Control device for internal combustion engine

Abstract

Control device (40) for an internal combustion engine (10), wherein the internal combustion engine comprises a fuel injection valve (30) configured to inject fuel into a cylinder, and a variable valve device (33, 34) configured to change the opening and closing times of at least one intake valve (31) and an exhaust valve (32), the control device for the internal combustion engine configured to control a fuel injection quantity based on an intake air quantity of the internal combustion engine, and to control the opening and closing times of the intake valve with the variable valve device based on an operating state of the internal combustion engine, wherein the control device for the internal combustion engine comprises: a determining unit,which is configured to determine whether the interior of a cylinder is in a state where fuel wetting is a concern, or whether the interior of the cylinder is in a droplet suspension state in which a large volume of suspended fuel droplets is generated when the engine is started with internal combustion; a first control unit configured to perform a first control as a control of the opening and closing timing with the variable valve device in order to reduce the intake air quantity when the determining unit determines that the interior of the cylinder is in a state where wetting is a concern; and a second control unit configured as a second control as the control of the opening and closing timing with the variable valve device in order to increase a temperature in the cylinder,when the unit of determination determines that the interior of the cylinder is in a droplet suspension state.

Description

Cross-Reference to Related ApplicationThis application is based on Japanese Patent Application No. 2018-213 189 filed on Nov. 13, 2018, and published under No. 2020-079 580 A.Technical FieldThe present disclosure relates to a control device applied to an internal combustion engine provided with a variable valve device that changes at least an opening timing and a closing timing of an intake valve and an exhaust valve.Prior ArtPatent Literature 1 discloses a control device that controls an opening timing and a closing timing of an intake valve or an exhaust valve for the purpose of reducing an emission amount of HC (hydrocarbon) in exhaust gas when an internal combustion engine is started. The control device disclosed in Patent Literature 1 controls the opening timing and the closing timing of the intake valve and the exhaust valve when the start of the internal combustion engine is detected based on a rotational speed of the internal combustion engine.JP 2005-146 917 A discloses the following: HC is to be decreased by reducing a wall flow rate in a combustion chamber even under the condition that a wall flow of an intake valve is large from a start timing before the buildup of a supercharging pressure to the timing after the start when the supercharging pressure is buildup. To this end, this control device of an engine includes an intake valve that opens and closes an intake passage, a variable valve mechanism that can variably control a valve lift volume and a valve timing of the intake valve, an ignition device for igniting sparks in a combustion chamber, and a fuel injection device that injects fuel from the intake passage toward the intake valve. In addition, the apparatus is provided with control means for controlling the fuel injection device so that the fuel is injected in an intake stroke at the start timing before the boost pressure is built up, and controlling the variable valve mechanisms so that an overlap volume of the intake valve and the exhaust valve is made larger than that until completion of the warm-up of the engine after the start timing when the boost pressure is built up, and controlling the ignition device so that ignition is performed at a stable combustion limit.JP 2002-327 651 A discloses providing a control device capable of suppressing instability of fuel combustion conditions in the combustion chamber of an internal combustion engine when exhaust gas is in the chamber at the time of fuel combustion to suppress generation of black smoke. At this time, the fuel injected into the combustion chamber is not easily atomized and remains in the liquid state when the temperature of the combustion chamber is low. Due to the combustion heat and the adhesion of the liquid fuel, black smoke may be generated in the exhaust gas. When the assumed temperature T of the combustion chamber falls below the value (fixed value a2) at which black smoke is generated, the valve timing of an intake valve is advanced and the amount of exhaust gas present in the chamber at the time of fuel combustion is adjusted stepwise. This exhaust gas raises the temperature in the chamber to promote atomization of the liquid fuel. In addition, the combustion temperature is lowered to suppress generation of black smoke. The black smoke suppression is performed in the described manner only when it is actually necessary so that the assumed temperature T falls below the predetermined value a2.Prior Art LiteraturePatent LiteraturePatent Literature 1: Japanese Patent No. JP 3 771 101 B2Summary of the InventionWhen the internal combustion engine is started, an amount of non-evaporated fuel in the cylinder increases, and an amount of HC and PN (Particulate Number) in the exhaust gas increases. In Patent Literature 1, the opening timing and the closing timing of the internal combustion engine are controlled without considering the state of fuel in the cylinder. Therefore, there is a problem that discharged HC and PN cannot be sufficiently reduced depending on the state of fuel.The present disclosure has been made in view of the above problems, and it is an object of the present invention to provide a control device for an internal combustion engine configured to increase an effect of reducing HC and PN in exhaust gas according to a state of fuel in the cylinder.To solve the above problems, the present disclosure relates to a control device that can be applied to an internal combustion engine. The internal combustion engine includes: a fuel injection valve configured to inject fuel into a cylinder; and a variable valve device configured to change an opening timing and a closing timing of at least one of the intake valve and an exhaust valve. The internal combustion engine control device is configured to control a fuel injection amount based on an intake air amount of the internal combustion engine and control the opening timing and the closing timing of the intake valve with the variable valve device based on an operation state of the internal combustion engine. The control device includes: a determination unit configured to determine whether an interior of a cylinder is in a state where fuel wetting is to be feared or the interior of the cylinder is in a droplet floating state where a large volume of floating droplets of fuel arises when the internal combustion engine is started; a first control unit configured to perform the first control as control of the opening timing and the closing timing with the variable valve device to reduce the amount of intake air when the determination unit determines that the interior of the cylinder is in the state where wetting is to be feared; and a second control unit configured to perform, as the control of the opening timing and the closing timing with the variable valve device, a second control to increase a temperature in the cylinder when the determination unit determines that the inside of the cylinder is in the droplet floating state.A state in which fuel in the cylinder is not sufficiently evaporated includes a state in which wetting is to be feared in which considerable concerns about fuel wetting exists, and a droplet floating state in which a large volume of floating droplets of fuel arises. Both conditions are factors that increase the amount of HC and PN emissions. Here, the state in which fuel wetting is to be feared is caused by the fuel injection amount being larger than an appropriate value, and the droplet floating state is caused by the cylinder at a low temperature. The above configuration is configured to determine whether the inside of the cylinder is in the state in which fuel wetting is to be feared or the inside of the cylinder is in the droplet floating state in which a large volume of floating droplets of fuel is generated when the internal combustion engine is started. Then, when it is determined that the inside of the cylinder is in the state where wetting is to be feared, the first control for reducing the intake air amount is performed as the control of the opening timing and the closing timing using the variable valve device. In this way, the fuel injection amount is reduced, and therefore fuel wetting in the cylinder is improved. Thus, HC and PN in the exhaust gas can be reduced. On the other hand, when it is determined that the inside of the cylinder is in the floating droplet state, the second control for increasing the temperature in the cylinder is performed as the control of the opening timing and the closing timing using the variable valve device. In this way, fuel in the cylinder is easily evaporated, and therefore fuel in the form of a floating droplet is reduced, and HC and PN in the exhaust gas can be reduced. As described above, the configuration makes it possible to perform appropriate control of the opening timing and the closing timing for reducing HC and PN according to the state of liquid in the cylinder. Therefore, the effect of reducing HC and PN in the exhaust gas can be enhanced.Brief Description of the DrawingsThe above and other objects, features and advantages of the present disclosure will become apparent from the following detailed description with reference to the accompanying drawings. It shows / show: FIG. 1 is a diagram of a machine system; FIG. 2 is a diagram showing a state of non-evaporated fuel in a cylinder; FIG. 3 is a view for explaining calculation of an amount of fuel generated in a non-evaporated state; FIG. 4 is a view showing a first controller and a second controller; FIG. 5 is a flowchart showing a method of start control of an engine; FIG. 6 is a time chart for explaining a transition of an operation state at the time when the engine is started; FIG. 7 is a view showing the second controller according to a modified example; FIG. 8 is a time chart showing a transition of an operating state of an engine according to a second embodiment; FIG. 9 is a flowchart showing a method of starting engine control of the engine; FIG. 10 is a time chart showing a change in an engine speed; and FIG. 11 is a flowchart showing a method for start control of the engine according to a third embodiment.DESCRIPTION OF THE EMBODIMENTSFirst EmbodimentHereinafter, with reference to the drawings, an engine control system will be described as an embodiment that implements an internal combustion engine according to the present disclosure. The engine control system includes an engine as an internal combustion engine mounted on a vehicle, and controls an operation of this engine.An engine 10 shown in FIG. 1 is a 4-stroke cylinder injection type gasoline engine. More specifically, the engine 10 is a four-cylinder engine and a 4-cylinder engine, respectively, and a cylinder block 11A is provided with four cylinders 21. In FIG. 1, only one cylinder 21 is shown, and the other cylinders are not shown in detail. A piston 35 is arranged in the cylinder 21 so as to be configured to reciprocate. Reciprocation of the piston 35 causes a crankshaft 28 (output shaft) provided in the cylinder block 11A to rotate. In the present embodiment, a space formed by the inner wall of the cylinder 21 and an upper surface (top) of the piston 35 is referred to as an inside of the cylinder.The engine 10 includes an intake passage 12 communicating with an intake port and allowing intake air to be taken into the cylinder to flow therethrough, and an exhaust passage 23 communicating with an exhaust port and allowing exhaust gas to be discharged from the cylinder 21 to flow therethrough.The intake port and the exhaust port are provided with an intake valve 31 and an exhaust valve 32, respectively, which open and close according to the rotation of the camshaft (not shown). The intake valve 31 and the exhaust valve 32 are provided with variable valve devices 33 and 34, respectively, which change the opening timing and the closing timings of the intake valve 31 and the exhaust valve 32, respectively. The variable valve devices 33 and 34 are configured to adjust a relative rotational phase between the crankshaft 28 and an intake camshaft, and a relative rotational phase between the crankshaft 28 and an exhaust camshaft. The variable valve devices 33 and 34 are configured to perform phase adjustment to the advance angle side and the retard angle side with respect to a predetermined reference position. A hydraulically driven valve train or an electrically driven variable valve device may be used as the variable valve devices 33 and 34.The engine 10 is provided with an injector 30 as a fuel injection valve for each cylinder 21, and fuel is directly injected into the cylinder from the injector 30. A fuel pressure sensor 37 that detects a pressure of fuel supplied to the injector 30 (hereinafter referred to as fuel pressure) is provided at a flow path through which fuel flows to the injector 30 from a fuel accumulator (not shown).A spark plug 22 is mounted on a cylinder head of the engine 10. A high voltage is applied to the spark plug 22 at a desired ignition timing by an ignition coil or the like (not shown). By applying this high voltage, a spark discharge is generated between opposing electrodes of the spark plug 22, and the fuel in the cylinder is ignited.The engine 10 is provided with a crank angle sensor 29 which outputs the crank angle signal for each predetermined crank angle when the engine 10 is in operation. A rotational speed of the crankshaft 28 may be detected as an engine rotational speed Ne with the crank angle signal from the crank angle sensor 29. The cylinder block 11A is provided with a water temperature sensor 38 that detects a temperature of cooling water.The intake passage 12 is provided with an airflow meter 13 that detects an amount of air taken into the cylinder as an intake air amount Ga. On a downstream side of the airflow meter 13, in the intake passage 12, a throttle valve 16 is provided, the opening degree of which is adjusted by a throttle actuator 15 such as a DC motor. In the intake passage 12, a surge tank 18 is provided on the downstream side of the throttle valve 16.The exhaust passage 23 is provided with catalytic converters 25 and 26. The catalytic converters 25 and 26 are composed of a three-way catalyst including an exhaust gas purification catalyst, a gasoline particulate filter (GPF) for removing PN in the exhaust gas, a 4-way GPF in which a catalyst is supported on the GPF, and the like.In the exhaust passage 23, an A / F sensor 24 for detecting an air-fuel ratio of exhaust gas is provided on the upstream side of the catalytic converters 25 and 26.The engine control system includes an ECU 40 as a control device. The ECU 40 is provided with a microcomputer including a CPU, a ROM, a RAM, and the like. The microcomputer executes various control programs stored in a ROM to thereby perform control of a fuel injection amount Q of the injector 30, control of an opening timing and a closing timing of the intake valve 31 and the exhaust valve 32, and control of an ignition timing of the spark plug 22 according to the engine operating state.The ECU 40 calculates the fuel injection amount Q according to the intake air amount Ga detected using the air flow meter 13 and the engine rotational speed Ne, and causes the injector 30 to perform fuel injection based on the fuel injection amount Q.The ECU 40 implements ISS restart control as start control of the engine 10 when a restart condition is satisfied. The ISS restart control automatically stops the engine 10 when a predetermined automatic stop condition is satisfied. In this automatic stop state, the ISS restart control starts the engine 10 using a starter 50 as a starting device when a predetermined restart condition is satisfied. The ECU 40 corresponds to a restart control unit.Here, in a state in which an amount of fuel in a non-evaporated state in the cylinder of the engine 10 is large, the amount of HC and PM in the exhaust gas tends to increase. Specifically, when the engine 10 is started, the catalysts included in the catalytic converters 25 and 26 are not activated. Therefore, there is a problem that HC and PM are not sufficiently purified and released into the atmosphere even when exhaust gas passes through the catalytic converters 25 and 26.FIG. 2 is a diagram illustrating states of non-evaporated fuel in the cylinder 21. (a) in FIG. 2 illustrates a state in which fuel wetting is caused in the cylinder 21. The fuel wetting is a state in which a large amount of fuel in the form of a liquid film in the cylinder adheres to the inner wall surface or the upper part of the piston 35. Further, (b) in FIG. 2 shows a droplet floating state in which an amount of fuel in the droplet floating state in the cylinder is large. The fuel in the droplet levitation state is fuel that floats as droplets in the air-fuel mixture in the cylinder. In either state, combustion of the air-fuel mixture in the cylinder deteriorates, causing an increase in HC and PM in the exhaust gas.In the present embodiment, in the cylinder, a state in which both the amount of fuel in the fuel wetting and the amount of fuel in the droplet floating state is small is defined as a normal state in which the state in which wetting is to be feared and the droplet floating state need not be considered. A state in which the amount of fuel in the fuel wetting is large and the amount of fuel in the droplet suspension state is large is defined as a state in which wetting is to be feared.When the engine 10 is started, the ECU 40 determines whether the inside of the cylinder is in the state in which wetting is to be feared or whether the inside of the cylinder is in the droplet floating state. The ECU 40 calculates the non-evaporated fuel amount WE, which is an index value indicating the amount of fuel generated in the non-evaporated state in the cylinder. Based on this non-evaporated fuel amount WE, the ECU 40 determines whether the inside of the cylinder is in the state in which wetting is to be feared or in the droplet floating state. More specifically, the non-evaporated fuel amount WE is calculated using at least one of the cooling water temperature Tw indicating the temperature of the cooling water detected by the water temperature sensor 38, the fuel injection amount Q, and the fuel pressure Pf detected by the fuel pressure sensor 37. The ECU 40 corresponds to a wetting amount calculation unit. (a) in FIG. 3 is a view for explaining the calculation of the non-evaporated fuel amount WE using the cooling water temperature Tw, in which the horizontal axis represents the cooling water temperature Tw and the vertical axis represents the non-evaporated fuel amount WE. As the cooling water temperature Tw becomes lower, fuel is less likely to be evaporated in the cylinder. Therefore, as the cooling water temperature Tw becomes lower, the non-evaporated fuel amount WE is set larger. In the present embodiment, when the non-evaporated fuel amount WE is larger than a first temperature determination value THa, it is determined that the inside of the cylinder is in the state in which wetting is to be feared. When the non-evaporated fuel amount WE is equal to or less than the first temperature determination value THa and is greater than a second temperature determination value THb, it is determined that the inside of the cylinder is in the droplet levitation state. The second temperature determination value THb is smaller than the first temperature determination value THa. When the amount of non-evaporated fuel WE is equal to or less than the second temperature determination value THb, it is determined that the inside of the cylinder is in a normal state. (b) in FIG. 3 is a view for explaining calculation of the non-evaporated fuel amount WE using the fuel injection amount Q, in which the horizontal axis shows the fuel injection amount Q and the vertical axis shows the non-evaporated fuel amount WE. As the fuel injection amount Q increases, the amount of fuel wetting in the cylinder tends to increase. Therefore, as the fuel injection amount Q becomes larger, the non-evaporated fuel amount WE is set larger. In the present embodiment, when the non-evaporated fuel amount WE is larger than a first injection amount determination value THc, it is determined that the inside of the cylinder is in the state where wetting is to be feared. When the non-evaporated fuel amount WE is equal to or less than the first injection amount determination value THc and is greater than a second injection amount determination value THd, it is determined that the inside of the cylinder is in the droplet levitation state. The second injection amount determination value THd is a value smaller than the first injection amount determination value THc. When the amount of non-evaporated fuel WE is equal to or less than the second injection amount determination value THd, it is determined that the inside of the cylinder is in the normal state. (c) in FIG. 3 is a view for explaining calculation of the non-evaporated fuel amount WE using the fuel pressure Pf, where the horizontal axis indicates the fuel injection pressure Pf and the vertical axis indicates the non-evaporated fuel amount WE. As the fuel pressure Pf becomes lower, fuel is less likely to be evaporated. Therefore, as the fuel pressure Pf becomes lower, the non-evaporated fuel amount WE is set larger. In the present embodiment, when the non-evaporated fuel amount WE is larger than a first fuel pressure determination value THe, it is determined that the inside of the cylinder is in the state where wetting is to be feared. When the non-evaporated fuel amount WE is equal to or less than the first fuel pressure determination value THe and is greater than a second fuel pressure determination value THf, it is determined that the inside of the cylinder is in the droplet levitation state. The second fuel pressure determination value THf is a value smaller than the first fuel pressure determination value THe. When the amount of non-evaporated fuel WE is equal to or less than the second fuel pressure determination value THf, it is determined that the inside of the cylinder is in a normal state. The ECU 40 corresponds to a determination unit.Instead of individually determining the state within the cylinder using the non-evaporated fuel amount WE shown in (a) to (c) in FIG. 3, a summation of the non-evaporated fuel amount WE may be used to determine the state within the cylinder. In this case, weighting may be assigned to each of the non-evaporated fuel amount WE calculated using the cooling water temperature Tw, the non-evaporated fuel amount WE calculated using the fuel injection amount Q, and the non-evaporated fuel amount WE calculated using the fuel pressure Pf. Further, the injection timing of the injector 30 or the engine rotational speed Ne may be used as a parameter for calculating the amount of non-evaporated fuel WE. As the injection timing of the injector 30 moves farther from the BDC, the distance from the injection port of the injector 30 to the piston 35 in the cylinder becomes smaller. Therefore, the amount of fuel adhering to the upper surface of the piston 35 increases, and the amount of non-evaporated fuel WE increases. As the engine speed Ne becomes higher, a waiting time until fuel injected into the cylinder evaporates becomes shorter. Therefore, the amount of non-evaporated fuel WE becomes larger.Next, with reference to FIG. 4, control of the opening timing and the closing timing of the intake and exhaust valves 31 and 32 when the interior of the cylinder is determined to be in the state where wetting is to be feared or in the droplet floating state will be described. FIG. 4 shows a transition of the valve opening amount IN of the intake valve 31 and a transition of the valve opening amount EX of the exhaust valve 32, the vertical axis shows a valve opening amount, and the horizontal axis shows a time transition.In this embodiment, an opening time A 1 of the intake valve 31 is set to the top dead center advance angle side (hereinafter referred to as TDC), and the closing time A 2 is set to the bottom dead center retard side (hereinafter referred to as BDC) when the inside of the cylinder is in the normal state in which it is not necessary to consider the state in which wetting is to be feared and the droplet floating state, as shown in (a) in FIG. 4. Further, in the present embodiment, the opening time B 1 of the exhaust valve 32 is set to the retard side of the BDC and the closing time B 2 is set to the advance side of the TDC in the normal state. Hereinafter, the control of the opening timing and the closing timing of the intake valve 31 and the exhaust valve 32 performed in the normal state will be referred to as a normal control.The state in which wetting is to be feared is a state in which the non-evaporated fuel amount WE is high, and therefore reducing the fuel injection amount Q is effective in improving the state in which wetting is to be feared. Therefore, when the ECU 40 determines that the interior of the cylinder is in the state where wetting is to be feared, the ECU 40 performs the first control for reducing the intake air amount Ga as the control of the opening timing and the closing timing of the intake valve 31 or the exhaust valve 32 using the variable valve devices 33 and 34. The ECU 40 corresponds to a first control unit.In this embodiment, as shown in (b) in FIG. 4, late closing control is performed as the first control such that the variable valve device 33 delays the closing timing A 2 of the intake valve 31 to be farther from the BDC than the closing timing A 2 in the normal control. In this way, in the intake stroke, the amount of intake air Ga filled in the cylinder becomes lower than that when the first control is not performed.Therefore, the fuel injection amount Q calculated using the intake air amount Ga decreases. Note that early closing control may be performed as the first control such that the variable valve device 33 advances the closing timing A 2 of the intake valve 31 to be farther from the BDC than the closing timing A 2 in the normal control.Vaporization of suspended droplets contained in the air-fuel mixture is promoted as the temperature inside the cylinder increases. Therefore, it is effective to increase the temperature in the cylinder to improve the droplet floating state. Therefore, the ECU 40 performs a second control to increase the temperature in the cylinder as a control of the opening timing and the closing timing of the intake and exhaust valves 31 and 32 using the variable valve devices 33 and 34. The ECU 40 corresponds to a second control unit.As shown in (c) in FIG. 4, the ECU 20, as the second control, changes the opening timing and the closing timing of the intake valve 31 such that the variable valve device 33 causes the closing timing A 2 of the intake valve 31 to be closer to the BDC than the closing timing A 2 in the normal control. In the present embodiment, the closing timing A 2 of the intake valve 31 is advanced so as to be closer to the BDC than the closing timing A 2 in normal control. In this way, the actual compression ratio increases in the compression stroke of the engine 10, so that the temperature inside the cylinder increases, and floating liquid particles or droplets can be easily evaporated.Next, the method of start control for the engine 10 will be described with reference to FIG. 5. The process shown in FIG. 5 is repeatedly executed by the ECU 40 in a predetermined cycle period.In step S 11, it is determined whether it is in the start period from the start of the engine 10 to a time when a predetermined period has elapsed. More specifically, it is determined whether it is in a period from a start of cranking of the engine 10 using the starter 50 caused by IG ON to the end of warming-up of the catalytic converters 25 and 26. For example, a determination may be made as to whether the warm-up of the catalytic converters 25 and 26 is completed by determining whether a predetermined time has elapsed since the engine 10 started.At step S12, the non-evaporated fuel amount WE is calculated as shown in (a) to (c) in FIG. 3. At step S 13, it is determined whether the inside of the cylinder is in the state in which wetting is to be feared using the non-evaporated fuel amount WE calculated at step S 13.When it is determined that the inside of the cylinder is in the state where wetting is to be feared, the process proceeds to step S 14, and the first control is performed. By the first control, the closing timing A2 of the intake valve 31 is delayed by the variable valve devices 33 and 34 compared with the closing timing A2 in the normal control from the BDC, and the intake air amount Ga is reduced. In this way, the fuel injection amount Q is reduced, and the in-cylinder fuel wetting is reduced.When it is determined at step S 13 that the inside of the cylinder is not in the state in which wetting is to be feared, the process proceeds to step S 15. At step S15, it is determined whether the interior of the cylinder is in the droplet floating state using the non-evaporated fuel amount WE calculated at step S12. When it is determined at step S 15 that the inside of the cylinder is in the droplet floating state, the process proceeds to step S 16.At step S 16, the second control is performed. By the second control, the closing timing A 2 of the intake valve 31 is brought closer to the BDC than the closing timing A 2 in the normal control, and the actual compression ratio in the compression stroke of the engine 10 increases. In this way, the temperature Tc in the cylinder rises and the amount of floating droplets in the cylinder decreases. In the present embodiment, in the period from the start of the engine 10 to the end of cranking using the starter 50, the determination of the first state in which wetting is to be feared or the determination of the droplet floating state is performed, and according to the determination result, the first and second controls are performed. In this way, the first and second controls may be started before a first explosion of the engine 10 occurs. Therefore, the effect of improving the state in which wetting is to be feared or the droplet floating state can be enhanced.When it is determined at step S 15 that the inside of the cylinder is not in the droplet floating state, the process proceeds to step S 17. In the case where the process proceeds to step S 17, the inside of the cylinder is in the normal state. Therefore, the normal control for fixing the opening timing and the closing timing of the intake valve 31 is performed. Subsequently, the series of processes shown in FIG. 5 is ended.Next, with reference to FIG. 6, the transition of the operation state at the start of the engine 10 will be described.At time t 1, a start request command is input to the ECU 40 when the driver turns ON the IG (ignition). In response, the crankshaft 28 is initially rotated in the time period t1-t2 by cranking the starter 50. The intake air amount Ga increases according to the engine speed Ne (crank speed) due to the flow of air in the intake passage 12.In FIG. 6, it is determined that the inside of the cylinder is in the state where wetting is to be feared in the period t1-t2. Therefore, the closing timing A 2 of the intake valve 31 is delayed by the first control compared with the closing timing A 2 in the normal control from the BDC. At time t 2, the first explosion of the engine 10 occurs, and the engine speed Ne increases.After the first explosion of the engine 10, the engine speed Ne increases above the crank speed, and the intake air amount Ga increases. At this time, the closing timing A 2 of the intake valve 31 is delayed more than that of the BDC. Therefore, an increase in the intake air amount Ga is suppressed. In (c) in FIG. 6, the intake air amount Ga shown by the broken line indicates the intake air amount Ga at the closing timing A 2 of the intake valve 31 caused by the normal control. By suppressing the increase in the intake air amount Ga, the fuel injection amount Q calculated by the ECU 40 becomes smaller than the fuel injection amount Q in the normal control. Therefore, the amount of HC and PN in the exhaust gas is reduced as compared with that in the case where normal control is performed. In (e) in FIG. 6, the emission amount of HC and PN shown by the broken line indicates the emission amount of HC and PN in the normal control.Thereafter, the intake air amount Ga becomes the adjustment amount of the throttle valve 16. In the present embodiment, after time t 3, it is determined that the inside of the cylinder is in the droplet floating state. Therefore, the second control is performed in which the closing timing of the intake valve 31 is closer to the BDC than the closing timing A 2 in the normal control. In this way, the actual compression ratio increases in the compression stroke of the engine 10, and the in-cylinder temperature Tc increases. Therefore, the amount of HC and PN in the exhaust gas is reduced as compared with that in the case where the normal control is performed. It is conceivable that the intake air amount Ga increases as the actual compression ratio increases. Note that the increase in the intake air amount Ga is suppressed by a reduction correction of the opening degree of the throttle valve 16. In (c) of FIG. 6, after time t 3, the intake air amount Ga in the normal control and the intake air amount Ga in the second control are shown in a displaced state for convenience of explanation.Thereafter, the amount of floating droplets in the cylinder decreases as the temperature Tc in the cylinder increases. Subsequently, at time t 4, the warm-up of the catalytic converters 25 and 26 is completed, and the start control for the engine 10 is completed.According to the first embodiment described above, the following effects can be produced.When the engine 10 is started, the ECU 40 determines whether the inside of the cylinder is in the state where wetting is to be feared in which concerns about fuel wetting exists, or the inside of the cylinder is in the droplet floating state in which a large volume of floating droplets of fuel arises. Then, when it is determined that it is in the state where there is a fear of wetting, the first control for reducing the intake air amount Ga is performed as the control of the opening timing and the closing timing using the variable valve devices 33 and 34. In this way, the fuel injection amount Q is reduced, and therefore, fuel wetting in the cylinder is reduced. Thus, HC and PN in the exhaust gas can be reduced. Further, when it is determined to be in the floating droplet state, the second control for increasing the in-cylinder temperature Tc is performed as the control of the opening timing and the closing timing using the variable valve devices 33 and 34. In this way, fuel in the cylinder is easily evaporated, and therefore fuel is reduced in the form of a droplet, and HC and PN in the exhaust gas can be reduced. As described above, the configuration makes it possible to perform the appropriate treatment for reducing HC and PN according to the state of fuel in the cylinder. Therefore, the effect of reducing HC and PN in the exhaust gas can be enhanced.The ECU 40 calculates the in-cylinder non-evaporated fuel amount WE based on at least one of the temperature of the engine 10, the fuel injection amount Q, and the fuel pressure Pf. Subsequently, based on the calculated non-evaporated fuel amount WE, the state in which wetting is to be feared and the droplet floating state are determined. In this way, the state in which wetting is to be feared and the droplet floating state can be easily determined according to the operating state of the engine 10.Modification of the First EmbodimentThe ECU 40 may perform control as the second control to increase a valve overlap duration in which both the intake valve 31 and the exhaust valve 32 are opened.In FIG. 7, the transition of the valve opening amount of each of the intake and exhaust valves 31 and 32 in the normal control is shown by a broken line, and the transition of the valve opening amount after the opening timing and the closing timing are changed by the second control is shown by a solid line. In (a) in FIG. 7, the ECU 40, as the second control, advances the opening time A 1 of the intake valve 31 relative to the TDC from the opening time A 1 in normal control. In this way, the valve overlap period OR1 in which both the intake valve 31 and the exhaust valve 32 are opened is increased. In this valve overlap period OR1, internal EGR is generated, in which exhaust gas flowing out from the inside of the cylinder into the exhaust passage 23 flows back into the cylinder from the exhaust port. In this way, the temperature Tc in the cylinder increases, and a floating droplet in the cylinder can be easily evaporated.In (b) in FIG. 7, the ECU 40 as the second control delays the closing time B 2 of the exhaust valve 32 relative to the TDC from the closing time B 2 in normal control. In this way, the valve overlap period OR2 in which both the intake valve 31 and the exhaust valve 32 are opened is increased. In this valve overlap period OR 2, internal EGR occurs in which exhaust gas discharged from the inside of the cylinder to the exhaust passage 23 is returned to the inside of the cylinder again. In this way, the temperature Tc in the cylinder increases, and a floating droplet in the cylinder can be easily evaporated.This modification also provides the similar effects to the first embodiment.The ECU 40 may determine whether the inside of the cylinder is in the state where wetting is to be feared or whether the inside of the cylinder is in the droplet floating state in a period after the engine 10 is stopped until the engine 10 is started. In this case, after an ISS restart control performs an automatic stop, for example, the non-evaporated fuel amount WE, the ECU 40 calculates the fuel pressure Pf using the cooling water temperature Tw or the fuel pressure Pf. Further, based on this calculated non-evaporated fuel amount WE, the ECU 40 determines whether the inside of the cylinder is in the state in which wetting is to be feared or in the droplet floating state. Subsequently, at the time when the ISS (idle start-stop) is restarted, the first or second control may be performed according to the state of the cylinder that has already been determined. In the present embodiment, the first or second control can be performed at the same time as the start of the engine 10.Second EmbodimentA second embodiment is different from the first embodiment as described below. The configurations having the same reference numerals as those in the first embodiment show the same configurations, and the description thereof will not be repeated.From the start of the engine 10, the pressure in the intake passage 12 is equivalent to the atmospheric pressure for a while. Therefore, the intake air amount Ga increases. When the intake air amount Ga reaches the adjustment amount of the throttle valve 16, the intake air amount Ga decreases. In FIG. 8, the pressure in the intake passage 12 is the atmospheric pressure Pa during the crank period P 0 of the engine 10, and after the first explosion occurs at time t 11, the pressure in the intake passage 12 decreases from the atmospheric pressure. Therefore, in the present embodiment, the ECU 40 determines that it (i.e., the inside of the cylinder) is in the state where wetting is to be feared when it is in the first period P 1 including the start time when the intake air amount Ga increases. When it is the second period P 2 following the first period P 1, it is determined to be in the droplet floating state.Next, the method of start control for the engine 10 according to the present embodiment will be described with reference to FIG. 9. The process shown in FIG. 9 is repeatedly executed by the ECU 40 in a predetermined cycle period.When it is determined at step S 11 that it is in the start period of the engine 10, the process proceeds to step S 20, and it is determined whether the engine 10 is in the first period P 1. The first control reduces the intake air amount Ga of the engine 10. Therefore, it is desirable to restrict the implementation of the first control to as short a duration as possible. Therefore, the duration of a combustion cycle after the first explosion occurs in the engine 10 after the engine 10 is set to its initial rotation by the starter 50 is defined as the first duration P 1 in which the first control is performed. The duration of the one first combustion cycle after the end of cranking is the duration of 72° CA (crank angle) from the first explosion, and in this duration, combustion is performed in each cylinder. In the present embodiment, the duration of the first combustion cycle after the end of cranking corresponds to the first duration P 1.When it is determined at step S 11 that it is the first duration P 1, the process proceeds to step S 14, and the first control for controlling the opening timing and the closing timing of the intake valve 31 is performed. Therefore, in the present embodiment, the first control is always performed at the start of starting the engine 10.When it is determined at step S 20 that it is not the first duration P 1, the process proceeds to step S 21, and it is determined whether it is the second duration P 2, which is the duration of the second combustion cycle after the first explosion. When the affirmative determination is made at step S 21, the process proceeds to step S 16, and the second control is performed.Further, at step S 21, when it is determined that it is not the duration of the second combustion cycle after the end of cranking, the process proceeds to step S 17, and the normal control that does not change the opening timing and the closing timing of the intake valve 31 and the exhaust valve 32 is performed. Subsequently, the series of processes shown in FIG. 9 is ended.According to the present embodiment described above, the following effects can be obtained.The ECU 40 determines that it is in a state in which wetting is to be feared when it is in the first period P 1 including the start of the engine 10. The ECU 40 determines that it is in a droplet levitation state when it is in the second duration following the first duration P 1. In this way, the first control and the second control are executed in order, and therefore, the effect of improving the wetting state in the cylinder can be enhanced.The ECU 40 determines the state in which wetting is to be feared in the duration of the first combustion cycle after the first explosion of the engine 10 as the first duration P 1 after the engine 10 is set to the initial rotation by the starter 50. Further, the ECU 40 determines the droplet levitation state in the duration following the duration of the one combustion cycle after the first explosion of the engine 10 as the second duration P 2. In this way, the configuration makes it possible to restrict the duration for executing the first control to the duration of the one combustion cycle after the first explosion of the engine 10. Therefore, the configuration makes it possible to shorten the time required for the engine rotational speed Ne to increase to the predetermined value when the engine 10 is started, and to improve the startability of the engine 10.Third EmbodimentA third embodiment is different from the first embodiment as described below. The configurations having the same reference numerals as those in the first embodiment show the same configurations, and the description thereof will not be repeated.When the engine 10 is restarted in the ISS restart control, it is necessary to minimize the vibration of the engine 10 during the start period. For example, if the engine rotational speed Ne largely fluctuates during the restart in the ISS restart control, there is a problem that the driver is more likely to notice this fluctuation. In FIG. 10, the actual compression ratio in the second control is increased at time t 21 in the period in which the engine speed Ne is increased after the first explosion. Therefore, overshoot occurs thereafter at the engine rotational speed Ne.On the other hand, it is highly likely that the catalytic converters 25 and 26 have already been activated by warming-up when the engine 10 is restarted in the ISS restart control. Therefore, in the present embodiment, the suppression of fluctuations in the engine rotational speed Ne when the engine 10 is restarted in the ISS restart control is prioritized. Further, the second control is performed after waiting for the engine speed Ne to stabilize (time t 22 in FIG. 10 ).Next, the method of start control for the engine 10 according to the present embodiment will be described with reference to FIG. 11. The process shown in FIG. 11 is repeatedly executed by the ECU 40 in a predetermined cycle period.When it is determined at step S 11 that it is in the start period of the engine 10, the process proceeds to step S 20, and it is determined whether the engine 10 is in the first period P 1. In addition, in this embodiment, the duration of a combustion cycle after the end of cranking is defined as the first duration P 1. When it is in the first period P 1, the process proceeds to step S 14, and the first control for controlling the opening timing and the closing timing of the intake valve 31 is performed.At step S 20, if not in the first period P 1, the process proceeds to step S 31, and it is determined whether the engine 10 is restarted with the ISS restart control. When the engine 10 is not started with the ISS restart control, the process proceeds to step S 16 to perform the second control. In this case, the duration following the duration of the one combustion cycle after the occurrence of the first explosion is defined as the second duration P 2.When the affirmative determination is made at step S 31, the process proceeds to step S 32, and it is determined whether the engine rotational speed Ne is stable. In the present embodiment, a difference between an engine rotational speed Ne (n-1) obtained at the previous calculation cycle and an engine rotational speed Ne (n) obtained at the current calculation cycle is calculated as a rotational speed difference ΔV. Subsequently, it is determined that the engine rotational speed Ne is stable when the calculated rotational speed difference ΔV is equal to or less than a predetermined speed difference determination value. On the other hand, it is determined that the engine rotational speed Ne is not stable when the rotational speed difference ΔV is larger than the speed determination value.When the negative determination is made at step S 32, the process proceeds to step S 14, and the first control is performed. Therefore, the reduction of the intake air amount Ga of the engine 10 continues with the first control. The reduction of the intake air amount Ga of the engine 10 in the first control is continued to thereby suppress an increase in the engine rotational speed Ne, and the stabilization of the engine rotational speed Ne can be expedited.Thereafter, at step S 32, each time the process of FIG. 11 is performed, it is determined whether the engine rotational speed Ne is stable. Subsequently, the process proceeds to step S 16 when it is determined at step S 32 that the engine rotational speed Ne is stable, and the second control is performed. Subsequently, the series of processes shown in FIG. 11 is ended.According to the present embodiment described above, the following effects can be obtained.After the engine 10 is set to the initial rotation in the starter 50 that rotates the crankshaft 28 of the engine 10, the ECU 40 determines the state in which wetting is to be feared in the period until the rotation speed of the engine 10 becomes stable as the first period P 1. Further, the ECU 40 determines the droplet floating state in the period after the engine rotational speed Ne becomes stable as the second period P 2. In this way, the configuration makes it possible to reduce emissions of HC and PN while suppressing excessive fluctuations in the engine rotational speed Ne when the engine 10 is started.When the engine 10 is restarted in the ISS restart control, the ECU 40 determines the state in which wetting is to be feared in the period until the engine rotational speed Ne becomes stable as the first period P 1. Further, the ECU 40 determines the droplet floating state in the period after the engine rotational speed Ne becomes stable as the second period P 2. When the engine 10 is not restarted in the ISS restart control, the state in which wetting is to be feared is determined as the first duration P 1 in the duration of the one combustion cycle after the first explosion of the engine 10. Further, the ECU 40 determines the droplet levitation state in the duration following the duration of the one combustion cycle after the first explosion as the second duration P 2. In this way, this configuration makes it possible to suppress the driver from feeling irritating due to the excessive variation in the engine rotational speed Ne in the restart control, and at the same time to reduce the emission of HC and PN.Modification of the Third EmbodimentWhen restarting the engine 10, the ECU 40 may determine the state in which wetting is to be feared in the period until the engine speed Ne becomes stable as the first period P 1 regardless of whether the ISS restart control is performed, and may determine the droplet floating state in the period after the engine rotational speed Ne becomes stable as the second period P 2. In this case, step S 31 of FIG. 11 may be omitted. Therefore, the process may proceed to step S 32 and may determine whether the engine rotational speed Ne is in a stable state when a negative determination is made at step S 20.Other EmbodimentsThe engine 10 may be configured to include only the variable valve device 33 that controls only the opening timing and the closing timing of the intake valve 31. In this case, the ECU 40, as the second control, may control the closing timing of the intake valve 31 to be closer to the BDC, or may advance the opening timing A 1 of the intake valve 31. In this way, the ECU 40 may perform control to increase the valve overlap period OR 1 in which both the intake valve 31 and the exhaust valve 32 are opened.The start period at which the ECU 40 performs the first control and the second control may continue from the start of cranking with the starter 50 until the elapse of a predetermined period regardless of the activity of the catalytic converters 25 and 26. In this case, the ECU 40 may determine whether it is in the start period at step S 11 based on a lapse of time from the start of cranking with the starter 50.The ECU 40 may determine whether the inside of the cylinder is in the state where wetting is to be feared or the inside of the cylinder is in the droplet floating state under the condition that the engine 10 is cold started.Engine 10 may be a port injected internal combustion engine.Although the disclosure has been described in accordance with the embodiments, it should not be construed that the present disclosure is limited to such embodiments or structures. The present disclosure encompasses various modifications and variations within the scope of equivalents. In addition, the various combinations and configurations that are preferred, other combinations and configurations, while including more, less, or only a single element, are also included within the spirit and scope of the present disclosure.

Claims

A control device (40) for an internal combustion engine (10), the internal combustion engine including a fuel injection valve (30) configured to inject fuel into a cylinder, and a variable valve device (33, 34) configured to change an opening timing and a closing timing of at least one intake valve (31) among the intake valve and an exhaust valve (32), the internal combustion engine control device configured to control a fuel injection amount based on an intake air amount of the internal combustion engine, and control the opening timing and the closing timing of the intake valve with the variable valve device based on an operation state of the internal combustion engine, wherein the internal combustion engine control device comprises: a determination unit configured to determine, whether an interior of a cylinder is in a state in which fuel wetting is to be feared or the interior of the cylinder is in a droplet floating state in which a large volume of floating droplets of fuel arises when the internal combustion engine is started; a first control unit configured to perform first control as control of the opening timing and the closing timing with the variable valve device to reduce the amount of intake air when the determination unit determines that the interior of the cylinder is in the state in which wetting is to be feared; and a second control unit configured to perform, as the control of the opening timing and the closing timing with the variable valve device, a second control to increase a temperature in the cylinder when the determination unit determines that the inside of the cylinder is in the droplet floating state.The control device for the internal combustion engine according to claim 1, wherein the first control unit is configured to perform, as the first control, an early closing control or a late closing control for separating the closing timing of the intake valve from a bottom dead center, and the second control unit is configured to perform, as the second control, a control to bring the closing timing of the intake valve closer to the bottom dead center or to increase a valve overlap at which both the intake valve and the exhaust valve are opened.The control device for the internal combustion engine according to claim 1 or 2, further comprising: a calculation unit configured to calculate an amount of non-evaporated fuel generated in the cylinder based on at least one of a temperature of the internal combustion engine, a fuel injection amount of the fuel injection valve, and a fuel pressure of fuel supplied to the fuel injection valve, wherein the determination unit is configured to determine whether the interior of the cylinder is in the state in which wetting is to be feared or the interior of the cylinder is in the droplet floating state based on the amount of non-evaporated fuel generated in the cylinder calculated by the calculation unit.The control device for the internal combustion engine according to claim 1 or 2, wherein the determination unit is configured to determine that the inside of the cylinder is in the state in which wetting is to be feared in a period from a start of the internal combustion engine to a time point at which a predetermined period has elapsed in a first period including the start of the internal combustion engine, and determine that the inside of the cylinder is in the droplet floating state in a second period following the first period.The control device for the internal combustion engine according to claim 4, wherein the determination unit is configured to determine that the inside of the cylinder is in the state of fear of wetting in a duration as the first duration that is a combustion cycle from a first explosion of the internal combustion engine after the internal combustion engine is initially rotated with a starter (50) to rotate an output shaft (28) of the internal combustion engine, and determine that the inside of the cylinder is in the droplet floating state in a duration as the second duration that follows the duration of the one combustion cycle after the first explosion.The control device for the internal combustion engine according to claim 4, wherein the determination unit is configured to determine that the inside of the cylinder is in the state in which wetting is to be feared in a duration as the first duration after the internal combustion engine is initially rotated with the starting device (50) to rotate the output shaft (28) of the internal combustion engine until a rotation speed of the internal combustion engine becomes stable, and determine that the inside of the cylinder is in the droplet floating state in a duration as the second duration after the rotation speed of the internal combustion engine becomes stable.The control device for the internal combustion engine according to claim 6, further comprising: a restart control unit configured to automatically stop the internal combustion engine when a predetermined automatic stop condition is satisfied, and subsequently automatically start the internal combustion engine when a predetermined restart condition is satisfied, wherein the determination unit is configured to determine that the inside of the cylinder is in the state in which wetting is to be feared in a period as the second period after the rotation speed of the internal combustion engine becomes stable under a condition that the internal combustion engine is started by the restart control unit, and determine that the inside of the cylinder is in the droplet floating state in a period as the second period after the rotation speed of the internal combustion engine becomes stable, The determination unit is configured to determine that the interior of the cylinder is in the droplet floating state in a duration as the first duration that is a duration of a combustion cycle after a first explosion of the internal combustion engine under a condition that the internal combustion engine is not started by the restart control unit, and determine that the interior of the cylinder is in the droplet floating state in a duration as the second duration that follows the duration of the one combustion cycle after the first explosion.

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