JP2017106371A - Internal combustion engine control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an internal combustion engine control device capable of curbing degradation of a fuel combustion state due to a positional relation between a fuel spray injected by a fuel injection valve and electric discharge generated by an ignition plug.SOLUTION: A control device (32) applied to an internal combustion engine (11) mounted with a fuel injection valve (18) and an ignition plug (19) comprises: an injection section which injects fuel with the fuel injection valve; an electric characteristic detection section which detects an electric characteristic of electric energy put into the ignition valve after the injection section starts fuel injection; a flux estimation section which estimates intensity of fluid flux around the ignition plug generated by the fuel injection through the fuel injection valve on the basis of the detected electric characteristic; and a control section which controls at least either an injection state or an electric discharge state in a manner that improves a fuel combustion state on the basis of the estimated intensity of the fluid flux.SELECTED DRAWING: Figure 1

Description

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

  In a direct injection 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 disposed so as to inject fuel downward from a substantially upper center of the combustion chamber into the fuel chamber. It has been known. In this spray guide type in-cylinder internal combustion engine, the ground electrode protruding into the spray range from the tip of the spark plug becomes an obstacle that blocks a part of the spray. Therefore, when the orientation of the ground electrode changes, the influence of spray shielding 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, a partially rich mixture is formed in the vicinity of the spark plug to ignite, so when the spray formation state changes depending on the orientation of the ground electrode, The formation state of the air-fuel mixture in the vicinity of the spark plug changes, and in some cases, the combustion state may deteriorate.

  Therefore, in the technique disclosed in Patent Document 1, when the combustion mode is the stratified combustion mode or the weak stratified combustion mode and the deterioration of the combustion state of the cylinder is detected, the fuel injection state (execution of split injection) is performed. And the injection start timing) and the discharge state of the spark plug (total discharge period, etc.) are controlled to improve the combustion state of the fuel.

JP 2009-24682 A

  In the technique disclosed in Patent Document 1, fuel combustion deterioration caused by excessive fuel spray injected by the fuel injection valve coming into contact with the spark plug, and fuel injection caused by the fuel spray not reaching the spark plug. The combustion state of the fuel is uniformly improved without distinguishing from the deterioration of combustion. However, the fuel combustion deterioration caused by excessive contact of the fuel spray injected by the fuel injection valve with the spark plug and the fuel combustion deterioration caused by the fuel spray not reaching the spark plug The improvement method is different. For this reason, in the technique disclosed in Patent Document 1, depending on the positional relationship between the spray of fuel injected by the fuel injection valve and the discharge generated by the spark plug, the effect of improving the combustion state of the fuel may be reduced. .

  The present invention has been made to solve the above-mentioned problems, and its main purpose is to burn the fuel due to the positional relationship between the fuel spray injected by the fuel injection valve and the discharge generated by the spark plug. An object of the present invention is to provide a control device for an internal combustion engine capable of suppressing deterioration of the 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 an ignition plug that discharges between electrodes in the combustion chamber, wherein discharge is performed by the ignition plug. An injection unit that injects the fuel by the fuel injection valve within a predetermined period including a start timing, and an electric characteristic of electric energy that is input to the spark plug after the fuel injection is started by the injection unit And estimating the strength of fluid flow in the vicinity of the spark plug generated by the fuel injection from the fuel injection valve based on the electrical characteristics detected by the electrical characteristics detection section and the electrical characteristics detected by the electrical characteristics detection section Based on the flow estimation unit and the strength of the fluid flow estimated by the flow estimation unit, an injection state in which fuel is injected by the fuel injection valve and the spark plug 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 fuel spray 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 where the spray of fuel injected from the fuel injection valve is away from the discharge generated by the spark plug becomes longer, and the fuel and the discharge can be satisfactorily in contact within the discharge period. However, the fuel may cause incomplete combustion or, in the worst case, misfire.

  In preparation for these cases, the present control device is provided with a flow estimation unit, and based on the electrical characteristics detected by the electrical property detection unit, the fluid in the combustion chamber generated by the fuel injection from the fuel injection valve The strength of the flow is estimated. Based on the estimated fluid flow strength, at least one of the injection state in which fuel is injected by the fuel injection valve and the discharge state in which discharge is performed by the spark plug is controlled by the control unit in a direction in which the combustion state of the fuel is improved. Is done. Since the positional relationship between the fuel spray injected by the fuel injection valve and the discharge generated by the spark plug can be inferred from the strength of the fluid flow, it corresponds to the positional relationship between the fuel spray and the discharge generated by the spark plug. Control can be performed. For this reason, it becomes possible to suppress the deterioration of the combustion state of the fuel due to 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 injection start time, the discharge period, and the magnitude | size of an electric current according to the strength of fluid flow. It is a control flowchart performed by the electronic control unit which concerns on this embodiment. It is a figure which shows the secondary voltage which changes when the spray of fuel and discharge contact according to the strength of fluid flow. It is a figure which shows the effect acquired by implementing this control when it is strong flow. It is a figure which shows the effect acquired by implementing this control when it is weak flow.

  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 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 the 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 part including the injector 18 and the ignition circuit unit 31 is controlled in accordance with.

  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 an injection unit and a control unit. In addition, the electronic control unit 32 corresponds to an electrical characteristic detection unit and a flow estimation 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 311a and a secondary winding 311b), 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 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-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 a secondary voltage detection unit) 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.

  The third power supply side terminal 315C is connected to the second power supply side terminal 314D of 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 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). To implement. The lean mode operating range is set to the lower rotation and low load side than the stoichiometric mode operating range. In the lean mode, less fuel is injected directly into the cylinder in the compression stroke than the stoichiometric mode described later, and ignition is performed. A stratified mixture is formed in the vicinity of the plug 19 and ignited. 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 lean mode. Specifically, when fuel is injected by the injector 18 within a predetermined period including the timing at which the spark plug 19 generates discharge, a period (hereinafter referred to as a discharge period) determined to cause the spark plug 19 to perform continuous discharge. During continuous operation, continuous discharge is maintained. Conventionally, when such stratified combustion is performed and the combustion state of the fuel deteriorates, the fuel injection state and the state of discharge generated in the spark plug 19 (hereinafter referred to as the discharge state) are controlled. By doing so, the deterioration of the combustion state of the fuel was suppressed. The injection state refers to the execution of divided injection that divides the injection amount originally injected by one fuel injection, the injection start timing, and the like, and the discharge state refers to the secondary current that flows to the spark plug 19. This corresponds to the size, the discharge period as the period during which the spark plug 19 is generating discharge, and the like.

  By the way, when the lean mode is performed, the fuel combustion state may deteriorate due to the positional relationship between the spray of fuel injected by the injector 18 and the discharge generated by the spark plug 19. For example, if the spray of fuel injected by the injector 18 excessively contacts the discharge generated by the spark plug 19, incomplete combustion may occur due to lack of oxygen, and in the worst case, misfire may occur. The state in which the spray of fuel injected by the injector 18 is in excessive contact with the discharge generated by the spark plug 19 is that the flow of fluid (hereinafter referred to as fluid flow) caused by the injection of fuel from the injector 18 occurs. It often occurs when strong (hereinafter referred to as strong flow). In such a strong flow situation, there is a possibility that the discharge generated by the spark plug 19 may blow out in addition to the above problem. 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 when the spark plug 19 generates a discharge, the fuel spray injected by the injector 18 is still away from the spark plug 19. Such a state often occurs when the fluid flow is weak (hereinafter referred to as weak flow). Therefore, the state in which the fuel spray injected from the injector 18 is away from the discharge generated by 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, misfire.

  In the prior art, no consideration is given to the above problem, and it is difficult to take countermeasures. Therefore, the electronic control unit 32 according to the present embodiment sets a discharge state that is set every time the engine 11 is started assuming an environment in which fuel is difficult to burn (hereinafter referred to as initial setting). Specifically, as shown in FIG. 3, the secondary current that flows through the spark plug 19 is set higher than normal so that a discharge can be generated even in a strong flow. In addition, a period during which the fuel spray injected from the injector 18 is long away from the discharge generated by the spark plug 19 is long (hereinafter referred to as a discharge period). (Name) is set longer than usual. Thus, after making the fuel combustible in any situation, the magnitude of the fluid flow generated by the fuel being injected from the injector 18 is estimated, and according to the estimated fluid flow strength Then, 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 an 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 time) is advanced. Thereby, since the fuel is injected from the injector 18 at an early stage, it is assumed that when the spark plug 19 generates a discharge, the fluid flow generated by the injection of fuel from the injector 18 is weakened.

  When it is estimated that the flow is weak, the secondary current flowing through the spark plug 19 is reduced and the discharge period is extended to the advance side. The reason why the secondary current flowing through the spark plug 19 is controlled to be small is that the fluid flow is weak, so that the discharge arc (discharge plasma) generated in the spark plug 19 is less likely to blow off. However, since the flow is weak, the state where the spray of fuel injected from the injector 18 is away from the discharge arc generated by the spark plug 19 becomes longer. Accordingly, by controlling the discharge period to be advanced to the advance side, a discharge arc is generated in the spark plug 19 at an early stage, and the discharge arc is extended in an arc shape by the fluid flow generated around the spark plug 19. As a result, the extended discharge arc can be brought into contact with the spray of fuel injected from the injector 18. In addition, by extending the discharge period, the spray of fuel injected until the end of discharge 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 intermediate flow), it is less likely that the discharge will blow out than in the strong flow, and the discharge will blow out more easily than in the weak flow. is assumed. For this reason, the secondary current flowing through the spark 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. In addition, since it is assumed that the fuel spray comes into contact with the spark plug 19 at the timing at which the spark plug 19 generates a discharge, the discharge period is set to the discharge period at the initial setting and the discharge period set at the strong flow. Set it shorter than either. As a result, it is possible to minimize the energy flowing through the spark plug 19.

  In the present embodiment, correction control of the spark plug 19 shown in FIG. The correction control of the spark plug 19 shown in FIG. 4 is repeatedly executed every time one combustion cycle is performed by the electronic control unit 32 during the period when 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 load of the engine 11 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. And it progresses to step S103 and refers to the operation mode which should be performed from an operation map based on the load and rotation speed of the engine 11 which were calculated by step S102. 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. If it is determined that the current operation state is an operation state in which the lean mode should be performed (low to medium rotation speed / low to medium required torque) (S104: YES), the process proceeds to step S105.

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

  In step S106, fuel is injected into the injector 18 based on the injection start time set in step S105. Similarly, the spark plug 19 is caused to discharge based on the ignition timing set in step S105. In step S107, it is determined whether or not the fluid flow strength in the operation state similar to the current operation state has already been estimated (any one of the strong flow estimation flag, the intermediate flow estimation flag, and the weak flow estimation flag is stored). To do. When it is determined that the strength of fluid flow in an operation state similar to the current operation state has already been estimated (S107: YES), this control is terminated. If it is determined that the fluid flow strength 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 fluid flow.

  For example, in the case of strong flow, the discharge arc generated by the spark plug 19 extends in an arc shape, and the secondary voltage V2 necessary for maintaining the discharge increases in the negative direction (secondary voltage). The absolute value of V2 increases). On the other hand, in the case of weak flow, the discharge arc generated in the spark plug 19 takes time to extend in an arc shape, and the length of the discharge arc generated between the electrodes of the spark plug 19 becomes relatively short. The secondary voltage V2 decreases in the negative direction. That is, the strength of fluid flow can be estimated from the magnitude of the secondary voltage V2 applied to the spark plug 19. However, when estimating the strength of fluid flow, the second and subsequent peaks of the secondary voltage V2 are narrowed down to the determination target. This is because a large amount of energy is required during the initial discharge of the spark plug 19, so that 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, when the fuel spray comes into contact with the spark discharge generated in the spark plug 19 and the fuel is combusted, the secondary voltage V2 may increase beyond the first threshold value Vh. Limit the period of strength estimation. Therefore, the secondary voltage V2 used in the process of estimating the strength of 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.

  From the above, in the present embodiment, the processing for estimating the strength of fluid flow is as follows. As shown in the right diagram of FIG. 5, the second and subsequent peaks of the detected secondary voltage V2 become smaller than the first threshold value Vh within the first determination period (the absolute value of the peak is the first threshold value). If it becomes larger than the absolute value of Vh), it is assumed that the fluidity is high. As shown in the left diagram of FIG. 5, the second and subsequent peaks of the detected secondary voltage V2 are larger than the second threshold value Vl within the first determination period (the absolute value of the peak is the second threshold value). If it becomes smaller than the absolute value of Vl), it is assumed that the flow is low. As described in the central diagram of FIG. 5, the second and subsequent peaks of the detected secondary voltage V2 are larger than the first threshold value Vh and smaller than the second threshold value Vl within the first determination period. In some cases, it is assumed to be an intermediate flow. The second threshold value Vl is set larger than the first threshold value 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 until a predetermined time elapses after the fuel is injected. 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. Advance and control the injection start timing to an earlier timing (advance side). And it progresses to step S111, the strong fluid estimation flag which shows having estimated that it is strong fluid is memorize | stored, and this control is complete | finished.

  If it is determined that the second and subsequent peaks of the secondary voltage V2 are greater 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. When it is determined that the second and subsequent peaks of the secondary voltage V2 have become larger than the second threshold value V1 (S112: YES), the process proceeds to step S113, the secondary current flowing through the spark plug 19 is reduced, and the discharge is performed. Extend the period to the advance side. And it progresses to step S114, the weak flow estimation flag which shows having estimated that it is weak flow is memorize | stored, and this control is complete | finished.

  When 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 be higher than that at the time of initial setting. It is set to be smaller and larger than the secondary current set at the time of weak flow. Further, the discharge period is set shorter than the initial setting and shorter than the discharge time set during the strong flow. In step S116, an intermediate flow estimation flag indicating that the intermediate flow is estimated is stored, and the present control is terminated.

  If it is determined that the current operating state is an operating state in which the lean mode should not be performed (high rotational speed and high required torque) (S104: NO), the process proceeds to step S117. In step S117, when 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, a stoichiometric (homogeneous combustion) mode is executed, and this control is terminated.

  Note that the processing content according to the fluid flow strength determined in this control is applied after the next combustion cycle as long as the lean mode continues.

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

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

  The result of actually improving the combustion state of the fuel is shown in FIG. The upper diagram of FIG. 6 shows how the combustion state of the fuel is changed by changing the timing at which the fuel is injected by the injector 18 under a situation where the fluid flow generated by the injection of the fuel from the injector 18 is strong. FIG. The combustion fluctuation rate indicated on the vertical axis in the upper diagram of FIG. 6 represents how much variation has occurred in the torque generated when the fuel is burned. Specifically, the injection rate or the like is 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. And the torque fluctuation value produced when the injected fuel combusts is calculated several 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 easily combusted (for example, in an intermediate flow environment). Then, a torque fluctuation value generated when the injected fuel burns is calculated a plurality of times (this data is 400 times), and an 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 obtained thereby corresponds to the combustion fluctuation rate.

  The upper diagram of FIG. 6 shows that the variation in torque fluctuation caused by fuel combustion is increased by controlling the injection start timing more retarded than the normal injection start timing (base injection start timing). . This is considered because the fuel is incompletely burned. On the other hand, it is shown that variation in torque fluctuation caused by fuel combustion is reduced by controlling the advance angle of the injection start timing relative to the base injection start timing. This shows that the fuel combustion state can be stabilized by advancing the fuel injection start timing.

  The lower diagram of FIG. 6 shows whether a misfire has occurred during the actual combustion of fuel in an environment of strong flow, or how the misfire occurrence rate has changed by changing the injection start timing. The lower diagram in FIG. 6 shows that misfire has occurred on the retarded side from the base injection start timing, whereas the misfire occurrence rate has been reduced to 0% by making the lead angle advance from the base injection start timing. Yes. The inventors have confirmed that the strength of the fluid flow in the vicinity of the spark plug 19 when the misfire occurrence rate becomes 0% was the strength of the fluid flow corresponding to the intermediate flow. Accordingly, when the injection start timing is advanced when it is estimated that the flow is strong, the strength of the fluid flow in the vicinity of the spark plug 19 can be reduced, so that the discharge generated by the spark plug 19 is blown off. And it is possible to stably burn the fuel.

  When the fluid flow is estimated to be weak, the secondary current flowing through the spark plug 19 is reduced. Thereby, the ignition energy at the time of generating discharge with the spark plug 19 can be saved.

  If the fluid flow is assumed to be weak, the discharge period is extended. As a result, the spray of fuel can be satisfactorily brought into contact with the discharge, and the fuel can be burned more reliably. FIG. 7 shows the result of actually improving the combustion state of the fuel for extending the discharge period. The upper diagram in FIG. 7 is a diagram showing how the combustion state of the fuel is changed by variously changing the discharge period under a situation where the fluid flow generated by the fuel injection from the injector 18 is weak. The upper diagram of FIG. 7 shows that the variation in torque fluctuation caused by burning the fuel becomes smaller as the discharge period is extended, and the combustion state of the fuel is actually improved. The lower diagram of FIG. 7 shows how the misfire occurrence rate is changed by changing the discharge period in an environment where the flow is weak. In the lower diagram of FIG. 7, it is shown that the misfire occurrence rate decreases as the discharge period is extended, and the misfire occurrence rate can be finally set to 0%.

  When it is estimated that the fluid flow is weak, the discharge period is extended to the advance side, so that the spark plug 19 is discharged early. As a result, the discharge arc is extended in a circular arc shape by the fluid flow generated around the spark plug 19, whereby the extended discharge arc can be brought into contact with the spray of fuel injected from the injector 18. It is possible to increase the frequency of contact with.

  When it is estimated that the fluid flow is an intermediate flow, the discharge period is set shorter than the discharge period set during the strong flow and the discharge period set during the weak flow. Further, the secondary current that flows through the spark plug 19 is set lower than the secondary current that flows through the spark plug 19 during strong flow and higher than the secondary current that flows through the spark plug 19 during weak flow. As a result, it is possible to minimize the secondary current necessary for generating a discharge in the spark plug 19.

  -Estimate the strength of fluid flow more accurately by determining how large the second and subsequent peaks of the secondary voltage V2 have elapsed from when fuel was injected until a predetermined time has elapsed. Is possible.

  -Every time the operation state becomes the lean mode, in the first process, the strength of the fluid flow caused by the injection of fuel from the injector 18 is estimated, and the combustion of the fuel is improved based on the strength of the fluid flow Control is performed in the direction to be performed. As a result, this control is performed particularly in the lean mode in which misfire is a concern, so that fuel misfire due to the strength of fluid flow can be suppressed.

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

  In the above embodiment, correction control is performed according to the strength of fluid flow in the lean mode. The lean mode in the above embodiment refers to the stratified combustion mode. However, the present invention is not limited to this, and even when the weak stratified combustion mode is set to the lean mode, correction control according to the strength of the fluid flow may be performed. In the weak stratified combustion mode, fuel injection is performed twice in the intake stroke and the compression stroke, but the fuel injection to be subjected to the correction control is fuel injection performed in the compression stroke. Further, not only in the lean mode but also in the stoichiometric mode, for example, correction control corresponding to the strength of the fluid flow may be performed. However, it is difficult to perform this correction control in the fuel injection in the intake stroke such as the stoichiometric mode in the above embodiment. Therefore, the target of performing 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 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 the above embodiment, the correction control is uniformly performed regardless of the operating state of the engine 11 in the state where the lean mode is being performed. In this regard, in addition to being in the lean mode, the operation region may be divided into a plurality of regions based on the required torque and the rotational speed, and correction control corresponding 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, an intermediate load / medium rotation region, and a low load / low rotation region, and the strength of 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 discharge, the fluid flow in the vicinity of the spark plug 19 is weakened. Therefore, it is possible to suppress blow-off of the discharge generated in the spark plug 19.

  In the above embodiment, when it is estimated that the flow is weak, the secondary current flowing through the spark plug 19 is reduced. In this regard, it is not always necessary to reduce the secondary current that flows through the spark plug 19 during weak flow.

  -In the said embodiment, when it was estimated that it was an intermediate flow, the discharge period was set shorter than both the discharge period set at the time of strong flow, and the discharge period set at the time of weak flow. In this regard, it is not always necessary to set the discharge period set during the intermediate flow shorter than the discharge period set during the strong flow and the discharge period set during the weak flow. For example, you may set longer than the discharge period set at the time of weak flow.

  In the above embodiment, when it is estimated that the flow is intermediate, the secondary current that flows through the spark plug 19 is lower than the secondary current that flows through the spark plug 19 during strong flow and flows through the spark plug 19 during weak flow. It was set higher than the secondary current. This need not be the above setting. However, if the current is set lower than the secondary current that flows through the spark plug 19 during weak flow, the discharge generated in the spark plug 19 may be blown out. Therefore, the secondary current is limited to be set high. Specifically, it may be set higher than the secondary current that flows through the spark plug 19 during strong flow.

  In the above-described embodiment, the processing content determined at the time of correction control (for example, when it is estimated that strong flow is assumed, the injection start timing is controlled to advance) is applied after the next combustion cycle. It was going to be. About this, you may implement the process according to the strength of the fluid flow estimated from the present combustion cycle. However, when the processing according to the strength of the fluid flow is performed from the current combustion cycle, the fuel has already been injected from the injector 18 and the spark plug 19 has been discharged, so the correction control in the above embodiment is performed. May not be appropriate. Therefore, the processing content corresponding to the strength of fluid flow is changed.

  Specifically, when it is estimated that the flow is strong, the current discharge generated by the spark plug 19 is stopped, and the discharge is started again after a predetermined time has elapsed. As a result, it is possible to obtain the same effect as the above-described another example in which the discharge start timing is delayed. If it is estimated that the flow is weak, the secondary current is attenuated over time, and the discharge period is extended to the retard side. Thereby, the energy flowing through the spark plug 19 can be suppressed to a low level, and the chance of the fuel spray contacting the discharge can be increased by extending the discharge period. When it is estimated that the flow is intermediate, the secondary current is attenuated with the passage of time, and the timing for terminating the discharge is advanced. As a result, the discharge can be terminated early, so that it is not necessary to put excessive energy into the spark plug 19.

  In this other example, when it was estimated that the fluid flow was strong, the current discharge generated in the spark plug 19 was stopped, and the discharge was started again after a predetermined time had elapsed. With regard to this, in consideration of the possibility that the fluid flow around the spark plug 19 is still strong when the spark plug 19 is caused to discharge again, when the discharge is discharged again, A secondary current larger than the secondary current may be passed. Thereby, it is possible to suppress the discharge of the discharge due to the fluid flow, and it is possible to more reliably maintain the discharge generated by the spark plug 19.

  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 continuous discharge, a discharge period is provided, and the discharge is terminated after the discharge period has elapsed. When performing multiple discharge, 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 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 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 values of the first threshold value Vh and the second threshold value Vl are also used for comparison determination.

  In the above embodiment, when the second and subsequent peaks of the secondary voltage V2 detected by the voltage detection path L2 are 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 are larger than the second threshold value V1, it has been estimated that the flow is low. Then, when the second and subsequent peaks of the secondary voltage V2 detected by the voltage detection path L2 are larger than the first threshold value Vh and larger than the second threshold value Vl, it is estimated that the flow is intermediate. Was.

  The method for estimating the strength of 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 change amount (for example, slope) of the secondary voltage V2 in the determination period is larger than the first predetermined change amount, 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 continuously increases. 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, when the absolute value of the change amount of the secondary voltage V2 within 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 within the second determination period, and the secondary voltage V2 does not change so much that it exceeds the second predetermined change amount. Further, if the absolute value of the change amount of the secondary voltage V2 within the second determination period is smaller than the first predetermined change amount and larger than the second predetermined change amount, it is assumed that the flow is intermediate. Also good. In the case of an intermediate flow, it is assumed that the injected fuel is in contact with the discharge, but the contact frequency is not as excessive as the strong flow. For this reason, the absolute value of the change amount of the secondary voltage V2 is smaller than the first predetermined change amount and larger than the second predetermined change amount because the fuel spray is in contact with the discharge.

  Thus, 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 within the second determination period.

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

Claims (15)

A fuel injection valve (18) for directly injecting fuel into the combustion chamber (11b);
A spark plug (19) for discharging between the electrodes in the combustion chamber;
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 of starting discharge by the spark plug;
An electrical property detection unit for detecting electrical properties of electrical energy input to the spark plug after the fuel injection is started by the injection unit;
Based on the electrical characteristics detected by the electrical characteristic detection unit, a flow estimation unit that estimates the strength of fluid flow in the vicinity of the spark plug generated by fuel being injected from the fuel injection valve;
Based on the strength of the fluid flow estimated by the flow estimation unit, the fuel combustion state improves at least one of an injection state in which fuel is injected by the fuel injection valve and a discharge state in which discharge is performed by the spark plug. A control unit for controlling the direction,
A control device for an internal combustion engine, comprising:   When the flow estimation unit estimates that the fluid flow is a strong strong flow, the control unit is configured to discharge the discharge state with the spark plug when the strong flow is weakened. 2. The control device for an internal combustion engine according to claim 1, wherein at least one of the two is controlled.   3. The internal combustion engine according to claim 2, wherein when the flow estimation unit estimates that the flow is strong, the control unit controls advance of a timing at which fuel is injected from the fuel injection valve. Engine control device.   4. The control unit according to claim 2, wherein when the flow estimation unit estimates that the strong flow is generated, the control unit performs a delay control on a timing at which the spark plug generates the discharge. 5. Control device for internal combustion engine.   When the flow estimation unit estimates that the flow is strong, the control 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 2, wherein the control device is generated.   The control unit performs control so that when the re-discharge is generated in the spark plug, a secondary current larger than a secondary current passed through the spark plug during the stopped discharge flows. The control device for an internal combustion engine according to claim 5.   The control unit extends a discharge period as a period for discharging by the spark plug when the flow estimation unit estimates that the fluid flow is weak and weak. The control device for an internal combustion engine according to any one of the above.   8. The control device for an internal combustion engine according to claim 7, wherein the control unit reduces a secondary current that flows through the spark plug when the flow estimation unit estimates that the flow is weak.   9. The control device for an internal combustion engine according to claim 7, wherein the control unit extends the discharge period to an advance side when the flow estimation unit estimates that the flow is weak. 9. .   When the flow estimation unit estimates that the fluid flow is an intermediate flow between a strong flow where the fluid flow is strong and a weak flow where the fluid flow is weak, discharge as a period for discharging by the spark plug 10. The internal combustion engine according to claim 1, wherein the period is set shorter than both the discharge period set during the strong flow and the discharge period set during the weak flow. Engine control device.   The control unit, when the flow estimation unit is inferred that the fluid flow is an intermediate flow between a strong flow and a weak flow, the secondary current that flows to the spark plug, 11. The method according to claim 1, wherein the current is set to be lower than the secondary current that flows through the spark plug during the strong flow and higher than the secondary current that flows through the spark plug during the weak flow. The control apparatus of the internal combustion engine described in 1. The internal combustion engine includes a secondary voltage detector (L2) that detects a secondary voltage applied to the spark plug,
The electrical characteristic detection unit acquires the secondary voltage detected by the secondary voltage detection unit,
The flow estimation unit has an absolute value of a peak after the second time of the secondary voltage acquired by the electrical characteristic detection unit within a first determination period after the fuel is injected into the fuel injection valve by the injection unit. When larger than the first threshold, it is estimated that the fluid flow is a strong strong flow, and after the fuel is injected into the fuel injection valve by the injection unit, the electrical characteristic detection unit within the first determination period. When the absolute value of the second and subsequent peaks of the acquired secondary voltage is smaller than a second threshold set smaller than the first threshold, it is estimated that the fluid flow is weak and weak. The control apparatus for an internal combustion engine according to any one of claims 1 to 11. The internal combustion engine includes a secondary voltage detector (L2) that detects a secondary voltage applied to the spark plug,
The electrical characteristic detection unit acquires the secondary voltage detected by the secondary voltage detection unit,
The flow estimation unit is a strong flow having a strong fluid flow when an absolute value of a change amount of the secondary voltage acquired by the electrical characteristic detection unit within a second determination period is larger than a first predetermined change amount. And the second predetermined change amount in which the absolute value of the change amount of the secondary voltage acquired by the electrical characteristic detection unit within the second determination period is set smaller than the first predetermined change amount. The control device for an internal combustion engine according to any one of claims 1 to 12, wherein the fluid flow is estimated to be a weak weak flow when the flow rate is smaller than a predetermined value.   The flow estimation unit divides the operation region of the internal combustion engine into a plurality of regions, and estimates the magnitude of the fluid flow generated by fuel injection from the fuel injection valve for each of the divided regions. The control device for an internal combustion engine according to any one of claims 1 to 13. The internal combustion engine is controlled to operate in a lean mode in which the air-fuel mixture is combusted in an air-excess state than the stoichiometric air-fuel ratio according to operating conditions.
The flow estimation unit estimates the magnitude of the fluid flow generated by fuel injection from the fuel injection valve every time the lean mode is set. The control device for an internal combustion engine according to claim 1.