Control device for internal combustion engine

Abstract

To enhance deterioration detection accuracy of a catalyst that eliminates NOx in an internal combustion engine that uses hydrogen as fuel.SOLUTION: An internal combustion engine 10 includes an SCR catalyst 41 provided in an exhaust pipe 90 to eliminate NOx included in exhaust gas, and performs lean combustion for burning a lean air-fuel mixture with an air-fuel ratio larger than a theoretical air-fuel ratio by using hydrogen as fuel. A control device 100 makes a deterioration diagnosis for detecting deterioration of the SCR catalyst 41. The control device 100 makes the deterioration diagnosis on the basis of elimination capacity of the SCR catalyst 41 during execution of NOx increase treatment. The NOx increase treatment is treatment for increasing the amount of NOx generated in a combustion chamber 17 of the internal combustion engine 10 compared to before execution of the NOx increase treatment.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] For example, Patent Document 1 describes a device for diagnosing an abnormality in a NOx purification catalyst provided in an exhaust passage of an internal combustion engine. This device calculates a NOx purification rate, which indicates the purification ability of the NOx purification catalyst, based on the NOx concentration upstream of the NOx purification catalyst and the NOx concentration downstream of the NOx purification catalyst. Then, an abnormality diagnosis of the NOx purification catalyst is performed based on the NOx purification rate. Note that this abnormality diagnosis may include, for example, detection of deterioration of the NOx purification catalyst. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-127990 Summary of the Invention [Problem to be solved by the invention]

[0004] In an internal combustion engine that uses hydrogen as fuel, NOx emissions can be reduced by performing lean combustion, which burns a lean mixture with an air-fuel ratio higher than the stoichiometric air-fuel ratio. However, if the NOx concentration in the exhaust gas is low, the accuracy of detecting deterioration of the catalyst that purifies NOx may decrease. [Means for solving the problem]

[0005] A control device for an internal combustion engine that solves the above problem is a control device that is applied to an internal combustion engine that includes an exhaust passage and a catalyst provided in the exhaust passage for purifying NOx contained in the exhaust, and that performs lean combustion using hydrogen as fuel to burn a lean mixture with an air-fuel ratio higher than the stoichiometric air-fuel ratio, and that performs deterioration diagnosis to detect deterioration of the catalyst. This control device performs the deterioration diagnosis based on the purification capacity of the catalyst when a NOx increase process is being performed, and the NOx increase process is a process that increases the amount of NOx generated in the combustion chambers of the internal combustion engine compared to before the NOx increase process was performed. [Effects of the Invention]

[0006] This control device for an internal combustion engine can improve the accuracy of detecting deterioration of a catalyst that purifies NOx in an internal combustion engine that uses hydrogen as fuel. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of an internal combustion engine and a drive system according to the first embodiment. [Figure 2] FIG. 2 is a flowchart showing the procedure of processing executed by the control device of the embodiment. [Figure 3] FIG. 3 is a flowchart showing the procedure of the process executed by the control device of the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] (First embodiment) A first embodiment of a control device for an internal combustion engine mounted on a vehicle will be described below.

[0009] <Configuration of internal combustion engine and drive system> 1, a vehicle 700 includes an internal combustion engine 10. The internal combustion engine 10 includes a cylinder block 11, a cylinder head 12, a head cover 13, and an oil pan .

[0010] A cylinder 16 is provided in the cylinder block 11. A piston 15 is disposed in the cylinder 16. The cylinder head 12 is provided with an intake port 30 that introduces intake air into a combustion chamber 17 of the internal combustion engine 10 and an exhaust port 70 that discharges exhaust gas from the combustion chamber 17. An intake valve 81 is provided in the intake port 30. A drive system for this intake valve 81 is provided with an intake-side variable valve timing mechanism 85, which is a variable valve mechanism that changes the valve timing of the intake valve 81.

[0011] An exhaust valve 82 is provided in the exhaust port 70. A drive system of this exhaust valve 82 is provided with an exhaust-side variable valve timing mechanism 86, which is a variable valve mechanism that changes the valve timing of the exhaust valve 82.

[0012] The cylinder head 12 is provided with a direct-injection type fuel injection valve 84 that directly injects hydrogen as fuel into the combustion chamber 17 during the compression stroke, and an ignition plug 23 . A crankcase 19 is provided below the cylinder block 11. The crankcase 19 houses a crankshaft 18, which is the output shaft of the internal combustion engine 10. An oil pan 14 that stores lubricating oil is provided below the crankcase 19.

[0013] An intake manifold 29 equipped with a surge tank 60 is connected upstream of the intake port 30, and the intake pipe 20 is connected upstream of the surge tank 60. The intake pipe 20, the surge tank 60, the intake manifold 29, and the intake port 30 form an intake passage of the internal combustion engine 10.

[0014] The intake pipe 20 is provided with, in order from upstream, an air cleaner 21, an air flow meter 51, a compressor wheel 24C of a supercharger 24 driven by exhaust gas discharged from the combustion chamber 17, an intercooler 27, a supercharging pressure sensor 54, and a throttle valve 28. The surge tank 60 is also provided with an intake pressure sensor 55. The opening of the throttle valve 28 is changed by an electric motor.

[0015] Furthermore, the portion of the intake pipe 20 upstream of the compressor wheel 24C and the portion downstream of the compressor wheel 24C are connected via a bypass passage 92. An air bypass valve 93, the opening of which is adjusted by an actuator, is provided in the bypass passage 92. The air bypass valve 93 is a valve that adjusts the amount of air flowing through the bypass passage 92, and the larger the opening of the air bypass valve 93, the larger the amount of air that bypasses the compressor wheel 24C and passes through the bypass passage 92. Therefore, the larger the opening of the air bypass valve 93, the lower the supercharging pressure of the intake air increased by the supercharger 24.

[0016] The air cleaner 21 filters the intake air taken into the intake pipe 20. The supercharger 24 supercharges the air in the intake pipe 20. The intercooler 27 cools the air after it has passed through the compressor wheel 24C. The throttle valve 28 adjusts the amount of intake air by adjusting the valve opening.

[0017] An air flow meter 51 detects the intake air amount GA. A boost pressure sensor 54 detects a boost pressure PTC, which is the pressure in the intake pipe 20 downstream of the compressor wheel 24C. An intake pressure sensor 55 detects an intake pressure PIM, which is the pressure in a surge tank 60.

[0018] An exhaust pipe 90 that constitutes an exhaust passage is connected downstream of the exhaust port 70. A housing that accommodates a turbine wheel 24T of the turbocharger 24 is connected midway through the exhaust pipe 90. The turbocharger 24 is a variable displacement turbocharger and is equipped with nozzle vanes 24N. The nozzle vanes 24N are driven by an actuator to adjust the flow velocity of the exhaust gas blown onto the turbine wheel 24T. By changing the opening degree of these nozzle vanes 24N, the supercharging pressure of the intake air increased by the turbocharger 24 changes.

[0019] An oxidation catalyst 40 is disposed in the exhaust pipe 90 downstream of the turbine wheel 24T of the turbocharger 24. In addition, a selective catalytic reduction catalyst 41, which is a catalyst that purifies NOx contained in the exhaust gas, is disposed in the exhaust pipe 90 downstream of the oxidation catalyst 40. Hereinafter, the selective catalytic reduction catalyst 41 will be referred to as an SCR (Selective Catalytic Reduction) catalyst 41.

[0020] A urea addition valve 43 is disposed in the exhaust pipe 90 between the oxidation catalyst 40 and the SCR catalyst 41. The urea addition valve 43 supplies urea water, which is a reducing agent containing an ammonia component, to the SCR catalyst 41. The urea water injected from the urea addition valve 43 is converted into ammonia through hydrolysis using exhaust heat, and is adsorbed by the SCR catalyst 41. NOx is then reduced and purified by the ammonia adsorbed by the SCR catalyst 41.

[0021] A first NOx sensor 57 that detects the concentration of NOx contained in the exhaust gas is provided in the exhaust pipe 90 between the oxidation catalyst 40 and the SCR catalyst 41. The first NOx sensor 57 detects a first NOx concentration N1, which is the NOx concentration in the exhaust gas before the NOx is purified by the SCR catalyst 41.

[0022] A second NOx sensor 58 that detects the concentration of NOx contained in the exhaust gas is provided in the exhaust pipe 90 downstream of the SCR catalyst 41. The second NOx sensor 58 detects a second NOx concentration N2, which is the NOx concentration in the exhaust gas after the NOx has been purified by the SCR catalyst 41.

[0023] The internal combustion engine 10 is equipped with an exhaust gas recirculation device (hereinafter referred to as the EGR device). The EGR device reduces the amount of NOx generated in the combustion chamber 17 by introducing a portion of the exhaust gas into the intake air to lower the combustion temperature of the air-fuel mixture. The EGR device includes an EGR passage 210 that connects the intake pipe 20 upstream of the compressor wheel 24C with the exhaust pipe 90 downstream of the SCR catalyst 41. The EGR device includes an EGR valve 220 that is provided in the EGR passage 210 and has an opening degree adjusted by an actuator. The EGR device also includes an EGR cooler 230 provided in the EGR passage 210. The opening degree of the EGR valve 220 is adjusted to regulate the amount of exhaust gas introduced from the exhaust pipe 90 into the intake pipe 20, i.e., the amount of EGR gas. The EGR cooler 230 also lowers the temperature of the exhaust gas flowing through the EGR passage 210.

[0024] The crankshaft 18 of the internal combustion engine 10 is mechanically connected to a carrier C of a planetary gear mechanism 300 that constitutes a power split device. A rotating shaft 310a of a first motor generator (hereinafter referred to as first MG) 310 is mechanically coupled to a sun gear S of the planetary gear mechanism 300.

[0025] Furthermore, a rotary shaft 320a of a second motor generator (hereinafter referred to as second MG) 320 and a driving wheel 340 are mechanically coupled to the ring gear R of the planetary gear mechanism 300. The driving wheel 340 is one of the wheels equipped on the vehicle 700. The wheel equipped on the vehicle 700 is provided with a hydraulic brake 510 that brakes the wheel. The brake 510 is a friction brake, and the operation thereof is controlled by the control system 500. The brake 510 may be an electric brake.

[0026] The first MG 310 functions as a generator that generates electricity using the engine output, and also functions as an electric motor that cranks the crankshaft 18 when the internal combustion engine 10 is started.

[0027] Second MG 320 functions as an electric motor that generates driving force for drive wheels 340, and also functions as a generator that generates electricity by regenerative braking when vehicle 700 is decelerating. The first MG 310 and the second MG 320 exchange power with the battery 470 via a PCU (Power Control Unit) 400. The PCU 400 includes a CPU that performs arithmetic processing, a memory that stores control programs and data, etc. The PCU 400 also includes a converter that boosts and outputs a DC voltage input from the battery 470, and an inverter that converts the DC voltage boosted by the converter into an AC voltage and outputs it to the first MG 310 and the second MG 320.

[0028] Battery 470 is connected to battery ECU 480. Battery ECU 480 includes a CPU that performs arithmetic processing, a memory that stores control programs and data, and the like, and manages the charging and discharging of battery 470. Battery ECU 480 acquires the state of battery 470 detected by sensors, that is, input current, output current, voltage, temperature, and the like. Then, based on the acquired data, battery ECU 480 calculates the remaining capacity, which is the current amount of stored power in battery 470, and the current full charge capacity of battery 470. Battery ECU 480 then calculates a value obtained by dividing the full charge capacity of battery 470 by the remaining capacity, and assigns the calculated value to the charging rate SOC of battery 470.

[0029] Thus, the vehicle 700 of this embodiment is a vehicle equipped with a hybrid system that includes an internal combustion engine and a motor generator as prime movers. The control device 100 controls the internal combustion engine 10. The control device 100 operates various devices to be operated, such as the throttle valve 28, the fuel injector 84, the spark plug 23, the intake-side variable valve timing mechanism 85, and the exhaust-side variable valve timing mechanism 86. The control device 100 also operates various devices to be operated, such as the air bypass valve 93, the actuator of the nozzle vane 24N, and the urea addition valve 43. The control device 100 also operates the PCU 400 to control the first MG 310 and the second MG 320. The control device 100 also operates the control system 500 to control the brake 510.

[0030] The control device 100 includes a CPU 110 that performs arithmetic processing, a memory 120 that stores control programs and data, and the like. The control device 100 performs various control-related processes by having the CPU 110 execute the programs stored in the memory 120. Although not shown, the control device 100 is made up of multiple control units, such as a control unit for the internal combustion engine 10, control units for the first MG 310 and the second MG 320, and a control unit for the brake 510.

[0031] The control device 100 receives detection signals from a boost pressure sensor 54, an intake pressure sensor 55, a first NOx sensor 57, and a second NOx sensor 58. The control device 100 also receives detection signals from various other sensors. For example, the control device 100 receives a detection signal from an air flow meter 51 that detects an intake air amount GA. The control device 100 also receives a detection signal from an accelerator operation amount sensor 52 that detects an accelerator operation amount ACCP, which is the amount of operation of an accelerator pedal that adjusts the output of the internal combustion engine 10. The control device 100 also receives a detection signal from a throttle sensor 53 that detects a throttle opening TA, which is the opening of the throttle valve 28. The control device 100 also receives detection signals from a vehicle speed sensor 56 that detects a vehicle speed SP of the vehicle 700 and a crank angle sensor 50 that detects a rotation angle (crank angle) of the crankshaft 18 to calculate the engine rotation speed NE. Control device 100 also receives a detection signal from pressure sensor 47 that detects fuel pressure P in a delivery pipe that distributes fuel to fuel injection valve 84. Control device 100 also receives a detection signal from temperature sensor 48 that detects fuel temperature THF in a delivery pipe that distributes fuel to fuel injection valve 84. Control device 100 also receives an output signal Sm1 from first rotation angle sensor 350 that detects the rotation angle of first MG 310 and an output signal Sm2 from second rotation angle sensor 360 that detects the rotation angle of second MG 320. Control device 100 also obtains the charging rate SOC of battery 470 from battery ECU 480.

[0032] The control device 100 calculates the engine load factor KL based on the engine speed NE and the intake air amount GA. The engine load factor KL is a parameter that determines the amount of air filled into the combustion chamber 17, and is the ratio of the amount of inflow air per combustion cycle of one cylinder to a reference inflow air amount. The reference inflow air amount is variably set according to the engine speed NE.

[0033] The control device 100 calculates the required torque required for the vehicle 700 to travel based on the accelerator operation amount ACCP and the vehicle speed SP. Then, the control device 100 controls the required output power Pe of the internal combustion engine 10 and the output torque of the first MG 310 and the second MG 320 so as to satisfy the required torque of the vehicle 700. For example, if the required output power Pe of the internal combustion engine 10 is "0" while the vehicle 700 is traveling, the control device 100 stops fuel injection from the fuel injection valve 84 and stops the ignition operation of the spark plug 23, thereby stopping the operation of the internal combustion engine 10. Then, the control device 100 performs electric traveling, in which the vehicle travels using the output torque of the second MG 320.

[0034] Hydrogen gas, which is fuel for the internal combustion engine 10, has a wider range of combustible mixtures than gasoline and can combust even lean mixtures. Therefore, the control device 100 performs lean combustion, which burns a lean mixture, which is a mixture with an air-fuel ratio higher than the stoichiometric air-fuel ratio, and adjusts the output of the internal combustion engine 10 through the following combustion control.

[0035] That is, the control device 100 sets a required injection amount Qd based on the required output Pe. The required injection amount Qd is a target value of fuel injected from the fuel injection valve 84. The control device 100 calculates a required air amount GAd, which is a target value of the intake air amount required to obtain the target air-fuel ratio AFt, based on the target air-fuel ratio AFt and the required injection amount Qd. The target air-fuel ratio AFt in this embodiment is a lean air-fuel ratio, for example, an excess air ratio λ=2.5 to 3.0. The control device 100 then controls the fuel injection valve 84 so as to obtain the required injection amount Qd. The control device 100 also controls the opening of the throttle valve 28 and the boost pressure of the turbocharger 24 so as to obtain the required air amount GAd. When controlling the boost pressure of the turbocharger 24, the control device 100 calculates a target boost pressure PTCp. Then, the control device 100 controls the opening of the air bypass valve 93 and the nozzle vane 24N so as to obtain the target boost pressure PTCp. In this way, in the internal combustion engine 10, the output is adjusted by changing the air-fuel ratio of the mixture through adjustment of the fuel injection amount and intake air amount.

[0036] The control device 100 sets a fuel injection start time Tis and a fuel injection end time Tie so that an amount of fuel corresponding to the required injection amount Qd is injected from the fuel injection valve 84. Calculation of the injection start time Tis and the injection end time Tie is well known. For example, the control device 100 calculates the injection start time Tis and the injection end time Tie based on the required injection amount Qd, the engine rotation speed NE, the fuel pressure P, the fuel temperature THF, and the like. Then, when the crank angle of the crankshaft 18 reaches the injection start time Tis, the control device 100 energizes the fuel injection valve 84 to open the fuel injection valve 84, thereby starting fuel injection. Then, when the crank angle of the crankshaft 18 reaches the injection end time Tie, the control device 100 stops energizing the fuel injection valve 84 to close the fuel injection valve 84, thereby ending fuel injection.

[0037] The control device 100 sets the ignition timing AFIN of the air-fuel mixture. Calculation of this ignition timing AFIN is well known. For example, the control device 100 calculates the ignition timing AFIN based on the engine speed NE, the engine load factor KL, a knocking correction value for suppressing knocking, and the like. Then, when the crank angle of the crankshaft 18 reaches the ignition timing AFIN, the control device 100 ignites the air-fuel mixture by causing the spark plug 23 to discharge a spark.

[0038] The control device 100 executes a fuel cut to stop fuel injection in the internal combustion engine 10 while the vehicle 700 is decelerating. This fuel cut is executed when the following execution condition is met. That is, when the accelerator depression amount ACCP is "0", the accelerator pedal is not depressed (accelerator off state), and the engine rotation speed NE is within a predetermined rotation speed range, the control device 100 stops fuel injection from the fuel injection valve 84. As is well known, when the accelerator pedal is operated or the engine rotation speed NE drops to a predetermined return rotation speed, the fuel cut is stopped and fuel injection from the fuel injection valve 84 is resumed.

[0039] When the accelerator operation amount ACCP is "0" and the engine is in the accelerator-off state, and the required output Pe for the internal combustion engine 10 corresponds to the value for idling operation, the control device 100 performs the idling operation of the internal combustion engine 10. This idling operation is performed while the vehicle 700 is running or stopped.

[0040] The control device 100 calculates the target valve timing of the intake valve 81 and the exhaust valve 82 based on the engine speed NE, the engine load factor KL, etc. Then, based on the target valve timing, etc., drive control of the intake-side variable valve timing mechanism 85 and the exhaust-side variable valve timing mechanism 86 is performed.

[0041] The control device 100 calculates a target EGR rate EGp, which is a command value for adjusting the amount of EGR gas introduced into the intake pipe 20, based on the engine operating state such as the engine speed NE and the engine load factor KL. The EGR rate is the ratio of the amount of EGR gas to the total amount of in-cylinder filling gas. Then, the control device 100 calculates a target opening EAt of the EGR valve 220 corresponding to the target EGR rate EGp based on the target EGR rate EGp, the intake air amount GA, etc., and controls the actuator of the EGR valve 220 so that the opening of the EGR valve 220 matches the target opening EAt.

[0042] <Deterioration diagnosis of SCR catalyst> The control device 100 performs a deterioration diagnosis of the SCR catalyst 41. In this deterioration diagnosis, a first average concentration NAV1, which is an average value of the first NOx concentration N1 detected by the first NOx sensor 57 during a predetermined sampling period, is calculated at each predetermined cycle and stored in the memory 120. Also, a second average concentration NAV2, which is an average value of the second NOx concentration N2 detected by the second NOx sensor 58 during the same sampling period, is calculated at each predetermined cycle and stored in the memory 120.

[0043] Then, the control device 100 calculates a NOx purification rate CF indicating the purification ability of the SCR catalyst 41 based on the following formula (1). NOx purification efficiency CF = (first average concentration NAV1 - second average concentration NAV2) / first average concentration NAV1 × 100 (%) (1) The second average concentration NAV2 used in calculating the NOx purification efficiency CF is preferably a value that takes into consideration the transport delay of exhaust gas.

[0044] That is, when the intake air amount GA is small, the flow velocity of the exhaust gas in the exhaust pipe 90 is slower than when the intake air amount GA is large, and so the time required for the exhaust gas to pass through the SCR catalyst 41 becomes longer. Therefore, the smaller the intake air amount GA, the longer the time it takes for the exhaust gas purification result, which was the first NOx concentration N1, to be reflected in the second NOx concentration N2. Therefore, for example, using the time point at which the first average concentration NAV1 substituted into the above equation (1) is stored as a reference, the second average concentration NAV2 stored at a time later than this reference timing by a predetermined time TR is substituted into the above equation (1). Note that the above time TR is set to be longer as the intake air amount GA becomes smaller.

[0045] The control device 100 then determines that the SCR catalyst 41 has deteriorated if the calculated NOx purification rate CF is equal to or less than a predetermined determination value ER, and determines that the SCR catalyst 41 has not deteriorated if the calculated NOx purification rate CF exceeds the determination value ER. In this embodiment, the deterioration diagnosis of the SCR catalyst 41 is performed once per trip, but the frequency with which the deterioration diagnosis is performed can be changed as appropriate. One trip refers to the period from when the vehicle driver turns on the ignition switch of the vehicle 700 until the next time he turns it off.

[0046] Incidentally, in the internal combustion engine 10 that uses hydrogen as fuel, lean combustion is performed in which a lean air-fuel mixture is burned as described above, thereby suppressing NOx emissions. Suppressing NOx emissions reduces the NOx concentration in the exhaust gas. A lower NOx concentration in the exhaust gas reduces the frequency with which NOx and the reducing agent come into contact in the SCR catalyst 41, thereby reducing the purification capability of the SCR catalyst 41. Therefore, the calculated NOx purification rate CF may be lower than the actual purification rate of the SCR catalyst 41, potentially reducing the accuracy of detecting deterioration of the SCR catalyst 41.

[0047] Furthermore, in an internal combustion engine 10 performing lean combustion, the NOx concentration in the exhaust gas is low, and therefore the amount of change in the second NOx concentration N2 associated with deterioration of the SCR catalyst 41 is small. Therefore, if the amount of change in the second NOx concentration N2 associated with deterioration of the SCR catalyst 41 is too small relative to the detectable range of NOx concentrations in the first NOx sensor 57 and the second NOx sensor 58, the following problem may occur. That is, it becomes difficult for the second NOx sensor 58 to correctly detect the change in the second NOx concentration N2 associated with deterioration of the SCR catalyst 41, and the accuracy of detecting deterioration of the SCR catalyst 41 may decrease.

[0048] Therefore, in this embodiment, when performing a deterioration diagnosis of the SCR catalyst 41, a NOx increase process is executed to increase the amount of NOx generated in the combustion chamber 17 of the internal combustion engine 10. Then, the deterioration diagnosis is executed based on the purification capacity of the SCR catalyst 41 when the NOx increase process is executed.

[0049] Fig. 2 shows the procedure of the process executed by the control device 100. The process shown in Fig. 2 is realized by the CPU 110 executing a program stored in the memory 120 of the control device 100 at predetermined intervals. Note that, below, the step number of each process is represented by a number preceded by "S."

[0050] 2, the control device 100 determines whether or not a deterioration detection condition for the SCR catalyst 41 is met (S100). The deterioration detection condition is a condition set for performing deterioration diagnosis when the NOx purification rate of the SCR catalyst 41 is high. The control device 100 determines that the deterioration detection condition is met when the following conditions (a), (b), and (c) are all met.

[0051] (a): The catalyst temperature THS is within a predetermined range. The catalyst temperature THS is the purification temperature of the SCR catalyst 41. The control device 100 estimates the catalyst temperature THS based on the engine speed NE, engine load factor KL, ignition timing AFIN, vehicle speed SP, etc. The lower limit of the predetermined range is the lowest temperature at which the SCR catalyst 41 is activated. If the temperature of the SCR catalyst 41 is too high, desorption of ammonia adsorbed on the SCR catalyst 41 may progress, or NOx may be generated in the SCR catalyst 41. Therefore, the upper limit of the predetermined range is the maximum temperature of the SCR catalyst 41 at which the desorption of ammonia and the generation of NOx can be kept within acceptable limits.

[0052] (b): The intake air amount GA is equal to or greater than the default value GAref. If the flow velocity of the exhaust gas passing through the SCR catalyst 41 is too fast, the time for which the NOx is purified by the SCR catalyst 41 is shortened, resulting in a decrease in the NOx purification rate. Therefore, the default value GAref is set in advance to an optimum value for the intake air amount GA that can prevent a decrease in the NOx purification rate.

[0053] (c): The required injection amount Qd is equal to or greater than the default value Qdref. When the required injection amount Qd is large, the amount of NOx generated in the combustion chamber 17 increases compared to when the required injection amount Qd is small. When the amount of NOx generated in the combustion chamber 17 increases, the NOx concentration in the exhaust increases, and the NOx purification rate of the SCR catalyst 41 increases. Therefore, an optimal value for the required injection amount Qd that can achieve a high NOx purification rate is set in advance as the default value Qdref.

[0054] In the process of S100, when it is determined that the deterioration detection condition for the SCR catalyst 41 is met (S100: YES), the control device 100 executes the process of S110. In the process of S110, the control device 100 executes the NOx increase process and the torque compensation process.

[0055] The NOx increasing process is a process for increasing the amount of NOx generated in the combustion chamber 17 compared to before the execution of the NOx increasing process. As the NOx increasing process, the control device 100 executes a reduction in the intake air amount and a retardation of the fuel injection timing.

[0056] The control device 100 reduces the intake air amount by correcting the required air amount GAd by the predetermined amount A. The predetermined amount A is an air amount that makes the air-fuel ratio of the mixture lower than the target air-fuel ratio AFt, and is an amount that can increase the amount of NOx generated in the combustion chamber 17 as much as possible within an allowable range while minimizing the impact on the engine operating state. That is, in a lean air-fuel ratio region where the air-fuel ratio of the mixture is higher than the stoichiometric air-fuel ratio, the amount of NOx generated in the combustion chamber 17 increases as the air-fuel ratio decreases, and the amount of NOx generated is maximized when the air-fuel ratio is slightly leaner than the stoichiometric air-fuel ratio. Therefore, the predetermined amount A is set so that the air-fuel ratio of the mixture is as close as possible to the air-fuel ratio that maximizes the amount of NOx generated, while minimizing the impact on the engine operating state within an allowable range. When the required air amount GAd is corrected downward by the predetermined amount A in this way, the control device 100 executes a process to reduce the opening of the throttle valve 28 so as to obtain the intake air amount after the correction.

[0057] The control device 100 also retards the fuel injection timing by correcting both the injection start timing Tis and the injection end timing Tie by a predetermined value B. The predetermined value B is an adaptive value that is set in advance to increase the amount of NOx generated in the combustion chamber 17.

[0058] The torque compensation process is a process for compensating for the decrease in torque of the internal combustion engine 10 that occurs as a result of the execution of the NOx increase process. As the torque compensation process, the control device 100 executes an increase in the required injection amount Qd and a retardation of the ignition timing.

[0059] The control device 100 increases the required injection amount Qd by correcting the required injection amount Qd by the predetermined amount C. The predetermined amount C is the following amount. That is, when the opening of the throttle valve 28 is reduced as part of the NOx increasing process, the pumping loss increases, and the torque transmitted to the crankshaft 18 of the internal combustion engine 10 decreases. The predetermined amount C is set to a fuel injection amount that compensates for this decrease in torque of the internal combustion engine 10. Note that the predetermined amount C may be changed depending on the amount of torque decrease due to the pumping loss.

[0060] The control device 100 also retards the ignition timing by correcting the ignition timing AFIN by a default value D. The default value D is the following value: When the NOx increase process is performed and the air-fuel ratio of the mixture decreases, the combustion speed of the mixture increases. Therefore, the timing at which the pressure in the cylinder of the internal combustion engine 10 reaches its maximum becomes earlier than the optimal timing for obtaining engine output, and as a result, the torque of the internal combustion engine 10 decreases. The default value D is set to an ignition timing correction value that compensates for such a decrease in torque of the internal combustion engine 10.

[0061] When the process of S110 is executed, the control device 100 determines whether or not the purification rate calculation condition is satisfied (S120). The purification rate calculation condition is a condition that permits calculation of the NOx purification rate CF. The control device 100 determines that the purification rate calculation condition is satisfied when the first NOx concentration N1 is equal to or greater than a predetermined judgment value N1ref. The judgment value N1ref is the minimum value of the first NOx concentration N1 necessary to accurately perform deterioration diagnosis of the SCR catalyst 41, and is a preset adaptive value.

[0062] Then, in the process of S120, when it is determined that the first NOx concentration N1 is equal to or greater than the reference value N1ref (S120: YES), the control device 100 executes the deterioration diagnosis of the SCR catalyst 41 described above.

[0063] If a negative judgment is made in S100 above, or if a negative judgment is made in the processing of S120 above, the control device 100 executes processing to reset both the currently calculated first average concentration NAV1 and second average concentration NAV2 to "0" (S140).

[0064] After executing the process of S130 and the process of S140, the control device 100 ends this process for the current execution cycle. <Actions and Effects of This Embodiment> (1-1) The control device 100 performs a deterioration diagnosis of the SCR catalyst 41 based on the NOx purification rate CF, which indicates the purification capability of the SCR catalyst 41 when the NOx increase processing is being performed. The NOx increase processing is a processing for increasing the amount of NOx generated in the combustion chamber 17 compared to before the execution of the NOx increase processing.

[0065] When performing deterioration diagnosis of the SCR catalyst 41 in this way, a NOx increase process is executed to increase the amount of NOx generated in the combustion chamber 17. Therefore, deterioration diagnosis of the SCR catalyst 41 is executed when the NOx concentration in the exhaust gas is high. Therefore, the accuracy of deterioration detection of the SCR catalyst 41 can be improved compared to when the NOx increase process is not executed.

[0066] (1-2) In a lean air-fuel ratio region where the air-fuel ratio of the mixture is greater than the stoichiometric air-fuel ratio, the smaller the air-fuel ratio, the greater the amount of NOx generated in the combustion chamber 17. Therefore, in the process of S110 shown in Fig. 2, the control device 100 executes a process to reduce the amount of intake air of the internal combustion engine 10 as the NOx increasing process. This reduction in the amount of intake air reduces the air-fuel ratio of the mixture, so the amount of NOx generated in the combustion chamber 17 can be increased.

[0067] (1-3) In order to perform a process of reducing the intake air amount as the NOx increasing process, the control device 100 executes a process of reducing the opening of the throttle valve 28 provided in the intake pipe 20 of the internal combustion engine 10. The control device 100 also executes a torque compensation process to compensate for the decrease in torque of the internal combustion engine 10 that accompanies the execution of the NOx increasing process. As this torque compensation process, the control device 100 executes a process of increasing the amount of fuel supplied to the combustion chamber 17.

[0068] As the NOx increasing process, a process for reducing the opening of the throttle valve 28 is executed, thereby reducing the intake air amount of the internal combustion engine 10. When the opening of the throttle valve 28 is reduced, pumping loss increases, and the torque (more specifically, the illustrated torque) transmitted to the crankshaft 18 of the internal combustion engine 10 decreases. Therefore, the control device 100 executes a process for increasing the amount of fuel supplied to the combustion chamber 17 by increasing the required injection amount Qd in the process of S110 shown in FIG. 2 as a torque compensation process for compensating for the decrease in torque of the internal combustion engine 10. When the amount of fuel supplied to the combustion chamber 17 is increased, the torque of the internal combustion engine 10 increases. Therefore, it is possible to suppress a decrease in torque of the internal combustion engine 10 due to the execution of the NOx increasing process.

[0069] (1-4) The internal combustion engine 10 is equipped with a fuel injection valve 84 that directly injects fuel into the combustion chamber 17 during the compression stroke. As the NOx increasing process, the control device 100 executes a process of delaying the injection start timing Tis at which fuel injection from the fuel injection valve 84 starts in the process of S110 shown in FIG.

[0070] When the injection start timing Tis is retarded, the time from when the fuel is injected to when it is ignited is shortened, and therefore the air-fuel mixture mixing time is shortened. When the air-fuel mixture mixing time is shortened, the fuel concentration distribution in the mixture is more likely to become uneven, resulting in regions in the combustion chamber 17 where the air-fuel ratio of the mixture is low. By burning this air-fuel mixture with a low air-fuel ratio, the amount of NOx generated in the combustion chamber 17 can be increased.

[0071] (1-5) The control device 100 executes torque compensation processing to compensate for the decrease in torque of the internal combustion engine 10 that accompanies the execution of the NOx increase processing. As this torque compensation processing, the control device 100 executes processing to retard the ignition timing of the air-fuel mixture.

[0072] When the air-fuel ratio of the mixture is reduced by executing the NOx increase processing, the combustion speed of the mixture increases. Therefore, the time when the pressure in the cylinders of the internal combustion engine 10 reaches a maximum becomes earlier than the optimal time for obtaining engine output, and as a result, the torque of the internal combustion engine 10 decreases. Therefore, in the processing of S110 shown in FIG. 2, the control device 100 of this embodiment executes processing to retard the ignition timing of the mixture as a torque compensation processing to compensate for such a decrease in torque of the internal combustion engine 10. Therefore, when the NOx increase processing is executed, the time when the pressure in the cylinders reaches a maximum approaches the optimal time for obtaining engine output. Therefore, the decrease in torque of the internal combustion engine 10 due to the execution of the NOx increase processing can be suppressed.

[0073] (Second embodiment) Next, a second embodiment of a control device for an internal combustion engine mounted on a vehicle will be described.

[0074] The present embodiment differs from the previous embodiment in the processing that the control device 100 executes prior to the processing of S120 shown in Fig. 2. The control device of this embodiment will be described below, focusing on these differences.

[0075] Fig. 3 shows a part of the procedure of the process executed by the control device 100. The process shown in Fig. 3 is realized by the CPU 110 executing a program stored in the memory 120 of the control device 100 at predetermined intervals.

[0076] 3, the control device 100 determines whether or not the deterioration detection conditions for the SCR catalyst 41 are met (S200). The control device 100 determines that the deterioration detection conditions are met when the following conditions (d), (e), and (f) are all met:

[0077] (d): The catalyst temperature THS is within a predetermined range. This condition (d) is the same as the above condition (a). (e): The accelerator is off.

[0078] (f): The battery 470 is chargeable. The control device 100 determines that the battery 470 is chargeable when the current state of charge SOC is equal to or less than a predetermined value E. The predetermined value E is an appropriate value for preventing the battery 470 from being overcharged.

[0079] In the process of S200, when it is determined that the deterioration detection condition for the SCR catalyst 41 is met (S200: YES), the control device 100 executes the process of S210. In the process of S210, the control device 100 determines whether or not the engine is currently idling (S210). If it is determined that the engine is currently idling (S210: YES), the control device 100 executes the process of S220.

[0080] In the process of S220, the control device 100 increases the required injection amount Qd as a NOx increasing process. That is, the control device 100 increases the amount of fuel supplied to the combustion chamber 17 by correcting the required injection amount Qd set during idle operation by the predetermined amount F. The predetermined amount F is an adaptive value that can increase the amount of NOx generated in the combustion chamber 17 during idle operation as much as possible within an allowable range while keeping the effect on the engine operating state within an allowable range.

[0081] Next, in the process of S230, control device 100 executes a process of decreasing the opening of throttle valve 28 and a process of increasing the amount of power generation of first MG 310 (S230). On the other hand, if it is determined in S210 that the engine is not idling (S210: NO), the control device 100 executes the process of S240.

[0082] In the process of S240, the control device 100 determines whether the above-mentioned conditions for executing fuel cut are met. If it is determined that the conditions for executing fuel cut are met (S240: YES), the control device 100 prohibits the execution of fuel cut in the process of S250. Then, the control device 100 performs combustion of the air-fuel mixture in the process of S260. When performing combustion of the air-fuel mixture in the process of S260, the control device 100 performs a process to increase the amount of NOx generated in the combustion chamber 17 as much as possible within an allowable range by burning an air-fuel mixture having a smaller air-fuel ratio than the above-mentioned lean mixture. The processes of S250 and S260 are NOx increasing processes that increase the amount of NOx generated in the combustion chamber 17.

[0083] After executing the process of S260, the control device 100 then executes the process of S270. In the process of S270, the control device 100 executes a process to decrease the opening of the throttle valve 28, a process to increase the amount of power generated by the second MG 320 by regenerative braking, and a process to increase the braking force of the wheels of the vehicle 700 (S270). As the process to increase the braking force of the wheels of the vehicle 700, the control device 100 executes a process to increase the braking force of the brake 510.

[0084] After completing the process of S270 or the process of S230, the control device 100 performs the process of S120 and subsequent steps shown in FIG. On the other hand, if a negative determination is made in the processing of S200 (S200: NO), the control device 100 performs the processing from S140 onwards shown in Fig. 2. Also, if a negative determination is made in the processing of S240 (S240: NO), the control device 100 ends this processing for the current execution cycle.

[0085] <Actions and Effects of This Embodiment> (2-1) The control device 100 executes the NOx increase processing and the deterioration diagnosis of the SCR catalyst 41 when the accelerator pedal, which adjusts the output of the internal combustion engine 10, is not depressed (accelerator off state). When the internal combustion engine 10 is idling due to the accelerator off, the control device 100 executes the processing of S220 shown in Fig. 3 as the NOx increase processing. That is, the control device 100 executes the processing to increase the amount of fuel supplied to the combustion chamber 17.

[0086] During idle operation, the amount of exhaust gas is small, and therefore the amount of NOx emitted from the combustion chamber 17 is also small. Therefore, this operating state is not suitable for diagnosing the deterioration of the SCR catalyst 41. In this regard, in this embodiment, a NOx increase process is executed to increase the amount of fuel supplied to the combustion chamber 17 while the internal combustion engine 10 is idling. When the amount of fuel supplied to the combustion chamber 17 is increased, the air-fuel ratio of the mixture decreases, and the amount of NOx generated in the combustion chamber 17 increases. In this way, deterioration diagnosis of the SCR catalyst 41 is performed with the amount of NOx generated increased, so deterioration diagnosis can be performed with high detection accuracy even during idle operation. Furthermore, compared to when deterioration diagnosis of the SCR catalyst 41 is not performed during idle operation, the number of opportunities to perform deterioration diagnosis can be increased.

[0087] (2-2) The control device 100 executes the NOx increasing process and the deterioration diagnosis of the SCR catalyst 41 when the accelerator pedal, which adjusts the output of the internal combustion engine 10, is not depressed and the engine is in an accelerator-off state. When the execution condition for fuel cut, which stops fuel injection in the internal combustion engine 10, is met due to the accelerator being off, the control device 100 executes the process of S250 and the process of S260 shown in Fig. 3 as the NOx increasing process. The process of S250 is a process that prohibits the execution of fuel cut even if the execution condition for fuel cut is met. The process of S260 is a process that burns an air-fuel mixture with a smaller air-fuel ratio than the above-mentioned lean air-fuel mixture.

[0088] Even when the conditions for executing a fuel cut that stops fuel injection in the internal combustion engine 10 are met, the control device 100 prohibits the execution of a fuel cut and executes a NOx increase process that burns a mixture with a lower air-fuel ratio than a lean mixture. When a mixture with a lower air-fuel ratio than the above-mentioned lean mixture is burned, the amount of NOx generated in the combustion chamber 17 increases. In this way, the deterioration diagnosis of the SCR catalyst 41 is performed with the amount of NOx generated increased, so that the deterioration diagnosis can be performed with high detection accuracy even in a situation where a fuel cut is executed due to an accelerator release. Furthermore, when the conditions for executing a fuel cut are met, the opportunities for performing the deterioration diagnosis of the SCR catalyst 41 can be increased compared to when the deterioration diagnosis of the SCR catalyst 41 is not performed.

[0089] (2-3) When the amount of fuel supplied to the combustion chamber 17 is increased as a NOx increasing process during idle operation, the torque of the internal combustion engine 10 increases. Also, when the NOx increasing process is performed when the conditions for executing fuel cut are met, and the air-fuel mixture is burned without performing fuel cut, the torque of the internal combustion engine 10 increases. In this regard, in this embodiment, during execution of the NOx increasing process, the control device 100 executes the process of S230 and S270 shown in FIG. 3 to execute a process to reduce the opening of the throttle valve 28. When the opening of the throttle valve 28 decreases, pumping loss increases, and therefore the torque transmitted to the crankshaft 18 of the internal combustion engine 10 decreases. This torque reduction makes it possible to suppress the increase in torque of the internal combustion engine 10 due to execution of the NOx increasing process.

[0090] (2-4) The crankshaft 18 of the internal combustion engine 10 is connected to the first MG 310, which functions as a generator, via the planetary gear mechanism 300. The drive wheels 340 are connected to the second MG 320, which also functions as a generator. The control device 100 then executes the process of S230 and the process of S270 shown in Fig. 3 to increase the amount of power generated by the first MG 310 and the second MG 320 during the execution of the NOx increasing process.

[0091] As described above, when the amount of fuel supplied to the combustion chamber 17 is increased as a NOx increasing process during idle operation, the torque of the internal combustion engine 10 increases. Furthermore, when the fuel cut execution condition is met as a NOx increasing process in which the air-fuel mixture is combusted without fuel cut, the torque of the internal combustion engine 10 increases. In this regard, in this embodiment, during execution of the NOx increasing process, a process is executed to increase the amount of power generated by the first MG 310 connected to the crankshaft 18 or the second MG 320 connected to the drive wheels 340. Therefore, the increase in torque of the internal combustion engine 10 due to execution of the NOx increasing process is absorbed by the increase in the amount of power generated by the first MG 310 or the second MG 320. Therefore, the increase in torque of the internal combustion engine 10 due to execution of the NOx increasing process can be suppressed.

[0092] (2-5) When the control device 100 executes the NOx increasing process by executing the process of S250 and the process of S260 shown in Fig. 3, the control device 100 executes the process of S270 shown in Fig. 3. That is, when the control device 100 executes the NOx increasing process, the control device 100 executes a process to increase the braking force of the brake 510 provided on the vehicle 700.

[0093] When the NOx increase process is executed in a situation where the conditions for executing a fuel cut are met, the air-fuel mixture is burned without a fuel cut. When the air-fuel mixture is burned, torque is generated from the internal combustion engine 10, which may reduce the sense of deceleration of the vehicle 700. In this regard, in this embodiment, when the NOx increase process is executed, the braking force of the brakes 510 provided on the wheels of the vehicle 700 is increased, thereby enhancing the sense of deceleration of the vehicle 700. Therefore, it is possible to prevent the sense of deceleration of the vehicle 700 from being reduced due to the execution of the NOx increase process.

[0094] <Example of change> The above-described embodiments can be modified as follows: The embodiments and the following modifications can be combined with each other within the scope of technical compatibility.

[0095] In the process of S110 shown in Figure 2, the opening of the throttle valve 28 is reduced in order to reduce the amount of intake air. Alternatively, the valve timing of the intake valve 81 or the valve timing of the exhaust valve 82 may be changed in order to reduce the amount of intake air. Furthermore, the opening of the nozzle vane 24N or the opening of the air bypass valve 93 may be changed in order to reduce the amount of intake air.

[0096] In the process of S110, the intake air amount is reduced as the NOx increasing process. Alternatively, the NOx increasing process may be performed by reducing the EGR amount by changing the target EGR ratio EGp to a value smaller than that before the NOx increasing process was performed, thereby increasing the amount of NOx generated in the combustion chamber 17.

[0097] In the NOx increasing process executed in the process of S110, either the reduction of the intake air amount or the retardation of the injection timing may be omitted. In the torque compensation process executed in the process of S110, either the increase in the required injection amount or the retardation of the ignition timing may be omitted.

[0098] The torque compensation process may be omitted from the process at S110. The deterioration detection conditions in the process of S100 shown in FIG. 2 may be changed as appropriate. Condition (f) may be omitted from the deterioration detection conditions in the process of S200 shown in Fig. 3. In this case, it is preferable to omit the increase in power generation amount in the processes of S230 and S270.

[0099] Of the processing executed in S230, either the processing for decreasing the opening of the throttle valve 28 or the processing for increasing the amount of power generated by the first MG 310 may be omitted. Of the processes executed in S270, at least one of the processes of decreasing the opening of the throttle valve 28, increasing the amount of power generated by the second MG 320 using regenerative braking, and increasing the braking force of the brake 510 may be omitted. Furthermore, the process of increasing the amount of power generated by the second MG 320 may be replaced with a process of increasing the amount of power generated by the first MG 310. Furthermore, in the process of S270, the braking force of a friction brake such as the brake 510 is increased in order to increase the braking force of the wheels of the vehicle 700. Furthermore, in order to increase such braking force, the increase in braking force by the brake 510 and the increase in braking force by the regenerative braking of the second MG 320 may be used in combination. Furthermore, instead of increasing the braking force by the brake 510, the braking force by the regenerative braking of the second MG 320 may be increased.

[0100] The processes of S210, S220, and S230 shown in FIG. 3 may be omitted. The processes of S240, S250, S260, and S270 shown in Fig. 3 may be omitted. In this case, if a negative determination is made in the process of S210, the series of processes shown in Fig. 3 may be terminated.

[0101] The first NOx concentration N1 may be estimated based on the required injection amount Qd, the intake air amount GA, or the like. The catalyst for purifying NOx may be a catalyst other than a selective reduction catalyst. For example, it may be a NOx storage reduction catalyst.

[0102] The internal combustion engine 10 may be provided with a port injection type fuel injection valve that injects fuel into the intake port 30. The internal combustion engine 10 may be equipped with either the intake side variable valve timing mechanism 85 or the exhaust side variable valve timing mechanism 86. Furthermore, the internal combustion engine 10 does not have to be equipped with either the intake side variable valve timing mechanism 85 or the exhaust side variable valve timing mechanism 86.

[0103] The internal combustion engine 10 does not have to be equipped with the supercharger 24. The turbocharger 24 does not have to include the nozzle vanes 24N. The exhaust pipe 90 does not have to include the bypass passage 92 and the air bypass valve 93.

[0104] The hybrid system of the vehicle is not limited to the one shown in FIG. 1, and other hybrid systems may be used. The number of motor generators provided in the vehicle can be changed as needed.

[0105] The vehicle may be equipped with only the internal combustion engine 10 as a prime mover. The control device 100 is not limited to a device equipped with a CPU and memory and executing software processing. For example, the control device 100 may be equipped with a dedicated hardware circuit, such as an ASIC, that performs hardware processing on at least a portion of the software processing performed in the above embodiments. That is, the control device 100 may include a processing circuit having any of the following configurations (a) to (c): (a) a processing circuit equipped with one or more processing devices that execute all of the above processing according to a program and one or more program storage devices, such as ROM, that store the program; (b) a processing circuit equipped with one or more processing devices and one or more program storage devices that execute part of the above processing according to a program, and one or more dedicated hardware circuits that execute the remaining processing; (c) a processing circuit equipped with one or more dedicated hardware circuits that execute all of the above processing. Program storage devices, i.e., computer-readable media, include any available media that can be accessed by a general-purpose or dedicated computer.

[0106] <Additional Notes> The technical ideas that can be understood from the above-described embodiment and modified examples will be described. [Appendix 1] A control device for an internal combustion engine that is equipped with an exhaust passage and a catalyst provided in the exhaust passage for purifying NOx contained in the exhaust, and that performs lean combustion using hydrogen as fuel to burn a lean mixture having an air-fuel ratio higher than the stoichiometric air-fuel ratio, and that performs deterioration diagnosis to detect deterioration of the catalyst, wherein the deterioration diagnosis is performed based on the purification capacity of the catalyst when a NOx increase process is being performed, and the NOx increase process is a process that increases the amount of NOx generated in the combustion chamber of the internal combustion engine compared to before the NOx increase process was performed.

[0107] [Appendix 2] The control device for an internal combustion engine according to appendix 1, wherein the NOx increasing process executes a process of reducing the amount of intake air of the internal combustion engine compared to before the NOx increasing process was executed. [Appendix 3] A control device for an internal combustion engine as described in Appendix 2, which executes a compensation process to compensate for the decrease in torque of the internal combustion engine that accompanies the execution of the NOx increase process, and as the compensation process, executes a process to retard the ignition timing of the mixture compared to before the compensation process was executed.

[0108] [Appendix 4] The NOx increase processing is a process of reducing the opening of a throttle valve provided in the intake passage of the internal combustion engine compared to before the NOx increase processing was executed, and a compensation process is executed to compensate for the decrease in torque of the internal combustion engine that accompanies the execution of the NOx increase processing, and as the compensation process, a process is executed to increase the amount of fuel supplied to the combustion chamber compared to before the compensation process was executed.

[0109] [Appendix 5] A control device for an internal combustion engine as described in any of Appendices 1 to 4, wherein the internal combustion engine is equipped with a fuel injection valve that directly injects fuel into a combustion chamber of the internal combustion engine during the compression stroke, and the NOx increase processing is a process that delays the injection start timing at which fuel injection from the fuel injection valve begins compared to before the NOx increase processing is executed.

[0110] [Appendix 6] A control device for an internal combustion engine as described in Appendix 1, which executes the NOx increase processing and the deterioration diagnosis when the accelerator pedal that adjusts the output of the internal combustion engine is not depressed and the accelerator is off, and when the internal combustion engine is idling due to the accelerator being off, executes the NOx increase processing by increasing the amount of fuel supplied to the combustion chamber compared to before the NOx increase processing was executed.

[0111] [Appendix 7] A control device for an internal combustion engine as described in Appendix 1 or Appendix 6, which executes the NOx increase processing and the deterioration diagnosis when the accelerator pedal that adjusts the output of the internal combustion engine is not depressed and the accelerator is off, and when the execution condition for fuel cut that stops fuel injection in the internal combustion engine is met due to the accelerator being off, the NOx increase processing is executed by prohibiting the execution of the fuel cut and performing a process to combust a mixture with a smaller air-fuel ratio than the lean mixture.

[0112] [Appendix 8] The control device for an internal combustion engine according to appendix 7, wherein when the NOx increasing process is executed, a process is executed to increase the braking force of the wheels of the vehicle compared to before the NOx increasing process was executed.

[0113] [Appendix 9] A control device for an internal combustion engine as described in any one of Appendices 6 to 8, which executes a process to reduce the opening of a throttle valve provided in the intake passage of the internal combustion engine during execution of the NOx increase process compared to before execution of the NOx increase process.

[0114] [Appendix 10] A control device for an internal combustion engine as described in Appendices 6 to 9, wherein the output shaft of the internal combustion engine is connected to a generator, and during execution of the NOx increase processing, a process is executed to increase the amount of power generated by the generator compared to before execution of the NOx increase processing. [Explanation of symbols]

[0115] 10...Internal combustion engine 17...Combustion chamber 18...Crankshaft 20...Intake pipe 23...Spark plug 24...Turbocharger 28...Throttle valve 40...Oxidation catalyst 41...Selective catalytic reduction catalyst (SCR catalyst) 43...Urea addition valve 57...No. 1 NOx sensor 58...Second NOx sensor 81...Intake valve 82...Exhaust valve 84...Fuel injection valve 90...Exhaust pipe 100...Control device 210...EGR passage 300...Planetary gear mechanism 310...First motor generator (first MG) 320...Second motor generator (second MG) 340...Drive wheels 470…Battery 510...Brake 700...vehicle

Claims

1. 1. A control device that is applied to an internal combustion engine that performs lean combustion using hydrogen as fuel to burn a lean mixture having an air-fuel ratio higher than the stoichiometric air-fuel ratio, the control device comprising: an exhaust passage; and a catalyst that is provided in the exhaust passage and that purifies NOx contained in exhaust gas. The control device performs deterioration diagnosis to detect deterioration of the catalyst, The deterioration diagnosis is performed based on the purification capacity of the catalyst when the NOx increasing process is being performed. The NOx increasing process is a process for increasing the amount of NOx generated in the combustion chamber of the internal combustion engine compared to before the NOx increasing process was executed. Control device for internal combustion engines.

2. As the NOx increasing process, a process is executed to reduce the intake air amount of the internal combustion engine compared to before the NOx increasing process is executed. The control device for an internal combustion engine according to claim 1.

3. performing a compensation process to compensate for a decrease in torque of the internal combustion engine due to the execution of the NOx increasing process; As the compensation process, a process is executed to retard the ignition timing of the air-fuel mixture compared to before the compensation process was executed. The control device for an internal combustion engine according to claim 2.

4. the NOx increasing process is a process of reducing the opening degree of a throttle valve provided in an intake passage of the internal combustion engine compared to before the NOx increasing process is executed, performing a compensation process to compensate for a decrease in torque of the internal combustion engine due to the execution of the NOx increasing process; As the compensation process, a process is executed to increase the amount of fuel supplied to the combustion chamber compared to before the compensation process was executed. The control device for an internal combustion engine according to claim 2.

5. the internal combustion engine is equipped with a fuel injection valve that directly injects fuel into a combustion chamber of the internal combustion engine during a compression stroke; As the NOx increasing process, a process is executed to retard the injection start timing at which fuel injection from the fuel injection valve is started compared to before the execution of the NOx increasing process. The control device for an internal combustion engine according to claim 1.

6. executes the NOx increase process and the deterioration diagnosis when an accelerator pedal that adjusts the output of the internal combustion engine is not depressed (accelerator-off state); When the internal combustion engine is idling due to the accelerator being released, the NOx increasing process is performed by increasing the amount of fuel supplied to the combustion chamber compared to before the NOx increasing process was performed. The control device for an internal combustion engine according to claim 1.

7. executes the NOx increase process and the deterioration diagnosis when an accelerator pedal that adjusts the output of the internal combustion engine is not depressed (accelerator-off state); When the execution condition for fuel cut for stopping fuel injection in the internal combustion engine is satisfied due to the accelerator release, the execution of the fuel cut is prohibited and a process for burning a mixture having an air-fuel ratio smaller than that of the lean mixture is executed as the NOx increasing process. The control device for an internal combustion engine according to claim 1.

8. When the NOx increasing process is executed, a process is executed to increase the braking force of the wheels of the vehicle equipped with the internal combustion engine compared to before the NOx increasing process was executed. The control device for an internal combustion engine according to claim 7.

9. During the execution of the NOx increasing process, a process is executed to reduce the opening of a throttle valve provided in an intake passage of the internal combustion engine compared to before the execution of the NOx increasing process.

8. The control device for an internal combustion engine according to claim 6 or 7.

10. an output shaft of the internal combustion engine is connected to a generator; During the execution of the NOx increase processing, a process is executed to increase the amount of power generated by the generator compared to before the execution of the NOx increase processing.

8. The control device for an internal combustion engine according to claim 6 or 7.

Images