JP2007120319A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure excellent fuel economy by using one fuel adding valve. <P>SOLUTION: A postprocessing system 20 is arranged in an exhaust passage of an internal combustion engine, and has an expansion chamber 22 in an upstream part. The exhaust passage is branched off into a first exhaust passage 24a and a second exhaust passage 24b on the downstream end of this expansion chamber 22. In this case, NOx storage reducing catalysts 25a and 25b and particulate filters 26a and 26b are respectively arranged in the respective exhaust passages 24a and 24b. For example, when NOx must be released from the NOx storage reducing catalyst 25a, fuel is added from the fuel adding valve 33 by closing the second exhaust passage 24b by an exhaust control valve 28b. <P>COPYRIGHT: (C)2007,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 When the fuel ratio becomes rich, a NO _x absorbent that releases stored NO _x is disposed in the first exhaust passage and the second exhaust passage, respectively, and in the first exhaust passage upstream of the NO _x absorbent and There is known an internal combustion engine in which a fuel addition valve is disposed in each of the second exhaust passages, and an exhaust control valve is disposed in each of the first exhaust passage and the second exhaust passage downstream of the NO _x absorbent (for example, (See Patent Document 1).

First exhaust passage and closes the exhaust control 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 in an internal combustion engine The fuel is added from a fuel addition valve disposed in the first exhaust passage in a state where the exhaust gas is retained in the first exhaust passage, whereby the air-fuel ratio of the exhaust gas in the first exhaust passage is kept rich, and the second the residence exhaust gas to the exhaust when to release the occluded NO _x from the placed _the NO _x absorbent in the passage second exhaust passage and closes the exhaust control valve disposed in the second exhaust passage In this state, the fuel is added from the fuel addition valve disposed in the second exhaust passage, so that the air-fuel ratio of the exhaust gas in the second exhaust passage is kept rich.
Japanese Patent Laid-Open No. 7-102947

However, this internal combustion engine has a problem that two fuel addition valves are required to release NO _x from each NO _x absorbent. A further major problem is that these fuel addition valves are located far away from the engine, so that the fuel supply pipe must be routed far away from the engine.

  In order to solve the above problems, according to the present invention, the aftertreatment device disposed in the engine exhaust passage is disposed in an exhaust gas inlet, aligned with the exhaust gas inlet, and larger than the exhaust gas inlet. An expansion chamber having a gas flow cross-sectional area, and a catalyst that defines a downstream end of the expansion chamber, and an exhaust passage that is one in the expansion chamber upstream of the catalyst from the upstream end surface with the upstream end surface of the catalyst as a boundary On the downstream side, when the fuel that is branched into the first exhaust passage and the second exhaust passage and is added from the fuel addition valve and flows into the expansion chamber from the exhaust gas inlet, the second exhaust passage is introduced. The exhaust passage is closed, and the first exhaust passage is closed when the fuel flows into the second exhaust passage.

  The number of fuel addition valves can be reduced while ensuring good fuel efficiency, and the attachment position of the fuel addition valves can be brought closer to the engine body.

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 has an exhaust gas inlet 21 communicating with the outlet of the exhaust turbine 7b, and an expansion chamber 22 that is aligned with the exhaust gas inlet 21 and has an exhaust gas flow cross-sectional area larger than that of the exhaust gas inlet 21. And a pair of exhaust branch pipes 23a and 23b connected to the downstream end of the expansion chamber 22, and a first exhaust passage 24a and a second exhaust passage in each of the exhaust pipes 23a and 23b. 24b is formed.

In the first exhaust passage 24a, the first NO _x storage reduction catalyst 25a, the first particulate filter 26a, the first oxidation catalyst 27a, and the first exhaust control valve driven by the actuator are sequentially arranged from the upstream side. 28a is disposed, a second NO _x storage reduction catalyst 25b is in the second exhaust passage 24b in this order from the upstream side, the second particulate filter 26b, the driven second oxidation catalyst 27b, and the actuator Two exhaust control valves 28b are arranged. The first exhaust passage 24a and the second exhaust passage 24b are joined to a common exhaust pipe 29 downstream of the first exhaust control valve 28a and the second exhaust control valve 28b.

The first exhaust passage 24a has a temperature sensor 30a for detecting the temperature of the first NO _x storage reduction catalyst 25a and a first pressure for detecting the differential pressure across the first particulate filter 26a. A differential pressure sensor 31a and a temperature sensor 32a for detecting the temperature of the exhaust gas discharged from the first oxidation catalyst 27a are disposed, and the second NO _x storage reduction catalyst 25b is provided in the second exhaust passage 24b. The temperature sensor 30b for detecting the temperature, the second differential pressure sensor 31b for detecting the differential pressure across the second particulate filter 26b, and the temperature of the exhaust gas discharged from the second oxidation catalyst 27b A temperature sensor 32b for detecting the above is disposed.

FIG. 2A shows a perspective view of the post-processing apparatus 20, and FIG. 20B shows a cross-sectional view of the post-processing apparatus 20 taken along line II-II in FIG. As shown in FIGS. 1 and 2, the expansion chamber 22 extends along the central axis of the exhaust gas inlet 21, and this expansion chamber 22 extends from the exhaust gas inlet 21 to the NOx storage reduction catalysts 25 a and 25 _b . It gradually expands toward the upstream end face. A downstream end both _the NO _x storage reduction catalyst 25a extending in the same plane of the expansion chamber 22 that this gradually expanded, are defined by the upstream end face of the 25b, is thus one in enlarged chamber 22 exhaust passage is to be branched to the first exhaust passage 24a and the second exhaust passage 24b on the downstream side from these upstream end face both _the NO _x storage reduction catalyst 25a, the upstream-side end face of 25b as a boundary.

  Further, as shown in FIGS. 1 and 2, the pair of exhaust branch pipes 23a and 23b are arranged symmetrically with respect to the plane including the central axis of the exhaust gas inlet 21, and accordingly, the first exhaust passage 24a. The second exhaust passage 24b is arranged symmetrically with respect to a plane including the central axis of the exhaust gas inlet 21.

  On the other hand, as shown in FIG. 1, a fuel addition valve 33 is disposed in the exhaust manifold 5, and fuel is added from the fuel addition valve 32 into the exhaust manifold 5. In an embodiment according to the invention, this fuel consists of light oil.

  The electronic control unit 40 comprises 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 30a, 30b, 32a and 32b, and the differential pressure sensors 31a and 31b are input to the input port 45 via the 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, and the fuel addition valve 33 via a corresponding drive circuit 48.

FIG. 3 shows another embodiment of the post-processing device 20. 4A shows a perspective view of the post-processing apparatus 20 shown in FIG. 3, and FIG. 4B shows a cross-sectional view of the post-processing apparatus 20 taken along line IV-IV in FIG. . In this embodiment, the expansion chamber 22 has a conical shape, and the NO _x storage-reduction catalyst 25 is composed of one straight flow type monolithic catalyst that extends the entire cross section of the internal space of the aftertreatment device 20.

The internal space of the aftertreatment device 20 is separated into two small spaces by a partition wall 34 extending downstream from the downstream end face of the NO _x storage reduction catalyst 25, and each small space is a first exhaust passage 24a. A second exhaust passage 24b is formed. The aftertreatment device 20 has a cylindrical shape as a whole, and therefore the first exhaust passage 24a and the second exhaust passage 24b have a semicircular cross section. In this embodiment, a first particulate filter 26a, a first oxidation catalyst 27a, and a first exhaust control valve 28a are disposed in the first exhaust passage 24a, and the second particulates are disposed in the second exhaust passage 24b. A curate filter 26b, a second oxidation catalyst 27b, and a second exhaust control valve 28b are disposed.

FIG. 5 shows the structure of the NO _x storage reduction catalyst 25a, 25b shown in FIG. 1 and the NO _x storage reduction catalyst 25 shown in FIG. In the embodiment shown in FIGS. 1 and 3, the NO _x storage reduction catalysts 25 a, 25 _b , 25 have a straight flow type, that is, a straight flow type honeycomb structure, and are straightly separated from each other by a thin partition wall 60. A plurality of exhaust gas flow passages 61 extending are provided. A catalyst carrier made of alumina, for example, is supported on both surfaces of each partition wall 60, and FIGS. 6A and 6B schematically show a cross section of the surface portion of the catalyst carrier 65. As shown in FIGS. 6A and 6B, the noble metal catalyst 66 is dispersedly supported on the surface of the catalyst carrier 65, and a layer of NO _x absorbent 67 is further provided on the surface of the catalyst carrier 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 catalyst 25a, 25b, 25 is referred to as the air-fuel ratio of the exhaust gas, the NO _x absorbent. 67 absorbs and releases NO _x when the air-fuel ratio of the exhaust gas is lean, and performs NO _x absorption / release action to release the absorbed NO _x when the oxygen concentration in the exhaust gas decreases.

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. 6 (A), NO is oxidized on platinum Pt 66 to become NO ₂ , and then absorbed into 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 and 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 33 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.

  7A and 7B show the structures of the particulate filters 26a and 26b shown in FIG. 7A shows a front view of the particulate filters 26a and 26b, and FIG. 7B shows a side sectional view of the particulate filters 26a and 26b. As shown in FIGS. 7A and 7B, the particulate filters 26a and 26b 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 26a and 26b 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. The structure of the particulate filters 26a and 26b shown in FIG. 3 is basically the same as the structure shown in FIGS. 7A and 7B except that the contour shape is a semicircular shape.

In the embodiment shown in FIGS. 1 and 3, for example, alumina is also provided on the peripheral wall surfaces of each exhaust gas inflow passage 70 and each exhaust gas outflow passage 71, that is, on both side surfaces of each partition wall 74 and on the inner wall surface of pores in the partition wall 74 As shown in FIGS. 6A and 6B, a noble metal catalyst 66 made of platinum Pt is dispersed and supported on the surface of the catalyst carrier 65. A layer of _x absorbent 67 is formed.

Therefore, when fuel is being 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 26a and 26b. 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 33.

  On the other hand, the particulate matter contained in the exhaust gas is collected on the particulate filters 26a and 26b 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 26a and 26b, 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 26a and 26b 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 filters 26a and 26b exceeds an allowable amount, that is, the difference between the particulate filters 26a and 26b detected by the differential pressure sensors 31a and 31b. When the pressure ΔP exceeds the allowable value, the fuel is added from the fuel addition valve 33 while maintaining the lean air-fuel ratio of the exhaust gas flowing into the particulate filters 26a and 26b, and the oxidation reaction heat of the added fuel causes the particulates to flow. The temperature of the curate filters 26a and 26b is raised, so that the deposited particulate matter is removed by oxidation.

In FIGS. 1 and 3, an oxidation catalyst or a three-way catalyst can be used in place of the NO _x storage reduction catalysts 25a and 25b. In this case, in the embodiment shown in FIG. 3, the oxidation catalyst or the three-way catalyst is formed from a straight flow type monolith catalyst. 1 and 3, particulate filters that do not carry the NO _x absorbent 67 may be used as the particulate filters 26a and 26b.

Then _the NO _x storage reduction catalyst 25a with reference to FIG. 8, 25b, _the NO _x absorbent 67 on 25, and the particulate filter 26a, the controlled release of the NO _x from _the NO _x absorbent 67 on 26b 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. 9 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. 8 is calculated by integrating the NO _x amount NOXA.

In the embodiment according to the present invention, the NO _x releasing action is alternately performed from the NO _x absorbent 67 in the first exhaust passage 24a and from the NO _x absorbent 67 in the second exhaust passage 24b. permissible value MAX is reached, one of the exhaust passage 24a of _the amount of NO _x ΣNOX absorbed in the _x absorbent 67 is shown in Figure 8, absorption of NO _x of _the NO _x absorbent 67 in 24b reaches the allowable value Will be. Therefore, at this time, it is determined that NO _x should be released from the NO _x absorbent 67 that has reached the allowable value. Amount of NO _x at this time is absorbed in the other of the NO _x absorbent 67 is half the tolerance. Note that in FIG. 8 X1 shows when the absorption of NO _x of _the NO _x absorbent 67 in the first exhaust passage 24a has reached the allowable value, X2 is absorption of NO _x in the second exhaust passage 24b This shows the time when the NO _x absorption amount of the agent 67 reaches an allowable value.

On the other hand, in FIG. 8, I indicates the first exhaust passage 24a, and II indicates the second exhaust passage 24b. As can be seen from FIG. 8, normally, that is, when the NO _x amount ΣNOX is lower than the allowable value MAX, both the first exhaust control valve 28a and the second exhaust control valve 28b are opened, and the first In both the exhaust passage 24a and the second exhaust passage 24b, exhaust gas having a lean air-fuel ratio flows. Therefore this time the one of the exhaust passage 24a, the absorption of the NO _x in the exhaust gas even in _the NO _x absorbent 67 in 24b is performed.

Now, first, the second exhaust control valve 28b is made to closed to when releasing the NO _x from the NO _x absorbent 67 is disposed in the first exhaust passage 24a as indicated by X1 in FIG. 8 Thereby, the second exhaust passage 24b is closed. As a result, the exhaust gas that has flowed into the expansion chamber 22 from the exhaust gas inlet 21 flows only into the first exhaust passage 24a. Next, after the second exhaust passage 24b is closed, when a predetermined first time Δt1 has passed, mist-like, that is, particulate fuel is added from the fuel addition valve 32, and this added fuel is particulate. And flows into the expansion chamber 22.

When the fine particles of the added fuel flow into the expansion chamber 22, these fine particles are decelerated and the inertia force of the fuel fine particles is weakened. At this time, as described above, the exhaust gas flows only into the first exhaust passage 24a. On the other hand, since the inertial force of the fuel fine particles is weakened at this time as described above, the fuel fine particles are placed on the exhaust gas. 1 in the exhaust passage 24a. Therefore without almost all of the fuel added is adhered on the upstream end face of the inner wall surface and the second NO _x storage reduction catalyst 25b of the expansion chamber 22, fed into the first exhaust passage 24a. The first time corresponds to a waiting time until the inflow of exhaust gas into the second exhaust passage 24b stops.

On the other hand, when a predetermined second time Δt2 elapses after the fuel is added, the second exhaust control valve 28b is opened, the second exhaust passage 24b is opened, and the first exhaust control valve 28a is opened. Is closed, and the first exhaust passage 24a is closed. That is, when fuel is added from the fuel addition valve 33, the fuel does not ride on the exhaust gas flow and immediately penetrate through the first exhaust passage 24a, but is delayed from the exhaust gas flow to the first exhaust passage. Advance in 24a. Next, this fuel temporarily adheres to the NO _x storage reduction catalyst 25a, the particulate filter 26a, and the oxidation catalyst 27a in the first exhaust passage 24a, and then evaporates.

That is, after the fuel is added from the fuel addition valve 33, if the first exhaust control valve 28a is closed too early, the added fuel will not advance further in the first exhaust passage 24a, so the NO _x storage reduction catalyst. The surface of the particulate filter 25a or the particulate filter 26a cannot be sufficiently utilized to hold the added fuel. On the other hand, if the first exhaust control valve 28a is closed too late after the fuel addition, the evaporated fuel is discharged to the outside. Will be. That is, the second time Δt2 is a time required to hold the fuel added from the fuel addition valve 33 in the first exhaust passage 24a.

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 28a needs to be closed. Therefore, as shown in FIG. 10A, the second time Δt2 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 25a and the particulate filter 26a, that is, the temperature Tc of the NO _x absorbent 67, the more easily the attached fuel evaporates. Therefore, as shown in FIG. The second time Δt2 is shortened as becomes higher. This second time Δt2 is stored in advance in the ROM 42 in the form of a map as shown in FIG. 10C as a function of the intake air amount Ga and the temperature Tc.

On the other hand, the first exhaust control valve 28a is closed, and the first exhaust control valve 28a is opened when a predetermined third time Δt3 elapses after the first exhaust passage 24a is closed. The first exhaust passage 24a is opened. First air of the NO _x storage-reduction catalyst 25a and the particulate exhaust gas filter 26a fuel adhering to the remaining in the first exhaust passage 24a is evaporated while the exhaust control valve 28a is closed ratio becomes rich, thereby NO _x absorbed in the absorbent 67 which do the NO _x is released and reduced. Therefore, the third time Δt3 is a time during which the air-fuel ratio of the exhaust gas in the first exhaust passage 24a can be kept rich.

As the temperature Tc of the NO _x absorbent 67 increases, the NO _x release and reduction action progresses. Therefore, as shown in FIG. 11A, the third time Δt3 becomes shorter as the temperature Tc increases. Further, even if the exhaust control valves 28a and 28b 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 24a. The air-fuel ratio of the exhaust gas in the exhaust passage 24a is quickly switched from rich to lean. In this case, as the amount of exhaust gas increases, that is, the amount of intake air Ga increases, the richer to leaner is switched earlier. Therefore, as the amount of intake air Ga increases, the third time Δt3 as shown in FIG. Is shortened. The third time Δt3 is stored in advance in the ROM 42 in the form of a map as shown in FIG. 11C as a function of the intake air amount Ga and the temperature Tc.

The same applies when the second exhaust passage 24b arranged _the NO _x absorbent in 67 as indicated by X2 should be released NO _x in FIG. 8. That is, when NO _x is to be released from the NO _x absorbent 67 disposed in the second exhaust passage 24b, the first exhaust passage 24a is closed and then a predetermined first time Δt1 has elapsed. The fuel is added from the fuel addition valve 33, and the first exhaust passage 24a is opened and the second exhaust passage 24b is closed when a predetermined second time Δt2 elapses after the fuel is added. Then, when the predetermined third time Δt3 has elapsed, the second exhaust passage 24b is opened.

  A feature of the present invention is that the first exhaust passage 24a and the second exhaust passage 24b are not immediately branched from the outlet of the exhaust turbine 7b or the common exhaust passage leading to the outlet, but the exhaust turbine 7b or the common exhaust passage leading to the outlet is connected to the first exhaust passage 24a and the second exhaust passage 24b via the expansion chamber 22. Thus, fuel consumption can be improved by forming the expansion chamber 22 immediately before the first exhaust passage 24a and the second exhaust passage 24b.

  That is, in the case where the first exhaust passage 24a and the second exhaust passage 24b are branched immediately from the outlet of the exhaust turbine 7b or the common exhaust passage leading to the outlet without providing such an expansion chamber 22, For example, in order to send the added fuel only into the first exhaust passage 24a, the fuel is added from the fuel addition valve 33 with the first exhaust control valve 28a fully opened and the second exhaust control valve 28b closed. When the added fuel is sent to the first exhaust passage 24a, the first exhaust control valve 28a is closed and the second exhaust control valve 28b is opened. In this case, at first glance, all the added fuel is sent into the first exhaust passage 24a, and then the first exhaust control valve 28a is closed so that the air-fuel ratio of the exhaust gas in the first exhaust passage 24a. Seems to be kept rich.

  However, actually, in order to send the added fuel only into the first exhaust passage 24a, the first exhaust control valve 28a is fully opened, and the second exhaust control valve 28b is closed, and the fuel addition valve 33 is used. Even if the fuel is added, the added fuel is in the form of fine particles, so that a part of the added fuel flows into the second exhaust passage 24b due to inertia, and on the inner wall surface of the second exhaust passage 24b. It adheres to etc. Next, when the second exhaust control valve 28b is fully opened, the adhered fuel is circulated in the second exhaust passage 24b.

Incidentally in this case, the air-fuel ratio of the exhaust gas in this adhering fuel second exhaust passage 24b does not become rich, therefore _the NO _x releasing action from _the NO _x absorbent 67 in the second exhaust passage 24b is Not done. That is, in this case, the attached fuel is wasted. On the other hand, when the expansion chamber 22 is provided as in the present invention, the fuel particles are decelerated in the expansion chamber 22 as described above, so that the inertial force is weakened. As a result, almost all of the fuel flows into the exhaust passages 24a and 24b that should flow into the exhaust gas flow, so that the fuel consumption can be improved.

  In the embodiment shown in FIG. 3, the partition wall 60 extending along the diameter of the catalyst 25 is arranged so as to align with the partition wall 34, and in the catalyst 25, the partition wall 60 extending along the diameter of the catalyst 25 is used. The first exhaust passage 24a and the second exhaust passage 24b are separated. That is, in the embodiment shown in FIG. 3, the first exhaust passage 24 a and the second exhaust passage 24 b are separated by the partition wall 60 and the partition wall 34 that extend along the diameter of the catalyst 25.

FIG. 12 shows an exhaust purification processing routine.
Referring to FIG. 12, 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 the absorption amount of NO _x .SIGMA.NOX is discriminated whether or not exceeded the allowable value MAX is, .SIGMA.NOX> NO in the first exhaust passage 24a proceeds to step 103, when it becomes a MAX _x absorbent 67 from the NO _x It is determined whether or not the flag I indicating that the battery should be released is set.

When it is determined in step 103 that the flag I is set, that is, when NO _x should be released from the NO _x absorbent 67 in the first exhaust passage 24a, the routine proceeds to step 104, where the flag I is reset. Next, at step 105, a first time Δt1 is calculated. Next, at step 106, the representative temperature Tc of the NO _x storage reduction catalyst 25 a and the particulate filter 26 a estimated from one or both of the temperatures detected by the temperature sensor 30 a and the temperature sensor 32 a and the intake air amount detected by the air flow meter 8. Based on Ga, the second time Δt2 is calculated from the map shown in FIG. Next, at step 107, the representative temperature Tc of the NO _x storage reduction catalyst 25 a and the particulate filter 26 a estimated from one or both of the temperatures detected by the temperature sensor 30 a and the temperature sensor 32 a and the intake air amount detected by the air flow meter 8. Based on Ga, the third time Δt3 is calculated from the map shown in FIG. Next, the routine proceeds to step 108.

In step 108, as shown in FIG. 8, first, the second exhaust control valve 28b is first closed, and then when the first time Δt1 calculated in step 105 has elapsed, the fuel from the fuel addition valve 33, that is, As the light oil is added, the NO _x amount ΣNOX is made zero. Next, when the second time Δt2 calculated in step 106 has elapsed, the first exhaust control valve 28a is closed, and the second exhaust control valve 28b is opened. Next, when the third time Δt3 calculated in step 107 has elapsed, the first exhaust control valve 28a is opened.

On the other hand, when it is determined in step 103 that the flag I is not set, that is, when NO _x should be released from the NO _x absorbent 67 in the second exhaust passage 24b, the routine proceeds to step 109, where the flag I is set. The Next, at step 110, a first time Δt1 is calculated. Next, at step 111, the representative temperature Tc of the NO _x storage reduction catalyst 25 _b and the particulate filter 26 b estimated from one or both of the temperatures detected by the temperature sensor 30 b and the temperature sensor 32 b and the intake air amount detected by the air flow meter 8. Based on Ga, the second time Δt2 is calculated from the map shown in FIG. Next, at step 112, the representative temperature Tc of the NO _x storage reduction catalyst 25b and the particulate filter 26b estimated from one or both of the temperatures detected by the temperature sensor 30b and the temperature sensor 32b and the intake air amount detected by the air flow meter 8 are used. Based on Ga, the third time Δt3 is calculated from the map shown in FIG. Next, the routine proceeds to step 108.

In step 108, as shown in FIG. 8, first, the first exhaust control valve 28a is first closed, and then fuel from the fuel addition valve 33 when the first time Δt1 calculated in step 110 has elapsed, that is, As the light oil is added, the NO _x amount ΣNOX is made zero. Next, when the second time Δt2 calculated in step 111 has elapsed, the second exhaust control valve 28b is closed, and the first exhaust control valve 28a is opened. Next, when the third time Δt3 calculated in step 112 has elapsed, the second exhaust control valve 28b is opened.

  By the way, piping a fuel supply pipe for adding fuel to the fuel addition valve 33 under the floor of a vehicle over a long distance is a sense of resistance. However, in the present invention, as shown in FIGS. 1 and 3, the fuel addition valve 33 can be disposed near the engine body, so the fuel supply pipe can be shortened.

  FIG. 13 shows a modification. In this modified example, one exhaust control valve 28 is arranged at the junction of the downstream end of the first exhaust passage 24a and the downstream end of the second exhaust passage 24b to the exhaust passage 29, and this one exhaust control valve 28 A state where both the first exhaust passage 24a and the second exhaust passage 24b are opened as shown by a solid line, and a state where only the first exhaust passage 24a is closed as shown by a broken line a, As shown by the broken line b, the state is switched to three states, that is, only the second exhaust passage 24b is closed.

1 is an overall view of a compression ignition type internal combustion engine. It is a figure which shows the post-processing apparatus of FIG. It is a general view of another Example of a compression ignition type internal combustion engine. It is a figure which shows the post-processing apparatus of FIG. 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 2nd time (DELTA) t2. It is a figure which shows 3rd time (DELTA) t3. It is a flowchart for performing exhaust gas purification processing. It is a figure which shows the modification of a compression ignition type internal combustion engine.

Explanation of symbols

5 exhaust manifold 20 exhaust post-treatment device 24a first exhaust passage 24b second exhaust passage 25a first NO _x storage reduction catalyst 25b second NO _x storage reduction catalyst 26a first particulate filter 26b second particulate Curate filter 27a First oxidation catalyst 27b Second oxidation catalyst 28a First exhaust control valve 28b Second exhaust control valve 33 Fuel addition valve

Claims (17)

  An aftertreatment device disposed in the engine exhaust passage includes an exhaust gas inlet, an enlarged chamber arranged in alignment with the exhaust gas inlet and having an exhaust gas flow cross-sectional area larger than the exhaust gas inlet, and the enlarged chamber And an exhaust passage that is one in the expansion chamber upstream of the catalyst and a first exhaust passage downstream from the upstream end surface with respect to the upstream end surface of the catalyst. When the fuel branched into the second exhaust passage and added from the fuel addition valve and flows into the expansion chamber from the exhaust gas inlet is caused to flow into the first exhaust passage, the second exhaust passage is closed, and the fuel An exhaust gas purification apparatus for an internal combustion engine, wherein the first exhaust passage is closed when the engine is caused to flow into the second exhaust passage.   The exhaust purification device of an internal combustion engine according to claim 1, wherein the expansion chamber is gradually expanded from the exhaust gas inlet toward the upstream end face of the catalyst.   The expansion chamber extends along a central axis of the exhaust gas inlet, and the first exhaust passage and the second exhaust passage are arranged symmetrically with respect to a plane including the central axis of the exhaust gas inlet. The exhaust emission control device for an internal combustion engine according to claim 1.   2. The internal combustion engine according to claim 1, wherein an internal space of the aftertreatment device is separated into two small spaces by a partition wall, and each of the small spaces forms a first exhaust passage and a second exhaust passage. Exhaust purification device.   5. The catalyst comprises a straight flow type monolith catalyst, the catalyst extends in the entire cross section of the internal space of the aftertreatment device, and the partition wall extends downstream from the downstream end face of the catalyst. 2. An exhaust gas purification apparatus for an internal combustion engine according to 1.   The exhaust emission control device for an internal combustion engine according to claim 1, further comprising at least one exhaust control valve for closing or opening the first exhaust passage and the second exhaust passage. When the air-fuel ratio of the inflowing exhaust gas lean occludes NO _x in the exhaust gas, the exhaust of _the NO _x absorbent when the air-fuel ratio of the exhaust gas flowing emits NO _x that are occluded becomes rich first The second exhaust passage is closed and the first exhaust passage is disposed in the passage and the second exhaust passage, respectively, and when NO _x is to be released from the NO _x absorbent disposed in the first exhaust passage. The fuel added from the fuel addition valve in a state where the fuel is opened is introduced into the first exhaust passage, and after the fuel is introduced into the first exhaust passage, of the air-fuel ratio of the exhaust gas in the exhaust passage closes the first exhaust passage in order to maintain the rich, the when releasing the NO _x from the NO _x absorbent arranged in the second exhaust passage first The exhaust passage is closed and the second exhaust passage is opened. The fuel added from the fuel addition valve is introduced into the second exhaust passage, and after the fuel is introduced into the second exhaust passage, the fuel causes the fuel to enter the second exhaust passage. 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the second exhaust passage is closed in order to keep the air-fuel ratio of the exhaust gas rich. An exhaust purification system of an internal combustion engine according to claim 7 in which the catalyst comprises _the NO _x storage-reduction catalyst carrying the _the NO _x absorbent. An exhaust purification system of an internal combustion engine according to claim 7 in which particulate filter carrying respectively the _the NO _x absorbent in the first exhaust passage and the second exhaust passage is located. When NO _x is to be released from the NO _x absorbent disposed in the first exhaust passage, the fuel is added from the fuel addition valve when a predetermined first time has elapsed after the second exhaust passage is closed. Is added, the second exhaust passage is opened and the first exhaust passage is closed when a predetermined second time has elapsed since the fuel was added, and then the predetermined third time When the time elapses, the first exhaust passage is opened, and when NO _x is to be released from the NO _x absorbent disposed in the second exhaust passage, the first exhaust passage is closed and then predetermined. The fuel is added from the fuel addition valve when the first time has elapsed, and the first exhaust passage is opened and the second exhaust passage is opened when the second predetermined time has elapsed since the fuel was added. 2 exhaust passages are closed, then An exhaust purification system of an internal combustion engine according to claim 7 in which the second exhaust passage is caused to open when the third time determined because has elapsed. When NO _x is to be released from the NO _x absorbent disposed in the first exhaust passage, the first time corresponds to a waiting time until the inflow of exhaust gas into the second exhaust passage stops. When NO _x is to be released from the NO _x absorbent disposed in the second exhaust passage, the first time corresponds to a waiting time until the inflow of exhaust gas into the first exhaust passage stops. The exhaust emission control device for an internal combustion engine according to claim 10. When NO _x is to be released from the NO _x absorbent disposed in the first exhaust passage, the second time is necessary to keep the fuel added from the fuel addition valve in the first exhaust passage. is the time, when it should be released NO _x from the NO _x absorbent arranged in the second exhaust passage is the second time holds fuel added from the fuel addition valve in the second exhaust passage The exhaust purification device for an internal combustion engine according to claim 10, which is a time required for the internal combustion engine.   13. The exhaust gas purification apparatus for an internal combustion engine according to claim 12, wherein the second time becomes shorter as the intake air amount increases. The exhaust gas purification apparatus for an internal combustion engine according to claim 12, wherein the second time becomes shorter as the temperature of the NO _x absorbent increases. When NO _x is to be released from the NO _x absorbent disposed in the first exhaust passage, the third time is a time during which the air-fuel ratio of the exhaust gas in the first exhaust passage is kept rich. When NO _x is to be released from the NO _x absorbent disposed in the second exhaust passage, the third time is a time during which the air-fuel ratio of the exhaust gas in the second exhaust passage is kept rich. The exhaust emission control device for an internal combustion engine according to claim 10.   16. The exhaust gas purification apparatus for an internal combustion engine according to claim 15, wherein the third time becomes shorter as the intake air amount increases. 16. The exhaust gas purification apparatus for an internal combustion engine according to claim 15, wherein the third time becomes shorter as the temperature of the NO _x absorbent increases.

Images