Abstract:
The fan assembly for a motor vehicle includes a plurality of radially extending blades each having a first rearwardly facing concave curvature extending along the entire length of the blade adjacent the leading edge and a forwardly facing concave curvature at the outer end of the blade adjacent the trailing edge to increase the cooling efficiency of the fan and decrease the noise produced during operation.

Description:
This application is a continuation in-part application of application Ser. No. 750,320 filed Dec. 14, 1976, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention is directed to a fan assembly more particularly to a cooling fan assembly for a motor vehicle. 
     2. Prior Art 
     Various prior art fan assemblies for motor vehicles have been proposed by which cooling air is drawn through a radiator core and passed over the engine of the vehicle. A fan assembly of this type is for example disclosed in the patent to Aiki et al U.S. Pat. No. 3,584,969 and assigned to the assignee of the present invention. Each blade of such a prior art fan assembly has a cross-sectional configuration wherein a curved center line of the blade as viewed in cross-section is defined by a radius of curvature the central point of which is positioned on the discharged side of the fan. This configuration may cause a whirl of air adjacent the trailing edge of the blade due to the arrangement of the engine block which resists the flow of cooling air. Therefore the cooling operating efficiency will be considerably reduced while the noise level will be increased. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide an improved fan assembly which obviates the various drawbacks mentioned above by increasing the cooling efficiency and decreasing the noise produced during the cooling operation. 
     The fan assembly according to the present invention includes a plurality of radially disposed fan blades each of which is provided with a rearwardly facing concave curvature extending the entire length of the blade adjacent the leading edge of the blade and a forwardly facing concave curvature at the outer end of the blade adjacent the trailing edge of the blade with the oppositely directing curvatures merging smoothly at the intermediate portion of the blade. 
     The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view showing the location of a fan assembly within the engine compartment of a vehicle between the radiator and the engine block. 
     FIG. 2 is a partial front view of a fan assembly according to the present invention showing a single blade. 
     FIG. 3 is a cross-sectional view of the fan blade according to the present invention taken substantially along the line II--II in FIG. 2. 
     FIG. 4 is a view similar to FIG. 3 showing the cross-sectional configuration of a prior art fan blade. 
     FIG. 5 is a view similar to FIG. 3 which more particularly shows the construction of the fan blade according to the present invention. 
     FIG. 6 is a view similar to FIG. 4 which schematically shows the flow of air according to a prior art fan assembly. 
     FIG. 7 is a view similar to FIG. 6 which schematically shows the flow of air according to the present invention. 
     FIGS. 8, 9 and 10 are graphs showing comparative experimental curves for a fan according to the present invention and a conventional fan. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, a fan assembly 1 is mounted on the drive shaft of an engine 3 between the engine 3 and the radiator 2. Thus the fan assembly is adapted to draw cooling air through the radiator core 2a of the radiator 2 and to discharge the air around the engine 3. 
     The fan assembly 1 includes a fan having a central boss 6, a peripheral annular flange 11 and a plurality of radially disposed blades 7, only one of which is illustrated in FIG. 2. The blades 7 which are integrally formed with the boss 6 and flange 11 may be formed of non-flexible material such as steel as well as from a flexible synthetic resin material. The trailing edge 8 of each curved blade 7 is provided with a reverse curvature toward the front surface 4 as shown in FIG. 5. More particularly the curved center line 9a of the blade 7 as viewed in cross-section is defined by two oppositely curved sections each having a different radius of curvature and an intermediate connecting section between the two oppositely curved sections. The center O 2  of the radius of curvature R 2  is located on the front side 4 of the blade 7 while the center O 1  of the radius of curvature R 1  is located on the rear side 5 of the blade 7. Thus the portion of the curved center line 9a adjacent the leading edge 9 of the blade 7 is defined by a curve having a radius R 1  while the portion of the curved center line 9a adjacent the trailing edge 8 of the blade 7 is defined by a curve having a radius R 2 . The intermediate section of the curved center line 9a at the intermediate portion 10 of the blade 7 is comprised of a line having oppositely directed curves adjacent each end which merge smoothly with the curved portions of the center line 9a having the radii of curvature R 1  and R 2 , respectively. The inflection line 10&#39; between the two oppositely curved portions is shown in FIG. 2 at an acute angle to the radius of the blade. Thus the root portion of the blade 7 has only a single radius of curvature R 1  and the outer portion of the blade has opposite radii of curvature R 1  and R 2 . 
     As shown in FIG. 3 the flow of air as indicated by the arrow W is curved due to the difference in pressure at the front and rear surfaces 4 and 5 of the blade 7. Thus the inflow and outflow angles α 1  and α 2  of air flow W will be different from flow angles β 1  and β 2  of air flows W 1  and W 2  to the leading edge 9 and from the trailing edge respectively by excess angles γ 1  and γ 2 , respectively. Therefore the following equations can be written: 
     
         γ.sub.1 =Δ.sub.1 -β.sub.1 
    
     
         α.sub.2 =β.sub.2 -α.sub.2 
    
     In FIG. 3 the angle of inclination of the blade 7 is designated θ and α is the angle of elevation of air flow. In order to reduce or prevent a whirl of air, especially around the trailing edge 8 of the blade 7 the curved center line 9a may be designed adjacent the air flows W 1  and W 2  taking into consideration the various above mentioned factors. 
     By constructing the blade 7 with the trailing edge 8 thereof curving towards the front surface 4 the flow of air past the trailing edge of the blade will occur without any undesirable whirl of air as best seen in FIG. 7. The a ial flow of air which occurs upon rotation of the fan blades is centrifugally urged by means of the forwardly curved portion adjacent the trailing edge 8 of the blade 7 which acts as a centrifugal fan. Therefore the air flows diagonally due to the composition of axial and centrifugal components. This results in the increase in the dynamic component of air flow between the fan assembly and the engine 3 to thereby effect an increase in the cooling efficiency for the vehicle engine. 
     A conventional blade is illustrated in FIGS. 4 and 6 wherein the curved center line 9a&#39; of the blade 7&#39; is defined by curves having radii of curvature R 1  &#39; and R 2  &#39;, the central points O 1  &#39; and O 2  &#39; of which are positioned at the same side of the rear surface 5&#39; of the blade 7&#39;. The pressure at the rear surface 5&#39; of the blade 7&#39; increases due to the position of the engine 3&#39; which resists the flow of air in the axial direction. Therefore the flow of air is urged toward the front side of the blade 7&#39; so that a part of the air which flows past the edge 8&#39; will flow upstream toward the front surface 4&#39; so as to define a low pressure are around the front surface 4&#39; adjacent the trailing edge 8&#39;. This results in a decrease in the quantity of air flowing around the engine 3&#39;. By constructing the blades according to the present invention, this disadvantage will be reduced. 
     The advantages of the present invention will be more clearly understood from the following experimental data comparing a fan according to the present invention with a conventional fan. 
     
         ______________________________________Factor         Present Invention                       Prior Art______________________________________Dimen- Outside Diametersions Of Fan       380          380Of Fan Diameter Of FanAssem- Boss         166          166bly   Number Of Blades       6            6 Width Of Blade              108 mm       108 mm Inclination Angle Of Blade     30°   30° R.sub.1 (R.sub.1 &#39;)              440 mm       440 mm O.sub.1 (O.sub.1 &#39;)              Side Of Rear Side Of Rear              Surface Of Blade                           Surface Of Blade R.sub.2 (R.sub.2 &#39;)              260 mm       340 mm O.sub.2 (O.sub.2 &#39;)              Side Of Front                           Side Of RearExperi-            Surface Of Blade                           Surface Of Blademental Fan Noise    94.5 dB      98.0 dBResults Fan Efficiency              57%          42%______________________________________ 
    
     In the above table, noise was measured at a distance of one meter from the front of the fan assembly when the fan was running at 3,250 rpm and the fan efficiency was measured with the fan running at 1,000 rpm. 
     More particularly, the advantages of the fan assembly according to the present invention as compared to a conventional fan will be better understood from the graphical illustrations in FIGS. 8, 9 and 10.