GB2296206A

GB2296206A - Improved dust separation apparatus

Info

Publication number: GB2296206A
Application number: GB9504504A
Authority: GB
Inventors: James Dyson; Andrew Walter Mcrae Thomson; Simon Mark Bickerstaff
Original assignee: Notetry Ltd
Current assignee: Dyson Technology Ltd
Priority date: 1994-12-21
Filing date: 1995-03-07
Publication date: 1996-06-26
Also published as: GB9425812D0; GB9504504D0; ZA9510864B

Abstract

The invention provides apparatus (10) for separating dirt or dust from an airflow. It comprises a frusto-conical cyclone (12) having tangential air inlet (16) located at the larger end of the cyclone (12), and a cone opening (18) located at the smaller end. A collector (20) is arranged so as to surround the cone opening (18) and has a base surface (24) facing towards the cone opening (18). According to a first aspect of the invention the distance between the cone opening (18) and the base surface (24) is either less than 8mm or between 30mm and 70mm. According to a second aspect of the invention, a deflecting plate (26, not shown) is located in the collector (20) between the cone opening (18) and the base surface (24). According to a third aspect of the invention, at least a portion of the base surface is conical or frusto-conical in shape. Each of these aspects of the invention allows the apparatus (10) to be reduced in size without substantially affecting the separation efficiency. <IMAGE>

Description

IMPROVED DUST SEPARATION APPARATUS The invention relates to apparatus for separating dirt or dust particles from an airflow by cyclonic means. The invention relates particularly, but not exclusively, to cyclonic dust separation apparatus for use in a vacuum cleaner.

Cyclonic dust separation apparatus typically comprises a frusto-conical cyclone having a tangential air inlet at the end having the larger diameter and a cone opening leading to a dirt or dust collector at the end having the smaller diameter. The dust collector is generally cylindrical in shape and is considerably larger in diameter than the cone opening, normally having a diameter of at least three times that of the cone opening. In operation, an airflow carrying dirt and dust with it enters the cyclone via the air inlet and, by virtue of the tangential orientation of the air inlet, is set into a swirling motion over the interior surface of the cyclone. Most of the air of the airflow escapes from the cyclone by passing towards the longitudinal axis of the cyclone and exiting via an exit passage arranged substantially centrally of the end of the cyclone having the larger diameter.The remainder of the airflow spirals towards the cone opening at increasing angular speeds carrying the dirt and dust with it and is ejected into the dust collector, whereupon the dirt and dust particles are flung towards the cylindrical wall of the collector. The dirt and dust particles then collect in the lower regions of the cylindrical wall, whilst the remainder of the airflow exits from the collector via the cone opening and the exit passage.

It is generally desirable for cyclonic dust separation apparatus to be relatively compact, particularly as regards the overall length of the apparatus, ie, the dimension parallel to the longitudinal axis of the cyclone. If the apparatus is used in a vacuum cleaner, compact dust separation apparatus reduced the overall dimensions of the complete cleaner and lowers the centre of gravity of the cleaner which, in turn, increases its stability. This is particularly advantageous in cylinder-type cleaners as well as upright-type vacuum cleaners.

It is an object of the present invention to provide dust separation apparatus which is relatively compact without any significant loss of dust separation efficiency.

According to a first aspect of the invention, there is provided apparatus as claimed in claim 1. A second aspect of the invention provides apparatus as claimed in claim 8 and a third aspect of the invention provides apparatus as claimed in claim 17. Advantageous features are set out in the subsidiary claims.

With regard to the first aspect of the invention, it has previously been assumed that as large a distance as possible between the base surface and the cone opening is desirable. This allows more volume in the collector for separated dirt and dust to accumulate before emptying is required and was also thought to reduce the likelihood of separated dirt and dust becoming re-entrained into the airflow. The distance between the base surface and the cone opening has therefore been limited merely by the desired overall dimensions of the machine of which the dust separation apparatus forms part. However, it has now been found that varying this distance can affect the separation efficiency of the apparatus.Maxima of separation efficiency for different sizes of cyclone and collector occur when the distance between the base surface and the cone opening lies in the range 30mm to 70mm. A particularly advantageous distance is 54mm. Surprisingly, a distance of less than 8mm, particularly around 4mm to 6mm, is highly efficient even though it was initially thought that such a small distance would adversely affect the airflow in the cyclone and collector. Reducing the distance between the base surface and the cone opening to 8mm or less therefore has an additionally advantageous effect on the overall dimensions of the apparatus without substantially detracting from the separation efficiency thereof. The centre of gravity of the separation apparatus is therefore lowered.

In some cases, it is not desirable for the base surface and the cone opening to be fixed at a relatively close spacing. For example, in some cases it will be necessary to provide as large a volume as possible for collection of separated dirt and dust and this would be preferably achieved by increasing the distance between the base surface and the cone opening. Tests have shown that this would normally result in a decrease in separation efficiency. However, further tests have shown that the separation efficiency can be increased again by placing a deflecting plate between the base surface and the cone opening, preferably immediately outside the cone opening at a spacing of approximately 2mm therefrom.The introduction of such a deflecting plate means that any desired spacing between the base surface and the cone opening can be adopted whilst still achieving an enhanced separation efficiency. This is the second aspect of the invention.

Dust separation apparatus of the type mentioned at the outset is often required to be located at an angle to a fixed surface. In the case of an upright-type vacuum cleaner, which is restricted in its overall height for practical reasons, the body of the cleaner containing the dust separation apparatus is tilted in use with respect to the cleaner head so as to facilitate the movement of the cleaner head over the surface to be cleaned. Also1 in cylinder-type vacuum cleaners, it is advantageous to position the centre of gravity as close as possible to the surface to be cleaned and this can be assisted by tilting the dust separation apparatus with respect to the said surface. However, the known generally cylindrical shape of the collector has previously imposed restrictions on the amount of tilting of the dust separation apparatus which can be achieved.

The greater the desired angle of tilt, the higher the dust separation apparatus must be, with respect to the fixed surface, to begin with.

The third aspect of the invention overcomes this problem by providing a collector having a base surface with a conical or frusto-conical portion. This allows the apparatus to be tilted without the need to raise the apparatus in the first place. The provision of a conical- or frustoconical-based collector has previously been dismissed as impractical because it was thought that separated dirt and dust would collect closer to the cone opening than in the standard flat-based collector, which would encourage separated dirt and dust to become re-entrained in the airflow. It has now been found that this is not the case and the separation efficiency of a conical- or frustoconical-based collector is very similar to that of a corresponding flat-based collector.The provision of a conical- or frustoconical-based collector and the consequential ability to tilt the dust separation apparatus with respect to the floor or another flat surface is highly desirable.

Embodiments of the various aspects of the invention will now be described with reference to the accompanying drawings, wherein: Figure la is a sectional side view of a first embodiment of apparatus for separating dirt or dust from an airflow according to a first aspect of the invention; Figure ib is a sectional side view, corresponding to part of Figure la, of a second embodiment of the first aspect of the present invention; Figure ic is a graph showing filtration efficiency test results for a 260mm cyclone with a flat-bottomed fine dust collector at varying distances from the cone opening; Figure 2a is a sectional side view of a first embodiment of apparatus for separating dirt or dust from an airflow according to a second aspect of the present invention; ; Figure 2b is a sectional side view, corresponding to part of Figure 2a, of a second embodiment of the second aspect of the invention; Figure 3a is a sectional side view of a first embodiment of apparatus for separating dirt or dust from an airflow according to a third aspect of the invention; Figures 3b and 3c are sectional side views, corresponding to part of Figure 3a, of second and third embodiments respectively of the third aspect of the invention; Figure 4a is a sectional side view, corresponding to Figure ib, of a third embodiment of the first aspect of the invention; and Figure 4b is a sectional side view, corresponding generally to Figures 3b and 3c, of a fourth embodiment of the third aspect of the invention.

Figure la shows apparatus 10 for separating dirt or dust from an airflow consisting of a frusto-conical cyclone 12 having an interior surface 14. An air inlet 16 is arranged at the end of the cyclone 12 having the larger diameter and the air inlet 16 communicates with the cyclone 12 so as to introduce air tangentially into the cyclone 12.

At the end of the cyclone 12 having the smaller diameter, ie. remote from the air inlet 16, there is a cone opening 18. Surrounding the cone opening 18 and sealed against the outer walls of the cyclone 12 is a collector 20 for collecting dirt and dust separated from the airflow. The main body of the collector 20 is generally cylindrical in shape although inclined walls 22 extend between the generally cylindrical portion and the cyclone 12. The collector 20 has a base surface 24 facing towards the cone opening 18, ie. remote from the main body of the cyclone 12.

In use, an airflow consisting of a stream of air having dirt and dust particles entrained therein enters the cyclone 12 via the inlet 16. Because of the tangential entry arrangement, the dirt-laden airflow takes up a swirling motion inside the cyclone 12 and spirals over the interior surface 14 of the cyclone 12 towards the cone opening 18 at ever-increasing angular speeds, with clean air escaping from the cyclone 12 by moving inwardly towards the longitudinal axis and upwardly towards an exit port 17. As soon as the remainder of the airflow enters the collector 20 via the cone opening 18, the dirt and dust particles entrained within the airflow are flung towards the side walls of the collector 20.The airflow, which is substantially free of dirt and dust particles, then exits the collector 20 via the cone opening 18 and leaves the cyclone 12 by means of the exit port 17 located substantially centrally of the end of the cyclone 12 having the larger diameter.

It has been found that, by varying the distance h between the base surface 24 and the cone opening 18, that the separation efficiency of the apparatus 10 can be improved. When the distance h is set at a value of between 30mm and 70mm, the separation efficiency increases. In particular, there is a peak in separation efficiency when the distance h is set at substantially 54mm.

It has also been found that the separation efficiency is particularly good if the distance h is reduced to less than 10mm. This is extremely surprising because it has previously been anticipated that such a small gap between the cone opening 18 and the base surface 24 would either restrict the airflow through the dirt or dust separation apparatus 10 or increase the likelihood of separated dirt or dust becoming re-entrained within the airflow. Tests have shown that this is not the case and that there is a particularly good separation efficiency when the distance h is between 4mm and 6mm. This arrangement is illustrated in Figure ib.

Test results showing the variation in separation efficiency for different distances between the base surface 24 and the cone opening 18 are shown in Figure 1c. The tests were carried out on apparatus incorporating a 260mm cone and a flat-bottomed collector positioned at varying distances from the cone opening.

The upper line shows the percentage of particles falling in the range 0. 3-0. 5ym present in the airflow after a standard test time, and the lower line shows the percentage of particles falling in the range 0. 5-1. OLm present after the standard test time. Clear minima can be seen at distances of 4mm-6mm and 54mm.

Figure 2a illustrates an embodiment of a second aspect of the invention. The apparatus 10 shown in Figure 2a corresponds almost identically to the apparatus 10 shown in Figure la. Corresponding reference numerals will therefore be used in connection with Figure 2a. There are two differences between the apparatus shown in Figure 2a and the apparatus shown in Figure la. Firstly, in Figure 2a, there is no specific distance requirement between the cone opening 18 and the base surface 24. In order to provide a larger volume inside the collector 20 for collecting dirt and dust particles separated from the airflow, the distance between the cone opening 18 and the base surface 24 can be as large as necessary. The second difference is the location of a deflecting plate 26 between the cone opening 18 and the base surface 24.The deflecting plate 26 is generally disc-shaped and the diameter of the deflecting plate 26 is substantially the same as the outer diameter of the cone opening 18, ie. the outer diameter of the wall of the cyclone 12 which surrounds the cone opening 18. This diameter is ideally substantially 25mm. The gap between the cone opening 18 and the deflecting plate 26 is substantially 2mm. This arrangement gives an enhanced separation efficiency irrespective of the distance between the cone opening 18 and the base surface 24.

The same effect is achieved irrespective of the shape of the collector 20. If the base surface 24 incorporates an inclined or frusto-conical portion 24a, the enhanced efficiency caused by the deflecting plate 26 appears to remain. Such an arrangement is illustrated in Figure 2b.

Figures 3a, 3b and 3c illustrate the third aspect of the invention.

The apparatus shown in Figure 3a corresponds closely to the apparatus shown in Figure la. The only difference between the apparatus shown in Figures la and 3a is the shape of the collector 20. In Figures 3a, the planar base surface 24 is replaced by a base surface 240 consisting of a frusto-conical portion 24a surrounding a planar circular portion 24b. (The cylindrical portions of the collector 20 shown in Figure la have also been reduced in height. ) The result is that the collector 20 shown in Figure 3a is substantially frusto-conical in shape. This allows the entire apparatus 10 to be rotated about an axis running along any diameter of the central portion 24b so as to tilt the apparatus 10 with respect to a fixed surface parallel to that axis.

It had previously been expected that dirt and dust separated from the airflow on entry into the collector 20 via the cone opening 18 would travel down the inclined surfaces 24a of the collector 20 and accumulate in the region of the central portion 24b. It was thought that such an accumulation would result in the separated dirt and dust being re-entrained into the airflow. However, tests have shown that this re-entrainment does not occur.

In the embodiment shown in Figure 3a, the distance between the cone opening 18 and the central portion 24b of the base surface 24' is substantially 54mm.

Furthermore, the angle of inclination a of the frusto-conical portion 24a with respect to the central portion 24b is substantially 50'. Also, the diameter of the central portion 24b is substantially identical to the diameter of the cone opening 18 and this is preferably substantially 25mm.

Various modifications and variations are possible within the context of this aspect of the invention: The distance between the cone opening 18 and the central portion 24b of the base surface 24' can be varied and, in particular, can be reduced to a distance of substantially 7mm. This spacing gives an increased separation efficiency. Such an arrangement is illustrated in Figure 3b.

A further alternative arrangement is illustrated in Figure 3c which shows the collector 20 having a frusto-conical portion 24a and a central circular portion 24b, but wherein the central circular portion 24b has a diameter k which is substantially larger than that of the cone opening 18. In the embodiment shown in Figure 3c, the diameter of the cone opening 18 is substantially 25mm, whereas the diameter of the circular central portion 24b is substantially 125mm.

Figures 4a and 4b illustrate an additional measure designed to reduce any possibility of dirt and dust collected in the collector 20 becoming re-entrained in the airflow circulating in the apparatus 10. This measure applies primarily in cases wherein the distance between the cone opening 18 and the base surface 24 is less than 8mm or wherein the base surface 24 is conical or frusto-conical in shape.

In order to reduce still further the possibility of dirt and dust located in the collector 20 from being re-entrained into the airflow, dirt and dust retaining means in the form of a wall 30 are provided on the base surface 24. The wall 30 is upwardly extending with respect to the base surface 24 and is substantially annular in shape, although other plan shapes could be utilised. The diameter d of the annular wall 30 is substantially 70mm but this could be varied within the range 30mm to 100mm. The height w of the wall 30 is substantially 55mm from the junction between the wall 30 and the base surface 24 but could be varied within the range 20mm to 60mm.

The wall 30 has a tapering cross-section as shown in Figure 4a. The thickness of the wall 30 is greater at the end thereof adjacent the junction with the base surface 24 than at the distal end. The upper end of the wall 30 is radiused to form a smooth finish.

When the annular wall 30 is provided in conjunction with a frusto-conical base surface 24 as shown in Figure 4b, the junction between the wall 30 and the base surface 24 is on the frusto-conical portion 24a of the base surface 24. However, if the central portion 24b is sufficiently large in diameter, the junction between the wall 30 and the base surface 24 can occur in the central planar portion 24b.

In operation, air exiting the cyclone 12 via the cone opening 18 causes dirt and dust particles entrained therein to be flung against the outer walls of the collector 20. The annular wall 30 prevents the dirt and dust particles from travelling towards the central portion of the base surface 24 and thereby reduces the possibility of dirt and dust particles becoming re-entrained into the airflow.

It is envisaged that cyclonic dust separation apparatus as described above can be used to advantage in a number of different situations. The application to which it is envisaged that the present invention is most likely to be applied is that of vacuum cleaning apparatus. Any of the three aspects of the invention described above can be used in an upright or cylinder-type vacuum cleaner in order to lower the centre of gravity and/or reduce the size of the apparatus as a whole. It is also likely that the apparatus described above will be used in conjunction with further cyclonic dust separation apparatus specifically designed to remove larger dust and fluff particles in a so-called "low efficiency" cyclone. The apparatus described above will therefore be intended to remove only the finer particles of dirt and dust entrained in the airflow.

However, it is also envisaged that the invention described above may well be utilised in other situations, for example the removal or dirt and dust particles from internal combustion engine emissions.

The principles described above are equally applicable to such situations and need not be used in combination with further cyclonic separation apparatus unless it is so desired.

Claims

1. Apparatus for separating dirt or dust from an airflow comprising a frusto-conical cyclone having a tangential air inlet located at or adjacent the end of the cyclone having the larger diameter and a cone opening located at the end of the cyclone having the smaller diameter, and a collector arranged so as to surround the cone opening and having a base surface facing towards the cone opening1 wherein the distance between the cone opening and the base surface is either less than 8mm or between 30mm and 70mm.

2. Apparatus as claimed in claim 1, wherein the base surface is substantially planar.

3. Apparatus as claimed in claim 2, wherein the distance between the cone opening and the base surface is measured parallel to the longitudinal axis of the cyclone.

4. Apparatus as claimed in claim 3, wherein the distance between the cone opening and the base surface is between 4mm and 6mm.

5. Apparatus as claimed in claim 3, wherein the distance between the cone opening and the base surface is between 45mm and 60mm.

6. Apparatus as claimed in claim 5, wherein the distance between the cone opening and the base surface is substantially 54mm.

7. Apparatus for separating dirt or dust from an airflow substantially as hereinbefore described with reference to Figures la and 1b of the accompanying drawings.

8. Apparatus for separating dirt or dust from an airflow comprising a frusto-conical cyclone having a tangential air inlet located at or adjacent the end of the cyclone having the larger diameter and a cone opening located at the end of the cyclone having the smaller diameter, and a collector arranged so as to surround the cone opening and having a base surface facing towards the cone opening, wherein a deflecting plate is located in the collector between the cone opening and the base surface.

9. Apparatus as claimed in claim 8, wherein the deflecting plate is circular.

10. Apparatus as claimed in claim 9, wherein the diameter of the deflecting plate is substantially the same as the outer diameter of the cone opening.

11. Apparatus as claimed in claim 9 or 10, wherein the diameter of the deflecting plate is substantially 25mm.

12. Apparatus as claimed in any one of claims 8 to 11, wherein the distance between the cone opening and the deflecting plate is less than 10mm.

13. Apparatus as claimed in claim 12, wherein the distance between the cone opening and the deflecting plate is substantially 2mm.

14. Apparatus as claimed in any one of claims 8 to 13, wherein the base surface of the collector is substantially planar.

15. Apparatus as claimed in any one of claims 8 to 13, wherein the base surface of the collector is frusto-conical.

16. Apparatus for separating dirt or dust from an airflow substantially as hereinbefore described with reference to Figures 2a and 2b of the accompanying drawings.

17. Apparatus for separating dirt or dust from an airflow comprising a frusto-conical cyclone having a tangential air inlet located at or adjacent the end of the cyclone having the larger diameter and a cone opening located at the end of the cyclone having the smaller diameter, and a collector arranged so as to surround the cone opening and having a base surface facing towards the cone opening, wherein at least a portion of the base surface is conical or frusto-conical in shape.

18. Apparatus as claimed in claim 17, wherein the base surface comprises a frusto-conical portion and a circular portion.

19. Apparatus as claimed in claim 18, wherein the diameter of the circular portion is substantially the same as that of the cone opening.

20. Apparatus as claimed in claim 18 or 19, wherein the diameter of the circular portion is between 20mm and 30mm.

21. Apparatus as claimed in claim 20, wherein the diameter of the circular portion is substantially 25mm.

22. Apparatus as claimed in claim 18, wherein the diameter of the circular portion is substantially greater than that of the cone opening.

23. Apparatus as claimed in claim 22, wherein the diameter of the circular portion is substantially 125mm.

24. Apparatus as claimed in any one of claims 18 to 23, wherein the circular portion is planar.

25. Apparatus as claimed in claim 24, wherein the distance between the cone opening and the planar circular portion is less than 8mm.

26. Apparatus as claimed in claim 25, wherein the distance between the cone opening and the planar circular portion is substantially 7mm.

27. Apparatus as claimed in any one of claims 17 to 26, wherein the conical or frusto-conical portion of the base surface is inclined at an angle of between 30 and 50 to the longitudinal axis of the cyclone.

28. Apparatus as claimed in claim 27, wherein the conical or frusto-conical portion of the base surface is inclined at an angle of substantially 40 to the longitudinal axis of the cyclone.

29. Apparatus as claimed in any one of claims 1 to 7 and claims 17 to 28, wherein the base surface comprises dust-retaining means spaced from the centre thereof.

30. Apparatus as claimed in claim 29, wherein the dust-retaining means comprise an upwardly-extending annular wall.

31. Apparatus as claimed in claim 30, wherein the wall extends upwardly from the junction thereof with the base surface for between 10mm and 60mm.

32. Apparatus as claimed in claim 31, wherein the wall extends upwardly from the junction thereof with the base surface for substantially 55mm.

33. Apparatus as claimed in any one of claims 30 to 32, wherein the diameter of the wall is between 30mm and 100mm.

34. Apparatus as claimed in claim 33, wherein the diameter of the wall is substantially 70mm.

35. Apparatus as claimed in any one of claims 30 to 34, wherein the thickness of the wall is greater at the end adjacent the junction with the base surface than at the end remote therefrom.

36. Apparatus as claimed in any one of claims 30 to 35, wherein the end of the wall remote from the junction with the base surface is radiused.

37. Apparatus for separating dirt or dust from an airflow substantially as hereinbefore described with reference to any of Figures 3a to 3c and 4a and 4b of the accompanying drawings.

38. A vacuum cleaner incorporating apparatus according to any one of the preceding claims.

39. A vacuum cleaner as claimed in claim 38, further comprising further apparatus for separating dirt or dust from the airflow, the said further apparatus being positioned upstream of the said apparatus.