GB2425078A

GB2425078A - Cyclonic separator with noise reducing feature

Info

Publication number: GB2425078A
Application number: GB0607824A
Authority: GB
Inventors: Hwa-Gyu Song; Jae-Man Joo; Jun-Hwa Lee; Jang-Keun Oh; Sung-Cheol Lee
Original assignee: Samsung Gwangju Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 2004-08-23
Filing date: 2005-04-14
Publication date: 2006-10-18
Anticipated expiration: 2025-04-14
Also published as: GB0607824D0; GB2425078B

Abstract

A cyclonic separating apparatus (300) includes a cyclone body (310) having a cyclone chamber (313) and a dust-collecting chamber (315). A cover unit (330) is connected to an upper portion of the cyclone body (310), and an openable door unit (350) is mounted to a lower portion of the cyclone body At least one noise-reducing rib (317, fig.3) is provided in an air discharge pipe (314, fig.3) of the cyclone chamber (313). The noise-reducing rib is preferably configured to be curved (as depicted in fig. 4) and also serves to convert the swirling motion of the air into a straightened flow.

Description

Cyclonic Separating Apparatus This invention relates to a cyclonic

separating apparatus, and to a vacuum cleaner having the same.

In a conventional cyclonic separating apparatus, dust-carrying air drawn in through a suction path is separated into "clean" air and impurities such as dust (hereinafter referred to as "dust").

The separated dust is passed through a dust discharge pipe and is collected in a dust-collecting chamber, and the "clean" air is discharged through an air discharge pipe to the outside of the cyclonic separating apparatus. As this happens, the "clean" air being discharged through the air discharge pipe becomes a whirling air current, and the flow of this whirling air current causes noise and a loss of pressure.

To overcome this disadvantage, an air discharge pipe configured to have an increasing diameter towards an air-inlet side thereof has been introduced (see KR 200 1-0099572). In another recent development (see WO 02067756) a streamlined slant body is disposed in the centre of an air discharge pipe. However, in each of these developments, the noise and loss of pressure due to the whirling air current generated at an outer wall of the air discharge pipe cannot be restrained.

Especially in the latter case, the streamlined slant body and the support structure therefor may obstruct the dust included in the air, thereby causing a blockage of the air discharge pipe.

An aim of the invention is to provide a cyclonic separating apparatus which operates with reduced noise and reduced loss of pressure.

The present invention provides a cyclonic separating apparatus comprising: a cyclone body including a cyclone chamber and a dust- collecting chamber; a cover unit connected to an upper portion of the cyclone body; an openable door unit mounted to a lower portion of the cyclone body; and at least one noise-reducing rib formed in an air discharge pipe of the cyclone chamber.

Advantageously, the or each noise-reducing rib protrudes from an inner wall of the air discharge pipe towards the centre thereof, and comprises a curved portion and a straight portion.

Preferably, the curved portion of the or each noise-reducing rib is disposed at an inlet of the air discharge pipe, and the straight portion thereof is disposed at an outlet of the air discharge pipe.

The curved portion of the or each noise-reducing rib may include a free end, the free end being rounded to avoid accumulation of dust.

Alternatively, the or each noise-reducing rib is provided on the inner wall of the air discharge pipe, extends from a predetermined distance from the top of the air discharge pipe, and has a predetermined dimension towards the centre of the air discharge pipe so as not to reach the centre of the air discharge pipe.

In a preferred embodiment, there there is a plurality of noise-reducing ribs provided at predetermined intervals on the inner wall of the air discharge pipe. Conveniently, there are four noise-reducing ribs.

Preferably, each noise-reducing rib has a width substantially 0.1 to 0.4 times as large as the inner diameter of the air discharge pipe.

Where the ribs extend from a position spaced from the top of the air discharge pipe, that pipe may have a substantially circular section, and the noise-reducing ribs may be formed on X and Y axes crossing the central longitudinal axis of the air discharge pipe.

The invention also provides a vacuum cleaner comprising: a cleaner body having a drive motor; a nozzle unit connected to the cleaner body to draw in dust from a surface to be cleaned; and a cyclonic separating apparatus detachably mounted to the cleaner body to separate the dust from dustcarrying air drawn in through the nozzle unit; wherein the cyclonic separating apparatus comprises a cyclone body including a cyclone chamber and a dust-collecting chamber, a cover unit connected to an upper portion of the cyclone body, an openable door unit mounted to a lower portion of the cyclone body, and at least one noise-reducing rib formed in an air discharge pipe of the cyclone chamber.

The or each noise-reducing rib may protrude from an inner wall of the air discharge pipe towards the centre thereof, and may comprise a curved portion and a straight portion.

The or each noise-reducing rib may be provided on the inner wall of the air discharge pipe, may extend from a predetermined distance from the top of the air discharge pipe, and may have a predetermined dimension towards the centre of the air discharge pipe so as not to reach the centre of the air discharge pipe.

The invention further provides a cyclonic separating apparatus comprising: a cyclone chamber; an air entry path for introducing dust- carrying air to the cyclone chamber, the cyclone chamber being such as to induce a rotating current to the dust-carrying air to separate that air into "clean" air and dust; an air discharge pipe defining a discharge path for discharging the "clean" air from the cyclone chamber; and a noise-reducing rib formed on the air discharge pipe in the air discharge path, the noise-reducing rib being configured to prevent the "clean" air from becoming a whirling air current in the air discharge pipe.

The invention will now be described in greater detail, by way of example, with reference to the drawings, in which: Figure 1 is a schematic perspective view showing a vacuum cleaner having a cyclonic separating apparatus constructed according to the invention; Figure 2 is an exploded perspective view of the cyclonic separating apparatus of Figure 1; Figure 3 is a perspective view showing the body of the apparatus of Figure 2; Figure 4 is an enlarged perspective view of a noise-reducing rib and an air discharge pipe of the apparatus of Figure 2; Figure 5 is a graph comparing the noise (in decibels) for an apparatus with and without the noise- reducing rib of Figure 4; Figure 6 is a graph comparing the noise (in decibels) and the loss of pressure for an apparatus with and without the noise-reducing rib of Figure 4; Figure 7 is a perspective view showing a modified noise-reducing rib; and Figure 8 is a graph comparing the noise (in decibels) for an apparatus with and without the noise- reducing rib of Figure 7.

In the following description, the same reference numerals are used for the same elements in the different drawings. The description is sufficiently detailed to provide a comprehensive understanding of the invention. Thus, it will be apparent that the invention can be carried out without all the details described. Also, well-known functions or constructions are not described in detail, since they would obscure the invention in unnecessary detail.

Referring to the drawings, Figure 1 shows a vacuum cleaner 200 having a cleaner body 250, a nozzle unit 210 for drawing in dust-carrying air from a surface to be cleaned, a handle 230 for manipulation of the vacuum cleaner, an extension pipe 220 connecting the nozzle unit to the handle, a flexible hose 240 connecting the handle to the cleaner body, and a cyclonic separating apparatus 300.

A drive motor (not shown), constituting a drive source for supplying a suction force, is mounted in the cleaner body 250. The cyclonic separating apparatus 300 is detachably mounted in the cleaner body 250 for centrifugally separating dust carried by drawn-in air.

Referring to Figure 2, the cyclonic separating apparatus 300 comprises a cover unit 330, a door unit 350 and a cyclone body 310. The cover unit 330 is removably mounted to an upper end of the cyclone body 310 to define a dust path (not shown) between a cyclone chamber 313 and a dust- collecting chamber 315 of the apparatus. The dust centrifuged from dust- carrying air in the cyclone chamber 313 is moved to the dust-collecting chamber 315 through the dust path. By separating the cover unit 330 from the cyclone body 310, the cyclone chamber 313 and the dust- collecting chamber 315 become accessible for a user to clean and manage. A suction path 331 is provided at the front central portion of the cover unit 330, the suction port being in fluid communication with the flexible hose 240 The door unit 350 is hinged at a lower end of the cyclone body 310 to be openable in the direction of the arrow G and closable in the direction of the arrow G' with respect to a hinge 351.

When the door unit 350 is open, a connection path 311 and the dustcollecting chamber 315 are open at the bottom ends thereof, so that dust collected in the connection path and the dust- collecting chamber is discharged by gravity.

The door unit 350 is opened in the following manner. A button 31 9a provided on a handle 319 is pressed, and a hook (not shown) which previously engaged one side of the door unit 350 is retracted. Accordingly, one end of the door unit 350 is rotated, in the direction of the arrow G with respect to the hinge 351. In order to close the door unit 350, the user rotates the door unit 350, in the direction of the arrow G', with respect to the hinge 351, so that the hook (not shown) is fastened to said one side of the door unit.

Referring to Figure 3, the cyclone body 310 comprises the connection path 311, the cyclone chamber 313, the dust-collecting chamber 315 and the handle 319. The connection path 311 is disposed in the middle of the cyclone body 310, and is connected to the suction path 331 (see Figure 2) so as to guide the dust-carrying air drawn in through the suction path towards the cyclone chamber 313. A filter-mounting hole 311a is provided in the connection path 311, a mesh filter M being mounted in the hole 311 a for filtering relatively fine dust particles. The connection path 311 is fluid communication with the drive source (not shown) via the mesh filter M. When the bottom of the connection path 311 is open, the dust collected in the connection path can fall, under gravity, and be discharged.

The cyclone chamber 313 is formed on the right (as shown in Figure 3) of the connection path 311 inside the cyclone body 310 to separate dust from the dust-carrying air using centrifugal force. Au air entry path 31 3a is formed in the bottom of the cyclone chamber 313, the air entry path being such as to let the dust-carrying air, drawn in through the suction path 331 and the connection path 311, flow into the cyclone chamber.

An air discharge pipe 314, having a substantially circular section, protrudes by a predetermined distance from the middle of the bottom of the cyclone chamber 313. The air discharge pipe 314 functions as a discharge path for "clean" air from which dust has been separated. The air discharge pipe 314 may be integrally formed with the cyclone chamber 313, or it can be formed as a separate part. The air discharge pipe 314 has four noise-reducing ribs 317 which will be described below.

The dust-collecting chamber 315 is disposed on the left (as shown in Figure 3) of the connection path 311 to collect the dust separated in the cyclone chamber 313. A blocking member 315a is provided at one side in the dust-collecting chamber 315 to prevent collected dust from flowing back to the cyclone chamber 313. The blocking member 315a is substantially arc shaped and curves downwards with respect to the dust-collecting chamber 315. As the bottom of the dust- collecting chamber 315 is open, the dust collected in the chamber can fall under gravity when the door unit 350 is opened, the dust thereby being discharged.

The handle 319 has a substantially flattened U-shape, and is mounted on the front of the cyclone body 310 for the user to grip when separating the cyclone body 250 from the cyclone body. The button 319a is disposed at a lower part of the handle 319. Inside the handle 319, a link member (not shown) is formed to connect the button 319a and the hook (not shown).

The structure and operation of the noise-reducing ribs 317 provided in the air discharge pipe 314 will now be described with reference to Figure 4. In order to decrease the noise generated by the "clean" air passing through the air discharge pipe 314 and to decrease the loss of pressure, four noise-reducing ribs 317 are mounted at an inner wall 314b of the air discharge pipe 314 at regular intervals. The noise-reducing ribs 317 can be separate members attached to the inner wall 314b of the air discharge pipe 314 by an adhesive, or can be integrally formed with the air discharge pipe so as to protrude from the inner wall.

Each noise-reducing rib 317 has a thickness t', and comprises a curved portion 3l7a and a straight portion 317c, the straight portion extending in the direction from an inlet 314a to an outlet 314c of the air discharge pipe 314. The curved portion 317a of each rib 317 is disposed at the inlet 314a of the air discharge pipe 314 and is curved in the direction of the arrow A to minimise the noise and the loss of pressure, the noise being that caused by collision of the "clean" air with that curved portion. The four noise-reducing ribs 317 are mounted to incline in the same direction on the inner wall 314b of the air discharge pipe 314.

The free end 31 7b of the curved portion 31 7a of each rib 317 is rounded to avoid dust accumulation. Accordingly, a rotating current of "clean" air flowing to the inlet 31 4a of the air discharge pipe 314 gradually loses its rotary power due to the curved portion 3 17a. Therefore, formation of a whirling air current, by collision of a rotary current of the "clean" air with the inner wall 314b of the air discharge pipe 314, can be prevented.

The straight portion 317c of each rib 317 is disposed at the outlet 314c of the air discharge pipe 314. The "clean" air that lost rotary power due to the associated curved portion 31 7a becomes a straight air current, and is guided to the outlet 314c of the air discharge pipe 314.

Presuming that reference numeral a' denotes the inner diameter of the air discharge pipe 314, the noise-reducing ribs 317 each have a width b' from the inner wall 314b of the air discharge pipe towards the centre. The width b' is approximately 0.1 to approximately 0.4 of the inner diameter a' of the air discharge pipe 314. That is, the width b' of each noisereducing rib 317 is less than the radius of the air discharge pipe 314, so that the ribs do not reach the centre of the air discharge pipe. The open central portion of the air discharge pipe 314 thus provides a discharge path for the "clean" air drawn into the inlet 3 14a of the air discharge pipe 314 for discharge to the outlet 31 4c of the air discharging pipe.

The operation of a vacuum cleaner having the structure shown in Figures 1 to 4 will now be described. As the drive motor is driven, a suction force is generated and transmitted to the nozzle unit 210 through the cyclonic separating apparatus 300. The nozzle unit 210 draws in dust from the surface to be cleaned together with air. The drawn-in air, including the dust, is guided to the suction path 331 of the cover unit 330 in the direction of the arrow F through the r4 nozzle unit 210, the extension pipe 220 and the flexible hose 240.

In the connection path 311, part of the dust-carrying air is passed through the mesh filter M and is discharged to the outside of the cyclonic separating apparatus 300 in the direction Fl through a discharge filter (not shown) disposed behind the cyclone body 310. The rest of the dust-carrying air is drawn into the air entry path 31 3a of the cyclone chamber 313 in the direction of the arrow F2.

The dust-carrying air rotates, ascending from the bottom of the cyclone chamber 313 to an upper part of the cover unit 330. The dust is separated out by centrifugal force and enters the dust- collecting chamber 315 in the direction of the arrow F3. The dust collected in the dust-collecting chamber 315 cannot flow back to the cyclone chamber 313 due to the blocking member 31 5a.

The "clean" air from which dust has been removed collides with the upper end of the cover unit 330, and so descends in the direction of the arrow F4 in a rotating manner. The descending air is discharged through the air discharge pipe 314 formed in the centre of the bottom of the cyclone chamber 313. Here, part of the rotary "clean" air is directly discharged through the centre of the air discharge pipe 314, whereas the rest of the rotary "clean" air loses rotary power as the curved portions 31 7a of the ribs 317 become straight, so that a straight air current passes along the straight portions 31 7c, and is discharged out of the air discharge pipe.

The "clean" air passed through the air discharge pipe 314 is discharged to the outside of the cyclonic separating apparatus 300 in the direction of the arrow F5 through the discharge filter (not shown) disposed behind the cyclone body 310.

When the vacuum cleaner is initially driven, the dust-carrying air drawn into the suction path 311 is mostly discharged through the mesh filter M. However, when the mesh filter M is blocked by dust, most of the dustcarrying air is drawn into the air entry path 31 3a of the cyclone chamber 313. This is because of the inherent properties of a fluid (here, the dust-carrying air), namely that a fluid flows to a side having relatively lower resistance. The presence of the mesh filter M, ensures that the pressure loss generated during the initial driving of the vacuum cleaner can be reduced.

The effect of the noise-reducing ribs 317 for reducing the noise and loss of pressure will now be described with reference to Figures 5 and 6.

As to the noise-reducing effect, by providing the noise-reducing ribs 317, the noise is reduced by 2.8dB in every frequency band, compared to when the noise-reducing ribs are not provided. In particular, at certain frequency bands (1.2 KHz, 2.4 KHz) the ribs 317 give rise to a considerable noise reduction of 16.9dB and 7.5dB respectively, when compared with the noise which would be expected, using flow analysis techniques, to be generated.

The effect of the noise-reducing ribs 317 for reducing the loss of pressure is as follows.

Referring to Figure 6, when the noise-reducing ribs 317 are provided, the loss of pressure is approximately 472 mmH2O. On the contrary, when the noise-reducing ribs 317 are not provided, the loss of pressure is approximately 527mmH20. Thus, the noise-reducing ribs 317 reduce the loss of pressure by approximately 55 mmH2O. In other terms, the loss of pressure is reduced by approximately 11% owing to the presence of the noise-reducing ribs 317.

Figure 7 shows a modified set of four noise-reducing ribs 417, the ribs being provided in an air discharge pipe 414, and extending from a distance d' from the top of the air discharge pipe.

Two of the ribs 417 are on the X axis of the pipe 414, and two are on the Y axis, the e X andY axes crossing at the central longitudinal axis of the air discharge pipe.

The noise-reducing ribs 417 are rectangular having a thickness ti', and are disposed on an inner wall 414a of the air discharge pipe 414. Assuming that reference numeral al' denotes the inner diameter of the air discharge pipe 414, the noise-reducing ribs 417 have a width bi' from the inner wall 414a towards the centre of the pipe. The width bi' is approximately 0.1 to approximately 0.4 of the inner diameter al' of the air discharge pipe 414. That is, the width bi' of each noise-reducing rib 417 is less than the radius of the air discharge pipe 414, so that the noise reducing ribs do not reach the centre of the air discharge pipe.

The noise-reducing ribs 417 are such as to prevent the "clean" air from becoming a whirling air current in the air discharge pipe 414. Accordingly, the noise caused by such a whirling air current can be reduced.

Figure 8 shows that, by providing the noise-reducing ribs 417, the noise is reduced by 3dB on the average in every frequency band, when compared to the situation when the noise-reducing ribs are not provided.

In particular, at certain frequency bands (1.2 KHz, 2.4 KHz) the ribs 417 give rise to a considerable noise-reduction of 15dB and 7dB respectively, when compared with the noise which would be expected, using flow analysis techniques, to be generated.

As can be appreciated, the noise-reducing ribs 317 and 41 7 can restrain the "clean" air from generating a whirling air current, thereby reducing the noise caused in the air discharge pipes 314 and 414 by such a whirling air current. Also, the loss of pressure is reduced. Accordingly, the user can work more comfortably due to the reduced noise. Moreover, cleaning efficiency is improved due to the reduced loss of pressure.

While the invention has been shown and described with reference to certain embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made. p

Claims

Claims 1. A cyclonic separating apparatus comprising: a cyclone body

including a cyclone chamber and a dust-collecting chamber; a cover unit connected to an upper portion of the cyclone body; an openable door unit mounted to a lower portion of the cyclone body; and at least one noise-reducing rib formed in an air discharge pipe of the cyclone chamber.
2. Apparatus of claim 1, wherein the or each noise-reducing rib protrudes from an inner wall of the air discharge pipe towards the centre thereof, and comprises a curved portion and a straight portion.
3. Apparatus as claimed in claim 2, wherein the curved portion of the or each noise-reducing rib is disposed at an inlet of the air discharge pipe, and the straight portion thereof is disposed at an outlet of the air discharge pipe.
4. Apparatus as claimed in claim 3, wherein the curved portion of the or each noise-reducing rib includes a free end, the free end being rounded to avoid accumulation of dust.
5. Apparatus as claimed in claim 1, wherein the or each noise-reducing rib is provided on the inner wall of the air discharge pipe, extends from a predetermined distance from the top of the air discharge pipe, and has a predetermined dimension towards the centre of the air discharge pipe so as not to reach the centre of the air discharge pipe.
6. Apparatus as claimed in anyone of claims 1 to 5, wherein there are a plurality of noise- reducing ribs provided at predetermined intervals on the inner wall of the air discharge pipe.
7. Apparatus as claimed in claim 6, wherein there are four noise-reducing ribs.
8. A cyclonic separating apparatus substantially as hereinbefore described with reference to, and as illustrated by, Figures 1 to 4 or Figures 1 to 3 as modified by Figure 7 of the drawings.

8. Apparatus as claimed in claim 6 or claim 7, wherein each noisereducing rib has a width substantially 0.1 to 0.4 times as large as the inner diameter of the air discharge pipe.

9. Apparatus as claimed in either of claims 7 and 8 when appendant to claim 5, wherein the air discharge pipe has a substantially circular section, and the noise-reducing ribs are formed on X and Y axes crossing the central longitudinal axis of the air discharge pipe.

10. A vacuum cleaner comprising: a cleaner body having a drive motor; a nozzle unit connected to the cleaner body to draw in dust from a surface to be cleaned; and a cyclonic separating apparatus detachably mounted to the cleaner body to separate the dust from dust-carrying air drawn in through the nozzle unit; wherein the cyclonic separating apparatus comprises a cyclone body including a cyclone chamber and a dustcollecting chamber, a cover unit connected to an upper portion of the cyclone body, an openable door unit mounted to a lower portion of the cyclone body, and at least one noise-reducing rib formed in an air discharge pipe of the cyclone chamber.

11. A vacuum cleaner as claimed in claim 10, wherein the or each noisereducing rib protrudes from an inner wall of the air discharge pipe towards the centre thereof and comprises a curved portion and a straight portion.

12. A vacuum cleaner as claimed in claim 10, wherein the or each noisereducing rib is provided on the inner wall of the air discharge pipe, extends from predetermined distance from the top of the air discharge pipe, and has a predetermined dimension towards the centre of the air discharge pipe so as not to reach the centre of the air discharge pipe.

13. A cyclonic separating apparatus comprising: a cyclone chamber; an air entry path for introducing dust-carrying air to the cyclone chamber, the cyclone chamber being such as to induce a rotating current to the dustcarrying air to separate that air into "clean" air and dust; an air discharge pipe defining a discharge path for discharging the "clean" air from the cyclone chamber; and a noise-reducing rib formed in the air discharge pipe in the air discharge path, the noise-reducing rib being configured to prevent the "clean" air from becoming a whirling air current in the air discharge pipe.

14. Apparatus as claimed in claim 13, wherein the noise-reducing rib is secured to, or integrally formed with, the air discharge pipe.

15. Apparatus as claimed in claim 13 or claim 14, wherein the noisereducing rib has a curved portion disposed at an inlet of the air discharge pipe, the curved portion being configured for gradual removal of rotary power from the air current in the air discharge pipe.

16. Apparatus as claimed in claim 15, wherein the noise-reducing rib also has a straight portion disposed at an outlet of the air discharge pipe, the straight portion being configured to direct the air current in a substantially straight direction towards the outlet of the air discharge pipe.

17. Apparatus as claimed in any one of claims 13 to 16, wherein the noisereducing rib has a width that is less than the radius of the air discharge pipe.

18. Apparatus as claimed in claim 13, wherein the noise-reducing rib is formed in the air discharge pipe and extends from a predetermined distance from an inlet of the air discharge pipe.

19. Apparatus as claimed in any one of claims 13 to 18, wherein there are a plurality of noise- reducing ribs provided at predetermined circumferential intervals on the air discharge pipe in the air discharge path.

20. A cyclonic separating apparatus substantially as hereinbefore described with reference to, and as illustrated by, Figures 1 to 4 or Figures 1 to 3 as modified by Figure 7 of the drawings.

21. A vacuum cleaner substantially as hereinbefore described with reference to, and as illustrated by, Figures 1 to 4 or Figures 1 to 3 as modified by Figure 7 of the drawings.

Amendments to the claims have been filed as follows 1. A cyclonic separating apparatus comprising: a cyclone chamber; an air entry path for introducing dust-carrying air to the cyclone chamber, the cyclonc chamber being such as to induce a rotating current to the dust- carrying air to separate that air into "clean" air and dust; an air discharge pipe defining a discharge path for discharging the "clean" air from the cyclone chamber; and a noise-reducing rib formed in the air discharge pipe in the air discharge path, the noise-reducing rib being configured to prevent the "clean" air from becoming a whirling air current in the air discharge pipe.

2. Apparatus as claimed in claim 1, wherein the noise-reducing rib is secured to, or integrally formed with, the air discharge pipe.

3. Apparatus as claimed in claim I or claim 2, wherein the noise-reducing rib has a curved portion disposed at an inlet of the air discharge pipe, the curved portion being configured for gradual removal of rotary power from the air current in the air discharge pipe.

4. Apparatus as claimed in claim 3, wherein the noise-reducing rib also has a straight portion disposed at an outlet of the air discharge pipe, the straight portion being configured to direct the air current in a substantially straight direction towards the outlet of the air discharge pipe.

5. Apparatus as claimed in any one of claims 1 to 4, wherein the noisereducing rib has a width that is less than the radius of the air discharge pipe.

6. Apparatus as claimed in claim 1, wherein the noise-reducing rib is formed in the air discharge pipe and extends from a predetermined distance from an inlet of the air discharge pipe.

7. Apparatus as claimed in any one of claims I to 6, wherein there are a plurality of noise- reducing ribs provided at predetermined circumferential intervals on the air discharge pipe in the air discharge path.