JP6677497B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for controlling an internal combustion engine.

  In a direct injection type internal combustion engine in which fuel is directly injected into a combustion chamber by a fuel injection valve, a technique called a spray guide system in which a fuel injection valve is arranged so as to inject fuel downward from substantially above the center of the combustion chamber into the fuel chamber. It has been known. In this spray guide type direct injection internal combustion engine, the ground electrode protruding into the spray range from the tip of the spark plug becomes an obstacle that blocks part of the spray. Therefore, when the direction of the ground electrode changes, the influence of the spray interruption by the ground electrode changes, and the spray formation state changes. In particular, in the stratified combustion mode in which fuel is injected in the compression stroke, or in the weak stratified combustion mode, since a partially rich mixture is formed near the ignition plug and ignited, if the spray formation state changes depending on the direction of the ground electrode, The state of formation of the air-fuel mixture near the spark plug changes, and in some cases, the combustion state may deteriorate.

  Therefore, in the technology described in Patent Document 1, when the combustion mode is the stratified combustion mode or the weakly stratified combustion mode, and when the deterioration of the combustion state of the cylinder is detected, the fuel injection state (the execution of the split injection) And the ignition start timing) and the discharge state of the spark plug (total discharge period, etc.) to improve the fuel combustion state.

JP 2009-24682 A

  According to the technology disclosed in Patent Document 1, deterioration of fuel combustion caused by excessive contact of the fuel spray injected by the fuel injection valve with the spark plug, and fuel deterioration caused by the fuel spray not reaching the spark plug occur. The aim is to uniformly improve the combustion state of the fuel without distinguishing between combustion deterioration. However, the deterioration of fuel combustion caused by excessive contact of the fuel spray injected by the fuel injection valve with the spark plug and the deterioration of fuel combustion caused by the fuel spray not reaching the spark plug depend on the combustion state of the fuel. Are different. For this reason, in the technology disclosed in Patent Document 1, the effect of improving the combustion state of the fuel may be reduced depending on the positional relationship between the fuel spray injected by the fuel injection valve and the discharge generated by the spark plug. .

  SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and a main object of the present invention is to combust a fuel due to a positional relationship between a fuel spray injected by a fuel injection valve and a discharge generated by an ignition plug. It is an object of the present invention to provide a control device for an internal combustion engine that can suppress deterioration of a state.

  The present invention is a control device applied to an internal combustion engine including a fuel injection valve that directly injects fuel into a combustion chamber, and a spark plug that discharges between electrodes in the combustion chamber, wherein discharge is performed by the spark plug. An injection unit for injecting the fuel by the fuel injection valve within a predetermined period including a start timing, and detecting an electric characteristic of electric energy input to the ignition plug after the fuel injection is started by the injection unit. And estimating, based on the electrical characteristics detected by the electrical characteristics detector, the strength of the fluid flow in the vicinity of the ignition plug caused by the injection of fuel from the fuel injection valve. Based on the flow estimating unit and the strength of the fluid flow estimated by the flow estimating unit, the injection state and the spark plug in which fuel is injected by the fuel injection valve. At least one of the discharge state to be conductive, characterized in that it comprises a control unit for controlling the direction of improving the combustion state of the fuel, the.

  When the spray of the fuel injected from the fuel injection valve passes, a flow occurs in the surrounding fluid (including air and vaporized fuel). Therefore, when the fluid flow around the spark plug is strong, the discharge generated in the spark plug may blow out. On the other hand, when the fluid flow is weak, the state in which the fuel spray injected from the fuel injection valve is far from the discharge generated by the spark plug becomes longer, and the fuel and the discharge can be satisfactorily contacted within the discharge period. The fuel may cause incomplete combustion or, in the worst case, misfire.

  In order to prepare for these cases, the control device includes a flow estimating unit, and based on the electric characteristics detected by the electric characteristic detecting unit, the fluid in the combustion chamber generated by the injection of fuel from the fuel injection valve. The flow strength is estimated. Then, based on the estimated strength of the fluid flow, at least one of the injection state in which the fuel is injected by the fuel injector and the discharge state in which the spark plug discharges is controlled by the control unit in a direction in which the combustion state of the fuel is improved. Is done. From the strength of the fluid flow, the positional relationship between the fuel spray injected by the fuel injection valve and the discharge generated by the spark plug can be estimated, so that the positional relationship between the fuel spray and the discharge generated by the spark plug can be determined. Control can be performed. For this reason, it is possible to suppress the deterioration of the combustion state of the fuel caused by the positional relationship between the fuel spray injected by the fuel injection valve and the discharge generated by the spark plug.

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 intensity | strength of a fluid flow by the injection start timing and the magnitude | size of a discharge period and electric current. 5 is a control flowchart executed by the electronic control unit according to the embodiment. It is a figure which shows the secondary voltage which changes when fuel spray and discharge contact, according to the intensity | strength of fluid flow. It is a figure showing the effect obtained by performing this control at the time of strong flow. It is a figure showing the effect obtained by performing this control at the time of weak flow.

  Referring to FIG. 1, an engine system 10 includes an engine 11 which 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 a main body of the engine 11. The combustion chamber 11b is provided so as to accommodate the piston 12 so as to be able to reciprocate. The water jacket 11c is a space through which a cooling liquid (also referred to as cooling water) can flow, and is provided so as to surround the periphery of the combustion chamber 11b.

  An intake port 13 and an exhaust port 14 are formed in a cylinder head at an upper portion of the engine block 11a so as to be able to communicate with the combustion chamber 11b. The cylinder head has an intake valve 15 for controlling a communication state between the intake port 13 and the combustion chamber 11b, an exhaust valve 16 for controlling a communication state between the exhaust port 14 and the combustion chamber 11b, and an intake valve. A valve driving 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 arranged near the ignition plug 19 and is provided so as to directly inject fuel into the combustion chamber 11b. The ignition plug 19 is provided so as to ignite the fuel mixture in the combustion chamber 11b.

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

  The EGR passage 23 is provided so 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 21 b (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 (the mixing ratio of exhaust gas in the gas before combustion sucked into the combustion chamber 11b) by its opening degree.

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

  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. Is provided with an air-fuel ratio sensor 40 (such as a linear A / F sensor) for detecting the air-fuel ratio.

  The engine system 10 includes an ignition circuit unit 31, an electronic control unit 32, and the like.

  The ignition circuit unit 31 is configured to generate a spark discharge at the spark plug 19 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 an operating state of the engine 11 (hereinafter referred to as “engine parameter”) acquired based on outputs of various sensors such as the crank angle sensor 33. The operation of each unit including the injector 18 and the ignition circuit unit 31 is controlled in accordance with this.

  Regarding ignition control, the electronic control unit 32 generates and outputs an ignition signal and an energy input period signal based on the acquired engine parameters. Such an ignition signal and an energy input period signal are optimal ignition timings and discharge currents (these vary depending on the state of gas in the combustion chamber 11b and the required output of the engine 11 (these vary depending on engine parameters)). (Ignition discharge current). Therefore, the electronic control unit 32 corresponds to an injection unit and a control unit. In addition, the electronic control unit 32 corresponds to an electric characteristic detecting unit and a flow estimating unit.

  The crank angle sensor 33 is a sensor for outputting a rectangular crank angle signal at every 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) a cooling water temperature that is the temperature of the cooling liquid flowing through the water jacket 11c, and is mounted on the engine block 11a.

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

  The throttle opening sensor 37 is a sensor that generates an output corresponding to the opening of the throttle valve 25 (throttle opening), and is built in the throttle actuator 26. The accelerator position sensor 38 is provided 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 311a and a secondary winding 311b), a DC power supply 312, a first switching element 313, an additional energy input circuit 322, It includes diodes 318a, 318b, and 318d, and a driver circuit 319.

  As described above, the ignition coil 311 includes the primary winding 311a and the secondary winding 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-ground side 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-ground side terminal) which is one end of the primary winding 311a. On the other hand, the other end of the primary winding 311a, that is, the low-voltage terminal (which may also be referred to as a ground terminal) is connected to the ground 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, the primary current flows in the primary winding 311a in the direction from the high voltage side terminal side to the low voltage side terminal side. ing.

  The high voltage side terminal (which may also be referred to as a non-ground side terminal) side of the secondary winding 311b is connected to the high voltage side terminal side of 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 supplies a secondary current (discharge current) to the ignition plug. 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 becomes 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 path L1 connecting the low voltage side terminal and the spark plug 19 includes a voltage detection terminal. The use path (corresponding to the secondary voltage detection unit) L2 is connected. The voltage detection path L2 is provided with resistors 320 and 321 for voltage detection. 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 between the resistor 320 and the resistor 321 (the figure number is omitted) 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) which is a MOS gate structure transistor, and has 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 (the first power supply side terminal 313C and the first ground side terminal 313E) of the first switching element 313. The first switching element 313 controls on / off of energization between the first power supply terminal 313C and the first ground 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 terminal 313E is connected to the ground.

  The energy addition 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 Semiconductor Field 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 terminal 314D and the second ground 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 terminal so as to allow a current to flow from the second ground terminal 314S of the second switching element 314 toward the low voltage terminal of the primary winding 311a. 314S.

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

  The third power supply terminal 315C is connected to a second power supply terminal 314D of the second switching element 314 via a diode 318c. The anode of the diode 318c is connected to the third power supply terminal 315C so as to allow current to flow from the third power supply terminal 315C of the third switching element 315 toward the second power supply terminal 314D of the second switching element 314. Connected to terminal 315C. The third ground terminal 315E of the third switching element 315 is connected to the ground.

  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 connecting the above-mentioned non-ground side output terminal of the DC power supply 312 and the third power supply side 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-mentioned non-ground side output terminal of the DC power supply 312. That is, the capacitor 317 is connected to the energy storage coil 316 in parallel with the third switching element 315. 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 to receive the engine parameters, 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. Have been. The driver circuit 319 converts the first control signal, the second control signal, and the third control signal into the first control terminal 313G, the second control terminal 314G, and the third control signal based on the received ignition signal and the energy input period signal. It is provided to output to three control terminals 315G.

  Specifically, the driver circuit 319 releases the stored energy from the capacitor 317 during the ignition discharge of the ignition plug 19 (this is started by turning off the first switching element 313) (this is the third switching element 315). Off and the second switching element 314 is turned on). The released stored energy becomes input energy and is supplied to the primary winding 311a from the low voltage side terminal side. As a result, a primary current caused by the input energy supplied during the ignition discharge flows through the primary winding 311a. Therefore, an additional component 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 in response thereto. Therefore, the secondary current is sufficiently secured to the extent that the ignition discharge can be maintained, and the continuous discharge is performed. Can be implemented.

  In such a configuration, the electronic control unit 32 switches between the 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). Is carried out. The operation range of the lean mode is set to a lower rotation speed and lower load than the operation range of the stoichiometric mode.In the lean mode, less fuel is directly injected into the cylinder in the compression stroke than in the stoichiometric mode described later, and ignition is performed. A stratified mixture is formed near the plug 19 to ignite. On the other hand, in the stoichiometric mode, fuel is directly injected into the cylinder during the intake stroke to form a homogeneous mixture and ignite. In short, fuel injection is performed in the compression stroke in the lean mode, and fuel injection is performed in the intake stroke in the stoichiometric mode.

  Continuous discharge is performed in a lean mode. Specifically, when fuel is injected by the injector 18 within a predetermined period including a timing at which a discharge occurs in the spark plug 19, a period (hereinafter, referred to as a discharge period) in which the spark plug 19 is to perform a continuous discharge is performed. ), A continuous discharge is maintained. Conventionally, when such stratified combustion is performed and the combustion state of the fuel is deteriorated, the state of fuel injection and the state of discharge (hereinafter, referred to as discharge state) generated in the spark plug 19 are controlled. By doing so, the deterioration of the combustion state of the fuel was suppressed. Note that the injection state corresponds to, for example, the execution of split injection that divides the injection amount originally injected in one fuel injection, the injection start timing, and the like, and the discharge state corresponds to the secondary current flowing through the spark plug 19. A size, a discharge period as a period during which discharge is generated in the ignition plug 19, and the like correspond.

  By the way, when the lean mode is performed, the combustion state of the fuel may be deteriorated due to the positional relationship between the fuel spray injected by the injector 18 and the discharge generated by the spark plug 19. For example, if the fuel spray injected by the injector 18 makes excessive contact with the discharge generated by the spark plug 19, insufficient combustion may occur due to lack of oxygen, and in the worst case, misfire may occur. The state in which the fuel spray injected by the injector 18 is in excessive contact with the discharge generated by the spark plug 19 is caused by the flow of the fluid (hereinafter referred to as the fluid flow) generated by the injection of the fuel from the injector 18. It often occurs when it is strong (hereinafter referred to as strong flow). In such a strong flow situation, besides the above-mentioned problem, there is a possibility that the discharge generated by the spark plug 19 may blow out. Note that the fluid in the present embodiment refers to air flowing in the combustion chamber or vaporized fuel.

  On the other hand, it is assumed that the fuel spray injected by the injector 18 is still separated from the spark plug 19 when the spark plug 19 generates a discharge. Such a state often occurs when the fluid flow is weak (hereinafter, referred to as weak flow). Accordingly, the state in which the fuel spray injected from the injector 18 is separated from the discharge generated in the spark plug 19 becomes longer, and the fuel spray and the spark discharge cannot be satisfactorily contacted within the discharge period in which the discharge occurs. The fuel may cause incomplete combustion or, in the worst case, cause misfire.

  In the prior art, no consideration is given to the above problem, and it is difficult to take measures against it. Therefore, the electronic control unit 32 according to the present embodiment sets the discharge state that is set each time the engine 11 is started, assuming an environment in which fuel is difficult to burn (hereinafter, referred to as an initial setting). Specifically, as shown in FIG. 3, the secondary current flowing through the spark plug 19 is set higher than normal so that a discharge can be generated even in a strong flow. In addition, in a case where the fuel flow is weak and the spray of the fuel injected from the injector 18 is separated from the discharge generated in the spark plug 19 for a long time, a period in which the fuel is discharged by the spark plug 19 (hereinafter referred to as a discharge period). (Name) is set longer than usual. Thereby, under any condition, the fuel can be burned, and the magnitude of the fluid flow generated by the injection of the fuel from the injector 18 is estimated. According to the estimated strength of the fluid flow, At least one of the fuel injection state when the fuel is injected and the discharge state discharged by the spark plug 19 is changed to the optimum state.

  For example, as shown in FIG. 3, when it is estimated that the flow is strong, the timing at which fuel is started to be injected by the injector 18 (hereinafter, referred to as injection start timing) is advanced. As a result, the fuel is injected from the injector 18 at an early stage. Therefore, when a discharge is generated in the spark plug 19, it is assumed that the fluid flow generated by the injection of the fuel from the injector 18 is weakened.

  When it is estimated that the flow is weak, the secondary current flowing through the ignition plug 19 is controlled to be small, and the discharge period is controlled to be extended to the advance side. The secondary current flowing through the spark plug 19 is controlled to be small because the flow of the fluid is weak, so that the discharge arc (discharge plasma) generated in the spark plug 19 is less likely to blow out. However, since the flow is weak, the state in which the fuel spray injected from the injector 18 is separated from the discharge arc generated in the spark plug 19 becomes longer. Therefore, by controlling the discharge period to be advanced to the advance side, a discharge arc is generated in the ignition plug 19 at an early stage, and the discharge arc is extended in an arc shape by the fluid flow generated around the ignition plug 19. This makes it possible to bring the extended discharge arc into contact with the fuel spray injected from the injector 18. Further, by extending the discharge period, the spray of the fuel injected until the discharge ends can satisfactorily come into contact with the discharge.

  When it is assumed that the fluid flow is neither strong nor weak (hereinafter referred to as an intermediate flow), discharge blowout is less likely to occur than during strong flow, and discharge blowout is more likely to occur than during weak flow. is assumed. For this reason, the secondary current flowing through the ignition plug 19 is set to be smaller than the secondary current at the time of initial setting and larger than the secondary current set at the time of weak flow. Further, it is assumed that the fuel spray comes into contact with the ignition plug 19 at the timing when the discharge is generated in the ignition plug 19, so that the discharge period is set to the discharge period in the initial setting and the discharge period set in the strong flow. Set shorter than either. This makes it possible to minimize the energy flowing to the spark plug 19.

  In the present embodiment, the electronic control unit 32 executes the correction control of the ignition plug 19 shown in FIG. The correction control of the ignition plug 19 shown in FIG. 4 is repeatedly executed each time one combustion cycle is performed by the electronic control unit 32 while the power of the electronic control unit 32 is 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 load of the engine 11 is calculated from the accelerator operation amount read in step S101. Further, the rotation speed of the engine 11 is calculated from the crank angle. Since there is a correlation between the crank angle and the rotation speed of the engine 11, the rotation speed of the engine 11 is calculated based on the correlation. Then, the process proceeds to step S103, and an operation mode to be executed is referred from an operation map based on the load and the rotation speed of the engine 11 calculated in step S102. Then, in step S104, based on the result of step S103, it is determined whether or not the current operating state is a state in which the lean mode should be performed. In the present embodiment, the lean mode is a so-called stratified combustion mode. When it is determined that the current operating state is the operating state in which the lean mode should be performed (low to medium rotational speed / low to medium required torque) (S104: YES), the process proceeds to step S105.

  In step S105, the injection start timing is set at which time in the compression stroke fuel injection is started from the injector 18 based on the referred operation map. Similarly, from the operation map referred to, the ignition timing and the magnitude of the secondary current flowing through the ignition plug 19 are set at which time in the compression stroke the electric discharge is caused in the ignition plug 19. At this time, in an operation state similar to the current operation state, the injection state or the discharge state correction processing (corresponding to any one of step S110, step S113, and step S115) according to the strength of the fluid flow already described later. Is applied, the setting after the correction processing is applied. If the correction processing of the ejection state or the discharge state in accordance with the strength of the fluid flow in the operation state similar to the current operation state is not performed, the above-described initial setting is performed. Then, the process proceeds to step S106.

  In step S106, the fuel is injected into the injector 18 based on the injection start timing set in step S105. Similarly, a discharge is generated in the spark plug 19 based on the ignition timing set in step S105. In step S107, it is determined whether the strength of the fluid flow in the operation state similar to the current operation state has already been estimated (one of the strong flow estimation flag, the intermediate flow estimation flag, and the weak flow estimation flag has been stored). I do. When it is determined that the strength of the fluid flow in the operation state similar to the current operation state has already been estimated (S107: YES), this control is ended. When it is determined that the strength of the fluid flow in the operation state similar to the current operation state has not been estimated yet (S107: NO), the process proceeds to step S108.

  In step S108, the secondary voltage V2 applied to the spark plug 19 is detected in the voltage detection path L2. This is a process for estimating the strength of the fluid flow.

  For example, in the case of strong flow, the discharge arc generated by the spark plug 19 expands in an arc shape, and the secondary voltage V2 required to maintain the discharge increases in the negative direction (secondary voltage). The absolute value of V2 increases). On the other hand, when the flow is weak, the discharge arc generated by the spark plug 19 takes a long time to extend in an arc shape, and the length of the discharge arc generated between the electrodes of the spark plug 19 is relatively short. The secondary voltage V2 decreases in the negative direction. That is, the strength of the fluid flow can be estimated from the magnitude of the secondary voltage V2 applied to the ignition plug 19. However, when estimating the strength of the fluid flow, the peak of the secondary voltage V2 after the second time is narrowed down to the determination target. Since the first discharge of the ignition plug 19 requires a large amount of energy, the first peak of the measured secondary voltage V2 may be smaller than the first threshold value Vh regardless of the strength of the fluid flow. (See FIG. 5). Further, even when the fuel spray comes into contact with the spark discharge generated in the ignition plug 19 and the fuel burns, the secondary voltage V2 may exceed the first threshold value Vh and increase. Limit the period for estimating strength. Therefore, the secondary voltage V2 used in the processing for estimating the strength of the fluid flow after step S109 is within the first determination period until a predetermined time (for example, 5 ° CA) elapses after the fuel is injected. This is the secondary voltage V2 excluding the detected first peak.

  As described above, in the present embodiment, the process of estimating the strength of the fluid flow is as follows. As shown in the right diagram of FIG. 5, within the first determination period, the second and subsequent peaks of the detected secondary voltage V2 are smaller than the first threshold Vh (the absolute value of the peak is equal to the first threshold). Vh is larger than the absolute value of Vh), it is assumed that the fluidity is high. As shown in the left diagram of FIG. 5, within the first determination period, the second and subsequent peaks of the detected secondary voltage V2 have become larger than the second threshold Vl (the absolute value of the peak is equal to the second threshold Vl). If it is smaller than the absolute value of Vl), it is assumed that the flow is low. As shown in the middle diagram of FIG. 5, within the first determination period, the peak of the detected secondary voltage V2 after the second time has become larger than the first threshold Vh and smaller than the second threshold Vl. In that case, it is assumed that the flow is intermediate. Note that the second threshold Vl is set to be larger than the first threshold Vh.

  Returning to the description of the flowchart shown in FIG. In step S109, it is determined whether or not the second and subsequent peaks of the secondary voltage V2 detected in step S108 have become smaller than the first threshold value Vh during a period from when fuel is injected until a predetermined time has elapsed. judge. If it is determined that the second and subsequent peaks of the secondary voltage V2 have become smaller than the first threshold value Vh before the predetermined time elapses after the fuel is injected (S109: YES), the process proceeds to step S110. Then, the injection start timing is controlled to an earlier timing (advance angle side). Then, the process proceeds to step S111 to store a strong flow estimation flag indicating that the strong flow is estimated, and ends the present control.

  When it is determined that the second and subsequent peaks of the secondary voltage V2 have become larger than the first threshold value Vh (S109: NO), the process proceeds to step S112. In step S112, it is determined whether or not the second and subsequent peaks of the secondary voltage V2 have become larger than the second threshold value Vl. If it is determined that the second and subsequent peaks of the secondary voltage V2 have become larger than the second threshold value Vl (S112: YES), the process proceeds to step S113, in which the secondary current flowing through the spark plug 19 is reduced and the discharge is performed. The period is extended to the advance side. Then, the process proceeds to step S114 to store a weak flow estimation flag indicating that it is estimated that the flow is weak, and ends the control.

  If it is determined that the second and subsequent peaks of the secondary voltage V2 have become smaller than the second threshold value Vl (S112: NO), the process proceeds to step S115, and the secondary current flowing through the spark plug 19 is set to a value lower than that at the time of the initial setting. It is set to be small and larger than the secondary current set at the time of weak flow. Further, the discharge period is set to be shorter than that at the time of the initial setting and shorter than the discharge time set at the time of strong flow. Then, the process proceeds to step S116, where an intermediate flow estimation flag indicating that the flow is estimated to be intermediate is stored, and the control is terminated.

  If it is determined that the current operation state is an operation state in which the lean mode should not be performed (high rotation speed / high required torque) (S104: NO), the process proceeds to step S117. In step S117, if any one of the flow estimation flags of step S111, step S114, and step S116 is stored, the stored flow estimation flag is reset, and the process proceeds to step S118. In step S118, the stoichiometric (homogenous combustion) mode is executed, and the present control ends.

  The processing content according to the fluid flow strength determined in this control is applied from the next combustion cycle onward as long as the lean mode continues.

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

  -If it is estimated that the flow is strong, the injection start timing is advanced. As a result, the fuel is injected from the injector 18 early, so that when the spark plug 19 generates a discharge, the fluid flow is weakened. Therefore, it is possible to suppress the blow-out of the discharge generated in the spark plug 19 and to improve the combustion state of the fuel.

  FIG. 6 shows the result of actually improving the combustion state of the fuel. The upper diagram of FIG. 6 shows how the combustion state of the fuel changes by changing the timing at which the fuel is injected by the injector 18 under various circumstances where the fluid flow generated by the injection of the fuel from the injector 18 is strong. FIG. The combustion fluctuation rate described on the vertical axis in the upper part of FIG. 6 indicates how much variation occurs in the torque generated when the fuel is burned. Specifically, the injection rate and the like are adjusted so that the strength of the target fluid flow is generated, and the fuel is injected into the injector 18 at an arbitrary injection start timing. Then, the torque fluctuation value generated when the injected fuel burns is calculated a plurality of times, and the standard deviation is calculated. On the other hand, the fuel is injected into the injector 18 at an arbitrary injection start timing in an environment in which the fuel is easy to burn (for example, in an intermediate flow environment). Then, the torque fluctuation value generated when the injected fuel is burned is calculated a plurality of times (this data is 400 times), and the average (average torque) of the torque fluctuation values generated each time is calculated. Then, the standard deviation is divided by the calculated average torque. The value thus obtained corresponds to the combustion fluctuation rate.

  The upper diagram in FIG. 6 shows that the variation in the torque fluctuation caused by the combustion of the fuel is increased by retarding the injection start timing from the normal injection start timing (base injection start timing). . This is considered to be due to incomplete combustion of the fuel. On the other hand, it is shown that, by controlling the injection start timing to be more advanced than the base injection start timing, variations in torque fluctuation caused by fuel combustion are reduced. From this, it is understood that the combustion state of the fuel can be stabilized by advancing the fuel injection start timing.

  The lower part of FIG. 6 shows whether a misfire has occurred during the actual combustion of the fuel in an environment of strong flow, and how the misfire occurrence rate has changed by changing the injection start timing. In the lower diagram of FIG. 6, it is shown that the misfire has occurred on the retard side from the base injection start timing, whereas the misfire occurrence rate has become 0% by advancing the base injection start timing from the base injection start timing. I have. It has been confirmed by the inventors that the strength of the fluid flow near the spark plug 19 when the misfire occurrence rate becomes 0% is the strength of the fluid flow corresponding to the intermediate flow. Therefore, when it is assumed that the fluid flow is strong, by advancing the injection start timing, the strength of the fluid flow near the spark plug 19 can be reduced, so that the discharge generated in the spark plug 19 blows out. And the fuel can be stably burned.

  If the fluid flow is estimated to be weak, the secondary current flowing through the spark plug 19 is reduced. This makes it possible to save ignition energy when the spark plug 19 generates a discharge.

  If the fluid flow is assumed to be weak, the discharge period is extended. This allows the fuel spray to satisfactorily come into contact with the discharge, thereby making it possible to burn the fuel more reliably. FIG. 7 shows the result of actually improving the combustion state of the fuel for extending the discharge period. The upper diagram of FIG. 7 is a diagram illustrating how the combustion state of the fuel has changed by variously changing the discharge period under the condition where the fluid flow generated by the injection of the fuel from the injector 18 is weak. The upper diagram in FIG. 7 shows that the longer the discharge period, the smaller the variation in torque fluctuation caused by burning the fuel, and the better the combustion state of the fuel is actually improved. The lower diagram of FIG. 7 illustrates how the misfire occurrence rate changes by changing the discharge period in a weakly flowing environment. The lower diagram of FIG. 7 shows that the longer the discharge period is, the lower the misfire occurrence rate is, and finally the misfire occurrence rate can be reduced to 0%.

  When it is estimated that the fluid flow is weak, the discharge period is extended to the advance side, thereby causing the spark plug 19 to generate a discharge at an early stage. Thus, by extending the discharge arc in an arc shape by the fluid flow generated around the ignition plug 19, the extended discharge arc can be brought into contact with the spray of the fuel injected from the injector 18, and the fuel and the discharge arc can be contacted. It is possible to increase the frequency of contact with.

  If the fluid flow is assumed to be an intermediate flow, the discharge period is set shorter than the discharge period set during strong flow and the discharge period set during weak flow. The secondary current flowing through the ignition plug 19 is set lower than the secondary current flowing through the ignition plug 19 during strong flow, and higher than the secondary current flowing through the ignition plug 19 during weak flow. As a result, it is possible to minimize the secondary current required for causing the spark plug 19 to generate a discharge.

  Estimating the strength of the fluid flow more accurately by determining how large the second and subsequent peaks of the secondary voltage V2 have been before the predetermined time has elapsed since the fuel was injected. Becomes possible.

  ・ Every time the operating state becomes the lean mode, the strength of the fluid flow generated by the injection of the fuel from the injector 18 is estimated in the first processing, and the combustion of the fuel is improved based on the strength of the fluid flow. The control is performed in the direction to be performed. Accordingly, by performing this control particularly in the lean mode in which a misfire is concerned, it is possible to suppress misfire of the fuel due to the strength of the fluid flow.

  The above-described embodiment can be modified and implemented as follows.

  In the above embodiment, the correction control according to the strength of the fluid flow was performed in the lean mode. Although the lean mode in the above-described embodiment indicates the stratified combustion mode, the present invention is not limited to this, and the correction control according to the strength of the fluid flow may be performed even when the weak stratified combustion mode is set to the lean mode. In the weak stratified charge combustion mode, fuel injection is performed twice during the intake stroke and the compression stroke. However, the fuel injection targeted for the correction control is the fuel injection performed during the compression stroke. Further, not only in the lean mode, but also in the stoichiometric mode, for example, the correction control according to the strength of the fluid flow may be performed. However, in the fuel injection in the intake stroke such as the stoichiometric mode in the above embodiment, it is difficult to perform the correction control. Therefore, the target of this correction control is limited to the stoichiometric mode in which fuel is injected in the compression stroke to form a homogeneous mixture.

  -In the said embodiment, the injector 18 was arrange | positioned in the vicinity of the ignition plug 19. In this regard, the injector 18 may be arranged to inject combustion into the combustion chamber 11b from the side of the combustion chamber 11b.

  In the above-described embodiment, the main control is uniformly performed in the lean mode regardless of the operating state of the engine 11. In this regard, in addition to the lean mode, the operating region may be divided into a plurality of regions based on the required torque and the rotation speed, and correction control according to the strength of the fluid flow may be performed for each of the divided regions. . For example, it may be divided into a high load / high rotation region, a medium load / medium rotation region, and a low load / low rotation region, and the strength of the fluid flow may be estimated for each of the divided regions.

  In the above embodiment, when it is estimated that the flow is strong, the injection start timing is advanced. In this regard, when it is estimated that the flow is strong, the timing at which discharge is started by the spark plug 19 (hereinafter, referred to as discharge start timing) may be retarded. As a result, the discharge start timing is delayed, so that when the spark plug 19 generates a discharge, the fluid flow near the ignition plug 19 is weakened. Therefore, it is possible to suppress the blow-out of the discharge generated in the ignition plug 19.

  In the above embodiment, when it is estimated that the flow is weak, the secondary current flowing through the ignition plug 19 is reduced. Regarding this, it is not always necessary to reduce the secondary current flowing through the spark plug 19 at the time of weak flow.

  In the above embodiment, when it is assumed that the flow is intermediate, the discharge period is set shorter than both the discharge period set during strong flow and the discharge period set during weak flow. In this regard, it is not necessary to set the discharge period set during the intermediate flow shorter than both the discharge period set during the strong flow and the discharge period set during the weak flow. For example, it may be set longer than the discharge period set at the time of weak flow.

  In the above embodiment, when it is assumed that the flow is intermediate, the secondary current flowing through the spark plug 19 is lower than the secondary current flowing through the ignition plug 19 during strong flow, and flows through the ignition plug 19 during weak flow. It was set higher than the secondary current. Regarding this, it is not always necessary to make the above setting. However, if the secondary current is set lower than the secondary current flowing through the spark plug 19 during the weak flow, the discharge generated in the spark plug 19 may be blown out. Therefore, only the secondary current is set to be higher. Specifically, it may be set higher than the secondary current flowing through the ignition plug 19 during strong flow.

  In the above embodiment, the processing content determined at the time of the correction control (for example, when it is estimated that the flow is strong, the injection start timing is controlled to be advanced) is applied after the next combustion cycle. I was going to. In this regard, a process may be performed according to the fluid flow strength estimated from the current combustion cycle. However, when the processing according to the strength of the fluid flow is performed from the current combustion cycle, the fuel is already injected from the injector 18 and the discharge is generated in the ignition plug 19, so the correction control in the above embodiment is performed. May not be appropriate. Therefore, the processing content according to the strength of the fluid flow is changed.

  Specifically, when it is estimated that the flow is strong, the discharge currently occurring in the ignition plug 19 is stopped, and the discharge is restarted after a predetermined time has elapsed. This makes it possible to obtain the same effect as that of the above-described another example in which the discharge start timing is retarded. When it is estimated that the flow is weak, the secondary current is attenuated with the passage of time, and the discharge period is controlled to be extended to the retard side. This makes it possible to reduce the amount of energy flowing through the ignition plug 19 and extend the discharge period, thereby increasing the chance that the fuel spray contacts the discharge. If it is assumed that the flow is intermediate, the secondary current is attenuated with the lapse of time, and the timing for ending the discharge is advanced. As a result, the discharge can be terminated early, so that it is not necessary to input excessive energy to the spark plug 19.

  In this alternative example, when it is estimated that the flow is strong, the discharge currently occurring in the spark plug 19 is stopped, and the discharge is restarted after a predetermined time has elapsed. Regarding this, in consideration of the possibility that the fluid flow around the spark plug 19 is still strong when the spark plug 19 is re-discharged, when discharging again, the discharge of the spark plug 19 into the spark plug 19 during the stopped discharge is considered. A secondary current larger than the secondary current may flow. This makes it possible to suppress the discharge from blowing off due to the fluid flow, and to more reliably maintain the discharge generated by the spark plug 19.

  In the above embodiment, the spark plug 19 generates a continuous discharge. In this regard, multiple discharges that generate spark discharges a plurality of times at the spark plug 19 may be performed. In the continuous discharge, a discharge period is provided, and the discharge is terminated after the discharge period has elapsed. When performing multiple discharges, instead of this discharge period, the number of discharges for which the discharge period elapses may be set, and after the discharge is generated in the spark plug 19 by the number of discharges, the discharge may be terminated.

  In the above embodiment, the strength of the fluid flow is estimated based on the secondary voltage V2 detected by the voltage detection path L2. In this regard, instead of detecting the secondary voltage V2, a secondary current may be detected, and the strength of the fluid flow may be estimated based on the detected secondary current.

  In the above embodiment, the strength of the fluid flow is estimated based on the second and subsequent peaks of the secondary voltage V2 detected by the voltage detection path L2. In this regard, the absolute value of the second and subsequent peaks of the detected secondary voltage V2 may be calculated, and the strength of the fluid flow may be estimated based on the calculated absolute value of the secondary voltage V2. In this case, the absolute value of each of the first threshold value Vh and the second threshold value Vl is also used for the comparison determination.

  In the above-described embodiment, when the second and subsequent peaks of the secondary voltage V2 detected by the voltage detection path L2 become lower than the first threshold value Vh, it is estimated that the flow is strong. In addition, when the second and subsequent peaks of the secondary voltage V2 detected by the voltage detection path L2 become larger than the second threshold value Vl, it is estimated that the flow is low. When the second and subsequent peaks of the secondary voltage V2 detected by the voltage detection path L2 are larger than the first threshold Vh and larger than the second threshold Vl, it is estimated that the flow is intermediate. Was.

  The method of estimating the strength of the fluid flow need not be limited to the above method. For example, a second determination period may be provided, and when the absolute value of the amount of change (for example, the slope) of the secondary voltage V2 during this determination period is larger than the first predetermined amount of change, it may be estimated that the flow is strong. 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 V2 increases continuously. When the contact frequency is excessively large, a change larger than the first predetermined change amount occurs in the secondary voltage V2 in the second determination period. On the other hand, if the absolute value of the change amount of the secondary voltage V2 during the second determination period is smaller than the second predetermined change amount, it may be estimated that the flow is weak. This is because the fuel spray does not come into contact with the discharge during the second determination period, and a large change does not occur in the secondary voltage V2 beyond the second predetermined change amount. If the absolute value of the change amount of the secondary voltage V2 during the second determination period is smaller than the first predetermined change amount and larger than the second predetermined change amount, it is estimated that the flow is intermediate. Is also good. In the case of the intermediate flow, the injected fuel is in contact with the discharge, but it is assumed that the frequency of the contact is not as excessive as the strong flow. Therefore, the absolute value of the change amount of the secondary voltage V2 is smaller than the first predetermined change amount, and is larger than the second predetermined change amount because the fuel spray contacts the discharge.

  As described above, the strength of the fluid flow generated by the fuel injection can be accurately estimated based on the amount of change in the secondary voltage V2 during the second determination period.

  11: engine, 11b: combustion chamber, 18: injector, 19: spark plug, 32: electronic control unit.

Claims (12)

A fuel injection valve (18) for directly injecting fuel into the combustion chamber (11b);
An ignition plug (19) for discharging between the electrodes in the combustion chamber;
A secondary voltage detector (L2) for detecting a secondary voltage applied to the ignition plug;
A control device (32) applied to an internal combustion engine (11) comprising:
An injection unit that injects the fuel by the fuel injection valve within a predetermined period including a timing at which discharge is started by the ignition plug;
After starting the fuel injection by the injection unit, an electrical characteristic detection unit that acquires the secondary voltage detected by the secondary voltage detection unit,
Based on the secondary voltage obtained by the electrical characteristic detection unit, a flow estimation unit that estimates the strength of the fluid flow near the ignition plug generated by the injection of fuel from the fuel injection valve,
Based on the strength of the fluid flow estimated by the flow estimating unit, the combustion state of the fuel is improved in at least one of an injection state in which fuel is injected by the fuel injection valve and a discharge state in which the spark plug discharges. A control unit for controlling the direction,
Bei to give a,
The flow estimating unit, after injecting fuel into the fuel injection valve by the injection unit, the absolute value of the second and subsequent peaks of the secondary voltage acquired by the electrical characteristic detection unit within the first determination period. When larger than the first threshold value, the fluid flow is estimated to be a strong strong flow, and after injecting fuel into the fuel injection valve by the injection unit, the electric characteristic detection unit within the first determination period. If the absolute value of the second and subsequent peaks of the obtained secondary voltage is smaller than the second threshold set smaller than the first threshold, the fluid flow is assumed to be weak weak flow,
The control unit is configured to, when the flow estimating unit estimates that the fluid flow is a strong strong flow, discharge the state by the spark plug at a time when the strong flow is weakened. Controlling the at least one of the two, and when the flow estimating unit is estimated that the fluid flow is a weak weak flow, extending the discharge period as a period for discharging by the spark plug , Control device. A fuel injection valve (18) for directly injecting fuel into the combustion chamber (11b);
An ignition plug (19) for discharging between the electrodes in the combustion chamber;
A secondary voltage detector (L2) for detecting a secondary voltage applied to the ignition plug;
A control device (32) applied to an internal combustion engine (11) comprising:
An injection unit that injects the fuel by the fuel injection valve within a predetermined period including a timing at which discharge is started by the ignition plug;
After starting the fuel injection by the injection unit, an electrical characteristic detection unit that acquires the secondary voltage detected by the secondary voltage detection unit,
Based on the secondary voltage obtained by the electrical characteristic detection unit, a flow estimation unit that estimates the strength of the fluid flow near the ignition plug generated by the injection of fuel from the fuel injection valve,
Based on the strength of the fluid flow estimated by the flow estimating unit, the combustion state of the fuel is improved in at least one of an injection state in which fuel is injected by the fuel injection valve and a discharge state in which the spark plug discharges. A control unit for controlling the direction,
Bei to give a,
The flow estimating unit is configured such that, when the absolute value of the amount of change in the secondary voltage acquired by the electrical characteristic detecting unit within the second determination period is larger than a first predetermined amount of change, the fluid flow is a strong strong flow. The absolute value of the change amount of the secondary voltage obtained by the electrical characteristic detection unit within the second determination period is set to be smaller than the first predetermined change amount. If smaller than, the fluid flow is assumed to be weak weak flow,
The control unit is configured to, when the flow estimating unit estimates that the fluid flow is a strong strong flow, discharge the state by the spark plug at a time when the strong flow is weakened. Controlling the at least one of the two, and when the flow estimating unit is estimated that the fluid flow is a weak weak flow, extending the discharge period as a period for discharging by the spark plug , Control device. Wherein, when said was estimated to be the strong flow by the flow estimating unit, according to claim 1 or 2 fuel from said fuel injection valve and controlling timing the advance to be injected Internal combustion engine control device. 4. The control unit according to claim 1, wherein, when the strong flow is estimated by the flow estimation unit, the timing at which the spark plug generates the discharge is retarded . 5. 2. The control device for an internal combustion engine according to claim 1 . The control unit, when the strong flow is estimated by the flow estimating unit, stops the discharge generated in the spark plug, and after a predetermined time has elapsed, re-discharges the spark plug. The control device for an internal combustion engine according to claim 1 , wherein the control device generates the control signal.   When the re-discharge is generated in the ignition plug, the control unit performs control so that a secondary current that is larger than a secondary current that flows to the ignition plug at the time of the stopped discharge flows. A control device for an internal combustion engine according to claim 5. Wherein, when said was estimated to be the weak fluidized by the flow estimating unit, according to any one of claims 1 to 6, characterized in that to reduce the secondary current flowing in the spark plug Internal combustion engine control device. Wherein, when said was estimated to be the weak fluidized by the flow estimating unit, according to any one of claims 1 to 7, characterized in that extending the discharge period to the advance side Control device for internal combustion engine. When the flow estimating unit estimates that the fluid flow is an intermediate flow between a strong strong flow and a weak weak flow, a discharge as a period for discharging by the spark plug is performed. The internal combustion engine according to any one of claims 1 to 8 , wherein a period is set shorter than any of the discharge period set at the time of the strong flow and the discharge period set at the time of the weak flow. Engine control device. The controller, when the flow estimating unit estimates that the fluid flow is an intermediate flow between a strong strong flow and a weak weak flow, a secondary current flowing through the spark plug, wherein the strong lower than the secondary current applied to the spark plug at the time of flow, any one of claims 1 to 9, characterized in that said set higher than the secondary current applied to the spark plug at the time of the weak flow 3. The control device for an internal combustion engine according to claim 1. The flow estimating unit may divide the operating region of the internal combustion engine into a plurality of regions, and estimate a magnitude of the fluid flow generated by the injection of fuel from the fuel injector for each of the divided regions. The control device for an internal combustion engine according to any one of claims 1 to 10 , characterized in that: The internal combustion engine is controlled to operate in a lean mode in which the air-fuel mixture is burned in a state in which the air is excessive than the stoichiometric air-fuel ratio depending on the operating condition,
The flow estimation unit according to any one of claims 1 to 11 , wherein the flow estimation unit estimates the magnitude of the fluid flow generated by injecting fuel from the fuel injection valve each time the lean mode is set. 2. The control device for an internal combustion engine according to claim 1.