Abstract:
A cooling fan having a circumferential ring. In ordinary fans of this type, deformation of fan blades causes the ring to buckle inward at locations between the blades. In one form of the invention, mass is added to the ring between the blades to counteract the buckling.

Description:
[0001]     The invention relates to cooling fans, particularly of the type wherein fan blades are supported at their blade tips by a circumferential ring. The invention reduces deformation of the ring.  
       BACKGROUND OF THE INVENTION  
       [0002]      FIG. 1  illustrates a motor vehicle  3 . Many such vehicles contain cooling fans, represented by block  6 . Two such fans are illustrated in  FIGS. 2 and 3 . Fan  9  has equally spaced blades. Fan  12  has unequally spaced blades.  
         [0003]     In examining these fans, the Inventors has observed that, in operation, and especially at the temperatures encountered in the engine compartment of the vehicle  3  in  FIG. 1 , the fans  9  and  12  experience deformation. The deformation reduces aerodynamic efficiency.  
         [0004]     In addition, the fans are designed to produce minimal noise, but the deformation increases the noise. How a fan produces noise can be understood by a simplified example.  
         [0005]     Every time a blade of a fan passes an observer, the blade delivers a small pressure pulse. One can easily prove this by listening to a ceiling fan. Every time a blade passes, a small whooshing sound is perceived. The sound is produced by a small pressure pulse.  
         [0006]     A ceiling fan is a low-speed fan. In a high-speed fan, such as that represented in  FIG. 1 , speeds can reach 2400 rpm, and higher. If the fan has five blades, as illustrated in  FIGS. 2 and 3 , then 12,000 pulses occur per minute (5×2,400), which correspond to about 200 pulses per second (12,000/60).  
         [0007]     The sequence of 200 pulses per second resembles roughly a sine wave of about the same frequency. Humans perceive these pulses as a hum or buzz at about 200 Hz.  
         [0008]     To reduce the hum or buzz, various approaches have been developed to reduce the size of the pressure pulses produced by the fans in question, and many have been quite successful. However, when the fans deform in operation as described above, the reduction in noise which was previously attained becomes somewhat compromised.  
         [0009]     Therefore, the Inventors has discovered that certain cooling fans, especially when operating in a high-temperature environment, experience a change in shape which causes a reduction in aerodynamic efficiency and also produces undesirable noise. The Inventors has developed strategies for mitigating these undesirable effects.  
       OBJECTS OF THE INVENTION  
       [0010]     An object of the invention is to provide an improved cooling fan.  
         [0011]     A further object of the invention is to provide a cooling fan which experiences reduced deformation in operation, particularly in a high-temperature environment.  
       SUMMARY OF THE INVENTION  
       [0012]     In one form of the invention, mass is added to a ring surrounding and connected to blades of a cooling fan.  
         [0013]     In one aspect, this invention comprises, an apparatus comprising a cooling fan having an array of swept fan blades surrounded by a ring connected to tips of the blades, and means for preventing deflection of the fan blades from causing inward buckling of the ring at locations between the tips.  
         [0014]     In still another aspect, this invention comprises an apparatus comprising: a cooling fan having fan blades whose tips support an outer ring, and masses embedded in the ring in sectors between the blades and constructed of material of greater density than the ring.  
         [0015]     In yet another aspect, this invention comprises an apparatus comprising: a cooling fan having a rotor which includes two elements: fan blades, and an annular ring supported by the blades, and one or more masses, distributed along the ring, such that greater mass is present between blades than radially outside the blades.  
         [0016]     In still another aspect, this invention comprises a cooling fan comprising: at least two fan blades having tips, and a structure spanning between, and connecting to, the tips of the two blades, the structure being more massive near its mid-point than near the tips.  
         [0017]     In yet another aspect, this invention comprises a cooling fan comprising: an array of fan blades, each having a tip, wherein all tips together define a tip circle, a ring which is connected to the tips at connection regions, lies outside the tip circle, and is more massive at mid-points between connection regions, than at the connection regions.  
         [0018]     In still another aspect, this invention comprises a method, comprising the steps of: performing a computer simulation of a cooling fan, which fan includes fan blades and a ring which surrounds the blades, is connected to the tips of the blades, and is unsupported between the tips, observing that, in operation, the ring bows inward at its unsupported regions, and adding simulated mass at the unsupported regions, and performing at least one additional simulation.  
         [0019]     In yet another aspect, this invention comprises a method comprising the steps of: maintaining a cooling fan which includes fan blades, and maintaining an outer ring, supported by the fan blades, which has a larger mass density between blades than at other places.  
         [0020]     In still another aspect, this invention comprises a cooling fan, comprising: at least two fan blades having tips, and a structure spanning between, and connecting to, the tips of the two blades, the structure being more massive at one location, compared to other locations.  
         [0021]     In yet another aspect, this invention comprises a cooling system for a vehicle, comprising: a cooling fan comprising a plurality of fan blades, and a motor for driving an annular ring surrounding the blades, the annular ring comprises at least one mass or weight between least two of the plurality of fan blades for improving performance of the cooling fan, and the annular ring comprises at least one sector between the at least two of the plurality of fan blades.  
         [0022]     In still another aspect, this invention comprises an apparatus, comprising: a fan having blades connected to a ring, wherein deformation occurs in the ring during operation, and means for reducing the deformation.  
         [0023]     Other objects and advantages of the invention will be apparent from the following description and the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]      FIG. 1  illustrates a prior-art cooling fan  6  in a motor vehicle  3 .  
         [0025]      FIGS. 2 and 3  illustrate two prior-art cooling fans.  
         [0026]      FIG. 4  illustrates a discovery made by the Inventor.  
         [0027]      FIG. 5  is an enlargement of region  36  in  FIG. 4 .  
         [0028]      FIG. 6  illustrates a simplified fan blade  63 .  
         [0029]      FIG. 6A  illustrates definitions of “axial plane” and “radial plane.” 
         [0030]      FIG. 7  illustrates deformation of the fan blade of  FIG. 6  under aerodynamic loading.  
         [0031]      FIG. 8  illustrates deformation of a collection of blades  63 .  
         [0032]      FIG. 9  illustrates a swept fan blade  86 .  
         [0033]      FIG. 9A  is a plan view of  FIG. 9 .  
         [0034]      FIG. 10  illustrates deformation of the fan blade of  FIG. 9 .  
         [0035]      FIG. 10A  is a plan view of  FIG. 10 .  
         [0036]      FIG. 10B  is a plan view of a view similar to that of  FIG. 9 , but with an added hypothetical cable C, which pulls point  95  radially inward.  
         [0037]      FIG. 11  illustrates a swept fan blade.  
         [0038]      FIG. 12  illustrates a swept fan blade which is not fully contained in axial plane  79 .  
         [0039]      FIG. 13  illustrates a definition of angle-of-attack.  
         [0040]      FIG. 14  illustrates deformation of the fan blade of  FIG. 12 .  
         [0041]      FIG. 15  illustrates, in simplified plan view, blades  160  and ring  155 .  
         [0042]      FIG. 16  is a perspective view of the apparatus of  FIG. 15 .  
         [0043]      FIG. 17  illustrates, in exaggerated view, how ring  155  is deformed when the tips of blades  160  move radially outward.  
         [0044]      FIG. 18  illustrates the deformation of  FIG. 17  in perspective view.  
         [0045]      FIG. 19  illustrates, in plan view, how added mass is located between blades  180 , and not in sectors  220 , which are radially outward of blades  160 .  
         [0046]      FIG. 20  illustrates plots, in radial coordinates, of mass versus position.  
         [0047]      FIG. 21  shows that the leading edge LE of one blade can lie directly behind the trailing edge TE of another blade.  
         [0048]      FIG. 22  illustrates ring  155 .  
         [0049]      FIG. 23  illustrates the rectangular cross section of ring  155  in  FIG. 22 .  
         [0050]      FIG. 24  illustrates webs W added to ring  155 .  
         [0051]      FIG. 25  illustrates, in cross-sectional view, two different ways in which the same amount of mass can be added to a ring.  
         [0052]      FIG. 26  indicates test data obtained from computer simulations. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0053]      FIG. 4  illustrates a discovery made by the Inventor.  FIG. 4  represents, in cross-section, the type of fan hub  15 , fan blade  18 , and fan ring  21  shown in  FIG. 3 .  FIG. 4  also shows a shroud side wall  24 , which is not shown in  FIG. 3 .  
         [0054]     The Inventors has observed that, during operation, the fan ring  21  deforms from position  30  to position  33 .  FIG. 5  is an enlargement of region  36  in  FIG. 4 .  FIG. 5  illustrates a movement in two directions by the fan ring  21 . Arrow  42  represents a radial movement, and arrow  45  represents an axial movement.  
         [0055]     Clearance between the fan  33  and the wall  24  has increased, allowing leakage.  
         [0056]     Some simple explanations explaining why these deformations occur will be given, with reference to  FIGS. 6-11 . First,  FIGS. 6 and 7  will be explained, establish a reference frame.  
         [0057]      FIG. 6  illustrates a simplified fan hub  60 , and an idealized fan blade  63 . Arrow  66  represents the collective forces imposed by aerodynamic loading. Arrow  70  represents the collective forces of centrifugal loading.  
         [0058]     The aerodynamic forces  66  tend to bend the idealized blade  63  into the phantom position  73  indicated in  FIG. 7 . However, the centrifugal forces  70  do not bend the idealized blade  63 , since all these forces are co-linear with the idealized blade  63 . (However, the centrifugal forces  70  can stiffen the idealized blade  63 .)  
         [0059]      FIG. 8  shows an array of idealized blades  63  extending from the hub  60 . If the aerodynamic loading  66  of  FIG. 6  is the only load applied to the idealized blade  63 , and if all blades  63  are identical, then all blades  63  in  FIG. 8  will bend equally into the phantom positions  73 , causing a small relative rotation of the fan ring  76  with respect to the hub  60 .  
         [0060]     The bending indicated in  FIGS. 6 and 7  changes the aerodynamic shape of the blades  63 , thus causing a change in aerodynamic behavior of the blade  63 . Of course, the blades  63  will probably be designed to anticipate this bending.  
         [0061]     The blade  63  just examined were non-swept, and were shown as aligned in axial planes. Plane  79  in  FIG. 6  represents an axial plane. An axial plane is parallel to the axis  82 .  FIG. 6A  sets forth a coordinate system which defines axial and radial planes. An axial plane contains the axis AA. A radial plane is defined by all radii emanating from a single point.  
         [0062]      FIG. 9  illustrates in simplified form a swept blade  86 , with straight leading edge  89  and a straight trailing edge  92 . Hub  60  is shown, for simplicity, as flat. The axial plane  79  of  FIG. 1  is shown for reference. Blade  86  is co-planar with the plane  79 .  FIG. 9A  is an elevational view, taken along arrows  9 A in  FIG. 9   
         [0063]      FIG. 10  shows the centrifugal loading force  70  of  FIG. 6 .  FIG. 10A  is an elevational view. In those Figs., force  70  tends to pull point  95  radially outward, in the direction of arrow  70 , as indicated in grossly exaggerated form. Force  70  may also result in movement of point  95  in a forward direction, parallel to arrow  98 , because of the reaction of parts of the blade  86  to the force  70 .  
         [0064]     One reason for the movement of point  95  is that no material is present in region  97  in  FIG. 10A . If, for example, material were present, represented by hypothetical cable C in  FIG. 10B , then the movement of point  95  may be reduced. But, as stated, no material performing the function of cable C is present in region  97  in  FIG. 10A .  
         [0065]     When the blade  86  is constructed with curved leading and trailing edges, similar types of deformation occur.  FIG. 11  illustrates such a blade  103 , but still aligned in an axial plane  79 . That is, the blade  103  is co-planar with axial plane  79 .  
         [0066]     The blades of the fans shown in  FIGS. 2 and 3  are not axially aligned as shown in  FIG. 11 , but are slanted as is blade  106  in  FIG. 12 . One reason is to give the blade  106  the proper angle-of-attack during operation.  FIG. 13  is a view of  FIG. 12 , taken along arrows  13 - 13 , and illustrates the basic idea of angle of attack.  
         [0067]     In  FIG. 13 , line  111  is an extension of the blade  106 . Arrow  112  represents an incoming air stream. Angle A represents the angle-of-attack.  
         [0068]      FIG. 14  illustrates one reason why the movement of point  95  in  FIG. 10  can be greater with a swept blade having a curved trailing edge  115  in  FIG. 14 . With such a trailing edge, material is absent in the region bounded by trailing edge  115  and dashed line  118 . Dashed line  18  lies in an analogous position to the straight trailing edge  92  in  FIG. 9 .  
         [0069]     Thus, with a curved trailing edge  115 , additional material is missing in addition to that of region  97  in  FIG. 10A . The additional material is that lying between trailing edge  115  in  FIG. 14  and dashed line  118 . That material, if present, could act as a web and absorb tensile load imposed by a force indicated by arrow  121  in  FIG. 14 . But such a web is not present in the blade shown in  FIG. 14 .  
         [0070]     Therefore, the preceding discussion has given a simplified explanation, based on observations made by the Inventor, of one set of reasons explaining why the deformation shown in  FIG. 4  can occur.  
         [0071]     The Inventors have further observed that specific types of deformation occur.  FIG. 15  illustrates schematically a fan, containing four blades  160 , a hub  150 , and a ring  155 , which connects to the tips of the blades  160 . Dots E, F, G, and H are reference points, and indicate points-of-attachments of the blades  160  to the ring  155 .  FIG. 16  illustrates the situation in perspective view, with the blades omitted for clarity.  
         [0072]     In operation, parts of the tips of the blades move radially outward, as explained in connection with  FIGS. 10 and 10 A above. This movement effectively lengthens the blades, as shown schematically in  FIG. 17 . Since the ring  155  is connected to the tips of the blades  160 , the ring is constrained to deform into the shape  1   55 A ( FIG. 17 ) indicated, which is, of course, shown in exaggerated form.  
         [0073]     The Inventors, through computer simulation, have found that a specific type of deformation occurs in the ring  155 , as shown in  FIG. 18 . The region of the ring  155  between points D and G, which points represent the junctions between the tips of blades (not shown) and the ring  155 , is drawn radially inward, as indicated by dashed line  170 . A similar observation applies to dashed line  172 , lying between points E and F.  
         [0074]     However, the part of the ring  155  at the trailing edge TE of a blade  160  bulges radially outward, as indicated by bulge  175  in  FIG. 18 .  
         [0075]     The inward and outward bulging is consistent with the exaggerated view shown in  FIG. 17 . Region  180  shows an inward bulge of the ring  155 , namely, the straight line between points D and E, compared with its rest position which is indicated by phantom ring  155 . This inward bulge in region  180  is consistent with bulge  170  in  FIG. 18 .  
         [0076]     On the other hand, region  190  in  FIG. 17  shows an outward bulge, consistent with outward bulge  175  in  FIG. 18 .  
         [0077]     To counteract the deformation illustrated in  FIGS. 17 and 18 , mass or weight was added to the ring  155 , at regions between the blades, but not at the blades themselves.  FIG. 19  illustrates the mass, as shaded sectors  210 . Four blades  160  are shown, and their spacing is not equal. That is, they are not  90  degrees apart. Other blade numbers can be used.  
         [0078]     Several significant features of the addition of mass  210  are the following.  
         [0079]     One is that the mass is preferably not added radially outward of the blades. That is, for example, mass is not added in sector  220  in  FIG. 19 , nor to any corresponding sector outside other blades.  
         [0080]     A second feature is that the mass need not be uniformly distributed.  FIG. 20  illustrates two types of mass distribution, wherein radial distance, such as distance D 1 , represents amount of mass, plotted as a function of position. For example, point P 1  represents an amount of mass added at angular position A 10 . Point P 12  represents an amount of mass added at angular position A 12 . Point P 1 o indicates that a larger mass is added at angular position A 10 , compared with point P 12 .  
         [0081]     Plot  230  indicates that the mass is lowest at the mid-point M between neighboring blades  160 . In another embodiment, plot  235  indicates that the mass is maximal at the mid-point M between neighboring blades  160 .  
         [0082]      FIG. 20  indicates a continuous distribution of mass. However, a continuous distribution is not seen as strictly necessary. Instead, mass can be added in discrete units, analogous to the wheel weights which are added to automotive wheels in a wheel-balancing process.  
         [0083]     A third feature is that the mass need not be uniformly distributed in the axial direction.  FIG. 21  illustrates this concept.  
         [0084]     In some fans, the leading edge of LE one blade can lie ahead of the trailing edge TE of an adjacent blade. It can expected that the bulging of the ring  155  will be different at the leading edge LE, compared with the trailing edge TE, despite the fact that the leading edge LE and the trailing edge TE lie on a common axial plane AP.  
         [0085]     Thus, different masses may be required at the leading edge LE, compared with the trailing edge TE.  
         [0086]     A fourth feature is that the bulging of  FIGS. 10 and 10 A is reduced by the outward centrifugal force due to the added mass in the ring. The reduction is not caused by stiffening the ring  155  in  FIG. 16 , at least not to the maximal extent possible.  FIGS. 22-24  illustrate this.  
         [0087]      FIG. 22  illustrates ring  155 .  FIG. 22  is a cut-away view, and indicates that the cross-section CS is rectangular. In one form of the invention, the mass  210  in  FIG. 19  is added by increasing the radial depth RD, or thickness, of the ring  155 .  
         [0088]     However, if stiffness of the ring  155  were to be increased, another approach would be taken. An increase in stiffness would require an increase in the moment-of-inertia of the ring, which would require fabrication of webs, such as webs W shown in  FIG. 24 . An example will illustrate the distinction.  
         [0089]      FIG. 25 , image  240 , shows the rectangular cross section  250  of the ring, which corresponds to cross section CS in  FIG. 23 . In  FIG. 25 , the cross section  250  is divided into nine squares for reference.  
         [0090]     Assume that the amount of material in the cross section  250  is to be doubled. Image  260  illustrates one possibility, wherein the radial depth RD is doubled. Nine squares have been added, making eighteen squares total. Image  270  illustrates another possibility, wherein webs W are formed. The additional nine squares are formed into webs W.  
         [0091]     Thus, material, or mass, can be added to the ring  155  in at least two ways. One way simply increases the thickness of the ring  155 , as in image  260  in  FIG. 25 . Another way increases the moment of inertia, as in image  270 . The latter approach increases stiffness more than does the former way.  
         [0092]     However, in one form of the invention, the webs W effectively decrease the inner diameter of the ring, obstructing airflow into the fan, which is not desired. Consequently, in one form of the invention, it is preferred to add mass without obstructing airflow, as in image  260  in  FIG. 25 .  
         [0093]     In one form of the invention, the additional mass shown in image  260  in  FIG. 25  can be viewed as occupying, or adding, minimal radial depth RD. That is, the additional mass is spread out, in the form of a cylindrical layer of uniform thickness represented by layer  260 A. This layer, being uniform in thickness, spreads out the additional mass in a layer of the smallest thickness possible, thereby increasing radial depth RD in the smallest amount.  
         [0094]     In contrast, the webs W in image  270  do not have this property of smallest increase in radial depth. Webs  270  could be re-arranged into the layer shown in image  260 , to thereby decrease radial depth.  
         [0095]     Thus, it should be understand that the sections or areas of ring  155  between adjacent blades that have additional weight or mass may comprise a different thickness or density than other areas of the ring  155 , and even within the same section (such as sectors  210 ) may comprise a density and/or thickness that changes across its cross-section.  
         [0096]     It is also possible to create a cylindrical layer of non-uniform radial depth. For example, small webs W of  FIG. 270  can be fabricated, with added material between the webs W.  
         [0097]     A fifth feature is that additional mass can be added by embedding a high-mass material, such as a metal such as lead, into the ring  155 . The high-mass material has a higher density than the ring  155 .  
         [0098]      FIG. 1  indicates a cooling fan located in the engine compartment of vehicle  3 . The Invention is applicable to fans generally, such as air conditioning fans and heating fans, and, if in a vehicle, whether located in the engine compartment or not.  
         [0099]     A sixth group of features is indicated in  FIG. 26 , which provides test data derived from computer simulations of various fans. In the leftmost column, “uniform” refers to a uniform thickness in the ring, such as 2 mm, 3 mm, and so on, corresponding to dimension RD in  FIG. 23 . The entry “3 mm in gaps” refers to a thickness arrangement of the type shown in  FIG. 19 , wherein gaps are present in the added mass. The third row, labeled “base,” refers to a baseline fan, against which the others are compared.  
         [0100]     The central column, labeled “mass,” refers to the amount of mass added.  
         [0101]     In the rightmost two columns, quotients are given, indicating the relative effectiveness of masses in reducing deflection. The basic idea is to divide the amount of reduction in deflection by the mass responsible for the reduction, to attain a Fig.-of-merit for each addition of mass.  
         [0102]     A seventh feature relates to positioning of the added mass. It was stated above that, in one embodiment, the additional mass does not occupy inwardly extending webs. However, in other embodiments, such webs, containing the added mass, can be used.  
         [0103]     In one embodiment, the ring sections are uniform in thickness. In other embodiments, the ring sections can be non-uniform in thickness.  
         [0104]     Mass need not be added to every ring section between adjacent blades. For example, a five-bladed fan may be used, and the spacing between blades need not be uniform. The non-uniform spacing is sometimes used to minimize acoustical noise.  
         [0105]     If two adjacent blades are very close, then the ring section between them will be short. Such a short ring section may experience only a small deflection. Added mass may not be needed for such a ring section.  
         [0106]     Thus, in some fans, some ring sections may contain added mass, and others may not.  
         [0107]     Inward deflection of a ring section may not be centered about the mid-point between the blades between which the ring spans. In such a case, the added mass may be added at the point of maximal deflection which, again, may not be the mid-point.  
         [0108]     The invention is applicable to raked blades. In one example of a raked blade, the leading edge progresses to the rear, that is, downstream, as one moves radially outward. In another example, the leading edge progresses to the front, that is, upstream, as one moves radially outward. In both examples, centrifugal force will tend to pull the blades into a pure radial position, and reduce the rake.  
         [0109]     The ring sections can be of varied cross section, such as rectangular, oval, J-shaped, or L-shaped with one or more rounded corners.  
         [0110]     A seventh feature is that inward deformation has been detected in the ring during operation of the fan. The invention applies added centrifugal force at selected points on the ring, to counteract the deformation. The added centrifugal force can be generated by addition of (1) a concentrated or distributed mass, (2) increased density at specific locations, (3) localized increases in thickness of the ring, or (4) other measures.  
         [0111]     Numerous substitutions and modifications can be undertaken without departing from the true spirit and scope of the invention. What is desired to be secured by Letters Patent is the invention as defined in the following claims.