JP2023175080A - Catalyst capacity detection device - Google Patents

Abstract

To determine capacity of a catalyst while suppressing increase in toxic substances in an exhaust gas.SOLUTION: A catalyst capacity detection device 10 includes: a catalyst 31 disposed in an exhaust passage 3 of an internal combustion engine 1 and having oxygen storage capacity; and an A/F sensor 32 disposed downstream from the catalyst 31 in the exhaust passage 3 to detect an oxygen concentration of an exhaust gas corresponding to an air-fuel ratio of a combustion chamber of the internal combustion engine 1. The catalyst capacity detection device calculates an inclination in correlation between the oxygen concentration and an oxygen density change speed from a value of the oxygen concentration detected by the A/F sensor 32 and determines capacity of the catalyst from the change of the inclination.SELECTED DRAWING: Figure 1

Description

The present invention relates to a catalyst performance detection device that determines the performance of a catalyst provided in an exhaust passage of an internal combustion engine.

Patent Document 1 and Patent Document 2 disclose that the catalyst installed in the exhaust passage of an internal combustion engine is controlled by executing active control that forcibly changes the air-fuel ratio to alternately switch richer and leaner than the stoichiometric air-fuel ratio. A catalyst deterioration diagnostic device for determining deterioration of oxygen storage capacity is disclosed.

JP2012-067636A International Publication No. 2012/160650

When performing active control that forcibly changes the air-fuel ratio to alternately switch richer and leaner than the stoichiometric air-fuel ratio, as in the catalyst deterioration diagnostic devices disclosed in Patent Document 1 and Patent Document 2, the stoichiometric air-fuel ratio The air-fuel ratio needs to fluctuate with a larger amplitude and period than the air-fuel ratio fluctuation in normal control that controls the injection amount of the injector so that Therefore, during the execution of the above active control, the amount of harmful substances discharged into the atmosphere may increase. In particular, in order to measure the maximum oxygen storage amount of the catalyst with the air-fuel ratio in a lean state in the active control described above, it is necessary to maintain the air-fuel ratio in a lean state for a long time, which is far from the stoichiometric air-fuel ratio, which is impossible with the above-mentioned normal control. During this period, nitrogen oxide emissions will continue to increase.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a catalyst ability detection device that can determine the ability of a catalyst while suppressing an increase in harmful substances in exhaust gas.

The catalytic ability detection device according to the present invention includes a catalyst that is disposed in an exhaust passage of an internal combustion engine and has an oxygen storage capacity, and a catalyst that is disposed downstream of the catalyst in the exhaust passage and that detects an air-fuel ratio in a combustion chamber of the internal combustion engine. A catalytic ability detection device comprising: an A/F sensor that detects the oxygen concentration in a corresponding exhaust gas; The method is characterized in that the slope is calculated, and the ability of the catalyst is determined from the change in the slope.

The present invention provides a detection value of the A/F sensor 32 obtained by normal control that controls the injector to maintain the stoichiometric air-fuel ratio without executing active control that alternately switches the air-fuel ratio to richer and leaner than the stoichiometric air-fuel ratio. Since the oxygen storage capacity of the catalyst is determined from the above, the capacity of the catalyst can be determined while suppressing the increase in harmful substances in the exhaust gas.

FIG. 2 is a diagram showing a control system of a catalyst ability detection device according to an embodiment of the present disclosure. 2 is a flowchart illustrating an example of a control routine that is executed by the control device of the catalyst capability detection device of the present embodiment to determine the capability of the catalyst. FIG. 2 is a correlation diagram showing an example of the distribution of the oxygen concentration of exhaust gas downstream of the catalyst and the oxygen concentration change rate.

The catalytic ability detection device 10 of this embodiment will be described below with reference to FIGS. 1 to 3. FIG. 1 is a diagram showing a control system of the catalyst ability detection device 10. As shown in FIG. The catalytic capacity detection device 10 is a device that determines the oxygen storage capacity of the three-way catalyst 31 provided in the exhaust passage 3 connected to the combustion chamber of the internal combustion engine 1. As shown in FIG. 1, an intake passage 2 and an exhaust passage 3 are connected to a combustion chamber of an internal combustion engine 1. The intake passage 2 includes an air flow meter 21 that detects the flow rate of intake air flowing through the intake passage 2, a throttle valve 22 that adjusts the flow rate of intake air, and a throttle valve opening sensor 23 that detects the opening degree of the throttle valve 22. is provided. The intake passage 2 is provided with an injector 24 that injects fuel near the combustion chamber. Note that the injector 24 may be provided at a position to directly inject fuel into the combustion chamber of the internal combustion engine 1.

The catalytic ability detection device 10 includes a three-way catalyst 31 and an A/F sensor 32 provided in the exhaust passage 3. The three-way catalyst 31 has an oxygen storage capacity, oxidizes hydrocarbons in exhaust gas into water and carbon dioxide, oxidizes carbon monoxide into carbon dioxide, and reduces nitrogen oxides to nitrogen. Therefore, the three-way catalyst 31 has a function of removing hydrocarbons, carbon monoxide, and nitrogen oxides from the exhaust gas. The three-way catalyst 31 exhibits its exhaust purification function to its fullest when the air-fuel ratio in the combustion chamber of the internal combustion engine 1 is at the stoichiometric air-fuel ratio. The A/F sensor 32 is provided downstream of the three-way catalyst 31 in the exhaust passage 3 and can detect the oxygen concentration of the exhaust gas downstream of the three-way catalyst 31. Since the oxygen concentration detected by the A/F sensor 32 corresponds to the air-fuel ratio in the combustion chamber of the internal combustion engine 1, the A/F sensor 32 can be used for monitoring the air-fuel ratio in the combustion chamber of the internal combustion engine 1.

The catalyst ability detection device 10 includes an ECU (Electronic Control Unit) 20 as a control device. Output signals are input to the ECU 20 from the crank angle sensor 11, accelerator opening sensor 4, air flow meter 21, throttle valve opening sensor 23, and A/F sensor 32 of the internal combustion engine 1. The throttle valve 22 and the injector 24 are controlled by the ECU 20.

The ECU 20 controls the opening of the throttle valve 22 based on the accelerator opening detected by the accelerator opening sensor 4 . Then, the ECU 20 calculates the air-fuel ratio of the combustion chamber of the internal combustion engine 1 from the value of the oxygen concentration of the exhaust gas detected by the A/F sensor 32, and adjusts the fuel injection amount of the injector 24 so that the stoichiometric air-fuel ratio is achieved. performs feedback control. Therefore, the air taken in from the atmosphere according to the opening degree of the throttle valve 22 is mixed with the fuel injected from the injector 24 so that the air-fuel ratio in the combustion chamber of the internal combustion engine 1 becomes the stoichiometric air-fuel ratio, and the internal combustion engine 1 1 into the combustion chamber. After the air-fuel mixture is combusted in the combustion chamber of the internal combustion engine 1, exhaust gas discharged from the combustion chamber to the exhaust passage 3 is purified by the three-way catalyst 31 and discharged from the exhaust passage 3 to the atmosphere.

The ECU 20 has a CPU, which is an arithmetic processing unit, and storage units such as RAM and ROM.The ECU 20 uses the primary storage function of the RAM and performs signal processing according to a program stored in advance in the ROM. Control 10. A control routine program for controlling the fuel injection amount of the injector 24 so that the air-fuel ratio in the combustion chamber of the internal combustion engine 1 becomes the stoichiometric air-fuel ratio is stored in the ROM of the ECU 20, and is executed in an extremely short cycle time of, for example, several milliseconds. executed repeatedly.

The ECU 20 performs control to determine the oxygen storage capacity of the three-way catalyst 31 in parallel with a control routine that controls the fuel injection amount of the injector 24 so that the air-fuel ratio in the combustion chamber of the internal combustion engine 1 becomes the stoichiometric air-fuel ratio. Also execute routines. FIG. 2 is a flowchart showing an example of a control routine that the ECU 20 executes to determine the oxygen storage capacity of the three-way catalyst 31. The control routine program shown in FIG. 2 is held in the ROM of the ECU 20, and is repeatedly executed in an extremely short cycle time of, for example, several milliseconds.

The control routine shown in FIG. 2 is executed after the internal combustion engine 1 is started until it is stopped. In the control routine shown in FIG. 2, first in step S1, the oxygen concentration of the exhaust gas is detected from the A/F sensor 32.

Next, the process proceeds to step S2, where it is determined whether the air-fuel ratio in the combustion chamber of the internal combustion engine 1 is near the stoichiometric air-fuel ratio. Specifically, it is determined whether the oxygen concentration value detected in step S1 is within a predetermined range above and below the value corresponding to the stoichiometric air-fuel ratio. If the oxygen concentration value detected in step S1 is not within a predetermined range, the process proceeds to step S3; if the oxygen concentration value detected in step S1 is within the predetermined range, the control routine is executed without proceeding to step S3. finish.

When the process proceeds from step S2 to step S3, the rate of change in oxygen concentration is calculated in step S3. The oxygen concentration change rate is calculated from the oxygen concentration value detected in step S1 and the oxygen concentration value of the exhaust gas detected in the previously executed control routine.

After calculating the rate of change in oxygen concentration in step S3, the process proceeds to step S4, where the value of the oxygen concentration detected in step S1, the value of the rate of change in oxygen concentration calculated in step S3, and the previously executed control routines are used. From the similarly obtained values of oxygen concentration and rate of change in oxygen concentration, a regression line is calculated as shown in FIG. 3. FIG. 3 is a correlation diagram showing an example of the distribution of oxygen concentration and oxygen concentration change rate. The horizontal axis of FIG. 3 is the oxygen concentration detected by the A/F sensor 32, and the vertical axis is the oxygen concentration change rate. In FIG. 3, the regression line calculated for the three-way catalyst 31 in a new state that has not deteriorated is shown by the dotted line L1, and the regression line calculated for the three-way catalyst 31 whose oxygen storage capacity has decreased due to deterioration is shown by the solid line L2. is indicated by a solid line L3.

Note that since the range near the stoichiometric air-fuel ratio is excluded in step S2, the points plotted within the rectangular area colored gray in FIG. 3 are not used in calculating the regression line in step S4. Only the points plotted outside the rectangular area colored gray in FIG. 3 are used to calculate the regression line in step S4. In the range near the stoichiometric air-fuel ratio, even if the three-way catalyst 31 deteriorates and the oxygen storage amount decreases, there is little effect on the rate of change in the oxygen concentration of the exhaust gas, so this is the target for calculating the regression line in step S4. It is removed from

After calculating the regression line in step S4, in step S5, the oxygen storage capacity of the three-way catalyst 31 is determined from the slope of the regression line calculated in step S4. In a typical three-way catalyst, when the oxygen storage capacity decreases due to catalyst poisoning or sintering, the oxygen adsorption/release rate decreases, and the oxygen concentration change rate decreases, changing from the dotted line L1 to the solid line L2 in Fig. 3. The slope of the regression line becomes smaller. Therefore, the oxygen storage capacity of the three-way catalyst 31 can be determined from the magnitude of the slope of the regression line calculated in step S4. In step S5, it may be determined that the three-way catalyst 31 has deteriorated when the magnitude of the slope of the regression line calculated in step S4 becomes smaller than a predetermined threshold value. However, depending on the catalyst specifications, when the catalyst deteriorates, the slope of the regression line may increase from the dotted line L1 to the solid line L3 in FIG. Therefore, in step S5, it may be determined that the three-way catalyst 31 has deteriorated when the magnitude of the slope of the regression line calculated in step S4 becomes larger than a predetermined threshold value.

In this way, the catalyst performance detection device 10 of this embodiment maintains the stoichiometric air-fuel ratio without executing active control that forcibly changes the air-fuel ratio to alternately switch the air-fuel ratio to richer and leaner than the stoichiometric air-fuel ratio. Since the oxygen storage capacity of the three-way catalyst 31 is determined from the detection value of the A/F sensor 32 obtained through normal control of the injector 24, the ability of the catalyst is determined while suppressing the increase in harmful substances in the exhaust gas. be able to.

In addition, the catalytic ability detection device 10 detects the ternary factor used in the control routine to control the injector 24 so that the air-fuel ratio in the combustion chamber of the internal combustion engine 1 becomes the stoichiometric air-fuel ratio based on the change in the slope of the regression line calculated in step S4. By correcting the amount of oxygen stored in the catalyst 31, the air-fuel ratio in the combustion chamber of the internal combustion engine 1 can be brought closer to the stoichiometric air-fuel ratio with even higher precision.

<Supplementary information on the embodiment>
The catalyst ability detection device of the present disclosure is not limited to the above-mentioned form, but can be implemented in various forms within the scope of the gist of the present disclosure. For example, an A/F sensor may be provided in the exhaust passage 3 upstream of the three-way catalyst 31 as well. In this case, feedback control may be performed to adjust the injection amount of the injector 24 using the detected value of the A/F sensor provided upstream of the three-way catalyst 31. Furthermore, if it is appropriate to calculate the regression curve in step S4 of the control routine shown in FIG. 2 due to the characteristics of the catalyst disposed in the exhaust passage 3, the regression curve is calculated instead of calculating the regression line in step S4. You may.

1 internal combustion engine, 2 intake passage, 3 exhaust passage, 4 accelerator opening sensor, 10 catalytic capacity detection device, 11 crank angle sensor, 20 ECU, 21 air flow meter, 22 throttle valve, 23 throttle valve opening sensor, 24 injector, 31 three-way catalyst, 32 A/F sensor.

Claims (1)

a catalyst disposed in an exhaust passage of an internal combustion engine and having oxygen storage capacity;
an A/F sensor that is disposed downstream of the catalyst in the exhaust passage and detects an oxygen concentration in exhaust gas that corresponds to an air-fuel ratio in a combustion chamber of the internal combustion engine;
A catalytic ability detection device comprising:
Catalytic ability detection characterized by calculating the slope of the correlation between the oxygen concentration and the oxygen concentration change rate from the oxygen concentration value detected by the A/F sensor, and determining the ability of the catalyst from the change in the slope. Device.