JP3536713B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an exhaust purifying apparatus for an internal combustion engine, the oxygen concentration in the exhaust gas air-fuel ratio of the exhaust gas flowing in detail absorbs NO _X in the exhaust gas when the lean, flows NO that releases absorbed NO _X when lowered
_{The present} invention relates to an exhaust gas purification device for an internal combustion engine using an _X storage reduction catalyst.

[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. _The NO _X storage reduction catalyst absorbs NO _X in the exhaust gas under a lean air-fuel ratio atmosphere, but absorbed N
When O _X amount is reaches the saturation amount increases can not be absorbed any more NO _X.

[0003] Therefore, the exhaust gas purifying apparatus using the _the NO _X storage reduction catalyst to release periodically _the NO _X storage reduction catalyst to reduce the oxygen concentration of the exhaust gas flowing into the by _the NO _X storage NO _X absorbed from the reduction catalyst There is a need. When the NO _X storage reduction catalyst is used as an exhaust gas purification device of a gasoline engine, for example, when the operating air-fuel ratio of the engine is reduced (that is, when the engine is operated at a rich air-fuel ratio), the oxygen concentration in the exhaust decreases and the exhaust gas decreases. unburned HC in, for CO components is increased, NO _X from the _the NO _X storage reduction catalyst is released, the released NO _X is HC on _the NO _X storage reduction catalyst,
Reduced by CO.

However, NO_XDize for storage reduction catalyst
Exhaust purification of internal combustion engines, such as
When used as a gasifier, the exhaust
It is necessary to lower the oxygen concentration of the gas. NO_XOcclusion
Uses a reduction catalyst as an exhaust purification device for diesel engines, etc.
The exhaust oxygen concentration to reduce_XOcclusion reduction
NO absorbed from the medium_XOne way to release
Is NO_XLiquid carbonization in the exhaust passage upstream of the storage reduction catalyst
A method for supplying a reducing agent such as hydrogen is known. NO_X
NO from storage reduction catalyst_XTo release NO_XOcclusion
When the reducing agent is supplied to the exhaust passage on the upstream side of the reduction catalyst,
The supplied reducing agent is dispersed in the exhaust gas and is_X
It flows into the storage reduction catalyst. NO is the reducing agent_XStorage reduction catalyst
Reacts with the oxygen in the exhaust gas to oxidize _XOcclusion
Atmospheric oxygen concentration of the reduction catalyst decreases, and NO_XOcclusion reduction
NO absorbed from the medium_XIs released. Also released
NO_XIs NO_XWith the reducing agent in the exhaust on the storage reduction catalyst
It is reduced and purified.

[0005] While not related to _the NO _X storage reduction catalyst, JP-A Examples of the apparatus for supplying the reducing agent to the upstream side of the exhaust passage of the reduction catalyst disposed in an exhaust passage 7-1903
There is one described in Japanese Patent Publication No. The device disclosed in the publication discloses a selective reduction catalyst capable of purifying NO _X by selectively reacting HC (hydrocarbon) and NO _X on a catalyst in an exhaust passage of a diesel engine when an exhaust air-fuel ratio is lean. It is configured to be arranged. The device of this publication is provided an injector for injecting hydrocarbons in the exhaust passage of the selective reduction catalyst upstream and supplies a hydrocarbon required for reduction of the NO _X selective reduction catalyst.

[0006]

However, when a reducing agent such as a hydrocarbon is supplied to the upstream side of the NO _X storage reduction catalyst, a problem different from that of the selective reduction catalyst may occur.
For example, when supplying hydrocarbon into the exhaust passage of the NO _X occluding and reducing catalyst upstream to release NO _X from _the NO _X storage reduction catalyst to reduce the air-fuel ratio of the exhaust gas flowing to the NO _X occluding and reducing catalyst Therefore, it becomes necessary to inject a relatively large amount of hydrocarbon into the exhaust passage in a short time. When a relatively large amount of hydrocarbons reaches the NO _X storage reduction catalyst at one time, a part of the reached hydrocarbons becomes NO.
NO without being used for purification of NO _X with _X storage reduction catalyst
There is a case where the gas passes through the _X storage reduction catalyst and flows downstream, which causes a problem that the exhaust properties deteriorate. In particular, when the exhaust gas temperature (the temperature of the NO _X storage reduction catalyst) is low, the activity of the NO _X storage reduction catalyst is reduced, so that heavy components (for example, components having 11 or more carbon atoms) in the supplied hydrocarbons Is N
Probability of flowing out to the O _X occluding downstream without reacting on the reduction catalyst becomes higher.

[0007] In the apparatus of JP-A-7-19031 discloses described above, and the HC adsorbent disposed in an exhaust passage of the NO _X occluding and reducing catalyst upstream, relatively transient large amount of HC exhausted from the engine at a low temperature However, it is not possible to prevent hydrocarbons injected into the exhaust passage downstream of the HC adsorbent from passing through the catalyst and flowing directly downstream at low temperatures.

[0008] NO_XFlow downstream after passing through the storage reduction catalyst
In order to purify the emitted hydrocarbons, NO_XOcclusion reduction
Oxidation catalyst is placed in the exhaust passage on the downstream side of the medium and NO_XOcclusion return
It is conceivable to oxidize hydrocarbons flowing out of the original catalyst
It is. However, actually, NO _XTo the downstream side of the storage reduction catalyst
NO at low temperatures when hydrocarbons flow out_XOcclusion reduction
Not only the temperature of the oxidation catalyst on the downstream side but also the catalyst is low.
You. At low temperatures, the activity of the oxidation catalyst also decreases.
NO if no_XHeavy coal discharged from the storage reduction catalyst
Hydrogen is not oxidized by the oxidation catalyst and flows downstream as it is.
There is a problem of getting out.

In view of the above problems, the present invention provides an exhaust gas purifying apparatus for an internal combustion engine capable of preventing the deterioration of exhaust properties due to the outflow of heavy hydrocarbons from the NO _X storage reduction catalyst which tends to occur particularly at low temperatures. It is intended to provide.

[0010]

[0011]

[0012]

[0013]

According to Means for Solving the Problems] The present invention, in an exhaust passage of an internal combustion engine, air-fuel ratio of the exhaust gas flowing into absorbs NO _X in the exhaust gas when the lean, the oxygen concentration of the exhaust air-fuel ratio flowing into supply and _the NO _X storage reduction catalyst releases the absorbed NO _X when lowered, the hydrocarbon as a reducing agent to exhaust gas flowing to the NO _X occluding and reducing catalyst when should be released NO _X from the _the NO _X storage reduction catalyst in the exhaust purification system of an internal combustion engine in which the reducing agent supply device, the place of, the disposed upstream of the exhaust passage of the NO _X occluding and reducing catalyst, and a hydrocarbon in the exhaust gas adsorbed after adsorption temperature increases adsorption An HC adsorbent that emits hydrocarbons, a combustion burner that burns hydrocarbons at a low engine exhaust temperature to generate combustion gas, and a combustion gas of the burner, which is an HC adsorbent upstream portion of the exhaust passage. HC adsorbent Wherein _the NO _X storage reduction catalyst and the exhaust gas purifying apparatus for an internal combustion engine having portion and a selectively switched introducible switching means, the between is provided.

That is, in the present invention , the HC adsorbent is disposed upstream of the NO _X storage reduction catalyst. When the temperature of the exhaust gas is low, the high temperature combustion gas from the burner is introduced into the exhaust passage, so that the temperature of the exhaust gas flowing into the NO _X storage reduction catalyst increases. Therefore, even when the engine exhaust gas is at a low temperature, the temperature of the NO _X storage reduction catalyst is kept high, and the supplied reducing agent is prevented from flowing to the downstream side of the NO _X storage reduction catalyst.

Further, in the present invention, the combustion gas from the burner can be selectively introduced into the exhaust passage portion upstream of the HC adsorbent and the exhaust passage portion downstream of the HC adsorbent. Therefore, for example, when the burner is ignited, the burner combustion gas is
By introducing unburned hydrocarbons generated at the time of ignition of the burner or hydrocarbons generated by poor burner ignition by introducing into the upstream side of the C adsorbent together with hydrocarbons discharged from the engine, HC
Adsorption can be performed by the adsorbent, and the emission of hydrocarbons to the atmosphere due to defective burner ignition or the like can be prevented. Further, by changing the combustion gases after stable combustion of the burner was confirmed in the exhaust passage part of the HC adsorbent downstream, NO _X
The storage reduction catalyst becomes hot in a short time. Hydrocarbons adsorbed to the HC adsorbent is HC adsorbent exhaust temperature rises and are released from the HC adsorbent becomes a high temperature, the temperature of the NO _X occluding and reducing catalyst is increased at this time, release hydrocarbons are prevented from hydrocarbons unpurified the NO _X occluding and reducing catalyst downstream now be reacted or oxidized NO _X on _the NO _X storage reduction catalyst is released.

[0016]

Embodiments of the present invention will be described below with reference to the accompanying drawings. (1) Reference Embodiment 1 Figure 1, in the case of applying the exhaust gas purifying apparatus for diesel engine for an automobile, first as a reference for understanding the present invention
FIG. 2 is a diagram illustrating a schematic configuration of the embodiment.

In FIG. 1, reference numeral 1 denotes an automobile diesel engine. Each cylinder exhaust port of the engine 1 is connected to a common exhaust passage 3 via an exhaust manifold 31.
Above the exhaust purification converter 10 is arranged. The converter 10 according to the present embodiment has NO
_{The X} storage reduction catalyst 7, the HC adsorbent 11, and the oxidation catalyst 13 are arranged in this order. The exhaust purification converter 10 will be described later. Reference numeral 9 in FIG. 1 denotes 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. As described below,
In the present embodiment, the fuel (light oil) of the engine 1 is used as a reducing agent. The reducing agent supply device 9 includes a fuel pump that pressurizes fuel supplied from an engine fuel system (not shown), a pressurized fuel supply source 92 that includes a flow control valve, and the like. The fuel is injected from the valve 91 into the exhaust passage 3.

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) of at controlling the reducing agent supply device 9 for injecting fuel into the exhaust passage 3.

An output port of the ECU 30 is connected to a reducing agent supply source 92 via a drive circuit (not shown).
1 controls the injection of the reducing agent (fuel). As described above, the exhaust gas purification converter 10 of this embodiment, in a single casing, NO _X occluding and reducing catalyst 7, HC adsorbent 11 from the exhaust inlet side, were placed oxidation catalyst 13 in this order through a small gap It is configured.

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. And noble 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 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, NO ₂ and NO ₂ produced by the above in the inflowing exhaust gas is absorbed in the catalyst while being further oxidized on platinum Pt, barium oxide acts as an absorbent Ba
O and combined with nitrate ions NO ₃ ^- diffuses into the catalyst in the form of. Therefore, under lean atmosphere, NO _X
Is absorbed in the form of nitrate in the NO _X storage reduction catalyst.

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 in the reverse direction. 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, NO ₂ is reduced by these components.

In this embodiment, the engine 1 is a diesel engine.
Because the engine is used, the exhaust air-fuel ratio of the engine is lean
During normal operation, NO in the exhaust passage 3_XStorage reduction catalyst 7
Exhaust gas with a lean air-fuel ratio flows into the_XIs NO
_XIt is absorbed by the storage reduction catalyst 7. In addition, exhaust purification converter
When the reducing agent is supplied to the exhaust passage 3 on the upstream side of the
O_XExhaust gas containing a reducing agent flows into the storage reduction catalyst 7,
Part of the reducing agent is NO_XAcid on the platinum Pt of the storage reduction catalyst 7
Reacts with element. Thereby, NO_XAtmosphere of storage reduction catalyst 7
As the oxygen concentration in the atmosphere decreases, oxidation of the reducing agent
Components such as unburned HC and CO are generated. Oxidation of reducing agent
NO_XThe oxygen concentration in the atmosphere of the storage reduction catalyst 7 decreases.
Then, NO is generated by the mechanism described above._XStorage reduction catalyst 7
From NO _XIs released and returned by the HC and CO components in the exhaust
Be exempted.

[0024] 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 this embodiment, since a diesel engine is used as the internal combustion engine 1, the fuel (light oil) of the engine 1 is used as a reducing agent in consideration of the convenience of replenishment and storage.

[0025] In this embodiment ECU30 calculates the amount of NO _X discharged from the engine 1 per unit time based on the example engine load condition (the fuel injection amount and the rotation speed). Then, the amount of NO _X obtained by multiplying the emission amount per unit time by a predetermined absorption rate is calculated as the NO _X absorption amount of the NO _X storage reduction catalyst 7 per unit time. ECU30 is, N by integrating the NO _X absorption amount per unit time
The amount of NO _X stored in the O _X storage reduction catalyst 7 is calculated, and every time the calculated stored NO _X amount reaches a predetermined value, the reducing agent is supplied from the reducing agent supply device 9 to the exhaust passage upstream of the exhaust purification converter 10. The regeneration operation of the NO _X storage reduction catalyst 7 is performed by supplying an agent (fuel). Thus, it saturated with NO _X absorbed _the NO _X storage reduction catalyst 7 is prevented from becoming unable to absorb the NO _X in more exhaust.

Next, the HC adsorbent 11 of this embodiment will be described. The HC adsorbent 11 of the present embodiment is, for example, Z
It is made of a porous zeolite such as SM5, and has a large number of small-diameter passages (cells) through which exhaust gas passes, like a normal catalyst carrier. HC adsorbent 11, the heavy hydrocarbon in the exhaust gas selectively adsorbed when the engine exhaust temperature is relatively low (e.g. when _the NO _X storage and reduction catalyst 7 and the activation temperature below the temperature of the oxidation catalyst 13) It has the property of converting the adsorbed heavy hydrocarbons into light hydrocarbons and releasing them when the temperature rises.

Since the HC adsorbent 11 is made of zeolite, a large number of pores are formed on the porous zeolite wall surface of the exhaust passage (cell) inside the adsorbent 11. The hydrocarbon molecules in the exhaust gas enter the pores of the wall surface when passing through the cell and are trapped. In this case, there is a correlation between the molecular weight of the hydrocarbon trapped in the pores and the wall pore diameter, and by adjusting the pore diameter of the wall, hydrocarbons in a specific molecular weight range can be selectively trapped on the wall. .

In the present embodiment, the relationship with the molecular weight of the trapped hydrocarbons is experimentally determined by changing the pore diameter of the zeolite porous used in advance, and the heavy hydrocarbons (for example, the components having carbon number C ≧ 11) are obtained. The zeolite pore diameter of the HC adsorbent 11 is adjusted so that the probability of trapping is increased. As a result, heavy hydrocarbons in the exhaust gas are selectively adsorbed on the HC adsorbent 11.

FIG. 2 is a diagram showing an example of the selective adsorption characteristics of heavy hydrocarbons of the HC adsorbent using zeolite.
FIG. 2 shows the amount of hydrocarbon components in the gas flowing into the HC adsorbent when the temperature of the HC adsorbent is maintained at a low temperature of about 100 ° C. (left side in FIG. 2) and the hydrocarbons in the gas after passing through the HC adsorbent. The results of measuring the component amounts (right side in FIG. 2) are shown for each carbon number. As shown in FIG. 2, the total amount of hydrocarbons in the gas after passing through the HC adsorbent has been reduced to about half, and it can be seen that about 50% of the hydrocarbons have been adsorbed on the HC adsorbent. Also, comparing the carbon number of the hydrocarbon component between the inflow gas and the gas after passing, it is found that light hydrocarbons (carbon number C ≦ 10)
Although there is almost no change in the amount of heavy hydrocarbons, the amount of heavy hydrocarbons (C> 11) is greatly reduced, indicating that heavy hydrocarbons are selectively adsorbed.

The HC adsorbent 11 of this embodiment selectively adsorbs heavy hydrocarbons in the exhaust gas as described above. However, when the temperature of the adsorbent rises, the adsorbed hydrocarbons increase in heat energy. From the pores. However, since zeolite also has a function as an oxidation catalyst, the adsorbed hydrocarbon is partially oxidized at the time of desorption, and the light hydrocarbon (C
≦ 10). That is, the HC adsorbent 11 of the present embodiment selectively adsorbs heavy hydrocarbons in exhaust gas at low temperatures, and converts the adsorbed heavy hydrocarbons to light hydrocarbons and emits them in exhaust gas when the temperature rises. It has the function to do.

The oxidation catalyst 13 of the present embodiment is obtained by forming a catalyst supporting layer of alumina on a monolithic carrier made of cordierite, for example, and supporting a catalyst component such as platinum Pt or palladium Pd on the supporting layer. used. The oxidation catalyst 13 oxidizes hydrocarbons in the exhaust gas to form H ₂
O, it converted to CO _2, but purifying, as the air-fuel ratio of the exhaust gas decreases (as the oxygen concentration decreases), also, as the catalyst temperature becomes lower oxidation capacity is reduced, in particular the activation temperature of the catalyst (for example, 300 In a region where the exhaust air-fuel ratio is equal to or lower than the theoretical air-fuel ratio at a temperature equal to or lower than (° C.), the heavy hydrocarbon component in the exhaust gas can hardly be oxidized.

In this embodiment, since a diesel engine is used as the internal combustion engine 1, the engine exhaust temperature is considerably lower than that of a gasoline engine. In particular, when the engine is under low load operation or when the engine is started, the exhaust gas temperature is low.
The temperatures of the _X storage reduction catalyst 7 and the oxidation catalyst 13 are also lowered in accordance with the exhaust gas temperature, and the activity as a catalyst is in a state of being reduced. Supplying to the NO _X occluding and reducing catalyst 7 relatively large amount of reducing agent (fuel) in a short time in order to perform the regenerating operation of the NO _X occluding and reducing catalyst 7 in this state, it is supplied in _the NO _X storage reduction catalyst 7 The entire amount of the reducing agent is not consumed,
Particularly, heavy hydrocarbons with low reactivity may flow out downstream of the catalyst 7.

In this case, the temperature of the oxidation catalyst 13 disposed downstream of the NO _X storage reduction catalyst 7 is also low and the activity as a catalyst is in a state of being reduced. In addition, since the oxygen concentration of the exhaust gas that has passed through the NO _X storage reduction catalyst 7 has been reduced, the oxidation catalyst 13 whose activity has been reduced may purify heavy hydrocarbons flowing out of the NO _X storage reduction catalyst 7. It is difficult. Also, in the exhaust gas temperature is low operating conditions, such as at engine startup and low load operation, there is a case where relatively large amount of hydrocarbons discharged from the engine 1, again passes through _the NO _X storage reduction catalyst 7 In some cases, hydrocarbons may flow downstream.

In the present embodiment, this problem is solved by disposing the HC adsorbent 11 between the NO _X storage reduction catalyst 7 and the oxidation catalyst 13. As described above, the HC adsorbent 11 of the present embodiment has a property of selectively adsorbing heavy hydrocarbons in exhaust gas at a low exhaust gas temperature. For this reason,
The heavy hydrocarbons that have flowed downstream without reacting on the NO _X storage reduction catalyst 7 at low engine temperatures are adsorbed by the HC adsorbent 11 and do not flow out downstream of the HC adsorbent 11. in this case,
Of the hydrocarbons that pass through the NO _X storage reduction catalyst 7 and flow downstream, some of the light hydrocarbons flow downstream without being adsorbed by the HC adsorbent, but the light hydrocarbons have high reactivity. Therefore, even if the oxidation catalyst 13 is at a low temperature, it is oxidized on the oxidation catalyst 13 and unpurified hydrocarbons are
It does not flow downstream.

In this embodiment, when the exhaust gas temperature of the engine rises from 250 ° C. to about 300 ° C., the HC adsorbent 1
From 1, the adsorbed hydrocarbons are released. However, in this case, the temperature of the oxidation catalyst 13 downstream of the adsorbent 11 has also risen, and the activity is high. As described above, hydrocarbons are partially oxidized and converted to light components on the HC adsorbent 11 during desorption. Therefore, when the exhaust gas temperature rises, a relatively large amount of hydrocarbons is released from the HC adsorbent 11, but these hydrocarbons are easily purified by the downstream oxidation catalyst 13.

As described above, in the present embodiment, the heavy hydrocarbon component in the exhaust gas is selectively adsorbed between the NO _X storage reduction catalyst 7 and the oxidation catalyst 13, and when the temperature rises, the adsorbed heavy carbon component is removed. By arranging the HC adsorbent 11 for converting hydrogen into light hydrocarbons and releasing the same, it is possible to prevent hydrocarbons from being released into the atmosphere when the exhaust gas temperature is low. Note that N
When fuel is supplied to the NO _X storage reduction catalyst 7 in order to release NO _X from the O _X storage reduction catalyst 7 and perform reduction purification, a comparison is made to reduce the oxygen concentration of the NO _X storage reduction catalyst 7. It is necessary to supply an extremely large amount of fuel in a short time.
In particular, it is preferable that in order to improve the purification rate of the absorbed NO _X in the NO _X occluding and reducing catalyst 7 is as high as possible in the hydrocarbon concentration in the exhaust gas during the regenerating operation. For this reason,
Hydrocarbon density in temporarily evacuated during even the fuel supply even when the exhaust gas temperature is high is much higher, the amount of heavy hydrocarbons flowing downstream without reacting with _the NO _X storage reduction catalyst 7 May increase. In this case, the exhaust gas after passing through the NO _X storage reduction catalyst 7 has a rich air-fuel ratio, and the oxygen concentration is low, so that the oxidation ability of the downstream oxidation catalyst 13 is reduced. May not be purified. However, in the present embodiment, since the HC adsorbent 11 is disposed between the NO _X storage reduction catalyst 7 and the oxidation catalyst 13, the heavy hydrocarbons flowing out of the NO _X storage reduction catalyst 7 Is temporarily absorbed. In this case, since the temperature of the HC adsorbent 11 is also high, the adsorbed hydrocarbon desorbs the HC adsorbent in a short time and flows out downstream. However, N from the NO _X storage reduction catalyst 7
For O _X release and reduction purification is completed in a short period of time, HC
When the desorption of hydrocarbons from the adsorbent 11 occurs, the fuel injection from the reducing agent supply device 9 has been completed, and the exhaust air-fuel ratio has returned to the lean air-fuel ratio. For this reason, the entire amount of the hydrocarbon desorbed from the HC adsorbent is purified on the oxidation catalyst 13 on the downstream side.

(2) Reference Embodiment 2 FIG. 3 is a diagram showing a schematic configuration of a second embodiment for reference of the present invention . 3, the same reference numerals as those in FIG. 1 indicate the same elements as those in FIG. In the present embodiment,
The only difference from the first embodiment is that a combustion type heater 50 is arranged in the exhaust passage 3 on the upstream side of the exhaust purification catalyst 10.

The heater 50 has a glow plug (not shown) and a burner for injecting the fuel of the engine into the glow plug, and operates according to a signal from the control circuit 30. The combustion heater 50 is used for injecting high-temperature combustion gas into the exhaust passage 3 when the exhaust gas temperature is low to heat the downstream NO _X storage reduction catalyst 7. In the present embodiment, by using the heater 50, even when the exhaust gas temperature is low, the temperature of the NO _X storage reduction catalyst 7 and the temperature of the oxidation catalyst 13 downstream thereof can be kept high. In addition, it is possible to reduce the amount of hydrocarbons flowing to the downstream side after passing through the NO _X storage reduction catalyst 7, and to completely purify the hydrocarbons flowing to the downstream side by the oxidation catalyst 13. .

However, when the combustion heater 50 is used, there is a problem that a relatively large amount of hydrocarbons is contained in the combustion gas when the combustion is unstable such as when the burner is ignited. Further, in the burner which is energized by energizing the glow plug to make it glow red by injecting fuel into the glow plug in this state as in the present embodiment, if the glow plug is disconnected or the state of insufficient red heat occurs, the burner injects the glow plug. Since the discharged fuel flows into the exhaust passage 3 without burning, there is a problem that a large amount of hydrocarbons reach the exhaust purification converter 10. In this case, since the low exhaust gas temperature, NO _X occluding and reducing catalyst 7 and the oxidation catalyst 1
In 3, the purification of hydrocarbons may be insufficient,
In the present embodiment, NO _X occluding and reducing catalyst 7 and the oxidation catalyst 13
The HC adsorbent 11 is disposed between the two. For this reason,
As in the first embodiment, the ignition failure of the burner and the hydrocarbons generated at the time of ignition are adsorbed by the HC adsorbent 11 and are prevented from flowing to the downstream side of the exhaust gas purification converter 10.

[0040] (3) Embodiment 4 of the present invention is a diagram illustrating a schematic configuration of implementation of the invention. 4, the same reference numerals as those in FIGS. 1 and 3 indicate the same elements as those in FIGS. In FIG. 4, 2
Reference numeral 0 denotes an exhaust gas purification converter provided in the exhaust passage 3. Converter of the present embodiment, NO _X occluding and reducing catalyst 7 on the upstream side in the same casing, is configured of arranging the oxidation catalyst 13 on the downstream side does not include the HC adsorbent.

In this embodiment, a separate HC adsorbent 1 is used.
1 is disposed in the exhaust passage on the upstream side of the exhaust purification converter 20, and converts the combustion gas of the combustion type heater 50 into the HC adsorbent 1.
3 three-way valve 5 that can be switched between upstream and downstream
This embodiment is different from the second embodiment in that 1 is provided. In the present embodiment, although the point performed by operating the heater 50 during the exhaust cold and _the NO _X storage reduction catalyst 7 heating the oxidation catalyst 13 is similar to the second embodiment, operation at the start of the heater (a burner ignition The second embodiment is different from the second embodiment in that the burner combustion gas is supplied to the exhaust passage on the upstream side of the HC adsorbent 11 after the ignition, and the burner combustion gas is supplied to the exhaust passage on the downstream side of the HC adsorbent 11 after ignition is completed. are doing.

That is, when the exhaust gas temperature is lower than the predetermined temperature, the control circuit 30 activates the heater 50 to ignite the burner. At this time, the three-way valve 51 sets the heater combustion gas to H
It is set at a position where it is supplied to the exhaust passage upstream of the C adsorbent 11. Thereby, a relatively large amount of hydrocarbons generated at the time of ignition of the burner is adsorbed by the HC adsorbent 11. In addition, even when a large amount of hydrocarbons are generated due to poor ignition, the hydrocarbons are adsorbed by the HC adsorbent 11, so that the low-temperature NO _X storage reduction catalyst 7 and the oxidation catalyst 1
3 is prevented from reaching a large amount of hydrocarbons.

On the other hand, when the burner ignition of the heater 50 is completed and the burner combustion is stabilized, the control circuit 30 switches the three-way valve 51 to set the burner combustion gas at a position to supply the burner combustion gas to the exhaust passage downstream of the HC adsorbent 11. . Thus, look like small hot burner combustion gas of the unburned hydrocarbons are supplied to the direct _the NO _X storage reduction catalyst 7 and the oxidation catalyst 13, the temperature of the _the NO _X storage and reduction catalyst 7 and the oxidation catalyst 13 is short The temperature rises to the activation temperature with time. The determination of the completion of the burner ignition of the heater 50 can be performed by, for example, providing a temperature sensor at the heater outlet and monitoring the burner combustion gas temperature. That is, after operating the heater, the control circuit 30 determines whether or not the burner combustion gas has risen to a predetermined temperature. If the temperature has reached the predetermined temperature, the control circuit 30 determines that the burner combustion has become stable. Then, the three-way valve 51 is switched. If the burner combustion gas temperature does not reach the predetermined temperature even after the predetermined period has elapsed, the control circuit 30 determines that a burner ignition failure has occurred,
Turn off fuel supply to the burner.

As described above, the heater 5 is provided by using the three-way valve 51.
Since the combustion gas at the start of operation 0 is introduced to the HC adsorbent 11, the hydrocarbons generated at the start of operation of the heater 50 and the hydrocarbons generated at a large amount when the burner ignition failure of the heater 50 occurs occur at a low temperature. passes through of the NO _X occluding and reducing catalyst 7 and the oxidation catalyst 13 is prevented from being discharged to the atmosphere.

[0045] In the present embodiment, to prevent a complete air hydrocarbon emissions by arranging _the NO _X storage reduction catalyst 7 oxidation catalyst 13 on the downstream side. However, in the present embodiment, unlike the first and second embodiments, the light hydrocarbons released after the temperature rise of the HC adsorbent 11 are NO _X
It flows into the storage reduction catalyst 7. Therefore, it emitted light hydrocarbons after reaching the activation temperature _the NO _X storage reduction catalyst 7
It is consumed in the reduction of oxidized, or NO _X by, NO
_It hardly flows out to the downstream side of the _X storage reduction catalyst 7. For this reason, in this embodiment, it is possible to prevent hydrocarbons from being released into the atmosphere without necessarily arranging the oxidation catalyst 13 on the downstream side of the NO _X storage reduction catalyst 7.

[0046]

According to the present invention, NO _X in the exhaust at low temperature, etc.
Storage reduction catalyst downstream hydrocarbon achieve the effect you allow prevented from flowing out.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a schematic configuration of an embodiment as a reference for understanding the present invention .

FIG. 2 is a diagram illustrating hydrocarbon adsorption characteristics of an HC adsorbent.

FIG. 3 is a diagram illustrating a schematic configuration of a second embodiment as a reference of the present invention .

4 is a diagram illustrating a schematic configuration of implementation of the invention.

[Explanation of symbols]

1 ... engine 3 ... exhaust passage 7 ... NO _X occluding and reducing catalyst 9 ... reducing agent supply device 11 ... HC adsorbent 13 ... oxidizing catalyst 50 ... combustion heater

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI F01N 3/20 F01N 3/20 L 3/28 301D 3/28 301 B01D 53/36 101B (72) Inventor Atsushi Tahara Toyota, Aichi Prefecture 1 Toyota Motor City, Toyota Motor Corporation (72) Inventor Kiyoshi Kobata 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Hiromichi Yanagihara 1 Toyota Motor Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (56) References JP-A-8-270439 (JP, A) JP-A-6-117220 (JP, A) JP-A-7-19031 (JP, A) (58) Fields studied (Int .Cl. ⁷ , DB name) F01N 3/08-3/28 B01D 53/94 B01J 23/58

Claims (1)

(57) [Claims] An exhaust air flowing into an exhaust passage of an internal combustion engine.
Ratio absorbs NO _X in the exhaust gas when the lean, flows to
Absorbed when the oxygen concentration of the exhaust air-fuel ratio decreases
And _the NO _X storage reduction catalyst that emits _X, the _the NO _X storage reduction catalyst
Flowing the NO _X occluding and reducing catalyst when should be released NO _X from medium
Reducing agent that supplies hydrocarbons as reducing agent
And an exhaust purification device for an internal combustion engine, wherein
Te, is disposed on the upstream side of the exhaust passage of the _the NO _X storage reduction catalyst
Adsorbs hydrocarbons in the exhaust and raises the temperature after adsorption
HC adsorbent that emits hydrocarbons adsorbed to the engine and combustion gas generated by burning hydrocarbons at low engine exhaust temperatures
A combustion burner to be burned and a combustion gas from the burner upstream of the HC adsorbent in the exhaust passage.
Side portion, the HC adsorbent and the NO _X storage reduction catalyst
Switching that can be introduced by selectively switching to the part between
Means for purifying exhaust gas of an internal combustion engine, comprising: