JPH06200737A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

(57) Abstract: OBJECTIVE the NO _X absorbent to remove NO _X in diesel engine exhaust, the exhaust gas purification efficiency by the low-temperature poisoning is caused by the SOF and the reducing agent in the exhaust to prevent a reduction . [Structure] An oxygen concentration sensor 10 for detecting the oxygen concentration of exhaust gas is provided in the exhaust passage 3 on the downstream side of the NO _X absorbent 15, and the oxygen concentration at a predetermined time after the start of the regeneration operation is detected. When the oxygen concentration is higher than a predetermined value, the ECU 20 determines that the low temperature poisoning of the NO _x absorbent has occurred, and the electric heater 16 heats the NO _x absorbent 15 to change the NO _x absorbent to the NO _x absorbent. A poisoning recovery process of burning the adhered SOF and the like is performed.

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 N in exhaust gas of a diesel engine.
The O _X on the Effective removable exhaust gas purification device.

[0002]

2. Description of the Related Art An example of this type of exhaust emission control device is disclosed in Japanese Patent Application Laid-Open No. 62-106826. The apparatus of the publication, NO _X absorbent absorbs NO _X in the presence of oxygen in an exhaust passage of a diesel engine (catalyst)
Is installed to absorb NO _X in the exhaust gas, and the NO
_{When the X} absorption efficiency is reduced, the exhaust gas is blocked from flowing into the absorbent and a gaseous reducing agent is supplied to release NO _X from the absorbent and reduce and purify the released NO _X. is there. That is, in the apparatus of this publication, the supplied reducing agent is burned by the catalytic action of the NO _X absorbent consume oxygen in the exhaust, the atmospheric oxygen concentration of the NO _X absorbent is lowered. Accordingly, it is the NO _X absorbed from _the NO _X absorbent is reduced and purified by the reducing agent is released.

[0003]

The exhaust gas of a diesel engine generally contains fine particles (diesel particulates) such as soluble organic matter (SOF) and soot (dry soot). These particles burn at high temperatures,
Although it vaporizes, the exhaust temperature of a diesel engine is generally lower than that of a gasoline engine, so NO in the exhaust passage.
_{When the X} absorbent is arranged, the fine particles such as SOF are NO.
So-called low temperature poisoning that adheres to and deposits on the _X absorbent occurs.

When low temperature poisoning due to SOF etc. occurs,
Since the surface of the NO _x absorbent is covered with SOF particles and the catalytic action is impeded, the above-mentioned reducing agent does not burn on the NO _x absorbent, and the oxygen in the exhaust gas is consumed even if the reducing agent is supplied. You will not be able to do it. Thus, release and reduction purification of the absorbed NO _X can not be performed in the NO _X absorbent, NO _X absorbing capacity of the NO _X absorbent is a problem that can not be removed of the NO _X in the exhaust gas becomes saturated.
In particular, when a liquid reducing agent such as light oil or kerosene having a relatively low volatility is used as the reducing agent, in addition to the above poisoning by SOF, the reducing agent that reaches the NO _x absorbent without vaporization causes NO _x. absorbent surface is covered, occurs cold poisoning by the reducing agent, further poisoning of the NO _X absorbent is likely to occur.

The present invention solves the above-mentioned problem of poisoning of the NO _X absorbent due to unburned components in the exhaust such as SOF and liquid reducing agent, and prevents the deterioration of exhaust purification efficiency of a diesel engine. It is intended to provide an exhaust emission control device.

[0006]

According to the present invention, NO _x is absorbed in the exhaust passage of a diesel engine when the air-fuel ratio of the inflowing exhaust gas is lean, and it is absorbed when the oxygen concentration of the inflowing exhaust gas decreases. place _the NO _X absorbent to release the NO _X, NO and introducing a reducing agent into the exhaust at a predetermined operating conditions
Combustion on the _X- absorbent consumes oxygen in the exhaust and NO _X
The NO _X with the release of NO _X absorbed from the absorbent
In an exhaust gas purification device of an internal combustion engine for reducing and purifying NOx, a means for detecting poisoning of a NO _x absorbent due to adhesion of unburned components in exhaust gas, and a means for heating the NO _x absorbent when the poisoning is detected. An exhaust gas purification apparatus for an internal combustion engine is provided, which is provided with a means for recovering poisoning.

[0007]

FUNCTION The SOF and liquid reducing agent attached to the NO _X absorbent burn and evaporate at high temperatures. In the present invention, when the poisoning detection means detects poisoning of the NO _x absorbent, the poisoning recovery means heats the NO _x absorbent. As a result, NO
SOF and liquid reducing agent covering the surface of the _X absorbent combustion, poisoning of the NO _X absorbent since it is removed from the surface of the NO _X absorbent is vaporized is eliminated.

[0008]

EXAMPLE An example in which the present invention is applied to a diesel engine will be described with reference to FIG. In FIG. 1, 1 is a diesel engine, 2 is an engine intake pipe, and 3 is an engine exhaust pipe. In this embodiment, a shutter valve 6 is provided on the intake pipe 2 of the engine.

[0009] The shutter valve 6 is in the form of intake 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 to be described later, predetermined during reduction operation The valve is closed to the opening,
The intake pipe 2 is throttled to reduce the amount of air taken into the engine. Reference numeral 7 denotes a step motor that opens and closes the shutter valve 6 in response to a signal from an electronic control unit (ECU) 20 described later, an actuator of an appropriate type such as a negative pressure actuator, and 8 an opening that detects the opening of the shutter valve. It is a sensor.

Further, an exhaust gas temperature sensor 13 and a reducing agent supply device 11 are arranged on the downstream side of the engine exhaust pipe 3, and the exhaust pipe 3 is further downstream of the NO _x absorbent 15.
Is connected to the casing that accommodates. Also, NO _X
An oxygen concentration sensor 10 using a lean mixture sensor that outputs a signal that continuously changes according to the oxygen concentration in the exhaust gas is provided in the exhaust pipe downstream of the absorbent 15.

The reducing agent supply device 11 includes a NO _x absorbent 15
An injection valve 11a for injecting a reducing agent is provided in the exhaust pipe 3 on the upstream side of, and a predetermined flow rate of the reducing agent is injected into the exhaust pipe 3 according to an input signal from the ECU 20. Any reducing agent may be used as long as it produces a reducing component such as hydrocarbon or carbon monoxide in the exhaust gas, and a gas such as hydrogen or carbon monoxide, propane,
Liquid or gaseous hydrocarbons such as propylene and butane, liquid fuels such as gasoline, light oil, and kerosene can be used. Since the diesel engine is used in the present embodiment, the same light oil as the fuel of the engine is used as the reducing agent, and the light oil is pressurized from the fuel tank of the engine (not shown) by the supply pump and supplied to the injection valve 11a. It

Reference numeral 20 in the drawing denotes an electronic control unit (ECU) of the engine 1. ECU 20 is a CPU
21, a RAM 22, a ROM 23, an input port 24, and an output port 25 are connected to each other by a bidirectional bus 26. The digital computer performs basic control such as fuel injection amount control of the engine. Is calculated and the injection amount of the reducing agent injection valve 11a is controlled. For these controls, the input port 24 of the ECU 20 receives an oxygen concentration signal in exhaust gas and an exhaust temperature signal from the oxygen concentration sensor 10 and the exhaust temperature sensor 13, and a shutter valve opening degree from the shutter valve opening degree sensor 8. In addition to the respective signals input, signals such as the engine speed and the accelerator opening are input from sensors not shown.

In this embodiment, the NO _x absorbent 15 is provided with an electric heater 16 for heating. Heater 16 is N
O exhaust inlet side of the _X absorbent 15 (the upstream side) provided on the end face, so as to heat the upstream-side end face of the energized _the NO _X absorbent 15 by a signal from the ECU 20. The heater 16 may be of a type embedded in the vicinity of the upstream end surface of the NO _X absorbent 15.

As the NO _x absorbent 15, for example, 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 15 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 exhaust air-fuel ratio mentioned above means here N
The exhaust passage on the upstream side of the O _X absorbent 15 and the engine combustion chamber,
It means the ratio of the total amount of air and the total amount of fuel supplied to the intake passage and the like. Therefore, when fuel or air is not supplied to the upstream exhaust passage of the NO _X absorbent 15, 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 the present embodiment, since the diesel engine is used, the exhaust air-fuel ratio during normal operation is lean, and the NO _X absorbent 15 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 15 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), the oxygen O ₂ is in the form of O ₂ ⁻ or O ^{2 −.} It adheres to the surface of platinum Pt. On the other hand, NO in the inflowing exhaust gas reacts with this O ₂ ⁻ or O ^{2 −} on the surface of platinum Pt to generate NO ₂
(2NO + O ₂ → 2NO ₂ ). Then, a part of the generated NO ₂ is oxidized on the platinum Pt, absorbed in the absorbent and combined with barium oxide BaO, and
As shown in ( ₃ ), it diffuses into the absorbent in the form of nitrate ion NO ₃ ⁻ . In this way, NO _X is absorbed in the NO _X absorbent 15.

Therefore, NO ₂ is produced on the surface of platinum Pt as long as the oxygen concentration in the inflowing exhaust gas is high, and NO ₂ is absorbed in the absorbent and nitrate ion NO ₃ unless the NO _X absorption capacity of the absorbent is saturated. ^- is generated. In contrast the oxygen concentration decreases and the amount of NO ₂ is reduced by reaction backward in the inflowing exhaust gas (NO ₃ ^- → NO ₂₎ proceeds to thus of the absorbent and nitrate ions NO ₃ ^- is NO ₂ Is released from the absorbent in the form of. Namely, when the oxygen concentration in the inflowing exhaust gas is released NO _X from _the NO _X absorbent 15 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.
^- or it is reacted with oxide and O ^2-, lowering the oxygen concentration in the exhaust to consume oxygen in the exhaust. Further, the NO released from the NO _X absorbent 15 due to the decrease in the oxygen concentration in the exhaust gas.
₂ is reduced by reacting with HC and CO as shown in Fig. 2 (B). 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. Accordingly HC in the inflowing exhaust gas, NO _X from _the NO _X absorbent 15 in a short time as CO components increase is released,
Will be reduced.

That is, HC and CO in the inflowing exhaust gas first react with O ₂ ⁻ or O ²⁻ on platinum Pt immediately to be oxidized, and then O ₂ ⁻ or O ²⁻ on platinum Pt are consumed. the HC, NO _X discharged from the released NO _X and the engine from the absorbent by CO is reduced even yet HC, any remaining CO is. Therefore, when low temperature poisoning occurs when SOF contained in the engine exhaust and the non-vaporized reducing agent adhere to the surface of the NO _x absorbent, oxygen consumption due to oxidation on the platinum Pt is hindered, and the oxygen concentration of the exhaust gas is reduced. sufficiently will not be able to reduce the release of above of the NO _X, reduction becomes not performed, removal of the NO _X in the exhaust gas can not be performed.

In the present embodiment, the occurrence of the low temperature poisoning is detected from the change in the output of the oxygen concentration sensor 10 after the supply of the reducing agent from the reducing agent supply device 11 is detected, and the poisoning recovery process is performed. . Then, the poisoning detection principle of the NO _X absorbent in this embodiment will be described with reference to FIG. FIG. 3 shows the difference in the temporal change in the exhaust oxygen concentration on the downstream side of the NO _x absorbent 15 after the supply of the reducing agent is different depending on the presence or absence of poisoning. If the NO _x absorbent is not poisoned (solid line in FIG. 3), as soon as the reducing agent reaches the NO _x absorbent, the oxygen in the exhaust gas is consumed by the oxidation reaction on the platinum Pt. The exhaust oxygen concentration on the side decreases rapidly.

However, when the low temperature poisoning occurs, as described above, the surface area of platinum Pt that can participate in the oxidation reaction due to the attachment of SOF or the like on the platinum Pt decreases, and the oxidation reaction on the platinum Pt decreases. Therefore, the decrease of the exhaust oxygen concentration on the downstream side becomes gentle, and the exhaust oxygen concentration becomes higher after a lapse of a fixed time (FIG. 3t _D ) after the start of supplying the reducing agent as the degree of poisoning (adhesion amount) increases ( (Figure 3, dotted line). In this embodiment, release of the NO _X absorbed in the NO _X absorbent by utilizing the above reduction purification operation (hereinafter, of the NO _X absorbent. Referred to as "regeneration" operation) during, after starting the reducing agent supply The exhaust oxygen concentration after a certain period of time is measured, and when the oxygen concentration is larger than the predetermined value A _0, it is determined that the NO _x absorbent is poisoned.

[0023] Figure 4 shows an example of a flowchart showing the poisoning determination operation described above of the NO _X absorbent. This routine is executed by the ECU 20 described above at regular intervals. When the routine starts in FIG. 4, step 4
In 01, it is determined whether or not the condition for executing the regeneration operation of the NO _X absorbent is satisfied. Here, the conditions for executing the regeneration of the NO _X absorbent are (1) the accelerator opening is equal to or less than a predetermined value,
In addition, the engine speed is equal to or higher than a predetermined value (that is, the engine is being braked), (2) The engine exhaust temperature is equal to or higher than a predetermined temperature (T _START ), (3)
The predetermined time has elapsed since the previous NO _x absorbent regeneration operation was performed, etc., and only when all the conditions (1) to (3) are satisfied, the NO _x absorbent regeneration from step 403 onward is performed. Do the operation.

Here, in order to regenerate the NO _x absorbent only during engine braking (condition (1) above), 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.
Further, the reason why the exhaust gas temperature is equal to or higher than the predetermined value (the above-mentioned condition (2)) is that the NO _X absorbent must reach the activation temperature at which the NO _X release and the reducing action are activated. The playback execution condition is that a predetermined time has passed since the previous playback operation was performed (the above condition (3)). The frequent playback operation is avoided and the playback operation is performed only when true playback is required. This is to do so.

Instead of the above condition (3), 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
_{The X} absorption amount is, for example, the ROM 23 of the ECU 20 as a function of the engine load (accelerator opening degree), the engine speed, and the like in advance of the NO _X emission amount from the engine per unit time.
Is stored in, determine the NO _X emissions by the function of the accelerator opening and the rotational speed at regular time intervals, are multiplied by certain coefficients in this of the NO _X absorbent in said predetermined time N
It is obtained by integrating as the amount of O _X absorption.

If any of the above-mentioned playback operation execution conditions is not satisfied in step 401, or if the above conditions are no longer satisfied during execution of the playback operation, step 41
9, 421 is executed, and the reproduction operation is stopped. Also,
If all the above conditions are satisfied in step 401, the regeneration operation of the NO _X absorbent 15 is executed in steps 403 to 407.

That is, in step 403, the counter T
Is incremented by 1, and in step 405 it is determined whether the value of the counter T is equal to or greater than a predetermined value T ₀ . The counter T is a counter indicating the time after the regeneration operation is started, and the predetermined value T ₀ is the number of times of routine execution corresponding to the time required for completely regenerating the NO _X absorbent. If T <T ₀ in step 405, it is determined that the NO _x absorbent has not been completely regenerated, and the process proceeds to step 407 to execute (continue) the regeneration operation. That is, in step 407, the shutter valve 6 of the engine intake pipe 2 is closed to a predetermined opening degree to throttle the intake air amount of the engine, and a predetermined amount of reducing agent is supplied from the reducing agent supply device 11 to the NO _X absorbent 15. To do.

The opening of the shutter valve is preset as a function of the engine speed in order to prevent abrupt deceleration, and this function is set in the ROM 23 of the ECU 20.
Are stored in the form of a numerical table. Step 407
Then, the opening setting value of the shutter valve 6 is read from the numerical table based on the engine speed, and the shutter valve actuator 7 is driven so that the opening detected by the shutter valve opening sensor 8 becomes equal to the above setting value. The shutter valve 6 is controlled to a predetermined opening. Further, the reducing agent supply amount is determined according to the engine intake air amount (the opening degree of the shutter valve 6 and the engine speed). If was T ≧ T ₀ in step 405, that is, the reproduction operation is considered to have a reducing and NO _X emission of the NO _X absorbent is performed for a predetermined time or more has been performed completely, the process proceeds to step 419 The intake shutter valve 6 is fully opened, the reducing agent supply from the reducing agent supply device 11 is stopped to end the regeneration operation, the counter T is cleared (= 0) in step 421, and the routine is ended.

Next, in steps 409 to 417, NO _{X is} carried out.
The presence or absence of poisoning of the absorbent is determined. That is, in step 409, it is determined whether the value of the counter T has reached the predetermined value T _D. Here, T _D is the number of times of routine execution corresponding to the time t _D in FIG. In step 409, T = T _D
If it is, the exhaust oxygen concentration A at the outlet of the NO _X absorbent 15 is read from the oxygen concentration sensor 10 in step 411, and in step 413, it is determined whether or not the oxygen concentration A is larger than a predetermined value A ₀ (FIG. 3). To be judged.

If A> A ₀ , NO as described above.
_Since it is considered that low temperature poisoning of the _X absorbent 15 is occurring, the flag F indicating that poisoning is occurring at step 415.
Set ₁ (= "1") and end the routine. If A ≦ A ₀ in step 413, it is considered that the NO _x absorbent 15 is not poisoned, so step 4
At 17, the flag F ₁ is reset (= “0”) and the routine ends. If T ≠ TD in step 409, the routine ends.

That is, by executing this routine, if the low temperature poisoning of the NO _X absorbent 15 is occurring, the flag F ₁ is set (= "1"), and if the low temperature poisoning is not occurring. Flag F ₁ is reset (= “0”). Next, the poisoning recovery process of this embodiment will be described with reference to FIG. FIG. 5 shows an example of a flowchart of poisoning recovery processing. This routine is similar to the routine of FIG.
Although it is executed by the CPU 20 at regular intervals, the execution interval of this routine is set to be considerably longer than the execution interval of the routine of FIG. Further, this routine may be executed each time the vehicle travels a fixed distance, instead of being executed every fixed time.

In this embodiment, the value of the flag F ₁ set by the routine of FIG. 4, whether or not the regeneration operation of the NO _X absorbent is being executed, and whether the exhaust temperature of the NO _X absorbent upstream side is a predetermined value or more is determined. The following poisoning recovery processing is performed accordingly. (1) N with the flag F ₁ set (= "1")
If O routine during playback operation of _X absorbent is performed (Fig. 5 step 501 and 503), by energizing a predetermined time to the heater 16 of the NO _X absorbent, heat the upstream end face of the NO _X absorbent 15 (Steps 505 to 509). SOF or the like attached to the surface of the NO _x absorbent burns and vaporizes at a high temperature (for example, 400 ° C. or higher). The NO _x absorbent regeneration operation is executed when the exhaust temperature rises above a predetermined value.
At this time, by heating with the heater 16, N
Temperature of O _X absorbent upstream end face beyond the temperature, the combustion of such SOF is started at the end face. As a result, the poisoning of the upstream end surface of the NO _x absorbent is recovered, so that the reducing agent is oxidized at the upstream end surface, and the NOx is generated by the combustion heat.
_X Absorber temperature rises. Due to this temperature rise, SOF combustion starts in the portion adjacent to the upstream end face, and poisoning recovery and reducing agent oxidation also occur in this portion. Thus, now the temperature rise due to oxidation reaction of the combustion with a reducing agent sequentially such a chain to SOF from upstream to downstream of the NO _X absorbent occurs, _the NO _X absorbent entire poisoning recovery To do.

(2) Flag F ₁ is set (= "1")
In the state where the NO _X absorbent regeneration operation is not being performed (NO
_When this routine is executed during the _X absorption operation (steps 501 and 503 in FIG. 5), it is determined whether or not the NO _x absorbent upstream side exhaust gas temperature is equal to or higher than a predetermined value (for example, 400 ° C.) (step 511). ), The following processing is performed according to the result.

When the exhaust gas temperature is equal to or higher than a predetermined value (for example, 400 ° C.), the SOF can be burned by heating the heater even when the regeneration operation is not being executed.
Steps 505 to 509 are executed to recover poisoning. When the exhaust gas temperature is lower than the predetermined value (for example, 400 degrees C), the process proceeds to step 513, and the set value T _START of the execution start exhaust gas temperature condition of the next regeneration operation execution start condition (step 401 in FIG. 4). Is set higher by a predetermined temperature T _A. As a result, even if the routine is not executed during the next regeneration operation and the heater 16 is not energized, the NO _x absorbent temperature rises to the temperature at which SOF combustion occurs due to the exhaust gas temperature and poisoning occurs. Recovery is performed.

It should be noted that if the steps 511 and 513 are executed again without the poisoning being recovered by the next execution of the regeneration operation, the exhaust temperature condition for starting the regeneration operation will be set higher by T _A. Therefore, when the next regeneration operation is executed, the SOF is surely burned and the poisoning is recovered. (3) If this routine is executed while the flag F ₁ is reset (= “0”), the poisoning has already been recovered, so the steps (1) and (2) above are not performed 51
5, the regeneration operation execution start exhaust gas temperature condition setting value T _START
Is returned to the initial value T _S0 ) and the routine ends.

[0036] As described above, by detecting the exhaust gas oxygen concentration of the NO _X absorbent downstream in the present embodiment, by executing the poisoning recovery process to determine the presence or absence of cold poisoning of the NO _X absorbent However, low temperature poisoning can be determined by other methods. FIG. 6 shows the configuration of an embodiment in which poisoning determination is performed based on the NO _X absorbent temperature. In FIG. 6, the same reference numerals as those in FIG. The present embodiment is different from the embodiment of FIG. 1 in that the oxygen concentration sensor 10 of FIG. 1 is not used and a temperature sensor 12 for measuring the temperature of the NO _x absorbent is provided instead. The temperature sensor 12 is inserted inside the NO _X absorbent on the downstream side by a predetermined distance from the upstream end surface of the NO _X absorbent 15, and measures the NO _X absorbent temperature at this portion.

Next, the principle of poisoning detection of this embodiment will be described with reference to FIGS. 7 (A) and 7 (B). FIG. 7 (A) shows the distribution of the adhered amount of SOF, reducing agent, etc. inside the NO _x absorbent after the exhaust gas has flowed for a certain period of time. As shown in FIG. 7 (A), the amount of SOF or the like attached is greatest near the upstream end face of the NO _x absorbent, and decreases toward the outlet side. This indicates that the surface area of platinum Pt that can contribute to the oxidation of the reducing agent decreases toward the upstream side of the NO _x absorbent due to the attachment of SOF and the like, and increases toward the downstream side. In addition, FIG. 7B shows NO when the NO _x absorbent is not poisoned (solid line) and when it is poisoned (dotted line).
_The NO _X absorbent during _X absorbent regenerating operation shows the temperature distribution inside. As can be seen from the figure, when poisoning does not occur (solid line), the reducing agent is most actively oxidized at the NO _x absorbent upstream end face, and reaches the NO _x absorbent downstream side. quantities temperature of the NO _X absorbent upstream end face is the highest since reducing the temperature the more becomes the downstream side is decreased.

On the other hand, when poisoning occurs (dotted line), the surface area of platinum Pt that can contribute to the reaction is small on the upstream end face, and therefore the oxidizing reaction of the reducing agent near the upstream side is reduced, The amount of reducing agent that reaches the downstream side without participating in the upstream side increases. In addition, the amount of SOF attached on the downstream side is smaller than that on the upstream side, and platinum P that can contribute to the reaction
Since the surface area of t is relatively large, the oxidizing reaction of the reducing agent becomes active. Therefore, on the downstream side rises as compared with the case where _the NO _X absorbent internal temperature does not occur poisoning. Therefore, it is possible to detect the presence or absence of poisoning of the NO _X absorbent by monitoring the increase in the internal temperature just downstream fixed distance from the upstream side end face of the NO _X absorbent.

[0039] Figure 8 shows an example of a flowchart showing the poisoning determining operation of the NO _X absorbent based on _the NO _X absorbent internal temperature in this example. This routine is also executed by the above-described ECU 20 at regular time intervals as in the routine of FIG. In FIG. 8, steps 801-807 and 81
9, 821 are steps 401 to 407, 419 of FIG.
Since it is the same as 421, only the parts different from FIG. 4 will be described here.

Step 809 in FIG. 8 is a determination as to whether or not a predetermined time or more has elapsed since the start of the reproduction operation. Where T
₁ is the number of times of execution of the routine corresponding to the time required for the temperature inside the NO _x absorbent to rise after the start of the regeneration operation to obtain the temperature distribution as shown in FIG. 7 (B). If the predetermined time has passed in step 809, step 81
Temperature sensor 12 upstream exhaust temperature t _in of the NO _X absorbent 15 from the exhaust temperature sensor 13 at 1, and in step 812
Is input from the internal temperature t _c of the NO _x absorbent 15. Next, at step 813, the NO _x absorbent internal temperature t _c input as above is more than the predetermined value Δt from the upstream side exhaust temperature t _in.
It is determined whether or not it is higher than ₀ .

If t _c ≧ t _in + Δt _{0 in} step 813, that is, the temperature distribution inside the NO _x absorbent is as shown by the dotted line in FIG. 7 (B), the NO _x absorbent is poisoned. If it is determined that it has occurred, the process proceeds to step 815 and the flag F ₁
Is set (= “1”). Also, t _c <t _in + Δt ₀
If it is, the temperature distribution is as shown by the solid line in FIG. 7 (B), so it is determined that poisoning has not occurred and step 81
7 and the flag F ₁ is reset (= "0"). As a result, as in the routine of FIG.
It can be judged by the value of ₁ .

In the present embodiment as well, the routine shown in FIG. 5 is executed at regular time intervals, and when it is determined that poisoning has occurred, the poisoning recovery process is carried out as shown in FIG. Similar to the example.

[0043]

As described above, the exhaust gas purifying apparatus of the present invention determines whether or not there is low temperature poisoning by the SOF of the NO _x absorbent or the liquid reducing agent, and recovers poisoning if poisoning occurs. By performing the treatment, it is possible to prevent the exhaust purification efficiency from decreasing and always keep the exhaust in a good state.

[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 absorption and release action of a NO _x absorbent.

3 is a diagram illustrating the poisoning detection principle of the NO _X absorbent in the embodiment of FIG.

FIG. 4 is a flow chart showing an operation for determining poisoning of the NO _X absorbent of the embodiment of FIG.

FIG. 5 is a flowchart showing poisoning recovery processing.

FIG. 6 is a diagram showing another embodiment of the exhaust emission control device of the present invention.

7 is a diagram illustrating the poisoning detection principle of the NO _X absorbent in the embodiment of FIG. 6.

FIG. 8 is a flowchart showing the operation of determining the poisoning of the NO _X absorbent of the embodiment of FIG.

[Explanation of symbols]

1 ... Diesel engine 2 ... Engine intake pipe 3 ... Engine exhaust pipe 6 ... Shutter valve 7 ... Actuator 8 ... Shutter valve opening sensor 10 ... Oxygen concentration sensor 11 ... Reductant supply device 12 ... NO _X absorbent temperature sensor 13 ... Exhaust gas Temperature sensor 15 ... NO _X absorbent 16 ... Heater 20 ... Electronic control unit (ECU)

Claims (1)

[Claims] In an exhaust passage of 1. A diesel engine, the air-fuel ratio of the inflowing exhaust absorbs NO _X when the lean, the _the NO _X absorbent oxygen concentration of the inflowing exhaust emits NO _X absorbed when reduced arrangement and, by introducing a reducing agent into the exhaust at a predetermined operating condition is burned on _the NO _X absorbent, the NO causes release the absorbed NO _X by consuming oxygen in the exhaust from _the NO _X absorbent _In an exhaust gas purification apparatus for an internal combustion engine for reducing and purifying _X , means for detecting poisoning of a NO _x absorbent due to unburned components in exhaust gas, and heating the NO _x absorbent when the poisoning is detected. An exhaust emission control device for an internal combustion engine, comprising: means for recovering poisoning.