Blade configuration for shrouded motor-driven fan

A motor-driven fan including a hub adapted to be driven by a motor, a plurality of fan blades provided on the hub to extend in radial directions, a shroud including a ring-shaped portion encircling the fan blades and stay members for supporting the ring-shaped portion, each of the fan blades being formed at a tip end thereof with a deflector which is bent in a direction of rotation of the fan by a width which increases from a leading edge to a trailing edge of the blade.

The present invention relates to a fan structure and more particularly to a 
fan blade configuration. 
Hithertofore, in the field of a shrouded fan which includes a motor-driven 
hub carrying a plurality of radially extending fan blades and a shroud 
having a ring-shaped portion encircling the fan blades and stay members 
for supporting the ring-shaped portion, there has been a problem of noise 
being produced by a stream of air impinging upon the interconnections 
between the ring-shaped portion and the stay members. Since the noise is 
caused by such air stream having a radially outward speed component, 
efforts have been made to suppress radially outward speed component. For 
example, Japanese utility model disclosure No. 55-35363 teaches to provide 
fan blades with beads at the tip portions thereof. Japanese utility model 
disclosure No. 55-90796 teaches to form flanges at the tip ends of the fan 
blades. Although efforts have thus been made in the past, they have not 
been successful to suppress the noise to a satisfactory extent. 
It is therefore an object of the present invention to provide a fan blade 
configuration which can eliminate the aforementioned problems in the 
conventional fan blades. 
Another object of the present invention is to provide a fan blade 
configuration which does not produce air stream noise when it is applied 
to a shrouded fan. 
According to the present invention, the above and other objects can be 
accomplished by a fan blade having a radially inner and tipends, and a 
leading and trailing edges, said fan blade being formed at the tip end 
with a deflector bent in forward direction by a width which increases from 
the leading edge to the trailing edge. According to a further aspect of 
the present invention, there is provided a motor-driven fan including a 
hub adapted to be driven by a motor, a plurality of fan blades provided on 
said hub to extend in radial directions, a shroud including a ring-shaped 
portion encircling the fan blades and stay members for supporting said 
ring-shaped portion, each of said fan blades being formed at a tip end 
thereof with a deflector which is bent in a direction of rotation of the 
fan by a width which increases from a leading edge to a trailing edge of 
the blade. Preferably, each fan blade is formed with a guide section which 
extends from said deflector in the direction of rotation of the fan and 
has a substantially straight cross-section.

Referring now to the drawings, particularly to FIGS. 1 and 2, there is 
shown a motor-driven fan which includes a motor 1 having an output shaft 
1a. A fan boss 3 is secured to the output shaft 1a of the motor 1 and 
carries a plurality of fan blades 10 which extend in radial directions. 
The fan further includes a shroud 4 which is comprised of a ring-shaped 
portion 5 encircling the fan blades 10 and a plurality of spiders or stay 
members 6 which are secured on one hand to the casing of the motor 1 and 
on the other hand connected to the ring-shaped portion 5 at junctions 7. 
Referring now to FIGS. 3 and 4, it will be noted that the fan blade 10 is 
secured to or integrally formed with the hub 3 and has a trailing edge 13 
and a leading edge 14. At the tip end, the fan blade 10 is formed with a 
deflector 12 which is an arcuately curved portion bent from the body of 
the fan blade in the forward direction or the direction of rotation of the 
fan. The deflector 12 has a width which increases gradually from the 
leading edge 14 to the trailing edge 13. A guide section 15 having a 
substantially straight cross-sectional configuration is formed to extend 
forwardly or in the direction of rotation of the fan from the deflector 
12. The guide section 15 also has a width which increases from the leading 
edge 14 to the trailing edge 13. 
The configuration of the deflector 12 may be represented in terms of an 
angle .alpha. which is as shown in FIG. 4 an angle between the surface of 
the body of the fan blade 10 and a line passing through the starting point 
and the ending point of the deflector 12. The angle .alpha. may be 
10.degree. to 60.degree., preferably 30.degree.. In the embodiment 
illustrated in the drawings, the radial dimension of the fan blade 10 is 
slightly decreased from the leading edge 14 to the trailing edge 13. The 
configurations of the fan blades 10 are found effective to deflect the air 
stream away from the junctions 7 in the shroud 4 so that it is possible to 
suppress or eliminate the noise which may otherwise be produced by the air 
stream impinging upon the shroud 4 at the junctions 7. 
The invention has thus been shown and described with reference to a 
specific embodiment, however, it should be noted that the invention is in 
no way limited to the details of the illustrated structures but changes 
and modifications may be made without departing from the scope of the 
appended claims.