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CENTRIFUGAL AIR BLOWER

Imported: 10 Mar '17 | Published: 27 Nov '08

Thomas G. Glore, Andrew L. Solinski, Justin Murnan, Robert L. Bilimek

USPTO - Utility Patents

Abstract

A centrifugal blower includes a main scroll portion and a scroll opening through which air is discharged. A transitional portion conducts air discharged through the scroll opening away from the blower. The transitional portion includes an internal passageway that provides for the smooth passage of air essentially without causing any abrupt changes in the direction of the flow of the air through the passageway. An impeller assembly can be mounted within the main scroll portion for rotation so as to circulate the air in a spiral path within the main scroll portion and force the air through the scroll opening and the passageway in the transitional portion. The impeller assembly can have a platen that has a perimeter and a plurality of impeller blades mounted at the platen for rotation with the platen. Each impeller blade can have a distal end that extends beyond the perimeter of the platen.

Description

CROSS-REFERENCE TO RELATED APPLICATION

The benefit of U.S. Provisional Application No. 60/940,224 filed on May 25, 2007 is claimed for this application.

BACKGROUND OF THE INVENTION

The present invention relates generally to centrifugal blowers. In particular, the invention relates to centrifugal blowers having a scroll-type casing or housing within which is disposed an impeller assembly that, upon rotation, draws air to the blower interior from the exterior of the blower, circulates the air in a spiral path within the scroll-type housing and then discharges the air back to the exterior of the blower through an opening in the scroll-type housing.

The need to move air exists in a variety of circumstances such as, for example, in connection with the operation of heating, air-conditioning and ventilating equipment as well as the operation of lawn-care and landscaping equipment. Centrifugal blowers are often used for that purpose. Typically, the centrifugal blowers include scroll-type casings or housings that provide enclosures within each of which is disposed an impeller assembly. Usually, the impeller assembly includes a plurality of vanes or blades that upon rotation of the impeller assembly moves or circulates the air within the blower housing in a spiral path and forces the air from the interior to the exterior of the blower housing through a discharge opening in the blower housing.

A centrifugal blower, however it may be powered, whether by electricity or the burning of fuel for example, can generate undesirable levels of noise as a result of the high-velocity circulation of the air within the blower. In addition, it can be the case that the internal structure of the centrifugal blower causes a portion of the circulating air within the blower to be recirculated past the blower discharge opening rather than be discharged from the blower through the blower discharge opening, thereby reducing the efficiency of the blower.

SUMMARY OF THE INVENTION

The following presents a simplified summary of the invention in order to provide a basic understanding of some example aspects of the invention. This summary is not an extensive overview of the invention. Moreover, this summary is not intended to identify critical elements of the invention nor delineate the scope of the invention. The sole purpose of the summary is to present some concepts of the invention in simplified form as a prelude to the more detailed description that is presented later.

According to one aspect, the present invention concerns a centrifugal air blower that incorporates certain features that reduce the noise levels generated by the circulation of air within the centrifugal blower and reduce the recirculation of air within the centrifugal blower compared to the case where these features are not present.

According to another aspect, the centrifugal blower comprises a main scroll portion having an internal surface and a scroll opening through which air can be discharged to the exterior of the centrifugal blower from within the main scroll portion. The internal surface of the main scroll portion has a progressively increasing radius beginning at an air discharge cut-off site at the internal surface of the main scroll portion that is located substantially adjacent a first side of the scroll opening and proceeding along the internal surface of the main scroll portion to a side of the scroll opening that is substantially opposite the first side of the scroll opening, whereby the air can be circulated in a spiral path along the internal surface of the main scroll portion of the blower. The blower also includes a transitional portion for conducting away from the centrifugal blower air discharged from within the main scroll portion through the scroll opening. The transitional portion includes: (a) an entry opening through which the air discharged from within the main scroll portion enters the transitional portion, the entry opening being essentially the same size as the scroll opening, and the main scroll portion and the transitional portion being joined to one another at the scroll opening and the entry opening, respectively; (b) an exit opening that is smaller than the entry opening in the transitional portion; and (c) a body portion joining the entry opening of the transitional portion and the exit opening of the transitional portion and providing an internal passageway for the air to exit from the main scroll portion. The internal passageway is constructed so as to provide for the smooth passage of air from the scroll opening in the main scroll portion past the air discharge cut-off site to the exit opening in the transitional portion essentially without causing any abrupt changes in the direction of the flow of the air through the passageway and at the air discharge cut-off site such as would result in the generation of unwanted noise.

According to a further aspect, the centrifugal blower, with or without a transitional portion as described in the previous paragraph, can include an impeller assembly mounted within the main scroll portion for rotation so as to circulate the air in a spiral path along the internal surface of the main scroll portion and force the air through the scroll opening and the passageway in the body portion of the transitional portion of the blower. The impeller assembly can have an axis of rotation that, in relation to the internal surface of the main scroll portion, is nearest the air discharge cut-off site at the internal surface of the main scroll portion. Also, the impeller assembly can comprise (a) a platen mounted for rotation about the axis of rotation and having a perimeter and (b) a plurality of impeller blades mounted at the platen generally radially to the axis of rotation of the platen for rotation with the platen. Each impeller blade can have a distal end that extends beyond the perimeter of the platen a distance such that the distal end of the impeller blade passes the air discharge cut-off site at the internal surface of the main scroll portion by an interval that is sufficiently small to maintain at substantially a minimum the recirculation of the air within the main scroll portion as the impeller blade passes the air discharge cut-off site.

According to yet another aspect, the exit opening of the transitional portion can be substantially cylindrical in cross-section. A tubular extension having a through opening the diameter of which is substantially equal to the cross-sectional diameter of the exit opening can be connected to the exit opening such that the exit opening and the through opening in the tubular extension are arranged in line with one another.

According to still another aspect, the interval by which the impeller blades pass the air discharge cut-off site at the internal surface of the main scroll portion can be no greater than approximately 2.5 millimeters.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Referring first to FIGS. 1 and 2 of the drawings, there are shown in FIG. 1 a first sub-assembly of an embodiment of a centrifugal air blower, indicated generally at 10, and in FIG. 2 a second sub-assembly of the same embodiment of the centrifugal air blower, indicated generally at 50. In FIGS. 1 and 2, internal faces or sides 12 and 52 of the first and second sub-assemblies, respectively, face the viewer so as to reveal certain parts of the first and second subassemblies that are located within the interior of the centrifugal air blower when the blower is assembled. In assembling the centrifugal air blower, the internal side 12 of the first sub-assembly 10 and the internal side 52 of the second sub-assembly 50 are brought together in a face-to-face attitude and the matching perimeters 14 and 54 of the first sub-assembly and the second sub-assembly, respectively, aligned with one another and brought into engagement so that the first sub-assembly and second sub-assembly can be secured to one another. Suitable complementary ears, lugs or the like, indicated at 16 on the first sub-assembly 10, and at 56 on the second sub-assembly 50 can be provided and appropriate fasteners employed thereat to secure the first sub-assembly to the second sub-assembly in a manner that will be familiar to those having ordinary skill in the art.

Legs 43 can be located at the exterior of the first and second sub-assemblies for supporting the centrifugal air blower in an upright position from a support surface. Also, a handle 42 can be located at the exterior of the first and second sub-assemblies whereby the centrifugal air blower can be carried and transported from place to place.

As can be seen in FIGS. 3 through 6, an air inlet screen 18 is be located at the external side of the first sub-assembly 10 that is opposite the internal side 12 of the first sub-assembly. The screen allows for the entry of air therethrough from the exterior of the centrifugal air blower to the interior of the air blower. Located within the first sub-assembly 10 adjacent the site where the air enters the first sub-assembly through the air inlet screen 18 is an impeller assembly, indicated generally at 40 and described in greater detail below, for drawing air from the exterior of the centrifugal blower through air inlet screen 18 to the interior of the blower, circulating the air within the blower and driving the air from the interior of the centrifugal air blower to the exterior of the air blower through a discharge assembly, also described in greater detail below. It is noted here that the impeller assembly 40 includes a substantially concave conical surface 42 that faces the interior of the centrifugal air blower.

Referring to FIG. 7, it can be seen that located at the internal side 52 of the second sub-assembly 50 is a supporting projection, indicated generally at 60, that projects or juts out, in a direction toward the impeller assembly 40 when the first and second sub-assemblies 10 and 50 are secured to one another as described above. The supporting projection 60 includes a substantially convex conical surface 62 that is dimensionally complementary with the substantially conical surface 42 of the impeller assembly so that the conical surface 62 is received within the concave recess that is created by the substantially conical surface 42 but is spaced apart from the substantially conical surface 42 when the first and second sub-assemblies 10 and 50 are secured to one another as described above.

Also as can best be seen in FIG. 7, the second sub-assembly 50 includes an external side, indicated generally at 58, that is opposite the internal side 52 of the second sub-assembly. The external side 58 is recessed at 59 to provide a site for the installation of a source of power such as an electric motor or fuel-driven engine not shown. The drive shaft of the source of power extends through the supporting projection 60 and is supported by the supporting projection. In this regard, a bushing 61 is located in the front wall of the supporting projection 60 and the drive shaft extends from the source of power through the bushing to the impeller assembly 40 and is secured to the impeller assembly for the purpose of rotating the impeller assembly. The variety of ways that suitable bushings, bearings, connecting elements and the like can be provided so that the drive shaft of the source of power can effectively and efficiently drive the impeller assembly 40 are familiar to those having ordinary skill in the art and, therefore, are not described here.

When assembled as described above, the embodiment of the centrifugal blower illustrated in the drawings comprises a main scroll portion that is formed by the curvilinear surfaces 22 and 62 of the first sub-assembly 10 and the second sub-assembly 50, respectively. The main scroll portion of the centrifugal blower has an internal surface 22, which is curvilinear, and a scroll opening, indicated generally at 24, through which air can be discharged from within the main scroll portion of the blower. As will be familiar to those having ordinary skill in the art, the curvilinear internal surface 22 of the main scroll portion is not of a constant radius. Rather, the internal surface 22 of the main scroll portion has a generally uniformly increasing radius. In particular, the internal surface 22 has a progressively increasing radius beginning at an air discharge cut-off site 26 at the internal surface of the main scroll portion that is located substantially adjacent a first side of the scroll opening 24 and proceeding along the internal surface 22 of the main scroll portion to a side 28 of the scroll opening 24 that is substantially opposite the first side of the scroll opening 24. By way of example, the internal surface 22 of the main scroll portion can have a progressively increasing radius of 6.5%, although increasing radii of greater and lesser than 6.5% can be employed. This progressively increasing radius in the internal surface 22 of the main scroll portion of the centrifugal blower results in the circulation of the air within the main scroll portion of the blower along a spiral path as the air is driven by the impeller assembly 40 to the scroll opening 24.

The centrifugal blower of the invention also includes a transitional portion, indicated generally at 30, for conducting away from the blower air discharged from within the main scroll portion of the blower through the scroll opening 24. The transitional portion 30 includes an entry opening 32 through which the air discharged from within the main scroll portion of the blower enters the transitional portion. The entry opening 32 of the transitional portion 30 is essentially the same size as the scroll opening 24, and the main scroll portion of the blower and the transitional portion 30 are joined together at the scroll opening 24 and the entry opening 32, respectively. The transitional portion 30 also includes an exit opening 34 that is smaller than the entry opening 32 in the transitional portion 30. A body portion 36 of the transitional portion 30 joins the entry opening 32 of the transitional portion and the exit opening 34 of the transitional portion and provides an internal passageway for the air to exit from the main scroll portion of the centrifugal blower through scroll opening 24.

The impeller assembly 40 of the centrifugal blower is mounted within the main scroll portion of the blower for rotation so as to draw air from the exterior of the blower through air inlet screen 18 into the interior of the main scroll portion of the blower, circulate the air within the main scroll portion and drive the air from within the main scroll portion through the scroll opening 24 and the passageway in the body portion 36 of the transitional portion 30 of the blower. The impeller assembly 40 has an axis of rotation 44, and, as described above, a drive shaft is located at that axis of rotation for driving the impeller assembly circularly within the main scroll portion of the blower. The axis of rotation 44 is located in relation to the internal surface 22 of the main scroll portion such that the axis of rotation is nearest the internal surface 22 at the air discharge cut-off site 26. Stated otherwise, the impeller assembly 40 in its rotation within the main scroll portion of the centrifugal blower will come nearest the internal surface 22 of the main scroll portion at the air discharge cut-off site 26.

The impeller assembly comprises a platen 46 and a plurality of impeller blades 48 that are mounted at the platen 46 at the side of the platen that faces the air inlet screen 18. The platen 46 has a perimeter 41 and is mounted within the main scroll portion of the centrifugal blower for rotation about the axis of rotation 44. The plurality of impeller blades 48 are mounted at the platen generally radially to the axis of rotation 44 of the platen for rotation with the platen. Each impeller blade 48 has a distal end 49 that extends beyond the perimeter 41 of the platen 46.

In operation, a drive shaft appropriately driven by the power source mounted at the recessed portion 59 of the external side 58 of the second sub-assembly 50 and connected to the impeller assembly 40 will cause the impeller assembly to rotate about the axis of rotation 44. The associated rotation of the impeller blades 48 will draw air from the exterior of the centrifugal blower through the air inlet 18 into the main scroll portion of the blower, causing the air to be circulated along a spiral path within the main scroll portion of the blower, out the scroll opening 24, through the entry opening 32 of the transitional portion 30, through the passageway in the body portion 36 of the transitional portion 30 and through the exit opening 34 in the transitional portion 30.

Because, as described above, the exit opening 34 of the transitional portion 30 is smaller than both the coinciding scroll opening 24 of the main scroll portion and the entry opening 32 of the transitional portion 30, the body portion 36 of the transitional portion 30 serves to provide an internal passageway that transitions the airflow cross-sectional area from the larger scroll opening 24 to the smaller exit opening 34. The embodiment of the invention illustrated in the drawings accomplishes this result by the construction of the internal passageway so as to provide for the smooth passage of air from the scroll opening 24 in the main scroll portion of the blower past the air discharge cut-off site 26 to the exit opening 34 in the transitional portion 30 essentially without causing any abrupt changes in the direction of flow of the air through the passageway and at the air discharge cut-off site such as would tend to cause the generation of unwanted noise. More specifically, based on the foregoing description, it will be understood that as the air circulates along the internal surface 22 of the main scroll portion of the centrifugal blower, the air is substantially prevented from circulating past the air discharge cut-off site 26 and is caused to be discharged from the centrifugal blower because of the close proximity between the air discharge cut-off site and the distal ends 49 of the impeller blades 48 as the blades rotate past the air discharge cut-off point. In some prior art blowers, an air discharge cut-off site is provided for this purpose in the form of a baffle-like component that has the undesirable characteristic of rather abruptly changing the direction of flow of at least a portion of the circulating air stream and thereby causing excessive noise to be generated. The present invention avoids that undesirable feature by providing for the smooth passage of air from the scroll opening in the main scroll portion of the blower past the air discharge cut-off site to the exit opening 34 without causing any abrupt changes in the direction of the flow of the circulating air through the passageway and at the air discharge cut-off site.

Undesirable noise is also reduced by extending the distal end 49 of each impeller blade 48 beyond the perimeter 41 of the platen 46 at which the impeller blades are mounted. This construction reduces the amount of noise that is generated by the rotating impeller blades, particularly where the distal ends 49 of the impeller blades pass by the air discharge cut-off site 26 compared to a construction where the ends of the impeller blades are substantially coextensive with the perimeter of the platen at which the blades are mounted. At the same time, the recirculation of air within the main scroll portion of the centrifugal blower is controlled and the efficient operation of the blower not compromised by having the distal end of each impeller blade pass the air discharge cut-off site 26 at the internal surface 22 of the main scroll portion of the blower by a distance or interval that is sufficiently small to maintain at substantially a minimum the recirculation of air within the main scroll portion as the impeller assembly rotates. A suitable distance or interval can be no more than approximately 2.5 millimeters.

In a particular aspect of the invention, the exit opening 34 of the transitional portion 30 of the centrifugal blower is substantially cylindrical in cross-section and a tubular extension 70 can be joined to the transitional portion 30 at the exit opening 34. The tubular extension 70 includes a through opening 71 the diameter of which is substantially equal to the cross-sectional diameter of the exit opening 34. The exit opening 34 and the through opening 71 in the tubular extension 70 are arranged in line with one another.

It will be understood that while a particular embodiment of the invention has been shown and described herein, the invention is not limited to that embodiment but covers and includes all modifications and variations that are encompassed by the following claims. By way of example, an impeller assembly as described can be employed with centrifugal blowers that do not include a transitional portion as illustrated in the drawings and a transitional portion as described can be employed with centrifugal blowers that include impeller assemblies different from the impeller assemblies illustrated in the drawings.

Claims

1. A centrifugal blower comprising:
a main scroll portion having an internal surface and a scroll opening through which air can be discharged to the exterior of the centrifugal blower from within the main scroll portion, the internal surface of the main scroll portion having a progressively increasing radius beginning at an air discharge cut-off site at the internal surface of the main scroll portion that is located substantially adjacent a first side of the scroll opening and proceeding along the internal surface of the main scroll portion to a side of the scroll opening that is substantially opposite the first side of the scroll opening, whereby the air can be circulated in a spiral path along the internal surface of the main scroll portion;
a transitional portion for conducting away from the centrifugal blower air discharged from within the main scroll portion through the scroll opening, the transitional portion including (a) an entry opening through which the air discharged from within the main scroll portion enters the transitional portion, the entry opening being essentially the same size as the scroll opening, and the main scroll portion and the transitional portion being joined to one another at the scroll opening and the entry opening, respectively, (b) an exit opening that is smaller than the entry opening in the transitional portion, and (c) a body portion joining the entry opening of the transitional portion and the exit opening of the transitional portion and providing an internal passageway for the air to exit from the main scroll portion, the internal passageway of the body portion being constructed so as to provide for the smooth passage of air from the scroll opening in the main scroll portion past the air discharge cut-off site to the exit opening in the transitional portion essentially without causing any abrupt changes in the direction of the flow of the air through the passageway and at the air discharge cut-off site such as would result in the generation of unwanted noise; and
an impeller assembly mounted within the main scroll portion for rotation so as to circulate the air in a spiral path along the internal surface of the main scroll portion and force the air through the scroll opening and the passageway in the body portion of the transitional portion, the impeller assembly having an axis of rotation that, in relation to the internal surface of the main scroll portion, is nearest the air discharge cut-off site at the internal surface of the main scroll portion, the impeller assembly comprising (a) a platen having a perimeter, the platen being mounted for rotation about the axis of rotation, and (b) a plurality of impeller blades mounted at the platen generally radially to the axis of rotation of the platen for rotation with the platen, each impeller blade having a distal end that extends beyond the perimeter of the platen a distance such that the distal ends of the impeller blades pass the air discharge cut-off site at the internal surface of the main scroll portion by an interval that is sufficiently small to maintain at substantially a minimum the recirculation of the air within the main scroll portion as the impeller blades pass the air discharge cut-off site.
a main scroll portion having an internal surface and a scroll opening through which air can be discharged to the exterior of the centrifugal blower from within the main scroll portion, the internal surface of the main scroll portion having a progressively increasing radius beginning at an air discharge cut-off site at the internal surface of the main scroll portion that is located substantially adjacent a first side of the scroll opening and proceeding along the internal surface of the main scroll portion to a side of the scroll opening that is substantially opposite the first side of the scroll opening, whereby the air can be circulated in a spiral path along the internal surface of the main scroll portion;
a transitional portion for conducting away from the centrifugal blower air discharged from within the main scroll portion through the scroll opening, the transitional portion including (a) an entry opening through which the air discharged from within the main scroll portion enters the transitional portion, the entry opening being essentially the same size as the scroll opening, and the main scroll portion and the transitional portion being joined to one another at the scroll opening and the entry opening, respectively, (b) an exit opening that is smaller than the entry opening in the transitional portion, and (c) a body portion joining the entry opening of the transitional portion and the exit opening of the transitional portion and providing an internal passageway for the air to exit from the main scroll portion, the internal passageway of the body portion being constructed so as to provide for the smooth passage of air from the scroll opening in the main scroll portion past the air discharge cut-off site to the exit opening in the transitional portion essentially without causing any abrupt changes in the direction of the flow of the air through the passageway and at the air discharge cut-off site such as would result in the generation of unwanted noise; and
an impeller assembly mounted within the main scroll portion for rotation so as to circulate the air in a spiral path along the internal surface of the main scroll portion and force the air through the scroll opening and the passageway in the body portion of the transitional portion, the impeller assembly having an axis of rotation that, in relation to the internal surface of the main scroll portion, is nearest the air discharge cut-off site at the internal surface of the main scroll portion, the impeller assembly comprising (a) a platen having a perimeter, the platen being mounted for rotation about the axis of rotation, and (b) a plurality of impeller blades mounted at the platen generally radially to the axis of rotation of the platen for rotation with the platen, each impeller blade having a distal end that extends beyond the perimeter of the platen a distance such that the distal ends of the impeller blades pass the air discharge cut-off site at the internal surface of the main scroll portion by an interval that is sufficiently small to maintain at substantially a minimum the recirculation of the air within the main scroll portion as the impeller blades pass the air discharge cut-off site.
2. A centrifugal blower comprising:
a main scroll portion having an internal surface and a scroll opening through which air can be discharged to the exterior of the centrifugal blower from within the main scroll portion, the internal surface of the main scroll portion having a progressively increasing radius beginning at an air discharge cut-off site at the internal surface of the main scroll portion that is located substantially adjacent a first side of the scroll opening and proceeding along the internal surface of the main scroll portion to a side of the scroll opening that is substantially opposite the first side of the scroll opening, whereby the air can be circulated in a spiral path along the internal surface of the main scroll portion; and
a transitional portion for conducting away from the centrifugal blower air discharged from within the main scroll portion through the scroll opening, the transitional portion including (a) an entry opening through which the air discharged from within the main scroll portion enters the transitional portion, the entry opening being essentially the same size as the scroll opening, and the main scroll portion and the transitional portion being joined to one another at the scroll opening and the entry opening, respectively, (b) an exit opening that is smaller than the entry opening in the transitional portion, and (c) a body portion joining the entry opening of the transitional portion and the exit opening of the transitional portion and providing an internal passageway for the air to exit from the main scroll portion, the internal passageway of the body portion being constructed so as to provide for the smooth passage of air from the scroll opening in the main scroll portion past the air discharge cut-off site to the exit opening in the transitional portion essentially without causing any abrupt changes in the direction of the flow of the air through the passageway and at the air discharge cut-off site such as would result in the generation of unwanted noise.
a main scroll portion having an internal surface and a scroll opening through which air can be discharged to the exterior of the centrifugal blower from within the main scroll portion, the internal surface of the main scroll portion having a progressively increasing radius beginning at an air discharge cut-off site at the internal surface of the main scroll portion that is located substantially adjacent a first side of the scroll opening and proceeding along the internal surface of the main scroll portion to a side of the scroll opening that is substantially opposite the first side of the scroll opening, whereby the air can be circulated in a spiral path along the internal surface of the main scroll portion; and
a transitional portion for conducting away from the centrifugal blower air discharged from within the main scroll portion through the scroll opening, the transitional portion including (a) an entry opening through which the air discharged from within the main scroll portion enters the transitional portion, the entry opening being essentially the same size as the scroll opening, and the main scroll portion and the transitional portion being joined to one another at the scroll opening and the entry opening, respectively, (b) an exit opening that is smaller than the entry opening in the transitional portion, and (c) a body portion joining the entry opening of the transitional portion and the exit opening of the transitional portion and providing an internal passageway for the air to exit from the main scroll portion, the internal passageway of the body portion being constructed so as to provide for the smooth passage of air from the scroll opening in the main scroll portion past the air discharge cut-off site to the exit opening in the transitional portion essentially without causing any abrupt changes in the direction of the flow of the air through the passageway and at the air discharge cut-off site such as would result in the generation of unwanted noise.
3. A centrifugal blower comprising:
a main scroll portion having an internal surface and a scroll opening through which air can be discharged to the exterior of the centrifugal blower from within the main scroll portion, the internal surface of the main scroll portion having a progressively increasing radius beginning at an air discharge cut-off site at the internal surface of the main scroll portion that is located substantially adjacent a first side of the scroll opening and proceeding along the internal surface of the main scroll portion to a side of the scroll opening that is substantially opposite the first side of the scroll opening, whereby the ait can be circulated in a spiral path along the internal surface of the main scroll portion; and
an impeller assembly mounted within the main scroll portion for rotation so as to circulate the air in a spiral path along the internal surface of the main scroll portion and force the air through the scroll opening, the impeller assembly having an axis of rotation that, in relation to the internal surface of the main scroll portion, is nearest the air discharge cut-off site at the internal surface of the main scroll portion, the impeller assembly comprising (a) a platen having a perimeter, the platen being mounted for rotation about the axis of rotation, and (b) a plurality of impeller blades mounted to the platen generally radially to the axis of rotation of the platen for rotation with the platen, each impeller blade having a distal end that extends beyond the perimeter of the platen a distance such that the distal ends of the impeller blades pass the air discharge cut-off site at the internal surface of the main scroll portion by an interval that is sufficiently small to maintain at substantially a minimum the recirculation of the air within the main scroll portion as the impeller blades pass the air discharge cut-off site.
a main scroll portion having an internal surface and a scroll opening through which air can be discharged to the exterior of the centrifugal blower from within the main scroll portion, the internal surface of the main scroll portion having a progressively increasing radius beginning at an air discharge cut-off site at the internal surface of the main scroll portion that is located substantially adjacent a first side of the scroll opening and proceeding along the internal surface of the main scroll portion to a side of the scroll opening that is substantially opposite the first side of the scroll opening, whereby the ait can be circulated in a spiral path along the internal surface of the main scroll portion; and
an impeller assembly mounted within the main scroll portion for rotation so as to circulate the air in a spiral path along the internal surface of the main scroll portion and force the air through the scroll opening, the impeller assembly having an axis of rotation that, in relation to the internal surface of the main scroll portion, is nearest the air discharge cut-off site at the internal surface of the main scroll portion, the impeller assembly comprising (a) a platen having a perimeter, the platen being mounted for rotation about the axis of rotation, and (b) a plurality of impeller blades mounted to the platen generally radially to the axis of rotation of the platen for rotation with the platen, each impeller blade having a distal end that extends beyond the perimeter of the platen a distance such that the distal ends of the impeller blades pass the air discharge cut-off site at the internal surface of the main scroll portion by an interval that is sufficiently small to maintain at substantially a minimum the recirculation of the air within the main scroll portion as the impeller blades pass the air discharge cut-off site.
4. The centrifugal blower of claim 1 wherein the exit opening of the transitional portion is substantially cylindrical in cross-section and a tubular extension having a through opening the diameter of which is substantially equal to the cross-sectional diameter of the exit opening is connected to the exit opening such that the exit opening and the through opening in the tubular extension are arranged in line with one another.
5. The centrifugal blower of claim 1 wherein the interval by which the impeller blades pass the air discharge cut-off site at the internal surface of the main scroll portion is no more than approximately 2.5 millimeters.
6. The centrifugal blower of claim 3 wherein the interval by which the impeller blades pass the air discharge cut-off site at the internal surface of the main scroll portion is no more than approximately 2.5 millimeters.
7. The centrifugal blower of claim 4 wherein the interval by which the impeller blades pass the air discharge cut-off site at the internal surface of the main scroll portion is no more than approximately 2.5 millimeters.
8. The centrifugal blower of claim 2 wherein the exit opening of the transitional portion is substantially cylindrical in cross-section and a tubular extension having a through opening the diameter of which is substantially equal to the cross-sectional diameter of the exit opening is connected to the exit opening such that the exit opening and the through opening in the tubular extension are arranged in line with one another.