AN EXTERNAL ROTOR BRUSHLESS DC MOTOR

Abstract: An external rotor brushless DC motor for use in a fan, or other similar application, the motor comprising: a stator assembly base having a base plate; a number of stator windings affixed to the stator assembly base; and circuitry associated with the motor, wherein the base plate is disposed between the circuitry and the stator windings.

Description: "An external rotor brushless DC motor" THIS INVENTION relates to an external rotor brushless DC motor For many years external rotor brushless DC motors have been manufactured in accordance with a conventional topography An example of such a conventional topography of a brushless DC motor is shown in Figure 1 of the accompanying drawings. The basic premise of this topogiaphy is that the stator assembly has a stator assembly base with a recess therein. The driving and control circuitry for the motor is attached to the stator assembly base in the recess, the stator windings being located above the circuitry such that the circuitry is sandwiched in the recess between the stator windings and the stator assembly base. Typically, the stator windings and the circuitry are permanently affixed to the stator assembly base. Despite drawbacks associated with this topography, there have been little or no attempts to deviate from the conventional described above since this type of motor was first made over 20 years ago There are a number of drawbacks associated with the abo\ e described conventional motor topography. These drawbacks all stem from the conventional location of the printed circuit board at a position between the stator assembly base and the stator windings For example, since the stator windings are almost always permanently affixed to the stator assembly base, it is extremely difficult to modify or repair the circuitry or components on the pπnted circuit boaid without at least partially damaging oi destroying the stator windings, or the assembly base It is often the case that it is cheaper to scrap a motor rather than to attempt to repair or maintain the circuitry associated with the motor A further diawback is that it is difficult to dissipate heat, generated by both the motor and the circuitry on the punted circuit boaid, away from the motor Another drawback is that it is difficult to seal the printed circuit board and the components theieon from the ingress of dust and moisture A further drawback is that it is also difficult to dissipate the heat, generated by both the motoi and the dnve cncuitiy on the punted cncuit board, which in many cases lestricts the power output of the motoi It is an object of the present invention to seek to provide an external rotor brushless DC motor which does not suffei fiom the above-mentioned drawbacks Accordingly, one aspect of the piesent invention provides an external rotor brushless DC motoi compiising a statoi assembh base having a base plate, a winding assembly affixed to the statoi assembK base, and ciicuitry associated with the motoi, wherein the base plate is disposed between the ciicuitry and the winding assembly and is piovided with a co\ eι to define an enclosuie, the circuitry being located between the base plate and the covei within the enclosuie which is hermetically sealed Pieferably, the ciicuitry is attached to 01 supported by the base plate Conveniently, the base plate comprises a substantially circular base plate havmg a substantially cylindrical side wall, the side wall defining a recess within which the circuitry is located. Advantageously, the stator assembly base include means foi supporting the stator windings. Preferably, the stator assembly base is manufactured from aluminium or any other mateπal with good thermal conduction Conveniently, the circuitry is in the form of a printed circuit board havmg a plurality of components mounted thereon, the components on the pπnted circuit board being positioned on eithei or both surfaces of the printed cncuit boaid. Preferably at least some, if not all of the high power dissipating components on the pπnted circuit board can overhang the printed circuit board and be attached to the assembly base P, hence conducting the heat directly into the assembly base, alternatively the heat dissipating components can be located over an aperture in the printed circuit boaid allowing them to be clamped to a piojecting area on the assembly base so conducting the heat into the assembly base Another aspect of the present invention provides a fan incorporating a motor embodying the present invention Advantageously, the fan has a frame which is manufactured from a plastic material or other low cost easily manufactured material Conveniently, the motor has a cover plate and the cover plate comprises a part of the fan housing which is so constructed that the outer edge of the assembly base is in the airflow of the fan and hence cooled by the said airflow. In order that the present invention may be more ieadily understood, embodiments thereof will now be described, by way of example, with reference to the accompanying drawings, m which: FIGURE 1 is a cross-section through a conventional brushless DC motor; FIGURE 2 is a cross-section through a first embodiment of an external rotor brushless DC motor according to the present invention, FIGURE 3 is a plan view of the brushless DC motor of Figure 2, FIGURE 4 is a ci oss-section thiough a second embodiment of an external rotor brushless DC motor according to the piesent invention, FIGURE 5 is a cioss-section thiough a thud embodiment of an external rotor brushless DC motoi according to the piesent invention, and FIGURE 6 is a schematic cioss-section through a fan having a plastics frame incorporating a brushless DC motor embodying the present invention RefeiTing now to Figuie 1, this shows a conventional topography of an external rotor brushless DC motoi 1 The motor 1 compπses a stator assembly and a rotor assembly The statoi assembly has a stator assembly base which compπses a substantially cπ culai base 2 having an outer upstanding cylindπcal side wall 3 A central cylindπcal column 4 is also upstanding from the centre of the circular base 2 and is concenriic with the cylindrical side wall 3 so as to define an annular space between the cyhndiical side wall 3 and the column 4 It is conventional for the dnving and contiol ciicuitry of the motoi to be housed within this annular space, typically on an annular pπnted circuit board 5 with the main surface of the punted cncuit board 5 which cames all the components 6 being onented toward the base 2 The printed circuit board 5 is typically permanently connected to and attached to a plurality of multipole stator laminations with windings aiound each pole forming a statoi winding assembly 7 which is attached to the statoi assembly base and, more particularly, to the exteπor of the column 4 dπectly above the base 2, the pπnted circuit board 5 thereby being sandwiched between the statoi winding assembly 7 and the base 2 The stator winding assembly 7 is permanently attached to the column 2 preferably by a thermoset iesin oi othei permanent adhesive It should be appreciated that the annulai space w ithin which the punted cncuit boaid 5 is to be affixed opens towaids the statoi w inding assembly 7 The rotoi assembly compnses a l otoi cup 8 having a senes of permanent magnet poles of opposite 9 aπanged ai ound the internal peπphery theieof The cup 8 is lotatabK engaged in the column 4 by means of a shaft 10 held between two pans of beanngs 1 1 within the column 4 The drawbacks associated with the above described conventional motor topography all stem from the conventional location of the printed circuit board at a position between the housing base 2 and the stator assembly 7 which are typically both permanently affixed together. It is, therefore, extremely difficult to modify or repair the circuitry or components on the printed circuit board without at least partially damaging or destroying the stator winding assembly or the bases. Other drawbacks include the difficulty of sealing the printed circuit board and the components thereon from the ingress of dust and moisture and the difficulty of dissipating heat, generated by both the motor and the circuitry on the printed circuit board, away from the motor and isolating the electronic components from the heat generated within the stator winding assembly 7. In order to address these problems, the present invention provides a departure from the conventional topography used in external rotor brushless DC motors. An example of a motor embodying the present invention in shown in Figure 2. Refeπing now to Figures 2 and 3 and using the same reference numerals used in connection with the conventional motor assembly shown in Figure 1, it will be apparent that the rotor assembly is no different and the stator winding assembly 7 is affixed to the column 4 in a conventional manner. However, the difference between the motor embodying the present invention and the conventional motor assembly shown in Figure 1 lies in the base portion of the stator assembly. The stator assembly base 20 of the motor 1 embodying the present invention comprises an effective inversion of the airangement shown in Figure 1. The stator assembly base 20 comprises a conventional column 4 upstanding from a circular base plate 21. A cylindrical side wall 22 projects from the base plate 21 in the opposite direction to the column 4, the side wall 22 thereby projecting away from the stator winding assembly 7, in the opposite direction to the column 4. Thus, there is no recess between the stator winding assembly 7 and the base plate 21 within which the printed circuit board 5 can be mounted. In contrast to the conventional topography, the side wall 22 which depends away from the stator winding assembly 7 defines a space on the opposite side of the base plate 21 to the stator winding assembly 7 within which the circuitry associated with the motor can be mounted. Thus, the recess defined by the side wall 22 and the base plate 21 opens away from the stator winding assembly 7. A cover plate 23 is seated on an internal step formed around the free edge of the side wall 22. An enclosure 24 is thereby defined between the base plate 21 and the cover plate 23 which is bounded by the side wall 22. Preferably, further bosses 25 or partition walls (not shown) are formed within the side wall 22 so as to provide, respectively, means by which the cover plate 23 can be secured to the base plate 21 and means to divide the main enclosure 24 into various sub-enclosures within the boundary of the side wall 22. In the embodiment of the motor show n in Figure 2, a printed circuit board 5 is attached to the base plate 21 The components 6 on the printed circuit board 5 are positioned on the opposite surface of the printed circuit board 5 to that adjacent the base plate 21 Therefore, the components 6 are readily accessible upon removal of the cover plate 23. Thus, the components 6 and circuitry of the printed circuit board 5 can be easily repaired or maintained without any need to cause damage to the winding assembly 7 or any other part of the stator assembly. Suitable wiring 7A connects the winding assembly 7 to the printed circuit board 5 through the base plate 21. The opening through which the wiring 7A passes thiough the base plate 21 is sealed by a rubber seal or the like. The provision of the enclosure 24, within which to mount the printed circuit board for the motor, on the opposite side of the base plate 21 to the stator windings 7 provides other advantages. The enclosure 24 is hermetically sealable by a rubber O-ring 33 or other similar sealing aπangement so as to protect the circuitry and components within the enclosure 24 from the ingress of dust or moisture. Additionally, the thermal transfer properties of the motor are enhanced in that heat from the motor can be more readily dissipated through the stator assembly, along the base plate 21, down the side wall 22 and from the cover plate 23. External heat sinks or the like may be connected to the cover plate 23 to facilitate further heat sinking. Preferably, the stator assembly base is manufactured from aluminium or any other thermally conductive material. A further embodiment of the invention would use the same motor construction using a plastic or non-conductive base, allowing the hermetic sealing of the electronic components Figure 4 shows anothei embodiment of the motoi m which one or more components 6A of the circuitry overhang the pπnted circuit board 5 so as to be attached directly to the base plate 21 hence conducting the heat directly into the base plate 21 This arrangement is especially advantageous for high power dissipating components. Figure 5 shows a further embodiment of the motor in which the printed circuit board 5 is provided with an aperture 26 through which an extension 27 from the base plate 21 projects A high power dissipating component 6A is located over the aperture 26 on the opposite surface of the printed circuit board 5 to the base plate 21 The extension 27 fiom the base plate 21 contacts the component 6A so as to provide a heat conduction path directly from the component 6A to the base plate 21 One particular application for motoi s embodying the present invention is in the field of fans and ventilation equipment, particularly axial flow fans. Fans having high power brushless DC motors typically have a frame manufactured from aluminium because it is not possible to utilise cheaper plastics materials due to the heat generated from the motoi However, when using a motoi embodying the present invention, it is possible to produce a fan 30 of hybrid construction having an aluminium stator assembly base 20 but with a plastics fiame 3 1 as shown in Figure 6 This is because the airflow cieated by the fan 30 will convect heat away from the motor 1. Airflow geneiated by the fan 30 passes over the side wall 22 of the stator assembly base 20 which compnses part of the heat transfer path away from the motor 1 Thus, the frame 3 1 of the fan 30 is subjected to less heat than would be experienced by a fan lncorpoiating a conventional brushless DC motor Preferably, the covei plate 23 foi the statoi assembly base 20 compπses a part of the fan housing 32 theieby pioviding an easy means by which the fan housing can be mechanically connected to the motoi 1 In the present specification "compuse" means "includes or consists of and "comprising" means "including oi consisting of The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims: CLAIMS 1 An external rotoi brushless DC motor compπsing a stator assembly base having a base plate, a winding assembly affixed to the statoi assembly base, and crrcmtry associated with the motor, wherein the base plate is disposed between the circuitry and the winding assembly and is provided with a cover to define an enclosure, the circuitry being located between the base plate and the cover within the enclosure which is hermetically sealed 2 A motor according to Claim 1, wherein the ciicuitry is attached to or supported by the base plate 3 A motor accoiding to Claim 1, wheiein the heat geneiating components of the circuitry are attached to the base plate 4 A motor according to any pieceding claim, wheiein the base plate compπses a base plate having a side wall, the side wall defining a lecess within which the ciicuitry is located 5 A motoi accoiding to any pieceding claim, wheiein the statoi assembly base include means foi supporting the winding assembk 6 A motoi accoiding to any pieceding claim, whei ein the statoi assembly base is manufactuied fiom aluminium oi othei thermal 1\ conductive material 7 \ motoi accoiding to any pieceding claim heiein the ciicuitry is in the form of a punted cncuit boaid having a pluiahty of components mounted thereon 8. A motor according to Claim 10, wherein some or all of the components on the printed circuit board are positioned on the opposite surface of the printed circuit board to that adjacent the base plate. 9. A motor according to Claim 10, wherein some or all of the components are positioned on the surface of the printed circuit board adjacent the base plate. 10. A motor according to Claim 10, wherein the components are positioned on both surfaces of the printed circuit board. 11. A motor according to any preceding claim, wherein high heat generating components overhang the edge of the printed circuit board and attach directly to the base plate hence conducting heat away from the component into the base plate. 12. A motor according to any preceding claim, wherein high heat generating components are located proximal an aperture in the printed circuit board, a projection from the base plate contacting at least one component through the aperture to conduct heat away from the component into the base plate. 13. A motor according to any preceding claim, w herein the winding assembly comprises a number of multipole stator laminations with windings. 14. A fan incorporating a motor according to any preceding claim. 15. A fan according to Claim 17 having a frame, w heiein the frame is manufactured from a plastics material 16. A fan according to Claim 17 or 18, wherein the motor has a cover plate and the cover plate comprises a part of the fan housing 17. An external rotor brushless DC motor comprising. a stator assembly base having a base plate, a winding assembly affixed to the stator assembly base; and circuitry associated with the motor, wherein the base plate is disposed between the circuitry and the winding assembly, and has a side wall depending away from the winding assembly , the side wall comprising part of a heat transfer path to dissipate heat away from the motoi 18. A motor according to Claim 17, wherein the circuitry is attached to or supported by the base plate 19. A motor according to Claim 17, wherein the heat generating components of the circuitry are attached to the base plate 20. A motor according to any one of Claims 17 to 19, wherein the side wall defines a recess within which the circuitry is located 21 A motor accoiding to any one of Claims 17 to 20, wherein the base plate is provided with a covei, the ciicuitry being located between the base plate and the cover. 22. A motor accoiding to any one of Claims 17 to 21 , wherein the circuitry is housed within an enclosui e 23. A motor according to Claim 22, wherein the enclosure is hermetically sealed. 24. A motor according to any one of Claims 17 to 23, wherein the stator assembly base include means for supporting the winding assembly 25. A motor according to any one of Claims 17 to 24, wherein the stator assembly base is manufactured from aluminium or other thermally conductive material. 26. A motor according to any one of Claims 17 to 25, wherein the circuitry is in the form of a printed circuit board having a plurality of components mounted thereon. 27. A motor according to Claim 26, wherein some or all of the components on the printed circuit board are positioned on the opposite surface of the printed circuit board to that adjacent the base plate 28. A motor according to Claim 26, wherein some oi all of the components are positioned on the surface of the printed circuit board adjacent the base plate. 29 A motor according to Claim 26, wheiein the components are positioned on both surfaces of the pπnted circuit boaid 30. A motor according to any one of Claims 17 to 29, wherein high heat generating components overhang the edge of the punted cncuit board and attach directly to the base plate hence conducting heat away from the component into the base plate 31. A motor according to any one of Claims 17 to 30, wherein high heat generating components are located proximal an apeiture in the printed circuit board, a projection from the base plate contacting at least one component through the aperture to conduct heat away from the component into the base plate. 32. A motor according to any one of Claims 17 to 31, wherein the winding assembly comprises a number of multipole stator laminations with windings. 33. A fan incorporating a motor according to any one of Claims 17 to 32. 34. A fan according to Claim 33 having a frame, wherein the frame is manufactured from a plastics material. 35. A fan according to Claim 33 or 34, wheiein the motor has a cover plate and the cover plate comprises a part of the fan housing. 36. A fan according to any one of Claims 33 to 35, wherein the side wall is within the air flow generated, in use, by the fan. 37. A fan for generating an airflow, the fan having a fan housing and an external rotor brushless DC motor, the motor comprising: a stator assembly base having a base plate; a winding assembly affixed to the stator assembly base; and circuitry associated with the motor, wherein the base plate is disposed between the circuitiy and the winding assembly and has a side wall depending away from the winding assembly, the side wall comprising part of a heat transfer path away from the motor and being within the airflow generated, in use, by the fan.

Inventors: RIDDOCH HENRY, RIDDOCH, HENRY
Applicants: NMB UK LTD, RIDDOCH HENRY, NMB (UK) LIMITED, RIDDOCH, HENRY
Application year: 2000
Main classification: H02K19
IPC codes: F04D29, H02K5, H02K7, H02K9, H02K11, H02K29