Title of Invention

"AXIAL FLOW FAN"

Abstract

An axial flow fan. is disclosed. The axial flow fan comprises a hub, a plurality of blades extending radially outwardly from the hub, and an outer band surrounding peripheral ends of the blades. The median sweep angle oi: each blade increases gradually from 0° along the outward radial direction. The leading sweep angle of eaah blade atarta from an angle less than 0°, increases "gradually and terminates at an angle more than 40°. The trailing swoop angle of each blade increases along the outward radial direction after it decreases frcuu an angle more than 0° alorjy the outward radlaJ. direction. The chord length of each blade gradually increases along the outward radial direction. The pitch angle of each k blade gradually decreases along the outward radial direction.

Full Text

AXIAL FLOW FAN BACKGROUND OF THE INVENTION Field of the invention The present: invention relates, in general, to axial flow fans for moving air axially by rotating a plurality of identical blades extending from a central hub and, more particularly, to an axial flow fan having a high efficiency and generating low noiso because the aweep anglo, the chord length and the pitch angle of each of the blades are designed to be harmonized. Description of the Prior Art As well known to those skilled in the art, an axial flow fan consists of a central hub and a plurality of blades extending from the hub, and moves air axially by means of the rotating bladua whiles being rotated by tho rot .rOtiny i'orco transmitted from a power source to the hub. The axial flow 5 fan serves to blow air forcibly to a heat exchanger so as to promote heat radiation from engine cooling water or air-conditioner coolant that is circulated through the heat exchanger, such aa a radiator ot u condemwr. ' Generally, Lha eixlul i'low fan in provided with a rjhroud that surrounds the blades and is fixed to a heat exchanger. shroud serves to guide air moved by the rotation of the blades so as to blow a larger amount of air to the heat exchanger and also is used to support a motor that generates driving force to rotate the blades. A conventional axial flow fan comprises a central hub connected with the driving shaft of a motor, a plurality of blades extending radially outwardly from the hub, and an outer band to which the peripheral ends of the blscios aro fixod. The axial flow fan is generally made of synthetic resin and formed into a single body. The fan band allows the blades to be restrained within the fan band by connecting Ihn irldu odgctfr) of the blades, thoroby preventing the! blades from being deformed. In the construction of the axial flow fan, the blades are directly concerned with the movement of air. Each of the blades has a streamlined cross section functioning to draw air from the front of the axial flow fan using pressure increase through the pressure face due to the rotation of the blades and to push the drawn air toward thy rear oi !:hfi axial flow fan. With regard to design for such an axial flow fan, the below-mentioned limitations follow* Since the axial flow fan may be usec. to cool a radiator for cooling an engine and a condenser for improving the performance of an air-conditioner, the axial flow fan should a sufficient; amount of airflow necessary for the cooling whila overcoming a drop In positive pressure due to the loads of the heat exchangers. Additionally, since a vehicle is provided with many electronic devices and the devices consume a large amount of energy, a blowing efficiency with regard to the Quantity of power that the electric motor of the fan consumes should be high. Further, pursuant to the noise restriction, the blowing noise shouid be small, Bonideu, tho axial flow fan must be frees from boing easily darcaged while being rotated in a high speed. Since the blades of the axial flow fan are most important so as to design the axial flow fan to satisfy the limitations, the shapa, the chord longth and the pitch anglo of each of fho blades are principal design factors. In order to satisfy tho limitations, various «xiai flow fans are proposed. In U.S. Pat. No. 4/569,631, there is proposed an axial flow fan whnroin the. loading edye cif a fan blade bar? a certain amount of" backward sweep angle at the root porLiou near the hub and a certain amount of forward uwuwp angle at the tip portion near t.he band and pitch anglos are dei'iaed along tho radial positions. In U.S. Pat. Wo. 4,684,324, there is proposed an axial flow,fan wherein with respect to the median line of each of the blades that ia obtained by joining the points circumferontially equidistant from its .leading edge and its trailing edge, a backward sweep angle is formed at the hub side of the blade, a forward sweep angle is formed at the radially outer side of the blade, and a position at which the sweep angle changes from a backward sweep angle to a forward sweep angle, its blade length and its pitch angle are defined. In U.S. Pat. No. 5,273,400, there is proposed an axial flow fan wherein its median aweep angle changes from a backward sweep angle to a forward sweep angle along a outwardly radial direction and its blade length, its piftch angle and its chamber angle are defined. In U.S. Pat, No. 5,393,199, there !is proposed an axial flow fan wherein thei median sweep angle 10 a forward swoop anglo all along liho oul.wurd radial direction, the sweep angle does not exceed 15" at tho outex end of the blade, a region in which a leading odge 14.no and a trailing edge line are parallel to a radial line exists, and the chord length doer eases after it increase:; along the outward radial direction. However, the above-described axial flow fane may improve the blowing efficjencies and reduce noises to a certain , i degree, but their blowing efficiencies are not improved sufficiently due to excessive sweep angle increases and cracks may be generated at their roots. SUMMARY OF THE INVENTION Accordingly, the present invention has boen made keeping in mind the above problems occurring in the prior art, and an abject of the present invention is to provide an axial flow fan, Improving the blowing efficiency and reducing noise by harmonising uhn ikidiqri ffiotonj, ouch an l;lu,s nwoop nnj.l.u of! tlm tan, tfott cvirvaturtm or l:hy leading and b:'n:I,:i.lug edge and ihcs pitch anglaa. In order to .accomplish the above object, the present i Invention providou an dxiul flow tun, cuupi'Jnluy a hub, a plurality of blades extending radially outwardly from the hub, and an outer band surrounding peripheral finds of the blades, wherein the median sweep angle of each blade increases gradually from 0° "along the outward radial direction, the leading sweep angle of each biade starts from an angle less than 0°, inaroaooa gradually arid terminates at an cmglo raoro than 40°, the trailing sweep angle of each blade increases along the outward radial direction after it decreases from an angle more than 0" along the outward radial direction, the chord length of each blade gradually increases along the outward radial direction, and the pitch angle of each blade gradually decreases along the outward radial direction. According to another embodiment, a point at which the i leading sweep angle of. each blade changes from a negative angle to a positive angle may be situated within the radially inward 50% of a length of the blade. According to a further embodiment, a skew angle of a radial line passing through a radially outer end of a median line of each of the blades may be less than skew angle of a radial line passing through a radially inner end of the leading edge line of each of the blades. In accordance with the present invention there is disclosed an axial flow fan, comprising a hub, a plurality of blades extending radially outwardly from the hub, and an outer band surrounding peripheral ends of the blades, -whoroin a median sweep angle of each blade increases gradually from 0° along the outward radial direction, a leading sweep angle of each blade starts from an angle less than 0°, increases gradually and terminates at an angle more than 40°, a trailing sweep angle of each blade increases along the outward radial direction after it decreases from an angle more than 0° along the outward radial direction, a chord length of each blade gradually increases along the outward radial direction, and a pitch angle of each blade gradually decreases along the outward radial direction. BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: Fig. 1 is a front view showing an axial flow fan according to the present invention; Fig 2 is a partial enlarged view of Fig. 1; Fig.3 is a cross section taken of along line Ill-Ill of Fig. 1; Fig. 4 is a partial enlarged view showing the sweep angle characteristics according to the present invention; Fig. 5 is a partial enlarged view showing the skew angle characteristics according to the present invention; Fig. 6 is a graph showing variation in sweep angle with regard to ration of the position in the blade to the chord length; Fig. 7 is a graph showing variation in chord length ratio with regard to ratio of the position in the blade to the chard length; and Fig. 8 is a graph showing variation in pitch angle with regard to ratio of the position in the blade to the chord length DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior requiremenrits in an axial flow , fan used in conjunction with an automobile are a high efficiency characteristic and a low noise characteristic. In order to allow the axial flow fan to have these characteristics, three principal design factors of the owoep angleo, the chord lengths and the pitch angles of each of the blades should be harmonized. The sweep angle S of the blade is a factor that represents the sweeping degree of the blade. Since the sweep angle S affects the blowing efficiency and noiiu,;, priority is yivHn to it in donign. Wlum thu othur. Cond:l I; i.oun rtivu identical, the greater the nwoop angle S in, the Iowa the noise and tho blowing efficiency are. Aa a result, when the sweep angle S is increased under the same conditions, rioige Is reduced, but tliu amount -ol' coiunnnod powor l.tt liicrii/inorJ iincl l"ltn strength of the fan should be increased because high-speed rotation 13 required. The chord length of the blade is a factor that represents the width of the blade In the direction at rotation. The chord length affects the amount of airflow and efficiency. That is, under the same conditions, the greater the chord length is, the greater the amount of airflow and efficiency become. However, in a range more than a certain amount of chord length, the greater the chord length is, the less the amount of airflow and efficiency become. The pitch angle a of the blades is a, factor that represents t.he gradient: of the blade. When the pitch angle a. is increased, the amount of airflow and efficiency are increased and rioiso is reduced. However, when the pitch angle a is more than a ' certain amount, oepurtitidn occury on the negative priKmure aurfaco, Uhuu roduciny tho omount of airflow and efficiency rapidly and increasing noise. As described above, tho above three factors affo»ct major characteristics of an axial fan, such as the amount of airflow, efficiency and noise. The required characteristics of an axial fan are satisfied when the factors are harmonized. An axial flow fan according' to the present invention is designed to have a high efficiency characteristic and a low noise characteristic by harmonizing the desiqn factors. Fig. 1 1fi n plan -vipiw showing f.hft axial flow fan. As shown in this drawing, the axial flow fan of the present invention, comprises a central hub 1, a plurality of blades 2 extending radially outwardly from the hub 1, and an outer band 3 to which the peripheral ends of the blades 2 are fixed. Before the axial flow fan is described in more detail, the terms used in the description are defined first, referring to Figs. 2 arid 3. When as shown in Fig. 3, a. leading edge 4a and a trailing edge 5o rtin icmpoutlvuly duflneid aa & froutiiiojfl; point; i.im,l i.\ rearmost point of a blade cross section with regard to the riirpoHnn nf rnraMnn, fls fihnwn irf Fig. ?, a 1 Priding prigp line 4 and a trailing edge line 5 may be defined as a line joining radially all the leading edges 4a and a lino radially joining all the trailing edges 5a. As shown in Fig. 2, a median line 6 is defined as a line obtained by joining the points that are circumferentially equidistant from the leading edge line 4 and t the trailing edge line 5. Meanwhile, a aweep arigel s (S1, SL and fT) i.u defined ac the interval angle between a tangent IV passing through a point in the above-defined lines (the median line 6, the leading edge line 4 and the trailing edge line b) and a radial line ilLr panning Lhrough tho r;ont:i;it 0 ol" \,im hub I, ami 1,1 iiltow angle pp is defined as a interval angle between a radial line RLIM joining the center of the hub 1 and the inner end IM of the median line 6 and ,a radial line RL(. passing through a point in the median line. In measurement of the a,:>ove angles, the angle measured along the direction of rotation is given a plus sign, while the angle measured along the opposite direction of rotation is given a minus sign. In addition, as shown in Fig. 3, a pitch angle a is defined as the interval angle between the line joining the loading edge la and the trailing edgo ba and the line lying in the direction ol rotation, uud u chord length W in defined an the distance between tho leading edge 4a and the trailing edge 5a. Further, rig shown in Fig. 5, a blado length (Ro-R1) in defined as Lhe distance between the inner end and the outer end of the blade, that is, the difference between the radium RO with regard to the outer end of the blade and the radius RI with regard to the inner end of the blade, and a position P of the blade ia defined as a difference (Rp-R1) bulwotm a radius; RP with regard to the point P and the radiua RI with regard to the inner end of the blado. In the axial flow fan of the present invention, the sweep angle S of the blade 2 should take a proper value so aa to prevent the reduction of efficiency and the reduction of noise. That is, the sweup angle S decreases in the portion near the hub 1 so as to improve efficiency and reinforce tho strength of the blade 2, while the sweep angle S of the blade 2 increases in the portion near the outer band 3 so as to reduce noise, in more detail, a median sweep angel SP defined as the interval angle between a tangent TP passing through a point P in the median line 6 and a radial line passing through tho conter 0 of t.ho hub 1 ia about, Zoro in tho Pwrtion near the inner end IM ol" the median line 6 and increases in tho portion near tho outer end OM of the median line C, The leading sweep angle 3U doilned liku tho median uwoop angle, has a minus value aL tho inner end IL of the leading edge line 4 (that is, SOL > SOM in Fig.4), increases along the leading edge line 4 and, finally, has at the outer end OL of the leading edge line 4 a value greater than the value of the median sweep angle ah the outer end 0M of the median lino 6 .(that in, fioi. > Ooi in Fig, 4) . In rmch a CHJIO, the leading sweep angle SOL at the outer end 0L of the leading edge line 4 ia made to be more than 40°, thereby reducing aoiae graatly. The trailing sweep angle GT, defined like Lho median sweop angle, has a plus value at the inner end IT of the trailing % edge line 5 (th'at is, Sri > 0 in Fig. 4), decreases gradually along the trailing edge line 5 to a certain point, and/ finally, increases from this point to the outer end Or of the trailing edge line 5, The graph of Fig. 6 illustrates variations of sweep angles of the blades of the present invention that prevents the • reduction tOi e1lcioitcy and reduces noiwo. In the mean time, Fig. 5 shows a skew angle characteristic of the blade of the axial flow fan according to an embodiment: of the present invention.Since the efficiency of the fan may be reduced when the blade 2 is excessivaly skewed, the skew angle BOn at the outer end On of tho median lino 6 is made to be leuw than the skew angle PIL at the inner end I,, of the leading edge line 4. On the other hand, sineo noise is increased when sknw angles in the loading edge lino 4 are excessively small, tina skow angle (Jot at the outer end OK of the leading edge line 4 is made to be greater than the skew angle PH. at the inner end 1L of the leading edge line 4 (that is, POL > Pn.) . Ps known from Figs, 4 and 6 and the below-described table 1, tne point at which a leading sweep angle SL changes from a miuura value to a plus value is made to be situated within radially inward 50% of the blade length (RO-R1) from the inner end IL of the leading edge lino 4, thus preventing the reduction of efficiency due to abrupt increase in sweep angle at the portion near the outer k end of the blade: Fig. 7 is a graph showing variation;; in cho-'d length of the blade 2 according to positions in the radial, direction. In this graph, a chord length ratio (WP/(Ro-R1) indicated in the vertical axis represents the ratio of the chord length to the blade length. AS known from this graph, in the axial flow fan, the further a position under consideration la moved to the radial direction from the hub 1, the greater the chord length W becomes. The graph of Fig. 7 is concerned with the axial flow fan having seven blades. As the number of the blades is increased, the chord length ratio {WP/ (R0-Rr) is decreased, while as the number of the blades is decreased/ chord length ratio (WP (Ro-RI) Is increased. Fl.g. B is a graph showing variations in pitch angle with regard to positions in the blade in the axial flow fan of the present invention. TAG axial flow fan serveo to move air front the front of Wie blAol3 tfl the 1-ftRj.- of the bladco. Cunh the movomont of air is generated.by pressure increase on the positive preaflure surface due to the rotation of the blades. Since according to the rotation of the blades, positive pressure is generated on the positive pressure surface and negative pressure is generated on the negative presure aurlviofi, thorn is roquitod rotating force/ that is, the driving force of a motor that may overcome the difference between pressures on the positive and negative pressure surfaces. It may be deduced from this fad: that as the difference between pressures on the positive and negative pressure surfaces is reduced, the rotating force required to drive the fan is, reduced, Lhua improving the efficiency of the axial flow fan. In the mean time, when the pitch angle a is excessively large/ the difference between pressures on the positive and negative pressure surfaces is increased by the separation generated on the negative' surface/ so that the efficiency of the fan is reduced. On the other hand, when the pitch angle a is excessively small, high-speed rotation is needod BO as to generate the required amount of airflow, so that; the raise of the fan is increased. In the axial flow fan, as shown in llg, 0, the pitch angle a of the fan is decreased, along t.ho outward direction oi' rotation. This is designed under the consideration that the speed of rotation is faster at the outer end portion of tha blade and the introducing angle T of air is small, although the axial flow fan is rotated at a single body. The pitch angle a of the blade is preferably set to be less than 20", Table 1 shows numerical values w:th regard to the principal design factors for each of tho Oladon of thy axial flow fan according to an onibodiinent of the present invention. Table 1 indicates sweep angles S, chord lengths W and pitch angles a according to the positions of the blade with regard to the blade lengths. The design factors are explained in more detail as follows. PIS known in Table 1, the median sweep angle SM of the blade increases from 0° to 43.6° along the outward radial direction, the loading sweep angle fit, Incroase from -l5.6° to » 47.3* along I he outward radla.1 direction, and tho t:.ro I .Liny sweep anglo S? of the blade increuaea to l0,3r' along the outward radial direction after it decreases from 15.2° to ,1.1.3° along i hn oulwnrrl radUil U! roof, .Ion tu,i far mi IMi? w,wh.lun wheru the position in tho Made per tho blacks .length is 0,125, TABLE 1 (Table Removed) In more detail, t;he median swoop angle ot the blade increases gradueilly from 0° to 43.6° along the outward radial direction so as to improve the efficiency of the ran and the strength of the blade. Additionally, the leading sweep angle SL starts from -15.6°, increases and changes to the positive value prior to the point at which' tho position in the blade per the bludo Umgth let 0.375 aud torminaLUM to 47.3" wore than 43.6° of the median sweep angle at the same position, thereby reducing noise at the outer ends of the blades. The chord length ratio (WP./ (R0-Rr) represents the chord length W along the direction of rotation and affects the amount of airflow and the efficiency of the fan. The chord length ratio (WP./(R0-R1) is designed to gradually increase from 0.47 at the inner end R1. of the blade 2 to 0.74 at the outer end of the blade 2, 'thereby allowing the relatively high rotational spec;d outer end to be uaed effectively. This enlarges the amount of airflow and improvoa the efficiency oi' the fan. Those chord length ratios (WP/ (Ro~Ri) are concerned with the axial flow fan having seven blades and vary with the number of the blades in the fan. The pitch angle a, as the gradient of the blades to the direction of rotation of the fan, that determines the incidence! nuqii,} T uT dil,r !M wcL t.o iiocM"t!,'iwij toward Urn outer end of the blade under the consideration, that the incidence anglo T is decreased because the rotating speed of the blade becomes faster toward the outm; end of thn b.l odo. Mnpuulally, sinew the pitch angle a at tha outer end of tho blade la designed to bo 17.0" not exceeding 20", reparation Its suppressed, thereby harmonizing the amount of airflow, the efficiency of the fan and the reduction of noise. Table 2 shows numerical valuefl with rogard to the principal design factors for each of the blades of the axial flow fan according to another embodiment of the present invention. TABLE 2 (Table Removed) The axicil flow fan according to thin umbodlmont; hus a relatively high rotational speed as compared with the axial-flow fan concerned with Table 1. When compared with those of. the axial flow fan of Table 1, the pitch angles are docniduoU somewhat in reverse proportion to, the rotational speed of the fan, while the other factors of the median sweep angle, the leading sweep angle SL, the trailing sweep angle Sr and the chord length ratio are set to be the same. As described abovi;, tho prowont .1 invention provl.doo an axial flow fan having a high efficiency and generating low noiae because the sweep angle, the chord length and the pitch angle of each of the blades are designed to he harmonized.. Although the preferred embodiment a of,: the pro-wiit invention have been disclosed for illustrative purposes/ those skilled in the art: will appreciate that various modi f icat ions, additions and substitutions are possible, without departing from the scope and spirit of the invention as (iisclofiod in the accompanying claims.- WE CLAIM: 1. An axial flow fan, comprising a hub, a plurality of blades extending radially outwardly from the hub, and an outer band surrounding peripheral ends of the blades, characterized in that a medium sweep angle of each blade increases gradually from 0° along the outward radial direction, a leading sweep angle of each blade starts from an angle less than 0° , increases gradually and terminates at an angle more than 40 ° , a trailing sweep angle of each .blade increases along the outward radial direction after it decreases from an angle more than 0° along the outward radial direction, a chord length of each blade gradually increases along the outward radial direction, and a pitch angle of each blade gradually decreases along the outward radial direction. 2. The fan as claimed in claim 1, wherein a point at which said leading sweep angle of each blade changes from a negative angle to a positive angle is situated within the radially inward 50% of a length of the blade. 3. The fan as claimed in claim 1, wherein a pitch angle at an outer end of each of said blades is less than 20°. 4. The fan as claimed in claim 1, wherein said hub, said blades and said outer band integrated into a single piece. 5. An axial flow fan substantially as herein described with reference to the foregoing description and the accompanying drawings.

Documents:

1586-del-1999-abstract.pdf

1586-del-1999-claims.pdf

1586-DEL-1999-Correspondence Others-(30-03-2011).pdf

1586-del-1999-Correspondence-Others-(18-03-2010).pdf

1586-DEL-1999-Correspondence-Others-(25-03-2011).pdf

1586-DEL-1999-Correspondence-Others-(28-03-2011).pdf

1586-del-1999-correspondence-others.pdf

1586-del-1999-correspondence-po.pdf

1586-del-1999-description (complete).pdf

1586-del-1999-drawings.pdf

1586-del-1999-form-1.pdf

1586-del-1999-form-19.pdf

1586-del-1999-form-2.pdf

1586-del-1999-form-3.pdf

1586-del-1999-form-5.pdf

1586-del-1999-gpa.pdf

1586-DEL-1999-Petition Others-(25-03-2011).pdf

1586-del-1999-petition-137.pdf

1586-del-1999-petition-138.pdf