Abstract:
A rotation angle sensor includes a rotatable magnet, at least one yoke located at a position to confront a magnetic pole, and a magnetic sensing device to sense magnetic flux density varying in accordance with a confronting area between the yoke and the magnet. The yoke is electrically connected with the magnetic sensing device through a nonmagnetic conductor.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a rotation angle sensor sensing a rotation angle of a rotary member, and more specifically to a rotation angle sensor sensing a throttle valve opening and an accelerator pedal opening of a vehicular engine. 
   U.S. Pat. No. 5,798,639 (corresponding to Published Japanese Patent Application Kokai No. H07(1995)-260412) shows a rotation angle sensor including a magnetic circuit and an electric circuit. The magnetic circuit is composed of a magnet provided in a rotary shaft rotating in accordance with a throttle valve opening, and yokes surrounding the magnet nearly over the full circumference. The electric circuit includes a magnetoelectric transducing element, such as a Hall effect device, disposed between the yokes, and a signal processing circuit. 
   The Hall effect device senses magnetic flux density varying in accordance with the rotation angle, in the magnetic circuit, and the signal processing circuit determines the rotation angle by processing a signal from the Hall effect device. 
   SUMMARY OF THE INVENTION 
   In this rotation angle sensor, the magnetic circuit of the yokes and the electric circuit of the magnetoelectric transducing element are isolated electrically by a structure retaining member made of nonmagnetic material such as high-polymer resin. In this arrangement, the magnetic circuit is not held equal in electric potential with respect to the electric circuit. 
   Therefore, an electric potential difference is generated in the magnetic circuit by electric charges stored in the magnetic circuit. This electric potential difference may cause electron generation or variation in positive hole density in the magnetoelectric transducing element and the signal processing circuit in the electric circuit. Consequently, operations of magnetoelectric transducing element and the signal processing circuit are changed, and the characteristic of the device is changed. 
   When, for example, electrons are induced in an N-type semiconductor region by this electric potential difference, the resistance of the N-type semiconductor region decreases. When electrons are induced in a P-type semiconductor region by this electric potential difference, the resistance of the P-type semiconductor region increases. In some cases, an inversion layer may be generated. 
   It is an object of the present invention to provide a rotation angle sensor which suppresses a change of the output characteristic, and enhances reliability. 
   According to the present invention, a rotation angle sensor comprises: a magnet rotatable about a rotation axis; a yoke located at a position to confront a magnetic pole of the magnet radially, and forming a magnetic circuit with the magnet; a magnetic sensing device to sense magnetic flux density varying in accordance with a confronting area between the yoke and the magnet; and a nonmagnetic conductor electrically connecting the yoke and the magnetic sensing device. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1A and 1B  are schematic views showing two different examples of a rotation angle sensor according to a first embodiment of the present invention. 
       FIG. 2  is a perspective view showing the rotation angle sensor of  FIG. 1   
       FIG. 3  is a plan view showing the rotation angle sensor shown in  FIG. 2 . 
       FIG. 4  is a sectional view taken along a section line F 4 -F 4  of  FIG. 2 . 
       FIG. 5  is a perspective view showing a rotation angle sensor according to a second embodiment of the present invention. 
       FIG. 6  is a plan view showing the rotation angle sensor shown in  FIG. 5   
       FIG. 7  is a sectional view taken along a section line F 7 -F 7  of  FIG. 5 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1A and 1B  show a rotation angle sensor according to a first or second embodiment of the present invention. This rotation angle sensor includes a Hall effect device  11  as a magnetoelectric transducing element or magnetic sensing device, and a yoke structure including yokes  12  and  13  for introducing magnetic flux generated by a magnet (not shown in  FIGS. 1A and 1B ) into the Hall effect device  11  disposed, between the yokes  12  and  13 . 
   The Hall effect device  11  is connected with a low electric potential side of power supply  101 , as shown in  FIG. 1A . Alternatively, the Hall effect device  11  is connected with a high electric potential side of power supply  102 , as shown in  FIG. 1B . The yokes  12  and  13  are connected to the low or high electric potential side of power supply  101  or  102  by a conductor  14  including at least one portion made of nonmagnetic conductive material such as copper or aluminum. Therefore, the Hall effect device  11  and each yoke  12  or  13  are electrically short-circuited, so that a electric potential difference therebetween is eliminated. At the same time the Hall effect device  11  and the yokes  12  and  13  are isolated magnetically. 
   The Hall effect device  11  is mounted on a lead frame  15 , and electrically connected to the lead frame  15  by wire bonding  16 . The Hall effect device  11  is molded in a resin package  17 . 
     FIGS. 2-4  show more in detail the connection between a yoke structure and a low or high electric potential side of power supply by a nonmagnetic conductor according to the first embodiment. This rotation angle sensor shown in  FIGS. 2˜4  is composed of a magnet  20 , a yoke structure including a pair of yokes  21  and  22 , a Hall effect device  23  serving as a magnetic sensing device, and a printed circuit board  25 . 
   The magnet  20  is in the form of a rectangle or a oval shape (or a shape of a racetrack). The magnet  20  extends from one end to the other in the lengthwise direction, and has magnetic poles in both ends, respectively. The magnet  20  produces magnetic flux to be sensed by the Hall effect device  23 . 
   The yoke structure forms the magnetic circuit with the magnet  20 . The yoke  21  is made of magnetic material such as pure iron (SUYB, SUYP) or Fe-Ni alloy, and arranged to conduct the magnetic flux generated by the magnet  20  to the Hall effect device  23 , as described later. The yoke  21  of this example includes a first pole piece portion  21 A and a first overhang portion  21 B. The first pole piece portion  21 A is in the form of an arcuate plate. The first pole piece portion  21 A confronts the magnet  20  radially across a predetermined constant radial gap. The first overhang portion  21 B is in the form of a flat plate, and extends radially inwardly from the first pole piece portion  21 A over the magnet  20 . The first overhang portion  21 B covers a part of the magnet  20  from above, and projects beyond the axis of the magnet  20 . The first overhang portion  21 B confronts the magnet  20  axially across a predetermined constant axial gap in the direction of the axis of the magnet  20 . 
   The yoke  22  is made of the magnetic material like the yoke  21 , located at a position diametrically opposite to the position of the yoke  21  to form the magnetic circuit, and arranged to conduct the magnetic flux generated by the magnet  20  to the Hall effect device  23 , as described later. Like the yoke  21 , the yoke  22  includes a second pole piece portion  22 A and a second overhang portion  22 B. The second pole piece portion  22 A is in the form of an arcuate plate. The second pole piece portion  22 A confronts the magnet  20  radially across a predetermined constant radial gap. The second overhang portion  22 B in the form of a flat plate extends radially inwardly from the second pole piece portion  22 A across the axis of the magnet  20 . The second overhang portion  22 B confronts the magnet  20  axially at a predetermined constant axial gap in the direction of the axis of the magnet  20 . 
   The second pole piece portion  22 A confronts the first pole piece portion  21 A diametrically across the magnet  20 . Each of the first and second pole piece portions  21 A and  22 A is curved in the form of a circular arc having a predetermined radius of curvature with respect to the rotation axis of the magnet  20 . Each pole piece portion  21 A or  22 A extends circumferentially around the axis of the magnet  20  through a substantially equal angle. In a cross section, each of the first and second pole piece portions  21 A and  21 B is in the form of a circular arc, and the angle subtended at the center by the arc of the second pole piece portion  22 A is substantially equal to that of the first pole piece portion  21 A. 
   The second overhang portion  22 B extends radially inwardly from the upper end of the second pole piece portion  22 A, like the first overhang portion  21 B, beyond the position of the axis of the magnet  20 , and overlaps the first overhang portion  21 B across a predetermined axial gap  26 . The Hall effect device  23  is disposed axially between the first and second overhang portions  21 B and  22 B, as best shown in  FIG. 4 . 
   The Hall effect device  23  is a component of an internal electric circuit. The Hall effect device  23  is mounted on a printed circuit board  25 , and disposed within the axial gap  26  between the first overhang portion  21 B below and the second overhang portion  22 B above. The Hall effect device  23  senses the magnetic flux in a direction parallel to the rotation axis of the magnet  20 , and perpendicular to the magnetizing direction of the magnet  20 . The Hall effect device  23  outputs a sensor signal proportional to the magnetic flux density in the magnetic circuit composed of the magnet  20 , and the yokes  21  and  22 . The Hall effect device  23  is connected to a signal processing circuit (not shown). The signal processing circuit processes the sensor signal indicative of the magnetic flux density introduced by the yokes  21  and  22 , and thereby determines the rotation angle. 
   The printed circuit board  25  supports the Hall effect device  23  at the position between the yokes  21  and  22 , as mentioned above. Moreover, the signal processing circuit (not shown) is formed on or in the printed circuit board. The board  25  is formed with a slot passing through the board  25 . The slot is curved in conformity with the curvature of the second pole piece portion  22 A of the yoke  22 , and arranged to receive the pole piece portion  22 A. The second pole piece portion  22 A passes through the slot of the board  25 . The second pole piece portion  22 A of the yoke  22  is fit in the slot so as to pass through the board  25 . 
   A conductive pattern  27  is formed on the printed circuit board  25 . In this example, the conductive pattern  27  includes an upper portion formed on a surface of the board  25 , and an inner portion formed within the slot, on inner side wall surfaces defining the slot. The upper portion of the conductive pattern  27  of this example is formed on the upper surface of the board  25 , in a region fringing the slot. A conductive pattern  28  is formed on the lower surface or back surface of the board  25 . The conductive pattern  28  is similar in the surface shape to the first overhang portion  21 B, as shown in  FIGS. 2 and 3 . The conductive pattern  28  confronts the upper surface of the first overhang portion  21 B. 
   The conductive patterns  27  and  28  are made of a nonmagnetic conductive material such as copper or aluminum. The conductive pattern  27  is electrically connected to the second pole piece portion  22 A of the yoke  22  inserted through the slot of the board  25  by, for example, one of welding, clamping, soldering, wire bonding, and nonmagnetic conductive adhesive. The conductive pattern  27  is connected to a wiring or interconnection pattern (not shown) formed on the upper surface of the printed circuit board  25 . The conductive pattern  27  is connected, through the wiring pattern, with the low electric potential side of power supply  101  or the high electric potential side of power supply  102  of the Hall effect device  23 . Therefore, the yoke  22  is electrically connected, through the conductive pattern  27  and the wiring pattern, to the low or high electric potential side of power supply  101  or  102  of the Hall effect device  23 . 
   The conductive pattern  28  is electrically connected through a through hole  29  formed in the printed circuit board  25 , to the wiring pattern on the upper surface of the board  25 , by, for example, one of welding, clamping, soldering, wire bonding, and nonmagnetic conductive adhesive. The through hole  29  extends through the board  25  from the lower surface to the upper surface of the board  25 . The wiring pattern is connected to the low or high electric potential side of power supply  101  or  102  connected with the Hall effect device  23 . Therefore, the yoke  21  is electrically connected, through the conductive pattern  28  and the wiring pattern, to the low or high electric potential side of power supply  101  or  102  of the Hall effect device  23 . 
   The yokes  21  and  22  are connected to the identical electric potential of power supply connected to the Hall effect device  23 . Therefore, when the yoke  21  is connected to the low electric potential side of power supply  101 , the yoke  22  is also connected to the low electric potential side of power supply  101 . When the yoke  21  is connected to the high electric potential side of power supply  102 , the yoke  22  is also connected to the high electric potential side of power supply  102 . Moreover, the signal processing circuit is connected to the low or high electric potential side of power supply  101  or  102  of the Hall effect device  23 . 
   In this arrangement, the yokes  21  and  22  guides the magnetic flux generated by the magnet  20 , to the Hall effect device  23 . The Hall effect device  23  generates the sensor signal indicative of the magnetic flux density introduced into the Hall effect device  23 . The sensor signal is proportional to the magnetic flux density. This rotation angle sensor can determine the rotation angle of the magnet  20 , i.e., the rotation angle of the rotary shaft rotating as unit with the magnet, by processing the sensor signal. 
   As described above, according to the first embodiment, the magnetic circuit of the yokes  21  and  22  is connected, by the nonmagnetic conductor ( 14 ,  27 ,  28 ), with the low or high electric potential side of power supply  101  or  102  of the electric circuit including the Hall effect device  23 . Therefore, the arrangement of the nonmagnetic conductor can act to eliminate an electric potential difference between the magnetic circuit and the electric circuit, and at the same time isolates the yokes and the magnetic sensing device magnetically. Therefore, this arrangement can protect the magnetoelectric transducing element from electrostatic destruction, and prevent resistance change and characteristic change of a semiconductor device due to electron generation or variation in positive hole density in the electric circuit. 
   The nonmagnetic conductor connects the magnetic circuit and the electric circuit by using one of welding, clamping, soldering, wire bonding, and nonmagnetic conductive adhesive. Therefore, this rotation angle sensor can ensure both the proper operation of the magnetic circuit and the electrical connection, without incurring magnetic interference. 
   The magnetoelectric transducing element can be electrically shielded by the magnetic circuit connected to a fixed electric potential. Therefore, this rotation angle sensor can prevent the accuracy in the measurement from being lowered by external electric field. 
     FIGS. 5˜7  show a rotation angle sensor according to a second embodiment of the present invention. In the second embodiment, a printed circuit board (PC board)  51  supporting the Hall effect device  13  has an arcuate end which abuts on the curved surface of the second pole piece portion  22 A of the yoke  22  with the interposition of a conductive pattern  52  of a nonmagnetic conductive material such as copper or aluminum. The arcuate end of the board  51  is formed in an arcuate shape fitting to the arcuate second pole piece portion  22 A. The conductive pattern  52  is formed on the end face of the arcuate end of the board  51 . The conductive pattern  52  is electrically connected with the second pole piece portion  22 A by one of welding, clamping, soldering, wire bonding, and nonmagnetic conductive adhesive. In the other points, the rotation angle sensor of the second embodiment is substantially identical to the sensor according to the first embodiment. The conductive pattern  52  is electrically connected to the wiring pattern formed on the surface of the board  51 , like the conductive patterns  27  and  28 . The wiring pattern is connected with the low or high electric potential side of power supply  101  or  102  connected with the Hall effect device  23 . Therefore, the conductive pattern  52  is electrically connected to the low or high electric potential side of power supply connected to the Hall effect device  23 . The conductive pattern  52  may include a first portion formed on the upper surface of the board  25  and a second portion formed on the end face of the board  25 , like the conductive pattern  27 . 
   The yokes  21  and  22  may be connected with the Hall effect device  23  by the nonmagnetic conductor printed directly on a structural member, such as a circuit board, of the electric circuit or the magnetic circuit. It is possible to reduce a electric potential difference between the yokes  21  and  22 , and the electric circuit, by taking a low electric potential side of power supply or a high electric potential side of power supply from a signal processing circuit arranged to take power from a generator (not shown) or a storage battery (not shown) connected with the yokes  21  and  22 . The number of Hall effect devices is not limited to one. The rotational angle sensor may includes two or more Hall effect devices. 
   This application is based on a prior Japanese Patent Application No. 2003-421036. The entire contents of the prior Japanese Patent Application No. 2003-421036 with a filing date of Dec. 18, 2003 are hereby incorporated by reference. 
   Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art in light of the above teachings. The scope of invention is defined with reference to the following claims.