DE10315264B4 - Exhaust emission-cleaning device and method for an internal combustion engine - Google Patents

Abstract

Emission cleaning device for the Exhaust gases of an internal combustion engine (1) with a storage reduction NOx catalyst (50a), which is capable of storing NOx, a reducing agent supply device (20) to the feeder Reductant to the Storage Reduction NOx Catalyst (50a) and an electronic control unit (22) for controlling the reducing agent supply device (20), wherein the storage reduction NOx catalyst (50a) not only NOx, but also SOx can store, that the absorption capacity reduced NOx and poisoning of the storage reduction NOx catalyst (50a) leads, through a recovery process under supply of Reducing agents can be eliminated, wherein, when the storage-reduction NOx catalyst (50a) is still in an aftertreatment phase in which noble metal substances of the Storage reduction NOx catalyst (50a) come into contact and chemically stabilized, the electronic control unit (22) the timing to carry a recovery process to control the start time and the duration of the recovery process on the basis of past Operating data of the internal combustion engine (1) determines.

Description

The The invention relates to an emission control device for the exhaust gases an internal combustion engine with a storage reduction NOx catalyst and to a process for the purification of the exhaust gases by means of a such a catalyst.

Various activities are undertaken to reduce the emission amount of nitrogen oxides (NOx) or other harmful Components of a lean burn internal combustion engine such as a diesel engine. One of these measures consists in the use of an exhaust emission cleaning device with a lean NOx catalyst and a reducing agent supply device is provided for cleaning an exhaust emission from the internal combustion engine with lean burn.

Of the Lean NOx catalyst is an exhaust emission purifying catalyst, which can primarily eliminate nitrogen oxides (NOx) present in the Exhaust emission are included. Described in more detail leads the Lean NOX catalyst an exhaust emission purge action for storage the nitrogen oxides (NOx) from the exhaust emission when the exhaust emission has a comparatively high oxygen concentration, and reducing of stored nitrogen oxides (NOx) to harmless nitrogen (N2) by causing a reaction of the NOx with unburned components (CO, HC) contained in the exhaust emission when the exhaust emission has a comparatively low oxygen concentration, that is if the exhaust gas entering the catalyst a comparatively low air-fuel ratio.

on the other hand For example, the reducing agent supply device is commonly used with an internal combustion engine lean burn provided in an oxygen excess state for insertion a reducing agent in the form of a motor fuel in the exhaust emission is operable to be discharged from the engine is to reduce the oxygen concentration of the exhaust emission and at the same time for feeding an unburned constituent in the form of hydrocarbons (motor fuel: HC) to the lean NOx catalyst for Promote the exhaust emission purifying action of the lean NOx catalyst.

Incidentally, the fuel supplied to the engine contains sulfur components, so that the exhaust emission from the engine contains sulfur oxide (SOx) such as SO ₂ and SO ₃ , and nitrogen oxides (NOx). The sulfur oxides (SOx) stored in the lean NOx catalyst together with the nitrogen oxides (NOx) tend to gradually change into chemically stable sulfates (BaSO ₄ ) accumulated in the lean NOx catalyst.

When the amount of sulfates (BaSO ₄ ) accumulated in the lean NOx catalyst, that is, the amount of sulfur oxides (SOx) stored in the catalyst becomes excessively large, the capability of the lean NOx catalyst for storage decreases the nitrogen oxides (NOx) resulting in the reduction of the exhaust emission purifying capability of the lean NOx catalyst. Namely, the lean NOx catalyst may be poisoned with the sulfur oxides (SOx), that is, it may suffer from so-called "SOx poisoning" which reduces the exhaust emission purifying efficiency.

In order to deal with the problem indicated above, a so-called "SOx poisoning elimination control" is started, which is started upon detecting the reduction of the exhaust gas emission ratio in order to provide the lean NOx catalyst with an appropriate amount of a reducing agent for promoting release of the sulfates (US Pat. BaSO ₄ ) to thereby eliminate the SOx poisoning and restore the original exhaust emission purification efficiency of the lean NOx catalyst.

Specifically, the SOx poisoning elimination control for supplying the exhaust emission purifying catalyst with a larger amount of the reducing agent than those used for promoting the reduction and release of nitrogen oxides (NOx), raising the temperature of the lean NOx catalyst, and considerably lowering the NOx Exhaust gas air-fuel ratio with the supply of the reducing agent to thereby promote the thermal decomposition and release of the sulfates (BaSO ₄ ), which constitute a poisoning ingredient for the lean NOx catalyst.

A extensive research by the inventors led to a disadvantage of SOx poisoning removal control, focusing on a period of After treatment of the lean NOx catalyst refers.

It should be noted that the above-discussed lean NOx catalyst generally has an aftertreatment period (a period of initial deterioration), which is a period from the moment of initial use of the lean NOx catalyst to the moment when the Catalytic substances of the noble metal, which are divided on the catalyst, in close contact with each other and are chemically stabilized. In other words, the aftertreatment period is a time sufficient for the lean NOx Kata lysator is required to complete its initial sintering process.

During the Post-treatment period, the catalytic substances of the precious metal with high uniformity distributed and the lean NOx catalyst has a higher ability for storing the nitrogen oxides (NOx) and sulfur oxides (SOx) as after the post-treatment period. The exhaust emission purifying properties of the lean NOx catalyst during the aftertreatment period are opposite to the nominal properties namely different namely differently. When a determination is made as to whether the lean NOx catalyst is at the SOx poisoning suffers or not based on its exhaust emission purification efficiency, obtained by detecting the state of exhaust emission with a sensor which is arranged in the exhaust passage of the engine tends to thus, exhaust emission purification efficiency obtained during After-treatment period to be high enough to determine that the catalyst does not suffer from SOx poisoning, even if the catalyst actually with a considerable one huge Amount of the poisoning ingredient is poisoned in the catalyst while the aftertreatment period is accumulated.

at the moment when the amount of reduction of exhaust emission purification efficiency becomes large enough is to determine that the lean NOx catalyst is involved in SOx poisoning suffers, then is detected, the SOx poisoning is serious with an oversized amount of the poisoning component accumulating in the lean NOx catalyst is. When the SOx poisoning elimination control would be started at this condition, the amount of the poisoning ingredient to be released be that big that an odor intensity the exhaust emission undesirable a permissible one exceed upper limit would, this means the concentration of released poisoning components would become undesirable Response height in accordance exceed the upper limit of the odor intensity.

From the documents DE 197 49 400 A1 . EP 0 898 061 A2 and WO 02/101209 A1 emission control devices are known for internal combustion engines, which have NOx reduction catalysts, which are continuously supplied with reducing agent in order to achieve a reduction of the incoming NOx in a continuous process. This type of catalysts is also described as SCR catalysts. The cited documents describe control means for calculating the optimum amount of reducing agent and supplying this amount of reducing agent to the catalysts.

task The invention is an emission control device for the exhaust gases an internal combustion engine, which has a storage reduction NOx catalyst has and it allows on the one hand unwanted odors minimize exhaust emissions and cause permanent deterioration of the storage reduction NOx catalyst by absorbed sulfur oxides to prevent.

These The object is achieved by an emission cleaning device according to claim 1 solved. With claim 7 is further an exhaust emission purification method for advantageously cleaning the exhaust emissions by means of a storage reduction NOx catalyst in accordance described with claim 1.

According to the exhaust emission purifying apparatus and method for one Internal combustion engine, which is described, is based on the determination of whether the poisoning elimination control is required or not, on the operating history of the internal combustion engine before the post-treatment period of the exhaust emission purification catalyst has expired. During the Aftertreatment period are the exhaust emission purifying properties the catalyst is not stable, so it is difficult to poison the state of the catalyst based on, for example, the exhaust emission purifying efficiency appreciate. Therefore, the poisoning state of the catalytic converter before the expiration the post-treatment period on the basis of the operating history estimated the internal combustion engine and determining if the poisoning elimination control applied should be based on the thus estimated poisoning status carried out of the catalyst.

The Exhaust emission cleaning device according to a preferred embodiment of this invention further has an exhaust gas component detection sensor, the downstream of the NOx catalyst is arranged to detect a NOx concentration of the exhaust gas, wherein the electronic control unit (ECU) controls the timing for performing a Recovery process of the NOx catalyst based on a Output signal of the exhaust gas component detection sensor determines when the post-treatment period has expired. Here, the exhaust gas component detection sensor a NOx sensor, an air-fuel ratio sensor, or an oxygen sensor be.

The method according to a preferred embodiment of the invention further comprises the Detecting a NOx concentration of the exhaust gas and determining the timing for performing a recovery process of the NOx catalyst based on the detected NOx concentration of the exhaust gas when the aftertreatment period has expired.

After this the after-treatment period of the exhaust emission-purifying catalyst has expired, the exhaust emission purifying properties become of the catalyst stabilized so that the amount of the poisoning constituent, which is accumulated in the catalyst can be accurately estimated can be based on a change the state of exhaust emission, that is, a change in exhaust emission purification efficiency of the catalyst. Accordingly, the odor intensity the exhaust emission before and after the end of the post-treatment period wherein the poisoning elimination control instruction means to appreciate the poisoning state of the exhaust emission purifying catalyst based on both the operating history of the internal combustion engine and the state of the exhaust emission is arranged. The state the exhaust emission can be represented be by a parameter that comes with a change the exhaust emission purification efficiency changes, such as a Concentration of NOx in the exhaust gas, an air-fuel ratio of Exhaust emission and an oxygen concentration in the exhaust emission. It should be noted that the use of the state of exhaust emission after the expiration of the post-treatment period for estimating the Poisoning state of the exhaust emission-cleaning catalyst not is essential and that another detection device than the Detecting means for detecting the state of the exhaust emission may be provided, so that the poisoning state of the catalyst after the end of the post-treatment period on the basis of a Output signal of this other detection device is estimated. For example, the poisoning state of the catalyst after the post-treatment period based on a history of operations estimated the internal combustion engine become. However, the state for the determination that the Poisoning elimination control is required after the expiration the post-treatment period to desirable Way different from the state for the determination before the expiration the post-treatment period.

at an advantageous arrangement of the exhaust emission cleaning device according to the above-described preferred form of the invention comprises the poisoning elimination control instruction means a first poisoning elimination control instruction means for Carry out a determination of whether the poisoning elimination control required is, based on the history of the operation of the internal combustion engine and a second poisoning control instruction means to perform a determination of whether the poisoning elimination control required is based on the state of the exhaust emission, wherein the Poison elimination control instruction means the poisoning elimination device for applying the poisoning elimination control in the post-treatment period of the exhaust emission purifying catalyst instructs when an off the first and second poisoning elimination control instruction means the investigation has made that the poisoning elimination control is required.

at an advantageous arrangement of the exhaust emission cleaning method according to the above described design of the invention, the poisoning elimination control in the after-treatment period of the exhaust emission purifying catalyst applied when it is determined that the poisoning elimination control is required, based on either the operating history the internal combustion engine or the state of the exhaust emission.

at the exhaust emission cleaning device and Process according to the above described advantageous arrangements of the above-described The invention becomes the poisoning state of the exhaust emission purifying catalyst estimated on the basis not only of the operating history of the engine, but also the state of the exhaust emission in the post-treatment period of the catalyst, and the poisoning elimination control becomes applied when the estimate based on either the operating history of the engine or the state of the exhaust emission indicates that the poisoning elimination control is required.

Namely, the estimation of the poisoning state of the catalyst based on the history of operation of the engine is an indirect estimate of the poisoning state of the catalyst. This estimation does not allow the application of poisoning elimination control at a suitable timing at which the exhaust emission purifying catalyst is poisoned with the poisoning ingredient whose concentration is considerably higher than a nominal value. Accordingly, a direct estimation of the poisoning state of the exhaust emission purifying catalyst based on the state of the exhaust emission from the catalyst in addition to the indirect estimation based on the history of operation of the engine enables the poisoning elimination control to be applied in response to a determination that the poisoning elimination control required on the basis of either direct or indirect estimation. This arrangement is effective for optimizing the moment when the poisoning elimination control is started.

at the above-described advantageous arrangement of the exhaust emission cleaning device is the Poisoning removal device preferably for applying the Poisoning elimination control in the after-treatment period of the exhaust emission purifying catalyst arranged to reduce an amount of the poisoning ingredient, which is released from the exhaust emission purifying catalyst, when the second poisoning control instruction means the investigation has made that the poisoning elimination control is required.

at the above-described advantageous arrangement of the exhaust emission cleaning method For example, the poisoning elimination control is preferably in the post-treatment period of the exhaust emission purifying catalyst applied to an amount of the poisoning constituents released from the exhaust emission purifying catalyst released when it is determined that the poisoning elimination control is required, based on the state of the exhaust emission.

The is called, that the poisoning elimination control in the post-treatment period in response to the determination by the second poison removal control instruction means, that the poisoning elimination control is required during the Reducing the amount of poisoning components is applied, which are released from the exhaust emission purifying catalyst. During this post-treatment period applied poisoning elimination control in response to the determination by the second poison removal control instructing means the catalyst can be poisoned with the poisoning ingredient, its concentration considerably higher than the nominal value is as indicated above. According tilts the amount of poisoning ingredient released from the catalyst in the poisoning elimination control to a large amount. The exhaust emission purifier and methods described above are for use the poisoning elimination control arranged to reduce the amount of Poisoning component in the situation indicated above to minimize the odor intensity of the released from the catalyst Reduce exhaust emissions. The amount of released poisoning ingredient should be represented be through a relationship in terms of the flow rate the exhaust emission and should not be interpreted as an absolute amount become.

The Exhaust emission cleaning device according to the above indicated advantageous arrangement is preferably arranged such after the poisoning elimination control by the poisoning elimination means in the after-treatment period of the exhaust emission purifying catalyst in response to the determination by the second poison removal control instructing means is applied, the poisoning elimination control required is the first poisoning elimination control instructing means the poisoning eliminator for applying the poisoning elimination control at an earlier Moment instructs as a moment in which the first poisoning control device instructs the poisoning eliminator to apply the poisoning elimination control.

The Exhaust emission cleaning method according to the above-described advantageous arrangement is preferably arranged such that after the application of the poisoning elimination control in the post-treatment period the exhaust emission purifying catalyst in response to a determination based on the state of exhaust emission that the poisoning elimination control is required, the poisoning elimination control appealing upon a determination that the poisoning elimination control required is, based on the history of the operation of the internal combustion engine at an earlier moment is applied as a moment when the poisoning elimination control in response to the above-indicated determination on the basis the state of the exhaust emission is applied.

Namely, as soon as the poisoning elimination control is applied by the poisoning removing means in the after-treatment period in response to the determination by the second poisoning elimination control instruction means that the poisoning elimination control is required, the exhaust emission purifying catalyst is liable to relatively serious poisoning with the poisoning ingredient as described above. In view of this tendency, it is preferable to change the state for determination by the first poisoning elimination control instruction means that the poisoning elimination control is required on the basis of the operation history of the internal combustion engine, so that the poisoning elimination control is based on the indirect estimation of the poisoning state of the catalyst the engine operating history applied at an earlier moment is applied. This arrangement he allows the application of the poisoning elimination control at an appropriate timing depending on the actual poisoning condition of the catalyst based on the engine operating history.

The Features, advantages and technical and industrial significance of this Invention will be better understood with reference to the following detailed description of the preferred Embodiments of the Invention.

1 Fig. 12 schematically illustrates an exhaust emission purifying apparatus according to an exemplary embodiment of this invention.

2 FIG. 12 shows an internal structure of a particulate filter used in the exhaust emission purifying apparatus of FIG 1 is provided.

3 11 is a view for explaining a method of determining whether or not a catalyst provided in the exhaust gas purifying apparatus is in its after-treatment period.

4 FIG. 16 is a graph for explaining a correlation between the amount of SOx accumulated in the catalyst and the concentration of the released SOx. FIG.

And 5 FIG. 12 is a view for explaining SOx poisoning elimination control for the exhaust emission odor control. FIG.

exemplary embodiments The present invention will be described with reference to the accompanying drawings described in detail.

It is understandable, that the arrangement of an internal combustion engine, only as a Example is discussed for that the principle of the present invention is applicable according to the desired specification changed can be.

First embodiment

An exhaust emission purifying apparatus according to a first embodiment of this invention is disposed in an exhaust system of a lean-burn engine, a typical example of which is a diesel engine. This exhaust emission purifying apparatus is provided with a catalyst 50 and a reducing agent supply device 20 Mistake.

The catalyst 50 includes a housing 51 and two exhaust emission purifying catalysts 50a . 50b in the case 51 are arranged. The catalyst 50 performs an exhaust emission purge action for purifying harmful substances contained in an exhaust emission emitted from the engine 1 is delivered.

The housing is described in detail 51 of the catalyst 50 downstream of a turbine housing of the internal combustion engine 1 and receives the exhaust emission purifying catalysts in the form of the storage reduction NOx catalyst 50a and the particulate filter 50b which are arranged in the order of description in the downstream direction of the exhaust emission. It will be understood that the term storage used herein means retention of a substance (solid, liquid, gas molecules) in the form of at least adsorption, adhesion, absorption, capture, occlusion and others. In the following description, the storage reduction NOx catalyst will be described 50a as a lean NOx catalyst 50a designated.

The lean NOx catalyst 50a , one of the two emission control catalysts 50a . 50b Performs an exhaust emission purifying action to eliminate mainly nitrogen oxides (NOx) from the exhaust emission. The lean NOx catalyst has been discussed in more detail 50a an exhaust emission purifying ability for absorbing the nitrogen oxides (NOx) in the exhaust emission when the exhaust emission reaches a comparatively high oxygen concentration, and reducing the absorbed nitrogen oxides (NOx) into harmless nitrogen (N2) by causing a reaction of the NOx with unburned components (CO, HC) contained in the exhaust emission when the exhaust emission has a comparatively low oxygen concentration, that is, when in the lean NOx catalyst 50a incoming exhaust emission has a comparatively low air-fuel ratio.

The lean NOx catalyst 50a It consists of a support formed of aluminum (Al 2 O 3), a noble metal such as platinum (Pt) and at least one substance selected from the group consisting of alkali metals such as potassium (K), sodium (Na), lithium ( Li) and cesium (Cs); Alkaline earth metals such as barium (Ba) and calcium (Ca); and rare earth elements such as Lantan (La) and Itrium (Y). The noble metal and the at least one substance indicated above are supported by the aluminum support.

In the internal combustion engine 1 With the lean burn provided with the exhaust emission purifying apparatus according to the present embodiment, the combustion of a fuel generally takes place in an oxygen excess state in which the oxygen concentration ration of exhaust emissions generated as a result of combustion is not likely to be reduced to a level at which the nitrogen oxides are reduced to nitrogen as described above. It should also be noted that the exhaust emission produced in the oxygen excess state contains only trace amounts of unburned components (CO, HC).

Accordingly, the exhaust emission purifying apparatus according to the present embodiment is provided with the reducing agent supply device 20 which is operable to introduce a reducing agent in the form of the engine fuel (HC) into the exhaust emission to lower the oxygen concentration of the exhaust emission and supply hydrocarbons (HC) as the unburned components to the exhaust emission, thereby the exhaust emission purifying action of the lean NOx catalyst 50a to promote. The reductant delivery device 20 will be described in detail.

The other exhaust emission purifying catalyst in the form of the particulate filter 50b performs an exhaust emission purge action for oxidizing and burning foreign matters such as soot contained in the exhaust emission. The particle filter is described in detail 50b with a filter 58 which carries an active oxygen releasing agent so that the foreign matter attached to the filter 58 accumulated or captured, are oxidized with the active oxygen and burned, whereby the foreign substances are eliminated.

The filter 58 has a honeycomb structure formed of cordierite or other porous material and has a variety of passages 55 . 56 that extend parallel to each other, as in 2 is shown. The honeycomb structure of the filter has been described in more detail 58 intake ports 55 by stuffing 55a closed at their downstream ends, and discharge channels 56 by stuffing 56a closed at their upstream ends. The inlet and outlet channels 55 . 56 are through thin partition walls 57 defined and in the LÄngs- and transverse direction of the filter 58 arranged.

The partition walls 57 have carrier layers formed of a suitable material such as aluminum (Al 2 O 3) on their outer surfaces and their internal pores. The support layers support a noble metal catalyst such as platinum (Pt) and the active oxygen release agent, which stores oxygen in the ambient atmosphere with a comparatively high oxygen concentration and releases the stored oxygen as active oxygen as the oxygen concentration in the ambient atmosphere decreases.

The Active oxygen release agent may comprise at least one substance, the chosen one is selected from the group consisting of alkali metals such as Potassium (K), sodium (Na), lithium (Li), cesium (Cs) and rubidium (Rb); Rlkalierdemetalle such as Barim (Ba), calcium (Ca) and strontium (Sr); rare earth metals such as lanthanum (La) and ytrium (Y); and transition metals such as cerium (Ce) and tin (Sn).

Preferably For example, the active oxygen release agent comprises at least one alkali metal and / or Alkalierdmetall with a higher tendency of ionization as calcium (Ca), that is at least one of potassium (K), lithium (Li), cesium (Cs), rubidium (Rb), barium (Ba) and strontium (Sr).

In the particulate filter constructed as described above 50b the exhaust emission flows through the intake ducts 55 , the partition walls 57 and the delivery channels 56 in this order, as indicated by arrows "a" in 2 is indicated, so that the foreign matter such as soot, which is contained in the exhaust emission, on the outer surfaces and in the pores of the partition walls 57 be caught when the exhaust emission through the partition walls 57 flowing. The foreign matter passing through the partition walls 57 are oxidized by active oxygen, the amount of which increases by several times the oxygen concentration of the exhaust emission is changed by the partition walls 57 passes through, whereby the foreign substances on the filter 58 to be burnt without producing a flame.

In the exhaust emission purifying apparatus of the present embodiment includes in the exhaust pipe 11 arranged catalyst 50 the storage reduction NOx catalyst 50a and the particulate filter 50b to eliminate the nitrogen oxides (NOx) and the foreign matters such as soot contained in the exhaust emission.

In the present embodiment, the lean NOx catalyst 50a and the particulate filter 50b arranged in series with each other so that the heat of reaction generated by the oxidation and reduction reaction, that in the lean NOx catalyst 50a is effected, is used to raise the temperature of the particulate filter 50b , and so that from the lean NOx catalyst 50a released active oxygen due to the oxidation and reduction reaction is applied through the particulate filter 50b to remove the foreign matter. It is understood from the foregoing description that the lean NOx catalyst 50a carries a substance similar to the active oxygen release agent. In this regard, the Ma ger NOx catalyst 50a so considered that it has a function of the active oxygen release agent.

Next, the reducing agent supply device 20 described, which is provided for promoting the exhaust emission cleaning actions of the exhaust emission purification catalysts 50a . 50b ,

The reductant delivery device 20 includes a reducing agent introduction valve 21 that with a section of the discharge line 11 connected upstream of the catalyst 50 located, and an electronic control unit (ECU) 22 , which is provided for controlling the opening and closing actions of the reducing agent introduction valve 21 ,

The reducing agent introduction valve 21 is an electrically operated shut-off valve which is opened at an appropriate timing for introducing an optimum amount of a reducing agent into the exhaust emission according to a predetermined reducing agent supply program stored in the electronic control unit 22 is stored. The reducing agent introduction valve 21 is also with a fuel supply system of the internal combustion engine 1 connected to introduce the fuel as the reducing agent in the exhaust emission.

The electronic control unit 22 determines the amount and timing of the introduction of the reducing agent based on the output signals of an air-fuel ratio sensor 23 and a NOx sensor 25 , the downstream of the catalyst 50 is arranged, output signals of the exhaust emission temperature sensors 24a . 24b , respectively upstream and downstream of the particulate filter 50b are arranged, and various operating history values of the internal combustion engine 1 , The electronic control unit 22 opens and closes the reducing agent introduction valve 21 according to the predetermined amount and timing of the introduction of the reducing agent.

As described above, the present exhaust emission purifying apparatus is arranged to control the reducing agent supply device 20 for introducing the engine fuel as the reducing agent into the exhaust emission to thereby lower the oxygen concentration of the exhaust emission passing through the catalyst 50 and to supply the exhaust gas emission with hydrocarbons (HC) as the unburned components for promoting the exhaust emission purifying actions of the exhaust emission purifying catalysts 50a . 50b ,

As discussed above with respect to the prior art, the lean NOx catalyst may 50a absorb the sulfur oxides (SOx) as well as the nitrogen oxides (NOx) contained in the exhaust emission. It becomes a considered mechanism of storage of sulfur oxides (SOx) by the lean NOx catalyst 50a described.

While the mechanism described is the mechanism by which the sulfur oxides (SOx) pass through the lean NOx catalyst 50a stored, it is assumed that the sulfur oxides (SOx) through the particulate filter 50b are stored by a mechanism similar to that of the lean NOx catalyst 50a because of the particle filter 50b the active oxygen release agent bears similar to that of the NOx catalyst 50a ,

When the exhaust gas emitted by the lean NOx catalyst 50a Oxygen in the form of O2 ^- or O- ² is deposited on the platinum (Pt) carried by the carrier in the exhaust emission oxygen-containing oxygen, which has a comparatively high air-fuel ratio. Like the nitrogen oxides NOx, therefore, the sulfur oxides (SOx) from the exhaust emission at the platinum (Pt) are oxidized to SO3 ^- or SO4 ^- .

The thus generated SO3 ^- or SO 4 ^- are further oxidized on the platinum Pt to sulfuric acid ions (SO4 ^-2), and the sulfuric acid ions (SO4 ^-2) are in the lean NOx catalyst 50a stored while sticking with barium oxide (Bao). The stored sulfuric acid ions (SO4 ^-2 ) gradually adhere to the barium ion (Ba ²⁺ ) to produce a chemically stable sulfate (BASO4).

The sulfur oxides (SOx) are considered to be in the lean NOx catalyst 50a stored in the manner described above. The sulphate (BASO4) produced in the storage of sulfur oxides (SOx) is likely to have a relatively large crystal size and a relatively high degree of chemical stability and is hardly decomposed. Accordingly, once in the lean NOx catalyst 50a stored sulfur oxides (SOx) are not easily released, but they are accumulated as sulfate (BASO4), even if the air-fuel ratio of the exhaust emission in the reduction and release of nitrogen oxides (NOx) is lowered.

Accordingly, the amount of barium oxide (BAO) that may contribute to the absorption and release of the nitrogen oxides (NOx) decreases with an increase in the amount of sulfate (BAO4) present in the lean NOx catalyst 50a is accumulated. Thus, the ability of the lean NOx catalyst becomes 50a for storing the nitrogen oxides (NOx) decreases as the amount of accumulated sulfates (BASO4) increases. At the same time, the amount of Aktivsauer stoffs, by the particle filter 50b is released, reduced and the surface of the filter, which can contribute to the oxidation and combustion of foreign matter, is also reduced. An excessively large amount of sulphates (BASO4) present in the lean NOx catalyst 50a namely accumulated, causes a so-called "SOx poisoning" of the two exhaust emission-cleaning catalysts 50a . 50b ,

In view of the above, the present exhaust emission purifying apparatus is arranged to eliminate SOx poisoning in the following manner. Initially, the catalyst 50 supplied with the reducing agent to the temperature of the catalyst 50 to raise to a height of about 500 to 700 ° C with heat generated by a reaction between the reducing agent and the catalytic substances, so that the accumulated barium sulfate (BASO4) is thermally decomposed to S03 ^- or SO4 ^- . Then that's through the catalyst 50 flowing through the exhaust emission again with the reducing agent supplied to maintain the oxygen concentration (air-fuel ratio) of the exhaust emission at a low level for a comparatively long time, so that the SO3 ^- or SO 4 ^-, which are produced by thermal decomposition of the barium sulfate (BAS4) to gaseous SO2 ^- Be reduced by a reaction with hydrocarbons (HC and carbon monoxide CO), which are included in the exhaust emission, whereby the gaseous SO2 ^{- is} released together with the exhaust emission from the catalyst 50 , That is, a so-called "SOx poisoning elimination control" is applied for restoring the original exhaust emission purifying capability of the catalyst 50 ,

In the present exhaust emission purifying apparatus, the poisoning elimination device is constituted by the reducing agent supply device 20 which is operable to supply the reducing agent for raising the temperature of the catalyst 50 and reducing and releasing the poisoning ingredients and the electronic control unit 22 which is operable to control the reducing agent supply device 20 ,

As described above, the present exhaust emission purifying apparatus is arranged to first the temperature of the catalyst 50 and then to supply the exhaust emission with the reducing agent for eliminating the SOx poisoning as in the reduction and release of the nitrogen oxides (NOx).

Like the timing at which the reducing agent is supplied to remove the nitrogen oxides (NOx) and foreign matters, the timing at which the catalyst becomes 50 that is poisoned with SOx is restored, that is, the timing at which the SOx poisoning elimination control is started or applied, controlled or detected in accordance with various control programs included in the electronic control unit 22 are stored.

Described in detail is the timing at which the SOx poisoning elimination control is applied, based on the outputs of the air-fuel ratio sensor 23 and the NOx sensor 25 , the downstream of the catalyst 50 is arranged, and the operational history values of the internal combustion engine 1 ,

However, it is necessary to use the post-treatment period (period of initial deterioration) of the lean NOx catalyst 50a and the particulate filter 50b to be considered in determining the timing of the application of SOx poisoning elimination control. The aftertreatment period becomes as a period from the moment of the initial use of the lean NOx catalyst 50a at the moment when the noble metal catalytic substances distributed on the catalyst come in close contact and are chemically stabilized. In other words, the aftertreatment period is a time required for the lean NOx catalyst 50a to complete his initial sintering.

In the post-treatment period, the catalytic substances of the noble metal are distributed with high uniformity and the catalyst 50 has a higher ability to store the nitrogen oxides (NOx) and sulfur oxides (SOx) than after the post-treatment period. The exhaust emission purifying properties of the catalyst 50 namely during the post-treatment period differ from the normal properties. In the post-treatment period, the exhaust emission purification efficiency of the catalyst tends to be 50 namely, to be relatively high, even if the catalyst 50 is actually poisoned with a considerable amount of sulfur oxides (SOx) accumulated therein.

When the SOx poisoning control is applied in response to a considerable amount of reduction of the exhaust emission purification efficiency of the catalyst 50 as detected on the basis of the output signals of the above-indicated many sensors, the timing at which the SOx poisoning control is started is delayed in the post-treatment period, so that the amount of the poisoning ingredient to be released in the post-treatment period is so it would be large that an odor intensity of the exhaust emission undesirably exceeds an allowable upper limit, that is, the concentration of released Ver The toxic components would undesirably exceed a threshold in accordance with the upper limit of odor intensity.

In view of the above disadvantage, the exhaust emission purifying apparatus according to the present embodiment is arranged such that the electronic control unit 22 stores a poisoning elimination control program that is formulated to appropriately determine the moment of release of the poisoning ingredients, that is, the timing of the beginning of the SOx poisoning elimination control, during the post-treatment period of the catalyst 50 and is further arranged to apply the SOx poisoning elimination control of the poisoning elimination control program to minimize the amount of odor generated in the SOx poisoning elimination control during the post-treatment period.

It is described in detail the poisoning elimination control program. The electronic control unit 22 determines if the catalyst 50 is in the aftertreatment period while the operational history values of the internal combustion engine 1 and the output of the NOx sensor 25 be taken into account.

The electronic control unit estimates in detail 22 the amount of SOx present in the catalyst 50 accumulated, based on the engine operating history values, the NOx concentration detects the exhaust emission downstream of the catalyst 50 based on the output of the NOx sensor 25 , compares the detected NOx concentration with a threshold determined by the estimated amount of SOx present in the catalyst 50 is accumulated (hereinafter simply referred to as "estimated amount of SOx poisoning") and makes a determination as to whether the catalyst is 50 is in the aftertreatment period or not according to a comparison result of the detected NOx concentration with the detected threshold value.

To carry out the determination, whether the catalyst 50 is in the aftertreatment period uses the electronic control unit 22 a data map, as in 3 is shown. This data map represents a relationship between the estimated amount of SOx poisoning and the above-indicated threshold value against which the detected NOx concentration is compared. In 3 the response value is represented by a curve A. Determining if the catalyst 50 Namely, whether or not it is in the post-treatment period is performed by determining whether a point passing through the NOx sensor 25 detected NOx concentration is defined, and the estimated amount of SOx poisoning are below the curve A or not.

Specifically, when the estimated amount of SOx poisoning is represented by a point "a" in FIG 3 is indicated, the exhaust emission purification efficiency is considered to be still high when the NOx concentration detected in this state is lower than the response value represented by the curve A, that is, when the detected NOx concentration is represented by a Point "b" in 3 is indicated. This is the catalyst 50 as still considered in the post-treatment period while being more or less poisoned with SOx. When the detected NOx concentration is higher than the threshold value, that is, represented by a point "c" in FIG 3 is indicated, it is considered that the exhaust emission purifying efficiency is excessively lowered due to SOx poisoning and that the post-treatment period has already expired. Thus, the determination of whether the catalyst 50 is in the aftertreatment period or not, are performed by comparing the detected NOx concentration represented by the output of the NOx sensor 25 with the response value determined based on the estimated amount of SOx poisoning and according to the data map stored in the electronic control unit 22 is stored.

In order to estimate the amount of SOx poisoning based on the engine operating history values, the present exhaust emission purifying apparatus is arranged to estimate the amount of sulfur oxides (SOx) generated based on at least one of cumulative amount of fuel consumption, cumulative amount of intake air, and cumulative operation time the internal combustion engine after the last Sox poisoning elimination control. When the internal combustion engine 1 When a vehicle is used, the amount of sox poisoning can be estimated by estimating the amount of generated sulfur oxides (SOx) based on at least one of the cumulative travel distance and the time of the vehicle and a cumulative amount of a change over time of the delivery internal combustion engine 1 ,

It is understandable that the preliminary investigation, whether the catalyst 50 is in the aftertreatment period or not, not the one using the data map of 3 is limited, which is described only for illustrative purposes. The determination may be made by another method, for example, based on at least one of: a cumulative time of use of the catalyst 50 ; a cumulative operating time of the engine 1 ; a Ku mulative amount of fuel consumption by the engine 1 ; a cumulative driving distance and time of a motor vehicle in which the engine 1 is installed. Thus, the determination of whether the catalyst 50 is in the aftertreatment period, carried out in various ways.

Then the electronic control unit selects 23 one of two ways of determining whether Sox poisoning control must be applied, depending on the state of the catalyst 50 that is, depending on whether the catalyst 50 is in the post-treatment period or not.

Described in detail, the electronic control unit begins 22 the sox poisoning elimination control based on the output of the Nox sensor 25 and the engine operating history value, respectively, when it is determined that the catalyst 50 is in the post-treatment period. When it is determined that the post-treatment period has expired, the electronic control unit starts 22 the SOX poisoning elimination control based on only the output of the NOX sensor 25 ,

In the determining manner based on the engine operating history values, the amount of sox poisoning is estimated on the basis of the engine operating history values, and the moment when the sox poisoning elimination control is started is determined according to a predetermined control routine. That is, the sox poisoning elimination control is applied or started at a moment when based on the estimation state of the soot poisoning of the catalyst 50 it is determined that the onset of SOx poisoning control is required.

That is, the amount of SOX poisoning is estimated based on at least one of the cumulative amount of fuel consumption by the engine 1 , the cumulative amount of engine intake air 1 , the cumulative travel distance of the vehicle etc. after the last application of the sox poisoning elimination control as described above. When the estimated amount of sox poisoning reaches a predetermined upper limit, that is, when the operating history of the engine 1 meets a predetermined condition, determines the electronic control unit 22 in that the SOX poisoning elimination control must be applied and establishes a first mark requiring the application of the sox poisoning elimination control. Thus, the electronic control unit serves 22 as a first poisoning elimination control instruction means in the present embodiment.

If the determination of whether the sox poisoning elimination control should be started, in the operating mode in response to the output signal of the Nox sensor 25 is carried out, the NOx concentration by the downstream of the catalyst 50 arranged NOx sensor 25 recorded and the amount of sox poisoning of the catalyst 50 is based on the output of the NOX sensor 25 estimated. The timing at which SOx poisoning elimination control is started is determined according to a predetermined control routine. That is, the SOx poisoning elimination control is applied or started at a moment when based on the estimated state of SOx poisoning of the catalyst 50 it is determined that the onset of SOx poisoning control is required.

That is, the amount of SOx poisoning and NOx concentration downstream of the catalyst 50 have the correlation described above, so that the electronic control unit 22 estimate the amount of SOx poisoning based on the NOx concentration downstream of the catalyst 50 passing through the NOx sensor 25 is detected. When the estimated amount of SOx poisoning is greater than a predetermined upper limit, the electronic control unit directs 22 a second mark requiring the application of SOx poisoning elimination control. Thus, the electronic control unit serves 22 as a second SOx poisoning elimination control instruction device in the present embodiment.

If the catalyst 50 is in the after-treatment period, the electronic control unit determines 22 in that the SOx poisoning elimination control must be applied when one of the first or second marks is established. In this case, the electronic control unit 22 the reducing agent supply device 20 to apply or start the SOx poisoning control. After the post-treatment period of the catalyst 50 has expired, instructs the electronic control unit 22 the reducing agent supply device 20 for applying the SOx poisoning elimination control when the second flag is established based on the output signal of the NOx sensor 25 ,

Namely, the poisoning elimination control program is formulated such that the SOx poisoning elimination control is started on the basis of both the engine operating history values and the output signal of the NOx sensor 25 before the post-treatment period of the catalyst 50 has expired and based on only the output of the NOx sensor 25 after the post-treatment period has gone.

For example, the following advantages are provided according to the present embodiment, wherein the determination as to whether the SOx poisoning elimination control should be applied or started is made depending on whether the catalyst 50 is in the post-treatment period or not:
If the determination of whether the SOx poisoning elimination control is required during the catalyst 50 is in the aftertreatment period based on the engine operating history values, the poisoning component may be released at an appropriate timing with a result of minimizing the odor intensity of the exhaust emission even in the aftertreatment period of the exhaust emission purifying catalysts 50a . 50b in which the exhaust emission purifying properties are not stable.

In the post-treatment period, the determination that SOx poisoning elimination control is required is delayed with respect to the actual moment of SOx poisoning when the determination is made on the output of the NOx sensor 25 founded. However, in the present embodiment, where the determination is based on the amount of SOx poisoning estimated on the basis of the engine operating history values, the first flag which requires the initiation of SOx poisoning elimination control is set at an appropriate timing, so that the concentration of the poisoning component released during the SOx poisoning elimination control can be reduced to a level not higher than the allowable upper limit.

Further, not only the engine operating history value (s) but also the output of the NOx sensor becomes 25 used to perform the determination whether the SOx poisoning elimination control is required before the after-treatment period has expired so that the SOx poisoning elimination control can be started, the second flag being established at a moment when the exhaust emission purifying catalysts 50a . 50b is poisoned with sulfur oxides (SOx) due to a large amount of the sulfur component contained in the fuel before the first flag is established based on the engine operating history value (s).

After the aftertreatment period has elapsed, the exhaust emission purifying properties of the exhaust emission purifying catalysts become 50a . 50b stabilized so that the amount of the poisoning constituent accumulated can be accurately estimated based on a change in the state of exhaust emission, that is, a change in exhaust emission purification efficiency. Therefore, the determination of whether to set the second flag or not is based on the output of the NOx sensor 25 after the post-treatment period, so that the SOx poisoning elimination control is applied depending on a change in the exhaust emission purifying efficiency of the exhaust emission purifying catalysts 50a . 50b as by the output of the NOx sensor 25 is represented. Accordingly, the SOx poisoning elimination control can be started at an optimal timing after the post-treatment period has expired.

Then is a second embodiment of present invention described. The second embodiment used in addition to the poisoning elimination control program described above a compensation program for setting the state for the determination based on the engine operating history value or values, whether SOx poisoning elimination control is required.

This equalization program is formulated such that once the second mark is established in the aftertreatment period, based on the output of the NOx sensor 25 According to the above-described poisoning elimination control program, the state for the determination based on the engine operation history value or the values as to whether the first flag should be established is set to change the moment at which the SOx poisoning elimination control is started.

More specifically, when the second flag requiring the beginning of SOx poisoning elimination control is established based on the output signal of the NOx sensor 25 before the end of the post-treatment period, the concentration of sulfur components contained in the fuel is considerably higher than a normal value, so that the concentration of released poisoning components is expected to be relatively high even after the following SOx poisoning elimination control based on of the engine operating history value (s). In view of this disadvantage, the present balancing program is formulated to advance the moment of setting the first mark based on the engine operating history value (s), thereby reducing the odor intensity of the exhaust emission during the subsequent SOx poisoning elimination control.

The compensation program will be further explained with respect to a specific example wherein the amount of SOx poisoning is estimated based on the cumulative amount of fuel consumption by the engine 1 as the engine history value after the last SOx poisoning elimination control. In this example, the equalization program is formulated to reduce the initially set cumulative amount of fuel consumption threshold by an appropriate amount, and then to compare the cumulative fuel consumption amount to the reduced response value (equalize response value). When the cumulative amount reaches the equalization threshold, it is determined that the SOx poisoning elimination control should be applied, that is, the first flag is set to start SOx poisoning elimination control. The threshold value coincides with an upper limit of the poisoning amount of the catalyst 50 with the sulfur oxides (SOx) match.

Thus, the equalization program used in the second embodiment is formulated such that once the determination required for SOx poisoning elimination control is made on the basis of the output of the NOx sensor 25 before the aftertreatment period has elapsed, the state (threshold) for the determination is set on the basis of the engine operating history value (s) to advance the moment of commencement of the subsequent SOx poisoning elimination control based on the engine operating history value (s) the exhaust emission in SOx poisoning elimination control due to the exposure of the catalyst 50 a relatively high concentration of the poisoning components.

Then is a third embodiment of this Invention described. The third embodiment uses in addition to the poisoning elimination control program described above an odor minimization program for applying SOx poisoning elimination control, to increase the amount of released poisoning ingredients reduce to minimize the odor intensity of the exhaust emission.

More specifically, the odor minimization program is formulated such that once the second mark is established in the post-treatment period based on the output of the NOx sensor 25 according to the poisoning elimination control program described above, the SOx poisoning elimination control according to this second mark is applied to minimize the amount of released poisoning ingredients.

Before the detailed explanation of this odor minimization program, a history used for checking the odor intensity of the exhaust emission will be explained with reference to FIG 4 described. In the course, the estimated amount of SOx poisoning, that is, the estimated amount of the accumulated sulfur oxides (SOx) is plotted along the abscissa, while the amount or concentration of the released poisoning components is plotted along the ordinate. A curve B in the graph represents a correlation between the amount of accumulated SOx and the concentration of the released poisoning ingredients, that is, it represents the concentration of the released poisoning ingredients in accordance with each value of the amount of the accumulated SOx. A threshold value of the concentration of released poisoning constituents, which in 4 is indicated with an upper limit (allowable maximum value) of the odor intensity of the catalyst 50 emitted exhaust emission match. When the SOx poisoning control is applied while the concentration of the released poisoning ingredients is higher than the threshold value, the odor intensity of the exhaust emission exceeds the upper limit. This upper limit of odor intensity may be set to a minimum concentration level of the released poisoning constituents that may be perceived as a smell by the human sense of smell.

It is understandable from the course of 4 in that, when the amount of accumulated SOx is relatively small (as indicated by the point "d"), the amount or concentration of the poisoning ingredients released in the SOx poisoning elimination control is less than that when applied in this state Response value in accordance with the upper limit of the odor intensity, so that the perceived odor intensity of the exhaust emission is almost zero in SOx poisoning elimination control.

If the amount of accumulated SOx is relatively large (as indicated by the point "e") exceeds the concentration of released poisoning components the Pickup value, so that a relatively high odor intensity of the exhaust emission is perceived.

However, if the second mark requiring SOx poisoning elimination control is established based on the output of the SOx sensor 25 in the post-treatment period of the catalyst 50 , is the SOx poisoning of the catalyst 50 more serious than if the first mark requiring SOx poisoning elimination control is set based on the engine operating history value (s). One Namely, the phenomenon where the second mark is established in the post-treatment period is similar to that when the SOx poisoning elimination control is applied to the state represented by the point e.

In the above-described state, the SOx poisoning elimination control causes the released exhaust emission to have a relatively high concentration of the poisoning components. In view of this disadvantage, the SOx poisoning elimination control required becomes based on the output of the NOx sensor 25 in the post-treatment period, applied according to the odor minimization program, to reduce the amount or concentration of the released poisoning ingredients below the threshold value in accordance with the upper limit or the maximum permissible value of the odor intensity.

Described in detail, the SOx poisoning elimination control according to the odor minimization program in the third embodiment is applied so that a period of time during which the reducing agent is supplied is shortened for decreasing the concentration of the released poisoning ingredients in view of a fact described below. That is, the SOx poisoning elimination control according to the normal poisoning elimination control program is applied by first supplying the reducing agent for raising the temperature of the catalyst 50 and decreasing the air-fuel ratio of the exhaust emission to promote release of the poisoning ingredients. The concentration of the poisoning ingredients released in this SOx poisoning elimination control changes substantially in proportion to the temperature of the catalyst 50 and the period of time during which the air-fuel ratio of the exhaust emission is kept at a lowered value (the period of time during which the exhaust emission is kept in a rich condition). In view of this, the time period during which the reducing agent is supplied is shortened in the initial stage of SOx poisoning elimination control according to the odor minimization program.

The reducing agent introduction valve 21 Namely, is set alternately in the open and closed states (on and off state), so that the opening time (on-time) is set relatively short in the initial stage of SOx poisoning elimination control, as in 5 is indicated, so that the temperature of the catalyst 50 is set lower than the SOx poisoning elimination control according to the normal poisoning elimination control program. Accordingly, the time period during which the air-fuel ratio is maintained at a lowered value is shortened by the amount or concentration of the catalyst 50 to liberate released poisoning ingredients so that the odor intensity of the exhaust emission in the SOx poisoning elimination control can be minimized.

The amount of poisoning ingredient released, which is reduced according to the present odor minimization program, is represented by a ratio of that amount to the flow rate of exhaust emission through the catalyst 50 therethrough. The open time of the reducing agent introduction valve 21 and the number of operations for introducing the reducing agent according to the odor minimization program are suitably determined by data obtained by experiments or experiments.

After an initial period of release of the poisoning ingredients to reduce the released amount according to the odor minimization program, the total amount of sulfur oxides (SOx) present in the catalyst is reduced 50 is accumulated. Therefore, the reducing agent is introduced according to the normal poisoning elimination control program in the following period of SOx poisoning elimination control.

Thus, the third embodiment is arranged to effect the specific control of the reducing agent introduction valve 21 for optimizing the SOx poisoning elimination control for minimizing the odor intensity of the exhaust emission when the SOx poisoning elimination control is required on the basis of the output signal of the NOx sensor 25 in the post-treatment period of the catalyst 50 ,

While the preferred embodiments of this invention are described in detail, it will be understood that that the invention is not limited to the details of the illustrated embodiments limited is, but to be executed with many changes can.

The poisoning elimination control used in the illustrated embodiments is formulated such that the determination of whether the SOx poisoning elimination control is required or not is made in the post-treatment period of the catalyst 50 is based not only on the engine operating history value or values, but also on the output of the NOx sensor 25 , The determination based on the output of the NOx sensor 25 however, is not essential and the SOx poisoning control can be applied in the post-treatment period responsive only to the first tag established based on the engine operating history value (s). Namely, the poisoning elimination control program of the present invention requires the application of the SOx poisoning elimination control in response to at least the first flag established based on the engine operating history value (s) while the exhaust emission purifying catalysts 50a . 50b are in the post-treatment period.

For example, the poisoning elimination control program may be formulated to select one of two mutually independent processing routines depending on whether or not the aftertreatment period has expired, so that the first processing routine is executed when the engine operating history value (s) are used to effect determination of whether the SOx poisoning elimination control is required while the second processing routine is executed when the output signal of the NOx sensor 25 is used to effect the determination.

Although the compensation program provided in the second embodiment is formulated to change the response value of the cumulative amount of fuel consumption by the engine 1 , the compensation according to the compensation program is not to a setting of the response value of the cumulative amount of the fuel injection into the engine 1 limited in it. For example, the threshold value of the cumulative amount of the intake air of the engine 1 is decreased in advancing the moment of the beginning of SOx poisoning elimination control when the determination of whether or not this control is required is based on the cumulative amount of the intake air. The response value of any other parameter of the motor 1 which can be used to estimate the amount of SOx poisoning of the catalyst 50 can be changed according to the compensation program.

While the illustrated embodiments are described with respect the poisoning elimination control for restoring the exhaust emission purifying catalysts, which are poisoned with sulfur oxides (SOx) that are in the exhaust emission are included, the poisoning ingredients are not according to the invention limited to sulfur oxides (SOx), but also include any other components with such Compositions that are lighter in the catalysts than nitrogen oxides (NOx) are stored.

In the illustrated embodiments, the output of the NOx sensor 25 used to estimate the amount of poisoning of the catalyst 50 , The amount of poisoning of the catalyst 50 however, can be estimated on the basis of the output of the air-fuel ratio sensor 23 or an oxygen sensor instead of the output of the NOx sensor 25 , Here, the determination as to whether the poisoning elimination control is required is also made based on the output of the air-fuel ratio sensor or the oxygen sensor and a prepared data map representing a correlation between the amount of the accumulated SOx and the sensor output. Thus, any detection means which can estimate the amount of poisoning of the exhaust emission purifying catalysts and the NOx sensor 25 are used as the detection means for detecting the state of exhaust emission from the catalyst in the present invention.

A poisoning condition of an exhaust emission purifying catalyst ( 50a . 50b ) in its after-treatment period is estimated on the basis of an operational history value of an engine, and the SOx poisoning elimination control is applied at the moment when it is determined based on the estimated poisoning state that the SOx poisoning elimination control is required. Furthermore, the determination of whether the SOx poisoning elimination control is required can be based on an output signal of a NOx sensor ( 25 ) are founded even in the post-treatment period. When the determination that the SOx poisoning control is required is performed in the after-treatment period based on the output signal of the NOx sensor (FIG. 25 ), this control is used to reduce the concentration of poisoning components released during the control. At this time, the determination based on the engine operation history value as to whether the following SOx poisoning elimination control should be applied is performed to advance the moment at which this subsequent control is applied.

As As described above, the present invention provides a Technique that allows the minimization of the odor intensity of an exhaust emission, the while a poisoning elimination control is issued to eliminate a poisoning of an exhaust emission purifying catalyst.

The present invention provides an apparatus and a method for purifying exhaust emission from an internal combustion engine, wherein a poisoning condition of the exhaust emission purifying catalyst in its after-treatment period is estimated on the basis of an operational history value of an engine and an SOx poisoning elimination control is applied at the moment when it is determined on the basis of the estimated poisoning state that the SOx poisoning elimination control is required, and a determination of whether the SOx poisoning elimination control should be applied can be based on an output signal of the NOx sensor, even in the post-treatment period. When the determination that the SOx poisoning elimination control is required is performed in the post-treatment period based on the output of the NOx sensor, this control is applied to reduce the concentration of a poisoning ingredient released during the control.

there the determination is based on the engine operating history value, whether the following SOx poisoning elimination control applied, to bring the moment forward, where the following control is applied. The device and procedure allow the Minimization of odor intensity the exhaust emission during the the poisoning elimination control of the exhaust emission purifying catalyst is delivered.

Claims (11)

Emission cleaning device for the exhaust gases of an internal combustion engine ( 1 ) with a storage reduction NOx catalyst ( 50a ) capable of storing NOx, a reducing agent supply device ( 20 ) for supplying reducing agent to the storage reduction NOx catalyst ( 50a ) and an electronic control unit ( 22 ) for controlling the reducing agent supply device ( 20 ), wherein the storage reduction NOx catalyst ( 50a ) can store not only NOx but also SOx which reduces the capacity of NOx and poison the storage reduction NOx catalyst ( 50a ), which can be eliminated by a regeneration process with supply of reducing agents, wherein, when the storage reduction NOx catalyst ( 50a ) is still in an aftertreatment phase, in the noble metal substances of the storage reduction NOx catalyst ( 50a ) and chemically stabilized, the electronic control unit ( 22 ) the timing for performing a recovery process for controlling the start time and the duration of the recovery process on the basis of past operating data of the internal combustion engine ( 1 ). Exhaust emission-cleaning device for an internal combustion engine ( 1 ) according to claim 1, characterized in that it further comprises an exhaust gas constituent detection sensor ( 25 ) downstream of the storage reduction NOx catalyst ( 50a ) is arranged to detect a NOx concentration of the exhaust gas, and the electronic control unit (ECU 22 ) the timing for performing a recovery process of the storage-reduction type NOx catalyst ( 50a ) based on an output signal of the exhaust gas constituent detection sensor ( 25 ) is determined when the post-treatment period has expired. Exhaust emission-cleaning device for an internal combustion engine ( 1 ) according to claim 2, characterized in that when the storage reduction NOx catalyst ( 50a ) is still in its after-treatment period, the electronic control unit (ECU 22 ) determines that a recovery process of the storage reduction NOx catalyst ( 50a ) is required when either the timing for performing a restoration based on an operational history of the engine or the output of the exhaust gas constituent detection sensor ( 25 ) exceeds a predetermined threshold. Exhaust emission-cleaning device for an internal combustion engine ( 1 ) according to claim 3, characterized in that when performing a recovery process on the basis of the output signal of the exhaust gas constituent detection sensor ( 25 ), a period of time during which the reducing agent is supplied is shortened to decrease the concentration of the released poisoning ingredients. Exhaust emission-cleaning device for an internal combustion engine ( 1 ) according to claim 3 or 4, characterized in that when a recovery process in response to the output signal of the exhaust gas constituent detection sensor ( 25 ), a time interval for performing a restoration process based on an operation history is shortened. Exhaust emission-cleaning device for an internal combustion engine ( 1 ) according to claim 2, characterized in that the exhaust gas constituent detection sensor ( 25 ) is a NOx sensor, an air-fuel ratio sensor or an oxygen sensor. Exhaust emission cleaning method for an internal combustion engine ( 1 ) with a storage reduction NOx catalyst ( 50a ) comprising the steps of: absorbing NOx contained in the exhaust gas that is caused by the engine ( 1 ), and Restoring the storage reduction NOx catalyst ( 50a by reducing the stored NOx and eliminating poisoning of the catalyst by means of the supply of a reducing agent; Estimating the timing for performing a recovery process of the storage reduction NOx catalyst ( 50a ) based on a history of the engine ( 1 ) when the storage reduction NOx catalyst ( 50a ) is still in its post-treatment period. Exhaust emission cleaning method for an internal combustion engine ( 1 ) according to claim 7, characterized by detecting a NOx concentration of the exhaust gas, and determining the timing for performing a recovery process of the storage reduction NOx catalyst ( 50a ) based on the detected NOx concentration of the exhaust gas when the post-treatment period has expired. Exhaust emission cleaning method for an internal combustion engine ( 1 ) according to claim 8, characterized in that when the storage reduction NOx catalyst ( 50a ) is still in its after-treatment period, it is determined that a recovery process of the storage-reduction type NOx catalyst ( 50a ) is required when either the timing to perform a restoration based on an operating history of the engine or the detected NOx concentration of the exhaust gas exceeds a predetermined threshold. Exhaust emission cleaning method for an internal combustion engine ( 1 ) according to claim 9, characterized in that when the performance of a recovery process is determined on the basis of the detected NOx concentration of the exhaust gas, the time period during which the reducing agent is supplied, is shortened to reduce the concentration of the released poisoning constituents. Exhaust emission cleaning method for an internal combustion engine ( 1 ) according to claim 9 or 10, characterized in that when a recovery process is performed in response to the detected NOx concentration of the exhaust gas, the time interval for performing a recovery process based on a history of operation is shortened.