JP4333612B2 - Exhaust gas purification device and exhaust gas purification catalyst - Google Patents

Description

  The present invention relates to an exhaust gas purification device and an exhaust gas purification catalyst for an internal combustion engine that is operated in a lean burn state in which fuel is leaner than the stoichiometric air-fuel ratio.

  In recent years, a lean burn engine in which the air-fuel ratio is a lean fuel has attracted attention. Here, the air-fuel ratio represents the ratio of air to fuel in the gas. When the air-fuel ratio of the exhaust gas is lean, it is difficult to purify NOx with a three-way catalyst that has been conventionally used for exhaust gas purification of a stoichiometric engine. For this reason, exhaust gas purification catalysts for lean burn engines have been studied. One of them is a catalyst described in JP-A-11-319564 (Patent Document 1). This publication describes an exhaust gas purifying catalyst comprising a porous carrier supporting an oxide of at least one NOx storage element selected from alkali metal, alkaline earth metal and rare earth metal and a catalyst noble metal. ing.

  According to the above publication, NOx can be efficiently purified even when the air-fuel ratio is lean by using the catalyst disclosed in the publication. The purification mechanism of the catalyst oxidizes NOx in the exhaust gas once when it is lean and traps it in the catalyst. When a certain amount of NOx is trapped, the oxygen concentration in the exhaust gas is reduced to absorb the absorbed NOx from the NOx storage agent. It is what is released.

  Japanese Patent Laid-Open No. 2002-70611 (Patent Document 2) stores the trapped NOx in an exhaust gas purification catalyst and a NOx trap catalyst provided upstream of the NOx trap catalyst in order to appropriately release and reduce the trapped NOx. There has been proposed an air-fuel ratio control device for an engine that supplies an amount of reducing agent that is not excessive or insufficient with respect to the amount of oxygen to a NOx trap catalyst.

JP 11-319564 A JP 2002-70611 A

  The content disclosed in Patent Document 1 is to temporarily release absorbed NOx from the catalyst, and the content disclosed in Document 2 relates to an efficient reduction device for released NOx. In any document, if the released NOx cannot be purified appropriately, the exhaust gas purification ability may be lowered.

  An object of the present invention is to provide an exhaust gas purification apparatus and an exhaust gas purification catalyst that solve the above-described problems and exhibit high NOx purification performance.

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine having an exhaust gas purification catalyst capable of capturing NOx in an exhaust gas flow path of an internal combustion engine into which an exhaust gas having a lean air-fuel ratio and a rich or stoichiometric exhaust gas flows. The NOx amount that can be captured when the oxygen concentration, CO concentration, hydrocarbon concentration, and hydrogen concentration of 0% are determined in advance, and the lean operation is controlled so that the NOx trapping amount in lean does not exceed the previously determined NOx amount There is to do. The amount of NOx trapped in lean can be estimated by a NOx sensor or the like.

  In the present invention, at least two exhaust gas purification catalysts are used, and the exhaust gas purification catalyst (the first stage exhaust gas purification catalyst) that first circulates the exhaust gas in lean has zero oxygen concentration, CO concentration, hydrocarbon concentration, and hydrogen concentration in the exhaust gas. When the lean operation control device determines that the trapped amount has reached a predetermined value that does not exceed the amount of NOx that can be trapped in%, the exhaust gas does not pass through the preceding exhaust gas purification catalyst, and the next exhaust gas purification catalyst (the latter exhaust gas purification catalyst). And an exhaust gas purifying apparatus for an internal combustion engine, characterized in that the exhaust gas is circulated.

  According to the exhaust gas purification method, the exhaust gas purification device, and the exhaust gas purification catalyst of the present invention, in an internal combustion engine that is operated in a lean burn state where the fuel is leaner than the stoichiometric air-fuel ratio, the NOx purification performance that occurs when switching to stoichiometric or rich is achieved. The decrease can be suppressed, and the amount of NOx emitted from the internal combustion engine can be suppressed.

  Normally, when the air-fuel ratio is switched from lean to stoichiometric or rich, it flows into the exhaust gas purification catalyst. The oxygen concentration decreases from a few percent (eg, 7%) to almost 0%. In the exhaust gas purification catalyst using the NOx occlusion element, trapped NOx is released. Therefore, NOx is discharged if the released NOx cannot be reduced and purified. However, if the release of trapped NOx can be avoided even if the oxygen concentration is reduced from several percent (for example, 7%) to 0%, NOx is reduced in the trapped state, so that NOx emission is prevented and effective. In the present specification, the present invention describes that the NOx trapped in the exhaust gas purification catalyst is released from the catalyst due to a decrease in the oxygen concentration in the gas phase.

  As a result of intensive studies by the inventor, when NOx is captured during lean and the air-fuel ratio is switched to stoichiometric or rich to purify the captured NOx, the amount of NOx that is captured while the air-fuel ratio of the exhaust gas is lean is in the exhaust gas. It was found that NOx detachment can be prevented by not exceeding the amount of NOx that can be captured when the oxygen concentration, CO concentration, hydrocarbon concentration, and hydrogen concentration are 0%.

That is, an exhaust gas purification catalyst capable of capturing NOx is provided in an exhaust gas flow path of an internal combustion engine into which an exhaust gas having a lean air-fuel ratio and a rich or stoichiometric exhaust gas flows, and when the air-fuel ratio is lean, the NOx in the exhaust gas In the exhaust gas purification device that captures NOx when the air-fuel ratio is stoichiometric or rich, the amount of NOx that is captured while the air-fuel ratio of the exhaust gas is lean is the oxygen concentration, CO concentration, An exhaust gas purification apparatus for an internal combustion engine is preferable, which includes a lean operation control device that controls the lean operation so as not to exceed the NOx amount that can be captured when the hydrocarbon concentration and the hydrogen concentration are 0%.

  As a specific method for determining the amount of NOx to be captured while the air-fuel ratio is lean, for example, the amount of NOx trapped by the exhaust gas purification catalyst when the oxygen concentration in the exhaust gas is set to 0% can be examined in advance. NOx reduction occurs when reducing agents such as CO, hydrocarbons, and hydrogen are included. Therefore, when examining the NOx trapping amount of the exhaust gas purification catalyst when the oxygen concentration is 0%, these reducing agent concentrations are also Set to 0%. Furthermore, since the NOx trapping amount depends on the temperature, it is preferable to investigate the NOx trapping amount in the exhaust gas temperature region used in the internal combustion engine, and map or formulate it to prepare for the lean operation control device.

  Specifically, when the lean NOx trapping amount is less than or equal to the NOx trapping amount when the oxygen concentration, CO concentration, hydrocarbon concentration and hydrogen concentration in the exhaust gas are 0%, specifically, for example, deterioration of the exhaust gas purification catalyst In consideration of the above, etc., it may be set to 1/4 of the NOx trapping amount before catalyst deterioration.

  Here, examples of means for estimating the lean NOx trapping amount include the following methods.

  First, there is a method of integrating the amount of NOx flowing into the exhaust gas purification catalyst in lean. Usually, the integrated value of the NOx amount is obtained by integrating the product of the NOx concentration in the exhaust gas and the air amount. Further, the NOx concentration in the exhaust gas can be estimated from the air-fuel ratio, and the air amount can be estimated from the air flow sensor or the engine speed and the engine exhaust amount. By examining the NOx trapping amount with respect to the NO amount flowing into the exhaust gas purification catalyst in advance, the NOx amount trapped by the exhaust gas purification catalyst can be estimated from the integrated value of the NOx amount flowing into the exhaust gas purification catalyst in lean.

  There is also a method for directly examining the amount of NOx trapped in the exhaust gas purification catalyst using a NOx sensor. Specifically, NOx sensors can be installed upstream and downstream of the exhaust gas purification catalyst, and the amount of NOx trapped by the exhaust gas purification catalyst can be determined from the difference in NOx concentration detected by the upstream and downstream NOx sensors. The NOx sensor can be estimated even if it is set on either the upstream or downstream side, but if it is installed on both, accurate estimation is possible.

Another simple method is to estimate the amount of NOx trapped in the exhaust gas purification catalyst by counting the lean operation time.

  Furthermore, the NOx trapping amount may depend on the exhaust gas temperature. Therefore, it is preferable that the lean operation end determination device performs the switching control by reflecting the inflowing exhaust gas temperature. Specifically, the amount of NOx trapped in the exhaust gas purification catalyst is estimated from the exhaust gas temperature and the NOx concentration flowing into the exhaust gas purification catalyst, and a predetermined amount below the NOx amount that can be captured when the oxygen concentration in the exhaust gas is 0% (for example, When it is determined that the ¼ amount has been reached, it is preferable to execute control to switch to rich operation.

  The exhaust gas temperature can be examined by installing an exhaust gas temperature sensor either upstream of the exhaust gas purification catalyst, inside the catalyst, or downstream of the catalyst. If it is installed inside the exhaust gas purification catalyst, it is preferable that the temperature of the catalyst itself can be directly known. The exhaust gas temperature can be estimated from the vehicle speed and the engine speed, but it is preferable to use an exhaust gas temperature sensor because temperature information can be obtained accurately.

  In stoichiometric or rich, reducing agents such as hydrocarbons and CO are supplied to the exhaust gas purification catalyst. However, in order to effectively use the reducing agent and improve fuel consumption, it is desirable to increase the amount of NOx captured by lean as much as possible.

  The amount of these reducing agents may be greater than the amount required to reduce lean trapped NOx. In addition, the lean time of the exhaust gas purification catalyst can be reduced by making the NOx trapping amount in the lean of the exhaust gas purification catalyst less than the NOx amount that can be supplemented even when the oxygen concentration, CO concentration, hydrocarbon concentration, and hydrogen concentration in the exhaust gas are 0%. It becomes too much, and stoichiometric or rich and lean are frequently repeated, and although the exhaust gas purification performance is good, there is a possibility that the fuel consumption deteriorates.

  On the other hand, when the lean time is lengthened, the NOx trapping amount of the exhaust gas purification catalyst in lean exceeds the NOx trapping amount that can be trapped even when the oxygen concentration, CO concentration, hydrocarbon concentration and hydrogen concentration in the exhaust gas are 0%. In addition, NOx release from the exhaust gas purification catalyst occurs during rich switching, and NOx may be discharged without being reduced and purified.

  Therefore, a method of using at least two exhaust gas purification catalysts and setting the NOx trapping amount in each lean to be equal to or less than the NOx trapping amount when the oxygen concentration, CO concentration, hydrocarbon concentration, and hydrogen concentration in the exhaust gas are 0% is adopted. Is possible.

  That is, an exhaust gas purification catalyst that first circulates exhaust gas in lean using at least two exhaust gas purification catalysts that capture NOx in exhaust gas even when the oxygen concentration, CO concentration, hydrocarbon concentration, and hydrogen concentration in the exhaust gas are 0% When the lean operation control device determines that the (pre-stage exhaust gas purification catalyst) exceeds the NOx amount that can be captured when the oxygen concentration and CO concentration, hydrocarbon concentration and hydrogen concentration in the exhaust gas are 0%, the exhaust gas to the pre-stage exhaust gas purification catalyst is reduced. An exhaust gas purification apparatus for an internal combustion engine, characterized in that the exhaust gas is circulated to the next exhaust gas purification catalyst (second-stage exhaust gas purification catalyst) without passing through.

  As a specific example, a switching valve is provided upstream of the upstream exhaust gas purification catalyst, and when the lean operation control device determines that the upstream exhaust gas purification catalyst has supplemented NOx of a predetermined value or more in lean, the switching valve is switched to the upstream exhaust gas purification catalyst. An exhaust gas purification apparatus for an internal combustion engine, characterized in that exhaust gas is circulated to a subsequent exhaust gas purification catalyst without passing the exhaust gas through the catalyst. By doing so, the lean operation time can be lengthened, and the reducing agent in the stoichiometric and rich gas can be used effectively, so that it is possible to achieve both the purification of exhaust gas and the improvement of fuel consumption.

The exhaust gas purification catalyst used in the present invention has a NOx trap. The NOx trapping material has a function of trapping NOx in the exhaust gas even when the oxygen concentration and CO concentration, hydrocarbon concentration and hydrogen concentration in the exhaust gas are 0%, and it absorbs NOx as a nitric acid compound or NOx Any adsorbent that chemically adsorbs as ₂ can be used.

The NOx trapping material includes at least one of an alkali metal or an alkaline earth metal, and at least any of Pt, Pd, and Rh for reducing the NOx oxide during lean and the trapped NOx during stoichiometric (rich) It is preferable that these are included. Moreover, although the alkali metal and alkaline-earth metal contained in a catalyst may be 1 type, it is suitable to combine 2 or more types according to the temperature range to capture | acquire. Furthermore, NOx can be effectively purified at the time of lean, stoichiometric or rich by using noble metals as Pt, Pd and Rh. It is considered that Pt is mainly effective in the NO oxidation reaction during lean, and Pd and Rh are mainly effective in the trapped NOx reduction reaction during stoichiometric (rich). Further, when Ce is contained as a rare earth element, hydrocarbons and CO are preferably purified in addition to NOx by oxygen storage and release in the vicinity of stoichiometry.

  As the method for preparing the exhaust gas purification catalyst, any of a physical preparation method such as an impregnation method, a kneading method, a coprecipitation method, a sol-gel method, an ion exchange method, and a vapor deposition method and a preparation method using a chemical reaction can be applied. As starting materials for the exhaust gas purification catalyst, various compounds such as nitric acid compounds, acetic acid compounds, complex compounds, hydroxides, carbonic acid compounds, organic compounds, metals, and metal oxides can be used.

  When Ti is contained in the exhaust gas purification catalyst, the NOx purification performance at the time of stoichiometric (rich) switching is further improved. This is thought to be because the trapped NOx reduction reaction is effective. The amount of Ti to be used is desirably 0.05 or more and 1 or less in molar ratio with respect to the total amount of alkali metal and alkaline earth metal contained in the exhaust gas purification catalyst. If the amount is less than 0.05, the effect of Ti does not appear. If the amount is too large, the active points of the NOx trapping material and the noble metal are covered.

The exhaust gas purification catalyst may use only the active component, but may support the active component on a porous carrier. It is considered that the active ingredient is highly dispersed by being supported on the porous carrier. As a result, the NOx purification performance at the time of stoichiometric (rich) switching is improved. The porous carrier may be further supported on the substrate. In this case, the amount of the porous carrier supported on 1 L of the substrate is preferably 50 g or more and 400 g or less, which is preferable for NOx purification performance at stoichiometric (rich) switching. If the loading amount of the porous carrier is less than 50 g, the effect of the porous carrier is insufficient, and if it is more than 400 g, the specific surface area of the porous carrier itself is reduced, and further, when the substrate is in a honeycomb shape, clogging occurs. It is because it becomes easy and is not preferable. As the porous carrier, in addition to alumina, metal oxides such as titania, silica, silica-alumina, zirconia, and magnesia, composite oxides, and the like can be used. Alumina is particularly optimal. Alumina is considered to have high heat resistance and a function of enhancing dispersion of active components such as NOx trapping materials and noble metals.

  The shape of the exhaust gas purifying catalyst according to the present invention can be applied in various shapes depending on applications. It can be applied to pellets, plates, granules, powders, etc., including honeycomb shapes obtained by coating exhaust gas purification catalysts carrying various components on honeycomb structures made of various materials such as cordierite, SiC, and stainless steel . In the case of a honeycomb shape, cordierite is optimal as the base material. However, if there is a risk that the catalyst temperature may increase, good results can be obtained even if a base material that is difficult to react with the catalyst component, such as a metal base, is used. Can do. In addition, good results can be obtained even when a honeycomb composed only of an exhaust gas purification catalyst is formed.

〔Example〕
Specific examples of the present invention will be described below. In addition, this invention is not restrict | limited by these Examples.

(NOx purification catalyst preparation method)
A cordierite honeycomb (400 cells / Inc ² ) was coated with a slurry made of alumina powder and an alumina precursor and made nitric acid acidic, and then dried and fired to obtain 1.9 mol of alumina per liter of apparent volume of the honeycomb. A coated alumina coated honeycomb was obtained. The alumina-coated honeycomb was impregnated with a Ce nitrate solution, dried at 200 ° C., and then fired at 600 ° C. for 1 hour. Next, the alumina supporting Ce is impregnated with a mixed solution of dinitrodiammine Pt nitric acid solution, dinitrodiammine Pd nitric acid solution, Rh nitrate solution, Na nitrate, Mg nitrate and titania sol, dried at 200 ° C., and subsequently 600 ° C. For 1 hour.

  Thus, catalyst A containing 190 g of alumina with respect to 1 L of honeycomb, and Ce: 27 g, Na: 18 g, Mg: 1.8 g, Ti: 4 g, Rh: 0.139 g, Pt: 2.792 g in terms of elements. Got.

(Catalyst performance evaluation method)
In order to evaluate the performance of the catalyst, a NOx purification performance test was conducted under the following conditions. A 6 cc honeycomb catalyst was fixed in a quartz glass reaction tube. This reaction tube was introduced into an electric furnace, and the heating was controlled so that the temperature of the gas introduced into the reaction tube was 450 ° C. The gas introduced into the reaction tube is
SV50,000 / h, model gas assuming exhaust gas when the car engine is operating rich (hereinafter rich model gas), and exhaust gas when the car Ecidin is performing lean burn operation The model gas (hereinafter referred to as lean model gas), the model gas in which the oxygen, hydrocarbon and hydrogen concentrations in the exhaust gas were set to 0% (hereinafter referred to as oxygen concentration 0% model gas) were used.

The composition of the rich model gas is NOx: 1000 ppm, C ₃ H ₆ : 0.2%, CO: 2%,
CO ₂ : 12%, H ₂ O: 10%, N ₂ : residual.

The composition of the lean model _{gas, NOx: 600ppm, CO 2:} 12%, O 2: 7%, H 2 O: 10%, N 2: was a residual.

The composition of the model gas having an oxygen concentration of 0% was NO: 600 ppm, CO ₂ : 12%, H ₂ O: 10%, N ₂ : residual.

The composition of the purge gas was CO ₂ : 12%, H ₂ O: 10%, N ₂ : residual.

In the measurement procedure, after rich model gas was circulated for 10 minutes, purge gas was circulated for 10 minutes to remove CO and C ₃ H ₆ . Next, an oxygen concentration 0% model gas was circulated and held for 60 minutes. The NOx concentration in each model gas (hereinafter referred to as inlet NOx concentration) before the catalyst inflow and the NOx concentration in each model gas (hereinafter referred to as outlet NOx concentration) after the catalyst flow are measured with a NOx meter, and the inlet NOx concentration and outlet NOx are measured. The change with time (inlet NOx concentration−outlet NOx concentration) with time was examined. While the difference is negative, NOx is captured. Therefore, the negative integrated value becomes the NOx trapping amount.

  The method for evaluating the performance of the catalyst by the above method is referred to as an evaluation method a.

(NOx trapping amount)
The NOx purification catalyst A was evaluated by the evaluation method a. The NOx trapping amount at 450 ° C. in the lean model gas was found to be 0.04 mol / L per catalyst unit volume when the NOx trapping amount in the 0% oxygen concentration model gas was determined. This value is the oxygen concentration in the exhaust gas at 450 ° C,
It becomes the limit amount (hereinafter referred to as NOx trapping amount when oxygen is 0%) at which the CO concentration, hydrocarbon concentration and hydrogen concentration are 0%.

  Note that the NOx trapping amount (0.04 mol / L) when the oxygen concentration was 0% corresponded to the NOx amount when lean model gas was allowed to flow slightly for 2 minutes. Therefore, when the rich gas was circulated after the lean model gas was circulated for 30 seconds, NOx was not released and the gas was reduced and purified.

From the above, the NOx trapping amount when the oxygen concentration is 0% is examined in advance, and the NOx trapping amount during the lean operation is made equal to or less than the NOx trapping amount when the oxygen is 0%, thereby reducing the oxygen concentration in the gas phase. Even in this case, the NOx trapped by the lean can be reduced and purified without leaving. Further, it is possible to determine the end of the lean operation by sequentially collecting information on the lean operation status (inlet NOx concentration, SV, etc.).

(Configuration diagram of internal combustion engine)
FIG. 1 is an overall configuration diagram showing an embodiment of an internal combustion engine equipped with an exhaust gas purification apparatus of the present invention. The purifying apparatus of the present invention includes a lean burnable engine 99, an air flow sensor 2, an intake system having a slot valve 3 and the like, an oxygen concentration sensor (or A / F sensor) 7, a catalyst-introducing gas temperature sensor 8, and a catalyst inlet NOx sensor 9. , A catalyst outlet NOx sensor 10, an exhaust gas purification catalyst 12, and the like, and an exhaust system and a control unit (ECU: Engine Control Unit) 11 and the like. The ECU includes an I / O as an input / output interface, an LSI, an arithmetic processing unit MPU, a storage device RAM and ROM storing a number of control programs, a timer counter, and the like.

The above exhaust purification device functions as follows. The intake air to the engine is filtered by the air cleaner 1 and then measured by the air flow sensor 2. The fuel is then injected from the injector 5 through the slot valve 3 and supplied to the engine 99 as an air-fuel mixture. The airflow sensor signal and other sensor signals are input to the ECU 11. The ECU 11 evaluates the operating state of the internal combustion engine and the state of the exhaust gas purification catalyst to determine the operating air-fuel ratio, and controls the injection time of the injector 5 to set the fuel concentration of the air-fuel mixture to a predetermined value. The air-fuel mixture sucked into the cylinder is ignited and burned by a spark plug 6 controlled by a signal from the ECU 11. The combustion exhaust gas is led to an exhaust purification system. In the exhaust purification system, an exhaust gas purification catalyst 12 is provided downstream of the three-way catalyst 13. The exhaust gas purification catalyst purifies NOx, HC, CO in the exhaust gas by the three-way catalyst function provided in the exhaust gas purification catalyst during stoichiometric operation, and purifies NOx by the NOx trapping ability during lean operation, and at the same time has a combustion function , HC,
Purify CO.

  Information on the amount of NOx to be captured while the air-fuel ratio of the exhaust gas is lean and information on the amount of NOx that can be captured when the oxygen concentration, CO concentration, hydrocarbon concentration, and hydrogen concentration in the exhaust gas are 0% are incorporated in the ECU 11 in advance. It is.

During the lean operation, the ECU 11 detects the NOx amount captured by the exhaust gas purification catalyst from the difference value of the NOx concentration measured by the catalyst inlet NOx sensor 9 and the catalyst outlet NOx sensor 10 and the air amount measured by the airflow sensor 2. Is estimated. The NOx amount is set in advance so as not to exceed the NOx trapping amount of 0% oxygen in the exhaust gas (for example, trapping when the oxygen concentration, CO concentration, hydrocarbon concentration and hydrogen concentration in the exhaust gas are 0%). When the ECU 11 determines that the amount of NOx that can be generated has reached ¼), the ECU 11 switches to the stoichiometric (rich) operation based on the determination and control signal of the ECU 11. By doing in this way, the discharge | emission amount of NOx in waste gas can be reduced effectively.

(Configuration diagram of exhaust gas purification device using switching valve)
An NOx sensor and a switching valve are provided upstream of the upstream exhaust gas purification catalyst so that the exhaust gas flows in this order (FIG. 2). At the lean time, the ECU estimates the amount of NOx trapped by the upstream exhaust gas purification catalyst based on information from the NOx sensor. Thereafter, when the ECU determines that the estimated value exceeds a predetermined value of the NOx trapping amount when oxygen is 0% (for example, 2/3 of the NOx trapping amount when oxygen is 0%), the changeover valve causes the upstream exhaust gas purification catalyst to The exhaust gas is switched to the downstream exhaust gas purification catalyst so that the exhaust gas flows. Then, the ECU starts estimating the amount of NOx captured by the post-exhaust gas purification catalyst based on the information of the NOx sensor. When the ECU determines that the NOx trapping amount of the rear exhaust gas purification catalyst exceeds a predetermined value of the NOx trapping amount when oxygen is 0%, the ECU switches the switching valve again so that the exhaust gas flows in the order of the front exhaust gas purification catalyst and the rear exhaust gas purification catalyst. And switch the air-fuel ratio to stoichiometric or rich. As a result, the NOx trapped by the upstream exhaust gas purification catalyst and the downstream exhaust gas purification catalyst is reduced and purified by a reducing agent such as CO.

  By doing so, the lean operation time can be lengthened, and the reducing agent in the stoichiometric and rich gas can be used effectively, so that it is possible to achieve both the purification of exhaust gas and the improvement of fuel consumption.

It is a block diagram which shows one embodiment of the exhaust gas purification apparatus of this invention. It is a block diagram which shows one embodiment of the exhaust gas purification apparatus of this invention using a switching valve.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Air cleaner, 2 ... Air flow sensor, 3 ... Slot valve, 5 ... Injector, 6 ... Spark plug, 7 ... Oxygen concentration sensor (or A / F sensor), 8 ... Catalyst entering gas temperature sensor, 9 ... Catalyst inlet NOx Sensors, 10 ... Catalyst outlet NOx sensor, 11 ... ECU, 12 ... Exhaust gas purification catalyst, 13 ... Three-way catalyst, 99 ... Engine.

Claims (6)

An exhaust gas purification catalyst capable of capturing NOx is provided in the exhaust gas flow path of the internal combustion engine in which the exhaust gas having a lean air-fuel ratio and the exhaust gas having a rich or stoichiometric air-fuel ratio alternately flows, and the NOx in the exhaust gas when the air-fuel ratio is lean An exhaust gas purifying device that reduces and purifies the captured NOx when the air-fuel ratio is rich or stoichiometric,
The exhaust gas purification device includes a lean operation control device, and the lean operation control device is configured such that, during the lean operation , the amount of NOx trapped by the purification catalyst is 0 in oxygen, CO, hydrocarbon, and hydrogen concentrations in the exhaust gas. An exhaust gas purifying apparatus for an internal combustion engine, wherein control for switching to rich operation is executed when the value becomes equal to or less than the NOx amount that can be captured at the time of% . An exhaust gas purification device according to claim 1 ,
The lean operation control device integrates the lean operation time and estimates the amount of NOx trapped by the exhaust gas purification catalyst. An exhaust gas purification device according to claim 1 ,
An exhaust gas temperature measuring device for measuring the temperature of the exhaust gas flowing into the exhaust gas purification catalyst in the exhaust gas flow path, and an exhaust gas concentration measuring device for measuring the NOx concentration of the exhaust gas flowing into the exhaust gas purification catalyst,
The lean operation control device estimates the NOx concentration captured by the exhaust gas purification catalyst from the exhaust gas temperature measured by the exhaust gas temperature measuring device and the NOx concentration in the exhaust gas, apparatus. An exhaust gas purifying device according to any one of claims 1 to 3 ,
The exhaust gas purifying apparatus for an internal combustion engine, wherein the exhaust gas purifying catalyst includes at least one of alkali metal or alkaline earth metal and at least one of Pt, Pd, and Rh. An exhaust gas purification device according to any one of claims 1 to 4 ,
An exhaust gas purification apparatus for an internal combustion engine, wherein a catalyst that captures NOx in an atmosphere having an oxygen concentration, a CO concentration, a hydrocarbon concentration, and a hydrogen concentration of 0% in the exhaust gas is employed as the exhaust gas purification catalyst. An exhaust gas purification catalyst capable of capturing a plurality of NOx is provided in the exhaust gas flow path of the internal combustion engine in which the exhaust gas having a lean air-fuel ratio and the rich or stoichiometric exhaust gas alternately flows, and in the exhaust gas when the air-fuel ratio is lean An exhaust gas purifying apparatus that supplements NOx of the catalyst to the catalyst and reduces and purifies the captured NOx when the air-fuel ratio is rich or stoichiometric.
The exhaust gas purification apparatus has a bypass exhaust gas flow path that bypasses the first purification catalyst closest to the internal combustion engine among the exhaust gas purification catalysts capable of capturing the plurality of NOx,
The exhaust gas purification device includes a lean operation control device,
In the lean operation control device, the NOx amount trapped by the first purification catalyst during the lean operation is less than the NOx amount that can be captured when the oxygen, CO, hydrocarbon, and hydrogen concentrations in the exhaust gas are 0%, respectively. The exhaust gas purifying apparatus for an internal combustion engine, wherein control for switching the exhaust gas flow path to the bypass flow path is executed when the value becomes.

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