JP2011226421A - Exhaust emission control device - Google Patents

Abstract

The present invention provides an exhaust gas purification apparatus capable of improving exhaust gas purification performance while suppressing a decrease in durability, an increase in pressure loss, and an increase in heat capacity.
An exhaust gas purification apparatus 20 is arranged in series with a front-stage catalyst 32 having a front-stage carrier 33 and a front-stage catalytic active material 34, and the front-stage catalyst 32, so that a rear-stage carrier 43 and a rear-stage catalyst are used. A post-stage catalyst 42 including a catalytically active material 44. The front carrier 33 is formed with a through hole 37. The amount of the first-stage catalytic active material 34 supported is equal to or greater than the amount of the second-stage catalytic active material 44 supported. The through hole 37 is formed so that the heat capacity of the front carrier 33 is smaller than the heat capacity of the rear carrier 43. The ratio of the through-hole 37 to the wall portion of the front carrier 33 is set based on the support limit mass, which is the maximum mass of the front catalyst active material 34 that can be supported per unit area in the front carrier 33.
[Selection] Figure 2

Description

  The present invention relates to an exhaust gas purification apparatus that is provided, for example, in an automobile and includes a catalyst.

  2. Description of the Related Art Conventionally, an automobile equipped with an engine (internal combustion engine) is provided with an exhaust gas purification device in an exhaust gas passage through which exhaust gas discharged from the engine flows. The exhaust gas purifying apparatus includes a catalyst for purifying unburned fuel, carbon monoxide, and nitrogen oxide (NOx) in the exhaust gas. An exhaust gas purification device having a tandem structure in which two catalysts are arranged in series has also been proposed (see, for example, Patent Document 1).

In the exhaust gas purification device having a structure including the catalyst arranged in the front stage and the catalyst arranged in the rear stage, further improvements should be made to the structure of the catalyst in the front stage and the catalyst in the rear stage from the viewpoint of improving exhaust gas purification performance. As an example of the above device, the catalyst in the front stage is formed so that it can be heated up to the activation temperature at an early stage with respect to the catalyst in the rear stage in order to improve the purification performance of exhaust gas immediately after the start of the automobile. Yes. Specifically, the heat capacity can be reduced by thinning the wall of the catalyst carrier in the previous stage or by reducing the capacity, and by increasing the surface area by increasing the number of cells of the carrier, it is easy to receive heat. It has been broken. The latter catalyst has a low cell density and uses a large capacity carrier, and is formed so as to purify exhaust gas that could not be treated with the former catalyst.

JP 2007-263055 A

  If the capacity is reduced in order to reduce the heat capacity of the catalyst in the preceding stage, the exhaust gas purification performance by the catalyst may be reduced. When the wall portion of the carrier is thinned, the durability may be reduced. If the cell density is increased (high cell density), the pressure loss may increase and the heat capacity may increase.

  For this reason, this invention is providing the exhaust gas purification apparatus which can improve the purification performance of exhaust gas, suppressing the fall of durability, the raise of pressure loss, and the increase in heat capacity.

  An exhaust gas purification apparatus according to a first aspect of the present invention is directed to a first catalyst comprising a first carrier, a first catalytically active substance supported on the first carrier, and the first catalyst. On the other hand, the second catalyst is arranged in series, and includes a second carrier comprising a second carrier and a second catalytically active substance carried on the second carrier. In the first carrier, a through-hole penetrating the wall portion is formed in the wall portion forming the first carrier. The amount of the first catalytically active substance supported is greater than or equal to the amount of the second catalytically active substance supported. The through hole is formed such that the heat capacity of the first carrier is smaller than the heat capacity of the second carrier. The ratio of the through hole to the wall is set based on a loading limit mass that is the maximum mass of the first catalytically active substance that can be supported per unit area in the first carrier.

  An exhaust gas purifying apparatus according to a second aspect of the present invention is the exhaust gas purifying apparatus according to the first aspect, wherein the through hole occupying the wall portion is configured such that the heat capacity of the first catalyst is smaller than the heat capacity of the second catalyst. The ratio and the loading amount of the first catalytically active substance are set.

  ADVANTAGE OF THE INVENTION According to this invention, the exhaust gas purification apparatus which can improve the purification performance of exhaust gas can be provided, suppressing the fall of durability, the raise of pressure loss, and the increase in heat capacity.

Schematic which shows an engine system provided with the exhaust gas purification apparatus of one Embodiment of this invention. Schematic which shows the state which decomposed | disassembled the front | former stage catalyst apparatus and back | latter stage catalyst apparatus which were shown by FIG. The perspective view which expands and shows a part of catalyst for the front | former stage shown by FIG. Schematic which shows an example of the preparation procedure of the front | former stage carrier shown by FIG. The graph which shows the purification | cleaning performance of the catalyst for a front | former stage in the case of changing the aperture ratio of the 1st, 2nd sheet member in the catalyst for a front | former stage shown by FIG.

  An exhaust gas purification apparatus according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a schematic diagram showing an engine system 10 including an exhaust gas purification device 20 of the present embodiment. The engine system 10 is used for an automobile as an example. As shown in FIG. 1, the engine system 10 includes an engine 11, an intake system 12, and an exhaust gas system 13.

  The engine 11 includes a cylinder 14 and a piston 15 and is a reciprocating internal combustion engine that uses gasoline as fuel. The intake system 12 includes an intake passage 16. The intake passage 16 takes air into the combustion chamber 17 of the engine 11.

  The exhaust gas system 13 includes an exhaust gas passage 18 that guides the exhaust gas G discharged from the engine 11 to the outside, and an exhaust gas purification device 20 that purifies the exhaust gas G flowing through the exhaust gas passage 18. The exhaust gas purification device 20 is incorporated in the exhaust gas passage 18. The exhaust gas G passes through the exhaust gas purification device 20. The exhaust gas G is purified by passing through the exhaust gas purification device 20.

  The exhaust gas purification device 20 is an example of the exhaust gas purification device referred to in the present invention. The exhaust gas purification device 20 includes a front-stage catalyst device 30 disposed upstream, a rear-stage catalyst device 40 disposed downstream of the front-stage catalyst device 30, and a housing that houses the front-stage catalyst device 30 and the rear-stage catalyst device 40. 60.

  The housing 60 constitutes a part of the exhaust gas passage 18. The upstream and downstream are defined along the direction in which the exhaust gas G flows. In the present embodiment, the exhaust gas G flows in one direction as indicated by arrows in the drawing. The front-stage catalyst device 30 and the rear-stage catalyst device 40 are arranged in series along the direction in which the exhaust gas G flows.

  FIG. 2 is a schematic view showing a state where the front-stage catalyst device 30 and the rear-stage catalyst device 40 are disassembled. As shown in FIG. 2, the front-stage catalyst device 30 includes a front-stage housing 31 and a front-stage catalyst 32. The pre-stage catalyst 32 is an example of the first catalyst referred to in the present invention. In FIG. 2, the decomposed upstream catalyst 32 is indicated by a two-dot chain line. The front-stage housing 31 has a cylindrical shape, and both end openings are arranged in the direction in which the exhaust gas G flows.

  The front-stage catalyst 32 includes a front-stage carrier 33 and a front-stage catalyst active material 34 supported on the front-stage carrier 33. In FIG. 2, a part of the pre-stage catalyst 32 is shown enlarged. As shown in an enlarged view in FIG. 2, the front carrier 33 has a plurality of passages 35 communicating from the opening 31 a at one end to the opening 31 b at the other end of the front housing 31 in a state of being accommodated in the front housing 31. Is a honeycomb structure. The front carrier 33 is an example of the first carrier referred to in the present invention. The exhaust gas G can pass through the upstream catalyst 32 from the opening 31a at one end to the opening 31b at the other end. The pre-stage catalyst 32 is an example of the first catalyst referred to in the present invention.

  FIG. 3 is an enlarged perspective view showing a part of the pre-stage catalyst 32. As described above, the front-stage catalyst 32 has a honeycomb structure including a plurality of passages 35 that allow the exhaust gas G to pass from the opening 31a at one end of the front-stage housing 31 to the opening 31b at the other end. As shown in FIG. 3, in the front carrier 33, a plurality of through holes 37 are formed in the wall portion 36 that defines the passage 35. The through holes 37 communicate adjacent passages 35 with each other. The through hole 37 is an example of a through hole as referred to in the present invention.

  An example of the preparation procedure of the upstream carrier 33 will be described. FIG. 4 is a schematic diagram showing an example of a procedure for creating the upstream carrier 33. As shown in FIG. 4, the front carrier 33 is a combination of the first sheet member 50 and the second sheet member 51 and the first and second sheet members 50 and 51 combined. It is formed by rounding into a roll shape.

  As shown in the figure, the first sheet member 50 has a thin sheet shape, and a plurality of through holes 37 penetrating the first sheet member 50 are formed. The second sheet member 51 is formed by folding a sheet member similar to the first sheet member 50. The through holes 37 formed in the first and second sheet members 50 and 51 become the through holes 37 formed in the front carrier 33.

  Here, the aperture ratio is the ratio of the area of the through hole 37 to the area of the range defined in the peripheral edges 54 and 55 on the upper surfaces 52 and 53 of the first and second sheet members 50 and 51.

  The front-stage catalyst active material 34 is supported on the front-stage carrier 33 configured as described above. The upstream catalytically active material 34 is an example of the first catalytically active material referred to in the present invention. FIG. 2 shows a state where the pre-stage catalytic active material 34 is supported. The front-stage catalytically active material 34 is carried on the surface of the front-stage carrier 33. Therefore, in other drawings, the reference numeral 34 indicates the surface of the front-stage carrier 33. Actually, as shown in FIG. 2, the front-stage catalyst active material 34 is supported on the surface of the front-stage carrier 33.

  Examples of the catalytically active substance include platinum Pt, palladium Pd, and rhodium Rh. In the present embodiment, platinum Pt, palladium Pd, and rhodium Rh are used as an example of the pre-stage catalytic active material. These three substances are mixed at a predetermined ratio.

  In FIG. 2, the decomposed rear-stage catalyst device 40 is indicated by a two-dot chain line. As shown in FIG. 2, the rear catalyst device 40 includes a rear housing 41 and a rear catalyst 42. The rear housing 41 has a cylindrical shape, and both ends thereof are arranged in the direction in which the exhaust gas G flows. In FIG. 2, a part of the rear catalyst 42 is shown in an enlarged manner.

  The post-stage catalyst 42 is an example of a second catalyst referred to in the present invention. As shown in an enlarged view in FIG. 2, the post-stage catalyst 42 includes a post-stage support 43 and a post-stage catalyst active material 44 carried on the post-stage support 43. The rear carrier 43 has a honeycomb structure including a plurality of passages 45 communicating from the opening 41 a at one end to the opening 41 b at the other end of the rear housing 41 when accommodated in the rear housing 41. The rear carrier 43 is not formed with a through hole in the wall portion like the front carrier 33. The post-stage carrier 43 is an example of a second carrier referred to in the present invention.

The latter catalytically active material is an example of the second catalytically active material referred to in the present invention. For example, platinum Pt, palladium Pd, and rhodium Rh ^* are used as the post-stage catalytic active material 44. These three substances are mixed at a predetermined ratio. The mixing ratio may be the same as that of the pre-stage catalyst 32, or may be a different ratio. Further, the post-stage catalytic active material 44 may be a material different from the pre-stage catalytic active material 34. The post-stage catalyst 42 is an example of a second catalyst referred to in the present invention.

  The relationship between the amount of the front-stage catalyst active material 34, the through-hole 37 formed in the front-stage carrier 33, and the rear-stage catalyst 42 will be described. The mass of the pre-stage catalyst 32 is a1. The mass of the post-stage catalyst 42 is b1. b1 is larger than a1 (a1 <b1). In this embodiment, the mass a1 of the upstream catalyst 32 is the sum of the mass of the upstream carrier 33 and the upstream catalytically active material 34. In this embodiment, the mass b1 of the post-stage catalyst 42 is the sum of the mass of the post-stage support 43 and the mass of the post-stage catalyst active material 44.

  The mass of the pre-stage catalytic active material 34 is a2. The mass of the post-stage catalytic active substance 44 is b2. In this embodiment, a2 is larger than b2 (a2> b2). The mass a2 of the pre-stage catalyst active material 34 is determined in accordance with the purification performance of the exhaust gas G required for the pre-stage catalyst 32.

  The surface area of the front carrier 33 is A. The surface area of the front carrier 33 will be specifically described. The surface area of the front carrier 33 is an area of a surface that may come into contact with the exhaust gas G flowing in the front carrier 33. As shown in FIG. 3, the surface area A includes four edge surfaces 55 that define the through holes 37 in addition to both surfaces of the first and second sheet members 50 and 51.

  Let L be the carrying limit mass of the carrier 33 for the previous stage. The support limit mass is the maximum mass of the pre-stage catalytic active material 34 that can be supported on a unit area in the pre-stage carrier 33. The carrying limit mass L is a predetermined value. Smin = a1 / L, where Smin is the surface area required for the front carrier 33, that is, the minimum surface area of the front carrier 33 that can contact the exhaust gas G. For this reason, A ≧ Smin. The through hole 37 is formed such that the surface area A of the front carrier 33 is equal to or greater than Smin.

  In this embodiment, A = Smin as an example. The only difference is that the through hole 37 is not formed in the front carrier 33, and when a carrier having the same structure (shape and size) as that of the front carrier 33 is assumed, the surface area of the virtual carrier is the through hole. It is more than Smin considering 37.

  FIG. 5 is a graph showing the purification performance of the pre-stage catalyst 32 when the opening ratios of the first and second sheet members 50 and 51 are changed in the pre-stage catalyst 32. The aperture ratio referred to here is the ratio of the area of the through hole 37 to the area in the range inside the peripheral edges 54 and 55 of the first and second sheet members 50 and 51 described above.

  The horizontal axis in FIG. 5 indicates the aperture ratio, and indicates that the aperture ratio increases as it proceeds to the right side in the figure. The vertical axis in FIG. 5 indicates the effect of reducing substances to be purified in the exhaust gas G. The substance to be purified is, for example, NOx or unburned fuel. The scale 1 on the vertical axis indicates that it has not been reduced. A value smaller than 1 on the scale (for example, 0.9, 0.7, etc.) indicates that the substance to be purified is reduced, and therefore the purification performance of the pre-stage catalyst 32 is improved. It is shown that.

  In FIG. 5, the amount (mass) of the substance to be purified in the exhaust gas having a structure with an aperture ratio of 0 (zero)% is used as a reference. The scale on the vertical axis indicates the ratio to the amount (mass) of the substance to be purified in the exhaust gas having a structure with an aperture ratio of 0%.

  For this reason, in the structure with an aperture ratio of 0%, the vertical axis indicates 1, that is, the substance to be purified is not reduced. 0.9 on the vertical axis indicates that the amount (mass) of the substance to be purified in the exhaust gas is 0 with respect to the amount (mass) of the substance to be purified in the exhaust gas having an opening ratio of 0% (scale is 1). .1 (10%) decrease.

  FIG. 5 shows that the exhaust gas purification performance of the pre-stage catalyst 32 is high near the position where the aperture ratio is P. The first and second sheet members 50 and 51 of this embodiment have an aperture ratio of P as an example. When the aperture ratio is P, the surface area A of the front carrier 33 is Smin.

  In the exhaust gas purification apparatus 20 configured as described above, the mass of the front stage carrier 33 is reduced by forming the through-hole 37 in the front stage carrier 33, and the mass a1 of the front stage catalyst 32 is changed to the mass b1 of the rear stage catalyst 42. Smaller than that. Therefore, the heat capacity of the front stage catalyst 32 can be made smaller than that of the rear stage catalyst 42. Therefore, the temperature of the front stage catalyst 32 can be raised earlier than that of the rear stage catalyst 42. In other words, the temperature can be raised quickly to the activation temperature of the pre-stage catalytic active material 34.

  Since the pre-stage catalytic active material 34 can be activated at an early stage, the exhaust gas can be purified by raising the temperature of the pre-stage catalyst device 30 quickly even immediately after the start of driving of the automobile. Then, the rear stage catalyst 42 purifies the exhaust gas that has not been treated by the front stage catalyst 32. Thus, since the exhaust gas purification device 20 functions early from the start of driving of the automobile, the exhaust gas purification performance is improved.

  Further, since the through-hole 37 is formed, the wall portion 36 is not thinned in order to reduce the weight of the front carrier 33, and therefore the durability of the front carrier 33 can be prevented from being lowered. it can. Further, since the through hole 37 is formed, the capacity of the front carrier 33 is not reduced, and therefore the exhaust gas purification performance is not lowered. Further, since the density of the passage 35 is not improved, the pressure loss is not improved.

  Further, since the mass a2 of the upstream catalytically active material 34 is larger than the mass b2 of the downstream catalytically active material 44, the purification performance of the upstream catalytic device 30 can be further enhanced. In the present embodiment, although a2> b2, it is not limited to this. For example, a2 = b2.

  The present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the above-described embodiments. For example, you may delete some components from all the components shown by embodiment mentioned above.

  DESCRIPTION OF SYMBOLS 20 ... Exhaust gas purification apparatus, 32 ... Pre-stage catalyst (first catalyst), 33 ... Pre-stage carrier (first carrier), 34 ... Pre-stage catalytic active substance (first catalytic active substance), 37 ... Through-hole , 42 ... latter stage catalyst (second catalyst), 43 ... latter stage carrier (second carrier), 44 ... latter stage catalyst active substance (second catalyst active substance).

Claims (2)

A first catalyst comprising a first carrier and a first catalytically active substance carried on the first carrier;
A second catalyst disposed in series with the first catalyst, the second catalyst comprising a second carrier and a second catalytically active substance carried on the second carrier. And
In the first carrier, a through-hole penetrating the wall is formed in the wall forming the first carrier,
The loading amount of the first catalytically active substance is not less than the loading amount of the second catalytically active substance,
The through hole is formed such that the heat capacity of the first carrier is smaller than the heat capacity of the second carrier,
The ratio of the through hole to the wall is set based on a loading limit mass that is a maximum mass of the first catalytically active substance that can be supported per unit area in the first carrier. Exhaust gas purification device. The ratio of the through-holes occupying the wall and the loading amount of the first catalytic active substance are set so that the heat capacity of the first catalyst is smaller than the heat capacity of the second catalyst. The exhaust gas purification apparatus according to claim 1.

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