Patent Publication Number: US-8983727-B2

Title: Steering control apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to an electric steering control apparatus that controls a motor for providing assist torque to a steering system of a motor vehicle or the like. More particularly, it relates to novel technical improvements in determining whether a motor output torque control unit is abnormal. 
     BACKGROUND ART 
     In the past, a electric steering control apparatus includes a main CPU and a sub CPU that are connected to each other by a data bus, a motor drive circuit that drives a motor in accordance with a drive signal from the main CPU, and a logic circuit that is inserted between the main CPU and the motor drive circuit, wherein the driving direction of the motor is limited by driving the logic circuit to control the passage of a driving direction signal from the main CPU by means of an output signal from the sub CPU (see, for example, a first patent document). 
     Now, reference will be made to the operation of the conventional apparatus as described in the above-mentioned first patent document. 
     The main CPU calculates the driving direction of the motor, etc., based on detection signals from various kinds of sensors such as a torque sensor, and sends the calculation result of the motor driving direction to the sub CPU through the data bus. 
     The sub CPU compares a steering torque signal from the torque sensor and the motor driving direction input from the main CPU with each other, determines, when both of them do not coincide with each other, that the main CPU is in failure (an abnormality occurrence state), and generates an output signal to inhibit the driving of the motor. 
     [First Patent Document] Japanese patent No. 2915234 
     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     The conventional steering control apparatus as constructed above has a problem that it is difficult for the apparatus to be applied to motor driving control in which the driving direction and the steering torque do not coincide with each other, such as, for example, external disturbance compensation control based on the angular velocity or the angular acceleration of the motor. 
     In addition, there has been a problem that it is also difficult for the apparatus to be applied to a three-phase motor in which the driving direction of the motor is not directly output from the main CPU to the motor drive circuit. 
     The present invention is intended to obviate the problems as referred to above, and has for its object to obtain a steering control apparatus which can achieve a sophisticated control function and the redundancy of a motor output torque control unit with a simple construction. 
     Means for Solving the Problems 
     A steering control apparatus according to the present invention includes a motor for providing assist torque to a steering system which is operated by a driver, a variety of kinds of sensors that detects at least a steering state of the steering system, and a processing unit that has an input processing section for taking in sensor detection signals from the variety of kinds of sensors and an output processing section for driving the motor, and provides an instruction command to the output processing section based on the sensor detection signals. The processing unit includes a motor target output torque calculation section that calculates a target output torque of the motor, and a motor output torque control unit that calculates an impression voltage to the motor by controlling a motor current flowing in the motor in a feedback manner so as to make an actual output torque of the motor coincide with the target output torque. The motor output torque control unit includes at least a plurality of main-calculation sections, and a plurality of sub-calculation sections corresponding to the main-calculation sections. Abnormality of the motor output torque control unit is determined based on individual calculation results of the plurality of main-calculation sections and the plurality of sub-calculation sections. 
     EFFECTS OF THE INVENTION 
     According to the present invention, the redundancy of the motor output torque control unit can be achieved with a simple construction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a steering control apparatus according to a first embodiment of the present invention (first embodiment). 
         FIG. 2  is an explanatory view showing the operation of a rotor angle calculator sub-calculation section according to the first embodiment of the present invention 1 (first embodiment). 
         FIG. 3  is an explanatory view showing the operation of the rotor angle calculator sub-calculation section according to the embodiment of the present invention 1 (first embodiment). 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     (Embodiment 1) 
     Hereinafter, a first embodiment of the present invention will be described while referring to the accompanying drawings. 
       FIG. 1  is a block diagram showing a steering control apparatus according to the first embodiment of the present invention. 
     In  FIG. 1 , the steering control apparatus comprises a torque sensor  1 , a processing unit  2 , a motor  3  and a resolver  4 . 
     The torque sensor  1  detects the steering state (steering torque Ts of a driver) of a steering system of a vehicle, and inputs it to the processing unit  2 . 
     The motor  3  is, for example, a synchronous motor of a permanent magnet field, and it is connected with the steering system that is operated by the driver, and is driven by a control signal based on the result of calculation of the processing unit  2  to provide assist torque to the steering system, thereby assisting a steering force of the driver. 
     The resolver  4  installed to the motor  3  functions as an angle sensor, and it detects rotor angular position information on the motor  3 , and inputs a detection signal related to a rotor angle to the processing unit  2 . 
     The processing unit  2  constitutes an essential portion of the steering control apparatus, and includes an input interface circuit (input processing section)  21  for taking in sensor detection signals from various kinds of sensors, a first microcontroller (first processing unit)  22  having a main CPU, a second microcontroller (second processing unit)  23  having a sub CPU, a current detection circuit  24  for detecting a phase current of the motor  3 , and an inverter  25   a  (output processing section) for driving the motor  3 , wherein a command is given to the inverter (the output processing section)  25   a  based on the sensor detection signals. 
     The first microcontroller  22  comprises a target output torque calculator main-calculation section  221   a , a motor output torque control unit  222 , an abnormality determination section  223   a , and a PWM calculation section  224   a.    
     The target output torque calculator main-calculation section  221   a  calculates a q-axis target current value Iq* corresponding to a target output torque of the motor  3  based on a detection signal (steering torque Ts) from the torque sensor  1 . 
     By controlling a motor current in a feedback manner, the motor output torque control unit  222  controls the PWM calculation section  224   a  so as to make the q-axis target current value Iq* (the target output torque of the motor  3 ), which is calculated by the target output torque calculator main-calculation section  221   a , and a q-axis detection current Iq (an actual output torque of the motor  3 ), which is calculated based on a detection signal (actual phase currents Iu, Iv) from the current detection circuit  24 , coincide with each other. 
     The abnormality determination section  223   a  determines, based on all the calculation results, whether the first microcontroller  22  or the second microcontroller  23  is abnormal, and generates a command to stop the inverter  25   a  to interrupt the supply of current to the motor  3  at an abnormal time. 
     The PWM calculation section  224   a  pulse width modulates a motor phase voltage signal (three-phase target impression voltage values Vu*, Vv* and Vw*) from the motor output torque control unit  222 , and supplies to the inverter  25   a  a PWM signal that is generated from the three-phase target impression voltage values Vu*, Vv*, Vw*. 
     The inverter  25   a  is driven by the PWM signal from the PWM calculation section  224   a  to drive the motor  3 . 
     The motor output torque control unit  222  comprises a feedback controller main-calculation section  225   a , an impression voltage calculator main-calculation section  226   a , a impression voltage calculator sub-calculation section  226   b , a rotor angle calculator main-calculation section  227   a , a detection current calculator main-calculation section  228   a , and a detected current calculator sub-calculation section  228   b.    
     The feedback controller main-calculation section  225   a  controls the motor current in a feedback manner based on the q-axis detection current Iq calculated from the detected values (the actual phase currents Iu, Iv) of the current detection circuit  24 . 
     The impression voltage calculator main-calculation section  226   a  converts a q-axis impression voltage value Vq* and a d-axis impression voltage value Vd* calculated by the feedback controller main-calculation section  225   a  into phase voltages of the motor  3  (three-phase target impression voltage values Vu*, Vv*, Vw*). 
     The impression voltage calculator sub-calculation section  226   b  determines abnormality of the impression voltage calculator main-calculation section  226   a  based on the three-phase target impression voltage values Vu*, Vv*, Vw*. 
     The rotor angle calculator main-calculation section  227   a  calculates a rotor angle (electrical angle) θ of the motor  3  based on an output signal of the resolver  4 . 
     The detection current calculator main-calculation section  228   a  converts a d-axis detection current Id and the q-axis detection current Iq based on the calculated rotor angle θ and the actual phase currents Iu, Iv of the motor  3  detected by the current detection circuit  24 . 
     The detection current calculator sub-calculation section  228   b  determines abnormality of the detection current calculator main-calculation section  228   a  based on the calculated rotor angle θ and actual phase currents Iv, Iw of the motor  3 . 
     On the other hand, the second microcontroller  23  is mutually connected to the first microcontroller  22  through a communication line  100 , and includes a target output torque calculator sub-calculation section  221   b , a feedback controller sub-calculation section  225   b , a rotor angle calculator sub-calculation section  227   b , a PWM abnormality determination section  224   b , an inverter output voltage abnormality determination section  25   b , and an abnormality determination section  223   b.    
     The target output torque calculator sub-calculation section  221   b  determines abnormality of the target output torque calculator main-calculation section  221   a  in the first microcontroller  22  based on the steering torque Ts detected by the torque sensor  1  and the q-axis target current value Iq* calculated by the target output torque calculator main-calculation section  221   a.    
     The feedback controller sub-calculation section  225   b  determines abnormality of the feedback controller main-calculation section  225   a  based on the d-axis impression voltage value Vd* and the q-axis impression voltage value Vq* calculated by the feedback controller main-calculation section  225   a  in the motor output torque control unit  222 . 
     The rotor angle calculator sub-calculation section  227   b  determines abnormality of the rotor angle calculator main-calculation section  227   a  based on input information (angular position detection signals sin θ, cos θ) to the rotor angle calculator main-calculation section  227   a  in the motor output torque control unit  222  and the rotor angle θ calculated by the rotor angle calculator main-calculation section  227   a.    
     The PWM abnormality determination section  224   b  determines abnormality of the PWM calculation section  224   a  in the first microcontroller  22  by supervising the period of a carrier wave by monitoring an impression voltage to the motor  3 . 
     The inverter output voltage abnormality determination section  25   b  determines abnormality of the inverter  25   a  by supervising a neutral point potential by monitoring the three-phase impression voltages Vu, Vv, Vw to the motor  3 . 
     The abnormality determination section  223   b  determines, similar to the abnormality determination section  223   a  in the first microcontroller  22 , the presence or absence of abnormality of the main-calculation sections from the calculation results of all the main-calculation sections and sub-calculation sections, and interrupts the driving of the motor  3  by the inverter  25   a  when abnormality is found even in either one of them. 
     As shown in  FIG. 1 , the processing unit  2  includes, as the plurality of main-calculation sections, the target output torque calculator main-calculation section  221   a , the feedback controller main-calculation section  225   a , the impression voltage calculator main-calculation section  226   a , the rotor angle calculator main-calculation section  227   a , and the detection current calculator main-calculation section  228   a.    
     In addition, the processing unit  2  also includes, as the plurality of sub-calculation sections corresponding to the main-calculation sections, the target output torque calculator sub-calculation section  221   b , the feedback controller sub-calculation section  225   b , the impression voltage calculator sub-calculation section  226   b , the rotor angle calculator sub-calculation section  227   b , and the detected current calculator sub-calculation section  228   b.    
     That is, the processing unit  2  includes a target output torque calculation section (the target output torque calculator main-calculation section  221   a  and the target output torque calculator sub-calculation section  221   b ), a feedback control section (the feedback controller main-calculation section  225   a  and the feedback controller sub-calculation section  225   b ), an impression voltage calculation section (the impression voltage calculator main-calculation section  226   a  and the impression voltage calculator sub-calculation section  226   b ), a rotor angle calculation section (the rotor angle calculator main-calculation section  227   a  and the rotor angle calculator sub-calculation section  227   b ), and a detection current calculation section (the detection current calculator main-calculation section  228   a  and the detection current calculator sub-calculation section  228   b ), all of which constitute redundant calculation sections, respectively. 
     In addition, in the processing unit  2 , the motor output torque control unit  222  at least has the impression voltage calculator main-calculation section  226   a  and the detection current calculator main-calculation section  228   a , which are main-calculation sections, and the impression voltage calculator sub-calculation section  226   b  and the detection current calculator sub-calculation section  228   b , which are sub-calculation section, and determines abnormality of the motor output torque control unit  222  based on the individual calculation results of the main-calculation sections and the sub-calculation sections. 
     In addition, here, by way of example, the impression voltage calculator sub-calculation section  226   b  and the detection current calculator sub-calculation section  228   b , which execute sub calculations being equivalent in processing contents to the main calculations and having a relatively large amount of calculations, are mounted in the first microcontroller  22  including the main CPU having a fast processing speed, and the other sub-calculation sections, which execute simplified sub calculations, are mounted in the second microcontroller  23  including the sub CPU having a processing speed slower than that of the main CPU. 
     Moreover, the motor  3  is not limited to the synchronous motor of the permanent magnet field, but may be motors other than an induction motor and a vector control motor. 
     In case where the motor  3  is a polyphase (e.g., three-phase) motor, as shown in the drawings, the impression voltage calculator main-calculation section  226   a  in the motor output torque control unit  222  calculates impression voltages to the individual phases of the polyphase motor, and the impression voltage calculator sub-calculation section  226   b  determines abnormality of the impression voltage calculator main-calculation section  226   a.    
     Further, regardless of the kind of the motor  3 , the rotor angle calculator main-calculation section  227   a  in the motor output torque control unit  222  calculates the rotor angle θ of the motor, and the rotor angle calculator sub-calculation section  227   b  in the second microcontroller  23  determines abnormality of the rotor angle calculator main-calculation section  227   a.    
     Specifically, the resolver  4 , functioning as the angle sensor, outputs angular position detection signals including information of sin θ and cos θ on the rotor angle θ of the motor  3 , and the rotor angle calculator main-calculation section  227   a  obtains the rotor angle θ from arctan (sin θ/cos θ) based on the angular position detection signals. 
     On the other hand, the rotor angle calculator sub-calculation section  227   b  obtains a separate rotor angle θ with a resolution of 45 degrees from eight sets of combinations of the polarity signs and the amplitude magnitude comparison relation of sin θ and cos θ, and determines abnormaility of the rotor angle calculator main-calculation section  227   a  by comparing the calculation results (rotor angle θ) of the main-calculation sections with the calculation results (rotor angle θ′) of the sub-calculation sections. 
     In addition, in case where a three-phase motor is used as the motor  3 , the detection current calculator main-calculation section  228   a  related to of in the motor output torque control unit  222  converts current detection values of at least two phases (actual phase currents Iu, Iv) of the motor  3  (three-phase motor) into two-axis direct currents (d-axis detection current Id and q-axis detection current Iq). 
     On the other hand, the detection current calculator sub-calculation section  228   b  in the motor output torque control unit  222  calculates two-axis direct currents without using, at least for one phase, a phase current (the actual phase current Iu in  FIG. 1 ) that is used by the detection current calculator main-calculation section  228   a.    
     That is, the detection current calculator sub-calculation section  228   b  converts the current detection values of at least two phases among individual phase currents of the motor  3  (three-phase motor) into two-axis direct currents, but at least one of the two phases used at this time includes a phase that is not used by the current main-calculation sections. 
     Also, in the motor output torque control unit  222 , the feedback controller main-calculation section  225   a  performs feedback control by converting the two-axis direct currents (Id, Iq) converted from the individual phase currents (Iu, Iv) of the motor  3  (three-phase motor) into two-axis direct current voltages (Vq*, Vd*), and the impression voltage calculator main-calculation section  226   a  related to the dq axes control converts the two-axis direct current voltages (Vq*, Vd*) into impression voltages (the three-phase target impression voltage values Vu*, Vv*, Vw*) to the individual phases of the motor  3  (three-phase motor). 
     Moreover, the impression voltage calculator sub-calculation section  226   b  in the motor output torque control unit  222  calculates an actual neutral point potential based on the three-phase target impression voltage values Vu*, Vv*, Vw* corresponding to the impression voltages impressed from the impression voltage calculator main-calculation section  226   a  to the motor  3  (three-phase motor), and determines, depending upon whether the neutral point potential is appropriate, whether the impression voltage calculator main-calculation section  226   a  is right or wrong. 
     Here, as will be described later, it is assumed that the individual sub-calculation sections check the main-calculation sections according to expressions or formulae different from those of the individual main-calculation sections. 
     Further, the first and second microcontrollers  22 ,  23  are connected to each other for mutual communications through the communication line  100 , and various data for determining the abnormalities of the individual main-calculation sections  221   a ,  225   a ,  227   a  in the first microcontroller  22  are input to the individual sub-calculation sections  221   b ,  225   b ,  227   b  in the second microcontroller  23  through the communication line  100 . 
     In addition, the abnormality determination sections  223   a ,  223   b  in the first and second microcontrollers  22 ,  23  each include an energization and deenergization control section that controls the supply and interruption of current to the motor  3 , and are constructed, as a fail-safe processing function of each energization and deenergization control section, such that when it is determined that at least one of the plurality of main-calculation sections  221   a ,  225   a ,  226   a ,  227   a ,  228   a  is abnormal, or when at least one of the inverter output voltage abnormality determination section  25   b  and the PWM abnormality determination section  224   b  makes an abnormality determination, the supply of current from the inverter  25   a  to the motor  3  is interrupted for the protection of the entire apparatus including the motor  3  and the steering system. 
     Further, at least one of the first and second microcontrollers  23  is provided with an energization and deenergization function check section that checks a function of energizing and deenergizing the motor  3  in association with the abnormality determination sections  223   a ,  223   b.    
     The energization and deenergization function check section is constructed such that it checks, as a check function upon activation, at least once whether the function of energizing and deenergizing the motor  3  operates normally, by means of the abnormality determination sections  223   a ,  223   b  before the driving control of the motor  3  after activation of the steering control apparatus is started, and when it is determined that the energization and deenergization function is abnormal, the driving control of the motor  3  is inhibited so as not to perform a steering control operation similarly for the protection of the entire apparatus including the motor  3  and the steering system. 
     Here, note that in  FIG. 1 , as a hardware construction, part of the sub-calculation sections among the plurality of main-calculation sections and sub-calculation sections are incorporated in the second microcontroller  23  different from the first microcontroller  22 , but all of the plurality of main-calculation sections and sub-calculation sections may be incorporated in one and the same microcontroller. 
     In addition, it is not limited to the specific construction example of  FIG. 1 , but an arbitrary part of the plurality of main-calculation sections and sub-calculation sections may be separately incorporated in the second microcontroller  23  different from the first microcontroller  22 . 
     Next, reference will be made to the processing operation of the steering control apparatus including a redundant system according to the first embodiment of the present invention. 
     First of all, in the first microcontroller  22 , the target output torque calculator main-calculation section  221   a  calculates the q-axis target current value Iq* for driving the motor  3  by performing predetermined calculation processing based on the steering torque Ts detected by the torque sensor  1 . 
     The q-axis target current Iq* calculated by the target output torque calculator main-calculation section  221   a  is input to the feedback controller main-calculation section  225   a , and at the same time to the target output torque calculator sub-calculation section  221   b  mounted in the second microcontroller  23  through the communication line  100 . 
     On the other hand, the rotor angle calculator main-calculation section  227   a  in the motor output torque control unit  222  calculates the rotor angle (electrical angle) θ based on the angular position detection signals sin θ, cos θ from the resolver  4  according to the calculation of arctan (sin θ/cos θ). 
     The rotor angle θ calculated by the rotor angle calculator main-calculation section  227   a  is supplied to the impression voltage calculator main-calculation section  226   a , the detection current calculator main-calculation section  226   a  and the detection current calculator sub-calculation section  228   b , and at the same time to the rotor angle calculator sub-calculation section  227   b  mounted in the second microcontroller  23  through the communication line  100 . Also, the angular position detection signals sin θ, cos θ used for the calculation of the electrical angle θ are supplied to the rotor angle calculator sub-calculation section  227   b  through the communication line  100 . 
     The detection current calculator main-calculation section  228   a  calculates the d-axis detection current Id and the q-axis detection current Iq based on the phase current values Iu, Iv detected by the current detection circuit  24  and the rotor angle θ calculated by the rotor angle calculator main-calculation section  227   a  by performing three-phase/two-phase conversion (dq conversion) by the use of the following expression (1). 
     
       
         
           
             
               
                 
                   
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     Deviations of the d-axis detection current Id and the q-axis detection current Iq after conversion calculated according to expression (1) above from two-axis target current values Id*, Iq*, respectively, are individually calculated, and are then input to the feedback controller main-calculation section  225   a.    
     The feedback controller main-calculation section  225   a  generates two-axis target impression voltage values Vd*, Vq* by performing PI control based on the deviations between the two-axis target current values Id*, Iq* and the two-axis detection current values Id, Iq according to the above-mentioned expression (1). 
     The two-axis target impression voltage values Vd*, Vq* are input to the impression voltage calculator main-calculation section  226   a . In addition, the q-axis target impression voltage value Vq* is input to the feedback controller sub-calculation section  225   b  mounted in the second microcontroller  23  through the communication line  100 . 
     The impression voltage calculator main-calculation section  226   a  calculates the three-phase target impression voltage values Vu*, Vv*, Vw* based on dq axes target impression voltage values Vd*, Vq* and the electrical angle θ by performing two-phase/three-phase conversion (dq inversion) by the use of the following expression (2). 
     
       
         
           
             
               
                 
                   
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     The three-phase target impression voltage values Vu*, Vv*, Vw* calculated by expression (2) above are input to the PWM calculation section  224   a  and the impression voltage calculator sub-calculation section  226   b.    
     The PWM calculation section  224   a  drives the motor  3  to produce the target output torque (required assist torque) by supplying a PWM signal generated based on the three-phase target impression voltage values Vu*, Vv*, Vw* to the inverter  25   a.    
     Next, reference will be made to the operation of the redundant system of the steering control apparatus according to the first embodiment of the present invention. 
     First of all, reference will be made to the abnormality determination (validity verification) operations of the target output torque calculator sub-calculation section  221   b , the PWM abnormality determination section  224   b  and the inverter output voltage abnormality determination section  25   b  in the second microcontroller  23  with respect to the target output torque calculator main-calculation section  221   a , the PWM calculation section  224   a  and the inverter  25   a  which are arranged outside of the motor output torque control unit  222  in the first microcontroller  22 . 
     In the second microcontroller  23 , the target output torque calculator sub-calculation section  221   b  performs interlocking based on the steering torque Ts detected by the torque sensor  1  and the q-axis target current Iq* input from the first microcontroller  22  through the communication line  100 . 
     The PWM abnormality determination section  224   b  supervises the carrier wave period of a motor drive signal by directly monitoring the pulse-width modulated three-phase impression voltages Vu, Vv, Vw to the motor  3  through the input interface circuit  21 . 
     Similarly, the inverter output voltage abnormality determination section  25   b  supervises the neutral point potential of the three-phase impression voltages Vu, Vv, Vw by directly monitoring the three-phase impression voltages Vu, Vv, Vw to the motor  3  through the input interface circuit  21 . 
     The operations of the above-mentioned target output torque calculator sub-calculation section  221   b , the PWM abnormality determination section  224   b  and the inverter output voltage abnormality determination section  25   b  verify the validity of the apparatus by solely using signals appearing outside of the first and second controllers  22 ,  23 . 
     That is, the target output torque calculator sub-calculation section  221   b  verifies the validity of the relation between the input signal (the q-axis target current value to the motor output torque control unit  222  and the steering torque Ts, and the PWM abnormality determination section  224   b  and the inverter output voltage abnormality determination section  25   b  verify the validity of the output signals (the phase voltages Vu, Vv, Vw to the motor  3 ) from the motor output torque control unit  222 . 
     Next, reference will be made to the abnormality determination (validity verification) operation of the calculation sections in the motor output torque control unit  222  while referring to  FIG. 2  and  FIG. 3  together with  FIG. 1 . 
       FIG. 2  and  FIG. 3  are explanatory views that show the operation of the rotor angle calculator sub-calculation section  227   b  in the second microcontroller  23 . 
       FIG. 2  and  FIG. 3  illustrate the rotor angle θ (regions R 1  through R 8 ) calculated by the rotor angle calculator sub-calculation section  227   b , and the individual regions R 1  through R 8  in  FIG. 2  and  FIG. 3  are set by eight sets of combinations of the polarity signs and the amplitude magnitude comparison results of sin θ and cos θ. 
     In  FIG. 1 , the feedback controller sub-calculation section  225   b , which determines abnormality of the feedback controller main-calculation section  225   a  in the first microcontroller  22 , is mounted in the second microcontroller  23 , as previously stated. 
     The feedback controller sub-calculation section  225   b  monitors whether the q-axis target impression voltage value Vq* input from the first microcontroller  22  through the communication line  100  is in a predetermined normal range, and determines, when the q-axis target impression voltage value Vq* deviates from the normal range, that the feedback controller main-calculation section  225   a  is abnormal. 
     On the other hand, the impression voltage calculator sub-calculation section  226   b , which determines abnormality of the impression voltage calculator main-calculation section  226   a , is mounted in the first microcontroller  22 , and monitors, based on whether the relation of the following expression (3) is satisfied, whether the neutral point potential of the three-phase target impression voltage values Vu*, Vv*, Vw* (the impression voltage calculator main-calculation section  226   a ).
 
 Vu*+Vv*+Vw*= 0  (3)
 
     When the above expression (3) is not satisfied, the impression voltage calculator sub-calculation section  226   b  determines that the impression voltage calculator main-calculation section  226   a  is abnormal. 
     On the other hand, the rotor angle calculator sub-calculation section  227   b , which determines abnormality of the rotor angle calculator main-calculation section  227   a  in the first microcontroller  22 , is mounted in the second microcontroller  23 , as previously stated. 
     The rotor angle calculator sub-calculation section  227   b  takes in the information (angular position detection signals sin θ, cos θ) input to the rotor angle calculator main-calculation section  227   a  from the resolver  4  and the rotor angle θ calculated by the rotor angle calculator main-calculation section  227   a  from the first microcontroller  22  through the communication line  100 , and the rotor angle calculator sub-calculation section  227   b  determines abnormality of the rotor angle calculator main-calculation section  227   a  based on the angular position detection signals sin θ, cos θ. 
     That is, the rotor angle calculator sub-calculation section  227   b  separately calculates the rotor angle θ′ (the regions R 1  through R 8 ) with a resolution of 45 degrees from the eight sets of combinations of the polarity signs and the amplitude magnitude comparison results of sin θ and cos θ, as illustrated in  FIG. 2  and  FIG. 3 , compares the rotor angle θ′ calculated by itself with the rotor angle θ calculated by the rotor angle calculator main-calculation section  227   a , and determines, based on whether the rotor angle θ is in a calculated region, whether the rotor angle calculator main-calculation section  227   a  is right or wrong. 
     Finally, the detection current calculator sub-calculation section  228   b , which determines abnormality of the detection current calculator main-calculation section  228   a , is mounted in the first microcontroller  22 , and calculates the d-axis detection current Id and the q-axis detection current Iq based on the actual phase current values Iv, Iw detected by the current detection circuit  24  and the rotor angle (electrical angle) θ calculated by the rotor angle calculator main-calculation section  227   a  by performing three-phase/two-phase conversion (dq conversion) by the use of the following expression (4). 
     
       
         
           
             
               
                 
                   
                     [ 
                     
                       
                         
                           
                             I 
                             d 
                           
                         
                       
                       
                         
                           
                             I 
                             q 
                           
                         
                       
                     
                     ] 
                   
                   = 
                   
                     
                       
                         2 
                       
                       ⁡ 
                       
                         [ 
                         
                           
                             
                               
                                 sin 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     θ 
                                     - 
                                     
                                       π 
                                       3 
                                     
                                   
                                   ) 
                                 
                               
                             
                             
                               
                                 - 
                                 
                                   sin 
                                   ⁡ 
                                   
                                     ( 
                                     
                                       θ 
                                       + 
                                       
                                         π 
                                         3 
                                       
                                     
                                     ) 
                                   
                                 
                               
                             
                           
                           
                             
                               
                                 sin 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     θ 
                                     + 
                                     
                                       π 
                                       6 
                                     
                                   
                                   ) 
                                 
                               
                             
                             
                               
                                 - 
                                 
                                   sin 
                                   ⁡ 
                                   
                                     ( 
                                     
                                       θ 
                                       + 
                                       
                                         
                                           5 
                                           ⁢ 
                                           π 
                                         
                                         6 
                                       
                                     
                                     ) 
                                   
                                 
                               
                             
                           
                         
                         ] 
                       
                     
                     · 
                     
                       [ 
                       
                         
                           
                             
                               I 
                               v 
                             
                           
                         
                         
                           
                             
                               I 
                               w 
                             
                           
                         
                       
                       ] 
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     The detection current calculator sub-calculation section  228   b  compares the dq conversion result according to expression (4) above with the dq conversion result of the detection current calculator main-calculation section  228   a  based on the above-mentioned expression (1), and determines, depending upon whether both of them coincide with each other, whether the detection current calculator main-calculation section  228   a  is right or wrong. 
     As described above, it is possible to verify all the main-calculation sections, which are divided into a plurality of sections in the processing unit  2 , by performing the calculation processing of the redundant system by the use of the plurality of sub-calculation sections corresponding to the plurality of the main-calculation sections. 
     Next, reference will be made to the driving control interruption operation of the motor  3  by means of the abnormality determination sections  223   a ,  223   b  with a fail safe function. 
     At least one of the abnormality determination sections  223   a ,  223   b  in the first and second microcontrollers  23  determines the presence or absence of abnormality of the main-calculation sections from all the above-mentioned calculation results of the main-calculation sections and the sub-calculation sections, and interrupts the driving of the motor  3  by the inverter  25   a  when it is determined that there is abnormality even in either one of them. 
     As a result, it is possible to protect the motor  3  and the entire apparatus, as previously stated. 
     In addition, at least one of the first and second microcontrollers  22 ,  23  performs an initial check operation upon activation in cooperation with the abnormality determination sections  223   a ,  223   b.    
     That is, as stated above, it is examined after activation whether the interruption functions of the abnormality determination sections  223   a ,  223   b  operate normally, and if there is abnormality, the supply of current from the inverter  25   a  to the motor  3  is interrupted so as to prevent the steering control. 
     Thus, it is possible to protect the motor  3  and the entire apparatus, as previously stated. 
     As described above, according to the first embodiment of the present invention, it is possible to achieve the redundant system of the motor output torque control unit  222  of a complicated construction for controlling, for example, the three-phase motor of the permanent magnet field on the dq axes with relative ease. 
     In the above-mentioned first embodiment, the current detection circuit  24  detects the two-phase currents (Iu, Iv), but it may be constructed to detect the three-phase currents (Iu, Iv, Iw). 
     In this case, there is an advantageous effect that abnormality of the current detection circuit  24  can also be determined in the detection current calculator sub-calculation section  228   b.    
     (Embodiment 2) 
     In the above-mentioned first embodiment, the sub calculations, which are equivalent in contents to the main calculations and relatively large in the calculation amounts, are executed in the first microcontroller  22  including the main CPU having a fast processing speed, and simplified sub calculations are executed in the second microcontroller  23  including the sub CPU having a processing speed slower than that of the main CPU, but it may be constructed such that processing of all the sub calculations are executed in the sub CPU (the second microcontroller  23 ) by using, as the sub CPU, one that can perform relatively high-speed processing. 
     In this case, there is an advantageous effect that a satisfactory verification can be made even if completely the same calculation expressions or formulae as those for the main calculations are used as the sub calculations. 
     For example, in the second microcontroller  23 , the rotor angle calculator sub-calculation section  226   b  can obtain the rotor angle θ from the angular position detection signals sin θ and cos θ by performing the same calculations as those for the main calculations without obtaining the rotor angle θ′ (see  FIG. 2  and  FIG. 3 ) comprising the eight sets of regions R 1  through R 8 , and determine abnormality of the rotor angle calculator main-calculation section  226   a  by comparing it with the calculation result of the main-calculation section. 
     Similarly, in the first microcontroller  22 , the detection current calculator sub-calculation section  228   b  performs the same calculations as those of the corresponding main-calculation section, converts the detected values of at least two phase currents among the individual phase currents of the three-phase motor into two-axis direct currents, and compares them with the calculation results of the corresponding main-calculation section, whereby abnormality of the detection current calculator main-calculation section  228   a  can be determined. 
     Also, the impression voltage calculator sub-calculation section  226   b  performs the same calculations as those of the corresponding main-calculation section, converts two-axis direct current voltages into respective phase impression voltages to the three-phase motor, and compares them with the calculation results of the corresponding main-calculation section, whereby abnormality of the impression voltage calculator main-calculation section  226   a  can be determined. 
     Further, although the first and second microcontrollers  22 ,  23  are used, all the main calculations and sub calculations may be carried out by one and the same microcontroller. 
     In this case, a satisfactory verification can be performed by setting the main calculations and the sub calculations to different calculation processings having equivalent contents, respectively. 
     In addition, in case where a single microcontroller is used, a sub CPU (second microcontroller  23 ) becomes unnecessary, and hence in addition to the above-mentioned advantageous effect, there is an advantageous effect that the redundant system can be achieved with a further simple construction. 
     (Embodiment 3) 
     Further, in the above-mentioned first embodiment, for example, the detection current calculator sub-calculation section  228   b  performs the dq conversion by using the above-mentioned expression (4) for a phase current different in phase from the above-mentioned expression (1) in the detection current calculator main-calculation section  228   a , but it may multiply a current or voltage of the same phase as that in the corresponding main-calculation section by a matrix with its phase shifted therefrom. 
     In this case, multiplication processing in the sub calculations is added, but the programming construct of the sub calculations can be made completely identical with that of the main calculations, so in addition to the above-mentioned advantageous effects, there is an advantageous effect that the creation of programs can be facilitated. 
     That is, the detection current calculator sub-calculation section  228   b  obtains a calculation result equivalent to that of a corresponding main-calculation section from at least two phase currents of the individual phase currents of the three-phase motor, and calculates two-axis direct currents by using a matrix different from that in the main-calculation section, whereby it is possible to determine abnormality of the main-calculation section based on a comparison thereof with the calculation result of the main-calculation section. 
     Similarly, the impression voltage calculator sub-calculation section  226   b  obtains a calculation result equivalent to that of a corresponding main-calculation section from two-axis direct current voltages from a feedback control section, and calculates individual phase impression voltages to the three-phase motor by using a matrix different from that in the main-calculation section, whereby it is possible to determine abnormality of the main-calculation section based on a comparison thereof with the calculation result of the corresponding main-calculation section.