Controller for hydrogen fuel internal combustion engine provided with scr catalyst, control method, and storage medium

Abstract

The present disclosure provides a controller (100) for an internal combustion engine (10). The internal combustion engine (10) includes a catalyst (41) arranged in an exhaust passage (90) to remove NOx from exhaust gas, and performs lean burn that burns a lean air-fuel mixture having an air-fuel ratio greater than a stoichiometric air-fuel ratio using hydrogen as a fuel. The controller (100) is configured to perform deterioration diagnosis that detects deterioration of the catalyst (41) based on a removal performance of the catalyst (41) during execution of NOx increase processing. The NOx increase processing includes increasing an amount of NOx generated in a combustion chamber (17) of the internal combustion engine (10) to be greater than an amount before the NOx increase processing is executed.

Description

Technical Field

[0001] The following description relates to a controller, control method, and storage medium for an internal combustion engine. Background Technology

[0002] Patent Document 1 discloses an example of an apparatus for diagnosing anomalies in a NOx removal catalyst disposed in the exhaust passage of an internal combustion engine. This apparatus calculates a NOx removal rate based on the NOx concentration upstream and downstream of the NOx removal catalyst, which indicates the removal performance of the NOx removal catalyst. Anomalies in the NOx removal catalyst are diagnosed based on the NOx removal rate. One example of anomaly diagnosis is detecting deterioration of the NOx removal catalyst.

[0003] List of citations

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2018-127990 Summary of the Invention

[0006] Technical issues

[0007] When hydrogen is used as fuel in an internal combustion engine, lean combustion is performed to reduce NOx emissions. This lean combustion involves burning a lean air-fuel mixture with an air-fuel ratio greater than the stoichiometric ratio. When the exhaust has a low concentration of NOx, the accuracy of detecting the degradation of the NOx removal catalyst may decrease.

[0008] Solution to the problem

[0009] A first aspect of this disclosure provides a controller for an internal combustion engine. The internal combustion engine includes an exhaust passage and a catalyst disposed on the exhaust passage to remove NOx from the exhaust. The internal combustion engine is configured to perform lean combustion using hydrogen as fuel to burn a lean air-fuel mixture having an air-fuel ratio greater than the stoichiometric air-fuel ratio. The controller is configured to perform a degradation diagnosis, based on the removal performance of the catalyst during the execution of a NOx-increasing treatment, to detect degradation of the catalyst. The NOx-increasing treatment includes increasing the amount of NOx generated in the combustion chamber of the internal combustion engine to a level greater than the amount of NOx before the NOx-increasing treatment was performed.

[0010] A second aspect of this disclosure provides a method for controlling an internal combustion engine. The internal combustion engine includes an exhaust passage and a catalyst disposed on the exhaust passage to remove NOx from the exhaust. The internal combustion engine is configured to perform lean combustion using hydrogen as fuel to burn a lean air-fuel mixture having an air-fuel ratio greater than the stoichiometric air-fuel ratio. The method includes performing a degradation diagnosis based on the removal performance of the catalyst during the execution of a NOx-increasing treatment. The NOx-increasing treatment includes increasing the amount of NOx generated in the combustion chamber of the internal combustion engine to a level greater than the amount of NOx before the NOx-increasing treatment was performed.

[0011] A third aspect of this disclosure provides a non-transitory computer-readable storage medium storing a program including instructions for performing a method for controlling an internal combustion engine. The internal combustion engine includes an exhaust passage and a catalyst disposed on the exhaust passage to remove NOx from the exhaust. The internal combustion engine is configured to perform lean combustion using hydrogen as fuel to burn a lean air-fuel mixture having an air-fuel ratio greater than the stoichiometric air-fuel ratio. The instructions include performing a degradation diagnosis to detect degradation of the catalyst based on the catalyst's removal performance during the execution of a NOx-increasing treatment. The NOx-increasing treatment includes increasing the amount of NOx generated in the combustion chamber of the internal combustion engine to a level greater than the amount of NOx before the NOx-increasing treatment was performed.

[0012] The controller for internal combustion engines using hydrogen as fuel has improved the accuracy of detecting the degradation of NOx removal catalysts. Attached Figure Description

[0013] [ Figure 1 ] Figure 1 This is a schematic diagram illustrating the configuration of the internal combustion engine and drive system according to the first embodiment; [ Figure 2 ] Figure 2 This is a flowchart illustrating the steps performed by the controller according to an embodiment; and [ Figure 3 ] Figure 3 This is a flowchart illustrating the steps performed by the controller according to the second embodiment. Detailed Implementation

[0014] First Embodiment

[0015] A first embodiment of a controller for an internal combustion engine installed in a vehicle will now be described.

[0016] Configuration of internal combustion engine and drive system

[0017] like Figure 1 As shown, vehicle 700 includes an internal combustion engine 10. The internal combustion engine 10 includes a cylinder block 11, a cylinder head 12, a cylinder head cover 13, and an oil pan 14.

[0018] The cylinder block 11 contains a plurality of cylinders 16. Each cylinder 16 contains a piston 15.

[0019] The cylinder head 12 includes an intake port 30 for drawing intake air into the combustion chamber 17 of the internal combustion engine 10 and an exhaust port 70 for expelling exhaust gas from the combustion chamber 17. The intake port 30 includes an intake valve 81. The drive system for the intake valve 81 includes an intake-side variable valve timing mechanism 85, which is a variable valve actuation mechanism that changes the valve timing of the intake valve 81.

[0020] An exhaust valve 82 is arranged in the exhaust port 70. The drive system of the exhaust valve 82 includes an exhaust-side variable valve timing mechanism 86, which is a variable valve actuation mechanism that changes the valve timing of the exhaust valve 82.

[0021] The cylinder head 12 is equipped with a spark plug 23 and a direct injection fuel injection valve 84. During the compression stroke, the fuel injection valve 84 directly injects hydrogen as fuel into the combustion chamber 17.

[0022] The crankcase 19 is located below the cylinder block 11. The crankcase 19 houses the crankshaft 18, which serves as the output shaft of the internal combustion engine 10. The oil pan 14 is located below the crankcase 19 to store lubricating oil.

[0023] The intake manifold 29, including the pressure regulator 60, is connected to the upstream portion of the intake port 30. The intake pipe 20 is connected to the upstream portion of the pressure regulator 60. The intake pipe 20, pressure regulator 60, intake manifold 29, and intake port 30 form the intake passage of the internal combustion engine 10.

[0024] The intake manifold 20 is equipped with, from upstream, an air filter 21, an air flow meter 51, a compressor impeller 24C of the forced intake device 24, an intercooler 27, a boost pressure sensor 54, and a throttle valve 28. The forced intake device 24 is driven by exhaust gas discharged from the combustion chamber 17. The intake pressure sensor 55 is located on the pressure regulator 60. The opening of the throttle valve 28 is changed by an electric motor.

[0025] In the intake pipe 20, the upstream and downstream portions of the compressor impeller 24C are fluidly connected by a bypass passage 92. An air bypass valve 93 is arranged in the bypass passage 92. The opening of the air bypass valve 93 is adjusted by an actuator. The air bypass valve 93 is configured to regulate the amount of air flowing through the bypass passage 92. As the opening of the air bypass valve 93 increases, the amount of air bypassing the compressor impeller 24C and flowing through the bypass passage 92 increases. Therefore, as the opening of the air bypass valve 93 increases, the boost pressure of the intake air increased by the forced intake device 24 decreases.

[0026] Air filter 21 filters the intake air drawn into intake manifold 20. Forced intake device 24 compresses the air in intake manifold 20. Intercooler 27 cools the air that has passed through compressor impeller 24C. Throttle valve 28 opening is adjusted to control intake air volume.

[0027] Air flow meter 51 detects the intake air volume GA. Booster pressure sensor 54 detects the boost pressure PTC, which is the pressure in the intake pipe 20 downstream of the compressor impeller 24C. Intake pressure sensor 55 detects the intake pressure PIM, which is the pressure in the pressure regulator 60.

[0028] The downstream side of the exhaust port 70 is connected to the exhaust pipe 90, which forms the exhaust passage. The exhaust pipe 90 is connected to the housing of the turbine impeller 24T, which houses the forced intake device 24. The forced intake device 24 is a variable displacement type and includes nozzle blades 24N. The nozzle blades 24N are driven by an actuator to regulate the flow velocity of the exhaust gas flowing toward the turbine impeller 24T. Changing the opening of the nozzle blades 24N changes the boost pressure of the intake air increased by the forced intake device 24.

[0029] An oxidation catalyst 40 is disposed on an exhaust pipe 90 downstream of the turbine impeller 24T of the forced intake device 24. A selective catalytic reduction catalyst 41 is disposed in the exhaust pipe 90 downstream of the oxidation catalyst 40 to remove NOx from the exhaust gas. Hereinafter, the selective catalytic reduction catalyst 41 is referred to as SCR catalyst 41.

[0030] A urea supply valve 43 is disposed in the exhaust pipe 90 between the oxidation catalyst 40 and the SCR catalyst 41 to supply urea water, which serves as a reducing agent containing ammonia, to the SCR catalyst 41. The urea water injected from the urea supply valve 43 is converted into ammonia through hydrolysis using exhaust heat and adsorbed onto the SCR catalyst 41. NOx is reduced and removed by the ammonia adsorbed on the SCR catalyst 41.

[0031] A first NOx sensor 57 is disposed in the exhaust pipe 90 between the oxidation catalyst 40 and the SCR catalyst 41 to detect the concentration of NOx in the exhaust gas. The first NOx sensor 57 detects a first NOx concentration N1, which is the NOx concentration in the exhaust gas before the NOx is removed by the SCR catalyst 41.

[0032] The second NOx sensor 58 is disposed in the exhaust pipe 90 downstream of the SCR catalyst 41 to detect the concentration of NOx in the exhaust gas. The second NOx sensor 58 detects a second NOx concentration N2, which is the NOx concentration after NOx removal by the SCR catalyst 41.

[0033] The internal combustion engine 10 includes an exhaust gas recirculation (EGR) device. The EGR device is configured to draw a portion of the exhaust gas into the intake passage to reduce the combustion temperature of the air-fuel mixture, thereby reducing the amount of NOx produced in the combustion chamber 17. The EGR device includes an EGR passage 210 that fluidly connects the intake manifold 20 upstream of the compressor impeller 24C to the exhaust manifold 90 downstream of the SCR catalyst 41. The EGR device includes an EGR valve 220 disposed on the EGR passage 210. The opening of the EGR valve 220 is adjusted by an actuator. The EGR device includes an EGR cooler 230 disposed on the EGR passage 210. Adjusting the opening of the EGR valve 220 controls the amount of exhaust gas drawn from the exhaust manifold 90 into the intake manifold 20, i.e., the amount of EGR gas. The EGR cooler 230 reduces the temperature of the exhaust gas flowing through the EGR passage 210.

[0034] The crankshaft 18 of the internal combustion engine 10 is mechanically connected to the planet carrier C of the planetary gear mechanism 300 included in the power distribution device.

[0035] The planetary gear mechanism 300 includes a sun gear S, which is mechanically coupled to the rotating shaft 310a of the first electric generator 310 (hereinafter referred to as the first MG).

[0036] The planetary gear mechanism 300 includes a ring gear R mechanically coupled to the rotating shaft 320a of the second electric generator 320 (hereinafter referred to as the second MG) and a drive wheel 340. The drive wheel 340 is one of the wheels of the vehicle 700. The wheels of the vehicle 700 are equipped with hydraulic brakes 510 configured to apply braking force to the wheels. Brakes 510 are friction brakes and are controlled by a control system 500. Alternatively, brakes 510 may be electric brakes.

[0037] The first MG310 is used as a generator to generate electricity using the output of the engine and as an electric motor to drive the crankshaft 18 when the internal combustion engine 10 is started.

[0038] The second MG320 is used as an electric motor to generate driving force for the drive wheels 340 and as a generator to generate electricity through regenerative braking during vehicle deceleration 700.

[0039] The first MG310 and the second MG320 send power to and receive power from the battery 470 via a power control unit (PCU) 400. The PCU 400 includes electronic components such as a CPU that performs computational processing and a memory that stores programs and data for control. The PCU 400 includes, for example, a converter and an inverter. The converter is configured to increase the DC voltage received from the battery 470 and output that voltage. The inverter converts the DC voltage from the converter to an AC voltage and outputs the AC voltage to the first MG310 and the second MG320.

[0040] Battery 470 is connected to battery ECU 480. Battery ECU 480 includes electronic components such as a CPU that performs computational processing and a memory that stores programs and data for control. Battery ECU 480 controls the charging and discharging of battery 470. Battery ECU 480 acquires the state of battery 470 detected by sensors. The state of battery 470 includes, for example, input current, output current, voltage, and temperature. Based on the acquired data, battery ECU 480 calculates the charge amount (i.e., the current charge amount of battery 470) and the current full charge amount of battery 470. Battery ECU 480 calculates the value by dividing the current charge amount of battery 470 by the full charge amount of battery 470 and assigns the calculated value to the state of charge (SOC) of battery 470.

[0041] As described above, the vehicle 700 of this embodiment includes a hybrid power system, which includes an internal combustion engine as a prime mover and an electric generator.

[0042] The internal combustion engine 10 is configured to be controlled by a controller 100. The controller 100 operates various devices, such as a throttle valve 28, a fuel injection valve 84, a spark plug 23, an intake-side variable valve timing mechanism 85, and an exhaust-side variable valve timing mechanism 86. The controller 100 also operates various devices, such as an air bypass valve 93, an actuator for the nozzle vanes 24N, and a urea supply valve 43. The controller 100 operates a PCU 400 to control the first MG 310 and the second MG 320. The controller 100 operates a control system 500 to control the brake 510.

[0043] The controller 100 includes electronic components such as a CPU 110 that performs computational processing and a memory 120 that stores programs and data for control. The controller 100 performs various control-related processes by having the CPU 110 execute a program stored in the memory 120, which includes instructions. The memory 120 corresponds to a non-transitory computer-readable storage medium. The CPU 110 may be a processing circuit. Although not shown, the controller 100 includes multiple control units, such as a control unit for the internal combustion engine 10, control units for the first MG310 and the second MG320, and a control unit for the brake 510.

[0044] The controller 100 receives detection signals from the boost pressure sensor 54, the intake pressure sensor 55, the first NOx sensor 57, and the second NOx sensor 58. The controller 100 also receives detection signals from other sensors. In one example, the controller 100 receives a detection signal from the air flow meter 51, which is configured to detect the intake air volume GA. The controller 100 receives a detection signal from the accelerator operation sensor 52, which is configured to detect the accelerator operation amount ACCP corresponding to the accelerator pedal operation amount. The accelerator pedal regulates the output of the internal combustion engine 10. The controller 100 receives a detection signal from the throttle sensor 53, which is configured to detect the throttle opening TA (i.e., the opening of the throttle valve 28). The controller 100 receives a detection signal from the vehicle speed sensor 56, which is configured to detect the vehicle speed SP of the vehicle 700, and a detection signal from the crank angle sensor 50, which is configured to detect the rotation angle (crank angle) of the crankshaft 18 to calculate the engine speed NE. The controller 100 receives a detection signal from a pressure sensor 47 configured to detect the fuel pressure P in the delivery pipe dispensing fuel to the fuel injection valve 84. The controller 100 receives a detection signal from a temperature sensor 48 configured to detect the fuel temperature THF in the delivery pipe dispensing fuel to the fuel injection valve 84. The controller 100 receives an output signal Sm1 from a first rotation angle sensor 350 configured to detect the rotation angle of a first MG310 and an output signal Sm2 from a second rotation angle sensor 360 configured to detect the rotation angle of a second MG320. The controller 100 obtains the state of charge (SOC) of the battery 470 from the battery ECU 480.

[0045] The controller 100 calculates the engine load rate KL based on the engine speed NE and the intake air volume GA. The engine load rate KL is a parameter that determines the amount of air charged into the combustion chamber 17, and is the ratio of the amount of air entering a cylinder to a reference amount of air entering for each combustion cycle. The reference amount of air entering is variably set according to the engine speed NE.

[0046] The controller 100 calculates the required torque for vehicle 700 to travel based on the accelerator operation (ACCP) and vehicle speed (SP). The controller 100 controls the required output Pe of the internal combustion engine 10 and the output torque of the first MG310 and the second MG320 to meet the required torque of vehicle 700. In one example, when vehicle 700 is traveling and the required output Pe of internal combustion engine 10 is zero, the controller 100 stops fuel injection from fuel injection valve 84 and stops ignition of spark plug 23 to stop the operation of internal combustion engine 10. The controller 100 then performs electric driving, where the vehicle uses the output torque of the second MG320 to travel.

[0047] Hydrogen is the fuel for the internal combustion engine 10. Compared to gasoline, hydrogen has a wider range of combustible air-fuel mixtures and can burn even in relatively lean air-fuel mixtures. The controller 100 performs lean combustion of the lean air-fuel mixture (whose air-fuel ratio is greater than the stoichiometric air-fuel ratio) and regulates the output of the internal combustion engine 10 by means of combustion control described below.

[0048] The controller 100 sets the required injection quantity Qd based on the required output Pe. The required injection quantity Qd is the target value of fuel injected from the fuel injection valve 84. Based on the target air-fuel ratio AFt and the required injection quantity Qd, the controller 100 calculates the required air quantity GAd, which is the target value of the intake air quantity used to obtain the target air-fuel ratio AFt. In this embodiment, the target air-fuel ratio AFt is, for example, a lean air-fuel ratio with an excess air ratio λ of 2.5 to 3.0. The controller 100 controls the fuel injection valve 84 to obtain the required injection quantity Qd. The controller 100 controls the opening of the throttle valve 28 and the boost pressure of the forced intake device 24 to obtain the required air quantity GAd. In the boost pressure control of the forced intake device 24, the controller 100 calculates the target boost pressure PTCp. The opening of the air bypass valve 93 and the opening of the nozzle blade 24N are controlled to obtain the target boost pressure PTCp. As described above, the output of the internal combustion engine 10 is adjusted by changing the air-fuel ratio of the air-fuel mixture through the adjustment of the fuel injection quantity and the intake quantity.

[0049] Controller 100 sets the fuel injection start timing Tis and the fuel injection stop timing Tie, causing the fuel injection valve 84 to inject fuel corresponding to the required injection quantity Qd. The fuel injection start timing Tis and the fuel injection stop timing Tie are calculated using known processing. In one example, controller 100 calculates the fuel injection start timing Tis and the fuel injection stop timing Tie based on the required injection quantity Qd, engine speed NE, fuel pressure P, and fuel temperature THF. When the crankshaft 18 reaches the fuel injection start timing Tis, controller 100 energizes the fuel injection valve 84, causing the fuel injection valve 84 to open and begin fuel injection. When the crankshaft 18 reaches the fuel injection stop timing Tie, controller 100 de-energizes the fuel injection valve 84, causing the fuel injection valve 84 to close and stop fuel injection.

[0050] Controller 100 sets the ignition timing AFIN of the air-fuel mixture. The ignition timing AFIN is calculated using known processing methods. In one example, controller 100 calculates the ignition timing AFIN based on engine speed NE, engine load rate KL, and a knock correction value to reduce knocking. When the crank angle of crankshaft 18 reaches the ignition timing AFIN, controller 100 causes spark plug 23 to discharge spark to ignite the air-fuel mixture.

[0051] The controller 100 performs a fuel cut-off procedure during vehicle 700 deceleration, stopping fuel injection into the internal combustion engine 10. The fuel cut-off procedure is performed when the following conditions are met: The controller 100 stops fuel injection from the fuel injection valve 84 when the accelerator pedal is depressed in the accelerator-off state and the engine speed NE is within a predetermined range. If the accelerator pedal is depressed or the engine speed NE decreases to a predetermined recovery speed, the execution of the fuel cut-off procedure is terminated. This restores fuel injection from the fuel injection valve 84.

[0052] When the accelerator operation quantity ACCP is zero in the accelerator off state and the required output Pe value of the internal combustion engine 10 corresponds to idle speed, the controller 100 causes the internal combustion engine 10 to idle. This idle operation is performed when the vehicle 700 is moving or stopped.

[0053] The controller 100 calculates the target valve timings for the intake valve 81 and exhaust valve 82 based on the engine operating state (e.g., engine speed NE and engine load rate KL). Based on the target valve timings, it controls the intake-side variable valve timing mechanism 85 and the exhaust-side variable valve timing mechanism 86.

[0054] The controller 100 calculates a target EGR rate EGp based on the engine operating state (e.g., engine speed NE and engine load rate KL). This target EGR rate is a command value used to adjust the EGR amount. The EGR amount is the amount of EGR gas drawn into the intake manifold 20. The EGR rate is the ratio of the EGR amount to the total amount of gas charged into the cylinder. The controller 100 calculates a target opening EAT of the EGR valve 220 corresponding to the target EGR rate EGp, and controls the actuator of the EGR valve 220 based on the target EGR rate EGp and the intake air volume GA, such that the opening of the EGR valve 220 is equal to the target opening EAT.

[0055] SCR catalyst degradation diagnosis

[0056] The controller 100 performs a degradation diagnosis on the SCR catalyst 41.

[0057] In degradation diagnosis, the average value of the first NOx concentration N1 detected by the first NOx sensor 57 during a predetermined sampling period is calculated as the first average concentration NAV1. The first average concentration NAV1 is stored in the memory 120 during each predetermined period. During the same sampling period, the average value of the second NOx concentration N2 detected by the second NOx sensor 58 is calculated as the second average concentration NAV2. The second average concentration NAV2 is stored in the memory 120 during each predetermined period.

[0058] The controller 100 calculates the NOx removal rate CF, which indicates the removal performance of the SCR catalyst 41, based on Equation 1.

[0059] Equation 1: NOx removal rate CF = (First average concentration NAV1 - Second average concentration NAV2) / First average concentration NAV1 × 100 (%)

[0060] Preferably, the second average concentration NAV2 used to calculate the NOx removal rate CF has a value that takes into account the exhaust flow delay.

[0061] More specifically, when the intake air volume GA is smaller than when it is larger, the exhaust gas flows at a lower velocity in the exhaust pipe 90. As a result, the exhaust gas requires a longer time to flow through the SCR catalyst 41. Therefore, as the intake air volume GA decreases, it takes a longer time to reflect the removal results of the exhaust gas with a first NOx concentration N1 in the second NOx concentration N2. In this regard, for example, the second average concentration NAV2 stored at a predetermined time TR after the first average concentration NAV1 used in Equation 1 is used as a reference time point. As the intake air volume GA decreases, the time TR is set to a longer duration.

[0062] When the calculated NOx removal rate CF is less than or equal to the predetermined judgment value ER, the controller 100 determines that the SCR catalyst 41 has deteriorated; conversely, when the calculated NOx removal rate CF is greater than the judgment value ER, the controller 100 determines that the SCR catalyst 41 has not deteriorated. In this embodiment, the deterioration diagnosis of the SCR catalyst 41 is performed once per cycle. However, the frequency of performing the deterioration diagnosis can be varied. A cycle refers to the time period from when the driver of vehicle 700 turns on the ignition switch to when the driver of vehicle 700 turns off the ignition switch.

[0063] As described above, when the fuel in the internal combustion engine 10 is hydrogen, lean combustion of a lean air-fuel mixture is performed. This reduces NOx emissions. When NOx emissions are reduced, the concentration of NOx in the exhaust gas decreases. When the concentration of NOx in the exhaust gas decreases, the frequency of contact between NOx and the reducing agent in the SCR catalyst 41 decreases. This adversely affects the removal performance of the SCR catalyst 41. As a result, the NOx removal rate CF may be calculated as lower than the actual removal rate of the SCR catalyst 41, and the accuracy of detecting the deterioration of the SCR catalyst 41 may decrease.

[0064] In the lean-burning internal combustion engine 10, the NOx concentration in the exhaust is relatively low, and the rate of change of the second NOx concentration N2 due to the deterioration of the SCR catalyst 41 is relatively small. The rate of change of the second NOx concentration N2 due to the deterioration of the SCR catalyst 41 may be too small relative to the NOx concentration range detectable by the first NOx sensor 57 and the second NOx sensor 58. In this case, the second NOx sensor 58 may have difficulty accurately detecting the change in the second NOx concentration N2 due to the deterioration of the SCR catalyst 41. This may lead to a decrease in the accuracy of detecting the deterioration of the SCR catalyst 41.

[0065] In this embodiment, when performing a degradation diagnosis on the SCR catalyst 41, a NOx increase treatment is performed to increase the amount of NOx generated in the combustion chamber 17 of the internal combustion engine 10. The degradation diagnosis is performed based on the removal performance of the SCR catalyst 41 during the NOx increase treatment.

[0066] Figure 2 The steps performed by the controller 100 are illustrated. The CPU 110 executes the program stored in the memory 120 of the controller 100 in each predetermined cycle. Figure 2 The steps are shown below. In the following description, the step number for each step is indicated by a number prefixed with "S".

[0067] exist Figure 2 In the series of steps shown, controller 100 determines whether the degradation detection conditions of SCR catalyst 41 are met (S100). The degradation detection conditions are set such that degradation diagnosis is performed when the NOx removal rate of SCR catalyst 41 is high. Controller 100 determines that the degradation detection conditions are met when all of the following conditions (a), (b), and (c) are met.

[0068] (a): The catalyst temperature THS is within a predetermined range. The catalyst temperature THS is the removal temperature of the SCR catalyst 41. The controller 100 estimates the catalyst temperature THS based on vehicle operating parameters such as engine speed NE, engine load rate KL, ignition timing AFIN, and vehicle speed SP. The lower limit of the predetermined range is the minimum temperature at which the SCR catalyst 41 is activated. When the temperature of the SCR catalyst 41 is too high, it may promote the desorption of ammonia from the SCR catalyst 41, or it may produce NOx in the SCR catalyst 41. The upper limit of the predetermined range is the highest temperature of the SCR catalyst 41 at which ammonia desorption and NOx production are limited to permissible values.

[0069] (b): The intake air volume GA is greater than or equal to the predetermined value GAref. If the exhaust flow velocity through the SCR catalyst 41 is too high, the NOx removal time of the SCR catalyst 41 is shortened. This leads to a decrease in the NOx removal rate. Therefore, the predetermined value GAref is preset to an appropriate value of the intake air volume GA to limit the decrease in the NOx removal rate.

[0070] (c): The required injection quantity Qd is greater than or equal to the predetermined value Qdref. Compared to a smaller required injection quantity Qd, a larger required injection quantity Qd results in the generation of a greater amount of NOx in combustion chamber 17. As the amount of NOx generated in combustion chamber 17 increases, the concentration of NOx in the exhaust gas increases. This leads to an increase in the NOx removal rate of the SCR catalyst 41. Therefore, the predetermined value Qdref is preset to an appropriate value for the required injection quantity Qd to maintain a high NOx removal rate.

[0071] In step S100, if it is determined that the degradation detection conditions of the SCR catalyst 41 are met (S100: Yes), the controller 100 executes step S110.

[0072] In step S110, the controller 100 performs NOx increase processing and torque compensation processing.

[0073] NOx enhancement treatment increases the amount of NOx produced in combustion chamber 17 to a level greater than before the NOx enhancement treatment was implemented. NOx enhancement treatment includes reducing intake air volume and delaying fuel injection timing.

[0074] The controller 100 reduces the required air volume GAd by a predetermined amount A for correction, thereby reducing the intake air volume. The predetermined amount A is the amount of air that makes the air-fuel ratio of the mixture less than the target air-fuel ratio AFt. Furthermore, the predetermined amount A allows the amount of NOx produced in the combustion chamber 17 to be maximized within permissible limits while limiting the impact on engine operating conditions. More specifically, in a lean air-fuel ratio range where the air-fuel ratio of the mixture is greater than the stoichiometric air-fuel ratio, the amount of NOx produced in the combustion chamber 17 increases as the air-fuel ratio decreases. The maximum amount of NOx is produced when the air-fuel ratio is slightly higher 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 produces the maximum amount of NOx. When the required air volume GAd is reduced by the predetermined amount A for correction, the controller 100 performs a process to reduce the opening of the throttle valve 28 to obtain the intake air volume obtained through this reduction correction.

[0075] The controller 100 delays the fuel injection start timing Tis and the fuel injection stop timing Tie by a predetermined value B for correction, thereby delaying the fuel injection timing. The predetermined amount B is set to a predetermined appropriate value for increasing the amount of NOx produced in the combustion chamber 17.

[0076] The torque compensation process compensates for the decrease in torque of the internal combustion engine 10 caused by the NOx increase treatment. The torque compensation process includes increasing the required injection quantity Qd and retarding the ignition timing.

[0077] The controller 100 increases the required injection quantity Qd by a predetermined amount C for correction. Thus, the required injection quantity Qd increases. The predetermined amount C is as follows. More specifically, when the throttle opening 28 is reduced as a NOx increase treatment, pumping losses increase. This results in a decrease in torque transmitted to the crankshaft 18 of the internal combustion engine 10. The predetermined amount C is set to compensate for this decrease in torque of the internal combustion engine 10. The predetermined amount C can be changed according to the amount of torque reduction due to pumping losses.

[0078] The controller 100 delays the ignition timing AFIN by a predetermined value D for correction. Thus, the ignition timing is delayed. The predetermined value D is as follows. More specifically, when NOx increase treatment is performed and the air-fuel ratio of the mixture decreases, the combustion rate of the mixture increases. Therefore, the cylinder pressure of the internal combustion engine 10 reaches its maximum value before reaching the optimal time for obtaining engine output. This results in a decrease in the torque of the internal combustion engine 10. The predetermined value D is set as an ignition timing correction value to compensate for this decrease in the torque of the internal combustion engine 10.

[0079] After executing step S110, the controller 100 determines whether the removal rate calculation conditions are met (S120). When the removal rate calculation conditions are met, the calculation of the NOx removal rate CF is allowed. The controller 100 determines that the removal rate calculation conditions are met when the first NOx concentration N1 is greater than or equal to the predetermined judgment value N1ref. The judgment value N1ref is the minimum value of the first NOx concentration N1 required for accurate SCR catalyst 41 degradation diagnosis. The judgment value N1ref is a predetermined appropriate value.

[0080] In step S120, if the first NOx concentration N1 is greater than or equal to the judgment value N1ref (S120: Yes), the controller 100 performs a degradation diagnosis of the SCR catalyst 41.

[0081] If a negative determination is made in S100 or S120, the controller 100 performs the process of resetting the currently calculated first average concentration NAV1 and second average concentration NAV2 to zero (S140).

[0082] When step S130 or S140 is executed, the controller 100 ends the processing in the current execution cycle.

[0083] Operation and advantages of this embodiment

[0084] (1-1) Controller 100 performs a degradation diagnosis of SCR catalyst 41 based on NOx removal rate CF, which indicates the removal performance of SCR catalyst 41 during NOx increase treatment. NOx increase treatment increases the amount of NOx generated in combustion chamber 17 to a level greater than that before NOx increase treatment was performed.

[0085] As described above, when performing a degradation diagnosis of the SCR catalyst 41, a NOx-increasing treatment is performed to increase the amount of NOx generated in the combustion chamber 17. Therefore, when the NOx concentration in the exhaust is high, a degradation diagnosis of the SCR catalyst 41 is performed. In this case, the degradation of the SCR catalyst 41 is detected with higher accuracy compared to when no NOx-increasing treatment is performed.

[0086] (1-2) Within the range of lean air-fuel ratios where the air-fuel ratio of the mixture is greater than the stoichiometric air-fuel ratio, the amount of NOx produced in combustion chamber 17 increases as the air-fuel ratio decreases. Figure 2 In step S110, the controller 100 performs a process to reduce the intake air volume of the internal combustion engine 10 as a NOx-increasing process. The reduction in the intake air volume lowers the air-fuel ratio of the mixture, thereby increasing the amount of NOx produced in the combustion chamber 17.

[0087] (1-3) The controller 100 performs a process to reduce the opening of the throttle valve 28 arranged on the intake manifold 20 of the internal combustion engine 10, thereby performing a process of reducing the intake air volume as a NOx-increasing process. Furthermore, the controller 100 performs a torque compensation process to compensate for the decrease in torque of the internal combustion engine 10 caused by the NOx-increasing process. The controller 100 also performs a process to increase the amount of fuel supplied to the combustion chamber 17 as a torque compensation process.

[0088] When a process for reducing the opening of the throttle valve 28 is performed as a NOx-increasing process, the intake air volume of the internal combustion engine 10 decreases. As the opening of the throttle valve 28 decreases, pumping losses increase. This results in a decrease in the torque (more specifically, the indicated torque) transmitted to the crankshaft 18 of the internal combustion engine 10. As a torque compensation process to compensate for this decrease in the torque of the internal combustion engine 10, in... Figure 2 In S110, the controller 100 increases the required injection quantity Qd to perform a process for increasing the amount of fuel supplied to the combustion chamber 17. When the amount of fuel supplied to the combustion chamber 17 increases, the torque of the internal combustion engine 10 increases. This limits the decrease in torque of the internal combustion engine 10 due to the NOx increase process.

[0089] (1-4) The internal combustion engine 10 includes a fuel injection valve 84 that injects fuel directly into the combustion chamber 17 during the compression stroke. Figure 2In step S110, the controller 100 performs a process to delay the fuel injection start timing Tis of the fuel injection valve 84 as a NOx increase process.

[0090] When the fuel injection start timing (Tis) is delayed, the time from fuel injection to ignition is shortened. As a result, the mixing time of the air-fuel mixture is shortened. When the mixing time of the air-fuel mixture is shortened, the fuel concentration distribution of the air-fuel mixture tends to be uneven. Therefore, the air-fuel ratio of the air-fuel mixture in a portion of combustion chamber 17 is relatively low. When an air-fuel mixture with a relatively low air-fuel ratio is burned, the amount of NOx produced in combustion chamber 17 increases.

[0091] (1-5) The controller 100 performs torque compensation processing to compensate for the decrease in torque of the internal combustion engine 10 caused by the NOx increase treatment. The controller 100 performs a process to delay the ignition timing of the air-fuel mixture as torque compensation processing.

[0092] When NOx increase treatment is performed and the air-fuel ratio of the mixture is reduced, the combustion rate of the mixture increases. Therefore, the cylinder pressure of the internal combustion engine 10 reaches its maximum value before the optimal time for obtaining engine output. This results in a decrease in the torque of the internal combustion engine 10. In this embodiment, in Figure 2 In step S110, the controller 100 performs a process to delay the ignition timing of the air-fuel mixture as a torque compensation process to compensate for the torque drop in the internal combustion engine 10. Therefore, the time when the cylinder pressure reaches its maximum value during the NOx increase treatment is close to the optimal timing for obtaining engine output. This limits the torque drop in the internal combustion engine 10 caused by the NOx increase treatment.

[0093] Second Embodiment

[0094] A second embodiment of a controller for an internal combustion engine installed in a vehicle will now be described.

[0095] This embodiment is executed Figure 2 The steps performed by the controller 100 before step S120 shown are different. The differences of the controller in this embodiment will be described in detail.

[0096] Figure 3 A portion of the steps performed by controller 100 is shown. Figure 3 The steps shown are executed by the CPU 110 in each predetermined cycle by executing the program stored in the memory 120 of the controller 100.

[0097] exist Figure 3In the series of steps shown, the controller 100 determines whether the degradation detection conditions of the SCR catalyst 41 are met (S200). The controller 100 determines that the degradation detection conditions are met when all of the following conditions (d), (e), and (f) are met.

[0098] (d): The catalyst temperature THS is within the predetermined range. Condition (d) is the same as condition (a).

[0099] (e): Acceleration is turned off.

[0100] (f): Battery 470 is rechargeable. When the current state of charge (SOC) is less than or equal to a predetermined value E, the controller 100 determines that battery 470 is rechargeable. The predetermined value E is an appropriate value used to prevent overcharging of battery 470.

[0101] In step S200, if it is determined that the degradation detection conditions of the SCR catalyst 41 are met (S200: Yes), the controller 100 executes step S210.

[0102] In step S210, the controller 100 determines whether the engine is idling (S210). If it is determined that the engine is idling (S210: Yes), the controller 100 executes step S220.

[0103] In step S220, the controller 100 performs a process of increasing the required injection quantity Qd as a NOx increase. More specifically, the controller 100 increases the required injection quantity Qd set during idling by a predetermined amount F for correction, thereby performing a process to increase the amount of fuel supplied to the combustion chamber 17. The predetermined amount F is an appropriate value used to allow the amount of NOx generated in the combustion chamber 17 during idling to increase to the maximum extent within permissible limits while limiting the impact on engine operating conditions to permissible limits.

[0104] In step S230, the controller 100 performs a process to reduce the opening of the throttle valve 28 and a process to increase the power generation of the first MG310 (S230).

[0105] In step S210, if it is determined that the engine is not idling (S210: No), the controller 100 executes step S240.

[0106] In step S240, the controller 100 determines whether the fuel cut-off processing execution conditions are met. If the fuel cut-off processing execution conditions are met (S240: Yes), the controller 100 prohibits the execution of the fuel cut-off processing in step S250. Then, in step S260, the controller 100 performs combustion of the air-fuel mixture. When performing combustion of the air-fuel mixture in step S260, the controller 100 combusts an air-fuel mixture with a smaller air-fuel ratio than the lean air-fuel mixture described above, thereby maximizing the amount of NOx generated in the combustion chamber 17 within permissible limits. Steps S250 and S260 correspond to the NOx increase processing that increases the amount of NOx generated in the combustion chamber 17.

[0107] After executing step S260, the controller 100 proceeds to step S270.

[0108] In step S270, the controller 100 performs processes for reducing the opening of the throttle valve 28, for increasing the electrical charge generated by the second MG320 through regenerative braking, and for increasing the braking force on the wheels of the vehicle 700 (S270). As a process for increasing the braking force on the wheels of the vehicle 700, the controller 100 performs a process for increasing the braking force of the brake 510.

[0109] When step S270 or S230 is completed, controller 100 starts execution from S120. Figure 2 The steps shown are for diagnosing the deterioration of SCR catalyst 41.

[0110] If a negative decision is made in step S200 (S200: No), then the controller 100 will start execution from S140. Figure 2 The steps are shown. If a negative decision is made in step S240 (S240: No), the controller 100 ends the processing in the current execution cycle.

[0111] Operation and advantages of this embodiment

[0112] (2-1) Controller 100 performs NOx increase treatment and SCR catalyst 41 degradation diagnosis when the accelerator pedal is not depressed and the accelerator is off. The accelerator pedal is configured to regulate the output of the internal combustion engine 10. When the internal combustion engine 10 is idling due to the accelerator off state, controller 100 performs... Figure 3 The step S220 shown is a NOx increase process. More specifically, the controller 100 performs a process to increase the amount of fuel supplied to the combustion chamber 17.

[0113] During idling, the amount of exhaust gas is very small. Therefore, the amount of NOx emitted from combustion chamber 17 is also very small. This operating condition is not suitable for the deterioration diagnosis of SCR catalyst 41. In this respect, in this embodiment, during the idling of internal combustion engine 10, a NOx-increasing treatment is performed to increase the amount of fuel supplied to combustion chamber 17. When the amount of fuel supplied to combustion chamber 17 increases, the air-fuel ratio of the mixture decreases. This results in an increase in the amount of NOx generated in combustion chamber 17. As described above, when the amount of NOx generated increases, the deterioration diagnosis of SCR catalyst 41 is performed. Therefore, deterioration diagnosis can be performed with high detection accuracy even during idling. This increases the number of deterioration diagnoses performed compared to a configuration where SCR catalyst 41 deterioration diagnosis is not performed during idling.

[0114] (2-2) Controller 100 performs NOx increase treatment and SCR catalyst 41 degradation diagnosis when the accelerator pedal is not depressed in the accelerator off state. The accelerator pedal is configured to regulate the output of the internal combustion engine 10. When the fuel cut-off treatment execution condition for stopping fuel injection in the internal combustion engine 10 is met due to the accelerator off state, controller 100 executes... Figure 3 Steps S250 and S260 are shown as NOx increase treatments. Step S250 prohibits fuel cut-off treatment even when the conditions for fuel cut-off treatment execution are met. Step S260 involves burning an air-fuel mixture with a smaller air-fuel ratio than a lean air-fuel mixture.

[0115] Even when the fuel cutoff procedure execution conditions for stopping fuel injection in the internal combustion engine 10 are met, the controller 100 performs a NOx increase procedure, thereby prohibiting the fuel cutoff procedure and burning an air-fuel mixture with a smaller air-fuel ratio than a lean air-fuel mixture. When burning an air-fuel mixture with a smaller air-fuel ratio than a lean air-fuel mixture, the amount of NOx generated in the combustion chamber 17 increases. As described above, when the amount of NOx generated increases, a degradation diagnosis of the SCR catalyst 41 is performed. Therefore, degradation diagnosis can be performed with high detection accuracy even when the fuel cutoff procedure is performed due to an accelerated shutdown state. With this configuration, the number of degradation diagnoses performed increases compared to a configuration where SCR catalyst 41 degradation diagnosis is not performed when the fuel cutoff procedure execution conditions are met.

[0116] (2-3) When NOx increase treatment is performed during idling to increase the amount of fuel supplied to combustion chamber 17, the torque of internal combustion engine 10 increases. Furthermore, as a NOx increase treatment performed when fuel cut-off treatment execution conditions are met, the torque of internal combustion engine 10 increases when the air-fuel mixture is burned without fuel cut-off treatment. In this regard, in this embodiment, during NOx increase treatment, the controller 100 performs... Figure 3The steps S230 or S270 shown are performed to reduce the opening of the throttle valve 28. When the opening of the throttle valve 28 decreases, pumping losses increase. This results in a decrease in torque transmitted to the internal combustion engine 10 via the crankshaft 18. The decrease in torque limits the increase in torque of the internal combustion engine 10 caused by the NOx increase treatment.

[0117] (2-4) The crankshaft 18 of the internal combustion engine 10 is connected to a first MG310, which serves as a generator, via a planetary gear mechanism 300. The drive wheel 340 is connected to a second MG320, which also serves as a generator. The controller 100 executes... Figure 3 The steps S230 or S270 shown are used to perform a process for increasing the power generation of the first MG310 and the second MG320 during the NOx increase process.

[0118] As described above, when a NOx-increasing treatment is performed during idling to increase the amount of fuel supplied to the combustion chamber 17, the torque of the internal combustion engine 10 increases. Furthermore, as a NOx-increasing treatment performed when the fuel cut-off treatment execution conditions are met, the torque of the internal combustion engine 10 increases when the air-fuel mixture is burned without a fuel cut-off treatment. In this respect, in this embodiment, during the NOx-increasing treatment, the power generation of the first MG310 connected to the crankshaft 18 and the power generation of the second MG320 connected to the drive wheel 340 are increased. Therefore, when the torque of the internal combustion engine 10 increases by performing the NOx-increasing treatment, this torque is absorbed by increasing the power generation of the first MG310 and the second MG320. Therefore, the increase in the torque of the internal combustion engine 10 due to the NOx-increasing treatment is limited.

[0119] (2-5) When controller 100 executes Figure 3 When steps S250 and S260 are shown to perform the NOx increase process, the controller 100 executes... Figure 3 The step S270 is shown. More specifically, when the NOx increase process is performed, the controller 100 performs a process to increase the braking force of the brake 510 mounted on the vehicle 700.

[0120] When the fuel cutoff condition is met and the NOx increase treatment is performed, the air-fuel mixture is burned without the fuel cutoff treatment. When the air-fuel mixture is burned, the internal combustion engine 10 generates torque. This may reduce the deceleration sensation of the vehicle 700. In this respect, in this embodiment, when the NOx increase treatment is performed, the braking force of the brakes 510 mounted on the vehicle 700 is increased. This increases the deceleration sensation of the vehicle 700. Therefore, the NOx increase treatment is unlikely to reduce the deceleration sensation of the vehicle 700.

[0121] Modify Example

[0122] The above embodiments can be modified as follows. The embodiments and the following modified examples can be combined, as long as the combined modified examples maintain technical consistency with each other.

[0123] Figure 2 The step S110 shown includes reducing the opening of the throttle valve 28 to reduce the intake air volume. Alternatively, to reduce the intake air volume, the valve timing of the intake valve 81 and the valve timing of the exhaust valve 82 can be changed. To reduce the intake air volume, the opening of the nozzle vane 24N or the opening of the air bypass valve 93 can be changed.

[0124] Step S110 includes reducing the intake air volume as a NOx-increasing treatment. Alternatively, as a NOx-increasing treatment, a process can be performed to change the target EGR rate EGp to a smaller value than that used before performing the NOx-increasing treatment, thereby reducing the EGR amount and thus increasing the amount of NOx produced in the combustion chamber 17.

[0125] One of reducing the intake volume and delaying the injection timing can be omitted from the NOx increase process performed in step S110.

[0126] One of increasing the required injection quantity and retarding the ignition timing can be omitted from the torque compensation process performed in step S110.

[0127] The torque compensation process can be omitted from step S110.

[0128] exist Figure 2 In step S100 shown, the degradation detection conditions can be changed.

[0129] exist Figure 3 In step S200, condition (f) can be omitted from the degradation detection conditions. In this case, preferably, the process for increasing power generation is omitted from steps S230 and S270.

[0130] In step S230, either reducing the opening of the throttle valve 28 or increasing the power generation of the first MG310 can be omitted.

[0131] At least one of the following can be omitted from the processing in step S270: reducing the opening of the throttle valve 28, increasing the electrical charge generated by the second MG320 through regenerative braking, and increasing the braking force of the brake 510. Increasing the electrical charge of the second MG320 can be changed to increasing the electrical charge of the first MG310. In step S270, to increase the braking force on the wheels of the vehicle 700, the braking force of the friction brake (such as brake 510) is increased. Alternatively, the braking force of brake 510 and the braking force of the regenerative braking of the second MG320 can be increased simultaneously to increase the braking force. Instead of increasing the braking force of brake 510, the braking force can be increased through the regenerative braking of the second MG320.

[0132] It can be omitted Figure 3 Steps S210, S220, and S230 are shown.

[0133] It can be omitted Figure 3 The steps S240, S250, S260, and S270 are shown. In this case, if a negative determination is made in step S210, then... Figure 3 The series of steps shown can be completed.

[0134] The first NOx concentration N1 can be estimated based on the required injection quantity Qd and the intake quantity GA.

[0135] The catalyst for NOx removal can be any catalyst other than a selective catalytic reduction catalyst. In one example, a NOx adsorption-reduction catalyst can be used.

[0136] The internal combustion engine 10 may include a port injection fuel injection valve that injects fuel into the intake port 30.

[0137] The internal combustion engine 10 may include only one of the intake-side variable valve timing mechanism 85 and the exhaust-side variable valve timing mechanism 86. The internal combustion engine 10 need not include both the intake-side variable valve timing mechanism 85 and the exhaust-side variable valve timing mechanism 86.

[0138] The internal combustion engine 10 does not need to include a forced intake device 24.

[0139] The forced air intake device 24 does not necessarily include nozzle blades 24N.

[0140] The exhaust pipe 90 need not include the bypass passage 92 and the air bypass valve 93.

[0141] Vehicle hybrid systems are not limited to Figure 1 The system shown may include other hybrid power systems.

[0142] The number of electric generators included in the vehicle can be changed.

[0143] The vehicle may consist of only the internal combustion engine 10 as the prime mover.

[0144] The controller 100 is not limited to a device that includes a CPU and memory and performs software processing. For example, the controller 100 may include dedicated hardware circuitry (e.g., an ASIC) that performs hardware processing on at least a portion of the processing executed by software in the embodiments. That is, the controller 100 may include processing circuitry having any of the following configurations (a) to (c): (a) The processing circuitry includes: at least one processor that performs all of the above-described processing according to a program; and at least one program storage device, such as a ROM, that stores the program. (b) The processing circuitry includes: at least one processor and at least one program storage device that perform some of the above-described processing according to a program; and at least one dedicated hardware circuitry that performs the remaining processing. (c) The processing circuitry includes at least one dedicated hardware circuitry that performs all of the above-described processing. The program storage device, i.e., the computer-readable medium, includes any medium accessible from a general-purpose computer or a special-purpose computer.

Claims

1. A controller for an internal combustion engine, the internal combustion engine including an exhaust passage and a catalyst, the catalyst being disposed on the exhaust passage to remove NOx from the exhaust gas. The internal combustion engine is configured to perform lean combustion, which uses hydrogen as fuel to burn a lean air-fuel mixture with an air-fuel ratio greater than the stoichiometric air-fuel ratio. The controller is configured to perform degradation diagnostics based on the catalyst's removal performance during the execution of NOx-increasing treatment, detecting catalyst degradation. in, The NOx increase treatment includes increasing the amount of NOx generated in the combustion chamber of the internal combustion engine to a level greater than the NOx level before the NOx increase treatment was performed.

2. The controller according to claim 1, wherein, The NOx increase treatment includes reducing the intake air volume of the internal combustion engine to a level lower than the intake air volume before the NOx increase treatment was performed.

3. The controller according to claim 2, wherein, The controller is configured to perform a compensation process that compensates for the decrease in torque of the internal combustion engine caused by the NOx increase process. The compensation process includes delaying the ignition timing of the air-fuel mixture compared to the ignition timing before the compensation process was performed.

4. The controller according to claim 2, wherein, The NOx increase treatment includes reducing the opening of the throttle valve arranged in the intake passage of the internal combustion engine to a smaller degree than the opening before the NOx increase treatment was performed. The controller is configured to perform a compensation process that compensates for the decrease in torque of the internal combustion engine caused by the NOx increase process. The compensation process includes increasing the amount of fuel supplied to the combustion chamber to a level greater than the amount of fuel before the compensation process was performed.

5. The controller according to any one of claims 1 to 4, wherein, The internal combustion engine includes a fuel injection valve that injects fuel directly into the combustion chamber of the internal combustion engine during the compression stroke. The NOx increase treatment includes delaying the injection start timing of the fuel injection valve from injecting fuel compared to the injection start timing before the NOx increase treatment was performed.

6. The controller according to claim 1, wherein, The controller is configured to perform the NOx increase processing and the degradation diagnosis in the accelerator pedal off state (when the accelerator pedal is not depressed), and the accelerator pedal is configured to regulate the output of the internal combustion engine. When the internal combustion engine is idling due to the acceleration shutdown state, the NOx increase treatment includes increasing the amount of fuel supplied to the combustion chamber to a greater amount than the amount of fuel before the NOx increase treatment was performed.

7. The controller according to claim 1 or 6, wherein, The controller is configured to perform the NOx increase processing and the degradation diagnosis in the accelerator pedal off state (when the accelerator pedal is not depressed), and the accelerator pedal is configured to regulate the output of the internal combustion engine. When the conditions for performing a fuel cut-off process to stop fuel injection in the internal combustion engine are met due to the accelerated shutdown state, the NOx increase treatment includes prohibiting the execution of the fuel cut-off process and burning an air-fuel mixture having a smaller air-fuel ratio than the lean air-fuel mixture.

8. The controller according to claim 7, wherein, The NOx increase treatment includes increasing the braking force on the wheels of the vehicle including the internal combustion engine to a level greater than the braking force before the NOx increase treatment was performed.

9. The controller according to any one of claims 6 to 8, wherein, The NOx increase treatment includes reducing the opening of the throttle valve arranged in the intake passage of the internal combustion engine to a smaller degree than before the NOx increase treatment was performed.

10. The controller according to any one of claims 6 to 9, wherein, The internal combustion engine includes an output shaft connected to a generator, and The NOx increase process includes increasing the generator's output to a level greater than the output before the NOx increase process was performed.

11. A method for controlling an internal combustion engine, the internal combustion engine including an exhaust passage and a catalyst, the catalyst being disposed on the exhaust passage to remove NOx from the exhaust, the internal combustion engine being configured to perform lean combustion, the lean combustion using hydrogen as fuel to burn a lean air-fuel mixture, the lean air-fuel mixture having an air-fuel ratio greater than the stoichiometric air-fuel ratio, the method comprising: Based on the catalyst's removal performance during the NOx increase treatment, a degradation diagnosis is performed to detect the catalyst's deterioration. The NOx increase treatment includes increasing the amount of NOx generated in the combustion chamber of the internal combustion engine to a level greater than the amount of NOx before the NOx increase treatment was performed.

12. A non-transitory computer-readable storage medium storing a program including instructions for performing a method for controlling an internal combustion engine, the internal combustion engine including an exhaust passage and a catalyst disposed on the exhaust passage to remove NOx from the exhaust, the internal combustion engine being configured to perform lean combustion using hydrogen as fuel to burn a lean air-fuel mixture, the lean air-fuel mixture having an air-fuel ratio greater than the stoichiometric air-fuel ratio. The instructions include: Based on the catalyst's removal performance during the NOx increase treatment, a degradation diagnosis is performed to detect the catalyst's deterioration. The NOx increase treatment includes increasing the amount of NOx produced in the combustion chamber of the internal combustion engine to a level greater than the amount of NOx produced before the NOx increase treatment was performed.

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