Drive unit and electrically assisted vehicle

Abstract

A drive unit (20) that can be used in an electrically assisted vehicle (10), wherein the drive unit (20) comprises: an electric motor (25) comprising an output shaft (2522) having an output gear (252A); a housing (21) that accommodates part or all of the electric motor (25); a pedal crankshaft (22) which passes through the housing (21), is rotatably mounted on the housing (21) and is provided with a driven gear (233); a transmission mechanism (40) that transmits a torque from the output gear (252A) of the electric motor (25) to the driven gear (233); and an output shaft of a resultant force (235) which is rotatable coaxially with the pedal crankshaft (22), wherein the output shaft of the resultant force (235) combines pedal power and support power of the electric motor (25), the transmission mechanism (40) includes: a retarder (24) which is rotatably mounted in the housing (21), and an idle gear (41) which is rotatably mounted in the housing (21), wherein the idle gear (41) is an element which does not decelerate or accelerate, wherein the retarder (24) increases the torque of the output shaft (2522) of the electric motor (25), and wherein the increased torque is transmitted via the idle gear (41) to the driven gear (233), wherein the electric motor (25) is mounted by the housing (21) such that the output shaft (2522) rotates about a first central axis (RC1), wherein the retarder (24) is mounted in the housing (21) in such a way that it is rotatable about a second central axis (RC2), and includes a first transmission gear (241), a second transmission gear (242) which has a smaller number of teeth than the first transmission gear (241), and a transmission shaft (243) which transmits a rotation of the first transmission gear (241) to the second transmission gear (242), wherein the idle gear (41) is mounted in the housing (21) in such a way that it is rotatable about a third central axis (RC3), and wherein the pedal crankshaft (22) runs through the housing (21) along a fourth central axis (RC1) and is supported by the housing (21) in such a way that it is rotatable about the fourth central axis (RC4), where a distance from a plane (61) containing the first central axis (RC1) and the fourth central axis (RC4) to the third central axis (RC3) is longer than a distance from the plane (61) to the second central axis (RC2), and wherein the idle gear (41) has a diameter that is shorter than either the diameter of the driven gear (233) or the diameter of the first transmission gear (241), wherein the idle gear (41) is engaged with each of the second transmission gear (242) of the retarder (24) and the driven gear (233).

Description

Background1. Technical area:

[0001] The present invention relates to a drive unit that can be attached to a vehicle frame of an electrically assisted vehicle, and to an electrically assisted vehicle including such a drive unit. 2. Description of related technology:

[0002] JP 2016-078 618 A discloses a drive unit usable in an electrically assisted vehicle, the drive unit comprising: an electric motor having an output shaft with an output gear; a housing enclosing part or all of the electric motor; a pedal crankshaft extending through the housing, rotatably supported by the housing, and provided with a driven gear; and a transmission mechanism transmitting torque of the output gear of the electric motor to the driven gear, the transmission mechanism comprising a decelerator and an idle gear.

[0003] Furthermore, an example of a vehicle that can move according to the power generated by a power source is an electric-assisted bicycle in which the power provided by a rider pedaling the bicycle is assisted by an electric motor (see, for example, Japanese Publication JP 2014-196080 A). An electric-assisted bicycle allows the electric motor to generate drive power according to the human power the rider applies to the pedals. Therefore, the electric-assisted bicycle can alleviate the burden on the rider, for example, while riding uphill or while carrying a load.

[0004] An electrically assisted bicycle includes a drive unit including an electric motor and the like. Known drive units include a drive unit of a type located in a rear wheel hub and a drive unit of a type mounted at the lower end of a vehicle frame (near a bottom bracket). Recently, the latter type of drive unit has become more established.

[0005] The electric-assisted bicycle disclosed in Japanese publication JP 2014-196080 A includes a drive unit mounted at a lower end of a vehicle frame. The drive unit includes a housing, an electric motor, a pedal crankshaft, and the like. The electric motor is housed in the housing and generates drive power that assists the rider's pedaling effort.

[0006] The pedal crankshaft is arranged to extend through the housing in a left-right direction of the vehicle. Pedals are attached to the pedal crankshaft via arms. The rotation of the pedal crankshaft is transmitted to the rear wheel via a drive pinion, a chain, a driven pinion, and the like. Further drive units are known from DE 10 2018 120 095 A1, DE 10 2017 217 307 A1, JP 4 056 130 B2, DE 11 2018 006 005 T5, and JP H08 - 295 284 A. Summary

[0007] In a drive unit of an electric-assisted bicycle, many components other than a battery, namely an electric motor, a decelerator, a pedal crankshaft, a control unit, and the like, are housed in a concentrated manner in a single housing. Some electric-assisted bicycles use a mounting system called a "center mount system," in which such a drive unit is mounted in a position corresponding to the position of a pedal crankshaft of a general bicycle.

[0008] This mounting system allows heavy mechanical and electronic components to be concentrated in a central lower section of the vehicle, thus improving the vehicle's weight balance. This mounting system allows many components to be concentrated in one housing, thus also allowing the drive unit to be mounted on many types of bicycle frames with minimal modification and at low cost.

[0009] Meanwhile, in the case where the drive unit in an electric-assisted bicycle is located at a position corresponding to the position of the pedal crankshaft in a general bicycle, a problem arises that the rear center length (the length between the pedal crankshaft and the rear wheel axle) is made longer than that of the general bicycle. Generally, in the case where the rear center length is made longer, handling agility is reduced.

[0010] For a vehicle type that travels on unpaved roads, such as a mountain bike or similar, it's important to ensure adequate minimum ground clearance (distance from the ground to the drive unit). If the minimum ground clearance is too short, the vehicle's travel range is limited, reducing performance.

[0011] In the case where the power unit has a large size, the parts around the power unit, such as a rear suspension, a battery, and the like, are restricted in the positional arrangement thereof.

[0012] The present invention provides a drive unit having a reduced size and an electrically assisted vehicle including such a drive unit. This object is achieved by a drive unit having the features of claim 1.

[0013] A drive unit according to one aspect of the present invention is usable in an electrically assisted vehicle. The drive unit includes an electric motor having an output shaft with an output gear; a housing housing part or all of the electric motor; a pedal crankshaft extending through the housing, rotatably supported by the housing, and provided with a driven gear; a transmission mechanism transmitting torque from the output gear of the electric motor to the driven gear; and a resultant power output shaft rotatable coaxially with the pedal crankshaft, the resultant power output shaft combining pedal power and assist power of the electric motor.The transmission mechanism includes a retarder, which is rotatably supported by the housing in the housing, and an idler gear, which is rotatably supported by the housing in the housing. The retarder increases the torque of the electric motor's output shaft, and the increased torque is transmitted to the driven gear via the idler gear.

[0014] To shorten the rear centerline length of the electric-assisted vehicle, it is conceivable to shorten the diameter of the driven gear provided on the pedal crankshaft. If a "dual-axis decelerator" is located between the driven gear on the pedal crankshaft and the electric motor, it becomes difficult to shorten the width of the drive unit in the axial direction. The decelerator includes the rotating shaft on which two gears with different diameters and different numbers of teeth are located in the axial direction. The dual-axis decelerator includes two such rotating shafts, and the two rotating shafts are located so that they are offset from each other in the axial direction. Therefore, the size of the dual-axis decelerator is increased in the axial direction.

[0015] According to one aspect of the present invention, the idler gear is used so that the diameter of the driven gear can be reduced, thus shortening the rear center length of the electric-assisted vehicle without increasing the width (size in the axial direction) of the drive unit. The use of the idler gear can also improve the degree of freedom of the positional arrangement of the electric motor, the decelerator, and the driven gear, thus further reducing the size of the drive unit.

[0016] The electric motor is supported by the housing such that the output shaft rotates about a first central axis. The decelerator is supported by the housing in the housing for rotation about a second central axis and includes a first transfer gear, a second transfer gear having a smaller number of teeth than the first transfer gear, and a transfer shaft that transmits rotation of the first transfer gear to the second transfer gear. The idler gear is supported by the housing in the housing for rotation about a third central axis. The pedal crankshaft extends through the housing along a fourth central axis and is supported by the housing for rotation about the fourth central axis.

[0017] The increased torque from the two transmission gears, which have different numbers of teeth, can be transmitted to the driven gear via the idle gear.

[0018] In one embodiment, the idle gear is engaged with each of the second retarder transfer gear and the driven gear.

[0019] The idle gear meshes with each of the second transfer gear and the driven gear, allowing torque from the retarder to be transmitted to the driven gear via the single idle gear. The presence of such an idle gear can slightly reduce the size of the driven gear.

[0020] In one embodiment, the first transmission gear of the retarder may be in engagement with the output gear of the electric motor.

[0021] Since the single retarder and single idler gear transmit the torque of the electric motor to the driven gear, the size of the drive unit can be reduced without using any additional gear.

[0022] A distance from a plane including the first center axis and the fourth center axis to the third center axis is longer than a distance from the plane to the second center axis, and the idler gear has a diameter shorter than each of a diameter of the driven gear and a diameter of the first transmission gear.

[0023] The idle gear is a member that does not decelerate or accelerate, and therefore only needs to be sized to realize power transmission between the decelerator and the driven gear. Therefore, the idle gear has a diameter shorter than each of the diameter of the first transmission gear of the decelerator and the diameter of the driven gear on the pedal crankshaft. The distance from the plane containing the first central axis and the fourth central axis to the third central axis is made larger than the distance from the plane to the second central axis, so that the idle gear, which has a relatively short diameter, can be arranged outside the first transmission gear. In other words, the first transmission gear, which has a relatively large diameter, can be located at a more inner position in the housing and can therefore be prevented from protruding outward.The housing may have an outer contour along the idler gear, which has a relatively short diameter, but not along the first transmission gear, which has a relatively long diameter. Therefore, the size of the drive unit can be reduced.

[0024] In one embodiment, a distance from the plane including the first central axis and the fourth central axis to a farthest point of the idler gear may be longer than each of a distance from the plane to a farthest point of the driven gear, a distance from the plane to a farthest point of the first transfer gear, and a distance from the plane to a farthest point of the driven gear, and the idler gear may have a diameter shorter than each of a diameter of the driven gear and a diameter of the first transfer gear.

[0025] The idler gear is a non-decelerating or accelerating element and therefore only needs to be sized to realize power transmission between the retarder and the driven gear. Therefore, the idler gear can have a diameter shorter than each of the diameters of the first retarder transmission gear and the driven gear on the pedal crankshaft. The distance from the plane containing the first central axis and the fourth central axis to the farthest point of the idler gear is made longer than each of the distance from the plane to the farthest point of the driven gear, the distance from the plane to the farthest point of the first transmission gear, and the distance from the plane to the farthest point of the driven gear.With this structure, the idle gear, which has a relatively short diameter, can be arranged outside the first transmission gear. In other words, the first transmission gear, which has a relatively long diameter, can be located at a more inner position in the housing and can therefore be prevented from protruding outward. The housing can have an outer contour along the idle gear, which has a relatively short diameter, but not along the first transmission gear, which has a relatively long diameter. Therefore, the size of the drive unit can be reduced.

[0026] In one embodiment, viewed in an axial direction parallel to the first central axis, a triangle having three axes among the first to fourth central axes as apices may have the remaining one axis disposed therein.

[0027] The gear rotating around the remaining one axis can be located at a more internal position in the housing, thus preventing the gear from protruding outward. This structure allows the size of the drive unit to be reduced.

[0028] In one embodiment, viewed in an axial direction parallel to the first central axis, the second central axis may be located in a triangle having the first central axis, the third central axis and the fourth central axis as apices.

[0029] The idle gear is a member that does not decelerate or accelerate, and therefore only needs to be sized to realize power transmission between the decelerator and the driven gear. Therefore, the idle gear can have a diameter shorter than either the diameter of the first transmission gear of the decelerator or the diameter of the driven gear on the pedal crankshaft. The second central axis is located in a triangle that has the first central axis, the third central axis, and the fourth central axis as apices. With this structure, the first transmission gear, which has a relatively long diameter, can be located at a more inward position in the housing and can therefore be prevented from protruding outward.The housing may have an outer contour along the idler gear, which has a relatively short diameter, but not along the first transmission gear, which has a relatively long diameter. Therefore, the size of the drive unit can be reduced.

[0030] In one embodiment, at least a portion of the driven gear may overlap the first transmission gear, viewed in an axial direction parallel to the first central axis.

[0031] The driven gear and the first transmission gear are positioned such that at least a portion of the driven gear and the first transmission gear overlap each other, thus bringing the second center axis and the fourth center axis closer to each other. With this structure, the first center axis and the fourth center axis can be brought closer to each other. The distance between the first center axis and the fourth center axis can be shortened, and therefore, the size of the drive unit in the front-rear direction can be reduced. The size of the drive unit in the front-rear direction is reduced, so that the space for the battery unit to be arranged in the down tube can be ensured.

[0032] In a vehicle with the battery unit located in the down tube, the battery unit is located in a space between the pedal crankshaft and the front wheel in the front-rear direction of the vehicle (in a front center section). Attempting to increase the battery capacity results in an increase in the size of the battery unit, and the front center length must be made longer accordingly. However, increasing the front center length poses a problem in that the vehicle's usability is reduced.

[0033] According to one embodiment of the present invention, the size of the drive unit is reduced in the front-rear direction, so that the degree of freedom of the positional arrangement of the battery unit can be increased. The battery unit with a large capacity can be easily arranged without increasing the front center length.

[0034] In one embodiment, at least a portion of a region in which the driven gear and the idle gear are engaged with each other, viewed in an axial direction parallel to the first central axis, may overlap the first transmission gear.

[0035] The first transmission gear, the idle gear, and the driven gear are positioned such that at least a portion of the area where the driven gear and the idle gear mesh with each other overlaps the first transmission gear. Consequently, the second center axis and the fourth center axis can be brought closer to each other. With this structure, the first center axis and the fourth center axis can be brought closer to each other. The distance between the first center axis and the fourth center axis can be shortened, and therefore the size of the drive unit in the front-rear direction can be reduced.

[0036] In one embodiment, viewed in an axial direction parallel to the first central axis, the third central axis may overlap the first transmission gear.

[0037] The idler gear and the retarder are positioned so that the third center axis and the first transmission gear overlap, thus bringing the second center axis and the third center axis closer together. With this structure, the first center axis and the fourth center axis can be brought closer together. The distance between the first center axis and the fourth center axis can be shortened, and therefore the size of the drive unit in the front-rear direction can be reduced.

[0038] In one embodiment, the pedal crankshaft may be provided with a one-way clutch.

[0039] The pedal crankshaft is provided with the one-way clutch, so that a structure can be provided in which forward rotation of the pedal crankshaft is transmitted to the drive pinion, but reverse rotation of the pedal crankshaft is not transmitted to the drive pinion.

[0040] An electrically assisted vehicle according to an embodiment of the present invention includes the drive unit described above.

[0041] The electric assisted vehicle includes the drive unit in which the driven gear on the pedal crankshaft has a short diameter, so that the rear center length of the electric assisted vehicle can be shortened.

[0042] The drive unit according to one embodiment of the present invention uses the idler gear, so the diameter of the driven gear can be reduced and therefore the rear center length of the electric-assisted vehicle can be shortened without increasing the width (size in the axial direction) of the drive unit. The use of the idler gear can improve the degree of freedom of the positional arrangement of the electric motor, the decelerator, and the driven gear, thus further reducing the size of the drive unit. Short description of the drawing Fig. 1 is a right side view of an electrically assisted bicycle 10 according to an embodiment of the present invention. Fig. 2 is a cross-sectional view showing an internal structure of a drive unit 20 included in the electrically assisted bicycle 10 according to an embodiment of the present invention. Fig. 3 is a view showing a positional relationship of components of the drive unit 20 according to an embodiment of the present invention. Fig. 4 is another view showing the positional relationship of the components of the drive unit 20 according to an embodiment of the present invention. Fig. 5 is yet another view showing the positional relationship of the components of the drive unit 20 according to an embodiment of the present invention. Fig. 6 is yet another view showing the positional relationship of the components of the drive unit 20 according to an embodiment of the present invention. Fig. 7 is a cross-sectional view showing a structure of a driven gear 233 and the vicinity thereof in the drive unit 20 according to an embodiment of the present invention. Fig. 8 is a cross-sectional view showing a structure of an electric motor 25 and the vicinity thereof in the drive unit 20 according to an embodiment of the present invention. Detailed description

[0043] Hereinafter, a drive unit and an electrically assisted vehicle incorporating the drive unit according to an embodiment of the present invention will be described with reference to the drawings. In the description of the embodiment, like components will have like reference numerals, and overlapping descriptions will be omitted. In the embodiment of the present invention, "front", "rear", "left", "right", "upper", and "lower" respectively refer to "front", "rear", "left", "right", "upper", and "lower" based on a state in which a rider sits on a saddle (seat) of the electrically assisted vehicle while facing a handle. The following embodiment is merely illustrative, and the present invention is in no way limited to the following embodiment. [Electrically assisted bicycle]

[0044] With reference to Fig. 1, an electrically assisted bicycle 10 will be described as an example of an electrically assisted vehicle according to an embodiment of the present invention. Fig. 1 is a right side view generally showing a structure of the electrically assisted vehicle 10.

[0045] The electrically assisted bicycle 10 includes a vehicle frame 12, a front wheel 14F, a rear wheel 14R, a handle 16, and a saddle 18. The electrically assisted bicycle 10 further includes a drive unit 20 and a battery unit 26.

[0046] The vehicle frame 12 includes a head tube 121, a top tube 122, a down tube 123, a seat tube 124 and a bracket 125.

[0047] The head tube 121 is located in a front portion of the vehicle frame 12 and extends in an up-down direction. A stem 27 is rotatably inserted into the head tube 121. A handle 16 is attached to an upper end of the stem 27. A front fork 28 is attached to a lower end of the stem 27. The front wheel 14F is rotatably attached to a lower end of the front fork 28. Namely, the front wheel 14F is supported by the vehicle frame 12 via the stem 27 and the front fork 28.

[0048] The top tube 122 is located at the rear of the head tube 121 and extends in a front-to-rear direction. A front end of the top tube 122 is connected to the head tube 121. A rear end of the top tube 122 is connected to the seat tube 124.

[0049] The down tube 123 is located on the rear side of the head tube 121 and extends in the front-to-rear direction. The down tube 123 is located below the top tube 122. A front end of the down tube 123 is connected to the head tube 121. In the Fig. In the example shown in Figure 1, a front portion of the down tube 123 is also connected to a front end portion of the top tube 122. A rear end of the down tube 123 is connected to the bracket 125.

[0050] The battery unit 26 is attached to the down tube 123. In the Fig. In the example shown in Figure 1, the battery unit 26 is mounted on the inside of the down tube 123. The battery unit 26 provides electrical power to the drive unit 20. The battery unit 26 includes a battery and a control circuit. The battery is a rechargeable battery that can be recharged and discharged. The control circuit controls the charging and discharging of the battery and also monitors the battery's output current, remaining battery level, and the like.

[0051] The seat tube 124 is located at the rear of the top tube 122 and the down tube 123 and extends in an up-down direction. A lower end of the seat tube 124 is connected to the bracket 125. The seat tube 124 extends upward from the bracket 125.

[0052] In the Fig. In the example shown in Figure 1, the seat tube 124 is bent in the up-down direction at a central position. As a result, a lower portion of the seat tube 124 extends in the up-down direction, while an upper portion of the seat tube 124 extends in a direction inclined with respect to the up-down direction.

[0053] A seat post 29 is inserted into the seat tube 124. The saddle 18 is attached to an upper end of the seat post 29.

[0054] The bracket 125 is arranged at a lower end of the vehicle frame 12. The bracket 125 supports the drive unit 20. The drive unit 20, mounted on the vehicle frame 12, generates drive power to be transmitted to a wheel (in this example, the rear wheel 14R). The details of the drive unit 20 are described below.

[0055] The vehicle frame 12 further includes a swing arm 30, a pair of connecting arms 303, and a suspension 304. The swing arm 30 includes a pair of chain stays 301 and a pair of seat stays 302.

[0056] The pair of chain stays 301 each extend in the front-rear direction. The pair of chain stays 301 are arranged side by side in the left-right direction. The rear wheel 14R is arranged between the pair of chain stays 301. The pair of chain stays 301 are arranged symmetrically on both sides. Therefore, Fig. 1 only the right chainstay 301.

[0057] A front end portion of each of the chainstays 301 is attached to the bracket 125. Namely, each chainstays 301 extends rearward from the bracket 125. Each chainstays 301 is arranged to be pivotable about an axis line extending in the left-right direction with respect to the bracket 125.

[0058] An axle 141 of the rear wheel 14R is non-rotatably fixed to a rear end portion of each chain stay 301. Namely, the rear wheel 14R is supported by the pair of chain stays 301 so as to be rotatable around the axle 141. In other words, the rear wheel 14R is supported by the vehicle frame 12. A multi-stage driven pinion 32 is fixed to the rear wheel 14R.

[0059] The pair of seat stays 302 each extend in the front-rear direction. The pair of seat stays 302 are arranged side by side in the left-right direction. The rear wheel 14R is arranged between the pair of seat stays 302. The pair of seat stays 302 are arranged symmetrically on both sides. Therefore, Fig. 1 only the right seat stay 302.

[0060] A rear end portion of the left seat stay 302 is connected to the rear end portion of the left chain stay 301. A rear end portion of the right seat stay 302 is connected to the rear end portion of the right chain stay 301.

[0061] The pair of connecting arms 303 each extends in the front-to-rear direction. The pair of connecting arms 303 are arranged side by side in the left-right direction. The seat tube 124 is arranged between the pair of connecting arms 303. The pair of connecting arms 303 are arranged symmetrically on both sides. Therefore, Fig. 1 only the right connecting arm 303.

[0062] Each of the link arms 303 is attached to the seat tube 124. Each link arm 303 is arranged to be pivotable about an axis line extending in the left-right direction with respect to the seat tube 124.

[0063] As viewed from a side view of the vehicle, a front end of each link arm 303 is located on the front side of the seat tube 124. As viewed from a side view of the vehicle, a rear end of each link arm 303 is located on the rear side of the seat tube 124.

[0064] A rear end portion of the right link arm 303 is attached to a front end portion of the right seat stay 302. The right link arm 303 is arranged to be pivotable about an axis line extending in the left-right direction with respect to the right seat stay 302.

[0065] A rear end portion of the left link arm 303 is attached to a front end portion of the left seat stay 302. The left link arm 303 is arranged to be pivotable about an axis line extending in the left-right direction with respect to the left seat stay 302.

[0066] The suspension 304 is arranged on the front side of the seat tube 124 and on the rear side of the down tube 123. An upper end portion of the suspension 304 is attached to the pair of link arms 303. The suspension 304 is arranged to be pivotable about an axis line extending in the left-right direction with respect to the pair of link arms 303. A lower end portion of the suspension 304 is attached to the bracket 125. The suspension 304 is arranged to be pivotable about an axis line extending in the left-right direction with respect to the bracket 125. The position at which the suspension 304 is attached to the bracket 125 is located on the front side of the position at which the seat tube 124 is attached to the bracket 125.

[0067] A drive pinion 34 is attached to the drive unit 20 via a support member 33. A chain is wound along the drive pinion 34 and the driven pinion 32. (drive unit)

[0068] With reference to Fig. 2, an example of the structure of the drive unit 20 is described. Fig. 2 is a cross-sectional view showing an example of an internal structure of the drive unit 20.

[0069] As in Fig. 2, the drive unit 20 includes a housing 21, a pedal crankshaft 22, a rotation shaft 23, a transmission mechanism 40, and an electric motor 25.

[0070] First, a structure of the housing 21 according to this embodiment will be described.

[0071] The housing 21 is attached to the clamp 125 via a plurality of clamping tools ( Fig. 1). The housing 21 includes a first housing 211, a second housing 212, and a cover 213. The first housing 211, the second housing 212, and the cover 213 are each formed of a metallic material (e.g., an aluminum alloy).

[0072] The first housing 211 is made to fit onto the second housing 212 from the left in the left-right direction. The first housing 211 and the second housing 212 are secured together by a plurality of clamping tools. As a result, a space 214 is formed between the first housing 211 and the second housing 212.

[0073] The cover 213 is made to fit onto the first housing 211 from the left in the left-right direction. The cover 213 and the first housing 211 are fastened together by a plurality of clamping tools. As a result, a space 215 enclosed by the cover 213 is formed to the left of the first housing 211. The motor 25 is housed in the space 215.

[0074] Now, a structure of the pedal crankshaft 22 according to this embodiment will be described.

[0075] The pedal crankshaft 22 is arranged to extend through the housing 21 in the left-right direction of the vehicle and is rotatably supported in the housing 21. A center axis line CL4 of the pedal crankshaft 22 extends in the left-right direction. Viewed in an axial direction of the pedal crankshaft 22 (in a thrust direction), the center axis line CL4 is a rotational center axis RC4 (fourth center axis) of the pedal crankshaft 22. The pedal crankshaft 22 is rotatable about the center axis line CL4 with respect to the housing 21.

[0076] The pedal crankshaft 22 extends through the housing 21 along the fourth central axis RC4 and is supported by the housing 21 for rotation about the fourth central axis RC4. In the housing 21, the pedal crankshaft 22 is rotatably supported by a pair of bearings 38L and 38R. The bearing 38L is located on the left side in the axial direction and is fixed to the first housing 211. The bearing 38R is located on the right side in the axial direction and is fixed to the second housing 212.

[0077] The pedal crankshaft 22 is arranged to pass through the rotation shaft 23. The rotation shaft 23 is housed in the housing 21. The details of the rotation shaft 23 are described below. A pair of left and right crank arms 35 (see Fig. 1) is attached to the pedal crankshaft 22. A pedal 37 (see Fig. 1) is attached to each of the crank arms 35.

[0078] Now, a structure of the electric motor 25 and the transmission mechanism 40 according to this embodiment will be described.

[0079] The electric motor 25 is housed in the housing 21 and is secured to the housing 21. The electric motor 25 generates drive power that assists the driving of the electrically assisted bicycle 10. The electric motor 25 includes a stator 251 and a rotor 252.

[0080] The stator 251 includes a plurality of coil supports 2512, around each of which a coil 2511 is wound. An iron core 2513 is inserted into each of the coil supports 2512. The stator 251 is located in the space 215. In this state, the stator 251 is fixed to the first housing 211.

[0081] A support member 253 is attached to the stator 251. The support member 253 is formed of a resin material. A plurality of bus bars (not shown) are embedded in the support member 253. The bus bars are each connected to the corresponding coil 2511. The transmission of electrical power to the bus bars is controlled, so that a magnetic force is generated in the stator 251.

[0082] The rotor 252 is located inside the stator 251. A center axis line CL1 of the rotor 252 is parallel to the center axis line CL4 of the pedal crankshaft 22. The rotor 252 is arranged parallel to the center axis line CL4 of the pedal crankshaft 22. Viewed in the axial direction of the pedal crankshaft 22, the center axis line CL1 is a rotational center axis RC1 (first center axis) of the rotor 252.

[0083] The rotor 252 includes a rotor main body 2521 and an output shaft 2522. An outer peripheral surface of the rotor main body 2521 is magnetized alternately with N poles and S poles in a circumferential direction.

[0084] The output shaft 2522 is arranged to pass through the rotor main body 2521. The output shaft 2522 is fixed to the rotor main body 2521. Namely, the output shaft 2522 is rotatable together with the rotor main body 2521.

[0085] In the housing 21, the output shaft 2522 is supported by the housing 21 to be rotatable about the first center axis RC1. The output shaft 2522 is supported by two bearings 42L and 42R to be rotatable about the center axis line CL1 with respect to the housing 21. The bearing 42L is fixed to the cover 213. The bearing 42R is located to the right of the rotor main body 2521 and is fixed to the first housing 211. The output shaft 2522 is arranged to pass through the first housing 211. A portion of the output shaft 2522 located in the space 214 has an output gear 252A formed therein. The output gear 252A is, for example, a helical gear.

[0086] 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 decelerator 24, an idle gear 41, and a rotating shaft 43. The transmission mechanism 40 transmits torque from the driven gear 252A of the electric motor 25 to a driven gear 233 described below.

[0087] The decelerator 24 is rotatably supported by the housing 21 and increases the torque of the output gear 252A of the electric motor 25. The decelerator 24 includes a first transmission gear 241, a second transmission gear 242, and a transmission shaft 243. A center axis line CL2 of the transmission shaft 243 is parallel to the center axis line CL4 of the pedal crankshaft 22. Namely, the transmission shaft 243 extends parallel to the center axis line CL4 of the pedal crankshaft 22. Viewed in an axial direction of the transmission shaft 243, namely, in the axial direction of the pedal crankshaft 22, the center axis line CL2 is a rotational center axis RC2 (second center axis) of the transmission shaft 243. In the housing 21, the decelerator 21 is supported by the housing so as to be rotatable about the second center axis RC2.

[0088] The first transmission gear 241 is located on a right portion of the transmission shaft 243 in the axial direction. A 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 around the center axis line CL2. The bearing 44L is fixed to the first housing 211. The bearing 44R is fixed to the second housing 212.

[0089] The first transmission gear 241 meshes with the output gear 252A of the electric motor 25. With this structure, the drive power generated by the electric motor 25 is transmitted from the output gear 252A to the first transmission gear 241.

[0090] A one-way clutch 244 is arranged 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 regulates the rotation of the first transmission gear 241 relative to the transmission shaft 243 in one direction. A rotational force of the output gear 252A acting in such a direction as to rotate the rear wheel 14R ( Fig. 1) of the electrically assisted bicycle 10 is transmitted to the transmission shaft 243 via the first transmission gear 241, while a rotational force of the driven gear 252A acting in such a direction as to rotate the rear wheel 14R backward is not transmitted to the transmission shaft 243. The one-way clutch 244 also prevents a forward rotational force of the pedal crankshaft 22 generated by the rider's human power from being transmitted to the electric motor 25.

[0091] The first transmission gear 241 has a longer diameter than that of the output gear 252A of the electric motor 25 and includes a larger number of teeth than that of the output gear 252A. Namely, the first transmission gear 241 is decelerated more than the output gear 252A.

[0092] The second transmission gear 242 is made of a metallic material (e.g., iron). The second transmission gear 242 is located on the transmission shaft 243.

[0093] The second transmission gear 242 is located at a different position from the first transmission gear 241 in the axial direction of the transmission shaft 243. The second transmission gear 242 has a shorter diameter than that of the first transmission gear 241 and includes a smaller number of teeth than that of the first transmission gear 241. The transmission shaft 243 and the second transmission gear 242 are integrally formed in this embodiment, but are not limited thereto. The second transmission gear 242 can be fixed to the transmission shaft 243 by a spline coupling (or by press fitting). The second transmission gear 242 is rotatable 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.

[0094] The idle gear 41 is formed of a metallic material (e.g., iron). The idle gear 41 is located on the rotating shaft 43. The idle gear 41 is fixed to the rotating shaft 43, for example, by a clamping tool, but is not limited thereto. The idle gear 41 may be fixed to the rotating shaft 43 by a spline coupling (or by interference fit). The idle gear 41 and the rotating shaft 43 may be integrally formed. The idle gear 41 is rotatable together with the rotating shaft 43.

[0095] A center axis line CL3 of the rotation shaft 43 is parallel to the center axis line CL4 of the pedal crankshaft 22. Namely, the rotation shaft 43 extends parallel to the center axis line CL4 of the pedal crankshaft 22. Viewed in an axial direction of the rotation shaft 43, namely, in the axial direction of the pedal crankshaft 22, the center axis line CL3 is a rotation center axis RC3 (third center axis) of the rotation shaft 43. In the housing 21, the idler gear 41 fixed by the rotation shaft 43 is supported by the housing 21 so as to be rotatable about the third center axis RC3.

[0096] The rotating shaft 43 is supported by two bearings 46L and 46R for rotation around the center axis line CL3. The bearings 46L and 46R are fixed to the first housing 211. The idle gear 41 is located closer to the bearing 46R than to the bearing 46L in the axial direction of the rotating shaft 43. The idle gear 41 meshes with the second transmission gear 242 of the decelerator 24. With this structure, the output torque of the electric motor 25 increased by the decelerator 24 is transmitted to the idle gear 41.

[0097] Now, a structure of the vicinity of the pedal crankshaft 22 will be described.

[0098] The rotation shaft 23 is arranged coaxially with the pedal crankshaft 22 and is rotatable together with the pedal crankshaft 22. The rotation shaft 23 includes a coupling shaft 231 and a one-way clutch 50.

[0099] The coupling shaft 231 has a cylindrical shape. The pedal crankshaft 22 is inserted into the coupling shaft 231. The coupling shaft 231 is arranged coaxially with the pedal crankshaft 22.

[0100] A left end portion of the coupling shaft 231 is coupled to the pedal crankshaft 22 through a spline 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.

[0101] A torque detection device 232 is arranged around the coupling shaft 231. The torque detection device 232 is supported by the coupling shaft 231 and is non-rotatable with respect to the first housing 211. The torque detection device 232 detects a torque generated in the coupling shaft 231 when the rider pedals. The torque detection device 232 is, for example, a magnetostrictive torque sensor. The torque detection device 232 outputs a signal corresponding to the detected torque to a controller mounted on a substrate 48. The controller refers to the torque detected by the torque detection device 232 to learn the state of the pedaling motion performed by the rider and control the electric motor 25.

[0102] The one-way clutch 50 is arranged to the right of the torque detection device 232 in the axial direction of the pedal crankshaft 22. The one-way clutch 50 is arranged on the pedal crankshaft 22 via the coupling shaft 231. The one-way clutch 50 is arranged coaxially with the pedal crankshaft 22. The one-way clutch 50 includes an inner member 51 and an outer member 52.

[0103] The inner member 51 of the one-way clutch 50 has a cylindrical shape. A right portion of the coupling shaft 231 is inserted into the inner member 51. The inner member 51 is arranged 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 a spline coupling or the like. As a result, the inner member 51 rotates together with the coupling shaft 231, regardless of whether the coupling shaft 231 rotates forward or backward. 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 function as a crank rotation input shaft that is integrally rotatable with the pedal crankshaft 22.

[0104] The outer member 52 of the one-way clutch 50 has a cylindrical shape. The pedal crankshaft 22 is inserted into the outer member 52. A plain bearing 49 is located between the outer member 52 and the pedal crankshaft 22. With this structure, the outer member 52 is rotatably mounted coaxially with the pedal crankshaft 22.

[0105] A locking mechanism as a one-way clutch mechanism is formed between the outer member 52 and the inner member 51. With this structure, a forward rotation force of the inner member 51 is transmitted to the outer member 52, while a reverse rotation force of the inner member 51 is not transmitted to the outer member 52. A forward rotation force of the outer member 52 generated by the rotation of the electric motor 25 is not transmitted to the inner member 51.

[0106] The outer member 52 is supported by the bearing 38R so as to be rotatable relative to the housing 21 about the center axis line CL4 of the pedal crankshaft 22. The outer member 52 is arranged to extend through the second housing 212. The drive pinion 34 is fixed to a portion of the outer member 25 located outside (right) of the housing 21.

[0107] The outer member 52 includes the driven gear 233. The driven gear 233 is arranged on the pedal crankshaft 22 via the one-way clutch 50 and the coupling shaft 231. The driven gear 233 is engaged with the idle gear 41. The driven gear 233 has a longer diameter than that of each of the second transmission gear 242 and the idle gear 41 and includes a larger number of teeth than those of each of the second transmission gear 242 and the idle gear 41. Namely, the driven gear 233 rotates at a lower speed than the speed of each of the second transmission gear 242 and the idle gear 41.The idle gear 41 is engaged with each of the second transmission gear 242 and the driven gear 233, so that the output torque of the electric motor 25 increased by the retarder 24 can be transmitted to the driven gear 233 via the single idle gear 41.

[0108] The outer member 52 transmits the resultant force of the human power (pedal power) transmitted to the coupling shaft 231 and the assisting drive power of the electric motor 25 to the drive pinion 34. The outer member 52 realizes a resultant force output shaft 235 that combines the human power input via the one-way clutch 50 and the assisting drive power input via the driven gear 233, and outputs the resultant force. The resultant force output shaft 235 rotates coaxially with the pedal crankshaft 22. The resultant force output shaft 235 is included in the rotation shaft 23. (Idle gear)

[0109] Now, the drive unit 20 including the idle gear 41 according to this embodiment will be described in more detail.

[0110] As described above, in the case where the drive unit in the electrically assisted bicycle is located at a position corresponding to the position of the pedal crankshaft of a general bicycle, there occurs a problem that the rear center length is made longer than that of the general bicycle.

[0111] To shorten the rear centerline length of the electric-assisted vehicle, it is conceivable to shorten the diameter of the driven gear provided on the pedal crankshaft. If a "dual-axis decelerator" is located between the driven gear and the electric motor, it becomes difficult to shorten the width of the drive unit in the axial direction. Two gears with different diameters and different numbers of teeth are arranged in the axial direction on the decelerator's rotating shaft. Therefore, the size of the rotating shaft in the axial direction tends to increase. The dual-axis decelerator includes two such rotating shafts, and the two rotating shafts are located so that they are offset from each other in the axial direction. Therefore, the size of the dual-axis decelerator is increased in the axial direction.

[0112] In this embodiment, the idle gear 41 is provided on a power transmission path between the decelerator 24 and the driven gear 233, so that the diameter of the driven gear 233 can be reduced. Even if the diameter of the driven gear 233 is reduced, the output torque of the electric motor 25 can be transmitted to the driven gear 233 via the idle gear 41. In this embodiment, the use of the idle gear 41 in this way allows the diameter of the driven gear 233 to be reduced, and therefore the rear center length of the electrically assisted bicycle 10 to be shortened without increasing the width (size in the axial direction) of the drive unit 20.The use of the idle gear 41 can also improve the degree of freedom of the positional arrangement of the electric motor 25, the decelerator 24 and the driven gear 233 and therefore further reduce the size of the drive unit 20.

[0113] Hereinafter, the positional arrangement of the components of the drive unit 20 will be described, which makes it possible to reduce the size of the drive unit 20.

[0114] Fig. 3 to Fig. 6 each show a positional arrangement of the components of the drive unit 20 as viewed in the axial direction. The axial direction is parallel to the first to fourth center axes RC1 to RC4.

[0115] As described above, the output shaft 2522 and the driven gear 252A of the electric motor 25 rotate around the first central axis RC1. The first transmission gear 241, the second transmission gear 242, and the transmission shaft 243 of the decelerator 24 rotate around the second central axis RC2. The idle gear 41 and the rotation shaft 43 rotate around the third central axis RC3. The pedal crankshaft 22 and the driven gear 233 rotate around the fourth central axis RC4. The diameter of the idle gear 41 is shorter than the diameter of the driven gear 233 and the diameter of the first transmission gear 241.

[0116] With reference to Fig. 3, a plane containing the first central axis RC1 and the fourth central axis RC4 is referred to as plane 61. In Fig. 3 represents a line (dashed line) along which plane 61 and the sheet of the figure intersect, the position of plane 61. This dashed line is a perpendicular line that intersects each of the first central axis RC1 and the fourth central axis RC4 at right angles and corresponds to a perpendicular line connecting the first central axis RC1 and the fourth central axis RC4. This is also for Fig. 4 applicable.

[0117] The distance from plane 61 to the third central axis RC3 is designated as d3. The distance from plane 61 to the second central axis RC2 is designated as d2. The distance d3 is greater than the distance d2. The idler gear 41 is located outside the retarder 24 in the housing 21.

[0118] The idle gear 41 is a member that does not decelerate or accelerate and therefore only needs to be sized to realize power transmission between the retarder 24 and the driven gear 233. Therefore, the idle gear 41 can have a diameter shorter than each of the diameter of the first transmission gear 241 of the retarder 24 and the diameter of the driven gear 233. The idle gear 41 and the retarder 24 are arranged such that the distance d3 is longer than the distance d2, and thus the idle gear 41, which has a relatively short diameter, can be arranged outside the first transmission gear 241. In other words, the first transmission gear 241, which has a relatively long diameter, can be located at a more inner position in the housing 21 and can therefore be prevented from protruding outward.The housing 21 may have an outer contour along the idler gear 41, which has a relatively short diameter, but not along the first transmission gear 241, which has a relatively long diameter. Therefore, the size of the drive unit 20 can be reduced. The size of the drive unit 20 in the up-down direction can be reduced, and therefore the minimum ground clearance of the electrically assisted bicycle 10 can be increased.

[0119] As in Fig. 3, the idle gear 41 is arranged at the bottom of the drive unit 20, so that the degree of freedom of the position arrangement of the suspension 304 ( Fig. 1) can be increased. The substantially same effect is also given in the case where the idle gear 41 is arranged at the top of the drive unit 20. However, in the case shown in Fig. 1, in which the suspension 304 is arranged above the drive unit 20, the position of the suspension 304 is influenced when the idle gear 41 is arranged at the top of the drive unit 20. The idle gear 41 is arranged below the drive unit 20, so that the degree of freedom of the positional arrangement of the suspension 304 can be increased.

[0120] With reference to Fig. 4, the positional relationship of the components of the drive unit 20 is further described.

[0121] The distance from plane 61 to a farthest point of the idler gear 41 is designated L3. The farthest point of the idler gear 41 is the position on a tip circle connecting the tips of the teeth of the idler gear 41 that is farthest from plane 61. The distance from plane 61 to a farthest point of the driven gear 252A is designated L1. The distance from plane 61 to a farthest point of the first transfer gear 241 is designated L2. The distance from plane 61 to a farthest point of the driven gear 233 is designated L4. The farthest point of the output gear 252A is the position on a tip circle connecting the tips of the teeth of the output gear 252A that is farthest from the plane 61.The farthest point of the first transmission gear 241 is the position on a tip circle connecting the tips of the teeth of the first transmission gear 241 that is farthest from the plane 61. The farthest point of the driven gear 233 is the position on a tip circle connecting the tips of the teeth of the driven gear 233 that is farthest from the plane 61.

[0122] Distance L3 is longer than each of the distances L1, L2, and L4. Specifically, distance L3 is made larger than distance L2, so that the idle gear 41, which has a relatively short diameter, can be arranged outside the first transmission gear 241. Namely, the first transmission gear 241, which has a relatively long diameter, can be arranged at a more inner position in the housing 21 and can therefore be prevented from protruding outward. With this structure, the size of the drive unit 20 can be reduced.

[0123] With reference to Fig. 5, the positional relationship of the components of the drive unit 20 is further described.

[0124] In the drive unit 20, a triangle is defined in the axial direction, having three axes among the first to fourth central axes RC1 to RC4 as apices. The remaining one axis among the first to fourth central axes RC1 to RC4 is located within the triangle. Fig. Figure 5 shows, as an example, a triangle 63 having the central axes RC1, RC3 and RC4 as apices, viewed in the axial direction. Fig. In the example shown in Figure 5, the second center axis RC2 of the first transmission gear 241 is located within the triangle 63, which has the center axes RC1, RC3, and RC4 as the apices. The first transmission gear 241, which has a relatively long diameter, is located at a more inner position in the housing 21, so that the first transmission gear 241 can be prevented from protruding outward. With this structure, the size of the drive unit 20 can be reduced.

[0125] Now, the positional relationship between the first transmission gear 241 of the decelerator 24 and the driven gear 233 will be described.

[0126] With reference to Fig. 3, in this embodiment, in the drive unit 20, viewed in the axial direction, the first transmission gear 241 and the driven gear 233 are arranged such that at least a part of the driven gear 233 overlaps the first transmission gear 241.

[0127] The driven gear 233 and the first transmission gear 241 are arranged such that at least a portion of the driven gear 233 and the first transmission gear 241 overlap each other, and thus the second center axis RC2 and the fourth center axis RC4 can be brought closer to each other. With this structure, the first center axis RC1 and the fourth center axis RC4 can be brought closer to each other. The distance between the first center axis RC1 and the fourth center axis RC4 can be shortened, and therefore the size of the drive unit 20 in the front-rear direction can be reduced.

[0128] The size of the drive unit 20 in the front-rear direction is reduced, so that a space for the down tube 123 ( Fig. 1) battery unit 26 to be arranged ( Fig. 1) can be ensured. In a vehicle with the battery unit located in the down tube, the battery unit is located in a space between the pedal crankshaft and the front wheel in the front-rear direction of the vehicle (located in a front center section). Attempting to increase the battery capacity results in an increase in the size of the battery unit, and the front center length must be extended accordingly. However, in the case where the front center length is extended, a problem arises that the operability of the vehicle is reduced.

[0129] According to this embodiment, the size of the drive unit 20 is reduced in the front-rear direction, so the degree of freedom of the positional arrangement of the battery unit 26 can be increased. The battery unit 26, which has a large capacity, can be easily arranged without increasing the front center length.

[0130] With reference to Fig. 6, the positional relationship between the first transmission gear 241 of the retarder 24, the idle gear 41 and the driven gear 233 will now be described.

[0131] In the drive unit 20, viewed in the axial direction, the driven gear 233 and the idle gear 41 are in an area 65 (black section in Fig. 6) mesh with each other. In this embodiment, the first transmission gear 241, the idle gear 41, and the driven gear 233 are arranged such that at least a portion of the region 65 in which the driven gear 233 and the idle gear 41 mesh with each other overlaps the first transmission gear 241.

[0132] The first transmission gear 241, the idle gear 41, and the driven gear 233 are arranged such that at least a portion of the region 65 where the driven gear 233 and the idle gear 41 mesh with each other overlaps the first transmission gear 241. Consequently, the second center axis RC2 and the fourth center axis RC4 can be brought closer to each other. With this structure, the first center axis RC1 and the fourth center axis RC4 can be brought closer to each other. The distance between the first center axis RC1 and the fourth center axis RC4 can be shortened, and therefore the size of the drive unit 20 in the front-rear direction can be reduced.

[0133] With reference to Fig. 6, the positional relationship between the third center axis RC3 and the first transmission gear 241 of the retarder 24 will now be described. The idle gear 41 rotates around the third center axis RC3.

[0134] In the drive unit 20, the third center axis RC3 overlaps the first transmission gear 241 in the axial direction. The idler gear 41 and the decelerator 24 are arranged so that the third center axis RC3 and the first transmission gear 241 overlap each other, and thus the second center axis RC2 and the third center axis RC3 can be brought closer to each other. With this structure, the first center axis RC1 and the fourth center axis RC4 can be brought closer to each other. The distance between the first center axis RC1 and the fourth center axis RC4 can be shortened, and therefore the size of the drive unit 20 in the front-rear direction can be reduced. (Support structure of the driven gear)

[0135] A structure that supports the driven gear 233 will now be described. Fig. 7 is a cross-sectional view showing an example of the structure of the driven gear 233 and its surroundings in the drive unit 20.

[0136] As described above, the driven gear 233 is provided in the outer member 52 of the one-way clutch 50. The drive pinion 34 is attached to a portion of the outer member 52 located outside (right) of the housing 21.

[0137] While the electrically assisted bicycle 10 is traveling with both the outer member 52 and the drive gear 34 rotating, a load is exerted from the drive gear 34 to the outer member 52. Due to the load from the drive gear 34, precession is caused in the outer member 52 including the driven gear 233. When the precession is large, a problem arises in that the meshing precision of the driven gear 233 and the idler gear 41 is reduced.

[0138] In this embodiment, two bearings 381R and 382R are provided as the bearing 38R that supports the outer member 52. The bearings 381R and 382R are each a rolling element bearing including an inner ring, an outer ring, and a rolling element. The outer ring of each of the bearings 381R and 382R is press-fitted into the second housing 212 of the housing 21, and the outer member 52 is clearance-fitted into the inner ring thereof.

[0139] In the left-right direction of the drive unit 20, the bearing 382R is located at an outer position, while the bearing 381R is located at an inner position. The bearings 381R and 382R may be in contact with each other or arranged separately.

[0140] The outer member 52 is supported by two bearings 381R and 382R, so that the rotational vibration of the outer member 52 can be reduced, and therefore the precession of the outer member 52 can be reduced. The reduction in precession can improve the meshing precision of the driven gear 233 and the idle gear 41. With this structure, the noise generated when the driven gear 233 and the idle gear 41 mesh with each other can be reduced, and the abrasion of the rotating shaft can be reduced. In addition, the sealability of the bearings 381R and 382R supporting the outer member 52 can be improved.

[0141] Now, the positional relationship between the drive pinion 34, the driven gear 233 and the bearings 381R and 382R will be described.

[0142] In the axial direction of the pedal crankshaft 22, the distance to the innermost position of the bearing 381R (left end portion of the bearing 381R) from a position 341 in the outer member 52 to which the drive pinion 34 is attached is denoted by a. In the axial direction of the pedal crankshaft 22, the distance from the attachment position 341 to the center of a portion where the driven gear 233 and the idle gear 41 mesh with each other is denoted by b. The relationship between distance a and distance b can be represented by Expression 1 below. a / b ≥ 0.5 ... Expression 1

[0143] The bearing 381R is located at an inner position in the left-right direction of the drive unit 20. As the position of the bearing 381R is farther away from the position 341 where the drive pinion 34 is mounted, the precession of the outer member 52 can be reduced more. The bearing 381R is arranged so that its left end portion is located within the middle position of the distance b in the left-right direction of the drive unit 20, and thus the precession of the outer member 52 can be reduced more.

[0144] The bearing 381R is located far from the position 341 where the drive pinion 34 is mounted, while the bearing 382R is arranged as close as possible to the mounting position 341, so that the precession of the outer member 52 can be reduced more. For example, the bearing 382R is arranged so that a left end portion thereof is located outside the center position of the distance b in the left-right direction of the drive unit 20. Consequently, the precession of the outer member 52 can be reduced more.

[0145] Bearings 381R and 382R can be the same size as each other or different sizes from each other.

[0146] A multi-row bearing can be used instead of bearings 381R and 382R. Examples of applicable multi-row bearings include, but are not limited to, a multi-row angular contact bearing, a multi-row deep groove bearing, and the like. A needle bearing can also be used instead of bearings 381R and 382R. (Heat dissipation structure)

[0147] Now, a structure will be described that dissipates the heat generated in the coils 2511 of the electric motor 25 to the outside. Fig. Fig. 8 is a cross-sectional view showing a structure of the electric motor 25 and the surroundings thereof in the drive unit 20. In the Fig. In the example shown in Fig. 8, a heat dissipation means 2515 (hatched section in Fig. 8). The heat dissipation means 2515 is provided between the coils 2511 wound around the coil supports 2512 of the stator 251 and the cover 213, so that the heat generated in the coils 2511 can be efficiently dissipated to the outside.

[0148] The heat dissipation agent 2515 may be formed of any material having high thermal conductivity. Examples of the material that can be used for the heat dissipation agent 2515 include highly thermally conductive epoxy resins and unsaturated polyester resins, each incorporating an alumina filler, but are not limited to any of these.

[0149] It is possible to dissipate heat even in the case where the entire circumference of each of the coils 2511 wound around the coil supports 2512 is covered with the heat dissipating agent 2515. However, in the case where the heat dissipating agent 2515 is provided to fill the space to cover the entire circumference of each of the coils 2511, a problem arises that the weight of the drive unit 20 is increased. In the case where the entire circumference of each of the coils 2511 is covered with the heat dissipating agent 2515, a mold to be filled with the heat dissipating agent 2515 is required, and therefore a problem arises that the production cost and the number of production steps are increased.

[0150] In this embodiment, the heat dissipation means 251 is provided only between the stator 251 and the cover 213, so that the heat generated in the coils 2511 can be efficiently dissipated to the outside while suppressing the increase in weight.

[0151] With reference to Fig. 8, the cover 213 in this embodiment includes an inner wall 2131. The cover 213 has a shape in which a left portion of each of the coil supports 2512, around each of which the coil 2511 is wound, is covered with the inner wall 2131 and an outer peripheral wall 2132 of the cover 213. During production of the drive unit 20, the heat dissipation agent 2515 is applied between the inner wall 2131 and the wall 2132 of the cover 213. The cover 213 having the heat dissipation agent 2515 applied thereto is attached to the first case 211 of the housing 21, and therefore, the structure including the heat dissipation agent 2515 between the coils 2511 and the cover 213 can be easily realized. A mold to be filled with the heat dissipating agent 2515 is not required, and therefore the production cost and the number of production steps can be reduced.

[0152] The cover 213 includes the inner wall 2131, so that when the heat dissipating agent 2515 is applied to the cover 213, the heat dissipating agent 2515 can be prevented from flowing into an area where the heat dissipating agent 2515 is not required. The left portion of each of the coil supports 2512, around which the coil 2511 is wound, is covered with the inner wall 2131 and the wall 2132 of the cover 213, so that the heat dissipating agent 2515 can be prevented from flowing to the rotor 252.

[0153] An embodiment of the present invention is described above. The present invention is not limited to the above-described embodiment. For example, in the above-described embodiment, the electric-assisted bicycle including the suspension is described as an example. The present invention is preferably also applicable to an electric-assisted bicycle without a suspension.

[0154] In the embodiment described above, the drive unit 20 ( Fig. 2) Four shafts, namely the output shaft 252A, the transmission shaft 243, the rotation shaft 43, and the pedal crankshaft 22. The number of shafts is not limited to four. The present invention is applicable to a drive unit including five or more shafts. For example, the present invention is applicable to a drive unit in which a gear is provided between the output gear 252A of the electric motor 25 and the first transmission gear 241 of the decelerator 24, and torque is transmitted from the output gear 252A to the first transmission gear 241 via the aforementioned gear.

[0155] In the embodiment described above, the entirety of the electric motor 25 is housed in the housing 21. The structure of the housing 21 is not limited to this. Only a part of the electric motor 25 may be housed in the housing 21. For example, a left portion of the first housing 211 may have an opening through which the electric motor 25 can pass, and the electric motor 25 may be mounted so that a part of it is located through the opening in the housing 21. In this case, the opening may be provided with a dust- and waterproof cover.

[0156] The cover 213 ( Fig.2) may be a part of the housing 21 and may be contained within the housing 21. The cover 213 may have a shape such that it covers a side surface of the electric motor 25, and the electric motor 25 may be supported by the cover 213. A shape in which the electric motor 25 is supported by the cover 213 is included in the shape in which the electric motor 25 is supported by the housing 21.

[0157] In the above-described embodiment, the two-wheeled electric-assisted bicycle is described as an example of the electric-assisted vehicle 10. The present invention is not limited to this. For example, the electric-assisted vehicle 10 may be an electric-assisted vehicle with three or more wheels.

[0158] In the embodiment described above, the drive wheel to which the human power generated by the rider's pedaling and the assist power generated by the motor are transmitted is the rear wheel. The present invention is not limited to this. The human power and the assist power may be transmitted to the front wheel or to both the front and rear wheels, depending on the shape of the electric-assisted bicycle.

[0159] In the embodiment described above, the vehicle is the electric-assisted bicycle, but it may alternatively be a vehicle other than the electric-assisted bicycle. The present invention is preferably applicable to any vehicle in which the drive unit must be reduced in size.

[0160] Illustrative embodiments of the present invention are described above.

[0161] A drive unit 20 according to an embodiment of the present invention is usable in an electrically assisted vehicle 10. The drive unit includes an electric motor 25 having an output shaft 252A having an output gear 252A; a housing 21 that houses part or all of the electric motor 25; a pedal crankshaft 22 extending through the housing 21, rotatably supported by the housing 21, and provided with a driven gear 233; a transmission mechanism 40 that transmits torque from the output gear 252A of the electric motor 25 to the driven gear 233; and a resultant force output shaft 235 rotatable coaxially with the pedal crankshaft 22, the resultant force output shaft 235 combining pedal power and assist power of the electric motor 25.The transmission mechanism 40 includes a retarder 24 rotatably supported by the housing 21 within the housing 21, and an idler gear 41 rotatably supported by the housing 21 within the housing 21. The retarder 24 increases the torque of the output shaft 252A of the electric motor 25, and the increased torque is transmitted to the driven gear 233 via the idler gear 41.

[0162] To shorten the rear center length of the electric-assisted vehicle 10, it is conceivable to shorten the diameter of the driven gear 233 provided on the pedal crankshaft 22. When a "dual-axis decelerator" is located between the driven gear 233 on the pedal crankshaft 22 and the electric motor 25, it becomes difficult to shorten the width of the drive unit 20 in the axial direction. Two gears with different diameters and different numbers of teeth are arranged in the axial direction on the decelerator's rotating shaft. Therefore, the size of the rotating shaft in the axial direction tends to increase. The dual-axis decelerator includes two such rotating shafts, and the two rotating shafts are located offset from each other in the axial direction. Therefore, the size of the dual-axis decelerator in the axial direction is increased.

[0163] According to one embodiment of the present invention, the idle gear 41 is used, so that the diameter 233 of the driven gear can be reduced, and therefore the rear center length of the electrically assisted vehicle 10 can be shortened without increasing the width (size in the axial direction) of the drive unit 20. The use of the idle gear 41 can also improve the degree of freedom of the positional arrangement of the electric motor 25, the decelerator 24, and the driven gear 233, and therefore further reduce the size of the drive unit 20.

[0164] In one embodiment, the electric motor 25 is supported by the housing 21 such that the output shaft 2522 rotates about a first central axis RC1. The decelerator 24 is supported by the housing 21 in the housing 21 such that it is rotatable about a second central axis RC2 and includes a first transmission gear 241, a second transmission gear 242 having a smaller number of teeth than the first transmission gear 241, and a transmission shaft 243 that transmits rotation of the first transmission gear 241 to the second transmission gear 242. The idler gear 41 is supported by the housing 21 in the housing 21 such that it is rotatable about a third central axis RC3. The pedal crankshaft 22 extends through the housing 21 along a fourth central axis RC4 and is supported by the housing 21 such that it is rotatable about the fourth central axis RC4.

[0165] The increased torque from the two transmission gears, which have different numbers of teeth, can be transmitted via the idle gear 41 to the driven gear 233.

[0166] According to the invention, the idle gear 41 is engaged with each of the second transmission gear 242 of the retarder 24 and the driven gear 233.

[0167] The idle gear 41 meshes with each of the second transmission gear 242 and the driven gear 233, so that the torque from the retarder 24 can be transmitted to the driven gear 233 via the single idle gear 41. The presence of such an idle gear 41 can slightly reduce the size of the driven gear 233.

[0168] In one embodiment, the first transmission gear 241 of the retarder 24 may mesh with the output gear 252A of the electric motor 25.

[0169] Since the single retarder 24 and the single idle gear 41 transmit the torque of the electric motor 25 to the driven gear 233, the size of the drive unit 20 can be reduced without using any additional gear.

[0170] In one embodiment, a distance d3 from a plane 61 including the first center axis RC1 and the fourth center axis RC4 to the third center axis RC3 is longer than a distance d2 from the plane to the second center axis RC2, and the idler gear 41 has a diameter shorter than each of a diameter of the driven gear 233 and a diameter of the first transmission gear 241.

[0171] The idle gear 41 is a member that does not decelerate or accelerate, and therefore only needs to be sized to realize power transmission between the decelerator 24 and the driven gear 233. Therefore, the idle gear 41 can have a diameter shorter than either the diameter of the first transmission gear 241 of the decelerator 24 or the diameter of the driven gear 233 on the pedal crankshaft 22. The distance d3 from the plane 61, which includes the first center axis RC1 and the fourth center axis RC4, to the third center axis RC3 is made larger than the distance d2 from the plane 61 to the second center axis RC2, so that the idle gear 41, which has a relatively short diameter, can be disposed outside the first transmission gear 241.In other words, the first transmission gear 241, which has a relatively large diameter, can be arranged at a more inner position in the housing 21 and can therefore be prevented from protruding outward. The housing 21 can have an outer contour along the idler gear 41, which has a relatively short diameter, but not along the first transmission gear 241, which has a relatively long diameter. Therefore, the size of the drive unit 20 can be reduced.

[0172] In one embodiment, a distance L3 from the plane 61 including the first center axis RC1 and the fourth center axis RC4 to a farthest point of the idler gear 41 may be longer than each of a distance L1 from the plane 61 to a farthest point of the driven gear 252A, a distance L2 from the plane 61 to a farthest point of the first transfer gear 241, and a distance L4 from the plane 61 to a farthest point of the driven gear 233, and the idler gear 41 may have a diameter shorter than each of a diameter of the driven gear 233 and a diameter of the first transfer gear 241.

[0173] The idle gear 41 is an element that does not decelerate or accelerate and therefore only needs to be of such a size to realize power transmission between the retarder 24 and the driven gear 233. Therefore, the idle gear 41 can have a diameter shorter than each of the diameter of the first transmission gear 241 of the decelerator 24 and the diameter of the driven gear 233 on the pedal crankshaft 22. The distance L3 from the plane 61, which includes the first center axis RC1 and the fourth center axis RC4, to the farthest point of the idle gear 41 is made longer than each of the distance L1 from the plane 61 to the farthest point of the driven gear 252A, the distance L2 from the plane 61 to the farthest point of the first transmission gear 241, and the distance L4 from the plane 61 to the farthest point of the driven gear 233.With this structure, the idle gear 41, which has a relatively short diameter, can be arranged outside the first transmission gear 241. In other words, the first transmission gear 241, which has a relatively long diameter, can be located at a more inner position in the housing 21 and can therefore be prevented from protruding outward. The housing 21 can have an outer contour along the idle gear 41, which has a relatively short diameter, but not along the first transmission gear 241, which has a relatively long diameter. Therefore, the size of the drive unit 20 can be reduced.

[0174] In one embodiment, viewed in an axial direction parallel to the first central axis RC1, a triangle having three axes among the first to fourth central axes RC1 to RC4 as apices may have the remaining one axis disposed therein.

[0175] The gear rotating around the remaining one axis can be located at a more inner position in the housing 21, and thus the gear can be prevented from protruding outward. With this structure, the size of the drive unit 20 can be reduced.

[0176] In one embodiment, viewed in an axial direction parallel to the first central axis RC1, the second central axis RC2 may be located in a triangle having the first central axis RC1, the third central axis RC3 and the fourth central axis RC4 as apices.

[0177] The idle gear 41 is a member that does not decelerate or accelerate, and therefore only needs to be sized to realize power transmission between the decelerator 24 and the driven gear 233. Therefore, the idle gear 41 can have a diameter shorter than each of the diameter of the first transmission gear 241 of the decelerator 24 and the diameter of the driven gear 233 on the pedal crankshaft 22. The second central axis RC2 is located in a triangle having the first central axis RC1, the third central axis RC3, and the fourth central axis RC4 as apices. With this structure, the first transmission gear 241, which has a relatively long diameter, can be located at a more inner position in the housing 21 and can therefore be prevented from protruding outward.The housing 21 may have an outer contour along the idler gear 41, which has a relatively short diameter, but not along the first transmission gear 241, which has a relatively long diameter. Therefore, the size of the drive unit 20 can be reduced.

[0178] In one embodiment, at least a portion of the driven gear 233 may overlap the first transmission gear 241, viewed in an axial direction parallel to the first central axis RC1.

[0179] The driven gear 233 and the first transmission gear 241 are arranged such that at least a portion of the driven gear 233 and the first transmission gear 241 overlaps with each other, and thus the second center axis RC2 and the fourth center axis RC4 can be brought closer to each other. With this structure, the first center axis RC1 and the fourth center axis RC4 can be brought closer to each other. The distance between the first center axis RC1 and the fourth center axis RC4 can be shortened, and therefore the size of the drive unit 20 in the front-rear direction can be reduced. The size of the drive unit 20 in the front-rear direction is reduced, so that the space for the battery unit 26 to be arranged in the down tube 123 can be ensured.

[0180] In a vehicle with the battery unit located in the down tube, the battery unit is located in a space between the pedal crankshaft and the front wheel in the front-rear direction of the vehicle (located in a front center section). Attempting to increase the battery capacity results in an increase in the size of the battery unit, and the front center length must be made longer accordingly. However, increasing the front center length results in a problem that reduces the vehicle's usability.

[0181] According to one embodiment of the present invention, the size of the drive unit 20 is reduced in the front-rear direction, so that the degree of freedom of the positional arrangement of the battery unit 26 can be increased. The battery unit 26, which has a large capacity, can be easily arranged without increasing the front center length.

[0182] In one embodiment, at least a portion of a region 65 in which the driven gear 233 and the idle gear 41 are engaged with each other, viewed in an axial direction parallel to the first central axis RC1, may overlap the first transmission gear 241.

[0183] The first transmission gear 241, the idle gear 41, and the driven gear 233 are positioned such that at least a portion of the region 65 where the driven gear 233 and the idle gear 41 mesh overlaps the first transmission gear 241. Consequently, the second center axis RC2 and the fourth center axis RC4 can be brought closer to each other. With this structure, the first center axis RC1 and the fourth center axis RC4 can be brought closer to each other. The distance between the first center axis RC1 and the fourth center axis RC4 can be shortened, and therefore the size of the drive unit 20 in the front-rear direction can be reduced.

[0184] In one embodiment, viewed in an axial direction parallel to the first central axis RC1, the third central axis RC3 may overlap the first transmission gear 241.

[0185] The idler gear 41 and the decelerator 24 are positioned so that the third center axis RC3 and the first transmission gear 241 overlap each other, and thus the second center axis RC2 and the third center axis RC3 can be brought closer to each other. With this structure, the first center axis RC1 and the fourth center axis RC4 can be brought closer to each other. The distance between the first center axis RC1 and the fourth center axis RC4 can be shortened, and therefore the size of the drive unit 20 in the front-rear direction can be reduced.

[0186] In one embodiment, the pedal crankshaft 22 may be provided with a one-way clutch 50.

[0187] The pedal crankshaft 22 is provided with the one-way clutch 50, so that a structure can be provided in which a forward rotation of the pedal crankshaft 22 is transmitted to the drive pinion 34, but a reverse rotation of the pedal crankshaft 22 is not transmitted to the drive pinion 34.

[0188] An electrically assisted vehicle 10 according to an embodiment of the present invention includes the drive unit 20 described above.

[0189] The electrically assisted vehicle 10 includes the drive unit 20 in which the driven gear 233 on the pedal crankshaft 22 has a short diameter so that the rear center length of the electrically assisted vehicle 10 can be shortened.

[0190] The present invention is particularly useful in the field of electrically assisted vehicles and drive units mountable on the electrically assisted vehicles.

Claims

[1] A drive unit (20) usable in an electrically assisted vehicle (10), the drive unit (20) comprising: an electric motor (25) including an output shaft (2522) having an output gear (252A); a housing (21) which houses part or all of the electric motor (25); a pedal crankshaft (22) extending through the housing (21), rotatably supported by the housing (21) and provided with a driven gear (233); a transmission mechanism (40) that transmits a torque of the driven gear (252A) of the electric motor (25) to the driven gear (233); and a resultant force output shaft (235) rotatable coaxially with the pedal crankshaft (22), the resultant force output shaft (235) combining pedal power and assist power of the electric motor (25), wherein the transmission mechanism (40) includes: a retarder (24) which is rotatably mounted in the housing (21) by the housing (21), and an idle gear (41) rotatably supported by the housing (21) in the housing (21), the idle gear (41) being a member that does not decelerate or accelerate, wherein the retarder (24) increases the torque of the output shaft (2522) of the electric motor (25), and wherein the increased torque is transmitted via the idle gear (41) to the driven gear (233), wherein the electric motor (25) is mounted by the housing (21) such that the output shaft (2522) rotates about a first central axis (RC1), wherein the retarder (24) is mounted by the housing (21) in the housing (21) so as to be rotatable about a second central axis (RC2), and includes a first transmission gear (241), a second transmission gear (242) having a smaller number of teeth than that of the first transmission gear (241), and a transmission shaft (243) transmitting rotation of the first transmission gear (241) to the second transmission gear (242), wherein the idle gear (41) is mounted by the housing (21) in the housing (21) so that it is rotatable about a third central axis (RC3), and wherein the pedal crankshaft (22) extends through the housing (21) along a fourth central axis (RC1) and is mounted by the housing (21) so that it is rotatable about the fourth central axis (RC4), wherein a distance from a plane (61) containing the first central axis (RC1) and the fourth central axis (RC4) to the third central axis (RC3) is longer than a distance from the plane (61) to the second central axis (RC2), and wherein the idle gear (41) has a diameter shorter than each of a diameter of the driven gear (233) and a diameter of the first transmission gear (241), wherein the idle gear (41) is engaged with each of the second transmission gear (242) of the retarder (24) and the driven gear (233). [2] The drive unit (20) of claim 1, wherein the first transmission gear (241) of the decelerator (24) is engaged with the output gear (252A) of the electric motor (25). [3] The drive unit (20) of claim 1 or 2, wherein a distance (L3) from a plane (61) including the first center axis (RC1) and the fourth center axis (RC4) to a farthest point of the idler gear (41) is longer than each of a distance (L1) from the plane (61) to a farthest point of the driven gear (252A), a distance (L2) from the plane (61) to a farthest point of the first transmission gear (241), and a distance (L4) from the plane (61) to a farthest point of the driven gear (233). [4] The drive unit (20) of any one of claims 1 to 3, wherein, viewed in an axial direction parallel to the first central axis (RC1), a triangle (63) having three axes among the first (RC1) to fourth central axes (RC4) as apices has the remaining one axis arranged therein. [5] The drive unit (20) of any one of claims 1 to 4, wherein, viewed in an axial direction parallel to the first central axis (RC1), the second central axis (RC2) is located in a triangle (63) having the first central axis (RC1), the third central axis (RC3) and the fourth central axis (RC4) as apices. [6] The drive unit (20) of any one of claims 1 to 5, wherein, viewed in an axial direction parallel to the first central axis (RC1), at least a part of the driven gear (233) overlaps the first transmission gear (241). [7] The drive unit (20) of any one of claims 1 to 6, wherein, viewed in an axial direction parallel to the first center axis (RC1), at least a part of a region in which the driven gear (233) and the idle gear (41) are engaged with each other overlaps the first transmission gear (241). [8] The drive unit (20) of any one of claims 1 to 7, wherein, viewed in an axial direction parallel to the first center axis (RC1), the third center axis (RC3) overlaps the first transmission gear (241). [9] The drive unit (20) of any one of claims 1 to 8, wherein the pedal crankshaft (22) is provided with a one-way clutch (50). [10] An electrically assisted vehicle (10) comprising the drive unit (20) according to any one of claims 1 to 9.

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