Abstract:
A detector for detecting a rotational angle of a gearshift lever. The detector includes a magnet that forms a magnetic flux in a predetermined direction along its surface. A magnetic resistance sensor generates a detection signal corresponding to the direction of the magnetic flux. The detected object is connected to the magnet or the magnetic resistance sensor. The magnet and the magnetic resistance sensor are rotated relatively to each other to generate the detection signal and obtain the rotational angle of the detected object. The magnetic resistance sensor is separated from an axis of rotation of the sensor or the magnet.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a rotational angle detector, and more particularly, to a rotational angle detector for detecting the rotational angle of, for example, a gearshift lever of an automobile.  
           [0002]    [0002]FIG. 1 is a schematic front view showing a prior art rotational angle detector  50 , and FIG. 2 is a cross-sectional view of the rotational angle detector  50 .  
           [0003]    The rotational angle detector  50  includes an annular magnet  51  rotated integrally with a gearshift lever (not shown). The magnet  51  is magnetized so that its magnetic flux extends in a direction perpendicular to the front and rear surfaces of the magnet  51 . In other words, the magnet  51  is polarized in the axial direction of the magnet  51  (direction perpendicular to the plane of FIG. 2). Accordingly, the magnetic flux extends upward or downward with respect to the plane of FIG. 2 at locations near the front and rear surfaces of the magnet  51 .  
           [0004]    A magnetic resistance sensor  52  is arranged at a position corresponding to the center of the magnet  51  to detect direction changes of the magnetic flux of the magnet  51 . When the gearshift lever is shifted and the magnet  51  is rotated by a predetermined angle, the magnetic resistance sensor  52  generates an analog output voltage in accordance with the direction of the magnetic flux, which changes in accordance with the rotational angle of the magnet  51 . More specifically, referring to FIG. 3, the analog output voltage has a waveform that is generally a sine wave. The linear portion of the output voltage wave is the detection range of the gearshift lever rotational angle.  
           [0005]    In the conventional rotational angle detector  50 , the linear portion of the analog output voltage waveform (sine wave) output from the magnetic resistance sensor  52  is short. Thus, the detection range of the rotational angle is less than 90°. The conventional rotational angle detector  50  thus cannot be employed if a detection range of 90° or more is required. Further, since a shaft connected with the gearshift lever is inserted through the middle of the magnet  51 , the positioning of the magnetic resistance sensor  52  along the axis of the magnet  51  is difficult.  
         SUMMARY OF THE INVENTION  
         [0006]    It is an object of the present invention to provide a rotational angle detector that enlarges the detection range and facilitates the positioning of the magnetic resistance sensor.  
           [0007]    To achieve the above object, in a first perspective, the present invention is a detector for detecting a rotational angle of a detected object. The detector includes a magnet having a surface. The magnet forms a magnetic flux in a predetermined direction along the surface. A magnetic resistance sensor generates a detection signal corresponding to the direction of the magnetic flux. The detected object is connected to one of the magnet and the magnetic resistance sensor, and the magnet and the magnetic resistance sensor are rotated relative to each other to generate the detection signal and obtain the rotational angle of the detected object. The magnetic resistance sensor is spaced from an axis of rotation of one of the sensor and the magnet.  
           [0008]    In a further perspective, the present invention is a detector for detecting a rotational angle of a detected object. The detector includes an annular magnet for forming a magnetic flux parallel to a predetermined radial direction of the magnet. A magnetic resistance sensor generates a detection signal corresponding to the direction of the magnetic flux. The detected object is connected to one of the magnet and the magnetic resistance sensor, and the magnet and the magnetic resistance sensor are rotated relatively to each other to generate the detection signal and obtain the rotational angle of the detected object. The magnetic resistance sensor is separated from an axis of rotation of one of the sensor and the magnet.  
           [0009]    In another perspective, the present invention is a detector for detecting a rotational angle of a detected object. The detector includes an annular magnet for forming a magnetic flux in a radial direction of the magnet. The magnet includes a first magnetic pole portion and a second magnetic pole portion located on the outer side of the first magnetic portion. The first magnetic pole portion has a north pole and a south pole, and the second magnetic pole portion has a south pole located in correspondence with the north pole of the first magnetic pole portion and a north pole located in correspondence with the south pole of the first magnetic pole portion. A magnetic resistance sensor generates a detection signal corresponding to the direction of the magnetic flux. The detected object is connected to one of the magnet and the magnetic resistance sensor, and the magnet and the magnetic resistance sensor are rotated relatively to each other to generate the detection signal and obtain the rotational angle of the detected object. The magnetic resistance sensor is separated from an axis of rotation of one of the sensor and the magnet.  
           [0010]    Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:  
         [0012]    [0012]FIG. 1 is a schematic front view showing a prior art rotational angle detector;  
         [0013]    [0013]FIG. 2 is a cross-sectional view showing the rotational angle detector of FIG. 1;  
         [0014]    [0014]FIG. 3 is a graph showing the relationship between the output voltage of a magnetic resistance sensor and the rotational angle of a magnet in the rotational angle detector of FIG. 1;  
         [0015]    [0015]FIG. 4A is a schematic front view showing a rotational angle detector according to a first embodiment of the present invention;  
         [0016]    [0016]FIG. 4B is a front view showing a magnetic resistance sensor of the rotational detector of FIG. 4A;  
         [0017]    [0017]FIG. 5A is a cross-sectional view showing the rotational angle detector of FIG. 4A;  
         [0018]    [0018]FIG. 5B is a side view showing the magnetic resistance sensor of the rotational angle detector of FIG. 4A;  
         [0019]    [0019]FIG. 6 is a graph showing the relationship between the output voltage of the magnetic resistance sensor and the rotational angle of a magnet in the rotational angle detector of FIG. 4A; and  
         [0020]    [0020]FIG. 7 is a circuit diagram of the magnetic resistance sensor. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    In the drawings, like numerals are used for like elements throughout.  
         [0022]    [0022]FIG. 4A is a schematic front view showing a rotational angle detector  11  according to a preferred embodiment of the present invention. The rotational angle detector  11  is arranged on a gearshift lever of an automobile to detect the position of the gearshift lever. FIG. 5A is a cross-sectional view showing the rotational angle detector  11 .  
         [0023]    The rotational angle detector  11  includes a magnet  12  magnetized in a predetermined direction, as shown by arrow H in FIG. 4A. The magnetization direction H is parallel to a center line CL.  
         [0024]    The magnet  12  is annular and has a central hole  13 . As shown by the broken lines of FIG. 5A, a shaft  14 , which is rotated when shifting the gearshift lever (not shown), is inserted through the hole  13 . The shift lever and the magnet  12  are rotated together with the shaft  14 .  
         [0025]    The magnet  12  is magnetized so that its magnetic flux F extends along the front surface  16   a  and rear surface  16   b  of the magnet  12 . In other words, the magnet  12  is polarized in the horizontal direction as viewed in FIG. 5A. The magnetic flux F of the magnet  12  extends along the front and rear sides of the magnet  12  from the left side to the right side, as viewed in FIG. 5A. Further, the magnetic flux F on the front and rear surfaces of the magnet  12  are parallel and extend in the direction of arrow H in FIG. 4A.  
         [0026]    [0026]FIG. 4A schematically shows the positional relationship between the north poles and the south poles of the magnet  12 . The magnet  12  includes an annular first magnetic pole portion  12   a  and an annular second magnetic pole portion  12   b , which extends about the first magnetic pole portion  12   a . The first magnetic pole portion  12   a  is defined at the inner side of the magnet  12 , and the second magnetic pole portion  12   b  is defined at the outer side of the magnet  12 .  
         [0027]    Half of the first magnetic pole portion  12   a  in the circumferential direction is polarized to the north pole, and the remaining half is polarized to the south pole. Half of the second magnetic pole portion  12   b  in the circumferential direction is polarized to the south pole, and the remaining half is polarized to the north pole. The south pole of the second magnetic pole portion  12   b  is located at the outer side of the north pole of the first magnetic pole portion  12   a . The north pole of the second magnetic pole portion  12   b  is located at the outer side of the south pole of the first magnetic pole portion  12   a . Referring to FIG. 5A, due to the positional relationship between the south and north poles in the magnetic pole portions  12   a ,  12   b , the magnetic field (magnetic flux F) formed on the front surface  16   a  of the magnet  12  is parallel to that formed on the rear surface  16   b  of the magnet  12 . FIG. 5A shows representative magnetic fluxes F.  
         [0028]    A magnetic resistance sensor  15  is located above one side (front surface  16   a ) of the magnet  12 , as viewed in FIG. 5A, at a position where the magnetic fluxes of the magnet  12  interlink. The magnetic resistance sensor  15  receives the magnetic flux F of the magnet  12  and generates a detection signal in accordance with the direction of the magnetic flux F. In the preferred embodiment, the magnetic resistance sensor  15  is arranged at a position spaced from the axis of the magnet  12 . More specifically, the magnetic resistance sensor  15  is opposed to the magnet  12  at a position located substantially midway between the outer circumference and inner circumference of the magnet  12 . In other words, the magnetic resistance sensor  15  is opposed to part of the magnet  12  at a location separated from the hole  13 .  
         [0029]    With reference to FIG. 7, the magnetic resistance sensor  15  includes four magnetic resistance elements R 1 , R 2 , R 3 , R 4  that are in full-bridged connection. The magnetic resistance elements R 1 -R 4  are each ferromagnetic and made of, for example, Ni—Co. Referring to FIGS. 4B and 5B, the magnetic resistance elements R 1 -R 4  are arranged at the side of the magnetic resistance sensor  15  that is closer to the inner circumference of the magnet  12 . As shown in FIG. 4B, the magnetic resistance elements R 2 , R 3  are arranged at an angle of 45° relative to a plane M 1  extending radially from the shaft  14 . The magnetic resistance elements R 1 , R 4  are arranged in another direction at an angle of 45° relative to the plane M 1 . As shown in FIG. 5B, the magnetic resistance elements R 1 , R 2  are arranged at an angle of 45° relative to a plane M 2  extending perpendicular to the axis of the shaft  14 . The magnetic resistance elements R 3 , R 4  are arranged in another direction at an angle of 45° relative to the plane M 2 .  
         [0030]    When the gearshift lever is shifted, the magnet  12  is rotated by a predetermined angle relative to the magnetic resistance sensor  15 . This changes the direction of the interlinking magnetic fluxes F relative to the magnetic resistance sensor  15 . The magnetic resistance sensor  15  generates an analog output voltage ΔV based on the change in the direction of the interlinking fluxes F. The output voltage ΔV is the differential voltage of the node potential between the resistance elements R 1 , R 2  and the node potential between the resistance elements R 3 , R 4 .  
         [0031]    With reference to FIG. 6, the waveform of the analog output voltage ΔV relative to the rotational angle of the magnet  12  is substantially a sine wave. The linear portion of the output voltage waveform corresponds to the detection range of the gearshift lever rotational angle. Referring to FIG. 4A, the rotational angle of the gearshift lever is set to 0° when the middle of the north pole of the first magnetic pole portion  12   a  or the middle of the south pole of the second magnetic pole portion  12   b  is aligned with the middle of the magnetic resistance sensor  15 . In other words, the rotational angle of the gearshift lever is set to 0° when the center line CL of the magnet  12  is aligned with a center line CS of the magnetic resistance sensor  15 .  
         [0032]    Referring to FIG. 6, the output voltage ΔV is detected at a range exceeding ±45° from rotational angle 0°. In other words, the detection range is greater than 90°. In FIG. 6, “P” indicates that the gearshift lever is in a parking position, “R” indicates that the gearshift lever is in a rear drive position, “N” indicates that the gearshift lever is in a neutral position, and “D” indicates that the gearshift lever is in a drive position.  
         [0033]    The advantages of the rotational angle detector  11  of the preferred embodiment are discussed below.  
         [0034]    (1) The magnet  12  of the rotational angle detector  11  is polarized in the horizontal direction. Thus, in comparison with the conventional magnet that is polarized in the vertical (axial) direction, the range in which the direction of the magnetic flux F of the magnet  12  relative to the magnetic resistance sensor  15  can be changed is greater. Accordingly, the sine wave showing the relationship between the output voltage ΔV of the magnetic resistance sensor  15  and the rotational angle of the magnet  12  is distorted, and an output voltage waveform having a long linear portion is obtained. As a result, the detection range of the magnetic resistance sensor  15  is enlarged.  
         [0035]    (2) The magnetic resistance sensor  15  of the rotational angle detector  11  is located at a position spaced from the hole  13 , which extends through the magnet  12 . Thus, the magnetic resistance sensor  15  does not interfere with the shaft  14  that is inserted through the hole  13 . This easily provides space for the magnetic resistance sensor  15  and facilitates the installation of magnetic resistance sensor  15 .  
         [0036]    (3) The first magnetic pole portion  12   a  and the second magnetic pole portion  12   b  are arranged about the axis of the magnet  12 . Thus, the positional relationship between the north pole and the south pole does not change regardless of whether the magnet  12  is engaged with the shaft  14  from its rear side or front side. This prevents the magnet  12  from being installed in the wrong direction.  
         [0037]    It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the present invention may be embodied in the following forms.  
         [0038]    A casing made of a ferromagnet, such as steel, may cover the magnet  12 . In this case, the casing reduces the influence of external magnetic fields on the magnet  12  and further stabilizes the detection of the rotational angle of the magnet  12 .  
         [0039]    The magnet  12  may be fixed, and the magnetic resistance sensor  15  may be rotated.  
         [0040]    The magnetic resistance sensor  15  may be arranged proximate to the inner circumference or outer circumference of the magnet  12 .  
         [0041]    The magnetic resistance elements R 1 -R 4  may be arranged on the side of the magnetic resistance sensor  15  that is closer to the outer circumference of the magnet  12 .  
         [0042]    The magnet  12  may have an arcuate form.  
         [0043]    The present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.