JP2018096341A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

It is an object of the present invention to suitably suppress deterioration of exhaust emission in an exhaust gas purification apparatus for an internal combustion engine including a first NSR catalyst, a second NSR catalyst, a bypass passage, and a flow path switching valve. .
In the case where A rich spike processing for reducing the NO _X occluded in the at least one of the first 1NSR catalyst and the 2NSR catalyst is performed, NO _X storage amount of the 2NSR catalyst is equal to or higher than a predetermined threshold value If so, the flow path switching valve is controlled so that the exhaust of the internal combustion engine bypasses the first NSR catalyst and flows into the second NSR catalyst. Further, in the above case where the rich spike control is executed, if it is less than _the NO _X storage amount is the predetermined threshold value of the 2NSR catalyst, to flow first 2NSR catalyst after the exhaust of the internal combustion engine via the first 1NSR catalyst The flow path switching valve is controlled.
[Selection] Figure 4

Description

The present invention relates to an exhaust purifying apparatus for an internal combustion engine, more particularly to an exhaust gas purifying apparatus comprising two of the NO _X storage reduction catalyst arranged in series (NSR (NOX Storage Reduction) catalyst).

  As an exhaust gas purification device for an internal combustion engine that is operated with lean combustion, an NSR catalyst, a three-way catalyst arranged downstream of the NSR catalyst, and an exhaust passage upstream of the NSR catalyst are branched, and three downstream of the NSR catalyst. An exhaust purification apparatus comprising: a bypass passage that joins an exhaust passage upstream of the original catalyst; and a flow path switching valve that switches an exhaust flow path so that exhaust flows through either the bypass passage or the NSR catalyst. When the air-fuel ratio is a lean air-fuel ratio, and when the exhaust air-fuel ratio is less than the stoichiometric air-fuel ratio and the exhaust temperature is less than a predetermined temperature, the exhaust flows through the NSR catalyst, the exhaust air-fuel ratio is less than the stoichiometric air-fuel ratio, and the exhaust temperature is predetermined. A device that controls a flow path switching valve so that exhaust flows through a bypass passage when the temperature is higher than the temperature is known (see, for example, Patent Document 1).

JP 05-340236 A JP 2000-303825 A

Here, the structure which arrange | positions an NSR catalyst instead of the above-mentioned three-way catalyst can be considered. That is, the first NSR catalyst is branched from the first NSR catalyst disposed in the exhaust passage of the internal combustion engine, the second NSR catalyst disposed in the exhaust passage downstream from the first NSR catalyst, and the exhaust passage upstream from the first NSR catalyst. Exhaust gas comprising a bypass passage that joins an exhaust passage downstream from the catalyst and upstream from the second NSR catalyst, and a flow path switching valve that switches the exhaust flow path so that the exhaust flows through either the bypass passage or the first NSR catalyst A purification device is conceivable. In such a configuration, when the reduction rich spike treatment for of the NO _X which is stored in the 1NSR catalyst or the 2NSR catalyst is performed, as in the prior art described above, the exhaust gas air-fuel ratio and the exhaust temperature If the flow path switching valve is controlled based on the above, exhaust emission may be deteriorated.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a rich spike in an exhaust gas purification apparatus for an internal combustion engine including a first NSR catalyst, a second NSR catalyst, a bypass passage, and a flow path switching valve. An object of the present invention is to provide a technique capable of suitably suppressing deterioration of exhaust emission during processing.

The present invention employs the following means in order to solve the above-described problems. That is, the exhaust gas purification apparatus for an internal combustion engine according to the present invention is a catalyst disposed in an exhaust passage of an internal combustion engine that is operated with lean combustion, and when the air-fuel ratio of the exhaust gas is a lean air-fuel ratio, NO _{X in the} exhaust gas is exhausted. A first NSR catalyst that desorbs the stored NO _X when the exhaust air-fuel ratio is a rich air-fuel ratio, and reduces the desorbed NO _X by the unburned fuel component in the exhaust; The catalyst is disposed in the exhaust passage downstream of the first NSR catalyst, and stores NO _X in the exhaust when the air-fuel ratio of the exhaust is a lean air-fuel ratio, and the air-fuel ratio of the exhaust is a rich air-fuel ratio and desorbed the NO _X that has been occluded when a second 2NSR catalyst for reducing the desorbed NO _X by unburned fuel components in exhaust gas, branches from the exhaust passage upstream of the first 1NSR catalyst The first NSR A bypass passage that joins the exhaust passage downstream from the medium and upstream from the second NSR catalyst, and a flow path switching valve that switches the exhaust passage so that exhaust flows through either the bypass passage or the first NSR catalyst , the air-fuel ratio of exhaust gas flowing through the upstream the exhaust passage of the branch portion of the bypass passage by the rich air-fuel ratio, reducing the NO _X occluded in the at least one of the first 1NSR catalyst and the second 2NSR catalyst and rich spike processing means for executing the rich spike processing for, by integrating _the amount of NO _X flowing out to the downstream side of the first 2NSR catalyst as a trigger at the end of the rich spike action by the rich spike processing means, integrated calculating means for calculating the NO _X emissions in the integrated NO _X emissions calculated by the calculating means is equal to or higher than a predetermined value When Tsu, wherein as the rich spike control is executed, a rich spike controller that controls the rich spike processing unit, an acquisition unit for acquiring _the NO _X storage amount of the first 2NSR catalyst, the rich spike processing There when executed, NO _X storage amount acquired by the acquisition means to control the flow path switching valve so that the exhaust equal to or greater than a predetermined threshold value flows through the bypass passage, acquired by the acquiring means that _the NO _X storage amount is so and a flow passage control unit for the exhaust is less than the predetermined threshold value to control the flow path switching valve so as to flow the first 1NSR catalyst.

  According to the present invention, in an exhaust gas purification apparatus for an internal combustion engine that includes a first NSR catalyst, a second NSR catalyst, a bypass passage, and a flow path switching valve, it is preferable to suppress deterioration of exhaust emission when performing rich spike processing. Can do.

It is a figure which shows schematic structure of the internal combustion engine to which this invention is applied, and its intake / exhaust system. When the first 2NO _X storage amount rich spike treatment in a state which is less than the predetermined threshold value is performed, the rich spike flag, bypass on / off, the 1NO _X storage amount, the 2NO _X storage amount, engine emissions HC amount FIG. 6 is a graph showing changes with time of the second NSR catalyst exhaust HC amount and the second NSR catalyst exhaust NO _X amount. When the first 2NO _X storage amount rich spike treatment in a state equal to or greater than a predetermined threshold is performed, the rich spike flag, bypass on / off, the 1NO _X storage amount, the 2NO _X storage amount, engine emissions HC amount FIG. 6 is a graph showing changes with time of the second NSR catalyst exhaust HC amount and the second NSR catalyst exhaust NO _X amount. It is a flowchart which shows the control procedure of the flow-path switching valve at the time of rich spike process execution.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which an exhaust gas purification apparatus according to the present invention is applied and its intake and exhaust system. An internal combustion engine 1 shown in FIG. 1 is a spark ignition type internal combustion engine that can switch between an operation for burning a stoichiometric air-fuel mixture (stoichiometric operation) and an operation for burning a lean air-fuel mixture (lean operation) ( A fuel injection valve 1a that directly injects fuel into a cylinder (not shown). The fuel injection valve 1a may be configured to inject fuel into the intake port of the internal combustion engine 1.

The internal combustion engine 1 is connected to the exhaust passage 2. A first catalyst casing 3 and a second catalyst casing 4 are arranged in the exhaust passage 2 from the upstream side in the exhaust flow direction. Further, the exhaust passage 2 is provided with a bypass passage 5 that branches from a portion upstream of the first catalyst casing 3 and merges with a portion downstream of the first catalyst casing 3 and upstream of the second catalyst casing 4. ing. Hereinafter, a portion of the exhaust passage 2 that extends from the branch portion of the bypass passage 5 to the joining portion with the bypass passage 5 via the first catalyst casing 3 is referred to as a main passage 20. In the exhaust passage 2, the flow for switching the exhaust flow path is arranged so that the arrangement flows in either the main passage 20 (first NSR catalyst) or the bypass passage 5 at the junction with the bypass passage 5. A path switching valve 6 is attached. The flow path switching valve 6 may be attached to a branch portion of the bypass passage 5 in the exhaust passage 2.

Here, the first catalyst casing 3 in the second catalyst casing 4, when the air-fuel ratio of the exhaust gas is lean air-fuel ratio occludes NO _X in the exhaust gas, when the air-fuel ratio of the exhaust gas is a rich air-fuel ratio Accommodates an NSR catalyst for desorbing the stored NO _X and reducing the desorbed NO _X by an unburned fuel component (for example, HC) in the exhaust gas. Hereinafter, the NSR catalyst accommodated in the first catalyst casing 3 is referred to as a first NSR catalyst, and the NSR catalyst accommodated in the second catalyst casing 4 is referred to as a second NSR catalyst.

The internal combustion engine 1 configured as described above is provided with an ECU (Electronic Control Unit) 7. The ECU 7 is an electronic control unit including a CPU, a ROM, a back RAM, and the like. ECU7 is first 1NO _X sensor 8, first 2NO _X sensor 9, the exhaust gas temperature sensor 10, crank position sensor 11, an accelerator position sensor 12, the various sensors and electrical connection, such as an air flow meter 13, the output signals of various sensors Can be entered. The first NO _X sensor 8 is disposed in a portion upstream of the second catalyst casing 4 in the exhaust passage 2 downstream from the junction with the bypass passage 5 and measures the NO _X concentration of the exhaust flowing into the second catalyst casing 4. . The second NO _X sensor 9 is disposed in the exhaust passage 2 downstream from the second catalyst casing 4 and measures the NO _X concentration of the exhaust gas flowing out from the second catalyst casing 4. The exhaust temperature sensor 10 is disposed in the exhaust passage 2 downstream from the second catalyst casing 4 and measures the temperature of the exhaust gas flowing out from the second catalyst casing 4. The crank position sensor 11 measures the rotational position of the crankshaft of the internal combustion engine 1. The accelerator position sensor 12 measures an operation amount (accelerator opening) of an accelerator pedal (not shown). The air flow meter 13 is attached to the intake passage 14 of the internal combustion engine 1 and measures the amount of air flowing through the intake passage 14 (intake air amount).

  The ECU 7 is electrically connected to various devices such as the fuel injection valve 1a and the flow path switching valve 6 so that these various devices can be electrically controlled. For example, the ECU 7 calculates the engine load factor (based on the intake air amount at full load) calculated based on the engine rotation speed calculated from the output signal of the crank position sensor 11 and the output signal (intake air amount) of the air flow meter 13. Based on the ratio of the actual intake air amount), the target fuel injection amount and target injection timing of the fuel injection valve 1a are calculated, and the fuel injection valve 1a is controlled according to the target fuel injection amount and target injection timing. At that time, if the engine operating state determined by the engine speed and the engine load factor is in the low rotation / low load factor region, the target fuel injection amount is determined so that the air-fuel ratio of the air-fuel mixture becomes the lean air-fuel ratio. Shall be. When the engine operating state is in the medium rotation / medium load factor region and the high rotation / high load factor region, the target fuel injection amount is determined so that the target air / fuel ratio becomes the stoichiometric air / fuel ratio.

Further, ECU 7 includes an exhaust flow rate which is calculated from the measured values and the fuel injection amount of the air flow meter 13, a NO _X concentration measured by the 2NO _X sensor 9, as parameters, a unit from the second catalyst casing 4 times The amount of NO _X flowing out into the engine is calculated and the amount of NO _X is integrated to calculate the integrated NO _X discharge amount (corresponding to “calculation means” according to the present invention). When the accumulated NO _X emission amount becomes equal to or greater than a predetermined value, the ECU 7 executes a rich spike process to reduce NO _X stored in at least one of the first NSR catalyst and the second NSR catalyst ( Equivalent to "rich spike control means" according to the present invention). The rich spike process here is a process for changing the air-fuel ratio of the exhaust to a rich air-fuel ratio by supplying fuel from the fuel injection valve 1a of the cylinder in the exhaust stroke. In the case where the fuel injection valve 1a is configured to inject fuel into the intake port, the rich spike process may be performed by setting the air-fuel ratio of the air-fuel mixture to a rich air-fuel ratio. In the configuration in which the fuel addition valve is attached to the exhaust passage 2 upstream from the branch portion between the main passage 20 and the bypass passage 5, the rich spike processing is performed by adding fuel into the exhaust from the fuel addition valve. It may be broken. When the ECU 7 executes the rich spike processing by the various methods described above, the “rich spike processing means” according to the present invention is realized. It should be noted that the above-mentioned accumulated NO _X emission amount is reset to “0” when the rich spike processing is completed.

Further, when the internal combustion engine 1 is in a lean operation, the ECU 7 controls the flow path switching valve 6 so that the exhaust flows through the main passage 20, thereby converting NO _X contained in the exhaust into the first NSR catalyst and the second NSR. Occluded by catalyst. Further, when the internal combustion engine 1 is stoichiometrically operated, the flow path switching valve 6 is controlled so that the exhaust gas flows through the bypass passage 5, thereby suppressing the thermal deterioration of the first NSR catalyst.

  In the present embodiment, the ECU 7 controls the flow path switching valve 6 during execution of the rich spike process in addition to the various controls described above. Below, the control method of the flow-path switching valve 6 at the time of execution of rich spike processing is described.

Here, as described above, when the internal combustion engine 1 is operated lean, the flow path switching valve 6 is controlled so that the exhaust flows through the main passage 20. At this time, if the NO _X storage amount of the first NSR catalyst is relatively small, substantially the entire amount of NO _{X in} the exhaust gas is stored in the first NSR catalyst. However, when the NO _X storage amount of the first NSR catalyst increases to some extent, so-called “breakthrough” occurs in which a part of NO _{X in} the exhaust gas is not stored in the first NSR catalyst but passes through the NSR catalyst. When such breakthrough of the NO _X storage capacity occurs, NO _X that has passed through the first NSR catalyst is stored in the second NSR catalyst.

In the case where rich spike processing in a state where the NO _X is not almost absorbed in the first 2NSR catalyst is performed, the exhaust flow path switching valve 6 is controlled to flow the bypass passage 5, Not included in the exhaust although part of the combusted fuel components can be consumed in order to reduce NO _X in the amount of very small that was stored in the first 2NSR catalyst, unburned fuel component of the remaining majority are consumed at the 2NSR catalyst Without flowing out of the second NSR catalyst. As a result, there is a risk that the amount of unburned fuel components discharged into the atmosphere increases.

On the other hand, when the rich spike process is executed in a state where NO _X is occluded in the second NSR catalyst, if the flow path switching valve 6 is controlled so that the exhaust flows through the main passage 20, it is included in the exhaust. because most unburned fuel component is consumed in the reduction of the NO _X that was stored in the first 1NSR catalyst, it may be difficult to reduce the NO _X that was stored in the first 2NSR catalyst. Further, since the unburned fuel component contained in the exhaust is consumed in the first NSR catalyst, the air-fuel ratio of the exhaust flowing into the second NSR catalyst becomes an air-fuel ratio in the vicinity of the theoretical air-fuel ratio, and is therefore stored in the second NSR catalyst. which was NO _X is desorbed, possibly the elimination NO _X flows out from the 2NSR catalyst without being reduced is. As a result, there is a possibility that the greater the amount of NO _X discharged into the atmosphere.

In the present embodiment, the flow path switching valve 6 is controlled when the rich spike process is executed in consideration of various situations as described above. First, when the rich spike operation is performed, NO _X storage amount of the 2NSR catalyst (hereinafter, referred to as "the 2NO _X storage amount") is less than the predetermined threshold value, and is conducting the main passage 20 bypassing The flow path switching valve 6 is controlled so that the passage 5 is blocked. Here, in the case where the 2NO _X storage amount rich spike treatment in a state which is less than the predetermined threshold value is performed, the state of rich spike flag, a state of the bypass passage 5, NO _X storage amount of the 1NSR catalyst ( hereinafter referred to as a "first 1NO _X storage amount"), a first 2NO _X storage amount, the amount of HC discharged from the internal combustion engine 1 (hereinafter referred to as) a "engine exhaust HC amount", is discharged from the 2NSR catalyst Over time (hereinafter referred to as “second NSR catalyst exhaust HC amount”) and NO _X amount exhausted from the second NSR catalyst (hereinafter referred to as “second NSR catalyst exhaust NO _X amount”). As shown in FIG. The term rich spike flag, in a state in which the engine 1 is lean operation, the accumulated NO _X emissions above is the on when equal to or greater than a predetermined value (when the rich spike control is started), This flag is turned off when the rich spike processing is completed. The predetermined threshold value here is be discharged into the atmosphere without NO _X less than the predetermined threshold value is reduced to a value deterioration of the exhaust emission is considered within an allowable range. Note that the predetermined threshold may be set to “0” from the viewpoint of suppressing the deterioration of exhaust emission as much as possible.

  In FIG. 2, when the rich spike flag is switched from off to on to start the rich spike processing (t1 in FIG. 2), the ECU 7 flows to maintain the bypass passage 5 in the cutoff state (bypass off). The path switching valve 6 is controlled. That is, the ECU 7 controls the flow path switching valve 6 so as to maintain the state where the main passage 20 is conducted and the bypass passage 5 is shut off.

When the rich spike process is started as the rich spike flag is switched from off to on, the air-fuel ratio of the exhaust discharged from the internal combustion engine 1 shifts from the lean air-fuel ratio to the rich air-fuel ratio, and the engine exhaust HC The amount increases. When such exhaust flows into the first NSR catalyst, the NO _X stored in the first NSR catalyst is reduced by the HC in the exhaust, so the first NO _X storage amount decreases. Thus, when the HC contained in the exhaust gas of a rich air-fuel ratio is consumed to reduce occluded NO _X of the 1NSR catalyst, the air-fuel ratio of the air-fuel ratio is near the stoichiometric air-fuel ratio of the exhaust gas discharged from the 1NSR catalyst become. When such exhaust near the stoichiometric air-fuel ratio flows into the second NSR catalyst, the NO _X stored in the second NSR catalyst is desorbed, but the desorbed NO _X is discharged from the second NSR catalyst without being reduced. . However, since the 2NO _X storage amount during the rich-spike treatment start is less than the predetermined threshold, the 2NSR catalyst discharge amount of NO _X becomes extremely small amount. In addition, since the amount of HC contained in the exhaust gas near the stoichiometric air-fuel ratio is extremely small, even if the HC contained in the exhaust gas is not consumed by the second NSR catalyst, the second NSR catalyst exhaust HC amount is extremely small. When the second NSR catalyst exhaust HC amount and the second NSR catalyst exhaust NO _X amount at the time of execution of the rich spike process are extremely small, the HC amount and NO _X amount discharged into the atmosphere are also extremely small. Therefore, it is possible to execute the rich spike process while suppressing the deterioration of the exhaust emission. Note that the rich spike processing is terminated when the first NO _X storage amount becomes “0”, and accordingly, the rich spike flag is switched from on to off (t2 in FIG. 2).

Next, rich when the spike processing is executed, if the first 2NO _X storage amount than the predetermined threshold value, as and bypass passage 5 main passage 20 is cut off is conducted, the flow switching valve 6 Was controlled. Here, in the case where the 2NO _X storage amount rich spike treatment in a state equal to or greater than a predetermined threshold is performed, the state of rich spike flag, a state of the bypass passage 5, and the 1NO _X storage amount, the 2NO FIG. 3 shows changes with time in the _X storage amount, the engine exhaust HC amount, the second NSR catalyst exhaust HC amount, and the second NSR catalyst exhaust NO _X amount.

In FIG. 3, when the rich spike flag is switched from off to on (t1 in FIG. 3), the ECU 7 switches the bypass passage 5 from the cutoff state (bypass off) to the conduction state (bypass on). The path switching valve 6 is controlled. That is, the ECU 7 controls the flow path switching valve 6 so as to switch from the state where the main passage 20 is turned on and the bypass passage 5 is turned off to the state where the main passage 20 is turned off and the bypass passage 5 is turned on. In that case, the rich air-fuel ratio exhaust gas discharged from the internal combustion engine 1 bypasses the first NSR catalyst and flows into the second NSR catalyst. That is, exhaust gas containing a relatively large amount of HC flows into the second NSR catalyst. As a result, storage NO _X of the 1NSR catalyst without being reduced, so that the occluded NO _X of the 2NSR catalyst is reduced. Along with this, the 1NO _X storage amount without decreasing, only the 2NO _X storage amount is decreased. Also, most of the HC contained in the exhaust gas of a rich air-fuel ratio described above, for consumption in order to reduce the occluded NO _X of the 2NSR catalyst, the 2NSR catalytic exhaust HC amount becomes very small amounts. In addition, by absorbing NO _X in the 2NSR catalyst is reduced as described above, the first 2NSR catalyst discharge amount of NO _X is also a very small amount. Thereafter, when the first 2NO _X storage amount becomes "0" (t10 in FIG. 3), ECU 7 is to switch to cut-off state the bypass passage 5 from a conductive state (on the bypass) (off bypass), the flow path switching The valve 6 is controlled. That, ECU 7 is once they become first 2NO _X storage amount is "0", in the same manner as FIG. 2 described above, by achieving reduction in occluded NO _X of the 1NSR catalyst, it is discharged into the atmosphere The amount of HC and the amount of NO _X were suppressed to a very small amount.

By the method shown in FIGS. 2 and 3, the control flow path switching valve 6 during the rich spike control execution is carried out, while suppressing the very small amount of HC amount and _the amount of NO _X discharged into the atmosphere, the 1NSR catalyst and or occluded NO _X of the 2NSR catalyst can be reduced.

  Hereinafter, the control procedure of the flow path switching valve 6 during execution of the rich spike process will be described with reference to FIG. FIG. 4 is a flowchart showing a processing routine that is repeatedly executed during the operation period of the internal combustion engine 1. This processing routine is stored in advance in the ROM of the ECU 7 or the like.

  In the processing routine of FIG. 4, the ECU 7 first determines whether or not the rich spike flag is on in the processing of S101. If a negative determination is made in the process of S101, the rich spike process has not been executed, so the ECU 7 proceeds to the process of S106 and performs normal control of the flow path switching valve 6. The normal control here means that, as described above, the flow path switching valve 6 is controlled so that the main passage 20 is conducted during the lean operation of the internal combustion engine 1, and the bypass passage 5 is used during the stoichiometric operation of the internal combustion engine 1. Is to control the flow path switching valve 6 so as to be conducted. When an affirmative determination is made in the process of S101, the rich spike process is being executed, and thus the ECU 7 executes the processes after S102.

In the process of S102, the ECU 7 acquires the second NO _X storage amount ΣNO _X 2 that is the NO _X storage amount of the second NSR catalyst (corresponding to “acquiring means” according to the present invention). It is assumed that the second NO _X storage amount ΣNO _X 2 is separately calculated and stored in the backup RAM or the like. At that time, the second NO _X storage amount ΣNO _X 2 is calculated by the following method, for example. First, when the air-fuel ratio of the exhaust gas flowing into the second NSR catalyst is lean, the output of the second NO _X sensor 9 is calculated from the inflow NO _X amount calculated based on the output signal of the first NO _X sensor 8 and the exhaust gas flow rate. by subtracting the outflow amount of NO _X is calculated on the basis of the signal and the exhaust flow rate, seek _the NO _X storage amount per unit time. Then, the ECU 7 may calculate the second NO _X storage amount ΣNO _X 2 by integrating the NO _X storage amount per unit time. On the other hand, when the air-fuel ratio of the exhaust gas flowing into the second NSR catalyst is equal to or lower than the stoichiometric air-fuel ratio, the NO _X desorption amount per unit time using the air-fuel ratio of the inflowing exhaust gas, the exhaust flow rate, the temperature of the second NSR catalyst, etc. as parameters. Ask for. Then, ECU 7 from the previous value of the 2NO _X storage amount, by subtracting the NO _X desorption amount per unit time may be calculating the first 2NO _X storage amount ΣNO _X 2.

In the process of S103, the ECU 7 includes a first 2NO _X storage amount ΣNO _X 2 obtained by the processing of the S102 it is determined whether or not a predetermined threshold value or more alpha. The predetermined threshold value α here is, as described above, when the deterioration of the exhaust emission is within the allowable range even if NO _X less than the predetermined threshold value α is not reduced by the second NSR catalyst and discharged into the atmosphere. It is a possible value.

If an affirmative determination is made in the process of S103, the ECU 7 proceeds to the process of S104, and controls the flow path switching valve 6 so that the bypass passage 5 is in a conductive state (bypass is on). In this case, as in the period from t1 to t10 in FIG. 3 described above, the rich air-fuel ratio exhaust gas discharged from the internal combustion engine 1 bypasses the first NSR catalyst and flows into the second NSR catalyst. As a result, while suppressing the very small amount of the 2NSR catalytic exhaust HC amount and the 2NSR catalyst discharge amount of NO _X can be reduced occlusion NO _X of the 2NSR catalyst.

If a negative determination is made in the process of S103, the ECU 7 proceeds to the process of S105, and controls the flow path switching valve 6 so that the bypass passage 5 is in a shut-off state (bypass is turned off). In this case, the rich air-fuel ratio exhaust gas discharged from the internal combustion engine 1 flows into the first NSR catalyst during the period from t1 to t2 in FIG. 2 described above or the period from t10 to t2 in FIG. Become. As a result, while suppressing the very small amount of the 2NSR catalytic exhaust HC amount and the 2NSR catalyst discharge amount of NO _X can be reduced occlusion NO _X of the 1NSR catalyst.

  Here, the “flow path control means” according to the present invention is realized by the ECU 7 executing the processes of S103 to S105 described above.

  If the flow path switching valve 6 at the time of executing the rich spike process is controlled by the procedure described above, the rich spike process can be performed while keeping the exhaust emission deterioration within an allowable range.

1 Internal combustion engine 1a Fuel injection valve 2 Exhaust passage 3 First catalyst casing 4 Second catalyst casing 5 Bypass passage 6 Flow path switching valve 7 ECU
8 The 1NO _X sensor 9 first 2NO _X sensor 10 exhaust gas temperature sensor

Claims (1)

A catalyst disposed in an exhaust passage of an internal combustion engine that is operated with lean combustion, and when the air-fuel ratio of the exhaust gas is a lean air-fuel ratio, it stores NO _X in the exhaust gas, and the air-fuel ratio of the exhaust gas is a rich air-fuel ratio and desorbed the NO _X that has been occluded when a first 1NO _X storage reduction catalyst that reduces the desorbed NO _X by unburned fuel components in exhaust gas,
A catalyst disposed in the exhaust passage downstream of the first 1NO _X storage reduction catalyst, when the air-fuel ratio of the exhaust gas is lean air-fuel ratio occludes NO _X in the exhaust gas, the air-fuel ratio of the exhaust gas rich A second NO _X storage reduction catalyst that desorbs the NO _X stored when it is at the air-fuel ratio and reduces the desorbed NO _X by the unburned fuel component in the exhaust;
Branched from the exhaust passage upstream of the first 1NO _X storage reduction catalyst, the bypass passage merging into the exhaust passage upstream of the first 1NO _X occluding and reducing catalyst downstream and the second 2NO _X storage reduction catalyst ,
The bypass passage or as the exhaust to one second 1NO _X either storage reduction catalyst flows, and a flow path switching valve for switching the exhaust passage,
By the air-fuel ratio of exhaust gas flowing through the upstream the exhaust passage of the branch portion of the bypass passage to the rich air-fuel ratio, at least one of said first 1NO _X storage reduction catalyst and the second 2NO _X storage reduction catalyst Rich spike processing means for performing rich spike processing for reducing the stored NO _x ;
A calculating means for calculating a cumulative NO _X emissions by accumulating the amount of NO _X flowing to the downstream side of the first 2NO _X storage reduction catalyst when it ends as a trigger of the rich spike action by the rich spike processing means,
Rich spike control means for controlling the rich spike processing means so that the rich spike processing is executed when the integrated NO _X emission amount calculated by the calculating means is equal to or greater than a predetermined threshold;
Obtaining means for obtaining the NO _X storage amount of the second NO _X storage reduction catalyst;
Wherein when the rich spike operation is performed, NO _X storage amount acquired by the acquisition means to control the flow path switching valve so that the exhaust equal to or greater than a predetermined threshold value flows through the bypass passage, the acquisition Flow path control means for controlling the flow path switching valve so that the exhaust flows through the first NO _X storage reduction catalyst if the NO _X storage amount acquired by the means is less than the predetermined threshold;
An exhaust emission control device for an internal combustion engine, comprising:

Images