Drive unit for power-assisted bicycle and power-assisted bicycle

Abstract

The invention relates to a drive unit for a power-assisted bicycle and a power-assisted bicycle. In the drive unit, the housing and the rotatable shaft contain different metal materials from each other; an outer peripheral portion of the dust seal is in contact with an inner peripheral portion of an opening of the housing, the opening allowing the rotatable shaft to pass through; an outer end of an inner peripheral portion of the opening of the housing in a rotation axis direction of the rotatable shaft includes a chamfered portion whose diameter increases toward an outer side of the opening; the dust seal includes a first lip covering the chamfered portion; and the dust seal does not protrude to the outside of the outermost portion of the opening in the rotation axis direction in the rotation axis direction.

Description

Technical Field

[0001] The present invention relates to a drive unit for an electric assist bicycle and an electric assist bicycle. Background Art

[0002] A variety of people, whether old or young, widely use bicycles as an easy means of transportation. In recent years, electric assist bicycles have been rapidly increasing, and with such electric assist bicycles, the power of the user's pedal strokes is assisted by an electric motor (for example, see Japanese Patent Laid-Open Publication No. 2007-230411).

[0003] Such an electric motor is supplied with electric power from a battery mounted on a vehicle (i.e., an electric assist bicycle) and thus generates a driving force. The electric assist bicycle causes the electric motor to generate a driving force corresponding to the power of the human body, specifically, the power provided by the user to the pedals, and thus reduces the load applied to the user, for example, when traveling on a slope or traveling with a load. Summary of the Invention

[0004] A drive unit for an electric assist bicycle includes a housing that houses an electric motor and a rotatable shaft that is partially exposed to the outside of the housing. For example, a crank arm is attached to the rotatable shaft.

[0005] When the housing and the rotatable shaft include different metal materials from each other, there is a problem that electrolytic corrosion (galvanic corrosion) easily occurs when water accumulates between the opening of the housing and the rotatable shaft.

[0006] It is required to suppress electrolytic corrosion of the drive unit of the electric assist bicycle.

[0007] This specification discloses a drive unit and an electric assist bicycle described in the following.

[0008] [Item 1]

[0009] A drive unit for an electric assist bicycle 1, the drive unit including:

[0010] An electric motor;

[0011] A housing that houses the electric motor;

[0012] A rotatable shaft that is rotatably supported by the housing and is partially exposed to the outside of the housing; and

[0013] An annular dust seal provided between the rotatable shaft and the housing, the dust seal suppressing dust from entering the inside of the housing from the outside of the housing,

[0014] wherein,

[0015] The housing and the rotatable shaft include different metal materials from each other.

[0016] The inner peripheral portion of the dust seal is in slidable contact with the rotatable shaft.

[0017] The outer peripheral portion of the dust seal is in contact with the inner peripheral portion of the opening of the housing, and the opening allows the rotatable shaft to pass through.

[0018] The outer end of the inner peripheral portion of the opening of the housing in the direction of the rotation axis of the rotatable shaft includes a chamfered portion, and the diameter of the chamfered portion increases toward the outside of the opening.

[0019] The dust seal includes a first lip covering the chamfered portion, and

[0020] The dust seal does not project outside the outermost portion of the opening in the direction of the rotation axis in the direction of the rotation axis.

[0021] In the case where the housing and the rotatable shaft include different metal materials from each other, when water accumulates between the opening of the housing and the rotatable shaft, electrolytic corrosion (galvanic corrosion) is likely to occur. The electrolytic corrosion can be suppressed to some extent by the coating applied to the opening. However, there are cases where the coating is not applied to the opening in a satisfactory manner. For example, in the case where the protrusion provided at the opening is thin, the coating is not applied to the protrusion in a satisfactory manner. According to an embodiment of the present invention, the dust seal includes a first lip covering the chamfered portion of the opening. The first lip covers the chamfered portion so that the electrolytic corrosion can be suppressed even when the coating is not applied to the opening in a satisfactory manner.

[0022] According to an embodiment of the present invention, the dust seal does not project outside the outermost portion of the opening in the direction of the rotation axis. With such an arrangement, the size of the drive unit in the width direction can be reduced.

[0023] A crank arm can be attached to the rotatable shaft. If the dust seal projects outside the opening of the housing, the dust seal will interfere with the crank arm or the like. Since the dust seal does not project outside the opening in this embodiment, the interference between the dust seal and the crank arm can be suppressed.

[0024] [Item 2]

[0025] The drive unit according to Item 1, wherein the first lip of the dust seal is formed to extend outward in the direction of the rotation axis while extending away from the rotatable shaft.

[0026] With such an arrangement, the chamfered portion of the opening can be suitably covered.

[0027] [Item 3]

[0028] The drive unit according to item 1 or item 2, wherein

[0029] A groove is provided in the inner peripheral portion of the opening along the circumferential direction of the opening, and

[0030] The outer peripheral portion of the dust-proof seal includes a second lip fitted into the groove.

[0031] Since the second lip of the dust-proof seal is fitted into the groove of the opening, the dust-proof seal can be fastened to the housing.

[0032] [Item 4]

[0033] The drive unit according to item 3, wherein

[0034] The opening includes a protrusion that serves as an outer wall of the groove in the direction of the rotation axis, and

[0035] The chamfered portion is provided at the protrusion.

[0036] Even when the paint is not applied to the opening in a satisfactory manner, the first lip covers the chamfered portion, thereby suppressing electrolytic corrosion.

[0037] [Item 5]

[0038] The drive unit according to item 3 or 4, wherein the second lip of the dust-proof seal is fitted into the groove by snap fit.

[0039] The dust-proof seal can be fastened to the housing by snap fit. In addition, water and dust entering the interior of the housing can be more effectively suppressed.

[0040] [Item 6]

[0041] The drive unit according to item 4, wherein the first lip and the second lip of the dust-proof seal hold the protrusion between the first lip and the second lip by elastic force.

[0042] With such an arrangement, it is not easy to form a gap between the first lip and the chamfered portion, thereby suppressing electrolytic corrosion more effectively. In addition, water and dust entering the interior of the housing can be more effectively suppressed.

[0043] [Item 7]

[0044] The drive unit according to item 1 or item 2, wherein the dust-proof seal is press-fitted into the opening.

[0045] The dust-proof seal is press-fitted into the opening, thereby being fastened to the housing.

[0046] [Item 8]

[0047] The drive unit according to any one of Items 1 to 7, wherein the inner peripheral portion of the dust seal includes a sealing lip that is in slidable contact with the rotatable shaft.

[0048] With such an arrangement, it is possible to suppress oil from flowing from the inside of the housing to the outside and water and dust from entering the inside from the outside of the housing.

[0049] [Item 9]

[0050] The drive unit according to Item 8, wherein the inner peripheral portion of the dust seal further includes a dust lip that is in slidable contact with the rotatable shaft and is positioned more outward in the direction of the rotation axis than the sealing lip.

[0051] With such an arrangement, it is possible to suppress dust from entering the inside from the outside of the housing.

[0052] [Item 10]

[0053] The drive unit according to any one of Items 1 to 9, wherein the housing contains a metallic material containing magnesium as a main component.

[0054] With such an arrangement, it is possible to reduce the weight of the drive unit.

[0055] [Item 11]

[0056] The drive unit according to any one of Items 1 to 10, wherein the rotatable shaft contains a metallic material containing iron as a main component.

[0057] With such an arrangement, it is possible to achieve the required rigidity and strength levels of the rotatable shaft at low cost.

[0058] [Item 12]

[0059] An electric assist bicycle including the drive unit according to any one of Items 1 to 11.

[0060] With such an arrangement, it is possible to realize an electric assist bicycle including a highly waterproof and compact drive unit.

[0061] In the case where the housing and the rotatable shaft of the drive unit are made of different metal materials, when water accumulates between the opening of the housing and the rotatable shaft, electrolytic corrosion (galvanic corrosion) is likely to occur. The electrolytic corrosion can be suppressed to some extent by the paint applied to the opening. However, there are cases where the paint is not applied to the opening in a satisfactory manner. For example, when the protrusion provided at the opening is thin, the paint is not applied to the protrusion in a satisfactory manner. According to an embodiment of the present invention, the dust seal includes a first lip covering the chamfered portion of the opening. The first lip covers the chamfered portion so that the electrolytic corrosion can be suppressed even when the paint is not applied to the opening in a satisfactory manner.

[0062] According to an embodiment of the present invention, the dust seal does not protrude outside the outermost portion of the opening in the rotational axis direction. With such an arrangement, the size of the drive unit in the width direction can be reduced.

[0063] The crank arm can be attached to the rotatable shaft. If the dust seal protrudes outside the opening of the housing, the dust seal will interfere with the crank arm or the like. Since the dust seal does not protrude outside the opening in this embodiment, the interference between the dust seal and the crank arm can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 is a right side view showing an electric assist bicycle 1 according to an embodiment of the present invention;

[0065] Figure 2 is a cross-sectional view showing an example of the internal structure of a drive unit 20 according to an embodiment of the present invention;

[0066] Figure 3 is a cross-sectional view showing a part of a housing 21 according to an embodiment of the present invention;

[0067] Figure 4 is a cross-sectional view showing an opening 261 of a housing 21 and a rotatable shaft 30 passing through the opening 261 according to an embodiment of the present invention;

[0068] Figure 5 is a perspective view showing a dust seal 60 taken along a plane parallel to the rotational axis direction D1 according to an embodiment of the present invention;

[0069] Figure 6 is a partially enlarged cross-sectional view of a drive unit 20 according to an embodiment of the present invention;

[0070] Figure 7 is a partially enlarged cross-sectional view of a drive unit 20 according to an embodiment of the present invention;

[0071] Figure 8is a cross-sectional view showing the positional relationship between the opening 261 of the housing 21 and the dust-proof seal 60 in the rotational axis direction D1 according to an embodiment of the present invention;

[0072] Figure 9 is a cross-sectional view showing the dust-proof seal 60 in a state where the dust-proof seal 60 is fastened to the inner peripheral portion 262 of the opening 261 by press-fitting according to an embodiment of the present invention. Detailed Description

[0073] Embodiments of the present invention will be described below with reference to the accompanying drawings. In the description of the embodiments, similar elements will be denoted by similar reference numerals, and repeated descriptions will be omitted. In the drawings, the letters F, Re, L, R, U, and D respectively represent front, rear, left, right, up, and down. The "front-rear" direction, "left-right" direction, and "up-down" direction of the power-assisted bicycle respectively indicate the front-rear direction, left-right direction, and up-down direction of a user sitting on the seat (saddle) of the power-assisted bicycle when facing the handlebars. The following embodiments are merely illustrative and do not limit the present invention in any way.

[0074] [Power-assisted Bicycle]

[0075] Figure 1 is a right side view of the power-assisted bicycle 1 according to an embodiment of the present invention.

[0076] The power-assisted bicycle 1 includes a main body frame 2 extending in the front-rear direction. The main body frame 2 includes a head tube 11, a down tube 12, an upper tube 14, a seat tube 16, a flat fork 18, a vertical fork 19, and a bracket 26. The head tube 11 is located at the front end of the main body frame 2. The handlebar 13 is rotatably inserted into the head tube 11. The handle 4 is fastened to the handlebar 13. The meter unit 5 for displaying various types of information about the power-assisted bicycle 1 is provided on the handle 4. The headlamp 59 is provided in front of the handle 4.

[0077] The front fork 15 is fastened to the bottom end of the handlebar 13. The bottom end of the front fork 15 supports the front wheel 6 serving as a steering wheel so that the front wheel 6 is rotatable.

[0078] The down tube 12 extends obliquely backward and downward from the head tube 11. The seat tube 16 extends upward from the rear end of the down tube 12. The flat fork 18 extends backward from the bottom end of the seat tube 16. The bracket 26 connects the rear end of the down tube 12, the bottom end of the seat tube 16, and the front end of the flat fork 18 to each other. The upper tube 14 is provided to connect the top of the head tube 11 and the top of the seat tube 16 to each other. The seat post 17 is inserted into the seat tube 16. The saddle 3 on which the user can sit is provided at the top end of the seat post 17.

[0079] The rear end of the swing arm 18 supports the rear wheel 7 that serves as a drive wheel, enabling the rear wheel 7 to rotate. The stand-up fork 19 extends obliquely backward and downward from the top of the seat tube 16. The bottom end of the stand-up fork 19 is connected to the rear end of the swing arm 18. A transmission 58 for changing the gear ratio is provided at the rear end of the swing arm 18. The transmission 58 may be provided near the pedal crankshaft 22. A speed sensor 55 detects the rotational speed of the rear wheel 7 and is provided on the rear part of the swing arm 18. The speed sensor 55 may be provided at the bottom of the front fork 15 to detect the rotational speed of the front wheel 6.

[0080] The drive unit 20 is provided on a bracket 26 that is located near the position at the center of the main body frame 2 of the vehicle (i.e., the power-assisted bicycle 1). The housing 21 of the drive unit 20 ( Figure 2 ) houses the motor 25, the MCU (motor control unit), the reduction gear 24 ( Figure 2 ) and so on. The pedal crankshaft 22 is supported by passing through the drive unit 20 in the left-right direction. Crank arms 35 are respectively provided at both ends of the pedal crankshaft 22. The pedals 37 are respectively rotatably supported at the ends of the crank arms 35.

[0081] The battery unit 56 for supplying power to the drive unit 20 etc. is mounted on the down tube 12. In Figure 1 the illustrated example, the battery unit 56 is provided inside the down tube 12. The down tube 12 may be hollow. At least a part of the down tube 12 may have a U-shaped cross-section, and the down tube 12 may be provided with a lid covering the U-shaped part.

[0082] The battery unit 56 may be located on the outer surface of the down tube 12. The battery unit 56 may be mounted on the bracket 26 or the seat tube 16. The battery unit 56 is detachable from the power-assisted bicycle 1.

[0083] The battery unit 56 includes a battery and a BMS (battery management system). The battery is a rechargeable battery. The MBS controls the charging / discharging of the battery and monitors the output current of the battery, the remaining battery capacity, etc.

[0084] The MCU of the drive unit 20 controls the operation of the motor 25 and also controls the operation of the various components of the power-assisted bicycle 1. The MCU includes a semiconductor integrated circuit such as a processor and a motor drive circuit. The rotation of the pedal crankshaft 22 generated by the user stepping on the pedal 37 is transmitted to the rear wheel 7 via the drive sprocket 34 and the chain 53. The MCU controls the motor 25 to generate a drive assist output corresponding to the rotational output of the pedal crankshaft 22 generated by the user stepping on the pedal 37. The auxiliary power generated by the motor 25 is transmitted to the rear wheel 7 via the drive sprocket 34 and the chain 53. A belt, a shaft, etc. may be used instead of the chain 53.

[0085] [Drive Unit]

[0086] For Figure 2 , an example of the configuration of the drive unit 20 will be described. Figure 2 is a cross-sectional view showing an example of the internal configuration of the drive unit 20.

[0087] As Figure 2 shown, the drive unit 20 includes a housing 21, a rotatable shaft 30, a transmission mechanism 40, and a motor 25.

[0088] First, the configuration of the housing 21 according to the present embodiment will be described.

[0089] The housing 21 is fastened to the bracket 26 by a plurality of fasteners (see Figure 1 ). The housing 21 includes a first housing 211, a second housing 212, and a lid 213. The housing 21 is formed of a metallic material (magnesium alloy) containing magnesium as a main component, for example. Using a metallic material containing magnesium as a main component can reduce the weight of the drive unit 20.

[0090] The first housing 211 is stacked on the second housing 212 in the left-right direction, more specifically, from the left. The first housing 211 and the second housing 212 are fastened to each other by a plurality of fasteners. As a result, a space 214 is formed between the first housing 211 and the second housing 212.

[0091] The lid 213 is stacked on the first housing 211 in the left-right direction, more specifically from the left. The lid 213 and the first housing 211 are fastened to each other by a plurality of fasteners. As a result, a space 215 covered by the lid 213 is formed to the left of the first housing 211. The motor 25 is accommodated in the space 215.

[0092] Now, the configuration of the rotatable shaft 30 according to the present embodiment will be described. The rotatable shaft 30 includes a pedal crankshaft 22 and a rotating shaft 23.

[0093] The rotatable shaft 30 penetrates the housing 21 in the vehicle left-right direction and is rotatably supported by the housing 21.

[0094] Figure 3 is a cross-sectional view showing a part of the housing 21. An opening 261 is provided in the first housing 211 of the housing 21. An opening 281 is provided in the second housing 212. Both the opening 261 and the opening 281 are cylindrical. The rotatable shaft 30 passes through the opening 261 and the opening 281, and thus a part of the rotatable shaft 30 is exposed to the outside of the housing 21.

[0095] The central axis CL4 of the pedal crankshaft 22 extends in the left-right direction. When viewed in the axial direction (thrust direction) of the pedal crankshaft 22, the central axis CL4 is the rotation center axis RC4 (the fourth central axis) of the pedal crankshaft 22. The pedal crankshaft 22 rotates relative to the housing 21 about the central axis CL4. The rotation center axis RC4 is the rotation axis of the rotatable shaft 30.

[0096] The rotatable shaft 30 including the pedal crankshaft 22 penetrates the housing 21 along the fourth central axis RC4 and is supported by the housing 21 so as to be rotatable about the fourth central axis RC4. The pedal crankshaft 22 is rotatably supported by the bearing pair 38L and 38R within the housing 21. The bearing 38L is located on the left side in the axial direction and is fastened to the first housing 211. The bearing 38R is located on the right side in the axial direction and is fastened to the second housing 212.

[0097] The pedal crankshaft 22 is positioned to penetrate the rotating shaft 23. The rotating shaft 23 is accommodated in the housing 21. The rotating shaft 23 will be described in detail below. A pair, more specifically, left and right crank arms 35 ( Figure 1 ) are attached to the pedal crankshaft 22. The pedals 37 ( Figure 1 ) are respectively attached to the crank arms 35.

[0098] The pedal crankshaft 22 is made of a metal material that contains iron as a main component, such as carbon steel, alloy steel, etc. Using such a metal material containing iron as a main component can achieve the required rigidity and strength levels of the pedal crankshaft 22 at low cost.

[0099] Now, the structure of the motor 25 and the transmission mechanism 40 according to the present embodiment will be described.

[0100] The motor 25 is accommodated in the housing 21 and is fastened to the housing 21. The motor 25 generates a driving force to assist the electric assist bicycle 1 in traveling. The motor 25 includes a stator 251 and a rotor 252.

[0101] The stator 251 includes a plurality of bobbins 2512, and coils 2511 are wound around each bobbin. The iron cores 2513 are inserted into each bobbin 2512. The stator 251 is located in the space 215. In this state, the stator 251 is fastened to the first housing 211.

[0102] The rotor 252 is located within the stator 251. The central axis CL1 of the rotor 252 is parallel to the central axis CL4 of the pedal crankshaft 22. That is, the rotor 252 is positioned parallel to the pedal crankshaft 22. When viewed in the axial direction of the pedal crankshaft 22, the central axis CL1 is the rotation center axis RC1 (the first central axis) of the rotor 252.

[0103] The rotor 252 includes a rotor main body 2521 and an output shaft 2522. The outer peripheral surface of the rotor main body 2521 is magnetized alternately with N poles and S poles.

[0104] The output shaft 2522 is positioned to penetrate the rotor main body 2521. The output shaft 2522 is fastened to the rotor main body 2521. That is, the output shaft 2522 rotates together with the rotor main body 2521.

[0105] The output shaft 2522 is supported by the housing 21 so as to be rotatable about a first central axis RC1 within the housing 21. The output shaft 2522 is supported by two bearings 42L and 42R so as to be rotatable about a central axis CL1 relative to the housing 21. The bearing 42L is fastened to the lid 213. The bearing 42R is located on the right side of the rotor main body 2521 and is fastened to the first housing 211. The output shaft 2522 is positioned to penetrate the first housing 211. An output gear 252A is formed on the right portion of the output shaft 2522. The output gear 252A is, for example, a helical gear.

[0106] The transmission mechanism 40 is housed in the housing 21. Specifically, the transmission mechanism 40 is located in the space 214. The transmission mechanism 40 includes a speed reducer 24, an idler gear 41, and a rotating shaft 43. The transmission mechanism 40 transmits the torque of the motor 25 to the rotating shaft 23.

[0107] The speed reducer 24 is rotatably supported by the housing 21 and increases the torque of the output gear 252A of the motor 25. The speed reducer 24 includes a first transmission gear 241, a second transmission gear 242, and a transmission shaft 243. The central axis CL2 of the transmission shaft 243 is parallel to the central axis CL4 of the pedal crankshaft 22. That is, the transmission shaft 243 extends parallel to the central axis CL4 of the pedal crankshaft 22. When viewed in the axial direction of the transmission shaft 243 (i.e., the axial direction of the pedal crankshaft 22), the central axis CL2 is the rotation central axis RC2 (second central axis) of the transmission shaft 243. The speed reducer 24 is supported by the housing 21 so as to be rotatable about the second central axis RC2 within the housing 21.

[0108] The first transmission gear 241 is located on the right portion of the transmission shaft 243 in the axial direction. The left portion of the transmission shaft 243 is rotatably supported by a bearing 44L. The first transmission gear 241 located on the right portion of the transmission shaft 243 is rotatably supported by a bearing 44R. The transmission shaft 243 and the first transmission gear 241 are supported by two bearings 44L and 44R so as to be rotatable about the central axis CL2. The bearing 44L is fastened to the first housing 211. The bearing 44R is fastened to the second housing 212.

[0109] The first transmission gear 241 meshes with the output gear 252A of the motor 25. With this arrangement, the driving force generated by the motor 25 is transmitted from the output gear 252A to the first transmission gear 241.

[0110] The one-way clutch 244 is located between the first transmission gear 241 and the transmission shaft 243. The one-way clutch 244 couples the transmission shaft 243 and the first transmission gear 241 to each other. The one-way clutch 244 restricts the rotation of the first transmission gear 241 relative to the transmission shaft 243 in one direction. The rotational force of the output gear 252A in the forward rotation direction of the rear wheel 7 (see Figure 1 ) of the power-assisted bicycle 1 is transmitted to the transmission shaft 243 via the first transmission gear 241, while the rotational force of the output gear 252A in the backward rotation direction of the rear wheel 7 is not transmitted to the transmission shaft 243. The one-way clutch 244 prevents the rotational force of the forward rotation of the pedal crankshaft 22 generated by the human power of the rider (i.e., the user) from being transmitted to the motor 25.

[0111] The first transmission gear 241 has a diameter larger than that of the output gear 252A of the motor 25 and has a number of teeth larger than that of the output gear 252A. That is, the first transmission gear 241 decelerates more than the output gear 252A.

[0112] The second transmission gear 242 is formed of a metal material (e.g., iron). The second transmission gear 242 is located on the transmission shaft 243. The second transmission gear 242 is located at a position different from that of the first transmission gear 241 in the axial direction of the transmission shaft 243. The second transmission gear 242 has a diameter smaller than that of the first transmission gear 241 and has a number of teeth smaller than that of the first transmission gear 241. The transmission shaft 243 and the second transmission gear 242 are integrally formed with each other in the embodiment, but are not limited thereto. The second transmission gear 242 can be fastened to the transmission shaft 243 by serrated coupling (or press-fitting). The second transmission gear 242 rotates together with the transmission shaft 243. The transmission shaft 243 transmits the rotation of the first transmission gear 241 to the second transmission gear 242.

[0113] The idler gear 41 is formed of a metal material (e.g., iron). The idler gear 41 is located on the transmission shaft 243. The idler gear 41 is fastened to the rotating shaft 43 by, for example, a fastener (but not limited thereto). The idler gear 41 can be fastened to the transmission shaft 243 by serrated coupling (or press-fitting). The idler gear 41 and the rotating shaft 43 can be integrally formed with each other. The idler gear 41 rotates together with the transmission shaft 243.

[0114] The central axis CL3 of the rotating shaft 43 is parallel to the central axis CL4 of the pedal crankshaft 22. That is, the rotating shaft 43 extends parallel to the central axis CL4 of the pedal crankshaft 22. When viewed in the axial direction of the rotating shaft 43 (i.e., the axial direction of the pedal crankshaft 22), the central axis CL3 is the rotational center axis RC3 (the third central axis) of the rotating shaft 43. The idler gear 41 fastened to the rotating shaft 43 is supported by the housing 21 so as to be rotatable within the housing 21 about the third central axis RC3.

[0115] The rotating shaft 43 is supported by two bearings 46L and 46R so as to be rotatable about the central axis CL3. The bearings 46L and 46R are fastened to the first housing 211. The idler gear 41 is positioned closer to the bearing 46R than to the bearing 46L in the axial direction of the rotating shaft 43. The idler gear 41 meshes with the second transmission gear 242 of the speed reducer 24. With such an arrangement, the output torque of the motor 25 increased by the speed reducer 24 is transmitted to the idler gear 41.

[0116] Now, the structure of the pedal crankshaft 22 and its vicinity will be described.

[0117] The rotating shaft 23 is positioned coaxially with the pedal crankshaft 22 and is rotatable together with the pedal crankshaft 22. The rotating shaft 23 includes a coupling shaft 231 and a one-way clutch 50.

[0118] The coupling shaft 231 is cylindrical. The pedal crankshaft 22 is inserted into the coupling shaft 231. The coupling shaft 231 is positioned coaxially with the pedal crankshaft 22.

[0119] The left end of the coupling shaft 231 is coupled to the pedal crankshaft 22 by means of a serrated coupling or the like. As a result, the coupling shaft 231 rotates together with the pedal crankshaft 22 regardless of whether the pedal crankshaft 22 rotates forward or backward.

[0120] The torque detector 232 is positioned around the coupling shaft 231. The torque sensor 232 is supported by the coupling shaft 231 and is non-rotatable relative to the first housing 211. When the rider performs pedal pedaling, the torque detector 232 detects the torque generated on the coupling shaft 231. The torque detector 232 is, for example, a torque sensor of a magnetostrictive system. The torque detector 232 outputs a signal corresponding to the detected torque to the MCU mounted on the circuit board 110. The MCU controls the motor 25 with reference to the torque detected by the torque detector 232 to grasp the state of the pedal pedaling performed by the rider. The external connection connector 130 is a connector that externally connects the drive unit 20 and external devices (such as the battery unit 56, the meter unit 5, etc.) to each other.

[0121] The one-way clutch 50 is located on the right side of the torque detector 232 in the axial direction of the pedal crankshaft 22. The one-way clutch 50 is provided on the pedal crankshaft 22 via the coupling shaft 231. The one-way clutch 50 is positioned coaxially with the pedal crankshaft 22. The one-way clutch 50 includes an inner member 51 and an outer member 52.

[0122] The inner member 51 of the one-way clutch 50 is cylindrical. The right portion of the coupling shaft 231 is inserted into the inner member 51. The inner member 51 is positioned coaxially with the coupling shaft 231. In this state, the right portion of the coupling shaft 231 is coupled to the inner member 51 by means of serrated coupling or the like. As a result, regardless of whether the coupling shaft 231 rotates forward or backward, the inner member 51 rotates together with the coupling shaft 231. That is, regardless of whether the pedal crankshaft 22 rotates forward or backward, the inner member 51 rotates together with the pedal crankshaft 22. The coupling shaft 231 and the inner member 51 act together as a crank rotation input shaft that can rotate integrally with the pedal crankshaft 22.

[0123] The outer member 52 of the one-way clutch 50 is cylindrical. The pedal crankshaft 22 is inserted into the outer member 52. The plain bearing 49 is located between the outer member 52 and the pedal crankshaft 22. With such an arrangement, the outer member 52 is positioned coaxially with the pedal crankshaft 22 and is rotatable.

[0124] A latch mechanism as a one-way clutch mechanism is formed between the outer member 52 and the inner member 51. With such an arrangement, the rotational force in the forward rotation direction of the inner member 51 is transmitted to the outer member 52, while the rotational force in the backward rotation direction of the inner member is not transmitted to the outer member 52. The rotational force in the forward rotation direction of the outer member 52 generated by the rotation of the motor 25 is not transmitted to the inner member 51.

[0125] The outer member 52 is supported by the bearing 38R so as to be rotatable about the central axis CL4 of the pedal crankshaft 22 relative to the housing 21. The outer member 52 is positioned to penetrate the second housing 212. The portion of the outer member 52 located outside the housing 21 (on the right side) has the drive sprocket 34 attached thereto.

[0126] The outer member 52 includes a driven gear 233. The driven gear 233 is provided on the pedal crankshaft 22 via the one-way clutch 50 and the coupling shaft 231. The driven gear 233 meshes with the idler gear 41. The driven gear 233 has a diameter larger than that of each of the second transmission gear 242 and the idler gear 41, and has a number of teeth larger than that of each of the second transmission gear 242 and the idler gear 41. That is, the rotational speed of the driven gear 233 is lower than that of each of the second transmission gear 242 and the idler gear 41. The idler gear 41 meshes with each of the second transmission gear 242 and the driven gear 233, so that the output torque increased by the speed reducer 24 of the motor 25 can be transmitted to the driven gear 233 via a single idler gear 41.

[0127] The outer member 52 transmits the combined force of the human power (the force for stepping on the pedal) transmitted to the coupling shaft 231 and the auxiliary driving force of the motor 25 to the drive sprocket 34. The outer member 52 realizes a combined-force output shaft 235 that combines the human power input via the one-way clutch 50 and the auxiliary driving force input via the driven gear 233 and outputs the combined force. The combined-force output shaft 235 rotates coaxially with the pedal crankshaft 22. The combined-force output shaft 235 is included in the rotating shaft 23.

[0128] [Dust seal]

[0129] The dust seal according to the present embodiment will now be described.

[0130] Figure 4 is a cross-sectional view showing the opening 261 of the housing 21 and the rotatable shaft 30 passing through the opening 261.

[0131] The rotatable shaft 30 is rotatably supported by the housing 21 via a bearing 38L. The outer ring of the bearing 38L is fastened to the housing 21. The movement of the bearing 38L in the rotational axis direction D1 of the rotatable shaft 30 is suppressed by the protrusion 273 of the housing 21 and snap rings 39 and 94.

[0132] An annular dust seal 60 is located between the opening 261 of the housing 21 and the rotatable shaft 30. The dust seal 60 closes the gap between the opening 261 and the rotatable shaft 30 and suppresses dust from entering the interior of the housing 21 from the outside of the housing 21.

[0133] In the present embodiment, the rotatable shaft 30 includes an adapter 92 that adjusts the diameter of the pedal crankshaft 22. The adapter 92 is fastened to the pedal crankshaft 22 by, for example, press fitting or serrated coupling and increases the diameter of a part of the pedal crankshaft 22. The dust seal 60 is in slidable contact with the adapter 92 of the rotatable shaft 30. The dust seal 60 may be in direct contact with the pedal crankshaft 22 of the rotatable shaft 30.

[0134] Figure 5 is a perspective view showing the dust seal cut along a plane parallel to the rotational axis direction D1 of the rotatable shaft 30. Figure 6 and Figure 7 each is a partial enlarged cross-sectional view of the drive unit 20 and shows in an enlarged form the Figure 4 region surrounded by the dashed line in Figure 7 The dust seal 60 is omitted. Figure 6 and Figure 7 The bearing 38L is omitted to easily understand the features of the present embodiment. In Figure 4 、 Figure 6 and Figure 7In the illustrated example, the left side of the rotational axis direction D1 of the rotatable shaft 30 is the outer side of the housing 21, and the right side of the rotational axis direction D1 is the inner side of the housing 21. The outer side of the housing 21 in the rotational axis direction D1 is the outer side of the opening 261.

[0135] As Figure 5 shown, the dust-proof seal 60 includes a body 61 and a metal ring (reinforcement ring) 67. The body 61 is formed of an elastomer such as synthetic rubber, for example. The metal ring 67 increases the rigidity of the dust-proof seal 60. A sealing lip 65 and a dust-proof lip 66 are provided in the inner peripheral portion 62 of the dust-proof seal 60. A first lip 71 and a second lip 72 are provided in the outer peripheral portion 63 of the dust-proof seal 60.

[0136] As Figure 6 shown, the sealing lip 65 and the dust-proof lip 66 provided in the inner peripheral portion 62 of the dust-proof seal 60 are in slidable contact with the adapter 92 of the rotatable shaft 30. The dust-proof lip 66 is positioned more outward than the sealing lip 65 in the rotational axis direction D1. The sealing lip 65 and the dust-proof lip 66 inhibit oil from flowing from the inside of the housing 21 to the outside of the housing 21, and also inhibit water and dust from entering the inside of the housing 21 from the outside of the housing 21.

[0137] The first lip 71 and the second lip 72 provided in the outer peripheral portion 63 of the dust-proof seal 60 are in contact with the inner peripheral portion 262 of the opening 261 of the housing 21.

[0138] In the inner peripheral portion 262 of the opening 261, a groove 271 is provided along the circumferential direction of the opening 261. The inner peripheral portion 262 includes a projection 272 as the outer wall of the groove 271 and a projection 273 as the inner wall of the groove 271 in the rotational axis direction D1. Each of the projection 272 and the projection 273 is formed to extend substantially toward the rotatable shaft 30 from the inner peripheral portion 262.

[0139] The second lip 72 of the dust-proof seal 60 is formed to extend away from the rotatable shaft 30 and is fitted into the groove 271 of the inner peripheral portion 262 of the opening 261. In this example, the second lip 72 is fitted into the groove 271 by snap fit. The second lip 72 is fitted into the groove 271 such that the dust-proof seal 60 can be fastened to the housing 21. Further, oil can be inhibited from flowing from the inside of the housing 21 to the outside of the housing 21, and water and dust can also be inhibited from entering the inside of the housing 21 from the outside of the housing 21.

[0140] The outer end 265 of the inner peripheral portion 262 of the opening 261 in the rotational axis direction D1 includes a chamfered portion 266 that is a C chamfer or an R chamfer. The chamfered portion 266 is formed to have a diameter that increases toward the outside of the opening 261. In the present embodiment, the chamfered portion 266 is provided at the projection 272.

[0141] The first lip 71 of the dust seal 60 is formed to extend away from the rotatable shaft 30 and at the same time extend outward in the direction D1 of the rotation axis. As Figure 6 shown, the first lip 71 covers the chamfered portion 266 of the opening 261. In the present embodiment, the expression "the first lip 71 covers the chamfered portion 266" may mean that the first lip 71 covers a part of the chamfered portion 266 or that the first lip 71 covers the entire chamfered portion 266.

[0142] In the case where the housing 21 and the rotatable shaft 30 include different metallic materials from each other, when water accumulates between the opening 261 of the housing 21 and the rotatable shaft 30, electrolytic corrosion (galvanic corrosion) is likely to occur. The electrolytic corrosion can be suppressed to some extent by the coating applied to the opening 261. However, in the case where the opening 261 has a certain shape, the coating may not be applied to the opening 261 in a satisfactory manner. For example, in the case where the protrusion 272 provided at the opening 261 is thin, the coating is not applied to the protrusion 272 in a satisfactory manner. According to the present embodiment, the dust seal 60 includes the first lip 71 that covers the chamfered portion 266 of the opening 261. The first lip 71 covers the chamfered portion 266 so that the electrolytic corrosion can be suppressed even when the coating is not applied to the opening 261 in a satisfactory manner.

[0143] The first lip 71 and the second lip 72 of the dust seal 60 hold the protrusion 272 therebetween by an elastic force. With such an arrangement, it is not easy to form a gap between the first lip 71 and the chamfered portion 266, and thus the electrolytic corrosion can be suppressed more effectively. In addition, the flow of oil from the inside of the housing 21 to the outside can be suppressed more effectively, and the entry of water and dust from the outside of the housing 21 into the inside can be suppressed more effectively.

[0144] Now, the positional relationship between the opening 261 of the housing 21 and the dust seal 60 in the direction D1 of the rotation axis will be described.

[0145] Figure 8 is a cross-sectional view showing the positional relationship between the opening 261 of the housing 21 and the dust seal 60 in the direction D1 of the rotation axis. In Figure 8 the example shown, the left side in the direction D1 of the rotation axis is the outside of the housing 21, and the right side in the direction D1 of the rotation axis is the inside of the housing 21. In Figure 8 , the one-dot chain line A1 shows the outermost position of the dust seal 60 in the direction D1 of the rotation axis. In Figure 8 , the dashed line A2 shows the outermost portion 267 of the opening 261 of the housing 21.

[0146] In the present embodiment, the dust seal 60 does not project outside the outermost portion 267 of the opening 261 in the rotational axis direction D1. With such an arrangement, the size of the drive unit 20 in the width direction (left - right direction) can be reduced.

[0147] Components such as the crank arm 35 are attached to the rotatable shaft 30. If the dust seal 60 projects outside the opening 261 of the housing 21, the dust seal 60 will interfere with the crank arm 35 or the like. Since the dust seal 60 does not project outside the opening 261 in the present embodiment, interference between the dust seal 60 and the crank arm 35 or the like can be suppressed.

[0148] The first lip 71 of the dust seal 60 covers the chamfered portion 266 in such a range that this range does not allow the dust seal 60 to project outside the outermost portion 267 of the opening 261. As long as the dust seal 60 does not project outside the outermost portion 267 of the opening 261, the first lip 71 can cover the entire chamfered portion 266.

[0149] In the above example, the dust seal 60 is fastened to the inner peripheral portion 262 of the opening 261 by snap - fit. Alternatively, the dust seal 60 can be fastened to the inner peripheral portion 262 by press - fitting.

[0150] Figure 9 is a cross - sectional view of the dust seal 60 showing the state where the dust seal 60 is fastened to the inner peripheral portion 262 of the opening 261 by press - fitting. In Figure 9 the example shown, the groove 271 is not provided in the inner peripheral portion 262, and the dust seal 60 is fastened to the inner peripheral portion 262 by press - fitting.

[0151] The outer end 265 of the inner peripheral portion 262 in the rotational axis direction D1 includes a chamfered portion 266. The first lip 71 of the dust seal 60 covers the chamfered portion 266 of the opening 261. With such an arrangement, electrolytic corrosion can be suppressed.

[0152] In the above embodiment, the drive unit 20 ( Figure 2 ) includes four shafts. More specifically, the output shaft 2522, the transmission shaft 243, the rotating shaft 43, and the rotatable shaft 30. The number of shafts is not limited to four. The present invention can be applied to a drive unit including more than four shafts. For example, the present invention can be applied to a drive unit in which a gear is located between the output gear 252A of the motor 25 and the first transmission gear 241 of the speed reducer 24 and torque is transmitted from the output gear 252A to the first transmission gear 241 via such a gear.

[0153] In the above embodiment, the drive unit 20 includes an idler gear 41. The present invention can be applied to a drive unit without an idler gear 41.

[0154] In the above embodiments, the entire motor 25 is accommodated in the housing 21. The configuration of the housing 21 is not limited thereto. Only a part of the motor 25 may be accommodated in the housing 21. For example, an opening through which the motor 25 can pass is provided in the left portion of the first housing 211, and the motor 25 can be attached such that this portion is located within the housing 21 through the opening. In this case, the opening may be covered with a lid to prevent dust and water from entering.

[0155] The lid 213 ( Figure 2 ) may be a part of the housing 21 and may be included in the housing 21. The lid 213 may be shaped to cover the side surface of the motor 25, and the motor 25 may be supported by the lid 213. Embodiments in which the motor 25 is supported by the lid 213 are included in embodiments in which the motor 25 is supported by the housing 21.

[0156] In the above embodiments, the present invention can be applied to the power-assisted bicycle 1 which is a two-wheeled vehicle. The present invention is not limited thereto and can be applied to a three-wheeled power-assisted bicycle.

[0157] In the above embodiments, the drive wheel to which the human power generated by the rider stepping on the pedals and the auxiliary power generated by the motor are transmitted is the rear wheel. The present invention is not limited thereto. Depending on the form of the power-assisted bicycle, the human power and the auxiliary power may be transmitted to the front wheel, or may be transmitted to both the front wheel and the rear wheel. The present invention can be applied to a power-assisted bicycle including a hub motor provided on the front wheel.

[0158] The illustrative embodiments of the present invention have been described above. This specification discloses the drive unit and the power-assisted bicycle described in the following.

[0159] [Item 1]

[0160] A drive unit 20 for a power-assisted bicycle 1, the drive unit 20 including:

[0161] A motor 25;

[0162] A housing 21 that houses the motor 25;

[0163] A rotatable shaft 30 that is rotatably supported by the housing 21 and is partially exposed to the outside of the housing 21; and

[0164] An annular dust-proof seal 60 provided between the rotatable shaft 30 and the housing 21, the dust-proof seal 60 suppressing dust from entering the interior of the housing 21 from the outside of the housing 21,

[0165] wherein,

[0166] The housing 21 and the rotatable shaft 30 include different metallic materials from each other,

[0167] The inner peripheral portion 62 of the dust seal 60 is in slidable contact with the rotatable shaft 30.

[0168] The outer peripheral portion 63 of the dust seal 60 is in contact with the inner peripheral portion 262 of the opening 261 of the housing 21, and the opening 261 permits the rotatable shaft 30 to pass through.

[0169] The outer end 265 of the inner peripheral portion 262 of the opening 261 of the housing 21 in the rotational axis direction D1 of the rotatable shaft 30 includes a chamfered portion 266, and the diameter of the chamfered portion 266 increases toward the outside of the opening 261.

[0170] The dust seal 60 includes a first lip 71 that covers the chamfered portion 266, and

[0171] the dust seal 60 does not project to the outside of the outermost portion 267 of the opening 261 in the rotational axis direction D1.

[0172] In the case where the housing 21 and the rotatable shaft 30 include different metal materials from each other, when water accumulates between the opening 261 of the housing 21 and the rotatable shaft 30, electrolytic corrosion (galvanic corrosion) is likely to occur. The electrolytic corrosion can be suppressed to some extent by the coating applied to the opening 261. However, there is a case where the coating is not applied to the opening 261 in a satisfactory manner. For example, in the case where the projection 272 provided at the opening 261 is thin, the coating is not applied to the projection 272 in a satisfactory manner. According to an embodiment of the present invention, the dust seal 60 includes a first lip 71 that covers the chamfered portion 266 of the opening 261. The first lip 71 covers the chamfered portion 266 so that the electrolytic corrosion can be suppressed even when the coating is not applied to the opening 261 in a satisfactory manner.

[0173] According to an embodiment of the present invention, the dust seal 60 does not project to the outside of the outermost portion 267 of the opening 261 in the rotational axis direction D1. With such an arrangement, the size of the drive unit 20 in the width direction can be reduced.

[0174] The crank arm 35 can be attached to the rotatable shaft 30. If the dust seal 60 projects to the outside of the opening 261 of the housing 21, the dust seal 60 will interfere with the crank arm 35 or the like. Since the dust seal 60 does not project to the outside of the opening 261 in this embodiment, the interference between the dust seal 60 and the crank arm 35 can be suppressed.

[0175] [Item 2]

[0176] The drive unit 20 according to item 1, wherein the first lip 71 of the dust seal 60 is formed to extend outward in the direction D1 of the rotation axis while extending away from the rotatable shaft 30.

[0177] With such an arrangement, the chamfered portion 266 of the opening 261 can be suitably covered.

[0178] [Item 3]

[0179] The drive unit 20 according to item 1 or item 2, wherein

[0180] A groove 271 is provided in the inner peripheral portion 262 of the opening 261 along the circumferential direction of the opening 261, and

[0181] The outer peripheral portion 63 of the dust seal 60 includes a second lip 72 fitted into the groove 271.

[0182] Since the second lip 72 of the dust seal 60 is fitted into the groove 271 of the opening 261, the dust seal 60 can be fastened to the housing 21.

[0183] [Item 4]

[0184] The drive unit 20 according to item 3, wherein

[0185] The opening 261 includes a protrusion 272 that is the outer wall of the groove 271 in the direction D1 of the rotation axis, and

[0186] The chamfered portion 266 is provided at the protrusion 272.

[0187] Even when the paint is not applied to the opening 261 in a satisfactory manner, the first lip 71 covers the chamfered portion 266, thus electrolytic corrosion can be suppressed.

[0188] [Item 5]

[0189] The drive unit 20 according to item 3 or item 4, wherein the second lip 72 of the dust seal 60 is fitted into the groove 271 by snap fit.

[0190] The dust seal 60 can be fastened to the housing 21 by snap fit. In addition, water and dust entering the interior of the housing 21 can be more effectively suppressed.

[0191] [Item 6]

[0192] The drive unit 20 according to item 4, wherein the first lip 71 and the second lip 72 of the dust seal 60 hold the protrusion 272 between the first lip 71 and the second lip 72 by an elastic force.

[0193] With such an arrangement, it is not easy to form a gap between the first lip 71 and the chamfered portion 266, so that electrolytic corrosion can be more effectively suppressed. In addition, water and dust entering the interior of the housing 21 can be more effectively suppressed.

[0194] [Item 7]

[0195] The drive unit 20 according to item 1 or item 2, wherein the dust seal 60 is press-fitted into the opening 261.

[0196] The dust seal 60 is press-fitted into the opening 261, so that it can be fastened to the housing 21.

[0197] [Item 8]

[0198] The drive unit 20 according to any one of items 1 to 7, wherein the inner peripheral portion 62 of the dust seal 60 includes a sealing lip 65 that is in slidable contact with the rotatable shaft 30.

[0199] With such an arrangement, it is possible to suppress oil from flowing out of the interior of the housing 21 to the outside and water and dust from entering the interior from the outside of the housing 21.

[0200] [Item 9]

[0201] The drive unit 20 according to item 8, wherein the inner peripheral portion 62 of the dust seal 60 further includes a dust lip 66 that is in slidable contact with the rotatable shaft 30 and is positioned more outward than the sealing lip 65 in the rotational axis direction D1.

[0202] With such an arrangement, it is possible to suppress dust from entering the interior from the outside of the housing 21.

[0203] [Item 10]

[0204] The drive unit 20 according to any one of items 1 to 9, wherein the housing 21 is made of a metal material containing magnesium as a main component.

[0205] With such an arrangement, the weight of the drive unit 20 can be reduced.

[0206] [Item 11]

[0207] The drive unit according to any one of items 1 to 10, wherein the rotatable shaft 30 is made of a metal material containing iron as a main component.

[0208] With such an arrangement, the required rigidity and strength levels of the rotatable shaft 30 can be achieved at low cost.

[0209] [Item 12]

[0210] An electric assist bicycle 1 including the drive unit 20 according to any one of items 1 to 11.

[0211] With such an arrangement, an electric assist bicycle 1 including a highly waterproof and compact drive unit 20 can be realized.

[0212] The present invention is particularly useful in the field of electric assist bicycles.

Claims

1. A drive unit for an electric-assisted bicycle, the drive unit comprising: Motor; a housing for accommodating the motor; a rotatable shaft rotatably supported by the housing and partially exposed to the outside of the housing; as well as an annular dust seal disposed between the rotatable shaft and the housing, the dust seal inhibiting dust from entering the interior of the housing from the exterior of the housing, in, The housing and the rotatable shaft comprise different metal materials from each other, The inner peripheral portion of the dust seal is in slidable contact with the rotatable shaft, an outer peripheral portion of the dust seal contacts an inner peripheral portion of an opening of the housing, the opening allowing the rotatable shaft to pass therethrough, an outer end of the inner peripheral portion of the opening of the housing in the rotation axis direction of the rotatable shaft includes a chamfered portion whose diameter increases toward the outside of the opening, The dust seal includes a first lip covering the chamfered portion, and The dust seal does not protrude outside the outermost portion of the opening in the rotation axis direction.

2. The drive unit according to claim 1, wherein: The first lip of the dust seal is formed to extend away from the rotatable shaft while extending outwardly in the rotation axis direction.

3. The drive unit according to claim 1 or 2, wherein A groove is provided in the inner peripheral portion of the opening along the circumferential direction of the opening, and The outer peripheral portion of the dust seal includes a second lip that fits into the groove.

4. The drive unit according to claim 3, wherein The opening includes a protrusion as an outer wall of the groove in the direction of the rotation axis, and The chamfered portion is provided at the protrusion. 5 . The drive unit according to claim 3 , wherein the second lip of the dust seal is fitted into the groove by hook fitting. 6 . The drive unit according to claim 4 , wherein the first lip and the second lip of the dust seal hold the protrusion between the first lip and the second lip by elastic force.

7. The drive unit according to claim 1 or 2, wherein the dust seal is press-fit into the opening. 8 . The drive unit according to claim 1 , wherein the inner peripheral portion of the dust seal includes a sealing lip slidably contacting the rotatable shaft. 9 . The drive unit according to claim 8 , wherein the inner peripheral portion of the dust seal further includes a dust lip slidably contacting the rotatable shaft and positioned further outward than the sealing lip in the rotation axis direction. 10 . The drive unit according to claim 1 , wherein the housing comprises a metal material containing magnesium as a main component. 11 . The drive unit according to claim 10 , wherein the rotatable shaft comprises a metal material containing iron as a main component.

12. An electric-assisted bicycle comprising a drive unit according to claim 1 or 2.

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