JP2845080B2 - 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, in particular, a gasoline engine or the like for a diesel engine or lean burn, the NO _X in the exhaust gas of an internal combustion engine causing combustion of lean air-fuel ratio The present invention relates to an exhaust purification device that can be removed effectively.

[0002]

2. Description of the Related Art An example of this type of exhaust gas purifying apparatus is disclosed, for example, in Japanese Patent Application Laid-Open No. 62-106826. The apparatus of this publication is to place the absorbent to absorb NO _X in the presence of oxygen in an exhaust passage of a diesel engine (catalyst) to absorb the NO _X in the exhaust gas, NO _X absorption ability of the absorbent is saturated to shut off the flow of exhaust gas into the absorbent supplying reducing agent to the absorbent when the is the NO _X released with the release of NO _X from the absorbent that so as to reduce and purify.

[0003]

Problems to be Solved by the Invention
In the exhaust purification device disclosed in Japanese Patent No. 6826, a gaseous reducing agent such as hydrogen is supplied to the NO _X absorbent in order to release NO _X from the NO _X absorbent and perform reduction purification (hereinafter referred to as “regeneration”). It is performed regeneration of the NO _X by the _the NO _X absorbent in an atmosphere under a rich air-fuel ratio.

However, during the regenerating operation of the NO _X absorbent in the apparatus of the above publication, when the atmosphere of the NO _X absorbent from the start of the supply of the reducing agent, such as take time to switch from lean to rich is elevated temperature of the NO _X absorbent by the combustion of the reducing agent on _the NO _X absorbent, there is a case where NO _X from _the NO _X absorbent before switching to rich atmosphere from being released. At this time, since the NO _X absorbent is not in a sufficient reducing atmosphere (rich atmosphere), the released NO _X
May not be sufficiently reduced and unpurified NO _X may be released to the atmosphere.

In order to prevent the unpurified NO _X from being released into the atmosphere, a large amount of a reducing agent is supplied and NO
_It is necessary to switch the atmosphere of _X absorbent richly,
In this case the atmosphere of the NO _X absorbent during regeneration becomes too rich (air-fuel ratio is too low), the ammonia reacts part of the NO _X released from _the NO _X absorbent is an excess of HC components (NH ₃ ) is produced, and this ammonia is released to the atmosphere.

On the other hand, as described below, generally in the NO _X atmosphere air-fuel ratio of the absorbent enough rich (i.e. the lower the air-fuel ratio) in a short time by performing complete regeneration at the time of regenerating operation of the NO _X absorbent It is known that can be. Therefore, in the exhaust purification apparatus and the like for a vehicle, to complete the shortest possible time in the reproduction operation of the NO _X absorbent, under possible rich atmosphere by increasing the supply amount of the reducing agent in order to prepare for the next of the NO _X absorbent it is preferred to carry out the regeneration of _the NO _X absorbent.

However, in the apparatus disclosed in the above publication, unpurified N
O_XOf reducing agent to prevent atmospheric release of ammonia and ammonia
Regeneration conditions such as supply amount are limited, and efficiency is reduced in a short time
Typical NO_XThe problem of not being able to perform absorbent regeneration
Occurs. The present invention provides NO_XNot purified during absorbent regeneration operation
NO_XTo solve the problem of atmospheric release of ammonia and ammonia
_XEfficient N in a short time by expanding the range of absorbent regeneration conditions
O _XExhaust purification of internal combustion engine that can perform absorbent regeneration
It is intended to provide a device.

[0008]

According to the present invention SUMMARY OF], in an exhaust passage of an internal combustion engine capable of performing combustion of the lean air-fuel ratio, the air-fuel ratio of the inflowing exhaust is absorbed inflowing exhaust the NO _X when the lean oxygen concentration to release the absorbed NO _X when the reduced NO _X in the absorbent arranged to absorb the NO _X in the exhaust gas, then NO _X exhaust air-fuel ratio flowing into the absorbent and absorbed in the rich NO _X in the exhaust purification system of an internal combustion engine to reduce and purify the NO _X with be released from _the NO _X absorbent and selective reducing agent to NO _X in the exhaust gas in the lean exhaust air-fuel ratio conditions downstream of the _the NO _X absorbent and _the NO _X selective reducing catalyst capable to be reacted, to flow into the _the NO _X absorbent
The exhaust air-fuel ratio to release NO _X absorbed in the rich that
Air-fuel of the exhaust gas flowing into the _the NO _X selective reducing catalyst Rutoki
Means for maintaining the ratio at a lean ratio .

[0009]

[Action] _the NO _X absorbent unpurified generated during the regenerating operation N
O _X and ammonia are simultaneously decomposed by selective reduction catalyst arranged in _the NO _X absorbent downstream _{N 2, H 2 O, CO} 2
NO _X and ammonia are not released to the atmosphere.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In FIG. 1, reference numeral 1 denotes an exhaust pipe of an internal combustion engine (not shown). In this embodiment, the exhaust pipe 1 has two branch passages 3.
a, 3b are provided, the exhaust gas temperature sensor 6 in the passage 3a from upstream, for generating a signal corresponding to the later-described reducing agent supply device 11 and _the NO _X absorbent 5, and the exhaust temperature,
An oxygen concentration sensor 7 that generates a continuous output corresponding to the oxygen concentration in the exhaust gas is provided. The exhaust passage 3b joins the exhaust passage 3a again downstream of the exhaust gas temperature sensor 6 and the oxygen concentration sensor 7. That is, the exhaust passage 3b plays a role of a bypass passage for flowing the exhaust to bypass the _the NO _X absorbent 5 on the downstream side.

Further, an exhaust switching valve 2 is provided at a branch portion of the exhaust passages 3a and 3b of the exhaust pipe 1, and the exhaust passage 3a
One of the exhaust passages 3a and 3b is closed to a predetermined opening degree.
The exhaust is distributed to the An actuator of an appropriate type, such as a negative pressure actuator for driving the switching valve 2 to a predetermined switching position by driving a switching valve 2 by a control signal from an engine control circuit (ECU) 20 to be described later, is shown in FIG. .

[0012] In this embodiment, the downstream side of the exhaust passage 3a of the NO _X absorbent 5, NO _X selective reduction catalyst 9 further described below in the exhaust pipe 1 downstream of the merging portion of 3b is provided. That is, the exhaust gas flowing through both the exhaust passages 3a and 3b flows into the NO _X selection catalyst 9. In the figure, reference numeral 20 denotes a control circuit (ECU) of the engine 1. ECU
Reference numeral 20 denotes a known digital computer having a configuration in which a CPU, a RAM, a ROM, an input port, and an output port are connected to each other via a bidirectional bus, and performs basic control such as fuel injection amount control of an engine. In this embodiment, the EC
U20 further drives the actuator 2a via a drive circuit (not shown), a negative pressure control valve, and the like to drive the exhaust switching valve 2
In addition to performing the switching position control, the reducing agent supply control from the reducing agent supply device 11 is performed. For these controls, the input ports of the ECU 20 are supplied with the exhaust gas temperature and the exhaust oxygen concentration from the exhaust gas temperature sensor 6 and the oxygen concentration sensor 7, respectively, and also show signals such as the engine speed and the accelerator opening, respectively. Not input from sensor.

[0013] The reducing agent supply device 11 is connected to the NO in the exhaust passage 3a.
Injection valve 11 for supplying a reducing agent to be described later on the upstream side of _X absorbent 5
a. Injector 11a is opened to the opening degree corresponding to the control signal of the ECU20 during playback operation of the NO _X absorbent 5, and supplies the amount of reducing agent in accordance with the opening to the exhaust passage 3a. _The NO _X absorbent 5 of the NO _X emission, the reducing agent used for reduction operations (playback operations), as long as it generates a hydrocarbon, reducing components such as carbon monoxide in the exhaust, hydrogen, carbon monoxide Gases such as carbon, liquid or gaseous hydrocarbons such as propane, propylene and butane, and liquid fuels such as gasoline, light oil and kerosene can be used. In the present embodiment, the reducing agent is supplied to the reducing agent supply device 11 from a supply source such as a container or a pump (not shown), and is supplied to the injection valve 11 according to a signal from the ECU 20.
a to the NO _x absorbent 5.

[0014] _the NO _X absorbent 5 uses a carrier such as alumina or the like, the carrier on, for example potassium K, sodium Na, alkali metal, barium Ba, alkaline earth such as calcium Ca, such as lithium Li, cesium Cs And at least one selected from rare earths such as lanthanum La and yttrium Y, and a noble metal such as platinum Pt. This _the NO _X absorbent 5 absorbs NO _X in the case the air-fuel ratio of the exhaust gas flowing is lean, the oxygen concentration is carried out to absorbing and releasing action of the NO _X that releases NO _X when lowered.

The above-mentioned exhaust air-fuel ratio is defined as N
O _X absorbent upstream of 5 exhaust passage and the engine combustion chamber is intended to mean the ratio of the total sum and the fuel respectively supplied amount of air in the intake passage or the like. Therefore, NO _X absorbent 5
When no fuel, reducing agent or air is supplied to the upstream exhaust passage of the engine, the exhaust air-fuel ratio becomes equal to the operating air-fuel ratio of the engine (air-fuel ratio in combustion in the engine combustion chamber).

In this embodiment, since an engine that performs combustion at a lean air-fuel ratio is used, the exhaust air-fuel ratio during normal operation is lean, and the NO _X absorbent 5 absorbs NO _{X in} the exhaust gas. . Also, when a reducing agent is introduced into the exhaust oxygen concentration is lowered, the release of _the NO _X absorbent 5 absorbs reducing agent performs a reducing agent supply device 11. The detailed mechanism of this absorption / release action is not clear in some parts. However, it is considered that this absorption / release action is performed by a mechanism as shown in FIG. Next, this mechanism will be described by taking as an example a case where platinum Pt and barium Ba are supported on a carrier, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths and rare earths.

That is, the inflow exhaust gas becomes considerably lean.
And the oxygen concentration in the inflow exhaust gas greatly increased, as shown in Fig. 6 (A).
These oxygen O_TwoIs O_Two ^-Or O^2-In the form of
It adheres to the surface of platinum Pt. On the other hand, NO in the inflow exhaust gas is
This O on the surface of platinum Pt_Two ^-Or O^2-Reacts with N
O_Two(2NO + O_Two→ 2NO_Two ). Then generated
NO_TwoSome of the oxygen is oxidized on platinum Pt and
FIG. 6 shows that while being absorbed by and binding to barium oxide BaO.
As shown in (A), nitrate ion NO_Three ^-Absorbent in the form of
Spreads in. NO in this way_XIs NO_XAbsorbent 5
Is absorbed into.

Therefore, as long as the oxygen concentration in the inflowing exhaust gas is high, NO ₂ is generated on the surface of the platinum Pt, and as long as the NO _x absorption capacity of the absorbent is not saturated, NO ₂ is absorbed in the absorbent and nitrate ions NO ₃ ^- is generated. On the other hand, when the oxygen concentration in the inflowing exhaust gas decreases and the amount of generated NO ₂ decreases, the reaction proceeds in the reverse direction (NO ₃ ⁻ → NO ₂ ), and thus the nitrate ion NO ₃ ⁻ in the absorbent becomes NO ₂ Released from the absorbent in the form of That is, the oxygen concentration in the inflowing exhaust gas is released NO _X from _the NO _X absorbent 5 when lowered.

On the other hand, if reducing components such as HC and CO are present in the inflowing exhaust gas, these components become oxygen O ₂ on platinum Pt.
^- or it is reacted with oxide and O ^2-, lowering the oxygen concentration in the exhaust to consume oxygen in the exhaust. Further, the NO ₂ released from the NO _X absorbent 5 due to a decrease in the oxygen concentration in the exhaust gas
Is reduced by reacting with HC and CO as shown in FIG. 6 (B). When NO ₂ is no longer present on the surface of the platinum Pt, NO ₂ is released from the absorbent one after another.

[0020] That is, HC in the inflowing exhaust gas, CO, first O ₂ on the platinum Pt ^- immediately react with oxidized or O ^2-, and then on the platinum Pt O ₂ ^- or O ^2- is consumed the HC, NO _X discharged from the released NO _X and the engine from the absorbent by CO is reduced even yet HC, any remaining CO is. Therefore, H in the inflow exhaust gas
C, NO _X released from _the NO _X absorbent when the amount of CO is not sufficient will be directly flowing downstream without being reduced.

Further, as described above, release of the NO _X, reduction (regeneration) when performing an operation, an atmosphere of the NO _X absorbent can complete regeneration is carried out in a short time as to reproduce rich conditions It is known that it can be done. This, NO _X absorbent nitrate ions into the NO ₃ ^- is absorbed in the form of the NO _X is N
In the form of O ₂ is released from _the NO _X absorbent (NO ₃ ^- → N
The reaction of O ₂ ) becomes more active as the atmosphere becomes richer,
The release rate of O _X is considered to become high.

On the other hand, when the degree of the rich atmosphere of the NO _X absorbent is large (that is, when the rich treatment is performed), a part of the released NO _X is reduced to N ₂ instead of being reduced to N ₂ , and excessive HC component is removed. It is also known that NH ₃ is produced by the reaction. Accordingly, the supply amount of the reducing agent at the time of regenerating operation of the NO _X absorbent must be controlled within a range that does not cause the occurrence of the above unpurified NO _X and ammonia, NO _X
The conditions for regeneration of the absorbent will be limited. In the present invention, by purifying both the unpurified NO _X and ammonia of the NO _X absorbent during regeneration by placing _the NO _X selective reducing catalyst on the downstream side of the _the NO _X absorbent, regeneration of the NO _X absorbent By expanding the range of conditions, efficient reproduction can be performed in a short time.

In this embodiment, NO_XOn the downstream side of the absorbent 5
NO arranged in exhaust pipe 1_XExamples of selective reduction catalyst 9
For example, a metal such as Cu is ion-exchanged with zeolite ZSM-5.
What is carried instead is used. NO_XSelective touch
The medium 9 is NO when an appropriate amount of HC exists in a lean atmosphere._X
To reduce N_TwoCan be converted to Furthermore, NO _X
The selective reduction catalyst 9 reacts with ammonia and NO in the presence of oxygen.
And 4NH_Three+ 4NO + O_Two→ 4N_Two+ 6H_TwoAmmonia is converted to N by the reaction of O 2_TwoIs known to convert to
ing. That is, NO_XSelective reduction catalyst 9 has a lean atmosphere
NO downside_XPurifying both ammonia and ammonia at the same time
Can be.

Next, the exhaust gas purifying operation of this embodiment will be described. In this embodiment, during normal operation the exhaust switching valve 2 is held in position to close the exhaust passage 3b of the bypass side, exhaust its entire amount flows into _the NO _X absorbent 5. Thereby, NO _X in the exhaust gas is absorbed by the NO _X absorbent 5,
The exhaust gas from which NO _X has been removed flows into the NO _X selective reduction catalyst 9. At this time, NO _X selective reduction catalyst 9 adsorbs slight HC contained in the exhaust into the pores of the zeolite.

[0025] Then, when a predetermined regenerating operation conditions described later is satisfied, the exhaust switching valve 2 is squeezed in the exhaust passage 3a side to a predetermined opening degree, thereby reducing the flow rate of the exhaust gas flowing into _the NO _X absorbent 5. As a result, the amount of the reducing agent required to make the exhaust gas flowing into the NO _X absorbent 5 have a rich air-fuel ratio is reduced. The reducing agent in an amount enough to be quite rich atmosphere of the NO _X absorbent 5 for the flow rate of the exhaust gas flowing into the NO _X absorbent is supplied from the reducing agent supply device 11. That is, the rich processing of the NO _X absorbent 5 is performed. At this time, since the exhaust passage 3b on the bypass side is fully opened, most of the exhaust gas flows through the exhaust passage 3b, so that the exhaust resistance does not increase and the operation of the engine is not affected.

Further, unpurified N which flows out at the beginning of the regeneration operation
O _X , ammonia and excess HC generated by the rich treatment flow out of the NO _X absorbent 5 into the exhaust passage 3a, and are mixed with the exhaust gas flowing through the exhaust passage 3b at a junction with the bypass-side exhaust passage 3b. After that, it flows into the NO _X selective reduction catalyst 9. For this reason, the rich air-fuel ratio exhaust gas flowing out of the NO _X absorbent 5 is diluted by a large amount of lean air-fuel ratio exhaust gas including unpurified NO _X flowing through the bypass side exhaust passage 3b, and the NO _X selective reduction catalyst The air-fuel ratio of the exhaust gas flowing into 9 becomes lean as a whole.

[0027] Accordingly lean atmosphere in _the NO _X selective reducing catalyst 9, and unpurified of the NO _X in the exhaust gas flowing, NO _X
Ammonia, HC generated by rich treatment of absorbent 5
Components and will be those HC components adsorbed on _the NO _X selective reducing catalyst 9 for exhaust gas temperature rise due to reaction heat during regeneration of the NO _X absorbent 5 is released simultaneously exist, in the exhaust The unpurified NO _X component reacts with ammonia and HC to purify both NO _X and ammonia at the same time.

Further, NO _X absorbent to a predetermined time elapses 5
When the regeneration of the exhaust gas is completed, the switching valve 2 moves to the position where the bypass side exhaust passage 3b is closed, and the exhaust gas is entirely NO.
Guided to the _X absorbent 5, absorption of NO _X is resumed. As described above, by arranging the _the NO _X selective reducing catalyst 9 on the downstream side of the NO _X absorbent 5, unpurified NO _X and ammonia, by simultaneously purifying HC components, the rich processing of _the NO _X absorbent 5 a short time it is possible to reproduce the _the NO _X absorbent. In addition, even at the time of the regenerating operation of _the NO _X absorbent 5 NO _X
Atmospheric release of the NO _X in the regenerating operation is prevented since it is possible to purify of the NO _X in the exhaust gas in the selective reduction catalyst 9.

A description will now be given reproduction conditions of the NO _X absorbent 5 in this embodiment. Generally, the activation temperatures of the NO _X absorbent 5 and the NO _X selective reduction catalyst 9 are different, and the NO _X selective reduction catalyst 9 usually requires a higher activation temperature than the NO _X absorbent 5. Therefore, in the present embodiment in consideration of both temperature and _the NO _X absorbent 5 and _the NO _X selective reducing catalyst 9, reproducing conditions of the NO _X absorbent 5 in accordance with the exhaust temperature detected by the exhaust temperature sensor 6 Has changed.

FIG. 2 is a map showing conditions for starting the regeneration operation of the NO _X absorbent 5 in this embodiment. The vertical axis in FIG. 2 shows the time T _the NO _X absorbent 5 is used in the NO _X absorbent. Time T becomes a value corresponding to the amount of NO _{X the} NO _X absorbent 5 is absorbed. The horizontal axis in FIG. 2 indicates the exhaust gas temperature, and N
O _X absorbent corresponding to 5 and the temperature of the NO _X selective reducing catalyst 9. Here, the temperature t _A is an exhaust gas temperature corresponding to the lower limit temperature (for example, about 250 ° C.) at which the NO _X absorbent 5 shows the activity, and the temperature t _B is the lower limit temperature (for example, about at about 250 ° C.) at which the NO _X selective reduction catalyst 9 shows the activity. Exhaust temperature corresponding to 350 ° C.). In this embodiment, when the exhaust gas temperature t is higher than t _B ,
O _X absorbent 5 and _the NO _X selective NO _X absorption amount T of the NO _X absorbent 5 both in a temperature region showing the activity of the reduction catalyst 9 of the NO _X absorbent 5 is larger than the first predetermined value T _A Reproduction is performed (FIG. 2, area I).

When the exhaust temperature t is between t _A and t _B , that is, when the NO _X absorbent 5 has reached the activation temperature but the NO _X selective reduction catalyst 9 has not reached the activation temperature. _the NO _X absorbent NO _X absorption amount T of 5 second predetermined value T _B is the (T _B> T _a) performs the reproduction of only _the NO _X absorbent 5 is greater than (2, region II), Region I and Region I
In I, the conditions are changed to regenerate the NO _X absorbent 5. Hereinafter, the reproduction operation in each area will be described.

[0032] (1) (for t ≧ t _B and T ≧ T _A) region I in the temperature range of t ≧ t _B are both reached the activation temperature of the _the NO _X absorbent 5 and _the NO _X selective reducing catalyst 9 N
When the NO _X absorption amount of the O _X absorbent 5 has increased to some extent (when T> T _A ), a normal regeneration operation is performed. That is, the exhaust switching valve 2 is switched to hold the exhaust passage 3 a at a predetermined position where the exhaust passage 3 a is almost fully closed, the flow rate of the exhaust gas passing through the NO _X absorbent 5 is reduced, and a predetermined amount of the reducing agent is supplied from the reducing agent supply device 11. supplying, performing the rich processing of the NO _X absorbent 5. Here, the NO _X absorption amount T _A is an absorption amount having a sufficient margin until the NO _X absorbent 5 is saturated.

(2) Region II (t _A ≦ t <t _B and T ≧
Since T For _{B) t A ≦ t <NO} X selective reduction catalyst 9 is in the temperature range of t _B does not reach the activation temperature, usually _the NO _X absorbent 5
If the condition of possible areas I without play so as to wait for the establishment, NO _X absorption of the NO _X absorbent 5 is _the NO _X absorbent 5 increases becomes a value that may be saturated ( for reproducing of the NO _X absorbent 5 only if T ≧ T _B).

Further, as it can be migrated to the region I and as fast as possible to raise the temperature of the NO _X selective reducing catalyst 9 in the case of executing the reproduction operation, performs an operation to raise the exhaust gas temperature t. That is, in the area II, when the reproduction operation is performed, the area I
Exhaust gas flow through the _the NO _X absorbent 5 holds the exhaust switching valve 2 to a position to increase than for. In addition, the supply amount of the reducing agent supplied from the reducing agent supply device 11 is also increased in accordance with the flow rate of the exhaust gas to activate the oxidation reaction of the reducing agent on the NO _X absorbent 5. As a result, the temperature of the exhaust gas flowing into the NO _X selective reduction catalyst 9 increases, and the temperature of the NO _X selective reduction catalyst 9 increases, so that the NO _X selective reduction catalyst 9 quickly reaches the activation temperature.

[0035] Incidentally, the reducing agent supply amount according to an output of the exhaust oxygen concentration sensor 7, the air-fuel ratio of the exhaust gas passing through the _the NO _X absorbent 5 may be feedback controlled so that the vicinity of the stoichiometric air-fuel ratio. Further, NO in the _X selective reducing catalyst 9 provided in advance an electric heater, further faster _the NO _X selective reducing catalyst 9 if to heat _the NO _X selective reducing catalyst 9 is energized when reproducing in the region II The temperature can be raised.

Further, NO _X after selective reduction catalyst 9 reaches the activation temperature and the exhaust switching valve 2 reducing agent supply device 11 is controlled as in the region I, normal playback operation of the NO _X absorbent 5 Is performed. FIG. 3 shows a flowchart for determining the reproduction condition. This routine is executed by the ECU 20 at predetermined time intervals, and the values of the regeneration operation execution flag F and the reducing agent supply control flag K are set according to the determined area.

In FIG. 3, steps 301 to 303 show the above-mentioned area determination operation. Steps 304 and 3
05 is a case where it is determined in Steps 301 to 303 that the condition is in the region I. In Step 304, the value of the regeneration operation execution flag F is set to “1”, and in Step 305, the value of the reducing agent supply amount flag K is set. The value is set to "1".

When the value of the flag F is set to "1", E
The exhaust switching valve 2 is maintained at a first predetermined degree of opening that almost completely closes the exhaust passage 3a by a routine (not shown) separately executed by the CU 20. Similarly, the flag K is "1" reducing agent supply amount from the reducing agent supply device 11 by a routine not shown separately performed by the is set ECU20 The corresponding to the opening degree of the exhaust switching valve 2 NO _X absorbent 5
Is controlled to an amount necessary to perform the rich processing.

Steps 306 and 307 correspond to step 301
To 303, when the condition is determined to be in the area II, the values of the flag F and the flag K are respectively set to “2”. As a result, the opening of the exhaust control valve 2 is maintained at the second predetermined opening which is larger than the first opening, and NO
_The flow rate of the exhaust gas passing through the _X absorbent 5 is set to a value larger than the region I. Further, the amount of the reducing agent supplied from the reducing agent supply device 11 is controlled to an amount necessary for performing the rich treatment of the NO _X absorbent 5 in accordance with the opening degree of the exhaust gas switching valve 2.

Steps 306 and 307 correspond to step 301
To 303, when the condition is determined to be in an area other than the areas I and II, the values of the flag F and the flag K are reset to zero. In this case, the regeneration operation of the NO _X absorbent 5 is not performed, and the exhaust switching valve 2 fully closes the bypass side exhaust passage 3 b to guide the entire amount of exhaust gas to the NO _X absorbent 5. Is stopped.

Next, another embodiment of the present invention will be described with reference to FIG. In this embodiment, new and that the secondary air supply system 15 for supplying secondary air to the bypass-side exhaust passage 3b is provided, and the exhaust temperature sensor 16 for detecting the _the NO _X selective reducing catalyst 9 inlet exhaust temperature Fig. 1
Configuration. As described above, the activation temperature of the NO _X selective reducing catalyst 9 is generally higher than the activation temperature of the NO _X absorbent 5, the regenerating operation of the NO _X absorbent 5 is preferably carried out at as high as possible exhaust gas temperature region. However, NO _X
Each of the absorbent 5 and _the NO _X selective reducing catalyst 9 is the use upper limit temperature, exhaust temperature and deterioration is accelerated beyond the upper limit temperature. Further, since the upper limit temperature of use of the NO _X selective reduction catalyst 9 is generally higher than the first use temperature of the NO _X absorbent 5, the upper limit of the exhaust temperature at the time of regeneration of the NO _X absorbent 5 is the upper limit temperature of the use of the NO _X selective reduction catalyst 9. It is regulated by.

[0042] In this embodiment, by lowering the supply to inflowing exhaust gas temperature of the secondary air to the NO _X selective reducing catalyst 9 has expanded the upper limit of the exhaust temperature during _the NO _X absorbent 5 play. In FIG. 4, the secondary air supply device 15 includes an appropriate pressurized air source 15a such as an air pump and a flow control valve 15b, and starts and stops the air pump 15a and opens the flow control valve 15b according to a control signal from the ECU 20. Is controlled, the secondary air is supplied to the bypass-side exhaust passage 3b under predetermined conditions.

FIG. 5 is a map similar to FIG. 2 showing the regeneration operation start condition and the secondary air introduction condition in this embodiment. In FIG. 5, t _A , t _B , T _A , T _B and region I,
II shows the same value as FIG. In addition, t _C is set to a temperature lower than the upper limit temperature of use of the NO _X selective reduction catalyst 9 with a margin, and is set to, for example, about 600 ° C. in the present embodiment.

[0044] In this embodiment, the regenerating operation of the NO _X absorbent 5 is controlled in accordance with the map of FIG. 5 independently of the supply control of secondary air. _The NO _X absorbent 5 playback operation and the area I of the present embodiment, the region II setting will be omitted here because FIG 2 is similar to FIG. 3. FIG. 5 shows a region III in which the secondary air is introduced. In this embodiment, NO
_When the exhaust gas temperature detected by the exhaust gas temperature sensor 6 at the outlet of the _X absorbent 5 exceeds the use upper limit temperature t _C of the NO _X selective reduction catalyst 9, regardless of the presence or absence of the regeneration operation of the NO _X absorbent 5 (ie, , Whether in region I or not). The supply amount of the secondary air is N
Based on the output of the O _X selective reduction catalyst 9 inlet exhaust temperature sensor 16, NO _X selective reduction catalyst 9 inlet temperature is feedback controlled by the ECU20 to be less than t _C.
Thus, when the reproduction operation of the NO _X absorbent 5 at the exhaust gas temperature is high is performed, NO _X selective reduction catalyst 9 even when _the NO _X absorbent 5 outlet exhaust temperature is increased by reproducing operations using upper limit temperature Since the temperature is kept below, deterioration is not accelerated.

[0045]

Exhaust purification apparatus of the present invention exhibits, NO _X absorbent downstream the NO _X and HC and the selectively degrades the NO _X by reacting _the NO _X selective reducing catalyst in the exhaust in lean exhaust conditions with placing, NO _X when _the NO _X absorbent regenerating operation
Maintain lean air-fuel ratio of exhaust gas flowing into the selective reduction catalyst
By you so that, in _the NO _X absorbent regenerating operation Initial
Generated unpurified NO _X and NO _X absorbent during regeneration operation
By _the NO _X selective reducing catalyst both with ammonia to raw
It becomes possible to purify. Therefore, according to the present invention,
If, expanding the range of playing conditions of the NO _X absorbent, effect in a short period of time
It is possible to perform efficient reproduction.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an embodiment of the present invention.

FIG. 2 is a diagram showing a reproduction operation start condition in the embodiment of FIG. 1;

FIG. 3 is a flowchart showing a determination of a reproduction condition in the embodiment of FIG. 1;

FIG. 4 is a view for explaining another embodiment of the present invention different from FIG. 1;

FIG. 5 is a view similar to FIG. 2, showing a reproduction operation start condition of the embodiment of FIG. 4;

FIG. 6 is a diagram illustrating the absorption and release action of the NO _X absorbent of the present invention.

[Explanation of symbols]

1 ... exhaust pipe 2 ... exhaust switching valve 3a, 3b ... branch exhaust passage 5 ... NO _X absorbent 6 ... exhaust gas temperature sensor 7 ... exhaust oxygen concentration sensor 9 ... NO _X selective reducing catalyst 11 ... reducing agent supply device 15 ... secondary Air supply device 20 ... Engine control circuit (ECU)

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-106826 (JP, A) JP-A-4-117136 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) F01N 3/24 F01N 3/08 F01N 3/18 F01N 3/20 F01N 3/28 301

Claims (1)

(57) [Claims] In an exhaust passage of claim 1 an internal combustion engine capable of performing combustion of the lean air-fuel ratio, the air-fuel ratio of the inflowing exhaust gas is the oxygen concentration of the inflowing exhaust absorbs NO _X when the lean absorbed when reduced NO by placing _the NO _X absorbent to release the _X to absorb NO _X in the exhaust gas, the causes subsequent _the NO _X absorbent NO _X which the exhaust air-fuel ratio flowing absorbed in the rich released from _the NO _X absorbent in the exhaust purification system of an internal combustion engine to reduce and purify NO _X, the NO _X in the downstream side of the absorber NO _X in the exhaust gas in the lean exhaust air-fuel ratio conditions may selectively reacting with a reducing agent _the NO _X selective reducing catalyst And the N
The exhaust air-fuel ratio flowing into the O _X absorbent in the rich absorbing
The NO _X in the _the NO _X selective reducing catalyst when to release the
Means for maintaining the air-fuel ratio of the inflowing exhaust gas lean .