JPH06200740A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To provide an exhaust emission control device for an internal combustion engine allowing the regeneration of an NOx absorbent to be completed efficiently in a short time and the consumption of a reducing agent to be reduced. CONSTITUTION:The exhaust flow flowing into an NOx absorbent 5 is reduced by an exhaust shutter valve 6 provided at the exhaust passage 3 of an engine, and a reducing agent is supplied from a reducing agent feeder 11 to perform the regeneration of the NOx absorbent 5. Prior to the start of regeneration, the reducing agent is supplied while holding the opening of the exhaust shutter valve 6 larger than that at the time of regeneration. The combustion of the reducing agent on the NOx absorbent 5 is thereby accelerated to raise the temperature of the NOx absorbent 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more particularly, to an exhaust gas of an internal combustion engine that burns a lean air-fuel ratio, such as a diesel engine or a gasoline engine that burns a lean mixture. The present invention relates to an exhaust emission control device that can effectively remove NO _X.

[0002]

2. Description of the Related Art As an example of this type of exhaust emission control device,
For example, the one disclosed in JP-A-62-106826.
There is. The device of the publication is installed in the exhaust passage of a diesel engine.
NO in the presence of oxygen_XAbsorbing NO_XAbsorbent (catalyst)
NO in exhaust gas_XIs absorbed and NO of the absorbent is
_XBlocks the inflow of exhaust gas to the absorbent when the absorption efficiency decreases.
By turning off and supplying a gaseous reducing agent,
Et NO_XReleased and NO released_XReduce
It purifies. That is, in the device of the same publication,
The supplied reducing agent is NO_XBurns due to the catalytic action of the absorbent
Consumes oxygen in the exhaust gas and NO_XAbsorber atmosphere Oxygen concentration
The degree decreases. As a result, NO_XAbsorbed by the absorbent
NO_XIs released and purified by reducing agent
Is.

[0003]

Generally [0005], by lowering the oxygen concentration in the atmosphere of the NO _X absorbent to release NO _X absorbed from _the NO _X absorbent, to reduction purification (hereinafter, this NO
"Regeneration" of NO _X absorbent for the operation of _X release and reduction purification
It is known that the time required for regeneration is greatly influenced by the temperature of the NO _x absorbent. That is, N
Since the release rate of the NO _X from O _X absorbent increases as the temperature of the NO _X absorbent is high, making it possible to more releases NO _X in _the NO _X absorbent in a short time as performing the reproduction operation at high temperatures Therefore, the reproduction can be completed in a short time.

Further, the NO _X absorption capacity (NO _X absorption amount per unit time) after performing the regeneration operation becomes larger as the amount of NO _X remaining in the NO _X absorbent becomes larger.
This means that, when the regeneration operation is performed for the same time, the NO _x absorbent capacity of the NO _x absorbent after regeneration increases as the temperature of regeneration increases. Therefore, the regeneration of the NO _x absorbent is completed in a short time, and the NO _x after regeneration is completed.
N at the time of reproduction in order to increase the NO _X absorbing capacity of the _X absorbent
It is necessary to provide means for raising the _Ox absorbent temperature.
However, in the above-mentioned conventional technique, since the temperature of the NO _X absorbent is not taken into consideration, there is a possibility that the capacity of the NO _X absorbent after regeneration cannot be kept sufficiently high.

[0005] As a means for raising the temperature of the NO _X absorbent, for example, it may be provided an electric heater in the NO _X absorbent,
A method of heating the _the NO _X absorbent by burner combustion gases provided burner in an exhaust passage of the NO _X absorbent upstream, N
O _X absorbent increases the reducing agent supply amount supplied to and a method of raising the temperature of the NO _X absorbent by the combustion of _the NO _X absorbent on the reducing agent. However, the method using a heater or a burner is disadvantageous in view of complication of the structure and increase of the apparatus cost, and it is preferable to raise the temperature of the NO _x absorbent by burning the reducing agent.

On the other hand, when the temperature of the NO _x absorbent is raised by burning the reducing agent, if the amount of oxygen flowing into the NO _x absorbent does not exist sufficiently, the reducing agent supply amount is increased to N.
Temperature of the NO _X absorbent for O _X absorbent on the no sufficient combustion is not increased. For example, in the above-mentioned conventional technique, although the temperature of the NO _x absorbent can be expected to rise to some extent by the combustion of the reducing agent, the reducing agent is supplied with the exhaust gas flowing into the NO _x absorbent blocked. and for which, due to lack of oxygen amount to increase the reducing agent supply amount causes no combustion of only the temperature of the NO _X absorbent is sufficiently increased, NO _X
In some cases, sufficient temperature rise of the absorbent cannot be obtained. In such a case, an increase in the supply amount of reducing agent is not tied to the temperature rise of the NO _X absorbent, issues only consumed amount of the reducing agent is increased occurs.

The present invention solves the above problems when the temperature of the NO _x absorbent is raised by burning the reducing agent, and provides an exhaust gas purification device capable of efficiently regenerating the NO _x absorbent in a short time. It is intended to be provided.

[0008]

According to the present invention, a lean system is provided.
The exhaust gas flowing into the exhaust passage of the internal combustion engine that burns at the air-fuel ratio
NO when the air-fuel ratio is lean_XAbsorbs the inflowing exhaust acid
NO absorbed when the elementary concentration decreased_XReleases NO
_XThe absorbent is placed and the NO_Xabsorption
NO by reducing the amount of oxygen flowing into the agent_XAbsorbent and reducing agent
To supply NO_XNO absorbed from the absorbent
_XAnd the released NO_XReduction purification
In the exhaust gas purification device for an internal combustion engine, the reducing agent supply
Sometimes NO _XStart supply of reducing agent to the amount of oxygen flowing into the absorbent
A means to adjust the amount of oxygen that is relatively high in the beginning
Provided is an exhaust emission control device for an internal combustion engine characterized by having
To be done.

Furthermore, according to the present invention, in an exhaust passage of an internal combustion engine causing combustion of lean air-fuel ratio, when the air-fuel ratio of the inflowing exhaust absorbs NO _X when the lean, the oxygen concentration of the inflowing exhaust drops the absorbed NO _X arranged _the NO _X absorbent to be released to supply the reducing agent at a predetermined operating conditions, the NO _X absorbent by closing the shut-off valve provided on the exhaust inlet of the _the NO _X absorbent by, in the exhaust purification system for an internal combustion engine to reduce and purify the released was NO _X with the release of NO _X absorbed from _the NO _X absorbent, by performing the supply of the reducing agent the shut-off valve before fully closed An exhaust emission control device for an internal combustion engine is provided.

[0010]

[Action] exhaust gas purifying apparatus of the present invention, by supplying the reducing agent to the NO _X absorbent, when achieving an increase in the temperature of the NO _X absorbent by the combustion of the reducing agent, the supply amount of the reducing agent and _the NO _X absorbent N by adjusting both the amount of oxygen flowing into the
To promote combustion of O _X absorbent on the reducing agent, thereby achieving an efficient increase in temperature of the NO _X absorbent.

That is, when the NO _x absorbent is regenerated, the amount of inflowing oxygen is reduced and the reducing agent is supplied to the NO _x absorbent.
_{In the} exhaust gas purification device that regenerates the _X absorbent, the oxygen amount adjusting means adjusts the amount of oxygen flowing into the reducing agent supply start stage to be relatively large. N when starting the supply of reducing agent
Since the combustion of O _X absorbent is supplied a sufficient amount of oxygen is _the NO _X absorbent on the reducing agent is promoted, the temperature of the NO _X absorbent is rapidly increased. The oxygen amount adjusting means performs regeneration with the temperature of the NO _x absorbent rising in order to reduce the amount of oxygen flowing in thereafter.

Further, in the exhaust purification apparatus that supplies a reducing agent to _the NO _X absorbent by closing the shut-off valve, the shut-off valve before fully closed a sufficient amount by supplying a reducing agent to _the NO _X absorbent Since the reducing agent is supplied to the NO _X absorbent while oxygen is being supplied, and the combustion of the reducing agent is promoted, the temperature of the NO _X absorbent rapidly rises. Next, since the shutoff valve is fully closed in this state, regeneration is performed with the temperature of the NO _x absorbent rising.

[0013]

Embodiments of the present invention will be described below with reference to the accompanying drawings. 1, without interrupting the flow of exhaust gas into _the NO _X absorbent, the present invention is an exhaust gas purification apparatus for reproducing of the NO _X absorbent by performing the supply of the reducing agent in a state with reduced exhaust gas flow rate The example when applied is shown.

In FIG. 1, 1 is a diesel engine,
Reference numeral 2 indicates an engine intake pipe, and 3 indicates an engine exhaust pipe.
Further, a NO _x absorbent 5 described later is connected to the exhaust pipe 3. In this embodiment, an exhaust shutter valve 6 is provided upstream of the NO _x absorbent 5 in the exhaust pipe 3 of the engine. The shutter valve 6 is a butterfly valve type that has a low exhaust resistance when fully opened, and is kept fully open during normal operation of the engine. When the NO _x absorbent 5 releases and releases NO _x , the shutter valve 6 closes to a predetermined opening degree. When the valve is closed, the exhaust pipe 3 is throttled to reduce the amount of air taken into the engine. 7a
Is a diaphragm type negative pressure actuator that drives the shutter valve 6 to open and close. The negative pressure actuator 7a is connected to a negative pressure source such as a vacuum pump (not shown) via a negative pressure control valve 7b, and an electronic control unit (E
A signal from the CU) 20 drives the negative pressure control valve 7b to change the negative pressure supplied to the negative pressure actuator 7a, thereby controlling the opening degree of the shutter valve 6.

A reducing agent supply device 11 is arranged between the shutter valve 6 of the engine exhaust pipe 3 and the NO _x absorbent 5, and an exhaust temperature sensor 12 is provided downstream of the NO _x absorbent 5. And an oxygen concentration sensor 13 are arranged.
In this embodiment, the oxygen concentration sensor 13 uses a lean mixture chassen that outputs a signal that continuously changes according to the oxygen concentration in the exhaust gas.

The reducing agent supply device 11 is equipped with an injection valve 11a for injecting the reducing agent into the exhaust pipe 3 upstream of the NO _x absorbent 5, and exhausts the reducing agent at a predetermined flow rate according to an input signal from the ECU 20. Inject into tube 3. The reducing agent may be one that generates a reducing component such as hydrocarbon or carbon monoxide in the exhaust gas, hydrogen, gas such as carbon monoxide, liquid or gaseous hydrocarbon such as propane, propylene, butane, Liquid fuels such as gasoline, light oil, and kerosene can be used.

Reference numeral 20 in the drawing denotes an electronic control unit (ECU) of the engine 1. ECU20 is CP
The U, RAM, ROM, and the input port and the output port are connected to each other by a bidirectional bus, which is a well-known digital computer that performs basic control such as fuel injection amount control of the engine. The opening control of the shutter valve 6 and the reducing agent injection amount control from the reducing agent injection valve 11a are performed. ECU20 for controlling these
An exhaust temperature signal and an oxygen concentration signal in the exhaust gas are input to the input port 24 of the exhaust temperature sensor 12 and the oxygen concentration sensor 13, respectively, and signals such as an engine speed and an accelerator opening degree are illustrated. Not input from the sensor.

As the NO _x absorbent 5, a carrier such as alumina is used. On this carrier, for example, potassium K, sodium Na, lithium Li, cesium Cs, an alkaline metal such as barium Ba, calcium Ca or an alkaline earth is used. At least one selected from rare earths such as lanthanum La and yttrium Y, and a noble metal such as platinum Pt are supported. 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.

Incidentally, the above-mentioned exhaust air-fuel ratio means here 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 fuel, reducing agent or air is not supplied to the upstream side exhaust passage of, 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 the diesel engine is used, the exhaust air-fuel ratio during normal operation is lean, and the NO _X absorbent 5 absorbs NO _{X in} the exhaust. Further, when the reducing agent is introduced into the exhaust gas and the oxygen concentration is lowered by the operation described later, the NO _X absorbent 5 releases 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 and releasing action is performed by the mechanism shown in FIG. Next, this mechanism will be described by taking as an example the 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, when the inflow exhaust becomes considerably lean, the oxygen concentration in the inflow exhaust greatly increases, and as shown in FIG. 2 (A), these oxygen O ₂ are in the form of O ₂ ^{− and} are present on the surface of the platinum Pt. Adhere to. On the other hand, NO in the inflowing exhaust gas reacts with O ₂ ⁻ on the surface of platinum Pt to become NO ₂ (2NO + O ₂ → 2
NO ₂ ). Then, a part of the generated NO ₂ is oxidized on the platinum Pt and absorbed in the absorbent to be barium oxide Ba.
While bound to O, it diffuses into the absorbent in the form of nitrate ion NO ₃ ⁻ as shown in FIG. 2 (A). In this way, NO _X is absorbed in the NO _X absorbent 5.

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 as long as the NO _X absorption capacity of the absorbent is not saturated, and nitrate ion NO ₃ ^- 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 in the inflowing exhaust gas is released NO _X from _the NO _X absorbent 5 when lowered.

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.
^- reacts with the oxidized, reducing the oxygen concentration in the exhaust to consume oxygen in the exhaust. In addition, the NO ₂ released from the NO _X absorbent 5 due to the decrease in the oxygen concentration in the exhaust gas is shown in FIG.
As shown in, it is reduced by reacting with HC and CO. When NO ₂ is no longer present on the surface of platinum Pt in this manner, NO ₂ is released from the absorbent one after another.

That is, the HC and CO in the inflowing exhaust gas first react with O ₂ ⁻ on the platinum Pt immediately to be oxidized, and then even if the O ₂ ⁻ on the platinum Pt is consumed, HC and CO are still present.
The HC, NO _X discharged from the released NO _X and the engine from the absorbent by CO is reduced if remaining. Also, releasing action of the NO _X from _the NO _X absorbent described above, since the temperature of the NO _X absorbent becomes higher active,
By maintaining a high temperature of the NO _X absorbent during regeneration, it is possible to perform complete regeneration by completely released in a short time is absorbed in _the NO _X absorbent was NO _X.

[0025] In this embodiment, before playing of the NO _X absorbent, by supplying oxygen controlled amount of the reducing agent to the NO _X absorbent, catalyzed by the platinum Pt of the NO _X absorbent Promotes combustion of the reducing agent. Thus, the temperature of the NO _X absorbent increases by performing the combustion of the reducing agent before the regenerating operation of the NO _X absorbent can be reproduced of the NO _X absorbent at high temperatures.

Next, the operation of raising the temperature of the NO _X absorbent of this embodiment will be described. ECU20 in the present embodiment closes the shutter valve 6 at the time of reproduction start operation to a relatively large first predetermined opening degree, with keeping relatively large amount of oxygen flowing into _the NO _X absorbent 5, _the NO _X absorbent 5 The reducing agent supply amount from the reducing agent supply device 11 is adjusted based on the output of the oxygen concentration sensor 13 so that the exhaust air-fuel ratio at the outlet becomes an optimum value for the combustion of the reducing agent (for example, the stoichiometric air-fuel ratio). Control. This causes combustion of a suitable reducing agent on _the NO _X absorbent 5, the temperature of the NO _X absorbent 5 increases.
Further, when the output of the downstream side exhaust temperature sensor 12 detects that the temperature of the NO _X absorbent 5 has risen due to the combustion of the reducing agent, the ECU 20 controls the shutter valve 6 to be smaller than the first predetermined opening degree. The valve is closed to the second predetermined opening, and N
O _X absorbent flow rate of the exhaust gas flowing into the 5 (oxygen) it reduces, reducing the amount of reducing agent required for oxygen consumption in the exhaust gas during the regeneration of the NO _X absorbent.

FIG. 3 is a flow chart showing the temperature raising and regeneration operations of the NO _X absorbent. This routine is executed by the above-mentioned ECU 20 at regular intervals. When the routine starts in FIG. 3, in step 301, the exhaust temperature T _EX downstream of the NO _X absorbent 5 and the exhaust oxygen concentration R _OX.
Are exhaust temperature sensor 12 and oxygen concentration sensor 13, respectively.
Further, the accelerator opening A _CC of the engine and the engine speed N are read from the respective sensors.

Next, at step 303, it is judged if the conditions for executing the NO _X absorbent regeneration operation are satisfied. Here, the conditions for executing the regeneration of the NO _X absorbent are (1)
The accelerator opening A _CC is less than or equal to a predetermined value and the engine speed N is more than or equal to a predetermined value (that is, the engine is being braked), (2) A predetermined time has elapsed since the previous NO _x absorbent regeneration operation was performed. The above condition is satisfied, and only when both of the above conditions are satisfied, the operation of raising the temperature of the NO _x absorbent and the regeneration of step 305 and thereafter are performed.

Here, in order to regenerate the NO _X absorbent only during engine braking (the above condition (1)), it is necessary to close the intake shutter valve and reduce the intake air amount during regeneration as described later. Therefore, if the regeneration is performed during the normal operation, a torque shock occurs and the drivability deteriorates.
The playback execution condition is that a predetermined time has elapsed since the previous playback operation was executed (the above condition (2)), and the playback operation is performed only when it is truly necessary to avoid frequent playback operations. This is to do so.

Instead of the above condition (2), NO _X
The condition for executing the regeneration operation may be that the NO _X absorption amount of the absorbent is equal to or greater than a predetermined value. NO _x absorbent NO
_{As the X} absorption amount, for example, the NO _X emission amount from the engine per unit time is stored in advance in the ROM of the ECU 20 as a function of the engine load (accelerator opening), the engine speed, etc. seeking NO _X emissions from the opening and the rotation speed by the above function, NO _X in _the NO _X absorbent in the fixed time are multiplied by certain coefficients in this
It is calculated by adding up the amount of absorption.

When the reproduction operation execution condition is satisfied in step 303, it is determined in step 304 whether the flag F is set (= "1"). Flag F
Is a flag that is set when the exhaust temperature T _EX becomes equal to or higher than a predetermined value T0 as described later (step 312),
Once set, it is not reset (= "0") until the reproduction operation is stopped (step 327). Step 3
When F = “1” in 04, the process proceeds to step 313 and NO.
_When the regeneration operation of the _X absorbent 5 is continued and F ≠ “1”, it is determined in step 305 whether the exhaust temperature T _EX is equal to or higher than the predetermined value T ₀ . Here, T ₀ is the exhaust gas temperature corresponding to the temperature of the NO _X absorbent sufficient to completely perform the regeneration in a short time, and is determined in advance by actual measurement or the like.

If T _EX <T ₀ in step 305, the temperature of the NO _x absorbent has not risen sufficiently, so the steps of heating the NO _x absorbent in steps 307 to 311 are performed. That is, in step 307, the shutter valve 6 is closed to the first predetermined opening degree to throttle the inflow of exhaust gas to the NO _X absorbent. In step 309, the opening of the injection valve 11 a of the reducing agent supply device 11 is controlled to supply the NO _x absorbent 5 with an amount of the reducing agent according to the exhaust oxygen concentration R _ox on the downstream side of the NO _x absorbent 5. Here, the reducing agent supply amount is feedback-controlled so that the downstream oxygen concentration R _OX becomes a predetermined value (for example, a theoretical air-fuel ratio equivalent value). Also, the shutter valve 6
At the above-mentioned first predetermined opening degree of NO, a sufficient amount of exhaust gas (oxygen) is supplied to the NO _x absorbent, and the exhaust gas flow rate becomes excessively large.
It is set within the range where the _X absorbent is not cooled. After the above operation is completed, in step 311, a counter C described later is executed.
Is cleared and the routine ends.

If T _EX ≧ T ₀ in step 305, the exhaust gas temperature is sufficiently high, or it is already in step 30.
Heating operation of the NO _X absorbent 7-311 is performed NO _X
Since the temperature of the absorbent has risen sufficiently, step 31
2-319 NO _x absorbent regeneration operation. That is, in step 312, the flag F is set, in step 313, the counter C representing the duration of the reproducing operation is incremented by 1, and in step 315, it is determined whether or not the counter C is equal to or greater than a predetermined value C ₀ . Here, the predetermined value C ₀ is the number of times of execution of the routine corresponding to the time sufficient to complete the regeneration of the NO _X absorbent. Also, step 3
Even if the exhaust gas temperature falls below the predetermined value T ₀ during execution of the regeneration operation due to the flag F being set in 12, the regeneration operation is continued by the above-mentioned step 304.

If C <C _{0 in} step 315, the process proceeds to step 317, the shutter valve 6 is closed to a second predetermined opening smaller than the first predetermined opening, and then in step 319, the reducing agent supply device. The reducing agent supply amount from 11 is controlled according to the downstream oxygen concentration R _OX . In this case, the reducing agent supply amount is set so that the downstream oxygen concentration R _OX becomes substantially zero.
That is, feedback control is performed so that the NO _X absorbent becomes a reducing atmosphere. If C ≧ C ₀ in step 315, the reproduction operation has already been performed for a sufficient time, and therefore the reproduction stop operation (steps 321 to 327) described later is executed.

Also, when the regenerating operation execution condition is not satisfied in step 303 (including the case where the condition is not satisfied due to a change in operating condition during regenerating operation execution), steps 321 to 327 are also executed. Stop the playback operation.
That is, in step 321, the counter C is cleared,
At step 323, the shutter valve 6 is fully opened, at step 325 the reducing agent supply from the reducing agent supply device 11 is stopped, and at step 327 the flag F is reset (= “0”).

FIG. 4 is a timing chart for explaining the above NO _x absorbent temperature raising regeneration operation. 4 (A), (B),
(C) is the flow rate of exhaust flowing into the NO _x absorbent,
The graph shows the temporal changes of the reducing agent supply amount and the exhaust gas temperature of the NO _x absorbent downstream side. When the regeneration operation execution condition is satisfied in FIG. 4 (point _{A in} FIG. 4), the shutter valve 6 is closed to the first predetermined opening degree, and the inflow exhaust amount is reduced accordingly (FIG. 4 (A)). the reducing agent is supplied to _the NO _X absorbent. As a result, the temperature of the NO _x absorbent rises and the exhaust gas temperature rises (FIG. 4 (C)). Next, when the exhaust gas temperature reaches the predetermined value T ₀ (point _{a in} FIG. 4), the shutter valve 6 is closed to the second predetermined opening degree, and the inflowing exhaust gas amount further decreases (FIG. 4 (A)). the feed rate is reduced to an amount just required for reproduction of the NO _X absorbent (Fig. 4 (B)). As a result, the NO _x absorbent is regenerated. Further, the predetermined time to start playback has elapsed (Fig. 4t _c points), playback with return to the shutter valve 6 terminates the fully open position (FIG. 4 (A)), the supply of the reducing agent is stopped ( Figure 4
(B)).

As described above, NO at the start of execution of the reproduction operation.
By promoting the combustion of the reducing agent on the _X absorbent, the NO _X absorbent can be regenerated at a high temperature, and the regeneration can be efficiently completed in a short time. In particular, when the NO _x absorbent is regenerated without stopping the inflow of the exhaust gas to the NO _x absorbent as in the present embodiment, the amount of the reducing agent for consuming oxygen in the inflowing exhaust gas is NO _x. It becomes greater than the amount of reducing agent needed to reduce and purify, the amount of the reducing agent for the oxygen consumption, to increase in proportion to the regenerating operation time of the NO _X absorbent as described above By increasing the temperature and completing the regeneration in a short time, the amount of reducing agent for oxygen consumption can be reduced, and the reducing agent consumption amount as a whole can be reduced.

Next, FIG. 5 shows another embodiment of the present invention.
The embodiment shown in FIG. 5 regenerates the NO _x absorbent by supplying the reducing agent in a state where the flow rate of the exhaust gas is reduced without blocking the inflow of the exhaust gas to the NO _x absorbent as in the embodiment of FIG. Although the present invention is applied to an exhaust emission control device that performs the above, the configuration of the device and the control method are different. In FIG. 5, FIG.
Elements designated by the same reference numerals as those in FIG. 1 indicate the same elements as those in FIG. 1, and therefore only the differences from the embodiment of FIG. 1 will be described here.

In this embodiment, an intake shutter valve 26 is provided in the intake pipe 2 of the engine 1 instead of the exhaust shutter valve 6 of FIG. 1 as a means for reducing the exhaust flow rate flowing into the NO _X absorbent. Like the exhaust shutter valve 6, the intake shutter valve 26 is of a butterfly valve type that has a small intake resistance when fully opened, and is closed during the regeneration operation of the NO _x absorbent to reduce the intake air amount (that is, exhaust flow rate) of the engine. Reduce. Reference numeral 27a is a diaphragm type negative pressure actuator that opens and closes the shutter valve 26. 27b is a negative pressure control valve, which is an ECU
A negative pressure from a negative pressure source such as a vacuum pump (not shown) is opened and closed by a signal from the negative pressure actuator 27.
intake shutter valve 2 by supplying to a.
Open and close 6. In the present embodiment, the intake shutter valve 26 is controlled to the fully open or fully closed position, and the intake air amount is controlled by controlling the air amount passing through the bypass passage 29 provided by bypassing the intake shutter valve 26. . A bypass control valve 30, which is an electromagnetic flow control valve, is provided in the bypass passage 29 for this purpose, and the bypass passage 29 is controlled by a signal from the ECU 20.
The amount of air passing through is adjusted.

Instead of providing the intake shutter valve 26, the exhaust flow rate may be reduced by the exhaust shutter valve as in FIG. Further, in the present embodiment, the reducing agent supply device 11 of FIG. 1 is not provided, and the reducing agent is supplied by injecting fuel into the cylinders of the diesel engine 1 at the end of the expansion stroke to remove unburned HC. Generate and N
It is supplied to the O _X absorbent 5.

Further, in the present embodiment, the exhaust temperature sensor 22
Is disposed in the exhaust inlet vicinity of the NO _X absorbent 5, more precisely is to detect the temperature of the NO _X absorbent itself, downstream of the embodiment similarly to _the NO _X absorbent 5 1 It is also possible to provide an exhaust gas temperature sensor in and to perform control based on the correlation between the exhaust gas temperature and the temperature of the NO _x absorbent 5. Next, the temperature raising and regeneration operation of the NO _X absorbent of this example will be described. FIG. 6 shows the exhaust gas flow rate and the fuel injection amount required to consume oxygen contained in the exhaust gas flow rate with respect to the temperature of the NO _x absorbent. When the temperature of the NO _x absorbent is low, only a part of the supplied fuel is burned, so that more fuel needs to be supplied in order to consume the same amount of oxygen. What is indicated by a dotted line I in FIG. 6 is the exhaust flow rate corresponding to the time when both the intake shutter valve and the bypass control valve are fully closed. Further, the solid line II shows the relationship between the exhaust gas flow rate at the time of regeneration and its theoretical value of oxygen consumption and the fuel supply amount necessary for NO _x reduction.

In this embodiment, when the condition for executing the NO _X absorbent regeneration operation is satisfied, the intake shutter valve 26 and the bypass control valve 30 are closed, and fuel injection during the expansion stroke is started. At this time, the fuel injection amount is determined according to FIG. 6 from the temperature of the NO _X absorbent 5 detected by the temperature sensor 22 and the exhaust flow rate (dotted line I in FIG. 6) when the shutter valve 26 and the bypass control valve 30 are fully closed. (For example, when the temperature of the NO _X absorbent 5 is 200 ° C., the point becomes point A in FIG. 6).
Next, in this state, it is detected from the output of the oxygen concentration sensor 13 that the exhaust oxygen concentration has started to decrease and from the output of the temperature sensor 22 that the temperature of the NO _x absorbent 5 has started to rise, or both. fuel on _the NO _X absorbent 5 opens the bypass control valve 30 in accordance with the temperature increase of the check after _the NO _X absorbent 5 that starts burning, increasing gradually exhaust flow Te. When the temperature of the NO _X absorbent 5 reaches a predetermined value T ₀ (400 degrees C in FIG. 6), the bypass control valve 30 is fully closed, and the fuel injection amount in the expansion stroke is necessary for regeneration based on the oxygen concentration sensor output. To a theoretical value (that is, a value at which the oxygen concentration R _OX becomes substantially zero) (FIG. 6, C
Point), the NO _x absorbent is regenerated in this state.

In the present embodiment, since the fuel is injected in the expansion stroke, a part of the injected fuel (light oil) adheres to the exhaust pipe and the arrival at the NO _x absorbent 5 is delayed. By controlling the fuel injection amount according to the output of the oxygen concentration sensor 13 after reaching the point C in FIG. 6, the fuel injection amount is reduced by the amount of arrival of the fuel adhering to the exhaust pipe (point D in FIG. 6). 7 and 8 show flowcharts of the temperature rising and regeneration operations of the NO _X absorbent. This routine is the same as the routine of FIG.
It is executed by the CU 20 at regular intervals.

In FIG. 7, when the routine starts, at step 701, the NO _x absorbent temperature T _N , the exhaust oxygen concentration R _OX , the engine accelerator opening A _CC , and the engine speed N are read from the temperature sensor 22, etc. 703
Then, it is determined whether or not the condition for executing the NO _X absorbent regeneration operation is satisfied. It should be noted that also in this embodiment, the reproduction operation execution condition is the same as that in step 303 in FIG.

When the playback operation execution condition is satisfied,
In step 705, the intake shutter valve 26 is fully closed. Steps 707 to 715 are steps that are executed only once when the first routine is executed according to the value of the flag G (steps 707 and 715) after the reproduction operation execution condition is satisfied. Step 707 to Step 715
By executing the above, the bypass control valve 30 is fully closed (step 711), and the fuel injection amount during the expansion stroke is determined from the temperature T _N of the NO _x absorbent 5 based on FIG. As a result, the state at point A in FIG. 6 is established.

Next, in step 717 of FIG. 8, flag F is set.
It is determined whether the operation of raising the temperature of the NO _X absorbent 5 is completed or not based on the value of. Flag F is N after the reproduction condition is satisfied.
This is a flag that is set when the O _X absorbent temperature T _N once exceeds the predetermined value T ₀ (steps 727, 72).
9). If the temperature raising operation has not been completed (Step 7
If F ≠ “1” in 17), NO is determined in step 719 due to a decrease in the oxygen concentration in the exhaust gas, an increase in the NO _X absorbent temperature T _N ,
It is determined whether or not the combustion of the fuel is started by the _X absorbent 5, and if the combustion is started, steps 721 to 7 are performed.
25 gradually open the bypass control valve 30 to NO _X
The temperature of the absorbent 5 is raised. That is, step 72
In No. 1, the temperature T _N of the NO _X absorbent 5 at the time of execution of this routine
And the temperature T _{N (i-1)} of the NO _X absorbent 5 during the execution of the previous routine
If the temperature is higher than the previous time, the opening V _B of the bypass control valve 30 is increased by a predetermined opening α to increase the exhaust gas flow rate. When the temperature is lower than the last time, the opening degree V _B of the bypass control valve 30 is decreased by α to prevent the temperature from decreasing. As a result, as shown in FIG.
The transition from point A to point B is gradually performed.

By executing steps 721 to 725, N
O_XTemperature T of absorbent 5_NIs a predetermined value T ₀When you reach
The flag F is set (= “1”) at steps 727 and 729.
Is NO_XThe operation to raise the temperature of the absorbent has been completed, and the next
From the time of execution of Chin, NO in steps 731 to 737_Xabsorption
The agent regeneration operation is executed (step 717). Playback operation
The bypass control valve 30 is fully closed (V_B← 0) and
(Step 731), the fuel injection amount is the exhaust oxygen concentration
Depending on the output of the oxygen concentration sensor 13 so that it becomes approximately zero
Feedback control is performed (step 733). Also,
If the reproduction operation continues for a predetermined time, steps 739 to 745
(FIG. 7) is executed and the reproduction operation is stopped.

As described above, by performing the temperature increasing operation of the NO _X absorbent 5, the delay in the arrival time of the injected fuel due to the adhesion of the exhaust pipe wall surface is corrected, and the appropriate temperature increasing operation of the NO _X absorbent becomes possible. . Next, FIG. 9 shows an embodiment in which the present invention is applied to an exhaust gas purification device that supplies a reducing agent by closing a shutoff valve provided at the NO _x absorbent inlet.

In this embodiment, the exhaust passage of the engine is
Two of the NO _X absorbent are arranged in parallel, at the time of reproduction of the NO _X in the exhaust gas only by closing the shut-off valve provided on the exhaust inlet of one of the NO _X absorbent other of the NO _X absorbent Remove. That is, in FIG. 9, two branch passages 3a to the exhaust pipe 3 of the engine, and 3b are provided, each of the exhaust passages _the NO _X absorbent 5a, 5b are arranged. Further, a switching type shutoff valve 36 is provided at a branch portion of the exhaust passages 3a and 3b. Reference numeral 37 is, for example, a solenoid actuator, which switches the shutoff valve 36 in response to a signal from the ECU 20 to close one of the branch passages 3a and 3b. Furthermore, NO _X absorbent 5
The exhaust temperature sensors 32a and 32b and the oxygen concentration sensor 33a, which are similar to those of the embodiment of FIG.
33b is provided. Further, NO _X absorbent reducing agent supply device 11 for supplying a reducing agent to the plurality of branched passages 3a, respectively injectors 11a, 11b to 3b, NO _X absorbent 5
A reducing agent can be selectively supplied to a and 5b.

[0050] In this embodiment, as described above, performs the regeneration of the NO _X absorbent and closes the shutoff valve provided in _the NO _X absorbent inlet, the shut-off valve when the exhaust gas temperature is low total Before closing, the reducing agent is supplied to the NO _x absorbent with the shut-off valve opened by a predetermined opening degree, thereby promoting the combustion of the reducing agent on the NO _x absorbent. FIG. 10 is a flow chart showing the temperature raising and regeneration operations of the NO _X absorbent. This routine is also similar to the routines of FIGS.
Is executed every fixed time.

When the routine starts in FIG. 10, it is determined in step 1001 which of the NO _X absorbents 5a and 5b is to be regenerated. In the present embodiment, even during the regenerating operation of one of the NO _X absorbent, it is possible to flow the exhaust on the other of the NO _X absorbent, Figure 1, during the regenerating operation of the engine brake as in the embodiment of FIG. 5 only restricted it not, either of the NO _X when the NO _X absorption amount of the absorbent exceeds a predetermined value, or _the NO _X absorbent regeneration operation when a predetermined time has elapsed since the previous regeneration operation To execute.

Next, at step 1003, the exhaust temperature temperature is set.
Sensors 32a and 32b and oxygen concentration sensors 33a and 33b.
Of these, the exhaust temperature T from the sensor that executes the regeneration operation_EX
And oxygen concentration R_OXIs read, and in step 1005,
Exhaust temperature T_EXIs a predetermined value T ₀It is determined whether or not
It T_EX<T₀If it is, block in step 1007.
NO to switch off valve 36 and regenerate_XAbsorbent branch passage
To a predetermined opening, and in step 1009, the reducing agent
To start supplying. Here, the amount of reducing agent supplied is
Oxygen concentration R read in step 1003_OXIs the theoretical air-fuel ratio phase
Feedback control is performed so that the value becomes equivalent. By this
No, no_XIn the presence of sufficient oxygen on the absorbent
Combustion of the active ingredient is promoted and NO_XAbsorbent temperature rises
It

When the temperature of the NO _x absorbent reaches or exceeds the predetermined value T ₀ (step 1005), steps 1011 and 101
3 is executed to regenerate the NO _X absorbent. That is, in step 1011 the shutoff valve 36 is fully closed, and in step 1013 the reducing agent supply amount is switched to the supply amount for the regeneration operation. Here, during the regenerating operation, the reducing agent supply amount is feedback-controlled so that the oxygen concentration R _OX becomes substantially zero.

Steps 1015 to 1023 are operations for stopping the reproduction, but since these steps are the same as those in the above-mentioned embodiment, the description thereof will be omitted.

[0055]

The exhaust gas purifying apparatus of the present invention promotes the combustion of the reducing agent on the NO _x absorbent before executing the regeneration operation of the NO _x absorbent, and the regeneration operation is performed at a high NO _x absorbent temperature. By doing so, the NO _x absorbent can be efficiently regenerated in a short time, and the reducing agent consumption amount can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of an exhaust emission control device of the present invention.

FIG. 2 is a diagram illustrating the NO _X absorption and release action of a NO _X absorbent.

FIG. 3 is a flow chart showing temperature raising and regeneration operations of the NO _X absorbent of the embodiment of FIG.

FIG. 4 is a timing diagram illustrating control according to the flowchart of FIG.

FIG. 5 is a diagram showing another embodiment of the exhaust emission control device of the present invention.

FIG. 6 is a diagram illustrating a temperature raising operation of the NO _X absorbent of the embodiment of FIG.

FIG. 7 is a part of a flow chart showing temperature raising and regeneration operations of the NO _X absorbent of the embodiment of FIG.

8 is a part of a flow chart showing a temperature raising and regeneration operation of the NO _X absorbent of the embodiment of FIG.

FIG. 9 is a diagram showing another embodiment of the exhaust emission control device of the present invention.

FIG. 10 is a flow chart showing temperature raising and regeneration operations of the NO _X absorbent of the embodiment of FIG. 9.

[Explanation of symbols]

1 ... Engine 2 ... Intake passage 3 ... Exhaust passage 5 ... NO _X absorbent 6 ... Exhaust shutter valve 11 ... Reductant supply device 12 ... Exhaust temperature sensor 13 ... Oxygen concentration sensor 26 ... Intake shutter valve 29 ... Bypass passage 30 ... Bypass Control valve

Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI Technical display location F01N 3/28 ZAB 301 H

Claims (2)

[Claims] 1. Exhaust gas from an internal combustion engine that burns lean air-fuel ratio
NO in the air passage when the air-fuel ratio of the exhaust gas is lean_XTo
Absorbed and absorbed when the oxygen concentration in the exhaust gas decreased
NO_XReleases NO_XAbsorbent is placed and the prescribed driving conditions
Under the situation, the NO_XTo reduce the amount of oxygen flowing into the absorbent
NO_XBy supplying a reducing agent to the absorbent, NO_XSucking
NO absorbed from the sorbent_XIs released and
NO_XIn an exhaust gas purification device for an internal combustion engine that reduces and purifies
And when the reducing agent is supplied, NO _XOxygen flowing into the absorbent
The amount was relatively high at the beginning of the supply of reducing agent and then decreased.
An internal combustion engine characterized by comprising oxygen adjusting means for
Exhaust purification device. In an exhaust passage of wherein the internal combustion engine causing combustion of lean air-fuel ratio, the air-fuel ratio of the inflowing exhaust absorbs NO _X when the lean, the absorbed NO _X when the oxygen concentration of the inflowing exhaust drops the _the NO _X absorbent to release disposed at predetermined operating conditions, by supplying a reducing agent to _the NO _X absorbent by closing the shutoff valve disposed in the exhaust inlet of the _the NO _X absorbent,
In the exhaust purification system of an internal combustion engine to reduce and purify the released was NO _X with the release of NO _X absorbed from _the NO _X absorbent, and characterized in that the supply of the reducing agent the shut-off valve before fully closed Exhaust gas purification device for internal combustion engine.