Control device for internal combustion engine

Abstract

To accurately perform correction corresponding to output deviation of an upstream side air-fuel ratio sensor.SOLUTION: The internal combustion engine 10 includes a three way catalyst 22 provided in an exhaust passage, an upstream air-fuel ratio sensor 40 provided on the exhaust upstream side of the three way catalyst 22, and a downstream air-fuel ratio sensor 50 provided on the exhaust downstream side of the three way catalyst 22. The CPU32 is configured to execute a correction process of making a correction corresponding to a deviation of the output of the upstream air-fuel-ratio sensor 40 based on the output of the upstream air-fuel-ratio sensor 40 and the output of the downstream air-fuel-ratio sensor 50 when the output of the downstream air-fuel-ratio sensor 50 indicates a value near the stoichiometric air-fuel-ratio during execution of an air-fuel-ratio control of controlling the air-fuel-ratio of the air-fuel mixture to an air-fuel-ratio near the stoichiometric air-fuel-ratio based on the output of the upstream air-fuel-ratio sensor 40.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] An internal combustion engine is provided with an exhaust passage provided with a three-way catalyst. An upstream air-fuel ratio sensor is provided upstream of the three-way catalyst, and a downstream air-fuel ratio sensor is provided downstream of the three-way catalyst. A control device for the internal combustion engine performs air-fuel ratio control based on the output of the upstream air-fuel ratio sensor to maintain the air-fuel ratio of the mixture at an air-fuel ratio close to the stoichiometric air-fuel ratio.

[0003] When hydrogen is contained in the exhaust gas, an output deviation occurs in which the output of the upstream air-fuel ratio sensor becomes richer than the actual air-fuel ratio. Therefore, the technology described in Patent Document 1 controls the exhaust air-fuel ratio upstream of the three-way catalyst to a rich air-fuel ratio that is richer than the stoichiometric air-fuel ratio. Then, the output of the upstream air-fuel ratio sensor is corrected according to the difference between the output of the upstream air-fuel ratio sensor and the output of the downstream air-fuel ratio sensor, which is detected after a reference time has elapsed since the rich air-fuel ratio was reached. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-185512 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in a rich atmosphere, the oxidation reaction of hydrogen in the three-way catalyst does not proceed easily, and therefore, the output deviation caused by hydrogen also occurs in the downstream air-fuel ratio sensor. Therefore, with the technology described in Patent Document 1, it is difficult to accurately perform correction corresponding to the output deviation of the upstream air-fuel ratio sensor. [Means for solving the problem]

[0006] A control device for an internal combustion engine that solves the above-mentioned problems is applied to an internal combustion engine that includes a three-way catalyst provided in an exhaust passage, an upstream air-fuel ratio sensor provided on the exhaust upstream side of the three-way catalyst, and a downstream air-fuel ratio sensor provided on the exhaust downstream side of the three-way catalyst. This control device executes a correction process that makes a correction corresponding to a deviation in the output of the upstream air-fuel ratio sensor based on the output of the upstream air-fuel ratio sensor and the output of the downstream air-fuel ratio sensor, when air-fuel ratio control is being executed to control the air-fuel ratio of an air-fuel mixture to an air-fuel ratio close to the stoichiometric air-fuel ratio based on the output of the upstream air-fuel ratio sensor. [Effects of the Invention]

[0007] According to the present invention, correction corresponding to the output deviation of the upstream air-fuel ratio sensor can be performed with high accuracy. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of an internal combustion engine and a control device according to one embodiment. [Figure 2] FIG. 2 is a block diagram showing the process executed by the control device of the embodiment. [Figure 3] FIG. 3 is a flowchart showing the procedure of processing executed by the control device of the embodiment. [Figure 4] FIG. 4 is a block diagram showing the process executed by the control device in the modified example of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of a control device for an internal combustion engine will be described with reference to FIGS. <Configuration of internal combustion engine> 1, the internal combustion engine 10 has four cylinders arranged in series: a first cylinder #1, a second cylinder #2, a third cylinder #3, and a fourth cylinder #4. The number and arrangement of the cylinders in the internal combustion engine 10 can be changed as appropriate. The internal combustion engine 10 is intended to be mounted on a vehicle.

[0010] Air in an intake passage 12 of an internal combustion engine 10 is drawn into each combustion chamber 14 of a first cylinder #1 to a fourth cylinder #4. A fuel injection valve 16 protrudes into the combustion chamber 14, and the mixture of fuel injected from the fuel injection valve 16 and air drawn into the combustion chamber 14 from the intake passage 12 is ignited by spark discharge from an ignition plug 18 and combusted.

[0011] The combusted air-fuel mixture is discharged as exhaust gas into an exhaust passage 20. A three-way catalyst 22 that purifies the exhaust gas is provided in the exhaust passage 20. An upstream air-fuel ratio sensor 40 is provided on the exhaust upstream side of the three-way catalyst 22. A downstream air-fuel ratio sensor 50 is provided on the exhaust downstream side of the three-way catalyst 22.

[0012] The upstream air-fuel ratio sensor 40 and the downstream air-fuel ratio sensor 50 are well-known limiting current oxygen sensors. This limiting current oxygen sensor is a sensor that obtains an output current as an output value corresponding to the oxygen concentration in the exhaust gas by providing a ceramic layer called a diffusion-controlling layer in the detection section of a concentration cell oxygen sensor. The limiting current oxygen sensor outputs a current of "0" when the air-fuel ratio, which is closely related to the oxygen concentration in the exhaust gas, is the stoichiometric air-fuel ratio. Furthermore, as the air-fuel ratio becomes richer, the output current increases in the negative direction, and as the air-fuel ratio becomes leaner, the output current increases in the positive direction.

[0013] The control device 30 includes a CPU 32, a memory 34, and the like, and performs various controls of the internal combustion engine 10 by the CPU 32 executing programs stored in the memory 34. The control device 30 operates various actuators such as the fuel injection valve 16 and the spark plug 18 to perform various controls of the internal combustion engine 10 .

[0014] In order to perform various controls, the control device 30 refers to an upstream output value ILF, which is the output value of the upstream air-fuel ratio sensor 40, and a downstream output value ILR, which is the output value of the downstream air-fuel ratio sensor 50. In order to perform various controls, the control device 30 also refers to the engine speed NE detected by the speed sensor 42, the intake air amount GA detected by the air flow meter 44, the cooling water temperature THW detected by the water temperature sensor 46, etc. The control device 30 calculates the engine load factor KL based on the engine speed NE, the intake air amount GA, etc.

[0015] In this embodiment, the excess air factor λ is used as a value indicating the air-fuel ratio, and the control device 30 calculates the upstream excess air factor λF by converting the upstream output value ILF using a map, and calculates the downstream excess air factor λR by converting the downstream output value ILR using a map.

[0016] <Air-fuel ratio control> The control device 30 executes well-known air-fuel ratio control to appropriately purify exhaust gas using the three-way catalyst 22. This air-fuel ratio control includes main air-fuel ratio control, which controls the air-fuel ratio of the mixture to a target air-fuel ratio based on the output of the upstream air-fuel ratio sensor 40, and sub air-fuel ratio control, which corrects values ​​involved in the main air-fuel ratio control using a sub-correction value calculated based on the output of the downstream air-fuel ratio sensor 50. In this embodiment, the target air-fuel ratio in the main air-fuel ratio control and the sub air-fuel ratio control is basically the stoichiometric air-fuel ratio. Therefore, the target value of the air excess ratio λ in the main air-fuel ratio control and the sub air-fuel ratio control is basically "λ = 1.0".

[0017] The main air-fuel ratio control is basically as follows. The control device 30 calculates a proportional term and an integral term and a derivative term as learned values ​​from the deviation between a target excess air ratio λFt, which is a target value for the air-fuel ratio of the mixture, and a proportional gain, an integral gain, and a derivative gain that have been experimentally determined in advance. Then, PID control is performed to calculate a correction value for the currently set fuel injection amount of the fuel injector 16 from the sum of the proportional term, the integral term, and the derivative term. Note that instead of PID control, feedback control such as PI control that calculates the correction value based on the proportional term and the integral term may be performed.

[0018] The control device 30 then corrects the fuel injection amount using the calculated correction value. For example, when the upstream excess air factor λF is greater than the target excess air factor λFt and the exhaust air-fuel ratio is lean, the fuel injection amount is corrected to be increased. On the other hand, when the upstream excess air factor λF is smaller than the target excess air factor λFt and the exhaust air-fuel ratio is rich, the fuel injection amount is corrected to be decreased. By controlling the upstream excess air factor λF to approach the target excess air factor λFt through such feedback control of the air-fuel ratio, the air-fuel ratio of the mixture is controlled to be an air-fuel ratio close to the stoichiometric air-fuel ratio.

[0019] The sub air-fuel ratio control is basically as follows. The control device 30 calculates a sub feedback value SFB as a proportional term and a sub learning value SFBG including an integral term and a differential term as a learned value from the deviation between the sub target excess air ratio λRt and the downstream-side excess air ratio λR, and a predetermined proportional gain, integral gain, and differential gain. Then, PID control is performed to calculate a sub correction value, which is a correction value for the currently set target excess air ratio λFt, from the sum of the proportional term, integral term, and differential term. Note that instead of PID control, feedback control such as PI control may be performed to calculate the sub correction value based on the proportional term and the integral term.

[0020] The control device 30 then corrects the target excess air factor λFt using the calculated sub-correction value. For example, when the downstream excess air factor λR is larger than the sub-target excess air factor λRt and the exhaust air-fuel ratio is lean, the target excess air factor λFt is corrected to change to a value on the rich side. On the other hand, when the downstream excess air factor λR is smaller than the sub-target excess air factor λRt and the exhaust air-fuel ratio is rich, the target excess air factor λFt is corrected to change to a value on the lean side. The main air-fuel ratio control is performed based on the target excess air factor λFt thus corrected with the sub-correction value. The target excess air factor λFt is a value corrected using the sub-correction value calculated based on the output of the downstream air-fuel ratio sensor 50, and is a value involved in air-fuel ratio control.

[0021] <Regarding correction for output deviations of the upstream air-fuel ratio sensor> If hydrogen is contained in the exhaust gas, an output deviation occurs in which the output of the upstream air-fuel ratio sensor 40 becomes richer than the actual air-fuel ratio. If such an output deviation occurs, the air-fuel ratio of the mixture adjusted by air-fuel ratio control will shift to the lean side, which may affect the purification performance of the three-way catalyst 22. Therefore, in this embodiment, a hydrogen estimation map is prepared in advance to estimate the hydrogen concentration H2C in the exhaust gas based on the engine operating state. Then, the upstream excess air factor λF is calculated based on the hydrogen concentration H2C calculated based on the hydrogen estimation map and the upstream output value ILF.

[0022] Here, an error may occur in the hydrogen concentration H2C obtained from the hydrogen estimation map due to aging of the internal combustion engine 10 or individual differences between the internal combustion engines 10. Therefore, when such an error occurs, it is not possible to sufficiently suppress the output deviation of the upstream air-fuel ratio sensor 40 caused by the hydrogen contained in the exhaust gas.

[0023] Here, when the air-fuel ratio of the mixture is controlled to an air-fuel ratio close to the stoichiometric air-fuel ratio, even if the exhaust contains hydrogen, the hydrogen is purified when passing through the three-way catalyst 22, and therefore the output of the downstream air-fuel ratio sensor 50 is not easily affected by the hydrogen. Therefore, when air-fuel ratio control is being executed to control the air-fuel ratio of the mixture to an air-fuel ratio close to the stoichiometric air-fuel ratio, if the output of the downstream air-fuel ratio sensor 50 indicates a value close to the stoichiometric air-fuel ratio, it can be considered as follows: That is, it can be considered that the hydrogen contained in the exhaust has been purified by the three-way catalyst 22, and the output of the downstream air-fuel ratio sensor 50 is not affected by the hydrogen.

[0024] Therefore, when the above conditions are met and it is considered that the output of the downstream air-fuel ratio sensor 50 is not affected by hydrogen, the control device 30 of this embodiment executes processing to correct the output of the upstream air-fuel ratio sensor 40 based on the output of the downstream air-fuel ratio sensor 50.

[0025] The correction performed by the control device 30 of this embodiment to deal with the output deviation of the upstream air-fuel ratio sensor 40 will now be described. FIG. 2 shows the processing that is realized by the CPU 32 executing the program stored in the memory 34.

[0026] The hydrogen concentration estimation processing unit M10 calculates the hydrogen concentration H2C by referring to the hydrogen estimation map described above, based on the engine rotation speed NE and the engine load factor KL. The output deviation correction value calculation circuit M20 calculates an output deviation correction value COR, which is a value by which the base excess ratio λFb is multiplied when calculating the upstream excess air ratio λF.

[0027] 3 shows the procedure of the process executed by the output deviation correction value calculation processing unit M20. This process is realized by the CPU 32 repeatedly executing a program stored in the memory 34 at predetermined intervals while the engine is running. In the following, step numbers are represented by numbers preceded by "S."

[0028] 3, the CPU 32 determines whether or not there is a learning history of the output deviation correction value COR for the current trip (S100). The trip is the period from when the ignition switch of the vehicle equipped with the internal combustion engine 10 is turned on to when it is turned off. Furthermore, if the processing of S170 described below has already been executed for the current trip, the CPU 32 determines that there is a learning history of the output deviation correction value COR.

[0029] If it is determined that there is no learning history (S100: NO), the CPU 32 determines whether or not the learning execution conditions for the output deviation correction value COR are met (S110). In the process of S110, the CPU 32 determines that the learning execution conditions are met when, for example, all of the following conditions (a) to (d) are met:

[0030] (a): The internal combustion engine 10 has finished warming up. (b): The engine speed NE is within a predetermined range. (c): The engine load factor KL is within a predetermined range.

[0031] (b): A predetermined time has elapsed since the sub air-fuel ratio control was started. In the process of S110, when it is determined that the learning execution condition is met (S100: YES), the CPU 32 determines whether or not the upstream excess air ratio condition is met (S120). In the process of S120, the CPU 32 determines that the upstream excess air ratio condition is met when, for example, the following condition (e) is met:

[0032] (e): Air-fuel ratio control is being executed to control the air-fuel ratio of the air-fuel mixture to an air-fuel ratio close to the stoichiometric air-fuel ratio. More specifically, the CPU 32 determines that the condition (e) is satisfied when the average value of the upstream excess air ratio λF calculated within a predetermined period is a value within a predetermined range centered around the air excess ratio λ=1.

[0033] In the process of S120, when it is determined that the upstream excess air ratio condition is met (S120: YES), the CPU 32 determines whether or not the downstream output value ILR is stable (S130).

[0034] In the process of S130, the CPU 32 determines that the downstream output value ILR is stable when, for example, the following condition (f) is satisfied. (f): The downstream-side output value ILR remains within a predetermined range for a predetermined period of time or longer. Note that "within the predetermined range" is a range that is synonymous with the output of the downstream-side air-fuel ratio sensor 50 indicating a value close to the stoichiometric air-fuel ratio, and refers to, for example, a state in which the output current of the downstream-side air-fuel ratio sensor 50 is within a predetermined range centered around "0."

[0035] In the process of S130, when it is determined that the downstream output value ILR is stable (S130: YES), the CPU 32 calculates the output difference ΔIL based on the following equation (1) (S140).

[0036] ΔIL = ILRAV - ILFAV…(1) ILRAV: Average value of downstream excess air ratio λR within a specified period ILFAV: Average value of upstream excess air ratio λF within a specified period The higher the hydrogen concentration in the exhaust gas, the greater the deviation of the upstream output value ILF toward the rich side, and therefore the absolute value of the output difference ΔIL becomes larger in the negative direction. Therefore, the greater the deviation of the upstream output value ILF toward the rich side, the greater the positive value of the output difference ΔIL becomes.

[0037] Next, the CPU 32 calculates the reference output difference ΔILref (S150). The reference output difference ΔILref is the output difference ΔIL calculated when all of the above conditions (a) to (f) are met in the reference internal combustion engine used to acquire the test data for creating the above-mentioned hydrogen estimation map. The memory 34 stores map data that describes the correspondence between the engine speed NE and engine load factor KL when the reference output difference ΔILref is calculated and the reference output difference ΔILref. In the processing of S150, the CPU 32 calculates the reference output difference ΔILref by referring to the map data based on the engine speed NE and engine load factor KL.

[0038] Next, the CPU 32 calculates the output difference ratio ΔILretio based on the following equation (2) (S160). ΔILretio=ΔIL / ΔILref…(2) ΔIL: Output difference calculated in S140 processing ΔILref: Reference output difference calculated by processing in S150 As described above, the greater the deviation of the upstream output value ILF toward the rich side, the greater the positive value of the output difference ΔIL. Therefore, the greater the deviation of the upstream output value ILF toward the rich side, the greater the positive value of the output difference ratio ΔILretio.

[0039] Next, the CPU 32 updates the output deviation correction value COR based on the following equation (3) (S170). COR=CORpre+{(ΔILretio-CORpre) / 2}…(3) CORpre: Output deviation correction value calculated in the previous S170 process ΔILretio: Output difference ratio calculated by S160 processing As shown in equation (3), the output deviation correction value COR is a smoothed value of the output difference ratio ΔILretio.

[0040] When the processing of S170 is completed, or when a positive judgment is made in the processing of S100, or when a negative judgment is made in any of the processing of S100, S110, S120, and S130, the CPU 32 temporarily terminates this processing.

[0041] 2 calculates the base excess ratio λFb by referring to a preset conversion map based on the upstream output value ILF and the hydrogen concentration HC calculated by the hydrogen concentration estimation processor M10. The upstream excess air ratio calculation processor M30 then calculates a value by multiplying the base excess ratio λFb by the output deviation correction value COR calculated by the output deviation correction value calculation processor M20. The upstream excess air ratio calculation processor M30 then substitutes the calculated value for the upstream excess air ratio λF.

[0042] The sub learning value calculation processing unit M50 calculates the sub learning value SFBG through the sub air-fuel ratio control described above. Furthermore, when the output deviation correction value calculation processing unit M20 updates the output deviation correction value COR, the sub learning value calculation processing unit M50 executes a correction process to correct the sub learning value SFBG. More specifically, the sub learning value calculation processing unit M50 corrects the sub learning value SFBG based on the following equation (4):

[0043] SFBG=SFBGpre-(COR / CORpre-1)…(4) SFBGpre: Sub-learning value before correction COR: Updated output deviation correction value CORpre: Output deviation correction value before update The sub-FB value calculation processing unit M60 calculates the sub-FB value SFB through the sub-air-fuel ratio control described above.

[0044] The target excess air ratio calculation circuit M70 calculates the target excess air ratio λFt based on the following equation (5). λFt=λFtb×{1 / (1+SFB+SFBG)}…(5) λFtb: Target excess air ratio base value SFB: Sub-FB value SFBG: Sub-learning value In this embodiment, the target excess air ratio base value λFtb is set to "1", but the target excess air ratio base value λFtb may be variably set based on the engine operating state.

[0045] <Actions and Effects of This Embodiment> (1) In the present embodiment, when air-fuel ratio control is being performed to control the air-fuel ratio of the mixture to an air-fuel ratio near the stoichiometric air-fuel ratio based on the output of the upstream air-fuel ratio sensor 40, if the output of the downstream air-fuel ratio sensor 50 indicates a value near the stoichiometric air-fuel ratio, the above-described correction process is executed. That is, a correction process is executed to make a correction corresponding to the output deviation of the upstream air-fuel ratio sensor based on the output of the upstream air-fuel ratio sensor 40 and the output of the downstream air-fuel ratio sensor 50. In this correction process, the base excess ratio λFb calculated based on the output value of the upstream air-fuel ratio sensor 40 is corrected by the output deviation correction value COR calculated based on the output of the upstream air-fuel ratio sensor 40 and the output of the downstream air-fuel ratio sensor 50. In this way, a correction corresponding to the output deviation of the upstream air-fuel ratio sensor 40 is made using the output of the downstream air-fuel ratio sensor 50, which is less susceptible to the influence of hydrogen, so that a correction corresponding to the output deviation of the upstream air-fuel ratio sensor 40 can be made with high accuracy.

[0046] (2) The difference between the output of the upstream side air-fuel ratio sensor 40 and the output of the downstream side air-fuel ratio sensor 50 reflects the magnitude of the output deviation of the upstream side air-fuel ratio sensor 40 . Therefore, as the above-mentioned correction process, the CPU 32 calculates the output difference ΔIL, which is the difference between the output of the upstream side air-fuel ratio sensor 40 and the output of the downstream side air-fuel ratio sensor 50. Then, the CPU 32 performs the above-mentioned correction using the output deviation correction value COR calculated using this output difference ΔIL. Therefore, the correction corresponding to the output deviation of the upstream side air-fuel ratio sensor 40 can be performed appropriately in accordance with the magnitude of the output deviation.

[0047] (3) Even if an output deviation due to hydrogen in the exhaust gas occurs in the upstream air-fuel ratio sensor 40, if the output of the downstream air-fuel ratio sensor 50 indicates a value close to the stoichiometric air-fuel ratio, the following state is reached. That is, the error in the overall air-fuel ratio control caused by the output deviation of the upstream air-fuel ratio sensor 40 is absorbed by the sub-correction value calculated in the sub air-fuel ratio control. Therefore, when making a correction corresponding to the output deviation of the upstream air-fuel ratio sensor 40, if the sub-correction value is not modified, the sub-correction value may become excessively large.

[0048] Therefore, the CPU 32 executes the following processing when performing sub air-fuel ratio control that corrects a value involved in air-fuel ratio control of the air-fuel ratio of the mixture using a sub correction value calculated based on the output of the downstream air-fuel ratio sensor 50. That is, when executing correction processing corresponding to the output deviation of the upstream air-fuel ratio sensor 40, the CPU 32 also executes processing to correct the sub learned value SFBG, which is the sub correction value, based on the above equation (4). Therefore, when performing correction corresponding to the output deviation of the upstream air-fuel ratio sensor 40, the sub learned value SFBG, which is one of the sub correction values, can be set to an appropriate value.

[0049] (4) In an internal combustion engine 10 that uses hydrogen as fuel, the hydrogen concentration in the exhaust gas increases when unburned hydrogen is produced. Therefore, deviations in the output of the upstream air-fuel ratio sensor 40 are likely to occur due to hydrogen in the exhaust gas. In this regard, in the present embodiment, the above-described correction process is executed, so that accurate corrections can be made to address deviations in the output of the upstream air-fuel ratio sensor 40 even in such an internal combustion engine 10 that uses hydrogen as fuel.

[0050] <Example of change> The above embodiment can be modified as follows. In this embodiment, the base excess rate λFb calculated based on the upstream output value ILF is corrected to compensate for the output deviation of the upstream air-fuel ratio sensor 40. However, other values ​​may also be corrected. For example, the CPU 32 may correct the upstream output value ILF using the output deviation correction value COR. The CPU 32 may also correct the injection amount of the fuel injector 16 using the output deviation correction value COR.

[0051] The hydrogen concentration estimation processing unit M10 may be omitted, and the upstream excess air ratio calculation processing unit M30 may calculate the upstream excess air ratio λF based on the upstream output value ILF and the output deviation correction value COR.

[0052] The output deviation correction value COR may be updated multiple times during one trip. The process of S170 shown in Fig. 3 may be omitted, and the output difference ratio ΔILretio calculated in the process of S160 may be substituted for the output deviation correction value COR.

[0053] Although the output difference ratio ΔILretio was calculated, the output difference ΔIL may be simply substituted into the output deviation correction value COR. As shown in Fig. 4, the block diagram shown in Fig. 2 may be partially modified. Note that the same processing units as those shown in Fig. 2 are denoted by the same reference numerals in Fig. 4.

[0054] The hydrogen concentration estimation processing unit M15 calculates the hydrogen concentration base value H2Cb by referring to the hydrogen estimation map based on the engine rotation speed NE and the engine load factor KL, and then multiplies the hydrogen concentration base value H2Cb by a concentration deviation correction value H2CH (described later) and assigns the resulting value to the hydrogen concentration H2C.

[0055] The concentration deviation correction value calculation processing unit M25 calculates the concentration deviation correction value H2CH. As described above, the higher the hydrogen concentration in the exhaust gas, the greater the deviation of the upstream output value ILF toward the rich side, and therefore the absolute value of the upstream output value ILF becomes larger in the negative direction. Therefore, the greater the deviation of the upstream output value ILF toward the rich side, the greater the positive value of the output difference ΔIL. The greater the positive value of the output difference ΔIL, the greater the positive value of the output difference ratio ΔILretio. Therefore, the output difference ratio ΔILretio reflects the magnitude of the deviation between the estimated hydrogen concentration value obtained from the map and the actual hydrogen concentration. In other words, the greater the output difference ratio ΔILretio, the greater the deviation of the actual hydrogen concentration from the estimated hydrogen concentration value. Therefore, the concentration deviation correction value calculation processing unit M25 executes the series of processes shown in FIG. 3, and in the process of S170, updates the concentration deviation correction value H2CH based on the following equation (6) instead of the above equation (3).

[0056] H2CH=H2CHpre+{(ΔILretio-H2CHpre) / 2}…(6) H2CHpre: Density deviation correction value calculated in the previous processing of S170 ΔILretio: Output difference ratio calculated by S160 processing As shown in equation (6), the density deviation correction value H2CH is a smoothed value of the output difference ratio ΔILretio.

[0057] The upstream excess air ratio calculation processing unit M35 calculates the upstream excess air ratio λF by referring to a preset conversion map based on the upstream output value ILF and the hydrogen concentration H2C calculated by the hydrogen concentration estimation processing unit M15.

[0058] The sub learning value calculation processing unit M55 calculates the sub learning value SFBG through the sub air-fuel ratio control described above. Furthermore, when the concentration deviation correction value calculation processing unit M25 updates the concentration deviation correction value H2CH, the sub learning value calculation processing unit M55 executes processing to correct the sub learning value SFBG. More specifically, the sub learning value calculation processing unit M50 corrects the sub learning value SFBG based on the following equation (7):

[0059] SFBG=SFBGpre-(λF / λFpre-1)…(7) SFBGpre: Sub-learning value before correction λF: The upstream excess air ratio calculated after updating the concentration deviation correction value H2CH λFpre: The upstream excess air ratio calculated before updating the concentration deviation correction value H2CH The value of "λFpre" is stored in the memory in association with each upstream output value ILF before the concentration deviation correction value H2CH is updated. When correcting the sub-learned value SFBG using equation (7), the sub-learned value calculation processing unit M55 acquires the value of "λF" and the value of "λFpre" for the same upstream output value ILF. Therefore, the value of "λF / λFpre" reflects the change in the calculated value of the upstream excess air factor λF before and after the concentration deviation correction value H2CH is updated. Therefore, the sub-learned value SFBG is appropriately corrected in accordance with the update of the concentration deviation correction value H2CH. Even in this modified example, the same functions and effects as those of the above embodiment can be obtained.

[0060] When performing the correction process to deal with the output deviation of the upstream air-fuel ratio sensor 40, the sub-learned value SFBG is corrected, but the sub-FB value SFB may also be corrected. The correction process for the sub-learned value SFBG may be omitted.

[0061] The fuel injection valve 16 is not limited to one that injects fuel into the combustion chamber 14. For example, it may be a fuel injection valve that injects fuel into the intake port of the internal combustion engine 10. The internal combustion engine 10 may be an internal combustion engine that uses a fuel other than hydrogen.

[0062] The control device 30 is not limited to a device equipped with a CPU and memory and executing software processing. For example, the control device 30 may be equipped with a dedicated hardware circuit, such as an ASIC, that performs hardware processing on at least a portion of the software processing performed in the above embodiments. That is, the control device 30 may include a processing circuit having any of the following configurations (a) to (c): (a) a processing circuit equipped with one or more processing devices that execute all of the above processing according to a program and one or more program storage devices, such as a ROM, that store the program; (b) a processing circuit equipped with one or more processing devices and one or more program storage devices that execute part of the above processing according to a program, and one or more dedicated hardware circuits that execute the remaining processing; (c) a processing circuit equipped with one or more dedicated hardware circuits that execute all of the above processing. Program storage devices, i.e., computer-readable media, include any available media that can be accessed by a general-purpose or dedicated computer. [Explanation of symbols]

[0063] 10...Internal combustion engine 12...Intake passage 14...Combustion chamber 16...Fuel injection valve 18...Spark plug 20...Exhaust passage 22...Three-way catalyst 30...Control device 32...CPU 34...Memory 40...Upstream air-fuel ratio sensor 42...Rotational speed sensor 44...Air flow meter 46...Water temperature sensor 50...Downstream air-fuel ratio sensor

Claims

1. A control device applied to an internal combustion engine including a three-way catalyst provided in an exhaust passage, an upstream air-fuel ratio sensor provided on the exhaust upstream side of the three-way catalyst, and a downstream air-fuel ratio sensor provided on the exhaust downstream side of the three-way catalyst, When an air-fuel ratio control is being performed to control the air-fuel ratio of the air-fuel mixture to an air-fuel ratio close to the stoichiometric air-fuel ratio based on the output of the upstream air-fuel ratio sensor, if the output of the downstream air-fuel ratio sensor indicates a value close to the stoichiometric air-fuel ratio, a correction process is performed to make a correction corresponding to an output deviation of the upstream air-fuel ratio sensor based on the output of the upstream air-fuel ratio sensor and the output of the downstream air-fuel ratio sensor. Control device for internal combustion engines.

2. The correction process is a process for correcting an excess air ratio calculated based on an output value of the upstream air-fuel ratio sensor. The control device for an internal combustion engine according to claim 1.

3. The correction process is a process of calculating a difference between the output of the upstream air-fuel ratio sensor and the output of the downstream air-fuel ratio sensor and performing the correction. The control device for an internal combustion engine according to claim 1.

4. performing sub-air-fuel ratio control to correct a value involved in the air-fuel ratio control using a sub-correction value calculated based on the output of the downstream-side air-fuel ratio sensor; When the correction process is performed, a process for correcting the sub-correction value is also performed. The control device for an internal combustion engine according to claim 1.

5. The internal combustion engine is a hydrogen-fueled internal combustion engine. The control device for an internal combustion engine according to claim 1.

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