# Patent

## Title
Multiblade air blower

## Abstract

A multiblade air blower has a multiblade impeller, an orifice, an axially overlaid portion, and an airflow collision prevention device. The multiblade impeller includes a main plate and a blade. The blade is provided at the main plate to form a blade inner periphery. The orifice has an open end and an orifice inner periphery. The open end is positioned toward the main plate from a blade end face. The orifice inner periphery has an inner diameter larger than that of the blade inner periphery, and guides air to the multiblade impeller. The axially overlaid portion is a part where the orifice and the blades are overlaid. The airflow collision prevention device is provided at the blade and at an inner side of the orifice inner periphery. The multiblade air blower suppresses loss of air distribution efficiency and increased noise.

## Background
This application is a continuation of U.S. patent application Ser. No. 12/096,278 filed Jun. 5, 2008 which is incorporated herein by reference in its entirety.


TECHNICAL FIELD
The present invention relates to multiblade air blowers of typically the type employed in ventilation fans installed in ceilings.
BACKGROUND ART
Conventional multiblade air blowers of this type have a structure in which the blade ends and orifice are axially overlaid. (Refer to Patent Document 1.)
The conventional multiblade air blower disclosed in Patent Document 1 is described below with reference to FIGS. 8A and 8B.
As shown in FIGS. 8A and 8B, multiblade air blower 101 includes multiblade fan 105 (hereafter referred to as “fan 105”), scroll casing 107, and orifice 110. Fan 105 includes round end plate 102 and a plurality of multiple blades 104. One end of each of blades 104 is fixed to one face periphery 103 of round end plate 102. The other ends of blades 104 are connected at their outer periphery. Scroll casing 107 houses fan 105, and guides air taken in from front inlet 106 of fan 105 in a centrifugal direction. One corner of inner periphery 108 of the other end of each blade 104 is notched so that tips 109 of blades 104 are overlaid on orifice 110. Orifice 110 configures front inlet 106.
In the above structure, blade inner diameter Db 1 and orifice inner diameter Do1 have the same dimensions, and multiblade air blower 101 has blades 104 that are long in the direction of rotational axis.
Next, another conventional multiblade air blower is disclosed (Refer to Patent Document 2.) The conventional multiblade air blower disclosed in Patent Document 2 is described below with reference to FIG. 9. As shown in FIG. 9, multiblade air blower 201 includes multiblade fan 205, fan motor 213, and scroll casing 207. Fan 205 has multiple blades 204. Fan 205 is fixed to motor shaft 212 of fan motor 213. Fan 205 is housed inside of scroll casing 207, and spiral scroll chamber 214 is formed around the outer periphery of fan 205.
In addition, scroll casing 207 includes intake side case plate 216 and motor side case plate 217. Intake side case plate 216 has air inlet 215. Motor side case plate 217 is positioned at the opposite side of intake side case plate 216 with fan 205 in between. A motor body of fan motor 213 is fixed to motor side case plate 217. Backflow suppression device 218 is provided at an outside of fan diameter Df2. Backflow suppression device 218 suppresses backflow of air in scroll chamber 214 to flow back from scroll chamber 214 to air inlet 215 via an intake space between fan 205 and intake side case plate 216.
This structure suppresses the backflow of air to air inlet 215 from scroll chamber 213 via space 220 between blades 204 and orifice 210. In addition, since blade inner diameter Db2 is smaller than orifice diameter Do2, airflow to tips 209 of blades 204 is enhanced.
Patent Document 1: Japanese Patent Unexamined Publication No. H10-185238
Patent Document 2: Japanese Patent Unexamined Publication No. 2002-161890
SUMMARY OF THE INVENTION
The present invention offers a multiblade air blower that suppresses backflow from a scroll chamber to air intake space of a multiblade impeller and disturbance of airflow at a blade end face. The present invention can thus offer the multiblade air blower that suppresses loss of air distribution efficiency and increased noise.
The multiblade air blower of the present invention includes the multiblade impeller, a casing, an orifice, an axially overlaid portion, and an airflow collision prevention device. The multiblade impeller includes a main plate and blades. The blade has a blade end face, and is provided at the main plate to form a blade inner periphery. The casing houses the multiblade impeller. The orifice includes an open end and an orifice inner periphery. The open end is positioned toward the main plate from the blade end face. The orifice inner periphery has an inner diameter larger than that of the blade inner periphery, and guides air to the multiblade impeller. The axially overlaid portion is a part where the orifice and the blades are overlaid. The blade has the airflow collision prevention device at an inner side of the orifice inner periphery. This structure suppresses backflow of air and airflow disturbance at high air volume. Accordingly, the multiblade air blower that suppresses loss of air distribution efficiency and increased noise is obtained.



BRIEF DESCRIPTION OF DRAWINGS
FIG. 1A is a side sectional view illustrating a multiblade air blower in accordance with a first exemplary embodiment of the present invention.
FIG. 1B is a front view of the multiblade air blower shown in FIG. 1A.
FIG. 2 is a side sectional view of a multiblade air blower in accordance with a second exemplary embodiment of the present invention.
FIG. 3 is a fragmentary perspective view of a multiblade impeller employed in the multiblade air blower show in FIG. 2.
FIG. 4A is a front view of a multiblade impeller employed in a multiblade air blower in accordance with a third exemplary embodiment of the present invention.
FIG. 4B is a rear view of the multiblade impeller shown in FIG. 4A.
FIG. 4C is a fragmentary perspective view of the multiblade impeller shown in FIG. 4A
FIG. 5 is a side sectional view of a multiblade air blower in accordance with a fourth exemplary embodiment of the present invention.
FIG. 6 is a side sectional view of a multiblade air blower in accordance with a fifth exemplary embodiment of the present invention.
FIG. 7 is a side sectional view of a multiblade air blower in accordance with a six exemplary embodiment of the present invention.
FIG. 8A is a side sectional view of a conventional multiblade air blower.
FIG. 8B is a fragmentary side sectional view of the multiblade air blower shown in FIG. 8A.
FIG. 9 is a side sectional view of a conventional multiblade air blower.



REFERENCE MARKS IN THE DRAWINGS


    
    
        1 Multiblade air blower
        2 Main plate
        3 Rotational axis
        4 Blade
        5 Multiblade impeller
        6 Casing
        7 Orifice
        8 Motor
        9 Scroll chamber
        10 Duct
        11 Open end
        12 Blade end face
        13 Axially overlaid portion
        14 Airflow collision prevention device
        15 Intake space
        16 Tongue portion
        17 Notched portion
        18 Forward-tilted portion
        19 Draft portion
        20 Curved portion
        25 Blade inner periphery
        28 Orifice inner periphery
        32 Blade end outer periphery
        33 Orifice outer periphery
        34 Clearance
    
    


DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Exemplary embodiments of the present invention are described below with reference to drawings.
First Exemplary Embodiment
FIGS. 1A and 1B show a multiblade air blower in the first exemplary embodiment of the present invention.
As shown in FIGS. 1A and 1B, multiblade air blower 1 (hereafter referred to as “air blower 1”) includes multiblade impeller 5 (hereafter referred to as “impeller 5”), casing 6, and orifice 7. Impeller 5 includes disc-shaped main plate 2 and a plurality of blades 4. One end of blade 4 is connected to outer periphery 2a of main plate 2, multiple blades 4 are disposed with space 30, which has a predetermined distance, in between. The other ends of blades 4 are connected and fixed to annular outer frame 22. The cross-sectional shape of each of blades 4 vertical to rotational axis 3, about which impeller 5 rotates, is a substantially circular arc. Blade inner periphery 25 is configured with inner peripheral end 24 of each blade 4 provided at outer periphery 2a of main plate 2. Blade outer periphery 27 is configured with outer peripheral end 26 of each blade 4. Impeller 5 is typically 180 mm in outer diameter, and 70 mm in height. In other words, the outer diameter of impeller 5 is the outer diameter of blade outer periphery 27. Casing 6 houses impeller 5, and is a spiral-shaped scroll casing. Orifice 7 guides air passing an inner face of orifice inner periphery 28 to impeller 5. Impeller 5 rotates by transmitting the drive force of electric motor 8, which is connected to impeller 5, to impeller 5. By the rotation of impeller 5, air led to impeller 5 through orifice 7 is fed to scroll chamber 9 via each space 30. The air fed to scroll chamber 9 is discharged to outside of air blower 1 through duct 10 connected to scroll chamber 9.
In air blower 1 shown in FIG. 1B, the cross-sectional shape of blade 4 vertical to rotational axis 3 is a circular arc of radius 14 mm and 1.5 mm in thickness. However, it is apparent that the cross-sectional shape of blade 4 is not limited to the shape shown in FIG. 1B as long as it is a shape that can smoothly change the direction of air flowing into spaces 30 from inner peripheral end 24 of blade 4 to outer peripheral ends 26 of blade 4. For example, blade 4 may have a cross-sectional shape of multiple circular arcs (not illustrated) or an air wheel shape (not illustrated) whose thickness changes from inner peripheral end 24 to outer peripheral end 26.
Orifice inner diameter Do, which is an inner diameter of orifice inner periphery 28, is 170 mm. Blade inner diameter Db, which is an inner diameter of blade inner periphery 25, is 160 mm. Orifice inner diameter Do is thus larger than blade inner diameter Db. In addition, open end 11 of orifice 7 is recessed for 5 mm toward main plate 2 from the level of blade end face 12. This forms axially overlaid portion 13 where orifice 7 and blades 4 are overlaid in the direction of rotational axis 3. Airflow collision prevention device 14 is also provided at orifice 7 side of blade 4. Airflow collision prevention device 14 is provided at an inner side of orifice inner periphery 28. In other words, airflow collision prevention device 14 is provided at a part toward rotational axis 3 from orifice inner periphery 28. Airflow collision prevention device 14 shown in FIG. 1A is configured with notched portion 17 in which a corner of each of blades 4 is notched.
A general characteristic of multiblade air blower 1 is that the main airflow arriving at impeller 5 at high air volume is formed at the side of main plate 2 with respect to the direction of rotational axis 3. Accordingly, airflow in the centrifugal direction is small at orifice 7 side of blades 4.
However, multiblade air blower 1 has airflow collision prevention device 14. Airflow collision prevention device 14 enables air, which is guided by orifice 7 in the direction of rotational axis 3 relative to blade end face 12, to flow to space 30 without being disturbed by corners of blades 4. This results in suppression of noise generated by the disturbance of airflow. At the same time, airflow in the centrifugal direction is also generated at orifice 7 side of blades 4 with respect to rotational axis 3. This achieves multiblade air blower 1 that suppresses noise generation and shows high air distribution efficiency.
In addition, multiblade air blower 1 has axially overlaid portion 13. This suppresses backflow of the air fed from blades 4 to scroll chamber 9 to intake space 15 of impeller 5 again through space 30 or clearance 34 between blades 4 and orifice 7. Accordingly, loss of air distribution efficiency and large noise generation are suppressed. This also eliminates the need for a complicated backflow prevention structure, such as by providing a longer distance between tongue portion 16 and blade outer periphery 27. A shorter distance is thus allowed between tongue portion 16 and blade outer periphery 27, leading to further suppression of loss of air distribution efficiency.
Furthermore, airflow collision prevention device 14 is configured with notched portion 17, as shown in FIG. 1A. If notched portion 17 is too large, the air distribution efficiency decreases due to insufficient area of blades 4 that effect air distribution. On the other hand, if notched portion 17 is too small, airflow collision prevention device 14 will not function effectively. In the light of these facts, notched portion 17 is formed by notching each blade 4 for 5 mm in the direction of rotational axis 3 and 5 mm in the radial direction of impeller 5.
Airflow collision prevention device 14 is thus simply configured by means of notched portion 17 to suppress any increased noise or loss of air distribution efficiency in multiblade air blower 1. At the same time, multiblade air blower 1 is achievable at low cost due to the simple structure of airflow collision prevention device 14.
In the above description, notched portion 17 has a shape 5 mm in the axial direction and 5 mm in the radial direction. However, the shape of notched portion 17 is not limited to this shape. The shape of notched portion 17 can be determined based on the balance between the air distribution efficiency and the airflow collision preventing function.
Axially overlaid portion 13 has the function of suppressing backflow of the air, which is fed to scroll chamber 9 from intake space 15 via space 30, to intake space 15 again via clearance 34. Accordingly, if a percentage of length Ld of axially overlaid portion 13 in length Lb of blade 4 in the axial direction is too large, effective length L=Lb−Ld of blades 4 that generate the main airflow distributed by impeller 5 is shortened. In other words, the air distribution efficiency of impeller 5 decreases if effective length L of blades 4 is short. On the other hand, if the percentage of length Ld in length Lb is too small, the function of suppressing backflow from scroll chamber 9 to intake space 15 does not work effectively. In the light of these facts, axial length Ld of axially overlaid portion 13 is set to 5 mm.
In the above description, axial length Ld of axially overlaid portion 13 is 5 mm. However, axial length Ld of axially overlaid portion 13 is not limited to 5 mm. The axial length Ld of the axially overlaid portion 13 can be determined based on the balance between the air distribution efficiency and the backflow suppressing function.
Second Exemplary Embodiment
FIGS. 2 and 3 show a multiblade air blower in a second exemplary embodiment of the present invention. The same components as those in the first exemplary embodiment are given the same reference marks to omit their detailed descriptions.
Airflow collision prevention device 14, shown in FIGS. 2 and 3, is provided at blade end face 12 side of blade 4, as in the first exemplary embodiment. Airflow collision prevention device 14 in the second exemplary embodiment is configured with forward-tilted portion 18 that is tilted forward in the direction of rotation (direction of arrow x) of impeller 5 at corner 29 of each blade 4 and at the inner side of orifice inner periphery 28. If forward-tilted portion 18 is too large, or the tilting angle is too large, the air distribution efficiency of multiblade air blower 1 decreases due to inhibition of air entering blades 4. If forward-tilted portion 18 or the tilting angle is too small, forward-tilted portion 18 cannot function effectively as airflow collision prevention device 14. In the light of these facts, forward-tilted portion 18 has an area of 5 mm in the direction of rotational axis 3 and 5 mm in the radial direction of impeller 5, and is tilted forward at an angle of 30° in the direction of rotation.
Airflow collision prevention device 14 is thus simply configured by means of forward-tilted portion 18 to prevent collision of airflow and suppress loss of air distribution efficiency, while suppressing any increased noise. In addition, forward-tilted portion 18 guides airflow to space 30. This improves the air distribution efficiency of multiblade air blower 1.
In the above description, forward-tilted portion 18 has a shape 5 mm in the direction of rotational axis 3 and 5 mm in the radial direction of impeller 5, and is tilted forward at an angle of 30° in the direction of rotation. However, the shape of forward-tilted portion 18 is not limited to this shape. The shape of forward-tilted portion 18 can be determined based on the balance between the air distribution efficiency and the airflow collision preventing function.
Third Exemplary Embodiment
FIGS. 4A, 4B, and 4C show a multiblade impeller employed in a multiblade air blower in the third exemplary embodiment of the present invention. The same components as those in the first and second exemplary embodiments are given the same reference marks to omit their detailed descriptions.
As shown in FIGS. 4A, 4B, and 4C, draft portion 19 that has a hole is provided at a part of main plate 2 where forward-tilted portion 18 is projected on main plate 2. The direction of forward-tilted portion 18 projected on main plate 2 is the direction of rotational axis 3. By providing draft portion 19 at multiblade impeller 5, impeller 5 can be molded using molds that only move in the direction of rotational axis 3 when impeller 5 is manufactured using resin molding. More specifically, since forward-tilted portion 18 extends like a window roof, the mold for forming this forward-tilted portion 18 can be released through this draft portion 19 when impeller 5 is molded. This enables molding of impeller 5 by using molds that move only in the direction of rotational axis 3. Accordingly, impeller 5 can be easily manufactured at low cost. Impeller 5 shown in FIGS. 4A, 4B, and 4C includes draft portion 19 that has an outline 3 mm larger than the area of forward-tilted portion 18 projected on main plate 2. This is designed for ease of machining of molds for manufacturing impeller 5 and ease of injection molding of impeller 5.
In the above description, draft portion 19 has the outline 3 mm larger than area of forward-tilted portion 18 projected on main plate 2. However, the shape of draft portion 19 is not limited to this shape. The shape of draft portion 19 can be determined based on ease of machining molds for manufacturing impeller 5, ease of injection molding of impeller 5, and also mechanical strength of impeller 5.
Fourth Exemplary Embodiment
FIG. 5 is a multiblade air blower in the fourth exemplary embodiment of the present invention. The same components as those in the first to third exemplary embodiments are given the same reference marks to omit their detailed descriptions.
As shown in FIG. 5, multiblade air blower 1 has predetermined clearance 34 between blade end outer periphery 32 and orifice outer periphery 33 that is the outer peripheral face of orifice 7. Clearance 34 has a substantially constant distance W. More specifically, blade 4 and orifice 7 are close to each other with the substantially constant distance of clearance 34.
In multiblade air blower 1 shown in FIG. 5, distance W between blade end outer periphery 32 and orifice outer periphery 33 is 3 mm. The dimension of distance W of clearance 34 is determined such that the balance of rotation of impeller 5 does not become uneven due to adhesion of dust and other matter to clearance 34 when multiblade air blower 1 is used as a ventilating fan. In addition, the dimension of distance W of clearance 34 is determined such that impeller 5 does not contact orifice 7 or tongue portion 16 during rotation.
With the above structure, the total extended distance of the closest portion of blade end outer periphery 32 and orifice outer periphery 33 becomes long. This suppresses backflow of air from scroll chamber 9 to intake space 15 through clearance 34 between blades 4 and orifice 7. Consequently, loss of air distribution efficiency of multiblade air blower 1 can be suppressed.
In the above description, distance W of clearance 34 is 3 mm. However, clearance 34 is not limited to 3 mm. The dimension of distance W of clearance 34 can be determined based on elements including the airflow collision preventing function, the balance of impeller 5 affected by adhesion of dust, and prevention of contact of impeller 5 with other surrounding members.
Fifth Exemplary Embodiment
FIG. 6 is a multiblade air blower in the fifth exemplary embodiment of the present invention. The same components as those in the first to fourth exemplary embodiments are given the same reference marks to omit their detailed descriptions.
Multiblade air blower 1 shown in FIG. 6 includes curved portion 20. Curved portion 20 is provided at orifice 7, and is protruding in a direction opposite to multiblade impeller 5. In addition, blade end outer periphery 32 is positioned inside curved portion 20. An inner face of curved portion 20 configure orifice outer periphery 33.
In multiblade air blower 1 shown in FIG. 6, curved portion 20 protrudes in the direction of rotational axis 3 for a dimension of protrusion Le=7 mm.
The above structure makes length Ld of axially overlaid portion 13 of orifice 7 and blade 4 further longer in the axial direction. This further suppresses backflow of air from scroll chamber 9 to intake space 15 via clearance 34 between blades 4 and orifice 7. Accordingly, loss of air distribution efficiency can be further suppressed.
In the above description, the dimension of protrusion Le of curved portion 20 is 7 mm. However, the dimension of protrusion Le of curved portion 20 is not limited to 7 mm. The dimension of protrusion Le of curved portion 20 can be determined based on the balance between the air distribution efficiency and the airflow collision preventing function. In addition, the dimension of protrusion Le can be determined based on other elements such as an outer shape of multiblade air blower 1.
In the fifth exemplary embodiment, blade 4 and orifice 7 may be close to each other with substantially constant distance W of clearance 34, as described in the fourth exemplary embodiment. If clearance 34 has substantially constant distance W, the total extended distance of the closest portion of blade end outer periphery 32 and orifice outer periphery 33 becomes further longer. This further increases the effect of suppressing backflow of air.
Sixth Exemplary Embodiment
FIG. 7 is a multiblade air blower in the sixth exemplary embodiment of the present invention. The same components as those in the first to fifth exemplary embodiments are given the same reference marks to omit their detailed descriptions.
As shown in FIG. 7, blade inner periphery 25 gradually becomes smaller toward main plate 2, and thus blade inner periphery 25 is tilted in multiblade air blower 1. Blade inner diameter Db at a side of main plate 2 is 150 mm, in multiblade air blower 1 shown in FIG. 7. Blade inner diameter Db at a side of orifice 7 is 160 mm.
In general, the main airflow is formed at the side of orifice 7 in the direction of rotational axis 3 of impeller 5 when air volume is low. However, the above structure enhances air to flow to the side of main plate 2 in the direction of rotational axis 3. This improves the air distribution efficiency of multiblade air blower 1.
In the above description, blade inner diameter Db at the side of main plate 2 is 150 mm. However, blade inner diameter Db at the side of main plate 2 is not limited to 150 mm. Blade inner diameter Db at the side of main plate 2 can be determined based characteristics of the multiblade air blower such as the air distribution efficiency and noise.
In the sixth exemplary embodiment, blade 4 and orifice 7 may be made close to each other with substantially constant distance W of clearance 34, as described in the fourth exemplary embodiment. In addition, orifice 7 may have curved portion 20 described in the fifth exemplary embodiment. By adding the structures described in the fourth and fifth exemplary embodiments to multiblade air blower 1 in the sixth exemplary embodiment, the present invention can offer multiblade air blower 1 with further improved characteristics including the air distribution efficiency.
INDUSTRIAL APPLICABILITY
The present invention suppresses backflow of air from a scroll chamber to a blade inner periphery via a space between blades or a space between the blades and an orifice, and also suppresses airflow disturbance at end faces of the blades. Accordingly, the present invention offers a multiblade air blower characterized by suppression of loss of air distribution efficiency and increased noise, which can be manufactured at low cost.

## Claims

1. A multiblade air blower comprising:
a multiblade impeller including:
a main plate; and
a plurality of blades, each of the plurality of blades has a blade end face, the plurality of blades being provided at the main plate, and the plurality of blades forming a blade inner periphery, the blade end face being an elongated portion contiguous to the blade;

a casing housing the multiblade impeller;
an orifice including:
an open end, an axial distance between an axially innermost position of the open end of the orifice and the main plate being smaller than an axial distance between an outermost end portion of the blade end face and the main plate; and
an orifice inner periphery having an inner diameter larger than that of an inner diameter of the blade inner periphery, the orifice inner periphery guiding air to the multiblade impeller; and
an airflow collision prevention device provided on each of the plurality of blades at an inner side of the orifice inner periphery, the airflow collision prevention device being a notched portion provided at a first corner between the blade end face and a blade inner peripheral end of each of the plurality of blades,


wherein a blade inner diameter is composed of a circumference connecting a second corner between the blade end face and an oblique line on each of the plurality of blades creating the notched portion of each of the plurality of blades, and the blade inner diameter and the orifice inner diameter have the same dimensions.

2. The multiblade air blower of claim 1,
wherein an axially overlaid portion where the orifice and each of the plurality of blades are overlaid is provided at a depression formed in a region from the second corner of the blade end face and an inside corner of an outermost end portion of the blade end face.

3. The multiblade air blower of claim 1 further comprising an annular outer frame, one end of the plurality of blades being provided at the main plate and an other end of the plurality of the blades being fixed to the annular outer frame, wherein the annular outer frame is disposed on a blade outer periphery of each of the plurality of blades outside a third corner between the blade outer periphery and an outermost end portion of the blade end face.

4. The multiblade air blower of claim 1 further comprising a curved portion provided at the orifice and protruding in a direction opposite to the multiblade impeller, a blade end outer periphery being provided at an inside corner of the blade end face, the blade end outer periphery being provided inside the curved portion, a distance of a clearance between the blade end outer periphery and the curved portion being constant.

5. The multiblade air blower of claim 1,
wherein the blade inner periphery gradually becomes smaller from the notched portion toward the main plate.

6. The multiblade air blower of claim 1,
wherein each of the plurality of the blade includes a first corner, a second corner, a third corner and a fourth corner in inner peripheral,
wherein the first corner and a second corner is connected by an oblique line,
wherein the second corner and the third corner is connected by a horizontal line,
wherein the third corner and the fourth corner is connected by a vertical line, the vertical line being parallel to an axial direction, and
wherein the blade end face extends horizontally from the fourth corner to blade outer periphery.

7. The multiblade air blower of claim 1,
wherein the blade includes a first side, a second side, a third side and a fourth side,
wherein the first side is the blade inner periphery,
wherein the second side is an outwardly inclined line extending from an end of the first side,
wherein the third side is a horizontal line outward extending from an end of the second side,
wherein the fourth side is a vertical line parallel to a rotational axis, extending from an end of the third side to opposite side of the main plate, and
wherein the blade outer periphery is a horizontal line outward extended from an end of the fourth side.

8. A multiblade air blower comprising:
a multiblade impeller including:
a main plate; and
a plurality of blades, each of the plurality of blades has a blade end face, the plurality of blades being provided at the main plate, and the plurality of blades forming a blade inner periphery, the blade end face being an elongated portion contiguous to the blade;

a casing housing the multiblade impeller;
an orifice including:
an open end, an axial distance between an axially innermost position of the open end of the orifice and the main plate being smaller than an axial distance between an outermost end portion of the blade end face and the main plate; and
an orifice inner periphery having an inner diameter larger than that of an inner diameter of the blade inner periphery, the orifice inner periphery guiding air to the multiblade impeller; and

an airflow collision prevention device provided on each of the plurality of blades at an inner side of the orifice inner periphery viewed from the direction perpendicular to the orifice inner diameter, the airflow collision prevention device being a notched portion provided at a first corner between the blade end face and a blade inner peripheral end of each of the plurality of blades, and the airflow collision prevention device comprises a straight edge connecting the blade end face and the blade inner peripheral end of each of the plurality of blades.

9. The multiblade air blower of claim 8,
wherein the blade inner periphery gradually becomes smaller from the notched portion toward the main plate.

10. A multiblade air blower comprising:
a multiblade impeller including:
a main plate; and
a plurality of blades, each of the plurality of blades has a blade end face, the plurality of blades being provided at the main plate, and the plurality of blades forming a blade inner periphery, the blade end face being an elongated portion contiguous to the blade;

a casing housing the multiblade impeller;
an orifice including:
an open end, an axial distance between an axially innermost position of the open end of the orifice and the main plate being smaller than an axial distance between an outermost end portion of the blade end face and the main plate; and
an orifice inner periphery having an inner diameter larger than that of an inner diameter of the blade inner periphery, the orifice inner periphery guiding air to the multiblade impeller; and

an airflow collision prevention device provided on each of the plurality of blades at an inner side of the orifice inner periphery viewed from the direction perpendicular to the orifice inner diameter, the airflow collision prevention device being a notched portion provided at a first corner between the blade end face and a blade inner peripheral end of each of the plurality of blades, and
wherein the blade inner periphery gradually becomes smaller from the notched portion toward the main plate.