JP4254484B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

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

As a catalyst 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 provided on the surface of a support made of alumina. A NO _x storage catalyst in which a layer of a NO _x storage agent made of metal is formed and a noble metal such as platinum is supported on the surface of the support is known. In this NO _X storage catalyst, when the NO _X storage catalyst is activated, NO _X contained in the exhaust gas is stored in the NO _X storage agent when the air-fuel ratio of the exhaust gas is lean, and the air-fuel ratio of the exhaust gas becomes rich. It is the the _the NO _X storage agent NO _X that was stored in is released and reduced.

By the way, absorbing and releasing action of such NO _X was considered the NO _X storing catalyst is not performed and does not activate, the _the NO _X storing catalyst to perform the absorption and release action of the thus NO _X As a result of repeated research by the present inventor, nitrogen monoxide NO contained in the exhaust gas is not stored in the NO _x storage agent unless the NO _x storage catalyst is activated, but nitrogen dioxide (NO ₂₎ contained in the exhaust gas. ) Was found to be stored in the NO _X storage agent even if the NO _X storage catalyst was not activated.

From this point of view, it ratio of NO ₂ with respect to NO _X in the exhaust gas when the the NO _X storing catalyst is not activated flowing into the NO _X storage catalyst is large of the NO _X storage catalyst by NO _X It can be seen that the purification rate increases.

The proportion of NO ₂ in the exhaust gas flowing into the NO _X storage catalyst as a way of increasing include the placing oxidation catalyst carrying a noble metal such as platinum on the upstream side of the NO _X storage catalyst (e.g., Patent Reference 1). In such an oxidation catalyst, NO in the exhaust gas is oxidized to NO ₂ by the oxidizing action of platinum.

JP 2002-89246 A JP 2000-345832 A International Publication No. 98/48153 Pamphlet

However, with such an oxidation catalyst, when the oxidation catalyst is not activated, NO in the exhaust gas can hardly be oxidized to NO ₂ , but rather NO ₂ in the exhaust gas can be reduced to NO. is there. Therefore, in the internal combustion engine described in Patent Document 1, when the oxidation catalyst and the NO _x storage catalyst are not activated, the NO _x purification rate is obtained by flowing the exhaust gas flowing through the oxidation catalyst into the NO _x storage catalyst. Will be low.

Accordingly, an object of the present invention is to provide an exhaust purification device for an internal combustion engine that can satisfactorily purify NO _{x in} exhaust gas even when the NO _x storage catalyst is not activated.

In order to solve the above problems, the first aspect of the present invention, is disposed _the NO _X storage catalyst with the noble metal and _the NO _X storage agent into the engine exhaust passage, when the the NO _X storing catalyst is not activated _the NO _X storage When the air-fuel ratio of the exhaust gas flowing into the catalyst is lean, nitrogen dioxide NO ₂ contained in the exhaust gas is stored in the NO _X storage agent, and flows into the NO _X storage catalyst when the NO _X storage catalyst is activated. When the air-fuel ratio of the exhaust gas is lean, the nitrogen oxide NO _x contained in the exhaust gas is occluded in the NO _x storage agent and the air-fuel ratio of the exhaust gas flowing into the NO _x storage catalyst is almost the stoichiometric air-fuel ratio or nitrogen oxides nO _X that is occluded becomes rich is released from _the nO _X storage agent, _the nO _X storage catalyst nitrogen dioxide nO ₂ is nitrogen monoxide nO in the exhaust gas discharged from the engine when not activated Suppressing reduction suppressing means from being reduced provided on the upstream side of the exhaust passage of the NO _X storage catalyst, was supported and noble metal is arranged on the upstream side of the _the NO _X storage catalyst be in the engine exhaust passage an oxidation catalyst And a bypass passage for bypassing the oxidation catalyst, and a flow rate adjusting valve for adjusting the flow rate of the exhaust gas flowing into the oxidation catalyst and the flow rate of the exhaust gas flowing into the bypass passage, _{When the X-} occlusion catalyst is not activated, the reduction suppression means controls the flow rate adjustment valve so that almost all of the exhaust gas discharged from the engine flows into the bypass passage .
In _the NO _X storage catalyst of the first aspect of the invention, when the NO _X storing catalyst is not activated, nitrogen dioxide NO ₂ in the exhaust gas flowing into the NO _X storage catalyst but is occluded in the NO _X storage catalyst, carbon monoxide Nitrogen NO is difficult to occlude. According to the first invention, when the NO _x storage catalyst is not activated, the reduction of nitrogen dioxide NO ₂ to nitric oxide NO is suppressed, so that the NO _x storage catalyst is contained in the inflowing exhaust gas. A large amount of NO _x can be occluded, and therefore NO _x in the exhaust gas can be purified well.

In order to solve the above-mentioned problem, in the second invention, noble metal and NO in the engine exhaust passage. _X NO with storage agent _X An occlusion catalyst is arranged and the NO _X NO when the storage catalyst is not activated _X Nitrogen dioxide NO contained in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into the storage catalyst is lean ₂ Is NO _X Occluded in the occluding agent, the NO _X NO when the storage catalyst is activated _X Nitrogen oxide NO contained in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into the storage catalyst is lean _X Is NO _X NO is stored in the storage agent _X NOx stored when the air-fuel ratio of the exhaust gas flowing into the storage catalyst becomes almost stoichiometric or rich _X Is NO _X NO released from the storage agent _X Nitrogen dioxide NO in exhaust gas exhausted from engine when storage catalyst is not activated ₂ NO reduction control means for suppressing the reduction of NO to NO _X The engine exhaust passage is provided in an upstream exhaust passage of the storage catalyst. The engine exhaust passage includes a trunk passage, an annular passage having both ends connected to a branch portion on the trunk passage, and the annular passage in one direction. A flow rate adjusting valve that adjusts the flow rate of the exhaust gas flowing in the direction opposite to the direction of the exhaust gas and the flow rate of the exhaust gas flowing through the main passage without flowing into the annular passage, _X An occlusion catalyst is provided in the annular passage, and an oxidation catalyst supporting a noble metal is provided in the annular passage. _X The NO is placed on one side of the storage catalyst _X When the storage catalyst is not active, the reduction suppressing means causes almost all of the exhaust gas discharged from the engine to pass through the annular passage. _X The flow rate adjustment valve is controlled so that the storage catalyst and the oxidation catalyst flow in this order.

In 3rd invention, in said 1st or 2nd invention, said NO _X Even when the storage catalyst is not activated, when the oxidation catalyst is activated, the control of the flow rate adjusting valve by the reduction suppressing means is stopped.
That is, according to the third invention, NO _X Only when the storage catalyst is not activated and the oxidation catalyst is not activated, the flow rate regulating valve is controlled by the reduction suppressing means.

In order to solve the above problems, in the fourth invention, noble metal and NO are contained in the engine exhaust passage. _X NO with storage agent _X An occlusion catalyst is arranged and the NO _X NO when the storage catalyst is not activated _X Nitrogen dioxide NO contained in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into the storage catalyst is lean ₂ Is NO _X Occluded in the occluding agent, the NO _X NO when the storage catalyst is activated _X Nitrogen oxide NO contained in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into the storage catalyst is lean _X Is NO _X NO is stored in the storage agent _X NOx stored when the air-fuel ratio of the exhaust gas flowing into the storage catalyst becomes almost stoichiometric or rich _X Is NO _X NO released from the storage agent _X Nitrogen dioxide NO in exhaust gas exhausted from engine when storage catalyst is not activated ₂ NO reduction control means for suppressing the reduction of NO to NO _X The reduction suppression means is provided in the exhaust passage upstream of the storage catalyst, and the NO. _X Having an HC adsorbent disposed upstream of the storage catalyst, the HC adsorbent adsorbs hydrocarbon HC contained in the exhaust gas flowing into the HC adsorbent when lower than the release start temperature, When the temperature is higher than the release start temperature, hydrocarbon HC adsorbed on the HC adsorbent is released, and the release start temperature is the NO. _X Higher than the temperature at which the storage catalyst is activated, _X When the storage catalyst is not activated, the hydrocarbon HC in the exhaust gas exhausted from the engine by the HC adsorbent is adsorbed, so that the hydrocarbon HC in the exhaust gas causes nitrogen dioxide NO. ₂ Is reduced to nitric oxide NO.

In order to solve the above problems, in the fifth aspect of the invention, noble metal and NO in the engine exhaust passage. _X NO with storage agent _X An occlusion catalyst is arranged and the NO _X NO when the storage catalyst is not activated _X Nitrogen dioxide NO contained in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into the storage catalyst is lean ₂ Is NO _X Occluded in the occluding agent, the NO _X NO when the storage catalyst is activated _X Nitrogen oxide NO contained in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into the storage catalyst is lean _X Is NO _X NO is stored in the storage agent _X NOx stored when the air-fuel ratio of the exhaust gas flowing into the storage catalyst becomes almost stoichiometric or rich _X Is NO _X NO released from the storage agent _X Nitrogen dioxide NO in exhaust gas exhausted from engine when storage catalyst is not activated ₂ NO reduction control means for suppressing the reduction of NO to NO _X It is provided in the exhaust passage on the upstream side of the storage catalyst, inside the engine exhaust passage, and the above NO _X An oxidation catalyst disposed upstream of the storage catalyst and supporting a noble metal, a bypass passage for bypassing the oxidation catalyst, a flow rate of exhaust gas flowing into the oxidation catalyst, and a flow rate of exhaust gas flowing into the bypass passage A HC adsorbent is provided on the bypass passage, and the HC adsorbent is contained in the exhaust gas flowing into the HC adsorbent when the temperature is lower than the discharge start temperature. The hydrocarbon HC contained in the HC is adsorbed, and if it is above the release start temperature, the hydrocarbon HC adsorbed on the HC adsorbent is released, _X When the storage catalyst is not activated, the reduction suppression means controls the flow rate adjustment valve so that almost all of the exhaust gas discharged from the engine flows into the bypass passage.

In order to solve the above-mentioned problem, in the sixth invention, noble metal and NO in the engine exhaust passage. _X NO with storage agent _X An occlusion catalyst is arranged and the NO _X NO when the storage catalyst is not activated _X Nitrogen dioxide NO contained in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into the storage catalyst is lean ₂ Is NO _X Occluded in the occluding agent, the NO _X NO when the storage catalyst is activated _X Nitrogen oxide NO contained in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into the storage catalyst is lean _X Is NO _X NO is stored in the storage agent _X NOx stored when the air-fuel ratio of the exhaust gas flowing into the storage catalyst becomes almost stoichiometric or rich _X Is NO _X NO released from the storage agent _X Nitrogen dioxide NO in exhaust gas exhausted from engine when storage catalyst is not activated ₂ NO reduction control means for suppressing the reduction of NO to NO _X The engine exhaust passage is provided in an upstream exhaust passage of the storage catalyst. The engine exhaust passage includes a trunk passage, an annular passage having both ends connected to a branch portion on the trunk passage, and the annular passage in one direction. A flow rate adjusting valve that adjusts the flow rate of the exhaust gas flowing in the direction opposite to the direction of the exhaust gas and the flow rate of the exhaust gas flowing through the main passage without flowing into the annular passage, _X An occlusion catalyst is provided in the annular passage, and an oxidation catalyst supporting a noble metal is provided in the annular passage. _X It is arranged on one side of the storage catalyst, and further the HC adsorbent is in the annular passage and NO. _X The HC adsorbent is disposed on the side opposite to the one side of the storage catalyst, and adsorbs and releases hydrocarbon HC contained in the exhaust gas flowing into the HC adsorbent when the HC adsorbent is lower than the release start temperature. When the temperature is higher than the start temperature, the hydrocarbon HC adsorbed on the HC adsorbent is released, and the NO _X When the storage catalyst is not activated, the reduction suppressing means allows almost all of the exhaust gas discharged from the engine to pass through the annular passage through the HC adsorbent, NO _X The flow rate adjustment valve is controlled so that the storage catalyst and the oxidation catalyst flow in this order.

In the seventh invention, in any one of the first to sixth inventions, when the NO _x storage catalyst is not activated, the carbon dioxide with respect to the nitric oxide NO generated when combustion is performed under a lean air-fuel ratio. A NO ₂ ratio increasing means for increasing the ratio of nitrogen NO ₂ is further provided.
According to the seventh invention, when the NO _x storage catalyst is not activated , the reduction of nitrogen dioxide NO ₂ to nitrogen monoxide NO is not only suppressed, but also in the exhaust gas discharged from the engine. purification for large proportion of the nitrogen dioxide nO ₂ with respect to nitrogen monoxide nO, more of the nO _X is stored in the nO _X storage catalyst, of the nO _X by _the nO _X storage catalyst definitive when _the nO _X storage catalyst is not activated The effect can be enhanced.

According to the present invention, even when the NO _X storage catalyst is not activated, the NO _X storage catalyst can store a large amount of NO _X in the inflowing exhaust gas, and therefore NO _X in the exhaust gas can be stored. It can be purified well.

  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 13 containing the oxidation catalyst 12 via the exhaust pipe 11. Is connected through an exhaust pipe 11 to a casing 15 containing a NO _x storage catalyst 14. Further, a bypass pipe 17 that bypasses the oxidation catalyst 12 branches from a branch portion 16 located on the exhaust pipe 11 upstream of the oxidation catalyst 12, and the bypass pipe 17 is connected between the oxidation catalyst 12 and the NO _x storage catalyst 14. Connected to the exhaust pipe 11. The branch portion 16 is provided with a flow rate adjusting valve 18 that adjusts the flow rate of the exhaust gas flowing into the oxidation catalyst 12 and the flow rate of the exhaust gas flowing into the bypass pipe 11. A reducing agent supply valve 19 for supplying a reducing agent made of, for example, hydrocarbons into the exhaust gas flowing through 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 20, and an electronically controlled EGR control valve 21 is disposed in the EGR passage 20. Further, an EGR cooling device 22 for cooling the EGR gas flowing through the EGR passage 20 is disposed around the EGR passage 20. In the embodiment shown in FIG. 1, the engine cooling water is guided into the EGR cooling device 22, 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 24, via a fuel supply pipe 23. Fuel is supplied into the common rail 24 from an electronically controlled fuel pump 25 with variable discharge amount, and the fuel supplied into the common rail 24 is supplied to the fuel injection valve 3 through each fuel supply pipe 23.

The electronic control unit 30 is composed of a digital computer, and is connected to each other by a bidirectional bus 31. A ROM (read only memory) 32, a RAM (random access memory) 33, a CPU (microprocessor) 34, an input port 35 and an output port 36. It comprises. The oxidation catalyst 12 and the NO _X storing catalyst 14 is attached a temperature sensor 26, 27 for detecting the temperature of the oxidation catalyst 12 and _the NO _X storage catalyst 14, respectively, the output signals of these temperature sensors 26 and 27 corresponding AD The signal is input to the input port 35 via the converter 37. 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, the input port 35 is connected to a crank angle sensor 42 that generates an output pulse every time the crankshaft rotates, for example, 15 °. 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 supply valve 19, the EGR control valve 21, and the fuel pump 25 through corresponding drive circuits 38.

The NO _x storage catalyst 14 shown in FIG. 1 is composed of a monolith catalyst, and a catalyst carrier made of alumina, for example, is supported on the base of the NO _x storage catalyst 14. 2A and 2B schematically show a cross section of the surface portion of the catalyst carrier 50. As shown in FIGS. 2A and 2B, the catalyst noble metal 51 is dispersedly supported on the surface of the catalyst carrier 50, and the NO _x storage agent 52 layer is further formed on the surface of the catalyst carrier 50. Is formed.

In this embodiment, platinum Pt is used as the catalyst noble metal 51, and the constituents of the NO _x storage agent 52 are, for example, alkali metals such as potassium K, sodium Na, cesium Cs, barium Ba, and calcium Ca. At least one selected from alkaline earths, rare earths such as lanthanum La and yttrium Y is used.

When the ratio of air and fuel (hydrocarbon) supplied to the engine intake passage, the combustion chamber 2 and the exhaust passage upstream of the NO _x storage catalyst 14 is referred to as the air-fuel ratio of the exhaust gas, the NO _x storage agent 52 If There if activated, i.e. when the air-fuel ratio of the exhaust gas the NO _X storing catalyst 14 is flowing into the NO _X storage catalyst if activated absorbs NO _X when the lean, the oxygen concentration in the exhaust gas falls performing absorption and release action of the NO _X to release the absorbed NO _X. When fuel (hydrocarbon) or air is not supplied into the exhaust passage upstream of the NO _x storage catalyst 14, the air-fuel ratio of the exhaust gas matches the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 2. In this case, the NO _x storage agent 52 absorbs NO _x when the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 2 is lean, and the oxygen concentration in the air-fuel mixture supplied into the combustion chamber 2 decreases. The absorbed NO _x will be released.

That is, the case where barium Ba is used as a component constituting the NO _x storage agent 52 will be described as an example. When the air-fuel ratio of the exhaust gas is lean, that is, when the oxygen concentration in the exhaust gas is high, the catalyst noble metal 51 is activated. 2A, the NO contained in the exhaust gas is oxidized on the platinum Pt 51 to become NO ₂ as shown in FIG. 2A, and then absorbed into the NO _X storage agent 52 and combined with the barium oxide BaO. It diffuses into the NO _x storage agent 52 in the form of nitrate ions NO ₃ ⁻ . In this way, NO _X is absorbed in the NO _X storage agent 52. Oxygen concentration in the exhaust _gas, NO ₂ is produced on the surface as long as the platinum Pt51 high, _the NO _X storage agent 52 of the NO _X absorbing capacity so long as NO ₂ not to saturate is absorbed in the NO _X absorbent 52 nitrate ions NO ₃ ^- is generated.

On the other hand, by making the air-fuel ratio in the combustion chamber 2 substantially the stoichiometric air-fuel ratio or rich, or by supplying the reducing agent from the reducing agent supply valve 19, the air-fuel ratio of the exhaust gas is substantially the stoichiometric air-fuel ratio or stoichiometric air-fuel. When the fuel ratio is increased, the oxygen concentration in the exhaust gas decreases, so that the reaction proceeds in the reverse direction (NO ₃ ⁻ → NO ₂ ), so that the nitrate ions NO ₃ ⁻ in the NO _X storage agent 52 are in the form of NO ₂ . Released from the NO _X storage agent 52. Next, the released NO _x is reduced by unburned HC and CO contained in the exhaust gas. In the above description, it has been described that NO _x is absorbed by the NO _x storage agent (that is, accumulates 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 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 the present specification, in particular, the storage performed when the NO _X storage catalyst is activated is referred to as “high temperature storage”. Further, the term “release” from the NO _X storage agent is used to include the meaning of “desorption” corresponding to “adsorption” in addition to “release” corresponding to “absorption”.

By the way, the oxidation ability of platinum Pt51 varies depending on the temperature. When the temperature of platinum Pt51 is low, the oxidation ability is low. For this reason, as shown in FIG. 3A, when the temperature of the NO _x storage catalyst 14 decreases, the oxidation rate from NO to NO ₂ by platinum Pt 51 (hereinafter referred to as “NO oxidation rate”) decreases. . In this embodiment, the temperature TC approximately 250 becomes the NO oxidation rate lower than ℃ of the NO _X storing catalyst 14 as can be seen from FIG. 3 (A) rapidly decreases, the temperature TC approximately 200 of the NO _X storage catalyst 14 At 0 ° C., the NO oxidation rate is approximately 50%. When NO oxidation rate is almost 50% in this embodiment, i.e. determines that the NO _X storing catalyst 14 when it is temperature TC approximately 200 ℃ (= Ts) of the NO _X storage catalyst 14 is activated Is done.

The nitrogen oxide NO _x in the exhaust gas is not absorbed by the NO _x storage agent 52 in the form of nitrogen monoxide NO, and is not absorbed by the NO _x storage agent 52 unless it is in the form of nitrogen dioxide NO ₂ . That is, nitrogen oxide NO _x contained in the exhaust gas is usually more nitric oxide NO, and this nitric oxide NO is not absorbed by the NO _x storage agent 52 unless it becomes nitrogen dioxide NO ₂ , that is, it is not oxidized. . To oxidize nitrogen monoxide NO is necessary that the catalytic noble metal 51 is activated, thus to purify the NO _X ever considered the catalyst precious metal 51 is required to have activated I came.

However the inventors of the present inventors have repeatedly studied this the NO _X storing catalyst 14, the nitrogen monoxide NO contained in the exhaust gas is platinum 51 is not activated, i.e. NO _X when storing catalyst 14 is not activated NO _X Although not absorbed by the storage agent 52, the nitrogen dioxide NO ₂ contained in the exhaust gas is, for example, NO in the form of nitrous acid NO ₂ ⁻ as shown in FIG. 2B even if the NO _x storage catalyst 14 is not activated. It was found that the _X occlusion agent 52 occludes. Also in this case, as in the case of the NO _X storing catalyst 14 is activated, or the nitrogen dioxide NO ₂ from being adsorbed in the NO _X absorbent 52, or either being absorbed in the NO _X absorbent 52 is not always It is not clear, and it is called “occlusion” that combines these adsorption and absorption. In the present specification, in particular, the storage performed when the NO _x storage catalyst is not activated is referred to as “low temperature storage”.

Thus _the NO _X storage since the catalyst 14 is nitrogen dioxide NO ₂ is occluded even without activated when the NO _X storing catalyst 14 is not activated, for example during starting of the engine after the interim pleasure the NO _X storing catalyst 14 It is preferable that the amount of nitrogen monoxide NO in the exhaust gas flowing into the exhaust gas is small and the amount of nitrogen dioxide NO ₂ in the exhaust gas is large. Therefore, in the present embodiment, it is possible to prevent NO ₂ in the exhaust gas from being reduced to NO before the exhaust gas discharged from the engine body 1 reaches the NO _x storage catalyst 14 in such a case. I am doing so.

Incidentally, as shown in FIG. 1, in the internal combustion engine of the present embodiment, the oxidation catalyst 12 is provided on the upstream side of the NO _x storage catalyst 14. The oxidation catalyst 12 is, for example, an exhaust gas that flows into the NO _X storage catalyst 14 by causing the added reducing agent to react reliably with oxygen when a reducing agent is added from the reducing agent addition valve 19 in the NO _X release process described later. In order to reduce the oxygen concentration in the gas, or the unburned HC or reducing agent reacts in the upstream portion of the NO _x storage catalyst 14 and only the temperature in the downstream portion rises, so the NO _x storage catalyst. 14 is provided to suppress the temperature distribution.

This oxidation catalyst 12 also carries platinum Pt, and its oxidation ability decreases as the temperature decreases. Accordingly, also in the oxidation catalyst 12, the oxidation rate from NO to NO ₂ by platinum Pt is the same as the NO oxidation rate by platinum of the NO _x storage catalyst 14 shown in FIG. On the other hand, when the oxidation catalyst 12 is not activated, that is, when the temperature of the oxidation catalyst 12 is lower than the activation temperature of platinum Pt, the platinum Pt supported on the oxidation catalyst 12 exhibits a reducing ability, and this reducing ability. Increases as the temperature of the oxidation catalyst 12 decreases. For this reason, as shown in FIG. 3B, when the oxidation catalyst 12 is not activated, the rate of reduction from NO ₂ to NO by platinum Pt (hereinafter referred to as “NO reduction rate”) when the temperature decreases. Rises. That is, when the oxidation catalyst 12 is not activated, the exhaust gas flows into the NO _X storing catalyst 14 through the oxidation catalyst 12, and nitrogen dioxide NO ₂ is reduced to nitrogen monoxide NO in the oxidation catalyst 12, the engine body The ratio of nitrogen monoxide NO in the exhaust gas flowing into the NO _x storage catalyst 14 is considerably higher than the ratio of nitric oxide NO in the exhaust gas discharged from 1 (= NO amount / NO _x amount). . Therefore, this time the NO _X storing catalyst 14 is not activated, the NO _X storing catalyst 14 can not absorb NO _X, thus becomes one NO _X purification rate by _the NO _X storage catalyst 14 is low.

Therefore, in the present embodiment, when the NO _x storage catalyst 14 and the oxidation catalyst 12 are not activated, the flow rate adjusting valve 18 bypasses the exhaust gas into the oxidation catalyst 12 and flows into the bypass pipe 17 (see FIG. 1). The position is moved to the position indicated by the solid line) and positioned at this bypass position. Thus, when the NO _x storage catalyst 14 and the oxidation catalyst 12 are not activated, the exhaust gas discharged from the engine body 1 flows directly into the NO _x storage catalyst 14 without passing through the oxidation catalyst 12, and thus in the exhaust gas. NO ₂ is reduced to NO. Accordingly, even when the the NO _X storing catalyst 14 and the oxidation catalyst 12 is not activated, it is possible to maintain a high purification rate of the NO _X by _the NO _X storage catalyst 14.

When the NO _x storage catalyst 14 is activated, the exhaust gas flowing into the NO _x storage catalyst 14 (hereinafter referred to as “inflow exhaust gas”) when combustion is performed at a lean air-fuel ratio is performed. NO _X is absorbed in the NO _X storage agent 52. However, the absorption when burned under a lean air-fuel ratio is continued, it would be NO _X absorbing capacity of the NO _X absorbent 52 is saturated during the NO _X by _the NO _X storage agent 52 and thus It becomes impossible. Therefore, in this embodiment, by supplying the reducing agent from the reducing agent supply valve 19 before the absorption capacity of the NO _X storage agent 52 is saturated, the air-fuel ratio of the inflowing exhaust gas is temporarily made substantially the stoichiometric air-fuel ratio or rich (hereinafter referred to as “rich”). to be referred to as "stoichiometric-rich"), thereby being so as to release the NO _X from _the NO _X storage agent 52 (NO _X emission process).

More specifically, in the present embodiment, the stored NO _X amount ΣNOX stored in the NO _X storage agent 52 of the NO _X storage catalyst 14 is calculated, and the calculated stored NO _X amount ΣNOX is a predetermined allowable value. air-fuel ratio of the exhaust gas is switched from lean to rich when it exceeds NX, whereby NO _X from absorbent 52 NO _X is released.

The amount of NO _x discharged from the engine body 1 per unit time is a function of the fuel injection amount Q and the engine speed N, and therefore the NO _x storage amount NOXA stored in the NO _x storage agent 52 per unit time is the fuel. This is a function of the injection amount Q and the engine speed N. In this embodiment, the NO _X storage amount NOXA per unit time corresponding to the fuel injection amount Q and the engine speed N is obtained in advance by experiments, and this NO _X storage amount NOXA is determined based on the fuel injection amount Q and the engine speed N. As shown in FIG. 4A, the function is stored in advance in the ROM 32 in the form of a map.

On the other hand, the NO _X storage rate KN in the NO _X storage agent 52 varies depending on the oxidation ability of the NO _X storage catalyst 14 and the oxidation catalyst 12, and therefore the temperature TC of the NO _X storage catalyst 14 and the temperature TO of the oxidation catalyst 12 Depends on. In this embodiment, the NO _X storage rate KN corresponding to the temperature TC of the NO _X storage catalyst 14 and the temperature TO of the oxidation catalyst 12 is experimentally obtained in advance, and this NO _X storage rate KN is determined as the NO _X storage catalyst. As a function of the temperature TC of 14 and the temperature TO of the oxidation catalyst 12, it is stored in advance in the ROM 32 in the form of a map as shown in FIG.

The actual NO _X storage amount in the NO _X storage agent 52 per unit time is represented by the product NOXA · KN of NOXA and NO _X storage rate KN, and this actual NO _X storage amount NOXA per unit time. The integrated value ΣNOX of KN represents the integrated storage NO _X amount stored in the NO _X storage agent 52.

However, while the NO _X storage catalyst 14 is not activated and the oxidation catalyst 12 is not activated, the NO _X storage amount per unit time is the NO ₂ in the exhaust gas discharged from the engine body 1 as described above. It depends on the amount. The amount of NO ₂ in the exhaust gas discharged from the engine body 1 is a function of the later-described EGR rate and the retard amount of the injection timing in addition to the fuel injection amount Q and the engine speed N. In the present embodiment, the NO ₂ occlusion amount NO2A per unit time corresponding to these parameters is obtained in advance by experiments and stored in advance in the ROM 32 in the form of a map. When the NO _x storage catalyst 14 is not activated and the oxidation catalyst 12 is not activated, the NO ₂ occlusion amount per unit time is used instead of the actual NO _x occlusion amount NOXA · KN per unit time described above. NO2A is added to the occluded amount of NO _X .SIGMA.NOX.

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 this embodiment, for example, by introducing a large amount of EGR gas into the combustion chamber 2, the lean degree of the air-fuel ratio of the exhaust gas discharged from the engine body 1 is made relatively small.

FIG. 5 shows a control routine for maintaining the NO _X purification capability of the NO _X storage catalyst 14, and this routine is executed by interruption every predetermined time.

Referring to FIG. 5, first, at step 101, the NO _X storage amount NOXA per unit time is calculated from the map shown in FIG. 4A, and the NO _X storage rate KN is calculated from the map shown in FIG. 4B. Calculated. Next, in step 102 and step 103, whether the temperature TC of the NO _x storage catalyst 14 is lower than a set temperature Tsc, for example 200 ° C., and whether the temperature TO of the oxidation catalyst 12 is lower than a set temperature Tso, for example 200 ° C. Each is determined. When TC <Tsc and TO <Tso, that is, when it is determined that both the NO _x storage catalyst 14 and the oxidation catalyst 12 are not activated, the routine proceeds to step 104, where the flow regulating valve 18 is moved to the bypass position. Rotated and maintained. As a result, the exhaust gas discharged from the engine body 1 is caused to flow into the NO _x storage catalyst 14 without passing through the oxidation catalyst 12, so that NO ₂ in the exhaust gas is reduced to NO in the oxidation catalyst 12. Is prevented. Next, at step 105, the NO ₂ storage amount NO2A per unit time is calculated from the map. In step 106, the integrated storage amount of NO _X ΣNOX that stored in the NO _X storing catalyst 14 by adding the NO ₂ stored amount NO2A per unit time ΣNOX is calculated.

In Steps 102 and 103, when it is determined that TC <Tsc and TO ≧ Tso, that is, when it is determined that the NO _x storage catalyst 14 is not activated but the oxidation catalyst 12 is activated, Proceeding to step 107, using the NO _X storage amount NOXA and NO _X storage rate calculated in step 101, the actual NO _X storage amount NOXA · KN per unit time is added to ΣNOX, integrated storage amount of NO _X ΣNOX is calculated.

When it is determined at step 102 that TC ≧ Tsc, that is, when it is determined that the NO _x storage catalyst 14 is activated, the routine proceeds to step 108 where the accumulated stored NO _x amount ΣNOX is the same as at step 107. Calculated. Then, the integrated storage amount of NO _X ΣNOX calculated in step 108 whether exceeds the allowable value NX is determined. When ΣNOX <NX, the control routine is terminated. On the other hand, when ΣNOX ≧ NX, the routine proceeds to step 110 where the NO _X releasing process is started.

FIG. 6 shows a processing routine of the NO _x releasing process started at step 110 in FIG.

Referring to FIG. 6, first, in step 121, the supply amount of the reducing agent necessary for setting the air-fuel ratio of the 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 judged if the reducing agent supply time calculated at step 122 has elapsed. When the reducing agent supply time has not elapsed, the routine returns to step 124. At this time, the supply of the reducing agent is continued, and the air-fuel ratio of the 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 52 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.

When the NO _x storage catalyst 14 and the oxidation catalyst 12 are not activated, the flow rate adjustment valve 18 is rotated to the bypass position and maintained at the bypass position, and under the lean air-fuel ratio. The ratio of nitrogen dioxide NO ₂ to the total nitrogen oxide NO _X generated when combustion is performed (hereinafter referred to as “NO ₂ ratio”) is the same engine operating state, that is, NO _{X at the} same rotational speed and the same torque. increase than that in the storage catalyst 14 activity (NO ₂ ratio increasing process) it may be.

The ratio of NO ₂ (= NO ₂ amount / NO _x amount) has been found to increase when slow combustion is performed. For example, the fuel injection timing is retarded or the EGR gas amount is increased. If at least one of pilot injection or premixed combustion is performed, the combustion becomes slow. Therefore, when the NO _x storage catalyst 14 and the oxidation catalyst 12 are not activated, slow combustion may be performed as compared to when the NO _x storage catalyst 14 or the oxidation catalyst 12 is activated in the same engine operating state.

Next, the case where the NO _x storage catalyst 14 shown in FIG. 1 comprises a particulate filter (hereinafter referred to as “filter”) will be described.

  FIGS. 7A and 7B show the structure of the filter 14. 7A shows a front view of the filter 14, and FIG. 7B shows a side sectional view of the filter 14. As shown in FIGS. 7A and 7B, the filter 14 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. In other words, in the exhaust gas inflow passage 60 and the exhaust gas outflow passage 61, each exhaust gas inflow passage 60 is surrounded by four exhaust gas outflow passages 61, and each exhaust gas outflow passage 61 is surrounded by four exhaust gas inflow passages 60. To be arranged.

  The filter 14 is formed of a porous material such as cordierite. Therefore, the exhaust gas flowing into the exhaust gas inflow passage 60 passes through the surrounding partition wall 64 as indicated by an arrow in FIG. And flows into the adjacent exhaust gas outflow passage 61.

When the NO _x storage catalyst is constituted by a particulate filter in this way, the peripheral wall surfaces of the exhaust gas inflow passages 60 and the exhaust gas outflow passages 61, that is, the pores on both side surfaces of the partition walls 64 and in the partition walls 64 are used. A catalyst carrier layer made of alumina is formed on the inner wall surface. As shown in FIGS. 2A and 2B, the catalyst noble metal 51 and the NO _x storage agent 52 are formed on the catalyst carrier 50. It is supported. In this case, platinum Pt is also used as the catalyst noble metal. The NO ₂ in the exhaust gas when _the NO _X storage catalyst is not activated even when the configure _the NO _X storage catalyst from the particulate filter is occluded in the NO _X storage catalyst as. The same of the NO _X emission process and the NO _X release processing for the NO _X storing catalyst 14 shown in FIGS. 5 and 6 in this case is carried out.

Further, when the NO _x storage catalyst is composed of a particulate filter, particulate matter contained in the exhaust gas is captured in the filter 14 and the captured particulate matter is sequentially burned by the exhaust gas heat. When a large amount of particulate matter accumulates on the filter 14, 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 19 to supply the oxidation catalyst 12 and the filter. 14 is burned, and the temperature of the filter 14 is increased, whereby the accumulated particulates are ignited and burned.

  8 and 9 show a second embodiment of the present invention. The internal combustion engine in the second embodiment is basically the same as that in the first embodiment, and the same reference numerals are assigned to the same components. In the internal combustion engine of the second embodiment, the exhaust passage on the downstream side of the exhaust turbine 7b of the exhaust turbocharger 7 is different from that of the first embodiment, and an exhaust purifier 70 is provided. The reducing agent supply valve is also provided at a position different from that in the first embodiment.

  FIG. 9 is an explanatory view schematically showing the exhaust gas purification device 70 shown in FIG. 8, and FIGS. 9A to 9C show that the flow rate adjustment valve 74 has a first operating position, a second operating position, The case in the neutral operating position is shown. In addition, the arrows in these drawings indicate the flow of exhaust gas.

As shown in FIG. 9, the exhaust gas purifier 70 includes main exhaust pipes (main passages) 71a and 71e, and annular branch pipes (annular passages) 71c and 71d connected to the main exhaust pipes 71a and 71e. . Annular branch pipes 71c, 71d is an oxidation catalyst 12, are coupled to both sides of the casing 72 with a built-in and the NO _X storing catalyst 14 described above. And the branch part 71b is provided in the connection part of the main exhaust pipes 71a and 71e and the annular branch pipes 71c and 71d. The annular branch pipes 71c and 71d branch from the branch part 71b and return to the branch part 71b again.

  The main exhaust pipes 71a and 71e are composed of an upstream partial exhaust pipe 71a upstream of the branch part 71b and a downstream partial exhaust pipe 71e downstream of the branch part 71b, and the annular branch pipes 71c and 71d are branched. It consists of a first partial annular branch pipe 71c that connects the portion 71b and one side of the casing 72, and a second partial annular branch pipe 71d that connects the branch portion 71b and the other side of the casing 72. A reducing agent supply valve 75 for supplying a reducing agent made of, for example, hydrocarbons into the exhaust gas flowing into the oxidation catalyst 12 is disposed in the first partial annular branch pipe 71c.

  A flow rate adjusting valve 74 is provided in the branch portion 71b. The operation of the flow rate adjusting valve 74 is controlled by a flow rate adjusting valve step motor 75 connected to the output port 37 of the ECU 30 via the corresponding drive circuit 38. The flow rate adjusting valve 74 continuously rotates around the center of the branch portion 71b, and the angle θ changes with respect to the axis line of the main exhaust pipes 71a and 71e, thereby flowing into the branch portion 71b from the upstream partial exhaust pipe 71a. Of the exhaust gas to be discharged, the flow rate of the exhaust gas flowing into the first partial annular branch pipe 71c or the second partial annular branch pipe 71d and the downstream partial exhaust pipe 71e is adjusted.

In particular, the flow rate adjusting valve 74 rotates roughly between three operating positions having different angles. These three operation positions are the first operation position shown in FIG. 9A, the second operation position shown in FIG. 9B, and the neutral operation position shown in FIG. 9C. . When the flow rate adjusting valve 74 is in the first operating position shown in FIG. 9A, most of the exhaust gas flowing from the upstream partial exhaust pipe 71a into the branch portion 71b flows into the first partial annular branch pipe 71c, The inside of the casing 72 passes through the oxidation catalyst 12 and the NO _x storage catalyst 14 in this order, flows to the second partial annular branch pipe 71d, and returns to the branch section 71b again. All the exhaust gas that has returned from the second partial annular branch pipe 71d to the branch section 71b again flows out to the downstream partial exhaust pipe 71e. In the following description, the direction in which the exhaust gas flows in the order of the oxidation catalyst 12 and the NO _x storage catalyst 14 will be described as the forward direction.

When the flow rate adjusting valve 74 is in the second operating position shown in FIG. 9B, most of the exhaust gas flowing from the upstream partial exhaust pipe 71a into the branch portion 71b is transferred to the second partial annular branch pipe 71d. flowed, NO _X storing catalyst 14 the casing 72, flows to the first partial annular branch pipe 71c to pass through in the order of the oxidation catalyst 12, returns to the branch portion 71b. All the exhaust gas that has returned from the first partial annular branch pipe 71c back to the branch section 71b flows out to the downstream partial exhaust pipe 71e. In the following description, the direction in which the exhaust gas flows in the order of the NO _x storage catalyst 14 and the oxidation catalyst 12 will be described as the reverse direction.

Furthermore, when the flow rate adjusting valve 74 is in the neutral operation position shown in FIG. 9C, most of the exhaust gas flowing from the upstream partial exhaust pipe 71a into the branch part 71b flows into the annular branch pipes 71c and 71d. Directly into the downstream partial exhaust pipe 71e. That is, when the flow control valve 74 is in the neutral operating position, the exhaust gas flows out to the downstream exhaust pipe 71e without passing through the oxidation catalyst 12 and _the NO _X storage catalyst 14.

In the NO _x releasing process of the present embodiment, when the NO _x storage catalyst 14 is activated, a small amount of exhaust gas flows forward through the annular branch pipes 71c and 71d, and most of the remaining exhaust gas flows through the annular branch pipe. The flow rate adjustment valve is controlled so as to flow directly to the downstream side exhaust pipe 71e without flowing into 71c and 71d. A small amount of reducing agent is added from the reducing agent addition valve 73 so that the air-fuel ratio of the exhaust gas flowing into the NO _x storage catalyst 14 becomes stoichiometric rich. When the exhaust gas to which the reducing agent is added flows into the oxidation catalyst 12, the unburned HC discharged from the engine body 1 and the reducing agent added from the reducing agent addition valve 73 react with oxygen, and the NO _x storage catalyst. The oxygen concentration of the exhaust gas flowing into the engine 14 is lowered. Thus, NO _X is released, which is occluded in the NO _X storing catalyst 14 is reduced by a reducing agent or fuel.

Here, in the first embodiment described above, when executing the NO _x releasing process, for example, by flowing a large amount of EGR gas into the combustion chamber 2, the flow rate of the exhaust gas flowing into the NO _x storage catalyst 14 is reduced. However, the amount of reducing agent required for the NO _x releasing treatment has been reduced. In the present embodiment, the operation position of the flow rate adjusting valve 74 is set such that a small amount of exhaust gas flows in the forward direction through the annular branch pipes 71c and 71d, so that a large amount of EGR gas does not flow into the combustion chamber 2. The flow rate of the exhaust gas flowing into the NO _x storage catalyst 14 can be reduced. Inflow of a large amount of EGR gas into the combustion chamber 2 may not be performed, for example, when the engine operating state is at a high load and high speed. Therefore, in the first embodiment, NO _X release processing is performed depending on the engine operating state. However, in this embodiment, the NO _x release process can be performed at any time.

By the way, as described above, when the NO _x storage catalyst 14 and the oxidation catalyst 12 are not activated, the exhaust gas is caused to flow into the NO _x storage catalyst 14 without passing through the oxidation catalyst 12, so that the NO ₂ by the oxidation catalyst 12 can be reduced. Reduction from NO to NO can be prevented. Therefore, in the present embodiment, when the NO _x storage catalyst 14 and the oxidation catalyst 12 are not activated, the flow rate adjustment valve 74 so that the exhaust gas discharged from the engine body 1 flows in the reverse direction through the annular branch pipes 71c and 71d. Is set as the second operating position. Exhaust gas annular branch pipe 71c, when the flow in the opposite direction 71d, to flow the exhaust gas is the NO _X storing catalyst 14, in the order of the oxidation catalyst 12, is the NO _X storing catalyst 14 is the exhaust gas without passing through the oxidation catalyst 12 Thus, the reduction of NO ₂ in the exhaust gas to NO is suppressed. Accordingly, even when the the NO _X storing catalyst 14 and the oxidation catalyst 12 is not activated, it is possible to maintain a high purification rate of the NO _X by _the NO _X storage catalyst 14.

In the present embodiment, as in the first embodiment, when the NO _x storage catalyst 14 and the oxidation catalyst 12 are not activated, the operation position of the flow rate adjustment valve 74 is set to the second operation position. In addition, slow combustion may be performed as compared to when the NO _x storage catalyst 14 or the oxidation catalyst 12 is active. Further, the NO _X storage catalyst 14 of the present embodiment may be a particulate filter.

FIG. 10 shows a third embodiment of the present invention. The internal combustion engine in the third embodiment is basically the same as that in the first embodiment, and the same reference numerals are assigned to the same components. In the present embodiment, an HC adsorbent 81 is provided upstream of the NO _x storage catalyst 14 instead of the oxidation catalyst. The HC adsorbent 81 is made of zeolite, and adsorbs hydrocarbon (HC) flowing into the HC adsorbent 81 when the temperature is lower than the release start temperature (for example, 200 ° C.), and starts the release. When the temperature rises above the temperature, the adsorbed HC is released. Further, no bypass pipe or flow rate adjusting valve is provided, and a reducing agent addition valve 82 is provided in the exhaust pipe 11 between the HC adsorbent 81 and the NO _x storage catalyst 14.

In the compression self-ignition internal combustion engine of the present embodiment, the air-fuel ratio of the exhaust gas discharged from the engine body 1 is basically lean, but there is no unburned hydrocarbon HC or the like in the exhaust gas. Instead, there is some hydrocarbon HC. In the above description, the NO ₂ ratio increasing process includes delaying the fuel injection timing, increasing the amount of EGR gas, performing pilot injection, or performing premixed combustion. When the NO ₂ ratio increasing process is performed, not only the ratio of NO _{2 in} the exhaust gas (= NO ₂ amount / NO _x amount) but also the amount of HC in the exhaust gas increases. .

For example, when the HC adsorbent 81 is not provided and the exhaust gas discharged from the engine body 1 directly flows into the NO _x storage catalyst 14, the exhaust gas discharged from the engine body 1 described above. The hydrocarbon HC inside reduces NO ₂ to NO. Therefore, in this case, if the NO _x storage catalyst 14 is not activated, the ratio of NO _{2 in} the exhaust gas decreases, and as a result, the NO _x purification rate by the NO _x storage catalyst 14 deteriorates.

On the other hand, in the present embodiment, when the NO _x storage catalyst 14 is not activated, such as when the internal combustion engine is cold started, the temperature of the HC adsorbent 81 is also equal to or lower than the release start temperature, and is thus discharged from the engine body 1. The hydrocarbon HC in the exhaust gas is adsorbed by the HC adsorbent 81. As a result, reduction of NO ₂ in the exhaust gas to NO is suppressed, and the NO _x purification rate by the NO _x storage catalyst 14 can be maintained high.

The release start temperature of the HC adsorbent 81 differs depending on the ratio of silica and alumina when synthesizing the zeolite. Therefore, the release of the HC adsorbent 81 is started by adjusting the ratio of silica and alumina at the time of production. The temperature can be adjusted. In the present embodiment, the release start temperature of the HC adsorbent 81 is adjusted to be higher than the activation temperature of the NO _x storage catalyst 14. As a result, after the NO _x storage catalyst 14 can oxidize and store nitrogen monoxide NO in the inflowing exhaust gas into nitrogen dioxide NO ₂ , hydrocarbon HC is released from the HC adsorbent 81. .

In addition, the exhaust gas purification apparatus in 3rd embodiment can be combined with the exhaust gas purification apparatus in 1st embodiment and 2nd embodiment. For example, when combined with the exhaust purification device in the first embodiment, the HC adsorbent is provided on the bypass pipe 17, _the NO _X storage exhaust gas when the NO _X storing catalyst 14 is not activated through the HC adsorbent By flowing into the catalyst 14, it is possible to suppress a decrease in the ratio of NO ₂ in the inflowing exhaust gas. Further, when combined with the exhaust emission control device in the second embodiment, the HC adsorbent is disposed in the casing 72 on the opposite side of the oxidation catalyst 12 with respect to the NO _x storage catalyst 14 (that is, oxidized in the casing 72). By arranging the catalyst 12, the NO _x storage catalyst 14, and the HC adsorbing material in this order), the exhaust gas flows into the NO _x storage catalyst 14 through the HC adsorbing material when the NO _x storage catalyst 14 is not activated. Therefore, a decrease in the ratio of NO ₂ in the inflowing exhaust gas can be suppressed.

It is a figure which shows the whole internal combustion engine. It is a diagram for explaining the absorbing action of the NO _X storage catalyst. It is a figure which shows the oxidation capability and reduction capability by platinum. I am a diagram showing a map for calculating a storage amount of NO _X. It is a flowchart of the NO _X purifying ability maintain control of the NO _X storage catalyst. Is a flow chart for performing the NO _X release process. It is a figure which shows a particulate filter. It is a figure which shows the whole internal combustion engine in 2nd embodiment. It is a figure which shows an exhaust gas purification device. It is a figure which shows the whole internal combustion engine in 3rd embodiment.

Explanation of symbols

3 ... fuel injection valve 4 ... intake manifold 5 ... exhaust manifold 12 ... oxidizing catalyst 14 ... NO _X storage catalyst 17 ... bypass pipe 18 ... flow control valve

Claims (7)

Is arranged _the NO _X storage catalyst in the engine exhaust passage and a noble metal and _the NO _X storage agent, when the the NO _X storing catalyst is not activated when the air-fuel ratio of the exhaust gas flowing into the NO _X storage catalyst is lean Nitrogen dioxide NO ₂ contained in the exhaust gas is stored in the NO _X storage agent, and when the NO _X storage catalyst is activated, the exhaust gas flows into the NO _X storage catalyst when the air-fuel ratio of the exhaust gas flowing into the NO _X storage catalyst is lean. NO nitrogen oxide NO _X is _the NO _X storing nitrogen oxides air-fuel ratio of the exhaust gas flowing into the NO _X storage catalyst with occluded is occluded becomes substantially stoichiometric or rich agents NO _X contained in the NO reduction suppression means that suppresses the reduction of nitrogen dioxide NO ₂ in the exhaust gas discharged from the engine when released from the _X storage agent and the NO _X storage catalyst is not activated to NO. _{X in} the exhaust passage upstream of the storage catalyst ,
An oxidation catalyst disposed in the engine exhaust passage upstream of the NO _x storage catalyst and carrying a noble metal, a bypass passage for bypassing the oxidation catalyst, a flow rate of exhaust gas flowing into the oxidation catalyst, A flow rate adjusting valve for adjusting the flow rate of the exhaust gas flowing into the bypass passage, and when the NO _x storage catalyst is not activated, the reduction suppressing means is configured to substantially reduce all of the exhaust gas discharged from the engine. An exhaust gas purification apparatus for an internal combustion engine that controls a flow rate adjustment valve so that the gas flows into the bypass passage . Is arranged _the NO _X storage catalyst in the engine exhaust passage and a noble metal and _the NO _X storage agent, when the the NO _X storing catalyst is not activated when the air-fuel ratio of the exhaust gas flowing into the NO _X storage catalyst is lean Nitrogen dioxide NO ₂ contained in the exhaust gas is stored in the NO _X storage agent, and when the NO _X storage catalyst is activated, the exhaust gas flows into the NO _X storage catalyst when the air-fuel ratio of the exhaust gas flowing into the NO _X storage catalyst is lean. NO nitrogen oxide NO _X is _the NO _X storing nitrogen oxides air-fuel ratio of the exhaust gas flowing into the NO _X storage catalyst with occluded is occluded becomes substantially stoichiometric or rich agents NO _X contained in the NO reduction suppression means that suppresses the reduction of nitrogen dioxide NO ₂ in the exhaust gas discharged from the engine when released from the _X storage agent and the NO _X storage catalyst is not activated to NO. _{X in} the exhaust passage upstream of the storage catalyst,
The engine exhaust passage includes a main passage, an annular passage whose both ends are connected to a branch portion on the main passage, and a flow rate of exhaust gas flowing in the one direction and in the opposite direction to the one direction. And a flow rate adjusting valve that adjusts the flow rate of the exhaust gas flowing through the main passage without flowing into the annular passage, and the NO _x storage catalyst is provided in the annular passage and the oxidation catalyst carrying a noble metal is is disposed an inside annular passage on one side of the of the nO _X storage catalyst, the nO _X when the storage catalyst is not activated, the almost all the annular passage nO in the exhaust gas the reducing suppressing means discharged from the engine An exhaust gas purification device for an internal combustion engine that controls a flow rate adjustment valve so that an _X storage catalyst and an oxidation catalyst flow in this order. When the _the NO _X storage catalyst is the oxidation catalyst even when not activated is activated, the control of the flow control valve by the reduction restraining means is stopped, the internal combustion engine according to claim 1 or 2 Exhaust purification device. Is arranged _the NO _X storage catalyst in the engine exhaust passage and a noble metal and _the NO _X storage agent, when the the NO _X storing catalyst is not activated when the air-fuel ratio of the exhaust gas flowing into the NO _X storage catalyst is lean Nitrogen dioxide NO ₂ contained in the exhaust gas is stored in the NO _X storage agent, and when the NO _X storage catalyst is activated, the exhaust gas flows into the NO _X storage catalyst when the air-fuel ratio of the exhaust gas flowing into the NO _X storage catalyst is lean. NO nitrogen oxide NO _X is _the NO _X storing nitrogen oxides air-fuel ratio of the exhaust gas flowing into the NO _X storage catalyst with occluded is occluded becomes substantially stoichiometric or rich agents NO _X contained in the NO reduction suppression means that suppresses the reduction of nitrogen dioxide NO ₂ in the exhaust gas discharged from the engine when released from the _X storage agent and the NO _X storage catalyst is not activated to NO. _{X in} the exhaust passage upstream of the storage catalyst,
The reduction suppression means has an HC adsorbent disposed in the engine exhaust passage and upstream of the NO _x storage catalyst, and the HC adsorbent becomes an HC adsorbent when the temperature is lower than the discharge start temperature. The hydrocarbon HC contained in the inflowing exhaust gas is adsorbed, and if it is higher than the release start temperature, the hydrocarbon HC adsorbed on the HC adsorbent is released, and the NO _x storage catalyst is activated at the release start temperature. When the NO _x storage catalyst is not activated, the hydrocarbon HC in the exhaust gas discharged from the engine is adsorbed by the HC adsorbent so that the hydrocarbon HC in the exhaust gas absorbs nitrogen dioxide. An exhaust purification device for an internal combustion engine, in which NO ₂ is suppressed from being reduced to nitric oxide NO. Is arranged _the NO _X storage catalyst in the engine exhaust passage and a noble metal and _the NO _X storage agent, when the the NO _X storing catalyst is not activated when the air-fuel ratio of the exhaust gas flowing into the NO _X storage catalyst is lean Nitrogen dioxide NO ₂ contained in the exhaust gas is stored in the NO _X storage agent, and when the NO _X storage catalyst is activated, the exhaust gas flows into the NO _X storage catalyst when the air-fuel ratio of the exhaust gas flowing into the NO _X storage catalyst is lean. NO nitrogen oxide NO _X is _the NO _X storing nitrogen oxides air-fuel ratio of the exhaust gas flowing into the NO _X storage catalyst with occluded is occluded becomes substantially stoichiometric or rich agents NO _X contained in the NO reduction suppression means that suppresses the reduction of nitrogen dioxide NO ₂ in the exhaust gas discharged from the engine when released from the _X storage agent and the NO _X storage catalyst is not activated to NO. _{X in} the exhaust passage upstream of the storage catalyst,
An oxidation catalyst disposed in the engine exhaust passage upstream of the NO _x storage catalyst and carrying a noble metal, a bypass passage for bypassing the oxidation catalyst, a flow rate of exhaust gas flowing into the oxidation catalyst, A flow rate adjusting valve for adjusting the flow rate of the exhaust gas flowing into the bypass passage, and an HC adsorbent is provided on the bypass passage, and the HC adsorbent is lower than a discharge start temperature. Adsorbs hydrocarbon HC contained in the exhaust gas flowing into the HC adsorbent, and releases hydrocarbon HC adsorbed on the HC adsorbent when the temperature is higher than the release start temperature, so that the NO _x storage catalyst is activated. It turned into and when not, the reducing suppressing means substantially all of the exhaust gas discharged from the engine to control the flow control valve so as to flow into the bypass passage, an exhaust purification system of an internal combustion engine. Is arranged _the NO _X storage catalyst in the engine exhaust passage and a noble metal and _the NO _X storage agent, when the the NO _X storing catalyst is not activated when the air-fuel ratio of the exhaust gas flowing into the NO _X storage catalyst is lean Nitrogen dioxide NO ₂ contained in the exhaust gas is stored in the NO _X storage agent, and when the NO _X storage catalyst is activated, the exhaust gas flows into the NO _X storage catalyst when the air-fuel ratio of the exhaust gas flowing into the NO _X storage catalyst is lean. NO nitrogen oxide NO _X is _the NO _X storing nitrogen oxides air-fuel ratio of the exhaust gas flowing into the NO _X storage catalyst with occluded is occluded becomes substantially stoichiometric or rich agents NO _X contained in the NO reduction suppression means that suppresses the reduction of nitrogen dioxide NO ₂ in the exhaust gas discharged from the engine when released from the _X storage agent and the NO _X storage catalyst is not activated to NO. _{X in} the exhaust passage upstream of the storage catalyst,
The engine exhaust passage includes a main passage, an annular passage whose both ends are connected to a branch portion on the main passage, and a flow rate of exhaust gas flowing in the one direction and in the opposite direction to the one direction. And a flow rate adjusting valve that adjusts the flow rate of the exhaust gas flowing through the main passage without flowing into the annular passage, and the NO _x storage catalyst is provided in the annular passage and the oxidation catalyst carrying a noble metal is An HC adsorbent is disposed in one side of the NO _x storage catalyst in the annular passage, and further, an HC adsorbent is disposed in the annular passage on the opposite side to the one side of the NO _x storage catalyst, and the HC adsorption The material adsorbs the hydrocarbon HC contained in the exhaust gas flowing into the HC adsorbent when it is lower than the release start temperature, and the hydrocarbon HC adsorbed on the HC adsorbent when the temperature is higher than the release start temperature. releasing said _the NO _X storage catalyst When not in gender of the nearly all of the exhaust gas the reducing suppressing means discharged from the engine to control the flow control valve so as to flow an annular passage HC adsorbent, NO _X storage catalyst, the order of the oxidation catalyst, an internal combustion engine Exhaust purification equipment. A NO ₂ ratio increasing means for increasing the ratio of nitrogen dioxide NO _{2 to} nitrogen monoxide NO generated when combustion is performed at a lean air-fuel ratio when the NO _x storage catalyst is not activated. The exhaust emission control device for an internal combustion engine according to any one of 1 to 6 .

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