Miniature axial fan

The invention relates to a miniature axial fan particularly of an axially compact construction, having a central motor driving a rotor disk with a housing surrounding the rotor disk in which an interior housing wall on the inflow side is cylindrical and extends past the axial center of the housing and then this cylinder wall expands outwardly to the outlet side of the housing to produce an enlargement of the flow cross-section. The housing has webs extending inwardly from the outlet side of the housing that carry the central driving motor with the rotor disk. A number of blades are mounted on the rotor disk which numbers differs from the number of webs.

The invention relates to a miniature axial fan according to the 
introductory part of claim 1. 
In the case of axial fans of such a small size, there is, in addition to 
the often required compactness, the requirement of a low noise level and 
of an air output that is sufficient for its use. Because of the given 
small outside dimensions that is not easy to achieve. In the range of 
these dimensions and below, there is therefore a struggle involving 
millimeters. If one parameter, one dimension is changed by a few 
millimeters in favor of one characteristic, this has a considerable effect 
on other characteristics and thus on the overall characteristics. 
On the basis of the European Patent Application 0100078, an axial fan is 
known that is suitable for developments of compact axial fans having a 
rotor disk diameter of below 100 mm. 
The inventive combination that is to be protected here used a part of the 
characteristics known from that text in combination with other measures 
that are specifically effective in the case of an axial fan of the 
initially mentioned small size. 
The invention is therefore based on the objective of developing a very 
small, relatively compact axial fan having a rotor disk driven by a 
concentric coaxial driving motor in such a way that, in the case of the 
small size offered here, it has a relatively good air output and a low 
noise level. 
The invention is achieved by the means listed in claim 1.

FIG. 1 shows a bent longitudinal section through the housing of a miniature 
fan according to the invention. Concentrically to the rotational axis 10, 
a bearing tube 17 is designed in a stepped way for stops of bearings and 
positioning of the stator body. 
The bearing tube 17 forms one piece with the flange 13, to which four webs 
5 connected distributed by 90.degree. that radially, in each case, extend 
into the center of a square side, continue there into a square flange 
plate 15, out of which the housing tube 4 or 1 extends axially with its 
cylindrical interior wall surface 3 to the inlet plane E. Radially outside 
the housing tube 1, the fastening columns 14 are provided that also extend 
out of the flange plate 15 from the outlet plane A axially to the inlet 
plane E. All these parts 17, 13, 5, 4, 1, 14, 15 are developed as a 
one-piece plastic injection molded part. The fastening column 14 that have 
the full axial length of the fan and have a compact construction, provide 
an excellent stiffness for the fastening of the minifan. In addition, by 
means of this design that inside and outside the flow duct, provides only 
one joint face (with respect to tools), an inexpensive tool becomes 
possible (sic - translator). The fastening bores 16 are let into the 
columns 14 concentrically. 
The enlarging spaces 18, 19 with the enlarging angles .gamma., .delta. at 
the outlet plane A that extend from the cylindrical part of the interior 
wall surface 3 to the outlet plane A, signify, first by means of their 
very small angle .delta., that the removing from the tool is ensured, by 
means of which, at the same time, also an increase of the cross-section is 
achieved, even though it is minimal. The cylindrical part of the interior 
wall surface 3, for reasons of manufacturing technology, at least in the 
case of the injection-molded piece, must have an incline for lifting-out, 
i.e., this cylindrical part is only essentially cylindrical (compare angle 
.delta.). The enlarging spaces 18 into the four corners of the square with 
the significantly larger enlarging angle .gamma. are known per se from the 
German Patent Text 17 28 338. The enlarging spaces 18 also extend 
conically (or also in steps) to the outlet plane A (from the direction of 
the cylindrical part 3 of the flow duct). 
The diagnonal wall of the enlarging spaces 18 is shown from the outside in 
FIG. 2 (compare number 27). Between the fastening columns 14 and the 
housing tube 1, continuous bridges 28 are provided that provide the 
stability of the columns 14 also to the housing tube 1. On the side of the 
inlet, the interior wall surface 3 has a rounded off area which in 
practice, in its real size, has a bending radius of about 4 to 5 mm. 
The real size of FIGS. 1 and 2 is therefore that of a cuboid of 
50.times.50.times.25 mm. In the present construction that is shown in FIG. 
1 and 2, the combination of an optimal flow duct, a relatively high 
stability of the housing structure, an economical manufacturability as a 
series product, also with dimensions of such a small size, is possibly of 
inventive significance. For this reason, measurements and proportions may 
also have this significance. The columns 14 that are developed as round 
bolts with the continuous fastening bolts 16 and the thin bridges 28 that 
nevertheless continue over the whole axial length of the housing radially 
to the thin housing ring 1, make possible an optimal construction also for 
a simple tool. 
In FIGS. 3, 4, 5, the bearing tube 17 and the flange 13 are constructed as 
shown in FIG. 1. The armature stampings of the stator are fitted onto the 
exterior (extreme-translator) step of the bearing tube 17, and strike 
against this step with insulating end plates. In the interior of the 
bearing tube, a pair of ball bearings is indicated in a known way that are 
braced axially with a spring for the bearing of a shaft that in a 
torsionally fixed way is connected with the outer rotor housing or the 
rotor disk hub. FIGS. 3 to 5 are constructed differently only with respect 
to this outer rotor cap and the rotor disk hub. In all three cases, 
identical blades 7 can be combined on a hub 21 into a rotor disk 2 Thus 
also the armature stampings are identical with the winding of a driving 
motor 6, also the electronic commutating system-immersing axially into the 
flange shell 13. 
In the case of axial fans of this small size, it is important, in the case 
of the relatively large driving motor 6, i.e., a relative large ratio of 
the rotor disk hubs--or the driving motor diameter--to the diameter of the 
rotor disk, i.e., that of the envelopes of the blade ends, to make the 
radial dimension of the blade relatively large, i.e., to construct the 
driving motor with the hub together for a small diameter of the interior 
flow wall. This interior flow wall is formed by the hub and the outer 
rotor. The object of FIGS. 3, 4, 5 is to provide conditions that are 
favorable in this respect; i.e. to achieve a certain output requirement 
and a secure fastening of the rotor disk blades 7 at the plastic hub, as 
well as of the fan wheel on the outer rotor and to nevertheless make 
available a sufficient air output. 
In FIG. 3, a plastic-bound magnet is used (or a ceramic magnet, but always 
still) of a relatively large thickness, over which a relatively thin 
bowl-shaped cap 33 of low retentivity is pulled. The rotor disk hub 21, 
with its cylindrical exterior part 22, completely reaches around the cap 
33, whereby a good anchoring is achieved by means of the fact that at the 
open end 24 of the bowl, the plastic is thickened, i.e., by means of the 
plastic a form-locking holding of the outer rotor is achieved by means of 
the fact that the injection molding takes place around it, wherebY the 
exterior part 22 with the radial wall 21 as a whole is combined into 
bowl-shaped hub and with the blades 7 into a rotor disk 2 that in the 
known way is developed in one part as an injection-molded part. 
FIG. 3 shows a further independently important economically advantageous 
method and structure to fix the rotor 2 on the shaft 12 by mere plastic 
injection molding. The soft-iron cap 33 with its inner axially bent 
collarlike rim 133 there is completely embedded in the plastic means. The 
internal surface 134 of said collar has a distance of about 0.5 to about 2 
mm to the shaft 12, preferably 0.6 mm. This distance or gap 137 is filled 
with plastic and the collar or rim is partly perforated, so that the 
plastic part 135 surrounds and penetrates the rim or collar 133. The gap 
is as small as possible so that plastic material, when injected, 
penetrates the gap. Because of heat problems the gap should not be larger 
than l to 2 mm. Said cylindrical collar surrounding said shaft is fixed 
with the rotor in any way. 
FIG. 4 shows a known, more costly method where a separate additional metal 
piece between the shaft and the collar is necessary. 
The method of FIG. 3 is important, independently of the type of fan or 
structure of the rotor housing. 
In FIG. 3, the internal rim of the rotor-holding reinforcement element 33 
is punched and bent in one step with the whole caplike element 33. 
FIG. 4 shows a cylindrical part 25 of a rotor disk hub that, only 
projecting out over a relatively small part, about one fourth of the axial 
length, reaches over the outer rotor of the driving motor. The bowl-shaped 
housing 33 of the outer rotor that is of low retentivity on it bottom side 
is reduced in its diameter in steps so that a cylindrical outer surface 
makes possible a press fit for the plastic hub 25, 26, in which case its 
outside diameter corresponds approximately to the outside diameter of the 
rotor bowl (or can- translator). In this way, with otherwise identical 
engine dimensions, a slightly larger cross-section is obtained by the 
elimination of the cylindrical exterior wall 22 of the plastic hub. 
Naturally, in the case of FIG. 4, the plastic hub with the radial front 
surface 26 and the cylindrical part 25 that is developed as a ring collar 
are injection-molded in one piece with the blades 7. In this case, this 
important expansion of the flow cross-section, i.e., reduction of the 
driving motor in its diameter including the rotor disk hub, takes place by 
such a reduced diameter. 
Should the mounting of this rotor disk on the outer rotor not be good 
enough, it may, as shown in FIG. 6, be held in addition (or also as an 
alternative) in the bottom of the outer rotor by means of journals that 
are upset by heating. This would make it possible that the cylindrical 
projection 25 can be eliminated. In that case, a cone-type tapering could 
be provided in the direction of the inlet plane E. The reason is that this 
type of cone-type tapering of the rotor disk hub in the direction of the 
inlet plane E would make possible an additional improvement of the flow 
behavior, particularly if, on the outside, the limiting housing wall were 
to extend at first cylindrically from the flow-in side, as is known on the 
basis of EP-0100 078-Al (EU-456). 
In principle, it can be stated that this hot upsetting of the rotor disk 
hub in the front side of the outer rotor cap, as shown in FIG. 6, is 
useful as an additional measure or as an alternative. There a 
glueing-together or riveting-together may also take place so that, in the 
area of the reduced diameter, as shown in FIG. 6, by means of a conical 
outer contour of the rotor disk hub or one that tapers in the direction of 
the inlet plane E, as a whole, clearance 71 is created. That is also shown 
on the right-hand side of FIG. 6 where it is shown clearly that the ring 
part was left out. 
If the rotor disk is made of a fiber-glass-reinforced plastic, this type of 
construction can be afforded. The blades will nevertheless adhere with the 
required stiffness to the only disk-shaped hub 56. If the rotor disk is a 
metallic punched bent part, it is advantageous to rivet the disk-shaped 
hub together with the rotor of the driving motor. 
FIG. 5 shows an additional variant, where by means of a radially deeper 
step, a further enlargement of the flow cross-section is achieved. 
By means of a more extensive reduction of the outer diameter of the housing 
50 to the cylindrical step 52, that there is reduced to a diameter of 50 
to 80%, because of the relatively small ring part 53 of the hub, that is 
still a sufficient amount of cross-section in order to achieve a perfect 
press fit not only on the outer surface 54 of the housing step 52, but in 
addition, because there is sufficient cross-section, the outer contour of 
the plastic hub with its overlapping ring part 53 can be constructed in 
such a way that it has a conical surface 65 that tapers in the direction 
of the inflow plane E, which again is favorable with respect to the flow, 
which is shown above in connection with FIG. 6, right-hand side. If the 
surface 65 extends axially at least over 1/3 of the flow duct length, this 
tapering is quite effective. Particularly by means of the concept of FIG. 
5 that is described in the following, this minimal length can be achieved 
in practice in the mass-produced product without any problems. In the case 
of this embodiment, less demands are made on the plastic that carries the 
one-piece rotor disk 2 with the blades 7, with the ring part 53, with the 
radial bottom wall 55 so that the plastic in this case may possibly be 
less expensive. In the case of FIG. 5, it is also provided that a 
rare-earth alloy, such as samarium cobalt, is used for the rotor magnet 
57. It is known that these types of magnets require a much smaller volume 
so that the permanent magnet in the tube radially may also be much thinner 
which, again in the case of the same air gap (the same magnetic conditions 
are a prerequisite), results in a further reduction of the outside 
diameter of the can 50. These advantageously small outside diameters of 
the driving rotor (in the case of the samarium-cobalt permanent magnet 
solution- used here) and the radially extensive reduction of the step 52 
(i.e., in the case of a ratio of the diameter of the step 52 to the 
diameter of the cylindrical part 50 of the outer rotor housing of 0.5 to 
0.8) results in an effective conical tapering of the engine rotor disk hub 
in the direction of the inlet plane E. Again, in the case of FIG. 5, the 
same rotor may be provided as in FIG. 3 or 4 so that therefore the same 
air gap diameter applies. It is shown that in the case of FIG. 5 the whole 
natural wall thickness of the rotor bundle with the parts 50 and 57 is 
about 1 to 2 mm, and in the case of FIG. 3, it is about 3 to 4 mm which 
signifies a reduction of diameter of about 4 mm which is very important in 
the case of this small size (hub diameter about 30 mm) because the flow 
cross-section is significantly improved by the enlargement and design. 
This concept of FIG. 5 is basically advantageous for miniature fans with a 
central motor, particularly with outside rotors, independently of the 
housing. It is also advantageous for miniature, so-called "motor rotor 
disks" (i.e. motors in which the rotor disk is placed on the motor). It is 
not only for rare-earth rotor magnets (with or without cobalt), but very 
effective for them. Weaker magnets signify a slightly larger "hub" 
diameter. 
In FIG. 6, on the left-hand side, a slightly different variant of a fan 
according to the invention is provided, in which a reduction of the 
outside diameter of the motor hub is visible. 
FIG. 6 shows an injection-molded plastic fan wheel 2 having a hub 19a which 
carries the evenly distributed blades 7 on its periphery. It is pressed 
over the hub part 70 of the outside rotor housing 22 that is reduced in 
its diameter and is fastened in a fitting way. The outside diameter of the 
plastic hub 21 corresponds largely to the outside diameter of the rotor 
housing 22 near its open end. 
The advantage of the plastic fan wheel is the fact that it results in an 
altogether cost-effective axial fan. It is also understandable that the 
outside diameter of the hub 21 is still smaller than this would be the 
case if this hub were to completely reach over the outside rotor of the 
driving brushless direct-current motor. Therefore the rotor constructed 
according to FIG. 6 with the fan wheel that is placed on it is 
advantageously used in very small axial fans, like the object of the 
present invention. The reason is that here, in the range of a rotor disk 
diameter of 30 to 60 mm with a coaxial "hub" motor, a minimal reduction of 
the rotor disk hub diameter is quite advantageous for the flow behavior 
(air volume/time and noise). 
Although it is shown in FIG. 6 that the central fastening part 32 is the 
bearing tube, it should be clear that for many usages the central 
fastening part could also consist of only the interior side of the iron 
core 58 of the stator. Thus, the stator iron could be used as a fastening 
either for the ball bearings 48, 48' or for the slide bearings 49 in the 
case of certain usages of the brushless direct-current motor. The printed 
circuit board 20, in this case, would be fastened by means of pins at the 
appropriate point of the stator. 
A further improvement of the structure consists of equipping the motor of 
FIG. 6 with the fan housing 37, the central fastening part 32, the flange 
30 as well as the webs 5 that are cast out of a single plastic part. 
Thus, in correspondence with this invention, an interior motor structure 
was shown for a brushless direct-current motor having an electronic 
driving system and a revolutions/min. control circuit that, on the inside 
of the motor, is fastened on a master board in such a way that it is 
possible to obtain in steps a smaller diameter at the closed end of the 
hub of the outside rotor than at the open end of the outside rotor. This 
type of diameter that becomes smaller in steps makes it possible that this 
type of motor be used for axial fans having a larger cross-section on the 
air inlet side of the fan, particularly in the case of a fan with smaller 
dimensions, as well as for usages where it is important that larger 
amounts of air be supplied at a higher pressure. 
FIG. 7 is a partial view of the rotor disk hub 2, particularly according to 
FIG. 3. The blades 7 are arranged in an unevenly distributed way at the 
circumference of the rotor disk hub 2. The clearance 75 (in this case 
about 3 mm) is varied in this case in order to reduce noise. The flow 
direction is indicated by the arrow 74. The inlet edges 71 of the blades 7 
are staggered by a first axial distance 61 from the inlet plane E in the 
direction of an Arrow 74 that indicates the flow direction. In the 
embodiment according to FIG. 3, for example, this distance 61 is 3 mm. The 
inlet edge is developed with a radius of about 0.6 mm. In the last third, 
the blade 7 is tapered and ends at the outlet edge 72 with a thickness of 
0.4 mm. The outlet edge 72 is set back by a second distance 62 in the 
opposite direction of the Arrow 74 from the inner web edge 59 of the webs 
5, namely preferably 4 mm (compare FIG. 3). The axial dimension 63 of the 
rotor disk 2 (according to FIG. 3) is about 20 mm. The inlet angle 
.epsilon. at the inflow side that is formed by the tangent line at the 
radial exterior side of the blade edge 71 and the inflow plane E, is 
located in the range of 25.degree. to 45.degree.. The adjusting angle 
.alpha. at the outflow side, formed by the tangent line at the radial 
exterior side of the blade edge 72 and the outflow side A, is 70.degree. 
to 90.degree. to preferably 80.degree.. 
FIG. 8 shows the blade 7 as a part-that is developed in a plane (and can, 
for example, be punched in this way). The blade 7 is developed on both 
sides of an axis 76 that has an angle of slope .beta. of about 45.degree. 
with respect to the blade root, with different radiuses R 1 and R 2. The 
diameters of the two bending cylinders on both sides around the axis 76 
are for 2.multidot.R 1=120 mm and 2.multidot.R 2=30 mm. In the case of a 
radial top view of the blade 7, the bend R 1 of the blade from the 
direction of the inlet edge 71 is at first slight and then changes into a 
more extensive bend R 2.