JP2006231248A - Exhaust gas purifying apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas purifying apparatus capable of obtaining the sufficient diffusion of gas on its downstream side and unnecessary to increase the amount of an expensive noble metal used. <P>SOLUTION: The exhaust gas purifying apparatus has a catalyst on an upstream side and a catalyst on a downstream side along the flow direction of an exhaust gas, and coating layers 102 and 112, which are formed by coating base material layers 101 and 111 with carrier particles having a noble metal preliminarily supported thereon, are formed on the respective catalysts. The average particle size of the carrier particles of the catalyst on the upstream side is larger than that of the catalyst on the downstream side and the amount of the noble metal per unit length and unit cell is the same in the catalyst on the upstream side and the catalyst on the downstream side. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust gas purification device for an internal combustion engine.

In general, an exhaust gas purifying apparatus for an internal combustion engine is a porous material made of a heat-resistant inorganic oxide such as alumina, on which a catalytic noble metal such as platinum is supported on the surface of a monolith-like heat-resistant carrier base material layer made of cordierite, for example. It has a structure that supports the carrier. Such an exhaust gas purification device oxidizes harmful carbon monoxide (CO) and hydrocarbon (HC) contained in the exhaust gas and converts them into harmless carbon dioxide (CO ₂ ) and water (H ₂ O) at the same time. Nitrogen oxide (NOx) can be reduced to be converted to harmless nitrogen (N ₂ ), so it is also called a three-way catalyst.

  The amount of each harmful component in the exhaust gas varies depending on the operating condition of the internal combustion engine. Further, in order to suppress the generation of NOx in the exhaust gas, a method of actively controlling the air-fuel ratio (hereinafter sometimes referred to as “A / F ratio”) to be stoichiometric or rich has been attempted. The component of the exhaust gas introduced into the exhaust gas purification device also changes by such control.

  On the other hand, inside the exhaust gas purification device, exhaust gas purification is gradually performed from the upstream side in the exhaust gas flow direction, so that the component of the gas flowing toward the downstream side also changes along the flow direction.

  Further, regarding the temperature, the temperature of the exhaust gas generated varies depending on the operating state of the internal combustion engine, and generally the temperature of the exhaust gas decreases toward the downstream side in the flow direction of the exhaust gas purification device.

In order to optimize the purification of exhaust gas in response to such changes, Patent Document 1 provides a first catalyst layer on the upstream side of the purification device and a second catalyst layer on the downstream side. A system is disclosed in which the components and amount of noble metal are changed between two catalyst layers to enhance the catalyst purification ability. Further, Patent Document 2 discloses a configuration in which the catalyst purification performance is improved by providing a gradient of the loading amount of the noble metal and the transition metal oxide from the upstream side toward the downstream side. Further, in Patent Document 3, the precious metal coat ratio of the upstream catalyst and the downstream catalyst is set to 1 <front side / back side ≦ 3, and in Patent Document 4, an upstream catalyst and a downstream catalyst are provided, It is said that a high NOx purification effect can be obtained by changing the amount of the composite oxide in the catalyst.
Japanese Patent Laid-Open No. 2004-283692 JP-A-9-122443 JP 2003-245523 A JP 2004-267843 A

  However, in the configuration disclosed in each of the above patent documents, from the viewpoint of diffusion of exhaust gas in the catalyst layer (hereinafter referred to as “coat layer”) formed on the base material layer, in particular, on the downstream side of the purification device. However, since the diffusion distance to the deep part of the coat layer is long and the gas is not sufficiently supplied to the inside of the coat layer, the purification rate of the catalyst may be lowered. This is because if the exhaust gas in the stoichiometric state continues to be discharged for a long time, most of the gas (hazardous components) is purified in the upstream part of the purification device, so the downstream gas (hazardous component) concentration is about several tens of ppm. Become. For this reason, the difference in concentration between the surface portion and the coating layer is reduced, and the amount of diffusion into the coating layer is reduced. Therefore, purification is hardly performed on the downstream side of the purification device, and the purification rate is lowered. On the other hand, in order to solve this problem, if the amount of catalyst supported on the downstream side is increased, the amount of expensive noble metal used increases, and the cost of the purification device increases.

  Accordingly, an object of the present invention is to provide an exhaust gas purification device that can obtain sufficient gas diffusion even on the downstream side of the purification device and that does not increase the amount of expensive noble metal used.

  In order to solve the above-mentioned problems, the present inventors coated porous carrier particles on which a noble metal is supported in advance on a base material layer, the coating layer has a three-dimensional structure, and an average of the carriers constituting this three-dimensional structure. It has been found that by making the particle size large on the upstream side in the flow direction of the exhaust gas and small on the downstream side, the diffusion distance is shortened on the downstream side, so that noble metals can be used effectively. In addition, by configuring the same unit length and amount of noble metal per unit cell on the upstream side and downstream side, an exhaust gas purifying device that obtains sufficient gas diffusion without increasing the amount of expensive noble metal used is configured. I found out that I can do it.

  Thus, the invention according to claim 1 is provided in the exhaust gas passage of the internal combustion engine, and includes the upstream catalyst and the downstream catalyst along the flow direction of the exhaust gas. An exhaust gas purifying apparatus comprising a coating layer having carrier particles previously loaded with a noble metal, wherein the average particle size of the carrier particles of the upstream catalyst is larger than the average particle size of the carrier particles of the downstream catalyst, The length and the amount of noble metal per unit cell are the same for the upstream side catalyst and the downstream side catalyst, and an object of the present invention is to solve the above problem by an exhaust gas purifying device.

  Here, the “average particle size” means an average particle size measured by a laser diffraction particle size distribution measuring device.

  According to a second aspect of the present invention, in the exhaust gas purifying apparatus according to the first aspect, the upstream catalyst and the downstream catalyst are integrally formed.

  According to a third aspect of the present invention, in the exhaust gas purifying apparatus according to the first aspect, the upstream side catalyst and the downstream side catalyst are spaced apart from each other.

  According to a fourth aspect of the present invention, in the exhaust gas purifying apparatus according to the third aspect, the number of cells of the upstream catalyst is larger than the number of cells of the downstream catalyst.

  According to a fifth aspect of the present invention, in the exhaust gas purifying device according to the third aspect, the upstream catalyst is larger than the downstream catalyst and is orthogonal to the flow direction with respect to the length along the flow direction of the exhaust gas. The upstream catalyst is smaller than the downstream catalyst with respect to the cross-sectional area in the surface direction, and the upstream catalyst is smaller than the downstream catalyst with respect to the number of cells.

  According to the invention described in claim 1, since the average particle diameter of the carrier particles is small in the downstream catalyst, the gas diffusion distance to the noble metal is shortened, and the diffusion amount can be increased even if the gas concentration is reduced. it can. Further, since the average particle diameter of the carrier particles is small in the downstream catalyst, the area density of the noble metal on the surface of the coat layer is increased. For this reason, sufficient purification is ensured even if the gas concentration is reduced. Accordingly, the purification rate of the entire exhaust gas purification device can be improved.

  On the other hand, the upstream catalyst having a large average particle size of the carrier particles traps poisonous substances against the catalyst such as phosphorus derived from engine oil and the like, so that poisonous substances reaching the downstream catalyst can be reduced. Therefore, even if carrier particles having a small average particle diameter are used in the downstream catalyst, clogging of the coating layer due to poisoning can be reduced. Therefore, it is possible to maintain a high purification capacity over a long period of time.

  In addition, since the coating layer is formed by coating a carrier on which a noble metal is supported in advance on the base material layer, the noble metal is evenly distributed even inside the coating layer when compared with the one in which the noble metal is supported after coating. Therefore, the oxygen storage capacity (hereinafter sometimes referred to as “OSC”) is large, and the catalyst purification window can be widened. Therefore, even if the A / F ratio varies, it is possible to maintain a good purification rate.

  Furthermore, since the average particle size of the carrier particles is large in the upstream catalyst, the surface noble metal loading density can be reduced, and the gap between the carrier particles is increased, increasing the amount of diffusion to the inside of the coat layer. The reaction amount on the surface layer decreases and the reaction amount on the inner side increases. Therefore, the local temperature gradient due to the difference in reaction heat between the central side and the peripheral side of the surface perpendicular to the exhaust gas flow direction in the coat layer can be alleviated, and the coating material peeling due to thermal strain can be suppressed. Can do.

  In addition, since the upstream length catalyst and the downstream side catalyst have the same unit length and the same amount of noble metal per unit cell, the amount of expensive noble metal used can be suppressed while maintaining the purification performance.

According to the invention described in claim 2, since the upstream catalyst and the downstream catalyst are integrally formed, the apparatus can be easily downsized. Further, when the exhaust gas purification device as a whole has the structure of the upstream catalyst of the present invention, that is, when the carrier particle has a three-dimensional structure with a large average particle diameter, the catalyst is provided with an O ₂ sensor, Although there is a problem that a low concentration cannot be detected, such a problem can also be solved by providing an O ₂ sensor in the configuration of the present invention, that is, a downstream catalyst having a small particle diameter.

  According to the invention described in claim 3, the upstream catalyst and the downstream catalyst are provided separately, and even if a part of the cells of the upstream catalyst is blocked, the downstream catalyst is not affected. Since it does not extend directly, it is possible to minimize a decrease in purification capacity and an increase in pressure loss. In addition, since the upstream catalyst and the downstream catalyst are formed separately, even when the mounting space on the vehicle is limited, it can be easily mounted separately and the space can be used effectively. it can.

  According to the invention described in claim 4, since the number of cells of the downstream catalyst is reduced from the number of cells of the upstream catalyst, it is easy to reduce the amount of noble metal used. Further, since the heat capacity of the downstream catalyst is reduced, the rate of rise of the downstream catalyst temperature is increased, and the exhaust gas purification performance immediately after startup is improved. Further, by reducing the number of cells, it is possible to further reduce the pressure loss, lower the back pressure, and improve the engine output.

  According to the fifth aspect of the present invention, since the number of cells of the downstream catalyst is further increased, the opportunity for reaction is increased and the exhaust gas purification rate is improved. Further, it is possible to suppress a decrease in engine power performance while improving the purification rate.

  Hereinafter, the best embodiment of the exhaust gas purifying apparatus of the present invention will be described more specifically with reference to the drawings.

  FIG. 1 is a system diagram showing an outline when the exhaust gas purifying apparatus of the present invention is used in a general gasoline engine. Normally, the system 50 is mounted on a vehicle. In FIG. 1, an air-fuel mixture supply unit 20 is shown on the left side of the engine 10, and an exhaust system is shown on the right side. In the air-fuel mixture supply unit 20, fuel and air mixed at a predetermined A / F ratio are supplied to the engine 10 and burned. Exhaust gas generated by combustion in each cylinder of the engine 10 is collected in the exhaust pipe 15 via the exhaust manifold 11 and guided to the exhaust gas purification device 30. In FIG. 1, “30” is used for convenience as a reference numeral indicating the exhaust gas purifying device. However, for the exhaust gas purifying apparatus according to the first embodiment to the fourth embodiment, which will be described later, reference numerals are appropriately used. The explanation is changed.

  Exhaust gas from which harmful substances have been purified by the exhaust gas purification device 30 is discharged from the exhaust pipe 16 into the atmosphere. The air-fuel mixture supply unit 20 is provided with a throttle valve 21, an air flow meter 22 is provided upstream thereof, and a throttle sensor 23 is provided in the vicinity of the throttle valve 21. Output signals from the meter 22 and the sensor 23 are sent to a motor electronic control unit (hereinafter referred to as “ECU”) 40.

An A / F sensor 24 and an O ₂ sensor 25 are respectively provided before and after the exhaust gas purification device 30 to determine the air-fuel ratio of the exhaust gas introduced into the purification device 30 and the oxygen concentration of the exhaust gas purified by the purification device 30. Detected. Detection signals from the A / F sensor 24 and the O ₂ sensor 25 are also sent to the ECU 40.

The ECU 40 receives detection signals from the air flow meter 22, the throttle sensor 23, the A / F sensor 24, and the O ₂ sensor 25, and adds signals from other sensors as necessary to calculate optimum control conditions. The engine 10 is controlled.

  FIG. 2 is a diagram schematically showing the configuration of the exhaust gas purification apparatus 100 according to the first embodiment. 2, the left side of the drawing is the exhaust pipe 15, that is, the upstream side in the exhaust gas flow direction, and the right side of the drawing is the exhaust pipe 16, that is, the downstream side in the exhaust gas flow direction. The illustrated exhaust gas purification device 100 includes a number of cells c1, c2, c3,... Penetrating from the upstream side to the downstream side. On the other hand, the exhaust gas purification apparatus 100 has an upstream catalyst 100A on the upstream side and a downstream catalyst 100B on the downstream side, both of which have different catalyst configurations and are integrally formed.

According to the exhaust gas purification apparatus 100 of the first embodiment, the upstream side catalyst 100A and the downstream side catalyst 100B are integrally formed, so that the apparatus can be easily downsized. Further, when the exhaust gas purifying apparatus as a whole has the structure of the upstream catalyst 100A, that is, when the catalyst has an O ₂ sensor in a three-dimensional structure with a large average particle diameter of the carrier particles, a low concentration is obtained. However, this problem can also be solved by providing the O ₂ sensor in the configuration of the present embodiment, that is, the downstream catalyst having a small particle diameter.

  Now, let Qf be the average particle size of the carrier in each cell of the upstream catalyst 100A. On the other hand, the average particle diameter of the carrier in each cell of the downstream side catalyst 100B is defined as Qr.

In the exhaust gas purification apparatus 100 of the first embodiment, between these Qf and Qr,
Qf> Qr
This relationship is established.

  FIG. 3 shows how the noble metal and the carrier form a coating layer in a part A of any one cell in the upstream catalyst 100A and a part B in any one cell in the downstream catalyst 100B. FIG. 3A schematically shows a cross section in the thickness direction of the coating layers 102 and 112 formed on the base material layers 101 and 111 of the upstream catalyst 100A, and FIG. 3B shows the downstream catalyst 100B. . In each figure, the exhaust gas passage extends from the left to the right above the coat layers 102 and 112.

  In the upstream catalyst 100A shown in FIG. 3A, a coating layer 102 made of a carrier having a large average particle diameter and a noble metal is formed on a base material layer 101. The carrier is preliminarily impregnated with a noble metal, and the carrier carrying the noble metal is coated on the base material layer 101 to form a coat layer 102. Therefore, the noble metal is uniformly dispersed in the depth direction from the surface layer portion 103 of the coat layer 102 to a portion close to the inner base material layer 101. With this configuration, the upstream catalyst 100A has a large average particle size of the carrier, so that the noble metal support density of the surface layer portion 103 can be reduced, and the gap between the carrier particles is increased, and the amount of diffusion to the inside of the coat layer 102 is increased. Since it increases, the reaction amount in the surface layer part 103 decreases, and the reaction amount on the inner side increases. Therefore, the local temperature gradient due to the difference in reaction heat between the central portion side and the peripheral portion side of the surface orthogonal to the exhaust gas flow direction in the coat layer 102 can be alleviated, and the peeling of the coating material due to thermal strain can be suppressed. be able to.

  In the downstream catalyst 100B shown in FIG. 3B, a coating layer 112 made of a carrier having a small average particle diameter and a noble metal is formed on the base material layer 111. Also in the downstream side catalyst 100B, the carrier is preliminarily impregnated with a noble metal, and the carrier carrying the noble metal is coated on the base layer 111 to form a coat layer 112. Therefore, also in the downstream catalyst 100B, the noble metal is uniformly dispersed in the depth direction from the surface layer portion 113 of the coat layer 112 to a portion close to the internal base material layer 111. Therefore, with this configuration, since the average particle diameter of the carrier particles is small in the downstream catalyst 100B, the gas diffusion distance to the noble metal is shortened, and the diffusion amount can be increased even if the gas concentration is reduced. Further, since the average particle size of the carrier particles is small, the area density of the noble metal on the coat layer surface portion 113 is increased. For this reason, sufficient purification is ensured even if the gas concentration is reduced. Accordingly, the purification rate of the entire exhaust gas purification device 100 can be improved.

  Furthermore, since the average particle size of the carrier is made larger in the upstream catalyst 100A than the downstream catalyst 100B, the upstream catalyst 100A having a large average particle size of the carrier particles has a poisoning substance for catalyst such as phosphorus derived from engine oil. It is possible to reduce the poisoning substances that are trapped and reach the downstream side catalyst 100B. Therefore, even if carrier particles having a small average particle diameter are used in the downstream catalyst 100B, clogging of the coating layer due to poisoning can be reduced. Therefore, it is possible to maintain a high purification capacity over a long period of time.

  In addition, since the coating layers 102 and 112 are formed by coating the base material layers 101 and 111 with a carrier preliminarily impregnated with a noble metal, when compared with those impregnated with a noble metal after coating, Since noble metal exists uniformly even inside the coat layer, the OSC is large and the catalyst purification window can be widened. Therefore, even if the A / F ratio varies, it is possible to maintain a good purification rate.

  In the exhaust gas purification apparatus 100 according to the first embodiment, the precious metal is the same amount per unit length of unit cell in the upstream catalyst 100A and the downstream catalyst 100B. By doing in this way, the usage-amount of an expensive noble metal can be suppressed, maintaining purification performance.

  In the exhaust gas purification apparatus 100 of the first embodiment shown in FIG. 3 described above, the precious metal and the carrier in the upstream catalyst 100A and the downstream catalyst 100B form the coat layers 101 and 111, and the operational effects thereof. The same applies to the exhaust gas purifying apparatuses 200, 300, and 400 according to the second to fourth embodiments described below.

  FIG. 4 is a diagram schematically showing the configuration of the exhaust gas purification apparatus 200 according to the second embodiment. 4, the left side of the drawing is the exhaust pipe 15, that is, the upstream side in the exhaust gas flow direction, and the right side of the drawing is the exhaust pipe 16, that is, the downstream side in the exhaust gas flow direction. In the illustrated exhaust gas purification device 200, an upstream catalyst 200A and a downstream catalyst 200B are formed separately, and both are arranged separately. Further, the upstream catalyst 200A and the downstream catalyst 200B are formed so that the lengths in the exhaust gas flow direction are substantially the same, and the cross-sectional areas in the plane direction orthogonal to the exhaust gas flow direction are also substantially the same. ing. The upstream catalyst 200A and the downstream catalyst 200B are covered with an outer tube 250 that communicates from the exhaust pipe 15 to the exhaust pipe 16.

  The upstream catalyst 200A includes a large number of cells c4, c5, c6,... Penetrating from the upstream side to the downstream side in the exhaust gas flow direction. On the other hand, the downstream catalyst 200B is also provided with a number of cells c7, c8, c9,... Penetrating from the upstream side to the downstream side along the exhaust gas flow direction. The number of cells c4, c5, c6,... Of the upstream catalyst 200A and the number of cells c7, c8, c9,. In the exhaust gas purification apparatus 200 having such a configuration, the exhaust gas flowing into the cells c4, c5, c6,... Of the upstream catalyst 200A from the exhaust pipe 15 is subjected to predetermined purification by the upstream catalyst 200A. After that, they once merge as one flow in the intermediate portion 251 of the outer tube 250 and are again guided into the cells c7, c8, c9,... Of the downstream catalyst 200B. The exhaust gas further subjected to predetermined purification in each of the cells c7, c8, c9,... Of the downstream side catalyst 200B is sent to the discharge pipe 16 and is discharged from there.

  The manner in which the precious metal, the support forms a coat layer, and the function and effect of the noble metal at any point A in the upstream catalyst 200A, and any point B in the downstream catalyst 200B, and the operational effects thereof are as described in FIG. This is the same as that in the exhaust gas purification apparatus 100. Therefore, the description is omitted here. Further, in the exhaust gas purification apparatus 200 according to the second embodiment, the noble metal is the same amount per unit length in the upstream catalyst 200A and the downstream catalyst 200B. By doing in this way, the usage-amount of an expensive noble metal can be suppressed, maintaining purification performance.

  According to the exhaust gas purification apparatus 200 according to the second embodiment, since the upstream catalyst 200A and the downstream catalyst 200B are provided separately, even if some cells of the upstream catalyst 200A are blocked, The downstream catalyst 200B is not directly affected. Accordingly, it is possible to minimize the decrease in purification ability and the increase in pressure loss. In addition, since the upstream catalyst 200A and the downstream catalyst 200B are formed separately, even when the mounting space on the vehicle is limited, it is easy to divide and mount the space effectively. be able to.

  FIG. 5 is a diagram schematically showing the configuration of the exhaust gas purification apparatus 300 according to the third embodiment. 5, the left side of the drawing is the exhaust pipe 15, that is, the upstream side in the exhaust gas flow direction, and the right side of the drawing is the exhaust pipe 16, that is, the downstream side in the exhaust gas flow direction. In the illustrated exhaust gas purifying apparatus 300, the upstream side catalyst 300A and the downstream side catalyst 300B are formed as separate bodies, and both are arranged apart from each other. Further, the upstream catalyst 300A and the downstream catalyst 300B are formed so that the lengths in the exhaust gas flow direction are substantially the same, and the cross-sectional areas in the plane direction perpendicular to the exhaust gas flow direction are also substantially the same. ing. The upstream catalyst 300 </ b> A and the downstream catalyst 300 </ b> B are covered with an outer tube 350 that communicates from the exhaust pipe 15 to the exhaust pipe 16.

  The upstream catalyst 300A includes a large number of cells c10, c11, c12,... Penetrating from the upstream side to the downstream side in the exhaust gas flow direction. On the other hand, the downstream catalyst 300B is also provided with a large number of cells c13, c14, c15,... Penetrating from the upstream side to the downstream side along the exhaust gas flow direction. The number of cells c10, c11, c12,... Of the upstream catalyst 300A is larger than the number of cells c13, c14, c15,. In other words, regarding the cross section in the plane direction orthogonal to the flow direction of the exhaust gas, the cross-sectional area of the cells c10, c11, c12,... Of the upstream catalyst 300A is that of the cells c13, c14, c15,. It is smaller than the cross-sectional area.

  In the exhaust gas purifying apparatus 300 having such a configuration, the exhaust gas flowing into the cells c10, c11, c12,... Of the upstream catalyst 300A from the exhaust pipe 15 is subjected to predetermined purification by the upstream catalyst 300A. After that, the flow is once merged as one flow in the intermediate portion 351 of the outer tube 350, and is again guided into the cells c13, c14, c15,... Of the downstream side catalyst 300B. The exhaust gas further subjected to predetermined purification in each of the cells c13, c14, c15,... Of the downstream side catalyst 300B is sent to the discharge pipe 16 and is discharged from there to the outside.

  The manner in which the noble metal, the carrier forms the coat layer, and the function and effect of the noble metal at the arbitrary point A in the upstream catalyst 300A, the arbitrary point B in the downstream catalyst 300B, and the effects thereof are as described in FIG. This is the same as that in the exhaust gas purification apparatus 100. Therefore, the description is omitted here. Further, in the exhaust gas purifying apparatus 300 according to the third embodiment, the noble metal is the same amount per unit length in the upstream catalyst 300A and the downstream catalyst 300B. However, since the downstream catalyst 300B has a smaller number of cells, the downstream catalyst 300B has a smaller amount of noble metal per unit volume. By doing in this way, the usage-amount of an expensive noble metal can be suppressed, maintaining purification performance.

  According to the exhaust gas purification apparatus 300 according to the third embodiment, since the upstream catalyst 300A and the downstream catalyst 300B are provided separately, even if a part of the cells of the upstream catalyst 300A is blocked, The downstream catalyst 300B is not directly affected. Accordingly, it is possible to minimize the decrease in purification ability and the increase in pressure loss. In addition, since the upstream catalyst 300A and the downstream catalyst 300B are formed separately, even when the mounting space on the vehicle is limited, it is easy to divide and mount the space, and effectively use the space. be able to. In addition, since the number of cells of the downstream catalyst 300B is smaller than the number of cells of the upstream catalyst 300A, it is easy to reduce the amount of noble metal used. Further, since the heat capacity of the downstream catalyst 300B is lowered, the temperature rise rate of the downstream catalyst 300B is increased, and the exhaust gas purification performance immediately after the start is improved. Further, by reducing the number of cells, it is possible to reduce the pressure loss more, lower the back pressure, and improve the engine output.

  FIG. 6 is a diagram schematically showing the configuration of the exhaust gas purification apparatus 400 according to the fourth embodiment. 6, the left side of the drawing is the exhaust pipe 15, that is, the upstream side in the exhaust gas flow direction, and the right side of the drawing is the exhaust pipe 16, that is, the downstream side in the exhaust gas flow direction. In the illustrated exhaust gas purification device 400, an upstream catalyst 400A and a downstream catalyst 400B are formed as separate bodies, and the two are separated from each other. Further, the upstream catalyst 400A and the downstream catalyst 400B are larger in length in the exhaust gas flow direction than the downstream catalyst 400B. Further, regarding the cross-sectional area in the plane direction orthogonal to the flow direction of the exhaust gas, the upstream catalyst 400A is formed to be smaller than the downstream catalyst 400B. The upstream side catalyst 400A and the downstream side catalyst 400B are covered with an outer tube 450 that communicates from the exhaust pipe 15 to the exhaust pipe 16.

  The upstream catalyst 400A includes a large number of cells c16, c17, c18,... Penetrating from the upstream side to the downstream side in the exhaust gas flow direction. On the other hand, the downstream catalyst 400B also includes a number of cells c19, c20, c21,... That penetrate from the upstream side to the downstream side in the exhaust gas flow direction. The number of cells c16, c17, c18,... Of the upstream catalyst 400A is smaller than the number of cells c19, c20, c21,. In other words, regarding the cross section in the plane direction orthogonal to the flow direction of the exhaust gas, the cross-sectional area of the cells c16, c17, c18,... Of the upstream catalyst 400A is the cell c19, c20, c21,. It is formed larger than the cross-sectional area.

  In the exhaust gas purification apparatus 400 having such a configuration, the exhaust gas flowing into the cells c16, c17, c18,... Of the upstream catalyst 400A from the exhaust pipe 15 is subjected to predetermined purification by the upstream catalyst 400A. After that, they once merge as one flow in the intermediate portion 451 of the outer tube 450 and are again guided into the cells c19, c20, c21,... Of the downstream side catalyst 400B. The exhaust gas further subjected to predetermined purification in each of the cells c19, c20, c21,... Of the downstream side catalyst 400B is sent to the discharge pipe 16 and is discharged from there.

  The manner in which the noble metal at any point A in the upstream catalyst 400A, the noble metal at the arbitrary point B in the downstream catalyst 400B, the support forms a coating layer, and the function and effect thereof are as described in FIG. This is the same as that in the exhaust gas purification apparatus 100. Therefore, the description is omitted here. Further, in the exhaust gas purification apparatus 400 according to the fourth embodiment, the noble metal is the same amount per unit length in the upstream catalyst 400A and the downstream catalyst 400B. However, since the number of cells in the upstream catalyst 400A is smaller, the upstream catalyst 400A is smaller in the amount of noble metal per unit volume.

  According to the exhaust gas purification apparatus 400 according to the fourth embodiment, since the upstream catalyst 400A and the downstream catalyst 400B are provided separately, even if some of the cells of the upstream catalyst 400A are blocked, The downstream catalyst 400B is not directly affected. Accordingly, it is possible to minimize the decrease in purification ability and the increase in pressure loss. In addition, since the upstream catalyst 400A and the downstream catalyst 400B are formed separately, even when the mounting space on the vehicle is limited, it is easy to divide and mount the space, and effectively use the space. be able to. In addition, since the number of cells of the downstream catalyst 400B is smaller than the number of cells of the upstream catalyst 400A, it is easy to reduce the amount of noble metal used. Further, since the heat capacity of the downstream catalyst 400B is reduced, the temperature increase rate of the downstream catalyst 400B is increased, and the exhaust gas purification performance immediately after the start is improved. Further, by reducing the number of cells, it is possible to reduce the pressure loss more, lower the back pressure, and improve the engine output. In addition, since the number of cells of the downstream side catalyst 400B further increases, the opportunity for reaction increases and the exhaust gas purification rate improves. Further, it is possible to suppress a decrease in engine power performance while improving the purification rate.

  In the exhaust gas purification apparatus 100, 200, 300, 400 of the present invention, the type of noble metal is not particularly limited, but any one of platinum (Pt), rhodium (Rh), and palladium (Pd), Or they can be used in combination. Among these, Pt and / or Rh can be preferably used.

  In the exhaust gas purification apparatuses 100, 200, 300, and 400 of the present invention, the type of the carrier is not particularly limited, but a porous material having a large surface area, such as ceria / alumina or zirconia, is preferably used. Can be used.

  It is preferable that the carrier particle diameter of the upstream catalyst 100A, 200A, 300A, 400A is twice or more the downstream carrier particle diameter. By taking such a particle size ratio, the purification ability of the exhaust gas purification devices 100, 200, 300, 400 of the present invention can be further enhanced.

  FIG. 7 is a diagram schematically showing the manufacturing process of the exhaust gas purifying devices 100, 200, 300, 400 of the present invention. A carrier powder A having a large average particle size is impregnated with a noble metal and coated on a substrate to be used upstream. On the other hand, a carrier powder B having a small average particle size is impregnated with a noble metal and coated on a substrate to be used on the downstream side. By firing the base material coated with the carrier carrying the noble metal, the upstream and downstream catalysts of the exhaust gas purification devices 100, 200, 300, and 400 can be obtained.

It is a system diagram showing an outline when the exhaust gas purification device of the present invention is used in a general gasoline engine. It is a figure showing roughly the composition of the exhaust gas purification device of a first embodiment. (A) is a figure which shows typically the thickness direction cross section of the coating layer formed on the base material layer of the upstream catalyst, and (B) is the downstream catalyst. It is a figure which shows roughly the structure of the exhaust-gas purification apparatus of 2nd embodiment. It is a figure which shows roughly the structure of the exhaust-gas purification apparatus of 3rd embodiment. It is a figure which shows roughly the structure of the exhaust-gas purification apparatus of 4th embodiment. It is a figure which shows typically the catalyst manufacturing process of an exhaust-gas purification apparatus.

Explanation of symbols

c1 to c20, c21... Cell 10 Engine 11 Exhaust Manifold 15 Exhaust Pipe 16 Exhaust Pipe 20 Mixture Supply Portion 21 Throttle Valve 22 Air Flow Meter 23 Throttle Sensor 24 A / F Sensor 25 O2 Sensor 40 ECU
50 System 101, 111 Base material layer 102, 112 Coat layer 103, 113 Surface layer part 30, 100, 200, 300, 400 Exhaust gas purification device 100A, 200A, 300A, 400A Upstream catalyst 100B, 200B, 300B, 400B Downstream side Catalyst 250, 350, 450 Outer tube 251, 351, 451 (outer tube) middle part

Claims (5)

The exhaust gas passage of the internal combustion engine is provided with an upstream catalyst and a downstream catalyst along the flow direction of the exhaust gas, and each of these catalysts has carrier particles previously supported with a noble metal on a base material layer. An exhaust gas purification device comprising a coat layer having,
The average particle size of the support particles of the upstream catalyst is larger than the average particle size of the support particles of the downstream catalyst,
The exhaust gas purifier according to claim 1, wherein the noble metal amount per unit length and unit cell is the same for the upstream catalyst and the downstream catalyst. The exhaust gas purification apparatus according to claim 1, wherein the upstream catalyst and the downstream catalyst are integrally formed. The exhaust gas purifying apparatus according to claim 1, wherein the upstream catalyst and the downstream catalyst are spaced apart from each other. The exhaust gas purification device according to claim 3, wherein the number of cells of the upstream catalyst is larger than the number of cells of the downstream catalyst. Regarding the length along the flow direction of the exhaust gas, the upstream catalyst is larger than the downstream catalyst, and the upstream catalyst is smaller than the downstream catalyst with respect to the cross-sectional area in the plane direction perpendicular to the flow direction. Yes,
The exhaust gas purification device according to claim 3, wherein the upstream catalyst is smaller than the downstream catalyst with respect to the number of cells.

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