Control device for internal combustion engine

Abstract

To suppress lowering of a residual amount of urea water.SOLUTION: A control device 100 controls an internal combustion engine 10 including: a fuel injection valve 18 for injecting hydrogen gas to be supplied into a cylinder 11; an SCR catalyst 24 located in an exhaust passage 21 and eliminating NOx; an urea water injection valve 23 located on the upstream side of the SCR catalyst 24 in the exhaust passage 21 and injecting urea water to the SCR catalyst 24; a tank 26 that stores urea water to be injected by the urea water injection valve 23; and a residual amount detection sensor 67 that detects a residual amount of the urea water stored in the tank 26. When the residual amount of the urea water is smaller than a predetermined set value, the control device controls an injection amount of hydrogen gas by the fuel injection valve 18 so that an excess air ratio in the cylinder 11 becomes equal to or greater than an excess ratio that is predetermined as a value larger than 1.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] The exhaust gas purification device for an internal combustion engine disclosed in Patent Document 1 includes an SCR catalyst, a urea water injector, and a tank. The SCR catalyst is located midway through the exhaust passage. The urea water injector is located upstream of the SCR catalyst. The tank stores urea water. The urea water injector injects the urea water stored in the tank toward the SCR catalyst. The SCR catalyst purifies NOx contained in the exhaust gas using ammonia derived from the urea water as a reducing agent. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-044528 Summary of the Invention [Problem to be solved by the invention]

[0004] An internal combustion engine that uses hydrogen gas as fuel is equipped with an exhaust purification device such as that disclosed in Patent Document 1 in order to purify NOx contained in the exhaust. While the internal combustion engine is operating, the amount of urea water stored in the tank may become low. If the amount of urea water becomes excessively insufficient, NOx will be discharged to the outside without being purified, making it difficult to continue operating the internal combustion engine. [Means for solving the problem]

[0005] A control device for an internal combustion engine to solve the above problem controls an internal combustion engine that is equipped with a fuel injection valve that injects hydrogen gas to be supplied into a cylinder, a selective reduction catalyst located in an exhaust passage and purifying NOx, a urea water injection valve located upstream of the catalyst in the exhaust passage and injecting urea water toward the catalyst, a tank that stores the urea water injected by the urea water injection valve, and a remaining amount detection sensor that detects the remaining amount of urea water stored in the tank, and if the remaining amount is less than a predetermined set value, a restriction process is executed to control the amount of hydrogen gas injected by the fuel injection valve so that the excess air ratio in the cylinder is equal to or greater than a predetermined specified excess ratio, which is a value greater than 1.

[0006] A control device for an internal combustion engine to solve the above problem has as its control target an internal combustion engine that is equipped with a fuel injection valve that injects hydrogen gas to be supplied into a cylinder, a selective reduction catalyst located in an exhaust passage and purifying NOx, a urea water injection valve located upstream of the catalyst in the exhaust passage and injecting urea water toward the catalyst, a tank that stores the urea water injected by the urea water injection valve, and a remaining amount detection sensor that detects the remaining amount of urea water stored in the tank, and when the remaining amount is less than a predetermined set value, a restriction process is executed to control the amount of hydrogen gas injected by the fuel injection valve so that the excess air ratio in the cylinder is larger than when the remaining amount is equal to or greater than the set value. [Effects of the Invention]

[0007] The control device for an internal combustion engine can suppress a decrease in the remaining amount of urea water. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram of an internal combustion engine. [Figure 2] FIG. 2 is a diagram showing the relationship between the excess air ratio and the amount of NOx produced. [Figure 3] 3 is a flowchart showing a processing procedure for engine control. [Figure 4]4 is a time chart showing an example of the transition of each parameter accompanying engine control. DETAILED DESCRIPTION OF THE INVENTION

[0009] An embodiment of a control device for an internal combustion engine will be described below with reference to the drawings. <General configuration of an internal combustion engine> As shown in FIG. 1, a vehicle 500 includes an internal combustion engine 10. The internal combustion engine 10 is a drive source for the vehicle 500. The internal combustion engine 10 includes an engine body 10A, a plurality of cylinders 11, a plurality of pistons 12, a plurality of connecting rods 13, and a crankshaft 14. Note that FIG. 1 shows only one of the plurality of cylinders 11. The same applies to the pistons 12 and the connecting rods 13. A piston 12 and a connecting rod 13 are provided for each cylinder 11. There are four cylinders 11 in total.

[0010] Cylinder 11 is a space defined in engine body 10A. Cylinder 11 is a space for burning a mixture of fuel and intake air. Piston 12 is located inside cylinder 11. Piston 12 reciprocates inside cylinder 11. Piston 12 is connected to crankshaft 14 via connecting rod 13. Crankshaft 14 rotates in response to the reciprocating motion of piston 12. Crankshaft 14 is an output shaft of internal combustion engine 10. Crankshaft 14 is connected to drive wheels 502 via an automatic transmission 501, a differential, etc.

[0011] The internal combustion engine 10 is equipped with a plurality of fuel injection valves 18. Note that FIG. 1 shows only one of the plurality of fuel injection valves 18. A fuel injection valve 18 is provided for each cylinder 11. The fuel injection valve 18 injects hydrogen gas as fuel. The fuel injection valve 18 supplies fuel directly into the cylinder 11 without passing through an intake passage 15, which will be described later.

[0012] The internal combustion engine 10 is equipped with a plurality of spark plugs 19. Note that FIG. 1 shows only one of the plurality of spark plugs 19. A spark plug 19 is provided for each cylinder 11. The tip of the spark plug 19 is located inside the cylinder 11. The spark plug 19 ignites the air-fuel mixture inside the cylinder 11.

[0013] The internal combustion engine 10 includes an intake passage 15 and a throttle valve 16. The intake passage 15 is a passage for introducing intake air into each cylinder 11. The intake passage 15 is connected to each cylinder 11. The throttle valve 16 is located midway through the intake passage 15. The opening of the throttle valve 16 is adjustable. The amount of intake air G changes depending on the opening of the throttle valve 16.

[0014] The internal combustion engine 10 includes an exhaust passage 21, an oxidation catalyst 22, a urea water injector 23, and a selective catalytic reduction catalyst (hereinafter referred to as an SCR catalyst 24). The exhaust passage 21 is a passage for discharging exhaust gas from each cylinder 11. The exhaust passage 21 is connected to each cylinder 11. The oxidation catalyst 22 is located midway through the exhaust passage 21. The oxidation catalyst 22 oxidizes components contained in the exhaust gas. The SCR catalyst 24 is located downstream of the oxidation catalyst 22 in the exhaust passage 21. The urea water injector 23 is located between the oxidation catalyst 22 and the SCR catalyst 24 in the exhaust passage 21. In other words, the urea water injector 23 is located upstream of the SCR catalyst 24 in the exhaust passage 21. The urea water injector 23 injects urea water into the SCR catalyst 24. The SCR catalyst 24 reduces NOx (nitrogen oxides) contained in the exhaust gas into nitrogen and water using ammonia derived from the urea water injected by the urea water injector 23 as a reducing agent. In other words, the SCR catalyst 24 purifies the NOx in the exhaust gas.

[0015] The internal combustion engine 10 includes a tank 26 and a connecting passage 28. The tank 26 stores the urea water to be injected by the urea water injector 23. In Fig. 1, an example of the liquid level of the urea water is indicated by a two-dot chain line. The connecting passage 28 connects the tank 26 and the urea water injector 23. The urea water stored in the tank 26 is supplied to the urea water injector 23 via the connecting passage 28.

[0016] The internal combustion engine 10 is equipped with a crank position sensor 61, an air flow meter 62, an air-fuel ratio sensor 63, a NOx sensor 64, and a remaining amount detection sensor 67. The crank position sensor 61 is located near the crankshaft 14. The crank position sensor 61 detects the rotational position R of the crankshaft 14. The air flow meter 62 is located upstream of the throttle valve 16 in the intake passage 15. The air flow meter 62 detects the intake air amount G. The air-fuel ratio sensor 63 is located upstream of the oxidation catalyst 22 in the exhaust passage 21. The air-fuel ratio sensor 63 detects the air-fuel ratio A of the mixture in the cylinder 11. The NOx sensor 64 is located between the oxidation catalyst 22 and the SCR catalyst 24. The NOx sensor 64 detects the NOx concentration M in the exhaust. The remaining amount detection sensor 67 is attached to the tank 26. The remaining amount detection sensor 67 detects the remaining amount W of urea, which is the remaining amount of urea water stored in the tank 26. Each of these sensors repeatedly transmits a signal corresponding to the information detected by itself to the control device 100, which will be described later.

[0017] The vehicle 500 is equipped with a vehicle speed sensor 71 and an accelerator sensor 72. The vehicle speed sensor 71 detects the traveling speed V of the vehicle 500. The accelerator sensor 72 detects the operation amount C of the accelerator pedal of the vehicle 500. Each of these sensors repeatedly transmits a signal corresponding to the information detected by itself to the control device 100 described below.

[0018] The vehicle 500 is equipped with an ignition switch 70 and an alert lamp 75. The ignition switch 70 is a switch that the occupant uses to instruct the internal combustion engine 10 to start. The ignition switch 70 is turned on or off in response to an operation by the occupant. The alert lamp 75 is a lamp that indicates that a first restriction process or a second restriction process, which will be described later, is being executed. The alert lamp 75 is provided on the meter panel.

[0019] <Control device> The vehicle 500 includes a control device 100. The control device 100 includes a processing circuit 101 including a CPU 111 and a ROM 112. The ROM 112 stores in advance various programs in which processes to be executed by the CPU 111 are described. The ROM 112 also stores in advance various data required for the CPU 111 to execute the various programs.

[0020] The control device 100 receives a signal from the ignition switch 70. Furthermore, while the ignition switch 70 is on, the control device 100 repeatedly receives signals from various sensors mounted on the vehicle 500. The control device 100 repeatedly calculates various parameters related to the state of the internal combustion engine 10 based on the received signals. For example, the control device 100 calculates the rotational speed of the crankshaft 14 based on the rotational position R of the crankshaft 14. The control device 100 also calculates the excess air ratio λ of the mixture in the cylinder 11 based on the air-fuel ratio A of the mixture in the cylinder 11. The excess air ratio λ represents the ratio of the actual air-fuel ratio A to the stoichiometric air-fuel ratio AS. In other words, when the excess air ratio λ is "1," combustion in the internal combustion engine 10 is stoichiometric combustion at the stoichiometric air-fuel ratio AS. When the excess air ratio λ is greater than 1, the combustion in the internal combustion engine 10 is lean combustion at an air-fuel ratio A that is leaner than the stoichiometric air-fuel ratio AS. Hereinafter, the excess air ratio λ of the mixture in the cylinder 11 will be simply referred to as the excess air ratio λ in the cylinder 11.

[0021] The control device 100 controls the internal combustion engine 10. While the ignition switch 70 is on, the control device 100 repeatedly calculates a target torque for the internal combustion engine 10 based on the traveling speed V of the vehicle 500 and the accelerator pedal operation amount C. The control device 100 then controls the internal combustion engine 10 based on the target torque. The control device 100 calculates a larger target torque value as the accelerator pedal operation amount C increases. When controlling the internal combustion engine 10, the control device 100 appropriately refers to signals from the above-mentioned sensors and information calculated therefrom.

[0022] <Relationship between excess air ratio λ and NOx> When controlling the internal combustion engine 10, the control device 100 may impose a limit on the excess air ratio λ in the cylinder 11. The relationship between the excess air ratio λ and the amount of NOx generated, which is the premise for imposing such a limit, will be described below. FIG. 2 shows the relationship between the excess air ratio λ and the amount of NOx generated in the internal combustion engine 10. Note that FIG. 2 representatively shows the range of excess air ratios λ from 1.2 to 3 among various excess air ratios λ. The amount of NOx generated is expressed, for example, as the weight ratio of NOx in the exhaust gas. As is well known, in the internal combustion engine 10, NOx is generated during the combustion reaction of hydrogen gas. The amount of NOx generated increases or decreases depending on the excess air ratio λ in the cylinder 11. While detailed illustration is omitted, when the internal combustion engine 10 is performing lean combustion, the amount of NOx generated is maximized when the excess air ratio λ is a specific maximum value slightly greater than 1. The specific maximum value is a value near 1.2. As shown in Fig. 2, as the excess air ratio λ is increased from a specific maximum value, the amount of NOx generated gradually decreases. When the excess air ratio λ reaches "3," the amount of NOx generated falls below the allowable value. The allowable value is the amount of NOx generated that can keep the amount of NOx emitted into the outside air below the regulated value even without injecting urea water from the urea water injector 23.

[0023] <Internal combustion engine control> While the ignition switch 70 is on, the control device 100 repeatedly executes engine control for operating the internal combustion engine 10 at a predetermined control period. The flow of a series of processes in this engine control will be described. The control period is the same period as the period in which the control device 100 calculates the target torque. The control period is, for example, one second.

[0024] As shown in Fig. 3, when starting engine control, the control device 100 first executes the processing of step S10. In step S10, the control device 100 determines whether the latest remaining amount W of urea detected by the remaining amount detection sensor 67 is less than a second set value W2. The second set value W2 is a predetermined fixed value. The second set value W2 is set as a value indicating that the remaining amount W of urea is considerably small. The second set value W2 is a value at which the vehicle 500 is allowed to travel. If the latest remaining amount W of urea is equal to or greater than the second set value W2 (step S10: NO), the control device 100 proceeds to the processing of step S20.

[0025] In step S20, the control device 100 determines whether the remaining amount W of urea referred to in step S10 is less than a first set value W1. The first set value W1 is a fixed value that is predetermined as a value greater than the second set value W2. The first set value W1 is determined as a value that indicates that the remaining amount W of urea has become so low that some kind of action is necessary. If the remaining amount W of urea is equal to or greater than the first set value W1 (step S20: NO), the control device 100 turns off the notification lamp 75 and proceeds to step S300.

[0026] In step S300, the control device 100 executes normal processing for the internal combustion engine 10. In this normal processing, the control device 100 controls the opening of the throttle valve 16, the amount of hydrogen gas injected by the fuel injector 18, and the ignition timing of the spark plug 19 based on the latest target torque without imposing any restrictions on the excess air ratio λ in the cylinder 11. The control device 100 uses various maps to set an optimal combination of each parameter so as to achieve the target torque. The control device 100 then continues control using the set control target values ​​for a fixed period of time corresponding to the control cycle. Additionally, in the normal processing, the control device 100 injects urea water from the urea water injector 23. The control device 100 increases the amount of urea water injected by the urea water injector 23 as the latest NOx concentration M detected by the NOx sensor 64 increases. After executing the normal processing described above for a fixed period of time corresponding to the control cycle, the control device 100 terminates the processing of step S300. Thereafter, the control device 100 temporarily ends the series of engine control processes. Then, the control device 100 executes the process of step S10 again. Note that the above-mentioned optimal combination takes into consideration, for example, prevention of pre-ignition and improvement of fuel economy. This also applies to the first and second restriction processes described below.

[0027] Now, in step S20, if the remaining amount W of urea is less than the first set value W1 (step S20: YES), the control device 100 turns on the notification lamp 75 and then proceeds to step S200.

[0028] In step S200, the control device 100 executes a first restriction process. In this first restriction process, the control device 100 imposes a first condition on the excess air ratio λ in the cylinder 11, and then controls the opening of the throttle valve 16, the amount of hydrogen gas injected by the fuel injection valve 18, and the ignition timing of the spark plug 19 based on the latest target torque. The first condition is that the excess air ratio λ in the cylinder 11 is equal to or greater than a first excess air ratio λ1. The control device 100 sets an optimal combination of the opening of the throttle valve 16, the amount of hydrogen gas injected by the fuel injection valve 18, and the ignition timing of the spark plug 19 while referring to various maps, etc., so as to satisfy this first condition and the target torque. The control device 100 then realizes control using the set control target values. That is, the control device 100 controls the opening of the throttle valve 16, the amount of hydrogen gas injected by the fuel injection valve 18, and the ignition timing of the spark plug 19 so as to satisfy the first condition. The first excess rate λ1 is a predetermined fixed value. The first excess rate λ1 is a value that is greater than the specific maximum value described in FIG. 2 and less than "3." The first excess rate λ1 is, for example, "2." In the first restriction process, the control device 100 injects urea water from the urea water injector 23, as in the normal process. The method for determining the injection amount of urea water at this time is the same as that described in the normal process. After executing the first restriction process as described above for a certain period of time corresponding to the control cycle, the control device 100 ends the process of step S200. Thereafter, the control device 100 temporarily ends the series of processes for engine control. Then, the control device 100 executes the process of step S10 again.

[0029] In step S10, if the remaining amount W of urea is less than the second set value W2 (step S10: YES), the control device 100 turns on the notification lamp 75 and then proceeds to step S100. At this time, the control device 100 turns on the notification lamp 75 in a different color from when the determination in step S20 is YES.

[0030] In step S100, the control device 100 executes a second restriction process. In this second restriction process, the control device 100 imposes a second condition on the excess air ratio λ in the cylinder 11, and then controls the opening of the throttle valve 16, the amount of hydrogen gas injected by the fuel injection valve 18, and the ignition timing of the spark plug 19 based on the latest target torque. The second condition is that the excess air ratio λ in the cylinder 11 is equal to or greater than a second excess ratio λ2. The control device 100 references various maps and sets an optimal combination of the opening of the throttle valve 16, the amount of hydrogen gas injected by the fuel injection valve 18, and the ignition timing of the spark plug 19 so as to satisfy the second condition and the target torque. The control device 100 then realizes control using the set control target values. That is, the control device 100 controls the opening of the throttle valve 16, the amount of hydrogen gas injected by the fuel injection valve 18, and the ignition timing of the spark plug 19 so as to satisfy the second condition. For example, the control device 100 fully opens the throttle valve 16 and injects hydrogen gas in an amount that meets the second condition. The second excess rate λ2 is a predetermined fixed value. In this embodiment, the second excess rate λ2 is "3." In the second restriction process, the control device 100 prohibits the urea water injector 23 from injecting urea water. That is, the control device 100 does not inject urea water in the second restriction process. After executing the second restriction process as described above for a certain period of time corresponding to the control cycle, the control device 100 ends the process of step S100. Thereafter, the control device 100 temporarily ends the series of processes for engine control. Then, the control device 100 executes the process of step S10 again.

[0031] In the above configuration, the first limiting process is also referred to as a limiting process, the first excess rate λ1 is also referred to as a specified excess rate, and the first set value W1 is also referred to as a set value. <Operation of the embodiment> FIG. 4 is a time chart showing an example of the transitions of the following three parameters during operation of the internal combustion engine 10. The three parameters are the remaining amount of urea W, the excess air ratio λ in the cylinder 11, and the amount of NOx produced. For ease of explanation, FIG. 4 shows an example in which the excess air ratio λ is constant before time T2, between time T2 and time T3, and after time T3. The transitions of the parameters shown in FIG. 4, including the transition of the excess air ratio λ, do not necessarily match the actual transitions.

[0032] As shown in FIG. 4A, at time T1 during operation of the internal combustion engine 10, the remaining amount of urea W is assumed to be equal to or greater than the first set value W1 (step S10: NO, step S20: NO). In this case, the control device 100 controls the internal combustion engine 10 through normal processing. That is, as shown in FIG. 4B, the control device 100 controls the internal combustion engine 10 without imposing any restrictions on the excess air ratio λ in the cylinder 11. In this case, for example, when the target torque is large, the control device 100 may control the internal combustion engine 10 by setting the excess air ratio λ in the cylinder 11 to a value close to a specific maximum value. Therefore, due to the relationship between the excess air ratio λ and the amount of NOx generated described in FIG. 2, the amount of NOx generated may increase during execution of normal processing, as shown in FIG. 4C. To purify such NOx, the amount of urea water consumed increases. As a result, as shown in FIG. 4A, the remaining amount of urea W may decrease at a relatively large rate during execution of normal processing.

[0033] As shown in (a) of FIG. 4, it is assumed that the remaining amount W of urea eventually becomes less than the first set value W1 and equal to or greater than the second set value W2 at time T2 (step S10: NO, step S20: YES). Then, after time T2, the control device 100 controls the internal combustion engine 10 by the first restriction process. That is, as shown in (b) of FIG. 4, the control device 100 controls the internal combustion engine 10 by setting the excess air ratio λ in the cylinder 11 to be equal to or greater than the first excess ratio λ1. Accordingly, as shown in (c) of FIG. 4, the amount of NOx generated after time T2 becomes smaller than before time T2. Accordingly, the amount of urea water consumed decreases. Then, as shown in (a) of FIG. 4, the rate of decrease of urea water becomes smaller.

[0034] As shown in (a) of FIG. 4, it is assumed that the remaining amount W of urea subsequently becomes less than the second set value W2 at time T3 (step S10: YES). Then, after time T3, the control device 100 controls the internal combustion engine 10 by the second restriction process. That is, the control device 100 controls the internal combustion engine 10 by setting the excess air ratio λ in the cylinder 11 to be equal to or greater than the second excess ratio λ2. Accordingly, as shown in (c) of FIG. 4, the amount of NOx generated in the internal combustion engine 10 is significantly reduced. Then, the amount of NOx generated becomes such that injection of urea water from the urea water injector 23 is no longer necessary. Taking this into account, the control device 100 prohibits injection of urea water from the urea water injector 23 in the second restriction process. Therefore, as shown in (a) of FIG. 4, the remaining amount W of urea does not decrease after time T3.

[0035] <Effects of the embodiment> (1) In the first and second restriction processes, the excess air ratio λ is increased to perform lean combustion in the cylinder 11. In this case, as described with reference to FIG. 2, the amount of NOx generated by fuel combustion decreases. Accordingly, the amount of urea water required to purify NOx decreases. Therefore, the amount of urea water injected by the urea water injector 23 can be reduced or stopped. Therefore, in the above configurations in which the first and second restriction processes are performed, the decrease in the remaining urea amount W can be suppressed when the remaining urea amount W becomes low. Here, if the remaining urea amount W becomes excessively insufficient, NOx will be discharged to the outside without being purified, making it difficult to continue operating the internal combustion engine 10. In this regard, if the decrease in the remaining urea amount W can be suppressed as in the above configuration, the time for which the internal combustion engine 10 can continue operating when the remaining urea amount W becomes low can be extended.

[0036] (2) Increasing the excess air ratio λ to perform lean combustion in the cylinder 11 reduces the torque that the internal combustion engine 10 can output. Therefore, when the first restriction process and the second restriction process are performed, the torque that the internal combustion engine 10 can output may not reach the target torque. In light of this, in the above configuration, when there is still some margin in the remaining urea amount W, the first restriction process is performed to moderate the restriction on the excess air ratio λ. This reduces the impact on the torque of the internal combustion engine 10. On the other hand, in the above configuration, when the remaining urea amount W becomes significantly low, the second restriction process is performed to strengthen the restriction on the excess air ratio λ. At the same time, in the above configuration, injection of urea water by the urea water injector 23 is prohibited. In this way, by changing the degree of restriction on the excess air ratio λ depending on the remaining urea amount W, it is possible to reduce the impact on the torque of the internal combustion engine 10 and suppress a decrease in the remaining urea amount W.

[0037] (3) When the excess air ratio λ is set to "3" or more, the amount of NOx generated by fuel combustion is almost zero. As a result, there is no need to inject urea water to purify NOx. In the above configuration, when the remaining urea amount W is significantly reduced, the second restriction process is performed. Then, the excess air ratio λ is set to "3" or more, and the injection of urea water by the urea water injector 23 is prohibited. This prevents further consumption of urea water. Therefore, the minimum remaining urea amount W can be maintained.

[0038] <Example of change> The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0039] The method for determining the first setting value W1 is not limited to the example in the above embodiment. The first setting value W1 may be determined to be any value that can appropriately define the circumstances under which the first restriction process is required to be executed.

[0040] The method for determining the second set value W2 is not limited to the example in the above embodiment. The second set value W2 may be determined to be any value that can appropriately define the circumstances under which the second restriction process is required to be executed.

[0041] The value of the first excess ratio λ1 is not limited to the example in the above embodiment. The first excess ratio λ1 may be set to a value that allows the first restriction process to impose an appropriate restriction on the air excess ratio λ, taking into account factors such as the first set value W1. The first excess ratio λ1 may be set to a value greater than "1." Furthermore, the first excess ratio λ1 may be set to a value greater than a specific maximum value.

[0042] The value of the second excess ratio λ2 is not limited to the example in the above embodiment. The second excess ratio λ2 may be set to a value that allows the second restriction process to impose an appropriate restriction on the air excess ratio λ, taking into account the second set value W2 and other factors. The second excess ratio λ2 may be set to a value greater than the first excess ratio λ1.

[0043] In the second restriction process, it is not essential to prohibit the injection of urea water from the urea water injector 23. Depending on the value of the second excess rate λ2, the injection of urea water may be necessary. In the above embodiment, the internal combustion engine 10 is controlled by imposing a two-stage restriction on the excess air ratio λ using the first set value W1 and the second set value W2. Alternatively, the internal combustion engine 10 may be controlled by imposing a three-stage restriction on the excess air ratio λ depending on the remaining amount W of urea.

[0044] In engine control, the second limiting process may be eliminated. In other words, in engine control, the excess air ratio λ may be limited to only one stage. When the air excess ratio λ is limited to only one stage as in the above modified example, the injection of urea water by the urea water injector 23 may be prohibited in conjunction with the imposition of the limit on the air excess ratio λ.

[0045] The configuration of the internal combustion engine 10 is not limited to the example of the above embodiment. For example, the fuel injection valve 18 may supply hydrogen gas into the cylinders 11 via the intake passage 15. The number of cylinders 11 may be changed. The internal combustion engine 10 may include both the following first and second elements. The first elements are the fuel injection valve 18 that injects hydrogen gas to be supplied into the cylinders 11, the SCR catalyst 24 located in the exhaust passage 21, and the urea water injector 23 that injects urea water into the SCR catalyst 24. The second elements are the tank 26 that stores urea water and the remaining amount detection sensor 67 that detects the remaining amount W of urea in the tank 26.

[0046] The overall configuration of the vehicle 500 is not limited to the example of the above embodiment. The vehicle 500 may include a motor generator in addition to the internal combustion engine 10 as a drive source for the vehicle 500.

[0047] The means for notifying the occupant that the first restriction process or the second restriction process is being executed is not limited to the notification lamp 75. A message or audio guidance may be displayed to indicate that the first restriction process or the second restriction process is being executed.

[0048] An execution switch may be provided in the passenger compartment of the vehicle 500. The execution switch is a switch that allows the occupant to instruct the execution of the first restriction process. The execution switch is turned on or off depending on the occupant's operation. In such a configuration, when the execution switch is turned on, the control device 100 may determine that the remaining urea amount W is less than the first set value W1 and perform the first restriction process. For example, if the remaining urea amount W is displayed on the meter panel, the occupant can determine for themselves whether or not it is necessary to save on the consumption of urea water. Then, the occupant can turn the execution switch on or off as needed.

[0049] With regard to the normal processing, an upper limit for the excess air ratio λ in the cylinder 11 may be set. For example, in the normal processing, a condition that the excess air ratio λ in the cylinder 11 be less than a first excess ratio λ1 may be set. In this case, comparing the normal processing and the first restriction processing, the following predetermined procedure is performed in the first restriction processing. That is, when the remaining urea amount W is less than the first set value W1 and equal to or greater than the second set value W2, the control device 100 controls the injection amount of hydrogen gas from the fuel injection valve 18 so that the excess air ratio λ in the cylinder 11 is larger than when the normal processing is performed when the remaining urea amount W is equal to or greater than the first set value W1. For example, the control device 100 performs this predetermined procedure even under the same target torque. Even with this configuration, the amount of NOx generated by fuel combustion is reduced in the first restriction processing compared to the normal processing. As a result, the amount of urea water required for NOx purification is reduced. Therefore, the amount of urea water injected by the urea water injector 23 can be reduced. Therefore, the decrease in the remaining urea amount W can be suppressed.

[0050] When adopting a configuration such as the above modified example, the first excess rate λ1 may not be a fixed value, but may be variably set depending on the driving state of the vehicle 500, etc. In this case, for example, the same first excess rate λ1 may be used under the condition that the target torque is the same between the normal processing and the first restriction processing. In this case, the first excess rate λ1 may be reduced as the target torque increases. In this case, it is possible to reduce the constraints on the torque of the internal combustion engine 10 that can be achieved by the first restriction processing, while suppressing a decrease in the remaining urea amount W when the first restriction processing is executed.

[0051] The processing circuit 101 is not limited to a circuit having a CPU and ROM and executing software processing. In other words, the processing circuit 101 may have any of the following configurations (a), (b), and (c):

[0052] (a) The processing circuit 101 includes one or more processors that execute various processes according to a computer program. The processor includes a CPU and memory such as RAM and ROM. The memory stores program code or instructions configured to cause the CPU to execute processes. Memory, i.e., computer-readable media, includes any available media that can be accessed by a general-purpose or special-purpose computer.

[0053] (b) The processing circuit 101 includes one or more dedicated hardware circuits for executing various processes, such as an application specific integrated circuit (ASIC) or an FPGA.

[0054] (c) The processing circuitry 101 includes a processor that executes some of the various processes in accordance with a computer program, and a dedicated hardware circuit that executes the remaining processes among the various processes. [Explanation of symbols]

[0055] 10...internal combustion engine 11...cylinder 18...fuel injection valve 21...exhaust passage 23...urea injection valve 24...SCR catalyst 26...tank 67...remaining amount detection sensor 100...control device

Claims

1. The control target is an internal combustion engine including: a fuel injection valve that injects hydrogen gas to be supplied into a cylinder; a selective reduction catalyst that is located in an exhaust passage and purifies NOx; a urea water injection valve that is located upstream of the catalyst in the exhaust passage and injects urea water toward the catalyst; a tank that stores the urea water injected by the urea water injection valve; and a remaining amount detection sensor that detects the remaining amount of urea water stored in the tank, when the remaining amount is equal to or greater than a predetermined second set value that is smaller than a predetermined first set value and is less than the first set value, execute a first limiting process to control the injection amount of hydrogen gas by the fuel injection valve so that the excess air ratio in the cylinder becomes equal to or greater than a predetermined first excess ratio that is greater than 1; If the remaining amount is less than the second set value, a second restriction process is executed to control the injection amount of hydrogen gas by the fuel injection valve so that the excess air ratio in the cylinder becomes equal to or greater than a second excess ratio that is a value greater than the first excess ratio. Control device for internal combustion engines.

2. In the second restriction process, the injection amount of hydrogen gas from the fuel injection valve is controlled so that the excess air ratio in the cylinder is 3 or more, and the injection of urea water from the urea water injection valve is prohibited. The control device for an internal combustion engine according to claim 1.

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