GB2055969A - Low Noise Centrifugal Blower - Google Patents

Abstract

In a centrifugal blower having a spiral housing 11 in which the fan wheel 12 is mounted approximately concentrically of the spiral housing, the involute wall portion 19 of the blower housing 11 terminates proximate the blower outlet 15 without a curved cut-off. Rather, the near extension wall portion 20 extends from the end of the involute wall portion 19 in a direction toward the blower outlet to define a channel 31 having an increasing radial spacing from the centre of the spiral housing towards the outlet. The elimination of the conventional cut-off reduces operating whistle. <IMAGE>

Description

SPECIFICATION Low Noise Centrifugal Blower The present invention relates generally, as indicated, to centrifugal blowers and, more particularly, to a means for reducing the noise of a centrifugal blower.

Centrifugal blowers or centrifugal fans (the terms blower and fan being used interchangeably herein) are, of course, well known devices for blowing air, or as desired, other fluids. As is described in the Marks' Standard Handbook for Mechanical Engineers, McGraw-Hill Book Company, New York, 1967, at pages 14-72 through 14-78, a centrifugal fan has a fan wheel and a casing or housing with a cutoff, an air inlet and an air outlet. The fan wheel is of generally cylindrical configuration having blades facing forward or backward relative to the direction of rotation thereof about the axis of the cylinder. The casing typically is generally spiral in shape to collect the air delivered from the fan wheel and to conduct the same in a spiral flow pattern to the outlet.

An example of a prior art centrifugal blower is illustrated in Figure 1 of this application. The blower 1 includes a cylindrical fan wheel 2 having a radial center 3 along its axis and a spiral shape blower housing 4 with a blower outlet 5 at one end thereof. The air inlet 6 to the fan wheel.

The spiral blower housing 4 has an approximate center of curvature or radial center, i.e. the theoretical center of the spiral thereof, not shown, but approximately falling in the vicinity of the radial center 3 of the fan wheel 2. The blower housing 4 has two wall portions which lead generally to the blower outlet 5; one of those wall portions 8 is that part of the spiral shape blower housing that is relatively far or remote from the spiral center, and the other wall portion 9 may be considered the involute wall portion, which generally curves inwardly along the track of the spiral toward the center thereof. Typically the fan wheel 2 is positioned such that it is relatively near the involute wall surface 9, but relatively far from the remote wall portion 8.With the fan wheel 2 so positioned, there is a generally annular spirally expanding flow path along which air may be blown by the rotating fan wheel 2 toward the blower outlet 5 for discharge from the latter in a generally linear flow direction or flow path. Linear is used herein to indicate a non-spirally confined flow path and may be a divergent one, as the air blown through the blower outlet 5 may diverge or expand upon so leaving.

In the past a cutoff 10 has been provided at the end of the involute wall portion 9 relatively proximate or extending into the blower outlet 5.

At least part of such cutoff 10 somewhat continues the involute curve of the spiral.

According to the above-mentioned text, Marks', such a cutoff is required in a centrifugal blower to provide a transition from the spiral air flow occurring in the housing to the relatively straightline discharge air flow through the blower outlet 5. In providing such transition, the typical cutoff, such as the cutoff 10 illustrated in Figure 1 , tends to cut off or to impede air flow through the clearance area between the cutoff and the fan wheel 2, which would ordinarily rotate in a counter-clockwise direction relative to the illustration of Figure 1.As is also described in such text, typically the blower outlet 5 would connect with a duct having a greater height dimension than the height of the blower outlet 5, such greater height dimension being, for example, equal to the distance between the wall portion 8 and the radial center 3 of Figure 1; and in such case, the cutoff 10 clearly impedes the flow of air into the outlet duct, not shown.

It has been discovered that the cutoff 10 of a typical conventional centrifugal blower contributes significantly to audible noise, notably an audible tone or whistle-like sound, of such prior art centrifugal blowers. Moreover, in accordance with the present invention, it has been discovered that by eliminating the cutoff in a centrifugal blower, such tone or whistle-like noise may be eliminated without unreasonably affecting the performance of the centrifugal blower and in many instances without having any significant effect on such performance.

Briefly, then, the invention is directed to a centrifugal blower and to a particular type of blower housing therefor, in which there is no such cutoff or like impediment to provide the allegedly required transition in the involute wall portion of the blower relatively proximate the blower outlet.

Rather, in the present invention an extension wall portion extends from the end of the involute wall portion in a direction toward the blower outlet, preferably terminating at the latter, with such extension wall portion, or least a major part thereof, traveling therealong in a direction toward such blower outlet having an increasing radial spacing from the spiral center of the spiral shape housing and/or the radial center of the fan wheel.

Although the total decibel noise level produced by an operating centrifugal blower in accordance with the present invention due to the major air flow therein will not be changed significantly, the noted tone or whistle-like sound, however, has been significantly reduced or eliminated by practicing the invention in centrifugal blowers.

The invention is further described with reference to the annexed drawing setting forth in detail a certain illustrative embodiment of the invention, this being indicative, however, of but one of the various ways in which the principles of the invention may be employed.

In the annexed drawing: Figure 1 is a side elevation view of a prior art cylindrical blower; Figure 2 is a side elevation view of a cylindrical blower in accordance with the present invention; Figure 3 is a front elevation view of a preferred embodiment of the invention looking generally in the direction of the arrows 3-3 of Figure 2; and Figure 4 is a top view of the preferred cylindrical blower looking generally in the direction of the arrows 44 of Figure 3.

Referring now in detail to the drawing, wherein like reference numerals designate like parts in the several figures, and initially to Figure 2, a centrifugal blower in accordance with the present invention is generally indicated at 11. The blower 11 includes a cylindrical fan wheel 12 of conventional design having a radial center 13 along its axis and a generally spiral shape blower housing 14 with a blower outlet 1 5 at one end of the housing.

The spiral blower housing 14 has an air inlet 16 in side wall 17. A wall portion 18 that is relatively remote or distant from the spiral center of the blower housing 14, which center may be in the vicinity of the radial center 13, extends to the blower outlet 15 forming part thereof. The blower housing 14 also has an involute wall portion 19, which, of course, is more proximate the radial center of the major spiral shape extent of the blower housing 14 than the remote wall portion 18.

Importantly, it will be seen in Figure 2 that there is no cuPoR continuing the general spriel shape of the involute wall portion 19 to provide a transition between the spiral flow and the straight-line or linear flow of air. Rather, an extension wall portion 20, which preferably has a linear extent, leads from its juncture with the involute wall portions 19, say approximately at the area designated 21, up to the blower outlet 1 5 at the end 22 of the extension wall portion.

Thus, it will be seen that there is no impediment in the centrifugal blower 1 11 similar to the cutoff vane of the prior art centrifugal blower 1. The actual outlet area of the blower outlet 1 5 may be considered to be the area bounded in part by the end 23 of the remote wall portion 18 and the end 22 of the extension wall portion 20, both of which open into a cutout 24 in a face plate 25 to which the blower housing 14 may be attached, say by spot welding, screws, etc. Moreover, even if the outlet area of the blower outlet 1 5 were considered to be that bounded by the end 23 of the remote wall portion 18 and the bottom of an outlet duct, not shown, which may line up approximately along a horizontal line drawn through the radial center 13, it will be appreciated that the extension wall portion 20 still will not provide the prior art cutoff transition in which the cutoff shape effectively continues the curve of the spiral of the blower housing 14.

The fan wheel 12 preferably is placed relatively proximate the involute wall portion 19 and relatively remote from the remote wall portion 18 so as to define an annular spirally enlarging space 30 from the area most proximate the closest part of the involute wall portion 19 or extension wall portion 20 to the blower fan wheel 12 traveling in the counterclockwise direction of rotation of the fan wheel toward the blower outlet 1 5. The exact position for the fan wheel 12 in the blower housing 14 may be determined experimentally or pragmatically in dependence on the desired performance of the centrifugal blower 11.In any event, it will clearly be desirable to have the fan wheel 12 a positioned relatively proximate, although with some clearance therebetween, the involute wail portion 1 9 and extension wall portion 20 and particularly the juncture area 21 thereof, while, on the other hand, being relatively remote from the remote wall portion 1 8 and the blower outlet 1 5.

Since the approximate radial center or spiral center of the spiral shape of the blower housing 14 and the radial center of the cylindrical fan wheel 12 are in the vicinity of one another, it will be seen that the major extent of the extension wall portion 20 in a direction thereof traveling toward the blower outlet 15 has an increasing radial spacing from such center. Therefore, the area 31, which may be referred to as the noncutoff area since there is no prior art cutoff there is, relatively open and unimpeded between the end 22 of the extension wall portion and the prnximate areas of the fan wheel 12.This open area 31 is provided in the centrifugal blower 11 regardless of whether the outer periphery of the fan wheel 12 is more proximate the involute wall portion 19, and particularly the juncture area 21 of the latter with the extension wall portion 20, or is more proximate the extension wall portion 20 at some point along its length, with this relationship being dependent, for example, on the location of the juncture 21 relative to the radial center 1 3 of the fan wheel and the actual slope of the extension wall portion 20, say, for example, with respect to the vertical.

Turning now briefly to Figures 3 and 4, in accordance with the best mode and preferred embodiment of the invention, a blower assembly 40 may be formed of two centrifugal blowers 1 a, 11 b identical with the centrifugal blower 11 described above with reference to Figure 2.

Reference numerals with suffixes a and b designate parts in blowers 11 a, 11 b corresponding to those parts designated by similar reference numerals in the blower 11 of Figure 2. Such blowers 1 a, 1 b may be attached to a common face plate 25 and may be further secured by a support strip 41. A single blower motor 42 mounted between blowers 1 a, 9 b provides motive force for rotating the two fan wheels 1 2a, 1 2b in the blower housings 1 4a, 1 4b. The air inlets 1 6a, 1 6b may be at opposite ends of the blower assembly 40, and, if desired, one or both of them may open toward the center of the blower assembly 40 to provide a cooling air flow over the motor 42 as air is drawn into the blowers. Air is blown through blower outlets 15a, 1 Sb of the respective blowers through respective cutouts 22a, 22b in the face plate 25.

The blower housing and improved blower of the invention may be used in vehicles and in other environments in which blown air is required.

Claims (8)

Claims

1. A centrifugal fan, comprising a fan wheel for blowing air, a housing for collecting air blown by said fan means, and a substantially unimpeded outlet in said housing for permitting substantially unimpeded outflow of blown air collected by said housing.

2. A fan according to claim 1, wherein said housing is a spiral housing having one wall portion remote from the spiral centre and leading toward said outlet, an involute wall portion close to such spiral centre, and an extension wall portion leading from said involute wall portion to said outlet, said extension wall portion having a substantial part thereof positioned with respect to said fan wheel so as not substantially to impede the flow of air in said housing.

3. A fan according to claim 2, wherein said extension wall portion is linear.

4. A fan according to claim 2 or 3, wherein said extension wall portion terminates at said outlet.

5. A fan according to claim 2, 3 or 4, wherein said fan comprises a generally cylindrical fan wheel positioned in said housing to blow air from an inlet in the side of the housing toward said outlet.

6. A fan according to claim 2, 3, 4 or 5, wherein said extension wall forms a channel of which increases in radial dimension in a direction toward said outlet.

7. A fan according to any one of claims 2-6 including two fan wheels each mounted in its own spiral housing and driven by a common drive motor.

8. A centrifugal fan substantially as hereinbefore described with reference to Figures 2 to 4 of the accompanying drawings.

8. A centrifugal fan substantially as hereinbefore described with reference to Figures 2-4 of the accompanying drawings.

New Claims or Amendments to Claims filed on 11 September 1980.

Superseded Claims 1 to 8.

New or Amended Claims:-

1. A centrifugal fan, comprising a fan wheel for blowing air, a housing for collecting air blown by said fan wheel and a substantially unimpeded outlet in said housing for permitting substantially unimpeded outflow of blown air collected by said housing, wherein said housing is a spiral housing having one wall portion remote from the spiral centre and leading toward said outlet, an involute wall portion close to such spiral centre, and an extension wall portion leading from said involute wall portion to said outlet, said extension wall portion having a substantial part thereof positioned with respect to said fan wheel so as not substantially to impede the flow of air in said housing.

2. A fan according to claim 1, wherein said extension wall portion is linear and tangential to the involute wall portion at the juncture of said involute and extension wall portions.

3. A fan according to claim 1 or 2, wherein said extension wall portion terminates at said outlet.

4. A fan according to claim 3, wherein said outlet is generally rectangular and the end of the wall portion which terminates at the outlet is parallel to the major axis of the outlet cross section.

5. A fan according to claim 1, 2, 3, or 4, wherein said fan comprises a generally cylindrical fan wheel positioned in said housing to blow air from an inlet in the side of the housing toward said outlet.

6. A fan according to any one of claims 1 to 5, wherein said extension wall forms a channel of which increases in radial dimension in a direction toward said outlet.

7. A fan according to any one of claims 1 to 6, including two fan wheels each mounted in its own spiral housing and driven by a common drive motor.