Abstract:
A diagnostic device capable of accurately diagnosing the soundness of a resolver circuit is provided. A shifter receives excitation signal and excitation signal; shifts the level of excitation signal, excitation signal, or both; and performs level shifting such that a period of time that starts with one of two times in which, in the vicinity of the peak value of excitation signal, excitation signal and excitation signal are at the same value and ends with the other of the two times is less than a prescribed threshold. A trigger generation circuit generates a trigger during said period of time. A control unit determines whether there is an abnormality in the resolver circuit on the basis of the trigger.

Description:
TECHNICAL FIELD 
     The present invention relates to a diagnostic device that detects an abnormality in a resolver circuit that calculates a rotational angle of a vehicular motor. 
     BACKGROUND ART 
     When a vehicular motor to be mounted on a vehicle, such as a plug-in hybrid electric vehicle (PHEV) or an electric vehicle (EV) is controlled, it is necessary to satisfy a functional safety standard of ISO 26262 Therefore, achieving the following safety goal is typically required. 
     (1) The motor does not rotate in a direction reverse to an intentional rotating direction (ASIL-C or D). 
     (2) The motor does not output unintentional torque and a rotational speed (ASIL-C or D). 
     In order to achieve the above safety goal, it is necessary to dispose a safety mechanism that stops drive of the motor when abnormal rotation of the vehicular motor is detected. 
     Ina conventional resolver circuit, based on output signals (SIN signal and COS signal) from a resolver, a resolver digital converter (RDC) calculates and outputs a rotational angle θ of a motor to an external microcomputer. The external microcomputer performs feedback control to the motor based on the rotational angle θ of the motor supplied from the RDC. 
     Therefore, in order to dispose the above safety mechanism, the resolver circuit that calculates the rotational angle θ of the vehicular motor is required to be sound. 
     Regarding this point, based on an interval between zero crossing points of an excitation signal to be supplied to an excitation coil of the resolver, it has been known a device that samples the output signals (SIN signal and COS signal) from the resolver and calculates sin θ and cos θ so as to detect an abnormality in the resolver circuit (for example, refer to Patent Literature 1). 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Patent No. 3402207 
     SUMMARY OF INVENTION 
     Technical Problem 
     In a diagnostic device disclosed in Paten Literature 1, even when there is an abnormality in an amplitude of an excitation signal, zero crossing points do not vary. Therefore, the abnormality in the amplitude of the excitation signal cannot be detected. In other words, in the conventional diagnostic device, soundness of a resolver circuit is sometimes not diagnosed accurately. 
     An object of the present invention is to provide a diagnostic device that can accurately diagnose soundness of a resolver circuit. 
     Solution to Problem 
     In order to achieve the above object, the present invention includes: a shifter configured to receive an excitation signal EXC+ to be input to a first end of an excitation coil of a resolver and the excitation signal EXC− to be input to a second end of the excitation coil, and shift a level of at least one of the excitation signal EXC+ and the excitation signal EXC− so that a period from first timing as a starting point to second timing as an end point becomes equal to or less than a predetermined threshold, the first timing and the second timing at which the excitation signal EXC+ and the excitation signal EXC− have a same value in a vicinity of a peak value of the excitation signal EXC+; a trigger generation circuit configured to generate a trigger during the period; and a control unit configured to diagnose whether there is an abnormality in a resolver circuit based on the trigger. 
     Advantageous Effects of Invention 
     According to the present invention, soundness of a resolver circuit can be accurately diagnosed. Problems, configurations, and effects other than the above descriptions will be clear in the following embodiments. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram of a configuration of a resolver system including a diagnostic device according to a first embodiment of the present invention. 
         FIG. 2  is a block diagram of a configuration of the diagnostic device according to the first embodiment of the present invention. 
         FIG. 3  is an explanatory graphical representation of an excitation signal generated by an RDC used in the diagnostic device according to the first embodiment of the present invention. 
         FIG. 4  is an explanatory graphical representation of operation of the diagnostic device according to the first embodiment of the present invention. 
         FIG. 5  is an explanatory graphical representation of operation of the diagnostic device according to the first embodiment of the present invention in a case where there is an abnormality in the RDC of a resolver circuit. 
         FIG. 6  is a block diagram of a configuration of a resolver system including a diagnostic device according to a second embodiment of the present invention. 
         FIG. 7  is a block diagram of a configuration of the diagnostic device according to the second embodiment of the present invention. 
         FIG. 8  is an explanatory graphical representation of a voltage value held by a sample-hold circuit and used for the diagnostic device according to the second embodiment of the present invention. 
         FIG. 9  is a block diagram of a configuration of a resolver system including a diagnostic device according to a third embodiment of the present invention. 
         FIG. 10  is a block diagram of the diagnostic device according to the third embodiment of the present invention. 
         FIGS. 11(A)  to (D) illustrate explanatory graphical representations of output signals, from a resolver, to be input into the diagnostic device according to the third embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     [First Embodiment] 
     A configuration and operation of a diagnostic device  100 A according to a first embodiment of the present invention will be described below using  FIGS. 1 to 5 . The diagnostic device  100 A is a device that detects an abnormality in a resolver circuit calculating a rotational angle θ of a vehicular motor. 
     First of all, an entire configuration of a resolver system including the diagnostic device  100 A according to the first embodiment of the present invention will be described using  FIG. 1 .  FIG. 1  is a block diagram of the configuration of the resolver system including the diagnostic device  100 A according to the first embodiment of the present invention. 
     The resolver system includes a motor M, a resolver  10 , a resolver circuit  20 , and the diagnostic device  100 A. 
     The motor M is a motor that drives the vehicle. 
     The resolver  10  is a typical angular sensor that detects the rotational angle θ of the motor M. The resolver  10  includes an excitation coil  11  (primary coil), and secondary coils  12  and  13 . The resolver  10  is coaxially attached to the motor M. 
     According to the present embodiment, an excitation signal EXC− of a sine wave is input into a first end of the excitation coil  11  (negative pole). An excitation signal EXC+ that is the inverted excitation signal EXC−, is input into a second end of the excitation coil  11  (positive pole). 
     Accordingly, a first end of the secondary coil  12  outputs an output signal SIN+ corresponding to the rotational angle θ of the motor. A second end of the secondary coil  12  outputs an output signal SIN− corresponding to the rotational angle θ of the motor. 
     Meanwhile, the secondary coil  13  is disposed so as to output an output signal that has a phase shifted from that of the secondary coil  12  by 90°. A first end of the secondary coil  13  outputs an output signal COS+. A second end of the secondary coil  13  outputs an output signal COS−. 
     The resolver circuit  20  includes a resolver digital converter (RDC)  21 . Here, the RDC  21  may be a resolver IC. 
     The RDC  21  generates the excitation signals EXC+ and EXC− so as to supply the excitation signals EXC+ and EXC− to the excitation coil  11  of the resolver  10  and the diagnostic device  100 A. The RDC  21  receives the output signals SIN+ and SIN− from the secondary coil  12  of the resolver  10  and receives the output signals COS+ and COS− from the secondary coil  13  of the resolver  10 . The RDC  21  calculates the rotational angle θ of the motor based on these output signals. 
     Based on the excitation signals EXC+ and EXC−, the diagnostic device  100 A detects an abnormality in an amplitude of each of the excitation signals EXC+ and EXC− so as to detect an abnormality in the resolver circuit  20 . A detailed description of the diagnostic device  100 A will be given later using  FIG. 2 . 
     Next, a configuration of the diagnostic device  100 A according to the first embodiment of the present invention will be described using  FIG. 2 .  FIG. 2  is a block diagram of the configuration of the diagnostic device  100 A according to the first embodiment of the present invention. 
     The diagnostic device  100 A includes a shifter  101 , a trigger generation circuit  102 , and a control unit  103 . 
     The shifter  101  receives the excitation signals EXC+ and EXC− and shifts levels of the excitation signals EXC+ and EXC− by +α and +β, respectively, so as to supply the level-shifted excitation signals (EXC+)+α and (EXC−)−β to the trigger generation circuit  102 . A detailed description of operation of the shifter  101  will be given later using  FIGS. 3 and 4 . 
     Based on the level-shifted excitation signals (EXC+)+α and (EXC−)−β, the trigger generation circuit  102  generates a trigger signal Trg that indicates timing of a peak of the excitation signal ESC+ so as to supply the trigger signal Trg to the control unit  103 . A detailed description of operation of the trigger generation circuit  102  will be given later using  FIG. 4 . 
     The control unit  103  includes, for example, a microcomputer. The control unit  103  includes a trigger signal input port  103   a , a cycle measuring unit  103   b , a cycle diagnosing unit  103   c , and a memory  103   d.    
     The trigger signal input port  103   a  receives the trigger signal Trg from the trigger generation circuit  102  so as to supply the trigger signal Trg to the cycle measuring unit  103   b.    
     The cycle measuring unit  103   b  measures a cycle of the trigger signal Trg so as to supply the measured value T Trg  to the cycle diagnosing unit  103   c.    
     The cycle diagnosing unit  103   c  determines that there is the abnormality in the resolver circuit  20  when the cycle T Trg  of the trigger signal Trg supplied from the cycle measuring unit  103   b  is different from a cycle T normal  that has already been stored in the memory  103   d . Here, the cycle T normal  is a cycle of the trigger signal Trg when the RDC  21  is normal. 
     Next, the excitation signals EXC+ and EXC− generated by the RDC  21  will be described using  FIG. 3 .  FIG. 3  is an explanatory graphical representation illustrating the excitation signals EXC+ and EXC− generated by the RDC  21  and used for the diagnostic device  100 A according to the first embodiment of the present invention. Note that, in  FIG. 3 , the horizontal axis represents time and the vertical axis represents a voltage value of the excitation signals. 
     According to the present embodiment, the excitation signal EXC− is a sine wave and the excitation signal EXC+ is an inverted excitation signal EXC−. 
     Next, operation of the diagnostic device  100 A according to the first embodiment of the present invention will be described using  FIG. 4 .  FIG. 4  is an explanatory graphical representation of the operation of the diagnostic device  100 A according to the first embodiment of the present invention. Note that, in  FIG. 4 , the horizontal axis represents time and the vertical axis represents a voltage value of the excitation signals. 
     The shifter  101  shifts level of the excitation signal EXC+ supplied from the RDC  21  by +α and shifts level of the excitation signal EXC− supplied from the RDC  21  by +β. That is, the excitation signals illustrated in  FIG. 4  are caused by moving the excitation signals illustrated in  FIG. 3  in the vertical direction in parallel. 
     Here, the excitation signal EXC+ and the excitation signal EXC− have the same voltage value at first timing and second timing in the vicinity of the peak value of the excitation signal EXC+. The shifter  101  shifts the levels of the excitation signals EXC+ and EXC− so that a period ΔT from the first timing (earlier) as a starting point T 1  to the second timing (later) as an endpoint T 2  becomes equal to or less than a predetermined threshold (for example, 2 μs). 
     That is, the shifter  101  shifts the levels of the excitation signals EXC+ and EXC− so that the excitation signals EXC+ and EXC− are substantially in close contact with each other. 
     Next, the trigger generation circuit  102  generates, as a trigger, a rectangular wave in which the voltage value has become a high level during the period ΔT. In  FIG. 4 , each of two rectangular waves is generated in the vicinity of timing of the peak of the excitation signal EXC+. The trigger generation circuit  102  inputs, as the trigger signal Trg, the two rectangular waves into the trigger signal input port  103   a.    
     The trigger signal input port  103   a  supplies the input trigger signal Trg to the cycle measuring unit  103   b.    
     After once the period ΔT becomes equal to or less than the predetermined threshold by the shifter  101 , the cycle measuring unit  103   b  compares the cycle T Trg  of the trigger signal Trg supplied from the cycle measuring unit  103   b  and the cycle T normal  that has already been stored in the memory  103   d . The cycle measuring unit  2103   b  determines that there is the abnormality in the RDC  21  of the resolver circuit  20  when the cycle T Trg  and the cycle T normal  are different from each other. 
     For example, when a difference between the cycle T Trg  and the cycle T normal  is equal to or more than the predetermined threshold, the cycle measuring unit  103   b  may determine that there is the abnormality in the RDC  21  of the resolver circuit  20 . 
     Next, operation of the diagnostic device  100 A in a case where there is the abnormality in the RDC  21  of the resolver circuit  20  using  FIG. 5 .  FIG. 5  is an explanatory graphical representation of the operation of the diagnostic device  100 A according to the first embodiment of the present invention in the case where there is the abnormality in the RDC  21  of the resolver circuit  20 . 
     In  FIG. 5 , since the abnormality occurs in the RDC  21 , an amplitude of the excitation signal (EXC+)+α is smaller than that in  FIG. 4 . In this case, since the excitation signal (EXC+) +α and the excitation signal (EXC−)+β do not cross each other, the trigger generation circuit  102  cannot generate the trigger signal. 
     That is, when the RDC  21  is normal, the trigger is generated in the predetermined cycle T Trg  as illustrated in  FIG. 4 . Meanwhile, when the RDC  21  is abnormal, no trigger is generated. 
     Accordingly, time of a predetermined threshold T out  or more has passed since the last trigger (rectangular wave having the high level) is generated. In this case, the cycle diagnosing unit  103   c  determines that there is the abnormality in the resolver circuit  20  so as to notify a motor control unit for controlling the motor M (not illustrated) of the determination. 
     The motor control unit corresponds to the notification from the cycle diagnosing unit  103   c  so as to cause the motor M to stop drive of the motor M. 
     As described above, according to the present embodiment, the abnormality in the amplitude of each of the excitation signals EXC+ and EXC− output from the RDC  21  of the resolver circuit  20  can be detected. Therefore, soundness of the resolver circuit can be accurately diagnosed. 
     [Second Embodiment] 
     Next, a configuration and operation of a diagnostic device  100 B according to a second embodiment of the present invention will be described using  FIGS. 6 to 8 . 
     First, an entire configuration of a resolver system including the diagnostic device  100 B according to the second embodiment of the present invention will be described using  FIG. 6 .  FIG. 6  is a block diagram of the configuration of the resolver system including the diagnostic device  100 B according to the second embodiment of the present invention. Note that portions in  FIG. 6  similar to those in  FIG. 1  are denoted with the same reference signs. 
       FIG. 6  is different from  FIG. 1  in that output signals SIN+ and SIN− of a secondary coil  12  of a resolver  10  and output signals COS+ and COS− of a secondary coil  13  of the resolver  10  are input into the diagnostic device  100 B.  FIG. 6  is also different from  FIG. 1  in that an AB pulse (encoder pulse), from an RDC  21 , corresponding to a rotational angle θ of a motor is input into the diagnostic device  100 B. 
     Next, the configuration of the diagnostic device  100 B according to the second embodiment of the present invention will be described using  FIG. 7 .  FIG. 7  is a block diagram of the configuration of the diagnostic device  100 B according to the second embodiment of the present invention. Note that portions in  FIG. 7  similar to those in  FIG. 2  are denoted with the same reference signs. 
     A sample-hold circuit  104  holds (samples and holds) a voltage value SH sin  of an output signal SIN(=(SIN+)−(SIN−)) from certain timing at which a voltage value of a trigger signal Trg becomes a high level (timing at which a trigger occurs) to timing at which the next trigger occurs, so as to supply the voltage value SH sin  to an AD port  103   g  of a control unit  103 . 
     Similarly, based on the trigger signal Trg, the sample-hold circuit  104  holds a voltage value SH cos  of an output signal COS from the certain timing at where the trigger occurs to the timing at which the next trigger occurs, so as to supply the voltage value SH cos  to an AD port  103   h  of the control unit  103 . 
     That is, the sample-hold circuit  104  holds the voltage value SH sin  of the output signal SIN of a resolver  10  and the voltage value SH sin  of the output signal COS of the resolver  10  at a peak of an excitation signal EXC (=(EXC+)−(ESC−)) for a predetermined period (trigger cycle T Trg ), so as to input the voltage values SH sin  and SH sin  into the AD ports  103   g  and  103   h , respectively. 
     Here, the voltage values held by the sample-hold circuit  104  and used for the diagnostic device  100 B according to the second embodiment of the present invention will be described using  FIG. 8 .  FIG. 8  is an explanatory graphical representation of the voltage values held by the sample-hold circuit  104  and used for the diagnostic device  100 B according to the second embodiment of the present invention. Note that, In  FIG. 8 , the horizontal axis represents time and the vertical axis represent voltage. 
     In  FIG. 8 , the trigger is generated at timing of the peak of the excitation signal EXC. Note that, in this example, the cycle in which the trigger occurs is 100 μs. 
     The sample-hold circuit  104  holds the voltage values of the output signals SIN and COS at the timing at which the trigger occurs. The voltage values that has been held by the sample-hold circuit  104  are constant during a period during which sample-hold has been performed (trigger cycle T Trg ). Accordingly, sampling of AD conversion can be performed at arbitrary timing during this period. 
     Referring back to  FIG. 7 , the AD port  103   g  converts the voltage value SH sin  (analog value) supplied from the sample-hold circuit  104  into a digital value so as to supplies the voltage value SH sin  (digital value) as an AD value to an AD value acquisition unit  103   i.    
     Similarly, the AD port  103   h  converts the voltage value SH cos  (analog value) supplied from the sample-hold circuit  104  into a digital signal so as to supply the voltage value SH cos  (digital value) as the AD value to the AD value acquisition unit  103   i.    
     The AD value acquisition unit  103   i  acquires the latest AD values SH sin  and SH cos  supplied from the AD port  103   g  so as to supply the latest AD values SH sin  and SH cos  to an angle calculating unit  103   j.    
     The angle calculating unit  103   j  calculates the rotation angle θ of the motor M at the timing at which the trigger occurs, based on the latest AD values SH sin  and SH cos  supplied from the AD value acquisition unit  103   i.    
     More specifically, the angle calculating unit  103   j  calculates a rotational angle (resolver angle) θ 1  of the motor M based on θ=tan −1  (SH sin /SH cos ). Here, tan an inverse function of tan. 
     The angle calculating unit  103   j  stores the calculated rotational angle θ 1  in a memory (RAM)  103   k.    
     Meanwhile, an AB pulse input port  103   f  receives the AB pulse from the RDC  21  of the resolver circuit  20  so as to supply the AB pulse to a real-time counter measuring unit  103   m.    
     The real-time counter measuring unit  103   m  measures, as a counter value, the number of pulses in the AB pulse per unit time so as to supply the counter value to the an angle conversion unit  103   p.    
     Here, based on the trigger signal Trg, an interruption generation unit  103   e  supplies an interruption signal to the angle conversion unit  103   p  at the timing at which the trigger occurs. 
     Based on the interruption signal, at the timing at which the trigger occurs, the angle conversion unit  103   p  converts the counter value supplied from the real-time counter measuring unit  103   m  into a rotational angle θ 2  of the motor M so as to store the rotational angle θ 2  in a memory  103   q.    
     An angle diagnosing unit  103   n  determines that there is an abnormality in the resolver circuit  20  when the rotational angle θ 1  of the motor M stored in the memory  103   k  and the rotational angle θ 2  of the motor M stored in the memory  103   q  are different from each other. In this case, the angle diagnosing unit  103   n  notifies a motor control unit (not illustrated) that there is the abnormality in the resolver circuit  20 . 
     The motor control unit corresponds to the notification from the angle diagnosing unit  103   n  so as to cause the motor M to stop drive of the motor M. 
     As described above, according to the present embodiment, an abnormality of the rotational angle of the motor M calculated by the resolver circuit  20  can be detected. Therefore, soundness of the resolver circuit can be accurately diagnosed. 
     [Third Embodiment] 
     Next, a configuration and operation of a diagnostic device  100 C according to a third embodiment of the present invention using  FIGS. 9 to 11 . 
     First, an entire configuration of a resolver system including the diagnostic device  100 C according to the third embodiment of the present invention will be described using FIG.  9 .  FIG. 9  is a block diagram of the configuration of the resolver system including the diagnostic device  100 C according to the third embodiment of the present invention. Note that, portions in  FIG. 9  similar to those in  FIG. 6  are denoted with the same reference signs. 
       FIG. 9  is different from  FIG. 6  in that an error signal Err from an RDC  21 , as a result of a self-diagnosis, is input into the diagnostic device  100 C 
     Next, the configuration of the diagnostic device  100 C according to the third embodiment of the present invention will be described using  FIG. 10 .  FIG. 10  is a block diagram of the configuration of the diagnostic device  100 C according to the third embodiment of the present invention. Note that portions in  FIG. 10  similar to those in  FIG. 7  are denoted with the same reference signs. 
     According to the present embodiment, an output signal diagnosing unit  103   s  detects an abnormality in any of output signals SIN and COS from a resolver  10 , based on the latest AD values SH sin+ , SH sin− , SH cos+ , and SH cos−  supplied from an AD value acquisition unit  103   i.    
     Here, the output signals, from the resolver  10 , to be input into the diagnostic device  100 C according to the third embodiment of the present invention will be described using  FIG. 11 .  FIG. 10  illustrates explanatory graphical representations of the output signals, from the resolver  10 , to be input into the diagnostic device  100 C according to the third embodiment of the present invention. 
       FIG. 11(A)  is a graphical representation of the output signals SIN+ and SIN−. In  FIG. 11(A) , the horizontal axis represents time and the vertical axis represents voltage. Here, the output signals SIN+ and SIN− can be expressed by the following expressions (1) and (2), respectively.
 
(SIN+)= V 0+ A *sin θ*sin ω t   (1)
 
(SIN−)= V 0− A *sin θ*sin ω t   (2)
 
     Note that the output signal SIN+ and the output signal SIN− are symmetrical with respect to V 0 . Reference symbols V 0 , A, θ, ω, and t represent an offset value, an amplitude, an rotational angle of a motor M (resolver angle), angular velocity of the motor M, and time, respectively. A reference symbol cot represents a phase of an excitation signal EXC. According to the present embodiment, V 0 =1.25 V and A=0.9 are used as recommended values for the RDC  21 . 
       FIG. 11(B)  is a graphical representation of the output signals COS+ and COS−. In  FIG. 11(B) , the horizontal axis represents time and the vertical axis represents voltage. Here, the output signals COS+ and COS− can be expressed by the following expressions (3) and (4)
 
(COS+)= V 0+ A *cos θ*sin ω t   (3)
 
(COS−)= V 0− A *cos θ*sin ω t   (4)
 
     Note that the output signal COS+ and the output signal COS− are symmetrical with respect to V 0 . 
       FIG. 11(C)  is a graphical representation of the output signal SIN(=(SIN+)−(SIN−)). In  FIG. 11(C) , the horizontal axis represents time and the vertical axis represents voltage. Here, the output signal SIN can be expressed by the following expression (5) with the expressions (1) and (2) 
     
       
         
           
             
               
                 
                   SIN 
                   = 
                   
                     
                       
                         ( 
                         
                           SIN 
                           ⁢ 
                           
                             + 
                           
                         
                         ) 
                       
                       - 
                       
                         ( 
                         
                           SIN 
                           - 
                         
                         ) 
                       
                     
                     = 
                     
                       2 
                       * 
                       A 
                       * 
                       sin 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       θ 
                       * 
                       sin 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       ω 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       t 
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     where 2*A represents an amplitude of the output signal SIN. 
       FIG. 11(D)  is a graphical representation of the output signal COS(=(COS+)−(COS−)). In  FIG. 11(D) , the horizontal axis represents time and the vertical axis represents voltage. Here, the output signal COS can be expressed by the following expression (6) with the expressions (3) and (4). 
     
       
         
           
             
               
                 
                   COS 
                   = 
                   
                     
                       
                         ( 
                         
                           COS 
                           ⁢ 
                           
                             + 
                           
                         
                         ) 
                       
                       - 
                       
                         ( 
                         
                           COS 
                           - 
                         
                         ) 
                       
                     
                     = 
                     
                       2 
                       * 
                       A 
                       * 
                       cos 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       θ 
                       * 
                       sin 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       ω 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       t 
                     
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
     where 2*A represents an amplitude of the output signal COS. 
     (Offset diagnosis) 
     Referring back to  FIG. 10 , the output signal diagnosing unit  103   s  determines whether the latest AD values SH sin+  and SH sin−  supplied from the AD value acquisition unit  103   i  satisfy the following expression (7).
 
 V 0−δ1&lt;((SIN+)+(SIN−))/2&lt; V 0+δ1.
 
 V 0−δ1&lt;( SH   sin+   +SH   sin− )/2&lt; V 0+δ1  (7)
 
     where δ 1  represents a predetermined threshold. 
     The output signal diagnosing unit  103   s  determines that there is an abnormality in any of the output signals SIN+ and SIN− from the resolver  10  when expression (7) is not satisfied. In this case, the output signal diagnosing unit  103   s  notifies an RDC error diagnosing unit  103   u  of the determination. 
     Similarly, the output signal diagnosing unit  103   s  determines whether the latest AD values SH cos+   0  and SH cos−  supplied from the AD value acquisition unit  103   i  satisfy the following expression (8).
 
 V 0−δ2&lt;((COS+) +(COS−) )/2&lt; V 0+δ2
 
 V 0−δ2&lt;( SH   cos+   +SH   cos− )/2&lt; V 0+δ2  (8)
 
     where δ 2  represents a predetermined threshold. 
     The output signal diagnosing unit  103   s  determines that there is an abnormality in any of the output signals COS+ and COS− from the resolver  10  when expression (8) is not satisfied. In this case, the output signal diagnosing unit  103   s  notifies an RDC error diagnosing unit  103   u  of the determination. 
     As a result, the output signal diagnosing unit  103   s  determines that there is the abnormality in any of the output signals SIN+, SIN−, COS+, and COS− when the absolute value of half of the sum of a value of the output signal SIN+ and a value of the output signal SIN− becomes more than a predetermined threshold or when the absolute value of half of the sum of a value of the output signal COS+ and a value of the output signal COS− becomes more than a predetermined threshold. 
     Meanwhile, when an abnormality occurs in the RDC  21 , an error information input port  103   t  receives, from the RDC  21 , the error signal Err as a result of a self-diagnosis so as to supply the error signal Err to the RDC error diagnosing unit  103   u.    
     The RDC error diagnosing unit  103   u  determines that there is the abnormality in the RDC  21  of the resolver circuit  20  when receiving the error signal of the RDC  21  from the error information input port  103   t  or when receiving, the output signal diagnosing unit  103   s , an notification in which there is the abnormality in any of the output signals COS+ and COS− from the resolver  10 . 
     That is, the RDC error diagnosing unit  103   u  compares the result diagnosed by the output signal diagnosing unit  103   s  and the error signal output from the RDC  21  so as to diagnose soundness of a diagnostic function of the RDC. 
     When determining that there is the abnormality in the RDC  21 , the RDC error diagnosing unit  103   u  notifies a motor control unit for controlling the motor M (not illustrated) of the determination. 
     The motor control unit corresponds to the notification from the RDC error diagnosing unit  103   u  so as to cause the motor M to stop drive of the motor M. 
     As described above, according to the present embodiment, accuracy for detecting the abnormality in the RDC  21  of the resolver circuit  20  can be improved. Therefore, soundness of the resolver circuit can be accurately diagnosed. 
     (Amplitude Diagnosis) 
     The output signal diagnosing unit  103   s  determines whether the latest AD values SH sin+  and SH sin−  supplied from the AD value acquisition unit  103   i  satisfy the following expression (9).
 
2* A− δ3&lt;SIN&lt;2* A+ δ3
 
2* A− δ3&lt;− SH   sin− &lt;2* A+ δ3  (9)
 
     where δ 3  represents a predetermined threshold. 
     The output signal diagnosing unit  103   s  determines there is the abnormality in any of the output signals SIN+ and SIN− from the resolver  10  when expression (9) is not satisfied. In this case, the output signal diagnosing unit  103   s  notifies an RDC error diagnosing unit  103   u  of the determination. 
     Similarly, the output signal diagnosing unit  103   s  determines whether the latest AD values SH cos+  and SH cos−  from the AD value acquisition unit  103   i  satisfy the following expression (10).
 
2* A− δ4&lt;COS&lt;2* A+ δ4
 
2* A− δ4&lt; SH   cos+   −SH   cos− &lt;2* A+ δ4  (10)
 
     Here, the output signal diagnosing unit  103   s  may determine whether the following expression (11) with expressions (9) and (10) is satisfied.
 
1&lt;√(SIN^2+COS^2)&lt;δ5  (11)
 
     where δ 5  is a predetermined threshold. 
     Whether the absolute value of a difference Δ(SIN^2+COS^2) between (SIN^2+COS^2) and the previously calculated value satisfies the following expression may be also determined.
 
|Δ(SIN^2+COS^2)|&gt;δ6  (12)
 
     where δ 6  is a predetermined threshold. 
     The output signal diagnosing unit  103   s  determines that there is the abnormality in the output signal when any of expressions (9) to (12) is not satisfied. Operation after the determination is similar to that of the above offset diagnosis. 
     As described above, according to the present embodiment, accuracy for detecting the abnormality in the RDC  21  of the resolver circuit  20  can be improved. Therefore, soundness of the resolver circuit can be accurately diagnosed. 
     The present invention is not limited to the above embodiments, and includes various modifications. For example, the above embodiments have been described in detail in order to easily understand the present invention. The present invention is not necessarily limited to including all the configurations having been described above. A part of a configuration in one embodiment can be replaced with a configuration in another embodiment. In addition, a configuration in one embodiment can be added to a configuration in another embodiment. With respect to a part of the configuration in each of the embodiments, additions, deletions, and replacements of the other configurations may be made. 
     For example, the configuration according to the second embodiment may be added to the configuration according to the first embodiment. Furthermore, the configuration according to the third embodiment may be added. 
     REFERENCE SIGNS LIST 
     
         
           10  resolver 
           11  excitation coil (primary coil) 
           12 ,  13  secondary coil 
           20  resolver circuit 
           21  RDC 
           100 A diagnostic device 
           101  shifter 
           102  trigger generation circuit 
           103  control unit 
           103   a  trigger signal input port 
           103   b  cycle measuring unit 
           103   c  cycle diagnosing unit 
           103   d  memory 
           103   e  interruption generation unit 
           103   f  AB pulse input port 
           103   g ,  103   h  AD port 
           103   i  AD value acquisition unit 
           103   j  angle calculating unit 
           103   k ,  103   q  memory 
           103   m  real-time counter measuring unit 
           103   n  angle diagnosing unit 
           103   p  angle conversion unit 
           103   s  output signal diagnosing unit 
           103   t  error signal input port 
           103   u  RDC error diagnosing unit 
         M motor