JP4577099B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

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

  An exhaust purification device for an internal combustion engine in which a reducing agent supply device is arranged in an exhaust passage upstream of the catalyst and exhaust gas is purified in the catalyst by the reducing agent supplied from the reducing agent supply device is known (see Patent Document 1). .

JP 2000-303826 A

  In such an exhaust purification device, in order to effectively use the reducing agent, it is preferable that the reducing agent is widely dispersed over the entire cross section of the exhaust passage. In this respect, if the exhaust passage space from the reducing agent supply device to the catalyst is large, the reducing agent can be widely dispersed.

  However, for example, under the vehicle floor, there is a limit to the location where the reducing agent supply device is installed, so the exhaust passage space from the reducing agent supply device to the catalyst cannot always be increased. For this reason, even if a reducing agent is simply added to the exhaust passage, there is a possibility that good dispersibility of the reducing agent cannot be ensured.

  Accordingly, an object of the present invention is to provide an exhaust purification device for an internal combustion engine that ensures good dispersibility of the reducing agent so that the reducing agent can be used effectively.

  In order to solve the above problems, according to a first aspect of the invention, an internal combustion engine in which a reducing agent supply device is disposed in an exhaust passage upstream of the catalyst and exhaust gas is purified in the catalyst by the reducing agent supplied from the reducing agent supply device. In the exhaust emission control device of an engine, a reducing agent holding member for temporarily adhering and holding the reducing agent is disposed in an exhaust passage upstream of the reducing agent supply device, and the reducing agent is directed from the reducing agent supply device to the reducing agent holding member. The reducing agent is temporarily attached and held on the reducing agent holding member, and then separated from the reducing agent holding member and supplied to the catalyst.

  According to a second aspect, in the first aspect, the reducing agent holding member is composed of a honeycomb structure.

  According to a third aspect, in the second aspect, the reducing agent holding member is composed of a particulate filter for collecting fine particles in the exhaust gas.

  According to a fourth aspect, in the first aspect, the reducing agent holding member is composed of a breathable plate member.

  According to a fifth aspect, in the fourth aspect, a particulate filter for collecting particulates in the exhaust gas is disposed in the exhaust passage upstream of the catalyst, and the reducing agent supply device and the A plate-like member is disposed in the exhaust passage between the particulate filter and the catalyst.

  It is possible to effectively use the reducing agent while ensuring good dispersibility of the reducing agent.

  FIG. 1 shows a case where the present invention is applied to a compression ignition type internal combustion engine. The present invention can also be applied to a spark ignition type internal combustion engine.

  Referring to FIG. 1, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is an electrically controlled fuel injection valve, 7 is an intake valve, 8 is an intake port, 9 Is an exhaust valve, and 10 is an exhaust port. The intake port 8 is connected to a surge tank 12 via a corresponding intake branch pipe 11, and the surge tank 12 is connected to a compressor 15 of an exhaust turbocharger 14 via an intake duct 13. A throttle valve 17 driven by a step motor 16 is disposed in the intake duct 13, and a cooling device 18 for cooling intake air flowing through the intake duct 13 is disposed around the intake duct 13. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 18 and the intake air is cooled by the engine cooling water. The intake air may be cooled by outside air.

  On the other hand, the exhaust port 10 is connected to an inlet of an exhaust turbine 21 of the exhaust turbocharger 14 via an exhaust manifold 19 and an exhaust pipe 20. The outlet of the exhaust turbine 21 is connected to the inlet of the catalytic converter 23 via the exhaust pipe 22, and the outlet of the catalytic converter 23 is connected to the exhaust pipe 24.

  In the example shown in FIG. 1, the catalytic converter 23 includes, for example, a single casing 25, and the reducing agent holding member 27 and the catalyst 28 are arranged in series in the casing 25 with a gap 26 in the exhaust gas flow direction. Is housed. A reducing agent supply valve 29 is disposed in the gap 25. Therefore, the reducing agent supply valve 29 is disposed upstream of the catalyst 28, and the reducing agent holding member 27 is disposed upstream of the reducing agent supply valve 29. The reducing agent supply valve 29 is connected via a reducing agent supply pipe 29a to an electrically controlled reducing agent pump 30 with variable discharge amount, and the reducing agent pump 30 is connected to a reducing agent tank 31 containing, for example, a liquid reducing agent. . The type of the reducing agent can be determined according to the type of the catalyst 28 and the exhaust gas component to be purified. For example, hydrocarbon such as light oil (fuel), urea, ammonia and the like can be used as the reducing agent.

  Further, referring to FIG. 1, the exhaust manifold 19 and the surge tank 12 are connected to each other via a recirculated exhaust gas (hereinafter referred to as EGR) passage 32, and an electrically controlled EGR control valve 33 is provided in the EGR passage 32. Be placed. A cooling device 34 for cooling the EGR gas flowing in the EGR passage 32 is disposed around the EGR passage 32.

  The fuel injection valve 6 is connected to a common fuel pressure accumulating chamber, that is, a common rail 35 via a fuel supply pipe 6a. The common rail 35 is connected to a fuel tank 37 via an electrically controlled fuel pump 36 having a variable discharge amount. A fuel pressure sensor 38 for detecting the fuel pressure in the common rail 35 is attached to the common rail 35, and the fuel pressure in the common rail 35 is set to a target fuel pressure based on the output signal of the fuel pressure sensor 38. The discharge amount of the pump 36 is controlled.

  The electronic control unit 40 is composed of a digital computer, and is connected to each other by a bidirectional bus 41. A ROM (read only memory) 42, a RAM (random access memory) 43, a CPU (microprocessor) 44, an input port 45 and an output port 46 are connected. It comprises. A pressure sensor 49 for detecting the pressure in the exhaust pipe 22 is attached to the exhaust pipe 22, and a load sensor 51 for detecting the depression amount of the accelerator pedal 50 is connected to the accelerator pedal 50. Output voltages of the fuel pressure sensor 38, the pressure sensor 49, and the depression amount sensor 51 are input to the input port 45 via the corresponding AD converters 47, respectively. Further, a crank angle sensor 52 that generates an output pulse every time the crankshaft rotates, for example, 10 ° is connected to the input port 45. The CPU 44 calculates the engine speed based on this output pulse. On the other hand, the output port 46 is connected to the fuel injection valve 6, the step motor 16, the reducing agent supply valve 29, the reducing agent pump 30, the EGR control valve 33, and the fuel pump 36 via corresponding drive circuits 48.

  The reducing agent holding member 27 is for temporarily attaching and holding the reducing agent supplied from the reducing agent supply valve 29. In the example shown in FIG. 2A, the reducing agent holding member 27 includes a particulate filter 27a for collecting fine particles mainly made of solid carbon contained in the exhaust gas. The particulate filter 27a 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. 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 27a is formed of a porous material such as cordierite. Therefore, the exhaust gas flowing into the exhaust gas inflow passage 60 passes through the surrounding partition wall 64 as shown by an arrow in FIG. It flows out into the adjacent exhaust gas outflow passage 61.

  In this case, the surface of the partition wall 64 positioned on the exhaust gas inflow passage 60 side is referred to as an exhaust gas inflow surface 65, and the surface of the partition wall 64 positioned on the exhaust gas outflow passage 61 side is referred to as an exhaust gas outflow surface 66. Passes through the exhaust gas inflow surface 65 and then through the exhaust gas outflow surface 66. In order to oxidize and remove the particulates deposited on the particulate filter 27a, for example, a particulate removing action for periodically raising the temperature of the particulate filter 27a while maintaining the air-fuel ratio of the exhaust gas flowing into the particulate filter 27a lean. Can be done. For example, a catalyst having an oxidation function may be supported on the particulate filter 27a.

On the other hand, the catalyst 28 is for purifying exhaust gas with the reducing agent supplied from the reducing agent supply valve 29. In the example shown in FIG. 2A, the catalyst 28 is composed of a selective reduction catalyst or a NO _X storage catalyst. The selective reduction catalyst selectively reduces NO _x in the exhaust gas even in an oxidizing atmosphere. The NO _X storage catalyst temporarily stores NO _X in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean, and stores the NO _X stored when the air-fuel ratio of the inflowing exhaust gas becomes the stoichiometric air-fuel ratio or rich. _X is released and reduced. In this specification, the ratio of the air, fuel, and reducing agent supplied to the exhaust passage upstream of a certain position of the exhaust passage, the combustion chamber, and the intake passage is referred to as the air-fuel ratio of the exhaust gas at that position. ing.

  The catalyst 28 is supported on a base material having a honeycomb structure. The substrate includes a plurality of exhaust flow passages extending in parallel to each other, and the exhaust flow passages are open at the upstream end and the downstream end. The substrate is also made of a porous material such as cordierite.

The case where the catalyst 28 is composed of a NO _X storage catalyst will be described as an example. Since the lean operation is continuously performed in the internal combustion engine, NO _X in the exhaust gas is stored in the NO _X storage catalyst at this time. Then, release the NO _X that is stored, at the time to be reduced, the air-fuel ratio of the exhaust gas flowing to the NO _X storage catalyst is fed a reducing agent so that the stoichiometric air-fuel ratio or rich, the result _the NO _X storage NO _X in the catalyst is released, and NO _X is reduced with this reducing agent. Further, in _the NO _X storage catalyst is stored is also sulfur e.g. SO _X, becomes the when releasing the SO _X, reduced as the air-fuel ratio of the exhaust gas flowing to the NO _X storage catalyst is the stoichiometric air-fuel ratio or rich Agent is supplied.

  When the reducing agent is to be supplied to the catalyst 28, the reducing agent is supplied from the reducing agent supply valve 29. In the embodiment according to the present invention, the supply axis of the reducing agent supply valve 29 is directed so that the reducing agent goes to the particulate filter 27a, and the reducing agent supply valve so that the reducing agent reaches the particulate filter 27a. 29 supply pressures are set. Accordingly, as shown in FIG. 2B, the reducing agent R is injected from the reducing agent supply valve 29 toward the particulate filter 27a, and this reducing agent adheres to the particulate filter 27a, particularly the exhaust gas outflow surface 66. Retained. In this case, it is preferable to inject the reducing agent R so as to spread over substantially the entire cross section of the particulate filter 27a.

  The reducing agent adhered and held on the particulate filter 27 a is separated from the particulate filter 27 a by the particulate filter 27 a itself, the heat of the exhaust gas, or by the exhaust gas flow, and then supplied to the catalyst 28.

  Thus, since the reducing agent is temporarily held in the particulate filter 27a and then supplied to the catalyst 28, the reducing agent can be widely dispersed without requiring a large dispersion space. Moreover, since the reducing agent receives a shearing force or collides with the particulate filter 27a when reversing the exhaust gas flow, or the reducing agent receives heat from the particulate filter 27a or the exhaust gas, the atomizing of the reducing agent is performed. Can be promoted. Therefore, the reducing agent can be effectively used in the catalyst 28 for exhaust gas purification.

  If a reducing agent is supplied to the particulate deposition layer formed on the particulate filter 27a, the reducing agent may penetrate into the particulate deposition layer, so that the reducing agent may not be effectively used for exhaust purification. However, in the embodiment according to the present invention, the reducing agent is supplied toward the exhaust gas outflow surface 66 of the particulate filter 27a, and the particulate deposit layer is hardly formed on the exhaust gas outflow surface 66. Does not occur.

  In addition, by performing the particulate removing action of the particulate filter 27a described above, the reducing agent remaining on the particulate filter 27a can be oxidized and removed. As a result, it is possible to prevent the reducing agent remaining on the particulate filter 27a from being deteriorated and fixed.

  3 and 4 show another embodiment according to the present invention.

  In the example shown in FIG. 3, the reducing agent holding member 27 is composed of a honeycomb structure 27b. Like the base material of the catalyst 28 described above, the honeycomb structure 27b includes a plurality of exhaust flow passages extending in parallel with each other, and the exhaust flow passages are open at the upstream end and the downstream end. . The honeycomb structure 27b can be formed of ceramic or metal.

  In this case, the reducing agent R is sprayed around the downstream end 27bd of the honeycomb structure 27b, and this reducing agent is adhered and held around the honeycomb structure 27b, particularly around the downstream end 27bd. Next, the reducing agent is separated from the honeycomb structure 27 b and supplied to the catalyst 28.

Another catalyst may be supported on the honeycomb structure 27b. As an additional catalyst in this case, in addition to the NO _X storage catalyst and the selective reduction catalyst described above, a catalyst having an oxidation function can be used. Alternatively, for example, a hydrolysis catalyst for producing ammonia from urea or an adsorption reforming catalyst for temporarily adsorbing and reforming hydrocarbons as a reducing agent can be used. In any case, the reducing agent can be modified by supporting the catalyst on the honeycomb structure 27b, and the reducing agent can be further effectively used for exhaust purification.

  Further, in the example shown in FIG. 3, the auxiliary catalyst 70 supported on the base material forming the honeycomb structure is accommodated in the casing 25 upstream of the honeycomb structure 27b. The auxiliary catalyst 70 is composed of a catalyst having an oxidation function, for example.

  On the other hand, in the example shown in FIGS. 4A, 4 </ b> B, and 4 </ b> C, the reducing agent holding member 27 is composed of a breathable plate-like member 27 c. The air-permeable plate-like member 27c is made of a porous material such as ceramic or foam filter. In this case, the reducing agent R is injected toward the downstream side surface 27cd of the air permeable plate member 27c, and this reducing agent is adhered and held on the air permeable plate member 27c, particularly the downstream side surface 27cd. Next, the reducing agent is separated from the gas permeable plate member 27 c and supplied to the catalyst 28.

  In the example shown in FIGS. 4A and 4B, the air permeable plate member 27 c is accommodated in the casing 25 upstream of the catalyst 28. In addition, in the example shown in FIG. 4A, the air-permeable plate-like member 27 c extends over almost the entire cross section of the casing 25. On the other hand, in the example shown in FIG. 4B, the breathable plate member 27c extends over a part of the cross section of the casing 25, and the reducing agent R is supplied from the reducing agent supply valve 29 to the breathable plate member. It is supplied toward 27c.

  On the other hand, in the example shown in FIG. 4C, the exhaust pipe 22 is connected to another casing 80, and the other casing 80 is connected to the casing 25 via the exhaust pipe 81. In another casing 80, a particulate filter 82 having the same configuration as the above-described particulate filter 27a is accommodated, and in the casing 25, the above-described catalyst 28 is accommodated. The reducing agent holding member 27 and the reducing agent supply valve 29 are disposed in the exhaust pipe 81. In this way, when the particulate filter 82 performs the particulate removing action, the reducing agent holding member 27 can suppress heat radiation from the particulate filter 82. Further, since the flow passage cross section of the exhaust pipe 81 is smaller than that of the casings 25 and 80 and therefore the linear flow velocity of the exhaust gas is high, the reducing agent attached and held on the air-permeable plate-like member 27c can be separated and atomized.

  FIG. 5 shows various embodiments of the breathable plate-like member 27c.

  In the example shown in FIG. 5A, the air-permeable plate-like member 27c is made of a non-woven fabric 91 bent in a wave shape along a concentric folding line 90. The nonwoven fabric 91 can be formed from heat resistant fibers such as metal fibers and glass fibers.

  On the other hand, in the example shown in FIG. 5B, the air-permeable plate-like member 27c is composed of a non-air-permeable plate material 94 such as metal in which a plurality of holes 93 are formed. In the example shown in FIG. 5C, the air permeable plate member 27c is composed of a plurality of air permeable plate members 95 arranged in series in the exhaust gas flow direction. A plurality of holes 96 are formed by folding the small pieces. In this way, the turbulence of the exhaust gas flow can be increased, and thus the diffusibility of the reducing agent can be increased.

1 is an overall view of an internal combustion engine. It is a figure for demonstrating the Example by this invention. It is a figure which shows another Example by this invention. It is a figure which shows another Example by this invention. It is a figure which shows another Example of a plate-shaped member.

Explanation of symbols

1 Engine Body 23 Catalytic Converter 27 Reducing Agent Holding Member 28 Catalyst 29 Reducing Agent Supply Valve

Claims (2)

In an exhaust gas purification apparatus for an internal combustion engine in which a reducing agent supply device is disposed in an exhaust passage upstream of the catalyst and exhaust gas is purified in the catalyst by the reducing agent supplied from the reducing agent supply device, an exhaust passage upstream of the reducing agent supply device A reducing agent holding member for temporarily adhering and holding the reducing agent is disposed therein, the reducing agent is supplied from the reducing agent supply device toward the reducing agent holding member, and the reducing agent is temporarily attached to the reducing agent holding member. An exhaust gas purification apparatus for an internal combustion engine that is detached from a reducing agent holding member and is supplied to a catalyst after being attached and held , wherein the reducing agent holding member is formed of a honeycomb structure . 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the reducing agent holding member comprises a particulate filter for collecting particulates in the exhaust gas .

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