Patent Publication Number: US-6659724-B2

Title: Axial fan for vehicles

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims priority of Japanese Patent Application No. 2001-31339, filed on Feb. 7, 2001, the contents being incorporated herein by reference, and a continuation of PCT/JP02/01048, filed Feb. 7. 2002. 
     TECHNICAL FIELD 
     The present invention relates to an axial fan, for vehicles, having a plurality of blades radially extending from a boss (hub). 
     BACKGROUND ART 
     A radiator, and a blower for blowing cold air onto the radiator, have usually been mounted on the portions where the air can be easily taken in, such as at the front end of the vehicle. Therefore, the blower is strongly affected by the air pressure caused by travelling of the vehicle. 
     Concretely speaking, the axial fan used for the blower is such that the air passes through in the axial direction. When the air pressure caused by travelling of the vehicle is received in the axial direction, therefore, the velocity differential becomes small between the surfaces of the blades and the air, and the resistance becomes small between the blade surfaces and the air. 
     In an idling condition in which the vehicle is at rest while the axial fan (blower) is in operation, on the other hand, the resistance is great between the blade surfaces and the air when there is almost no air pressure caused by travelling of the vehicle. On the root side of the blades  212  where the peripheral velocity is small, therefore, the air flow peels off the surfaces of the blades  212  and stalls. As shown in FIG. 7, therefore, the air that is blown fails to flow in the axial direction but flows in an outer radial direction. 
     As the air that is blown flows in the outer radial direction, the spatial size W 1  through which the air substantially flows becomes smaller than the spatial size Wo in which the air substantially flows when the air that is blown is flowing in the axial direction, resulting in a decrease in the blow rate and in the fan efficiency of the blower. 
     This phenomenon (problem) occurs particularly conspicuously when there exists a wall surface having a large air resistance, such as an engine, on the downstream side of the axial fan. 
     DISCLOSURE OF THE INVENTION 
     In view of the above-mentioned points, therefore, it is an object of the present invention to provide an axial fan for vehicles, which suppresses a drop in the flow rate that occurs when the air that is blown does not flow in the axial direction but flows in the outer radial direction. 
     In order to accomplish the above-mentioned object according to one aspect of the present invention, there is provided an axial fan  210 , having a plurality of blades  212  radially extending from a boss  211  to blow the air to a heat exchanger  100  mounted on the vehicle, wherein the axial end surface  211   a  of the boss  211  on the negative pressure side  212  of the blades  212  is so constituted that the air flows toward the root side of the blades  212  from the side of the axial end surface  211   a.    
     Due to the air flowing toward the root side of the blades  212  from the side of the axial end surface  211   a , therefore, the resistance decreases between the air and the blade surfaces on the root side of the blades  212 , making it possible to prevent a stall on the root side of the blades  212 . It is, therefore, possible to effectively make the air on the front side of the boss  211  flow toward the outer direction (toward the blades  212 ) and, hence, to suppress a drop in the flow rate. 
     According to another aspect of the present invention, there is provided an axial fan  210 , having a plurality of blades  212  radially extending from a boss  211  to blow the air to a heat exchanger  100  mounted on the vehicle, wherein the front edges  212   b  of the blades  212  are deviated toward the upstream side in the air stream beyond the axial end surface  211   a  at the axial end of the boss  211  as viewed from a direction at right angles to the axial direction of the boss  211 . 
     It is thus made possible for the air to flow from the side of the axial end surface  211   a  toward the root side of the blades  212 . Due to the air flowing toward the root side of the blades  212  from the side of the axial end surface  211   a , therefore, the resistance decreases between the air and the blade surfaces on the root side of the blades  212 . It is, therefore, allowed to effectively guide the air on the front side of the boss  211  toward the outer direction (toward the blades  212 ) and, hence, to suppress a drop in the flow rate. 
     The invention can be more fully understood from the accompanying drawings and from the description of preferred embodiments of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is a side view of an axial fan according to a first embodiment of the present invention; 
     FIG. 1B is a front view of the axial fan according to the first embodiment of the present invention; 
     FIG. 2 is a side view schematically illustrating the axial fan according to the first embodiment of the present invention; 
     FIG. 3A is a perspective view of the axial fan according to the first embodiment of the present invention; 
     FIG. 3B is a sectional view along the line III—III in FIG. 3A; 
     FIG. 4 is a graph illustrating the fan efficiency, static pressure and drive torque of the fan for the flow rate; 
     FIG. 5A is a side view of the axial fan according to a second embodiment of the present invention; 
     FIG. 5B is a front view of the axial fan according to the second embodiment of the present invention; 
     FIG. 5C is a view illustrating a major portion A of FIG. 5A on an enlarged scale; 
     FIG. 6 is a sectional view of the blade and boss of the axial fan according to the second embodiment of the present invention; and 
     FIG. 7 is a side view of an axial fan according to a prior art. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     (First Embodiment) 
     In this embodiment, the axial fan, for vehicles, of the invention is adapted to a blower that blows cooling air onto the radiator of a vehicle. FIG. 1 is a view schematically illustrating a state where a blower  200  according to the embodiment is mounted, and FIG. 2 is a schematic abstract view of FIG.  1 A. 
     In FIG. 1A, a radiator  100  is a heat exchanger for cooling cooling water by exchanging the heat between the air and the cooling water of an engine E/G, and the blower  200  is a blower means for blowing cold air onto the radiator  100 . The radiator  100  and the blower  200  are, usually, mounted on the portions where the air can be easily taken in, such as the front end of the vehicle. 
     Here, the radiator  100  comprises a plurality of flat tubes  111  through which the cold water flows and corrugated fins (not shown) arranged among the tubes  111  to increase the area for conducting heat to the air. Upon brazing the fins and tubes  111  together, there is constituted a radiator core for exchanging the heat between the cooling water and the air. 
     In this embodiment, the tubes  111  are extending up and down, and header tanks  120  are arranged at the end portions being communicated with the tubes  111 . Here, the header tank  120  on the upper end side, on the surface of the paper, is for distributing the cold water to the tubes  111 , and the header tank  120  on the lower end side, on the surface of the paper, is for collecting and recovering the cold water after having exchanged heat. 
     Referring to FIG. 1B, further, the blower  200  comprises an axial fan  210  constituted by a plurality of blades  212  radially extending from a boss  211 , and a shaft  220  (see FIG. 1A) for rotating the axial fan  210 . The shaft  220  obtains power from the crankshaft (not shown) of the engine E/G. 
     A metallic sleeve (not shown) is mounted in a portion of the boss  211  in which the shaft  220  is inserted, and the boss  211  and the blades  212  are integrally molded together by using a resin (polypropylene in this embodiment). 
     Therefore, the words “the boss  211  and the blades  212  are integrally molded together by using a resin” referred to in this specification do not necessarily mean that the boss  211  as a whole is made of a resin. However, the boss  211  as a whole may be made of a resin, as a matter of course. 
     Here, the axial fan stands for the one with which the gas (air) passes through in the axial direction as specified under JIS (Japanese Industry Standard) B 0132-1012. 
     In this embodiment as shown in FIG. 2, front edges  212   b  of the blades  212  which are ridges of negative-pressure surfaces  212   a  (see FIG. 3B) of the blades  212  are deviated toward the upstream side in the air stream beyond the axial end surface  211   a  at the end in the axial direction of the boss  211 . 
     Concretely speaking, as shown in FIGS. 3A and 3B, nearly one-half region of the blade  212  on the root side (boss  211  side) and on the front edge  212   b  side, is protruded toward the upstream side in the air stream beyond the axial end surface  211   a  positioned on the side of the negative-pressure surface  212   a.    
     The negative-pressure surface of the blade stands for the surface of the blade opposite to the surface (pressure surface) facing the flow of the air as is disclosed in, for example, Fluid Engineering (Published by Tokyo University). The front edge of the blade stands for a front edge of the blade in a direction in which it travels as disclosed in the above-mentioned literature. 
     On the root side of the blade  212 , further, a portion protruding toward the upstream in the air stream beyond the axial end surface  211   a  is connected from the root side of the blade  212  to the axial end surface  211   a  describing a smoothly curved surface  213  as shown in FIG.  3 A. When viewed from the axial direction of the boss  211 , the curved surface  213  is so formed that a contour line  213   a  of the curved surface  213  describes a streamline shape or a wing shape as shown in FIG.  1 B. 
     Here, as described in the above-mentioned literature, the streamline shape stands for a shape which hardly permits the occurrence of peeling between the air stream and the body (curved surface  213  in this embodiment), and the wing shape stands for a shape which produces a lift which is considerably greater than the air resistance. 
     In FIGS. 1A and 2, a shroud  230  covers a gap between the axial fan  210  and the radiator  100 . Therefore, the air blown out by the axial fan  210  is not sucked by the axial fan  210 , i.e., the air is prevented from circulating around the axial fan  210 , and the flow rate to the radiator  100  is prevented from decreasing. 
     Next, described below are the advantages of this embodiment. 
     In this embodiment, the front edges  212   b  of the blades  212  are deviated toward the upstream side in the air stream beyond the axial end surface  211   a  as viewed from the direction at right angles with the axial direction of the boss  211  and, hence, air is allowed to flow toward the root side of each blade  212  from the side of the axial end surface  211   a.    
     Due to the air flowing from the side of the axial end surface  211   a  toward the root side of the blades  212  (see FIGS.  2  and  1 B), therefore, the resistance decreases between the air and the blade surfaces on the root side of the blades  212  making it possible to suppress the stalling on the root side of each blade  212 . 
     It is thus made possible to prevent air flowing in the outer radial direction, to suppress a decrease in the size of a space through which the air substantially flows, and to suppress a decrease in the flow rate and in the fan efficiency of the blower  200 . 
     Further, the root side of each blade  212  is continuous to the axial end surface  211   a  through the smoothly curved surface  213 , enabling the air to smoothly flow from the side of the axial end surface  211   a  toward the root side of each blade  212 . Thus, the resistance is further decreased between the air and the blade surfaces on the root side of each blade  212 , reliably suppressing the stall on the root side of the blades  212 . 
     Further, the curved surface  213  is so formed that the contour  213   a  of the curved surface  213  describes a streamline shape or a wing shape as viewed from the axial direction of the boss  211 , enabling the air to flow smoothly from the side of the axial end surface  211   a  toward the root side of each blade  212 . 
     Besides, the curved surface  213  is the one that is curved like a dome contributing to increasing the mechanical strength on the root side of each blade  212 . 
     FIG. 4 is a graph of test results and illustrates the fan efficiency, static pressure and drive torque of the fan for the blow rate. As will be obvious from this graph, the axial fan according to this embodiment exhibits both improved static pressure and improved fan efficiency using the same torque as that of the axial fan of the prior art. 
     The words “fan efficiency” and “static pressure” have been defined under JIS B 0132, and the testing methods thereof comply with JIS B 8340. 
     (Second Embodiment) 
     According to this embodiment as shown in FIGS. 5 and 6, a skirt portion  213   b  extends from the curved surface  213  so as to be continuous to the pressure surface side of the blade  212  and expands toward the outer peripheral side, the skirt portion  213   b  being formed from the front edge of the blade  212  toward the rear edge side thereof. 
     This enables the air to smoothly flow from the upstream side to the downstream side. 
     (Other Embodiments) 
     In the above-mentioned embodiments, the axial fan for vehicles of the invention is adapted to cooling the radiator  100 . The invention, however, is not limited thereto only but can be adapted to the blowers for the condensers and for other heat exchangers. 
     According to the invention, as will be obvious from the above-mentioned embodiments, the air is permitted to easily flow from the side of the axial end surface  211   a  toward the root side of each blade  212 , suppressing stalling on the root side of the blades  212 . Therefore, the effect of the boss  211  (flow rate of the air from the side of the axial end surface  211   a  toward the root side of the blades  212 ) decreases as the diameter of the boss  211  decreases with respect to the outer diameter D of the axial fan  210 . 
     Accordingly, the invention exhibits its effect more conspicuously for the axial fans having a large ratio (d/D) of the diameter of the boss  211  to the outer diameter D of the axial fan  210 . According to a study by the present inventors, it has been confirmed that the invention is particularly effective for axial fans having ratios d/D of not smaller than 0.35. 
     The invention was described above in detail with reference to particular embodiments. It should, however, be noted that a person skilled in the art would be capable of changing and modifying the invention in a variety of ways without departing from the scope and spirit of the invention.