Abstract:
A motor controller comprises a PWM demodulation processor for re storing speed command value Vr from PWM command signal Si, a rotatio n control section for generating drive value Dd of a motor according to the speed command value Vr, a power drive section for generating driving vol tages Uo, Vo and Wo to energize and drive a motor winding according to the drive value Dd, a rotation speed calculating section for generating dete cted speed value Vd as an information signal to be transmitted to outside, and a PWM modulation processor for generating PWM information signal Fp pulse-width modulated by detected speed value Vd. The PWM modul ation processor outputs the PWM information signal Fp generated in sync hronization with the PWM command signal.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a motor controller for controlling a rotation speed and the like of a motor according to a command from a host controller, a brushless motor equipped with the motor controller, and a motor control system including a host controller and this brushless motor. In particular, the invention relates to the motor controller for controlling a rotation speed of the motor according to a speed command signal that is pulse-width modulated (“PWM”), the brushless motor, and the motor control system. 
       BACKGROUND ART 
       [0002]    A technique of controlling a fan motor mounted to a vehicle with a host controller such as an electric control unit (“ECU”), for instance, is disclosed in patent literature 1, as one example of hitherto available motor control systems including such motor controllers. The host controller in this literature supplies a rotation speed command of a fan in a form of PWM signal to a brushless motor equipped with a drive control circuit. The drive control circuit thus rotates the fan at a rotation speed corresponding to a duty factor of the PWM signal. Besides, for instance, patent literature 2 discloses a structure in which a motor control unit outputs a rotation detection signal to a host controller in addition to a rotation speed command in a form of PWM signal. 
         [0003]    Incidentally, there is growing number of cases in recent years for such motor control systems that are controlled by digital signals using pulse signals. There increases a possibility with such digital processing to cause adverse influence to other apparatuses due to electromagnetic radiation of noises attributable to pulse signals while providing flexibility in the processing. In the case of the above motor control system mounted to a vehicle, for instance, electromagnetic noises are radiated from a main motor body, a power supply, control lines, and the like which give rise to a risk of adverse influence to such devices as a radio mounted to the vehicle. 
         [0004]    Certain means have been used to suppress the influence of noises of this kind, such as installing a noise eliminating circuit using capacitors and inductance elements, shielding a source of the noise emission, and providing a structure that enables feeding lines and control lines as short as possible. In addition, patent literature 3 discloses a method of reducing spurious electromagnetic emission in a vehicle by transmitting signals using a cable of twisted-pair structure to cancel out magnetic fields generated by the propagating signals. 
         [0005]    In the methods for reducing electromagnetic emission such as those discussed above associated with the noise eliminating circuit, shielding means, and the cables of twisted-pair structure, however, there remain some drawbacks that they increase a number of the circuit components and shielding members for the noise preventive measures, and necessitate special cable materials like the twisted-pair cables. There is also a problem with the structure of shortening the feeding lines and control lines because they impose limitations on the mounting flexibility of the power supply, motor and the like. 
       CITATION LIST 
     Patent Literature 
       [0006]    PTL 1: Unexamined Japanese Patent Publication No. 2008-148542 
         [0007]    PTL 2: Unexamined Japanese Patent Publication No. 2011-130532 
         [0008]    PTL 3: Unexamined Japanese Patent Publication No. 2009-104907 
       SUMMARY OF THE INVENTION 
       [0009]    A motor controller of the present invention is a control device configured to receive a PWM command signal formed of a pulse-width modulated rotation speed command, and control a motor to rotate of at a speed corresponding to the rotation speed command. The motor controller comprises a PWM demodulation processor for demodulating the PWM command signal and restoring the rotation speed command as a speed command value, a rotation control section for generating a drive value of the motor according to the speed command value, a power drive section for generating a driving voltage to energize and drive a winding of the motor according to the drive value, an information signal generator for generating an information signal to be transmitted to outside, and a PWM modulation processor for generating a PWM information signal that is pulse-width modulated by the information signal. The PWM modulation processor is configured to generate the PWM information signal synchronized with the PWM command signal and output the same. 
         [0010]    A brushless motor of the present invention has a structure comprising a rotor, a stator provided with a three-phase winding, and the motor controller of this invention for energizing and driving the winding. 
         [0011]    Furthermore, a motor control system of the present invention comprises the brushless motor of this invention, and a host controller configured to control rotation of the brushless motor by outputting a PWM command signal to the brushless motor and receiving a PWM information signal from the brushless motor. 
         [0012]    According to the configurations stated above, magnetic field radiated from a transmission line of the PWM command signal and magnetic field radiated from a transmission line of the PWM information signal become generally opposite to each other in their directions at all the time, since the PWM command signal is synchronized with the PWM information signal, which can equalize pulse periods of both these signals. Unwanted emissions radiated from both transmission lines are thus cancelled out, and spurious emissions can be reduced. 
         [0013]    As stated above, the motor controller, the brushless motor and the motor control system of the present invention can reduce the spurious emissions simply by synchronizing the pulse periods of the PWM command signal received at the motor side and the PWM information signal sent out from the motor side. Accordingly, the present invention can provide the motor controller, the brushless motor, and the motor control system with an advantage of reducing the spurious emissions with the simple structures not requiring any special component and material for the noise preventive measures. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0014]      FIG. 1  is a block diagram of a motor control system according to one exemplary embodiment of the present invention. 
           [0015]      FIG. 2  is a block diagram of a PWM demodulation processor and a PWM modulation processor of a motor controller according to the exemplary embodiment of the present invention. 
           [0016]      FIG. 3A  is a graphic diagram showing a waveform of PWM command signal Si in the motor controller. 
           [0017]      FIG. 3B  is a graphic diagram showing timing of pulse start signal Ps in the motor controller. 
           [0018]      FIG. 3C  is a graphic diagram showing a waveform of PWM information signal Fp in the motor controller. 
           [0019]      FIG. 4  is a sectional view of a brushless motor according to one exemplary embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0020]    Description is provided hereinafter of a motor controller, a brushless motor and a motor control system according to exemplary embodiments of the present invention with reference to the accompanying drawings. 
       Exemplary Embodiment 
       [0021]      FIG. 1  is a block diagram of motor control system  100  according to one exemplary embodiment of the present invention. Motor control system  100  described in this embodiment has a structure including brushless motor  50  provided with motor controller  10  of the present invention. 
         [0022]    As shown in  FIG. 1 , motor control system  100  of this embodiment has a structure including brushless motor  50 , and host controller  11  used to control brushless motor  50 . In this embodiment, brushless motor  50  is so constructed that it includes internally mounted circuit components that constitute motor controller  10 , details of which will be described later. In other words, motor controller  10  in brushless motor  50  controls rotation of motor  40 , as shown in  FIG. 1 . 
         [0023]    Motor  40  includes a rotor and a stator provided with windings  56 , and the rotor rotates when windings  56  are energized. Description given in this embodiment is an example of brushless motor  50  in which motor  40  is driven with a three-phase source having U-phase, V-phase and W-phase that are offset by 120 degrees from one another. Motor  40  has windings  56  to make three-phase operation, which include winding  56 U driven in the U-phase, winding  56 V driven in the V-phase and winding  56 W driven in the W-phase. 
         [0024]    Motor controller  10  supplies a drive voltage of a predetermined waveform to each phase of windings  56 . As a result, the rotor rotates at a rotation speed according to rotational control of motor controller  10 . Motor  40  is additionally provided with a sensor for detecting a rotating position and rotation speed of the rotor in order to carry out such rotational control. In this exemplary embodiment, motor  40  has three position detection sensors  49  such as hall elements disposed to locations corresponding to the individual phases for detecting a rotating position of the rotor. Sensor signal Det is supplied to motor controller  10  from position detection sensors  49 . 
         [0025]    Motor controller  10  is also in signal communication with host controller  11  through signal transmission lines  19  shown in  FIG. 1 . 
         [0026]    Host controller  11  is located in an apparatus to which brushless motor  50  is mounted, for example, and it is configured of a microcomputer, a digital signal processor (“DSP”), or the like device. In an instance that brushless motor  50  is an electrical component mounted to a vehicle, host controller  11  may be a controller like an ECU. A command for controlling rotation of motor  40  is delivered from such host controller  11  to motor controller  10  through signal transmission lines  19 . On the other hand, information of brushless motor  50  is delivered from motor controller  10  to host controller  11  through signal transmission lines  19 . 
         [0027]    In this exemplary embodiment, a rotation speed command that directs a rotation speed of motor  40  is delivered to motor controller  10  as a command from host controller  11 . The rotation speed directed by the rotation speed command is hence delivered through signal transmission line  19   s  as pulse-width modulated PWM command signal Si. 
         [0028]    In addition, predetermined information is delivered from motor controller  10  to host controller  11 . Description is provided in this embodiment by taking an example in which the information to be delivered is information of a detected rotation speed. That is, motor controller  10  delivers information indicating the detected rotation speed as an information signal to host controller  11 . Here, the detected rotation speed means a rotation speed of motor  40  detected by motor controller  10 , and it represents an actual rotation speed. This information signal is pulse-width modulated, and delivered as PWM information signal Fp to host controller  11  through signal transmission line  19   f  in the same manner as the PWM command signal Si. A numerical figure denoting number of revolutions per minute (rpm) is used, for instance, for the rotation speed command and the detected rotation speed. 
         [0029]    A structure of motor controller  10  is described next. Motor controller  10  includes rotation control section  12 , PWM drive circuit  14 , inverter  15 , position detecting section  16 , rotation speed calculating section  17 , PWM demodulation processor  20 , and PWM modulation processor  30 . As stated previously, sensor signal Det is supplied to motor controller  10  from each of three position detection sensors  49  disposed to motor  40 . In addition, motor controller  10  is connected with host controller  11  via signal transmission lines  19  through which the PWM signal is transmitted. 
         [0030]    First, sensor signal Det is supplied from position detection sensors  49  to position detecting section  16 . Position detecting section  16  detects position information of the individual phases from the sensor signal Det that varies according to changes in the magnetic polarity with rotation of the rotor. For instance, position detecting section  16  detects timing at which sensor signal Det shows zero-crossing at a point of time when the magnetic polarity changes, and outputs position detection signal Pd based on this detected timing. In other words, a rotating position of the rotor can be detected by using the detected timing since the rotating position corresponds to the detected timing. The position detection signal Pd may be in a form of pulse signal showing such detected timing, as a specific example. Position detecting section  16  supplies position detection signal Pd corresponding to each of the phases to rotation speed calculating section  17 . 
         [0031]    Rotation speed calculating section  17  calculates a rotation speed of the rotor, for instance by differential operation, based on the rotating position provided by position detection signals Pd. Rotation speed calculating section  17  supplies calculated rotation speeds in the order of time sequence as detected speed values Vd to rotation control section  12  and PWM modulation processor  30 . Although what has been described in this exemplary embodiment is one example in which detected speed values Vd are generated based on sensor signal Det from position detection sensors  49 , it may instead be a structure configured to detect the rotor speed by using a speed detecting means and generate detected speed values Vd according to a result of this detection. In other words, detected speed values Vd only need to be values or signals in a time series that show speeds actually detected on the rotating motor. In this exemplary embodiment, rotation speed calculating section  17  also functions as an information signal generator for generating an information signal delivered to the outside. 
         [0032]    On the other hand, PWM demodulation processor  20  receives PWM command signal Si delivered from host controller  11 , and carries out demodulation of this pulse-width modulated signal. By this demodulating operation, PWM demodulation processor  20  restores speed command value Vr in the order of time sequence from the received PWM command signal Si. PWM command signal Si is in a form of pulse signal composed of pulses having pulse-widths corresponding to the rotational speed directed by host controller  11 , i.e. the rotation speed command. PWM demodulation processor  20  demodulates PWM command signal Si by detecting pulse-widths, or duty factors corresponding to the pulse-widths, of individual pulses of the PWM command signal Si. PWM demodulation processor  20  then outputs speed command value Vr restored by the demodulation operation in the order of time sequence. The rotation speed command of host controller  11  is thus restored as speed command value Vr by the above operation of PWM demodulation processor  20 . 
         [0033]    Speed command value Vr is supplied to rotation control section  12 . 
         [0034]    Rotation control section  12  is also supplied with detected speed value Vd calculated by rotation speed calculating section  17 . Rotation control section  12  generates drive value Dd representing a driving quantity for windings  56 , based on speed command value Vr and detected speed value Vd. To be specific, rotation control section  12  obtains a deviation in speed between speed command value Vr representing the speed command and detected speed value Vd indicating the detected speed corresponding to the actual speed. Rotation control section  12  then generates drive value Dd representing an amount of torque corresponding to the deviation in the speed, by which to bring the actual speed to conform to the commanded speed. Rotation control section  12  supplies this drive value Dd to PWM drive circuit  14 . 
         [0035]    PWM drive circuit  14  generates driving waveforms for the individual phases to drive windings  56 , pulse-width modulates each of the generated driving waveforms, and outputs them as driving pulse signals Dp. The driving waveforms are sinusoidal waves when windings  56  are driven with sine-wave voltages, or the driving waveforms are rectangular waves when driven with rectangular-pulse voltages. Amplitude of the driving waveforms is determined according to drive value Dd. PWM drive circuit  14  thus makes pulse-width modulation of the driving waveforms generated for each of the phases as modulation signals, and supplies to inverter  15  these driving pulse signals Dp forming pulse train that are pulse-width modulated by the driving waveforms. 
         [0036]    Inverter  15  energizes and drives windings  56  by supplying power to windings  56  in the individual phases based on driving pulse signals Dp. Inverter  15  includes a switching element connected to a positive side and another switching element connected to a negative side of the power supply for each of the U-phase, V-phase and W-phase. Driving output Uo of U-phase is connected to winding  56 U, driving output Vo of V-phase is connected to winding  56 V, and driving output Wo of W-phase is connected to winding  56 W. The switching elements are turned on and off in the individual phases by their corresponding driving pulse signals Dp. Drive voltage are thus supplied from the power supply through the turned-on switching elements, and then from the driving outputs to individual windings  56 . The supply of these drive voltages causes driving currents to flow through windings  56 . Here, individual windings  56  are energized by the driving currents corresponding to the driving waveforms since driving pulse signals Dp are the signals that are pulse-width modulated by the driving waveforms. 
         [0037]    PWM drive circuit  14  and inverter  15  make up power drive section  13 . As discussed above, power drive section  13  drives motor  40  by energizing windings  56  in the individual phases according to drive value Dd. 
         [0038]    With the structure illustrated above, a feedback control loop is formed to control rotation speed of the rotor in a manner to follow speed command value Vr. 
         [0039]    In addition, PWM modulation processor  30  is provided in this exemplary embodiment. PWM modulation processor  30  generates PWM information signal 
         [0040]    Fp by carrying out pulse-width modulation by detected speed value Vd supplied as information signal in the order of time sequence. In order for PWM modulation processor  30  to carry out such pulse-width modulation, PWM demodulation processor  20  supplies to PWM modulation processor  30  with pulse start signal Ps indicating start timing of the individual pulses to be sent out, and pulse-period signal Pw indicating cyclic periods of the individual pulses. PWM modulation processor  30  determines pulse widths of the pulses to be sent out based on detected speed value Vd and pulse-period signal Pw, and sequentially generates pulses that go on only for the periods of these pulse-widths from pulse start signal Ps. The pulse train generated in this manner is sent to host controller  11  through signal transmission line  19   f  as PWM information signal Fp. 
         [0041]    In particular, the structure in this embodiment is so configured that the pulse periods and the phases of PWM information signal Fp are synchronizing with the pulse periods and the phases of PWM command signal Si. In other words, the periods of PWM command signal Si are synchronized with the periods of PWM information signal Fp by using pulse-period signal Pw, and the phase of PWM command signal Si is synchronized with the phase of PWM information signal Fp by the timing of pulse start signal Ps. According to this exemplary embodiment, magnetic field radiated from signal transmission line  19   f  of PWM information signal Fp becomes generally opposite in the direction to magnetic field radiated from signal transmission line  19   s  of PWM command signal Si, by virtue of the structure configured above. As a result, unwanted emissions radiated from both signal transmission lines  19  are cancelled out, and the spurious emissions can hence be reduced. 
         [0042]    Described next pertains to a detailed structure of PWM demodulation processor  20  and PWM modulation processor  30 . 
         [0043]      FIG. 2  is a block diagram showing an exemplary structure of PWM demodulation processor  20  and PWM modulation processor  30  of motor controller  10  according to this embodiment of the invention. In addition,  FIG. 3A  to  FIG. 3C  are graphic diagrams showing signal waveforms and the like in main points of motor controller  10 .  FIG. 3A  shows a signal waveform of PWM command signal Si in a solid line,  FIG. 3B  shows timing of pulse start signal Ps in a solid line, and  FIG. 3C  shows a signal waveform of PWM information signal Fp, also in a solid line. 
         [0044]    As shown in  FIG. 2 , clock signal Ck is supplied to PWM demodulation processor  20  and PWM modulation processor  30 . The clock signal Ck is a pulse signal of regular cyclic periods, of which a frequency is substantially higher than frequencies of PWM command signal Si and PWM information signal Fp. For example, both the frequencies of PWM command signal Si and PWM information signal Fp are set at 500 Hz, and the frequency of clock signal Ck is set at 1 MHz. In the example shown in  FIG. 2 , the structure is so configured that it generates the PWM signal by counting clock signal Ck with a counter. 
         [0045]    To begin with, PWM demodulation processor  20  includes leading-edge detecting section  21 , edge-cycle detecting section  22 , duty factor calculating section  23 , and speed command calculating section  24 , as shown in  FIG. 2 . 
         [0046]    In PWM demodulation processor  20 , PWM command signal Si delivered from host controller  11  is supplied to leading-edge detecting section  21  and duty factor calculating section  23 . PWM command signal Si is a pulse train of period Tp, and a time duration of each period Tp is made up of on-period Ton of a high level and off-period Toff of a low level, as shown in  FIG. 3A . A pulse width that forms this on-period Ton is modulated by a value of the rotation speed command. In other words, the rotation speed command can be restored by detecting a duty factor, which is a ratio of on-period Ton to the time duration of period Tp.  FIG. 3A  illustrates an example in which a value of the rotation speed command becomes larger as time passes, and on-period Ton of each pulse, i.e. the duty factor, becomes larger as the rotation speed command speed becomes larger. 
         [0047]    Leading-edge detecting section  21  detects timing of a rising edge when each pulse of PWM command signal Si rises from an off state to an on state, and generates edge detection signal Pe based on this timing. The timing of this edge detection signal Pe corresponds to the start timing of each of the pulses that constitute PWM command signal Si, as shown in  FIG. 3B . The generated edge detection signal Pe is supplied to edge-cycle detecting section  22  and duty factor calculating section  23 . This edge detection signal Pe is also supplied to PWM modulation processor  30  as pulse start signal Ps. Leading-edge detecting section  21  configured to operate in the above manner is provided in this embodiment as one example of an edge timing detector for detecting timing of an edge that changes into a given direction. 
         [0048]    Edge-cycle detecting section  22  detects a cyclic period of edge detection signals Pe supplied sequentially from leading-edge detecting section  21 . In this exemplary structure, edge-cycle detecting section  22  has a counter for counting a number of clock signals Ck. Edge-cycle detecting section  22  detects the cyclic period of edge detection signals Pe by having the counter count the number of clocks between successive edge detection signals Pe. The counter of edge-cycle detecting section  22  operates in this manner to detect the number of counts Ntp in the interval of period Tp, as shown in  FIG. 3B . This detected number of counts Ntp corresponds to period Tp of each of the pulses that constitute PWM command signal Si. The number of counts Ntp is supplied to duty factor calculating section  23 , as well as to PWM modulation processor  30  as pulse-period signal Pw. 
         [0049]    In this exemplary structure, duty factor calculating section  23  also has a counter for counting the number of clock signals Ck. The counter in duty factor calculating section  23  starts counting at the timing of edge detection signals Pe, continues the counting for duration of on-period Ton of PWM command signal Si, and detects a number of counts Non in the on-period Ton, as shown in  FIG. 3B . Furthermore, duty factor calculating section  23  calculates a ratio of the numbers of counts Non to the number of counts Ntp. This ratio corresponds to the duty factor of PWM command signal Si. PWM command signal Si is hence demodulated by calculating this ratio. In addition, speed command calculating section  24  restores the rotation speed command as speed command value Vr from the ratio calculated by duty factor calculating section  23 . 
         [0050]    Assume that a number of counts Ntp is  2 , 000  and a number of counts Non is 1,000, for instance, the ratio becomes 0.5 and hence a duty factor of 50%. Speed command calculating section  24  restores a rotation speed command as being 1,000 (rpm) from the duty factor of 50%, for example, or 500 (rpm) if the duty factor is 25%. 
         [0051]    Next, PWM modulation processor  30  includes duty factor calculating section  31 , modulation count-number calculating section  32  and timer output section  33 , as shown in  FIG. 2 . 
         [0052]    Duty factor calculating section  31  calculates a duty factor used to carry out pulse-width modulation from detected speed value Vd supplied to it. For example, duty factor calculating section  31  calculates a duty factor corresponding to a rotation speed indicated by detected speed value Vd, such that the duty factor is 50% when detected speed value Vd is 1,000 (rpm), or the duty factor is 25% when value Vd is 500 (rpm). 
         [0053]    Modulation count-number calculating section  32  calculates a pulse width of the on-period of PWM information signal Fp based on a pulse period indicated by pulse-period signal Pw supplied to it and a duty factor provided from duty factor calculating section  31 . More specifically, modulation count-number calculating section  32  calculates a number of counts Mon for generating PWM information signal Fp by multiplying a number of counts Ntp indicated by pulse-period signal Pw by the duty factor. 
         [0054]    Duty factor calculating section  31  and modulation count-number calculating section  32  constitute pulse-width calculating section  34 . That is, pulse-width calculating section  34  calculates the pulse width of the on-period of PWM information signal Fp based on detected speed value Vd and a cyclic period of edges detected by edge-cycle detecting section  22 . 
         [0055]    Timer output section  33  generates a signal formed of pulse train that becomes on state only for a period corresponding to number of counts Mon from the timing of pulse start signal Ps periodically responding to pulse-period signal Pw, as shown in  FIG. 3C . To be specific, timer output section  33  in this exemplary structure has a counter for counting a number of clock signals Ck. The counter in timer output section  33  starts counting at the timing of pulse start signal Ps, and continues the counting up to the number of counts Mon. Timer output section  33  outputs PWM information signal Fp that stays at an on state during a period wherein the counting continues, and switches to an off state from the point when the counting ends. Timer output section  33  also functions as a PWM information signal generator for generating and outputting PWM information signal Fp based on a pulse width calculated by pulse-width calculating section  34  and pulse start signal Ps provided from leading-edge detecting section  21 . 
         [0056]    PWM demodulation processor  20  and PWM modulation processor  30  in this exemplary embodiment are configured as discussed above. In other words, the timing at which each pulse of PWM information signal Fp rises is based on pulse start signal Ps restored from PWM command signal Si. Accordingly, phases of the individual pulses of PWM information signal Fp are synchronized with phases of the pulses of PWM command signal Si. Moreover, a period of each individual pulse of PWM information signal Fp is based on period Tp restored from PWM command signal Si. Thus, periods of the individual pulses of PWM information signal Fp are also synchronized with periods of the pulses of PWM command signal Si. By virtue of synchronization of PWM information signal Fp with PWM command signal Si, the magnetic field radiated from signal transmission line  19   f  of PWM information signal Fp becomes generally opposite in direction of the magnetic field radiated from signal transmission line  19   s  of PWM command signal Si. Unwanted emissions radiated from both signal transmission lines  19  are thus cancelled, thereby achieving a reduction of the spurious emissions. 
         [0057]    In this exemplary embodiment, an information signal transmitted with PWM information signal Fp is detected speed value Vd. Here, detected speed value Vd becomes nearly equal to speed command value Vr, when the rotation speed of the rotor controlled according to the rotation speed command of host controller  11  comes to reach a speed directed by this rotation speed command. In other words, a waveform of PWM information signal Fp becomes generally similar to a waveform of PWM command signal Si when the rotation speed reaches the directed speed. Two such signals of similar waveforms are transmitted through both of signal transmission lines  19   s  and  19   f.  The magnetic fields radiated from both these signal lines therefore become similar with their direction opposite to each other, thereby cancelling out the unwanted emissions more effectively, and further improving the effect of reducing the spurious emissions. 
         [0058]    It is also feasible to employ a structure configured to avoid leading-edge detecting section  21  from outputting pulse start signal Ps during a period when leading-edge detecting section  21  does not detect any edge, and to avoid timer output section  33  from outputting PWM information signal Fp during the same period in conjunction with it. The structure so configured can reduce a frequency of sending PWM information signal Fp needlessly, thereby improving further the effect of reducing the spurious emissions, since PWM information signal Fp is output only when PWM command signal Si is received. 
         [0059]    Although what has been described above is an example of structure including PWM demodulation processor  20  and PWM modulation processor  30  made up by using counters and the like devices, it is also possible to form the structure with microcomputers or the like devices. That is, the functions of PWM demodulation processor  20  and PWM modulation processor  30  described above may be replaced with a program that can be installed into the structure to execute the above processes. Moreover, the structure discussed above is one example configured to modulate a pulse width of on-period starting at a rising point of the pulse as a reference. However, the structure can be such that it uses a falling point of the pulse as the reference, or modulates a pulse width of off-period. In essence, the structure only needs to have motor controller  10  that is capable of generating and sending out PWM information signal Fp in synchronization with PWM command signal Si it receives. 
         [0060]    Next, description is provided of a detailed structure of brushless motor  50 . 
         [0061]      FIG. 4  is a sectional view of brushless motor  50  according to one exemplary embodiment of the present invention. In this exemplary embodiment, description is given of an example of inner-rotor type brushless motor  50  having a rotor disposed rotatable to an interior side of a stator. 
         [0062]    As shown in  FIG. 4 , brushless motor  50  includes stator  51 , rotor  52 , circuit board  53  and motor case  54 . Motor case  54  is formed of a metal having a sealed cylindrical shape, and brushless motor  50  has such a structure that stator  51 , rotor  52  and circuit board  53  are disposed inside motor case  54 . 
         [0063]    In  FIG. 4 , stator  51  is constructed by having windings  56  of individual phases wound around stator core  55 . Stator core  55  has a plurality of protruding poles that protrude inward. Stator core  55  has an outer periphery of generally a cylindrical shape, which is fixed to motor case  54 . Rotor  52  is inserted in stator  51  with a gap between them. Rotor  52  holds permanent magnet  58  of a cylindrical shape on an outer periphery of rotor frame  57 , and is disposed rotatably around rotary shaft  60  supported by bearings  59 . In other words, stator  51  and rotor  52  are disposed such that end surfaces of the protruding poles of stator core  55  confront an outer peripheral surface of permanent magnet  58 . Motor  40  is thus constructed by having stator  51  of such configuration and rotor  52  supported by bearings  59 . 
         [0064]    In addition, this brushless motor  50  has circuit board  53  disposed inside motor case  54 , with various circuit components  41  mounted on circuit board  53 . These circuit components  41  concretely configure motor controller  10  for driving and controlling motor  40 . Additionally, position detection sensors  49  like hall elements are mounted to circuit board  53  for detecting a rotating position of rotor  52 . Support member  61  is attached to stator core  55 , and circuit board  53  is fixed within motor case  54  via this support member  61 . End portions of individual windings  56 U,  56 V and  56 W of U-phase, V-phase and W-phase are individually tapped out from stator  51  to serve as lead wires  56   a,  which are connected individually to circuit board  53 . 
         [0065]    Signal transmission lines  19  are also extended out of brushless motor  50  for connection with host controller  11 . 
         [0066]    When a power supply voltage and PWM command signal Si are supplied from the outside to brushless motor  50  constructed as above, a drive current flows to windings  56  from motor controller  10  formed on circuit board  53 , which in turn generates magnetic field from stator core  55 . The magnetic field from stator core  55  and magnetic field of permanent magnet  58  produce an attractive force and a repulsive force corresponding to polarities of these magnetic fields, and these forces make rotor  52  rotate around rotary shaft  60 . 
         [0067]    As described above, the motor controller of the present invention includes a PWM demodulation processor for demodulating a PWM command signal and restoring a rotation speed command as a speed command value, a rotation control section for generating a drive value of a motor according to the speed command value, a power drive section for generating a driving voltage to energize and drive a winding of the motor according to the drive value, an information signal generator for generating an information signal to be transmitted to outside, and a PWM modulation processor for generating a PWM information signal that is pulse-width modulated by the information signal. The PWM modulation processor is configured to generate and output the PWM information signal that is synchronized with the PWM command signal. 
         [0068]    The brushless motor of the present invention includes a rotor, a stator provided with windings for three-phases and the motor controller of this invention for energizing and driving the winding. 
         [0069]    Furthermore, the motor control system of the present invention includes the brushless motor of this invention, and a host controller configured to control rotation of the brushless motor by outputting a PWM command signal to and receiving a PWM information signal from the brushless motor. 
         [0070]    According to the configurations described above, magnetic field radiated from the transmission line of the PWM command signal and magnetic field radiated from the transmission line of the PWM information signal become generally opposite to each other in their directions at all the time, because both pulse periods of the PWM command signal and the PWM information signal become equal. Unwanted emissions radiated from both these transmission lines are thus cancelled out, and spurious emissions can be reduced. Thus provided according to the present invention are the motor controller, the brushless motor, and the motor control system capable of reducing the spurious emissions with simple structures not requiring any special component and material for noise preventive measures. 
       INDUSTRIAL APPLICABILITY 
       [0071]    The motor controller, brushless motor and motor control system of the present invention are suitable for motors for an electrical component of which a reduction of spurious emissions is especially needed since they are capable of reducing unwanted emissions, and that they are also useful for motors used in electrical apparatuses.