JP2013129338A - Power unit for saddle riding type electric vehicle and saddle riding type electric vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power unit for saddle riding type electric vehicle which is excellent in cooling performance of a controller and a stator and, moreover, has a high flexibility for arranging members.SOLUTION: The power unit 40 for saddle riding type electric vehicle includes: an electric motor 5 which has a rotor 52 and the stator 51; a transmission mechanism 60; a controller 70; and a case 41 for housing them, wherein the case 41 includes a case body 42 disposed on the lateral side of a rear wheel 4 in one direction of the axis direction of an axle 4a and a cover 43 disposed on the lateral side of the case body 42, the case body 42 and the cover 43 are joined to form a housing chamber S2 which houses at least one side of the stator 51 or the controller 70 and is filled with a gas, and heat transfer facilitation parts 48, 49 for facilitating the transfer of heat from a joint part 45 of the case body 42 close to the rear wheel 4 to a joint part 46 of the cover 43 away from the rear wheel are disposed.

Description

  The present invention relates to a power unit for a straddle-type electric vehicle and a straddle-type electric vehicle.

In recent years, straddle-type electric vehicles such as electric motorcycles using an electric motor as a power source have been developed.
In such a straddle-type electric vehicle, an electric motor and a controller that controls the electric motor are housed inside the power unit, and a cable extending from the electric motor and the controller is led out of the power unit. This power unit is assembled by attaching a cover to the case body.

  When assembling the power unit, the electric motor and the controller are preferably attached to the case body. This is because, when these are attached to the cover, an extra length is required for the cable by the moving distance when the cover is attached to the case main body, compared to the case of attaching to the case main body.

  Incidentally, since a large current flows through the controller and the stator of the electric motor during operation, the amount of heat generated is large. For this reason, these members need to be cooled. Therefore, the electric motorcycle described in Patent Document 1 is arranged with the controller facing the side surface of the rear wheel, and the controller is cooled by the air flow generated by the rear wheel.

JP 2004-352208 A

By the way, in an electric motorcycle, a seat on which a passenger sits is provided in front of the rear wheel. Therefore, the airflow flowing from the front during traveling of the electric motorcycle is blocked by the seat and the members constituting the seat. Therefore, fresh air is not supplied around the rear wheels. Therefore, in the electric motorcycle of Patent Document 1 in which the controller is disposed so as to face the rear wheel, there is room for improvement in the cooling performance of the controller.
Further, since the area facing the rear wheel is a limited area, the position where the controller is arranged is limited. For this reason, in the electric motorcycle described in Patent Document 1, even if it is attempted to change the position of the electric motor, the speed reducer, etc. in order to improve the cooling performance and the riding comfort, the arrangement position is limited.

  Accordingly, an object of the present invention is to provide a power unit of a straddle-type electric vehicle having excellent cooling performance of a controller and a stator and having a high degree of freedom in arranging members, and a straddle-type electric vehicle including the same. .

To achieve the above object, the power unit of the saddle-ride type electric vehicle of the present invention is
An electric motor having a rotor and a stator, and receiving the supply of electric power to rotate the output shaft;
A transmission mechanism for transmitting the driving force of the output shaft of the electric motor to an axle to which a rear wheel is attached;
A controller for controlling the supply of electric power to the electric motor;
A case housing the electric motor, the transmission mechanism, and the controller;
The case is
In one direction of the axial direction of the axle, including a case body provided on the side of the rear wheel, and a cover provided on the side of the case body,
The case body and the cover are joined to form a storage chamber filled with gas for storing at least one of the stator or the controller,
There is provided a heat transfer promoting portion that promotes heat transfer from the joint portion of the case body close to the rear wheel to the joint portion of the cover that is separated from the rear wheel.

According to the power unit of the saddle-ride type electric vehicle according to the present invention, the heat transfer promotion unit that promotes heat transfer transmits the heat transmitted from the stator or the controller to the case body to the cover side having high cooling performance. For this reason, the power unit of the saddle riding type electric vehicle excellent in cooling performance can be provided.
Further, since cooling is performed by a cover that is always in contact with fresh air, there is no need to provide a special mechanism in the power unit, and the position of the controller and the stator is not restricted. Therefore, it is possible to provide a power unit for a straddle-type electric vehicle having a high degree of freedom in arranging members, such as arranging members with priority on ride comfort.

In the power unit of the saddle riding type electric vehicle according to the present invention,
The case body and the cover are joined by a plurality of fastening members,
The heat transfer promoting part may be an enlarged part having a larger area than a surrounding part between the plurality of fastening means on the surface where the case main body and the cover are joined.

  According to the power unit of the saddle riding type electric vehicle according to the present invention, heat transfer is promoted by the enlarged portion having an area larger than that of the surrounding portion of the joint surfaces joined by the fastening member. In this way, a power unit for a straddle-type electric vehicle having a simple configuration and excellent cooling performance can be provided. Moreover, since a special member is not provided inside the power unit as the heat transfer promoting portion, the degree of freedom of arrangement of the stator and the controller can be further increased.

In the power unit of the saddle riding type electric vehicle according to the present invention,
The heat transfer promoting part may be a seal member that is provided between the joint part of the case body and the joint part of the cover and has excellent heat transfer characteristics for sealing the storage chamber.

  According to the power unit of the saddle riding type electric vehicle according to the present invention, the seal member excellent in heat transfer characteristics that does not hinder heat transfer is employed. In this way, a power unit for a straddle-type electric vehicle having a simple configuration and excellent cooling performance can be provided. Moreover, since a special member is not provided inside the power unit as the heat transfer promoting portion, the degree of freedom of arrangement of the stator and the controller can be further increased.

In the power unit of the saddle riding type electric vehicle according to the present invention,
The heat transfer promoting part is a seal member excellent in heat transfer characteristics,
The sealing member may be configured to be provided in the enlarged portion and seal around the fastening member.

  According to the power unit of the saddle riding type electric vehicle according to the present invention, the enlarged portion is firmly joined by the fastening member, and the seal member is strongly pressed against the enlarged portion, so that the heat from the case body to the cover can be further increased. Communication is facilitated.

In the power unit of the saddle riding type electric vehicle according to the present invention,
The sealing member having excellent heat transfer characteristics may include at least one of a liquid gasket, a metal gasket, and a paper or resin gasket containing a large amount of carbon fiber.

In the power unit of the saddle riding type electric vehicle according to the present invention,
The metal gasket may be coated with expanded graphite.

According to the power unit of the saddle riding type electric vehicle according to the present invention,
Heat-transfer from the case body to the cover is further promoted by coating expanded graphite having excellent heat transfer characteristics on a highly rigid and highly durable metal gasket.

  In order to achieve the above object, a straddle-type electric vehicle according to the present invention includes the power unit described above.

  According to the straddle-type electric vehicle according to the present invention, it is possible to provide a straddle-type electric vehicle that is excellent in cooling performance of the controller and the stator and that has a high degree of freedom in arranging the members.

1 is a left side view of an electric motorcycle according to a first embodiment of the present invention. FIG. 3 is a left side view of a state where some parts such as a body cover of the electric motorcycle are removed. Fig. 3 is a right side view of a rear portion of the electric motorcycle. It is a partial sectional view of a power unit and a rear wheel, and shows the state which looked at the power unit and the rear wheel from the upper part. It is a side view of a power unit shown in the state where a cover was opened. It is sectional drawing of the power unit in the surface containing a controller. It is a figure similar to FIG. 6 of the power unit which concerns on the modification of this invention.

The first embodiment of the present invention will be specifically described below with reference to the drawings.
FIG. 1 is a left side view of an electric motorcycle 1 which is a straddle-type electric vehicle according to a first embodiment of the present invention. In this embodiment, an electric motorcycle 1 including a scooter will be described as an example of a saddle riding type electric vehicle. The electric motorcycle 1 can travel with a load placed on the front part and the rear part, and is suitable for use as a cargo handling vehicle.

  In the following description, the front, rear, top and bottom, and left and right directions are in a reference posture corresponding to a state in which the electric motorcycle 1 is traveling straight on a horizontal plane, and the driver when the driver is facing forward. Based on this viewpoint. In addition, the configuration of the electric motorcycle 1 will be described with reference to the electric motorcycle 1 that stands upright, the front wheels 3 and the rear wheels 4 are in contact with the road surface A1, and the driver is not on the vehicle.

  The electric motorcycle 1 includes a body frame 2, a front wheel 3, a rear wheel 4, an electric motor 5, a battery 6, and a vehicle body cover 7. The electric motor 5 is driven by the electric power supplied from the battery 6. The rear wheel 4 is driven by the output of the electric motor 5. Hereinafter, the entire structure of the electric motorcycle 1 will be described in order from the front of the vehicle body.

FIG. 2 is a left side view of the electric motorcycle 1 with some parts such as the body cover 7 removed.
The electric motorcycle 1 has a head pipe 8 disposed at the front upper portion of the electric motorcycle 1. A steering shaft 9 is rotatably inserted into the head pipe 8. A pair of left and right front forks 10 are attached to the lower end of the steering shaft 9. The front wheel 3 is attached to the front fork 10.

A handle 11 is attached to the upper end portion of the steering shaft 9. The driver can turn the steering shaft 9, the front fork 10 and the front wheel 3 around the axis of the steering shaft 9 by operating the handle 11.
A grip 12 is provided at each of the left and right ends of the handle 11 (only the left grip is shown). The right grip constitutes the throttle grip. The driver can adjust the output of the electric motor 5 by turning the throttle grip.

  As shown in FIG. 1, a meter 13 is provided near the center of the handle 11. A loading platform 14 is disposed below the meter 13. The loading platform 14 is fixed to the head pipe 8. The load of the load loaded on the loading platform 14 mainly acts on the front wheel 3 via the head pipe 8 and the steering shaft 9. A headlamp 15 is fixed to the bottom of the loading platform 14.

  As shown in FIG. 2, the electric motorcycle 1 includes a vehicle body frame 2 that extends rearward from the head pipe 8. The body frame 2 is formed using a steel pipe member or the like. The vehicle body frame 2 includes a down tube 19 and a frame main body 20 disposed behind the down tube 19. The down tube 19 extends obliquely downward and rearward from the lower portion of the head pipe 8. In the side view, the frame body 20 extends rearward from the lower end portion of the down tube 19, and an intermediate portion of the vehicle in the front-rear direction X <b> 1 is formed in an S shape.

  A pair of frame main bodies 20 are provided on the left and right with respect to a center line extending in the front-rear direction. The frame body 20 includes a first frame portion 21, a second frame portion 22, a third frame portion 23, and a fourth frame portion 24. The first frame portion 21 extends substantially straight rearward from the lower end portion of the down tube 19 in a side view, and is slightly inclined rearward and upward.

  The second frame portion 22 is formed in an S shape in a side view. The second frame portion 22 includes a lower end portion 22a, an intermediate portion 22b, and an upper end portion 22c. The lower end portion 22 a of the second frame portion 22 is formed in a curved shape and is connected to the rear end portion of the first frame portion 21. The intermediate part 22b of the second frame part 22 extends straight from the lower end part 22a obliquely rearward and upward. In side view, the inclination angle of the intermediate portion 22b with respect to the first frame portion 21 is, for example, about 45 degrees. The upper end portion 22c of the second frame portion 22 is formed in a curved shape and is connected to the intermediate portion 22b.

  The third frame portion 23 extends linearly from the upper end portion 22c, and is slightly inclined rearward and upward. The fourth frame portion 24 extends rearward from the intermediate portion 22 b of the second frame portion 22, is bent obliquely rearward and upward in the middle, and is connected to the intermediate portion of the third frame portion 23.

  As shown in FIG. 1, the electric motorcycle 1 includes a vehicle body cover 7 attached to the vehicle body frame 2. The vehicle body cover 7 includes a front cover 25 that covers the head pipe 8, a lower cover 26 that extends rearward from the lower portion of the front cover 25, and a rear cover 27 that is disposed behind the front cover 25.

  The front cover 25 surrounds a part of the steering shaft 9 and the head pipe 8, and surrounds the down tube 19. The lower cover 26 extends rearward from the lower portion 25a of the front cover 25, and covers the first frame portion 21 and the lower end portion 22a of the second frame portion 22 from the lower side and the left and right sides. A footrest 28 is disposed at the upper end of the lower cover 26. The footrest portion 28 is provided for the driver to place his / her feet, and is formed substantially flat.

  The rear cover 27 as a whole is formed in a shape extending obliquely upward and rearward from the rear portion 26a of the lower cover 26. The rear cover 27 covers the area of the second frame portion 22 excluding the lower end portion 22a from the front and both left and right sides. The rear cover 27 covers the third frame portion 23 and the fourth frame portion 24 from both the front and left and right sides.

  A seat 29 is disposed above the rear cover 27. While the electric motorcycle 1 is traveling, the feet of the driver sitting on the seat 29 are placed on the footrest portion 28. In the front-rear direction X1, the footrest portion 28 is disposed between the rear surface 25b of the front cover 25 and the front end portion 29a of the seat 29. The seat 29 is disposed above the second frame portion 22, disposed above a portion of the third frame portion 23, and disposed above a portion of the fourth frame portion 24. . A space surrounded by the seat 29 and the rear cover 27 defines an accommodation space S1.

  As shown in FIG. 2, a battery 6 as a power source for the electric motor 5 is disposed in the accommodation space S <b> 1 below the seat 29. The battery 6 is disposed between the pair of left and right second frame portions 22. The battery 6 is a rechargeable secondary battery. The battery 6 is formed in a substantially rectangular shape in a side view, and the length (height) in the vertical direction Z1 of the vehicle is longer than the length (width) in the front-rear direction X1. The battery 6 is disposed in a posture inclined rearward and obliquely upward, and is supported by the vehicle body frame 2. The upper part 6 a of the battery 6 is disposed between the first bracket 31 and the support bracket 37.

  FIG. 3 is a right side view of the rear portion of the electric motorcycle 1. The electric motorcycle 1 includes a power unit 40 that is pivotally supported on the vehicle body frame 2 by a pivot shaft 51. The power unit 40 is disposed below the third frame portion 23 and to the right of the rear wheel 4 in a side view. The rear portion 47 b of the power unit 40 is connected to the third frame portion 23 via the shock absorber 32. Thereby, the shock when the power unit 40 swings is attenuated and absorbed by the shock absorber 32. The power unit 40 has a length in the front-rear direction X1 that is greater than a length in the up-down direction Z1 in a side view.

  FIG. 4 is a partial cross-sectional view of the power unit 40 and the rear wheel 4 and shows a state in which the power unit 40 and the rear wheel 4 are viewed from above. As shown in FIG. 4, the electric motorcycle according to the present embodiment is provided with a power unit 40 on the right side of the rear wheel 4. The power unit 40 accommodates the transmission mechanism 60, the electric motor 5, and the controller 70 therein.

  The controller 70 is electrically connected to the battery 6 via the harness 71. The controller 70 is electrically connected to the electric motor 5 through the power supply line 72. An aluminum substrate 73 (see FIG. 6) and a resin case 74 covering the aluminum substrate 73 are provided. On the aluminum substrate 73, a driver circuit such as an inverter circuit and a control circuit 75 (see FIG. 6) are fixed. The inverter circuit converts DC power from the battery 6 (see FIG. 2) into AC power and supplies it to the electric motor 5.

  The control circuit 75 includes a CPU, a RAM, and a ROM, and controls the inverter circuit so that an output corresponding to the amount of throttle operation by the driver is generated in the electric motor 5. A power semiconductor element that generates a large amount of heat and constitutes an inverter circuit or the like is directly attached to the aluminum substrate 73. Thereby, heat from the power semiconductor element is efficiently transferred to the aluminum substrate 73.

  The electric motor 5 includes a stator 51 that is fixed to the power unit 40 and electrically connected to the controller 70, and a rotor 52 that is rotatably supported by the power unit 40 and has a rotor shaft 53. The electric motor 5 is rotated by the controller 70 and drives the rear wheel 4.

  The transmission mechanism 60 includes an input shaft 61 integral with the rotor shaft 53 of the rotor 52, an output shaft 62 integral with the axle 4a of the rear wheel 4, an intermediate shaft 63, and a gear case 64 that rotatably accommodates these. I have. A gear is fixed to the outer periphery of each of the input shaft 61, the output shaft 62 and the intermediate shaft 63. The gear of the input shaft 61 meshes with the gear of the intermediate shaft 63, and the gear of the intermediate shaft 63 meshes with the gear of the output shaft 62.

  Thereby, the rotational force input to the input shaft 61 is transmitted to the output shaft 62 via the intermediate shaft 63. Thereby, when the rotor 52 is rotationally driven by the electric power supplied from the battery 6, the rear wheel 4 is driven via the transmission mechanism 60.

  The power unit 40 accommodates the transmission mechanism 60, the electric motor 5, and the controller 70 inside the case 41. A case main body 42 extending in the front-rear direction, a cover 43 disposed on the right side of the case main body 42, and a support portion 44 provided on the left side of the case main body 42 on the front side of the rear wheel 4 are provided.

  The case main body 42 is opened on the right side, and the cover 43 is joined to the case main body 42 so as to cover the opening, whereby the housing chamber S2 formed between the case main body 42 and the cover 43 is sealed. . This accommodation room S2 is filled with air.

  The case body 42 includes a bottom wall 42a extending in the front-rear direction on the rear wheel 4 side, and a side wall 42b protruding from the bottom wall 42a to the cover 43 side. The main body side joining surface 45 in contact with the cover 43 of the side wall 42b and the cover side joining surface 46 in contact with the case main body 42 of the cover 43 are formed on a flat surface so as to be in surface contact with each other.

  Further, the controller 70 and the stator 51 of the electric motor 5 are fixed to the bottom wall 42a of the case main body 42 by screws 80 as fastening members. In addition, the area | region which contacts the controller 70 of the bottom wall 42a is made into the flat surface, and is in surface contact with the controller 70. FIG. Thereby, the heat generated by the controller 70 is easily transmitted to the bottom wall 42a.

  Thus, in the present embodiment, the controller 70 and the stator 51 are not attached to the cover 43 but are attached to the bottom wall 42a exposed from the opening of the case main body 42. For this reason, when removing the cover 43, the extra length of the harness 71 required for making the cover 43 follow the controller 70 and the stator 51 is not required, and the assembly is easy.

  FIG. 5 is a side view of the power unit 40 shown with the cover 43 opened. As shown in FIG. 5, a screw hole 47 is provided in the side wall 42 b of the case body 42. A screw 81 (see FIG. 4) for screwing the cover 43 to the case main body 42 is inserted into the screw hole 47.

  Further, in the side wall 42b, the screw hole forming portion 48 provided with the screw hole 47 is an enlarged portion having a larger area than the surrounding portion on the surface shown in FIG. Further, in the side wall 42b, the controller covering portion 49 near the controller 70 is an enlarged portion having a larger area than the side wall 42b in other regions.

  FIG. 6 is a cross-sectional view of the power unit 40 in a plane including the controller 70. The cover 43 is fixed to the case main body 42 by screwing a screw 81 into the screw hole 47 in a state where the cover side joint surface 46 is aligned with the main body side joint surface 45. A plurality of heat radiating ribs 43a are provided on the surface of the cover 43 opposite to the case main body 42 along the front-rear direction.

  In the power unit 40 configured as described above, since the surface of the cover 43 is always in contact with fresh outside air, the cooling performance is high. Further, the heat generated by the controller 70 is transmitted from the flat surface to the bottom wall 42a, and is transmitted from the bottom wall 42a to the side wall 42b to the cover 43 side. At this time, the controller cover part 49 is formed thicker than the other side wall 42 b, and serves as a heat transfer promoting part that promotes heat transfer from the case body 42 to the cover 43.

  Further, heat generated in the stator 51 is also transmitted to the bottom wall 42a, and is transmitted to the cover 43 through the side wall 42b. At this time, the screw hole forming portion 48 is formed thicker than the other region of the side wall 42 b, and serves as a heat transfer promoting portion that promotes heat transfer from the case main body 42 to the cover 43.

  As described above, according to the power unit 40 according to the present embodiment, the cooling performance away from the rear wheel 4 from the main body side joining surface 45 of the case main body 42 on the rear wheel 4 side by the controller covering portion 49 and the screw hole forming portion 48. The heat transfer to the cover side joint surface 46 of the cover 43 having a high height is promoted. For this reason, the power unit 40 of the electric motorcycle excellent in cooling performance can be provided.

  Further, the power unit 40 according to the present embodiment is configured so as to release heat to the cover 43 that originally has high cooling efficiency by using a part of the side wall 42b, such as the controller cover portion 49 and the screw hole forming portion 48. Yes. For this reason, a mechanism such as a special cooling fin for cooling is not required in the power unit 40, and it is not necessary to arrange the controller 70 and the stator 51 in a specific place, so that the degree of freedom of arranging the members is high. A power unit 40 for an electric motorcycle can be provided. Therefore, for example, the arrangement positions of the controller 70 and the electric motor 5 can be designed with priority given to the ride comfort of the vehicle, and an electric motorcycle excellent in ride comfort and cooling performance can be provided.

  Further, the power unit 40 according to the present embodiment promotes the transfer of heat from the case main body 42 to the cover 43 by the screw hole forming part 48 and the controller cover part 49 that are in contact with the cover side joint surface 46 in a larger area than the surrounding area. doing. By promoting the heat transfer with such a simple configuration, the power unit 40 of the electric motorcycle having a higher degree of freedom in arranging members can be provided without providing a mechanism for promoting heat transfer inside the power unit 40. Can be provided.

  In the above-described embodiment, an example in which the cover 43 is attached to the case main body 42 via the screw 81 has been described. However, the present invention is not limited to this. For example, the cover 43 may be joined to the case body 42 by bolts and nuts, rivets, or the like.

  Further, in the above-described embodiment, the controller cover portion 49 and the screw hole forming portion 48 in which a part of the side wall 42b is thick has been described as an example of promoting heat transfer to the cover 43. It is not limited to these.

  For example, a sealing member that seals the storage chamber S <b> 2 between the main body side joining surface 45 and the cover side joining surface 46 may be a sealing member having excellent heat transfer characteristics. As a sealing member having excellent heat transfer characteristics, a liquid gasket, a metal gasket, or a paper or resin gasket containing a large amount of carbon fiber can be employed. Among these, a metal gasket is particularly preferable. Of the metal gaskets, a metal gasket made of copper or iron is preferably coated with expanded graphite.

  The sealing member may be disposed between the body-side joining surface 45 of the case body 42 and the cover-side joining surface 46 of the cover 43 so as to surround the screw hole 47 of the screw hole forming portion 48.

  In this way, heat transfer from the case main body 42 to the cover 43 may be promoted by a seal member having excellent heat transfer characteristics provided between the main body side bonding surface 45 and the cover side bonding surface 46.

  In addition, a water channel connected to an external radiator may be formed between the main body side bonding surface 45 and the cover side bonding surface 46, and heat transfer from the case main body 42 to the cover 43 may be promoted by the water channel.

  In the above-described embodiment, the power unit 40 has been described with an example including the controller cover portion 49 and the screw hole forming portion 48 that promote the transfer of heat generated in the controller 70 and the stator 51 to the cover 43. In addition, the controller 70 or the stator 51 may be configured so as to promote the transfer of heat generated to the cover 43.

  In the above-described embodiment, in order to improve the cooling efficiency of the cover 43, the example in which the heat radiating rib is provided on the cover 43 has been described. However, the present invention is not limited to this. For example, as shown in FIG. 7, the size of the cover 43 </ b> A itself may be made larger than that sufficient to accommodate the controller 70 and the electric motor 5, and the surface area of the cover 43 </ b> A may be increased. Also by this, the cooling efficiency of the cover 43A can be improved.

  In the above-described embodiment, the example in which the power unit 40 is disposed on the right side of the rear wheel 4 has been described. However, the power unit 40 may be disposed on the left side of the rear wheel 4.

  In the above embodiment, the present invention is applied to an electric motorcycle. However, the present invention may be applied to other than an electric motorcycle such as an electric tricycle as long as it is a saddle type vehicle.

  In addition, various design changes can be made within the scope of matters described in the claims.

4: Rear wheel, 4a: Axle, 40: Power unit, 41: Case, 42: Case main body, 42a: Bottom wall, 42b: Side wall, 43: Cover, 44: Support part, 45: Main body side joint surface (joint part) 46: cover side joint surface (joint part), 47: screw hole, 48: screw hole forming part (enlarged part), 49: controller cover part (enlarged part), S2: housing chamber, 5: electric motor, 51: Stator, 52: rotor, 53: rotor shaft, 60: transmission mechanism, 61: input shaft, 62: output shaft, 63: intermediate shaft, 64: gear case, 70: controller, 71: harness, 72: feeder line, 73: Aluminum substrate, 74: resin case, 75: control circuit, 80: screw (fastening member)

Claims (7)

An electric motor having a rotor and a stator, and receiving the supply of electric power to rotate the output shaft;
A transmission mechanism for transmitting the driving force of the output shaft of the electric motor to an axle to which a rear wheel is attached;
A controller for controlling the supply of electric power to the electric motor;
A case housing the electric motor, the transmission mechanism, and the controller;
The case is
In one direction of the axial direction of the axle, including a case body provided on the side of the rear wheel, and a cover provided on the side of the case body,
The case body and the cover are joined to form a storage chamber filled with gas for storing at least one of the stator or the controller,
A power unit for a straddle-type electric vehicle, comprising: a heat transfer promoting portion that promotes heat transfer from a joint portion of the case body near the rear wheel to a joint portion of the cover that is separated from the rear wheel. The case body and the cover are joined by a plurality of fastening members,
2. The straddle-type electric motor according to claim 1, wherein the heat transfer promoting part includes an enlarged part having a larger area than a surrounding part between the plurality of fastening means on a surface where the case main body and the cover are joined. Vehicle power unit.   2. The saddle riding according to claim 1, wherein the heat transfer promoting portion includes a seal member that is provided between the joint portion of the case body and the joint portion of the cover and has excellent heat transfer characteristics for sealing the housing chamber. Type electric vehicle power unit. The heat transfer promoting part includes a seal member having excellent heat transfer characteristics,
The power unit of a straddle-type electric vehicle according to claim 2, wherein the seal member is provided in the enlarged portion and seals around the fastening member.   The power unit of a straddle-type electric vehicle according to claim 3 or 4, wherein the sealing member having excellent heat transfer characteristics includes at least one of a liquid gasket, a metal gasket, and a paper or resin gasket containing a large amount of carbon fiber. .   The power unit of a straddle-type electric vehicle according to claim 5, wherein the metal gasket is coated with expanded graphite.   A straddle-type electric vehicle comprising the power unit according to any one of claims 1 to 6.

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