External rotor motors and their power tools

Abstract

This invention discloses an external rotor motor, comprising an axially extending shaft, an external rotor assembly connected to the shaft, and an inner stator assembly located between the shaft and the external rotor assembly. The external rotor assembly includes a housing fixed to the shaft, and the inner stator assembly includes a stator core housed within the housing and a bracket supporting the stator core. The shaft passes through the stator core, and one axial end of the shaft is supported by the bracket. The housing has an annular sidewall located on the outer side of the housing and an end wall connected to the annular sidewall. The end wall is fixed to the shaft, and the annular sidewall has several cold-extruded blades, which can improve the heat dissipation effect of the external rotor motor.

Description

[Technical Field]

[0001] This invention relates to the field of motor technology, and in particular to an external rotor motor and the power tool thereof. [Background Technology]

[0002] Traditional garden tool external rotor motors use an axial fan added to the motor axis for axial cooling, or a centrifugal fan added to one side of the rotor for radial cooling. Both cooling methods operate on the same principle: as the motor rotor rotates, the fan rotates as well, and airflow is directed from the other side of the motor towards the fan side.

[0003] The enameled wire, as the main heat-generating component during motor operation, experiences a relatively high temperature rise, along with the entire stator core. However, due to the high slot fill factor designed for motors, there is essentially little space within the stator core slots after the winding, making it difficult for cooling airflow to reach the fan side from the other side. Simultaneously, because the stator core and windings are very close to the rotor magnets, some heat is conducted to the rotor magnets. However, since the rotor magnets are largely not involved in the overall cooling system, their temperature rise is quite high. The neodymium iron boron magnets used in existing motors exhibit demagnetization at high temperatures, significantly impacting the matching between the motor and the electronic control system, as well as the motor's performance. Therefore, the cooling effect of traditional fan structures is limited.

[0004] Therefore, it is indeed necessary to provide an improved external rotor motor and its power tool to overcome the shortcomings of the prior art. [Summary of the Invention]

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide an external rotor motor and its power tool that can improve the heat dissipation effect of the motor.

[0006] The present invention solves the problems of the prior art by adopting the following technical solution: an external rotor motor, including a rotating shaft extending along the axial direction, an external rotor assembly connected to the rotating shaft, and an inner stator assembly located between the rotating shaft and the external rotor assembly. The external rotor assembly includes a housing fixed on the rotating shaft. The inner stator assembly includes a stator core housed in the housing and a bracket supporting the stator core. The rotating shaft passes through the stator core and one axial end of the rotating shaft is supported by the bracket.

[0007] A further improvement is as follows: the housing has an annular sidewall located on the outside of the housing and an end wall connected to the annular sidewall. The end wall is fixed on the rotating shaft. The annular sidewall is cold-extruded and includes grooves evenly distributed circumferentially and several cold-extruded blades located between the grooves. The blades include an arc-shaped blade surface adjacent to the grooves.

[0008] A further improvement is as follows: the outer rotor assembly includes a magnet frame and several magnets that are attached to the inner wall of the annular sidewall. The magnet frame abuts against the end wall and fixes the magnets. The magnets are evenly distributed circumferentially on the inner wall of the blade.

[0009] A further improvement is as follows: the magnet has a circumferential length a1, the blade has a first circumferential length b1 and a second circumferential length b2, the first circumferential length b1 is less than the second circumferential length b2, and the circumferential length a1 of the magnet is less than or equal to the first circumferential length b1.

[0010] A further improvement is as follows: The circumferential surface of the shell has a center c1. Starting from the center c1, an arbitrary center line c2 of the magnet is drawn on the magnet. Then, a tangent line c3 is drawn perpendicularly along the outer wall of the magnet on the center line c2. The tangent line c3 is still on the circumferential surface of the shell. The first circumferential length b1 has a first endpoint b11 and a second endpoint b12. The second circumferential length b2 has a third endpoint b21 and a fourth endpoint b22. The first endpoint b11 is adjacent to the third endpoint b21, and the second endpoint b12 is adjacent to the fourth endpoint b22. The first endpoint b11 and the third endpoint b21 are connected to obtain a straight line c4. The angle between the tangent line c3 and the straight line c4 is between 15 degrees and 49 degrees.

[0011] A further improvement is that the end wall includes an opening that connects the interior and exterior of the housing.

[0012] A further improvement is as follows: the inner stator assembly includes insulating end plates installed at both ends of the stator core and windings wound on the insulating end plates, wherein the insulating end plates insulate and separate the windings from the stator core.

[0013] A further improvement is that the inner stator assembly further includes a first bearing housed within the housing, and the rotating shaft is supported on the end wall by the first bearing.

[0014] A further improvement is as follows: the inner stator assembly further includes a second bearing and a retaining ring located within the bracket, the rotating shaft is supported on the bracket by the second bearing, and the retaining ring fixes the second bearing within the bracket.

[0015] A further improvement is that the inner stator assembly also includes screws and a pressure plate, with the pressure plate being fixedly connected to the bracket by the screws.

[0016] A further improvement is that the power tool includes any one of the external rotor motors described in the above improvement schemes.

[0017] Compared with the prior art, this application has one or more of the following beneficial effects:

[0018] 1. The annular sidewall is cold-extruded and includes grooves evenly distributed circumferentially and several cold-extruded blades located between the grooves. The blades include arc-shaped blade surfaces adjacent to the grooves. Compared with the stamping process of traditional axial fans, this invention uses cold extrusion molding, which is simpler. 2. Making the housing into a fan shape can not only meet the original performance and ensure the magnet is attached, but also greatly reduce the temperature rise of the motor and improve the heat dissipation effect of the external rotor motor.

[0019] 3. By making the housing into a fan shape, the original fan weight is eliminated, reducing the overall weight of the external rotor motor and lowering the cost of the motor. Reducing the position of the fan in the axial direction also makes the external rotor motor smaller, which is conducive to the current market pursuit of lightweight and small size.

[0020] 4. When the circumferential length a1 of the magnet is less than or equal to the first circumferential length b1, the magnet is in the airflow path, and the heat of the magnet will be carried away by the airflow, which reduces the overall temperature of the external rotor motor and improves the heat dissipation effect. Under the same conditions, compared with the condition that the circumferential length a1 of the magnet is not limited to be less than or equal to the first circumferential length b1, the temperature rise can be reduced by 20%.

[0021] 5. The angle between the tangent c3 and the straight line c4 is between 15 degrees and 49 degrees. At this angle, the heat dissipation effect can be improved by more than 25% compared to outside this angle range, and the heat dissipation effect is optimal. [Attached Image Description]

[0022] The specific embodiments of this application will be described in further detail below with reference to the accompanying drawings:

[0023] Figure 1 This is a three-dimensional schematic diagram of the external rotor motor in a preferred embodiment of the present invention;

[0024] Figure 2 yes Figure 1 The exploded view of the external rotor motor shown;

[0025] Figure 3 yes Figure 2 A three-dimensional schematic diagram of the housing in an external rotor motor is shown.

[0026] Figure 4 yes Figure 2 A three-dimensional schematic diagram of the housing, magnets, and magnet frame assembly in an external rotor motor;

[0027] Figure 5 yes Figure 4 A cross-sectional view of the combination shown;

[0028] Figure 6 yes Figure 5 A magnified view of part A in the combination shown.

[0029] Meaning of the reference numerals in the diagram:

[0030] 100, External rotor motor; 10, Rotary shaft; 20, External rotor assembly

[0031] 21. Shell 211, Annular sidewall 2111, Blade

[0032] 2112, Groove 21111, Arc-shaped blade surface 212, End wall

[0033] 2121, Opening; 22, Magnetic frame; 23, Magnetic steel.

[0034] 30. Inner stator assembly; 31. Stator core; 32. Bracket

[0035] 33. Insulating end plate; 34. Winding; 35. First bearing

[0036] 36. Second bearing; 37. Retaining ring; 38. Screw

[0037] 39. Pressure plate a1, circumferential length a11, fifth end point

[0038] a12, sixth endpoint b1, first circumferential length b11, first endpoint

[0039] b12, second endpoint b2, second circumferential length b21, third endpoint

[0040] b22, fourth endpoint c1, center c2, center line

[0041] c3, tangent c4, straight line

Detailed Implementation Methods

[0042] The technical solutions of this application will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0043] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0044] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0045] Please see Figures 1 to 2 As shown, an embodiment of this application relates to an external rotor motor 100, including an axially extending shaft 10, an external rotor assembly 20 connected to the shaft, and an inner stator assembly 30 located between the shaft and the external rotor assembly. The external rotor assembly 20 includes a housing 21 fixed to the shaft. The inner stator assembly 30 includes a stator core 31 housed within the housing 21 and a bracket 32 ​​supporting the stator core 31. The shaft 10 passes through the stator core 31, and one axial end of the shaft 10 is supported by the bracket 32. The external rotor assembly 20 is fixed to the shaft 10, and the shaft 10 rotates relative to the inner stator assembly 30 as the external rotor assembly 20 rotates.

[0046] Please see Figure 3 As shown, the housing 21 has an annular sidewall 211 located on the outer side of the housing 21 and an end wall 212 connected to the annular sidewall 211. The end wall 212 is fixed to the rotating shaft 10. The end wall 212 includes an opening 2121, which connects the interior and exterior of the housing. The annular sidewall 211 is cold-extruded and includes grooves 2112 evenly distributed circumferentially and several cold-extruded blades 2111 located between the grooves 2112. The blades 2111 include an arc-shaped blade surface 21111 adjacent to the grooves 2112. The traditional process for making axial flow fans is stamping, while the present invention uses cold extrusion molding, which is a simpler process.

[0047] Traditional external rotor motors use axial fans for heat dissipation, allowing airflow to pass through the stator core and enameled wire from one end to the fan end, achieving a cooling effect. However, due to the relatively small wire slots of the motor itself, coupled with the high fill factor of the winding slots and the problem of enamel dripping, the actual heat dissipation from one side to the other is limited. As a comparison, the inventors found through experiments that the temperature rise of a traditional motor during normal operation is 120K.

[0048] In an embodiment of this invention, the inventors made the housing into a fan shape, which satisfies the original performance requirements and ensures the adhesion of the magnets. Slots were then cut into the remaining parts. In principle, because the housing is shaped like blades, the slotted portion is very close to the stator core and enameled wire, greatly improving heat dissipation efficiency. Furthermore, it is no longer limited by the high slot fill factor. Simultaneously, the airflow path passes beside the magnets, which also participate in the heat dissipation system and become a major part of the heat dissipation, resulting in significant optimization of temperature rise. Through experiments, the inventors found that the motor temperature rise during normal operation is 80K, greatly reducing the temperature rise and improving the heat dissipation effect of the external rotor motor.

[0049] In addition, by making the fan out of the casing, the original fan weight is eliminated, the overall weight of the external rotor motor is reduced, and the cost of the motor is lowered. Reducing the position of the fan in the axial direction also makes the motor smaller, which is conducive to the current market pursuit of lightweight and small size.

[0050] Please see Figure 2 and Figure 3 As shown, the inner stator assembly 30 includes insulating end plates 33 installed at both ends of the stator core 31 and windings 34 wound on the insulating end plates 33. The insulating end plates 33 insulate and separate the windings 34 from the stator core 31.

[0051] The winding 34 may further include a coil and an adhesive integrally formed on the coil. The adhesive is preferably epoxy resin. Epoxy resin contains various polar groups and highly reactive epoxy groups, thus exhibiting strong adhesion to materials with high surface activity. Simultaneously, the cohesive strength of the cured epoxy is also very high, resulting in high adhesive strength. Furthermore, epoxy resin produces virtually no low-molecular-weight volatiles during curing, exhibits low volume shrinkage, and possesses good corrosion resistance and dielectric properties, making it a preferred choice for integral molding with the coil. Of course, adhesives can be, but are not limited to, acrylic resins, polyurethane, phenolic resins, and other resins with similar properties. In the external rotor motor of this application, the winding is three-phase and is formed by winding multiple strands of enameled wire or copper strips into a cylindrical, slotless structure.

[0052] Furthermore, the inner stator assembly also includes a first bearing 35 housed within the housing 21, through which the shaft 10 is supported on the end wall 212. The inner stator assembly also includes a second bearing 36 and a retaining ring 37 located within the bracket, with the shaft supported on the bracket 32 ​​via the second bearing, and the retaining ring securing the second bearing within the bracket 32. The inner stator assembly also includes screws 38 and a pressure plate 39, the pressure plate being securely connected to the bracket via the screws.

[0053] Please see Figure 4As shown, in a preferred embodiment of the present invention, the outer rotor assembly 20 includes a magnet frame 22 and several magnets 23 that are attached to the inner wall of the annular sidewall 211. The magnet frame 22 abuts against the end wall 212 and fixes the magnets 23. The magnets 23 are evenly distributed circumferentially on the inner wall of the blade 2111. All the magnets are tightly attached to the housing, ensuring high bonding strength.

[0054] Please see Figures 5 to 6 As shown, the magnet 23 has a circumferential length a1, and the blade 2111 has a first circumferential length b1 and a second circumferential length b2. The first circumferential length b1 is smaller than the second circumferential length b2. The circumferential length a1 of the magnet 23 is less than or equal to the first circumferential length b1. At this time, the magnet 23 is in the airflow path, and the heat of the magnet 23 will be carried away by the wind, reducing the overall temperature of the external rotor motor and improving the heat dissipation effect. Under the same conditions, compared with the condition that the circumferential length a1 of the magnet 23 is not limited to be less than or equal to the first circumferential length b1, the temperature rise can be reduced by 20%.

[0055] In addition, the magnet 23 has a tile-like structure and is made of neodymium iron boron material. Of course, the structure of the magnet 23 is not limited here. As long as the magnet satisfies that its circumferential length a1 is less than or equal to the first circumferential length b1, the magnet material is not limited to neodymium iron boron material. As long as this effect is achieved, it can be selected.

[0056] Please see Figure 5 and Figure 6 As shown, Figure 6 for Figure 5In the enlarged view of part A, we can see that the circumferential surface of the housing 21 has a center c1. Starting from the center c1, an arbitrary center line c2 is drawn on the magnet 23. Then, a tangent line c3 is drawn perpendicularly to the outer wall of the magnet along the center line c2, perpendicular to the center line c2, and the tangent line c3 is still on the circumferential surface of the housing 21. The circumferential length a1 has a fifth endpoint a11 and a sixth endpoint a12; the first circumferential length b1 has a first endpoint b11 and a second endpoint b12; and the second circumferential length b2 has a third endpoint b21 and a fourth endpoint b22. The first endpoint b11 is adjacent to the third endpoint b21, and the second endpoint b12 is adjacent to the fourth endpoint b22. Connecting the second endpoint b12 and the fourth endpoint b22 and extending them to obtain a straight line c4, the angle between the tangent c3 and the straight line c4 is between 15 degrees and 49 degrees. At this angle range, the heat dissipation effect can improve the temperature rise by more than 25%, and the heat dissipation effect is optimal. If the angle is too small, such as less than 15 degrees, the airflow will be blocked too much by the inner wall of the casing, resulting in a large loss of airflow efficiency. If the angle is too large, such as more than 49 degrees or even close to the angle of the parallel magnet, the effective path is too short and the airflow is limited, resulting in poor heat dissipation effect.

[0057] See Table 1 below for the experimental results of testing a conventional motor and the external rotor motor of this application. It can be seen that when the conventional motor (motor axial length is 124mm) is working, the motor temperature rises by 120K and the cost decreases to 0. However, the motor using the structure of this application has a motor temperature rise of 80K, a cost reduction of 2%, and the axial length can be reduced to 114mm in the original structure of the conventional motor.

[0058] Experimental results Traditional motor The motor in this application Motor temperature rise / K 120 80 Cost reduction / % 0 2 Axial length / mm 124 114

[0059] Table 1

[0060] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0061] Although embodiments of this application have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the claims and their equivalents.

Claims

1. An outer rotor motor comprising an axle extending in an axial direction, an outer rotor assembly connected to the axle, and an inner stator assembly located between the axle and the outer rotor assembly, the outer rotor assembly comprising a housing fixed to the axle, the inner stator assembly comprising a stator core accommodated in the housing and a support supporting the stator core, the axle penetrating the stator core and an axial end of the axle being supported by the support; characterized in that: The shell is provided with an annular side wall outside the shell and an end wall connected to the annular side wall, the end wall is fixed on the rotating shaft, the annular side wall is cold extruded and formed, and includes grooves uniformly distributed in the circumferential direction and a plurality of blades between the grooves, the blades include arc blade surfaces adjacent to the grooves; the outer rotor assembly further includes a magnetic steel frame and a plurality of magnetic steels fitted to the inner wall of the annular side wall, the magnetic steel frame abuts against the end wall and fixes the magnetic steels, and the magnetic steels are uniformly distributed in the circumferential direction on the inner wall of the blades.

2. An external rotor electric machine according to claim 1, characterized in that: The magnetic steel has a circumferential length a1, the blade has a first circumferential length b1 and a second circumferential length b2, the first circumferential length b1 is smaller than the second circumferential length b2, and the circumferential length a1 of the magnetic steel is smaller than or equal to the first circumferential length b1.

3. An external rotor electric machine according to claim 2, characterized in that: The circumferential surface of the shell has a center c1, a center line c2 of any one of the magnetic steels is drawn from the center c1 on the magnetic steel, then a tangent c3 is drawn vertically on the outer wall of the magnetic steel on the center line c2, and the tangent c3 is still on the circumferential surface of the shell; the first circumferential length b1 has a first end point b11 and a second end point b12, the second circumferential length b2 has a third end point b21 and a fourth end point b22, the first end point b11 is adjacent to the third end point b21, and the second end point b12 is adjacent to the fourth end point b22, a straight line c4 is obtained by connecting and extending the second end point b12 and the fourth end point b22, and the included angle between the tangent c3 and the straight line c4 is between 15 degrees and 49 degrees.

4. The external rotor electric machine of claim 1, wherein: The end wall includes an opening, and the opening communicates the inside of the shell with the outside.

5. The external rotor electric machine of claim 1, wherein: The inner stator assembly includes insulating end plates mounted at both ends of the stator core and windings wound on the insulating end plates, and the insulating end plates insulate and separate the windings and the stator core.

6. The external rotor electric machine of claim 1, wherein: The inner stator assembly further includes a first bearing accommodated in the shell, and the rotating shaft is supported on the end wall through the first bearing.

7. An external rotor electric machine according to claim 6, characterized in that: The inner stator assembly further includes a second bearing and a retainer ring in the bracket, the rotating shaft is supported on the bracket through the second bearing, and the retainer ring fixes the second bearing in the bracket.

8. An external rotor electric motor as claimed in claim 6, characterised in that: The inner stator assembly further includes a screw and a pressing plate, and the pressing plate is fixedly connected to the bracket through the screw.

9. A power tool characterized by: The electric tool includes the outer rotor motor according to any one of claims 1-8.

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