Impeller for axial flow fan and axial flow fan using the same

There is provided an impeller for an axial flow fan, which includes a plurality of blades arranged in a circumferential direction. In each of the blades, with respect to a center point of a chord length of the blade, a leading edge side shape of the blade and a trailing edge side shape of the blade are line-symmetric, and a shape of the blade at one face side is different from a shape of the blade at the other face side.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an impeller for an axial flow fan, and an axial flow fan using the impeller, and more particularly, to an impeller which maintains an air flow characteristic in a normal rotation direction without a significant deterioration in the air flow characteristic even in a case of rotating in a reverse direction, and an axial flow fan using the impeller.

2. Description of the Related Art

Axial flow fans have been used for blowing or cooling of electronic devices such as home appliances and information devices.

Electronic devices such as personal computers and copy machines include a number of electronic components accommodated in a relatively small casing. Therefore, heat generated from the electronic components stays in the casing, possibly resulting in destroying the electronic components. Thermal destruction causes a big problem for the device. For this reason, a ventilation hole is provided on the side wall or ceiling of the casing of the electronic device. The heat generated in the casing is discharged from the ventilation hole to the outside. Also, axial flow fans have been used as cooling means for electronic devices.

FIG. 7is a front view showing a related-art axial flow fan.

The axial flow fan is disclosed in JP-A-H8-303391, andFIG. 8is a cross-sectional view taken along a line B-B′ of a blade shown inFIG. 7. The blade shape of the axial flow fan shown inFIGS. 7 and 8configures a forward swept blade. In order to increase an air flow, the blade shape is bent with respect to a rotation direction (normal rotation direction) such that a pressure surface side becomes a concave surface.

Some axial flow fan is rotatable in a reverse direction to change an air flow direction such that the axial flow fan can be used not only for blowing but also for exhaust. Since the related-art axial flow fan as shown inFIGS. 7 and 8has the blade shape for increasing an air flow with respect to the normal rotation direction, in a case of rotating the axial flow fan in the reverse direction, the air flow characteristic is significantly deteriorated as compared to the case of the normal rotation direction.

Meanwhile, there is a known bi-directional axial blower which is rotatable in a normal direction and a reverse direction and is called as a jet fan for air ventilation of a tunnel or the like (see JP-A-2009-097430, for example). The jet fan is configured to have the same air flow characteristic even if an air flow direction is changed between the normal direction and the reverse direction. Therefore, it is possible to send air forward or backward in a tunnel according to the internal environment situation of the tunnel.

FIG. 9is a cross-sectional view showing a blade of the axial blower of JP-A-2009-097430.

As shown inFIG. 9, the blade is S-shaped, and has a point symmetrical shape with respect to a point A (the center of the blade chord). The thickness of the blade has the maximum value h at the position of the point A, and is 8% to 14% with respect to the blade chord length L. The edge has a shape having a radius of curvature r of 0.25% to 0.35% with respect to the length L of the blade chord. At the position as the apex of warping, a distance X from a front end (or rear end) of the blade is about 10% with respect to the length L of the blade chord, and the height C of the warping at that position is about 2% with respect to the blade chord length. An axial flow fan having this blade shape has the same air flow characteristic in both of normal rotation and reverse rotation.

As in the axial blower disclosed in JP-2009-097430, if a blade shape is S-shaped and has a point symmetrical shape, even if the rotation direction is changed, the same air flow characteristic can be achieved. However, in this case, the air flow characteristic in the normal rotation direction is deteriorated as compared to the axial flow fan disclosed in JP-A-H8-303391. For this reason, in a case where a high air flow characteristic in the normal rotation direction is required, a blower as disclosed in JP-A-2009-097430 may not satisfy that requirement.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an impeller which can maintain an air flow characteristic in a normal rotation direction of an axial flow fan while suppressing a significant deterioration in the air flow characteristic even in a case of rotating in a reverse direction by designing the shape of the impeller, and an axial flow fan using the impeller.

According to an aspect of the present invention, there is provided an impeller for an axial flow fan, comprising: a plurality of blades arranged in a circumferential direction. In each of the blades, with respect to a center point of a chord length of the blade, a leading edge side shape of the blade and a trailing edge side shape of the blade are line-symmetric, and a shape of the blade at one face side is different from a shape of the blade at the other face side.

In the above impeller, the shape of the blade at the one face side may be defined by a concave shape having an arc shape with a predetermined radius of curvature, and the shape of the blade at the other face side may be defined by a convex shape having an arc shape with a predetermined radius of curvature.

In the above impeller, the one face side may be a pressure face side during a normal rotation of the impeller.

According to another aspect of the present invention, there is provided an axial flow fan comprising: the above impeller; a motor configured to rotate the impeller; and a casing which accommodates the impeller, and includes a base portion supporting the motor.

According to the above configuration, it is possible to provide an impeller which can maintain an air flow characteristic in a normal rotation direction of an axial flow fan while suppressing a significant deterioration in the air flow characteristic even in a case of rotating the axial flow fan in a reverse direction, and an axial flow fan using the impeller.

DETAILED DESCRIPTION

Hereinafter, an illustrative embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1is a sectional view of a center of an axial flow fan according to an illustrative embodiment of the present invention, andFIG. 2is a plan view showing an impeller3of the axial flow fan shown inFIG. 1.

An axial flow fan1includes an impeller3having a plurality of blades4arranged in a circumferential direction, a motor2configured to rotate the impeller3, and a casing6which accommodates the impeller3and has a base portion7supporting the motor2.

The base portion7is fixed to the casing6by a plurality of spokes8. If the impeller3rotates according to rotation of the motor2, air is suctioned from an inlet of the casing6, passes through the gaps between the blades4and the inside of the casing6, and is discharged from an outlet of the casing6.

The impeller3includes a cylindrical hub5, and the plurality of blades4arranged on an outer circumferential surface of the hub5. The blades4(five blades in an example shown inFIG. 2) are arranged at a regular interval in the circumferential direction. All of the blades4have the same shape and are formed integrally with the hub5by injection molding of a thermoplastic resin.

The blades4are forward swept blades in which the leading edges10of the blades4moves more forward than the roots of the blades4when normally rotating in a rotation direction of an arrow9inFIG. 2. However, in another illustrative embodiment, the blades4may be configured as sweptback blades=). InFIG. 1, the normal rotation direction of a blade at a front side is shown by an arrow ofFIG. 1.

FIG. 3is a cross-sectional view taken along a line A-A′ of a blade shown inFIG. 2, andFIG. 4is a view for explaining the cross-sectional view ofFIG. 3.FIG. 5is an enlarged view showing a leading edge portion (portion surrounded by a circle inFIG. 3) of the blade shown inFIG. 3.

FIGS. 3 and 4are cross-sectional views which are taken along the line A-A′ of the blade shown inFIG. 2(a cross section taken by cutting the vicinity of the outer circumferential portion of the blade along the outer circumference) and seen from a direction “B”. InFIGS. 3 and 4, an upper side is the outlet side, and a lower side is the inlet side. The normal rotation direction of the blade4is shown by the arrow9ofFIG. 3.

InFIG. 3, a straight line connecting the leading edge10and a trailing edge11is a blade chord line12. The length L of the blade chord line12is a blade chord length. There are shown a pressure surface13of the blade4and a suction surface14of the blade4during normal rotation.

The center portion of the surface of the pressure surface13of the blade4is formed in an arc having a predetermined radius of curvature R2, and the center of the radius of curvature R2is provided at a side of the pressure surface13of the blade4. In other words, the center portion of the surface of the pressure surface13of the blade4has a concave shape (a shape where the center portion of the pressure surface13becomes convex toward a side of the suction surface14).

Both ends of the pressure surface13of the blade4are formed in an arc having a predetermined radius of curvature R1(FIG. 5), and the center of the radius of curvature R1is provided at a side of the suction surface14of the blade4. In other words, the both ends of the pressure surface13of the blade4are convex toward the side of the pressure surface13.

That is, the surface of the pressure surface13of the blade4is formed by a curved surface where the arcs having the radius of curvature R1and the arc having the radius of curvature R2are connected (a curved surface whose end portions are convex and whose center portion is concave). One of the connection positions of the arcs are shown by a point A inFIG. 4, and the connection positions are distant from the both end portions of the blade4by a length of ⅕ of the length L of the blade chord line12.

Meanwhile, the center portion of the surface of the suction surface14of the blade4is formed in an arc having a predetermined radius of curvature R4, and both end sides of the suction surface14of the blade4are formed in arcs having a predetermined radius of curvature R3(FIG. 5). The center of the radius of curvature R3and the center of the radius of curvature R4are provided at a side of the pressure surface13of the blade4. In other words, the suction surface14of the blade4is convex toward the side of the suction surface14at any position.

That is, the surface of the suction surface14of the blade4is formed from a curved surface where the arcs having the radius of curvature R3and the arc having the radius of curvature R4are connected. One of the connected positions of the arcs is shown by a point B inFIG. 4. The point B is a point where a straight line passing the point A and extending in a rotation axis direction of the blade4intersects with the suction surface14.

As the values of R1to R4with respect to the length L of the blade chord line12, the following values are preferable.R1is 0.6 to 0.8 times of the length LR2is 70 to 90 times of the length LR3is 3 to 4 times of the length LR4is 4 to 5 times of the length L

As shown in the cross-sectional view ofFIG. 5, in the cross-sectional view of the blade end portion, a length X from the blade chord line12to the surface of the pressure surface13is larger than a length Y from the blade chord line12to the surface of the suction surface14. Further, as shown in the cross-sectional view ofFIG. 3, at the center portion of the blade, the length X from the blade chord line12to the surface of the pressure surface13is almost equal to the length Y from the blade chord line12to the surface of the suction surface14. In other words, a relation of (X≧Y) is satisfied.

Also, as shown inFIG. 3, the blade4has a line-symmetric shape with an axis passing through a center point15of the blade chord length L and perpendicular to the blade chord line12, as a symmetry axis16.

An attachment angle of the blade4represents an angle which is formed by the blade chord line12which is a straight line connecting the leading edge10of the blade4and the trailing edge11of the blade4, and a plane perpendicular to a rotation axis line. The attachment angle of the blade4generally depends on the position of the blade4in a radial direction. An attachment angle at the root side (portion which is attached to the hub5) of the blade4is 33°, and an attachment angle at the tip end side of the blade4is smaller than the attachment angle at the root side of the blade4. For example, the attachment angle at the tip end side is 75% to 80% of the attachment angle at the root side (portion which is attached to the hub5) of the blade4.

FIG. 6is a graph showing the air flow rate Q-static pressure characteristics of the axial flow fan1of the present illustrative embodiment having the blade shape shown inFIG. 2and an axial flow fan of a comparative example.

The axial flow fan of the comparative example has a blade shape bent with respect to a rotation direction for increasing an air flow such that a pressure surface side is convex, as shown inFIG. 8. The attachment angle at the root side of each blade is 62°, and the attachment angle at the tip end side of the blade is smaller than the attachment angle at the root side of the blade (here, the attachment angle at the tip end side of the blade is set to 65% of the attachment angle at the root side of the blade). Also, even in the comparative example, similarly toFIG. 2, the number of blades is five and the blades are forward swept blades.

InFIG. 6, solid lines represent air flow rate-static pressure characteristics during normal rotation, and broken lines represent air flow rate-static pressure characteristics during reverse rotation.

As shown inFIG. 6, the maximum static pressure of the axial flow fan1of the illustrative embodiment is slightly lower than that of the axial flow fan of the comparative example, but the maximum air flow rate of the axial flow fan1shows an increase from that of the axial flow fan of the comparative example. This is because the attachment angle of the blade of the axial flow fan1of the illustrative embodiment is smaller than the attachment angle of the blade of the comparative example.

The axial flow fan of the comparative example represents a characteristic in which the maximum air flow rate during reverse rotation is about 79% of that during normal rotation, whereas the axial flow fan of the present illustrative embodiment represents a characteristic in which the maximum air flow rate during reverse rotation is about 90% of that during normal rotation. That is, as compared to the axial flow fan of the comparative example, the axial flow fan of the present illustrative embodiment is slightly worse in the maximum static pressure, but shows an increase in the maximum air flow rate, and has the characteristic in which the maximum air flow rate during reverse rotation is about 90% of that during normal rotation.

Accordingly, the axial flow fan of the present illustrative embodiment has an optimized blade shape, and thus can maintain an air flow characteristic in a normal rotation direction while suppressing a significant deterioration in the air flow characteristic even in a case of rotating in a reverse direction.

Herein, in the above-described illustrative embodiment, although the number of blades is five, the present invention is not limited thereto. Further, the values of the shape and size of the blade are merely preferable examples, and can be variously changed within the scope of the claims.

The shape of each blade may be a forward swept blade or a sweptback blade.

Further, the blades may have any shape as long as a shape at one face side is different from a shape at the other (opposite) face side, and its variation is not limited to that shown inFIG. 3. For example, the shape of the pressure surface during normal rotation may have any shape as long as it is different from the shape of the suction surface, and thus may be a concave shape or a planar or convex shape. Similarly, the shape of the suction surface during the normal rotation may have any shape as long as it is different from the shape of the pressure surface, and thus may be a convex shape or a planar or concave shape.