Centrifugal fan and air conditioner provided with the same

In a centrifugal fan, when an angle defined by a tangential line to a camber line at an intersection point between the camber line and an arc around a rotation axis, and a tangential line to the arc at the intersection point on a blade cross section passing a front edge and a rear edge of a blade is a blade angle, the blade has at least one of a decreasing shape and a fixed shape. The decreasing shape is such that the blade angle decreases as the intersection point is shifted toward the rear edge on the camber line on a front edge side portion of a shroud side blade cross section. The fixed shape is such that the blade angle is fixed, even if the intersection point is shifted toward the rear edge on the camber line on the front edge side portion of the shroud-side blade cross section.

TECHNICAL FIELD

The present invention relates to a centrifugal fan, and an air conditioner provided with the same.

BACKGROUND ART

Conventionally, a centrifugal fan has been used as a fan of an indoor unit of an air conditioner. In the centrifugal fan, when an impeller is rotated by a fan motor, air is sucked into a case of the indoor unit through a suction port of the indoor unit. The sucked air is guided to an air suction port of a shroud of the impeller along an inner circumferential surface of a bell mouth. In the following, a stream of air guided to the air suction port along the inner circumferential surface of the bell mouth is called as a main stream.

The main stream of air is ejected to the outside (in a direction to be away from a rotation axis of the impeller) from the impeller by a plurality of blades arranged circumferentially between a hub and the shroud. A main part of the air ejected from the impeller is blown into the room through a blow-out port of the indoor unit. However, a part of the air ejected from the impeller is refluxed toward the bell mouth through a space between the outer circumferential surface of the shroud and the case within the case of the indoor unit. The refluxed air merges with the main stream while passing through a gap between the outer circumferential surface of the bell mouth and the inner circumferential surface of the shroud. In the following, a stream of air that is refluxed as described above, and merges with the main stream while passing through a gap between the outer circumferential surface of the bell mouth and the inner circumferential surface of the shroud is called as a reflux stream (a leakage stream).

The aforementioned reflux stream has a high air velocity. Therefore, when the reflux stream passing through the gap collides against the front edges of the blades, noise increases. Further, the reflux stream has large fluctuations in air velocity (air velocity is largely fluctuated). Therefore, the pressure generated on the blade surfaces near the reflux stream is likely to be unstable. Fluctuations in pressure on the blade surfaces are a factor of noise increase.

In particular, in a centrifugal fan having a reduced thickness accompanied by reduction of the thickness of an indoor unit, the channel of the main stream is narrowed. However, it is necessary to secure substantially the same volume of the main stream as the volume in an indoor unit in which the thickness is not reduced. In the centrifugal fan having a reduced thickness, the volume of the reflux stream tends to increase. Therefore, the ratio of the reflux stream with respect to the main stream increases. As a result, the influence of the reflux stream on the main stream increases. In view of the above, it is important to suppress the influence by the reflux stream.

Patent Literature 1 proposes a technique for reducing noise by reducing a reflux stream (a leakage stream). The centrifugal fan disclosed in Patent Literature 1 is provided with a plurality of main blades disposed between a hub and a shroud, and a plurality of small blades formed on the outer circumferential surface of the shroud, wherein the camber line of a shroud-side blade element of each of the main blades is concaved toward the pressure surface, or a front-edge side portion of a shroud-side blade element of each of the main blades with respect to the camber line is tilted in the rotating direction. Patent Literature 1 describes that a pressure raising effect by the small blades reduces a pressure difference between the region on the back surface of the shroud and the region of the bell mouth channel. This makes it possible to reduce the flow rate of the reflux stream, and to reduce the air velocity on the shroud side portion of the front-edge-side portion of each of the main blades. Further, Patent Literature 1 describes forming the shape of the main blades as described above allows for the streams to follow the main blades. Patent Literature 1 describes the aforementioned configuration makes it possible to reduce noise.

However, in the configuration of the centrifugal fan disclosed in Patent Literature 1, it may be impossible to sufficiently reduce the volume of the reflux stream, and it may be impossible to obtain a sufficient noise reduction effect. Further, in the configuration of the centrifugal fan disclosed in Patent Literature 1, the weight of the fan may increase by addition of the small blades, and the cost may also increase.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

An object of the invention is to provide a centrifugal fan that enables to reduce noise due to a reflux stream, while suppressing an increase in the weight and the cost.

A centrifugal fan of the present invention comprises an impeller rotating around a rotation axis and a bell mouth guiding air to the impeller. The impeller includes a shroud provided to have a gap between the shroud and an end of the bell mouth in a circumferential direction and a plurality of blades arranged along a circumferential direction of the shroud, and assembled to the shroud.

In a blade cross section passing a front edge of the blade and a rear edge of the blade, when an angle between a tangential line to a camber line at an intersection point of the camber line and an arc around the rotation axis, and a tangential line to the arc at the intersection point is defined as a blade angle, the blade has at least one of a decreasing shape and a fixed shape. The decreasing shape being such that the blade angle decreases as the intersection point is shifted toward the rear edge side on the camber line in a portion of the front edge side in the blade cross section of the shroud side. The fixed shape being such that the blade angle is fixed even if the intersection point is shifted toward the rear edge side on the camber line in a portion of the front edge side in the blade cross section of the shroud side.

DESCRIPTION OF EMBODIMENTS

In the following, a centrifugal fan51according to one embodiment of the present invention, and an indoor unit31of an air conditioner provided with the centrifugal fan51are described referring to the drawings.

[Configuration of Indoor Unit of Air Conditioner]

The indoor unit31of the air conditioner in the embodiment illustrated inFIG. 1andFIG. 2is a cassette-type indoor unit embedded in a ceiling. The indoor unit31is provided with a substantially rectangular parallelepiped case33to be embedded in an opening formed in a ceiling35, and a decorative panel47mounted on the lower portion of the case33. The decorative panel47has a larger size than the case33in plan view, and is exposed inside the room in a state that the opening of the ceiling is covered. The decorative panel47has a rectangular suction port39formed in the middle of the decorative panel47, and four elongated rectangular blow-out ports37formed along the respective sides of the suction port39.

The indoor unit31is provided with a centrifugal fan (turbo fan)51, a fan motor11, a heat exchanger43, a drain pan45, and an air filter41within the case33. The centrifugal fan51includes an impeller23and a bell mouth25. The fan motor11is fixed substantially at the middle of a top plate of the case33. A shaft13of the fan motor11extends in the up-down direction.

The heat exchanger43has a flat shape with a small thickness. The heat exchanger43is disposed to surround the periphery of the impeller23in a state that the heat exchanger43stands upright from the dish-shaped drain pan45extending along the lower end of the heat exchanger43. The drain pan45accommodates water droplets generated in the heat exchanger43. The accommodated water is discharged through an unillustrated drainage channel.

The air filter41has a size capable of covering the inlet of the bell mouth25. The air filter41is disposed along the suction port39between the bell mouth25and the suction port39. The air filter41traps dust in the air when the air sucked into the case33through the suction port39passes through the air filter41.

The indoor unit31in the embodiment has a reduced thickness. Accompanied by thinning of the indoor unit31, the thickness of the impeller23of the centrifugal fan51is also reduced in the rotation axis A direction. As a result, the indoor unit31has a structure such that noise is likely to occur due to a reflux stream C. Specifically, it is conceived that the flow rate of the reflux stream C is proportional to the size of a gap G, and a pressure difference (a pressure loss of the indoor unit). In the indoor unit31having a reduced thickness, the pressure difference is likely to increase, regardless that the size of the gap G is retained unchanged. This is because the air velocity increases and the pressure loss increases in order to obtain the same volume of air in the indoor unit31having a reduced thickness as in an indoor unit31in which the thickness is not reduced. As a result, the reflux stream C is likely to increase in the indoor unit31having a reduced thickness.

As illustrated inFIG. 1toFIG. 3, the impeller23includes a hub15, a shroud19, and a plurality of blades21. The impeller23rotates around the rotation axis A. The hub15is fixed to the lower end of the shaft13of the fan motor11. The hub15has a circular shape around the rotation axis A in plan view.

The shroud19is disposed to face the front side F with respect to the hub15in the rotation axis A direction of the shaft13. The shroud19includes an air suction port19aopened in a circular shape around the rotation axis A. The outer diameter of the shroud19increases toward the rear side R in the rotation axis A direction.

As illustrated inFIG. 1, the bell mouth25is disposed to face the front side F with respect to the shroud19in the rotation axis A direction. The bell mouth25includes an opening25a(suction port25a) passing in the rotation axis A direction. A part of the bell mouth25on the rear side R is inserted into the shroud19through the air suction port19ain a state that a predetermined gap is formed between the rear side part of the bell mouth25, and a perimeter19eof the air suction port19aof the shroud19. According to this configuration, the bell mouth25is operable to guide air sucked toward the rear side R through the opening25ato the air suction port19aof the shroud19.

As illustrated inFIG. 3, a plurality of blades21are arranged around the rotation axis A between the hub15and the shroud19. Each of the blades21is a backward blade configured such that the blade21is tilted in the direction opposite to the rotational direction DR (tilted backward) radially of the hub15. In the embodiment, each of the blades21has a three-dimensional shape such that the blade21extends in the rotation axis A direction while being twisted between the hub15and the shroud19. Alternatively, each of the blades21may not be twisted as described above. As illustrated inFIG. 3andFIG. 4, a rear edge62of each of the blades21has a plurality of concavity and convexity72. The concavity and convexity72may be omitted.

As illustrated inFIG. 3,FIG. 4,FIG. 5A, andFIG. 5B, each of the blades21includes a negative pressure surface21A (blade inner surface21A) facing radially inward of the impeller23, a positive pressure surface21B (blade outer surface21B) facing radially outward of the impeller23, a front edge61as a front side edge when the impeller23is rotated, and the rear edge62as a rear side edge when the impeller23is rotated. Further, an end edge21F of each of the blades21on the front side F is joined to the inner surface of the shroud19. An end edge21R of each of the blades21on the rear side R is joined to the inner surface of the hub15.

As illustrated inFIG. 4, andFIG. 5A, the front edge61of the blade21includes a front area61F and a rear area61R. The front edge61further includes an end61aon the front side F, the other end61con the rear side R, and a bent portion61bformed between the one end61aand the other end61c. The front area61F is an area from the one end61ato the bent portion61b, and the rear area61R is an area from the other end61cto the bent portion61b. The one end61aof the front edge61is connected to an end of the end edge21F. The other end61cof the front edge61is connected to an end of the end edge21R. The front edge61has a bent shape at the bent portion61b. The tilt angle of the front area61F with respect to the rotation axis A is larger than the tilt angle of the rear area61R with respect to the rotation axis A. The front area61F is tilted in a direction away from the rotation axis A with respect to the rotation axis A, as the front area61F extends from the bent portion61btoward the one end61a.

In the embodiment, all the blades21have the same shape. Specifically, each of the blades21has a feature on the blade angle β to be described later in order to reduce noise due to the reflux stream C. In the centrifugal fan51, not all the blades21may have the feature on the blade angle β, but at least one of the blades21may have the feature on the blade angle β. It is, however, preferable that all the blades21have the feature on the blade angle β to be described later on a shroud19side portion of the blade21in order to enhance the noise reduction effect.

FIG. 4is a sectional view for describing a main stream and a reflux stream. When the impeller23is rotated by the fan motor11, air is sucked into the case33of the indoor unit31through the suction port39of the indoor unit31. The sucked air is guided to the air suction port19aof the shroud19of the impeller23along the inner circumferential surface of the bell mouth25. The air of main stream M guided to the air suction port19aalong the inner circumferential surface of the bell mouth25is ejected to the outside (in a direction away from the rotation axis A) from the impeller23by the blades21arranged circumferentially between the hub15and the shroud19. A main part of the air ejected from the impeller23is blown into the room through the blow-out ports37of the indoor unit31.

A part of air ejected from the impeller23is refluxed toward the bell mouth25through the space between the outer circumferential surface of the shroud19and the case33within the case33of the indoor unit31, and forms the reflux stream C (a leakage stream C) passing through the gap G between the outer circumferential surface of the bell mouth25and the inner circumferential surface of the shroud19. The reflux stream C merges with the main stream M after passing through the gap G.

FIG. 6is a graph illustrating a relationship between the radial position r and the blade angle β of the blade21in the embodiment.FIG. 7Ais a sectional view illustrating a shroud-19-side blade cross section S1in the embodiment.FIG. 7Bis a sectional view illustrating a blade cross section S2at the middle of the span (at the middle of the blade height in the rotation axis A direction) in the embodiment.FIG. 7Cis a sectional view illustrating a hub-side blade cross section S3in the embodiment. The horizontal axis of the graph illustrated inFIG. 6denotes the radial position r of an arc around the rotation axis A. The origin O side of the horizontal axis is the front edge61side of the blade21, and the side away from the origin O of the horizontal axis is the rear edge62side of the blade21. The arc around the rotation axis A is indicated by the two-dotted chain line inFIG. 7AtoFIG. 7C, for instance.

In the embodiment, it is assumed that the angle defined by the tangential line L1to the camber line CL at the intersection point P between the camber line CL and an arc around the rotation axis A, and the tangential line L2to the arc at the intersection point P on a blade cross section passing the front edge61and the rear edge62of the blade21is the blade angle β. The camber line CL is indicated by the broken line in each ofFIG. 7AtoFIG. 7C.

The broken line indicating the blade angle β of the shroud19side portion of the blade21inFIG. 6indicates a change in the blade angle β when the intersection point P is shifted from the front edge61to the rear edge62on the camber line CL on the shroud-19-side blade cross section S1illustrated inFIG. 7A. In the sectional view ofFIG. 7A, five intersection points P1to P5are illustrated as the intersection point P. However, the broken line illustrated inFIG. 6is a line obtained by plotting the blade angle β at multitudes of intersection points P including the intersection points P1to P5.

Further, the shroud-19-side blade cross section S1illustrated inFIG. 7Ais a blade cross section of a boundary portion B1between the shroud19and the blade21illustrated inFIG. 9(joint portion B1between the shroud19and the blade21). Specifically, the shroud-19-side blade cross section S1is a blade cross section of the boundary portion B1between the inner circumferential surface of the shroud19and the end edge21F of the blade21on the front side F. The blade cross section S1illustrated inFIG. 7Ais a blade cross section obtained by projecting a blade cross section of the boundary portion B1, which is curved along the inner circumferential surface of the shroud19on a plane orthogonal to the rotation axis A in the rotation axis A direction.

Further, the hub-15-side blade cross section S3illustrated inFIG. 7Cis a blade cross section of a boundary portion B2between the hub15and the blade21illustrated inFIG. 9(joint portion B2between the hub15and the blade21). Specifically, the hub-15-side blade cross section S3is a blade cross section of the boundary portion B2between the inner surface of the hub15, and the rear edge21R of the blade21on the rear side R. In the embodiment, the end edge21R of the blade21on the rear side R and the inner surface of the hub jointed to the end edge21R are plane orthogonal to the rotation axis A. When the end edge21R of the blade21on the rear side R is curved, it is possible to obtain the blade cross section S3illustrated inFIG. 7Cby projecting a blade cross section of the boundary portion B2, which is curved along the end edge21R, on a plane orthogonal to the rotation axis A in the rotation axis A direction.

Further, the blade cross section S2at the middle of the span illustrated inFIG. 7Bis a blade cross section at the middle of the blade height in the rotation axis A direction. Specifically, the blade cross section S2is a blade cross section obtained by cutting the blade21along a plane passing through the middle of the blade height of the rear edge62of the blade21, and orthogonal to the rotation axis A.

Further, in the embodiment, as illustrated inFIG. 6andFIG. 7A, the area of the blade21closer to the front edge61than the intermediate point (middle) of the length of the camber line CL on the blade cross section S1is called as a front-edge-61-side portion PL of the blade cross section S1. The area of the blade21closer to the rear edge62than the intermediate point (middle) of the length of the camber line CL on the blade cross section S1is called as a rear-edge-62-side portion PT of the blade cross section S1.

As illustrated by the broken line inFIG. 6, the blade21has a decreasing shape such that the blade angle β decreases as the intersection point P is shifted toward the rear edge62on the camber line CL on the front edge61-side portion PL of the shroud-19-side blade cross section S1.

Forming the blade21to have the aforementioned decreasing shape on the front-edge-61-side portion PL of the shroud-19-side blade cross section S1makes it possible to form a shroud-19-side area on the negative pressure surface21A of the blade21where the negative pressure is high at a position away from the front edge and on the rear edge side.

FIG. 8is a sectional view for describing that an area N where the negative pressure is high is formed at a position away from the front edge and on the rear edge side. InFIG. 8, the solid line circle on the negative pressure surface21A indicates the area N where the negative pressure is high in the embodiment, and the broken line circle on the negative pressure surface21A indicates an area N of a blade where the negative pressure is high in a conventional centrifugal fan to be described later. As illustrated inFIG. 8, in the embodiment, the blade21has the aforementioned decreasing shape on the front-edge-61-side portion PL of the shroud-19-side blade cross section S1. This makes it possible to form the area N on the negative pressure surface21A of the blade21where the negative pressure is high at a position away from the front edge61and on the rear edge62side, unlike a conventional configuration. Thus, in the embodiment, it is possible to weaken the force of sucking the reflux stream C. According to this configuration, the flow rate of the reflux stream C decreases. This makes it possible to reduce noise due to the reflux stream C (noise caused by interference between the main stream and the reflux stream).

The area N on the negative pressure surface21A of the blade21where the negative pressure is high coincides with the area where the negative pressure is highest. The invention, however, is not limited to the above. In the embodiment, as far as it is possible to form the area N on the negative pressure surface21A where the negative pressure is high at a position closer to the rear edge62, another area where the negative pressure is higher than the negative pressure on the aforementioned area N may be formed on the rear-edge-62-side portion PT, for instance.

Further, in the embodiment illustrated inFIG. 6, the blade21has such a shape that the blade angle β continues to decrease from the front edge61to the rear edge62on the shroud-19-side blade cross section S1. As described above, in the embodiment, the blade21has a shape such that the blade angle β continues to decrease. Therefore, for instance, as compared with a configuration in which the blade angle β increases on the rear-edge-62-side portion, it is easy for airstreams to follow up to the rear edge62on the negative pressure surface. This is advantageous in suppressing separation of airstreams in the vicinity of the rear edge62.

Further, in the embodiment illustrated inFIG. 6, the blade21includes an area where the degree of decrease of the blade angle β decreases, as the intersection point P is shifted from the front edge61toward the rear edge62on the camber line CL on the front-edge-61-side portion PL of the shroud-19-side blade cross section S1. Specifically, as illustrated inFIG. 6, on the front-edge-61-side portion PL of the blade cross section S1, the broken line indicating the blade angle β includes a curve which is convex leftward and downward. Specifically, the gradient extending in the obliquely rightward and downward direction on the former half area of the front-edge-61-side portion PL (area closer to the origin O) is larger than the gradient extending in the obliquely rightward and downward direction on the latter half area of the front-edge-61-side portion PL (area farther away from the origin O). As described above, in the embodiment, the blade21is configured such that the gradient of decrease of the blade angle β on the area closer to the front edge61is made relatively large within the front-edge-61-side portion PL, and the blade21includes an area where the gradient of decrease of the blade angle β decreases toward the rear edge62on the front-edge-61-side portion PL. Specifically, locally increasing the degree of decrease of the blade angle β on the area closer to the front edge61is advantageous in enhancing the effect of forming an area where the negative pressure is high at a position away from the front edge61and on the rear edge62side. Meanwhile, forming an area where the degree of decrease of the blade angle β is moderate toward the rear edge62makes it possible to prevent an excessive decrease in the shroud-19-side blade load on the negative pressure surface. This is advantageous in keeping the shroud-19-side blade load to a certain degree of force on the negative pressure surface.

In the embodiment illustrated inFIG. 6, the degree of decrease of the blade angle β decreases, as the intersection point P is shifted from the front edge61toward the rear edge62on the camber line CL substantially on the entire area of the front-edge-61-side portion PL of the shroud-19-side blade cross section S1. Alternatively, the area where the degree of decrease of the blade angle β decreases may not be formed on the entire area of the front-edge-61-side portion PL, but may be formed only on a part of the front-edge-61-side portion PL.

For instance, in the second modification illustrated inFIG. 10Bto be described later, the area where the degree of decrease of the blade angle β decreases on the front-edge-61-side portion PL is not formed on the entire area of the front-edge-61-side portion PL. The area where the degree of decrease of the blade angle β decreases on the front-edge-61-side portion PL is not formed on the latter half area of the front-edge-61-side portion PL, but is formed on the former half area of the front-edge-61-side portion PL. On the latter half area of the front-edge-61-side portion PL, the blade angle β does not decrease even if the intersection point P is shifted toward the rear edge62on the camber line CL, but is made constant.

Further, in the embodiment described inFIG. 6, the rear-edge-62-side portion PT on the shroud-19-side blade cross section S1includes an area where the degree of decrease of the blade angle β increases, as the intersection point P is shifted toward the rear edge62on the camber line CL. Specifically, as illustrated inFIG. 6, on the rear-edge-62side portion PT of the blade cross section S1, the broken line indicating the blade angle β is a curve which is convex rightward and upward. Specifically, the gradient extending in the obliquely rightward and downward direction on the latter half area of the rear-edge-62-side portion PT (the area farther away from the origin O) is larger than the gradient extending in the obliquely rightward and downward direction on the former half area of the rear-edge-62-side portion PT (the area closer to the origin O). As described above, forming an area where the degree of decrease of the blade angle β increases on the rear-edge-62-side portion PT makes it easy for airstreams to follow the negative pressure surface on the rear-edge-62-side portion PT. This is advantageous in preventing separation of airstreams on the rear-edge-62-side portion PT.

In the embodiment illustrated inFIG. 6, the degree of decrease of the blade angle β increases, as the intersection point P is shifted toward the rear edge62on the camber line CL substantially on the entire area of the rear-edge-62-side portion PT on the shroud-19-side blade cross section S1. Alternatively, an area where the degree of decrease of the blade angle β increases may not be formed on the entire area of the rear-edge-62-side portion PT, but may be formed only on a part of the rear-edge-62-side portion PT.

For instance, in the second modification illustrated inFIG. 10Bto be described later, on the rear-edge-62-side portion PT, an area where the degree of decrease of the blade angle β increases is not formed on the entire area of the rear-edge-62-side portion PT. The area where the degree of decrease of the blade angle β increases is not formed on the former half area of the rear-edge-62-side portion PT, but is formed on the latter half area of the rear-edge-62-side portion PT. On the former half area of the rear-edge-62-side portion PT, the blade angle β does not decrease, even if the intersection point P is shifted toward the rear edge62on the camber line CL, but is made constant.

In the embodiment, the shroud-19-side blade cross section S1illustrated inFIG. 7Amay not necessarily be a blade cross section of the boundary portion B1between the shroud19and the blade21. As far as the blade cross section21is a shroud-19-side blade cross section of the blade21, the blade cross section S1is not specifically limited. In the embodiment, the shroud-19-side portion of the blade21may be the following area. Specifically, as illustrated inFIG. 9, the shroud-19-side portion of the blade21may be an area B3having a predetermined width W from the boundary portion B1between the shroud19and the blade21in a direction away from the shroud19. The predetermined width W is substantially equal to the distance D between an end25eof the bell mouth25and the shroud19. A blade cross section which passes the front edge61and the rear edge62and is formed along the boundary portion B1between the shroud19and the blade21may be selected within the area B3, and a blade cross section obtained by projecting the selected blade cross section on a plane orthogonal to the rotation axis A in the rotation axis A direction may be set as the blade cross section S1.

Providing the feature on the blade angle β on the shroud-19-side portion of the blade21as described above is advantageous in weakening the force of sucking the reflux stream C. Specifically, the following advantageous effects are obtained. The width of the reflux stream C immediately after the reflux stream C passes through the gap G between the outer circumferential surface of the bell mouth25and the inner circumferential surface of the shroud19is substantially equal to the distance D between the end25eof the bell mouth25and the inner circumferential surface of the shroud19. The reflux stream C impinges on the blade21shortly after passing through the gap G. Therefore, the area of the blade21affected by the reflux stream C is associated with the width of the reflux stream C. In view of the above, providing the aforementioned feature on the blade angle β on the area B3having the predetermined width W, which is substantially equal to the distance D between the end25eof the bell mouth25and the shroud19, is advantageous in weakening the force of sucking the reflux stream C.

Preferably, the blade cross section S1obtained by projecting a selected blade cross section on a plane orthogonal to the rotation axis A in the rotation axis A direction may have the aforementioned feature on the blade angle β, even if any blade cross section along the boundary portion B1is selected within the area B3.

Further, in the embodiment, the solid line indicating the blade angle β of the hub-15-side portion inFIG. 6indicates a change in the blade angle β when the intersection point P is shifted from the front edge61to the rear edge62on the camber line CL on the hub-15-side blade cross section S3inFIG. 7C. As illustrated inFIG. 6, the blade angle β of the hub-15-side portion is illustrated by a line (curve) extending in the obliquely rightward and upward direction, and increases as the intersection point is shifted from the front edge61toward the rear edge62. The invention, however, is not limited to the above.

Further, in the embodiment, the one-dotted chain line indicating the blade angle β at the middle of the span inFIG. 6indicates a change in the blade angle β when the intersection point P is shifted from the front edge61to the rear edge62on the camber line CL on the blade cross section S2at the middle of the span inFIG. 7B. As illustrated inFIG. 6, the blade angle β at the middle of the span is illustrated by a line (curve) extending in the obliquely rightward and upward direction, and increases as the intersection point is shifted from the front edge61toward the rear edge62. The invention, however, is not limited to the above.

Next, the feature on a blade121in a conventional centrifugal fan is briefly described.FIG. 11is a graph illustrating a relationship between the radial position r and the blade angle β of the blade121in a conventional centrifugal fan.FIG. 12Ais a sectional view illustrating a shroud-side blade cross section S11in the conventional centrifugal fan.FIG. 12Bis a sectional view illustrating a blade cross section S12at the middle of the span in the conventional centrifugal fan.FIG. 12Cis a sectional view illustrating a hub-side blade cross section S13in the conventional centrifugal fan.

The broken line indicating the blade angle β of the shroud side portion inFIG. 11indicates a change in the blade angle β when the intersection point P is shifted from a front edge161to a rear edge162on the camber line CL on the shroud-side blade cross section S11inFIG. 12A. The one-dotted chain line indicating the blade angle β at the middle of the span inFIG. 11indicates a change in the blade angle β when the intersection point P is shifted from the front edge161to the rear edge162on the camber line CL on the blade cross section S12at the middle of the span inFIG. 12B. The solid line indicating the blade angle β of the hub side portion inFIG. 11indicates a change in the blade angle β when the intersection point P is shifted from the front edge161to the rear edge162on the camber line CL on the hub-side blade cross section S13inFIG. 12C. The blade cross sections S11to S13are blade cross sections at the same positions as the blade cross sections S1to S3in the embodiment.

As illustrated inFIG. 11, in the conventional centrifugal fan, in any one of the shroud-side blade cross section S11of the blade121, the blade cross section S12at the middle of the span of the blade121, and the hub-side blade cross section of the blade121, the blade angle β is illustrated by a line (curve) extending in the obliquely rightward and upward direction, and increases as the intersection point is shifted from the front edge161toward the rear edge162. Therefore, in the conventional centrifugal fan, an area N on the negative pressure surface21A of the blade121where the negative pressure is high is located at a position close to the front edge161. As a result, unlike the embodiment, the reflux stream is sucked with a large force. Consequently, as compared with the embodiment, the flow rate of the reflux stream increases and noise due to the reflux stream increases.

In the foregoing, an embodiment of the invention is described. The invention, however, is not limited to the embodiment. Various modifications and improvements are applicable as far as such modifications and improvements do not depart from the gist of the invention.

In the embodiment illustrated inFIG. 6, the blade21has such a shape that the blade angle β continues to decrease from the front edge61to the rear edge62on the shroud-19-side blade cross section S1. The invention, however, is not limited to the above. For instance, the blade21may have the shapes of the first to fifth modifications illustrated inFIG. 10AtoFIG. 10E. InFIG. 10AtoFIG. 10E, only the blade angle β on the shroud-19-side blade cross section S1is illustrated, and illustration of the blade angle β on the blade cross section S2at the middle of the span, and the blade angle β on the hub-15-side blade cross section S3is omitted.

The blade21of the first modification illustrated inFIG. 10Ahas a decreasing shape such that the blade angle β decreases, as the intersection point P is shifted toward the rear edge62on the camber line CL on the front-edge-61-side portion PL of the shroud-19-side blade cross section S1, and has an increasing shape such that the blade angle β increases, as the intersection point P is shifted toward the rear edge62on the camber line CL on the rear-edge-62-side portion PT of the shroud-19-side blade cross section S1.

The blade21of each one of the third to fourth modifications illustrated inFIG. 10CtoFIG. 10Dhas a fixed shape such that the blade angle β is fixed even if the intersection point P is shifted toward the rear edge62on the camber line CL on the front-edge-61-side portion PL of the shroud-19-side blade cross section S1.

The blade21of each one of the third to fifth modifications illustrated inFIG. 10CtoFIG. 10Dhas a fixed shape such that the blade angle β is fixed even if the intersection point P is shifted toward the rear edge62on the camber line CL on the front-edge-61-side portion PL of the shroud-19-side blade cross section S1.

The blade21of the third modification illustrated inFIG. 10Cincludes an area where the blade angle β decreases, as the intersection point P is shifted toward the rear edge62on the camber line CL on the rear-edge-62-side portion PT of the shroud-19-side blade cross section S1.

The blade21of the fourth modification illustrated inFIG. 10Dincludes an area where the blade angle β increases, as the intersection point P is shifted toward the rear edge62on the camber line CL on the rear-edge-62-side portion PT of the shroud-19-side blade cross section S1.

The blade21of the fifth modification illustrated inFIG. 10Eincludes an area where the blade angle β decreases, as the intersection point P is shifted toward the rear edge62on the camber line CL, and an area where the blade angle β increases, as the intersection point P is shifted toward the rear edge62on the camber line CL, on the rear-edge-62-side portion PT of the shroud-19-side blade cross section S1.

Further, in the embodiment, all the blades21have the same shape. The invention, however, is not limited to the above. Any configuration is applicable, as far as at least one of the blades21has the decreasing shape, the fixed shape, or a shape obtained by combining the decreasing shape and the fixed shape.

Further, the embodiment is applied to a case, in which the centrifugal fan51is incorporated in a ceiling-embedded indoor unit. The invention, however, is not limited to the above. The inventive centrifugal fan is also applicable to the other types of indoor units such as indoor units installed at a high place including ceiling-suspended indoor units, air handling units, or rooftop units; and indoor units placed on the floor.

The following is a summary of the foregoing embodiment.

The centrifugal fan of the embodiment comprises an impeller rotating around a rotation axis and a bell mouth guiding air to the impeller. The impeller includes a shroud provided to have a gap between the shroud and an end of the bell mouth in a circumferential direction and a plurality of blades arranged along a circumferential direction of the shroud, and assembled to the shroud.

In a blade cross section passing a front edge of the blade and a rear edge of the blade, when an angle between a tangential line to a camber line at an intersection point of the camber line and an arc around the rotation axis, and a tangential line to the arc at the intersection point is defined as a blade angle, the blade has at least one of a decreasing shape and a fixed shape. The decreasing shape being such that the blade angle decreases as the intersection point is shifted toward the rear edge side on the camber line in a portion of the front edge side in the blade cross section of the shroud side. The fixed shape being such that the blade angle is fixed even if the intersection point is shifted toward the rear edge side on the camber line in a portion of the front edge side in the blade cross section of the shroud side.

According to the aforementioned configuration, the blade has at least one of the decreasing shape and the fixed shape in a portion of the front edge side in the blade cross section of the shroud side. The camber line, which is an element that defines the blade angle, is a line connecting positions on the blade cross section equally distanced away from a positive pressure surface and a negative pressure surface. Because the blade has at least one of the decreasing shape and the fixed shaped in a portion of the front edge side in the blade cross section of the shroud side, it becomes possible to weaken the blade load of a shroud side and front edge side portion on the negative pressure surface of the blade. Thus, it is possible to form an area on the negative pressure surface of the blade where the negative pressure is high at a position away from the front edge and on the rear edge side. Therefore, it is possible to weaken the force of sucking a reflux stream (a leakage stream). Thus, it is possible to reduce the flow rate of the reflux stream. This is advantageous in reducing noise due to the reflux stream (noise caused by interference between the main stream and the reflux stream).

Further, in the embodiment, it is possible to reduce noise due to a reflux stream without adding small blades, unlike the conventional art. This is advantageous in suppressing an increase in the weight and the cost.

In the embodiment, a portion of the front edge side in the blade cross section is a portion closer to the front edge than the intermediate point of the camber line, and a portion of the rear edge side in the blade cross section is a portion closer to the rear edge than the intermediate point of the camber line.

In the centrifugal fan, the blade may have a shape combining the decreasing shape and the fixed shape in a portion of the front edge side in the blade cross section of the shroud side.

In the centrifugal fan, preferably, the blade has a shape such that the blade angle continues to decrease from the front edge to the rear edge in the blade cross section of the shroud side.

In the aforementioned configuration, the blade has such a shape that the blade angle continues to decrease. Therefore, as compared with a configuration, in which the blade angle increases in a portion of the rear edge side, for instance, the aforementioned configuration makes it easy for airstreams to follow up to the rear edge on the negative pressure surface. This is advantageous in suppressing separation of airstreams in the vicinity of the rear edge.

In the centrifugal fan, preferably, the blade is provided with an area where a degree of decrease of the blade angle decreases as the intersection point is shifted from the front edge toward the rear edge on the camber line in a portion of the front edge side in the blade cross section of the shroud side.

In the aforementioned configuration, the blade is configured such that the gradient of decrease of the blade angle on the area closer to the front edge is made relatively large within the portion of the front edge side, and the blade includes an area where the gradient of decrease of the blade angle decreases toward the rear edge in the portion of the front edge side. Specifically, locally increasing the degree of decrease of the blade angle on the area closer to the front edge makes it possible to enhance the effect of forming an area where the negative pressure is high at a position away from the front edge and on the rear edge side. Meanwhile, forming an area where the degree of decrease of the blade angle is moderate toward the rear edge makes it possible to prevent an excessive decrease in the shroud-side blade load on the negative pressure surface. This is advantageous in keeping the shroud-side blade load to a certain degree of force on the negative pressure surface.

In the centrifugal fan, preferably, the blade is provided with an area where a degree of decrease of the blade angle increases as the intersection point is shifted toward the rear edge on the camber line in a portion of the rear edge side in the blade cross section of the shroud side.

According to the aforementioned configuration, making the degree of decrease of the blade angle large on the portion of the rear edge side makes it easy for airstreams to follow the negative pressure surface on the portion of the rear edge side. This is advantageous in suppressing separation of airstreams on the rear-edge-side portion.

In the centrifugal fan, a shroud side portion of the blade may be the following area, for instance. Specifically, the shroud side portion of the blade may be an area having a predetermined width from a boundary portion between the shroud and the blade in a direction away from the shroud, and the predetermined width may be equal to a distance between the end of the bell mouth and the shroud.

Providing the aforementioned feature on the blade angle on the shroud side portion is advantageous in weakening the force of sucking a reflux stream. Specifically, the following advantageous effects are obtained. The width of the reflux stream immediately after the reflux stream passes through the gap between the outer circumferential surface of the bell mouth and the inner circumferential surface of the shroud is substantially equal to the distance between the end of the bell mouth and the inner circumferential surface of the shroud. The reflux stream impinges on the blade shortly after passing through the gap. Therefore, the area of the blade affected by the reflux stream is associated with the width of the reflux stream. In view of the above, providing the aforementioned feature on the blade angle on the area having the predetermined width, which is equal to the distance between the end of the bell mouth and the shroud, is advantageous in weakening the force of sucking the reflux stream.

In the centrifugal fan, preferably, the plurality of blades may have the same shape each other.

In the aforementioned configuration, all the blades have the aforementioned feature on the blade angle on the shroud side portion. This is advantageous in weakening the force of sucking the reflux stream on each of the blades.

The air conditioner of the embodiment is provided with the centrifugal fan having the aforementioned configuration. Therefore, the air conditioner of the embodiment is advantageous in reducing noise.