Catalyst deterioration detection device for internal combustion engines

Abstract

To provide a catalyst deterioration detection device for an internal combustion engine capable of accurately determining whether a catalyst deteriorates.SOLUTION: A catalyst deterioration detection device for an internal combustion engine includes: an air-fuel ratio sensor provided in an exhaust passage of the internal combustion engine; a learning section for learning responsiveness of the air-fuel ratio sensor on the basis of an output value from the air-fuel ratio sensor when fuel injection amount of the internal combustion engine is changed; a calculation section for correcting the output value from the air-fuel ratio sensor on the basis of the learning and calculating oxygen storage amount of a catalyst provided in the exhaust passage on the basis of the corrected output value; and a determination section for determining whether the catalyst deteriorates on the basis of the oxygen storage amount of the catalyst.SELECTED DRAWING: Figure 4

Description

[Technical field]

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

[0002] A catalyst is provided in the exhaust passage to purify exhaust gas discharged from an internal combustion engine. There is a technique for detecting catalyst deterioration using an air-fuel ratio sensor provided upstream of the catalyst and an oxygen sensor provided downstream of the catalyst (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2004-346767 A Summary of the Invention [Problem to be solved by the invention]

[0004] A catalyst has the function of storing oxygen. Catalyst deterioration may be determined based on the amount of oxygen stored in the catalyst. The calculation result of the amount of oxygen changes depending on the responsiveness of the air-fuel ratio sensor. As a result, there is a risk of erroneously detecting catalyst deterioration. Therefore, the object of the present invention is to provide a catalyst deterioration detection device for an internal combustion engine that can accurately determine whether or not the catalyst has deteriorated. [Means for solving the problem]

[0005] The above object is to provide an exhaust passage for an internal combustion engine. and outputs an output value according to the air-fuel ratio. An air-fuel ratio sensor and a fuel injection amount of the internal combustion engine The air-fuel ratio is changed by varying between a first amount and a second amount. a learning unit that learns the responsiveness of the air-fuel ratio sensor based on an output value of the air-fuel ratio sensor at the time of detection of the exhaust gas from the exhaust gas; a calculation unit that corrects the output value of the air-fuel ratio sensor based on the learning and calculates an oxygen storage amount of a catalyst provided in the exhaust passage based on the corrected output value; and a determination unit that determines whether the catalyst has deteriorated based on the oxygen storage amount of the catalyst. an output value of the air-fuel ratio sensor becomes a first value in response to the fuel injection amount being the first amount, and an output value of the air-fuel ratio sensor becomes a second value in response to the fuel injection amount being the second amount, and the learning unit learns the responsiveness of the air-fuel ratio sensor based on a gradient of the output value when the output value of the air-fuel ratio sensor changes between the first value and the second value, or learns the responsiveness of the air-fuel ratio sensor based on a time during which the output value of the air-fuel ratio sensor changes between the first value and the second value.This can be achieved by a catalyst deterioration detection device for an internal combustion engine. Effect of the Invention

[0006] It is possible to provide a catalyst deterioration detection device for an internal combustion engine that can ensure a sense of deceleration. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram illustrating an engine system. [Diagram 2] FIG. 2 is a schematic diagram illustrating the relationship between the amount of oxygen stored in the catalyst and emissions in the exhaust gas. [Diagram 3] FIG. 3 is a diagram illustrating an example of a time chart. [Figure 4] FIG. 4 is a diagram illustrating an example of a time chart. [Diagram 5] FIG. 5 is a flowchart illustrating the processing performed by the ECU. [Figure 6] FIG. 6 is a diagram illustrating a time chart in the modified example. [Figure 7] FIG. 7 is a diagram illustrating a time chart in the second embodiment. [Figure 8] FIG. 8 is a flowchart illustrating the processing executed by the ECU. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] First Embodiment Hereinafter, a catalyst deterioration detection device for an internal combustion engine according to the present embodiment will be described with reference to the drawings. Fig. 1 is a schematic diagram illustrating an engine system 100. The engine system 100 has an internal combustion engine 10, an air-fuel ratio sensor 20, a catalyst 22, an oxygen sensor 24, and an ECU (Electronic Control Unit) 50. The internal combustion engine 10 may be a gasoline engine or a diesel engine.

[0009] As shown in FIG. 1, the internal combustion engine 10 has a cylinder block 40 , a cylinder head 41 , a fuel injector 42 , a piston 44 , a crankshaft 46 , an intake valve 47 , an exhaust valve 48 , and a spark plug 49 .

[0010] The cylinder block 40 is provided with a water jacket 40a and a crank angle sensor 25. The water jacket 40a stores cooling water. A crankshaft 46 is housed within the cylinder block 40. One end of a connecting rod 45 is connected to a piston 44, and the other end is connected to the crankshaft 46. A combustion chamber 43 is defined by the cylinder block 40, the cylinder head 41, and the piston 44. The crank angle sensor 25 detects the rotation angle of the crankshaft 46.

[0011] The cylinder head 41 is attached on top of the cylinder block 40. The cylinder head 41 is provided with an intake valve 47, an exhaust valve 48, a fuel injector 42, and an ignition plug 49. The fuel injector 42 performs in-cylinder injection. The fuel injector 42 is provided in the intake passage 12, and may perform port injection.

[0012] The intake passage 12 and the exhaust passage 14 are connected to the cylinder head 41. In the intake passage 12, an air cleaner 15, an air flow meter 16, and a throttle valve 18 are provided in this order from the upstream side. The air cleaner 15 removes dust and other particles from the air in the intake passage 12 to purify the air. The air flow meter 16 detects the flow rate of air in the intake passage 12. The throttle valve 18 adjusts the flow rate of air. The larger the opening of the throttle valve 18, the greater the air flow rate. The smaller the opening of the throttle valve 18, the smaller the air flow rate.

[0013] In the exhaust passage 14, an air-fuel ratio (A / F) sensor 20, a catalyst 22, and an oxygen sensor 24 (O2 sensor) are provided in this order from the upstream side. The air-fuel ratio sensor 20 detects, for example, the air-fuel ratio linearly and outputs an electric signal according to the air-fuel ratio. The catalyst 22 is, for example, a three-way catalyst, and contains ceria (CeO2) and the like.

[0014] The oxygen sensor 24 is, for example, a sensor using a zirconia element, and detects the air-fuel ratio. The oxygen sensor 24 switches the electric signal (voltage) around the stoichiometric air-fuel ratio (14.7). For example, the voltage output by the oxygen sensor 24 is high at an air-fuel ratio higher than the stoichiometric air-fuel ratio (lean) and is low at an air-fuel ratio lower than the stoichiometric air-fuel ratio (rich). An air-fuel ratio sensor may be provided downstream of the catalyst 22 instead of the oxygen sensor 24.

[0015] 1, one catalyst 22 is provided in one exhaust passage 14, an air-fuel ratio sensor 20 is provided upstream of the catalyst 22, and an oxygen sensor 24 is provided downstream of the catalyst 22. For example, the internal combustion engine 10 may be provided with a plurality of branched exhaust passages 14 corresponding to the number of cylinders of the internal combustion engine 10. The air-fuel ratio sensor 20, the catalyst 22, and the oxygen sensor 24 may be provided in each of the branched portions of the exhaust passage 14. Also, the air-fuel ratio sensor 20, the catalyst 22, and the oxygen sensor 24 may be provided in a portion of the exhaust passage 14 where the branched passages merge into one or two passages.

[0016] Air in the intake passage 12 is introduced into the combustion chamber 43 in response to the opening of the intake valve 47. The fuel injector 42 injects fuel into the combustion chamber 43. A mixture of fuel and air is generated in the combustion chamber 43. The spark plug 49 ignites the mixture. The combustion of the mixture causes the piston 44 to move downward. Power is transmitted from the piston 44 to the crankshaft 46, which then rotates. The rotation of the crankshaft 46 and the combustion of the mixture cause the piston 44 to reciprocate up and down. When the exhaust valve 48 opens, the exhaust gas after combustion is discharged into the exhaust passage 14, purified by the catalyst 22, and discharged outside the vehicle.

[0017] The catalyst 22 has the function of storing and releasing oxygen. When the air-fuel ratio of the mixture is lean, the catalyst 22 adsorbs and retains the oxygen in the exhaust. Nitrogen oxides (NOx) in the exhaust are reduced. When the air-fuel ratio is rich, the catalyst 22 releases the retained oxygen into the exhaust. Carbon monoxide (CO), hydrocarbons (HC), etc. in the exhaust are oxidized.

[0018] As the catalyst 22 deteriorates, the oxygen storage capacity (OSC) of the catalyst 22 decreases. As the amount of oxygen held by the catalyst 22 decreases, it becomes difficult to sufficiently purify NOx. In addition, the amount of oxygen released by the catalyst 22 also decreases. As a result, it becomes difficult to sufficiently purify CO and the like. Therefore, the deterioration of the catalyst 22 is judged based on the OSC of the catalyst 22.

[0019] 2 is a schematic diagram illustrating the relationship between the amount of oxygen stored in the catalyst 22 and emissions in the exhaust. The horizontal axis indicates the maximum value Cmax of the amount of oxygen stored in the catalyst 22. The vertical axis on the right indicates the amount of non-methane hydrocarbons (NHMC) in the exhaust. The vertical axis on the left indicates the amount of NOx in the exhaust.

[0020] The larger Cmax shown by the curve in Figure 2 is, the lower the NMHC and NOx in the exhaust gas. This is because the exhaust gas is purified by the catalyst 22. On the other hand, the lower Cmax is, the higher the NMHC and NOx in the exhaust gas. This is because the catalyst 22 deteriorates and the exhaust gas is not sufficiently purified. Cth is the threshold value for the amount of oxygen stored. When the maximum value Cmax of the amount of oxygen stored becomes equal to or less than the threshold value Cth, the catalyst 22 is determined to be deteriorated.

[0021] The ECU 50 includes a central processing unit (CPU), a random access memory (RAM), a read only memory (ROM), and other storage devices, and performs various controls by executing programs stored in the ROM and the storage devices.

[0022] The ECU 50 acquires the air flow rate detected by the air flow meter 16 and the rotation angle of the crankshaft 46 detected by the crank angle sensor 25. The ECU 50 controls the fuel injection amount from the fuel injector 42, the ignition timing of the spark plug 49, and the opening degree of the throttle valve 18. The ECU 50 receives electrical signals from the air-fuel ratio sensor 20 and the oxygen sensor 24. The ECU 50 acquires the air-fuel ratio of the internal combustion engine 10 based on the electrical signal input from the air-fuel ratio sensor 20.

[0023] The ECU 50 controls the air-fuel ratio by increasing or decreasing the fuel injection amount. The ECU 50 switches the air-fuel ratio between rich and lean according to the output value (voltage) of the oxygen sensor 24. The ECU 50 functions as a learning unit that learns the responsiveness of the air-fuel ratio sensor 20 when the fuel injection amount is changed. The ECU 50 functions as a calculation unit that calculates the maximum oxygen storage amount Cmax of the catalyst 22 from the output value of the air-fuel ratio sensor 20 when the air-fuel ratio is made rich and lean. The ECU 50 functions as a determination unit that determines whether the catalyst 22 has deteriorated by comparing Cmax with the threshold value Cth in FIG. 2.

[0024] 3 is a time chart illustrating an example in which the ECU 50 controls the air-fuel ratio and calculates Cmax. From the top, FIG. 3 shows the air-fuel ratio (A / F), the output voltage of the oxygen sensor 24, and the oxygen storage amount (OSA) of the catalyst 22.

[0025] The upper part of Fig. 3 is a time chart of the air-fuel ratio. The dashed line is the target value of the air-fuel ratio (target A / F) determined by the ECU 50. The broken line is the air-fuel ratio (actual A / F) when there is little response delay in the air-fuel ratio sensor 20, which is measured in advance, for example, when the air-fuel ratio sensor 20 is manufactured. The solid line is the air-fuel ratio (A / F output value) detected by the air-fuel ratio sensor 20 mounted on the vehicle.

[0026] As shown in the middle of FIG. 3, the output voltage of the oxygen sensor 24 switches between approximately 0V and approximately 1V. When the air-fuel ratio is lean, the catalyst 22 stores oxygen in the exhaust, causing the oxygen concentration in the exhaust to decrease. The output voltage of the oxygen sensor 24 is higher than when the air-fuel ratio is lean, at approximately 1V. When the OSC of the catalyst 22 reaches its limit, oxygen is not stored in the catalyst 22 and remains in the exhaust, causing the oxygen concentration in the exhaust to increase. The output voltage of the oxygen sensor 24 drops from 1V. In response to the change in the output voltage of the oxygen sensor 24, the ECU 50 switches the target A / F from lean to rich.

[0027] When the air-fuel ratio is rich, the catalyst 22 releases oxygen into the exhaust gas, causing the oxygen concentration in the exhaust gas to rise. The output voltage of the oxygen sensor 24 is approximately 0V. When the OSC of the catalyst 22 reaches its limit, the amount of oxygen released from the catalyst 22 decreases. The oxygen concentration in the exhaust gas decreases, and the output voltage of the oxygen sensor 24 increases. In response to the change in the output voltage of the oxygen sensor 24, the ECU 50 switches the target A / F from rich to lean. The ECU 50 controls the amount of fuel injection in accordance with the target A / F, and adjusts the air-fuel ratio to the target A / F.

[0028] 3 shows a schematic diagram of the oxygen storage amount (OSA) of the catalyst 22. If the air-fuel ratio is lean, the catalyst 22 stores oxygen, so the oxygen storage amount increases. If the air-fuel ratio is rich, the catalyst 22 releases oxygen, so the oxygen storage amount decreases.

[0029] The ECU 50 calculates the oxygen storage amount (OSA) using the following formula. OSA=0.23×ΔA / F×Fuel injection amount (1) ΔA / F is the difference between the air-fuel ratio detected by the air-fuel ratio sensor 20 and the stoichiometric air-fuel ratio, and 0.23 is the mass fraction of oxygen in air.

[0030] The ECU 50 calculates the amount of oxygen stored in the catalyst 22, X1, by integrating the OSA during a lean period, such as P1 in Fig. 3. The ECU 50 calculates the amount of oxygen released from the catalyst 22, X2, by integrating the OSA during a rich period, such as P2 in Fig. 3.

[0031] The ECU 50 calculates the maximum oxygen storage amount Cmax as the average value of the oxygen storage amount X1 and the oxygen release amount X2. That is, Cmax is expressed by the following formula. Cmax = (X1 + X2) / 2 (2)

[0032] As described above, an abnormality in the catalyst 22 is detected by comparing the calculated Cmax with the threshold value Cth in Fig. 2. However, as shown by the solid line in the upper part of Fig. 3, the A / F output value lags behind the target A / F and the actual A / F.

[0033] The OSA of the catalyst 22 is calculated by the above formula (1). Due to the response delay of the air-fuel ratio sensor 20, ΔA / F in formula (1) becomes a smaller value, and OSA also becomes smaller, compared to the case where there is no response delay. Cmax calculated by formula (2) also becomes smaller. As Cmax becomes smaller, it may become smaller than the threshold value Cth in FIG. 2. The catalyst 22 is determined to be abnormal. For example, even if the catalyst 22 has sufficient purification capacity, Cmax may become smaller than the threshold value Cth due to the response delay of the air-fuel ratio sensor 20, and it may be determined to be abnormal. In this embodiment, the responsiveness of the air-fuel ratio sensor 20 is learned, so that the abnormality of the catalyst 22 is accurately determined.

[0034] 4 is a diagram illustrating a time chart, and is an example including learning of the responsiveness of the air-fuel ratio sensor 20. From the top, it shows a basic fuel injection amount, a target air-fuel ratio (target A / F) and the corresponding fuel injection amount, and an output value (A / F output value) of the air-fuel ratio sensor 20. In period P4, feedback control of the air-fuel ratio is performed. Period P3 is located immediately before period P4, and learning of the responsiveness of the air-fuel ratio sensor 20 is performed.

[0035] In period P3, the ECU 50 does not determine a target A / F, but forcibly changes the air-fuel ratio by changing the basic fuel injection amount between F1 and F2. F1 corresponds to an air-fuel ratio of 14.1, for example. F2 corresponds to an air-fuel ratio of 15.1, for example, and is smaller than F1. As the basic fuel injection amount changes from F1 to F2, the A / F output value changes from 14.1 to 15.1. Due to a delay in the response of the air-fuel ratio sensor 20, it takes time T1 for the A / F output value to approach 15.1 from 14.1. The A / F output value is close to 15.1 for time T2, and is saturated at 15.1.

[0036] In response to the change in the basic fuel injection amount from F2 to F1, the A / F output value changes from 15.1 to 14.1. Due to a delay in the response of the air-fuel ratio sensor 20, it takes time T3 for the A / F output value to approach 14.1 from 15.1. The A / F output value is close to 14.1 for time T4 and saturates at 14.1. The ECU 50 switches the basic fuel injection amount from F1 to F2 and from F2 to F1, for example, twice, within the period P3, to learn the response of the air-fuel ratio sensor 20. Specifically, the ECU 50 acquires the time (T1 and T2) until the A / F output value reaches a target value (for example, 15.1 and 14.1), the rate of change (slope) of the A / F output value until it reaches the target value, and the like.

[0037] In period P4 after period P3, the ECU 50 changes the target A / F between, for example, 14.1 and 15.1, and sets the fuel injection amount to a value corresponding to the target A / F, thereby performing feedback control of the air-fuel ratio. The fuel injection amount changes between F3 and F4. F3 is the fuel injection amount corresponding to an air-fuel ratio of 14.1. F4 is the fuel injection amount corresponding to an air-fuel ratio of 15.1, and is smaller than F3. The A / F output value changes with a delay from the target A / F. In period P4, the ECU 50 changes the air-fuel ratio twice, from 14.1 to 15.1 and from 15.1 to 14.1.

[0038] The ECU 50 corrects the A / F output value based on the learning. Figure 4During this period, times such as T5 and T7 where the A / F output value changes greatly are ignored, and only the A / F output values ​​close to the target value are used, such as at times T6 and T8. As another example, the slope of the actual A / F (the broken line at the top of Figure 3) during times where the A / F output value changes greatly is obtained, and a value calculated from this slope is used in place of the A / F output value during times T5 and T7. As yet another example, the time until the A / F output value reaches the target value (for example, T1) is determined, and the actual A / F value corresponding to this time is substituted for the A / F output value. Using the corrected A / F output value results in a large ΔA / F.

[0039] Fig. 5 is a flowchart illustrating the process performed by the ECU 50. The ECU 50 changes the fuel injection amount, for example, between F1 and F2 in Fig. 4 (step S10, period P3 in Fig. 4). The ECU 50 learns the responsiveness of the air-fuel ratio sensor 20 (step S12).

[0040] The ECU 50 sets the target A / F to, for example, 14.1 and 15.1 as shown in FIG. 4, and controls the fuel injection amount so that the target A / F is realized (step S14, period P4 in FIG. 4). The ECU 50 calculates the OSA using equation (1), and calculates the maximum oxygen storage amount Cmax using equation (2) (step S16). At this time, the A / F output value is corrected based on learning of the responsiveness of the air-fuel ratio sensor 20, and the corrected value is substituted into equation (1) to calculate the OSA. The ECU 50 calculates the oxygen storage amount X1 and the oxygen release amount X2 by integrating the OSA, and calculates Cmax using equation (2). The accuracy of Cmax can be improved by learning the responsiveness of the air-fuel ratio sensor 20 and correcting the A / F output value.

[0041] The ECU 50 determines whether Cmax is less than the threshold value Cth (step S18). If the determination is affirmative (Yes), the ECU 50 determines that the catalyst 22 is abnormal (step S20). If the determination is negative (No), the ECU 50 determines that the catalyst 22 is normal (step S22). This ends the process.

[0042] According to the first embodiment, the ECU 50 learns the responsiveness of the air-fuel ratio sensor 20 when the fuel injection amount is changed. The ECU 50 corrects the output value of the air-fuel ratio sensor 20 based on the learning. The ECU 50 calculates OSA and Cmax using the corrected value. By correcting the output value, the absolute value of ΔA / F in the formula (1) is likely to become larger than before the correction. The OSA also becomes a large value, and the absolute values ​​of X1 and X2 obtained from the integration of the OSA become larger. Compared to Cmax without correction, Cmax after correction becomes larger. In other words, Cmax shifts to the right in FIG. 2. Therefore, Cmax becomes equal to or larger than the threshold value Cth, and the catalyst 22 is likely to be determined to be normal (step S22 in FIG. 5). It is possible to suppress the catalyst 22 having a purification ability from being erroneously determined to be abnormal. It is possible to accurately determine whether the catalyst 22 is deteriorated or not.

[0043] In period P3 in FIG. 4, the ECU 50 changes the basic fuel injection amount without determining a target A / F. This suppresses the influence of feedback control of the air-fuel ratio, and allows learning of the responsiveness of the air-fuel ratio sensor 20 to changes in the fuel injection amount. In period P4, the ECU 50 determines a target A / F, feedback controls the air-fuel ratio, and sets the fuel injection amount to F3 and F4. During the feedback control of the air-fuel ratio, the ECU 50 determines whether the catalyst 22 is abnormal. By learning the responsiveness in period P3 immediately before period P4, the accuracy of determining whether the catalyst 22 is abnormal is improved.

[0044] 4, the basic fuel injection amount is switched between F1 and F2 multiple times. The ECU 50 learns the responsiveness of the air-fuel ratio sensor 20 from all of the multiple switchings, thereby improving the accuracy of abnormality determination. The responsiveness may be learned from one switching.

[0045] In the period P4 in Fig. 4, the fuel injection amount is switched between F3 and F4 multiple times. The ECU 50 may calculate Cmax in both of the multiple switchings, or may calculate Cmax in one of the multiple switchings. For example, the fuel injection amount may be switched multiple times, and the average value of Cmax for each switching may be compared with the threshold value Cth. This improves the accuracy of abnormality determination.

[0046] The basic fuel injection amount F1 in the period P3 may be a value corresponding to an air-fuel ratio of 14.1 or may be another value. The basic fuel injection amount F2 may be a value corresponding to an air-fuel ratio of 15.1 or may be another value. The target A / F in the period P4 may be 14.1 and 15.1 or may be a value other than these.

[0047] (Modification) FIG. 6 is a diagram illustrating a time chart in the modified example. In FIG. 6, in addition to FIG. 4, a time chart of a fuel cut flag (F / C flag) is shown at the top. In a period P3 for learning the responsiveness, the ECU 50 switches the F / C flag between on and off, for example, four times. The basic fuel injection amount F2 is the fuel injection amount when the F / C flag is on, and is, for example, 0. The ECU 50 performs the process of FIG. 5 in the modified example as well. In step S14 in FIG. 5, the ECU 50 learns the responsiveness of the air-fuel ratio sensor 20 when the F / C flag is switched between on and off.

[0048] <Second embodiment> 7 is a diagram illustrating a time chart in the second embodiment. In the second embodiment, periods P5 and P6 are arranged in this order. The first half of period P5 is designated as P5a. The first half of period P6 is designated as P6a. During periods P5a and P6a, learning of the responsiveness of the air-fuel ratio sensor 20 is performed.

[0049] FIG. 8 is a flowchart illustrating the process executed by the ECU 50. The process of FIG. 8 includes step S24 in addition to the process of FIG. 5. The ECU 50 does not determine a target A / F, and sets the basic fuel injection amount to F2. The ECU 50 learns the responsiveness of the air-fuel ratio sensor 20 when the air-fuel ratio becomes lean from the A / F output value (steps S10 and S12 of FIG. 8, period P5a of FIG. 7). The ECU 50 sets the target A / F to, for example, 15.1, and sets the fuel injection amount to F4 corresponding to the target A / F (step S14, period P5).

[0050] The ECU 50 determines whether or not the learning of responsiveness and the control of the air-fuel ratio to the target A / F have been performed on both the lean side and the rich side of the air-fuel ratio (step S24). Here, the control on the rich side has not ended. Therefore, the determination is negative, and the ECU 50 returns to step S10.

[0051] The ECU 50 does not determine a target A / F, and sets the basic fuel injection amount to F1. From the A / F output value, the responsiveness of the air-fuel ratio sensor 20 when the air-fuel ratio becomes rich is learned (steps S10 and S12, period P6a). The ECU 50 sets the target A / F to, for example, 14.1, and sets the fuel injection amount to F4 corresponding to the target A / F (step S14, period P6).

[0052] The ECU 50 determines whether learning of responsiveness and control of the air-fuel ratio to the target A / F have been performed on both the lean side and the rich side of the air-fuel ratio (step S24). The determination here is positive, and the ECU 50 proceeds to step S16.

[0053] The ECU 50 corrects the A / F output values ​​during periods P6 and P8, and calculates Cmax from the A / F output values ​​using equations (1) and (2) (step S16). The ECU 50 compares Cmax with a threshold value Cth to determine whether the catalyst 22 has deteriorated (steps S18, S20, and S22).

[0054] According to the second embodiment, the catalyst 22 having a purification ability is prevented from being erroneously determined to be abnormal. It is possible to determine whether the catalyst 22 has deteriorated with high accuracy. When the air-fuel ratio is changed once to the lean side and once to the rich side, the responsiveness is learned and the abnormality is determined. The processing speed is improved compared to the first embodiment.

[0055] Although a preferred embodiment of the present invention has been described in detail above, the present invention is not limited to such a specific embodiment, and various modifications and variations are possible within the scope of the gist of the present invention described in the claims. [Explanation of symbols]

[0056] 10 Internal combustion engine 12 Intake passage 14 Exhaust passage 15 Air cleaner 16 Air flow meter 18 Throttle valve 20 Air-fuel ratio sensor 22 Catalyst 24 Oxygen sensor 25 Crank angle sensor 40 Cylinder block 40a Water Jacket 41 Cylinder head 42 Fuel injection valve 43 Combustion chamber 44 Piston 45 Connecting rod 46 Crankshaft 47 Intake valve 48 Exhaust valve 49 Spark plug 50 ECU 100 Engine System

Claims

[Claim 1] an air-fuel ratio sensor provided in an exhaust passage of the internal combustion engine and outputting an output value corresponding to the air-fuel ratio; a learning unit that learns a responsiveness of the air-fuel ratio sensor based on an output value of the air-fuel ratio sensor when the air-fuel ratio changes by changing a fuel injection amount of the internal combustion engine between a first amount and a second amount; a calculation unit that corrects an output value of the air-fuel ratio sensor based on the learning, and calculates an oxygen storage amount of a catalyst provided in the exhaust passage based on the corrected output value; A determination unit that determines whether the catalyst is deteriorated based on an oxygen storage amount of the catalyst, the output value of the air-fuel ratio sensor becomes a first value in response to the fuel injection amount being the first amount, the output value of the air-fuel ratio sensor becomes a second value in response to the fuel injection amount being the second amount, a learning unit that learns the responsiveness of the air-fuel ratio sensor based on a gradient of the output value of the air-fuel ratio sensor when the output value of the air-fuel ratio sensor changes between the first value and the second value, or that learns the responsiveness of the air-fuel ratio sensor based on a time over which the output value of the air-fuel ratio sensor changes between the first value and the second value.

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