Abstract:
A control device of a motor used in, for example, electric power steering control of a vehicle has to monitor the operation thereof to execute such a processing as stopping the control without delay upon detection of error. However, conventional monitoring devices have a disadvantage of taking a long time period the detection or not being able to detect an error of no output. A three-phase inverter circuit  52  having a substantially constant operation period is employed. The inverter  52  outputs an output waveform also at the moment of not driving the motor  2.  An inverter period monitoring circuit  555  is provided to monitor a period of the output waveform. When the period comes to be too large or too small as compared with a carrier period of the inverter, an alarm is outputted, and control of the inverter is stopped.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a motor control device and, more particularly, to a control device of a motor acting to assist in driving a steering wheel of a vehicle.  
         [0003]     2. Description of the Related Art  
         [0004]     In the description hereinafter, an electric steering device that adds an assisting power to a steering device of a vehicle is taken as an example. However, the present invention is not limited to a steering device, but may be applied generally to a control device functioning to drive an electric motor with an inverter from a DC power supply.  
         [0005]     As for an electric power steering device of vehicles, it is foreseen that the occurrence of error in the control device of a motor during the operation (generally an inverter is used) immediately invites dangerous situations, so that it is desirable to detect the error as soon as possible, for example, within one cycle of the inverter.  
         [0006]     The following motor control device is disclosed in the Japanese Patent No. 2501030. With reference to  FIGS. 1 and 3 ( b ) of this Japanese Patent, a terminal voltage of a motor to be driven by an inverter is monitored and, further, with reference to  FIGS. 1 and 3 ( a ), a drive signal of switching element that drives the motor is monitored. In this motor control device, when the state of those inverter and switching element driving the motor continues for not less than a predetermined time period, an error is determined, and the feed of an electric power to the motor drive circuit is interrupted.  
         [0007]     In the art of this Japanese Patent No. 251030, an output state only when a drive circuit makes outputs is monitored, so that a state of no output is not determined to be abnormal. However, the fault that a drive circuit cannot make outputs takes place relatively often as a mode of faults. Therefore, it cannot be said that this motor control device detects various faults with accuracy, thus a disadvantage exists in that this device is not always useful in practical use.  
         [0008]     Moreover, in the case where a drive circuit continues to make outputs for a long time period takes place during actual driving, it is sometimes the case that a return torque is exerted on a steering wheel at all times, for example, as a result of running at high speed on a circular test course. To prevent the malfunction in such a case, it is necessary to set a time period on which an error is determined to be rather long. Consequently, a further disadvantage exists in that it takes a long time period to determine the error.  
         [0009]     Furthermore, the motor control device disclosed in the mentioned Japanese Patent No. 2501030 shows only the case where a drive circuit is a single-phase inverter. Thus, a yet further disadvantage exists in that this drive circuit is not always effective in the case of a three-phase or poly-phase inverter.  
       SUMMARY OF THE INVENTION  
       [0010]     Since the mentioned conventional motor control device is arranged as described above, a problem exists in that errors cannot be detected in the case of such a type of fault that no output is sent from a drive apparatus to a motor, or in the case where an output voltage from a motor drive circuit is fixed at L level due to ground fault or short circuit fault in the internal part of the motor or in wiring to the motor. Moreover, another problem exists in that the application method in the case where a drive circuit is a three-phase inverter is not shown. A further problem exists in that it takes a long time period to determine an error.  
         [0011]     The invention was made to solve the above-discussed problems, and has an object of obtaining a motor control device in which a drive circuit is a three-phase inverter operating in a substantially constant period, and which is provided with a monitoring circuit capable of detecting an error even in the case of such a type of fault that no output is sent from a drive apparatus to a motor or in the case where an output voltage from a motor drive circuit is fixed at L level due to ground fault or short circuit fault in the internal part of the motor or in wiring to the motor.  
         [0012]     The invention has a further object of obtaining a motor control device enabling the determination of error in a short time period, for example, about one periodic time of an inverter.  
         [0013]     A motor control device according to the invention includes:  
         [0014]     a poly-phase inverter of not less than three phases that is connected to a DC power supply having a voltage H of a vehicle, and performs a PWM operation controlled at a predetermined range of output duty ratio in a substantially constant carrier period, whereby there exists a period in which all voltages of output phase come to be 0 in synchronization or H in synchronization during one periodic time;  
         [0015]     an inverter period monitoring circuit that monitors a periodic time of an output voltage waveform of the mentioned inverter, and that determines a fault of the mentioned inverter and outputs a signal when the mentioned periodic time comes to be not less than a predetermined magnification or not more than a predetermined magnification with respect to the mentioned carrier period; and  
         [0016]     an alarm circuit that gives a notice of alarm with the mentioned signal to a driver who operates the mentioned vehicle.  
         [0017]     According to the invention, it is possible to detect an error of a three-phase inverter or error of a micro-controller within a time period nearly equal to a PWM carrier period with a simple circuit arrangement, resulting in improvement in safety of the vehicle.  
         [0018]     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]      FIG. 1  is a block diagram of a motor control device according to a first preferred embodiment of the present invention.  
         [0020]      FIG. 2  is a chart showing a waveform of each section at the normal time of the motor control device of  FIG. 1 .  
         [0021]      FIG. 3  is a chart showing a waveform of each section at the time of error of the motor control device of  FIG. 1 .  
         [0022]      FIG. 4  is a block diagram of a motor control device according to a second embodiment of the invention.  
         [0023]      FIG. 5  is a chart showing a waveform of each section at the normal time of the motor control device of  FIG. 4 .  
         [0024]      FIG. 6  is a chart showing a waveform of each section at the time of error of the motor control device of  FIG. 4 .  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
     Embodiment 1  
       [0025]      FIG. 1  is a block diagram of a motor control device according to a first preferred embodiment of the present invention. Referring to the drawing, a motor  2  is mounted onto a steering device of a vehicle, not shown, and is connected to an output terminal of a motor control device (hereinafter, it may be referred to as “controller” as well)  1  that is fed with an electric power from a battery  4  of the vehicle. The motor  2  is a DC brushless motor. Furthermore, to excite a phase corresponding to an angle position of a magnetic pole of the motor  2 , the motor control device receives signals from a rotor angle sensor  3  that detects a rotor angle of the motor  2 . In addition, the rotor angle sensor  3  is shown as an example of a supply source of signals, and a signal supply source is not limited to this rotor angle sensor  3 .  
         [0026]     The controller  1  includes an interface  51  that receives signals from the outside; a first micro-controller  56  that executes the control based on outputs from an interface  51 ; a gate drive circuit  53  that is controlled by the first micro-controller  56 ; a three-phase inverter circuit  52  that is controlled by the gate drive circuit  53 , and drives the motor  2 ; switch means  54 , e.g., relay for interrupting the feed of power from the battery  4  to the three-phase inverter  52 ; an output voltage monitoring circuit  55  that picks up an output voltage from the three-phase inverter  52 , and inputs periods thereof to the first micro-controller  56  as a waveform capable of being measured; and a second micro-controller  57  for monitoring/inspecting an electric power steering device containing the first micro-controller  56 . Although a tree-phase inverter is described as an example herein, the same description can be made with respect to any poly-phase inverter of not less than three phases.  
         [0027]     Both first and second micro-controllers  56 ,  57 , in addition to the execution of the above-described respective controls, measure a period of waveforms, which the inverter period monitoring circuit  55  outputs, based on their own clock signal periods respectively. The output voltage monitoring circuit  55 , the above-described period measurement circuits, not shown, of the first and second micro-controllers  56 ,  57 , and a section that executes processing such as alarm output that is made after the detection of error form a so-called inverter period monitoring circuit  555  according to the invention. For conveniences of description, a voltage of the battery  4  is established to be H volt.  
         [0028]     The three-phase inverter circuit  52  outputs a voltage waveform on a regular basis irrespective of whether or not a steering wheel is being turned, or irrespective of whether or not the motor  2  generates a torque during an engine key, not shown, of this vehicle being ON.  
         [0029]     The output voltage monitoring circuit  55  includes capacitors C 1 , C 2 , C 3  that are connected to output terminals V 1 , V 2 , V 3  of the three-phase inverter circuit  52 , buffers B 1 , B 2 , B 3  that are connected to these capacitors, and an AND gate  55 A that receives outputs from the buffers B 1 , B 2 , B 3 .  
         [0030]     An output from the AND gate  55 A are inputted to the first and second micro-controllers  56 ,  57 .  
         [0031]     Now, operations of the motor control device of  FIG. 1  are described. The first micro-controller  56  executes the control of outputting a signal to the gate drive circuit  53  based on a rotor angle signal generated by the rotor angle sensor  3 , converting a DV voltage that is supplied form the battery  4  to a three-phase AC voltage with the three-phase inverter circuit  52 , and supplying this three-phase AC voltage to the motor  2 .  
         [0032]     The method of driving an inverter of the three-phase inverter circuit  52  is executed by mutually driving upper and lower switching elements that form each arm based on the so-called PWM of triangle wave comparison. A duty ratio of driving each arm is limited within a predetermined range so as not to be a value close to 0% and not to be a value close to 100% (for example, it is controlled so as to be not less than 5% and not more than 95%) . As a result, without regard to a value of outputs, there is a time period in which all voltages of each phase come to be L or H during one period. An AND gate  55 A of the output voltage monitoring circuit  55  outputs H (voltage of the battery) to an output terminal VO when all voltages of each phase come to be H, while outputs L (herein, 0 volt) other than this case.  
         [0033]      FIG. 2  is an output waveform chart of the three-phase inverter circuit  52  for explaining operations of the output voltage monitoring circuit  55  of  FIG. 1 . An output voltage VO from the output voltage monitoring circuit  55  comes to be H during a time period in which output phase voltages V 1 , V 2 , V 3  from the three-phase inverter  52  are H. A period T of VO (for example, a time period between rise edges of VO) is a PWM carrier period (taken as t) of the three-phase inverter circuit  52 , and herein is substantially a constant value as described above. The first micro-controller  56  measures the period T of an output from the output voltage monitoring circuit  55  with a timer  56 X contained therein, not shown, and determines that it is normal on the supposition that T is within a predetermined range. A predetermined range herein is preferably a range, for example, 0.5 to twice as long as a period t of a carrier frequency of the three-phase inverter circuit  52 .  
         [0034]     When any fault such as output ground fault on the way of wiring to the motor  2  occurs (for example, when the ground fault takes place on V 2  line as shown in  FIG. 3 ), VO becomes constant at L level, and T is out of the mentioned predetermined range (no signal is outputted to VO in the case of  FIG. 3 ) and the first micro-controller  56  determines it is abnormal.  
         [0035]     Each output terminal of the three-phase inverter  52  is AC-coupled to the output voltage monitoring circuit  55  via the capacitors C 1 , C 2 , C 3 . Even if each phase voltage is constant at H level or at L level, input voltages to the mentioned buffers B 1 , B 2 , B 3  come to be at L level, thereby enabling to detect errors.  
         [0036]     When the output voltage monitoring circuit  55  determines an error, the first micro-controller  56  opens the switch means  54  and instructs output interruption to the three-phase inverter circuit  52  via the gate drive circuit  53  (or stops outputting a control signal to the gate drive circuit  53 ). Further, a driver will be notified of the error with an alarm, not shown. In this manner, even in the case of such a type of fault that any output is not sent from the three-phase inverter circuit  52 , it is possible to avoid the danger of continuing to drive without being informed of the occurrence of error.  
         [0037]     In the meantime, the second micro-controller  57  receives the signal VO of the output voltage monitoring circuit  55  as well. When a period of this signal is measured based on a period of an internal clock in the same manner as described above and is compared with the mentioned magnification having been (preliminarily determined eventually to judge a fault, the second micro-controller  57  opens the switch means  54 , interrupts the supply of power source to the three-phase inverter  52  and inhibits it from sending outputs in the same manner as in the first micro-controller  56 . The switch means  54  is arranged to ON drive based on AND of the instruction of the first micro-controller  56  and the instruction of the second micro-controller  57  (that is, becomes ON only when both of them instruct ON). Accordingly, even if the first micro-controller  56  makes the ON instruction of the switch means  54 , the second micro-controller can make the OFF instruction (vice versa). Thus, it is possible to prevent the motor  2  from being abnormally energized due to run-away of the first micro-controller  56 .  
         [0038]     In addition, instead of interrupting the feed of an electric power to the three-phase inverter circuit  52 , the similar effect can be obtained with the arrangement of interrupting power supply to the gate drive circuit  53 . In the case of the fault that any element of the three-phase inverter circuit  52  is brought in short circuit, outputs are continuously sent even after the power supply to the gate drive circuit  53  has been interrupted, and therefore it becomes necessary to detect this fault itself with another detection means. It is, however, possible to use, for example, a semi-conductor switching element of smaller current capacity as the switch means  54 .  
         [0039]     Furthermore, instead of monitoring an output voltage from the three-phase inverter  52 , the similar effect can be obtained with the arrangement of monitoring outputs from the gate drive circuit  52  or output ports of the first micro-controller  56 . Although it is difficult to detect a fault that an error takes place in inverter output (for example, element fault) despite that there is no error in outputs from the gate drive circuit  53  or in output ports of the first micro-controller  56 , it is possible to monitor signals of less noise easily as compared with the case of directly monitoring a power section, which results in stable operation.  
         [0040]     In the explanation of  FIG. 1 , a period T of the output voltage monitoring circuit  55  is monitored with an internal clock of the first micro-controller  56 . However, for example, in the case of run-away of the first micro-controller, a PWM period t comes to be shorter, and the internal clock also goes wrong, resulting in the possibility that the first micro-controller  56  detects no error. Even in such a case, the second micro-controller  57  detects the error, so that it is possible to detect the error as a whole system. Thus, a PWM period is measured on the basis of a clock itself that generates a periodic time of PWM, and further a PWM period is measured on the basis of a clock different from the clock that generates a periodic time of PWM, thereby improving reliability of the system.  
         [0041]     In addition, to prevent detection of any error during a time period from the time of starting a vehicle (shortly after an engine key being ON) until the three-phase inverter circuit  52  has got in the stable operation, it is a matter of course that a waiting time is secured in monitoring sequence of the first and second micro-controllers  56 ,  57 .  
       Embodiment 2  
       [0042]      FIG. 4  is block diagram of a motor control device according to a second embodiment of the invention. In the drawing, the same reference numerals indicate the same or like parts as those in  FIG. 1 , and detailed description thereof is omitted. With reference to  FIG. 4 , an output voltage monitoring circuit  550  includes: resistors of the same value as output terminals V 1 , V 2 , V 3  of a three-phase inverter circuit  52  to which the resistors are connected (all resistors are referred to as R); a resistor R 2  applying an arbitrary bias; first and second comparators CP 1 , CP 2  connected to these resistors; and a flip-flop FF receiving outputs from the comparators CP 1 , CP 2 .  
         [0043]     As compared with the output voltage monitoring circuit  55  of  FIG. 1  according to the foregoing first embodiment, the output voltage monitoring circuit  550  of  FIG. 4  is DC-coupled to power feed lines of the motor  2  with the three resistors R.  
         [0044]     The output voltage monitoring circuit  550  monitors a voltage obtained by addition of all voltages of each phase. That is, letting each phase voltage be V 1 , V 2 , V 3 , and an input voltage to the comparators CP 1 , CP 2  be V 4 , then V cc  is a predetermined constant voltage, for example, a power supply voltage.  
         [0045]     Letting {a resistance value obtained by connecting R 1  and (⅓)·R in parallel} be Z, 
 
 R′=Z/{R   2 + Z}   (1) 
 
         [0046]     Letting {a resistance value obtained by connecting R 1 , R 2 , and (½)·R in parallel} be Z, 
 
 R″={Y}I{R+Y}   (2) 
 
then, 
 
 V   4 = R′V   cc   +R″ ( V   1 + V   2 + V   3 )   (3) 
 
         [0047]     The above-mentioned V 4  is compared with voltages of VTH 1 , VTH 2  having been preliminarily set, and a waveform thereof is shaped. Thereafter, an output from one comparator is inputted to a set terminal S of the flip-flop FF, and an output from the other comparator is inputted to a reset terminal R of the flip-flop FF. The voltages of VTH 1 , VTH 2  are at a level appropriate to cut off the peak of a waveform of V 4  obtained by the addition of V 1 , V 2 , V 3  as indicated in  FIGS. 5 and 6 . It is a matter of course that this level depends on a voltage of the battery  4 , thus enabling to determine it preliminarily.  
         [0048]     In the normal case, as shown with Q of  FIG. 5 , a rise edge can be obtained from the flip-flop FF with a PWM carrier period T, and it is possible to determine a fault depending on whether or not a period is out of a predetermined range in the same manner as in the foregoing first embodiment. On the other hand, at the time of an error such as ground fault on the output side of the three-phase inverter circuit  52 , VO comes not to exceed either threshold value of VTH 1  or VTH 2 , as shown in  FIG. 6 , and an output from the flip-flop is not inverted. Thus, it is possible to detect the error.  
         [0049]     In the descriptions heretofore, a motor acting to assist turning a steering wheel of a vehicle is taken as an example. However, the motor control device according to the invention is not limited to the one that can be mounted onto a vehicle, and can be applied to any other control devices, on conditions that the motor control device is driven by an inverter of a substantially constant period, and a duty ratio of driving each arm is limited to be in a predetermined range from a value not close to 0% up to a value not close to 100%, and that as a result there is a time period in which all voltages of each phase come to be L or H during one periodic time without regard to a value of output.  
         [0050]     It is to be understood that the invention is not limited to the above-mentioned embodiments and that various changes and modifications may be made without departing from the technical scope of the invention.