IMPELLER FOR AN AXIAL FLOW FAN AND AXIAL FLOW FAN

Abstract

An impeller for an axial flow fan includes a plurality of blades arranged around a rotating shaft and a hub portion having a side peripheral portion surrounding the rotating shaft as viewed from a direction parallel to the rotating shaft, wherein an end portion on the rotating shaft side of each of the plurality of blades is coupled to the side peripheral portion, the plurality of blades includes a blade having a first type of shape and a blade having a second type of shape, and a thickness of the end portion on the rotating shaft side in the rotating shaft direction of the first type of shape is greater than the thickness of the end portion on the rotating shaft side in the rotating shaft direction of the second type of shape.

Description

BACKGROUND

Technical Field

The present disclosure relates to an impeller for an axial flow fan and an axial flow fan, and more particularly to an impeller for an axial flow fan and an axial flow fan for a compressible fluid.

Background

Examples of an axial flow turbo type fluid machine treating a compressible fluid such as a gas include an axial flow fan. Noise occurs in the axial flow fan. The largest noise occurring in the axial flow fan is fluid noise. Examples of fluid noise include a swirling sound as broadband noise and a blade sound (wind noise produced by rotating blades) as discrete frequency noise. Noise reduction has been addressed for many years. Generally, the level of fluid noise tends to increase with an increase in rotational speed.

JP Unexamined Patent Application Publication No. 05-044691 discloses a structure of an axial turbomachine blade having a fillet provided at a portion connecting a blade back surface and a platform. The structure disclosed in JP Unexamined Patent Application Publication No. 05-044691 reduces secondary loss of flow and improves efficiency by configuring the fillet such that a rear half portion of the fillet has a smaller curvature radius than a front half portion of the fillet at a sharp change point in curvature radius serving as a boundary between the front half portion of the fillet and the rear half portion of the fillet.

Examples of noise occurring in the above-described axial flow fan include not only noise caused by a fluid (hereinafter referred to as fluid noise) but also noise caused by vibration generated by excitation by a motor (hereinafter referred to as vibration noise). Vibration noise is generated by resonance of blades, casings, and the like at a specific rotational speed. Vibration noise is mainly generated by resonance in a nodal circle zero-order natural vibration mode (umbrella mode) where all blades of the axial flow fan vibrate in the same phase in the axial direction.

SUMMARY

The present disclosure is related to providing an impeller for an axial flow fan and an axial flow fan capable of generating a relatively small amount of noise.

In accordance with one aspect of the present disclosure, an impeller for an axial flow fan comprises a plurality of blades arranged around a rotating shaft and a hub portion having a side peripheral portion surrounding the rotating shaft as viewed from a direction parallel to the rotating shaft, wherein an end portion on the rotating shaft side of each of the plurality of blades is coupled to the side peripheral portion, the plurality of blades includes a blade having a first type of shape and a blade having a second type of shape, and a thickness of the end portion on the rotating shaft side in the rotating shaft direction of the first type of shape is greater than the thickness of the end portion on the rotating shaft side in the rotating shaft direction of the second type of shape.

Preferably, the number of blades having the first type of shape out of the plurality of blades is two or more, and each of the blades having the first type of shape is adjacent to other blade having the first type of shape around the rotating shaft.

Preferably, the number of blades having the first type of shape of the plurality of blades is two or more, and the plurality of blades are arranged in a state where the blades having the first type of shape are located at asymmetric positions.

Preferably, each of the plurality of blades comprises a first surface facing a suction port of a gas and a second surface facing an exhaust port of the gas, and the first type of shape has a part located at the end portion on the rotating shaft side, at least one of the first surface and the second surface has a portion coupled to the side peripheral portion through a curved surface at the end portion on the rotating shaft side.

Preferably, the curved surface has a recessed shape recessed toward the inside of the blade.

Preferably, the curved surface has a fillet surface shape.

In accordance with another aspect of the present disclosure, an axial flow fan comprises an impeller for an axial flow fan according to any one of the above aspects and a casing rotatably supporting the impeller for an axial flow fan around the rotating shaft, wherein a motor rotating the impeller for an axial flow fan is attached to the casing.

Preferably, the motor is an motor of outer rotor type, and a rotor yoke of the motor is attached to the hub portion.

In accordance with another further aspect of the present disclosure, an impeller for an axial flow fan comprises a plurality of blades arranged around a rotating shaft and a hub portion having a side peripheral portion surrounding the rotating shaft, wherein an end portion on the rotating shaft side of each of the plurality of blades is coupled to the side peripheral portion, the plurality of blades includes a blade having a first type of shape and a blade having a second type of shape, and the shape of the end portion on the rotating shaft side in the rotating shaft direction of the first type of shape is different from the shape of the end portion on the rotating shaft side in the rotating shaft direction of the second type of shape.

The present disclosure can provide an impeller for an axial flow fan and an axial flow fan capable of generating a relatively small quantity of noise.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an axial flow fan according to an embodiment of the present disclosure;

FIG. 2 is a perspective view illustrating an impeller of the axial flow fan according to the present embodiment;

FIG. 3 is a view of the impeller viewed from a rotating shaft direction;

FIG. 4 is a sectional view taken along line A-A of FIG. 3;

FIG. 5 is a view of the impeller viewed from a direction vertical to the rotating shaft;

FIG. 6 is a view of a blade having a first type of shape and a blade having a second type of shape, both being arranged side by side;

FIG. 7 is a perspective view illustrating an axial flow fan according to a modification of the present embodiment;

FIG. 8 is a view illustrating the impeller of the axial flow fan according to the present modification viewed from the rotating shaft direction; and

FIG. 9 is a graph illustrating a relationship between a frequency at which resonance occurs in an umbrella mode and vibration acceleration.

DETAILED DESCRIPTION

Hereinafter, an axial flow fan according to an embodiment of the present disclosure will be described.

Note that the direction of the coordinate system illustrated in each figure is common to all figures. Specifically, the X axis, the Y axis, and the Z axis are orthogonal to each other.

Embodiment

FIG. 1 is a perspective view of an axial flow fan according to an embodiment of the present disclosure.

As illustrated in FIG. 1, an axial flow fan 1 includes an impeller (impeller for an axial flow fan) 2 and a casing 5 supporting the impeller 2. The impeller 2 is rotatably supported by the casing 5 around a rotating shaft 2a relative to the casing 5. A motor 8 is attached to the casing 5. The motor 8 rotates the impeller 2 relative to the casing 5.

The rotating shaft 2a of the impeller 2 is parallel to the Z axis. In the figure, the position through which the rotating shaft 2a passes is illustrated by a reference character. Hereinafter, the Z-axis direction may be referred to as a rotating shaft direction. The XY plane of the coordinate system illustrated in FIG. 1 is a plane perpendicular to the rotating shaft direction.

The axial flow fan 1 is configured to rotate the impeller 2 thereby to blow a gas such as air (as an example of a compressible fluid) in a negative direction along the Z axis as viewed from the origin of the coordinate system illustrated in FIG. 1 (in a direction from the front side to the rear side of the axial flow fan 1 in FIG. 1).

The casing 5 includes a substantially circular hole portion as viewed from the rotating shaft direction. The impeller 2 is accommodated inside the hole portion. The casing 5 surrounds a side portion of the impeller 2.

In the present embodiment, the motor 8 is an motor of outer rotor type. The motor 8 includes a stator, a rotor yoke to be described later, a shaft to be described later, and an unillustrated magnet. The stator of the motor 8 is retained by a motor base portion located at a substantially center of the hole portion of the casing 5. The motor base portion is coupled via several spokes and thereby fixed to a portion around the casing 5. The motor base portion is located on an exhaust port (positive pressure side) serving as an exhaust port of a gas when the impeller 2 rotates in a normal rotation direction. The spokes connect between the exhaust port and the motor base portion of the casing 5. Specifically, the axial flow fan 1 has a configuration that a part of the air blowing passage is blocked by the spokes on the exhaust port. The impeller 2 is attached to the casing 5 from an intake port (negative pressure side) serving as a suction port of a gas when the impeller 2 rotates in the normal rotation direction.

Rotation of the motor 8 causes the impeller 2 to rotate relative to the casing 5, and then the axial flow fan 1 functions. More specifically, air is sucked from the intake port of the casing 5, passes through the impeller 2 inside the casing 5, and is then discharged from the exhaust port of the casing 5.

FIG. 2 is a perspective view illustrating the impeller 2 of the axial flow fan 1 according to the present embodiment. FIG. 3 is a view of the impeller 2 viewed from the rotating shaft direction. FIG. 4 is a sectional view taken along line A-A of FIG. 3. FIG. 5 is a view of the impeller 2 viewed from a direction vertical to the rotating shaft.

FIGS. 2 and 3 illustrate the impeller 2 viewed from the suction port of the gas. FIG. 5 illustrates the impeller 2 viewed from the X-axis direction. FIG. 4 illustrates the rotating shaft 2a through the use of a one-dot chain line.

The impeller 2 includes a hub portion 11 and a plurality of blades 21 to 27 arranged around the rotating shaft 2a (in a peripheral direction). The plurality of blades 21 to 27 are coupled to the hub portion 11. In the present embodiment, for example, seven blades 21 to 27 are provided. The impeller 2 is formed by integrally molding the hub portion 11 and the plurality of blades 21 to 27, for example, by injection molding of a thermoplastic resin.

As illustrated in FIG. 4, the hub portion 11 has a cup shape and includes a substantially flat lid portion 13 provided on the suction port of the gas and a side peripheral portion 15 surrounding the lid portion 13. A part of the hub portion 11 on the suction port of the gas serves as the substantially flat lid portion 13. The side peripheral portion 15 of the hub portion 11 has a cylindrical shape. The side peripheral portion 15 has an inclined surface 15b on the intake port. The inclined surface 15b is gently inclined so as to be tapered as approaching the intake port. The lid portion 13 is coupled to an end portion on the intake port of the side peripheral portion 15, namely, an end portion of the inclined surface 15b.

A rotor yoke 41 serving as a rotor of the motor 8 is provided inside the hub portion 11. The rotor yoke 41 is fixed to the lid portion 13 of the hub portion 11. The rotor yoke 41 is made of, for example, a ferromagnetic member such as iron. The rotor yoke 41 has a cylindrical shape, namely, a cup shape, and blocks the suction port. The inner side surface of the rotor yoke 41 includes an unillustrated magnet attached so as to face the stator of the motor 8.

A shaft 43 of the motor 8 is fixed to a center portion of the rotor yoke 41 as viewed from the rotating shaft direction. The shaft 43 is rotatably supported by the stator of the motor 8. The impeller 2 rotates the shaft 43 as the rotating shaft 2a. More specifically, the impeller 2 is rotatably retained relative to the casing 5 in a state of being attached to the shaft 43 of the motor 8 of the casing 5.

Seven blades 21 to 27 are arranged at substantially equal spacings in a direction around the rotating shaft 2a (in a peripheral direction). Each of the blades 21 to 27 has roughly the same shape, except as detailed below. Each end portion of the blades 21 to 27 on the side of the rotating shaft 2a is coupled to the side peripheral portion 15 of the hub portion 11. As illustrated in FIG. 4, each of the blades 21 to 27 includes a first surface 31 facing the suction port of the gas and a second surface 32 facing the exhaust port of the gas. Each of the blades 21 to 27 is inclined and attached to the hub portion 11 so as to flow a gas from the intake port to the exhaust port according to the rotation direction of the impeller 2.

In the present embodiment, each of the seven blades 21 to 27 has one of the two types of shape. More specifically, four blades 21 to 24 of the seven blades 21 to 27 have a first type of shape. The remaining three blades 25 to 27 of the seven blades 21 to 27 have a second type of shape.

Each of the blades 21 to 24 having the first type of shape is arranged so as to be adjacent to another one of the blades 21 to 24 of the same type around the rotating shaft 2a. As illustrated in FIG. 3, the blades 21 to 24 having the first type of shape are disposed at asymmetric positions with respect to an arbitrary plane (more specifically, a plane perpendicular to an XY plane passing through a rotation center of the impeller 2 as viewed from the rotating shaft direction) including the rotating shaft 2a. In other words, the blades 21 to 24 having the first type of shape are not equally spaced but rather disproportionately spaced around the rotating shaft 2a. As used herein, the term “asymmetric” refers to being asymmetric in terms of rotational symmetry or in terms of bust symmetry. Whether or not the blades have rotational symmetry is determined, for example, by the presence or absence of symmetry around the rotating shaft 2a serving as the rotation center of the impeller 2. Whether or not the blades have bust symmetry is determined, for example, by the presence or absence of symmetry assuming that a plane perpendicular to the XY plane passing through the rotating shaft 2a serving as the rotation center of the impeller 2 is used as a mirror.

FIG. 6 is a view of a blade 24 having the first type of shape and a blade 27 having the second type of shape, both being arranged side by side.

In FIG. 6, the upper part illustrates a cross section passing through the rotating shaft 2a of the blade 24, and the lower part illustrates a cross section passing through the rotating shaft 2a of the blade 27.

As illustrated in FIG. 6, a thickness t1 of a root portion (end portion on the rotating shaft 2a side) of a blade having a first type of shape (for example, the shape of the blade 24) in the rotating shaft direction is greater than a thickness t2 of a root portion of a blade having a second type of shape (for example, the shape of the blade 27) in the rotating shaft direction. Specifically, in the present embodiment, a fillet portion 35 is provided at a coupling portion between a first surface 31 of the blades 21 to 24 having a first type of shape and a side peripheral portion 15. Instead of the fillet portion 35, a corner portion 36 is provided at a connection portion between the first surface 31 of the blades 25 to 27 having a second type of shape and the side peripheral portion 15.

As illustrated in FIG. 4, the fillet portion 35 is configured so as to connect between the first surface 31 of the blades 21 to 24 and the side peripheral portion 15 via a surface curved concavely toward the inside of the blades. In other words, the first type of shape has a fillet surface shape at a root portion of the blades 21 to 24 coupled to the side peripheral portion 15 from the first surface 31. Further, in other words, the blade thickness (size between the first surface 31 and the second surface 32) of each of the blades 21 to 24 having the first type of shape is larger, by the amount of the fillet portion 35 provided, than the blade thickness of each of the blades 25 to 27 having the second shape.

In the present embodiment, the fillet portion 35 is formed so as to contact the first surface 31 of each of the blades 21 to 24 and the surface of the side peripheral portion 15, respectively, but the present disclosure is not limited to this. The impeller 2 has a diameter of about 110 millimeters and the fillet portion 35 is an arc-shaped curved surface having a cross section radius of about 2 millimeters, but the sizes are not limited to these. In addition, the cross section of the fillet portion 35 is not limited to the arc-shaped curved surface.

The fillet portion 35 is formed so as to extend along an outer peripheral surface of the side peripheral portion 15 toward the intake port from a portion near the exhaust port of the root portion of each of the blades 21 to 24. In other words, each of the blades 21 to 24 includes two side portions radially extending from the side peripheral portion 15, and the fillet portion 35 extends from one side portion to another side portion of each of the blades 21 to 24.

In the present embodiment, an inclined surface 15b is formed on the intake port of the opening portion 15c (end portion) of the side peripheral portion 15, and the angle between the inclined surface 15b and the first surface 31 of the blades 21 to 24 is relatively small. The fillet portion 35 is formed between a position near the exhaust port and a position in front of the inclined surface 15b. Specifically, the fillet portion 35 is located between the opening portion 15c of the side peripheral portion 15 and the inclined surface 15b in the rotating shaft direction. Note that instead of the inclined surface 15b, the fillet portion 35 may be formed over the entire area between the first surface 31 of the blades 21 to 24 and the surface of the side peripheral portion 15. Note also that the fillet portion 35 may also be formed between the inclined surface 15b and the first surface 31.

As described above, in the present embodiment, the four blades 21 to 24 of the seven blades 21 to 27 have the first shape, and the thickness of the root portion is greater than that of the blades 25 to 27 having the second shape. For this reason, the natural frequency of each of the blades 21 to 24 having the first shape is different from the natural frequency of each of the blades 25 to 27 having the second shape. The seven blades 21 to 27 has a mixture of blades having one type of the two types of shape and blades having another type of shape. Thus, the balance of the natural frequency of each of the blades 21 to 27 is uneven as a whole in the impeller 2. As a result, resonance due to the umbrella mode at a specific frequency is hardly excited, and remarkable noise is less likely to occur.

The four blades 21 to 24 having the first shape are disposed to be adjacent to each other. The fillet portion 35 is provided at an asymmetric position around the rotating shaft 2a. Thus, the present embodiment can increase the degree of uneven balance of natural frequency of the blades 21 to 27 and can largely reduce or eliminate the vibration peak level of the resonance frequency.

Note that in order to suppress resonance due to the umbrella mode, for example, it is also conceivable to increase the thickness of all the blades thereby increasing the rigidity of the blades. However, it is conceivable that such measures may increase the weight of the impeller or may increase the manufacturing cost due to an increase in material costs and the like. For this reason, the present embodiment is more preferable for suppressing resonance due to the umbrella mode.

[Description of Modification]

FIG. 7 is a perspective view illustrating an axial flow fan 101 according to a modification of the present embodiment. FIG. 8 is a view illustrating an impeller 102 of the axial flow fan 101 according to the present modification viewed from the rotating shaft direction.

The axial flow fan 101 has the same structure as the axial flow fan 1 of the above-described embodiment except that the impeller 102 has only one blade having the first shape.

As illustrated in FIG. 8, the impeller 102 includes seven blades 21 to 27, each having one of the two types of shape. Only the blade 21 of the seven blades 21 to 27 has the first type of shape. The remaining six blades 22 to 27 of the seven blades 21 to 27 have the second type of shape.

In the axial flow fan 101 illustrated in FIGS. 7 and 8, one blade 21 of the seven blades 21 to 27 has a first shape and the thickness of the root portion is greater than that of the other blades 22 to 27. Thus, as in the above-described embodiment, resonance due to the umbrella mode at a specific frequency hardly occurs or is eliminated.

Note that in the present modification, only one blade 21 has the fillet portion 35, and thus can easily maintain balance as a rotating body of the impeller 2.

In the axial flow fan, one of the typical vibrations is generated when an excitation force frequency of the motor 8 coincides with the nodal circle zero-order natural vibration mode (umbrella mode) of the blade. In the natural frequency, each blade vibrates in the same phase in the rotating shaft direction. In order to suppress occurrence of vibration due to the umbrella mode, it is conceivable to increase the thickness of the blades thereby to increase the rigidity of the blades. However, such measures increase the weight of the impeller and increase the material cost. Further, the magnetic center of the motor portion in the rotating shaft direction needs to be adjusted or subjected to design changes.

In the present embodiment, without being biased by the common sense notion that “all the blades have the same shape and have an even rigidity”, the fillet portion 35 is provided in the root of some of the blades. The fillet portion 35 increases the natural frequency of the blade and reduces the vibration level when resonance occurs. The unevenness of balance of natural frequency as a blade group can violate the principle that each blade easily vibrates in the same phase, and can suppress or eliminate vibration from occurring in the umbrella mode. Thus, the present embodiment can suppress occurrence of remarkable resonance sound in a relatively wide range of rotational speeds from high speed to low speed.

The fillet portion 35 may have a simple shape and may be provided only in some of the blades 21 to 27, and thus can suppress an increase in weight of the blade and can suppress an increase in material cost. In addition, suppression of resonance occurrence can reduce design changes on the magnetic center of the motor portion in the rotating shaft direction.

Note that in the present embodiment, a curved surface is formed so as to curve along a boundary between the blades 21 to 24 and the side peripheral portion 15 so that the thickness of the blades 21 to 24 having the first shape is greater than that of the other blades 25 to 27. Thus, changes in the air flow rate characteristics due to the presence or absence of such a curved surface are small and abnormal sound can be prevented from occurring without lowering the fluidity of the gas. Further, the recessed shape of the curved surface can further reduce the changes in the air flow rate characteristics due to the presence or absence of the curved surface. Furthermore, the curved surface is the fillet portion 35 having the fillet surface shape and formed along the side peripheral portion 15, and thus is hardly affected by changes in the air flow rate characteristics due to the presence or absence of the fillet portion 35 and can prevent occurrence of abnormal noise without lowering the fluidity of the gas.

FIG. 9 is a graph illustrating a relationship between a frequency at which resonance occurs in the umbrella mode and vibration acceleration.

In FIG. 9, the solid line indicates the magnitude of the vibration acceleration of the impeller 2 according to the above-described embodiment; the dashed line indicates the magnitude of the vibration acceleration of the impeller 102 of the axial flow fan 101 according to the modification of the above-described embodiment; and the dotted line indicates the magnitude of the vibration acceleration of the impeller of the axial flow fan with none of the blades having the fillet portion.

FIG. 9 illustrates simulation results obtained by calculating an average value of axial acceleration on the surface of each blade when electromagnetic excitation force in the rotating shaft direction is applied to a position where a magnet is located after modeling each of the impellers 2 and 102.

In the case of the impeller with none of the blades having the fillet portion, the peak frequency where a vibration acceleration peak occurred was 477 hertz (hereinafter may be referred to as [Hz]) and the vibration acceleration at that time was 9.24 meters per second (hereinafter may be referred to as [m/s²]).

In the case of the impeller 102 according to the modification, the peak frequency was 476 [Hz] and the vibration acceleration was 6.83 [m/s²].

The impeller 2 had two peaks. In the case of the first peak, the peak frequency was 482 [Hz] and the vibration acceleration was 4.84 [m/s²]. In the case of the second peak, the peak frequency was 523 [Hz] and the vibration acceleration was 4.90 [m/s²].

It can be confirmed from the above simulation results that the above-described embodiment and modification can suppress occurrence of resonance due to the umbrella mode in comparison with the structure with none of the blades having the fillet portion. More specifically, the impeller 2 according to the above-described embodiment can reduce acceleration by 47.6% in comparison with the structure with none of the blades having the fillet portion. The impeller 102 according to the modification can reduce acceleration by 26.1% in comparison with the structure with none of the blades having the fillet portion.

[Others]

The number of fan blades is not limited to 7. The shape of the blade can be variously changed.

The total number of blades is odd. Of them, the number of blades having the first type of shape is preferably half of the number obtained by adding 1 or subtracting 1 to or from the total number of blades. At this time, the blades having the first type of shape are disposed in an asymmetric position with respect to an arbitrary plane including the rotating shaft to provide a more uneven balance of natural frequency as the entire impeller, thereby providing resonance suppression. Alternatively, at this time, each of the blades having the first type of shape is disposed so as to be adjacent to another blade having the first type of shape around the rotating shaft, to provide a more uneven balance of natural frequency as the entire impeller, thereby providing large resonance suppression.

The fillet portion is provided on a negative pressure side of the blades having the first shape, but is not limited to this. The fillet portion may be provided on a positive pressure side of the blades to obtain a similar resonance suppression effect. More specifically, the fillet portion 35 may be formed not only on the side of the first surface 31 but also on the side of the second surface 32 or on both sides of the first surface 31 and the second surface 32.

The fillet portion 35 may be formed from one side portion to another side portion of each of the blades 21 to 24 or may be formed halfway from one side portion to another side portion.

Instead of the fillet portion, the root portion of the blade having the first shape may include another portion having another shape so that the thickness of the root portion of the blade having the second shape is greater than that of the blade having the first shape. Specifically, instead of the fillet surface shape, the blade having the first shape may be configured to partially increase the thickness of the root portion by providing a rib shape, the rib being standingly disposed at an end portion on the rotating shaft side so as to radially extend from the side peripheral portion to connect between the side peripheral portion and the surface of the blade. This configuration can also provide an uneven balance of natural frequency of the blades to obtain resonance suppression effects. Preferably, instead of the fillet surface shape, a portion allowing at least one of the first surface and the second surface to be coupled to the side peripheral portion through the curved surface may be formed. The curved surface formed in the portion can suppress the changes in the air flow rate characteristics due to the presence or absence of the portion. At this time, the curved surface is more preferably concaved. This can more greatly suppress the changes in the air flow rate characteristics.

The motor may be of an inner rotor type. In this case, the diameter of the hub portion can be reduced. Instead of providing the axial flow fan with a motor, the impeller may be configured to rotate by attaching the hub portion of the impeller to the rotating shaft rotated by a driving force of a motor located outside the casing.

The above-described embodiments are to be considered in all respects as illustrative and not restrictive. The scope of the present disclosure is defined not by the above description but by the scope of the claims, and it is intended to include the meanings equivalent to the scope of the claims and all modifications within the scope.

Claims

1. An impeller for an axial flow fan comprising:

a plurality of blades arranged around a rotating shaft; and

a hub portion having a side peripheral portion surrounding the rotating shaft, wherein

an end portion on the rotating shaft side of each of the plurality of blades is coupled to the side peripheral portion,

the plurality of blades includes a blade having a first type of shape and a blade having a second type of shape, and

a thickness of the end portion on the rotating shaft side in the rotating shaft direction of the first type of shape is greater than the thickness of the end portion on the rotating shaft side in the rotating shaft direction of the second type of shape.

2. The axial flow fan impeller according to claim 1, wherein

the number of blades having the first type of shape of the plurality of blades is two or more, and

each of the blades having the first type of shape is adjacent to other blade having the first type of shape around the rotating shaft.

3. The axial flow fan impeller according to claim 1, wherein

the number of blades having the first type of shape of the plurality of blades is two or more, and

the plurality of blades are arranged in a state where the blades having the first type of shape are located at asymmetric positions.

4. The axial flow fan impeller according to claim 1, wherein

each of the plurality of blades comprises a first surface facing a suction port of a gas;

and a second surface facing an exhaust port of the gas, and the first type of shape has a part located at the end portion on the rotating shaft side, at least one of the first surface and the second surface has a portion coupled to the side peripheral portion through a curved surface at the end portion on the rotating shaft side.

5. The axial flow fan impeller according to claim 4, wherein

the curved surface has a recessed shape recessed toward the inside of the blade.

6. The axial flow fan impeller according to claim 4, wherein

the curved surface has a fillet surface shape.

7. A axial flow fan comprising:

an axial flow fan impeller according to claim 1; and

a casing rotatably supporting the axial flow fan impeller around the rotating shaft, wherein

a motor rotating the axial flow fan impeller is attached to the casing.

8. The axial flow fan according to claim 7, wherein

the motor is an motor of outer rotor type, and

a rotor yoke of the motor is attached to the hub portion.

9. An axial flow fan impeller comprising:

a plurality of blades arranged around a rotating shaft; and

a hub portion having a side peripheral portion surrounding the rotating shaft, wherein

an end portion on the rotating shaft side of each of the plurality of blades is coupled to the side peripheral portion,

the plurality of blades includes a blade having a first type of shape and a blade having a second type of shape, and

the shape of the end portion of the first type of shape is different from the shape of the end portion in the rotating shaft direction of the second type of shape on the rotating shaft side.