JPH0893684A - Centrifugal blower - Google Patents

Abstract

(57) [Summary] (Modified) [Purpose] To obtain a centrifugal blower that can cool an electric motor more efficiently and has higher efficiency. [Structure] Centrifugal fan unit F having a cylindrical outer diameter, having an intake port 3 in the central portion on one side and an exhaust port 4 on the other side.
And a cylindrical casing C accommodating the centrifugal fan unit F
And an electric motor for accommodating and arranging the centrifugal fan portion F on the intake port 3 side in the tubular casing C, having an outer diameter smaller than the inner diameter of the tubular casing C, and rotatingly driving the centrifugal fan portion C. M and. The side of the cylindrical casing C on which the electric motor M is arranged is the suction port 1, and the side of the cylindrical casing C on which the centrifugal fan part F is arranged is the discharge port 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is provided with a centrifugal fan section and an electric motor for rotationally driving the centrifugal fan section in a cylindrical casing, wherein one opening of the cylindrical casing serves as a suction port and the other opening serves as a discharge port. Centrifugal blower.

[0002]

2. Description of the Related Art A centrifugal fan portion of a centrifugal blower is provided with an intake port at a central portion on one side thereof, and discharges a pressurized fluid in a radial direction. At this time, the electric motor that rotationally drives the centrifugal fan is arranged and fixed on the side opposite to the intake port of the centrifugal fan. Although this configuration is a general configuration for a centrifugal blower, the discharge port of the centrifugal fan must be provided with a structural part such as a volute, which causes a problem that the entire blower becomes large in the radial direction.

Therefore, there has been proposed a structure in which a centrifugal fan section and an electric motor are arranged inside a cylindrical casing, and one opening of this cylindrical casing is used as a suction port and the other opening is used as a discharge port. . In this case, the intake port of the centrifugal fan unit is made to correspond to one opening of the cylindrical casing, and the electric motor is arranged on the side opposite to the intake port of the centrifugal fan unit. The outer diameter of the electric motor is configured to be smaller than the inner diameter of the cylindrical casing, and due to this difference in diameter, a discharge passage for the fluid pressurized by the centrifugal fan is formed between the outer diameter of the electric motor and the inner diameter of the cylindrical casing. To do. As a result, when the centrifugal fan part is driven to rotate by the electric motor, the fluid is sucked from the suction port of the cylindrical casing, the gas flows into the centrifugal fan part from the suction port of the centrifugal fan part, and the fluid is pressurized. Is discharged from the discharge port of the cylindrical casing through the discharge flow path.

References for this type of technology include Japanese Patent Laid-Open Nos. 63-100298 and 63-100299.
There is a gazette.

[0005]

As described above, the centrifugal fan and the electric motor arranged in the cylindrical casing can reduce the diameter of the blower as a whole, and further, the suction port and the discharge port in the axial direction. Is effective because it can be placed. However, the conventional one directly incorporates the conventional basic configuration in which the electric motor is arranged on the discharge port side of the centrifugal fan.

As is well known, the centrifugal fan section and the electric motor radiate a considerable amount of heat. And, as compared with a centrifugal fan, an electric motor is generally weak against heat.

In constructing this type of centrifugal blower, how to efficiently dissipate this heat and to cool it is an important issue.

An object of the present invention is to obtain a centrifugal blower which can cool an electric motor more efficiently.

Another object of the present invention is to obtain a centrifugal fan with higher efficiency.

[0010]

The present invention has been made in order to achieve the above-mentioned object, and is characterized in that a centrifugal fan unit and an electric motor are arranged in a tubular casing. The electric motor is located on the intake side of the fan. Then, an intake passage is formed between the outer diameter of the electric motor and the inner diameter of the cylindrical casing, the side of the cylindrical casing on which the electric motor is arranged serves as the suction port, and the other side of the cylindrical casing serves as the discharge port. is there.

According to a preferred embodiment of the present invention, a rectifying plate is provided in at least a part of the intake passage. This rectifying plate may be formed integrally with the outer frame of the electric motor, or may also serve as a fixing member for fixing the electric motor inside the tubular casing.

Further, according to a preferred embodiment of the present invention, at least the suction port of the suction port and the discharge port have a diameter smaller than the inner diameter of the cylindrical casing.

According to a preferred embodiment of the present invention, the surface of the centrifugal fan section of the electric motor facing the intake port has a shape in which the flow path of the fluid sucked into the suction section gradually decreases in cross section. To do.

[0014]

According to the above-mentioned structure, by rotating the centrifugal fan portion by the electric motor, the fluid flows in through the suction port of the cylindrical casing and is formed between the outer diameter of the electric motor and the inner diameter of the cylindrical casing. It reaches the intake port of the centrifugal fan unit through the intake flow path. The fluid that has flowed into the intake port of the centrifugal fan unit is pressurized by the centrifugal fan, discharged from the exhaust port, and discharged from the discharge port provided on the other side of the cylindrical casing.

Therefore, the electric motor is first cooled by the gas of lower temperature sucked from the suction port, and the electric motor is cooled more effectively and efficiently.

In a centrifugal fan, it is generally known that when the temperature of the suction fluid rises, the fluid adiabatically compresses and the discharge pressure rises. According to the above configuration, the electric motor is arranged on the suction side of the centrifugal fan unit, and the gas flowing along the surface of the electric motor M efficiently absorbs the heat generated by the electric motor due to the action of the tubular casing, and the temperature Is a higher value. Therefore, the temperature of the gas flowing into the centrifugal fan unit has a higher value, and from the above, it can be expected that the discharge pressure becomes higher. From this point,
The above arrangement is extremely rational.

Further, if a rectifying plate is arranged in the intake passage formed between the outer diameter of the electric motor and the inner diameter of the cylindrical casing, the gas flowing into the centrifugal fan can be rectified in advance, so that the gas can be rectified. The suction flow is stable, and a more efficient centrifugal blower can be obtained. Also here,
If this rectifying plate is attached to the electric motor, the rectifying plate acts as a cooling fin of the electric motor, and the cooling efficiency of the electric motor is further increased.

Further, by making the suction port smaller than the inner diameter of the cylindrical casing, the gas sucked from the suction port is rapidly expanded and decelerated, so that the turbulence of the suction flow of the gas is alleviated. It is possible to obtain an efficient centrifugal blower. Furthermore, if this is combined with the above-mentioned rectifying plate, the suction flow of gas into the centrifugal fan section will be remarkably stable, and further improvement in efficiency can be expected.

Further, the surface of the centrifugal fan part of the electric motor facing the intake port is shaped so that the flow path of gas sucked into the intake port is gradually reduced in cross-section. Before being sucked in, the gas is contracted and accelerated. As a result, flow separation can be prevented and turbulence can be prevented from occurring, so that an efficient centrifugal blower can be obtained.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a cut front view of a centrifugal blower showing an embodiment of the present invention, and FIG. 2 is a cut side view showing this FIG. 1 cut along the line 2-2. The external appearance of this centrifugal blower has a substantially cylindrical shape, and a suction port 1 having a small diameter is formed on one surface in the axial direction and a discharge port 2 is formed on the other side. F is a centrifugal fan part having a cylindrical outer shape, which is provided with an intake port 3 on one side surface and an exhaust port 4 on the other side surface, and M is an electric motor. C is a cylindrical casing that houses the centrifugal fan unit F and the electric motor M therein. When disposing the centrifugal fan unit F and the electric motor M inside the casing C, the electric motor M is arranged on the intake port 3 side of the centrifugal fan unit F. The cylindrical casing C may be integrated, but in consideration of the assemblability, for example, the cylindrical casing C is divided into two in the axial direction or appropriately divided into a plurality of parts.

The outer diameter of the centrifugal fan portion F is substantially the same as the inner shape of the casing C. The centrifugal fan portion F is fitted and fixed in the casing C, and if necessary, fixed by a fixing means such as a screw. There is. The electric motor M has an outer diameter smaller than the inner diameter of the casing C, and is fixedly arranged in the central portion of the casing C by a fixed plate 5 that also serves as a flow straightening plate. As shown in FIG. 2, the fixed plate 5 that also serves as the current plate is an outer frame 9 of the electric motor M.
In addition, a plurality of the motors M are radially provided, whereby the electric motor M is stably arranged and fixed in the central portion of the casing C.

Reference numerals 6a and 6b denote centrifugal impellers constituting the centrifugal fan unit F. In the case of this embodiment, the impeller has a two-stage structure. 7 is these impellers 6a, 6
It is an impeller casing which accommodates b. Impeller 6a, 6
Each of b is fixed to the rotating shaft 8 of the electric motor M.

In the case of this embodiment, the electric motor M employs a fully closed type induction motor, 9 is an outer frame of the electric motor M, and 10 is a stator fitted inside the outer frame 9. The stator winding 11 is provided. Reference numeral 12 denotes a rotor arranged inside the stator 10 and fixed to the rotary shaft 8. 13,
14 is a load side bracket, an anti-load side bracket,
Rotary bearings 15 and 1 provided on the brackets 13 and 14, respectively.
A rotary shaft 8 is rotatably held via 6. This electric motor M has the same structure as a general induction motor, but differs from a general induction motor in that the anti-load side bracket 14 is provided with a thrust bearing 17 for supporting the thrust load of the rotary shaft 8.

By disposing the electric motor M in the central portion of the casing C, intake passages 20a, 20b, 20c are formed around the electric motor M with the inner diameter of the casing C. As a matter of course, a sufficient space required by the centrifugal fan unit F is secured between the intake port 3 of the centrifugal fan unit F and the load side bracket 13 of the electric motor M. At this time, the surface of the centrifugal fan portion F of the electric motor M on the side facing the intake port 3, that is, the outer surface of the load-side bracket 13 has a flow path cross section in which the flow path of the gas sucked into the suction port 3 is gradually increased. Is reduced. The shape may be linearly reduced, or may be curvilinearly reduced. Desirably, it is curvilinearly reduced as shown in this embodiment.

When the electric motor M is rotationally driven and the impellers 6a and 6b are rotationally driven with the above structure, gas is sucked from the intake port 3. As a result, gas is sucked from the suction port 1. The gas sucked from the suction port 1 is separated from the outer frame 9 of the electric motor M and the casing C by the intake passage 20a formed by the inner diameter of the casing C and the anti-load side bracket 14 of the electric motor M as shown by the arrow. Is distributed to the intake flow passage 20b formed by the above, is merged in the intake flow passage 20c formed by the casing C and the impeller casing 7 of the centrifugal fan unit F, and is guided to the intake port 3 of the centrifugal fan unit F. The gas flowing in from the intake port 3 of the centrifugal fan F is pressurized by the impeller 6 a, then pressurized by the impeller 6 b, and discharged from the exhaust port 4. Then, it is guided to the discharge port 2 by the casing C and discharged from here.

With the above arrangement, the electric motor M is first cooled by the gas of lower temperature sucked from the suction port 1, and the electric motor M is cooled more effectively and efficiently. . As described above, the electric motor M is weaker to heat than the centrifugal fan unit F. With the above-described configuration, the electric motor M, which requires more cooling, can be cooled with the gas having a lower temperature, and the arrangement is extremely rational.

It is generally known that in a centrifugal fan, when the temperature of the suction fluid rises, the fluid adiabatically compresses and the discharge pressure rises. In the case of this embodiment, the electric motor M is arranged on the suction side of the centrifugal fan unit F, and the gas flowing along the surface of the electric motor M by the action of the casing C efficiently absorbs the heat generated by the electric motor M, and its temperature is reduced. Is a higher value. Therefore, the temperature of the gas flowing into the centrifugal fan unit F has a higher value, and therefore, it can be expected that the discharge pressure becomes higher. From this point,
The above arrangement is extremely rational.

Further, in the above-described embodiment, since the straightening vane 5 is arranged in the intake passage 20b formed between the outer frame 9 of the electric motor M and the inner diameter of the cylindrical casing C,
The gas flowing into the centrifugal fan unit F can be rectified in advance, the suction flow of the gas is stabilized, and a more efficient centrifugal blower can be obtained. Further, here, since the current plate 5 is attached to the electric motor M, the current plate 5 functions as a cooling fin of the electric motor M, and the cooling efficiency of the electric motor M is further increased.

Further, since the suction port 1 is smaller than the inner diameter of the cylindrical casing C, the gas sucked from the suction port 1 expands in the casing C and is decelerated. Therefore, the turbulence of the gas suction flow is alleviated, and a more efficient centrifugal blower can be obtained. Furthermore, according to the embodiment, the combination of this and the flow regulating plate 5 makes the suction flow of the gas into the centrifugal fan unit F extremely stable,
It is possible to further improve efficiency.

Furthermore, by making the surface of the centrifugal fan portion of the electric motor facing the intake port into a shape in which the flow path of the gas sucked into the intake port is gradually reduced in cross section, the centrifugal fan part is formed. Before being sucked in, the gas is contracted and accelerated. As a result, flow separation can be prevented and turbulence can be prevented from occurring, so that an efficient centrifugal blower can be obtained.

Further, according to the above embodiment, the electric motor M
The thrust bearing 17 is arranged at the shaft end on the side opposite to the load.
The centrifugal blower unit F drives the impellers 6a and 6b to rotate, thereby generating a thrust force T that causes the impellers 6a and 6b to move to the intake port 3 side. The thrust force T tends to increase due to an increase in the discharge air volume of the centrifugal blower F, an increase in the discharge pressure, or an increase in the number of revolutions for these reasons. The thrust bearing 17 supports the thrust force and reduces the load on the bearings 15 and 16. By adopting the configuration in which the electric motor M is arranged on the intake port 3 side of the centrifugal fan unit F, the thrust bearing 17 can be arranged on the anti-load side bracket 14 of the electric motor M, and the thrust force can be supported with a simple structure. , As a result bearing 15,
The effect of being able to reduce the burden of 16 can be obtained,
From this point of view, it can be said that the arrangement of the electric motor M and the centrifugal fan unit F in the embodiment is extremely rational.

FIG. 3 is an enlarged view of the bearing portion on the anti-load side of FIG. 1, and shows the case where the pivot bearing is adopted as the thrust bearing 17. That is, the metal 17a is arranged in the anti-load side bracket 14, the conical hole 17b is opened in the center of the end of the rotary shaft 8, and the sphere 17c is arranged between the conical hole 17b and the metal 17a. And the force T
It was intended to receive.

FIG. 4 shows another example of the thrust bearing 17, which is called a pad type, and is a ring-shaped pad made of a material such as carbon between the end surface of the rotary shaft 8 and the metal 17a. 17d is arranged to receive the thrust force T on the surface.

FIG. 5 shows still another example of the thrust bearing 17, which is a modification of the pivot bearing 17 shown in FIG. 3, in which a receiving plate 17e is provided with a protrusion 17f, which is provided on the rotary shaft 8. The thrust force T is received by contacting the shaft end of the.

The thrust bearing 17 is not limited to the above, but various types can be used.

The configuration of the above embodiment is also desirable in terms of cooling the bearing. That is, the gas sucked from the suction port 1 is
At this time, the anti-load side bracket 14 and the accompanying anti-load side bearing 16 and thrust bearing 17 are cooled. Further, the gas suction flow passes through the outer frame 9 of the electric motor M and the intake flow path 20b formed by the cylindrical casing C,
The electric motor 5 is cooled. The suction flow that has passed through the intake flow path 20b on the outer periphery of the outer frame 9 of the electric motor M further flows along the load side bracket 13 and flows into the intake port 3 of the centrifugal fan unit F, and at this time, the load side bracket 13 And the bearing 15 attached thereto is cooled. As described above, in the embodiment, due to the suction pressure of the centrifugal blower section F, the suction flow is such that the non-load side brackets 14 and 13 on the load side.
Flowing along. As a result, the bearings are appropriately cooled, and the load-side bearing 15 and the anti-load-side bearing 16 receive the radial load, and the thrust bearing 17 receives the axial thrust load. The bearing load per area is reduced and the life of the bearing can be extended.

FIG. 6 is a cut-away front view showing another embodiment of the present invention. The load side bracket 13 and the anti-load side bracket 14 of the electric motor M are also provided with fins 13a and 14a in consideration of rectification and cooling. It is provided. Further, the casing C is configured so that the cross section thereof gradually increases on both the suction port 1 side and the discharge port 2 side. FIG. 7 shows the anti-load side bracket 14, which is indicated by an arrow A1 in FIG.
It is the perspective view seen from the side. FIG. 8 shows the load side bracket 13.
FIG. 7 is a perspective view seen from the arrow A2 side in FIG. FIG. 9 is an enlarged sectional view showing the positional relationship between the bracket fins 13a of the load side bracket 13 and the impeller 6a of the centrifugal blower section F.

As shown in FIGS. 6 and 7, the central portion of the surface of the anti-load side bracket 14 has a projection 1 having a spherical tip.
4b, and the bracket fins 1 for cooling and rectifying are radially formed from the protrusions 14b as shown in FIG.
4a extends toward the outer frame 9 side. Generally, gas is introduced into the suction port 1 through various pipes. The gas flow sucked from this pipe has the highest flow velocity near its center.

According to the structure of this embodiment, the flow near the center of the projection 14b is provided on the anti-load bracket 14.
It hits and becomes a stagnation state. Then, the gas flow having a relatively low flow velocity around it is guided to the outer peripheral side of the outer frame 9 of the electric motor M by the radially extending fins 14a. As a result, the gas suction flow is smoothed, the performance is less deteriorated, and the flow is guided to the outside of the outer frame 9 of the electric motor M.

When a turbulent flow of gas flows into the centrifugal fan section F, the impeller efficiency drops sharply. According to this embodiment, as shown in FIGS. 6 and 8, fins 13a for rectifying the turbulence of the flow immediately before the impeller flow is attached to the surface of the load side bracket 13. The number of the fins 13a is set to be relatively prime to the number of the blades of the impellers 6a and 6b in order to avoid acoustic interference with the impeller 2.
In this way, the cooling performance of the load side bracket 13 can be improved and the load side bearing 15 can be cooled more efficiently. When the outlet portion of the fin 13a is too close to the intake port 3 of the centrifugal fan unit F, it interferes with the pressure fluctuation near the inlet of the impeller 6a generated due to the finite number of blades of the impeller 6a, which causes noise. appear. Therefore, as shown in FIG. 9, the outlet portion of the fin 13a is located inside the impeller intake port 3. Furthermore, in order to prevent separation of the intake air flow that flows into the impellers 6a and 6b, the load side bracket 1
The shape of 3 is a smooth shape toward the impeller intake port 3, as shown in FIG.

FIG. 10 is a further improvement of the one shown in FIG. 6, in which the fin 14 of the anti-load side bracket 14 is shown.
FIG. 9A is a cross-sectional view when the shapes of a and fins 13a of the load side bracket 13 are changed. That is, the fins 14a of the anti-load side bracket 14 and the load side bracket 1
The end portions of the fins 13a of No. 3 are extended to the casing C and connected to the casing C to reinforce the support of the electric motor M.

FIG. 11 is a sectional view showing still another embodiment, in which a current plate 5 is additionally arranged in an intake passage 20b constituted by the inner diameter of the casing C and the outer diameter of the outer frame 9. . FIG. 12 is a perspective view of the outer frame 9 and the anti-load side bracket 14 of the electric motor M when FIG. 11 is viewed from the direction of arrow A3. In this embodiment, since the length of the intake flow passage 20b on the outer periphery of the outer frame 9 of the electric motor M is long, a rectifying plate 5 is provided to rectify the suction flow in order to prevent the performance from deteriorating due to the occurrence of disturbances. I am trying to The number of the rectifying plates 5 is the same as the number of the fins 13a on the load side bracket 13, and the distance between the two is as small as possible. The current plate 5 has a linear shape in the axial direction, and the distance between the fins 14a of the anti-load side bracket 14 and the current plate 5 is minimized.

FIG. 13 is a sectional view showing still another embodiment. In this embodiment, when the electric motor M and the centrifugal fan portion F are housed in the casing C, the sound absorbing material 21 is provided on the entire inner peripheral surface of the casing C. Is provided, and the electric motor M and the centrifugal fan unit F are surrounded by the casing C via the sound absorbing material 21,
This is intended to reduce noise. In this case, in particular, since the sound absorbing material 21 is arranged between the casing C and the centrifugal fan unit F, the high-frequency components of the impellers 6a and 6b are absorbed.

In the above embodiments, the centrifugal fan unit F has the two-stage structure of the impellers 6a and 6b. However, the number of stages is not limited in the present invention, and the one-stage structure may be used. Alternatively, it may have a multi-stage configuration of three or more stages.

Further, although the case where the casing C is cylindrical has been described as an example, the casing C need not be circular in particular as long as it is cylindrical, and may be polygonal, for example. Furthermore, the case where the suction port 1 and the discharge port 2 are opened in the axial direction with respect to the casing C has been described, but this may be, for example, at a right angle to the axial direction or in an oblique direction, There is no limit to the direction.

[0046]

As is apparent from the above description, according to the present invention, the electric motor can be cooled more efficiently,
A more efficient centrifugal blower can be obtained.

[Brief description of drawings]

FIG. 1 is a cutaway front view showing one embodiment of the present invention.

FIG. 2 is a side view showing FIG. 1 taken along line 2-2.

FIG. 3 is a partially cutaway front view showing the anti-load side bearing portion of FIG. 1 in an enlarged manner.

FIG. 4 is a partial front view showing another example of the anti-load side bearing portion.

FIG. 5 is a partial front view showing still another example of the anti-load side bearing portion.

FIG. 6 is a cut front view showing a second embodiment of the present invention.

7 is a perspective view showing an anti-load side bracket of the electric motor in FIG.

8 is a perspective view showing a load side bracket of the electric motor in FIG.

9 is an enlarged cross-sectional view showing the positional relationship between the load side bracket of the electric motor and the impeller of the centrifugal fan unit in FIG.

FIG. 10 is a cut front view showing a third embodiment of the present invention.

FIG. 11 is a cut front view showing a fourth embodiment of the present invention.

12 is a perspective view of an anti-load side bracket and an outer frame of the electric motor in FIG.

FIG. 13 is a cut front view showing a fifth embodiment of the present invention.

[Explanation of symbols]

F ... Centrifugal fan part, M ... Electric motor, C ... Cylindrical casing, 1 ... Suction port, 2 ... Discharge port, 3 ... Intake port, 4 ... Exhaust port, 5 ... Fixed plate (rectifying plate), 6a, 6b ... Centrifugal Impeller,
7 ... Impeller casing, 8 ... Rotating shaft, 9 ... Outer frame, 13 ...
Load side bracket, 14 ... Anti-load side bracket, 15,
16 ... Rotary bearing, 17 ... Thrust bearing, 20a, 20
b, 20c ... Intake passage, 21 ... Sound absorbing material

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kengo Hasegawa 7-1, 1-1 Higashi Narashino, Narashino City, Chiba Prefecture Hitachi Keiyo Engineering Co., Ltd. (72) Masayuki Fujio 7-1, 1-1 Higashi Narashino, Narashino City, Chiba Stocks Hitachi Industrial Products Division

Claims (8)

[Claims] 1. A centrifugal fan part having an outer diameter of a cylindrical shape, having an intake port at one side center part and an exhaust port at the other side part, and a tubular casing accommodating the centrifugal fan part. An electric motor that is housed and arranged in the tubular casing on the intake port side of the centrifugal fan portion, has an outer diameter that is smaller than the inner diameter of the tubular casing, and that rotationally drives the centrifugal fan portion. A centrifugal blower in which the side of the tubular casing on which the electric motor is arranged serves as a suction port, and the side of the tubular casing on which the centrifugal fan unit is arranged serves as a discharge port. 2. The centrifugal blower according to claim 1, wherein an intake passage of the centrifugal fan portion is formed between the inner diameter of the cylindrical casing and the outer diameter of the electric motor. 3. The centrifugal blower according to claim 2, wherein at least a part of the intake passage is provided with a rectifying plate that rectifies the flow of gas passing through the intake passage. 4. The centrifugal blower according to claim 3, wherein the current plate is formed integrally with the outer frame of the electric motor. 5. The straightening plate also serves as a fixing member for fixing the electric motor inside the cylindrical casing.
The described centrifugal blower. 6. The centrifugal blower according to claim 1, wherein the suction port has a diameter smaller than the inner diameter of the cylindrical casing. 7. The centrifugal blower according to claim 1, wherein both the suction port and the discharge port are smaller in diameter than the inner diameter of the cylindrical casing. 8. The surface of the centrifugal fan portion of the electric motor facing the air inlet has a shape in which the flow passage of gas sucked into the suction inlet gradually decreases in cross section. 1. The centrifugal blower according to 1.