US 3891349 A
A cooling fan formed of two sheet metal layers joined to a centrally contained spider arm. The configuration of the resulting blade is streamlined or an airfoil in cross section. In constructing the fan the surface pieces are normally spaced from the central support arm and during assembly are forced together and joined to the arm. The resulting stress imposed on the leading and trailing edges of the surface sheets reduces vibratory stresses in the blade. In one embodiment the trailing edge of one of the sheets is permitted to slide along the surface of the other sheet when the other sheet is decambering due to centrifugal and aerodynamic forces generated by rotation of the fan. The result is to vary the moment arm of the restraining forces imposed on the decambering trailing portion of the flexing sheet, thus giving better control of the decambering rate of that sheet.
Description (OCR text may contain errors)
United States Patent [191 Woollenweber, .11 r.
 3,891,349 ]*June 24, 1975  Assignee: Wallace-Murray Corporation, New
[ Notice: The portion of the term of this patent subsequent to June 24, 1991, has been disclaimed.
 Filed: Feb. 22, 1972  Appl. No.: 227,922
8,734 4/1908 France 416/240 152,416 lO/l920 United Kingdom 416/210 450,992 7/1936 United Kingdom 416/210 Primary Examiner-Everette A. Powell, Jr. Attorney, Agent, or Firm-Thomas J. Greer, Jr.
[5 7] ABSTRACT A cooling fan formed of two sheet metal layers joined to a centrally contained spider arm. The configuration of the resulting blade is streamlined or an airfoil in cross section. In constructing the fan the surface pieces are normally spaced from the central support arm and during assembly are forced together and joined to the arm. The resulting stress imposed on the leading and trailing edges of the surface sheets reduces vibratory stresses in the blade. In one embodiment the trailing edge of one of the sheets is permitted to slide along the surface of the other sheet when the other sheet is decambering due to centrifugal and aerodynamic forces generated by rotation of the fan. The result is to vary the moment arm of the restraining forces imposed on the decambering trailing portion of the flexing sheet, thus giving better control of the decambering rate of that sheet.
8 Claims, 9 Drawing Figures sum PATENTED JUN 2 4' I975 1 COOLING FAN CONSTRUCTION AND METHOD OF MAKING SAME BACKGROUND OF THE INVENTION airfoil or streamlined cross-sectioned configuration,
and the method of making the same. 1
In the automotive and truck industry the goal sought for cooling fans has been that of achieving a highly efficient fan blade capable of moving large quantities of air in accordance with engine cooling requirements without generating excessive noise; capable of being produced in an economical manner, and capable of having a long service life.
In the past it has been recognized that an airfoil or streamlined cross-sectional configuration for a fan would give a greater efficiency at low speeds and less noise at higher speeds than the commonly used fan construction of the present day, which is a curved plate fastened to a single or double spider arm. The reason for the extensive use of the latter constructions isthe relative economy inherent in the single blade construction versus the airfoil or streamlined construction.
Therefore, the industry has chosen to live with excesor bonding sheets together in the desired shape, as by brazing or welding, such practices being relatively expensive.
A concept of the present invention is to take two sheets of metal, with at least one of the sheets having a curved cross-sectional configuration, and place these sheets on either side of a spider arm. The two sheets are drawn together and fastened to the supporting spider arm by appropriate means such as rivets so that the edge portions of both sheets remain discrete but are placed in a continuous compressive stress similar to the edge portions of a Belleville spring when it is compressed. One resulting benefit due to-the support given by one sheet to the other along the edge portions is the prevention of flutter or high frequency vibratorystresses which may be set up in the blade along the edge portions. Where a streamlined cross-sectional configuration is desired, both sheets may be curved somewhat in excess of their desired final shape. The assembly prostress. I In another embodiment the lower or pressure side sheet is extended beyond the rear edge of the upper' BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of the upstream side of an engine cooling fan embodying the present invention.
cess will provide some straightening and the edge FIG. 5 is a plan view of the upstream side of a different embodiment of the present invention.
FIG. 6 is an enlarged sectional view of an arm and blade of the fan of FIG. 5 taken alongline 6--6. FIG. 7 is a sectional'exploded view of the construction illustrated in FIG. 6 prior to assembly.
FIG. 8 is a sectional partial view of a modification of the.leading edge relationship of the present invention.
FIG. 9 is a sectional partial'view of a slight modificay tion of the trailing edge configuration of the construction of FIG. 6.
' DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring initially to FIG. 1 there is illustrated a cool ing-fan generally referred to by the numeral 10"com'- posed of a spider 12 having a hub portion 13 and aplurality of spider arms 14. These arms are oriented perpendicularly to the axis of rotation ofthe fan. Joined to the spider arms are a plurality of fan blade constructions ge'nerally designated as 16.
As seen in FIGS. 2 and 3 each blade 16 is constructed of a front sheet 18 and a rear sheet 20 joined by rivets 22 to the spider arm 14. It willbe noted from the illustration of FIG. 3 that the front sheet 18 is curved to the desiredfinal shape whereas the rear sheet 20, which may be of thinner stock, is straight prior to assembly. In some/instances rear sheet 20) could be pre-curved to a lesser degree than front sheet 18 and still accomplish the objectives of this invention or,'if sheets 18 and 20 were of the'same thickness, sheet 18 could be curved to a greater degree than the desired finalconfiguration and would then be straightened somewhat during'assembly with sheet 20.
To assemble the'fan bladesthe' front sheet 18 and rear sheet20are locatedin a spaced sandwich relation ship to the spider arm 14 and then forced into contin guity with the spider arm 14 wIhilethe rivets 22 are in'- serted and are formedinto place. As can be noted from the illustrated spider arm cross section 14 the front and rear surfaces of thei' spider arml may be shaped to conform to the desiredcu'rvature of the final product. The curvature desi'redin FIG. Z'isthat of an airfoil'configuration in which thebuter surface of the back sheet is concave in its configuration and the outer surface of theback sheetis concave; in its configuration as viewed in cross section.
A FIG. 4 illustrates a different configuration that can be I obtained. In this illustration components corresponding to those in FIGS. 2 and 3 are given the same numeral with a subscript a. In this case the cross-sectional configuration is streamlined in that the outer surfaces of the front and rear sheets are both convex as viewed in cross section. The configuration of FIG. 4 may be assembled in the same manner as that of FIG. 2.
FIGS. 5 through 7 illustrate the application of the present invention to a flexible bladed fan which results in greater strength and a more desirable flexing action of the blades. The fan is geneally designated as and is composed of a spider 112 which is itself made up of a hub portion 113 and a plurality of spider arms 114.
3 Fastened to the spider arms are blade constructions Lookihg to the cross-sectional FIGS. 6 and 7 it is seen that each blade 116 of the fan consists of a semi-rigid resilient front sheet 118 and a flexibly resilient rear sheet 120 joined to the spider arm 114 by means of a plurality of rivets 122. As will be seen in these FIG- URES the rear sheet 120 is preferably of a thinner cross section than the front sheet 118 and extends to its trailing edge of a distance d 1 beyond the trailing edge 124 of front sheet 118. The trailing edge of front sheet 118 is spaced a distance m 1 from the rearmost line of rivets 122 and constitutes the pivot edge about which the portion d 1 will rotate during flexure. Therefore the distance m 1 would also constitute the moment arm of the resisting force imposed by the trailing edge of the front sheet 118 against such flexure.
Because it has become recognized as desirable in the fan art that the greatest rate of decambering flexing should occur initially during the rotative cycle of the fan (e.g., duringthe transition of the vehicle from idle to beginning speed) and then diminish so that no flexing into opposite camber will occur. It is desirable to proportion sheets 118 and 120 such that some flexing does occur in the rearward portion of 118 near its trailing edge 124but not as much as occurs in sheet 120. The result of this relationship is that as the extending portion (1, of sheet 120 flexes forwardly it will urge the trailing edge of 124 of front sheet 118 forwardly also, which will cause this trailing edge to slide along the extending portion d, by a distance shown as Am, this will increase the moment arm of the trailing edge 124 to a new value shown as m which in effect will increase the resistance to flexure against the portion d, as the fan increases its speed. Thus, with this type of construction all of the benefits of an airfoil shape will be derived plus the additional benefit of a variable flexing rate which can be controlled and tailored to fit the requirements of aparticular cooling problem.
Under some conditions, such as a desire'for a finer leading edge,.or the desire to protect the "thinner rear sheet from damage to its leading edge it may be advantageous to carry the leading .edge of the front sheet 20 over that of the rear sheet as shown. in FIG. 8.
lnsome applications of the FIG. v6'construction it may be found that unwanted and unduly high stress concentrations may occur at the line engagement of trailing edge 124 on sheet 120. Under such conditions it may be desirable to curlthe trailing edge somewhat as shown in FIG. 9. By having front sheet 118a engage rear sheet 1204 at the curved trailing edge 124a a rolling as well as sliding line of contact will occur in the vicinity of 125a when the sheet 120a flexes. This will help to prevent the build-up of high stress concentrations.
i The terms front and rear, and upper and lower as used in the specification and claims are for the purposes of relating various components to each other and are not intended to fix the construction of the invention in a particular spatial relationship.
1. A fan blade construction adapted for use in cooling systems for automotive and truck applications, said construction including,
a. an elongated spider arm,
b. a pair of sheet metal, elongated sheets of generally rectangular configuration, each sheet having a leading lengthwise edge and a trailing lengthwise edge,
c. said sheets being of a width greater than the width of said spider arm,
d. said sheets each being secured to said spider arm, to sandwich the spider arm, the longitudinal axis of the arm and the said sheets being substantially par-' allel,
e. at least one of said sheets being convex with respect to said spider arm,
f. at least one of said leading lengthwise edges of said pair of sheets resiliently abuting the other sheet of 3. The fan blade construction of claim 1 wherein at least one of said trailing lengthwise edges of said pair of sheets resiliently abuts the other sheet of said pair of sheets, whereby force would have to be exerted to displace the resiliency abutting trailing lengthwise edge from the sheet against which it abuts.
4. The fan blade construction of claim 3 wherein said trailing lengthwise edges abut each other.
5. The fan blade construction of claim 2 wherein at least one of said trailing lengthwise edges of said pair of sheets resiliently abuts the other sheet of said pair of sheets, whereby force would have to be exerted to displace ,the resiliently abutting trailing lengthwise edge from the sheet against which it abuts.
6. The fan blade construction of claim 3 wherein one of said trailing lengthwise edges has a curled portion, curving away from the sheet which it abuts, to thereby reduce stress concentrations.
7. The fan blade construction of claim 1 wherein said sheets are of different degrees of resiliency.
8. The fan blade construction of claim 5 wherein said sheets are of different degrees of resiliency.