JP2008101565A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance an NOx purification performance by keeping the temperature of an NOx absorbent. <P>SOLUTION: This exhaust emission control device comprises a first exhaust passage 22a and a second exhaust passage 22b branched from the exhaust passage 21 of an internal combustion engine. NOx storage/reduction catalysts 23a, 23b and particulate filters 24a, 24b are disposed in the exhaust passages 22a, 22b, respectively. The length of the exhaust passage from the branch part Z to the second NOx storage/reduction catalyst 23b disposed in the second exhaust passage 22b is longer than the length of the exhaust passage from the branch part Z to the first NOx storage/reduction catalyst 23a disposed in the first exhaust passage 22a. The exhaust gas flowing in the first exhaust passage 22a is guided around the second NOx storage/reduction catalyst 23b and the second particulate filter 24b and kept heated. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

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

Comprising a first exhaust passage and a second exhaust passage branched from a common exhaust passage, when the air-fuel ratio of the inflowing exhaust gas is lean occludes NO _x in the exhaust gas, sky of the exhaust gas flowing ratio is disposed respectively a _the NO _x absorbent to release the NO _x that is occluded becomes rich in the first exhaust passage and the second exhaust passage, disposed on the second exhaust passage from the branch portion of the above is the second of the NO _x in the exhaust passage length to the absorbent longer form than the exhaust passage length from the branch portion of the above to the first of the NO _x absorbent arranged in the first exhaust passage has, NO _x A fuel addition valve is disposed in each of the first exhaust passage upstream of the absorbent and the second exhaust passage, and exhaust control is performed in each of the first exhaust passage downstream of the NO _x absorbent and the second exhaust passage. An internal combustion engine in which a valve is arranged is known (see, for example, Patent Document 1).

First exhaust in the internal combustion engine by adding fuel from the fuel addition valve disposed in the first exhaust passage when to release the NO _x occluding from _the NO _x absorbent arranged in the first exhaust passage When the air-fuel ratio of the exhaust gas in the passage is made rich so that the stored NO _x is released from the NO _x absorbent disposed in the second exhaust passage, the fuel is added from the fuel addition valve disposed in the second exhaust passage. Is added to enrich the air-fuel ratio of the exhaust gas in the second exhaust passage.
JP2003-307127A

By the way, when the exhaust passage length from the branch portion from the common exhaust passage to each NO _x absorbent is formed to have different lengths as in this internal combustion engine, the second NO _x absorbent disposed at the longer passage length is used. As a result, the temperature decreases, and as a result, the activity of the second NO _x absorbent is lowered, resulting in a problem that the NO _x purification rate is lowered.

In order to solve the above problems, according to the present invention, the first exhaust passage and the second exhaust passage branched from the common exhaust passage are provided, and when the air-fuel ratio of the inflowing exhaust gas is lean, the exhaust gas occluding NO _x in the air-fuel ratio of the inflowing exhaust gas is disposed respectively in _the NO _x absorbent within the first exhaust passage and the second exhaust passage that releases NO _x that are occluded becomes rich In the internal combustion engine, a fuel addition valve is disposed in a common exhaust passage upstream of the branch portion of the first exhaust passage and the second exhaust passage, and a second exhaust passage disposed in the second exhaust passage from the branch portion. first lengthened than the exhaust passage length to _the NO _x absorbent disposed in the exhaust passage length to _the NO _x absorbent from the branch portion into the first exhaust passage, it flows through the first exhaust passage the exhaust gas Te Shirubebii the second of the NO _x absorbent around by the exhaust gas It is to be kept warm 2 of the NO _x absorbent.

The NO _x purification rate can be improved.

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 via the intake duct 6, and the inlet of the compressor 7 a is connected to the air cleaner 9 via the air flow meter 8. An electronically controlled throttle valve 10 is arranged in the intake duct 6, and a cooling device 11 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 11, 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 exhaust aftertreatment device 20.

  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 12, and an electronically controlled EGR control valve 13 is disposed in the EGR passage 12. A cooling device 14 for cooling the EGR gas flowing in the EGR passage 12 is disposed around the EGR passage 12. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 14, 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 16 through a fuel supply pipe 15. Fuel is supplied into the common rail 16 from an electronically controlled fuel pump 17 with variable discharge amount, and the fuel supplied into the common rail 16 is supplied to the fuel injection valve 3 through each fuel supply pipe 15.

The exhaust aftertreatment device 20 includes a common exhaust passage 21 connected to the outlet of the exhaust turbine 7b, and a first exhaust passage 22a and a second exhaust passage 22b branched from the common exhaust passage 21 at a branch portion Z. It comprises. The in the first exhaust passage 22a first NO _x storage-reduction catalyst 23a in this order from the upstream side, the first exhaust control valve 26a driven by the first particulate filter 24a and the actuator 25a are arranged, the second the exhaust passage 22b second NO _x storage reduction catalyst 23b in this order from the upstream side, the second exhaust control valve 26b which is driven by the second particulate filter 24b and the actuator 25b are arranged. The first exhaust passage 22a and the second exhaust passage 22b are joined to a common exhaust pipe 27 downstream of the first exhaust control valve 26a and the second exhaust control valve 26b. As can be seen from FIG. 1, the exhaust passage length from the branch portion Z to the second NO _x storage reduction catalyst 23b is formed longer than the exhaust passage length from the branch portion Z to the first NO _x storage reduction catalyst 23a. .

If the exhaust passage length from the branch portion Z to the second NO _x storage reduction catalyst 23b is longer than the exhaust passage length from the branch portion Z to the first NO _x storage reduction catalyst 23a in this way, the exhaust gas There the temperature of the exhaust gas is decreased while flowing through the second exhaust passage 22b, also a low temperature thus to the temperature of the second NO _x storage reduction catalyst 23b and the second particulate filter 24b. As a result, the activities of the second NO _x storage reduction catalyst 23b and the second particulate filter 24b are lowered, and the exhaust purification performance is thus lowered.

Therefore, in the present invention, in order to improve the exhaust purification performance by maintaining the second NO _x storage reduction catalyst 23b and the second particulate filter 24b at a high temperature, the inside of the first exhaust passage 22a as shown in FIG. a second NO _x storage reduction catalyst 23b and the through second particulate filter 24b the exhaust gas Te Shirubebii around the second NO _x storage reduction catalyst 23b and the second particulate filter 24b of the exhaust gas flowing through the heat insulation Like to do.

  On the other hand, in the first exhaust passage 22a, a temperature sensor 28a for detecting the temperature of the first particulate filter 24a and a first differential pressure for detecting the differential pressure across the first particulate filter 24a. A sensor 29a is disposed, and a temperature sensor 28b for detecting the temperature of the second particulate filter 24b and a pressure difference across the second particulate filter 24b are detected in the second exhaust passage 22b. The second differential pressure sensor 29b is arranged.

  Further, as shown in FIG. 1, in the common exhaust passage 21 upstream of the branch portion Z of the first exhaust passage 22a and the second exhaust passage 22b, in the exhaust manifold 5 in the embodiment shown in FIG. A common fuel addition valve 30 is arranged for the first exhaust passage 22 a and the second exhaust passage 22 b, and fuel is added from the fuel addition valve 30. In an embodiment according to the invention, this fuel consists of light oil.

  The electronic control unit 40 is composed of a digital computer, and is connected to each other by a bidirectional bus 41. A ROM (read only memory) 42, a RAM (random access memory) 43, a CPU (microprocessor) 44, an input port 45 and an output port 46 are connected. It comprises. The output signals of the air flow meter 8, the temperature sensors 28a and 28b, and the differential pressure sensors 29a and 29b are input to the input port 45 via corresponding AD converters 47, respectively. The accelerator pedal 49 is connected to a load sensor 50 that generates an output voltage proportional to the depression amount L of the accelerator pedal 49, and the output voltage of the load sensor 50 is input to the input port 45 via the corresponding AD converter 47. Is done. Further, a crank angle sensor 51 that generates an output pulse every time the crankshaft rotates, for example, 15 ° is connected to the input port 45. On the other hand, the output port 46 is connected to the fuel injection valve 3, the throttle valve 10 drive device, the EGR control valve 13, the fuel pump 17, the actuators 25 a and 25 b, and the fuel addition valve 30 through corresponding drive circuits 48.

FIG. 2 shows the structure of the NO _x storage reduction catalyst 23a, 23b. In the embodiment shown in FIG. 2, the NO _x storage reduction catalysts 23 a and 23 b have a honeycomb structure and include a plurality of exhaust gas flow passages 61 separated from each other by thin partition walls 60. A catalyst carrier made of alumina, for example, is supported on both surfaces of each partition wall 60, and FIGS. 3A and 3B schematically show a cross section of the surface portion of the catalyst carrier 65. As shown in FIGS. 3A and 3B, a noble metal catalyst 66 is dispersedly supported on the surface of the catalyst support 65, and a layer of NO _x absorbent 67 is further formed on the surface of the catalyst support 65. Is formed.

In the embodiment according to the present invention, platinum Pt is used as the noble metal catalyst 66, and the components constituting the NO _x absorbent 67 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 reduction catalysts 23a, 23b is referred to as the air-fuel ratio of the exhaust gas, the NO _x absorbent 67 is air-fuel ratio of the exhaust gas is absorbed 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 to decrease.

That is, the case where barium Ba is used as a component constituting the NO _x absorbent 67 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. 3 (A), NO is oxidized on platinum Pt 66 to become NO ₂ , and then is absorbed in the NO _x absorbent 67 and combined with barium oxide BaO in the form of nitrate ions NO ₃ ^−. _{x Diffuses in the} absorbent 67. In this way, NO _x is absorbed in the NO _x absorbent 67. Oxygen concentration in the exhaust _gas, NO ₂ is produced on the surface as long as the platinum Pt66 high, _the NO _x absorbent 67 of the NO _x absorbing capability as long as NO ₂ not to saturate been absorbed in the NO _x absorbent 67 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 67, as shown in the ion NO ₃ ^- is released from the NO _x absorbent 67 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 67. However becomes saturated the absorption of NO _x capacity of the NO _x absorbent 67 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 67 and thus End up. Therefore, 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 30 before the absorption capacity of the NO _x absorbent 67 is saturated, and thereby the NO _x absorbent 67. NO _x is released from the gas.

  4A and 4B show the structures of the particulate filters 24a and 24b. 4A shows a front view of the particulate filters 24a and 24b, and FIG. 4B shows a side sectional view of the particulate filters 24a and 24b. As shown in FIGS. 4A and 4B, the particulate filters 24a and 24b have a honeycomb structure and include a plurality of exhaust flow passages 70 and 71 extending in parallel with each other. These exhaust flow passages include an exhaust gas inflow passage 70 whose downstream end is closed by a plug 72 and an exhaust gas outflow passage 71 whose upstream end is closed by a plug 73. In addition, the hatched part in FIG. Therefore, the exhaust gas inflow passages 70 and the exhaust gas outflow passages 71 are alternately arranged via the thin partition walls 74. In other words, in the exhaust gas inflow passage 70 and the exhaust gas outflow passage 71, each exhaust gas inflow passage 70 is surrounded by four exhaust gas outflow passages 71, and each exhaust gas outflow passage 71 is surrounded by four exhaust gas inflow passages 70. Arranged so that.

The particulate filters 24a and 24b are formed of a porous material such as cordierite, for example. Therefore, the exhaust gas flowing into the exhaust gas inflow passage 70 is surrounded by the surrounding partition walls as shown by arrows in FIG. It flows out into the adjacent exhaust gas outflow passage 71 through the inside of 74.
In the embodiment according to the present invention, catalyst carriers made of alumina, for example, are also provided on the peripheral wall surfaces of the exhaust gas inflow passages 70 and the exhaust gas outflow passages 71, that is, on both side surfaces of the partition walls 74 and on the pore inner wall surfaces of the partition walls 74. are supported, are supported noble metal catalysts 66 made of platinum Pt in this way on the surface of the catalyst carrier 65 shown in FIG. 3 (a) and (B) is dispersed, of the NO _x absorbent 67 A layer is formed.

Therefore, when combustion is performed under a lean air-fuel ratio, NO _x in the exhaust gas is also absorbed in the NO _x absorbent 67 on the particulate filters 24a and 24b. This _the NO _x absorbent 67 is absorbed in the NO _x is also released by the addition of fuel from the fuel addition valve 30.

  On the other hand, the particulate matter contained in the exhaust gas is collected on the particulate filters 24a and 24b and sequentially oxidized. However, when the amount of collected particulate matter is larger than the amount of particulate matter to be oxidized, the particulate matter gradually accumulates on the particulate filters 24a and 24b, and in this case, the amount of particulate matter deposited increases. Decreasing engine output. 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 filters 24a and 24b is raised to about 600 ° C. under excess air, the deposited particulate matter is oxidized and removed.

  Accordingly, in the embodiment according to the present invention, when the amount of the particulate matter deposited on the particulate filters 24a and 24b exceeds an allowable amount, that is, the difference between the particulate filters 24a and 24b detected by the differential pressure sensors 29a and 29b. When the pressure ΔP exceeds the allowable value, the fuel is added from the fuel addition valve 30 while maintaining the air-fuel ratio of the exhaust gas flowing into the particulate filters 24a, 24b lean, and the oxidation reaction heat of the added fuel increases the particulates. The temperature of the curate filters 24a and 24b is raised so that the deposited particulate matter is removed by oxidation.

In FIG. 1, the NO _x storage reduction catalysts 23a and 23b can be omitted. In addition, as the particulate filters 24 a and 24 b in FIG. 1, particulate filters that do not carry the NO _x absorbent 67 can be used. However, it is necessary that the NO _x absorbent 67 is disposed in both the first exhaust passage 22a and the second exhaust passage 22b. Therefore, in other words, the exhaust passage length from the branch portion Z to the second NO _x absorbent 67 disposed in the second exhaust passage 22b is the same as the exhaust passage length described above. It can be said that it is formed longer than the length of the exhaust passage to the first NO _x absorbent 67 arranged in one exhaust passage 22a.

The exhaust gas contains not only NO _x but also SO ₂ , and this SO ₂ is oxidized at platinum Pt 66 shown in FIGS. 3A and 3B to become SO ₃ . Next, this SO ₃ is absorbed in the NO _x absorbent 67 and bonded to the barium oxide BaO, while diffusing into the NO _x absorbent 67 in the form of sulfate ions SO ₄ ²⁻ to produce stable sulfate BaSO ₄ . To do. However, since the NO _x absorbent 67 has a strong basicity, this sulfate BaSO ₄ is stable and difficult to decompose. If the air-fuel ratio of the exhaust gas is simply made rich, the sulfate BaSO ₄ is not decomposed and remains as it is. Remains. Thus will be sulfates BaSO ₄ increases as NO _x time to absorbent 67 has elapsed, that the amount of NO _{x the} NO _x absorbent 67 can absorb as thus to time has elapsed is reduced Become.

However, _if the air-fuel ratio of the exhaust gas is made rich while the temperature of the NO _x absorbent 67 is raised to an SO _x release temperature of about 600 ° C. or higher, SO _x is released from the NO _x absorbent 67. And the air-fuel ratio to be rich Thus while in the embodiment according to the present invention increases the temperature of the NO _x absorbent 67 to release SO _x temperature when the amount of SO _x is increased, which is absorbed in _the NO _x absorbent 67 ing.

Then _the NO _x storage-reduction catalyst 23a with reference to FIG. 5, _the NO _x absorbent 67 on 23b, and the particulate filter 24a, the controlled release of the NO _x from _the NO _x absorbent 67 on 24b will be described.

Amount of NO _x discharged from the engine per unit time changes in accordance with the engine operating state, therefore changes according to the operating state of the NO _x amount engine is absorbed in _the NO _x absorbent 67 per unit time . Is stored in advance in ROM42 in the form of a map shown in FIG. 6 as a function of the NO _x amount NOXA is required torque TQ and engine speed N which is absorbed per unit time in _the NO _x absorbent 67 in this embodiment of the present invention The NO _x amount ΣNOX absorbed in the NO _x absorbent 67 shown in FIG. 5 is calculated by integrating the NO _x amount NOXA.

On the other hand, in FIG. 5, I indicates the first exhaust passage 22a, and II indicates the second exhaust passage 22b. As can be seen from FIG. 5, normally, when the NO _x amount ΣNOX is lower than the allowable value MAX, both the first exhaust control valve 26a and the second exhaust control valve 26b are opened, and the first In both the exhaust passage 22a and the second exhaust passage 22b, exhaust gas having a lean air-fuel ratio flows. Therefore this time the one of the exhaust passage 22a, the absorption of the NO _x in the exhaust gas even in _the NO _x absorbent 67 in 22b is performed.

Now, the fuel from the fuel addition valve 30 so as to release the NO _x from the NO _x absorbent 67 when the NO _x absorbed in the absorbent 67 the amount of NO _x ΣNOX exceeds the allowable value MAX as indicated by X1 in Fig. 5 Added. The added fuel is in the form of mist, that is, fine particles. The mist-added fuel is placed in the exhaust gas flow and circulates in the common exhaust passage 21, and then in the first exhaust passage 22a and the second exhaust. It flows into the passage 22b. At this time, the added fuel that has flowed into the first exhaust passage 22a and the second exhaust passage 22b does not immediately pierce through the first exhaust passage 22a and the second exhaust passage 22b. The first exhaust passage 22a and the second exhaust passage 22b move forward with a delay with respect to the flow.

In the present invention, as described above, the length of the exhaust passage from the branch portion Z to the NO _x absorbent 67 disposed in the second exhaust passage 22b is disposed in the first exhaust passage 22a from the branch portion Z. Since it is formed longer than the exhaust passage length to the NO _x absorbent 67, the added fuel first reaches the first NO _x absorbent 67 in the first exhaust passage 22a and then for a while. The second NO _x absorbent 67 in the two exhaust passages 22b is reached. That is, the arrival time of the added fuel to the first NO _x absorbent 67 in the first exhaust passage 22a and the arrival time of the added fuel to the second NO _x absorbent 67 in the second exhaust passage 22b There will be a time difference between the two.

When the added fuel reaches the NO _x storage reduction catalyst 23a in the first exhaust passage 22a, the added fuel temporarily adheres to the NO _x storage reduction catalyst 23a and the particulate filter 24a and then evaporates.
By the way, in the embodiment according to the present invention, when fuel is added from the fuel addition valve 30 at X1 in FIG. 5, the second exhaust control valve 26b is set when a predetermined first time Δt1 has elapsed since the fuel addition. While maintaining the fully open state, the first exhaust control valve 26a is closed and the first exhaust passage 22a is closed. When the first exhaust control valve 26a is closed after the fuel is added in this way, the added fuel that has flowed into the first exhaust passage 22a is held in the first exhaust passage 22a.

In this case, if the first exhaust control valve 26a is closed too early after fuel addition from the fuel addition valve 30, the added fuel will not advance further in the first exhaust passage 22a, so NO _x storage reduction. The surface of the catalyst 23a and the particulate filter 24a cannot be sufficiently utilized to hold the added fuel. On the other hand, if the first exhaust control valve 26a is closed too late after adding the fuel, the evaporated fuel will be discharged to the outside. It will be discharged. That is, the first time Δt1 is a time required to hold the fuel added from the fuel addition valve 30 in the first exhaust passage 22a.

In this case, the faster the exhaust gas flow rate, that is, the larger the intake air amount, the more the added fuel advances. Therefore, the larger the intake air amount, the faster the first exhaust control valve 26a needs to be closed. Therefore, as shown by the solid line in FIG. 7A, the first time Δt1 is shortened as the intake air amount Ga increases. On the other hand, the higher the temperature Tc of the NO _x storage reduction catalyst 23a and the particulate filter 24a, that is, the temperature Tc of the NO _x absorbent 67, the more easily the attached fuel evaporates. Therefore, as shown in FIG. The higher the is, the shorter the first time Δt1 is. The first time Δt1 is stored in advance in the ROM 42 in the form of a map as shown in FIG. 7C as a function of the intake air amount Ga and the temperature Tc.

On the other hand, when the first exhaust control valve 26a is closed and a predetermined second time Δt2 elapses after the first exhaust passage 23a is closed, the first exhaust control valve 26a is opened. The first exhaust passage 22a is opened. While the first exhaust control valve 26a is closed, the fuel adhering to the NO _x storage reduction catalyst 23a and the particulate filter 24a evaporates and the exhaust gas remaining in the first exhaust passage 22a is empty. ratio becomes rich, thereby NO _x absorbed in the absorbent 67 which do the NO _x is released and reduced. Therefore, the second time Δt2 is a time during which the air-fuel ratio of the exhaust gas in the first exhaust passage 22a can be kept rich. Release reduction action enough time to be held in the rich long NO _x becomes good.

As the temperature Tc of the NO _x absorbent 67 increases, the NO _x release / reduction action proceeds. Therefore, as shown in FIG. 8A, the second time Δt2 decreases as the temperature Tc increases. Further, even if the exhaust control valves 26a and 26b are fully closed, there is a slight leak. When such a leak occurs, the exhaust gas having a lean air-fuel ratio flows into the first exhaust passage 22a. The air-fuel ratio of the exhaust gas in the exhaust passage 22a is quickly switched from rich to lean. In this case, the more the exhaust gas amount is increased, that is, the more the intake air amount Ga is, the faster the switch is made from rich to lean. Therefore, as the intake air amount Ga increases as shown in FIG. Is shortened. The second time Δt2 is stored in advance in the ROM 42 in the form of a map as shown in FIG. 8C as a function of the intake air amount Ga and the temperature Tc.

  On the other hand, as shown in FIG. 5, when the first exhaust control valve 26a is opened and the first exhaust passage 22a is opened, the second exhaust control valve 26b is closed and the second exhaust control valve 26b is closed. The exhaust passage 22b is closed. That is, while the first exhaust control valve 26a is closed, the added fuel that has flowed into the second exhaust passage 22b advances in the second exhaust passage 22b, and the first exhaust control valve 26a When the second exhaust control valve 26b is closed when the valve is opened, the added fuel is held in the second exhaust passage 22b.

In other words, in the present invention, when the second exhaust control valve 26b is closed when the total time of the first time Δt1 and the second time Δt2 has elapsed after the addition of fuel, the added fuel enters the second exhaust passage 22b. The exhaust passage length from the branch portion Z to the second NO _x absorbent 67 is maintained so that in the embodiment shown in FIG. 1, the exhaust passage length from the branch portion Z to the second NO _x storage reduction catalyst 23b is It has been established. As a result, as shown in FIG. 5, the air-fuel ratio of the exhaust gas staying in the second exhaust passage 22b becomes rich while the second exhaust control valve 26b is closed, whereby the second exhaust control valve 26b becomes rich. the second of the NO _x absorbed in the absorbent 67 which do the NO _x in the exhaust passage 22b of is released and reduced.

  When the second exhaust control valve 26b is closed, a predetermined target time during which the second exhaust control valve 26b can keep the air-fuel ratio of the exhaust gas in the second exhaust passage 22b rich has elapsed. The valve is kept closed until it is closed, and the valve is opened when the predetermined target time elapses. In the example shown in FIG. 5, this target time is the second time Δt2.

After release of the NO _x from the first of the NO _x absorbent 67 and the second exhaust passage 22b second of the NO _x absorbent 67 in the in the first exhaust passage 22a is completed, again in X2 of FIG. 5 When the amount of NO _x ΣNOX absorbed in the NO _x absorbent 67 exceeds the allowable value MAX, NO _x release control is performed in the same manner as described above.

  A feature of the present invention is that when one of the exhaust control valves 26a and 26b is temporarily closed after fuel addition, the time during which the air-fuel ratio of the exhaust gas is kept rich is lengthened. In this case, the added fuel is sent to the first exhaust passage 22a and the second exhaust passage 22b. When the added fuel is fed into both the first exhaust passage 22a and the second exhaust passage 22b, the added fuel is sent to either the first exhaust passage 22a or the second exhaust passage 22b. The fuel consumption can be improved as compared with the case where the fuel is fed into the vehicle.

  That is, for example, in order to send the added fuel only into the first exhaust passage 22a, the fuel is supplied from the fuel addition valve 30 with the first exhaust control valve 26a fully opened and the second exhaust control valve 26b closed. When the added fuel is fed into the first exhaust passage 22a, the first exhaust control valve 26a is closed and the second exhaust control valve 26b is opened. In this case, at first glance, all the added fuel is sent into the first exhaust passage 22a, and then the first exhaust control valve 26a is closed so that the air-fuel ratio of the exhaust gas in the first exhaust passage 22a. Seems to be kept rich.

  However, in practice, in order to send the added fuel only into the first exhaust passage 22a, the first exhaust control valve 26a is fully opened, and the second exhaust control valve 26b is closed, and the fuel addition valve 30 is used. Even if the fuel is added, the added fuel is in the form of fine particles. Therefore, a part of the added fuel flows into the second exhaust passage 22b due to inertia, and on the inner wall surface of the second exhaust passage 22b. It adheres to etc. Next, when the second exhaust control valve 22b is fully opened, the adhered fuel is circulated in the second exhaust passage 22b.

Incidentally in this case, the air-fuel ratio of the exhaust gas in this adhering fuel second exhaust passage 22b does not become rich, therefore _the NO _x releasing action from _the NO _x absorbent 67 in the second exhaust passage 22b is Not done. That is, in this case, the attached fuel is wasted. In contrast, in the present invention it is effectively used for both _the NO _x releasing respectively fed the added fuel into the first exhaust passage 22a and the second exhaust passage 22b may be able to improve the fuel consumption and thus become.

Next, temperature rise control of the particulate filters 24a and 24b, particulate combustion control, and SO _x release control from the NO _x absorbent 67 will be described with reference to FIG. Particulate filter 24a shown in the period I as shown in Figure 9, the 24b before the temperature rise control, that is the normal operation from time to time the fuel addition valve 30 to release the NO _x from the NO _x absorbent 67 Fuel is being added.

When the differential pressure ΔP detected by the differential pressure sensors 29a and 29b exceeds the allowable value Po, the temperature increase control of the particulate filters 24a and 24b is performed over the period I. This temperature increase control is the same as the NO _x release control shown in FIG. 5, that is, the first exhaust control valve 26a is temporarily closed every time fuel is added as shown in FIG. The second exhaust control valve 26b is temporarily closed. In this case, the fuel is added to such an extent that the air-fuel ratio of the exhaust gas becomes substantially the stoichiometric air-fuel ratio, and the temperatures of the particulate filters 24a and 24b are indicated by Tc in FIG. 9 by the oxidation reaction heat of the added fuel. To rise. In this case, the oxidization reaction of the added fuel is promoted by the retention of the added fuel due to the valve closing action of the exhaust control valves 26a and 26b, thereby improving the fuel consumption.

When the temperature increase control of the particulate filters 24a and 24b is completed, particulate combustion control is performed over a period II under a lean air-fuel ratio as shown in FIG. This combustion control is the same as the NO _x release control shown in FIG. 5, that is, as shown in FIG. 11, every time fuel addition is performed, the first exhaust control valve 26a is temporarily closed and then the second control is continued. The exhaust control valve 26b is temporarily closed. In this case, fuel is added in an amount necessary to maintain the temperature of the particulate filters 24a and 24b at approximately 600 ° C. or higher. In this case, both the exhaust control valves 26a and 26b may be kept fully open.

When the particulate combustion control is completed, the SO _x release control from the NO _x absorbent 67 is performed over a period III as shown in FIG. This SO _x release control is the same as the NO _x release control shown in FIG. 5, that is, after the first exhaust control valve 26a is temporarily closed every time fuel is added as shown in FIG. This is done by temporarily closing the second exhaust control valve 26b. In this case, the fuel is added so that the air-fuel ratio of the exhaust gas becomes a rich air-fuel ratio, and the SO _x is released from the NO _x absorbent 67 by the added fuel. Therefore, as shown in FIG. 9, when SO _x release control is performed, the amount of absorbed SO _x absorbed in the NO _x absorbent 67 gradually decreases. In this case, the exhaust control valves 26a, releasing action of the SO _x by residence of adding fuel by the closing action of 26b is promoted, it fuel is made to improve the.

FIG. 13 shows an exhaust purification processing routine.
Referring to FIG. 13, first, at step 100, the NO _x amount NOXA absorbed 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 absorbed in the NO _x absorbent 67. Next, at step 102, it is judged if the absorbed NO _x amount ΣNOX has exceeded the allowable value MAX. If ΣNOX> MAX, the routine proceeds to step 103.

  In step 103, a first time Δt1 is calculated from the map shown in FIG. 7C based on the temperature Tc of the particulate filter 24a detected by the temperature sensor 28a and the intake air amount Ga detected by the air flow meter 8. The Next, at step 104, the second time Δt2 is calculated from the map shown in FIG. 8C based on the temperature Tc of the particulate filter 24a detected by the temperature sensor 28a and the intake air amount Ga detected by the air flow meter 8. Is done. Next, the routine proceeds to step 105.

  In step 105, fuel is first added as shown in FIG. Next, after the fuel is added, the first exhaust control valve 26a is closed when the first time Δt1 calculated in step 103 has elapsed. Next, when the second time Δt2 calculated in step 104 has elapsed, the first exhaust control valve 26a is opened, and the second exhaust control valve 26b is closed. Next, the second exhaust control valve 26b is opened when the second time Δt2 has elapsed.

Next, at step 106, it is judged if the differential pressure ΔP detected by the differential pressure sensors 29a, 29b has exceeded the allowable value Po. When the differential pressure ΔP exceeds the allowable value Po, the routine proceeds to step 107, where the temperature rise control of the particulate filters 24a, 24b is performed over the period I shown in FIG. Next, the routine proceeds to step 108, where particulate combustion control is performed over a period II shown in FIG. 9, and then at step 109, SO _x release control is performed over a period III shown in FIG.

As shown in FIG. 1, each exhaust control valve 26a, 26b is particulated to improve the controllability by reducing the dead space between the particulate filters 24a, 24b corresponding to the exhaust control valves 26a, 26b, respectively. It is disposed immediately after the filters 24 a and 24 b, in other words, immediately after the NO _x absorbent 67.

Further, in the example shown in FIG. 14, the first exhaust control valve 26a is disposed in the first exhaust passage 22a upstream of the first NO _x storage reduction catalyst 23a, and the second exhaust upstream of the second NO _x storage reduction catalyst 23b. The second exhaust control valve 26b is disposed in the exhaust passage 22b. Exhaust fuel addition also in this case is in the first exhaust passage 22a when closing the first exhaust control valve 26a when attached to the first NO _x storage reduction catalyst 23a and the first particulate filter 24a gas is held rich, the second exhaust passage when closing the second exhaust control valve 26b when the added fuel adheres to the second NO _x storage reduction catalyst 23b and the second particulate filter 24b The exhaust gas in 22b is kept rich. Also in this example, each exhaust control valve 26a, 26b is disposed immediately before the NO _x storage reduction catalyst 23a, 23b in order to reduce the dead space between the corresponding NO _x storage reduction catalyst 23a, 23b.

Well As described above, according to the present invention or second NO _x storage reduction catalyst 23b and the second particulate filter 24b, to improve the exhaust purification performance by holding the second of the NO _x absorbent 67 to a high temperature Further, as shown in FIGS. 1 and 14, the exhaust gas flowing in the first exhaust passage 22a is moved around the second NO _x storage reduction catalyst 23b and the second particulate filter 24b, that is, the second NO _x absorption. The second NO _x storage reduction catalyst 23b and the second particulate filter 24b, that is, the second NO _x absorbent 67 are kept warm by the exhaust gas guided around the agent 67.

Specifically, as shown in FIGS. 1 and 14, the second NO _x storage reduction catalyst 23b and the second particulate filter 24b, that is, the second NO _x absorbent 67 and the like are arranged concentrically. The inner cylinder A and the outer cylinder B are formed into a double pipe structure. A first exhaust passage 22a is formed between the inner cylinder A and the outer cylinder B, and A second exhaust passage 22b is formed. Further, in the embodiment shown in FIGS. 1 and 14, the second exhaust passage 22b branched at the branch portion Z passes through the side of the first exhaust passage 22a, and then passes through the outer cylinder B to pass through the inner cylinder A. The second exhaust passage 22b extending from the inner cylinder A to the downstream side extends through the outer cylinder B to the side of the first exhaust passage 22a to the common exhaust pipe 27.

In the embodiment shown in FIGS. 1 and 14, the first NO _x storage reduction catalyst 23 a and the first particulate filter 24 a are incorporated, that is, the first NO _x absorbent 67 is incorporated. the first exhaust passage 22a portion and a second NO _x storage reduction catalyst 23b and the second incorporates a particulate filter 24b, that is, the second exhaust passage with a built-in second of the NO _x absorbent 67 The portion 22b is arranged in series on the same straight line under the floor of the vehicle.

On the other hand, in the embodiment shown in FIG. 15, the first NO _x storage reduction catalyst 23a and the first particulate filter 24a are incorporated, that is, the first NO _x absorbent 67 is incorporated. 1 of the exhaust passage 22a is arranged so that the side of the engine body 1 extends vertically downward from the vicinity of the exhaust turbine 7b, and the second NO _x storage reduction catalyst 23b and the second particulate filter 24b. , That is, the second exhaust passage 22b portion containing the second NO _x absorbent 67 is disposed so as to extend in the horizontal direction under the floor of the vehicle.

FIG. 16 shows still another embodiment. In this embodiment, since the first NO _x storage reduction catalyst 23a and the first particulate filter 23a are also kept at a high temperature, the exhaust gas flowing in the second exhaust passage 22b is used as the first NO _x storage reduction catalyst. 23a and the first particulate filter 24a around, i.e. first _the NO _x absorbent by the exhaust gas Te Shirubebii around 67 first NO _x storage reduction catalyst 23a and the first particulate filter 24a, that is, the first The NO _x absorbent 67 is also kept warm.

Also in this embodiment, as shown in FIG. 16, the inner cylinder C around the first NO _x storage reduction catalyst 23a and the first particulate filter 24a, that is, around the first NO _x absorbent 67 is arranged concentrically. And the outer cylinder D. The second exhaust passage 22b is formed between the inner cylinder C and the outer cylinder D, and the first exhaust is formed in the inner cylinder C. A passage 22a is formed. Also in this embodiment, the first exhaust passage 22a branched at the branch portion Z passes through the side of the second exhaust passage 22b and then extends through the outer cylinder D toward the inner cylinder C. Further, the first exhaust passage 22a extending downstream from the inner cylinder C extends through the outer cylinder D, extends laterally from the second exhaust path 22b, and then passes through the outer cylinder B toward the inner cylinder A. It extends.

In this embodiment, the first NO _x storage reduction catalyst 23a and the first particulate filter 24a are incorporated, that is, the first exhaust passage 22a portion containing the first NO _x absorbent 67 is incorporated. And the second NO _x storage reduction catalyst 23b and the second particulate filter 24b, that is, the second exhaust passage 22b portion containing the second NO _x absorbent 67 is located under the floor of the vehicle. They are arranged in series on the same straight line.

On the other hand, in the embodiment shown in FIG. 17, similarly to the embodiment shown in FIG. 15, the first NO _x storage reduction catalyst 23a and the first particulate filter 24a are built-in, that is, the first NO _x. The first exhaust passage 22a portion containing the absorbent 67 is disposed so that the side of the engine body 1 extends vertically downward from the vicinity of the exhaust turbine 7b, and the second NO _x storage reduction catalyst. has a built-in 23b and the second particulate filter 24b, that is, the second exhaust passage 22b portion incorporates a second of the NO _x absorbent 67 is disposed so as to extend in the horizontal direction in the floor of the vehicle Yes.

FIG. 18 shows another embodiment of the NO _x release control method. Also in this embodiment, normally, that is, when the NO _x amount ΣNOX is lower than the allowable value MAX, both the first exhaust control valve 26a and the second exhaust control valve 26b are opened, and the first exhaust In both the passage 22a and the second exhaust passage 22b, a lean air-fuel ratio exhaust gas flows. Therefore this time the one of the exhaust passage 22a, the absorption of the NO _x in the exhaust gas even in _the NO _x absorbent 67 in 22b is performed.

Figure in 18 absorbed in the NO _x absorbent 67 as indicated by X1 the amount of NO _x ΣNOX fuel is added from the fuel addition valve 30 so as to release the NO _x from the NO _x absorbent 67 exceeds the allowable value MAX The added fuel flows in the exhaust gas flow and flows through the common exhaust passage 21, and then flows into the first exhaust passage 22a and the second exhaust passage 22b. Next, after the fuel is added, the first exhaust control valve 26a is closed while the second exhaust control valve 26b is fully opened when a predetermined first time Δt1 has elapsed, and the first exhaust control valve 26b is closed. The passage 22a is closed. When the first exhaust control valve 26a is closed after the fuel is added in this way, the added fuel that has flowed into the first exhaust passage 22a is held in the first exhaust passage 22a.

On the other hand, when the first exhaust control valve 26a is closed and a predetermined second time Δt2 elapses after the first exhaust passage 22a is closed, the first exhaust control valve 26a is opened. The first exhaust passage 22a is opened. While the first exhaust control valve 26a is closed, the fuel adhering to the NO _x storage reduction catalyst 23a and the particulate filter 24a evaporates and the exhaust gas remaining in the first exhaust passage 22a is empty. ratio becomes rich, thereby NO _x absorbed in the absorbent 67 which do the NO _x is released and reduced.

On the other hand, when the fuel is added from the fuel addition valve 30 at X1 in FIG. 18, the air-fuel ratio of the exhaust gas in the second exhaust passage 22b becomes rich as described above, and therefore, the inside of the second exhaust passage 22b. NO _x is also released from the NO _x absorbent 67. However fuel evaporated from _the NO _x storage-reduction catalyst 23b and the particulate filter 24b since the second exhaust control valve 26a is held in the fully opened state without staying in the second exhaust passage 22b, in this case by thus As shown in FIG. 18, the rich time becomes shorter than the rich time of the air-fuel ratio of the exhaust gas in the first exhaust passage 22a. Thus _the NO _x releasing reducing action from _the NO _x absorbent 67 in the second exhaust passage 22b is slightly weaker than the _the NO _x releasing reducing action from _the NO _x absorbent 67 in the first exhaust passage 22a.

  When fuel is added from the fuel addition valve 30 at X2 in FIG. 18, the second exhaust control valve 26b is now predetermined in order to hold the added fuel in the second exhaust passage 22b after the fuel addition. The valve is closed when the third time Δt3 has elapsed, and is opened when a predetermined second time Δt2 has elapsed after the valve is closed. Accordingly, at this time, as shown in FIG. 18, the rich time of the air-fuel ratio of the exhaust gas in the second exhaust passage 22b becomes longer than the rich time of the air-fuel ratio of the exhaust gas in the first exhaust passage 22a.

On the other hand, at X3 in FIG. 18, the first exhaust control valve 26a is temporarily closed after fuel addition. That is, the exhaust passage is temporarily closed after the fuel addition from the fuel addition valve 30 in this embodiment, first each time the air-fuel ratio of the exhaust gas so as to release the NO _x from the NO _x absorbent 67 is made rich The first exhaust passage 22a and the second exhaust passage 22b are alternately switched.

1 is an overall view of a compression ignition type internal combustion engine. FIG. 3 is a side cross-sectional view of a NO _x storage reduction catalyst. It is sectional drawing of the surface part of a catalyst support | carrier. It is a figure which shows the structure of a particulate filter. It is a time chart which shows the timing of fuel addition, and the on-off valve timing of an exhaust control valve. It is a diagram showing a map of the absorption amount of NO _x NOXA. It is a figure which shows 1st time (DELTA) t1. It is a figure which shows 2nd time (DELTA) t2. It is a time chart which shows temperature rising control etc. of a particulate filter. It is a time chart which shows the timing of fuel addition, and the on-off valve timing of an exhaust control valve. It is a time chart which shows the timing of fuel addition, and the on-off valve timing of an exhaust control valve. It is a time chart which shows the timing of fuel addition, and the on-off valve timing of an exhaust control valve. It is a flowchart for performing exhaust gas purification processing. It is a figure which shows the modification of an exhaust gas aftertreatment apparatus. It is a figure which shows another Example of an exhaust gas aftertreatment apparatus. It is a figure which shows another Example of an exhaust-gas aftertreatment apparatus. It is a figure which shows another Example of an exhaust-gas aftertreatment apparatus. It is a time chart which shows another Example of NOx discharge _| release control.

Explanation of symbols

5 exhaust manifold 20 exhaust post-treatment device 21 common exhaust passage 22a first exhaust passage 22b second exhaust passage 23a first NO _x storage reduction catalyst 23b second NO _x storage reduction catalyst 24a first particulate filter 24b Second particulate filter 26a First exhaust control valve 26b Second exhaust control valve 30 Fuel addition valve A, C Inner cylinder B, D Outer cylinder

Claims (10)

Comprising a first exhaust passage and a second exhaust passage branched from a common exhaust passage, when the air-fuel ratio of the inflowing exhaust gas is lean occludes NO _x in the exhaust gas, sky of the exhaust gas flowing In the internal combustion engine in which the NO _x absorbent that releases the stored NO _x when the fuel ratio becomes rich is disposed in the first exhaust passage and the second exhaust passage, respectively, the first exhaust passage and the second exhaust passage A fuel addition valve is disposed in the common exhaust passage upstream of the branch portion of the exhaust passage, and the length of the exhaust passage from the branch portion to the second NO _x absorbent disposed in the second exhaust passage is branched. The exhaust gas flowing from the first exhaust passage to the first NO _x absorbent disposed in the first exhaust passage is longer than the exhaust passage length, and the exhaust gas flowing in the first exhaust passage is formed around the second NO _x absorbent. the exhaust gas Te Shirubebii among which is adapted to keep warm the second of the NO _x absorbent Exhaust emission control device of the engine. The second NO _x absorbent is surrounded by a double pipe structure including an inner cylinder and an outer cylinder, a second exhaust passage including the second NO _x absorbent is formed in the inner cylinder, and the inner The exhaust emission control device for an internal combustion engine according to claim 1, wherein a first exhaust passage is formed between the cylinder and the outer cylinder. Exhaust of an internal combustion engine according to claim 1 which is adapted to keep warm the second exhaust by the exhaust gas of the exhaust gas have electrically beauty to the first of the NO _x absorbent around flowing passage first of the NO _x absorbent Purification equipment. The first NO _x absorbent is surrounded by a double pipe structure including an inner cylinder and an outer cylinder, a first exhaust passage including the first NO _x absorbent is formed in the inner cylinder, and the inner The exhaust emission control device for an internal combustion engine according to claim 3, wherein a second exhaust passage is formed between the cylinder and the outer cylinder. Claim that the second exhaust passage portion where the first exhaust passage portion that incorporates the first of the NO _x absorbent incorporates the second of the NO _x absorbent arranged in series on the same straight line in the floor of the vehicle 2. An exhaust emission control device for an internal combustion engine according to 1. The first exhaust passage portion containing the first NO _x absorbent is disposed on the side of the engine body, and the second exhaust passage portion containing the second NO _x absorbent is disposed below the floor of the vehicle. The exhaust emission control device for an internal combustion engine according to claim 1. An exhaust purification system of an internal combustion engine according to claim 1, the NOx storage reduction catalyst carrying respectively the _the NO _x absorbent in the first exhaust passage and the second exhaust passage is located. An exhaust purification system of an internal combustion engine according to claim 1, particulate filter carrying respectively the _the NO _x absorbent in the first exhaust passage and the second exhaust passage is located.   2. The internal combustion engine according to claim 1, wherein an exhaust control valve for closing or opening the first exhaust passage and the second exhaust passage is disposed in each of the first exhaust passage and the second exhaust passage. Exhaust purification device. The exhaust emission control device for an internal combustion engine according to claim 9, wherein each exhaust control valve is arranged immediately after the corresponding NO _x absorbent.

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