JPH07259541A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

(57) [Summary] [Objective] During the regeneration operation, the amount of the reducing agent supplied to the NO _x absorbent is appropriately controlled to efficiently regenerate the NO _x absorbent. [Structure] The exhaust passage 3 of the internal combustion engine 1 is branched into two N
O _X absorbent 5a, and 5b are connected in parallel. The exhaust flow is switched by the exhaust switching valves 2 and 22, and one of the NO _x
NO that reduces the flow rate of exhaust gas passing through the absorbent and reduces the flow rate of exhaust gas from the reducing agent supply nozzles 12a and 12b.
Regeneration is performed by supplying a reducing agent to the _X absorbent. Each N
O _X absorbent downstream oxygen concentration sensor 7a, and 7b, the oxidation catalyst 101a downstream thereof, and 101b provided further controlled based on the reducing agent supply amount to the output of the oxygen concentration sensor at the time of reproduction. During the regeneration, the oxygen component entering from the other branch passage is consumed by the oxidation catalyst and does not reach the oxygen concentration sensor, so that the reducing agent supply amount can be accurately controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, and more particularly, to exhaust NO _{x in} an exhaust gas of an internal combustion engine that burns at a lean air-fuel ratio, such as a diesel engine or a gasoline engine that performs lean combustion. The present invention relates to an exhaust purification device that can be effectively removed.

[0002]

2. Description of the Related Art An example of this type of exhaust emission control device is disclosed in Japanese Patent Application Laid-Open No. 62-106826. The apparatus of the publication, the absorbent which absorbs NO _X in the presence of oxygen in an exhaust passage of a diesel engine (catalyst) connected two parallel, NO in the exhaust gas led to the exhaust to one of the NO _X absorbent Absorb _X. Further, when the NO _X absorbing capacity of the absorber NO _X absorption of one of the NO _X absorbent above increases is saturated, the exhaust switching valve, the saturation led to a flow of exhaust other of the NO _X absorbent while blocking the influx of exhaust into _the NO _X absorbent, it supplies a reducing agent to this _the NO _X absorbent. Thus, the saturated _the NO _X absorbent NO _X is released, the released NO _X is in the (herein that is reduced and purified by the reducing agent, the reduction and purification and NO _X emission from this _the NO _X absorbent The operation is called "NO _x absorbent regeneration operation". That is, in the device of the publication, the regeneration operation of the two NO _x absorbents is alternately performed.

[0003] In the apparatus of JP-A Sho 62-106826, the amount of reducing agent supplied to the NO _X absorbent during the regenerating operation of the NO _X absorbent is a fixed amount, NO in _the NO _X absorbent
_No control is made according to the _X absorption state. For this reason,
There is a problem that regeneration of the NO _X absorbent becomes insufficient due to insufficient supply of the reducing agent, or the reducing agent not used for regeneration is released into the atmosphere due to excessive supply of the reducing agent. .

This problem is caused by the NO _x absorbent regeneration operation.
This can be solved by controlling the reducing agent supply amount so that the air-fuel ratio of the exhaust gas that has passed through the NO _X absorbent becomes close to the stoichiometric air-fuel ratio. That is, when the reducing agent supply amount to _the NO _X absorbent is insufficient, it is impossible to consume all the oxygen in the exhaust gas flowing into _the NO _X absorbent, the air-fuel ratio of the exhaust gas passing through the _the NO _X absorbent Is lean. Also, N
When the amount of the reducing agent supplied to the O _X absorbent is excessive, a part of the supplied reducing agent is not consumed in the regeneration operation and flows out to the downstream side. Therefore, the air-fuel ratio of the exhaust gas passing through the NO _X absorbent is increased. Will be rich. On the other hand, if the amount of the reducing agent supplied to the NO _x absorbent is appropriate, the oxygen in the exhaust is completely consumed by the reducing agent, and the supplied reducing agent is the oxygen consumption in the exhaust, air-fuel ratio of the exhaust gas passing through the _the NO _X absorbent to be completely consumed in the reduction and purification of the released NO _X is because become near the stoichiometric air-fuel ratio.

For this reason, for example, an oxygen concentration sensor for detecting the oxygen concentration in the exhaust gas is provided on the NO _x absorbent outlet side, and the oxygen concentration of the exhaust gas passing through the NO _x absorbent is determined based on the output of this oxygen concentration sensor. By controlling the reducing agent supply amount from the reducing agent supply device so that it becomes a value near the theoretical air-fuel ratio equivalent value, it becomes possible to appropriately control the reducing agent supply amount.

[0006]

However, when the oxygen concentration sensor is provided on the NO _x absorbent outlet side to control the reducing agent supply amount as described above, a problem may occur. Hereinafter, this problem will be described with reference to FIG.
FIG. 6 is a diagram showing a configuration in the case where an oxygen concentration sensor is provided at the NO _x absorbent outlet as described above, and the reducing agent supply amount is controlled based on the output of the oxygen concentration sensor. In FIG. 6, reference numeral 1 is an internal combustion engine that performs lean air-fuel ratio operation, and 3 is an exhaust passage of the engine 1. The exhaust passage 3 branches into two exhaust passages 3a and 3b on the downstream side, and an exhaust switching valve 2 is provided at a branch point of the branch passages 3a and 3b. By switching the exhaust switching valve 2, the exhaust passage 3a or Most of the engine exhaust can be guided to one side of 3b.

In addition, in each of the branch passages 3a and 3b
Is the NO in the exhaust gas when the inflowing oxygen concentration is lean._X
And absorbs when the oxygen concentration of the inflowing exhaust gas decreases.
NO _XReleases NO_XProvided with absorbents 5a, 5b
ing. In FIG. 6, what is indicated by 12a and 12b is
NO during playback operation_XSupply a reducing agent to the absorbents 5a, 5b
Reducing agent supply nozzle, 7a and 7b are branch passages
3a and 3b NO_XProvided on the outlet side of the absorbents 5a, 5b
It is an oxygen concentration sensor. Furthermore, the branch passages 3a, 3b
Are merged again on the downstream side of the oxygen concentration sensors 7a and 7b.
At the junction of the branch passages 3a and 3b, the above-mentioned exhaust switching valve
A downstream exhaust switching valve 22 similar to that of No. 2 is provided.

In the configuration shown in FIG. 6, when regenerating one of the NO _x absorbents (for example, the NO _x absorbent 5a), the exhaust switching valves 2 and 22 are switched to the positions shown by the solid line in the figure. Most of the exhaust gas of the engine 1 is made to flow to the NO _x absorbent 5b side,
Make the absorption of NO _X in the exhaust gas in _the NO _X absorbent 5b, NO
The flow rate of the exhaust gas flowing into the _X absorbent 5a is significantly reduced.
Also, to reproduce this time to supply the reducing agent from the reducing agent feed nozzle 12a in _the NO _X absorbent 5a _the NO _X absorbent 5a. Further, other of the NO _X absorbent _(the NO _X absorbent 5b
When the NO _x absorption amount of the NO _x absorption capacity increases and the NO _x absorption capacity approaches saturation, the exhaust switching valves 2 and 22 are switched to the positions shown by the dotted lines in FIG. 6 to regenerate the NO _x absorbent (NO _x absorbent). 5a) absorbs NO _x in the exhaust gas. Further, at this time, the reducing agent is supplied from the reducing agent supply nozzle 12b to the NO _x absorbent 5
b to regenerate the NO _x absorbent 5b. That, _the NO _X absorbent 5a, 5b in the configuration of FIG. 6 performs alternately reproduced, during one of the playback performs NO _X absorbent in the exhaust gas in the other of the NO _X absorbent.

However, in the configuration as shown in FIG.
_X absorbent 5a, in order to proper amount of reducing agent supplied to 5b, the reducing agent supply nozzle 12a, the _the NO _X absorbent 5a reducing agent supply amount from 12b, 5b outlet side of the oxygen concentration sensor 7a, 7b If feedback control is performed based on the output, there is a problem that the amount of the reducing agent supplied is generally excessive and the amount of unused reducing agent released to the atmosphere increases.

As a result of examination by the applicants of the present application, this problem is
When regenerating the O _X absorbent, the oxygen concentration detected by the oxygen concentration sensor provided at the NO _X absorbent outlet on the regeneration side is NO _X.
It has been found to occur to indicate an oxygen concentration higher than the oxygen concentration of the exhaust gas that has passed through the absorbent. in this way,
The reason why the oxygen concentration sensor on the regeneration side indicates an oxygen concentration higher than the oxygen concentration of the exhaust gas passing through the NO _X absorbent is considered to be as follows.

[0011] that is, NO in order at the time of _X absorbent regeneration to reduce the amount of reducing agent to consume oxygen component in the exhaust gas, the flow rate of the exhaust gas flowing to _the NO _X absorbent side for reproducing the exhaust switching valve 2 , 22 greatly reduces the amount. Therefore, the exhaust flow velocity is significantly reduced in the branch passage on the NO _x absorbent side during regeneration. Further, the supply of the reducing agent makes the exhaust oxygen concentration in this branch passage extremely low. Thus, both the branch passages 3a, results a difference occurs in the oxygen concentration of exhaust in 3b, the exhaust switching valve 22 portion of the merging portion, NO _X absorbent side of the oxygen concentration in the absorbing high side (NO _X 2) oxygen contained in the exhaust gas moves toward the side where the oxygen concentration is low (the NO _x absorbent side during regeneration) by diffusion. On the other hand, on the NO _x absorbent side during regeneration, the exhaust flow velocity is significantly reduced as described above. Therefore, the oxygen that has entered through the exhaust switching valve 22 diffuses in the branch passage on the NO _x absorbent side during regeneration and flows backward, and finally reaches the oxygen concentration sensor position. 7 instructions are actually N
The phenomenon occurs in which the concentration of oxygen in the exhaust gas that has passed through the _Ox absorbent becomes higher.

[0012] Figure 7 is a result of measuring the oxygen concentration of the NO _X absorbent _(the NO _X absorbent 5a) side branch passage 3a each portion actually inserted an oxygen concentration sensor at each position in the playback 6 Is shown. In FIG. 7, section I shows the oxygen concentration in the section from the exhaust switching valve 2 to the NO _x absorbent 5a inlet, and section II shows the NO concentration from the NO _x absorbent 5a inlet to the outlet.
Oxygen concentration in the section inside the _X absorbent, and section III is N
The oxygen concentration in the section from O _X absorbent 5a outlet to the downstream side exhaust switching valve 22 respectively show (see FIG. 6). Figure 7
As shown in, the supplied reducing agent in the interval I is still oxygen concentration in the exhaust gas because it does not react with oxygen in the exhaust is high, by the catalytic action of the NO _X absorbent in the section II in the exhaust and reducing agent Since oxygen reacts and oxygen is consumed, the oxygen concentration drops to about zero. However, at the end of the section II (near the end surface on the downstream side of the NO _X absorbent 5a), the oxygen concentration starts to rise again, and in the section III, the downstream side exhaust switching valve 2
The oxygen concentration increases as it approaches 2. That is, it is understood that the oxygen concentration in the exhaust gas tends to increase on the downstream side of the NO _x absorbent as it approaches the exhaust gas switching valve 22 due to the diffusion of oxygen molecules entering through the exhaust gas switching valve 22. In FIG. 7, the dotted line indicates the branch passage 3
The results when the exhaust gas is switched using only the upstream exhaust gas switching valve 2 without providing the downstream exhaust gas switching valve 22 at the confluence of a and 3b are shown. In this case, the amount of oxygen entering the order no downstream exhaust switching valve 22 is further increased, the oxygen concentration in _the NO _X absorbent downstream side is further increased. Also, although not shown, it has been found that the same reduction occurs due to the diffusion of oxygen from the atmosphere side even when the branch passages 3a and 3b are individually opened to the atmosphere without being joined.

Originally, it is necessary to control the amount of the reducing agent supplied to the NO _x absorbent based on the oxygen concentration near the center of section II in FIG. However, in the configuration as shown in FIG. 6, since the reducing agent supply amount is controlled based on the oxygen concentration in the section III portion higher than that in the section II, the reducing agent supply amount becomes excessive. Occurs. This problem,
The problem can be solved by inserting an oxygen concentration sensor into the NO _x absorbent so that the oxygen concentration in section II in FIG. 7 is accurately detected. However, since the NO _X absorbent becomes extremely hot during engine operation, inserting the oxygen concentration sensor into the NO _X absorbent causes a problem of sensor durability. Also, NO
Inserting the sensor into the _X absorbent is not preferable to produce a problem such as decrease in mechanical strength of itself _the NO _X absorbent.

[0014] The present invention has been made in view of the above problems, without inserting the sensor into _the NO _X absorbent, the oxygen concentration sensor disposed in _the NO _X absorbent downstream oxygen concentration of exhaust passing through the _the NO _X absorbent It is an object of the present invention to provide means for making it possible to accurately detect.

[0015]

According to the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine which operates in a lean air-fuel ratio, wherein two branch passages connected in parallel to each other are provided in an exhaust passage of the internal combustion engine, the disposed on each of the branch passages, the air-fuel ratio of the exhaust flowing absorbs NO _X in the exhaust gas when the lean and _the NO _X absorbent to the exhaust oxygen concentration to release NO _X absorbed when reduced An exhaust switching valve capable of individually reducing the exhaust flow rate flowing into the NO _x absorbent, and a reducing agent supply device capable of individually supplying the reducing agent to each of the NO _x absorbent. , after the and a oxygen concentration sensor for detecting oxygen concentration of the exhaust gas in the downstream side branch passages of each of the NO _X absorbent, to absorb NO _X in the exhaust gas to one of the _the NO _X absorbent, the exhaust the one of the NO _X absorption by switching valve Reducing the flow rate of the exhaust gas flowing to the agent, by supplying a reducing agent to one of the NO _X absorbent said from the reducing agent supply device based on the output of the oxygen concentration sensor,
The operation of reducing and purifying the released NO _X with the release of NO _X absorbed from one of the NO _X absorbent said, in the exhaust purification apparatus for an internal combustion engine which performs for said alternating _the NO _X absorbent, the branch passage downstream An exhaust gas purifying apparatus for an internal combustion engine is provided, which is provided with an oxygen consuming means for consuming oxygen flowing back to the oxygen concentration sensor.

[0016]

When the NO _x absorbent is regenerated, oxygen flowing back from the downstream side toward the oxygen concentration sensor due to diffusion is consumed by the oxygen consuming means. Therefore, oxygen flowing backward from the downstream side is prevented from reaching the oxygen concentration sensor,
_The NO _X absorbent oxygen concentration of the exhaust gas oxygen concentration sensor near the time of reproduction, _the NO _X absorbent oxygen concentration of exhaust passing through the (7, section II central portion) substantially equal to the oxygen concentration sensor output NO _X It accurately represents the oxygen concentration of the exhaust gas that has passed through the absorbent.

[0017]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows the configuration of an embodiment of the exhaust emission control device of the present invention. In FIG. 1, the same reference numerals as those in FIG.
Shows the same element as. In FIG. 1, reference numeral 1 denotes an internal combustion engine capable of performing lean air-fuel ratio combustion, such as a diesel engine or a lean-burn gasoline engine, and 3 denotes an exhaust passage of the internal combustion engine 1. The exhaust passage 3 is provided with two branch passages 3a and 3b. As will be described later, the passages 3a and 3b absorb NO _X in the exhaust gas when the inflowing exhaust air-fuel ratio is lean, so that the exhaust gas is exhausted. The NO _x absorbents 5a and 5b, which release the absorbed NO _x when the oxygen concentration of the NO _x is reduced, are connected respectively.

Further, an exhaust switching valve 2 is provided at a branch portion of the passages 3a and 3b of the exhaust passage 3, and any one of the exhaust passages 3a and 3b is closed to a predetermined opening degree to exhaust passages 3a and 3b.
The exhaust is distributed to. For example, when the exhaust switching valve 2 is switched to the position shown by the solid line in FIG. 1, most of the exhaust gas flows into the side of the branch passage 3b, and the flow rate of the exhaust gas flowing into the side of the branch passage 3a is reduced. Further, when the exhaust switching valve 2 is switched to the position shown by the dotted line in FIG. 1, most of the exhaust gas flows into the branch passage 3a side, and the flow rate of exhaust gas flowing into the branch passage 3b side is reduced. Reference numeral 2a in the drawing denotes an actuator of an appropriate type such as a negative pressure actuator for driving the switching valve 2 by a control signal from an engine control circuit (ECU) 20 to be described later to take a predetermined switching position. is there.

Further, the branch passages 3a and 3b are merged again on the downstream side of the NO _x absorbents 5a and 5b, and an exhaust switching valve 22 similar to the exhaust switching valve 2 and an actuator 22a are provided at this confluent portion. Has been. The exhaust gas switching valve 22 operates in conjunction with the exhaust gas switching valve 2 to prevent the exhaust gas from the other branch passage from flowing back to the branch passage on the side of the NO _X absorbent being regenerated.

Further, on the upstream side of the NO _x absorbents 5a, 5b in the branch passages 3a, 3b, a reducing agent supply nozzle for supplying the reducing agent from the reducing agent supply device 11 described later to the NO _x absorbents 5a, 5b, 12a respectively. , 12b are connected. Further, 7a and 7b in FIG. 1 respectively indicate the branch passages 3
a is an oxygen concentration sensor disposed on the downstream side of the NO _x absorbents 5a and 5b. Oxygen concentration sensors 7a and 7b are N
O _X absorbent 5a, it detects the oxygen concentration in the exhaust gas passing through the 5b. In this example, as described later, the NO _x absorbent 5 was used.
N being regenerated from the reducing agent supply device 11 during regeneration of a and b.
O _X absorbent 5a, the reducing agent supply amount supplied to 5b, the oxygen concentration sensor 7a, is controlled in accordance with the output of 7b.

Further, in this embodiment, the oxidation catalysts 101a and 101b as oxygen consuming means are provided on the downstream side of the oxygen concentration sensors 7a and 7b in the respective branch passages 3a and 3b. Reference numeral 20 in the drawing denotes a control circuit (ECU) of the engine 1. ECU20 is CPU, RAM, RO
It comprises a well-known digital computer in which M, an input port, and an output port are connected to each other by a bidirectional bus, and performs basic control such as fuel injection amount control of the engine. Further, in the present embodiment, the ECU 20 further controls the actuator 2 via a drive circuit (not shown), a negative pressure control valve, etc.
a and 22a are driven to control the switching position of the exhaust gas switching valves 2 and 22, and the reducing agent supply amount from the reducing agent supply device 11 is controlled based on the outputs of the oxygen concentration sensors 7a and 7b. For these controls, the oxygen concentration signals from the oxygen concentration sensors 7a and 7b are input to the input port of the ECU 20, and signals such as the engine speed and the engine intake air amount are input from sensors not shown. There is.

The oxidation catalysts 101a and 101b are, for example, a honeycomb-shaped metal carrier carrying an oxidation catalyst such as platinum Pt or palladium, and as will be described later, the branch passages 3a and 3b are passed through the exhaust switching valve 22. By reacting the oxygen flowing back from the downstream side with the reducing agent in the exhaust gas passing through the oxidation catalyst, the oxygen acts as an oxygen consuming means for consuming the oxygen flowing backward from the downstream side.

The reducing agent supply device 11 controls the flow rate of the reducing agent supplied from the reducing agent supply source 13 to the reducing agent supply nozzles 12a and 12b. Adjusting control valves 14a, 14b and
Check valves 15a and 15b for preventing exhaust gas backflow are provided between the nozzles 12a and 12b and the control valves 14a and 14b. The control valves 14a and 14b are used for NO _X described later.
When absorbent 5a, 5b of the reproduction operation, taking a predetermined opening in response to a control signal of the ECU 20, and supplies the amount of reducing agent in accordance with the degree of opening _the NO _X absorbent 5a, to 5b.

[0024] _the NO _X absorbent 5a, 5b of the NO _X emission, the reducing agent used for reduction operations (playback operations), as long as it generates a reduction component and the hydrocarbon component such as carbon monoxide in the exhaust gas Of course, a gas such as hydrogen or carbon monoxide, a liquid or gaseous hydrocarbon such as propane, propylene or butane, or a liquid fuel such as gasoline, light oil or kerosene can be used.

As the NO _x absorbents 5a and 5b, for example, a carrier such as alumina is used, and on this carrier, for example, potassium metal such as potassium K, sodium Na, lithium Li, cesium Cs, barium Ba, calcium Ca, or the like. At least one selected from rare earths such as alkaline earth, lanthanum La and yttrium Y, and a noble metal such as platinum Pt are supported. This _the NO _X absorbent 5a, 5
b absorbs NO _X in the case the air-fuel ratio of the exhaust gas flowing is lean and releases the NO _X when the oxygen concentration is reduced NO _X
It absorbs and releases.

The above-mentioned exhaust air-fuel ratio is N in this case.
O _X absorbent 5a, upstream of the exhaust passage and the engine combustion chamber 5b, shall mean the sum of the respective supply air amount in the intake passage or the like, the ratio of the sum of the fuel and a reducing agent.
Therefore, NO _X absorbent 5a, the fuel in the upstream side exhaust passage 5b, the exhaust air-fuel ratio in the case of the reducing agent or air is not supplied is equal to the operating air-fuel ratio of the engine (air-fuel ratio in the combustion in the engine combustion chamber).

In this embodiment, since the engine that burns lean air-fuel ratio is used, the exhaust air-fuel ratio during normal operation is lean, and the NO _x absorbents 5a, 5b are NO in the exhaust gas.
Absorb _X. Further, when the reducing agent is introduced into the exhaust gas from the reducing agent supply device 11 and the oxygen concentration decreases, the NO _x absorbents 5a and 5b release the absorbed reducing agent. There are some points where the detailed mechanism of this absorption / release action is not clear. However, it is considered that this absorbing / releasing action is performed by the mechanism shown in FIG. Next, regarding this mechanism, platinum Pt and barium B are deposited on the carrier.
The case of supporting a will be described as an example, but the same mechanism can be obtained by using other noble metal, alkali metal, alkaline earth, or rare earth.

That is, the inflow exhaust becomes considerably lean.
And the oxygen concentration in the exhaust gas increased significantly, as shown in Fig. 5 (A).
As these oxygen O₂Is O₂ ^-Or O^2-In the form of
It adheres to the surface of platinum Pt. On the other hand, the NO in the exhaust gas is
This O on the surface of platinum Pt₂ ^-Or O^2-Reacts with N
O₂Becomes (2NO + O₂→ 2 NO₂ ). Then generated
NO₂Part of the inside of the absorbent while being oxidized on platinum Pt
While being absorbed by and bound to barium oxide BaO,
As shown in (A), nitrate ion NO₃ ^-Absorbent in the form of
Diffuse in. NO in this way_XIs NO_XAbsorbent 5
It is absorbed in a and 5b.

Therefore, NO ₂ is produced on the surface of platinum Pt as long as the oxygen concentration in the inflowing exhaust gas is high, and NO ₂ is absorbed in the absorbent and nitrate ion NO ₃ unless the NO _X absorption capacity of the absorbent is saturated. ^- is generated. In contrast the oxygen concentration decreases and the amount of NO ₂ is reduced by reaction backward in the inflowing exhaust gas (NO ₃ ^- → NO ₂₎ proceeds to thus of the absorbent and nitrate ions NO ₃ ^- is NO ₂ Is released from the absorbent in the form of. That is, the oxygen concentration when decreases _the NO _X absorbent 5a of the inflowing exhaust, NO _X is to be released from 5b.

On the other hand, when reducing components such as HC and CO are present in the inflowing exhaust gas, these components are 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 absorbents 5a, 5b due to the decrease of the oxygen concentration in the exhaust gas is reduced by reacting with HC and CO as shown in FIG. 5 (B). In this way, NO _{2 is} deposited on the surface of platinum Pt.
When NO is absent, the absorbent releases NO _{2 one} after another.

That is, HC and CO in the inflowing exhaust gas are first reacted with O ₂ ⁻ or O ²⁻ on platinum Pt immediately to be oxidized, and then O ₂ ⁻ or O ²⁻ on platinum Pt are consumed. the HC, NO _X flowing into NO _X released from the absorbent by CO, and with the exhaust gas is reduced even yet HC, any remaining CO is. In this embodiment, by operating the exhaust switching valves 2 and 22, the NO _x absorbents 5a and 5a are alternated.
It absorbs and releases bNO _x . That is, in this embodiment, by supplying a large part of the exhaust to one of the NO _X absorbent (eg 5a) to absorb NO _X by the operation of the exhaust switching valve 2, 22. Further, when the NO _X absorption of the NO _X absorbent 5a performs predetermined time NO _X absorption preset come increases, the exhaust switching the exhaust switching valve 2, 22 to the other of the NO _X absorbent 5b flow, NO with _X to reduce the flow rate of the exhaust gas flowing into the absorbent 5a, _the NO _X absorbent 5a by supplying reducing agent from the reducing agent feed nozzle 12a in _the NO _X absorbent 5a
Play. In addition, after a predetermined time has elapsed after switching, NO
If NO _X absorption amount of _X absorbent 5b comes increased performs switching of the exhaust switching valve 2, 22 again, resume the NO _X absorbent by _the NO _X absorbent 5a flowing exhaust into _the NO _X absorbent 5a side At the same time, the NO _x absorbent 5b is regenerated.

In this embodiment, in order to reduce the amount of reducing agent used to regenerate the NO _x absorbents 5a and 5b, the exhaust switching valves 2 and 22 are switched to the position where the NO _x absorbent is regenerated. The amount of reducing agent required to consume the oxygen in the exhaust is reduced and the reduction is performed based on the output of the oxygen concentration sensor provided on the outlet side of the NO _X absorbent during regeneration. The amount of reducing agent supplied from the agent supply device 11 is controlled so that an appropriate amount of reducing agent is supplied to the NO _x absorbent.

FIG. 2 shows the NO of this embodiment._XAbsorbent 5a, 5
It is a flowchart which shows the reproduction operation control of b. Book roux
Chin is set by the engine control circuit (ECU) 20 at a predetermined time
It is executed every interval. The routine starts in FIG.
Then, in step 201, it is currently NO._XRunning absorption
NO_XWhether or not the conditions for executing the absorbent regeneration operation are satisfied
Is determined. Where NO_XAbsorbent regeneration operation execution section
The matter is NO_XAbsorption time (previous NO _XChange the absorbent
(Elapsed time since) exceeds the specified time,
The engine exhaust temperature is above a certain value,
If any of the above
The process proceeds to step 221, and the time counter T
After setting the value of the switching flag F of the exhaust switching valve to zero,
End the routine. NO in above_XAbsorbent NO_Xabsorption
The time is judged as NO_XAbsorbent NO _XAbsorption
NO only when is increased to some extent_XRegenerate the absorbent
This is to avoid frequent playback operations.
The exhaust temperature is judged by NO when the exhaust temperature is low.
_XSince the temperature of the absorbent itself is also low, it is necessary to supply the reducing agent.
NO when paid_XNO from absorbent_XRelease rate is low
It is not possible to perform efficient playback operation.
It

Therefore, in this embodiment, the reproduction operation from step 203 to step 219 is executed only when both of the above conditions are satisfied in step 201.
That is, when the NO _X absorbent regeneration condition is satisfied in step 201, it is determined in step 203 whether or not the value of the switching flag F of the exhaust switching valve is set to 1,
When F ≠ 1, in step 205, the exhaust switching valves 2 and 22
Is switched to reduce the flow rate of the exhaust gas flowing into the branch passage on the NO _x absorbent side where the regeneration condition is satisfied to a predetermined amount, and then the value of the flag F is set to 1 in step 207, and then the process proceeds to step 209. If F = 1 in step 203, the exhaust switching valve is not switched, and step 21 is directly executed.
Go to 1. The switching flag F is a flag used to switch the exhaust switching valves 2 and 22 only once after the regeneration condition of the NO _X absorbent is satisfied.

In step 209, the condition for ending the reproduction operation is satisfied.
Indicates whether or not it is standing. That is, step 2
In 09, the value of the clock counter T is the predetermined value T₀Or not
Judged, T ≧ T₀If so, the control of the reducing agent supply device 11
Set the set value R of the control valve 14a (or 14b) to zero
Then, the process proceeds to step 219, and the control of the reducing agent supply device 11 is performed.
It controls the opening of the valve 14a (or 14b).
In this case, since R = 0, both control valves 14a and 14b are
It is fully closed. ). Here, the predetermined value T₀Is NO _Xabsorption
The time required to regenerate the agent, NO_XType of absorbent,
The size is set in advance by experiments or the like. Sanawa
Then, at step 211, the elapsed time T after the start of the reproducing operation is
Is over the specified playback execution time, and
If the raw operation has been performed for a predetermined time, step 2
Control valve 14a (or 14b) of the reducing agent supply device 10
NO when fully closed_XStop the supply of reducing agent to the absorbent.

If it is determined in step 209 that the predetermined reproduction operation execution time has not elapsed, the routine proceeds to step 211.
Then, the oxygen concentration C in the exhaust gas is read from the oxygen concentration sensor (7a or 7b) arranged downstream of the NO _X absorbent on the side where the regeneration operation is performed, and in step 212, this oxygen concentration C is calculated theoretically. It is determined whether or not the oxygen concentration C _ST corresponding to the air-fuel ratio is equal to or higher (that is, the exhaust air-fuel ratio is lean).

In step 212, the exhaust air-fuel ratio detected by the oxygen concentration sensor (7a or 7b) is lean (C ≧
If it is C _ST ), step 213 is executed, the opening degree of the control valve (14a or 14b) of the reducing agent supply device is increased by a constant amount α, and the reducing agent supply amount is increased. Further, when the exhaust air-fuel ratio is rich in step 212, step 215 is executed, the control valve opening degree is reduced by a fixed amount β, and the reducing agent supply amount is reduced. Here, α and β are constant values set in advance. The values of α and β may be the same, but by setting the difference between the values of α and β, NO _x
The air-fuel ratio of the exhaust gas passing through the absorbent can be maintained on the rich side or lean side of the stoichiometric air-fuel ratio. For example α>
By setting β, the exhaust air-fuel ratio is maintained on the slightly rich side of the stoichiometric air-fuel ratio.

In step 217 after execution of the above operation, the value of the clock counter T is incremented by 1, and in step 219, step 213 or 215 is performed.
The control valve opening degree R set by is output to a drive circuit (not shown). By executing the above routine, during _the NO _X absorbent regeneration reducing agent supply amount as the downstream exhaust air-fuel ratio becomes the stoichiometric air-fuel ratio based on the oxygen concentration sensor output of _the NO _X absorbent downstream is feedback controlled. Therefore, the outputs of the oxygen concentration sensors 7a and 7b are the NO _x absorbent 5a and the output.
It is necessary to accurately detect the oxygen concentration in the exhaust gas passing through 5b.

As described above, in the present embodiment, the oxidation passages 3a and 3b on the downstream side of the oxygen concentration sensors 7a and 7b are provided with the oxidation catalysts 101a and 101b as oxygen consuming means. Therefore, NO _X oxygen during regeneration of the absorption medium through the downstream exhaust switching valve 22 oxygen from the branch passage side in the NO _X absorbent comes diffused, oxide catalyst 101a, 101b
Is supplied from the reducing agent supply device, and NO _x
It is consumed by reacting with the reducing agent passing through the absorbent and does not reach the oxygen concentration sensors 7a and 7b. Therefore, the oxygen concentration sensor 7a in the regenerating operation, the output of 7b becomes possible to accurately reflect the air-fuel ratio of the exhaust gas passing through the _the NO _X absorbent,
Oxygen concentration sensor 7a, by controlling the reducing agent supply amount on the basis of the output of 7b, it is possible to supply the appropriate amount of the reducing agent to _the NO _X absorbent.

Next, the configuration of another embodiment of the present invention is shown in FIG. In the embodiment of FIG. 1, the branch passages 3a and 3b between the oxygen concentration sensors 7a and 7b and the exhaust switching valve 22 are provided with the oxidation catalysts, respectively. However, as shown in FIG. The difference is that instead of providing an independent oxidation catalyst in each of the branch passages 3a and 3b, an exhaust switching valve 102 in which an oxidation catalyst is integrated and incorporated into an exhaust switching valve is used.

That is, the exhaust switching valve 102 of the present embodiment.
As shown in FIG. 3 (B), is a honeycomb-shaped metal carrier 102b having an oxidation catalyst supported in the center of a disc-shaped valve body 102a.
The exhaust gas that has passed through the NO _x absorbent flows through the catalyst carrier to the confluence portion. The invasion of oxygen into the branch passage on the NO _x absorbent side during regeneration is caused only by diffusion due to the concentration difference, and the amount thereof is relatively small. Therefore, even if the oxidation catalyst has a relatively small capacity, it can sufficiently prevent oxygen from reaching the oxygen concentration sensors 7a and 7b. Therefore, in the embodiment of FIG. 3, a small-capacity oxidation catalyst is integrally incorporated in the exhaust gas switching valve to prevent oxygen from reaching the oxygen concentration sensors 7a and 7b without hindering the operation of the switching valve. There is.
According to this embodiment, there is an advantage that the same effect as that of the embodiment of FIG. 1 can be achieved with a simple structure.

FIG. 4 is a diagram showing the configuration of still another embodiment of the present invention. In the embodiment of FIG. 1, oxygen concentration sensors are provided in the respective branch passages, but in the present embodiment, a single oxygen concentration sensor 107 is used for both NO _x absorbents 5.
The difference is that the reducing agent supply amount is controlled during regeneration of a and b. In FIG. 4, ports 103a and 103b are provided at the inlets of the NO _x absorbents 5a and 5b, and are connected to the inlet port of the switching valve 105 that works with the exhaust switching valve 2 via pipes 104a and 104b. . Further, the outlet port of the switching valve 105 has a small capacity NO _x absorbent 106,
Similarly, the small capacity oxidation catalyst 108 and the exhaust pump 109 are connected to an exhaust port 110 provided at the confluence of the branch passages 3a and 3b.

Further, in this embodiment, a single oxygen concentration sensor 107 is provided in the pipe connecting the NO _X absorbent 106 and the oxidation catalyst 108. Exhaust switching valve 22 on the downstream side is not provided in the present embodiment, switching of the exhaust for _the NO _X absorbent regeneration is carried out only by the upstream exhaust switching valve 2. In this embodiment, the switching valve 105 in conjunction with the upstream exhaust switching valve 2, of the NO _X absorbent side in the regenerating operation port (103a or 103b) _the NO _X absorbent 10
Connect to 6. As a result, a part of the mixture of the exhaust gas and the reducing agent flowing into the NO _x absorbent being regenerated is exhausted by the exhaust pump 10.
It is sucked by 9 and passes through the NO _X absorbent 106.

Therefore, the NO _x absorbent 106 is supplied with exhaust gas having the same reducing agent concentration as that supplied to the NO _x absorbent during regeneration, so that the oxygen concentration at the outlet of the NO _x absorbent 106 is , The exhaust oxygen concentration at the outlet of the NO _x absorbent during regeneration is approximately the same. Further, the oxygen diffused from the exhaust port 110 is consumed by the oxidation catalyst 108,
The oxygen concentration sensor 107 does not reach the oxygen concentration sensor 1
The oxygen concentration in the exhaust gas near 07 is approximately the same as the oxygen concentration in the exhaust gas that has passed through the NO _X absorbent during regeneration.

Therefore, based on the output of the oxygen concentration sensor 107, the same control as in FIG. 2 is performed, so that the reducing agent supply amount at the time of regeneration of the NO _x absorbent is appropriately controlled. According to this embodiment, there is an advantage that the number of oxygen concentration sensors used can be reduced and simple control can be performed. In each of the above-mentioned embodiments, the oxidation catalyst is used as the oxygen consuming means for preventing the oxygen diffused from the downstream side from reaching the oxygen concentration sensor. The oxygen consuming means is not limited, and any oxygen consuming means can be used as long as it can react oxygen with a reducing agent. For example, the oxygen consumption means, even with _the NO _X absorbent small volume instead of the oxidation catalyst it is possible to obtain the same effect.

[0046]

According to the present invention, the oxygen concentration sensor for detecting the exhaust oxygen concentration at the NO _x absorbent outlet is provided with the oxygen consuming means for preventing the oxygen diffused from the downstream side from reaching the oxygen concentration sensor. Thus, when alternately regenerating two NO _X absorbents connected in parallel to the exhaust passage, the reducing agent supply amount to the NO _X absorbent can be determined based on the oxygen concentration sensor output on the downstream side of the NO _X absorbent being regenerated. It is possible to control accurately,
It is possible to prevent insufficient regeneration due to insufficient supply of the reducing agent to the NO _X absorbent and release of unused reducing agent to the atmosphere due to excessive supply of the reducing agent.

[Brief description of drawings]

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

FIG. 2 is a flowchart showing an example of NO _X absorbent regeneration control in the embodiment of FIG.

FIG. 3 is a diagram illustrating a configuration of an embodiment different from FIG. 1 of the present invention.

FIG. 4 is a diagram illustrating the configuration of yet another embodiment of the present invention.

FIG. 5 is a diagram illustrating the NO _X absorption and release action of a NO _X absorbent.

FIG. 6 is a diagram illustrating a problem of the conventional technique.

FIG. 7 is a diagram illustrating a problem of the conventional technique.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2, 22 ... Exhaust gas switching valve 3 ... Exhaust passage 3a, 3b ... Branch passage 5a, 5b ... NO _X absorbent 7a, 7b ... Oxygen concentration sensor 11 ... Reductant supply device 20 ... Engine control circuit 101a, 101b ... Oxidation catalyst (oxygen consuming means)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location B01D 53/94 F01N 3/08 ZAB A 3/10 ZAB A 3/24 ZAB E F02D 35/00 301 G (72) Inventor Shinya Hirota 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor ▲ Yuji Sakaki Harajoji, Nagakute-cho, Aichi-gun, Aichi Prefecture In-house

Claims (1)

[Claims] 1. An exhaust gas purification apparatus for an internal combustion engine that performs lean air-fuel ratio operation, comprising two branch passages connected in parallel to an exhaust passage of the internal combustion engine, and the branch passages respectively arranged in the branch passages. NO air-fuel ratio of the exhaust flowing absorbs NO _X in the exhaust gas when the lean exhaust oxygen concentration to release NO _X absorbed when reduced
_{An X-} absorbent, an exhaust switching valve capable of individually reducing the exhaust flow rate flowing into the NO _X absorbent, and a reduction capable of individually supplying a reducing agent to each of the NO _X absorbent. a agent supply device, and a oxygen concentration sensor for detecting oxygen concentration of the exhaust gas in the downstream side branch passage of the respective of the NO _X absorbent was absorbed NO _X in the exhaust gas to one of the _the NO _X absorbent after, the exhaust by the switching valve to reduce the flow rate of the exhaust gas flowing into one of the NO _X absorbent said, supplying the reducing agent to one of the NO _X absorbent said from the reducing agent supply device on the basis of the output of said oxygen concentration sensor to, in the exhaust purification apparatus for an internal combustion engine for performing the above _the NO _X absorbent the released NO _X alternately operation to reduce and purify with the release of NO _X absorbed from one of the NO _X absorbent said, the branch passage Downstream to front An exhaust gas purification device for an internal combustion engine, characterized in that an oxygen consuming means for consuming backflowing oxygen is provided in the oxygen concentration sensor.