Control device and control method for an internal combustion engine

Abstract

A machine control device initiates a fuel injection process to introduce an air-fuel mixture, containing fuel injected by a fuel injector, into the exhaust port without combusting the air-fuel mixture in the cylinder, while the crankshaft of an internal combustion engine is rotating. If the oxygen concentration of the exhaust gas, which has passed through a three-way catalyst, decreases during the execution of the fuel injection process, the machine control device initiates a stop process to halt the fuel injection.

Description

Background1. Field of InterestThe following description relates to a control device and a control method for an internal combustion engine.2. Description of the Related ArtU.S. Pat. No. 2014 / 0 041 362 A1 discloses a spark-ignition internal combustion engine. This internal combustion engine is equipped with a three-way catalyst and a filter that collects particulates. The three-way catalyst is disposed in the exhaust passage. The filter is disposed in the exhaust passage on the downstream side of the three-way catalyst. US 2012 / 0 310 512 A1 discloses an operating mode in which a fuel-air mixture is conveyed into the exhaust gas region uncombusted in order to provide additional heat at the catalyst by an exothermic reaction. EP 1 625 300 B1 discloses that an oxygen sensor can be used downstream of the catalyst in order to detect, in a corresponding operating mode, whether the oxygen content falls due to the reaction at the catalyst. In addition, DE 10 2016 124 427 A1 teaches the use of a downstream oxygen sensor for detecting the oxygen storage capacity of the upstream catalytic converter.In US 2014 / 0 041 362 A1, a fuel introduction process is performed to increase the temperature of the three-way catalyst while the vehicle is sliding, thereby burning and removing the particulates deposited in the filter. In the fuel introduction process, the fuel injection is performed with the spark discharge of the spark plug stopped. Subsequently, the air-fuel mixture is introduced into the exhaust passage without being burned in the cylinder. The unburned air-fuel mixture flows from the exhaust passage into the three-way catalyst and is burned in the three-way catalyst. The heat generated by the combustion increases the temperature of the three-way catalyst and also increases the temperature of the gas flowing from the three-way catalyst into the filter. This increases the filter temperature to the ignition point of the particles. Consequently, the particulates deposited in the filter are burned and removed.During the above-described combustion operation of the internal combustion engine, the air-fuel ratio sensor installed in the exhaust passage detects the air-fuel ratio of the air-fuel mixture burned in the cylinder, and air-fuel ratio feedback control is executed according to the detection result of the air-fuel ratio. Specifically, by correcting the fuel injection amount by the air-fuel ratio feedback control, the deviation of the fuel injection amount of the fuel injection valve is compensated.In contrast, in the execution of the fuel introduction process, the air-fuel ratio feedback control cannot be executed because the in-cylinder combustion is stopped. Therefore, the amount of fuel actually injected from the fuel injection valve (actual injection amount) may deviate from the amount (commanded injection amount) commanded by the control device. Consequently, the actual injection amount may exceed the commanded injection amount so that the fuel concentration in the air-fuel mixture increases to such an extent that the air-fuel ratio of the unburned air-fuel mixture flowing into the exhaust passage becomes richer than the stoichiometric air-fuel ratio. This is likely to result in the following disadvantages.When unburned air-fuel mixture having a high fuel concentration flows into the three-way catalyst due to execution of the fuel introduction process, the fuel in the air-fuel mixture is burned using not only the oxygen contained in the air-fuel mixture but also the oxygen stored in the three-way catalyst. When this reduces the oxygen storage amount of the three-way catalyst, a part of the fuel contained in the air-fuel mixture can easily pass through the three-way catalyst without being burned due to the lack of oxygen, so that the emission may deteriorate.Summary of the InventionThis summary is provided to introduce a selection of concepts in a simplified form that are described in more detail below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to serve as an aid in determining the scope of the claimed subject matter.A first aspect of the invention relates to a control device for an internal combustion engine having the features of claim 1. the internal combustion engine includes a fuel injection valve, a cylinder into which an air-fuel mixture containing the fuel injected by the fuel injection valve is introduced, an ignition device that ignites the air-fuel mixture introduced into the cylinder by a spark, an exhaust passage through which the gas discharged from inside the cylinder flows, a three-way catalyst provided in the exhaust passage, and a sensor provided in the exhaust passage and detecting a state of an oxygen concentration of exhaust gas corresponding to a gas having passed through the three-way catalyst. The control device is configured to execute: a fuel introduction process for introducing the air-fuel mixture containing the fuel injected by the fuel injection valve into the exhaust passage in a state in which a crankshaft of the internal combustion engine rotates without combusting the air-fuel mixture in the cylinder; and a stop process for stopping the fuel introduction process when the oxygen concentration detected by the sensor has changed from a lean state to a rich state with respect to the oxygen concentration at a stoichiometric air-fuel ratio during the execution of the fuel introduction process.A second aspect of the invention relates to a control method for an internal combustion engine having the features of claim 4. the internal combustion engine includes a fuel injection valve, a cylinder into which an air-fuel mixture containing the fuel injected by the fuel injection valve is introduced, an ignition device that ignites the air-fuel mixture introduced into the cylinder by a spark, an exhaust passage through which the gas discharged from inside the cylinder flows, a three-way catalyst provided in the exhaust passage, and a sensor provided in the exhaust passage and detecting a state of an oxygen concentration of exhaust gas corresponding to a gas having passed through the three-way catalyst. The control method includes: introducing the air-fuel mixture including the fuel injected by the fuel injection valve into the exhaust passage in a state in which a crankshaft of the internal combustion engine rotates without combusting the air-fuel mixture in the cylinder; and stopping the fuel introduction process when the oxygen concentration detected by the sensor has changed from a lean state to a rich state with respect to the oxygen concentration at a stoichiometric air-fuel ratio during execution of the fuel introduction process.Other features and aspects will become apparent from the following detailed description, drawings and claims.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is a schematic diagram showing the configuration of a hybrid vehicle equipped with a control device for an internal combustion engine according to an embodiment of the present disclosure. FIG. 2 is a flowchart showing a flow of catalyst temperature increase control executed by the control device. FIG. 3 is a timing chart showing the operation of the embodiment. FIG. 4 is a schematic diagram showing the exhaust system of an internal combustion engine in a modification of the embodiment. FIG. 5 is a flowchart showing a flow of catalyst temperature increase control in a modification of the embodiment.In the figures and the detailed description, the same reference numerals refer to the same elements. The figures may not be to scale, and the relative size, proportions, and representation of the elements in the figures may be exaggerated for clarity, illustration, and simplicity.Detailed DescriptionThis description provides a thorough understanding of the described methods, apparatus, and / or systems. Modifications and equivalents of the described methods, devices, and / or systems will be apparent to one of ordinary skill in the art. The sequences of operations are exemplary and may be changed as apparent to those skilled in the art, except for operations that necessarily occur in a particular order. Descriptions of functions and constructions known to those skilled in the art may be omitted.Example embodiments may take various forms and are not limited to the examples described. However, the examples described are accurate and complete, and will fully convey the full scope of the disclosure to those skilled in the art.A control device 100 for an internal combustion engine 10 according to an embodiment will now be described with reference to FIGS. 1, 2 to 3.FIG. 1 shows a hybrid vehicle (hereinafter referred to as a vehicle) 500 including a spark-ignition internal combustion engine 10 to which the control device 100 of the present embodiment is adapted. As shown in FIG. 1, the vehicle 500 has two motor generators, i.e., a first motor generator 71 and a second motor generator 72, which can be used as both a motor and a generator. Moreover, the vehicle 500 includes a battery 77, a first inverter 75, and a second inverter 76. when the first motor generator 71 and the second motor generator 72 operate as generators, the battery 77 stores the power generated by the first and second motor generators 71, 72. When the first motor generator 71 and the second motor generator 72 operate as motors, the battery 77 supplies the energy stored in the battery 77 to the first and second motor generators 71, 72. The first inverter 75 regulates the amount of energy transferred between the first motor generator 71 and the battery 77. The second inverter 76 adjusts the amount of energy transferred between the second motor-generator 72 and the battery 77.The vehicle 500 includes a first planetary gear mechanism 40. the first planetary gear mechanism 40 includes a sun gear 41 corresponding to an external gear and a ring gear 42 corresponding to an internal gear arranged coaxially with the sun gear 41. Between the sun gear 41 and the ring gear 42, planetary gears 43 are provided which mesh with the sun gear 41 and the ring gear 42. The planet gears 43 are supported by a carrier 44 for rotation and rotation. The carrier 44 is coupled to a crankshaft 14 that corresponds to the output shaft of the internal combustion engine 10. The sun gear 41 is coupled to the first motor-generator 71. The ring gear 42 is connected to a ring gear shaft 45. The ring gear shaft 45 is coupled to drive wheels 62 via a reduction mechanism 60 and a differential mechanism 61. In addition, the ring gear shaft 45 is coupled to the second motor-generator 72 via the second planetary gear mechanism 50.The second planetary gear mechanism 50 includes a sun gear 51 corresponding to an external gear and a ring gear 52 corresponding to an internal gear arranged coaxially with the sun gear 51. Between the sun gear 51 and the ring gear 52, planetary gears 53 are provided which mesh with the sun gear 51 and the ring gear 52. Each planet gear 53 is rotatable, but cannot rotate. The ring gear 52 is connected to the ring gear shaft 45. The sun gear 51 is connected to the second motor-generator 72.The internal combustion engine 10 has a plurality of cylinders 11. In the intake passage 15, a throttle valve 16 that adjusts the intake air amount is provided. The intake passage 15 branches on the downstream side of the throttle valve 16 to correspond to each of the cylinders 11. The branch portions of the intake passage 15 are connected to the intake ports 15a provided for the respective cylinders 11. Each intake passage 15a is provided with a fuel injection valve 17. Each cylinder 11 is provided with an igniter 19. The igniter 19 ignites the air-fuel mixture sucked into the cylinder 11 by a spark discharge. Further, the internal combustion engine 10 is provided with an exhaust passage 21 serving as a discharge passage for exhaust gas generated by the combustion of the air-fuel mixture in each cylinder 11. In the exhaust passage 21, a three-way catalyst 22 configured to purify exhaust gas is provided. Further, in the exhaust passage 21 downstream of the three-way catalyst 22, a filter 23 for collecting particulates in the exhaust gas is provided.In the internal combustion engine 10, the air-fuel mixture containing fuel injected from the fuel injection valves 17 is introduced into the cylinders 11. When the igniter 19 ignites the air-fuel mixture, combustion occurs in the cylinder 11. The exhaust gas resulting from the combustion is discharged from the inside of the cylinder 11 into the exhaust passage 21. In the three-way catalyst 22, oxidation of HC and CO in the exhaust gas and reduction of NOx take place. Moreover, the filter 23 traps particulates in the exhaust gas to purify the exhaust gas.The vehicle 500 includes the engine control device 100, an engine control device 300, and a vehicle control device 200. The engine control device 100 performs various types of control of the internal combustion engine 10. The motor control device 300 performs various types of control of the first motor generator 71 and the second motor generator 72. The vehicle control device 200 controls the engine control device 100 and the motor control device 300 in a central manner. In addition, the vehicle 500 is equipped with a battery monitoring device 400 that monitors the state of charge (SOC) of the battery 77.The battery monitoring device 400 is connected to the battery 77. The battery monitoring device 400 includes a central processing unit (CPU) and a memory. The battery monitoring device 400 receives the current IB, the voltage VB, and the temperature TBof the battery 77. the battery monitoring device 400 calculates the state of charge SOC of the battery 77 by causing the CPU to execute programs stored in the memory, based on at least the current IB, the voltage VB, and the temperature TB.The motor control device 300 is connected to the first inverter 75 and the second inverter 76. The motor control device 300 includes a central processing unit (CPU) and a memory. The motor control device 300 controls the amount of power supplied from the battery 77 to the first motor generator 71 and the second motor generator 72, and the amount of power supplied to the battery 77 from the first motor generator 71 and the second motor generator 72 (i.e., charge amount) by causing the CPU to execute programs stored in the memory.The engine control device 100, the motor control device 300, and the battery monitoring device 400 are connected to the vehicle control device 200 via communication terminals. The vehicle control device 200 also includes a central processing unit (CPU) and a memory. The vehicle control device 200 executes various types of control by causing the CPU to execute programs stored in the memory.The vehicle control device 200 receives the state of charge SOC of the battery 77 from the battery monitoring device 400. The vehicle control device 200 is connected to an accelerator pedal sensor 86 that detects the amount of depression of the accelerator pedal by the driver (accelerator pedal operation amount ACC), a vehicle speed sensor 87 that detects the vehicle speed SP corresponding to the travel speed of the vehicle 500, and a power switch 88. The vehicle control device 200 receives output signals from sensors and switches. The power switch 88 corresponds to a switch for activating the system of the hybrid vehicle 500. When the operator turns on the power switch 88, the vehicle 500 is in a ready-to-drive state.The vehicle control device 200 calculates the required power of the vehicle corresponding to the required value of the driving force of the vehicle 500 based on the accelerator operation amount ACC and the vehicle speed SP. In addition, the vehicle control device 200 calculates the engine required torque, the first motor required torque, and the second motor required torque based on the required performance of the vehicle, the state of charge SOC, and the like. The engine required torque corresponds to a required value of the output torque of the internal combustion engine 10. the first motor required torque corresponds to a required value of the drive torque or the regenerative torque of the first motor generator 71. the second motor required torque corresponds to a required value of the drive torque or the regenerative torque of the second motor generator 72. the engine control device 100 controls the output of the internal combustion engine 10 according to the engine required torque. The engine control device 300 performs torque control required for driving the vehicle 500 by performing torque control of the first motor generator 71 and the second motor generator 72 according to the required torque of the first motor and the required torque of the second motor.The machine control device 100 includes a central processing unit (hereinafter, referred to as a CPU) 110 and a memory 120 that stores programs and data used for control. The CPU 110 executes programs stored in the memory 120 to execute various types of engine control.The engine control device 100 is connected to an air flow meter 81, a coolant temperature sensor 82, and a crank angle sensor 85. The air flow meter 81 corresponds to an intake air amount sensor that detects an intake air amount GA. The coolant temperature sensor 82 detects a coolant temperature THW corresponding to the temperature of the coolant of the internal combustion engine 10. The crank angle sensor 85 detects the rotation angle of the crankshaft 14. the engine control device 100 receives output signals from the above-described sensors. The engine control device 100 is also connected to a first air-fuel ratio sensor 83 provided in the exhaust passage 21 on the upstream side of the three-way catalyst 22, and a second air-fuel ratio sensor 84 provided in the exhaust passage 21 between the three-way catalyst 22 and the filter 23. The engine control device 100 also receives output signals from the above-described sensors.The first air-fuel ratio sensor 83 and the second air-fuel ratio sensor 84 are sensors that detect the state of the oxygen concentration of the exhaust gas and output signals proportional to the oxygen concentration of the exhaust gas. The first air-fuel ratio sensor 83 detects an upstream side air-fuel ratio Afu indicating the oxygen concentration of the exhaust gas flowing into the three-way catalyst 22. The second air-fuel ratio sensor 84 detects a downstream side air-fuel ratio Afd indicating the oxygen concentration of the exhaust gas (hereinafter referred to as exhaust gas) after passing through the three-way catalyst 22. The engine control device 100 is also connected to a temperature sensor 89 provided in the exhaust passage 21 between the three-way catalyst 22 and the filter 23. The temperature sensor 89 detects a catalyst outlet gas temperature THe corresponding to the temperature of the exhaust gas after passing through the three-way catalyst 22. The engine control device 100 also receives output signals from this sensor.The engine control device 100 calculates an engine speed NE based on an output signal Scr of the crank angle sensor 85. in addition, the engine control device 100 calculates an engine load factor KL based on the engine speed NE and the intake air amount GA. The engine load factor KL corresponds to the ratio of the actual cylinder inflow air amount to the cylinder inflow air amount when the internal combustion engine 10 is in a steady state operating state with the throttle valve 16 fully opened at the actual engine speed NE. The cylinder inflow air amount corresponds to the air amount flowing into each cylinder 11 in the intake stroke.The engine control device 100 calculates a catalyst temperature Tsc corresponding to the temperature of the three-way catalyst 22 and a filter temperature Tf corresponding to the temperature of the filter 23, based on the catalyst outlet gas temperature THe and various kinds of engine operating conditions such as the intake charging efficiency and the engine speed NE. In addition, the engine control device 100 calculates a PM deposit amount Ps based on the engine speed NE, the engine load factor KL, the filter temperature Tf, and the like. The PM deposition amount Ps corresponds to the amount of particulates deposited on the filter 23.Moreover, the engine control device 100 performs air-fuel ratio feedback control that corrects the fuel injection amount of the fuel injection valve 17 based on the detection values of the first air-fuel ratio sensor 83 and the second air-fuel ratio sensor 84.The vehicle control device 200 requests the engine control device 100 to stop the combustion operation of the internal combustion engine 10 when the vehicle 500 is in a stopped state or traveling at a low speed, provided that the state of charge SOC of the battery 77 is above a certain required charge value. When a request to stop the combustion operation is made, the engine control device 100 stops both the fuel injection of the fuel injection valve 17 and the spark discharge of the ignition device 19 to stop the combustion operation of the internal combustion engine 10.As described above, the collected particulates in the exhaust gas are deposited on the filter 23 provided in the exhaust passage 21. As the deposition amount of particulates increases, the filter 23 may clog. In order to burn and remove the particulates deposited on the filter 23, the temperature of the filter 23 needs to be higher than or equal to the ignition point of the particulates. The three-way catalyst 22 is disposed in the exhaust passage 21 on the upstream side of the filter 23. As the temperature of the three-way catalyst 22 (catalyst temperature) rises, the temperature of the gas flowing from the three-way catalyst 22 to the filter 23 also rises. Due to the heat absorption by the high temperature gas flowing in, the temperature of the filter 23 also rises, and therefore, the increase in the temperature of the three-way catalyst 22 burns the particulates deposited on the filter 23. Therefore, in the present embodiment, when the deposition amount of the particulates in the filter 23 is increased, catalyst temperature increase control is executed to increase the catalyst temperature to combust and remove the particulates deposited on the filter 23.FIG. 2 shows the flow of the catalyst temperature increase control. The series of processes illustrated in FIG. 2 is started when the combustion operation of the internal combustion engine 10 is stopped and the rotation of the crankshaft 14 is stopped. This process is implemented by the CPU 110 executing programs stored in the memory 120 of the machine control device 100. In the following description, the number of each step is represented by the letter S followed by a numeral.When this process is started, the CPU 110 first determines whether there is a temperature increase request of the three-way catalyst 22 (S 100). In the present embodiment, the CPU 110 determines that there is a temperature increase request of the three-way catalyst 22 when the PM deposition amount Ps is larger than a predetermined specified amount and the catalyst exit gas temperature THe is lower than the regeneratable temperature of the filter 23.If it is determined that there is no temperature increase request of the three-way catalyst 22 (S 100: NO), the CPU 110 ends the current process. In contrast, if it is determined that there is a temperature increase request of the three-way catalyst 22 (S 100: YES), the CPU 110 starts drive control (S 110). The drive control corresponds to control that rotates the crankshaft 14 with the power of the first motor generator 71 in a state where the combustion operation of the internal combustion engine 10 is stopped. When the drive control for rotating the crankshaft 14 is started, intake and exhaust are performed in each cylinder 11.In the drive control, the rotation speed of the first motor-generator 71 is controlled so that the engine rotation speed NE becomes equal to or higher than a specified temperature increase rotation speed γ. The temperature increase speed γ corresponds to an engine speed at which the flow rate of the air discharged into the exhaust passage 21 corresponds to the minimum flow rate required to increase the catalyst temperature.After starting the drive control, the CPU 110 starts a fuel introduction process. In the fuel introduction process, the fuel injection of the fuel injection valve 17 is performed in a state where the spark discharge of the ignition device 19 is stopped. The fuel injection amount of the fuel injection valve 17 during execution of the fuel introduction process is controlled so that the air-fuel ratio of the air-fuel mixture is leaner than the stoichiometric air-fuel ratio.At the beginning of the fuel introduction process, intake and exhaust are performed in each cylinder 11 via the drive control. The air-fuel mixture containing the fuel injected from the fuel injection valve 17 is thus introduced into the exhaust passage 21 uncombusted. Since the unburned air-fuel mixture flows into the three-way catalyst 22 and is burned in the three-way catalyst 22, the catalyst temperature increases.Next, the CPU 110 determines whether the downstream side air-fuel ratio Afd has indicated a decrease in the oxygen concentration of the exhaust gas (S 130). In the present embodiment, if the downstream side air-fuel ratio Afd starts changing to a rich side value during the execution of the fuel introduction process, the CPU 110 determines that the downstream side air-fuel ratio Afd indicates a decrease in the oxygen concentration of the exhaust gas.If the downstream side air-fuel ratio Afd indicates a decrease in the oxygen concentration (S 130: YES), the CPU 110 stops the fuel introduction process by stopping the fuel injection from the fuel injection valve 17 (S 150). The CPU 110 also stops the drive control (S 160). Then, the CPU 110 ends the current process.On the other hand, if the downstream side air-fuel ratio Afd does not indicate a decrease in the oxygen concentration of the exhaust gas (S 130: NO), the CPU 110 determines whether the catalyst exhaust gas temperature THe is equal to or higher than a specified determination temperature α (S 140). The determination temperature α is set to a temperature higher than the above-mentioned regeneratable temperature.If the catalyst exit gas temperature THe is lower than the prescribed determination temperature α (S 140: NO), the CPU 110 repeatedly executes the process after S 130. If the catalyst outlet gas temperature THe is equal to or higher than the specified determination temperature α (S 140: YES), the CPU 110 stops the fuel introduction process by stopping the fuel injection from the fuel injection valve 17 (S 150). The CPU 110 also stops the drive control (S 160). Then, the CPU 110 ends the current process. In this process, the process of S 130 and the process of S 150 correspond to a stop process for stopping the fuel introduction process when the detection value of the sensor indicates a decrease in the oxygen concentration of the discharge gas during the execution of the fuel introduction process.Now, the operation and advantages of the present embodiment will be described.FIG. 3 shows a manner in which the fuel introduction process is executed. In this case, the actual fuel amount injected by the fuel injection valve 17 is larger than the injection amount instructed by the engine control device 100. In addition, the fuel concentration in the air-fuel mixture is high enough to make the air-fuel ratio of the unburned air-fuel mixture introduced into the exhaust passage 21 richer than the stoichiometric air-fuel ratio.As shown in FIG. 3, in a case where the combustion operation of the internal combustion engine 10 is in a stopped state at a time point t 1, if there is a temperature increase request of the three-way catalyst 22, the catalyst temperature increase control is executed to start the fuel introduction process. At the beginning of the fuel introduction process, the drive control is also started.Execution of the fuel introduction process causes unburned air-fuel mixture having a high fuel concentration to flow into the three-way catalyst 22 as described above. Then, the fuel reacts with oxygen contained in the air-fuel mixture to be burned. The combustion of the fuel brings the three-way catalyst 22 into a reducing atmosphere. The three-way catalyst 22 thus releases the stored oxygen. A part of the oxygen released from the three-way catalyst 22 is burned by reacting with the fuel that has not reacted with the oxygen contained in the air-fuel mixture, and the remaining oxygen flows out from the three-way catalyst 22 into the exhaust passage 21.As described above, even when an unburned air-fuel mixture having a high fuel concentration flows into the three-way catalyst 22 by the execution of the fuel introduction process, oxygen is released from the three-way catalyst 22, so that the oxygen concentration of the exhaust gas flowing out of the three-way catalyst 22 is high. Therefore, the downstream side air-fuel ratio Afd after the time point t 1 indicates a significantly leaner air-fuel ratio than that during the combustion operation of the internal combustion engine 10.When the oxygen storage amount of the three-way catalyst 22 decreases during the execution of the fuel introduction process, the amount of oxygen released from the three-way catalyst 22 also decreases. This reduces the amount of oxygen released from the three-way catalyst 22 and flowing into the exhaust passage 21 without reacting with the fuel. Thus, the oxygen concentration of the exhaust gas flowing out of the three-way catalyst 22 starts to decrease (time t 2). Therefore, the value of the downstream side air-fuel ratio Afd representing the lean limit value starts to change toward the rich side. If the fuel introduction process is continued after the time point t 2, a part of the fuel supplied to the three-way catalyst 22 starts passing through the three-way catalyst 22 without being burned because the amount of oxygen released from the three-way catalyst 22 is absent.Thus, in the present embodiment, the CPU 110 stops the fuel introduction process by stopping the fuel injection from the fuel injection valve 17 at the time when the value of the downstream side air-fuel ratio Afd starts changing to the rich side during the execution of the fuel introduction process. Thereby, the deterioration of the emissions by the unburned fuel passing through the three-way catalyst 22 is restricted.The above-described embodiment may be modified as follows. The above-described embodiment and the following modifications may be combined as long as the combined modifications remain technically consistent.In the above-described embodiment, the second air-fuel ratio sensor 84 that outputs a signal proportional to the oxygen concentration of the exhaust gas is provided as a sensor for detecting the state of the oxygen concentration of the exhaust gas that has passed through the three-way catalyst 22.Alternatively, as shown in FIG. 4, an oxygen sensor 184 that detects only the presence or absence of oxygen in the exhaust gas may be provided as a sensor for detecting the state of the oxygen concentration of the exhaust gas that has passed through the three-way catalyst 22. The oxygen sensor 184 is characterized in that its output voltage changes rapidly when the air-fuel ratio changes over the stoichiometric air-fuel ratio. That is, if the air-fuel ratio of the air-fuel mixture is richer than the stoichiometric air-fuel ratio and no oxygen is present in the exhaust gas, the oxygen sensor 184 provides an output voltage of about 1 volt. The downstream air-fuel ratio Afg detected by the oxygen sensor 184 at this time indicates a rich state in which oxygen is not present in the exhaust gas. In addition, if the air-fuel ratio of the air-fuel mixture is leaner than the stoichiometric air-fuel ratio and oxygen is present in the exhaust gas, the oxygen sensor 184 provides an output voltage of about 0 volts. The downstream air-fuel ratio Afg detected by the oxygen sensor 184 at this time indicates a lean state in which oxygen is in the exhaust gas.Subsequently, by executing the process of S 200 shown in FIG. 5 in place of the process of S 130 in the flow of the catalyst temperature increase control described in FIG. 2, it is determined whether the oxygen concentration of the discharge gas has decreased during the execution of the fuel introduction process. That is, the CPU 110 determines whether the downstream side air-fuel ratio Afg has changed from a lean state to a rich state at S 200. If the downstream side air-fuel ratio Afg has changed from a lean state to a rich state (S 200: YES), the CPU 110 determines that the oxygen concentration of the exhaust gas has decreased, and stops the fuel introduction process by stopping the fuel injection from the fuel injection valve 17 (S 150). The CPU 110 also stops the drive control (S 160). Then, the CPU 110 ends the current process.In contrast, if the downstream side air-fuel ratio Afg has not changed from a lean state to a rich state (S 200: NO), the CPU 110 determines whether the catalyst outlet gas temperature THe is equal to or higher than a specified determination temperature α (S 140). If the catalyst outlet gas temperature THe is lower than the prescribed determination temperature α (S 140: NO), the CPU 110 repeatedly executes the process of S 200. In this modification, the process of S 200 and the process of S 150 correspond to a stop process for stopping the fuel introduction process when the detection value of the sensor indicates a decrease in the oxygen concentration of the discharge gas during the execution of the fuel introduction process.Also in the modification described above, when the oxygen concentration of the discharge gas that has passed through the three-way catalyst 22 decreases during the execution of the fuel introduction process, the stop process is executed to stop the fuel introduction process. Thereby, the deterioration of the emissions by the unburned fuel passing through the three-way catalyst 22 is restricted.During the fuel introduction process is executed, the spark discharge of the ignition device 19 is stopped. Moreover, during execution of the fuel introduction process, the spark discharge of the ignition device 19 may be performed in a period in which the air-fuel mixture in the cylinder 11 is not burned. For example, if a spark discharge is performed when the piston in the cylinder 11 is near the bottom dead center, the air-fuel mixture in the cylinder 11 is not burned. Therefore, even if the spark discharge is performed during the execution of the fuel introduction process, the fuel injected from the fuel injection valve 17 can be introduced from the inside of the cylinder 11 into the exhaust passage 21 without being burned.In the above-described embodiment, the fuel introduction process is executed by the fuel injection into the intake passage 15a by the fuel injection valve 17. Alternatively, it is also possible to execute the fuel introduction process by fuel injection into the cylinder 11 in an internal combustion engine having a direct injection type fuel injection valve that injects fuel into the cylinder 11.The present disclosure may be adapted to a system other than the hybrid vehicle system shown in FIG. 1 as long as the rotational speed of the crankshaft 14 is controlled by driving an engine.The present disclosure may be adapted for vehicles that do not have a power source other than the internal combustion engine. Also in this case, the crankshaft is rotated by the power transmitted from the driven wheels if the vehicle is running without performing combustion of the air-fuel mixture in the cylinder, that is, if the vehicle is coasting. Therefore, the temperature of the three-way catalyst may be increased if the fuel introduction process is executed while the vehicle is coasting and the crankshaft is rotating.The machine control device 100 is not limited to a device that includes the CPU 110 and the memory 120 and executes software processing. For example, dedicated hardware circuitry (such as an ASIC) may be provided that executes at least a portion of the software processing performed in each of the embodiments described above. That is, the machine control device 100 may be modified as long as it has any one of the following configurations (a) to (c). (a) A configuration including a processor that executes all of the above-described processes according to programs and a program storage device such as a memory that stores the programs. (b) A configuration including a processor and a program storage device that execute a part of the above-described processes according to the programs and a dedicated hardware circuit that executes the remaining processes. (c) A configuration including a dedicated hardware circuit that executes all of the above-described processes. A plurality of software processing circuits each including a processor and a program storage device, and a plurality of dedicated hardware circuits may be provided. That is, the above processes may be performed in any manner as long as the processes are performed by a processing circuit including at least one of a set of one or more software processing circuits and a set of one or more dedicated hardware circuits.Various changes in form and detail may be made in the above examples without departing from the spirit and scope of the claims and their equivalents. The examples are for the purpose of description only and not of limitation. Descriptions of features in each example are to be considered applicable to similar features or aspects in other examples. Suitable results may be achieved if sequences are performed in a different order and / or if components in a described system, architecture, device, or circuit are combined differently and / or replaced or supplemented by other components or their equivalents. The scope of the disclosure is defined not by the detailed description, but by the claims and their equivalents. All variations within the scope of the claims and their equivalents are included in the disclosure.

Claims

A control device (100) for an internal combustion engine (10), the internal combustion engine (10) comprising a fuel injection valve (17), a cylinder (11) into which an air-fuel mixture with fuel injected by the fuel injection valve (17) is introduced, an ignition device (19) that ignites the air-fuel mixture introduced into the cylinder (11) by a spark, an exhaust passage (21) through which a gas discharged from inside the cylinder (11) flows, a three-way catalyst (22) provided in the exhaust passage (21), and a sensor (84, 184) provided in the exhaust passage (21) and detecting a state of an oxygen concentration of exhaust gas corresponding to a gas having passed through the three-way catalyst (22), and the control device (100) is configured to:, To execute: a fuel introduction process for introducing the air-fuel mixture containing the fuel injected by the fuel injection valve (17) into the exhaust passage (21) in a state in which a crankshaft (14) of the internal combustion engine (10) rotates without burning the air-fuel mixture in the cylinder (11); and a stop process for stopping the fuel introduction process when the oxygen concentration detected by the sensor (84, 184) has changed from a lean state to a rich state with respect to the oxygen concentration at a stoichiometric air-fuel ratio during execution of the fuel introduction process.The control device (100) for an internal combustion engine (10) according to claim 1, wherein the sensor corresponds to an air-fuel ratio sensor (84) that outputs a signal proportional to the oxygen concentration of the exhaust gas, and the control device (100) is configured to stop the fuel introduction process when the oxygen concentration detected by the air-fuel ratio sensor (84) has changed from a lean state to a rich state during the execution of the fuel introduction process with respect to the oxygen concentration at a stoichiometric air-fuel ratio.The control device (100) for an internal combustion engine (10) according to claim 1, wherein the sensor corresponds to an oxygen sensor (184) that detects only the presence or absence of oxygen in the exhaust gas, and the control device (100) is configured to stop the fuel introduction process when the detection value of the oxygen sensor (184) changes from a value indicating the presence of oxygen to a value indicating the absence of oxygen during the execution of the fuel introduction process.A control method for an internal combustion engine (10), the internal combustion engine (10) comprising a fuel injection valve (17), a cylinder (11) into which an air-fuel mixture with fuel injected by the fuel injection valve (17) is introduced, an ignition device (19) that ignites the air-fuel mixture introduced into the cylinder (11) by a spark, an exhaust passage (21) through which a gas discharged from inside the cylinder (11) flows, a three-way catalyst (22) provided in the exhaust passage (21), and a sensor (84, 184) provided in the exhaust passage (21) and detecting a state of an oxygen concentration of discharge gas corresponding to a gas having passed through the three-way catalyst (22), The control method includes: introducing the air-fuel mixture including the fuel injected by the fuel injection valve (17) into the exhaust passage (21) in a state in which a crankshaft (14) of the internal combustion engine (10) rotates without burning the air-fuel mixture in the cylinder (11); and stopping the fuel introduction process when the oxygen concentration detected by the sensor (84, 184) has changed from a lean state to a rich state with respect to the oxygen concentration at a stoichiometric air-fuel ratio during execution of the fuel introduction process.

Images