CN114389396A

CN114389396A - Brushless motor

Info

Publication number: CN114389396A
Application number: CN202111539620.9A
Authority: CN
Inventors: 付鑫; 王海军; 杨晓辉; 王洪磊; 孟繁悦; 吴太晖
Original assignee: General Coal Research Institute Co Ltd
Current assignee: General Coal Research Institute Co Ltd
Priority date: 2021-12-15
Filing date: 2021-12-15
Publication date: 2022-04-22

Abstract

The present invention provides a brushless motor, comprising: casing, stator module, rotor subassembly and first heat conduction spare, stator module is located the casing and links to each other with the casing, and the rotor subassembly cooperatees with stator module, and the rotor subassembly rotationally links to each other with the casing, and at least part of rotor subassembly is located the casing, and first heat conduction spare links to each other with casing and stator module respectively to be used for the heat transfer to the external world with stator module production. The first heat-conducting piece absorbs heat generated in the operation of the stator assembly, the first heat-conducting piece transfers the absorbed heat to the machine shell, and finally the machine shell transfers the heat to the external environment. Through first heat-conducting piece and casing with the inside heat transfer of motor to the external world, avoided the heat at the inside accumulation of motor, the casing is sealed with the subassembly, avoids the inside motor that leads to with the external environment contact problem by pollutions such as dust, greasy dirt, also makes the motor can use in extreme environment such as pit, has expanded the use scene of motor.

Description

Brushless motor

Technical Field

The invention relates to the technical field of motors, in particular to a brushless motor.

Background

With the breakthrough of artificial intelligence technology, higher demands are put on the intelligent operation and unmanned operation of underground equipment. The robot technology is used as a physical execution terminal of an intelligent mine, wherein a motor-based driver technology is one of key technologies of the robot. The outer rotor brushless motor is widely applied to different types of robot platforms, but the problems of dust, accumulated water and other external factor pollution and the safe heat dissipation of the motor exist in the underground working environment, and higher requirements are provided for the structural design of the outer rotor brushless motor.

In the related art, the open-shell motor has a low heat dissipation effect under a static condition or when air convection is poor, and the inside of the motor is easily polluted due to the design of the open-shell motor. The air-cooled heat dissipation motor solves the problem that the passive heat dissipation efficiency of an open shell type motor is low, but the problem that the interior of the motor is polluted can be brought. The water-cooling heat dissipation motor has a good heat dissipation effect and avoids the problem that the interior of the motor is polluted, but a heat dissipation system formed by a pipeline, a water pump and an external heat radiator is large in size, not only occupies the internal space of the motor, but also increases the weight of the motor.

Disclosure of Invention

The present invention is based on the discovery and recognition by the inventors of the following facts and problems:

among the correlation technique, open shell type motor realizes stator winding's heat dissipation through the air convection of external environment and motor inside, and the radiating efficiency is low and lead to the inside quilt of motor to pollute easily, still can't use in the scene that needs carry out sealed design to the motor, has great limitation. Air-cooled heat dissipation motor uses the fan to accelerate the circulation of air with the external world in the motor, but can bring the inside pollution problem of motor and can't apply under the sealed scene equally. The water-cooling heat dissipation motor exchanges liquid serving as a heat carrier inside and outside the motor through a pipeline, but a complex conduit water pump system is needed, so that the cost, the mechanism complexity and the weight of the motor are increased.

The present invention is directed to solving, at least to some extent, one of the technical problems in the related art.

Therefore, the embodiment of the invention provides a brushless motor, which has a good heat dissipation effect under the premise of sealing the interior of the motor, and the heat dissipation design part occupies a small space in the motor and has low cost.

The brushless motor of the embodiment of the invention comprises: the heat-conducting device comprises a machine shell, a stator assembly, a rotor assembly and a first heat-conducting piece, wherein the stator assembly is positioned in the machine shell and is connected with the machine shell, the rotor assembly is matched with the stator assembly, the rotor assembly is rotatably connected with the machine shell, at least part of the rotor assembly is positioned in the machine shell, and the first heat-conducting piece is respectively connected with the machine shell and the stator assembly and is used for transferring heat generated by the stator assembly to the outside.

According to the brushless motor provided by the embodiment of the invention, the first heat conducting piece absorbs heat generated in the operation of the stator assembly, the first heat conducting piece transfers the absorbed heat to the machine shell, and finally the machine shell transfers the heat to the external environment. The heat inside the motor is transferred to the outside through the first heat conducting piece and the shell, so that the heat accumulation inside the motor is avoided, and the heat dissipation of the motor is realized. And the casing seals the subassembly, avoids the inside problem by pollution such as dust, greasy dirt of motor that leads to with the external environment contact of motor inside, also makes the motor can use in extreme environment such as pit, has expanded the use scene of motor.

Therefore, the brushless motor of the embodiment of the invention solves the heat dissipation problem of the motor in a sealed scene, and expands the use scene of the motor.

In some embodiments, the casing includes a first casing cover, a second casing cover, and a barrel-shaped member with openings at two ends, the first casing cover and the second casing cover are respectively located at the openings of the barrel-shaped member, and the first casing cover, the barrel-shaped member, and the second casing cover are sequentially connected to form the generally cylindrical casing.

In some embodiments, the first heat-conducting member is located between the second housing cover and the stator assembly, and the first heat-conducting member is a heat-conducting plate or a heat-conducting pipe.

In some embodiments, the first heat-conducting member is a heat-conducting plate, a surface of the heat-conducting plate away from the second housing cover is in contact with the stator assembly, and a surface of the heat-conducting plate close to the second housing cover is attached to a surface of the second housing cover close to the heat-conducting plate.

In some embodiments, the stator assembly includes a plurality of stator coil windings arranged in a ring shape, and a gap is formed between adjacent stator coil windings, and the brushless motor further includes a second heat-conducting member in contact with the first heat-conducting member, and at least a part of the second heat-conducting member is filled in the gap.

In some embodiments, the second heat-conducting member is positioned between the first heat-conducting member and the stator assembly, a first major surface of the second heat-conducting member is in contact with an end of the stator coil winding adjacent the second heat-conducting member, and a second major surface of the second heat-conducting member is in contact with the first heat-conducting member.

In some embodiments, the first major surface of the second heat conducting member is a flat surface or a curved surface matching the shape of the surface of the stator assembly on the side adjacent to the second heat conducting member.

In some embodiments, the second thermally conductive member is a thermally conductive gel.

In some embodiments, the first housing cover defines a central through-hole, and the rotor assembly includes a sleeve fitted in the central through-hole.

In some embodiments, the enclosure is a ferrous alloy enclosure.

Drawings

Fig. 1 is a schematic view of a brushless motor according to an embodiment of the present invention.

Fig. 2 is an exploded schematic view of a brushless motor according to an embodiment of the present invention.

Fig. 3 is a schematic view of a stator assembly of a brushless motor according to an embodiment of the present invention before being filled with a thermally conductive gel.

Fig. 4 is a first schematic view of a stator assembly of a brushless motor of an embodiment of the present invention after filling with a thermally conductive gel.

Fig. 5 is a second schematic view of a stator assembly of a brushless motor of an embodiment of the invention after filling with a thermally conductive gel.

Reference numerals:

the machine shell 1, a first shell cover 101, a central through hole 1011, a barrel-shaped part 102, a second shell cover 103, a first annular part 1031 and a second annular part 1032;

stator assembly 2, stator coil winding 201, air gap 2011;

the rotor assembly 3, the surrounding part 301, the connecting part 302 and the shaft sleeve 3021;

a first heat-conductive member 4;

a second heat-conducting member 5.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.

A brushless motor according to an embodiment of the present invention will be described below with reference to the accompanying drawings.

As shown in fig. 1 and 2, a brushless motor according to an embodiment of the present invention includes: casing 1, stator module 2, rotor subassembly 3 and first heat conduction piece 4, stator module 2 is located casing 1 and links to each other with casing 1, rotor subassembly 3 cooperatees with stator module 2, rotor subassembly 3 rotationally links to each other with casing 1, rotor subassembly 3 at least part is located casing 1, first heat conduction piece 4 links to each other with casing 1 and stator module 2 respectively to a heat transfer to the external world that is used for producing stator module 2.

It should be understood that the cooperating parts of the rotor assembly 3 and the stator assembly 2 are located in the casing 1, and the rotor assembly 3 and the casing 1 are rotatably connected, and both together form a seal. In other words, the casing 1 seals the rotor assembly 3, the first heat conducting member 4 and the part of the rotor assembly 3 cooperating with the rotor assembly 3, so as to avoid the contact between the inside of the motor and the external environment, and prevent the pollutants from entering the inside of the motor and affecting the operation of the motor.

The casing 1 also protects the external environment, for example, in extreme environments such as an underground scene with methane, and prevents the external environment from exploding due to factors such as static electricity inside the motor. The problem of brushless motor need be in the use under sealed prerequisite is solved, expand the use scene of motor, improve the multi-adaptability of motor.

Alternatively, as shown in fig. 2, the stator assembly 2 is fixedly mounted to the casing 1. The rotor assembly 3 includes a surrounding portion 301 and a connecting portion 302, the upper end of the surrounding portion 301 is connected to the connecting portion 302, and the connecting portion 302 is rotatably mounted on the casing 1. The connecting part 302 hermetically penetrates the casing 1 and is arranged outside the casing 1, the upper end of the connecting part 302 is arranged outside the casing 1, and the lower end of the connecting part 302 is arranged inside the casing 1. The surrounding portion 301 is sleeved on the periphery of the stator assembly 2, so that the rotor assembly 3 and the stator assembly 2 are used in cooperation.

Further, as shown in fig. 2, the stator assembly 2 is located above the first heat conducting member 4, the stator assembly 2 is indirectly contacted with the upper end of the first heat conducting member 4, and the lower end of the first heat conducting member 4 is directly contacted with the casing 1. The first heat-conducting piece 4 absorbs heat generated by the operation of the stator assembly 2, the first heat-conducting piece 4 transfers the absorbed heat to the machine shell 1 through the contact with the machine shell 1, and the machine shell 1 transfers the heat transferred by the first heat-conducting piece 4 to the external environment.

Therefore, the first heat conducting member 4 and the housing 1 form a heat dissipation structure, and the heat inside the motor is transferred to the outside under the sealing condition of the brushless motor according to the embodiment of the present invention, so as to prevent the motor from being overheated due to the accumulation of heat inside the motor, thereby affecting the use of the motor and indirectly enhancing the working performance of the motor.

According to the brushless motor provided by the embodiment of the invention, the first heat-conducting piece 4 absorbs heat generated in the operation of the stator assembly 2, the first heat-conducting piece 4 transfers the absorbed heat to the machine shell 1, and finally the machine shell 1 transfers the heat to the external environment. The heat inside the motor is transferred to the outside through the first heat conducting piece 4 and the shell 1, so that the accumulation of the heat inside the motor is avoided, and the heat dissipation of the motor is realized. And the casing 1 seals the subassembly, avoids the inside problem of being polluted by dust, greasy dirt etc. of motor that leads to with the contact of external environment in the motor, also makes the motor can use in extreme environment such as pit, has expanded the use scene of motor.

In some embodiments, as shown in fig. 2, the housing 1 includes a first housing 101, a second housing 103, and a barrel 102 with two open ends, the first housing 101 and the second housing 103 are respectively located at the open ends of the barrel 102, and the first housing 101, the barrel 102, and the second housing 103 are connected in sequence to form the substantially cylindrical housing 1.

Alternatively, as shown in fig. 2, the barrel 102 is open at both ends and cylindrical, and the opening of the barrel 102 is circular. The first cover 101 is fitted to an opening at the upper end of the tub 102, and the first cover 101 is located at the opening at the upper end of the tub 102 and is coupled to the tub 102. The second cover 103 is fitted to an opening at the lower end of the barrel 102, and the second cover 103 is attached to the barrel 102 at the opening at the lower end of the barrel 102.

Further, as shown in fig. 1 and 2, the second housing cover 103 is provided with a first ring member 1031 and a second ring member 1032 positioned in the barrel member 102, the first ring member 1031 has an inner diameter and an outer diameter larger than those of the second ring member 1032, and a central axis of the first ring member 1031, a central axis of the second ring member 1032, and a central axis of the second housing cover 103 are coaxially arranged. The stator assembly 2 is fitted over the first ring member 1031, the lower end of the connecting portion 302 is rotatably connected to the second ring member 1032, and the connecting portion 302 rotates about the central axis of the second ring member 1032.

In some embodiments, the first heat-conducting member 4 is located between the second housing cover 103 and the stator assembly 2, and the first heat-conducting member 4 is a heat-conducting plate or a heat-conducting pipe.

It should be understood that, as shown in fig. 2, the first heat conduction member 4 is used for transferring heat generated by the stator assembly 2, the first heat conduction member 4 is located between the second housing cover 103 and the stator assembly 2, the first heat conduction member 4 is in direct contact with the second housing cover 103, and heat generated by the stator assembly 2 is absorbed by the first heat conduction member 4 and then transferred to the second housing cover 103, and then transferred to the external environment through the second housing cover 103.

Alternatively, the first heat conducting member 4 is a ring-shaped heat conducting pipe (not shown), which is disposed on the second housing cover 103 and located between the outer wall of the first ring member 1031 and the inner wall of the barrel member 102.

In some embodiments, as shown in fig. 1 to 5, the first heat-conducting member 4 is a heat-conducting plate, the surface of the heat-conducting plate away from the second housing cover 103 is in contact with the stator assembly 2, and the surface of the heat-conducting plate close to the second housing cover 103 is attached to the surface of the second housing cover 103 close to the heat-conducting plate.

It should be understood that, the heat-conducting plate compares the heat-conducting pipe, and the periphery of heat-conducting pipe is the arc, leads to the contact of heat-conducting pipe and second shell lid 103 less, and its radiating effect is lower, consequently chooses for use the heat-conducting plate to regard as the heat-conducting medium between stator module 2 and the second shell lid 103.

Optionally, the heat conducting plate is an annular VC soaking plate, the heat conducting plate is sleeved on the first annular member 1031, and the lower surface of the heat conducting plate is attached to the upper surface of the second housing cover 103. The radial distance between the inner wall and the outer wall of the heat-conducting plate is the same as the radial distance from the outer wall of the first ring member 1031 to the inner wall of the barrel member 102, thereby increasing the heat-conducting area between the first heat-conducting member 4 and the second housing cover 103.

In some embodiments, as shown in fig. 2 to 5, the stator assembly 2 includes a plurality of stator winding 201 arranged in a ring shape, a gap 2011 is formed between adjacent stator winding 201, the brushless motor further includes a second heat-conducting member 5 in contact with the first heat-conducting member 4, and at least a part of the second heat-conducting member 5 is filled in the gap 2011.

It should be understood that the second heat-conducting member 5 fills the gap 2011 between the adjacent stator coil windings 201, so that the heat generated inside the stator assembly 2 is transferred to the first heat-conducting member 4 through the second heat-conducting member 5, thereby further improving the heat-conducting efficiency of the stator assembly 2.

Alternatively, as shown in fig. 2 to 5, a plurality of stator coil windings 201 are arranged at intervals around the central axis of the first ring member 1031, with a gap 2011 between adjacent stator coil windings 201. The second heat conductive member 5 includes a filling portion connected to the main heat transfer portion, the filling portion being located in the gap 2011 of the adjacent stator coil winding 201, and the main heat transfer portion being located below the stator coil winding 201, the main heat transfer portions being in direct contact with the stator coil winding 201 and the heat conductive plate, respectively.

Therefore, a small portion of the heat generated by the operation of the plurality of stator coil windings 201 is absorbed by the filling portion and transferred to the main heat transfer portion, and a large portion of the heat is absorbed by the main heat transfer portion directly through the contact of the stator coil windings 201 with the main heat transfer portion. The heat of the main heat transfer portion is transferred to the heat conductive plate by direct contact with the heat conductive plate, and then transferred to the second housing cover 103, and finally released into the external environment.

In some embodiments, the second heat-conducting member 5 is located between the first heat-conducting member 4 and the stator assembly 2, a first main surface of the second heat-conducting member 5 is in contact with an end of the stator coil winding 201 near the second heat-conducting member 5, and a second main surface of the second heat-conducting member 5 is in contact with the first heat-conducting member 4.

It is to be understood that the first main surface of the second heat conduction member 5 is a surface of the main heat transfer portion in contact with the stator coil winding 201, and the second main surface of the second heat conduction member 5 is a lower surface of the main heat transfer portion.

Alternatively, as shown in fig. 2 and 5, the lower surface of the main heat transfer part is a plane, and the lower surface of the main heat transfer part is attached to the upper surface of the heat-conducting plate, so that the heat transfer efficiency between the main heat transfer part and the heat-conducting plate is further increased.

In some embodiments, the first major surface of the second heat conducting member 5 is a plane or a curved surface matching the shape of the surface of the stator assembly 2 on the side close to the second heat conducting member 5.

Alternatively, when the first main surface of the second heat conductive member 5 is a flat surface, the lower end of the stator coil winding 201 is in contact with the first main surface of the second heat conductive member 5.

Alternatively, when the first main surface of the second heat-conducting member 5 is a curved surface matching the lower end of the stator assembly 2, the contact area between the second heat-conducting member 5 and the stator coil winding 201 is larger, and the heat-conducting effect is better, compared with the case where the first main surface of the second heat-conducting member 5 is a flat surface.

It should be understood that the lower end of the stator coil winding 201 is an arc-shaped protrusion, and thus, the curved surface matching the lower ends of the plurality of stator coil windings 201 is wavy. In other words, the upper surface of the main heat transfer portion is provided with a plurality of arc-shaped grooves matched with the arc-shaped protrusions, and the plurality of arc-shaped grooves correspond to the plurality of stator coil windings 201 one to one.

In some embodiments, the second thermally conductive member 5 is a thermally conductive gel.

It should be understood that the heat-conducting gel is fluid at a high-temperature state, so that the gap 2011 of the stator assembly 2 filled with the heat-conducting gel is facilitated, and the gap 2011 is filled with the heat-conducting gel, and is kept stand, cooled and condensed into a solid state, so that the operation is simple.

Alternatively, the first heat-conducting member 4 is a heat-conducting plate and the second heat-conducting member 5 is a heat-conducting gel. Therefore, by using the first heat conducting member 4, the second heat conducting member 5 and the second housing cover 103 as the heat dissipation structure, the brushless motor of the embodiment of the invention can dissipate heat efficiently in a sealed scene, and the heat dissipation structure occupies a smaller internal space of the motor and is lower in cost.

In some embodiments, as shown in fig. 1 and 2, the first housing cover 101 defines a central through hole 1011, and the rotor assembly 3 includes a sleeve 3021 fitted in the central through hole 1011.

It should be understood that the shaft sleeve 3021 is the connecting portion 302 in the above embodiment, the shaft sleeve 3021 is rotatably fitted in the central through hole 1011 and the second annular member 1032, and the gap between the shaft sleeve 3021 and the central through hole 1011 is sealed.

Alternatively, as shown in fig. 2, the lower end of the shaft sleeve 3021 is located in the second annular member 1032, a bearing is fitted around the shaft sleeve 3021, and the shaft sleeve 3021 is rotatably coupled via the bearing in the second annular member 1032. The upper end of the shaft sleeve 3021 penetrates through the central through hole 1011 and is disposed outside the housing 1, and the gap between the shaft sleeve 3021 and the central through hole 1011 is filled with sealing oil.

In some embodiments, the enclosure 1 is a ferrous alloy enclosure.

It is understood that the ferroalloy is obtained by smelting pig iron, scrap steel, ferrosilicon, ferromanganese, carburant, copper and inoculant in an electric furnace, modifying and inoculating in front of the furnace, and finally casting, molding and cooling. Since there are many flammable gases such as methane in the well, and the explosion-proof safety of the motor needs to be considered in order to avoid the generation of sparks, static electricity, etc., the housing 1 of the brushless motor according to the embodiment of the present invention is made of an iron alloy explosion-proof material.

In the description of the present invention, it is to be understood that the terms "central," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," "circumferential," and the like are used in the orientations and positional relationships indicated in the drawings for convenience in describing the invention and to simplify the description, and are not intended to indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and are therefore not to be considered limiting of the invention.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.

In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally formed; may be mechanically coupled, may be electrically coupled or may be in communication with each other; they may be directly connected or indirectly connected through intervening media, or they may be connected internally or in any other suitable relationship, unless expressly stated otherwise. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

In the present invention, unless otherwise expressly stated or limited, the first feature "on" or "under" the second feature may be directly contacting the first and second features or indirectly contacting the first and second features through an intermediate. Also, a first feature "on," "over," and "above" a second feature may be directly or diagonally above the second feature, or may simply indicate that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature may be directly under or obliquely under the first feature, or may simply mean that the first feature is at a lesser elevation than the second feature.

In the present disclosure, the terms "one embodiment," "some embodiments," "an example," "a specific example," or "some examples" and the like mean that a specific feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present disclosure. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.

Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.

Claims

1. A brushless motor, comprising:

a housing;

the stator assembly is positioned in the machine shell and is connected with the machine shell;

a rotor assembly cooperating with the stator assembly, the rotor assembly being rotatably coupled to the housing, at least a portion of the rotor assembly being located within the housing;

the first heat conducting piece is respectively connected with the shell and the stator assembly and used for transferring heat generated by the stator assembly to the outside.

2. The brushless electric machine of claim 1, wherein the housing comprises a first housing cover, a second housing cover, and a barrel-shaped member with openings at both ends, the first housing cover and the second housing cover are respectively located at the openings of the barrel-shaped member, and the first housing cover, the barrel-shaped member, and the second housing cover are sequentially connected to form the substantially cylindrical housing.

3. The brushless electric machine of claim 2, wherein the first thermally conductive member is positioned between the second housing cover and the stator assembly, the first thermally conductive member being a thermally conductive plate or tube.

4. The brushless electric machine of claim 3, wherein the first thermally conductive member is a thermally conductive plate, a surface of the thermally conductive plate distal from the second housing cover contacts the stator assembly, and a surface of the thermally conductive plate proximal to the second housing cover abuts a surface of the second housing cover proximal to the thermally conductive plate.

5. The brushless electric machine of claim 1, wherein the stator assembly comprises a plurality of stator coil windings arranged in a ring shape with a gap between adjacent ones of the stator coil windings, the brushless electric machine further comprising a second thermally conductive member in contact with the first thermally conductive member, at least a portion of the second thermally conductive member filling the gap.

6. The brushless electric machine of claim 5, wherein the second thermally conductive member is positioned between the first thermally conductive member and the stator assembly, a first major surface of the second thermally conductive member being in contact with an end of the stator winding proximate the second thermally conductive member, and a second major surface of the second thermally conductive member being in contact with the first thermally conductive member.

7. The brushless electric machine of claim 6, wherein the first major surface of the second thermally conductive member is planar or curved to match a shape of a surface of the stator assembly on a side thereof adjacent to the second thermally conductive member.

8. The brushless electric machine of claim 5, wherein the second thermally conductive member is a thermally conductive gel.

9. The brushless electric machine of claim 2, wherein the first housing cover defines a central through-hole, and the rotor assembly includes a bushing that fits within the central through-hole.

10. The brushless electric machine of any of claims 1-9, wherein the housing is a ferrous alloy housing.