Abstract:
A rotation angle detector for detecting rotation angle of a rotator to be measured is provided. The detector includes a magnet which is fixed to the rotator to be measured and is rotated with the rotator to be measured and plural magnetic detection means respectively arranged at a prescribed angle, for detecting intensity of magnetic field generated by the magnet and outputting signals of electric charge based on the intensity of magnetic field. The detector further includes drive means for driving the plural magnetic detection means, where the drive means is capable of simultaneously changing magnetic sensitivities of the plural magnetic detection means in the same ratio. The detector further includes rotation angle calculation means for calculating rotation angle of the rotator to be measured based on signals output from the plural magnetic detection means.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a US national stage filing of patent cooperation treaty (PCT) Appln. No. PCT/JP2007/067783 (WO2008/050550), filed Sep. 13, 2007, which claims priority to Japanese patent application No. 2006-289881, filed on Oct. 25, 2006, the entire content of which are incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    This invention relates to a rotation angle detector for detecting rotation angle of a rotator to be measured. Especially, this invention relates to the rotation angle detector in which effect of disturbance factor such as change of temperature or the like, on output signals of plural magnetic detection means or the like, can be reduced. 
       BACKGROUND ART 
       [0003]    Conventionally, as a rotation angle detector, the device is developed into which a magnet fixed to a rotator and magnetic detectors for detecting strength of the magnet are assembled, and, by rotating the rotator with the magnet relatively to the magnetic detection means, the rotation angle is detected, and which is utilized in various fields, for example, engine of vehicle, steering wheel, DC motor, or the like. Especially, the rotation angle detector in which hall elements are used as magnetic detection means, is developed and utilized. 
         [0004]    And it is known that, in the magnetic detection means, magnetic strength to be detected is considerably varied by change of temperature or the like. Accordingly, in the rotation angle detector in which such magnetic detection means are utilized, the rotation angle to be detected has been affected by accident error caused by change of temperature or the like. Therefore, the rotation angle detector in which the rotation angle is detected without being affected by the change of temperature or the like, has been proposed. 
         [0005]    In Patent document 1, there is proposed a rotation angle sensor including a drive circuit in which drive currents of hall elements are respectively controlled by applying similar constant currents as drive currents to the two hall elements, so that signal ratio of signals detected by each of hall elements is maintained constant. 
         [0006]      FIG. 5  shows the drive circuit of the hall elements which are provided in a rotation angle sensor proposed in Patent document 1. As shown in  FIG. 5 , the hall voltages of the two hall elements  34   a  and  34   b  are respectively detected by drive detection circuits  50   a  and  50   b.  And the drive detection circuits  50   a  and  50   b  respectively comprise hall element drive part  51 , hall voltage detection part  52  and detected voltage amplifying part  53 . 
         [0007]    Patent document 1: Japanese Patent Application Publication Hei11-295022 
       DISCLOSURE OF THE INVENTION 
     Problem to be Solved 
       [0008]    However, in the Patent Document 1, since, as shown in  FIG. 5 , in the hall element drive part  51 , the drive current values of the two hall elements  34   a  and  34   b  are determined by resistances R 51   a  and R 51   b,  there has been a problem that strictly equal current values can hardly be applied to the two hall elements  34   a  and  34   b  respectively because of the difference of initial resistance values caused by variation of parts of resistances  51   a  and  51   b.  Furthermore, there has been a problem that, since effect on the resistance R 51   a  and R 51   b  and Op-Amp Circuits (operational amplifier circuits) A 51   a  and A 51   b  caused by change of temperature are different from each other, the signal ratio of signals detected by the hall elements  34   a  and  34   b  can hardly be constant. 
         [0009]    The present invention is made for solving these problems described above, whose purpose is to provide a rotation angle detector in which plural magnetic detection means such as hall elements are serially connected and, by applying the same drive current to each of the magnetic detection means, accident error of detection can be eliminated. 
       Means to Solve the Problem 
       [0010]    To solve the conventional problems described above, the invention described below is provided. 
         [0011]    A rotation angle detector according to the first embodiment of the present invention is the rotation angle detector for detecting the rotation angle of the rotator to be measured, comprising: 
         [0012]    a magnet which is fixed to a rotator to be measured and is rotated with the rotator to be measured, 
         [0013]    plural magnetic detection means respectively arranged at a prescribed angle, for detecting intensity of magnetic field generated by the magnet and outputting signals of electric charge based on the intensity of magnetic field, 
         [0014]    drive means for driving the plural magnetic detection means, capable of simultaneously changing magnetic sensitivities of the plural magnetic detection means in the same ratio, and 
         [0015]    rotation angle calculation means for calculating rotation angle of the rotator to be measured based on the signals output from the plural magnetic detection means. 
         [0016]    In use of this, the signals whose absolute values are equal can be output from magnetic detection means such as the plural hall elements included in the rotation angle detector. Accordingly, accident error of rotation angle detection caused by disturbance such as change of temperature, variation of electric source, or the like can be eliminated. 
         [0017]    A rotation angle detector according to the second embodiment of the present invention is the rotation angle detector according to the first embodiment of the present invention, wherein, in the drive means, plural magnetic detection means are serially connected and the drive currents of all of the magnetic detection means are maintained equal constant values. 
         [0018]    In use of this, the same drive currents can be applied to the magnetic detection means such as the plural hall elements included in the rotation angle detector. Accordingly, effect on the plural magnetic detection means caused by the disturbance such as change of temperature, variation of electric source, or the like can be the same, and absolute values of the signals output by the plural magnetic detection means can be equal. Namely, the accident error in detection of rotation angle caused by the disturbance such as change of temperature, variation of electric source, or the like can be eliminated. 
         [0019]    A rotation angle detector according to the third embodiment of the present invention is the rotation angle detector according to the first or second embodiment of the present invention whose drive means comprises signal adjustment means for adjusting the signals output from the magnetic detection means into optimized signals within a prescribed range by changing the drive currents. 
         [0020]    In use of this, the same arbitrary signal gain can be provided to the plural magnetic detection means included in the rotation angle detector from outside. Namely, by adjusting the signals output from the magnetic detection means into optimized signals, the accident error can be eliminated. 
         [0021]    A rotation angle detector according to the fourth embodiment of the present invention is the rotation angle detector according to the third embodiment of the present invention whose signal adjustment means changes all of the drive currents of the plural magnetic detection means into equal current values by changing one reference voltage for preset reference resistance. 
         [0022]    In use of this, since the reference voltage is changed, the signals output from the magnetic detection means can be adjusted into optimized signals. 
         [0023]    A rotation angle detector according to the fifth embodiment of the present invention is the rotation angle detector according to the fourth embodiment of the present invention, whose reference voltage is generated by rectifying pulse width modulation signal. 
         [0024]    In use of this, by converting pulse width modulation signal (PWM signal) as digital signal generated in use of microcomputer or the like, into analogue signal, desirable reference voltage can easily be generated. 
         [0025]    For example, when a magnet made from NdFeB (neodymium, ferrous, boron) is used as the magnet; the magnet is demagnetized by around −0.1%/° C. accompanied by the change of temperature. And sensitivities of hall elements also are decreased by around −0.1%/° C. Accordingly, when they are used in the temperature ambience within the range of 120° C., between −40° C. and 80° C., they are respectively changed by around 12%, and the change of the signal intensities need to be expected by around 20%. 
         [0026]    On the other hand, dynamic range needs to be optimized in signal processing. Namely, signal amplitude obtained as electric signal is constantly optimized. In the case that AD conversion (analogue signal to digital signal) is done by computer, resolution comes to a problem. 
         [0027]      FIG. 6  shows one example of the output signal of the hall element when the magnet is rotated. The rotation angle of magnet θ is shown in horizontal axis and the output signal V of the hall element is shown in vertical axis. In the case of 10 bit AD conversion, since, when V in  FIG. 6  is input to AD conversion in full range, it comes to the full range with amplitude of 90°, resolution of 90° C./1024=0.09° is obtained. However, in the case that the signal amplitude is increased or deceased by the change of temperature descried above, upper and lower parts of sinusoidal wave are lost (range over) when it is increased. And, when it is decreased, apparent full range is decreased, for example, when the signal amplitude is changed by 80%, amplitude of 90/1024/0.8=0.11° is obtained, and measurement accuracy is reduced. 
         [0028]    Accordingly, it is preferable that signal gain is optimized correspondingly to the change of temperature under the operational environment of the rotation angle detector. Since the increase and decrease of the magnetic force and sensitivities of hall elements caused by the change of temperature are physically determined, the settings of sensitivities need to be set correspondingly to the temperature in use of temperature measurement means provided in the rotation angle detector. 
         [0029]    A rotation angle detector according to the sixth embodiment of the present invention is the rotation angle detector according to any one from the first to fifth embodiment of the present invention, wherein the magnetic detection means consists of the hall elements and the drive means consists of the means to drive the hall elements with constant currents. 
       EFFECT OF THE INVENTION 
       [0030]    According to the present invention, the same drive currents can be output to the magnetic detection means such as the plural hall elements included in the rotation angle detector. Accordingly, effects of disturbance such as change of temperature, variation of electric source, or the like on the plural magnetic detection means can the same, and the signal ratio of signals output from the plural magnetic detection means can be constant. Namely, the accident error in detection of rotation angle caused by the disturbance such as change of temperature, variation of electric source, or the like can be eliminated. 
         [0031]    Furthermore, the same arbitrary signal gain can be provided to the plural magnetic detection means included in the rotation angle detector from outside. Namely, by adjusting signals output from the magnetic detection means into optimized signals, the accident error can be eliminated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]      FIG. 1  shows one example of exterior configuration of the rotation angle detector to which the present invention is applicable; 
           [0033]      FIG. 2  shows the output signals of the hall elements  13   a  and  13   b  shown in  FIG. 1 ; 
           [0034]      FIG. 3  shows one example of the drive circuit of the hall elements  13   a  and  13   b;    
           [0035]      FIG. 4  shows one example of exterior configuration of another rotation sensor to which the present invention is applicable; 
           [0036]      FIG. 5  shows the drive circuit of the hall elements provided in the conventional rotation angle sensor; and 
           [0037]      FIG. 6  shows one example of the output signal of the hall element. 
       
    
    
     EXPLANATION OF THE REFERENCE NUMERALS 
       [0038]      10 ,  30  . . . rotation sensor 
         [0039]      11 ,  31  . . . rotator 
         [0040]      12  . . . ring magnet 
         [0041]      13   a,    13   b,    33   a,    33   b . . .  hall element 
         [0042]      14 ,  34  . . . rotation center axis 
         [0043]      20 ,  40  . . . drive circuit 
         [0044]      21  . . . hall element drive part 
         [0045]      22  . . . reference voltage adjustment part 
         [0046]      23  . . . operational amplifier 
         [0047]      24  . . . reference resistance 
         [0048]      25  . . . MCU (Micro Control Unit) 
         [0049]      26  . . . LPF (low pass filter) 
         [0050]      32  . . . disk magnet 
         [0051]      50  . . . rotation angle calculation part 
       DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0052]    One embodiment of the present invention is explained referring to the figures. However, the explanations described below are only for explanation, and range of the present invention is not limited to them. Accordingly, although it is possible for person having ordinary skill in the art to apply embodiments in which each or all of the components are substituted for the equivalents, these embodiments are included in the range of the present invention. 
         [0053]      FIG. 1  shows one example of exterior configuration of the rotation angle detector to which the present invention can be applied. In the description below, the rotation angle detector is called as a rotation sensor. 
         [0054]    As shown in  FIG. 1 , the rotation sensor  10  comprises a ring magnet  12 , hall element  13   a,  hall element  13   b,  drive circuit  20  (not depicted in the figure) and rotation angle calculation part  50  (not depicted in the figure), for detecting the rotation angle of the rotator  11 . The ring magnet  12  is magnetized in the circle direction with two pairs of North Pole and South Pole alternately formed with each other. And the ring magnet  12  is fixed to the rotator  11  and is rotated with the rotator  11 . In this sensor, a shaft which is vertical to the magnetic sensitive surface of the ring magnet  12  is fixed in the center of the ring magnet  12  in the diameter direction, as a rotation center axis  14 . Although the ring magnet  12  is magnetized in the circle direction in this case, the ring magnet  12  can be magnetized also in the parallel direction to the rotation center axis (Z axis direction). 
         [0055]    The hall elements  13   a  and  13   b  are arranged so that the change of intensity of magnetism in the vertical direction to the diameter direction of the ring magnet  12  can be detected. In this sensor, the hall elements  13   a  and  13   b  are arranged outside of the circle of the ring magnet  12  so that normal to the rotation center axis  14  on the magnetic sensitive surface substantially is declined by an angle of 45°. 
         [0056]    In this case, the hall voltage V generated to the hall elements arranged in the magnetic field is expressed by the equation (1) described below, with the hall sensitivity which is determined by hall coefficient, shape of the hall elements, or the like denoted by α, with magnetic flux density in the magnetic field generated by the magnet or the like denoted by B, and with drive current of the hall elements denoted by I. 
         [0000]        V=α×B×I   (1) 
         [0057]    Namely, in the case that the hall sensitivity α is constant, the hall voltage V is proportionate to the magnetic flux density B and the drive current I. Since the hall voltage V is proportionate to the drive current I even though the magnetic flux density B is constant, this relation is called as sensitive magnetic properties (gain). 
         [0058]    And change of the magnetic flux density B of the ring magnet  12  in the circle direction on the surface parallel to the magnetic sensitive surface of the ring magnet  12  is expressed by the equation (2) described below. In this case, Bo is constant number and fixed value because of the ring magnet  12 . 
         [0000]        B=B   0  ×sin θ  (2) 
         [0059]    Accordingly, in the case that the drive current I of the hall elements is constant, it is found out that the hall voltage V of the hall elements  13   a  and  13   b  is proportionate to the magnetic flux density B. 
         [0060]    Then, the outputs of the hall elements  13   a  and  13   b  are explained. 
         [0061]      FIG. 2  shows the outputs of the hall elements  13   a  and  13   b  in  FIG. 1 . As shown in the figure, when the rotator  11  is rotated with the ring magnet  12  by an angle of θ, hall voltages V 13a  and V 13b , the signals output from the hall elements  13   a  and  13   b,  are expressed by the equation (3) and (4) described below. In this case, V a  and V b  are constant amplitude values of output signals of the hall elements  13   a  and  13   b.    
         [0000]        V   13a   =V   a ×sin θ  (3) 
         [0000]        V   13b   =V   b ×cos θ  (4) 
         [0062]    Accordingly, the rotation angle θ of the rotator  11  is expressed by the equation (7) described below. 
         [0000]      θ=tan −1 ( V   b   V   13a   /Va V   13b )  (7) 
         [0063]    As described above, the rotation sensor  10  detects the rotation angle θ of the rotator  11  based on the signal ratio of the output signals of the hall elements  13   a  and  13   b.  Accordingly, as far as the drive currents I a  and I b  of the hall elements  13   a  and  13   b  are equal values, even if the drive current I (=I a =I b ) is changed by the disturbance, the rotation angle θ of the rotator  11  is accurately detected based on the signal ratio of the output signals of the hall elements  13   a  and  13   b  without being affected by the drive currents. 
         [0064]    Then, the drive circuit which is provided in the rotation sensor  10  for outputting the hall voltages of the hall elements  13   a  and  13   b,  is explained. 
         [0065]      FIG. 3  shows one example of the drive circuit of the hall elements  13   a  and  13   b  in  FIG. 1 . As shown in  FIG. 3 , the drive circuit  20  includes the hall element drive part  21  and the reference voltage adjustment part  22 . 
         [0066]    The hall element drive part  21  is for driving the hall elements  13   a  and  13   b  with constant current and includes the operational amplifier  23  and the reference resistance  24 . And the hall elements  13   a  and  13   b  are serially connected. When the reference voltage Vref is input to the non-inverting input terminal of the operational amplifier  23 , since the hall elements  13   a  and  13   b  are serially connected, the drive current I of the hall elements  13   a  and  13   b  is expressed by the equation (8) described below. In this case, the resistance value of the reference resistance  24  is denoted by Rref. 
         [0000]      I=I a   =I   b   =Vref/Rref   (8) 
         [0067]    The reference voltage adjustment part  22  is for adjusting the reference voltage Vref input to the operational amplifier  23 , and includes MCU (Micro Control Unit)  25  and low pass filter  26 . PWM signal generated by the MCU  25  is rectified by the low pass filter (LPF)  26  for being generated as a signal of the reference voltage Vref and is input to the operational amplifier  23 . 
         [0068]    By adjusting the pulse width of the PWM signal generated by the MCU  25 , the reference voltage Vref is changed. 
         [0069]    Accordingly, by adjusting the reference voltage Vref, the drive current I of the hall elements  13   a  and  13   b  is changed, and the drive current I is adjusted so that the output signals of the hall elements  13   a  and  13   b  are optimized. 
         [0070]    The rotation angle θ is calculated by the rotation angle calculation part  50  based on the output signals of the hall elements  13   a  and  13   b  output by the drive circuit  20  according to the equation (7) described above. 
         [0071]    In the rotation sensor  10  described above, the hall elements  13   a  and  13   b  corresponds to the magnetic detection means of the present invention, the ring magnet  12  corresponds to the magnet of the present invention, the drive circuit  20  corresponds to the drive means of the present invention, the rotation angle calculation part  50  corresponds to the rotation angle calculation means, and the reference voltage adjustment part  22  corresponds to the signal adjustment means of the present invention. 
         [0072]    As described above, since the drive circuit  20  in which hall elements  13   a  and  13   b  are serially connected is provided in the rotation sensor  10 , constant drive current I can be applied to the hall elements  13   a  and  13   b.  Accordingly, effects of disturbance such as change of temperature, variation of electric source, or the like on the plural magnetic detection means can be the same, and the signal ratio of signals output from the plural magnetic detection means can be constant. Namely, the accident error of rotation angle detection caused by the disturbance such as change of temperature, variation of electric source, or the like, can be eliminated. 
         [0073]    Furthermore, the same arbitrary signal gain (for example, reference voltage Vref) can be provided from outside. Namely, by adjusting signals output from the hall elements  13   a  and  13   b  into optimized signals, the accident error of detection can be eliminated. 
         [0074]    Furthermore, as described above, in the reference voltage adjustment part  22 , the reference voltage is adjusted with the analogue signal into which the digital signal is converted by adjusting the digital signal, however, analogue signal can be directly adjusted. 
         [0075]      FIG. 4  shows one example of the exterior configuration of another rotation sensor to which the present invention can be applied. As shown in  FIG. 4 , the rotation sensor  30  comprises disk magnet  32 , hall element  33   a,  hall element  33   b  and drive circuit  40  (not depicted in the figure), for detecting the rotation angle of the rotator  31 . The disk magnet  32  is magnetized in the circle direction and has a pair of North Pole and South Pole. And the disk magnet  32  is fixed to the rotator  31  and is rotated with the rotator  31 . In this sensor, a shaft which is vertical to the magnetic sensitive surface of the disk magnet  32  is fixed in the center of the disk magnet  32  in the diameter direction, as a rotation center axis  34 . 
         [0076]    The hall elements  33   a  and  33   b  are arranged so that the change of intensity of magnetism in the vertical direction to the diameter direction of the disk magnet  32  can be detected. In this sensor, the hall elements  33   a  and  33   b  are arranged outside of the circle of the disk magnet  32  so that normal to the rotation center axis on the magnetic sensitive surface substantially is declined by an angle of 90°. 
         [0077]    And, as similar to the drive circuit  20  in  FIG. 3 , in the drive circuit  40 , the hall elements  33   a  and  33   b  are serially connected. 
         [0078]    Even if it has a configuration described above, since the drive circuit  40  in which hall elements  33   a  and  33   b  are serially connected is provided in the rotation sensor  10 , the same drive current I can be applied to the hall elements  33   a  and  33   b.  Accordingly, effects of disturbance such as change of temperature, variation of electric source, or the like, on the plural magnetic detection means can be similar, and the signal ratio of signals output from the plural magnetic detection means can be constant. Namely, the accident error in the detection of the rotation angle caused by the disturbance such as change of temperature, variation of electric source, or the like, can be eliminated. 
         [0079]    Furthermore, the same arbitrary signal gain (for example, reference voltage Vref) can be provided from outside. Namely, by adjusting signals output from the hall elements  33   a  and  33   b  into optimized signals, the accident error of detection can be eliminated.