GB2569589A - Dirt separator and vacuum cleaner - Google Patents

Abstract

A dirt separator comprising fluid path 28 configured to direct fluid flow through at least two layers of fluid permeable electrically conductive mesh 50 and into downstream dirt separation stage 8. Preferably, downstream separator and an upstream separator are cyclonic separators. Preferably, there are at least ten layers of mesh, and two or three layers of mesh are placed immediately adjacent to form a plurality of agglomerator sheets spaced by 2-4mm. Preferably, apertures in respective mesh layers are out of alignment and the grid of each mesh is non orthogonal between layers to increase fluid path to trap more dirt. Preferably, mesh is woven, has a pitch of 0.5-3mm and occupies 30-60% of available cross sectional area. Preferably, mesh comprises an agitator to loosen adhered dirt. Mesh is used in a vacuum cleaner. Conductive mesh allows electrostatically charged dirt to lose charge and detach, and separate layers reduce pressure drop.

Description

The present invention relates to a dirt separator, for instance a dirt separator of the kind that may be used in a vacuum cleaner.

In a dirt separator, there is often a trade-off between separation efficiency and pressure drop - the separation efficiency can be increased (for instance by using a finer filter medium, or by increasing the number of cyclones in a cyclonic separator) but this generally results in a larger pressure drop across the separator. This in turn can affect the volume of fluid which can be drawn through the separator. Conversely, the pressure drop across a separator can be reduced so as to increase the volumetric flow rate of fluid, but this generally results in less entrained dirt being separated from that fluid.

It is therefore desirable to find a way by which the separation efficiency of a cyclonic separator can be increased while mitigating the resultant increase in pressure drop, or by which the pressure drop can be reduced while mitigating the resultant decrease in efficiency.

It is an object of the present invention to provide this, and/or to provide an improved or alternative dirt separator or vacuum cleaner.

According to a first aspect of the present invention there is provided a dirt separator comprising a fluid path configured to direct a fluid flow through at least two layers of fluid-permeable electrically-conductive mesh and into a downstream dirt separation stage.

The inventors of the present application have discovered that when a fluid flow with entrained dirt passes through a layer of fluid-permeable mesh, some of the finer entrained dirt adheres to the mesh through electrostatic attraction. As the dirt builds up on the mesh it clumps together, and over time clumps of dirt detach from the mesh. These clumps then enter the downstream dirt separation stage, where due to their size they can be captured more easily then the fine dirt that they are made up of.

The use of mesh to clump some of the finer dirt together means that less loose fine dirt is left to be separated by the downstream dirt separation stage. That separation stage can therefore be tailored towards coarser dirt, which generally allows for a smaller pressure drop. The present invention can therefore provide a reduction in pressure drop with less (if any) of a reduction in separation efficiency, or conversely can provide an increase in separation efficiency with less (if any) of an increase in pressure drop.

The mesh being electrically conductive can allow clumps of dirt to detach more easily therefrom. This can reduce the pressure drop across the layers of mesh which could occur if buildup of dirt began to constrict fluid flow through the mesh.

The use of two layers of mesh provides a greater total surface area of mesh upon which fine dirt can accumulate (thereby magnifying the above effect and the advantages offered thereby) while allowing the diameter of the flow path to be smaller than if the entire surface area of the mesh was provided in a single sheet. Also, the pressure drop across two layers of mesh can be lower than if the total surface area of mesh was provided in a single layer.

Furthermore, the resistance to flow offered by the upstream layer(s) of mesh can act to spread fluid flow out across the cross section of the fluid path, providing more even flow from which more dirt can adhere to the downstream layer(s) of mesh. In contrast, if the fluid flow through the fluid flow path took the form of a fast jet in the central portion thereof, relatively little fluid may reach the outer region of the mesh (meaning that relatively little fine dirt adheres to the mesh) and fluid flow in the central region may have sufficient velocity to prevent dirt from accumulating.

The electrically conductive mesh may be a metallic mesh, for instance a mesh made of metal or metallised plastic, or another type of conductive mesh such as a mesh made from carbon fibre.

Said downstream dirt separation stage may be a cyclonic separation stage.

A cyclonic separator can allow clumps of fine dirt to be separated with advantageous ease (e.g. with advantageously minimal pressure drop). In contrast, in embodiments of the invention where the downstream dirt separation stage is a filter, clumps of dirt may break apart upon contact with the filter, contributing to clogging of the filter and the pressure drop caused thereby.

The dirt separator may further comprise a dirt separation stage upstream of said layers of mesh.

The upstream dirt separation stage may separate particularly large particles of dirt, preventing those particles from impacting the mesh and damaging it, or becoming lodged in the mesh and clogging it.

The upstream dirt separation stage may be, for example, a coarse filter or mesh, a cyclonic separation stage, or another type of inertial separation stage such as a baffle chamber.

The dirt separator may comprise at least 10 of said layers of fluid-permeable electrically-conductive mesh.

For instance, the dirt separator may comprise at least 15 or at least 20 of said layers. Increasing the number of sheets of mesh provides a greater total surface area of mesh upon which fine dirt can accumulate, while allowing the diameter of the flow path to be smaller than if the entire surface area of mesh was provided as a single sheet. Furthermore, a greater number of layers of mesh can spread the flow across the cross section of the fluid path (as noted above) to an increased extent.

At least two of said layers of mesh may be positioned immediately adjacent to one another along the fluid path.

For instance, said at least two layers may be positioned less than 2mm apart or less than 1mm apart. In some embodiments, said at least two layers may be in contact with one another,

With the layers of mesh positioned immediately adjacent to each other, fluid flow through the downstream layer(s) of mesh is affected by the presence of the upstream layer(s). Accordingly, an upstream layer may introduce short-lived low-level turbulence into the flow, and this turbulence may allow better circulation of fluid around a downstream layer, meaning that more dirt from the fluid can adhere to the downstream layer.

The layers of mesh may be arranged into a plurality of agglomerator sheets which are spaced apart from one another along the fluid path, each agglomerator sheet comprising no more than three and no fewer than two layers of mesh positioned immediately adjacent to one another.

As noted above, layers of mesh being immediately adjacent to one another can improve the amount of dirt which collects on the mesh. However, when a group of mesh layers are positioned immediately adjacent to one another, the pressure drop across them can be larger than when the layers are spaced apart. Accordingly, positioning the mesh layers in spaced-apart groups of two or three may provide the best compromise between dirt collection and pressure drop.

The agglomerator sheets may be spaced apart by between 1mm and 6mm, for instance between 2mm and 4mm.

This may provide an advantageous compromise between (a) the agglomerator sheets being positioned close enough together for the total space occupied thereby to be acceptably low, and (b) the agglomerator sheets being spaced apart far enough for the fluid flow to recover therebetween (thereby reducing total pressure drop) and far enough apart to minimise the risk of risk of clumps of dirt becoming trapped therebetween.

Within each agglomerator sheet, a first mesh layer may define a set of apertures which are out of alignment with the apertures of a second mesh layer.

The apertures in the layers of mesh of the agglomerator sheet(s) being out of alignment means that more of the fluid flow passes close enough to the mesh for dirt to be attracted thereto. In contrast, if the apertures were aligned then fluid could flow through the centres of the apertures, remaining far enough away from any part of the mesh for dirt attraction to be minimal.

The first and second mesh layers may form respective grids, the grid formed by the first mesh layer being non-orthogonal to the grid formed by the second mesh layer when viewed along the fluid path.

This may provide reduce the manufacturing tolerances required for the apertures of the first and second mesh layers to be out of alignment. This is discussed in more detail later.

When viewed along the fluid path, each layer of mesh may block between 30% and 60% of the available cross sectional area.

For instance, each layer of mesh may block between 40% and 50% of the available cross sectional area.

This may provide an advantageous compromise, providing sufficient surface area which is blocked by material of the mesh by to which fine dirt can adhere, while still leaving sufficient area unblocked to avoid too large a pressure drop across that layer.

Each layer of mesh may have a pitch of less than 3mm, for instance less than 2mm.

A relatively small pitch can allow the material of the mesh, to which fine dirt can adhere, to be more evenly distributed across the area of the mesh. In contrast, if the mesh had a large pitch then less of the fluid flowing therethrough would come close enough to the material of the mesh to adhere thereto.

Each layer of mesh may have a pitch of at least 0.5mm.

This may reduce cost of the mesh, and/or may allow the mesh to be stronger and thus more resistant to impact from relatively large particles of entrained dirt. Furthermore, the resultant increase in pore size may reduce the risk of the mesh becoming clogged.

Each layer of mesh is formed from a plurality of overlaid or woven fibres.

This may allow the mesh to be produced advantageously quickly or easily. However, in other embodiments the mesh may be a perforated (for instance punched or etched) sheet.

The dirt separator may comprise an agitator for agitating the layers of mesh to loosen dirt adhered thereto.

This can assist with detachment of clumped dirt from the mesh, either during use or as a cleaning step. The agitator may directly agitate the mesh, or may indirectly agitate the mesh by agitating another component such that shock or vibration propagates to the mesh.

The agitator may be, for example, a piezoelectric element configured to vibrate the layers of mesh. As another example, the agitator may be a spring-loaded hammer arranged to provide a shock to a portion of the separator.

As an alternative, the dirt separator may be arranged such that normal operation imparts sufficient shock to the layers of mesh to loosen dirt. For example, the separator may have a lid which can be opened to empty collected dirt from the separator, and the lid may reach a ‘hard stop’ in the open position with sufficient force to shake the separator and thereby loosen dirt adhered to the mesh.

According to a second aspect of the present invention there is provided a vacuum cleaner comprising a dirt separator according to any preceding claim.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a perspective view of a known vacuum cleaner;

Figure 2 is a cross-sectional side view of a dirt separator of the vacuum cleaner of Figure 1;

Figure 3 is a schematic cross-sectional side view of a dirt separator of a vacuum cleaner according to an embodiment of the invention;

Figure 4 shows a portion of a layer of mesh from the dirt separator of Figure 3, viewed in the direction of fluid flow therethrough; and

Figure 5 shows a portion of an agglomerator plate of the dirt separator of Figure 3, viewed in the direction of fluid flow therethrough.

Throughout the description and drawings, corresponding reference numerals denote corresponding features.

Figures 1 and 2 show a known vacuum cleaner 1. The vacuum cleaner 1 has a dirt separator 2 which has an air inlet 3 in fluid communication with a cleaner head 4 via a rigid wand 5. The dirt separator 2 comprises a primary cyclonic separation stage 6, a downstream separation stage in the form of a secondary cyclonic separation stage 8, a sock filter 10, and an air outlet 12 which leads to a vacuum motor (not visible) housed in a rear casing 13 of the vacuum cleaner 1 which is positioned above a pistol grip 14.

The primary separation stage 6 has a single cyclone chamber 20 formed by an upper portion of a transparent bin 22, a porous cylindrical shroud 24 which forms an air outlet for the primary separation stage, and a primary dirt collection chamber 26 formed by a lower portion of the bin 22 and an openable lid 27. Behind the shroud 24 is an air flow path 28 of annular cross section, surrounding a generally cylindrical wall 40 which is positioned concentrically inside the bin 22 and leads to the secondary separation stage 8.

The secondary separation stage 8 has a plurality of cyclone chambers 30 arranged in parallel. The cyclone chambers 30 have respective tangential inlets 32 which branch off from the air flow path 28, open ends 34 configured as dirt outlets, and air outlets in the form of vortex finders 36. The secondary separation stage 8 also has a secondary dirt collection chamber 38 which is defined by the generally cylindrical wall 40 and the openable lid 27.

In use, dirt-laiden air is drawn into the vacuum cleaner 2 through the inlet 3, for instance from a cleaner head attached thereto. The air then spirals around the cyclone chamber 20 of the primary separation stage 6, where coarse dirt is separated from the air by centrifugal action and falls into the primary dirt collection chamber 26. Air from which coarse dirt has been separated then passes through the shroud 24, through the air flow path 28 and into the secondary separation stage 8. The air then splits into a series of streams, each of which enters one of the cyclone chambers 30 through its inlet 32 and forms a cyclone therein. Finer dirt is separated by centrifugal action and falls out of the open end 34 of the cyclone chamber into the secondary dirt collection chamber 38, while air from which the finer dirt has been removed exits the cyclone chamber 30 through its vortex finder 36. From the vortex finders 36, the separate streams of air re-combine and are directed downwards through the filter 10, which removes any remaining entrained dirt, before passing along the air outlet 12 to the vacuum motor. Intermittently, the lid 27 is opened to allow dirt to be emptied out of the dirt collection chambers 26, 28, and the filter 10 is washed to remove dirt collected thereby.

Figure 3 shows a schematic of a dirt separator 2 of a vacuum cleaner according to an embodiment of the invention. The vacuum cleaner of this embodiment is similar to the vacuum cleaner of Figure 1, therefore only the differences will be described here. It should be noted that although Figure 3 only shows the front portion of the dirt separator, the primary and secondary separation stages 6, 8 are arranged generally circumferentially around a longitudinal axis 42 of the separator 2.

The separator 2 of this embodiment has an array of ten annular agglomerator plates 50 positioned in the air flow path 28 circumferentially around the longitudinal axis 42. With the agglomerator plates 50 so positioned, the primary separation stage 6 is located upstream of the agglomerator plates 50 and the secondary separation stage 8 is located downstream of the agglomerator plates. In this embodiment the agglomerator plates 50 are substantially the same as one another, with the exception that those plates which are positioned towards the bottom (from the perspective of Figure 2) have a smaller outer diameter to accommodate the shape of the upper portion of the shroud 24. In this embodiment, the agglomerator plates are spaced apart from one another by a distance of 4mm.

Each agglomerator plate 50 comprises first and second layers of fluid-permeable metallic mesh, which in this case are substantially identical to one another. Figure 4 shows a portion of a first layer 52a of this mesh, which in this embodiment is formed from lengths of fibre 54a, 54b. The lengths of fibre 54a, 54b of this embodiment are lengths of stainless steel wire which are arranged into warp wires 54a and weft wires 54b which are woven together. The warp wires 54a and weft wires 54b are arranged perpendicularly to each other, giving the mesh 52a the form of a rectangular grid which defines an array of rectangular pores or apertures 56. In this case the warp wires 54a and the weft wires 54b have the same spacing as each other, therefore the layer of mesh 52a forms a square grid with square array of square apertures 56.

In this case the pitch of the mesh (i.e. the space between centrelines of adjacent lengths of wire 54a, 54b) is 1mm, and the diameter of the lengths of wire is 0.25mm. Accordingly, when viewed along the air flow path 28 (i.e. from the perspective of Figure 4) the layer of mesh 52a blocks around 45% of the total available area, with the combined area of the apertures 56 making up the remaining 55%.

Figure 5 shows a portion of an agglomerator plate 50, showing both first and second layers of mesh 52a, 52b, viewed along the flow path 28 in the direction of fluid flow (i.e. upwards from the perspective of Figure 3). The second layer of mesh 52b is positioned immediately adjacent to the first layer of mesh 52a, downstream thereof. In this embodiment the first and second layers of mesh 52a, 52b are in plane parallel contact with one another.

It is noteworthy that substantially all the apertures 56 of the first layer of mesh 52a are out of alignment with the apertures 56’ of the second layer of mesh 52b (although in a few locations 58 the apertures 56, 56’ approach alignment). In this embodiment, this lack of alignment is achieved by the respective grids formed by the layers of mesh 52a, 52b being non orthogonal when viewed along the air flow path 28. In this case, the respective grids are positioned at around 45 degrees to one another.

Non-alignment of the apertures 56, 56’ could instead be achieved with the respective grids being parallel or perpendicular to one another when viewed along the air flow path 28, for instance by positioning the apertures 56’ of the second mesh layer 52b behind the intersections between the warp fibres 54a and weft fibres 54b of the first layer. However, due to the fine pitch of the mesh layers 52a, 52b, manufacturing tolerances meaning one layer was moved by 0.5mm horizontally and vertically (from the perspective of Figures 4 and 5) relative to the other would mean that the apertures 56, 56’ were in complete alignment. In contrast, in this embodiment relative movement of the two mesh layers 52a, 52b due to manufacturing tolerances would have negligible effect on the non-alignment of the apertures 56, 56’.

In use, as air (from which coarse dirt has been removed by the primary separation stage 6) passes up the air flow passage 28 and runs through the apertures 56, 56’ in the layers of mesh 52a, 52b that make up the agglomerator plates 50. As the air passes through the plates 50, some of the fine dust entrained therein adheres to the mesh layers 52a, 52b of the agglomerator plates 50 through electrostatic attraction. At first, this simply results in less entrained dirt reaching the secondary separation stage

8. However, as use continues, the fine dirt builds up on the mesh 52a, 52b of the agglomerator plates 50 and forms clumps which eventually detach from the mesh. Those clumps then pass along the air flow passage 28 and enter the secondary separation stage 8. Since the clumps have larger mass than the individual particles that they are made up of, they are more easily removed in the cyclone chambers 30 of the secondary separation stage 8.

In some embodiments the air flow through the agglomerator plates 50 may be sufficient to detach clumps of dirt therefrom so as to avoid the mesh 52a, 52b becoming clogged. In this embodiment, however, means are provided to impart a shock to the separator so as to shake the layers of mesh 52a, 52b so as to shake clumps of dirt off them. In this case the lid 27 is opened by sliding the bin 22 downwards relative to the shroud 24, wall 40 and secondary separation stage 8, which also has the effect of sliding a wiping member 60 across the shroud 24 so as to clean the shroud, as described in GB2546543 (which is incorporated herein by reference). When the bin 22 reaches the end of its downward travel, and also when it is pushed upwards again and reaches the position shown in Figure 3, the bin reaches a ‘hard stop’ and stops suddenly. These sudden stops impart a shock to the dirt separator 2 which propagates to the agglomerator plates 50 and shakes clumps of dirt therefrom. The clumps of dirt then fall into a further dirt collection chamber 62 formed between the wall 40 and an annular extension 64 depending from the bottom of the shroud. The clumps of dirt can then be emptied from the further dirt collection chamber 62, along with dirt from the primary and secondary dirt collection chambers 26, 38, when the lid 27 is open.

In a modification of the above described embodiment, an ultrasonic transducer is positioned on the wall 40 adjacent to the agglomerator plates 50. The ultrasonic transducer can be activated, for instance when emptying the dirt collection chambers 26, 38, 62, so as to vibrate the agglomerator plates and shake clumps of dirt therefrom.

It will be appreciated that numerous modifications to the above described embodiments may be made without departing from the scope of invention as defined in the appended claims. For instance, although in the above embodiment each layer of mesh forms a square grid with an array of square apertures, in other embodiments each layer may take any other suitable form. For example, one or more of the layers of mesh may take the form of a triangular grid (for instance woven from three sets of parallel wires positioned at 60 degrees to the wires of each of the other sets) forming an array of triangular apertures. As another example, one or more layers of mesh may take the form of a perforated or etched sheet forming a honeycomb-like structure.

Claims (15)

1. A dirt separator comprising a fluid path configured to direct a fluid flow through at least two layers of fluid-permeable electrically-conductive mesh and into a downstream dirt separation stage.

2. A dirt separator according to claim 1 wherein said downstream dirt separation stage is a cyclonic separation stage.

3. A dirt separator according to claim 1 or 2 further comprising a dirt separation stage upstream of said layers of mesh.

4. A dirt separator according to any preceding claim comprising at least 10 of said layers of fluid-permeable electrically-conductive mesh.

5. A dirt separator according to any preceding claim wherein at least two of said layers of mesh are positioned immediately adjacent to one another along the fluid path.

6. A dirt separator according to claim 5 wherein the layers of mesh are arranged into a plurality of agglomerator sheets which are spaced apart from one another along the fluid path, each agglomerator sheet comprising no more than three and no fewer than two layers of mesh positioned immediately adjacent to one another.

7. A dirt separator according to claim 6 wherein the agglomerator sheets are spaced apart by between 2mm and 4mm.

8. A dirt separator according to claim 6 or 7 wherein within each agglomerator sheet, a first mesh layer defines a set of apertures which are out of alignment with the apertures of a second mesh layer.

9. A dirt separator according to claim 8 wherein the first and second mesh layers form respective grids, the grid formed by the first mesh layer being non-orthogonal to the grid formed by the second mesh layer when viewed along the fluid path.

10. A dirt separator according to any preceding claim wherein when viewed along the fluid path, each layer of mesh blocks between 30% and 60% of the available cross sectional area.

5

11. A dirt separator according to any preceding claim wherein each layer of mesh has a pitch of less than 3mm

12. A dirt separator according to any preceding claim wherein each layer of mesh has a pitch of at least 0.5mm.

13. A dirt separator according to any preceding claim wherein each layer of mesh is formed from a plurality of overlaid or woven fibres.

14. A dirt separator according to any preceding claim further comprising an agitator for 15 agitating the layers of mesh to loosen dirt adhered thereto.

15. A Vacuum cleaner comprising a dirt separator according to any preceding claim.