Fan wheel with cup shaped hub

A fan wheel has a cup shaped hub having an outer cup wall with a plurality of vanes and a cup bottom connectable with a shaft of a drive and provided at its inner side with a plurality of ribs defining a plurality of fields therebetween. The cup bottom in the region of the fields has a plurality of depressions extending from its inner side and having a width approximately 70% of a thickness of the cup bottom.

BACKGROUND OF THE INVENTION 
The present invention relates to a fan wheel with a cup shaped hub with a 
cup wall provided with a plurality of radially extending vanes and a cup 
bottom connected with a shaft of a drive motor. 
Fan wheels of the above mentioned general type are known in the art. In a 
known fan wheel the cup bottom has substantially the same thickness as the 
cup wall. When such a fan wheel is fixedly connected with the shaft of the 
drive motor, the magnetic force fluctuations occurring in the electric 
motor due to the armature grooves extending through the magnetic field can 
propagate through the shaft to the hub and radiated through the vanes as 
sound transmitted air. The flutes tone produced in this way has a 
frequency of approximately 630 Hz depending on the size of the hub and is 
disturbing especially when the fan is used for ventilation of the cooling 
device for the internal combustion engine of a motor vehicle. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a fan 
wheel which avoids the disadvantages of the prior art. 
In keeping with these objects and with others which will become apparent 
hereinafter, one feature of the present invention resides, briefly stated, 
in a fan wheel which has a cup shaped hub with a plurality of ribs 
provided on its cup bottom and defining fields therebetween, wherein in 
accordance with the present invention the cup bottom in the region of the 
above mentioned fields has depressions extending from their inner side and 
having a depth corresponding to at least 70% of the thickness of the cup 
bottom. 
When the fan wheel is designed in accordance with the present invention it 
avoids the disadvantage of the prior art. 
The fan wheel in accordance with the present invention in the regions of 
the field and therefore the vibrations in this region are eliminated. 
Thereby the disturbing operational noise disappears. 
The frequency f, for example 630 Hz, is calculated as follows: 
EQU f=Z.multidot.n/60 
wherein Z is a number of the grooves, n is a rotary speed in revolutions 
per minute. 
The passing wavelength 
EQU .lambda.=c/f 
c is the speed of sound in m/s. Here 
EQU .lambda.=340 m/s/360 Hz=0.54 m. 
This equation takes place when the half diameter 
EQU D=.lambda./4. Here: 
EQU D=0.54 m/4=0.135 m. 
Since the motor size and the fan size cannot be changed (required values 
for performing the objective), therefore with these features the hub is 
determined acoustically or in other words made acoustically "soft". 
In accordance with another feature of the present invention the 
depressions, as seen in the circumferential direction of the hub, extend 
from one rib to another neighboring rib. 
In accordance with still a further feature of the present invention, the 
fields between the neighboring ribs are provided with throughgoing 
openings. Preferably, the throughgoing openings extend in a radial 
direction and are slot-shaped. 
The width of the slots measured in the circumferential direction of the hub 
can amount to maximum 3 mm. 
Finally the free ends of the vanes are connected without another by a ring 
which surrounds the hub. 
The novel features which are considered as characteristic for the invention 
are set forth in particular in the appended claims. The invention itself, 
however, both as to its construction and its method of operation, together 
with additional objects and advantages thereof, will be best understood 
from the following description of specific embodiments when read in 
connection with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
A fan wheel in accordance with the present invention is identified as a 
whole with reference 10 in FIG. 1. It has a cup shaped hub 20 clearly 
shown in FIG. 2. 
The hub 12 has a cup wall 16 provided with a plurality of vanes 18 on its 
outer side 14. The vanes 18 are connected on their free ends by a circular 
ring 20. A cup bottom 22 is connected with a ring shaped wall 14 and 
extends in a radial direction of the fan wheel 10. A greater part of an 
electrical drive motor 24 is accommodated in the cup 12. It is shown in 
FIG. 2 in dash-dot lines and identified with reference numeral 24. 
The electric drive motor 22 has a drive or armature shaft 26 extending from 
it. The cup bottom 22 of the cup 12 of the fan wheel 10 is mounted on the 
free end of the shaft 26. For this purpose the shaft 26 extends through 
the cup bottom to the region of a central reinforcement 28. The mounting 
is performed by a mounting nut 30 which is screwed on a not shown threaded 
pin of the armature shaft 26. Thereby the hub 12 and therefore the fan 
wheel 10 is fixedly connected with the shaft 26 and the fan wheel rotates 
together with the not shown armature of the electric motor 24. 
As shown in FIG. 2, the cup shape hub 12 is provided with ribs 32 on its 
inner side, both in the region of the inner wall of the cup as well 
extending in the region of the cup bottom 22. As seen in the 
circumferential direction of the hub, they are arranged at a distance from 
one another and extend radially on the cup bottom 22 as can be seen in 
FIG. 1. Fields 34 of the cup bottom 22 is formed between neighboring ribs 
32. The fields have substantially the shape of the segments which, when 
seen in FIG. 1 shown in the cup shape of the hub 12. As can be seen from 
FIG. 2, the cup bottom in the region of the field 34 has depressions 36 
extending from its inner side. The depressions 36 have a depth 38 at least 
equal to 70% of the thickness 40 of the cup bottom as shown in FIG. 3. 
As can be also seen from FIG. 3 that a remaining thickness 42 of the cup 
bottom 22 in the region of the depressions 36, as compared with the ribs 
32, is very small. Therefore a certain elasticity of the fan wheel in the 
region of the bottom 22 is produced. As a result, a tendency to vibrations 
is obtained. Furthermore, the hub is thereby determined acoustically. As 
shown in FIG. 1, the depressions 36 extend between the ribs 32 over the 
whole distance between two neighboring ribs 32. As can also be seen from 
FIG. 1, the fields 34 between the neighboring ribs 32 have through-going 
passages 44. The passages 44 are preferably radial and slot shaped. 
The slots 44 have a maximum width 46 equal to 3 mm as considered in the 
circumferential direction of the hub 12. This is shown in FIG. 4. The 
slots, with the remaining thin wall 38 in the region of the fields 34, 
must form a reliably protection against spring water from the outer side 
of the cup bottom 22. In the event of excessively wide slots 44 it can 
penetrate through cooling air opening 50 in the end wall 51 of the 
electric drive motor 24 which faces the cup bottom 22. The spring water 
can whirl through the motor vehicle from the street. The ventilating 
device with the fan wheel 10 can be used for the ventilation of the 
cooling device of an internal combustion engine of a motor vehicle. Due to 
the rotatable fan wheel, in connection with the low width of the slots 44, 
it is reliably prevented that the spray water flows through the 
ventilating openings 50 into the electric motor 22 and can damage it. 
It will be understood that each of the elements described above, or two or 
more together, may also find a useful application in other types of 
constructions differing from the types described above. 
While the invention has been illustrated and described as embodied in a fan 
wheel, it is not intended to be limited to the details shown, since 
various modifications and structural changes may be made without departing 
is any way from the spirit of the present invention. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
from the standpoint of prior art, fairly constitute essential 
characteristics of the generic or specific aspects of this invention.