MULTIBLADE FAN

Abstract

To provide a multiblade fan that enables an improvement in noise characteristics or blowing performance. The multiblade fan includes a scroll type casing that has a bell-mouthed inlet and an impeller housed in the casing. The impeller includes a plurality of blades and a rotation axis m oriented toward the inlet of the casing. The blades are annularly arranged. In the multiblade fan, a center axis of the inlet and the rotation axis of the impeller are arranged at a tilt angle to each other and in any one of an intersecting positional relationship and a skew-lines positional relationship so that a space between the inlet and the impeller increases from the rotation axis of the impeller toward an outlet of the casing.

Description

TECHNICAL FIELD

The present invention relates to a multiblade fan, and more particularly, to a multiblade fan capable of improving noise characteristics or blowing performance.

BACKGROUND ART

A typical multiblade fan includes a scroll type casing having a bell-mouthed inlet and an impeller housed in the casing. The impeller is a multiblade impeller (sirocco fan) that includes a plurality of annularly arranged blades and that is housed in the casing with a rotation axis of the impeller oriented toward the inlet of the casing.

In a structure where a center axis of the inlet and the rotation axis of the impeller are coaxially arranged, an inertial force is exerted on air flown into the impeller through the inlet. Hence, airflow inside the impeller is likely to be deflected toward a main plate (a plate that supports blades). Then, the velocity distribution (velocity distribution of air blowing out of the spaces between the blades) of the air passing through between the blades (space between the blades) becomes nonuniform in the axial direction of the impeller. Because this causes the velocity of flow to be likely to fluctuate, pressure differential of air or a level of air turbulence increases, which can result in louder noise or degradation in blowing performance.

When the multiblade fan is constructed in this manner, air is incident on a blade at an acute (sharp) incident angle when the air flows into the impeller to pass through between the blades. Because this causes the impeller to function insufficiently, it is possible that the multiblade fan provides its blowing performance insufficiently.

In view of the above circumstances, conventional multiblade fans have adopted a configuration in which an inlet is deformed depending on an inflow velocity of air (see Patent Document 1), a configuration in which end portions of blades are tapered (see Patent Document 2), and the like. In the multiblade fans having these configurations, an airflow rate near the end portions of the blades is increased, making velocity distribution of air inside an impeller uniform. This improves performance of the blowers.

Another conventional multiblade fan has adopted a configuration of causing a space between an impeller and a bell-mouthed inlet to vary in a rotation direction (see Patent Document 3). This configuration makes velocity distribution of air inside the impeller uniform, thereby improving performance of the blower. However, these configurations are disadvantageous in that because the shape of a casing is complicated or it is difficult to release the casing from a die, cost of production increases.

The multiblade fan uses a scroll type casing that is expanded by a predetermined degree to recover a static pressure. Accordingly, when a position where air is sucked is changed, velocity of airflow inside the impeller is changed, thereby changing the deflection of the airflow that is deflected toward the main plate. Hence, changing the shape of the blades of the impeller is disadvantageous in being insufficiently effective. This is because the changing the shape of the blades is effective for a target airflow; however, there are produced losses in air flows other than the target airflow. It is also necessary to determine the shape of the blades while taking its influences over an all-around rotation of the impeller into consideration.

PRIOR ART DOCUMENT

Patent Document

• Patent document 1: Japanese Patent Application Laid-open No. 2000-179496
• Patent document 2: Japanese Patent Application Laid-open No. 2006-200525
• Patent document 3: Japanese Patent Application Laid-open No. 1995-228128

DISCLOSURE OF INVENTION

Problem to be Solved by the Invention

It is an object of the present invention to provide a multiblade fan capable of improving noise characteristics or blowing performance.

Means for Solving Problem

To achieve the object, a multiblade fan according to the present invention includes a scroll type casing that includes a bell-mouthed inlet and an impeller that includes a plurality of annularly arranged blades and a rotation axis oriented toward the inlet and that is housed in the casing. A center axis of the inlet and the rotation axis of the impeller are arranged to make a tilt angle and in either one of a mutually intersecting positional relationship and a mutually skewed positional relationship, so that a space between the inlet and the impeller is increased from the rotation axis of the impeller toward an outlet of the casing.

Effect of the Invention

In a multiblade fan according to an aspect of the present invention, a space between an inlet and an impeller increases from a rotation axis of the impeller toward an outlet of a casing. This configuration permits air that has flown into the impeller through the inlet to flow in a gentle curve inside the impeller to pass through between blades. This causes velocity distribution (deflection of airflow) of intake air inside the impeller and an incident angle of the intake air on a blade to relatively change, thereby making the velocity distribution of air having passed through between the blades uniform in the axial direction of the rotation axis of the impeller. Hence, the noise characteristics and the blowing performance are advantageously improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional plan view depicting a multiblade fan according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view taken along line A-A of the multiblade fan depicted in FIG. 1.

FIG. 3 is a schematic explanatory diagram illustrating how the multiblade fan depicted in FIG. 1 works.

FIG. 4 is a schematic explanatory diagram illustrating how the multiblade fan depicted in FIG. 1 works.

FIG. 5 is a graph illustrating noise characteristics for different spaces between an inlet and an impeller.

FIG. 6 is a graph illustrating results of performance tests of multiblade fans.

FIG. 7 is a graph illustrating results of performance tests of multiblade fans.

FIG. 8 is a schematic explanatory diagram of the configuration of the multiblade fan depicted in FIG. 1.

FIG. 9 is a schematic explanatory diagram of a modification of the multiblade fan depicted in FIG. 1.

FIG. 10 is a schematic explanatory diagram of another modification of the multiblade fan depicted in FIG. 1.

FIG. 11 is a schematic configuration diagram of a conventional multiblade fan.

FIG. 12 is a schematic explanatory diagram illustrating how the multiblade fan depicted in FIG. 11 works.

BEST MODES FOR CARRYING OUT THE INVENTION

Exemplary embodiments of the present invention are described in detail below with reference to the accompanying drawings. The present invention is not limited to the exemplary embodiments. Elements of the embodiments include all equivalents that do not depart from the spirit and scope of the invention in its broadest form. The plurality of modifications of the embodiments mentioned below can be arbitrarily combined within the range that will occur to those skilled in the art.

[Multiblade Fan]

A multiblade fan 1 is a blower that includes a multibladed wheel (sirocco fan). The multiblade fan 1 is applied to, for example, an air conditioning system, a duct fan, and a ventilating fan. The multiblade fan 1 can be of a single inlet type or a double inlet type. In the present embodiment, the multiblade fan 1 of a single inlet type will be described as an example.

The multiblade fan 1 includes a casing 2, an impeller 3, and a drive motor 4 (see FIG. 1 and FIG. 2).

The casing 2 is, for example, a scroll type casing. The casing 2 includes a main body 21, an inlet 22, and an outlet 23. The main body 21 assumes a scroll-like shape in plan view. The inlet 22 is a bell-mouthed inlet defined in a side surface (axially upper surface of the scroll-like shape) of the main body 21, at a center of the scroll-like shape. The outlet 23 is defined in a circumferential surface (coiled surface of the scroll-like shape) of the main body 21. The casing 2 is made of, for example, resin and formed by die molding.

The impeller 3 is a multibladed wheel (sirocco fan) that includes a plurality of blades 31 that are annularly arranged. The impeller 3 includes a rotary shaft m that is oriented toward the inlet 22 of the casing 2 and a circumferential surface that is oriented along the circumference of the casing 2. For example, in the present embodiment, the impeller 3 is constructed by annularly arranging the blades 31 along the rim of a substantially disc-shaped main plate 32 at predetermined intervals and fixing the blades 31 to the main plate 32. In this manner, a bladed wheel made of the blades 31 is formed on the main plate 32. An annular member 33 serving as reinforcement is fit in end portions (end portions on the side opposite from the main plate 32) of the blades 31. The impeller 3 is housed in the casing 2 with the end portions of the blades 31 oriented toward the inlet 22 and with a circumferential surface of the bladed wheel oriented along the circumference of the casing 2.

The drive motor 4 is a motor that drives the impeller 3 to rotate. The drive motor 4 is inserted into the casing 2 through the bottom surface of the casing 2 to be coupled to the main plate 32 of the impeller 3. On/off control of the drive motor 4 is performed by using, for example, an external switch.

When the drive motor 4 is driven to rotate the impeller 3, air is sucked into the main body 21 through the inlet 22 of the casing 2. The air passes through the multiblade fan 1 such that air pressure is increased by the impeller 3 and then recovered to a static pressure through the scroll-like shape of the casing 2, and then the air is blown out to the outside through the outlet 23 of the casing 2. Air is blown by the multiblade fan 1 in this manner.

[Positional Relationship Between Inlet and Impeller]

Generally, (1) in a configuration where a center axis l of an inlet and a rotation axis m of an impeller are coaxially arranged, an inertial force is exerted on air that have flown into the impeller through the inlet (see FIG. 11). This makes airflow inside the impeller to be deflected toward a main plate. When the airflow is deflected in this manner, velocity distribution (velocity distribution of air blowing out of spaces between the blades) of air that passes through between blades (the spaces between blades) of the impeller becomes nonuniform in the axial direction of the impeller. Because this makes the airflow velocity to be likely to fluctuate, pressure differential of air or a level of air turbulence increases, which can result in louder noise, blowing performance degradation, or the like. This configuration also causes (2) air to be incident on a blade at an acute (sharp) incident angle δ when the air flows into the impeller to pass through between blades (see FIG. 12). Because this causes the impeller to function insufficiently, it is possible that the multiblade fan fails to provide its blowing performance sufficiently.

To this end, in the multiblade fan 1, the center axis l of the inlet 22 of the casing 2 and the rotation axis m of the impeller 3 are arranged in (a) an intersecting positional relationship where they intersect with each other at a tilt angle φ or in (b) a skew-lines positional relationship where they are skewed relative to each other (see FIG. 2). In other words, the positional relationship between the inlet 22 and the impeller 3 are set such that the center axis l of the inlet 22 and the rotation axis m of the impeller 3 are not coaxial with each other (not on a single axis). Meanwhile, the center axis l of the inlet 22 is a center axis of the bell-mouthed inlet of the inlet 22.

A space L between the inlet 22 and the blades 31 of the impeller 3 increases toward the outlet 23 of the casing 2 due to the positional relationship between the inlet 22 and the impeller 3 (see FIG. 1 and FIG. 2). For example, in the present embodiment, the space L between an opening surface of the inlet 22 and an end (an end of one of the blades 31 near the inlet 22) of the one of the blades 31 of the impeller 3 increases from the rotation axis m of the impeller 3 toward the outlet 23 of the casing 2. The space L can be arbitrarily set according to specifications for the multiblade fan 1 or the like.

When the multiblade fan 1 is configured in this manner, because the space L between the inlet 22 and the impeller 3 increases from the rotation axis m of the impeller 3 toward the outlet 23 of the casing 2, air that has flown into the impeller 3 through the inlet 22 is allowed to flow in a gentle curve inside the impeller 3 (see FIG. 3). When air flows in this manner, an airflow rate around the blades 31 near the inlet 22 increases. Accordingly, velocity distribution of air that passes through between the blades 31, 31 is more uniform in the axial direction of the impeller 3 as compared with that of the configuration in which airflow is deflected toward the main plate (see FIG. 11). This results in an improvement in noise characteristics and blowing performance.

This configuration also causes air to flow into the blades 31 at a less acute incident angle δ inside the impeller 3 (see FIG. 4). Accordingly, the velocity distribution of air that passes through between the blades 31, 31 is more uniform as compared with that of the configuration in which air flows into the blades at the acute (sharp) angle δ (see FIG. 12). Hence, the impeller 3 can provide its function sufficiently, thereby improving blowing performance of the multiblade fan 1.

In the casing 2 that has the scroll-like shape, an opening area of an air passage in the main body 21 is maximized near the outlet 23 (see FIG. 1). This causes air near the outlet 23 to flow at a relatively high airflow rate, thereby increasing an airflow rate of air that passes through between the blades 31 of the impeller 3, which increases the magnitude of the inertia force. As a result, the velocity distribution of the air that passes through between the blades 31, 31 is further deflected toward the main plate. Hence, by increasing the space L between the inlet 22 and the impeller 3 at this position toward the outlet 23 (see FIG. 2), the velocity distribution of intake air inside the impeller 3 and the incident angle δ on one of the blades 31 are changed by a large extent. This makes the velocity distribution, which can otherwise be largely deflected toward the main plate, of the air passing through between the blades 31, 31 effectively uniform. Accordingly, noise characteristics are efficiently improved.

Meanwhile, it is preferable to set the position where the space L between the inlet 22 and the impeller 3 is maximized as required based on the scroll-like shape of the casing 2 or the like. For example, an arc angle θ [°]that indicates a rotation angle of the impeller 3 about the rotation axis m of the impeller 3 relative to a reference direction, which is parallel to the axial direction of the outlet 23 of the casing 2 in plan view of the impeller 3, can be defined (see FIG. 1). The arc angle θ can be set so that favorable noise characteristics are obtained with the configuration depicted in FIG. 2 (the configuration in which the center axis l of the inlet 22 of the casing 2 and the rotation axis m of the impeller 3 are arranged at the tilt angle φ to each other and in any one of the intersecting positional relationship and the skew-lines positional relationship).

FIG. 5 depicts a relationship between the arc angle θ and the noise characteristics. In the drawing, the noise characteristics are given as a difference in noise level relative to a reference noise level (0 [dB]), which is a noise level of the conventional example. Meanwhile, the conventional example has the configuration in which the center axis l of the inlet and the rotation axis m of the impeller are coaxially arranged (φ=0) (see FIG. 11). As depicted in the drawing, the noise characteristics are improved most where θ=270 [°], in which θ is the arc angle. This position corresponds to the position near the outlet 23 of the casing 2. Accordingly, it is revealed that by setting the space L between the inlet 22 and the impeller 3 to be maximized near the outlet 23 of the casing 2, the noise characteristics of the multiblade fan 1 are efficiently improved.

[Performance Test]

FIG. 6 and FIG. 7 are graphs illustrating results of performance tests of the multiblade fans. Performance tests for (1) blowing performance (performance measured by static pressure) and (2) noise characteristics have been performed on the present embodiment.

The multiblade fan of the conventional example subjected to the performance tests has the configuration in which the center axis l of the inlet and the rotation axis m of the impeller are coaxially arranged (φ=0) (see FIG. 11). The multiblade fan 1 of the present embodiment has the configuration in which the center axis l of the inlet 22 of the casing 2 and the rotation axis m of the impeller 3 are arranged at the tilt angle φ to each other and in any one the intersecting positional relationship and the skew-lines positional relationship as well as in which the space L between the inlet 22 and the impeller 3 is maximized near the outlet 23 of the casing 2 (θ=270 [°]) (see FIG. 1 and FIG. 2).

As illustrated in the results of the tests, the multiblade fan 1 of the present embodiment is improved in blowing performance and noise characteristics as compared with the multiblade fan of the conventional example. For example, the multiblade fan 1 of the present embodiment is increased in static pressure by approximately 10 [Pa] and decreased in noise level by approximately 1 [dB] under the same airflow rate.

[Effect]

As described above, this multiblade fan 1 is constructed such that (1) the space L between the inlet 22 and the impeller 3 increases from the rotation axis m of the impeller 3 toward the outlet 23 of the casing 2 (see FIG. 1 and FIG. 2). This configuration permits air that has flown into the impeller 3 through the inlet 22 to flow in a gentle curve inside the impeller 3 to pass through between the blades 31, 31 (see FIG. 3). When air flows in this manner, the velocity distribution (deflection of airflow) of intake air inside the impeller 3 and the incident angle δ of the intake air on one of the blades 31 are relatively changed, thereby making the velocity distribution of air having passed through between the blades 31, 31 uniform in the axial direction of the rotation axis of the impeller 3. This advantageously improves the noise characteristics and the blowing performance of the multiblade fan 1.

Particularly near the outlet 23, because an airflow rate of air that passes through between the blades 31, 31 of the impeller 3 increases, the magnitude of the inertia force increases, which causes the velocity distribution of the air that passes through between the blades 31, 31 to be more deflected toward the main plate. Accordingly, by setting the space L between the inlet 22 and the impeller 3 at this position large, the velocity distribution of intake air inside the impeller 3 and the incident angle δ of the intake air on the one of the blades 31 are changed by a large extent. As a result, the velocity distribution, which can otherwise be largely deflected toward the main plate, of the air passing through between the blades 31, 31 is effectively made uniform. This advantageously improves the noise characteristic effectively.

The space L between the inlet 22 and the impeller 3 is adjusted because (2) the center axis l of the inlet 22 and the rotation axis m of the impeller 3 are arranged at the tilt angle φ to each other and in any one of the intersecting positional relationship and the skew-lines positional relationship. Put another way, the space L is adjusted by adjusting the positional relationship between the center axis l of the inlet 22 and the rotation axis m of the impeller 3. This space L causes the velocity distribution of intake air inside the impeller 3 and the incident angle δ on one of the blades 31 to be relatively changed, making the velocity distribution of air passing through between the blades 31, 31 uniform. Hence, there is obtained an advantage that the velocity distribution of air passing through between the blades 31, 31 can be made more uniform with a simple configuration as compared with that of a configuration in which dimensions and/or shapes of the impeller and the bell-mouthed inlet are complicatedly changed.

[Modifications]

The multiblade fan 1 can employ any one of the following configurations (see FIG. 8 to FIG. 10) to adjust the positional relationship between the center axis l of the inlet 22 and the rotation axis m of the impeller 3 (they are arranged at the tilt angle φ to each other and in any one of the intersecting positional relationship and the positional relationship).

FIG. 8 depicts a configuration in which both the center axis l of the inlet 22 and the rotation axis m of the impeller 3 are tilted relative to the main body 21, thereby adjusting the positional relationship (tilt angle φ) between the center axis l of the inlet 22 and the rotation axis m of the impeller 3. This configuration is advantageous in that the tilt angle φ can be attained more easily in terms of design as compared with a configuration in which only any one of the center axis l of the inlet 22 and the rotation axis m of the impeller 3 are tilted relative to the main body 21.

For example, in the present embodiment, a mating portion of an outer periphery of the bell-mouthed inlet of the inlet 22 and a wall surface of the main body 21 includes a stepped portion so that the bell-mouthed inlet of the inlet 22 is tilted relative to the wall surface of the main body 21 (see FIG. 2). The drive motor 4 is attached to the main body 21 such that the rotation axis of the drive motor 4 is tilted relative to the wall surface of the main body 21. The impeller 3 is attached to the drive motor 4. Hence, both the center axis l of the inlet 22 and the rotation axis m of the impeller 3 are tilted relative to the main body 21.

However, the configuration is not limited thereto. Alternatively, the positional relationship between the center axis l of the inlet 22 and the rotation axis m of the impeller 3 can be adjusted by arranging only any one of the center axis l of the inlet 22 and the rotation axis m of the impeller 3 to be tilted relative to the main body 21 (see FIG. 9 and FIG. 10).

For example, FIG. 9 depicts a configuration in which only the center axis l of the inlet 22 is tilted relative to the main body 21. In this configuration, a component that is formed by simple die molding can be used to form the inlet 22 of the main body 21. Accordingly, this configuration is advantageous in that the positional relationship between the center axis l of the inlet 22 and the rotation axis m of the impeller 3 can be adjusted in a simple and less expensive manner.

FIG. 10 depicts another exemplary configuration in which only the rotation axis m of the impeller 3 (the rotation axis of the drive motor 4) is tilted relative to the main body 21. This configuration is advantageous in that the positional relationship between the center axis l of the inlet 22 and the rotation axis m of the impeller 3 can be adjusted in a simple and less expensive manner without changing an outer dimension of the main body 21.

INDUSTRIAL APPLICABILITY

As set forth hereinbefore, a multiblade fan according to the present invention is useful in enabling an improvement in noise characteristics or blowing performance.

EXPLANATIONS OF LETTERS OR NUMERALS

1 multiblade fan, 2 casing, 21 main body, 22 inlet, 23 outlet, 3 impeller, 31 blade, 32 main plate, 33 annular member, 4 drive motor

Claims

1. A multiblade fan comprising:

a scroll type casing that includes a bell-mouthed inlet; and

an impeller that includes a plurality of annularly arranged blades and a rotation axis oriented toward the inlet and that is housed in the casing, wherein

a center axis of the inlet and the rotation axis of the impeller are arranged to make a tilt angle and in either one of a mutually intersecting positional relationship and a mutually skewed positional relationship, so that a space between the inlet and the impeller is increased from the rotation axis of the impeller toward an outlet of the casing.

2. The multiblade fan according to claim 1, wherein a positional relationship between the center axis of the inlet and the rotation axis of the impeller is adjusted by arranging the center axis of the inlet to be tilted relative to a main body of the casing.

3. The multiblade fan according to claim 1, wherein a positional relationship between the center axis of the inlet and the rotation axis of the impeller is adjusted by arranging the rotation axis of the impeller to be tilted relative to a main body of the casing.