JP4374518B2 - Exhaust gas purification control device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification control device for an internal combustion engine in which a plurality of catalysts or a plurality of catalyst groups are arranged in series in an exhaust passage.
[0002]
[Prior art]
In recent years, in order to improve the exhaust gas purification ability of an engine, there is one in which two exhaust gas purification catalysts are installed in series in the middle of an engine exhaust pipe. In this system, air-fuel ratio sensors (or oxygen sensors) are installed on the upstream side of the upstream catalyst and the downstream side of the downstream catalyst, respectively, and the air-fuel ratio of the exhaust gas flowing into the upstream catalyst is detected by the upstream sensor. Then, air-fuel ratio feedback control (main feedback control) is performed so as to make this coincide with the target air-fuel ratio, and the air-fuel ratio of the exhaust gas that has passed through the downstream catalyst is detected by the downstream sensor, and this is detected downstream. Sub-feedback control is performed to correct the upstream target air-fuel ratio so as to match the target air-fuel ratio.
[0003]
[Problems to be solved by the invention]
However, since the conventional air-fuel ratio feedback system cannot detect the air-fuel ratio of the exhaust gas flowing out from the upstream catalyst (the air-fuel ratio of the exhaust gas flowing into the downstream catalyst), the upstream catalyst and the downstream catalyst It is impossible to perform air-fuel ratio feedback control in which the state of each is evaluated individually. For this reason, exhaust gas purification using two catalysts efficiently cannot be performed, and the effect of improving the exhaust gas purification rate is small compared to using two catalysts.
[0004]
Therefore, an air-fuel ratio sensor (or oxygen sensor) is also installed between the upstream catalyst and the downstream catalyst, and the air-fuel ratio of the exhaust gas flowing out from the upstream catalyst (the air-fuel ratio of the exhaust gas flowing into the downstream catalyst) ) And the detection result is reflected in the sub-feedback control (upstream target air-fuel ratio).
[0005]
The present inventors have developed this system for practical use. In the process, the following new technical problems have been found. Currently, the system developed by the present inventors uses an upstream catalyst based on sub-feedback control based on the output of the air-fuel ratio sensor downstream of the upstream catalyst and the output of the air-fuel ratio sensor downstream of the downstream catalyst. The target air-fuel ratio control range (rich side guard value and lean side guard value) by this sub-feedback control is corrected by a broken line (comparative example) in FIG. The target air-fuel ratio is corrected within this control range. Generally, the control range of the upstream target air-fuel ratio is set in consideration of the upstream catalyst, and therefore, if the target air-fuel ratio is corrected within this control range, the exhaust gas purification rate of the upstream catalyst will be good. Although the air-fuel ratio of the exhaust gas flowing into the downstream catalyst varies relatively depending on the engine operation state and the state of the upstream catalyst, the control range of the target air-fuel ratio is fixed to a constant value, The air-fuel ratio of the exhaust gas flowing into the downstream catalyst may deviate from the appropriate range, and further, it takes time for the air-fuel ratio deviating from the appropriate range to return to the appropriate range. Therefore, depending on the engine operating condition, the exhaust gas purification rate of the downstream catalyst may decrease, and the exhaust emission may increase.
[0006]
The present invention has been made in view of such circumstances. Therefore, the object of the present invention is to efficiently purify exhaust gas by efficiently using a plurality of catalysts (or catalyst groups) arranged in series in the exhaust passage. It is possible to provide an exhaust gas purification control apparatus for an internal combustion engine that can increase the exhaust gas purification rate.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, an exhaust gas purification control apparatus according to claim 1 of the present invention includes a first sensor for detecting an air-fuel ratio or rich / lean of exhaust gas flowing into an upstream catalyst, and an outflow from the upstream catalyst. A second sensor for detecting the air-fuel ratio or rich / lean of the exhaust gas to be discharged and a third sensor for detecting the air-fuel ratio or rich / lean of the exhaust gas flowing out from the downstream side catalyst are provided. The target air-fuel ratio is set based on the output of the two sensors and / or the output of the third sensor, and the control range of the target air-fuel ratio is switched based on the output of the second sensor and the output of the third sensor. In this way, the control range of the target air-fuel ratio can be switched so that the exhaust gas purification rate of the entire system becomes high while detecting the purification states of both the upstream catalyst and the downstream catalyst. The exhaust gas can be purified efficiently by using both the catalyst and the downstream catalyst efficiently.
[0008]
In general, the exhaust gas purification rate of the catalyst varies depending on the lean / rich component adsorption state of the catalyst, and when the catalyst adsorption state is near the stoichiometric condition, the rich component (HC, CO, etc.) and lean component (NOx) in the exhaust gas. Etc.) can be purified most efficiently, and the highest exhaust gas purification rate can be obtained.
[0009]
Therefore, as described in claim 2, when both the outputs of the second sensor and the third sensor are rich, at least the rich-side guard value in the control range of the target air-fuel ratio is switched to a guard value with a small rich degree. When both the sensor and the third sensor output are lean, at least the lean side guard value of the control range may be switched to a guard value with a small lean degree.
[0010]
That is, when both the outputs of the second sensor and the third sensor are rich, the adsorption state of the upstream catalyst and the downstream catalyst is both rich, and the rich component in the exhaust gas flowing out from each catalyst is reduced. There is a tendency to increase relatively. In this case, at least the rich side guard value in the control range of the target air-fuel ratio is switched to a guard value with a small rich degree. As a result, the control range of the target air-fuel ratio is shifted to a leaner side than usual, and the richness of the air-fuel ratio of the exhaust gas is suppressed, so that the upstream catalyst and the downstream catalyst are saturated and adsorbed with rich components. Is prevented, and the ability to purify rich components of exhaust gas is secured.
[0011]
On the other hand, when both the outputs of the second sensor and the third sensor become lean, the adsorption state of both the upstream catalyst and the downstream catalyst becomes lean, and the lean component in the exhaust gas flowing out from each catalyst is reduced. There is a tendency to increase relatively. In this case, at least the lean side guard value in the control range of the target air-fuel ratio is switched to a guard value with a small lean degree. As a result, the control range of the target air-fuel ratio is shifted to a richer side than usual, and the lean degree of the air-fuel ratio of the exhaust gas is suppressed, so that the upstream catalyst and the downstream catalyst are saturated and adsorbed with the lean component. And the ability to purify the lean components of the exhaust gas is secured.
[0012]
In this case, as in the third aspect, when the control range of the target air-fuel ratio is switched, the switching value may be set according to the output of the second sensor and / or the third sensor. In this way, the correction amount of the target air-fuel ratio by switching the control range of the target air-fuel ratio can be made an appropriate amount according to the state (rich / lean degree) of the upstream side catalyst and the downstream side catalyst. Accuracy can be improved.
[0013]
Further, as in claims 4 and 5, the control gain of the sub feedback control for setting the target air-fuel ratio may be switched based on the output of the second sensor and the output of the third sensor. In this way, it is possible to change the target air-fuel ratio with good response by switching the control gain of the sub feedback control in accordance with the state of the upstream catalyst and the state of the downstream catalyst, and both the upstream catalyst and the downstream catalyst. Can be efficiently used to purify exhaust gas.
[0014]
In this case, as in the sixth aspect, when the control gain is switched, the switching value may be set according to the output of the second sensor and / or the third sensor. In this way, the control gain can be set to an appropriate gain according to the state (rich / lean degree) of the upstream catalyst and the downstream catalyst, and the control accuracy can be improved.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. First, a schematic configuration of the entire engine control system will be described with reference to FIG. An air cleaner 13 is provided at the most upstream portion of the intake pipe 12 of the engine 11 which is an internal combustion engine, and an air flow meter 14 for detecting the intake air amount is provided downstream of the air cleaner 13. A throttle valve 15 and a throttle opening sensor 16 for detecting the throttle opening are provided on the downstream side of the air flow meter 14.
[0016]
Further, a surge tank 17 is provided on the downstream side of the throttle valve 15, and an intake pipe pressure sensor 18 for detecting the intake pipe pressure is provided in the surge tank 17. The surge tank 17 is provided with an intake manifold 19 for introducing air into each cylinder of the engine 11, and a fuel injection valve 20 for injecting fuel is attached in the vicinity of the intake port of the intake manifold 19 of each cylinder. .
[0017]
On the other hand, in the middle of the exhaust pipe 21 (exhaust passage) of the engine 11, an upstream catalyst 22 and a downstream catalyst 23 such as a three-way catalyst for reducing CO, HC, NOx, etc. in the exhaust gas are installed in series. Yes. Further, a first sensor 24, a second sensor 25, and a third sensor 26 are installed on the upstream side and downstream side of the upstream catalyst 22 and on the downstream side of the downstream catalyst 23, respectively. In this case, the first sensor 24 is an air-fuel ratio sensor (linear A / F sensor) that outputs a linear air-fuel ratio signal corresponding to the air-fuel ratio of the exhaust gas flowing into the upstream catalyst 22, and the second sensor 25. As the third sensor 26, an oxygen sensor whose output voltage is inverted according to the rich / lean of the exhaust gas flowing out from the catalysts 22 and 23 is used. The second sensor 25 and / or the third sensor 26 may be an air-fuel ratio sensor (linear A / F sensor), like the first sensor 24. Of course, an oxygen sensor is used as the first sensor 24. Also good.
[0018]
A cooling water temperature sensor 27 that detects the cooling water temperature and a crank angle sensor 28 that detects the engine rotation speed are attached to the cylinder block of the engine 11.
[0019]
These various sensor outputs are input to an engine control circuit (hereinafter referred to as “ECU”) 29. This ECU 29 is mainly composed of a microcomputer, and serves as an air-fuel ratio feedback control means for feedback-controlling the air-fuel ratio by executing the programs shown in FIGS. 2 to 5 stored in a built-in ROM (storage medium). To play a role. The processing contents of each program will be described below.
[0020]
[Calculation of fuel injection amount]
The fuel injection amount calculation program in FIG. 2 is a program for setting the required fuel injection amount TAU through air-fuel ratio feedback control, and is executed at every predetermined crank angle. When this program is started, first, at step 101, the basic fuel injection amount TP is calculated from a map or the like based on the operation state parameters such as the current intake pipe pressure and the engine rotation speed. It is determined whether or not a fuel ratio feedback condition is satisfied. Here, the air-fuel ratio feedback condition is that the engine cooling water temperature is equal to or higher than a predetermined temperature, the engine operating state is not in a high rotation / high load region, and the air-fuel ratio feedback condition when all these conditions are satisfied. Is established.
[0021]
If it is determined in step 102 that the air-fuel ratio feedback condition is not satisfied, the process proceeds to step 106, the air-fuel ratio correction coefficient FAF is set to “1.0”, and the process proceeds to step 105. In this case, feedback correction of the air-fuel ratio is not performed.
[0022]
On the other hand, if it is determined in step 102 that the air-fuel ratio feedback condition is satisfied, the routine proceeds to step 103, where a target air-fuel ratio setting program shown in FIG. The air-fuel ratio λTG is set, and in the next step 104, the air-fuel ratio correction coefficient FAF is determined according to the deviation between the output of the first sensor 24 upstream of the upstream catalyst 22 (the air-fuel ratio of the exhaust gas) and the target air-fuel ratio λTG. Is calculated.
[0023]
Thereafter, in step 105, the fuel injection amount TAU is calculated by the following equation using the basic fuel injection amount TP, the air-fuel ratio correction coefficient FAF, and other correction coefficients FALL, and this program is terminated.
TAU = TP × FAF × FALL
[0024]
[Target air-fuel ratio setting]
Next, the processing contents of the target air-fuel ratio setting program of FIG. 3 executed in step 103 of FIG. 2 will be described. This program is a program that executes sub-feedback control for setting the target air-fuel ratio λTG based on the output of the second sensor 25 and the output of the third sensor 26.
[0025]
When this program is started, first, in step 201, the target voltage setting program of FIG. 4 is executed, and a second map is output according to the output voltage of the third sensor 26 (the air-fuel ratio downstream of the downstream catalyst 23). The target voltage Vtg of the sensor 25 is set. The map characteristic of the target voltage Vtg indicates that the target voltage of the second sensor 25 increases as the output voltage of the third sensor 26 increases in a region where the output voltage of the third sensor 26 is within a predetermined range (A <output voltage <B). In a region where Vtg is low and the output voltage of the third sensor 26 is less than or equal to the predetermined value A, the target voltage Vtg of the second sensor 25 is constant at the upper limit value, and the output voltage of the third sensor 26 is greater than or equal to the predetermined value B Then, the target voltage Vtg of the second sensor 25 is constant at the lower limit value.
[0026]
After setting the target voltage Vtg, the process proceeds to step 202 in FIG. 3, and the state of the upstream catalyst 22 depends on whether the output voltage VOX2 of the second sensor 25 disposed downstream of the upstream catalyst 22 is higher or lower than the target voltage Vtg. Is rich or lean, and if it is lean, the routine proceeds to step 203, where it is determined whether or not the previous time was also lean. If both the previous time and the current time are lean, the routine proceeds to step 204, where the rich integral amount λIR is calculated from a map or the like according to the current intake air amount. After calculating the rich integral amount λIR, the process proceeds to step 205, the target air-fuel ratio λTG is corrected to the rich side by λIR, and then the process proceeds to step 213.
[0027]
If the previous time is rich and the current time is reversed to lean, the process proceeds to step 206, where the skip amount λSKR to the rich side is determined from a map or the like according to the output of the third sensor 26 (the adsorption state of the downstream side catalyst 23). calculate. After calculating the rich skip amount λSKR, the process proceeds to step 207, the target air-fuel ratio λTG is corrected to the rich side by λIR + λSKR, and then the process proceeds to step 213.
[0028]
On the other hand, if it is determined in the skip 202 that the output voltage VOX2 of the second sensor 25 is higher than the target voltage Vtg (the state of the upstream catalyst 22 is rich), the process proceeds to step 208, and was the previous time also rich? Determine whether or not. If both the previous time and the current time are rich, the process proceeds to step 209, and the lean integral amount λIL is calculated from a map or the like according to the current intake air amount. After calculating the lean integral amount λIL, the process proceeds to step 210, the target air-fuel ratio λTG is corrected to the lean side by λIL, and then the process proceeds to step 213.
[0029]
Further, when the previous time is lean and the current time is richly reversed, the process proceeds to step 211, and the skip amount λSKL to the lean side is determined from a map or the like according to the output of the third sensor 26 (adsorption state of the downstream side catalyst 23). calculate. After calculating the lean skip amount λSKL, the process proceeds to step 212, the target air-fuel ratio λTG is corrected to the lean side by λIL + λSKL, and then the process proceeds to step 213.
[0030]
In step 213, a target air-fuel ratio guard processing program shown in FIG. 5 to be described later is executed to limit the target air-fuel ratio λTG upstream of the upstream catalyst 22 to a predetermined control range, and then the routine proceeds to step 214 where the upstream air-fuel ratio at that time The rich / lean of the side catalyst 22 is memorized and the program is terminated.
[0031]
[Target air-fuel ratio guard process]
Next, the processing content of the target air-fuel ratio guard processing program of FIG. 5 executed in step 213 of FIG. 3 will be described. This program plays a role corresponding to the target air-fuel ratio guard means in the claims. When this program is started, first, in step 301, the rich / lean of the output of the second sensor 25 (the state of the upstream catalyst 22) and the rich / lean of the output of the third sensor 26 (the state of the downstream catalyst 23) / The rich side guard value Grich and the lean side guard value Glean of the target air-fuel ratio λTG are set by a table according to the combination with lean. At this time, the combinations of the output of the second sensor 25 and the output of the third sensor 26 are classified into the following four types (1) to (4).
[0032]
(1) When both the outputs of the second sensor 25 and the third sensor 26 are rich, the rich-side guard value Grich is switched to a guard value Rmin having a lower richness than usual, and the lean-side guard value Glean is changed from normal. Switch to a guard value Lmax with a large lean degree. Note that the lean guard value Glean may be set to the normal value Lav.
[0033]
(2) When the output of the second sensor 25 is lean and the output of the third sensor 26 is rich, the rich side guard value Grich and the lean side guard value Glean are switched to the normal values Rav and Lav, respectively.
[0034]
(3) When both the outputs of the second sensor 25 and the third sensor 26 are lean, the lean side guard value Glean is switched to a guard value Lmin having a leaner degree than usual, and the rich side guard value Grich is changed from normal. Switch to a guard value Rmax with a high degree of richness. The rich side guard value Grich may be set to the normal value Rav.
[0035]
(4) When the output of the second sensor 25 is rich and the output of the third sensor 26 is lean, the rich side guard value Grich and the lean side guard value Glean are switched to normal values Rav and Lav, respectively. Rav is set to an intermediate value between Rmax and Rmin, and Lav is set to an intermediate value between Lmax and Lmin.
[0036]
After setting the rich-side guard value Grich and the lean-side guard value Glean as described above, the process proceeds to step 302 and updated in any one of steps 205, 207, 210, and 212 of the target air-fuel ratio setting program of FIG. The target air-fuel ratio λTG is subjected to a guard process using the rich guard value Grich and the lean guard value Glean. That is, if the target air-fuel ratio λTG before guard processing is within the range of both guard values Grich and Glean, the target air-fuel ratio λTG before guard processing is used as it is as the final target air-fuel ratio λTG. If the previous target air-fuel ratio λTG is shifted to the rich side from the rich-side guard value Grich, the final target air-fuel ratio λTG is replaced with the rich-side guard value Grich. Further, if the target air-fuel ratio λTG before the guard process is shifted to the lean side from the lean-side guard value Glean, the final target air-fuel ratio λTG is replaced with the lean-side guard value Glean. As a result, the target air-fuel ratio λTG is limited between the rich side guard value Grich and the lean side guard value Glean.
[0037]
An execution example of the air-fuel ratio feedback control of the present embodiment described above will be described with reference to the time chart of FIG. In the time chart of FIG. 6, the behavior of the comparative example is indicated by a broken line.
[0038]
In the comparative example, the rich side / lean side guard values Grich and Glean are fixed to constant values. Since the air-fuel ratio of the exhaust gas flowing into the downstream catalyst 23 varies relatively depending on the engine operation state and the state of the upstream catalyst 22, the rich side / lean side guard values Grich and Glean of the target air-fuel ratio λTG become constant values. If it is fixed, the air-fuel ratio of the exhaust gas flowing into the downstream catalyst 23 may deviate from the appropriate range, and further, it takes time for the air-fuel ratio deviating from the appropriate range to return to the appropriate range. . For this reason, depending on the engine operating condition, the exhaust gas purification rate of the downstream catalyst 23 may decrease, and the exhaust emission may increase.
[0039]
On the other hand, in this embodiment, the combination of the rich / lean output of the second sensor 25 (the state of the upstream catalyst 22) and the rich / lean output of the third sensor 26 (the state of the downstream catalyst 23). Accordingly, the rich side / lean side guard values Grich and Glean are switched.
[0040]
For example, during the period (1) in FIG. 6, the outputs of the second sensor 25 and the third sensor 26 are both rich. In this state, the adsorption states of the upstream catalyst 22 and the downstream catalyst 23 are both rich, and the rich components in the exhaust gas flowing out from the catalysts 22 and 23 tend to be relatively large.
[0041]
Therefore, when both the outputs of the second sensor 25 and the third sensor 26 are rich, the rich-side guard value Grich is switched to a guard value Rmin that is less rich than usual. As a result, the control range of the target air-fuel ratio λTG is shifted to the leaner side than usual, and the richness of the air-fuel ratio of the exhaust gas is suppressed, so that the upstream catalyst 22 and the downstream catalyst 23 are saturated and adsorbed with rich components. And the ability to purify rich components of exhaust gas is ensured.
[0042]
Further, during the period {circle around (3)} in FIG. 6, the outputs of the second sensor 25 and the third sensor 26 are both lean. In this state, the adsorption states of the upstream catalyst 22 and the downstream catalyst 23 are both lean, and the lean components in the exhaust gas flowing out from the catalysts 22 and 23 tend to be relatively large.
[0043]
Therefore, when both the outputs of the second sensor 25 and the third sensor 26 are lean, the lean side guard value Glean is switched to a guard value Lmin having a smaller lean degree than usual. As a result, the control range of the target air-fuel ratio λTG is shifted to a richer side than usual, and the lean degree of the air-fuel ratio of the exhaust gas is suppressed, so that the upstream catalyst 22 and the downstream catalyst 23 are saturated and adsorbed with lean components. This prevents the lean component of the exhaust gas from being purified.
[0044]
Further, during the periods (2) and (4) in FIG. 6, one output of the second sensor 25 and the third sensor 26 is lean, and the other output is rich. In this state, the rich / lean in the adsorption state of the upstream catalyst 22 and the downstream catalyst 23 are opposite to each other. Therefore, the upstream catalyst 22 and the downstream catalyst 23 are used in a well-balanced manner, and the exhaust gas rich component and lean are used. Ingredients can be purified efficiently.
[0045]
Therefore, when one output of the second sensor 25 and the third sensor 26 is lean and the other output is rich, the rich side guard value Grich and the lean side guard value Glean are switched to the normal values Rav and Lav, respectively. As a result, the control range of the target air-fuel ratio λTG is set so that the stoichiometric is the center, and the air-fuel ratio of the exhaust gas is controlled so that the stoichiometric is the center, so that the upstream catalyst 22 and the downstream catalyst 23 Is used in a well-balanced manner to efficiently purify the rich and lean components of the exhaust gas.
[0046]
In the present embodiment, the switching values Rmin, Rav, Rmax of the rich side guard value GRich and the switching values Lmin, Lav, Lmax of the lean side guard value Glean are fixed values. You may make it set with a map or numerical formula etc. according to the output of the sensor 25, and / or the output of the 3rd sensor 26. FIG. In this way, the correction amount of the target air-fuel ratio λTG by switching the guard value can be set to an appropriate amount according to the state (rich / lean degree) of the upstream catalyst 22 and the downstream catalyst 23, and the control accuracy Can be improved.
[0047]
In the present embodiment, the guard value of the target air-fuel ratio λTG is switched according to the combination of the rich / lean output of the second sensor 25 and the rich / lean output of the third sensor 26. In addition, depending on the combination of the rich / lean of the output of the second sensor 25 and the rich / lean of the output of the third sensor 26, the control gain of the sub feedback (for example, the skip amount λSKR, λSKL of the target air-fuel ratio λTG and / or The integration amounts λIR and λIL may be switched.
[0048]
In this way, the control gain can be switched according to the state of the upstream catalyst 22 and the state of the downstream catalyst 23 to change the target air-fuel ratio λTG with good response, so the upstream catalyst 22 and the downstream catalyst 23 can be changed. Both of these can be used efficiently and exhaust gas can be purified efficiently. In this case, the switching value of the control gain may be a fixed value, but may be set by a map or a mathematical formula according to the output of the second sensor 25 or the output of the third sensor 26.
[0049]
Further, both the control range of the target air-fuel ratio λTG and the control gain of the sub feedback control are switched according to the combination of the rich / lean output of the second sensor 25 and the rich / lean output of the third sensor 26. May be.
[0050]
In the present embodiment, the target voltage Vtg of the second sensor 25 is set according to the output voltage of the third sensor 26 (the air-fuel ratio downstream of the downstream catalyst 23) by the target air-fuel ratio setting program of FIG. 2 The target air-fuel ratio λTG is set by determining whether the upstream catalyst 22 is rich or lean depending on whether the output voltage VOX2 of the sensor 25 is higher or lower than the target voltage Vtg. The setting method may be variously changed. For example, one of the second sensor 25 and the third sensor 26 is selected according to the engine operating state, the state of each of the catalysts 22 and 23, and the output of the sensor. The target air-fuel ratio λTG may be set based on the above.
[0051]
The system configuration in FIG. 1 is an embodiment in which two catalysts 22 and 23 are arranged in series in the exhaust pipe 21, but three or more catalysts are arranged and divided into two catalyst groups. The present invention may be applied by regarding each catalyst group as one catalyst.
[0052]
In addition, the scope of application of the present invention is not limited to an exhaust purification system using only a three-way catalyst. The present invention can be applied to an exhaust purification system or a three-way catalyst combining a three-way catalyst and another catalyst (such as a NOx catalyst). The present invention may be applied to an exhaust purification system using only a catalyst other than the above.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an entire engine control system showing an embodiment of the present invention. FIG. 2 is a flowchart showing a process flow of a fuel injection amount calculation program. FIG. 3 is a process flow of a target air-fuel ratio setting program. FIG. 4 is a flowchart showing a process flow of a target voltage setting program. FIG. 5 is a flowchart showing a process flow of a target air-fuel ratio guard process program. FIG. 6 is a second sensor output, a third sensor output, and a target sky. Time chart showing behavior of fuel ratio and target air-fuel ratio guard value
DESCRIPTION OF SYMBOLS 11 ... Engine (internal combustion engine), 12 ... Intake pipe, 20 ... Fuel injection valve, 21 ... Exhaust pipe (exhaust passage), 22 ... Upstream catalyst, 23 ... Downstream catalyst, 24 ... First sensor, 25 ... Second Sensors 26... Third sensor 29. ECU (air-fuel ratio feedback control means, target air-fuel ratio guard means).

Claims (6)

In an internal combustion engine in which a plurality of catalysts or a plurality of catalyst groups are arranged in series in an exhaust passage,
A first sensor for detecting an air-fuel ratio or rich / lean of exhaust gas flowing into a catalyst or a catalyst group (hereinafter referred to as “upstream catalyst”) disposed on the upstream side;
A second sensor for detecting the air-fuel ratio or rich / lean of the exhaust gas flowing out from the upstream catalyst;
A third sensor for detecting an air-fuel ratio or rich / lean of exhaust gas flowing out from a catalyst or catalyst group (hereinafter referred to as “downstream catalyst”) disposed on the downstream side;
An air-fuel ratio in which a target air-fuel ratio is set based on the output of the second sensor and / or the output of the third sensor, and the air-fuel ratio is feedback controlled based on a deviation between the target air-fuel ratio and the output of the first sensor Feedback control means;
Target air-fuel ratio guard means for limiting the target air-fuel ratio to a predetermined control range,
The exhaust gas purification control apparatus for an internal combustion engine, wherein the target air-fuel ratio guard means switches the control range based on the output of the second sensor and the output of the third sensor. The target air-fuel ratio guard means switches at least the rich side guard value in the control range to a guard value with a small rich degree when both the outputs of the second sensor and the third sensor are rich, and the second sensor and 2. The exhaust gas purification control apparatus for an internal combustion engine according to claim 1, wherein when both the outputs of the third sensors are lean, at least the lean side guard value of the control range is switched to a guard value with a small lean degree. . 3. The target air-fuel ratio guard means sets the switching value according to the output of the second sensor and / or the third sensor when switching the control range. An exhaust gas purification control device for an internal combustion engine. The control gain switching means for switching the control gain of the sub-feedback control for setting the target air-fuel ratio based on the output of the second sensor and the output of the third sensor is provided. 4. An exhaust gas purification control apparatus for an internal combustion engine according to any one of 3 above. In an internal combustion engine in which a plurality of catalysts or a plurality of catalyst groups are arranged in series in an exhaust passage,
A first sensor for detecting an air-fuel ratio or rich / lean of exhaust gas flowing into a catalyst or a catalyst group (hereinafter referred to as “upstream catalyst”) disposed on the upstream side;
A second sensor for detecting the air-fuel ratio or rich / lean of the exhaust gas flowing out from the upstream catalyst;
A third sensor for detecting an air-fuel ratio or rich / lean of exhaust gas flowing out from a catalyst or catalyst group (hereinafter referred to as “downstream catalyst”) disposed on the downstream side;
An air-fuel ratio in which a target air-fuel ratio is set based on the output of the second sensor and / or the output of the third sensor, and the air-fuel ratio is feedback controlled based on a deviation between the target air-fuel ratio and the output of the first sensor Feedback control means;
An internal combustion engine comprising: control gain switching means for switching a control gain of sub feedback control for setting the target air-fuel ratio based on an output of the second sensor and an output of the third sensor Exhaust gas purification control device. 6. The internal combustion engine according to claim 4, wherein the control gain changing unit sets the switching value according to the output of the second sensor and / or the third sensor when the control gain is switched. Engine exhaust gas purification control device.

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