JPH09322480A - Motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the cooling performance of a motor while the increase of the axial direction dimension is suppressed. SOLUTION: A centrifugal fan 35 is attached to the right side part of the rotary shaft 32 of a rotor 31 so as to be surrounded by the inner circumferential parts of the coil ends 30a of the stator coils 30. If the centrifugal fan 35 is turned in a direction of an arrow A by the rotation of the rotor 31, the air in the space surrounded by the inner circumferential parts of the coil ends on an exhaust outlet 25 side is sent to the outer circumference side and air flows shown by arrows B, C and D are produced in a frame 21. At that time, a negative pressure is produced in a part linked with a gap between the rotor 31 and a stator 27 and the air flowing into a part surrounded by the inner circumferential parts of the coil ends 30a on a suction inlet 24 side as shown by the arrow C is ventilated through the gap.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor with improved cooling performance.

[0002]

For example, in a squirrel cage induction motor, for example, a rotor 1 having end fins 2 provided on both axial end faces thereof as shown in FIG. 9 is widely used. This is an integrally molded cage conductor and end fins 2 made by aluminum die casting.
At the same time as the rotation of, the end fins 2 cause an air flow to cool the motor.
However, in this structure, the end fins 2 have only allowed the air in the space in the inner peripheral portion of the stator coil 4 wound around the stator 3 to flow.

Therefore, as shown in FIG. 10, the centrifugal fan 7 is attached to the rotary shaft 5 of the rotor 1 so as to be located between the rotor 1 and the stator 3 and the end wall portion (bearing bracket) 6a of the frame 6. Has also been done. In this case, the frame 6 has an exhaust port 8 facing the outer peripheral portion of the centrifugal fan 7.
Is provided, and the bearing bracket 6 on the side opposite to the exhaust port 8 is provided.
An intake port 9 is provided at a. And centrifugal fan 7
When air is taken into the frame 6 from the intake port 9 due to the rotation of the stator 3, the air flows through the ventilation passage 10 between the stator 3 and the frame 6 toward the exhaust port 8 to cool the stator 3. Done. The air near the rotor 1 is also made to flow by the end fins 2, and the air blown by the centrifugal fan 7 causes air to flow through the ventilation passage 10 and the exhaust port 9 as well.
Therefore, the rotor 1 is cooled.

However, in this case, since the centrifugal fan 7 is mounted between the rotor 1 and the stator 3 and the bearing bracket 6a and attached to the rotary shaft 5, the motor becomes large in size in the axial direction. .

On the other hand, in the permanent magnet type motor, since an annular permanent magnet for field magnetism is attached to the outer peripheral portion of the rotor core to form the rotor, there is a situation in which the end fins cannot be integrally formed on the rotor. In this case, a cooling fan is attached to the outside of the frame and air is blown from one end of the frame to the other end to cool the motor. FIG. 11 shows a circulation pattern of air in the frame 11 in such a permanent magnet type motor. In the figure, each arrow shows the flow of air in the frame 11, the direction of the arrow corresponds to the flow direction, and the length of the arrow corresponds to the flow velocity. Therefore, in the figure, what can be seen as dots indicates that there is almost no air flow.

In the figure, an intake port 12 is provided on the left end surface of the frame 11 in the drawing, and a cooling fan is provided outside the frame 11 on the intake port 12 side (not shown). . An exhaust port 13 is provided on the peripheral wall portion of the frame 11 on the side opposite to the intake port 12.

As is apparent from FIG. 11, most of the air flowing into the frame 11 from the intake port 12 due to the rotation of the cooling fan collides with the coil end 14a directly or on the outer periphery of the coil end 14a. Department and frame 11
Flows into the space between and, and heads for the ventilation path 16 between the stator 15 and the frame 11. Then, the air that has flowed into the ventilation passage 16 is discharged to the outside of the frame 11 from the exhaust port 13 toward the exhaust port 13 side at a relatively high speed.

On the other hand, a part of the air flowing into the frame 11 from the intake port 12 collides with the coil end 14a and flows into the space of the inner peripheral portion of the coil end 14a. However, since the gap between the rotor 17 and the stator 15 is narrow and almost no air flows in this gap, the air that has flowed into the space of the inner peripheral portion of the coil end 14a hardly flows into that space. It becomes a stagnation state. Also on the exhaust port 13 side, of the air around the coil end 14a, part of the air on the outer peripheral side of the coil end 14a is pulled by the air flowing from the intake port 12 side through the ventilation passage 16 and exhausted. Although it is discharged from the mouth 13 to the outside, most of it does not flow and is in a widely stagnation state around the coil end 14a.

Therefore, in the motor having the above structure, the outer peripheral portion of the stator 15 is cooled by the air flowing through the ventilation passage 16, but the inner peripheral portion is not cooled, and most of the heat generated in the rotor 17 is generated. No heat is dissipated. Therefore, there is a problem that the temperature of the entire motor rises and the insulators, the lubricant in the bearing, and the like are significantly deteriorated.

Further, in recent years, in permanent magnet type motors, in order to achieve miniaturization, weight reduction, high output, etc., permanent magnets made of rare earth metal type compounds having a large energy product, for example, neodymium type compounds, have been adopted. There is. This type of permanent magnet has an extremely small electric resistance as compared with the ferrite magnets that have been generally used so far, and therefore eddy currents are easily generated, and therefore heat is easily generated. However, as described above, even if the cooling fan is provided outside the frame, the air does not circulate in the vicinity of the rotor, and the temperature rise of the field permanent magnet provided on the outer circumference of the rotor cannot be sufficiently suppressed. there were.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a motor capable of improving the cooling performance while suppressing an increase in the axial size of the motor.

[0012]

A motor according to a first aspect of the present invention comprises a stator having a stator coil wound around it, and a permanent magnet for a field arranged inside the stator with a slight gap. And a centrifugal fan provided in the vicinity of the field permanent magnet on the rotating shaft of the rotor.

According to this structure, the air in the inner peripheral portion of the stator coil, that is, the portion facing the gap between the stator and the rotor is exhausted to the outside in the radial direction by the centrifugal fan. Air can be circulated, and the rotor can be efficiently cooled even if the rotor heats up due to the generation of an eddy current in the field permanent magnet.

The centrifugal fan may be arranged at the inner peripheral portion of the coil end of the stator coil (claim 2). In this case, since the centrifugal fan is originally located on the inner peripheral portion of the coil end, which is a space portion, it can be compactly arranged in the axial direction, and when the stator coil is provided at a different axial position. It is smaller than the whole.

When a permanent magnet made of a rare earth metal-based material is used as the field permanent magnet, the energy product is large, so that the motor can be made compact, lightweight and high in output. In this case, since the permanent magnet composed of a rare earth metal-based material has a small electric resistance, an eddy current is likely to be generated, which causes a relatively large temperature rise when the motor is driven. Since the air near the rotor is made to flow, heat is efficiently radiated from the rotor (claim 3).

If the outer peripheral side end of the centrifugal fan blade is made substantially parallel to the inner peripheral side of the coil end of the stator coil,
The centrifugal fan can be made as large as possible, and the blowing performance of the centrifugal fan can be improved (claim 4). Then, when the main plate of the centrifugal fan is inclined outward in the axial direction from the inner peripheral side toward the outer peripheral side, the air blown by the rotation of the centrifugal fan flows smoothly along the outer periphery of the coil end. Item 5).

Further, when a through hole penetrating in the axial direction is provided in the main plate of the centrifugal fan, the air in the axially outer portion of the centrifugal fan flows through the through hole to the inner side of the centrifugal fan in the axial direction, and the bearing. A flow of air in the part can be generated (claim 6).

At this time, if the through hole provided in the main plate of the centrifugal fan is inclined in the rotation direction of the centrifugal fan from the inner side to the outer side in the axial direction, the through hole is inclined due to the rotation of the centrifugal fan. Since the air is blown and the air in the through holes flows toward the inner side in the axial direction, the air circulation in the bearing portion is improved (claim 7).

Further, by forming the centrifugal fan with a material having a thermal conductivity higher than that of the rotating shaft of the rotor, the heat of the rotating shaft can be radiated through the centrifugal fan, and the cooling of the rotating shaft and, by extension, the bearing. Can be efficiently cooled (Claim 8). In addition, if an annular projection extending outward in the axial direction is provided on the outer peripheral edge of the main plate of the centrifugal fan, a balance weight for rotor balance adjustment (plus balance adjustment) is provided along the inner circumferential surface of the annular projection. It can be made hard to come off by mounting, and in the case of negative balance adjustment, it can be easily adjusted by scraping an appropriate amount of the annular protrusion (claim 9).

When a groove extending in the axial direction is provided on the outer peripheral surface of the rotor as in the motor of claim 10, the air flows through the groove, so that the rotor and the stator are cooled more satisfactorily. can do. Moreover, in the case where the rotor is provided with the field permanent magnet on the outer periphery of the rotor core, the generation of the eddy current is suppressed by the formation of the groove portion on the outer peripheral surface of the field permanent magnet, and the heat generation amount of the rotor is suppressed. Therefore, heat generation of the rotor can be effectively suppressed as a whole.

When a through hole is provided in the rotor so as to penetrate therethrough in the axial direction as in the motor of the eleventh aspect, air is allowed to circulate in the through hole, and heat generated in the rotor is transferred from the inside. Can be cooled. In addition, if an external fan-shaped cooling fan is provided on the opposite side of the rotary shaft from the centrifugal fan, air can be forcibly blown into the motor frame toward the centrifugal fan side, so that cooling is further enhanced. The performance can be improved (claim 12).

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION

(1) First Embodiment Hereinafter, a first embodiment of the present invention (claims 1, 2, 3, 4,) will be described.
(Corresponding to 5 and 8) will be described with reference to FIGS. 1 and 2. In FIG. 1 showing the entire configuration, a motor frame 2
Bearing brackets 23 each having a bearing 22 mounted inside are provided in the center of both end faces of 1, respectively, one side of which is
In this case, on the left side of the drawing, intake ports 24 are formed intermittently along the circumferential direction at a portion near the outer circumference of the bearing bracket 23. The frame 21 has the intake port 24.
The exhaust port 25 is intermittently provided on the side opposite to the
Is provided.

A rib 26 projecting inward and extending in the axial direction is provided on the inner peripheral surface of the frame 21 at a central portion in the axial direction. A stator 27 is arranged on the inner peripheral portion of the rib 26. As a result, an air passage 28 is formed between the frame 21 and the stator 27.

The stator 27 is composed of an annular stator core 29 fitted to the ribs 26, and a stator coil 30 wound around the stator core 29. The coil end 30a of the stator coil 30 largely protrudes from the stator core 29 in the axial direction (the horizontal direction in FIG. 1). A rotor 31 is arranged inside the stator 27 so as to face the stator core 29 with a slight gap. The rotor 31 includes a rotating shaft 3 made of, for example, an iron material, which is supported by the bearings 22 and 22.
The rotor core 33 is provided on the outer circumference of the rotor core 2, and the field permanent magnet 34 is provided on the outer circumference of the rotor core 33. In this case, the field permanent magnet 34 is formed of a compound of rare earth metal, such as neodymium.

A centrifugal fan 35 is attached to the rotary shaft 32 at the inner peripheral portion of the coil end 30a of the stator coil 30 on the right side in FIG. The centrifugal fan 35 is made of a material having a higher thermal conductivity than the rotating shaft 32, for example, aluminum, and as shown in FIG. 2, a main plate 36 having a boss portion 36a fitted and fixed to the rotating shaft 32. On its surface (the surface on the side of the rotor core 33) is provided with a plurality of blades 37, in this case, nine blades 37 protruding at equal intervals.

At this time, the main plate 36 is not perpendicular to the axial direction, but is inclined from the boss portion 36a toward the outer peripheral side in the axial outer direction (right side in FIG. 1).
In this case, the main plate 36 is inclined so that a slight gap is generated between the virtual surface extending the outer periphery and the coil end 30a. Further, the nine blades 37 are inclined rearward from the boss portion 36a toward the outer periphery with respect to the rotation direction of the rotating shaft 32 (shown by an arrow A), and the outer peripheral side end portions 37a thereof are stators. It is formed so as to be substantially parallel to the inner peripheral side of the coil end 30a of the coil 30. As a result, the centrifugal fan 35 having the largest size is connected to the coil end 30a.
It is possible to attach it to the rotary shaft 32 so as to be located on the inner peripheral portion of the.

Next, the operation of the above configuration will be described. When the motor (stator coil 30) having the above configuration is energized,
A magnetic field is generated in the stator core 29, and as the magnetic field rotates, the rotor 31 rotates and the centrifugal fan 35 attached to the rotating shaft 32 rotates in the direction of arrow A. By the rotation of the centrifugal fan 35, the inner peripheral side of the surface of the centrifugal fan 35,
That is, the air in the inner peripheral portion of the coil end 30a on the right side in FIG. 1 is blown out to the outer peripheral side, and the air flows as shown by arrows B, C, and D in the frame 21.

At this time, a negative pressure is applied to the portion connected to the gap between the rotor 31 and the stator 27, and the air flowing into the space of the inner peripheral portion of the coil end 30a on the intake port 24 side as shown by the arrow C is the stator. It flows through the gap between 27 and the rotor 31. Then, together with the air flowing from the intake port 24 side in the ventilation passage 28,
Due to the blowing action of the centrifugal fan 35, the air is discharged from the exhaust port 25 to the outside as shown by the arrow D.

Further, since the main plate 36 of the centrifugal fan 35 is inclined outward in the axial direction from the boss portion 36a toward the outer circumference, the air blown by the centrifugal fan 35 is smoothly moved along the outer circumference of the coil end 30a. It comes to the exhaust port 25.

Here, heat is generated in the rotor 31 portion by generating an eddy current in the rotor core 29 and the field permanent magnet 34. In the present embodiment, however, the field permanent magnet 34 is a rare earth metal. There is a circumstance that the heat generation is relatively large due to the fact that it is a system. However, this heat is radiated satisfactorily by the air flowing through the gap between the rotor 31 and the stator 27. Moreover, since the centrifugal fan 35 has a larger thermal conductivity than the rotating shaft 32,
The heat generated in the rotor 31 portion and the heat generated in the bearing 22 portion are easily transmitted to the centrifugal fan 35 via the rotating shaft 32, and the centrifugal fan 35 can efficiently radiate heat.

Therefore, according to this embodiment, the centrifugal fan 3
5, the air circulates well in the gap between the rotor 31 and the stator 27. Therefore, even if the end fin cannot be formed in the rotor 31 or the heat generation of the permanent magnet 34 for field magnetism becomes large, Can be efficiently cooled.

Since the centrifugal fan 35 is provided at the inner peripheral portion of the coil end 30a, the centrifugal fan 35 can be compactly arranged in the portion that is originally the space portion, and FIG. Compared with the conventional one shown in
This can be done without increasing the axial length of the motor.

(2) Second to Seventh Embodiments FIG. 3 shows the second embodiment (corresponding to claim 6) of the present invention. The difference from the first embodiment is that the main plate 36 of the centrifugal fan 35 is different. A plurality of, for example, nine through holes 41 penetrating in the axial direction
Is provided. In this case, centrifugal fan 3
5, the air on the back surface side of the centrifugal fan 35 flows to the front surface side through the through hole 41 as indicated by an arrow E, so that an air flow is generated around the bearing 22 to cool the bearing 22 portion. Can be planned.

In this case, as in the third embodiment (corresponding to claim 7) shown in FIG. 4, the through hole 42 is inclined from the front surface side to the back surface side in the rotation direction of the centrifugal fan 35 shown by the arrow A. With such a configuration, as the centrifugal fan 35 rotates, the through holes 42 exhibit a blowing action due to the inclination thereof, so that the air inside the through holes 42 flows from the outer side toward the inner side in the axial direction. Therefore, the air around the bearing 22 is more likely to flow, and the cooling effect of the bearing 22 portion is improved.

Although not shown in the drawing, in the configuration of the first embodiment, a second centrifugal fan having the same shape as the centrifugal fan 35 is axially outside the centrifugal fan 35, and its blades face the bearing 22. It is also possible to provide it on the rotary shaft 32. In this case, the air around the bearing 22 is blown toward the exhaust port 25 by the second centrifugal fan.
The part can be cooled. Alternatively, blades may be added to the back surface of the main plate 36 of the centrifugal fan 35 in the first embodiment.

FIG. 5 shows a fourth embodiment (corresponding to claim 9) of the present invention, which is different from the first embodiment in that the back side, that is, the shaft is provided at the outer peripheral edge portion of the main plate 36 of the centrifugal fan 35. An annular protrusion 51 extending outward in the direction is formed integrally with the main plate 36. This makes it easier to adjust the balance (dynamic balance) of the rotor 31. That is, for example, in the case of the positive balance adjustment, the balance weight 52 is attached to the annular protrusion 5.
By mounting the balance weight 52 along the inner peripheral surface of the No. 1, centrifugal force can prevent the balance weight 52 from jumping out in the outer peripheral direction. Further, in the case of the negative balance adjustment, the annular projection 51 can be easily adjusted by scraping it off by an appropriate amount.

FIG. 6 shows a fifth embodiment (corresponding to claim 10) of the present invention. The difference from the first embodiment is that the outer peripheral surface of the rotor 31, that is, the permanent magnet 34 for field magnet is axially oriented. That is, there are formed a plurality of grooves 61 extending in the direction.
In this case, the rotation of the centrifugal fan 35 allows the air to flow in the groove 61 from the intake port 24 side toward the exhaust port 25 side, so that the cooling performance is improved and the rotor 31 and the stator 27 are cooled well. To be done.

Further, when the motor is driven, an eddy current is generated in the field permanent magnet 34, but the eddy current is generated in the area divided by each groove 61 and is subdivided and reduced. Therefore, the amount of heat generated by the field permanent magnet 34 is also reduced. Therefore, in combination with the improvement of the cooling performance described above, the heat generation of the field permanent magnet 34 can be further suppressed.

The groove 61 may be skewed. In this case, from the end surface of the rotor 31 on the intake port 24 side to the exhaust port 25
If it is skewed toward the end face on the side opposite to the rotation direction of the rotor 31 shown by the arrow A, air easily flows in the groove 61, and the heat radiation from the field permanent magnet 34 and the stator 27 is efficiently performed. Well done.

FIG. 7 shows a sixth embodiment of the present invention (corresponding to claim 11). In this embodiment, the inside of the rotor 31 is
In this case, a plurality of through holes 71 penetrating in the axial direction are provided inside the rotor core 33. As a result, the rotation of the centrifugal fan 35 causes the air to flow through the through hole 71 from the intake port 24 side toward the exhaust port 25 side, so that heat is exchanged between the air and the rotor core 33, and the rotor core 33 is heat-exchanged. 33 (rotor 31) can be cooled from the inside.

The through hole 71 is also formed in the groove 6 described above.
Skew may be performed in the same manner as in No. 1, and in this case as well, the groove 61
It is possible to obtain the same operation and effect as when tilting. The through hole 71 may be provided at the boundary between the rotor core 33 and the field permanent magnet 34, or may be provided at the boundary between the rotor core 33 and the rotary shaft 32.

FIG. 8 shows a seventh embodiment (corresponding to claim 12) of the present invention. In this embodiment, an outer fan-shaped cooling is provided on the rotation shaft 32 of the rotor 31 on the opposite side of the centrifugal fan 35. A fan 81 is provided. That is, in addition to the configuration of the first embodiment, the fan casing 82 is provided on the outer surface of the end surface of the frame 21 on the intake port 24 side so that it projects outward from the end surface of the frame 21 on the intake port 24 side. A cooling fan 81 is fixed to the end of the provided rotary shaft 32 so as to be located inside the fan casing 82.
It is adapted to rotate integrally with the rotary shaft 32.

When the cooling fan 81 rotates as the rotor 31 rotates, the air outside the frame 21 is blown to the cooling fan 81 and forcedly flows into the frame 21 from the intake port 24. Become. Then, a part of this air flows into the ventilation passage 28 and is discharged from the exhaust port 25 to the outside of the frame 21, and a part of the remaining air flows into the space of the inner peripheral portion of the coil end 30 a of the stator coil 30. . On the other hand, in the frame 21, as the centrifugal fan 35 provided on the exhaust port 25 side rotates, the air in the space at the inner peripheral portion of the coil end 30a on the intake port 24 side moves to the stator 27. The gas flows from the intake port 24 side to the exhaust port 25 side through the gap between the rotor 31 and
5 is discharged to the outside of the frame 21.

Therefore, the cooling fan 81 and the centrifugal fan 3
As a result, the amount of air flowing through the frame 21 increases due to the action with the motor 5, and as a result, heat is efficiently exchanged in each part of the motor, so that the cooling performance of the motor is further improved.

[0045]

As is apparent from the above description, according to the motor of the present invention, the eddy current is generated in the field permanent magnet by forming the rotor with the field permanent magnet on the outer periphery of the rotor core. Even if there is a situation in which the temperature easily increases, the centrifugal fan allows cooling air to flow in the gap between the rotor and the stator, so that the rotor can be cooled.

When the centrifugal fan is provided on the rotating shaft of the rotor so as to be located on the inner peripheral portion of the coil end of the stator coil as in the motor of claim 2, the axial length of the motor is increased. Instead, the cooling air can be made to flow in the gap between the rotor and the stator, and the excellent practical effect of improving the cooling performance can be achieved.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional side view of an entire configuration showing a first embodiment of the present invention.

2A is a front view of a centrifugal fan, and FIG. 2B is a vertical cross-sectional side view of the centrifugal fan.

FIG. 3 is an enlarged vertical sectional side view of a centrifugal fan portion showing a second embodiment.

FIG. 4 is a partially enlarged front view of a centrifugal fan showing a third embodiment.

FIG. 5 is a view corresponding to FIG. 2B showing a fourth embodiment.

FIG. 6 is a side view of a rotor portion showing a fifth embodiment.

FIG. 7 is a vertical sectional side view of a rotor portion showing a sixth embodiment.

FIG. 8 is a view corresponding to FIG. 1 showing a seventh embodiment.

FIG. 9 is a diagram corresponding to FIG. 1 showing a conventional example.

FIG. 10 is a view corresponding to FIG. 1 showing another conventional example.

FIG. 11 is a view showing another conventional example and showing a circulation pattern of air in a frame.

[Explanation of symbols]

In the figure, 27 is a stator, 30 is a stator coil, and 30a.
Is a coil end, 31 is a rotor, 32 is a rotating shaft, 33 is a rotor core, 34 is a permanent magnet for field, 35 is a centrifugal fan, 36 is a main plate, 37 is a blade, 37a is an outer peripheral side end portion, 4
1, 42 are through holes, 51 is an annular protrusion, 61 is a groove, 71 is a through hole, and 81 is a cooling fan.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroki Ito 2-3-10 Nanishi, Nishi-ku, Nagoya-shi, Aichi Toshiba A ・ VEE Co., Ltd. Nagoya Office (72) Inventor Isao Kishimoto Hole in Seto City, Aichi Prefecture 991 Tamachi, Toshiba Aichi factory

Claims (12)

[Claims] 1. A stator comprising a stator coil wound thereon, and a rotor having a permanent magnet for a field arranged inside the stator with a slight air gap between the stator and the rotating shaft of the rotor. A motor characterized in that a centrifugal fan is provided near the permanent magnet for field magnet. 2. The motor according to claim 1, wherein the centrifugal fan is located on the inner circumference of the coil end of the stator coil. 3. The motor according to claim 2, wherein the field permanent magnet is made of a rare earth metal-based material. 4. The motor according to claim 1, wherein an outer peripheral side end of the centrifugal fan blade is substantially parallel to an inner peripheral side of a coil end of the stator coil. 5. The motor according to claim 1, wherein the main plate of the centrifugal fan is inclined outward in the axial direction from the inner peripheral side toward the outer peripheral side. 6. The motor according to claim 1, wherein the main plate of the centrifugal fan is provided with a plurality of through holes penetrating in the axial direction. 7. The through hole provided in the main plate of the centrifugal fan,
The motor according to claim 6, wherein the motor is inclined from the inner side to the outer side in the axial direction in the rotation direction of the centrifugal fan. 8. The motor according to claim 1, wherein the centrifugal fan is made of a material having a thermal conductivity higher than that of the rotating shaft of the rotor. 9. The motor according to claim 1, wherein an outer peripheral edge portion of the main plate of the centrifugal fan is provided with an annular projection extending outward in the axial direction. 10. The motor according to claim 1, wherein an outer peripheral surface of the rotor is provided with a groove extending in the axial direction. 11. The motor according to claim 1, wherein a plurality of through holes penetrating in the axial direction are provided inside the rotor. 12. The motor according to claim 1, further comprising an outer fan-shaped cooling fan provided on the opposite side of the rotary shaft of the rotor from the centrifugal fan.