JP2019019817A - Exhaust emission control device - Google Patents

Abstract

To provide an exhaust emission control device capable of early raising a temperature of a second catalyst from start of an engine and thus enhance purification efficiency of exhaust gas earlier than ever before, even when providing a first catalyst and the second catalyst through which exhaust gas from the first catalyst passes.SOLUTION: An exhaust emission control device 3 includes an exhaust emission control catalyst 32 for purifying exhaust gas from an exhaust manifold 29. The exhaust emission control catalyst 32 includes: a first catalyst 34 for purifying the exhaust gas from the exhaust manifold 29; and a second catalyst 35 for purifying the exhaust gas that has passed through the first catalyst 34. Heat capacity of the first catalyst 34 is smaller than that of the second catalyst 35. The heat capacity of the second catalyst 35 is 184-322 J/K under a temperature environment of 25°C. The heat capacity of the first catalyst 34 is 20 J/K or less under the temperature environment of 25°C.SELECTED DRAWING: Figure 8

Description

  The present invention relates to an exhaust gas purification apparatus including an exhaust gas purification catalyst that purifies exhaust gas from an exhaust manifold.

  Conventionally, in order to purify exhaust gas discharged from an engine, an exhaust gas purification device is connected to the exhaust manifold. The exhaust gas purifying apparatus includes a catalyst that purifies exhaust gas from an exhaust manifold, and the catalyst includes a metal catalyst that purifies the exhaust gas and a carrier (catalyst carrier) that supports the metal catalyst.

  For example, in Patent Document 1, as such an exhaust gas purification device, an exhaust gas purification device including a first catalyst that purifies exhaust gas from an exhaust manifold and a second catalyst that purifies exhaust gas that has passed through the first catalyst. Is disclosed. In this exhaust gas purification apparatus, the first catalyst has a smaller heat capacity than the second catalyst. Thereby, the temperature of the first catalyst can be raised quickly, and the exhaust performance at the time of engine start can be improved.

Japanese Patent Laying-Open No. 2015-165095

  However, even with the configuration as disclosed in Patent Document 1, at the stage of activation of the first catalyst at the time of starting the engine, the exhaust gas passing through the first catalyst receives heat from the reaction of the exhaust gas in the first catalyst. However, more heat than the amount of heat input may be absorbed by the first catalyst itself. That is, when the heat of the exhaust gas is deprived much by the first catalyst, the temperature of the exhaust gas that passes through the first catalyst and travels toward the second catalyst may be lower than when the first catalyst is not provided. As a result, the time from when the engine is started to the activation of the second catalyst is delayed, and the time from when the engine is started until the predetermined purification efficiency is reached may be longer than when the first catalyst is not provided. .

  The present invention has been made in view of such a point, and even when the first catalyst and the second catalyst through which the exhaust gas from the first catalyst passes are provided, the second catalyst is started from the start of the engine. It is an object of the present invention to provide an exhaust gas purification apparatus that can raise the temperature of the exhaust gas at an early stage and increase the purification efficiency of the exhaust gas earlier than before.

  In view of the above problems, as a result of extensive studies by the inventor, if the heat capacity of the first catalyst is made extremely smaller than the heat capacity of the second catalyst, the exhaust gas from the exhaust manifold passes through the first catalyst. Furthermore, it was considered that the heat of exhaust gas can be suppressed from being taken away by the first catalyst. Heretofore, it has been considered that when the heat capacity of the catalyst is extremely reduced, the size of the catalyst becomes extremely small, so that there is almost no exhaust gas purification performance. However, as is clear from the experiments described later by the inventor, new knowledge has been obtained that the first catalyst can sufficiently contribute to the purification of exhaust gas even if the first catalyst is extremely smaller than the second catalyst. .

  The present invention is based on the inventor's new knowledge, the exhaust gas purification device is an exhaust gas purification device including an exhaust gas purification catalyst for purifying exhaust gas from an exhaust manifold, and the exhaust gas purification catalyst is A first catalyst that purifies the exhaust gas from the exhaust manifold, and a second catalyst that purifies the exhaust gas that has passed through the first catalyst, wherein the heat capacity of the first catalyst is greater than the heat capacity of the second catalyst. The heat capacity of the second catalyst is 184 to 322 J / K under a temperature environment of 25 ° C., and the heat capacity of the first catalyst is 20 J / K or less under a temperature environment of 25 ° C. To do.

  According to the present invention, the heat capacity of the second catalyst is in the range of the heat capacity of a general catalyst used in a vehicle, whereas the heat capacity of the first catalyst is extreme with respect to the heat capacity of the second catalyst. Is less than 20 J / K. Thus, even when a relatively low temperature exhaust gas passes through the first catalyst from the exhaust manifold when the engine is started, the first catalyst is heated up early because the first catalyst has a small heat capacity as described above. In addition, since the heat of the exhaust gas that passes through the first catalyst is not easily deprived by the first catalyst, the temperature of the second catalyst is also raised quickly following the first catalyst by the heat of the exhaust gas that has passed through the first catalyst. Can do. As a result, the first catalyst is activated earlier than when the engine is started, and the second catalyst is also activated earlier than before, so that the exhaust gas purification efficiency is increased earlier than when the engine is started. be able to.

  Here, since the heat capacity of the first catalyst is 20 J / K or less under a temperature environment of 25 ° C., the size of the first catalyst is considerably smaller than that of the conventional catalyst. For this reason, a 1st catalyst can be arrange | positioned easily, without providing the space for arrange | positioning a 1st catalyst newly. When the heat capacity of the first catalyst exceeds 20 J / K, as is apparent from the results of experiments conducted by the inventors, which will be described later, the second catalyst starts from the start of the engine more than when the first catalyst is not provided. It has been found that the time until activation becomes longer.

  Here, for example, the first catalyst may be disposed in an exhaust manifold or an exhaust pipe upstream of the second catalyst, but as a more preferable aspect, the exhaust gas purifying device includes the first and second catalysts. And a metal housing that houses the first and second catalysts therein, and exhaust gas from the exhaust manifold flows into the housing, and upstream of the exhaust gas. The inlet side cone part in which the cross section of the exhaust gas channel is expanded from the downstream side, the body part that is continuous with the inlet side cone part, and the gas channel cross section of the exhaust gas is constant, and is continuous with the body part. From the upstream to the downstream, an outlet side cone portion having a reduced exhaust gas flow path cross section is formed, the first catalyst is disposed in the inlet side cone portion, and the second catalyst is The body part It is located in.

  According to this aspect, the 2nd catalyst is arrange | positioned at the trunk | drum of the housing of a catalytic converter like the conventional catalyst. On the other hand, since the first catalyst is smaller in size than the second catalyst, the first catalyst can be arranged in an exhaust pipe or the like. In this aspect, the first catalyst is located in the inlet cone portion. Is arranged. Thereby, compared with the case where the 1st catalyst is arrange | positioned to an exhaust pipe, the 1st catalyst which is a large diameter and short along the flow path can be arrange | positioned at an exhaust gas purification apparatus. As a result, the pressure loss of the exhaust gas passing through the first catalyst can be reduced.

  The carrier for supporting the metal catalyst of the first catalyst (catalyst carrier) may be either a carrier made of a ceramic material or a carrier made of a metal material. In a more preferred embodiment, the first catalyst is A carrier made of a metal material carries a metal catalyst for purifying exhaust gas.

  For example, the specific heat of a metal material such as stainless steel used for the carrier is generally smaller than that of a ceramic material such as cordierite used for the carrier. Therefore, according to this aspect, the 1st catalyst which satisfy | fills the heat capacity requirements of the 1st catalyst mentioned above can be obtained easily by making the support | carrier of a 1st catalyst into the support | carrier consisting of a metal material.

  In addition, since the first catalyst is an extremely small catalyst as compared with conventional catalysts, the carrier made of a ceramic material is easily cracked by a thermal shock or the like. In this embodiment, the carrier made of a metal material is used. Such cracks can be avoided. Further, when the first catalyst is disposed in the inlet cone portion of the metal housing of the catalytic converter, the inlet cone portion of the housing and the first catalyst carrier can be easily joined by welding.

  As a more preferable aspect, the carrier has a disk shape, and includes an outer peripheral portion, an inner peripheral portion formed inside the outer peripheral portion, and between the outer peripheral portion and the inner peripheral portion. A plurality of holes are formed in the direction in which the exhaust gas passes, and the first gas passage part in which the metal catalyst is supported on the wall surface forming each hole, and the direction in which the exhaust gas passes inside the inner peripheral part. A second gas passage portion that is a hollow portion formed along the cross-sectional area of the flow path through which the exhaust gas of the first gas passage portion flows, and the flow path of the flow path through which the exhaust gas of the second gas passage portion flows. The ratio of the cross-sectional area of the flow path through which the exhaust gas of the second gas passage portion flows to the total cross-sectional area with respect to the cross-sectional area is 3.5 to 25%.

  According to this aspect, the speed of the exhaust gas flowing toward the first catalyst is high in the center, and the second gas passage portion exists at that position. Since the first gas passage portion is formed with a plurality of holes and the second gas passage portion is a hollow portion, the second gas passage portion has a lower pressure loss of the exhaust gas than the first gas passage portion, and The exhaust gas easily flows through the two gas passages. As a result, the flow rate of the exhaust gas flowing through the second gas passage is secured while the flow rate is increased, and the exhaust gas flows through the central portion of the second catalyst. As a result, the central portion of the second catalyst is heated at an early stage, and the heat at the time of the temperature increase is uniformly transmitted from the central portion to the surroundings. The temperature can be raised. In addition, when the exhaust gas passes through the first gas passage portion, the temperature of the first gas passage portion is increased, and the heated heat is transmitted to the exhaust gas passing through the second gas passage portion.

  Here, when the ratio of the cross-sectional area described above is less than 3.5%, the flow rate of the exhaust gas flowing through the second gas passage portion decreases, and thus the temperature increase effect of the second catalyst may not be sufficiently expected. . On the other hand, when the ratio of the cross-sectional area exceeds 25%, the flow rate of the exhaust gas flowing through the first gas passage portion of the first catalyst is reduced, so that the temperature raising effect of the first catalyst is reduced. Thereby, the temperature rising effect of the second catalyst may not be fully expected.

  According to the present invention, even if the first catalyst and the second catalyst through which the exhaust gas from the first catalyst pass are provided, the temperature of the second catalyst is raised quickly from the time of engine start, and the exhaust gas purification efficiency Can be raised earlier than before.

It is a typical key map for explaining the exhaust gas purification device concerning a 1st embodiment of the present invention. It is a typical perspective view of the 1st catalytic converter of the exhaust gas purification apparatus shown in FIG. FIG. 3 is a schematic plan view of a first catalyst shown in FIG. 2. It is a typical conceptual diagram for demonstrating the exhaust gas purification apparatus which concerns on 2nd Embodiment of this invention. FIG. 5 is a schematic plan view of a first catalyst shown in FIG. 4. 4 is a schematic plan view of a first catalyst of Example 2 and Example 3. FIG. 6 is a schematic plan view of a first catalyst of Example 4. FIG. It is the graph which showed the HC50% purification | cleaning arrival time of the waste gas which passed the 1st catalytic converter which concerns on Examples 1-4 and Comparative Examples 1-3. It is the graph which showed the relationship between the heat capacity of the 1st catalyst of Examples 1-4 and Comparative Examples 1-3, and HC50% purification | cleaning arrival time of the waste gas which passed the 1st catalytic converter. It is the graph which measured the change of the exhaust gas temperature after passing the 1st catalyst of Examples 1 and 3 and Comparative Examples 1-3. It is the graph which showed the relationship between the area ratio of the 2nd gas passage part of the 1st catalyst of Examples 5-7 and Comparative Examples 4 and 5, and HC50% purification arrival time of the exhaust gas which passed the 1st catalytic converter. 6 is a graph showing the relationship between the area ratio of the second gas passage part of the first catalyst of Examples 5 to 7 and Comparative Example 5 and the temperature rise temperature of the first catalyst.

[First Embodiment]
Hereinafter, an exhaust gas purifying apparatus according to a first embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a schematic conceptual diagram for explaining an exhaust gas purifying apparatus 3 according to an embodiment of the present invention. FIG. 2 is a schematic perspective view of a first catalytic converter 30 of the exhaust gas purifying apparatus 3 shown in FIG. It is. In FIG. 2, the housing 33 is shown in a halved state to show the inside of the first catalytic converter 30.

  As shown in FIG. 1, the exhaust gas purification device 3 according to this embodiment is a device that is attached downstream of the engine 2 and purifies the exhaust gas after combustion by the engine 2. The engine 2 may be either a gasoline engine or a diesel engine. In the present embodiment, a gasoline direct injection engine is illustrated in FIG. 1 as an example.

  In the engine 2, the air sucked through the intake valve 25 enters the combustion chamber formed by the cylinder block 21 and the piston 22 and is mixed with the fuel (gasoline) injected by the fuel injection valve 28. The mixed air-fuel mixture is ignited by the spark plug 27 and burned in the combustion chamber, and the exhaust gas after combustion is discharged from the exhaust manifold 29 via the exhaust valve 26.

  The exhaust gas exhausted by the exhaust manifold 29 is purified by the exhaust gas purification device 3. Specifically, the exhaust gas purification device 3 is connected to the first catalytic converter 30 via the exhaust pipe 36 at the downstream side of the first catalytic converter 30 connected to the exhaust manifold 29 and the first catalytic converter 30. A second catalytic converter 37. The first catalytic converter 30 is disposed, for example, in an engine room (not shown) of the vehicle, and the second catalytic converter 37 is disposed, for example, under the floor of the vehicle (not shown).

  The first catalytic converter 30 includes an exhaust gas purification catalyst 32 that purifies the exhaust gas from the exhaust manifold 29, and a housing 33 that houses the exhaust gas purification catalyst 32. Similarly, the second catalytic converter 37 includes an exhaust gas purification catalyst 38 for further purifying exhaust gas that could not be purified by the first catalytic converter 30, and a housing 39 for housing the exhaust gas purification catalyst 38. The housings 33 and 39 are made of a metal material such as stainless steel, carbon steel, or aluminum, for example.

  As shown in FIG. 2, the housing 33 of the first catalytic converter 30 is formed with an entrance side cone portion 33 a, a body portion 33 b, and an exit side cone portion 33 c. The inlet-side cone portion 33a has a cone shape in which the exhaust gas from the exhaust manifold 29 flows in and the cross section of the exhaust gas flow path is enlarged from the upstream side to the downstream side of the exhaust gas. The body portion 33b is formed continuously with the inlet-side cone portion 33a on the upstream side where the exhaust gas flows, and has a cylindrical shape with a constant cross section of the exhaust gas. The outlet side cone portion 33c is formed continuously with the body portion 33b on the upstream side where the exhaust gas flows, and has a cone shape in which the cross section of the exhaust gas flow path is reduced from the upstream side to the downstream side of the exhaust gas.

  In the present embodiment, the exhaust gas purification catalyst 32 of the first catalytic converter 30 includes a first catalyst 34 that purifies the exhaust gas from the exhaust manifold 29 and a second catalyst 35 that purifies the exhaust gas that has passed through the first catalyst 34. ing. The first catalyst 34 is disposed in the entrance cone portion 33a, and the second catalyst 35 is disposed in the body portion 33b.

  In the present embodiment, since the engine 2 is a gasoline engine, the first catalyst 34 and the second catalyst 35 are hydrocarbon (HC), carbon monoxide (CO), nitride oxide (NOx) of exhaust gas of the gasoline engine. ) Is a three-way catalyst. On the other hand, when the internal combustion engine is a diesel engine, the first catalyst 34 and the second catalyst 35 are oxidation catalysts that remove carbon monoxide (CO), hydrocarbons (HC), and the like. The exhaust gas purification catalyst 38 accommodated in the second catalytic converter 37 is also set to the same catalyst as the first and second catalysts 34 and 35 according to the type of the internal combustion engine.

  The first catalyst 34 and the second catalyst 35 are obtained by carrying a metal catalyst for purifying exhaust gas on a carrier (catalyst carrier). These carriers may be made of either a ceramic material or a metal material, more preferably a metal material. The metal material is preferably a material having heat resistance and corrosion resistance, and examples thereof include stainless steel and aluminum.

  Here, for example, the specific heat of a metal material such as stainless steel as a carrier material is smaller than that of a ceramic material such as cordierite as a carrier material. As a result, by using the carrier of the first catalyst 34 as a carrier made of a metal material, a catalyst that satisfies the conditions of the heat capacity of the first catalyst 34 as described later can be easily manufactured. In addition to this, since the first catalyst 34 satisfies the condition of an extremely small heat capacity as will be described later, a carrier made of a ceramic material is easily cracked by a thermal shock or the like. Cracks can be avoided.

  As shown in FIGS. 2 and 3, the carrier of the first catalyst 34 has a disk shape, and a plurality of cells (holes) through which exhaust gas passes are inside a ring-shaped metal frame (outer peripheral portion) 34 a. It is a formed structure. Specifically, in the first catalyst 34, a metal band 34b bent in a wave shape and a plate-shaped metal band 34c are overlapped and wound inside the metal frame 34a to form a plurality of cells. Forming.

  On the other hand, in the present embodiment, the carrier of the second catalyst 35 is a columnar carrier made of a ceramic material and having a structure in which a plurality of cells through which exhaust gas passes are formed. Examples of the ceramic material include a porous ceramic material mainly containing any one of alumina, zirconia, cordierite, titania, silicon carbide, silicon nitride, and the like. The same applies to the carrier of the exhaust gas purification catalyst 38.

  The metal catalyst of the 1st catalyst 34 and the 2nd catalyst 35 is granular, and is carry | supported via the ceramic material on the inner wall surface which forms these cells. As the metal serving as the metal catalyst, a noble metal containing at least one of platinum, rhodium, and palladium is selected. Examples of the ceramic material that supports the catalyst metal on the carrier include zirconia and alumina, ceria and alumina, or a mixed material of ceria-zirconia and alumina. When the metal catalyst is supported on the carrier, it can be obtained by coating the carrier on the slurry containing the ceramic material and the metal catalyst described above and firing the slurry.

  In the present embodiment, the heat capacity of the first catalyst 34 is smaller than the heat capacity of the second catalyst 35. Specifically, the heat capacity of the first catalyst 34 is 20 J / K or less under a temperature environment of 25 ° C., and the heat capacity of the second catalyst 35 is 184 to 322 J / K under a temperature environment of 25 ° C.

  The range of the heat capacity of the second catalyst 35 is the heat capacity of the catalyst that is generally applied according to the displacement of the engine of a commercially available vehicle. This heat capacity can be selected by appropriately selecting the above-described materials and the like. Can fall within the range. When the heat capacity of the second catalyst 35 is less than 184 J / K, the size (heat capacity) of the second catalyst 35 is too small, and thus the exhaust gas purification performance is not sufficient. On the other hand, when the heat capacity of the second catalyst 35 exceeds 322 J / K, the size (heat capacity) of the second catalyst 35 is too large. Become.

  According to this embodiment, the heat capacity of the first catalyst 34 is 20 J / K or less, which is extremely small with respect to the heat capacity of the second catalyst 35. Therefore, even when a relatively low temperature exhaust gas passes through the first catalyst 34 from the exhaust manifold 29 when the engine 2 is started, the first catalyst 34 has a small heat capacity as described above, and therefore, compared with the conventional catalysts. The temperature of the first catalyst 34 is raised early.

  Further, the heat of the exhaust gas passing through the first catalyst 34 is not easily deprived by the first catalyst 34 because the heat capacity of the first catalyst 34 is small, and reaction heat with the metal catalyst is added to the heat of the exhaust gas. Therefore, the heat of the exhaust gas that has passed through the first catalyst 34 can also raise the temperature of the second catalyst 35 early after the start of the engine 2 following the first catalyst 34. As a result, since the first catalyst 34 is activated early from the time of starting the engine 2 and the second catalyst 35 is also activated earlier than before, the exhaust gas purification efficiency is increased early. be able to. Furthermore, since the metal catalyst of the first catalyst 34 plays a part in the purification of exhaust gas, the reaction heat of the metal catalyst of the second catalyst 35 can be suppressed as compared with the case where the first catalyst 34 is not provided. As a result, deterioration of the metal catalyst in the second catalyst 35 can be suppressed.

  When the heat capacity of the first catalyst 34 exceeds 20 J / K, the time from when the engine 2 is started until the second catalyst 35 is activated becomes longer than when the first catalyst 34 is not provided. From the viewpoint of manufacturing, the heat capacity of the first catalyst 34 is preferably 3 J / K or more.

  Furthermore, since the heat capacity of the first catalyst 34 is 20 J / K or less under a temperature environment of 25 ° C., the size of the first catalyst is considerably smaller than that of a conventional general catalyst. For this reason, the first catalyst 34 can be easily arranged without newly providing a space for arranging the first catalyst 34.

  In particular, in the present embodiment, the second catalyst 35 is disposed in the body portion 33b of the housing 33 of the first catalytic converter 30 and the first catalyst 34 is disposed in the entry-side cone portion 33a as in the conventional catalyst. Has been. Thereby, compared with the case where the 1st catalyst 34 is arrange | positioned to an exhaust pipe, the 1st catalyst with a big diameter and short length along the flow path of waste gas can be arrange | positioned. As a result, the pressure loss of the exhaust gas passing through the first catalyst 34 can be reduced.

  In addition, since the exhaust gas passes through the first catalyst 34 and is rectified on the upstream side of the second catalyst 35, the velocity gradient of the exhaust gas toward the second catalyst 35 can be moderated. The velocity distribution can be smoothed.

  As described above, the carrier of the first catalyst 34 is made of a metal material. Thus, when the first catalyst 34 is disposed on the entrance side cone portion 33a of the metal housing 33, the entrance side cone portion 33a and the carrier of the first catalyst 34 can be easily joined by welding. .

[Second Embodiment]
FIG. 4 is a schematic conceptual diagram for explaining an exhaust gas purifying apparatus according to a second embodiment of the present invention, and FIG. 5 is a schematic plan view of the first catalyst 34A shown in FIG. The exhaust gas purifying apparatus according to the second embodiment is different from the first embodiment in the shape of the first catalyst 34A, and thus has the same function as other members of the catalyst purifying apparatus according to the first embodiment. Components are denoted by the same reference numerals, and detailed description thereof is omitted.

  The first catalyst 34A according to the second embodiment is obtained by carrying a metal catalyst for purifying exhaust gas on a carrier (catalyst carrier) 34 'made of the above-described metal material. The carrier 34 ′ has a disk shape and includes a metal frame (outer peripheral part) 34 a and a ring-shaped inner peripheral part 34 e formed inside the metal frame 34 a. The first catalyst 34A further includes a first gas passage 34f and a second gas passage 34g.

  The first gas passage portion 34f is formed between the metal frame 34a and the inner peripheral portion 34e, and the first gas passage portion 34f has a plurality of cells (holes) 34h, 34h,. Specifically, the plurality of cells 34h are formed by overlapping and winding a wave-like bent metal strip 34b and a plate-like metal strip 34c, as in the first embodiment. Yes. Similarly to the first embodiment, each cell 34h is formed in the direction in which the exhaust gas passes, and each cell 34h carries the metal catalyst shown in the first embodiment.

  The second gas passage portion 34g is a hollow portion formed along the direction in which the exhaust gas passes inside the inner peripheral portion 34e. The first gas passage portion 34f and the second gas passage portion 34g It is partitioned by the part 34e. Further, as shown in FIG. 5, the second gas passage part 34 g is arranged at a position facing the central part 35 a of the second catalyst 35.

  In the present embodiment, the exhaust gas of the second gas passage part 34g with respect to the sum of the cross-sectional area of the flow path through which the exhaust gas in the first gas passage part 34f flows and the cross-sectional area of the flow path in which the exhaust gas of the second gas passage part 34g flows. The ratio of the cross-sectional area of the flow path through which the gas flows is 3.5 to 25%.

  The flow path through which the exhaust gas flows in the first gas passage portion 34f is a plurality of cells 34h, and the cross-sectional area of the flow path is the same as the area of the plurality of cells 34h in the virtual cross section orthogonal to the direction in which the exhaust gas flows. The total area. Specifically, the cross-sectional area is determined from the area of the region surrounded between the metal frame 34a and the inner peripheral portion 34e in the plan view shown in FIG. 5, and the metal strip 34b and the plate-shaped metal strip. This is the area obtained by subtracting the cross-sectional area of 34c.

  On the other hand, the flow path through which the gas of the second gas passage section 34g passes is the hollow section itself, and the cross-sectional area of the flow path is the area of the hollow section in the virtual cross section orthogonal to the direction in which the exhaust gas flows. Specifically, this cross-sectional area is the area of a region surrounded by the inner peripheral portion 34e in the plan view shown in FIG.

  According to the second embodiment, the axis of the disc-shaped first catalyst 34A and the columnar second catalyst 35 coincide with each other, and the velocity of the exhaust gas flowing toward the first catalyst 34A as shown in FIG. The center is high, and the second gas passage part 34g exists at that position. The first gas passage portion 34f is formed by a plurality of hole cells (holes) 34h, 34h,..., And the second gas passage portion 34g is a hollow portion, so the second gas passage portion 34g Compared to the portion 34f, the pressure loss of the exhaust gas is small, and the exhaust gas easily flows through the second gas passage portion 34g.

  As a result, while ensuring the flow rate of the exhaust gas flowing through the second gas passage portion 34g, the flow velocity is increased, and this exhaust gas flows into the central portion 35a of the second catalyst 35. As a result, the temperature of the central portion 35a of the second catalyst 35 is raised early, and the heat at the time of the temperature rise is uniformly transferred from the central portion 35a to the outer peripheral portion 35b, so that the second catalyst 35 is activated early. The temperature can be raised early. Since the exhaust gas also passes through the first gas passage portion 34f and the metal catalyst in the first gas passage portion 34f is activated by the exhaust gas, the temperature of the first gas passage portion 34f is increased, and this temperature increase is performed. The generated heat is transmitted to the exhaust gas passing through the second gas passage part 34g.

  In particular, in the present embodiment, the second catalyst 35 can be activated early and the temperature can be raised by setting the above-described cross-sectional area ratio within the above-described range. When the ratio of the cross-sectional area is less than 3.5%, the flow rate of the exhaust gas flowing through the second gas passage portion 34g of the first catalyst 34A decreases, as is apparent from the experiment of the inventor described later. For this reason, the temperature raising effect of the second catalyst 35 may not be sufficiently expected. On the other hand, when the ratio of the cross-sectional area exceeds 25%, the flow rate of the exhaust gas flowing through the first gas passage portion 34f of the first catalyst 34A decreases, and the temperature increase effect of the first catalyst 34A decreases. End up. Also in this case, the temperature raising effect of the second catalyst 35 may not be fully expected.

  Examples of the present invention will be described below.

<Example 1>
As shown below, the first catalytic converter 30 shown in FIG. 2 was produced. First, a carrier having the shape shown in FIG. 3 was prepared as a carrier (metal substrate) for the first catalyst 34. Specifically, the carrier of the first catalyst 34 is a carrier (metal carrier) made of disk-shaped stainless steel having a diameter of 80 mm and a length of 2 mm, and the thickness of the ring-shaped metal frame (outer peripheral part) 34 a. Is 1.0 mm, the thickness of the corrugated metal strip 34 b and the plate-shaped metal strip 34 c is 30 μm, the number of cells per square inch is 600, and the weight of the carrier is It was 11.5 g.

  Next, as a metal catalyst, a slurry of ceria-zirconia containing rhodium particles in a predetermined ratio was coated on the carrier, dried at 120 ° C., and calcined at 500 ° C. As a result, the carrier was coated with a coat layer weighing 1.3 g, of which the rhodium weight was approximately 0.1 g.

  The heat capacity of the obtained first catalyst 34 was calculated from the weight of the carrier and the coat layer and the specific heat of each material. The specific heat of the stainless steel as the carrier material is 0.46 J / g · K in a temperature environment of 25 ° C., and the specific heat of the ceria-zirconia after firing contained in the coat layer is in a temperature environment of 25 ° C. And 0.77 J / g · K. Therefore, the heat capacity of the first catalyst 34 of Example 1 was 6.3 J / K under a temperature environment of 25 ° C. Since the rhodium content in the first catalyst 34 is very small, the heat capacity of rhodium is not taken into consideration.

  Next, as a second catalyst 35, a ceramic carrier made of cordierite having a diameter of 103 mm is coated with a ceria-zirconia slurry containing platinum and rhodium particles as a metal catalyst, and the same as the first catalyst. , Dried and fired. The second catalyst 35 includes 1.8 g of granular platinum and 0.2 g of granular rhodium as a metal catalyst. Note that, similarly to the first catalyst 34, the heat capacity of the second catalyst 35 was calculated. The heat capacity of the second catalyst 35 is 322 J / K under a temperature environment of 25 ° C.

  Next, the first catalyst 34 is welded to the entrance side cone portion 33a of the housing 33, and then the body portion 33b is welded to the entrance side cone portion 33a, and then the second catalyst 35 is attached to the body portion 33b by Aaron ceramics (registered). Trademark). Finally, the outlet cone portion 33c was welded to the body portion 33b. As a result, a first catalytic converter 30 according to Example 1 was obtained.

<Example 2>
A first catalytic converter was produced in the same manner as in Example 1. The first catalytic converter of the second embodiment is different from that of the first embodiment in that a first catalyst 34B shown in FIG. 6A is used. Specifically, the carrier (metal substrate) of the first catalyst 34B is a carrier (metal carrier) made of disc-shaped stainless steel having a diameter of 80 mm and a length of 10 mm, and a ring-shaped metal frame (outer peripheral part). ) 34a has a thickness of 1.0 mm. Next, a strand made of stainless steel having a total length of 500 mm and a diameter of 0.12 mm was processed into a coil with a diameter of 5 mm, and a total of eight coils 34 d were produced by stacking five of these, as shown in FIG. What fixed these coils 34d inside the metal frame (outer peripheral part) 34a was used as the carrier for the first catalyst of Example 2. The weight of this carrier was 20.3 g.

  As in Example 1, this support was coated with a slurry containing rhodium at a predetermined ratio, dried at 120 ° C., and calcined at 500 ° C. As a result, a coating layer having a weight of 3.0 g was formed on the carrier, and the weight of rhodium was about 0.1 g. From the weight of the carrier and the coat layer, the heat capacity of the obtained first catalyst 34B was calculated in the same manner as in Example 1. The heat capacity of the first catalyst 34B of Example 2 was 11.7 J / K under a temperature environment of 25 ° C.

<Example 3>
A first catalytic converter was produced in the same manner as in Example 1. The first catalytic converter of Example 3 is different from that of Example 1 in that the first catalyst 34B shown in FIG. 6A is used. The first catalyst of Example 3 is the same as that of Example 2. It is a catalyst of the shape. Specifically, the carrier (metal substrate) of the first catalyst 34B is a disc-shaped stainless steel carrier (metal carrier) having a diameter of 70 mm and a length of 10 mm, and a ring-shaped metal frame 34 a (outer peripheral part). ) Is 1.0 mm. Next, in the same manner as in Example 2, a strand made of stainless steel having a total length of 500 mm and a diameter of 0.12 mm was processed into a coil having a diameter of 5 mm, and a total of eight coils 34d were prepared by stacking five of them. What fixed these coils 34d inside the metal frame (outer peripheral part) 34a was used as the carrier for the first catalyst of Example 3. The weight of this carrier was 17.8 g.

  As in Example 1, this support was coated with a slurry containing rhodium at a predetermined ratio, dried at 120 ° C., and calcined at 500 ° C. As a result, a coating layer having a weight of 2.6 g was formed on the carrier, and the weight of rhodium was about 0.1 g. From the weight of the carrier and the coat layer, the heat capacity of the obtained first catalyst 34B was calculated in the same manner as in Example 1. The heat capacity of the first catalyst 34B of Example 3 was 10.2 J / K under a temperature environment of 25 ° C.

<Example 4>
A first catalytic converter was produced in the same manner as in Example 1. The first catalytic converter of the fourth embodiment is different from that of the first embodiment in that a first catalyst 34C shown in FIG. 6B is used. Specifically, the carrier (metal substrate) of the first catalyst 34C is a disk-shaped stainless steel carrier (metal carrier) having a diameter of 80 mm and a length of 10 mm, and a ring-shaped metal frame (outer peripheral part). The thickness of 34a is 1.0 mm. Next, in the same manner as in Example 2, a strand made of stainless steel having a total length of 500 mm and a diameter of 0.12 mm was processed into a coil having a diameter of 5 mm, and a total of 10 coils 34d were prepared by stacking five of these. As in Example 2, the first catalyst carrier of Example 4 was obtained by fixing these coils 34d inside the metal frame (outer peripheral part) 34a. The weight of this carrier was 20.3 g.

  As in Example 1, this support was coated with a slurry containing rhodium at a predetermined ratio, dried at 120 ° C., and calcined at 500 ° C. As a result, a coating layer weighing 2.8 g was formed on the carrier, of which the rhodium weight was about 0.1 g.

  From the weights of the carrier and the coat layer, the heat capacity of the obtained first catalyst 34C was calculated in the same manner as in Example 1. The heat capacity of the first catalyst 34C of Example 4 was 11.5 J / K under a temperature environment of 25 ° C.

<Comparative Example 1>
A first catalytic converter was produced in the same manner as in Example 1. The comparative example 1 is different from the first embodiment in that the first catalyst is not provided in the first catalytic converter.

<Comparative example 2>
A first catalytic converter was produced in the same manner as in Example 1. The first catalytic converter of Comparative Example 2 is different from that of Example 1 in that the length of the carrier shown in FIG. 3 is 10 mm, and the other carrier structures are the same. The weight of this carrier was 41.2 g.

  The carrier was coated with the same slurry as in Example 1, dried at 120 ° C. and calcined at 500 ° C. As a result, a coat layer having a weight of 4.7 g was formed on the carrier, and the weight of rhodium was about 0.1 g. From the weight of the carrier and the coat layer, the heat capacity of the obtained first catalyst was calculated in the same manner as in Example 1. The heat capacity of the first catalyst of Comparative Example 2 was 22.7 J / K under a temperature environment of 25 ° C.

<Comparative Example 3>
A first catalytic converter was produced in the same manner as in Example 1. The first catalytic converter of Comparative Example 3 is different from that of Example 2 in the structure of the first catalyst. A metal frame made of ring-shaped stainless steel having a diameter of 80 mm, a length of 10 mm, and a thickness of 1.0 mm was prepared. Next, a cylindrical body having a diameter of 78 mm and a length of 10 mm is cut out from the portion where the second catalyst carrier cell is formed, and the cut cylindrical body is inserted into a ring-shaped metal frame and fixed with Aaron ceramics. This was used as the carrier of Comparative Example 3.

  The carrier was coated with the same slurry as in Example 1, dried at 120 ° C. and calcined at 500 ° C. As a result, a coating layer was formed on the carrier, and the weight of rhodium was about 0.3 g. From the weight of the carrier and the coat layer, the heat capacity of the obtained first catalyst was calculated in the same manner as in Example 1. The heat capacity of the first catalyst of Comparative Example 3 was 28.8 J / K under a temperature environment of 25 ° C.

〔Evaluation test〕
The first catalytic converters of Examples 1 to 4 and Comparative Examples 1 to 3 were each connected from the engine to an exhaust pipe having a bypass path. In the engine, the air-fuel mixture was burned under the stoichiometric condition of the inflow air amount of the engine (ie, corresponding to the exhaust gas amount) of 25 g / sec, and the exhaust gas adjusted to the exhaust gas temperature of 450 ° C. was caused to flow through the exhaust pipe. After that, switching to the bypass path, the exhaust gas flowing in the exhaust pipe was circulated through the bypass path, and the exhaust gas was passed through the first catalytic converter. The time until the HC purification efficiency of the exhaust gas discharged from the first catalytic converter reaches 50% from the start of the engine was measured. The results are shown in FIG. 7 and FIG. In this evaluation test, the timing for switching to the bypass path is assumed to be when the engine is started.

  FIG. 7 is a graph showing the HC 50% purification arrival time of the exhaust gas that has passed through the first catalytic converter according to Examples 1 to 4 and Comparative Examples 1 to 3. FIG. 8 is a graph showing the relationship between the heat capacities of the first catalysts of Examples 1 to 4 and Comparative Examples 1 to 3 and the HC50% purification arrival time of the exhaust gas that has passed through the first catalytic converter.

  Furthermore, the temperature of the exhaust gas that passed through the first catalyst in the first catalytic converters of Examples 1 and 3 and Comparative Examples 1 to 3 was measured after switching to the bypass path (from the time of engine start). The result is shown in FIG. FIG. 9 is a graph showing changes in exhaust gas temperature after passing through the first catalysts of Examples 1 and 3 and Comparative Examples 1 to 3.

[Result 1]
As shown in FIG. 7, the HC50% purification arrival time of the first catalytic converters of Examples 1 to 4 was shorter than that of Comparative Example 1. This is considered to be because, in Examples 1 to 4, unlike Comparative Example 1, purification efficiency was improved by further arranging the first catalyst upstream of the second catalyst.

  However, as shown in FIG. 7, in Comparative Examples 2 and 3, the HC50% purification arrival time of the first catalytic converter is higher than that of Comparative Example 1 even though the first catalyst is disposed upstream of the second catalyst. It became long. As shown in FIG. 9, the temperature of the exhaust gas of Comparative Examples 2 and 3 in 2 to 7 seconds after the engine start was lower than that of Examples 1 and 3.

  From this, since the heat capacities of Comparative Examples 2 and 3 are larger than the heat capacities of the first catalysts of Examples 1 to 4, in Comparative Examples 2 and 3, when the exhaust gas passes through the first catalyst, It is thought that a lot of exhaust gas heat was taken away by the catalyst. Thereby, in Comparative Examples 2 and 3, compared with Examples 1 and 3, the temperature of the exhaust gas reaching the second catalyst is lower at the initial stage (2 to 7 seconds) after the engine is started. It is thought that the temperature rise by the exhaust gas of 2 catalyst became late. As a result, as shown in FIG. 8, it can be said that in Comparative Examples 2 and 3 in which the heat capacity of the first catalyst is small compared to Examples 1 to 4, the HC50% purification arrival time of the first catalytic converter is longer. .

  On the other hand, as shown in FIG. 9, the exhaust gas temperatures of Examples 1 and 3 are substantially the same as the exhaust gas temperature of Comparative Example 1 until about 6 seconds from the time of engine start. This is because in Examples 1 and 3, the heat capacity of the first catalyst is smaller than that in Comparative Examples 2 and 3, so that the amount of heat of the exhaust gas that is deprived (heat absorbed) by the first catalyst is small. It is thought that the heat at the time of reaction due to activation was input to the exhaust gas. Therefore, in the 1st catalytic converter of Examples 1-4, it is thought that the 2nd catalyst can be heated up early, hardly receiving the influence of the heat absorption of the exhaust gas by the 1st catalyst. As shown in FIG. 9, after 6 seconds from the start of the engine, in Examples 1 and 3, the temperature of the exhaust gas that has passed through the first catalyst (that is, the second catalyst flows into the second catalyst) due to the activation of the first catalyst. It can be said that the temperature of the exhaust gas is higher than that of Comparative Example 1, the temperature of the second catalyst is raised to a higher temperature, and the purification of the exhaust gas by the second catalyst is promoted.

  From the above results, as shown in FIG. 8, if the heat capacity of the first catalyst is 20 J / K or less in a temperature environment of 25 ° C., the second catalyst can be activated early together with the first catalyst. I can say that.

<Example 5>
A first catalytic converter was produced in the same manner as in Example 1. First, a carrier having the shape shown in FIG. 5 was prepared as a carrier (metal substrate) for the first catalyst. Specifically, the carrier 34 ′ of the first catalyst 34A is a carrier (metal carrier) made of disc-shaped stainless steel having an outer diameter of 80 mm, an inner diameter of 30 mm, and a length of 2 mm, and a ring-shaped metal frame (outer periphery). Part) 34a has a thickness of 1.0 mm, and the inner peripheral part 34e has a thickness of 30 μm. The thickness of the corrugated metal strip 34b and the plate-shaped metal strip 34c forming the first gas passage portion 34f is 30 μm, and the number of cells (number of holes) per square inch is 600, The weight of the carrier was 11.0 g.

  As in Example 1, this support was coated with a slurry containing rhodium at a predetermined ratio, dried at 120 ° C., and calcined at 500 ° C. As a result, a coating layer having a weight of 1.0 g was formed on the carrier, and the weight of rhodium was about 0.10 g. From the weight of the carrier and the coat layer, the heat capacity of the obtained first catalyst 34A was calculated in the same manner as in Example 1. The heat capacity of the first catalyst 34A of Example 5 was 6.6 J / K under a temperature environment of 25 ° C. The specific heat of the stainless steel as the carrier material is 0.46 J / g · K in a temperature environment of 25 ° C., and the specific heat of the ceria-zirconia after firing contained in the coat layer is in a temperature environment of 25 ° C. And 1.5 J / g · K. Further, the exhaust gas of the second gas passage part 34g with respect to the total cross-sectional area of the cross-sectional area of the flow path through which the exhaust gas in the first gas passage part 34f flows and the cross-sectional area of the flow path in which the exhaust gas of the second gas passage part 34g flows. The ratio of the cross-sectional area of the flow channel (hereinafter referred to as “the area ratio of the cavity”) was 14%.

<Example 6>
A first catalytic converter was produced in the same manner as in Example 5. The difference from Example 5 is that the inner diameter of the carrier 34 ′ of the first catalyst 34A is 15 mm, and the weight of the carrier is 11.4 g. Further, a coat layer having a weight of 1.2 g was formed on the carrier in the same manner as in Example 5, and the weight of rhodium contained in the coat layer was about 0.11 g. From the weight of the carrier and the coating layer, the heat capacity of the obtained first catalyst 34A was calculated in the same manner as in Example 5. The heat capacity of the first catalyst 34A of Example 5 was 7.0 J / K under a temperature environment of 25 ° C. The area ratio of the cavity was 3.5%.

<Example 7>
A first catalytic converter was produced in the same manner as in Example 5. The difference from Example 5 is that the inner diameter of the carrier 34 'of the first catalyst 34A is 40 mm, and the weight of the carrier is 10.1 g. Further, a coating layer having a weight of 1.0 g was formed on this carrier in the same manner as in Example 5, and the weight of rhodium contained in the coating layer was about 0.10 g. From the weight of the carrier and the coating layer, the heat capacity of the obtained first catalyst 34A was calculated in the same manner as in Example 5. The heat capacity of the first catalyst 34A of Example 5 was 6.2 J / K under a temperature environment of 25 ° C. The area ratio of the hollow portion was 25%.

<Comparative example 4>
A first catalytic converter was produced in the same manner as in Example 5. Comparative Example 4 is different from Example 5 in that the first catalyst is not provided in the first catalytic converter. Therefore, the catalytic converter of Comparative Example 4 is the same as that of Comparative Example 1.

<Comparative Example 5>
A first catalytic converter was produced in the same manner as in Example 5. The comparative example 5 is different from the fifth embodiment in that the first catalyst 34 having no hollow portion shown in FIG. 3 is used. Therefore, Comparative Example 5 is an example included in the present invention. The weight of the support of the first catalyst 34 of Comparative Example 5 was 11.6 g. Further, a coating layer was formed on this carrier in the same manner as in Example 5, and the weight of rhodium contained in 1.2 g of the coating layer was about 0.11 g. From the weight of the carrier and the coating layer, the heat capacity of the obtained first catalyst 34 was calculated in the same manner as in Example 5. The heat capacity of the first catalyst 34 of Comparative Example 5 was 7.1 J / K under a temperature environment of 25 ° C.

  For the first catalytic converters of Examples 5 to 7 and Comparative Examples 4 and 5, the same evaluation test as in Example 1 was performed, and the HC purification efficiency of the exhaust gas discharged from the first catalytic converter was The time to reach 50% was measured. The result is shown in FIG. FIG. 10 shows the relationship between the area ratio of the second gas passage part of the first catalyst of Examples 5 to 7 and Comparative Examples 4 and 5 and the HC50% purification arrival time of the exhaust gas that passed through the first catalytic converter. It is a graph.

  Furthermore, the temperature increase temperature of the first catalyst 10 seconds after the exhaust gas passed through the first catalyst of Examples 5 to 7 and Comparative Example 5 was measured. The result is shown in FIG. FIG. 11 is a graph showing the relationship between the area ratio of the second gas passage portion of the first catalyst of Examples 5 to 7 and Comparative Example 5 and the temperature rise temperature of the first catalyst.

[Result 2]
As shown in FIG. 10, the HC50% purification arrival time of the first catalytic converters of Examples 5 to 7 and Comparative Example 5 was shorter than that of Comparative Example 4. This is probably because, in Examples 5 to 7 and Comparative Example 5, unlike the comparative example 4, the purification efficiency was improved by further arranging the first catalyst upstream of the second catalyst.

  Furthermore, the HC50% purification arrival time of the catalytic converters of Examples 5 to 7 was shorter than that of Comparative Example 5. This is because, in Examples 5 to 7, compared with Comparative Example 5, it was possible to flow exhaust gas having a high flow rate through the second gas passage part in the central part of the second catalyst in a short time. Conceivable. In this way, the exhaust gas that has passed through the second gas passage part of the first catalyst flows toward the central part of the second catalyst, the central part of the second catalyst is heated up early, and the heat at the time of the temperature rise Is thought to have been transmitted around from its central part. And if the area ratio of a cavity part is ensured 3.5% or more, it is thought that such an effect can be expected.

  Furthermore, as shown in FIG. 11, the temperature rise of the first catalysts of Examples 5 to 7 was lower than that of Comparative Example 5. This is considered to be because the flow rate of the exhaust gas flowing through the first gas passage portion decreased as the area ratio of the cavity portion increased. And if the area ratio of a cavity part is ensured 25% or less, it is thought that the flow volume of the waste gas which flows through a 1st gas passage part can be ensured, and the temperature rising effect by a 1st catalyst can be anticipated.

  Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention described in the claims. Design changes can be made.

  In the present embodiment, the first catalyst is disposed in the first catalytic converter. However, for example, the heat capacity of the first catalyst can be satisfied, and the activation of the first catalyst allows the exhaust gas at a higher temperature to be discharged from the second catalyst. The first catalyst may be provided further upstream of the first catalytic converter.

2: Engine, 29: Exhaust manifold, 3: Exhaust gas purification device, 30: First catalytic converter (catalytic converter), 32: Exhaust gas purification catalyst, 33: Housing, 33a: Entrance cone portion, 33b: Body portion, 33c: Outlet cone portion, 34, 34A, 34B, 34C: first catalyst, 34a: metal frame (outer peripheral portion), 34e: inner peripheral portion, 34f: first gas passage portion, 34g: second gas passage portion, 34h : Cell (hole), 35: Second catalyst

Claims (4)

An exhaust gas purification device including an exhaust gas purification catalyst for purifying exhaust gas from an exhaust manifold,
The exhaust gas purification catalyst includes a first catalyst that purifies the exhaust gas from the exhaust manifold, and a second catalyst that purifies the exhaust gas that has passed through the first catalyst,
The heat capacity of the first catalyst is smaller than the heat capacity of the second catalyst,
The heat capacity of the second catalyst is 184 to 322 J / K under a temperature environment of 25 ° C.,
The exhaust gas purification apparatus according to claim 1, wherein the heat capacity of the first catalyst is 20 J / K or less under a temperature environment of 25 ° C. The exhaust gas purifying apparatus includes a catalytic converter including the first and second catalysts and a metal housing that houses the first and second catalysts therein.
Into the housing, exhaust gas from the exhaust manifold flows, and an inlet side cone portion in which a cross section of the exhaust gas channel is enlarged from upstream to downstream of the exhaust gas,
A body part that is continuous with the inlet cone part and has a constant cross-section of the exhaust gas flow path;
Continuing from the body part, from the upstream side of the exhaust gas to the downstream side, an outlet side cone part in which the cross section of the exhaust gas channel is reduced, and is formed,
The first catalyst is disposed in the entry side cone part,
The exhaust gas purifying apparatus according to claim 1, wherein the second catalyst is disposed in the body portion.   The exhaust gas purifying apparatus according to claim 1 or 2, wherein the first catalyst is a carrier made of a metal material and carrying a metal catalyst for purifying exhaust gas. The carrier has a disc shape,
An outer periphery,
An inner periphery formed inside the outer periphery;
Between the outer peripheral portion and the inner peripheral portion, a plurality of holes are formed in a direction in which the exhaust gas passes, and a first gas passage portion in which the metal catalyst is supported on a wall surface forming each of the holes,
A second gas passage part that is a hollow part formed along the direction in which the exhaust gas passes inside the inner peripheral part,
The flow through which the exhaust gas in the second gas passage section flows relative to the total cross-sectional area of the cross-sectional area of the flow path in which the exhaust gas in the first gas passage section flows and the cross-sectional area in the flow path in which the exhaust gas in the second gas passage section flows. The exhaust gas purification apparatus according to claim 3, wherein the ratio of the cross-sectional area of the road is 3.5 to 25%.

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