portion 81B of the output shaft 81. The second sprocket 43 is restricted from moving in the axial direction toward the inner race 83A by a step 81D formed between the first portion 81A and the second portion 81B. The circlip 142 is attached to the third portion 81 </ b> C of the output shaft 81.

  FIG. 7A is a cross-sectional view of the damper 141 cut along a plane including the axis La of the damper 141. FIG. 7B is a side view of the damper 141. The damper 141 has an annular shape as a whole. The damper 141 has a large diameter portion 141A and a small diameter portion 141B. The large diameter portion 141A and the small diameter portion 141B are integrally formed. The damper 141 is formed with a shaft hole 141C along the axis La. The output shaft 81 is inserted into the shaft hole 141C of the damper 141.

  The diameter of the large diameter portion 141A of the damper 141 is, for example, 20 to 40 mm. The diameter of the small diameter portion 141B of the damper 141 is, for example, 10 to 30 mm. The diameter of the shaft hole 141C is, for example, 5 to 25 mm. The magnitude | size (refer code | symbol 141b of Fig.7 (a)) of the axis | shaft La direction of the damper 141 is 5-20 mm, for example. The damper 141 is formed of an elastic member. Specifically, the damper 141 is made of, for example, urethane resin. The damper 141 is attached to the first portion 81A of the output shaft 81 so that the shaft 141La and the shaft L of the output shaft 81 coincide with each other. The size of the damper 141 in the axis La direction is slightly larger than the size in the axial direction of the first portion 81 of the output shaft 81 (see reference numeral 81Ab in FIG. 4).

  Hereinafter, as shown in FIG. 7, the inner peripheral surface (the surface constituting the shaft hole 141 </ b> C) of the surface of the damper 141 is referred to with reference numeral 141 </ b> D. The outer peripheral surface of the large-diameter portion 141A of the damper 141 is referred to with reference numeral 141E. The outer peripheral surface of the small diameter portion 141B of the damper 141 is referred to with reference numeral 141F. Of the surface of the damper 141, the bottom surface constituting the large diameter portion 141A (that is, the right side surface in a state where the damper 141 is attached to the drive unit 40) is referred to by reference numeral 141G. Of the surface of the damper 141, the bottom surface constituting the small diameter portion 141B (that is, the left side surface in a state where the damper 141 is attached to the drive unit 40) is referred to by reference numeral 141H.

  The inner peripheral surface 141C of the damper 141 preferably has a uniform diameter. Thereby, when the damper 141 is attached to the output shaft 81, the damper 141 can rotate around the axis L with respect to the output shaft 81.

  Referring to FIG. 6 again, the damper 141 is attached to the output shaft 81. The damper 141 is sandwiched between the second sprocket 43 and the inner race 83 </ b> A and is elastically compressed in the axial direction of the output shaft 81. Thereby, in the attachment state of the damper 141, the magnitude | size 141a of the axial direction of the damper 141 is slightly contracted rather than the magnitude | size 141b of the damper 141 in the state before the attachment shown to Fig.7 (a).

  The inner peripheral surface 141D of the damper 141 is in contact with the outer peripheral surface 81Aa of the output shaft 81. The outer peripheral surface 141E of the large-diameter portion 141A of the damper 141 is in contact with the outer peripheral surface 46B of the chain 46 to be wound. Further, the first surface 141G of the surface of the damper 141 facing the one end of the output shaft 81 in the axial direction of the output shaft 81 is in contact with the second sprocket 43. The first surface 141G is a flat surface extending from the inner peripheral surface 141D to the outer peripheral surface 141E. Of the surface of the damper 141, the second surface 141H facing the other end of the output shaft 81 in the axial direction of the output shaft 81 is in contact with the right side surface 83F of the inner race 83A.

  As described above, the second sprocket 43 is attached to the output shaft 81 by a spline structure. The second sprocket 43 rotates integrally with the output shaft 81.

  The circlip 142 is an annular plate member having a notch in a part of the circumference.

  FIG. 8 is an exploded perspective view of the sprocket mounting mechanism 140. The damper 141 and the second sprocket 43 are fitted into the output shaft 81, and the circlip 142 is attached to the output shaft 81, so that the second sprocket 43 is fixed to the output shaft 81. At this time, since the spline formed on the inner periphery of the second sprocket 43 and the spline 81Ba formed on the second portion 81B mesh with each other, the second sprocket 43 cannot rotate with respect to the output shaft 81. Therefore, the sprocket attachment mechanism 140 can be formed only through an easy operation of simply attaching the damper 141, the second sprocket 43, and the circlip 142 to the output shaft 81.

  Further, since the damper 141 is not fixed by baking or bonding to any of the members of the output shaft 81, the second sprocket 43, and the inner race 83A, the parts can be easily replaced when the damper 141 is consumed. be able to.

  As shown in FIG. 8, when the circlip 142 is attached to the third portion 81C, the circlip 142 is pushed into the boundary portion between the third portion 81C and the second portion 81B. As a result, the second sprocket 43 can slightly move in the direction of the axis L between the step 81D and the circlip 142 in the second portion 81B. That is, the second sprocket 43 may rattle between the step 81D and the circlip 142. This rattling may cause abnormal noise. However, the size 141b of the damper 141 in the axis L direction is slightly larger than the size Ab of the first portion 81 in the axis L direction, and the damper 141 is always elastically compressed in the axial direction. The movement of the second sprocket 43 in the axial direction can be restricted by contacting the second sprocket 141. As a result, it is possible to suppress the generation of noise due to the shakiness of the second sprocket 43 in the axial direction.

  With reference to FIG. 6 again, the state where the chain 46 is wound around the second sprocket 43 will be described. Since the damper 141 includes a large diameter portion 141A and the outer peripheral surface 141E of the large diameter portion 141A can contact the outer peripheral surface 46B of the chain 46, the chain 46 wound around the second sprocket 43 is It will be in contact with the large diameter portion 141A. Therefore, when the chain 46 rotates, the damper 141 acts as a cushioning material between the chain 46 and the second sprocket 43, and as a result, the generation of abnormal noise during the traveling of the battery-assisted bicycle 1 is suppressed. Can do.

  In the traveling state of the battery-assisted bicycle 1 (that is, the rotation state of the chain 46), a force that is pressed toward the center of the second sprocket 43 acts on the chain 46 due to the tension applied to the chain 46. The damper 141 is formed of an elastic member. Therefore, in the rotating state of the chain 46, as shown in FIG. 6, the chain 46 is in a state of biting into the outer peripheral surface 141E of the large diameter portion 141A of the damper 141. In other words, the large-diameter portion 141A of the damper 141 is elastically compressed in the direction perpendicular to the axis L while the battery-assisted bicycle 1 is traveling. Since the damper 141 is elastically compressed in the direction perpendicular to the axis L, the chain 46 receives an elastic force in the outer radial direction of the second sprocket 43 from the damper 141. Therefore, it is possible to more reliably suppress the generation of abnormal noise between the chain 46 and the second sprocket 43.

  In the sprocket mounting mechanism 140 of the present embodiment, since the second sprocket 43 is fixed to the output shaft 81 by the circlip 142, the output shaft 81 is compared with the case where the second sprocket 43 is fixed by a bolt or the like. Among them, the length protruding to the right of the second sprocket 43 (that is, the axial size 1Ca of the third portion 81C shown in FIG. 6) can be reduced. As a result, the size of the drive unit 40 in the left-right direction can be reduced.

  In the present embodiment, since the diameter of the inner peripheral surface 141D of the damper 141 is a uniform size, the damper 141 can rotate relative to the output shaft 81 and the second sprocket 43 in the axial direction. Therefore, the inner peripheral surface 141D of the damper 141 is uniformly worn regardless of the irregularities of the splines provided on the outer peripheral surface 81Aa of the output shaft 81. As a result, a highly durable damper 141 can be obtained.

  In the present embodiment, the first surface 141G of the damper 141 is in contact with the second sprocket 43. The first surface 141G is a flat surface extending from the output shaft 81 to the outer peripheral surface 141E. Since the first surface 141G which is a plane is along the plane constituting the second sprocket 43, the damper 141 is deformed along the second sprocket 43 when the damper 141 is deformed by receiving the pressing force from the chain 46. be able to. Therefore, the deformation direction of the damper 141 can be restricted to a direction perpendicular to the axis L, and as a result, the durability of the damper 141 can be enhanced.

  The drive unit 40 of the present embodiment is a drive unit 40 mounted on the battery-assisted bicycle 1, and includes an electric motor 61, an output shaft 81 that rotates by the driving force of the electric motor 61, and an outer peripheral surface 81 </ b> Aa of the output shaft 81. And an inner race 83A that rotates integrally with the output shaft 81, a second sprocket 43 that is attached to one end of the output shaft 81, and that transmits the driving force of the electric motor 61 to the wound chain 46, and an output An annular damper 141 is mounted on the shaft 81 and positioned between the second sprocket 43 and the inner race 83A. Of the surface of the damper 141, the first surface 141G facing the one end of the output shaft 81 in the direction of the axis L of the output shaft 81 contacts the second sprocket 43. Of the surface of the damper 141, the second surface 141H facing the other end of the output shaft 81 in the direction of the axis L of the output shaft 81 contacts the inner race 83A.

  According to the above configuration, the annular damper 141 is fitted on the output shaft 81. Of the surface of the damper 141, the first surface 141G facing the one end of the output shaft 81 in the direction of the axis L of the output shaft 81 contacts the second sprocket 43, and among the surfaces of the damper 141, the output shaft 81 The second surface 141H facing the other end of the output shaft 81 in the direction of the axis L contacts the inner race 83A. Therefore, when the chain 46 is wound around the second sprocket 43 and the chain 46 is rotated, the damper 141 restricts the movement of the output shaft 81 of the second sprocket 43 in the direction of the axis L. Accordingly, it is possible to suppress the generation of abnormal noise due to the movement of the second sprocket 43 in the direction of the axis L. That is, it is possible to suppress the generation of abnormal noise due to the fixing method of the second sprocket 43.

  The damper 141 of this embodiment is provided in a state of being elastically compressed in the direction of the axis L.

  According to the above configuration, since the damper 141 is provided in a state of being elastically compressed in the direction of the axis L, it is more effective that the second sprocket 43 moves in the direction of the axis L of the output shaft 81. Is suppressed. Therefore, the generation of abnormal noise due to the movement of the second sprocket 43 in the direction of the axis L can be more effectively suppressed.

  The second sprocket 43 of the present embodiment is fixed to the output shaft 81 by being sandwiched between a circlip 142 provided on the output shaft 81 and a damper 141.

  According to said structure, since the 2nd sprocket 43 is being fixed to the output shaft 81 with the circlip 142, the attachment operation | work of the 2nd sprocket 43 and the circlip 142 can be performed easily. Further, since the second sprocket 43 is fixed to the output shaft 81 by the circlip 142, it is opposite to the inner race 83A of the second sprocket 43 as compared with the case where the second sprocket 43 is fixed using a nut or the like. The length of the output shaft 81C protruding in the direction can be shortened. As a result, the size of the drive unit 40 in the direction of the axis L can be reduced.

  The first surface 141G of the damper 141 of the present embodiment is positioned so as to be in contact with the second sprocket 43 from the inner periphery of the first surface 141G to the outer periphery of the first surface 141G.

  According to the above configuration, the first surface 141G of the damper 141 is positioned so as to be in contact with the second sprocket 43 from the inner periphery of the first surface 141G to the outer periphery of the first surface 141G. The damper 141 can be deformed along the second sprocket 43 when deformed by receiving the pressing force from the chain 46. Therefore, the deformation direction of the damper 141 can be restricted to a direction perpendicular to the axis L of the output shaft 81, and as a result, the durability of the damper 141 can be improved.

  The damper 141 of the present embodiment is not fixed to any of the output shaft 81, the second sprocket 43, and the inner race 83A. Further, the damper 141 of the present embodiment is rotatably mounted on the output shaft 81.

  According to the configuration described above, the damper 141 is not fixed to any of the output shaft 81, the second sprocket 43, and the inner race 83A, and thus operations such as baking and bonding of the damper 141 are not necessary. Therefore, the operation of attaching the damper 141 to the output shaft 81 can be easily performed.

  Further, according to the above configuration, the damper 141 is not fixed to any of the output shaft 81, the second sprocket 43, and the inner race 83A. Therefore, when the output shaft 81 rotates, the damper 141 can rotate relative to the output shaft 81 and the second sprocket 43 around the axis L of the output shaft 81 as a rotation center. Since the damper 141 can rotate relative to the output shaft 81 and the second sprocket 43, even if the outer peripheral surface 81Aa of the output shaft 81 is uneven, the inner peripheral surface 141D of the damper 141 is used as the output shaft. Regardless of the unevenness of the outer peripheral surface 81Aa of 81, the wear will be uniform. Therefore, according to the configuration described above, the highly durable damper 141 can be obtained.

  Furthermore, according to the above configuration, the damper 141 is not fixed to any of the output shaft 81, the second sprocket 43, and the inner race 83A, so that the parts of the damper 141 can be easily replaced.

  The diameter of the inner peripheral surface 141D of the damper 141 of the present embodiment is a uniform size.

  According to the above configuration, since the diameter of the inner peripheral surface 141D of the damper 141 is a uniform size, the damper 141 has the axis L of the output shaft 81 as the center of rotation with respect to the output shaft 81 and the second sprocket 43. It can rotate relatively. Therefore, the inner peripheral surface 141D of the damper 141 is uniformly worn regardless of the unevenness of the outer peripheral surface 81Aa of the output shaft 81. Therefore, according to the configuration described above, the highly durable damper 141 can be obtained.

  The inner race 83 </ b> A of the present embodiment is a member included in the rolling bearing 83 in which the output shaft 81 is inserted and rotates integrally with the output shaft 81.

  According to the above configuration, the inner race 83A is a member included in the rolling bearing 83 into which the output shaft 81 is inserted and rotates integrally with the output shaft 81. The movement of the damper 141 in the direction can be restricted.

  The inner peripheral surface 141 </ b> D of the damper 141 according to the present embodiment is in contact with the outer peripheral surface 81 </ b> Aa of the output shaft 81. At least a part of the outer peripheral surface of the damper 141 of the present embodiment is positioned so as to be in contact with the chain 46.

  According to the above configuration, the annular damper 141 is mounted on the output shaft 81 and is positioned between the second sprocket 43 and the inner race 83A. Since the inner peripheral surface 141D of the damper 141 is in contact with the outer peripheral surface 81Aa of the output shaft 81 and at least a part of the outer peripheral surface of the damper 141 can contact the chain 46, the chain 46 is wound around the second sprocket 43. When the chain 46 is rotated, the damper 141 acts as a cushion material. Therefore, it is possible to suppress the generation of abnormal noise between the chain 46 and the second sprocket 43 when the chain 46 is rotated.

  The damper 141 according to the present embodiment is formed integrally with the large diameter portion 141A on the inner race 83A side of the large diameter portion 141A and is positioned smaller than the large diameter portion 141A. And a small-diameter portion 141B having a diameter.

  According to the above configuration, the portion of the damper 141 that meshes with the chain 46 is the large-diameter portion 141A, while the portion that does not contact the chain 46 is the small-diameter portion 141B, so the entire damper 141 is large. Compared to the case where the diameter is the same as the diameter portion 141A, the damper 141 is easily deformed. Therefore, when the chain 46 is wound around the second sprocket 43 and the chain 46 comes into contact with the large-diameter portion 141A of the damper 141, the large-diameter portion 141A is deformed and the chain 46 is likely to bite into the large-diameter portion 141A. It has become. Therefore, when the chain 46 is wound around the second sprocket 43 and the chain 46 is rotated, the damper 141 acts more effectively as a cushioning material, and as a result, a more excellent noise suppression effect is obtained.

  The damper 141 of this embodiment is formed of an elastic member.

  According to said structure, since the damper 141 is formed with the elastic member, the drive unit 40 can be formed cheaply. Moreover, since the damper 141 is formed of an elastic member, the damper 141 is easily deformed, and the damper 141 can effectively act as a cushioning material.

  Since the battery-assisted bicycle 1 of the present embodiment includes the drive unit 40 described above, it is possible to suppress the generation of abnormal noise between the chain 46 and the second sprocket 43 when the chain 46 is rotated. .

  The attachment mechanism 140 of the second sprocket 43 of the present embodiment is attached to the output shaft 81, an inner race 83 </ b> A that is fixed to the outer peripheral surface 81 </ b> Aa of the output shaft 81 and rotates integrally with the output shaft 81, and one end of the output shaft 81. The second sprocket 43, the chain 46 wound around the second sprocket 43, an annular damper 141 mounted on the output shaft 81 and positioned between the second sprocket 43 and the inner race 83A. Have. Of the surface of the damper 141, the first surface 141G facing the one end of the output shaft 81 in the direction of the axis L of the output shaft 81 contacts the second sprocket 43. Of the surface of the damper 141, the second surface 141H facing the other end of the output shaft 81 in the direction of the axis L of the output shaft 81 contacts the inner race 83A.

  According to the above configuration, the annular damper 141 is fitted on the output shaft 81. Of the surface of the damper 141, the first surface 141G facing the one end of the output shaft 81 in the direction of the axis L of the output shaft 81 contacts the second sprocket 43, and among the surfaces of the damper 141, the output shaft 81 The second surface 141H facing the other end of the output shaft 81 in the direction of the axis L contacts the inner race 83A. Therefore, when the chain 46 wound around the second sprocket 43 is rotated, the damper 141 restricts the movement of the output shaft 81 of the second sprocket 43 in the direction of the axis L. Accordingly, it is possible to suppress the generation of abnormal noise due to the movement of the second sprocket 43 in the direction of the axis L. That is, it is possible to suppress the generation of abnormal noise due to the fixing method of the second sprocket 43.

[Other Embodiments]
Hereinafter, modified embodiments of the present invention will be described.

  In the present embodiment, the damper 141 has been described as including the large-diameter portion 141A and the small-diameter portion 141B, but is not particularly limited thereto. For example, the diameter of the outer peripheral surface of the damper 141 may be constant. In this case, the portion corresponding to the small diameter portion 141B of the present embodiment has the same diameter as the portion corresponding to the large diameter portion 141A. However, from the point that the chain 46 is easy to bite in the direction of the axis L at the portion of the outer peripheral surface of the damper 141 that contacts the chain 46 (the portion corresponding to the large diameter portion 141A of the present embodiment), the damper 141 is It is preferable that the large diameter portion 141A and the small diameter portion 141B are configured. Further, since the space for providing the left portion of the damper 141 (the portion corresponding to the small diameter portion 141B of the present embodiment) is narrow, the left portion of the damper 141 has a smaller diameter than the right portion from the viewpoint of increasing the degree of design freedom. It is preferable that

  In the present embodiment, it has been described that the first surface 141G constituting the large-diameter portion 141A of the damper 141 is a flat surface and is attached along the side surface of the second sprocket 43, but at least the outer peripheral surface of the damper 141 is If a part can contact with the chain 46, it is not limited to this. For example, the right side of the outer peripheral surface of the damper 141 with respect to the chain 46 may have a smaller diameter than the chain contact portion. However, when the damper 141 is deformed by receiving a pressing force from the chain 46, if the first surface 141G is a plane along the side surface of the second sprocket 43, the deformation direction of the damper 141 is perpendicular to the axis L. As a result, the durability of the damper 141 can be enhanced. Therefore, the first surface 141G is preferably a flat surface along the side surface of the second sprocket 43.

  In the present embodiment, the damper 141 has been described as an elastic member, but the present invention is not particularly limited thereto. When the damper 141 is not an elastic member, the damper 141 is not elastically compressed in the axial direction. Further, even when the chain 46 is wound around the large-diameter portion 141A of the damper 141, the damper 141A is hardly compressed toward the direction of the axis L. However, since the effect of suppressing the movement of the second sprocket 43 in the axial direction can be enhanced by elastically compressing the damper 141 in the axial direction, the damper 141 is preferably formed of an elastic member. In addition, when the chain 46 is wound around the large-diameter portion 141A of the damper 141, the damper 141A is compressed in the direction of the axis L, so that the function of the damper 141 as a cushioning material is enhanced. 141 is preferably formed of an elastic member.

  In the present embodiment, the damper 141 has been described as being in contact with both the outer peripheral surface 81Aa of the output shaft 81 and the chain 46, but this is not an essential configuration of the present invention. The damper 141 may not be in contact with both the outer peripheral surface 81Aa of the output shaft 81 and the chain 46. Even in this case, since the damper 141 is sandwiched between the second sprocket 43 and the inner race 83A and is elastically compressed in the axial direction, the second sprocket 43 is moved in the axial direction (rattle). Can suppress abnormal noise. However, in order to suppress abnormal noise generated between the chain 46 and the second sprocket 43 in addition to suppressing abnormal noise due to the axial movement of the second sprocket 43, the damper 141 may be It is preferable that both the outer peripheral surface 81Aa and the chain 46 are in contact.

  In the present embodiment, it has been described that the diameter of the inner peripheral surface 141D of the damper 141 is constant and rotates around the axis L with respect to the output shaft 81, but is not particularly limited thereto. For example, as shown in FIG. 9, when the spline 81Ac of the output shaft 81 is formed up to the first portion 81A to which the damper 141 is attached, the inner peripheral surface 141D of the damper 141 has unevenness along the spline 81Ac. The output shaft 81 and the damper 141 may be spline-coupled. In this case, the damper 141 cannot rotate with respect to the output shaft 81. When the damper 141 cannot rotate with respect to the output shaft 81, the convex portion of the spline of the output shaft 81 comes into contact with a certain portion of the damper 141. That is, there will be a portion of the inner peripheral surface 141D of the damper 141 where the wear due to the spline convex portion of the output shaft 81 and a portion where the wear due to the spline convex portion does not occur. Therefore, the wear of the damper 141 becomes uneven, and the durability of the damper 141 may be reduced. In view of this point, it is preferable that the diameter of the inner peripheral surface 141 </ b> D of the damper 141 is constant and is rotatable with respect to the output shaft 81. In addition, it is preferable that the diameter of the inner peripheral surface 141D of the damper 141 is constant from the viewpoint that the molding of the damper 141 is easy.

  In the present embodiment, it has been described that the second surface 141H constituting the small diameter portion 141B of the damper 141 is in contact with the surface 83F constituting the inner race 83A of the bearing 83, but is not particularly limited thereto. The second surface 141H is not limited to the inner race 83A, but may be fixed to the outer peripheral surface of the output shaft 81 and be in contact with a member that rotates integrally with the output shaft 81. For example, an annular first member may be provided on the right side of the inner race 83A as a member with which the second surface 141H is in contact. However, it is preferable that the second surface 141H is in contact with the inner race 83A from the point that it is not necessary to separately provide a member in contact with the second surface 141H.

  In the present embodiment, the circlip 142 is fitted to the output shaft 81 on the right side of the second sprocket 43 and the second sprocket 43 is fixed by the circlip 142, but the second sprocket 43 is It may be fixed by means other than the circlip 142. For example, the second sprocket 43 may be fixed using a bolt or the like. However, from the viewpoint of reducing the size of the drive unit 40 in the left-right direction, it is preferable to fix the second sprocket 43 by the circlip 142 and shorten the length of the output shaft 81.

  In the present embodiment, it has been described that the drive unit 40 includes the three shafts of the crankshaft 41, the motor shaft 64, and the output shaft 81. However, the drive unit having a configuration in which the motor shaft and the output shaft are integrated (that is, The sprocket mounting structure of the present invention can be applied even to a drive unit including a crankshaft and a motor output shaft. When the drive unit includes two shafts, the chain 46 contacting the outer peripheral surface 46B of the chain 46 is wound around the sprocket of the motor output shaft. Therefore, the sprocket mounting structure of the present invention is applied to the sprocket of the motor output shaft. It is preferable to apply.

1 Electric Assist Bicycle 40 Drive Unit 43 Second Sprocket 46 Chain 81 Output Shaft (Drive Shaft)
83 Rolling bearing 83A Inner race 140 Sprocket mounting mechanism 141 Damper 141G First surface 141H Second surface 142 Circlip

Claims (12)

A drive unit mounted on a battery-assisted bicycle,
A motor,
A drive shaft that is rotated by the driving force of the motor;
A first member fixed to the outer peripheral surface of the drive shaft and rotating integrally with the drive shaft;
A sprocket attached to one end of the drive shaft and transmitting the driving force of the motor to a wound chain;
An annular damper mounted on the drive shaft and positioned between the sprocket and the first member;
Have
Of the surface of the damper, a first surface facing one end of the drive shaft in the axial direction of the drive shaft is in contact with the sprocket,
A drive unit in which a second surface of the surface of the damper facing the other end of the drive shaft in the axial direction of the drive shaft is in contact with the first member. The drive unit according to claim 1, wherein
The damper is a drive unit provided in a state of being elastically compressed in the axial direction. The drive unit according to claim 2,
The sprocket is a drive unit that is sandwiched between a circlip provided on the drive shaft and the damper and fixed to the drive shaft. In the drive unit according to any one of claims 1 to 3,
The drive unit, wherein the first surface is positioned so as to be in contact with the sprocket from an inner periphery of the first surface to an outer periphery of the first surface. In the drive unit according to any one of claims 1 to 4,
The damper is not fixed to any of the drive shaft, the sprocket and the first member,
The drive unit, wherein the damper is rotatably mounted on the drive shaft. The drive unit according to claim 5,
A drive unit in which a diameter of an inner peripheral surface of the damper is a uniform size. In the drive unit according to any one of claims 1 to 6,
The first member includes a bearing having an inner race that rotates integrally with the drive shaft while the drive shaft is inserted therein.
The drive unit in which the inner race of the first member contacts the damper. In the drive unit according to any one of claims 1 to 7,
The inner peripheral surface of the damper is in contact with the outer peripheral surface of the drive shaft,
At least a part of the outer peripheral surface of the damper is a drive unit positioned so as to be in contact with the chain. The drive unit according to claim 8,
The damper has a large-diameter portion positioned so as to mesh with the chain, and a small-diameter having a smaller diameter than the large-diameter portion, formed integrally with the large-diameter portion on the first member side of the large-diameter portion. And a drive unit. In the drive unit according to any one of claims 1 to 9,
The damper is a drive unit formed of an elastic member.   A battery-assisted bicycle comprising the drive unit according to any one of claims 1 to 10. A drive shaft;
A first member fixed to the outer peripheral surface of the drive shaft and rotating integrally with the drive shaft;
A sprocket attached to one end of the drive shaft;
A chain wound around the sprocket;
An annular damper mounted on the drive shaft and positioned between the sprocket and the first member;
Have
Of the surface of the damper, a first surface facing one end of the drive shaft in the axial direction of the drive shaft is in contact with the sprocket,
A sprocket mounting mechanism in which a second surface of the surface of the damper that faces the other end of the drive shaft in the axial direction of the drive shaft contacts the first member.

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