Control device for internal combustion engine and control method for internal combustion engine

Abstract

To suppress stall of an internal combustion engine caused by catalyst neutralization processing.SOLUTION: The electronic control unit is configured to determine whether an oxygen concentration detected by the oxygen sensor is equal to or higher than a predetermined first threshold value, and when the oxygen concentration is equal to or higher than the predetermined first threshold value, execute a catalyst neutralization process of supplying fuel to the internal combustion engine in a fuel-rich atmosphere to consume at least a portion of oxygen stored in the catalyst. It is determined whether or not the oxygen concentration detected by the oxygen sensor has increased from a value less than a predetermined second threshold value smaller than the predetermined first threshold value to the predetermined second threshold value or more within a predetermined time after fuel cut for stopping fuel injection during operation of the internal combustion engine is finished and fuel injection is restarted, and when the oxygen concentration has increased to the predetermined second threshold value or more, the operation amount of the exhaust gas recirculation device is corrected so that the exhaust gas recirculation amount decreases.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present disclosure relates to a control device for an internal combustion engine and a control method for an internal combustion engine. [Background technology]

[0002] A catalyst is provided in the exhaust passage of an internal combustion engine to purify the exhaust. For example, a three-way catalyst made of a ceramic carrier carrying precious metals such as platinum, rhodium, and palladium is provided in the exhaust passage of a gasoline engine, and the three-way catalyst purifies carbon monoxide (CO), nitrogen oxides (NOx), and hydrocarbons (HC) in the exhaust.

[0003] When the oxygen concentration inside a three-way catalyst increases due to a fuel cut, which temporarily stops fuel injection while the internal combustion engine is running, the catalyst's NOx purification performance declines. When the fuel cut ends and fuel injection resumes, the oxygen concentration in the three-way catalyst gradually declines, neutralizing the catalyst, but until then, the catalyst's NOx purification performance declines. For this reason, when the oxygen concentration downstream of the three-way catalyst declines, the exhaust air-fuel ratio is made fuel-rich, and excess fuel is supplied to the three-way catalyst, oxidizing the oxygen stored in the three-way catalyst, a process known as catalyst neutralization. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-35796 Summary of the Invention [Problem to be solved by the invention]

[0005] Here, internal combustion engines are equipped with an exhaust gas recirculation device (hereinafter also referred to as "EGR device") that recirculates a portion of the exhaust gas to the intake side. The EGR device reduces the amount of oxygen in the intake air by mixing exhaust gas with a low oxygen concentration into the intake air, which lowers the combustion temperature and reduces the amount of NOx produced. The catalyst neutralization process operates when fuel cut ends and fuel injection resumes, so the amount of air is small. As a result, during the catalyst neutralization process, the amount of exhaust gas recirculated by the EGR device (hereinafter also referred to as "EGR amount") becomes extremely small.

[0006] However, if the fuel cut is performed for an extremely short period of time, the catalyst neutralization process may start after the end of the fuel cut. In this case, the fuel-rich state caused by the catalyst neutralization process and the decrease in the amount of oxygen caused by the exhaust gas (hereinafter referred to as "EGR gas") introduced by the EGR device may overlap, causing the internal combustion engine to stall due to the decrease in oxygen concentration.

[0007] The present disclosure has been made in consideration of the above-mentioned problems, and an object of the present disclosure is to provide a control device for an internal combustion engine and a control method for an internal combustion engine that are capable of suppressing stalling of the internal combustion engine due to catalyst neutralization processing. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, according to one aspect of the present disclosure, a control device for an internal combustion engine includes an internal combustion engine, an intake passage and an exhaust passage connected to the internal combustion engine, a catalyst provided in the exhaust passage, an oxygen sensor that detects an oxygen concentration downstream of the catalyst, and an exhaust gas recirculation device that circulates a portion of the exhaust gas to the intake side. The control device for an internal combustion engine includes an exhaust gas recirculation processing unit that controls the exhaust gas recirculation device based on an operating state of the internal combustion engine, and determines whether the oxygen concentration detected by the oxygen sensor is equal to or greater than a predetermined first threshold value, and when the oxygen concentration is equal to or greater than the predetermined first threshold value, controls the exhaust gas recirculation device to operate in a rich atmosphere that is richer in fuel than the stoichiometric air-fuel ratio. and a catalyst neutralization processing unit that executes a catalyst neutralization process that supplies the fuel to the internal combustion engine and consumes at least a portion of the oxygen stored in the catalyst, wherein the catalyst neutralization processing unit determines whether or not the oxygen concentration detected by the oxygen sensor has risen from a value less than a predetermined second threshold that is smaller than the predetermined first threshold to equal to or greater than the predetermined second threshold within a predetermined time after a fuel cut that stops fuel injection during operation of the internal combustion engine has ended and fuel injection has been resumed, and if the oxygen concentration has risen to equal to or greater than the predetermined second threshold, corrects the operating amount of the exhaust gas recirculation device so that the amount of exhaust gas recirculation is reduced.

[0009] Further, in order to solve the above-mentioned problems, according to another aspect of the present disclosure, there is provided a method for controlling an internal combustion engine including an internal combustion engine, an intake passage and an exhaust passage connected to the internal combustion engine, a catalyst provided in the exhaust passage, an oxygen sensor that detects an oxygen concentration downstream of the catalyst, and an exhaust gas recirculation device that circulates a portion of the exhaust gas to the intake side, the method comprising the steps of: controlling the exhaust gas recirculation device based on an operating state of the internal combustion engine; determining whether or not the oxygen concentration detected by the oxygen sensor is equal to or greater than a predetermined first threshold; and, if the oxygen concentration is equal to or greater than the predetermined first threshold, producing a rich atmosphere that is richer in fuel than the stoichiometric air-fuel ratio. The present invention provides a control method for an internal combustion engine, which performs a catalyst neutralization process by supplying the fuel to the internal combustion engine in an ambient atmosphere and consuming at least a portion of the oxygen stored in the catalyst; and when a fuel cut that stops fuel injection during operation of the internal combustion engine ends and fuel injection is resumed, it is determined whether the oxygen concentration detected by the oxygen sensor has increased from a value less than a predetermined second threshold that is smaller than the predetermined first threshold to equal to or greater than the predetermined second threshold, and if the oxygen concentration has increased to equal to or greater than the predetermined second threshold, correcting an operation amount of the exhaust gas recirculation device so as to reduce the amount of exhaust gas recirculation. [Effects of the Invention]

[0010] As described above, according to the present disclosure, it is possible to suppress stalling of the internal combustion engine caused by the catalyst neutralization process. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram illustrating an example of the configuration of an internal combustion engine to which a control device for an internal combustion engine according to an embodiment of the present disclosure can be applied; [Figure 2] 2 is a block diagram showing an example of the configuration of a control device for an internal combustion engine according to the embodiment; FIG. [Figure 3] 3 is a flowchart showing an example of a control method for the internal combustion engine according to the embodiment. [Figure 4] 3 is a flowchart showing an example of a control method for the internal combustion engine according to the embodiment. [Figure 5]FIG. 10 is an explanatory diagram showing the operation of the present disclosure. [Figure 6] FIG. 10 is an explanatory diagram showing an example to which the present disclosure is not applied. [Figure 7] FIG. 1 is an explanatory diagram showing an example to which the present disclosure is applied. DETAILED DESCRIPTION OF THE INVENTION

[0012] Preferred embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant description will be omitted.

[0013] <1. Overall structure of the internal combustion engine> First, the overall configuration of an internal combustion engine to which an internal combustion engine control device according to an embodiment of the present disclosure can be applied will be described.

[0014] FIG. 1 is a schematic diagram showing an example of the overall configuration of an internal combustion engine 10. The internal combustion engine 10 shown in FIG. 1 is, for example, a spark-ignition direct injection gasoline engine that is mounted on a vehicle such as an automobile. The internal combustion engine 10 has one or more cylinders 11. For ease of understanding, only one cylinder 11 is shown in FIG. 1.

[0015] A piston 13 is slidably provided in the cylinder 11. A combustion chamber defined by the inner peripheral surface of the cylinder 11 and the crown surface of the piston 13 is formed in part of the cylinder 11.

[0016] Each cylinder 11 is equipped with a fuel injector 15 and a spark plug 17. The fuel injector 15 is an injection device that directly injects atomized fuel into the combustion chamber of the cylinder 11. Fuel is supplied to the fuel injector 15 from a fuel supply device (not shown), and the fuel injector 15 opens and injects the fuel in response to a signal output from a control device 50. The spark plug 17 generates a spark in response to the signal output from the control device 50 and ignites the air-fuel mixture formed in the cylinder 11. This causes the piston 13 to reciprocate, which rotates a crankshaft connected to the piston 13 via a connecting rod (not shown), thereby outputting driving torque.

[0017] An intake passage 23 and an exhaust passage 25 are connected to the cylinder 11. The intake passage 23 is provided with an air filter 31, an air flow meter 33, and a throttle valve 35, in this order from upstream to downstream in the intake air flow. The air filter 31 removes foreign matter from the intake air. The air flow meter 33 measures the flow rate of the intake air. The throttle valve 35 is driven by a control device 50 to adjust the opening area of ​​the intake passage 23 and regulate the flow rate of air introduced into the cylinder 11 through the intake passage 23. An intake valve 19 is provided at the opening where the intake passage 23 connects to the cylinder 11. The intake valve 19 opens and closes the opening in conjunction with the rotation of the crankshaft of the internal combustion engine 10.

[0018] The exhaust passage 25 is provided with an air-fuel ratio sensor 41, an oxygen sensor 43, and a three-way catalyst 45. The air-fuel ratio sensor 41 measures the air-fuel ratio (A / F) of the exhaust gas upstream of the three-way catalyst 45. The oxygen sensor 43 measures the oxygen concentration of the exhaust gas downstream of the three-way catalyst 45. In this embodiment, the air-fuel ratio sensor 41 and the oxygen sensor 43 each output a larger voltage value as the oxygen concentration of the exhaust gas decreases. Note that the air-fuel ratio sensor 41 and the oxygen sensor 43 may be of any type as long as they are capable of measuring the oxygen concentration.

[0019] The three-way catalyst 45 oxidizes hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas and reduces nitrogen oxides (NOx) in the exhaust gas to convert them into water vapor (HO), carbon dioxide (CO2), and nitrogen (N2). However, in addition to its catalytic function, the three-way catalyst 45 may also function as a gasoline particulate filter (GPF) that collects particulate matter (PM) in the exhaust gas.

[0020] The internal combustion engine 10 also includes an exhaust gas recirculation device (EGR device) 47. The EGR device 47 includes an exhaust gas recirculation passage (hereinafter also referred to as an "EGR passage") 48 that connects the exhaust passage 25 and the intake passage 23, and an exhaust gas recirculation valve (EGR valve) 49 that adjusts the opening area of ​​the EGR passage 48. The EGR valve 49 is controlled by a control device 50 based on the operating state of the internal combustion engine 10 to adjust the opening area and regulate the flow rate of exhaust gas circulated from the exhaust passage 25 to the intake passage 23. The EGR passage 48 is connected to the exhaust passage 25 upstream of the three-way catalyst 45, but may also be connected to the exhaust passage 25 downstream of the three-way catalyst 45.

[0021] The control device 50 includes a processor such as a CPU (Central Processing Unit) and storage elements such as a RAM (Random Access Memory) and a ROM (Read Only Memory), and functions as a device that controls the operation of the internal combustion engine 10 by the processor executing a computer program. The computer program is a computer program that causes the processor to execute the operations to be performed by the control device 50, which will be described later. The computer program executed by the processor may be recorded on a recording medium that functions as a storage unit (memory) 53 provided in the control device 50, or may be recorded on a recording medium built into the control device 50 or any recording medium that can be externally attached to the control device 50.

[0022] Recording media for recording computer programs include magnetic media such as hard disks, floppy disks, and magnetic tapes, optical recording media such as CD-ROMs (Compact Disk Read Only Memory), DVDs (Digital Versatile Disks), and Blu-ray (registered trademark), magneto-optical media such as floptical disks, memory elements such as RAMs and ROMs, flash memories such as USB (Universal Serial Bus) memories and SSDs (Solid State Drives), and other media capable of storing programs.

[0023] Note that part or all of the control device 50 may be configured with updatable firmware or the like, or may be a program module or the like that is executed by instructions from a CPU or the like.

[0024] 2. Internal combustion engine control device Next, the control device 50 that controls the internal combustion engine 10 will be described. The control device 50 sets control targets for the internal combustion engine 10 based on information transmitted from various sensors, and controls the operation of the internal combustion engine 10 based on the set control targets. The control device 50 outputs control signals to the throttle valve 35, the fuel injector 15, the spark plug 17, the EGR valve 49, etc., to control the output torque and engine speed.

[0025] The control device 50 is configured to be able to acquire sensor signals from the air flow meter 33, the air-fuel ratio sensor 41, and the oxygen sensor 43, as well as from an accelerator sensor 55, a vehicle speed sensor 57, and an engine speed sensor 59. The accelerator sensor 55 detects the amount of operation of the accelerator pedal operated by the driver of the vehicle. The vehicle speed sensor 57 detects the vehicle speed. The engine speed sensor 59 detects the engine speed, which is the rotational speed of the crankshaft of the internal combustion engine 10.

[0026] 2 is an explanatory diagram showing an example of the configuration of the control device 50 shown in FIG. 1. The control device 50 includes a processing unit 51 and a storage unit 53. The processing unit 51 is configured with one or more processors such as CPUs. The storage unit 53 is configured to be able to communicate with the processing unit 51. The storage unit 53 stores programs executed by the processing unit 51, parameters used in various calculations, detection data, information on calculation results, etc. A part of the storage unit 53 is used as a work area for the processing unit 51.

[0027] The control device 50 is configured to be able to acquire sensor signals output from the air flow meter 33, the air-fuel ratio sensor 41, the oxygen sensor 43, the accelerator sensor 55, the vehicle speed sensor 57, and the engine speed sensor 59. In the illustrated example, the various sensors are directly connected to the control device 50, but information indicated by the sensor signals of the various sensors may be acquired from another controller via an in-vehicle network (not shown).

[0028] The processing unit 51 includes an engine control unit 61, an exhaust gas recirculation processing unit 63, and a catalyst neutralization processing unit 65. The functions of these units are realized by a processor executing a computer program. Note that some of the engine control unit 61, the exhaust gas recirculation processing unit 63, and the catalyst neutralization processing unit 65 may be configured using hardware such as analog circuits.

[0029] (Engine Control Unit) The engine control unit 61 controls the operation of the internal combustion engine 10. The engine control unit 61 sets a target torque, which is a target value of the output torque to be output from the internal combustion engine 10, and sets a target intake amount, a target fuel injection amount, and a target ignition timing based on the target torque. For example, the engine control unit 61 calculates the target torque based on the accelerator opening and engine speed by referring to a torque map stored in advance in the memory unit 53. Note that if there are other driving elements that use the output torque of the internal combustion engine 10, the engine control unit 61 sets the target torque by further adding the torque used by the other driving elements.

[0030] Furthermore, the engine control unit 61 sets a target intake air amount, a target fuel injection amount, and a target ignition timing by referring to an intake air amount map, an injection amount map, and an ignition timing map stored in advance in the memory unit 53. The target intake air amount is a target value of the amount of intake air introduced into the cylinder 11 of the internal combustion engine 10, and is set in proportion to the magnitude of the target torque. The target fuel injection amount is a target value of the amount of fuel injected and supplied into the cylinder 11 by the fuel injector 15. Basically, the target fuel injection amount is set according to the target intake air amount so that the ratio of fuel to air in the mixture is a constant ratio (theoretical air-fuel ratio). The target ignition timing is a target value of the timing at which the mixture formed in the cylinder 11 is ignited. For example, with respect to the top dead center of the piston 13 of the internal combustion engine 10 as a reference, the more the ignition timing is retarded, the lower the combustion efficiency of the mixture.

[0031] The engine control unit 61 controls the drive of the throttle valve 35, the fuel injector 15, and the spark plug 17 based on the set target intake air amount, target fuel injection amount, and target ignition timing. This controls the output torque and engine speed output from the internal combustion engine 10. For example, the engine control unit 61 sets a target opening of the throttle valve 35 based on the target intake air amount and engine speed, and drives the throttle valve 35 to rotate. The engine control unit 61 also sets a drive duty ratio of the fuel injector 15 based on the target fuel injection amount, and controls the current supplied to the fuel injector 15. The engine control unit 61 also supplies current to the spark plug 17 in accordance with the target ignition timing.

[0032] Furthermore, the engine control unit 61 executes a fuel cut to stop the supply of fuel to the internal combustion engine 10 depending on the running state of the vehicle. For example, the engine control unit 61 executes a fuel cut when the vehicle is decelerating and the accelerator opening is zero. The fuel cut ends when the accelerator opening exceeds zero or when the engine speed drops to a predetermined threshold, and fuel injection is resumed.

[0033] (Exhaust gas recirculation processing unit) The exhaust gas recirculation processor 63 controls the operation of the EGR valve 49 based on the operating state of the internal combustion engine 10. For example, the exhaust gas recirculation processor 63 determines the target opening (target operation amount) of the EGR valve 49 by referring to an EGR map that defines the target opening (target operation amount) of the EGR valve 49 according to the engine speed and the target torque of the internal combustion engine 10, and controls the EGR valve 49 so that the opening of the EGR valve 49 becomes the target opening. The exhaust gas recirculation processor 63 basically keeps the EGR valve 49 closed during fuel cut. However, the exhaust gas recirculation processor 63 may open the EGR valve 49 as part of a diagnostic process for the EGR device 47. Furthermore, the exhaust gas recirculation processor 63 maintains the EGR valve 49 closed during a catalyst neutralization process.

[0034] (Catalyst neutralization treatment unit) The catalyst neutralization processing unit 65 performs catalyst neutralization processing to consume at least a portion of the oxygen stored in the three-way catalyst 45. The catalyst neutralization processing unit 65 determines whether the oxygen concentration detected by the oxygen sensor 43 (hereinafter also referred to as the "downstream oxygen concentration") is equal to or greater than a predetermined first threshold, and if the downstream oxygen concentration is equal to or greater than the predetermined first threshold, the catalyst neutralization processing unit 65 consumes the oxygen in the three-way catalyst 45 by supplying fuel to the internal combustion engine 10 in a rich atmosphere that is richer in fuel than the stoichiometric air-fuel ratio.

[0035] The predetermined first threshold is a threshold for determining whether the amount of oxygen stored in the three-way catalyst 45 has become excessive, and may be set to any appropriate value. Normally, the execution of a fuel cut causes the amount of oxygen stored in the three-way catalyst 45 to become excessive, so the predetermined first threshold is set to an appropriate value based on the downstream oxygen concentration that increases as a result. Therefore, generally, the catalyst neutralization process is executed when fuel injection is resumed after a fuel cut.

[0036] In addition, the catalyst neutralization processing unit 65 determines whether the downstream oxygen concentration detected by the oxygen sensor 43 has risen from a value less than a predetermined second threshold value, which is smaller than the predetermined first threshold value, to a predetermined second threshold value or higher within a predetermined time after the fuel cut has ended and fuel injection has resumed, and if the downstream oxygen concentration has risen to a predetermined second threshold value or higher, corrects the operation amount of the EGR valve 49 (EGR reduction correction) so that the exhaust gas recirculation amount (EGR amount) is reduced.

[0037] For example, if the driver of the vehicle releases the accelerator pedal for only 1 to 3 seconds and a fuel cut is executed within a short time, it is conceivable that the downstream oxygen concentration will exceed the predetermined first threshold value after the fuel cut ends and fuel injection is resumed. If the catalyst neutralization process is executed at this timing, the EGR amount will be maintained due to the operation delay of the EGR valve 49, and the fuel-rich state due to the catalyst neutralization process and the decrease in the amount of oxygen due to the EGR gas introduced by the EGR device 47 will overlap, which may cause a stall (misfire) of the internal combustion engine 10 due to a significant decrease in the oxygen concentration.

[0038] Therefore, if the downstream oxygen concentration rises from a value less than a predetermined second threshold value that is smaller than the predetermined first threshold value to equal to or greater than the predetermined second threshold value within a predetermined time after the fuel cut ends and fuel injection is resumed, the catalyst neutralization processing unit 65 predicts the start of catalyst neutralization processing and reduces the EGR amount. This brings the EGR amount closer to zero before the start of catalyst neutralization processing, making it possible to suppress stalling of the internal combustion engine 10.

[0039] The predetermined second threshold value is set to a value that exceeds the range of fluctuation of the downstream oxygen concentration during normal driving after the catalyst neutralization process is completed and fuel injection control and EGR control are resumed, thereby detecting a state in which the downstream oxygen concentration begins to rise even though the vehicle is in a normal driving state after the fuel cut is completed.

[0040] In this embodiment, whether the downstream oxygen concentration is equal to or greater than a predetermined first threshold corresponds to whether the output voltage of the oxygen sensor 43 is equal to or less than a predetermined first voltage threshold. Also, whether the downstream oxygen concentration has increased from a value less than a predetermined second threshold that is smaller than the predetermined first threshold to equal to or greater than the predetermined second threshold corresponds to whether the output voltage of the oxygen sensor 43 has decreased from a value exceeding the predetermined second voltage threshold to equal to or less than the predetermined second voltage threshold.

[0041] <3. Example of operation of the control device for an internal combustion engine> So far, we have explained an example of the configuration of the internal combustion engine control device 50. Next, we will explain an example of the operation of the internal combustion engine control device 50.

[0042] 3 and 4 are flowcharts showing an example of processing operations performed by the control device 50. The flowcharts shown in FIGS. 3 and 4 are constantly executed when the internal combustion engine 10 is started.

[0043] After completing the start of the internal combustion engine 10 (step S11), the engine control unit 61 of the control device 50 starts fuel injection control and EGR control of the internal combustion engine 10 (step S13). For example, the engine control unit 61 acquires a sensor signal from the accelerator sensor 55 and a sensor signal from the engine speed sensor 59, and calculates a target torque based on the accelerator opening and the engine speed. When the vehicle is in automatic driving in which acceleration is automatically controlled by a computer, information on required acceleration set by the computer may be used instead of information on the accelerator opening.

[0044] The engine control unit 61 sets a target intake air amount, a target fuel injection amount, and a target ignition timing based on the set target torque. The exhaust gas recirculation processing unit 63 determines a target opening (target operation amount) of the EGR valve 49 according to the engine speed and the target torque of the internal combustion engine 10. The engine control unit 61 controls the drive of the throttle valve 35, the fuel injector 15, the spark plug 17, and the EGR valve 49 based on the set target intake air amount, target fuel injection amount, target ignition timing, and target opening.

[0045] Next, the catalyst neutralization processing unit 65 determines whether or not the internal combustion engine 10 is in a fuel cut state (step S15). If the catalyst neutralization processing unit 65 does not determine that the internal combustion engine 10 is in a fuel cut state (S15 / No), the process proceeds to step S25, and the determination of step S15 is repeated unless it is determined that the internal combustion engine 10 has stopped.

[0046] On the other hand, when it is determined that the internal combustion engine 10 is in a fuel cut (S15 / Yes), the catalyst neutralization processing unit 65 determines whether or not a catalyst neutralization processing execution condition is met (step S17). In this embodiment, the catalyst neutralization processing unit 65 determines, as the catalyst neutralization processing execution condition, whether or not the downstream oxygen concentration measured by the oxygen sensor 43 is equal to or greater than a predetermined first threshold. For example, the catalyst neutralization processing unit 65 determines whether or not the output voltage of the oxygen sensor 43 is equal to or less than a predetermined first voltage threshold corresponding to the first threshold of the downstream oxygen concentration. During fuel cut, fuel injection control is stopped, and the EGR valve 49 is basically closed. However, as a diagnostic process for the fuel injection system or the EGR device 47, a small amount of fuel injection or an opening operation of the EGR valve 49 may be performed.

[0047] If the catalyst neutralization processing unit 65 determines that the downstream oxygen concentration is equal to or greater than a predetermined first threshold and that the catalyst neutralization processing execution condition is met (S17 / Yes), it sets a condition fulfillment flag and determines whether or not fuel cut has ended (step S19).If the catalyst neutralization processing unit 65 does not determine that fuel cut has ended (S19 / No), it repeats the determination of step S19 until fuel cut ends.

[0048] When it is determined that the fuel cut has ended (S19 / Yes), the catalyst neutralization processing unit 65 executes the catalyst neutralization processing (step S21). When the fuel cut ends and fuel injection control is resumed, the catalyst neutralization processing unit 65 executes the fuel supply to the internal combustion engine 10 in a rich atmosphere that is richer in fuel than the stoichiometric air-fuel ratio. As a result, unburned fuel is supplied to the three-way catalyst 45, and the oxygen in the three-way catalyst 45 is consumed.

[0049] On the other hand, if the catalyst neutralization processing unit 65 determines that the downstream oxygen concentration is less than the predetermined first threshold and the catalyst neutralization processing execution condition is not satisfied (S17 / No), it determines whether or not the fuel cut has ended (step S25). If the catalyst neutralization processing unit 65 does not determine that the fuel cut has ended (S25 / No), it returns to step S17, and proceeds to step S19 if the catalyst neutralization processing execution condition is satisfied before the fuel cut ends.

[0050] On the other hand, when it is determined that the fuel cut has ended (S25 / Yes), the catalyst neutralization processing unit 65 starts counting a timer (step S27) and determines whether a condition for executing an EGR amount reduction correction, which corrects the operation amount of the EGR valve 49 so as to reduce the EGR amount, is satisfied (step S29). In this embodiment, the catalyst neutralization processing unit 65 determines, as a condition for executing the EGR amount reduction correction, whether the downstream oxygen concentration detected by the oxygen sensor 43 has increased from a value less than a predetermined second threshold to a value equal to or greater than the predetermined second threshold. For example, the catalyst neutralization processing unit 65 determines whether the output voltage of the oxygen sensor 43 is equal to or less than a predetermined second voltage threshold corresponding to the second threshold of the downstream oxygen concentration. Here, it is determined whether the downstream oxygen concentration is predicted to be equal to or greater than a predetermined first threshold and whether the catalyst neutralization processing can be executed.

[0051] If the downstream oxygen concentration remains below the predetermined second threshold and it is not determined that the condition for executing the EGR amount reduction correction is met (S29 / No), the catalyst neutralization processing unit 65 determines whether a predetermined time has elapsed since the start of timer counting in step S27 (step S31). The predetermined time may be set to any appropriate value taking into consideration the time during which an increase in the downstream oxygen concentration due to a short-term fuel cut may occur, which is determined in advance by a simulation using an actual machine, for example.

[0052] If the catalyst neutralization processing unit 65 determines that the predetermined time has elapsed (S31 / Yes), it is unlikely that the execution of the catalyst neutralization processing will be started, and so the process proceeds directly to step S23. On the other hand, if the catalyst neutralization processing unit 65 does not determine that the predetermined time has elapsed (S31 / No), it returns to step S29 and repeatedly determines whether the EGR amount reduction correction execution condition is met until the predetermined time has elapsed. If the catalyst neutralization processing unit 65 determines that the downstream oxygen concentration has increased from a value less than the predetermined second threshold to a value equal to or greater than the predetermined second threshold and the EGR amount reduction correction execution condition is met (S29 / Yes), it calculates a correction coefficient for the operation amount of the EGR device 47 (step S33).

[0053] It is also possible to set the target opening of the EGR valve 49 to zero when the conditions for executing the EGR amount reduction correction are met. However, in this case, the execution time of EGR control would be shortened, which may lead to a deterioration in fuel economy. In this embodiment, the catalyst neutralization processing unit 65 sets the correction coefficient by linear interpolation according to the downstream oxygen concentration, with the coefficient set to 0 when the downstream oxygen concentration is a predetermined first threshold and the coefficient set to 1 when the downstream oxygen concentration is a predetermined second threshold. This reduces the EGR amount as the timing to start the catalyst neutralization processing approaches, allowing the EGR amount to approach zero when the catalyst neutralization processing starts. Furthermore, because EGR control is continued until the timing to start the catalyst neutralization processing approaches, a deterioration in fuel economy can be suppressed.

[0054] In addition, in order to avoid interfering with the self-diagnosis of the EGR device, which involves opening the EGR valve 49 during fuel cut, the catalyst neutralization processing unit 65 activates the EGR reduction correction only during normal driving when fuel cut is not in progress.

[0055] After the correction coefficient is determined, the catalyst neutralization processing unit 65 executes the EGR amount reduction correction (step S35). For example, the exhaust gas recirculation processing unit 63 multiplies the target opening of the EGR valve 49 calculated based on the EGR map by the correction coefficient to set the corrected target opening, and controls the drive of the EGR valve 49.

[0056] Next, the catalyst neutralization processing unit 65 determines whether or not a catalyst neutralization processing execution condition is satisfied (step S37). In this embodiment, the catalyst neutralization processing unit 65 determines, as the catalyst neutralization processing execution condition, whether or not the downstream oxygen concentration measured by the oxygen sensor 43 is equal to or greater than a predetermined first threshold. If the catalyst neutralization processing unit 65 determines that the downstream oxygen concentration is less than the predetermined first threshold and the catalyst neutralization processing execution condition is not satisfied (S37 / No), the process returns to step S33 and continues the EGR amount reduction correction. On the other hand, if the catalyst neutralization processing unit 65 determines that the downstream oxygen concentration is equal to or greater than the predetermined first threshold and the catalyst neutralization processing execution condition is satisfied (S37 / Yes), the catalyst neutralization processing unit 65 executes the catalyst neutralization processing (step S21).

[0057] The processing of steps S15 to S37 described above continues until the operation of the internal combustion engine 10 stops.

[0058] <4. Effect> Next, the operation of the present disclosure will be described with reference to FIGS.

[0059] 5 shows examples of the fuel cut flag F_fcut, throttle opening Slt, target EGR amount EGR_tgt, actual EGR amount EGR_act, target air-fuel ratio A / F_tgt, actual air-fuel ratio A / F_act, and output voltage V_o2_r of the oxygen sensor 43 when the downstream oxygen concentration becomes equal to or higher than a predetermined first threshold during fuel cut and catalyst neutralization processing is executed. During normal vehicle running, the internal combustion engine 10 is feedback controlled so that the output voltage V_o2_r of the oxygen sensor 43 becomes the target value V_o2_r_tgt, thereby achieving an exhaust air-fuel ratio that increases the purification efficiency of the three-way catalyst 45.

[0060] In the example shown in FIG. 5 , when the fuel cut flag F_fcut is set, the throttle opening Slt decreases, and fuel injection is stopped, causing the actual air-fuel ratio A / F_act to increase. This increases the amount of oxygen stored in the three-way catalyst 45, causing the output voltage V_o2_r of the oxygen sensor 43 to decrease. When the output voltage V_o2_r of the oxygen sensor 43 becomes equal to or less than a predetermined first voltage threshold V_o2_r_A corresponding to the first downstream oxygen concentration threshold, fuel injection is resumed after the fuel cut ends in a fuel-rich atmosphere with a decreased target air-fuel ratio A / F_tgt, and the oxygen in the three-way catalyst 45 is consumed. As the target EGR amount EGR_tgt is set to zero upon the start of the fuel cut, the actual EGR amount EGR_act gradually decreases due to an operation delay. However, because the actual EGR amount EGR_act becomes zero at the start of the catalyst neutralization process, the oxygen concentration of the intake air does not decrease significantly during the catalyst neutralization process, preventing the internal combustion engine 10 from stalling.

[0061] 6 and 7 show examples of the fuel cut flag F_fcut, throttle opening Slt, target EGR amount EGR_tgt, actual EGR amount EGR_act, target air-fuel ratio A / F_tgt, actual air-fuel ratio A / F_act, and output voltage V_o2_r of oxygen sensor 43 when fuel cut ends in a short time, the downstream oxygen concentration becomes equal to or greater than a predetermined first threshold after a delay, and catalyst neutralization processing is executed. Fig. 6 shows an example when the EGR amount reduction correction of the present disclosure is not executed, and Fig. 7 shows an example when the EGR amount reduction correction of the present disclosure is executed.

[0062] 6 and 7, when the fuel cut flag F_fcut is set, the throttle opening Slt decreases, fuel injection is stopped, and the actual air-fuel ratio A / F_act increases. Although the target EGR amount EGR_tgt is set to zero when the fuel cut starts, the target EGR amount EGR_tgt is restored in a short time, and the actual EGR amount EGR_act is maintained without a significant decrease due to the operation delay.

[0063] In the example shown in Figure 6, EGR reduction correction is not performed, so when the output voltage V_o2_r of the oxygen sensor 43 becomes equal to or less than the first voltage threshold V_o2_r_A corresponding to the first threshold value of the downstream oxygen concentration, the target EGR amount EGR_tgt is set to zero, but due to an operation delay, the actual EGR amount EGR_act does not decrease immediately, and the fuel-rich state due to the catalyst neutralization process and the decrease in oxygen concentration due to EGR control overlap, which may cause the internal combustion engine 10 to stall.

[0064] 7, the EGR amount reduction correction is performed, and the target EGR amount EGR_tgt is corrected to decrease when the output voltage V_o2_r of the oxygen sensor 43 drops from a value exceeding a predetermined second voltage threshold V_o2_r_B corresponding to the second threshold value of the downstream oxygen concentration to a predetermined second voltage threshold V_o2_r_B or less before the output voltage V_o2_r of the oxygen sensor 43 drops to a predetermined second voltage threshold V_o2_r_B or less, ... first voltage threshold V_o2_r_A or less, which corresponds to the first threshold value of the downstream oxygen concentration. Therefore, the actual EGR amount EGR_act has already decreased when the output voltage V_o2_r of the oxygen sensor 43 drops to a first voltage threshold V_o2_r_A or less, and a decrease in the oxygen concentration of the intake air caused by the fuel-rich state due to the catalyst neutralization process and the decrease in the oxygen concentration due to the EGR control are suppressed, thereby making it possible to suppress a stall of the internal combustion engine 10.

[0065] <5. Effects> As described above, the control device 50 for an internal combustion engine according to this embodiment includes the exhaust gas recirculation processing unit 63 that controls the EGR device 47 based on the operating state of the internal combustion engine 10, and the catalyst neutralization processing unit 65 that determines whether the downstream oxygen concentration detected by the oxygen sensor 43 is equal to or greater than a predetermined first threshold, and, if the downstream oxygen concentration is equal to or greater than the predetermined first threshold, executes a catalyst neutralization process that supplies fuel to the internal combustion engine 10 in a fuel-rich atmosphere and consumes at least a portion of the oxygen stored in the three-way catalyst 45. The catalyst neutralization processing unit 65 determines whether the downstream oxygen concentration detected by the oxygen sensor 43 has increased from a value less than a predetermined second threshold that is smaller than the predetermined first threshold to equal to or greater than the predetermined second threshold within a predetermined time after a fuel cut that stops fuel injection during operation of the internal combustion engine 10 ends and fuel injection is resumed, and if the downstream oxygen concentration has increased to equal to or greater than the predetermined second threshold, corrects the operation amount of the EGR device 47 so as to reduce the actual EGR amount. Therefore, the decrease in the oxygen concentration of the intake air caused by the fuel-rich state due to the catalyst neutralization process and the decrease in the oxygen concentration due to the EGR control overlapping is suppressed, and the stall of the internal combustion engine 10 can be suppressed.

[0066] In this embodiment, the catalyst neutralization processing unit 65 sets the correction coefficient by linear interpolation according to the downstream oxygen concentration, with the coefficient being 0 when the downstream oxygen concentration is a predetermined first threshold and the coefficient being 1 when the downstream oxygen concentration is a predetermined second threshold. Therefore, it is possible to suppress a stall of the internal combustion engine 10 while suppressing deterioration in fuel efficiency caused by setting the EGR amount to zero.

[0067] In this embodiment, the predetermined second threshold is set to a value that exceeds the range of fluctuations in the downstream oxygen concentration after the catalyst neutralization process is completed, thereby preventing the EGR amount from being erroneously reduced due to fluctuations in the downstream oxygen concentration that may occur during normal vehicle running.

[0068] In this embodiment, the exhaust gas recirculation treatment unit 63 closes the EGR valve 49 during the catalyst neutralization process. This reliably prevents a decrease in the oxygen concentration of the intake air due to EGR control during the catalyst neutralization process, thereby suppressing stalling of the internal combustion engine 10.

[0069] Although the preferred embodiments of the present disclosure have been described in detail above with reference to the accompanying drawings, the technology of the present disclosure is not limited to such examples. It is clear that a person skilled in the art of the technology to which the present disclosure pertains can conceive of various modified or altered examples within the scope of the technical ideas described in the claims, and it is understood that these also naturally fall within the technical scope of the present disclosure. [Explanation of symbols]

[0070] 10: Internal combustion engine 11: Cylinder 23: Intake passage 25: Exhaust passage 35: Throttle valve 41: Air-fuel ratio sensor 43: Oxygen sensor 45:Three-way catalyst 47:EGR device 49: EGR valve 50: Control device 61: Engine control unit 63: Exhaust gas recirculation processing unit 65: Catalyst neutralization processing unit

Claims

1. An internal combustion engine control device for controlling an internal combustion engine including an internal combustion engine, an intake passage and an exhaust passage connected to the internal combustion engine, a catalyst provided in the exhaust passage, an oxygen sensor that detects an oxygen concentration downstream of the catalyst, and an exhaust gas recirculation device that circulates a portion of the exhaust gas to the intake side, an exhaust gas recirculation processing unit that controls the exhaust gas recirculation device based on an operating state of the internal combustion engine; a catalyst neutralization processing unit that determines whether or not the oxygen concentration detected by the oxygen sensor is equal to or greater than a predetermined first threshold, and, if the oxygen concentration is equal to or greater than the predetermined first threshold, supplies the fuel to the internal combustion engine in a fuel-rich atmosphere that is richer than the stoichiometric air-fuel ratio, and performs a catalyst neutralization process that consumes at least a portion of the oxygen stored in the catalyst, The catalyst neutralization processing unit determines whether the oxygen concentration detected by the oxygen sensor has risen from a value less than a predetermined second threshold value that is smaller than the predetermined first threshold value to equal to or greater than the predetermined second threshold value within a predetermined time after a fuel cut that stops fuel injection during operation of the internal combustion engine has ended and fuel injection has resumed, and if the oxygen concentration has risen to equal to or greater than the predetermined second threshold value, corrects the operating amount of the exhaust gas recirculation device so that the amount of exhaust gas recirculation is reduced.

2. 2. The control device for an internal combustion engine according to claim 1, wherein the catalyst neutralization processing unit sets a correction coefficient by linear interpolation according to the oxygen concentration, with the coefficient being 0 when the oxygen concentration is the predetermined first threshold value and the coefficient being 1 when the oxygen concentration is the predetermined second threshold value.

3. The control device for an internal combustion engine according to claim 1 , wherein the predetermined second threshold value is set to a value that exceeds a fluctuation range of the oxygen concentration after the catalyst neutralization process is completed.

4. The control device for an internal combustion engine according to claim 1 , wherein the exhaust gas recirculation processing unit closes the exhaust gas recirculation valve during the catalyst neutralization process.

5. A method for controlling an internal combustion engine including an internal combustion engine, an intake passage and an exhaust passage connected to the internal combustion engine, a catalyst provided in the exhaust passage, an oxygen sensor that detects an oxygen concentration downstream of the catalyst, and an exhaust gas recirculation device that circulates a portion of the exhaust gas to the intake side, the method comprising: controlling the exhaust gas recirculation device based on an operating state of the internal combustion engine; determining whether or not the oxygen concentration detected by the oxygen sensor is equal to or greater than a predetermined first threshold, and if the oxygen concentration is equal to or greater than the predetermined first threshold, supplying the fuel to the internal combustion engine in a fuel-rich atmosphere that is richer than the stoichiometric air-fuel ratio, and performing a catalyst neutralization process that consumes at least a portion of the oxygen stored in the catalyst; determining whether or not the oxygen concentration detected by the oxygen sensor has risen from a value less than a predetermined second threshold value that is smaller than the predetermined first threshold value to equal to or greater than the predetermined second threshold value within a predetermined time period after a fuel cut that stops fuel injection during operation of the internal combustion engine has ended and fuel injection has been resumed, and if the oxygen concentration has risen to equal to or greater than the predetermined second threshold value, correcting an operation amount of the exhaust gas recirculation device so as to reduce the exhaust gas recirculation amount; A control method for an internal combustion engine.

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