JPH07224788A - Sirocco fan - Google Patents

Abstract

PURPOSE:To obtain a sirocco fan for which abnormal sound (siren sound) generated by the rotation of the rotor is reduced and the decrease of efficiency is lessened. CONSTITUTION:The nose 10 as the starting point of an air path is so shaped that the radial gap between the nose 10 of the intermediate part 10a with which the air stream with a large velocity collides and the rotor 2 is made larger in the height of the nose 10 and the gap is made gradually smaller from the intermediate part 10a toward both ends of the nose 10 (port side end and motor side end), corresponding to the air velocity distribution at the outlet of the blades 6. The radius of curvature (nose R) at the nose 10 is made larger at the intermediate part 10a than both ends of the nose.

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 equipped with a scroll casing, which is suitable for use in, for example, an air conditioner for automobiles.

[0002]

2. Description of the Related Art A multi-blade fan is a centrifugal impeller (hereinafter abbreviated as impeller) in which a large number of blades are arranged at equal intervals in the circumferential direction, a motor for rotating the impeller, and a periphery of the impeller. It is composed of a scroll casing that forms a spiral ventilation passage, and because it is compact and lightweight, and is capable of high pressure and large air volume, it is used in various air conditioners including automobile air conditioners. In this multi-blade blower, the wind speed distribution on the outer circumference (blade exit) of the impeller is not uniform, and as shown in FIG.
A wind speed difference ΔV occurs between before and after 0 and between the blades, and the wind speed becomes higher between the blades. Therefore, an air mass is formed between the blades at the outlet of the blade 100, and the air mass collides with the nose portion 200 of the scroll casing in a pulsed manner to generate an abnormal noise (siren sound).

Therefore, as a measure for reducing the siren noise, as shown in FIG. 27, a nose gap (nose portion 2
00 and the impeller 300), and
As shown in FIG. 8, a method of forming the nose portion 200 obliquely with respect to the rotating direction of the impeller 300 is known. When the nose gap is increased, the air mass formed between the blades diffuses and merges, so that the wind speed difference ΔV decreases in the rotating direction of the impeller 300, and the wind speed distribution becomes uniform. Therefore, the peak value of the siren sound decreases as the nose gap increases. Further, when the nose portion 200 is formed obliquely with respect to the rotation direction of the impeller 300, the nose portion 200 has a predetermined length in the rotation direction of the impeller 300, so that air generated between the blades is Since the mass passes through the nose portion 200 for a predetermined length in the rotation direction, it is possible to reduce the peak value of the pulse-like siren sound.

[0004]

However, when the nose gap is enlarged or the nose portion 200 is provided obliquely, there arises a problem that the fan efficiency is lowered due to the reduction of the air volume and the total pressure. The present invention has been made based on the above circumstances, and an object of the present invention is to provide a multi-blade blower that reduces abnormal noise generated during rotation of an impeller and reduces a decrease in fan efficiency due to the reduction of the abnormal noise. In offer.

[0005]

In order to achieve the above object, in claim 1, an impeller having a large number of blades arranged at regular intervals in the circumferential direction, and a nose portion around the impeller. A scroll casing that forms a spiral ventilation path as a starting point and is provided with an air suction port on one surface in the height direction of the impeller, and is arranged on the opposite side of the suction port in the height direction of the impeller. And a motor for applying a rotational force to the impeller, and the nose portion is set between the impeller and a portion of the nose portion, which corresponds to the wind velocity distribution at the blade outlet, to which an air flow having a high wind velocity hits. The larger radial gap,
The technical means is to have a shape such that the gap is small at the portion where the air flow having a low wind velocity hits.

According to a second aspect of the present invention, in the multiblade blower according to the first aspect, the nose portion is located between the suction port side end portion and the motor side end portion of the nose portion in the height direction of the impeller. The technical means is that the gap is large in the middle part of the above, and the gap is gradually reduced from the middle part toward the suction port side end part and the motor side end part.

According to a third aspect of the present invention, in the multiblade blower according to the first or second aspect, the gap at the suction port side end portion of the nose portion is L1, and the nose portion at the motor side end portion is the gap. Is L2, the gap at the middle portion of the nose portion is L3, and the outer diameter of the impeller is D. 0.06 × D <L0 <0.08 × D The L0 satisfying this relationship is used as a reference. When the values are used, it is a technical means that the following relationship is established among the L1, the L2, the L3 and the L0. L1> 0.6.times.L0, L2> 0.7.times.L0, and 1.
1 x L0 <L3 <1.7 x L0

According to a fourth aspect of the present invention, an impeller having a large number of blades arranged at regular intervals in the circumferential direction, and a spiral ventilation passage having a nose portion as a starting point are formed around the impeller. A scroll casing provided with air suction ports on both sides in the height direction, and a motor that is arranged on the opposite side of one of the suction ports in the height direction of the impeller and applies a rotational force to the impeller. The nose portion, corresponding to the wind speed distribution at the blade outlet, in the portion where the air flow with a high wind speed hits, the radial gap set with the impeller becomes large, In the area where a small air flow hits,
The technical means is to provide the shape so that the gap becomes smaller.

According to a fifth aspect of the present invention, in the multiblade blower according to the fourth aspect, the nose portion is between a central portion of the nose portion and one of the suction port side end portions in the height direction of the impeller, and The gap is large in each intermediate portion between the central portion and the motor-side end portion, and the suction port-side end portion, the motor-side end portion, and the central portion from one of the intermediate portions toward the central portion. The technical means is that the gap is gradually reduced.

According to a sixth aspect of the present invention, in the multiblade blower according to the fourth or fifth aspect, the gap at the suction port side end of the nose portion is L1, and the gap at the motor side end portion of the nose portion is L1. L2, the gap at each intermediate portion of the nose portion is L3, and the outer diameter of the impeller is D
0.06 × D <L0 <0.08 × D When L0 satisfying this relation is used as a reference value, the following relations are established between L1, L2, L3 and L0. That is the technical means. L1> 0.6.times.L0, L2> 0.7.times.L0, and 1.
1 x L0 <L3 <1.7 x L0

[0011]

In the first aspect, the radial gap between the nose portion of the scroll casing and the impeller is not constant in the height direction of the impeller, but is set according to the wind velocity distribution at the blade outlet. Therefore, the nose portion is provided in such a shape that the gap becomes large at a portion where the air flow having a high wind velocity hits and the gap becomes small at a portion where the air flow having a low wind velocity hits.

According to a second aspect of the present invention, the nose portion according to the first aspect has a large gap at an intermediate portion between the suction port side end portion and the motor side end portion in the height direction of the impeller, and the suction is performed from the intermediate portion. The gap is gradually reduced toward the mouth side end and the motor side end.

According to a third aspect of the present invention, in the multiblade blower according to the first or second aspect, gaps are provided at both ends (suction port side end and motor side end) and an intermediate part of the nose part in the height direction of the impeller. Is defined by the reference value L0. In addition,
The reference value L0 is defined by the outer diameter D of the impeller in the nose shape when the gap is constant in the height direction of the impeller.

In the fourth aspect, the radial gap between the nose portion of the scroll casing and the impeller is not constant in the height direction of the impeller, but is set according to the wind velocity distribution at the blade outlet. Therefore, the nose portion is provided in such a shape that the gap becomes large at a portion where the air flow having a high wind velocity hits and the gap becomes small at a portion where the air flow having a low wind velocity hits.

According to a fifth aspect of the present invention, the nose portion according to the fourth aspect is provided between the central portion in the height direction of the impeller and one suction port side end portion, and between the central portion and the motor side end portion. The gap is large in each intermediate portion, and the gap is gradually reduced from the intermediate portion toward one suction port side end portion, the motor side end portion, and the central portion.

According to a sixth aspect, in the multi-blade blower according to the fourth or fifth aspect, both end portions (one suction port side end portion and one motor side end portion) of the nose portion in the height direction of the impeller and each intermediate portion are provided. The gap at is defined by the reference value L0. The reference value L0 is defined by the outer diameter D of the impeller when the gap is constant in the height direction of the impeller.

[0017]

EXAMPLE An example of the present invention will be described below with reference to FIGS. FIG. 1 is a perspective view showing a nose portion of a scroll casing. As shown in FIGS. 2 and 3 (A-A cross-sectional view of FIG. 2), the multi-blade blower 1 of the present embodiment includes an impeller 2,
It is composed of a scroll casing (hereinafter abbreviated as casing) 3 and a motor 4.

The impeller 2 is composed of a bottom plate 5 to which the rotational force of the motor 4 is transmitted, a number of blades 6 fixed to the bottom plate 5, and an annular holding ring 7 for holding each blade 6. There is. The bottom plate 5 is fixed to the rotation shaft 4a by tightening the nut 8 by fitting the rotation shaft 4a of the motor 4 to the boss portion 5a provided in the central portion. In order to reduce the protrusion of the motor 4, the bottom plate 5 has a shape in which the central portion having the boss portion 5a is recessed inward from the outer peripheral portion. The blades 6 have a circular arc-shaped cross section (see FIG. 1) and are annularly arranged at the outer peripheral end of the bottom plate 5 at a constant pitch. The retaining ring 7 connects the upper ends (opposite sides of the bottom plates 5) of the blades 6 and holds the blades 6 at equal intervals.

The casing 3 forms a spiral ventilation passage S around the impeller 2, is divided into two in the width direction of the ventilation passage S (vertical direction in FIG. 3), and has an air intake port. The bell casing 9 is formed of an upper casing 3a and a lower casing 3b supporting the motor 4. In this casing 3, as shown in FIG. 2, the spiral portion of the ventilation passage S starts winding one point of the nose portion 10 which is the starting point of the ventilation passage S, and has a constant spread angle from the one point of the nose portion 10. It is composed of a formed scroll curve.

The motor 4 is a bell mouth 9 of the casing 3.
The impeller 2 is rotated by transmitting the rotational force to the bottom plate 5 which is arranged on the opposite side to and fitted to the rotary shaft 4a.

Next, the nose portion 10 of the casing 3 will be described in detail. Generally, the wind velocity distribution at the outlet of the blade 6 of the air flow generated by the rotation of the impeller 2 is sucked from the bell mouth 9 in the height direction of the impeller 2 (the vertical direction of FIG. 4) as shown in FIG. Wings where air flows smoothly 6
The wind speed becomes smaller on the upper side of the blade 6 outlet where the air flow direction becomes the largest at the center of the outlet and the air flow direction changes greatly, and on the lower side of the blade 6 outlet where the resistance increases due to the flow along the bottom plate 5. It has been known.

Therefore, the nose portion 10 of this embodiment has the blade 6
Corresponding to the wind velocity distribution at the outlet, as shown in FIG. 5, in the height direction of the nose portion 10 (vertical direction in FIG. 5), the portion where the air flow with the highest wind velocity hits (hereinafter referred to as the intermediate portion 10a) The radial gap between the nose portion 10 and the impeller 2 (hereinafter referred to as the nose G) is increased at the intermediate portion 10
Nose G gradually increases from a toward both ends of the nose portion 10.
Is provided in a shape such that The position of the intermediate portion 10a is slightly lower than the central portion of the nose portion 10 (closer to the end portion on the motor 4 side) because the air sucked from the bell mouth 9 flows obliquely downward from the outlet of the blade 6. .

Further, in the height direction of the nose portion 10, the nose G
In the conventional nose portion shape (shape shown by the broken line in FIG. 6) in which the constant is constant, the optimum nose G (L0) is defined by the following relationship in terms of fan efficiency and noise. However, the outer diameter of the impeller 2 is D (see FIG. 6).

[Equation 1] 0.06D <L0 <0.08D

On the other hand, the nose portion 10 of this embodiment
As shown in Fig. 6, the nose G at the suction port side end is
1, L2 is the nose G at the end of the motor 4 side, and L3 is the nose G at the intermediate portion 10a, L1, L2, and L3 have the following relationship with L0 above (Equation 2 to Equation 4). )
Are specified to satisfy.

[0025]

[Equation 2] L1> 0.6 × L0

[Equation 3] L2> 0.7 × L0

## EQU00004 ## 1.1.times.L0 <L3 <1.7.times.L0

However, on the downstream side of the ventilation passage S from the nose portion 10, the gap between the impeller 2 and the inner wall surface of the casing 3 becomes gradually constant in the width direction of the ventilation passage S as it goes downstream from the nose portion 10. It is provided in. Then, the position where the gap becomes maximum is provided so as to gradually move from the middle part 10a of the nose part 10 to a lower position in the period from the nose part 10 until the gap becomes constant, as shown in FIG. There is. Note that FIG. 8 shows the casing 3 at a position corresponding to each point (-) position shown in FIG. 7.
Shows the shape of the inner wall surface (indicates the moving direction of the maximum gap position).

As shown in FIG. 9, the nose portion 10 has a radius of curvature (hereinafter referred to as nose R) which is the middle portion 10.
It is provided so that it is the largest at a and becomes gradually smaller toward both ends of the nose portion 10.

Next, the operation of this embodiment will be described. Impeller 2
The air sucked from the bell mouth 9 by the rotation of
A wind velocity distribution as shown in FIG. 4 is generated at the outlet of the blade 6. On the other hand, in the nose portion 10 of the casing 3, the nose G at the intermediate portion 10a, which is hit by the air flow having the highest wind speed, is larger than the nose G at both ends of the nose portion 10, and the nose R is at the nose portion. The intermediate portion 10a is provided so as to be larger than both end portions of 10.

Generally, the relationship between the nose G and the nose R and the peak value reduction amount of the siren sound and the fan efficiency is as follows.
As shown in FIG. 10, it is known that as the nose G and the nose R increase, the peak value reduction amount of the siren sound increases (that is, the siren sound decreases), and the fan efficiency decreases. For reference, the data measured by using the multiblade blower 1 in a vehicle air conditioner are shown in FIGS. 11 and 12. The data shown in FIG. 11 are obtained by measuring the relationship between the nose G and the peak value of the siren sound when the nose R = 7.5 mm (constant) in the FACE mode and the FOOT mode. The data shown in FIG.
The relationship between the nose R and the peak value of the siren sound when the value is constant is measured in the FACE mode and the FOOT mode, respectively. However, the divergence angle of the casing 3 is 6.0 °, and the blade tip average outlet wind speed in each outlet mode is constant.

As described above, the siren sound peak value can be reduced by increasing the nose G and the nose R, but it is better to reduce the nose G and the nose R in terms of fan efficiency. Therefore, as in the present embodiment, by making the nose G and the nose R in the intermediate portion 10a, which are hit by the air flow having a high wind velocity, larger than both ends of the nose portion 10, the siren sound peak value can be effectively reduced. (See FIG. 13). Also, the nose part 1
Since the nose G and the nose R are set to be smaller at both ends of 0 than the intermediate part 10a, it is possible to reduce the decrease in fan efficiency.

Further, since the maximum gap position downstream from the nose portion 10 is provided so as to gradually move to a lower position along the airflow flowing through the ventilation passage S, the reduction in fan efficiency can be further reduced. it can.

Here, a conventional nose portion shape in which the nose G is constant in the height direction of the nose portion 10 (see FIG. 14),
With the shape of the nose portion 10 of the present invention (see FIG. 15) in which the nose G is set according to the wind speed distribution at the outlet of the blade 6, the relationship between the nose G and the siren sound, total pressure, and fan efficiency is FAC.
The data measured respectively in the E mode and the FOOT mode are shown in FIGS. However, the outer diameter D of the impeller 2 =
φ150, height of nose part H = 90 mm, nose R =
As shown in FIG. 16, the nose G is set to 9.0 mm (constant), and the gap between the impeller 2 and the nose portion 10 on a straight line connecting the rotation center A1 of the impeller 2 and the center A2 of the nose R. Is.

Further, in the shape of the nose portion 10 of the present invention, the intermediate portion 10a having the maximum nose G is located at a position 30 mm from the end portion on the motor 4 side (the lower end portion in FIG. 15).
The nose G at 0a is set to be 2 mm larger than the nose G at the end on the motor 4 side and 5 mm larger than the nose G at the end on the suction port side (upper end in FIG. 15). In addition,
The shape of the nose portion 10 of the present invention is measured with reference to the nose G at the end of the motor 4 side.

Next, a second embodiment of the present invention will be described. In this embodiment, in order to improve the workability of the nose portion 10, the nose R is constant in the height direction of the nose portion 10. However, as for the nose R, in order to reduce the siren sound, the nose R at both ends of the nose portion 10 is increased,
It is better to match the nose R of the intermediate portion 10a.

Next, a third embodiment of the present invention will be described. FIG. 23 is an explanatory diagram showing the moving direction of the maximum gap position. In the first embodiment, the maximum gap position downstream of the nose portion 10 is provided so as to gradually move to a position lower than the nose portion 10 downstream, but in the present embodiment, the maximum gap position is the nose portion 10. It is provided so as to move further downstream in the same position (see FIG. 23).
This facilitates the processing of the casing 3.

Next, a fourth embodiment of the present invention will be described. FIG. 24 is a sectional view showing the shape of the nose portion 10. In the first embodiment, the intermediate portion 10a having the maximum nose G is located below the central portion of the nose portion 10 (closer to the end portion on the motor 4 side), but the wind speed distribution at the outlet of the blade 6 is shown in FIG. If it is different from the distribution, it may be changed according to the wind speed distribution. For example, when the airflow with the highest wind velocity hits the suction port side from the central portion of the nose portion 10, as shown in FIG. 24, the nose G is above the central portion of the nose portion 10 (close to the suction inlet side end portion). You may provide so that it may become the maximum.

Next, a fifth embodiment of the present invention will be described. FIG. 25 is a schematic cross-sectional view of the multiblade blower 1. The multiblade blower 1 of this embodiment has suction ports 9a and 9b on both sides of the casing 3.
The casing 3 is provided with two impellers 2
Are connected in the height direction. In this multi-blade blower 1, since air is sucked from both sides of the casing 3, the nose portion 10 of the casing 3 has different wind speeds on the suction port 9a side and the motor 4 side from the central portion of the nose portion 10. A large air stream hits.

Therefore, the nose portion 10 has a central portion which is a boundary between the two impellers 2 and a portion on which one of the suction ports 9a is provided with an air flow having a high wind speed, and the central portion and the motor 4.
At a portion (hereinafter referred to as an intermediate portion 10a) where an airflow having a high wind velocity hits between the side end portion (the other suction port 9b side end portion),
The nose G is increased, and the nose G is increased at the one end on the suction port 9a side, the end on the motor 4 side, and the central part.
Is provided in a shape such that

In the nose portion 10, one suction port 9a
If the nose G at the side end is L1, the nose G at the side end of the motor 4 is L2, and the nose G at each intermediate portion 10a is L3, L1, L2, and L3 are as described in the first embodiment. It is defined to satisfy the following relationship (Equation 5 to Equation 7) with the optimum nose G L0 (see FIG. 6).

[0040]

[Equation 5] L1> 0.6 × L0

[Equation 6] L2> 0.7 × L0

[Equation 7] 1.1 × L0 <L3 <1.7 × L0

However, on the downstream side of the ventilation passage S from the nose portion 10, the gap between the impeller 2 and the inner wall surface of the casing 3 becomes gradually constant in the width direction of the ventilation passage S as it goes downstream from the nose portion 10. It is provided in. The position where the gap becomes maximum is provided so as to gradually move from each intermediate portion 10a toward the central portion along the air flow until the gap becomes constant from the nose portion 10. Moreover, the nose R in the nose part 10 is
It is provided so that it is the largest in each intermediate portion 10a and becomes gradually smaller toward the central portion and both end portions of the nose portion 10.

Even when air inlets 9a and 9b are provided on both sides of the scroll casing 3 as in the present embodiment, the wind speed distribution at the outlet of the blade 6 can be dealt with as in the first embodiment. By setting the nose G, it is possible to reduce the siren sound and reduce the decrease in fan efficiency.

[0043]

The multi-blade blower of the present invention is provided so as to increase the gap at the nose portion which is hit by an air flow having a high wind speed, so that siren noise can be reduced. In addition, since the gap is provided so as to be small in the nose portion where the air flow having a low wind velocity hits, it is possible to reduce the decrease in fan efficiency.

[Brief description of drawings]

FIG. 1 is a perspective view showing a nose portion of a scroll casing.

FIG. 2 is a cross-sectional view of a multi-blade blower.

3 is a cross-sectional view taken along the line AA of FIG.

FIG. 4 is a diagram showing a wind speed distribution at a blade outlet.

FIG. 5 is a sectional view showing the shape of a nose portion.

FIG. 6 is a cross-sectional view showing a conventional nose portion shape and a nose portion shape of this embodiment.

FIG. 7 is a cross-sectional view near the nose portion.

FIG. 8 is a diagram showing a moving direction of a maximum gap position.

9 is a perspective view of a nose portion showing a nose R. FIG.

FIG. 10 is a graph showing the relationship between the nose G and the nose R, the siren sound, and the fan efficiency.

FIG. 11 is a graph showing the relationship between the nose G and the peak value of the siren sound.

FIG. 12 is a graph showing the relationship between the nose R and the peak value of the siren sound.

FIG. 13 is a graph showing a relationship between a siren sound generation frequency and a siren sound peak value.

FIG. 14 is a view showing a nose G in a conventional nose portion shape.

FIG. 15 is a view showing the shape of the nose portion of the present invention.

16 is a sectional view showing the position of the nose G. FIG.

FIG. 17 is a graph showing the relationship between the nose G and the siren sound measured in the FACE mode.

FIG. 18 is a graph showing the relationship between the nose G and the siren sound measured in the FOOT mode.

FIG. 19 is a graph showing the relationship between the nose G and the total pressure measured in the FACE mode.

FIG. 20 is a graph showing the relationship between the nose G and the total pressure measured in the FOOT mode.

FIG. 21 is a graph showing the relationship between the nose G and the fan efficiency in the FACE mode.

FIG. 22 is a graph showing the relationship between the nose G and the fan efficiency in the FOOT mode.

FIG. 23 is a diagram showing a moving direction of a maximum gap position (third embodiment).

FIG. 24 is a sectional view showing the shape of the nose portion (fourth embodiment).

FIG. 25 is a cross-sectional view showing the shape of the nose part of a double-suction multiblade blower (fifth embodiment).

FIG. 26 is a diagram showing a wind speed distribution in the circumferential direction of an impeller.

FIG. 27 is a diagram showing a wind speed distribution when the nose G is increased (prior art).

FIG. 28 is a view showing a case where a nose portion is obliquely provided with respect to an impeller (prior art).

[Explanation of symbols]

 1 multi-blade blower 2 impeller 3 scroll casing 4 motor 6 blade 9 bell mouth (suction port) 9a one suction port 9b the other suction port 10 nose part 10a middle part S ventilation path

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Koji Ito 1-1, Showa-cho, Kariya city, Aichi Prefecture Nihon Denso Co., Ltd. (72) Inventor Teruhiko Kameoka 1-1-cho, Showa-machi, Kariya city, Aichi prefecture Nihon Denso Co., Ltd. Within the corporation

Claims (6)

[Claims] 1. An impeller in which a large number of blades are arranged at regular intervals in the circumferential direction, and a spiral ventilation path is formed around the impeller with a nose portion as a starting point, and the height of the impeller is increased. A scroll casing provided with an air suction port on one side in the direction, and a motor that is arranged on the opposite side of the suction port in the height direction of the impeller and applies a rotational force to the impeller, the nose The part corresponds to the wind speed distribution at the blade outlet,
The radial gap set between the impeller and the impeller is large in the part where the airflow with high wind speed hits, and the gap is small in the part where the airflow with low wind speed hits. A multi-blade blower characterized by that. 2. The multiblade blower according to claim 1, wherein the nose portion is an intermediate portion between the suction port side end portion and the motor side end portion of the nose portion in the height direction of the impeller. The gap is large, and the gap is gradually reduced from the intermediate portion toward the suction port side end portion and the motor side end portion. 3. The multiblade blower according to claim 1 or 2, wherein the gap at the end of the nose portion on the suction port side is L
1, the gap at the motor side end of the nose portion is L2, the gap at the intermediate portion of the nose portion is L3, and the outer diameter of the impeller is D. 0.06 × D <L0 <0.08 × D When L0 satisfying this relationship is used as a reference value, the following relationship is established between L1, L2, L3 and L0. L1> 0.6.times.L0, L2> 0.7.times.L0, and 1.
1 x L0 <L3 <1.7 x L0 4. An impeller comprising a large number of blades arranged at regular intervals in the circumferential direction, and a spiral ventilation path is formed around this impeller with a nose portion as a starting point, and the height of the impeller is increased. A scroll casing provided with air inlets on both sides in the direction, and a motor disposed on the opposite side of one of the inlets in the height direction of the impeller, which gives a rotational force to the impeller, The nose portion corresponds to the wind speed distribution at the blade outlet,
The air gap with a high wind velocity hits a large radial gap with the impeller, and the air gap with a low wind velocity hits the gap. A multi-blade blower characterized by that. 5. The multi-blade blower according to claim 4, wherein the nose portion is between the central portion of the nose portion and one of the suction port side end portions in the height direction of the impeller, and the central portion. And the motor-side end portion, the gap is large in each intermediate portion, and the gap gradually increases from each of the intermediate portions toward the suction port-side end portion, the motor-side end portion, and the central portion. It is characterized in that it is provided in a small shape. 6. The multiblade blower according to claim 4 or 5, wherein the gap at the suction port side end portion of the nose portion is L
1, the gap at the motor side end of the nose portion is L2, the gap at each intermediate portion of the nose portion is L3, and the outer diameter of the impeller is D, and 0.06 × D < L0 <0.08 × D When L0 satisfying this relationship is used as a reference value, the following relationship is established between L1, L2, L3 and L0. L1> 0.6.times.L0, L2> 0.7.times.L0, and 1.
1 x L0 <L3 <1.7 x L0