Patent Grant
9163524
The present application claims priority to United Kingdom Patent Application No. 1105726.2 filed Apr. 4, 2011, which is incorporated herein by reference.
The present invention relates to a turbine suitable for, but not limited to, use in a variable geometry turbocharger.
Turbochargers are well known devices for supplying air to the intake of an internal combustion engine at pressures above atmospheric pressure (boost pressures). A conventional turbocharger essentially comprises a housing in which is provided an exhaust gas driven turbine wheel mounted on a rotatable shaft connected downstream of an engine outlet manifold. A compressor impeller wheel is mounted on the opposite end of the shaft such that rotation of the turbine wheel drives rotation of the impeller wheel. In this application of a compressor, the impeller wheel delivers compressed air to the engine intake manifold. A power turbine also comprises an exhaust gas driven turbine wheel mounted on a shaft, but in this case the other end of the shaft is not connected to a compressor. For instance, in a turbocompound engine, two turbines are provided in series, both driven by the exhaust gases of the engine. One turbine drives a compressor to deliver pressurised air to the engine and the other, the “power turbine”, generates additional power which is then transmitted to other components via a mechanical connection, such as a gear wheel to transmit power to the engine crankshaft, or via other types of connection, for instance a hydraulic or electrical connection.
In some applications, it may be desirable to be able to control the flow and/or or speed of flow of gas through an inlet of the turbine, which in turn affects the speed of rotation of the turbine wheel. Such control may be achieved by varying a geometry of the turbine, for example a geometry of the inlet of the turbine. One approach to varying the geometry may be to vary the orientation of vanes or other structures located in the turbine inlet, for example to change the angle of attack of gas flowing through the inlet relative to the turbine wheel. Another approach might be to control an axial width of the inlet by appropriate movement of an axially moveable wall member.
A potentially new approach to the variation of a geometry of a turbine involves providing the inlet of the turbine with a number of axially offset inlet portions defined by one or more baffles or the like located within that inlet. The opening or closing (i.e. blocking or unblocking) of one or more of these inlet portions is controlled by appropriate movement of an axially moveable sleeve, moveable along an outside diameter, or an inside diameter (depending on the particular embodiment), of the inlet portions. This new approach may be advantageous in terms of simplicity of design and implementation, and an associated reduction in costs. However, although theoretically a workable approach, a basic implementation of this approach may have performance-related problems in practice. These problems may relate, for example, to gas flowing through inlet portions that should be blocked, axial expansion of gas reducing energy available for rotation of the turbine wheel, and a non-continuous response (i.e. a step-wise response) of gas flow speed associated with movement of the sleeve.
It is an object of the present invention to obviate or mitigate one or more of the problems associated with existing turbines, whether identified herein or elsewhere, or to provide an alternative to an existing turbine.
According to an aspect of the invention, there is provided a variable geometry turbine comprising: a turbine wheel mounted for rotation about a turbine axis within a housing, the housing defining an annular inlet surrounding the turbine wheel and defined between first and second inlet sidewalls; and a ring-like seal axially movable across the annular inlet to vary the size of a gas flow path through the annular inlet, the annular inlet being divided into at least two axially offset inlet portions.
The seal may be provided adjacent a free end of, and/or attached to, a sleeve that is (also) axially moveable (e.g. across the inlet). At least a part of the ring-like seal may be located in-between the sleeve and the inlet portions, or a structure defining the inlet portions.
The seal may extend axially to an extent equal to or greater than: an axial width of one, more or all inlet portions; or an axial width of one, more or all inlet portions, plus an axial width of one, more, or all baffles that divides the inlet to form those portions.
An axial extent of the seal may be flush with an axial extent of the free end of the sleeve.
An axial extent of the seal may extend beyond an axial extent of the free end of the sleeve.
An axial extent of a free end of the seal (e.g. a free axial end, not attached to a structure for supporting or effecting movement of the seal) may vary in magnitude around a circumference of the seal to define a plurality of recesses and/or protrusions located around the circumference of the free end of the seal.
A maximum in the variation in magnitude of the axial extent may be substantially equal to: an axial width of an inlet portion; or an axial width of an inlet portion plus an axial width of a baffle that divides the inlet to define an inlet portion; or an axial width of an inlet passage through an inlet portion.
An inlet portion may comprise one or more vanes or other structures dividing the inlet portion into one or more inlet passages, and wherein the variation in magnitude of the axial extent of the seal is such that a number of protrusions and/or recesses is: greater than the number of vanes or other structures dividing the inlet portion into one or more inlet passages, and/or greater than the number of inlet passages.
The variable geometry turbine may further comprise a plurality of apertures distributed about at least a portion of a circumference of the seal (e.g. a portion of the seal that extends beyond the free end of a sleeve, if a sleeve is present).
A circumferential position of at least one aperture may be different from a circumferential position of a least one axially adjacent recess; and/or a circumferential position of each one a plurality of apertures may be different from a circumferential position of each one of a plurality of respective axially adjacent recesses.
The seal may be constructed and arranged to allow for expansion and/or compression in a radial direction, whilst still maintaining seal functionality, and wherein the seal is constructed and arranged to, at least in use, be in contact with a structure defining the inlet portions due to a resilience and/or shape of the seal.
The seal may be constructed and arranged to allow for expansion and/or compression in a radial direction, whilst still maintaining seal functionality, and wherein the seal is constructed and arranged to, in use, allow for compression in a radial direction due to a gas flow pressure acting on the seal.
The compression may be sufficient in magnitude to bring the seal into contact with a structure defining the inlet portions.
The seal may be constructed and arranged to limit the compression to a diameter that exceeds or substantially equates to a diameter of the inlet portions (e.g. by 5 mm or less, 4 mm or less, 3 mm or less, 2 mm or less, 1 mm or less, or 0.5 mm or less). A limitation may be provided in the form of a gap in a circumference of the seal that extends at least partially in the axial direction.
The seal may be provided adjacent a free end of a sleeve that is (also) axially moveable (e.g. across the inlet). Alternatively and/or additionally, the seal may be attached to the sleeve.
An inner diameter of the sleeve and/or seal may be greater than an outer diameter of the inlet portions.
The variable geometry turbine may form a part of a turbocharger, and for example (or more specifically) a variable geometry turbocharger.
Advantageous and preferred features of the invention will be apparent from the following description.
Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
Referring to
The turbine housing 5 has an exhaust gas inlet volute 9 located annularly around the turbine wheel 4 and an axial exhaust gas outlet 10. The compressor housing 7 has an axial air intake passage 11 and a compressed air outlet volute 12 arranged annularly around the compressor wheel 6. The turbocharger shaft 8 rotates on journal bearings 13 and 14 housed towards the turbine end and compressor end respectively of the bearing housing 3. The compressor end bearing 14 further includes a thrust bearing 15 which interacts with an oil seal assembly including an oil slinger 16. Oil is supplied to the bearing housing from the oil system of the internal combustion engine via oil inlet 17 and is fed to the bearing assemblies by oil passageways 18.
In use, the turbine wheel 4 is rotated by the passage of exhaust gas from the annular exhaust gas inlet 9 to the exhaust gas outlet 10, which in turn rotates the compressor wheel 6 which thereby draws intake air through the compressor inlet 11 and delivers boost air to the intake of an internal combustion engine (not shown) via the compressor outlet volute 12.
The turbine 22 is also shown as comprising a turbine wheel 29 mounted on a turbine shaft 30 for rotation about a turbine axis. Gas passing over the turbine wheel 29 causes rotation of that wheel 29, and as a result torque is applied to the shaft 30 to drive a compressor wheel (or other structure) attached to an opposite end of the shaft (for example the compressor of
The speed of the turbine wheel 29 is largely dependent upon the velocity and pressure of the gas passing through the annular inlet 21. For a fixed mass flow of gas flowing into the inlet 21, the gas velocity and pressure is a function of the inlet portions 26a, 26b, 26c that are open (i.e. not blocked by the sleeve 28). Thus, movement of the cylindrical sleeve 28 may be undertaken to at least partially close (i.e. block) or at least partially open (i.e. unblock) one or more of the inlet portions 26a, 26b, 26c, to control the velocity and pressure of the gas and, in turn, to control the speed of rotation of the turbine wheel 29.
In
A ring-like seal 42 is, to the best of the applicant's knowledge, only ever used between two cylindrical surfaces which move relative to one another. The use of the ring seal 42 in the arrangement shown in
The seal 42 may have any appropriate form (for example any appropriate axial length), and, as will be discussed in more detail further below, may allow for a degree of radial expansion or compression to take into account thermal affects and/or gas pressure on the seal during use due to gas flow towards and through the inlet. Preferably, the seal comprises, or is formed from or with, a nickel/iron based alloy. This will allow the seal to maintain structural integrity when exposed to the high temperatures that are present in a turbine inlet of a turbocharger.
It will be appreciated that seals with other cross-sectional shapes may be used as and where appropriate.
The inclusion of a seal between the cylindrical sleeve and the inlet portions has been described above as being advantageous. However, depending on how the seal is constructed and arranged (which includes positioned), gas may still unintentionally flow through inlet portions that should be blocked.
It will be appreciated that the exact nature (e.g. length) of the axial extent may be dependent on a particular application, or the configuration of the inlet portions and the structures that define those inlet portions. Generally speaking, this seal may extend axially to an extent equal to or greater than an axial width of one more or all inlet portions, or extend axially to an extent equal to or greater than an axial width of one, more or all inlet portions plus an axial width of one, more or all baffles (or other structures) that divides the inlet to form those portions. If the inlet portions have different axial widths, the axial extent may be equal to the smallest axial width (with or without the width of an adjacent baffle). In any event, the seal is still ring-like, as would be apparent when the seal is viewed end-on. However, with increasing axial extent (e.g. length), the seal may additionally be described as having a sleeve-like shape, or a sleeve that seals.
In one embodiment, the seal may extend axially to such an extent that the seal extends over and covers or blocks all inlet portions that are (or can ever be) covered or blocked by the sleeve. If and when appropriately sealed or blocked by such a seal, there may be no need to provide other seals upstream of the inlet, for example a seal in-between the sleeve and an actuation arrangement for that sleeve. This may reduce costs for the turbine as a whole.
Another benefit of providing a seal having an axial extent which is flush with an axial extent of a free end of the sleeve, is that axial expansion of gas is not possible in a gap that would otherwise be provided between the axial extent of the seal and the axial extent of the sleeve. Axial expansion of gas reduces the energy available for rotation of the downstream turbine wheel, and so preventing or limiting such axial expansion may improve efficiency and/or performance.
Although not visible in
Because the axial extent of a leading end of the seal varies in magnitude around a circumference of the seal, the opening or closing of the inlet portions is not undertaken in a harsh, abrupt step-wise manner, as might be the case if the axial extent exhibited no variation. An absence of axial variation might result in associated or related step-wise characteristic in the performance of the turbine as a whole. In contrast, axial variation ensures that the opening or closing of the inlet portions may be undertaken more gradually, which obviates or mitigates such a step-wise characteristic.
Referring to
An inlet portion may comprise one or more vanes or other structures dividing the inlet portion into one or more inlet passages. The variation in magnitude of the axial extent in the circumferential direction (e.g. a pitch or wavelength 82) may be synchronised in some way with a location of the one or more vanes or other structures, or a spacing between the one or more vanes or other structures. The synchronisation may extend or continue around the circumference of the seal. For example, the synchronisation may be such that the variation in magnitude is in phase with the location of the vanes or other structures. Alternatively or additionally, an area defined between a maximum and minimum axial extent may be equal to an area defined between vanes or other structures in the vicinity of the variation. In other words, an area defined by recesses (or in other words between protrusions) of the leading end of the seal may be equal to an area of the opening or opening of inlet portions or inlet passages through those inlet portions. This may ensure that when a leading edge of the leading end of the seal is aligned with a baffle that divides the inlet, gas flow through an inlet portion which the seal has partially closed is optimised. The synchronisation may be used in combination with the concept described above relating to the maximum in the variation in magnitude of the axial extent.
Referring to
Alignment of a single vane throat area with a radially overlying recess of the seal may only be important if the number of recesses is effectively equal to the number of vanes. It will be appreciated that this does not necessarily need to be the case in all embodiments. In alternative embodiments, more recesses may be desired for example. In this case, the same basic theory can be applied as discussed above, i.e. the total flow area defined by the recesses may be substantially similar or equal to the total flow area defined by the combination of all of the vane throats. The shape of the profile of the end of the seal defined by one or more recesses and/or protrusions can be tailored to meet a specific requirement. For example, in addition or in the alternative to the profiles shown in
Referring to
As discussed above, it may be advantageous in certain embodiments for the axial depth of recesses of a seal to be substantially equal to the spacing between adjacent baffles within the turbine inlet (possibly including the width of one baffle). In such embodiments, it may also be advantageous that at least one or more, more preferably most, or all, of the baffles should have substantially equal axial spacing within the inlet (i.e. so that the inlet portions have equal axial widths).
In some embodiments the recesses at the end of the seal need not all be the same shape, size or have equal spacing. However, it is generally preferred that their combined cross-sectional area relative to gas flow through the turbine inlet should be substantially equal to the cross-sectional area of the throat area of at least one annular array of inlet gas passages defined by the vanes in a given inlet portion.
The concept of variation in an axial extent of a seal may be alternatively or additionally described or defined in many other ways, as will now be discussed.
An axial extent of a leading end of the seal varies in magnitude around a circumference of the seal. This results in a plurality of recesses and/or protrusions being defined around the circumference of the leading end of the seal. The recesses (which may, in any embodiment, be defined as spaces between protrusions, or cut-outs, or cut-aways) extend through the entire thickness or the sleeve. The recesses and/or protrusions are present to, upon movement of the sleeve, selectively block or expose (e.g. close or open) at least a part of inlet portions, or inlet passages provided in those portions by other structures.
In a known prior art sleeve, a leading portion (i.e. not a leading end, but next to the leading end) of the sleeve extends further in an axial direction than another, adjacent portion (e.g. an outer diameter portion) to accommodate a vane structure upon appropriate movement of the sleeve. However, an axial extent of a leading end of the prior art sleeve does not vary in magnitude around a circumference of the sleeve. Instead, the axial extent defines a circular structure. In this prior art sleeve, a plurality of recesses and/or protrusions are not defined around the circumference of the leading end of the sleeve.
As discussed above, a variation in magnitude of the axial extent in the circumferential direction (e.g. a pitch or wavelength) may be synchronised in some way with a location of one or more vanes or other structures that divide an inlet portion into a number of inlet passages. In theory, such synchronisation, which corresponds to appropriate alignment of the recesses of the seal with the structures dividing the inlet portions, may be readily achievable. However, in practice, this may not be the case. In some instances, it may be difficult to ensure that the required alignment is undertaken during manufacture or installation of the sleeve, seal and inlet arrangement, or to maintain such alignment during use of the arrangement. If the alignment (i.e. synchronisation) is not achieved and maintained, modelling has shown that the efficiency of the arrangement as a whole is vastly reduced. For instance, only a small misalignment can have a great and adverse affect on the flow of gas through the inlet. In summary, it has been found that the efficiency is extremely sensitive to even slight misalignment. It is therefore desirable to obviate or mitigate this sensitivity—i.e. it is desirable to desensitise the arrangement to misalignment of the recesses (or other profiling) of the seal relative to structures defining passages through inlet portions, or the passages themselves.
Two solutions to the above-mentioned problems are proposed. One solution is to desensitise the arrangement to misalignment by increasing the number of recesses provided in the leading end of the seal, such that the number of recesses (and/or protrusions) is greater than the number of vanes or other structures dividing the inlet portion into one or more inlet passages, and/or greater than the number of inlet passages defined by those structures. The total area defined by the total number of recesses might, as described above, be equal to the total throat area defined by the vanes or other structures. Alternatively, the area might be different. By increasing the number of recesses (and/or protrusions) the effects of misalignment are greatly reduced, while the benefits of providing the recesses are maintained.
Another solution to the above-mentioned problem, which may be used independently of, or in conjunction with, the increase in the number of recesses, is the provision of a plurality of apertures distributed about a circumference of a portion of the seal that extends beyond the free end of a sleeve. The apertures are not recesses in the end of the seal, but are instead holes passing through the seal, at a distance from the end of the seal. It has been found that the presence of these apertures results in a desensitisation of the alignment of the recesses relative to the inlet passages defined in the inlet portions by vanes or other structures. This desensitisation may be further improved by ensuring that a circumferential position of at least one of those apertures is different from a circumferential position of at least one axially adjacent recess (i.e. a recess that is adjacent to the aperture in the axial direction). More generally, a circumferential position of each one of a plurality of apertures may be different from a circumferential position of each one of a plurality of respective axially adjacent recesses, further improving the desensitisation.
In general, in order for the seals discussed above to provide an optimum sealing functionality, the seal should, at least in use, come into contact with (or at least be in close proximity with) the baffles or other structures dividing the inlet into one or more inlet portions. This allows for appropriate sealing off of inlet portions through which gas should not flow. One way of achieving this would be to ensure that the seal is biased into contact with those structures. The biasing may be achieved by an appropriate construction and/or arrangement of the seal itself, such that the seal is partly sprung or otherwise biased to urge itself against the structure or structures defining the inlet portions. This may generally be described as the seal being constructed and arranged to have a particular resilience and/or shape to achieve this affect. The term “resilient” is used to include the situation where the seal expands or contracts in a radial direction due to, for example, gas flow pressure, or thermal effects, but can return to its original shape. This assures that the seal has a prolonged life, and does not function on only one, or a limited number of, occasions.
In another embodiment, the seal may be constructed and arranged to be in contact (or urged into contact) with the structures defining inlet portions when the turbine is in use, and in particular when gas is flowing towards the seal, and exerting a gas pressure on that seal. The seal may be constructed and arranged so that when gas pressure is acting on this seal, the seal is compressed in a radially direction to come into contact with the structures defining the inlet portions, thus providing the appropriate seal. This may be achieved by the seal having one or more overlapping circumferential portions, or a circumferential gap that extends axially along the seal (e.g. see
The seal 102 can be configured and arranged in one of a number of ways to achieve the desired functionality. For example, the seal can be constructed and arranged to have a particular degree of radial compression for a particular applied gas pressure or range of gas pressures. However, care should be taken to ensure that the seal 102 is not urged against the baffles 23a, 23b to such an extent that movement of the sleeve 28 and the attached seal 102 becomes either impossible, or impossible to achieve without excessive wear being caused to one or both of the seal 102 and baffles 23a, 23b. To overcome this problem, the seal 102 may be alternatively or additionally constructed and arranged to limit the degree or extent of compression to a diameter that substantially equates to, or exceeds, a diameter of the inlet portions 26a, 26b, 26c (which equates to the outer diameter of the baffles 23a, 23b defining those inlet portions 26a, 26b, 26c). It will be appreciated that the limitation should not be such that there is an excessive gap left in-between the limit of the compression of the seal 102 and the outer diameter of the baffles 23a, 23b, or otherwise the seal 102 will provide an unsatisfactory sealing functionality. The limitation may be decided upon by balancing the amount of wear that is likely to be incurred by the seal 102 during use against the reduction in sealing performance that would be experienced by providing an ever increasing gap between the limitation of the seal's 102 compression and the baffles 23a, 23b.
In one embodiment, the limitation can be realised by providing a gap in the circumference of the seal that extends in the axial direction, as already described above (e.g. see
Thus far, a seal has been described as being located between a sleeve and one or more structures that define the inlet portions, at least when the seal is moved across the inlet. Other arrangements are possible, in which a seal is employed. In such arrangements, a sleeve might not be required.
In
Although the arrangements of
Even though the seals in
In one or more embodiments, one, more or all inlet portions may comprise one or more vanes or other structures, having the same or different configurations, dividing the inlet portion into one or more inlet passages. One or more inlet portions may be free of vanes or other structures that would otherwise divide the inlet portion.
The sleeve and or seal may be free of vanes. It is known in the prior art to provide a sleeve (which has no seal that is moveable with the sleeve) with vanes, for example to affect the angle of attack of gas flowing past the vanes. However, it is important to note that such a sleeve is cylindrical, and this cylinder is then provided with vanes. In other words, an axial extent of a leading end of the prior art sleeve does not vary in magnitude around a circumference of the sleeve. In this prior art sleeve, a plurality of recesses and/or protrusions are not defined around the circumference of the leading end of the sleeve. Instead, vanes protrude from a circular face of that sleeve. Thus, the features of the known sleeve are not the same as the axial variation in the leading end of the seal as described herein.
Preferentially, the sleeve (if used) and/or seal surrounds the inlet portions, which has been found to give an improved aerodynamic performance. In other words, the inner diameter of the sleeve (if used) and/or seal is greater, or substantially equates to, than an outer diameter (or outer radial extent) of the inlet portion or portions. In another embodiment, the sleeve (if used) and/or seal may be surrounded by the inlet portions. In other words, the outer diameter of the sleeve (if used) and/or seal may be less than, or substantially equates to, an inner diameter of the inlet portion or portions. In another embodiment, the sleeve (if used) and/or seal may be moveable through the inlet portion or portions. In other words, the diameter (e.g. inner or outer, or average diameter) of the sleeve (if used) and/or seal may be less than an outer diameter of the inlet portion or portions, and greater than an inner diameter of the inlet portion or portions.
The extent of the sleeve and/or seal in the radial direction (which may be described as a thickness of the sleeve or seal) may be small, to reduce aerodynamic load on the sleeve and/or seal, or actuators for moving the sleeve (to which the seal is attached). ‘Small’, may be defined as being less than an axial width of the annular inlet, or less than an axial width of an inlet portion or passageway. For example, the sleeve and/or seal may be less than 5 mm thick, less than 4 mm thick, less than 3 mm thick, less than 2 mm thick, or less than 1 mm thick, for example approximately 0.5 mm thick or less.
Typically, exhaust gas flows to the annular inlet from a surrounding volute or chamber. The annular inlet is therefore defined downstream of the volute, with the downstream end of the volute terminating at the upstream end of the annular inlet. As such, the volute transmits the gas to the annular inlet, while the gas inlet passages or portions of the present invention receive gas from the volute. In some embodiments, the first and second inlet sidewalls which define the annular inlet are continuations of walls which define the volute. The annular inlet may be divided into at least two axially offset inlet passages or portions by one or more baffles located in the annular inlet, and which are therefore positioned downstream of the volute.
The turbine of the present invention has been illustrated in the Figures using a single flow volute, however it is applicable to housings that are split axially, whereby gas from one or more of the cylinders of an engine is directed to one of the divided volutes, and gas from one or more of the other cylinders is directed to a different volute. It is also possible to split a turbine housing circumferentially to provide multiple circumferentially divided volutes, or even to split the turbine housing both circumferentially and axially. It should be appreciated, however, that an axially or circumferentially divided volute is distinguished from the multiple gas inlet passages or portions present in the turbine of the present invention. For example, the gas inlet passages or portions relate to a nozzle structure arranged to accelerate exhaust gas received from the volute towards the turbine, and optionally to adjust or control the swirl angle of the gas as it accelerates. The multiple gas inlet passages or portions forming part of the present invention may be further distinguished from a divided volute arrangement in that, while the gas inlet passages or portions receive gas from the volute (or divided volute), and split the gas into an array of paths directed on to the turbine, a divided volute receives gas from the exhaust manifold so as to retain the gas velocity in gas pulses resulting from individual engine cylinder opening events.
It will be appreciated that axially offset inlet passages or portions include inlet passages or portions with different axial positions and/or inlet passages with different axial extents. Axially offset inlet passages or portions may be spaced apart, adjacent or axially overlapping.
The term ‘free end’ has been used herein to describe, for example, an end of the sleeve. The ‘free end’ will, as shown in the Figures, be the functional end of the sleeve—i.e. the end of the sleeve that is moveable within and/or across the inlet. The sleeve and/or seal are moveable across the inlet, and across and/or over at least one, more or all of the structures (e.g. baffles) that divide the inlet into portions, thus allowing one, more or all of those inlet portions to be selectively blocked or unblocked.
Terms such as ‘radial’ and ‘axial’ have been used herein, for example to describe movement of a sleeve, or the orientation of a structure. ‘Axial’ generally refers to the direction along which the turbine shaft (i.e. the shaft attached to the turbine wheel) extends, or a direction parallel to that shaft. ‘Radial’ is a direction substantially perpendicular to the direction along which the turbine shaft (i.e. the shaft attached to the turbine wheel) extends, or a direction parallel to that perpendicular direction.
Embodiments have thus far been described in relation to a turbine of a variable geometry turbocharger. A variable geometry turbocharger may be a particularly suitable application for the embodiments of the turbine, since a variable geometry turbocharger requires reliable operation, and needs to provide and maintain operational efficiency in order to meet end user requirements. The described embodiments assist in achieving this. However, the turbine might be used in other fields, for example in any field where a variable geometry turbine is required, and in particular in fields where the problems discussed above exist.
From a reading of this disclosure, it may be apparent to the skilled person that various modifications may be made to one or more embodiments disclosed herein, without departing from the scope of the claims that follow.
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