WO2023146419A1

WO2023146419A1 - Washing appliance

Info

Publication number: WO2023146419A1
Application number: PCT/NZ2023/050004
Authority: WO
Inventors: Wayne Andrew Mason; Robert Effingham LAWRENCE; Paul CHRISTIAANS; Liam David BARKER
Original assignee: Fisher & Paykel Appliances Limited
Priority date: 2022-01-28
Filing date: 2023-01-28
Publication date: 2023-08-03

Abstract

A washing appliance such as a dishwasher of the drawer-style, and a filter plate, filter and sump therefore. The filter plate of the washing appliance comprises a central inner opening to surround a wash pump, a perforated region towards the outer edge of the filter plate configured to filter wash liquid, and a filter opening in the perforated region of the filter plate, the filter opening for the insertion of a filter through the filter plate. The filter opening is at least partially located in a radial bulge of the filter plate.

Description

WASHING APPLIANCE

Field of the invention

The present invention relates to washing appliances and more particularly, though not solely, to wash systems within washing appliances that recirculate wash liquid during a washing cycle. In particular, the wash system of the invention is suitable for use in a dishwasher, including a drawer-type dishwasher.

Background of the invention

The wash system of our DISHDRAWER™ drawer-type dishwasher, as disclosed for example in WO1 993012706A1 and WO1998033426A1 (the disclosures of which are hereby incorporated by reference), includes a wash pump that is centrally located in the base of the wash tub. In one model of our DISHDRAWER™ dishwasher, the wash pump draws wash liquid in radially beneath a large, annular stainless steel "coarse" filter plate covering much of the base of the wash tub. The coarse filter plate has an annular region of perforations near its outer edge through which recirculating wash liquid passes to the underside of the coarse filter plate, then radially inwardly toward the wash pump over an annular heating plate surrounding the wash pump. The heated wash liquid then flows into the wash pump inlet and then upwardly through a central aperture in the coarse filter plate out of the wash pump via an impeller mounted within a spray arm. Soil, dirt or other particles too large to pass through the perforations in the coarse filter plate are washed into a drain sump located beneath an opening in the coarse filter plate and which is provided with a removable "fine" mesh filter strainer for capturing the large particles.

WO1 993012706A1 and WO1998033426A1 show dishwashers suitable for installation as drawers. An overarching constraint of drawer-type dishwashers is that the entire wash system is designed so that vertical height utilisation is minimised. The removable fine mesh filter strainer captures fine particles, is configured to be removed by the user, and the sump connects, through conduits, to the drain pump to allow draining of wash water. It is important that the seals around the fine mesh filter strainer ensure separation of filtered particles from the wash water. As a result of the wash pump requirement for a large intake area, and in order to successfully operate with a low liquid volume and a minimal suction head, the height available to incorporate the system that filters the wash liquid prior to it entering the wash pump inlet is reduced as compared with conventional (i.e., non-drawer-type or "drop-door") dishwashers.

W02016130027A1 (the disclosure of which is hereby incorporated by reference) also describes a dishwasher suitable for mounting in a drawer. It does not use an annular filter plate. Instead, it introduces a smaller filter plate insert in only a portion of the wash tub, the filter plate insert surrounding a filter for fine particles and conduits for directing the water from a sump beneath the filter plate back to the spray arm. The volume of water required compared to WO1993012706 is reduced because the path of the wash liquid around the machine is limited. In particular, the wash path is restricted to a series of low height conduits from the smaller filter plate back to the wash pump. WO2016130027 explains that it avoids the use of a large, annular coarse filter plate because the entire volume beneath the filter plate forms a part of the water flow passage from wash tub to wash pump, requiring a relatively large volume of washing liquid. The cylindrical microfilter for fine particles is placed into the sump using an inverted 'U'- shaped opening in its mesh wall to slide axially over a correspondingly-shaped drain inlet hood to form a labyrinth seal between the mesh wash and a mating slot in the drain inlet hood. This is then locked into place by the drain filter which has gripping projections which pass through the floor of the microfilter and lock rotationally into place with protruding hooks of the tub base. While effective, the seal at the drain inlet could be improved

The above-described wash systems, while performing satisfactorily, could be improved. For example, the volume of washing liquid required for a wash cycle and its associated energy and detergent requirement is relatively high. It is therefore an object of the present invention to provide a washing appliance which will go at least some way towards overcoming the above disadvantages, such as providing a washing appliance able to wash effectively while using less water, providing a sump filter with an improved seal with the drain inlet, or which will at least provide the public with a useful choice.

Summary of the invention

According to a first aspect the present invention consists in a ring-shaped filter plate for a washing appliance the filter plate comprising: a central inner opening to surround a wash pump; a perforated region towards the outer edge of the filter plate configured to filter wash liquid; and a filter opening in the perforated region of the filter plate, the filter opening for the insertion of a filter through the filter plate, wherein the filter opening is at least partially located in a radial bulge of the filter plate.

The use of a filter plate with a radial bulge containing the opening for the insertable filter enables the filter plate to provide a reduced length fluid flow return path back to the wash pump impeller, because there is a shorter distance from the perforated region to the centre of the filter plate, while also ensuring good filtration by having the insertable filter align with wash flow path in the perforated region and ensuring the filter has a strong seal around its periphery. The reduced radius of the filter plate outside the filter opening sector means that less water is needed because the area below the filter plate (that must be filled with wash liquid to ensure the pump operates efficiently) is less than that of a constant radius filter plate surrounding the filter opening.

Optionally further comprising a step on the inner side of the perforated region, the step separating an inner region at a higher level and the perforated region at a lower level.

The step provides an improved wash fluid flow as the water must enter through the lower perforated section while the inner section provides an upper edge of the wash fluid intake and the step provides a barrier to ensure "clean" or smooth (i.e., non-turbulent) flow of wash liquid towards the wash pump. The step is a relatively short transition between a first level and a second level to create a clear delineation between the sections. Although it may be vertical, the step is preferably at an angle of approximately 45 degrees.

Optionally the filter opening is circular and extends substantially from the inner edge of the perforated region to the outer edge of the filter plate.

Having the filter opening, and therefore the filter, span substantially across the entire radial width of the perforated region of the filter plate ensures that the filter is able to capture and store substantially all of the dirt or particles filtered by the filter plate perforated region.

Optionally further comprising a support structure at its outer periphery, the support structure configured to rest against a base of a dishwasher washing tub in use.

Optionally the support structure comprises a step and a lip, the lip curling inwards to increase the vertical stiffness of the outer periphery. The edge of the filter plate must be capable of supporting the filter plate in position against the wash base tub, as well as providing a seal so that wash fluid cannot bypass the perforated region on its path to the pump. The strengthening of the outer edge of the filter plate into a support structure allows the main span of the filter plate to flex, or elastically deform, effectively stressing or tensioning the filter plate once locked into position. The shaping of the periphery to provide this seal reduces the number of components involved in the assembly.

Optionally further comprising a locking means around the central inner opening, wherein the locking means is configured to interface with a complementary locking means around the wash pump.

The use of a locking means such as a locknut around the inner opening provides an effective method of securing the filter plate in place. In particular, in combination with the support structure at the outer edge of the filter plate, two strong points of contact are formed between the filter plate and the wash tub base, tensioning the filter plate and providing a required stiffness to resist the forces applied during washing while reducing leakage at the inner opening and outer edge of the filter plate.

Optionally further comprising a flange surrounding the filter opening, the flange configured to provide a contact surface for the filter when inserted.

A flange surrounding the filter opening provides reinforcement and rigidity to the filter plate around the filter opening/mating interface with the filter so that the filter plate retains its shape in use as well as ensuring a strong and/or reliable connection so that fluid cannot flow through a seal formed between the filter and the filter plate. Preferably the filter plate has a downwards step surrounding the flange.

According to another aspect the present invention consists in a washing appliance comprising: a washing tub for holding wash liquid and having a washing space adapted to receive items for washing, the washing tub comprising a base with a sump for collecting wash liquid; a wash pump and a drain pump, the wash pump having a wash liquid inlet in fluid connection with the washing tub, and a wash liquid outlet in fluid connection with a spray arm to direct wash liquid into the washing space, and the drain pump having a drain liquid inlet in fluid connection with the sump; and a filter plate according to the first aspect, the filter plate separating the wash liquid inlet of the wash pump from the washing space and the filter opening located above the sump.

Optionally a centrally-located pump assembly is provided, comprising the wash pump and the drain pump on a common drive shaft.

Optionally the base of the washing tub comprises a ring-shaped depression, wherein at least some of the perforated region of the filter plate is located in, or is positioned above, the ringshaped depression.

Having at least some of the perforated region of the filter plate in or positioned above a depression ensures that, in use, there is fluid on both sides of at least some of the perforated region of the filter plate, and that a non-turbulent liquid intake path to the wash pump is provided.

Optionally the base of the washing tub comprises an inner portion between the wash pump and the ring-shaped depression, the inner portion forming the lower surface of the wash pump wash liquid inlet, wherein the inner portion is substantially horizontal.

Optionally further comprising an annular heater forming, or below, a portion of the inner portion of the base of the washing tub.

A substantially flat and horizontal wash liquid intake lower surface reduces the length of the wash liquid intake and allows a more compact design because the depression can have a larger vertical separation from the wash liquid intake lower surface without increasing the height of the base assembly or the filter plate.

Optionally the annular heater is a tubular sheath heating element brazed or welded to an annular plate.

The use of a tubular sheath heating element brazed or welded to the underside of an annular plate allows control over the shape of the upper surface of the heating element, so that it can be flush with the lower surface of the wash pump wash liquid inlet. Control is achieved by the design of the annular plate to which the heating element is welded or brazed.

Optionally the base of the washing tub comprises an outer ledge surrounding the filter plate, the ledge sloping downwardly, inwardly towards the outer wall of the ring-shaped depression. It is important that wash liquid is given a short path from the wash space back to the wash pump liquid intake. Advantageously the improvements made to the filter plate have reduced the path length of the wash liquid from the filter plate to the intake, however the (average) distance that the wash liquid must flow to reach the filter plate, in particular the filter plate's perforated region, is also an important feature, and this is potentially lengthened due to the reduction of the filter plate radius. The provision of a raised (relative to the filter plate and/or annular depression) and sloped outer ledge ensures that falling water is quickly returned to the surface of the filter plate and reduces the volume of water required to fill the base of the wash tub.

Optionally further comprising one or more drainage channels in the depression, each drainage channel sloped along its length to encourage washing fluid to move towards the sump.

One or more channels in the base of the depression ensure that water held in the depression during a wash cycle will drain fully during the drain cycle. Advantageously one of the same channels is used to position a contoured insert which forms the outer edges and sides of the wash space within the wash tub, and can improve contact between the filter plate and the wash tub base by acting as an intermediary therebetween.

Optionally further comprising a partial floor portion, preferably of stainless steel, for the washing tub, the partial floor portion having a central opening that mates with the channel in the base of the washing tub and extending along the base of the washing tub and meeting the wall of the washing tub, locating between the outer edge of the filter plate and the base of the washing tub.

Optionally further comprising a compressible seal between the partial floor portion and the base of the washing tub, the compressible seal located in a slot formed in the tub base, the slot formed in a closed loop and being overlapped by the partial floor portion.

Optionally the compressible seal is hollow.

Optionally further comprising a filter configured to be removably inserted into the sump, the filter passing through the filter plate when inserted and removed.

Optionally the filter is a cylindrical shaped filter with a bottom surface which locks to the base of the washing tub. Optionally the washing appliance is a dishwasher.

Optionally the features of the washing appliance may include any one or more of the preceding optional features.

According to another aspect the present invention consists in a washing appliance comprising: a washing tub for holding wash liquid and having a washing space adapted to receive items for washing, the washing tub comprising a base with a sump for collecting wash liquid; a wash pump and a drain pump, the wash pump having a wash liquid inlet in fluid connection with the washing tub, and a wash liquid outlet in fluid connection with a spray arm to direct wash liquid into the washing space, and the drain pump having a drain liquid inlet in fluid connection with the sump; and a ring shaped filter plate surrounding the pump assembly, the filter plate separating the wash liquid inlet of the wash pump from the washing space, an outer region of the filter plate perforated to allow wash liquid to flow to the wash pump; wherein the filter plate has a radial bulge extending to encircle the sump.

According to another aspect the present invention consists in a washing appliance comprising: a washing tub for holding wash liquid and having a washing space adapted to receive items for washing, the washing tub comprising a base with a sump for collecting wash liquid; a wash pump and a drain pump, the wash pump having a wash pump liquid inlet in fluid connection with the washing tub, and a wash liquid outlet in fluid connection with a spray arm to direct wash liquid into the washing space, and the drain pump having a drain liquid inlet in fluid connection with the sump; and the base of the washing tub having a ring-shaped channel surrounding the pump assembly, the channel providing a fluid source for the wash pump liquid inlet, and wherein the channel has a radial bulge to encircle the sump.

Preferably comprising a perforated filter plate positioned at least in part in the channel, the filter plate separating the wash liquid inlet of the wash pump from the washing space

According to another aspect the present invention consists in a dishwasher sump for receiving a cylindrical filter having an outlet seal, the dishwasher sump comprising: a base with an alignment feature, and a cylindrical wall having a drain outlet, either a surface of the drain outlet or the drain seal being horizontally tapered, wherein, in use, the alignment feature mates with a corresponding feature of the cylindrical filter and rotation of the cylindrical filter in a first direction urges the outlet seal against the drain outlet surface.

The use of a drain outlet or drain seal with a horizontal taper and an alignment feature ensures that, when a suitable filter is inserted, an effective seal is formed between the filter and the drain and it is easy to rotationally engage and disengage the filter without soil escaping from the filter via an opening for the drain outlet. This is because, in contrast to hypothetical engagement features located at the outer edge of the sump and filter, the alignment feature has relatively small, so can be manufactured with low tolerances, accurately positioning the filter. Once the filter is in such a position the tapered surfaces ensure that rotation precisely aligns and tightly seals the filter in place on the drain outlet.

Advantageously the locking arrangement minimises any internal fittings or components, maximising the filter's effective internal volume.

Preferably the alignment feature is at least one protrusion or recess to mate with a corresponding recess or protrusion in the cylindrical filter, or vice versa. Most preferably it is a central pin. Preferably the sump has a securing means for securing the filter vertically. Preferably the securing means comprises a plurality of feet, bayonets, or protruding ledges. Preferably these are at the bottom edge of the side wall of the sump and are configured to mate with corresponding protruding ledges or feet on the filter. These provides additional support against vertical movement of the filter. Preferably the feet or bayonets are sloped to encourage the filter downwards when locking. Preferably the alignment feature is in the centre of the base, centrally located, or in the centre of the filter. Preferably the drain outlet surface is horizontally and vertically tapered so that progressive rotation of the filter in the first direction simultaneously increases seal compression both horizontally and vertically.

According to another aspect the present invention consists in a filter for a sump in a dishwasher, the sump having a tapered surface on a drain outlet, the filter comprising: a circular base, a circular lid, and at least one wall extending between the base and lid, each wall comprising fine mesh filter portions; an alignment feature on the circular base; and a moulded seal at the drain outlet, wherein in use the central alignment feature mates with a corresponding feature of the sump and rotation of the cylindrical filter in a first direction urges the outlet seal against the tapered surface of the drain outlet.

Preferably the lid has an array of apertures to allow wash fluid or liquid to flow into the filter but to restrict fluid from directly flowing out. Preferably the lid and the mesh body are reversibly detachable to allow cleaning of the filter and/or removal of soil or dirt from the filter. Preferably the lid and mesh body are rotatable and/or removable from the sump as a single unit. Preferably the alignment feature is a protrusion or recess to mate with a recess or protrusion in the filter or vice versa. Preferably the filter is cylindrical.

Preferably the filter comprises a plurality of feet or protruding ledges at the bottom edge of the wall, to mate with corresponding protruding ledges or feet in the sump. This provides additional support against vertical movement of the filter. Preferably the filter, most preferably the lid of the filter, has a ledge configured to connect with or attach to a filter plate in use. Preferably the moulded seal is an o-ring, an over-moulded seal, or an over-moulded o-ring. Preferably the circular base is continuous across the bottom of the wall(s), the circular base lacking any large apertures which may allow soil to escape. Preferably the filter comprises a ledge, the ledge preferably removably connectable between the circular lid and the wall. Preferably the ledge is an upturned truncated cone with an aperture at the apex of the cone. This restricts the ability of soil to float out of the filter once captured. Preferably the filter comprises one or more notches. Preferably the notch is attached or part of one of the feet. The notch interacts with a protrusion on the sump to click, or provide haptic feedback to the user, when the filter is correctly positioned. Preferably the alignment feature is central, centrally located, or in the centre of the filter.

This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more of said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth. The term "comprising" as used in this specification and claims means "consisting at least in part of". When interpreting each statement in this specification that includes the term "comprising", features other than that or those prefaced by the term may also be present. Related terms such as "comprise" and "comprises" are to be interpreted in the same manner.

Brief Description of the drawings

FIGURE 1 shows a diagrammatic form of a dishwashing appliance suitable for a drawer or cabinet.

FIGURE 2 shows an exploded view of a dishwasher incorporating the filter plate of the present invention.

FIGURE 3 shows a partial cross-section of the base of a dishwasher showing the filter plate.

FIGURE 4 shows A) a top view of the filter plate arranged in a dishwasher, B) a horizontal crosssection view of the filter plate along the centre of the filter plate, C) detail of the outer and edges, and D) detail of the inner edge.

FIGURE 5 shows a partial isometric view of the base of the dishwasher including filter plate and sump, with a cross-section to view the base beneath the filter plate.

FIGURE 6 shows A) a filter to be positioned in the sump, where the mesh has been removed to allow visibility inside the filter, B) the sump in which the filter may be placed and C) the filter placed in the sump.

FIGURE 7 shows an exploded view of the filter of Figure 6.

Detailed description

The washing appliance 100 incorporating wash system and filter plate according to an embodiment of the present invention is illustrated in Figure 1. The washing appliance 100 includes a wash (or washing) tub 101 (which incorporates all wash system components, such as spray arm, wash pump, and filtration and wash liquid flow passages) having a base 102 and either one continuous side wall or separate, connected side walls surrounding or enclosing a wash chamber or wash space 104. Wash tub 101 is fitted with a front panel 105 having a handle (not shown) and is slidably mounted within a cabinet 106 in a drawer-style arrangement. The wash chamber 104 has an open top and is withdrawn from the cabinet in the direction of the arrow to allow loading and unloading of, for example, dishes and is retracted within cabinet 106 while washing occurs. A wash system is fitted within wash tub 101.

The washing appliance 100 is usually constructed with a height dimension approximately half that of conventional front-loading domestic washing appliances. In this form it can be used alone or as one of a number, more usually one of a vertically-stacked pair of such washing appliances, as shown in WO1998033426A1. The wash system could be incorporated within other types of dishwashing machines such as conventional "drop door" dishwashers or "table- top"/benchtop/worktop-style dishwashers. The wash system could also be incorporated into other types of washing appliance such as front- or top-loading, or even drawer-style, laundry washing machines. To achieve an effective washing space within the wash chamber 104 of such a reduced height washing appliance 100, it is important that the wash system has a compact vertical height.

A surface 114 within the wash tub forms at least part of the floor of the wash chamber or wash space 104 and includes a ring-shaped filter plate (not identified in Figure 1) forming a separation or boundary between the wash chamber or wash space and a wash system volume beneath the filter plate and above a wash tub base 102. The liquid intake of the wash pump 107 is formed in the wash system volume, while the outer part of the filter plate 1 has a perforated region to allow water to pass through to the liquid intake while stopping at least large particles of dirt from entering the liquid intake. Preferably, the inner part of the filter plate is non-perforated.

A rotatable spray arm 115 is also provided in the wash tub 101, generally in a lower portion of the wash space 104, above surface 114. Spray arm 115, as is well known, is for directing wash liquid or fluid, such as a water and detergent mixture, from the wash pump in a spray pattern onto the dishes or other items in wash space 104 for removing soil therefrom. Racking (not shown) is provided within the wash tub above the height of the spray arm to hold, for example, dishes. Flexible electrical wiring and plumbing 111 couples the wash tub 101 to the relevant terminations within cabinet 106 in a manner enabling the withdrawal and retraction of the wash tub from/into the cabinet while also enabling power and clean water to be provided to the wash tub, soiled water to be removed from the wash tub and optionally, control signals to be relayed to/from the appliance. A user interface unit 112 to enable a user to activate various functions or wash programmes of the dishwasher may be mounted in the cabinet 106, in the wash tub 101 (such as on the upper surface of front panel 105, as shown) or may be provided remotely. User input from the user interface unit is provided to a dishwasher controller 113 provided in the cabinet or wash tub and which may be programmed to generate, in response to user-input instructions, electronic control signals for various machine components such as display(s), motor(s), heating element(s) and valve(s) during cycles of machine operation such as pre-wash, washing, rinsing, and drying.

Figure 2 shows an exploded view of the base region of a wash tub. The wash system of the dishwasher includes a pump assembly comprising a drain pump 108 and a wash pump 107, a heating device/element 109, preferably an annular heating device surrounding the pump assembly, and a sump 110 to hold a filtration system and connect to a drain, all generally positioned in a lower portion of the wash tub. The wash tub surface 114 preferably includes a first opening 117. The pump assembly can be fitted and secured in this first opening. The pump assembly is preferably a combined wash pump 107 and drain pump 108 with separate wash pump impeller 127 and drain pump impeller 126 mounted on a common shaft 125, wherein the geometry of the impellers and the chambers in which they are rotated ensures that shaft rotation in a first direction effectively activates only the wash pump and shaft rotation in the opposite direction effectively activates only the drain pump. Preferably the pump assembly, comprising the rotor 60 (shown in Figure 3), drive shaft 125, and connected drain pump impeller 126 and wash pump impeller 127 is removable from the first opening. This allows simple cleaning, or repair of the rotor and impellers unit. However different wash pumps will work with the filter plate described herein.

The first opening 117 is preferably formed in a stator assembly or motor housing component 120 which forms, or is also inserted into, part of base 102. The motor housing component (including the stator, drain pump cavity, and ducts connecting to the tub sump and to the drain) is fixed into, or forms part of, the surface 114 of the tub base 102. In the described embodiment, the wash tub 101 is moulded from a plastics material such that the side wall(s) 103 are formed separately from base 102 and the tub is formed with a hole into which base 102 is inserted and sealed during assembly. Alternatively, base 102 could be integrally formed with the side wall(s) 103, for example by plastics injection moulding. In further embodiments inserts may be used to provide a stainless-steel finish to elements in the wash tub. Preferably though, the substantially vertical side wall of the wash tub may be formed from folded/formed/welded sheet stainless steel with a partial tub floor portion (19 - see Figure 3 and description below) formed, attached or welded at, and extending inwardly from, the lower periphery of the four connected side walls. The partial tub floor portion 19 is adapted to be attached to base 102, to thereby attach the tub to base 102, having a central opening therein that exposes most of base 102 which thereby forms the remainder of the tub floor. Thus, partial tub floor portion 19 effectively forms an inwardly-directed flange at the base end of the tub side walls.

Figure 3 shows an aspect of the lower part of the washing tub and wash chamber 104. The wash flow liquid path is forced by the wash pump. Beginning, for example, at the wash pump impeller 127, the wash liquid is pumped from a wash pump chamber 128 beneath the impeller 127 into the spray arm 115. In the spray arm 115 the wash liquid is directed, by spraying apertures or nozzles 116 in an upper surface of the spray arm into the wash chamber to wash the dishes in the rack (not shown). The wash liquid then falls down inside the wash chamber 104, or down the walls of the wash chamber toward or into the tub base 102. The shape of the tube base 102 includes a ring-shaped depression 10 and the sump 110 (not shown in Figure 3) into which water flows, as they are relatively deep compared to the rest of the wash tub base 102. The inlet 129 to the wash pump and wash pump chamber 128 is fed by an annular passageway or plenum 80 with the lower surface formed by the tub base. An outer portion of the plenum has a heating element 109 to heat the water, preferably beneath or forming a flush surface. The sump has a conduit connecting it to the drain pump 108 and then an outlet for draining liquid from the machine.

Because of the low volume of water used for each wash/rinse cycle, only a low suction head is available for wash pump 107. This means only a small pressure drop can be tolerated which means the pump velocity intake must be low.

The filter plate 1 separates the wash chamber 104 of the dishwasher from the wash pump chamber 128 or at least the plenum 80 from the wash chamber 104. A series of apertures in the filter plate 1 allows wash water or liquid to pass through this separation while providing a level of filtration to remove soil or dirt or any large particles from the wash liquid. Figure 3 shows the filter plate extending out from the centre of the dishwasher (where the pump assembly is located). The inner portion or region 11 of the filter plate preferably forms the upper surface of the wash pump plenum 80 and is non-perforated (i.e., impervious to the washing liquid). The outer portion or region 12 of the filter plate has a plurality of holes or apertures or perforations 2. Preferably this perforated region spans the outer portion of the filter plate. These can be relatively coarse, so that they stop large pieces of soil or dirt or other particles passing into the wash pump (and potentially blocking the pump or spray arm), while allowing liquid and smaller soil/food particles to flow relatively freely. The inner section allows a less turbulent flow of liquid to the wash pump, as well as restricting the flow of any air into the wash pump, because the apertures are confined to the outer region.

To ensure that this perforated region 12 remains as clear as possible for the liquid to flow through the wash water flow path is preferably configured (by the shape of the tub and the angle of the spray arm jets) to create a clearing effect on the filter plate 1 ahead of the spray arm 115 as it rotates. For this purpose, a sluicing jet may be provided at an edge of the spray arm's lower surface (as best seen in Figure 2), angled at least partially downwardly at the filter plate. Large soil particles are pushed radially around the perforated surface 12 by the water flow, preferably with a lip of the filter plate 1 or tub base 102 at the outside edge of the filter plate ensuring they remain on the filter plate. The particles are pushed by the wash fluid around the filter plate to drain sump 110 which is provided with a passive filter or strainer 50 for collecting these larger particles. This action puts particular pressure on the seals of the filter or strainer 50 as it sits within the flow of most of the water during a wash cycle. As with filter systems found in conventional dishwashers, the strainer or filter 50 will require regular clearing and/or cleaning by the user.

Surprisingly, the inventors have found that effective wash performance is possible with reduced water usage through the use of a radial bulge 5 in the filter plate 1. When the filter plate 1 is positioned in the depression or recess 10 in the base 102 of the wash chamber 104 the depression 10 also has a radial bulge. The radial bulge 5 provides an area with a relatively large radius to hold a large filter 50 for use in filtering particles from the wash water, while providing a relatively smaller outer radius for the ring-shaped depression 10 so that less water is required to fill the depression, and therefore less water is required to provide appropriate water levels to run the wash pump 107.

Figure 4 shows a view of the filter plate 1 from above with spray arm 115 in location on the wash pump 107. In this embodiment the outer region 12 containing apertures 2 extends from step 15 to the outer edge 13 of the filter plate 1. The filter 50 is located within this outer region 12, with the filter plate 1 extending around it to provide a suitable filter opening, and preferably a ledge for the filter 50 to sit on or connect to. Preferably the opening also has a mating surface to allow the filter to mate securely with the filter plate 1. Preferably this ledge or flange ensures a strong and/or effective connection between the filter plate 1 and the filter or strainer 50 reducing the ability for soil or dirt to pass between them. Preferably the filter 50 connects or secures to the base of the tub 102, forcing the flanges or mating surfaces of the filter plate 1 and filter 50 together, or holding them in contact. Preferably the filter opening is partially in the radial bulge, with the remainder of the filter opening extending across the outer region, towards or to step 15, or from the inner edge of the perforated region to the outer edge of the filter plate. As the filter 50 sits in the sump in use, the sump extends across substantially the same area as filter opening 50.

The shape of the outer edge 13 of the filter plate is tear or tear drop shaped, preferably having a curved point, that is generally circular with a lobe or radial bulge to extend around the filter. The radial bulge 5 forms an outwardly-projecting lobe from a substantially annular filter plate 1. Because of the inner cut-out or opening 14 to fit around the wash pump assembly the filter plate 1 as a whole is ring- or annulus-shaped - that is, it is substantially planar and forms a full revolution or 360 degrees about an axis through an inner opening 14 spaced radially from its outer edge 13. It will be understood that throughout this document where ring-shaped or annular is used the outer edge or periphery may be non-circular, as may the inner opening shape. The inner opening 14 is shaped to fit the shape of the wash assembly that it surrounds, and so is generally circular. The ring-shape provides rigidity to the filter plate 1, ensuring the seals to the wash tub 102 and around removable filter 50 remain strong or sealed, so that the filter plate is able to effectively filter the washing fluid through the apertures as well as providing a quick and/or short and/or efficient return path to the wash pump for wash liquid throughout the wash chamber.

The remaining outer edge 13 (e.g., away from the radial bulge 5) of the filter plate may also not be completely circular (although it is preferably substantially circular, or circular outside specific regions). Figure 4 shows a removed or shortened segment 16 of the filter plate 1 opposite the filter 50, in this case at the front of the dishwasher. This segment 16 is removed to increase the space beneath the dishwasher to enable a toe-space beneath the unit (for lower drawers in a stacked, double-drawer version) which is necessary for some kitchen designs, although other reasons may also require changes or variations to the geometry. The base of the wash tub extends to the wall where the segment of filter plate is not present. The filter plate 1 then has an outer edge 13 forming an annular shape along the majority of the filter plate 1, so that all, or a majority, of the circumference of the filter plate 1, or at least of outer region 12 containing apertures 2, has a radius less than the maximum radius at the filter 50. At the opening for the filter 50 the filter plate 1 extends to surround the opening. The exact shape of the outer edge of connecting portion 7 of the filter plate between the annular section of the filter plate 1 and the bulge 5 extending around the filter 50 may be varied. In the embodiment of Figure 4 the outer edge 7 has been selected to have a substantially straight edge.

The radial bulge 5 at the periphery of the filter plate has a radius greater than the remaining filter plate creating a larger sector in that area of the filter plate 1. The radial bulge 5 or lobe in the filter plate 1 provides additional space in the filter plate for an opening for a filter. In particular, this space is further from the centre of the filter plate, so that when the filter plate is positioned in the dishwasher the depth beneath the opening for filter 50 is maximised, allowing a large filter 50 to be used. The additional space is useful because the annular heating element 109 limits the ability to have a deep sump (or other features) closer to the pump assembly.

The filter plate 1 may be formed from a metal plate covered by a large number of closely- spaced holes in the perforated region through which wash liquid and smaller soil particles may pass. The filter plate provides a relatively coarse level of filtering to the wash liquid and the holes are of the order of 0.7 to 1.0 mm in diameter. The holes 2 in filter plate 1 may be acid- etched so that rough or sharp hole edges may be avoided. Filter plate 1 is provided with an opening 3 to enable drain filter 50 to pass therethrough. The recessed edge of opening 3 may also be provided with a flexible or elastomeric seal 4. An o-ring 64 may be placed between the opening 3 and the tub base 102 or surface on which it sits to ensure a strong seal.

The filter plate preferably has a step 15 between inner region 11 and outer region 12. The step lowers the outer region 12 of the filter plate into a depression of the wash tub base 102 so that the wash liquid intake (through the perforated region) is drawn at a lower level than the wash pump plenum 80. This restricts the ability of air to enter the wash pump system, as water is typically present up to a level slightly above the top of the plenum or the lock nut 62 of the filter plate 1. The step also ensures that the annular plenum 80 is more separated, or more clearly separated, from wash liquid flow around the wash tub or depression 10, helping provide clean (non-turbulent) flow of wash liquid towards the wash pump. The step is a relatively short transition between a first level and a second level to create a clear delineation between the sections. Although the step may be vertical, it is preferably at an angle of approximately 45 degrees, or at least 30 degrees or at least 45 degrees and is preferably substantially parallel to the base 102 below it. The height of the step is preferably between 5-10 mm, most preferably at least 6 mm high. A higher step is preferable as it provides improved separation, however the top of the step is set by the level of the motor and motor housing 120 plus plenum 80 above it, while the level of the base of the step 15 is driven by the depth available in the wash tub and water requirements. The perforated region preferably extends between the step and the outer edge of the filter plate.

The filter plate 1 has a connection means 62 to the wash tub at its central opening 6. This secures the filter plate 1 in place, preferably to the pump assembly 118. The connection means 60 preferably comprises at least a ledge 61 on filter plate 1 and a locking means. The ledge 61 on the filter plate may be formed by a fold or hemmed edge at the inner opening. Preferably the ledge 61 comprises a step 136, substantially horizontal portion 137 and a hem 135 as shown in Figure 4D. The locking means is preferably a lock nut 62 which secures, screws down, or rotationally locks onto the pump assembly to hold the filter plate in contact with the pump assembly, preferably the rotor chimney of the pump assembly which is suspending above base 102 to support the spray arm bearing. An o-ring seal 64 between the pump assembly and the filter plate helps to ensure air is not introduced at this high connection point. Tightened the locking means flexes or plastically deforms the central part of the filter downwards, stressing or tensioning the filter plate 1, the stress or tension biasing the outer edge downwardly into position against the wash tub base 102.

The washing appliance may be constructed in a range of sizes. In a preferred embodiment, suitable for standard dishwasher widths, the following measurements may be used (measurements provided plus or minus 2 mm). The inner opening 3 diameter is 75 mm with a 20 mm flange surrounding it to allow connection of the lock nut or securing means. The diameter of the circular portion is 364 mm (radius 182 mm). The maximum radius of the radial bulge is 209 mm. The radial bulge preferably increases the filter plate radius by at least 5% or at least 10%. However, the radial bulge may increase the filter plate radius up to 20%, between 5% and 20%, between 12% and 17%, or by 15%. The flat portion at the front of the filter plate in the drawer has a minimum radius of 163 mm. Step 13 has a diameter of 237 mm at its low point. The height of the filter plate is 17 mm (from high point at inner opening 3 to low point at outer edge 13). When secured in the washing tub this height may reduce due to the deformation or flexing of the filter plate 1.

Figures 3 and 4B, 4C and 4D shows the outer edge 13 of the filter plate is strengthened vertically, to support the filter plate as well as ensuring wash liquid is unable to bypass the filter plate perforations by flowing between the filter plate 1 and the wash tub base 102. Preferably the strengthening is achieved by bending or moulding the outer edge 13 of the filter plate to from a support structure which has a relatively high vertical stiffness or strength. In Figure 4B and 4C this is achieved by (moving away from the centre of the dishwasher) an upwards step 131 to a short substantially horizontal section 132 and then a vertical drop 133. This creates a substantially box-shaped section, or creates a substantially square corner, giving the outer edge 13 vertical stiffness or resistance to plastic deformation. The end of the outer edge 13 is then coiled inwards to produce section 134, which also helps to avoid injury to a user. In embodiments, a seal or rubber component (not shown) is attached or part of the outer edge of the filter plate to improve contact or reduce rubbing between the filter plate 1 and wash tub base 102. As seen in Figure 4B the filter plate 1 has a falling shape or cross-section profile from the inside to the outer edge. This profile may appear flatter when installed in the wash tub due to the central part of the filter plate flexing downwardly in use.

Partial tub floor portion 19, preferably formed of stainless steel, may be positioned between the filter plate 1 and the base 102 of the washing appliance or machine. This may be contacted below by a compressible, preferably hollow or tubular, seal or o-ring 130, positioned in a groove or slot 138 formed in the tub base 102 to block wash liquid from flowing radially outwardly on base 102. Groove or slot 138 is formed in a closed loop enclosing the filter opening, overlapped by the partial tub floor portion 19 so that the slot is formed to approximately correspond to the peripheral shape and size of filter plate 1 as it also has a radial bulge to accommodate the filter's position. Screws or other connection means fasten the partial tub floor portion 19 (and therefore the entire wash tub) to base 102, compressing seal 130 therebetween. If seal 130 is hollow, it is better able to compress to the desired thickness so as not to deform partial tub floor portion 19 and therefore filter plate 1, while better spreading and therefore minimising the force exerted onto base 102, and also enabling the seal to deform sufficiently to maintain sealing contact along/around the entire length/circumference of slot 138.

Partial tub floor portion 19 has a first, radially inner edge configured to sit in channel 17 and a second, radially outer edge extending up the side 103 of the wash tub. As mentioned above, the radially outer edge 13 of filter plate 1 is, in use, biased downwardly so that section 134 is compressed against the upper side of partial tub floor portion 19, optionally with a seal (for example an extruded elastomeric seal) in between, attached to edge 13, for improved corrosion resistance. Preferably tub floor portion 19 is formed integrally with, and/or is welded to the side walls 103. As side walls 103, tub floor portion 19 and filter plate 1 may all be formed from stainless-steel, the internal surfaces visible to a user during operation of the appliance may be completely stainless steel, thus providing improved aesthetic appeal and wear/stain resistance.

Figure 5 shows an isometric view of the section of the washing tub near the removable filter 50 with a cross-section to view beneath the filter plate 1. The radial increase between the normal radius and the radial bulge 5 around the filter plate can be of general shape, in the present case it is substantially straight. Alternatively, it could be more bulbous, only expanding close to the radial bulge. This embodiment has a ledge 4 formed in the filter plate 1 to surround the removable filter 50 in the sump. This ledge or flange provides a mating surface for the lid of the filter 50, in use. This combined with a locking means, for instance as described below, for the filter 50 to the wash tub base, provides a series of strong seals around the filter 50 to prevent captured soil or dirt in the filter 50 from re-entering the wash fluid. The ledge is preferably created by a step down in the filter plate 1. Because the outer perimeter of the filter opening meets the outer edge 13 of the filter plate 1 directly, the step 131 of this portion will be larger than the step 131 of the remaining perimeter which steps down to the outer region 12 with apertures.

Figure 5 also shows the annular heating plate 109 which surrounds the pump assembly 118 in the plenum 80. As shown in Figure 2 it preferably also surrounds, or sits at, or on, the outer surface of stator assembly 120. The annular heating plate is located inside the filter plate outer region with apertures to ensure that all liquid (which is preferably water with detergent or other cleaning component) flowing into the wash pump 107 has been heated (in the relevant part of the wash cycle). At this point the filter plate 1 has a flat profile forming the upper surface of the liquid intake 129 and plenum 80. The profile may be slightly sloped up towards the central opening where the wash pump sits. The location of the heating plate 109 places a restriction on the device, due to the height required for the heater, so that the step 15 in the filter plate 1 and the depression 10 in the base 102 occur substantially just outside the outer edge 119 of the heating plate 109 (as some additional support/protective elements are required adding additional width around the heating plate 109). The heater plate also restricts the filter opening from moving closer to the centre of the filter plate 1 because the heater plate must contact the wash fluid so cannot be above the sump.

The heating plate 109 is preferably formed from a tubular sheathed heating element which is welded, or preferably brazed, to an annular plate 111. This allows the shape of the heating element to be controlled or selected by the choice of the annular plate. Preferably the annular plate is chosen to be substantially flush with the base 102 of the washing tub and substantially flat and horizontal when mounted in a drawer arrangement. The flatness of the heating element 109 and the flush base 102 surrounding it allows the flow path between the wash impeller and the outer region of the filter plate to be relatively short and have a relatively low height, helping minimise the space used. The short path also means that less liquid is sitting in the plenum 80 in use, so that less water/liquid overall can be used. A preferred tubular sheathed element comprises an aluminium sheath containing a resistance wire for providing heat and Magnesium oxide as compressed insulation. This element is brazed onto an Aluminium heat spreading plate which is brazed onto an annular stainless-steel plate which forms the surface of the heating plate 109.

In the ring-shaped depression 10 of Figure 5 the first 17 and second 18 channels are visible. The height of the two channels will vary around the circumference of the channels 17/18, to have a slope towards the sump at all points. At the sump 110 the wash liquid meets the mesh side walls of the filter 50. The sump 110 substantially spans the distance between the heating plate 109 and the outer edge or wall 103 of the dishwasher, with the small amount of additional space required for support structures and to accommodate sub-surface features such as tubing. This is because it is advantageous to have as large a filter 50 as possible, to increase the amount of water filtered in each wash cycle and to avoid the filter 50 filling up quickly. The strengthened outer edge 12 of the filter plate 1 is aligned with the outer edge of the sump 50 so that there is substantially no space between them, allowing the step portion 131 to directly drop to the flange or ledge 4 to support the filter 50.

The outer edge 13 of the filter plate 1 rests at or near the outer edge of depression 10. There is a corresponding step up at the outer edge of the depression to form the channel in which the filter plate 1 sits. Outside this step 9 the washing tub base 102 angles towards the wall 103 of the washing machine. There may be further sloped portions or steps, for instance step 40 between the circular portion of the base 102 and the square sides 103. The sloped region 41 of the base encourages wash liquid to return to the depression, and therefore quickly return to the wash pump, minimising the amount of water needed to fill the wash pump intake. This takes the place of a wider filter plate in prior art systems. While a greater angle or slope may encourage liquid to flow more quickly this would increase the height of the region, which sits under the spray arm 115 and may impact performance.

Returning to Figure 3 we can follow the radial outline of the base 102 of the tub from the wash pump in the centre to the outer edge, recognising that the annular nature means this is substantially similar around the dishwasher. The first portion is substantially flat and horizontal, forming the lower surface of the wash pump intake 129 and plenum 80. The heating element 109 is preferably embedded flush into this surface, so as avoid disturbing the flow of wash liquid to the wash pump. Outside the heating element 109 there is a depression 10 with a step or lip at the inner and outer edges. This depression provides a space for the collection of wash liquid, and for the filter plate 1 apertures to sit in. The depression preferably has one, two, or a plurality, of channels 17, 18 for encouraging wash liquid to the sump. As discussed above the depression preferably has a radial bulge around the sump portion of the depression, allowing a larger filter to be used while collecting water quickly enough to supply to wash pump. Outside the outer edge of the depression is a sloped or angled surface, or plurality of surfaces, leading to the wash tub wall 103.

Figures 6A to 6C and Figure 7 show the removable drain filter 50. Drain filter 50 preferably comprises a substantially cylindrical filter mesh 51 and a lid 52, which are reversibly connectable together. The mesh 51 and lid 52 are preferably secured together with a securing means or device such as clip 67. This enables the lid 52 to be removed to allow collected material to be removed from the filter 50, while allowing the lid and mesh to be connected and disconnected from the sump in one unit. Drain filter 50 is arranged with its axis substantially perpendicular to the plane of filter plate 1 and tub base 102. While a cylindrical filter 50 is preferred to maximise the use of space it is possible that a small angle (from vertical) is present in the outside wall of the filter while remaining substantially cylindrical.

Figure 7 shows an exploded view where lid 52 is preferably formed as a welded cup, with an upper portion having a series of apertures 58 to allow water in and a surrounding wall with larger apertures 53 to allow soil and larger food/soil particles to pass in for capture, and a lower frustoconical portion 65 with a central aperture 66. This conical barrier 65 allows particles to pass easily into the filter but prevents floating of particles out. Alternative shapes may be used, preferably they have a generally downwards slope to encourage water or soil to flow into the filter and a central aperture. The central aperture is preferably as large as or slightly larger than the openings 53 so that material is not trapped in the lid 52. Welding the two pieces of the lid together simplifies use, however separate interlocking or connecting pieces could also be used.

The drain filter lid 52 preferably has an angled upper surface with a plurality of apertures. The perforated surface 58 is adapted to reduce any flow of trapped particles out of the drain filter. Beneath the upper surface the drain filter lid 52 includes a substantially cylindrical filter wall containing a series of openings 53, larger than lid openings 58. Openings 53 may have dimensions of about 10 mm by 10 mm, for example, through which large soil particles may progress from filter plate 1 into the filter or strainer 50, pushed by the flow of wash liquid. Particles too large to pass through openings 52 will remain on filter plate 1 and be removed manually. The lid or frame 53 has an annular rim or lip 59 which extends out to contact the filter plate when positioned on the filter plate 1.

The filter mesh 51 is preferably a stainless-steel mesh. The filter mesh 51 has much smaller holes in its mesh surface than the size of the holes 2 in filter plate 1. The hole size in the mesh may be between about 0.1 and about 0.5 mm in diameter, most preferably 0.2 to 0.3 mm (60 - 80 wires/inch). The filter mesh 51 is maintained in its cylindrical shape by a frame 54 which may extend about the top and bottom circular edges and may include reinforcing beams extending between the top and bottom edges. The frame 54 preferably forms or provide the securing means between the lid 52 and mesh 51, such as an opening or protrusion to engage with clip 67, so that the lid 52 connects to the frame 54 to hold the mesh and lid in relative positions. An opening or outlet 55 is provided in the cylindrical wall of the filter mesh 51 to enable soil particles within the drain filter to exit the sump region via the drain pump inlet. There is preferably a labyrinth filter 63 at or near the mouth of the outlet 55 to stop large particles passing into the drain pump inlet to avoid blockages. The labyrinth filter 63 preferably comprises a plurality of blades or spines mounted to or protruding from the floor 68 of the filter. The drain outlet 55 is formed by or attached to frame 54 in the region defining the edges.

Drain filter 50 may be removed by rotating and then lifting the filter, generally held by the lid. The user should occasionally remove the drain filter for cleaning and for removing large soil particles trapped in the filter mesh 51.

Sufficient rotation (clockwise from above, for example) of the drain filter 50 (which rotates the lid and mesh together) reaches a detent position or end-stop stable position so that the drain filter outlet 55 is aligned with a drain inlet 70 in the sump 110. Surprisingly the inventors have found that leakage at the outlet of the filter to the drain pump inlet can be problematic, such as in prior art cases where labyrinth seals and/or sliding inserts are used. The inventors have found that a, preferably central, alignment feature 73 in connection with a tapered face 71 at the drain inlet provides a secure and gently closing seal and allows the inside of the filter to be substantially empty - maximising storage of soil, dirt, or particles, avoiding holes in the base of the filter and allowing the mesh and lid to be insertable as a single unit. This means that the filter base 68 can be completely, or at least substantially, continuous (having no holes) between the walls of the mesh, and allows significant flexibility in the design of features on the base, for instance to improve filtering or water flow.

Figure 6B shows the base of the sump 110 with the filter 50 removed. The base 76 of the sump 110 has a central pin 73 and a tapered face 71 at the drain outlet 55. The tapered face thickens or changes thickness along a curve. The face 71 has at least one, and preferably two tapers, a horizontal (that is, in horizontal cross-section, or when viewed in a substantially horizontal direction, or in a direction substantially perpendicular to base 76 of the sump) taper 72, in this case thickening left to right and a vertical (the is, in vertical cross-section, or when viewed in a substantially horizontal direction, or in a plane parallel to base 76, or along the axis of the drain outlet 55) taper thickening bottom to top. The central pin or protrusion 73 provides a locating feature when the filter is inserted. Because the dimension of the central pin 73 is relatively small (between 5 mm and 15 mm diameter and 5 mm and 15 mm height, most preferably 7 mm diameter by 10 mm height), and it is at centre of the filter it can be manufactured to a tight tolerance, ensuring the filter is easily positioned accurately. When the filter 50 is positioned on the pin rotation of the filter rotates the drain outlet of the filter against the tapered surfaces. The horizontal tapered surface then works to reduce the installation resistance until the filter is in in an optimum position, down and against the turn. An additional benefit of this arrangement is that the rotation is very smooth until at or near locking into position, making it clear to a user that the filter has locked into position properly and avoiding misalignment between the drain inlet face and the filter outlet.

Figure 6A shows the filter out of the sump, to allow visibility inside the filter the mesh wall has been removed. The filter outlet has an outside face 56 which preferably has a seal 57. The seal 57 may be an o-ring or other seal and is preferably on over-moulded seal arranged in a recess (not visible) on the face 56 of the filter/drain outlet. The seal is preferably made of an elastomeric material and improves the connection and water tightness of the seal between the filter and the drain inlet 70. While the seal could alternatively be placed on the drain outlet it is preferably to be on the filter 50 so as to be more easily replaced if it wears. The filter has an alignment feature 83, preferably located at the centre of, or centrally within, the filter which may be a protrusion or recess to mate with the central feature 73 of the sump. Preferably the central alignment feature 83 is a recess or socket into which the central feature, in particular a central protrusion can locate. In a less preferred embodiment the central alignment feature 83 may be an opening into which the central feature sits, however this would create a hole in the base of the filter 50, so the opening is preferably covered.

Figure 6C shows the filter in place in the sump. There is a horizontal gap between the filter and the sump because the filter plate is not shown in this view. There will also be a gap between the walls of the sump and the filter, to allow wash liquid to pass through sump during the wash cycle and collect around the sump for draining as well as providing flow to a turbidity sensor located in the sump. The gap is sized to avoid blockage from soil, but also to avoid additional water usage. The arrows on lip 59 demonstrate the lock and unlock direction of the filter (although this could be reversed if desired). The channels 17, 18 in the floor of the tub 102, which return water to the sump, are also visible and allow the sump to drain fully.

Figure 6A and 6B also show complementary features 74, 75 on the outside wall of the filter 50 and the inner wall of the sump 110. Feet or protrusions 75 extend outwards from the wall of the filter and engage or lock in use to the complementary protrusions 74 on the inner wall of the sump 110. These work together to stop or limit the ability of the filter to rise upwards when in use because the locking rotation of the filter moves feet 75 beneath protrusions 74. The protrusions, which may be bayonets, are preferably angled or have planar drafts so that the filter is pulled down (towards the base of the sump) as it is rotated. Alternative vertical positioning means are possible. Because the positioning of the filter 50 in the centre of the sump is controlled by the central pin or protrusion and the drain outlet face the radial tolerances required for these protrusions and feet are reduced allowing for easier construction.

The filter and sump may also have a securing device or indicator means/device for indicating when the filter is in the locked position. This is advantageous as it provides the user feedback that the filter is correctly located and ensures that the filter outlet aligns with the drain - improving flow. The indicator means or device may be an increased friction element or a blocking wall, for instance at the end of the protrusions 74 in the sump to stop further rotation of the filter. Preferably the indicator means comprises one or more additional protrusion 77 on the sump which interact with one or more complementary notches 78 or recesses in one or more of the feet 75. The notch 78 preferably has a spring element, such as a living hinge, or partially flexible connection to or with the feet 75 such that it is reversibly deformable, wherein it deforms to allow the protrusion 77 to pass into notch 78, before returning to its original shape in which the protrusion 77 is held in the notch 78. In this way a click or spring is felt by the user when the filter is rotated and locked into position. Preferably there are two notches 78 and protrusions 77. As shown in Figure 6A the notch is formed in the foot or bayonet of the filter with an undercut 79 in the foot beneath it to provide deformability.

Claims

1. A ring-shaped filter plate for a washing appliance, the filter plate comprising: a central inner opening to surround a wash pump; a perforated region towards the outer edge of the filter plate configured to filter wash liquid; and a filter opening in the perforated region of the filter plate, the filter opening for the insertion of a filter through the filter plate, wherein the filter opening is at least partially located in a radial bulge of the filter plate.

2. The filter plate of claim 1, further comprising a step on the inner side of the perforated region, the step separating an inner region at a higher level and the perforated region at a lower level.

3. The filter plate of claim 1 or claim 2, wherein the filter opening is circular and extends substantially from the inner edge of the perforated region to the outer edge of the filter plate.

4. The filter plate of any one of the preceding claims, further comprising a support structure at its outer periphery, the support structure configured to rest against a base of a dishwasher washing tub in use.

5. The filter plate of claim 4, wherein the support structure comprises a step and a lip, the lip curling inwards to increase the vertical stiffness of the outer periphery.

6. The filter plate of any one of the preceding claims, further comprising a locking means around the central inner opening, wherein the locking means is configured to interface with a complementary locking means around the wash pump.

7. The filter plate of any one of the preceding claims, further comprising a flange surrounding the filter opening, the flange configured to provide a contact surface for the filter when inserted.

8. A washing appliance comprising: a washing tub for holding wash liquid and having a washing space adapted to receive items for washing, the washing tub comprising a base with a sump for collecting wash liquid; a wash pump and a drain pump, the wash pump having a wash liquid inlet in fluid connection with the washing tub, and a wash liquid outlet in fluid connection with a spray arm to direct wash liquid into the washing space, and the drain pump having a drain liquid inlet in fluid connection with the sump; and a filter plate as claimed in any one of the preceding claims, the filter plate separating the wash liquid inlet of the wash pump from the washing space and the filter opening located above the sump.

9. The washing appliance of claim 8, wherein the base of the washing tub comprises a ring-shaped depression, wherein at least some of the perforated region of the filter plate is located in, or is positioned above, the ring-shaped depression.

10. The washing appliance of claim 9, wherein the base of the washing tub comprises an inner portion between the wash pump and the ring-shaped depression, the inner portion forming the lower surface of the wash pump wash liquid inlet, wherein the inner portion is substantially horizontal.

11. The washing appliance of claim 10, further comprising an annular heater forming, or below, a portion of the inner portion of the base of the washing tub.

12. The washing appliance of any one of claims 9 to 11, wherein the base of the washing tub comprises an outer ledge surrounding the filter plate, the ledge sloping downwardly, inwardly towards the outer wall of the ring-shaped depression.

13. The washing appliance of any one of claims 9 to 12, further comprising one or more drainage channels in the depression, each drainage channel sloped along its length to encourage washing fluid to move towards the sump.

14. The washing appliance of claim 13, further comprising a partial floor portion, preferably of stainless steel, for the washing tub, the partial floor portion having a central opening that mates with the channel in the base of the washing tub and extending along the base of the washing tub and meeting the wall of the washing tub, locating between the outer edge of the filter plate and the base of the washing tub.

15. The washing appliance of claim 14, further comprising a compressible seal between the partial floor portion and the base of the washing tub, the compressible seal located in a slot formed in the tub base, the slot formed in a closed loop and being overlapped by the partial floor portion.

16. The washing appliance of claim 15, wherein the compressible seal is hollow.

17. The washing appliance of any one of claims 8 to 16, further comprising a filter configured to be removably inserted into the sump, the filter passing through the filter plate when inserted and removed, wherein the filter is a cylindrical-shaped filter with a bottom surface which locks to the base of the washing tub.

18. The washing appliance of any one of claims 8 to 17, wherein the washing appliance is a dishwasher.

19. A washing appliance comprising: a washing tub for holding wash liquid and having a washing space adapted to receive items for washing, the washing tub comprising a base with a sump for collecting wash liquid; a wash pump and a drain pump, the wash pump having a wash liquid inlet in fluid connection with the washing tub, and a wash liquid outlet in fluid connection with a spray arm to direct wash liquid into the washing space, and the drain pump having a drain liquid inlet in fluid connection with the sump; and a ring shaped filter plate surrounding the pump assembly, the filter plate separating the wash liquid inlet of the wash pump from the washing space, an outer region of the filter plate perforated to allow wash liquid to flow to the wash pump; wherein the filter plate has a radial bulge extending to encircle the sump.