WO1999005770A1

WO1999005770A1 - Axial flux rotary micromotor and local forced-air cooling device constructed therewith

Info

Publication number: WO1999005770A1
Application number: PCT/IL1998/000333
Authority: WO
Inventors: Josef Buckshtein; Oleg Michailov
Original assignee: Josef Buckshtein; Oleg Michailov
Priority date: 1997-07-24
Filing date: 1998-07-16
Publication date: 1999-02-04
Also published as: IL121387A0

Abstract

Axial flux rotary micromotor and local forced-air cooling device has a flat, ring stator (2) with stator coils (12) and one or two flat, ring shaped, squirrel cage rotors (3). A thin sliding bearing (8) is positioned between active stator and rotor surfaces. The axial flux micromotor has a very small air gap (G1/G2) between active stator and rotor surfaces, which enables increased micromotor power per mass unit. The axial flux micromotor incorporates into a very compact, local forced air cooling device under the principal 'motor outside-fan inside', i.e. the fan blades are secured to the rotor rings. The axial flux micromotor is constructed without a central shaft and provides more homogeneous air flux density on cooled electronic components.

Description

AXIAL FLUX ROTARY MICROMOTOR AND LOCAL FORCED-AIR COOLING DEVICE CONSTRUCTED THEREWITH

The present invention relates to axial flux electrical micromotors of very flat construction. The invention also relates to local forced-air cooling devices constructed with such electrical micromotors.

Generally speaking, a flat micromotor requires a very small air gap between the stator and rotor active surfaces. In conventional radial-flux cylindrical, or axial-flux disk, micromotor constructions, the air gap depends to a great extent on the micromotors detail tolerances and on the precision of the bearings rotatably mounting the rotor with respect to the stator. Such constructions typically permit air gaps in the order of 1mm.

An object of the present invention _.s to provide a novel electrical micromotor which permits very small air gaps to be attained between the rotor and stator . Another object of the present invention is to provide a local forced-air cooling device including the novel electrical micromotor .

According to one aspect of the present invention, there is provided an electrical micromotor, comprising: a stator having a flat surface; a rotor having a flat surface adjacent to and coaxial with the stator; and a low-friction thin sliding bearing between the stator and rotor flat surface spacing them apart and defining an axially-extending air gap between them.

According -to further features in the described preferred embodiments, the low-friction thin sliding bearing defines an axially-extending air gap of less than 1mm, more particularly, in the order of 0.05 to 0.1mm, which is substantially smaller than the air gaps permitted by conventional electrical micromotor constructions.

According to further features in the discribed preferred embodiments, the low-friction sliding bearing comprises a stator bearing ring engaging the stator, and a rotor bearing ring engaging the rotor and having a face in contact with a face of the stator bearing ring. As more particularly described, the contacting faces of the two bearing rings include conical surfaces self-centering the rotor with respect to the stator.

Several embodiments of the invention are described below for purposes of example.

According to some described embodiments, the rotor assembly includes a single rotor, and the stator assembly includes two stators secured together on opposite sides of the rotor, with a low-friction thin sliding bearing between each stator and the rotor. In one described embodiment, both stators include magnetic cores and windings, and in a second described embodiment, one stator includes a magnetic core and windings, and the other stator includes only a magnetic core.

According to other described embodiments, the rotor assembly includes two rotors located on opposite sides of the stator, with a low-friction thin sliding bearing between each rotor and its respective side of the stator.

In one described embodiment, the two rotors are secured together by an inner bush extending axially through the stator; and in another described embodiment, the two rotors are secured together by an outer bush extending axially around the stator and the two rotors.

As will be described more particularly below, such an electrical micromotor construction permits very small air gaps to be attained, in the order of 0.05 to 0.1mm, which enables increase micromotor power per mass unit. In addition, it enables the micromotor to be constructed without a central shaft. Particularly the latter advantage permits the micromotor to be incorporated into a very compact local air-forced cooling device for cooling electronic components, for example.

According to another aspect of the present invention, therefore, there is provided an air-cooling device comprising an electrical micromotor as described above, and a plurality of fan blades secured to the rotor ring for circulating a cooling fluid in heat-exchange relationship with respect to an element to be cooled. Further features and advantages of the invention will be apparent from the description below.

The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:

Fig. 1 is a longitudinal sectional view illustrating one form of electrical micromotor constructed in accordance with the present invention;

Fig. 2 is an exploded fragmentary view more particularly illustrating the main components in the electrical micromotor of Fig. 1;

Fig. 3 is a longitudinal sectional view illustrating a second form of electrical micromotor constructed in accordance with the present invention;

Fig. 4 is a fragmentary top plan view of the stator in the electrical micromotor of Fig. 3;

Fig. 5 is a sectional view along line V—V of Fig. 4;

Fig. 6 is a longitudinal sectional view illustrating a third form of electrical micromotor constructed in accordance with the present invention;

Fig. 7 is a longitudinal sectional view illustrating a fourth form of electrical micromotor constructed in accordance with the present invention;

Fig. 8 is a diagramatic view illustrating an important advantage in the electrical micromotor of the present invention, permitting the micromotor to be constructed as modular units and assembled in any desired number according to the micromotor power requirements for any particular application;

Fig. 9 is a partial sectional view illustrating one form of local forced-air cooling device constructed with the novel micromotor of the present invention;

Fig. 10 is a partial sectional view illustrating a second form of local forced-air cooling device constructed with the electrical micromotor of the present invention;

Fig. 11 is a partial sectional view illustrating a third form of local forced-air cooling device constructed with an electrical micromotor in accordance with the present invention; and

Fig. 12 is a partial top plan view illustrating the heat sink and the cooling blades in the cooling device of Fig. 11.

The electrical micromotor illustrated in Figs. 1 and 2 comprises a stator assembly, generally designated 2, and a rotor assembly, generally designated 3, rotatably mounted with respect to the stator assembly. The stator assembly 2 includes a stator core 4 having flat surfaces at its opposite sides; and the rotor assembly 3 includes two rotors 5, 6, having flat surfaces located adjacent to and coaxial with stator core 4 on opposite sides of the stator core. The two rotor cores 5, 6 are joined together to rotate as a unit by an internal bush 7. A low-friction sliding bearing, generally designated 8, spaces the flat surfaced rotor core 5 from the respective flat surface of the stator core 4 to define an axially-extending air gap •/., between them; and another low-friction sliding bearing generally designated 9 spaces the flat surface of rotor 6 from the flat surface at the respective side of stator core 4 to define an axially-extending air gap

Fig. 2 more particularly illustrates the construction of the stator core 4, the rotor 5, and the low-friction sliding bearing 8 between them. It will be appreciated that the rotor 6 on the opposite side of the stator core 4 and the low-friction sliding bearing 9 between them, are of similar construction.

As seen in Fig. 2, stator core 4 includes a magnetic core 10 constituted of a wrapped laminated ring and formed with a plurality of radially-extending slots 11 receiving coils 12 to define poles 13 at both sides of the magnetic core.

Rotor 5 is of a squirrel-cage construction. It includes a wrapped laminated cylindrical core 15 having electrically-conductive rings 16, 17 on the inner and outer cylindrical faces, respectively, and a plurality of electrically-conductive bars 18 extending radially through the laminated cylindrical core and electrically connected to the electrically-conductive rings.

The low-friction thin sliding bearing 8 between rotor 5 and stator core 4 comprises two bearing rings, namely, bearing ring 20 secured to the stator core 4, and bearing ring 21 secured to the rotor 5. Each bearing ring 20, 21, is formed with a thickened inner peripheral section 20a, 21a, a thickened outer peripheral section 20b, 21b, and a thin intermediate "^■ section 20c, 21c. The thickened peripheral sections of the two bearing rings 20, 21, are used for securing them to the stator core 4 and rotor 5, respectively; whereas the thin intermediate sections 20c, 21c are used for spacing the rotor 5 with respect to the stator core 4. The outer surface of the inner peripheral section 20a of bearing ring 20, and the inner surface of the inner peripheral section 21a of bearing ring 21, are formed with complementary conical surfaces which are effective to self-center the rotor 5 with respect to the stator core 4.

The construction illustrated in Figs. 1 and 2 permits very small axial air gaps «.. , V- between the two rotors 5, 6 and the stator core 4, considerably less than the 1mm previously attainable in conventional constructions. Thus, the illustrated construction permits air gaps in the order of 0.1 to 0.05mm. Such small air gaps provide more micromotor power, small windings dimentions, and high reliability.

Another important advantage in the construction illustrated in Figs. 1 and 2 is that it does not require a central output shaft, as in a conventional electrical micromotor, for conveying the torque to a utilization device. Thus, the central bush 7 joining the two rotors 5, 6 together could be integrally formed with fan blades, as will be described more fully below particularly with respect to Figs. 9 and 10, to provide a very compact and efficient forced-air cooling device.

Figs. 3-5 illustrate another construction in which there is a single stator, generally designated 52 and the rotor assembly, generally designated 53, includes two rotors 55 and 56 located on opposite sides of the stator 52. The two rotors 55, 56 are of the squirrel-cage construction described above with respect to Figs. 1 an 2, and are joined together by an internal bush 57 so as to rotate as a unit.

The stator core 52, however, is of a different construction. It comprises a magnetic core 60 constituted of a laminated magnetic path of circular sheets 61 extending in the radial direction and stacked in the axial direction, as best seen in Fig. 3. The outer diameters of all the sheets 61 are equal, but the inner diameters increase from the center sheet in the stack towards the outer sheets at the opposite sides of the stack. In addition, as best seen in Fig. 4, the inner periphery of the laminated assembly is formed with a plurality of radially-extending slots 62 for receiving the stator windings 63 which enclose the outer peripheries of the stacked assembly. Slots 62 thus define magnetic poles 64 at the inner periphery of the assembly.

At the inner periphery of the laminated assembly, the sheets are divided into two groups bent axially in opposite directions, as best seen in Figs. 3 and 5, to define poles 64a facing in one direction, and poles 64b facing in the opposite direction. A stator bearing ring 65 is secured between the two oppositely-facing poles 64a, 64b and is firmly bonded to these poles by a plastic material, such as an epoxy resin. This resin pots the laminated sheets including their bent-out poles 64a, 64b and the bearing ring 65, but leaves the inner periphery of the stator bearing ring 65 exposed. The inner periphery of stator bearing ring 65 is formed with a conical surface 65a. It contacts complementarily-shaped conical rotor bearing rings 66a, 66b, to define the gaps •/.. , -/_ between the rotors and the stator.

It will thus be seen that the electrical micromotor construction illustrated in Figs. 3-5 also provides the advantages of an ultra flat structure enabling the attainement of very small gaps - , , between the stator and the two rotors, as in the constructions described above with respect to Figs. 1-2. The Figs. 3-5 construction also enables the electrical micromotor to be built in a shaftless manner with its central portion available for the provision of fan blades in an air-cooling device, or for coupling in a modular fasion to another type of utilization device.

Fig. 6 illustrates another electrical micromotor 30, also including a stator assembly generally designated 32 and a rotor assembly generally designated 33. In this case, however, the stator assembly 32 includes two stators 34, 35, secured together in a common housing 36; and the rotor assembly 33 includes a single rotor 37 coupled to an inner bush 38.

Each of the stators 34, 35, includes a core 40, 41, of similar construction as core 10 in the electrical micromotor of Figs. 1 and 2, except that the slots for placing the windings 42, 43, are formed only on one side of each laminated core, namely the side facing the rotor 37. Each stator 34, 35, further includes a low-friction bearing ring 44, 45, of similar construction as bearing ring 11 in the electrical micromotor of Figs . 1 and 2.

Rotor 37 also includes a low-friction bearing ring 48, 49, on its opposite flat faces in contact with bearing rings 46, 47 of the two stators. Bearing rings 48 and 49 are of generally the same construction as bearing ring 10 in Figs. 1 and 2, except that they are integrally connected with the connecting bush 38. The inner peripheries of each pair of bearing rings are also formed with complimentary conical surfaces, corresponding to surfaces 20c and 21c in Fig. 2, to self-center the rotor 37 with respect to the two stators 34 and 35.

Rotor 37 is preferrably also of the squirrel-cage construction as described above with respect to Figs. 1 and 2.

Fig. 7 illustrates an electrical micromotor of a similar construction as in Fig. 6, except that only one stator 34' includes a stator winding 42' on its laminated core 40'; the other, contra-stator 35' includes only a laminated core 41', and no stator windings thereon. In addition, the rotor 37' between the two stators 34' and 35' is preferrably of a printed circuit construction, including an insulating base with electrical circuitry printed on both of its opposite faces. In all other respects, the electrical micromotor illustrated in Fig. 7 is of the same construction as described above with respect to Fig. 6.

Fig. 8 diagramatically illustrates how the novel electrical micromotor may be used as a modular unit, to be assembled in any desired number, according to the power requirements of any particularl load. As shown in Fig. 8, the mechanism is represented by bush 70. Bush 70 is adapted to be coupled to a plurality of electrical micromotors 72a—72n, which may be of any of the constructions described above with respect to Figs. 1-7. Thus, in these electrical micromotors, the bush 73 of each electrical micromotor is used for coupling the micromotor to the common bush 70. All the electrical micromotors 72a-72n may be coupled to the common bush 70 in any suitable manner.

Figs. 9-12 illustrate how the above-described electrical micromotors may be used in forced-air cooling devices particularly for cooling electronic components.

Fig. 9 illustrates a forced-air cooling device, generally designated 80, for cooling an electronic component 81. For this purpose, the electrical micromotor, generally designated 82, which may be of any of the constructions described above with respect to Figs. 1-7, utilizes the internal bush 83 coupled to the rotors of the electrical micromotor for driving a plurality of fan blades 84 occupying the central region of the electrical micromotor. The air-cooling device further includes a heat sink 85 to which the stator assembly of the electrical micromotor is secured for cooling the electronic component 81.

The cooling device illustrated in Fig. 9 thus not only provides a very efficient and compact electrical micromotor for forced-air cooling the electronic component 81 , but also a more efficient air velocity profile for cooling this member. Thus, in a conventional cooling device, wherein the fan blades are formed externally of the electrical micromotor, the fan blades produce an annular air stream because the electrical micromotor is located at the center of the cooling device; therefore, the annular air stream must be deflected towards the component to be cooled, or must be somewhat spaced from the component so that the annular air stream spreads to cover the electronic component. In the novel construction illustrated in Fig. 9, however, wherein the fan blades 84 occupy the central area of the forced-air cooling device, the fan blades concentrate the air flow directly towards the electrical component 81 and the heat sink 85, even though the fan blades are closely spaced to the heat sink.

Fig. 10 illustrates forced-air cooling device 90 for cooling a printed circuit board 91. The cooling device also includes an electrical micromotor 92, of any of the above-described constructions, in which the rotor is coupled to an internal bush 93 formed with the fan blades 94.

In the constructions illustrated in Figs. 9 and 10, the electrical micromotor circulates the cooling air by inlet axial fan. Figs. 11 and 12 illustrate another construction of cooling device wherein the electrical micromotor is embodied in an outlet centrifugal fan, in which the fan blades draw the cooling air through the heat sink for cooling the electronic component.

Thus, as shown particularly in Fig. 11, the cooling device 100 is used for cooling a high power electronic component 101 also located centrally of the electrical micromotor 102. In this case, the electrical micromotor 102 is preferrably of the two-rotor construction as described above with respect to Figs. 1 and 2, for example, except that the two rotors are coupled not by an inner bush (7, Fig. 1), but rather by an external bush 106.

Thus, the external bush 106 carries the fan blades 107. In this case, however, the heat sink 105 is located in the central region of the electrical micromotor 102, and the fan blades 107, secured to the external rotary bush 106, are axially spaced from the electrical micromotor, so as to draw the cooling air through the heat sink for cooling the electronic component 101 carried by the heat sink.

While the invention has been described with respect to several preferred embodiments, it will be appreciated that these are set forth merely for purposes of example. Thus, many variations in the construction of the electrical micromotor may be used, e.g. variations in the construction of the stators, rotors, or the external coupling from the rotor. In addition, other utilization devices may be driven by the electrical micromotor, e.g. gears, pumps, and the like. Many other variations, modifications and applications of the inevntion will be apparent.

Claims

WHAT IS CLAIMED IS:

1. A flat electrical micromotor, comprising: a stator having a flat surface; a rotor having a flat surface adjacent to and coaxial with said stator; and a low-friction sliding bearing between said stator and rotor flat surfaces spacing them apart and defining an axially-extending air gap between them.

2. The electrical micromotor according to Claim

1 , wherein said low-friction sliding bearing defines an axially extending air gap of less than 1 mm.

3. The electrical micromotor according to Claim

2, wherein said low-friction sliding bearing defines an axially-extending air gap of the order of 0.05-0.1 mm.

4. The electrical micromotor according to any one of Claims 1-3, wherein said low-friction sliding bearing comprises: a stator bearing ring engaging said stator, and a rotor bearing ring engaging said rotor and having a face in contact with a face of said stator bearing ring.

5. The electrical micromotor according to Claim 4, wherein said contacting faces of said bearing rings include conical surfaces self-centering said rotor with respect to said stator.

6. The elbtrical micromotor according to Claim 5, wherein each of said bearing rings is formed with thickened inner and outer peripheral sections for securing them to the stator and rotor, respectively, and a thin intermediate section for spacing the rotor flat surface with respect to the stator flat surface.

7. The elctrical micromotor according to any one of Claims 1-6, wherein said rotor includes a single rotor, and said stator assembly includes two stators secured together on opposite sides of the rotor, with a low-friction sliding bearing between each stator flat surface and the rotor flat surface.

8. The electrical micromotor according to Claim 7, wherein both stators include magnetic cores and windings .

9. The elfctrical micromotor according to Claim 8, wherein one stator includes a magnetic core and windings, and the other stator includes only a magnetic core.

10. The electrical micromotor according to any one of Claims 7-9, wherein said rotor is of a squirrel-cage construction, including: a laminated cylindrical assembly of magnetic ribbons having electrically-conductive rings on the inner and outer diameter of the cylindrical assembly; and a plurality of electrically-conductive bars extending radially through said laminated cylindrical assembly and electrically connected to said electrically-conductive rings .

11. The elctrical micromotor according to any one of Claims 7-9, wherein said rotor is of a printed circuit construction including an insulating base and printed circuitry coils on the opposite faces of said insulating base.

12. The electrical micromotor according to Claim 1 , wherein said rotor assembly includes two rotors located on opposite sides of the stator with a low-friction sliding bearing between each rotor flat surface and its respective side of the stator flat surface.

13. The electrical micromotor according to Claim 12, wherein the two rotors are secured together by an inner bush extending axially through the stator.

14. The electrical micromotor according to Claim 12, wherein the rotors are connected together by an outer bush extending axially around the stator and the two rotors .

15. The electrical micromotor according to any one of Claims 12-14, wherein said stator includes: a laminated magnetic assembly of axially-extending sheets of increasing diameter, and stator windings received in slots formed in the opposite sides of the laminated magnetic assembly; said low-friction sliding bearing including a stator bearing ring secured over each side of the laminated assembly of the stator and the stator winding thereof, and a rotor bearing ring secured to each of the rotors.

16. The electrical micromotor according to any one of Claims 12-15, wherein said rotor is of a squirrel-cage construction, including: a laminated cylindrical assembly of magnetic ribbons having electrically-conductive rings on the inner and outer faces of the cylindrical assembly; and a plurality of electrically-conductive bars extending radially through said laminated cylindrical assembly and electrically connected to said electrically-conductive rings .

17. The electrical micromotor according to Claim

16, wherein said stator includes a laminated magnetic assembly of radially-extending sheets stacked in the axial direction and each formed with a central opening; the laminated assembly having an inner section formed with radially-extending slots defining magnetic poles, and an outer section receiving stator windings between said poles.

18. The electrical micromotor according to Claim

17, wherein a number of the sheets of the inner section of the laminated magnetic assembly are bent axially in one direction, and the remaining sheets in the inner section of the laminated magnetic assembly are bent axially in the opposite direction; said low-friction sliding bearing including an axially-extending bearing ring joining all the axially-bent sheets of the laminated magnetic assembly, and a bearing ring for each of the rotors and having surfaces in contact with surfaces at the opposite ends of said bearing ring of the stator.

19. The electrical micromotor according to Claim 18, wherein said bearing rings on the rotors are of conical configuration, and the opposite ends of the stator bearing ring are each formed with a conical surface at its inner periphery in contact with the conical bearing rings of the rotors .

20. The electrical micromotor according to any one of Claims 1-19, wherein said rotor is coupled to a utilization device.

21. The electrical micromotor according to Claim 20, wherein said utilization device comprises fan blades secured to the inner periphery of said rotor.

22. The electrical micromotor according to Claim 20, wherein said utilization device comprises fan blades secured to the outer periphery of said rotor.

23. The electrical micromotor according to Claim 20, wherein said rotor includes a bush formed with splines on its inner surface, and said utilization device includes a shaft formed with splines on its outer surface to be coupled via said splines to the bush of the electrical micromotor.

24. A forced-air cooling device, comprising; an electrical micromotor according to any one of Claims 1-19 and a plurality of fan blades secured to said rotor for circulating a cooling fluid in heat-exchange relationship with respect to a member to be cooled.

25. The forced-air cooling device according to Claim 24, wherein the cooling device further includes a heat sink to be placed in heat-exchange relationship to the member to be cooled and located in the path of the cooling fluid circulated by said fan blades.

26. The forced-air cooling device according to Claim 25, wherein said fan blades are carried by the inner periphery of the rotor, and said heat sink is axially aligned with said fan blades so as to be cooled by the cooling fluid circulated by said fan blades.

27. The forced-air cooling device according to Claim 26, wherein said heat sink includes a surface facing away from said fan blades for receiving the member to be cooled.

28. The forced-air cooling device according to Claim 26, wherein said heat sink includes a surface facing, and aligned with, said fan blades for receiving the member to be cooled.

29. The forced-air cooling device according to Claim 25, wherein said fan blades are carried by the outer periphery of the rotor ring, and said heat sink is radially aligned with said fan blades so as to be cooled by the cooling fluid circulated by the fan blades.

30. The forced-air cooling device accroding to Claim 29, wherein said heat sink includes a cavity centrally thereof for receiving the member to be cooled, and a plurality of radiator blades extending radially outwardly of said cavity and aligned with said fan blades.

31. An electrical micromotor according to any one of Claims 1-23, substantially as described with reference to and as illustrated in Figs. 1-8 of the accompanying drawings .

32. A forced-air cooling device according to any one of Claims 24-30 substantially as described with reference to and as illustrated in Figs. 9-12 of the accompanying drawings.