Deterioration degree estimation system

Abstract

To estimate a deterioration degree of a three way catalyst while suppressing a discharge amount of NOx.SOLUTION: An air flow meter configured to detect an intake air amount of an engine, a three-way catalyst disposed in an exhaust passage of the engine and configured to store oxygen, an air fuel ratio sensor disposed in an exhaust passage on an upstream side of the three-way catalyst, a NOx sensor disposed in the exhaust passage on a downstream side of the three-way catalyst and configured to detect an amount of ammonia in the exhaust, and an estimation device configured to estimate a degree of deterioration of the three-way catalyst; The estimation device includes: an acquisition unit which acquires a detected rich air-fuel ratio which is a detected air-fuel ratio in a state where the detected air-fuel ratio of the air-fuel ratio sensor indicates a rich air-fuel ratio, a detected intake air amount detected by an air flow meter, and a detected ammonia amount detected by an NOx sensor; and a deterioration degree estimation system which estimates the degree of deterioration on the basis of the detected rich air-fuel ratio, the detected intake air amount, and the detected ammonia amount and estimates the degree of deterioration to be greater as the detected ammonia amount is smaller with respect to the detected rich air-fuel ratio and the detected intake air amount.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a deterioration degree estimation system. [Background technology]

[0002] There is a technique for calculating the maximum oxygen storage capacity of a three-way catalyst and estimating the degree of deterioration of the three-way catalyst based on the maximum oxygen storage capacity (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-241652 Summary of the Invention [Problem to be solved by the invention]

[0004] To calculate the maximum oxygen storage capacity, the three-way catalyst must be changed from an oxygen-depleted state to an oxygen-saturated state, which may result in increased NOx emissions.

[0005] Therefore, an object of the present invention is to provide a deterioration degree estimation system that can estimate the deterioration degree of a three-way catalyst while suppressing NOx emissions. [Means for solving the problem]

[0006] The above object can be achieved by a deterioration degree estimation system comprising: an air flow meter that detects the amount of intake air of an engine; a three-way catalyst that is arranged in an exhaust passage of the engine and is capable of storing oxygen; an air-fuel ratio sensor that is arranged in the exhaust passage upstream of the three-way catalyst; a NOx sensor that is arranged in the exhaust passage downstream of the three-way catalyst and is capable of detecting the amount of ammonia in the exhaust; and an estimation device that estimates a degree of deterioration of the three-way catalyst, wherein the estimation device includes: an acquisition unit that acquires a detected rich air-fuel ratio that is the detected air-fuel ratio, a detected intake air amount detected by the air flow meter, and a detected ammonia amount detected by the NOx sensor when the detected air-fuel ratio of the air-fuel ratio sensor indicates a rich air-fuel ratio; and an estimation unit that estimates the degree of deterioration based on the detected rich air-fuel ratio, the detected intake air amount, and the detected ammonia amount, and that estimates the degree of deterioration to be larger the smaller the detected amount of ammonia is relative to the detected rich air-fuel ratio and the detected intake air amount.

[0007] The acquisition unit may acquire at least three detected rich air-fuel ratios having different values, and the detected intake air amount and the detected ammonia amount corresponding to each of the at least three detected rich air-fuel ratios, and the estimation unit may estimate the degree of deterioration based on the at least three detected rich air-fuel ratios and the detected intake air amount and the detected ammonia amount corresponding to each of the at least three detected rich air-fuel ratios.

[0008] The exhaust passage may include an upstream catalyst capable of storing oxygen and a downstream catalyst disposed downstream of the upstream catalyst, the three-way catalyst being the downstream catalyst, and the air-fuel ratio sensor being disposed between the upstream catalyst and the downstream catalyst, and the estimation device may include a control unit that executes rich active processing to cause the detected air-fuel ratio to reciprocate between the stoichiometric air-fuel ratio and the rich air-fuel ratio at least three times by switching a target air-fuel ratio of the engine from a rich air-fuel ratio to a lean air-fuel ratio when the detected air-fuel ratio becomes equal to or less than a judgment value indicating a rich air-fuel ratio, and switching the target air-fuel ratio from the lean air-fuel ratio to the rich air-fuel ratio when the detected air-fuel ratio becomes equal to or greater than the stoichiometric air-fuel ratio, and a switching unit that switches the judgment value to a different value when the detected air-fuel ratio becomes equal to or less than the judgment value while the rich active processing is being executed.

[0009] The acquisition unit may acquire, as the detected rich air-fuel ratio, a minimum value of the detected air-fuel ratio from when the detected air-fuel ratio becomes equal to or less than the determination value until when the detected air-fuel ratio becomes equal to or greater than the stoichiometric air-fuel ratio, and may acquire, as the detected ammonia amount, a maximum value of the ammonia amount from when the detected air-fuel ratio becomes equal to or less than the determination value until when the detected air-fuel ratio becomes equal to or greater than the stoichiometric air-fuel ratio.

[0010] The estimation device may include an upstream catalyst estimation unit that estimates the degree of deterioration of the upstream catalyst based on the maximum oxygen storage capacity of the upstream catalyst, and the upstream catalyst estimation unit may estimate the degree of deterioration of the upstream catalyst when the temperature of the downstream catalyst is higher than a predetermined temperature, and the estimation unit may estimate the degree of deterioration of the downstream catalyst when the temperature of the downstream catalyst is equal to or lower than the predetermined temperature. [Effects of the Invention]

[0011] It is possible to provide a deterioration degree estimation system that can estimate the deterioration degree of a three-way catalyst while suppressing NOx emissions. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram of a deterioration degree estimation system. [Figure 2]FIG. 2A is a flowchart illustrating the deterioration degree estimation control, and FIG. 2B is a map defining the relationship between the detected rich air-fuel ratio and the detected ammonia amount according to the detected intake air amount and the deterioration degree of the downstream catalyst. [Figure 3] FIG. 3 is a timing chart illustrating the deterioration degree estimation control. [Figure 4] FIG. 4 is a flowchart of a modified example of deterioration degree estimation control. [Figure 5] FIG. 5 is a flowchart illustrating the rich active process. [Figure 6] FIG. 6 is a timing chart of a modified example of the deterioration degree estimation control. DETAILED DESCRIPTION OF THE INVENTION

[0013] [Outline of the deterioration degree estimation system] FIG. 1 is a schematic diagram of a deterioration degree estimation system 1. The deterioration degree estimation system 1 is mounted on, for example, a vehicle, but is not limited to this and may also be mounted on a vessel or other device other than a vehicle. The deterioration degree estimation system 1 includes an engine 1a and an ECU (Electric Control Unit) 50. The engine 1a has an engine body 2, an intake passage 10, and an exhaust passage 20. The engine body 2 has a plurality of cylinders 3. Each cylinder 3 is provided with an in-cylinder injection valve 4 and an ignition plug 5. Note that instead of or in addition to the in-cylinder injection valve 4, a port injection valve may be provided.

[0014] The intake passage 10 includes an intake manifold 11 connected to the engine body 2, and an intake pipe 12 located upstream of the intake manifold 11. A throttle valve 13 that adjusts the amount of intake air is provided in the intake pipe 12. An air flow meter 14 is provided upstream of the throttle valve 13 in the intake pipe 12. The air flow meter 14 detects the amount of intake air.

[0015] The exhaust passage 20 includes an exhaust manifold 21 connected to the engine body 2, and an exhaust pipe 22 downstream of the exhaust manifold 21. An upstream catalyst 31 is arranged between the exhaust manifold 21 and the exhaust pipe 22. A downstream catalyst 32 is arranged in the exhaust pipe 22. An upstream air-fuel ratio sensor 41 is provided at the junction of branch sections connected to each cylinder of the exhaust manifold 21. A downstream air-fuel ratio sensor 42 is provided in the exhaust pipe 22 downstream of the upstream catalyst 31. A NOx sensor 43 is provided in the exhaust pipe 22 downstream of the downstream catalyst 32. The upstream air-fuel ratio sensor 41 detects the air-fuel ratio of the exhaust gas flowing into the upstream catalyst 31. The downstream air-fuel ratio sensor 42 detects the air-fuel ratio of the exhaust gas discharged from the upstream catalyst 31 and flowing into the downstream catalyst 32. The output value of the NOx sensor 43 correlates with the amount of NOx in the exhaust gas in a lean atmosphere, and correlates with the amount of ammonia in the exhaust gas in a rich atmosphere. Therefore, when exhaust gas having a rich air-fuel ratio that is smaller than the stoichiometric air-fuel ratio flows into the downstream catalyst 32 , the output value of the NOx sensor 43 correlates with the amount of ammonia discharged from the downstream catalyst 32 .

[0016] The upstream catalyst 31 and downstream catalyst 32 are three-way catalysts containing catalytic metals such as platinum (Pt), palladium (Pd), and rhodium (Rh) and having oxygen storage capacity. The three-way catalyst, with its catalytic activity and oxygen storage capacity, purifies NOx and HC according to the amount of oxygen stored. When the air-fuel ratio of the exhaust gas flowing into the three-way catalyst is lean (higher than the stoichiometric air-fuel ratio), the three-way catalyst stores oxygen in the exhaust gas if the amount of oxygen stored in the three-way catalyst is small. This reduces and purifies NOx in the exhaust gas. As the amount of oxygen stored in the three-way catalyst increases, the concentrations of oxygen and NOx in the exhaust gas flowing out of the three-way catalyst increase. When the air-fuel ratio of the exhaust gas flowing into the three-way catalyst is rich (rich air-fuel ratio), the oxygen stored in the three-way catalyst is released if the amount of oxygen stored in the three-way catalyst is large, and HC in the exhaust gas is oxidized and purified. When the amount of oxygen stored in the three-way catalyst decreases, the concentration of HC in the exhaust gas flowing out of the three-way catalyst increases, and ammonia is produced from NOx in the three-way catalyst.

[0017] Here, ammonia produced in the three-way catalyst is produced by the following reaction in a rich atmosphere. N2+3H2→2NH3+reaction heat Therefore, the lower the temperature of the three-way catalyst, the more the heat of reaction is released, and the more ammonia is produced. Also, the higher the pressure of the exhaust gas flowing into the three-way catalyst, the more the reaction proceeds in the direction of decreasing the total number of molecules, and the more ammonia is produced.

[0018] The ECU 50 includes a central processing unit (CPU), random access memory (RAM), read-only memory (ROM), flash memory, and other storage devices, and performs various controls by executing programs stored in the ROM and storage devices. The ECU 50 controls the intake air amount, fuel injection amount, ignition timing, and the like based on the amount of operation of the accelerator pedal and brake pedal operated by the driver, the engine speed and load of the engine 1a, and the like. The ECU 50 receives the detected air-fuel ratios detected by the upstream air-fuel ratio sensor 41 and the downstream air-fuel ratio sensor 42, respectively, and the output value of the NOx sensor 43. The ECU 50 is an example of an estimation device that estimates the degree of deterioration of the downstream catalyst 32, which will be described in detail later. The ECU 50 functionally realizes an acquisition unit and an estimation unit, which will be described in detail later.

[0019] The ECU 50 controls the engine 1a so that the air-fuel ratio of the exhaust gas discharged from the engine 1a becomes a target air-fuel ratio. Specifically, the ECU 50 controls the air-fuel ratio of the exhaust gas discharged from the engine 1a mainly by feedback controlling the fuel injection amount so that the air-fuel ratio detected by the upstream air-fuel ratio sensor 41 becomes the target air-fuel ratio.

[0020] [Deterioration degree estimation control] Deterioration degree estimation control executed by the ECU 50 will be described. FIG. 2A is a flowchart illustrating the deterioration degree estimation control. In the following description, when the term "detected air-fuel ratio" is simply referred to, it means the air-fuel ratio detected by the downstream air-fuel ratio sensor 42. The ECU 50 determines whether the detected air-fuel ratio is equal to or less than a determination value (step S1). The determination value is a value indicating a rich air-fuel ratio. Specifically, when the target air-fuel ratio of the engine 1a is a rich air-fuel ratio and the upstream catalyst 31 is in an oxygen-depleted state, the detected air-fuel ratio of the downstream air-fuel ratio sensor 42 becomes a rich air-fuel ratio equal to or less than the determination value. If the determination in step S1 is No, this control ends.

[0021] If the answer is Yes in step S1, the ECU 50 switches the target air-fuel ratio of the engine 1a to a lean air-fuel ratio (step S2). Here, even after the target air-fuel ratio has been switched to the lean air-fuel ratio, rich air-fuel ratio exhaust gas continues to flow into and be discharged from the downstream catalyst 32 until a predetermined time has elapsed. The ECU 50 acquires a detected rich air-fuel ratio, which is the air-fuel ratio of the rich air-fuel ratio exhaust gas flowing into the downstream catalyst 32 and is a detected air-fuel ratio, a detected intake air amount detected by the air flow meter 14, and a detected ammonia amount detected by the NOx sensor 43 (step S3). Step S3 is an example of processing executed by the acquisition unit.

[0022] Next, the ECU 50 estimates the deterioration degree of the downstream catalyst 32 based on the detected rich air-fuel ratio, the detected intake air amount, and the detected ammonia amount obtained by referring to the map of FIG. 2B (step S4). FIG. 2B is a map that defines the relationship between the detected rich air-fuel ratio and the detected ammonia amount according to the detected intake air amount, and the deterioration degree of the downstream catalyst 32. The larger the detected rich air-fuel ratio, the closer the detected rich air-fuel ratio is to the stoichiometric air-fuel ratio. The smaller the detected rich air-fuel ratio, the greater the detected rich air-fuel ratio. The smaller the detected rich air-fuel ratio and the larger the detected intake air amount, the greater the detected ammonia amount. According to the map of FIG. 2B, the smaller the detected rich air-fuel ratio and the detected ammonia amount relative to the detected rich air-fuel ratio and the detected intake air amount, the greater the deterioration degree of the downstream catalyst 32 is estimated to be. Note that the deterioration degree of the downstream catalyst 32 may be estimated using, for example, an arithmetic expression that uses the detected rich air-fuel ratio, the detected intake air amount, and the detected ammonia amount as arguments. Step S4 is an example of processing executed by the estimation unit.

[0023] FIG. 3 is a timing chart illustrating deterioration degree estimation control. FIG. 3 shows changes in the intake air amount, the detected air-fuel ratio of the downstream air-fuel ratio sensor 42, and the amount of ammonia in the exhaust gas discharged from the downstream catalyst 32. For example, the ECU 50 controls the intake air amount and the target air-fuel ratio according to the operating state of the engine 1a, and the detected air-fuel ratio is maintained at the stoichiometric air-fuel ratio (time t0). When the upstream catalyst 31 enters an oxygen-starved state, the detected air-fuel ratio decreases. When the detected air-fuel ratio becomes equal to or less than a determination value D, the target air-fuel ratio is switched to a lean air-fuel ratio (time t1). After a predetermined time lag has elapsed since the detected air-fuel ratio became equal to or less than the determination value D, the detected air-fuel ratio begins to increase (time t2). When the detected air-fuel ratio switches from decreasing to increasing, the detected air-fuel ratio reaches its minimum value. The ECU 50 acquires this minimum value as the detected rich air-fuel ratio R described above, and acquires the intake air amount when the detected air-fuel ratio becomes the detected rich air-fuel ratio R as the detected intake air amount G. After that, the exhaust gas having the detected rich air-fuel ratio R passes through the downstream catalyst 32, and the amount of ammonia becomes a maximum value (time t3). The ECU 50 acquires this maximum value as the detected ammonia amount N. After that, the detected air-fuel ratio becomes the stoichiometric air-fuel ratio (time t4).

[0024] As described above, the ECU 50 estimates the degree of deterioration of the downstream catalyst 32 based on the detected rich air-fuel ratio R, the detected intake air amount G, and the detected ammonia amount N. Therefore, for example, since it is not necessary to bring the downstream catalyst 32 into an oxygen saturated state, the degree of deterioration of the downstream catalyst 32 can be estimated while suppressing NOx emissions.

[0025] The detected rich air-fuel ratio R is the minimum value of the detected air-fuel ratio from when the detected air-fuel ratio becomes equal to or less than the judgment value D until it becomes the stoichiometric air-fuel ratio. The detected ammonia amount N is the maximum value of the ammonia amount from when the detected air-fuel ratio becomes equal to or less than the judgment value D until it becomes the stoichiometric air-fuel ratio again. Therefore, the detected rich air-fuel ratio R and the detected ammonia amount N correspond with high precision, and the accuracy of estimating the deterioration degree of the downstream catalyst 32 is improved.

[0026] The ECU 50 acquires the intake air amount when the detected air-fuel ratio becomes the detected rich air-fuel ratio R as the detected intake air amount G, but is not limited to this. There is a predetermined time lag between the intake air whose amount is detected by the air flow meter 14 being discharged from the engine body 2 and flowing into the downstream catalyst 32 as exhaust. Therefore, the ECU 50 may acquire the intake air amount detected by the air flow meter 14 the amount of the above-mentioned time lag before the detected air-fuel ratio becomes the detected rich air-fuel ratio R as the detected intake air amount. In this case, the time lag may be calculated according to operating conditions such as the intake air amount and engine speed. The deterioration degree estimation control described above may also be performed for a configuration in which the upstream catalyst 31 is not provided.

[0027] [Modification of Deterioration Degree Estimation Control] Next, a description will be given of a modified example of the deterioration degree estimation control executed by the ECU 50. In this modified example, the ECU 50 functionally realizes an acquisition unit, an estimation unit, a control unit, a switching unit, and an upstream catalyst estimation unit, which will be described in detail later.

[0028] FIG. 4 is a flowchart of a modified example of deterioration degree estimation control. The ECU 50 determines whether the temperature of the downstream catalyst 32 is equal to or lower than a predetermined temperature (step S11). The predetermined temperature is the upper limit of the temperature of the downstream catalyst 32 at which the amount of ammonia produced in the downstream catalyst 32 when, for example, rich air-fuel ratio exhaust gas flows into the downstream catalyst 32 is such that the accuracy of estimating the deterioration degree of the downstream catalyst 32 is ensured. As described above, the amount of ammonia produced in the downstream catalyst 32 increases as the temperature of the downstream catalyst 32 decreases. For example, the temperature of the downstream catalyst 32 may be estimated as the intake air volume decreases. Alternatively, the amount of heat transferred to the downstream catalyst 32 may be estimated taking into account the amount of heat transferred from the engine main body 2 to the exhaust port, the exhaust passage 20, and the upstream catalyst 31, and the temperature of the downstream catalyst 32 may be estimated based on the amount of heat transferred to the downstream catalyst 32. Alternatively, a temperature sensor may be provided in the downstream catalyst 32 to acquire the temperature of the downstream catalyst 32. Alternatively, the temperature of the downstream catalyst 32 may be acquired, estimated, or calculated using a known method.

[0029] If the answer is Yes in step S11, the ECU 50 executes a rich active process described below (step S12). Step S12 is an example of a process executed by a control unit. Next, the ECU 50 acquires the detected rich air-fuel ratio, the detected intake air amount, and the detected ammonia amount while executing the rich active process (step S13), and estimates the degree of deterioration of the downstream catalyst 32 (step S14). Step S13 is an example of a process executed by an acquisition unit. Step S14 is an example of a process executed by an estimation unit.

[0030] If the answer is No in step S11, the ECU 50 executes rich-lean active processing (step S15), which will be described later. Next, the ECU 50 calculates the maximum oxygen storage amount of the upstream catalyst 31 while executing the rich-lean active processing (step S16), and estimates the degree of deterioration of the upstream catalyst 31 based on the maximum oxygen storage amount (step S17). Step S17 is an example of processing executed by the upstream catalyst estimation unit.

[0031] 5 is a flowchart illustrating the rich active processing. The ECU 50 switches the target air-fuel ratio to a rich air-fuel ratio (step S21). The ECU 50 determines whether the detected air-fuel ratio has become equal to or less than the determination value (step S22). If the result in step S22 is No, step S21 is executed again. If the result in step S22 is Yes, the ECU 50 switches the determination value to a different value (step S23), which will be described in detail later. Next, the ECU 50 switches the target air-fuel ratio to a lean air-fuel ratio (step S24). The ECU 50 determines whether the detected air-fuel ratio has become equal to or greater than the stoichiometric air-fuel ratio (step S25). If the result in step S25 is No, step S24 is executed again.

[0032] If the answer is Yes in step S25, the ECU 50 determines whether the detected air-fuel ratio has already reciprocated three times between the stoichiometric air-fuel ratio and the judgment value during execution of the rich active processing (step S26). For example, the ECU 50 may count the number of times the target air-fuel ratio is switched from a rich air-fuel ratio to a lean air-fuel ratio during execution of the rich active processing as the number of reciprocations. The ECU 50 may count the number of times the judgment value is switched during execution of the rich active processing as the number of reciprocations. The ECU 50 may count the number of times the detected air-fuel ratio falls below the judgment value during execution of the rich active processing as the number of reciprocations. The ECU 50 may count the number of times the detected air-fuel ratio changes from less than the stoichiometric air-fuel ratio to equal to or greater than the stoichiometric air-fuel ratio during execution of the rich active processing as the number of reciprocations. If the answer is No in step S26, step S21 is executed again. If the answer is Yes in step S26, the rich active processing ends. Therefore, the judgment value is switched to different values ​​three times during execution of the rich active processing.

[0033] Fig. 6 is a timing chart of a modified example of deterioration degree estimation control. Fig. 6 shows changes in the intake air amount, the air-fuel ratio detected by the downstream air-fuel ratio sensor 42, the amount of ammonia in the exhaust gas discharged from the downstream catalyst 32, and the amount of ammonia and NOx discharged from the upstream catalyst 31. In the example of Fig. 6, rich active processing is executed first, and then rich-lean active processing is executed. In rich active processing, the amount of ammonia in the exhaust gas discharged from the downstream catalyst 32 is shown. In rich-lean active processing, the amount of ammonia and NOx in the exhaust gas discharged from the upstream catalyst 31 is shown.

[0034] As described above, when the temperature of the downstream catalyst 32 is equal to or lower than the predetermined temperature, the rich active processing is executed (time t11). When the rich active processing is executed, the target air-fuel ratio is switched to a rich air-fuel ratio, the upstream catalyst 31 enters an oxygen-starved state, and the detected air-fuel ratio decreases. When the detected air-fuel ratio becomes equal to or lower than the judgment value D1, the target air-fuel ratio is switched to a lean air-fuel ratio, the detected air-fuel ratio increases, and the detected rich air-fuel ratio R1 and the detected ammonia amount N1 are acquired. When the detected air-fuel ratio becomes equal to or higher than the stoichiometric air-fuel ratio, the target air-fuel ratio is switched to a rich air-fuel ratio, and the detected air-fuel ratio decreases. When the detected air-fuel ratio becomes equal to or lower than the judgment value D2 to which the judgment value D1 is switched, the target air-fuel ratio is switched to a lean air-fuel ratio, the detected air-fuel ratio increases, and the detected rich air-fuel ratio R2 and the detected ammonia amount N2 are acquired. When the detected air-fuel ratio becomes equal to or higher than the stoichiometric air-fuel ratio, the target air-fuel ratio is switched to a rich air-fuel ratio, and the detected air-fuel ratio decreases. When the detected air-fuel ratio becomes equal to or less than the judgment value D3 to which the judgment value D2 is switched, the target air-fuel ratio is switched to the lean air-fuel ratio, the detected air-fuel ratio increases, and the detected rich air-fuel ratio R3 and the detected ammonia amount N3 are acquired. When the detected air-fuel ratio becomes equal to or more than the stoichiometric air-fuel ratio, the rich active processing ends (time t12).

[0035] 6 illustrates a case where the detected intake air amount G1 is constant during execution of the rich active processing, and the judgment value D1 is maximum and the judgment value D3 is minimum among the judgment values ​​D1 to D3. Therefore, among the detected rich air-fuel ratios R1 to R3, the detected rich air-fuel ratio R1 is maximum and the detected rich air-fuel ratio R3 is minimum. Among the detected ammonia amounts N1 to N3, the detected ammonia amount N3 is maximum and the detected ammonia amount N1 is minimum. Note that the order in which the judgment values ​​are switched is not limited to the order in which the judgment values ​​gradually decrease as shown in FIG. 6.

[0036] The ECU 50 estimates the degree of deterioration of the downstream catalyst 32 based on the detected rich air-fuel ratios R1 to R3, the detected ammonia amounts N1 to N3, and the detected intake air amount G1, which are data acquired three times. For example, the ECU 50 may refer to the map of Fig. 2B and estimate an average value of the degrees of deterioration estimated based on the detected rich air-fuel ratio R1, the detected ammonia amount N1, and the detected intake air amount G1, the detected rich air-fuel ratio R2, the detected ammonia amount N2, and the detected intake air amount G1, and the detected rich air-fuel ratio R3, the detected ammonia amount N3, and the detected intake air amount G1, as the final degree of deterioration of the downstream catalyst 32. The ECU 50 may estimate the degree of deterioration of the downstream catalyst 32 based on the average value of the detected rich air-fuel ratios R1 to R3, the average value of the detected ammonia amounts N1 to N3, and the detected intake air amount G1. The ECU 50 may refer to the map of FIG. 2B and calculate a regression line by the least squares method from the detected rich air-fuel ratio R1, the detected ammonia amount N1, and the detected intake air amount G1, the detected rich air-fuel ratio R2, the detected ammonia amount N2, and the detected intake air amount G1, and the detected rich air-fuel ratio R3, the detected ammonia amount N3, and the detected intake air amount G1, and estimate the degree of deterioration based on this regression line.

[0037] In this way, by estimating the deterioration degree of the downstream catalyst 32 based on data acquired multiple times, the accuracy of estimating the deterioration degree is improved. The accuracy of estimating the deterioration degree is also improved by switching the determination value to a different value. This is because by switching the determination value to a different value, at least a plurality of detected rich air-fuel ratios having different values ​​and a plurality of detected ammonia amounts having different values ​​are acquired.

[0038] Also in this modification, the detected rich air-fuel ratios R1 to R3 are the minimum values ​​of the detected air-fuel ratio from when the detected air-fuel ratio becomes equal to or less than the determination values ​​D1 to D3 until it reaches the stoichiometric air-fuel ratio. The detected ammonia amounts N1 to N3 are the maximum values ​​of the ammonia amounts from when the detected air-fuel ratio becomes equal to or less than the determination values ​​D1 to D3 until it reaches the stoichiometric air-fuel ratio. This improves the accuracy of estimating the deterioration degree.

[0039] In the above example, the data is acquired three times, but it may be acquired two times or four times or more. In consideration of the accuracy of estimating the degree of deterioration, it is preferable that the data be acquired three times or more. Furthermore, if the intake air amount changes while the rich active processing is being executed, multiple detected intake air amounts with different values ​​corresponding to the acquired multiple detected rich air-fuel ratios are acquired.

[0040] When the temperature of the downstream catalyst 32 rises above a predetermined temperature, rich-lean active processing is executed to estimate the degree of deterioration of the upstream catalyst 31 (time t13). When rich-lean active processing is executed, the target air-fuel ratio is set to a rich air-fuel ratio, the upstream catalyst 31 enters an oxygen-starved state, and the detected air-fuel ratio decreases. When the detected air-fuel ratio falls below a determination value RD indicating a rich air-fuel ratio, the target air-fuel ratio is switched to a lean air-fuel ratio, and the detected air-fuel ratio increases, but the amount of ammonia emitted from the upstream catalyst 31 temporarily increases. When the upstream catalyst 31 enters an oxygen-saturated state and the detected air-fuel ratio becomes equal to or exceeds a determination value LD indicating a lean air-fuel ratio, the target air-fuel ratio is switched to a rich air-fuel ratio, and the detected air-fuel ratio decreases, but the amount of NOx emitted from the upstream catalyst 31 temporarily increases. In this way, after the detected air-fuel ratio has fluctuated between the determination value RD and the determination value LD multiple times, if the detected air-fuel ratio becomes equal to or lower than the stoichiometric air-fuel ratio with the target air-fuel ratio set to the rich air-fuel ratio, the rich-lean active processing ends (time t14). Note that FIG. 6 illustrates a case in which the detected intake air amount G2 is constant while the rich-lean active processing is being executed. The ECU 50 calculates the maximum oxygen storage amount of the upstream catalyst 31 based on the detected intake air amount G2 from when the target air-fuel ratio is switched from the rich air-fuel ratio to the lean air-fuel ratio until when it is switched from the lean air-fuel ratio to the rich air-fuel ratio. The ECU 50 estimates the degree of deterioration of the upstream catalyst 31 based on the maximum oxygen storage amount.

[0041] As described above, when the temperature of the downstream catalyst 32 is higher than the predetermined temperature, the degree of deterioration of the upstream catalyst 31 is estimated. Here, because the upstream catalyst 31 is closer to the engine body 2 than the downstream catalyst 32, it is considered that the upstream catalyst 31 is hotter than the downstream catalyst 32. Therefore, when the temperature of the downstream catalyst 32 is higher than the predetermined temperature, it is considered that the temperature of the upstream catalyst 31 is equal to or higher than the activation temperature of the upstream catalyst 31. When the temperature of the upstream catalyst 31 is equal to or higher than the activation temperature, the maximum oxygen storage amount of the upstream catalyst 31 is calculated with high accuracy. Therefore, the accuracy of estimating the degree of deterioration of the upstream catalyst 31 is improved. As described above, when the temperature of the downstream catalyst 32 is equal to or lower than the predetermined temperature, the accuracy of estimating the degree of deterioration of the upstream catalyst 31 is improved, and when the temperature of the downstream catalyst 32 is higher than the predetermined temperature, the accuracy of estimating the degree of deterioration of the upstream catalyst 31 is improved.

[0042] Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as described in the claims. [Explanation of symbols]

[0043] 1. Deterioration degree estimation system 31 Upstream catalyst 32 Downstream catalyst (three-way catalyst) 42 Downstream air-fuel ratio sensor (air-fuel ratio sensor) 43 NOx sensor 50 ECU (estimation device, acquisition unit, estimation unit, control unit, switching unit, upstream catalyst estimation unit)

Claims

1. an air flow meter that detects the amount of intake air of the engine; a three-way catalyst capable of storing oxygen, which is disposed in an exhaust passage of the engine; an air-fuel ratio sensor disposed in the exhaust passage upstream of the three-way catalyst; a NOx sensor that is disposed in the exhaust passage downstream of the three-way catalyst and is capable of detecting an amount of ammonia in the exhaust gas; an estimation device for estimating a deterioration degree of the three-way catalyst; Equipped with The estimation device includes: an acquisition unit that acquires a detected rich air-fuel ratio, a detected intake air amount detected by the air flow meter, and a detected ammonia amount detected by the NOx sensor when the detected air-fuel ratio of the air-fuel ratio sensor indicates a rich air-fuel ratio; an estimation unit that estimates the degree of deterioration based on the detected rich air-fuel ratio, the detected intake air amount, and the detected ammonia amount, and estimates the degree of deterioration to be larger as the detected ammonia amount is smaller relative to the detected rich air-fuel ratio and the detected intake air amount, Deterioration degree estimation system.

2. the acquisition unit acquires at least three detected rich air-fuel ratios having different values, and the detected intake air amount and the detected ammonia amount corresponding to each of the at least three detected rich air-fuel ratios, 2. The deterioration degree estimation system according to claim 1, wherein the estimation unit estimates the deterioration degree based on the at least three detected rich air-fuel ratios and the detected intake air amount and the detected ammonia amount corresponding to each of the at least three detected rich air-fuel ratios.

3. an upstream catalyst capable of storing oxygen and a downstream catalyst disposed downstream of the upstream catalyst in the exhaust passage; the three-way catalyst is the downstream catalyst; the air-fuel ratio sensor is disposed between the upstream catalyst and the downstream catalyst; The estimation device includes: a control unit that executes a rich active process to cause the detected air-fuel ratio to reciprocate between the stoichiometric air-fuel ratio and the rich air-fuel ratio at least three times by switching a target air-fuel ratio of the engine from a rich air-fuel ratio to a lean air-fuel ratio when the detected air-fuel ratio becomes equal to or less than a determination value indicating a rich air-fuel ratio, and by switching the target air-fuel ratio from a lean air-fuel ratio to a rich air-fuel ratio when the detected air-fuel ratio becomes equal to or greater than the stoichiometric air-fuel ratio; 3. The deterioration degree estimation system according to claim 2, further comprising: a switching unit that switches the determination value to a different value when the detected air-fuel ratio becomes equal to or less than the determination value during execution of the rich active processing.

4. 4. The deterioration degree estimation system according to claim 3, wherein the acquisition unit acquires, as the detected rich air-fuel ratio, a minimum value of the detected air-fuel ratio from when the detected air-fuel ratio becomes equal to or less than the determination value until when the detected air-fuel ratio becomes equal to or more than the stoichiometric air-fuel ratio, and acquires, as the detected ammonia amount, a maximum value of the ammonia amount from when the detected air-fuel ratio becomes equal to or less than the determination value until when the detected air-fuel ratio becomes equal to or more than the stoichiometric air-fuel ratio.

5. the estimation device includes an upstream catalyst estimation unit that estimates a degree of deterioration of the upstream catalyst based on a maximum oxygen storage amount of the upstream catalyst, the upstream catalyst estimation unit estimates a deterioration degree of the upstream catalyst when the temperature of the downstream catalyst is higher than a predetermined temperature; 5. The deterioration degree estimation system according to claim 4, wherein the estimation unit estimates the deterioration degree of the downstream catalyst when the temperature of the downstream catalyst is equal to or lower than the predetermined temperature.

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