JP2018096215A - Control device for internal combustion engine - Google Patents

Abstract

Even when an ozone supply device fails, an increase in combustion noise is suppressed while suppressing the occurrence of misfire and the like. A control device for an internal combustion engine includes a control unit that controls a fuel injection valve 31, a spark plug 16, and an ozone supply device. The controller sequentially injects the main fuel and the ignition assist fuel from the fuel injection valve, and causes the air-fuel mixture formed by the injection of the ignition assist fuel to be flame-propagated and combusted by the spark plug, and the remaining fuel is premixed. Compressive self-ignition combustion. In addition, when it is determined by the failure diagnosis unit that the ozone supply device has failed and the engine operating state is within the ozone supply region, and the combustion stability is low, the injection timing and ignition timing of the ignition assist fuel are low. Is advanced and the injection ratio of the ignition assist fuel is increased. When the combustion noise is large, the injection ratio of the ignition assist fuel is increased and the injection timing and ignition timing of the ignition assist fuel are not changed. [Selection] Figure 16

Description

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

  Conventionally, an internal combustion engine that performs premixed compression auto-ignition combustion is known. In such an internal combustion engine, it has been proposed to supply ozone into the combustion chamber in order to achieve stable self-ignition of the air-fuel mixture.

  Further, in such an internal combustion engine, when the ozone supply device that supplies ozone into the combustion chamber fails, the self-ignition of the air-fuel mixture in the combustion chamber does not occur stably, resulting in a decrease in thermal efficiency or misfire. Thus, it has been proposed that when the ozone supply device fails, the target air-fuel ratio is changed to the rich side in order to maintain premixed compression self-ignition combustion (for example, Patent Document 1).

JP 2014-169664 A JP 2007-263065 A

  By the way, in order to reduce the combustion noise in the premixed compression auto-ignition combustion, it has been proposed to supply ozone from the ozone supply device to the combustion chamber. As a specific method, for example, ozone is supplied into the combustion chamber in a layered manner. As a result, the air-fuel mixture self-ignites early in the region where the ozone concentration is high, and the air-fuel mixture self-ignites later in the region where the ozone concentration is low, so the self-ignition timing of the air-fuel mixture in the combustion chamber is dispersed, As a result, combustion noise is reduced.

  On the other hand, when the ozone supply device fails, the self-ignition timing of the air-fuel mixture in the combustion chamber is not dispersed and combustion noise increases. Moreover, even if the target air-fuel ratio is changed to the rich side at the time of failure of the ozone supply device as in Patent Document 1, the auto-ignition timing is not dispersed, and thus increase in combustion noise cannot be suppressed.

  The present invention has been made in view of such a problem, and an object thereof is to suppress an increase in combustion noise while suppressing the occurrence of misfire or the like even when the ozone supply device fails. An object of the present invention is to provide a control device for an internal combustion engine.

  The present invention has been made to solve the above problems, and the gist thereof is as follows.

  (1) A fuel injection valve that directly injects fuel into the combustion chamber, an ignition plug that ignites an air-fuel mixture in the combustion chamber, and an ozone supply device that supplies ozone directly or indirectly into the combustion chamber. A control device for an internal combustion engine for controlling the internal combustion engine, the combustion stability detection unit detecting a parameter value representing combustion stability, a combustion noise detection unit detecting a parameter value representing combustion noise, A failure diagnosis unit that performs failure diagnosis of the ozone supply device; and a control unit that controls the fuel injection valve, the spark plug, and the ozone supply device, wherein the control unit injects main fuel from the fuel injection valve. And the ignition assist fuel are sequentially injected, and the air-fuel mixture formed by the injection of the ignition assist fuel is flame-propelled and combusted by the spark plug and generated by the flame-propagation combustion. It is possible to execute ignition assist control for controlling the injection amount and injection timing of the main fuel and the ignition assist fuel and the ignition timing by the spark plug so that the remaining fuel is premixed compression self-ignition combustion using the generated heat. The control unit supplies ozone from the ozone supply device when the engine operating state is within a predetermined ozone supply region, and the control unit determines that the ozone supply device has failed by the failure diagnosis unit. When the engine operating state is within the ozone supply region, the value of the parameter representing the combustion stability detected by the combustion stability detector is a value on the unstable side of the predetermined first threshold value. Sometimes, the injection timing of the ignition assist fuel and the ignition timing are advanced and the total fuel injection is performed as compared with the case where the value is more stable than the first threshold value. The ratio of the injection amount of the ignition assist fuel with respect to the engine is increased, and the control unit determines that the ozone supply device has failed by the failure diagnosis unit and the engine operating state is within the ozone supply region. Is a value on the side where the noise is smaller than the second threshold when the value of the parameter representing the combustion noise detected by the combustion noise detector is a value on the side where the noise is larger than the predetermined second threshold The control device for an internal combustion engine, which increases the ratio of the injection amount of the ignition assist fuel to the total fuel injection amount and does not change the injection timing and the ignition timing of the ignition assist fuel.

  ADVANTAGE OF THE INVENTION According to this invention, even when an ozone supply apparatus fails, the control apparatus of the internal combustion engine which can suppress the increase in combustion noise, suppressing generation | occurrence | production of misfire etc. is provided.

FIG. 1 is a schematic view of an entire internal combustion engine according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of the engine body. 3A, 3B, and 3C are schematic views of a cylinder of the internal combustion engine as viewed from the cylinder head side. FIG. 4 is a diagram illustrating an operation region in which operation in each operation mode is performed. 5A and 5B are diagrams showing changes in lift amounts of the intake valve and the exhaust valve. FIG. 6 is a diagram showing the relationship between the crank angle, the fuel injection amount, the ignition timing, and the heat generation rate when the ignition assist is performed and the premixed gas is subjected to compression self-ignition combustion. FIG. 7 is a diagram showing the relationship between the crank angle and the heat generation rate when ozone is supplied so that a concentration difference is spatially generated in the combustion chamber. FIG. 8 is a flowchart showing a control routine of basic combustion control with ozone supply from the ozone supply device. FIG. 9 is a diagram showing the relationship between the crank angle and the heat generation rate when the ozone supply device fails. FIG. 10 is a diagram showing the relationship between the crank angle and the heat generation rate when the combustion noise cannot be sufficiently reduced due to the failure of the ozone supply device. FIG. 11 is a diagram showing the relationship between the crank angle and the heat generation rate in the case where the premixed gas misfires without causing compression autoignition combustion due to a failure of the ozone supply device. FIG. 12 is a diagram illustrating a relationship between ΔCOV obtained by subtracting the first threshold value from the COEP value of IMEP and the advance side correction amount of the ignition timing and ignition timing of the ignition assist fuel. FIG. 13 is a diagram illustrating a relationship between ΔCOV obtained by subtracting the first threshold value from the COEP value of IMEP and the increase correction amount of the ignition assist injection ratio. FIG. 14 is a diagram illustrating a relationship between ΔCNL obtained by subtracting the second threshold value from the CNL value and the increase correction amount of the ignition assist injection ratio. FIG. 15 is a flowchart showing a control routine for correction control of the ignition assist fuel injection amount, injection timing, and ignition timing. FIG. 16 is a flowchart showing a control routine of control at the time of failure that is performed when the ozone supply device is out of order. FIG. 17 is a flowchart illustrating a control routine for normal control that is performed when the ozone supply device is operating normally without a failure.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, the same reference numerals are assigned to similar components.

≪Description of the internal combustion engine as a whole≫
First, a configuration of an internal combustion engine 1 in which a control device according to an embodiment of the present invention is used will be described with reference to FIGS. 1 to 3A. FIG. 1 is a schematic configuration diagram of an internal combustion engine 1 using gasoline as fuel. FIG. 2 is a schematic cross-sectional view of the engine body 10 of the internal combustion engine 1. FIG. 3A is a schematic perspective view of the cylinder 11 as viewed from the cylinder head side.

  As shown in FIGS. 1 and 2, the internal combustion engine 1 includes an engine body 10, a variable valve mechanism 20, a fuel supply device 30, an intake system 40, an exhaust system 50, an EGR mechanism 60, and a control device 70.

  The engine body 10 includes a cylinder block 12 in which a plurality of cylinders 11 are formed, and a cylinder head 13. A piston 14 that reciprocates in each cylinder 11 is disposed in each cylinder 11. A combustion chamber 15 in which the air-fuel mixture burns is formed in the cylinder 11 between the piston 14 and the cylinder head 13. The cylinder head 13 is provided with an ignition plug 16 for igniting the air-fuel mixture in the combustion chamber 15 near the center of each cylinder 11.

  An intake port 17 and an exhaust port 18 are formed in the cylinder head 13. The intake port 17 and the exhaust port 18 communicate with the combustion chamber 15 of each cylinder 11. An intake valve 21 is disposed between the combustion chamber 15 and the intake port 17, and the intake valve 21 opens and closes the intake port 17. Similarly, an exhaust valve 22 is disposed between the combustion chamber 15 and the exhaust port 18, and the exhaust valve 22 opens and closes the exhaust port 18.

  The variable valve mechanism 20 includes an intake variable valve mechanism 23 that opens and closes an intake valve 21 of each cylinder, and an exhaust variable valve mechanism 24 that opens and closes an exhaust valve 22 of each cylinder. The intake variable valve mechanism 23 can control the opening timing, closing timing, and lift amount of the intake valve 21. Similarly, the exhaust variable valve mechanism 24 can control the opening timing, closing timing, and lift amount of the exhaust valve 22. These variable valve mechanisms 23 and 24 are configured to change the valve opening timing and the like by opening and closing the intake valve 21 and the exhaust valve 22 by an electromagnetic actuator. Alternatively, the variable valve mechanisms 23 and 24 are configured to change the valve opening timing or the like by changing the relative phase of the camshaft with respect to the crankshaft or changing the cam profile by hydraulic pressure or the like. Also good.

  The fuel supply device 30 includes a fuel injection valve 31, a delivery pipe 32, a fuel supply pipe 33, a fuel pump 34, and a fuel tank 35. The fuel injection valve 31 is disposed in the cylinder head 13 so as to inject fuel directly into the combustion chamber 15 of each cylinder 11. In particular, in the present embodiment, the fuel injection valve 31 is disposed adjacent to the ignition plug 16 so that the electrode portion of the ignition plug 16 is located in or near the fuel injection region X from the fuel injection valve 31. It is arranged near the center.

  The fuel injection valve 31 is connected to a fuel tank 35 via a delivery pipe 32 and a fuel supply pipe 33. A fuel pump 34 that pumps the fuel in the fuel tank 35 is disposed in the fuel supply pipe 33. The fuel pumped by the fuel pump 34 is supplied to the delivery pipe 32 via the fuel supply pipe 33 and is directly injected into the combustion chamber 15 from the fuel injection valve 31 as the fuel injection valve 31 is opened. The

  The intake system 40 includes an intake branch pipe 41, a surge tank 42, an intake pipe 43, an air cleaner 44, a compressor 5a of the exhaust turbocharger 5, an intercooler 45, and a throttle valve 46. The intake port 17 of each cylinder 11 communicates with a surge tank 42 via a corresponding intake branch pipe 41, and the surge tank 42 communicates with an air cleaner 44 via an intake pipe 43. The intake pipe 43 is provided with a compressor 5a of an exhaust turbocharger 5 that compresses and discharges intake air flowing through the intake pipe 43, and an intercooler 45 that cools the air compressed by the compressor 5a. The intercooler 45 is disposed on the downstream side of the compressor 5a in the flow direction of the intake air. The throttle valve 46 is disposed in the intake pipe 43 between the intercooler 45 and the surge tank 42. The throttle valve 46 is rotated by a throttle valve drive actuator 47, whereby the opening area of the intake passage can be changed. The intake port 17, the intake branch pipe 41, the surge tank 42, and the intake pipe 43 form an intake passage that supplies intake gas to the combustion chamber 15.

  The exhaust system 50 includes an exhaust manifold 51, an exhaust pipe 52, a turbine 5 b of the exhaust turbocharger 5, and an exhaust aftertreatment device 53. The exhaust port 18 of each cylinder 11 communicates with an exhaust manifold 51, and the exhaust manifold 51 communicates with an exhaust pipe 52. The exhaust pipe 52 is provided with a turbine 5 b of the exhaust turbocharger 5. The turbine 5b is driven to rotate by the energy of the exhaust gas. The compressor 5a of the exhaust turbocharger 5 and the turbine 5b are connected by a rotating shaft. When the turbine 5b is driven to rotate, the compressor 5a rotates with this, and the intake air is compressed. The exhaust pipe 52 is provided with an exhaust aftertreatment device 53 on the downstream side in the exhaust flow direction of the turbine 5b. The exhaust aftertreatment device 53 is a device for purifying exhaust gas and discharging it into the outside air, and includes various exhaust purification catalysts for purifying harmful substances, filters for collecting harmful substances, and the like. The exhaust port 18, the exhaust manifold 51, and the exhaust pipe 52 form an exhaust passage for exhausting exhaust gas from the combustion chamber 15.

  The EGR mechanism 60 includes an EGR pipe 61, an EGR control valve 62, and an EGR cooler 63. The EGR pipe 61 is connected to the exhaust manifold 51 and the surge tank 42 so as to communicate with each other. The EGR pipe 61 is provided with an EGR cooler 63 that cools the EGR gas flowing in the EGR pipe 61. In addition, the EGR pipe 61 is provided with an EGR control valve 62 that can change the opening area of the EGR passage formed by the EGR pipe 61. By controlling the opening degree of the EGR control valve 62, the flow rate of the EGR gas recirculated from the exhaust manifold 51 to the surge tank 42 is adjusted.

  The control device 70 includes an electronic control unit (ECU) 71 and various sensors. The ECU 71 is composed of a digital computer, and is connected to each other via a bidirectional bus 72, a RAM (random access memory) 73, a ROM (read only memory) 74, a CPU (microprocessor) 75, an input port 76, and An output port 77 is provided.

  The cylinder head 13 is provided with an in-cylinder pressure sensor 81 for detecting the pressure in each cylinder 11 (in-cylinder pressure). Further, the delivery pipe 32 is provided with a fuel pressure sensor 82 for detecting the pressure of fuel in the delivery pipe 32, that is, the pressure (injection pressure) of fuel injected from the fuel injection valve 31 into the cylinder 11. . The intake pipe 43 is provided with an air flow meter 83 for detecting the flow rate of the air flowing through the intake pipe 43 on the upstream side of the compressor 5a of the exhaust turbocharger 5 in the intake flow direction. The throttle valve 46 is provided with a throttle opening sensor 84 for detecting the opening (throttle opening). In addition, the surge tank 42 is provided with an intake pressure sensor 85 for detecting the pressure of the intake gas in the surge tank 42, that is, the pressure (intake pressure) of the intake gas sucked into the cylinder 11. Further, the surge tank 42 is provided with an intake air temperature sensor 86 for detecting the temperature of the intake gas in the surge tank 42, that is, the temperature of the intake gas sucked into the cylinder 11 (intake air temperature). The outputs of the in-cylinder pressure sensor 81, the fuel pressure sensor 82, the air flow meter 83, the throttle opening sensor 84, the intake pressure sensor 85, and the intake air temperature sensor 86 are input to the input port 76 via the corresponding AD converter 78. .

  A load sensor 88 that generates an output voltage proportional to the amount of depression of the accelerator pedal 87 is connected to the accelerator pedal 87, and the output voltage of the load sensor 88 is input to the input port 76 via the corresponding AD converter 78. The Therefore, in this embodiment, the depression amount of the accelerator pedal 87 is used as the engine load. The crank angle sensor 89 generates an output pulse every time the crankshaft of the engine body 10 rotates, for example, 15 degrees, and this output pulse is input to the input port 76. The CPU 75 calculates the engine speed from the output pulse of the crank angle sensor 89.

  On the other hand, the output port 77 of the ECU 71 is connected to each actuator that controls the operation of the internal combustion engine 1 via a corresponding drive circuit 79. In the example shown in FIGS. 1 and 2, the output port 77 includes the spark plug 16, the intake variable valve mechanism 23, the exhaust variable valve mechanism 24, the fuel injection valve 31, the fuel pump 34, the throttle valve drive actuator 47, and The EGR control valve 62 is connected. The ECU 71 outputs a control signal for controlling these actuators from the output port 77 to control the operation of the internal combustion engine 1.

≪Explanation of ozone supply device≫
In addition, the internal combustion engine 1 according to the present embodiment includes a discharge plug 91 provided in the cylinder head 13 as shown in FIGS. 1 and 3A. One discharge plug 91 is provided in each cylinder 11 so as to face the combustion chamber 15 of each cylinder 11, and oxygen in the combustion chamber 15 is converted into ozone by discharge (silent discharge, corona discharge, streamer discharge, etc.). And ozone is supplied into the combustion chamber 15. Therefore, the discharge plug 91 functions as an ozone supply device that supplies ozone into the combustion chamber 15. The discharge plug 91 is connected to an output port 77 of the ECU 71 via a corresponding drive circuit 79. Therefore, the discharge plug 91 is controlled by the ECU 71.

  In the present embodiment, as shown in FIG. 3A, the discharge plug 91 is arranged with a bias with respect to the center of the cylinder 11. In addition, the discharge plug 91 has an opening (hereinafter referred to as a “combustion chamber opening”) 17a of one of the two intake ports 17 communicating with the combustion chamber 15 of each cylinder 11 to the combustion chamber 15. And the combustion chamber opening 18a of one of the two exhaust ports 18 communicating with the combustion chamber 15 of each cylinder 11 (an exhaust port disposed on the side corresponding to the one intake port). Has been placed. In the present embodiment, the intake gas sucked from one combustion chamber opening 17a of the intake port 17 and the intake gas sucked from the other combustion chamber opening 17b are difficult to mix in the combustion chamber 15. In addition, an intake port 17 is formed so that the intake gas sucked from the combustion chamber openings 17 a and 17 b causes a tumble flow in the combustion chamber 15.

  By configuring the intake port 17 and the discharge plug 91 in this way, it is possible to cause a spatial concentration difference in the combustion chamber 15 to the ozone supplied by the discharge plug 91. That is, when ozone is generated during the intake stroke by the discharge plug 91, the intake gas (intake gas present in the region on the right side of the cylinder 11 in FIG. 3A) sucked from one combustion chamber opening 17a of the intake port 17 is contained. The ozone concentration can be made higher than the ozone concentration in the intake gas sucked from the other combustion chamber opening 17b of the intake port 17 (intake gas existing in the left region of the cylinder 11 in FIG. 3A).

  In addition, the method of supplying ozone so that a density | concentration difference may produce spatially in the combustion chamber 15 is not restricted to the method as mentioned above. For example, as shown in FIG. 3B, two intake airs communicating with the combustion chamber 15 of each cylinder 11 so that ozone is contained in the intake gas mainly sucked into the combustion chamber 15 from one combustion chamber opening 17a. The discharge plug 91 may be provided only in one intake port of the ports 17. Further, as shown in FIG. 3C, the combustion chamber 15 of each cylinder 11 is filled with ozone so that the intake gas sucked into the combustion chamber 15 from both of the combustion chamber openings 17a and the combustion chamber openings 17b is contained. One discharge plug 91 may be provided for each of the two intake ports 17 that communicate with each other, and the amount of ozone generated by each discharge plug 91 may be varied.

  Although not shown, the ozone supply device may be configured to inject ozone generated in advance into the combustion chamber 15 or the intake port 17 by an ozone injection valve or the like. Also in this case, ozone is injected from the ozone injection valve so that a concentration difference spatially occurs in the combustion chamber 15. In any case, the ozone supply device may be configured in any manner as long as ozone can be supplied directly or indirectly into the combustion chamber.

≪Explanation of control device functions≫
Next, functions of the control device 70 configured as described above will be described. The control device 70 includes a combustion stability detection unit, a combustion noise detection unit, a failure diagnosis unit, and a control unit.

The combustion stability detection unit detects a parameter value representing the combustion stability of the air-fuel mixture in the combustion chamber 15. In the present embodiment, the combustion stability detector is configured by the in-cylinder pressure sensor 81 and the ECU 71. Specifically, in this embodiment, the combustion stability detection unit calculates an indicated mean effective pressure (hereinafter referred to as “IMEP”) based on the in-cylinder pressure detected by the in-cylinder pressure sensor 81. In addition, a COV (Coefficient of Variance) is calculated as the calculated IMEP variation rate. The COV is calculated based on, for example, the following formula (1) from the standard deviation σ of IMEP in a plurality of cycles and the average value μ of IMEP in the plurality of cycles.
COV = σ / μ × 100 [%] (1)

  The COV calculated in this way indicates the combustion stability of the air-fuel mixture, and the smaller the value of COV, the higher the combustion stability. Therefore, when the value of COV is smaller than a predetermined threshold (for example, 3%), it can be said that the value of COV is a value on the stable side with respect to the predetermined threshold. In this case, if the threshold value is set appropriately, the combustion stability of the air-fuel mixture is high, and it can be said that the possibility that the air-fuel mixture does not burn and misfires is low. On the other hand, when the value of COV is larger than the predetermined threshold, it can be said that the value of COV is a value on the unstable side with respect to the predetermined threshold. In this case, if the threshold value is set appropriately, the combustion stability of the air-fuel mixture is low, and it can be said that there is a high possibility that the air-fuel mixture does not burn and misfires.

  In this embodiment, the IMEP COV calculated based on the in-cylinder pressure detected by the in-cylinder pressure sensor 81 is used as a parameter representing the combustion stability of the air-fuel mixture. However, the IMEP COV is not necessarily used as a parameter representing the combustion stability of the air-fuel mixture, and another parameter may be used. Specific examples of the other parameters include, for example, variations between cycles such as the temperature, pressure, and air-fuel ratio of the exhaust gas discharged from the combustion chamber.

  The combustion noise detection unit detects the value of a parameter representing combustion noise caused by combustion generated in the combustion chamber 15. In the present embodiment, the combustion noise detection unit is configured by the in-cylinder pressure sensor 81 and the ECU 71. Specifically, in this embodiment, the combustion noise detection unit calculates CPL (Cylinder Pressure Level) based on the in-cylinder pressure detected by the in-cylinder pressure sensor 81, and calculates the calculated CPL and the engine body 10. A combustion noise level (hereinafter referred to as “CNL”) is calculated from the structural attenuation.

  The calculated CNL indicates the combustion noise caused by the combustion generated in the combustion chamber 15, and the smaller the CNL value, the lower the combustion noise. Therefore, when the value of CNL is smaller than the predetermined threshold, it can be said that the value of CNL is a value on the side where noise is smaller than the predetermined threshold. On the other hand, when the value of CNL is larger than the predetermined threshold, it can be said that the value of CNL is a value on the side where noise is larger than the predetermined threshold.

  In the present embodiment, CNL calculated based on the in-cylinder pressure detected by the in-cylinder pressure sensor 81 is used as a parameter representing combustion noise caused by the combustion generated in the combustion chamber 15. However, it is not always necessary to use CNL as a parameter representing the combustion stability of the air-fuel mixture, and another parameter may be used. Therefore, for example, a knock sensor may be provided in the engine body 10 and the combustion noise may be calculated based on the output of the knock sensor.

  The failure diagnosis unit performs failure diagnosis of the ozone supply device described above. In the present embodiment, the failure diagnosis unit is configured by the in-cylinder pressure sensor 81 and the ECU 71.

  By the way, when ozone is supplied to the combustion chamber 15, the self-ignition timing of the premixed gas is advanced as will be described later. For this reason, the auto-ignition timing of the premixed gas changes between when ozone is supplied into the combustion chamber 15 by the ozone supply device and when ozone is not supplied. Therefore, the failure diagnosis unit calculates the self-ignition timing based on the in-cylinder pressure detected by the in-cylinder pressure sensor 81 in each of the cases where ozone is supplied into the combustion chamber 15 by the ozone supply device and when ozone is not supplied. calculate. And when ozone is supplied into the combustion chamber 15 by the ozone supply device and when the ozone is not supplied, the ozone supply device has failed when the auto-ignition timing of the premixed gas changes greatly beyond a predetermined threshold value. It is determined that it has not occurred. On the other hand, when ozone is supplied into the combustion chamber 15 by the ozone supply device and when ozone is not supplied, the ozone supply is performed when the auto-ignition timing of the premixed gas changes only smaller than a predetermined threshold value. It is determined that a failure has occurred in the device.

  In the present embodiment, the failure diagnosis of the ozone supply device is performed based on the self-ignition timing of the premixed gas calculated based on the in-cylinder pressure detected by the in-cylinder pressure sensor 81. However, the failure diagnosis of the ozone supply device does not necessarily have to be performed in this manner, and may be performed in another manner. Therefore, for example, an ozone sensor capable of detecting ozone in the combustion chamber 15 or the intake port 17 may be provided, and failure diagnosis of the ozone supply device may be performed based on the output of the ozone sensor.

  Based on the outputs of the various sensors and the outputs of the above-described combustion stability detector, combustion noise detector, and failure diagnostic unit, the control unit controls the fuel so that desired combustion can be performed in the combustion chamber 15. The injection valve 31, the spark plug 16, and the ozone supply device are controlled. Specific combustion control by the control unit will be described in detail below.

≪Basic combustion control≫
Next, with reference to FIGS. 4-6, the basic combustion control by the control part of the control apparatus 70 of this embodiment is demonstrated. In the present embodiment, the control unit of the control device 70 has two operation modes, a spark ignition operation mode (hereinafter referred to as “SI operation mode”) and a compression self-ignition operation mode (hereinafter referred to as “CI operation mode”). The internal combustion engine is operated.

  In the SI operation mode, the control unit of the control device 70 basically forms a premixed gas near the stoichiometric air fuel ratio or near the stoichiometric air fuel ratio in the combustion chamber 15 and ignites the premixed gas with the spark plug 16. As a result, the premixed gas is subjected to flame propagation combustion in the combustion chamber 15.

  Further, in the CI operation mode, the control unit of the control device 70 basically forms a pre-air mixture with an air-fuel ratio leaner than the stoichiometric air-fuel ratio (for example, about 30 to 40) in the combustion chamber 15, The mixture is burned by compression ignition. In particular, in this embodiment, a stratified premixed gas having a combustible layer at the center of the combustion chamber 15 and an air layer around the inner wall surface of the cylinder 11 is formed as the premixed gas.

  Premixed compression auto-ignition combustion can be performed even when the air-fuel ratio is lean as compared with flame propagation combustion, and can be performed even when the compression ratio is increased. Therefore, by performing premixed compression auto-ignition combustion, fuel efficiency can be improved and thermal efficiency can be improved. In addition, since premixed compression self-ignition combustion has a lower combustion temperature than flame propagation combustion, generation of NOx can be suppressed. Furthermore, since there is sufficient oxygen around the fuel, the generation of unburned HC can be suppressed.

  In premixed compression self-ignition combustion, a reaction time is required until the air-fuel mixture self-ignites in the combustion chamber 15, and when the engine speed increases, the reaction time required for the air-fuel mixture to self-ignite. Can not be secured. For this reason, the operation in the SI operation mode is performed in a region where the engine rotation speed is high. Further, if the engine load increases and the torque generated by the internal combustion engine increases, pre-ignition occurs, knocking occurs, and good self-ignition combustion cannot be performed. For this reason, the operation in the SI operation mode is performed even in a region where the engine load is high. As a result, in the present embodiment, if the engine operating state ascertained from the engine load and the engine speed is within the self-ignition region RR surrounded by the solid line in FIG. If it is in a region outside the ignition region RR, the internal combustion engine is operated in the SI operation mode.

  Next, control of the variable valve mechanism 20, the ignition plug 16, and the fuel injection valve 31 in the CI operation mode of the present embodiment will be described with reference to FIGS.

  In order to perform the premixed compression self-ignition combustion, it is necessary to raise the in-cylinder temperature to a temperature at which the premixed gas can be self-ignited, and the premixed gas is moved into the combustion chamber 15 as in the SI operation mode. Therefore, it is necessary to make the in-cylinder temperature higher than in the case of all the flame propagation combustion. Therefore, in this embodiment, for example, as shown in FIGS. 5A and 5B, during the CI operation mode, the exhaust variable valve mechanism 24 is configured so that the exhaust valve 22 is opened not only in the exhaust stroke but also in the intake stroke as necessary. Is controlling. In this way, by performing the opening operation of the exhaust valve twice to open the exhaust valve 22 again during the intake stroke, the high-temperature exhaust gas discharged from a certain cylinder during the exhaust stroke is discharged during the immediately following intake stroke. The cylinder can be sucked back. Thus, the in-cylinder temperature is raised, and the in-cylinder temperature of each cylinder 11 is maintained at a temperature at which premixed compression self-ignition combustion can be performed.

  As shown in FIG. 5A, if the exhaust valve 22 is opened when the lift amount of the intake valve 21 is small, a large amount of exhaust gas can be sucked back into the own cylinder, so that the in-cylinder temperature can be greatly increased. it can. On the other hand, as shown in FIG. 5B, if the exhaust valve 22 is opened after the lift amount of the intake valve 21 has increased to some extent, the exhaust gas is sucked back after a certain amount of air (fresh air) is sucked into the cylinder. As a result, the amount of exhaust gas sucked back into the cylinder can be suppressed and the increase in the in-cylinder temperature can be suppressed. In this way, the increase range of the in-cylinder temperature can be controlled according to the timing at which the exhaust valve opening operation is performed twice.

  In addition, in the present embodiment, the air-fuel mixture is ignited by the spark plug 16 even in the CI operation mode. More specifically, when the premixed gas is compressed and ignited and combusted in the combustion chamber 15, the ignition plug 16 performs an ignition assist so that a part of the fuel is flame-propagated and combusted, and the heat generated by the flame-propagating combustion is used. By forcibly raising the in-cylinder temperature, ignition assist self-ignition combustion is performed in which the remaining fuel is premixed compression self-ignition combustion. By performing such an ignition assist and causing the premixed gas to undergo compression self-ignition combustion, it becomes easy to control the self-ignition timing of the premixed gas to an arbitrary timing.

  FIG. 6 is a diagram showing the relationship between the crank angle, the fuel injection amount, the ignition timing, and the heat generation rate when the ignition assist is performed and the premixed gas is subjected to compression self-ignition combustion. Heat generation rate (dQ / dθ) [J / deg. [CA] is the amount of heat per unit crank angle generated by the combustion of the air-fuel mixture, that is, the amount of heat generation Q per unit crank angle. The solid line (heat generation rate pattern A) in the figure shows the transition of the heat generation rate when the ignition assist is performed and the premixed mixture is subjected to compression self-ignition combustion. Shows the transition of the heat generation rate when the premixed gas is subjected to compression self-ignition combustion without performing the ignition assist.

  As shown in FIG. 6, in the case where ignition assist is performed and the premixed mixture is subjected to compression self-ignition combustion, main fuel injection by the fuel injection valve 31, injection of ignition assist fuel by the fuel injection valve 31, and ignition Ignition by the plug 16 is performed sequentially.

  The main fuel is injected at an arbitrary time during the compression stroke from the intake stroke (in the example of FIG. 6, about −50 [deg. ATDC]). The main fuel injection amount is preferably at least half of the total fuel injection amount in each cycle. A premixed gas is formed in the combustion chamber 15 by the injection of the main fuel. In the example shown in FIG. 6, the main fuel is injected only once during the compression stroke. However, the main fuel may be injected in a plurality of times.

  The ignition assist fuel is injected at an arbitrary time in the latter half of the compression stroke after the main fuel is injected (about -10 [deg. ATDC] in the example of FIG. 6). Due to the injection of the ignition assist fuel, a rich air-fuel mixture rich in air-fuel ratio is formed around the spark plug 16 than the pre-air mixture formed in the combustion chamber 15 by the main fuel injection.

  The ignition plug 16 is ignited at an arbitrary timing in the latter half of the compression stroke after the ignition assist fuel is injected (about -8 [deg. ATDC] in the example of FIG. 6). As a result, the rich air-fuel mixture (ignition assist fuel) formed around the spark plug 16 is ignited, and the rich air-fuel mixture is mainly burned and burned. As shown by the heat generation rate pattern A1 in FIG. 6, heat is generated by the flame propagation combustion of the rich mixture, and the in-cylinder temperature is forcibly raised by the generated heat, thereby premixing. Qi (main fuel) is compressed and ignited. Heat is generated as shown by the heat generation rate pattern A2 in FIG. 6 by the compression auto-ignition combustion of the premixed gas. As a result, in the combustion chamber 15 in which flame propagation combustion and compression self-ignition combustion occur, the heat generation rate changes as shown by the heat generation rate pattern A.

  As described above, in the present embodiment, the control unit of the control device 70 sequentially performs the injection of the main fuel and the injection of the ignition assist fuel from the fuel injection valve 31 and ignites the air-fuel mixture formed by the injection of the ignition assist fuel. The injection amount, injection timing, and ignition timing of the main fuel and the ignition assist fuel are controlled so that the plug 16 causes flame propagation combustion and the remaining fuel is premixed compression self-ignition combustion using heat generated by the flame propagation combustion. It can be said that the ignition assist control can be executed.

  As described above, by performing the ignition assist and causing the premixed gas to undergo compression self-ignition combustion, it becomes possible to easily control the ignition timing of the premixed gas to an arbitrary timing. In addition, since a part of the fuel is subjected to flame propagation combustion, the amount of fuel consumed by the compression auto-ignition combustion is reduced. For this reason, combustion noise can be reduced compared with the case where all the fuel is consumed by premixed compression auto-ignition combustion. The reason why the combustion noise can be reduced in this way will be described below.

When the premixed gas is subjected to compression self-ignition combustion, the fuel diffused in the combustion chamber 15 self-ignites at multiple points at the same time, so the combustion speed becomes faster than when flame propagation combustion occurs, and the combustion period Becomes shorter. Therefore, when the premixed gas is subjected to compression self-ignition combustion as shown in the heat generation rate pattern B shown by the one-dot chain line in FIG. 6, the peak value of the heat generation rate pattern and the initial auto-ignition combustion of the heat generation rate pattern Each of the slopes at (d ² Q / (dθ) ² ) tends to be relatively large.

  Combustion noise has a correlation with the peak value of this heat release rate pattern and the slope at the beginning of autoignition combustion, and the greater the peak value of the heat release rate pattern, the greater the slope at the beginning of autoignition combustion, the greater the noise. Become. Therefore, when the premixed gas is subjected to compression self-ignition combustion, combustion noise increases compared to when the premixed gas is subjected to flame propagation combustion.

On the other hand, when the ignition mixture is executed and the premixed gas is subjected to compression self-ignition combustion, the peak value of the heat generation rate pattern and the heat generation rate as shown in the heat generation rate pattern A indicated by the solid line in FIG. Each of the inclinations (d ² Q / (dθ) ² ) in the early stage of autoignition combustion of the pattern is smaller than that of the heat release rate pattern B. For this reason, combustion noise can be reduced when ignition assist is performed and the premixed gas is subjected to compression self-ignition combustion.

≪Reduction of combustion noise using ozone supply device≫
By the way, when the premixed gas is subjected to compression self-ignition combustion, the fuel diffused in the combustion chamber 15 is self-ignited at the same time at many points. Therefore, even when the ignition assist as described above is performed, there is a problem that combustion noise increases compared to the case where the premixed gas is subjected to flame propagation combustion.

As described above, in the heat generation rate pattern A indicated by the solid line in FIG. 6, each of the peak value of the heat generation rate pattern and the slope (d ² Q / (dθ) ² ) in the initial stage of autoignition combustion of the heat generation rate pattern. Is smaller than the heat release rate pattern B. However, the peak value and the slope at the initial stage of autoignition combustion are still relatively large, and the combustion noise cannot be said to be sufficiently small.

  Here, as a method of reducing the combustion noise by reducing each of the peak value of the heat generation rate pattern and the inclination in the early stage of auto-ignition combustion, ozone is used so that a concentration difference occurs spatially or temporally in the combustion chamber 15. There is a method in which compression auto-ignition combustion is generated step by step by supplying a time difference.

  The ozone supplied into the combustion chamber 15 is decomposed when the temperature in the combustion chamber 15 rises to a predetermined temperature (for example, about 500 [K] to 600 [K]), and generates oxygen radicals which are a kind of active species. Let It is known that oxygen radicals act on fuel molecules to increase the self-ignitability of the fuel. The greater the amount of oxygen radicals present in the combustion chamber 15, the earlier the self-ignition timing of the premixed gas.

  Therefore, by supplying ozone so that a concentration difference occurs spatially in the combustion chamber 15, premixing that exists in a region where the ozone concentration (more strictly speaking, oxygen radical concentration) is relatively high in the combustion chamber 15. The self-ignition timing of the premixed gas existing in the region where the ozone concentration is relatively low in the combustion chamber 15 can be delayed with respect to the self-ignition timing of the gas. That is, by supplying ozone so that a concentration difference spatially occurs in the combustion chamber 15, it is possible to cause compression auto-ignition combustion in stages with a time difference.

  On the other hand, for example, when the ozone concentration in the combustion chamber 15 is equal to or higher than a predetermined value, the primary fuel injection is performed, and then the secondary fuel injection is performed after the ozone concentration is reduced to a value lower than the predetermined value. Even if ozone is supplied so that a concentration difference occurs with time in the combustion chamber 15, compression auto-ignition combustion can be caused stepwise by providing a time difference.

  FIG. 7 shows a premixed compression with ignition assist without changing the total amount of fuel injected from the fuel injection valve 31 while supplying ozone during the intake stroke so that a spatial concentration difference occurs in the combustion chamber 15. It is the figure which showed the relationship between the crank angle at the time of implementing self-ignition combustion, and a heat release rate.

  In FIG. 7, the heat generation rate pattern C1 is a heat generation rate pattern when the rich mixture formed by the ignition assist fuel is subjected to flame propagation combustion, and is a heat generation rate pattern similar to the heat generation rate pattern A1 described above. is there. The heat generation rate pattern C21 is a heat generation rate pattern when the premixed gas present in the region where the ozone concentration is relatively high in the combustion chamber 15 is subjected to compression self-ignition combustion. The heat release rate pattern C22 is a heat release rate pattern when the premixed gas present in the region where the ozone concentration is relatively low in the combustion chamber 15 is subjected to compression self-ignition combustion. The heat generation rate pattern C is an actual heat generation rate pattern obtained by adding the heat generation rate pattern C1, the heat generation rate pattern C21, and the heat generation rate pattern C22.

  When ozone is supplied so as to cause a concentration difference in the combustion chamber 15, as shown in the heat generation rate pattern C21, the premixed gas existing in the region where the ozone concentration is relatively high in the combustion chamber 15 is first. Cause self-ignition. And as shown in the heat release rate pattern C22, the premixed gas existing in the region where the ozone concentration is relatively low in the combustion chamber 15 is delayed and causes self-ignition. As a result, combustion in a region where the ozone concentration is relatively high in the combustion chamber 15 and combustion in a region where the ozone concentration is relatively low in the combustion chamber 15 occur in a dispersed manner.

  The peak value of each of the heat generation rate pattern C21 and the heat generation rate pattern C22 and the inclination in the initial stage of autoignition combustion are smaller than the peak value of the heat generation rate pattern A shown in FIG. This is because the amount of fuel contributing to the formation of the heat generation rate pattern C21 and the amount of fuel contributing to the formation of the heat generation rate pattern C22 are compared with the amount of fuel contributing to the formation of the heat generation rate pattern A. This is because the amount of fuel igniting at the same time is dispersed, and the amount of fuel ignited at the same time is dispersed. As a result, as shown in FIG. 7, the peak value of the heat generation rate pattern C, which is an actual combustion waveform, and the slope at the initial stage of autoignition combustion are also larger than the peak value of the heat generation rate pattern A and the slope at the initial stage of autoignition combustion Get smaller.

  Therefore, combustion noise can be reduced by providing a time difference in this manner and causing compression auto-ignition combustion in stages. Therefore, in the present embodiment, when the operation mode is the CI operation mode, ozone with a target ozone supply amount corresponding to the engine operation state is supplied into the combustion chamber 15 so that compression auto-ignition combustion occurs in stages with a time difference. Like to do.

  In the present embodiment, when the operation mode is the CI operation mode, ozone is supplied from the ozone supply device so that compression auto-ignition combustion occurs in stages. Therefore, in this embodiment, if the engine operating state is within the auto-ignition region RR surrounded by the solid line in FIG. 4, ozone is supplied from the ozone supply device. Therefore, the self-ignition region RR surrounded by a solid line in FIG. 4 can also be referred to as an ozone supply region in which ozone is supplied.

  However, it is not always necessary to supply ozone by the ozone supply device when the operation mode is the CI operation mode. The combustion noise increases in the CI operation mode in a region where the engine load is particularly high in the self-ignition region RR of FIG. Therefore, ozone may be supplied from the ozone supply device only in a region where the load is high in the self-ignition region RR of FIG. In this case, a region having a high load in the self-ignition region RR in FIG. 4 is an ozone supply region in which ozone is supplied.

≪Basic combustion control flowchart≫
FIG. 8 is a flowchart showing a control routine of basic combustion control with ozone supply from the ozone supply device. The illustrated control routine is performed by interruption at regular time intervals.

  Referring to FIG. 8, first, in step S <b> 11, the engine operating state is detected using the engine load detected by the load sensor 88 and the engine speed calculated based on the crank angle sensor 89. Next, in step S12, it is determined whether or not the current engine operating state detected in step S11 is within the self-ignition region RR. If it is determined in step S12 that the current engine operating state is within the auto-ignition region RR, the process proceeds to step S13.

  In step S13, the total fuel injection amount IM is calculated based on the engine load and the like detected by the load sensor 88. The total fuel injection amount IM is calculated based on the engine load using, for example, a map that defines the relationship between the engine load and the total fuel injection amount stored in the ROM 74 of the ECU 71. The total fuel injection amount IM is set so as to increase as the engine load increases.

  Next, in step S14, a ratio R of the injection amount IMa of the ignition assist fuel with respect to the total fuel injection amount IM is calculated. For example, the ratio R is set to increase as the engine load decreases. This is because, as the engine load decreases, the amount of intake air decreases, and the temperature and pressure of the premixed gas decreases, making it difficult for compression auto-ignition combustion to occur. Therefore, when the engine load decreases, compression auto-ignition combustion The injection amount of the ignition assist fuel is increased so as to make it easier to generate.

  Next, in step S15, based on the total fuel injection amount IM calculated in step S13 and the ignition assist injection ratio R calculated in step S14, the main fuel injection amount IMm and the ignition assist fuel injection amount IMa are obtained. Calculated. Next, in step S16, based on the engine load and the engine speed using a predetermined map stored in the ROM 74 of the ECU 71, the main fuel injection timing Tm, the ignition assist fuel injection timing Ta, and the spark plug. 16 is calculated. The injection timing of the main fuel, the injection timing of the ignition assist fuel, and the ignition timing are set so as to be advanced as the engine speed increases, for example.

  Next, in step S17, it is determined whether or not the current engine operating state is within the ozone supply region. In the present embodiment, as described above, since the ozone supply region and the auto-ignition region RR are the same, in step S17, the current engine operating state is always within the ozone supply region, and the process proceeds to step S18. In step S18, the supply amount to be supplied from the ozone supply device is calculated. Specifically, for example, since the combustion noise increases as the engine load increases, the ozone supply amount is calculated such that the ozone supply amount increases as the engine load increases.

  On the other hand, as described above, when the ozone supply region is a partial region within the auto-ignition region RR, it may be determined in step S17 that the current engine operation state is not within the ozone supply region. In this case, the process proceeds from step S17 to step S19, and the ozone supply amount from the ozone supply device is set to zero.

  If it is determined in step S12 that the current engine operating state is not within the self-ignition region RR, the process proceeds to step S20. In step S20, the fuel injection valve 31, the spark plug 16, and the like are controlled so that the combustion in the combustion chamber 15 is performed in the SI operation mode.

≪Ozone supply device failure≫
By the way, if the ozone supply device fails and ozone cannot be sufficiently supplied from the ozone supply device into the combustion chamber 15, the combustion noise cannot be reduced sufficiently, or the premixed gas is compressed. There is a risk of misfire without being able to self-ignite and burn. Hereinafter, such a phenomenon will be described with reference to FIG.

  FIG. 9 is a diagram showing the relationship between the crank angle and the heat generation rate when the ozone supply device fails. A heat generation rate pattern C indicated by a broken line in FIG. 9 indicates a heat generation rate pattern in the case where the ozone supply device has not failed, and is the same as the heat generation rate pattern C in FIG. On the other hand, the heat release rate pattern D indicated by the solid line and the heat release rate pattern E indicated by the alternate long and short dash line in FIG. 9 indicate the heat release rate pattern in the case where the ozone supply device has failed.

  As in the present embodiment, when ozone is supplied so as to produce a spatial density difference in the combustion chamber 15, if the actual ozone supply amount becomes smaller than the target ozone supply amount, The difference in ozone concentration in the water becomes smaller than usual. Therefore, the self-ignition timing of the premixed gas existing in the region where the ozone concentration is relatively high in the combustion chamber 15 and the self-ignition timing of the premixed gas existing in the region where the ozone concentration is relatively low in the combustion chamber 15. And the time difference becomes shorter. As a result, combustion in a region where the ozone concentration is relatively high in the combustion chamber 15 and combustion in a region where the ozone concentration is relatively low in the combustion chamber 15 occur without being sufficiently dispersed. In particular, when the actual ozone supply amount becomes almost zero due to a failure of the ozone supply device, there is no spatial concentration difference in ozone in the combustion chamber 15 and combustion is not dispersed. For this reason, as indicated by the solid line D in FIG. 9, the peak value of the heat generation rate pattern and the inclination in the initial stage of the auto-ignition combustion cannot be sufficiently reduced, and the combustion noise cannot be sufficiently reduced.

  On the other hand, when ozone is supplied into the combustion chamber 15 from the ozone supply device, compression autoignition combustion is likely to occur earlier than when ozone is not supplied into the combustion chamber 15 from the ozone supply device. As described above, when the generation of compression auto-ignition combustion becomes earlier than an appropriate time, sufficient engine output cannot be obtained. For this reason, when ozone is supplied into the combustion chamber 15 from the ozone supply device, the time at which the compression mixture ignition combustion of the premixed gas occurs is compared with a case where ozone is not supplied into the combustion chamber 15 from the ozone supply device. The fuel injection timing and the like are controlled so as to be delayed. Specifically, for example, the injection timing of the main fuel is retarded.

  On the other hand, when the actual ozone supply amount becomes smaller than the target ozone supply amount due to the failure of the ozone supply device, the fuel injection timing and the like are controlled so that the timing at which the compression mixture ignition combustion of the premixed gas occurs is delayed. Despite this, compression self-ignition combustion is less likely to occur. As a result, the time of occurrence of compression auto-ignition combustion of the premixed gas is delayed, and in some cases, compression auto-ignition combustion of the premixed gas does not occur (misfire). In this way, when misfire occurs, only flame propagation combustion by ignition assist occurs, and thus a heat generation rate pattern as shown by a one-dot chain line E in FIG.

  Thus, if the ozone supply device fails, an increase in combustion noise or misfire of compression auto-ignition combustion of the premixed gas occurs, making it difficult to continue the operation of the internal combustion engine. Therefore, it is desirable to suppress an increase in combustion noise while suppressing the occurrence of misfire, etc., so that the operation of the internal combustion engine can be continued even when the ozone supply device fails.

≪Relationship between combustion noise and misfire and ignition assistance≫
Referring to FIG. 10, a case where combustion noise cannot be sufficiently reduced due to a failure of the ozone supply device will be considered. FIG. 10 is a diagram showing the relationship between the crank angle and the heat generation rate when the combustion noise cannot be sufficiently reduced due to the failure of the ozone supply device. The heat generation rate pattern D indicated by the alternate long and short dash line in FIG. 10 shows the heat generation rate pattern when the ozone supply device fails and combustion noise cannot be sufficiently reduced, and the heat generation rate pattern in FIG. The same as pattern D. Further, the injection timing, injection amount, and ignition timing of the main fuel and the ignition assist fuel indicated by the alternate long and short dash line in FIG. 10 are the same as the injection timing, injection amount, and ignition timing shown in FIG.

  On the other hand, the injection amounts of the main fuel and the ignition assist fuel indicated by the solid line in FIG. 10 are the same as the injection amounts of the main fuel and the ignition assist fuel indicated by the one-dot chain line in FIG. However, the injection amount of the main fuel is small and the injection amount of the ignition assist fuel is increased. That is, in the example indicated by the solid line in FIG. 10, the ratio of the injection amount of the ignition assist fuel to the total fuel injection amount is increased compared to the example indicated by the alternate long and short dash line in FIG. 10.

  In FIG. 10, the heat generation rate pattern F1 is a heat generation rate pattern when the rich mixture formed by the ignition assist fuel is flame-propagated and combusted, and the heat generation rate pattern F2 is the premixing formed by the main fuel. It is a heat release rate pattern when Qi is compressed auto-ignition combustion. As described above, in the example shown by the solid line in FIG. 10, the injection amount of the ignition assist fuel is larger than in the example shown by the alternate long and short dash line in FIG. For this reason, the amount of heat generated by the flame propagation combustion of the rich air-fuel mixture formed by the ignition assist fuel increases, and thus the heat generation rate in the heat generation rate pattern F1 increases overall. On the other hand, in the example shown by the solid line in FIG. 10, the injection amount of the main fuel is smaller than in the example shown by the one-dot chain line in FIG. For this reason, the calorific value generated by the compression auto-ignition combustion of the premixed gas formed by the main fuel is reduced, so that the heat generation rate in the heat generation rate pattern F2 is reduced as a whole. As a result, in the combustion chamber 15, the heat generation rate changes as shown by the heat generation rate pattern F.

  Here, as can be seen from FIG. 10, in the heat generation rate pattern F, the peak value of the heat generation rate pattern and the slope in the initial stage of autoignition combustion are smaller than in the heat generation rate pattern D. For this reason, in the heat release rate pattern F, the combustion noise is smaller than in the heat release rate pattern D. Therefore, when the combustion noise cannot be sufficiently reduced due to a failure of the ozone supply device, the combustion noise is sufficiently reduced by increasing the ratio of the injection amount of the ignition assist fuel to the total fuel injection amount. Will be able to.

  Next, with reference to FIG. 11, a case will be considered in which the premixed gas cannot be subjected to compression self-ignition combustion due to a failure of the ozone supply device and misfires. FIG. 11 is a diagram showing the relationship between the crank angle and the heat generation rate in the case where the premixed gas misfires without causing compression autoignition combustion due to a failure of the ozone supply device. A heat generation rate pattern E indicated by a one-dot chain line in FIG. 11 shows a heat generation rate pattern when the ozone supply device fails and misfire occurs, and is similar to the heat generation rate pattern E in FIG. . Further, the injection timing, injection amount, and ignition timing of the main fuel and ignition assist fuel indicated by the one-dot chain line in FIG. 11 are the same as the injection timing, injection amount, and ignition timing shown in FIG.

  On the other hand, the injection amounts of the main fuel and the ignition assist fuel indicated by the solid line in FIG. 11 are the same as the injection amounts of the main fuel and the ignition assist fuel indicated by the one-dot chain line in FIG. However, the injection amount of the main fuel is small and the injection amount of the ignition assist fuel is increased. That is, in the example shown by the solid line in FIG. 11, the ratio of the injection amount of the ignition assist fuel to the total fuel injection amount is increased compared to the example shown by the alternate long and short dash line in FIG. In addition, the injection timing and ignition timing of the ignition assist fuel indicated by the solid line in FIG. 11 are advanced compared to the injection timing and ignition timing of the ignition assist fuel indicated by the one-dot chain line in FIG.

  In FIG. 11, the heat generation rate pattern G1 is a heat generation rate pattern when the rich mixture formed by the ignition assist fuel is subjected to flame propagation combustion, and the heat generation rate pattern G2 is the premixing formed by the main fuel. It is a heat release rate pattern when Qi is compressed auto-ignition combustion. As described above, in the example shown by the solid line in FIG. 11, the injection timing and the ignition timing of the ignition assist fuel are advanced compared to the example shown by the alternate long and short dash line in FIG. 11. For this reason, flame propagation combustion by the rich air-fuel mixture formed by the ignition assist fuel occurs earlier than the example shown by the alternate long and short dash line. As a result, in the heat generation rate pattern G1 when the rich air-fuel mixture burns and propagates through the flame, the time when the peak occurs is advanced and approaches TDC. Since the peak of the temperature and pressure in the combustion chamber 15 due to the rise of the piston 14 is TDC, the peak of the temperature and pressure in the combustion chamber 15 is increased by bringing the peak of the heat generation rate pattern G1 close to TDC. Can do.

  In addition, the fuel injection amount of the ignition assist fuel is larger in the example shown by the solid line in FIG. 11 than in the example shown by the alternate long and short dash line in FIG. For this reason, the amount of heat generated by the flame propagation combustion of the rich air-fuel mixture formed by the ignition assist fuel increases, and thus the heat generation rate in the heat generation rate pattern G1 increases overall. As a result, the peak value in the heat generation rate pattern G1 increases, and the temperature and pressure in the combustion chamber 15 at the time when the peak occurs in the heat generation rate pattern G1 can be increased.

  Thus, by advancing the injection timing and ignition timing of the ignition assist fuel, it is possible to increase the temperature and pressure peaks in the combustion chamber 15 due to the flame propagation combustion of the rich mixture. In addition, by increasing the injection amount of the ignition assist fuel, the temperature and pressure in the combustion chamber 15 when the flame propagation combustion of the rich mixture is occurring can be increased. As a result, the temperature and pressure in the combustion chamber 15 can be increased at the timing at which the compression mixture of the premixed gas should be generated, and the premixed gas will eventually be misfired without performing the compression ignition combustion. This can be suppressed. Therefore, when the premixed mixture cannot be combusted by compression auto-ignition combustion due to a failure of the ozone supply device, the ignition assist fuel injection timing and ignition timing are advanced, and the ignition assist fuel relative to the total fuel injection amount is advanced. By increasing the injection ratio of the injection amount, it is possible to suppress the premixed gas from being misfired without compression self-ignition combustion.

≪Control when ozone supply device fails≫
Therefore, paying attention to the above-described relationship between combustion noise and misfire and ignition assist, in the present embodiment, the control unit of the control device 70 performs the following control.

  In other words, the control unit of the control device 70 determines that the ozone supply device has failed by the failure diagnosis unit and the IMEP detected by the combustion stability detection unit when the engine operating state is within the ozone supply region. When the value of COV is greater than a predetermined first threshold (for example, 3%) (that is, the value on the unstable side), the value is smaller than the first threshold (that is, the value on the stable side). Compared to a certain time), the injection timing and ignition timing of the ignition assist fuel are advanced, and the ratio of the injection amount of the ignition assist fuel to the total fuel injection amount is increased.

  In particular, in this embodiment, when the COV value of IMEP is larger than the first threshold value, the injection timing and the ignition timing of the ignition assist fuel are advanced more greatly as the COV value increases. This means that the larger the value of COV is, the more unstable the combustion is. Thus, the larger the value of COV is, the more the combustion timing of the ignition assist fuel is advanced. The increase in the temperature and pressure in the chamber 15 can be matched to the increase in the temperature and pressure in the combustion chamber 15 by motoring, so that compression auto-ignition combustion can be more easily generated.

  In addition, when the COEP value of IMEP is larger than the first threshold value, the ratio of the injection amount of the ignition assist fuel to the total fuel injection amount is increased more as the COV value becomes larger. As described above, the larger the value of COV means that the combustion is more unstable. In this way, the larger the value of COV, the larger the amount of heat generated by the combustion of the ignition assist fuel. Compressive self-ignition combustion can be more easily generated.

  FIG. 12 is a diagram illustrating a relationship between ΔCOV obtained by subtracting the first threshold value from the COEP value of IMEP and the advance side correction amount of the ignition timing and ignition timing of the ignition assist fuel. As can be seen from FIG. 12, the larger the COV of IMPE, that is, the greater the value of COPE of IMPE exceeds the first threshold value, the larger the advance side correction amount of the ignition assist fuel injection timing and ignition timing. As a result, as ΔCOV increases, the ignition assist fuel injection timing and ignition timing are advanced more greatly. The advance side correction amount calculated in this way is used to correct the ignition assist fuel injection timing Ta and ignition timing Tig calculated in step S16 of FIG. 8 to the advance side.

  FIG. 13 shows ΔCOV obtained by subtracting the first threshold value from the COV value of IMEP and an increase correction amount of the ratio of the injection amount of the ignition assist fuel to the total fuel injection amount (hereinafter referred to as “an increase correction amount of the ignition assist injection ratio). FIG. As can be seen from FIG. 13, as ΔCOV increases, that is, as the value of COPE of IMPE increases beyond the first threshold value, the increase correction amount of the ignition assist injection ratio increases. As a result, as ΔCOV increases, the ratio of the injection amount of the ignition assist fuel to the total fuel injection amount increases. The increase correction amount of the ignition assist injection ratio calculated in this way is used to correct the ratio R of the injection amount of the ignition assist fuel with respect to the total fuel injection amount calculated in step S14 of FIG. 8 to the increase side. .

  In the present embodiment, the first threshold value is a predetermined constant value. However, the first threshold value is not necessarily a constant value, and may be set so as to change according to the engine load or the like.

  In addition, the control unit of the control device 70 determines that the ozone supply device has failed by the failure diagnosis unit and the CNL detected by the combustion noise detection unit when the engine operating state is within the ozone supply region. When the value is larger than a predetermined second threshold (that is, when the noise is larger), the value is smaller than when the value is smaller than the second threshold (that is, when the noise is smaller). Thus, although the ratio of the injection amount of the ignition assist fuel to the total fuel injection amount is increased, the injection timing of the ignition assist fuel and the ignition timing are not changed.

  In particular, in the present embodiment, when the CNL value is larger than the second threshold value, the ratio of the ignition assist fuel injection amount to the total fuel injection amount is greatly increased as the CNL value increases. As the CNL value increases, the combustion noise increases. Thus, as the CNL value increases, the ratio of the injection amount of the ignition assist fuel to the total fuel injection amount is increased. The proportion of fuel used can be reduced, so that combustion noise can be further reduced.

  FIG. 14 is a diagram illustrating a relationship between ΔCNL obtained by subtracting the second threshold value from the CNL value and the increase correction amount of the ignition assist injection ratio. As can be seen from FIG. 14, as ΔCNL increases, that is, as the value of CNL exceeds the second threshold, the increase correction amount of the ignition assist injection ratio increases. As a result, as ΔCNL increases, the ratio of the injection amount of the ignition assist fuel to the total fuel injection amount increases. The increase correction amount of the ignition assist injection ratio calculated in this way is used to correct the ratio of the injection amount of the ignition assist fuel with respect to the total fuel injection amount calculated in step S14 of FIG. 8 to the increase side.

  In the present embodiment, the second threshold value is a predetermined constant value. However, the second threshold value is not necessarily a constant value, and may be set so as to change according to the engine load or the like. In this case, since the driver can allow the combustion noise to increase when the engine load is large, the second threshold value is set so as to increase as the engine load increases, for example.

≪Control when ozone supply device is normal≫
By the way, even if the ozone supply device is not broken, combustion noise may increase. This occurs, for example, when the actual actual compression ratio is higher than the target actual compression ratio and as a result, the compression auto-ignition combustion of the premixed gas suddenly occurs. Alternatively, for example, the temperature of the intake gas supplied into the combustion chamber 15 is higher than the expected intake gas temperature, and as a result, the compression auto-ignition combustion of the premixed gas suddenly occurs.

  Moreover, even if the ozone supply device is not out of order, the premixed gas may not be able to be subjected to compression self-ignition combustion and may misfire. This occurs, for example, when the actual actual compression ratio is lower than the target actual compression ratio, and as a result, the temperature and pressure in the combustion chamber 15 do not sufficiently increase to such an extent that the premixed gas undergoes compression self-ignition combustion. . Alternatively, for example, the temperature of the intake gas supplied into the combustion chamber 15 is lower than the expected intake gas temperature, and as a result, the temperature in the combustion chamber 15 sufficiently rises to such an extent that the premixed gas undergoes compression self-ignition combustion. Caused by not doing.

  Therefore, in the present embodiment, when the ozone supply device has not failed, the control of the control device 70 is performed when the combustion noise increases or the premixed gas cannot be subjected to compression self-ignition combustion and misfires. The section adjusts the amount of ozone supplied by the ozone supply device. When the combustion noise increases, by increasing the ozone supply amount by the ozone supply device, the generation timings of the heat generation rate pattern C21 and the heat generation rate pattern C22 shown in FIG. 7 can be separated from each other, and as a result As a result, combustion noise can be further reduced. Further, when the premixed gas cannot be compressed and self-ignited and combusted and misfires, the premixed gas existing in the region where the ozone concentration is high is easily ignited by increasing the ozone supply amount by the ozone supply device. As a result, it is possible to suppress the premixed gas from being misfired without performing compression self-ignition combustion.

  However, there is a limit to the amount of ozone supplied by the ozone supply device, and ozone exceeding a certain amount cannot be supplied. Therefore, even if the ozone supply amount by the ozone supply device is increased, the combustion noise cannot be sufficiently reduced, or the premixed gas cannot be combusted by compression self-ignition and is misfired. In some cases, measures other than increasing the amount of ozone supplied by the ozone supply device are necessary. However, at this time, if the ratio of the injection amount of the ignition assist fuel to the total fuel injection amount is increased, or the ignition timing of the ignition assist fuel or the ignition timing by the spark plug 16 is advanced, NOx or smoke in the exhaust gas Increase in fuel efficiency or fuel consumption. For this reason, in this embodiment, if the ozone supply device has not failed, even if the combustion noise increases or the premixed gas cannot be combusted by compression autoignition and misfires, the total fuel The ratio of the injection amount of the ignition assist fuel to the injection amount is not increased, and the injection timing of the ignition assist fuel and the ignition timing by the spark plug 16 are not advanced.

  On the other hand, when the ozone supply device has not failed, there are some factors as described above when the combustion noise increases or the premixed gas cannot be burned by compression autoignition and misfires. Therefore, in the present embodiment, measures are taken in accordance with this factor. For example, if the actual actual compression ratio is different from the target actual compression ratio and combustion noise increases or misfire occurs, the actual compression ratio is estimated based on the output of the in-cylinder pressure sensor 81 and the actual The closing timing of the intake valve 21 is controlled so that the compression ratio becomes the target compression ratio.

<< Flowchart of correction control >>
Hereinafter, specific control performed by the control device 70 will be described with reference to FIGS. 15 to 17.

  FIG. 15 is a flowchart showing a control routine for correction control of the ignition assist fuel injection amount, injection timing, and ignition timing. The illustrated control routine is performed by interruption at regular time intervals.

  Referring to FIG. 15, first, in step S21, it is determined whether or not the current engine operating state is within the self-ignition region RR. If it is determined in step S21 that the current engine operating state is not within the auto-ignition region RR, the control routine is terminated. On the other hand, if it is determined in step S21 that the current engine operating state is within the self-ignition region RR, the process proceeds to step S22.

  In step S22, it is determined whether or not the current engine operating state is within the ozone supply region. If it is determined in step S22 that the current engine operating state is not within the ozone supply region, the control routine is terminated. On the other hand, if it is determined in step S22 that the current engine operating state is within the ozone supply region, the process proceeds to step S23.

  In step S23, it is determined whether or not it is determined by the failure diagnosis unit of the control device 70 that the ozone supply device has failed. If it is determined in step S23 that the ozone supply device has failed, the process proceeds to step S24. In step S24, the failure control shown in FIG. 16 is performed. On the other hand, if it is determined in step S23 that the ozone supply device has not failed, the process proceeds to step S25. In step S25, the normal time control shown in FIG. 17 is performed.

  FIG. 16 is a flowchart showing a control routine of control at the time of failure that is performed when the ozone supply device is out of order. The illustrated control routine is executed when the control routine of FIG. 15 reaches step S24.

  Referring to FIG. 16, first, in step S31, it is determined whether misfire has occurred in the compression self-ignition combustion of the premixed gas. Specifically, in step S31, for example, it is determined whether or not the value of IMEP COV is equal to or greater than a first threshold value. If it is determined in step S31 that misfire has occurred, for example, if it is determined that the value of COEP in IMEP is equal to or greater than the first threshold value, the process proceeds to step S32.

  In step S32, it is determined whether the injection timing and ignition timing of the ignition assist fuel have reached the advance side limit values. This advance side limit value is set based on the relationship with the timing when the main fuel injection ends. That is, when the fuel injection valve 31 performs the injection a plurality of times, an interval of a certain time or more is required from the completion of the previous injection to the start of the subsequent injection. Also, if the time from the completion of the previous injection to the start of the subsequent injection is short, the fuel injected by both injections interferes with each other and the stability in combustion of each fuel deteriorates. The limit value on the advance side is set in consideration of these, and is specifically set based on the injection completion timing of the main fuel, the fuel injection pressure, the engine speed, and the like.

  If it is determined in step S32 that the injection timing and ignition timing of the ignition assist fuel have not reached the advance side limit values, the routine proceeds to step S33. In step S33, the ignition assist fuel injection timing Ta and ignition timing Tig set in step S16 of FIG. 8 are advanced based on the map shown in FIG. 12, and the control routine is terminated. On the other hand, if it is determined in step S32 that the injection timing and ignition timing of the ignition assist fuel have reached the advance side limit values, the routine proceeds to step S34.

  In step S34, it is determined whether the ratio R of the injection amount of the ignition assist fuel with respect to the total fuel injection amount (hereinafter referred to as “ignition assist injection ratio”) has reached the limit value on the increase side. This limit value on the increase side is set based on the relationship with the amount of NOx and smoke discharged from the engine body 10. That is, when the injection amount of the ignition assist fuel increases, the proportion of fuel burned by flame propagation combustion increases. Further, the amount of NOx and smoke generated is larger in the flame propagation combustion than in the compression self-ignition combustion of the premixed gas. For this reason, when the injection amount of the ignition assist fuel increases, the amount of NOx and smoke discharged from the engine body 10 increases. Therefore, an increase limit value is set for the ignition assist injection ratio R so that the amount of NOx and smoke discharged from the engine body 10 does not increase beyond a certain level. The limit value on the increase side may be a predetermined constant value or a value that varies depending on the engine load or the like.

  If it is determined in step S34 that the ignition assist injection ratio R has not reached the increase limit value, the process proceeds to step S35. In step S35, the ignition assist injection ratio R set in step S14 of FIG. 8 is increased and corrected based on the map as shown in FIG. 13, and the control routine is ended. On the other hand, if it is determined in step S34 that the ignition assist injection ratio R has reached the increase limit value, the process proceeds to step S36. In step S36, the compression auto-ignition combustion of the premixed gas is terminated, spark ignition combustion (SI combustion) is performed, and the control routine is terminated.

  On the other hand, if it is determined in step S31 that no misfire has occurred in the compression self-ignition combustion of the premixed gas, for example, if it is determined that the value of COV of IMEP is less than the first threshold value, the process proceeds to step S37. Proceed with

  In step S37, it is determined whether or not a large combustion noise is generated by the compression auto-ignition combustion of the premixed gas. Specifically, in step S37, for example, it is determined whether or not the CNL value is equal to or greater than a second threshold value. If it is determined in step S37 that no significant combustion noise has occurred, for example, if it is determined that the value of CNL is less than the second threshold value, the control routine is terminated. On the other hand, if it is determined in step S37 that a large combustion noise is occurring, for example, if it is determined that the CNL value is greater than or equal to the second threshold, the process proceeds to step S38. In step S38, as in step S34, it is determined whether or not the ignition assist injection ratio R has reached the increase limit value.

  If it is determined in step S38 that the ignition assist injection ratio R has not reached the limit value on the increase side, the process proceeds to step S39. In step S39, the ignition assist injection ratio R set in step S14 of FIG. 8 is increased and corrected based on the map as shown in FIG. 14, and the control routine is terminated. On the other hand, if it is determined in step S38 that the ignition assist injection ratio R has reached the increase limit value, the process proceeds to step S40. In step S40, the compression auto-ignition combustion of the premixed gas is terminated, spark ignition combustion (SI combustion) is performed, and the control routine is terminated.

  FIG. 17 is a flowchart illustrating a control routine for normal control that is performed when the ozone supply device is operating normally without a failure. The illustrated control routine is executed when the control routine of FIG. 15 reaches step S25.

  Referring to FIG. 17, first, in step S51, it is determined whether or not misfire has occurred in the compression auto-ignition combustion of the premixed gas as in step S31 of FIG. If it is determined in step S51 that a misfire has occurred, the process proceeds to step S52.

  In step S52, it is determined whether or not the ozone supply amount from the ozone supply device has reached a limit value. The limit value of the ozone supply amount is set based on, for example, the upper limit value of the ozone amount that can be supplied per unit time in terms of the performance of the ozone supply device. If it is determined in step S52 that the ozone supply amount from the ozone supply device has not reached the limit value, the process proceeds to step S53. In step S53, the ozone supply amount calculated in step S18 of FIG. 8 is corrected to increase, and the control routine is terminated. On the other hand, if it is determined in step S52 that the ozone supply amount from the ozone supply device has reached the limit value, the process proceeds to step S54. In step S54, devices other than the ozone supply device, the fuel injection valve 31, and the spark plug 16 are controlled so as to suppress misfire, and the ozone supply amount from the ozone supply device, such as the closing timing of the intake valve 21, and the ignition. Parameters other than the assist fuel injection timing and ignition timing, and the ignition assist injection ratio are controlled.

  On the other hand, if it is determined in step S51 that no misfire has occurred, the process proceeds to step S55. In step S55, as in step S37 of FIG. 16, it is determined whether or not a large combustion noise is generated by the compression auto-ignition combustion of the premixed gas. If it is determined in step S55 that no significant combustion noise has occurred, the control routine is terminated. On the other hand, if it is determined in step S55 that a large combustion noise is occurring, the process proceeds to step S56. In step S56, as in step S52, it is determined whether the ozone supply amount from the ozone supply device has reached a limit value. When it is determined that the ozone supply amount from the ozone supply device has not reached the limit value, the process proceeds to step S57. In step S57, as in step S53, the ozone supply amount is corrected to increase, and the control routine is terminated. On the other hand, if it is determined in step S56 that the ozone supply amount from the ozone supply device has reached the limit value, the process proceeds to step S58. In step S58, as in step S54, devices other than the ozone supply device, the fuel injection valve 31, and the spark plug 16 are controlled, and the control routine is terminated.

1 0 Internal combustion engine 10 Engine body 15 Combustion chamber 16 Spark plug 31 Fuel injection valve 71 Electronic control unit (ECU)
91 Discharge plug (ozone supply device)

Claims (1)

An internal combustion engine comprising a fuel injection valve that directly injects fuel into a combustion chamber, an ignition plug that ignites an air-fuel mixture in the combustion chamber, and an ozone supply device that supplies ozone directly or indirectly into the combustion chamber A control device for an internal combustion engine for controlling
A combustion stability detector that detects a value of a parameter that represents combustion stability; a combustion noise detector that detects a value of a parameter that represents combustion noise; a failure diagnostic unit that performs a failure diagnosis of the ozone supply device; and the fuel A control unit for controlling the injection valve, the spark plug, and the ozone supply device;
The control unit sequentially performs injection of main fuel and injection of ignition assist fuel from the fuel injection valve, and causes an air-fuel mixture formed by the injection of the ignition assist fuel to be flame-propagated and combusted by the spark plug and the flame. Ignition assist control is performed to control the injection amount and injection timing of the main fuel and the ignition assist fuel and the ignition timing by the spark plug so that the remaining fuel is premixed compression auto-ignition combustion using the heat generated by the propagation combustion. Is possible,
The controller is configured to supply ozone from the ozone supply device when the engine operating state is within a predetermined ozone supply region,
The control unit determines the combustion stability detected by the combustion stability detection unit when the failure diagnosis unit determines that the ozone supply device has failed and the engine operating state is within the ozone supply region. When the value of the parameter indicating the property is a value on the unstable side with respect to the predetermined first threshold value, the injection timing of the ignition assist fuel and the ignition are compared with the value on the stable side with respect to the first threshold value. Advancing the timing and increasing the ratio of the injection amount of the ignition assist fuel to the total fuel injection amount,
The control unit determines the combustion noise detected by the combustion noise detection unit when the failure diagnosis unit determines that the ozone supply device has failed and the engine operating state is within the ozone supply region. When the value of the parameter to be represented is a value on the side where the noise is larger than the predetermined second threshold value, the ignition assist fuel relative to the total fuel injection amount is compared with a value on the side where the noise is smaller than the second threshold value. A control device for an internal combustion engine, which increases the ratio of the injection amount of the engine and does not change the injection timing of the ignition assist fuel and the ignition timing.

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