JP2010196496A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress a decrease in the NO<SB>x</SB>reducing performance of a NO<SB>x</SB>storage reduction catalyst used in an exhaust emission control device. <P>SOLUTION: In this exhaust emission control device 10, when it is determined that the NO<SB>x</SB>storage reduction catalyst 16 is poisoned with hydrocarbon (HC) by performing NO<SB>x</SB>storage reduction catalyst purifying treatment, HC purge treatment for removing the HC according to the NO<SB>x</SB>storage capacity of the NO<SB>x</SB>storage reduction catalyst 16 is performed. After that, NO<SB>x</SB>reducing treatment for enriching an air-fuel ratio of exhaust gas is performed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

In recent years, internal combustion engines mounted on automobiles and the like, in particular, diesel engines and lean burn engines that can burn an oxygen-rich mixture (a so-called lean air-fuel mixture having a lower fuel concentration than the stoichiometric air-fuel ratio). In a gasoline engine, a technique for purifying nitrogen oxides (NO _x ) contained in the exhaust gas of the internal combustion engine is desired.

In response to such demands, a technique for arranging a NO _X storage material in the exhaust system of an internal combustion engine has been proposed. As one of the NO _X storage materials, an exhaust purification device using an NO _X storage reduction catalyst that stores and reduces nitrogen oxides (NO _X ) is known (for example, Patent Document 1). _The NO _X storage and reduction type catalyst, a noble metal catalyst having an oxidation function, and _the NO _X storage material having _the NO _X storage function, such as an alkali metal, which is configured to holding the, and _the NO _X storage in the exhaust by these , Two functions of NO _X release and purification are exhibited.

This _the NO _X storage and reduction type catalyst, when the air ratio of the exhaust gas flowing is lean state (low fuel concentration than the stoichiometric air fuel ratio) can be oxidized to nitrogen dioxide nitrogen monoxide in the exhaust gas by the noble metal catalyst, This nitrogen dioxide is stored as nitrate in the NO _X storage material. On the other hand, when the air-fuel ratio of the exhaust is rich (fuel concentration higher than the stoichiometric air-fuel ratio), nitrate is decomposed from the NO _X storage material and NO _X is released, and this NO _X is a precious metal catalyst. It is reduced to nitrogen by unburned hydrocarbons, carbon monoxide, etc. in the exhaust gas by catalytic action.

Therefore, in the exhaust system with _the NO _X storage reduction catalyst, when the air-fuel ratio of the exhaust gas reaches a predetermined amount _the NO _X storage amount is increased in _the NO _X storage reduction catalyst when it is lean, in the internal combustion engine By adjusting the air-fuel ratio of the air-fuel mixture to be burned, a rich spike is executed that brings the air-fuel ratio of the exhaust into a rich state in a spike manner (short time) in a short cycle. This rich spike treatment, the exhaust amounts of hydrocarbons (HC) and carbon monoxide (CO) unburned gas or the like is discharged, these unburned gases act on _the NO _X storage reduction catalyst as a reducing agent As a result, the stored NO _X is reduced, and NO _X can be stored again.

JP 2000-161105 A

However, in stratified combustion or lean combustion in an internal combustion engine at low rotation and low load, such as during idling, a state in which a large amount of HC is contained in the exhaust gas exhausted from the internal combustion engine occurs, which causes NO _X storage. The reduced catalyst may be poisoned by HC.

  Specifically, when a high concentration of HC comes in contact with the surface of the noble metal catalyst and an HC layer is formed on the noble metal catalyst, the catalytic reaction rate for oxidizing HC by oxygen in the exhaust gas decreases, and further accumulation of HC occurs. It is thought that a vicious cycle occurs in which the HC layer becomes thick. For this reason, even if a large amount of oxygen is present in the exhaust because the air-fuel ratio of the exhaust is made lean, if the thick HC layer is formed at one end, the removal of HC by oxidation does not proceed, It is thought that a thick HC layer is maintained.

In the state where the surface of the noble metal catalyst is covered by the HC layer, even if the rich spike is executed, NO _X released in the exhaust gas, it is prevented from coming into contact with the noble metal catalyst by a thick HC layer In some cases, the NO _X reduction performance of the NO _X storage reduction catalyst is deteriorated, so that the NO _X reduction is not sufficiently performed.

The present invention has been made in consideration of the above-described facts, and an object of the present invention is to suppress a reduction in NO _X reduction performance of a NO _X storage reduction catalyst used in an exhaust purification device.

In order to achieve the above object, an invention according to claim 1 is provided in an exhaust passage of an internal combustion engine, stores NO _X in exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean, and empties the inflowing exhaust gas. and _the NO _X storage and reduction type catalyst ratio is to reduce NO _X which has been occluded during the rich N _2, and adjusting means for adjusting the air-fuel ratio of the exhaust gas, by raising the temperature of the _the NO _X storage reduction catalyst Recovery means for recovering from a poisoned state by hydrocarbons, poisoning determining means for determining whether or not the NO _x storage reduction catalyst is poisoned by hydrocarbons, and said poisoning determining means wherein when _the NO _X storage reduction catalyst is determined to be in the poisoned state, the NO _X occluding reduction catalyst after controlling the recovery means so as to recover from the poisoned state, the air-fuel ratio of the exhaust by To enrich And control means for controlling the adjusting means, an exhaust gas purification device provided with.

The recovery means recovers the poisoning state by the hydrocarbon by raising the temperature of the NO _X storage reduction catalyst. As a method for raising the temperature of the this _the NO _X storage reduction catalyst, a method of the air-fuel ratio of the exhaust is lean state, to inject fuel into the exhaust gas flowing to the NO _X occluding and reducing catalyst within the range of the lean, the lean method for heating directly _the NO _X storage reduction catalyst in a state under the like.

According to the invention described in claim 1, when _the NO _X storage reduction catalyst is determined to be in the poisoned state of being poisoned by hydrocarbons by poisoning determining means, raising the _the NO _X storage reduction catalyst After the recovery means is controlled to recover from the hydrocarbon poisoning state by heating, the adjustment means is controlled to make the air-fuel ratio of the exhaust rich.
Therefore, before the NO _X reduction performance of the NO _X occluding and reducing catalyst by poisoning by hydrocarbon is lowered, _the NO _X storage reduction catalyst is recovered from the poisoned, drops of the NO _X reduction performance is suppressed .

By controlling the recovery means, the NO _X storage amount of the NO _X storage reduction catalyst increases while the poisoning state of the NO _X storage reduction catalyst by the hydrocarbon is being recovered. Therefore, the invention according to claim 2 includes a derivation means for deriving the NO _X occlusion amount of the NO _X storage reduction catalyst, and the control means is controlled by the derivation means when controlling the recovery means. When the derived NO _X storage amount exceeds a predetermined reference amount, the control of the recovery means is interrupted, and the adjustment means is controlled to make the air-fuel ratio of the exhaust rich. As this reference amount, an upper limit value at which the NO _X storage reduction catalyst in a poisoned state with hydrocarbons can store NO _X may be determined in advance. For this reason, the NO _X reduction performance of the NO _X storage reduction catalyst is suppressed, and the NO _X discharge to the outside air is further suppressed.

When _the NO _X storage reduction catalyst is determined to be in the poisoned state of being poisoned by hydrocarbons by poisoning determining means, _the NO _X storage reduction catalyst which this has been determined that poisoning condition, further NO There are cases where it is difficult to perform _X occlusion. Therefore, in the invention according to claim 3, the control means, when the NO _X occlusion amount derived by the derivation means before controlling the recovery means exceeds the reference amount, The adjusting means is controlled so as to make the air-fuel ratio rich. Therefore, while suppressing the emission of the NO _X to the outside air, and NO _X reduction performance degradation can be suppressed.

According to the present invention, when it is determined by the poisoning determination means that the NO _X storage reduction catalyst is in a poisoned state poisoned by hydrocarbons, the NO _X storage reduction catalyst is heated to raise the temperature. After the recovery means is controlled to recover from the poisoning state by hydrogen, the adjustment means is controlled to make the air-fuel ratio of the exhaust rich, so that the NO _X reduction performance reduction of the NO _X storage reduction catalyst is suppressed. .

It is a figure which shows schematic structure of the exhaust gas purification apparatus concerning embodiment of this invention. An example of the NO _X occluding and reducing catalyst purification process executed by the CPU of the exhaust gas purification apparatus according to an embodiment of the present invention is a flow chart showing. In _the NO _X storage reduction catalyst purification process executed by the CPU of the exhaust gas purification apparatus according to an embodiment of the present invention, she is a flow chart illustrating an example of the HC purge process. In Test Example shows for the peak intensity assigned to the nitrate of the NO _X occluding and reducing catalyst, and the ratio of the peak intensity assigned to the nitrate reduction processed of the NO _X occluding and reducing catalyst, and reducing the temperature, the relationship FIG.

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.

  As shown in FIG. 1, the exhaust purification device 10 of the present embodiment includes an internal combustion engine 12. Examples of the internal combustion engine 12 include a gasoline lean burn engine, a diesel engine, a hybrid-lean burn engine, and a hybrid-diesel engine.

The internal combustion engine 12 is connected to an exhaust pipe 14 that exhausts exhaust gas generated by the fuel in the internal combustion engine 12 to the outside. On the exhaust passage of the exhaust pipe 14, NO _X storage reduction catalyst 16 is provided.

_The NO _X storage reduction catalyst 16 is a catalyst air-fuel ratio of the exhaust gas flowing the occluding NO _X in the exhaust gas when the lean, reducing NO _X when the air-fuel ratio of the exhaust gas had been occluded during the rich is there.

Specifically, the NO _X storage reduction catalyst 16 is configured to hold a noble metal catalyst (such as platinum) having an oxidation function and a NO _X storage material having a NO _X storage function, and NO _X in the exhaust gas. Two functions of _X occlusion and NO _X reduction are demonstrated. Examples of the NO _X storage material include alkaline earth metals and alkali metals. When the air-fuel ratio of the inflowing exhaust gas is lean (fuel concentration lower than the stoichiometric air-fuel ratio), the NO _X storage reduction catalyst 16 is oxidized by the noble metal catalyst to oxidize nitrogen monoxide (NO) in the exhaust gas. Nitrogen (NO ₂ ) is formed, and this nitrogen dioxide is stored as nitrate in the NO _X storage material. On the other hand, when the air-fuel ratio of the exhaust is rich (fuel concentration higher than the stoichiometric air-fuel ratio), nitrate is decomposed from the NO _X storage material and NO _X is released, and this NO _X is a precious metal catalyst. It is reduced to nitrogen by unburned hydrocarbons, carbon monoxide, etc. in the exhaust gas by catalytic action.

Herein, the term air-fuel ratio of the exhaust gas state (rich state) is rich is not necessarily indicate only to rich combustion in the cylinder of an internal combustion engine 12, it is flowing into _the NO _X storage reduction catalyst 16 The ratio of the amount of air supplied to the exhaust gas and the amount of fuel (including the amount burned in the cylinder) is close to the stoichiometric air-fuel ratio (stoichiometric state), or the fuel amount is richer than the stoichiometric air-fuel ratio. It means being in a state. This amount of fuel also includes the amount of fuel that is added directly into the exhaust pipe 14 (in this embodiment, fuel that is added to the exhaust by the fuel injection valve 20 described later).

Similarly, the state in which the air-fuel ratio of the exhaust gas is lean (lean state) does not necessarily indicate only lean combustion in the cylinder of the internal combustion engine 12, but in the exhaust gas flowing into the NO _X storage reduction catalyst 16 The ratio of the air amount to the fuel amount is a lean state where the fuel amount is smaller than the stoichiometric air-fuel ratio. Similar to the above, this amount of fuel includes the amount of fuel added directly into the exhaust pipe 14.

As the NO _X storage reduction catalyst 16, for example, a catalyst coating layer made of aluminum oxide, titanium oxide or the like is provided on a monolith catalyst formed of cordierite, silicon carbide (SiC), ultra-thin plate stainless steel, etc. on the layer of platinum, a catalyst metal such as palladium, include structural obtained by holding the _the NO _X storage material such as barium. The monolith catalyst structural material carrier has a large number of cells, and the catalyst coat layer provided on the inner wall of the cells has a large surface area to enhance the contact efficiency with the exhaust gas.

In the present embodiment, the case where only the NO _X storage reduction catalyst 16 is provided on the exhaust gas exhaust path by the exhaust pipe 14 will be described. However, the exhaust gas of the NO _X storage reduction catalyst 16 will be described. Further, an oxidation catalyst, a three-way catalyst, a DPF (diesel particulate filter), and the like may be further provided on one or both of the upstream side and the downstream side in the discharge direction.

On the exhaust path of the exhaust pipe 14, the exhaust upstream side of the _the NO _X storage reduction catalyst 16, fuel injection valve 20 for adding fuel is provided in the exhaust. Further, the exhaust path of the exhaust gas by this exhaust pipe 14, the NO _X in the occlusion-reduction catalyst 16 from the exhaust upstream side, and the exhaust downstream side of the fuel injection valve 20, the air-fuel ratio of the exhaust from the exhaust gas component An air-fuel ratio sensor 22 for detecting the above is provided.

In addition, a bed temperature detection sensor 24 for measuring the bed temperature of the NO _X storage reduction catalyst 16 is provided at an installation location of the NO _X storage reduction catalyst 16 on the exhaust gas exhaust path by the exhaust pipe 14. Is provided.

  The internal combustion engine 12 is provided with a fuel injection valve 12A that injects fuel into the combustion chamber. The fuel injection valve 12A may be configured to inject fuel directly into the combustion chamber depending on the structure of the internal combustion engine 12, or may be configured to inject fuel into the inflow path of the mixed gas into the combustion chamber. Good.

  Further, the exhaust purification apparatus 10 is provided with an electronic control unit (hereinafter referred to as ECU) 18 for controlling the entire apparatus.

  The fuel injection valve 12A, the air-fuel ratio sensor 22, and the bed temperature detection sensor 24 are connected to the ECU 18 so that signals can be exchanged. The ECU 18 is connected to an unillustrated engine speed sensor 34 for detecting the engine speed from the rotation of the crankshaft so as to be able to exchange signals. In addition to such sensors, sensors necessary for engine control such as a vehicle speed sensor are connected to the ECU 18 so as to be able to exchange signals.

  In addition to the components shown in FIG. 1, various components, various sensors, and the like are mounted on the exhaust purification device 10 and are connected to the ECU 18 so as to be able to send and receive signals as appropriate. In FIG. Only the connection and configuration of the directly related parts are shown.

The ECU 18 includes both a CPU (central processing unit) 18A, a ROM (read only memory) 18D, a RAM (random access memory) 18C, an I / O (input / output control circuit) 18E, and a backup RAM (random access memory) 18B. It is configured as a known microcomputer connected to each other by a directional bus. In the ROM 18D, application programs such as a NO _X storage reduction catalyst purification processing routine described later are stored in advance. In addition to the above applications, various control maps are stored in the ROM 18D. The control map, even if the exhaust HC amount estimation map can purify HC amount estimation map, an exhaust amount of NO _X estimating map or the like. Details of each map will be described later.

The RAM 18C stores output signals from the sensors, calculation results of the CPU 18A, and the like. As the calculation result, for example, the NO _X storage amount of the NO _X storage reduction catalyst 16 derived at the time of each processing in the CPU 18A, the HC poisoning amount, and the like can be cited. These data, latest signal from each sensor is input, a new every time _the NO _X storage amount and HC poisoning amount and the like are derived in CPU 18a, (overwrite) is rewritten to the latest data.
The backup RAM 18B is a nonvolatile memory that can store data even after the internal combustion engine 12 stops moving. The various calculation results stored in the RAM 18C are stored in the backup RAM 18B as needed and updated to the latest data.

The CPU 18A operates according to an application program stored in the ROM (not shown), and executes NO _X storage reduction type catalyst purification processing in addition to known basic control such as fuel injection control and ignition timing control of the internal combustion engine 12. To do. In this _the NO _X storage reduction catalyst purification treatment, when _the NO _X storage and reduction type catalyst 16 is judged to be poisoned state of being poisoned by hydrocarbons (HC), the NO _X in the _the NO _X storage reduction catalyst 16 after performing the HC purge treatment for removing HC in accordance with the storage amount, to perform the NO _X reduction process to make the air-fuel ratio of the exhaust gas rich.

Hereinafter, the NO _X storage reduction catalyst purification process executed by the CPU 18A of the exhaust purification apparatus 10 configured as described above will be described. 2 and 3 are flowcharts showing an example of the flow of the NO _X occluding and reducing catalyst purification process routine performed by the CPU18A of the exhaust gas purifying apparatus 10 according to this embodiment.

Note that the _the NO _X storage reduction catalyst purifying process routine is a control integrated into the overall control of the internal combustion engine 12, it is repeatedly executed at predetermined time intervals.

In the normal operation control, the CPU 18A executes the NO _X storage reduction catalyst purification processing routine shown in FIG. 2 at a predetermined cycle predetermined as the NO _X storage reduction catalyst purification processing time interval. Proceed to

In step 100, the previously calculated HC poisoning amount (hereinafter referred to as “previously calculated HC poisoning amount”) Q _HCn−1 , and the previously calculated NO _X storage amount (hereinafter, “previous calculation NO _X storage amount”) Q _NOXn-1 is read from the RAM 18C.

The “previous calculated HC poisoning amount Q _HCn−1 ” indicates the poisoning amount by HC of the NO _X storage reduction catalyst 16 obtained during the previous HC poisoning amount calculation process. Further, this 'previously calculated _the NO _X storage amount _{Q NOxn-1',} shows _the NO _X storage amount of the NO _X occluding and reducing catalyst 16 obtained in the preceding _the NO _X storage amount calculation processing.

In the next step 102, the HC poisoning amount Q _HCn and the NO _X storage amount Q _NOxn of the NO _X storage reduction catalyst 16 during the processing of step 102 are calculated.

The HC poisoning amount Q _HCn at the time of the processing of step 102 of the NO _X storage reduction catalyst 16 is calculated from the following equation (1), for example.

Q _HCn = Q _HCn-1 + q _HC -f (T) (1)

In the above formula (1), Q _HCn represents the HC poisoning amount of the NO _X storage reduction catalyst 16 during the step 102 treatment. Q _HCn-1 indicates the previously calculated HC poisoning amount. q _HC represents the amount of HC contained in the exhaust gas flowing into the NO _X storage reduction catalyst 16 (hereinafter referred to as “exhaust HC amount”). f (T) is, HC purification performance at the bottom temperature T of the NO _X storage reduction catalyst 16 (hereinafter, referred to as "capable of purifying HC amount" hereinafter).

The previously calculated HC poisoning amount Q _HCn−1 read in step 100 is used as the previously calculated HC poisoning amount Q _HCn−1 in the equation (1).

The exhaust HC amount q _HC is, for example, experimentally determined in advance by engine speed, the amount of fuel injected from the fuel injection valve 12A, the amount of fuel added from the fuel injection valve 20, and the NO _X storage reduction type. Using the air-fuel ratio of the exhaust gas flowing into the catalyst 16 as a parameter, an exhaust HC amount estimation map in which these parameters are associated with the exhaust HC amount q _HC is stored in the ROM 18D.
Then, when the process of step 102, engine speed sensor 34, the air-fuel ratio sensor 22, and the fuel injection of each engine speed inputted from the valve 12A, NO _X occluding and reducing air-fuel ratio of the inflowing exhaust into the catalyst 16, From the injection amount of fuel injected from the fuel injection valve 12A and the addition amount of fuel added from the fuel injection valve 20, information indicating the exhaust HC amount q _HC corresponding to the values of these parameters is obtained as the exhaust HC amount. What is necessary is just to derive | lead-out by reading from an estimation map.
The parameters used in this exhaust HC amount estimation map are not limited to the above parameters. Further, the method for estimating the exhaust HC amount is not limited to the above method, and other known methods may be used.

The above can purify HC amount shows a can purify HC amount in the environment temperature T of the NO _X occluding and reducing catalyst 16. For this purifiable HC amount, for example, a purifiable HC amount estimation map in which temperature information indicating the bed temperature of the NO _X storage reduction catalyst 16 and information indicating the purifiable HC amount at the bed temperature are associated in advance. Stored in the ROM 18D. Then, at the time of the processing in step 102, the purifiable HC amount is derived by reading information indicating the purifiable HC amount corresponding to the temperature information input from the bed temperature detection sensor 24 from the purifiable HC amount estimation map. do it.

  The method for deriving the purifiable HC amount may employ a method using a function, and is not limited to a method using a map.

Further, in the present embodiment, in the derivation of the can purify HC amount, the bed temperature of the NO _X storage reduction catalyst 16 is input from the bed temperature sensor 24 for measuring the bed temperature of the NO _X occluding and reducing catalyst 16 directly The case where the signal is obtained by the above signal has been described. However, the method for obtaining the bed temperature of the NO _X storage reduction catalyst 16 is not limited to such a method. For example, in the exhaust pipe 14, NO _X storage reduction catalyst 16 from the exhaust upstream side, NO _X occluding region provided with the reduction catalyst 16, and NO _X either from storage reduction catalyst 16 in the exhaust downstream side in one place or the like, provided with a temperature sensor for measuring the exhaust gas temperature in the exhaust pipe 14, the exhaust gas temperature measured by these temperature sensors may estimate the bed temperature of the NO _X occluding and reducing catalyst 16.

On the other hand, the NO _X storage amount Q _NOxn when the NO _X storage reduction catalyst 16 is processed in Step 102 is calculated from the following equation (2), for example.

Q _NOxn = Q _NOxn-1 + q _NOx (2)

In the above formula _{(2), Q NOxn} shows _the NO _X storage amount at the time of the step 102 processing of the NO _X occluding and reducing catalyst 16. Q _NOxn-1 represents the previously calculated NO _X storage amount. q _NOx indicates the amount of NO _X contained in the exhaust gas flowing into the NO _X storage reduction catalyst 16 (hereinafter referred to as “exhaust NO _X amount”).

The previously calculated NO _X storage amount Q _NOxn−1 read in step 100 is used as the previously calculated NO _X storage amount Q _NOxn−1 in the equation (2).

The exhaust NO _x amount q _NOx is, for example, previously determined by experimentally engine speed, the amount of fuel injected from the fuel injection valve 12A, the amount of fuel added from the fuel injection valve 20, and NO _X storage reduction. the air-fuel ratio of the exhaust gas flowing into the mold the catalyst 16 as a parameter, and these parameters, stored and exhaust amount of NO _{X q NOx,} the exhaust amount of NO _X estimation map that associates to ROM18D. During the process of step 106, the engine speed input from each of the engine speed sensor 34, the air-fuel ratio sensor 22, the fuel injection valve 12 </ b> A, and the fuel injection valve 20, and the NO _X occlusion reduction type catalyst 16 flowed. Information indicating the exhaust NO _x amount q _NOx corresponding to the air-fuel ratio of the exhaust, the injection amount of the fuel injected from the fuel injection valve 12A, and the addition amount of the fuel added from the fuel injection valve 20 is read from the map. It may be derived by this.
The parameters used for the map are not limited to the above parameters. Further, the method of estimating the exhaust amount of NO _X is not limited to the above method may be used other known methods. For example, the NO _X sensor for measuring the NO _X concentration in the exhaust gas is configured to be provided upstream of the NO _X storage reduction catalyst 16 in the exhaust pipe 14 in the exhaust direction and downstream of the fuel injection valve 20 in the exhaust direction, by reading the signal input from the NO _X sensor, it may be calculated exhaust amount of NO _X.

In the next step 104, the HC poisoning amount Q _HCn and the NO _X storage amount Q _NOxn of the NO _X storage reduction catalyst 16 calculated in step 102 are stored in the RAM 18C. At this time, already by overwriting the information indicating the HC poisoning amount it has been stored and _the NO _X storage amount RAM 18c, rewrites the information to the latest information.

In the next step 106, it is determined whether or not the NO _X storage reduction catalyst 16 is in a poisoned state in which HC is poisoned. This “poisoned state” means that even if the air-fuel ratio of the exhaust is made rich, NO _X reduction is blocked by the HC layer (or adsorbed HC) formed on the NO _X storage reduction catalyst 16 and NO _X storage is performed. The state in which the NO _X reduction performance of the reduction catalyst 16 is deteriorated is shown.

Determination of the step 106, HC poisoning amount _{Q HCn} stored in RAM18C in step 104, to determine whether it exceeds a predetermined amount _{Q HC-rq} a predetermined, the predetermined amount _{Q HC-rq} If it exceeds, it may be determined that the poisoning state is caused by HC.

The fixed amount Q _HC-rq is a threshold value of the HC adsorption amount that causes deterioration of the NO _X reduction performance in the NO _X storage reduction catalyst 16, and when the HC adsorption amount exceeds this value, the NO _X storage reduction catalyst 16 NO _X reduction performance by adsorbed HC to deterioration, that is, poisoned. This fixed amount may be measured in advance and stored in the ROM 18D.

If the result in step 106 is affirmative, the process proceeds to step 108.
In step 108, _the NO _X storage reduction catalyst 16 in to said poison state, it is determined whether or not a difficult state of performing the further _the NO _X storage in該被poisoned. The determination in step 108 is made by determining whether or not the NO _X storage amount Q _NOx stored in the RAM 18C in step 104 exceeds a predetermined reference value Q _NOx−rq1 .

This reference value Q _NOx-rq1 represents the upper limit value of the NO _X storage reduction catalyst 16 in the HC poisoning state that can _store NO _X. That is, when the NO _X storage amount of the poisoned NO _X storage reduction catalyst 16 exceeds the reference value Q _NOx-rq1 , it is difficult to perform NO _X reduction. The reference value Q _NOx-rq1 may be measured in advance and stored in the ROM 18D.

If the determination in step 108 is negative, the process proceeds to step 110, and after performing the HC purge process for recovering the NO _X storage reduction catalyst 16 from the poisoning state by HC, the process returns to step 100. That is, when the NO _X storage reduction catalyst 16 is poisoned by HC and can store NO _X , the HC purge process is performed. Details of this HC purge process will be described later (FIG. 3).

On the other hand, if the result in step 108 is affirmative, the routine proceeds to step 112, where NO _X reduction processing is started.

And the NO _X reduction process, the air-fuel ratio of the exhaust gas flowing from the exhaust pipe 14 into _the NO _X storage reduction catalyst 16, a spike to a short period (short time) rich state (theoretical air-fuel ratio close state or theory In this control, the amount of fuel is greater than the air-fuel ratio.

Specifically, for example, the air-fuel ratio of the exhaust gas flowing into the NO _X storage reduction catalyst 16 is controlled by controlling the fuel injection valve 12A so as to inject fuel in a short cycle from the fuel injection valve 12A. Is temporarily set to a predetermined target rich air-fuel ratio.
That is, “start the NO _X reduction process” indicates that in this embodiment, intermittent fuel injection from the fuel injection valve 12A is started.

In the present embodiment, in the NO _X reduction process, a case where the fuel injection valve 12A is controlled will be described. However, fuel is intermittently added from the fuel injection valve 20 into the exhaust pipe 14 in a short cycle. a by controlling the fuel injection valve 20, the air-fuel ratio of the exhaust gas flowing to the NO _X occluding and reducing catalyst 16 may be a rich air-fuel ratio temporarily predetermined target. Further, both the fuel injection valve 12A and the fuel injection valve 20 may be controlled.

Through the process of step 112, air-fuel ratio of exhaust gas flowing into _the NO _X storage reduction catalyst 16 is made rich state in a short period, thereby, NO _X reduction start that has been occluded in _the NO _X storage reduction catalyst 16 Will be. Specifically, nitrate is decomposed from the NO _X storage material in the NO _X storage reduction catalyst 16 and NO _X is released, and this NO _X is caused by uncatalyzed hydrocarbons and monoxide in the exhaust gas by the catalytic action of the noble metal catalyst. The process of reducing to nitrogen by carbon or the like is started.

In the next step 113, a negative determination is repeated until a predetermined time has elapsed after the start of the NO _X reduction process in step 112, and if the determination is affirmative, the routine proceeds to step 114. As the predetermined time in step 113, for example, an arbitrary time may be determined in advance according to the number of fuel injections intermittently injected by NO _X reduction processing, the injection amount, the engine speed, and the like.

In the next step 114, the previously calculated HC poisoning amount Q _HCn-1 and the previously calculated NO _X storage amount Q _NOxn-1 are read from the RAM 18C. Therefore, in step 114, the HC poisoning amount and NO _X storage amount calculated in the most recently processed step out of the processing in step 102, the processing in step 204 described later, or the processing in step 116 described later. Will be read.

In the next step 116, the HC poisoning amount Q _HCn and the NO _X storage amount Q _NOxn of the NO _X storage reduction catalyst 16 at the time of the processing of step 116 are calculated.

The HC poisoning amount Q _HCn of the NO _X storage reduction catalyst 16 during the processing of step 116 is _calculated from, for example, the above formula (1) (Q _HCn = Q _HCn−1 + q _HC −f (T)). do it.

In the process of step 116, Q _HCn in equation (1) may be the HC poisoning amount of the NO _X storage reduction catalyst 16 during the process of step 116. Q _HCn-1 may be the previously calculated HC poisoning amount read in step 114.

Further, as q _HC and f (T), the exhaust HC amount and the purifiable HC amount calculated in step 116 may be used.

That is, q _HC and f (T) are engine parameters input from each of the various parameters (engine speed sensor 34, air-fuel ratio sensor 22, fuel injection valve 12A, and fuel injection valve 20) obtained in step 116. From the rotational speed, the air-fuel ratio of the exhaust gas flowing into the NO _X storage reduction catalyst 16, the amount of fuel injected from the fuel injection valve 12A, and the amount of fuel added from the fuel injection valve 20). The estimation method used in 102 may be obtained from the exhaust HC amount estimation map and the purifiable HC amount estimation map.

Further, the NO _X storage amount Q _NOxn at the time of the processing of step 116 of the NO _X storage reduction catalyst 16 may be calculated from the following equation (3).

_{Q NOxn = Q NOxn-1 +} q NOx -q NOx-red ··· (3)

In the formula _{(3), Q NOxn} shows _the NO _X storage amount at the time of the step 116 processing of the NO _X occluding and reducing catalyst 16. Q _NOxn-1 represents the previously calculated NO _X storage amount. q _NOx indicates the amount of NO _X contained in the exhaust gas flowing into the NO _X storage reduction catalyst 16 (hereinafter referred to as “exhaust NO _X amount”). q _NOx-red shows the NO _X reduction amount.

The previous calculated NO _X storage amount Q _NOxn−1 read in step 114 is used as the previous calculated NO _X storage amount Q _NOxn−1 in the equation (3).

Exhaust amount of NO _{X q NOx} stores various parameters (engine speed sensor 34 obtained at the process of step 116, the air-fuel ratio sensor 22, the fuel injection valves 12A, and the engine speed inputted from each of the fuel injection valve 20, Step 102 is performed using the air-fuel ratio of the exhaust gas flowing into the NO _X storage reduction catalyst 16, the amount of fuel injected from the fuel injection valve 12A, and the amount of fuel added from the fuel injection valve 20). in using the method of estimating the exhaust amount of NO _{X q NOx} using, it may be obtained from the exhaust amount of NO _X estimation map.

The NO _X reduction amount q _NOx-red in the formula (3) is reduced by the NO _X storage reduction catalyst 16 when the NO _X reduction process started in Step 112 is performed for a predetermined time in Step 113. It shows the reduction amount of that NO _X.

The NO _X reduction amount _{q NOx-red,} for example, HC poisoning amount _Q information indicating _HCn, NO _X occluding and reducing by NO _X reduction treatment of step 112 is performed for a predetermined time as shown in step 113 A reduced NO _X amount estimation map that associates information indicating the reduced NO _X amount reduced by the type catalyst 16 is stored in advance in the ROM 18D. Then, the information indicating the reduced NO _X amount corresponding to the HC poisoning amount Q _HCn at the time of the processing of step 116 obtained in step 116 may be obtained by reading from the reduced NO _X amount estimation map.
As a method of estimating the NO _X reduction amount is reduced _the amount of NO _X for _the NO _X storage reduction catalyst 16 NO _X reduction process of step 112 is reduced by executing a predetermined time shown in step 113 Is not limited to the above method, and other known methods may be used.

In the next step 118, the HC poisoning amount Q _HCn and the NO _X storage amount Q _NOxn calculated in step 116 are stored in the RAM 18C. At this time, it rewrites the latest information by overwriting the information that indicates the HC poisoning amount and _the NO _X storage amount already stored in the RAM 18c.

In the next step 120, it is determined whether or not to end the NO _X reduction process. Determination in step 120, whether _the NO _X storage amount stored in RAM18C in step 118, has become a certain amount _{(Q NOx-end)} than to NO _X reduction termination criterion in _the NO _X storage reduction catalyst 16 What is necessary is just to judge affirmative when it is less than this fixed amount.

When the result of step 120 is negative and it is determined that the NO _X reduction process is not terminated, the routine returns to step 112, where the NO _X storage amount stored in the RAM 18C at step 118 is the NO _X storage reduction catalyst 16. NO _X reduction and end regarded the predetermined amount _{(Q NOx-end)} and until less than, repeats the processing of step 112 to step 120.

On the other hand, if the result in step 120 is affirmative, the process proceeds to step 122, and after the NO _X reduction process started in step 112 is completed, the process returns to step 100.

If the result in Step 106 is negative, the process proceeds to Step 124. In step 124, it is determined whether or not the NO _X storage reduction catalyst 16 that is not in the poisoned state is in a state that requires NO _X reduction. The determination in step 124 is to determine whether or not the NO _X storage amount Q _NOxn stored in the RAM 18C in step 104 is greater than the saturated storage amount (Q _NOx−rq2 ) in the NO _X storage reduction catalyst 16. Judgment can be made. The saturated occlusion amount is an upper limit value of the NO _x occlusion amount that can be occluded by the NO _x occlusion reduction type catalyst 16 that is not poisoned by HC. Needless to say, the saturated occlusion amount Q _NOx-rq2 is larger than the reference value Q _NOx-rq1 described in step 108, and may be measured and stored in the ROM 18D in advance.

  If the result in step 124 is negative, the process returns to step 100. If the result is positive, the process proceeds to step 112.

  Next, the HC purge process executed in step 110 will be described.

  As shown in FIG. 3, in the HC purge process, in step 200, the HC purge process is started.

The HC purge process is a process for recovering the NO _X storage reduction catalyst 16 from the poisoned state by HC.

The poisoned by the HC, as described above, shows a state in which the HC layer has been formed by the NO _X storage reduction catalyst 16 a high concentration of HC contacts, and the air fuel ratio of the exhaust gas to a rich state NO _X reduction is prevented by NO _X reduction performance and shows a state in which deteriorated by also HC layer.

The _the NO _X storage reduction catalyst 16, as a method to recover from the poisoned by the HC, while maintaining the air-fuel ratio of the exhaust gas flowing to the NO _X occluding and reducing catalyst 16 to the lean state, _the NO _X storage reduction type A method of raising the ambient temperature of the catalyst 16 to a high temperature range of 400 ° C. or higher can be mentioned. Using this method, the HC which has been adsorbed to the NO _X occluding and reducing catalyst 16, the reaction proceeds with the oxygen in the exhaust, which HC that was adsorbed by is purified (purge).

In this embodiment, CPU 18a in step 200, the exhaust gas flowing into _the NO _X storage reduction catalyst 16, spike controls the fuel injection valve 20 so as to add the fuel in a short period from the fuel injection valve 20 By doing so, the temperature of the exhaust gas flowing into the NO _X storage reduction catalyst 16 is raised. Then, by raising the exhaust temperature, the temperature of the NO _X storage reduction catalyst 16 is raised. The fuel addition from the fuel injection valve 20 is adjusted so that the air-fuel ratio of the exhaust gas to which the fuel is added is within a lean range.

In the present embodiment, in HC purging process, by adding a spike fuel in a short period from the fuel injection valve 20 to the exhaust gas flowing into _the NO _X storage reduction catalyst 16, _the NO _X storage reduction catalyst 16 using the method of raising the temperature of, but provided with a heating device for heating the _the NO _X storage reduction catalyst 16 directly, the empty燃日of the exhaust gas flowing into the _the NO _X storage reduction catalyst while the lean state A method of heating the NO _X storage reduction catalyst 16 by the heating device may be used.

  As described above, when the process of step 200 is executed and the HC purge process is started, the HC purge process is started.

  In the next step 201, a negative determination is repeated until a predetermined time has elapsed after the start of the HC purge process in step 200. If the determination is affirmative, the process proceeds to step 202. As the predetermined time in step 201, for example, an arbitrary time can be determined in advance according to the number of times of addition of fuel intermittently added from the fuel injection valve 20 by the HC purge process, the addition amount, the engine speed, and the like. That's fine.

In the next step 202, the previously calculated HC poisoning amount Q _HCn-1 and the previously calculated NO _X storage amount Q _NOxn-1 are read from the RAM 18C. Therefore, in step 202, the processing of the previous step 202, the process of step 102, or in the process of step 116, HC poisoning amount calculated in the most recently processed steps and _the NO _X storage amount is read Will be.

In the next step 204, the HC poisoning amount Q _HCn and the NO _X storage amount Q _NOxn of the NO _X storage reduction catalyst 16 during the processing of step 204 are calculated.

The HC poisoning amount Q _HCn at the time of the step 204 processing of the NO _X storage reduction catalyst 16 is _calculated from, for example, the above equation (1) (Q _HCn = Q _HCn−1 + q _HC −f (T)). do it.

In the process of this step 204, Q _HCn in equation (1) may be the HC poisoning amount of the NO _X storage reduction catalyst 16 at the time of the step 204 process. Q _HCn-1 may be the previously calculated HC poisoning amount read in step 204.

Further, as q _HC and f (T), the exhaust HC amount and the purifiable HC amount calculated in step 204 may be used, respectively.

That is, q _HC and f (T) are engine parameters inputted from the various parameters (engine speed sensor 34, air-fuel ratio sensor 22, fuel injection valve 12A, and fuel injection valve 20) obtained during the processing of step 204. rotational speed, NO _X occluding and reducing air-fuel ratio of the inflowing exhaust into the catalyst 16, the injection quantity of fuel injected from the fuel injection valve 12A, and from the addition amount of fuel added from the fuel injection valve 20), the steps The estimation method used in 102 may be obtained from the exhaust HC amount estimation map and the purifiable HC amount estimation map.

Further, the NO _X storage amount Q _NOxn of the NO _X storage reduction type catalyst 16 at the time of the processing of step 204 may be calculated from, for example, the above formula (2) (Q _NOxn = Q _NOxn-1 + q _NOx ).

In the process of step 204, wherein _{(2), Q NOxn} may if _the NO _X storage amount at the time of the step 204 processing of the NO _X occluding and reducing catalyst 16. Q _NOxn−1 may be the previously calculated NO _X storage amount read in step 204.

_As the _{q NOx,} calculated in step 204, it may be used an exhaust amount of NO _X. That is, the exhaust amount of NO _{X q NOx} is input from each of the step 204 various parameters obtained during the processing of the (engine speed sensor 34, the air-fuel ratio sensor 22, the fuel injection valves 12A, and the fuel injection valve 20 engine speed, by using _the NO _X storage reduction air-fuel ratio of the inflowing exhaust into the catalyst 16, the injection quantity of fuel injected from the fuel injection valves 12A, and the fuel injected from the fuel injection valve 20 an injection amount) , using the method of estimating the exhaust amount of NO _{X q NOx} used in step 102 may be obtained from the exhaust amount of NO _X estimation map.

In the next step 206, the HC poisoning amount Q _HCn and the NO _X storage amount Q _NOxn calculated in step 204 are stored in the RAM 18C. At this time, already by overwriting the information indicating the HC poisoning amount it has been stored and _the NO _X storage amount RAM 18c, rewrites the information to the latest information.

Here, even during the HC purge process execution, _the NO _X storage to _the NO _X storage reduction catalyst 16 proceeds.
Therefore, in the next step 208, it is determined whether or not the NO _X storage reduction catalyst 16 in the poisoned state by HC is in a state where it is difficult to perform further NO _X storage in the poisoned state. . The determination in step 208 is determined by determining whether the NO _X storage amount stored in the RAM 18C in step 206 exceeds the reference value Q _NOx−rq1 used in the determination in step 108.

If the determination in step 208 is affirmative, the process proceeds to step 210, the HC purge process started in step 200 is interrupted, and then the process returns to step 112. Thus, HC purge process is interrupted, NO _X reduction process is started.

On the other hand, if the result in Step 208 is negative, the routine proceeds to Step 212, where it is determined whether or not to end the HC purge process. Determination of step 212, or HC poisoning amount stored in RAM18C in step 206 has reached the predetermined amount _{(Q HC-end)} than to HC purging termination criterion in _the NO _X storage reduction catalyst 16 What is necessary is just to judge affirmative when it is less than this predetermined amount.

If the result of step 212 is negative and it is determined that the HC purge process is not to be terminated, the process returns to step 200, and the HC poisoning amount stored in the RAM 18C at step 206 is the HC poisoning amount in the NO _X storage reduction catalyst 16. The processes of Step 200 to Step 212 are repeated until the amount is less than a predetermined amount (Q _HC-end ) regarded as the end of the purge process.

  On the other hand, when the result in step 212 is affirmative, the routine proceeds to step 214, and after the HC purge process started in step 200 is completed, this routine is terminated.

As described above, according to the exhaust purification apparatus 10 of the present embodiment, the NO _X storage reduction catalyst 16 is poisoned by hydrocarbons (HC) by executing the NO _X storage reduction catalyst purification process. When it is determined that the poisoning state is present, after performing an HC purge process for removing HC in accordance with the NO _X storage amount of the NO _X storage reduction catalyst 16, the NO _X reduction for enriching the exhaust air-fuel ratio is performed. Execute the process.

For this reason, before the NO _X reduction performance is reduced by HC poisoning, the NO _X storage reduction catalyst 16 is recovered from the poisoning state by HC, and the NO _X reduction performance reduction is suppressed.

Further, _the NO _X storage reduction catalyst 16 when it is determined that poisoning state of being poisoned by HC, that the _the NO _X storage reduction catalyst 16 in this poisoned performs _the NO _X storage further If the state is difficult, the NO _X reduction process is preferentially executed, and then the HC purge process for recovering from the poisoned state by HC is performed. Therefore, while suppressing the emission of the NO _X to the outside air, and NO _X reduction performance degradation can be suppressed.

Further, since the _the NO _X storage to _the NO _X storage reduction catalyst 16 progresses even during HC purging process, _the NO _X storage amount of the NO _X occluding and reducing catalyst 16 during HC purging process, HC poisoned When it is determined that the upper limit of the NO _X storage reduction type catalyst 16 that can store NO _X is exceeded, the HC purge process is interrupted, the NO _X reduction process is preferentially executed, and then the HC purge process is performed again. Do.
Therefore, while suppressing the NO _X reduction performance degradation and, emissions of the NO _X in the outside air is further suppressed.

Further, NO _X reduction process, when _the NO _X storage reduction catalyst 16 is not poisoned by the HC, _the NO _X storage amount of the _the NO _X storage reduction catalyst 16, _yet-the NO _X storage reduction of poisoned The NO _X reduction process is executed only when the NO _X saturated storage amount in the type catalyst 16 is exceeded. For this reason, the NO _X reduction process is executed efficiently, leading to a reduction in fuel consumption.

<Test example>
Hereinafter, the present invention will be described in more detail with reference to test examples. However, the present invention is not limited to the following test examples unless the gist of the present invention is exceeded.

(Test Example 1)
In a solution obtained by adding 50 g of Al ₂ O ₃ powder to 200 ml of water and stirring, a dinitrodiamine platinum nitric acid solution whose platinum content was adjusted so that the supported amount of platinum was 2% by mass was added and stirred for 1 hour. It dried by heating at 10 degreeC for 10 hours. Further, the powder A was obtained by baking at 500 ° C. for 2 hours.
Next, 120 ml of pure water was added to 30 g of the powder A, and lithium acetate adjusted so that the amount of occlusion material supported per 120 g of powder A was 0.3 mol was added thereto, followed by heating at 120 ° C. for 2 hours. Evaporated and solidified. Further, the NO _X storage reduction catalyst was prepared by firing at 500 ° C. for 2 hours.

The prepared NO _X storage reduction catalyst was pretreated by leaving it in a mixed gas (10% H ₂ , 90% N ₂ ) for 15 minutes in an environment of 400 ° C. Then, the NO _X storage reduction catalyst that has been subjected to the pretreatment is left in a diluent gas (1% NO, 10% O ₂ , 89% N ₂ ) for 60 minutes, so that NO _X in the state of storing NO _{X is} stored. _{An X} storage reduction catalyst (NO _X storage reduction catalyst A) was prepared.

Moreover, the _the NO _X storage was _the NO _X storage reduction catalyst A described above adjusted, by standing diluent gas _{(1% C 3 H 6,} 10% O 2, 89% N 2) 60 minutes in, by HC A NO _X storage reduction catalyst (HC poisoning-NO _X storage reduction catalyst B) in a poisoned state was prepared.

For each of the prepared NO _X storage reduction catalyst A and HC poisoning-NO _X storage reduction catalyst B, 200 ° C., 300 ° C., and under a mixed gas (10% H ₂ , 90% N ₂ ) by leaving each 15 minutes under 400 ° C. environment subjected to NO _X reduction treatment, respectively, reducing the treated -NO _X storage reduction catalyst a, and reduced processed -HC poisoning -NO _X storage reduction catalyst B.

The _the NO _X storage reduction catalyst A, the reduction processed -NO _X storage reduction catalyst A, and for each of the reduction processed -HC poisoning -NO _X storage reduction catalyst B, performs IR measurement, 1580 cm around ^-1 The peak intensity attributed to the nitrate was measured.

4 shows, to the peak intensity attributed to the nitrate of the NO _X storage reduction catalyst A, and the peak intensity attributed to the nitrate reduction processed -NO _X storage reduction catalyst A, and the reduction temperature, the relationship Shown as diagram 50.
Further, to the peak intensity attributed to the nitrate of the NO _X storage reduction catalyst A, and the peak intensity attributed to the nitrate reduction processed -HC poisoning -NO _X storage reduction catalyst B, a reduction temperature, the relationship Is shown as diagram 52.

As shown in the diagram 50 of Figure 4, the reduction-processed -NO _X storage reduction catalyst A, the NO _X reduction rate of 200 ° C. is about 90%. On the other hand, as shown in the diagram 52, the reduction processed -HC poisoning -NO _X storage reduction catalyst B is, NO _X reduction rate of the same 200 ° C. is about 15%, NO by HC poisoning _X It can be seen that the reduction performance is significantly degraded.

According to the exhaust purification apparatus 10 of the present embodiment, the NO _X storage reduction catalyst purification process is executed, and thus the NO _X storage reduction catalyst 16 is poisoned by hydrocarbons (HC). When it is determined, after performing HC purge processing for removing HC in accordance with the NO _X storage amount of the NO _X storage reduction catalyst 16, NO _X reduction processing for enriching the air-fuel ratio of the exhaust is performed. Therefore, according to the exhaust gas purifying apparatus 10 of the present embodiment, it can be said that decrease of the NO _X reduction due HC poisoning is effectively inhibited.

10 exhaust gas purification device 12 an internal combustion engine 12A fuel injection valve 14 exhaust pipe 16 NO _X occluding and reducing catalyst 18 ECU
18A CPU
20 Fuel injection valve

Claims (5)

Provided in an exhaust passage of an internal combustion engine, the air-fuel ratio of the exhaust gas flowing into the occluding NO _X in the exhaust gas when the lean, the NO _X when the air-fuel ratio of the exhaust gas was occluded during the rich flowing into N ₂ and _the NO _X storage and reduction type catalyst that reduces,
Adjusting means for adjusting the air-fuel ratio of the exhaust;
Recovery means for recovering from a poisoned state by hydrocarbons by raising the temperature of the NO _X storage reduction catalyst;
Poisoning determination means for determining whether or not the NO _X storage reduction catalyst is poisoned by hydrocarbons;
Wherein when the _the NO _X storage reduction catalyst is determined to be in the poisoned by poisoning determining means, said _the NO _X storage reduction catalyst after controlling the recovery means so as to recover from the poisoned state, Control means for controlling the adjusting means to make the air-fuel ratio of the exhaust rich;
Exhaust gas purification device. Derivation means for deriving the NO _X storage amount of the NO _X storage reduction catalyst;
The control means interrupts the control of the recovery means when the NO _X occlusion amount derived by the derivation means exceeds a predetermined reference amount while controlling the recovery means, and the exhaust means The exhaust emission control device according to claim 1, wherein the adjusting means is controlled to make the air-fuel ratio of the exhaust gas rich. The control means includes
2. The control unit controls the adjustment unit so that the air-fuel ratio of the exhaust gas becomes rich when the NO _X storage amount derived by the deriving unit exceeds the reference amount before controlling the recovery unit. The exhaust emission control device according to 2. The exhaust emission control device according to claim 2 or 3, wherein the reference amount is an upper limit value at which the poisoned NO _X storage reduction catalyst can store NO _X. It said recovery means includes an exhaust purification device according to any one of claims 1 to 4, characterized in that the injection means for injecting fuel into exhaust gas flowing into the _the NO _X storage reduction catalyst.

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