Controller, control method, and storage medium for a hydrogen fuelled internal combustion engine provided with a SCR catalyst

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 combustion, which burns a lean air-fuel mixture having an air-fuel ratio greater than a stoichiometric air-fuel ratio using hydrogen as fuel. The controller (100) is configured to execute a deterioration diagnosis that detects deterioration of the catalyst (41) based on a removal performance of the catalyst (41) during execution of a NOx increasing process. The NOx increasing process includes increasing an amount of NOx produced in a combustion chamber (17) of the internal combustion engine (10) to be greater than before execution of the NOx increasing process.

Description

CONTROLLER, CONTROL METHOD, AND STORAGE MEDIUM FOR A HYDROGEN FUELLED INTERNAL COMBUSTION ENGINE PROVIDED WITH A SCR CATALYST

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

[0002] Patent Literature 1 discloses an example of a device that diagnoses an anomaly of a NOx removal catalyst arranged in an exhaust passage of an internal combustion engine. The device calculates a NOx removal rate, which indicates the removal performance of the NOx removal catalyst, based on a NOx concentration upstream of the NOx removal catalyst and a NOx concentration downstream of the NOx removal catalyst. The anomaly diagnosis is performed on the NOx removal catalyst based on the NOx removal rate. An example of the anomaly diagnosis is detection of deterioration in the NOx removal catalyst.

[0003] Japanese Laid-Open Patent Publication No. 2018-127990

[0004] When hydrogen is used as a fuel in the internal combustion engine, lean combustion, which burns a lean air-fuel mixture having an air-fuel ratio greater than a stoichiometric air-fuel ratio, is performed to reduce emission of NOx. When the exhaust gas has a low concentration of NOx, the accuracy of detecting deterioration of the NOx removal catalyst may decrease.

[0005] A first aspect of the present disclosure provides a controller for an internal combustion engine. The internal combustion engine includes an exhaust passage and a catalyst arranged on the exhaust passage to remove NOx from an exhaust gas. The internal combustion engine is configured to perform lean combustion that uses hydrogen as a fuel to burn a lean air-fuel mixture, which has an air-fuel ratio greater than a stoichiometric air-fuel ratio. The controller is configured to execute a deterioration diagnosis that detects deterioration of the catalyst based on a removal performance of the catalyst during execution of a NOx increasing process. The NOx increasing process includes increasing an amount of NOx produced in a combustion chamber of the internal combustion engine to be greater than before execution of the NOx increasing process.

[0006] A second aspect of the present disclosure provides a method for controlling an internal combustion engine. The internal combustion engine includes an exhaust passage and a catalyst arranged on the exhaust passage to remove NOx from an exhaust gas. The internal combustion engine is configured to perform lean combustion that uses hydrogen as a fuel to burn a lean air-fuel mixture, which has an air-fuel ratio greater than a stoichiometric air-fuel ratio. The method includes executing a deterioration diagnosis that detects deterioration of the catalyst based on a removal performance of the catalyst during execution of a NOx increasing process. The NOx increasing process includes increasing an amount of NOx produced in a combustion chamber of the internal combustion engine to be greater than before execution of the NOx increasing process.

[0007] A third aspect of the present disclosure provides a non-transitory computer readable storage medium storing a program including an instruction to execute a method for controlling an internal combustion engine. The internal combustion engine includes an exhaust passage and a catalyst arranged on the exhaust passage to remove NOx from an exhaust gas. The internal combustion engine is configured to perform lean combustion that uses hydrogen as a fuel to burn a lean air-fuel mixture, which has an air-fuel ratio greater than a stoichiometric air-fuel ratio. The instruction includes executing a deterioration diagnosis that detects deterioration of the catalyst based on a removal performance of the catalyst during execution of a NOx increasing process. The NOx increasing process includes increasing an amount of NOx produced in a combustion chamber of the internal combustion engine to be greater than before execution of the NOx increasing process.

[0008] The controller for an internal combustion engine that uses hydrogen as fuel increases the accuracy of detecting deterioration of the NOx removal catalyst.

[0009] Fig. 1 is a schematic diagram showing the configuration of an internal combustion engine and a drive system according to first embodiment;Fig. 2 is a flowchart showing a procedure of steps executed by a controller according to the embodiment; andFig. 3 is a flowchart showing a procedure of steps executed by a controller according to a second embodiment.

[0010] First Embodiment

[0011] A first embodiment of a controller for an internal combustion engine mounted on a vehicle will now be described.

[0012] Configuration of Internal Combustion Engine and Drive System

[0013] As shown in Fig. 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 14.

[0014] Cylinders 16 are arranged in the cylinder block 11. A piston 15 is arranged in each cylinder 16.

[0015] The cylinder head 12 includes an intake port 30 that draws 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. The intake port 30 includes an intake valve 81. The drive system of the intake valve 81 includes an intake-side variable valve timing mechanism 85 that is a variable valve actuation mechanism that changes valve timing of the intake valve 81.

[0016] 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 valve timing of the exhaust valve 82.

[0017] The cylinder head 12 is provided with an ignition plug 23 and a fuel injection valve 84 of a direct-injection type. The fuel injection valve 84 directly injects hydrogen as fuel into the combustion chamber 17 during a compression stroke.

[0018] A crankcase 19 is arranged below the cylinder block 11. The crankcase 19 accommodates a crankshaft 18, which is an output shaft of the internal combustion engine 10. The oil pan 14 is arranged below the crankcase 19 to store lubricant.

[0019] An intake manifold 29 including a surge tank 60 is connected to an upstream portion of the intake port 30. An intake pipe 20 is connected to an upstream portion 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.

[0020] The intake pipe 20 is provided with an air cleaner 21, an airflow meter 51, a compressor wheel 24C of a forced induction device 24, an intercooler 27, a boost pressure sensor 54, and a throttle valve 28 arranged sequentially in order from the upstream side. The forced induction device 24 is driven by exhaust gas discharged from the combustion chamber 17. An intake pressure sensor 55 is arranged on the surge tank 60. The open degree of the throttle valve 28 is changed by an electric motor.

[0021] In the intake pipe 20, an upstream portion of the compressor wheel 24C and a downstream portion of the compressor wheel 24C are fluidly connected by a bypass passage 92. An air bypass valve 93 is arranged in the bypass passage 92. The open degree of the air bypass valve 93 is adjusted by an actuator. The air bypass valve 93 is configured to adjust the amount of air flowing through the bypass passage 92. As the open degree of the air bypass valve 93 increases, the amount of air bypassing the compressor wheel 24C and flowing through the bypass passage 92 increases. Therefore, as the open degree of the air bypass valve 93 increases, boost pressure of the intake air increased by the forced induction device 24 decreases.

[0022] The air cleaner 21 filters intake air drawn into the intake pipe 20. The forced induction device 24 compresses air in the intake pipe 20. The intercooler 27 cools the air that has passed through the compressor wheel 24C. The open degree of the throttle valve 28 is adjusted to control the intake air amount.

[0023] The airflow meter 51 detects an intake air amount GA. The boost pressure sensor 54 detects a boost pressure PTC, which is the pressure of the intake pipe 20 downstream of the compressor wheel 24C. The intake pressure sensor 55 detects an intake air pressure PIM, which is the pressure of the surge tank 60.

[0024] The downstream side of the exhaust port 70 is connected to an exhaust pipe 90 forming an exhaust passage. The exhaust pipe 90 is connected to a housing accommodating a turbine wheel 24T of the forced induction device 24. The forced induction device 24 is of a variable displacement type and includes a nozzle vane 24N. The nozzle vane 24N is driven by an actuator to adjust the flow speed of the exhaust gas flowing to the turbine wheel 24T. The open degree of the nozzle vane 24N is changed to change the boost pressure of intake air increased by the forced induction device 24.

[0025] An oxidation catalyst 40 is arranged on the exhaust pipe 90 downstream of the turbine wheel 24T of the forced induction device 24. A selective catalytic reduction catalyst 41 is arranged in the exhaust pipe 90 downstream of the oxidation catalyst 40 to remove NOx from the exhaust gas. In the description hereafter, the selective catalytic reduction catalyst 41 is referred to as the SCR catalyst 41.

[0026] A urea supply valve 43 is arranged in the exhaust pipe 90 between the oxidation catalyst 40 and the SCR catalyst 41 to supply urea water, which is a reducing agent containing an ammonia component, to the SCR catalyst 41. Urea water injected from the urea supply valve 43 is changed into ammonia through hydrolysis using exhaust heat and is adsorbed to the SCR catalyst 41. NOx is reduced and removed by the ammonia adsorbed to the SCR catalyst 41.

[0027] A first NOx sensor 57 is arranged in the exhaust pipe 90 between the oxidation catalyst 40 and the SCR catalyst 41 to detect the concentration of NOx contained in the exhaust gas. The first NOx sensor 57 detects a first NOx concentration N1, which is the concentration of NOx in the exhaust gas before NOx is removed by the SCR catalyst 41.

[0028] A second NOx sensor 58 is arranged in the exhaust pipe 90 downstream of the SCR catalyst 41 to detect the concentration of NOx contained in the exhaust gas. The second NOx sensor 58 detects a second NOx concentration N2, which is the concentration of NOx after NOx removal of the SCR catalyst 41.

[0029] The internal combustion engine 10 includes an exhaust gas recirculation device (hereinafter, referred to as the EGR device). The EGR device is configured to draw some of the exhaust gas into the intake passage to decrease 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 pipe 20 upstream of the compressor wheel 24C to the exhaust pipe 90 downstream of the SCR catalyst 41. The EGR device includes an EGR valve 220 arranged on the EGR passage 210. The open degree of the EGR valve 220 is adjusted by an actuator. The EGR device includes an EGR cooler 230 arranged on the EGR passage 210. The open degree of the EGR valve 220 is adjusted to control the amount of exhaust gas drawn from the exhaust pipe 90 into the intake pipe 20, that is, the amount of EGR gas. The EGR cooler 230 decreases the temperature of the exhaust gas flowing through the EGR passage 210.

[0030] The crankshaft 18 of the internal combustion engine 10 is mechanically coupled to a carrier C of a planetary gear mechanism 300, which is included in a power split device.

[0031] The planetary gear mechanism 300 includes a sun gear S mechanically coupled to a rotation shaft 310a of a first motor generator 310 (hereafter, referred to as the first MG).

[0032] The planetary gear mechanism 300 includes a ring gear R mechanically coupled to a rotation shaft 320a of a second motor generator 320 (hereafter, referred to as the second MG) and a drive wheel 340. The drive wheel 340 is one of wheels of the vehicle 700. A wheel of the vehicle 700 is provided with a hydraulic brake 510 configured to apply braking force to the wheel. The brake 510 is a friction brake and is controlled by a control system 500. Alternatively, the brake 510 may be an electric brake.

[0033] The first MG 310 is used as an electric generator that generates power using output of the engine and as an electric motor that performs cranking of the crankshaft 18 when starting the internal combustion engine 10.

[0034] The second MG 320 is used as an electric motor that generates driving force of the drive wheel 340 and as an electric generator that generates power by regenerative braking during deceleration of the vehicle 700.

[0035] The first MG 310 and the second MG 320 send and receive power to and from a battery 470 through a power control unit (PCU) 400. The PCU 400 includes an electronic component such as a CPU performing a calculation process and memory storing programs and data for controlling. The PCU 400 includes, for example, a converter and an inverter. The converter is configured to increase direct current voltage received from the battery 470 and output the voltage. The inverter converts the direct current voltage of the converter into alternating current voltage and outputs the alternating current voltage to the first MG 310 and the second MG 320.

[0036] The battery 470 is connected to a battery ECU 480. The battery ECU 480 includes an electronic component such as a CPU performing a calculation process and memory storing programs and data for controlling. The battery ECU 480 controls the charging and discharging of the battery 470. The battery ECU 480 obtains a state of the battery 470 detected by a sensor. The state of the battery 470 is, for example, input current, output current, voltage, and temperature. The battery ECU 480 calculates a charge amount, that is, the present charge amount of the battery 470, and the present fully-charged amount of the battery 470 based on the obtained data. The battery ECU 480 calculates a value by dividing the present charge amount of the battery 470 by the fully-charged amount of the battery 470 and assigns the calculated value to the state of charge SOC of the battery 470.

[0037] As described above, the vehicle 700 of the present embodiment includes a hybrid system including an internal combustion engine and a motor generator as prime movers.

[0038] The internal combustion engine 10 is configured to be controlled by a controller 100. The controller 100 operates various devices such as the throttle valve 28, the fuel injection valve 84, the ignition plug 23, the intake-side variable valve timing mechanism 85, and the exhaust-side variable valve timing mechanism 86. The controller 100 operates further various devices such as the air bypass valve 93, the actuator of the nozzle vane 24N, and the urea supply valve 43. The controller 100 operates the PCU 400 to control the first MG 310 and the second MG 320. The controller 100 operates the control system 500 to control the brake 510.

[0039] The controller 100 includes an electronic component such as a CPU 110 performing calculation process and memory 120 storing a program and data for controlling. The controller 100 executes processes related to various controls by executing the program stored in the memory 120 and including an instruction with the CPU 110. The memory 120 corresponds to a non-transitory computer readable storage medium. The CPU 110 may be processing circuitry. Although not shown, the controller 100 includes multiple control units such as a control unit of the internal combustion engine 10, a control unit of the first MG 310 and the second MG 320, and a control unit of the brake 510.

[0040] 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 an example, the controller 100 receives a detection signal from the airflow meter 51 configured to detect the intake air amount GA. The controller 100 receives a detection signal from an accelerator operation sensor 52 configured to detect an accelerator operation amount ACCP corresponding to the operation amount of an accelerator pedal. The accelerator pedal adjusts output of the internal combustion engine 10. The controller 100 receives a detection signal from a throttle sensor 53 configured to detect a throttle open degree TA, which is the open degree of the throttle valve 28. The controller 100 receives a detection signal from a vehicle speed sensor 56 configured to detect vehicle speed SP of the vehicle 700 and a detection signal from a crank angular sensor 50 configured to detect a rotation angle (crank angle) of the crankshaft 18 to calculate engine speed NE. The controller 100 receives a detection signal from a pressure sensor 47 configured to detect fuel pressure P of a delivery pipe distributing fuel to the fuel injection valves 84. The controller 100 receives a detection signal from a temperature sensor 48 configured to detect fuel temperature THF of the delivery pipe distributing fuel to the fuel injection valves 84. The controller 100 receives an output signal Sm1 from a first rotation angle sensor 350 configured to detect the rotation angle of the first MG 310 and an output signal Sm2 from a second rotation angle sensor 360 configured to detect the rotation angle of the second MG 320. The controller 100 obtains the state of charge SOC of the battery 470 from the battery ECU 480.

[0041] The controller 100 calculates an engine load ratio KL based on the engine speed NE and the intake air amount GA. The engine load ratio KL is a parameter that determines the amount of air charged in the combustion chamber 17 and is the ratio of an inflow air amount in one cylinder to a reference inflow air amount per combustion cycle. The reference inflow air amount is variably set in accordance with the engine speed NE.

[0042] The controller 100 calculates a request torque needed for the vehicle 700 to travel based on the accelerator operation amount ACCP and the vehicle speed SP. The controller 100 controls a request output Pe of the internal combustion engine 10 and output torques of the first MG 310 and the second MG 320 so that the request torque of the vehicle 700 is satisfied. In an example, when the vehicle 700 is traveling and the request output Pe of the internal combustion engine 10 is zero, the controller 100 stops fuel injection from the fuel injection valve 84 and stops the ignition operation of the ignition plug 23 to stop the operation of the internal combustion engine 10. The controller 100 performs electric traveling in which the vehicle travels using output torque of the second MG 320.

[0043] Hydrogen gas, which is the fuel of the internal combustion engine 10, has a wide range of combustible air-fuel mixtures compared to gasoline and can be burned even in a relatively lean air-fuel mixture. The controller 100 performs lean combustion, which burns a lean air-fuel mixture having an air-fuel ratio greater than the stoichiometric air-fuel ratio, and adjusts output of the internal combustion engine 10 through the combustion control described below.

[0044] The controller 100 sets the requested injection amount Qd based on the request output Pe. The requested injection amount Qd is a target value of the fuel injected from the fuel injection valve 84. Based on a target air-fuel ratio AFt and the requested injection amount Qd, the controller 100 calculates a requested air amount GAd, which is a target value of the intake air amount for obtaining the target air-fuel ratio AFt. In the present embodiment, the target air-fuel ratio AFt is, for example, a lean air-fuel ratio with air excess ratio λ of 2.5 to 3.0. The controller 100 controls the fuel injection valve 84 to obtain the requested injection amount Qd. The controller 100 controls the open degree of the throttle valve 28 and the boost pressure of the forced induction device 24 to obtain the requested air amount GAd. In the boost pressure control of the forced induction device 24, the controller 100 calculates a target boost pressure PTCp. The open degree of the air bypass valve 93 and the open degree of the nozzle vane 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 adjustment of the fuel injection amount and the intake air amount.

[0045] The controller 100 sets a fuel injection start timing Tis and a fuel injection stop timing Tie so that the fuel injection valve 84 injects fuel corresponding to the requested injection amount Qd. The fuel injection start timing Tis and the fuel injection stop timing Tie are calculated by a known process. In an example, the controller 100 calculates the fuel injection start timing Tis and the fuel injection stop timing Tie based on the requested injection amount Qd, the engine speed NE, the fuel pressure P, and the fuel temperature THF. When the crank angle of the crankshaft 18 reaches the fuel injection start timing Tis, the controller 100 energizes the fuel injection valve 84 so that the fuel injection valve 84 opens and starts fuel injection. When the crank angle of the crankshaft 18 reaches the fuel injection stop timing Tie, the controller 100 stops energizing the fuel injection valve 84 so that the fuel injection valve 84 closes and stops the fuel injection.

[0046] The controller 100 sets ignition timing AFIN of the air-fuel mixture. The ignition timing AFIN is calculated by a known process. In an example, the controller 100 calculates the ignition timing AFIN based on the engine speed NE, the engine load ratio KL, and a knocking correction value for reducing occurrence of knocking. When the crank angle of the crankshaft 18 reaches the ignition timing AFIN, the controller 100 performs spark discharge of the ignition plug 23 to ignite the air-fuel mixture.

[0047] The controller 100 executes a fuel cut-off process that stops fuel injection in the internal combustion engine 10 during deceleration of the vehicle 700. The fuel cut-off process is executed when the following execution condition is satisfied. When the accelerator operation amount ACCP is zero in an acceleration-off state, in which the accelerator pedal is not depressed, and the engine speed NE is in a predetermined range, the controller 100 stops injection of fuel from the fuel injection valve 84, thereby executing the fuel cut-off process. If the accelerator pedal is depressed or the engine speed NE is decreased to a predetermined recovery rotation speed, execution of the fuel cut-off process is terminated. This resumes fuel injection from the fuel injection valve 84.

[0048] When the accelerator operation amount ACCP is zero in the acceleration-off state and the value of the request output Pe of the internal combustion engine 10 corresponds to idling, the controller 100 performs idling of the internal combustion engine 10. The idling is performed when the vehicle 700 is traveling or is stopped.

[0049] The controller 100 calculates target valve timings of the intake valve 81 and the exhaust valve 82 based on engine operation states such as the engine speed NE and the engine load ratio KL. The intake-side variable valve timing mechanism 85 and the exhaust-side variable valve timing mechanism 86 are controlled based on the target valve timings or the like.

[0050] The controller 100 calculates a target EGR ratio EGp, which is an instruction value for adjusting an EGR amount, based on the engine operation states such as the engine speed NE and the engine load ratio KL. The EGR amount is an amount of EGR gas drawn into the intake pipe 20. The EGR ratio is a ratio of the EGR amount to the total amount of gas charged in the cylinder. The controller 100 calculates a target open degree EAt of the EGR valve 220 corresponding to the target EGR ratio EGp and controls the actuator of the EGR valve 220 so that the open degree of the EGR valve 220 becomes equal to the target open degree EAt based on the target EGR ratio EGp and the intake air amount GA.

[0051] SCR Catalyst Deterioration Diagnosis

[0052] The controller 100 performs a deterioration diagnosis on the SCR catalyst 41.

[0053] In the deterioration diagnosis, an average value of the first NOx concentration N1 detected by the first NOx sensor 57 during a predetermined sampling period is calculated as a first average concentration NAV1. The first average concentration NAV1 is stored in the memory 120 in each predetermined cycle. During the same sampling period, an average value of the second NOx concentration N2 detected by the second NOx sensor 58 is calculated as a second average concentration NAV2. The second average concentration NAV2 is stored in the memory 120 in each predetermined cycle.

[0054] The controller 100 calculates a NOx removal rate CF, which indicates the removal performance of the SCR catalyst 41, based on Equation 1.

[0055] Equation 1: NOx Removal Rate CF = (First Average Concentration NAV1 - Second Average Concentration NAV2) / First Average Concentration NAV1 × 100 (%)

[0056] It is preferred that the second average concentration NAV2, which is used in the calculation of the NOx removal rate CF, have a value taking into consideration the flow delay of exhaust gas.

[0057] More specifically, when the intake air amount GA is small as compared to when the intake air amount GA is large, the exhaust gas flows in the exhaust pipe 90 at a lower speed. As a result, it takes the exhaust gas longer to flow through the SCR catalyst 41. Therefore, as the intake air amount GA decreases, it takes a longer time to reflect a removal result of the exhaust gas having the first NOx concentration N1 on the second NOx concentration N2. In this regard, for example, with reference to the point in time when the first average concentration NAV1 used in Equation 1 is stored, the second average concentration NAV2 that is stored at a predetermined time TR after the reference point in time is used in Equation 1. As the intake air amount GA decreases, the time TR is set to a longer time.

[0058] The controller 100 determines that the SCR catalyst 41 has deterioration when the calculated NOx removal rate CF is less than or equal to a predetermined determination value ER, and determines that the SCR catalyst 41 does not have deterioration when the calculated NOx removal rate CF is greater than the determination value ER. In the present embodiment, the deterioration diagnosis of the SCR catalyst 41 is performed once per trip. However, the frequency of performing the deterioration diagnosis may be changed. A trip refers to a period from when the driver of the vehicle 700 switches on the ignition switch until the driver of the vehicle 700 switches off the ignition switch.

[0059] As described above, when the fuel of the internal combustion engine 10 is hydrogen, the lean combustion, which burns a lean air-fuel mixture, is performed. This reduces emission of NOx. When emission of NOx is reduced, the concentration of NOx in the exhaust gas is decreased. When the concentration of NOx in the exhaust gas is decreased, NOx contacts the reducing agent in the SCR catalyst 41 less frequently. This adversely affects the removal performance of the SCR catalyst 41. As a result, the NOx removal rate CF may be calculated to be lower than the actual removal ratio of the SCR catalyst 41, and the accuracy of detecting deterioration of the SCR catalyst 41 may be decreased.

[0060] In the internal combustion engine 10 performing the lean combustion, the concentration of NOx in the exhaust gas is relatively low, and a change rate of the second NOx concentration N2 due to deterioration of the SCR catalyst 41 is relatively small. The change rate of the second NOx concentration N2 due to deterioration of the SCR catalyst 41 may be excessively small as compared to a range of NOx concentration detectable by the first NOx sensor 57 and the second NOx sensor 58. In such a case, it is difficult for the second NOx sensor 58 to correctly detect a change in the second NOx concentration N2 due to deterioration of the SCR catalyst 41. This may result in a decrease in the accuracy of detecting deterioration of the SCR catalyst 41.

[0061] In the present embodiment, when the deterioration diagnosis is performed on the SCR catalyst 41, a NOx increasing process is executed to increase the amount of NOx produced in the combustion chamber 17 of the internal combustion engine 10. The deterioration diagnosis is executed based on the removal performance of the SCR catalyst 41 during execution of the NOx increasing process.

[0062] Fig. 2 shows a procedure of steps executed by the controller 100. The steps shown in Fig. 2 are executed by the CPU 110 executing programs stored in the memory 120 of the controller 100 in each predetermined cycle. In the following description, the step number of each step is represented by a numeral provided with an “S” prefix.

[0063] In a series of the steps shown in Fig. 2, the controller 100 determines whether a deterioration detection condition of the SCR catalyst 41 is satisfied (S100). The deterioration detection condition is set so that the deterioration diagnosis is performed when the NOx removal rate of the SCR catalyst 41 is high. When all of the following conditions (a), (b), and (c) are satisfied, the controller 100 determines that the deterioration detection condition is satisfied.

[0064] (a): A catalyst temperature THS is within a predetermined range. The catalyst temperature THS is a removal temperature of the SCR catalyst 41. The controller 100 estimates the catalyst temperature THS based on operation parameters of the vehicle such as the engine speed NE, the engine load ratio KL, the ignition timing AFIN, and the vehicle speed SP. The lower limit value of the predetermined range is the minimum temperature at which the SCR catalyst 41 is active. When the temperature of the SCR catalyst 41 is excessively high, removal of ammonia from the SCR catalyst 41 may be facilitated, or NOx may be produced in the SCR catalyst 41. The upper limit value of the predetermined range is the maximum temperature of the SCR catalyst 41 at which the removal of ammonia and the production of NOx are limited to an allowable value.

[0065] (b): The intake air amount GA is greater than or equal to a predetermined value GAref. If the flow speed of the exhaust gas flowing through the SCR catalyst 41 is excessively high, the time for the SCR catalyst 41 to remove NOx shortens. This results in a decrease in the NOx removal rate. Thus, the predetermined value GAref is set, in advance, to an appropriate value of the intake air amount GA to limit a decrease in the NOx removal rate.

[0066] (c): The requested injection amount Qd is greater than or equal to a predetermined value Qdref. When the requested injection amount Qd is large, a greater amount of NOx is produced in the combustion chamber 17 than when the requested injection amount Qd is small. When the amount of NOx produced in the combustion chamber 17 is increased, the concentration of NOx in the exhaust gas is increased. This results in an increase in the NOx removal rate of the SCR catalyst 41. Thus, the predetermined value Qdref is set, in advance, to an appropriate value of the requested injection amount Qd to maintain a high NOx removal rate.

[0067] In the step of S100, if it is determined that the deterioration detection condition of the SCR catalyst 41 is satisfied (S100: YES), the controller 100 executes the step of S110.

[0068] In the step of S110, the controller 100 executes the NOx increasing process and a torque compensation process.

[0069] The NOx increasing process increases the amount of NOx produced in the combustion chamber 17 to be greater than before execution of the NOx increasing process. The NOx increasing process includes decreasing the intake air amount and retarding the fuel injection timing.

[0070] The controller 100 decreases the requested air amount GAd by a predetermined amount A for correction, thereby decreasing the intake air amount. The predetermined amount A is an air amount with which the air-fuel ratio of a mixture is less than the target air-fuel ratio AFt. Also, the predetermined amount A allows the amount of NOx produced in the combustion chamber 17 to be maximally increased within an allowable range while limiting the effects on the engine operation states. More specifically, in a range of a lean air-fuel ratio in which the air-fuel ratio of the mixture is greater than the stoichiometric air-fuel ratio, as the air-fuel ratio decreases, the amount of NOx produced in the combustion chamber 17 is increased. When the air-fuel ratio is slightly leaner than the stoichiometric air-fuel ratio, the maximum amount of NOx is produced. Thus, when the effect on the engine operation states is limited to the allowable range, the predetermined amount A is set so that the air-fuel ratio of the mixture maximally approaches an air-fuel ratio at which the maximum amount of NOx is produced. When the requested air amount GAd is decreased by the predetermined amount A for correction, the controller 100 executes a process for decreasing the open degree of the throttle valve 28 to obtain the intake air amount that is obtained by the decrease correction.

[0071] The controller 100 retards the fuel injection start timing Tis and the fuel injection stop timing Tie by a predetermined value B for correction, thereby retarding 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.

[0072] The torque compensation process compensates for a decrease in torque of the internal combustion engine 10 due to execution of the NOx increasing process. The torque compensation process includes increasing the requested injection amount Qd and retarding the ignition timing.

[0073] The controller 100 increases the requested injection amount Qd by a predetermined amount C for correction. Thus, the requested injection amount Qd is increased. The predetermined amount C is as follows. More specifically, when the open degree of the throttle valve 28 is decreased as the NOx increasing process, pumping loss is increased. 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 a fuel injection amount for compensating for such a decrease in torque of the internal combustion engine 10. The predetermined amount C may be changed in accordance with the amount of torque decreased due to pumping loss.

[0074] The controller 100 retards the ignition timing AFIN by a predetermined value D for correction. Thus, the ignition timing is retarded. The predetermined value D is as follows. More specifically, when the NOx increasing process is executed and the air-fuel ratio of the mixture is decreased, the combustion speed of the mixture is increased. Consequently, the pressure of the cylinder of the internal combustion engine 10 reaches a maximum before the optimal time for obtaining the engine output. This results in a decrease in torque of the internal combustion engine 10. The predetermined value D is set to an ignition timing correction value for compensating for such a decrease in torque of the internal combustion engine 10.

[0075] After executing the step of S110, the controller 100 determines whether a removal rate calculation condition is satisfied (S120). When the removal rate calculation condition is satisfied, calculation of the NOx removal rate CF is permitted. When the first NOx concentration N1 is greater than or equal to the predetermined determination value N1ref, the controller 100 determines that the removal rate calculation condition is satisfied. The determination value N1ref is the minimum value of the first NOx concentration N1 necessary for accurately performing the deterioration diagnosis of the SCR catalyst 41. The determination value N1ref is a predetermined appropriate value.

[0076] In the step of S120, if the first NOx concentration N1 is greater than or equal to the determination value N1ref (S120: YES), the controller 100 executes the deterioration diagnosis of the SCR catalyst 41.

[0077] If a negative determination is made in S100 or S120, the controller 100 executes a process for resetting the first average concentration NAV1 and the second average concentration NAV2 that are presently calculated to zero (S140).

[0078] When the step S130 or S140 is executed, the controller 100 terminates the process in the present execution cycle.

[0079] Operation and Advantage of Present Embodiment

[0080] (1-1) The controller 100 performs the deterioration diagnosis of the SCR catalyst 41 based on the NOx removal rate CF, which indicates the removal performance of the SCR catalyst 41 during execution of the NOx increasing process. The NOx increasing process increases the amount of NOx produced in the combustion chamber 17 to be greater than before execution of the NOx increasing process.

[0081] As described above, when performing the deterioration diagnosis of the SCR catalyst 41, the NOx increasing process is executed to increase the amount of NOx produced in the combustion chamber 17. Thus, the deterioration diagnosis of the SCR catalyst 41 is performed when the concentration of NOx in the exhaust gas is high. In this case, deterioration the SCR catalyst 41 is detected at a higher accuracy than when the NOx increasing process is not executed.

[0082] (1-2) In a range of a lean air-fuel ratio in which the air-fuel ratio of the mixture is greater than the stoichiometric air-fuel ratio, as the air-fuel ratio decreases, the amount of NOx produced in the combustion chamber 17 is increased. In the step S110 shown in Fig. 2, the controller 100 executes a process for decreasing the intake air amount of the internal combustion engine 10 as the NOx increasing process. The decrease in the intake air amount decreases the air-fuel ratio of the mixture, thereby increasing the amount of NOx produced in the combustion chamber 17.

[0083] (1-3) The controller 100 executes a process for decreasing the open degree of the throttle valve 28 arranged on the intake pipe 20 of the internal combustion engine 10 to execute a process for decreasing the intake air amount as the NOx increasing process. Additionally, the controller 100 executes the torque compensation process for compensating for a decrease in torque of the internal combustion engine 10 due to execution of the NOx increasing process. The controller 100 executes a process for increasing the amount of fuel supplied to the combustion chamber 17 as the torque compensation process.

[0084] When the process for decreasing the open degree of the throttle valve 28 is executed as the NOx increasing process, the intake air amount of the internal combustion engine 10 is decreased. When the open degree of the throttle valve 28 is decreased, pumping loss is increased. This results in a decrease in torque (more specifically, indicated torque) of the internal combustion engine 10 transmitted to the crankshaft 18. As the torque compensation process for compensating for such a decrease in torque of the internal combustion engine 10, in the S110 shown in Fig. 2, the controller 100 increases the requested injection amount Qd to execute the process for increasing the amount of fuel supplied to the combustion chamber 17. When the amount of fuel supplied to the combustion chamber 17 is increased, torque of the internal combustion engine 10 is increased. This limits the decrease in torque of the internal combustion engine 10 due to execution of the NOx increasing process.

[0085] (1-4) The internal combustion engine 10 includes the fuel injection valve 84 that directly injects the fuel into the combustion chamber 17 during a compression stroke. In the step S110 shown in Fig. 2, the controller 100 executes a process for retarding the fuel injection start timing Tis, at which the fuel injection valve 84 starts injecting fuel, as the NOx increasing process.

[0086] When the fuel injection start timing Tis retards, the time from when the fuel is injected until the fuel is ignited shortens. As a result, the mixing time of the air-fuel mixture shortens. When the mixing time of the air-fuel mixture shortens, the fuel concentration distribution of the air-fuel mixture tends to be uneven. Thus, the air-fuel ratio of the air-fuel mixture is relatively small in part of the combustion chamber 17. When the air-fuel mixture having the relatively small air-fuel ratio is burned, the amount of NOx produced in the combustion chamber 17 is increased.

[0087] (1-5) The controller 100 executes the torque compensation process for compensating for a decrease in torque of the internal combustion engine 10 due to execution of the NOx increasing process. The controller 100 executes a process for retarding the ignition timing of the air-fuel mixture as the torque compensation process.

[0088] When the NOx increasing process is executed and the air-fuel ratio of the mixture is decreased, the combustion speed of the mixture is increased. Consequently, the pressure of the cylinder of the internal combustion engine 10 reaches a maximum before the optimal time for obtaining the engine output. This results in a decrease in torque of the internal combustion engine 10. In the present embodiment, in the step S110 shown in Fig. 2, the controller 100 executes a process for retarding the ignition timing of the air-fuel mixture as the torque compensation process, which compensates for a decrease in torque of the internal combustion engine 10. Thus, the time when the pressure of the cylinder reaches a maximum during execution of the NOx increasing process is close to the optimal timing for obtaining the engine output. This limits the decrease in torque of the internal combustion engine 10 due to execution of the NOx increasing process.

[0089] Second Embodiment

[0090] A second embodiment of a controller for an internal combustion engine mounted on a vehicle will now be described.

[0091] The present embodiment differs in steps executed by the controller 100 prior to the step of S120 shown in Fig. 2. The controller of the present embodiment will be described focusing on the differences.

[0092] Fig. 3 shows part of a procedure of steps executed by the controller 100. The steps shown in Fig. 3 are executed by the CPU 110 executing programs stored in the memory 120 of the controller 100 in each predetermined cycle.

[0093] In a series of the steps shown in Fig. 3, the controller 100 determines whether a deterioration detection condition of the SCR catalyst 41 is satisfied (S200). When all of the following conditions (d), (e), and (f) are satisfied, the controller 100 determines that the deterioration detection condition is satisfied.

[0094] (d): The catalyst temperature THS is within a predetermined range. The condition (d) is the same as the condition (a).

[0095] (e): The acceleration is off.

[0096] (f): The battery 470 is rechargeable. When the state of charge SOC is presently less than or equal to a predetermined value E, the controller 100 determines that the battery 470 is rechargeable. The predetermined value E is an appropriate value to avoid overcharging of the battery 470.

[0097] In the step of S200, if it is determined that the deterioration detection condition of the SCR catalyst 41 is satisfied (S200: YES), the controller 100 executes the step of S210.

[0098] In the step of 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 the step of S220.

[0099] In the step of S220, the controller 100 executes increasing the requested injection amount Qd as the NOx increasing process. More specifically, the controller 100 increases a requested injection amount Qd that is set during idling by a predetermined amount F for correction, thereby performing a process for increasing the amount of fuel supplied to the combustion chamber 17. The predetermined amount F is an appropriate value for allowing the amount of NOx produced in the combustion chamber 17 during idling to be maximally increased within an allowable range while limiting the effects on the engine operation states is limited to an allowable range.

[0100] In the step of S230, the controller 100 executes a process for decreasing the open degree of the throttle valve 28 and a process for increasing the amount of power generated by the first MG 310 (S230).

[0101] In the step of S210, if it is determined that the engine is not idling (S210: NO), the controller 100 executes the step of S240.

[0102] In the step of S240, the controller 100 determines whether the fuel cut-off process execution condition is satisfied. If the fuel cut-off process execution condition is satisfied (S240: YES), the controller 100 prohibits execution of the fuel cut-off process in the step of S250. Then, in the step of S260, the controller 100 performs combustion of the air-fuel mixture. When performing combustion of the air-fuel mixture in the step of S260, the controller 100 burns the air-fuel mixture having a smaller air-fuel ratio than the lean air-fuel mixture described above so that the amount of NOx produced in the combustion chamber 17 is maximally increased within an allowable range. The steps of S250 and S260 correspond to the NOx increasing process that increases the amount of NOx produced in the combustion chamber 17.

[0103] After execution of the step of S260, the controller 100 proceeds to the step of S270.

[0104] In the step of S270, the controller 100 executes a process for decreasing the open degree of the throttle valve 28, a process for increasing the amount of power generated by the second MG 320 through regenerative braking, and a process for increasing braking force on the wheel of the vehicle 700 (S270). As the process for increasing the braking force on the wheel of the vehicle 700, the controller 100 executes a process for increasing braking force of the brake 510.

[0105] When the step of S270 or S230 is completed, the controller 100 executes the steps shown in Fig. 2 from S120 to perform the deterioration diagnosis of the SCR catalyst 41.

[0106] If a negative determination is made in the step of S200 (S200: NO), the controller 100 executes the steps shown in Fig. 2 from S140. If a negative determination is made in the step of S240 (S240: NO), the controller 100 terminates the process in the present execution cycle.

[0107] Operation and Advantage of Present Embodiment

[0108] (2-1) The controller 100 executes the NOx increasing process and the deterioration diagnosis of the SCR catalyst 41 in an acceleration-off state in which an accelerator pedal is not depressed. The accelerator pedal is configured to adjust the output of the internal combustion engine 10. When the internal combustion engine 10 is idling due to the acceleration-off state, the controller 100 executes the step of S220 shown in Fig. 3 as the NOx increasing process. More specifically, the controller 100 executes a process for increasing the amount of fuel supplied to the combustion chamber 17.

[0109] The amount of the exhaust gas is small during idling. Accordingly, the amount of NOx discharged from the combustion chamber 17 is small. This operation state is not suitable for the deterioration diagnosis of the SCR catalyst 41. In this regard, in the present embodiment, during idling of the internal combustion engine 10, the NOx increasing process is executed to increase the amount of fuel supplied to the combustion chamber 17. When the amount of fuel supplied to the combustion chamber 17 is increased, the air-fuel ratio of the mixture is decreased. This results in an increase in the amount of NOx produced in the combustion chamber 17. As described above, when the amount of NOx produced is increased, the deterioration diagnosis of the SCR catalyst 41 is performed. Thus, the deterioration diagnosis is performed at a high detection accuracy even during idling. This increases the number of times of executing the deterioration diagnosis as compared to a configuration that does not execute the deterioration diagnosis of the SCR catalyst 41 during idling.

[0110] (2-2) The controller 100 executes the NOx increasing process and the deterioration diagnosis of the SCR catalyst 41 in an acceleration-off state in which an accelerator pedal is not depressed. The accelerator pedal is configured to adjust the output of the internal combustion engine 10. When the fuel cut-off process execution condition for stopping fuel injection in the internal combustion engine 10 is satisfied due to the acceleration-off state, the controller 100 executes the steps of S250 and S260 shown in Fig. 3 as the NOx increasing process. The step of S250 prohibits execution of the fuel cut-off process even when the fuel cut-off process execution condition is satisfied. The step of S260 burns an air-fuel mixture having a smaller air-fuel ratio than the lean air-fuel mixture.

[0111] Even when the fuel cut-off process execution condition, which stops fuel injection in the internal combustion engine 10, is satisfied, the controller 100 executes the NOx increasing process prohibiting execution of the fuel cut-off process and burning the air-fuel mixture having a smaller air-fuel ratio than the lean air-fuel mixture. When the air-fuel mixture having a smaller air-fuel ratio than the lean air-fuel mixture is burned, the amount of NOx produced in the combustion chamber 17 is increased. As described above, when the amount of NOx produced is increased, the deterioration diagnosis of the SCR catalyst 41 is performed. Thus, the deterioration diagnosis is performed at a high detection accuracy even when the fuel cut-off process is executed due to the acceleration-off state. With this configuration, the number of times of executing the deterioration diagnosis is increased as compared to a configuration that does not execute the deterioration diagnosis of the SCR catalyst 41 when the fuel cut-off process execution condition is satisfied.

[0112] (2-3) When the NOx increasing process is executed during idling to increase the amount of fuel supplied to the combustion chamber 17, torque of the internal combustion engine 10 is increased. Also, as the NOx increasing process that is executed when the fuel cut-off process execution condition is satisfied, when the air-fuel mixture is burned without execution of the fuel cut-off process, torque of the internal combustion engine 10 is increased. In this regard, in the present embodiment, during execution of the NOx increasing process, the controller 100 executes the step of S230 or S270 shown in Fig. 3 to execute a process for decreasing the open degree of the throttle valve 28. When the open degree of the throttle valve 28 is decreased, pumping loss is increased. This results in a decrease in torque of the internal combustion engine 10 transmitted to the crankshaft 18. The decrease in torque limits an increase in torque of the internal combustion engine 10 due to execution of the NOx increasing process.

[0113] (2-4) The crankshaft 18 of the internal combustion engine 10 is connected to the first MG 310, which is used as an electric generator, via the planetary gear mechanism 300. The drive wheel 340 is connected to the second MG 320, which is used as an electric generator. The controller 100 executes the step of S230 or S270 shown in Fig. 3 to execute the process for increasing the amount of power generated by the first MG 310 and the second MG 320 during execution of the NOx increasing process.

[0114] As described above, when the NOx increasing process is executed during idling to increase the amount of fuel supplied to the combustion chamber 17, torque of the internal combustion engine 10 is increased. Also, as the NOx increasing process that is executed when the fuel cut-off process execution condition is satisfied, when the air-fuel mixture is burned without execution of the fuel cut-off process, torque of the internal combustion engine 10 is increased. In this regard, in the present embodiment, during execution of the NOx increasing process, the amount of power generated by the first MG 310, which is connected to the crankshaft 18, and the amount of power generated by the second MG 320, which is connected to the drive wheel 340, are increased. Therefore, when torque of the internal combustion engine 10 is increased by execution of the NOx increasing process, the torque is absorbed by increasing the amount of power generated by the first MG 310 and the second MG 320. Thus, an increase in torque of the internal combustion engine 10 due to execution of the NOx increasing process is limited.

[0115] (2-5) When the controller 100 executes the steps of S250 and S260 shown in Fig. 3 to execute the NOx increasing process, the controller 100 executes the step of S270 shown in Fig. 3. More specifically, when executing the NOx increasing process, the controller 100 executes the process for increasing braking force of the brake 510 mounted on the vehicle 700.

[0116] When the fuel cut-off process execution condition is satisfied and the NOx increasing process is executed, the air-fuel mixture is burned without execution of the fuel cut-off process. When the air-fuel mixture is burned, the internal combustion engine 10 generates torque. This may reduce the sensation of deceleration of the vehicle 700. In this regard, in the present embodiment, when executing the NOx increasing process, braking force of the brake 510 mounted on the vehicle 700 is increased. This increases the sensation of deceleration of the vehicle 700. Thus, the NOx increasing process is less likely to decrease the sensation of deceleration of the vehicle 700.

[0117] Modified Examples

[0118] The above-described embodiments may be modified as follows. The embodiments and the following modified examples can be combined as long as the combined modified examples remain technically consistent with each other.

[0119] The step of S110 shown in Fig. 2 includes decreasing the open degree of the throttle valve 28 to decrease the intake air amount. Alternatively, to decrease the intake air amount, the valve timing of the intake valve 81 and the valve timing of the exhaust valve 82 may be changed. To decrease the intake air amount, the open degree of the nozzle vane 24N or the open degree of the air bypass valve 93 may be changed.

[0120] The step of S110 includes decreasing the intake air amount as the NOx increasing process. Alternatively, as the NOx increasing process, a process for changing the target EGR ratio EGp to a value smaller than that used before execution of the NOx increasing process may be executed to decrease the EGR amount, thereby increasing the amount of NOx produced in the combustion chamber 17.

[0121] One of the decreasing of the intake air amount and the retarding of the injection timing may be omitted from the NOx increasing process executed in the step of S110.

[0122] One of the increasing of the requested injection amount and the retarding of the ignition timing may be omitted from the torque compensation process executed in the step of S110.

[0123] The torque compensation process may be omitted from the step of S110.

[0124] In the step of S100 shown in Fig. 2, the deterioration detection condition may be changed.

[0125] In the step of S200 shown in Fig. 3, the condition (f) may be omitted from the deterioration detection condition. In this case, it is preferred that the process for increasing power generation amount is omitted from the steps of S230 and S270.

[0126] In the step of S230, one of the decreasing of the open degree of the throttle valve 28 and the increasing of the amount of power generated by the first MG 310 may be omitted.

[0127] At least one of the decreasing of the open degree of the throttle valve 28, the increasing of the amount of power generated by the second MG 320 through regenerative braking, and the increasing of braking force of the brake 510 may be omitted from the process of S270. The increasing of the amount of power generated by the second MG 320 may be changed to increasing of the amount of power generated by the first MG 310. In the step of S270, to increase braking force on the wheel of the vehicle 700, braking force of a friction brake such as the brake 510 is increased. Alternatively, braking force of the brake 510 and braking force of regenerative braking of the second MG 320 may both be increased to increase the braking force. Instead of increasing the braking force by the brake 510, the braking force may be increased by regenerative braking of the second MG 320.

[0128] Steps S210, S220, and S230 shown in Fig. 3 may be omitted.

[0129] Steps S240, S250, S260, and S270 shown in Fig. 3 may be omitted. In this case, if a negative determination is made in step S210, the series of the steps shown in Fig. 3 may end.

[0130] The first NOx concentration N1 may be estimated based on the requested injection amount Qd and the intake air amount GA.

[0131] The catalyst removing NOx may be other than a selective catalytic reduction catalyst. In an example, a NOx adsorption reduction catalyst may be used.

[0132] The internal combustion engine 10 may include a fuel injection valve of a port injection type that injects fuel into the intake port 30.

[0133] 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 does not necessarily have to include the intake-side variable valve timing mechanism 85 and the exhaust-side variable valve timing mechanism 86.

[0134] The internal combustion engine 10 does not necessarily have to include the forced induction device 24.

[0135] The forced induction device 24 does not necessarily have to include the nozzle vane 24N.

[0136] The exhaust pipe 90 does not necessarily have to include the bypass passage 92 and the air bypass valve 93.

[0137] The vehicle hybrid system is not limited to the one shown in Fig. 1 and may include other hybrid systems.

[0138] The number of motor generators included in the vehicle may be changed.

[0139] The vehicle may include only the internal combustion engine 10 as a prime mover.

[0140] The controller 100 is not limited to a device that includes a CPU and a memory and executes a software process. For example, the controller 100 may include a dedicated hardware circuit (such as ASIC) executing a hardware process on at least part of the processes executed by the software in the embodiment. That is, the controller 100 may include processing circuitry that has any one of the following configurations (a) to (c). (a) Processing circuitry includes at least one processor that executes all of the above-described processes according to programs and at least one program storage device such as a ROM that stores the programs. (b) Processing circuitry includes at least one processor and at least one program storage device that execute part of the above-described processes according to the programs and at least one dedicated hardware circuit that executes the remaining processes. (c) Processing circuitry includes at least one dedicated hardware circuit that executes all of the above-described processes. The program storage device, that is, a computer readable medium, includes any medium that can be accessed from a general-purpose computer or a dedicated computer.

Claims

1. A controller for an internal combustion engine including an exhaust passage and a catalyst arranged on the exhaust passage to remove NOx from an exhaust gas, the internal combustion engine being configured to perform lean combustion that uses hydrogen as a fuel to burn a lean air-fuel mixture, which has an air-fuel ratio greater than a stoichiometric air-fuel ratio, and the controller being configured to execute a deterioration diagnosis that detects deterioration of the catalyst based on a removal performance of the catalyst during execution of a NOx increasing process, wherein the NOx increasing process includes increasing an amount of NOx produced in a combustion chamber of the internal combustion engine to be greater than before execution of the NOx increasing process.

2. The controller according to claim 1, wherein the NOx increasing process includes decreasing an intake air amount of the internal combustion engine to be less than before execution of the NOx increasing process.

3. The controller according to claim 2, wherein the controller is configured to execute a compensation process that compensates for a decrease in torque of the internal combustion engine due to execution of the NOx increasing process, and the compensation process includes retarding an ignition timing of the air-fuel mixture as compared to before execution of the compensation process.

4. The controller according to claim 2, wherein the NOx increasing process includes decreasing an open degree of a throttle valve arranged in an intake passage of the internal combustion engine to be less than before execution of the NOx increasing process, the controller is configured to execute a compensation process that compensates for a decrease in torque of the internal combustion engine due to execution of the NOx increasing process, and the compensation process includes increasing an amount of the fuel supplied to the combustion chamber to be greater than before execution of the compensation process.

5. The controller according to any one of claims 1 to 4, wherein the internal combustion engine includes a fuel injection valve that directly injects the fuel into the combustion chamber of the internal combustion engine during a compression stroke, and the NOx increasing process includes retarding an injection start timing at which the fuel injection valve starts to inject the fuel as compared to before execution of the NOx increasing process.

6. The controller according to claim 1, wherein the controller is configured to execute the NOx increasing process and the deterioration diagnosis in an acceleration-off state in which an accelerator pedal is not depressed, the accelerator pedal being configured to adjust an output of the internal combustion engine, and the NOx increasing process includes increasing an amount of the fuel supplied to the combustion chamber to be greater than before execution of the NOx increasing process when the internal combustion engine is idling due to the acceleration-off state.

7. The controller according to claim 1 or 6, wherein the controller is configured to execute the NOx increasing process and the deterioration diagnosis in an acceleration-off state in which an accelerator pedal is not depressed, the accelerator pedal being configured to adjust an output of the internal combustion engine, and when a condition for executing a fuel cut-off process that stops fuel injection in the internal combustion engine is satisfied due to the accelerator-off state, the NOx increasing process includes prohibiting 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 increasing process includes increasing a braking force on a wheel of a vehicle including the internal combustion engine to be greater than before execution of the NOx increasing process.

9. The controller according to any one of claims 6 to 8, wherein the NOx increasing process includes decreasing an open degree of a throttle valve arranged in an intake passage of the internal combustion engine to be less than before execution of the NOx increasing process.

10. The controller according to any one of claims 6 to 9, wherein the internal combustion engine includes an output shaft connected to an electric generator, and the NOx increasing process includes increasing an amount of power generated by the electric generator to be greater than before execution of the NOx increasing process.

11. A method for controlling an internal combustion engine including an exhaust passage and a catalyst arranged on the exhaust passage to remove NOx from an exhaust gas, the internal combustion engine being configured to perform lean combustion that uses hydrogen as a fuel to burn a lean air-fuel mixture, which has an air-fuel ratio greater than a stoichiometric air-fuel ratio, the method comprising: executing a deterioration diagnosis that detects deterioration of the catalyst based on a removal performance of the catalyst during execution of a NOx increasing process, wherein the NOx increasing process includes increasing an amount of NOx produced in a combustion chamber of the internal combustion engine to be greater than before execution of the NOx increasing process.

12. A non-transitory computer readable storage medium storing a program including an instruction to execute a method for controlling an internal combustion engine, the internal combustion engine including an exhaust passage and a catalyst arranged on the exhaust passage to remove NOx from an exhaust gas, the internal combustion engine being configured to perform lean combustion that uses hydrogen as a fuel to burn a lean air-fuel mixture, which has an air-fuel ratio greater than a stoichiometric air-fuel ratio, the instruction including executing a deterioration diagnosis that detects deterioration of the catalyst based on a removal performance of the catalyst during execution of a NOx increasing process, and the NOx increasing process includes increasing an amount of NOx produced in a combustion chamber of the internal combustion engine to be greater than before execution of the NOx increasing process.

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