JP2000240428A - Exhaust gas emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the NOX purification efficiency of an NOX occlusion reduction catalyst. SOLUTION: An NOX occlusion reduction catalyst 7 is arranged in the exhaust passage 3 of an engine 1 to absorb NOX contained in exhaust gas of an engine under lean air-fuel ratio operation. When an NOX occlusion amount of the catalyst 7 attains a predetermined decision value, a reducing agent (diesel oil) is injected in an exhaust passage on the upper stream side of the catalyst 7 through a reducing agent feed nozzle 91 and NOX is emitted from the catalyst 7 for reduction purification. The decision value is set such that an emission amount of unpurified NOX due to exudation under absorption of NOX is decreased to a predetermined low value. This constitution, since emission of unpurified NOX through discharge or exudation owing to the increase of an occlusion NOX amount is suppressed to a low value, remarkably improves the NOX purification efficiency of the whole of the NOX occlusion reduction catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

Relates to an exhaust purifying apparatus of the present invention is an internal combustion engine TECHNICAL FIELD OF THE INVENTION The exhaust air-fuel ratio flows into the details absorbs NO _X in the exhaust gas when the lean, the oxygen concentration in the inflowing exhaust gas drops The present invention relates to an exhaust gas purification device for an internal combustion engine provided with a NO _X storage reduction catalyst that releases sometimes absorbed NO _X.

[0002]

BACKGROUND ART exhaust air-fuel ratio of the inflowing absorbs NO _X in the exhaust gas when the lean, NO _X occluding and reducing catalyst the oxygen concentration in the inflowing exhaust gas to release NO _X absorbed when reduced intellectual Have been. An example of an exhaust gas purifying apparatus for an internal combustion engine using this type of NO _X storage reduction catalyst is described in, for example, Japanese Patent Application Laid-Open No. Hei 6-200738.

In the device disclosed in the publication, a NO _X storage reduction catalyst is disposed in an exhaust passage of an engine operable at a lean air-fuel ratio, and when the engine is operated at a lean air-fuel ratio, NO _X in exhaust gas is discharged.
To absorb, _the NO _X storage NO _X absorption amount of the reduction catalyst is a liquid or gas as a reducing agent from the reducing agent feed nozzle disposed on an upstream side of the exhaust passage of the NO _X occluding and reducing catalyst when reaching a predetermined value hydrocarbon And the like are injected into the exhaust gas. When the reducing agent with the exhaust to the NO _X occluding and reducing catalyst is supplied, NO _X is oxygen concentration in the exhaust gas absorbed from _the NO _X storage reduction catalyst for reduction by oxidation on _the NO _X storage reduction catalyst reducing agent Released. Further, the released NO _X reacts with the reducing agent in the exhaust gas on the catalyst to be reduced and purified.

[0004]

[SUMMARY OF THE INVENTION However, NO _X from the JP-A as in the 6-200738 discloses a device, there by supplying reducing agent to the NO _X occluding and reducing catalyst at the time intervals _the NO _X storage reduction catalyst When the emission of NO and the reduction and purification are performed, the overall NO _X purification rate may not be improved depending on the time interval of the supply of the reducing agent.

Usually, NO_XSupply reducing agent to storage reduction catalyst
NO_XNO from storage reduction catalyst _XRelease and reduction purification
(Hereinafter, “NO_XRegeneration operation of storage reduction catalyst
Is called NO)_XNO absorbed by the storage reduction catalyst
_XExecuted when the volume reaches a certain level,
This NO_XNO absorption level_XAbsorption reduction catalyst absorbs
NO_XDetermined based on the amount of absorption (saturation)
It is. That is, NO_XNO of storage reduction catalyst_XAbsorption capacity
Make the most of NO_XActual operation of regeneration of storage reduction catalyst
To keep row frequency low, use as much NO as possible_X
Is NO_XRegeneration operation is performed after absorption by the storage reduction catalyst
Is preferred. Therefore, usually, a playback operation is performed.
NO_XNO absorption level_XSaturation amount of storage reduction catalyst
A relatively high level (eg, NO
_X(About 70% of the saturation of the storage reduction catalyst)
Is done.

However, when the regeneration operation of the NO _X storage reduction catalyst is executed after waiting for the NO _X absorption amount of the NO _X storage reduction catalyst to reach a relatively high level, the overall purification of NO _X It has proven difficult to significantly increase the rate. For example, during the regeneration operation of the conventional NO _X storage reduction catalyst, it is considered that NO _X released from the NO _X storage reduction catalyst is completely purified by the supplied reducing agent, and unpurified NO _X is not released downstream. I was However, in practice, it has been found that unpurified NO _X may be released to the downstream side of the catalyst during the regeneration operation of the NO _X storage reduction catalyst.

As mentioned above, when the reducing agent is supplied, NO
_XOxygen concentration near the storage reduction catalyst decreases and NO_XOcclusion reduction
NO from catalyst_XIs released. However, the catalyst
NO _XRelease rate was not constant and oxygen concentration decreased
Immediately after (immediately after starting the supply of the reducing agent), a relatively large amount of N
O_XIs released, after which the relatively low release rate is almost uniform
NO in degrees_XHas been found to be released. This, return
NO immediately after starting supply of base agent_XN absorbed from the storage reduction catalyst
O_XIs rapidly released as "NO_XVomiting "
To call it, NO_XNO in spitting_XRelease
The output (release speed) is NO_XNO of storage reduction catalyst_XOcclusion
Quantity, ie NO_XNO absorbed in the storage reduction catalyst_X
The larger the amount, the larger. Therefore, NO_XOcclusion reduction
Medium regeneration operation with relatively high NO_XPerform at the storage level
NO if you try to_XReleased by the exhalation of
Large amount of unpurified NO_XTemporarily reduces the amount of reducing agent in the exhaust
And the N released immediately after the start of the supply of the reducing agent.
O_XIs unpurified and NO_XOutflow downstream of the storage reduction catalyst
Become so. NO_XIs short after starting the supply of reducing agent
Ends in hours, then NO_XRelease rate is relatively low
After the end of the discharge, the reducing agent in the exhaust
There will be no shortage. Therefore, NO_XOcclusion reduction
Medium NO_XReducing agent even when the storage amount is at a relatively high level
After a certain period of time has passed since the start of supply, unpurified NO_X
Will stop flowing.
NO for each line_XUnpurified NO from the storage reduction catalyst_XLeaks
Average NO as a whole_XPurification rate above a certain level
The problem that cannot be raised arises.

Further, in the NO _X storage reduction catalyst, the above NO _X
A phenomenon called "NO _X seepage" has been discovered in addition to the exhalation. Conventionally, the NO _X storage reduction catalyst is NO _X
Storage amount exhaust air-fuel ratio unless reaching the saturation amount is believed to absorb NO _X in the exhaust gas if lean. However, in practice it has been found that NO _X absorbing capacity of the NO _X occluding and reducing catalyst gradually decreases as _the NO _X storage amount of the NO _X occluding and reducing catalyst is increased. Therefore, NO _X
Also _the NO _X storage amount of storage reduction catalyst is a much lower than the saturation amount, NO _X in the occluding and reducing catalyst downstream is not absorbed in the catalyst NO _X is flowing. Also, this NO
_X runoff increases as _the NO _X storage amount of the NO _X occluding and reducing catalyst is increased, the downstream side in the NO _X in the exhaust gas and _the NO _X storage amount reaches the saturation amount not at all absorbed in the NO _X occluding and reducing catalyst To be leaked to In this way, when the exhaust air-fuel ratio is lean, a phenomenon in which an amount of NO _X corresponding to the NO _X storage amount flows out downstream of the catalyst without being purified is referred to as “NO _X seepage”.

As described above, NO_XRegeneration of storage reduction catalyst
Sometimes NO_XOf unpurified NO flowing out due to the discharge of water
_XAnd NO under lean air-fuel ratio_XFlow by oozing
Unpurified NO emitted_XNO both_XOcclusion reduction catalyst
NO_XIt increases according to the occlusion amount. For this reason,
NO_XWhen the storage amount reaches a relatively high level, N
O _XExhaust gas that performs the regeneration operation of the storage reduction catalyst
In the purifier, NO_XRelease by spitting and seeping out
Unpurified NO issued_XBecause, to some extent over the whole
NO as_XPurification rate cannot be improved.

[0010] The present invention has been made in view of the above problems, preventing deterioration of the NO _X purification rate by discharging or exudation of the NO _X,
And its object is to provide an exhaust purification system of an internal combustion engine that can significantly improve the NO _X purification rate.

[0011]

According to the first aspect of the present invention,
According to this, the exhaust gas flowing into the exhaust passage of the internal combustion engine is
NO in exhaust when air-fuel ratio is lean_XAbsorb and inflow
Absorbed when the oxygen concentration in the exhaust gas decreases_X
Releases NO_XThe storage reduction catalyst and the NO_XOcclusion reduction
NO when the exhaust air-fuel ratio flowing into the medium is lean_XOcclusion return
By supplying a reducing agent to the source catalyst, NO_XOcclusion reduction
With reducing the oxygen concentration in the exhaust gas flowing into the catalyst
And the released NO_XReducing agent supply device to reduce and purify
In the exhaust gas purifying apparatus for an internal combustion engine provided with:_X
The storage reduction catalyst is supplied immediately after the start of the supply of the reducing agent.
Unpurified NO that is not reduced by the reducing agent_XThe downstream side
And the unpurified NO_XThe amount is NO_XAbsorption of storage reduction catalyst
NO collected_XThe reducing agent supply device increases according to the amount
Is NO_XNO absorbed by the storage reduction catalyst_XQuantity is predetermined
NO when level is reached_XUsing a reducing agent for the storage reduction catalyst
Supply the predetermined NO _XThe absorption level is determined by the reducing agent
NO at the start of supply_XUnpurified NO from the storage reduction catalyst
_XThe release amount is set to be less than the predetermined value.
An exhaust gas purification device for an internal combustion engine is provided.
You.

That is, according to the first aspect of the present invention, NO
Every time the amount of NO _X absorbed by the _X storage reduction catalyst reaches a predetermined level, a regeneration operation of the NO _X storage reduction catalyst is performed.
However, this predetermined level is set to a considerably lower level than in the past so that the unpurified NO _X amount flowing out by the discharge of NO _X at the start of the regeneration operation is maintained at a predetermined low value. As a result, in the present invention, the regeneration operation is performed at a very short interval as compared with the related art, but the emission amount of unpurified NO _X due to the discharge at the start of the regeneration operation is suppressed to an extremely low value. The overall NO _X purification rate can be greatly improved. Note that NO _X
The reducing agent supply to storage reduction catalyst may be performed by injecting a reducing agent consisting of _the NO _X storage reduction catalyst upstream of the exhaust passage to hydrocarbon (HC) and the like, in a short time a rich air-fuel ratio of the engine By driving, unburned HC in exhaust gas,
This may be done by increasing the CO component.

According to the invention described in claim 2, the internal combustion engine
The air-fuel ratio of the inflowing exhaust
Sometimes NO in exhaust_XAbsorbs oxygen in the incoming exhaust
NO absorbed when the concentration decreases_XReleases NO_X
The storage reduction catalyst and the NO_XExhaust gas flowing into the storage reduction catalyst
NO when the air-fuel ratio is lean_XUsing a reducing agent for the storage reduction catalyst
NO by supplying_XExhaust flowing into the storage reduction catalyst
Reduced oxygen concentration in air and released NO
_XInternal combustion engine equipped with a reducing agent supply device for reducing and purifying
In the exhaust gas purification apparatus, the NO_XThe storage reduction catalyst is
NO absorbed even if the incoming exhaust air-fuel ratio is lean_Xamount
Amount of unpurified NO_XDischarge downstream
And the reducing agent supply device has NO_XAbsorbed by storage reduction catalyst
NO _XNO when quantity reaches a predetermined level_X
A reducing agent is supplied to the storage reduction catalyst, and the predetermined NO_Xabsorption
The amount level is determined by the above NO under lean air-fuel ratio exhaust._XSucking
Unpurified NO from storage reduction catalyst_XRelease amount is less than predetermined value
Internal combustion engine characterized by being set to be below
An exhaust purification system for a Seki is provided.

That is, also in the second aspect of the present invention, the regeneration operation of the NO _X storage reduction catalyst is performed every time the NO _X amount absorbed by the NO _X storage reduction catalyst reaches a predetermined level. However, in the present invention, the predetermined level is conventionally set so that the unpurified NO _X amount flowing out due to the exudation of NO _X due to the increase in the NO _X storage amount of the NO _X storage reduction catalyst is maintained at a predetermined low value. It is set to a considerably lower level. As a result, in the present invention, the regeneration operation is performed at a very short interval as compared with the related art, but the amount of unpurified NO _X released due to NO _X seeping is suppressed to an extremely low value. As a result, the purification rate of NO _X can be greatly improved. In the present invention, NO
The supply of the reducing agent to the _X storage reduction catalyst may be performed by injecting the reducing agent into the exhaust passage or by operating the engine at a rich air-fuel ratio for a short time.

[0015] The level of the NO _X storage amount at which the regeneration operation of the NO _X storage reduction catalyst is started may be a value at which the unpurified NO _X amount by discharging according to the first aspect of the present invention becomes equal to or less than a predetermined value, or the level of the stain according to the present invention. If the unpurified NO _X amount by discharging is set to a lower value which is equal to or less than a predetermined value, the emission of unpurified NO _X can be reduced more completely.

According to the third aspect of the present invention, the reducing agent supply device includes a reducing agent supply nozzle for injecting a reducing agent into an exhaust passage on an upstream side of the NO _X storage reduction catalyst.
_When the exhaust air-fuel ratio flowing into the _X storage reduction catalyst is lean, a predetermined amount of reducing agent is supplied into the exhaust each time the NO _X amount absorbed by the NO _X storage reduction catalyst reaches the predetermined level. An exhaust gas purifying apparatus for an internal combustion engine according to claim 1 or 2 is provided.

That is, in the third aspect of the invention, NO
The supply of the reducing agent to the _X storage reduction catalyst is performed by injecting the reducing agent into the exhaust gas from a reducing agent supply nozzle disposed in the exhaust passage on the upstream side of the NO _X storage reduction catalyst. This makes it possible to significantly improve the purification rate of the NO _X even in difficult diesel engine be operated at a rich air-fuel ratio.

According to the fourth aspect of the present invention, the injection amount and the injection rate of the reducing agent from the reducing agent supply nozzle are set according to the time interval at which the supply of the reducing agent is performed. Item 3. An exhaust gas purification device for an internal combustion engine according to item 3 is provided. That is, in the invention according to claim 4, the injection rate and the injection amount of the reducing agent from the reducing agent supply nozzle are set according to the execution interval of the regeneration operation. In the present invention, since the regeneration operation is performed at a shorter interval than in the related art, if the same amount of the reducing agent is injected as in the related art during each regeneration operation, the consumption of the reducing agent is greatly increased. In the present invention, NO
_{Since the} regeneration operation is performed when the NO _X storage amount of the _X storage reduction catalyst is at a low level, the amount of the reducing agent required for the regeneration operation is small. Therefore, in the present invention, the amount of the reducing agent supplied at the time of the regeneration operation depends on the time interval of the regeneration operation, that is, the amount of N stored in the NO _X storage reduction catalyst at the time of the regeneration operation.
Depending on the amount of O _X excess and deficiency is set so as not to cause.
This also reduces the amount of reducing agent injected from the reducing agent supply nozzle during each regeneration operation, but if this small amount of reducing agent is injected into the exhaust for a long time, the reducing agent is diluted into the exhaust. As a result, the oxygen concentration of the NO _X storage reduction catalyst cannot be reduced. Therefore, in the present invention, the injection rate of the reducing agent from the reducing agent supply nozzle is set according to the injection amount (that is, according to the execution interval of the regeneration operation), and the concentration of the reducing agent in the exhaust gas is maintained sufficiently high. Like that. As a result, even if the time interval of the regeneration operation is set short, an increase in the consumption of the reducing agent is suppressed, and complete regeneration of the NO _X storage reduction catalyst is performed.

[0019]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram showing a schematic configuration of an embodiment of the exhaust gas purification apparatus of the present invention. In FIG. 1, reference numeral 1 denotes an internal combustion engine. In this embodiment, a diesel engine is used as the internal combustion engine 1, and each cylinder exhaust port of the engine is connected to a common exhaust passage 3 via an exhaust manifold 31. Further, a NO _X storage reduction catalyst 7 described later is arranged on the exhaust passage 3. 9 in FIG.
Is a reducing agent supply device that supplies a reducing agent to the NO _X storage reduction catalyst 7 during the NO _X storage reduction catalyst 7 regeneration operation. The reducing agent supply device, comprising a _the NO _X storage reduction the reducing agent feed nozzle 91 disposed in an exhaust inlet near the catalyst 7 NO _X
By injecting a reducing agent into the exhaust gas flowing into the storage reduction catalyst 7, the oxygen concentration in the exhaust gas flowing into the NO _X storage reduction catalyst 7 is reduced, and the NO _X absorbed from the catalyst 7 is released and released. to reduce and purify the NO _X. As described below, in the present embodiment, the fuel (diesel oil) of the engine 1 is used as the reducing agent. The reducing agent supply device 9 includes:
The pressurized fuel supplied from the fuel system, which is connected to an engine fuel system (not shown),
Inject into.

In FIG. 1, reference numeral 30 denotes an electronic control unit (ECU) of the engine 1. In the present embodiment, the ECU 3
Reference numeral 0 denotes a microcomputer having a known configuration including a RAM, a ROM, and a CPU. The microcomputer 0 performs basic control such as a fuel injection amount and a fuel injection timing of the engine 1 and also controls a reducing agent supply device 9 to be described below. N from _X storage reduction catalyst 7
O _X release and reduction purification operation (NO _X catalyst regeneration operation of the reduction catalyst) is carried out.

The NO _X storage-reduction catalyst 7 of the present embodiment comprises, for example, potassium K and sodium Na on a carrier such as alumina.
, Lithium Li, at least one component selected from alkali metals such as cesium Cs, alkaline earths such as barium Ba and calcium Ca, and rare earths such as lanthanum La, cerium Ce and yttrium Y, and platinum Pt. Noble metal is supported. The NO _X storage reduction catalyst converts NO _X (NO ₂ , NO) in the exhaust gas into nitrate ions NO when the air-fuel ratio of the inflowing exhaust gas is lean.
₃ ^- absorbed in the form of, performing absorption and release action of the NO _X that releases NO _X concentration of oxygen absorbed to decrease the inflow exhaust gas.

The mechanism of the absorption and release will be described below by taking platinum Pt and barium Ba as an example, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths and rare earths. When the oxygen concentration in the inflowing exhaust gas increases (that is, when the air-fuel ratio of the exhaust gas becomes a lean air-fuel ratio), these oxygens become
₂ ^- or deposited at O ^2- form, NO _X in the exhaust gas platinum P
O ₂ on t ^- or react with O ^2-, thereby NO ₂ is produced. Further, barium oxide BaO NO ₂ and NO ₂ produced by the above in the inflowing exhaust gas is to function as an absorbent is absorbed by the catalyst while being further oxidized on the platinum Pt
Diffuses in the catalyst in the form of ^- bound nitrate ions NO ₃ while the. Therefore, in a lean atmosphere, NO _X in the exhaust gas is absorbed in the NO _X storage reduction catalyst in the form of nitrate.

When the oxygen concentration in the inflowing exhaust gas decreases (ie, when the air-fuel ratio of the exhaust gas decreases), the amount of NO ₂ generated on the platinum Pt decreases, so that the reaction proceeds in the reverse direction, and the catalyst proceeds. The nitrate ion NO ₃ ⁻ in the inside is released from the NO _X storage reduction catalyst in the form of NO ₂ . In this case, if components such as HC and CO are present in the exhaust gas, platinum Pt
Above, these components reduce NO ₂ .

[0024] In this embodiment, the exhaust air-fuel ratio of the engine for diesel engine is used as the engine 1 is lean, the normal operation of the exhaust passage 3 NO _X occluding and reducing catalyst 7
NO _X in the exhaust gas flowing the exhaust of a lean air-fuel ratio in the NO
It is absorbed by the _X storage reduction catalyst 7. When the reducing agent is supplied to the exhaust passage 3 on the upstream side of the NO _X storage reduction catalyst 7, NO
The _X occluding and reducing catalyst 7 flows is contained reductant exhaust, part of the reducing agent reacts with oxygen on the platinum Pt of the NO _X occluding and reducing catalyst 7. Thereby, the oxygen concentration in the atmosphere of the NO _X storage reduction catalyst 7 decreases, and components such as unburned HC and CO are generated by oxidation of the reducing agent. When the atmospheric oxygen concentration of the NO _X occluding and reducing catalyst 7 by oxidation of the reducing agent decreases, HC of _the NO _X storage NO _X from the reducing catalyst 7 is released in the exhaust by a mechanism mentioned above, it is reduced by CO component.

[0025] The _the NO _X storage reduction and release of the NO _X from the catalyst, the reducing agent used in the reduction purification operation (reproducing operation of the NO _X occluding and reducing catalyst), the reducing components and HC such as H ₂ in the exhaust, A substance that generates a CO component is used, and for example, a gas such as hydrogen and carbon monoxide, a liquid or gaseous hydrocarbon such as propane, propylene, and butane, and a liquid fuel such as gasoline, light oil, and kerosene can be used. In the present embodiment, since a diesel engine is used as the internal combustion engine 1, the fuel (diesel oil) of the engine 1 is used as a reducing agent in consideration of the convenience of replenishment and storage. The reducing agent supply device 9 receives the fuel supplied from the fuel pump (not shown) of the engine 1 from the reducing agent supply nozzle 91 via a shutoff valve and a flow control valve (not shown) to the upstream side of the NO _X storage reduction catalyst 7. for reproducing of the NO _X occluding and reducing catalyst 7 by supplying the exhaust passage.

As described above, NO_XStorage reduction catalyst 7 is returned
When the reducing agent is not supplied from the base agent supply device 9
(Ie when the incoming exhaust air-fuel ratio is lean)
NO in_XAnd returned to the exhaust gas from the reducing agent supply device 9
When the oxygen concentration of the exhaust gas supplied and supplied decreases,
NO collected_XTo release and purify. For this reason, the conventional N
O_XNO absorbed by the storage reduction catalyst 7_XUnless saturated with
Unpurified NO downstream _XWill not be released
Was obtained.

[0027] However, in the actual operation saturated with NO _X storage is the reduction catalyst described above "NO _X of the discharge," said NO because the phenomenon occurs, which is referred to as "NO stains out of _{X" X} occluding and reducing catalyst has absorbed NO _X Unpurified N even if not
O _X is it found that may be released to the downstream side. In this specification, referred to as "discharging of the NO _X" a phenomenon that unpurified of the NO _X is released into _the NO _X storage reduction catalyst downstream of the regeneration operation early of the NO _X occluding and reducing catalyst as described above, _the NO _X storage The phenomenon that unpurified NO _X is released downstream of the NO _X storage reduction catalyst while the reduction catalyst is absorbing NO _X in the exhaust gas (that is, when the inflowing exhaust air-fuel ratio is lean) is referred to as “NO _X seepage”. To distinguish them.

The reason why the exhalation and exudation of NO _X occurs is not clear at present, but is presumed to be due to the phenomenon described below. First, the reason why the discharge of NO _X occurs will be described. As described above, the NO _X storage reduction catalyst
The O _X held in the form of nitrates. At this time, nitrate ions move by diffusion from the surface of the absorbent (eg, BaO) in the NO _x storage reduction catalyst to form nitrate. For this reason, during the absorption of NO _X , the nitrate ion concentration on the absorbent surface is higher than the internal nitrate ion concentration. In this state, when the regenerating operation of the NO _X storage reduction catalyst is started and the atmospheric oxygen concentration on the surface of the absorbent rapidly decreases, high concentration nitrate ions near the surface of the absorbent are simultaneously released from the absorbent in the form of NO _2. Become so. Therefore, immediately after the start of the regeneration operation, a relatively large amount of NO _X is released from the NO _X storage reduction catalyst in a short time, and a temporary shortage of the reducing agent occurs.
Some of the released NO _X is considered to be to be released leaving _the NO _X storage reduction catalyst downstream of unpurified.

After the nitrate ions near the surface of the absorbent are released, the nitrate ions retained inside the absorbent move to the surface and are released in the form of NO _2. Since the release rate of NO ₂ from the agent is determined by the moving speed of nitrate ions inside the absorbent, the release rate is relatively low, and there is no shortage of reducing agent. Therefore, it is the discharging of the NO _X which _the NO _X storage reduction NO _X temporarily unpurified immediately after the start of the regenerating operation of the catalyst is released to the downstream side is caused.

The amount of NO _X released by the discharge is
It becomes larger as the concentration of nitrate ions on the surface of the absorbent is higher. Therefore, NO _X occluding and reducing _the amount of NO _X absorbed in the catalyst (N
O _X storage amount) unpurified of the NO _X released by discharging the more is to increase. Further, oozing of the NO _X is _the NO _X storage reduction NO _X absorbed by the absorbent of the catalyst
It is considered that the increase in the amount causes a decrease in the NO _X storage capacity of the absorbent. As described above, nitrate ions generated on platinum Pt of the NO _X storage reduction catalyst move from the surface of the absorbent to the inside by diffusion. Therefore, when the NO _X storage amount of the NO _X storage reduction catalyst increases and the nitrate ion concentration inside the absorbent increases, the nitrate ion hardly diffuses inside, and the nitrate ion concentration on the absorbent surface increases. As a result, the reaction of NO ₂ → NO ₃ ⁻ on the platinum Pt hardly occurs, and NO _X in the exhaust gas is not absorbed by the NO _X storage reduction catalyst. Therefore, of the NO _X occluding and reducing catalyst NO _X
Unpurified of the NO _X during absorption flowing downstream without being absorbed in the NO _X occluding and reducing catalyst as _the NO _X storage amount increases
The amount will increase.

Also, NO_XMaximum NO of storage reduction catalyst_XSucking
The storage amount (saturation amount) is low even under lean air-fuel ratio.
As it goes down (becomes richer), it goes down.
Therefore, NO_XRelatively large amount of NO in storage reduction catalyst_XBut
If it is occluded, the exhaust air-fuel ratio will change due to changes in operating conditions.
Decreases and NO_XWhen the saturation amount of the storage reduction catalyst decreases
Is the amount of stored NO that exceeds the saturation amount._XIs NO_XOcclusion reduction
It is released from the catalyst. Therefore, even if the exhaust
NO is the air-fuel ratio_XNO storage reduction catalyst_XAbsorbing
NO even if the air-fuel ratio drops_XFrom storage reduction catalyst
NO over the saturation amount_XWill be released. This
Of course, NO_XNO of storage reduction catalyst _XLarge storage capacity
Unpurified NO_XThe amount will also increase.

[0032] In the present embodiment, NO _X in the storage reduction catalyst N
O _X produced during the absorption the two types of unpurified NO _X released together is referred to as the exudation of NO _X. By the way, N
The amount of unpurified of the NO _X released by and O _X discharged and exudation are both increased as _the NO _X storage amount of the NO _X occluding and reducing catalyst is increased. For this reason, if the regeneration operation is performed every time the NO _X storage amount of the NO _X storage reduction catalyst reaches a relatively high value as in the related art, NO _X is discharged by exhalation and exudation. The unpurified NO _X amount becomes large, and the N
The O _X purification rate may not be able to sufficiently improve.

Therefore, in the present embodiment, the NO _X storage amount for determining whether or not the regeneration operation is necessary, which has been set based on the NO _X saturation amount of the NO _X storage reduction catalyst (for example, 70% of the saturation amount) in the past, is set. NO from the NO _X storage reduction catalyst
To prevent the release of unpurified of the NO _X by _the amount of NO _X unpurified released by _X spitting or exudation is set to a low value to be equal to or less than the predetermined value, the whole of the NO _X occluding and reducing catalyst the NO _X purification rate as being greatly improved.

In this embodiment, NO is determined in advance by an experiment._XSucking
NO of storage reduction catalyst_XStorage amount and NO_XVomiting, seeping out
Unpurified NO_XFind the relationship with the amount of release.
From this relationship, both unpurified NO_XTotal release
Is less than the predetermined value_XMaximum storage amount (regeneration
Operation execution determination value), and NO in actual operation. _X
Every time the storage amount reaches the regeneration operation execution determination value.
_XThe regeneration operation of the storage reduction catalyst is performed. NO_XSpitting
Unpurified NO due to bleeding and seepage_XEmission allowance
Is NO as a whole_XPurification rate (ie, over a period of time
NO_X(The average value of the purification rate) to the desired value
Set, but conventionally achievable NO_XGreater than purification rate
In order to achieve a high purification rate, in this embodiment, unpurified
NO_XIs set very small. This
Therefore, in this embodiment, NO_XRegeneration operation of storage reduction catalyst
Is a very low value (eg less than 10% of saturation)
), And NO at very short intervals compared to the past.
_XThe regeneration operation of the storage reduction catalyst is performed. This
As a result, NO_XSpitting immediately after the start of the storage reduction catalyst regeneration operation
Unpurified NO released by discharging_XQuantity, and NO_XOcclusion
NO for increased volume _XReleased by oozing during absorption
Unpurified NO_XThe amount will be suppressed to a lower value.
In addition, the exhaust air-fuel ratio decreased due to changes in engine operating conditions.
NO NO Occlusion_XThe amount does not exceed the saturation amount
Unpurified NO due to air-fuel ratio change_XRelease is also prevented
Become like

FIG. 2 is a timing chart for explaining the effect of improving the purification rate in the exhaust gas purification apparatus of the present embodiment. FIG.
The solid line, the concentration of NO _X in the exhaust gas in _the NO _X storage reduction catalyst 7 outlet when executing a reproduction operation at short intervals as an exhaust gas purifying apparatus of the present embodiment and the dotted line as in the conventional exhaust gas purifying device The graph shows the NO _X concentration in the exhaust gas at the outlet of the NO _X storage reduction catalyst 7 when the regeneration operation is performed at relatively long intervals. Further, the straight line I in FIG. 2 NO _X
2 shows the NO _X concentration in the exhaust gas flowing into the storage reduction catalyst 7 (FIG. 2 shows a case where the NO _X concentration in the inflow exhaust gas is constant).

First, in the case of a conventional exhaust gas purification device (dotted line)
In the description below, conventionally, relatively NO_XStorage reduction catalyst
NO_XThe regeneration operation is performed until the storage amount increases to a large value.
Not done. Therefore, NO_XThe storage amount of the storage reduction catalyst is
Unpurified NO due to exudation as it increases_XRelease
As shown by the dotted line A in FIG.
O_XThe concentration gradually increases. NO_XOcclusion amount
Reach a predetermined value (for example, about 70% of the saturation amount)
Then, the reducing agent is supplied and NO_XRegeneration operation of storage reduction catalyst
Is executed (dotted line in FIG. 2, point B).
NO at the time of operation _XRegeneration operation due to relatively large storage capacity
Exhausted large amount of unpurified NO at start_XIs released
(Dotted line in FIG. 2, part C). Not purified by spitting
NO_XRelease is completed in a short time, and when regeneration is completed, N
O_XExit NO of storage reduction catalyst_XAlthough the concentration decreases, its
After NO_XAs the storage amount increases, the outlet NO_Xconcentration
(Dotted line in FIG. 2, D portion). For this reason, conventional exhaust
In the purifier, the area of the lower part of the dotted line in FIG.
A relatively large amount of unpurified NO corresponding to_XIs NO_XOcclusion reduction
Will be released downstream of the catalyst,
NO_XNO of storage reduction catalyst_XPurification rate is low
U.

[0037] In contrast, the exhaust gas purification device (Figure 2 solid lines), the reproduction operation at short intervals each time _the NO _X storage amount of the NO _X occluding and reducing catalyst reaches a very low value of the present embodiment (FIG. 2
(Solid line, point B '). Therefore, NO _X emission unpurified by exudation in NO _X absorption (FIG. 2 solid line, A '
Part) and the release of unpurified NO _X due to the discharge at the start of the regeneration operation (solid line in FIG. 2, C ′) both have small values. As a result, the unpurified NO _X amount released from the NO _X storage reduction catalyst as a whole becomes a very small amount corresponding to the area of the lower part of the solid line in FIG. 2, and the conventional exhaust gas purification device (dotted line in FIG. 2) is NO _X purification efficiency of the entire significantly so improved as compared to.

FIG. 3 is a flow chart for explaining the NO _X storage reduction catalyst regeneration operation of the present embodiment. This operation is performed by a routine executed by the ECU 30 at regular intervals. In FIG. 3, in step 301, the current NO _X storage amount CNOX of the NO _X storage reduction catalyst 7 is calculated.

[0039] In this embodiment, NO _X storage amount CNOX is calculated based on the operating state of the engine. N generated per unit time (for example, the execution interval of the operation in FIG. 3) from the institution
O _X amount is determined by the engine load conditions (e.g., the fuel injection amount and the rotation speed). Therefore, in this embodiment, pre-engine was operated by changing the load conditions, and measuring the NO _X generation amount in each load conditions, for example, a fuel injection amount and the rotational speed and the ECU30 in the form of a numerical table using the It is stored in ROM.
In step 301, the fuel injection amount calculated by the fuel injection amount calculation routine separately executed by the ECU 30 every time the operation is performed, and the engine speed are used from the previous operation execution to the current operation execution by using the above numerical table. calculating the amount of NO _X generated from the engine. Then, a value obtained by multiplying the generated amount by a predetermined constant (the ratio of NO _X absorbed by the NO _X storage reduction catalyst 7 to NO _{X in} the exhaust gas) is added to CNOX. As a result, the value of CNOX is reduced to the NO _X storage reduction catalyst 7.
Is a value corresponding to the NO _X amount occluded in the fuel cell.

In this embodiment, the fuel injection amount and the rotational speed
The value calculated according to_XNO of the storage reduction catalyst 7_X
It is used as the storage amount CNOX.
After the operation, the integrated value of the fuel injection amount, the integrated value of the rotational speed,
Or the engine is running at a relatively high speed
In this case, the engine operating time after the previous regeneration operation _X
The calculation may be simplified using the storage amount CNOX.

Further, in the NO _X absorption of the NO _X occluding and reducing catalyst 7 as shown in FIG. 2, _the NO _X storage concentration of NO _X reducing catalyst 7 in the exhaust at the outlet is NO in _the NO _X storage reduction catalyst for seepage _X Increases according to the amount of occlusion. Thus, for example, _the NO _X storage reduction catalyst 7 NO _X in the exhaust gas outlet
By placing detectable NO _X concentration sensor concentrations, NO _X
The NO _X concentration detected by the concentration sensor may be used as CNOX. After calculating the NO _X storage amount CNOX of the NO _X storage reduction catalyst 7 as described above, step 303
Then, the calculated NO _X storage amount CNOX becomes the predetermined value CNOX.
_It is determined whether ₀ has been reached. Here, CNOX ₀
Is, NO _X occluding amount of unpurified NO _X emitted by reduction catalyst 7 exudation (NO _X in occluding and reducing catalyst 7 in the exhaust gas at the outlet NO _X concentration) maximum is below a predetermined value N
O _X storage amount, or either smaller one of the NO _X occluding and reducing catalyst 7 regeneration amount of unpurified NO _X released by the operation at start discharging (concentration) up to _the NO _X storage amount becomes less than predetermined quantity Is set. The allowable value of the released unpurified NO _X amount is determined from a desired NO _X purification rate. Further, the value of CNOX ₀ is preferably determined by an experiment using an actual NO _X storage reduction catalyst 7.

If CNOX ≧ CNOX ₀ in step 303, a predetermined amount of fuel is injected from the reducing agent supply nozzle 91 of the reducing agent supply device 9 in step 305, and NO
The regeneration of the _X storage reduction catalyst 7 is performed. Further, after the reproduction operation end, the value of the NO _X storage amount CNOX step 305 is reset. Note that the injection amount of the reducing agent (diesel oil in the present embodiment) injected from the reducing agent supply nozzle 91 is a sufficient amount of HC and CO to purify the entire NO _X storage amount CNOX of the NO _X storage reduction catalyst. The component is set to the minimum amount that can be generated. By setting the supply amount of the reducing agent in accordance with the NO _X storage amount of the NO _X storage reduction catalyst at the time of performing the regeneration operation in this manner, in the present embodiment, the amount of the reducing agent injected in one regeneration operation is low. Can be suppressed. Therefore, despite performing playback operation in a very short time interval in the present embodiment, the consumption of the reducing agent is slightly over conventional (i.e., to purify NO _X which have been released while the conventional unpurified (By an amount corresponding to the amount of reducing agent used). Further, in the present embodiment, since the regeneration operation is performed at extremely short time intervals, it is necessary to inject a required amount of the reducing agent from the nozzle 91 in a short time. In addition, since the amount of the reducing agent injected in one regeneration operation is relatively small, if the small amount of the reducing agent is injected over a long time, the injected reducing agent is diluted by the exhaust gas and the exhaust gas is exhausted. The concentration of the reducing agent therein cannot be sufficiently increased. Therefore, in this embodiment, the injection amount of the reducing agent from the reducing agent feed nozzle 91 is set in accordance with execution interval of the reproduction operation (reproduction operation at the start of the NO _X storage amount), further nozzles 91
Is set in consideration of both the injection amount and the regeneration operation execution interval. As a result, it is possible to supply the required amount of reducing agent in the required concentration in the exhaust gas flowing into the NO _X storage reduction catalyst in one regeneration operation.

In this embodiment, the reducing agent supply nozzle 9
Although the reducing agent is supplied to the NO _X storage reduction catalyst from 1,
In order to prevent dilution by exhaust gas and allow a sufficient concentration of the reducing agent to reach the NO _X storage reduction catalyst 7, the reducing agent supply nozzle 9
It is desirable to dispose 1 at a position as close as possible to the upstream side of the NO _X storage reduction catalyst 7.

[0044]

According to the invention described in each claim, NO _X
Prevents decrease the exhaust purification efficiency for unpurified NO _X by NO _X out discharging and stains from storage-reduction catalyst exhibits the common effects that it is possible to greatly improve the exhaust purification efficiency.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of an embodiment in which the present invention is applied to a diesel engine.

FIG. 2 is a diagram illustrating the effect of improving the NO _X purification rate according to the present invention.

FIG. 3 is a flowchart illustrating an embodiment of a regeneration operation of the NO _X storage reduction catalyst according to the present invention.

[Explanation of symbols]

1 ... diesel engine 3 ... exhaust passage 7 ... NO _X occluding and reducing catalyst 9 ... reducing agent supply device 30 ... electronic control unit (ECU) 91 ... reducing agent supply nozzle

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Atsushi Tahara 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Masaaki Kobayashi 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation F Terms (reference) 3G091 AA12 AA18 AA28 AB06 BA14 BA33 CA18 CA19 CB02 CB08 DA01 DA02 DB06 DB08 DB10 EA01 EA08 EA30 EA33 FB10 FB11 FB12 FC02 GB01X GB02W GB03W GB04W GB05W GB06W GB10X GB16X HA37

Claims (4)

[Claims] 1. An inflow engine disposed in an exhaust passage of an internal combustion engine.
NO in exhaust when the air-fuel ratio of exhaust is lean_XAbsorb
And absorbs when the oxygen concentration in the incoming exhaust falls.
NO_XReleases NO_XThe storage reduction catalyst and the NO_XSucking
NO when the exhaust air-fuel ratio flowing into the storage reduction catalyst is lean
_XBy supplying a reducing agent to the storage reduction catalyst, NO_X
Decrease oxygen concentration in exhaust gas flowing into storage reduction catalyst
With the released NO_XOf reducing agent to reduce and purify wastewater
The exhaust gas purifying apparatus for an internal combustion engine, comprising:_XThe storage reduction catalyst is used immediately after the start of the supply of the reducing agent.
The unpurified N which is not reduced by the supplied reducing agent
O_XTo the downstream side, and the unpurified NO_XThe amount is NO _XOcclusion
NO absorbed by the reduction catalyst_XThe reducing agent supply device increases according to the amount._XAbsorbed by the storage reduction catalyst
NO_XNO when quantity reaches a predetermined level_XOcclusion
A reducing agent is supplied to the reduction catalyst, and the predetermined NO_XThe absorption level is determined by
NO at the time_XUnpurified NO from the storage reduction catalyst_XRelease amount
Is set to be equal to or less than the predetermined value.
An exhaust purification device for an internal combustion engine. Wherein the air-fuel ratio of the exhaust gas is disposed in an exhaust passage of an internal combustion engine inlet absorbs NO _X in the exhaust gas when the lean, the NO _X in which the oxygen concentration in the exhaust gas absorbed when drops flowing The NO _X storage reduction catalyst to be released and the NO _X storage reduction catalyst when the exhaust air-fuel ratio flowing into the NO _X storage reduction catalyst is lean
By supplying a reducing agent to the _X storage reduction catalyst, NO _X
With lowering the oxygen concentration in the exhaust gas flowing into the storage-reduction catalyst, in an exhaust gas purification apparatus for an internal combustion engine having a reducing agent supply device for reducing and purifying the released NO _X, the NO _X storage reduction catalyst flows Even if the exhaust air-fuel ratio is lean, the amount of unpurified NO _X that increases in accordance with the absorbed NO _X amount is released to the downstream side, and the reducing agent supply device is absorbed by the NO _X storage reduction catalyst. When the NO _X amount reaches a predetermined level, a reducing agent is supplied to the NO _X storage reduction catalyst, and the predetermined NO _X absorption level is equal to the unpurified NO _X storage reduction catalyst under lean air-fuel ratio exhaust. exhaust purification system of an internal combustion engine, wherein a NO _X emissions are set to be less than a predetermined value. Wherein the reducing agent feeder, the _the NO _X storage on the upstream side of the exhaust passage of the reduction catalyst with a reducing agent feed nozzle for injecting the reducing agent, the exhaust air-fuel ratio is lean flowing to the NO _X occluding and reducing catalyst internal combustion engine according to claim 1 or claim 2 supplied to the exhaust a predetermined amount of reducing agent each time _the NO _X storage amount of NO _X absorbed in the reduction catalyst reaches the predetermined level when the Exhaust purification equipment. 4. The exhaust gas of an internal combustion engine according to claim 3, wherein the injection amount and the injection rate of the reducing agent from the reducing agent supply nozzle are set in accordance with a time interval at which the supply of the reducing agent is performed. Purification device.