Motor unit for use in electric bicycles, and electric bicycle

A motor unit for use in electric bicycles, the motor unit comprising: a motor having a rotary shaft; a unit case to house the rotary shaft partially; an input shaft arranged in the unit case to penetrate through the unit case and to be rotatable around an axis; an input body configured to rotate along with the input shaft; an output body configured to rotate around the axis upon receiving rotational force of the input body; and a control board housed in the unit case and configured to control rotation of the motor. The unit case includes: a first heat dissipating portion connected to a first surface of the control board; and a second heat dissipating portion connected to a second surface opposite from the first surface of the control board.

TECHNICAL FIELD

The present disclosure generally relates to a motor unit for use in electric bicycles and also relates to an electric bicycle.

BACKGROUND ART

Patent Literature 1 discloses an electric bicycle including a motor unit (i.e., an electric assist bicycle). In that motor unit, a motor is housed in a unit case that forms its shell. The unit case includes a motor case to house the motor. This motor case is resin-molded along with a stator of the motor by a molding technique.

The motor unit known from Patent Literature 1 described above still has room for improvement in terms of its capability of dissipating the heat generated when the motor is activated.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

It is therefore an object of the present disclosure to provide a motor unit with improved heat dissipation capability for electric bicycles and also provide an electric bicycle including such a motor unit.

A motor unit according to one aspect of the present disclosure is designed to be used in electric bicycles. The motor unit includes a motor and a unit case to which the motor is fitted. The motor includes: a stator; a rotor arranged to be surrounded with the stator; a rotary shaft fixed to the rotor; and a metallic cup having an opening and configured to house the stator and the rotor at least partially. An inner peripheral surface of the metallic cup is in pressure contact with the stator.

An electric bicycle according to another aspect of the present disclosure includes the motor unit according to the one aspect; and at least one wheel to which rotational force is transmitted from the motor of the motor unit.

DESCRIPTION OF EMBODIMENTS

Exemplary Embodiment

An electric bicycle1according to an exemplary embodiment is implemented as an electric assist bicycle. An electric bicycle1according to the exemplary embodiment includes: a frame10; a motor unit3used for electric bicycles (hereinafter simply referred to as a “motor unit3”) which is mounted on the frame10; and two wheels11which are rotatably coupled to the frame10. The two wheels11are a front wheel111and a rear wheel112. The rear wheel112is driven in rotation by the driving force supplied from the motor unit3.

Note that in the following description, the respective directions, including the forward/backward directions and the rightward/leftward directions, are herein defined with respect to the rider of the electric bicycle1. Specifically, the direction in which the rider who is riding the electric bicycle1travels by pedaling the electric bicycle1is the forward direction, and the opposite direction thereof is the backward direction. The direction pointing to the left when viewed from the rider is the leftward direction, and the direction pointing to the right when viewed from him or her is the rightward direction. The respective constituent elements thereof will be described in detail.

As shown inFIG.1, the frame10includes a head tube101, a top tube102, a down tube103, a seat tube104, seat stays105, chain stays106, and a bracket2.

The frame10(i.e., the respective parts that form the frame10) is typically made of a metal such as aluminum or stainless steel, which may contain a non-metallic material as well. Alternatively, the entire frame10may also be made of a non-metallic material. Thus, the frame10may be made of any material without limitation.

A handlebar stem12is inserted rotatably into the head tube101. At the bottom of the handlebar stem12, provided are forks121, on which the front wheel111is mounted rotatably. To the top of the handlebar stem12, fixed are handlebars122.

A front end portion of the top tube102is fixed to the head tube101. A rear end portion of the top tube102is fixed onto the seat tube104. Into a hole at the top of the seat tube104, inserted is a tube132extending downward from a saddle13. Fixing the tube132onto the seat tube104allows the saddle13to be fixed. To the bottom of the seat tube104, fixed is the bracket2.

A front end portion of the down tube103is further fixed to the head tube101. A rear end portion of the down tube103is fixed to the bracket2.

Below the bracket2, fixed is the motor unit3. To a rear end portion of the bracket2, fixed are respective front end portions of the chain stays106.

To a rear end portion of the top tube102, fixed are respective front end portions of the seat stays105. The respective rear end portions of the seat stays105are coupled to the respective rear end portions of the chain stays106. The rear wheel112is mounted rotatably on their coupling portions. On the down tube103, a battery15for supplying power to the motor unit3is mounted removably.

Next, the motor unit3will be described.

As shown inFIGS.2A and2B, the majority of the shell of the motor unit3is formed by a unit case4. As shown inFIG.3, a motor5, operating as a drive source for driving the wheels11in rotation, is fitted into the unit case4. The unit case4houses: a speed reducer31to which the rotational force of the motor5is transmitted; and a control board35for controlling the rotation of the motor5. The unit case4further houses an input shaft6, an input body7, an output body8, and other members.

To the outer surface of the unit case4, fitted is a metallic cup57having the shape of a bottomed cylinder for housing principal parts of the motor5. The metallic cup57has an opening, of which an opening edge portion574is coupled to the unit case4.

Parts (such as a portion of a rotary shaft51to be described later), not housed in the metallic cup57, of the motor5are housed in the unit case4. A plurality of first mount pieces401and a plurality of second mount pieces402, all of which are to be fixed to the bracket2, protrude from the outer surface of the unit case4.

The unit case4includes a first divided part41forming a left half of the unit case4and a second divided part42forming a right half of the unit case4. The plurality of first mount pieces401protrudes from the first divided part41and the plurality of second mount pieces402protrudes from the second divided part42. A hollow unit case4is formed by joining the first divided part41and the second divided part42together.

As shown inFIGS.3and4and other drawings, the first divided part41has a space which is opened rightward. This space forms the left half of the housing space of the unit case4. The first divided part41has a wall415in a region to face the motor5. The wall415has a circular through hole412and an arc-shaped through hole413, which is concentric with the through hole412. Part (specifically, the rotary shaft51to be described later) of the motor5is inserted into the through hole412. A power supply cable for the motor5and a resin portion molding the cable are passed through the through hole413.

The second divided part42has a space which is opened leftward. This space forms the right half of the housing space of the unit case4. The first divided part41and the second divided part42are joined together such that their respective spaces communicate with each other.

The metallic cup57provided for the motor5includes: a circular bottom wall572; a peripheral wall573extended from the peripheral edge of the bottom wall572; and an opening edge portion574formed in a flange shape at the tip of the peripheral wall573(seeFIGS.5and6). The peripheral wall573is extended along the thickness of the bottom wall572.

The metallic cup57is typically made of aluminum. However, this is only an example and should not be construed as limiting. Alternatively, the metallic cup57may also be made of iron, a magnesium alloy, titanium, or any other suitable material.

The opening edge portion574having an annular shape has: a plurality of screw holes575arranged circumferentially at intervals; a plurality of protrusions576also arranged circumferentially at intervals; and an annular groove577(seeFIG.6).

The plurality of screw holes575are provided to receive a plurality of screws571to be screwed thereto one to one. The plurality of protrusions576are provided to position the metallic cup57by being fitted into recesses on the outer surface of the first divided part41. The groove577is provided to receive an O-ring49. The groove577is provided over the entire circumference of the opening edge portion574.

The groove577is located radially inside of (i.e., closer to the center of the opening of the metallic cup57than) the plurality of screw holes575and the plurality of protrusions576. The profile of the groove577is not a perfect circle but is bent radially inward in regions where the screw holes575and the protrusions576are provided (seeFIG.6). This allows the motor unit3according to this embodiment to decrease the external dimension of the opening edge portion574of the metallic cup57. However, this is only an example of the present disclosure and should not be construed as limiting. Alternatively, the groove577may also be formed to have a perfect circular profile.

To fix the metallic cup57onto the outer surface of the first divided part41, a plurality of screws571may be inserted through the opening of the first divided part41(seeFIG.4) and screwed into their corresponding screw holes575through the first divided part41. This allows the opening edge portion574of the metallic cup57to be hermetically fixed onto the outer surface of the first divided part41via the O-ring49with elasticity. Interposing the O-ring49between the metallic cup57and the unit case4achieves the advantage of reducing the transmission of vibrations.

As shown inFIG.3, the motor5includes: a circular columnar rotary shaft51; a rotor52coupled to the rotary shaft51to rotate along with the rotary shaft51; and a circular cylindrical stator53arranged to surround the rotor52.

The metallic cup57houses an axial part of the rotary shaft51(specifically, an axial half of the rotary shaft51), the rotor52, and a part of the stator53(specifically, most of the stator53). Through the opening of the metallic cup57, the rest of the rotary shaft51(specifically, the other axial half of the rotary shaft51) and the rest of the stator53(specifically, a resin molded part of the stator53) protrude.

On the inner surface of the bottom wall572of the metallic cup57, provided is a recess578to receive a bearing552. The bearing552is provided to rotatably support an axial end portion of the rotary shaft51. The other axial end portion of the rotary shaft51is rotatably supported by another bearing551placed in another recess428provided on the inner surface of the second divided part42.

On the outer peripheral surface of a portion, protruding from the metallic cup57, of the rotary shaft51, formed are teeth54to mesh with the speed reducer31.

In the motor unit3according to this exemplary embodiment, an inner peripheral surface570of the metallic cup57(i.e., the inner peripheral surface of the metallic peripheral wall573) is, over the entire circumference thereof, in pressure contact with the outer peripheral surface530of the stator53sufficiently closely. As used herein, bringing the inner peripheral surface570of the metallic cup57into pressure contact with the stator53means bringing, with pressure, the inner peripheral surface570of the metallic cup57into contact with the stator53. Between the inner peripheral surface570of the metallic cup57and the outer peripheral surface530of the stator53, applied is pressure that causes the inner peripheral surface570and the outer peripheral surface530to be pressed against each other.

The metallic cup57is thermally inserted to the stator53. Specifically, the metallic cup57is fitted onto the stator53after having been heated and expanded. When the metallic cup57shrinks as its temperature decreases after that, the metallic cup57is brought into pressure contact with the stator53closely. The inner peripheral surface570of the metallic cup57is an annular continuous metallic surface. The inner peripheral surface570of the metallic cup57makes, over the entire circumference thereof, close contact under pressure with the outer peripheral surface530of the stator53.

A non-resin-molded part of the outer peripheral surface530of the stator53is the metallic surface535. The stator53is resin-molded not entirely but only partially such that at least the metallic surface535is exposed on the outer periphery thereof. The metallic surface535is the outer peripheral surface of an iron core533of the stator53. A coil534wound around the iron core533is resin-molded.

As can be seen, in the motor unit3according to the exemplary embodiment, the stator53is resin-molded entirely but a part thereof. That part includes a portion, designed to be in pressure contact with the inner peripheral surface570of the metallic cup57, of the stator53(i.e., the outer peripheral surface530of the stator53).

Thus, the heat generated inside the motor5is directly transferred from the stator53to the metallic cup57and is efficiently dissipated through the metallic cup57into the open air. The surface of the metallic cup57may be exposed to the air blowing against the electric bicycle traveling. As will be described later with respect to variations, the stator53does not have to be resin-molded.

As shown inFIG.5, an anti-rotation pin48is provided between the metallic cup57and the stator53. On the outer peripheral surface530of the stator53, a linear groove538is formed to which part of the pin48is fitted. On the inner peripheral surface570of the metallic cup57, a linear groove579is formed to which another part of the pin48is fitted (seeFIG.6).

The pin48is arranged parallel to the axis of the motor5(i.e., the axis of the rotary shaft51). Fitting the pin48between the metallic cup57and the stator53allows the relative rotation of the metallic cup57with respect to the stator53to be checked with more reliability.

In addition, in the motor unit3according to the exemplary embodiment, the stator53includes a portion531protruding through the opening of the metallic cup57(seeFIG.4). This portion531serves as a guide when the O-ring49is attached.

The foregoing description is focused on the structure of the motor5. Next, various types of mechanisms to be housed in the unit case4will be described.

As shown inFIG.3, in the unit case4, the input shaft6is housed to be rotatable around the axis60thereof. The first divided part41has a through hole411into which the input shaft6is inserted. The second divided part42also has a through hole421into which the input shaft6is inserted.

To both end portions of the input shaft6, fixed are crank arms18. To the tip of each of these crank arms18, attached rotatably is a pedal181(seeFIG.1). The rider may apply manual rotational force to the input shaft6by pumping the pedals181.

In the unit case4, the input body7is arranged along the outer peripheral surface of the input shaft6. The input body7is a cylindrical member and rotates along with the input shaft6.

The input body7is divided into a first input body71and a second input body72. The first input body71is coupled to the input shaft6in the first divided part41. The second input body72is coupled to the first input body71in the second divided part42. The second input body72transmits rotational force to the output body8.

The output body8is a cylindrical member and is arranged rotatably along the outer peripheral surface of the input shaft6. One end portion of the output body8passes through the through hole421of the second divided part42to protrude out of the unit case4.

A front sprocket191is fixed to the portion, protruding out of the unit case4, of the output body8. The front sprocket191rotates along with the output body8. A rear sprocket192is fixed to a hub of the rear wheel112(seeFIG.1). A chain193is hung around between the front sprocket191and the rear sprocket192.

As shown inFIG.3, in the unit case4, a one-way clutch32is arranged to be located between the input body7and the output body8. The one-way clutch32is configured to, when rotational force is applied in an accelerating direction to the input body7, transmit the rotational force to the output body8and is also configured to, when rotational force is applied in a decelerating direction to the input body7, stop transmitting the rotational force to the output body8. As used herein, the “accelerating direction” refers to the direction in which the electric bicycle1is accelerated in its traveling direction, and the “decelerating direction” is opposite from the accelerating direction.

The output body8includes a web81and a rim82as its integral members. The web81protrudes radially outward with respect to the output body8. The rim82is continuous with a radially outer end portion of the web81. On the outer peripheral surface of the rim82, formed are teeth83to mesh with the speed reducer31.

The speed reducer31housed in the unit case4is configured to reduce the number of revolutions of the motor5and transmit reduced rotational force to the output body8.

The speed reducer31includes a rotary shaft310and a first transmission gear311and a second transmission gear312, both of which are supported by the rotary shaft310.

The first transmission gear311is a cylindrical member to receive the rotational force from the rotary shaft51of the motor5. On the outer peripheral surface of the first transmission gear311, formed are teeth313to mesh with the teeth54of the rotary shaft51.

The rotary shaft310is housed rotatably in the unit case4such that its axis is aligned with the rightward/leftward direction. One end portion of the rotary shaft310is supported rotatably by a bearing314arranged in the second divided part42.

The first transmission gear311is coupled to the rotary shaft310via a one-way clutch315.

The one-way clutch315is configured to, when rotational force is applied in an accelerating direction to the first transmission gear311, transmit the rotational force to the rotary shaft310and is also configured to, when rotational force is applied in a decelerating direction to the first transmission gear311, stop transmitting the rotational force to the rotary shaft310.

The second transmission gear312is fixed to the rotary shaft310so as to rotate along with rotary shaft310. The second transmission gear312transmits the rotational force transmitted from the first transmission gear311via the rotary shaft310to the teeth83of the output body8. On the outer peripheral surface of the second transmission gear312, formed are teeth316to mesh with the teeth83.

The motor unit3according to the exemplary embodiment has such a configuration. Thus, when the input shaft6rotates in the accelerating direction as the rider pumps the pedals181of the electric bicycle1, the first input body71and the second input body72also rotate along with the input shaft6. When the rotational force in the accelerating direction of the second input body72is transmitted to the output body8via the one-way clutch32, the output body8and the front sprocket191rotate in the accelerating direction. As the front sprocket191rotates in the accelerating direction, its rotational force is transmitted via the chain193to the rear sprocket192, thus causing the rear sprocket192to rotate in the accelerating direction and thereby driving the rear wheel112in rotation in the accelerating direction.

In addition, the motor unit3according to the exemplary embodiment may apply the rotational force output from the motor5to the output body8as will be described below.

As the rotary shaft51of the motor5rotates in the accelerating direction, the first transmission gear311engaged with rotary shaft51also rotates in the accelerating direction. The rotational force in the accelerating direction of the first transmission gear311is transmitted to the rotary shaft310and the second transmission gear312via the one-way clutch315, thus causing the second transmission gear312to rotate in the accelerating direction. The rotational force in the accelerating direction of the second transmission gear312is transmitted to the output body8. To the output body8, transmitted in combination are the rotational force produced by the motor5and the rotational force generated by the rider who is pumping the pedals181.

In the electric bicycle1according to the exemplary embodiment, a control unit included in the control board35controls the rotation of the motor5in accordance with a torque applied to the input shaft6and the number of revolutions per unit time of the input shaft6. The torque applied to the input shaft6is detected by a torque detector33housed in the unit case4. The torque detector33is a magnetostriction torque detector including a magnetostriction generation unit331formed on the outer peripheral surface of the first input body71and a coil332arranged at a very narrow interval from the magnetostriction generation unit331.

The number of revolutions per unit time of the input shaft6is detected by a rotation detector34. The rotation detector34is an optical rotation detector including a rotator341that rotates along with the input body7and an optical sensor342arranged at a very narrow interval from the rotator341.

The control unit of the control board35may include, for example, a microcomputer and controls the operation of the respective constituent elements by executing a program stored on a storage medium such as a read-only memory (ROM). A known control unit may be used as appropriate as this control unit.

In the motor unit3according to the exemplary embodiment having such a configuration, the heat in the stator53is directly transferred to the metallic cup57through the metallic surface535and then is dissipated efficiently from the outer surface of the metallic cup57. In addition, since the amount of the resin used as its material is reduced, the motor unit3may have a lighter overall weight.

Next, some variations of the motor unit3and electric bicycle1according to the exemplary embodiment will be described. In the following description of variations, any constituent element, having the same function as a counterpart of the exemplary embodiment described above, will be designated by the same reference numeral as that counterpart's, and a detailed description thereof will be omitted herein.

FIG.7illustrates a cross section of a first variation of the motor unit3. In the motor unit3shown inFIG.3and other drawings, the stator53is resin-molded partially. Meanwhile, according to the first variation of the motor unit3, the stator53is not resin-molded.

That is to say, neither the iron core533of the stator53nor the coil534wound around the iron core533is resin-molded. The metallic surface535constituted by the outer peripheral surface of the iron core533and the inner peripheral surface570of the metallic cup57are in close contact with each other with pressure that causes these surfaces535,570to be pressed against each other.

In the first variation of the motor unit3, the stator53is not resin-molded, and therefore, the motor5may have an even lighter overall weight. Meanwhile, if the stator53is resin-molded entirely but the metallic surface535(i.e., in the embodiment shown inFIG.3and other drawings), the advantages are achieved in that a steep increase in the temperature of the stator53is reduced due to the heat storage property of the resin portion, the resin portion reduces noise and vibrations, and the resin portion increases the degree of insulation between the coil534and the metallic cup57.

FIG.8illustrates a cross section of a second variation of the motor unit3. The motor unit3shown inFIG.3and other drawings is a so-called “uniaxial motor unit.” On the other hand, the second variation of the motor unit3is a biaxial motor unit3.

In the second variation of the motor unit3, the motor unit3includes a second output body310B, which is different from the output body8.

A first end portion of the second output body310B is located in the unit case4. The second output body310B is supported rotatably by a bearing3191B arranged in the first divided part41and a bearing3192B arranged in the second divided part42.

A second end portion of the second output body310B protrudes out of the unit case4. To the second end portion of the second output body310B, fixed is a sprocket194B. A chain193is hung around the sprocket194B.

On the outer peripheral surface of the second output body310B, mounted via a one-way clutch317B is a gear318B with a large diameter. The gear318B meshes with the teeth54on the rotary shaft51of the motor5.

In the electric bicycle1including the second variation of the motor unit3, when the rotary shaft51of the motor5rotates in the accelerating direction while the rider is traveling by pumping the pedals181, the gear318B rotates in the accelerating direction and the rotational force is transmitted via the one-way clutch317B to the second output body310B and then is further transmitted to the chain193.

Next, a third variation of the motor unit3will be described with reference toFIG.9.

In the third variation of the motor unit3, the first divided part41of the unit case4made of a metallic material includes, as an integral part thereof, a first heat dissipating portion414. A portion of the first divided part41is formed to be thicker than a surrounding portion thereof. That thicker portion of the first divided part41constitutes the first heat dissipating portion414made of a metallic material and bulging inward in the unit case4.

The first heat dissipating portion414is connected to a first surface351along the thickness of the control board35via a first thermally conductive sheet91serving as a thermally conductive member9. As used herein, if something is “connected to” anything else, then the two things may naturally be directly in contact with each other with no other member interposed between them but may also be indirectly connected together with another member interposed between them. A contact surface between the thermally conductive member9and the control board35is at a side of the first divided part41with respect to a mating surface45of the first and second divided parts41,42.

The thickness of the control board35is the thickness of a printed wiring board354included in the control board35and corresponds to the rightward/leftward direction in the third variation of the motor unit3. The first surface351of the control board35is one surface along the thickness of the printed wiring board354and forms a principal part thereof. A second surface352of the control board35is another surface along the thickness of the printed wiring board354and forms a principal part thereof.

The control board35further includes a plurality of electrical components353assembled together on the printed wiring board354. The plurality of electrical components353includes not only capacitors3532and integrated circuits3533, for example, but also heat generating elements3531which tend to generate heat particularly easily. Examples of the heat-generating elements3531include not only a switching element such as a field-effect transistor (FET), a diode, and a coil, which are used to supply power to the motor5, but also various types of resistors and connectors, for example.

The second divided part42of the unit case4includes a second heat dissipating portion424as an integral part thereof. In the third variation of the motor unit3, a portion of the second divided part42is formed to be recessed inward with respect to a surrounding portion thereof. The bottom of the recessed portion of the second divided part42constitutes the second heat dissipating portion424made of a metallic material and bulging inward in the unit case4.

The second heat dissipating portion424is connected to the second surface352of the control board35via a second thermally conductive sheet92serving as a thermally conductive member9. The second surface352is a surface facing the opposite direction from the first surface351.

A plurality of heat-generating elements3531is in contact with the second thermally conductive sheet92. The heat generated by the plurality of heat generating elements3531is efficiently dissipated from the outer surface of the unit case4via the second thermally conductive sheet92and the second heat dissipating portion424.

Note that the number of the heat generating elements3531in contact with the second thermally conductive sheet92does not have to be plural but may also be singular. Also, a single or plurality of heat generating elements3531may be in contact with the first thermally conductive sheet91. A single or a plurality of heat generating elements3531may be in contact with each of the first thermally conductive sheet91and the second thermally conductive sheet92.

As can be seen, in the third variation of the motor unit3, the first heat dissipating portion414forming an integral part of the unit case4is connected to the first surface351of the control board35and the second heat dissipating portion424forming an integral part of the unit case4is connected to the second surface352of the control board35. Since the heat generated from the control board35(e.g., the heat generated by the heat generating elements3531) is efficiently dissipated from both sides thereof along its thickness, the motor unit3for use in electric bicycles may have its heat dissipation capability improved.

In the third variation of the motor unit3, the control board35may have its heat dissipation capability improved, and the plurality of heat generating elements3531may be assembled together on the printed wiring board354at narrower intervals, thus reducing the size of the control board35.

As shown inFIG.9, in the third variation of the motor unit3, when viewed along the thickness of the control board35(i.e., when viewed in the rightward/leftward direction), the first heat dissipating portion414and the second heat dissipating portion424are both located to overlap with the heat generating elements3531. This allows the heat generated by the heat generating elements3531to be efficiently dissipated via the first heat dissipating portion414and the second heat dissipating portion424. The first heat dissipating portion414and the second heat dissipating portion424may be each located so as to partially overlap with the heat generating elements3531.

As shown inFIG.9, when viewed along the thickness of the control board35, the first heat dissipating portion414is located to overlap with the second heat dissipating portion424. In the third variation of the motor unit3, a portion of the control board35(specifically, a side edge portion, located more distant from the input shaft6, of the control board35) is sandwiched from both sides between the first heat dissipating portion414and the second heat dissipating portion424. This not only improves the heat dissipation capability of the control board35but also allows the control board35to be fixed with more reliability, thus improving the vibration resistance of the motor unit3. The first heat dissipating portion414needs to be located to at least partially overlap with the second heat dissipating portion424.

In the third variation of the motor unit3, the thermally conductive member9includes both the first thermally conductive sheet91and the second thermally conductive sheet92. However, this is only an example of the present disclosure and should not be construed as limiting. Alternatively, the thermally conductive member9may include either the thermally conductive sheet91or the second thermally conductive sheet92, with the other sheet omitted.

If the thermally conductive member9does not include the first thermally conductive sheet91, the first heat dissipating portion414is directly in contact with the first surface351of the control board35. If the thermally conductive member9does not include the second thermally conductive sheet92, the second heat dissipating portion424is directly in contact with the second surface352of the control board35.

Also, in the third variation of the motor unit3, the first thermally conductive sheet91and the second thermally conductive sheet92are formed out of mutually different sheet members. However, this is only an example of the present disclosure and should not be construed as limiting. Alternatively, the first thermally conductive sheet91and the second thermally conductive sheet92may also be formed out of the same sheet member. That is to say, a part of the sheet member constituting the thermally conductive member9may serve as the first thermally conductive sheet91and another part of the sheet member may serve as the second thermally conductive sheet92.

Note that the first to third variations described above are some of numerous variations. In the metallic cup57, at least part of the stator53and at least part of the rotor52need to be housed. In the exemplary embodiment and the first to third variations thereof, part of the stator53protrudes from the opening of the metallic cup57. However, this is only an example of the present disclosure and should not be construed as limiting. Alternatively, the stator53may be entirely housed in the metallic cup57. In the exemplary embodiment and the first to third variations thereof, the electric bicycle equipped with the motor unit3is implemented as a so-called “electric assist bicycle.” However, this is only an example of the present disclosure and should not be construed as limiting. Alternatively, the electric bicycle may also be an e-bike designed to drive the wheels11in rotation with only the rotational force of the motor5. Furthermore, the electric bicycle according to the exemplary embodiment and the first to third variations includes two wheels11. However, the number of the wheels11provided is not limited to any particular number but may also be three, for example.

Furthermore, in the exemplary embodiment and the first to third variations thereof, the metallic cup57and the stator53are fixed to each other by thermal insertion technique. Optionally, an adhesive may be further applied between the metallic cup57and the stator53(e.g., between the inner peripheral surface570of the metallic cup57and the outer peripheral surface530of the stator53). That is to say, the metallic cup57and the stator53may be fixed to each other not only by thermal insertion but also with an adhesive as well. Alternatively, the metallic cup57may be brought into pressure contact with the stator53by any technique other than thermal insertion (e.g., by press fitting). Still alternatively, the metallic cup57and the stator53may be fixed to each other not only by the alternative technique but also with an adhesive as well.

As can be seen easily from the foregoing description of an exemplary embodiment and its variations, a motor unit (3) according to a first aspect is designed to be used in electric bicycles. The motor unit (3) includes a motor (5) and a unit case (4) to which the motor (5) is fitted. The motor (5) includes: a stator (53); a rotor (52) arranged to be surrounded with the stator (53); a rotary shaft (51) fixed to the rotor (52); and a metallic cup (57) to house the stator (53) and the rotor (52) at least partially. The metallic cup (57) has an opening. An inner peripheral surface (570) of the metallic cup (57) is in pressure contact with the stator (53).

In the motor unit (3) according to the first aspect, the heat generated from the stator (53) is transferred to the metallic cup (57) that is in pressure contact with the stator (53) and may be efficiently dissipated through the metallic cup (57). This improves the heat dissipation capability of the motor unit (3) for use in electric bicycles. In addition, the motor unit (3) according to the first aspect may have its overall weight further lightened by adopting the metallic cup (57).

A motor unit (3) according to a second aspect may be implemented in combination with the first aspect. In the motor unit (3) according to the second aspect, at least part of an outer peripheral surface (530) of the stator (53) is a metallic surface (535). The inner peripheral surface (570) of the metallic cup (57) is in pressure contact with the metallic surface (535).

In the motor unit (3) according to the second aspect, the inner peripheral surface (570) of the metallic cup (57) is in pressure contact with the metallic surface (535), of which the properties make the surface sufficiently smooth and easy to transfer heat. This allows the heat to be transferred easily between the metallic cup (57) and the stator (53), thus achieving excellent heat dissipation capability.

A motor unit (3) according to a third aspect may be implemented in combination with the first or second aspect. In the motor unit (3) according to the third aspect, the stator (53) is resin-molded entirely but a particular part thereof. The particular part includes a portion, with which the metallic cup (57) is in pressure contact, of the stator (53).

In the motor unit (3) according to the third aspect, providing the resin-molded portion that partially covers the stator (53) reduces not only a steep increase in the temperature of the stator (53) but also vibrations as well. In addition, the presence of the resin-molded portion also increases the degree of insulation between the stator (53) and the metallic cup (57).

A motor unit (3) according to a fourth aspect may be implemented in combination with any one of the first to third aspects. The motor unit (3) according to the fourth aspect further includes a speed reducer (31) to which rotational force of the motor (5) is transmitted. The speed reducer (31) is housed in the unit case (4).

In the motor unit (3) according to the fourth aspect, the motor (5) and the speed reducer (31) are provided as a unit.

A motor unit (3) according to a fifth aspect may be implemented in combination with the fourth aspect. The motor unit (3) according to the fifth aspect further includes an O-ring (49) interposed between the unit case (4) and the metallic cup (57). The metallic cup (57) has an opening edge portion (574), against which the O-ring (49) is pressed.

In the motor unit (3) according to the fifth aspect, the O-ring (49) may increase the degree of close contact between the metallic cup (57) and the unit case (4) and also reduce the transmission of vibrations as well.

A motor unit (3) according to a sixth aspect may be implemented in combination with the fifth aspect. In the motor unit (3) according to the sixth aspect, the stator (53) includes a portion (531) protruding from the metallic cup (57) through the opening.

In the motor unit (3) according to the sixth aspect, the portion (531), protruding from the metallic cup (57), of the stator (53) may serve as a guide when the O-ring (49) is fitted.

A motor unit (3) according to a seventh aspect may be implemented in combination with any one of the first to sixth aspects. In the motor unit (3) according to the seventh aspect, the metallic cup (57) is thermally inserted into the stator (53).

In the motor unit (3) according to the seventh aspect, the metallic cup (57) may be brought into pressure contact with the stator (53) sufficiently closely.

A motor unit (3) according to an eighth aspect may be implemented in combination with any one of the first to seventh aspects. In the motor unit (3) according to the eighth aspect, the motor (5) further includes a bearing (552) configured to rotatably support the rotary shaft (51). A portion of the metallic cup (57) has a recess (578) to receive the bearing (552).

In the motor unit (3) according to the eighth aspect, a structure for receiving the bearing (552) may be constituted by a part of the metallic cup (57), thus further lightening the weight of the motor unit (3).

An electric bicycle (1) according to a ninth aspect includes the motor unit (3) according to any one of the first to eighth aspects; and at least one wheel (11) to which rotational force is transmitted from the motor (5) of the motor unit (3).

The electric bicycle (1) according to the ninth aspect may improve the heat dissipation capability of the motor unit (3) and have a much lighter weight as well.

As can also be seen easily from the foregoing description of an exemplary embodiment and its variations (e.g., the third variation, among other things), a motor unit (3) according to a tenth aspect is designed to be used in electric bicycles and includes: a motor (5) having a rotary shaft (51); a unit case (4) to house the rotary shaft (51) partially; an input shaft (6) arranged in the unit case (4) to penetrate through the unit case (4) and to be rotatable around an axis (60); an input body (7) arranged around an outer peripheral surface of the input shaft (6) and configured to rotate along with the input shaft (6); an output body (8) arranged along the outer peripheral surface of the input shaft (6) and configured to rotate around the axis (60) upon receiving rotational force of the input body (7); and a control board (35) housed in the unit case (4) and configured to control rotation of the motor (5). The unit case (4) includes: a first heat dissipating portion (414) connected to a first surface (351) of the control board (35); and a second heat dissipating portion (424) connected to a second surface (352) of the control board (35). The second surface (352) is opposite from the first surface (351).

In the motor unit (3) according to the tenth aspect, the heat generated in the control board (35) may be efficiently dissipated from both sides via the first heat dissipating portion (414) and the second heat dissipating portion (424), thus improving the heat dissipation capability of the motor unit (3) for use in electric bicycles.

A motor unit (3) according to an eleventh aspect may be implemented in combination with the tenth aspect. The motor unit (3) according to the eleventh aspect further includes a thermally conductive member (9) arranged in the unit case (4). The thermally conductive member (9) is arranged between the first heat dissipating portion (414) and the control board (35) and/or between the second heat dissipating portion (424) and the control board (35).

In the motor unit (3) according to the eleventh aspect, the heat generated in the control board (35) may be dissipated more efficiently through the thermally conductive member (9).

A motor unit (3) according to a twelfth aspect may be implemented in combination with the eleventh aspect. In the motor unit (3) according to the twelfth aspect, the control board (35) includes an electrical component (353). The thermally conductive member (9) is in contact with the electrical component (353).

In the motor unit (3) according to the twelfth aspect, the heat generated by the electrical component board (353) may be dissipated efficiently through the thermally conductive member (9).

A motor unit (3) according to a thirteenth aspect may be implemented in combination with any one of the tenth to twelfth aspects. In the motor unit (3) according to the thirteenth aspect, the control board (35) includes a heat generating element (3531). At least one of the first heat dissipating portion (414) or the second heat dissipating portion (424) is arranged to overlap with the heat generating element (3531) when viewed along the thickness of the control board (35).

In the motor unit (3) according to the thirteenth aspect, the heat generated by the heat generating element (3531), of which the temperature tends to increase particularly significantly on the control board (35), may be dissipated even more efficiently.

A motor unit (3) according to a fourteenth aspect may be implemented in combination with any one of the tenth to thirteenth aspects. In the motor unit (3) according to the fourteenth aspect, the first heat dissipating portion (414) is arranged to overlap with the second heat dissipating portion (424) when viewed along the thickness of the control board (35).

In the motor unit (3) according to the fourteenth aspect, the control board (35) is sandwiched from both sides between the first heat dissipating portion (414) and the second heat dissipating portion (424). This not only improves the heat dissipation capability but also allows the control board (35) to be fixed with more reliability, thus eventually increasing the vibration resistance of the motor unit (3).

An electric bicycle (1) according to a fifteen aspect includes the motor unit (3) according to any one of the tenth to fourteenth aspects; and at least one wheel (11) to which rotational force is transmitted from the motor (5) of the motor unit (3).

The electric bicycle (1) according to the fifteen aspect may improve the heat dissipation capability of the motor unit (3) for use in electric bicycles.

REFERENCE SIGNS LIST