JPH11107739A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the consumption quantity of reducing agent by causing highly efficient reduction work by preventing Nox from being occluded in a catalyst during low load running. SOLUTION: In this device, an exhaust emission passage E is branched into three exhaust emission passages, first through third passages E1, E2 and E3 provided with switch valves 13A, 13B and 13C respectively, and reduction agent adding devices 4A and 4B are arranged upperstream of the first and second exhaust emission passages respectively, and occluding reduction catalysts 1A and 2A are provided in the first and second passages respectively. When the load on an engine 35 is a specified value or less, the switch valves of the first and second passages are closed, and the switch valve of the third passage us opened to directly discharge exhaust emission gas G. When the load is more than the specified value, the switch valve of the third passage is closed, and the switch valve of either the first or second passage is opened so that oxidation occlusion works by means of a catalyst in the passage, and reduction agent R is added to the closed passage of the other switch valve from a reduction adding device to make a catalyst backstream of the reduction agent adding device perform reduction occlusion work. Thus, their respective oxidation occlusion work and reduction releasing work of the first and second catalysts are alternatively conducted by operating switch valves.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus having a storage reduction catalyst interposed in an exhaust passage of an internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, NOx is oxidized and stored at an air-fuel ratio corresponding to gas lean, and the stored NO is stored in a gas-rich reducing atmosphere or an atmosphere burning at a stoichiometric air-fuel ratio.
A storage reduction catalyst for reducing and removing x is known. For example, in Japanese Patent Application Laid-Open No. HEI 8-19728, a catalyst device including two sets of an oxidation catalyst, a nitrogen dioxide trapping agent, and a reduction catalyst is provided, and an opening / closing valve is alternately opened and closed, and a trapping action by an open side catalyst is provided. There is disclosed a technique for purifying exhaust gas by continuously performing a reducing operation by supplying a reducing gas to a catalyst on a closed side.

[0003] However, in these techniques, oxidation storage is performed even during low-load operation in which NOx is less generated, and after a long-time low-load operation, a large amount of reducing agent needs to be injected. There is a problem that it increases.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an exhaust gas purifying apparatus for an internal combustion engine which can perform an efficient reducing operation to reduce the consumption of a reducing agent.

[0005]

According to the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine in which an occlusion reduction catalyst is provided in an exhaust path of the internal combustion engine. , And first to third switching valves are interposed in each of the first to third exhaust passages, and occlusion reduction catalysts are interposed in each of the first and second exhaust passages. In addition, a reducing agent addition device is provided upstream of the first device.
The third to third switching valves close the first and second exhaust passages when the load of the internal combustion engine is equal to or lower than a predetermined value, and open the third switching valve to transfer exhaust gas to the third exhaust passage. When the load is equal to or more than a predetermined value, the third exhaust passage is closed, only one of the first and second switching valves is opened, and the exhaust passage is interposed in the opened exhaust passage. The catalyst is configured to perform an oxidative occlusion action, and the reduction action of the catalyst disposed on the side of the first and second exhaust passages where the open switching valve is disposed is performed. As described above, a reducing agent (for example, city gas) is added from the reducing agent adding device provided in the exhaust passage, and the first and second switching valves are alternately opened and closed, so that the first and second switching valves are alternately opened and closed. The first and second catalysts are characterized in that they are configured to alternately perform the oxidizing / occluding action and the reducing / releasing action of the second catalyst ( Corresponding to 1, 2). The present invention is configured as described above, and in a region where the load of the internal combustion engine is equal to or less than a predetermined value and the NOx concentration in the exhaust gas is low, the exhaust gas does not flow through the storage reduction catalyst, so that the load is changed from a low load to a high load. It is not necessary to use a large amount of a reducing agent. Further, there is an effect that the catalyst use time can be reduced by the time of the low load operation.

Here, it is desirable that the flow resistance of the bypass passage (that is, the exhaust passage on the side where the catalyst is not interposed) is equal to the flow resistance of the exhaust passage where the catalyst is interposed.
This prevents a change in the engine back pressure due to the switching.

Further, the exhaust gas purifying apparatus for an internal combustion engine according to the present invention is an exhaust gas purifying apparatus for an internal combustion engine in which an occlusion reduction catalyst is provided in the exhaust path of the internal combustion engine, wherein the exhaust path is branched into three exhaust paths by a switching valve. (One of them is an exhaust passage for bypass at low load), and a reducing agent addition line joins upstream of the two exhaust passages interposing a storage reduction catalyst upstream of the catalyst. The addition line is open from the reducing agent supply source via the oxidation catalyst to the upstream side of the storage reduction catalyst, and the upstream side of the oxidation catalyst of the reducing agent addition line from the other exhaust passage downstream of the switching valve. The branched branch lines join together, and the branch line introduces a part of the exhaust gas flowing through the exhaust passage on the other side downstream of the switching valve to supply a reducing agent supplied through the reducing agent addition line. After partial oxidation, the partial acid And the reducing agent is configured so as to be added to the storage-reduction catalyst which is interposed in the exhaust passage on the side to which the reducing agent addition line merge (corresponding to FIG. 3 and 4).

[0008] According to this structure, the exhaust gas is mixed with the reducing agent, and the oxidation catalyst has a high reducing power of CO (carbon monoxide).
NOx is supplied after being partially oxidized,
Can be reduced.

Further, the exhaust gas purifying apparatus for an internal combustion engine according to the present invention is configured such that when an internal combustion engine (for power generation) such as a gas engine and a boiler are used in a cogeneration system or the like, the occlusion reduction is performed in an exhaust passage of the internal combustion engine. In an exhaust gas purifying apparatus for an internal combustion engine provided with a catalyst, the exhaust passage is branched into three exhaust passages via a switching valve (one of the exhaust passages is for bypass at low load), and an absorption reduction catalyst is interposed. It is characterized in that a reducing agent addition device is provided on each of the two exhaust passages upstream of the catalyst, and a boiler exhaust gas supply line for supplying boiler exhaust gas is provided in the reducing agent addition device (FIG. 5). Corresponding to).

Here, the excess exhaust gas for reducing the stored nitrogen oxides of the rich exhaust gas of the boiler is supplied to the catalyst side storing the nitrogen oxides. Is preferred.

[0011] In this configuration, the stored NOx can be reduced efficiently by burning the boiler in an excess fuel atmosphere to generate CO and adding the exhaust gas as a reducing agent.

The exhaust gas purifying apparatus for an internal combustion engine according to the present invention has a stoichiometric air-fuel ratio with an engine that burns in a gas lean state (lean combustion engine) when two engines are used in a cogeneration system or the like. Two engines, a combustion engine (stoichiometric combustion engine or rich combustion engine), are provided so as to be able to operate simultaneously, and a storage reduction catalyst is interposed in each of the exhaust passages of those engines, and a switching valve is provided upstream of each catalyst. An exhaust passage is branched to be interposed, one end of which is communicated between the switching valve of the other exhaust passage and the catalyst, and the exhaust gas of the engine burning in the gas lean state (lean combustion engine) flows into one of the catalysts. To perform an oxidative occlusion action, and the exhaust of an engine (stoichiometric combustion engine) that burns at the stoichiometric air-fuel ratio flows into the other catalyst and is reduced and released. Do use, has a valve switching operation means for controlling said switching valve so as to perform the exhaust gas purification switched alternately and reducing release effect and oxidation occluding effect (FIGS. 6 and 7
Corresponding to).

In this case, since one engine is operated in a gas lean state, the fuel consumption of the engine can be reduced as compared with the case where both engines are operated at the stoichiometric air-fuel ratio. Further, since the exhaust gas of the engine burning at the stoichiometric air-fuel ratio is used as the reducing agent, it is not necessary to use the reducing agent.

[0014] With the above structure, lean occlusion gas (NOx in lean exhaust gas atmosphere)
And the stoichiometric combustion gas (which releases and reduces stored NOx in that atmosphere) flows alternately,
Oxidation and occlusion and reduction and release of Ox are performed continuously to purify exhaust gas.

When the present invention having the above configuration is implemented, an engine that burns at the stoichiometric air-fuel ratio (stoichiometric combustion engine) is provided with a load sensor for detecting a load and a rotational speed sensor for detecting a rotational speed. A main oxygen sensor is provided in an exhaust passage of a burning engine (stoichiometric combustion engine), and sub oxygen sensors are provided downstream of the storage reduction catalyst. Output lines of these sensors are connected to a control device. The control device includes: a main feedback calculating unit that reads a signal of the main oxygen sensor to calculate a main feedback amount; a sub feedback calculating unit that reads a signal of the sub oxygen sensor to calculate a sub feedback amount; Number sensor signal, main feedback calculation means output and sub feed An air ratio control valve operating means for controlling the air ratio control valve based on the output of the lock calculating means, a valve switching operating means for calculating a switching time to control the switching valve, and a sub feedback control constant storage means. The sub-feedback control constant storage means stores a sub-feedback control constant for the storage reduction catalyst used immediately before switching the switching valve, and
It is configured to read the previous sub-feedback control constant for the storage reduction catalyst that is to be interposed in the exhaust passage of an engine that burns at the stoichiometric air-fuel ratio after switching the switching valve (stoichiometric combustion engine). Is preferable (corresponding to FIGS. 6 and 7).

By providing such a control device, in addition to being able to set the air-fuel ratio of the stoichiometric combustion engine to an optimum air-fuel ratio according to the state of the catalyst, by providing the sub-feedback control constant storage means, Second, when the optimum sub-feedback constant of the two storage reduction catalysts is significantly different, the time required for the sub-feedback control to stabilize after switching the switching valve can be significantly reduced.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, an exhaust passage E for exhausting an exhaust gas G of an engine 35 (internal combustion engine) has three exhaust passages (first to third exhaust passages) via first to third switching valves 13A to 13C, respectively. Passages) E1, E2, E3, and the first and second exhaust passages E1, E2 are provided with storage reduction catalysts 1A, 1B, respectively. Further, addition devices (reducing agent addition devices) 4A and 4B for adding the reducing agent R are provided upstream of the catalysts 1A and 1B in the first and second exhaust passages E1 and E2, respectively. The flow resistance of the third exhaust passage E3 is determined by the first or second exhaust passages E1 and E2 with the catalyst 1A or 1B interposed therebetween.
It is configured to be equivalent to.

In the above configuration, when the load of the engine 35 is a low load that is equal to or less than a predetermined value (NOx is equal to or less than the regulation value), the third switching valve 13C is opened, and the first and second switching valves 13A and 13A are opened. 13B is closed, the exhaust gas G is passed through the catalyst 1A,
1B is bypassed. On the other hand, if the load on the engine 35 is equal to or greater than the predetermined value, the third switching valve 13C is closed, and either one of the first or second switching valves 13A and 13B,
For example, the first switching valve 13A is opened, and the first exhaust passage E
The exhaust gas G is caused to flow through the first catalyst 1 to occlude NOx in the first catalyst 1A (the catalyst provided in the open exhaust passage). Then, in the other exhaust passage E2 (the side of the first and second exhaust passages where the closed switching valve is interposed), the reducing agent R (for example, city gas) is supplied to the second addition device 4A.
(The reducing agent addition device provided in the exhaust passage) is added to reduce and release NOx stored in the second catalyst 1B.

After a lapse of a predetermined time, the first and second switching valves 13A and 13B are opened and closed, and the second and first adding devices 4 are opened.
By switching the addition of the reducing agent to B, 4A, catalysts 1A, 1A
The oxidizing / occluding action and the reducing / releasing action of B are performed alternately and continuously.

FIG. 2 is a flowchart showing the switching valve and the reducing agent adding device in the embodiment of FIG.
Referring to FIG. 1, first, it is determined whether the load of the engine 35 is equal to or less than a predetermined value (NOx is equal to or less than a regulation value) (FIG. 2: step S31). If YES, the first and second switching valves 13A and 13B are closed to close the first and second exhaust passages E1 and E2, and the third switching valve 13C is opened (step S32). Thus, the exhaust gas of the engine 35 is allowed to flow only to the third exhaust passage E3, and the storage reduction catalyst is bypassed. As a result, none of the catalysts 1A and 1B occlude NOx, so that the consumption amount of the reducing agent is reduced by the amount of NOx occluded at a low load. Further, the catalyst usage time can be reduced by the time at the time of low load.

On the other hand, if the load of the engine 35 is equal to or greater than the predetermined value (NO in step S31), taking into account that the oxidation and occlusion actions and the reduction and release actions of the catalysts 1A and 1B are performed alternately to the same extent, At that point, NO
It is determined whether to store x (step S33), the third switching valve 13C is closed to close the third exhaust passage E3, and the switching valve determined in step S33 is opened (step S34). The catalyst provided in the open exhaust passage performs an oxidative occlusion function, and the catalyst is reduced by the reducing agent addition device provided in the exhaust passage on the side where the closed switching valve is provided. The agent is added.

Hereinafter, the processes of steps S31 to S34 are repeated while taking into consideration that the oxidizing / occluding action and the reducing / releasing action of the catalysts 1A and 1B are performed to the same extent.

In the embodiment shown in FIG. 3, the exhaust passage E for discharging the exhaust gas G of the engine 35 is connected to the switching valve 13.
The exhaust gas is branched into three exhaust passages E1, E2, and E3 via AC, and the storage reduction catalyst 1 is provided in each of the exhaust passages E1 and E2.
A and 1B are interposed. Then, the supply line (reducing agent addition line) of the reducing agent R is branched into two lines L1 and L2 via the flow rate regulating valve 15, and each of the valves 16A and 16B, the check valves c and c, Through c, c and the oxidation catalysts 39A, 39B, they are connected to addition devices 4A, 4B installed upstream of the first and second catalysts 1A, 1B.

Switching valves 13A, 13 in exhaust passages E1, E2
B, from upstream of the oxidation catalysts 39B, 39A of the reducing agent addition lines L2, L1 to the other exhaust passages, respectively,
The exhaust gas G is branched and led. In other words, the oxidation catalysts 39A, 39A of the reducing agent addition lines L1, L2.
On the upstream side of B, branch lines E2-D and E1-D branched from the other exhaust passage downstream of the switching valve 13 merge (represented by symbols L1-P and L2-P, respectively). Further, the exhaust passage E3 is for bypass at a low load, and is controlled in the same manner as described above.

For example, when the exhaust gas G flows from the exhaust passage E to one of the exhaust passages E1 by the switching valves 13A and 13B, NOx is oxidized and stored in the storage reduction catalyst 1A. The exhaust gas G does not flow in the other exhaust passage E2. Then, to supply the reducing agent to the reducing agent addition line L2 in the exhaust passage E2, the on-off valve 16B opens in conjunction with the switching valves 13A and 13B, and the reducing agent R (hydrocarbon) metered by the adjusting valve 15 is supplied. It is supplied to the reducing agent supply line L2 side. Here, the reducing agent R flowing through the reducing agent addition line L2 is mixed with the exhaust gas G branched off from the exhaust passage E1 (a part of the exhaust gas flowing through the other exhaust passage downstream of the switching valve is introduced). Is partially oxidized to CO (carbon monoxide) by the oxidation catalyst 39B and added to the upstream of the catalyst 1B from the second addition device 4B (the side where the partially oxidized reducing agent joins the reducing agent addition line). Is added to the storage-reduction catalyst interposed in the exhaust passage. In the reduction catalyst 1B, the reduced release action is efficiently performed by the added CO and the like.

The mode of control according to the present embodiment will be described with reference to FIG. In the initial start state, for example, the switching valve 1
Reference numeral 3 opens to the E1 side, and the on-off valve 16B is opened. In step S1, it is determined whether or not a predetermined time t1 (s) has elapsed. If No, the routine of step S1 is repeated, and if Yes, the on-off valve 16B in step S2.
Close. Then, the switching valve 13A is opened in step S3, and the switching valve 13B is closed in step S9. Then, in step S4, the on-off valve 16A is opened. The exhaust gas G does not flow to the exhaust passage E1 side, and the reducing agent R and a part of the exhaust gas branch from the exhaust passage E2 side to the line L1 to oxidize the oxidation catalyst 39A.
, And flows into the catalyst 1A from the addition device 4A, and the stored NOx is reduced and released. Meanwhile, NOx is oxidized and stored in the catalyst 1B on the exhaust passage E2 side.

Then, in step S5, a predetermined time t1
(S) It is determined whether or not the time has elapsed. If No, the routine of Step S5 is repeated. If Yes, the on-off valve 16A is closed in Step S6, the switching valve 13B is opened in Step S7, and Step S10 is performed. To close the switching valve 13A,
In step S8, the on-off valve 16B is opened. Then, the process returns to step S1.

In the embodiment shown in FIG.
Are connected to the three exhaust passages E1, E via the switching valves 13A-C.
2 and E3, and the storage reduction catalysts 1A and 1B are interposed in the exhaust passages E1 and E2, respectively.
Upstream of A and 1B, reducing agent addition devices 4A and 4B are provided. On the other hand, in the boiler 38, the supplied fuel gas F and the air A are adjusted and combusted in an excess fuel atmosphere, and the exhaust gas line is divided into two by the blower 18 and the flow rate adjusting valves 15A and 15B are respectively operated. It is interposed and connected to the reducing agent addition devices 4A and 4B. Note that, similarly to the above, the exhaust passage E3 is a bypass line for exhaust gas at the time of low load.

The exhaust gas G flows to one exhaust passage, for example, E2 side by the switching valves 13A and 13B, and NOx is stored by the catalyst 1B interposed in the passage E2. Then, on the other exhaust passage E1 side, the exhaust gas (containing a large amount of CO) of the boiler 38 burned in the excess fuel atmosphere is metered by the regulating valve 15A and added from the adding device 4A, and is added to the catalyst 1A. NOx occluded in the fuel cell is reduced and removed.
At this time, when the CO of the boiler exhaust gas is larger than the stored NOx, the excess CO flows to the opposite catalyst 1B to be oxidized (the regulating valve 15A is "closed" and the regulating valve 15B is "open"). . In this way, when a predetermined amount of NOx is stored in the catalyst 1B or at regular intervals, the switching valves 13A and 13B
Thus, the storage side and the reduction side are switched to purify the exhaust gas continuously. Next, in the embodiment shown in FIG. 6, two engines, a lean combustion engine (engine burning in a gaseous state) 35A and a stoichiometric combustion engine (engine burning at stoichiometric air-fuel ratio) 35B, can be operated in parallel. The air A and the fuel gas F are mixed and supplied to the respective engines by the mixer 37. The exhaust passages E1 of the engines 35A and 35B,
The storage reduction catalysts 1A and 1B are interposed in E2, respectively. Switching valves 13A and 13B are interposed in the upstream passages of the respective catalysts 1A and 1B, and the exhaust passages E3 and E4 are branched. One end is communicated between the switching valve and the catalyst (13B / 1B, 13A / 1A) of the other exhaust passages E2, E1.

The stoichiometric combustion engine 35B has
A load sensor 36 for detecting the engine load and a rotation sensor 6 for detecting the number of revolutions are provided, and an air ratio control valve 17 for controlling the air ratio is provided in the fuel gas supply line, bypassing the mixer 37. . On the other hand, a main oxygen sensor 8 is provided in the exhaust passage E2 of the stoichiometric combustion engine 35B, and sub oxygen sensors 9A and 9B are provided downstream of the catalysts 1A and 1B, respectively. Further, a control device 20 is provided so as to be connected to these sensors 36, 6, 8, 9A, and 9B.

The control device 20 includes a main oxygen sensor reading means 26 connected to the main oxygen sensor 8,
A main feedback amount calculating means 27 for calculating a main feedback amount based on a signal of the main oxygen sensor reading means 26, and sub oxygen sensor reading means 31A, 31 connected to the sub oxygen sensors 9A, 9B, respectively.
B, a sub-feedback calculating means 32 for calculating a sub-feedback amount based on signals from the sub oxygen sensors 31A and 31B, a load sensor reading means 21 connected to a load sensor 36, and a rotation connected to the rotation sensor 6. Number sensor reading means 22 is provided. Then, the signals of the load sensor reading means 21 and the rotation sensor reading means 22 and the main feedback calculation means 2
7 and an output of the sub-feedback calculating means 32, an air ratio control valve calculating means 24 for calculating the opening of the air ratio control valve 17 is provided. An air ratio control valve operating means 25 for operating the control valve 17 is provided.

Further, the sub feedback operation means 32
A sub-feedback control constant storage means 34 for storing the control constant calculated in the step (1) and a switching time calculation means 28 for calculating the switching time are provided, and a switching valve for operating the switching valves 13A and 13B according to a signal from the switching time calculation means. Actuating means 2
9 and a sub oxygen sensor signal switching means 33 for instructing a signal switching of the sub oxygen sensor in the sub oxygen sensor reading means 31A and 31B and the sub feedback control constant storing means 34 based on a signal of the switching time calculating means 28. .

Here, the sub feedback and the main feedback are controls for changing the delay time of the main feedback and the like so that the air-fuel ratio comes to the catalyst window according to the signal of the sub oxygen sensor. This is used in an exhaust gas purification system using a three-way catalyst.

Hereinafter, the mode of the switching control will be described with reference to FIG. First, it is determined in step S11 whether main feedback has been established. If No, go back and
If Yes, the sub-oxygen feedback (A) learning value is read from the sub-feedback control constant storage means 34 in step S12, and sub-oxygen feedback is started in step S13. In step S14, it is determined whether a predetermined time t (s) has elapsed. If No, the process returns to the previous step. If Yes, the sub-feedback (A) control constant is stored in the control constant storage unit 34 in step S15.
Then, in step S16, the switching valves 13A and 13B are switched, and in step S17, the sub oxygen sensor is switched (to B). Then, the sub oxygen feedback learning value (B) is read in step S18, and the sub oxygen feedback is started in step S19. At step S20, a predetermined time t
(S) It is determined whether or not the time has elapsed.
If it is s, the sub feedback (B) is performed in step S21.
The control constants are saved, and the switching valves 13A, 1
3B, and switches the sub oxygen sensor to (A) in step S23.
), And returns to step S12.

In this way, every time the switching valves 13A and 13B are switched, the previous sub-feedback control constant of the catalyst to be newly interposed on the exhaust passage side of the engine 35B is read. The time required to stabilize the control is shortened accordingly.

When two engines are operated in parallel in a cogeneration system or the like, the total fuel consumption of the two engines can be reduced by operating one of the engines in lean burn. In this case, since the exhaust gas of the engine burning at the stoichiometric air-fuel ratio is used as the reducing agent, no separate reducing agent is required.

[0037]

The present invention is configured as described above,
The following effects are obtained. (1) When the load is less than a predetermined value, the N
In the region where the Ox concentration is low, since the exhaust gas does not flow through the storage reduction catalyst, it is possible to save a reducing agent for processing NOx stored at a low load. And, by reducing the catalyst usage time by the time of low load operation,
The life of the storage reduction catalyst can be extended. (2) Efficient reduction can be achieved by using a partial oxidation catalyst or boiler-rich exhaust gas. (3) When two engines are used in combination, one of the engines is operated in a lean state (lean burn) using the storage reduction catalyst, and the other is operated at the stoichiometric air-fuel ratio (stoichiometric). As a result, the fuel consumption of the engine in the entire two engines can be reduced, and NOx can be efficiently removed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of the present invention.

FIG. 2 is a flowchart showing a control mode according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of a second embodiment of the present invention.

FIG. 4 is a flowchart showing a control mode of the embodiment of FIG. 3;

FIG. 5 is a sectional view showing a third embodiment of the present invention.

FIG. 6 is a sectional view showing the configuration of a fourth embodiment of the present invention.

FIG. 7 is a flowchart illustrating a control mode according to the embodiment of FIG. 6;

[Explanation of symbols]

 1, 1A, 1B ... storage reduction catalyst 3 ... closing plate 4A, 4B ... reducing agent addition device 6 ... rotation speed sensor 8 ... main oxygen sensor 9A, 9B ... sub oxygen sensor DESCRIPTION OF SYMBOLS 11 ... Bypass 13A, 13B, 13C ... Switching valve 15 ... Flow control valve 16 ... On-off valve 17 ... Air ratio control valve 20 ... Control device 25 ... Air ratio control valve Operating means 27: Main feedback calculating means 29: Switching valve operating means 32: Sub-feedback calculating means 34: Sub-feedback control constant storage means 35, 35A, 35B: Engine 36: Load Sensor 37 ・ ・ ・ Mixer 38 ・ ・ ・ Boiler 39A, 39B ・ ・ ・ Oxidation catalyst

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI F01N 3/24 ZAB F01N 3/24 ZABE

Claims (7)

[Claims] In an exhaust gas purifying apparatus for an internal combustion engine in which a storage reduction catalyst is provided in the exhaust passage of the internal combustion engine, the exhaust passage is connected to the exhaust passage.
The first to third exhaust passages are branched, and the first to third exhaust passages are respectively provided with first to third switching valves.
A storage reduction catalyst is interposed in each of the second exhaust passages and a reducing agent addition device is provided upstream thereof, and the first to third switching valves are provided when the load of the internal combustion engine is equal to or less than a predetermined value. The first and second exhaust passages are closed, and the third switching valve is opened to allow exhaust gas to flow only to the third exhaust passage. If the load is equal to or more than a predetermined value, the third exhaust passage is closed. , And only one of the first and second switching valves is opened, and the catalyst provided in the open exhaust passage performs an oxidative occlusion action. The reducing agent is supplied from the reducing agent adding device provided in the exhaust passage so as to perform the reducing action of the catalyst provided on the side of the second exhaust passage on which the closed switching valve is provided. The first and second switching valves are alternately opened and closed to switch between the first and second switching valves. Exhaust purification system of an internal combustion engine, characterized by being configured so as to perform the reduction and release action as oxygen storage function of the catalyst alternately. 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein city gas is used as said reducing agent. 3. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein a reducing agent obtained by partially oxidizing hydrocarbons with an oxidation catalyst is used as said reducing agent. 4. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein rich exhaust gas from a boiler is used as said reducing agent. 5. The system according to claim 1, wherein an excess of the rich exhaust gas of the boiler for reducing the stored nitrogen oxides is supplied to a catalyst side storing the nitrogen oxides. 4. An exhaust gas purification device for an internal combustion engine according to 4. 6. An engine that burns in a gas lean state and an engine that burns at a stoichiometric air-fuel ratio are provided so as to be simultaneously operable, and an occlusion reduction catalyst is interposed in an exhaust passage of each of the engines. The exhaust passage is branched by interposing a switching valve upstream of each catalyst, and one end thereof is communicated between the switching valve of the other exhaust passage and the catalyst, and the exhaust gas of the engine burning in the gas lean state is exhausted by the catalyst. To perform the oxidative occlusion action, and the other catalyst receives the exhaust of the engine burning at the stoichiometric air-fuel ratio to perform the reductive release action, and alternately switches between the oxidative occlusion action and the reduction release action. An exhaust gas purifying apparatus for an internal combustion engine, comprising valve switching operation means for controlling the switching valve so as to purify exhaust gas. 7. An engine burning at the stoichiometric air-fuel ratio is provided with a load sensor for detecting a load and a rotational speed sensor for detecting a rotational speed, and a main oxygen sensor is provided in an exhaust passage of the engine burning at the stoichiometric air-fuel ratio. Sub oxygen sensors are provided on the downstream side of the storage reduction catalyst, respectively, and the output lines of these sensors communicate with a control device.
Main feedback calculation means for reading a signal of the main oxygen sensor and calculating a main feedback amount;
Sub-feedback calculating means for reading a signal from the sub-oxygen sensor and calculating a sub-feedback amount; air ratio control based on signals from the load sensor and the speed sensor, an output from the main feedback calculating means, and an output from the sub-feedback calculating means. Air ratio control valve operating means for controlling the valve, valve switching operating means for calculating the switching time to control the switching valve, and sub feedback control constant storage means, the sub feedback control constant storage means, Storing a sub-feedback control constant for the storage reduction catalyst used immediately before switching the switching valve, and interposing the sub feedback control constant in an exhaust passage of an engine burning at a stoichiometric air-fuel ratio after switching the switching valve. To read the previous sub-feedback control constant for the storage reduction catalyst Exhaust purifying apparatus according to claim 6 which have been made.