US3628882A

US3628882A - Centrifugal fan structure

Info

Publication number: US3628882A
Application number: US886627A
Authority: US
Inventors: Arne Lennart Nilsson
Original assignee: Electrolux AB
Current assignee: Electrolux AB
Priority date: 1968-12-20
Filing date: 1969-12-19
Publication date: 1971-12-21
Anticipated expiration: 1988-12-21
Also published as: DE6942947U; CH505298A; DE1955585A1; NL160915C; DK125109B; FR2026620A1; NL160915B; NL6917313A; GB1271808A; DE1955585B2; SE330061B

Abstract

This invention relates to a centrifugal fan having a rotatable fan wheel and stationary diaphragm disposed within a housing having an air inlet and outlet as its opposite ends. The diaphragm is spaced from the end of the housing having the air outlet to form a diffuser chamber. The air inlet of the housing cooperates with an axially disposed inlet of the fan wheel through which air is discharged radially outward to an outlet at the periphery of the fan wheel. The outer periphery of the diaphragm is spaced from the housing to form an annular discharge opening through which air at a high velocity passes from the outlet of the fan wheel to the diffuser chamber. In order to reduce the velocity of the air discharged from the fan wheel to transform its dynamic pressure to static pressure, a helical spring of annular form is disposed in the outer peripheral portion of the diffuser chamber.

Description

United States Patent [72] lnventor Arne Lennart Nilsson Stockholm, Sweden [21] Appl. No. 886,627 [22] Filed Dec. 19, 1969 [45] Patented Dec. 21, 1971 [73] Assignee Aktienbolaget Electrolux Stockholm, Sweden [32] Priority Dec. 20, 1968 [33] Sweden [31 1 "526/68 [54] CENTRIFUGAL FAN STRUCTURE 4 Claims, 9 Drawing Figs.

[52] U.S.Cl 415/119, 4l5/l99,415/122 [51] Int. Cl ..F04b 39/00, F04d 17/12 [50] Field of Search 415/119, 121, 122,219, 199; 230/117 VC [56] References Cited UNITED STATES PATENTS 993,985 5/1911 Harker 417/369 1,361,107 12/1920 Smoot 415/121 1,988,951 1/1935 Korittke 248/26 Primary ExaminerHenry F. Raduazo Att0rney-Edmund A. Fenander ABSTRACT: This invention relates to a centrifugal fan having a rotatable fan wheel and stationary diaphragm disposed within a housing having an air inlet and outlet as its opposite ends. The diaphragm is spaced from the end of the housing having the air outlet to form a diffuser chamber. The air inlet of the housing cooperates with an axially disposed inlet ofthe fan wheel through which air is discharged radially outward to an outlet at the periphery of the fan wheel. The outer periphery of the diaphragm is spaced from the housing to form an annular discharge opening through which air at a high velocity passes from the outlet of the fan wheel to the diffuser chamber. In order to reduce the velocity of the air discharged from the fan wheel to transform its dynamic pressure to static pressure, a helical spring of annular form is disposed in the outer peripheral portion of the diffuser chamber.

PATENTEU UEEZI l9?! SHEET 1 OF 4 FIG/- FIG. 3

PATENTEU 05221 um 3,628,882

sum 2 [1F 4 PATENIED M221 m 3.628.882

SHEET 3 [1F 4 PAIENIEUnzczmn 3528, 532

SHEET u [1F 4 1.0 2.0 -m /mm Q-EFF'ICIENCY H -5UCT/ON mm. WATER COLUMN CENTRIFUGAL FAN STRUCTURE BACKGROUND OF THE INVENTION 1. Field of the Invention Centrifugal fans having fan wheels of the centrifugal type have been provided for certain applications, such as for vacuum cleaners, for example, in which the fan wheels are driven at relatively high speeds to produce a high vacuum with comparatively high speeds to produce a high vacuum with comparatively small quantities of air.

2. Description of the Prior Art In centrifugal fans the fan wheel and a stationary diaphragm or fan screen are disposed within a housing having an air inlet and air outlet. The inlet of the housing cooperates with an inlet at one side of the rotatable fan wheel at the vicinity of its axis of rotation. The diaphragm is disposed between the fan wheel and a transverse wall of the housing in which the outlet is formed, the space between the diaphragm and such outlet wall defining a diffuser chamber.

Air is discharged from the outlet of the fan wheel at its outer periphery into the diffuser chamber through an annular air discharge opening formed between the outer periphery of the diaphragm and the housing. The air introduced into the diffuser chamber in this manner flows therethrough to .the axially disposed outlet of the housing.

Air is discharged from the outlet of the fan wheel at a relatively high velocity. It is desirable to transform the velocity head of such discharged air, which is at a relatively great dynamic pressure, into pressure head before the air flows to a succeeding stage of a multistage centrifugal fan. It usually has been the practice heretofore to employ stationary vanes or blades of helical form to decrease the velocity of the discharged air and convert its dynamic pressure to static pressure. Such helically shaped blades provide air channels which increase in cross section in a direction toward the outlet of the housing to promote a rapid decrease in velocity of the air flowing through a diffuser chamber. Even when the stationary helically shaped blades are streamlined, objectionable energy losses occur due to air shocks and air turbulence which cannot be avoided. Further, the rapid rate at which the velocity of the discharged air is reduced develops objectionable fan noise.

Further, a number of factors, such as the number, shape and length of the stationary blades or vanes determine the conditions under which the centrifugal fan functions most efficiently. Hence, a centrifugal fan having a specific stationary blade or fan system performs best for a particular speed of the fan wheel and other working conditions for which the stationary blade system has been designed. When the working conditions and speed of the fan wheel change, the energy losses of the stationary blade system usually become greater and the fan wheel operates at a higher noise level which is objectionable.

While centrifugal fans having stationary helically shaped blades or vane systems are suitable for single-stage centrifugal fans, they are objectionable in multistage centrifugal fans because the coefficient of eft'iciency of such multistage fans is materially reduced. In order to provide a stationary helically shaped blade system that is completely effective, the radial distance between the blades of the fan wheel and the stationary helically shaped vanes must be comparatively great so that the fan housing will be relatively large relative to the fan diameter, which makes it costly to fabricate.

SUMMARY OF THE INVENTION It is an object of my invention to provide an improved centrifugal fan in which the velocity of the air discharged from the fan wheel is effectively reduced to transform its dynamic pressure to static pressure. I accomplish this by providing a centrifugal fan having a diffusion chamber in which air-permeable structure is provided, such air-permeable structure providing shock resistance to air in axial, tangential and radial directions in its path of flow through the diffuser chamber to the outlet of the fan housing.

The air-permeable structure in the preferred embodiment comprises a helical spring of annular form which is disposed about the outer peripheral portion of the diffuser chamber at the vicinity of the annular discharge opening formed between the fan housing and outer periphery of the diaphragm or fan screen.

With this construction air discharged at a relatively high velocity from the outlet of the fan wheel and having a circular motion flows through the annular discharge opening into the diffuser chamber and strikes the individual turns of the helical spring which may be referred to as elements and function to break down the airstream discharged from the fan wheel outlet into a multiplicity of smaller airstreams. In this manner the velocity of the air flowing into the diffuser chamber is effectively reduced at the immediate vicinity at which the highvelocity air is introduced into this chamber. The individual turns or elements of the helical spring also function to change the circular motion of the air toward a straight line motion in a radial direction toward the axially disposed outlet of the fan housing.

BRIEF DESCRIPTION OF THE DRAWING In the drawing, FIG. 1 is a perspective view, partly broken away and in section, of a single-stage centrifugal fan embodying my invention;

FIG. 2 is a sectional view of the centrifugal fan shown in FIG. 1;

FIG. 3 is a sectional view taken at line 3-3 of FIG. 2;

FIG. 4 is a sectional view similar to FIG. 2 illustrating a twostage centrifugal fan embodying my invention;

FIG. 5 is a view, partly broken away and in section, taken at line 5-5 of FIG. 4;

FIGS. 6 and 7 are views similar to FIG. 5 illustrating other embodiments of my invention; FIG. 6A is a fragmentary sectional view taken at line 6A-6A of FIG. 6; and

FIG. 8 shows curves diagrammatically illustrating the performance characteristics of a fan system embodying the invention and another fan system for purposes of comparison, the performance characteristics being obtained when the fan systems are incorporated in horizontal tank-type vacuum cleaners.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 to 3 of the drawing, I have shown my invention as applied to a single-stage centrifugal fan 10 having a rotary fan or fan wheel 11 fixed to a shaft 12 adapted to be driven by a suitable electric motor (not shown). The fan wheel 11, which is provided with spaced radially disposed blades or vanes 9, is disposed within a housing 14 which forms a suctioncreating fan chamber 15.

The housing 14 includes

walls

16 and 17 which are transverse to the axis of the shaft 12 and normal or perpendicular thereto. Rotating movement imparted to the shaft 12 causes fan wheel II to draw air through an inlet 18. in the wall 16 into the housing 14. A stationary diaphragm or fan screen 19 is fixed in position alongside the fan wheel 11 at the side thereof opposite the inlet 18 formed in the wall 16. Air drawn through the inlet 18 in the wall 16 passes through a cooperating inlet 20 at one side of the fan wheel 11 and is discharged radially outward toward the outlet 21 at the outer periphery of the fan wheel.

An outlet 22 is formed in the wall 17 which is spaced from the diaphragm or fan screen 19 to form a diffuser chamber 23. The outer periphery of the diaphragm 19 is spaced from the annular portion of the housing 14 to form an annular discharge opening 24 from the outlet 21 of the fan wheel 1 I to the diffuser chamber 23. A plurality of essentially straight blades or vanes 25 are provided in the diffuser chamber 23 which extend radially outward from the outlet 23 in wall 17 toward the outer peripheral portion of the chamber 23.

In accordance with my invention I provide a helical spring 26 of annular form in the outer peripheral portion of the diffuser chamber 23 in the path of flow of air passing through the annular discharge opening 24 from the outlet 21 of the fan wheel 11. In a broad sense the helical spring 26 serves as airpermeable structure which functions to provide shock resistance to air in axial, tangential and radial directions in its path of flow to the outlet 22 of the fan housing 14.

The high-velocity air passing through the air discharge opening 24, which has a. circular motion, strikes and impinges the individual turns or elements of the helical spring 26 and breaks down the air passing into the outer peripheral portion of the diffuser chamber 23 into a multiplicity of small airstreams. In FIG. 3 the circular motion of the air passing through the annular air discharge opening 24 is indicated schematically by the arrows A and the resulting multiplicity of the small airstreams formed after striking the turns of the helical spring 26 are indicated schematically by the arrows B. Hence, the helical spring 26 functions to change the circular motion of air represented by the arrows A to an essentially straight line motion represented by the arrows B in which the small airstrearns flow radially inward in the diffuser chamber 23 to the outlet 22 of the fan housing 14. Such change in the motion of the air is aided by the essentially straight blades 25 which extend radially inward from the helical spring 26 toward the air outlet 22.

The important function of the helical spring 26 is that it provides shock resistance to the impinging air to transform its dynamic pressure to static pressure and in so doing materially reduces the velocity of the air which requires energy. I have discovered that the shock losses that result when air flows through the helical spring 26 to reduce its velocity is materially less than the total shock loss that results when the velocity of air is reduced by helically shaped stationary blades in the manner described above.

In FIGS. 4 and I have illustrated a two-stage centrifugal fan 110 in which each stage 1100 and 11% is like the singlestage centrifugal fan shown in FIGS. 1 to 3 and just described. The centrifugal fan 110 includes fan wheels 1110 and lllb fixed to a shaft 112 adapted to be driven by an electric motor (not shown). The tandem fan wheels 111a and lb are disposed within housings 114a and 114b, respectively, which form suction-creating chambers 115a and lb.

The housings 114a and l14b include

walls

116a, 117a and ll7b which are transverse to the axis of the shaft 112 and normal or perpendicular thereto. The

walls

116a, 117a and 1l7b are formed with openings 118a, 112a and 112b, respectively. The

wall openings

118a and 122a cooperate with inlets 120a and 120i; at one side of the fan wheels Illa and 11 lb, respectively. Air is discharged radially outward in the fan wheels Illa and lllb toward the outlets 121a and 121b, respectively, at the outer peripheries of the fan wheels,

Stationary diaphragms 119a and 11% are fixed in position between the fan wheels 111a and Illb and housing walls 117a and 1117b, respectively, to form diffuser chambers 123a and 12312 in which are provided essentially straight blades 125a and 1.25!) like the blades 25 in the first described embodiment. The outer peripheries of the diaphragrns 119a and 11912 are spaced from the annular portions of the housings 114a and 114b, respectively, to form annular discharge openings 124a and 12412.

As in the embodiment of FIGS. 1 to 3, I provide helical springs 126a and 126k of annular form in the outer peripheral portions of the

difiuser chambers

123a and 123b, respectively, each of which functions in the same manner as the helical spring 26 in the first-described embodiment of FIGS. 1 to 3. The velocity of the air discharged from the outlet 121a of the fan wheel 1110 in the first stage 110a is effectively reduced by the helical spring 1260 to transform its dynamic pressure to static pressure before the air flows through the opening 1220 in the housing wall 117a into the second stage [10b of the centrifugal fan 110. With this arrangement the performance of the two-stage centrifugal fan 110 is substantially improved, as will be explained presently.

In FIGS. 6 and 6A, similar to FIG. 5, I have shown a further embodiment of my invention in which parts similar to those shown in the embodiment of FIGS. 4 and 5, are referred to by the same reference numerals to which has been added. In FIG. 6 I provide a plurality of

helical coils

2260, 226b, 226e, 226d and 226a which are of annular form. The helical coil 226e is disposed in the diffuser chamber 223 adjacent to the air outlet 222, the coil 226a is disposed in the outer peripheral portion of the diffuser chamber 223 and the coils 226b, 226v and 2264 are disposed between the inner and outer coils 226e and 2260, respectively. As best seen in FIG. 6A, the essentially straight blades 225 are notched at 2251: to provide openings through which the

helical coils

226e, 226d and 226a can pass.

In FIG. 7, which is similar to FIG. 6, l have shown a further embodiment of my invention which is provided with two

helical coils

326a and 326e, one of which is disposed at the outer peripheral portion of the diffuser chamber 212 and the other of which is disposed in the diffuser chamber adjacent to the air outlet 322.

In FIG. 8 I show curves illustrating the performance characteristics plotted from test data for two fan systems which will be referred to as fan system I" and fan system 2." The embodiment shown in FIGS. 4 and 5 and described above embodies fan system I and a modification of the embodiment of FIGS. 4 and 5, in which the helical coils 126a and [26b are omitted, embodies fan system 2. The two fan systems I and 2 were tested in a motor-fan unit incorporated in a horizontal tank-type vacuum cleaner, the same electric motor being employed in testing each fan system. The motor-fan unit was attached to an equalization vessel provided with an aerometer and outlet to measure the vacuum.

The curves in FIG. 8 represent the efficiency and vacuum H-curves for the horizontal tank-type vacuum cleaner adapted for operation with the fan systems 1 and 2, respectively. The test data obtained for the purpose of comparing the performance characteristics of the two fan systems were taken at essentially the same electrical power input (watts) to the motor while supplying electrical energy thereto at the same operating voltage. In this way the test data for the two fan systems indicated changes in performance characteristics attributable only to differences between the fan systems I and 2.

As previously stated, FIG. 8 illustrates curves representing the performance characteristics for a complete vacuum cleaner structure. In practical use such vacuum cleaner is adapted to move a variable quantity of air q per unit interval of time in a range represented along the abscissa in FIG. 8 from the intersection thereof with the ordinate to the region of the reference character q. Within practically the entire operating range it will be seen that the vacuum performance curve H, for fan system I is higher than the vacuum performance curve H, for fan system 2.

The increased suction capacity shown by fan system I embodying my invention is thus due to the higher degree of efficiency of this fan system compared with fan system 2. This is apparent in FIG. 8 which shows the efficiency curves n l and n 2 for vacuum cleaners adapted for operation with fan systems I and 2, respectively.

A feature of my invention that is realized is that my improved centrifugal fan is substantially quieter in operation than centrifugal fans of the kind heretofore provided. This reduction in sound level is in a range of 4 to 6 dBA. This reduction in sound level can be attributed to the fact that a large part of the sound generated when the velocity of the air is reduced by the helical springs is at a relatively high frequency outside the audible range.

It will be understood that, instead of providing one or more helical coils of annular form in the diffuser chamber of a centrifugal fan in the manner illustrated and described above, other air-permeable structure can be employed which functions in the same manner as the helical springs and provides shock resistance to air in axial, tangential and radial directions in its path of flow through the diffuser chamber to reduce the velocity of the air by transforming its dynamic pressure to static pressure.

I claim:

1. Centrifugal fan structure comprising a. a centrifugal fan having a rotatable fan wheel formed with an air inlet at one side thereof at the vicinity of its axis of rotation and an outlet at the outer periphery thereof,

b. a diaphragm transverse to said axis having one side thereof spaced from and facing the side of said fan which is opposite said inlet,

. means providing a housing for said fan wheel and said diaphragm which includes an annular portion and a first wall transverse to said axis which has an inlet cooperating with said fan wheel inlet and a second wall transverse to said axis which has an axially disposed air outlet and is spaced from the opposite side of said diaphragm to form a diffuser chamber,

d. the outer periphery of said diaphragm being spaced from the annular portion of said housing to form an annular discharge opening from the outlet of said fan wheel to said diffuser chamber, and

e. helical spring means of annular form which is disposed in said diffuser chamber and provides shock resistance to air in axial tangential and radial directions in its path of flow from said annular discharge opening to the outlet of said housing.

2. Centrifugal fan structure as set forth in claim 1 in which said helical spring means of annular form is disposed at the outer peripheral portion of said diffuser chamber at the vicinity of said annular discharge opening.

3. Centrifugal fan structure as set forth in claim 1 including a plurality of blades which are distributed in said diffuser chamber and extend radially outward from the air outlet of said fan housing toward said helical spring means.

4. Centrifugal fan structure comprising a. a centrifugal fan having a rotatable fan wheel formed with an air inlet at one side thereof at the vicinity of its axis of rotation and an outlet at the outer periphery thereof,

c. means providing a housing for said fan wheel and said diaphragm which includes an annular portion and a first wall transverse to said axis which has an inlet cooperating with said fan wheel inlet and a second wall transverse to said axis which has an axially disposed air outlet and is spaced from the opposite side of said diaphragm to form a diffuser chamber,

e. a plurality of helical spring means of annular form which are disposed in said diffuser chamber and provide shock resistance to air in axial, tangential and radial directions in its path of flow from said annular discharge opening to the outlet of said housing, said helical spring means being at different radial distances from the axially disposed air outlet of said fan housing.

UNITED STATES PATENT omits (IERTiFICATE 0F CORRECHON Patent No. 3, 4 Dated December 21, 1971 Invent0 Arne Lennart Nilsson It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover sheet [73-] Assignee, "Aktienbolagetfil, v

should read Aktiebolaget in the ABSTRACT, line 31-, "as" should read at Column 1, lines 8 and 9, canoel "high speeds to product a high vacuum with comparatively"; line 67, "diffusion" should read diffuser Column 3, line 47,

"112a" should read 122a and "ll2b" should read' l22b Column 4 line 1, after "618,9, insert FIG. 6 being line 17 "212" should read 323 Column 5, line 22, after axial", insert a comma.

Signed and sealed this 14th day of November 1972.

(SEAL) Attest:

EDWARD MBFLETCHERJJR. o ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM USCOMM-DC 00376-Pu9 n ,5. GOVERNMENT PRINTING OFFICFVI I969 U-SGIPJSJ,

Claims

1. Centrifugal fan structure comprising a. a centrifugal fan having a rotatable fan wheel formed with an air inlet at one side thereof at the vicinity of its axis of rotation and an outlet at the outer periphery thereof, b. a diaphragm transverse to said axis having one side thereof spaced from and facing the side of said fan which is opposite said inlet, c. means providing a housing for said fan wheel and said diaphragm which includes an annular portion and a first wall transverse to said axis which has an inlet cooperating with said fan wheel inlet and a second wall transverse to said axis which has an axially disposed air outlet and is spaced from the opposite side of said diaphragm to form a diffuser chamber, d. the outer periphery of said diaphragm being spaced from the annular portion of said housing to form an annular discharge opening from the outlet of said fan wheel to said diffuser chamber, and e. helical spring means of annular form which is disposed in said diffuser chamber and provides shock resistance to air in axial tangential and radial directions in its path of flow from said annular discharge opening to the outlet of said housing.

4. Centrifugal fan structure comprising a. a centrifugal fan having a rotatable fan wheel formed with an air inlet at one side thereof at the vicinity of its axis of rotation and an outlet at the outer periphery thereof, b. a diaphragm transverse to said axis having one side thereof spaced from and facing the side of said fan which is opposite said inlet, c. means providing a housing for said fan wheel and said diaphragm which includes an annular portion and a first wall transverse to said axis which has an inlet cooperating with said fan wheel inlet and a second wall transverse to said axis which has an axially disposed air outlet and is spaced from the opposite side of said diaphragm to form a diffuser chamber, d. the outer periphery of said diaphragm being spaced from the annular portion of said housing to form an annular discharge opening from the outlet of said fan wheel to said diffuser chamber, and e. a plurality of helical spring means of annular form which are disposed in said diffuser chamber and provide shock resistance to air in axial, tangential and radial directions in its path of flow from said annular discharge opening to the outlet of said housing, said helical spring means being at different radial distances from the axially disposed air outlet of said fan housing.