JP2845068B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, and more particularly, to an exhaust gas purifying apparatus for an internal combustion engine which burns at a lean air-fuel ratio, such as a diesel engine or a gasoline engine which burns a lean mixture. the NO _X on effective removable exhaust gas purification device.

[0002]

2. Description of the Related Art As an example of this type of exhaust gas purification apparatus,
For example, the one disclosed in JP-A-62-106826
There is. The device disclosed in this publication is used in exhaust passages of diesel engines.
NO in the presence of oxygen_XNO that absorbs_XAbsorbent (catalyst)
NO in exhaust_XAnd the NO of the absorbent
_XIf the absorption efficiency decreases, the flow of exhaust gas into the absorbent is blocked.
Supply of gaseous reducing agent to the
NO_XAnd released NO_XReduce
It purifies. That is, in the device of the publication,
The supplied reducing agent is NO_XCombustion by the catalysis of the absorbent
Consumes oxygen in the exhaust_XAtmosphere oxygen concentration of absorbent
Degree decreases. Thereby, NO_XAbsorbed by the absorbent
NO_XIs released and reduced and purified by the reducing agent.
It 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
"Play" _X release and manipulation of the reduced and purified in _the NO _X absorbent
Manipulation is called), the time required for regeneration are known to be greatly affected 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 Reproduction can be completed in a short time.

Further, (NO _X absorption amount per unit time) NO _X absorbing capacity after regeneration operation carried out from the larger the smaller the amount of the NO _X remaining in _the NO _X absorbent,
This is when performing reproduction operation of the same time, it means that the NO _X absorbing capacity of the NO _X absorbent after regeneration enough to reproduce at a high temperature increases. Therefore, to complete the regeneration of the short time _the NO _X absorbent and the regenerated NO
_In order to increase the NO _X absorption capacity of the _X absorbent, N
O _X absorbent temperature is necessary to provide a means for raising the.
However, in the above-described prior art, for _the NO _X absorbent temperature is not considered, and there is a possibility that when it becomes impossible to maintain sufficiently high capacity of the NO _X absorbent after regeneration occurs.

[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, considering the increase in complexity and device cost structure, the method according to the heater and the burner is disadvantageous, it is preferable to raise the temperature of the NO _X absorbent by the combustion of the reducing agent.

On the other hand, if raising the temperature of the NO _X absorbent by the combustion of the reducing agent also increases the reducing agent supply amount and oxygen amount flowing into _the NO _X absorbent is not sufficiently present N
Temperature of the NO _X absorbent for O _X absorbent on the no sufficient combustion is not increased. For example, in the above-described related art, although the temperature increase of the degree of _the NO _X absorbent by the combustion of the reducing agent can be expected, performing the supply of the reducing agent while blocking the flow of exhaust gas into _the NO _X absorbent Therefore, even if the supply amount of the reducing agent is increased, the shortage of the oxygen amount does not cause the combustion for sufficiently raising the temperature of the NO _X absorbent, and the NO _X
In some cases, a sufficient temperature rise of the absorbent may not 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.

[0007] The present invention is to solve the above problems in the case of raising the temperature of the NO _X absorbent by the combustion of the reducing agent, the exhaust gas purifying apparatus capable of playing in a short time efficiently _the NO _X absorbent It is intended to provide.

[0008]

According to the present invention, there is provided a lean engine.
The inflow exhaust gas flows 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 incoming exhaust acid
NO absorbed when the element concentration decreases_XReleases NO
_XAn absorbent is disposed, and under predetermined operating conditions, the NO_Xabsorption
NO by reducing the amount of oxygen flowing into the agent_XReducing agent in absorbent
By supplying NO_XNO absorbed from absorbent
_XAnd the released NO_XThe reduction purification
The exhaust gas purifying apparatus for an internal combustion engine,
Sometimes NO _XStart supplying the reducing agent with the amount of oxygen flowing into the absorbent
A relatively large amount of oxygen in the initial stage
Provided is an exhaust gas purification device for an internal combustion engine, characterized by comprising:
Is 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 gas purification 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 By adjusting both the amount of oxygen flowing into
To promote combustion of O _X absorbent on the reducing agent, thereby achieving an efficient increase in temperature of the NO _X absorbent.

[0011] That is, during reproduction of the NO _X absorbent, by which to reduce the amount of oxygen flowing to supply the reducing agent NO
_{In the} exhaust gas purifying apparatus for regenerating the _X absorbent, the oxygen amount adjusting means adjusts the amount of oxygen flowing in the initial stage of the supply of the reducing agent so as to be relatively large. At the start of reducing agent supply, N
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. Oxygen-amount adjustment means, the temperature of the NO _X absorbent to reduce the amount of oxygen then flows is performed reproduced while elevated.

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 oxygen reducing agent to the NO _X absorbent is supplied in a state of being supplied, the combustion of the reducing agent is promoted, the temperature of the NO _X absorbent is rapidly increased. Then, the shut-off valve in this condition because fully closed, reproduction in a state where the temperature of the NO _X absorbent is increased is performed.

[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 in the case of applying is shown.

In FIG. 1, 1 is a diesel engine,
2 denotes an intake pipe of the engine, and 3 denotes an exhaust pipe of the engine.
Further, the exhaust pipe 3 is connected to _the NO _X absorbent 5 will be described later. In this embodiment, on the upstream side of the NO _X absorbent 5 in the exhaust pipe 3 of the engine exhaust shutter valve 6 is provided. Shutter valve 6 is in the form of exhaust resistance less butterfly valve fully open state during normal operation of the engine is held fully opened, release of the NO _X from _the NO _X absorbent 5, to a predetermined degree of opening during reduction operation closed The exhaust valve 3 is throttled to reduce the amount of air taken into the engine. 7a
Is a diaphragm type negative pressure actuator for driving 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.
The opening of the shutter valve 6 is controlled by changing the negative pressure supplied to the negative pressure actuator 7a by driving the negative pressure control valve 7b according to a signal from the CU 20.

A reducing agent supply device 11 is disposed 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 provided.
In the present embodiment, the oxygen concentration sensor 13 uses a lean mixture that outputs a signal that continuously changes according to the oxygen concentration in the exhaust gas.

The reducing agent supply device 11 is provided with an injection valve 11a for injecting the reducing agent to the upstream side of the exhaust pipe 3 of the NO _X absorbent 5, the exhaust predetermined flow rate of the reducing agent in accordance with an input signal from the ECU20 Inject into tube 3. Any reducing agent may be used as long as it 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 or butane, Liquid fuels such as gasoline, light oil and kerosene can be used.

In FIG. 1, reference numeral 20 denotes an electronic control unit (ECU) of the engine 1. ECU 20 is CP
A known digital computer having a configuration in which a U, a RAM, a ROM, and an input port and an output port are connected to each other by a bidirectional bus, performs basic control such as fuel injection amount control of an engine. The opening degree control of the shutter valve 6 and the control of the reducing agent injection amount from the reducing agent injection valve 11a are performed. ECU 20 for these controls
An input port 24 receives an exhaust temperature signal and an oxygen concentration signal in the exhaust from the exhaust temperature sensor 12 and the oxygen concentration sensor 13, respectively, and also shows signals such as engine speed and accelerator opening, respectively. Not input from sensor.

[0018] _the NO _X absorbent 5 uses a carrier such as alumina or the like, the carrier on, for example potassium K, sodium Na, alkali metal, barium Ba, alkaline earth such as calcium Ca, such as lithium Li, cesium Cs And at least one selected from rare earths such as lanthanum La and yttrium Y, and a noble metal such as platinum Pt. This _the NO _X absorbent 5 absorbs NO _X in the case the air-fuel ratio of the exhaust gas flowing is lean, the oxygen concentration is carried out to absorbing and releasing action of the NO _X that releases NO _X when lowered.

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

In this embodiment, since a 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 gas. Further, when the oxygen concentration is introduced a reducing agent into the exhaust gas decreases, the emission of the NO _X absorbent 5 absorbs reducing agent performed by the operation described below. The detailed mechanism of this absorption / release action is not clear in some parts. However, it is considered that this absorption / release action is performed by a mechanism as shown in FIG. Next, this mechanism will be described by taking as an example a case where platinum Pt and barium Ba are supported on a carrier, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths and rare earths.

That is, when the inflowing exhaust gas becomes considerably lean, the oxygen concentration in the inflowing exhaust gas greatly increases, and as shown in FIG. 2A, the oxygen O ₂ is converted into O ₂ ^-in the form of O ₂ ^{− on} the surface of the platinum Pt. Adheres to On the other hand, NO in the inflowing exhaust gas is O ₂ on the surface of the platinum Pt ^- reacted with, and _{NO 2 (2NO + O 2 →} 2
NO ₂ ). Next, a part of the generated NO ₂ is absorbed in the absorbent while being oxidized on platinum Pt, and barium oxide Ba is absorbed.
While bonding with the O, nitrate ions NO ₃ as shown in FIG. 2 (A) ^- is diffused in the absorbent in the form of. In this way, NO _X is absorbed in the NO _X absorbent 5.

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

On the other hand, if reducing components such as HC and CO are present in the inflowing exhaust gas, these components become oxygen O ₂ on platinum Pt.
^- reacts with the oxidized, reducing the oxygen concentration in the exhaust to consume oxygen in the exhaust. 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 (1), it is reduced by reacting with HC and CO. When NO ₂ is no longer present on the surface of the platinum Pt, NO ₂ is released from the absorbent one after another.

[0024] That is, HC in the inflowing exhaust gas, CO, first O ₂ on the platinum Pt ^- it is immediately reacted with oxidized, then O ₂ on the platinum Pt ^- yet even is consumed HC, CO
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 keeping the temperature of the NO _X absorbent high during regeneration, it is possible to completely release NO _X absorbed by the NO _X absorbent in a short time and perform complete regeneration.

[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 reducing agent combustion. 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, a description will be given of a temperature rise operation of the NO _X absorbent in this embodiment. 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 supply amount of the reducing agent from the reducing agent supply device 11 is determined 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, by the combustion of the reducing agent, NO if the temperature of the _X absorbent 5 that has risen is detected by the output of the downstream exhaust gas temperature sensor 12, ECU 20 is first the smaller first predetermined opening the shutter valve 6 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 operation of raising the temperature and regenerating the NO _X absorbent. This routine is executed by the ECU 20 at regular intervals. When the routine starts in FIG. 3, in step 301, the exhaust gas temperature T _EX downstream of the NO _X absorbent 5 and the exhaust oxygen concentration R _OX
Are respectively an exhaust gas temperature sensor 12 and an oxygen concentration sensor 13
Then, the accelerator opening A _CC and the engine speed N of the engine are read from the respective sensors.

[0028] Next, the regenerating operation conditions of the NO _X absorbent in step 303 whether or not satisfied is determined. Here, the regeneration execution condition of the NO _X absorbent is (1)
Accelerator opening A _CC is equal to or less than a predetermined value, and engine speed N is equal to or more than a predetermined value (that is, engine braking is being performed). (2) A predetermined time since the previous NO _X absorbent regeneration operation was performed There it has passed a, performs an operation of heating the regeneration of step 305 following _the NO _X absorbent only when a condition is satisfied the conditions are both.

[0029] Here, to conduct the regeneration of _the NO _X absorbent only during engine braking (the condition (1)), it is necessary to reduce the amount of intake air by closing the intake shutter valve as described later at the time of reproduction Therefore, if the regeneration is performed during the normal operation, a torque shock occurs and the drivability is deteriorated.
Also, the fact that the predetermined time has elapsed since the last execution of the reproduction operation (the above condition (2)) is set as the reproduction execution condition, because the frequent reproduction operation is avoided and the reproduction operation is performed only when the reproduction is truly required. It is to do it.

It should be noted that instead of the above condition (2), NO _X
The NO _X absorption amount of the absorbent is equal to or greater than a predetermined value may be the execution condition of the reproduction operation. NO of _the NO _X absorbent
_X absorption, for example, advance the engine load emissions of the NO _X from the engine per unit time (accelerator opening) and is stored in ECU20 the ROM as a function of the engine speed or the like, an accelerator at regular time intervals 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 determined by integrating the amount of absorption.

If 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 gas 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
If F = "1" in 04, the process proceeds to step 313 and is NO
_{If the} operation of regenerating the _X absorbent 5 is continued and F１ “1”, it is determined in step 305 whether or not the exhaust gas temperature T _EX is equal to or higher than a predetermined value T ₀ . Here, T ₀ is an exhaust gas temperature corresponding to the temperature of the NO _x absorbent sufficient for performing regeneration in a short time, and is determined in advance by actual measurement or the like.

[0032] When a T _EX <T ₀ in step 305, the temperature of the NO _X absorbent to perform heating operation of the NO _X absorbent steps 307-311 since not sufficiently increased. That is, in step 307, and closes the shutter valve 6 to a first predetermined opening throttling the flow of exhaust gas into _the NO _X absorbent. At step 309 by controlling the opening degree of the injection valve 11a of the reducing agent supply device 11 supplies the amount of reducing agent in accordance with the exhaust gas oxygen concentration R _OX of the NO _X absorbent 5 downstream 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 value corresponding to a stoichiometric air-fuel ratio). Also, the shutter valve 6
The first predetermined opening degree, NO _X sufficient amount of exhaust in the absorbent (oxygen) is supplied, and an exhaust flow rate becomes excessive NO
It is set within a range where the _X absorbent is not cooled. After the end of the above operation, in step 311, a counter C described later is used.
Is cleared, and the routine ends.

If T _EX ≧ T ₀ in step 305, the exhaust gas temperature is sufficiently high,
Heating operation of the NO _X absorbent 7-311 is performed NO _X
Since the temperature of the absorbent has risen sufficiently, step 31
Perform regenerating operation of the NO _X absorbent 2-319. That is, in step 312 the flag F is set, the counter C which represents the duration of the reproduction operation in step 313 plus 1 counts up, in step 315 the counter C is determined whether a predetermined value C ₀ or more. Here, the predetermined value C ₀ is the number of executions of the routine corresponding to a time sufficient for the regeneration of the NO _X absorbent to be completed. 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 at 12, the regeneration operation is continued in step 304 described above.

[0034] The shutter valve 6 proceeds to step 317 in the case of C <C ₀ is closed to the first predetermined opening smaller than the second predetermined opening in step 315, then the reducing agent supply device in step 319 The supply amount of the reducing agent 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 _the NO _X absorbent is feedback controlled so that the reducing atmosphere. If C ≧ C ₀ in step 315, the reproduction operation has already been performed for a sufficient time, and the reproduction stop operation (steps 321 to 327) described later is executed.

Also, if the regeneration operation execution condition is not satisfied in step 303 (including the case where the operation state changes during execution of the regeneration operation and the condition is not satisfied), steps 321 to 327 are also executed. To stop the playback operation.
That is, in step 321, the counter C is cleared,
In step 323, the shutter valve 6 is fully opened, and in step 325, the supply of the reducing agent from the reducing agent supply device 11 is stopped. In step 327, the flag F is reset (= "0").

[0036] FIG. 4 is a timing diagram illustrating the above of the NO _X absorbent ZaiNoboru temperature regeneration operation. 4 (A), (B),
(C) is the flow rate of the exhaust gas flowing to _the NO _X absorbent, respectively,
Reducing agent supply amount illustrates temporal changes of the NO _X absorbent downstream exhaust temperature. When the regeneration operation execution condition is satisfied in FIG. 4 (point _{A in} FIG. 4), the shutter valve 6 closes to the first predetermined opening, and the inflow exhaust amount decreases accordingly (FIG. 4A). the reducing agent is supplied to _the NO _X absorbent. Accordingly, the temperature of the NO _X absorbent increases, the exhaust gas temperature rises (FIG. 4 (C)). Then, when the exhaust temperature reaches a predetermined value T ₀ (Fig. 4t _a point), the shutter valve 6 is closed by the inflowing exhaust gas quantity to a second predetermined opening is further reduced (FIG. 4 (A)), a reducing agent the feed rate is reduced to an amount just required for reproduction of the NO _X absorbent (Fig. 4 (B)). Thus regeneration of the NO _X absorbent is carried out. 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 ( FIG.
(B)).

As described above, when starting the execution of the reproduction operation, NO
By promoting the combustion of the reducing agent on the _X absorbent, the NO _X absorbent is regenerated at a high temperature, and the regeneration can be completed efficiently in a short time. In particular, NO _X amount of reducing agent to consume the oxygen in the exhaust gas flowing in the case of without stopping the flow of exhaust gas into the absorbent the regeneration of _the NO _X absorbent is NO _X as in this embodiment 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 the reducing agent for consuming oxygen can be reduced, and the amount of the reducing agent consumed can be reduced as a whole.

Next, FIG. 5 shows another embodiment of the present invention.
Embodiment shown in FIG. 5 performs the supply of the reducing agent in a state with reduced exhaust gas flow rate without interrupting the flow of exhaust gas into the embodiment similarly to _the NO _X absorbent in Figure 1, regeneration of _the NO _X absorbent This is a case in which the present invention is applied to an exhaust gas purifying apparatus that performs the above, but the configuration and control method of the apparatus are different. In FIG. 5, FIG.
Elements denoted by the same reference numerals as those in FIG. 1 indicate the same elements as in FIG. 1, and therefore, only the differences from the embodiment of FIG. 1 will be described here.

[0039] In this embodiment, as a means for throttling the flow rate of the exhaust gas flowing into _the NO _X absorbent is provided an intake shutter valve 26 in the intake pipe 2 of the engine 1 in place of the exhaust shutter valve 6 in Figure 1. Intake shutter valve 26 is in the form of intake resistance less butterfly valve when fully opened like the exhaust shutter valve 6, the intake air amount of the engine closed during the regenerating operation of the NO _X absorbent (i.e., the exhaust gas flow rate) Reduce. Reference numeral 27a denotes a diaphragm type negative pressure actuator for driving the opening and closing of the shutter valve 26. 27b is a negative pressure control valve,
20 is opened / closed by a signal from the vacuum pump 20 to reduce the negative pressure from a negative pressure source such as a vacuum pump (not shown) to the negative pressure actuator 27.
supply to the intake shutter valve 2
6 is opened and closed. In this embodiment, the intake shutter valve 26 is controlled to the fully open or fully closed position, and the amount of intake air is controlled by controlling the amount of air passing through a bypass passage 29 provided to bypass the intake shutter valve 26. . The bypass passage 29 is provided with a bypass control valve 30 including an electromagnetic flow control valve for this purpose.
The amount of air passing through is adjusted.

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

In this 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 May be provided with an exhaust gas temperature sensor, and control may be performed based on the correlation between the exhaust gas temperature and the temperature of the NO _X absorbent 5. Next, the operation of raising the temperature of the NO _X absorbent and the regeneration operation of the present embodiment will be described. FIG. 6 is a view of a fuel injection amount required to consume the oxygen contained in the exhaust flow rate and the exhaust flow rate given for the temperature of the NO _X absorbent. Since the temperature of the NO _X absorbent is not only burn part of the lower and the supplied fuel in order to consume the same amount of oxygen, it is necessary to supply more fuel. The dotted line I in FIG. 6 shows the exhaust flow rate corresponding to the time when both the intake shutter valve and the bypass control valve are fully closed. Further, the shown by the solid line II shows the relationship between the exhaust flow rate and the theoretical value of the fuel supply amount required for the reduction of the oxygen consumption and NO _X at the time of reproduction.

[0042] When the regenerating operation conditions of the NO _X absorbent is established in this embodiment closes the intake shutter valve 26 and the bypass control valve 30, starts the fuel injection during the expansion stroke. 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 the point A in FIG. 6).
Then, to detect one or both of the temperature of the NO _X absorbent 5 from the output of that temperature sensor 22 that the exhaust oxygen concentration from the output of the oxygen concentration sensor 13 is started reduced in this state began to rise 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 ° C. in FIG. 6), the bypass control valve 30 is fully closed, and the fuel injection amount in the expansion stroke is required for regeneration based on the output of the oxygen concentration sensor. (That is, a value at which the oxygen concentration R _OX becomes substantially zero) (FIG. 6, C
Points), playback of the NO _X absorbent is performed in this state.

[0043] In this embodiment, because a fuel injection of the expansion stroke, part of the injected fuel (light oil) is delayed arrival to _the NO _X absorbent 5 attached to the exhaust pipe. 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 the fuel attached to the exhaust pipe (point D in FIG. 6). FIGS. 7 and 8 show flowcharts of the above-mentioned NO _X absorbent temperature raising and regeneration operation. This routine is also similar to the routine of FIG.
This is executed by the CU 20 at regular intervals.

[0044] In FIG. 7, the routine in step 701 when started _the NO _X absorbent temperature T _N, the exhaust oxygen concentration R _OX, accelerator opening A _CC of the engine, the engine speed N is read from the temperature sensor 22 and the like, step 703
Then, it is determined whether the condition for executing the NO _X absorbent regeneration operation is satisfied. Note that also in this embodiment, the reproduction operation execution conditions are the same as in step 303 in FIG.

When the reproduction operation execution condition is satisfied,
In step 705, the intake shutter valve 26 is fully closed. Steps 707 to 715 are executed once at the time of the first routine execution after the regeneration operation execution condition is satisfied according to the value of the flag G (steps 707 and 715). Step 707 to Step 715
By the execution, the bypass control valve 30 is fully closed (step 711), the fuel injection amount at the time of the expansion stroke is determined from the temperature T _N of the NO _X absorbent 5 with reference to FIG. Thereby, the state at the point A in FIG. 6 is established.

Next, in FIG.
Whether the temperature rise operation of the NO _X absorbent 5 is completed is determined by the value. The flag F is set to N after the regeneration condition is satisfied.
O _X absorbent temperature T _N is a flag that is set when it is once more a predetermined value T ₀ (step 727,72
9). If the temperature raising operation has not been completed (step 7
In step 719, F ≠ “1”) is set to NO due to a decrease in the oxygen concentration in the exhaust gas and an increase in the NO _X absorbent temperature _TN.
It is determined whether or not the combustion of the fuel with the _X absorbent 5 has been started.
25, the bypass control valve 30 is gradually opened to release NO _X
The temperature of the absorbent 5 is increased. That is, step 72
In FIG. 1, the temperature T _N of the NO _X absorbent 5 at the time of execution of the current routine
And the temperature T _{N (i-1)} of the NO _X absorbent 5 at the time of execution of the last routine.
Compared bets, increasing the exhaust flow rate increases the opening degree V _B of the bypass control valve 30 by a predetermined angle α in the case where the temperature is higher than the previous. Also, the opening degree V _B of the bypass control valve 30 is decreased by α when the temperature is lower than the previous to prevent a decrease in temperature. As a result, FIG.
The transition from the point A to the point B is performed gradually.

By executing steps 721 to 725, N
O_XTemperature T of absorbent 5_NIs a predetermined value T ₀When you reach
In steps 727 and 729, the flag F is set (= "1").
NO_XThe operation to raise the temperature of the absorbent is completed, and the next
NO at steps 731 to 737_Xabsorption
An agent regeneration operation is performed (step 717). Playback operation
, The bypass control valve 30 is fully closed (V_B← 0) and
(Step 731), the fuel injection amount is determined by the exhaust oxygen concentration.
According to the output of the oxygen concentration sensor 13 so as to be substantially zero
Feedback control is performed (step 733). Also,
Steps 739 to 745 when the reproduction operation continues for a predetermined time
(FIG. 7) is executed, and the reproduction operation is stopped.

[0048] As described above, it is possible _the NO _X absorbent 5 temperature rise operation temperature rise operation delay of arrival time corrected appropriate _the NO _X absorbent by the exhaust pipe wall adhesion of the injected fuel by performing the . Next in Figure 9, the present invention, showing an example of applying the exhaust gas purifying apparatus for supplying and closes the reducing agent shut-off valve provided in _the NO _X absorbent inlet.

In this embodiment, in the exhaust passage of the engine,
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 denotes a solenoid actuator, for example, 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, 32b and the oxygen concentration sensor 33a, which are the same as those in the embodiment of FIG.
33b are 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, 5b can be selectively supplied with a reducing agent.

[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, by supplying the reducing agent to the NO _X absorbent in the state where only the opening a predetermined opening the shutoff valve, to promote combustion of the reducing agent on _the NO _X absorbent. FIG. 10 is a flowchart showing the above-mentioned NO _X absorbent temperature raising and regeneration operation. This routine is executed by the ECU 20 similarly to the routines of FIGS.
Is executed at regular intervals.

[0051] When the routine starts in Fig. 10, step 1001 in _the NO _X absorbent 5a, whether to perform regenerating operation of the 5b is determined. 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 Execute

Next, at step 1003, the exhaust gas temperature
Sensors 32a, 32b and oxygen concentration sensors 33a, 33b.
Of these, the exhaust temperature T_EX
And oxygen concentration R_OXIs read, and in step 1005,
The exhaust temperature T_EXIs a predetermined value T ₀Is determined
You. T_EX<T₀In step 1007,
NO for switching valve stop 36 and regenerating_XAbsorbent branch passage
Side is closed to a predetermined opening, and the reducing agent is
Start supplying. Here, the supply amount of the reducing agent is determined in the above-described step.
Oxygen concentration R read in step 1003_OXIs the stoichiometric air-fuel ratio phase
Feedback control is performed so as to be the equivalent value. This
No_XOn the absorbent in the presence of sufficient oxygen
Combustion of base agent is promoted, NO_XAbsorbent temperature rises
You.

When the temperature of the NO _X absorbent becomes equal to or higher than the predetermined value T ₀ (step 1005), steps 1011 and 101 are performed.
3 is executed, reproduction of the NO _X absorbent is carried out. 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 regeneration operation, the supply amount of the reducing agent is feedback-controlled so that the oxygen concentration R _OX becomes substantially zero.

Steps 1015 to 1023 are operations for stopping the reproduction. These steps are the same as those in the above-described embodiment, and therefore the description is omitted.

[0055]

[Effect of the Invention An exhaust gas purifying apparatus of the present invention, prior to the regenerating operation of the NO _X absorbent to promote combustion of the reducing agent on _the NO _X absorbent, the regeneration operation at higher _the NO _X absorbent temperature by was performed, performs reproduction efficient _the NO _X absorbent in a short time, an effect capable of reducing the reducing agent consumption.

[Brief description of the drawings]

FIG. 1 is a view showing one embodiment of an exhaust gas purification apparatus of the present invention.

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

FIG. 3 is a flowchart showing a temperature raising and regeneration operation of the NO _X absorbent of the embodiment of FIG. 1;

FIG. 4 is a timing chart illustrating control according to the flowchart of FIG. 3;

FIG. 5 is a view showing another embodiment of the exhaust gas purification apparatus of the present invention.

FIG. 6 is a view for explaining a temperature raising operation of the NO _X absorbent of the embodiment of FIG. 5;

FIG. 7 is a part of a flowchart showing a temperature raising and regeneration operation of the NO _X absorbent of the embodiment of FIG. 5;

FIG. 8 is a part of a flowchart showing a temperature raising and regeneration operation of the NO _X absorbent of the embodiment of FIG. 5;

FIG. 9 is a view showing another embodiment of the exhaust gas purification apparatus of the present invention.

FIG. 10 is a flowchart showing the operation of raising the temperature and regenerating 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 ... reducing agent supply device 12 ... exhaust gas temperature sensor 13 ... oxygen concentration sensor 26 ... intake shutter valve 29 ... bypass passage 30 ... Bypass Control valve

────────────────────────────────────────────────── (5) Int.Cl. ⁶ Identification symbol FI F01N 3/28 301 F01N 3/28 301H (56) References JP-A-62-106826 (JP, A) JP-A-48-61813 (JP, A) (58) Fields surveyed (Int. Cl. ⁶ , DB name) F01N 3/08 F01N 3/18 F01N 3/24 F01N 3/28 301

Claims (2)

(57) [Claims] 1. An exhaust system for an internal combustion engine that performs combustion at a lean air-fuel ratio.
NO when the air-fuel ratio of the inflow exhaust gas is lean in the air passage_XTo
Absorbed and absorbed when oxygen concentration of inflow exhaust decreased
NO_XReleases NO_XArrange the absorbent and follow the specified operating conditions
Under the case, the NO_XBy reducing the amount of oxygen flowing into the absorbent
NO_XBy supplying the reducing agent to the absorbent, NO_XSucking
NO absorbed from the absorbent_XAnd release the
NO_XExhaust purification device for internal combustion engines
When the reducing agent is supplied. _XOxygen flowing into the absorbent
The amount was relatively large at the beginning of the reductant supply and decreased thereafter.
Internal combustion engine provided with an oxygen amount adjusting means for causing
Exhaust purification equipment. 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 purification device for an internal combustion engine.