Patent Description:
For the pursuit of better dynamic performance and energy source diversity, it gradually becomes a trend to drive a mechanical device by a motor. The motor needs to be cooled by a cooling system so as to avoid overheat of the motor. The related cooling system cools the motor by arranging a cooling channel in a motor housing, while an end of a stator of the motor cannot exchange heat with a cooling liquid in the cooling channel, so that the temperature of the end of the stator of the motor is higher than those of other parts of the stator, i.e., the temperature of the stator is uneven. Thus, the increase of output power of the motor is limited.

The related cooling system solves the uneven temperature of the stator by directly spraying or splashing the cooling liquid onto the end of the stator. However, the stator needs to possess a cooling liquid resistance as the cooling liquid directly touches the stator, and also, a spraying system needs to be added, thus increasing a manufacturing cost of a power assembly.

<CIT> relates to a motor drive control apparatus, on which a switching element for performing drive control of the motor is mounted, includes: a heat sink placed on the front side or rear side of the motor; and a housing that is coupled to the heat sink and couples the heat sink to the frame or that covers the switching element mounted on the heat sink, and wherein an abutment surface between the housing and the heat sink is located on a single plane intersecting with the direction of the rotation axis of the motor, and screw holes and for coupling the frame, the heat sink and the housing to each other are provided such that the positions in the circumferential direction of the screw holes and correspond to each other.

<CIT> relates to a stator for an electrodynamic machine, in particular an electric motor, which contains a stator packet with a first stator end and a second stator end. Furthermore, the stator assembly comprises at least one web insulation with at least one winding support element to accommodate a stator coil. A heat conductive support device with at least one support element is provided, whereby the support element is at least partially disposed in the winding support element.

To this end, the present disclosure provides a power assembly, so as to prevent an uneven temperature of a stator and to improve a cooling efficiency of a motor without increasing a manufacturing cost of the stator.

The present invention is defined in the independent claims, and the preferable features according to the present invention are defined in the dependent claims.

By arranging the heat conductive element between the end of the stator and the transmission housing, the heat exchange between the end of the stator and the transmission housing is accelerated, thereby ensuring the cooling rate of the end of the stator. Thus, the temperature of the end of the stator is prevented from being higher than those of other parts of the stator, and the uneven temperature of the stator is avoided. Moreover, by adding the cooling channel of the end of the stator, the cooling efficiency of the motor is further improved. Moreover, the end of the stator does not need to touch a cooling liquid in the transmission housing, the stator does not need to possess a cooling liquid resistance, and also, a spraying system does not need to be added, thereby reducing the manufacturing cost of the power assembly.

It is to be understood that both the foregoing general description and the following detailed description are illustrative and explanatory only and are not restrictive of the present disclosure, as claimed.

All specific technical features in all examples described in specific embodiments may be combined in various ways under no contradictions, for example, different specific technical features may be combined to form different embodiments. To avoid unnecessary repetition, various possible combinations of all specific technical features in the present disclosure are not described separately.

In a specific embodiment, a power assembly may be a power assembly for any mechanical device to drive the mechanical device. For example, the power assembly may be a power assembly for a spindle of a lathe to drive the spindle of the lathe to rotate. For example, the power assembly may also be a power assembly for a drilling machine to drive a drill to rotate. For example, the power assembly may also be a power assembly for an all-terrain vehicle to drive wheels of the all-terrain vehicle to rotate so as to drive the all-terrain vehicle to move. To facilitate description, that the power assembly is the power assembly for the all-terrain vehicle is taken as an example.

Referring to <FIG>, a power assembly <NUM> may include: a transmission <NUM>, a motor <NUM>, a heat conductive element <NUM> and a differential <NUM>. The transmission <NUM> includes a transmission housing <NUM>, a transmission input shaft <NUM> and a transmission output shaft <NUM>. The transmission input shaft <NUM> is arranged in the transmission housing <NUM> and rotatably connected to the transmission housing <NUM>. A through hole is formed in the transmission housing <NUM>. An output shaft of the motor <NUM> passes through the through hole to be connected to the transmission input shaft <NUM>, so as to transmit power to the transmission input shaft <NUM>. The transmission output shaft <NUM> is arranged in the transmission housing <NUM>, and the transmission output shaft <NUM> is rotatably connected to the transmission housing <NUM>. A plurality of first gears are arranged on the transmission input shaft <NUM>. A plurality of second gears are arranged on the transmission output shaft <NUM>. The first gears and the second gears may be meshed to form a plurality of gear transmission pairs. The transmission input shaft <NUM> transmits power to the transmission output shaft <NUM> through the gear transmission pairs. A housing of the differential <NUM> is fixedly connected to the transmission housing <NUM>. The transmission output shaft <NUM> is connected to an input shaft of the differential <NUM> and transmits power to the differential <NUM>. The differential <NUM> transmits the power acquired from the transmission output shaft <NUM> to half axles of wheels, so as to drive the wheels to rotate and hence to drive the all-terrain vehicle to move. By changing a transmission ratio of the gear transmission pairs between the transmission input shaft <NUM> and the transmission output shaft <NUM>, a transmission ratio of the transmission <NUM> may be changed, such that the all-terrain vehicle can possess a relatively high driving force at different vehicle speeds. In some embodiments of the present disclosure, the first gears are slidably arranged on the transmission input shaft <NUM>, and different first gears may be meshed with the second gears by sliding the first gears, so that the transmission ratio of the transmission is changed. In some embodiments of the present disclosure, the first gears and the second gears keep a meshed state all the time, the second gears are rotatably connected to the transmission output shaft <NUM>, and an engagement sleeve is arranged on the transmission output shaft <NUM> and slidably connected to the transmission output shaft <NUM>. By sliding the engagement sleeve, different second gears are circumferentially fixed to the transmission output shaft <NUM>, so that different second gears drive the transmission output shaft <NUM> to rotate, and thus the transmission ratio of the transmission <NUM> is changed. The transmission housing <NUM> accommodates a lubricating oil, the first gears and the second gears are immersed in the lubricating oil, and the lubricating oil cyclically flows so as to lubricate all the transmission parts, and also to lower temperatures of all the transmission parts, e.g., temperatures of the first gears and the second gears, thus preventing the first gears and the second gears from an overheat damage. It should be noted that only illustrative descriptions are made for the structure of the transmission <NUM>, and except the manual transmission as described above, the transmission <NUM> may be other forms of transmissions. For example, the transmission <NUM> may be an electronic control hydraulic automatic transmission, an electronic control mechanical stepless automatic transmission or a dual-clutch transmission.

The motor <NUM> includes a motor housing <NUM>, a rotor <NUM>, a stator <NUM> and a motor output shaft <NUM>. The motor housing <NUM> has an open end and a closed end opposite to the open end. Specifically, the motor housing <NUM> is a housing having an opening in one side, the motor housing <NUM> is connected to an outer surface of the transmission housing <NUM>, and the opening of the motor housing <NUM> is covered by the outer surface of the transmission housing <NUM>, so that an enclosed accommodating space is formed between the outer surface of the transmission housing <NUM> and the motor housing <NUM>, i.e., the transmission housing <NUM> serves as a cover of the motor housing <NUM>, and no additional motor cover is needed. Thus, the power assembly <NUM> is more compact in structure and smaller in size. The rotor <NUM> is rotatably arranged in the motor housing <NUM>, the stator <NUM> is fixed in the motor housing <NUM>, and the stator <NUM> is arranged on a peripheral outer side of the rotor <NUM>. The stator <NUM> drives the rotor <NUM> to rotate under the action of electromagnetic induction, and the rotor <NUM> is connected to the motor output shaft, so the motor output shaft is driven by the rotor <NUM> to rotate.

The heat conductive element <NUM> is arranged between an end of the stator <NUM> and the transmission housing <NUM>, and transmits heat of the end of the stator <NUM> to the transmission housing <NUM>, then the transmission housing <NUM> is cooled by the lubricating oil in the transmission housing <NUM>, and thus the end of the stator <NUM> is cooled. According to the invention, one end of the heat conductive element <NUM> is in contact with the end of the stator <NUM>, the heat conductive element <NUM> exchanges heat with the end of the stator <NUM> by thermal conduction, the other end of the heat conductive element <NUM> is in contact with the outer surface of the transmission housing <NUM>, and the heat conductive element <NUM> exchanges heat with the transmission housing <NUM> by thermal conduction. In some embodiments of the present disclosure, which are outside the scope of the invention, one end of the heat conductive element <NUM> is in contact with the end of the stator <NUM>, the heat conductive element <NUM> exchanges heat with the end of the stator <NUM> by thermal conduction, the other end of the heat conductive element <NUM> is a preset distance from the outer surface of the transmission housing <NUM>, and the heat conductive element <NUM> exchanges heat with the outer surface of the transmission housing <NUM> by thermal convection of air. In some embodiments of the present disclosure, one end of the heat conductive element <NUM> is a preset distance from the end of the stator <NUM>, the heat conductive element <NUM> exchanges heat with the end of the stator <NUM> by thermal convection of air, the other end of the heat conductive element <NUM> is a preset distance from the outer surface of the transmission housing <NUM>, and the heat conductive element <NUM> exchanges heat with the outer surface of the transmission housing <NUM> by thermal convection of air.

By arranging the heat conductive element <NUM> between the end of the stator <NUM> and the transmission housing <NUM>, the heat exchange between the end of the stator <NUM> and the transmission housing <NUM> is accelerated, thereby ensuring the cooling rate of the end of the stator <NUM>. Thus, the temperature of the end of the stator <NUM> is prevented from being higher than those of other parts of the stator <NUM>, and the uneven temperature of the stator <NUM> is avoided. Moreover, by adding a cooling channel of the end of the stator, the cooling efficiency of the motor <NUM> is further improved. Moreover, the end of the stator <NUM> does not need to touch a cooling liquid in the transmission housing <NUM>, and thus the stator <NUM> does not need to possess a cooling liquid resistance. Furthermore, an oil spraying system also does not need to be provided, thereby reducing a manufacturing cost of the power assembly.

In some embodiments, referring to <FIG>, the heat conductive element <NUM> includes a heat conductive rib <NUM>, the heat conductive rib <NUM> is arranged on the outer surface of the transmission housing <NUM> and at a periphery of the through hole, and the heat conductive rib <NUM> is a preset distance from the end of the stator <NUM>, so that the end of the stator <NUM> exchanges heat with the heat conductive rib <NUM> by thermal convection of air, and the heat conductive rib <NUM> exchanges heat with the transmission housing <NUM> by thermal conduction. The heat conductive rib has a large contact area with hot air, thereby accelerating the heat exchange between the end of the stator <NUM> and the heat conductive rib <NUM>, and hence increasing the cooling rate of the end of the stator <NUM>. Thus, the temperature of the end of the stator <NUM> is prevented from being higher than those of other parts of the stator <NUM>, and the uneven temperature of the stator <NUM> is avoided.

In some embodiments of the present disclosure, a cooling fan is further arranged to the motor output shaft <NUM> and rotates along with rotation of the motor output shaft <NUM>, so as to enable the air to flow from the end of the stator <NUM> to the heat conductive rib <NUM>, thereby accelerating the heat exchange between the end of the stator <NUM> and the heat conductive rib <NUM>. Thus, the temperature of the end of the stator <NUM> is prevented from being higher than those of other parts of the stator <NUM>, and the uneven temperature of the stator <NUM> is avoided.

In some embodiments, as shown in <FIG>, an accommodating chamber <NUM> is formed in the outer surface of the transmission housing <NUM>, the through hole is formed in a bottom wall of the accommodating chamber <NUM>, the open end of the motor housing <NUM> is connected to a peripheral wall of the accommodating chamber <NUM>, and the heat conductive rib <NUM> is arranged on the bottom wall of the accommodating chamber <NUM>.

According to the invention, referring to <FIG> and <FIG>, the heat conductive element <NUM> includes a heat conductive washer <NUM>, one end of the heat conductive washer <NUM> is in contact with the transmission housing <NUM>, and the other end of the heat conductive washer <NUM> opposite to the one end of the heat conductive washer <NUM> is in contact with the end of the stator <NUM>.

Further, a thermal conductivity of the heat conductive washer <NUM> is higher than that of the air, and the heat conductive washer <NUM> is made of an insulating material. In some embodiments of the present disclosure, the thermal conductivity of the heat conductive washer is <NUM> W/(m·K), and the thermal conductivity of the heat conductive washer is <NUM> times that of the air. The heat conductive washer <NUM> enables the end of the stator <NUM> to exchange heat with the transmission housing <NUM> by thermal conduction. The thermal conductivity of the heat conductive washer <NUM> is greater than that of the air, thereby accelerating the heat exchange between the end of the stator <NUM> and the transmission housing <NUM>, and hence increasing the cooling rate of the end of the stator <NUM>. Thus, the temperature of the end of the stator <NUM> is prevented from being higher than those of other parts of the stator <NUM>, and the uneven temperature of the stator <NUM> is avoided. Moreover, the heat conductive washer <NUM> is made of the insulating material, thereby increasing the cooling rate of the end of the stator <NUM>, and also realizing an overall plastic packaging of the end of the stator <NUM>, so as to achieve an electrical isolation between the end of the stator <NUM> and the transmission housing <NUM>.

Further, as shown in <FIG>, the heat conductive washer <NUM> is annular, the transmission housing <NUM> has a cooling ring face <NUM> matched with the heat conductive washer <NUM> in shape, and the heat conductive washer <NUM> is fitted with the cooling ring face <NUM>, thereby enlarging a contact area between the heat conductive washer <NUM> and the transmission housing <NUM>, accelerating the heat exchange between the end of the stator <NUM> and the transmission housing <NUM>, and hence further increasing the cooling rate of the end of the stator <NUM>.

In some embodiments, as shown in <FIG>, the power assembly further includes the differential <NUM>, and the housing of the differential <NUM> is fixedly connected to the transmission housing <NUM>.

Further, the accommodating chamber <NUM> is formed in the outer surface of the transmission housing <NUM>, the through hole is formed in the bottom wall of the accommodating chamber <NUM>, the open end of the motor housing <NUM> is connected to the peripheral wall of the accommodating chamber, and the cooling ring face <NUM> is arranged on the bottom wall of the accommodating chamber <NUM>. Further, referring to <FIG> and <FIG>, the heat conductive washer <NUM> covers the end of the stator <NUM>, thereby increasing the cooling rate of the end of the stator <NUM>, and also realizing the overall plastic packaging of the end of the stator <NUM>, so as to realize the electrical isolation between the end of the stator <NUM> and the transmission housing <NUM>.

In some embodiments, referring to <FIG> and <FIG>, the heat conductive element <NUM> includes the heat conductive rib <NUM> and the heat conductive washer <NUM>, the heat conductive rib <NUM> is fixed to the outer surface of the transmission housing <NUM>, the first end of the heat conductive washer <NUM> is in contact with the heat conductive rib <NUM>, and the second end of the heat conductive washer <NUM> opposite to the first end of the heat conductive washer <NUM> is in contact with the end of the stator <NUM>. A part, in contact with the heat conductive rib <NUM>, of the first end of the heat conductive washer <NUM> exchanges heat with the heat conductive rib <NUM> by thermal conduction, and another part, not in contact with the heat conductive rib <NUM>, of the first end of the heat conductive washer <NUM> exchanges heat with the transmission housing <NUM> by thermal convection of air, i.e., the end of the stator <NUM> exchanges heat with the transmission housing <NUM> by thermal conduction and by thermal convection of air at the same time, thereby further increasing the cooling rate of the end of the stator <NUM>. Thus, the temperature of the end of the stator <NUM> is prevented from being higher than those of other parts of the stator <NUM>, and the uneven temperature of the stator <NUM> is avoided. Further, a plurality of heat conductive ribs <NUM> are provided, i.e., the plurality of heat conductive ribs <NUM> are arranged on the outer surface of the transmission housing <NUM> and surround the through hole, thereby enlarging a contact area between the heat conductive washer <NUM> and the heat conductive ribs <NUM>, and also enlarging the contact area between the heat conductive ribs <NUM> and the hot air, so as to further increase the cooling rate of the end of the stator <NUM>, and to avoid the uneven temperature of the stator <NUM>.

Further, referring to <FIG> and <FIG>, a heat conductive boss <NUM> fitted with the heat conductive rib <NUM> is arranged on the end of the heat conductive washer <NUM> in contact with the heat conductive rib <NUM>. In the case that the plurality of heat conductive ribs <NUM> are provided at intervals, a plurality of heat conductive bosses <NUM> are also provided at intervals, and the heat conductive bosses <NUM> that are arranged at intervals and the heat conductive ribs <NUM> that are arranged at intervals are fitted in an alternated manner and in contact with each other. By providing the heat conductive boss <NUM> on the end of the heat conductive washer <NUM> in contact with the heat conductive rib <NUM>, the contact area between the heat conductive washer <NUM> and the heat conductive rib <NUM> is enlarged, thus accelerating the thermal conduction between the heat conductive washer <NUM> and the heat conductive rib <NUM>. Therefore, the cooling rate of the end of the stator <NUM> is increased, and the uneven temperature of the stator <NUM> is avoided.

In some embodiments, an input end of the transmission input shaft <NUM> blocks the through hole of the transmission housing <NUM>. The input end of the transmission input shaft <NUM> is just an end of the transmission input shaft <NUM> connected to the motor output shaft <NUM>. Specifically, as shown in <FIG>, an overall dimension (for example, an outer diameter) of the input end of the transmission input shaft <NUM> is greater than an overall dimension (for example, an inner diameter) of the through hole of the transmission housing <NUM>, thereby preventing the lubricating oil in the transmission housing <NUM> from flowing out of the through hole. A spline hole <NUM> is formed in the input end of the transmission input shaft <NUM>, and an overall dimension (for example, an inner diameter) of the spline hole <NUM> is not greater than that of the through hole of the transmission housing <NUM>. An end of the motor output shaft <NUM> passes through the through hole to be inserted in the spline hole <NUM>, and a spline is arranged on the end of the motor output shaft <NUM> to enable the motor output shaft to be circumferentially connected to the transmission input shaft <NUM>, so as to drive the transmission input shaft <NUM> to rotate.

In some embodiments, as shown in <FIG>, the transmission <NUM> further includes a lubricating oil pump <NUM>, the lubricating oil in the transmission housing <NUM> is driven by the lubricating oil pump <NUM> to cyclically flow in the lubricating oil pump <NUM>, and heat is distributed evenly in the lubricating oil due to the flow of the lubricating oil, thereby preventing heat from being concentrated in a certain part of the transmission <NUM>, and increasing a cooling rate of the lubricating oil. Thus, the cooling rate of the end of the stator <NUM> is increased, and the uneven temperature of the stator <NUM> is avoided. Further, a movement speed of a drive part in the lubricating oil pump <NUM> is positively correlated with a rotation speed of the motor output shaft <NUM>, i.e., the movement speed of the drive part of the lubricating oil pump <NUM> is regulated according to the rotation speed of the motor output shaft <NUM>, thereby controlling a cyclical flow speed of the lubricating oil in the transmission housing <NUM>, and the higher the rotation speed of the motor output shaft <NUM> is, the higher the cyclical flow speed of the lubricating oil is. In some embodiments of the present disclosure, the lubricating oil pump <NUM> is a gear pump, the drive part in the lubricating oil pump <NUM> includes two meshed drive gears, namely a driving gear and a driven gear, and the drive gears rotate to squeeze the lubricating oil out of the lubricating oil pump <NUM>, thereby driving the lubricating oil to cyclically flow. Rotation speeds of the drive gears are positively correlated with the rotation speed of the motor output shaft <NUM>. In some embodiments of the present disclosure, the lubricating oil pump <NUM> is a piston pump, the drive part in the lubricating oil pump <NUM> is a drive piston, and the drive piston reciprocates linearly to drive the lubricating oil to cyclically flow. Taking that the lubricating oil pump <NUM> is the gear pump as the example, illustrative descriptions are made for the implementation mode of enabling the rotation speed of the gear pump to be positively correlated with the rotation speed of the motor output shaft <NUM> as follows.

In some embodiments of the present disclosure, the driving gear in the lubricating oil pump <NUM> is connected to the transmission input shaft <NUM> through a mechanical transmission structure, i.e., the driving gear in the lubricating oil pump <NUM> acquires power from the transmission input shaft <NUM> through the mechanical transmission structure so as to drive the lubricating oil to cyclically flow, the rotation speed of the driving gear is positively correlated with the rotation speed of the transmission input shaft <NUM>, and the rotation speed of the transmission input shaft <NUM> is identical with the rotation speed of the motor output shaft <NUM>, so that the rotation speed of the lubricating oil pump <NUM> is positively correlated with the rotation speed of the motor output shaft <NUM>.

In some embodiments of the present disclosure, the gear pump further includes a drive motor, a motor driver and a rotation speed sensor. The drive motor is connected to a storage battery of the all-terrain vehicle to acquire electric energy, an output shaft of the drive motor is connected to the driving gear of the gear pump to drive the driving gear to rotate, the rotation speed sensor is configured to get the rotation speed of the transmission input shaft, the rotation speed sensor is connected to the motor driver and transmits data of the rotation speed of the transmission input shaft to the motor driver, and the motor driver controls the rotation speed of the output shaft of the drive motor according to the got rotation speed of the transmission input shaft, thereby controlling the rotation speed of the driving gear of the gear pump, i.e., controlling the rotation speed of the driving gear of the gear pump according to the rotation speed of the transmission input shaft, and hence enabling the rotation speed of the lubricating oil pump <NUM> to be positively correlated with the rotation speed of the motor output shaft <NUM>.

In some embodiments, the lubricating oil pump is an individual pump, i.e., the lubricating oil pump is a pump integrating an internal power supply, or the lubricating oil pump directly acquires electric energy from a battery module of the vehicle, thereby allowing the rotation speed of the lubricating oil to be constant and not correlated with the rotation speed of the motor output shaft.

In some embodiments, as shown in <FIG>, the outer surface of the transmission housing <NUM> is recessed to form the accommodating chamber <NUM>, the accommodating chamber <NUM> is configured to accommodate the end of the stator <NUM>, and the heat conductive rib <NUM> is arranged on a chamber wall of the accommodating chamber <NUM>. The accommodating chamber <NUM> is formed to enlarge a surface area of the heat conductive rib <NUM>, thereby accelerating the heat exchange between the end of the stator <NUM> and the heat conductive rib <NUM>. Thus, the cooling rate of the end of the stator <NUM> is further increased, and the uneven temperature of the stator <NUM> is avoided. In some embodiments of the present disclosure, one end of the motor housing <NUM> is an open end, an overall dimension (for example, an inner diameter) of the accommodating chamber <NUM> is equal to an overall dimension (for example, an outer diameter) of the open end of the motor housing <NUM>, the open end of the motor housing <NUM> abuts against the accommodating chamber <NUM>, and the wall surface of the accommodating chamber <NUM> covers an opening of the motor housing <NUM>, thereby preventing dust or liquid drops from entering the motor through the opening of the motor housing <NUM> and adhering to the rotor <NUM> or the stator <NUM>, and hence prolonging the service life of the motor <NUM>. Meanwhile, the accommodating chamber is formed to reduce the dimension of the power assembly <NUM> in an axial direction of the motor output shaft <NUM>, thereby making the structure of the power assembly <NUM> more compact, and hence facilitating the arrangement of the power assembly <NUM> in the all-terrain vehicle.

Embodiments of the present disclosure further provide an all-terrain vehicle <NUM>, as shown in <FIG>. The all-terrain vehicle <NUM> includes a wheel and the power assembly according to the above embodiments of the present disclosure. The power assembly is connected to the wheel and configured to drive the wheel to rotate.

The wheel includes a front wheel <NUM> and a rear wheel <NUM>, and the differential <NUM> is connected to the rear wheel <NUM>, so as to drive the rear wheel <NUM> to rotate and hence to drive the all-terrain vehicle <NUM> to move.

Claim 1:
A power assembly (<NUM>), comprising:
a transmission (<NUM>) comprising a transmission housing (<NUM>) and a transmission input shaft (<NUM>) rotatably connected to the transmission housing (<NUM>), the transmission housing (<NUM>) having a through hole;
a motor (<NUM>) comprising:
a motor housing (<NUM>) having an open end and a closed end opposite to the open end, and the open end being connected to the transmission housing (<NUM>);
a rotor (<NUM>) rotatably arranged in the motor housing (<NUM>);
a motor output shaft (<NUM>) having an end connected to the rotor (<NUM>) and another end passing through the through hole to be connected to the transmission input shaft (<NUM>); and
a stator (<NUM>) fixed in the motor housing (<NUM>) and arranged on a peripheral outer side of the rotor (<NUM>); and
a heat conductive element (<NUM>) arranged between an end of the stator (<NUM>) and the transmission housing (<NUM>),
wherein the heat conductive element (<NUM>) comprises a heat conductive washer (<NUM>), one end of the heat conductive washer (<NUM>) is in contact with the transmission housing (<NUM>), and the other end of the heat conductive washer (<NUM>) opposite to the one end of the heat conductive washer (<NUM>) is in contact with the end of the stator (<NUM>),
wherein the heat conductive washer (<NUM>) is annular, the transmission housing (<NUM>) has a cooling ring face (<NUM>) matched with the heat conductive washer (<NUM>) in shape, and the heat conductive washer (<NUM>) is fitted with the cooling ring face (<NUM>),
characterized in that the heat conductivity of the heat conductive washer (<NUM>) is higher than a thermal conductivity of air, and the heat conductive washer (<NUM>) is made of an insulating material, wherein an accommodating chamber (<NUM>) is formed in an outer surface of the transmission housing (<NUM>), the through hole is formed in a bottom wall of the accommodating chamber (<NUM>), the open end of the motor housing (<NUM>) is connected to a peripheral wall of the accommodating chamber (<NUM>), and the cooling ring face (<NUM>) is arranged on the bottom wall of the accommodating chamber (<NUM>).