WO2001011206A2

WO2001011206A2 - Perforated acoustic silencer for electrical motors

Info

Publication number: WO2001011206A2
Application number: PCT/TR1999/000037
Authority: WO
Inventors: Ridvan Egin; Cüneyt ÖZTÜRK; Emin SÖNMEZ; Mithat ERGÜN
Original assignee: Türk Elektrik Endüstrisi A.Ş.
Priority date: 1999-08-11
Filing date: 1999-08-11
Publication date: 2001-02-15
Also published as: WO2001011206A3; AU5457199A

Abstract

The present invention is related to a fan silencer that attenuates the continuously fluctuating sound waves without being propagated and that lowers the acoustic energy emerging in the near field, within the hydrodynamic near field of the suction fan particularly used in electrical vacuum cleaner motors. The silencer essentially consists of an annular set (13) surrounding the suction fan (2) which forms a barrier between the suction fan and the fan clow side wall (12). On this set (13) exist one or more than one rows of circular holes (8). The silencer (7) can be fixed inside the suction fan cover (3) or on the surface (14) of the air diffuser (6) that faces the suction fan.

Description

PERFORATED ACOUSTIC SILENCER FOR ELECTRICAL MOTORS

The present invention is related to a fan silencer which attenuates the continuously fluctuating waves before being propagated, and which reduces the acoustic energy emerging within the hydrodynamic nearfield area of the suction fan which is a radial fan particularly used in electrical vacuum cleaners.

The fan groups integrated to the electrical motors for different purposes consist of various parts. For instance, for the vacuum cleaner motors, a fan assembly consists of an air diffuser, a fan and a fan cover. The air sucked in through the fan cover inlet is accelerated by the fan and exhausted from the fan outlet.

The noise of the air accelerated by the fan is generally tried to be suppressed by using passive absorption techniques. Furthermore, flow errors that may enhance the air borne noise, such as turbulence and jet-effect, should be avoided in the design while determining the dimensions of the fan and the fan cover.

Another way to reduce the fan noise is using indirect methods such as lowering the r.p.m.

The object of the present invention is to attenuate the sound waves created by the radial fan assemblies in the electrical motors and to lower the air borne noise level by reducing the acoustic energy and thus, to regulate the acoustic emission.

A preferred embodiment of the perforated acoustic silencer realised to achieve this object is illustrated in the attached drawings for exemplary purposes, wherein:

Figure 1; is a schematic view of the wet & dry electrical vacuum cleaner fan assembly.

Figure 2; is the overall view of the silencer; Figure 3; is the view of the silencer as mounted on the fan cover; Figure 4; is cross section view of the silencer as mounted on the fan cover; Figure 5; is cross section view of the silencer in the wet & dry vacuum cleaner; Figure 6; is the view of the silencer showing it in a state of being mounted on the fan cover by using the sagging method;

Figure 7; is the view showing the lugs forming the skirt (tail) of the silencer; Figure 8; is the view showing the installation of the silencer on the channels provided on the air diffuser.

The numerals used for the parts shown in the drawings are as follows:

1. Fan cover (mounting) stopper

2. Suction fan

3. Suction fan cover 4. Motor body

5. Fan cover air inlet

6. Air diffuser

7. Silencer,

8. Hole 9. Silencer skirt

10. Sagging

11. Silencer skirt lugs

12. Fan cover side walls

13. Annular set 14. Air diffuser surface

15. Mounting channel on the air diffuser

The silencer (7) of the invention essentially consists of an annular set (13) placed inside the fan assembly and around the suction fan (2) forming a barrier between the suction fan (2) and the fan cover side wall (12) (Figure 2). The silencer (7) is characterized with one or more rows of holes (8) on the said set (13). The said holes (8) are preferably circular. The silencer (7) can be made of various metals, or plastics material.

The said silencer (7) is placed in the suction fan cover (3). The skirt (9) of the silencer is fitted on the base of the fan cover (Figure 3 and Figure 4). The height and the distance of the silencer (7) from the side walls may vary depending on the way of implementation and construction.

In the preferred embodiment of the invention, the diameters of the holes (8) arranged in two rows on the silencer (7) also vary according to the way of implementation and construction.

Although it has been observed that the most effective result is obtained by arranging the holes (8) in two rows, the number of the rows may vary, in order to meet the specific requirements of different practises.

The function of the silencer (7) is to attenuate the continuously fluctuating waves without being propagated within the hydrodynamic near field and to lower the acoustic energy emerging in the near field.

The sound waves exhibit a continuos variation in the near field. It is possible to attenuate the sound waves and to lower the acoustic energy, within the said near field. As providing this by means of a perforated structure, shall also ensure the reduction in the back pressure, it is considered to be a substantially effective method. Here the aim is to attenuate the sound waves without causing any negative impact on the dynamic behaviour of the fluid or on the fan performance.

The ability of attenuation of the perforated acoustic silencer (7) varies inversely proportionally to the cross section area and wave length and directly proportionally to the peripheral length, number and depth of the perforated holes of the silencer (7). Accordingly; when:

P: no. of perforated holes

1= peripheral length of the acoustic silencer

A= Cross section area of the perforated holes

ΔLi: attenuation ability of the silencer (7) h= depth of perforated holes λ = sound wavelength;

then, it is possible to foresee its attenuation ability from the formula (1) given below:

ΔJ_; -I— (i) A χ

Further more, the reflection and transmission angles of the sound waves from the perforated structure are also important.

When,

is taken as

P_R = P_Re-^ja*^+K> (3)

P_τ = P_Te^}a*^+K° (4) then: PT=PI+PR

Since: θ₀= incoming wave angle = reflected wave angle

θ_x - transmitted wave angle,

then;

sin 0ι ₌ ___ ₍₅₎ sin θ₀ z₀

Here, when it is considered that:

P z₀ = p₀c = (6)

a r a (7)

it will be seen that the angles of positioning are effective on the reflected and transmitted sound waves as well as on their velocity. For this reason the effectiveness of the acoustic silencer will vary depending on;

• The hole diameters, sectional area and hole depth,

• Number and lay-out of the holes,

• The silencer peripheral length and its distance from the source of noise,

• Positioning angle of the silencer and the perforated holes. The silencer (7) may be made of metal, or plastic material. The assembly process of the silencer (7) to the fan cover (3) may be performed before the assembly line, in order to provide facility. By selecting the silencer skirt (9) exterior diameter, in conformity with the inner diameter of the fan cover (3) or with the circular ribs existing on the base of the fan cover, concentricity can be facilitated. Moreover, in case there is a certain inclination at the base of the fan cover (3), it is preferable that the silencer skirt (9) is also in line with the said inclination. Various methods can be employed for the assembly of the silencer (7) on the fan cover (3).

One of the said methods is locating the silencer skirt (9) to the fan cover base, using the appropriate adhesive (Figure 4). Another method is providing the fixation of the silencer skirt (9) by a sagging (10) to be made inwards at several points or peripherally on the fan cover (3) exterior diameter (Figure 6). In this practise, the silencer skirt (9) can be placed inside the fan cover (3) with or without locating it on the fan cover (3) base by using the appropriate adhesive.

Another approach stipulates the formation of lugs (11) on the silencer skirt, in case a silencer made of metal is used (Figure 7). Assembly is provided by welding the said lugs (11) on the fan cover (3).

The silencer can also be fixed on the surface (14) of the air diffuser (6).

For this purpose, sectional or peripheral channels (15) are formed on the said surface to provide the engagement of the edges of the silencer (Figure 8). The said channels (15) can be formed on the air diffuser surface (14) in a divided (sectional) form depending on the profile of air diffuser exterior diameter. By means of the said channels (15) formed on the air diffuser surface:

• Fixation guide rails by means of which the silencer can easily be mounted on the air diffuser surface, are formed. • The complexity of the air diffuser mould by mounting the silencer later, is prevented.

• By choosing the suitable channel base height, the gap required for the air flow between the air diffuser and the silencer is provided.

• By choosing the suitable silencer and channel profiles, the diffuser/silencer fixation is provided (One of these profiles is shown in Figure 8 as an example).

Claims

1. A perforated acoustic silencer for electrical motors that is placed within the fan assembly in order to lower the air noise of the radial fan groups assembled to electrical motors, characterized with an annular set (13) surrounding the suction fan (2) which forms a barrier between the suction fan and the fan cover side wall (12) and with more than one holes (8) perforated on the periphery of the said set.

2. An acoustic silencer as claimed in Claim 1, characterized in that the holes (8) are circular.

3. An acoustic silencer as claimed in Claims 1 and 2, characterized in that there are more than one rows of perforated holes that are parallel to each other, on the said set (13).

4. An acoustic silencer as claimed in Claims 1 to 3, characterized with a peripheral skirt (9) provided in order to locate the silencer by using the appropriate adhesive (7) to the base of the fan cover (3).

5. An acoustic silencer as claimed in Claims 1 to 4, characterized with the saggings (10) formed at more than one points or peripherally on the exterior of the fan cover side wall (12) in order to provide the fixation of the silencer skirt (9) on the base of the fan cover (3).

6. An acoustic silencer as claimed in Claims 1 to 3, characterized with the skirt lugs (11) providing the fixation of the silencer (7) made of metallic material to the base of the fan cover (3) by welding. An acoustic silencer as claimed in Claims 1 to 6, characterized with the channels (15) providing the mounting of the silencer (7) on the surface (14) of the air diffuser (6) that faces the suction fan.