JP2000009094A - Impeller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To hardly cause separation in the inside of a channel between blades and lower noises by lowering the maximum value of blade height to which camber height and the thickness of the blades are added. SOLUTION: This impeller is equipped with a plurality of blades 20 annually arranged on a main plate and an auxiliary plate connecting the other end of the blade 20, the blade 20 is such that its shape in a cross section cut by a surface perpendicular to a rotary shaft comprises a closed curve that vertically symmetrical thickness distribution is added to a camber line 21, and the camber line 21 is formed into a structure that its maximum camber position is positioned except for the center of a chord, for example, positioned within 70% from a front edge. Therefore, camber from the front edge to the maximum camber position is loosened, thus separation in this part is hardly produced, and also an effect can be obtained that a separation range in the vicinity of a rear edge is reduced and an effective cannel between blades can be widely retained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-blade blower used for home air conditioners and the like, and more particularly to a resin-molded impeller.

[0002]

2. Description of the Related Art As shown in FIG. 6, a conventional multi-blade blower of this type has a structure in which an impeller 2 is housed in a spiral casing 1. As shown in FIG. 7, the impeller 2 has a structure in which the blades 4 are annularly arranged on the main plate 3, and the other end is held by the sub plate 5. The shape of the sub-plate 5 is often a ring shape for integrally forming the impeller. A boss 6 is provided at the center of the main plate 3, and a drive shaft 8 of a motor 7 is provided.
Is linked to A suction port 9 is provided on a casing surface of the impeller 2 opposite to the sub-plate 5, and a bell mouth 10 is formed so that air can flow in smoothly. A discharge port 11 is formed at an end of the casing 1.

In such a configuration, by rotating the impeller in the direction of arrow 12 using a motor, the air sucked from the suction port 9 is blown out from the impeller 2 in the centrifugal direction, and the flow is transmitted through the casing 1. To perform the operation of blowing out from the discharge port 11 in one direction.

As the blades 4 of the impeller 2, an airfoil having a certain thickness distribution is often used as shown in FIG. Reference numeral 13 denotes an end on the side where the flow enters, which is called a leading edge.
4 is an end on the side where the flow flows out, and is called a trailing edge. Leading edge 13
The length L of a straight line connecting the trailing edge 14 and the trailing edge 14 represents the length of the blade and is called a chord. There are various well-known airfoils such as the NACA airfoil. The airfoil most commonly used in a multi-blade blower has an arc of the leading edge 13 and an arc of the trailing edge 14 as shown in FIGS. Are connected on the convex side 15 and the concave side 16 by arcs, respectively, so-called simple airfoil. This airfoil is provided with a vertically symmetric thickness distribution on both sides of a reference circular arc 17, and this circular arc 17 is called a warp line. In the case of a vertically symmetric thickness distribution, circles each having a center on a warp line are arranged as shown in FIG. 9, and the envelope forms an airfoil. That is, at the point P whose distance from the leading edge 13 along the chord is Lp, the radius Rp of the circle 19 having the center at the point P becomes the thickness of the blade, and is added to both surfaces of the warp line 17.

As described above, various airfoils having a vertically symmetrical thickness distribution can be defined and configured according to the size of the circles arranged on the warp line 17 and the arrangement thereof and the shape of the warp line itself. Here, the radii of the arcs forming the leading edge 13 and the trailing edge 14 are particularly called a leading edge radius and a trailing edge radius.

[0008] In the case of the simplified airfoil shown in FIG. 8, the airfoil has the largest thickness at the center of the airfoil and becomes thinner at both ends, so that the thickness distribution has a local maximum point at the center. The distance H between the chord and the warp line 17 is referred to as a warp height. In the case of a simple airfoil, the warp height is greatest at the center of the chord, that is, at a position 50% from the leading edge. Further, a distance Hb from the chord to the convex surface of the blade is referred to as a blade height. In the case of the simple wing type, the blade height also becomes maximum at the center of the chord.

As shown in FIG. 8, an angle β1 between the warp line 17 and the circumferential direction at the leading edge 13 is called an entrance angle, and an angle β2 between the warp line 17 and the circumferential direction at the trailing edge 14 is called an exit angle. . In a typical multi-blade blower of this type, the inlet angle β1
Is set to 80 to 90 degrees, and the exit angle β2 is set to 160 to 170 degrees.

[0008]

However, in the conventional multi-blade blower described above, there is a problem that the flow does not sufficiently follow the blade and large separation occurs, thereby lowering the blowing efficiency and increasing noise. That is, as shown in FIG. 8, the convex side 15 of the blade 4 is greatly curved, but the flow cannot flow along the blade 4 and separates in the vicinity of the center of the chord where the warp height H is the largest. , A large peeling area 18 is formed. The flow between the blades of the impeller is expected to ideally all flow along the blade surface, but in practice, such separation occurs. Where and what separation area occurs depends on the shape of the blade and the operating point of the blower and cannot be determined unconditionally. However, the deviation between the inflow at the leading edge 13 and the inlet angle β1 is large, and the curvature of the blade is large. Hardness is a major factor in peeling. That is, since the entrance angle β1 is set at 80 to 90 degrees,
If the relative velocity of the inflow is substantially in the radial direction, the inflow will flow smoothly along the blade. However, in the case of this type of multi-blade fan, the angle of the incoming flow is the inlet angle β
Since the flow is often smaller than 1, the flow is pressed against the concave side 16 of the blade 4, causing separation on the convex side 15 as shown in FIG. 8. This is more remarkable as the chord L is shorter and the blades 4 are more curved.

The separation region 18 is a region in which turbulence is strong and vortices are concentrated, which causes noise, narrows an effective flow path between blades, and increases passage resistance. Has become.

[0010]

In order to solve the above-mentioned problems, a multi-blade blower according to the present invention comprises a sub-plate in which a plurality of blades are annularly arranged on a main plate and the other end of the blades is connected. The blade has a blade shape in a cross section cut along a plane perpendicular to the rotation axis, and is configured by a closed curve obtained by adding a thickness distribution symmetrically to a warp line, and the warp line has a maximum warp position other than the center of the chord. , For example, 70% from the leading edge.

According to the above invention, since the maximum warpage position is shifted to the trailing edge side of 70%, the curve from the front edge to the maximum warpage position becomes gentle, so that peeling at this portion can be made hard to occur. . Furthermore, since the distance from the maximum warpage position to the trailing edge is short, even if separation occurs in this part, it flows out of the blade before growing as a large separation area, so the effect of narrowing the effective flow path between the blades Is also smaller.

As described above, by reducing the flow separation from the wing surface, high performance can be maintained over a wide operating point.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An impeller according to a first aspect of the present invention includes a sub-plate in which a plurality of blades are annularly arranged on a main plate and the other end of the blade is connected to the sub-plate. The blade shape in a cross section cut along a plane perpendicular to the axis is configured by a closed curve in which a vertical symmetric thickness distribution is added to the warp line, and the warp line has a maximum warp position other than the center of the chord. Has taken.

According to the above configuration, since the maximum warpage of the warp line is shifted from the center of the chord, the height of the warp near the center of the chord where the thickness of the blade is the largest is generally reduced. The maximum value of the blade height including the blade thickness is also reduced. That is, the blade height can be kept low without changing the inlet angle, the outlet angle, the height of the warp line, etc., so that the curvature of the entire blade is reduced and the curvature of the inter-blade flow path can be reduced. . Therefore, the separation in the flow path between the blades is less likely to occur, and the effect of reducing noise is obtained.

The impeller according to a second aspect of the present invention is the impeller according to the first aspect, wherein the maximum warping position of the warp line of the blade is 60 to 70% from the leading edge.

The impeller according to a third aspect of the present invention is the impeller according to the first aspect, wherein the maximum warping position of the warpage line of the blade is 30 to 40% from the leading edge.

According to a fourth aspect of the present invention, there is provided an impeller comprising: a plurality of blades arranged in a ring on a main plate; and a sub-plate connecting the other ends of the blades. The blade shape in a cross section cut along a plane perpendicular to the rotation axis, smaller than the sub-plate side, is configured by a closed curve in which a thickness distribution symmetrical to the warp line is added to the vertical line, and the warp line is the maximum warp position toward the main plate side. Has a configuration near the trailing edge.

According to the above-mentioned structure, the blade becomes a so-called tapered blade in which the blade chord is longer toward the main plate. The tapered blade has a short chord on the sub-plate side serving as a suction port and a wide opening, and the main plate side serving as a main flow has a long chord blade to efficiently blow air. By changing the maximum warp position between the main plate side and the sub plate side, a blade shape that allows easy integral molding of resin becomes possible. Therefore, it is possible to make use of both the effect of lowering the noise by shifting the maximum warping position to the trailing edge side and the effect of the tapered blade.

The impeller according to a fifth aspect of the present invention is the impeller according to any one of the first to fourth aspects, wherein a warp line of the blade is constituted by two cubic curves.

According to a sixth aspect of the present invention, there is provided an impeller comprising: a plurality of blades arranged in a ring on a main plate; and a sub-plate connecting the other ends of the blades, wherein the blades are perpendicular to a rotation axis. The blade shape in the cross section cut by the plane is constituted by a closed curve obtained by adding a vertically symmetrical thickness distribution to an arc-shaped warp line, and the thickness distribution is provided at two places near 30% and 70% from the leading edge. It has a configuration with a maximum point.

According to the above configuration, the combination of the vertically symmetrical thickness distribution having the maximum point at about 30% and about 70% from the leading edge and the arc-shaped warping line makes the convex side near the center of the chord flat. Become. Therefore, the flow path between the blades is widened, so that not only the air volume performance can be improved, but also the peeling is less likely to occur on the trailing edge side of the blade convex side. In addition, since the area becomes smaller even when it occurs, the performance degradation can be reduced.

According to a seventh aspect of the present invention, there is provided an impeller comprising a plurality of blades arranged in a ring on a main plate, and a sub-plate connecting the other ends of the blades, wherein the blades are perpendicular to a rotation axis. The blade shape in the cross section cut by the plane is composed of a closed curve with an asymmetric thickness distribution added above and below the arc-shaped warp line, the thickness distribution on the convex side has a local maximum point from the trailing edge of the chord, The thickness distribution on the concave side has a maximum point near the center of the chord.

According to the above configuration, the convex side of the blade has a moderate warp from the leading edge to a position where the thickness becomes maximum due to the combination of the thickness distribution having the maximum point on the trailing edge side and the arc-shaped warping line. In this case, peeling at this portion can be made difficult to occur. Furthermore, since the distance from the position where the thickness is the maximum to the trailing edge is short, even if separation occurs in this part, it flows out of the blade before growing as a large separation area, so the effective flow path between the blades is reduced. The effect of narrowing is also reduced.

As described above, by reducing the flow separation from the wing surface, high performance can be maintained over a wide operating point.

An impeller according to an eighth aspect of the present invention includes a sub-plate in which a plurality of blades are annularly arranged on a main plate, and a sub-plate connecting the other ends of the blades, wherein the blades are perpendicular to a rotation axis. The blade shape in the cross section cut by the plane is constituted by a closed curve in which an asymmetric thickness distribution is added above and below the arc-shaped warp line, and the thickness distribution on the convex side is approximately 30% and 70% from the leading edge.
It has a local maximum point at one place, and the thickness distribution on the concave side has a configuration with one local maximum point near the center.

According to the above configuration, the convex side of the blade is relatively flat near the center of the chord due to the combination of the thickness distribution having the maximum points at around 30% and 70% from the leading edge and the arc-shaped warpage. Shape. Therefore, the flow path between the blades is widened, so that not only the air volume performance can be improved, but also the peeling is less likely to occur on the trailing edge side of the blade convex side. Also,
Even in the case of occurrence, the area is reduced, so that a decrease in performance can be reduced.

[0027]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is an enlarged view of a blade of an impeller according to Embodiment 1 of the present invention. As in the conventional example, the blades 20 of the impeller housed in the spiral casing are arranged in an annular shape on the main plate, and have a structure in which the other end is supported by the sub plate. Here, the blade 20 has a maximum warp position of the warp line 21 closer to the trailing edge than the center of the chord. In particular,
For the chord length L, the maximum warping position is at a distance Lh from the leading edge, and the value of Lh / L is 0.6 to
A position of about 0.7, that is, 60 to 70% from the leading edge is appropriate. An airfoil is formed by adding a vertically symmetric thickness distribution to the warp line 21.

In general, the thickness distribution of the airfoil has a small thickness at the leading edge and the trailing edge, and has a maximum thickness near the center of the chord. Therefore, this airfoil, whose maximum warp position is shifted to the trailing edge side, has a lower blade height near the center of the chord due to the lower warpage and a lower height at the maximum warp position due to the reduced thickness. Has become. In other words, the airfoil has a reduced blade height without changing the inlet angle, outlet angle, and warp height of the blade.

The flow of the airflow around the blade 20 will be described. As shown in FIG. 1, the flow flowing from the leading edge 22 is
The blade 20 flows into the convex side 24 and the concave side 25 of the blade 20 separately, and flows out from the trailing edge 23. At this time, the angle flowing into the blade 20 is determined by the absolute speed of the flow and the rotation speed of the impeller,
In general, the angle often goes from the concave side 25 to the convex side 24 of the blade 20. Normally, the entrance angle of the blade 20 is set to a value that does not largely deviate in consideration of the inflow angle. Since the flow on the concave side 25 of the blade 20 is pressed against the blade 20 by the rotation of the impeller, peeling is less likely to occur. On the other hand, the flow on the convex side 24 flows along the curvature of the blade 4, so that if the curvature is too tight, it will not be able to follow the flow and will be separated. In the configuration of the present invention, the curvature from the leading edge 22 to the maximum warpage position is moderated because the maximum warpage position is shifted to the trailing edge side and the blade height is reduced. Therefore, the separation of the flow during this period is very small.

On the other hand, from the maximum warp position to the trailing edge, the curve is steeper than in the first half. However, since the blade height is low and the blade is close to the trailing edge 23, even if peeling occurs, It does not form a large separation area between the wings,
Immediately, it flows out of the impeller. Therefore, high performance can be realized without narrowing the effective flow path between the blades.

When the maximum warping position of the warp line 21 is brought to a position 30 to 40% from the front edge, the curve from the front edge 22 of the convex side 24 to the maximum warp position becomes slightly sharp. Since the pressure recovery region from the warped position to the trailing edge 23 has a gentle curve, peeling hardly occurs.
Therefore, if the entrance angle is appropriately set, there is no peeling in the first half part or it is possible to keep the peeling small, so that a good flow with little peeling as a whole can be realized.

The shape of the warp line 21 can be expressed using an arbitrary curve. However, when three parameters of the entrance angle, the exit angle, and the maximum warpage position are used as parameters, the curve from the leading edge to the maximum warpage position is used. By expressing each of the distance from the maximum warpage position to the trailing edge by a cubic curve, a warp line can be uniquely determined.

(Embodiment 2) FIG. 2 is an enlarged view of a blade of an impeller according to Embodiment 2 of the present invention. The structure of the impeller is the same as that of the first embodiment, and the blades 26 are arranged in an annular shape on the main plate.
The other end is supported by a sub-plate. This impeller is
It is a so-called tapered blade in which the inner diameter of the blade 26 on the main plate side is smaller than that on the sub-plate side. That is, if the inner diameter of the blade 26 is Rh on the main plate side and Rs on the sub plate side, Rs> Rh. Therefore, if the front edge on the main plate side is 27, the front edge on the sub-plate side is 28, and the intermediate front edge is 29.
It is represented by Here, the warp line 21 is constant from the main plate side to the sub plate side, and the maximum warp position is set on the main plate side closer to the trailing edge than the chord center as in the first embodiment. Such tapered blades having different blade inner diameters on the main plate side and the sub plate side reduce inflow resistance by expanding the sub plate side serving as an inflow port, and utilize the long chord on the main plate side serving as a main flow of the flow. To provide effective blowing.

With the common warp line 21, the maximum warp position is set near the trailing edge on the main plate side, and the maximum warp position is continuously changed on the sub-plate side so as to be near the center of the chord. Thereby, a blade shape having no twist in the span direction from the main plate side to the sub plate side is obtained, and the integral molding of the resin is facilitated.

Therefore, there is a merit that the efficiency of the tapered type blade and the effect of suppressing the peeling by shifting the maximum warp position to the trailing edge side can be realized, and the blade can be easily formed integrally with the resin.

Incidentally, any curve such as a cubic curve can be used as the curve representing the warp line 21 as in the first embodiment.

(Embodiment 3) FIG. 3 is an enlarged view of a blade of an impeller according to Embodiment 3 of the present invention. The structure of the impeller is the same as that of the first embodiment, and the blades 31 are arranged in an annular shape on the main plate.
The other end is supported by a sub-plate. The wings 31
This is a shape obtained by adding a vertically symmetric thickness distribution to the arc-shaped warp line 32. This thickness distribution is about 30% from the leading edge 22 and 7
The distribution shape has a local maximum value at two locations near 0%. The thicknesses D1 and D2 of the blade 31 at points L1 and L2 from the leading edge shown in FIG. 3 are the maximum values of the thickness distribution.

In the above configuration, the thickness between the two local maximum points is naturally smaller than the local maximum point.
The shape of No. 4 is almost flat near the center, and the concave side 25
Has a sharp center curve. Convex side 24 of blade 31
As the bulge of the blade becomes small and the flow path between the blades is widened, not only the air volume performance can be improved, but also the peeling is less likely to occur on the trailing edge 23 side of the blade convex surface side 24. Further, even when it occurs, the peeled area becomes smaller, so that an increase in noise and the like can be suppressed.

On the other hand, even if the concave surface 25 is slightly curved, the flow acts in the direction in which the flow is pressed against the blades 31, so that large separation does not occur.

(Embodiment 4) FIG. 4 is an enlarged view of a blade of an impeller according to Embodiment 4 of the present invention. The structure of the impeller is the same as that of the first embodiment, and the blades 33 are annularly arranged on the main plate.
The other end is supported by a sub-plate. The wings 33
It is composed of a closed curve in which an asymmetric thickness distribution is added above and below the arc-shaped warp line 32, the thickness distribution on the convex side 24 has a maximum point from the trailing edge of the chord, and the thickness distribution on the concave side 25 is It has a maximum point near the center of the string. FIG.
Is the maximum thickness position at a distance L3 from the leading edge, and the thickness T3 of the convex side 24 of the blade 33 at this point is the maximum value.

In the above configuration, the curvature from the leading edge 22 to the maximum thickness position is moderated because the maximum thickness position of the convex surface 24 is shifted to the rear edge side. Therefore, the separation of the flow during this period is very small.

On the other hand, the curve from the maximum thickness position to the trailing edge 23 becomes steeper than the front half, but the trailing edge 23
Due to the closeness, the separation does not form a large separation area between the blades even if separation occurs, and immediately flows out of the impeller. Therefore, there is an effect that a large air volume can be realized without narrowing the effective flow path between the blades.

Further, since the same thickness distribution as that of the conventional simple airfoil can be used for the arcuate warp line for the shape of the concave side 25, the blade having little separation between the blades can be formed by merely changing the thickness distribution of the convex side 24. It can be easily made.

(Embodiment 5) FIG. 5 is an enlarged view of a blade of an impeller according to Embodiment 5 of the present invention. The structure of the impeller is the same as that of the first embodiment, and the blades 34 are arranged in an annular shape on the main plate.
The other end is supported by a sub-plate. The wings 34
This is a shape in which an asymmetric thickness distribution is added above and below the arc-shaped warp line 32. The convex side 24 of this asymmetrical thickness distribution has local maximum points at two positions, around 30% and 70% from the leading edge. The thickness distribution on the concave side 25 has one local maximum near the center. Distance L4 from the leading edge shown in FIG.
The thicknesses T4 and T5 of the convex side 24 of the blade 34 at points L5 and L5 are the maximum values.

In the above configuration, since the thickness between the two maximum points on the convex side 24 is naturally smaller than the maximum point, the thickness of the convex side 24 is combined with the arc-shaped warpage line 32. The shape is almost flat near the center. In other words, the bulge on the convex side 24 of the blade 34 is reduced and the flow path between the blades is widened, so that not only the air volume performance can be improved, but also the peeling is less likely to occur on the trailing edge 23 side of the blade convex side 24. In addition, even when it occurs, the peeled area becomes small, so that an effect of suppressing an increase in noise and the like can be obtained.

Further, since the same thickness distribution as that of the conventional simple airfoil can be used for the arcuate curved line of the concave side 25, the blade having high air volume performance can be easily obtained only by changing the thickness distribution of the convex side 24. Can be made.

[0048]

As described above, according to the blade of the impeller of the present invention, the maximum warpage of the warp line is shifted from the center of the chord, so that the blade is generally thickest near the center of the chord. The height of the blade, which is the sum of the height of the blade and the height of the blade, also decreases. Therefore, the separation in the flow path between the blades is less likely to occur, and the effect of reducing noise is obtained.

Further, by adopting a so-called tapered blade in which the chord of the blade is longer on the main plate side, and by changing the maximum warp position on the main plate side and the sub plate side, the blade shape is easy to integrally mold resin. Becomes possible. Therefore, it is possible to make use of both the effect of lowering the noise by shifting the maximum warping position to the trailing edge side and the effect of the tapered blade.

Further, the combination of a vertically symmetrical thickness distribution having local maximum points at around 30% and 70% from the leading edge and an arc-shaped warpage makes the convex side near the center of the chord relatively flat. Since the flow path between the blades is widened, an effect of improving the air volume performance can be obtained.

Further, in a wing shape in which an asymmetric thickness distribution is added to the upper and lower sides of the arc-shaped warp line, a combination of the thickness distribution having a local maximum point on the trailing edge side of the convex surface and the arc-shaped warp line allows a maximum from the leading edge. Since the warpage to the warped position becomes gentle, an effect of making it difficult to cause peeling at this portion is obtained.

Further, in a wing shape in which an asymmetric thickness distribution is added above and below the arc-shaped warp line, the thickness distribution having local maximum points at around 30% and 70% from the leading edge on the convex side, and the arc-shaped warp line By the combination of the above, since the vicinity of the center of the chord has a relatively flat shape, the flow path between the blades is widened, and the effect of improving the air volume performance can be obtained.

[Brief description of the drawings]

FIG. 1 is an enlarged view of a blade of an impeller according to a first embodiment of the present invention.

FIG. 2 is an enlarged view of an impeller blade according to a second embodiment of the present invention.

FIG. 3 is an enlarged view of an impeller blade according to a third embodiment of the present invention.

FIG. 4 is an enlarged view of an impeller blade according to a fourth embodiment of the present invention.

FIG. 5 is an enlarged view of an impeller blade according to a fifth embodiment of the present invention.

FIG. 6 is a plan view of a conventional multi-blade blower.

FIG. 7 is a longitudinal sectional view of a conventional multi-blade fan.

FIG. 8 is an enlarged view of a blade of an impeller in a conventional multi-blade blower.

FIG. 9 is an explanatory diagram of a blade thickness distribution of an impeller in a conventional multi-blade fan.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 casing 2 impeller 3 main plate 20 blade 21 warp line 22 leading edge 23 trailing edge 26 blade 27 leading edge on main plate side 28 leading edge on sub plate side 29 front edge at intermediate portion 31 blade 32 warp line 33 blade 34 blade

Claims (8)

[Claims] 1. A plurality of blades are annularly arranged on a main plate, and a sub plate connecting the other ends of the blades is provided. The blades have a blade shape in a cross section cut along a plane perpendicular to a rotation axis. An impeller for a multi-blade blower, comprising a closed curve obtained by adding a vertically symmetric thickness distribution to a warp line, wherein the warp line has a maximum warp position other than the center of the chord. 2. The maximum warp position of the warp line of the blade is 6 degrees from the leading edge.
The impeller of a multi-blade blower according to claim 1, which is located at a position of 0 to 70%. 3. The maximum warp position of the warp line of the blade is 3 from the leading edge.
The impeller of a multi-blade blower according to claim 1, which is located at a position of 0 to 40%. 4. A plurality of blades are arranged in an annular shape on a main plate, and a sub-plate is provided for connecting the other end of the blade. The blade has an inner diameter smaller on the main plate side than on the sub-plate side. The blade shape in the cross section cut by the vertical plane is constituted by a closed curve obtained by adding a vertically symmetrical thickness distribution to the warp line, and the warp line has a maximum warp position on the main plate side closer to the trailing edge of the multi-blade blower. Impeller. 5. An impeller for a multi-blade blower according to claim 1, wherein a warp line of the blade is constituted by two cubic curves. 6. A blade having a plurality of blades arranged in an annular shape on a main plate and a sub-plate connecting the other ends of the blades, wherein the blades have a blade shape in a cross section cut along a plane perpendicular to a rotation axis. It is composed of a closed curve in which a vertically symmetric thickness distribution is added to an arc-shaped warp line, and the thickness distribution is around 30% from the leading edge and 70%
An impeller of a multi-blade blower with local maximums in two places. 7. A plurality of blades are arranged in an annular shape on a main plate, and a sub plate connecting the other ends of the blades is provided. The blades have a blade shape in a cross section cut along a plane perpendicular to a rotation axis. It is composed of a closed curve with an asymmetrical thickness distribution added above and below the arcuate warp line.The thickness distribution on the convex side has a maximum point from the trailing edge of the chord, and the thickness distribution on the concave side is the center of the chord. An impeller of a multi-blade blower with a local maximum point. 8. A plurality of blades are annularly arranged on a main plate, and a sub plate connecting the other ends of the blades is provided, wherein the blades have a blade shape in a cross section cut along a plane perpendicular to a rotation axis. It is composed of a closed curve with an asymmetrical thickness distribution added above and below the arcuate warp line. The thickness distribution on the convex side has local maximum points at around 30% and 70% from the leading edge, and the concave side on the concave side. The thickness distribution is for an impeller of a multi-blade blower with one maximum point near the center.