Multi-channel disc valve assembly

A multi-channel disc valve assembly including: a first inlet chamber having a first inlet port; a second inlet chamber having a second inlet port; a multi-channel mixing chamber body having at least one first chamber opening fluidly communicable with the first inlet chamber and at least one second chamber opening fluidly communicable with the second inlet chamber; a first disc valve sub-assembly positioned between the first inlet chamber and the multi-channel mixing chamber body, the first disc valve sub-assembly including a first movable disc; and a second disc valve sub-assembly positioned between the second inlet chamber and the multi-channel mixing chamber body, the second disc valve sub-assembly including a second movable disc; the first and second movable discs being rotatable to respectively alter fluid flow pathways from the first inlet chamber to the multi-channel mixing chamber body and from the second inlet chamber to the multi-channel mixing chamber body.

CROSS REFERENCE TO RELATED APPLICATIONS

This non-provisional patent application claims priority under 35 U.S.C. § 119(a) from Patent Application No. 1808925.0 filed in United Kingdom on May 31, 2018 and Patent Application No. 1808977.1 filed in United Kingdom on Jun. 1, 2018.

FIELD

The present invention relates to a multi-channel disc valve assembly suitable but not necessarily exclusively for use in automotive cooling fluid control systems. The invention further relates to a multi-channel disc valve system, and to a method of assembling such a multi-channel disc valve system.

BACKGROUND

To provide multi-way valves for selectably controlling fluid flow around a system in a compact manner, there is currently a limited range of choices. Multi-way ball valves are available, but are also bulky and relatively expensive to manufacture due to the precision required to create a fluid-tight seal.

Such ball valve arrangements also typically require a plurality of actuators to control each ball individually, which further increases the complexity of manufacture of such an apparatus.

Furthermore, in order to provide suitable fluid-tightness, existing multi-way valves must be produced as a single unit. This limits the utility of multi-way valves, since a bespoke valve arrangement must be created for each different application.

As more complicated cooling arrangements are required, particularly in automotive contexts where hybrid vehicles are provided, which require additional cooling for batteries, for example, there is a greater need for cost-effective and simple multi-way valve arrangements to be provided.

The present invention seeks to provide a multi-channel disc valve assembly which overcomes these issues.

SUMMARY

According to a first aspect of the invention, there is provided a multi-channel disc valve assembly comprising: a first inlet chamber having a first inlet port; a second inlet chamber having a second inlet port; a multi-channel mixing chamber body having at least one first chamber opening fluidly communicable with the first inlet chamber and at least one second chamber opening fluidly communicable with the second inlet chamber, the multi-channel mixing chamber body having a plurality of outlet ports; a first disc valve sub-assembly positioned between the first inlet chamber and the multi-channel mixing chamber body, the first disc valve sub-assembly comprising a first movable disc; and a second disc valve sub-assembly positioned between the second inlet chamber and the multi-channel mixing chamber body, the second disc valve sub-assembly comprising a second movable disc; the first and second movable discs being rotatable to respectively alter a fluid flow pathway from the first inlet chamber to the multi-channel mixing chamber body and a fluid flow pathway from the second inlet chamber to the multi-channel mixing chamber body.

A disc valve assembly will be typically much cheaper and more durable than an equivalent ball valve assembly. However, the structure of disc valves makes them much more difficult to up-scale for multi-way diversion of fluid through a system, and as such, only single-stage disc valves are presently available. The present invention has found that a modified central mixing chamber structure allows for multi-way input therein whilst utilising disc valves. The movable discs can be rotated to achieve selective control over the fluid flow.

Optionally, a relative configuration between the first movable disc and the or each first chamber opening may be different to a relative configuration between the second movable disc and the or each second chamber opening.

Preferably, the first disc valve sub-assembly may comprise a first sealing element which has a matching shape to the or each first chamber opening, the first sealing element being positioned between the first movable disc and the multi-channel mixing chamber body.

The first sealing element may include a first static plate against which the first movable disc is rotatable.

The first static plate may be formed as a disc having at least one aperture which is matched to the or each first chamber opening.

The second disc valve sub-assembly may comprise a second sealing element which has a matching shape to the or each second chamber opening, the second sealing element being positioned between the second movable disc and the multi-channel mixing chamber body.

Preferably, the second sealing element may include a second static plate against which the second movable disc is rotatable.

The second static plate may be formed as a disc having at least one aperture which is matched to the or each second chamber opening.

The provision of the matched sealing element to the chamber openings ensures that there is no leakage from the first or second inlet chamber into the wrong outlet chamber. This can be a significant issue for pressurised fluid. The easiest way to construct such an arrangement would be to provide a static disc as part of each disc valve sub-assembly which can compress the sealing element against the multi-channel mixing chamber body, whilst providing a flat surface against which the movable disc can rotate freely.

Optionally, at least one of the first and second movable discs may have a quarter-circle aperture therethrough.

A quarter opening provides the option for four-way control of flow through each of the ends of the multi-channel mixing chamber body, which allows for the complex flow pathway configurations of the present invention to be achieved.

In one embodiment, the multi-channel mixing chamber body may have two said outlet ports.

A two-outlet port arrangement allows for the creation of a four-way mixing assembly, which is a successful arrangement within the sphere of ball valve assemblies.

In an alternative embodiment, the multi-channel mixing chamber body may have three said outlet ports.

Preferably, a first end of the multi-channel mixing chamber body may comprise three said first chamber openings corresponding with the three said outlet ports, and wherein a second end of the multi-channel mixing chamber body comprises two said second chamber openings corresponding with two of the three said outlet ports.

A three-outlet port arrangement is also a successful arrangement used in ball valve assemblies, and is of particular use in hybrid vehicular technologies, where coolant fluid may be required for at least three components of a cooling system thereof. The specific arrangement of the five-way mixing assembly can result in divergent flows and mixed flows, which may achieve pressurisation gains which may be necessary for successful operation of the system.

Preferably, the first inlet chamber, multi-channel mixing chamber body, and second inlet chamber may be provided in a stacked configuration.

A stacked configuration is primarily useful as a means of creating a space-efficient apparatus allowing for ready integration into existing applications. Furthermore, it can allow for ready replacement of the central mixing chamber assembly as part of a modular system, which can reduce manufacturing costs as only this component need be replaced to provide a bespoke fluid flow configuration.

The assembly may further comprise a shaft which is engaged with the first and second movable discs to permit simultaneous rotation thereof.

The multi-channel disc valve assembly may preferably further comprise an actuator which is drivably coupled, preferably via the shaft, to drive both of the first and second movable discs, which may be a brushless DC electric motor.

Simultaneous rotation of the movable discs has the benefit of removing the requirement to provide independent actuators for each movable disc, which is otherwise necessary in corresponding ball valve arrangements. One shaft can be used to produce the complex flow pathway arrangements, which is driven by one actuator. This reduces both the cost and complexity of the multi-channel disc valve assembly.

Preferably, the multi-channel mixing chamber body may comprise a shaft-receiving bore extending therethrough for receiving the shaft.

The provision of a central bore through the multi-channel mixing chamber body not only improves the support of the shaft in situ, but also assists in creating the advantageous stacked arrangement of the assembly.

The assembly may also comprise a multi-part valve casing, a first valve casing part being provided for the first inlet chamber, a second valve casing part being provided for the second inlet chamber, and a third valve casing part being provided for the multi-channel mixing chamber body.

Using a multi-part casing further improves the ability to modularise the assembly, permitting the selective insertion of an appropriate multi-channel mixing chamber body without needing to replace the inlet chambers for each new system.

Optionally, each of the first movable disc and second movable disc may be formed from a ceramic material.

The multi-channel mixing chamber body may comprise a plurality of fluidly-noncommunicable chamber body portions.

The use of fluidly-noncommunicable body portions improves the resistance of the assembly to leakage between the various fluid-flow pathways defined as the movable discs rotate.

According to a second aspect of the invention, there is provided a multi-channel disc valve system comprising: a first inlet chamber having a first inlet port; a second inlet chamber having a second inlet port; a mixing chamber assembly comprising: a multi-channel mixing chamber body having at least one first chamber opening fluidly communicable with the first inlet chamber and at least one second chamber opening fluidly communicable with the second inlet chamber, the multi-channel mixing chamber body having a plurality of outlet ports; a first disc valve sub-assembly positioned at a first end of the multi-channel mixing chamber body, the first disc valve sub-assembly comprising a first movable disc; a second disc valve sub-assembly positioned at a second end of the multi-channel mixing chamber body, the second disc valve sub-assembly comprising a second movable disc; and a drive transmission means which is engaged with the first and second movable discs; and an actuator drivably coupled to the drive transmission means; the first and second movable discs respectively alter a fluid flow pathway from the first inlet chamber to the multi-channel mixing chamber body and a fluid flow pathway from the second inlet chamber to the multi-channel mixing chamber body.

Preferably, the mixing chamber assembly may be fluidly communicable with the first and second inlet chambers such that a relative configuration between the first movable disc and the or each first chamber opening is different to a relative configuration between the second movable disc and the or each second chamber opening when the drive transmission means is driven by the actuator.

A system having a single actuator which is able to drive both movable discs, and having a complex relationship between the chamber openings of the multi-channel mixing chamber body and the first and second movable discs, provides a cost-effective and durable mechanism by which a variable fluid control system can be achieved, which is particularly suitable for use in vehicular contexts, and in particular for electric and/or hybrid electric vehicles where many components require cooling.

A plurality of different said mixing chamber assemblies may be provided, each mixing chamber assembly being selectably engagable in fluid communication with the first and second inlet chambers to provide different fluid flow pathway configurations between the first inlet chamber and multi-channel mixing chamber body and between the second inlet chamber and the multi-channel mixing chamber body.

Selectable engagement of a standardised set of inlet chambers with a desired configuration of multi-channel mixing chamber advantageously reduces the cost of manufacture of the disc valve assembly, since a smaller percentage of the components of the assembly must be created specifically for the application.

According to a third aspect of the invention, there is provided a method of assembling a multi-channel disc valve system preferably in accordance with the second aspect of the invention, the method comprising the steps of: a] engaging the first inlet chamber at the first end of the multi-channel mixing chamber body of the mixing chamber assembly; b] engaging the second inlet chamber at the second end of the multi-channel mixing chamber body of the mixing chamber assembly; c] connecting the shaft to the actuator; and d] securing the actuator, first inlet chamber, mixing chamber assembly and second inlet chamber together via a valve casing.

The assembly of a modular multi-channel disc valve system in which the central assembly can be manufactured and assembled with standardized inlet chambers significantly reduces the complexity of producing a customized disc valve system, particularly for an automotive cooling system.

According to a fourth aspect of the invention, there is provided a multi-channel disc valve assembly comprising: a first inlet chamber having a first inlet port; a second inlet chamber having a second inlet port; a multi-channel mixing chamber body having at least one first chamber opening fluidly communicable with the first inlet chamber and at least one second chamber opening fluidly communicable with the second inlet chamber, the multi-channel mixing chamber body having a plurality of outlet ports; a first disc valve sub-assembly positioned between the first inlet chamber and the multi-channel mixing chamber body, the first disc valve sub-assembly comprising a first static disc and a first movable disc, the first movable disc being rotatable relative to the first static disc; a second disc valve sub-assembly positioned between the second inlet chamber and the multi-channel mixing chamber body, the second disc valve sub-assembly comprising a second static disc and a second movable disc, the second movable disc being rotatable relative to the second static disc; and a shaft which is engaged with the first and second movable discs, the shaft being drivable to simultaneously rotate the first and second movable discs to respectively alter a fluid flow pathway from the first inlet chamber to the multi-channel mixing chamber body and a fluid flow pathway from the second inlet chamber to the multi-channel mixing chamber body.

The assembly may further comprise an actuator which is drivably coupled to drive both of the first and second movable discs.

DETAILED DESCRIPTION

Referring toFIG. 1, a multi-channel disc valve assembly, referenced globally at10, is shown which is suitable for, in particular, fluid flow control of coolant fluid within an automotive context. This may be of particular use for hybrid or electric vehicle systems, where cooling fluid may need to be diverted between many different systems, such as the battery, electronic control system, and so on, during operation of the vehicle.

The multi-channel disc valve assembly10comprises first and second inlet chambers12a,12b, each having an inlet port14a,14bvia which fluid can be introduced to the first and second inlet chambers12a,12brespectively. These components may be common to any multi-channel disc valve assembly10constructed in accordance with the present invention.

The central components positioned between the first and second inlet chambers12a,12bcan be collectively considered to be a mixing chamber assembly16, and may be bespoke depending upon the application of the multi-channel disc valve assembly10. The multi-channel disc valve assembly10is therefore preferably formed from a plurality of modules which may be interchangeable and/or selectably interengagable, with the mixing chamber assembly16being different for different uses of the multi-channel disc valve assembly10.

The mixing chamber assembly16comprises a multi-channel mixing chamber body18, which has a plurality of outlet ports20x,20y,20z. As indicated inFIG. 1, there are three outlet ports20x,20y,20zin the present arrangement, forming a five-way multi-channel disc valve assembly10. Alternative arrangements could, of course be provided; a four-way multi-channel disc valve assembly may be particularly useful in which a multi-channel mixing chamber body includes only two outlet ports, but the multi-channel disc valve assembly can be scaled according to requirements. In particular, a six-way assembly, in which there are four outlet ports, and a seven-way assembly, in which there are five outlet ports, may be readily achievable, and arrangements with even more outlet ports are also possible. Furthermore, it may be possible to introduce arrangements having more than two inlet ports, if the system were to be scaled further.

The multi-channel mixing chamber body18has first and second ends22a,22bwhich are respectively associated with the first and second inlet chambers12a,12b. Each of the first and second ends22a,22bis associated with a plurality of chamber openings which are respectively communicable with outlet chambers of the multi-channel mixing chamber body18.

The multi-channel mixing chamber body18here comprises a plurality of fluidly-noncommunicable chamber body portions which define the three outlet chambers24x,24y,24zof the present arrangement, corresponding with the three outlet ports20x,20y,20z. There is also provided a shaft-receiving bore26which extends through the centre of the multi-channel mixing chamber body18.

The first outlet chamber24xhere has a single upper chamber opening28x—best illustrated in the legend ofFIG. 3—which is positioned at the first end22aof the multi-channel mixing chamber body. As such, it is only possible for fluid to be directed through the first outlet port20xfrom the first inlet port14a, provided the fluid pathway therebetween is unsealed. The chamber opening28xmay be formed as a quarter-circle, for example.

The second outlet chamber24yhere has upper and lower chamber openings28y,30ywhich are respectively positioned at the first and second ends22a,22bof the multi-channel mixing chamber body. The upper and lower chamber openings28y,30ypreferably have different dimensions, with the upper chamber opening28ybeing shaped as a half-circle, and the lower chamber opening30ybeing formed as a quarter-circle.

The third outlet chamber24zalso has upper and lower chamber openings28z,30zwhich are respectively positioned at the first and second ends22a,22bof the multi-channel mixing chamber body. Again, the upper and lower chamber openings28z,30zpreferably have different dimensions, with the upper chamber opening28zbeing shaped as a quarter-circle, and the lower chamber opening30zbeing formed as a three-quarter-circle.

Selective opening and closure of the chamber openings28x,28y,28z,30y,30zpermits the fluid flow pathways through the multi-channel mixing chamber body18from the first and second inlet chambers12a,12bto be altered. This can be achieved by the use of disc valves.

A first disc valve sub-assembly32ais provided which comprises at least a first movable disc34awhich has a disc body36ahaving at least one aperture38atherethrough. The first disc valve sub-assembly32ais positionable between the first inlet chamber12aand the first end22aof the multi-channel mixing chamber body18to permit the changing of the fluid flow into the three upper chamber openings28x,28y,28z.

The first disc valve sub-assembly32apreferably also includes a static plate against which the first movable disc34ais rotatable, which is preferably formed as a first static disc40ahaving a plurality of apertures42awhich match the configuration of the upper chamber openings28x,28y,28z. It is also preferred that a first sealing element44ais provided which prevents leakage between the first movable disc34aand the multi-channel mixing chamber body18, and this is preferably positioned between the first static disc40aand the multi-channel mixing chamber body18, having an aperture configuration which corresponds with that of the first static disc40a.

A second disc valve sub-assembly32bis also provided which comprises at least a second movable disc34bwhich has a disc body36bhaving at least one aperture38btherethrough. The second movable disc34bpreferably has an identical shape or form to the first movable disc34a. The second disc valve sub-assembly32bis positionable between the second inlet chamber12band the second end22bof the multi-channel mixing chamber body18to permit the changing of the fluid flow into the two lower chamber openings30y,30z.

The second disc valve sub-assembly32bpreferably also includes a static plate against which the second movable disc34bis rotatable, which is preferably formed as a second static disc40bhaving a plurality of apertures42bwhich match the configuration of the lower chamber openings30y,30z. It is also preferred that a second sealing element44bis provided which prevents leakage between the second movable disc34band the multi-channel mixing chamber body18, and this is preferably positioned between the second static disc40band the multi-channel mixing chamber body18, having an aperture configuration which corresponds with that of the second static disc40b.

Each of the first and second movable discs34a,34bmay preferably be formed from a ceramic material. The first and second static discs40a,40bmay also be formed from a similar or identical material to the first and second movable discs34a,34b.

The first and second sealing elements44a,44bmay preferably be formed from a flexible or resilient sealing material, such as rubber or an elastomeric material, and may include a locator46a,46bwhich is able to locate the sealing element44a,44bwith respect to its respective static disc40a,40band/or to the multi-channel mixing chamber body18.

FIG. 2ashows the multi-channel disc valve assembly10inclusive of the valve casing48, which is connected at one end to an actuator50, preferably a brushless DC electric motor, which is able to control the rotation of the movable discs34a,34b. Preferably, the valve casing48is formed in three parts: a first valve casing part52abeing provided for the first inlet chamber12a, a second valve casing part52bbeing provided for the second inlet chamber12b, and a third valve casing part52cbeing provided for the multi-channel mixing chamber body18. This allows the multi-channel disc valve assembly10to be assembled in a modular manner, and potentially allows the third valve casing part52cto be selected according to the desired function of the multi-channel disc valve assembly10.

The cross-section through the multi-channel disc valve assembly10ofFIG. 2aalong line A-A can be seen inFIG. 2b, in which the drive transmission means of the actuator50can be seen. The actuator50is here coupled to a shaft54which extends through the first inlet chamber12a, the first disc valve sub-assembly32a, the multi-channel mixing chamber body18, and the second disc valve assembly32b. This arrangement illustrates the advantage of a stacked assembly in which the first inlet chamber12a, the multi-channel mixing chamber body18, and the second inlet chamber12bare linearly aligned; the shaft54can engage with both the first and second movable discs34a,34b, coupling their rotational motion, and allowing the assembly10to be constructed with only a single actuator50. The shaft54is preferably supported through the multi-channel mixing chamber body18by the shaft-receiving bore26thereof. Preferably, such a stacked assembly will have symmetric inlet ports14a,14b, with the intermediate mixing chamber assembly16being adapted according to the needs of the flow.

As can be seen inFIG. 2b, first, second and third mixing chambers24x,24y,24zare provided which are associated with the three outlet ports20x,20y,20z; when the first and/or second aperture38a,38bof the movable discs34a,34bis aligned with the corresponding chamber opening28x,28y,28z,30y,30zof the mixing chambers24x,24y,24z, a fluid flow pathway can be achieved to direct a fluid in the multi-channel disc valve assembly10along a desired direction.

Driving of the actuator50will result in rotation of the shaft54, which will result in simultaneous rotation of the movable discs34a,34b. The effect of this rotation can be seen inFIGS. 3 and 4.

InFIG. 3, the upper and lower circles indicate the shapes of the first and second static discs40a,40brespectively, with the shaded quarter-circle indicating the relative position of the apertures38a,38bof the first and second movable discs34a,34brespectively.

In a first rotational position, indicated by the top-centre images in each ofFIGS. 3 and 4, which can be considered to be a rotational phase of 0°, the first aperture38aof the first movable disc34ais aligned with the upper chamber opening28yof the second mixing chamber24y, and the second aperture38bof the second movable disc34bis aligned with the lower chamber opening30zof the third mixing chamber24z. As such, there is a fluid flow pathway from the first inlet port14ato the second outlet port20y, and a fluid flow pathway from the second inlet port14bto the third outlet port20z.

Rotation of the first and second movable discs34a,34bin a clockwise direction, that is, to an effective phase of 90°, is shown in the right-hand image in each ofFIGS. 3 and 4. The first aperture38ais aligned with the upper chamber opening28xof the first mixing chamber24x, whilst, although the second movable disc34bhas been rotated, its aperture38bremains aligned to the lower chamber opening30zof the third mixing chamber24z. As such, there is a fluid flow pathway from the first inlet port14ato the first outlet port20x, and a fluid flow pathway from the second inlet port14bto the third outlet port20z.

Both of these configurations result in divergent fluid flows through the multi-channel disc valve assembly10.

Further rotation of the first and second movable discs34a,34bin a clockwise direction, that is, to an effective phase of 180°, is shown in the lower-centre image in each ofFIGS. 3 and 4. The first aperture38ais aligned with the upper chamber opening28zof the third mixing chamber24z, and the second aperture38bremains aligned to the lower chamber opening30zof the third mixing chamber24z. As such, there is a fluid flow pathway from both the first inlet port14aand second inlet port14bto the third outlet port20z, resulting in mixing of the fluids transported therethrough.

Further rotation of the first and second movable discs34a,34bin a clockwise direction, that is, to an effective phase of 270°, is shown in the left-hand image in each ofFIGS. 3 and 4. The first aperture38ais aligned with the upper chamber opening28yof the second mixing chamber24y, and the second aperture38bbecomes aligned to the lower chamber opening30yof the second mixing chamber24y. As such, there is a fluid flow pathway from both the first inlet port14aand second inlet port14bto the second outlet port20y, resulting in mixing of the fluids transported therethrough.

One of the advantages of the multi-channel disc valve assembly10is that it is possible to provide a multi-channel disc valve system in which the first inlet chamber12aand second inlet chamber12bare standardised, with only the mixing chamber assembly16being replaced to alter the fluid flow properties thereof. The first and second disc valve sub-assemblies32a,32bare preferably provided as part of the mixing chamber assembly16, since the form of the disc valve sub-assemblies32a,32bwill likely be dependent on the forms of the mixing chamber openings.

Furthermore, it may be possible to provide a plurality of different said mixing chamber assemblies, with each mixing chamber assembly being selectably engagable in fluid communication with the first and second inlet chambers12a,12bto provide different fluid flow pathway configurations between the first inlet chamber12aand multi-channel mixing chamber body18and between the second inlet chamber12band the multi-channel mixing chamber body18. This effectively provides the modular set-up allowing the creation of disc valve assemblies which are bespoke to the application required.

The multi-channel disc valve may be assembled by engaging the first inlet chamber12aat the first end22aof the multi-channel mixing chamber body18of the mixing chamber assembly16, and engaging the second inlet chamber12bat the second end22bof the multi-channel mixing chamber body18of the mixing chamber assembly16. The shaft54can then be connected to the actuator50and the actuator50, first inlet chamber12a, mixing chamber assembly16and second inlet chamber12bcan be secured together via the valve casing48.

Whilst the above-described arrangement utilises a single actuator having a linear output shaft, it will be apparent that an alternative drive transmission means for actuating the first and second movable discs could be provided. For example, a linked gear train could be provided, allowing the first and second inlet chambers to be positioned side-by-side. Alternatively, a plurality of actuators could be provided, allowing independent control of the fluid flow through the multi-channel disc valve assembly.

Similarly, it may be useful, in some arrangements, for there to be no mixing chamber coincident with all of the possible rotational phases of the movable discs. In such a scenario, it may be useful to provide a blocking element which prevents fluid flow into the mixing chamber assembly even where the aperture of the movable disc is aligned thereto.

It will also be appreciated that, although the selective direction of fluid within the system has been achieved in the present invention by mismatching of the upper and lower chamber openings relative to the apertures of the movable discs, it is possible to mismatch the apertures of the movable discs to one another in order to achieve the same effect, for example, by misalignment of the rotational phases of the apertures relative to one another. Indeed, a relative configuration between the first movable disc and the or each first chamber opening and the second movable disc and the or each second chamber opening may be the same, with the selective fluid flow being achieved by, for example, a complex internal geometry of the mixing chamber.

It is therefore possible to provide a multi-channel disc valve assembly which is suitable for providing selective direction of a fluid, such as a cooling fluid in automotive contexts, from two inlets to a plurality of different outlets. This is achieved by selecting different inlet profiles from the inlet chambers thereof into a mixing chamber assembly, and providing movable discs to provide selective control over the fluid communication therebetween. Where a stacked arrangement is provided, this control can also be achieved by the use of a single actuator and output shaft arrangement, reducing the cost and complexity of producing such an assembly.

The words ‘comprises/comprising’ and the words ‘having/including’ when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components, but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

The embodiments described above are provided by way of examples only, and various other modifications will be apparent to persons skilled in the field without departing from the scope of the invention as defined herein.