Abstract:
A cooling fan for automobiles which is drivable by an electric motor includes a plurality of blades, each having distal and proximal ends inclined at attachment angles larger than an attachment angle at which an intermediate portion of the blade is inclined, thereby reducing noises produced by the cooling fan.

Description:
This is a continuation of application Ser. No. 319,280, filed Nov. 9, 1981, now abandoned. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a fan, which can be used in a variety of applications, but is particularly useful when used as a motor-driven fan for supplying cooling air to an automobile&#39;s radiator. 
     BACKGROUND OF THE INVENTION 
     The present inventors have studied air flows caused while a fan is rotating since fan noises are generated by air flows particularly when the latter are disturbed irregularly. Upon observation of air flows during rotation of a conventional fan with the aid of a styrene particle method, it was found that no main air flow is present over a considerable area at the tip of each blade of the fan, the main air flow being defined as an air flow (indicated at U in FIG. 4) in an axial direction of the fan while the latter is rotating. An oil film method was used to observe air flows along the surfaces of fan blades. As a result, it was also found that air flows mainly in a radial direction (shown at R in FIG. 5) at the tip of each blade of the prior fan. On the basis of these experiments, the present inventors have concluded that conventional fans produce noises due to air flow distrubances at the tip of each fan blade. To confirm such conclusion, air flow disturbances during rotation of a fan were measured by a hot wire anemometer, and main air flow distribution was measured by a three-hole Pitot tube. The results of such measurements indicated that air flow is greatly disturbed and gets stalled at the blade tip. The foregoing conclusion was therefore justified. 
     An air flow at the tip of each fan blade is considered to be disturbed by the following reasons: As shown in FIG. 1, air is believed to flow in streams a around the blade tip 1e from front to rear surfaces of the blade. It is also considered that air is caused to flow from a base end portion 1g to the tip 1e of each blade 1a as indicated at b in FIG. 2. Where the fan 1 is used with a shroud 3 as illustrated in FIG. 3, the blade tip 1e traverses a boundary layer on a wall of the shroud, causing air flow disturbances at the blade tip 1e. 
     U.S. Pat. No. 3,914,068 (corresponding to West German Pat. No. 2203353) discloses a cooling fan for automobiles. The known fan has blades, each including a tip or distal end inclined at an angle greater than that at which a proximal end of the blade is inclined, an arrangement which will deliver a sufficient amount of air to an internal combustion engine even when the latter rotates at low speeds. 
     A fan according to the present invention is of the type driven by an electric motor at a constant output thereof. Where the prior fan having a greater blade angle at the blade tip than at the proximal end is to be driven by a motor having a constant output, the absolute value of the blade angle at the proximal end is required to be considerably small. This is because, with the greater blade angle at the blade tip, energy from the motor consumed at the blade tip is increased and energy consumed at the proximal end is reduced accordingly. It has been known that if the blade angle at the proximal end of the blade is too small, no effective work is done at the proximal end and the proximal end of the blade causes air flow to be disturbed producing noises at an increased sound pressure level. Therefore, the prior fan as a whole cannot reduce noises to a large extent since the proximal ends of the blades produce larger noises, though noises are slightly reduced at the blade tips. 
     SUMMARY OF THE INVENTION 
     The present invention has been made with the foregoing in view. It is an object of the present invention to increase the cooling efficiency of a fan without requiring an increase in the output of a motor for driving the fan, and to lower the noise level of the fan as a whole. 
     The above object can be achieved by having a blade angle larger at proximal and distal ends of a blade than at an intermediate portion thereof. By way of comparison with U.S. Pat. No. 3,914,068, the present invention can be characterized in that the blade angle is larger at both the proximal and distal ends of the blade than at the intermediate portion thereof, and the blade angle at the distal end may not necessarily be greater than that at the proximal end in order to achieve the foregoing object. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 through 3 are views illustrative of streams of air at the tip of a blade of a cooling fan; 
     FIG. 4 is a schematic view of an automotive engine room in which a cooling fan according to the present invention is mounted; 
     FIG. 5 is a front elevational view of the cooling fan shown in FIG. 4; 
     FIG. 6 is a cross-sectional view taken along line VI--VI of FIG. 5; 
     FIG. 7 is a cross-sectional view taken along line VII--VII of FIG. 5; 
     FIG. 8 is a graph indicative of angles of attachment of a blade of the fan shown in FIG. 4; 
     FIG. 9 is a graph indicative of degrees of noise reduction gained by the cooling fan shown in FIG. 4; 
     FIG. 10 is a graph indicative of ratios between attachment angles of cooling fans according to the present invention; 
     FIG. 11 is a graph indicative of degrees of noise reduction attained by the cooling fans described with reference to FIG. 10; 
     FIG. 12 is a graph indicative of ratios of amounts of air supplied by the cooling fans described with reference to FIG. 10 to an amount of air supplied by a conventional cooling fan; 
     FIG. 13 is a graph showing various performances of the cooling fan shown in FIG. 4 as incorporated in an automotive radiator; 
     FIGS. 14 and 15 are graphs indicative of other ratios between attachment angles of cooling fan blades; 
     FIGS. 16 and 17 are front elevational views of cooling fans according to other embodiments; 
     FIG. 18 is a fragmentary cross-sectional view of a cooling fan according to still another embodiments; 
     FIGS. 19 and 20 are fragmentary perspective views of cooling fans in accordance with other embodiments; 
     FIG. 21 is a fragmentary cross-sectional view of a cooling fan according to still another embodiment; 
     and FIG. 22 is a front elevational view of a cooling fan according to still another embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment according to the present invention will be described. In FIG. 4, a cooling fan 1 made of synthetic resin, or a metal such as aluminum or iron is rotatively driven by a motor 2 coupled therewith to generate an air flow flowing through a radiator 4 and guided by a shroud 3. The motor 2 is attached by a stay (not shown) to the shroud 3, which is secured to brackets (not shown) of the radiator 4. The radiator 4 comprises an upper tank 4a for supplying coolant water from an engine 5 to a core 4b in which the heat of the water is radiated, and a lower tank 4c for delivering the cooled water from the core 4b to the engine 5. Designated at 6 is a hood for the automotive engine room, 7 a bumper, 8 a grille for passage of air therethrough, 9 an under plate for the engine room, and V a direction of travel of air while the automobile is running. 
     As shown in FIG. 5, the cooling fan 1 comprises blades 1a and a boss 1b which are formed integrally with each other as illustrated in FIG. 6. Each blade 1a has a cross section as shown in FIG. 7. The blade 1a has a leading edge 1c and a trailing edge 1d that are connected by a straight line extending at an attachment angle of β to a direction Q of rotation of the fan 1 and hence the boss 1b. Since the leading edge 1c coincides with the trailing edge 1d at a tip or distal end portion ie, no such attachment angle can be determined at the tip 1e in the above manner. However, an attachment angle βt at the tip le should be determined by plotting an attachment angle β at any desired position in the radial direction R and by extrapolating the angle as shown in FIG. 8. 
     It is known that as the attachment angle β increases, the speed of travel of main air flow also increases in a range in which the attachment angle β is not excessively large. To obtain a higher speed of the main air flow at the tip 1e of the fan blade 1a, the attachment angle β at the tip 1e is larger than that at an intermediate portion or average-diameter portion 1f as shown by the solid line B in FIG. 8. Designated at Dt, Dm, Dh in FIG. 8 are a diameter as taken between opposite tips 1e, an average diameter of the fan blades 1a, and a diameter as take between opposite proximal end portions 1g or a diameter of the boss 1b. 
     The curve indicated by the solid line A in FIG. 8 is illustrative of attachment angles β of a blade of a conventional cooling fan. Study of the curve A indicates that the attachment angles β of the prior fan are progressively smaller toward the tip of the blade. Upon measuring levels of noises produced by the conventional fan A and the fan B of the present invention, it has been confirmed that the fan B produces less noises in substantially the full range of frequencies as illustrated in FIG. 9. The sound pressure level around the frequency 1 KHz, which most annoys automobile passengers, is greatly reduced, and hence the fan 1 operates considerably quietly at such frequency. The fan 1 used in the experiment, the results of which are shown in FIG. 9, had four blades 1a, with Dt being 300 mm, Dh 90 mm, and the motor 2 had an input power of 45 Watt and rotated at 1,850 r.p.m. The fan system had an air flow resistance such that the amount of air delivered was 1,000 m 3  /h at a pressure of 5.4 mm Ag. The attachment angles of the fan B are as follows: βh=24 degrees,βm=12 degrees and βt=28 degrees. 
     The fan 1 according to the present invention should not be limited to the foregoing specifications, and may be of a variety of shapes other than that shown in FIG. 8. 
     FIG. 10 shows curves C, D, E, F, G, which indicate ratios β/βm of various fans, where β is an attachment angle at the tip and the base of the fans and βm is an attachment angle at the average-diameter portion, β being larger than βm. The fan with the ratio H has an attachment angle βt at the tip which is smaller than the attachment angle βm at the average-diameter portion. THe fan with the ratio G has a constant attachment angle β at the tip, with the ratio β/βm from the intersection of the curves F and G to the base being equal to that of the curve F. As can be seen from FIG. 10, the attachment angles at the tip of the fans E and G are smaller than those at the base of these fans. As described below, it has been confirmed that the fans C, D, E, F, G have lower noise levels than those of the prior fan A and the fan H having the smaller attachment angle βt at the tip 1e than that of the prior fan A. 
     FIG. 11 illustrates noise levels of the fans A, B, C, D, E, F, G, and H plotted against the ratio βt/βm between the attachment angle βm at the average-diameter portion 1f and the attachment angle βt at the tip 1e. Study of the graph of FIG. 11 clearly indicates that the fans B, C, D, E, F, and G with the ratio βt/βm greater than 1 produce less noises. Where the ratio βt/βm is too large, that is, where the attachment angle βt at the tip 1e is excessively large, the air flow at the tip 1e of the fan blade is subjected to separation and becomes disturbed, resulting in a higher noise level. For that reason, the ratio βt/βm should preferably be 5 or below. 
     To confirm the experimental results shown in FIG. 11, the present inventors measured air flow disturbances for the fans A, B, C, D, E, F, G, and H with a hot wire anemometer, and also measured air speed distribution for the main air flow with a three-hole Pipot tube. The results of such measurements showed that with the fans B, D, E, and F, that is, with the ratio βt/βm in the range of from 1.5  to 3.5, the air flow disturbance at the fan blade tip 1e is held to a minimum and the speed of the main air flow is maximum, while the fan C with the greater rario βt/βm is subjected to increased air flow disturbances at the blade tip 1e, which have once been reduced. 
     The fans A, B, C, D, E, F, G, and H have different attachment angles βh at the proximal end portion 1g than the attachment angles βm at the average-diameter portion 1f. However, measurement of air flow disturbances with a hot wire anemometer indicated that the ratio βh/βm does not greatly affect air flow disturbances. It has been recognized though that as the attachment angle βh at the base portion 1g is increased, i.e., as the ratio βh/βm is increased, the air flow disturbances are gradually reduced, and where the attachment angle βh is too small, the fan blade 1a does not perform effective work, resulting in a disturbed air flow and hence an increased sound pressure level. The ratio βh/βm should preferably be 1.4 or greater. 
     A fan having a reduced noise level would be unacceptable if the noise level reduction were accompanied by a reduction in the amount of air delivered by the fan. The present inventors therefore studied the effects which the ratio βt/βm has on the amount of air delivered. FIG. 12 shows the results of measurements for determining such effects. A review of FIG. 12 shows that the fans B, C, D, E, F, and G with the ratios βt/βm being 1 or more deliver a greater amount of air than that delivered by the conventional fan A. The vertical axis of the graph of FIG. 12 is indicative of ratios of the amounts of air delivered by the fans of the present invention to the amount of air supplied by the conventional fan A. 
     The reasons why the fans B, C, D, E, F, and G of the invention deliver increased amounts of air as shown in FIG. 12 are considered as follows: Whereas no effective main air flow is generated at the blade tip 1e of the prior fan A, the fans B through G with the attachment angles being larger according to the invention permit an effective main air flow to be generated at their blade tip 1e, and prevent disturbed air flows from being produced at their base portions by having larger attachment angles at the base portions than at the average-diameter portions. 
     The experiments illustrated in FIGS. 11 and 12 are based on comparison between fans having the same size and driven by a motor 2 with a constant output. With the fans having the ratio βt/βm of 1 or higher, the amount of work done by the tip of each blade is increased by a reduction in the amount of work done by the average-diameter portion, resulting in a constant amount of work done bodily by the fans. Therefore, the attachment angle at the average-diameter portion of the fans according to the invention is smaller than that of the conventional fan as illustrated in FIG. 8. Even with the amount of work done by the average-diameter portion being reduced, no substantial reduction in the main air flow (Volume of air) is caused as the air flow around the average-diameter portion is stable. As a consequence, an increase in the main air flow at the blade tip makes up for the reduction in the main air flow at the average-diameter portion and results in an overall increase in the main air flow across the fans. As described above, the fan with attachment angles from the average-diameter portion 1f to the tip 1e being varied according to the curve C in FIG. 8 is required to be driven by a motor capable of producing an output greater than that produced by a motor for driving the fan A. 
     The fans according to the present invention are particularly useful when used for cooling automotive radiators. Such usefulness of the fans of the invention will be described below with reference to FIG. 13, which shows noise levels (shown by the curves A 1 , B 1 ), static pressures or differential pressures between the front and rear of the fans (shown by the curves A 2 , B 2 ), and efficiencies of the fans (shown by the curves A 3 , B 3 ) plotted against amounts of air delivered with respect to the fan B of the present invention and the prior fan 4 as simulatively installed in the engine room as illustrated in FIG. 4. Comparison between the curves A 1 , B 1  indicative of the noise level shows that the noise level (curve B 1 ) of the fan of the invention is lower than the noise level (curve A 1 ) of the conventional fan. Comparison between the curves indicative of the static pressure characteristics and fan efficiencies indicates that the static pressure (curve B 2 ) and the efficiency (curve B 3 ) of the fan according to the present invention are greater than those of the prior fan in the region in which the amount of air delivered is greater than the point Y . It is preferable that the point Y corresponds to the idling mode of operation of the automobile, and the point, for example X, at which the fan efficiency is greater than that at the point Y, corresponds to the running mode of operation of the automobile which requires maximum cooling of the engine. With such an arrangement, the noise level at the point Y for the idling of the automobile is greatly reduced as can be seen from comparison between the curves A 1  and B 1 . The engine is subjected to the maximum degree of cooling at the point X near the maximum fan efficiency. Accordingly, the noise is reduced while the automobile is at rest with the engine idling, a feature which is advantageous since large noises produced during engine idling would be annoying. The fan according to the present invention is especially useful as a cooling fan for automotive radiators. 
     While the present invention has been described as being applied to one preferred form, the invention is applicable to a variety of modified forms. 
     Provided that the attachment angle βt at the blade tip 1e is larger than the attachment angle βm at the average-diameter portion 1f, the attachment angle β therebetween may be varied rectilinearly as shown at I in FIG. 14 or may be varied along a curve of a multiple degree. The attachment β may not be minimum at the average-diameter portion 1f, but may become minimum at a position displaced from the average-diameter portion 1f a little toward the tip 1e or the base 1g as shown by the curve K or L in FIG. 15. 
     While in the foregoing embodiment the blades 1a are integral with the boss 1b, the blades 1a may be in the form of iron sheets and separate from the boss 1b as illustrated in FIGS. 16 and 17, in which case the blades 1a and the boss 1b are connected together by revetting or spot-welding. The diameter (of the boss) Dh between opposite blade base portions should be determined as shown. 
     The fan 1 thus constructed may include members for preventing air from flowing in streams around the blade tip 1e shown at a in FIG. 1. FIG. 18 shows a ring 1h on the blade tip 1e for preventing such air streams. The blade tip 1e shown in FIG. 19 has a wall 1i for preventing air from flowing around the blade tip 1e. As shown in FIG. 20, a wall 1j for preventing air streams from flowing around the blade tip may be mounted on one side of the blade 1a. 
     While the blade 1a extends perpendicularly from the boss 1b as shown in FIG. 6, the blade 1a may be inclined in a forward direction as shown in FIG. 21 or may be included in a rearward direction. With the blade 1a thus inclined, an air flow toward the blade tip 1e is improved. To further improve such an air flow toward the blade tip 1e, the blades 1a may be swept forward in the direction of rotation of the fan as shown in FIG. 22, or may be swept backward in the direction of rotation of the fan. The present invention is applicable to stationary blades when incorporated in a fan equipped with such stationary blades. 
     Although in the embodiment shown in FIG. 4 the fan 1 is located rearward of the radiator 4 to draw air through the latter, the fan 1 may be disposed in front of the radiator 4 to blow air into the latter. The fan 1 according to the present invention should not be limited to use for cooling radiators, but is applicable in a wide variety of fans and blowers. 
     With the arrangement of the present invention, the fan has an attachment angle that is greater at a blade tip than at an average-diameter position to cause a large main air flow to be produced at the blade tip, thus reducing air flow disturbances at the blade tip and hence reducing noises due to such air flow disturbances.