The present invention relates to an axial flow fan.
Japanese Utility Model Registration No. 3089140 (U.S. Patent Application Publication No. 2003/0123988) discloses in
Japanese Utility Model Registration No. 3089140 (U.S. Patent Application Publication No. 2003/0123988) describes that vortices 23 are generated at the radially end portion 13 of the blade as shown in
An object of the present invention is to provide an axial flow fan in which an amount of dropping at the inflection point appearing in air volume-static pressure characteristics may be reduced and noise may also be reduced as compared to conventional axial flow fans.
An axial flow fan according to the present invention includes an impeller, a housing, and a motor. The impeller includes a hub having an annular peripheral wall portion, and a plurality of blades. Each blade has a base portion which is integrally fixed to an outer wall of the peripheral wall portion of the hub. The blades extend outwardly in a radial direction of the peripheral wall portion from the outer wall of the peripheral wall portion, and are disposed at an interval in a circumferential direction of the peripheral wall portion. The housing has a cylindrical air channel in which the impeller rotates. The motor is fixed to the housing and includes a rotary shaft having a front end portion and a rear end portion. The impeller is fixed to the front end portion of the rotary shaft.
The blade used in the present invention has the following features. In order to identify the shape of the blade, an imaginary line is assumed. The imaginary line passes one end of the base portion of the blade positioned on the rear end side of the rotary shaft and extends in parallel to an axial line of the rotary shaft along an outer peripheral surface of the peripheral wall portion. The base portion of the blade is inclined in a direction from the one end of the base portion to the other end thereof so as to be gradually away from the imaginary line in a rotation direction of the impeller and curved so as to be convex in a direction opposite to the rotation direction. The blade has a curved portion formed in the vicinity of a radially outer end portion positioned opposite to the base portion in the radial direction of the hub. The curved portion is convex in the rotation direction, or is concave in the direction opposite to the rotation direction. The curved portion extends along the radially outer end portion from a rear end edge of the blade to the vicinity of a front end edge of the blade. The rear end edge is positioned on a side where the one end of the base portion of the blade is positioned and extends in the radial direction. The front end edge of the blade is positioned on a side where the other end of the base portion of the blade is positioned and extends in the radial direction. The width of the curved portion in the radial direction and depth of a concave portion formed in the curved portion are determined so as to gradually decrease from the rear end edge of the blade to the front end edge thereof.
With the above configuration, it is possible to reduce the amount of dropping at the inflection point appearing in air volume-static pressure characteristics and reduce noise as compared to a conventional axial flow fan in which a projecting edge is formed over the entire length of the radially outer end portion of the blade. The effects obtained in the present invention were confirmed by experiments.
It is preferable that the shape of the blade be determined such that outer surface portions positioned on both sides of the curved portion in the radial direction exist in the same curved surface. In other words, it is preferable that one outer surface portion positioned on one side of the curved portion exist on an extended surface of the other outer surface portion positioned on the other side of the curved portion. By defining the shape of the curved portion in this manner, it is possible to increase the inflection point appearing in air volume-static pressure characteristics and reduce noise as compared to the conventional axial flow fan in which a projecting edge is formed.
It is preferable that, as the impeller is viewed from the front end portion of the rotary shaft toward the rear end portion thereof, an outline of the rear end edge of the blade be curved to be convex in the rotation direction at a position corresponding to the curved portion. By defining the shape in this manner, it is possible to reduce the amount of dropping at the inflection point appearing in air volume-static pressure characteristics and reduce noise.
Assuming that the outer diameter of the impeller is R, it is preferable that the deepest point of the concave portion be positioned within a range from 0.8R to 0.95R. When the deepest point of the concave portion exists at a position closer to the base portion relative to the radial position corresponding to 0.8R, the inflection point of the air volume—static pressure characteristics decreases.
Assuming that the number of blades is N, it is preferable that the length L of the curved portion as measured in the circumferential direction of the peripheral wall portion of the hub be in a range from 2πR/(2.8N) to 2πR/(1.5N). If the length L of the curved portion as measured in the circumferential direction is less than 2πR/(2.8N), the air volume is reduced to cause an increase in the amount of dropping at the inflection point of the air volume-static pressure characteristics. If the length L of the curved portion as measured in the circumferential direction is more than 2πR/(1.5N), the inflection point of the air volume-static pressure characteristics decreases as a whole, leading to an increase of noise.
It is preferable that the maximum value for the width of the curved portion be in a range from 0.15R to 0.20R. If the maximum value for the width of the curved portion is less than 0.15R, the air volume is reduced to cause an increase in the amount of dropping at the inflection point of the air volume-static pressure characteristics, leading to an increase of noise. If the maximum value for the width of the curved portion is more than 0.20R, the inflection paint of the air volume-static pressure characteristics decreases, leading to an increase of noise.
Further, it is preferable that the maximum value for the depth D of the concave portion of the curved portion be in a range from 0.02R to 0.05R. If the maximum value for the depth D of the concave portion of the curved portion is less than 0.02R, the amount of dropping at the inflection point of the air volume static pressure characteristics is increased to increase noise. If the maximum value for the depth D of the concave portion of the curved portion is more than 0.05R, the inflection point of the air volume—static pressure characteristics significantly decreases to increase noise. Specifically, the maximum value for the depth D of the curved portion may preferably be 1 to 2 mm.
According to the present invention, it is possible to reduce the amount of dropping at the inflection point appearing in air volume-static pressure characteristics than in a conventional axial flow fan in which a projecting edge is formed over the entire length of the radially outer end portion of the blade, which further leads to a reduction in noise.
An embodiment of an axial flow fan according to the present invention will be described in detail hereinbelow with reference to the accompanying drawings.
Each blade 5 has the following features. In order to identify the shape of the blade 5, an imaginary line PL is assumed to pass one end 5Aa of the base portion 5A of the blade 5 positioned on the rear end side of the rotary shaft 8 and extending in parallel to the axial line X of the rotary shaft 8 along the outer peripheral surface of the peripheral wall portion 6A. As shown in
Each blade 5 used in the present embodiment has a curved portion 4 as shown in
Further, the shape of the blade 5 is defined such that outer surface portions 5Ea and 5Eb positioned on both sides of the curved portion 4 in the radial direction exist in the same curved surface, in other words, the outer surface portion 5Eb exists on an extended surface of the outer surface portion 5Ea as viewed from the rear end edge 5C side. By defining the shape in this manner, it is possible to reduce the amount of dropping at the inflection point appearing in air volume-static pressure characteristics and reduce noise as compared to a conventional axial flow fan in which a projecting edge is formed.
When the impeller 7 is viewed from the front end portion of the rotary shaft 8 to the rear end portion thereof (i.e., as shown in
As shown in
As shown in
It is preferable that the maximum value for the width W of the curved portion 4 be in a range from 0.15R to 0.20R. If the maximum value for the width W of the curved portion 4 is less than 0.15R, the air volume is reduced to cause an increase in the amount of dropping at the inflection point of the air volume—static pressure characteristics as a whole, leading to an increase of noise. If the maximum value for the width W of the curved portion 4 is more than 0.20R, the inflection point of the air volume-static pressure characteristics decreases as a whole, leading to an increase of noise. Further, it is preferable that the maximum value for the depth D of the concave portion 4A of the curved portion 4 be in a range from 0.02R to 0.05R. If the maximum value for the depth D of the concave portion 4A of the curved portion 4 is less than 0.02R, the air volume is reduced to cause an increase in the amount of dropping at the inflection point of the air volume-static pressure characteristics, leading to an increase of noise. If the maximum value for the depth D of the concave portion 4A of the curved portion 4 is more than 0.05R, the inflection point of the air volume-static pressure characteristics decreases as a whole, leading to an increase of noise.
Assuming that the number of blades is N, it is preferable that the length L of the curved portion 4 as measured in the circumferential direction of the peripheral wall portion 6A of the hub 6 be in a range from 2πR/(2.8N) to 2πR/(1.5N). If the length L of the curved portion 4 as measured in the circumferential direction is less than 2πR/(2.8N), the air volume is reduced to cause an increase in the amount of dropping at the inflection point of the air volume-static pressure characteristics, leading to an increase of noise. If the length L of the curved portion 4 as measured in the circumferential direction is more than 2πR/(1.5N), the inflection point of the air volume-static pressure characteristics decreases, leading to an increase of noise.
According to the present embodiment, it is possible to increase the static pressure and air volume in a practicable operating range as compared to a conventional axial flow fan in which a projection edge is formed in the entire radially outer end portion of the blade, thereby reducing noise.
Next, results of a test for confirming meritorious effects of the axial flow fan according to the present embodiment will be described.
The radius R of the impellers of the axial flow fans used in the test was 43 mm, and rotation speed thereof was 4,400 [min−1]. In the axial flow fan according to the present embodiment, the deepest point of the concave portion 4A of the curved portion 4 was set at a position of 0.9R assuming that the outer diameter of the impeller 7 is R. Further, the length L of the curved portion 4 was set to 2πR/(1.5N), the width W of the curved portion 4 was set to 0.19R, and the maximum value for the depth D of the concave portion 4A was set to 0.03R.
As can be seen from the results shown in
It has been confirmed by the tests that even though the number of blades, the outer diameter of the impeller, the rotation speed of the impeller, and the number and shape of the webs are different, the same result is obtained.
While certain features of the invention have been described with reference to example embodiments, the description is not intended to be construed in a limiting sense. Various modifications of the example embodiments, as well as other embodiments of the invention, which are apparent to persons skilled in the art to which the invention pertains are deemed to lie within the spirit and scope of the invention.
Number | Date | Country | Kind |
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2008-326283 | Dec 2008 | JP | national |