JP2000204937A - Exhaust gas control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To high-efficiently regenerate a storage type NOx catalyst gas a discharge of H2 S (a reduction material of a sulfur component) is suppressed. SOLUTION: A storage type NOx catalyst 6A and an auxiliary catalyst 6B having oxygen storage capacity are arranged in the exhaust passage of an internal combustion engine. By regulating an air-fuel ratio of exhaust gas by an atmosphere regulating means 24, a sulfur component in exhaust gas stored from the storage type NOx catalyst 6A is discharged. This constitution, when the storage type NOx catalyst 6A is regenerated by a discharge of a sulfur component from the storage type NOx catalyst 6A, oxidizes a reduction material of the sulfur component discharged from the storage type NOx catalyst 6A by oxygen stored in the auxiliary catalyst 6B, whereby a discharge of the sulfur component to an external part of the reduction material is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention, harmful components in the exhaust gas, in particular, provided with a catalytic converter for purifying NO _X, an exhaust gas purifying apparatus.

[0002]

At present, have been developed lean-burn internal combustion engine capable to achieve further improvement of fuel efficiency, the NO _X in the exhaust gas generated during such lean combustion in the internal combustion engine, are equipped conventionally It is difficult to purify using a three-way catalyst (having a three-way function near stoichio).

[0003] Therefore, the lean NO _X catalyst can purify the NO _X even in an oxidizing atmosphere of oxygen in the exhaust gas becomes excessive have been developed. Such lean NO _X catalyst, in an oxidizing atmosphere to occlude NO _X in the exhaust gas, has a function of oxygen concentration capable of leaving the NO _X occluding When lowered, purify NO _X in the exhaust gas by this feature (Storage type lean NO _X catalyst, trap type lean NO _X catalyst; hereinafter, referred to as NO _X catalyst).

[0004] Specifically, lean NO_XThe catalyst is oxygen enriched
In excessive atmosphere, NO in exhaust gas _XOxidizes NO
_XIs stored as nitrate, while the oxygen concentration is low.
In the atmosphere, lean NO_XNitrate and exhaust gas stored in the catalyst
Reacts with CO in the gas to decompose nitrate,
NO_XHas a function of desorbing.

[0005]

Incidentally, since sulfur components are contained in fuel and lubricating oil, the exhaust gas also contains sulfur components. Therefore, the NO _X catalyst
With occlude NO _X with excess oxidizing atmosphere having an oxygen concentration, such sulfur components also will be occluded. That is, the sulfur components contained in fuel or lubricating the oil is burned, further oxidized to become SO ₃ on NO _X catalyst, occluding for this part of the SO ₃ is further on NO _X catalyst NO _X by reaction with wood is being occluded in the NO _X catalyst is sulfuric acid salt.

Therefore, NO_XCatalysts include nitrate and sulfur
And sulfates, but sulfates are better than nitrates.
Also has high stability as salt, NO_XThe temperature of the catalyst is sufficient
If it does not increase, even in an atmosphere with a reduced oxygen concentration,
Is decomposed only partially, so NO_XAccumulate in catalyst
The amount of sulfate increases with time. Therefore, NO _X
NO of catalyst_XThe storage capacity decreases with time, and NO_XTouch
Medium NO_XThe purification efficiency will be reduced (this is
Poisoning).

As a technique for preventing such S poisoning,
For example, Japanese Patent Laid-Open No. 7-217474, while estimating the amount of accumulated sulfate in the NO _X catalyst, when the amount of the sulfate exceeds the allowable amount, and the catalyst allowed to warm to NO _X catalyst the atmosphere around to promote the decomposition of occluded sulfate on the catalyst by the atmosphere which can reduce sulfate (reducing atmosphere) to release the sulfur component, recovering the NO _X purification efficiency of the catalyst (reproduction) A technique for causing this to occur is disclosed.

[0008] In such a technique, however, a part of the sulfate is reduced excessively and becomes hydrogen sulfide (H ₂ S) in such a reducing action. The amount of H ₂ S generated increases as the reducing atmosphere is strengthened. That is, as to enhance the reducing atmosphere, increasing the reduction substance such as HC, moreover emissions H ₂ S along with the NO _X catalyst occluded sulfur component (sulfate) is a large amount of release also increases You have to do it. For this reason, in view of the suppression of H ₂ S emission, it is difficult to enhance the reducing atmosphere to release the sulfur component stored in the NO _X catalyst more quickly and efficiently, and in a limited time. it is also difficult to reproduce of the NO _X catalyst.

Further, even by placing the normal three-way catalyst for purifying the above H ₂ S downstream of the NO _X catalyst, since such a three-way catalyst oxygen storage amount is small, during the playback process It is difficult to oxidize all generated H ₂ S. The present invention has been in view conceived of these problems, while suppressing the emission of sulfur component (H ₂ S), and the regeneration of the NO _X catalyst can be performed efficiently, the exhaust gas purifying device The purpose is to provide.

[0010]

Therefore, in the exhaust gas purifying apparatus according to the first aspect of the present invention, a storage NOx catalyst and an auxiliary catalyst having an oxygen storage capacity are provided in an exhaust passage of the internal combustion engine. By adjusting the air-fuel ratio of the exhaust gas by the atmosphere adjusting means, a sulfur component in the occluded exhaust gas is released from the occluded NOx catalyst.

Thus, when the storage NOx catalyst is regenerated by releasing the sulfur component from the storage NOx catalyst, the reducing substance of the sulfur component released from the storage NOx catalyst is reduced by the oxygen stored in the auxiliary catalyst. Because of being oxidized, the release of the reducing substance of the sulfur component to the outside can be suppressed.

Further, in the exhaust gas purifying apparatus according to claim 2, in the apparatus according to claim 1, the oxygen storage capacity of the auxiliary catalyst is about 400 to 600 cc per liter of catalyst capacity as measured by an oxygen pulse method. It is set to become. Thereby, the reducing substance of the sulfur component released from the storage NOx catalyst can be reliably oxidized.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. First, an exhaust gas purifying apparatus as one embodiment of the present invention will be described with reference to FIGS. The internal combustion engine equipped with this exhaust gas purification device
It is configured as shown in FIG.
An internal combustion engine that performs each exhaust stroke during one working cycle,
That is, the engine is a four-cycle engine, a spark ignition type, and is configured as a direct injection internal combustion engine (direct injection engine) that directly injects fuel into a combustion chamber.

An intake passage 2 and an exhaust passage 3 are connected to the combustion chamber 1 so that they can communicate with each other. The intake passage 2 and the combustion chamber 1 are connected by an intake valve 4, and the exhaust passage 3 and the combustion chamber 1 are connected to each other. The communication is controlled by the exhaust valves 5, respectively. The intake passage 2 is provided with an air cleaner and a throttle valve (not shown).
Is provided with an exhaust gas purifying device main body 6 and a muffler (muffler) (not shown) which will be described later.

The injector (fuel injection valve) 8
In order to inject fuel directly into the combustion chamber 1 in the cylinder, the opening is arranged to face the combustion chamber 1. Naturally, the injectors 8 are provided for each cylinder. For example, if the engine of the present embodiment is an in-line four-cylinder engine, four injectors 8 are provided.

With such a configuration, the air sucked through the air cleaner (not shown) according to the opening degree of the throttle valve (not shown) is drawn into the combustion chamber 1 by opening the intake valve 4, and the vertical vortex (Inverse tumble flow) The intake air generated and the fuel directly injected from the injector 8 based on a signal from an electronic control unit (ECU) 20 as a control means are mixed, and the ignition plug 7 Is ignited at an appropriate timing to cause combustion and generate engine torque. Then, exhaust gas is discharged from the combustion chamber 1 to the exhaust passage 3, and CO, HC, and NO in the exhaust gas are exhausted by the exhaust gas purifying device main body 6. _After purifying the three harmful components _x , they are muffled by mufflers and released to the atmosphere.

The engine is provided with various sensors, and detection signals from the sensors are sent to the ECU 20. For example, the upstream portion of the exhaust gas purifying apparatus main body 6 of the exhaust passage 3 NO _X sensor 9 (hereinafter, referred to as upstream NO _X sensor 9) is provided,
Further, NO _X sensor 10 (hereinafter, referred to as the downstream NO _X sensor 10) to the downstream portion of the lean NO _X catalyst 6A to be described later is provided. These upstream NO _X sensor 9
The information detected by the downstream NO _X sensor 10 is sent to a NO _X purification efficiency calculating means 21 provided as a function of the ECU 20 described later. In FIG. 2, the upstream NO _X sensor 9 is disposed far away from the exhaust gas purifying device main body 6, but the position of the upstream NO _X sensor 9 may be a portion immediately upstream of the exhaust gas purifying device main body 6. .

In this engine, the mode of fuel injection is as follows.
A super-lean operation mode (compression lean operation mode) in which fuel is injected during the compression stroke and operation is performed in a very lean state (air-fuel ratio is 25 or more) by stratified combustion in which spray is collected near the ignition plug 7 and burned. ), The fuel is injected during the intake stroke, and the combustion in the combustion chamber 1 is premixed and combusted in a uniform air-fuel mixture state to operate the fuel in a lean state (lean air-fuel ratio smaller than 24). and operation mode (intake lean operation mode), and the air-fuel ratio is performed a feedback control based on the O ₂ sensor information such as a near stoichiometric air-fuel ratio stoichiometric operation mode (stoichiometric feedback operation mode), rich I of the fuel An enrichment operation mode (open loop mode) for performing operation in a state (that is, the air-fuel ratio is smaller than the stoichiometric air-fuel ratio) is provided.

The operation in the super lean operation mode and the lean operation mode is referred to as lean operation, the operation in the stoichiometric operation mode is referred to as stoichiometric operation (stoichiometric air-fuel ratio operation), and the operation in the enrich operation mode is referred to as rich operation. . This operation mode is selected based on the engine speed Ne and the effective pressure Pe indicating the load state. When the engine speed Ne is low and the load Pe is small, the compression lean operation mode is selected, and the engine lean mode is selected. Rotation speed Ne
As the load Pe increases, the intake lean operation mode, the stoichiometric feedback operation mode, and the open loop mode are selected.

Next, the exhaust gas purifying apparatus main body 6 according to this embodiment will be described. As shown in FIG. 2, the exhaust gas purifying apparatus main body 6 includes a lean NO _x catalyst (storage type NO _x) having a three-way function provided in separate casings.
Catalyst) 6A and high oxygen storage capacity (OSC: Oxidat)
A three-way catalyst (auxiliary catalyst) 6B having an ion storage capacity is arranged in series in this order in the flow direction of the exhaust gas.

The oxygen storage capacity of the three-way catalyst 6B is set higher than that of the conventional three-way catalyst, and the oxygen storage capacity per liter of the catalyst capacity is 400 as measured by the oxygen pulse method.
It is set to be ~ 600cc. Here, a measuring device and a measuring method of the oxygen storage capacity by a general oxygen pulse method will be described.

As shown in FIG. 3, the apparatus for measuring the oxygen storage capacity by the oxygen pulse method uses a sample tube 56 for holding a sample (here, a three-way catalyst) and a gas (H) in the sample tube 56.
e, air, H ₂ ) and the sample tube 5
The discharge pipe 61 is configured to include a discharge passage 61 that discharges gas from the sample tube 6 and a heating furnace 57 that heats the sample tube 56 to a predetermined temperature. The supply passage 60 has its upstream side connected to the He introduction path 60a, the Air introduction path 60b, and the H ₂ introduction path 60c via the switching cock 52, and its downstream side connected to the sample tube 56 via the connector 55. By connecting the switching cock 52, any one of He, air, and H ₂ can be supplied to the sample in the sample tube 56.

In the supply passage 60 between the switching cock 52 and the sample tube 56, the supply passage 6
A flow meter 51a for detecting the flow rate of gas flowing through the inside of the chamber 0, and an oxygen pulse introduction unit 53 for introducing oxygen in a pulse shape into the supply passage 60 when measuring the oxygen storage capacity are provided. Also,
At the time of measuring the oxygen storage capacity, the side that supplies the gas flowing through the supply passage 60 to the sample in the sample tube 56 and the discharge passage 61
A flow path switching cock 54 is provided so as to connect the supply path 60 and the discharge path 61 so that the flow path can be switched to the side bypassing the sample tube 56 so as to flow to the side.

The discharge passage 61 on the downstream side of the flow path switching cock 54 is provided with a flow meter 51b for detecting the flow rate of gas flowing through the discharge passage 61 in order from the upstream side. A purge cock 58 that discharges a gas into the atmosphere is provided. Then, a thermal conductivity detector 59 for detecting the thermal conductivity of the gas passing through the sample tube 56.
Is provided.

Next, a method of measuring the oxygen storage capacity by the oxygen pulse method using such a measuring device will be described. First, before starting measurement of oxygen storage capacity, a pretreatment is performed to remove oxygen already stored in the sample. In this pretreatment, a sample is put into the sample tube 56, the sample tube 56 is connected to the measuring device main body side (specifically, the supply passage 60 and the exhaust passage 61) via the connector 55, and the heating furnace 57 is set. . Then, the switching cock 52 is switched to the H ₂ introduction path 60c side, and H ₂ is introduced into the sample tube 56,
The sample is kept at about 450 ° C. for 30 minutes.

In this case, the flow rate of the gas introduced into the sample tube 56 is controlled by the flow meter 51a so as to be a predetermined flow rate. Further, the purge cock 58 is opened, and the gas flowing through the exhaust passage 61 is discharged to the atmosphere. By such a treatment, the oxygen stored in the sample is reacted with H ₂ to desorb oxygen from the sample, so that the sample does not store oxygen.

Next, the switching cock 52 is connected to the He introduction path 60a.
Side, He is introduced into the sample tube 56,
Hold for one minute and cool the sample to room temperature. By such a process, H ₂ supplied in the above-described process to desorb oxygen from the inside of the sample is purified by He. By performing such a pretreatment, the oxygen storage capacity of the sample can be measured more accurately.

Next, the actual oxygen storage amount is measured. When the oxygen storage amount is measured, oxygen is introduced in a pulse form from the oxygen pulse introduction unit 53 into the supply passage 60, and oxygen is supplied to the sample in the sample tube 56. Thereafter, after the oxygen storage of the sample is in a steady state (saturated state), oxygen is supplied from the oxygen pulse introduction unit 53 a predetermined number of times (for example, twice).
Then, oxygen is supplied to the sample in the sample tube 56, and the process ends.

When measuring the oxygen storage amount, the introduction of gas from the switching cock 52 is stopped, and the purge cock 58 is closed. The thermal conductivity is detected by the thermal conductivity detector 59 every time oxygen is supplied in a pulse form from the oxygen pulse introduction unit 53 into the supply passage 60.
In addition, the flow path switching cock 54 is switched to a side that bypasses the sample tube 56 to calibrate the oxygen amount.

In the calibration of the oxygen amount, the relationship between the oxygen amount supplied in a pulse form from the oxygen pulse introduction unit 53 and the area of the peak detection value detected by the thermal conductivity detector 59 with respect to the oxygen amount is obtained. . Then, based on the relationship between the amount of oxygen obtained by the calibration of the amount of oxygen and the area of the peak detection value, the average of the area of the peak detection value detected by the thermal conductivity detector 59 after the sample enters a steady state. The oxygen storage stored in the sample is determined from the area difference between the value and the area of the peak detection value detected by the thermal conductivity detector 59 each time oxygen is supplied from the oxygen pulse introduction unit 53 before the sample enters a steady state. The amount is converted, and the oxygen storage amount per liter of sample (ccO ₂ / Lcat), that is, the oxygen storage capacity of the sample can be calculated from the total amount. Note that ccO ₂ / Lcat
L indicates liter.

Next, the oxygen storage capacity of the three-way catalyst 6B was measured by the oxygen pulse method at 400 to 600 cc O ₂ / L.
The reason for setting to cat will be described. Here, FIG.
Are three types with different oxygen storage capacity (about 200, about 400,
About 600ccO ₂ / Lcat) of the three-way catalyst, respectively installed downstream of the NO _X catalyst of the same specifications, these of the NO _X
Catalyst were allowed to S poisoning to the same extent, and the temperature of the air-fuel ratio (A / F) of 12, NO _X catalyst around of the NO _X catalyst to about 700
It shows the release behavior of H ₂ S from each three-way catalyst during the regeneration treatment when the regeneration treatment was performed at 10 ° C. for 10 minutes. Incidentally, about 200ccO ₂ / three-way catalyst having an oxygen storage capacity of Lcat that many three-way catalysts which are generally commercially available about the oxygen storage capacity 150~250ccO ₂ /
Since it is set to Lcat, it is regarded as a general three-way catalyst (conventional product) conventionally used.

As shown in FIG. 4, a conventional product of about 200
ccO to the three-way catalyst having an oxygen storage capacity of ₂ / Lcat, in the three-way catalyst having an oxygen storage capacity of about 400ccO ₂ / Lcat about 1/2, about 600ccO ₂ / L
about eight times less for a three-way catalyst having an oxygen storage capacity of cat
, The amount of H ₂ S released can be reduced. That is, at least the oxygen storage capacity of the three-way catalyst is about 400 c.
if cO ₂ / Lcat above, can halve the amount of released H ₂ S than conventional products, as enhance the oxygen storage capacity of the three-way catalyst, it can reduce the emission of H ₂ S.

Therefore, in order to increase the oxygen storage capacity and reduce the amount of H ₂ S released, it is conceivable to increase the amount of an oxygen storage agent (for example, ceria CeO ₂ ) added to the catalyst component. However, in the impregnation method, which is generally performed as a method for supporting the catalyst component on the catalyst substrate, the catalyst component is slurried when the catalyst component is supported on the catalyst substrate, but the viscosity of the slurry is determined by adding an oxygen storage agent. The higher the amount, the higher the viscosity, and the higher the viscosity, the more difficult it becomes to support the catalyst component on the substrate.

Therefore, the production of the catalytic converter and the H_Two
Considering the reduction rate of the amount of S released, about 400 to 600
ccO_Two/ Lcat sets the oxygen storage capacity of the three-way catalyst
Is desirable. Therefore, the three-way catalyst in the present embodiment
6B is an additive having oxygen storage capacity, for example, ceria C
eO_TwoIs added in an amount of 10 to 1 per liter of catalyst volume.
Within the range of 00 g, the oxygen of the three-way catalyst 6B can be reduced.
400-600ccO storage capacity _TwoSet to / Lcat
I am trying to.

[0035] With this configuration, CO in the exhaust gas generated during the stoichiometric air-fuel ratio operation, the HC and NO _x, the lean NO
_x catalyst (hereinafter, the NO _x catalyst hereinafter) as well as cleaned by the three-way function and a three-way catalyst 6B of 6A, is adapted to purify by the NO _x catalyst 6A for NO _x in the exhaust gas generated during lean operation . Further, by installing a three-way catalyst 6B having a high oxygen storage capacity to the exhaust gas downstream of the NO _x catalyst 6A, this three-way catalyst 6B, NO
_x CO that could not be purified by the catalyst 6A,
It is possible to oxidize HC and hydrogen sulfide H ₂ S (reducing substance of sulfur component) which is generated in a small amount during the regeneration control of the NO _x catalyst 6A. This is a three-way catalyst 6B
Has a high oxygen storage capacity, so that H ₂ S, CO, and HC can be oxidized by oxygen stored during lean operation (when the exhaust gas air-fuel ratio is lean).

At this time, the three-way catalyst 6B causes N
₂ is oxidized to NO _X (N ₂ + 1 / 2O ₂ → 2N
O) Nothing like that. This is because the oxidation reaction of N ₂ usually occurs only in a high-temperature atmosphere of 1000 ° C. or higher because the reaction rate is low. Well, NO _x catalyst 6A is alumina A
l ₂ O ₃ as a base material, a catalyst component having a three-way function together with a catalyst component having a NO _x purification function is supported on this base material so that they are mixed, and the NO _x purification function and the three-way function And at the same time. Here, when focusing on NO _X purification function, the NO _X purification function, the NO _X occluded on the catalyst in a lean atmosphere, then, NO in the exhaust gas by the occluded NO _X release and decomposition in a rich atmosphere _It purifies _X and is a so-called occlusion type lean NO _X catalyst. For example, at least one of barium Ba and potassium K as an occlusion material and at least one of platinum Pt and palladium Pd as noble metals are used. It is configured to carry.

[0037] In the exhaust gas purifying apparatus according to the present embodiment, the atmospheric adjustment control for adjusting the ambient atmosphere of the NO _X catalyst 6A, and resurrection control and regeneration control.
Here, resurrection and control is, NO _X purification efficiency of the NO _X catalyst 6A by occlusion of the NO _X is occluded when reduced NO
The _X desorbed a control to restore the NO _X purification efficiency, regeneration control A, NO _X catalyst 6A to SO _X is occluded NO _X purification efficiency was occluded when lowered SO _X
Which is a control for reproducing the NO _X catalyst 6A desorbed. Desorption of SO _X from the NO _X catalyst is also referred to as S purge.

Therefore, the ECU 20 of the internal combustion engine provided with the exhaust gas purifying apparatus according to the present embodiment has the configuration shown in FIG.
As shown in the functional block diagram, the upstream NO _X sensor 9, based on the detection value of the downstream NO _X sensor 10 NO
A NO _X purification efficiency calculating means 21 for calculating the NO _X purification efficiency of the _X catalyst 6A, the NO _X purification efficiency determination unit 22 determines whether it is necessary to either control the resurrection control and regeneration control, various An operation mode setting means 23 for selecting an operation mode based on detection information or the like from the sensors 28,
Operation and the fuel injection control means 25 for controlling the driving of the injector 8 is provided in accordance with the mode, NO _X purification with efficiency determination unit 22, described later additional fuel injection control unit 27
Thus, an atmosphere adjusting means 24 is provided which can set the periphery of the NO _X catalyst 6A to either an atmosphere suitable for desorbing NO _X (reducing atmosphere) or an atmosphere suitable for desorbing SO _X. .

Further, the ECU 20, the upstream-side NO _X sensor 9 as described above, the downstream NO _X sensor 10, along with the detection information from the various sensors 28 is inputted, the timer 2
The count value is input from 9. Here, the fuel injection control means 25 includes the normal fuel injection control means 2.
6 and additional fuel injection control means 27. The additional fuel injection control means 27 is provided when the recovery control determining means 22A determines that the recovery control is necessary, and when the regeneration control determining means 22B determines that the regeneration control is necessary, Each controls the operation of the fuel injection valve 8 so that additional fuel injection is performed.

The additional fuel injection for the recovery control is NO _X
In order to desorb NO _X stored in the catalyst 6A, NO
_{In order to make} the vicinity of the _X catalyst 6A have a rich atmosphere with a reduced oxygen concentration (for example, A / F = about 13), and to perform additional fuel injection for regeneration control so as to desorb SO _X , NO _In the vicinity of the _X catalyst 6A, a rich atmosphere (for example, A / F = about 12) in which the oxygen concentration is further reduced and the degree of reduction is higher than that in the reactivation control and the temperature is set to a predetermined temperature (for example, about 650 ° C.) or more. Is set to

[0041] Here, the additional fuel injection for regeneration control, was injected fuel is reliably combusted NO _X catalyst 6A
Is set to a high temperature atmosphere in the vicinity of the middle of the expansion stroke of each cylinder to the end of the exhaust stroke (a period in which the engine output is not affected), and is performed in a period in which the additional fuel can self-ignite and burn. The injection start timing is set. With such a configuration, in the exhaust gas purifying apparatus as one embodiment of the present invention, for example, as shown in the flowchart of FIG. 5, the recovery control (Steps S10 to S50) and the regeneration control based on the determination of the recovery control determining means 22A. Reproduction control based on the judgment of the judgment means 22B (step S60
Step S100) is performed.

First, the resurrection control will be described. In step S10, the lean operation cumulative time T _LS is calculated from the count value read from the timer 29 (see FIG. 1), and the process proceeds to step S20, where the lean operation cumulative time T _LS is calculated. Is longer than the recovery control determination time T _{LS 0} (for example, 60 seconds). As a result, when it is determined that the lean operation cumulative time T _LS is longer than the recovery control determination time T _LS0 , it is determined that the recovery control is necessary, and the lean operation cumulative time T _LS is reset to 0 and the step S30 is performed. Proceed to. On the other hand, when it is determined that the lean operation cumulative time T _LS is equal to or less than the recovery control determination time T _LS0 , the recovery control is not required yet, and the process returns to step S10 in the next control cycle.

[0043] This, NO in the _X catalyst 6A, the operation in the lean operation mode such as compressed lean operation mode and the intake lean operation mode is performed gradually since _the NO _X storage amount increases, thus NO _X NO _X occluded in catalyst 6A
It is determined whether or not it is necessary to perform the resurrection control in order to restore the NO _X purification efficiency of the NO _X catalyst 6A by desorbing the NOx catalyst 6A. The determination is made based on whether or not the operation cumulative time) T _LS has _{exceeded a} predetermined time (recovery control determination time T _LS0 ).

Then, in step S30, the rich spike timer is turned on, and at the same time, the process proceeds to step S40, in which a resurrection control mode (rich spike mode) is executed. Fuel injection (rich spike) is performed, and the process proceeds to step S50. Note that the rich spike timer is calculated by the resuming control determining means 22A based on the count value read from the timer 29 (see FIG. 1).

In step S50, the rich spike timer value T counted by the rich spike timer
_L is greater or not than the additional fuel injection time T ₁ of the for a given resurrection control is determined. As a result, when the rich spike timer value T _L is determined to be greater than the additional fuel injection time T ₁ proceeds to step S60 (regeneration control).

Meanwhile, if the rich spike timer value T _L is determined to be less additional fuel injection time T _1, the flow returns to step S40, the rich spike timer value T _L is greater than the additional fuel injection time T ₁ Until then, the rich spike mode (step S40) is maintained. Thus, during the predetermined additional fuel injection time T _1, and the rich spike is performed, revived control ends.

With this resurrection control, NO_XOf catalyst 6A
The vicinity is a rich atmosphere and NO _XOccluded in catalyst 6A
NO_XIs desorbed, so NO_XN by catalyst 6A
O_XAlthough the purification efficiency is increased, it takes a certain amount of time
Judgment time for control) T_LS0Every time the resurrection control is performed
NO_XThe catalyst 6A contains SO_XOccluded as sulfate
Sulfate once absorbed is released in the recovery control
NO_XWith catalyst 6A, SO_X
The occlusion amount increases, and accordingly, NO_XCatalyst 6A
NO_XPurification efficiency also decreases. For this reason, the playback system
The stored SO is determined by the usage determining means 22B._XNO_XTouch
Regeneration control for detachment from the medium 6A (steps S60 to S60)
Step S100) is performed.

That is, after the end of the resurrection control, step S60
In due to the NO _X catalyst 6A after resurrection controlled by NO _X purification efficiency calculating means 21 NO _X purification efficiency eta [η = (A ₁ -
_{A 2) / A 1, A} 1: upstream NO _X sensor detection value,
A ₂ : detected value of the downstream NO _X sensor], it is determined in step S70 whether or not the NO _X purification efficiency η after the recovery control is smaller than the regeneration control determination value a.

As a result of this determination, if it is determined that the NO _X purification efficiency η after the restoration control is not smaller than the regeneration control determination value a, the regeneration control is not yet necessary, so that step S10 is performed in the next control cycle. The processing from step S10 to step S70 is repeated until the NO _X purification efficiency η after the restoration control becomes smaller than the regeneration control determination value a.

On the other hand, if it is determined that the NO _X purification efficiency η after the recovery control is smaller than the regeneration control determination value a, N
NO _X by O _X catalyst 6A to SO _X is occluded
Since the purification efficiency has decreased and it is considered that regeneration control is necessary, the process proceeds to step S80, where the regeneration process timer is turned on, and the process proceeds to step S90, where the regeneration process mode is executed. The reproduction processing timer is calculated by the reproduction control determination means 22B based on the count value read from the timer 29 (see FIG. 1).

Then, in step S90, the regeneration processing mode is executed, additional fuel injection (S purge) for regeneration control is performed by the additional fuel injection control means 27, and the routine proceeds to step S100. At step S100, playback processing timer value T _R to be counted by the reproduction process timer, whether greater than the additional fuel injection time T ₂ of the for a given regeneration control is determined, as a result, the reproduction process timer value T _{If R} is determined to be greater than the additional fuel injection time T ₂ regeneration control is terminated, whereas, if the reproduction process timer value T _R is determined to be the additional fuel injection time T ₂ or less, the step S90 to return, to the rich spike timer value T _R is greater than the additional fuel injection time T _2, the reproduction process mode (step S90) is maintained.

In this way, the regeneration process is performed for a fixed time (additional fuel injection time T ₂ ), and the regeneration control ends. Accordingly, when the NO _X purification efficiency η after the resurrection control becomes smaller than the regeneration control determination value a, the regeneration processing mode for a fixed time (additional fuel injection time T ₂ ) causes N
Near the O _X catalyst 6A is a rich atmosphere, and a predetermined temperature (e.g., about 650 ° C.) is equal to or greater than, NO _X catalyst 6A occluded in the SO _X is desorbed, thus, NO
NO _X purification efficiency by _X catalyst 6A is adapted to be raised (reproduced).

In this reducing atmosphere, NO_X
SO desorbed from catalyst 6A_XIs excessively reactive
Quantity of H_TwoS is oxidized by the high oxygen storage type three-way catalyst 6B
SO again_X(2H_TwoS + 3O_Two→ 2SO
_Two+ 2H_TwoO) It is discharged outside. Therefore, this implementation
According to the exhaust gas purifying device according to the embodiment, the high oxygen storage type
H generated during the regeneration control by the three-way catalyst 6B_TwoS to S
O_XAnd oxidize to the outside _TwoSuppressing S emission
There is an advantage that you can.

[0054] Further, in the reproduction process, SO _X in the NO _X catalyst 6A and more richer than the conventional air-fuel ratio
Of H ₂ S is reduced by the three-way catalyst 6B
Therefore, there is no need to set the degree of enrichment of the air-fuel ratio low in consideration of H ₂ S emission. For this reason, the time required for the regeneration process is reduced, and the NO _X
It is possible to regenerate the purification efficiency η of the catalyst 6A, and there is also an advantage that deterioration in fuel efficiency due to the regeneration process can be suppressed.

[0055] Further, HC that has not been purified by a three-way function of the NO _X catalyst 6A, for also CO, it is possible to oxidize by a three-way catalyst 6B, HC, an advantage that a further reduction can be performed in CO emissions is there. Incidentally, the exhaust gas purifying apparatus main body 6 of this embodiment is installed the NO _x catalyst 6A and three-way catalyst 6B and to each in separate casings, it is not limited thereto, for example, NO _x
The catalyst 6A and the three-way catalyst 6B may be provided in one casing. In this case as well, the downstream side NO
_X sensor 10 is disposed between the the NO _x catalyst 6A and a three-way catalyst 6B.

[0056] Further, the exhaust gas purifying apparatus main body 6 is equipped with a conventional three-way catalyst downstream of the NO _x catalyst 6A, it may be further configured to include the three-way catalyst of high oxygen storage-type downstream thereof. Further, in the exhaust gas purifying apparatus according to each of the above-described embodiments, a high oxygen storage type three-way catalyst is used to oxidize H ₂ S, but an oxidation catalyst may be used. Further, the exhaust gas purifying apparatus according to each embodiment described above, the resurrection control, although to perform the additional fuel injection by adding the fuel injection control means 27 to the vicinity of the NO _X catalyst in a rich atmosphere, revived control However, the method for setting the vicinity of the NO _X catalyst to a rich atmosphere is not limited to this, and a method such as switching the operation mode to the rich side may be used.

[0057] Further, the exhaust gas purifying apparatus according to the embodiments described above, in the regeneration control, and the vicinity of the NO _X catalyst in a rich atmosphere, and added by the additional fuel injection control unit 27 in order to raise the exhaust gas temperature fuel injection However, the method of raising the exhaust gas temperature is not limited to this. For example, rich operation, ignition timing is retarded, or another device (for example, an electrically heated catalyst) is used. Or other methods.

[0058] Further, the exhaust gas purifying apparatus according to each embodiment described above, in order to calculates the NO _X purification efficiency of the NO _X catalyst is provided with the NO _X sensor on the upstream side and the downstream side of the NO _X catalyst, not limited thereto, and detecting the amount of NO _X in the exhaust gas discharged from the exhaust gas purifying apparatus main body 6 is provided one NO _X sensor on the downstream side of the NO _X catalyst is supplied to the exhaust gas purifying apparatus main body 6 that _the amount of NO _X in the exhaust gas,
The NO _X amount may be set in advance according to the operating conditions (a value stored in the ECU), and the deterioration of the NO _X catalyst may be estimated by comparing the detected value of the NO _X sensor with the memory value.

Further, the exhaust gas purifying apparatus according to each of the above embodiments has been described as applied to a direct injection internal combustion engine. However, the present invention is not limited to this. Can.

[0060]

As described above in detail, according to the exhaust gas purifying apparatus according to the first and second aspects of the present invention, it is possible to suppress the emission of the reducing substance of the sulfur component released from the storage type NOx catalyst to the outside. It is possible to reduce the air-fuel ratio
There is an advantage that the regeneration of the Ox catalyst can be performed efficiently, and the deterioration of fuel efficiency due to the regeneration processing of the storage NOx catalyst can be suppressed.

[Brief description of the drawings]

FIG. 1 is a block diagram schematically showing a main configuration of a control system of an internal combustion engine as one embodiment of the present invention.

FIG. 2 is a schematic diagram showing an overall configuration of an internal combustion engine as one embodiment of the present invention.

FIG. 3 is a diagram showing an overall configuration of a measuring device when measuring oxygen storage capacity in a general oxygen pulse method.

FIG. 4 is a diagram showing the release behavior of H ₂ S when a regeneration treatment is performed on three types of catalysts having different oxygen storage capacities.

FIG. 5 is a flowchart showing a recovery control and a regeneration control in the internal combustion engine as one embodiment of the present invention.

[Description of Signs] 3 Exhaust passage 6 Exhaust gas purification device main body 6A Lean NO _X catalyst (storage type NO _X catalyst) 6B Three-way catalyst (auxiliary catalyst) 20 Electronic control unit (ECU) 21 NO _X purification efficiency calculating means 22 NO _X Purification efficiency determination means 22A Recovery control determination means 22B Regeneration control determination means 23 Operation mode setting means 24 Atmosphere adjustment means 26 Normal fuel injection control means 27 Additional fuel injection control means

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F01N 3/24 F01N 3/24 ER F02D 41/02 305 F02D 41/02 305 41/04 305 41/04 305C (72) Inventor Kazuo Koga 5-33-8 Shiba, Minato-ku, Tokyo Inside Mitsubishi Motors Industry Co., Ltd. (72) Inventor Uniform 5-33-8 Shiba 5-chome, Minato-ku, Tokyo Mitsubishi Motors Corporation (72) Inventor Masao Hori 992, Nishioki, Akihama-ku, Abashiri-ku, Himeji-shi, Hyogo 1 Inside ICT Inc. Shin Makoto Horiuchi 992, Nishioki, Okihama-shi, Aboshi-ku, Himeji-shi, Hyogo F-term (reference) in ICT Corporation 3G091 AA12 AA17 AA24 AA28 AB02 AB06 BA03 BA11 BA14 BA15 BA19 BA20 BA32 BA33 CA18 CB02 CB03 DA02 DA04 DB06 DB10 DB13 DC01 EA30 EA33 EA34 FB10 FB11 FB12 FC01 GB03W GB06W GB07W HA08 HA09 HA36 HA37 HA04 3G301 HA01 PE04

Claims (2)

[Claims] 1. An occlusion type NOx catalyst which is interposed in an exhaust passage of an internal combustion engine and stores NOx in exhaust gas flowing in an oxidizing atmosphere and releases the stored NOx in a reducing atmosphere. Atmosphere adjusting means for adjusting the air-fuel ratio of the inflowing exhaust gas to release the sulfur component in the exhaust gas stored in the storage NOx catalyst, and an exhaust passage downstream of the storage NOx catalyst, An exhaust gas purifying apparatus, comprising: an auxiliary catalyst having an oxygen storage capacity capable of oxidizing a reducing substance of the sulfur component released from the type NOx catalyst. 2. The oxygen storage capacity of the auxiliary catalyst is set such that the oxygen storage capacity per liter of catalyst capacity is about 400 to 600 cc as measured by the oxygen pulse method. 2. The exhaust gas purifying apparatus according to claim 1.