JP6442928B2 - Ignition system for internal combustion engines - Google Patents

Description

  The present invention relates to an ignition system used in an internal combustion engine.

  In recent years, in order to improve the fuel efficiency of an internal combustion engine for automobiles, studies are being made on technologies relating to combustion control of lean fuel (lean burn engine) or EGR for returning combustion gas to a cylinder of the internal combustion engine. In these technologies, the ignition plug is continuously discharged for a certain time near the ignition timing, or a multiple ignition method / AC ignition method in which the ignition plug continuously discharges a plurality of times at the ignition timing of the internal combustion engine. Various ignition systems for effectively burning the fossil fuel contained in the air-fuel mixture, such as the DCO system to be used, have been studied.

  Since ignition systems based on these methods are required to maintain a large discharge current, the voltage applied to the primary coil (primary side of the ignition coil) is boosted by a DC-DC converter or the like (see Patent Document 1). ).

JP2012-167665A

  In the above case, the ignition signal at the start of discharge or the ignition signal after the start of discharge may be longer than the normal ignition signal due to a signal abnormality from the ECU. At this time, because of the high voltage, current may flow excessively to a switching element such as an IGBT (insulated gate bipolar transistor) that cuts off and conducts current flowing to the primary coil. As a result, the power consumption of the IGBT increases and may be damaged.

  The present invention has been made to solve the above-mentioned problems, and its main object is to suppress damage to switching elements in an ignition system that performs continuous discharge or multiple discharge with an ignition plug. It is.

  Hereinafter, means for solving the above-described problems and the operation and effects thereof will be described.

  The present invention is an ignition system for an internal combustion engine, comprising an ignition plug for generating a spark discharge for igniting a combustible air-fuel mixture in a combustion chamber of the internal combustion engine, a primary coil and a secondary coil, and the secondary coil An ignition coil for applying a voltage to the ignition plug, a voltage applying means for applying a predetermined voltage to the primary coil, a first switching element for cutting off and conducting a primary current flowing through the primary coil, and the first By controlling the driving of the switching element, the discharge executing means for executing continuous discharge or multiple discharge by the spark plug, and connected between the voltage applying means and the primary coil, the primary current flowing to the primary coil A second switching element for cutting and conducting; a cathode connected between the second switching element and the primary coil; and an anode grounded A diode, and primary current control means for controlling the second switching element so that a current flowing through the primary coil falls within a first predetermined region during driving of the first switching element by the discharge execution means. It is characterized by.

  According to the above configuration, the ignition coil includes the primary coil and the secondary coil. A predetermined voltage is applied to the primary coil by the voltage applying means. The current flowing to the primary coil is controlled to be cut off and conducted by turning the first switching element ON / OFF. By controlling the first switching element and controlling the primary current by the discharge execution means, the spark plug is caused to execute continuous discharge or multiple discharge.

  In this internal combustion engine ignition system, a second switching element is further provided between the voltage applying means and the primary coil. A diode having a cathode connected and an anode grounded is provided between the second switching element and the primary coil. At this time, during the driving of the first switching element, the second switching element is controlled by the primary current control means so that the primary current falls within the first predetermined region. For example, during driving of the first switching element, when the primary current flowing through the primary coil exceeds the upper limit value of the first predetermined region, the primary current is cut by the primary current control means. In the meantime, current is supplied through a diode whose anode is grounded, and the primary current slowly drops. When the primary current falls below the lower limit value of the first predetermined region, the primary current is supplied again by the primary current control means. By doing so, the primary current can be stored in the first predetermined region. As a result, damage can be suppressed without excessive current flowing through the first switching element.

1 is a diagram illustrating a circuit configuration of an internal combustion engine ignition system (first embodiment). FIG. 4 is a timing chart showing an ignition signal, a primary current, a secondary current, and power consumption (first embodiment). 3 is a timing chart showing an ignition signal, a primary current, and a secondary current (first embodiment). It is a figure which shows the circuit structure of the ignition system for internal combustion engines (modified example of 1st Embodiment). It is a figure which shows the circuit structure of the ignition system for internal combustion engines (2nd Embodiment). It is a timing chart showing an ignition signal, a primary current, and a secondary current (second embodiment). It is a figure which shows the circuit structure of the ignition system for internal combustion engines (3rd Embodiment). 10 is a timing chart showing an ignition signal, a primary current, and a secondary current (third embodiment). It is a flowchart which shows the control program of a current control circuit (3rd Embodiment). It is a figure which shows the circuit structure of the ignition system for internal combustion engines (modified example). It is a figure which shows the circuit structure of the ignition system for internal combustion engines (modified example).

(First embodiment)
The present embodiment will be described with reference to the drawings. An ignition system 10 for an internal combustion engine shown in FIG. 1 includes two ignition coils 19A and 19B, two IGBTs 15A and 15B (corresponding to a first switching element), a spark plug 20, and a DC-DC converter 12 (voltage applying means). Corresponding to the above).

  The battery 11 and the DC-DC converter 12 are connected in series. The DC-DC converter 12 is applied with a voltage of about 12 (V) to 24 (V) from the battery 11, and based on this, the voltage is boosted to about 40 (V) to about 90 (V).

  The output side of the DC-DC converter 12 is branched and connected to a first end of a primary coil 16A included in the ignition coil 19A and a first end of a primary coil 16B included in the ignition coil 19B. The ignition coil 19A includes a secondary coil 17A and an iron core 18A in addition to the primary coil 16A, and the ignition coil 19B has a similar configuration. The second ends of the primary coils 16A and 16B are connected to the collector terminals of the IGBTs 15A and 15B (corresponding to the first switching element), respectively, and the emitter terminals of the IGBTs 15A and 15B are grounded through a current detection circuit such as a resistor. Has been.

The first ends of the secondary coils 17A and 17B are each grounded to a ground potential. On the other hand, the second ends of the secondary coils 17A and 17B are connected to the cathode sides of the diodes 14A and 14B. The anode side of the diodes 14A and 14B is connected to the spark plug 20.
The diodes 14A and 14B are provided to prevent preignition. Specifically, the anode sides of these diodes 14A and 14B are connected and joined together, and the joined current path is connected to the input terminal of the spark plug 20. That is, each of the secondary coils 17A and 17B is connected to one common spark plug 20, and the spark plug 20 has a voltage that allows current to flow from both the ignition coils 19A and 19B to the secondary coils 17A and 17B. Are added and applied. The arrow of the secondary current I2 in FIG. 1 indicates that the direction flowing from the secondary coils 17A and 17B to the spark plug 20 is the positive direction. Therefore, when the primary currents I1_1 and I1_2 flowing through the primary coils 16A and 16B are cut off, the secondary current I2 flowing through the spark plug 20 from the ground potential grounded to the spark plug 20 becomes a negative value.

  The ECU 13 (corresponding to the discharge execution means) includes a CPU, an I / O circuit, a memory circuit, a clock circuit, and the like. The ECU 13 is connected separately from each of the IGBTs 15A and 15B. The ECU 13 generates ignition signals IGT_1 and IGT_2 based on the input information, outputs them to the gate terminals of the IGBTs 15A and 15B, and controls the driving of the IGBTs 15A and 15B. Information relating to the operation state of the internal combustion engine (hereinafter referred to as operation state information) is appropriately input to the I / O circuit from various ECUs or sensors provided in each part of the automobile. The operating state information includes injector operation information, information from the crank angle sensor, and the like, and the ECU 13 recognizes information on the load state and the rotational speed of the internal combustion engine based on these information. And ECU13 sets each ignition signal IGT_1 and IGT_2 based on these information.

  Since the phases of the ignition signals IGT_1 and IGT_2 transmitted from the ECU 13 do not coincide with each other and are input to the IGBTs 15A and 15B, the IGBTs 15A and 15B are driven synchronously so that when one is ON, the other is OFF. Will be.

  Here, a MOSFET 21 (corresponding to the second switching element) is connected between the output terminal of the DC-DC converter 12 and the first ends of the primary coils 16A and 16B. Specifically, the drain terminal of the MOSFET 21 is connected to the output terminal of the DC-DC converter 12, and the source terminal of the MOSFET 21 is connected to the first end of the primary coil 16A.

  The cathode of the diode 22 is connected between the source terminal of the MOSFET 21 and the first ends of the primary coils 16A and 16B, and the anode of the diode 22 is grounded. The gate terminal of the MOSFET 21 is connected to a current control circuit 23 (corresponding to primary current control means). The current control circuit 23 is composed of a microcomputer, a drive circuit, and the like.

  The current control circuit 23 is connected to a current detection circuit 24 (corresponding to primary current detection means), and the current detection circuit 24 is connected to the respective emitter terminals of the two IGBTs 15A and 15B. The current detection circuit 24 includes a current sensor. Therefore, based on the current detected by the current detection circuit 24, the current control circuit 23 performs ON / OFF control of the MOSFET 21, and controls the primary currents I1_1 and I1_2 flowing to the primary coils 16A and 16B, respectively.

  Next, control executed by the ECU 13 and the current control circuit 23 in the present embodiment will be described.

  FIG. 2 is a timing chart showing operations of the ECU 13 and the current control circuit 23 in the present embodiment. This figure shows waveforms of primary currents I1_1 and I1_2 flowing in IGT_1, IGT_2 and IGBTs 15A and 15B transmitted from the ECU 13, respectively, waveforms of the secondary current I2 generated when the primary currents I1_1 and I1_2 are cut off, and consumption of the IGBT 15A Each power is shown.

  The ignition signals IGT_1 and IGT_2 transmitted asynchronously by the ECU 13 are each composed of a first pulse with a long time interval and a subsequent pulse that occurs intermittently with a short time interval. The first pulse is set such that the primary current I1_1 reaches the preset upper set value A. Accordingly, the primary current I1_1 due to the first pulse is set to be larger than the primary current I1_1 due to the subsequent pulse. The primary current I1_2 is similarly set.

  When the IGBTs 15A and 15B are driven by the ignition signals IGT_1 and IGT_2, primary currents I1_1 and I1_2 are intermittently generated in the primary coils 16A and 16B.

  At this time, in each of the secondary coils 17A and 17B, the fluctuation of the magnetic flux is continuously generated in synchronization with the primary currents I1_1 and I1_2, and a high voltage is continuously output. Therefore, a voltage obtained by synthesizing both high voltages is applied to the input terminal of the spark plug 20, and the secondary current I2 flows continuously.

  At this time, when the ignition plug 20 starts to discharge, if the ignition signals IGT_1 and IGT_2 transmitted to the IGBTs 15A and 15B become longer than the normal ignition signal due to a signal abnormality from the ECU 13, etc., the dotted line of the primary current I1_1 As shown in FIG. 5, excessive increase of the primary current I1_1 is allowed. As a result, the power consumption of the IGBT 15A increases rapidly and is damaged. For this reason, by providing another current control circuit 23 that does not depend on the ignition signals IGT_1 and IGT_2, damage to the IGBTs 15A and 15B is suppressed.

  The current control circuit 23 receives the magnitude of the current detected by the current detection circuit 24. At the start of the discharge of the spark plug 20, when either one of the primary currents I1_1 and I1_2 detected by the current detection circuit 24 rises above the preset upper set value A, the MOSFET 21 is turned off. Control. At this time, a current is supplied through the diode 22 whose anode is grounded, and the primary currents I1_1 and I1_2 slowly drop. Thereafter, the MOSFET 21 is controlled to be ON when the lower set value B is exceeded. By this control, the primary currents I1_1 and I1_2 are controlled between the upper set value A and the lower set value B (corresponding to the second predetermined area). At this time, the upper set value A is set as an upper limit within a range where there is no possibility of damaging the IGBTs 15A and 15B, and the lower set value B is set as a value obtained by reducing the upper set value A by a predetermined value.

  After starting the discharge of the spark plug 20, the upper set value A is changed to the upper set value C set lower (FIG. 3), and the lower set value B set lower than the lower set value D ( Change to FIG. The same control is performed so that both the primary currents I1_1 and I1_2 transition between the upper set value C and the lower set value D (corresponding to the first predetermined range). As a result, the secondary current I2 is controlled so that no discharge interruption occurs.

  With the above configuration, the current control circuit 23 of the internal combustion engine ignition system 10 according to the present embodiment has the following effects.

  The upper set value A of the primary currents I1_1 and I1_2 at the start of discharge of the spark plug 20 is set higher than the upper set value C after the start of discharge. Therefore, the primary currents I1_1 and I1_2 can be increased, and the output voltage to the spark plug 20 can be increased in response to the current values. As a result, the spark plug 20 can be easily discharged.

  The current control circuit 23 monitors the primary currents I1_1 and I1_2 detected by the current detection circuit 24, and according to the preset upper set value A and lower set value B or upper set value C and lower set value D. Then, ON / OFF control of the MOSFET 21 is performed. By doing so, the primary currents I1_1 and I1_2 are controlled between the upper set value A and the lower set value B or between the upper set value C and the lower set value D. Since the current control circuit 23 is a circuit that does not depend on the ECU 13, even if the IGBTs 15A and 15B continue to be ON due to a signal abnormality of the ECU 13, the current control circuit 23 suppresses the primary currents I1_1 and I1_2 from rising. For this reason, the power consumption of the IGBTs 15A and 15B is suppressed, leading to suppression of damage.

  In addition, the said embodiment can also be changed and implemented as follows.

  At the start of discharge of the spark plug 20, the upper set value A of the primary current is set to be higher than the upper set value C after the start of discharge. In this regard, the upper set value A may be made equal to the upper set value C. By doing so, there is no difference in control between the start of the discharge of the spark plug 20 and the start of the discharge, and the control can be further simplified. Further, the upper set values A and C may be set as target values for the primary current. According to such a configuration, the primary current can be accurately controlled to the target value.

  The first ends of the secondary coils 17A and 17B are each grounded to the ground potential. In this regard, as shown in FIG. 4, the first end of the primary coil 16 and the first end of the secondary coil 17 may be connected. By doing so, the ignition system 10 can be simplified.

(Second Embodiment)
Hereinafter, the second embodiment will be described with reference to the drawings with a focus on differences from the first embodiment.

  In the first embodiment, the current detection circuit 24 is connected between the emitter terminals of the IGBTs 15A and 15B and the ground point, and the primary currents I1_1 and I1_2 are detected. In the present embodiment, as shown in FIG. 5, a current detection circuit 31 (corresponding to a secondary current detection means) is connected between the first ends of the secondary coils 17A and 17B and the ground point.

  The ignition signals IGT_1 and IGT_2 are respectively input to the IGBTs 15A and 15B with a predetermined time interval. At this time, the magnitudes of the primary currents I1_1 and I1_2 are estimated from the magnitudes of the secondary currents I2_1 and I2_2 detected by the current detection circuit 31, and the secondary currents I2_1 and I2_2 are set to a reference current value β ( If it is smaller than that in FIG. 6, the time interval between the primary currents I1_1 and I1_2 is extended. Note that the secondary currents I2_1 and I2_2 induced by blocking the primary currents I1_1 and I1_2 have negative values. Therefore, in the graph of the secondary currents I2_1 and I2_2 in FIG. 6, the negative direction is the increasing direction of the secondary currents I2_1 and I2_2. Thus, the primary currents I1_1 and I1_2 are controlled to some extent so that the secondary currents I2_1 and I2_2 are both larger than the preset reference current value β. The maximum peak ranges of the reference current value β and the secondary currents I2_1 and I2_2 at this time correspond to the third predetermined region in the claims.

  As shown by the dotted line portion in the secondary current I2_1, the secondary current I2_1 changes every moment due to changes in the airflow in the combustion chamber, and in some cases, the secondary current I2_1 cannot be maintained and there is a risk of misfire. A similar event can occur in the secondary current I2_2.

  Therefore, when each of the secondary currents I2_1 and I2_2 becomes smaller than the reference current value β, the current control circuit 32 predicts an increase in the primary current necessary for suppressing the decrease. And based on the prediction, the length of the time interval of the ignition signals IGT_1 and IGT_2 is extended. At this time, the maximum extension time is an extension time in a range where the IGBTs 15A and 15B are not likely to be damaged. By this control, it is possible to suppress a decrease in each of the secondary currents I2_1 and I2_2.

  The current control circuit 32 is provided with a limit current value γ in addition to the reference current value β. When the secondary currents I2_1 and I2_2 decrease below the limit current value γ, the limit values are set such that it becomes difficult to discharge the spark plug 20 and misfire. The reference current value β is between the maximum peak of the secondary currents I2_1 and I2_2 when not affected by external factors such as airflow changes and the limit current value γ, more specifically, the maximum peak of the secondary current. It is set at the center between the limit current value γ.

  With the above configuration, the current control circuit 32 of the internal combustion engine ignition system 30 according to the present embodiment has the following effects.

  The change of the secondary current I2 can be monitored by connecting the current detection circuit 31 to the first ends of the secondary coils 17A and 17B. Therefore, even if each of the secondary currents I2_1 and I2_2 decreases beyond the reference current value β, it is possible to suppress the decrease by extending the length of each time interval of the ignition signals IGT_1 and IGT_2. . At this time, the maximum peaks of the secondary currents I2_1 and I2_2 are reduced by the reduced amount, but the discharge state of the spark plug 20 can be maintained as long as the minimum peak does not fall below the limit current value γ. It becomes.

  In addition, the said embodiment can also be changed and implemented as follows.

  The current detection circuit 31 is connected to the first ends of the secondary coils 17A and 17B. In this regard, a current detection circuit 31 may be connected between the junction of the current paths on the anode side of the diodes 14A and 14B and the spark plug 20. By doing so, the current path connected to the current detection circuit 31 can be reduced, and the structure can be simplified.

  The secondary currents I2_1 and I2_2 are controlled so as to be within the maximum peak ranges of the reference current value β and the secondary currents I2_1 and I2_2. In this regard, although the reference current value β is set at the center between the maximum peak of the secondary currents I2_1 and I2_2 and the limit current value γ, the reference current value β is not limited thereto. The reference current value β may be provided anywhere as long as it is between the maximum peak of the secondary currents I2_1 and I2_2 and the limit current value γ.

(Third embodiment)
Hereinafter, the third embodiment will be described with reference to the drawings with a focus on differences from the first embodiment.

  In the first embodiment, the current detection circuit 24 is connected between the emitter terminals of the IGBTs 15A and 15B and the ground point, and the primary currents I1_1 and I1_2 are detected. Also in this embodiment, as shown in FIG. 7, the current detection circuit 24 is connected between the emitter terminals of the IGBTs 15A and 15B and the ground point. This configuration is the same as that of the first embodiment, but in addition, the current detection circuit 41 is also connected between the first ends of the secondary coils 17A and 17B and the ground point. With this configuration, the primary currents I1_1 and I1_2 and the secondary currents I2_1 and I2_2 can be detected.

  At this time, as shown in FIG. 8, the current control circuit 42 sets the upper set value C and the lower set value D for the primary currents I1_1 and I1_2, respectively. When the magnitude of the current exceeds the upper set value C, the MOSFET 21 is turned off to suppress the current rise. And when it reduces exceeding the lower side setting value D, the reduction | decrease in an electric current is prevented by turning ON MOSFET21.

  When the minimum peaks of both the secondary currents I2_1 and I2_2 are larger than the reference current value β, the same control as in the first embodiment is performed. However, with only that control, if either one of the secondary currents I2_1 and I2_2 decreases beyond the reference current value β due to changes in the airflow in the combustion chamber, there is a risk of misfire due to failure to deal with. (I2_1 dotted line). In preparation for such a case, the control described below is performed in addition to the present embodiment.

  FIG. 9 shows a flowchart of secondary current control performed by the current control circuit 42.

  First, the current detection circuit 41 is caused to detect the magnitudes α of the secondary currents I2_1 and I2_2 flowing through the secondary coils 17A and 17B, respectively (S1). Then, it is determined whether the absolute value of the magnitude α of the detected secondary currents I2_1 and I2_2 is smaller than the reference current value β (S2). When the absolute value of the magnitude α of the secondary currents I2_1 and I2_2 is not smaller than the reference current value β, the process returns to the detection (S1) of the magnitude α of the secondary currents I2_1 and I2_2 (S2: NO). When the absolute value of the magnitude α of the secondary currents I2_1 and I2_2 is smaller than the reference current value β, the upper set value C and the lower set value D are set to the upper set values set at the start of discharge of the spark plug 20. The value A and the lower set value B are changed (S3: YES).

  With the configuration described above, the current control circuit 42 of the internal combustion engine ignition system 40 according to the present embodiment has the following effects.

  When the minimum peaks of both the secondary currents I2_1 and I2_2 are larger than the reference current value β (FIG. 8), the primary currents I1_1 and I1_2 are within the preset upper set value C and lower set value D. Is controlled so that For this reason, the secondary currents I2_1 and I2_2 are controlled to a predetermined range as long as they are not affected by external factors.

  When either one of the secondary currents I2_1 and I2_2 decreases beyond the reference current value β, the upper set value C and the lower set value D set in advance in the primary currents I1_1 and I1_2 are set to the upper side. Change to value A and lower set value B. By so doing, it is possible to increase the primary currents I1_1 and I1_2, respectively, and to suppress the decrease in the secondary currents I2_1 and I2_2.

  In addition, the said embodiment can also be changed and implemented as follows.

  The current detection circuit 41 is connected to the first ends of the secondary coils 17A and 17B. In this regard, a current detection circuit 31 may be connected between the junction of the current paths on the anode side of the diodes 14A and 14B and the spark plug 20. By doing so, the current path connected to the current detection circuit 31 can be reduced, and the structure can be simplified.

  When either one of the secondary currents I2_1 and I2_2 decreases beyond the reference current value β, the upper set value C and the lower set value D set in advance in the primary current are changed to the upper set value A and It was supposed to be changed to the lower set value B. In this regard, the set values after the change need not be limited to the upper set value A and the lower set value B. If there is no risk of damage to the IGBTs 15A and 15B and each of the secondary currents I2_1 and I2_2 can be controlled so as not to be smaller than the limit current value γ, the upper set value A and the lower set value B are limited. There is no.

  About each said embodiment, you may change as follows and may implement.

  In the above embodiments, the supplied voltage is obtained by boosting the voltage of the battery 11 by the DC-DC converter 12. About this, you may change to the high voltage battery 61 used with a hybrid vehicle as shown in FIG. In this case, not only the total voltage (maximum pressure) of the high voltage battery 61 but also a part of the voltage may be used. By doing so, boosting by the DC-DC converter 12 is not necessary, and the structure can be simplified.

  The current control circuits 23, 32, and 42 in each embodiment are configured by a microcomputer, a drive circuit, and the like, and control the primary currents I1_1 and I1_2 and the secondary currents I2_1 and I2_2. With respect to this, the control performed by the current control circuits 23, 32, 42 may be contracted by the CPU in the ECU 13 or the DC-DC converter 12 without installing the current control circuits 23, 32, 42 in the circuit. . By doing so, the structure can be simplified.

  In each embodiment, the MOSFET 21 and the IGBT 15 are used as switching elements that control the primary currents I1_1 and I1_2. This may be changed to a power transistor, a thyristor, a triac, or the like.

  In each embodiment, the ignition coil 19A and the ignition coil 19B are provided. About this, the structure (multiple ignition system) provided with only one ignition coil 19 may be sufficient. Even in this case, the current control circuits 23, 32, and 42 in the respective embodiments are limited to the primary current between the preset upper set value A and the lower set value B or between the upper set value C and the lower set value D. The MOSFET 21 is controlled so that I1 is contained. By doing so, the structure can be simplified.

  The present ignition system is not limited to the DCO system and the multiple ignition system, but can be applied to an AC ignition system as shown in FIG. In the ignition system 70, a diode 77 and a capacitor 78 are connected in parallel to both ends (input end and output end) of the IGBT 76 of the igniter 74 as shown in the figure. The spark plug 20 is connected in parallel to the secondary coil 73 of the ignition coil 75 and wired so that a discharge operation is performed regardless of the polarity of the output voltage of the secondary coil 73.

  In such an ignition system 70, when the primary current reaches a specified value with the IGBT 76 in the ON state, the IGBT 76 is switched OFF, and charging and discharging of electric charge are repeated between the primary coil 71 and the capacitor 78 to vibrate the primary current. Let At this time, the spark plug 20 repeats discharge while alternately switching the polarity direction during the vibration period in which the primary current vibrates. As described above, also in the present ignition system 70, the discharge operation is continued for a certain period as in the DCO ignition system 10.

  In such an ignition system 70, the voltage boosted in the DC-DC converter 12 must be set so that the voltage applied to the spark plug 20 can be discharged with both positive and negative polarities. As a result, if the voltage is maintained within a certain range, the amount of charge accumulated in the capacitor 78 is also set to the designed value, so that the maximum peak of the primary current reaches the upper set value A or the upper set value C. Become.

  In this case, ON / OFF control of the MOSFET 21 is performed by the current control circuit 23, and the primary current falls between the upper set value A and the lower set value B or between the upper set value C and the lower set value D. For this reason, the continuous discharge operation at the spark plug 20 is reliably performed without excessively increasing the power consumption of the IGBT 76.

  DESCRIPTION OF SYMBOLS 12 ... DC-DC converter (voltage application means), 13 ... ECU (discharge execution means), 15A, 15B ... IGBT (first switching element), 16A, 16B, 71 ... Primary coil, 17A, 17B, 73 ... Secondary Coil, 19A, 19B, 75 ... ignition coil, 20 ... spark plug, 21 ... MOSFET (second switching element), 22 ... diode, 23 ... current control circuit (primary current control means).

Claims (8)

A spark plug (20) for generating a spark discharge for igniting a combustible mixture in a combustion chamber of an internal combustion engine;
An ignition coil (19, 75) comprising a primary coil (16, 71) and a secondary coil (17, 73), and applying a voltage to the spark plug by the secondary coil;
A DC-DC converter (12) for boosting a predetermined voltage and applying it to the primary coil;
A first switching element (15) for cutting off and conducting a primary current flowing to the primary coil;
Discharge controlling means (13) for controlling the driving of the first switching element to execute continuous discharge or multiple discharge by the spark plug;
A second switching element (21) connected between the DC-DC converter and the primary coil for cutting off and conducting a primary current flowing to the primary coil;
A diode (22) having a cathode connected between the second switching element and the primary coil and an anode grounded;
Primary current control means (23, 32, 42) for controlling the second switching element so that the current flowing through the primary coil falls within a first predetermined range during driving of the first switching element by the discharge execution means; ,
With
The ignition system for an internal combustion engine , wherein the primary current control means does not depend on an ignition signal (IGT_1, IGT_2) for igniting the ignition plug . The primary current control means has a first predetermined current flowing in the primary coil during drive control of the first switching element by the discharge execution means for causing the spark plug to execute the continuous discharge or the multiple discharge. The ignition system for an internal combustion engine according to claim 1, wherein the second switching element is controlled so as to be within a range. Primary current detection means (24, 41) for detecting the primary current flowing in the primary coil;
The said primary current control means controls the said 2nd switching element so that the said primary current detected by the said primary current detection means may be settled in the said 1st predetermined area, The Claim 1 or 2 characterized by the above-mentioned. Ignition system for internal combustion engines. Secondary current detection means (31, 41) for detecting a secondary current flowing in the secondary coil,
The primary current control means (32, 42) controls the second switching element based on the secondary current detected by the secondary current detection means so that the primary current falls within the first predetermined range. The ignition system for an internal combustion engine according to claim 1 or 2 , characterized in that: 5. The internal combustion engine ignition system according to claim 4 , wherein the primary current control means estimates the current value of the primary current from the current value of the secondary current detected by the secondary current detection means. The primary current control means disconnects the primary current when the current value of the primary current exceeds the upper limit value of the first predetermined region, and conducts when the current value of the primary current falls below the lower limit value of the first predetermined region. The ignition system for an internal combustion engine according to any one of claims 1 to 5 , wherein the primary current is controlled within a first predetermined range. Upon discharge start of the spark plug, the primary current control means (23), according to claim, characterized in that for controlling the primary current to a second predetermined region which is set to a large current region than the first predetermined zone 6 An ignition system for an internal combustion engine according to 1. A secondary current detecting means for detecting a secondary current flowing in the secondary coil;
The primary current control means (32, 42), when the current value of the secondary current detected by the secondary current detection means deviates from a third predetermined range, during driving of the switching element, by the primary current control means, in any one of claims 1 to 7, characterized in that to suppress the deviation from the third predetermined range by controlling the second switching element An ignition system for an internal combustion engine as described.

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