# Patent

## Title
Electric vehicle

## Abstract

An electric vehicle capable of protecting a coupling portion between a wheel and an axle from disturbance. An electric vehicle includes an axle that is a hollow cylindrical shaft passing substantially coaxially through a wheel in a manner extending from both sides of the wheel. A motor shaft is inserted into a hollow portion of the axle substantially coaxially with the axle in a manner extending from both ends of the axle. In this case, a motor is connected to a base end of the motor shaft extending from one end of the axle. Between the wheel and the motor, there are provided a coupling portion for coupling between the one end of the axle and the wheel, and a labyrinth structure for sealing between the wheel and the motor in a manner surrounding the coupling portion.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 USC 119 to Japanese Patent Application No. 2011-081263 filed Mar. 31, 2011 the entire contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electric vehicle in which an output of a motor is transmitted to an axle through a reduction mechanism, thereby rotating a wheel.
2. Description of Background Art
In the past, various electric vehicles have been proposed in which an output of a motor is transmitted to an axle through a reduction mechanism, thereby rotating a wheel.
For example, in JP-A No. H10-89439, there is proposed a structure in which a motor, a reduction mechanism, and a wheel are coaxially connected to an axle (a drive shaft) in this order. One end of the drive shaft toward which the motor is located, and the other end toward which the wheel is located, are each fastened by a nut.
However, in JP-A No. H10-89439, a motor shaft and the reduction mechanism are disposed on the one side, leading to a weight imbalance. In addition, the nut for fastening the wheel to the drive shaft is exposed to a side surface of the wheel on the other side. For this reason, the nut might be affected by disturbance such as stones scattered by the wheel during the operation of an electric vehicle or access to the nut by a person such as an occupant.
SUMMARY AND OBJECTS OF THE INVENTION
Accordingly, the present invention has been made in view of the problems in the related art, and an object of an embodiment of the present invention is to provide an electric vehicle in which a coupling portion between a wheel and an axle can be protected from disturbance while a motor and a reduction mechanism are disposed in such a manner so as to be distributed one on each side of the wheel.
In order to accomplish the above-mentioned object, a feature of an embodiment of the present invention is that, in an electric vehicle (10) in which an output of a motor (16) is transmitted to an axle (52) through a reduction mechanism (160) in order to rotate a wheel (90), with the axle (52) being a hollow cylindrical shaft passing substantially coaxially through the wheel (90) in a manner extending from both sides of the wheel (90). The motor (16) has a motor shaft (16a) inserted into a hollow portion of the cylindrical shaft (52) substantially coaxially with the cylindrical shaft (52) in a manner extending from both ends of the cylindrical shaft (52). The motor (16) is connected to a base end of the motor shaft (16a) extending from one end of the cylindrical shaft (52) with the reduction mechanism (160) being connected to a leading end of the motor shaft (16a) extending from the other end of the cylindrical shaft (52). A coupling portion (192) is provided for coupling between the one end of the cylindrical shaft (52) and the wheel (90), and a sealing portion (190, 194) is provided for sealing between the wheel (90) and the motor (16) in a manner surrounding the coupling portion (192), are provided between the wheel (90) and the motor (16).
According to an embodiment of the present invention, the coupling portion (192) is composed of a threaded portion formed at the one end of the cylindrical shaft (52); and a nut (172) threaded onto the threaded portion for coupling between the wheel (90) and the cylindrical shaft (52).
According to an embodiment of the present invention, a motor case (44) is provided for storing the motor (16); and a first bearing (194) is inserted between the motor case (44) and the wheel (90) in a manner surrounding the motor shaft (16a), the cylindrical shaft (52), and the coupling portion (192). The first bearing (194) relatively rotatably mounts the motor case (44) to the wheel (90).
According to an embodiment of the present invention, a portion (195) of the motor case (44) opposite the coupling portion (192) is tapered so as to deviate from the nut (172).
According to an embodiment of the present invention, a motor module (46) is composed of the motor (16) and the motor case (44) with a reduction mechanism module (50) composed of the reduction mechanism (160) and a reduction mechanism case (48) for storing the reduction mechanism (160). A second bearing (254) is inserted between the reduction mechanism case (48) and the wheel (90) in a manner surrounding the motor shaft (16a) and the cylindrical shaft (52). The second bearing (254) relatively rotatably mounts the reduction mechanism case (48) to the wheel (90).
According to an embodiment of the present invention, a labyrinth structure (252) is formed between the reduction mechanism case (48) and the wheel (90) in a manner surrounding the second bearing (254).
According to an embodiment of the present invention, a brake (260) is provided for braking rotation of the wheel (90). The brake (260) is disposed in a hollow portion between the labyrinth structure (252) provided between the reduction mechanism case (48) and the wheel (90), and the second bearing (254).
According to an embodiment of the present invention, a third bearing (198, 200) is inserted between the motor case (44) and the motor shaft (16a). The third bearing (198, 200) relatively rotatably supports the motor case (44) on the motor shaft (16a) with a sealing being applied to at least one of the first to third bearings (194, 198, 200, 254).
According to an embodiment of the present invention, the sealing portion (190, 194) is a labyrinth structure (190) formed between the motor case (44) and the wheel (90) in a manner surrounding the first bearing (194), and/or the sealed first bearing (194).
According to an embodiment of the present invention, a hole portion (214) or a bolt head (282) is provided at the leading end of the motor shaft (16a). The hole portion (214) allows insertion of a screw-driver or a hex wrench.
According to an embodiment of the present invention, the reduction mechanism (160) is provided with a first gear (216) formed at the leading end of the motor shaft (16a) and a second gear (220) disposed forwardly of the motor shaft (16a), the second gear (220) engaging with the first gear (216). A reduction shaft (218) is disposed forwardly of and substantially parallel to the cylindrical shaft (52) and the motor shaft (16a), and substantially coaxially connected to the second gear (220). A third gear (222) is formed on the side of the reduction shaft (218) toward the wheel (90) with a fourth gear (224) being substantially coaxially connected to the cylindrical shaft (52) on the other end of the cylindrical shaft (52), the fourth gear (224) engaging with the third gear (222). A hole portion (286) or a bolt head (288) is provided at an end of the reduction shaft (218) toward the second gear (220). The hole portion (286) allows insertion of a screw-driver or a hex wrench.
According to an embodiment of the present invention, a sealing member (232) is inserted between the other end of the cylindrical shaft (52) and the motor shaft (16a).
According to an embodiment of the present invention, a double-sided swing arm (14) is provided for supporting the motor shaft (16a), the cylindrical shaft (52), and the wheel (90) by respectively supporting the motor (16) and the reduction mechanism (160).
According to an embodiment of the present invention, the motor is connected to the base end of the motor shaft on one side of the wheel, and on the other side, the reduction mechanism is connected to the leading end of the motor shaft. Thus, weight balance is easily achieved. In addition, between the wheel and the motor, the coupling portion couples between the one end of the cylindrical shaft, serving as the axle, and the wheel. Also, the sealing portion seals between the wheel and the motor in a manner surrounding the coupling portion. Consequently, the coupling portion is disposed within a sealed space sealed by the sealing portion. This allows protection of the coupling portion from disturbance, such as stones scattered by the wheel during travel of the electric vehicle or access to the nut by a person such as an occupant.
According to an embodiment of the present invention, the motor shaft is inserted into the hollow portion of the cylindrical shaft substantially coaxially with the cylindrical shaft. Thus, the structure of the shaft for rotating the wheel has a double structure of the motor shaft and the cylindrical shaft, thereby allowing an increase in stiffness of the shaft.
Also, the wheel, the cylindrical shaft, and the motor shaft are substantially coaxially disposed. The motor and the reduction mechanism are each connected to the motor shall. Further, the reduction mechanism is connected to the wheel through the cylindrical shaft and the coupling portion. Consequently, a drive system of the wheel, from the motor to the wheel through the motor shaft, the reduction mechanism, the cylindrical shaft, and the coupling portion, is disposed on the axis of the wheel. Thus, the drive system can be compactly disposed on the wheel without protruding the drive system from both sides of the wheel. In addition, flexibility in the space around the wheel is increased. Also, in the reduction mechanism, the torque of the wheel can be easily increased in accordance with the rotational drive force of the motor.
According to an embodiment of the present invention, the coupling portion is composed of: the threaded portion formed at the one end of the cylindrical shaft; and the nut threaded onto the threaded portion, thereby allowing easy coupling between the cylindrical shaft and the wheel.
Also, the coupling portion is provided within the sealed space between the wheel and the motor which is sealed by the sealing portion. Thus, intrusion of mud, etc. from the outside can be avoided, thereby eliminating the need for forming the nut with a coarse pitch to provide resistance to thread stripping. Consequently, the nut can be formed with a fine pitch so that the tightening accuracy can be increased.
According to an embodiment of the present invention, the first bearing is inserted between the motor case and the wheel, thereby allowing a further increase in stiffness of the drive system.
According to an embodiment of the present invention, the portion of the motor case opposite the coupling portion is tapered so as to deviate from the nut. Thus, the motor case (the motor in the motor case) can be brought close to the wheel. Consequently, even if the nut comes loose during travel of the electric vehicle, the nut can be tightened by contact between the tapered portion and the nut, so that the motor case can be further compactly stored on the wheel.
According to an embodiment of the present invention, the second bearing is inserted between the reduction mechanism case and the wheel, thereby allowing a still further increase in stiffness of the drive system.
According to an embodiment of the present invention, the labyrinth structure is formed between the reduction mechanism case and the wheel in a manner surrounding the second bearing. Thus, intrusion of dust, etc. from the outside can be avoided.
According to an embodiment of the present invention, the brake is provided in the hollow portion between the labyrinth structure and the second bearing, thereby enabling efficient braking of rotation of the wheel while eliminating external environmental influences.
According to an embodiment of the present invention, the third bearing is inserted between the motor case and the motor shaft. Thus, by the application of sealing to at least one of the first to third bearings, intrusion of dust, etc. from the outside is effectively avoided, so that the coupling portion or the brake can be reliably protected from the disturbance. Also, sealing of the first to third bearings allows easy and efficient sealing between the wheel and both of the motor module and the reduction mechanism module.
According to an embodiment of the present invention, the sealing portion is the labyrinth structure formed between the motor case and the wheel in a manner surrounding the first bearing, and/or the sealed first bearing. Thus, intrusion of dust, etc. from the outside can be reliably and efficiently avoided.
According to an embodiment of the present invention, the hole portion or the bolt head is formed at the leading end of the motor shaft. Thus, rotational force is transmitted to the cylindrical shaft through the reduction mechanism by rotating the hole portion with a screw-driver or a hex wrench while fixing the nut, or rotating the bolt head with a wrench. Thus, large tightening force can be generated in the coupling portion by small rotational force.
According to an embodiment of the present invention, the hole portion or the bolt head is formed at the end of the reduction shaft toward the second gear. Thus, rotational force is transmitted to the cylindrical shaft by rotating the hole portion with a screw-driver or a hex wrench while fixing the nut, or rotating the bolt head with a wrench. Also in this case, large tightening force can be generated in the coupling portion by small torque.
According to an embodiment of the present invention, the sealing member is inserted between the other end of the cylindrical shaft and the motor shaft, thereby reducing the difference between the rotational speed of the motor shaft and the rotational speed of the cylindrical shaft reduced by the reduction mechanism and allowing an increase in durability.
According to an embodiment of the present invention, the motor and the reduction mechanism are supported by the double-sided swing arm. Thus, the motor shaft, the cylindrical shaft, and the wheel can be supported on both sides.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.



BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:
FIG. 1 is a left side view of a two-wheeled electric vehicle according to the present embodiment;
FIG. 2 is a right side view of the two-wheeled electric vehicle of FIG. 1;
FIG. 3 is a schematic plan view of a motor module, a reduction mechanism module, a motor shaft, an axle, and a rear wheel which are supported by a double-sided swing arm;
FIG. 4 is a partially-exploded perspective view of a left arm of the swing arm of FIG. 3;
FIG. 5A is a side view of an arm portion of FIG. 4; and FIG. 5B is a sectional view of the arm portion of FIG. 4;
FIG. 6 is an exploded perspective view of the motor module of FIG. 3;
FIG. 7 is a sectional view of the motor module, the reduction mechanism module, the motor shaft, the axle, and the rear wheel of FIG. 3;
FIG. 8 is a sectional view illustrating an alternative construction of the reduction mechanism module of FIG. 7;
FIG. 9 is a sectional view illustrating an alternative construction of the reduction mechanism module of FIG. 7;
FIG. 10 is a sectional view illustrating an alternative construction of the reduction mechanism module of FIG. 7;
FIG. 11 is a sectional view illustrating an alternative construction of the reduction mechanism module of FIG. 7;
FIG. 12 is a right side view of the two-wheeled electric vehicle, illustrating an alternative construction in terms of coupling between the swing arm and the reduction mechanism module; and
FIG. 13 is a schematic plan view of the swing arm, the motor module, the reduction mechanism module, the motor shaft, the axle, and the rear wheel, illustrating the alternative construction of FIG. 12.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter, a preferred embodiment of an electric vehicle according to the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a left side view of a two-wheeled electric vehicle (electric vehicle) 10 according to this embodiment. FIG. 2 is a right side view of the two-wheeled electric vehicle 10.
The two-wheeled electric vehicle 10 is a scooter type two-wheeled vehicle having a step floor 12, in which a rear wheel WR is driven by rotational drive force of a motor 16 (see FIG. 3) provided in a swing arm 14. A high-voltage (for example, 72 V) main battery 18 for supplying electric power to the motor 16 has a plurality of modules with a plurality of battery cells connected in series.
A head pipe 24 rotatably journaling a steering stem 22 is coupled to an upper end of a main frame 20. A pair of left and right front forks 26l and 26r rotatably journaling a front wheel WF is mounted to the steering stem 22. The front wheel WF can be steered by a steering handlebar 28 mounted to an upper portion of the steering stem 22 and having an accelerator grip. The steering handlebar 28 is provided with a throttle sensor 30 that detects an accelerator grip turning angle, i.e., an accelerator opening.
A pair of left and right side frames 32l and 32r extending rearwardly of a vehicle body are connected to the main frame 20. Rear frames 34l and 34r extending upwardly and rearwardly of the vehicle body are connected to the pair of left and right side frames 32l and 32r. Pivot plates 38l and 38r formed with a swing arm pivot 36 are mounted to rear portions of the side frames 32l and 32r. 
A front end 42 of the double-sided swing arm 14 that supports the rear wheel WR with both left and right arms 40l and 40r is swingably journaled to the swing arm pivot 36. The rear wheel WR is rotatably journaled through an axle 52 (see FIG. 3) to a motor case 44 (a motor module 46 including the motor case 44) on the left side and a reduction mechanism case 48 (a reduction mechanism module 50 including the reduction mechanism case 48) on the right side, which serve as rear ends of the swing arm 14. The motor case 44 and the reduction mechanism case 48 are suspended from the rear frames 34l and 34r by rear suspensions 54l and 54r, respectively. Also, a taillight 56 is provided on the rear frames 34l and 34r. 
A side stand 58 is provided on the pivot plate 38l. The side stand 58 has a side-stand switch 60 that outputs a detection signal when the side stand 58 is stored in a predetermined position.
Air introduction pipes 62l and 62r are connected to a front portion of the main battery 18. A suction fan 64 is provided on a rear portion of the main battery 18. The suction fan 64 allows air to be introduced into the main battery 18 from the air introduction pipes 62l and 62r and discharged rearwardly of the vehicle body. Thus, heat generated by the main battery 18 can be cooled by outside air.
A storage space 66 is provided between the pair of left and right rear frames 34l and 34r. A low-voltage (for example, 12 V) sub-battery 70, which is charged from the main battery 18 or from an external source, is stored in a storage space bottom 68 protruding downward from the storage space 66. Also, the storage space 66 is provided with a PDU (Power Drive Unit) 72 that transforms direct current supplied from the main battery 18 into alternating current to supply the current to the motor 16. A DC-DC down converter (hereinafter referred to as a down converter) 74 is provided at the rear of the storage space 66. A rider's seat 76, also serving as a lid of the storage space 66, is provided above the storage space 66. The rider's seat 76 is provided with a seat switch 78 that operates to output a seating signal when a rider sits on the seat 76. It should be noted that an electric power supply line 80 for supplying alternating current to the motor 16 from the PDU 72 is provided between the storage space 66 and the motor 16.
A bracket 82 is coupled to a front portion of the head pipe 24. A headlight 84 is mounted to a front end of the bracket 82. Also, a meter unit 86 for showing the vehicle speed or the like is provided in the vicinity of the steering handlebar 28.
Next, a construction around the rear wheel WR of the two-wheeled electric vehicle 10 will be described in relation to the double-sided swing arm 14 with reference to FIGS. 1 to 7.
The swing arm 14 is, as described above, the double-sided swing arm that supports the rear wheel WR with both the left and right arms 40l and 40r. 
More specifically, the front end 42 (a fifth arm portion and an eighth arm portion) of the swing arm 14 is composed of a hollow cylinder portion 42a allowing insertion of the swing arm pivot 36; arm portions 42l and 42r respectively extending rearward from both the left and right sides of the cylinder portion 42a; and a connection portion 42b connecting between both the left and right arm portions 42l and 42r. 
The left arm 40l extends from the front end 42 to the left side (one side) of a wheel 90 constituting the rear wheel WR serving as a wheel assembly. In other words, the arm 40l is composed of the above-described arm portion 42l; an arm portion 92 (a connection portion, a third arm portion) coupled to a rear portion of the arm portion 42l in a vehicle width direction; an arm portion 94 (a connection portion, a fourth arm portion) coupled to the arm portion 92 in the vehicle width direction; and the motor case 44 coupled to a rear portion of the arm portion 92 in the vehicle width direction.
Also, the motor case 44 is composed of a storage portion 44a (a first arm portion) that is formed with a recessed portion allowing the reception of the motor 16; and a lid portion 44b (a second arm portion) that covers the storage portion 44a in the vehicle width direction with the motor 16 received in the recessed portion of the storage portion 44a, thereby closing the motor 16 in cooperation with the storage portion 44a. Therefore, the motor 16 is disposed in the storage portion 44a, and the storage portion 44a is covered with the lid portion 44b to constitute the motor case 44, so that the motor module 46 including the motor 16 and the motor case 44 is constituted.
The arm portions 42l, 92, 94, the storage portion 44a, and the lid portion 44b are coupled to one another in the vehicle width direction (the left-right direction in FIG. 3) of the two-wheeled electric vehicle 10.
More specifically, plate-like portions 96a and 96b extend vertically from a rear end of the arm portion 42l. Also, the arm portion 92 is a plate-like member, of generally substantially C-shaped cross-section, formed in such a manner that a front end thereof covers a rear end of the arm portion 42l and the left side of the plate-like portions 96a and 96b. On the right side of the arm portion 92, plate-like portions 98a and 98b extend vertically. Furthermore, the arm portion 94 is a plate-like member, of substantially C-shaped cross section, opposed to the arm portion 92 of substantially C-shaped cross section. On the left side of the arm portion 94, plate-like portions 100a and 100b extend vertically opposite to the plate-like portions 98a and 98b, respectively. Moreover, on a front end of the storage portion 44a, arm portions 102a and 102b extend forwardly toward the plate-like portions 98a and 98b of the arm portion 92.
Therefore, with front ends of the plate-like portions 98a and 98b superposed on rear ends of the plate-like portions 96a and 96b, bolts 110a and 110b are respectively inserted into bores 108a and 108b formed in the front ends of the plate-like portions 98a and 98b, and threaded into nuts 112a and 112b welded and fixed to the rear ends of the plate-like portions 96a and 96b in the vehicle width direction, thereby allowing coupling between the arm portion 42l and the arm portion 92 in the vehicle width direction.
Also, with central portions of the plate-like portions 98a and 98b superposed on the plate-like portions 100a and 100b, bolts 118a to 118c are inserted into a total of three bores 114a to 114c (two bores 114a and 114b of the plate-like portion 98a and a single bore 114c of the plate-like portion 98b) formed in the central portions of the plate-like portions 98a and 98b, and three bores 116a to 116c formed opposite to the three bores 114a to 114c, respectively, in the plate-like portions 100a and 100b, and threaded into weld nuts 120a to 120c fixed to the plate-like portions 100a and 100b, thereby allowing coupling between the arm portion 92 and the arm portion 94 in the vehicle width direction.
Furthermore, with rear ends of the plate-like portions 98a and 98b superposed on leading ends of the arm portions 102a and 102b, bolts 126a and 126b are inserted into bores 122a and 122b formed in the rear ends of the plate-like portions 98a and 98b, respectively, and threaded into threaded bores 124a and 124b formed in the leading ends of the arm portions 102a and 102b, respectively, thereby allowing coupling between the arm portion 92 and the arm portions 102a and 102b (the storage portion 44a including the arm portions 102a and 102b) in the vehicle width direction.
Moreover, four threaded holes 128a to 128d are circumferentially formed in the storage portion 44a that is substantially circular in side view. Also, bores 130a to 130d are formed opposite to the threaded holes 128a to 128d, respectively, in the substantially disk-shaped lid portion 44b (see FIG. 6). Therefore, with the bores 130a to 130d aligned with the threaded holes 128a to 128d, bolts 132a to 132d are inserted into the bores 130a to 130d and threaded into the threaded holes 128a to 128d, respectively, thereby allowing coupling between the lid portion 44b and the storage portion 44a in the vehicle width direction.
It should be noted that the bottom of the storage portion 44a is machined flat, and the bottom of the lid portion 44b is also machined flat so as to correspond to the bottom of the storage portion 44a. Also, an arm portion 102c extends rearward on a rear portion of the storage portion 44a. The rear suspension 54l is connected to a bore 124c formed in a leading end portion of the arm portion 102c. 
An expanded portion 134 expanding forward is formed at a portion in between the arm portions 102a and 102b of the storage portion 44a. Also, an expanded portion 136 expanding forward, which corresponds to the expanded portion 134, is formed on the lid portion 44b. 
The motor 16 is an inner rotor type three-phase motor that is composed of a motor shaft 16a substantially coaxially inserted into the hollow cylindrical axle 52 (see FIG. 7); a rotor 16b substantially coaxially connected to the motor shaft 16a; and an annular stator 16c surrounding the rotor 16b. The motor 16 is stored in the motor case 44 by fixing the stator 16c to the recessed portion of the storage portion 44a and disposing, within the stator 16c, the rotor 16b with the motor shaft 16a passing therethrough (see FIGS. 3, 5, and 6). In this case, bus bar connecting terminals 138a to 138c (connecting portions), facing forward, are provided at a portion of the motor 16 toward the expanded portions 134 and 136, in such a manner so as to be sandwiched between the expanded portions 134 and 136.
As described above, the arm portions 92 and 94 of substantially C-shaped cross section are coupled to each other in the vehicle width direction, thereby forming a longitudinally-extending hollow portion 140 at the C-shaped portions by coupling between the respective arm portions 92, 94 (see FIGS. 5A and 5B). Also, the electric power supply line 80 runs from the PDU 72 (see FIGS. 1 to 3). The electric power supply line 80 extends downwardly from the rear of the storage space 66 storing the PDU 72 and passes the side of the arm portion 42l of the swing arm 14 to enter the hollow portion 140 through between leading ends 142a and 142b of the arm portion 94 which is upwardly curved in an arc, and reach the connecting terminals 138a to 138c. 
In this case, the electric power supply line 80 is composed of bus bars 80a to 80c as a three-phase line. The bus bars 80a to 80c, between the storage space 66 and the leading ends 142a and 142b of the arm portion 94, are externally electrically insulated by an insulating sheath 144. Within the hollow portion 140, a supporting member 150 of substantially C-shaped cross section made of an electrical insulating material is fixed to the arm portion 94 by threaded engagement of a screw 146 with a nut 148. Thus, the bus bars 80a to 80c are supported by the supporting member 150 in such a way so as to prevent contact with the arm portions 92 and 94. Also, bores 154a to 154c allowing insertion of screws 152a to 152c are formed in leading ends of the bus bars 80a to 80c toward the motor 16.
Therefore, the screws 152a to 152c are inserted into the bores 154a to 154c and threaded into threaded bores 156a to 156c formed in the connecting terminals 138a to 138c, respectively, thereby allowing fixation (connection) of the bus bars 80a to 80c to the connecting terminals 138a to 138c, respectively. Consequently, the rotor 16b and the motor shaft 16a can be driven to rotate by supplying three-phase alternating current to the motor 16 from the PDU 72 through the bus bars 80a to 80c and the connecting terminals 138a to 138c. 
On the other hand, the right arm 40r extends from the front end 42 to the right side (the other side) of the wheel 90 (see FIGS. 2 and 3). In other words, the arm 40r is composed of the above-described arm portion 42r, and the reduction mechanism case 48 coupled to a rear portion of the arm portion 42r. 
Also, the reduction mechanism case 48 is composed of a first storage portion 48a that is provided on the right side of the wheel 90 and formed with a recessed portion allowing the reception of a reduction mechanism 160; a second storage portion 48b that is coupled to the first storage portion 48a in the vehicle width direction in such a manner as to surround a side portion of the reduction mechanism 160; and a lid portion 48c (a seventh arm portion) that covers the second storage portion 48b in the vehicle width direction with the reduction mechanism 160 disposed in the first and second storage portions 48a and 48b (sixth arm portions), thereby closing the reduction mechanism 160 in cooperation with the first and second storage portions 48a and 48b. Therefore, the reduction mechanism 160 is disposed in the first and second storage portions 48a and 48b, and the second storage portion 48b is covered with the lid portion 48c to constitute the reduction mechanism case 48, so that the reduction mechanism module 50 including the reduction mechanism 160 and the reduction mechanism case 48 is formed.
In the arm 40r, the arm portion 42r, the first storage portion 48a, the second storage portion 48b, and the lid portion 48c are coupled to one another in the vehicle width direction.
More specifically, a plate-like portion 162 that is V-shaped in side view extends rearward from a rear end of the arm portion 42r. Also, arm portions 164a and 164b extend toward the plate-like portion 162 from the first storage portion 48a. Therefore, bolts 166a and 166b are inserted into two bores, not shown, of the plate-like portion 162 and threaded into threaded holes, not shown, of the arm portions 164a and 164b, respectively, thereby allowing coupling between the plate-like portion 162 (of the arm portion 42r) and the arm portions 164a and 164b (of the first storage portion 48a) in the vehicle width direction. Also, the first storage portion 48a, the second storage portion 48b, and the lid portion 48c can be sequentially coupled in the vehicle width direction by using bolts not shown or the like.
It should be noted that an arm portion 164c extends rearward on a rear portion of the first storage portion 48a. The rear suspension 54r is connected to a bore 168 formed in a leading end portion of the arm portion 164c. The rear suspension 54r is connected to the arm portion 164c forwardly with respect to the rear suspension 54l in a plan view of FIG. 3.
The reduction mechanism 160 is connected to the motor shaft 16a extending to the right side of the wheel 90. Also, the reduction mechanism 160 rotates the axle 52 at a rotational speed lower than that of the motor shaft 16a rotated by driving of the motor 16, thereby rotating the rear wheel WR including the wheel 90 connected to the axle 52.
Next, a more concrete explanation of the wheel 90, and the motor module 46 and the reduction mechanism module 50 respectively disposed on the left and right sides of the wheel 90, will be made with reference to a sectional view of FIG. 7.
The hollow cylindrical axle 52 passes substantially coaxially through the wheel 90 constituting the rear wheel WR serving as the wheel assembly. In this case, the outer and inner diameters of a left-hand portion of the axle 52 passing through the wheel 90 are smaller than those of a right-hand portion thereof connected to the reduction mechanism 160. Consequently, the axle 52 is formed as a cylindrical shaft having a shoulder. Also, a portion on an outer peripheral surface of the axle 52 which passes through the wheel 90 is subjected to spline processing to engage spline grooves of the wheel 90 (see FIGS. 3 and 7). Further, a thread groove (threaded portion), not shown, is formed at a left end (one end) of the axle 52 protruding slightly from the wheel 90. Therefore, with a washer 170 attached to the axle 52, a nut 172 is threaded onto the thread groove, thereby allowing coupling between the wheel 90 and the axle 52. It should be noted that the thread groove, the washer 170, and the nut 172 constitute a coupling portion 192 for coupling the wheel 90 and the axle 52.
The motor shaft 16a is substantially coaxially inserted into the axle 52 so as to extend on both sides from both ends of the axle 52. In this case, the motor shaft 16a is formed as a columnar shaft having a shoulder so as to conform to the shape of a hollow portion of the axle 52.
The motor shaft 16a passes through the rotor 16b of the motor 16. A thread groove, not shown, is formed at a left end of the motor shaft 16a protruding leftward from the rotor 16b. With a washer 174 attached to the motor shaft 16a, a nut 176 is threaded onto the thread groove, thereby allowing coupling between the motor shaft 16a and the rotor 16b. Also, a removable cap 180 is disposed at a central portion of the lid portion 44b, opposite to the left end of the motor shaft 16a. 
Also, on the side of the storage portion 44a toward the wheel 90, there are provided annular protruding portions 182 and 184 protruding toward the wheel 90 in such a manner as to surround the motor shaft 16a. On the side of the wheel 90 toward the storage portion 44a, there are provided, between the above-described protruding portions 182 and 184, annular protruding portions 186 and 188 protruding toward the storage portion 44a in such a manner so as to surround the motor shaft 16a. 
In this case, between the protruding portion 184 of the storage portion 44a and the protruding portion 188 of the wheel 90 is a labyrinth structure 190.
Also, a bearing 194 (a first bearing) is disposed between the protruding portions 182 and 186 provided inwardly with respect to the protruding portions 184 and 188. The motor case 44 (the motor module 46) is supported in a relatively rotatable manner with respect to the wheel 90 by the bearing 194. Consequently, the labyrinth structure 190 prevents stones, etc. scattered by the rear wheel WR during operation of the two-wheeled electric vehicle 10 from being directly splashed onto the bearing 194. It should be noted that a seal bearing is employed as the bearing 194 to seal a space toward the motor shaft 16a. 
Furthermore, a portion of the protruding portion 182 opposite the nut 172 is formed as a tapered portion 195 that is tapered so as to deviate from the nut 172 (so as to spread toward the nut 172).
Moreover, a portion of the motor shaft 16a which is in between the rotor 16b and the axle 52 is formed with a shoulder. A collar 196 is attached to the shoulder. Also, a bearing 198 is inserted between the rotor 16b, the collar 196, and the protruding portion 182. On the other hand, a bearing 200 is attached between the side of the rotor 16b toward the cap 180, and the lid portion 44b. The motor case 44 is supported in a relatively rotatable manner with respect to the motor shaft 16a and the rotor 16b by the bearings 198 and 200. It should be noted that the bearings 198 and 200 are also seal bearings.
On the other hand, the right end of the motor shall is supported through bearings 210 and 212 by the second storage portion 48b and the lid portion 48c. 
The reduction mechanism 160 is composed of a gear portion 216 (a first gear) formed at a portion of the motor shaft 16a which is in between the bearings 210 and 212; a reduction shaft 218 disposed forwardly with respect to the motor shaft 16a and the axle 52, and substantially parallel to the motor shaft 16a and the axle 52; a gear 220 (a second gear) disposed on the side of the reduction shaft 218 toward the lid portion 48c, and engaging with the gear portion 216; a gear portion 222 (a third gear) formed on the side of the reduction shaft 218 toward the wheel 90; and a gear 224 (a fourth gear) disposed on a right end of the axle 52 and engaging with the gear portion 222.
Also, within the reduction mechanism case 48, both ends of the reduction shaft 218 are supported through bearings 226 and 228 by the first storage portion 48a and the lid portion 48c. The gear 224 is fixed through a bearing 230 to the right end of the axle 52 and the second storage portion 48b. Further, the reduction mechanism 160 is injected with oil so as to prevent seizing up of the gear portions 216 and 222 and the gears 220 and 224. Therefore, oil seals 232 and 234 are inserted between the right end of the axle 52 and the motor shaft 16a, and between the side of the first storage portion 48a toward the wheel 90, and the axle 52, respectively.
An annular recessed portion 240 is formed at a portion of the wheel 90 opposite the first storage portion 48a. Also, an annular recessed portion 242 is formed opposite to the annular recessed portion 240 on the side of the first storage portion 48a toward the wheel 90. Thus, annular protruding portions 244 and 246 protruding toward the first storage portion 48a in a manner surrounding the axle 52 are formed on a right side surface of the wheel 90. Also, annular protruding portions 248 and 250 protruding toward the wheel 90 in a manner surrounding the axle 52 are formed on the side of the first storage portion 48a toward the wheel 90.
In this case, a labyrinth structure 252 is formed between the protruding portion 246 of the wheel 90 and the protruding portion 250 of the first storage portion 48a. The labyrinth structure 252 seals a space on the inside of the protruding portions 246 and 250 formed by the annular recessed portions 240 and 242.
Also, a bearing 254 (a second bearing) serving as a seal bearing is provided between the axle 52 and each of the protruding portions 244 and 248 formed inwardly with respect to the protruding portions 246 and 250, respectively. The reduction mechanism case 48 (the reduction mechanism module 50) is supported in a relatively rotatable manner with respect to the wheel 90 by the bearing 254.
Furthermore, a drum brake 260 is provided toward the annular recessed portion 240 in the sealed space formed by the labyrinth structure 252, in such a manner as to surround the axle 52.
The drum brake 260 is a well-known drum brake mechanism, and composed of a drum 262 attached to the wheel 90, a leading shoe 266 mounted with a lining 264, and a trailing shoe 270 mounted with a lining 268. In this case, a spring member, not shown, is inserted between the leading shoe 266 and the trailing shoe 270. When the leading shoe 266 and the trailing shoe 270 are longitudinally moved away from each other against the tension of the spring member by a hydraulic cylinder or the like, the lining 264 of the leading shoe 266 and the lining 268 of the trailing shoe 270 press against the drum 262, thereby enabling braking of rotation of the wheel 90 attached with the drum 262.
It should be noted that in this embodiment, a disc brake may of course be used in place of the drum brake 260 as long as it can brake the rotation of the wheel 90.
The two-wheeled electric vehicle 10 according to this embodiment is constructed as above. Next, mounting/removal of the rear wheel WR, the motor module 46, and the reduction mechanism module 50 to/from the two-wheeled electric vehicle 10, and replacement (both of mounting and removal) thereof will be described with reference to FIGS. 1 to 7.
First of all, mounting of the rear wheel WR, the motor module 46, and the reduction mechanism module 50 to the two-wheeled electric vehicle 10 will be described.
Firstly, the reduction mechanism module 50 with the motor shaft 16a and the axle 52 mounted is mounted to the two-wheeled electric vehicle 10. In this case, an operator couples the plate-like portion 162 and the arm portions 164a and 164b in the vehicle width direction by inserting the bolts 166a and 166b into the two holes of the plate-like portion 162 extending from the arm portion 42r of the swing arm 14, and threading the bolts 166a and 166b into the threaded holes, not shown, of the arm portions 164a and 164b provided on the reduction mechanism module 50. Also, the operator attaches the drum brake 260 to the axle 52 and then connects the rear suspension 54r to the bore 168 of the arm portion 164c. 
Next, the rear wheel WR serving as the wheel assembly is mounted to the axle 52.
In this case, the operator mounts the rear wheel WR to the axle 52 in such a manner that the spline structure formed on the left end of the axle 52 fits the spline grooves formed in the wheel 90. It should be noted that the bearing 194 is also previously attached to the wheel 90.
And then the operator tightens the nut 172 with a wrench with the rear wheel WR fixed.
Next, the operator mounts the motor module 46 to the motor shaft 16a. 
In this case, the operator attaches the collar 196 to the motor shaft 16a, and then mounts the motor module 46 to the motor shaft 16a in such a manner that the motor shaft 16a is inserted into the hollow portion (the central axis) of the rotor 16b. Then after the cap 180 is removed from the lid portion 44b and the washer 174 is attached to the motor shaft 16a, the nut 176 is threaded onto the thread groove of the motor shaft 16a so as to fix the motor shaft 16a and the rotor 16b. After fixing the motor shaft 16a and the rotor 16b, the operator mounts the cap 180 to the lid portion 44b and then mounts the rear suspension 54l to the bore 124c of the arm portion 102c. 
Next, the arm portions 42l, 92, and 94, and the motor case 44 are coupled in the vehicle width direction.
In this case, firstly, the bus bars 80a to 80c and the connecting terminals 138a to 138c are connected to each other. That is, the screws 152a to 152c are inserted into the bores 154a to 154c and threaded into the threaded bores 156a to 156c of the connecting terminals 138a to 138c, respectively, thereby connecting the bus bars 80a to 80c and the connecting terminals 138a to 138c. 
Next, the arm portion 92 and the arm portion 42l are coupled to each other in the vehicle width direction. Also, the arm portion 92 and the arm portions 102a and 102b are coupled to each other in the vehicle width direction.
In this case, the bolts 126a and 126b are inserted into the bores 122a and 122b of the plate-like portions 98a and 98b of the arm portion 92 and threaded into the threaded bores 124a and 124b of the arm portions 102a and 102b, thereby allowing coupling between the arm portion 92 and the arm portions 102a and 102b in the vehicle width direction. Also, the bolts 110a and 110b are inserted into the bores 108a and 108b of the plate-like portions 98a and 98b and threaded into the nuts 112a and 112b, respectively, thereby allowing coupling between the arm portion 42l and the arm portion 92 in the vehicle width direction.
Furthermore, with the bus bars 80a to 80c supported by the supporting member 150, the bolts 118a to 118c are inserted into the bores 114a to 114c and the bores 116a to 116c and threaded into the weld nuts 120a to 120c, respectively, thereby allowing coupling between the arm portion 92 and the arm portion 94 in the vehicle width direction. Also, the bus bars 80a to 80c can be supported within the hollow portion 140 without making contact with inner walls of the arm portions 92 and 94.
In the above-described manner, the rear wheel WR, the motor module 46, and the reduction mechanism module 50 can be mounted to the two-wheeled electric vehicle 10.
Next, as to removal of the rear wheel WR, the motor module 46, and the reduction mechanism module 50 from the two-wheeled electric vehicle 10, it can be performed by reversing the above-described mounting procedure.
In this embodiment, the left arm 40l of the swing arm 14 can be separated into the arm portions 42l, 92, 94, and the motor case 44. Also, in side view, the outer periphery or outside of the rear wheel WR is a separation point (a separation point between the arm portion 42l and the arm portion 92). Consequently, the motor module 46 and the rear wheel WR can be removed in one direction by releasing the coupling in the vehicle width direction of the arm portions 42l, 92, and 94. It should be noted that the concept of the outer periphery of the rear wheel WR is not limited to the outer periphery itself but includes the vicinity of the outer periphery (portions of a diameter slightly smaller or larger than the outside diameter of the rear wheel WR).
Also, replacement of the rear wheel WR, the motor module 46, and the reduction mechanism module 50 can be easily performed by adopting the above-described mounting and removal procedures.
As described above, in the two-wheeled electric vehicle 10 according to this embodiment, the motor 16 is disposed on the left side (one side) of the wheel 90, while the reduction mechanism 160 is disposed on the right side (the other side) of the wheel 90. In this case, the motor shaft 16a passes through the hollow portion of the axle 52 connected to the wheel 90 to extend from both ends of the axle 52. Also, the rotor 16b of the motor 16 is connected to the left end of the motor shaft 16a, while the reduction mechanism 160 is connected to the right end of the motor shaft. In this manner, the motor 16 is disposed on one side of the wheel 90, and on the other side of the wheel 90 is the reduction mechanism 160, thereby easily achieving a weight balance. In addition, the motor shaft 16a is inserted into the hollow portion of the axle 52 substantially coaxially with the axle 52. Thus, the shaft for rotating the wheel 90 has a double structure of the motor shaft 16a and the axle 52, thereby allowing an increase in stiffness of the shaft.
Also, the wheel 90, the axle 52, and the motor shaft 16a are substantially coaxially disposed. The motor 16 and the reduction mechanism 160 are each connected to the motor shaft 16a. Further, the reduction mechanism 160 is connected to the wheel 90 through the axle 52. Consequently, a drive system of the wheel 90, from the motor 16 to the wheel 90 through the motor shaft 16a, the reduction mechanism 160, and the axle 52, is disposed on the axis of the wheel 90. Thus, the drive system can be compactly disposed on the wheel 90 without protruding the drive system to the left or right side of the wheel 90. In addition, flexibility in the space around the wheel 90 is increased. Also, in the reduction mechanism 160, the torque of the wheel 90 can be easily increased in accordance with the rotational drive force of the motor 16.
In this manner, in this embodiment, the periphery of the wheel 90 is constructed as above, thereby allowing the realization of the two-wheeled electric vehicle 10 in which weight balance is easily achieved and the drive system, such as the motor 16, can be compactly disposed on the wheel 90.
Also, by achieving weight balance as described above, it is possible to support the wheel 90, the axle 52, and the motor shaft 16a on both sides through the motor module 46 including the motor 16 and the reduction mechanism module 50 including the reduction mechanism 160, without unnecessary reinforcement (increase in stiffness) or increase in weight of the double-sided swing arm 14.
Furthermore, the motor 16 is modularized as the motor module 46, and the reduction mechanism 160 is modularized as the reduction mechanism module 50, thereby facilitating the mounting/removal of the motor module 46 (the motor 16) and the reduction mechanism module 50 (the reduction mechanism 160) to/from the wheel 90 or the replacement thereof, and allowing prevention of dust contamination with the adhesion or deposition of foreign particles, such as dirt and dust, to the motor 16 or the reduction mechanism 160.
Moreover, the motor module 46 is relatively rotatably mounted to the wheel 90 through the bearing 198, and the reduction mechanism module 50 is relatively rotatably mounted to the wheel 90 through the bearing 254. Thus, mounting/removal of the motor module 46 and the reduction mechanism module 50 to/from the wheel 90 or replacement thereof can be further facilitated.
Also, the rear suspensions 54l and 54r are mounted to the motor module 46 and the reduction mechanism module 50, respectively. Thus, the shock due to uneven roads or the like is effectively absorbed, thereby allowing an improvement in the occupant ride quality of the two-wheeled electric vehicle 10.
Furthermore, the left end of the motor shaft 16a is fixed to the rotor 16b, and the right end of the motor shaft is supported by the bearings 210 and 212 provided on the reduction mechanism 160, thereby allowing an improvement in the operational efficiency of mounting/removal of the rotor 16b and the reduction mechanism 160 to/from the motor shaft 16a or replacement thereof.
Moreover, the reduction shaft 218, the gear 220, and the gear portion 222, which are major portions of the reduction mechanism 160, are provided in front of the axle 52 and the motor shaft 16a. Consequently, the center of gravity of the reduction mechanism 160 is located forward with respect to the axle 52 and the motor shaft 16a, so that the two-wheeled electric vehicle 10 having an excellent weight balance can be realized.
Also, the drum brake 260 is disposed on the right side of the wheel 90 in a state of passing through the axle 52 and the motor shaft 16a. This allows reliable braking of rotation of the wheel 90 while achieving weight balance.
Also, in the two-wheeled electric vehicle 10 according to this embodiment, the left side (the left arm 40l) of the swing arm 14 with respect to the wheel 90 is composed of the plurality of arm portions 42l, 92, and 94 and the motor case 44 which can be separated. Thus, the wheel 90 and the motor 16 can be removed or mounted in one direction just by removing the arm portions 92 and 94 from the two-wheeled electric vehicle 10, on the left side of the wheel 90. In other words, removal or mounting of the rear wheel WR (the wheel assembly) and the motor case 44 can be easily performed from the left side of the wheel 90 by removing the arm portions 92 and 94 from the two-wheeled electric vehicle 10. Thus, the operational efficiency of mounting and removal of the wheel 90 and the motor 16 can be improved. Further, since the motor case 44 is one element of the left arm 40l, it is possible to suppress an increase in the number of components.
In this manner, in this embodiment, the periphery of the wheel 90 is constructed as above, thereby allowing the realization of the two-wheeled electric vehicle 10 in which weight balance is easily achieved and the operational efficiency of mounting, removal, and replacement of the wheel 90 and the motor 16 can be improved.
Furthermore, the electric power supply line 80 is provided within the hollow portion 140 of the arm portions 92 and 94 connected to the motor case 44, thereby allowing proper protection of the electric power supply line 80 and enhancing the appearance in the portion of the two-wheeled electric vehicle 10 where the swing arm 14 is located. Also, even if the arm portions 92 and 94 are each made of a metal material, the supporting member 150 prevents contact between the inner walls of the arm portions 92 and 94 and the electric power supply line 80. Thus, shorts in the electric power supply line 80 can be reliably prevented.
Also, the connecting terminals 138a to 138c provided on the motor 16 and the bus bars 80a to 80c composing the electric power supply line 80 are connected to each other in front of the motor case 44. Thus, a connecting region between the motor 16 and the electric power supply line 80 can be protected. In this manner, the connecting terminals 138a to 138c serve as portions for fixing the bus bars 80a to 80c, thereby facilitating mounting of the bus bars 80a to 80c to the connecting terminals 138a to 138c. 
The arm portions 42l, 92, and 94 and the motor case 44 are coupled to one another in the vehicle width direction. Thus, an operator, while being on the left of the two-wheeled electric vehicle 10, can perform removal/mounting or replacement of the wheel 90 and the motor 16, thereby allowing an improvement in operational efficiency while reducing the operator's work burdens. Also, the arm portions 42l, 92, and 94 and the motor case 44 are coupled to one another in the vehicle width direction. Thus, it is only necessary to remove only the element of an operation object, so that the operational efficiency can be further improved. Also, the arm portions 92 and 94 are coupled to each other in the vehicle width direction, thereby allowing reliable formation of the hollow portion 140 for insertion of the electric power supply line 80.
Furthermore, the arm portions 42l, 92, and 94 and the motor case 44 are coupled to one another in the vehicle width direction by using the plurality of bolts 110a, 110b, 118a to 118c, 126a, 126b, 132a to 132d, the nuts 112a and 112b, and the weld nuts 120a to 120c. Thus, the operator can further efficiently perform the mounting/removal or replacement operation.
The right side (the right arm 40r) of the swing arm 14 with respect to the wheel 90 is also composed of the arm portion 42r and the reduction mechanism case 48 which can be separated. Therefore, removal/mounting of the reduction mechanism 160 from/to the two-wheeled electric vehicle 10 or replacement thereof can be performed on the right side of the wheel 90. Also in this case, the operational efficiency of mounting, removal, and replacement of the reduction mechanism 160 can be improved.
Also, the reduction mechanism case 48 is designed to serve as an element of the arm 40r, thereby allowing suppression of an increase in the number of components. Further, since the arm portion 42r and the reduction mechanism case 48 are coupled in the vehicle width direction by the bolts 166a and 166b, it is only necessary to remove only the reduction mechanism case 48, so that the operational efficiency can be improved.
Moreover, the bottom of the motor case 44 is formed substantially flat Thus, contact of the lower surface of the motor case 44 with the ground can be suppressed.
Furthermore, in the two-wheeled electric vehicle 10 according to this embodiment, as described above, the motor 16 is connected to the left end of the motor shaft 16a which is one end of the wheel 90, and on the other side thereof, the reduction mechanism 160 is connected to the right end of the motor shaft. Thus, weight balance is easily achieved. In addition, between the wheel 90 and the motor case 44, the left end of the axle 52 and the wheel 90 are coupled to each other by the coupling portion 192. Also, the labyrinth structure 190 seals the space in between the wheel 90 and the motor case 44 in a manner surrounding the coupling portion 192. Consequently, the coupling portion 192 is disposed in the sealed space sealed by the labyrinth structure 190. Thus, the coupling portion 192 can be protected from disturbance such as stones scattered by the rear wheel WR during travel of the two-wheeled electric vehicle 10 or access to the nut 172 by a person such as an occupant. Also, intrusion of mud, etc. from the outside can be avoided, thereby eliminating the need for forming the nut 172 with a coarse pitch to provide resistance to thread stripping. Therefore, the nut 172 can be formed with a fine pitch so that the tightening accuracy can be increased.
Also, the coupling portion 192 is composed of the threaded groove formed in the outer peripheral surface of the axle 52, the washer 170, and the nut 172 threaded onto the threaded groove. Thus, coupling between the axle 52 and the wheel 90 can be easily performed.
Also, the bearing 194 is inserted between the motor case 44 and the wheel 90, thereby allowing a further increase in stiffness of the drive system.
The portion (the tapered portion 195) of the motor case 44 opposite the coupling portion 192 is tapered so as to deviate from the nut 172. Thus, the motor case 44 (the motor 16 in the motor case 44) can be brought close to the wheel 90, so that the motor case 44 can be further compactly stored in the wheel 90.
Also, in the case of the nut 172 of the right-hand thread type, even if the nut 172 comes loose during the operation of the two-wheeled electric vehicle 10, the contact between the tapered portion and the nut 172 allows the nut 172 to be automatically tightened by the operation of the two-wheeled electric vehicle 10 because the rear wheel WR rotates in a direction to tighten the nut 172.
Also, the bearing 254 is inserted between the reduction mechanism case 48 and the wheel 90, thereby allowing a still further increase in stiffness of the drive system.
Further, the labyrinth structure 252 is formed between the reduction mechanism case 48 and the wheel 90 in a manner surrounding the bearing 254. Thus, intrusion of dust, etc. from the outside can be avoided. Also, the drum brake 260 is provided in the hollow portion between the labyrinth structure 252 and the bearing 254, thereby enabling efficient braking of rotation of the wheel 90 while eliminating external environmental influences.
Also, if the bearings 198 and 200 are inserted between the motor case 44 and the motor shaft 16a and all bearings 194, 198, 200, and 254 are seal bearings, intrusion of dust, etc. from the outside is effectively avoided, thereby allowing reliable protection of the coupling portion 192 or the drum brake 260 from disturbance, and easy and efficient sealing between the wheel 90 and each of the motor module 46 and the reduction mechanism module 50.
Also, the oil seal 232 is inserted between the right end of the axle 52 and the motor shaft 16a, thereby reducing the difference between the rotational speed of the motor shaft 16a and the rotational speed of the axle 52 reduced by the reduction mechanism 160 and allowing an increase in durability.
Next, modifications of this embodiment will be described with reference to FIGS. 8 to 13.
FIG. 8 illustrates a case where a hole portion 214 allowing insertion of a screw-driver or a hex wrench is formed in a right end of the motor shaft, and a cap 280 is attached to a portion of the lid portion 48c opposite the hole portion 214.
In this modification, at the time of tightening the nut 172 by an operator, the operator removes the cap 280 to insert the screw-driver or the hex wrench into the hole portion 214. On the other hand, the operator fixes the nut 172 with a wrench, and in this state, rotates the motor shaft 16a by using the screw-driver or the hex wrench. Then small rotational force of the motor shaft 16a generated by the screw-driver or the hex wrench is transmitted to the axle 52 through the gear portion 216, the gear 220, the reduction shaft 218, the gear portion 222, and the gear 224, thereby generating large tightening force in the coupling portion 192. Consequently, the nut 172 can be easily tightened against the wheel 90 with the large tightening force.
In this manner, in the modification of FIG. 8, the hole portion 214 is formed in the right end of the motor shaft. Thus, rotational force is transmitted to the axle 52 through the reduction mechanism 160 by rotating the hole portion 214 with a screw-driver or a hex wrench while fixing the nut 172. Consequently, large tightening force can be generated in the coupling portion 192 by small rotational force.
FIG. 9 illustrates a case where the cap 280 is attached to the lid portion 48c, while a bolt head 282 is provided on a right end of the motor shaft. Also in this case, rotational force is transmitted to the axle 52 through the reduction mechanism 160 by fixing the nut 172 with one wrench and, with the cap 280 removed, rotating the bolt head 282 with the other wrench. Thus, large tightening force can be generated in the coupling portion 192 by small rotational force. Consequently, the nut 172 can be easily tightened against the wheel 90 with the large tightening force.
FIG. 10 illustrates a case where a cap 284 is attached to the lid portion 48c, while a hole portion 286 allowing insertion of a screw-driver or a hex wrench is provided at a right end of the reduction shaft 218. Also in this case, a large tightening force, which, although not as large as those of the structures of FIGS. 8 and 9, is to some extent larger relative to small rotational force generated in the hole portion 286, can be generated in the coupling portion 192 by fixing the nut 172 with a wrench, and, with the cap 284 removed, inserting a screw-driver or a hex wrench into the hole portion 286 and rotating the reduction shaft 218. Consequently, the nut 172 can be tightened against the wheel 90.
FIG. 11 illustrates a case where the cap 284 is attached to the lid portion 48c, while a bolt head 288 is provided on a right end of the reduction shaft 218. Also in this case, a large tightening force, which is to some extent larger relative to small rotational force generated in the bolt head 288, can be generated in the coupling portion 192, in the same manner as the case of FIG. 10, by fixing the nut 172 with one wrench, and, with the cap 284 removed, rotating the bolt head 288 using the other wrench. Consequently, the nut 172 can be tightened against the wheel 90.
FIGS. 12 and 13 illustrate a case where four arm portions 290 extend forward from the first storage portion 48a; a plane rear end 292 is formed at a leading end of the plate-like portion 162, opposite to the arm portions 290; and a plurality of bolts 294 are inserted into bores, not shown, longitudinally formed in the rear end 292, and threaded into threaded holes, not shown, of the arm portions 290, thereby longitudinally coupling the plate-like portion 162 and the respective arm portions 290 with the four bolts 294. This coupling in the longitudinal direction in which the two-wheeled electric vehicle 10 travels allows the realization of coupling capable of resisting shear force (force applied in the longitudinal direction).
Although the present invention has been described by using the preferred embodiment, the technical scope of the present invention is not limited to the scope described in the foregoing embodiment. It is obvious to those skilled in the art that the foregoing embodiment may be variously altered or improved. It will be apparent from the description of the appended claims that a form obtained by altering or improving the embodiment can also be included in the technical scope of the present invention.

## Claims

1. An electric vehicle wherein an output of a motor is transmitted to an axle through a reduction mechanism in order to rotate a wheel, comprising:
a hollow cylindrical shaft forming the axle, said hollow cylindrical shaft passing substantially coaxially through the wheel in a manner extending from both sides of the wheel;
a motor shaft inserted into a hollow portion of the cylindrical shaft substantially coaxially with the cylindrical shaft in a manner extending from both ends of the cylindrical shaft;
said motor being connected to a base end of the motor shaft extending from one end of the cylindrical shaft;
said reduction mechanism being connected to a leading end of the motor shaft extending from the other end of the cylindrical shaft; and
a coupling portion for coupling between the one end of the cylindrical shaft and the wheel, and a sealing portion for sealing between the wheel and the motor in a manner surrounding the coupling portion, said coupling portion and said sealing portion being provided between the wheel and the motor,
wherein the coupling portion is composed of a threaded portion formed at the one end of the cylindrical shaft; and a nut threaded onto the threaded portion for coupling between the wheel and the cylindrical shaft.

2. The electric vehicle according to claim 1, and further comprising:
a motor case for storing the motor; and
a first bearing inserted between the motor case and the wheel in a manner surrounding the motor shaft, the cylindrical shaft, and the coupling portion, the first bearing relatively rotatably mounting the motor case to the wheel.

3. The electric vehicle according to claim 2, wherein a portion of the motor case opposite the coupling portion is tapered so as to deviate from the nut.

4. The electric vehicle according to claim 3, and further comprising:
a motor module composed of the motor and the motor case;
a reduction mechanism module composed of the reduction mechanism and a reduction mechanism case for storing the reduction mechanism; and
a second bearing inserted between the reduction mechanism case and the wheel in a manner surrounding the motor shaft and the cylindrical shaft, the second bearing relatively rotatably mounting the reduction mechanism case to the wheel.

5. The electric vehicle according to claim 4, and further comprising a third bearing inserted between the motor case and the motor shaft, the third bearing relatively rotatably supporting the motor case on the motor shaft, wherein sealing is applied to at least one of the first to third bearings.

6. The electric vehicle according to claim 3, wherein the sealing portion is a labyrinth structure formed between the motor case and the wheel in a manner surrounding the first bearing, and/or the sealed first bearing.

7. The electric vehicle according to claim 2, and further comprising:
a motor module composed of the motor and the motor case;
a reduction mechanism module composed of the reduction mechanism and a reduction mechanism case for storing the reduction mechanism; and
a second bearing inserted between the reduction mechanism case and the wheel in a manner surrounding the motor shaft and the cylindrical shaft, the second bearing relatively rotatably mounting the reduction mechanism case to the wheel.

8. The electric vehicle according to claim 7, wherein a labyrinth structure is formed between the reduction mechanism case and the wheel in a manner surrounding the second bearing.

9. The electric vehicle according to claim 8, and further comprising a brake for braking rotation of the wheel, wherein the brake is disposed in a hollow portion between the labyrinth structure provided between the reduction mechanism case and the wheel, and the second bearing.

10. The electric vehicle according to claim 7, and further comprising a third bearing inserted between the motor case and the motor shaft, the third bearing relatively rotatably supporting the motor case on the motor shaft, wherein sealing is applied to at least one of the first to third bearings.

11. The electric vehicle according to claim 2, wherein the sealing portion is a labyrinth structure formed between the motor case and the wheel in a manner surrounding the first bearing, and/or the sealed first bearing.

12. The electric vehicle according to claim 2, wherein a hole portion or a bolt head is provided at the leading end of the motor shaft, the hole portion allowing insertion of a screw-driver or a hex wrench.

13. The electric vehicle according to claim 2, wherein the reduction mechanism is provided with:
a first gear formed at the leading end of the motor shaft;
a second gear disposed forwardly of the motor shaft, the second gear engaging with the first gear;
a reduction shaft disposed forwardly of and substantially parallel to the cylindrical shaft and the motor shaft, and substantially coaxially connected to the second gear;
a third gear formed on the side of the reduction shaft toward the wheel; and
a fourth gear substantially coaxially connected to the cylindrical shaft on the other end of the cylindrical shaft, the fourth gear engaging with the third gear,
wherein a hole portion or a bolt head is provided at an end of the reduction shaft toward the second gear, the hole portion allowing insertion of a screw-driver or a hex wrench.

14. The electric vehicle according to claim 1, wherein a hole portion or a bolt head is provided at the leading end of the motor shaft, the hole portion allowing insertion of a screw-driver or a hex wrench.

15. The electric vehicle according to claim 1, wherein the reduction mechanism is provided with:
a first gear formed at the leading end of the motor shaft;
a second gear disposed forwardly of the motor shaft, the second gear engaging with the first gear;
a reduction shaft disposed forwardly of and substantially parallel to the cylindrical shaft and the motor shaft, and substantially coaxially connected to the second gear;
a third gear formed on the side of the reduction shaft toward the wheel; and
a fourth gear substantially coaxially connected to the cylindrical shaft on the other end of the cylindrical shaft, the fourth gear engaging with the third gear,
wherein a hole portion or a bolt head is provided at an end of the reduction shaft toward the second gear, the hole portion allowing insertion of a screw-driver or a hex wrench.

16. The electric vehicle according to claim 1, wherein a sealing member is inserted between the other end of the cylindrical shaft and the motor shaft.

17. The electric vehicle according to claim 1, and further comprising a double-sided swing arm for supporting the motor shaft, the cylindrical shaft, and the wheel by respectively supporting the motor and the reduction mechanism.

18. An output for an electric vehicle comprising:
an axle having a hollow cylindrical shaft, said hollow cylindrical shaft passing substantially coaxially through a wheel in a manner extending from both sides of the wheel;
a motor shaft inserted into a hollow portion of the cylindrical shaft substantially coaxially with the cylindrical shaft in a manner extending from a first end and a second end of the cylindrical shaft;
a motor being connected to a base end of the motor shaft extending from the first end of the cylindrical shaft;
a reduction mechanism operatively connected to rotate the wheel, said reduction mechanism being connected to a leading end of the motor shaft extending from the second end of the cylindrical shaft; and
a coupling portion for coupling between the first end of the cylindrical shaft and the wheel, and a sealing portion for sealing between the wheel and the motor in a manner surrounding the coupling portion,
wherein the coupling portion is composed of a threaded portion formed at the one end of the cylindrical shaft; and a nut threaded onto the threaded portion for coupling between the wheel and the cylindrical shaft.