Muffler for impeller with rearwardly curved blades

Abstract

A high speed centrifugal air impeller assembly with rearwardly curved blades has it impeller backplate directly cooperating with an adjacent housing wall portion to provide a narrow annular sound attenuating passageway from an impeller chamber to a motor and discharge chamber.

Description

RELATED APPLICATIONS

Provisional Application No. 60/508,325, titled “Internal Muffler for Backward Inclined Blower” filed Oct. 2, 2003, inventor David A. Curtis, incorporated herein by reference.

BACKGROUND OF INVENTION

This invention relates to a high speed centrifugal air impeller with rearwardly curved blade and more particularly to sound attenuation means therefore. Impellers of the type under consideration are relatively low flow high speed devices, which operate in the neighborhood of a blade tip speed up to approximately 550 feet per second.

Air flow is three dimensional. Air enters the impeller axially through inlet openings in the housing and impeller. In the plane of rotation there is a circulation that flows outwardly and is collected by the housing for approximately 300 degrees of rotation. Typically an outlet section makes up the remaining flow, usually a cylindrical section whose axis is substantially tangent to the impeller outer diameter.

As will be apparent, the high speed operation of these devices results in substantial noise generation. One method of noise reduction used involved the provision of an impeller housing having two discrete chambers, one containing the impeller and the other the air outlet or discharge section. Thus, a muffler effect can be provided for by means of a rapidly changing cross-sectional opening. In the prior art a divider piece is provide in one design and cooperates with the impeller backplate to define a narrow annular opening spaced radially inwardly from the housing wall but interconnecting the impeller and discharge chambers. Sound waves passing through the opening along with the air are substantially attenuated. The additional part, however, adds significantly to manufacturing cost and assembly complexity and the overall cost of the impeller assembly is adversely affected.

It is the general object of the present invention to provide a high speed centrifugal air impeller assembly having rearwardly curved blades with improved sound attenuation means which can be manufactured at economic advantage and which also enhances impeller performance.

In fulfillment of the foregoing object and in accordance with the present invention, an impeller housing is provided with air inlet and discharge openings. An air impeller with an annular backplate is disposed in the housing with a circumaxially spaced series of long narrow rearwardly inclined air moving blades on its backplate and with its inlet opening in communication with the housing inlet opening. The annular backplate of the impeller cooperates with an annular potion of the housing inner surface to define a narrow annular passageway and discrete chambers on opposite sides thereof. Although the impeller may be otherwise driven, it preferably has its backplate connected with and driven by an electric motor mounted in the chamber on the side opposite the blades. With this arrangement, the air flow created by the impeller blades is constrained to flow through the narrow annular passageway connecting the impeller and motor chambers and the sound waves accompanying the flow are substantially attenuated in flow through the passageway. It should also be noted that the air flow is not required to reverse direction on reaching the housing wall in order to flow radially inwardly and then through the annular passageway as the prior art design. Confinement of the motor in its chamber within the housing also contributes significantly to overall sound reduction.

DESCRIPTION OF DRAWINGS

FIG. 1 of the drawings shows a prior art design in sectional schematic form,

FIG. 2 illustrates the improved design of the present invention also in sectional schematic form.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring initially to FIG. 1, it will be observed that an impeller housing is indicated generally at 10. Mating upper and lower cup-shaped members form a generally cylindrical housing with an annular third housing member 15 clamped therebetween. The member 15 has a radially inwardly projecting annular extension 16 which cooperates with an impeller backplate 18 to define an annular passageway 20 spaced radially inwardly from the inner wall of the housing 10. The extension 16 and the backplate 18 cooperatively define upper and lower chambers 22 and 24 in the housing and the latter carries a circumaxially spaced series of long narrow rearwardly curved air moving blades 26,26. A housing inlet opening 28 receives an inlet member 30 of the impeller and the air is conducted generally radially outwardly where it is forced to reverse direction at the housing wall and travels radially inwardly before passing through the passageway 20 to the upper chamber 22. The chamber 22 contains electric motor 32 driving the impeller through connection with backplate 18 and a discharge opening 34, which extends in a direction generally tangent to the housing wall.

As will be apparent, a degree of sound attenuation will be realized with the design of FIG. 1. As mentioned above, however, it will also be apparent that the third housing part 15 will add substantial cost in manufacturing and assembly time. Further, the inefficient reversing flow pattern is obviously detrimental to impeller performance.

Referring now to FIG. 2, the improved impeller assembly of the present invention has a housing indicated generally at 40 which may vary widely in form but which preferably comprises a pair of mating cup-shaped members 42,44 as in FIG. 1. The members 42,44 are attached directly to each other at their open ends to provide a desirably simple two part construction. At the junction between the members on the interior surface of the housing a narrow annular portion 46 thereof is provided irrespective of the remaining configuration of the housing. This portion of the housing cooperates with an enlarged backplate 48 to define a narrow annular air passageway 50 for the passage of air and the attenuation of accompanying noise. The backplate also serves to define a lower chamber 52 which houses an impeller 54 and from which air flows through the passageway 50 to an upper chamber. The lower surface of the backplate 48 also carries a circumaxial series of long narrow rearwardly inclined air moving blades 56,56 and an inlet tube 58 which is received in inlet opening 60 in the lower wall of the housing member 44. As will be apparent, air drawn inwardly through the inlet tube 58 will be discharged radially outward from the impeller blades and will then make a direct right angle turn through the passageway 50 without any reversal in flow and resulting turbulence.

As mentioned above, various configurations may be employed for the chambers 52, 54. In this regard it should be observed that the diameter of the narrow annular portion which defines the opening 50 in cooperation with the backplate 48 should in all cases be at least as large as that of the inlet chamber 52.

The upper chamber 54 preferably houses an electric motor 62 for rotating the backplate of the impeller and thus driving the impeller. Also located in the chamber 54 is a discharge tube which has its axis substantially tangent to the wall of the housing. As mentioned confining the electric motor in the housing also serves to reduce noise generated by the assembly.

Claims

1. A high speed centrifugal air impeller assembly with rearwardly curved blades and with sound attenuation means; said impeller comprising a housing defining air inlet and air discharge openings, an air impeller with an annular backplate carrying a circumaxially spaced series of long narrow rearwardly inclined air moving blades on one side disposed in the housing with it inlet opening in communication with the housing inlet opening, said backplate also defining discrete impeller and motor chambers in the housing, an electric motor mounted in the motor chamber on an opposite and discharge side of the backplate in driving relationship therewith, said housing having an annular portion of its inner surface adjacent said backplate and said backplate having an outer diameter slightly less than the inner diameter of said housing annular portion to define therewith a narrow annular air passageway immediately adjacent the housing inner surface and which interconnects the impeller and motor chambers and provides sound attenuation during the passage of impeller discharge air therethrough.

2. A high speed centrifugal air impeller as set forth in claim 1 wherein the ratio of the annular area between the backplate and housing to that of the annular area between the blade tips and housing falls in the range 0.10 to 0.50.

3. A high speed centrifugal air impeller as set forth in claim 1 wherein the impeller is operated at a tip speed up to approximately 550 feet per second.

4. A high speed centrifugal air impeller as set forth in claim 1 wherein the backplate extends substantially beyond the outer diameter of the blades.

5. A high speed centrifugal air impeller as set forth in claim 1 wherein the housing is formed of a pair of mating cup shaped parts, and wherein said annular portion of the inner surface of the housing resides at the junction of the two parts.

6. A high speed centrifugal air impeller assembly with rearwardly curved blades and with sound attenuation means; said impeller comprising a housing defining air inlet and air discharge chambers respectively having inlet and discharge openings, an air impeller with an annular backplate carrying a circumaxially spaced series of long narrow rearwardly inclined air moving blades on one side disposed in the housing with its inlet opening in communication with the housing inlet opening, said housing also having an annular portion at its inner surface adjacent said backplate with a diameter slightly greater than that of the backplate and at least as large as that of the inlet chamber to define a narrow annular air passageway adjacent the housing inner surface interconnecting the inlet and discharge chambers and providing sound attenuation during the passage of impeller discharge air therethrough

7. A high speed centrifugal air impeller as set forth in claim 6 wherein the ratio of the annular area between the backplate and housing to that of the annular area between the blade tips and housing falls in the range 0.10 to 0.50.

8. A high speed centrifugal air impeller as set forth in claim 6 wherein the impeller is operated at a tip speed up to approximately 550 feet per second.

9. A high speed centrifugal air impeller as set forth in claim 6 wherein the backplate extends substantially beyond the outer diameter of the blades.

10. A high speed centrifugal air impeller as set forth in claim 6 wherein the housing is formed of a pair of mating cup shaped parts, and wherein said annular portion of the inner surface of the housing resides at the junction of the two parts.