Patent Publication Number: US-2019195713-A1

Title: Operation  processing  apparatus,  torque  sensor  and  power  steering  apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is based on Japanese Patent Application No. 2017-249501 filed on Dec. 26, 2017, the disclosure of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to an operation processing apparatus that calculates a torque value based on an output signal from a sensor element, a torque sensor and a power steering apparatus. 
     BACKGROUND OF THE INVENTION 
     In a power steering apparatus or the like for a vehicle, multipolar magnets are provided at both ends of a torsion bar, magnetic flux in accordance with the positional displacement of these multipolar magnets is detected by a magnetic sensor, a twist angle (relative twist angle) generated in the torsion bar is calculated from the detected magnetic flux, and a torque sensor is used to detect the torque value from this twist angle. The driver can steer with a small steering force by driving a motor or hydraulic apparatus based on the torque value detected by this torque sensor to assist the steering force of the steering wheel. 
     PRIOR ART 
     Patent Literature 
     [PATENT LITERATURE 1] JP Laid-Open Patent Application No. 2017-44683 
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     In the torque sensor disclosed in Patent Literature 1, a first rotational angle sensor is provided in correspondence with a first multipolar ring magnet that is attached to an input shaft and that can rotate synchronously with the input shaft, and a second rotational angle sensor is provided in correspondence with a second multipolar ring magnet that is attached to an output shaft and that can rotate synchronously with the output shaft. Furthermore, the rotational angle of the input shaft is computed based on a sensor signal output from the first rotational angle sensor, the rotational angle of the output shaft is computed based on a signal output from the second rotational angle sensor, and a relative angle (twist angle between the input shaft and the output shaft) Δθ is computed by calculating the difference between these. Furthermore, the steering torque is calculated based on the relative angle Δθ. 
     The sensor signals output from the first rotational angle sensor and the second rotational angle sensor each include a sine wave signal (sin signal) and a cosine wave signal (cos signal) indicating the respective rotational angles of the input shaft (first multipolar ring magnet) and the output shaft (second multipolar ring magnet), and each of the rotational angles is computed from an arctangent operation (atan operation) using the sine wave signal and the cosine wave signal. That is to say, in addition to finding the rotational angle of the input shaft by calculating the arctangent (atan) from the sensor signals (sin signal and cos signal) output from the first rotational angle sensor, it is necessary to find the rotational angle of the output shaft by also similarly calculating the arctangent (atan) from the sensor signals (sin signal and cos signal) output from the second rotational angle sensor. Consequently, the problems exist that the circuit size of the operation processing circuit necessary for arctangent operation processing becomes large, and the power consumption in the angle detection apparatus including the operation processing circuit becomes large. In addition, a large number of clock cycles is taken in calculating the arctangent (atan), so the operation processing time in the operation processing circuit becomes long. 
     In consideration of the foregoing, it is an object of the present invention to provide an operation processing apparatus, which can calculate the relative angle (twist angle) of two coaxial rotational shafts in a short time and can reduce the power consumption in the operation processing circuit that accomplishes this calculation process, a torque sensor equipped with this operation processing apparatus, and a power steering apparatus equipped with this torque sensor. 
     Means for Solving the Problem 
     In order to resolve the above problems, the present invention provides an operation processing apparatus that computes torque generated in a first rotation shaft and a second rotation shaft connected via a torsion bar and arranged coaxially by using a first output signal including a first sine wave signal and a first cosine wave signal output from a first magnetic sensor element in accordance with rotation of the first rotation shaft, and a second output signal including a second sine wave signal and a second cosine wave signal output from a second magnetic sensor element in accordance with rotation of the second rotation shaft. The operation processing apparatus includes a phase difference calculation part that computes the relative phase difference between the first rotation shaft and the second rotation shaft from the first output signal and the second output signal based on the Equation (1) below, and a torque calculation part that computes the torque from a relative twist angle that is expressed as a difference in rotational angles between the first rotation shaft and the second rotation shaft and that is found based on a correlation between the relative phase differences computed by the phase difference calculation part. 
       [Formula 1] 
         C   PD =√{square root over (( S   S1   −S   S2 ) 2 +( S   C1   −S   C2 ) 2 )}  (1)
 
     In Equation (1), C PD  indicates the relative phase difference, S S1  indicates the first sine wave signal, S C1  indicates the first cosine wave signal, S S2  indicates the second sine wave signal and S C2  indicates the second cosine wave signal. 
     In this specification, a “sine wave signal” also includes signals (approximate sine wave signals) expressed by waveforms extremely close to waveforms of ideal sine waves (distortion ratio within 30%), besides signals expressed by waveforms of ideal sine waves. In addition, in this specification, a “cosine wave signal” also includes signals (approximate cosine wave signals) expressed by waveforms extremely close to waveforms of ideal cosine waves (distortion ratio within 30%), besides signals expressed by waveforms of ideal cosine waves. The distortion ratio is measured by separating the ideal component and the distorted component of the signal using a method such as Fourier analysis or the like and using an evaluable distortion ratio measurement apparatus. In addition, the sine wave signal and the cosine wave signal are intended to allow the phase difference thereof to deviate within 90 deg±20 deg. 
     The above-described operation processing apparatus further includes a memory part that stores the correlation between the relative twist angles and the relative phase differences in advance. The torque calculation part can compute the torque from the relative twist angle found based on the correlation stored in the memory part and the relative phase difference computed by the phase difference calculation part, and the relative twist angle may be preferably 10° or less. 
     The present invention provides a torque sensor that includes the above-described operation processing apparatus, a first magnetic field generation part that is provided on the first rotation shaft and rotates integrally with the first rotation shaft, a second magnetic field generation part that is provided on the second rotation shaft and rotates integrally with the second rotation shaft, and a magnetic sensor part that includes the first magnetic sensor element and the second magnetic sensor element. The first magnetic field generation part and the second magnetic field generation part tare multipolar magnets such that the different magnetic poles are arranged alternately in a radial direction, the first magnetic sensor element outputs the first output signal in accordance with the magnetic field generated from the first magnetic field generation part, and the second magnetic sensor element outputs the second output signal in accordance with the magnetic field generated from the second magnetic field generation part. 
     In the above-described torque sensor, each of the first magnetic sensor element and the second magnetic sensor element may be a TMR element, a GMR element, an AMR element or a Hall element. 
     The present invention provides a power steering apparatus that includes a power generation part that gives power to a steering mechanism for steering and assists the steering power of the steering, the above-described torque sensor, and a control part that drives the power generation part in accordance with the torque detected by the torque sensor. 
     Effects of the Invention 
     With the present invention, it is possible to provide an operation processing apparatus that can calculate the relative angle (twist angle) of two rotational shafts arranged coaxially in a short time and that can reduce the power consumption in the operation processing circuit that accomplishes the operation processing, a torque sensor equipped with the operation processing apparatus and a power steering apparatus equipped with the torque sensor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing the schematic configuration of a torque sensor according to the embodiment of the present invention. 
         FIG. 2  is a block diagram showing the schematic configuration of a magnetic detection apparatus in the embodiment of the present invention. 
         FIG. 3  is a circuit diagram schematically showing the circuit configuration of a 1 st -1 Wheatstone bridge circuit in the embodiment of the present invention. 
         FIG. 4  a circuit diagram schematically showing the circuit configuration of a 1 st -2 Wheatstone bridge circuit in the embodiment of the present invention. 
         FIG. 5  a circuit diagram schematically showing the circuit configuration of a 2 nd -1 Wheatstone bridge circuit in the embodiment of the present invention. 
         FIG. 6  a circuit diagram schematically showing the circuit configuration of a 2 nd -2 Wheatstone bridge circuit in the embodiment of the present invention. 
         FIG. 7  is a perspective view showing the schematic configuration of an MR element as a magnetic sensor element in the embodiment of the present invention. 
         FIG. 8  is a cross-sectional view showing the schematic configuration of the MR element as a magnetic sensor element in the embodiment of the present invention. 
         FIG. 9  is a schematic diagram showing the configuration of an electric power-assisted steering apparatus provided with the torque sensor according to the embodiment of the present invention. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     The embodiment of the present invention will be described in detail with reference to the drawings  FIG. 1  is a perspective view showing the schematic configuration of a torque sensor according to this embodiment;  FIG. 2  is a block diagram showing the schematic configuration of a magnetic detection apparatus in this embodiment;  FIGS. 3 ˜ 6  are circuit diagrams schematically showing the circuit configuration of a 1 st -1 Wheatstone bridge circuit, a 1 st -2 Wheatstone bridge circuit, a 2 nd -1 Wheatstone bridge circuit and a 2 nd -2 Wheatstone bridge circuit in this embodiment of the present invention; and  FIG. 7  and  FIG. 8  are a perspective view and a cross-sectional view showing the schematic configuration of an MR element as a magnetic sensor element in this embodiment. In this embodiment, a torque sensor used in an electric power-assisted steering apparatus for a vehicle will be described as an example. 
     A torque sensor  1  according to this embodiment is provided with a first multipolar magnet  2 A that is provided on one end of an input shaft  102 A (one end on an output shaft  102 B side) connected to a steering wheel  101 , a second multipolar magnet  2 B provided on one end of the output shaft  102 B (one end on the input shaft  102 A side) connected to the input shaft  102 A via a torsion bar  102 C, and a magnetic detection apparatus  3  that includes a first magnetic detection apparatus  3 A arranged to face the first multipolar magnet  2 A and a second magnetic detection apparatus  3 B arranged facing the second multipolar magnet  2 B. 
     The first multipolar magnet  2 A and the second multipolar magnet  2 B are rotatably provided on one end of the input shaft  102 A and one end of the output shaft  102 B about a rotational axis RA. The multipolar magnets  2 A,  2 B rotate about the rotational axis RA while interlocked with the rotation of the input shaft  102 A and the output shaft  102 B. 
     The first multipolar magnet  2 A and the second multipolar magnet  2 B have a plurality of pairs of N poles and S poles, and the N poles and S poles are arranged radially (in a ring shape) alternately with each other. The first multipolar magnet  2 A and the second multipolar magnet  2 B generate magnetic fields based the magnetization each possesses. In this embodiment, the number of poles of the first multipolar magnet  2 A and the second multipolar magnet  2 B is 15, but the number of poles of the first multipolar magnet  2 A and the second multipolar magnet  2 B is not limited to this. 
     The first magnetic detection apparatus  3 A is arranged to face the first multipolar magnet  2 A, and detects the magnetic field produced by the first multipolar magnet  2 A. The second magnetic detection apparatus  3 B is arranged to face the second multipolar magnet  2 B, and detects the magnetic field produced by the second multipolar magnet  2 B. As described below, the torque sensor  1  according to this embodiment can find the torque based on the respective outputs of the first magnetic detection apparatus  3 A and the second magnetic detection apparatus  3 B. 
     The magnetic detection apparatus  3  has the first magnetic detection apparatus  3 A, the second magnetic detection apparatus  3 B and an operation processor  3 C. The first magnetic detection apparatus  3 A includes a first magnetic sensor  31 A that outputs a sensor signal based on changes in the magnetic field accompanying rotation of the first multipolar magnet  2 A. The second magnetic detection apparatus  3 B includes a second magnetic sensor  31 B that outputs a sensor signal based on changes in the magnetic field accompanying rotation of the second multipolar magnet  2 B. 
     The first magnetic sensor  31 A and the second magnetic sensor  31 B each include at least one magnetic detection element and may include a pair of magnetic detection elements connected in series. In this case, the first magnetic sensor  31 A has a 1 st -1 Wheatstone bridge circuit  311 A and a 1 st -2 Wheatstone bridge circuit  312 A that include the first magnetic detection element and the second magnetic detection element connected in series, and the second magnetic sensor  31 B has a 2 nd -1 Wheatstone bridge circuit  311 B and a 2 nd -2 Wheatstone bridge circuit  312 B that include the first magnetic detection element and the second magnetic detection element connected in series. The first magnetic sensor  31 A and the second magnetic sensor  31 B may also have a half bridge circuit that includes only the first magnetic detection element pair and does not include the second magnetic detection element pair, respectively, in place of the 1 st -1 Wheatstone bridge circuit  311 A, the 1 st -2 Wheatstone bridge circuit  312 A, the 2 nd -1 Wheatstone bridge circuit  311 B and the 2 nd -2 Wheatstone bridge circuit  312 B. 
     As shown in  FIG. 3 , the 1 st -1 Wheatstone bridge circuit  311 A of the first magnetic sensor  31 A includes a power source port V 11 , a ground port G 11 , two output ports E 111  and E 112 , a first pair of magnetic detection elements R 111  and R 112  connected in series, and a second pair of magnetic detection elements R 113  and R 114  connected in series. One end of each of the magnetic detection elements R 111  and R 113  is connected to the power source port V 11 . The other end of the magnetic detection element R 111  is connected to one end of the magnetic detection element R 112  and to the output port E 111 . The other end of the magnetic detection element R 113  is connected to one end of the magnetic detection element R 114  and to the output port E 112 . The other end of each of the magnetic detection elements R 112  and R 114  is connected to the ground port G 11 . A power source voltage of a predetermined magnitude is applied on the power source port V 11 , and the ground port G 11  is connected to ground. 
     As shown in  FIG. 4 , the 1 st -2 Wheatstone bridge circuit  312 A of the first magnetic sensor  31 A has has the same configuration as the 1 st -1 Wheatstone bridge circuit  311 A and includes a power source port V 12 , a ground port G 12 , two output ports E 121  and E 122 , a first pair of magnetic detection elements R 121  and R 122  connected in series, and a second pair of magnetic detection elements R 123  and R 124  connected in series. One end of each of the magnetic detection elements R 121  and R 123  is connected to the power source port V 12 . The other end of the magnetic detection element R 121  is connected to one end of the magnetic detection element R 122  and to the output port E 121 . The other end of the magnetic detection element R 123  is connected to one end of the magnetic detection element R 124  and to the output port E 122 . The other end of each of the magnetic detection elements R 122  and R 124  is connected to the ground port G 12 . A power source voltage of a predetermined magnitude is applied on the power source port V 12 , and the ground port G 12  is connected to ground. 
     As shown in  FIG. 5 , the 2 nd -1 Wheatstone bridge circuit  311 B of the second magnetic sensor  31 B has has the same configuration as the 1 st -1 Wheatstone bridge circuit  311 A and includes a power source port V 21 , a ground port G 21 , two output ports E 211  and E 212 , a first pair of magnetic detection elements R 211  and R 212  connected in series, and a second pair of magnetic detection elements R 213  and R 214  connected in series. One end of each of the magnetic detection elements R 211  and R 213  is connected to the power source port V 21 . The other end of the magnetic detection element R 211  is connected to one end of the magnetic detection element R 212  and to the output port E 211 . The other end of the magnetic detection element R 213  is connected to one end of the magnetic detection element R 214  and to the output port E 212 . The other end of each of the magnetic detection elements R 212  and R 214  is connected to the ground port G 21 . A power source voltage of a predetermined magnitude is applied on the power source port V 21 , and the ground port G 21  is connected to ground. 
     As shown in  FIG. 6 , the 2 nd -2 Wheatstone bridge circuit  312 B of the second magnetic sensor  31 B has has the same configuration as the 2 nd -1 Wheatstone bridge circuit  311 B and includes a power source port V 22 , a ground port G 22 , two output ports E 221  and E 222 , a first pair of magnetic detection elements R 221  and R 222  connected in series, and a second pair of magnetic detection elements R 223  and R 224  connected in series. One end of each of the magnetic detection elements R 221  and R 223  is connected to the power source port V 22 . The other end of the magnetic detection element R 221  is connected to one end of the magnetic detection element R 222  and to the output port E 221 . The other end of the magnetic detection element R 223  is connected to one end of the magnetic detection element R 224  and to the output port E 222 . The other end of each of the magnetic detection elements R 222  and R 224  is connected to the ground port G 22 . A power source voltage of a predetermined magnitude is applied on the power source port V 22 , and the ground port G 22  is connected to ground. 
     In this embodiment, as all of the magnetic detection elements R 111 ˜R 124  and R 211 ˜R 224  included in the 1 st -1 Wheatstone bridge circuit  311 A, the 1 st -2 Wheatstone bridge circuit  312 A, the 2 nd -1 Wheatstone bridge circuit  311 B and the 2 nd -2 Wheatstone bridge circuit  312 B, MR elements such as TMR elements, GMR elements, AMR elements or the like, or magnetic detection elements such as Hall elements, can be used, and using TMR elements is particularly preferable. TMR elements and GMR elements have magnetization fixed layers in which the magnetization direction is fixed, free layers in which the magnetization direction changes in accordance with the direction of an applied magnetic field, and nonmagnetic layers positioned between the magnetization fixed layers and the free layers. 
     Specifically, as shown in  FIG. 7 , the MR element has a plurality of lower electrodes  41 , a plurality of MR films  50  and a plurality of upper electrodes  42 . The plurality of lower electrodes  41  is provided on a substrate (not shown in the drawings). Each of the lower electrodes  41  has an elongated shape. A gap is formed between two lower electrodes  41  adjacent in the lengthwise direction of the lower electrodes  41 . The MR films  50  are respectively provided near the two ends in the lengthwise direction on the top surface of the lower electrodes  41 . As shown in  FIG. 8 , the MR films  50  have a roughly circular shape in a plan view, and include a free layer  51 , a nonmagnetic layer  52 , a magnetization fixed layer  53  and an antiferromagnetic layer  54  layered in that order from the lower electrode  41  side. The free layer  51  is electrically connected to the lower electrode  41 . The antiferromagnetic layer  54  is configured by antiferromagnetic materials, and by causing exchange coupling with the magnetization fixed layer  53 , serves the role of fixing the direction of magnetization of the magnetization fixed layer  53 . The plurality of upper electrodes  42  is provided on top of the plurality of MR films  50 . Each upper electrode  42  has an elongated shape, is arranged on two of the lower electrodes  41  adjacent in the lengthwise direction of the lower electrodes  41 , and electrically connects the antiferromagnetic layers  54  of two adjacent MR films  50 . The MR films  50  may be configured to have the free layer  51 , the nonmagnetic layer  52 , the magnetization fixed layer  53  and the antiferromagnetic layer  54  layered in that order from the upper electrode  42  side. In addition, the antiferromagnetic layer  54  may be omitted, by making the magnetization fixed layer  53  a so-called self-pinned type fixed layer (Synthetic Ferri Pinned layer, or SFP layer) having a layered ferri structure of a ferromagnetic layer/nonmagnetic intermediate layer/ferromagnetic layer, with the two ferromagnetic layers antiferromagnetically coupled. 
     In the TMR elements, the nonmagnetic layer  52  is a tunnel barrier layer. In the GMR elements, the nonmagnetic layer  52  is a nonmagnetic conductive layer. In the TMR elements and GRM elements, the resistance value changes in accordance with the angle of the direction of magnetization of the free layer  51  with respect to the direction of magnetization of the magnetization fixed layer  53 , the resistance value becomes a minimum when this angle is 0° (when the magnetization directions are mutually parallel), and the resistance value becomes a maximum when the angle is 180° (the magnetization directions are mutually antiparallel). 
     In  FIGS. 3-6 , when the magnetic detection elements R 111 ˜R 124  and R 211 ˜R 224  are TMR elements or GMR elements, the magnetization direction of the magnetization fixed layers  53  thereof are indicated by the filled arrows. In the 1 st -1 Wheatstone bridge circuit  311 A of the first magnetic sensor  31 A, the magnetization directions of the magnetization fixed layers  53  of the magnetic detection elements R 111 ˜R 114  are parallel to a first direction D 1 , and the magnetization direction of the magnetization fixed layers  53  of the magnetic detection elements R 111  and R 114  and the magnetization direction of the magnetization fixed layers  53  of the magnetic detection elements R 112  and R 113  are mutually antiparallel directions. In addition, in the 1 st -2 Wheatstone bridge circuit  312 A, the magnetization directions of the magnetization fixed layers  53  of the magnetic detection elements R 121 ˜R 124  are parallel to a second direction D 2  orthogonal to the first direction D 1 , and the magnetization directions of the magnetization fixed layers  53  of the magnetic detection elements R 121  and R 124  and the magnetization direction of the magnetization fixed layers  53  of the magnetic detection elements R 122  and R 123  are mutually antiparallel directions. 
     In the 2 nd -1 Wheatstone bridge circuit  311 B of the second magnetic sensor  31 B, the magnetization directions of the magnetization fixed layers  53  of the magnetic detection elements R 211 ˜R 214  are parallel to the first direction D 1 , and the magnetization direction of the magnetization fixed layers  53  of the magnetic detection elements R 211  and R 214  and the magnetization direction of the magnetization fixed layers  53  of the magnetic detection elements R 212  and R 213  are mutually antiparallel directions. In addition, in the 2 nd -2 Wheatstone bridge circuit  312 B, the magnetization directions of the magnetization fixed layers  53  of the magnetic detection elements R 221 ˜R 224  are parallel to the second direction D 2  orthogonal to the first direction D 1 , and the magnetization direction of the magnetization fixed layers  53  of the magnetic detection elements R 221  and R 224  and the magnetization direction of the magnetization fixed layers  53  of the magnetic detection elements R 222  and R 223  are mutually antiparallel directions. 
     In the first magnetic sensor  31 A and the second magnetic sensor  31 B, the electric potential difference between the output ports E 111 , E 112 , E 121  and E 122  and the output ports E 211 , E 212 , E 221  and E 222  changes in accordance with changes in the direction of the magnetic field accompanying rotation of the input shaft  102 A and the output shaft  102 B, and a 1 st -1 sensor signal S 1-1 , a 1 st -2 sensor signal S 1-2 , a 2 nd -1 sensor signal S 2-1  and a 2 nd -2 sensor signal S 2-2  are output as signals expressing the magnetic field intensity. 
     Difference detectors  331 A and  332 A output a signal corresponding to the potential difference between the output ports E 111  and E 112  to a first operation part  32 A and a second operation part  32 B as the 1 st -1 sensor signal S 1-1 . Difference detectors  331 B and  332 B output a signal corresponding to the potential difference between the output ports E 121  and E 122  to the first operation part  32 A and the second operation part  32 B as the 1 st -2 sensor signal S 1-2 . The difference detector  331 B outputs a signal corresponding to the potential difference between the output ports E 211  and E 212  to the operation processing part  3 C as the 2 nd -1 sensor signal S 2-1 . The difference detector  332 B outputs a signal corresponding to the potential difference between the output ports E 221  and E 222  to the operation processing part  3 C as the 2 nd -2 sensor signal S 2-2 . 
     As shown in  FIG. 3  and  FIG. 4 , the magnetization direction of the magnetization fixed layers  53  of the magnetic detection elements R 111 ˜R 114  in the 1 st -1 Wheatstone bridge circuit  311 A and the magnetization direction of the magnetization fixed layers  53  of the magnetic detection elements R 121 ˜R 124  in the 1 st -2 Wheatstone bridge circuit  312 A are mutually orthogonal. In this case, the waveform of the 1 st -1 sensor signal S 1-1  is a cosine waveform depending on the rotational angle θ 1  of the first multipolar magnet  2 A, and the waveform of the 1 st -2 sensor signal S 1-2  is a sine waveform depending on the rotational angle θ 1  of the first multipolar magnet  2 A. That is to say, the 1 st -1 sensor signal S 1-1  can be called the first cos signal, and the 1 st -2 sensor signal S 1-2  can be called the first sin signal. 
     As shown in  FIG. 5  and  FIG. 6 , the magnetization direction of the magnetization fixed layers  53  of the magnetic detection elements R 211 ˜R 214  in the 2 nd -1 Wheatstone bridge circuit  311 B and the magnetization direction of the magnetization fixed layers  53  of the magnetic detection elements R 221 ˜R 224  in the 2 nd -2 Wheatstone bridge circuit  312 B are mutually orthogonal. In this case, the waveform of the 2 nd -1 sensor signal S 2-1  is a cosine waveform depending on the rotational angle θ 2  of the second multipolar magnet  2 B, and the waveform of the 2 nd -2 sensor signal S 2-2  is a sine waveform depending on the rotational angle θ 2  of the second multipolar magnet  2 B. That is to say, the 2 nd -1 sensor signal  524  can be called the second cos signal, and the 2 nd -2 sensor signal S 2-2  can be called the second sin signal. 
     The operation processor  3 C has a phase difference calculator  31 C that calculates the relative phase difference C PD  of the input shaft  102 A and the output shaft  102 B based on the equation (1) below, from the first cos signal (Cos θ 1 ) and the first sin signal (Sin θ 1 ) output by the first magnetic sensor  31 A, and the second cos signal (Cos θ 2 ) and the second sin signal (Sin θ 2 ) output by the second magnetic sensor  31 B, and a torque calculator  32 C that computes the torque generated in the input shaft  102 A and the output shaft  102 B on the basis of the relative phase difference C PD . 
       [Formula 2] 
         C   PD =√{square root over (( S   S1   −S   S2 ) 2 +( S   C1   −S   C2 ) 2 )}  (1)
 
     In Equation (1), C PD  indicates the relative phase difference, S S1  indicates the first sin signal, S C1  indicates the first cos signal, S S2  indicates the second sin signal and S C2  indicates the second cos signal. 
     Here, the respective phases (rotational angle) P IN  and P OUT  of the input shaft  102 A and the output shaft  102 B can be expressed by equations (2) and (3) below. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Formula 
                      
                     
                         
                     
                      
                     3 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     P 
                     IN 
                   
                   = 
                   
                     
                       
                         
                           
                             ( 
                             
                               S 
                               
                                 S 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                             
                             ) 
                           
                           2 
                         
                         + 
                         
                           
                             ( 
                             
                               S 
                               
                                 C 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                             
                             ) 
                           
                           2 
                         
                       
                     
                     = 
                     
                       
                         
                           
                             ( 
                             
                               sin 
                                
                               
                                   
                               
                                
                               
                                 θ 
                                 1 
                               
                             
                             ) 
                           
                           2 
                         
                         + 
                         
                           
                             ( 
                             
                               cos 
                                
                               
                                   
                               
                                
                               
                                 θ 
                                 1 
                               
                             
                             ) 
                           
                           2 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
             
               
                 
                   
                     P 
                     OUT 
                   
                   = 
                   
                     
                       
                         
                           
                             ( 
                             
                               S 
                               
                                 S 
                                  
                                 
                                     
                                 
                                  
                                 2 
                               
                             
                             ) 
                           
                           2 
                         
                         + 
                         
                           
                             ( 
                             
                               S 
                               
                                 C 
                                  
                                 
                                     
                                 
                                  
                                 2 
                               
                             
                             ) 
                           
                           2 
                         
                       
                     
                     = 
                     
                       
                         
                           
                             ( 
                             
                               sin 
                                
                               
                                   
                               
                                
                               
                                 θ 
                                 2 
                               
                             
                             ) 
                           
                           2 
                         
                         + 
                         
                           
                             ( 
                             
                               cos 
                                
                               
                                   
                               
                                
                               
                                 θ 
                                 2 
                               
                             
                             ) 
                           
                           2 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     In Equations (2) and (3), P IN  indicates the phase of the input shaft  102 A, Pour indicates the phase of the output shaft  102 B, S S1  indicates the first sin signal, S C1  indicates the first cos signal, S S2  indicates the second sin signal and S C2  indicates the second cos signal. 
     When the relative twist angle Δθ between the input shaft  102 A and the output shaft  102 B is 0 (zero), the relative phase difference C PD  between the input shaft  102 A and the output shaft  102 B indicated by Equation (1) also becomes 0 (zero). In this case, torque is not generated in the input shaft  102 A and the output shaft  102 B. On the other hand, when the relative twist angle Δθ between the input shaft  102 A and the output shaft  102 B is not 0 (zero), the relative phase difference C PD  between the input shaft  102 A and the output shaft  102 B is expressed by Equation (4) below. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Formula 
                      
                     
                         
                     
                      
                     4 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       
                         
                           C 
                           PD 
                         
                         = 
                         
                           
                             
                               
                                 ( 
                                 
                                   
                                     sin 
                                      
                                     
                                         
                                     
                                      
                                     
                                       θ 
                                       1 
                                     
                                   
                                   - 
                                   
                                     sin 
                                      
                                     
                                       ( 
                                       
                                         
                                           θ 
                                           1 
                                         
                                         + 
                                         Δθ 
                                       
                                       ) 
                                     
                                   
                                 
                                 ) 
                               
                               2 
                             
                             + 
                             
                               
                                 ( 
                                 
                                   
                                     cos 
                                      
                                     
                                         
                                     
                                      
                                     
                                       θ 
                                       1 
                                     
                                   
                                   - 
                                   
                                     cos 
                                      
                                     
                                       ( 
                                       
                                         
                                           θ 
                                           1 
                                         
                                         + 
                                         Δθ 
                                       
                                       ) 
                                     
                                   
                                 
                                 ) 
                               
                               2 
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           
                             
                               
                                 
                                   
                                     
                                       ( 
                                       
                                         sin 
                                          
                                         
                                             
                                         
                                          
                                         
                                           θ 
                                           1 
                                         
                                       
                                       ) 
                                     
                                     2 
                                   
                                   + 
                                   
                                     
                                       ( 
                                       
                                         sin 
                                          
                                         
                                           ( 
                                           
                                             
                                               θ 
                                               1 
                                             
                                             + 
                                             Δθ 
                                           
                                           ) 
                                         
                                       
                                       ) 
                                     
                                     2 
                                   
                                   - 
                                   
                                     2 
                                      
                                     
                                       ( 
                                       
                                         sin 
                                          
                                         
                                             
                                         
                                          
                                         
                                           
                                             θ 
                                             1 
                                           
                                           · 
                                           
                                             sin 
                                              
                                             
                                               ( 
                                               
                                                 
                                                   θ 
                                                   1 
                                                 
                                                 + 
                                                 Δθ 
                                               
                                               ) 
                                             
                                           
                                         
                                       
                                       ) 
                                     
                                   
                                   + 
                                   
                                     
                                       ( 
                                       
                                         cos 
                                          
                                         
                                             
                                         
                                          
                                         
                                           θ 
                                           1 
                                         
                                       
                                       ) 
                                     
                                     2 
                                   
                                   + 
                                 
                               
                             
                             
                               
                                 
                                   
                                     
                                       ( 
                                       
                                         cos 
                                          
                                         
                                           ( 
                                           
                                             
                                               θ 
                                               1 
                                             
                                             + 
                                             Δθ 
                                           
                                           ) 
                                         
                                       
                                       ) 
                                     
                                     2 
                                   
                                   - 
                                   
                                     2 
                                      
                                     
                                       ( 
                                       
                                         cos 
                                          
                                         
                                             
                                         
                                          
                                         
                                           
                                             θ 
                                             1 
                                           
                                           · 
                                           
                                             cos 
                                              
                                             
                                               ( 
                                               
                                                 
                                                   θ 
                                                   1 
                                                 
                                                 + 
                                                 Δθ 
                                               
                                               ) 
                                             
                                           
                                         
                                       
                                       ) 
                                     
                                   
                                 
                               
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           
                             
                               
                                 - 
                                 2 
                               
                                
                               
                                 ( 
                                 
                                   sin 
                                    
                                   
                                       
                                   
                                    
                                   
                                     
                                       θ 
                                       1 
                                     
                                     · 
                                     
                                       sin 
                                        
                                       
                                         ( 
                                         
                                           
                                             θ 
                                             1 
                                           
                                           + 
                                           Δθ 
                                         
                                         ) 
                                       
                                     
                                   
                                 
                                 ) 
                               
                             
                             - 
                             
                               2 
                                
                               
                                 ( 
                                 
                                   cos 
                                    
                                   
                                       
                                   
                                    
                                   
                                     
                                       θ 
                                       1 
                                     
                                     · 
                                     
                                       cos 
                                        
                                       
                                         ( 
                                         
                                           
                                             θ 
                                             1 
                                           
                                           + 
                                           Δθ 
                                         
                                         ) 
                                       
                                     
                                   
                                 
                                 ) 
                               
                             
                             + 
                             2 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           
                             
                               
                                 
                                   
                                     
                                       - 
                                       2 
                                     
                                      
                                     
                                       ( 
                                       
                                         
                                           - 
                                           1 
                                         
                                         / 
                                         2 
                                       
                                       ) 
                                     
                                      
                                     
                                       ( 
                                       
                                         
                                           cos 
                                            
                                           
                                             ( 
                                             
                                               
                                                 θ 
                                                 1 
                                               
                                               + 
                                               
                                                 θ 
                                                 1 
                                               
                                               + 
                                               Δθ 
                                             
                                             ) 
                                           
                                         
                                         - 
                                         
                                           cos 
                                            
                                           
                                             ( 
                                             
                                               
                                                 θ 
                                                 1 
                                               
                                               - 
                                               
                                                 θ 
                                                 1 
                                               
                                               - 
                                               Δθ 
                                             
                                             ) 
                                           
                                         
                                       
                                       ) 
                                     
                                   
                                   - 
                                   
                                     2 
                                      
                                     
                                       ( 
                                       
                                         1 
                                         / 
                                         2 
                                       
                                       ) 
                                     
                                   
                                 
                               
                             
                             
                               
                                 
                                   
                                     ( 
                                     
                                       
                                         cos 
                                          
                                         
                                           ( 
                                           
                                             
                                               θ 
                                               1 
                                             
                                             + 
                                             
                                               θ 
                                               1 
                                             
                                             + 
                                             Δθ 
                                           
                                           ) 
                                         
                                       
                                       - 
                                       
                                         cos 
                                          
                                         
                                           ( 
                                           
                                             
                                               θ 
                                               1 
                                             
                                             - 
                                             
                                               θ 
                                               1 
                                             
                                             - 
                                             Δθ 
                                           
                                           ) 
                                         
                                       
                                     
                                     ) 
                                   
                                   + 
                                   2 
                                 
                               
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           
                             2 
                              
                             
                               ( 
                               
                                 1 
                                 - 
                                 
                                   cos 
                                    
                                   
                                     ( 
                                     Δθ 
                                     ) 
                                   
                                 
                               
                               ) 
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           
                             
                               2 
                                
                               
                                 ( 
                                 
                                   2 
                                    
                                   
                                     
                                       sin 
                                        
                                       
                                         ( 
                                         
                                           Δθ 
                                           / 
                                           2 
                                         
                                         ) 
                                       
                                     
                                     2 
                                   
                                 
                                 ) 
                               
                             
                           
                           = 
                           
                             2 
                              
                             
                               sin 
                                
                               
                                 ( 
                                 
                                   Δθ 
                                   / 
                                   2 
                                 
                                 ) 
                               
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     Here, when the relative twist angle Δθ between the input shaft  102 A and the output shaft  102 B is sufficiently small (for example, when Δθ is 10° or less, and preferably 5° or less), sin θ 1  can be close to θ 1 , so the relative phase difference C PD  and the relative twist angle Δθ between the input shaft  102 A and the output shaft  102 B have a predetermined correlation indicated in Equation (4) above. 
     Consequently, the relative phase difference C PD  between the input shaft  102 A and the output shaft  102 B is calculated by the phase difference calculator  31 C from the first cos signal (Cos θ 1 ) and the first sin signal (Sin θ 1 ) output from the first magnetic sensor  31 A, and the second cos signal (Cos θ 2 ) and the second sin signal (Sin θ 2 ) output from the second magnetic sensor  31 B, and through this the relative twist angle Δθ can be found based on the correlation (Equation (4)) between the relative phase difference C PD  of the input shaft  102 A and the output shaft  102 B and the relative twist angle Δθ. Furthermore, the torque generated in the input shaft  102 A and the output shaft  102 B can be calculated by the torque calculator  32 C based on the relative twist angle Δθ. The relative twist angle Δθ may also be found by preparing a table or the like indicating the correlation between the relative phase difference C PD  and the relative twist angle Δθ in advance and referring to the table or the like. 
     The torque calculator  32 C calculates the torque generated in the input shaft  102 A and the output shaft  102 B based on the relative twist angle Δθ found from the above-described correlation (Equation (4)). That is to say, if the relative twist angle Δθ between the input shaft  102 A and the output shaft  102 B connected via the torsion bar  102 C is obtained, the torque can be calculated through a commonly known calculation method using the cross-sectional secondary polar moment, the transverse electricity coefficient, the length, the diameter and the like of the torsion bar  102 C. 
     The operation processing part  3 C may also include a memory part (not illustrated), in addition to the phase difference calculator  31 C and the torque calculator  32 C. The memory part stores the torque generated in the input shaft  102 A and output shaft  102 B calculated by the torque calculator  32 C and a table indicating the correlation between the relative phase difference C PD  of the input shaft  102 A and the output shaft  102 B and the relative twist angle Δθ, and the like. The operation processor  3 C may be configured from a microcomputer, an Application Specific Integrated Circuit (ASIC) or the like, for example, that is capable of realizing operation processing of the relative phase difference C PD , the relative twist angle Δθ and the torque. 
     In the torque sensor  1  having the above configuration, when the first multipolar magnet  2 A and the second multipolar magnet  2 B rotate accompanying rotation of the input shaft  102 A and the output shaft  102 B, the magnetic fields of the first multipolar magnet  2 A and the second multipolar magnet  2 B change. The resistance values of the magnetic detection elements R 111 ˜R 124  and R 211 ˜R 224  of the first magnetic sensor  31 A and the second magnetic sensor  31 B change in accordance with changes in the magnetic field, and the first cos signal (Cos θ 1 ) and first sin signal (Sin θ 1 ) and the second cos signal (Cos θ 2 ) and second sin signal (Sin θ 2 ) are output in accordance with the potential difference between the respective output ports E 111 , E 112 , E 121 , E 122 , E 211 , E 212 , E 221  and E 222 . Furthermore, the relative phase difference C PD  between the input shaft  102 A and the output shaft  102 B is calculated by the phase difference calculator  31 C, and the torque is calculated by the torque calculator  32 C based on the relative twist angle Δθ found from the correlation with the relative phase difference C PD . 
     In this manner, with the torque sensor  1  according to this embodiment, it is possible to compute the torque without accomplishing arctangent (atan) operation processing by the operation processor  3 C, so it is not necessary to enlarge the circuit scale of the operation processing circuit, and it is possible to reduce the power consumption in the torque sensor  1 . In addition, it is not necessary to accomplish arctangent (atan) operation processing that requires a large number of clock cycles, so it is possible to compute the torque in an extremely short time. 
     Next, the configuration of an electric power-assisted steering that uses the rotational angle detection apparatus according to this embodiment will be described.  FIG. 9  is a schematic configuration diagram of an electric power-assisted steering apparatus that uses the torque sensor according to this embodiment 
     An electric power-assisted steering apparatus  100  is provided with a steering wheel  101 , a steering shaft  102 , the torque sensor  1  according to this embodiment, a first universal joint  103 , a lower shaft  104 , a second universal joint  105 , a pinion shaft  106 , a steering gear  107 , tie rods  108  and knuckle arms  109 . The knuckle arms  109  are respectively attached to the front wheels  110 R and  110 L of the vehicle. 
     The steering force with which the driver steers the steering wheel  101  is conveyed to the steering shaft  102 . The steering shaft  102  includes an input shaft  102 A and an output shaft  102 B. One end of the input shaft  102 A is connected to the steering wheel  101 , and the other end is connected to one end of the output shaft  102 B via the torque sensor  1 . Accordingly, the steering force conveyed to the output shaft  102 B of the steering shaft  102  is conveyed to the lower shaft  104  via the first universal joint  103  and is conveyed to the pinion shaft  106  via the second universal joint  105 . The steering force conveyed to the pinion shaft  106  is conveyed to the tie rods  108  via the steering gear  107 , the steering force conveyed to the tie rods  108  is conveyed to the knuckle arms  109 , and the front wheels are steered. 
     A steering assist mechanism  111  that conveys a steering assist force to the output shaft  102 B is connected to the output shaft  102 B of the steering shaft  102 . The steering assist mechanism  111  is provided with a reduction gear  112  that is connected to the output shaft  102 B and configured by a worm gear mechanism or the like, an electric motor  113  that is connected to the reduction gear  112  and generates the steering assist force, and an electric power-assisted steering (EPS) control part  114  that is fixedly supported to the housing of the electric motor  113 . 
     When the steering wheel  101  is steered by the driver of the vehicle and this steering force is conveyed to the steering shaft  102 , the input shaft  102 A rotates in a direction corresponding to the steering direction. Accompanying this rotation, the end of the torsion bar  102 C on the input shaft  102 A side rotates, and the first multipolar magnet  2 A provided on the input end of the torsion bar  102 C rotates. The resistance values of the magnetic detection elements R 111 ˜R 124  of the first magnetic sensor  31 A change in accordance with the change in the magnetic field accompanying rotation of the first multipolar magnet  2 A, and the first cos signal (Cos θ 1 ) and first sin signal (Sin θ 1 ) are output to the operation processor  3 C in accordance with the respective potential differences between the output ports E 111 , E 112 , E 121  and E 122 . 
     On the other hand, the steering force that causes the input shaft  102 A to rotate is conveyed to the end on the output shaft  102 B side via twisting (elastic deformation) of the torsion bar  102 C, and the output shaft  102 B rotates. That is to say, the input shaft  102 A and the output shaft  102 B are relatively displaced in the rotational direction. Through this, the second multipolar magnet  2 B provided on the output end of the torsion bar  102 C rotates. The resistance values of the magnetic detection elements R 211 ˜R 224  of the second magnetic sensor  31 B change in accordance with changes in the magnetic field accompanying rotation of the second multipolar magnet  2 B, and the second cos signal (Cos θ 2 ) and second sin signal (Sin θ 2 ) are output to the operation processor  3 C in accordance with the respective potential differences between the output ports E 211 , E 212 , E 221  and E 222 . 
     The phase difference calculator  31 C of the operation processor  3 C calculates the relative phase difference C PD  by the first cos signal (Cos θ 1 ), the first sin signal (Sin θ 1 ), the second cos signal (Cos θ 2 ) and the second sin signal (Sin θ 2 ), and computes the relative twist angle Δθ from the predetermined correlation. Then, the torque calculator  32 C computes the torque based on the relative twist angle Δθ. The torque calculated by the torque calculator  32 C is output to the EPS control part  114 , and the EPS control part  114  computes the electric current command value based on the torque value from the torque calculator  32 C, the vehicle speed from a vehicle speed sensor and the motor rotation angle from the electric motor. Then, a three-phase alternating current in accordance with this electric current command value is generated and supplied to the electric motor, and a steering assist force is generated in the electric motor. 
     In the electric power-assisted steering apparatus  100  having the above-described configuration, the torque value necessary for generating the steering assist force is computed by the torque sensor  1  according to this embodiment. In this torque sensor  1 , it is possible to compute the torque value without accomplishing arctangent (atan) operation processing by the operation processor  3 C, and it is possible to compute the torque value in an extremely short time with small power consumption. Consequently, with the electric power-assisted steering apparatus  100  according to this embodiment, a competent steering assist force can be generated in accordance with steering of the steering wheel  101  by the driver. 
     The above-described embodiment is disclosed in order to facilitate understanding of the present invention and is not disclosed to limit the present invention. Accordingly, the various elements disclosed in the above-described embodiment include all design modifications and equivalents that fall within the technical scope of the present invention. 
     DESCRIPTION OF REFERENCE SYMBOLS 
     
         
           1  Torque sensor 
           2 A First multipolar magnet (first magnetic field generator) 
           2 B Second multipolar magnet (second magnetic field generator) 
           3  Magnetic detection apparatus 
           3 A First magnetic detection apparatus 
           31 A First magnetic sensor 
           3 B Second magnetic detection apparatus 
           31 B Second magnetic sensor 
           3 C Operation processor (operation processing apparatus) 
           31 C Phase difference calculator 
           32 C Torque calculator 
           100  Electric power-assisted steering apparatus 
           102 A Input shaft (first rotation shaft) 
           102 B Output shaft (second rotation shaft) 
           102 C Torsion bar 
           113  Electric motor (power generator) 
           114  EPS control part (controller)