Abstract:
A motor abnormality detection apparatus is capable of performing the abnormality detection of a motor ( 5 ) without supplying a special electric current thereto for abnormality detection in an ordinary control state. A motor control device ( 100 ) controls the motor ( 5 ) through vector control which is described by a two-phase rotating magnetic flux coordinate system having the direction of a field current as a d-axis direction and a direction orthogonal to the d-axis direction as a q-axis direction. A motor abnormality detection part ( 100   h ) ( 100   h ) performs an abnormality determination of the motor based on target impression voltages (Vd*, Vq*) impressed on the motor ( 5 ).

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a motor abnormality detection apparatus used for abnormality detection of a brushless motor and an electric power steering control system equipped with such a motor abnormality detection apparatus.  
           [0003]    2. Description of the Related Art  
           [0004]    Conventionally, brushless motors are used in electric power steering systems or the like. In such electric power steering systems or the like, it is necessary to always perform the detection of faults or failures such as a break or disconnection of a motor power line, etc., in order to prevent abnormality in steering assist torque, i.e., the output torque of a brushless motor.  
           [0005]    In general, a brushless motor control apparatus performs arithmetic calculations such as the calculation of d-axis and q-axis (hereinafter called “dq-axis”) target currents based on a command torque, the detection of motor currents of respective phases (for instance, u phase, v phase and w phase), the dq conversion (hereinafter called “uvw to dq transformation) of currents, the calculation of current deviations, the calculation of command voltage values, dq inversion (hereinafter called “dq to uvw transformation”), and PWM control pattern outputs. The respective detected phase currents are converted or transformed from three phases into two phases (i.e., dq conversion or uvw to dq transformation), and are subjected to feedback control so that their d-axis component and q-axis component become equal to a d-axis target current and a q-axis target current, respectively.  
           [0006]    Here, note that the d-axis component of a current means a reactive or wattless current. When the motor is a synchronous motor with a constant magnitude of excitation magnetic field, the q-axis component of a current supplied to the motor is proportional to the torque of the motor. Therefore, in the current feedback control, in case of the synchronous motor, it is generally controlled such that the d-axis component of the detected current becomes zero and the q-axis component becomes equal to a target value of the output torque.  
           [0007]    For instance, in an apparatus disclosed in Japanese patent application laid-open No. 2000-184772, abnormality determination is performed by supplying a current to the d axis of a brushless motor.  
           [0008]    In this apparatus, however, operation efficiency reduces due to the fact that a d-axis current, which is usually controlled to be zero, is supplied to the motor in order to detect abnormality or fault in the motor. On the other hand, if abnormality detection processing is carried out at constant time intervals to avoid the reduction in efficiency, there will be generated a delay in abnormality detection.  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention is intended to obviate the problems as referred to above, and has for its object to provide a motor abnormality detection apparatus and an electric power steering control system equipped with such a motor abnormality detection apparatus in which abnormality in a motor can be detected under an ordinary control state without supplying a special current to the motor for abnormality detection.  
           [0010]    Bearing the above object in mind, the present invention resides in a motor abnormality detection apparatus in which a motor is controlled through vector control which is described by a two-phase rotating magnetic flux coordinate system having the direction of a field current as a d-axis direction and a direction orthogonal to the d-axis direction as a q-axis direction. The apparatus includes an abnormality detection part for making a determination of abnormality in said motor based on target impression voltages impressed on said motor. According to the present invention, it is possible to carry out the detection of abnormality in the motor in an ordinary control state. In addition, it is possible to provide an electric power steering control system equipped with such a motor abnormality detection apparatus which is capable of detecting abnormality in a motor which generates an assist force for power steering under an ordinary control state without the need of supplying a current to the motor for the purpose of abnormality detection.  
           [0011]    The above and other objects, features and advantages of the present invention will become more readily apparent to those skilled in the art from the following detailed description of preferred embodiments of the present invention taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a view illustrating the construction of an electric power steering control system equipped with a motor abnormality detection apparatus in accordance with a first embodiment of the present invention.  
         [0013]    [0013]FIG. 2 is a control block diagram functionally illustrating an example of the electric power steering control system using a permanent magnet brushless motor (hereinafter called a PM brushless motor) as a steering assist motor according to the first embodiment of the present invention.  
         [0014]    [0014]FIG. 3 is a vector diagram used for explaining the operation of the brushless motor according to the first embodiment of the present invention.  
         [0015]    [0015]FIG. 4 is used to explain the operation of the first embodiment of the present invention, and is a flow chart explaining the processing performed by a motor abnormality detection part  100   h  of FIG. 2.  
         [0016]    [0016]FIG. 5 is a view functionally illustrating an example of an electric power steering control system using a PM brushless motor as a steering assist motor according to a second embodiment of the present invention.  
         [0017]    [0017]FIG. 6 is used to explain the operation of the second embodiment of the present invention, and is a flow chart explaining the processing performed by a motor abnormality detection part  100   h  of FIG. 5.  
         [0018]    [0018]FIG. 7 is a view functionally illustrating an example of an electric power steering control system using a PM brushless motor as a steering assist motor according to a third embodiment of the present invention.  
         [0019]    [0019]FIG. 8 is used to explain the operation of the third embodiment of the present invention, and is a flow chart explaining the processing performed by a motor abnormality detection part  100   h  of FIG. 7.  
         [0020]    [0020]FIG. 9 is a view functionally illustrating an example of an electric power steering control system using a PM brushless motor as a steering assist motor according to a fourth embodiment of the present invention.  
         [0021]    [0021]FIG. 10 is used to explain the operation of the fourth embodiment of the present invention, and is a flow chart explaining the processing performed by a motor abnormality detection part  100   h  of FIG. 9.  
         [0022]    [0022]FIG. 11 is a view functionally illustrating an example of an electric power steering control system using a PM brushless motor as a steering assist motor according to a fifth embodiment of the present invention.  
         [0023]    [0023]FIG. 12 is used to explain the operation of the fifth embodiment of the present invention, and is a flow chart explaining the processing performed by a motor abnormality detection part  100   h  of FIG. 11. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]    Hereinafter, preferred embodiments of the present invention will be described in detail while referring to the accompanying drawings.  
         [0025]    Embodiment 1.  
         [0026]    Now, a first embodiment of the present invention will be described below in detail with particular reference to FIGS. 1 through 4. FIG. 1 is a view illustrating the construction of an electric power steering system to which a motor abnormality detection apparatus in accordance with a first embodiment of the present invention is applied. As shown in FIG. 1, a motor  5  for generating steering assist torque is connected through a speed reduction gear  4  with one end of a steering shaft  2  which is connected at the other end thereof with a steering wheel  1 . Also, connected with the steering shaft  2  is a torque sensor  3  for detecting the steering torque of the steering wheel  1  and generating an output signal representative of the detected torque value.  
         [0027]    A controller  100  determines a steering assist torque based on the steering torque of the steering wheel  1  detected by the torque sensor  3  and the speed of a vehicle detected by a vehicle speed sensor  6 , and serves to assist the steering operation of the steering wheel  1  by driving the motor  5  to generate the steering assist torque thus determined. Note that in FIG. 1, reference numerals  7  and  8  designate a battery and an ignition switch, respectively.  
         [0028]    [0028]FIG. 2 functionally illustrates an example of a control block diagram of an electric power steering control system using a permanent magnet brushless motor (hereinafter called a PM brushless motor) as a steering assist motor according to the first embodiment. In FIG. 2, a reference numeral  100  designates a microcomputer corresponding to the controller  100  shown in FIG. 1 for performing steering assist control, and a software configuration of the microcomputer  100  is illustrated therein as various functional blocks. In FIG. 2, the microcomputer  100  includes a q-axis target current calculation part  100   a , a d-axis target current setting part  100   b , a position calculation part  100   c , a dq conversion (or uvw to dq transformation) part  100   d , a current control part  100   e , a dq inversion (or dq to uvw transformation) part  100   f , an angular velocity calculation part  100   g , and a motor abnormality detection part  100   h.    
         [0029]    The q-axis target current calculation part  100   a  performs predetermined calculations based on the torque detection signal of the torque sensor  3 , which detects the steering torque of the steering wheel  1 , and the vehicle speed detection signal of the vehicle speed sensor  6 , which detects the vehicle speed, determines a q-axis target current value Iq* for driving the PM brushless motor  5 , and supplies the q-axis target current value Iq* thus determined to the current control part  100   e.    
         [0030]    The d-axis target current setting part  100   b  supplies a d-axis target current Id to the current control part  100   e  as a zero current.  
         [0031]    The position calculation part  100   c  determines an electrical angle θ through calculations based on the positional detection signal of a position sensor  103  representative of the rotational position of the PM brushless motor  5 , and supplies the electrical angle θ thus determined to the angular velocity calculation part  100   g , the uvw to dq transformation part  100   d  and the dq to uvw transformation part  100   f.    
         [0032]    The angular velocity calculation part  100   g  determines a motor electrical angular velocity ω e  through calculations based on the electrical angle θ, and supplies it to the motor abnormality detection part  100   h.    
         [0033]    The uvw to dq transformation part  100   d  performs three-phase to two-phase transformation (dq conversion or uvw to dq transformation) based on three-phase current values (Iu, Iv, Iw) detected by current sensors  102   a ,  102   b  and  102   c  and the electrical angle θ by using the following expression (1), and supplies d-axis and q-axis (dq-axis) currents (Id, Iq) thus obtained to the current control part  100   e .  
               [         Id           Iq         ]     =           2   3                  [           cos                 θ           cos                   (     θ   -       2   3        π       )             cos                   (     θ   +       2   3        π       )                   -   sin                   θ             -   sin                     (     θ   -       2   3        π       )               -   sin                     (     θ   +       2   3        π       )             ]                [         Iu           Iv           Iw         ]             (   1   )                               
 
         [0034]    The current control part  100   e  performs proportional and integral (PI) control based on deviations between the dq-axis target currents (Id*, Iq*) and the corresponding detected dq-axis currents (Id, Iq), and generates dq-axis target impression voltages (Vd*, Vq*).  
         [0035]    The dq to uvw transformation part  100   f  performs two-phase to three-phase transformation (dq inversion or dq to uvw transformation) based on the dq-axis target impression voltages (Vd*, Vq*) and the electrical angle θ by using the following expression (2) to generate three-phase target impression voltages (Vu*, Vv*, VW*), which are supplied to a drive part  101  in the form of a PWM actuator.  
               [           Vu   *               Vv   *               Vw   *           ]     =               2   3                         [         1       0             -     1   2               3     2               -     1   2             -       3     2             ]                  [           cos                 θ             -   sin                   θ               sin                 θ           cos                 θ           ]                [           Vd   *               Vq   *           ]             (   2   )                               
 
         [0036]    Next, a method for detecting abnormality in a motor according to this embodiment will be described below. A circuit equation (the following expression (3)) for the motor  5  represented by d-q coordinates is well-known.  
               [         Vd           Vq         ]     =         [           R   +     pL   d               -     ω   e            L   q                   ω   e          L   d             R   +     pL   q             ]                [           I   d               I   q           ]     +     [         0               ω   e          Φ   a             ]               (   3   )                               
 
         [0037]    where Vd represents a d-axis armature voltage; Vq represents a q-axis armature voltage; R represents an armature resistance; Φ a  represents {square root}{square root over ( )} (3/2)·Φ′ a ; Φ′ a  represents an armature winding interlinkage magnetic flux maximum value; p represents a differential operator (d/dt); Id represents a d-axis armature current; Iq represents a q-axis armature current; ω e  represents an electrical angular velocity; Ld represents a d-axis inductance; and Lq represents a q-axis inductance.  
         [0038]    Here, note that FIG. 3 is a vector diagram of expression (3) above. When the number of revolutions per minute of the motor is equal to or less than a prescribed value, a combined or synthesized voltage vector Va of the d-axis armature voltage Vd and the q-axis armature voltage Vq becomes an operating point in a voltage limiting circle, as shown in a vector diagram of FIG. 3A.  
         [0039]    In addition, when the angular velocity of the motor increases from the state of FIG. 3A, the synthesized voltage vector Va becomes an operating point on the voltage limiting circle, as shown in a vector diagram of FIG. 3B.  
         [0040]    Moreover, when the angular velocity of the motor further increases from the state of FIG. 3B, the q-axis current Iq decreases, i.e., the motor output torque decreases, and the synthesized voltage vector Va becomes an operating point on the voltage limiting circle, as shown in a vector diagram of FIG. 3C.  
         [0041]    Since in the electric power steering control system, the motor  5  is directly connected with the steering wheel  1  through the speed reduction gear  4 , the most part of rotation of the motor  5  is in a stopped state or a low-speed rotating state, and hence the synthesized voltage vector Va becomes an operating point within the voltage limiting circle. However, upon abrupt steering operation such as urgent avoidance operation, etc., the motor  5  is caused to rotate at a speed higher than an idling speed by means of an external force so that the synthesized voltage vector Va becomes an operating point on the voltage limiting circle.  
         [0042]    Therefore, in the electric power steering control system, it is possible to perform accurate abnormality detection by making a determination as to whether the synthesized voltage vector Va of the d-axis armature voltage Vd and the q-axis armature voltage Vq becomes an operating point on the voltage limiting circle when the angular velocity of the motor is below a predetermined value.  
         [0043]    Here, note that in the electric power steering control system, the rotation of the motor  5  is almost stopped or performed at a low speed, and hence even in cases where the system is constructed such that abnormality determination is made only below a predetermined angular velocity of the motor, it is possible to perform abnormality detection at all times under the ordinary steering condition except for abrupt steering operation such as urgent avoidance operation, etc.  
         [0044]    In this first embodiment, abnormality determination is carried out based on whether the magnitude or length of the synthesized voltage vector Va is less than a predetermined voltage with the angular velocity of the motor being equal to a predetermined value or below.  
         [0045]    [0045]FIG. 4 is a flow chart explaining the processing performed by the motor abnormality detection part  100   h . In step S 10 , the d-axis target voltage Vd* and the q-axis target voltage Vq* output from the current control part  100   e  and the motor electrical angular velocity ω e  output from the angular velocity calculation part  100   g  are read into the motor abnormality detection part  100   h , and then the control flow advances to step S 11 . In step S 11 , the sum of squares Va* of the dq-axis target voltages is calculated by the motor abnormality detection part  100   h  through arithmetic calculations, and the control flow advances to step S 12 . In step S 12 , it is determined whether the motor electrical angular velocity ω e  is less than a predetermined number of revolutions per minute. When the motor electrical angular velocity ω e  is less than the predetermined number of revolutions per minute, the control flow advances to step S 13 , whereas when it is equal to or greater than the predetermined number of revolutions per minute, a return to step S 10  is performed.  
         [0046]    In step S 13 , it is determined whether the sum of squares Va of the dq-axis target voltages is equal to or greater than a predetermined value. When the sum of squares Va* of the dq-axis target voltages is equal to or greater than the predetermined value, an abnormality timer is counted up in step S 14 , whereas when it is less than the predetermined value, the abnormality timer is reset in step S 15 .  
         [0047]    Subsequently, in step S 16 , it is determined whether an abnormal state continues for a predetermined time, that is, the count value of the abnormality timer has reached a prescribed value. When the count value of the abnormality timer has not yet reached the prescribed value, a return to step S 10  is carried out.  
         [0048]    When it is determined in step S 16 , by repeating step S 10  through step S 16 , that the abnormal state continues for the predetermined time, that is, the count value of the abnormality timer has reached the prescribed value, it is assumed that there is abnormality, and the control on the brushless motor  5  is stopped in step S 17 .  
         [0049]    In the electric power steering control system as constructed above in which provision is made for the motor abnormality detection part  100   h , abnormality such as a break of a motor power line, a failure of the drive part  101 , failures of the current sensors  102   a ,  102   b  and  102   c , etc., can be detected in the ordinary control state.  
         [0050]    In addition, since abnormality determination is performed only below the predetermined motor electrical angular velocity, it is possible to prevent misjudgments even in cases where the dq-axis synthesized voltage vector Va can take an operating point on the voltage limiting circle in the normal operating condition as in the electric power steering control system.  
         [0051]    Although the above-mentioned first embodiment is constructed such that a determination of abnormality is made when the sum of squares Va* of the dq-axis target voltages is equal to or greater than the predetermined value, abnormality in the motor may instead be determined when the synthesized voltage vector of the dq-axis target voltages becomes an operating point on the voltage limiting circle.  
         [0052]    In the first embodiment, the detection of motor abnormality in the electric power steering control system has been described, but the present invention can also be used for the detection of abnormality in a motor used in systems or fields other than electric power steering control systems.  
         [0053]    In addition, in cases where the present invention is used for detecting abnormality in a motor in a system in which the synthesized voltage vector of the dq-axis voltages can not become an operating point on the voltage limiting circle, it is possible to perform abnormality detection at all times irrespective of the angular velocity of the motor.  
         [0054]    Embodiment 2.  
         [0055]    Now, reference will be made to an electric power steering control system in accordance with a second embodiment of the present invention while referring to FIGS. 5 and 6 of the accompanying drawings. In the second embodiment, the motor abnormality detection part  100   h  performs a determination of abnormality in a motor based on the d-axis target voltage Vd* output from the current control part  100   e.    
         [0056]    [0056]FIG. 5 functionally illustrates an example of an electric power steering control apparatus in which a PM brushless motor is used as a steering assist motor, in accordance with a second embodiment of the present invention. In FIG. 5, the same parts as those of the first embodiment shown in FIG. 2 are identified by the same symbols while omitting an explanation thereof. This second embodiment additionally includes, as new components, a steering angle sensor  9  for detecting the rotational angle of the steering wheel  1 , and a steering angular velocity calculation part  100   i  for calculating a steering angular velocity ω (i.e., the angular velocity of the steering wheel  1 ) from the steering angle detected by the steering angle sensor  9 , and supplying it to the motor abnormality detection part  100   h.    
         [0057]    Here, note that from expression (3) above, the d-axis armature voltage Vd when the d-axis armature current Id is controlled to zero (i.e., Id=0) is represented by the following expression (4). 
           V   d =ω e   ·L   q   ·I   q   (4) 
         [0058]    [0058]FIG. 6 is a flow chart explaining the processing performed by the motor abnormality detection part  100   h  according to the second embodiment. In step S 20 , the d-axis target voltage Vd* output from the current control part  100   e  and the steering angular velocity ω output from the steering angular velocity calculation part  100   i  are read into the motor abnormality detection part  100   h , and then the control flow advances to step S 21 . In step S 21 , it is determined whether the steering angular velocity ω is less than a predetermined number of revolutions per minute. When the steering angular velocity ω is less than the predetermined number of revolutions per minute, the control flow advances to step S 22 , whereas when it is equal to or greater than the predetermined number of revolutions per minute, a return to step S 20  is performed.  
         [0059]    In step S 22 , it is determined whether the d-axis target voltage Vd* is outside a predetermined range. When the d-axis target voltage Vd* is outside the predetermined range, an abnormality timer is counted up in step S 23 , whereas when it is within the predetermined range, the abnormality timer is reset in step S 24 . Here, in order to prevent mis-detections, the above-mentioned predetermined range as set beforehand is set to be wider than a voltage range into which the d-axis armature voltage Vd, which is obtained from expression (4) above under the condition of the steering angular velocity ω being less than the above-mentioned predetermined number of revolutions pre minute, can fall.  
         [0060]    Subsequently, in step S 25 , it is determined whether an abnormal state continues for a predetermined time, that is, the count value of the abnormality timer has reached a prescribed value. When the count value of the abnormality timer has not yet reached the prescribed value, a return to step S 20  is carried out.  
         [0061]    When it is determined in step S 25 , by repeating step S 20  through step S 25 , that the abnormal state continues for the predetermined time, that is, the count value of the abnormality timer has reached the prescribed value, it is assumed that there is abnormality, and the control on the brushless motor  5  is stopped in step S 26 .  
         [0062]    In the electric power steering control system as constructed above in which provision is made for the motor abnormality detection part  100   h , abnormality such as a break of a motor power line, a failure of the drive part  101 , failures of the current sensors  102   a ,  102   b  and  102   c , etc., can be detected at all times.  
         [0063]    Moreover, since abnormality determination is performed only below a predetermined steering angular velocity (i.e., the predetermined number of revolutions pre minute), it is possible to prevent mis-detections even in a special case where the motor  5  is caused to rotate at a speed higher than an idling speed by means of an external force as in the electric power steering control apparatus.  
         [0064]    Although in the above-mentioned second embodiment, the processing of counting up the abnormality timer is performed when the d-axis target voltage Vd* is outside the predetermined range as set beforehand, the abnormality timer may instead be counted up when the d-axis target voltage Vd* is saturated or reached.  
         [0065]    In this second embodiment, the detection of motor abnormality in the electric power steering control system has been described, but the present invention can also be used for the detection of abnormality in a motor used in systems or fields other than electric power steering control systems.  
         [0066]    Embodiment 3.  
         [0067]    Reference will be made to an electric power steering control system in accordance with a third embodiment of the present invention while referring to FIGS. 7 and 8 of the accompanying drawings. In the third embodiment, the motor abnormality detection part  100   h  determines that the motor  5  is abnormal when a deviation between the d-axis target voltage Vd* output from the current control part  100   e  and the d-axis armature voltage Vd obtained from the motor electrical angular velocity ω e  and the q-axis current Iq using expression (4) above is greater than a prescribed value.  
         [0068]    [0068]FIG. 7 functionally illustrates an example of the electric power steering control apparatus in which a PM brushless motor is used as a steering assist motor, in accordance with the third embodiment of the present invention.  
         [0069]    [0069]FIG. 8 is a flow chart explaining the processing performed by the motor abnormality detection part  100   h  of FIG. 7 according to the third embodiment. In step S 30 , the d-axis target voltage Vd* output from the current control part  100   e , the motor electrical angular velocity ω e  output from the angular velocity calculation part  100   g  and the q-axis current Iq output from the uvw to dq transformation part  100   d  are read into the motor abnormality detection part  100   h , and then the control flow advances to step S 31 .  
         [0070]    In step S 31 , a d-axis armature voltage Vd that satisfies expression (4) is calculated by the motor abnormality detection part  100   h  through arithmetic calculations.  
         [0071]    In step S 32 , a deviation ΔVd between the d-axis target voltage Vd* output from the current control part  100   e  and the d-axis armature voltage Vd obtained in step S 31  is calculated.  
         [0072]    In step S 33 , it is determined whether the absolute value |ΔAV| of the deviation ΔVd is greater than a determination threshold. When the absolute value |ΔVd| of the deviation ΔVd is greater than the determination threshold, an abnormality timer is counted up in step S 34 , whereas when it is equal to or less than the determination threshold, the abnormality timer is reset in step S 35 .  
         [0073]    Subsequently, in step S 36 , it is determined whether an abnormal state continues for a predetermined time, that is, the count value of the abnormality timer has reached a prescribed value. When the count value of the abnormality timer has not yet reached the prescribed value, a return to step S 30  is carried out.  
         [0074]    When it is determined in step S 36 , by repeating step S 30  through step S 36 , that the abnormal state continues for the predetermined time, that is, the count value of the abnormality timer has reached the prescribed value, it is assumed that there is abnormality, and the control on the brushless motor  5  is stopped in step S 37 .  
         [0075]    In the electric power steering control system as constructed above in which provision is made for the motor abnormality detection part  100   h , abnormality such as a break of a motor power line, a failure of the drive part  101 , failures of the current sensors  102   a ,  102   b  and  102   c , etc., can be detected at all times.  
         [0076]    In the third embodiment, the detection of motor abnormality in the electric power steering control system has been described, but the present invention can also be used for the detection of abnormality in a motor used in systems or fields other than electric power steering control systems.  
         [0077]    In the third embodiment, the motor abnormality detection part  100   h  determines that the motor  5  is abnormal when the deviation between the d-axis target voltage Vd* output from the current control part  100   e  and the d-axis armature voltage Vd obtained from expression (4) is greater than the prescribed value, but the d-axis armature voltage Vd as shown in the following expression (5) may be calculated while taking into consideration the d-axis armature current Id from expression (3) above, and a determination of abnormality in the motor  5  may be made when a deviation between the d-axis armature voltage Vd and the d-axis target voltage Vd* is greater than a prescribed value. This serves to make it possible to perform a more accurate abnormal determination. 
           V   d   =R·I   d −ω e   ·L   q   ·I   q   (5) 
         [0078]    where R represents an armature resistance; Id represents a d-axis armature current; ω e  represents an electrical angular velocity; Lq represents a q-axis inductance; and Iq represents a q-axis armature current.  
         [0079]    In this case, it is necessary to input the d-axis current Id from the uvw to dq transformation part  100   d  to the motor abnormality detection part  100   h  of FIG. 7.  
         [0080]    Embodiment 4.  
         [0081]    Reference will be made to an electric power steering control system in accordance with a fourth embodiment of the present invention while referring FIGS. 9 and 10 of the accompanying drawings. In this fourth embodiment, the motor abnormality detection part  100   h  performs a determination of abnormality in a motor based on the q-axis target voltage Vq* output from the current control part  100   e.    
         [0082]    [0082]FIG. 9 functionally illustrates an example of the electric power steering control apparatus in which a PM brushless motor is used as a steering assist motor, in accordance with the fourth embodiment of the present invention.  
         [0083]    Here, note that from expression (3) above, the q-axis armature voltage Vq when the d-axis armature current Id is controlled to zero (i.e., Id=0) is represented by the following expression (6). 
           V   q   =R·I   q +ω e ·Φ a   (6) 
         [0084]    [0084]FIG. 10 is a flow chart explaining the processing performed by the motor abnormality detection part  100   h  according to the fourth embodiment. In step S 40 , the q-axis target voltage Vq* output from the current control part  100   e  and the motor electrical angular velocity ω e  output from the angular velocity calculation part  100   g  are read into the motor abnormality detection part  100   h , and then the control flow advances to step S 41 . In step S 41 , it is determined whether the motor electrical angular velocity ω e  is less than a predetermined number of revolutions per minute as set beforehand. When the motor electrical angular velocity ω e  is less than the predetermined number of revolutions per minute, the control flow proceeds to step S 42 , whereas when it is equal to or greater than the predetermined number of revolutions per minute, a return to step S 40  is performed.  
         [0085]    In step S 42 , it is determined whether the q-axis target voltage Vq* is outside a predetermined range as set beforehand. When the q-axis target voltage Vq* is outside the predetermined range, an abnormality timer is counted up in step S 43 , whereas when it is within the determination range, the abnormality timer is reset in step S 44 . Here, in order to prevent mis-detections, the above-mentioned predetermined range as set beforehand is set to be wider than a voltage range into which the q-axis armature voltage Vq, that is obtained from expression (5) above under the condition of the motor electrical angular velocity ω e  being less than the above-mentioned predetermined number of revolutions pre minute, can fall.  
         [0086]    Subsequently, in step S 45 , it is determined whether an abnormal state continues for a predetermined time, that is, the count value of the abnormality timer has reached a prescribed value. When the count value of the abnormality timer has not yet reached the prescribed value, a return to step S 40  is carried out.  
         [0087]    When it is determined in step S 45 , by repeating step S 40  through step S 45 , that the abnormal state continues for the predetermined time, that is, the count value of the abnormality timer has reached the prescribed value, it is assumed that there is abnormality, and the control on the brushless motor  5  is stopped in step S 46 .  
         [0088]    In the electric power steering control system as constructed above in which provision is made for the motor abnormality detection part  100   h , abnormality such as a break of a motor power line, a failure of the drive part  101 , failures of the current sensors  102   a ,  102   b  and  102   c , etc., can be detected at all times.  
         [0089]    Moreover, since abnormality determination is performed only below the predetermined motor electrical angular velocity, mis-detections can be prevented.  
         [0090]    Although in the above-mentioned fourth embodiment, the processing of counting up the abnormality timer is performed when the q-axis target voltage Vq* is outside the predetermined range as set beforehand, the abnormality timer may instead be counted up when the q-axis target voltage Vq* is saturated or reached.  
         [0091]    In the fourth embodiment, the detection of motor abnormality in the electric power steering control system has been described, but the present invention can also be used for the detection of abnormality in a motor used in systems or fields other than electric power steering control systems.  
         [0092]    Embodiment 5.  
         [0093]    Reference will be made to an electric power steering control system in accordance with a fifth embodiment of the present invention while referring to FIGS. 11 and 12 of the accompanying drawings. In this fifth embodiment, the motor abnormality detection part  100   h  determines that the motor  5  is abnormal when a deviation between the q-axis target voltage Vq* output from the current control part  100   e  and the q-axis armature voltage Vq obtained from the motor electrical angular velocity ω e  and the q-axis current Iq using expression (6) above is greater than a prescribed value.  
         [0094]    [0094]FIG. 11 functionally illustrates an example of the electric power steering control apparatus in which a PM brushless motor  5  is used as a steering assist motor, in accordance with the fifth embodiment of the present invention.  
         [0095]    [0095]FIG. 12 is a flow chart explaining the processing performed by the motor abnormality detection part  100   h  according to the fifth embodiment. In step S 50 , the q-axis target voltage Vq* output from the current control part  100   e , the motor electrical angular velocity ω e  output from the angular velocity calculation part  100   g  and the q-axis current Iq output from the uvw to dq transformation part  100   d  are read into the motor abnormality detection part  100   h , and then the control flow advances to step S 51 .  
         [0096]    In step S 51 , a q-axis armature voltage Vq that satisfies expression (6) above is calculated by the motor abnormality detection part  100   h  through arithmetic calculations.  
         [0097]    In step S 52 , a deviation ΔVd between the q-axis target voltage Vq* output from the current control part  100   e  and the q-axis armature voltage Vq obtained in step S 51  is calculated.  
         [0098]    In step S 53 , it is determined whether the absolute value |ΔVq| of the deviation ΔVq is greater than a determination threshold. When the absolute value |ΔVq| of the deviation ΔVq is greater than the determination threshold, an abnormality timer is counted up in step S 54 , whereas when it is equal to or less than the determination threshold, the abnormality timer is reset in step S 55 .  
         [0099]    Subsequently, in step S 56 , it is determined whether an abnormal state continues for a predetermined time, that is, the count value of the abnormality timer has reached a prescribed value. When the count value of the abnormality timer has not yet reached the prescribed value, a return to step S 50  is carried out.  
         [0100]    When it is determined in step S 56 , by repeating step S 50  through step S 56 , that the abnormal state continues for the predetermined time, that is, the count value of the abnormality timer has reached the prescribed value, it is assumed that there is abnormality, and the control on the brushless motor  5  is stopped in step S 57 .  
         [0101]    In the electric power steering control system as constructed above in which provision is made for the motor abnormality detection part  100   h , abnormality such as a break of a motor power line, a failure of the drive part  101 , failures of the current sensors  102   a ,  102   b  and  102   c , etc., can be detected at all times.  
         [0102]    In the fifth embodiment, the detection of motor abnormality in the electric power steering control system has been described, but the present invention can also be used for the detection of abnormality in a motor used in systems or fields other than electric power steering control systems.  
         [0103]    In the fifth embodiment, the motor abnormality detection part  100   h  determines that the motor  5  is abnormal when the deviation between the q-axis target voltage Vq* output from the current control part  100   e  and the q-axis armature voltage Vq obtained from expression (6) is greater than the prescribed value, but the q-axis armature voltage Vq as shown in the following expression (7) may instead be calculated while taking into consideration the d-axis armature current Id from expression (3) above, and a determination of abnormality in the motor  5  may be made when a deviation between the q-axis armature voltage Vq and the q-axis target voltage Vq* is greater than a prescribed value. This serves to make it possible to perform a more accurate abnormal determination. 
           V   q =ω e   ·L   d   ·I   d   +R·I   q +ω d ·Φ a   (7) 
         [0104]    where R represents an armature resistance; Id represents a d-axis armature current; ω e  represents an electrical angular velocity; Lq represents a q-axis inductance; and Iq represents a q-axis armature current.  
         [0105]    In this case, it is necessary to input the d-axis current Id from the uvw to dq transformation part  100   d  to the motor abnormality detection part  100   h  of FIG. 11.  
         [0106]    As described above, according to the present invention, the detection of abnormality in a motor can be performed in an ordinary control state.  
         [0107]    In addition, it is possible to obtain an electric power steering control system equipped with such a motor abnormality detection apparatus which is capable of detecting abnormality in a motor that generates an assist force for power steering under an ordinary control state without supplying a current to the motor for the purpose of abnormality detection.  
         [0108]    While the invention has been described in terms of preferred embodiments, those skilled in the art will recognize that the invention can be practiced with modifications within the spirit and scope of the appended claims.