Abstract:
A rotation angle sensor is provided, including a casing, and a magnet positioned in the casing. The magnet has a first magnetic pole end and a second magnetic pole end. First and second yokes are positioned at a first predetermined space relative to the first magnetic pole end of the magnet, and a third yoke is positioned at a predetermined space relative to the second magnetic pole end of the magnet. The third yoke is further positioned between the magnet and an extending portion of the first yoke, and is also positioned between the magnet and an extending portion of the second yoke. A first signal output element, which is positioned between the third yoke and the extended portion of the first yoke, outputs a first signal corresponding to an area ratio between the magnet and the first yoke. A second signal output element, which is positioned between the third yoke and the extended portion of the second yoke, outputs a second signal corresponding to an area ratio between the magnet and the second yoke. In addition, a magnetic shielding portion is positioned above the magnet, wherein the magnetic shielding portion interrupts leakage magnet flux of the magnet, and wherein the magnetic shielding portion and the third yoke are integrally formed of a single-piece construction.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to sensors for sensing a rotation angle, and more particularly to sensors that sense a rotation angle or open degree of a throttle valve installed in an air intake manifold of an internal combustion engine. 
     2. Description of the Background Art 
     Generally speaking, a throttle valve is installed in an air intake manifold of an internal combustion engine, and a rotation angle sensor detects an open angle of the throttle valve. A detecting signal of the rotation angle sensor is routed to an engine control unit, which signal indicates an intake air amount of the engine. The engine control unit calculates a fuel injection amount corresponding to the intake air amount. The rotation angle sensor has a potentiometer, which is comprised of a resistant element and a brush for detecting the open angle of the throttle valve. The brush is connected with a rotational shaft (a throttle shaft). When the brush moves on the resistant element, the open angle of the throttle valve can be detected by a resistant value change of the resistant element. However, because the brush may be isolated from the resistant element, the detecting signal of the rotation angle sensor has the potential for being suddenly interrupted. Also, when the brush or the resistant element is used for a long period of time, the rotation angle sensor cannot keep its durability and life because of the wearing away of the brush or the resistant element. 
     A Japanese Patent Application First Publication No. Heisei 9-189509, published on Jul. 22, 1997, exemplifies a previously proposed rotation angle sensor with three poles, having a first yoke, a second yoke, and a third yoke surrounding a magnet, and a first Hall element installed between the first yoke and the third yoke, and a second Hall element installed between the second yoke and the third yoke. 
     In the disclosed Japanese Patent Application First Publication, the rotation angle sensor is shown in FIG. 9. A throttle body  1  has a throttle valve (not shown) which rotates with a valve shaft  2 . The throttle body  1  has also a fit portion  1 A, which forms a cylindrical shape surrounding the projection end of the valve shaft  2 . The fit portion  1 A is fixed to a cylindrical portion  3 A of a yoke mounting member  3 . The valve shaft  2  is made of a high strength metal material, which is installed on the bearings in the throttle body  1 . 
     The yoke mounting member  3  includes a casing in conjunction with the throttle body  1 , which has the cylindrical portion  3 A opening in the downward direction, a partition portion  3 B covering on the top end of the cylindrical portion  3 A, a circuit board installing space  3 C on the upper portion of the partition portion  3 B, a magnet installing space  3 D on the lower portion of the partition portion  3 B, and a connector portion  3 E projecting in the outside diameter direction of the cylindrical portion  3 A. 
     A magnet  4  is installed in the magnet installing space  3 D of the yoke mounting member  3 . The magnet has circular ended portions in the lengthwise direction, parallel ended portions in the width direction, and a through hole  4 A extending in the axial direction of the valve shaft  2 . By inserting and crimping the projecting end of the valve shaft  2  into the through hole  4 A, the magnet  4  is fixed to the valve shaft  2 . 
     The first yoke  5  is installed in the yoke-mounting member  3 . The first yoke  5  has a circular magnet portion  5 A opposed to the circular portions of the magnet  4 , and an extending portion  5 B extending from the magnet portion  5 A to the circuit board installing space  3 C, and shaped like a letter L. The extending portion  5 B covers a Hall element  8  from above. The extending portion  5 B of the first yoke  5  leads a magnetic flux from the magnet  4  to the first Hall element  8 . 
     The second yoke  6  is installed in the yoke-mounting member  3 . The second yoke  6  has a circular magnet portion  6 A opposed to the circular portions of the magnet  4 , and an extending portion  6 B extending from the magnet portion  6 A to the circuit board installing space  3 C, and shaped like a letter L. The extending portion  6 B covers a Hall element  9  from above. The extending portion  6 B of the second yoke  6  leads a magnetic flux from the magnet  4  to the second Hall element  9 . 
     The third yoke  7  is installed in the yoke-mounting member  3 . The third yoke  7  has a circular magnet portion  7 A opposed to the circular portions of the magnet  4 . An extending portion  7 B extends from the magnet portion  7 A along the surface of a circuit board  10  on the partition portion  3 B of the yoke mounting portion  3 , which extending portion  7 B is installed below the extending portions  5 B,  6 B. 
     The first Hall element  8  for a first signal output means is installed on the circuit board  10 , which circuit board is positioned between the extending portion  5 B of the first yoke  5  and the extending portion  7 B of the third yoke  7 . The first signal is output proportional to a magnetic flux density through a first closed flux path which is comprised of the magnet  4 , the first yoke  5 , and the third yoke  7 . 
     The second Hall element  9  for a second signal output means is installed on the circuit board  10 , which stands between the extending portion  6 B of the second yoke  6  and the extending portion  7 B of the third yoke  7 . The second signal is output proportional to a magnetic flux density through a second closed flux path which is comprised of the magnet  4 , the second yoke  6 , and the third yoke  7 . 
     The circuit board  10  is installed in the circuit board installing space  3 C, which includes an insulating material such as a ceramic. The Hall elements  8 , 9  are positioned on the circuit board  10 . The circuit board  10  is connected to the end of more than one terminal  11 , which extends toward the connector  3 E. The circuit board  10  is connected to a signal processing circuit (not shown) by the terminal  11 . 
     The circuit installing space  3 C of the yoke-mounting member  3  is sealed with a cover  12 , which may be a resin plate. Packing  13  is installed between the cover  12  and the circuit installing space  3 C, which packing includes an elastic member. 
     A magnetic shielding plate  14  is buried in the partition portion  3 B of the yoke mounting member  3 , which interrupts a leakage flux and reduces the effect of a leakage magnetic field to the Hall elements  8 , 9 . 
     In the above-mentioned the rotation angle sensor, when the valve shaft  2  rotates to the throttle valve openings, the magnet  4  which is fixed on the valve shaft  2  also moves. Then, because each area ratio of the circular portion of the magnet  4  relative to the circular magnet portion  5 A or the circular portion of the magnet  4  relative to the circular magnet portion  6 A changes, the magnetic flux density through the yoke  5 , 6  changes. 
     Each Hall element  8 , 9  outputs a signal proportional to the magnetic flux density to the signal processing circuit through the circuit board  10  and terminal  11 . Therefore, the valve shaft opening is detected by the signal processing circuit. 
     Incidentally, in the above-mentioned rotation angle sensor, because the magnetic shielding plate  14  is buried in the partition portion  3 B of the yoke mounting member  3 , this requires preparations for many parts. Also, when the yoke-mounting member  3  is made, because the magnetic shielding plate  14  must be molded in the partition portion  3 B, it causes inconvenience in the workability. 
     In addition, the Hall elements  8 , 9  are contained on the circuit board  10  of the circuit installing space  3 C, which is located above the partition portion  3 B of the yoke mounting member  3 . When the yoke-mounting member  3  is mounted on the cylindrical fit portion  1 A of the throttle body  1 , it results in an undesirably increased size of the sensor. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide an improved rotation angle sensor which can reduce the effect of the leakage magnetic field and improve the detecting sensitivity of the throttle valve opening and be miniaturized by reducing the number of parts. 
     It is also an object of the invention to provide a yoke for a rotation angle sensor, which has a magnetic shielding plate and third yoke in one piece. 
     In order to achieve these and other objects, a rotation angle sensor is provided, including a casing and a magnet positioned in the casing. The magnet has a first magnetic pole end and a second magnetic pole end, and first and second yokes are positioned at a first predetermined space relative to the first magnetic pole end of the magnet. A third yoke positioned at a predetermined space relative to the second magnetic pole end of the magnet, the third yoke further positioned between the magnet and an extending portion of the first yoke, and also positioned between the magnet and an extending portion of the second yoke. A first signal output element is positioned between the third yoke and the extended portion of the first yoke, the first signal output element for outputting a first signal corresponding to an area ratio between the magnet and the first yoke. A second signal output element is positioned between the third yoke and the extended portion of the second yoke, the second signal output element for outputting a second signal corresponding to an area ratio between the magnet and the second yoke. A magnetic shielding portion is positioned above the magnet, wherein the magnetic shielding portion interrupts leakage magnet flux of the magnet, and wherein the magnetic shielding portion and the third yoke are integrally formed of a single-piece construction. 
     In a further aspect of the present invention, a yoke construction for a rotation angle sensor is provided, including a magnet has a first magnetic pole end and a second magnetic pole end. First yoke and second yokes-are positioned at a first predetermined space relative to the first magnetic pole end of the magnet. A third yoke has a circular magnet portion, which circular magnet portion of the third yoke is positioned at a second predetermined space relative to second magnetic pole end of the magnet. A magnetic shielding portion positioned above the magnet, the magnetic shielding portion has a substantially semicircular shape. 
     In a further aspect of the present invention, a yoke construction for a rotation angle sensor is provided, including a magnet has a first magnetic pole end and a second magnetic pole end. A first yoke and a second yoke are positioned at a first predetermined space relative to the first magnetic pole end of the magnet. A third yoke has a circular magnet portion, which circular magnet portion of the third yoke is positioned at a second predetermined space relative to second magnetic pole end of the magnet. A magnetic shielding portion is positioned above the magnet, and the magnetic shielding portion has a substantially U shape and includes a notch as a shaft inserting portion. 
     In a further aspect of the present invention, a rotation angle sensor is provided, including a casing, and a magnet is positioned in the casing, said magnet having a first magnetic pole end and a second magnetic pole end. First and second yokes are positioned at a first predetermined space relative to the first magnetic pole end of the magnet. A third yoke is positioned at a second predetermined space relative to the second magnetic pole end of the magnet. Each of the first and second yokes includes a circular magnet portion and an extending magnet portion. Each the extending magnet portion is positioned at a greater radial distance from the magnet than each the circular magnet portions, respectively. 
     As a result, the improved rotation angle sensor can reduce the effect of the leakage magnetic field and improve the detecting sensitivity of the throttle valve opening and be miniaturized by reducing the number of parts. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a vertical sectional view of the rotation angle sensor according to a first embodiment of the present invention. 
     FIG. 2 is a horizontal sectional view in the direction of arrows II—II FIG.  1 . 
     FIG. 3 is a perspective view of the first yoke, the second yoke, the third yoke, and the magnet according to the first embodiment of the present invention. 
     FIG. 4 is a plan view of the first yoke, the second yoke, the third yoke, and the magnet according to the first embodiment of the present invention. 
     FIG. 5 is a perspective view of the first yoke, the second yoke, the third yoke, and the magnet according to a second embodiment of the present invention. 
     FIG. 6 is a plan view of the first yoke, the second yoke, the third yoke, and the magnet according to the second embodiment of the present invention. 
     FIG. 7 is a perspective view of the first yoke, the second yoke, the third yoke, and the magnet according to a third embodiment of the present invention. 
     FIG. 8 is a perspective view of the first yoke, the second yoke, the third yoke, and the mag according to a fourth embodiment of the present invention. 
     FIG. 9 is a vertical sectional view of a rotation angle sensor according to a prior art. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A more detailed description of embodiments of the present invention is given below. A first embodiment shows a rotation angle sensor as shown in FIGS. 1-4. 
     A yoke-mounting member  21  forms the outside shape of the rotation angle sensor, which includes a casing in conjunction with throttle body  1 . The yoke mounting member  21  has a cylindrical portion  21 A opening in the downward direction, a partition portion  21 B covering on the top end of the cylindrical portion  21 A, a connector portion  21 C projecting from the outside diameter direction of the cylindrical portion  21 A. 
     A magnet  22  is installed in the cylindrical portion  21 A. The magnet  22  has magnetic poles in both sides of the lengthwise direction. Also, the magnet  22  has circular ended portions  22 A,  22 B in the lengthwise direction, parallel ended portions  22 C,  22 D in the width direction, and a through-Hall  22 E extending in the axial direction of the valve shaft  2 , as shown FIG.  2 . By inserting and crimping the projection end of a valve shaft  2  into the through-Hall  22 E, the magnet  22  is fixed to the valve shaft  2 . 
     A first yoke  23  is installed in the yoke-mounting member  21 . The first yoke  23  has a circular magnet portion  23 A extending at an angle, which has a constant clearance relative to the circular ended portion  22 A of the magnet  22 . The first yoke  23  also has an extending portion  23 B extending from the end of the circular magnet portion  23 A in a direction along the perimeter to a circular magnet portion  25 A of a third yoke  25 , as shown from FIGS. 2-4. The tip of the extending portion  23 B is positioned relative to the circular magnet portion  25 A of the third yoke  25  in the direction along the outside diameter. The extending portion  23 B of the first yoke  23  leads a magnetic flux from the magnet  22  to a first Hall element  27 . 
     A second yoke  24  is installed in the yoke-mounting member  21 . The second yoke  24  has a circular magnet portion  24 A extending at an angle, which has a constant clearance relative to the circular ended portion  22 A of the magnet  22 . The second yoke  24  also has an extending portion  24 B extending from the end of the circular magnet portion  24 A in a direction along the perimeter to the circular magnet portion  25 A of the third yoke  25 . The tip of the extending portion  24 B is positioned relative to the circular magnet portion  25 A of the third yoke  25  in the direction along the outside diameter. The extending portion  24 B of the second yoke  24  leads a magnetic flux from the magnet  22  to a second Hall element  28 . 
     The third yoke  25  is buried in the cylindrical portion  21 A of the yoke mounting member  21 , and is kept at a slight clearance to circular magnet portions  23 A,  24 A in the direction of the perimeter. The third yoke  25  has the circular magnet portion  25 A expanding approximately 180-degree. 
     When the central portion of the circular ended portion  22 A is positioned at a midpoint between the circular magnet portion  23 A and the circular magnet portion  24 A, a rotation angle ±⊖ of the magnet  22  (the valve shaft  2 ) shows a “0” point as shown FIG.  2 . When the magnet  22  rotates to the right, the rotation angle shows a positive direction (+⊖). When the magnet  22  rotates to the left, the rotation angle shows a negative direction (−⊖). The magnet  22  (the valve shaft  2 ) can rotate ±45-degree, and when the rotation angle ⊖ is +45 degree, it corresponds to a maximum opening of the throttle valve. 
     A magnetic shielding plate  26  and the third yoke  25  have a single-piece construction. The magnetic shielding plate  26  is coupled to one end of the circular magnet portion  25 A in the direction of the length, and forms a half-circle (a fan-shape). The magnetic shielding plate  26  reduces the effect of a leakage magnet flux to the outside by passing a leakage magnet flux from the magnet  22 . 
     The first Hall element  27  for a first signal output means is installed between the outside of the circular magnet portion  25 A of the third yoke  25  and the extending portion  23 B of the first yoke  23  as shown FIGS.  3 , 4 . The first signal is output proportional to a magnetic flux density through a first closed flux path which includes the magnet  22 , the first yoke  23 , and the third yoke  25 . 
     The second Hall element  28  for a second signal output means is installed between the outside of the circular magnet portion  25 A of the third yoke  25  and the extending portion  24 B of the second yoke  24 . The second signal is output proportional to a magnetic flux density through a second closed flux path which includes the magnet  22 , the second yoke  24 , and the third yoke  25 . 
     More than one terminal  29  extends in a connector portion  21 C of the yoke mounting member  21 , which is connected to the first Hall element  27  and the second Hall element  28  with a lead wire (not shown). 
     In the above-mentioned first embodiment, the rotation angle sensor has three poles which is comprised of the yokes  23 ,  24 , and  25 . When the valve shaft  2  rotates, the circular ended portion  22 A of the magnet  22  rotates within rotation angles ±⊖(±45-degree), which is also kept a constant clearance to the circular magnet portions  23 A,  24 A as shown FIG.  2 . The circular ended portion  22 A of the magnet  22  is positioned relative to the circular magnet portion  23 A, 24 A, and the whole of the circular ended portion  22 B is positioned to the circular magnet portion  25 A. Therefore, a magnet flux of the magnet  22  is lead through the first yoke  23  and the third yoke  25  to the first Hall element  27 , and through the second yoke  24  and the third yoke  25  to the second Hall element  28 . The first signal is output from the first Hall element  27  corresponding to the magnetic flux density through the yokes  23 ,  25 . The second signal is output from the second Hall element  28  corresponding to the magnetic flux density through the yokes  24 ,  25 . Furthermore, the signal processing circuit is connected to the outside by a connector portion  21 C, which outputs detecting signals corresponding to rotation angle±⊖ by manipulating the first signal and the second signal, and therefore can detect rotation angles±⊖ of the valve shaft  2 . 
     Also, in the above-mentioned first embodiment, the magnetic shielding plate  26  and the circular magnet portion  25 A of the third yoke  25  have a single-piece construction. Since the magnetic shielding plate  26  is buried in the partition portion  21 B of the yoke-mounting member  21 , this eliminates the need of the magnetic shielding plate  14  aside from the third yoke  7  as shown the prior art. This means a reduced number of parts, and improves the convenience in the workability. 
     On the other hand, because the magnetic shielding plate  26  can suppress the leakage flux of the magnet  22  to the first yoke  23  or the second yoke  24 , each of the first signal and the second signal from Hall elements  27 , 28  is not affected by fluctuations of the leakage flux. 
     Also, since the first Hall element  27  is installed between the outside of the circular magnet portion  25 A of the third yoke  25  and the extending portion  23 B of the first yoke  23 , and the second Hall element  28  is installed between the outside of the circular magnet portion  25 A of the third yoke  25  and the extending portion  24 B of the second yoke  24 , the magnetic shielding plate  26  can interrupt the effect of the leakage flux to the extending portion  23 B of the first yoke  23  and the extending portion  24 B of the yoke  24 , and can reduce the effect of the leakage flux to Hall elements  27 ,  28  for detecting rotation anglesie accurately. 
     Furthermore, since the first Hall element  27  is installed between the outside of the circular magnet portion  25 A of the third yoke  25  and the extending portion  23 B of the first yoke  23 , and the second Hall element  28  is installed between the outside of the circular magnet portion  25 A of the third yoke  25  and the extending portion  24 B of the second yoke  24 , the yoke mounting member  21  may be made thinner than the prior art, which installs Hall elements on the yoke mounting member. This means a reduction in size of the Hall of the rotation angle sensor. 
     In the second embodiment as shown FIGS. 5-6, the first yoke  31  has a circular magnet portion  31 A and an extending portion  31 B which extends from one end of the circular magnet portion  31 A to and along the outside of a circular magnet portion  33 A of the third yoke  33 . 
     The second yoke  32  has a circular magnet portion  32 A and an extending portion  32 B which extends from one end of the circular magnet portion  32 A to and along the outside of a circular magnet portion  33 A of the third yoke  33 . 
     The third yoke  33  has the circular magnet portion  33 A, which is kept at a slight clearance relative to the extending portions  31 B,  32 B in the direction along the perimeter. The third yoke  33  also has plate projections  33 B,  33 B, which extend from the circular magnetic portion  33 A in the direction to the perimeter of the circular magnet portion  32 A. Each of the plate projections  33 B,  33 B extends radially to the extending portion  31 B of the first yoke  31  or the extending portion  32 B of the second yoke  32 , offset in the axial direction. 
     A magnetic shielding plate  34  and the third yoke  33  have a single-piece construction. The magnetic shielding plate  34  is formed on the upper end of the circular magnet portion  33 A, and has a fan-shape. The magnetic shielding plate  34  reduces the effect of a leakage magnet flux to the outside by passing a leakage magnet flux from the magnet  22 . 
     A first Hall element  35  for a first signal output means is installed between the plate projection  33 B of the third yoke  33  and the extending portion  31 B of the first yoke  31 . The magnet flux detecting direction of the first Hall element  35  is installed in the direction of the axis. 
     A second Hall element  36  for a second signal output means is installed between the plate projection  33 B of the third yoke  33  and the extending portion  32 B of the second yoke  32 . The magnet flux detecting direction of the second Hall element  36  is installed in the direction of the axis. 
     In the above-mentioned second embodiment, the rotation angle sensor has similar effects as same as the first embodiment. Furthermore, because the magnetic pole direction of the magnet  22  goes straight to the magnet flux detecting direction of Hall elements  35 ,  36 , it can reduce the effect of the leakage magnet flux better than the first embodiment. 
     In a third embodiment shown in FIG. 7, a third yoke  41  has a circular magnet portion  41 A which is kept at a slight clearance relative to the extending portion  23 B of the first yoke  23  and the extending portion  24 B of the second yoke  24  along the direction of the perimeter. 
     A magnetic shielding plate  42  and the third yoke  41  have a single-piece construction. The magnetic shielding plate  42  is formed on the upper end of the circular magnet portion  41 A, which shielding plate has the shape of a letter “U” and has a notch which is a shaft inserting portion  42 A. The magnetic shielding plate  42  prevents leaking of the magnetic flux of the magnet  22  to the outside. 
     A first Hall element  43  for the first signal output means is installed between the circular magnet portion  41 A of the third yoke  41  and the extending portion  23 B of the first yoke  23 . 
     A second Hall element  44  for the second signal output means is installed between the circular magnet portion  41 A of the third yoke  41  and the extending portion  24 B of the second yoke  24 . 
     In the above-mentioned third embodiment, the rotation angle sensor has similar effects as same as the first embodiment. In addition, because the magnetic shielding plate  42  has the shaft-inserting portion  42 A, a valve shaft  2 ′ is fixed on the magnet  22 , and can be projected from the rotation angle sensor to the outside. Therefore, an open/close operation of the throttle valve can be made stable by installing a hysteresis generating structure on the top end of the throttle valve. 
     In a fourth embodiment shown in FIG. 8, the third yoke  51  has a circular magnet portion  51 A which is kept at a slight clearance relative to the circular magnet portion  31 A of the first yoke  31  and the circular magnet portion  32 A of the second yoke  32  in the direction of the perimeter. The third yoke  51  also has plate projections  51 B,  51 B extending from the circular magnet portion  51 A. 
     A magnetic shielding plate  52  and the third yoke  51  have a single-piece construction. The magnetic shielding plate  52  is formed on the upper end of the circular magnet portion  51 A, which shielding plate has the shape like a letter “U”, and has a notch which is a shaft inserting portion  52 A. The magnetic shielding plate  52  prevents from leaking of the magnetic flux of the magnet  22  to the outside. 
     A first Hall element  53  for the first signal output means is installed between the plate projection  51 B of the third yoke  51  and the extending portion  31 B of the first yoke  31 . 
     A second Hall element  54  for the second signal output means is installed between the plate projection  51 B of the third yoke  51  and the extending portion  32 B of the second yoke  32 . 
     In the above-mentioned fourth embodiment, the rotation angle sensor has similar effects as same as the second embodiment. In addition, because the magnetic shielding plate  52  has the shaft-inserting portion  52 A, a valve shaft  2 ′ fixed on the magnet  22 , which can be projected from the rotation angle sensor to the outside. Therefore, an open/close operation of the throttle valve can be made stable by installing a hysteresis generating structure on the top end of the throttle valve. 
     Further, instead of comprising of the throttle body  1  and the yoke mounting member  21  for the casing in the above-mentioned embodiments, the casing may include a bottom plate which acts as a lid on the cylindrical portion  21 A of the yoke mounting member  21 . In this case, an open/close lever is installed on the side of the yoke mounting member  21 , which can open/close relatively to the valve shaft  2 . 
     The entire contents of Japanese Patent Application No. TOKUGANHEI 10-088111, filed Mar. 17, 1998 is incorporated herein by reference. The foregoing description of preferred embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. These embodiments were chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents.