Shrouding for engine cooling fans

Shrouded engine cooling fan in which the interface between an outer stationary shroud fixed with respect to a radiator and an inner and rotating shroud fixed to the tips of the fan blades define a generally toroidal chamber in which a vortex of air is generated in response to the rotational drive of said fan that acts as a seal to block the flow of recirculation air from the fan discharge to the fan entrance over a wide range of fan operating points to increase fan operating efficiency and reduce fan generated noises.

FIELD OF THE INVENTION 
This invention relates to shrouded engine cooling fans and, more 
particularly to a multi-bladed cooling fan having new and improved 
relatively rotatable shrouding which is operative to retard the 
recirculation of fan discharge air into the fan inlet over a wide range of 
fan operating points to thereby improve fan efficiency and to reduce fan 
generated noises. 
DESCRIPTION OF RELATED ART 
Various fan designs for engine cooling utilize special fixed and rotatable 
shrouding which is intended to make the fan pump air with high efficiency 
and without generating excessive noise. Among these are shroud 
arrangements that have stationary shrouding that is fixed with respect to 
an engine heat dissipating radiator and rotatable shrouding fixed to the 
tips of the fan blading that operates within the fixed shrouding. In U.S. 
Pat. No. 4,329,946, assigned to the assignee of this invention and hereby 
incorporated by reference a fan with a rotatable shroud is immersed within 
a fixed shroud in a design that provides effective blockage of a 
recirculation air path occurring between the two shrouds. This blockage 
however is optimally effective in a narrow range of fan operating points 
and occurs at the discharge side of the rotatable fan with fan discharged 
air blocking an annular clearance path between the rotating and fixed 
shrouds. The operating point of a fan is defined as the ratio of the air 
flow rate to the pressure rise. While this prior construction provides 
efficient and quiet pumping it is highly sensitive to fan operating point 
and effectiveness at points outside of a very narrow range of fan 
operating points is materially reduced since blockage falls and 
considerable volumes of air can recirculate to the fan inlet so that fan 
noise abatement and pumping efficiency is reduced. 
SUMMARY OF THE INVENTION 
In the present inention a bellmouthed rotating ring shroud is fixed to the 
tips of the blades of an engine cooling fan and is immersed in a 
cooperating stationary shroud. These shrouds have an interface 
configuration that uses the pressure differential and entrained air flow 
in a generally toroidal chamber in an annular clearance passage between 
the shrouds to generate a vortex of air. This vortex acts as a seal to 
block a majority of air that would otherwise recirculate from the high 
pressure to the low pressure side of the fan. With this new and improved 
recirculation blockage the fan does not have to repump air so that fan 
efficiency and noise abatement are optimized. This invention is effective 
for substantially all fan operating points and particularly effective when 
the fan is immersed within a cylindrical ejector so that an additional air 
seal is formed at the discharge end of the fixed and rotatable shrouding. 
With this dual seal arrangement recirculating flow at the operating point 
of the fan where the rear seal is effective is optimally blocked because 
the vortex front seal blocks recirculation bypassing the rear seal. At the 
other fan operation points where the effectiveness of the rear seal is 
reduced or marginal, the vortex seal continues to provide a highly 
effective seal. In the preferred embodiment of the invention, the vortex 
of air generated in the vortex chamber acts as a localized area of high 
pressure that blocks the pathway of recirculating air flow adjacent the 
periphery of a bellmouth inlet of the rotating shroud to provide a full 
time front seal. This full time front seal also blocks forward entrance of 
the vortex seal chamber so that large quantities of air flowing into the 
fixed shrouding through the radiator are routed into the entrance of the 
rotating ring shroud.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Turning now in greater detail to the drawings there is shown in FIG. 1 a 
conventional radiator 10 adapted to be operatively mounted in an engine 
compartment of a vehicle for cooling the fluid coolant circulated 
therethrough. The radiator is mounted to upper and lower supports 12 and 
14 which also serve as the supporting structure for a shrouded engine 
cooling fan assembly 15 to which this invention is drawn. This assembly 
includes a shell-like outer shroud 16 molded from a suitable plastics 
material having a rectilinear face plate 18 bounded by a peripheral and 
forwardly extending wall 20 providing good radiator coverage such as 
between lines L--L in FIG. 1. Mounting ears 22 and 24 respectively 
extending upward and downward from wall 20 provide means to secure the 
outer shroud and thus the fan assembly to the supports 12 and 14 with ears 
24 being inserted in laterally spaced slots 26, one of which is not shown, 
in the lower support 14 while the upper ears 22 receive fasteners 30 that 
thread into the upper support 12. The face plate 18 has a planar interior 
surface 32 which faces the radiator and extends inwardly from the 
peripheral wall 20 to a doubled stepped and rearwardly extending 
cylindrical ejector 34. FIG. 2 illustrates a cross section of part of 
ejector 34 which has a large diameter step 36 integral with and extending 
rearwardly from the face plate and a reduced diameter step 38 continuing 
from the large diameter step to a terminal annular end 40. The cylindrical 
reduced diameter step forms the discharge end of the fixed fan shroud. 
The large diameter step 36 of the cylindrical ejector 34 accommodates the 
outwardly flaring bellmouth 44 providing the inlet of a rotatable shroud 
46 that is secured to the tips of the blades 47 of a multiple bladed 
cooling fan 48. The fan 48 is supported for rotation within shoud 16 by 
the output shaft of an electric motor 52. This motor is in turn centrally 
supported within the stationary shroud 16 by a support collar 54 and three 
or more spokes 56 radiating therefrom to attachment with three or more 
arcuately spaced ears 58 projecting axially from the reduced diameter step 
38 of the outer shroud 16. As best shown in FIG. 2 the bellmouth of the 
rotatable shroud has an annular forward surface 60 at the entrance thereof 
that is smooth and substantially coplanar with the forward surface 32 of 
the outer shroud 16 to enhance the flow of air from the fixed outer shroud 
into the rotatable shroud. With this configuration, and with the forward 
air seal described below, the flow is attached and will tend to remain 
attached with no appreciable induced turbulence. From this forward surface 
the bellmouth arcs inwardly and rearward to a cylindrical skirt 64 that 
has a terminal end 68 that is inboard of the terminal end 40 of the fixed 
shroud as shown in FIG. 2. The diameter of the rotatable shroud is 
correspondingly smaller than that of the fixed shroud 16 all along the 
axial length thereof to provide an annular clearance passage 70 
therebetween through which discharge air normally has a tendency to 
recirculate. The radially extending fan blades 47 extend from a central 
drive hub 72 to connection with the cylindrical skirt 64 of the rotatable 
shroud so that this shroud rotates with the fan. With this construction 
air discharged by the fan when driven by the motor at certain operating 
speeds will have a significant radial component, here diagrammatically 
shown by arrow A, which partially blocks the clearance passage 70 at the 
discharge side of the fan. This embarrassment to recirculation air flow 
allows the fan to pump with higher efficiency since there is reduced 
pumping of recirculation air. Also the fan pumps with reduced noise since 
reduced amounts of recirculation air turning into the bellmouth and 
turbulence which may result therefrom is decreased as pointed out in 
greater detail in prior U.S. Pat. No. 4,329,946 cited above. Importantly 
in this invention the shroud construction is such that a forward air block 
is formed that further inhibits the flow of recirculation air for a wide 
range of fan operating points which materially extends the limited range 
of blockage provided by the extending ejector 38 and the rotatable shroud. 
As best shown in FIG. 2 a vortex chamber 78 is formed between the bellmouth 
of the rotating shroud and the large diameter step 36 of the fixed shroud 
16. This generally toroidal chamber is basically defined by the concavely 
curved outer wall 80 of the bellmouth 44 of the rotating shroud and the 
concavely curved inner wall 82 of the large diameter step of the outer 
shroud 16. This vortex chamber has a front restricted entrance 84 defined 
by the annular clearance between the outer peripheral edge 88 of the 
bellmouth 44 and the facing inner wall 89 of the fixed outer shroud 18. A 
restricted rear entrance 90 for chamber 78 is defined between the apex 92 
of the annular constriction 94, triangular in cross section, formed on the 
interior of the large diameter step of the outer shroud. With this 
construction a convex 96 of air is generated from the action of 
recirculating air flow impinging on the rotating shroud side of the 
chamber 78 and by heat exchanger air flowing into the fixed shroud. The 
resulting vortex acts as a ring of high pressure that blocks the pathway 
of recirculating air flow so that the fan does not repump discharged air 
resulting in improved fan efficiency and flow distribution. Importantly in 
this invention this vortex block embarrasses the recirculation flow for 
substantially all fan operating points which extends well beyond the 
limited blockage provided by the immersion of the rotating shroud within 
the fixed shroud. In addition to blocking the recirculation air path the 
air vortex blocks the front annular entrance 84 so that quantities of air 
entering the fixed shroud through the radiator 10 routes into the 
bellmouth 44 instead of into the ejector as diagrammatically illustrated 
by flow arrow B. 
While a preferred embodiment of the invention has been shown and described 
other embodiments will be now apparent to those skilled in the art. For 
example the vortex seal chamber can be made so that the inlet 90 can be 
defined by a rounded edge instead of the annular apex 92 with any such 
modification ensuring the formation of a vortex of flow to block 
recirculating flow for a wide range of fan speeds and operating points. 
Also the full rotating ring shroud can be replaced by segments of the ring 
shroud or winglets attached to each of the blades so that all of the seal 
geometry is present. Vortex formation, stability and magnitude of vortex 
pressure may be enhanced through use of small scale aerodynamic devices in 
the vortex chamber. These devices can be in the form of circular scoring 
in the surfaces of the vortex chamber similar to rifling of gun barrels, 
or could take form as small bladelets formed on the walls thereof.