CA1253188A - Axial-flow fan - Google Patents

Abstract

AXIAL-FLOW FAN

ABSTRACT OF THE DISCLOSURE
An axial-flow fan, particularly a small fan which is axially compact, with a scroll plate surrounding the impeller and whose inner contour has a cylindrical configuration in the vicinity of the axial median plane. The outside of the rotor housing at its closed end is provided with a step-wise reduction in the outer diameter thereof, allowing the outside of this portion of the rotor housing to serve as a hub for mounting and driving a fan wheel.

Description

;~ ~53~3 NHI.-PMG-02 Canada AXIAL - I; LOW ~AN

BA5:~XCROUND OY TtJE INVENTION
The pre~ent Invention relates to an uxial-flow f~n, par~icularly to a ~mull fan which is uxially compact, with a ~croll plate or hou~ing surroundin the impell~r und whose inner contour has a cylindrical configuration in the vicinity of the uxilll m~dian plune und extends both towards the inlet side und the outlet ~ide in u polygon~l, particularly square profile de~cribin~ th~
impell~r dianleter und uccompanied by the formation o~ corner area~, ancl with a central, co~ l core formed by the dr~ve motor, ~he impeller hub und the mounting flung~e for the d~ive motor, whereby the core hag a surfuce ~onicully taperin~ towurds the inlet ~ide.
Such ~xiul-flow fans are u~ed in a preferred m~nner for coolin~ ~leetrical ~nd electronic eqwpment ~nd ins~all~tions, particularly where very compuct fan dimension~ ~nd low noi~e wtth high air outpu~ ar~ r~quir~d. Tha dimen~ion~
of th~ flm~ which can be u~ed ul such d~vic~s are limited by the av~ilsble s~ructur~l sp~ce. Thus, it i~ not po~sible to increQ~e the climen6is~n~ In order to increase the outputof such f~s.
Arl uxial-flow fan of the aforementioned type is known (DOS ~9 40 650), in which rel~tively hiL~,h air outputs are obtained in that on the inlet side the impeller hub i~ provided-with a ring suruce conically tap~rirlg towards the end face. The sc~oll pl~te i9 cylindrical in the vicinity of the axi~l mediurl plune while lel~ving a small gap to th~ fan blades and widen~ to u squ~re ~hupe by w~lls sloping in the corner ureaa both towards the ir;let ~ide und tow~ the outlet side and extendin~ symmetrically to the axilll m~ditln plllne.
Due to the euct that in the equipment in question, ever-smaller electricul ndlor electronic components ur~ bein~ increasingly used, the cll~ings or hou~ing~i of such t:quipment c~n also be mude ever-sm~lller. This meuns Lor the ~mall fsns of tJIe type considered herein thut the efficiency is limited by t~le opposin~ dynamic pressures in the installation ureas.

12S 3~ 8 8 NilL-PMG-02 Canada Brushless direct current motors also are used in axial-flow fans, but many axial-flow fans are installed in electronic appliances to serve as ventilators where there is a size restric-tion. Thus, the external dimensions of the~casing jacket are likely predetermined and fixed. This becomes critical in very small ventilators, because of the proportion of the diameter of the motor to the diameter of the surrounding fan housing.
Because of this, there is a limit to the amount of radial dimen-sion available for the fan blades. It is important, therefore, that the air input be as efficient as possible to maximize the air delivery of the fan even in spite of static pressures often encountered in fan installations. This invention is advanta-geously useful for brushless direct current motors used in both axial-flow fans and in disk storage drives.

la ~BJECTS OF T~E INVENTION ~ ~ ~ 3 ~ ~ 8 An object of the presen~ invention ~6 ~he~e~ore ~o p~o~ide an axial-~low ~an, which ha~ a higher e~iclency than the kno~
fans of this type and in whioh ~hl~ i~ achieved without incre~-ing ~he ex~ern~l dimension~ of ~he ~nown fans, Another object of the invention i~ to provide ~ hrushless direc~ curren~ ~oto~ system having a rotor of simple design usable as ~ bo~s for carrying and drl~ing a fan wheel for a plur~lit~ of fan blades directly attached or welded to t~e bos~, the bos~ bein~ driven by a high ~u~ bearing system.
Still ano~her ob~ect of ~he lnven~ion i~ to provide a brush~
le~s dlrect current motor of the outer ~otor type ~hat includes a step~wiae sm~ller dia~eter on the clo~ed end o the o~er rotor th~n the diameter ~t the open end ~hereof ~uch that ~or use in driving di~k~, disks of ht~ndardized bores may be driven and for u~e in axial-flow f~n~, ~he inlet ~ide may have a be~er ~low st~ucture to per~it higher volu~es of a~r or a~ le~st permit a pres~ ~it of ~ ~n h~ over the clo~ed end of the hou~ing without increahing the overall di~meter o~ the rotor ~ou~in~.
9DUY~3~ ~F IH~. IN~V~TION
~ ne aspect of the inven~ion r~ides hroadl~ ln ~ brushles~
direct current motor ~y~tem, ~he system includln~ an outer rotor type mot~r comprising: a cup-~h~ped rotor houaing compri~lng sheet material ~nd h~ving permanent magnet ~pparatus ~isposed a~
the rocor hou~ing, the housing having a ~haft coneen~ric~lly mounte~ therein extending lnternally thereo~, the outer portion o the housin~ hein~ formed as a drive bo~s to r~eelve at lea~t one load mem~e~ ~or the dlrect drivlng ~hereof~ a bearing system ln the motor recelvlng the sha~t so a6 to rotate the rotor ho~sing~ ~tator apparatus ~oncentrically mounting t~e bearing sy8~e~1 wlthin the ~otor, ~he rotor housing being mounted ~o 8~3 rotate ~round the peri.phery of ~he sta~or flpparatus and separa~ed by an annul~r air gap; and the ou~side of the rotor housin~ at i~9 closed end being pro~ided with a step-wise reduction ln ~he ou~er dia~e~er ~hereof, allowing the ou~lde o~ thi~ portion of the rotor hou~ing ~o ~erve as a hub for mounti~ and driving a fan wheel.
~ nother aspect of the invention re~ides in u cup-shaped rotor housing with inserted perm~nent m~gnet ~pp~r~tus, the cup being a one piece deep drawn sheet and having ~ ~ha~t concentri-cally ~oun~ed therein extending internQlly thereof, ~he ou~er por~ion o~ t~e hou~in~ being formed as a drive bo3s to receive at least one load member for the direc~ drivin~ thereof; a be~ring syste~ in ~he motor reeeiving t'ne ~haf~ 80 a~ to rotate the ~o~or hou~ingi s~ator appAr~tu~ concentrically mountin~ the be~ring system wi~hin ~he motort ~he ro~or hou~in~ bein~ mou~ted to rotA~e around the per~phery of the stato~ app~ratus and separated by an ~ir gap; and the out~id~ of the r~tor hou~in~ ~t its clo~ed end being prc,vided wi~h a step~wiRe reductiol:~ in ~he ou~er diamete~ thereo~7 allowing the outside of ~hi~ portiorl of the rotor hou~in~; ~o serve as a hub for moun~ing and drivin~ a plurali~y of ~an blades.
B~ providing a ~tru~hless di~ect cur~ent motor ~yst~m having ~n outer ro~or, and having ~t le~st one ~ta~ion~ry ~witch ~upport-ingly mo~nted on the ~otor ~tato~ the~e ohJect6 ~re solved, accordin~ to the invention, by mounting the electronic drive 8yst~m on the ~tator within the çloaed e~d of the outer rotor hou~ing, Thu~, ac~.ordlng to ~he invention, the electronic drive sy~tem c~n constltute ~ pArt of the motor in a bru.qhle~ direct current mo~or ~ystem. An a~ially ~ompact structural unit i~

2a ~;~53~
NHL-PMC-02 Canada provided which lends itself to many applications. It will be seen that the structure allows a larger axial distance between bearings to provide a strong bearing system. According to a preferred embodiment, the drive shaft is surrounded by means which hold the bearings that in turn support the rotatable motor shaft. The means is disposed in the motor housing. A circuit component board is connected to the means and is preferably constructed as an annular, plate-shaped member to support one or both sides of at least part of the electronic drive system. The dimensions of the annular component board are expediently adapted to the motor housing. Also a plurality of such members can be disposed one over another in accordance with the height of the available axial space. In such a way the motor system may provide a closed unit with only lead lines extendlng outwardly for connection to an outside source of power. In operation, the space-saving overall arrangement is reliable. The system also includes means for dissipating heat and it allows a step-wise construction on the hub side of the motor, advantageous for uses of the motor in a~ial-flow fans.
The problem relating to efficiency is solved in that the axial length of the conical annular surface amounts to at least 1/3 of the hub length and in that with respect to the axial median plane, the scroll plate is asymmetricaL in the corner areas and is constructed cylindrically over a longPr distance from the axial median plane to the inlet side than to the outlet side.
It has been discovered that these measures lead to a considerable improv~ement in the performance, without having to modify the external dimensions of the axial-Elow fans. It has also been found that the improved action does not occur to any NHL-PMG-02 Canad~

noticeable extent, i.e., occurs only ~arely, unless the axial length of the conical ring surface corresponds to at leas~ one third of the total hub length. Only the combination of the two features mention~d above leads to the surprising improvement, which will be further explained hereinafter. As a result of the measures according to the present invention, on the inlet side a wall is formed over a relatively long path (in the area of the cylindrical configuration of the scroll plate), which surrounds the fan blades in a circular manner even in the corner areas, so that the air drawn in, even in the cas~ of high dynamic pressures on the outlet side, cannot leave the fan blades in a radially outward direction before reaching the half of the air guidance path located on the outlet side.
According to an advantageous further developmen~, the cylindrical portion o the scroll plate passes over into a rounded-off intake portion at the outer edge area directed towards the inlet side. This leads to a wider intake cross section on the inlet side, which passes over only gradually narrowing into the flow duct portion bounded by the cylindrical part of the scroll plate.

N~IL-PMG-02 Canad~

lt i~ thereby advantageous i~ the radius of curvature of the rounded intake por~ion is chosen relatively large and in fact somewhat larger or eqllal to 1/3 of the distance between the axial median plune and the ~nlet side.
A ~imilar action can also be obtained if the cylindr~cal portion of the scroll plate passes over into the inlet ~ide by way ot` a chamfer. it has al80 been found that if the scroll plate is cylindrical over the entire distance between the ~ucial median plane and the inlet side, a considerable improvement in output can ~till be achieved.
BRIE~ DESCRlPTlON OF THE DEIAWINCS
These and o~hel objects, fe~ture~ and advantages of the pres~nt invention will become more ~pparent from the followin~ description when tuken in connection with the accompanying drawing which ~hows, for purpose~ of illu6tration only, several emboc~iment~ in accorcance with the pre~ent invention, and wherein:
~ igure 1 i~ an elevationul view of the inlet side oî an axi~l-flow fan according to the pregent invention;
Figure 2 is a cro~s-sectibnal view taken along line 1l-11 through the a~ Ylow fan of Figure 1;
Figura 3 is a cro~s-section~l view of B d~tail of ~ corner area of a modified con~truction in ~ccordance with the pre~ent irlvention;
Fi~ure 4 i~ u cross-sectional view of a detail of ~ corner areu of still ~nother modi~ied con~truction in accordance with the pre6ent invention;
Figure 5 i9 a diugrum illu~trating the curve~ of the quantity oY ai~
~ain~t ~tatic pressure measured in an axial flow fan according to the present inven~ion and also in an axial flow fan of the prior art;
Figure 6 is a longitudinul uxial cros4-sectional view, similur to Figure 4 through an ~xial fan in uccordance with the present invention illustra~ing two modifications, shown in actu~l size;
Figure 7 is a cross-sectiorlal view, similar to Figure 6, of a smaller version, also in actuul size and illustrating certain constructive details theIeor;
Figure 8 is a cross-s~ctional view through a still further modified embodiment of ~n axiul fan in accordance with the present invention;

NEIL-PMG-02 C~nad~
~ ~ 5 3~ ~ ~

Figure 9 is a diagram of air output curves for two different ro~ational speed ranges;
Figure 10 is a radial plan view on a rotor blade whereby only a single blade is shown in order to clearly define ~he blade;
Figure 11 is a side sectional view, similar to Figure 6, of another embodiment utilizing the invention in an axLal-10w fan where radial blades are attached directly to the outer rotor and the housing is asymmetrical in section;
Figure 12 is a side sectional view, similar to Figure 6, of yet another embodiment utilizing the invention in an axial-flow fan where a fan wheel is inserted with its hub press-fit over the outer rotor and the housing is asymmetrical in section; and Figure 13 is a side sectional view, similar to Figure 6, of still a third embodiment utili2ing the invention in an axial-flow fan in a manner similar to that shown in Figure 12, except that the housing is symmetrical in section.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawing wherein like reference numerals are used to designate corresponding parts in the various views thereof, and more particularly to Figure 1, an axial-flow fan i9 generally designated in this figure by reference numeral 1 which, as a result o its small external dimensions and compact construc-tion, is preferably used for cooling purposes in electronic or electrical equipment. The impeller is installed into a scroll plate or housing generally designated by reference numeral 2.
The fan blades 4 and motor casing 3 can also be seen in Figure 1.
Viewed over the axial depth, the scroll plate or housing 2 has a partial area, in which it extends cylindrically and concentrically to the fan axis B and is desLgnated by re~erence QZ53~88 NHL-PMG-02 Canada numeral 5. From the cylindrical area 5, the scroll pla~e or housing 2 passes over into a square form in the direetion towards the inlet side as also towards the outlet side, whereby mounting holes 7 are located in the resulting corner areas 6.
The cross sec~ion of Figure 2 through half of an axial fan according to the present invention shows that the motor casing 3, serving as a hub, is provided with an annular surface 10 conically tapering towards the inlet side 9, whereby the fan blades 4 also extend over this annular ~urface 10. The motor is constructed in a manner known as such. The coil ends 13, which are mounted on a ring 12 and which are sealed off at the front by means of a protective cover 14 made from an insulating material, surround the stator 19, which in turn is supported by means of a tubular member 23 and a sliding bearing 22 with respect to shaft 15. The shaft 15 is fixed to the motor casin$ 3 by means of the bush 11. Externally, the casing 3 is constructed in one piece as a short-circuit rotor motor, whose bars pass in a manner, known as such, through the laminated plates 16 of the rotor. The fan blades 4 are then fi~ed to the outer periphery of the motor casing 3, which is constructed as hu~.

:12S3~88 NIIL-PMG-02 Canad~

The cylindrically extending area 5 of the scroll plate 2 delimit~ the inner space in which the impeller is arranged, in the axial median plane A.
Towards the inlet side 9, scroll plate 2 extends over a leng~h a2, which is greater than half the distance al from the axial median plane A to the inlet side 9. Towards the outlet side 8, the scroll plate in the corner areas extends from the axial median plane A with a sloping wall 17, so that an overall asymmetrical construction with respect to the axial median plane A between the inlet side half and the outlet side half of the axial-flow fan re~ults. Th~ cylindrical areu 5, in the embodiment of Figur~ 2, pa~es over into a rounded-off intake portion 18, whose radius of curvature X is approximately one-third of the distance al from the axial median plane A
to the inlet side 9. lt has been found that if the cylindrically extencling area 5 is advanced relatively f~r up to the inlet side, the fan performance can be improved. This can be attributed to the fact th~t in the construction according to the present invention, the fan blades 4 are surrounded over a re~atively large axial area by the cylindrical area 5 of the scroll plute 2, so that the air seized by the fan blades is unable ahead of the cro~s-sectional narrowing in the axial median plane, with dynamic pressures prevailing on the outlet side 8, to escape this counterpressure in th~t the air escape~
~he movement by the fan blades 4 radially outwardly and would thus be forced again toward the inlet side, as is the case with the known copstructions.
In the embodiment of Figure 3, which also shows a cross section through a corner area of the scroll plute, the cylindrical area 5a extends over the entire distunce between the axial median plane A and the inlet side 9. The output can be increased in this case as also with an axial-flow fan, whose cylindlqcal area 5b pusses over into the outer edge area towards the inlet side 9 by way of a chamfer 24 (cf. Figrure 4), compared with the prior art axial-f1Ow fans.
Figure 5 shows the characteristic curves 20a and 20b of the novel axial-flow fan compared with characteristic CUl'VeS 21a and 21b of a p~ior NHL-PMG-02 Canada ~2~18~

art fan (DOS 29 40 650); it is apparent from these curve.s that. particularly in the case of high counterpres~ures (the pressure i~ plotted along the ordinate), a considerable improvement in the sutput and performance can be achieved with the f~m according to the present invention. The curve pLairs 20a and 21a as well as 20b and 21 b which belong together, represent thereby comparative measurements, carried out with two diferent impeller frequencies.
The curves 20a and 21a are plotted at a frequency of 60 Hz, while the curves 20b and 21b are plotted at a ~requency of 50 Hz. The quantity of air i~ plotted along the abscissn axis.
lt has also been found that an even more marked improvement of the characteristics can be obtained at higher speeds, which is apparent from the gre~ter deviatio-ls in the curves 20a and 21a plotted for ~ frequency of 60 Hz, as compared with the deviations of curves 20b and 21 b, plotted at a frequency o~ only 50 Hz and thus at lower fan ~peed~. Consequ~ntly, the effec~ according to the present invention occurs in particular in the case of high-speed fans, especially with direct-current fans having a speed over 3000 rpm. These fans are particulariy suitable for cooling and ventilating electrical and electronic equipment, as described hereinabove.
The inlet channel according to Figure 2 has a circumferential rounded-off edge with a rela~ively large inlet radius R while in the construction according to Figure 3 the inlet radius has a theoretical value equal to zero. Howèver, the embodiments according to Figures 3 and 2 are alternative to one another, i.e., the pre~ent invention so far provides a construction according to Figure 2 with a relatively large inlet radius 6 having the half-diameter R or a cylindrical surface of the channel up to the inlet plane 9 in Figure 3. Figure 4 illustrates only ~ small widening angle of the cylindrical surface 5b toward the inlet side in the form of the cone surace 24; it starts, for example~ at 1/8 of the axial housing length from the inlet plane 9 and has a value of about 60~. Figure 6 now illustrates a modifïcation of the cone surlace lO of Figure 2 which also forms part of the present invention.

~;~5~3~88 IIL-PMG-02 Canada The embodiment of Figure 6 includes a portion cyl~nd~cally off~et in the axial area of the closed outer rotor bottom, i.e., reduced in the diameter thereof, having the cylindrical surf'ace 65 which widens step-like after the length ll to the full r~tor diameter d2 of the hub 66. The blades 63 are butt-welded, for example, by condenser discharge onto the rotor cap 61 which is deep-drawn of soft magnetic metal so that the larger cro~s section 0xi~t~ in th~ in~low direction 60 (as in the case of the cone lO of Figur~ 2).
The rotor pot section 65 which is reduced in diameter, thus acts like a strongly defined inlet cone of the rotor hub or of the t'lange--whichever exist4 in the center on the inlet side.
The channel wall 67 which only for manufacturing tolerance~ i~ not exaetly cylindrieal, extends toward the inlet side from the center plasle A by a distance a2 which i8 significantly larger than the axially ramaining cylindrical length of the channel wall 67. On the outlet side, the eylindrical wall 67 now pas~es over in the square corner areas (in axial plan view on the housing according to FiguIe 1) into the channel enlargement with the wall contour 68 (like the wall 17 in the case of Figures 2, 3 and 4); this feature can be varied in a further modifïcation in that in lieu of the inclined corner walls 68 (which icl ~ coaxial cone surface only in special ca~es), one provides radially and axially ex~ending walls 69 which form complete corner pockets a~ a result of their sudden strong widening in the mentioned corner areas whereas in the case of the graclual transition by the inclined corner waUs 68, somethin~ like a "half-corner pocket" is formed. The variation of the ~nlet contour ot' the housing according to Figures 2, 3 and 4 is also possible in the case of Figures 6, 7 and 8. However, the shape illustrated in Fi~ure 6 is optimized with a view toward manufacture, noise and output; on the other hand, the valqations of the outlet channel configuration (Pigures 2, 3, and 4--reference numeral 17) can also be replaced by a contour corresponding to the walls 69--Figure 6.

~.;2S3~ NHL-PMG-02 Canada It i~ lmpor~ant ~or the pres~nt invention tha~ a maximum cro~ section is available in the inlet ar~, above all that a cross-sectional enlargement about the rotor hub i~ attained, and that on the outlet side a~ large ag possible an enlargement of the flow cross section is attained by the channel walls 67, respectively, 68 or 69 and the hub contour 66 whereby the ratio of the len~ths a2 + a3/2a1 should have a m~nimum value of about 0. 3, preferably about 0.5. The optimum at 0.5, however, is not aharply defined.
lf, for example, for manufacturing reasons, one cannot make the diameter of the rotor, i.e., the outer diameter of the rotor blade 63 suf-ficiently close to the inner diameter of the wall 67, the ratio a2 + a3/2a1 must be larger. It may then, for example, lie optimally at about 0. 6.
The ratio 11/2al has a minimum value of 0.3.
Figure 7 illustrate~ further details which are more clearly visible by the cross-hatching. lrl this figure, one can see the housing with the outer annular wall 74 which pa~ses over into square fastening lugs corresponding to the illustration in Figure 1 in one-piece with the fastening webs 75 arlà
flange 76 as well as the bearing tube 77, 78 and 79. More particularly, the entire structure ia a one-pi~e plastic die-casting or molded part, preferably with an interior width enlarged in the diameter with respect to the cen~er part 78 within the area of the bearings 72 and 73 of the plastic bearing tube ~for the installation of the bearing]. Because the fan of the present invention is driven by a collectorless d.c. motor, especially a so-called two-pulse motor,` particul4rly if' one deals with ~ fan of small dimensiona as shown in its actual ~ize in Figure 7 and even smaller, it is not easy to accommodate the electronics in the motor area, i.e., either in the flange 76 or as in the case of Figure 7, within the area of the closed rotor bottom 71.
With collectorless d.c. fans with one- or two-pulsed operation, one uses particularly few electronio elements and the latter can be favorably accommodated in the drive hub of the fan. A~ the same time, they produce relatively little heat so that with a collectorless d.c. motor for the drive of JL;~j3~ NIIL-PMG-02 Can~da the fan, the be~ring ~ube 77, 78 and 79 can be made of plastic material, particularly with a one- or two-pulsed collectorless d.c. mo~or. The plastic bearing tube has sufficient durability and maint~ins the tolerance over a long length o~ life because the heating from the motor loses and the electronics i8 so small that one can provide a plastic bearing support tube for the bearing and very advantageously can make the same economically in one piece with the remaining housing.
Figure 8 illustrates a similar construction as Figure 6 and 7 with offset-like pockets 81 and 80 on the inlet and outlet plane, with sloping corner walls 84 on the inlet side and sloping corner walls sa on the outlet ~ide. It i8 again deci~ive that the point of transition 85 from the wic!ening wall 84 into the cylindrical wall 87 on the inlet side is at a greater di3tance from the center plane A than the point 86 where the transition takes place on the outlet side from the cylindsr wall 87 into the corner enlargement wall 88. The offset recess which leads to the formation of the corner pockets 81 snd 89 ia favorable from a manufacturing point of view and assures a better maintenance of the dimensions of the one-piece plastic housing which, as to the rest7 is constructed as in Figure 7; namely, in one piece inclusive the beuring tube and consisting o~ plastic muterial.
Figure 9 illustrates clearly that a small widening into the corners on the inlet si~1e, as ahown to scale in Figure 4, entai1s a vel~y advantageous configuration of the curve at a slightly higher pressure requirement while with decided rnaximum pressure, the differences from the different contour of the inlet opening disappeur, but in the middle pressure range where the pructical applications lie, a relatively large radius of curvature of the circum-ferential contour (as indicated in Figrure 2) clearly prs)duces still an additional improvement .
In particular, it can be seen that the asymmetry of the outer hous~slg, as viewed from the center plane A, in conjunction with the inlet cone (for exumple accordinL~ to Figure 2 or ~Iso in the modilïcation accord-ing to Figures 6, 7 und 8) 3~ 3 NIIL-PMG-02 C~nada is very favor~ble (differenee of curvec~ from curves ~, ~ and ~ ) . The curve (x corresponds to ~ symmetrical housing whereby a pronounced cone hub was also provided in the inflow area, as described in the Japanese Patent Application 54/133638 or in the U.S. Patent 4,373,161.
One obtains generally a further improvement of the characteristic curve und also of the noise if one constructs the contour of the blades 23, reapectively, 83, 63, 73 or 123 as shown in Figure lO in such a manner that the angle at the blade root on the inlet side ~i which is formed by the tangent to the blade root on the inlet side (i.e., at the blade surface thereat) and the innow plane (a~ alao to any of the other planes which are parallel to the innow pl~n~ which may be E, El, E2) is smaller than tht angle c~l on th~
ou~let side (at the blade root). The blade angle ~O~ at the radial outside on the inlet side (formed aguin by the tangent to thia blade edge and its angle to the inlet plane) i9 smaller than the blade angle at the radial outer edge on the outlet side ~a In other words ~i is smaller than cYi and ~a is smaller than C~ a~ whereby the conditions, as illustrated in Figure 1O, are optimal for a fan according to Figure 2, i.e., for Figures 1, 2, 3 and 4 and similar condition~ are valid in the case of Figures 6, 7 and 8; however, cYi is approximately egual to ct a in that cuse.
The blade curvature is approximately that o~ a cylindrical surface.
In all of these cases, the angle ~ i passes over continuously into the angle ~ a and the ang~le c~i into the angle cYa in the approximately radially directed conto~ur of the inlet and outlet edges. The true radial extent of the blades ha~l to be considered thereby, and it i8 to be t~ken into conaicleration in this case that Figure 1 is shown approximately in actual size whereas Figure 2 i9 shown enlarged by about 1.5 as also Figures 3 and 4, and thut Figures 6 and ~ are shown in their actual size whereas Figure 8 is illustrated in twice its sizeO Figure 10, shown in its actual size, belongs to Figures 2 und 1.

lZ 5~3~ 88 NHL-PMG-02 Canada Each of the motors shown in Figures 11, 12 and 13 have a fan housing 17' that forms the outer extremes and provides structure for mounting the motor and an wheel or fan blades. The housing 17' dimensions are predetermined according to the standards in the industry, and the housing 17' may have small dimensions where the square outside faces have a length of about 80 mm. The fan housing 17 t includes a central cylindrical portion indicated by 17b', and emanating from that toward the inlet side is an inclined wall section 17a'. The inclined wall section 17a' is provided on at lPast four diagonally opposite corners of an externally squ~re fan housing 17'.
Returning to Figure 11, it can be seen that by means of this arrangemen~, a broader inlet cross section is obtained over the entire inlet zone of the axial-flow fan. The front edges of the fan blades 23' extend into this cross section, and they are brought up approximately to the forward end face of the fan housing 17' with their Ieading edges. At their inner edges, the fan blades are welded to the rotor housing 14', particularly at the drive boss 70'. The fan blades 23' may be welded convention-ally to the rotor housing 14' by a special process disclosed in German Patent 16 28 349. The fan blades are made of very thin sheet steel, and are arranged equally around the periphery, and a very large free inlet region is obtained which ~s enlarged even more by the provision between the angled dashed line L and the inclined wall 17a'.
Because the fan housing 17', as can be seen from Figure 11, is provided, on the four diagonally opposite corners of the externally square fan housing 17', with corner pockets 18', the inclined wall sections 17a' of which emanate from the central cylindrical middle piece 17b', the inlet cross section is 1~

~ ~ 5 3~ ~ ~ NHL-PMG-02 c additionally enlarged at these four corners. It has been ound that an axial-10w fan constructed in this way has advantages over conven~ional kinds of construction~ especially if it must operate against high static pressures in the installed condition.
In such instance, the fan yields surprisingly larger amounts of air.
The wielding process or attaching the fan blades 23' to the rotor housing 14' as described in the aforementioned German patent, is useful for mass production and generally requires a very large, expensive welding machine. If axial-flow fans are to be produced in smaller quantities, or if they are to be produced in locations far distant from ~he welding machine, it is much 1PSS expensive to produce a fan wheel of molded plastic. There, the blades distributed evenly about the periphery of the hub, are molded along with the hub to form a uni~.
The invention of this application, however, also lends itself to use in axial-flow fans having the unitized molded plastic fan wheel. Such a motor is shown in Figure 12, and the molded plastic fan wheel 19' having a hub 19a' which carries the evenly distributed fan blades 23a' about its periphery, i9 applied to the rotor housing 14l by being press-fit over the reduced hub portion 70' at the rotor housing 14' and secured in a suitable manner. Co~paring this ~tructure with that in Figure 11, it will be seen that the angled dashed line L, if drawn in the structure of Figure 12, would be substantially vertical.
That is, the outer diameter o the plastic hub 19a' is substan-tially the same as the outer diameter of the rotor housing 14' near its open end.
The advantage of the plastic fan wheel, of course, is that it results in an axial-fan of overall less expense than that 3'3~ N~IL-I'MG-02 Canada shown in Figure 11. It can be understood, however, that the outer diameter of the hub 19a' is still of a smaller dimension than had it been placed over the rotor o~ a conven~ional DC
brushless motor. Thus, this invention finds advantageous use in this application, also.
The motor structure shown in Figure 13 is similar to that in Figure 12 excep-t for one important difference. It will be noted in Figure 12 that the central cylindrical mid piece 17b' is flanked by an inclined wall 17a' toward the inlet side and an inclined wall 17CI toward the outlet side. By Lnspection, it will be seen that the wall 17a' is shorter and at a slightly larger angle to the mid-piece than the wall 17c'. Such a fan housing is referred to as an asymmetrical housing. In contrast, the structure in Figure 13 is a symmetrical housing where the angle and length of the walls 17al and 17c' flanking the central cylindrical mid-wall 17b' are substantially the same length and of the same angle with respect to the mid-piece wall. The reduced diameter hub 70l finds advan ageous use in both of these s~.ructure 5 .
I~ has b~en indicated that the bearing system in a brushless DC motor for direct drive of magnetic disks must be of high quality and accuracy. Hence, the motor ~hown in Figure 11, in which the load on the hub 70' i9 a plurality of magnet-lc disks>
is shown with spaced apart ball bearings 48' and ~8". These bearings are held securely within the bearing tube 44' which constitutes the central holding means 22'. Not all requirements for brushless DC motors, however, are as rigid as those for direct drive of magnetic disks. In this connection, it will be noted in the axial fans shown of Figures 11, 12 and 13, that spaced apart ball bearings are shown in the motor lla' in FigurP

NHL-PMG-02 Canada ~ Z 5 3~ ~ ~
ll whereas sleeve bearings 49' are shown iTl motors llb' and llc' in Figures 12 and 13 respectively.
Although the central holding means 22' is shown to be the bearing tube 44' in the drawings, it should be understood that for many applications, it would be acceptable for the central holding means to comprise merely of the inside of the stator iron core 58'. Thus, the stator iron could provide the support for either the ball bearings 48', 48" or the sleeve bearing~ 49' in certain applications of the DC brushless motor. The component board 20' would then be supported by means of pins to the stator in a suitable location.
A further modification of the structure is in providing the motors llb~ and llc' of Figures 12 and 13, respectively, with the fan housing 17', the central holding means 22', the flange 30a', and ~he supporting s~ruts as a one-piece molded plastic. At present, such structure has limited applications and is thought to be useful only in the instance of a two-pulse brushless DC
motor, especîally a reluctance torque motor having auxillary torques, all resulting in high efficiency and low heat generation. Heretofore, plastic has been used only in the very inexpensive ins~allations, because heat is destructive to the rigidity of the plastic structure. With the more highly eficient DC brushless motors with low heat gen~ration, however, a plastic structure is now practical for certain other applications.
Thus, there has been provided in accordance with this invention an internal motor structure for a bruchless direct current motor system including the electronic drive system and r.p.m. control circuit mounted on a component board internally of the motor ln such a manner as to enable a step-wise smaller NHL-PMG-02 Canada ~ ~ 5 3~ ~ ~

diameter on the closed end of the hub of the outer rotor than the diameter of the open end of the outer rotor. Such step-wise smaller diameter allows for such a motor to be used in the direct drive of magnetic disks, where the disks have standardized bores, and in axial-fans where a larger cross section on the air input side of the fan, particularly a fan of small dimensions, to be used in applications where it is important to deliver higher volumes of air at higher pressures. Some principal advantages of such a motor structu~2 are (1) axial c~mpactness, (2) easy access to the electronic circuit board during motor production and repair, and (3) independency of the diameter of the drive boss to the s~ator and air gap.
The cross section created by the cylindrical s~rface 65 is very critical to the flow therethrough, especially when the fan is v~ry small and having an area of preferably of about 92 square millimeters.
Although we have shown and described ~hi~ invention in connection with certain embodiments, alternatives, modifications, and variations may be apparent to those skllled in the art in view of the ~oregolng description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as ~all within the spirit and scope of the appended claims.

Claims (12)

1. THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
   OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
   l. A brushless direct current motor system, said system including an outer rotor type motor comprising:
   a cup-shaped rotor housing comprising sheet material and having permanent magnet means disposed at said rotor housing, said housing having a shaft concentrically mounted therein extending internally thereof, the outer portion of said housing being formed as a drive boss to receive at least one load member for the direct driving thereof;
   a bearing system in said motor receiving said shaft so as to rotate said rotor housing;
   stator means concentrically mounting said bearing system within said motor, said rotor housing being mounted to rotate around the periphery of said stator means and separated by an annular air gap; and the outside of said rotor housing at its closed end being provided with a step-wise reduction in the outer diameter thereof, allowing the outside of this portion of the rotor housing to serve as a hub for mounting and driving a fan wheel.
2. 2. A system according to Claim 1 wherein said outer rotor housing is extended axially such that the outer diameter of said drive boss is independent of the diameter of the rotor housing rotatable around said stator.
3. 3. A system according to Claim 1 wherein said bearing system includes a pair of axially spaced apart bearing members concentrically mounting said shaft in said motor for rotation of said outer rotor housing.
4. 4. A system according to Claim 1 wherein said fan wheel is a unitized assembly including a hub and radially extending fan blades mounted thereon uniformly around the periphery and wherein said hub is dimensioned to be press fit over the reduced diameter hub of said outer rotor.
5. 5. A system according to Claim 4 wherein the diameter of the hub of said fan wheel is not greater than the diameter of the cup-shaped rotor housing at its open end.
6. 6. A system according to Claim 5 wherein said system is part of an axial-flow fan and further comprising an outer fan housing of multi-corner profile, said housing having a central cylindrical portion surrounding the fan blade, said housing being broadened on the exhaust side of the cylindrical central portion by corner pockets into the regular multi-corner profile, said profile circumscribing the outer diameter of the fan wheel.
7. 7. A system according to Claim 6 wherein said corner pockets are formed by inclined walls which extend from said central cylindrical portion.
8. 8. A system according to Claim 7 wherein the inclined wall on the air inlet side is axially shorter than and at a different angle from the inclined wall on the outlet side of the central cylindrical portion, forming an asymmetrical cross section in the fan housing.
9. 9. A system according to Claim 8 wherein the inclined walls on both the inlet and outlet sides of the central cylindrical portion are of substantially the same angle and length to each other, forming a symmetrical cross section in the fan housing.
10. 10. A system according to Claim 8 wherein said fan wheel has a pressed on fan hub whereby the diameter of at least a portion of the system is reduced.
11. 11. A brushless direct current motor system, said system including an outer rotor type motor comprising:
    
    a cup-shaped rotor housing with inserted permanent magnet means, said cup being a one piece deep drawn sheet and having a shaft concentrically mounted therein extending internally thereof, the outer portion of said housing being formed as a drive boss to receive at least one load member for the direct driving thereof;
    a bearing system in said motor receiving said shaft so as to rotate said rotor housing;
    stator means concentrically mounting said bearing system within said motor, said rotor housing being mounted to rotate around the periphery of said stator means and separated by an air gap; and the outside of said rotor housing at its closed end being provided with a step-wise reduction in the outer diameter thereof, allowing the outside of this portion of the rotor housing to serve as a hub for mounting and driving a plurality of fan blades.
12. 12. A system according to Claim 1 wherein said air gap is cylindrical in shape.