JP2005171805A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of excellently purifying NOx in inflow exhaust gas, even when the temperature of a NOx catalyst is lower than the NO oxidation starting temperature. <P>SOLUTION: This exhaust emission control device is provided with a NOx storage means for carrying a NOx occlusion agent 55 and a noble metal catalyst 54 in an engine exhaust passage. The NOx occlusion agent performs the NOx occlusion-emission action when the temperature of the noble metal catalyst is the NO oxidation starting temperature or more. A NOx occlusion means has a small quantity carrying area 56 and a large quantity carrying area 57. A carrying quantity of the noble metal catalyst per unit volume in the small quantity carrying area, is less than a carrying quantity of the noble metal catalyst per unit volume in the large quantity carrying area. The small quantity carrying area and the large quantity carrying area are arranged so that exhaust gas flowing in the NOx occlusion means, passes through the large quantity carrying area after passing through the small quantity carrying area. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

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

As a means for purifying nitrogen oxide (NO _x ) contained in exhaust gas when combustion is performed under a lean air-fuel ratio, an alkali metal or alkaline earth is formed on the surface of a support made of alumina. forming a layer of the NO _X absorbent comprising a metal or the like, it is known more NO _X catalyst a noble metal catalyst supported on a carrier surface, such as platinum.

At a temperature at which platinum supported on the NO _x catalyst can oxidize nitric oxide (NO) to nitrogen dioxide (NO ₂ ) under a lean atmosphere (hereinafter referred to as “NO oxidation start temperature”), NO _x When the temperature of the catalyst has reached, when the air-fuel ratio of exhaust gas flowing into the NO _x catalyst (hereinafter referred to as “inflow exhaust gas”) is lean, NO _x contained in the inflow exhaust gas is stored as the NO _x storage agent. occluded within, the air-fuel ratio of the inflowing exhaust gas is substantially stoichiometric or rich (hereinafter referred to as "stoichiometric-rich") When the NO _X absorbent NO _X that was stored in is released, the inflow exhaust It is reduced by a reducing agent (for example, unburned fuel or carbon monoxide (CO)) present in the gas (hereinafter, the action of the NO _x storage agent is referred to as “absorption / release action”).

Here, the NO _x storage agent stores nitrogen dioxide (NO ₂ ) in the exhaust gas in a lean atmosphere and releases NO ₂ stored in a rich atmosphere. NO Although the exhaust gas flowing into the _X catalyst also include NO not only NO ₂ as NO _X, NO _X NO by the oxidation action of platinum in the case the temperature is above NO oxidation start temperature of the platinum catalyst NO since it is oxidized to _2, NO contained in the exhaust gas flowing into the NO _X catalyst as a result is also occluded in _the NO _x storage material.

However, when the temperature of the NO _x catalyst is lower than the NO oxidation start temperature of platinum, the oxidizing action of platinum is low, and NO in the exhaust gas flowing into the NO _x catalyst is not oxidized to NO ₂ . Therefore, NO _X in the exhaust upstream of the catalyst disposed NO oxidation catalyst, NO even if the temperature of the _X catalyst is lower than the NO oxidation start temperature of the platinum, NO in the exhaust gas discharged from the pre-engine body by the NO oxidation catalyst There has been proposed an exhaust purification device that increases the NO _x purification rate of the NO _x catalyst by oxidizing the gas to NO ₂ (Patent Document 1).

JP 2002-89246 A JP 2001-62294 A JP 2003-13732 A Japanese Patent No. 3374999 JP 2001-289035 A JP 2000-157867 A

However, platinum supported in the NO _X catalyst, when the temperature of the NO _X catalyst is lower than the NO oxidation start temperature of the platinum, the NO in the inflow exhaust gas to the NO _X catalyst just can not oxidized to NO ₂ Or, NO ₂ in the inflowing exhaust gas is reduced to NO. Therefore, as disclosed in Patent Document 1, provided with a NO oxidation catalyst in the exhaust upstream of the NO _X catalyst, even if the proportion of NO ₂ in the inflowing exhaust gas to the NO _X catalyst, NO _X NO ₂ is reduced to NO in the catalyst. As a result, NO _X in the exhaust gas is less likely to be occluded into _the NO _x storage material, is NO _X purification rate by the NO _X catalyst and low when the temperature of the NO _X catalyst is lower than the NO oxidation start temperature of the platinum It was.

Accordingly, an object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine that can effectively purify NO _x in the inflowing exhaust gas even when the temperature of the NO _x catalyst is lower than the NO oxidation start temperature of the noble metal catalyst. Is to provide.

In order to solve the above problems, the first aspect of the invention, comprising a _the NO _X storage means for carrying the _the NO _X storage agent and a noble metal catalyst in the engine exhaust passage, the _the NO _X storage agent, the temperature of the noble metal catalyst occluding NO _X in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into _the NO _X storage means when it is NO oxidation start temperature or higher is lean, the air-fuel ratio of the exhaust gas flowing into _the NO _X storage means substantially releasing NO _X that is occluded in the NO _X absorbent when the stoichiometric air-fuel ratio or rich, the _the NO _X storage means, and a small amount carrying region and a large amount carrying region, per unit volume in the small amount carrying region in the exhaust purification system of smaller internal combustion engine than the amount of the noble metal catalyst per unit volume amount of the noble metal catalyst in the large amount holding region, a small amount carrying region and multimeric carrying weight region areas above the NO _X absorption Exhaust gas flowing into the unit is provided so as to pass through the large amount holding region above the passes over the small amount carrying region.
When the oxidation / reduction ability of the noble metal catalyst is high, when the temperature of the noble metal catalyst is lower than the NO oxidation start temperature, that is, when the temperature of the NO _x storage means carrying the noble metal catalyst is lower than the NO oxidation start temperature. The NO ₂ in the exhaust gas flowing into the NO _x storage means is reduced to NO by the noble metal catalyst. Since _the NO _X storage agent can not be occluded only a NO _2, can not occlude thus reduced NO, thus is NO _X purifying ability of _the NO _X storage means decreases. According to the first aspect of the present invention, a small amount supporting region with a small amount of noble metal catalyst supported per unit volume is provided. When the amount of the noble metal catalyst supported is small, the activity of the noble metal catalyst is weakened due to the strong basicity of the NO _x storage agent, and therefore the oxidation / reduction ability is low. For this reason, when the temperature of the noble metal catalyst is lower than the NO oxidation start temperature in the small amount supported region, the reduction from NO ₂ to NO by the noble metal catalyst can be suppressed, and NO ₂ can be stored in the NO _X storage agent. It is possible to suppress a decrease in the NO _X purification ability of the _X storage means. Further, since the exhaust gas passes over the small amount supporting region before passing over the large amount supporting region, NO ₂ may be reduced to NO in the large amount supporting region before the exhaust gas passes over the small amount supporting region. Is prevented.
Further, in the small amount carrying region, when the temperature of the noble metal catalyst, that is, the temperature of the NO _x storage means is equal to or higher than the NO oxidation start temperature and the air-fuel ratio of the exhaust gas flowing into the NO _x storage means is almost the stoichiometric air fuel ratio or rich. In addition, the reduction capability of reducing NO _X released from the NO _X storage agent to N ₂ is not high, and NO _X flows downstream of the exhaust gas in the small amount carrying region. However, according to the first aspect of the invention, the exhaust gas containing NO _x that has passed over the small amount carrying region passes over the large amount carrying region, so that NO _x that has not been reduced in the small amount carrying region in this large amount carrying region is removed. Can be reduced to N ₂ .

According to a second invention, in the first invention, the NO _X storage means comprises one NO _X catalyst supporting a NO _X storage agent and a noble metal catalyst, and the small amount supporting region and the large amount supporting region are the one of the above one. It is provided in the NO _x catalyst.

According to a third aspect, in the second aspect, the small amount supporting region is provided in an upstream portion of the NO _X catalyst, and the large amount supporting region is located downstream of the upstream portion of the NO _X catalyst. Provided in the downstream portion.

According to a fourth invention, in the second invention, the NO _x catalyst comprises an inflow passage through which exhaust gas flows in and an outflow passage through which exhaust gas flows out, and a partition wall is provided between the inflow passage and the outflow passage. The exhaust gas that has flowed into the inflow passage flows to the outflow passage through the partition wall, and the small amount carrying region is provided on the inflow passage side on the surface of the partition wall, The carrying region is provided on the surface of the partition wall and on the outflow passage side.

According to a fifth invention, in the first invention, the NO _x storage means comprises two NO _x catalysts arranged in series in the engine exhaust passage, each NO _x catalyst comprising a NO _x storage agent and a noble metal catalyst. The NO _x catalyst arranged upstream is provided with the small amount carrying region, and the NO _x catalyst arranged downstream is provided with the large amount carrying region.

  In a sixth invention, in any one of the first to fifth inventions, the amount of the noble metal catalyst supported per unit volume in the small amount support region is at least when the temperature of the noble metal catalyst is equal to or higher than the NO oxidation start temperature. Less than the amount set to be optimal when considering the oxidation / reduction ability of the noble metal catalyst.

To solve the above problem, in the seventh aspect of the invention, there is provided a _the NO _X storage means comprising a noble metal catalyst and _the NO _X storage agent, and a small amount carrying region is small supported amount of noble metal catalyst per unit volume, unit with _the NO _X storage means having a large amount carrying region is large amount of the noble metal catalyst per volume, in the exhaust purification method for an internal combustion engine for purifying NO _X contained in the exhaust gas, the temperature of the noble metal catalyst is the NO oxidation When the temperature is lower than the starting temperature, the exhaust gas flowing into the NO _X storage means passes over the small amount supporting region before passing over the large amount supporting region, and the NO _X storage agent in the small amount supporting region is used. Occludes NO ₂ .
According to the seventh aspect of the invention, in the small amount support region, when the temperature of the noble metal catalyst is lower than the NO oxidation start temperature, the reduction of NO ₂ to NO by the noble metal catalyst is suppressed. For this reason, when the temperature of the noble metal catalyst is lower than the NO oxidation start temperature, the small amount is supported by passing over the small amount supporting region before the exhaust gas passes over the large amount supporting region that reduces NO ₂ to NO. Since NO ₂ can be stored in the NO _X storage agent in the region, it is possible to suppress a decrease in the NO _X purification ability of the NO _X storage means.

According to the first to sixth inventions, when the temperature of the noble metal catalyst, that is, the temperature of the NO _x storage means is lower than the NO oxidation start temperature, NO ₂ in the inflowing exhaust gas is converted into the NO _x storage agent in the small amount carrying region. it is possible that the temperature of and the noble metal catalyst can be occluded to reduce the released NO _X from _the NO _X storage agent in a large amount carrying region in the case of more NO oxidation start temperature, the temperature of _the NO _X storage means noble metal catalyst while maintaining the NO _X purifying ability of _the NO _X storage means when it is in the NO oxidation start temperature or higher, the temperature is also good inflow exhaust even if lower than the NO oxidation start temperature of the noble metal catalyst of the NO _X occluding means NO _x in the gas can be purified.
According to the seventh invention, the temperature of the noble metal catalyst also it is possible to suppress the reduction of the NO _X purifying ability of _the NO _X storage means when lower than the NO oxidation start temperature, NO _X in the well inflow exhaust gas Can be purified.

  FIG. 1 shows a case where the present invention is applied to a compression self-ignition internal combustion engine. The present invention can also be applied to a spark ignition type internal combustion engine.

Referring to FIG. 1, 1 is an engine body, 2 is a combustion chamber of each cylinder, 3 is an electronically controlled fuel injection valve for injecting fuel into each combustion chamber 2, 4 is an intake manifold, and 5 is an exhaust manifold. Respectively. The intake manifold 4 is connected to the outlet of the compressor 7 a of the exhaust turbocharger 7 through the intake duct 6, and the inlet of the compressor 7 a is connected to the air cleaner 8. A throttle valve 9 driven by a step motor is arranged in the intake duct 6, and a cooling device 10 for cooling intake air flowing in the intake duct 6 is arranged around the intake duct 6. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 10 and the intake air is cooled by the engine cooling water. On the other hand, the exhaust manifold 5 is connected to the inlet of the exhaust turbine 7 b of the exhaust turbocharger 7, and the outlet of the exhaust turbine 7 b is connected to the casing 12 containing the NO _x catalyst 11. A reducing agent addition valve 13 for adding a reducing agent made of, for example, hydrocarbons to the exhaust gas flowing in the exhaust manifold 5 is disposed at the outlet of the collecting portion of the exhaust manifold 5.

  The exhaust manifold 5 and the intake manifold 4 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 14, and an electronically controlled EGR control valve 15 is disposed in the EGR passage 14. An EGR cooling device 16 for cooling the EGR gas flowing in the EGR passage 14 is disposed around the EGR passage 14. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 16, and the EGR gas is cooled by the engine cooling water. On the other hand, each fuel injection valve 3 is connected to a fuel reservoir, so-called common rail 18 via a fuel supply pipe 17. Fuel is supplied into the common rail 18 from an electronically controlled fuel pump 19 with variable discharge amount, and the fuel supplied into the common rail 18 is supplied to the fuel injection valve 3 via each fuel supply pipe 17.

The electronic control unit 30 is composed of a digital computer, and is connected to each other by a bidirectional bus 31. It comprises. The the NO _X catalyst 11 is attached a temperature sensor 20 for detecting the temperature of the NO _X catalyst 11, the output signal of the temperature sensor 20 is input to the AD converter 37 the input port 35 via a corresponding. A load sensor 41 that generates an output voltage proportional to the amount of depression of the accelerator pedal 40 is connected to the accelerator pedal 40, and the output voltage of the load sensor 41 is input to the input port 35 via the corresponding AD converter 37. The Further, a crank angle sensor 42 that generates an output pulse every time the crankshaft rotates, for example, 15 ° is connected to the input port 35. On the other hand, the output port 36 is connected to the fuel injection valve 3, the step motor for driving the throttle valve 9, the reducing agent addition valve 13, the EGR control valve 15, and the fuel pump 19 through corresponding drive circuits 38.

2A and 2B show the structure of the NO _x catalyst 11 shown in FIG. Incidentally, FIG. 2 (A) shows a front view of the NO _X catalyst 11, FIG. 2 (B) shows a side cross-sectional view of the NO _X catalyst 11. As shown in FIGS. 2A and 2B, the NO _x catalyst 11 has a honeycomb structure and includes a plurality of exhaust flow passages 50 extending in parallel to each other. The exhaust flow passages 50 are partition walls. 51.

The base 52 of the partition wall 51 of the NO _x catalyst 11 is made of, for example, cordierite or the like, and a carrier 53 made of alumina, for example, is provided on the base 52. 3A and 3B schematically show a cross section of the surface portion of the carrier 53. FIG. As shown in FIGS. 3A and 3B, a noble metal catalyst 54 is dispersedly supported on the surface of the carrier 53, and a layer of NO _x storage agent 55 is formed on the surface of the carrier 53. Has been.

In the present embodiment, platinum (Pt) is used as the noble metal catalyst 54, and examples of the components constituting the NO _x storage agent 55 include alkali metals such as potassium (K), sodium (Na), and cesium (Cs), At least one selected from alkaline earths such as barium (Ba) and calcium (Ca), and rare earths such as lanthanum (La) and yttrium (Y) is used.

When the ratio of air and fuel (hydrocarbon) supplied into the engine intake passage, the combustion chamber 2 and the exhaust passage upstream of the NO _x catalyst 11 is called the air-fuel ratio of the exhaust gas, the NO _x storage agent 55 if NO oxidation initiation temperature or higher temperature of below, i.e. the exhaust gas temperature of the NO _X catalyst 11 flows into the NO _X catalyst if NO oxidation start temperature or higher (hereinafter referred to as "inflow exhaust gas") of air absorbs NO _X when the lean performs absorbing and releasing action of the NO _X that releases NO _X concentration of oxygen absorbed to decrease in the inflowing exhaust gas.

The case where barium (Ba) is used as a component constituting the NO _X storage agent 55 will be described as an example. When the air-fuel ratio of the inflowing exhaust gas is lean, that is, when the oxygen concentration in the inflowing exhaust gas is high, the temperature of the platinum 54 If NO is higher than the NO oxidation start temperature, the NO contained in the inflowing exhaust gas is oxidized on the platinum 54 to become NO ₂ as shown in FIG. 3A, and then absorbed into the NO _x storage agent 55. It diffuses into the NO _x storage agent 55 in the form of nitrate ions (NO ₃ ⁻ ) while being combined with barium oxide (BaO). In this way, NO _x is absorbed in the NO _x storage agent 55. NO ₂ is produced on the surface of the oxygen concentration is as high as platinum 54 in the inflowing exhaust gas, NO _X unless NO ₂ to NO ₂ absorption capacity is not saturated the absorbent 55 is absorbed in the NO _X absorbent 55 nitrate ions (NO ₃ ⁻ ) is generated.

On the other hand, the inflow exhaust gas is obtained by making the air-fuel ratio in the combustion chamber 2 substantially the stoichiometric air-fuel ratio or rich (hereinafter referred to as “stoichiometric rich”) or by supplying the reducing agent from the reducing agent supply valve 13. When the air-fuel ratio of the gas is stoichiometrically rich, the oxygen concentration in the inflowing exhaust gas decreases, so that the reaction proceeds in the reverse direction (NO ₃ ⁻ → NO ₂ ), thereby causing nitrate ions (NO ₃ in the NO _X storage agent 55). ^- ) Is released from the NO _x storage 55 in the form of NO ₂ . Next, the released NO _x is reduced by unburned HC and CO contained in the inflowing exhaust gas. In the above description, it has been described that NO _x is absorbed by the NO _x storage agent 55 (that is, accumulated in the form of nitrate or the like). However, whether NO _x is actually absorbed or adsorbed ( That is, it is not always clear whether NO _x is surface adsorbed in the form of NO ₂ or the like, and the term occlusion including both the concepts of absorption and adsorption is used. In this specification, in particular, the occlusion performed when the temperature of the NO _x catalyst 11 is equal to or higher than the NO oxidation start temperature is referred to as “high temperature occlusion”. The term “release” from the NO _x storage agent 55 is also used to include the meaning of “desorption” corresponding to “adsorption” in addition to “release” corresponding to “absorption”.

Incidentally, the ability of platinum 54 to oxidize NO to NO ₂ (hereinafter referred to as “NO oxidation ability”) varies depending on the temperature, and the lower the temperature of platinum 54, the lower the NO oxidation ability. For this reason, as shown in FIG. 3, when the temperature of the NO _x catalyst 11 decreases, the oxidation rate from NO to NO ₂ by platinum 54 (hereinafter referred to as “NO oxidation rate”) decreases. In this embodiment, when the temperature of the NO _x catalyst 11 becomes lower than about 250 ° C., the NO oxidation rate decreases rapidly, and when the temperature of the NO _x catalyst 11 becomes about 200 ° C., the NO oxidation rate becomes about 50 percent. In this embodiment, the temperature of the NO _x catalyst 11 when the NO oxidation rate becomes approximately 50 percent is set to the NO oxidation start temperature (approximately 200 ° C. (= Ts)).

Well, NO _X in the inflowing exhaust gas is not stored in the NO _X storage agent 55 in the form of nitric oxide (NO), are occluded in the NO _X absorbent 55, if the form of nitrogen dioxide (NO _2). The NO _x contained in the inflowing exhaust gas usually contains not only NO ₂ but also a lot of NO, and this NO is not absorbed by the NO _x storage agent 55 unless it is oxidized to NO ₂ . NO _X catalyst 11 to NO in the oxidation to NO ₂ is required that the temperature of the noble metal catalyst 54 is in the NO oxidation start temperature or higher, so this until the noble metal catalyst 54 to purify the NO _X It has been considered that the temperature needs to be equal to or higher than the NO oxidation start temperature.

However, as a result of the inventor's repeated research on the NO _x catalyst 11, NO contained in the inflowing exhaust gas has a temperature of the platinum 54 not higher than the NO oxidation start temperature, that is, the temperature of the NO _x catalyst 11 is NO. The NO _x storage agent 55 does not store unless the oxidation start temperature is exceeded, but the NO ₂ contained in the inflowing exhaust gas is not shown in FIG. 3B even if the temperature of the NO _x catalyst 11 does not exceed the NO oxidation start temperature. It has been found that the NO _x storage agent 55 stores, for example, in the form of nitrous acid (NO ₂ ⁻ ) as shown in FIG. Also in this case, as in the case where the temperature of the NO _X catalyst 11 is in the NO oxidation start temperature or higher, or the nitrogen dioxide NO ₂ from being adsorbed in the NO _X absorbent 55, or the NO _X absorbent 55 Whether it is absorbed or not is not always clear, and the term “occlusion” that combines these adsorption and absorption is used. In this specification, in particular, the occlusion performed when the temperature of the NO _x catalyst 11 is lower than the NO oxidation start temperature is referred to as “low temperature occlusion”.

The temperature is in the NO _X absorbent 55 nitrous acid is lower than the NO oxidation start temperature of the NO _X catalyst 11 (NO ₂ ^-) NO ₂ occluded as the temperature NO oxidation start temperature of the NO _X catalyst 11 If it rises to the above, it will be changed into nitrate ion (NO ₃ ⁻ ), and thus will be stored in the NO _X storage agent 55 in the form of nitrate ion (NO ₃ ⁻ ).

By the way, when the temperature of the platinum 54 is lower than the NO oxidation start temperature, if the activity of the platinum is high, that is, if the oxidation / reduction ability of the platinum is high, the platinum 54 can not only oxidize NO to NO _2. , resulting in a reduction of the NO ₂ to NO. Therefore, in such a case, if the activity of the platinum 54 in the NO _x catalyst is high, the NO ₂ in the exhaust gas flowing into the NO _x catalyst is reduced to NO by the platinum 54 before being stored in the NO _x storage agent 55 at a low temperature. Will be. The reduced NO is not stored in the NO _X storage agent 55, and therefore, exhaust gas containing a large amount of NO flows out from the NO _X catalyst.

Therefore, in order to increase the low temperature storage capacity of NO ₂ of the NO _x storage agent when the temperature of the platinum 54 is lower than the NO oxidation start temperature, the activity of platinum is weakened, and in such a case, the NO ₂ by the platinum is reduced. It is necessary to reduce the ability to reduce NO to NO.

On the other hand, in the conventional type of the NO _X catalyst, and optimally oxidizing NO in the inflowing exhaust gas to NO ₂ when the air-fuel ratio of the inflowing exhaust gas when it is NO oxidation start temperature or higher is lean _the NO _X storage agent the NO _X when the air-fuel ratio of the inflowing exhaust gas is released from _the NO _X storage agent when a stoichiometric-rich with NO _X is as likely to be occluded as easily reduced to N _2, the intensity of the activity of platinum That is, the oxidation / reduction ability of platinum is set. That is, in the conventional NO _x catalyst, the oxidation / reduction ability of platinum is optimal for storing / reducing NO _x in the exhaust gas flowing into the NO _x catalyst when the temperature of the platinum is equal to or higher than the NO oxidation start temperature. It is set to be. Thus, when the oxidation / reduction ability of platinum is set, naturally, even when the temperature of platinum 54 is lower than the NO oxidation start temperature, the oxidation / reduction ability of platinum is high, and the exhaust gas flowing into the NO _x catalyst NO ₂ in is reduced to NO, as a result, the purification rate of the NO _X when the temperature is lower than the NO oxidation start temperature of the platinum 54 has been has become low.

Therefore, in the present embodiment, as shown in FIG. 4, the downstream portion 57 of the carrier 53 of the NO _X catalyst 11 carrying the NO _X storage agent 55 and the noble metal catalyst 54 is replaced with the conventional NO _X catalyst 11 described above. strong region active platinum to the same extent, i.e. conventional NO _X catalyst high and oxidation-reduction ability comparable to platinum region (hereinafter, referred to as "high redox ability region") and at the same time as, NO _X occluding The upstream portion 56 of the carrier 53 of the NO _x catalyst 11 carrying the agent 55 and the noble metal catalyst 54 is oxidized in a region where the platinum activity is weaker than that in the high oxidation / reduction ability region, that is, in the platinum oxidation than in the high oxidation / reduction ability region.・ A region with low reducing ability (hereinafter referred to as “low oxidation / reducing ability region”). Accordingly, the exhaust gas flowing into the NO _x catalyst 11 passes over the low oxidation / reduction ability region 56 and then passes over the high oxidation / reduction ability region 57.

Here, the NO _x storage agent 55 is basic, and the stronger the basicity of the platinum 54 is, the weaker the activity of the platinum 54 is. In other words, when the type and loading amount of the NO _x storage agent 55 are constant, the activity of the platinum 54 is weakened as the loading amount of the platinum 54 per unit volume is smaller. Therefore, in the NO _x catalyst 11 of the present embodiment, the amount of platinum supported per unit volume in the low oxidation / reduction capacity region 56 is smaller than the amount of platinum supported per unit volume in the high oxidation / reduction capacity region 57. It is said. Specifically, the amount of platinum 54 supported per unit volume in the high oxidation / reduction capacity region (mass loading region) 57 is larger than 2 g / l as in the conventional NO _x catalyst, whereas the low oxidation The amount of platinum 54 supported per unit volume in the reducing capacity region (small amount supporting region) 56 is set to 2 g / l or less.

In the low oxidation / reduction capacity region 56 formed in this way, when the temperature of the NO _x catalyst 11 is lower than the NO oxidation start temperature, the activity of the platinum 54 is weak and the reduction of NO ₂ to NO by platinum is performed. Therefore, NO ₂ in the exhaust gas flowing through the low oxidation / reduction capacity region 56 is reliably stored in the NO _X storage agent 55. Therefore, NO _X purification ability temperature of the NO _X catalyst 11 by the NO _X catalyst 11 when lower than the NO oxidation initiation temperature is elevated.

This is shown in FIG. FIG. 5 shows the NO _x purification rate (in the outflowing exhaust gas) of the conventional NO _x catalyst (catalyst A in the figure) in which the supported amount of platinum 54 is 5 g / l when the temperature of the NO _x catalyst is 150 ° C. and the amount of NO _X / inflow amount of NO _X in the exhaust gas), in which NO _X catalyst 11 in this embodiment (as compared with the NO _X purification rate of the catalyst B) in FIG. As can be seen from FIG. 5, when the temperature of the NO _x catalyst is 150 ° C., that is, lower than the NO oxidation start temperature, the NO _x purification rate of the NO _x catalyst 11 (catalyst B) of the present embodiment is the catalyst A. higher than of the NO _X purification rate.

Further, when the temperature of the NO _x catalyst 11 becomes equal to or higher than the NO oxidation start temperature, when the air-fuel ratio of the inflowing exhaust gas is lean, it flows in both the low oxidation / reduction capacity region 56 and the high oxidation / reduction capacity region 57. The NO _X in the exhaust gas can be stored in the NO _X storage agent 55. In the high oxidation / reduction capacity region 57, since the oxidation ability of platinum 54 is high, NO ₂ in the exhaust gas can be oxidized to NO ₂ and NO ₂ can be stored in the NO _X storage agent 55. In the reducing capacity region 56, the oxidizing ability of the platinum 54 sufficient to oxidize most of the NO in the exhaust gas to NO ₂ is exhibited, so that all the areas are the high oxidizing / reducing ability area 57. similar to the conventional NO _X catalyst, the NO _X in the inflowing exhaust gas can be occluded in the NO _X absorbent 55.

This is shown in FIG. FIG. 6 shows the NO _x purification rate of the catalyst A shown in FIG. 5 and the NO _x catalyst 11 of the present embodiment (same as the catalyst B shown in FIG. 5) when the temperature of the NO _x catalyst is 300 ° C. it is a comparison of the of the NO _X purification rate. As can be seen from FIG. 6, even when the temperature of the NO _x catalyst is 300 ° C., that is, when the temperature of the NO _x catalyst is equal to or higher than the NO oxidation start temperature, the NO _x catalyst 11 (catalyst B) of the present embodiment. It can be seen that the NO _x purification rate is comparable to the NO _x purification rate of the conventional NO _x catalyst (catalyst A).

On the other hand, when the temperature of the NO _X catalyst 11 becomes equal to or higher than the NO oxidation start temperature, if the air-fuel ratio of the inflowing exhaust gas is stoichiometric rich, the NO ₂ stored in the NO _X storage agent 55 is stored in the NO _X storage. Released from the agent 55. In the low oxidation / reduction ability region 56, the activity of platinum 54 is weaker than that of the high oxidation / reduction ability region 57 as described above, and the reduction ability to reduce NO _x released from the NO _x storage agent 55 to N ₂ is high. Absent. Therefore, as described above, when the air-fuel ratio of the inflowing exhaust gas is made stoichiometric rich, the exhaust gas containing some NO flows from the low oxidation / reduction capacity region 56 of the NO _x catalyst 11 to the exhaust downstream. .

However, in the NO _x catalyst 11 of the present embodiment, the high oxidation / reduction capacity region 57 is provided downstream of the low oxidation / reduction capacity region 56. Therefore, when the temperature of the NO _X catalyst 11 is equal to or higher than the NO oxidation start temperature, if the air-fuel ratio of the inflowing exhaust gas is stoichiometric rich, the NO _X catalyst 11 over the low oxidation / reduction capacity region 56 The exhaust gas containing NO that has passed passes over the high oxidation / reduction capacity region 57. When the temperature of the NO _x catalyst 11 is equal to or higher than the NO oxidation start temperature, the ability to reduce NO _x to N ₂ in the high oxidation / reduction ability region 57 is high, and thus high oxidation is performed from above the low oxidation / reduction ability region 56. · NO _X contained in the exhaust gas flowing into the reducing ability region 57 above is reduced to N _2. Therefore, according to the present embodiment, when the temperature of the NO _x catalyst 11 is equal to or higher than the NO oxidation start temperature, if the air-fuel ratio of the inflowing exhaust gas is stoichiometric rich, the low oxidation / reduction capacity region 56 and NO _x is released from the NO _x storage agent 55 in the high oxidation / reduction capacity region 57, and the released NO _x is reduced and purified to N ₂ well.

Thus, according to the NO _X catalyst 11 of the present invention, the temperature of the NO _X catalyst 11 while maintaining the purification performance of the NO _X in the case where NO oxidation start temperature or higher of a noble metal catalyst 54, of the NO _X catalyst 11 The NO _x purification ability when the temperature is lower than the NO oxidation start temperature of the noble metal catalyst 54 can be enhanced.

In the above embodiment, the amount of platinum 54 supported per unit volume in the low oxidation / reduction capacity region 56 is less than the amount of platinum 54 supported per unit volume in the high oxidation / reduction capacity region 57. Although the oxidation / reduction ability of the platinum 54 in the low oxidation / reduction ability region 56 is lowered, the oxidation / reduction ability of the platinum 54 may be lowered by strengthening the basicity of the NO _x storage agent 55. To enhance the basicity of the NO _X absorbent 55, to increase the loading amount of the NO _X absorbent 55 to the carrier 53 per unit volume, and strong basic by substance used as _the NO _X storage agent 55 substances For example, use of alkali metals such as cesium (Cs), potassium (K), and sodium (Na) can be used.

By the way, when the temperature of the NO _x catalyst 11 is lower than the NO oxidation start temperature, or when the temperature of the NO _x catalyst 11 is higher than the NO oxidation start temperature and the air-fuel ratio of the inflowing exhaust gas continues to be lean, _the NO _X storage capacity of the NO _X absorbent 55 is saturated, making it impossible to occlude NO _X by more _the NO _X storage agent 55. Therefore, in this embodiment, before the NO _X storage capacity of the NO _X storage agent 55 is saturated, the air-fuel ratio of the inflowing exhaust gas is temporarily stoichiometric rich by adding the reducing agent from the reducing agent addition valve 13, As a result, NO _X is released from the NO _X storage agent 55 (NO _X release processing).

More specifically, in this embodiment, the stored NO _X amount ΣNOX stored in the NO _X storage agent 55 of the NO _X catalyst 11 is calculated, and the calculated stored NO _X amount ΣNOX is a predetermined allowable value NX. When the temperature of the NO _x catalyst 11 is equal to or higher than the NO oxidation start temperature, the air-fuel ratio of the inflowing exhaust gas is switched from lean to stoichiometric rich, whereby the NO _x storage agent 55 NO _x is released from the gas.

NO _X amount exhausted from the engine body 1 per unit time is a function of the fuel injection amount Q and the engine speed N, thus the inflow amount of NO _X NOXA of the inflowing exhaust gas to the NO _X catalyst per unit time This is a function of the fuel injection amount Q and the engine speed N. Inflow amount of NO _X NOXA per unit time in accordance with the fuel injection amount Q and engine speed N in the present embodiment is obtained by experiment, the function of the inflow amount of NO _X NOXA fuel injection amount Q and the engine speed N As a map in advance in the ROM 32.

On the other hand, the NO _X storage rate KN to the NO _X storage agent 55 changes according to the temperature Tc of the NO _X catalyst 11. Therefore, in the present embodiment, the relationship between the NO _X storage rate KN and the temperature Tc of the NO _X catalyst is obtained in advance by experiments and stored in advance in the ROM 32 as a map. _The NO _X storage amount per unit time to _the NO _X storage agent 55 is represented by the product of the NOXA and KN.

On the other hand, when the temperature Tc of the NO _x catalyst 11 is lower than the NO oxidation start temperature, only the NO ₂ in the inflowing exhaust gas is occluded in the NO _x storage agent as described above. For this reason, in such a case, it is preferable to reduce the proportion of NO in NO _x in the inflowing exhaust gas and increase the proportion of NO ₂ . Therefore, in this embodiment, when the temperature Tc of the NO _x catalyst 11 is lower than the NO oxidation start temperature, the ratio of NO ₂ to NO generated when combustion is performed under a lean air-fuel ratio is expressed as NO _x. When the temperature Tc of the catalyst 11 is equal to or higher than the NO oxidation start temperature, compared with the ratio of NO ₂ (= NO ₂ amount / NO amount) in the same engine operating state, that is, at the same speed and the same torque. so that increase (NO ₂ ratio increasing process).

This ratio of NO ₂ has been found to increase with slow combustion, for example, retarding the fuel injection timing, increasing the EGR gas amount, performing pilot injection, or premixing Combustion becomes slow when at least one of the air combustion is performed. Therefore, in the present embodiment, when the temperature of the NO _x catalyst 11 is lower than the NO oxidation start temperature, as the NO ₂ ratio increasing process, the combustion is performed more slowly than in other temperature regions in the same engine operating state. .

Even when the temperature Tc of the NO _x catalyst 11 is lower than the NO oxidation start temperature, the NO _x occlusion amount of the NO _x catalyst 50 increases because NO ₂ is occluded in the NO _x occlusion agent 55. In this case, the NO _X storage amount per unit time varies depending on the NO ₂ amount in the exhaust gas discharged from the engine body 1. The amount of NO ₂ in the exhaust gas discharged from the engine body 1 is a function of the EGR rate (the ratio of EGR gas in the intake gas), the retard amount of the injection timing, etc. in addition to the fuel injection amount Q and the engine speed N It is. In the present embodiment, the NO ₂ storage amount NO2A per unit time corresponding to these parameters is obtained in advance by experiments and stored in the ROM 32 in advance in the form of a map. When the temperature Tc of the NO _x catalyst 11 is lower than the NO oxidation start temperature, the NO ₂ occlusion amount NO2A per unit time is replaced by the occluded NO _x amount ΣNOX instead of the NO _x occlusion amount NOXA · KN per unit time described above. Is added to

FIG. 7 shows a control routine for optimally maintaining the NO _x purification capacity of the NO _x catalyst 11, and this routine is executed by interruption every predetermined time.

Referring to FIG. 7, first, at step 101, it is judged if the NO _x release flag XN is set. The NO _X release flag XN is a flag that is set when the NO _X release process is to be executed (XN = 1) and is not set otherwise (XN = 0). When it is determined that the NO _X release flag XN is not set, the routine proceeds to step 102 where the temperature sensor 20 detects the temperature Tc of the NO _X catalyst 11. Next, at step 103, it is determined whether or not the temperature Tc of the NO _x catalyst 11 detected at step 102 is lower than the NO oxidation start temperature Ts. If it is determined in step 103 that the temperature Tc of the NO _x catalyst 11 is lower than the NO oxidation start temperature Ts (Tc <Ts), the process proceeds to step 104.

In step 104, an NO ₂ ratio increasing process is executed, and for example, at least one of retarding the fuel injection timing, increasing the EGR gas amount, performing pilot injection, or performing premixed gas combustion. One is done. Next, at step 105, the NO ₂ occlusion amount NO2A per unit time is calculated from the map described above. In step 106, the NO ₂ storage amount NO2A per unit time calculated in step 105 is added to ΣNOX, and an integrated value ΣNOX of the NO _X storage amount is calculated.

On the other hand, if it is determined in step 103 that the temperature Tc of the NO _x catalyst 11 is equal to or higher than the NO oxidation start temperature Ts (Tc ≧ Ts), the routine proceeds to step 107. In step 107, the inflow amount of NO _X NOXA and _the NO _X storage rate KN per unit each time from the map described above is calculated. Next, at step 108, the integrated value ΣNOX of the NO _X storage amount is calculated by adding the NO _X storage amount NOXA · KN per unit time calculated at step 107 to ΣNOX. Next, at step 109, it is determined whether or not the integrated value ΣNOX of the NO _X absorption amount exceeds the allowable value NX. When ΣNOX ≦ NX, the control routine is terminated. On the other hand, when ΣNOX> NX, the NO _X flag XN is set in step 110 (XN = 1). When the NO _X release flag XN is set, the routine proceeds from step 101 to step 111 when the next routine is executed, and the NO _X release process is executed.

FIG. 8 shows a processing routine of the NO _x releasing process performed in step 111 of FIG.

Referring to FIG. 8, first, at step 121, the supply amount of the reducing agent necessary for setting the air-fuel ratio of the inflowing exhaust gas to a rich air-fuel ratio of about 13, for example, is calculated. Next, at step 122, the supply time of the reducing agent is calculated. The supply time of this reducing agent is usually 10 seconds or less. Next, at step 123, supply of the reducing agent from the reducing agent supply valve 13 is started. Next, at step 124, it is determined whether or not the supply time of the reducing agent calculated at step 122 has elapsed. When the supply time of the reducing agent has not elapsed, step 124 is repeated. At this time, the supply of the reducing agent is continued, and the air-fuel ratio of the inflowing exhaust gas is maintained at a rich air-fuel ratio of about 13. On the other hand, when the supply time of the reducing agent has elapsed, that is, when the NO _x releasing action from the NO _x storage agent 55 is completed, the routine proceeds to step 125 where the supply of the reducing agent is stopped, and then proceeds to step 126 and ΣNOx. Is cleared, and the NO _X release flag XN is reset in step 127 (XN = 0).

In the NO _x releasing process, it has been described that the air-fuel ratio of the inflowing exhaust gas is temporarily stoichiometrically rich by supplying the reducing agent from the reducing agent supply valve 13, but compression auto-ignition is performed as in the present embodiment. When the internal combustion engine is used, the lean degree of the air-fuel ratio of the exhaust gas discharged from the engine body 1 is usually very large. Therefore, in order to make the air-fuel ratio of the inflowing exhaust gas stoichiometric and rich, a large amount of reducing agent is required. Must be supplied from the reducing agent supply valve 13. Therefore, in the present embodiment, for example, by introducing a large amount of EGR gas into the combustion chamber 2 or performing post injection, the lean degree of the air-fuel ratio of the exhaust gas discharged from the engine body 1 is made relatively small. The reducing agent is added from the reducing agent addition valve 13 to this.

Next, a second embodiment in which the NO _x catalyst 11 shown in FIG. 1 is formed of a particulate filter (hereinafter referred to as “filter”) will be described.

  FIGS. 9A and 9B show the structure of the filter 11. 9A shows a front view of the filter 11, and FIG. 9B shows a side cross-sectional view of the filter 11. As shown in FIGS. 9A and 9B, the filter 11 has a honeycomb structure and includes a plurality of exhaust flow passages 60 and 61 extending in parallel with each other. These exhaust flow passages include an exhaust gas inflow passage 60 whose downstream end is closed by a plug 62 and an exhaust gas outflow passage 61 whose upstream end is closed by a plug 63. In addition, the hatched part in FIG. Therefore, the exhaust gas inflow passages 60 and the exhaust gas outflow passages 61 are alternately arranged via the thin partition walls 64.

  The base body 65 of the partition wall 64 of the filter 11 is formed of a porous material such as cordierite, so that the exhaust gas flowing into the exhaust gas inflow passage 60 is surrounded by the surroundings as shown by arrows in FIG. Through the partition wall 64 and into the adjacent exhaust gas outflow passage 61.

When the NO _x catalyst 11 is constituted by a particulate filter in this way, alumina is formed on the peripheral wall surfaces of the exhaust gas inflow passages 60 and the exhaust gas outflow passages 61, that is, on both side surfaces of the base 65 of each partition wall 64. As shown in FIGS. 3 (A) and 3 (B), the noble metal catalyst 54 and the NO _x storage agent 55 are supported on the carriers 66 and 67. . In this case, platinum is used as the noble metal catalyst 54.

FIG. 10 is a diagram schematically showing a portion surrounded by a dotted line X in FIG. 9B. As can be seen from FIG. 10, the carrier 66 on the peripheral wall surface of the exhaust gas inflow passage 60, that is, the carrier 66 on the base 65 of the partition wall 64 facing the exhaust gas inflow passage 60 is used as the low oxidation / reduction capacity region. The carrier 67 on the peripheral wall surface of the passage 61, that is, the carrier 68 on the base 64 of the partition wall 64 facing the exhaust gas outflow passage is used as a high oxidation / reduction ability region. Specifically, in the present embodiment, the carrying amount per unit volume of platinum 54 carried on the carrier 66 on the peripheral wall surface of the exhaust gas inflow passage 60 is transferred to the carrier 67 on the peripheral wall surface of the exhaust gas outflow passage 61. Although the amount of platinum 54 supported is smaller than the amount supported per unit volume, the basicity of the NO _x storage agent 55 supported on the carrier 66 is more basic than the basicity of the NO _x storage agent 55 supported on the support 67. May be strong.

As described above, the exhaust gas flowing into the exhaust gas inflow passage 60 flows into the adjacent exhaust gas outflow passage 61 through the surrounding partition wall 64 as indicated by an arrow in FIG. The inflowing exhaust gas passes over the low oxidation / reduction ability region 66 provided on the peripheral wall surface of the exhaust gas inflow passage 60 and then the high oxidation / reduction ability region 67 provided on the peripheral wall surface of the exhaust gas outflow passage 61. Pass over. Therefore, similarly to the exhaust gas purifying apparatus of the first embodiment, when the temperature of the filter 11 is NO oxidation start temperature or higher, the air-fuel ratio of the inflowing exhaust gas is NO _X in the inflowing exhaust gas when the lean low When the air-fuel ratio of the inflowing exhaust gas is stoichiometric rich, the low oxidation / reduction capacity region 66 and the high oxidation / reduction capacity are stored in the NO _x storage agent in the oxidation / reduction capacity region 66 and the high oxidation / reduction capacity region 67. is NO _X is released from _the NO _X storage agent in the ability region 67, these two areas, NO _X released by the platinum 54 present particularly high redox potential region 67 is reduced to N _2. On the other hand, when the temperature of the filter 11 is lower than the NO oxidation start temperature, NO ₂ in the inflowing exhaust gas is occluded in the NO _x storage agent 55 mainly in the low oxidation / reduction capacity region 66. In this case as well, the NO _X purification capability maintenance control similar to the NO _X purification capability maintenance control of the NO _X catalyst 11 shown in FIGS. 7 and 8 is performed.

When the NO _x catalyst 11 is composed of a particulate filter, particulate matter contained in the inflowing exhaust gas is captured in the filter 11 and the captured particulate matter is sequentially burned by the exhaust gas heat. . When a large amount of particulate matter accumulates on the filter 11, the temperature of the exhaust gas discharged from the engine body 1 is increased, or the reducing agent is supplied from the reducing agent supply valve 13 and burned by the filter 11. In other words, by raising the temperature of the filter 11, the accumulated particulates are ignited and combusted.

FIG. 11 shows an exhaust emission control device according to a third embodiment of the present invention. As shown in FIG. 11, in the third embodiment, two NO _X catalysts 70 and 72 are provided on the engine exhaust passage as NO _X storage means. That is, the outlet of the exhaust turbine 7b is connected to the casing 71 with a built-in upstream NO _X catalyst 70, the exhaust downstream of the upstream-side NO _X catalyst 70 casing 73 incorporating a downstream NO _X catalyst 72 is connected. Each of the NO _X catalysts 70 and 72 is provided with a carrier 53 such as alumina on the base 52 as in the NO _X catalyst 11 of the first embodiment, and the noble metal catalyst 54 and the NO _X occlusion on the surface of the carrier 53. An agent 55 is carried.

On the other hand, unlike the NO _x catalyst 11 of the first embodiment, all of the support of the upstream NO _x catalyst 70 is in the low oxidation / reduction capacity region, and all of the support of the downstream NO _x catalyst 72 is highly oxidized and reduced. It is a reducing capacity area. In the present embodiment, the supported amount per unit volume of the noble metal catalyst supported on the support of the upstream side NO _x catalyst 70 is determined from the supported amount per unit volume of the noble metal catalyst supported on the support of the downstream side NO _x catalyst 72. Although it is assumed is small, than basic of the NO _X absorbent 55 carried the basic of the NO _X absorbent 55 is supported on a carrier of the upstream-side NO _X catalyst 70 to the carrier of the downstream NO _X catalyst 72 You may make it strong.

Exhaust gas discharged from the engine body 1 flows into the downstream NO _X catalyst 72 after passing through the upstream NO _X catalyst 70. That is, in this embodiment, the exhaust gas flowing into the high redox ability region provided after passing the low oxidation-reduction potential region above provided upstream NO _X catalyst 70 on the downstream side NO _X catalyst 72 To do. Therefore, similarly to the exhaust gas purifying apparatus of the first embodiment, when the temperature of both the NO _X catalyst 70, 72 is NO oxidation start temperature or more, the air-fuel ratio of the exhaust gas flowing into the upstream-side NO _X catalyst 70 During lean, NO _x in the exhaust gas is occluded by the NO _x storage agent 55 carried by the upstream NO _x catalyst 70 and the downstream NO _x catalyst 72 and flows into the upstream NO _x catalyst 70. air-fuel ratio is _the NO _X storage agent from NO _X provided upstream NO _X catalyst 70 and the downstream NO _X catalyst 72 when the stoichiometric-rich is released, these both NO _X catalyst 70 and 72, in particular downstream The released NO _x is reduced to N ₂ by the platinum 54 present in the NO _x catalyst 72. On the other hand, when the temperatures of the NO _X catalysts 70 and 72 are lower than the NO oxidation start temperature, NO ₂ in the inflowing exhaust gas is mainly stored in the NO _X storage agent 55 in the upstream NO _X catalyst 70. In this case as well, the NO _X purification capability maintenance control similar to the NO _X purification capability maintenance control of the NO _X catalyst 11 shown in FIGS. 7 and 8 is performed.

It is a figure which shows the whole internal combustion engine. It is a diagram for explaining the configuration of the NO _X catalyst. It is a diagram illustrating a NO _X purification action by the NO _X catalyst. FIG. 4 is an enlarged cross-sectional view schematically showing the inside of a broken line IV in FIG. 2. Heating of the NO _X catalyst is a diagram showing the difference of the NO _X purification rate by the NO _X catalyst definitive at 0.99 ° C.. Heating of the NO _X catalyst is a diagram showing the difference of the NO _X purification rate by the NO _X catalyst definitive at 300 ° C.. 3 is a flowchart of NO _X purification capacity maintenance control of the NO _X catalyst. Is a flow chart for performing the NO _X release process. It is a figure for demonstrating the structure of a particulate filter. FIG. 10 is an enlarged cross-sectional view schematically showing the inside of a broken line X in FIG. 9. 3 shows an exhaust emission control device according to a third embodiment of the present invention.

Explanation of symbols

3 ... fuel injection valve 4 ... intake manifold 5 ... exhaust manifold 7 ... exhaust turbocharger 11 ... NO _X catalyst 13 ... reducing agent feed valve 20 ... Temperature sensor

Claims (7)

Comprising a _the NO _X storage means for carrying the _the NO _X storage agent and a noble metal catalyst in the engine exhaust passage, the _the NO _X storage agent to _the NO _X storage means when the temperature of the noble metal catalyst is the NO oxidation start temperature or higher When the air-fuel ratio of the inflowing exhaust gas is lean, NO _x in the exhaust gas is occluded, and when the air-fuel ratio of the exhaust gas flowing into the NO _x occlusion means is almost the stoichiometric air-fuel ratio or rich, it is occluded by the NO _x storage agent. the NO _X by being released, the _the NO _X storage means, and a small amount carrying region and a large amount carrying region, per unit volume amount of the noble metal catalyst per unit volume in the small amount carrying region is in the large amount of carrying region In the exhaust gas purification device for an internal combustion engine, which is less than the amount of the noble metal catalyst supported,
The exhaust gas purifying apparatus for an internal combustion engine provided so that the exhaust gas flowing into the NO _x storage means passes over the small amount support region and then passes over the large amount support region. . 2. The NO _x storage means includes one NO _x catalyst that supports a NO _x storage agent and a noble metal catalyst, and the small amount supporting region and the large amount supporting region are provided in the one NO _x catalyst. Exhaust gas purification device for internal combustion engine. The small amount carrying region is provided on the upstream side portion of the NO _X catalyst, the large amount carrying region according to claim 2 which is provided on the downstream side portion of the NO _X catalyst located in the exhaust downstream than the upstream side portion An exhaust purification device for an internal combustion engine. The NO _X catalyst; and a bleed passage inlet passage and an exhaust gas exhaust gas flows to flow out, the exhaust gas flowing into the inflow passage with the partition wall is provided between these inlet passages and outlet passages Flows through the partition to the outflow passage, the small amount carrying region is provided on the inflow passage side on the surface of the partition, and the large amount carrying region is on the surface of the partition and flows out. The exhaust emission control device for an internal combustion engine according to claim 2, provided on the passage side. The NO _X storage means includes two NO _X catalysts arranged in series in the engine exhaust passage, and each NO _X catalyst carries a NO _X storage agent and a noble metal catalyst, and is arranged upstream. An exhaust purification system of an internal combustion engine according to claim 1 in which the large amount carrying region is provided in the NO _X catalyst arranged downstream together with the small amount carrying region is provided in the NO _X catalyst.   The amount of noble metal catalyst supported per unit volume in the small amount loading region is set to be optimal when considering the oxidation / reduction ability of the noble metal catalyst at least when the temperature of the noble metal catalyst is equal to or higher than the NO oxidation start temperature. The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 5, wherein the exhaust gas purification device is less than a predetermined amount. A _the NO _X storage means comprising a noble metal catalyst and _the NO _X storage agent, a small amount and carrying region is small supported amount of noble metal catalyst per unit volume, and a large amount carrying region is large amount of the noble metal catalyst per unit volume In an exhaust gas purification method for an internal combustion engine that purifies NO _x contained in exhaust gas using a NO _x storage means having
When the temperature of the noble metal catalyst is lower than the NO oxidation start temperature, the exhaust gas flowing into the NO _X storage means passes over the small amount supporting region before passing over the large amount supporting region, and the small amount supporting An exhaust purification method for an internal combustion engine in which NO ₂ is stored in the NO _X storage agent in the region.

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