Axial flow fan

Abstract

To provide an axial flow blower capable of improving ventilation efficiency.SOLUTION: An axial flow blower 9 comprises, inside the cylindrical casing 1, an electric motor 2, an axial flow fan 6 that is composed of a plurality of blades 4 attached to a rotational shaft P1 of the electric motor 2 and a hub part 5 and can rotate in both forward and reverse directions, a hub cone part 7 that rectifies an air flow from the axial flow fan 6, and a stay part 8 that is fixed to the casing 1 and supports the hub cone part 7. The stay part 8 includes an upstream stay part 8a located on the axial flow fan 6 side, and a downstream stay part 8b located on the downstream side of the upstream stay part 8a along the rotational axis P1. In a cylindrical cross section of the stay part 8, the downstream stay part 8b is arranged offset from the upstream stay part 8a along a rotational direction of the rotational axis P1 so that an angle formed between a straight line connecting the upstream stay part 8a and the downstream stay part 8b and the rotational axis P1 is an absolute outflow angle of air having passed through the axial flow fan.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an axial flow fan for tunnel ventilation equipment, which has forward and reverse operation and is used in tunnels to expel harmful substances such as soot, carbon monoxide, and nitrogen oxides emitted by automobiles and to supply fresh air. [Background technology]

[0002] Conventionally, this type of axial flow fan has been installed on the ceiling mainly for ventilation of automobile tunnels, and the one described in Patent Document 1 is known for flowing a large volume of air.

[0003] FIG. 4 is a diagram showing the structure of a conventional axial flow fan 109.

[0004] As shown in Figure 4, axial flow blower 109 is equipped with: an electric motor 102 inside a cylindrical casing 101; a motor stay portion 103 that supports electric motor 102; an axial flow fan 106 that is rotatable in both forward and reverse directions A and B and is composed of a plurality of blades 104 and a hub portion 105 that are attached to a rotation axis P3 of electric motor 102; a hub cone portion 107 that rectifies the flow of air from axial flow fan 106; and stay portions 108 (upstream stay portion 108a and downstream stay portion 108b) that are fixed to casing 101 and support hub cone portion 107. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-265825 Summary of the Invention [Problem to be solved by the invention]

[0006] In such a conventional axial flow fan 109, stay portions 108 for supporting the hub-cone portion 107 are arranged in multiple rows (two rows: upstream stay portion 108a and downstream stay portion 108b). Therefore, the multiple rows of stay portions 108 are arranged overlapping with each other in the direction of the rotation axis P3, and the collision of the swirling flow with the stay portions 108 causes similar separation across the multiple rows. This poses a problem of increased pressure loss due to flow separation at the stay portions 108, resulting in reduced blowing efficiency. The blowing efficiency indicates how much of the motor's output power (axial power) is converted into work (air volume and static pressure). Increased pressure loss results in wasted energy consumption, reducing blowing efficiency.

[0007] SUMMARY OF THE INVENTION The present invention is intended to solve the above-mentioned problems of the prior art, and has an object to provide an axial flow fan capable of improving the air blowing efficiency. [Means for solving the problem]

[0008] To achieve this object, the axial flow blower of the present invention includes, inside a cylindrical casing, an electric motor, an axial flow fan that is rotatable in both forward and reverse directions and that is composed of a hub and multiple blades attached to the rotating shaft of the electric motor, a hub cone portion that rectifies the flow of air from the axial flow fan, and a stay portion that is fixed to the casing and supports the hub cone portion. The stay portion includes, on the downstream side of the axial flow fan, an upstream stay portion located on the axial flow fan side, and a downstream stay portion located downstream of the upstream stay portion along the rotational axis, and the downstream stay portion is disposed offset relative to the upstream stay portion along the rotational direction of the rotational axis so that, in a cylindrical cross section of the stay portion parallel to the rotational axis, the angle between the rotational axis and a line connecting the upstream stay portion and the downstream stay portion is the absolute outflow angle of air that has passed through the axial flow fan. This achieves the desired object. [Effects of the Invention]

[0009] According to the present invention, an axial flow fan capable of improving the air blowing efficiency can be obtained. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram for explaining an axial flow fan according to a first embodiment of the present invention. [Figure 2] FIG. 2(a) is a vertical cross-sectional view of the axial flow fan, and FIG. 2(b) is a cylindrical cross-sectional view parallel to the rotation axis of the stay portion for explaining the airflow to the stay portion. [Figure 3] FIG. 3(a) is a vertical cross-sectional view of an axial flow fan according to a comparative example, and FIG. 3(b) is a cylindrical cross-sectional view parallel to the rotation axis of the stay portion for explaining the airflow to the stay portion. [Figure 4] FIG. 4 is a schematic diagram for explaining a conventional axial flow fan. DETAILED DESCRIPTION OF THE INVENTION

[0011] The axial flow fan according to the present invention comprises, inside a cylindrical casing, an electric motor, an axial flow fan that is rotatable in both forward and reverse directions and that is composed of a hub and a plurality of blades attached to the rotary shaft of the electric motor, a hub cone portion that rectifies the flow of air from the axial flow fan, and a stay portion that is fixed to the casing and supports the hub cone portion. The stay portion includes an upstream stay portion located on the axial fan side on the downstream side of the axial flow fan, and a downstream stay portion located downstream of the upstream stay portion along the rotary shaft, and the downstream stay portion is disposed offset relative to the upstream stay portion along the rotary shaft so that, in a cylindrical cross section of the stay portion parallel to the rotary shaft, the angle formed between the rotary shaft and a line connecting the upstream stay portion and the downstream stay portion is the absolute outflow angle of air that has passed through the axial flow fan.

[0012] With this configuration, the swirling air from the axial fan that collides with the upstream stay section is decelerated by the collision before colliding with the downstream stay section. This reduces pressure loss due to the collision compared to when the swirling air directly collides with the downstream stay section. As a result, the air-blowing efficiency of the axial fan is improved. Therefore, the air-blowing efficiency of the axial fan can be improved compared to when multiple rows of stay sections are installed in the same straight line in the rotational axis direction.

[0013] In the axial flow fan according to the present invention, the stay portions are arranged so that the angle formed between the rotation axis and a line connecting a first midpoint between the upstream end and downstream end of the upstream stay portion and a second midpoint between the upstream end and downstream end of the downstream stay portion is the absolute outflow angle. This arrangement allows the swirling flow impinging on the upstream stay portion to be decelerated by the collision, and most of the decelerated flow impinges on the downstream stay portion. This reduces pressure loss due to the collision compared to when the swirling flow directly impinges on the downstream stay portion. As a result, the blowing efficiency of the axial flow fan is improved. Therefore, the blowing efficiency of the axial flow fan can be improved compared to when multiple rows of stay portions are arranged on the same straight line in the direction of the rotation axis.

[0014] Furthermore, in the axial flow fan according to the present invention, the stay portions are arranged with a predetermined gap between the upstream stay portion and the downstream stay portion in a cylindrical cross section parallel to the rotation axis of the stay portions. This ensures the strength to support the hub cone portion 7, thereby suppressing fluctuations in the position of the stay portions due to airflow and achieving a stay portion arrangement with high airflow efficiency.

[0015] Furthermore, in the axial flow fan according to the present invention, the stay portions may be arranged such that, in a cross section perpendicular to the rotating shaft, a line connecting the casing-side end of the upstream stay portion to the hub-cone-side end and a line connecting the casing-side end of the downstream stay portion to the hub-cone-side end are parallel to each other. This allows the stay portions to maintain the same positional relationship with respect to the incoming swirling flow from the hub-cone-side end to the casing-side end. As a result, when the stay portions are aligned with the absolute outflow angle of the incoming swirling flow with a high flow velocity, much of the flow, including the swirling flow in the vicinity, is decelerated by impinging on the upstream stay portion, and the decelerated flow impinges on the downstream stay portion. This reduces pressure loss due to impingement compared to when the swirling flow directly impinges on the downstream stay portion. As a result, the blowing efficiency of the axial flow fan can be improved compared to when multiple rows of stay portions are arranged in the same straight line in the rotating shaft direction.

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0017] (Embodiment 1) First, an outline of an axial flow fan 9 according to a first embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is a schematic diagram for explaining an axial flow fan 9 according to a first embodiment of the present invention.

[0018] An axial flow fan 9 is a ventilation device installed in automobile tunnels to expel harmful substances such as soot, carbon monoxide, and nitrogen oxides emitted by automobiles and to send fresh air into the tunnel. As shown in Figure 1, the axial flow fan 9 is equipped with an axial flow fan 6 that can rotate in both directions, forward and reverse, to blow air in both direction A, which is the forward direction, and direction B, which is the opposite direction to direction A. For example, if direction A is the forward direction (forward direction), direction B is the reverse direction. This allows the blowing direction to be switched according to changes in the traffic volume of automobiles passing through the tunnel, the direction of natural wind, or a fire that breaks out inside the tunnel.

[0019] Specifically, as shown in Figure 1, the axial flow fan 9 is configured with a casing 1, an electric motor 2, a motor stay section 3 that supports the electric motor 2, an axial flow fan 6 consisting of a plurality of blades 4 and a hub section 5, a hub cone section 7 that straightens the airflow, and a stay section 8 that supports the hub cone section. The axial flow fan 6 rotates about a rotation axis P1. The following description assumes a situation in which the axial flow fan 9 blows air in direction A, focusing on the components located downstream of the electric motor 2. Note that a situation in which the axial flow fan 9 blows air in direction B has the same corresponding relationship as the situation in direction A, so a description thereof will be omitted.

[0020] The casing 1 has openings at both ends that are cylindrical or rectangular. The casing 1 is installed, for example, by hanging it from the ceiling of a tunnel using mounting brackets. The casing 1 also has an internal sound-absorbing section made of sound-absorbing material, a perforated plate, etc. The central axis of the casing 1 is coaxial with the rotation axis P1 of the axial flow fan 6.

[0021] The electric motor 2 is installed on the inner surface of the casing 1 via a motor stay 3. The electric motor 2 has the function of rotating the axial fan 6 and reversing the direction of rotation. For example, the electric motor 2 may rotate the rotation axis P1 clockwise or counterclockwise. The axial fan 6 is connected to the electric motor 2 downstream in the direction of the rotation axis P1 via the rotation axis P1.

[0022] The motor stay portion 3 supports the electric motor 2 by placing it on its upper surface, and is attached to the lower part of the casing 1.

[0023] The axial fan 6 is composed of multiple blades 4 and a hub 5, and the cylindrical cross section of the blades 4 is formed to have an airfoil shape or a bilaterally symmetrical shape. The axial fan 6 is connected adjacent to the electric motor 2, downstream of the electric motor 2 in the direction of the rotation axis P1, via the rotation axis P1. Here, the axial fans 6 are connected to both the downstream and upstream sides of the electric motor 2. In other words, since two axial fans 6 are installed point-symmetrically around the center of the electric motor 2, airflow can be generated with the same volume even when the airflow direction is reversed. Note that the axial fans 6 may be installed on only one of the discharge side or suction side of the electric motor 2.

[0024] Six blades 4 are attached to the hub portion 5, and the cross section of the blades 4 is an axisymmetric airfoil shape. The number of blades 4 may be three to five, and the cross section of the blades 4 may be an asymmetric airfoil shape.

[0025] The hub portion 5 is cylindrical in shape and has a plurality of blades 4 attached at equal intervals in the circumferential direction. The hub portion 5 is connected to the electric motor 2 at a position adjacent to the electric motor 2, downstream in the direction of the rotation axis P1, via the rotation axis P1.

[0026] The hub cone portion 7 is located downstream of the axial fan 6 and is supported by the stay portion 8. The hub cone portion 7 has a shape that combines a cylindrical portion and a hemispherical portion. More specifically, the hub cone portion 7 is configured by combining a cylindrical portion that is attached to the downstream side of the direction of the rotation axis P1 of the electric motor 2 at a position adjacent to the axial fan 6, and a hemispherical portion that is located downstream of the cylindrical portion. The hub cone portion 7 also has an internal sound-absorbing portion that is made of sound-absorbing material, a perforated plate, etc. The hub cone portion 7 may have an approximately conical shape either entirely or in its cylindrical portion.

[0027] The stay portion 8 is a member that fixes the hub cone portion 7 to the casing 1. The stay portion 8 includes two rows of upstream stay portions 8a located downstream of the axial fan 6: upstream stay portions 8a located on the axial fan 6 side; and downstream stay portions 8b located downstream of the upstream stay portions 8a along the rotation axis P1. The four upstream stay portions 8a and four downstream stay portions 8b that make up the stay portion 8 extend circumferentially from the hub cone portion 7 at equal intervals in a vertical cross section normal to the rotation axis P1, and are fixed to the inner surface of the casing 1. The stay portion 8 is installed so that the distance between the upstream stay portions 8a and the downstream stay portions 8b (the distance in the direction of the rotation axis P1 when the axial flow fan 9 is viewed from the side) is 0.5 to 1.0 times the length of the hub cone portion 7 in the direction of the rotation axis P1. Stay portion 8 is arranged so that, in a vertical cross section normal to rotation axis P1, a line connecting the casing 1 side end of upstream stay portion 8a and the hub cone portion 7 side end and a line connecting the casing 1 side end of downstream stay portion 8b and the hub cone portion 7 side end are parallel to each other (see FIG. 2). The detailed arrangement (relationship) of upstream stay portion 8a and downstream stay portion 8b of stay portion 8 will be explained in detail in the flow phenomenon section below.

[0028] In the axial flow blower 9 configured in this way, when the electric motor 2 is driven, the axial flow fan 6 rotates in either direction A (forward direction) or direction B (reverse direction). As the axial flow fan 6 rotates, air is drawn in through an opening in the casing 1 and expelled from an opening on the opposite side. This allows harmful substances such as soot, carbon monoxide, and nitrogen oxides from automobiles that fill the tunnel to be expelled, and fresh air to be blown in. It also allows harmful gases or smoke resulting from fires and other emergencies to be expelled from the tunnel.

[0029] Next, with reference to Figure 2, we will explain how pressure loss caused when a swirling flow collides with the stay portion 8 in the axial flow fan 9 is reduced. Figure 2(a) is a vertical cross-sectional view of the axial flow fan 9, and Figure 2(b) is a cylindrical cross-sectional view parallel to the rotation axis P1 of the stay portion 8 for explaining the airflow to the stay portion 8. Note that the cylindrical cross section Q1 in Figure 2(a) is a cross section along the side of the cylinder parallel to the rotation axis P1, that is, the side of the cylinder with the rotation axis P1 as its central axis, and shows a cross section at a position on the casing 1 side where the flow velocity is generally high.

[0030] Figure 2(b) is a conceptual diagram of the vectors of airflow generated from the blades 4 as the axial fan 6 rotates in the cylindrical cross section Q1 shown in Figure 2(a) in the airflow direction A. For convenience, Figure 2(b) shows only one of the multiple blades 4 that make up the axial fan 6.

[0031] As shown in Figure 2(b), the absolute outlet velocity c1 of the airflow exiting the blades 4 of the axial fan 6 is the resultant velocity of the circumferential velocity u1 of the blades 4 and the relative velocity w1 of the airflow as seen from the blades 4. The angle between the direction of the flow with absolute outlet velocity c1 and the rotation axis P1 represents the absolute outlet angle r1. Here, the circumferential velocity u1 represents the circumferential velocity at the cylindrical cross section Q1 of the axial fan 6. The relative velocity w1 represents the outlet velocity from the blades 4 as seen from the rotating blades 4. The two rows of stay members 8 (upstream stay member 8a and downstream stay member 8b) that secure the hub cone member 7 are arranged so that the angle between the line connecting the upstream stay member 8a, located on the blade 4 side of the axial fan 6, and the downstream stay member 8b, located downstream of the upstream stay member 8a, and the rotation axis P1 is equal to the absolute outlet angle r1. In other words, the upstream stay member 8a and the downstream stay member 8b are arranged on the same straight line in the direction of the flow with absolute outlet velocity c1. More specifically, the straight line connecting the upstream stay portion 8a and the downstream stay portion 8b is, for example, a straight line passing through a first midpoint M1 between the upstream end portion 8a1 and the downstream end portion 8a2 of the upstream stay portion 8a and a second midpoint M2 between the upstream end portion 8b1 and the downstream end portion 8b2 of the downstream stay portion 8b.

[0032] Here, the upstream end 8a1 of the upstream stay portion 8a is the upstream side surface of the upstream stay portion 8a, and the downstream end 8a2 is the downstream side surface of the upstream stay portion 8a. The upstream end 8b1 of the downstream stay portion 8b is the upstream side surface of the downstream stay portion 8b, and the downstream end 8b2 is the downstream side surface of the downstream stay portion 8b. If the cylindrical cross section of the stay portion 8 is rectangular, the midpoint is the center point of the rectangle.

[0033] The flow with absolute exit velocity c1 exiting the blade 4 collides with the upstream stay portion 8a located on the blade 4 side, causing separation, and exits behind the upstream stay portion 8a with a wake velocity d1 that is smaller than the absolute exit velocity c1. The wake velocity d1 indicates the velocity of the flow that separates from the flow with absolute exit velocity c1 exiting the blade 4 toward the downstream stay portion 8b in the direction of the flow with absolute exit velocity c1 exiting the blade 4. The flow with the exiting wake velocity d1 collides with the downstream stay portion 8b and separates. This reduces pressure loss compared to when the flow exits the blade 4 and separates by directly colliding with the downstream stay portion 8b without colliding with the upstream stay portion 8a (a comparative example described later). The positional relationship between the upstream stay portion 8a and the downstream stay portion 8b in the cylindrical cross section Q1, where the flow velocity is high, remains unchanged from the hub-cone portion 7 to the casing 1, and the pressure loss is more effectively reduced on the casing 1 side where the flow velocity is high. Furthermore, since a flow with a high flow velocity causes a larger pressure loss due to collision than a flow with a low flow velocity, the configuration of the first embodiment can achieve a greater effect of reducing pressure loss.

[0034] As a comparative example, a case where air flows out from the blades 4 of the axial fan 6 and directly collides with the downstream stay portion 8b without colliding with the upstream stay portion 8a, and is then separated will be described with reference to FIG. 3. FIG. 3 is a conceptual diagram for explaining the flow of air in an axial flow fan 29 according to the comparative example. Specifically, FIG. 3(a) is a vertical cross-sectional view of the axial flow fan 29 according to the comparative example, and FIG. 3(b) is a cylindrical cross-sectional view of the stay portion 28, for explaining the flow of air to the stay portion 28. Note that the cylindrical cross section Q2 in FIG. 3(a) is a cross section along the side surface of a cylinder parallel to the rotation axis P2, i.e., along the side surface of a cylinder with the rotation axis P2 as its central axis, and shows a cross section at a position on the casing 21 side where the air velocity is generally high.

[0035] Figure 3(b) is a conceptual diagram of the vectors of the airflow generated from the blades 24 in the cylindrical cross section Q2 shown in Figure 3(a) as the axial fan 26 rotates in the airflow direction A. For convenience, Figure 3(b) shows only one of the multiple blades 24 that make up the axial fan 26.

[0036] As shown in FIG. 3, the axial flow fan 29 according to the comparative example differs from that shown in FIG. 2 in that the straight line connecting the two rows of upstream stay portions 28a and downstream stay portions 28b that make up the stay portion 28 is positioned on the rotation axis P2, but the other configurations are similar to those of the axial flow fan 9 shown in FIGS. 1 and 2.

[0037] In the axial flow blower 29 according to the comparative example, as shown in FIG. 3(a), the axial flow fan 26 is configured to have a plurality of blades 24 and a hub portion 25, and a stay portion 28 is provided on the outer periphery of the hub cone portion 27, which supports and fixes the hub cone portion 27 to the casing 21.

[0038] In the axial flow fan 29, as shown in Fig. 3(b), the first midpoint M3 of the upstream stay portion 28a and the second midpoint M4 of the downstream stay portion 28b are located on a line passing through the rotation axis P2 in a vertical cross section normal to the rotation axis P2, and as shown in Fig. 3(a), they extend in the same direction and are fixed to the casing 21, so they overlap when viewed from the direction of the rotation axis P2. Note that when the cylindrical cross section of the stay portion 28 is rectangular, the first midpoint M3 is the midpoint of a line connecting the upstream end 28a1 and the downstream end 28a2 of the upstream stay portion 28a, and the second midpoint M4 is the midpoint of a line connecting the upstream end 28b1 and the downstream end 28b2 of the downstream stay portion 28b.

[0039] As shown in FIG. 3(b), the absolute outflow velocity c2 of the airflow exiting the blades 24 of the axial fan 26 is the resultant velocity of the circumferential velocity u2 of the blades 24 and the relative velocity w2 of the airflow as seen from the blades 24, and the angle between the direction of the flow having the absolute outflow velocity c2 and the rotation axis P2 indicates the absolute outflow angle r2. Here, the circumferential velocity u2 indicates the circumferential velocity at the cylindrical cross section Q2 of the axial fan 26. The relative velocity w2 indicates the outflow velocity from the blades 24 as seen from the rotating blades 24. The absolute outflow velocity c2 exiting the blades 24 is similar in magnitude to the absolute outflow velocity c1 exiting the blades 4 shown in FIG. 2.

[0040] A flow having an absolute outflow velocity c2 that flows out from blades 24 of axial fan 26 collides with and separates from upstream stay portion 28a and downstream stay portion 28b, and flows out from each stay portion 28 at a wake velocity d2. At this time, the flow that collides with downstream stay portion 28b has absolute outflow velocity c2 that flows out from blade 24 without colliding with upstream stay portion 28a, and therefore experiences a greater pressure loss than when a flow that collides with upstream stay portion 28a and has a wake velocity d2 that is slower than the absolute outflow velocity c2 collides with downstream stay portion 28b. In other words, axial flow blower 29 according to the comparative example has a problem in that pressure loss increases due to flow separation at stay portion 28, resulting in reduced blowing efficiency.

[0041] For this reason, in this embodiment, the stay portion 8 constituting the axial flow fan 9 is arranged such that the downstream stay portion 8b is shifted relative to the upstream stay portion 8a along the rotation direction of the rotation axis P1 so that the angle formed between the rotation axis P1 and a line connecting the first midpoint M1 of the upstream stay portion 8a and the second midpoint M2 of the downstream stay portion 8b is the absolute outflow angle r1.

[0042] The straight line connecting the upstream stay portion 8a and the downstream stay portion 8b is not limited to a straight line connecting the first midpoint M1 of the upstream stay portion 8a and the second midpoint M2 of the downstream stay portion 8b, but may be a straight line connecting the upstream end portion 8a1 of the upstream stay portion 8a and the downstream end portion 8b2 of the downstream stay portion 8b, or may be a straight line connecting the downstream end portion 8a2 of the upstream stay portion 8a and the upstream end portion 8b1 of the downstream stay portion 8b. In other words, the downstream stay portion 8b may be shifted relative to the upstream stay portion 8a along the rotational direction of the rotation axis P1 so that the absolute outflow angle r1 is a first angle (minimum angle) formed between the rotation axis P1 and a straight line connecting the upstream end portion 8a1 of the upstream stay portion 8a and the downstream end portion 8b2 of the downstream stay portion 8b, or a second angle (maximum angle) formed between the rotation axis P1 and a straight line connecting the downstream end portion 8a2 of the upstream stay portion 8a and the upstream end portion 8b1 of the downstream stay portion 8b.

[0043] As described above, the axial flow fan 9 according to the first embodiment can provide the following effects.

[0044] (1) An axial flow blower 9 includes, inside a cylindrical casing 1, an electric motor 2, an axial flow fan 6 that is rotatable in both forward and reverse directions and is composed of a hub portion 5 and a plurality of blades 4 attached to a rotation axis P1 of the electric motor 2, a hub cone portion 7 that rectifies the flow of air from the axial flow fan 6, and a stay portion 8 that is fixed to the casing 1 and supports the hub cone portion 7. The stay portion 8 includes, on the downstream side of the axial flow fan 6, an upstream stay portion 8a located on the axial flow fan 6 side and a downstream stay portion 8b located downstream of the upstream stay portion along the rotation axis P1, and the downstream stay portion 8b is disposed offset from the upstream stay portion 8a along the rotation direction of the rotation axis P1 so that, in a cylindrical cross section of the stay portion 8 parallel to the rotation axis P1, the angle formed between the rotation axis P1 and a straight line connecting the upstream stay portion 8a and the downstream stay portion 8b is equal to the absolute outflow angle r1 of the air that has passed through the axial flow fan 6.

[0045] With this configuration, the swirling air from the axial fan 6 that collides with the upstream stay portion 8a is decelerated by the collision before colliding with the downstream stay portion 28b. This reduces pressure loss due to the collision compared to when the swirling air directly collides with the downstream stay portion 8b. As a result, the air-blowing efficiency of the axial flow fan 9 is improved. Therefore, the air-blowing efficiency of the axial flow fan 9 can be improved compared to when multiple rows of stay portions 28 are installed on the same straight line in the direction of the rotation axis P2.

[0046] (2) In the axial flow fan 9, the stay portions 8 are arranged so that the angle between the rotation axis P1 and a line connecting a first midpoint M1 between the upstream end 8a1 and the downstream end 8a2 of the upstream stay portion 8a and a second midpoint M2 between the upstream end 8b1 and the downstream end 8b2 of the downstream stay portion 8b is an absolute outflow angle r1. This arrangement reduces the speed of the swirling flow that strikes the upstream stay portion 8a, and most of the decelerated flow strikes the downstream stay portion 8b. This reduces pressure loss due to the impact compared to when the swirling flow directly strikes the downstream stay portion 28b. This improves the blowing efficiency of the axial flow fan 9. Therefore, the blowing efficiency of the axial flow fan 9 can be improved compared to when multiple rows of stay portions 28 are arranged on the same straight line in the direction of the rotation axis P2.

[0047] (3) In the axial flow fan 9, the stay portion 8 is arranged with a predetermined gap (a gap of 0.5 to 1.0 times the length of the hub-cone portion 7 in the direction of the rotation axis P1) between the upstream stay portion 8a and the downstream stay portion 8b in the cylindrical cross section Q1 parallel to the rotation axis P1 of the stay portion 8. This ensures the strength to support the hub-cone portion 7, thereby suppressing fluctuations in the position of the stay portion 8 due to air blowing, and achieving an arrangement of the stay portion 8 with high air blowing efficiency.

[0048] (4) In the axial flow fan 9, the stay portion 8 is arranged so that, in a cross section perpendicular to the rotation axis P1, the line connecting the casing 1-side end of the upstream stay portion 8a and the hub-cone portion 7-side end of the downstream stay portion 8b is parallel to the line connecting the casing 1-side end of the downstream stay portion 8b and the hub-cone portion 7-side end of the downstream stay portion 8b. This arrangement allows the stay portion 8 to maintain the same positional relationship with respect to the incoming swirling flow from the hub-cone portion 7-side end to the casing 1-side end. As a result, when the absolute outflow angle r1 of the incoming swirling flow with a high flow velocity is adjusted, most of the flow, including the swirling flow in the vicinity, is decelerated by impinging on the upstream stay portion 8a, and the decelerated flow impinges on the downstream stay portion 8b. Therefore, pressure loss due to impingement is reduced compared to when the swirling flow directly impinges on the downstream stay portion 28b. As a result, the blowing efficiency of the axial flow fan 9 can be improved compared to when multiple rows of stay portions 28 are arranged on the same line in the direction of the rotation axis P2.

[0049] The present invention has been described above based on the embodiments, but the present invention is not limited to the above embodiments, and it can be easily inferred that various improvements and modifications are possible within the scope of the invention without departing from the spirit of the invention.

[0050] In the axial flow fan 9 according to the first embodiment, the stay portions 8 are arranged in two rows (upstream stay portions 8a and downstream stay portions 8b), but this is not limited to this. For example, the stay portions may be arranged in three or more rows. Specifically, the axial flow fan according to a modified example having three rows of stay portions on the downstream side of the axial flow fan will be described, but the configuration other than the stay portions is the same as that of the first embodiment.

[0051] In the axial flow blower according to the modified example, if the stay sections downstream of the axial flow fan are referred to as the first stay section, the second stay section, and the third stay section in that order from the stay section closest to the axial flow fan in the downstream direction, the stay sections are arranged so that the relationship between the first stay section and the second stay section and the relationship between the second stay section and the third stay section are the same as the relationship between the upstream stay section 8a and the downstream stay section 8b in the first embodiment. In other words, the stay sections in the modified example are arranged such that the second stay section is offset from the first stay section along the rotational direction of the rotational shaft so that the angle between the rotational axis and a line connecting the midpoints of the first stay section and the second stay section is the absolute outflow angle, and the third stay section is offset from the second stay section along the rotational direction of the rotational shaft so that the angle between the rotational axis and a line connecting the midpoints of the second stay section and the third stay section is the absolute outflow angle. This arrangement reduces the speed of the swirling flow that strikes the stay section on the upstream side, and much of the decelerated flow strikes the stay section on the downstream side. This reduces pressure loss due to impingement compared to when the swirling flow directly strikes the stay section on the downstream side. This improves the blowing efficiency compared to an axial flow fan with three rows of stays aligned in the same line in the direction of the rotation axis. The same is true for an axial flow fan with four or more rows of stays installed downstream of the axial flow fan. [Industrial Applicability]

[0052] As described above, the axial flow fan of this embodiment has a structure that suppresses pressure loss due to collision of the swirling flow flowing inside the casing with the stay portion that supports the hub cone portion, thereby improving blowing efficiency and making it useful as an axial flow fan. [Explanation of symbols]

[0053] 1 casing 2 electric motor 3 Motor stay 4 Feathers 5 Hub 6 Axial Fan 7 Hub cone part 8 Stay part 8a Upstream stay 8a1 Upstream end 8a2 Downstream end 8b Downstream stay 8b1 Upstream end 8b2 Downstream end 9 Axial blower M1 first midpoint M2 second midpoint u1 Circumferential speed w1 relative velocity c1 Absolute outflow velocity d1 Wake velocity r1 Absolute outflow angle P1 rotation axis Q1 Cylindrical cross section 21 Casing 24 Feather 25 Hub section 26 Axial fan 27 Hub cone part 28 Stay part 28a Upstream stay 28a1 Upstream end 28a2 Downstream end 28b Downstream stay 28b1 Upstream end 28b2 Downstream end 29 Axial blower M3 first midpoint M4 second midpoint u2 Circumferential speed w2 relative velocity c2 Absolute outflow velocity d2 Wake velocity r2 Absolute outflow angle P2 rotation axis Q2 Cylindrical cross section 101 Casing 102 Electric motor 103 Motor stay part 104 Feather 105 Hub part 106 Axial Fan 107 Hub cone part 108 Stay part 108a Upstream stay 108b Downstream stay 109 Axial blower P3 rotation axis

Claims

1. An axial flow fan including: an electric motor; an axial flow fan that is rotatable in both forward and reverse directions and that is made up of a plurality of blades and a hub portion attached to a rotary shaft of the electric motor; a hub cone portion that rectifies the flow of air from the axial flow fan; and a stay portion that is fixed to the casing and supports the hub cone portion, the stay portion includes, on a downstream side of the axial flow fan, an upstream stay portion located on the axial flow fan side, and a downstream stay portion located downstream of the upstream stay portion along the rotation shaft, and the downstream stay portion is disposed so as to be shifted relative to the upstream stay portion along the rotation direction of the rotation shaft so that, in a cylindrical cross section of the stay portion parallel to the rotation shaft, an angle formed between the rotation shaft and a straight line connecting the upstream stay portion and the downstream stay portion becomes an absolute outflow angle of air that has passed through the axial flow fan.

2. 2. The axial flow fan according to claim 1, wherein the stay portions are disposed such that an angle formed between the rotation axis and a straight line connecting a first midpoint between the upstream end and the downstream end of the upstream stay portion and a second midpoint between the upstream end and the downstream end of the downstream stay portion is the absolute outflow angle.

3. 3. The axial flow fan according to claim 1, wherein the stay portion is disposed with a predetermined gap between the upstream stay portion and the downstream stay portion in a cylindrical cross section of the stay portion parallel to the rotation axis.

4. 3. The axial flow fan according to claim 1, wherein the stay portion is arranged such that, in a vertical cross section of the rotation shaft, a straight line connecting the casing side end of the upstream stay portion and the hub cone portion side end and a straight line connecting the casing side end of the downstream stay portion and the hub cone portion side end are parallel to each other.

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