Abstract:
A self-diagnosis means is provided with a fan motor comprising a stator on which a stator coil is mounted, a rotor comprising a permanent magnet and a fan, a Hall device for detecting magnetic pole position of the permanent magnet and a current control means for controlling rotation of the rotor by controlling current to be fed to the stator coil. In an embodiment, the self-diagnosis means judges if the fan motor has drawn to the life. In another embodiment, the self-diagnosis means interrupts the current to be fed to the stator coil when the rotational speed is higher than an allowable value, and restarts the current automatically to return the fan motor into normal operation when the rotational speed is not higher than the allowable value.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention concerns a fan motor. More particularly, the present invention concerns a fan motor provided with a self-diagnosis means.  
           [0003]    2. Description of the Prior Art  
           [0004]    A fan motor being used comprises a stator, a rotor, a Hall device, a microcomputer and a current control circuit. The stator has a stator coil mounted on it. The rotor comprises a permanent magnet and a fan, and is rotatably supported to oppose the stator coil. The Hall device detects magnetic pole position of the permanent magnet. The microcomputer processes output of the Hall device. The current control circuit receives the output of the microcomputer and controls the operation of the rotor by controlling current to be fed to the stator coil.  
           [0005]    Such fan motor is installed, for example, in a casing of electronic equipments, and is an important component that discharges heat inside of the casing to assure the safe operation of the electronic equipments. Accordingly, life of the fan motor has an important effect on lives of the electronic equipments in the casing in which the fan motor is installed.  
           [0006]    A life of a fan motor is estimated based on results of continuous running tests for a large number of samples. However, there is a problem that it is difficult to exactly determine a life of an individual fan motor being actually in use, based only on the results of the continuous running tests using samples, since lives of fan motors scatter according to the service conditions.  
           [0007]    In the meantime, some fan motors are provided with protection circuits. The protection circuit detects rotational speed of the fan motor from an output voltage of the Hall device, judges that the fan motor is being incurred an overload when the detected rotational speed is lower than the reference value and stops the fan motor. However, there is a problem that such protection circuit does not work as protection means in an abnormal case when the rotational speed of the fan motor becomes higher than an allowable value, by some reason, and a voltage induced in the stator coil exceeds the withstand voltage of a semiconductor device in a current control circuit.  
         SUMMARY OF THE INVENTION  
         [0008]    It is an object of the present invention to solve the above problems and provide a fan motor provided with a self-diagnosis means.  
           [0009]    It is another object of the present invention to provide a fan motor provided with a self-diagnosis means that judges that the fan motor has drawn to the life.  
           [0010]    It is still another object of the present invention to provide a fan motor provided with a self-diagnosis means that functions as a protection means for control circuit devices.  
           [0011]    To achieve the above object, the present invention provide an fan motor comprising a stator on which a stator coil is mounted, a rotor comprising a permanent magnet and a fan and being rotatably supported to oppose the stator coil, a Hall device for detecting magnetic pole position of the permanent magnet, and a current control means for controlling rotation of the rotor by controlling current to be fed to the stator coil, characterized in that there is provided a self-diagnosis means for detecting the state of the fan motor, based on the result of which operation of the fan motor is controlled through the current control means.  
           [0012]    This fan motor is capable to be controlled autonomously, since the self-diagnosis means detects the state of the fan motor, based on the result of which the operation of the fan motor is controlled through the current control means.  
           [0013]    Further to achieve the above object, the self-diagnosis means comprises a current detection circuit for detecting a currently flowing current value in the stator coil, a current signal processing means for processing the currently flowing current value, and a memory means for processing and storing a steady state current value, in which the currently flowing current value is compared with the steady state current value, and the fan motor is judged to have drawn to the life if the difference between the currently flowing current value and the steady state current value exceeds a predetermined value.  
           [0014]    The fan motor provided with such self-diagnosis means can be replaced properly when it has drawn to the life, and consequently, the lives of the electronic equipments for which the fan motor is provided can be lengthened, since the currently flowing current value is compared with the steady state current value, and the fan motor is judged to have drawn to the life if the difference between the currently flowing current value and the steady state current value exceeds the predetermined value.  
           [0015]    Still further to achieve the above object, the self-diagnosis means comprises a reference voltage generator means for generating a predetermined reference voltage, a F/V converter means for transforming a rotational speed detected from an output voltage of the Hall device into a voltage proportional to the rotational speed, a comparator means for comparing the reference voltage with the voltage proportional to the rotational speed, in which the current to be fed to the stator coil is interrupted when the voltage proportional to the rotational speed is higher than the reference voltage, and the current to be fed to the stator coil is restarted automatically to return the fan motor into normal operation when the voltage proportional to the rotational speed is less than or equal to the reference voltage.  
           [0016]    The fan motor provided with such self-diagnosis means can be prevented from an accident in which a semiconductor device in the current control means is destroyed, since when the rotational speed of the fan motor becomes higher than an allowable value, the current fed to the stator coil is interrupted, the rotational speed of the rotor is lowered and a voltage induced in the stator coil is kept below the withstand voltage of the semiconductor device in the current control means,  
           [0017]    Other objects, characteristics and advantages of the present invention will become apparent from the following detailed description referring to the attached drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is a block diagram of a control system of the first embodiment of the fan motor according to the present invention.  
         [0019]    [0019]FIG. 2 is a block diagram of a current signal processing means of the control system shown in FIG. 1.  
         [0020]    [0020]FIG. 3 is a flowchart of the current signal processing means shown in FIG. 2.  
         [0021]    [0021]FIG. 4 is a block diagram of a control system of the second embodiment of the fan motor according to the present invention.  
         [0022]    [0022]FIG. 5 is a flowchart of the microcomputer shown in FIG. 4. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]    Preferred embodiments of the fan motor according to the present invention are explained referring to the attached drawings.  
         [0024]    [0024]FIG. 1 is a block diagram of a control system of the first embodiment of the fan motor according to the present invention. In the drawing,  1  is a Hall device,  2  is a microcomputer containing a current signal processing means  2 - 2 ,  3  is a current control circuit that is a current control means,  4  is a current detection circuit,  5  is a stator coil and  6  is a memory device that is a memory means.  
         [0025]    A magnetic pole position signal of a permanent magnet of a rotor detected by the Hall device  1  is transmitted into a current control signal generator part  2 - 1  in the microcomputer  2 . The current control signal generator part  2 - 1  processes the input magnetic pole position signal and transmits the resultant signal into the current control circuit  3 . An output of the current control circuit  3  is transmitted into the stator coil  6  through the current detection circuit  4 . Thus, a current controlled based on the output of the Hall device  1  flows through the stator coil  5  to rotate the rotor, and the operation of the fan motor is controlled accordingly.  
         [0026]    A current flowing through the stator coil  5  differs in individual fan motor in use, Accordingly, it is difficult to evaluate a variation in the current in a long term of operation only by examining its effective value, So, in the present embodiment, the current is detected, compared with that of steady state, and a variation in current is evaluated.  
         [0027]    The current detection circuit  4  is composed of a resistance element. A voltage drop in the current detection circuit  4  is transmitted into the current signal processing means  2 - 2  in the microcomputer  2  as a current signal.  
         [0028]    Construction of the current signal processing means  2 - 2  is shown in FIG. 2. In the drawing,  10  is a zero timing generator means that receives an output voltage of the Hall device  1  and generates zero timing signal  12  is a sampling means,  13  is a timing signal generator means,  14  is an A/D converter means,  16  is a comparator means,  6  is the memory device,  3  is the current control circuit and  4  is the current detection circuit.  
         [0029]    Operation of the current signal processing means  2 - 2  shown in FIG. 2 is as follows. An output voltage Vout (corresponding to a currently flowing current value in the stator coil  6 ) of the current detection circuit  4  is transmitted into the sampling means  12 . The sampling means  12  samples the output voltage Vout in accordance with the timing signal transmitted from the timing signal generator means  13 , and transmits the sampled output voltage Vout into the A/D converter means  14 . The A/D converter means  14  transforms the sampled output voltage Vout into a digital value Ic. A zero timing of the sampling is determined by a zero timing signal transmitted from the zero timing generator means  10 .  
         [0030]    The digital value Ic corresponding to the currently flowing current value transmitted from the A/D converter means  14 , a digital value Iref corresponding to the current value in the steady state stored in the memory device  6  and the zero timing signal transmitted from the zero timing generator means  10  are put into the comparator means  15 . The comparator means  15  compares the digital value Ic with the digital value Iref starting from the zero timing signal. If the difference between the digital value Ic and the digital value Iref is greater than a predetermined reference value E, then the comparator means  15  judges that the fan motor draws to its life and transmits a signal into the current control circuit  3  to stop current. Consequently, the fan motor is stopped.  
         [0031]    The current signal processing means  2 - 2  shown in FIG. 2 can be controlled with a control program prepared and stored before hand in the microcomputer  2 .  
         [0032]    Process in the current signal processing means  2 - 2  is explained referring to the flowchart shown in FIG. 5.  
         [0033]    The zero timing generator means  10  generates the zero timing signal synchronized with a signal from the Hall device  1 . (S 1 )  
         [0034]    The timing signal generator means  13  receives the zero timing signal and generates the timing signal. (S 2 )  
         [0035]    The sampling means  12  receives the timing signal and samples the output voltage Vout of the current detection circuit  4 . (S 3 )  
         [0036]    The A/D converter means  14  transforms the output voltage Vout, corresponding to the currently flowing current value, sampled by the sampling means  12 , into the digital value Ic, and transmits the digital value Ic into the comparator means  15 . (S 4 )  
         [0037]    On the other hand, the digital value Iref corresponding to the current value in the steady state stored in the memory device  6  is transmitted into the comparator means  15 , starting from the zero timing signal and synchronized with the timing signal from the timing signal generator means  13 . (S 5 )  
         [0038]    The comparator means  15  compares the digital value Ic with the digital value Iref starting from the zero timing signal. If the difference between the digital value Ic and the digital value Iref is greater than the predetermined reference value E for judging the life, then the comparator means  15  judges that the fan motor draws to its life and transmits a signal into the current control circuit  3  to stop current and the fan motor is stopped. On the contrary, if the difference between the digital value Ic and the digital value Iref does not exceed the reference value E, then the procedure returns into initial step (S 1 ) without transmitting the signal for stopping current into the current control circuit  8 . (S 6 )  
         [0039]    Additionally, the reference value E for judging the life of the fan motor should be set with a certain degree of allowance, since a current flowing through a stator coil differs in individual fan motor in use.  
         [0040]    In the first embodiment of the fan motor according to the present invention as explained above, the current value currently flowing through the stator coil  5  is compared with the current value in steady state stored in the memory device  6 . In case that the difference between the current value currently flowing and the current value in steady state is greater than a predetermined reference value E, the comparator means judges that the fan motor draws to its life and transmits a signal into the current control circuit  3  to stop current. Consequently, the fan motor is stopped. Accordingly, it is possible to replace the fan motor in operation before it wears out, and thus the life of the electronic equipments in the casing in which the fan motor is installed can be lengthened.  
         [0041]    [0041]FIG. 4 is a block diagram of a control system of the second embodiment of the fan motor according to the present invention. In the drawing,  1  is a Hall device,  20  is a microcomputer,  22  is a control computer,  23  is a current control circuit that is a current control means,  24  is a current control switching circuit,  5  is a stator coil,  26  is a F/V converter means for transforming an output frequency of the Hall device into voltage,  27  is a comparator means,  28  is a reference voltage generator means and  214  is a drive control signal means.  
         [0042]    In the control system shown in FIG. 4, an output signal of the Hall device  1  is transmitted into the control computer  22 . This signal is transformed into a pulse signal and transmitted into the current control circuit  23 . Output signal of the current control circuit  23  is transmitted into the current control switching circuit  24 , and then into the stator coil  5  to rotate the rotor in a predetermined rotational speed in a predetermined rotational direction.  
         [0043]    On the other hand, the output of the Hall device  1  is also transmitted into the F/V converter means  26 , from which an output voltage Vc proportional to the rotational speed of the rotor is transmitted into the comparator means  27 . In the comparator means  27 , the output voltage Vc of the F/V converter means  26  is compared with a reference voltage Vref generated from the reference voltage generator means  28 . If the output voltage Vc is lower than the reference voltage Vref, then an affirmation signal YES is transmitted into the drive control signal means  214 . If the drive control signal means  214  receives the affirmation signal YES, and if the pulse signal is generated in the control computer  22 , then the drive control signal means  214  transmits a continue drive command signal into the current control circuit  23 .  
         [0044]    On the contrary, if the output voltage Vc is equal to or higher than the reference voltage Vref, then an affirmation signal YES is not transmitted into the drive control signal means  214 . Accordingly, the continue drive command signal is not transmitted from the drive control signal means  214 , and the fan motor is decelerated. When the output voltage Vc of the F/V converter means  26  becomes lower than the reference voltage Vref again, the continue drive command signal is transmitted from the comparator means  27  into the current control circuit  23 , and the fan motor is controlled to return into normal operation.  
         [0045]    Composing elements, such as the control computer  22 , the F/V converter means  26 , the comparator means  27 , the reference voltage generator means  28  and the drive control signal means  214 , used to carry out the above procedure can be included in the microcomputer  20 , and the procedure can be operated by a computer program loaded in the microcomputer  20 .  
         [0046]    [0046]FIG. 5 is a flowchart of the microcomputer  20 .  
         [0047]    With the rotation of the fan motor, a voltage is generated in the Hall device  1 . The control computer  22  receives the voltage generated in the Hall device  1  and generate a pulse signal, (S 15 ) This pulse signal is transmitted into the drive control signal means  214 .  
         [0048]    The output voltage of the Hall device  1  is also transmitted into the F/V converter means  26 . The F/V converter means  26  transforms the frequency of the wave form of the output voltage into the voltage Vc proportional to the rotational speed of the fan motor. (S 12 )  
         [0049]    The reference voltage generator means  28  generates the reference voltage Vref. (s 13 )  
         [0050]    The comparator means  27  compares the voltage Vc with the reference voltage Vref If the voltage Vc is lower than the reference voltage Vref, the comparator means  27  transmits the affirmation output YES into the drive control signal means  214 . (S 14 )  
         [0051]    If the pulse signal is transmitted from the control computer  22  is ascertained. (S 16 )  
         [0052]    If the pulse signal is transmitted from the control computer  22 , and if the affirmation output YES is transmitted from the comparator means  27 , the drive control signal means  214  transmits the continue drive command signal into the current control circuit  23 . (S 17 )  
         [0053]    As a result, a current feed signal is transmitted from the current control circuit  28  into the current control switching circuit  24 , current is fed to the stator coil  5  and the rotor of the fan motor continues to rotate. (S 18 )  
         [0054]    After that, the flow returns to the start S 11  and the process is repeated.  
         [0055]    In case that the rotational speed rises during the operation of the fan motor, and the output voltage Vc of the F/V converter means  26  becomes equal to or higher than the reference voltage Vref, then the comparator means  27  selects a denial output NO. If it is the case, no output signal is transmitted into the drive control signal means  214 . Accordingly, since the continue drive command signal is not transmitted from the drive control signal means  214  into current control circuit  23 , the current control circuit  23  stops to transmit the current feed signal into a semiconductor device in the current control switching circuit  24 . Consequently, the current into the stator coil  5  is interrupted, the rotor is not driven and the fan motor is decelerated. The execution returns to the start S 11  and the process is repeated,  
         [0056]    In case that the current into stator coil  6  is interrupted and the rotor is decelerated, the output voltage Vc from the F/V converter means  26  lowers. Comparing the output voltage Vc with the reference voltage Vref in the comparator means  27 , if the output voltage Vc becomes less than the reference voltage Vref, the comparator means  27  again selects the affirmation signal YES and transmits it into the drive control signal means  214 . Then, the continue drive command signal is transmitted from the drive control signal means  214  into the current control circuit  28 , a normal current control signal is transmitted from the current control signal generate circuit  28  into the current control switching circuit  24 , a normal current is fed to the stator coil  5  and the fan motor returns automatically into normal operation state.  
         [0057]    Additionally, the reference voltage Vref is determined such that a rotational speed of the fan motor remains within a range in which a voltage, caused by a back electromotive force in the stator coil  6  and applied to a semiconductor control device of the current control switching circuit  24 , does not exceed the withstand voltage of the semiconductor control device. Thus, the rotational speed can be reduced before the semiconductor control device is destroyed by the back electromotive force in the stator coil, and an accident can be prevented from occurring.  
         [0058]    In the second embodiment of the fan motor according to the present invention as explained above, the fan motor is provided with an automatic return function by which, if the voltage Vc, obtained by transforming the output signal of the Hall device  1  by the F/V converter means  26 , and proportional to the rotational speed of the fun motor, exceeds the reference voltage Vref, then the current fed to the stator coil  5  is interrupted to decelerate the fun motor, and if the voltage Vc becomes equal to or less than reference voltage Vref, then feeding of the current to the stator coil  5  is restarted to return the fun motor into normal operation.  
         [0059]    Accordingly, it is possible to prevent such an accident in which semiconductor device in the current control circuit is destroyed when the rotational speed of the fan motor becomes higher than an allowable value.  
         [0060]    The invention has been described in terms of preferred embodiments. However, those skilled in the art will recognize that many variations of such embodiments exist. Such variations are intended to be within the scope of the present invention.