Exhaust purification device

Abstract

The invention relates to an exhaust gas purification device. The generation of cracks in the exhaust gas purification catalyst can be suppressed by reducing thermal shock acting on the exhaust gas purification catalyst. An exhaust gas purification device (3) is provided with a catalytic converter (30) that purifies exhaust gas from an exhaust manifold (29). The first catalytic converter (30) is provided with: a porous body (34) comprising a metal material through which exhaust gas from the exhaust manifold (29) passes; and an exhaust gas purification catalyst (32) that purifies the exhaust gas that has passed through the porous body (34). An exhaust gas purification catalyst (32) is an electrically heated catalyst in which a pair of electrodes (35, 35) is attached to a catalyst body (31). A plurality of through holes are formed in the porous body (34) so as to extend from the upstream side to the downstream side of the exhaust gas, the surface of the porous body (34) is a surface in which the metal material is exposed, and the thermal capacity ratio of the porous body (34) to the catalyst main body (31) is 8% to 23% (inclusive) in a temperature environment of 25 DEG C.

Description

Technical Field

[0001] The present invention relates to an exhaust gas purification device. Background Art

[0002] To purify the exhaust gas (exhaust gas) emitted from the engine, an exhaust purification device is connected to the exhaust manifold. The exhaust purification device includes an exhaust purification catalyst that purifies the exhaust gas from the exhaust manifold. The exhaust purification catalyst consists of a metal catalyst that purifies the exhaust gas and a carrier that supports the metal catalyst (catalyst carrier).

[0003] For example, Patent Document 1 proposes a catalytic converter as such an exhaust purification device. The catalytic converter includes a first catalyst that purifies exhaust gas from the exhaust manifold and a second catalyst that purifies exhaust gas after passing through the first catalyst. The heat capacity of the first catalyst is smaller than that of the second catalyst. This catalytic converter allows the first catalyst to be heated up earlier, thereby improving exhaust performance during engine startup.

[0004] [Prior art literature]

[0005] [Patent Document]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-019817 Summary of the Invention

[0007] However, for example, during rapid vehicle acceleration, the exhaust gas flow rate increases, and the exhaust gas passing through the first catalyst rapidly heats up due to catalyst activation. Consequently, if the rapidly heated exhaust gas reaches the second catalyst, the exhaust gas purification catalyst serving as the second catalyst may be rapidly heated. As a result, it is conceivable that a thermal shock may act on the exhaust gas purification catalyst, causing cracks in the exhaust gas purification catalyst.

[0008] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a catalyst purification device capable of suppressing the occurrence of cracks in the exhaust gas purification catalyst by reducing the degree of thermal shock acting on the exhaust gas purification catalyst.

[0009] In view of the above-mentioned problems, the exhaust purification device of the present invention is provided with a catalytic converter for purifying the exhaust gas from the exhaust manifold. The catalytic converter comprises: a porous body made of a metal material through which the exhaust gas from the exhaust manifold passes; and an exhaust purification catalyst for purifying the exhaust gas that has passed through the porous body. The exhaust purification catalyst is an electrically heated catalyst in which a pair of electrodes are mounted on a catalyst body. The porous body is formed with a plurality of through holes along the upstream side to the downstream side of the exhaust gas. The surface of the porous body is a surface on which the metal material is exposed. Under a temperature environment of 25°C, the heat capacity ratio of the porous body to the catalyst body is not less than 8% and not more than 23%.

[0010] According to the present invention, by reducing the degree of thermal shock acting on the exhaust gas purification catalyst, it is possible to suppress the occurrence of cracks in the exhaust gas purification catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a schematic conceptual diagram for explaining the exhaust gas purification device according to the present embodiment.

[0012] Figure 2 yes Figure 1 Schematic perspective view of a first catalytic converter of the exhaust gas purification system shown.

[0013] Figure 3 (a) is Figure 2 , and (b) is a schematic plan view of the porous body shown in (a).

[0014] Figure 4 This is a graph showing the relationship between the bed temperature, the temperature of the exhaust gas passing through the first catalytic converter, and cracks generated in the exhaust gas purification catalyst when the first catalytic converters of Examples 1 and 2 and Comparative Examples 1 and 2 are used.

[0015] Figure 5 (a) is a graph showing the relationship between the heat capacity ratio of the first catalytic converter of Example 1, Example 2 and Comparative Example 2 and the reduction in the heating rate, and (b) is a graph showing the relationship between the heat capacity ratio of the first catalytic converter of Example 1, Example 2 and Comparative Example 2 and the pressure loss increase rate.

[0016] Description of Reference Numerals

[0017] 2: Engine; 29: Exhaust manifold; 3: Exhaust purification device; 30: First catalytic converter (catalytic converter); 31: Catalyst body; 32: Exhaust purification catalyst; 33: Housing; 33a: Inlet tapered portion; 33b: Trunk; 33c: Outlet tapered portion; 34, 34A: Porous body; 34h, 34hs, 34ht: Through-hole; 34s: Central region; 34t: Peripheral region; 35: Electrode. DETAILED DESCRIPTION

[0018] [First embodiment]

[0019] The following reference Figures 1 to 5 An exhaust gas purification device according to an embodiment of the present invention will be described. Figure 1 Schematic conceptual diagram for explaining the exhaust gas purification device 3 according to the embodiment of the present invention. Figure 2 yes Figure 1 Schematic perspective view of the first catalytic converter 30 of the exhaust purification device 3 shown in FIG. Figure 2 In FIG. 1 , in order to show the interior of the first catalytic converter 30 , the housing 33 is shown in a half-split state.

[0020] like Figure 1 As shown, the exhaust gas purification device 3 of this embodiment is installed downstream of the engine 2 and purifies the exhaust gas after combustion in the engine 2. The engine 2 can be any of a gasoline engine and a diesel engine. In this embodiment, as an example, Figure 1 A gasoline direct injection engine is exemplified in FIG.

[0021] In the engine 2, air drawn in through an intake valve 25 flows into a combustion chamber formed by a cylinder block 21 and a piston 22, and mixes with fuel (gasoline) injected by a fuel injection valve 28. The mixed air-fuel mixture is ignited by a spark plug 27 in the combustion chamber and combusted. The exhaust gas after the combustion is discharged from an exhaust manifold 29 through an exhaust valve 26.

[0022] The exhaust gas discharged from the exhaust manifold 29 is purified by the exhaust gas purification device 3. Specifically, the exhaust gas purification device 3 includes a first catalytic converter 30 connected to the exhaust manifold 29, and a second catalytic converter 37 connected to the first catalytic converter 30 downstream of the first catalytic converter 30 via an exhaust pipe 36. The first catalytic converter 30 is disposed, for example, in the engine compartment (not shown) of the vehicle, and the second catalytic converter 37 is disposed, for example, under the floor of the vehicle (not shown).

[0023] The first catalytic converter 30 includes a porous body 34 made of a metal material through which exhaust gas from the exhaust manifold 29 passes; an exhaust purification catalyst 32 that purifies the exhaust gas from the exhaust manifold 29; and a housing 33 that houses the exhaust purification catalyst 32. Similarly, the second catalytic converter 37 includes an exhaust purification catalyst 38 that further purifies exhaust gas not completely purified by the first catalytic converter 30; and a housing 39 that houses the exhaust purification catalyst 38. The porous body 34 and housings 33 and 39 are made of a metal material such as stainless steel, carbon steel, or aluminum.

[0024] like Figure 2As shown, the exhaust purification catalyst 32 is an electrically heated catalyst in which a pair of electrodes 35, 35 are mounted on a catalyst body 31. The catalyst body 31 has a cylindrical shape having a honeycomb structure. Each electrode 35 is comb-shaped and has a plurality of wiring portions 35a extending in the circumferential direction of the catalyst body 31. The plurality of wiring portions 35a are spaced apart in the axial direction of the catalyst body 31 and fixed by a fixing portion 35c. The plurality of wiring portions 35a of each electrode 35 are connected by a connecting portion 35b. By passing an electric current through the pair of electrodes 35, the catalyst body 31 can be resistively heated, and the metal catalyst of the exhaust purification catalyst 32 can be activated.

[0025] The housing 33 of the first catalytic converter 30 is formed with an inlet tapered portion 33a, a trunk portion 33b, and an outlet tapered portion 33c. The inlet tapered portion 33a, into which the exhaust gas from the exhaust manifold 29 flows, has a tapered shape in which the exhaust gas flow cross-section expands from the upstream to the downstream of the exhaust gas. The trunk portion 33b is formed on the upstream side of the exhaust gas flow, connected to the inlet tapered portion 33a, and has a cylindrical shape in which the exhaust gas flow cross-section is constant. The outlet tapered portion 33c is formed on the upstream side of the exhaust gas flow, connected to the trunk portion 33b, and has a tapered shape in which the exhaust gas flow cross-section decreases from the upstream to the downstream of the exhaust gas. In this embodiment, the porous body 34 is arranged in the inlet tapered portion 33a, and the exhaust purification catalyst 32 is arranged in the trunk portion 33b. As a result, the axis of the disc-shaped porous body 34 and the axis of the exhaust purification catalyst 32 can be aligned. As a result, the exhaust gas that has passed through the porous body 34 and absorbed heat can be made to flow into the exhaust purification catalyst 32 uniformly.

[0026] In this embodiment, since the engine 2 is a gasoline engine, the exhaust purification catalyst 32 is a three-way catalyst that purifies hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) in the gasoline engine's exhaust. On the other hand, if the internal combustion engine is a diesel engine, the exhaust purification catalyst 32 is an oxidation catalyst that removes carbon monoxide (CO) and hydrocarbons (HC). Furthermore, the exhaust purification catalyst 38 housed in the second catalytic converter 37 is also provided with a catalyst similar to the exhaust purification catalyst 32, depending on the type of internal combustion engine.

[0027] The catalyst body 31 of the exhaust purification catalyst 32 is a catalyst body comprising a metal catalyst for purifying exhaust gas, supported on a carrier (catalyst carrier). The carrier 31a is a honeycomb-shaped carrier. A plurality of through-holes extending along the axis of the carrier 31a are formed therein. The carrier 31a is composed of a ceramic material, such as a porous ceramic material primarily composed of alumina, zirconium dioxide, cordierite, titanium dioxide, silicon carbide, or silicon nitride. The same applies to the carrier of the exhaust purification catalyst 38.

[0028] In the present embodiment, the carrier 31a is composed of a SiC-based ceramic material. The so-called SiC-based ceramic material is a material with SiC as the main material. As long as the conductivity of the carrier 31a can be ensured, other ceramic materials may be further contained. In the present embodiment, since the carrier 31a is composed of a SiC-based ceramic material, the catalyst body 31 can be energized by the electrode 35. A metal catalyst containing at least one of platinum, rhodium and palladium is supported on the wall surface forming the honeycomb structure of the carrier 31a. When the metal catalyst is supported on the carrier, it can be obtained by applying a slurry containing the above-mentioned ceramic material and the metal catalyst to the carrier and sintering it.

[0029] like Figure 3 As shown in Figure (a), the porous body 34 is a disc-shaped carrier with multiple through-holes formed within an annular metal frame (outer periphery) 34a for the passage of exhaust gas. Specifically, a wavy metal strip 34b and a plate-shaped metal strip 34c are wound in an overlapping manner within the metal frame 34a. Consequently, multiple through-holes 34h are formed in the porous body 34, extending from upstream to downstream along the exhaust gas flow.

[0030] In this embodiment, the heat capacity of the porous body 34 is smaller than that of the catalyst body 31. Specifically, at a temperature of 25°C, the heat capacity ratio of the porous body 34 to the catalyst body 31 is 8% or more and 23% or less. For example, the heat capacity of the catalyst body 31 at a temperature of 25°C is in the range of 184 to 322 J / K, while the heat capacity of the porous body 34 at a temperature of 25°C is in the range of 14.7 to 74.1 J / K. This heat capacity range corresponds to the heat capacity of catalysts used in engines of typical commercially available vehicles. By appropriately selecting the materials described above, the heat capacity can be controlled within this range.

[0031] According to this embodiment, exhaust gas flowing from the exhaust manifold 29 into the first catalytic converter 30 passes through the porous body 34 before reaching the exhaust purification catalyst 32, where it is purified. Because the exhaust purification catalyst 32 is an electrically heated catalyst, it can be heated by passing current between a pair of electrodes 35 when the engine 2 is started. Thus, even when relatively low-temperature exhaust gas reaches the exhaust purification catalyst 32 when the engine 2 is started, the heated exhaust purification catalyst 32 is activated early. As a result, exhaust purification efficiency can be improved from the moment the engine 2 is started.

[0032] On the other hand, during rapid acceleration of the vehicle, the engine 2 speed increases, and relatively high-temperature exhaust gas flows from the exhaust manifold 29 into the first catalytic converter 30. Furthermore, as the amount of exhaust gas flowing into the exhaust manifold 29 increases, the activation degree of the exhaust purification catalyst 32 also increases, resulting in a state where the temperature easily rises rapidly.

[0033] Even in such a state, in this embodiment, since the metal material is exposed on the surface of the porous body 34, the heat of the relatively high-temperature exhaust gas flowing into the first catalytic converter 30 can be absorbed by the porous body 34. As a result, excessive activation of the exhaust purification catalyst 32 arranged downstream of the exhaust gas can be suppressed. As a result, the degree of thermal shock acting on the exhaust purification catalyst 32 is reduced, thereby suppressing the occurrence of cracks in the exhaust purification catalyst 32. In order to achieve such an effect, according to the inventor's experiments described later, the heat capacity ratio of the porous body 34 to the catalyst body 31 is 8% or more under a temperature environment of 25°C. In addition, as the heat capacity ratio increases, the pressure loss of the exhaust gas passing through the porous body 34 increases, so the heat capacity ratio of the porous body 34 to the catalyst body 31 is 23% or less. The appropriate range of their heat capacity ratios will be explained in the following examples.

[0034] In addition, if Figure 3 As shown, when viewing the porous body 34A from above, the heat capacity per unit area of the circular central region 34s of the porous body 34A is greater than the heat capacity per unit area of the annular peripheral region 34t surrounding the central region 34s. "Heat capacity per unit area" refers to the value obtained by dividing the heat capacity of the entire region under a temperature environment of 25°C by the area of the region when viewed from above. The flow velocity of exhaust gas flowing into the central region 34s is higher than that of the peripheral region 34t, and the flow rate of this exhaust gas is also greater. Therefore, by increasing the heat capacity of the central region 34s, the heat of the exhaust gas passing through the central region 34s can be efficiently absorbed. This can suppress the temperature rise of the center of the exhaust purification catalyst 32 when viewed from above, thereby reducing the degree of thermal shock to the catalyst body 31.

[0035] More specifically, the porous body 34A comprises a wave-shaped metal strip 34bt (34bs) and a plate-shaped metal strip 34ct (34cs) wound in an overlapping manner within a circular, ring-shaped metal frame 34a. The spacing between the waves of the metal strip 34bs in the central region 34s is smaller than the spacing between the waves of the metal strip 34bt in the peripheral region 34t. Consequently, when viewing the porous body 34 from above, the opening area of the through-holes 34hs formed in the central region 34s is smaller than the opening area of the through-holes 34ht formed in the peripheral region 34t. Furthermore, the number of through-holes 34hs per unit area in the central region 34s is greater than the number of through-holes 34ht per unit area in the peripheral region 34t. In addition to the above-mentioned effects, by increasing the number of through holes 34hs corresponding to the reduction in the opening area of the central region 34s, the exhaust pressure loss can be reduced while ensuring the heat capacity of the central region 34s.

[0036] [Example]

[0037] The following describes embodiments of the present invention.

[0038] <Example 1>

[0039] As shown below, we created Figure 2 The first catalytic converter 30 shown. As a porous body 34. As the porous body 34, a circular plate-shaped porous body made of stainless steel with a diameter of 70 mm and a length of 10 mm was produced. The thickness of the annular metal frame 34a is 1.0 mm. The thickness of the wavy metal strip 34b and the plate-shaped metal strip 34c is 30 μm. The number of cells (the number of through holes) per square inch of the porous body 34 is 600. The mass of the porous body 34 is 41.0 g. The heat capacity of the porous body 34 is 18.9 J / K under a temperature environment of 25°C. Next, a slurry of ceria-zirconium dioxide containing rhodium particles in a specified proportion as a metal catalyst is applied to a SiC substrate (carrier), dried, and then sintered. The mass of the catalyst body 31 thus obtained is 244 g. The heat capacity of the catalyst body 31 is 174 J / K under a temperature environment of 25°C. Under a temperature environment of 25° C., the heat capacity ratio of the porous body 34 to the catalyst body 31 is 11%.

[0040] <Example 2>

[0041] The first catalytic converter 30 was produced in the same manner as in Example 1. The difference from Example 1 was that the length of the porous body 34 was 15 mm. The mass of the porous body 34 was 62.0 g. The heat capacity of the porous body 34 was 28.6 J / K at a temperature of 25°C.

[0042] <Comparative Example 1>

[0043] A first catalytic converter was produced in the same manner as in Example 1. The difference from Example 1 was that the porous body 34 was not provided.

[0044] <Comparative Example 2>

[0045] A first catalytic converter was produced in the same manner as in Example 1. The difference from Example 1 was that the length of the porous body 34 was 5 mm. The mass of the porous body 34 was 21.0 g. The heat capacity of the porous body 34 was 9.7 J / K at a temperature of 25°C.

[0046] Evaluation test

[0047] The first catalytic converters of Example 1, Example 2 and Comparative Example 1 and Comparative Example 2 were respectively connected to an exhaust pipe having a bypass path, and the bypass path came from an engine with an exhaust volume of 2.5L. Next, a test was carried out under rapid acceleration conditions for 500 cycles, with the process of changing the engine speed from 1000rpm to 3000rpm as one cycle. At this time, it was confirmed whether cracks occurred in the catalyst body. In addition, the bed temperature of these catalyst bodies and the temperature change (maximum heating rate) at a position 5mm downstream from the porous body were measured. The results are shown in Figure 4 Next, the temperature increase rate reduction of Example 1, Example 2, and Comparative Example 2 was measured based on the maximum temperature increase rate of Comparative Example 1. The results are shown in the following Tables 1 and Figure 5 (a) Based on the exhaust pressure loss of Comparative Example 1, the pressure loss increase rates of Example 1, Example 2, and Comparative Example 2 were measured. The results are shown in Tables 1 and Figure 5 (b) As a reference example, the catalytic converter of Comparative Example 1 was tested under rapid acceleration conditions for 500 cycles, with one cycle consisting of changing the engine speed from 1000 rpm to 2900 rpm. The results are shown in Table 1.

[0048] Table 1

[0049]

[0050] Results and Investigations

[0051] The catalyst bodies of Examples 1 and 2 did not develop cracks, but the catalyst bodies of Comparative Examples 1 and 2 developed cracks. This is believed to be because, under rapid acceleration conditions, in Examples 1 and 2, the heat of the exhaust gas was fully absorbed by the porous body, and therefore, the catalyst bodies of Examples 1 and 2 did not develop cracks. In addition, when the engine speed was changed from 1000 rpm to 2900 rpm as in the reference example, it was believed that due to the low exhaust temperature and low exhaust flow rate, the catalyst body did not develop cracks even when the catalytic converter of Comparative Example 1 was used. From this perspective, in order to prevent the catalyst body from developing cracks, as in the reference example, Figure 5 As shown in (a), the heat capacity ratio of the porous body to the catalyst body is 8% or more, more preferably 11% or more. Figure 5 As shown in (b), taking into account the pressure loss of the porous body, the heat capacity ratio of the porous body to the catalyst body is 23% or less, more preferably 16% or less.

Claims

1. An exhaust purification device, characterized in that: This is an exhaust gas purification device equipped with a catalytic converter that purifies exhaust gas from the exhaust manifold. The catalytic converter comprises: a porous body made of a metal material through which exhaust gas from the exhaust manifold passes; and an exhaust gas purification catalyst for purifying the exhaust gas having passed through the porous body, The exhaust gas purification catalyst is an electrically heated catalyst having a pair of electrodes mounted on a catalyst body. The porous body has a plurality of through holes formed along the upstream side to the downstream side of the exhaust gas, and the surface of the porous body is a surface where the metal material is exposed. Under a temperature environment of 25° C., a heat capacity ratio of the porous body to the catalyst body is 8% or more and 23% or less.

2. The exhaust gas purification device according to claim 1, characterized in that: The catalytic converter includes a metal casing that houses the porous body and the exhaust gas purification catalyst. As the housing, there are formed: an inlet tapered portion into which the exhaust gas from the exhaust manifold flows and into which a flow path cross section of the exhaust gas expands from an upstream side toward a downstream side of the exhaust gas; a trunk portion connected to the inlet-side tapered portion and having a constant exhaust flow path cross section; and The outlet tapered portion is connected to the trunk portion and has a flow path cross section of the exhaust gas that decreases from the upstream to the downstream of the exhaust gas. The porous body is arranged in the inlet tapered portion, The exhaust gas purification catalyst is arranged in the trunk portion.

3. The exhaust gas purification device according to claim 2, characterized in that: The porous body is in the shape of a circular plate, In a plan view of the porous body, a heat capacity per unit area of a central region of the porous body is larger than a heat capacity per unit area of a peripheral region surrounding the central region.

4. The exhaust gas purification device according to claim 3, characterized in that: In a plan view of the porous body, the opening area of the through-holes formed in the central region is smaller than the opening area of the through-holes formed in the peripheral region. The number of through holes per unit area in the central region is greater than the number of through holes per unit area in the peripheral region.

5. The exhaust gas purification device according to claim 1, characterized in that: The catalyst body has a honeycomb-shaped carrier made of a SiC-based ceramic material.

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