JP2005163594A - Exhaust emission control device for compression ignition internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To determine degree of deterioration of NO<SB>x</SB>occlusion catalyst in an exhaust emission control device for a compression ignition internal combustion engine. <P>SOLUTION: A fuel adding valve 14, a HC adsorption catalyst 11, and a NO<SB>x</SB>occlusion catalyst 12 are arranged in order toward a downstream side in an engine exhaust passage. When particulate fuel is added in exhaust gas for discharging NO<SB>x</SB>from the NO<SB>x</SB>occlusion catalyst 12, it is determined that the HC adsorption catalyst 11 is deteriorated if air fuel ratio of gaseous component in exhaust gas flowing out of the HC adsorption catalyst 11 does not become rich or the time being held rich gets shorter as compared with that of the non-deteriorated HC adsorption catalyst 11 even if it becomes rich. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an exhaust emission control device for a compression ignition type internal combustion engine.

An HC adsorption catalyst for adsorbing hydrocarbons contained in the exhaust gas, that is, HC, is disposed in the engine exhaust passage, and when the air-fuel ratio of the inflowing exhaust gas is lean, the NO _x contained in the exhaust gas is occluded. internal combustion engine in which the oxygen concentration in the exhaust gas is arranged the NO _X storing catalyst to release the NO _X occluded when drops HC adsorption catalyst downstream of the engine exhaust passage that flows is known (e.g. Patent Document 1). In this internal combustion engine, HC generated when combustion is performed under a lean air-fuel ratio is adsorbed by the HC adsorption catalyst, and NO _x generated at this time is stored in the NO _x storage catalyst.

However such when using the NO _X storing catalyst should emit NO _X from the NO _X storing catalyst before _the NO _X storage ability of the NO _X storage catalyst is saturated by increasing the supply amount of this fuel NO _X fuel ratio of the exhaust gas flowing into the storage catalyst capable of reducing the NO _X that NO _X from storage catalyst to release NO _X and release if rich.
However, if the air-fuel ratio is changed from lean to rich each time NO _X is released from the NO _X storage catalyst, fuel consumption increases.

However, in the above-described HC adsorption catalyst, when the temperature of the HC adsorption catalyst is near the activation temperature, that is, near 200 ° C., the oxidation reaction of the adsorbed HC becomes active, and as a result, oxygen in the exhaust gas is consumed rapidly. In addition, the oxygen concentration in the exhaust gas rapidly decreases. Therefore, at this time, if a small amount of fuel is additionally supplied, the air-fuel ratio of the exhaust gas can be made rich. Therefore, in the above-mentioned internal combustion engine, it is detected whether or not a sufficient amount of oxygen is consumed in the HC adsorption catalyst, and the exhaust gas air-fuel ratio is made rich when a sufficient amount of oxygen is consumed in the HC adsorption catalyst. Thus, NO _X is released from the NO _X storage catalyst.
JP 2003-97255 A

However time the temperature of the HC adsorbing catalyst becomes near the activation temperature, that is, timing is limited to a sufficient amount of oxygen is consumed in the HC adsorbing catalyst, required viewed from NO _X release action from the NO _X storing catalyst not a temperature of the HC adsorption catalyst to the activation temperature in time, the NO _X from the NO _X storing catalyst when it becomes necessary to release the NO _X from the NO _X storing catalyst in an internal combustion engine described above with thus There is a problem that it cannot be released. In addition, if the HC adsorption catalyst deteriorates, it affects the NO _x releasing action from the NO _x storage catalyst, so it is necessary to determine whether the HC adsorption catalyst has deteriorated. No judgment is made at all.

In order to solve the above problems, according to the present invention, a fuel addition means for adding particulate fuel into the exhaust gas, and an exhaust gas disposed in the engine exhaust passage downstream of the fuel addition means are included in the exhaust gas. Exhaust gas that adsorbs NO _x contained in the exhaust gas when the air-fuel ratio of the HC adsorption catalyst that adsorbs hydrocarbons and the exhaust gas that is disposed in the engine exhaust passage downstream of the HC adsorption catalyst and is lean is lean air-fuel ratio; and a the nO _X storing catalyst to release the nO _X occluding becomes the stoichiometric air-fuel ratio or rich, the exhaust gas so as to release the nO _X from _the nO _X storage catalyst when the HC adsorption catalyst is not deteriorated in air-fuel ratio of the gaseous components in the exhaust gas when the particulate fuel is added to flow out from the HC adsorption catalyst is maintained at the rich during the interim pleasure with becomes rich during the releasing NO _X from the NO _X storing catalyst Therefore, when the particulate fuel is added to the exhaust gas, the air-fuel ratio of the gaseous component in the exhaust gas flowing out from the HC adsorption catalyst does not become rich or even if it becomes rich When the HC adsorption catalyst is shorter than when the HC adsorption catalyst is not deteriorated, it is determined that the HC adsorption catalyst has deteriorated.

It is possible to reliably release NO _x from the NO _x storage catalyst and determine whether the HC adsorption catalyst has deteriorated.

FIG. 1 shows an overall view of a compression 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 inlet of the HC adsorption catalyst 11. The outlet of the HC adsorption catalyst 11 is connected to the NO _x storage catalyst 12 through the exhaust pipe 13. The exhaust manifold 5 is provided with a fuel addition valve 14 for adding mist-like, that is, particulate fuel to the exhaust gas. In an embodiment according to the invention, this fuel consists of light oil.

  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 15, and an electronically controlled EGR control valve 16 is disposed in the EGR passage 15. A cooling device 17 for cooling the EGR gas flowing in the EGR passage 15 is disposed around the EGR passage 15. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 17, and the EGR gas is cooled by the engine cooling water. On the other hand, each fuel injection valve 3 is connected to a common rail 19 via a fuel supply pipe 18. Fuel is supplied into the common rail 19 from an electronically controlled variable discharge amount fuel pump 20, and the fuel supplied into the common rail 19 is supplied to the fuel injection valve 3 via each fuel supply pipe 18.

The electronic control unit 30 is composed of a digital computer, and is connected to each other by a bidirectional bus 31. It comprises. A temperature sensor 21 for detecting the temperature of the HC adsorption catalyst 11 is attached to the HC adsorption catalyst 11, and an air-fuel ratio sensor 22 for detecting the air-fuel ratio of the gaseous component in the exhaust gas is provided in the exhaust pipe 13. Be placed. Output signals from the temperature sensor 21 and the air-fuel ratio sensor 22 are input to the input port 35 via the corresponding AD converters 37. Further, the NO _X storing catalyst 12 has a differential pressure sensor 23 is attached for detecting the differential pressure of the NO _X storage catalyst 12, the output signal of the differential pressure sensor 23 via a corresponding AD converter 37 To the input port 35.

  A load sensor 41 that generates an output voltage proportional to the depression amount L 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. . 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 fuel addition valve 14, the EGR control valve 16 and the fuel pump 20 through corresponding drive circuits 38.

FIG. 2 shows another embodiment of the compression ignition type internal combustion engine. In this embodiment, an air-fuel ratio sensor 22 for detecting the air-fuel ratio of the gaseous component in the exhaust gas is disposed in the exhaust pipe 24 connected to the outlet of the NO _x storage catalyst 12.

First, the NO _x storage catalyst 12 shown in FIGS. 1 and 2 will be described. The NO _x storage catalyst 12 is supported on a monolithic carrier or pellet-like carrier having a three-dimensional network structure, or has a honeycomb structure. It is carried on a particulate filter. In this way, the NO _x storage catalyst 12 can be supported on various carriers. Hereinafter, the case where the NO _x storage catalyst 12 is supported on a particulate filter will be described.

3A and 3B show the structure of the particulate filter 12a carrying the NO _x storage catalyst 12. FIG. 3A shows a front view of the particulate filter 12a, and FIG. 3B shows a side sectional view of the particulate filter 12a. As shown in FIGS. 3A and 3B, the particulate filter 12a 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, each of the exhaust gas inflow passages 60 and the exhaust gas outflow passages 61 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. Arranged so that.

The particulate filter 12a is formed of a porous material such as cordierite, so that the exhaust gas flowing into the exhaust gas inflow passage 60 is contained in the surrounding partition wall 64 as shown by an arrow in FIG. Through the exhaust gas outflow passage 61 adjacent thereto.
When the NO _x storage catalyst 12 is thus supported on the particulate filter 12 a, 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 partition walls 64 and the partition walls 64. A catalyst support made of alumina, for example, is supported on the inner wall surfaces of the pores, and FIGS. 4A and 4B schematically show a cross section of the surface portion of the catalyst support 45. As shown in FIGS. 4A and 4B, a noble metal catalyst 46 is dispersedly supported on the surface of the catalyst carrier 45, and a layer of NO _x absorbent 47 is further provided on the surface of the catalyst carrier 45. Is formed.

In the embodiment according to the present invention, platinum Pt is used as the noble metal catalyst 46, and the constituents of the NO _x absorbent 47 are, for example, alkali metals such as potassium K, sodium Na, cesium Cs, barium Ba, calcium Ca. At least one selected from alkaline earths such as these, lanthanum La, and rare earths such as 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 storage catalyst 12 is referred to as the air-fuel ratio of the exhaust gas, the NO _x absorbent 47 air absorbs NO _X when the lean, the oxygen concentration in the exhaust gas performs the absorbing and releasing action of the NO _X that releases NO _X absorbed and reduced.

That is, the case where barium Ba is used as a component constituting the NO _x absorbent 47 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, it is contained in the exhaust gas. As shown in FIG. 4 (A), NO is oxidized on platinum Pt 46 to become NO ₂ , and then absorbed into the NO _x absorbent 47 and combined with barium oxide BaO in the form of nitrate ions NO ₃ ^−. It diffuses into the _X absorbent 47. In this way, NO _x is absorbed in the NO _x absorbent 47. Exhaust oxygen concentration in the gas is NO ₂ with high long as the surface of the platinum Pt46 are generated, _the NO _X absorbent 47 of the NO _X absorbing capacity so long as NO ₂ not to saturate is absorbed in the NO _X absorbent 47 nitrate ions NO ₃ ^- is generated.

On the other hand, when the air-fuel ratio of the exhaust gas is made rich or stoichiometric, the oxidation concentration in the exhaust gas decreases, so that the reaction proceeds in the reverse direction (NO ₃ ⁻ → NO ₂ ). (B) nitrate in _the NO _X absorbent 47, as shown in the ion NO ₃ ^- is released from _the NO _X absorbent 47 in the form of NO _2. Next, the released NO _x is reduced by unburned HC and CO contained in the exhaust gas.

Thus, when the air-fuel ratio of the exhaust gas is lean, that is, when combustion is performed under the lean air-fuel ratio, NO _X in the exhaust gas is absorbed into the NO _X absorbent 47. However becomes saturated is NO _X absorbing capacity of the NO _X absorbent 47 during the combustion of the fuel under a lean air-fuel ratio is continued, no longer able to absorb NO _X by _the NO _X absorbent 47 and thus End up. Accordingly, in the embodiment according to the present invention, the air-fuel ratio of the exhaust gas is temporarily made rich by adding fuel from the fuel addition valve 14 before the absorption capacity of the NO _x absorbent 47 is saturated, and thereby the NO _x absorbent 47. NO _x is released from the gas.

Well, NO _X from _the NO _X absorbent 47 to the oxygen concentration in the exhaust gas and the air-fuel ratio of the exhaust gas by adding the fuel from the fuel addition valve 14 to the rich decreased as described above is released, release been NO _X is reduced by the unburned HC, CO contained in the exhaust gas. In this case, if the added fuel is to be a liquid theoretically even if the air-fuel ratio of the exhaust gas becomes rich without lowering the oxygen concentration in the exhaust gas, thus NO _X from the absorbent 47 NO _X release do not do. Further, when the fuel is liquid, NO _X is not reduced. That is, in order to release NO _X from the NO _X absorbent 47 and reduce the released NO _X , the air-fuel ratio of the gaseous component in the exhaust gas flowing into the NO _X storage catalyst 12 must be made rich.

In the present invention, the fuel added from the fuel addition valve 14 is in the form of fine particles, and some of the fuel is in the form of gas, but a substantial part is in the liquid state. Upstream of the NO _X storage catalyst 12 as fuel in the present invention has been added fuel oxygen concentration of the thus during even particulate exhaust gas flowing into the lowered vital the NO _X storing catalyst 12 becomes gaseous The HC adsorption catalyst 11 is disposed on the side. Next, the HC adsorption catalyst 11 will be described.

  The HC adsorption catalyst 11 is made of a material having a large specific surface area having a pore structure such as zeolite, and the base of the HC adsorption catalyst 11 shown in FIG. 1 is made of mordenite, which is a kind of zeolite. 5A to 5D schematically show a cross section of the surface portion of the HC adsorption catalyst 11. 5B shows an enlarged view of a portion B in FIG. 5A, FIG. 5C shows the same cross section as FIG. 5B, and FIG. The enlarged view of D section in 5 (C) is shown. As can be seen from FIGS. 5B and 5C, the surface of the HC adsorption catalyst 11 has an uneven rough surface shape. On the surface having this rough surface shape, as shown in FIG. 5D. A large number of pores 51 are formed, and a noble metal catalyst 52 made of platinum Pt is dispersed and supported.

  When particulate fuel is added from the fuel addition valve 14, a part of the fuel evaporates to become a gaseous state, but a substantial part is adsorbed on the surface of the substrate 50 in the form of particulates. FIGS. 5A and 5B show how the fuel fine particles 53 are adsorbed. Thus, the fuel adsorption rate when the fuel is adsorbed in the liquid form is considerably higher than the adsorption rate of the gaseous fuel. The amount of particulate fuel that can be adsorbed by the HC adsorption catalyst 11 increases as the temperature of the HC adsorption catalyst 11 decreases as shown in FIG.

The fuel fine particles 53 adsorbed on the surface of the substrate 50 are gradually evaporated to become gaseous fuel. This gaseous fuel is mainly composed of HC having a large number of carbon atoms. When the HC having a large number of carbons evaporates, it is cracked on the acid sites on the zeolite surface or on the noble metal catalyst 52, and is reformed to HC having a small number of carbons. Next, the reformed gaseous HC flows into the NO _x storage catalyst 12.

FIG. 7 shows the amount of fuel added from the fuel addition valve 14 and the air-fuel ratio A / F of the gaseous component in the exhaust gas. 7A shows the air-fuel ratio A / F of the gaseous component in the exhaust gas flowing into the HC adsorption catalyst 11, and FIG. 7B shows the NO _x storage catalyst flowing out from the HC adsorption catalyst 11. 12 shows the air-fuel ratio A / F of the gaseous component in the exhaust gas flowing into the exhaust gas 12, and (C) shows the air-fuel ratio A / F of the gaseous component in the exhaust gas flowing out of the NO _x storage catalyst 12. Yes.

In the embodiment according to the present invention, when NO _x should be released from the NO _x storage catalyst 12, as shown in FIG. 7, the fuel is added from the fuel addition valve 14 in a pulse shape over a plurality of times with a time interval. When fuel is added from the fuel addition valve 14, a part of the fuel evaporates, so the oxygen concentration in the exhaust gas becomes low, and thus flows into the HC absorption catalyst 11 as shown in FIG. The air-fuel ratio A / F of the gaseous component in the exhaust gas becomes small. However, since a considerable portion of the added fuel is liquid, the air-fuel ratio A / F of the gaseous component in the exhaust gas flowing into the HC adsorption catalyst 11 does not become so small that it becomes rich.

  On the other hand, when fuel is added from the fuel addition valve 14, the fuel particulates are adsorbed by the HC adsorption catalyst 11, and then the fuel is gradually evaporated from the fuel particulates, cracked and reformed as described above. A part of the fuel evaporated from the fuel fine particles or the reformed fuel is oxidized by reacting with oxygen contained in the exhaust gas, thereby reducing the oxygen concentration in the exhaust gas. On the other hand, surplus fuel, that is, surplus HC is discharged from the HC adsorption catalyst 11, and as a result, the air-fuel ratio A / F of the gaseous component in the exhaust gas flowing out from the HC adsorption catalyst 11 becomes slightly rich.

  The fuel is gradually evaporated from the fuel particulates adsorbed on the HC adsorption catalyst 11, and the air-fuel ratio A / F of the gaseous components in the exhaust gas flowing out from the HC adsorption catalyst 11 until the adsorbed fuel particulates become a small amount. Keeps getting slightly richer. Accordingly, as shown in FIG. 7B, the air-fuel ratio A / F of the gaseous component in the exhaust gas flowing out from the HC adsorption catalyst 11 over a considerable time after the fuel addition operation from the fuel addition valve 14 is completed. F keeps getting slightly richer.

Air-fuel ratio A / F of the gaseous components in the exhaust gas flowing into the NO _X storing catalyst 12 flows out from the HC adsorbing catalyst 11 NO _X from the NO _X storing catalyst 12 becomes rich is released, the released NO _X is Reduced by unburned HC and CO. In this case, as described above, the unburned HC flowing into the NO _x storage catalyst 12 is reformed in the HC adsorption catalyst 11, and thus the released NO _x is satisfactorily reduced by the unburned HC. Figure 7 while the releasing action and the reducing action of the NO _X from the NO _X storing catalyst 12 as can be seen from (C) is being performed, NO _X gaseous air-fuel ratio A component in the exhaust gas flowing out from the storage catalyst 12 / F is maintained substantially at the stoichiometric air-fuel ratio.

  By the way, when the HC adsorption catalyst 11 is used for a long period of time, the zeolite constituting the base of the HC adsorption catalyst 11 is thermally destroyed, hydrocarbons with a large molecular weight are fixedly deposited, the acid point of the zeolite and platinum The HC adsorption catalyst 11 gradually deteriorates due to a decrease in the activity of Pt. When the HC adsorption catalyst 11 deteriorates, the ability to adsorb and hold particulate fuel decreases and the ability to crack evaporated HC also decreases. As a result, the generation amount of gaseous HC decreases and the gaseous HC having a small molecular weight is reduced. It becomes difficult to generate.

  FIG. 8 shows the air-fuel ratio A / F of the gaseous component in the exhaust gas when the same amount of fuel as in FIG. 7 is added. (A), (B), and (C) in FIG. 8 show the air-fuel ratio A / F of the gaseous component in the exhaust gas at the same location as (A), (B), and (C) in FIG. ing. Further, curves a in FIGS. 8B and 8C represent the curves shown in FIGS. 7B and 7C, respectively, and these curves a are obtained when the HC adsorption catalyst 11 is not deteriorated. Is shown.

  On the other hand, when the HC adsorption catalyst 11 deteriorates, the curves shown in FIGS. 8B and 8C change from a to b, further deteriorate from b to c, and further deteriorate from c to d. That is, when the HC adsorption catalyst 11 deteriorates, the ratio of gasification of the added particulate fuel decreases, so that the gas in the exhaust gas flowing out from the HC adsorption catalyst 11 as shown in FIG. The time Δt1 during which the air-fuel ratio A / F of the gaseous component is maintained rich becomes gradually shorter. Further, when the HC adsorption catalyst 11 is further deteriorated, the air-fuel ratio A / F does not become rich. In this case, the air-fuel ratio A / F and the stoichiometric air-fuel ratio at the time when the HC adsorption catalyst 11 becomes the smallest as the HC adsorption catalyst 11 deteriorates. The difference ΔA / F1 increases.

Further, as shown in FIG. 8C, when the time Δt1 during which the air-fuel ratio A / F of the gaseous component in the exhaust gas flowing out from the HC adsorption catalyst 11 is kept rich becomes short, the NO _X storage catalyst 12 The time Δt2 during which the air-fuel ratio A / F of the gaseous component in the exhaust gas flowing out from the exhaust gas is substantially maintained at the stoichiometric air-fuel ratio becomes short, and the HC adsorption catalyst 11 deteriorates when the HC adsorption catalyst 11 further deteriorates. The difference ΔA / F2 between the air-fuel ratio A / F and the stoichiometric air-fuel ratio when it becomes the smallest becomes larger.

  In FIGS. 8B and 8C, Δt1 and Δt2 are substantially equal, and ΔA / F1 and ΔA / F2 are substantially equal. Therefore, as Δt1 and Δt2 become shorter as shown in FIG. 9A, the degree of deterioration of the HC adsorption catalyst 11 becomes larger, and ΔA / F1 and ΔA / F2 become larger as shown in FIG. 9B. As the time goes on, the degree of deterioration of the HC adsorption catalyst 11 increases. The actual degree of deterioration of the HC adsorption catalyst 11 is as shown in FIG. 9C by combining FIGS. 9A and 9B. Therefore, the degree of deterioration of the HC adsorption catalyst 11 can be determined by detecting Δt1, Δt2, ΔA / F1, and ΔA / F2.

That is, in the present invention, particulate fuel into exhaust gas in order to release the NO _X from the NO _X storing catalyst 12 when the HC adsorption catalyst 11 is not deteriorated as shown by the curve a shown in FIG. 8 (B) There the air-fuel ratio of the gaseous components in the exhaust gas flowing out from the HC adsorbing catalyst 11 is maintained rich during the interim pleasure with become rich when it is added, the exhaust gas so as to release the NO _X from the NO _X storing catalyst 12 Whether or not the air-fuel ratio A / F of the gaseous component in the exhaust gas flowing out from the HC adsorption catalyst 11 when the particulate fuel is added becomes rich (curve d in FIG. 8B) or rich Even when the HC adsorbing catalyst 11 has become shorter, the HC adsorbing catalyst 11 is judged to have deteriorated when the time during which the HC adsorbing catalyst is maintained is shorter than when the HC adsorbing catalyst is not deteriorated (curves b and c in FIG.

  Since the air-fuel ratio of the gaseous component in the exhaust gas can be determined from the gaseous component in the exhaust gas, it is determined whether or not the air-fuel ratio of the gaseous component in the exhaust gas flowing out from the HC adsorption catalyst 11 has become rich. A sensor that detects a gaseous component in the exhaust gas can be used as the determination means. In the embodiment according to the present invention, as shown in FIGS. 1 and 2, an air-fuel ratio sensor 22 is used as the determination means. This air-fuel ratio sensor 22 is generally used in which platinum thin film electrodes are formed on both sides of zirconia, one platinum thin film electrode is exposed to the atmosphere, and the other platinum thin film electrode is exposed to exhaust gas through a diffusion layer. The air-fuel ratio sensor 22 generates an output signal corresponding to the air-fuel ratio of the gaseous component in the exhaust gas.

  In the embodiment shown in FIG. 1, an air-fuel ratio sensor 22 is arranged so that the air-fuel ratio of the gaseous component in the exhaust gas flowing out from the HC adsorption catalyst 11 can be detected, and based on the output signal of this air-fuel ratio sensor 22. It is then determined whether or not the air-fuel ratio of the gaseous component in the exhaust gas flowing out from the HC adsorption catalyst 11 has become rich.

On the other hand, as shown in FIGS. 7B and 7C, when the air-fuel ratio A / F of the gaseous component in the exhaust gas flowing out from the HC adsorption catalyst 11 is slightly rich, the NO _x storage catalyst 12 is used. The air-fuel ratio A / F of the gaseous component in the exhaust gas flowing out from the exhaust gas is almost the stoichiometric air-fuel ratio. Therefore, in the embodiment shown in FIG. 2, the air-fuel ratio sensor 22 is arranged so that the air-fuel ratio of the gaseous component in the exhaust gas flowing out from the NO _x storage catalyst 12 can be detected. When the air-fuel ratio of the gaseous component in the exhaust gas is substantially the stoichiometric air-fuel ratio, it is determined that the air-fuel ratio of the gaseous component in the exhaust gas flowing out from the HC adsorption catalyst is rich.

Next, the entire exhaust gas purification process including the NO _X release control from the NO _X storage catalyst 12 and the deterioration determination of the HC adsorption catalyst 11 will be described.
In the embodiment according to the present invention, the NO _X amount NOXA stored per unit time in the NO _X storage catalyst 12 is stored in advance in the ROM 32 as a function of the required torque TQ and the engine speed N in the form of a map shown in FIG. The NO _X amount ΣNOX stored in the NO _X storage catalyst 12 is calculated by integrating the NO _X amount NOXA. Further, in the embodiment according to the present invention, the air-fuel ratio A / F of the gaseous component in the exhaust gas flowing into the NO _X storage catalyst 12 is temporarily made rich every time the NO _X amount ΣNOX reaches the allowable value NX, As a result, NO _X is released from the NO _X storage catalyst 12.

  Further, the fuel addition amount necessary to enrich the air-fuel ratio A / F of the gaseous component in the exhaust gas flowing out from the HC adsorption catalyst 11 increases as the air-fuel ratio becomes leaner, and the exhaust gas amount, that is, the intake air It increases as the amount increases. On the other hand, the air-fuel ratio and the intake air amount are functions of the required torque TQ and the engine speed N. Therefore, in the embodiment according to the present invention, the fuel addition amount AQ is a function of the required torque TQ and the engine speed N as shown in FIG. Is stored in advance in the ROM 32 in the form of a map shown in FIG.

  As shown in FIG. 6, in the HC adsorption catalyst 11, the amount of fuel that can be adsorbed changes according to the temperature of the HC adsorption catalyst 11, so it is necessary to determine the amount of fuel added in consideration of this. For example, the amount of fuel that can be adsorbed increases as the temperature of the HC adsorption catalyst 11 decreases, so that the amount of fuel addition can be increased as the temperature of the HC adsorption catalyst 11 decreases.

On the other hand, the particulate matter contained in exhaust gas is trapped on the particulate filter 12a carrying the the NO _X storing catalyst 12, is sequentially oxidized. However, when the amount of the collected particulate matter is larger than the amount of the particulate matter to be oxidized, the particulate matter gradually accumulates on the particulate filter 12a. In this case, the engine output increases when the amount of the particulate matter deposited increases. Will be reduced. Therefore, when the amount of accumulated particulate matter increases, the deposited particulate matter must be removed. In this case, when the temperature of the particulate filter 12a is raised to about 600 ° C. under excess air, the deposited particulate matter is oxidized and removed.

  Therefore, in the embodiment according to the present invention, when the amount of the particulate matter deposited on the particulate filter 12a exceeds the allowable amount, the temperature of the particulate filter 12a is raised under the lean air-fuel ratio of the exhaust gas, thereby The deposited particulate matter is removed by oxidation. Specifically, in the embodiment according to the present invention, when the differential pressure ΔP before and after the particulate filter 12a detected by the differential pressure sensor 23 exceeds the allowable value PX, it is determined that the amount of the deposited particulate matter exceeds the allowable amount. At this time, while maintaining the lean air-fuel ratio of the exhaust gas flowing into the particulate filter 12a, the fuel is added from the fuel addition valve 14, and the temperature of the particulate filter 12a is increased by the oxidation reaction heat of the added fuel. The temperature rise control is performed.

FIG. 11 shows an exhaust purification processing routine.
Referring to FIG. 11, first, at step 100, the NO _X amount NOXA stored per unit time is calculated from the map shown in FIG. Next, at step 101, this NOXA is added to the NO _X amount ΣNOX stored in the NO _X storage catalyst 12. Then whether step 102 occluded amount of NO _X .SIGMA.NOX has exceeded the allowable value NX is discriminated, .SIGMA.NOX> fuel addition processing and judging the deterioration of the fuel adding valve 14 proceeds to step 103, when it becomes NX is performed. Two examples of this fuel addition process and deterioration determination are shown in FIGS.
Next, at step 104, the differential pressure sensor 23 detects the front-rear differential pressure ΔP of the particulate filter 12a. Next, at step 105, it is judged if the differential pressure ΔP has exceeded the allowable value PX, and when ΔP> PX, the routine proceeds to step 106 where temperature increase control of the particulate filter 12a is performed.

  Referring to FIG. 12, first, at step 200, the fuel addition amount AQ is calculated from the map shown in FIG. Next, at step 201, fuel, that is, light oil, is added from the fuel addition valve 14 in accordance with the fuel addition amount AQ. Next, at step 202, Δt1 and ΔA / F1 are detected based on the output signal of the air-fuel ratio sensor 22 in the embodiment shown in FIG. 1, and based on the output signal of the air-fuel ratio sensor 22 in the embodiment shown in FIG. Δt2 and ΔA / F2 are detected. Next, at step 203, the degree of deterioration of the HC adsorption catalyst 11 is calculated from the relationship shown in FIG. Next, at step 204, ΣNOX is cleared.

FIG. 13 and FIG. 14 show another embodiment. FIG. 13A shows the amount of fuel added when NO _X should be released from the NO _X storage catalyst 12, and usually the amount of fuel shown in FIG. 13A is added. Figure 13 when this embodiment should be released then the NO _X storing catalyst 12 from NO _X because lack of fuel addition amount may be the cause when it is determined that the HC adsorption catalyst 11 has deteriorated (B) As shown in FIG. 5, it is determined again whether or not the particulate fuel added to the exhaust gas has increased and the HC adsorption catalyst 11 has deteriorated.

At this time, if it is determined that the HC adsorption catalyst 11 has not deteriorated, it is considered that it is caused by a shortage of the fuel addition amount, and thereafter, the increased amount is held as shown in FIG. 13 (B). The In contrast, added fuel per one time as shown in FIG. 13 (C) from subsequent the NO _X storing catalyst 12 when it is determined that the HC adsorbing catalyst this time is deteriorated when releasing the NO _X The amount can be reduced or the number of fuel additions can be reduced. That is, the amount of added fuel is made to decrease in order to from the NO _X storing catalyst 12 not expect adsorption of fuel release NO _X.

FIG. 14 shows a fuel addition and deterioration determination routine for executing this embodiment.
Referring to FIG. 14, it is first determined whether or not a deterioration recheck condition is satisfied. Since it is not normally a recheck condition, the process proceeds to step 301. In step 301, the fuel addition amount AQ is calculated from the map shown in FIG. Next, at step 302, the final fuel addition amount AQ (= AQ · K) is calculated by multiplying the fuel addition amount AQ by the correction coefficient K. The correction coefficient K is initially set to 1.0.

  Next, at step 303, fuel, that is, light oil, is added from the fuel addition valve 14 according to the final fuel addition amount AQ. Next, at step 304, Δt1 and ΔA / F1 are detected based on the output signal of the air-fuel ratio sensor 22 in the embodiment shown in FIG. 1, and based on the output signal of the air-fuel ratio sensor 22 in the embodiment shown in FIG. Δt2 and ΔA / F2 are detected. Next, at step 305, it is judged from the relationship shown in FIG. 9C whether or not the degree of deterioration of the HC adsorption catalyst 11 exceeds a predetermined degree, that is, whether or not the HC adsorption catalyst 11 has deteriorated. When it is determined that the HC adsorption catalyst 11 has not deteriorated, the routine proceeds to step 307, where ΣNOX is cleared. On the other hand, when it is determined that the HC adsorption catalyst 11 has deteriorated, the routine proceeds to step 306, where it is determined that rechecking should be performed.

If it is determined that rechecking is to be performed, it is determined in step 300 whether or not the operation state is the same as when it is determined that rechecking is to be performed. The fuel addition amount AQ is calculated from the map shown in (B). Next, at step 309, the final fuel addition amount AQ (= AQ · K ₀ ) is calculated by multiplying the fuel addition amount AQ by the correction coefficient K ₀ . This correction coefficient K ₀ is set to a value larger than 1.0.

  Next, at step 310, fuel, that is, light oil, is added from the fuel addition valve 14 in accordance with the final fuel addition amount AQ. At this time, the amount of fuel added is increased as shown in FIG. Next, at step 311, Δt 1 and ΔA / F 1 are detected based on the output signal of the air-fuel ratio sensor 22 in the embodiment shown in FIG. 1, and based on the output signal of the air-fuel ratio sensor 22 in the embodiment shown in FIG. Δt2 and ΔA / F2 are detected. Next, at step 312, it is determined from the relationship shown in FIG. 9C whether or not the deterioration degree of the HC adsorption catalyst 11 exceeds a predetermined degree, that is, whether or not the HC adsorption catalyst 11 has deteriorated.

Correction coefficient K proceeds to step 311 when the HC adsorption catalyst 11 is determined not to be degraded is a K _0. That is, the subsequent addition amount is the addition amount shown in FIG. On the other hand, when it is determined that the HC adsorption catalyst 11 has deteriorated, the routine proceeds to step 307, where the fuel addition amount is decreased as shown in FIG.

1 is an overall view of a compression ignition type internal combustion engine. It is a general view which shows another Example of a compression ignition type internal combustion engine. It is a figure which shows the structure of a particulate filter. 2 is a cross-sectional view of a surface portion of a catalyst carrier of an NO _x storage catalyst. FIG. It is sectional drawing of the surface part of the catalyst support | carrier of HC adsorption catalyst. It is a figure which shows the amount of fuel adsorption. It is a figure which shows the change of the air fuel ratio of the gaseous component in exhaust gas. It is a figure which shows the change of the air fuel ratio of the gaseous component in exhaust gas. It is a figure which shows a deterioration degree. It is a diagram showing a map such as occluded amount of NO _X NOXA. It is a flowchart for performing exhaust gas purification processing. It is a flowchart for performing a fuel addition process and deterioration determination. It is a figure which shows the addition pattern of a fuel. It is a flowchart for performing a fuel addition process and deterioration determination.

Explanation of symbols

4 ... intake manifold 5 ... exhaust manifold 7 ... exhaust turbocharger 11 ... HC adsorption catalyst 12 ... NO _X storing catalyst 14 ... fuel addition valve

Claims (7)

A fuel addition means for adding particulate fuel into the exhaust gas, an HC adsorption catalyst disposed in the engine exhaust passage downstream of the fuel addition means to adsorb hydrocarbons contained in the exhaust gas, and the HC absorbing the air-fuel ratio of the exhaust gas air-fuel ratio of the exhaust gas flowing disposed adsorbing catalyst downstream of the engine exhaust passage at the time of lean of occluding NO _X contained in the exhaust gas flowing becomes the stoichiometric air-fuel ratio or rich HC when the by comprising a the nO _X storing catalyst to release the nO _X was, particulate fuel is added to exhaust gas so as to release the nO _X from _the nO _X storage catalyst when the HC adsorption catalyst is not deteriorated air-fuel ratio of the gaseous components in the exhaust gas flowing out from the adsorption catalyst is maintained rich during the interim pleasure with becomes richer, addition particulate fuel into exhaust gas in order to release the NO _X from the NO _X storing catalyst If the air-fuel ratio of the gaseous component in the exhaust gas flowing out from the HC adsorption catalyst does not become rich or becomes rich, the time during which it remains rich is shorter than when the HC adsorption catalyst is not deteriorated. An exhaust emission control device for a compression ignition type internal combustion engine in which it is determined that the HC adsorption catalyst has deteriorated.   The base of the HC adsorption catalyst is made of zeolite, and a noble metal catalyst made of platinum is supported. The HC adsorption catalyst gradually evaporates and evaporates after adsorbing and holding the particulate fuel added to the exhaust gas. The exhaust emission control device for a compression ignition type internal combustion engine according to claim 1, which has a function of cracking fuel. When the air-fuel ratio of the gaseous component in the exhaust gas flowing out from the HC adsorption catalyst becomes rich when particulate fuel is added to the exhaust gas to release NO _x from the NO _x storage catalyst, it is kept rich. 2. The exhaust gas purification apparatus for a compression ignition type internal combustion engine according to claim 1, wherein it is determined that the degree of deterioration of the HC adsorption catalyst is greater as the time for which the operation is performed is shorter. When particulate fuel is added to the exhaust gas to release NO _x from the NO _x storage catalyst, it becomes the smallest when the air-fuel ratio of the gaseous component in the exhaust gas flowing out from the HC adsorption catalyst does not become rich. 2. The exhaust gas purification apparatus for a compression ignition type internal combustion engine according to claim 1, wherein it is determined that the degree of deterioration of the HC adsorption catalyst is larger as the difference between the current air-fuel ratio and the stoichiometric air-fuel ratio is larger.   An air-fuel ratio sensor capable of detecting the air-fuel ratio of the gaseous component in the exhaust gas flowing out from the HC adsorption catalyst is disposed in the engine exhaust passage downstream of the HC adsorption catalyst, and the HC adsorption catalyst is based on the output signal of the air-fuel ratio sensor. 2. An exhaust emission control device for a compression ignition internal combustion engine according to claim 1, wherein it is determined whether or not the air-fuel ratio of the gaseous component in the exhaust gas flowing out from the exhaust gas has become rich. _The NO _X storage downstream of the catalyst in the engine exhaust passage an air-fuel ratio sensor capable of detecting an air-fuel ratio of the gaseous components in the exhaust gas flowing out from the NO _X storing catalyst arranged, an exhaust gas detected by the air-fuel ratio sensor 2. The exhaust gas purification of a compression ignition type internal combustion engine according to claim 1, wherein it is determined whether or not the air-fuel ratio of the gaseous component in the exhaust gas flowing out from the HC adsorption catalyst becomes rich based on the air-fuel ratio of the gaseous component. apparatus. When it is determined that the HC adsorption catalyst has deteriorated, it is determined again whether the HC adsorption catalyst has deteriorated by increasing the amount of particulate fuel added to the exhaust gas so as to release NO _X from the NO _X storage catalyst. and, HC exhaust purification of a compression ignition type internal combustion engine according to claim 1 to reduce the fuel amount when the adsorption catalyst should be released NO _X from then _the NO _X storage catalyst when it is again determined if has deteriorated apparatus.

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