JP4506544B2 - Exhaust gas purification device for compression ignition type internal combustion engine - Google Patents

Description

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

  When the air-fuel ratio of the exhaust gas flowing to purify NOx contained in the exhaust gas is lean, the NOx contained in the exhaust gas is occluded and the occluded NOx is released when the oxygen concentration in the inflowing exhaust gas decreases. An internal combustion engine is known in which an NOx storage catalyst is disposed in an engine exhaust passage. In this internal combustion engine, NOx generated when combustion is performed under a lean air-fuel ratio is stored in the NOx storage catalyst.

  By the way, when such a NOx storage catalyst is used, it is necessary to release NOx from the NOx storage catalyst before the NOx storage capacity of the NOx storage catalyst is saturated. In this case, the air-fuel ratio of the exhaust gas flowing into the NOx storage catalyst is made rich. In this case, NOx can be released from the NOx storage catalyst and the released NOx can be reduced. Therefore, in the conventional internal combustion engine, the air-fuel ratio in the combustion chamber is made rich in order to release NOx from the NOx storage catalyst, or the fuel is supplied into the engine exhaust passage upstream of the NOx storage catalyst and flows into the NOx storage catalyst. The air-fuel ratio of the gas is made rich.

  By the way, in order to release NOx satisfactorily from the NOx storage catalyst, it is necessary to allow the rich gas-fuel ratio exhaust gas that has been sufficiently gasified to flow into the NOx storage catalyst. In this case, if the air-fuel ratio in the combustion chamber is made rich, exhaust gas having a rich gas-fuel ratio that has been sufficiently gasified flows into the NOx storage catalyst, so that NOx can be released well from the NOx storage catalyst. However, when the air-fuel mixture is made rich in the combustion chamber, there is a problem that a large amount of soot is generated, and the air-fuel ratio of the exhaust gas discharged from the combustion chamber is made rich by injecting additional fuel during the expansion stroke or exhaust stroke. Then, so-called bore flushing occurs in which the injected fuel adheres to the inner wall surface of the cylinder bore.

  On the other hand, when fuel is injected into the engine exhaust passage upstream of the NOx storage catalyst, no soot or bore flushing occurs as described above. However, when the fuel is injected into the engine exhaust passage upstream of the NOx storage catalyst, the injected fuel is not sufficiently gasified, and therefore NOx cannot be discharged from the NOx storage catalyst satisfactorily. There is.

  On the other hand, an internal combustion engine is known in which an HC adsorption catalyst for adsorbing hydrocarbons contained in exhaust gas, that is, HC, is disposed in an engine exhaust passage upstream of the NOx storage catalyst (see Patent Document 1). In this internal combustion engine, HC generated when combustion is performed under a lean air-fuel ratio is adsorbed by the HC adsorption catalyst, and NOx generated at this time is stored in the NOx storage catalyst.

By the way, in this internal combustion engine, when the temperature of the HC adsorption catalyst is near the activation temperature, that is, around 200 ° C., the oxidation reaction of the adsorbed HC becomes active, and as a result, oxygen in the exhaust gas is consumed rapidly. The oxygen concentration in the exhaust gas decreases rapidly. Therefore, at this time, if a small amount of fuel is additionally supplied, the air-fuel ratio of the exhaust gas can be made rich. Therefore, in this internal combustion engine, it is detected whether or not a sufficient amount of oxygen is consumed in the HC adsorption catalyst, and the exhaust gas air-fuel ratio is made rich when a sufficient amount of oxygen is consumed in the HC adsorption catalyst. NOx is released from the NOx storage catalyst.
JP 2003-97255 A

  However, in this internal combustion engine, the air-fuel ratio in the combustion chamber is made rich, and fuel is not injected into the engine exhaust passage, so the above-described problems occur. Further, in this internal combustion engine, the time when the temperature of the HC adsorption catalyst becomes close to the activation temperature, that is, the time when a sufficient amount of oxygen is consumed in the HC adsorption catalyst is limited, so that the NOx releasing action from the NOx storage catalyst. Therefore, when the temperature of the HC adsorption catalyst does not reach the activation temperature at the necessary time, it is therefore impossible to release NOx from the NOx storage catalyst when it is necessary to release NOx from the NOx storage catalyst. There's a problem.

  The object of the present invention is to release NOx well from the NOx storage catalyst even when fuel is supplied into the engine exhaust passage upstream of the NOx storage catalyst when NOx should be released from the NOx storage catalyst. An object of the present invention is to provide an exhaust emission control device for a compression ignition type internal combustion engine.

  In order to achieve the above object, according to the present invention, fuel addition means for adding particulate fuel into the exhaust gas, and the exhaust gas disposed in the engine exhaust passage downstream of the fuel addition means are included in the exhaust gas. When the air-fuel ratio of the HC adsorption oxidation catalyst that adsorbs and oxidizes hydrocarbons and the exhaust gas that is disposed in the engine exhaust passage downstream of the HC adsorption oxidation catalyst is lean, occludes inflow of NOx contained in the exhaust gas A NOx storage catalyst that releases stored NOx when the air-fuel ratio of the exhaust gas that is exhausted becomes the stoichiometric air-fuel ratio or rich, and when NOx should be released from the NOx storage catalyst, particulate fuel is added from the fuel addition means. By sending the added particulate fuel to the HC adsorption oxidation catalyst, the air-fuel ratio of the exhaust gas flowing into the NOx storage catalyst is made rich, and at this time, the HC adsorption oxidation catalyst The temperature of the fuel is controlled to be within a predetermined optimum temperature range that is optimal for oxidizing HC. Further, at this time, the amount of particulate fuel added from the fuel addition means flows into the HC adsorption oxidation catalyst. The air-fuel ratio of the exhaust gas is set to an amount that becomes a rich air-fuel ratio smaller than the rich air-fuel ratio flowing into the NOx storage catalyst, and the added particulate fuel is adsorbed after being adsorbed by the HC adsorption oxidation catalyst Most of the spent fuel is oxidized in the HC adsorption oxidation catalyst and the exhaust gas emptied into the NOx storage catalyst for a longer time than the time during which the air-fuel ratio of the exhaust gas flowing into the HC adsorption oxidation catalyst is made rich. The fuel ratio is made rich.

  When NOx should be released from the NOx storage catalyst, NOx can be released well from the NOx storage catalyst.

FIG. 1 shows an overall view of a compression ignition type internal combustion engine.
Referring to FIG. 1, 1 is an engine body, 2 is a combustion chamber of each cylinder, 3 is an electronically controlled fuel injection valve for injecting fuel into each combustion chamber 2, 4 is an intake manifold, and 5 is an exhaust manifold. Respectively. The intake manifold 4 is connected to the outlet of the compressor 7 a of the exhaust turbocharger 7 through the intake duct 6, and the inlet of the compressor 7 a is connected to the air cleaner 8. A throttle valve 9 driven by a step motor is arranged in the intake duct 6, and a cooling device 10 for cooling intake air flowing in the intake duct 6 is arranged around the intake duct 6. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 10 and the intake air is cooled by the engine cooling water. On the other hand, the exhaust manifold 5 is connected to the inlet of the exhaust turbine 7 b of the exhaust turbocharger 7, and the outlet of the exhaust turbine 7 b is connected to the exhaust pipe 11. The exhaust manifold 5 is provided with a fuel addition valve 12 for adding a mist-like, that is, particulate fuel to the exhaust gas. In an embodiment according to the invention, this fuel consists of light oil.

  The exhaust manifold 5 and the intake manifold 4 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 13, and an electronically controlled EGR control valve 14 is disposed in the EGR passage 13. A cooling device 15 for cooling the EGR gas flowing in the EGR passage 13 is disposed around the EGR passage 13. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 15, 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 17 through a fuel supply pipe 16. Fuel is supplied into the common rail 17 from an electronically controlled fuel pump 18 with variable discharge amount, and the fuel supplied into the common rail 17 is supplied to the fuel injection valve 3 through each fuel supply pipe 16.

  The electronic control unit 20 comprises a digital computer and is connected to each other by a bidirectional bus 21. A ROM (read only memory) 22, a RAM (random access memory) 23, a CPU (microprocessor) 24, an input port 25 and an output port 26 are connected. It comprises. As shown in FIG. 1, a load sensor 31 that generates an output voltage proportional to the depression amount L of the accelerator pedal 30 is connected to the accelerator pedal 30, and the output voltage of the load sensor 31 passes through a corresponding AD converter 27. Input to the input port 25. Further, a crank angle sensor 32 that generates an output pulse every time the crankshaft rotates, for example, 15 ° is connected to the input port 25. On the other hand, the output port 26 is connected to the fuel injection valve 3, the step motor for driving the throttle valve 9, the fuel addition valve 12, the EGR control valve 14, and the fuel pump 18 through corresponding drive circuits 28.

  As shown in FIG. 1, a post-treatment device 40 for purifying harmful components in exhaust gas, particularly NOx, is attached to the exhaust pipe 11. FIG. 2 shows an enlarged view of the post-processing device 40. Referring to FIG. 2, a main exhaust pipe 41 is connected to the exhaust pipe 11, and an HC adsorption oxidation catalyst 42 is disposed in the main exhaust pipe 41. Further, a NOx storage catalyst 43 is disposed in the main exhaust pipe 41 downstream of the HC adsorption oxidation catalyst 42. The main exhaust pipe 41 bypasses the HC adsorption oxidation catalyst 42, that is, the main exhaust pipe 41 upstream of the HC adsorption oxidation catalyst 42 and downstream of the HC adsorption oxidation catalyst 42 and upstream of the NOx storage catalyst 43. An exhaust bypass pipe 44 connecting the inside is attached.

  A flow path switching valve device 45 is disposed in the main exhaust pipe 41 and the exhaust bypass pipe 44 upstream of the HC adsorption oxidation catalyst 42. In the first embodiment shown in FIG. 2, the flow path switching valve device 45 includes an exhaust control valve 46 disposed in the main exhaust pipe 42 upstream of the HC adsorption oxidation catalyst 42, and an exhaust disposed in the exhaust bypass pipe 44. It comprises a control valve 47 and an actuator 48 for driving these exhaust control valves 46, 47, and this actuator 48 is connected to the output port 26 via a drive circuit 28 shown in FIG. When one of these exhaust control valves 46 and 47 is opened, the other is closed. That is, when the exhaust control valve 46 is opened, the exhaust control valve 47 is closed, and when the exhaust control valve 47 is opened, the exhaust control valve 46 is closed.

  As shown in FIG. 2, a temperature sensor 49 for detecting the temperature of the HC adsorption / oxidation catalyst 42 is attached to the HC adsorption / oxidation catalyst 42, and the output signal of the temperature sensor 49 corresponds to the corresponding AD conversion shown in FIG. The data is input to the input port 25 via the device 27. Further, a differential pressure sensor 50 for detecting a differential pressure across the NOx storage catalyst 43 is attached to the NOx storage catalyst 43, and an output signal of the differential pressure sensor 50 is input via a corresponding AD converter 27. Input to port 25.

  In FIG. 2, when the exhaust control valve 46 is opened and the exhaust control valve 47 is closed, all the exhaust gas is circulated in the main exhaust pipe 41, that is, the HC adsorption oxidation catalyst 42. In this way, the flow path of the exhaust gas flowing through the HC adsorption oxidation catalyst 42, that is, the flow path of the exhaust gas extending through the HC adsorption oxidation catalyst 42 is the main stream as shown by the broken arrow in the embodiment shown in FIG. It is called a road. On the other hand, when the exhaust control valve 47 is opened and the exhaust control valve 46 is closed, all the exhaust gas bypasses the main exhaust pipe 41 and flows through the exhaust bypass pipe 44. In this way, the exhaust gas flow path that bypasses the HC adsorption oxidation catalyst 42, that is, the exhaust gas flow path in the exhaust bypass pipe 44, is a sub-flow path as shown by the broken arrow in the embodiment shown in FIG. It is called.

  First, the NOx occlusion catalyst 43 shown in FIGS. 1 and 2 will be described. This NOx occlusion catalyst 43 is supported on a monolithic carrier or pellet-like carrier having a three-dimensional network structure, or has a honeycomb structure. It is carried on a filter. As described above, the NOx storage catalyst 43 can be supported on various carriers. Hereinafter, the case where the NOx storage catalyst 43 is supported on the particulate filter will be described.

  3A and 3B show the structure of the particulate filter 43a carrying the NOx storage catalyst 43. FIG. 3A shows a front view of the particulate filter 43a, and FIG. 3B shows a side sectional view of the particulate filter 43a. As shown in FIGS. 3A and 3B, the particulate filter 43a has a honeycomb structure and includes a plurality of exhaust flow passages 60 and 61 extending in parallel with each other. These exhaust flow passages include an exhaust gas inflow passage 60 whose downstream end is closed by a plug 62 and an exhaust gas outflow passage 61 whose upstream end is closed by a plug 63. In addition, the hatched part in FIG. Therefore, the exhaust gas inflow passages 60 and the exhaust gas outflow passages 61 are alternately arranged via the thin partition walls 64. In other words, each of the exhaust gas inflow passages 60 and the exhaust gas outflow passages 61 is surrounded by four exhaust gas outflow passages 61, and each exhaust gas outflow passage 61 is surrounded by four exhaust gas inflow passages 60. Arranged so that.

The particulate filter 43a is made of, for example, a porous material such as cordierite. Therefore, the exhaust gas flowing into the exhaust gas inflow passage 60 is contained in the surrounding partition wall 64 as indicated by an arrow in FIG. Through the exhaust gas outflow passage 61 adjacent thereto.
When the NOx storage catalyst 43 is supported on the particulate filter 43a in this way, the peripheral wall surfaces of the exhaust gas inflow passages 60 and the exhaust gas outflow passages 61, that is, on both side surfaces of the partition walls 64 and in the partition walls 64. A catalyst carrier made of alumina, for example, is supported on the inner wall surfaces of the pores. FIGS. 4A and 4B schematically show a cross-section of the surface portion of the catalyst carrier 70. As shown in FIGS. 4A and 4B, a noble metal catalyst 71 is dispersedly supported on the surface of the catalyst carrier 70, and a layer of NOx absorbent 72 is further provided on the surface of the catalyst carrier 70. Is formed.

In the embodiment according to the present invention, platinum Pt is used as the noble metal catalyst 71, and the components constituting the NOx absorbent 72 are, for example, alkali metals such as potassium K, sodium Na, cesium Cs, barium Ba, and calcium Ca. At least one selected from rare earths such as alkaline earth, lanthanum La, and yttrium Y is used.
When the ratio of air and fuel (hydrocarbon) supplied into the engine intake passage, the combustion chamber 2 and the exhaust passage upstream of the NOx storage catalyst 43 is referred to as the air-fuel ratio of the exhaust gas, the NOx absorbent 72 has the air-fuel ratio of the exhaust gas. When NO is lean, NOx is absorbed, and when the oxygen concentration in the exhaust gas decreases, NOx is absorbed and released so that the absorbed NOx is released.

That is, the case where barium Ba is used as a component constituting the NOx absorbent 72 will be described as an example. When the air-fuel ratio of the exhaust gas is lean, that is, when the oxygen concentration in the exhaust gas is high, the NO contained in the exhaust gas 4A is oxidized on platinum Pt 71 to become NO ₂ as shown in FIG. 4 (A), and then is absorbed into the NOx absorbent 72 and combined with barium oxide BaO to form a NOx absorbent in the form of nitrate ions NO ₃ ^−. It diffuses into 72. In this way, NOx is absorbed into the NOx absorbent 72. As long as the oxygen concentration in the exhaust gas is high, NO ₂ is generated on the surface of the platinum Pt 71. As long as the NOx absorption capacity of the NOx absorbent 72 is not saturated, NO ₂ is absorbed in the NOx absorbent 72 and nitrate ions NO ₃ ⁻ are generated. 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 ). As shown in (B), nitrate ions NO ₃ ⁻ in the NOx absorbent 72 are released from the NOx absorbent 72 in the form of NO ₂ . Next, the released NOx 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, NOx in the exhaust gas is absorbed into the NOx absorbent 72. However, if combustion under a lean air-fuel ratio is continuously performed, the NOx absorbent capacity of the NOx absorbent 72 is saturated during that time, and therefore the NOx absorbent 72 cannot absorb NOx. Therefore, in the embodiment according to the present invention, the air-fuel ratio of the exhaust gas is temporarily made rich by adding the fuel from the fuel addition valve 12 before the absorption capacity of the NOx absorbent 72 is saturated, and thereby the NOx absorbent 72 to the NOx. To be released.

  Now, as described above, when the air-fuel ratio of the exhaust gas is made rich by adding fuel from the fuel addition valve 12, NOx is released from the NOx absorbent 12, and the unburned HC in which the released NOx is contained in the exhaust gas. , Reduced by CO. In this case, assuming that the added fuel is liquid, theoretically, NOx is not released from the NOx absorbent 72 even if the air-fuel ratio of the exhaust gas becomes rich. Further, when the fuel is liquid, NOx is not reduced. That is, in order to release NOx from the NOx absorbent 72 and reduce the released NOx, the air-fuel ratio of the gaseous component in the exhaust gas flowing into the NOx storage catalyst 43 must be made rich.

  In the embodiment according to the present invention, the fuel added from the fuel addition valve 12 is in the form of fine particles, and some of the fuel is in the form of gas but most is in the liquid state. Therefore, in the embodiment according to the present invention, when NOx is to be released from the NOx absorbent 72, the exhaust gas containing fuel added from the fuel addition valve 12 is used as the main flow passage shown in FIG. Even if most of the added fuel is liquid, the fuel flowing into the NOx storage catalyst 43 is in a gaseous state. Next, the HC adsorption oxidation catalyst 42 will be described.

  FIG. 5 shows a side sectional view of the HC adsorption oxidation catalyst 42. As shown in FIG. 5, the HC adsorption oxidation catalyst 42 has a honeycomb structure and includes a plurality of exhaust gas flow passages 73 extending straight. The HC adsorption oxidation catalyst 42 is made of a material having a large specific surface area having a pore structure such as zeolite, and the base of the HC adsorption oxidation catalyst 73 shown in FIG. 5 is made of mordenite, which is a kind of zeolite. FIGS. 6A to 6D schematically show a cross section of the surface portion of the base 74 of the HC adsorption oxidation catalyst 42. 6B shows an enlarged view of a portion B in FIG. 6A, FIG. 6C shows the same cross section as FIG. 6B, and FIG. The enlarged view of D section in 6 (C) is shown. As can be seen from FIGS. 6B and 6C, the surface of the HC adsorption oxidation catalyst 42 has an uneven rough surface shape, and the surface having this rough surface shape is as shown in FIG. 6D. In addition, a large number of pores 75 are formed, and a precious metal catalyst 76 made of platinum Pt is dispersed and supported.

  When particulate fuel is added from the fuel addition valve 12, a part of the fuel evaporates into a gaseous state, but most of the fuel is adsorbed on the surface of the substrate 74 in the form of particulates. FIGS. 6A and 6B show how the fuel fine particles 77 are adsorbed. Thus, the fuel adsorption rate when the fuel is adsorbed in the liquid form is considerably higher than the adsorption rate of the gaseous fuel. Note that the adsorption amount of the particulate fuel that can be adsorbed by the HC adsorption oxidation catalyst 42 increases as the temperature of the HC adsorption oxidation catalyst 42 decreases as shown in FIG. 7A. Further, when the space velocity with respect to the exhaust gas flow in the HC adsorption oxidation catalyst 42 (= volume velocity of the exhaust gas / volume of the HC adsorption oxidation catalyst bed) increases, that is, when the flow velocity of the exhaust gas increases, the HC adsorption oxidation catalyst 42 added from the fuel addition valve 12 Of the fuel, the amount of gasified fuel and the amount of particulate fuel that passes through the exhaust flow passage 73 in the NOx adsorption oxidation catalyst 42 increase. Accordingly, the amount of particulate fuel that can be adsorbed by the HC adsorption oxidation catalyst 42 decreases as the space velocity increases as shown in FIG. 7B.

  Next, as shown in FIGS. 6C and 6D, the fuel fine particles 77 adsorbed on the surface of the substrate 50 are gradually evaporated to become gaseous fuel. This gaseous fuel is mainly composed of HC having a large number of carbon atoms. When the HC having a large number of carbons evaporates, it is cracked on the acid sites on the zeolite surface or on the noble metal catalyst 76, and is reformed to HC having a small number of carbons. This reformed gaseous HC is immediately oxidized by reacting with oxygen in the exhaust gas. In this way, most of the fuel fine particles 77 adsorbed on the surface of the substrate 74 react with oxygen in the exhaust gas, so almost all the oxygen contained in the exhaust gas is consumed. As a result, the oxygen concentration in the exhaust gas decreases and NOx is released from the NOx storage catalyst 43.

  On the other hand, at this time, gaseous HC remains in the exhaust gas, and the air-fuel ratio of the exhaust gas is rich. The gaseous HC flows into the NOx storage catalyst 43, and the NOx released from the NOx storage catalyst 43 is reduced by the gaseous HC.

  FIG. 8 shows the amount of fuel added from the fuel addition valve 12 and the air-fuel ratio A / F of the exhaust gas during engine low speed and low load operation. 8A shows the air-fuel ratio A / F of the exhaust gas flowing into the HC adsorption oxidation catalyst 42, and FIG. 8B flows out from the HC adsorption oxidation catalyst 42 and flows into the NOx storage catalyst 43. The air-fuel ratio A / F of the exhaust gas is shown, and (C) shows the air-fuel ratio A / F of the exhaust gas flowing out from the NOx storage catalyst 43.

  In the embodiment according to the present invention, when NOx should be released from the NOx storage catalyst 43, a drive signal consisting of a plurality of continuous pulses is supplied to the fuel addition valve 12, as shown in FIG. While the fuel is being supplied, the fuel is continuously added. While the fuel is being supplied from the fuel addition valve 12, the air-fuel ratio of the exhaust gas flowing into the HC adsorption oxidation catalyst 42 becomes a considerably rich air-fuel ratio of 5 or less as shown in FIG.

  On the other hand, when fuel is added from the fuel addition valve 12, the fuel particulates are adsorbed by the HC adsorption oxidation catalyst 42, and then the fuel is gradually evaporated from the fuel particulates, cracked and reformed as described above. A part of the fuel evaporated from the fuel fine particles or the reformed fuel reacts with oxygen contained in the exhaust gas and is oxidized, thereby lowering the oxygen concentration in the exhaust gas. On the other hand, surplus fuel, that is, surplus HC is discharged from the HC adsorption oxidation catalyst 42, and as a result, the air-fuel ratio A / F of the exhaust gas flowing out from the HC adsorption oxidation catalyst 42 becomes slightly rich. That is, the air-fuel ratio A / F of the exhaust gas flowing out from the HC adsorption oxidation catalyst 42 is reduced until the fuel gradually evaporates from the fuel fine particles adsorbed on the HC adsorption oxidation catalyst 42 and the adsorbed fuel fine particles become a small amount. It continues to be slightly richer. Therefore, as shown in FIG. 8 (B), the air-fuel ratio A / F of the exhaust gas flowing out from the HC adsorption oxidation catalyst 42 is very small for a considerable time after the fuel addition operation from the fuel addition valve 12 is completed. Continue to be rich.

  When the air-fuel ratio A / F of the exhaust gas flowing out from the HC adsorption oxidation catalyst 42 and flowing into the NOx storage catalyst 43 becomes rich, NOx is released from the NOx storage catalyst 43, and the released NOx is reduced by unburned HC and CO. The In this case, as described above, the unburned HC flowing into the NOx storage catalyst 43 is reformed in the HC adsorption oxidation catalyst 42, and thus the released NOx is satisfactorily reduced by the unburned HC. As can be seen from FIG. 8C, the air-fuel ratio A / F of the exhaust gas flowing out from the NOx storage catalyst 43 is substantially equal to the stoichiometric air-fuel ratio while the NOx storage catalyst 43 releases and reduces the NOx. Maintained.

  Thus, in the present invention, when the air-fuel ratio of the exhaust gas flowing into the NOx storage catalyst 43 is made rich in order to release NOx from the NOx storage catalyst 43, the particulate fuel is added from the fuel addition valve 12 and at this time The amount of the particulate fuel added is less than half the rich air-fuel ratio in the example shown in FIG. 8, in which the air-fuel ratio of the exhaust gas flowing into the HC adsorption oxidation catalyst 42 is smaller than the rich air-fuel ratio flowing into the NOx storage catalyst 43. Is set to an amount.

  On the other hand, the particulate fuel added at this time is adsorbed by the HC adsorption / oxidation catalyst 42, and most of the adsorbed fuel is oxidized in the HC adsorption / oxidation catalyst 42, and the exhaust gas flowing into the HC adsorption / oxidation catalyst 42 becomes empty. In the example shown in FIG. 8, the air-fuel ratio of the exhaust gas flowing into the NOx storage catalyst 43 becomes rich for a time longer than the time when the fuel ratio is made rich, in the example shown in FIG.

  Thus, in the present invention, the particulate fuel added from the fuel addition valve 12 is once adsorbed and held in the HC adsorption oxidation catalyst 42, and then the adsorbed and held particulate fuel is gradually evaporated from the HC adsorption oxidation catalyst 42. Thus, the air-fuel ratio of the exhaust gas flowing into the NOx storage catalyst 43 over a long time is made rich. In this case, in order to release as much NOx as possible from the NOx storage catalyst 43, the time during which the air-fuel ratio of the exhaust gas flowing into the NOx storage catalyst 43 is made rich should be lengthened. It is necessary to increase as much as possible the amount of fuel adsorbed and held in the tank.

  For example, in a compression ignition type internal combustion engine in which the intake air amount is 10 (g) per second during engine low speed and low load operation, for example, when particulate fuel is injected from the fuel addition valve 12 for about 400 msec, the NOx storage catalyst 43 is injected. It has been found that the air-fuel ratio of the exhaust gas flowing into the gas reaches a rich air twist ratio of about 14.0 over about 2 seconds, and at this time, NOx is favorably released from the NOx storage catalyst 43. At this time, the air-fuel ratio of the exhaust gas immediately downstream of the fuel addition valve 12, that is, the air-fuel ratio of the exhaust gas flowing into the HC adsorption oxidation catalyst 42 becomes a rich air-fuel ratio of about 4.4.

  More specifically, in this compression ignition type internal combustion engine, the air-fuel ratio A / F is about 30 at the time of engine low speed and low load operation, and therefore A / F = 10 (g / sec) / F = 30. Is F = 1/3 (g / sec). On the other hand, in order to generate 14 rich air-fuel ratios, since A / F = 10 (g / sec) / F = 14, 5/7 (g / sec) of fuel is required. Therefore, the amount of additional fuel to be added from the fuel addition valve 12 to generate a rich air-fuel ratio of 14 is 5/7 (g / sec) -1/3 (g / sec) = 8/21 (g / sec) Therefore, in order to generate a rich air-fuel ratio of 14 over 2 seconds, 16/21 (g) of fuel must be added from the fuel addition valve 12. If this fuel is added in 400 msec, then the air-fuel ratio of the exhaust gas becomes approximately 4.4.

  Thus, in this internal combustion engine, when the rich air-fuel ratio of 14 is generated for 2 seconds during engine low speed and low load operation, the fuel addition valve 12 must supply 16/21 (g) of fuel. In this case, if this amount of fuel is to be supplied in a shorter time, for example, 100 msec, the injection pressure of the fuel addition valve 12 must be increased. However, when the injection pressure of the fuel addition valve 12 is increased, the amount of fuel to be gasified increases because the fine particles of fuel at the time of injection are promoted, and thus the amount of fuel adsorbed by the HC adsorption oxidation catalyst 42 decreases. Thus, when the amount of fuel adsorbed to the HC adsorption oxidation catalyst 42 decreases, the time during which the air-fuel ratio becomes rich becomes shorter. On the other hand, if the supply amount per unit time is reduced in supplying 16/21 (g) of fuel, for example, if the fuel addition time from the fuel addition valve 12 is 1000 msec, the unit from the HC adsorption oxidation catalyst 42 is reduced. The amount of fuel evaporation per hour decreases, and the air-fuel ratio of the exhaust gas becomes difficult to become rich. FIG. 9 illustrates this.

  That is, FIG. 9 shows the air-fuel ratio A / F of the exhaust gas flowing into the HC adsorption oxidation catalyst 42 when the fuel addition time τ (msec) from the fuel addition valve 12 is changed, and the exhaust gas flowing out from the HC adsorption oxidation catalyst 42. A temperature rise amount ΔT of the gas, an exhaust HC amount G discharged from the NOx storage catalyst 43, and a rich time Tr of the exhaust gas flowing into the NOx storage catalyst 43 are shown.

  As described above, if the fuel addition time from the fuel addition valve 12 is shortened, the amount of fuel adsorbed to the HC adsorption oxidation catalyst 42 is reduced. As a result, the amount of fuel evaporated from the HC adsorption oxidation catalyst 42 decreases, so the HC oxidation action weakens, the temperature increase amount ΔT decreases, and the rich time decreases. At this time, the amount of fuel carried away by the exhaust gas flow among the fuel supplied from the fuel addition valve 12 increases, so the exhaust HC amount G increases.

  On the other hand, if the fuel addition time from the fuel addition valve 12 is lengthened, the amount of adsorbed fuel per unit time to the HC adsorption oxidation catalyst 42 decreases as described above. As a result, the amount of fuel evaporated from the HC adsorption oxidation catalyst 42 decreases, so the HC oxidation action weakens, the temperature increase amount ΔT decreases, and the rich time decreases. On the other hand, since the HC continues to evaporate from the HC adsorption oxidation catalyst 42 even after the NOx releasing action from the NOx storage catalyst 43 is completed, the exhaust HC amount G increases.

  If the added fuel is discharged into the atmosphere when the fuel is added from the fuel addition valve 12, the fuel is completely wasted. Therefore, the discharged amount of the added fuel into the atmosphere, that is, the discharged HC amount G is the allowable value Go. It is necessary to suppress to the following. If the discharged HC amount G is less than or equal to the allowable value Go, from another viewpoint, it means that the HC undergoes an oxidation reaction and sufficiently consumes oxygen. Therefore, the discharged HC amount G is equal to the allowable value Go. The following corresponds to the fact that the temperature rise amount ΔT is greater than or equal to a predetermined set value ΔTo.

  That is, when adding fuel from the fuel addition valve 12, it is necessary to determine the addition time τ of the added fuel so that the exhaust HC amount G is less than the allowable value Go and the temperature rise amount ΔT is greater than the set value ΔTo. Therefore, in the embodiment according to the present invention, the addition time τ of the added fuel is set between approximately 100 (msec) and approximately 700 (msec). Expressing this as the air-fuel ratio A / F, the air-fuel ratio A / F when the addition time τ is 100 (msec) is approximately 1, and the air-fuel ratio A / F when the addition time τ is 700 (msec) is approximately Therefore, in the embodiment according to the present invention, the addition amount of the particulate fuel added from the fuel addition valve 12 to release NOx from the NOx storage catalyst 43 flows into the HC adsorption oxidation catalyst 42 in the engine low speed and low load operation. That is, the air-fuel ratio of the exhaust gas to be set is set to an amount from about 1 to about 7.

  FIG. 10 shows the air-fuel ratio at the same place as in FIG. 8 during engine high speed and high load operation. 7A and 7B, the temperature of the HC adsorption oxidation catalyst 42 is higher during the engine high speed and high load operation than in the engine low speed and low load operation, and the space velocity with respect to the exhaust gas flow in the HC adsorption oxidation catalyst 42 is increased. As can be seen, the amount of fuel that can be adsorbed by the HC adsorption oxidation catalyst 42 is considerably reduced. Therefore, as can be seen from a comparison between FIG. 10 and FIG. 8, the amount of fuel added from the fuel addition valve 12 is smaller in the engine high speed and high load operation than in the engine low speed and low load operation.

  As shown in FIG. 10, the air-fuel ratio is about 20 at the time of engine high-speed and high-load operation, so that the air-fuel ratio of the exhaust gas can be made rich even if the added fuel is reduced. However, the time during which the air-fuel ratio of the exhaust gas can be made rich is considerably shorter than that during engine low speed and low load operation.

Figure 11 (A) represents the amount of fuel AQ added from the fuel adding valve 12 to when releasing the NOx from the NOx storing catalyst 43, the amount of fuel added AQ _1, AQ _2, AQ _3, AQ ₄ , AQ ₅ , AQ ₆ in order. In FIG. 11A, the vertical axis TQ represents the output torque, and the horizontal axis N represents the engine speed. Therefore, the fuel amount AQ to be added increases as the output torque TQ increases, that is, the HC adsorption oxidation catalyst 42. The temperature decreases as the engine temperature increases, and decreases as the engine speed N increases, that is, the flow rate of the exhaust gas increases. The fuel amount AQ to be added is stored in advance in the ROM 22 in the form of a map as shown in FIG.

Next, NOx release control will be described with reference to FIGS.
FIG. 12A shows the change in the NOx amount ΣNOX stored in the NOx storage catalyst 43 during the engine low speed and low load operation, and the timing when the air-fuel ratio A / F of the exhaust gas is made rich to release NOx. FIG. 12B shows the change of the NOx amount ΣNOX stored in the NOx storage catalyst 43 during the engine high-speed and high-load operation, and the timing for enriching the air-fuel ratio A / F of the exhaust gas for NOx release. Yes.

  The amount of NOx discharged from the engine per unit time changes according to the operating state of the engine, and therefore the amount of NOx stored in the NOx storage catalyst 43 per unit time also changes according to the operating state of the engine. In the embodiment according to the present invention, the NOx amount NOXA stored in the NOx storage catalyst 43 per unit time is stored in advance in the ROM 22 as a function of the required torque TQ and the engine speed N in the form of a map shown in FIG. The NOx amount ΣNOX stored in the NOx storage catalyst 43 is calculated by integrating the NOx amount NOXA.

  On the other hand, in FIGS. 12A and 12B, MAX represents the maximum NOx occlusion amount that the NOx occlusion catalyst 43 can occlude, and NX represents the allowable value of the NOx amount that can be occluded by the NOx occlusion catalyst 43. ing. Therefore, as shown in FIGS. 12A and 12B, when the NOx amount ΣNOX reaches the allowable value NX, the air-fuel ratio A / F of the exhaust gas flowing into the NOx storage catalyst 43 is temporarily made rich, thereby NOx is released from the NOx storage catalyst 43.

  As described above, the amount of fuel that can be adsorbed by the HC adsorption oxidation catalyst 42 during the engine low speed and low load operation increases, so the amount of fuel added from the fuel addition valve 12 increases. When the fuel addition amount is increased in this way, a large amount of NOx can be released from the NOx storage catalyst 43. That is, in this case, even when a large amount of NOx is occluded in the NOx occlusion catalyst 43, all the occluded NOx can be released, so the allowable value NX is a high value as shown in FIG. In the example shown in 12 (A), the value is slightly lower than the maximum NOx occlusion amount.

  On the other hand, since the amount of fuel adsorbed by the HC adsorption oxidation catalyst 42 is reduced during engine high speed and high load operation, the amount of fuel added from the fuel addition valve 12 is reduced as described above. When the fuel addition amount is reduced in this way, only a small amount of NOx can be released from the NOx storage catalyst 43. That is, in this case, if a small amount of NOx is stored in the NOx storage catalyst 43, the stored NOx must be released, so the allowable value NX is considerably low as shown in FIG. In the example shown in B), the value is 1/3 or less of the allowable value NX in the engine low speed and low load operation shown in FIG.

FIG. 13B shows an allowable value NX determined according to the operating state of the engine. In FIG. 13B, the allowable value NX is NX ₁ , NX ₂ , NX ₃ , NX ₄ , NX ₅ , gradually decreases in the order of NX _6. In FIG. 13B, the vertical axis TQ indicates the engine output torque, and the horizontal axis N indicates the engine speed. Therefore, it can be seen from FIG. 13B that the allowable value NX decreases as the output torque TQ increases, that is, as the engine load increases, and decreases as the engine speed N increases. The allowable value NX shown in FIG. 13B is stored in advance in the ROM 22 in the form of a map as shown in FIG.

  Since the allowable value NX decreases as the engine load increases or the engine speed increases, the frequency at which the particulate fuel is added from the fuel addition valve 12 to release NOx from the NOx storage catalyst 43 depends on the engine load. Increases as the engine speed increases or as the engine speed N increases. That is, as shown in FIGS. 12A and 12B, the frequency at which the particulate fuel is added during the engine high speed and high load operation is considerably higher than during the engine low speed and low load operation.

  On the other hand, the particulate matter contained in the exhaust gas is collected on the particulate filter 43a carrying the NOx storage catalyst 43 and is sequentially oxidized. However, when the amount of the collected particulate matter is larger than the amount of the particulate matter to be oxidized, the particulate matter gradually accumulates on the particulate filter 43a. In this case, if the amount of the particulate matter deposited increases, the engine output Will be reduced. Therefore, when the amount of accumulated particulate matter increases, the deposited particulate matter must be removed. In this case, when the temperature of the particulate filter 43a is raised to about 600 ° C. under excess air, the deposited particulate matter is oxidized and removed.

  Therefore, in the embodiment according to the present invention, when the amount of the particulate matter deposited on the particulate filter 43a exceeds the allowable amount, the temperature of the particulate filter 43a is raised under the lean air-fuel ratio of the exhaust gas, thereby The deposited particulate matter is removed by oxidation. Specifically, in the embodiment according to the present invention, when the differential pressure ΔP before and after the particulate filter 43a detected by the differential pressure sensor 50 exceeds the allowable value PX, it is determined that the amount of the deposited particulate matter exceeds the allowable amount. At this time, fuel is added from the fuel addition valve 12 while maintaining the air-fuel ratio of the exhaust gas flowing into the particulate filter 43a lean, and the temperature of the particulate filter 43a is increased by the oxidation reaction heat of the added fuel. The temperature rise control is performed.

FIG. 14 shows an exhaust purification processing routine.
Referring to FIG. 14, first, at step 100, the NOx amount NOXA stored per unit time is calculated from the map shown in FIG. 13 (A). Next, at step 101, this NOXA is added to the NOx amount ΣNOX stored in the NOx storage catalyst 43. Next, at step 102, an allowable value NX is calculated from the map shown in FIG. Next, at step 103, it is judged if the stored NOx amount ΣNOX has exceeded the allowable value NX. When ΣNOX> NX, the routine proceeds to step 104, where the NOx release flag indicating that NOx should be released from the NOx storage catalyst 43 is set. Set. Next, the routine proceeds to step 105, where NOx purification processing is performed. Next, at step 106, the differential pressure sensor 50 detects the differential pressure ΔP across the particulate filter 43a. Next, at step 107, it is determined whether or not the differential pressure ΔP exceeds the allowable value PX. When ΔP> PX, the routine proceeds to step 108 where temperature rise control of the particulate filter 43a is performed.

  As described above, if the HC oxidation action in the HC adsorption oxidation catalyst 42 is weak, the air-fuel ratio of the exhaust gas flowing into the NOx storage catalyst 43 does not become rich, and the air-fuel ratio of the exhaust gas flowing into the NOx storage catalyst 43 is reduced. In order to make it rich, it is necessary to increase the amount of HC to be oxidized as much as possible by promoting the oxidizing action of HC in the HC adsorption oxidation catalyst 42. FIG. 15A shows the relationship between the amount of HC oxidized in the HC adsorption oxidation catalyst 42, that is, the amount of HC oxidation and the temperature Tc of the HC adsorption oxidation catalyst 42.

  As shown in FIG. 7A, when the temperature of the HC adsorption oxidation catalyst 42 increases, the adsorption amount of the particulate fuel adsorbed on the HC adsorption oxidation catalyst 42 decreases. As the amount of particulate fuel adsorbed decreases, the amount of HC oxidized in the HC adsorption oxidation catalyst 42 decreases. Therefore, as shown in FIG. 15A, the amount of HC oxidation increases the temperature Tc of the HC adsorption oxidation catalyst 42. It decreases. On the other hand, when the temperature Tc of the HC adsorption oxidation catalyst 42 is decreased, the adsorption amount of the particulate fuel is increased, but the activity of the noble metal catalyst is decreased, so that the HC oxidation amount is also decreased as shown in FIG.

That is, the temperature range of the HC adsorption oxidation catalyst 42 in which the amount of HC oxidation increases, in other words, the optimum temperature range optimal for oxidizing HC is 100 ° C. to 200 ° C. as indicated by X in FIG. It is between a lower limit temperature T ₁ between 0 ° C. and an upper limit temperature T ₂ between 300 ° C. and 400 ° C. On the other hand, Y in FIG. 15B indicates the range of the temperature Td of the NOx storage catalyst 43 in which the NOx storage amount of the NOx storage catalyst 43 is good. As can be seen from comparison with FIG. The range Y is higher than the optimum temperature range X.

  In some embodiments according to the present invention, when NOx should be released from the NOx storage catalyst 43, the temperature Tc of the HC adsorption oxidation catalyst 42 is controlled to be approximately within the optimum temperature range X. In this embodiment, when NOx should be released from the NOx storage catalyst 43, the temperature Tc of the HC adsorption oxidation catalyst 42 is controlled to be accurately within the optimum temperature range X.

Therefore, the description will be started from an embodiment in which the temperature Tc of the HC adsorption oxidation catalyst 42 is controlled to be approximately within the optimum temperature range X when NOx should be released from the NOx storage catalyst 43 next.
As described above, in order to release NOx from the NOx storage catalyst 43, it is necessary to add particulate fuel from the fuel addition valve 12 and to send exhaust gas containing the particulate fuel to the HC adsorption oxidation catalyst 42. However, when always exhaust gases leave as circulating in HC adsorbing oxidation catalyst 42 the temperature of the HC adsorbing oxidation catalyst 42 exceeds the upper limit temperature T ₂ of the optimum temperature range X.

  Therefore, in the first embodiment, as shown in FIG. 16 in the post-treatment device 40 shown in FIG. 2, during the normal operation in which the particulate fuel is not added from the fuel addition valve 12, that is, the empty twist ratio of the exhaust gas is In the lean state, the flow path switching valve device 45 causes the flow path of the exhaust gas to be a secondary flow path that bypasses the HC adsorption oxidation catalyst 42, and particulate fuel is added from the fuel addition valve 12 to release NOx from the NOx storage catalyst 43. When this is done, the flow path switching valve device 45 switches the exhaust gas flow path to the main flow path extending through the HC adsorption oxidation catalyst 42.

And exhaust flow paths are sub-passage gas exhaust gas to the upper limit temperature T ₂ temperatures below Tc the optimum temperature range X by reduction of HC -AO catalyst 42 in order not to pass through the HC adsorbing oxidation catalyst 42 Maintained. Thus the temperature Tc of the HC adsorbing oxidation catalyst 42 even when the flow path of the exhaust gas so as to release NOx from the NOx storing catalyst 43 is switched to the main passage from the auxiliary flow path and the optimum temperature range X of the upper limit temperature T ₂ less Thus, a good NOx release reduction action from the NOx storage catalyst 43 can be performed. In this case, the temperature Tc of the HC adsorption oxidation catalyst 42 may be lower than the lower limit temperature T ₁ of the optimum temperature range X. Therefore, in this embodiment, the temperature Tc of the HC adsorption oxidation catalyst 42 is approximately as described above. It is controlled to be within the optimum temperature range X.

FIG. 17 shows the NOx purification processing routine performed in step 105 of FIG. 14 in order to execute this embodiment.
Referring to FIG. 17, first, at step 200, it is judged if the NOx release flag is set. When the NOx release flag is set, the routine proceeds to step 201, where the flow path switching valve device 45 switches the exhaust gas flow path from the sub flow path to the main flow path only during the NOx release action period. Next, at step 202, the fuel amount AQ to be added is calculated from the map shown in FIG. 11B. Next, at step 203, the fuel of the amount AQ calculated from the map, that is, light oil, is added from the fuel addition valve 12. Next, at step 204, the NOx release flag is reset.

FIG. 18 shows another embodiment. Also in this embodiment, the exhaust gas flow path is switched from the sub flow path to the main flow path during the NOx releasing action as in the embodiment shown in FIG. 16, but in this embodiment, in addition to this flow path switching action, the HC adsorption oxidation catalyst When the temperature Tc of 42 becomes equal to or lower than the lower limit temperature T ₁ of the optimum temperature range X, the exhaust gas flow path is switched from the sub flow path to the main flow path. When the exhaust gas flow path is switched from the sub flow path to the main flow path, the temperature Tc of the HC adsorption oxidation catalyst 42 rises, so that the temperature Tc of the HC adsorption oxidation catalyst 42 can be maintained relatively well within the optimum temperature range X. Become.

FIG. 19 shows a NOx purification processing routine performed in step 105 of FIG. 14 in order to execute this embodiment.
Referring to FIG. 19, first, at step 210, it is judged if the NOx release flag is set. It is judged whether it is lower than the lower limit temperature T ₁ of the temperature Tc is the optimum temperature range X of the HC adsorbing oxidation catalyst 42 detected by the temperature sensor 49 proceeds to step 211 when the NOx releasing flag has not been set . When Tc <T _1, the routine proceeds to step 202 where the flow path switching valve device 45 switches the exhaust gas flow path from the sub flow path to the main flow path as long as Tc <T ₁ .

  On the other hand, when it is determined in step 210 that the NOx release flag is set, the routine proceeds to step 213, where the flow path switching valve device 45 switches the exhaust gas flow path from the sub flow path to the main flow path only during the NOx release action period. It is done. Next, at step 214, the fuel amount AQ to be added is calculated from the map shown in FIG. 11B. Next, at step 215, the fuel of the amount AQ calculated from the map, that is, light oil, is added from the fuel addition valve 12. Next, at step 216, the NOx release flag is reset.

  FIG. 20 shows still another embodiment. FIG. 20 shows a change in the engine load L in addition to the air-fuel ratio and the flow path. In this embodiment as well, as in the embodiment shown in FIG. 16, the exhaust gas flow path is switched from the sub flow path to the main flow path during the NOx releasing action. In this embodiment, in addition to this flow path switching action, the engine load L is The exhaust gas flow path is switched from the sub-flow path to the main flow path when it rapidly decreases, that is, when deceleration operation is performed.

That is, when the temperature of the HC adsorption oxidation catalyst 42 rises once and the inflow of exhaust gas to the HC adsorption oxidation catalyst 42 is stopped, the HC adsorption oxidation catalyst 42 is maintained at a high temperature, and therefore the temperature Tc of the HC adsorption oxidation catalyst 42 is maintained. May exceed the upper limit temperature T ₂ of the optimum temperature range X. On the other hand, the exhaust gas temperature is low during deceleration operation. Therefore, in this embodiment, in order to cool the HC adsorption oxidation catalyst 42 with the low temperature exhaust gas, the flow path of the exhaust gas is switched from the sub flow path to the main flow path during the deceleration operation.

FIG. 21 shows a NOx purification processing routine performed in step 105 of FIG. 14 in order to execute this embodiment.
Referring to FIG. 21, first, at step 220, it is judged if the NOx release flag is set. When the NOx release flag is not set, the routine proceeds to step 211, where it is judged if the vehicle is decelerating. When the vehicle is decelerating, the routine proceeds to step 222, where the flow path switching valve device 45 switches the exhaust gas flow path from the sub flow path to the main flow path only during the deceleration period.

  On the other hand, when it is determined in step 220 that the NOx release flag is set, the routine proceeds to step 223, where the flow path switching valve device 45 switches the exhaust gas flow path from the sub flow path to the main flow path only during the NOx release action period. It is done. Next, at step 224, the fuel amount AQ to be added is calculated from the map shown in FIG. 11B. Next, at step 225, the fuel of the amount AQ calculated from the map, that is, light oil, is added from the fuel addition valve 12. Next, at step 226, the NOx release flag is reset.

FIG. 22 shows still another embodiment. Also in this embodiment, the exhaust gas flow path is switched from the sub flow path to the main flow path during the NOx releasing action as in the embodiment shown in FIG. 16, but in this embodiment, in addition to this flow path switching action, the HC adsorption oxidation catalyst Even when the temperature Tc of 42 becomes equal to or lower than the lower limit temperature T ₁ of the optimum temperature range X, the exhaust gas passage is switched from the sub passage to the main passage, and the temperature Tc of the HC adsorption oxidation catalyst 42 is further changed to the optimum temperature range. When the deceleration operation is performed when the temperature is equal to or higher than the upper limit temperature T _{2 of} X, the flow path of the exhaust gas is switched from the sub flow path to the main flow path. That is, in this embodiment, as compared with the embodiment shown in FIGS. 20 and 21, the temperature Tc of the HC adsorption oxidation catalyst 42 is suppressed from being lowered more than necessary due to the cooling action by the low temperature exhaust gas during the deceleration operation. be able to.

FIG. 23 shows the NOx purification processing routine performed in step 105 of FIG. 14 in order to execute this embodiment.
Referring to FIG. 23, first, at step 230, it is judged if the NOx release flag is set. When NOx releasing flag has not been set or lower or not than the lower limit temperature T ₁ of the temperature Tc is the optimum temperature range X of the HC adsorbing oxidation catalyst 42 proceeds to step 231 is determined. When Tc <T _1, the routine jumps to step 234 and the flow path switching valve device 45 switches the exhaust gas flow path from the sub flow path to the main flow path only while Tc <T ₁ .

On the other hand, when it is determined in step 231 that Tc ≧ T ₁ , the routine proceeds to step 232, where it is determined whether or not the temperature Tc of the HC adsorption oxidation catalyst 42 is higher than the upper limit temperature T ₂ of the optimum temperature range X. When the tc> T ₂ whether the deceleration operation proceeds to step 232 is determined. When the vehicle is decelerating, the routine proceeds to step 234, where the flow path switching valve device 45 switches the exhaust gas flow path from the sub flow path to the main flow path only during the deceleration period.

  On the other hand, when it is determined at step 230 that the NOx release flag is set, the routine proceeds to step 235, where the flow path switching valve device 45 switches the exhaust gas flow path from the sub flow path to the main flow path only during the NOx release action period. It is done. Next, at step 236, the fuel amount AQ to be added is calculated from the map shown in FIG. 11B. Next, at step 237, the fuel of the amount AQ calculated from the map, that is, light oil, is added from the fuel addition valve 12. Next, at step 238, the NOx release flag is reset.

  24 to 26 show modifications of the post-processing device 40 shown in FIG. In the modification shown in FIG. 24, the main exhaust pipe 41 is divided into two passages 52, 53 that are arranged in parallel by a partition wall 51, and the HC adsorption oxidation catalyst 42 is arranged in one passage 52. As shown in FIG. 24, the passage 52 forms a main flow path, and the other passage 53 forms a sub flow path. Further, in this modification, the exhaust control valve 54 of the flow path switching valve device 45 is disposed at the junction of both the passages 52 and 53 downstream of the HC adsorption oxidation catalyst 42. The exhaust control valve 54 is switched to a position indicated by a solid line or a position indicated by a broken line, whereby the exhaust gas flow path is switched to either the main flow path or the sub flow path.

  In the modification shown in FIG. 25, the bypass pipe 55 is branched from the main exhaust pipe 41 upstream of the HC adsorption oxidation catalyst 42, and the branched bypass pipe 55 is joined again to the main exhaust pipe 41 downstream of the branch portion. An exhaust control valve 56 of the flow path switching valve device 45 is disposed in the main exhaust pipe 41 between the branch portion and the junction portion of the bypass pipe 55. When the exhaust control valve 56 is fully opened, the main exhaust pipe 41 forms a main flow path, and when the exhaust control valve 56 is closed, the bypass pipe 55 forms a sub flow path.

  That is, in this embodiment, the exhaust gas flow path is constituted by a main flow path that goes into the HC adsorption oxidation catalyst 42 and a sub flow path that reaches the HC adsorption oxidation catalyst 42 through a flow path longer than the main flow path. The exhaust control valve 56 switches the exhaust gas flow path to either the main flow path or the sub flow path. When the exhaust gas is circulated in the sub-flow channel, the exhaust gas temperature is lowered while the exhaust gas is circulated, and thus the relatively low temperature exhaust gas flows into the HC adsorption oxidation catalyst 42.

  In the modification shown in FIGS. 24 and 25, the switching action of the exhaust gas flow path is performed using any one of the NOx purification processing routines shown in FIG. 17, FIG. 19, FIG.

  26, in addition to the bypass passage 44 that bypasses the HC adsorption oxidation catalyst 42, a second bypass passage 57 that bypasses the NOx storage catalyst 43 is further provided. The second bypass passage 57 and the NOx storage are provided. Exhaust control valves 58 and 59 are arranged at the inlet of the catalyst 43, respectively. In this embodiment, the normal exhaust control valve 58 is closed and the exhaust control valve 59 is open. At this time, the exhaust control valves 46 and 47 are controlled to open and close so that the flow path of the exhaust gas becomes the main flow path or the sub flow path. It is switched to either one of the flow paths. Further, the exhaust control valve 46 and the exhaust control valve 58 are opened, and the exhaust control valve 59 is closed, thereby forming a cooling flow path that bypasses the NOx storage catalyst 43 after extending through the HC adsorption oxidation catalyst 42. The

As shown in FIG. 27, in this embodiment, the exhaust gas flow path is switched to the main flow path, the sub flow path, or the cooling flow path. That is, when NOx is released and when the temperature Tc of the HC adsorption oxidation catalyst 42 becomes lower than the lower limit temperature T ₁ of the optimum temperature range X, the exhaust gas flow path is switched from the sub flow path to the main flow path. On the other hand, when the deceleration operation is performed, in the embodiment shown in FIG. 27, if the temperature Tc of the HC adsorption oxidation catalyst 42 is higher than the upper limit temperature T ₂ of the optimum temperature range X, the exhaust gas flow path becomes the cooling flow path. Is switched to.

  When the exhaust gas flow path is switched to the cooling flow path, the HC adsorption oxidation catalyst 42 is cooled by the low temperature exhaust gas. At this time, however, the low-temperature exhaust gas bypasses the NOx storage catalyst 43, so that the NOx storage catalyst 43 is kept at a high temperature. Therefore, as can be seen from FIG. 15B, the NOx storage catalyst 43 maintains a high NOx storage amount. Can do.

FIG. 28 shows a NOx purification processing routine performed in step 105 of FIG. 14 in order to execute this embodiment.
Referring to FIG. 28, first, at step 240, it is judged if the NOx release flag is set. When NOx releasing flag has not been set or lower or not than the lower limit temperature T ₁ of the temperature Tc is the optimum temperature range X of the HC adsorbing oxidation catalyst 42 proceeds to step 241 is determined. When Tc <T _1, the routine proceeds to step 242 where the flow path switching valve device 45 switches the exhaust gas flow path from the sub flow path to the main flow path as long as Tc <T ₁ .

On the other hand, when it is judged at step 241 that Tc ≧ T ₁ , the routine proceeds to step 243, where it is judged if the temperature Tc of the HC adsorption oxidation catalyst 42 is higher than the upper limit temperature T ₂ of the optimum temperature range X. When the tc> T ₂ whether the deceleration operation proceeds to step 244 is determined. When it is during deceleration operation, the routine proceeds to step 245, where the flow path switching valve device 45 switches the flow path of the exhaust gas from the sub flow path to the cooling flow path only during the deceleration period.

  On the other hand, when it is determined in step 240 that the NOx release flag is set, the routine proceeds to step 246, where the flow path switching valve device 45 switches the exhaust gas flow path from the sub flow path to the main flow path only during the NOx release action period. It is done. Next, at step 247, the fuel amount AQ to be added is calculated from the map shown in FIG. 11B, and then at step 248, the fuel of the amount AQ calculated from the map, that is, light oil, is added from the fuel addition valve 12. Next, at step 249, the NOx release flag is reset.

  FIG. 29 shows another type of post-processing device 40, and FIGS. 30 and 31 show modifications of the post-processing device 40, respectively. These post-treatment devices 40 have a common point in that they comprise a first adsorption oxidation catalyst 42a and a second adsorption oxidation catalyst 42b in which HC adsorption oxidation catalysts are arranged in parallel, and the flow path of the exhaust gas is the first. The first flow path extending inside the HC adsorption oxidation catalyst 42a and the second flow path extending inside the second HC adsorption oxidation catalyst 42b are formed, and the flow path switching valve device 45 changes the flow path of the exhaust gas to the first flow path or the first flow path. It is switched to either one of the two flow paths, and temperature sensors 49a and 49b are attached to the HC adsorption oxidation catalysts 42a and 42b, respectively.

  Next, each post-treatment device will be described more specifically. In the post-treatment device 40 shown in FIG. 29, the exhaust passage from the outlet of the exhaust pipe 11 to the NOx storage catalyst 43 forms a first flow path. The exhaust passage is divided into a passage 80 and a second passage 81 forming a second flow path. An exhaust control valve 46 and a first HC adsorption oxidation catalyst 42a are disposed in the first passage 80, and An exhaust control valve 47 and a second HC adsorption oxidation catalyst 42b are disposed in the two passages 81.

  Further, in the aftertreatment device 40 shown in FIG. 30, the exhaust passage from the outlet of the exhaust pipe 11 to the NOx storage catalyst 43 forms a first passage 83 and a second passage that form a first passage by the partition wall 82. The exhaust control valve 46 and the first HC adsorption oxidation catalyst 42a are disposed in the first passage 83, and the exhaust control valve is disposed in the second passage 84. 47 and the second HC adsorption oxidation catalyst 42b are arranged.

  On the other hand, in the aftertreatment device 40 shown in FIG. 31, the exhaust passage extending downstream from the outlet of the exhaust pipe 11 forms the first passage 85 forming the first passage and the second passage forming the second passage. The exhaust control valve 46, the first HC adsorption oxidation catalyst 42 a, and the first NOx storage catalyst 43 a are disposed in the first passage 85, and the second passage 86 has the second passage 86. An exhaust control valve 47, a second HC adsorption oxidation catalyst 42b, and a second NOx storage catalyst 43b are arranged. In this modification, differential pressure sensors 50a and 50b are attached to the NOx storage catalysts 43a and 43b, respectively.

In the aftertreatment device 40 shown in FIG. 29 to FIG. 31, the exhaust gas always flows through one of the HC adsorption oxidation catalysts 42a or 42b. In the embodiment shown in FIG. 32, the exhaust gas is exhausted when the temperature Tc ₁ of the first HC adsorption oxidation catalyst 42a becomes equal to or higher than the upper limit temperature T ₂ of the optimum temperature range X when the exhaust gas flows in the first flow path. When the gas flow path is switched from the first flow path to the second flow path, and the exhaust gas flows through the second flow path, the temperature Tc ₂ of the second HC adsorption oxidation catalyst 42b is within the optimum temperature range X. It is switched to the first flow path flow path of the exhaust gas from the second flow path when it is the upper limit temperature T ₂ above.

  When such a channel switching operation is performed, the temperature of the HC adsorption oxidation catalyst in the channel through which exhaust gas flows is within the optimum temperature range X, as shown in FIG. Even if it performs, a favorable rich air fuel ratio can be formed.

FIG. 33 shows the NOx purification processing routine performed in step 105 of FIG. 14 in order to execute this embodiment.
Referring to FIG. 33, first, at step 200, it is judged if the exhaust gas flow path is the first flow path. When the exhaust gas flow path is the first flow path, the routine proceeds to step 201, where it is determined whether or not the temperature Tc ₁ of the first HC adsorption oxidation catalyst 42a has become equal to or higher than the upper limit temperature T ₂ of the optimum temperature range X. . When Tc ₁ ≦ T _2, the routine jumps to step 205. On the other hand, when Tc ₁ > T ₂ , the routine proceeds to step 202 where the exhaust gas flow path is switched from the first flow path to the second flow path, and then proceeds to step 205.

On the other hand, when it is determined in step 200 that the exhaust gas passage is not the first passage, the routine proceeds to step 203 where the temperature Tc ₂ of the second HC adsorption oxidation catalyst 42b becomes equal to or higher than the upper limit temperature T ₂ of the optimum temperature range X. It is determined whether or not. When Tc ₂ ≦ T _2, the routine jumps to step 205. On the other hand, when Tc ₂ > T ₂ , the routine proceeds to step 204 where the exhaust gas flow path is switched from the second flow path to the first flow path, and then proceeds to step 205.

  In step 205, it is determined whether or not a NOx release flag is set. When the NOx release flag is set, the routine proceeds to step 206, where the fuel amount AQ to be added is calculated from the map shown in FIG. 11B, and then at step 207, the amount of fuel AQ calculated from the map, that is, light oil, is calculated. It is added from the fuel addition valve 12. Next, at step 208, the NOx release flag is reset.

FIG. 34 shows another embodiment. In this embodiment, the flow path switching action similar to that of the embodiment shown in FIG. 32 is performed. In this embodiment, in addition to the flow path switching action, the exhaust gas is flowing in the first flow path, and the second HC. is switched to the second flow path flow path of the exhaust gas from the first flow path when the deceleration operation when the upper limit temperature T ₂ above the temperature Tc ₂ is the optimum temperature range X of -AO catalyst 42b is performed, the exhaust gas flow channel second flow of exhaust gas when but the deceleration operation is performed when the temperature is an upper limit temperature T ₂ above the optimum temperature range X of the first HC -AO catalyst 42a by flowing a second flow path The path is switched to the first flow path.

That is, for example, when the temperature Tc _{1 of} the first HC adsorption oxidation catalyst 42 a exceeds the upper limit temperature T ₂ of the optimum temperature range X, the flow path of the exhaust gas is switched from the first flow path to the second flow path. The first HC adsorption oxidation catalyst 42a may continue to be at a high temperature. Therefore, when the deceleration operation is performed in such a case, the low-temperature exhaust gas is sent to the first flow path during the deceleration period to decrease the temperature Tc ₁ of the first HC adsorption oxidation catalyst 42a.

FIG. 35 shows the NOx purification processing routine performed in step 105 of FIG. 14 in order to execute this embodiment.
Referring to FIG. 35, first, at step 210, it is judged if the exhaust gas flow path is the first flow path. When the exhaust gas flow path is the first flow path, the routine proceeds to step 211, where it is determined whether or not the temperature Tc ₁ of the first HC adsorption oxidation catalyst 42a has become equal to or higher than the upper limit temperature T ₂ of the optimum temperature range X. . If it is determined at this time that Tc ₁ > T ₂ , the routine proceeds to step 212 where the flow path of the exhaust gas is switched from the first flow path to the second flow path, and then the routine proceeds to step 221.

On the other hand, when it is determined in step 211 that Tc ₁ ≦ T ₂ , the routine proceeds to step 213, where the temperature Tc _{2 of} the second HC adsorption oxidation catalyst 42b in which the circulation of the exhaust gas is stopped is the optimum temperature range X. or not if it is the upper limit temperature T ₂ or more is discriminated. When Tc ₂ ≦ T _2, the routine jumps to step 221. On the other hand, when Tc ₂ > T ₂ , the routine proceeds to step 214 where it is judged if the vehicle is decelerating. When the vehicle is not decelerating, the process proceeds to step 221. On the other hand, when the deceleration operation is being performed, the routine proceeds to step 215, where the exhaust gas flow path is switched from the first flow path to the second flow path during the deceleration operation.

On the other hand, when it is determined in step 210 that the exhaust gas passage is not the first passage, the routine proceeds to step 216, where the temperature Tc ₂ of the second HC adsorption oxidation catalyst 42b becomes equal to or higher than the upper limit temperature T ₂ of the optimum temperature range X. It is determined whether or not. If it is determined at this time that Tc ₂ > T ₂ , the routine proceeds to step 217, where the exhaust gas flow path is switched from the second flow path to the first flow path, and then proceeds to step 221.

On the other hand, when it is determined in step 216 that Tc ₂ ≦ T ₂ , the routine proceeds to step 218, where the temperature Tc _{1 of} the first HC adsorption oxidation catalyst 42a in which the flow of exhaust gas is stopped is the optimum temperature range X. or not if it is the upper limit temperature T ₂ or more is discriminated. When Tc ₁ ≦ T _2, the routine jumps to step 221. On the other hand, when Tc ₁ > T ₂ , the routine proceeds to step 219, where it is judged if the vehicle is decelerating. When the vehicle is not decelerating, the process proceeds to step 221. On the other hand, when the vehicle is decelerating, the routine proceeds to step 220 where the exhaust gas flow path is switched from the second flow path to the first flow path during the deceleration operation.

  In step 221, it is determined whether or not a NOx release flag is set. When the NOx release flag is set, the routine proceeds to step 222, where the fuel amount AQ to be added is calculated from the map shown in FIG. 11B, and then at step 223, the amount of fuel AQ calculated from the map, that is, light oil, is calculated. It is added from the fuel addition valve 12. Next, at step 224, the NOx release flag is reset.

  FIG. 36 shows still another type of post-processing device 40, and FIG. 37 shows a modification of the post-processing device 40. As shown in FIGS. 36 and 37, these aftertreatment devices 40 are provided with a bypass passage 90 that branches from the main exhaust pipe 41 and returns to the branched position, and the bypass passage 90 and the main exhaust pipe 41 are connected to each other. A flow path switching valve 92 of the flow path switching valve device 45 is disposed at the junction.

  In the aftertreatment device 40 shown in FIG. 36, the HC adsorption oxidation catalyst 42 and the NOx storage catalyst 43 are disposed in the bypass passage 90, and the flow direction of the exhaust gas is changed by the switching action of the flow path switching valve 92 so that the exhaust gas is HC. The flow direction is switched between the forward flow direction that flows into the NOx storage catalyst 43 after passing through the adsorption oxidation catalyst 42 and the reverse flow direction in which the exhaust gas flows into the HC adsorption oxidation catalyst 42 after passing through the NOx storage catalyst 43.

  On the other hand, in the aftertreatment device 40 shown in FIG. 37, the first HC adsorption oxidation catalyst 42a, the NOx occlusion catalyst 43, and the second HC adsorption oxidation catalyst 42b are arranged in this order in the bypass passage 90. Due to the switching action of the switching valve 92, the flow direction of the exhaust gas is the forward flow direction in which the exhaust gas flows into the second HC adsorption oxidation catalyst 42b after passing through the NOx storage catalyst 43 following the first HC adsorption oxidation catalyst 42a. Then, after the exhaust gas passes through the NOx storage catalyst 43 following the second HC adsorption oxidation catalyst 42b, the exhaust gas is switched to one of the reverse flow directions flowing into the first HC adsorption oxidation catalyst 42a. 36 and 37, the position of the flow path switching valve 92 when the exhaust gas flow direction becomes the forward flow direction is shown by a solid line, and the flow path when the exhaust gas flow direction becomes the reverse flow direction. The position of the switching valve 92 is indicated by a broken line.

FIG. 38 shows an embodiment of the NOx purification processing method for the post-processing device 40 shown in FIG. Referring to FIG. 38, in this embodiment, when the flow direction of the exhaust gas is the forward flow direction, the flow direction of the exhaust gas when the temperature Tc of the HC adsorption oxidation catalyst 42 becomes equal to or higher than the upper limit temperature T ₂ of the optimum temperature range X. Is switched from the forward flow direction to the reverse flow direction, and when the temperature Tc of the HC adsorption oxidation catalyst 42 falls below the lower limit temperature T ₁ of the optimum temperature range X when the exhaust gas flow direction is the reverse flow direction, the flow direction of the exhaust gas Is switched from the reverse flow direction to the forward flow direction.

  When the flow direction of the exhaust gas is switched to the reverse flow direction, the HC adsorption oxidation catalyst 42 located downstream of the NOx storage catalyst 43 functions as a sweeper that adsorbs HC that has passed through the NOx storage catalyst 43. End. Further, in this NOx purification processing method, as can be seen from FIG. 38, the air-fuel ratio is made rich only when the exhaust gas flow direction is the forward flow direction, and the NOx releasing action is performed.

FIG. 39 shows a NOx purification processing routine performed in step 105 of FIG. 14 in order to execute this embodiment.
Referring to FIG. 39, first, at step 300, it is judged if the flow direction of the exhaust gas is the forward flow direction. The flow direction of the exhaust gas is whether it is the upper limit temperature T ₂ above the temperature Tc of the HC adsorbing oxidation catalyst 42 proceeds to step 301 of the optimum temperature range X when a forward flow direction is determined. When the tc ≦ T ₂ jumps to step 305. In contrast Tc> T ₂ to become the flow direction of the exhaust gas proceeds to step 302 is switched from the forward flow direction in the backflow direction.

In contrast, whether the direction of flow of the exhaust gas in step 300 is equal to or less than the lower limit temperature T ₁ of the temperature Tc is the optimum temperature range X of the HC adsorbing oxidation catalyst 42 proceeds to step 303, when it is determined not to be a forward flow direction Is determined. The time Tc <is the the flow direction of the exhaust gas proceeds to step 304 determines that becomes T ₁ is switched from reverse flow direction in the forward flow direction.

  In step 305, it is determined whether or not a NOx release flag is set. When the NOx release flag is set, the routine proceeds to step 306, where the fuel amount AQ to be added is calculated from the map shown in FIG. 11B, and then at step 307, the amount of fuel AQ calculated from the map, that is, light oil, is calculated. It is added from the fuel addition valve 12. Next, at step 308, the NOx release flag is reset.

FIG. 40 shows an embodiment of the NOx purification processing method for the post-processing device 40 shown in FIG. Referring to FIG. 40, in this embodiment, when the flow direction of the exhaust gas is the forward flow direction, when the temperature Tc ₁ of the first HC adsorption oxidation catalyst 42a becomes equal to or higher than the upper limit temperature T ₂ of the optimum temperature range X, the exhaust gas is exhausted. When the gas flow direction is switched from the forward flow direction to the reverse flow direction and the exhaust gas flow direction is the reverse flow direction, the temperature Tc ₂ of the second HC adsorption oxidation catalyst 42b becomes equal to or higher than the upper limit temperature T ₂ of the optimum temperature range X. When this happens, the flow direction of the exhaust gas is switched from the reverse flow direction to the forward flow direction.

FIG. 41 shows the NOx purification processing routine performed in step 105 of FIG. 14 in order to execute this embodiment.
Referring to FIG. 41, first, at step 310, it is judged if the flow direction of the exhaust gas is the forward flow direction. When the flow direction of the exhaust gas is the forward flow direction, the routine proceeds to step 311 where it is determined whether or not the temperature Tc ₁ of the first HC adsorption oxidation catalyst 42a has become equal to or higher than the upper limit temperature T ₂ of the optimum temperature range X. When Tc ₁ ≦ T _2, the routine jumps to step 315. On the other hand, when Tc ₁ > T ₂ , the routine proceeds to step 312 where the flow direction of the exhaust gas is switched from the forward flow direction to the reverse flow direction, and then proceeds to step 315.

On the other hand, when it is determined in step 310 that the exhaust gas flow direction is not the forward flow direction, the routine proceeds to step 313, where the temperature Tc ₂ of the second HC adsorption oxidation catalyst 42b becomes equal to or higher than the upper limit temperature T ₂ of the optimum temperature range X. It is determined whether or not. When Tc ₂ ≦ T _2, the routine jumps to step 315. On the other hand, when Tc ₂ > T ₂ , the routine proceeds to step 314 where the flow direction of the exhaust gas is switched from the reverse flow direction to the forward flow direction, and then proceeds to step 315.

  In step 315, it is determined whether or not a NOx release flag is set. When the NOx release flag is set, the routine proceeds to step 316, where the fuel amount AQ to be added is calculated from the map shown in FIG. 11B, and then at step 317, the amount of fuel AQ calculated from the map, that is, light oil, is calculated. It is added from the fuel addition valve 12. Next, at step 318, the NOx release flag is reset.

1 is an overall view of a compression ignition type internal combustion engine. It is an enlarged view of the post-processing apparatus shown by FIG. It is a figure which shows the structure of a particulate filter. It is sectional drawing of the surface part of the catalyst support | carrier of a NOx storage catalyst. It is side surface sectional drawing of HC adsorption oxidation catalyst. It is sectional drawing of the surface part of the catalyst support | carrier of HC adsorption oxidation catalyst. It is a figure which shows the amount of fuel adsorption. It is a figure which shows the change of the air fuel ratio of exhaust gas. It is a figure which shows the relationship between fuel addition time and the air-fuel ratio A / F of exhaust gas, temperature rise amount (DELTA) T, exhausted HC amount G, and rich time Tr. It is a figure which shows the change of the air fuel ratio of exhaust gas. It is a figure which shows the fuel addition amount. It is a figure which shows NOx discharge | release control. It is a figure which shows the map etc. of occlusion NOx amount NOXA. It is a flowchart for performing exhaust gas purification processing. It is a figure which shows HC oxidation amount and NOx occlusion amount. It is a figure for demonstrating the NOx purification processing method. It is a flowchart for performing the NOx purification processing method shown by FIG. It is a figure for demonstrating the NOx purification processing method. It is a flowchart for performing the NOx purification processing method shown by FIG. It is a figure for demonstrating the NOx purification processing method. FIG. 21 is a flowchart for executing the NOx purification processing method shown in FIG. 20. FIG. It is a figure for demonstrating the NOx purification processing method. It is a flowchart for performing the NOx purification processing method shown by FIG. It is a figure which shows the modification of the post-processing apparatus shown by FIG. It is a figure which shows the modification of the post-processing apparatus shown by FIG. It is a figure which shows the modification of the post-processing apparatus shown by FIG. It is a figure for demonstrating the NOx purification processing method. It is a flowchart for performing the NOx purification processing method shown in FIG. It is a figure which shows another type of post-processing apparatus. It is a figure which shows the modification of the post-processing apparatus shown by FIG. It is a figure which shows the modification of the post-processing apparatus shown by FIG. It is a figure for demonstrating the NOx purification processing method. It is a flowchart for performing the NOx purification processing method shown by FIG. It is a figure for demonstrating the NOx purification processing method. FIG. 35 is a flowchart for executing the NOx purification processing method shown in FIG. 34. FIG. It is a figure which shows another type of post-processing apparatus. It is a figure which shows the modification of the post-processing apparatus shown by FIG. It is a figure for demonstrating the NOx purification processing method. It is a flowchart for performing the NOx purification processing method shown by FIG. It is a figure for demonstrating the NOx purification processing method. It is a flowchart for performing the NOx purification processing method shown by FIG.

Explanation of symbols

2 Combustion chamber 3 Fuel injection valve 11 Exhaust pipe 12 Fuel addition valve 42 HC adsorption oxidation catalyst 43 NOx occlusion catalyst 45 Flow path switching valve device

Claims (18)

  Fuel addition means for adding particulate fuel into the exhaust gas, and an HC adsorption oxidation catalyst that is disposed in the engine exhaust passage downstream of the fuel addition means and that adsorbs and oxidizes hydrocarbons contained in the exhaust gas And when the air-fuel ratio of the exhaust gas that is disposed and flows into the engine exhaust passage downstream of the HC adsorption oxidation catalyst is lean, the air-fuel ratio of the exhaust gas that stores and flows in NOx contained in the exhaust gas is the stoichiometric air-fuel ratio or A NOx occlusion catalyst that releases NOx occluded when it becomes rich, and when NOx should be released from the NOx occlusion catalyst, the particulate fuel added by adding the particulate fuel from the fuel addition means is adsorbed to the HC By sending it to the oxidation catalyst, the air-fuel ratio of the exhaust gas flowing into the NOx storage catalyst is made rich, and at this time, the temperature of the HC adsorption oxidation catalyst is used to oxidize HC. The amount of particulate fuel added from the fuel addition means at this time is controlled so as to be within an appropriate predetermined optimum temperature range, and the air-fuel ratio of the exhaust gas flowing into the HC adsorption oxidation catalyst is NOx. The amount is set to a rich air-fuel ratio smaller than the rich air-fuel ratio flowing into the storage catalyst, and the added particulate fuel is adsorbed by the HC adsorption oxidation catalyst, and most of the adsorbed fuel is adsorbed by HC. The air-fuel ratio of the exhaust gas flowing into the NOx storage catalyst is made rich for a longer time than the time during which the air-fuel ratio of the exhaust gas that is oxidized in the oxidation catalyst and flows into the HC adsorption oxidation catalyst is made rich. Exhaust gas purification device for compression ignition type internal combustion engine.   The amount of particulate fuel added from the fuel addition means for releasing NOx from the NOx storage catalyst during engine low speed low load operation is such that the air-fuel ratio of the exhaust gas flowing into the HC adsorption oxidation catalyst is approximately 1 to approximately 7 The exhaust gas purification apparatus for a compression ignition type internal combustion engine according to claim 1, wherein the exhaust gas purification apparatus is set to an amount of   The exhaust purification device for a compression ignition type internal combustion engine according to claim 1, wherein the NOx storage catalyst is supported on a particulate filter for capturing and oxidizing particulate matter contained in the exhaust gas.   2. An exhaust emission control device for a compression ignition type internal combustion engine according to claim 1, wherein the temperature of the HC adsorption oxidation catalyst is controlled within the optimum temperature range by changing a flow path of exhaust gas flowing in the engine exhaust passage.   The exhaust gas flow path is constituted by a main flow path toward the HC adsorption oxidation catalyst and a sub flow path that bypasses the HC adsorption oxidation catalyst or passes through a flow path longer than the main flow path and reaches the HC adsorption oxidation catalyst. The exhaust gas purification apparatus for a compression ignition type internal combustion engine according to claim 4, further comprising a flow path switching valve device for switching the flow path of the exhaust gas to either the main flow path or the sub flow path.   During normal operation when the particulate fuel is not added by the fuel addition means, the exhaust gas flow path is a sub-flow path, and when the particulate fuel is added by the fuel addition means, the exhaust gas flow path is the main flow path. 6. An exhaust emission control device for a compression ignition type internal combustion engine according to claim 5, wherein   The exhaust gas purification apparatus for a compression ignition type internal combustion engine according to claim 6, wherein the flow path of the exhaust gas is switched to the main flow path when the temperature of the HC adsorption oxidation catalyst falls below the optimum temperature range during the normal operation.   The exhaust gas purification apparatus for a compression ignition internal combustion engine according to claim 6, wherein when the deceleration operation is performed during the normal operation, the flow path of the exhaust gas is switched to the main flow path.   The compression ignition type internal combustion engine according to claim 6, wherein when the deceleration operation is performed during the normal operation, the flow path of the exhaust gas is switched to the main flow path when the temperature of the HC adsorption oxidation catalyst is equal to or higher than the optimum temperature range. Exhaust purification device.   In addition to the main flow channel and the sub flow channel, an exhaust gas flow channel is provided with a cooling flow channel that extends through the HC adsorption oxidation catalyst and then bypasses the NOx storage catalyst. During normal operation when no action is taken, the exhaust gas flow path is set as a sub-flow path, and when particulate fuel is added by the fuel addition means, the exhaust gas flow path is switched to the main flow path. 6. The exhaust gas purification apparatus for a compression ignition internal combustion engine according to claim 5, wherein when the deceleration operation is performed, the exhaust gas flow path is switched to the cooling flow path.   The first adsorbing oxidation catalyst and the second adsorbing oxidation catalyst in which the HC adsorbing oxidation catalyst is arranged in parallel, and the exhaust gas flow path extending in the first HC adsorbing oxidation catalyst and the second HC. 5. A flow path switching valve device for switching an exhaust gas flow path to either the first flow path or the second flow path, comprising a second flow path extending through the adsorption oxidation catalyst. An exhaust emission control device for a compression ignition type internal combustion engine.   When the temperature of the first HC adsorption oxidation catalyst exceeds the optimum temperature range when the exhaust gas is flowing in the first flow path, the flow path of the exhaust gas is switched from the first flow path to the second flow path. When the temperature of the second HC adsorption oxidation catalyst becomes equal to or higher than the optimum temperature range when the exhaust gas is flowing in the second flow path, the flow path of the exhaust gas is changed from the second flow path to the first flow path. The exhaust gas purification apparatus for a compression ignition type internal combustion engine according to claim 11, wherein   When exhaust gas is flowing in the first flow path and the temperature of the second HC adsorption oxidation catalyst is equal to or higher than the optimum temperature range, when the deceleration operation is performed, the flow path of the exhaust gas is changed from the first flow path to the second flow path. When the decelerating operation is performed when the exhaust gas is flowing in the second flow path and the temperature of the first HC adsorption oxidation catalyst is equal to or higher than the optimum temperature range, the flow path of the exhaust gas is changed to the flow path. The exhaust gas purification apparatus for a compression ignition internal combustion engine according to claim 11, wherein the exhaust gas purification apparatus is switched from two flow paths to the first flow path.   2. An exhaust emission control device for a compression ignition type internal combustion engine according to claim 1, wherein the temperature of the HC adsorption oxidation catalyst is controlled within the optimum temperature range by changing the flow direction of the exhaust gas flowing in the engine exhaust passage.   The exhaust gas flow direction is either a forward flow direction in which the exhaust gas flows into the NOx storage catalyst after passing through the HC adsorption oxidation catalyst, or a reverse flow direction in which the exhaust gas flows into the HC adsorption oxidation catalyst after passing through the NOx storage catalyst. The exhaust gas purification device for a compression ignition type internal combustion engine according to claim 14, further comprising a flow direction switching valve device for switching to one side.   When the exhaust gas flow direction is the forward flow direction and the temperature of the HC adsorption oxidation catalyst exceeds the optimum temperature range, the exhaust gas flow direction is switched from the forward flow direction to the reverse flow direction, and the exhaust gas flow direction is the reverse flow direction. 16. The exhaust gas purification apparatus for a compression ignition type internal combustion engine according to claim 15, wherein the flow direction of the exhaust gas is switched from the reverse flow direction to the forward flow direction when the temperature of the HC adsorption oxidation catalyst becomes equal to or lower than the optimum temperature range. .   The HC adsorption catalyst comprises a first HC adsorption oxidation catalyst and a second HC adsorption oxidation catalyst, and the exhaust gas flows in the direction of flow after the exhaust gas passes through the NOx storage catalyst following the first HC adsorption oxidation catalyst. In the forward flow direction flowing into the second HC adsorption oxidation catalyst, and the reverse flow direction in which the exhaust gas flows into the first HC adsorption oxidation catalyst after passing through the NOx storage catalyst following the second HC adsorption oxidation catalyst. The exhaust gas purification device for a compression ignition type internal combustion engine according to claim 14, further comprising a flow direction switching valve device for switching.   When the flow direction of the exhaust gas is the forward flow direction and the temperature of the first HC adsorption oxidation catalyst exceeds the optimum temperature range, the flow direction of the exhaust gas is switched from the forward flow direction to the reverse flow direction. 18. The compression ignition type according to claim 17, wherein when the direction is the reverse flow direction and the temperature of the second HC adsorption oxidation catalyst is equal to or higher than the optimum temperature range, the flow direction of the exhaust gas is switched from the reverse flow direction to the forward flow direction. An exhaust purification device for an internal combustion engine.

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