Cooling fan for electric motors

The present invention provides an improved rotor and end connector for an induction motor. The end connector adjoins a rotor core. The rotor core includes a plurality of spaced ventilation openings and defines an aperture for capturing a motor shaft. The end connector should preferably surround and be concentric with the inner ventilation openings. To increase ventilation efficiency, the end connector has a plurality of spaced fan blades. Each of the fan blades has a sloping inner surface and backward curving outer surface. The backward curving outer surface is substantially perpendicular to the end connector, and directs air flow radially outward.

BACKGROUND OF THE INVENTION 
This invention relates to cooling fans for electric motors and generators 
and more particularly to improved rotor and end connectors for induction 
motors having precisely shaped fan blades to maximize ventilation 
efficiency, without diminishing the strength of the blades. 
Dynamoelectric machines, particularly high speed induction electric motors, 
produce a lot of heat, particularly in the rotor winding and the 
laminations of steel that make up the body of the rotor. Various attempts 
have been made to provide ventilation at one end of the rotor using radial 
fan blades. For example, in U.S. Pat. No. 821,249 (Lundell), the patentee 
states that he attempts to improve ventilation of a dynamoelectric machine 
by providing end plates having web-like arms which appear to force air 
through a flange to cool the winding. 
According to U.S. Pat. No. 1,628,086 (Warner), the patentee includes a fan 
in an electric motor. The fan appears to force air around one end of the 
coils in order to cool the motor coils and field laminations. 
Similarly, the patentee of U.S. Pat. No. 3,075,106 (Chi) states that he 
uses an improved rotor to cool a hermetic refrigeration motor-compressor 
unit. According to the patentee, the rotor has a plurality of impeller 
blades at each end, with the outer portion of each blade leading the inlet 
portion in the direction of rotation of the rotor. The patentee also 
states that the impeller blades direct refrigerant cooling fluid into 
contact with the winding end turns to transfer heat away from the motor. 
None of the foregoing attempts, however, appears to provide a satisfactory 
solution to the problem of providing a suitable cooling fan for an 
induction motor. 
SUMMARY OF THE INVENTION 
The present invention provides an improved rotor for an induction motor, 
comprising a rotor core and an end connector. The rotor core defines an 
aperture for capturing a motor shaft and includes a plurality of spaced 
ventilation openings. The end connector comprises a ring of conductive 
material, and cooperates with the plurality of spaced ventilation openings 
on the rotor core. The end connector ring should preferably surround and 
be concentric with the ring of ventilation openings. To increase 
ventilation efficiency, the end connector ring has a plurality of spaced 
fan blades. Each of the fan blades has backward curving inner and outer 
surfaces, with the outer surface substantially perpendicular to the end 
connector. 
The present invention also provides a fan blade for inclusion in or 
attachment to an end connector of a rotor for an electric induction motor. 
The fan blade comprises a bottom edge and a top edge, with the bottom edge 
wider than the top edge. The fan blade also has an inner surface, an outer 
surface, a leading edge and a trailing edge. The inner surface curves from 
the wider bottom edge to the narrower top edge. The outer surface is 
substantially perpendicular to the bottom edge, permitting the outer 
surface to move air along a predetermined path. The leading edge 
preferably forms an entry angle of between about 20.degree. and about 
40.degree. with respect to a tangent point at the tip of the blade. The 
trailing edge preferably is inwardly biased or offset with respect to the 
outer surface of the fan blade. 
The invention, together with further objects and attendant advantages, will 
be best understood by reference to the following detailed description 
taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawings, FIG. 1 shows a side view of a rotor generally 
designated by the reference numeral 10 including at each end an improved 
end connector 12, 14 of the present invention. As shown in FIG. 2, the end 
connector 12, 14 adjoins a rotor core 16. The rotor core 16 defines a 
central aperture 20 for capturing a motor shaft 22 (FIG. 1), and includes 
a plurality of spaced ventilation openings 24 located within the inside 
diameter of the end connector 12, 14. The end connector 12, 14 has 
extending therefrom a plurality of fan blades 26. These airfoil-shaped fan 
blades 26 have a geometry arrived at through experimentation in order to 
maximize air circulating efficiency, while preserving mechanical strength 
of the fan blades 26, and their attachment to the end connector 12, 14, 
and maintaining desired low noise levels. 
The geometry of the fan blades 26 can best be understood by reference to 
FIGS. 3, 4 and 5. Referring to FIGS. 3-5, each fan blade 26 includes a top 
edge 28, a bottom edge 30, an inner face 32, an outer face 34 (FIG. 4), a 
leading edge 36 (FIG. 3) and a trailing edge 38 (FIG. 4). As best shown in 
FIG. 5, the fan blade 26 is tapered in cross-section: the inner surface 32 
curves backwardly from the bottom edge 30 to the top edge 28, as shown in 
FIG. 5. On the other hand, the outer surface 34 is substantially 
perpendicular with respect to the plane defined by the bottom edge 30. The 
dimensions vary according to the size and turning speed of the rotor. For 
example, for a motor designed to have the rotor turn at about 3600 rpm 
with a 12.5 inch diameter rotor, the bottom edge 30 should be about 5/8 
inch thick and the top edge 28 should be 3/16 inch thick. The inner 
surface 32 should slope evenly from the bottom edge 30 to the top edge 28. 
This inner surface 32 allows the fan blade to preserve mechanical strength 
while diminishing overall thickness, weight and bulk of the fan blades 26. 
The outer surface 34, as stated above, is essentially perpendicular to the 
bottom edge 30 and therefore to the end connector. The outer surface 34 is 
also preferably substantially parallel to the plane defined by the motor 
shaft 22, as may be seen in FIG. 1. The substantially backward curved 
vertical outer surface 34 directs air flow radially outward (FIG. 1). In 
order to aid ventilation, the laminations comprising the rotor 10 core 
have spaces between packets of laminations. These spaces (not shown) act 
as radial vents to allow air to blow outward to maintain a cooler rotor 
temperature. This lower temperature helps to reduce electrical resistance 
in the rotor, thereby improving the efficiency of the motor. 
Importantly, the leading edge 36 of the fan blade 26 is shaped and 
positioned on the end connectors 12, 14 so that the tip 40 of the blade 
forms an angle of between 20.degree. and 40.degree. from the tangent 
formed at the tip of the blade, as shown in FIG. 6. Preferably, the angle 
formed by the tangent ranges from about 20.degree. to about 30.degree., 
although an angle of between about 24.degree. to about 26.degree. appears 
optimal, based upon experiments conducted thus far. Of course, the exact 
angle formed by the tangent at the point of the tip 40 of the fan blade 26 
may be varied depending on the size and duty of the particular motor, and 
a person of ordinary skill designing an end connector 12, 14 can vary the 
entry angle of the fan blades 26 and their placement on the end connector 
12, 14 to optimize the cooling and ventilating power of the improved end 
connectors 12, 14. 
In addition, the trailing edge 38 tapers beyond the actual trailing edge of 
the outer face 34 of the blade 26, as shown in FIG. 4, and is biased 
inwardly with respect to the longitudinal curve defined by the blade. This 
shape helps reduce the rotational forces on the blade 26 without 
substantially diminishing the air current. 
The fan blades 26 may be individually cast or forged and welded to the end 
connectors 12, 14. Alternatively, and preferably, the fan blades should be 
integrally cast with the end connectors 12, 14. If cast, the end connector 
12, 14 as cast should be designed so that the casting includes a plurality 
of preferably oval shaped metal risers 42, as shown in FIG. 2. These metal 
risers 42 stay molten while other parts of the casting are cooling and 
solidifying. This allows shrinkage to occur in the casting without 
distorting the end connectors 12, 14. Once the casting has cooled, the 
risers 42 may be cut off. The casting should also preferably include a 
plurality of pins 44 spaced around the periphery of the outer ring 18 
between adjacent fan blades 26. The pins 44 have washers or other weights 
(not shown) placed thereon to properly balance the end connectors 12, 14. 
Once the desired balance is achieved, the ends of the pins 44 are 
flattened using a hammer to secure the washers in place and prevent them 
from sliding off. 
Having described the invention and how it is made, a person of ordinary 
skill can now readily understand how the improved end connectors 12, 14 
and rotor 10 of the present invention operate. When the rotor 10 is being 
turned by the inductive forces in the induction motor, the fan blades 
create air currents. Some air passes through the plurality of ventilation 
openings 24 in the rotor core 16 which permits air to blow through spaces 
in the rotor (not shown). An air current also passes around the outside of 
the rotor 10 and provides a cooling air current to the stator core and 
winding. The design of the fan blades 26 provides higher ventilating 
efficiency because of the shape and orientation of the fan blade 26 
described above. Additionally, the improved aerodynamic fan design seems 
to produce less noise. The tapered blade thickness provides substantial 
mechanical strength to withstand the effects of rotational forces at the 
base of the fan blade 26. Additionally, the ventilation openings 24, which 
allow air to enter through spaces in the rotor laminations, obviate the 
need for fluted shafts. Also, because air can enter axially through the 
end connectors 12, 14 at both ends, increased cooling results, permitting 
extended core length. 
Various modifications and changes to the preferred embodiment described 
above will be apparent to those skilled in the art. Such changes and 
modifications can be made without departing from the spirit and scope of 
the present invention, and it is therefore intended that such changes and 
modifications be covered by the following claims including all equivalents 
.