JP6577772B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for controlling 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 techniques, a multiple ignition method / AC ignition method in which the ignition plug discharges a plurality of times at the ignition timing of the internal combustion engine, or a DCO method in which the ignition plug is continuously discharged for a certain time near the ignition timing. Various ignition systems for effectively burning fuel contained in an air-fuel mixture have been studied.

  In an ignition system in which a spark plug discharges a plurality of times, a discharge abnormality may occur during the first discharge. Therefore, when it is detected that a discharge abnormality has occurred in the spark plug, a technique for stopping the discharge at the time when the discharge abnormality has occurred and starting charging the power necessary for the subsequent ignition discharge has already been made. It is disclosed (see Patent Document 1).

JP 2009-287521 A

  However, in the technique disclosed in Patent Document 1, it is possible to stop the discharge when the abnormal discharge has occurred, but a plurality of predetermined discharges are performed regardless of whether or not the fuel is actually ignited. Is done. For this reason, energy is supplied to the spark plug in excess of the energy required for ignition, and there is still room for improvement.

  The present invention has been made to solve the above-mentioned problems, and a main object of the present invention is to provide an ignition system in which a continuous discharge or a plurality of discharges are executed in a predetermined period during one combustion stroke by an ignition plug. The object is to reduce the energy supplied to the spark plug.

  The present invention is a control device applied to an internal combustion engine comprising: a fuel injection valve that directly injects fuel into a combustion chamber; and a spark plug that generates a discharge by voltage induction generated in a drive circuit. During a single combustion stroke of the engine, by controlling the drive circuit, the spark plug performs a continuous discharge or a plurality of discharges in a predetermined period by the spark plug, and the discharge is performed by the discharge execution means. An injection unit that injects the fuel by the fuel injection valve, a discharge state detection unit that detects a state of discharge that the discharge execution unit is causing the spark plug to perform, and the injection unit is the fuel The state of the discharge detected by the discharge state detection means as to whether or not the fuel injected by the injection valve has come into contact with the discharge being executed by the discharge execution means. And determining means for determining based on the above, and ending means for terminating the discharge being executed by the discharge executing means when the determining means determines that the fuel has contacted the discharge. Features.

  According to the above configuration, the control device is applied to an internal combustion engine that includes a fuel injection valve that directly injects fuel into the combustion chamber, and a spark plug that generates discharge by voltage induction generated in the drive circuit. . This control device is provided with a discharge execution means, and controls the drive circuit during one combustion stroke of the internal combustion engine to cause the spark plug to execute continuous discharge or a plurality of discharges in a predetermined period. . When the discharge is executed by the discharge execution means, the fuel is injected from the fuel injection valve by the injection means. At this time, when the spray of injected fuel comes into contact with the discharge generated in the spark plug, the state of the discharge changes. This discharge state is detected by a discharge state detecting means. Therefore, based on the state of the discharge detected by the discharge state detection means, it is determined whether or not the fuel spray injected from the fuel injection valve by the determination means has come into contact with the discharge of the spark plug. When the injected fuel comes into contact with the spark plug discharge, the fuel is likely to ignite. Therefore, when it is determined by the determination means that the fuel has come into contact with the discharge generated at the spark plug, the discharge of the spark plug is ended by the end means because the ignition of the fuel has occurred. Thereby, the energy supplied to the spark plug can be reduced.

1 is a schematic diagram of an internal combustion engine and a control device thereof according to the present embodiment. FIG. 2 is a schematic circuit diagram around an ignition circuit unit shown in FIG. 1. It is a figure which shows the fuel-injection time and discharge start time in weak stratified combustion mode. It is a control flowchart performed by ECU concerning this embodiment. It is a figure which shows the secondary voltage which changes when spraying of fuel and discharge contact. It is a figure which shows the change of a secondary voltage in case the ignition of fuel is favorable. It is a figure which shows the change of a secondary voltage when the ignition of fuel is slow. It is a figure which shows the relationship between the time of contact of fuel spray and discharge, and the time when combustion was observed.

  Referring to FIG. 1, an engine system 10 includes an engine 11 that is a spark ignition type internal combustion engine. A combustion chamber 11b and a water jacket 11c are formed inside an engine block 11a constituting the main body of the engine 11. The combustion chamber 11b is provided to accommodate the piston 12 so as to be capable of reciprocating. The water jacket 11c is a space through which a coolant (also referred to as cooling water) can flow, and is provided so as to surround the combustion chamber 11b.

  An intake port 13 and an exhaust port 14 are formed in the cylinder head, which is an upper portion of the engine block 11a, so as to communicate with the combustion chamber 11b. The cylinder head includes an intake valve 15 for controlling the communication state between the intake port 13 and the combustion chamber 11b, an exhaust valve 16 for controlling the communication state between the exhaust port 14 and the combustion chamber 11b, A valve drive mechanism 17 for opening and closing the valve 15 and the exhaust valve 16 at a predetermined timing is provided.

  Further, an injector (corresponding to a fuel injection valve) 18 and a spark plug 19 are mounted on the engine block 11a. In the present embodiment, the injector 18 is disposed in the vicinity of the spark plug 19 and is provided so as to inject fuel directly into the combustion chamber 11b. The spark plug 19 is provided so as to ignite the fuel mixture in the combustion chamber 11b.

  An intake manifold 21 a is connected to the intake port 13. A surge tank 21b is disposed upstream of the intake manifold 21a in the intake air flow direction. An exhaust pipe 22 is connected to the exhaust port 14.

  The EGR passage 23 is provided such that a part of the exhaust gas discharged to the exhaust pipe 22 can be introduced into the intake air by connecting the exhaust pipe 22 and the surge tank 21b (EGR is an abbreviation for Exhaust Gas Recirculation). is there). An EGR control valve 24 is interposed in the EGR passage 23. The EGR control valve 24 is provided so as to be able to control the EGR rate (exhaust gas mixing ratio in the pre-combustion gas sucked into the combustion chamber 11b) by its opening.

  A throttle valve 25 is interposed in the intake pipe 21 upstream of the surge tank 21b in the intake air flow direction. The opening degree of the throttle valve 25 is controlled by the operation of a throttle actuator 26 such as a DC motor. Further, an air flow control valve 27 for generating a swirl flow or a tumble flow is provided in the vicinity of the intake port 13.

  The exhaust pipe 22 is provided with a catalyst 41 such as a three-way catalyst for purifying CO, HC, NOx, etc. in the exhaust gas, and the air-fuel ratio of the air-fuel mixture is detected upstream of the catalyst 41 with exhaust gas as a detection target. An air-fuel ratio sensor 40 (linear A / F sensor or the like) is provided for detecting the above.

  The engine system 10 includes an ignition circuit unit (corresponding to a drive circuit) 31, an electronic control unit 32, and the like.

  The ignition circuit unit 31 is configured to cause the spark plug 19 to generate a spark discharge for igniting the fuel mixture in the combustion chamber 11b. The electronic control unit 32 is a so-called engine ECU (ECU is an abbreviation for Electronic Control Unit), and is based on outputs of various sensors such as a crank angle sensor (corresponding to a crank angle detection means and a rotation speed detection means) 33. The operation of each part including the injector 18 and the ignition circuit unit 31 is controlled in accordance with the operating state of the engine 11 (hereinafter, abbreviated as “engine parameter”).

  Regarding the ignition control, the electronic control unit 32 generates and outputs an ignition signal and an energy input period signal based on the acquired engine parameter. The ignition signal and the energy input period signal are the optimum ignition timing and discharge current (depending on the state of the gas in the combustion chamber 11b and the required output of the engine 11 (which varies depending on the engine parameters)). Ignition discharge current). Therefore, the electronic control unit 32 corresponds to a discharge execution unit and an injection unit. In addition, the electronic control unit 32 corresponds to a discharge state detection unit, a determination unit, and an end unit.

  The crank angle sensor 33 is a sensor for outputting a rectangular crank angle signal for each predetermined crank angle of the engine 11 (for example, at a cycle of 30 ° CA). The crank angle sensor 33 is mounted on the engine block 11a. The cooling water temperature sensor 34 is a sensor for detecting (acquiring) the cooling water temperature that is the temperature of the coolant flowing through the water jacket 11c, and is attached to the engine block 11a.

  The air flow meter 35 is a sensor for detecting (acquiring) the intake air amount (the mass flow rate of the intake air introduced into the combustion chamber 11b through the intake pipe 21). The air flow meter 35 is attached to the intake pipe 21 upstream of the throttle valve 25 in the intake air flow direction. The intake pressure sensor 36 is a sensor for detecting (acquiring) intake pressure, which is the pressure in the intake pipe 21, and is attached to the surge tank 21b.

  The throttle opening sensor 37 is a sensor that generates an output corresponding to the opening (throttle opening) of the throttle valve 25 and is built in the throttle actuator 26. The accelerator position sensor 38 is provided so as to generate an output corresponding to the accelerator operation amount.

<Configuration around the ignition circuit unit>
Referring to FIG. 2, the ignition circuit unit 31 includes an ignition coil 311 (including a primary winding 311 a and a secondary winding 311 b), a DC power supply 312, a first switching element 313, an additional energy input circuit 322, Diodes 318a, 318b, and 318d and a driver circuit 319 are provided.

  As described above, the ignition coil (corresponding to the ignition coil) 311 includes the primary winding (corresponding to the primary coil) 311a and the secondary winding (corresponding to the secondary coil) 311b. As is well known, the ignition coil 311 is configured to generate a secondary current in the secondary winding 311b by increasing or decreasing the primary current flowing through the primary winding 311a.

  A non-grounded output terminal (specifically, a + terminal) of the DC power supply 312 is connected to a high voltage side terminal (which may also be referred to as a non-grounded side terminal) which is one end of the primary winding 311a. On the other hand, the low voltage side terminal (which may also be referred to as a ground side terminal) side which is the other end of the primary winding 311 a is connected to the ground side via the first switching element 313. That is, the DC power supply 312 is provided so that when the first switching element 313 is turned on, a primary current flows in the direction from the high-voltage side terminal side to the low-voltage side terminal side in the primary winding 311a. ing.

  The high voltage side terminal (which may also be referred to as a non-ground side terminal) side in the secondary winding 311b is connected to the high voltage side terminal side in the primary winding 311a via a diode 318a. The diode 318a prohibits the flow of current in the direction from the high-voltage side terminal side of the primary winding 311a to the high-voltage side terminal side of the secondary winding 311b, and spark plugs the secondary current (discharge current). The anode is connected to the high voltage side terminal side of the secondary winding 311b so as to define the direction from 19 to the secondary winding 311b (that is, the current I2 in the figure has a negative value).

  On the other hand, the low voltage side terminal (which may also be referred to as a ground side terminal) side of the secondary winding 311b is connected to the spark plug 19, and a voltage detection is provided in a path L1 connecting the low voltage side terminal and the spark plug 19. A use path (corresponding to the secondary voltage detection means) L2 is connected. The voltage detection path L2 includes voltage detection resistors 320 and 321. One end of the resistor 320 is connected to the path L1, and the other end is connected to the resistor 321. One end of the resistor 321 is connected to the resistor 320, and the other end is connected to the ground side. A node (not shown in the figure) between the resistor 320 and the resistor 321 is connected to an electronic control unit 32 described later. The secondary voltage V2 applied to the spark plug 19 is detected by such a voltage detection path L2.

  The first switching element 313 is an IGBT (Insulated Gate Bipolar Transistor) that is a MOS gate structure transistor, and includes a first control terminal 313G, a first power supply side terminal 313C, and a first ground side terminal 313E. ing. A diode 318d is connected in parallel to both ends of the first switching element 313 (first power supply side terminal 313C and first ground side terminal 313E). The first switching element 313 controls on / off of energization between the first power supply side terminal 313C and the first ground side terminal 313E based on the first control signal input to the first control terminal 313G. It is configured. In the present embodiment, the first power supply side terminal 313C is connected to the low voltage side terminal side of the primary winding 311a. The first ground side terminal 313E is connected to the ground side.

  The additional energy input circuit 322 includes a second switching element 314, a third switching element 315, an energy storage coil 316, a capacitor 317, and a diode 318c.

  The second switching element 314 is a MOSFET (Metal Oxide Field Effect Effect Transistor), and has a second control terminal 314G, a second power supply side terminal 314D, and a second ground side terminal 314S. The second switching element 314 controls on / off of energization between the second power supply side terminal 314D and the second ground side terminal 314S based on the second control signal input to the second control terminal 314G. It is configured.

  In the present embodiment, the second ground side terminal 314S is connected to the low voltage side terminal side of the primary winding 311a via the diode 318b. The diode 318b has an anode connected to the second ground side terminal so as to allow current to flow from the second ground side terminal 314S of the second switching element 314 toward the low voltage side terminal side of the primary winding 311a. 314S is connected.

  The third switching element 315 is an IGBT that is a MOS gate structure transistor, and includes a third control terminal 315G, a third power supply side terminal 315C, and a third ground side terminal 315E. The third switching element 315 controls on / off of energization between the third power supply side terminal 315C and the third ground side terminal 315E based on the third control signal input to the third control terminal 315G. It is configured.

  In the present embodiment, the third power supply side terminal 315C is connected to the second power supply side terminal 314D in the second switching element 314 via the diode 318c. The diode 318c has an anode on the third power supply side so as to allow current to flow from the third power supply side terminal 315C in the third switching element 315 to the second power supply side terminal 314D in the second switching element 314. It is connected to the terminal 315C. The third ground side terminal 315E of the third switching element 315 is connected to the ground side.

  The energy storage coil 316 is an inductor provided to store energy when the third switching element 315 is turned on. The energy storage coil 316 is interposed in a power line that connects the above-described non-grounded output terminal of the DC power supply 312 and the third power supply terminal 315C of the third switching element 315.

  The capacitor 317 is connected in series with the energy storage coil 316 between the ground side and the above-described non-ground side output terminal of the DC power supply 312. That is, the capacitor 317 is connected in parallel with the third switching element 315 with respect to the energy storage coil 316. The capacitor 317 is provided to store energy when the third switching element 315 is turned off.

  The driver circuit 319 is connected to the electronic control unit 32 so as to receive the engine parameter, the ignition signal, and the energy input period signal output from the electronic control unit 32. The driver circuit 319 is connected to the first control terminal 313G, the second control terminal 314G, and the third control terminal 315G so as to control the first switching element 313, the second switching element 314, and the third switching element 315. Has been. The driver circuit 319 sends the first control signal, the second control signal, and the third control signal to the first control terminal 313G, the second control terminal 314G, and the first control signal based on the received ignition signal and energy input period signal, respectively. Three control terminals 315G are provided for output.

  Specifically, the driver circuit 319 releases stored energy from the capacitor 317 during the ignition discharge of the spark plug 19 (which is started by turning off the first switching element 313) (this is the third switching element 315). Is turned off and the second switching element 314 is turned on). The released stored energy becomes input energy and is supplied from the low voltage side terminal side to the primary winding 311a. Thereby, the primary current resulting from the input energy supplied during the ignition discharge flows through the primary winding 311a. Therefore, the additional amount accompanying the flow of the primary current is superimposed on the secondary current generated in the secondary winding 311b. As described above, the primary current is sequentially added by the energy stored in the capacitor 317, and the secondary current is sequentially added correspondingly. Therefore, the secondary current is sufficiently secured to maintain the ignition discharge, and the continuous discharge is performed. Can be implemented.

  In such a configuration, the electronic control unit 32 performs the weak stratified combustion mode (lean mode) and the homogeneous combustion mode (stoichiometric mode) according to the crank angle (rotational speed of the engine 11) and the required torque (load). Perform switching. The operation region in the weak stratified combustion mode is set to a lower rotation / low load side than the operation region in the homogeneous combustion mode. In the weak stratified combustion mode, a relatively small amount of fuel is taken in as shown in FIG. The fuel is directly injected into the cylinder during the stroke, and more fuel than the fuel injected during the intake stroke during the compression stroke is directly injected into the cylinder for a short period of time to form a stratified mixture near the spark plug 19 and ignite. On the other hand, in the homogeneous combustion mode, the fuel injection amount is increased and fuel is directly injected into the cylinder during the intake stroke to form a homogeneous mixture and ignite. In short, in the weak stratified combustion mode, the injection is performed in two steps of the intake stroke and the compression stroke, and in the homogeneous combustion mode, the injection is performed in the intake stroke.

  Continuous discharge is carried out in the weak stratified combustion mode. Specifically, it is performed when the fuel is injected by the injector 18 during the compression stroke, and the continuous discharge is maintained for a predetermined period until the time when the fuel spray and the discharge are assumed to be in sufficient contact. The period from the start of discharge by the spark plug 19 to the end of fuel combustion corresponds to the combustion stroke. For this reason, continuous discharge is performed in a predetermined period during the combustion stroke. Conventionally, continuous discharge is performed for a predetermined period regardless of whether or not the fuel is actually ignited, so that the energy is supplied to the spark plug 19 more than the energy necessary for the ignition of the fuel. .

  In order to save this extra energy supplied to the spark plug 19, in this embodiment, the electronic control unit 32 performs discharge control of the spark plug 19 shown in FIG. The discharge control of the spark plug 19 shown in FIG. 4 is repeatedly executed at a predetermined cycle by the electronic control unit 32 while the electronic control unit 32 is powered on.

  When this control is started, first, in step S101, the accelerator operation amount detected by the accelerator position sensor 38 and the crank angle detected by the crank angle sensor 33 are read. Then, the process proceeds to step S102.

  In step S102, the required torque is calculated from the accelerator operation amount read in step S101. Further, the rotational speed of the engine 11 is calculated from the crank angle. Since the crank angle and the rotational speed of the engine 11 have a correlation, the rotational speed of the engine 11 is calculated based on the correlation. Then, the process proceeds to step S103, and based on the required torque and the rotational speed calculated in step S102, it is determined whether or not the weak stratified combustion mode should be performed with reference to the operation map. If it is determined that the weak stratified combustion mode should not be performed (high rotational speed and high required torque) (S103: NO), the process proceeds to step S111, the homogeneous combustion mode is executed, and this control is terminated. . If it is determined that the weak stratified combustion mode should be performed (low rotational speed and low required torque) (S103: YES), the process proceeds to step S104.

  In step S104, a predetermined injection timing is set for which timing of the compression stroke the fuel is to be injected from the injector 18 from the referenced operation map. Similarly, a predetermined ignition timing is set as to which discharge is to be generated in the spark plug 19 at the timing of the compression stroke from the operation map referred to in the same manner. Then, the process proceeds to step S105.

  In step S105, spark discharge is generated in the spark plug 19 based on the predetermined ignition timing set in step S104. Then, the process proceeds to step S106, and fuel is injected into the injector 18 based on the predetermined injection timing set in step S104. In step S107, control is performed so that the discharge being performed by the spark plug 19 can be maintained, and continuous discharge is performed.

  In step S108, it is determined based on the change in the secondary voltage whether or not the fuel spray injected from the injector 18 has come into contact with the discharge of the spark plug 19. As shown in FIG. 5, when the fuel spray comes into contact with the discharge at a subsequent peak except for the first peak where the discharge is started by the spark plug 19, the value falls below the threshold value Vj (negative value). (See A in FIG. 5). That is, the absolute value of the secondary voltage is larger than the absolute value of the threshold value Vj (which can be said to be a positive threshold value). Therefore, in the present embodiment, whether or not the fuel spray is in contact with the discharge is determined based on whether or not the second and subsequent peaks of the secondary voltage are smaller than the threshold value Vj. At this time, the threshold value Vj is set as a secondary voltage that is assumed to decrease at a minimum when the fuel spray comes into contact with the discharge.

  This threshold value Vj is a variable value. For example, the threshold value Vj is set smaller as the crank angle approaches the top dead center (TDC). This will be described with reference to FIGS. FIG. 6 shows a case where the contact timing between the fuel spray and the discharge is earlier than the contact timing between the fuel spray and the discharge shown in FIG. Compared to FIG. 7, in FIG. 6, the second peak lower than the threshold value Vj is detected in a state where the crank angle is advanced (see crank angle CA2). However, in FIG. 7, since the fuel spray and the discharge are not yet in contact at the crank angle CA2, the secondary voltage is maintained at a large value as compared with FIG. However, the secondary voltage decreases as the crank angle approaches TDC, even though the fuel spray and the discharge are not yet in contact. This is because the airflow in the combustion chamber 11b has an influence. Therefore, if the threshold value Vj is set to a fixed value, the secondary voltage may be smaller than the threshold value Vj even though the fuel spray and the discharge are not in contact with each other during the period when the crank angle approaches TDC. . For this reason, like the threshold value Vj described in FIG. 7, the threshold value Vj is set smaller as the crank angle approaches TDC. In FIG. 7, fuel spray and discharge are in contact with each other at the crank angle CA4, and the secondary voltage is smaller than the threshold value Vj at the crank angle CA4.

  Further, the threshold value Vj is set smaller as the rotational speed of the engine 11 is higher. This is because as the rotational speed of the engine 11 increases, the airflow in the combustion chamber 11b increases and the secondary voltage applied to the spark plug 19 decreases. The setting of the threshold value Vj is also changed depending on the air-fuel ratio in the combustion chamber 11b. As the air-fuel ratio output by the air-fuel ratio sensor 40 is leaner, the ignition of the fuel is more difficult. Therefore, by setting the threshold value Vj to be smaller, the discharge is maintained for a longer time and the occurrence of misfire is suppressed.

  If it is determined that the fuel spray is not in contact with the discharge (S108: NO), it is determined that the fuel has not yet ignited, and the process proceeds to step S110 to determine whether continuous discharge has been performed for a predetermined period. If it is determined that continuous discharge has not been performed for a predetermined period (S110: NO), the process returns to step S107, assuming that continuous discharge continues. When it is determined that the continuous discharge has been performed for a predetermined period (S110: YES), the process proceeds to step S109, the continuous discharge is terminated, and this control is terminated.

  If it is determined that the fuel spray has come into contact with the discharge (S108: YES), the continuous discharge ends after a predetermined period of time as shown in FIGS. FIG. 8 shows the relationship between the time when the fuel spray and discharge are in contact with the time when the combustion flame actually occurs. FIG. 8 is a correlation diagram obtained by the inventor actually analyzing the video by using the visualization engine. According to FIG. 8, the earlier the contact timing between spray and discharge, the earlier the combustion flame generation time, and the later the contact timing between spray and discharge, the later the combustion flame generation timing. For this reason, the combustion flame generation timing, that is, the fuel ignition timing, reflects the contact timing between the spray and the discharge. Therefore, the ignition timing of the fuel can be estimated from the contact timing between the spray and the discharge. In addition, the combustion flame is slightly delayed from the contact timing of the fuel spray and discharge. Therefore, in this embodiment, in order to ignite the fuel more reliably, continuous discharge is performed until the fuel ignition timing. Therefore, the predetermined time is set as a time until the ignition timing of the fuel estimated from FIG. 8 based on the time when it is determined that the fuel spray and the discharge are in contact with each other.

  This predetermined time is variable. For example, the longer the air-fuel ratio detected by the air-fuel ratio sensor 40 is, the more difficult it is to ignite the fuel, so the predetermined time is set longer. Alternatively, as the injection amount of the fuel injected from the injector 18 during the compression stroke increases, the fuel cannot be sufficiently mixed with the air until it comes into contact with the discharge of the spark plug 19, and the ignition of the fuel fails due to the lack of air ( The predetermined time is set longer because there is a risk of rich misfire).

  Next, the operation of the engine system will be described with reference to FIG.

  Based on the accelerator operation amount detected by the accelerator position sensor 38 and the crank angle detected by the crank angle sensor 33, it is assumed that the electronic control unit 32 implements the weak stratified combustion mode from the operation map.

  First, a relatively small amount of fuel is directly injected into the cylinder in the intake stroke from the injector 18. Thereafter, a large secondary current is caused to flow through the spark plug 19 at a predetermined ignition timing set based on the operation map referred to by the electronic control unit 32 to cause discharge (see crank angle CA1). At this time, the secondary voltage detected from the voltage detection path L2 reaches the first peak. When a discharge occurs in the spark plug 19, a continuous discharge is subsequently performed so that the discharge of the spark plug 19 is not interrupted. Further, after the spark plug 19 is discharged, fuel is injected from the injector 18 at a predetermined injection timing set based on the operation map (see FIG. 3). Specifically, more fuel than that injected during the intake stroke in the compression stroke is directly injected into the cylinder for a short period of time to form a stratified mixture in the vicinity of the spark plug 19.

  After the fuel injection, when the detected secondary voltage reaches a peak lower than the threshold value Vj (see crank angle CA2), it is determined by the electronic control unit 32 that the fuel spray and discharge are in contact. In order to cause the ignition of the fuel more reliably, the discharge generated in the spark plug 19 is stopped after a predetermined time has elapsed since it was determined that the fuel spray and the discharge contacted each other (see crank angle CA3).

  With the above configuration, the electronic control unit 32 according to this embodiment has the following effects.

  Whether or not the fuel injected from the injector 18 has come into contact with the discharge of the spark plug 19 is determined based on the secondary voltage detected by the voltage detection path L2. When it is determined that the fuel injected from the injector 18 and the discharge of the spark plug 19 are in contact with each other, the discharge of the spark plug 19 is terminated. When the fuel injected from the injector 18 comes into contact with the discharge of the spark plug 19, the fuel is likely to ignite. Therefore, when it is determined that the fuel has come into contact with the discharge generated in the spark plug 19, the discharge of the spark plug 19 is terminated because the ignition of the fuel has occurred, thereby reducing the energy supplied to the spark plug 19. It becomes possible to do.

  When the second and subsequent peaks of the secondary voltage detected from the voltage detection path L2 are lower than the threshold value Vj, it is determined that the fuel spray is in contact with the discharge generated in the spark plug 19. When the spray of fuel injected by the injector 18 comes into contact with the discharge of the spark plug 19, the secondary voltage decreases. Therefore, when the measured secondary voltage is smaller than the threshold value Vj, it can be determined that the fuel spray has come into contact with the discharge of the spark plug 19. In addition, since a large amount of energy is required during the initial discharge of the spark plug 19, the absolute value of the first peak of the measured secondary voltage may be smaller than the threshold value Vj. Therefore, if the determination is made including the first peak, it may be erroneously determined that the contact between the discharge of the spark plug 19 and the fuel spray occurs at the first peak. For this reason, it is possible to more accurately determine that the fuel spray has contacted the discharge of the spark plug 19 by targeting the second and subsequent peaks of the measured secondary voltage.

  The threshold value Vj is set smaller as the crank angle detected by the crank angle sensor 33 is on the retard side. The secondary voltage applied to the spark plug 19 decreases as the crank angle approaches the top dead center due to the airflow generated in the combustion chamber 11b. Therefore, by setting the threshold value Vj to be smaller as the crank angle is retarded, it is possible to suppress the possibility of erroneous determination of contact between fuel spray and discharge.

  -When the rotational speed of the engine 11 is high, the airflow generated in the combustion chamber 11b becomes strong, and the secondary voltage applied to the spark plug 19 becomes small. For this reason, the higher the rotational speed of the engine 11, the smaller the threshold value Vj can be set to suppress the possibility of erroneous determination of contact between fuel spray and discharge.

  -The leaner the air-fuel ratio detected by the air-fuel ratio sensor 40, the more difficult it is to ignite the fuel. Therefore, it is necessary to continue the discharge generated by the spark plug 19 for a long time. Therefore, by reducing the threshold value Vj and making it difficult to establish the contact determination between the fuel spray and the discharge, the discharge generated in the spark plug 19 can be continued for a long time, and the fuel can be ignited more reliably. .

  The discharge of the spark plug 19 is terminated after a predetermined time has elapsed since it was determined that the fuel injected by the injector 18 contacted the discharge generated in the spark plug 19. For example, when the air-fuel ratio in the combustion chamber 11b is on the lean side, there is a possibility that the fuel will not ignite immediately even if it contacts the spark plug 19. Assuming such a case, even if it is determined that the fuel injected from the injector 18 has come into contact with the discharge of the spark plug 19, the discharge of the spark plug 19 is not terminated until a predetermined time elapses. It is possible to cause ignition of the fuel.

  -About a predetermined time, it is extended, so that the air fuel ratio which is the ratio of the fuel with respect to the air in the combustion chamber 11b is a lean side. The smaller the proportion of fuel present in the combustion chamber 11b, the more difficult the ignition. For this reason, the ignition time of the fuel can be more reliably generated by extending the discharge time of the spark plug 19 as the air-fuel ratio is on the lean side.

  The predetermined time is extended as the amount of fuel injected by the injector 18 increases. If the amount of fuel injected from the injector 18 is large, the fuel injected before contact with the discharge of the spark plug 19 cannot be sufficiently mixed with the air, and the ignition of the fuel may fail due to insufficient air. Yes (rich misfire). Therefore, since there is a possibility that the ignition of the fuel cannot be performed immediately due to the lack of air as the injection amount of the injected fuel increases, by extending the discharge of the spark plug 19, the air amount has a concentration sufficient for the ignition of the fuel. It becomes possible to perform discharge until it becomes.

  The spark plug 19 is discharged prior to the fuel injection performed by the injector 18. Since the injector 18 directly injects the fuel into the combustion chamber 11b, if the fuel injection is performed before the discharge occurs, the fuel spray may pass before the spark plug 19 causes the discharge. For this reason, discharge is generated by the spark plug 19 prior to fuel injection. Thereby, it is possible to suppress the possibility that the fuel spray does not come into contact with the discharge generated in the spark plug 19.

  Accumulated energy is released from the capacitor 317 during the ignition discharge of the spark plug 19. The released stored energy becomes input energy and is supplied from the low voltage side terminal side to the primary winding 311a. As a result, the primary current resulting from the input energy supplied during the ignition discharge is passed through the primary winding 311a, and the secondary current generated in the secondary winding 311b is added to the primary current through the primary current. Minutes are superimposed. For this reason, even if there is little energy sequentially supplied to the spark plug 19 after the start of discharge, the secondary current is ensured sufficiently to maintain the discharge, and continuous discharge can be performed.

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

  In the present embodiment, contact determination between fuel spray and discharge is performed during weak stratified combustion. In this regard, not only during weak stratified combustion but if the fuel is injected by the injector 18 when discharge is being performed by the spark plug 19, for example, during the stoichiometric combustion in which fuel is injected during stratified combustion or compression stroke, You may perform the contact determination of spraying and discharge.

  In the above embodiment, the injector 18 is disposed in the vicinity of the spark plug 19. About this, the injector 18 may be arrange | positioned so that combustion may be injected in the combustion chamber 11b from the side of the combustion chamber 11b. In this case, if the distance between the injector 18 and the spark plug 19 is greater than that in the above embodiment, the spark plug 19 may cause a discharge after fuel injection by the injector 18.

  In the above embodiment, the spark plug 19 causes continuous discharge. About this, you may implement the multiple discharge which produces a spark discharge in the spark plug 19 several times. In the continuous discharge, the discharge is terminated after a predetermined time has elapsed when the fuel spray and the discharge come into contact with each other. When performing the multiple discharge, instead of the predetermined time, the discharge may be terminated after the spark discharge is performed a first predetermined number of times set as the number of discharges for which the predetermined time elapses. Similarly, the continuous discharge is assumed to be performed for a predetermined period in the combustion stroke, but instead of this predetermined period, the multiple discharge is performed for the second predetermined number of times set as the number of discharges for which the predetermined period elapses. It is good also as a thing. The predetermined period is not limited to a period in which so-called continuous discharge is performed, but may be a period that is longer than a case in which only instantaneous discharge is performed and that can end discharge halfway. . Further, the discharge can be immediately terminated when the fuel spray and the discharge come into contact with each other.

  In the above embodiment, whether or not the fuel spray injected by the injector 18 has come into contact with the discharge of the spark plug 19 is determined based on the secondary voltage detected by the voltage detection path L2. In this regard, instead of detecting the secondary voltage, the secondary current is detected, and it is determined whether or not the fuel spray injected by the injector 18 is in contact with the discharge of the spark plug 19 based on the detected secondary current. May be.

  In the above embodiment, when the second and subsequent peaks of the secondary voltage detected by the voltage detection path L <b> 2 become lower than the threshold value Vj, the fuel spray injected by the injector 18 is discharged from the spark plug 19. It was determined that the contact was made. In this regard, when the absolute value of the second and subsequent peaks of the detected secondary voltage is calculated, and the calculated absolute value of the secondary voltage is greater than the absolute value of the threshold value Vj (that is, a positive threshold value) In addition, it may be determined that the fuel spray injected by the injector 18 has come into contact with the discharge of the spark plug 19.

  In the above embodiment, when the secondary voltage detected by the voltage detection path L2 becomes lower than the threshold value Vj, it is determined that the fuel spray injected by the injector 18 has come into contact with the discharge of the spark plug 19. It was. In this regard, a determination period is provided, and when the absolute value of the change amount (for example, slope) of the secondary voltage in the determination period is larger than the predetermined change amount, the fuel spray injected by the injector 18 is discharged from the spark plug 19. You may determine with having contacted discharge. When the fuel spray injected by the injector 18 comes into contact with the discharge of the spark plug 19, the absolute value of the secondary voltage continuously increases. Accordingly, when the fuel spray comes into contact with the discharge of the spark plug 19, a change larger than a predetermined change amount occurs in the secondary voltage in the determination period. Therefore, the contact between the fuel spray and the discharge of the spark plug 19 can be determined by making the absolute value of the change amount of the secondary voltage within the determination period larger than the predetermined change amount.

  In the above embodiment, when the secondary voltage detected by the voltage detection path L2 becomes lower than the threshold value Vj, it is determined that the fuel spray injected by the injector 18 has come into contact with the discharge of the spark plug 19. It was. Regarding this, there is a difference obtained by subtracting the absolute value of the secondary voltage that is assumed when the fuel spray does not come into contact with the discharge of the spark plug 19 from the absolute value of the secondary voltage detected by the voltage detection path L2. If it is greater than the predetermined value, it may be determined that the fuel spray injected by the injector 18 has come into contact with the discharge of the spark plug 19. When the fuel spray injected by the injector 18 comes into contact with the discharge of the spark plug 19, the absolute value of the secondary voltage measured in comparison with the absolute value of the secondary voltage in the case of no contact increases. Therefore, the difference obtained by subtracting the absolute value of the secondary voltage assumed when the fuel spray does not come into contact with the discharge of the spark plug 19 from the absolute value of the secondary voltage actually measured by the voltage detection path L2. When larger than the predetermined value, it is possible to determine contact between fuel spray and spark plug 19 discharge.

  DESCRIPTION OF SYMBOLS 11 ... Engine, 11b ... Combustion chamber, 18 ... Injector, 19 ... Spark plug, 31 ... Ignition circuit unit, 32 ... Electronic control unit

Claims (12)

A fuel injection valve (18) for directly injecting fuel into the combustion chamber (11b);
A spark plug (19) for generating discharge by voltage induction generated in the drive circuit (31);
A control device (32) applied to an internal combustion engine (11) comprising:
Discharge executing means for controlling the drive circuit during a single combustion stroke of the internal combustion engine to execute continuous discharge or multiple discharges in a predetermined period by the spark plug;
Injection means for injecting the fuel by the fuel injection valve when the discharge is executed by the discharge execution means;
A discharge state detection means for detecting a state of discharge that the discharge execution means causes the spark plug to execute;
Based on the state of the discharge detected by the discharge state detection means, whether or not the fuel injected by the fuel injection valve by the injection means has come into contact with the discharge being executed by the discharge execution means. Determination means for determining
Ending means for terminating the discharge being executed by the discharge executing means when the determining means determines that the fuel has come into contact with the discharge;
A control device for an internal combustion engine, comprising: The drive circuit is
An ignition coil (311) comprising a primary coil (311a) and a secondary coil (311b) magnetically coupled to each other, and applying a voltage to the spark plug by the secondary coil;
Secondary voltage detection means (L2) for detecting a secondary voltage induced in the secondary coil based on a change in magnetic flux generated in the primary coil;
With
The discharge state detection means acquires the secondary voltage detected by the secondary voltage detection means,
The determination means determines that the fuel is in contact with the discharge when the absolute value of the second and subsequent peaks of the secondary voltage acquired by the discharge state detection means is greater than a positive threshold value. The control apparatus for an internal combustion engine according to claim 1, wherein the control apparatus is an internal combustion engine. The internal combustion engine includes crank angle detection means (33) for detecting a crank angle based on angle pulses at predetermined equal angular intervals synchronized with rotation of the crankshaft,
3. The control apparatus for an internal combustion engine according to claim 2, wherein the positive threshold value is set to be larger as the crank angle detected by the crank angle detection means is on the retard side. The internal combustion engine includes rotational speed detection means (33) for detecting the rotational speed of the crankshaft of the internal combustion engine,
4. The control apparatus for an internal combustion engine according to claim 2, wherein the positive threshold value is set to be larger as the rotational speed of the internal combustion engine detected by the rotational speed detection means is higher. The internal combustion engine includes an air-fuel ratio sensor (40) that detects an air-fuel ratio that is a ratio of the fuel to air in the combustion chamber,
5. The control device for an internal combustion engine according to claim 2, wherein the positive threshold is set to be larger as the air-fuel ratio detected by the air-fuel ratio sensor is leaner. . The drive circuit is
An ignition coil (311) comprising a primary coil (311a) and a secondary coil (311b) magnetically coupled to each other, and applying a voltage to the spark plug by the secondary coil;
Secondary voltage detection means (L2) for detecting a secondary voltage induced in the secondary coil based on a change in magnetic flux generated in the primary coil;
With
The discharge state detection means acquires the secondary voltage detected by the secondary voltage detection means,
The determination means determines that the fuel has come into contact with the discharge when the absolute value of the change amount in the determination period of the secondary voltage acquired by the discharge state detection means is larger than a predetermined change amount. 6. The control device for an internal combustion engine according to claim 1, wherein the control device is an internal combustion engine. The drive circuit is
An ignition coil (311) comprising a primary coil (311a) and a secondary coil (311b) magnetically coupled to each other, and applying a voltage to the spark plug by the secondary coil;
Secondary voltage detection means (L2) for detecting a secondary voltage induced in the secondary coil based on a change in magnetic flux generated in the primary coil;
With
The discharge state detection means acquires the secondary voltage detected by the secondary voltage detection means,
The determination means has a difference obtained by subtracting the absolute value of the secondary voltage assumed when the fuel is not in contact with the discharge from the absolute value of the secondary voltage acquired by the discharge state detection means. The control apparatus for an internal combustion engine according to claim 1, wherein when it is greater than a predetermined value, it is determined that the fuel has come into contact with the discharge.   The ending means discharges the discharge after a predetermined time elapses after the determination means determines that the fuel injected by the injection means has contacted the discharge executed by the discharge execution means. The control device for an internal combustion engine according to any one of claims 1 to 7, wherein the control device is terminated.   9. The control apparatus for an internal combustion engine according to claim 8, wherein the predetermined time is extended as the air-fuel ratio, which is a ratio of the fuel to the air in the combustion chamber, becomes leaner.   The control apparatus for an internal combustion engine according to claim 8 or 9, wherein the predetermined time is extended as the injection amount of the fuel injected by the injection means increases.   11. The internal combustion engine according to claim 1, wherein the discharge execution unit causes the spark plug to generate the discharge prior to the fuel injection performed by the injection unit. Control device. A drive circuit applied to the control device for an internal combustion engine according to any one of claims 1 to 11,
An ignition coil (311) comprising a primary coil (311a) and a secondary coil (311b) magnetically coupled to each other, and applying a voltage to the spark plug by the secondary coil;
A first switching element (313) that disconnects and conducts a primary current flowing to the primary coil and causes the spark plug to start the discharge;
During the discharge started by the operation of the first switching element, the primary coil is energized in a direction opposite to the energization direction by the first switching element from the low voltage side terminal side of the primary coil, thereby An additional energy input circuit (322) for continuing the discharge while maintaining energization of the next coil in the same direction as started by the operation of the first switching element;
A drive circuit comprising: