US 3356154 A
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Description (OCR text may contain errors)
1967 R. CASSIDY 3,
FLEXIBLE BLADE ENGINE COOLING FAN Filed Nov. 16, 1966 ROBE/PT L. CASS/DY INVENTOR ORNEY5 United States Patent Ofiice ENGINE COOLING FAN Westland, Mich., assiguor to Ford Dearborn, Micln, a corporation of ABSTRACT OF THE DISCLOSURE The present invention relates to a flexible cooling fan assembly of the type comprising a hub having asymmetrically disposed arms extending outwardly therefrom, the arms being twisted so as to have an angle of attack with respect to the air flow. The arms are combined with flexible curved blades which are mounted thereon by rivets or the like and suitable laminated reinforcements. The reinforcements are constructed and arranged to provide stress relief for the blades as they attempt to attain planar relationshipwith the hub upon high speed rotation of the fan.
This invention relates to a flexible blade engine cooling fan.
Summary of the invention It has long been recognized that engine cooling fans in which the blades are of a fixed pitch decrease in air moving efliciency and therefore engine cooling efliciency as the speed of the engine and the speed of the vehicle is increased. At high vehicle speeds, the cooling efliciency is relatively low because the ram effect of the air flowing through the radiator passages and over the engine block is more than suflicient to provide the necessary cooling effect. There have been several proposals made in the prior art of means for reducing engine cooling fan drag as the speed of the engine and the vehicle increases. Among these, has been a proposal to provide an engine cooling fan having flexible blades, the pitch of the blades being responsive to air and centrifugal forces which cause the pitch of the blades to decrease as the speed of the fan is increased. U.S. Patent 2,149,267 to Bouvy et al. and 3,044,557 to Posh are representative of this tym of fan.
lexible fan have not achieved commercial success because the designs available have not been able to achieve optimum production design and optimum fan endurance. It is an object of the present invention to provide a flexible cooling fan which meets both of the necessary criteria for commercial acceptability.
The foregoing has been accomplished by providing an engine cooling fan having a central planar hub and a plurality of rigid arms extending outwardly of the hub. Each arm has mounted thereon a flexible blade. Each blade has a flat leading portion overlying the arm with the plane of the flat portion intersecting the plane of the hub at an angle. Each blade has a curved trailing portion extending laterally of its flat portion and curved away from the plane of the hub. An important feature of the present invention is the provision of lamina means for mounting the blade on the arm, the lamina means comprising an insulation plate interposed between each arm and blade flat leading portion and a cap plate overlying the blade flat leading portion. Securing means, such as rivets or the like, secure each arm, insulation plate, blade flat portion and cap plate in the laminated relationship. A further important feature is that each cap plate is provided with a curved trailing edge laterally spaced from the securing means and extending longitudinally of the cap plate. The cap plate is curved at its trailing edge to provide for stress concentration relief as the blade curved 3 3,356,154 Patented Dec. 5, 1967 portion is flexed toward the rotation of the fan.
Other objects, advantages and features of the present invention will become more apparent as this description proceeds particularly when considered in conjunction with the accompanying drawings, wherein:
FIG. 1 is a plan view of an engine cooling fan embodying the present invention;
FIG. 2 is a side elevational view of FIG. 1; and
FIG. 3 is an enlarged sectional view taken along line 3-3 of FIG. 1.
plane of the planar hub upon Detailed description Referring now in detail to the drawing, there is shown generally at 11 an engine cooling fan adapted for use on a motor vehicle engine. The fan comprises a spider or central planar hub 12 and a plurality of rigid arms 13 extending outwardly of the hub. The arms 13 are preferably asymmetrically disposed and in this respect follow conventional design practice.
Each arm 13 has mounted thereon a flexible or resilient blade 14 having a substantially flat portion 15, see FIG. 3, overlying the arm. The blade 14 has a curved trailing portion 16 extending laterally of the flat portion 15 and curved rearwardly away from the plane of the hub, see FIG. 2.
Thefiexible blades 14 are mounted on their respective arms 13 by lamina means comprising an insulation plate 17, which may be a pressure sensitive aluminum foil tape, and a cap plate or reinforcement member 18, which may be formed of sheet metal.
Securing means, such as rivets 19, or the like, secure each arm 13, insulating plate 17, blade flat portion 15 and cap plate 18 in laminated relationship. A best seen in FIG. 3, each cap or reinforcing plate 18 has a curved trailing edge 21 laterally spaced from the rivets 19 and extending longitudinally of the cap plate. This is an important feature, as will be explained.
Each arm 13 has a twisted base section 22 adjoining the arm to the hub 12 so that the plane of each arm is at an angle to the plane of the hub. This means that the leading edge of each arm in the direction of rotation of the fan as indicated by the arrow in FIG. 1, is forward of the trailing edge of the arm so as to to form an attack angle relative to the direction of air flow as indicated by the arrow in FIG. 2. A flat portion of each blade 15 lies adjacent the forward face, again with reference to the direction of relative air flow as shown by the arrow in FIG. 2, of the arm 13. The direction of curvature of the curved portion 16 of each blade is rearwardly of the plane of rotation of the fan or of the fan hub.
As a result of the foregoing construction and arrangement, the blades 14 will by the action of the air pressure and centrifugal forces acting on the flexible portions of the blades, have tendency to flatten out as the rotational speed of the fan is increased. In effect, the pitch the higher rate of fan rotation, thus making more horsepower available for propelling the vehicle.
The importance of the curved trailing edges 21 on the cap plates 18 is that as the fan blades flex away from the arm 13, the portions of the blades adjacent the curved edges 21 roll around the edges 21 thereby shifting the point of stress concentration outwardly from the rivets 19 as the fan speed is increased. This prevents the buildup of metal fatigue on the blades at any single line of contact with the cap or reinforcing plates and results in much greater fan endurance.
It will be understood that the invention is not to be limited to the exact construction shown and described, but that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.
1. An engine cooling fan having a central planar hub and a plurality of rigid arms extending outwardly of said hub,
a plurality of flexible blades each having a fiat leading portion overlying an arm with the plane of the flat portion intersecting the plane of the hub at an angle thereto,
each blade having a curved trailing portion extending laterally of its flat portion and curved away from the plane of said hub,
a spacer plate interposed between each arm and blade flat leading portion and an outermost cap plate overlying said blade flat leading portion,
securing means securing each arm, spacer plate, blade flat portion and cap plate in laminated relationship,
and each cap plate having a curved trailing edge closely adjacent to said securing means extending longitudinally of said cap plate and away from the plane of the blade therebeneath,
said cap plate curved trailing edge providing stress relief for said blade curved portion adjacent said securing means as the latter is flexed about said curved trailing edge toward the plane of said planar hub upon rotation of said fan.
2. An engine cooling fan according to claim 1 in which the arms are asymmetrically positioned around said hub.
3. An engine cooling fan having a central planar hub and a plurality of rigid fiat arms extending asymmetrically of said hub,
each arm having a twisted base section joining the arm to the hub so that the plane ot'each arm is at an angle to the plane of said hub,
a plurality of flexible blades each having a flat portion at the leading edge thereof and a curved trailing portion extending laterally of its flat portion,
a first plate member interposed between the blade flat portion and an adjacent surface of an arm and an outermost cap plate overlying said blade flat portion,
securing means securing each arm, first plate member,
blade flat portion and cap plate in laminated relationship,
and each cap plate having a curved trailing edge closely adjacent to said securing means,
said blade curved trailing portions upon rotation of said fan seeking a parallel planar relationship to the plane of said hub,
said cap plate curved trailing edges providing stress relief for said blades adjacent said securing means as the latter bend around said cap plate curved trailing edges upon said blades seeking parallel planar relationship to said hub.
References Cited UNITED STATES PATENTS 2,032,224 2/1936 Paton -1605 2,149,267 3/1939 Bouvy et al. 170-160.5 2,766,964 10/1956 Almquist et al.
3,044,557 7/1962 Posh 170--l60.5 3,289,924 12/1966 Weir 170160.5 X
EVERETTE A. POWELL, 111., Primary Examiner.
EDGAR W. GEOGHEGA'N, Examiner.
Disclaimer 3,356,154.Robert L. Oassidy, Westland, Mich. FLEXIBLE BLADE EN- GINE COOLING FAN. Patent dated Dec. 5, 1967. Disclaimer filed Sept. 17, 1970, by the assignee, Ford Motor Company. Hereby enters this disclaimer to claims 1, 2 and 3 of said patent.
[Oficial Gazette January 12, I971]