Reactor manufacturing method

Abstract

A method of manufacturing a reactor includes a pair of coils and a pair of core units of partial I-shaped cores with gap members butted together and mounted in the coils. The respective ends of the I-shaped cores are pressed against the ends of a pair of U-shaped cores. The U-shaped cores and the I-shaped cores are formed by pressing powder in movable dies that preheat any burrs formed during pressing to be positioned in a direction different from the winding axis direction to avoid any contact with the coil.

Claims

1. A method of manufacturing a reactor comprising a plurality of partial cores that form a closed magnetic path, the method comprising steps of: (a) putting in a magnetic powder to an I-shaped core press-molding die including a fixed die and movable dies, moving the movable dies closer to each other, and pressing the magnetic powder to shape a first partial core of the plurality of partial cores which forms a magnetic path passing through a hollow core-insertion part of a coil and which has a pressed face surface of the first partial core; (b) putting in the magnetic powder to U-shaped core press-molding die including a second fixed die and second movable dies, moving the second movable dies closer to each other, and pressing the magnetic powder in a predetermined press direction to shape a second partial core of the plurality of partial cores which forms a magnetic path passing through an exterior of the hollow core-insertion part of the coil and which has a pressed face surface of the second partial core orthogonal to the predetermined press direction; (c) inserting the first partial core in the hollow core-insertion part of the coil such that the pressed face surface of the first partial core is oriented orthogonal to a winding axis direction of the coil; and (d) butting the second partial core against the first partial core disposed in the hollow core-insertion part of the coil to form the closed magnetic path, and forming the plurality of partial cores, wherein a cross-sectional area of a leg-portion end face of the second partial core is smaller than a cross-sectional area of the first partial core.

2. The reactor manufacturing method according to claim 1, the step (d) further comprising butting the second partial core against the first partial core such that the pressed face surface of the second partial core is oriented orthogonal to the pressed face surface of the first partial core.

3. The reactor manufacturing method according to claim 1, the step (a) further comprising pressing and shaping the first partial core to have a first magnetic path end face, and the step (b) further comprising pressing and shaping the second partial core to have a second magnetic path end face with a different area size from the first magnetic path end face of the first partial core which is disposed in a manner facing with the second magnetic path end face when the second partial core is butted against the first partial core.

4. The reactor manufacturing method according to claim 3, the step (b) further comprising shaping the second partial core such that the second magnetic path end face has a smaller area size than the first magnetic path end face and has a smaller dimension than the first magnetic path end face in a direction orthogonal to the pressed face surface of the second partial core.

5. The reactor manufacturing method according to claim 3, the step (d) further comprising providing a first gap between the first partial core and the second partial core such that the first magnetic path end face and the second magnetic path end face are faced with each other with the first gap therebetween in the hollow core-insertion part of the coil.

6. The reactor manufacturing method according to claim 1, the step (a) further comprising shaping the first partial core such that a cross-sectional shape of the first partial core parallel to the pressed face surface of the first partial core becomes substantially similar to a cross-sectional shape of the hollow core-insertion part of the coil.

7. The reactor manufacturing method according to claim 1, wherein the coil comprises a pair of coils disposed side by side in a manner parallel to each other, the first partial core comprises at least a pair of I-shaped cores, the second partial core comprises a pair of U-shaped cores having a first leg-portion and a second leg-portion disposed in a manner parallel to each other, the step (c) further comprising inserting and disposing at least one of the I-shaped cores in the hollow core-insertion part of each of the pair of coils, and the step (d) further comprising disposing the respective first leg-portions of the pair of U-shaped cores and the respective second leg-portions thereof so as to face with each other and to butt against each other through the I-shaped core inserted and disposed in the hollow core-insertion part of the coil.

8. The reactor manufacturing method according to claim 7, the step (c) further comprising inserting a plurality of I-shaped cores in the hollow core-insertion part of each coil in a manner disposed side by side in the winding axis direction.

9. The reactor manufacturing method according to claim 8, the step (c) further comprising providing each second gaps forming the closed magnetic path between the adjoining I-shaped cores.

10. The reactor manufacturing method according to claim 9, wherein providing each first gaps between the respective first and second leg-portions of the U-shaped core and the I-shaped cores, and disposing all of the first and second gaps in the hollow core-insertion part of the coil.

11. The reactor manufacturing method according to claim 10, wherein each of the pair of coils has a rectangular wire folded at a right angle at four locations in each turn and wound in a square shape.

12. The reactor manufacturing method according to claim 1, wherein providing the pressed face surface of the second partial core with a step portion across a whole edge of the pressed face surface of which height is 1 mm or less.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a plane view illustrating a reactor according to an embodiment of the present invention;

(2) FIG. 2 is a plane view illustrating a core unit in solo provided in the reactor according to the embodiment of the present invention;

(3) FIG. 3 is an exploded perspective view illustrating a plurality of partial cores configuring the core unit according to the embodiment of the present invention in an exploded manner;

(4) FIG. 4 is a diagram illustrating a cross section taken along a line A-A in FIG. 1;

(5) FIGS. 5A-5C are diagrams each illustrating an outline of a pressing process of an I-shaped core and a U-shaped core by a press shaping die;

(6) FIG. 6A is a diagram illustrating a press shaping die for the I-shaped core as viewed from the top;

(7) FIG. 6B is a diagram illustrating a press shaping die for the U-shaped core as viewed from the top;

(8) FIG. 7 is a cross-sectional view of a straight core part and an I-shaped core according to a modified example of the embodiment of the present invention;

(9) FIGS. 8A-8E are diagrams each illustrating a structure of a U-shaped core according to another modified example of the embodiment of the present invention; and

(10) FIGS. 9A-9B are diagrams each illustrating a structure of a U-shaped core according to the other modified example of the embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(11) An explanation will now be given of a reactor and a manufacturing method thereof according to an embodiment of the present invention with reference to the accompanying drawings.

(12) FIG. 1 is a plane view illustrating a reactor 1 of this embodiment. The reactor 1 is, for example, a large-capacity reactor utilized for a drive system, etc., of a hybrid vehicle or an electric vehicle, and as illustrated in FIG. 1, includes a coil 10 and a core unit 20. FIG. 2 is a plan plane view illustrating the core unit 20 in solo. FIG. 3 is an exploded perspective view illustrating a plurality of partial cores configuring the core unit 20 in an exploded manner. FIG. 4 is a diagram illustrating a cross section taken along a line A-A in FIG. 1. In the following explanation, the vertical direction in FIG. 1 is defined as an X direction, the horizontal direction orthogonal to the vertical direction is defined as a Y direction, and a direction orthogonal to the vertical direction and the horizontal direction and perpendicular to the paper plane is defined as a Z direction. The reactor 1 can be disposed and directed in any direction when used.

(13) The reactor 1 is fixed in an unillustrated heat-dissipation casing which is formed of a lightweight metal having a high thermal conductivity, e.g. an aluminum alloy, and having a retaining space formed in a substantially rectangular shape. A filler is filled between the reactor 1 and the heat-dissipation casing. A resin which is relatively soft and which has a high thermal conductivity is suitable as the filler in order to ensure the heat-dissipation performance of the reactor 1 and to suppress a transmission of vibration from the reactor 1 to the heat-dissipation casing.

(14) The coil 10 employs a structure in which straight coils 12 and 14 with the same structure are disposed in parallel with each other and respective one ends thereof are coupled by an unillustrated wiring. For example, the straight coils 12 and 14 are each an edgewise coil having a rectangular wire folded at right angle at four locations in each turn and wound in a substantially square shape. As illustrated in FIG. 4, the straight coil 12 or 14 has a hollow core part 15 of which shape (hereinafter, referred to as a hollowpart shape) is a substantially rectangular shape with rounded four corners appeared when the straight coil is cut in the direction orthogonal to the winding axis direction (X direction). Note that the terminals of each straight coil 12 or 14 coupled with a load are omitted in the figure in order to simplify the drawing.

(15) As illustrated in FIGS. 1 to 3, the core unit 20 has a plurality of partial cores butted against one another, thereby fainting a substantially annular closed magnetic path. The partial cores forming the closed magnetic path are a pair of I-shaped core groups 22 and a pair of U-shaped cores 24.

(16) The I-shaped core group 22 includes three I-shaped cores 22a arranged in one direction, and the adjoining I-shaped cores 22a (adjoining end faces 22p) are respectively bonded and fixed together through a predetermined gap member 26 (unillustrated in FIG. 3).

(17) The pair of I-shaped core groups 22 structured as explained above have respective I-shaped cores 22a inserted and disposed in the parts of the straight coils 12 and 14 in a manner directed in the winding axis direction (X direction). The gap member 26 is, for example, a tabular member formed of a nonmagnetic material (various ceramics like alumina or resins). The I-shaped core 22a is a magnetic powder compact formed of a powder magnetic core, but the powder magnetic core may be a ferrite magnetic core instead. The U-shaped core 24 is a partial core of substantially U-shape and includes a first leg portion 24a and a second leg portion 24b arranged in parallel with each other, and a connecting portion 24c connecting the first and the second leg portion 24a and 24b. The U-shaped core 24 is formed of the same material as that of the I-shaped core 22a. The pair of U-shaped cores 24 are disposed in such a way that the respective first leg portions 24a and the respective second leg portions 24b face with each other via the I-shaped core group 22. That is, the core unit 20 has the respective leg portions of the pair of U-shaped cores 24 butted against each other through the I-shaped core group 22, thereby forming a substantially annular closed magnetic path having each partial core as a magnetic path.

(18) A leg-portion end face 24aa of the first leg portion 24a and the end face 22p of the I-shaped core 22a facing with the leg-portion end face 24aa are bonded and fixed together through a gap member 28 (unillustrated in FIG. 3). Moreover, a leg-portion end face 24bb of the second leg portion 24b and the end face 22p facing with the leg-portion end face 24bb are bonded and fixed together through the gap member 28. Those gap members 28, that are, the gaps between the leg-portion end face 24aa or the leg-portion end face 24bb and the end face 22p are disposed in the hollow core part 15 of the straight coil 12 or 14.

(19) In this embodiment, the gap members 26 or 28 are present in all magnetic paths between the adjoining partial cores. Since all gap members 26 or 28 are disposed in the hollow core part 15 of the straight coil 12 or 14, a loss of the magnetic flux due to a leakage can be suppressed when the magnetic flux flows into the adjoining partial core.

(20) FIGS. 5A to 5C are diagrams illustrating an outline of the pressing of the I-shaped core 22a and the U-shaped core 24 by a press-molding die. As illustrated in FIG. 5A, a press-molding die 30 includes a fixed die 32 that surrounds the horizontal direction of a work-piece, and a pair of top and bottom movable dies 34 that respectively seal the top and bottom openings of the fixed die 32. Magnetic powders are put in a cavity defined by the fixed die 32 and the top and the bottom movable dies 34. After the magnetic powders are put in, the top and the bottom movable dies 34 are moved relative to each other in a direction coming close to each other (the direction of an arrow P), as illustrated in FIG. 5B, and thus the magnetic powders in the cavity are compressed and pressed, and thus the I-shaped core 22a or the U-shaped core 24 is formed.

(21) The movable dies 34 are fitted to the fixed die 32 by, for example, loose fitting since the movable dies 34 slide in the vertical direction in the fixed die 32. Accordingly, there is an extremely tiny clearance between the side wall of the fixed die 32 and the pressing face of the movable die 34. Even though such a clearance is extremely tiny, the magnetic powders enter in such a clearance at the time of compression and pressing, and as illustrated in FIG. 5C, the magnetic powders having entered such a clearance remain as burr on the end face (pressed face) 22p of the I-shaped core 22a or a pressed face 24p of the U-shaped core 24. The pressed face 22p and 24p are each a surface of the I-shaped core 22a and the U-shaped core 24 pressed by the pressing face of the movable die 34, and the term burr in this embodiment mainly means an unnecessary objects running in the direction orthogonal to the press face 22p and 24p.

(22) FIG. 6A is a diagram illustrating a press-molding die 30 for the I-shaped core 22a as viewed from the top. It should be noted that in FIG. 6A and in FIG. 6B to be discussed later, a clearance between the fixed die 32 and the movable die 34 is illustrated in exaggerated manner for the purpose of explanation. As illustrated in FIG. 6A, the fixed die 32 for the I-shaped core 22a is formed in a substantially rectangular aperture shape having four rounded corners. Moreover, the movable dies 34 for the I-shaped core 22a are each formed in a substantially rectangular columnar shape having four rounded corners, and are capable of sealing respective top and bottom rectangular openings formed in the fixed die 32. However, there is an extremely tiny clearance between the side face of the fixed die 32 and the pressing face of the movable die 34. Accordingly, when the top and the bottom movable dies 34 are moved relative to each other in the direction of an arrow P1 (see FIGS. 3 and 6A) and the magnetic powders are compressed and pressed, the magnetic powders having entered in the clearance remain as burr on the pressed face 22p of the I-shaped core 22a. In FIG. 5, only one burr left on the pressed face 22p is illustrated for simplifying the illustration.

(23) As illustrated in FIG. 3, the I-shaped core 22a is inserted and disposed in the hollow core part 15 of the straight coil 12 or 14 such that the pressed face 22p is oriented orthogonal to the winding axis direction (X direction) of the coil 12 or 14. As a result, the burr on the pressed face 22p runs mainly in the winding axis direction. Accordingly, it is unnecessary to set a clearance between the I-shaped core 22a and the hollow core part 15 for avoiding a contact of the burr against the coil. This makes it possible to design a large cross-sectional area of the I-shaped core 22a, which is advantageous for a high-inductance designing. In other words, since a clearance for avoiding a contact of the burr against the coil is unnecessary, the hollow core part 15 of the coil (see FIG. 1) can be made small, which is advantageous for a downsizing design of the coil.

(24) Moreover, as illustrated in FIG. 4, the I-shaped core 22a is designed to have a similar cross-sectional shape to the shape of the hollow core part 15 of the straight coil 12 or 14. In other words, a cross-sectional shape of the I-shaped core 22a orthogonal to the winding axis direction is made substantially similar to a shape of the hollow core part of the coil which appears when the coil is cut in a direction orthogonal to the winding axis direction. Accordingly, the clearance between the I-shaped core 22a and the hollow core part 15 can be made small, and the large cross-sectional area of the I-shaped core 22a can be designed.

(25) More specifically, as illustrated in FIG. 4, the I-shaped core 22a is designed to have a substantially rectangular cross-section with four rounded corners which is slightly off set from the whole hollow shape of the hollow core part 15. It is unnecessary to design the cross-sectional shape of the I-shaped core 22a so as to have perfect similarity to the hollow shape of the straight coil 12 or 14. For example, the four corners of the substantially rectangular cross-section of the I-shaped core 22a illustrated in FIG. 4 can be formed as a curved face instead of the rounded face. By this way, the clearance between the I-shaped core 22a and the hollow core part 15 can be made small, and the large cross-sectional area of the I-shaped core 22a can be designed.

(26) FIG. 6B is a diagram illustrating a press-molding die 30 for the U-shaped core 24 as viewed from the top. As illustrated in FIG. 6B, a fixed die 32 for the U-shaped core 24 is formed in a U-shaped aperture shape having respective rounded corners. Moreover, movable dies 34 for the U-shaped core 24 are each formed in a U-shaped polygonal column shape having respective rounded corners, and are capable of sealing respective vertical U-shaped openings formed in the fixed die 32. In the press-molding die 30 for the U-shaped core 24, there is also an extremely tiny clearance between the side wall of the fixed die 32 and the pressing faces of the movable dies 34. Hence, when the top and the bottom movable dies 34 are moved relative to each other in the direction of an arrow P2 (see FIGS. 3 and 6B), and the magnetic powders are compressed and pressed, the magnetic powders having entered the clearance remain as burr on the pressed face 24p of the U-shaped core 24. In FIG. 5, only one burr left on the pressed face 24p is illustrated in order to simplify the illustration.

(27) As illustrated in FIG. 3, the U-shaped core 24 has two large step portions D1 on a plane orthogonal to the winding axis direction (X direction). One step portion D1 is formed since the height in the X direction of an end face 24aa of the first leg portion 24a and that of the side face 24cc of the connecting portion 24c differ from each other. Similarly, other step portion D1 is formed since the height in the X direction of an end face 24bb and that of the side face 24cc of the connecting portion 24c differ from each other. (Step portions D1 are illustrated in only FIG. 3 for the matter of simplification). In the conventional technology, when the U-shaped core 24 is compressed and pressed by a pair of movable dies that can move relative to each other in the lengthwise direction (X direction) of the leg portion, it is necessary to adopt a multi-stage press molding die which is, for example, complex and takes costs. In contrast, according to this embodiment, the pair of movable dies 34 that can move relative to each other in the direction of the arrow P2 (Z direction), that is orthogonal to the winding axis direction (X direction), is used for compressing and pressing the magnetic powders.

(28) In either one of the I-shaped core 22a and the U-shaped core 24, the thickness of the powder compact pressed between the top and the bottom movable dies 34 becomes uniform in the pressing direction and has no step portion, i.e., flat in this direction. Therefore, a multi-stage press molding die which is complex and takes costs becomes unnecessary. That is, the I-shaped core 22a and the U-shaped core 24 can be pressed and formed by a die with a simple structure. This is advantageous from the standpoint of costs (e.g., initial costs and the maintenance costs of the die).

(29) As illustrated in FIG. 3, the U-shaped core 24 has the pressed face 24p disposed in a manner parallel with the winding axis direction (X direction) so that the remaining burr run mainly in the direction (Z direction) orthogonal to the winding axis direction. In other words, the pressed face 24p and the pressed face 22p of the I-shaped core 22a are disposed in directions orthogonal to each other. Here, each tip of the first leg portion 24a or the second leg portion 24b is inserted and disposed in the hollow core part 15 of the straight coil 12 or 14, and thus there is a concern that the burr remaining near the leg-portion end faces 24aa and 24bb may damage the insulation layer of the straight coil 12 or 14. Hence, as illustrated in FIG. 4, the U-shaped core 24 has the height dimension (Z direction) of the leg-portion end faces 24aa and 24bb designed so as to be shorter than the height dimension of the substantially rectangular cross-section (or pressed face 22p) of the I-shaped core 22a, and thus a sufficient clearance for avoiding the burr is ensured between the respective tips of the first leg portion 24a, the second leg portion 24b and the hollow core part 15.

(30) In this embodiment, the planar shape of the leg-portion end faces 24aa and 24bb differs from the planar shape of the pressed face 22p. That is, the area size each of the leg-portion end faces 24aa and 24bb is smaller than the area size of the pressed face 22p. Moreover, the cross-sectional area size of the U-shaped core 24 is smaller than the cross-sectional area size of the I-shaped core 22a.

(31) In a case the cross-sectional area size and planar shape, etc., of adjoining partial cores differ as explained above, a reduction of the inductance is concerned due to, for example, the leakage of the magnetic flux. However, it is appropriate if the cross-sectional area of the U-shaped core 24 and the planar shape and area of the leg-portion end faces 24aa and 24bb be designed in consideration of a relationship between the DC superimpose characteristic necessary for the specification and the reduction of the DC superimpose characteristic due to magnetic saturation, and the differences in the cross-sectional area of the I-shaped core 22a and the planar shape and area of the pressed face 22p are not always a problem. For example, the U-shaped core 24 is one obtained by eliminating a part (where magnetic fluxes hardly pass through) of a U-shaped core model having the same cross-sectional area as that of the I-shaped core 22a, and thus it is designed so that the inductance does not decrease substantially. In this case, the superimposition of the U-shaped core 24 is reduced, contributing to the weight saving of the reactor 1.

(32) The above explanation was for an example embodiment of the present invention. The embodiment of the present invention is not limited to the above explanation, and can be changed as needed within the scope of the technical thought defined in the appended claims. For example, in the above-explained embodiment, the gap members 26 or 28 are bonded and fixed at all magnetic paths between the adjoining partial cores, but in another embodiment, air gaps may be employed instead of such gap members.

(33) FIG. 7 is a cross-sectional view (corresponding to a cross-section taken along the line A-A in FIG. 1) of a straight coil 12z (or 14z) and an I-shaped core 22a7 of the reactor 1 according to a modified example of the above-explained embodiment. As illustrated in FIG. 7, the straight coil 12z or 14z is an edgewise coil having a rectangular wire wound in a spiral manner and having an annular cross-section. Moreover, the I-shaped core 22aZ is in a columnar shape having a circular cross-section similar to the hollow (circular shape) of the straight coil 12z and 14z. Hence, according to this modified example, also, the clearance between the hollow core part 15 and the I-shaped core 22aZ can be as small as possible, and thus the cross-sectional area of the I-shaped core 22aZ can be designed largely.

(34) Moreover, according to the above-explained embodiment, a thickness of the U-shaped core 24 in the direction of the arrow P2 (Z direction) that is a pressing direction is uniform and has no step portion. Accordingly, it can be pressed and molded by a die with a simple structure. Meanwhile, depending on the type of the core, the U-shaped core has a step portion in the Z direction. FIGS. 8A to 8E are diagrams illustrating au-shaped core according to another modified example of the reactor 1 of the embodiment and a structure of a U-shaped core 24Y having a step portion in the Z direction. More specifically, 8A and 8B are a plane view of the U-shaped core 24Y according to another modified example, and a side view thereof, respectively. FIG. 8C is a cross-sectional view taken along a line B-B in FIG. 8A. FIGS. 8D and 8E are enlarged cross-sectional view illustrating areas C and D in FIG. 8C, respectively.

(35) As illustrated in FIGS. 8A to 8E, a pressed face 24pY of the U-shaped core 24Y is provided with a step portion D2 across the whole edge thereof. By this step portion D2, the pressed face 24 pY has an edge lower than the rest of the face. That is to say, the U-shaped core 24Y of this another modified example has step portions not only in the X direction but also the Z direction, that is, the steps D1 and D2. However, the height of the step portion D2 in the Z direction is remarkably smaller than the height of the step portions D1 in the X direction, and is, for example, equal to or smaller than 5% relative to the thickness of the U-shaped core 24Y in the z direction (when thickness is 20 mm, equal to or smaller than 1 mm, and when thickness is 40 mm, equal to or smaller than 2 mm). Such a small step equal to or smaller than 5% (e.g., equal to or larger than 1 mm and equal to or smaller than 2 mm) relative to the thickness does not make the structure of a die complex. Therefore, the U-shaped core 24Y of another modified example is compressed and pressed in the direction of the arrow P2 (Z direction) as similar to the U-shaped core 24 of the above embodiment.

(36) That is, also in another modified example, simplification of the structure of a die is mainly focused without taking the press direction (X direction) of the I-shaped core 22a into consideration, and the die of the U-shaped core 24Y is designed. In the U-shaped core 24Y of another modified example, the lower portion at the edge has a high surface pressure at the time of compression and molding, the compression density becomes high, thereby enhancing the strength. Hence, according to another modified example, breaking and chipping of the edge is further suppressed.

(37) Here, according to the present application, substantially flat plane includes a pressed face having a small step portion which does not substantially make the structure of a die complex (e.g., the pressed surface having a step portion smaller than 5% (e.g., equal to or larger than 1 mm and equal to or smaller than 2 mm) to the thickness of the core).

(38) FIGS. 9A and 9B illustrate a structure of a U-shaped core 24X which is a U-shaped core of the reactor 1 according to the other modified example of the above-explained embodiment and which has a step portion also in the Z direction. More specifically, FIGS. 9A and 9B are a plane view of the U-shaped core 24X of the other modified example and a side view thereof, respectively. As illustrated in FIGS. 9A and 9B, a pressed face 24pX of the U-shaped core 24X includes pressed faces 24aX and 24bX on respective leg portions, and a pressed face 24cX on an interconnection portion that interconnects the respective leg portions together, and step D3 is formed between the pressed face 24aX, 24bX and the pressed face 24cX. The step height of the step D3 in the Z direction is suppressed to be a height that does not substantially make the structure of a die complex (e.g., equal to or smaller than 5% relative to the thickness of the U-shaped core 24X in the Z direction (e.g., equal to or larger than 1 mm and equal to or smaller than 2 mm)) like the modified example illustrated in FIGS. 8A to 8E. According to the modified example illustrated in FIGS. 9A and 9B, the cross-sectional area of, for example, the interconnection portion of the U-shaped core 24X can be increased by adding the step portion D3, and thus it is advantageous for suppressing a reduction of the DC superimpose characteristic by magnetic saturation. Although in the modified example illustrated in FIGS. 9A and 9B, the step portion D3 is formed at the one pressed face 24pX, the step portion D3 may be added to both pressed faces 24pX.

(39) While the above features of the present invention teach apparatus, process and an improved reactor, it can be readily appreciated that it would be possible to deviate from the above embodiments of the present invention and, as will be readily understood by those skilled in the art, the invention is capable of many modifications and improvements within the scope and spirit thereof. Accordingly, it will be understood that the invention is not to be limited by the specific embodiments but only by the spirit and scope of the appended claims.