Abstract:
A voltage regulator for an a.c. generator produces a power generation ratio signal having a duty ratio corresponding to the current supply to the field winding of the a.c. generator. This power generation ratio signal is applied to an external apparatus through a signal wire. The duty ratio of the power generation ratio signal is more than 10% when the a.c. generator is normal. When abnormality is detected, the power generation ratio signal is partly masked by an abnormality detection signal so that the duty ratio of the power generation signal is reduced to be less than 10% and this change may be detected by the external apparatus. Alternatively, the power generation ratio signal may be transmitted only intermittently when the abnormality is detected.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
         [0001]    This application is based on and incorporates herein by reference Japanese Patent Application No. 2001-261095 filed Aug. 30, 2001.  
         FIELD OF THE INVENTION  
         [0002]    The present invention relates to a control apparatus and method for controlling an alternating current generator mounted on vehicles, and more particularly to the control apparatus and method which outputs abnormality information to an external apparatus.  
           [0003]    It is recently proposed to use the power generation ratio of an alternating current (a.c.) generator as a parameter in an engine control thereby to stabilize idling rotation of the engine. In JP-U-60-18120, an a.c. generator is constructed to output to an external electronic apparatus a field coil voltage signal from the junction between its field coil and its voltage regulator through a current limiting resistor. The external apparatus is thus enabled to estimate mechanical torque or the like of the generator from the power generation ratio of the generator and control an idle control valve of an engine for stabilizing the engine idle speed.  
           [0004]    The external apparatus requires as much information as possible for engine control. Such information includes, in addition to the power generation ratio, malfunction indicative of malfunction of the generator. However, because the field coil voltage signal does not include such information other than the power generation ratio, additional signal wires must be added to the field coil voltage signal wire. It is not desirable to increase signal wires, because wiring the signal wires becomes complicated and breakage and shorting of the signal wires become more likely.  
         SUMMARY OF THE INVENTION  
         [0005]    It is therefore an object of the present invention to provide an a.c. generator control apparatus and method which enables detection of malfunction of an a.c. generator without increasing signal wires.  
           [0006]    According to the present invention, current supply to a field winding of an a.c. generator is turned on and off in a variable duty ratio within a predetermined range at every predetermined cycle period thereby to regulate an output voltage of the generator. A power generation ratio output signal is produced in a pulse form having a duty ratio corresponding to the duty ratio of the current supply to the field winding. The output signal is transmitted to an external apparatus through a signal wire. The output signal transmitted to the external apparatus is changed depending on whether an abnormality in the a.c. generator is detected. The change of the output signal may be a change of the duty ratio of the output signal to a duty ratio that is outside the predetermined range. Alternatively, the change may be a stop of transmission of the output signal to the external apparatus for a period longer than the predetermined cycle period. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings:  
         [0008]    [0008]FIG. 1 is a circuit diagram showing a vehicle a.c. generator regulator apparatus according to the first embodiment of the present invention;  
         [0009]    [0009]FIG. 2 is a signal diagram showing a mode of generation of a power generation ratio signal in a normal condition in the first embodiment;  
         [0010]    [0010]FIG. 3 is a signal diagram showing a mode of generation of the power generation ratio signal in an abnormal condition in the first embodiment;  
         [0011]    [0011]FIG. 4 is a signal diagram showing a mode of generation of the power generation ratio signal in the abnormal condition in the second embodiment of the present invention; and  
         [0012]    [0012]FIG. 5 is a circuit diagram showing an external signal receiver circuit used in the third embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0013]    (First Embodiment)  
         [0014]    Referring first to FIG. 1, a vehicle a.c. generator  1  has three-phase stator windings  11  wound in a stator (not shown), a rectifier circuit  12  which full-wave rectifies output voltages of the stator windings  11 , a field winding  13  wound in a rotor (not shown), and a voltage regulator apparatus  3  which controls a field current supplied to the field winding  13  thereby to regulate the output voltage of the rectifier circuit  12 . The a.c. generator  1  has an output terminal (B-terminal) connected to a battery  2  and various electric loads (not shown) in a vehicle. The a.c. generator  1  further has an output terminal (FX-terminal) and an input terminal (CX-terminal). Those terminals are connected to an external electronic control unit (ECU)  4  to transmit a power generation ratio signal to the ECU  4  and to receive a control signal from the ECU  4 , respectively.  
         [0015]    The voltage regulator apparatus  3  is for regulating the output voltage at the B-terminal to a regulated voltage (for instance 14 volts). It includes a power transistor  20 , a flywheel diode  21 , a pulse generator  22 , an external signal receiver circuit  23 , a power supply circuit  24 , an abnormality detection circuit  25 , a transistor  26 , comparators  27 ,  28 , a NAND circuit  29 , an inverter circuit  30 , a Zener diode  31 , resistors  33  through  36 , and a capacitor  37 .  
         [0016]    The power transistor  20  is connected in series with the field winding  13  to turn on and off the field current supplied to the field winding  13 . The flywheel diode  21  is connected in parallel with the field winding  13  to flywheel the field current when the transistor  20  turns off.  
         [0017]    The pulse generator  22  is constructed to generate a periodic signal which is a composite of a triangular signal of a peak voltage 5 volts and of a cycle period t 0  and a pulse signal of a peak voltage 8 volts of period t 1  (t 0 /10) in each period t 0 . The external signal receiver circuit  23  is constructed to receive the control signal applied from the ECU  4  through the CX-terminal. The power supply circuit  24  is constructed to start supplying an operating voltage to various circuits in the voltage regulator apparatus  3 , when the control signal is received by the external signal receiver circuit  23 .  
         [0018]    The abnormality detection circuit  25  is constructed to detect abnormality in the a.c. generator  1  and generate an abnormality detection signal of a predetermined period and duty ratio, when any abnormality is detected.  
         [0019]    The voltage at the B-terminal is divided by the resistors  32  and  33  and applied to the non-inverting input of the comparator  28 , and a reference voltage Vr is applied to the inverting input of comparator  28 . The voltage Vr is set to correspond to a regulated voltage to which the output voltage of the rectifier circuit  12  is regulated. The output voltage of the comparator  28  is smoothed by a smoothing circuit comprised of the resistor  34  and the capacitor  37  and applied to the inverting input of the comparator  27 . The comparator  27  is connected to the pulse generator  22  to receive the periodic signal at its non-inverting input. The Zener diode  31  has a breakdown voltage of 5 volts to regulate the voltage applied to the inverting input of the comparator  27  to be 5 volts at maximum. The output signal produced from the comparator  27  is applied to the base of the power transistor  20 . As a result, the transistor  20  is turned on by a minimum duty ratio of 10%, even when the voltage applied to the inverting input of the comparator  27  is at the highest, that is, 5 volts.  
         [0020]    The collector of the transistor  20  is connected to the field coil  13  and the NAND circuit  29  through the inverter circuit  30 . The abnormality detection circuit  25  is also connected tot he NAND circuit  29 . Thus, the NAND circuit  29  masks a part of the output signal of the inverter circuit  30  by the abnormality detection signal of the abnormality detection circuit  25 . The output of the NAND circuit  29  is connected to the base of the transistor  26 , the collector and the emitter of which are connected to the FX-terminal through the resistor  36  and grounded, respectively. Thus, the transistor  26  is provided to transmit the on/off output signal of the power transistor  20 , which indicates the power generation ratio. The signal wire connecting the FX-terminal and the ECU  4  is terminated by a pull-up resistor  40  in the ECU  4 .  
         [0021]    [0021]FIG. 2 shows a pulse generator output signal Sa, an inverter output signal Sb produced from the pulse generator circuit  22 , an abnormality detection signal Sc produced from the abnormality detection circuit  25  and a power generation ratio signal Sd produced from the FX-terminal, when the a.c. generator  1  is operating normally.  
         [0022]    In operation, when the control signal indicating a start of electric power generation is applied to the CX-terminal from the ECU  4  distanced from the a.c. generator  1 , the power supply circuit  22  starts supplying power with which the voltage regulator apparatus  3  operatios to control the field current supplied to the field winding  13  by the power transistor  20 . As long as the a.c. generator  1  is operating normally, that is, no abnormality is detected by the abnormality detection circuit  25 , the power generation ratio signal Sd corresponds to the inverter output signal Sb indicative of the on/off operation (duty ratio) of the power transistor  20  as shown in FIG. 2.  
         [0023]    When any abnormality occurs, the abnormality detection signal Sc is applied to the NAND circuit  29 . As shown in FIG. 3, this signal Sc is set to have a period t 2  shorter than the period t 1  (10% minimum duty ratio) of the periodic signal Sa which is generated at every period t 0 . As a result, the duty ratio of the power generation ratio signal Sd applied to the ECU  4  through the FX-terminal becomes less than the duty ratio (10%) of the pulse signal Sa.  
         [0024]    The voltage regulator apparatus  3  thus reduces the duty ratio of the power generation ratio signal Sd to be lower than the predetermined minimum duty ratio (10%) of the field current. The ECU  4  is thus enabled to check for any abnormality in the a.c. generator  1  from the duty ratio of the power generation ratio signal Sd. Further, the ECU  4  is capable of checking the operating condition of the a.c. generator  1  from the period t 0  of the power generation ratio signal Sd. That is, as long as the power generation ratio signal Sd is received from the FX-terminal at every period t 0 , it can be confirmed that the power transistor  20  is not in the open-malfunction and the a.c. generator  1  is continuing the power generating operation even when the duty ratio (period t 2 ) is less than 10%.  
         [0025]    (Second Embodiment)  
         [0026]    In this second embodiment, the abnormality detection circuit  25  is constructed to generate the abnormality detection signal in the waveform different from that in the first embodiment.  
         [0027]    The abnormality detection circuit  25  generates an abnormality detection signal Sc shown in FIG. 4, when any abnormality is detected. The abnormality detection signal Sc continues to hold a high level and a low level alternately. The period t 3  of these levels are much longer than the period t 0  of the pulse signal Sa. The power generation ratio signal Sd is applied to the ECU  4  through the FX-terminal only when the abnormality detection signal Sc is at the high level. The ECU  4  is thus enabled to detect any abnormality in the a.c. generator  1  by checking whether the power generation ratio signal Sd is applied from the FX-terminal, because the power generation ratio signal Sd continues to be at the low level for the period t 3  when the abnormality occurs. The ECU  4  is also capable of checking the power generation ratio from the power generation ratio signal Sd.  
         [0028]    (Third Embodiment)  
         [0029]    In this third embodiment, the external signal receiver circuit  23  is constructed to generate the reference voltage Vr applied to the inverting input of the comparator  28  and to detect abnormality of the signal wire connecting the CX-terminal and the ECU  4 . Therefore, the NAND circuit  29  shown in FIG. 1 has another (third) input to receive this abnormality detection signal from the external signal receiver circuit  23 .  
         [0030]    As shown in FIG. 5, the external signal receiver circuit  23  has a resistor  100 , a voltage comparator  102 , a high-time counter  104 , a period counter  106 , a pulse width modulation (PWM) duty calculation circuit  108 , a duty latch  110 , a D/A converter  112 , a period check circuit  120 , a monitor timer  122  and an alarm pulse generator  124 .  
         [0031]    The CX-terminal is connected to the non-inverting input of the comparator  102  through the resistor  100 . The comparator  102  compares the control signal applied from the ECU  4  to its non-inverting input and indicative of the regulated output voltage in the form of the PWM signal with the reference voltage V 1  applied to its inverting input. The high-time counter  104  counts the period of time of the high level in the received PWM signal. The period counter  106  counts the period of the PWM signal. The PWM duty ratio calculation circuit  108  calculates the duty ratio of the PWM signal from the two counted periods. The calculated duty ratio is stored in the duty latch  110  and then converted into an analog voltage by the A/D converter  112 . This analog voltage is applied as the reference voltage Vr of the comparator Vr in FIG. 1. Thus, by varying the duty ratio of the PWM signal applied from the ECU  4 , the reference voltage Vr and hence the resulting regulated voltage of the a.c. generator  1  can be varied correspondingly.  
         [0032]    The period check circuit  120  checks whether the period of the PWM signal counted by the period counter  106  is within a predetermined range. If the signal wire connecting the CX-terminal and the ECU  4  is broken or shorted to other conductive parts, the counted period of the PWM signal increases over or decreases below the predetermined range. The check circuit  120  in such a case determines that the PWM signal is abnormal. The monitor timer  122  measures the period of time in which the abnormality detected by the check circuit  120  continues. If the measured abnormality period reaches a predetermined period, the alarm pulse generator  124  generates an alarm pulse as an abnormality detection signal. This alarm pulse may be the signal Sc of the period t 2  (less than 10% duty ratio) as in the first embodiment or the signal Sc of the long period t 3  as in the second embodiment. In the case of generating the signal Sc of the second embodiment, the abnormality in the control signal applied from the ECU  4  can be notified to the ECU  4  in addition to notifying the power generation condition of the a.c. generator  1 .  
         [0033]    The present invention should not be limited to the above disclosed embodiments, but may be implemented in many other ways. For instance, the abnormality may be notified by a signal of a predetermined duty ratio, which is larger than the maximum duty ratio (for instance 90%) of the power generation ratio signal. This large duty signal may be used solely or in addition to the small duty signal of the first embodiment to notify the abnormality. The periods of the high level signal and the low level signal used in the second embodiment may be varied in dependence on the types of detected abnormality.