Patent Description:
Traditionally, hard floor cleaning has involved first vacuuming the floor, followed by mopping it. Vacuuming removes the fine dust and coarse dirt, while mopping removes any very fine dust and stains.

There are now many available appliances on the market that claim to vacuum and mop in one go, and this is what is referred to by a "wet vacuum cleaner". Many of these appliances have a vacuum nozzle for picking up the coarse dirt by means of an airflow and a (wet) cloth or brush for removing the stains. These wet cloths or brushes can be pre-wetted or can be wetted by the consumer but also in some cases they can be wetted by the appliance (by means of a liquid but also by means of steam).

The wet vacuum cleaner then needs to be able to collect moist dirt from the floor and transport it to the dirt container. This is achieved using the airflow generated by a motor and fan arrangement. The moist dirt and liquid in the form of droplets needs to be separated from the airflow. The moist dirt and liquid enters the dirt container whereas the remaining airflow passes through the fan and any post-filtering units, and exits the appliance.

It is known to use labyrinths and filters or cyclone units to separate liquid and moist dirt from the air flow. This invention relates in particular to the use of a cyclone.

In cyclonic systems, centrifugal forces arise by rotating air inside a chamber. The air flows in a helical pattern, for example beginning at the top of the cyclone chamber and ending at the bottom, before exiting the cyclone through the center of the cyclone and out of the top. Particles and liquid droplets dragged along in the rotating stream have too much inertia to follow the tight curve of the air flow path, and will strike the outside wall, then move along the wall to the bottom of the cyclone chamber (or enter a separate dirty water chamber) where they can be removed.

Cyclones are widely used as a way to separate dry particles from air. However, the use of a cyclone for separating water droplets (and dirt particles) from air is more difficult, because the water tends to creep to the exit along with the main air flow. The main challenge for the use of a cyclone with a wet flow is thus to guide the water along the walls of the cyclone unit towards a collector while preventing water becoming airborne again.

One issue for cyclonic devices is that in addition to the primary helical flow, there are secondary airflow patterns which arise, leading for example to the transport of water drops towards and along the top of the cyclone chamber. When water reaches the top, it can flow to the outlet of the cyclone unit (the output for example extends into the chamber from the top), giving an ineffective separation.

Another issue is the size of water droplets. A cyclone unit for example has an inlet conduit that couples to an opening in the cyclone housing, in particular with a tangential component of the direction of the inlet conduit. It has been found that the connection between the inlet conduit and the opening in the cyclone housing can promote formation of large static water droplets. When these are eventually dislodged they can become airborne as a finer mist, which is then carried to the main air flow outlet, again giving a reduction in efficiency of the water separation.

<CIT>, <CIT>, <CIT> and <CIT> each disclose a wet and dry floor cleaning system using a cyclone unit.

There remains a need for an improved cyclone unit design for use in a wet vacuum cleaner.

According to examples in accordance with an aspect of the invention, there is provided a wet vacuum cleaner, comprising:.

This wet vacuum cleaner makes use of a cyclone unit to separate water (and debris) from the flow generated by the suction of the motor and fan. The cyclone is generated around a cyclone axis and travels in the direction from the surface (e.g. a top) towards a spaced apart opposite end (e.g. a bottom). The main flow inlet to the cyclone unit is spaced apart from the surface. This means that a secondary flow towards the surface (e.g. towards the top, and in addition to the helical flow towards the bottom) is less able to cause liquid to attach to the inner face of the surface, from where it can run down to the main flow outlet and be drawn out with the main air flow. Thus, this design reduces the amount of water that is entrained in the main outlet flow. The spacing is preferably a step or transition at or near the location of the main flow inlet.

Note that the terms "top" and "bottom" used in this application are not intended to refer to gravitational orientations. The top of the outer housing may be considered to be the end nearest which the main flow entry is provided, and the bottom of the outer housing may be considered to be the end nearest the debris collection outlet or chamber.

The cyclone unit for example has first and second ends, spaced along the direction of the cyclone axis. A first end may for example be a debris collection end and a second end may include or comprise the surface defined above. A collection outlet from the outer housing may be provided, or else there may be a collection area or chamber within the outer housing.

The main flow outlet is for example positioned at a greater spacing from the surface than the main flow inlet. Thus, the flow within the cyclone unit is generally away from the surface towards the collection outlet.

The dirt inlet is for example for attachment to a vacuum cleaner head or other vacuum cleaner accessory.

The opening of the main flow inlet does not need to be circular. The "effective hydraulic inlet diameter" may be taken to be the diameter for a circle with the same area as the opening. The area of the opening may be considered to be the area of the missing portion of the outer wall which forms the inlet. This area may be the area of a curved (missing) wall portion, or it may be approximated as the best fit planar surface to the outer contour of the opening.

An outlet conduit is for example provided which in one example extends from the surface into a central region of the outer housing, and the main flow outlet (i.e. the entrance to a main flow outlet conduit) is at the end of the outlet conduit.

This outlet conduit for example defines a vortex finder within the outer housing, and the main flow outlet (at the end of the outlet conduit) is located at a position centrally within the interior volume of the outer housing. This is a typical configuration for a cyclone unit.

The main flow inlet is for example spaced internally from the surface by a separation distance between <NUM> and <NUM>. The spacing needed is preferably small so the total appliance is small and therefore easy to store and handle.

A main flow inlet conduit is for example provided which connects to the opening in the outer housing. It typically defines a flow direction which is partly radially inwardly directed and partly circumferentially (i.e. tangentially) directed around the outer housing, to give a compact overall design. The airflow is for example mostly tangential and partly radial. main flow inlet conduit extends in a direction offset from the perpendicular to the cyclone axis and facing towards the surface.

This means that the primary input flow is inclined towards the surface (e.g. towards the top). This reduces the pressure difference between the inside and outside of the cyclonic flow near the surface, so that any droplets which have collected on the inner face of the surface (e.g. the top) are still subjected to a drag force and thus do not collect and flow towards the main flow outlet. A tangential component of the primary input flow is maintained.

The main flow inlet conduit may extend in a direction offset by <NUM> to <NUM> degrees from the perpendicular to the cyclone axis.

The transition between the main flow inlet conduit and the outer housing may have, at least for a portion of the opening facing away from the surface, a radius of curvature of at least <NUM>.

This avoids sharp intersection edges at the locations where water drops may form. If locations are present where large water drops cannot flow, it has been found that they will eventually be broken into small droplets once dislodged, and then flow to the main flow outlet. The use of large curvature surfaces prevents this.

The part of the opening facing the away from the surface (e.g. the bottom) is the area where most liquid enters the separation system. Thus, it is desirable to prevent large water droplets collecting in this region.

The radius of curvature may be at least <NUM>, for example at least <NUM>, for example at least <NUM>.

The main flow inlet conduit may have a first cross sectional area, and the area of the opening is a larger, second, cross sectional area.

In this way, there is a flow area increase at the transition from the flow inlet conduit to the cyclone unit. This reduces the flow speed. This measure may be designed to prevent water droplets of a size suitable for collection being broken up into smaller droplets, which can more easily flow to the outlet.

The second cross sectional area is for example at least <NUM> times the first cross sectional area. It may be at least <NUM> times, for example at least <NUM> times, for example at least <NUM> times the first cross sectional area.

The main flow outlet may extend parallel to the cyclone axis. At least a portion of the outer housing is for example cylindrical, around the cyclone axis.

The invention provides a wet vacuum cleaner which uses a cyclone unit for separating liquid and particles from a suction flow. The main flow inlet to the cyclone chamber is spaced internally from its respective end by a separation distance. This separation distance is at least <NUM> times the effective hydraulic inlet diameter of the main flow inlet. This assists in preventing formation of large droplets which can follow a path to the main flow outlet.

The invention relates specifically to the design of a cyclone unit of a wet vacuum cleaner. Before describing the cyclone unit in detail, an example will be given of the general configuration of a wet vacuum cleaner.

<FIG> shows a wet vacuum cleaner <NUM>, comprising a vacuum cleaner head <NUM>, and a motor <NUM> and a fan <NUM> for delivering suction to the vacuum cleaner head.

A cyclone unit <NUM> is provided for separating liquid and particles from a flow generated by the suction of the motor and fan.

The motor for example comprises a bypass motor. This type of motor can tolerate water content in the air flow, because the drawn in air flow is not used for motor cooling and is isolated from the motor parts. Instead, ambient air is drawn in to the motor for cooling purposes.

The cyclone unit <NUM> is part of a wet dirt management system, which dirt may included additional filters. The dirt management system has a collection chamber for collecting the separated moisture and dirt. This may be an internal part of the cyclone unit or there may be a separate a waste water collection reservoir to which the cyclone unit connects. An outlet filter <NUM> may for example be provided between the outlet flow of the cyclone and the motor and fan as shown.

The cyclone unit has a cyclone axis of rotation <NUM>. This axis may be aligned parallel with the general length axis of the vacuum cleaner (as in the case in <FIG>), but this is not essential. The axis of rotation <NUM> may instead be perpendicular to the general length axis or oriented in other ways. The cyclone unit has an inlet opening, and the flow direction through the inlet opening is perpendicular to the cyclone axis <NUM>, with a predominantly tangential and partly radially inward direction, to promote the desired helical flow condition within the cyclone unit.

A collection volume <NUM> is for example below the cyclone chamber (when the vacuum cleaner is upright) so that water is collected under gravity.

There is a handle <NUM> at the opposite end to the head <NUM>.

The vacuum cleaner shown is a stick vacuum cleaner so that in use the head <NUM> forms the only contact with the surface to be vacuumed. Of course, it may be an upright vacuum cleaner or a canister vacuum cleaner. The invention relates to design features of the cyclone unit, and may be applied to any wet vacuum cleaner.

The user may be required to deliver water to the surface being vacuumed independently of the vacuum cleaner. However, the wet dirt management system may instead also include a clean water reservoir for delivering water to the vacuum nozzle.

The vacuum cleaner head for example has a rotary brush to which water is delivered from the clean water reservoir, and hence also has an inlet for receiving water from the clean water reservoir. The vacuum cleaner head is specifically designed to pick up wet dirt and optionally also perform the floor wetting.

<FIG> shows in schematic form the general known configuration of a cyclone unit <NUM>.

The cyclone unit comprises an outer housing <NUM> having an outer side wall <NUM>, a first end <NUM> and a second end <NUM> spaced apart along the cyclone axis <NUM>. The second end <NUM> forms a surface (which will thus also be referred to as reference <NUM>) which closes the internal volume of the cyclone unit at that end. Thus, the surface <NUM> is at one end of the cyclone unit along the cyclone axis.

The surface <NUM> is shown in <FIG> (and in the other figures) to be a flat surface. However, this is not necessary. The surface <NUM> may have a more complex three dimensional shape.

The first end <NUM> may be considered to be the bottom and the second end <NUM> may be considered to be the top, without implying any particular orientation of the cyclone unit.

A main flow inlet <NUM> is provided to the outer side wall <NUM> of the housing <NUM>, comprising an opening in the outer housing. The opening has an effective hydraulic inlet diameter as discussed above, namely the diameter for a circle with the same area as the opening.

The opening may be considered to be a missing portion of the outer side wall <NUM>. This missing portion has an area. This area may thus be considered to be the area of the missing portion of the outer side wall. If the outer side wall is cylindrical, the missing portion will be a portion of a cylindrical surface. However, the area may instead be determined as a smaller planar area which is a closest approximation to the shape of the inlet.

A main flow inlet conduit <NUM> connects to the opening in the outer housing. The main flow inlet <NUM> and the main flow inlet conduit <NUM> are only shown schematically in <FIG>. In particular, the main flow inlet conduit <NUM> is shown as radially directed, whereas in practice the main flow inlet has a predominantly tangential direction as well as a radial direction, as will be seen more clearly below. The direction of flow created by the main flow inlet conduit <NUM> is designed to create the desired helical flow conditions within the cyclone unit.

A main flow outlet <NUM> is provided from the outer housing <NUM> closer to the first end <NUM> than the main flow inlet <NUM>. Thus, the main flow outlet is nearer the bottom. An outlet conduit <NUM> extends from the second end <NUM> into a central region of the outer housing. The main flow outlet <NUM> is at the end of the outlet conduit <NUM>. This outlet conduit <NUM> and the main flow outlet <NUM> for example define a vortex finder.

A collection outlet <NUM> is provided from the outer housing <NUM> for the collection of moisture and debris. However the outer housing may itself instead define a collection chamber.

Dirt and water should not be able to come back to the cyclone as soon as they have passed the collection outlet <NUM>. The vortex finder has a shape to guarantee a stable vortex/cyclone. The position of the vortex finder relative to the main flow inlet in part determines the separation performance.

<FIG> is used to show a first issue which arises in this design.

There is a primary rotational flow <NUM> from the main flow inlet <NUM> to the main flow outlet <NUM>, but there is also a secondary air flow pattern <NUM>, which is able to transport liquid towards and along the second end <NUM> (the top). This is shown as droplets <NUM>. When water upwardly reaches the second end <NUM>, it can flow down the outlet conduit <NUM> and eventually be sucked out from the main flow outlet <NUM>, reducing the effectiveness of the liquid separation.

<FIG> is used to show a second issue which arises in this design.

Where the main flow inlet conduit <NUM> couples to the opening in the outer wall of the housing, the formation of large static water droplets may arise, as represented by droplet <NUM>. When these are eventually dislodged they can become airborne as a finer mist, which is then carried to the main air flow outlet, again giving a reduction in efficiency of the water separation.

<FIG> shows first and second design features relating to these issues.

In accordance with a first design feature, the main flow inlet <NUM> is spaced internally below the second end of the outer housing <NUM>, by a separation distance d1. This separation distance is greater than <NUM> times the effective hydraulic inlet diameter defined above. The main flow inlet is generally still at the second end of the cyclone unit (i.e. closer to the second end that the first end and closer to the second end than a central location along the cyclone axis) but with a spacing.

The separation distance may be more than <NUM> times, for example more than <NUM> times, for example more than <NUM> times the effective hydraulic inlet diameter. It is preferably also below <NUM> times the effective hydraulic inlet diameter, to avoid a significant increase in the axial length of the cyclone unit.

The spacing may thus be between <NUM> and <NUM> times, more preferably between <NUM> and <NUM> times, and most preferably between <NUM> and <NUM> times the effective hydraulic inlet diameter.

The example of <FIG> shows a cyclone unit with a cylindrical side wall and a planar top wall, hence a planar surface <NUM>. In such a case, the spacing d1 is simple to define. However, for a non planar surface <NUM> the spacing is less easily defined. The aim of the spacing is to prevent a secondary flow towards the surface <NUM> (e.g. towards the top), in addition to the helical flow towards the outlet, causing liquid to attach to the inner face of the surface.

The spacing is thus preferably near the main flow inlet <NUM>, i.e. at a radially outward part of the surface <NUM>, where the surface <NUM> connects to the outer side wall.

The design is such that there is at least a part of the surface <NUM> which is positioned along the axis <NUM> spaced by a distance of d1 or more than d1 from the top of the main flow inlet <NUM>.

The separation distance is thus between the top of the main flow inlet and a portion of the surface <NUM>, i.e. the underside face of the second end. Thus, the spacing may be considered as the axial distance between the nearest (top) part of the inlet and the highest part of the cyclone chamber (if it has a non-planar second end).

For a non-planar second end, the spacing d1 is preferably present within the outer <NUM>%, or within the outer <NUM>% or within the outer <NUM>% or within the outer <NUM>% of the radius of the surface <NUM> from the axis <NUM>. Thus, the step is provided at or near the outer side wall, and hence at or near the main flow inlet <NUM>.

By displacing the main flow inlet from the second end in this way, the secondary flow discussed above towards the second end (i.e. towards the top) is less able to cause liquid to attach to the inner surface of the second end. Thus, this design reduces the amount of water that is entrained in the main outlet flow.

The main flow inlet <NUM> is for example spaced internally below the second end <NUM> by a separation distance between <NUM> and <NUM>. The spacing needed is relatively small so does not require significant additional space.

<FIG> shows that the main flow inlet conduit <NUM> extends in a direction offset from the perpendicular to the cyclone axis and facing towards the second end. The offset is by an angle θ as shown.

By moving the main flow inlet downwards, an easier path for the secondary flow is created. By directing the main inlet flow conduit slightly upwardly, the secondary flow is counteracted by reducing the pressure difference between the inside and the outside of the cyclone at the location of the second end. This in turn prevents any droplets that may have ended up at the second end to experience less or inward drag force.

Thus, the primary input flow is made to be inclined towards the second end (i.e. towards the top, second end).

The flow inlet conduit may extend in a direction offset by an angle θ in the range <NUM> to <NUM> degrees from the perpendicular to the cyclone axis. An optimum is found in the range <NUM> to <NUM> degrees.

<FIG> shows a cross section of a cyclone unit with these design features.

In addition, <FIG> shows a third design feature.

The main flow inlet conduit <NUM> can be seen with a circular cross section <NUM> with a first cross sectional area. The hydraulic area of the opening <NUM>, as defined above, is a larger, second, cross sectional area.

In this way, there is a flow area increase at the transition from the flow inlet conduit <NUM> to the cyclone unit. This reduces the flow speed. This measure may be designed to prevent water droplets of a size suitable for collection being broken up into smaller droplets, which can more easily flow to the outlet.

The main flow inlet conduit has a constant cross sectional area until it reaches the first intersection with the outer housing. From that point, the cross sectional area expands to reduce the air inlet speed. The separation process needs a certain flow speed, but when the speed is too high, larger water droplets will be broken down into droplets that are more able to travel with the airstream. The area expansion just at the entrance into the cyclone chamber prevents this issue.

<FIG> shows a view along the cyclone axis <NUM> of the junction between the outer side wall <NUM> and the main flow inlet conduit. It shows that the main flow inlet conduits approaches the opening <NUM> tangentially.

A fourth design feature relates to the interface between the outer side wall <NUM> and the main flow inlet conduit <NUM>. The fourth design feature is that inlet should gradually evolve into the housing. A gradual shape ensures that liquid enters the cyclone volume in a controlled manner. A sharp edge at the inlet tends to result in accumulation of larger drops breaking down into smaller drops, which eventually lead to water on the outlet conduit <NUM> (i.e. the vortex finder).

<FIG> shows a conventional transition between the main flow inlet conduit <NUM> and the outer side wall <NUM>. The abrupt edges in region <NUM> have been found to cause the collection of large droplets.

<FIG> shows the modification to the transition between the main flow inlet conduit <NUM> and the outer side wall <NUM> in accordance with this fourth feature. In region <NUM>, the part of the inlet facing the first end (i.e. the bottom area) is the area where most liquid enters the separation system. A minimum radius of curvature is set in this area. The radius of curvature may be at least <NUM>, for example at least <NUM>, for example at least <NUM>, for example at least <NUM>.

In general, larger edge radii are preferable. The radius may be at least as large as the capillary length (aka capillary constant) which (for pure water) is around <NUM>. Thus, for a vacuum cleaner application, the liquid can be assumed to be water (with some contaminants and possibly cleaning aid) and hence the radius of curvature can be defined in absolute terms. However, the physical effect under consideration is the formation and dispersal of droplets, and this depends not only on the surface shape but also on the liquid characteristics. The capillary length is a length scaling factor that relates gravity and surface tension, and it governs the behavior of menisci, based on the equilibrium between surface forces and gravity.

In particular, the capillary length is the typical size scale of droplets below which surface tension will tend to keep the droplets from breaking up by external forces. If the wall on which the liquid is flowing has a radius of curvature which is larger than this typical droplet size scale, the droplet movement will not be significantly hampered. If the radius of curvature is smaller however, the liquid needs to deform considerably causing it to be slowed or even pinned depending on the advancing contact angle.

<FIG> shows a view from within the cyclone chamber looking through the main flow inlet <NUM> into the main flow inlet conduit. The curvature in region <NUM> is represented.

<FIG> shows an external side view of the same design as <FIG>. It shows the inclination angle θ.

<FIG> shows a view from above the cyclone unit, with a top section removed, to show the transition between the main flow inlet conduit <NUM> and the outer side wall <NUM>.

As mentioned above, the ends of the cyclone unit do not need to be planar. <FIG> shows some alternative representative shapes for the surface <NUM> which closes the cyclone unit at the inlet end (termed the second end in the description above). In each case, at least a portion of the surface is spaced from the inlet opening by at least the spacing discussed above.

<FIG> shows a planar surface as in the examples above.

<FIG> shows a sloped conical surface. The radially innermost part of the conical surface has a spacing greater than the defined minimum spacing. Thus, there is a portion of the surface which has the required spacing. The minimum spacing may be reached before the radially innermost part, for example it may be reach even at the radially outermost <NUM>%, or <NUM>% or <NUM>% of the surface (as discussed above).

<FIG> represents a possible limit for the slope of the surface <NUM>, in that the desired effect may be lost if the slope in any less (i.e. if the second end is any flatter). The minimum slope angle is for example <NUM> degrees, for example <NUM> degrees, for example <NUM> degrees.

<FIG> shows a stepped surface with an initial step to a radially outermost flat portion and then a radially innermost sloped portion. There is again a portion of the surface which has the required spacing. This required spacing may arise at the initial step (near the main flow inlet) or it may arise at a position along the sloped portion.

<FIG> shows a surface with an initial step and a raised part near the outlet. The raised part may perform no function in the flow control and thus may be ignored. In any case, there is again a portion of the surface which has the required spacing and that portion is at the radial outer portion of the surface.

<FIG> shows a surface with an initial step and a sunken part near the outlet. The sunken part may perform no function in the flow control and thus may be ignored. In any case, there is again a portion of the surface which has the required spacing, and that portion is at the radial outer portion of the surface.

<FIG> shows a curved surface. It is sufficiently steep that the desired spacing arises sufficient outwardly from the axis <NUM>.

Thus, there are many possible shapes of the surface that may perform the functions described above in controlling the overall flow characteristics.

Claim 1:
A wet vacuum cleaner (<NUM>), comprising:
a dirt inlet;
a motor (<NUM>) and fan (<NUM>) for delivering suction to the dirt inlet;
a cyclone unit (<NUM>) for separating liquid and particles from a flow generated by the suction of the motor and fan, the cyclone unit having a cyclone axis (<NUM>) of rotation, wherein the cyclone unit comprises:
an outer housing (<NUM>) having an outer side wall (<NUM>) having an opening and an end surface (<NUM>) forming a boundary of an internal volume of the cyclone unit and which connects to the outer side wall (<NUM>), the end surface being at end of the cyclone unit along the cyclone axis;
a main flow inlet (<NUM>) to the opening in the outer side wall having an effective hydraulic inlet diameter;
a main flow inlet conduit (<NUM>) which connects to the main flow inlet (<NUM>), and
a main flow outlet (<NUM>) from the outer housing,
the main flow inlet (<NUM>) is at said one end of the cyclone unit but spaced internally from the end surface (<NUM>) by a separation distance (d1) of at least <NUM> times the effective hydraulic inlet diameter, characterized in that
the main flow inlet conduit (<NUM>) extends in a direction offset from the perpendicular to the cyclone axis and facing towards the end surface.