Abstract:
An internal combustion engine control apparatus includes: an ignition coil including a primary coil and a secondary coil that are magnetically coupled to each other; a first switch element for turning on and off a current to the primary coil; and a spark plug, for igniting an air-fuel mixture in an internal combustion engine by using a spark discharge caused by switching the first switch element from the ON state to the OFF state. The internal combustion engine control apparatus is configured to: determine occurrence of one of an abnormality in a discharge voltage and a misfire of the spark plug, when the calculated time duration in which a voltage of the primary coil after the switching of the first switch element from the ON state to the OFF state is above a predetermined comparison reference voltage does not fall within an allowable range.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an internal combustion engine control apparatus including a spark plug which is driven by a current interruption-type ignition circuit, for igniting an air-fuel mixture in an internal combustion engine, in particular, a technology of detecting an abnormality in a discharge voltage and a misfire of the spark plug. 
         [0003]    2. Description of the Related Art 
         [0004]    In recent years, a high compression-ratio technology and a gasoline in-cylinder direct injection technology become more and more important in order to improve fuel efficiency of an internal combustion engine (gasoline engine). When a compression ratio is increased, however, a pressure in a spark discharge gap in a spark plug is increased to disadvantageously increase a discharge voltage of the spark plug. Moreover, when the gasoline in-cylinder direct injection is performed, a difference in density is likely to be generated in an air-fuel mixture. Thus, large spark energy is required to ignite the air-fuel mixture. 
         [0005]    When the spark energy increases, electrodes of the spark plug are likely to wear. As a result, if the electrodes wear, the spark discharge gap becomes wider to increase the discharge voltage of the spark plug. Accordingly, there is a fear in that the discharge voltage of the spark plug exceeds a dielectric withstand voltage to cause dielectric breakdown of the spark plug. Moreover, when the discharge voltage of the spark plug exceeds a magnetically induced voltage which can be generated by an ignition coil, the spark plug cannot generate the spark discharge and therefore cannot ignite the air-fuel mixture. 
         [0006]    As a related-art internal combustion engine control apparatus which solves the problem described above, there exits one configured to measure the discharge voltage of the spark plug to obtain a degradation state of the spark plug (for example, see Japanese Patent Application Laid-open No. 2013-177881). 
         [0007]    However, the related art has the following problems. 
         [0008]    According to Japanese Patent Application Laid-open No. 2013-177881, although a state in which the discharge voltage of the spark plug becomes high can be obtained, a state in which the discharge voltage becomes abnormally low or the occurrence of a spark plug misfire cannot be obtained. Moreover, in order to detect the abnormality in the discharge voltage and the misfire of the spark plug, special elements such as a zener diode which withstands a high voltage are required. Further, an additional wiring for connecting the above-mentioned elements to a secondary coil at a high voltage and insulating processing are required. Thus, costs disadvantageously increase. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention has been made to solve the problems described above and has an object to provide an internal combustion engine control apparatus at low costs, which is capable of detecting an abnormality in a discharge voltage and a misfire of a spark plug. 
         [0010]    According to one embodiment of the present invention, there is provided an internal combustion engine control apparatus, including: an ignition coil including a primary coil and a secondary coil that are magnetically coupled to each other; a first switch element for turning on a current to the primary coil when the first switch element is brought into an ON state, and turning off the current to the primary coil when the first switch element is brought into an OFF state; a control computing section for controlling switching between the ON state and the OFF state of the first switch element; and a spark plug, which is to be driven by a current-interruption type ignition circuit, for igniting an air-fuel mixture in an internal combustion engine by using a spark discharge caused by a magnetically induced voltage generated in the secondary coil by switching of the first switch element from the ON state to the OFF state, in which the control computing section is configured to: calculate a time duration in which a voltage of the primary coil after the switching of the first switch element from the ON state to the OFF state is above a predetermined comparison reference voltage; and determine occurrence of one of an abnormality in a discharge voltage of the spark plug and a misfire of the spark plug when the calculated time duration does not fall within an allowable range. 
         [0011]    According to one embodiment of the present invention, by measuring the discharge voltage of the spark plug based on the time duration in which the voltage of the primary coil is above the predetermined comparison reference voltage, the internal combustion engine control apparatus capable of detecting the abnormality in the discharge voltage and the misfire of the spark plug can be obtained at low costs. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is an exemplary diagram of a circuit configuration of an internal combustion engine control apparatus according to a first embodiment of the present invention. 
           [0013]      FIG. 2  is a timing chart of the internal combustion engine control apparatus according to the first embodiment of the present invention. 
           [0014]      FIG. 3  is a timing chart of the internal combustion engine control apparatus according to the first embodiment of the present invention in the case where a discharge voltage of a spark plug has an abnormality. 
           [0015]      FIG. 4  is a timing chart of the internal combustion engine control apparatus according to the first embodiment of the present invention in the case where the spark plug is in a misfire state. 
           [0016]      FIG. 5  is a graph showing a relationship between a time duration in which a primary coil voltage V 1  is above a comparison reference voltage and the discharge voltage of the spark plug in the internal combustion engine control apparatus according to the first embodiment of the present invention. 
           [0017]      FIG. 6  is a graph showing a relationship between a charging voltage of a capacitor and the discharge voltage of the spark plug in the internal combustion engine control apparatus according to the first embodiment of the present invention. 
           [0018]      FIG. 7  is an exemplary diagram of a circuit configuration of an internal combustion engine control apparatus according to a second embodiment of the present invention. 
           [0019]      FIG. 8  is a timing chart of the internal combustion engine control apparatus according to the second embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    Now, an internal combustion engine control apparatus according to exemplary embodiments of the present invention is described referring to the accompanying drawings. In the drawings, the same or corresponding parts are denoted by the same reference symbols for description. 
       First Embodiment 
       [0021]      FIG. 1  is an exemplary diagram of a circuit configuration of an internal combustion engine control apparatus according to a first embodiment of the present invention. The internal combustion engine control apparatus according to the first embodiment includes a control computing section  10 , a first switch element  20 , an ignition coil  30 , a spark plug  40 , and a voltage detecting circuit  50 . As the control computing section  10 , an engine control unit (ECU) for a vehicle is used. 
         [0022]    The ignition coil  30  includes a primary coil  30   a  and a secondary coil  30   b  which are magnetically coupled to each other so as to generate a spark discharge in a spark discharge gap in the spark plug  40 . The first switch element  20  is turned on and off based on a control signal (hereinafter referred to as “Igt signal”) from the control computing section  10  to control a flow (ON) and interruption (OFF) of a primary coil current I 1 . 
         [0023]    The voltage detecting circuit  50  includes a comparator  51 , voltage-dividing resistors  52 ,  53 ,  54 , and  55 , a resistor  56 , a diode  57 , a capacitor  58 , and a second switch element  59 . The voltage detecting circuit  50  detects a primary coil voltage V 1 . 
         [0024]    The comparator  50  compares the primary coil voltage V 1  and a predetermined comparison reference voltage V 0 . In practice, instead of directly comparing the primary coil voltage V 1  and the comparison reference voltage V 0  with each other, the comparator  51  compares a voltage V 1 ′ which is set by the primary coil voltage V 1  and the voltage-dividing resistors  54  and  55 , and a voltage V 0 ′ (=V 0 ×V 1 ′/V 1 ) which is set by a power supply voltage and the voltage-dividing resistors  52  and  53 , as illustrated in  FIG. 1 . 
         [0025]    An output from the comparator  51  is brought into an open collector state when the primary coil voltage V 1  is above the comparison reference voltage V 0 . When the output from the comparator  51  is in the open collector state, the capacitor  58  is charged from a power supply through the resistor  56 . On the other hand, when the primary coil voltage V 1  is equal to or lower than the comparison reference voltage V 0 , the output from the comparator  51  is set at a GND level. Therefore, the capacitor  58  is not charged, and a charging voltage Vs before the voltage V 1  becomes equal to or lower than the comparison reference voltage V 0  is maintained. The diode  57  serves to prevent the capacitor  58  from discharging. 
         [0026]    As a result, the charging voltage Vs of the capacitor  58  increases in proportion to a time duration in which the primary coil voltage V 1  is above the comparison reference voltage V 0 . Moreover, the control computing section  10  enables the capacitor  58  to discharge by controlling the second switch element  59  connected in parallel to the capacitor  58 . Therefore, the control computing section  10  resets the charging voltage Vs of the capacitor  58  to 0 V in advance before turning on the first switch element  20  so that a value of the charging voltage Vs itself can be made proportional to the time duration in which the primary coil voltage V 1  is above the comparison reference voltage V 0 . 
         [0027]    As described above, the control computing section  10  controls the second switch element  59  and measures the charging voltage Vs of the capacitor  58 . As a result, the control computing section  10  can obtain the time duration in which the primary coil voltage V 1  is above the comparison reference voltage V 0 . 
         [0028]      FIG. 2  is a timing chart of the internal combustion engine control apparatus according to the first embodiment of the present invention. The control computing section  10  sets a signal VR at a high level to bring the second switch element  59  into an energized (ON) state. In this manner, the charging voltage Vs of the capacitor  58  is reset to 0 V in advance. 
         [0029]    At a time T 1 , when the level of the Igt signal output from the control computing section  10  becomes high, the first switch element  20  is turned on to start the flow of the primary coil current I 1  through the primary coil  30   a . Simultaneously, the control computing section  10  sets the signal VR at a low level to bring the second switch element  59  into an interrupted (OFF) state. 
         [0030]    At a time T 2 , when the level of the Igt signal output from the control computing section  10  becomes low, the first switch element  20  is turned off to interrupt the primary coil current I 1  which flows through the primary coil  30   a . As a result, a magnetic flux in the ignition coil  30  rapidly changes to cause a change in the primary coil voltage V 1  and a secondary coil voltage V 2  due to electromagnetic induction. 
         [0031]    Specifically, the secondary coil voltage V 2  starts gradually decreasing at the time T 2 . The primary coil voltage V 1  has a high peak voltage immediately after the time T 2  and then gradually increases. The high peak voltage of the primary coil voltage V 1  is a surge voltage generated due to a primary coil leakage inductance caused when the perfect coupling between the primary coil  30   a  and the secondary coil  30   b  fails. The voltage which gradually increases after the generation of the surge voltage is a voltage generated by the primary coil  30   a  and the secondary coil  30   b  which form a transformer having a winding turns ratio N. At this time, a change amount ΔV 1  in the primary coil voltage V 1  and a change amount ΔV 2  in the secondary coil voltage V 2  have a relationship: |ΔV 1 |=|ΔV 2 |/N. 
         [0032]    The voltage detecting circuit  50  compares the primary coil voltage V 1  and the comparison reference voltage V 0 . When the primary coil voltage V 1  exceeds the comparison reference voltage V 0 , the output from the comparator  51  is brought into the open collector state. As a result, the capacitor  58  is charged to increase the charging voltage Vs. 
         [0033]    At a time T 3 , when a magnetically induced voltage generated in the secondary coil  30   b  exceeds a discharge voltage Vb 1  in the spark discharge gap in the spark plug  40 , a spark discharge is caused in the spark plug  40 . As a result, the secondary coil voltage V 2  rapidly converges to a glow/arc discharge voltage. With the convergence of the secondary coil voltage V 2 , the primary coil voltage V 1  also rapidly drops to become a voltage V 1   a  lower than the comparison reference voltage V 0 . 
         [0034]    Further, at the time T 3 , when the primary coil voltage V 1  becomes equal to or lower than the comparison reference voltage V 0 , the output from the comparator  51  is set at the GND level. As a result, the charging for the capacitor  58  is stopped. After the time T 3 , a charging voltage Vs 1  at the time T 3  is maintained. In this manner, the capacitor  58  is charged only for a time duration t 1 . 
         [0035]    The comparison reference voltage V 0  may be set so as to be lower than the primary coil voltage V 1  during the time duration t 1  and higher than the voltage V 1   a  during the glow/arc discharge time period, for example, to about 100 V. 
         [0036]    At a time T 4 , when the spark discharge of the spark plug  40  ends, the primary coil voltage V 1  and the secondary coil voltage V 2  both converge to about 0 V. 
         [0037]    At a time T 5  after elapse of a predetermined time period from the time T 2 , the control computing section  10  reads the charging voltage Vs 1  of the capacitor  58 . 
         [0038]    At a time T 6  after the reading of the charging voltage Vs 1  of the capacitor  58  is completed (or after elapse of a predetermined time period from the time T 5 ), the control computing section  10  sets the signal VR at the high level to bring the second switch element  59  into a conductive (ON) state. In this manner, the capacitor  58  is discharged to reset the charging voltage Vs to 0 V. 
         [0039]      FIG. 3  is a timing chart of the internal combustion engine control apparatus according to the first embodiment of the present invention in the case where a discharge voltage Vb of the spark plug  40  has an abnormality.  FIG. 3  differs from  FIG. 2  referred to above in the discharge voltage Vb, mainly in an operation from a time T 3 ′ to a time T 4 ′. The operation at the times except for the time period from the time T 2 ′ to the time T 3 ′ is the same as that illustrated in  FIG. 2 , and therefore the description thereof is herein omitted. 
         [0040]    At the time T 3 ′, when the magnetically induced voltage generated in the secondary coil  30   b  exceeds a discharge voltage Vb 2  in the spark discharge gap in the spark plug  40 , the spark discharge is caused in the spark plug  40 . As a result, the secondary coil voltage V 2  rapidly converges to the glow/arc discharge voltage. 
         [0041]    The discharge voltage Vb 2  illustrated in  FIG. 3  is larger than the discharge voltage Vb 1  illustrated in  FIG. 2 . A time duration t 2  illustrated in  FIG. 3  is longer than the time duration t 1  illustrated in  FIG. 2 , whereas a charging voltage Vs 2  of the capacitor  58  at the time T 3 ′ is higher than the charging voltage Vs 1  illustrated in  FIG. 2 . 
         [0042]    At the time T 4 ′, when the spark discharge in the spark plug  40  ends, the primary coil voltage V 1  and the secondary coil voltage V 2  both converge to about 0 V. 
         [0043]    As described above, even when the discharge voltage Vb of the spark plug  40  becomes high, the discharge voltage Vb of the spark plug  40  can be detected by measuring the time duration in which the primary coil voltage V 1  is above the comparison reference voltage V 0  based on the charging voltage Vs of the capacitor  58 . Moreover, even when the discharge voltage Vb is low, the discharge voltage Vb of the spark plug  40  can be detected by using the same method. 
         [0044]      FIG. 4  is a timing chart of the internal combustion engine control apparatus according to the first embodiment of the present invention in the case where the spark plug  40  is in a misfire state without causing dielectric breakdown.  FIG. 4  differs from  FIG. 2  referred to above mainly in an operation from a time T 3 ″ to a time T 4 ″. The operation at the times except for the time period from the time T 2 ″ to the time T 3 ″ is the same as that illustrated in  FIG. 2 , and therefore the description thereof is herein omitted. 
         [0045]    In the case where dielectric breakdown does not occur in the spark discharge gap in the spark plug  40 , the spark discharge is not caused in the spark discharge gap in the spark plug  40 . Therefore, a sudden voltage drop occurs neither in the primary coil voltage V 1  nor in the secondary coil voltage V 2 , and the primary coil voltage V 1  and the secondary coil voltage V 2  both have a gentle waveform as illustrated in  FIG. 4 . A time period in which the primary coil voltage V 1  is above the comparison reference voltage V 0  becomes extremely long as represented by a time duration t 3 . As a result, the capacitor  58  is continuously charged over the long time duration t 3 . After the capacitor  58  is charged to a charging voltage Vs 3  which is the same as the power supply voltage, the charging voltage of the capacitor  58  does not become any higher. 
         [0046]    As described above, by measuring the time duration in which the primary coil voltage V 1  is above the comparison reference voltage V 0  based on the charging voltage Vs of the capacitor  58 , the misfire of the spark plug  40  can also be detected. 
         [0047]      FIG. 5  is a graph showing a relationship between the time duration in which the primary coil voltage V 1  is above the comparison reference voltage V 0  and the discharge voltage Vb of the spark plug  40  in the internal combustion engine control apparatus according to the first embodiment of the present invention.  FIG. 6  is a graph showing a relationship between the charging voltage Vs of the capacitor  58  and the discharge voltage Vb of the spark plug  40  in the internal combustion engine control apparatus according to the first embodiment of the present invention. 
         [0048]    As described above, by measuring the time duration in which the primary coil voltage V 1  is above the comparison reference voltage V 0  based on the charging voltage Vs of the capacitor  58 , the abnormality in the discharge voltage and the misfire of the spark plug  40  can be detected.  FIGS. 5 and 6  are exemplary relationship graphs for determining the abnormality in the spark plug  40  based on the time duration or the charging voltage Vs in a specific manner. 
         [0049]    In  FIG. 5 , when a time duration t is equal to or smaller than a first threshold value, it is determined that there is a possibility of a leak discharge occurring at a location other than the spark discharge gap in the spark plug  40 . When the time duration t is larger than a second threshold value (&gt;first threshold value) and is equal to or smaller than a third threshold value described below, it is determined that the discharge voltage Vb is abnormally high due to wear of electrodes of the spark plug  40 . Further, when the time duration t is larger than the third threshold value (&gt;second threshold value), it is determined that the spark plug  40  is in a misfire state without causing the spark discharge. 
         [0050]    In the internal combustion engine control apparatus according to the first embodiment, the charging voltage Vs of the capacitor  58  is approximately proportional to the time duration in which the primary coil voltage V 1  is above the comparison reference voltage V 0 . Therefore, based on the charging voltage Vs instead of the time duration t as shown in  FIG. 6 , the leak discharge of the spark plug  40 , the abnormality in the discharge voltage Vb, and the misfire can be determined by using the same technique. 
         [0051]    When the abnormality in the discharge voltage or the misfire is detected, it is possible to prevent uncombusted gasoline from being released out of an internal combustion engine by, for example, warning a driver by displaying the result of detection on a warning indicator of a vehicle or stopping fuel injection controlled by the ECU. 
         [0052]    As described above, according to the first embodiment, the abnormality in the discharge voltage and the misfire of the spark plug can be detected by measuring the time duration in which the primary coil voltage is above the predetermined comparison reference voltage based on the charging voltage of the capacitor. 
         [0053]    Further, according to the first embodiment, no additional circuit is required for the secondary coil of the ignition coil. Therefore, the internal combustion engine control apparatus can be configured using general low-voltage components without requiring an element which withstands a high voltage. Further, a component and a wiring are not required for a high-voltage side, and a wiring is required only for the primary coil having a low voltage. Thus, the voltage detecting circuit can be realized by general-purpose components for a low voltage. Thus, the costs can be reduced. 
       Second Embodiment 
       [0054]      FIG. 7  is an exemplary diagram of a circuit configuration of an internal combustion engine control apparatus according to a second embodiment of the present invention. The internal combustion engine control apparatus illustrated in  FIG. 7  differs from that illustrated in  FIG. 1  according to the first embodiment described above in that a regulator circuit  60  for regulating the operation of the voltage detecting circuit  50  is further provided. The remaining configuration is the same as that illustrated in  FIG. 1 . 
         [0055]    The regulator circuit  60  includes comparators  61  and  62 , and resistors  63 ,  64 , and  65 . The regulator circuit  60  regulates the voltage detecting circuit  50  of the first embodiment described above so that the voltage detecting circuit  50  responds only to the first spark discharge but not to the subsequent spark discharges even in the case where the spark discharge is caused in the spark plug  40  for a plurality of times. With the regulator circuit  60 , the discharge voltage Vb of the spark plug  40  can be more precisely determined. 
         [0056]      FIG. 8  is a timing chart of the internal combustion engine control apparatus according to the second embodiment of the present invention.  FIG. 8  differs from  FIG. 2  referred to above mainly in an operation from the time T 3  to the time T 5 . The operation at the times except for the time period from the time T 3  to the time T 5  is the same as that illustrated in  FIG. 2 , and therefore the description thereof is herein omitted. 
         [0057]    At the time T 3 , the magnetically induced voltage generated in the secondary coil  30   b  exceeds the discharge voltage Vb 1  in the spark discharge gap in the spark plug  40 , and then transitions to the glow/arc discharge. Thereafter, at a time T 7 , the glow/arc discharge is sometimes blown out by an airflow in a combustion chamber. 
         [0058]    In this case, an electromotive force of the secondary coil  30   b  increases, for example, due to electromagnetic energy stored in the ignition coil  30 . At a time T 9 , the secondary coil  30   b  exceeds a discharge voltage Vb 1 ′ of the spark plug  40  again to transition to the glow/arc discharge. As a result, the primary coil voltage V 1  exceeds the comparison reference voltage V 0  again. Thus, the time duration measured by the voltage detecting circuit  50  includes not only the time duration t 1  which needs to be measured actually but also a time duration t 4 . 
         [0059]    Thus, in the second embodiment, the regulator circuit  60  is further provided. As a result, even in the case where the spark discharge is repeatedly caused as described above, only the first time duration t 1  is detected without detecting the second time duration t 4 . In this manner, the discharge voltage Vb of the spark plug  40  can be more precisely determined. 
         [0060]    At the time T 3  in  FIG. 8 , when a (−) input of the comparator  61  of the regulator circuit  60  becomes approximately 0 V and an output from the comparator  61  is in the open collector state, the charging voltage Vs of the capacitor  58  is applied to the (−) input of the capacitor  62  through the resistor  63 . The applied charging voltage Vs is a voltage Vc illustrated in  FIG. 8 . As a result, the output from the comparator  62  is set at the GND level to prevent the primary coil voltage V 1  from being applied to a (+) input of the comparator  51 . The resistors  64  and  65  are voltage-dividing resistors for generating a small voltage value which is not 0 V, for the comparison with the charging voltage Vs of the capacitor  58 . 
         [0061]    The control computing section  10  sets the signal VR at the high level to reset the charging voltage Vs of the capacitor  58  to 0 V. In this manner, the voltage Vc illustrated in  FIG. 8  is also reset to 0 V to recover the regulator circuit  60  into an initial state. 
         [0062]    As described above, according to the second embodiment, even in the case where the spark discharge is repeatedly caused in the spark plug for a plurality of times, only the first discharge voltage is detected to enable more precise detection of the abnormality in the discharge voltage and the misfire of the spark plug. 
         [0063]    In the first and second embodiments, the method of measuring the time duration in which the primary coil voltage V 1  is above the comparison reference voltage V 0  based on the charging voltage Vs of the capacitor  58  has been described. However, the time duration may be directly measured by, for example, using a time measurement function of a microcomputer mounted in the ECU. Even in this case, the second and subsequent time durations (t 4 ) are ignored by the ECU. In this manner, only the first discharge voltage can be measured in the case where the spark discharge is repeatedly caused for a plurality of times.