Abstract:
A spiral exchanger has a winding axis and comprises an outer sheet and an inner sheet secured to one another in a fastening plane before winding and delimiting a space for a fluid between them. The outer sheet and the inner sheet are wound on themselves and each comprises a plurality of flexible areas and a plurality of rigid areas, the flexible areas being more flexible than the rigid areas during folding. The flexible areas and the rigid areas are extended along the winding axis, and at least one flexible area of the outer sheet and at least one flexible area of the inner sheet that delimit the space between them form a pair of flexible areas that are aligned in a same radial direction.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to FR 11 60354, filed Nov. 15, 2011. 
       TECHNICAL FIELD 
       [0002]    The invention relates to a spiral exchanger, and to a portion of an exhaust that includes such an exchanger. Furthermore, the invention relates to a method for manufacturing a spiral exchanger. 
       BACKGROUND OF THE INVENTION 
       [0003]    Several types of spiral exchangers exist in the state of the art. Typically, such exchangers are formed by two superimposed sheets that are then wound and arranged in an exhaust duct of an internal combustion engine. 
         [0004]    In one type of spiral exchanger, the sheets are spaced apart with spacers. For example, application FR 2 810 726 A1 discloses a spiral exchanger that is made by two sheets spaced apart that have, on their surfaces across from the inner spacing elements and the opposite surface, respectively, outer spacing elements that are arranged so that the inner and outer spacing elements of one sheet bear on the corresponding inner and outer spacing elements of the other sheet. The spacing elements have substantially the same shape. In application FR 2 809 483 A1, a metal strip having spacing elements is formed by folding the edges, which are then connected to one another by welding. The folded metal strip is then wound to form the spiral exchanger. 
         [0005]    Application FR 2 874 080 A1 relates to an exchanger comprising two wound metal sheets. The metal sheets are provided with spacing elements in the form of serrations distributed on the surface thereof. Furthermore, the inlet and outlet for the fluid, for example water, of the device are done at a center of the spiral. This means that the inlet and outlet tubes will exit on either side of the exchanger and have a complicated trajectory, which is therefore costly. Typically, the water circulating in such an exchanger is at most at a temperature of 130° C., and therefore significantly below that of the exhaust gas that heats the water. The fact that there are differential expansions between these water tubes and exhaust tubes may cause wear of the materials after extended use. 
         [0006]    Generally, when two metal sheets are wound on one another, the metal sheet on the outer side is always longer than the inner sheet for an equivalent number of winding turns due to its thickness and/or the space between the two metal sheets. If the two metal sheets are welded before winding, for example as in application FR 2 809 483 A1, deformations will appear on the inner sheet. As a result, in the prior art, the sheets are often welded during or after winding, for example such as in application FR 2 810 726 A1. Nevertheless, welding during winding poses manufacturing problems, in particular for thin sheets. In fact, thin sheets cannot be welded using an electric arc and it is not possible to consider seam welding due to problems of accessing the heel that returns current. Furthermore, laser welding is difficult. The welding problem becomes increasingly complicated if it is necessary to perform intermediate welds between two side welds. 
         [0007]    The aim of the present invention is to overcome the drawbacks of the state of the art and in particular to use a spiral exchanger that is easy to manufacture, light, and inexpensive. 
       SUMMARY OF THE INVENTION 
       [0008]    A spiral exchanger has a winding axis and comprises an outer sheet and an inner sheet secured to one another in a fastening plane before winding and delimiting a space for a fluid between them. The outer sheet and the inner sheet are wound on themselves and each comprises a plurality of flexible areas and a plurality of rigid areas. The flexible areas are more flexible than the rigid areas during folding. The flexible areas and the rigid areas are extended along the winding axis, and at least one flexible area of the outer sheet and at least one flexible area of the inner sheet that delimit the space between them form a pair of flexible areas that are aligned in a same radial direction. 
         [0009]    The spiral exchanger includes one or more of the following exemplary features: the flexible areas of the outer sheet and/or the inner sheet are substantially rectilinear; the majority of the flexible areas, in particular all of the flexible areas, of the outer sheet form, with a respective flexible area of the inner sheet, a pair of flexible areas that are aligned in a same radial direction; considered in cross-section in the direction of winding, the rigid areas are formed by flats and the flexible areas are formed by hollow profiles and edges between the hollow profiles and the flats, the hollow profiles in particular being formed toward the winding axis; each flexible area, in particular each hollow profile, of the outer sheet has, over the entire width of the outer sheet in the direction of the winding axis, a rectilinear part that is located at the fastening plane, and in that each flexible area, in particular each edge, of the inner sheet, has, over its entire length parallel to the winding axis, at least one rectilinear portion that is located in the fastening plane to form a plurality of hinges in the fastening plane; a plurality of rigid areas, in particular a plurality of flats, of the outer sheet is provided with at least one hollow portion, each hollow portion bearing against a rigid area of the inner sheet; the exchanger comprises at least one fluid inlet opening to introduce fluid into the space and at least one fluid outlet opening to remove fluid from the space, the inlet opening(s) and outlet opening(s) being arranged at a first end of one of the outer sheet or the inner sheet in the winding direction, the first end being opposite a second end at which the winding began; the space is U-shaped, W-shaped, or zigzagged, having substantially rectilinear branches; the outer sheet and the inner sheet are fastened to one another respectively between two branches; the outer sheet and the inner sheet have a respective cut-out between two branches; an average passage diameter in the space decreases between the inlet opening(s) and the outlet opening(s); each branch has a substantially constant width and the width of the branches in the direction of the winding axis of the at least two adjacent branches decreases one relative to the other; and/or the outer sheet and/or the inner sheet is/are made up of a metal sheet. 
         [0010]    Furthermore, in another embodiment, a portion of an exhaust includes such an exchanger. 
         [0011]    Additionally, a method for manufacturing a spiral exchanger comprises the following steps: stamping, in an outer sheet and an inner sheet, a plurality of flexible areas and a plurality of rigid areas, the flexible areas being more flexible than the rigid areas during folding, and the flexible areas and the rigid areas being elongated along the winding axis; aligning the outer sheet and the inner sheet such that at least one flexible area of the outer sheet and at least one flexible area of the inner sheet form a pair of flexible areas that are aligned with one another; permanently fastening the outer sheet to the inner sheet at predetermined locations to form a space between them; and winding the outer sheet and the inner sheet to form the spiral exchanger. 
         [0012]    The method includes one or more of the following exemplary features: considered in the direction of winding, the rigid areas are formed by flats and the flexible areas are formed by hollow profiles and edges between the hollow profiles and the flats, during the winding steps the hollows are oriented toward the winding axis; at least one of the outer or inner sheets comprises a fluid inlet opening for introducing fluid into the space and at least one fluid outlet opening for removing fluid from the space, the sheets having a first end in the winding direction in which the openings are arranged, the winding step starting with a second end opposite the first end; the space formed is U-shaped, W-shaped, or zigzagged, the space having substantially rectilinear branches, the method also comprising a step for cutting the outer and inner sheets between at least two adjacent branches to form a cut-out; and/or the method comprises steps for forming an exchanger according to the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    Other features and advantages of the present invention will emerge from the description thereof provided below, in reference to the drawings, which illustrates several non-limiting embodiments and in which: 
           [0014]      FIG. 1  is a perspective view of the two sheet metal sheets for a spiral exchanger according to the invention; 
           [0015]      FIG. 2  is an exploded schematic view of two sheet metal sheets for a spiral exchanger according to the invention; 
           [0016]      FIG. 3  is a side view of two sheet metal sheets for an exchanger according to the invention before connection of the two sheets; 
           [0017]      FIG. 4  is a side view of the two sheet metal sheets for an exchanger according to the invention after connection of the two sheets; 
           [0018]      FIG. 5  is a longitudinal cross-sectional view of a portion of the two sheet metal sheets of an exchanger according to the invention after connection of the two sheets; 
           [0019]      FIG. 6  is a cross-sectional view in the radial plane of a spiral exchanger according to the invention after a winding turn; 
           [0020]      FIG. 7  is a cross-sectional view in a radial plane of the exchanger during mounting in an exhaust; 
           [0021]      FIG. 8  is a schematic perspective view of an outer sheet metal sheet for a spiral exchanger according to a second embodiment; and 
           [0022]      FIG. 9  is a top view of an outer sheet metal sheet of another embodiment for a spiral exchanger according to the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    A first embodiment will be described using  FIGS. 1 to 5 .  FIGS. 1 to 5  schematically show an elongated element of an exchanger  1  before winding to form a spiral exchanger. The element  1  comprises two sheet metal sheets  10 ,  20 , in particular an outer sheet  10  and an inner sheet  20  that are fastened to one another. During winding of the element  1  around the winding axis X (see  FIG. 6 ), the inner sheet  20  is radially inside relative to the outer sheet  10 . 
         [0024]    The element  1  has a winding direction Y in which the element  1  is wound. The winding direction Y is substantially orthogonal to the winding axis X. The length of the element  1  is defined in the winding direction Y and the width of the element  1  is defined in the direction of the winding axis X. 
         [0025]    The inner sheet  20  has a thickness d i  larger than a thickness d e  of the outer sheet  10 . Typically, the sheets have a thickness between 0.05 mm and 0.5 mm, in particular between 0.10 mm and 0.4 mm. The winding of these sheet metal sheets  10 ,  20  requires less effort than winding sheet metal sheets having a higher thickness, for example metal sheets having a thickness from 0.6 mm to 1 mm. 
         [0026]    The outer sheet  10  and the inner sheet  20  have undergone a deformation step, for example stamping, and after that deformation each have a plurality of flexible areas  12 ,  22  and a plurality of rigid areas  14 ,  24 . The rigid  14 ,  24  and flexible areas  12 ,  22  are elongated parallel to the winding axis X and orthogonally to the winding direction Y. The flexible  12 ,  22  and rigid  14 ,  24  areas are arranged alternately in the winding direction Y. The flexible  12 ,  22  and rigid  14 ,  24  areas extend over the entire width of the element  1 . 
         [0027]    The shape and arrangement of the rigid  14 ,  24  and flexible areas  12 ,  22  are clearly shown in  FIG. 5 . During the deformation, a plurality of flats  15 ,  25 , a plurality of edges  16 ,  26 , and a plurality of hollow profiles  17 ,  27  are respectively formed in the outer sheet  10  and the inner sheet  20 . The edges  16 ,  26  are arranged between the flats  15 ,  25  and the hollow profiles  17 ,  27 . The flats  15 ,  25  form the rigid areas  14 ,  24  and the edges  16 ,  26 , and the hollow profiles  17 ,  27  form the flexible areas  12 ,  22 . The flexible areas  12  of the outer sheet  10  have, in the winding direction Y, a smaller width relative to the length of the flexible areas  22  of the inner sheet  20 . 
         [0028]    In the outer sheet  10 , the hollow profile  17  has, in the winding direction Y, a smaller width relative to the width of the flats  15 . For example, the flats  15  of the outer sheet  10  have a width that is substantially twice the width of the hollow profiles  17 . 
         [0029]    In the inner sheet  20 , the hollow profiles  27  have, in the winding direction Y, a width larger than the width of the flats  25 . For example, the hollow profiles  27  of the inner sheet  20  have a width that is substantially twice the width of the flats  25 . 
         [0030]    In the embodiment of  FIGS. 1 to 5 , the width of the flats  25  of the inner sheet  20  substantially corresponds to the width of the hollow profile  17  of the outer sheet  10 , and the width of the flats  15  of the outer sheet  10  corresponds substantially to the width of the hollow profiles  27  of the inner sheet  20 . 
         [0031]    The outer sheet  10  and the inner sheet  20  are arranged one on the other before they are connected, such that the flexible areas  12 ,  22 , in particular the hollow profiles  17 ,  27 , are placed substantially across from one another. 
         [0032]    The outer sheet  10  is fastened to the inner sheet  20  in a fastening plane S before winding of the element  1 . For example, the outer sheet  10  is fastened to the inner sheet  20  by a weld. When the sheets  10 ,  20  are fastened to one another, a space  30  is formed between the outer sheet and the inner sheet  20  (see  FIG. 5 ). 
         [0033]    The space  30  is provided for circulation of a fluid, for example water. For a fluid circulating in the space  30 , a minimum passage section  32  is defined by the space between the hollow profile  17  of the outer sheet  10  and the edges  26  of the inner sheet  20 . 
         [0034]    As shown in  FIG. 5 , each flexible area  12 , and therefore each hollow profile  17 , of the outer sheet  10  has, over its entire length along the winding axis X, a rectilinear portion that is located at the fastening plane S. Additionally, the edges  26  and the flats  25  of the inner sheet  20  are in the fastening plane S. 
         [0035]    In the winding direction Y, the element  1  comprises a first end  34  and a second end  35 . At the first end  34  of the element  1 , two openings  36 ,  37  are provided in a connection area  38  of the outer sheet  10 , including a first or inlet opening  36  to allow fluid to enter the space  30  and a second or outlet opening  37  to allow the fluid to leave the space  30 . The connection area  38  extends along the direction of the winding axis X, and the openings  36 ,  37  are provided in a connection flat having a larger width than the flats  15 . In another embodiment, the distance between the openings  36 ,  37  along the winding axis X is larger or smaller relative to the embodiments shown in  FIG. 1 . 
         [0036]    The outer sheet  10  is welded to the inner sheet  20  along a weld line  39  (dotted line in  FIG. 1 ), which is done such that the space  30  between the two elongated sheets  10 ,  20  is generally U-shaped, whereof the branches  40 ,  42  are oriented toward the first end  34 , where the inlet and outlet openings  36 ,  37  are arranged. A longitudinal portion  44  of the weld line  39  is arranged between the branches  40 ,  42 . Therefore, during use of the element  1 , the fluid, after entering the space through the first opening  36 , passes through the first branch  40  toward the second end  35  to go from the first branch  40  to the second branch  42  in which the fluid passes through the element  1  from the second end  35  to the second opening  37 . 
         [0037]    The rigid areas  14  of the outer sheet  10  have hollow portions  46 , in particular in the flats  15 . At the hollow portions  46 , the outer sheet  10  bears on the inner sheet  20 , in particular on the flats  25 . The hollow portions  46  are made to stabilize the space  30  of the element  1 , in particular to prevent the space  30  from collapsing. In the embodiment of  FIG. 1 , the hollow portions  46  of the outer sheet  10  are respectively aligned, in the branches  40 ,  42 , in the winding direction Y. Nevertheless, in other embodiments, the hollow portions  46  in the rigid areas  14  may be arranged randomly. 
         [0038]    The assembly of the spiral exchanger is described below. 
         [0039]    In a first step, the outer  10  and inner  20  sheets are stamped to form the flexible areas  12 ,  22  and the rigid areas  14 ,  24 . Then, the outer and inner sheets are arranged such that the flexible areas  12 ,  22  and the rigid areas  14 ,  24  are respectively positioned across from one another (see  FIGS. 3 and 4 ). The outer sheet  10  is placed relative to the inner sheet  20  such that the passage of the fluid is ensured, and the passage section  32  of the fluid is constant even after the winding. 
         [0040]    Next, the outer  10  and inner  20  sheets are fastened to each other by a weld running alongside the weld line  39 ,  44  to seal the space  30  between the two sheets relative to the outside of that space and to form the U-shaped trajectory for a fluid passing through the space  30 . The outer sheet  10  and the inner sheet  20  can be fastened to one another using a seam weld, laser weld, or, for example, brazing. 
         [0041]    In a subsequent step, as shown in  FIG. 6 , the second end  35  of the element  1  is fastened to a central tube  48  to wind the element  1  from the second end  35 . The outer sheet  10  is radially outside the inner sheet  20  during the winding. Once the element  1  is wound, the openings  36 ,  37  are turned outward. A passage  50  is formed between the outer sheet of a layer and the inner sheet of the successive layer of the wound element  1 , through which the exhaust gas passes to transfer its heat to the fluid circulating in the space  30  of the element  1 . In an embodiment, the central tube  48  is obstructed. 
         [0042]    During the winding, the folding of the outer sheet  10  is done in the flexible areas  12 , in particular in the rectilinear portion of the fastening plane S in the hollow profiles  17 . The inner sheet  20  is folded at the edges  26 . The folding axis will then be situated between the hollow profiles  17  of the outer sheet  10  and the adjacent edges  26  of the inner sheet  20  in the fastening plane S. In the outer sheet  10 , the flexible areas  12  are a reserve of material to make it possible, during winding of the element  1 , to elongate the outer sheet  10 . In any case, the edges  26  of the inner sheet  20  and the hollow profiles  17  of the outer sheet  10  behave like a hinge during winding of the element  1 . The respective deformations of the outer sheet  10  and the inner sheet  20  are therefore different from one another, to allow elongation of the outer sheet relative to the inner sheet during winding of the element  1 . The number of winding layers varies and depends on the use of the exchanger. During winding, the passage section  32  does not change significantly. 
         [0043]      FIG. 7  shows the mounting of the exchanger in half-shells  52 ,  54  of an exhaust. Tubes  56  are fastened to the inlet opening  36  and the outlet opening  37  and are connected to tubes  58  of one of the half-shells  54  of the exhaust. Once assembled, the half-shells  52 ,  54  constitute a part of the exhaust system of a combustion engine. To that end, the assembly of the element  1  and the tube  48  is placed in half-shells  52 ,  54 , and a fluid is injected through the tubes  56 ,  58  into the space  30  of the element  1 . 
         [0044]    In one embodiment, the distance between the openings  36 ,  37  may be reduced. For example, the openings may be positioned such that the exchanger is less sensitive to dimensional variations between the exchanger and the half-shells  52 ,  54 . In fact, in an exchanger without fluid vaporization, the outer and inner sheets  10 ,  20  are at the temperature of the fluid while the half-shells  52 ,  54  are close to the temperature of the exhaust gas passing through the half-shells. 
         [0045]    In other embodiments, which are described relative to  FIGS. 8 and 9 , a fluid circulating in the exchanger is vaporized and overheated. 
         [0046]      FIG. 8  schematically illustrates an element  101  of an exchanger provided to vaporize fluid. The elements of the embodiment of  FIG. 8  that are identical or perform the same function as those of the embodiment of  FIGS. 1 to 7  will be designated using the same references plus 100. 
         [0047]    In the same way, it has flexible areas  112  and rigid areas  114  to allow winding with controlled deformations. The same principle as in the embodiment of  FIGS. 1 to 7  is used. As in the embodiment  FIGS. 1 to 7 , a space to guide the fluid between the two sheets  110  is generally U-shaped with a first branch  140  and a second branch  142 . Unlike  FIG. 1 , the first branch  140  and the second branch  142  are separated from one another by a longitudinal cut-out  160  in the winding direction Y. A width L 1  of the first branch  140  bearing the inlet opening  136  is larger than the width L 2  of the second branch  142  bearing the outlet opening  137 . A passage section for the fluid in the space in the second branch  142  is then smaller than a passage section of the fluid in the space in the first branch  140 . The width L 2  of the second branch  142  is between 10% and 80% smaller, in particular between 20% and 60% smaller, than the width L 1  of the first branch  140 . In one embodiment, the width L 2  of the second branch  142  is 33% smaller than the width L 1  of the first branch  140  for a mass flow of 30 liters/hour. 
         [0048]    In fact, during operation of the exchanger, the fluid enters in liquid form into the inlet opening  136 , passes through the first branch  140 , turns around at the second end  135 , passes through the second branch  142 , and leaves through the outlet opening  137  in gas form. 
         [0049]      FIG. 9  illustrates another embodiment of an element  201  for a spiral exchanger. In particular,  FIG. 9  shows an exchanger for vaporizing a fluid.  FIG. 9  is a schematic top view of an outer sheet  210  of an element  201 . The elements of the embodiment of  FIG. 9  that are identical or perform the same function as those of the embodiment of  FIGS. 1 to 7  will be designated using the same references plus 200. 
         [0050]    The outer sheet  210  has flexible areas  212  and rigid areas  214  that are arranged alternatingly in the direction of winding Y. 
         [0051]    The space between the inner and outer sheets  210  is formed such that the fluid is guided by a W-shaped trajectory (shown upside down in  FIG. 9 ). The element  204  therefore has four branches  240 ,  241 ,  242  and  243 . In other embodiments, the element has more than four branches. The branches  240 ,  241 ,  242  and  243  respectively extend in the winding direction Y and have, between two respective adjacent branches, cut-outs  260 ,  262 ,  264  to separate one of the branches from the other adjacent branches. The inner and outer sheets  210  are cut by the cut-outs  260 ,  262 ,  264 . The first branch  240  is connected to the second branch  241  at the second end  235 , the second branch  241  is connected to the third branch  242  at the first end  234 , and the third branch  242  is connected to the fourth and final branch  243  at the second end  235 . 
         [0052]    The element  201  has an inlet opening  236  and an outlet opening  237 . The inlet opening  236  is arranged at the first end  234  of the first branch  240 . The outlet opening  237  is arranged in a fourth branch  243  at the first end  234 . In fact, during operation of the exchanger, the fluid enters in liquid form into the inlet opening  236  and exits through the outlet opening  337  in gas form. 
         [0053]    The branches have, in the direction of the winding axis, a width L 1 , L 2 , L 3 , L 4 , the width of the branches  240 ,  241 ,  242 ,  243  decreasing gradually in that order. For example, the width L 2  of the second branch  241  is decreased by 33% relative to the width L 1  of the first branch  240 . The widths L 3 , L 4  of the third branch  242  and the fourth branch  243 , respectively, are approximately half the width L 1  of the first branch  240 . In an embodiment, the first branch  240  has a width L 1  of approximately 50 mm. 
         [0054]    Contrary to the embodiment presented relative to  FIGS. 1 to 8 , the hollow portions  246  and the rigid areas  214  of the branches  240 ,  241 ,  242 ,  243 , where the rigid area  214  of the outer sheet  210  bears against the rigid area of the inner sheet, are not aligned in the winding direction Y to create more perturbations of the fluid. 
         [0055]    During operation of the exchangers for the vaporization of  FIGS. 8 and 9 , the fluid is introduced into the element  101 ,  201  of the exchanger at a temperature of from 80° C. to 100° C. and vaporizes, while absorbing the heat given off by the exhaust gases. The evaporation takes considerable energy from the exhaust gases, and the temperatures of the outer and inner sheets in that area are therefore the same as that of the fluid. Next, the vapor from the fluid will behave like a gas as it overheats. The final temperature of the overheated vapor is approximately 200° C. to 500° C. or more depending on the pressure. Near the outlet  237  of the vapor, the temperature of the sheets of the exchanger is comprised between the vapor and that of the exhaust gas. The exchanger thus has a high temperature gradient between the fluid inlet in the exchanger (90° C. to 100° C.) and the fluid outlet (400 to 650° C.). For that reason, the cut-outs  60 ,  260 ,  262 ,  264  are formed in the elements  101 ,  201 , as the heat expansion of each branch is different. 
         [0056]    In gaseous form, the fluid for example has a volume 1,680 times larger than that in liquid form, which means that at an equal mass flow, the volume flow rate is much higher, and therefore its speed is higher. The final speed of the vapor is a very important parameter in correctly vaporizing and overheating the vapor. In fact, the greater the speed, the more the heat exchanges at the wall of the space between the two sheets are good. That is why the passage section offered to the steam is reduced. In the embodiments of  FIGS. 8 and 9 , this reduction is proportional to the width of the branches. This makes it possible to increase the speed, and therefore further increase the heat exchanges. 
         [0057]    For example, in the element of  FIG. 9 , the first branch  240  has a first area that corresponds to an area in which the fluid is heated until the first microbubbles appear (beginning of vaporization). Next, the vaporization will effectively take place in the second branch  241 . The movement of the fluid is accelerated in the second branch  241  by narrowing the passage section to favor vaporization. In the third branch  242  and the fourth branch  243 , the vapor is transformed from a wet or saturated vapor to an overheated vapor. There again, decreasing the passage section makes it possible to increase the speed of the vapor, and thus the turbulence and therefore the heat exchange. 
         [0058]    The fluid circulating in the exchanger according to the invention is water or another liquid. In one embodiment, the liquid is an organic fluid, for example ethanol. 
         [0059]    Generally, the exchanger according to the invention allows great flexibility. In some embodiments, the passage section of the fluid is managed over the course of the latter&#39;s conversion into overheated vapor. In other embodiments, the passage sections are varied depending on the anticipated temperatures of the exhaust gas. According to one embodiment, the length of the sheet metal sheets in the winding direction is varied as a function of the desired vapor quality and available energy in the exhaust gas. 
         [0060]    Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.