JP2008232055A - Exhaust emission control system for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To change direction of flow of exhaust gas flowing in a NOx selective reduction catalyst and a particulate filter according to demand. <P>SOLUTION: An oxidation catalyst 12 is provided in an engine exhaust gas passage and a change over valve device 13 is provided on an outlet of the oxidation catalyst 12. Flow direction of exhaust gas can be changed over to first flow I flowing into the particulate filter 1 after flowing out of the NOx selective reduction catalyst 15 and second flow II flowing in the NOx selective reduction catalyst 15 after flowing out of the particulate filter 16 by changing over action of the change over valve device 13. Flow is changed over to either of the first flow I or the second flow II according to demand on the NOx selective reduction catalyst 15 and the particulate filter 16. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

Engine exhaust passage an oxidation catalyst in this order from the upstream side in the particulate filter, the internal combustion engine arranged to _the NO _x selective reduction catalyst are known (e.g., see Patent Document 1). In this internal combustion engine, when the amount of particulate matter collected on the particulate filter exceeds the allowable amount, the amount of HC supplied to the oxidation catalyst is increased, and at this time, the oxidation reaction heat generated in the oxidation catalyst The temperature of the particulate filter is raised to burn the particulate matter on the particulate filter, thereby regenerating the particulate filter.
JP 2005-140111 A

By the way, in this internal combustion engine, for example, when the amount of HC supplied to the oxidation catalyst is increased in order to warm up the NO _x selective reduction catalyst at the time of engine startup, the internal combustion engine has a particulate filter in the middle. However, the temperature of the NO _x selective reduction catalyst does not rise easily, so it is difficult to warm up the NO _x selective reduction catalyst early.

Thus, in this internal combustion engine, there is a requirement that the particulate filter must be raised to a temperature necessary for regeneration, for example, and that the NO _x selective reduction catalyst must be warmed up early, for example. There is a request. However, this internal combustion engine has a problem that it cannot properly cope with each requirement for the NO _x selective reduction catalyst and the particulate filter.

In order to solve the above problem, according to the present invention, an oxidation catalyst is disposed in an engine exhaust passage, and an outlet of the oxidation catalyst is connected to an exhaust passage portion whose flow direction can be switched via a switching valve device. A NO _x selective reduction catalyst capable of selectively reducing NO _x with ammonia in the part and a particulate filter for collecting particulate matter are arranged in series, and the flow of exhaust gas in the exhaust passage part is switched. can be switched to the second flow that flows through the flow after _the NO _x selective reduction catalyst the first flow and a particulate filter that flows through the flow after the particulate filter and _the NO _x selective reduction catalyst by the switching action of the valve device, Switching between the first flow and the second flow is made according to the demand for the NO _x selective reduction catalyst and the particulate filter.

The demand for the NO _x selective reduction catalyst and the particulate filter can be appropriately dealt with.

FIG. 1 shows an overall view of a compression ignition type internal combustion engine.
Referring to FIG. 1, 1 is an engine body, 2 is a combustion chamber of each cylinder, 3 is an electronically controlled fuel injection valve for injecting fuel into each combustion chamber 2, 4 is an intake manifold, and 5 is an exhaust manifold. Respectively. The intake manifold 4 is connected to the outlet of the compressor 7 a of the exhaust turbocharger 7 via the intake duct 6, and the inlet of the compressor 7 a is connected to the air cleaner 9 via the intake air amount detector 8. A throttle valve 10 driven by a step motor is disposed in the intake duct 6, and a cooling device 11 for cooling intake air flowing through the intake duct 6 is disposed around the intake duct 6. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 11, and the intake air is cooled by the engine cooling water.

On the other hand, the exhaust manifold 5 is connected to the inlet of the exhaust turbine 7 b of the exhaust turbocharger 7. The outlet of the exhaust turbine 7 b is connected to the inlet of the oxidation catalyst 12. The outlet of the oxidation catalyst 12 is connected to an exhaust passage portion 14 whose flow direction can be switched via a switching valve device 13. An NO _x selective reduction catalyst 15 capable of selectively reducing NO _x with ammonia and a particulate filter 16 for collecting particulate matter are arranged in series in the exhaust passage portion 14.

  More specifically, a switching valve 18 driven by an actuator 17 is disposed at the outlet of the oxidation catalyst 12, and a discharge port 19 is formed on the opposite side of the switching valve 18 from the outlet of the oxidation catalyst 12. The discharge port 19 is connected to an oxidation catalyst 21 through an exhaust pipe 20. On the other hand, on both sides of the switching valve 18, a first outflow inlet 22 that is one end of the exhaust passage portion 14 and a second outflow inlet 23 that is the other end of the exhaust passage portion 14 are disposed facing each other. Yes.

When the switching valve 18 is in the first position shown by the solid line in FIG. 1, the exhaust gas that has flowed through the oxidation catalyst 12 flows into the exhaust passage portion 22 from the first outlet / inlet 22, and the NO _x selective reduction catalyst 15. Then, it flows through the particulate filter 16 and flows into the discharge port 19 from the second outlet 23 and then flows into the oxidation catalyst 21 through the exhaust pipe 20.

On the other hand, when the switching valve 18 is in the second position indicated by the broken line in FIG. 1, the exhaust gas that has flowed through the oxidation catalyst 12 flows into the exhaust passage portion 22 from the second outlet / inlet 23, and the particulate filter 16. Then, the gas flows through the NO _x selective reduction catalyst 15 and flows from the first outlet 22 into the outlet 19, and then flows into the oxidation catalyst 21 through the exhaust pipe 20.

That is, after the flow of the exhaust gas in the exhaust passage portion 14 flows through the first flow I and the particulate filter 16 flowing through the flow after the particulate filter 16 to _the NO _x selective reduction catalyst 15 by the switching action of the switching valve device 13 Switching to the second flow II flowing through the NO _x selective reduction catalyst 15 is possible. In the present invention, the flow is switched to either the first flow I or the second flow II according to the demands on the NO _x selective reduction catalyst 15 and the particulate filter 16.

As shown in FIG. 1, an HC supply valve 24 for supplying hydrocarbons, that is, HC into the exhaust gas flowing in the exhaust manifold 5 is disposed in the exhaust manifold 5. In addition, urea supply valves 25 and 26 are disposed in the exhaust passage portions 14 on the upstream side and the downstream side of the NO _x selective reduction catalyst 15 as viewed from the exhaust gas flow direction I, respectively.

These urea supply valves 25 and 26 are connected to a urea aqueous solution tank 29 via a supply pipe 27 and a supply pump 28. The urea aqueous solution stored in the urea aqueous solution tank 29 is injected into the exhaust gas flowing in the exhaust passage portion 14 from the urea supply valves 25 and 26 located on the upstream side by the supply pump 28, and ammonia generated from the urea (( The NO _x contained in the exhaust gas is reduced in the NO _x selective reduction catalyst 15 by NH ₂ ) CO + H ₂ O → 2NH ₃ + CO ₂ ).

  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 30, and an electronically controlled EGR control valve 31 is disposed in the EGR passage 30. A cooling device 32 for cooling the EGR gas flowing in the EGR passage 30 is disposed around the EGR passage 30. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 32, 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 34 via a fuel supply pipe 33, and this common rail 34 is connected to a fuel tank 36 via an electronically controlled variable discharge pump 35. The fuel stored in the fuel tank 36 is supplied into the common rail 34 by the fuel pump 35, and the fuel supplied into the common rail 34 is supplied to the fuel injection valve 3 through each fuel supply pipe 33.

The electronic control unit 40 comprises a digital computer and is connected to each other by a bidirectional bus 41. A ROM (read only memory) 42, a RAM (random access memory) 43, a CPU (microprocessor) 44, an input port 45 and an output port 46 are connected. It comprises. The _the NO _x selective reducing catalyst 15 is attached a temperature sensor 37 for detecting the bed temperature of the NO _x selective reduction catalyst 15, AD converter output signal of the temperature sensor 37 and intake air amount detector 8 respectively corresponding to It is input to the input port 45 via 47. A load sensor 51 that generates an output voltage proportional to the depression amount L of the accelerator pedal 50 is connected to the accelerator pedal 50, and the output voltage of the load sensor 51 is input to the input port 45 via the corresponding AD converter 47. Is done. Further, a crank angle sensor 52 that generates an output pulse every time the crankshaft rotates, for example, 15 ° is connected to the input port 45. On the other hand, the output port 46 is connected to the fuel injection valve 3, the step motor for driving the throttle valve 10, the actuator 17 for driving the switching valve 18, the HC supply valve 24, the urea supply valves 25 and 26, and the supply via corresponding drive circuits 48. Connected to the pump 28, the EGR control valve 31 and the fuel pump 35.

The oxidation catalyst 12 carries a noble metal catalyst such as platinum, for example. The oxidation catalyst 12 functions to convert NO contained in the exhaust gas into NO ₂ and oxidize HC contained in the exhaust gas. . That is, NO ₂ is more oxidizable than NO. Therefore, when NO is converted to NO ₂ , the oxidation reaction of the particulate matter captured on the particulate filter 16 is promoted, and the NO _x selective reduction catalyst 15 The reduction action by ammonia is promoted. On the other hand, when HC is oxidized, the exhaust gas temperature is raised by the heat of oxidation reaction of HC.

As the particulate filter 16, a particulate filter that does not carry a catalyst can be used, or a particulate filter that carries a precious metal catalyst such as platinum, for example, can also be used. On the other hand, the NO _x selective reduction catalyst 15 can be composed of an ammonia adsorption type Fe zeolite having a high NO _x purification rate at a low temperature, or can be composed of a titanium / vanadium catalyst having no ammonia adsorption function. . The oxidation catalyst 21 carries a noble metal catalyst made of platinum, for example, and this oxidation catalyst 21 functions to oxidize ammonia leaked from the NO _x selective reduction catalyst 15.

  FIG. 2 shows a routine for switching the flow direction in the exhaust passage portion 14 to either the first flow I or the second flow II by the switching valve 18. Next, the flow direction switching control according to the present invention will be described with reference to this routine.

  Referring to FIG. 2, first, at step 60, it is judged if the particulate filter 16 should be regenerated. When the particulate filter 16 is to be regenerated, the routine proceeds to step 61 where the flow is switched to the second flow II. At this time, HC is supplied from the HC supply valve 24, and the exhaust gas whose temperature is increased by the oxidation reaction heat of HC in the oxidation catalyst 12 is sent to the particulate filter 16. Thus, the temperature of the particulate filter 16 can be easily raised to the regeneration temperature.

At this time, the NO ₂ generated in the oxidation catalyst 12 promotes the oxidizing action of the particulate matter. Note that the switching valve 18 is held at the position indicated by the broken line in FIG. 1 until the regeneration of the particulate filter 16 is completed, and the second flow II is maintained. When the regeneration of the particulate filter 16 is completed, the process proceeds from step 60 to step 62.

In step 62, it is determined whether or not the bed temperature TC of the NO _x selective reduction catalyst 15 is lower than a predetermined lower limit temperature T ₁ , for example, 200 ° C., based on the detected value of the temperature sensor 37, and the NO _x selective reduction catalyst. 15 bed temperature TC of when less than the lower limit temperature T ₁ of switched to the first flow I proceeds to step 63. Since the exhaust gas flowing through the oxidation catalyst 12 is immediately fed to _the NO _x selective reduction catalyst 15 at this time _the NO _x selective reduction catalyst 15 is warmed up quickly. As long as TC <T ₁ , the switching valve 18 is held at the position indicated by the solid line in FIG. 1, and the first flow I is maintained. Next, when the bed temperature TC of the NO _x selective reduction catalyst 15 becomes higher than the lower limit temperature T ₁ , the routine proceeds from step 62 to step 64.

In step 64, it is determined whether or not the bed temperature TC of the NO _x selective reduction catalyst 15 is lower than a predetermined upper limit temperature T ₂ , for example, 500 ° C. When the bed temperature TC of the NO _x selective reduction catalyst 15 is lower than the upper limit temperature T ₂ , the routine proceeds to step 65, where it is judged if the vehicle is decelerating. When it is not during deceleration operation, the processing cycle is completed. On the other hand, at the time of decelerating operation, the routine proceeds to step 66 where the current flow is the first flow I to the second flow II, and the current flow is the second flow II. To the first flow I. That is, when the bed temperature TC of the NO _x selective reduction catalyst 15 is T ₁ ≦ TC <T ₂ , that is, during normal operation, the first flow I and the second flow II are alternately switched every time deceleration operation is performed. Then, urea is supplied from urea supply valves 25 and 26 located on the upstream side after switching.

That is, when the NO _x selective reduction catalyst 15 is composed of a zeolite-based catalyst, the NO _x selective reduction catalyst 15 has extremely high ammonia adsorption performance. Therefore, in this case, ammonia generated from the supplied urea is adsorbed only on the upstream side of the NO _x selective reduction catalyst 15, and thus the entire catalyst cannot be used effectively for NO _x purification. Therefore, the flow direction is periodically switched, and urea is supplied from the urea supply valves 25 and 26 located on the upstream side every time the flow direction is switched, so that ammonia is adsorbed to the entire NO _x selective reduction catalyst 15 and thereby NO _x selective reduction. the entire catalyst 15 so as to effectively utilize for _the NO _x purification.

In the case where it is important to ensure a high NO _x purification rate without alternately switching the flow direction every time the deceleration operation is performed, the ratio of maintaining the first flow I is increased, and NO ₂ is used. When importance is attached to the oxidizing action of the particulate matter, the ratio maintained in the second flow II can also be increased.

  On the other hand, as can be seen from FIG. 1, when the switching valve 18 is switched, the exhaust gas flowing out from the oxidation catalyst 12 flows directly into the discharge port 19 in the middle of switching, and then is exhausted into the atmosphere. However, during the deceleration operation, the fuel supply is stopped. Therefore, even if the switching valve 18 is switched at this time, no harmful exhaust gas is discharged into the atmosphere. Therefore, in the embodiment according to the present invention, the switching action of the switching valve 18 is performed during the deceleration operation. In this case, the switching valve 18 can be switched when the exhaust gas amount is small, for example, during idling, instead of during deceleration.

On the other hand, when it is determined at step 64 that the bed temperature TC of the NO _x selective reduction catalyst 15 is higher than the upper limit temperature T ₂ , the routine proceeds to step 67 where it is determined whether or not the deceleration operation is being performed. When the vehicle is decelerating, the routine proceeds to step 68 where the flow is switched to the first flow I, and when the vehicle is not decelerating, the flow proceeds to step 69 where the flow is switched to the second flow II.

That is, when the bed temperature TC of the NO _x selective reduction catalyst 15 becomes higher than the upper limit temperature T ₂ , the NO _x purification rate decreases, and at this time, the temperature of the NO _x selective reduction catalyst 15 needs to be lowered. In this case, when the second flow II is used, the NO _x selective reduction catalyst 15 is located downstream of the particulate filter 16, so the bed temperature of the NO _x selective reduction catalyst 15 is lowered. Therefore, when the bed temperature TC of the NO _x selective reduction catalyst 15 becomes higher than the upper limit temperature T ₂ during normal operation, the flow is switched to the second flow II.

On the other hand, since the fuel supply is stopped during the deceleration operation, the exhaust gas temperature decreases. At this time, switching to the first flow I can effectively cool the NO _x selective reduction catalyst 15. Therefore, the bed temperature TC of the NO _x selective reduction catalyst 15 is higher than the upper limit temperature T ₂ , and when the deceleration operation is performed at this time, the first flow I is switched during the deceleration operation.

When the particulate filter 16 carries a noble metal catalyst and HC is supplied from the HC supply valve 24 to warm up the NO _x selective reduction catalyst 15, the oxidation catalyst 12 and the particulate filter 16 are used. Both generate heat of oxidation reaction of HC. Therefore, in this case, switching to the first flow I is preferable because the NO _x selective reduction catalyst 15 can be warmed up early.

1 is an overall view of a compression ignition type internal combustion engine. It is a flowchart for performing switching control of a flow direction.

Explanation of symbols

4 Intake manifold 5 Exhaust manifold 7 Exhaust turbocharger 12, 21 Oxidation catalyst 13 Switching valve device 14 Exhaust passage part 15 NO _x selective reduction catalyst 16 Particulate filter 24 HC supply valve 25, 26 Urea supply valve

Claims (7)

An oxidation catalyst is disposed in the engine exhaust passage, an outlet of the oxidation catalyst is connected to an exhaust passage portion whose flow direction can be switched via a switching valve device, and NO _x is selectively selected by ammonia in the exhaust passage portion. A reducible NO _x selective reduction catalyst and a particulate filter for collecting particulate matter are arranged in series, and the flow of exhaust gas in the exhaust passage portion is selectively reduced by NO _x by the switching action of the switching valve device. for the first stream and can be switched to the particulate filter and a second stream flowing through the flow after _the NO _x selective reduction catalyst, _the NO _x selective reduction catalyst and the particulate filter to flows through the flow after the particulate filter catalyst An exhaust gas purification apparatus for an internal combustion engine that switches between the first flow and the second flow as required.   2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein when the particulate filter is to be regenerated, the particulate flow is switched to the second flow. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the first flow is switched to when the temperature of the NO _x selective reduction catalyst is lower than a predetermined lower limit temperature. A urea supply valve is disposed in the exhaust passage portion on the upstream side and downstream side of the NO _x selective reduction catalyst as viewed from the flow direction of the exhaust gas. The urea supply valve is alternately switched to the first flow and the second flow. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein urea is supplied from a urea supply valve located on the side.   The exhaust emission control device for an internal combustion engine according to claim 4, wherein the engine is switched from the first flow to the second flow or from the second flow to the first flow during deceleration operation. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein when the temperature of the NO _x selective reduction catalyst is higher than a predetermined upper limit temperature, the second flow is switched to.   The exhaust gas purification apparatus for an internal combustion engine according to claim 6, wherein the flow is switched to the first flow during the deceleration operation.

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