JP3487209B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more specifically, when the inflowing exhaust air-fuel ratio is lean, it absorbs NO _x in the exhaust gas and the oxygen concentration in the inflowing exhaust gas is reduced. The present invention relates to an exhaust emission control device for an internal combustion engine equipped with a NO _X storage reduction catalyst that releases NO _X that is sometimes absorbed.

[0002]

2. Description of the Related Art There is known a NO _X storage reduction catalyst that absorbs NO _X in exhaust gas when the inflowing exhaust air-fuel ratio is lean and releases the absorbed NO _X when the oxygen concentration in the inflowing exhaust gas decreases. Has been. An example of an exhaust gas purification device for an internal combustion engine using this type of NO _X storage reduction catalyst is disclosed in Japanese Patent Laid-Open No. 6-200738.

[0003] The apparatus of this publication, the _the NO _X storage reduction catalyst disposed in an exhaust passage of an operable engine at a lean air-fuel ratio, NO _X in the exhaust gas when the engine is operated at a lean air-fuel ratio
When the amount of NO _x absorbed and reduced by the NO _x storage reduction catalyst reaches a predetermined value, a liquid or gaseous hydrocarbon as a reducing agent is discharged from the reducing agent supply nozzle arranged in the exhaust passage on the upstream side of the NO _x storage reduction catalyst. Etc. 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 Is 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 In some cases, when the NOx emission and the reduction purification are performed, the overall NO _x purification rate may not be good depending on the time interval of the reducing agent supply.

Normally, NO_XSupplying a reducing agent to the storage reduction catalyst
Then NO_XNO from storage reduction catalyst _XRelease and reduction purification
Operation to perform (hereinafter, "NO_XRegeneration operation of storage reduction catalyst
"Work") is NO_XNO absorbed by the storage reduction catalyst
_XIt is executed when the amount reaches a certain level,
This NO_XAbsorption level is NO_XAbsorption by storage reduction catalyst
NO_XDetermined based on the amount of absorption (saturation amount) saturated with
Be done. That is, NO_XNO of storage reduction catalyst_XAbsorption capacity
To make the most of NO_XActual operation of regeneration of storage reduction catalyst
In order to keep the line frequency low, as much NO as possible_X
Is NO_XThe regeneration operation is executed after being absorbed by the storage reduction catalyst.
Preferably. So, normally, you should execute the playback operation.
NO_XAbsorption level is NO_XSaturation amount of storage reduction catalyst
A relatively high level with a certain amount of margin (eg NO
_XSet to about 70% of the saturation amount of the storage reduction catalyst)
To be done.

However, when the NO _X storage reduction catalyst regeneration operation is executed after waiting until the NO _X absorption amount of the NO _X storage reduction catalyst reaches a relatively high level, purification of NO _X as a whole is performed. It has proven difficult to significantly increase the rate. For example, it is considered that the NO _x released from the NO _x storage reduction catalyst is completely purified by the supplied reducing agent during the regeneration operation of the conventional NO _x storage reduction catalyst, and unpurified NO _x is not released downstream. Was there. However, in fact, 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 described above, when the reducing agent is supplied, NO
_XThe oxygen concentration near the storage reduction catalyst decreases and NO_XStorage reduction
NO from catalyst_XIs released. However, from the catalyst
NO _XRelease rate was not constant and oxygen concentration decreased
Immediately after (immediately after the supply of the reducing agent), a relatively large amount of N
O_XIs emitted, and thereafter is relatively uniform and has a relatively low emission rate
NO in degrees_XHas been found to be released. This return
NO immediately after starting the supply of the base material_XN absorbed from the storage reduction catalyst
O_XThe phenomenon of sudden release of "NO_XSpit out of
NO to call_XNO in exhaling_XRelease
Output (release rate) 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
Regeneration operation of medium is relatively high NO_XRun at storage level
NO if you try_XReleased by the exhalation of
Large amount of unpurified NO_XTemporarily reduces the reducing agent in the exhaust gas.
And N released immediately after starting the supply of reducing agent
O_XRemains unpurified NO_XOutflow to the downstream side of the storage reduction catalyst
Become so. NO_XSpitting out is short after starting the supply of reducing agent
Ends in time, then NO_XRelease rate is relatively low
After the discharge is finished, the reducing agent in the exhaust gas
There will be no shortage. Therefore, NO_XOcclusion reduction
Medium NO_XReducing agent even if the storage amount is at a relatively high level
If a certain amount of time has passed after the start of supply, unpurified NO_X
Will stop flowing out, but in this case, the playback operation
NO for each line_XUnpurified NO from the storage reduction catalyst_XIs leaked
Therefore average NO as a whole_XPurification rate above a certain level
There is a problem that cannot be raised.

Further, in the NO _X storage reduction catalyst, the above NO _X
A phenomenon referred to as "exuding of NO _X" in addition to the discharge have been found of. Conventionally, 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. In addition, 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 Will 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 to the downstream side of the catalyst without being purified is called “NO _X ooze out”.

As mentioned above, NO_XRegeneration of storage reduction catalyst
Sometimes NO_XUnpurified NO that flows out when exhaling
_XAmount and NO under lean air-fuel ratio_XFlowing out of
Unpurified NO out_XBoth amount is NO_XOf storage reduction catalyst
NO_XIt increases according to the amount of occlusion. For this reason,
NO_XN when the storage amount reaches a relatively high level
O _XExhaust gas adapted to perform regeneration operation of storage reduction catalyst
NO in the purification device_XRelease by exhaling and seeping out
Unpurified NO issued_XFor a certain degree or more
NO as_XThe purification 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,
It is an object of the present invention to provide an exhaust gas purification device for an internal combustion engine that can significantly improve the NO _x purification rate.

[0011]

According to the invention described in claim 1 SUMMARY OF THE INVENTION, the air-fuel ratio of the exhaust gas is disposed in the exhaust passage flows into the internal combustion engine to absorb NO _X in the exhaust gas when the lean, flows NO _x absorbed when the oxygen concentration in the exhaust decreased
By supplying the _the NO _X storage reduction catalyst which releases a reducing agent to the NO _X occluding and reducing catalyst when the exhaust air-fuel ratio is lean flowing into the _the NO _X storage reduction catalyst and flows into _the NO _X storage reduction catalyst exhaust While reducing the oxygen concentration in the inside,
In an exhaust gas purification device for an internal combustion engine, comprising a reducing agent supply device that reduces and purifies the released NO _x , the NO _x storage reduction catalyst is not reduced by the supplied reducing agent immediately after starting the supply of the reducing agent. releasing unpurified NO _X downstream, yet-purifying amount of NO _X is increased in response to the absorbed amount of NO _X in _the NO _X storage reduction catalyst, results in discharging of the NO _X, the reducing agent supply device, NO _The reducing agent is supplied to the NO _X storage reduction catalyst when the amount of NO _X absorbed by the _X storage reduction catalyst reaches a predetermined level, and the predetermined NO _X absorption amount level is the above-mentioned at the time of starting the supply of the reducing agent. Provided is an exhaust gas purification device for an internal combustion engine, wherein an amount of unpurified NO _x released that flows out when NO _x is discharged from a NO _x storage reduction catalyst is set to be a predetermined value or less.

That is, in the invention described in claim 1, NO
Every time the amount of NO _X absorbed by the _X storage reduction catalyst reaches a predetermined level, the NO _X storage reduction catalyst is regenerated.
However, as _the amount of NO _X unpurified flowing out by discharging the predetermined level at the start of reproduction operation NO _X is maintained at a predetermined low value is set to a much lower level compared to the prior art. As a result, in the present invention, the regeneration operation is executed at an extremely short interval as compared with the prior art, but the amount of unpurified NO _X released due to the discharge at the start of the regeneration operation is suppressed to an extremely low value. The purification rate of NO _x as a whole can be significantly improved. In addition, NO _X
The reducing agent may be supplied to the storage reduction catalyst by injecting a reducing agent composed of hydrocarbon (HC) or the like into the exhaust passage on the upstream side of the NO _X storage reduction catalyst, or the engine may be operated at a rich air-fuel ratio for a short time. By operating, unburned HC in exhaust gas,
It may be performed by increasing the CO component.

According to the invention described in claim 2, the oxygen concentration in the exhaust gas air-fuel ratio of the exhaust gas is disposed in an exhaust passage of the internal combustion engine flows to absorb NO _X in the exhaust gas when the lean, flows By supplying a reducing agent to the NO _X storage reduction catalyst that releases the absorbed NO _X when it has decreased, and a reducing agent to the NO _X storage reduction catalyst when the exhaust air-fuel ratio flowing into the NO _X storage reduction catalyst is lean. _X The oxygen concentration in the exhaust flowing into the storage reduction catalyst is reduced, and the released NO _X
In the exhaust gas purification device for an internal combustion engine, which comprises a reducing agent supply device for reducing and purifying NOx, the NO _X storage reduction catalyst is an amount that increases according to the absorbed NO _X amount even if the inflowing exhaust air-fuel ratio is lean. releasing unpurified of the NO _X in the downstream
Cause oozing of NO _X, the reducing agent supply device, NO _X
When the amount of NO _X absorbed by the storage reduction catalyst reaches a predetermined level, a reducing agent is supplied to the NO _X storage reduction catalyst, and the predetermined NO _X absorption level is the NO _X under lean air-fuel ratio exhaust. For NO _x seepage from the storage reduction catalyst
There is provided an exhaust gas purification device for an internal combustion engine, wherein the amount of unpurified NO _x released more outflow is set to be a predetermined value or less.

That is, also in the second aspect of the 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, this predetermined level in the present invention as _the amount of NO _X unpurified flowing out by exudation of the NO _X due to the increase in _the NO _X storage amount of the NO _X occluding and reducing catalyst is maintained at a predetermined low value, the conventional It is set to a considerably lower level in comparison. As a result, in the present invention, the regeneration operation is executed at a much shorter interval than in the conventional case, but the amount of unpurified NO _X released due to NO _X oozing is suppressed to an extremely low value, so As a result, the purification rate of NO _x can be significantly improved. Note that in the present invention as well, NO
The reducing agent may be supplied to the _X storage reduction catalyst by injecting the reducing agent into the exhaust passage or by operating the engine for a short time at the rich air-fuel ratio.

The level of the NO _X storage amount for starting the regeneration operation of the NO _X storage reduction catalyst is the value at which the unpurified NO _X amount by the discharge of the invention of claim 1 becomes a predetermined value or less, or the stain of the present invention. _{If the} amount of unpurified NO _{x due to} discharge is set to a lower value, whichever is lower, the release of unpurified NO _x can be more completely reduced.

According to the third aspect of the present invention, the reducing agent supply device includes a reducing agent supply nozzle for injecting the reducing agent into the exhaust passage on the 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 gas every time the NO _X amount absorbed by the NO _X storage reduction catalyst reaches the predetermined level. An exhaust gas purification device for an internal combustion engine according to claim 1 or 2 is provided.

That is, in the invention described in claim 3, NO
Supply of the reducing agent to the _X occluding and reducing catalyst is carried out by injecting a reducing agent into the exhaust gas from the reducing agent feed nozzle disposed in the exhaust path of the NO _X occluding and reducing catalyst upstream. As a result, the NO _x purification rate can be significantly improved even in a diesel engine that is difficult to operate at a rich air-fuel ratio.

According to the invention described in claim 4, the injection amount and injection rate of the reducing agent from the reducing agent supply nozzle are set according to the time interval in which the reducing agent is supplied. An exhaust gas purification device for an internal combustion engine according to item 3 is provided. That is, in the invention described in 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 executed at a shorter interval than in the conventional case, if the same amount of reducing agent as in the conventional case is injected during each regeneration operation, the reducing agent consumption amount increases significantly. Further, 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 reducing agent required for the regeneration operation is small. Therefore, in the present invention, the amount of the reducing agent supplied during the regeneration operation depends on the time interval of the regeneration operation, that is, the N stored in the NO _X storage reduction catalyst during 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.However, if this small amount of reducing agent was injected into the exhaust gas over a long period of time, the reducing agent would dilute into the exhaust gas. As a result, the oxygen concentration of the NO _X storage reduction catalyst cannot be lowered. Therefore, in the present invention, the reducing agent injection rate 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 reducing agent concentration in the exhaust gas is maintained sufficiently high. I am trying. As a result, even if the time interval of the regeneration operation is set to be short, an increase in the consumption amount of the reducing agent is suppressed and the NO _X storage reduction catalyst is completely regenerated.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION 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 an exhaust emission control device of the present invention. In FIG. 1, reference numeral 1 denotes an internal combustion engine. In the present 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.
It is shown in a reducing agent supply device for supplying the reducing agent to the NO _X occluding and reducing catalyst 7 during _the NO _X storage reduction catalyst 7 playback 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 by the catalyst 7 is released and released. Reduces and purifies NO _X. As will be described later, in this embodiment, the fuel (diesel oil) of the engine 1 is used as the reducing agent. The reducing agent supply device 9 is
The pressurized fuel supplied from the fuel system, which is connected to an engine fuel system (not shown), is discharged from the reducing agent supply nozzle 91 to the exhaust passage 3
To inject.

Reference numeral 30 in FIG. 1 is an electronic control unit (ECU) of the engine 1. In this embodiment, the ECU 3
Reference numeral 0 denotes a microcomputer having a well-known configuration including a RAM, a ROM, and a CPU, which performs basic control of the fuel injection amount, fuel injection timing, etc. of the engine 1 and also controls the reducing agent supply device 9 to be described later in NO. 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. It carries a precious metal. 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 this absorption and release will be described below by taking the case of using 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 the lean air-fuel ratio), these oxygens are O 2 on the platinum Pt.
₂ ^- or deposited at O ^2- form, NO _X in the exhaust gas platinum P
Reacts with O ₂ ⁻ or O ^{2 −} on t, which produces NO ₂ . 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
It diffuses into the catalyst in the form of nitrate ions NO ₃ ⁻ while being bound with. 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 (that is, the air-fuel ratio of the exhaust gas decreases), the amount of NO ₂ produced on the platinum Pt decreases, so that the reaction proceeds in the opposite direction and the catalyst 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 HC, CO, etc. are present in the exhaust gas, platinum Pt
NO ₂ is reduced by these components above.

In this embodiment, since the diesel engine is used as the engine 1, the exhaust air-fuel ratio of the engine is lean, and the NO _x storage reduction catalyst 7 in the exhaust passage 3 is in normal operation.
Lean air-fuel ratio exhaust flows into the exhaust and NO _x in the exhaust is NO
It is absorbed by the _X storage reduction catalyst 7. Further, 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. As a result, the oxygen concentration in the atmosphere of the NO _X storage reduction catalyst 7 decreases, and the components such as unburned HC and CO are generated due to the 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.

As the reducing agent used for the release of NO _X from the NO _X storage reduction catalyst and the reduction purification operation (regeneration operation of the NO _X storage reduction catalyst), a reducing component such as H ₂ or HC in exhaust gas, A substance that produces a CO component is used, and for example, a gas such as hydrogen or carbon monoxide, a liquid or gaseous hydrocarbon such as propane, propylene, butane, or a liquid fuel such as gasoline, light oil, or kerosene can be used. In this embodiment, since the diesel engine is used as the internal combustion engine 1, the fuel (diesel oil) of the engine 1 is used as the reducing agent in consideration of the refueling and storage stools. The reducing agent supply device 9 is an upstream side of the NO _X storage reduction catalyst 7 from the reducing agent supply nozzle 91 via a cutoff valve and a flow rate adjusting valve (not shown) for fuel supplied from a fuel pump (not shown) of the engine 1. The NO _x storage reduction catalyst 7 is regenerated by supplying it to the exhaust passage.

As mentioned above, NO_XStorage reduction catalyst 7 is returned
When the reducing agent is not supplied from the original material supply device 9
Exhaust (that is, when the inflowing exhaust air-fuel ratio is lean)
NO in_XAbsorbed and returned from the reducing agent supply device 9 to the exhaust gas
When the base agent is supplied and the oxygen concentration of the inflowing exhaust gas decreases,
NO collected_XRelease and purify by reduction. Therefore, the conventional N
O_XNO absorbed by the storage reduction catalyst 7_XUnless saturated with
Unpurified NO on the downstream side _XThought not to be released
It was taken.

[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 when not performing
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 during absorption reduction catalyst the NO _X in the exhaust gas (i.e. exhaust gas air-fuel ratio of the inflowing when lean) "oozing of the NO _X" a phenomenon in which NO _X unpurified the NO _X occluding and reducing catalyst downstream is released To distinguish between the two.

The reason why the NO _x is exhaled and exuded is not clear at present, but it is presumed that it is due to the phenomenon described below. First, the reason why NO _X is discharged will be described. As described above, the NO _X storage reduction catalyst has absorbed N
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 the inside to form nitrate. For this reason, the nitrate ion concentration on the surface of the absorbent is higher than the internal nitrate ion concentration during the absorption of NO _X. When the regeneration operation of the NO _X storage reduction catalyst is started in this state and the atmospheric oxygen concentration on the surface of the absorbent drops sharply, the 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, causing a temporary shortage of the reducing agent,
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 rate of NO ₂ release from the agent is controlled by the rate of movement of nitrate ions inside the absorbent, the rate of release 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 exhalation is
The higher the nitrate ion concentration on the surface of the absorbent, the larger it becomes. Therefore, the amount of NO _X absorbed by the NO _X storage reduction catalyst (N
The larger the O _X storage amount), the larger the amount of unpurified NO _X that is released by the discharge. 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 this occurs because the NO _x storage capacity of the absorbent decreases as the amount increases. As described above, the nitrate ions generated on the 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, it becomes difficult for the nitrate ions to diffuse inside, and the nitrate ion concentration on the absorbent surface increases. As a result, the reaction of NO ₂ → NO ₃ ⁻ on platinum Pt is less likely to occur, and NO _X in the exhaust gas is not absorbed by the NO _X storage reduction catalyst. Therefore, the NO _X storage reduction 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 quantity will increase.

In addition, NO_XMaximum NO of storage reduction catalyst_XSucking
Storage amount (saturation amount) is low even under lean air-fuel ratio
It decreases as it goes down (as it goes to the rich side).
Therefore, NO_XA relatively large amount of NO in the storage reduction catalyst_XBut
If stored, the exhaust air-fuel ratio may change due to changes in operating conditions.
Is lowered and NO_XWhen the saturation level of the storage reduction catalyst decreases
Is the stored NO that exceeds the saturation amount._XIs NO_XStorage reduction
It will be released from the catalyst. Therefore, even if exhaust is
Air-fuel ratio and NO_XStorage reduction catalyst is NO_XAbsorbing
Even if the air-fuel ratio decreases, NO_XFrom storage reduction catalyst
NO that exceeds saturation_XWill be released. This
In case of, NO_XNO of storage reduction catalyst _XLarge storage capacity
Unpurified NO released as much_XThe quantity will also increase.

In this embodiment, N of the NO _X storage reduction catalyst is used.
The above two types of unpurified NO _x emissions that occur during O _x absorption are collectively referred to as NO _x leaching. 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. Therefore, than had to perform a reproducing operation for each of _the NO _X storage amount of the NO _X occluding and reducing catalyst as in the prior art to reach a relatively high value, it is released by the the exudation discharging of the NO _X The amount of unpurified NO _x becomes large and the total N
In some cases, the O _x purification rate cannot be improved sufficiently.

Therefore, in this 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 conventional NO _X storage reduction catalyst (for example, 70% of the saturation amount). NO from 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 As a result, the NO _x purification rate is greatly improved.

In this embodiment, NO is previously determined by an experiment._XSucking
NO of storage reduction catalyst_XStorage amount and NO_XExhalation, exudation
Unpurified NO due to shii_XFind the relationship with the amount released.
And from this relationship both unpurified NO_XTotal amount released
Is less than or equal to a predetermined value NO_XMaximum storage capacity (regeneration
Operation execution judgment value) is set, and NO in actual driving. _X
NO is stored every time the stored amount reaches the judgment value for execution of the regeneration operation.
_XThe regeneration operation of the storage reduction catalyst is executed. NO_XSpit out
Unpurified NO due to exudation_XEmission allowance
Is NO as a whole_XPurification rate (ie in a certain period
NO in_XSo that the average value of the purification rate) becomes the desired value
Set, but conventionally achievable NO_XGreater than purification rate
In order to achieve a high purification rate, unpurified in this embodiment.
NO_XThe allowable value of the release amount of is set to be extremely small. This
Therefore, in this embodiment, NO_XRegeneration operation of storage reduction catalyst
Is a very low value (eg less than 10% of saturation)
Is set to about), and NO is set at an extremely short interval compared to the past.
_XThe regeneration operation of the storage reduction catalyst comes to be executed. This
By this, NO_XSuction immediately after starting the regeneration operation of the storage reduction catalyst
Unpurified NO released by discharge_XQuantity and NO_XOcclusion
NO to increase quantity _XReleased by exudation during absorption
Unpurified NO_XThe amount will be suppressed to a low value.
In addition, the exhaust air-fuel ratio decreased due to changes in engine operating conditions.
In case of occlusion NO_XAmount did not exceed saturation
Therefore, unpurified NO due to changes in the air-fuel ratio_XRelease is also prevented
Like

FIG. 2 is a timing chart for explaining the effect of improving the purification rate in the exhaust purification system of this embodiment. Figure 2
The solid line indicates the NO _X concentration in the exhaust gas at the outlet of the NO _X storage reduction catalyst 7 when the regeneration operation is executed at short intervals as in the exhaust gas purification apparatus of the present embodiment, and the dotted line indicates the NO _X concentration in the exhaust gas purification apparatus of the related art. The respective NO _x concentrations in the exhaust gas at the outlet of the NO _x storage reduction catalyst 7 when the regeneration operation is executed at relatively long intervals are shown. The straight line I in FIG. 2 is NO _x.
The NO _x concentration in the exhaust gas flowing into the storage reduction catalyst 7 is shown (FIG. 2 shows the case where the NO _x concentration in the exhaust gas is constant).

First, in the case of the conventional exhaust emission control device (dotted line)
The conventional method is relatively NO._XStorage reduction catalyst
NO_XThe regenerating operation continues until the occlusion amount increases to a large value.
Not done. Therefore, NO_XThe storage amount of the storage reduction catalyst
Unpurified NO due to seepage as it increases_XThe amount released
As shown by A in the dashed line in FIG.
O_XThe concentration gradually increases. Also, NO_XStorage capacity
Reach a specified value (for example, about 70% of saturation)
Then, the reducing agent is supplied and NO_XRegeneration operation of storage reduction catalyst
Is executed (dotted line in Fig. 2, point B), but in this case also
NO when executing the work _XRegeneration operation due to relatively large storage capacity
A large amount of unpurified NO due to spitting at the start_XIs released
(Fig. 2, dotted line, part C). Unpurified by spitting
NO_XIs released in a short time, and when the regeneration is completed, N
O_XOutlet NO of storage reduction catalyst_XThe concentration decreases, but that
After NO_XThe outlet NO again as the storage amount increases_Xconcentration
Increases (dotted line in FIG. 2, part D). Because of this, conventional exhaust
In the purification device, the area of the lower part of the dotted line in FIG. 2 as a whole
Relatively large amount of unpurified NO equivalent to_XIs NO_XStorage reduction
It will be released to the downstream side of the catalyst, and as a whole
NO_XNO of storage reduction catalyst_XThe purification rate will be 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
The solid line, point B ') is executed. For this reason, unpurified NO _X release due to seepage during NO _X absorption (solid line in FIG. 2, A ′)
(Part) and the unpurified NO _x emission (solid line in FIG. 2, C ′) due to the discharge at the start of execution of the regeneration operation both have small values. As a result, the amount of unpurified NO _X released from the NO _X storage reduction catalyst as a whole becomes an extremely small amount corresponding to the area of the lower portion of the solid line in FIG. 2, and the conventional exhaust purification device (FIG. 2, dotted line). As a result, the NO _x purification efficiency as a whole will be greatly improved.

FIG. 3 is a flow chart for explaining the operation of regenerating the NO _X storage reduction catalyst 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.

In this embodiment, the NO _X storage amount CNOX is calculated based on the operating state of the engine. N generated from the engine per unit time (for example, the operation execution interval of FIG. 3)
The O _X amount is determined by the engine load condition (for example, the fuel injection amount and the rotation speed). Therefore, in the present embodiment, the engine is operated under different load conditions in advance, the NO _X generation amount under each load condition is measured, and the ECU 30 is operated in the form of a numerical table using, for example, the fuel injection amount and the rotation speed. It is stored in ROM.
In step 301, from the fuel injection amount calculated in the fuel injection amount calculation routine executed separately by the ECU 30 each time the operation is executed, and the engine speed from the previous operation execution time to the current operation execution time using the above numerical value table. calculating the amount of NO _X generated from the engine. Then, a value obtained by multiplying the generated amount by a predetermined constant (a ratio of NO _X absorbed in the NO _X storage reduction catalyst 7 in NO _{X in} the exhaust gas) is added to CNOX. As a result, the value of CNOX is reduced by the NO _X storage reduction catalyst 7
The value corresponds to the amount of NO _X stored in the.

In this embodiment, the fuel injection amount and the rotation speed are set.
The value calculated according to_XNO of the storage reduction catalyst 7_X
Although used as the storage amount CNOX, for example, the previous playback
The cumulative value of the fuel injection amount after the operation, the cumulative value of the number of revolutions,
Or the engine is running at a relatively high speed
In this case, the engine operating time after completion of the previous regeneration operation is NO. _X
The storage amount may be used as CNOX to simplify the calculation.

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 It 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. From the above, after calculating the NO _X storage amount CNOX of the NO _X storage reduction catalyst 7, step 303
Then, the calculated NO _X storage amount CNOX is the predetermined value CNOX.
_It is determined whether ₀ has been reached. Here, CNOX ₀
Is the maximum N at which the amount of unpurified NO _X released by the exudation of the NO _X storage reduction catalyst 7 (NO _X concentration in the exhaust gas at the outlet of the NO _X storage reduction catalyst 7) becomes a predetermined value or less.
The smaller one of the O _X storage amount or the maximum NO _X storage amount at which the amount (concentration) of the unpurified NO _X released by discharge at the start of the regeneration operation of the NO _X storage reduction catalyst 7 becomes a predetermined amount or less. Is set. The allowable value of the unpurified NO _X amount released is determined from the 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 X} storage reduction catalyst 7 is regenerated. Further, after the regeneration operation is completed, in step 305, the value of the NO _X storage amount CNOX is reset. The injection amount of the reducing agent (diesel oil in this embodiment) injected from the reducing agent supply nozzle 91 is sufficient to purify the total amount of the NO _X storage amount CNOX of the NO _X storage reduction catalyst HC, CO. It is set to the minimum amount that can produce the component. In this way, by setting the reducing agent supply amount according to the NO _X storage amount of the NO _X storage reduction catalyst at the time of executing the regeneration operation, the amount of the reducing agent injected in one regeneration operation is low in the present embodiment. It can be suppressed. For this reason, in the present embodiment, although the regenerating operation is performed at an extremely short time interval, the reducing agent consumption is slightly smaller than that in the conventional case (that is, the NO _X that has been conventionally discharged without being purified is purified. The amount of reducing agent used to increase the amount). Further, in the present embodiment, since the regeneration operation is executed at an extremely short time interval, it is necessary to inject the required amount of reducing agent from the nozzle 91 in a short time. Further, since the amount of reducing agent injected in one regeneration operation is relatively small, injecting this small amount of reducing agent over a long period of time causes the injected reducing agent to be diluted by the exhaust gas and exhausted. It becomes impossible to sufficiently increase the concentration of the reducing agent therein. Therefore, in the present embodiment, the injection amount of the reducing agent from the reducing agent supply nozzle 91 is set according to the execution interval of the regeneration operation (NO _X storage amount at the start of the regeneration operation), and the nozzle 91
The injection rate is set in consideration of both the injection amount and the regeneration operation execution interval. This makes it possible to supply the required amount of reducing agent in one regeneration operation at the required concentration into the exhaust gas flowing into the NO _X storage reduction catalyst.

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 the dilution due to the exhaust gas and reach the NO _x storage reduction catalyst 7 with a sufficient concentration of the reducing agent, the reducing agent supply nozzle 9
It is desirable to arrange 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
It is possible to prevent the exhaust purification efficiency from being lowered due to the unpurified NO _x due to the discharge or ooze of NO _x from the storage reduction catalyst, and it is possible to significantly improve the exhaust purification efficiency.

[Brief description of 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 for explaining 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]

DESCRIPTION OF SYMBOLS 1 ... Diesel engine 3 ... Exhaust passage 7 ... NO _X storage reduction catalyst 9 ... Reductant supply device 30 ... Electronic control unit (ECU) 91 ... Reductant supply nozzle

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaaki Kobayashi 1 Toyota-cho, Toyota-shi, Aichi Toyota Motor Co., Ltd. (56) References JP 10-2213 (JP, A) JP 10-71325 (JP, A) JP-A-6-200738 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) F01N 3/08-3/36

Claims (4)

(57) [Claims] 1. A 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 and _the NO _X storage reduction catalyst to release, NO _X when the exhaust air-fuel ratio is lean flowing into the _the NO _X storage reduction catalyst
By supplying a reducing agent to the storage reduction catalyst, the oxygen concentration in the exhaust gas flowing into the NO _x storage reduction catalyst is reduced, and a reducing agent supply device for reducing and purifying the released NO _x is provided for an internal combustion engine. In the exhaust emission control device, the NO _x storage reduction catalyst is an unpurified N that is not reduced by the supplied reducing agent immediately after starting the supply of the reducing agent.
The O _X discharged to the downstream side, yet-purifying amount of NO _X is increased in response to the absorbed amount of NO _X in _the NO _X storage reduction catalyst, of the NO _X discharge failure
When the amount of NO _x absorbed by the NO _x storage reduction catalyst reaches a predetermined level, the reducing agent supply device supplies the reducing agent to the NO _x storage reduction catalyst, and the predetermined NO _x absorption level, the discharging of the NO _X from the _the NO _X storage reduction catalyst at the start the reducing agent supply
Ri exhaust purifying apparatus for an internal combustion engine unpurified NO _X release amount is characterized in that it is set to be less than a predetermined value flowing. 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 and _the NO _X storage reduction catalyst to release, NO _X when the exhaust air-fuel ratio is lean flowing into the _the NO _X storage reduction catalyst
By supplying a reducing agent to the storage reduction catalyst, the oxygen concentration in the exhaust gas flowing into the NO _x storage reduction catalyst is reduced, and a reducing agent supply device for reducing and purifying the released NO _x is provided for an internal combustion engine. in the exhaust purification apparatus, wherein _the NO _X storage reduction catalyst of the NO _X to release the unpurified of the NO _X amount which increases with the amount of NO _X exhaust air-fuel ratio is absorbed even lean flowing into the downstream side Bleed out
Flip, the reducing agent supply device, _the NO _X storage amount of NO _X absorbed in the reduction catalyst supplies the reducing agent to the NO _X occluding and reducing catalyst when reaching a predetermined level, the predetermined of the NO _X absorption level It is exuded of the NO _X from the _the NO _X storage reduction catalyst under a lean air-fuel ratio exhaust
Exhaust purification system of an internal combustion engine, characterized in that unpurified NO _X emissions flowing out is set to be less than a predetermined value by. 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 3. The internal combustion engine according to claim 1 or 2, wherein a predetermined amount of reducing agent is supplied into the exhaust gas every time the amount of NO _x absorbed by the NO _x storage reduction catalyst reaches the predetermined level. Exhaust purification device. 4. The exhaust gas of an internal combustion engine according to claim 3, wherein an injection amount and an injection rate of the reducing agent from the reducing agent supply nozzle are set according to a time interval in which the reducing agent is supplied. Purification device.