JP2005211868A - Catalyst structure in exhaust purification apparatus and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a catalyst structure in an exhaust purification device capable of activating a catalyst by suppressing a temperature distribution at a low cost.
A method of manufacturing a catalyst structure in an exhaust emission control device includes a step of adjusting a ceramic material so as to obtain a desired material suitable for the catalyst structure, and a number of continuous adjustments of the adjusted ceramic material in an extrusion direction. A step of extruding into a substantially cylindrical shape having a passage with a full length L (1) and a diameter D (1), and applying a pressing force P to the structure molded in this shape in the extruding direction and before extrusion Applying a twisting force in the direction opposite to each other in the direction and the back direction to form a final shape having a total length shorter than L (1) and a diameter larger than D (1); Firing the finished structure.
[Selection] Figure 4

Description

  The present invention relates to a purification device provided in an exhaust system of an internal combustion engine, and more particularly to a catalyst structure in an exhaust purification device that is provided in an exhaust system and purifies harmful components in exhaust gas.

  In a diesel engine or a gasoline engine that performs lean combustion, an operation region in which an air-fuel mixture with a high air-fuel ratio (lean atmosphere) is used for combustion and the engine is operated occupies most of the entire operation region. In this type of engine (internal combustion engine), generally, an NOx absorbent (catalyst) that absorbs nitrogen oxides (NOx) in the presence of oxygen is provided in the exhaust system.

  Further, fine particles such as carbon discharged from a diesel engine are called PM (Particulate Matter), and many techniques have been developed for the removal thereof. For example, there is an exhaust particle processing apparatus in which an exhaust trap with a filter-like catalyst is interposed in an exhaust passage. This trap with catalyst self-combusts exhaust particulates deposited by the catalytic action. Techniques related to these are disclosed in the following publications.

  Japanese Laid-Open Patent Publication No. 10-249968 (Patent Document 1) discloses a ceramic spiral honeycomb structure having a unique shape that can be used not only for a catalyst carrier but also for dust collection and smoke removal particularly at high temperatures. In this ceramic spiral honeycomb structure, a large number of adjacent honeycomb-shaped through holes are spirally curved while maintaining a predetermined distance from each other. In addition, this ceramic spiral honeycomb structure is provided with a graphic aperture in which a number of regular polygonal or circular holes are regularly arranged in a square or hexagonal symmetry in a ceramic powder sheet or thin plate molded product. Through-holes formed by laminating a plurality of ceramic molded products, each of which is shifted little by little without rotating the figure of the opening part so that the center of each hole moves along a constant curvature circumference. However, it is manufactured by forming a honeycomb laminated body that is curved in a spiral shape, and sintering and integrating the ceramic portions.

According to this ceramic spiral honeycomb structure, a large number of through holes are spirally curved, and when this is installed in the passage of the combustion exhaust gas, the exhaust gas passes along the ceramic wall when passing through the spiral through hole. You will be forced to turn. Therefore, the gas receives a cyclonic centrifugal force proportional to the square of the flow velocity and the reciprocal of the spiral radius of curvature, and collides with the inner wall of the through hole. Fine particles such as oil smoke and dust contained in the exhaust gas are separated from the gas. They are separated by the difference in specific gravity and adhere to the inner wall.
Japanese Patent Laid-Open No. 10-249968

  However, in the ceramic spiral honeycomb structure disclosed in Patent Document 1, a large number of ceramic powder sheets or thin plate products are sequentially shifted little by little, and all the through holes formed by stacking the apertures are spiral. It is necessary to bend into a shape. The manufacturing cost of the ceramic spiral honeycomb laminate manufactured by such a manufacturing method becomes expensive. In addition, as shown in FIG. 1 of Patent Document 1, this ceramic powder sheet-like or thin-plate molded product has an assembly of regular hexagonal openings in an elliptical outer frame, and the position of the assembly. Eccentric from the center of the ellipse. Therefore, it has a part where the aggregate of the opening part does not exist, and the ratio of the total area of the part of the opening part to the outer shape frame is lower than the case where the whole outer shape frame has the opening part. become. For this reason, the pipe resistance of the exhaust gas is increased, and the performance of the internal combustion engine may be deteriorated.

  Further, when a catalytic converter is configured using such a structure, it is necessary to raise the temperature of the catalyst to a high temperature using exhaust gas because of the temperature characteristics of the catalyst. In the ceramic spiral honeycomb structure disclosed in Patent Document 1, the temperature rise effect by the exhaust gas cannot be expected in a portion that does not have the aggregate of the opening portions. Furthermore, since the aggregates of the apertures are arranged asymmetrically, the temperature distribution becomes large and the catalyst cannot be activated uniformly.

  The present invention has been made in order to solve the above-described problems, and an object of the present invention is to provide a catalyst structure in an exhaust purification apparatus capable of activating a catalyst without temperature distribution at a low production cost, and its It is to provide a manufacturing method.

  A catalyst structure according to a first invention is a catalyst structure in an exhaust gas purification apparatus for an internal combustion engine. This catalyst structure has a number of communication passages in the flow direction of exhaust gas from the internal combustion engine. The communication path in the peripheral part is formed in a spiral shape having a longer communication path than the communication path in the central part of the flow in a plane perpendicular to the flow direction.

  According to the first invention, in order to purify exhaust gas from a diesel engine, for example, an NSR (NOx Storage Reduction) catalyst that absorbs NOx or / and PM that is fine particles of carbon and the like are removed and NOx is absorbed. A DPNR (Diesel Particulate NOx Reduction) catalyst is provided as a catalyst for the internal combustion engine. These catalysts are activated when they reach a high temperature, exhibit a desired purification function, and purify exhaust gas. When the catalyst is cold, the temperature of the catalyst is raised using the exhaust gas from the internal combustion engine. In such a case, the catalyst structure according to the first invention has a large number of communication passages in the flow direction of the exhaust gas from the internal combustion engine. Heat exchange is performed when passing through this communication path, and the temperature of the catalyst is increased. About this communicating path, the length of the pipe line is long and the length of the pipe line is long, and the length of the pipe line is short and the length of the pipe line is short. In the case of a conventional catalyst structure in which all of the communication passages penetrate uniformly and straightly, the flow rate of exhaust gas is higher in the central part and the flow rate of exhaust gas is lower in the peripheral part. Then, since there is a difference in flow rate, the temperature for achieving the catalyst activation temperature becomes longer as the temperature is lower at the outer peripheral portion. In the catalyst structure according to the first aspect of the present invention, the pipe length is longer at the peripheral portion and the pipe length is shorter at the central portion. Since the exothermic time due to chemical reaction is long, the temperature rise can be promoted. Further, in the central portion, the residence time is short even if the flow rate of the exhaust gas is large, so that the temperature difference from the peripheral portion can be suppressed. As a result, it is possible to provide a catalyst structure in an exhaust purification device that can activate the catalyst without temperature distribution.

  A catalyst structure according to a second invention is a catalyst structure in an exhaust gas purification apparatus for an internal combustion engine. This catalyst structure has a substantially cylindrical shape. The flow direction of the exhaust gas from the internal combustion engine is provided so as to be substantially the length direction of the cylinder. The catalyst structure has a large number of communication passages communicating with each other in a substantially cylindrical length direction. The communication path in the peripheral part is formed in a spiral shape in which the length of the communication path is longer than the communication path in the central part of the flow in the cross section of the substantially cylindrical shape.

  According to the second invention, when the NSR catalyst or the DPNR catalyst is cold, the temperature of the catalyst is raised using the exhaust gas from the internal combustion engine. In such a case, the catalyst structure according to the second aspect of the present invention has a substantially cylindrical shape, and the flow direction of the exhaust gas from the internal combustion engine is substantially the length direction of the cylindrical column, and the substantially soot particles. A number of communication paths are provided in the longitudinal direction. Heat exchange is performed when passing through this communication path, and the temperature of the catalyst is increased. About this communication path, the length of the pipe line is longer and the length of the pipe line is longer, and the length of the pipe line is longer in the center part of the cross section of the cylinder. It is getting shorter. In the catalyst structure according to the second invention, since the pipe length is longer in the peripheral portion and the pipe length is shorter in the central portion, the residence time is long in the peripheral portion even if the flow rate of the exhaust gas is small. The temperature rise can be promoted. Further, in the central portion, the residence time is short even if the flow rate of the exhaust gas is large, so that the temperature difference from the peripheral portion can be suppressed. As a result, it is possible to provide a catalyst structure in an exhaust purification device that can activate the catalyst without temperature distribution.

  In the catalyst structure according to the third invention, in addition to the configuration of the first or second invention, a part of the communication path is closed on the upstream side in the exhaust gas flow direction. In addition, the communication passages other than a part are closed on the downstream side in the exhaust gas flow direction.

  According to the third aspect of the present invention, for example, in the case of a DPNR catalyst, a part of the upstream side of many communication pipes is blocked and the downstream side of the other communication pipes is closed. However, the pipe length of the peripheral part where the exhaust gas flow rate is small can be made longer than the central part, and the temperature difference can be suppressed.

  A catalyst structure according to a fourth invention is a catalyst composed of a plurality of catalyst structures, wherein the catalyst structure according to the structure of the first or second invention is used as the previous catalyst structure. .

  According to the fourth invention, in order to purify exhaust gas from a diesel engine, for example, at least two catalyst bodies of an NSR catalyst that absorbs NOx and a DPNR may be provided in series in this order. In such a case, the catalyst structure according to the first invention or the catalyst structure according to the second invention is adopted for the preceding stage NSR catalyst that is required to have a shorter overall length. Even if it is short, an NSR catalyst having a long pipe length can be realized. As a result, even if the total length is short, it is possible to provide an NSR catalyst that can raise the temperature in a short time and can exhibit a desired purification function.

  A catalyst structure according to a fifth aspect of the present invention is a catalyst composed of a plurality of catalyst structures, wherein the catalyst structure according to the structure of the third aspect of the invention is used as a subsequent catalyst structure.

  According to the fifth invention, in order to purify exhaust gas from a diesel engine, for example, at least two catalyst bodies of an NSR catalyst that absorbs NOx and a DPNR may be provided in series in this order. In such a case, the catalyst structure according to the third aspect of the present invention is adopted as the DPNR catalyst in the subsequent stage, and a DPNR catalyst having a long pipe length can be realized even if the total length of the DPNR catalyst is short. As a result, even if the total length is short, it is possible to provide a DPNR catalyst capable of raising the temperature in a short time and exhibiting a desired purification function.

  A manufacturing method according to a sixth aspect of the invention is a method for manufacturing a catalyst structure in an exhaust gas purification apparatus for an internal combustion engine. The manufacturing method includes a step of adjusting a ceramic material to a desired material suitable for the catalyst structure, a step of extruding the ceramic material into a desired shape having a number of communication paths in the extrusion direction, and a desired shape. A step of applying a pressing force in the extrusion direction and applying a twisting force in a direction opposite to each other in the forward direction and the backward direction of extrusion to form a desired final shape; Firing the structure molded into the desired final shape.

  According to the sixth invention, the ceramic material adjusted to a desired material is extruded into a substantially cylindrical shape having a large number of communication passages, and a pressing force is applied in the extrusion direction, and in the forward and backward directions of extrusion. Twists against each other. For this reason, the outer peripheral portion of the substantially cylindrical cross section is bent in a large spiral shape, and the length of the pipeline is long, and the central portion of the substantially cylindrical cross section is bent in a small spiral shape, and the length of the pipeline is shortened. Yes. As a result, it is possible to provide a method for producing a catalyst structure in an exhaust purification device that can activate a catalyst without temperature distribution at a low production cost.

  A manufacturing method according to a seventh aspect of the present invention is a method for manufacturing a catalyst structure in an exhaust gas purification apparatus for an internal combustion engine. In this manufacturing method, a ceramic material is adjusted to a desired material suitable for the catalyst structure, and the ceramic material is extruded into a desired shape having a large number of communication paths in the extrusion direction and pressed in the extrusion direction. A step of forming a desired final shape by applying a torsional force in a direction opposite to each other in the forward direction and the backward direction of extrusion, and firing the structure molded in the desired final shape Including the step of.

  According to the seventh invention, the ceramic material adjusted to a desired material is extruded into a substantially cylindrical shape having a large number of communication passages, a pressing force is applied in the extrusion direction, and the forward and backward directions of extrusion are Twist in the opposite direction. For this reason, the outer peripheral portion of the substantially cylindrical cross section is bent in a large spiral shape, and the length of the pipeline is long, and the central portion of the substantially cylindrical cross section is bent in a small spiral shape, and the length of the pipeline is shortened. Yes. As a result, it is possible to provide a method for producing a catalyst structure in an exhaust purification device that can activate a catalyst without temperature distribution at a low production cost.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

  An embodiment in which a catalyst structure in an exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention is applied to a diesel engine system will be described. First, a diesel engine system to which this catalyst structure is applied will be described. This diesel engine system combines a high-pressure common rail fuel injection device, a large-capacity electronically controlled EGR (Exhaust Gas Recirculation) cooler, and a DPNR catalyst in order to realize clean exhaust of the diesel engine, and PM and NOx are continuously and simultaneously. It is a system to reduce.

  In FIG. 1, an internal combustion engine (hereinafter referred to as an engine) 1000 is an in-line four-cylinder diesel engine system including a fuel supply system 100, a combustion chamber 200, an intake system 300, an exhaust system 400, and the like as main parts.

  The fuel supply system 100 includes a supply pump 110, a common rail 120, a fuel injection valve 130, a shutoff valve 140, a metering valve 160, a fuel addition nozzle 170, an engine fuel passage 800, an addition fuel passage 810, and the like.

  The supply pump 110 pumps fuel from the fuel tank, raises the pumped fuel to a high pressure, and supplies the pumped fuel to the common rail 120 via the engine fuel passage 800. The common rail 120 functions as a pressure accumulation chamber that holds (accumulates) the high-pressure fuel supplied from the supply pump 110 at a predetermined pressure, and distributes the accumulated fuel to each fuel injection valve 130. The fuel injection valve 130 includes an electromagnetic solenoid therein, and is appropriately opened to inject fuel into the combustion chamber 200.

  The supply pump 110 supplies a part of the fuel pumped from the fuel tank to the fuel addition nozzle (reducing agent injection nozzle) 170 via the added fuel passage 810. In the addition fuel passage 810, a shutoff valve 140 and a metering valve 160 are sequentially arranged from the supply pump 110 toward the fuel addition nozzle 170. The shutoff valve 140 shuts off the added fuel passage 810 in an emergency and stops the fuel supply. The metering valve 160 controls the pressure (fuel pressure) of the fuel supplied to the fuel addition nozzle 170. The fuel addition nozzle 170 is a mechanical on-off valve that opens when a fuel pressure (for example, 0.2 MPa) equal to or higher than a predetermined pressure is applied and injects fuel into the exhaust system 400 (exhaust port 410). That is, by controlling the fuel pressure upstream of the fuel addition nozzle 170 by the metering valve 160, desired fuel is injected and supplied (added) from the fuel addition nozzle 170 at an appropriate timing.

  The intake system 300 forms a passage (intake passage) for intake air supplied into each combustion chamber 200. The exhaust system 400 is configured by connecting various passage members such as an exhaust port 410, an exhaust manifold 420, a catalyst upstream side passage 430, and a catalyst downstream side passage 440 in order from upstream to downstream, and exhaust discharged from each combustion chamber 200. A gas passage (exhaust passage) is formed.

  Further, the engine 1000 is provided with a known supercharger (turbocharger) 500. The turbocharger 500 includes two turbine wheels 520 and a turbine wheel 530 that are connected via a shaft 510. One turbine wheel (intake side turbine wheel) 530 is exposed to intake air in the intake system 300, and the other turbine wheel (exhaust side turbine wheel) 520 is exposed to exhaust in the exhaust system 400. The turbocharger 500 having such a configuration performs so-called supercharging in which the intake side turbine wheel 530 is rotated using the exhaust flow (exhaust pressure) received by the exhaust side turbine wheel 520 to increase the intake pressure.

  In the intake system 300, the intercooler 310 provided in the turbocharger 500 forcibly cools the intake air whose temperature has been increased by supercharging. The throttle valve 320 provided further downstream than the intercooler 310 is an electronically controlled on-off valve whose opening degree can be adjusted steplessly, and the flow area of the intake air is reduced under predetermined conditions. The function of adjusting (reducing) the supply amount of the intake air is provided.

  Further, the engine 1000 is formed with an exhaust gas recirculation passage (EGR passage) 600 that bypasses the upstream (intake system 300) and the downstream (exhaust system 400) of the combustion chamber 200. The EGR passage 600 has a function of returning a part of the exhaust to the intake system 300 as appropriate. The EGR passage 600 is opened and closed steplessly by electronic control, and an EGR valve 610 that can freely adjust the flow rate of exhaust gas flowing through the passage, and EGR for cooling the exhaust gas that passes (refluxs) through the EGR passage 600. A cooler 620 is provided.

  In the exhaust system 400, a catalyst composed of an NSR catalyst 460 and a DPNR catalyst 470 is provided downstream of the exhaust side turbine wheel 520 (between the catalyst upstream side passage 430 and the catalyst downstream side passage 440).

The NSR catalyst 460 is an NOx storage reduction catalyst. For example, alumina (Al ₂ O ₃ ) is used as a carrier, and potassium (K), sodium (Na), lithium (Li), cesium Cs, and the like are formed on this carrier. It is constituted by supporting a rare earth metal such as alkali metal, barium Ba, calcium Ca, alkaline earth such as lanthanum (La), yttrium (Y), and noble metal such as platinum Pt.

The NSR catalyst 460 absorbs NOx in a state where a large amount of oxygen is present in the exhaust gas, has a low oxygen concentration in the exhaust gas, and a large amount of reducing component (for example, unburned component (HC) of fuel). In the existing state, NOx is reduced to NO ₂ or NO and released. NO NOx released as NO ₂ or NO, the N ₂ is further reduced due to quickly reacting with HC or CO in the exhaust. Incidentally, HC and CO are oxidized to H ₂ O and CO ₂ by reducing NO ₂ and NO. That is, if the oxygen concentration and HC component in the exhaust gas introduced into the NSR catalyst 460 are appropriately adjusted, HC, CO, and NOx in the exhaust gas can be purified.

  The DPNR catalyst 470 is configured by combining a porous ceramic structure with a NOx storage reduction catalyst. The exhaust gas from the engine 100 is oxidized and reduced by the catalyst while passing through the gaps in the ceramics, and is then chemically changed into a harmless gas and discharged.

  PM is temporarily collected by a porous catalyst during lean combustion with lean oxygen (at the same time, and at the same time is oxidized and purified by active oxygen generated when NOx is occluded and oxygen in the exhaust gas. NOx is temporarily stored in the catalyst during lean combustion, and then reduced and purified by instantaneous rich combustion (concentrated air-fuel ratio combustion with less oxygen), and PM is stored in NOx during rich combustion. It is oxidized and purified by the active oxygen generated during the process.

  Various sensors are attached to each part of the engine 1000, and signals related to the environmental conditions of each part and the operating state of the engine 1000 are output.

  For example, the rail pressure sensor 700 outputs a detection signal corresponding to the fuel pressure stored in the common rail 120. The fuel pressure sensor 710 outputs a detection signal corresponding to the pressure (fuel pressure) Pg of the fuel introduced into the metering valve 160 among the fuel flowing through the added fuel passage 810. The air flow meter 720 outputs a detection signal corresponding to the flow rate (intake amount) Ga of intake air downstream of the throttle valve 320 in the intake system 300. The air-fuel ratio (A / F) sensor 730 outputs a detection signal that continuously changes in accordance with the oxygen concentration in the exhaust downstream of the catalyst casing of the exhaust system 400. Similarly, the exhaust temperature sensor 740 outputs a detection signal corresponding to the exhaust temperature (exhaust temperature) Tex at the downstream of the catalyst casing of the exhaust system 400.

  The accelerator opening sensor 750 is attached to the accelerator pedal of the engine 1000, and outputs a detection signal corresponding to the depression amount Acc of the pedal. The crank angle sensor 760 outputs a detection signal (pulse) every time the output shaft (crankshaft) of the engine 1000 rotates by a certain angle. Each of these sensors 700 to 760 is electrically connected to an electronic control unit (ECU) 1100.

  The ECU (Electronic Control Unit) 1100 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), a backup RAM, a timer, a counter, and the like, and an A / D (Analog / Digital). ) An external input circuit including a converter and an external output circuit are connected by a bidirectional bus.

  The ECU 1100 configured as described above inputs detection signals from the various sensors via an external input circuit, and performs basic control for fuel injection and the like of the engine 1000 based on these signals, as well as a reducing agent (as a reducing agent). Various controls relating to the operating state of the engine 1000 are executed, such as control of addition of a reducing agent (fuel) relating to determination of addition timing and supply amount for the functioning fuel) addition.

  Next, an outline of the basic principle of fuel addition executed by the ECU 1100 will be described.

  In general, in a diesel engine, the oxygen concentration of a mixture of fuel and air used for combustion in a combustion chamber is in a high concentration state in most operating regions.

The oxygen concentration of the air-fuel mixture used for combustion is usually reflected directly in the oxygen concentration in the exhaust gas after subtracting the oxygen supplied for combustion. If the oxygen concentration (air-fuel ratio) in the air-fuel mixture is high The oxygen concentration (air-fuel ratio) in the exhaust gas basically increases similarly. On the other hand, as described above, the NOx storage reduction catalyst absorbs NOx The higher the oxygen concentration in the exhaust gas, the NOx A low NO ₂
Alternatively, since it has a characteristic of being reduced to NO and released, NOx is absorbed as long as oxygen in the exhaust is in a high concentration state. However, when there is a limit amount in the NOx absorption amount of the catalyst and the catalyst absorbs the limit amount of NOx, NOx in the exhaust gas is not absorbed by the catalyst and passes through the catalyst casing.

Therefore, in an internal combustion engine such as the engine 1000 having the fuel addition nozzle 170, fuel is added to the upstream of the catalyst 450 of the exhaust system 400 through the fuel addition nozzle 170 at an appropriate time (hereinafter referred to as exhaust addition). Thus, the oxygen concentration in the exhaust gas is reduced and the amount of reducing component (HC, etc.) is increased. Then, the catalyst 450 reduces and releases the NOx absorbed so far to NO ₂ or NO, and recovers (regenerates) its own NOx absorption ability. As described above, the released NO ₂ and NO react with HC and CO to be quickly reduced to N ₂ .

  At this time, for the catalyst 450 that reduces and purifies the NOx absorbed by itself in the above-described manner, the reduction is performed by the amount of reducing component (fuel concentration) in the exhaust gas flowing into the catalyst casing and the oxygen concentration (air-fuel ratio). The efficiency of purification will be determined.

  Therefore, the engine 1000 performs fuel addition (fuel addition control) to the exhaust system 400 so that an appropriate amount of reducing component and air-fuel ratio in the exhaust gas can be stably obtained.

  FIG. 2 shows the detailed structure of the catalyst 450. As shown in FIG. 2, an NSR catalyst 460 is provided via a gap 480 on the upstream side (engine 1000 side) of the DPNR catalyst 470 formed of a porous ceramic structure for removing PM of exhaust gas. . In particular, the length of the NSR catalyst 460 is often restricted in the direction in which the exhaust gas flows, and needs to be shortened in the flow direction of the exhaust gas. In the following description, the case where the catalyst structure according to the present embodiment is applied to the NSR catalyst 460 will be described, but the catalyst structure may be applied to the DPNR catalyst 470 and other catalysts.

  The NSR catalyst 460 in FIG. 2 has a characteristic that it is not activated unless the temperature rises. Therefore, when the engine 1000 is cold started, the temperature of the NSR catalyst 460 is raised using the exhaust gas. At this time, the NSR catalyst 460 is a porous ceramic structure having a substantially circular cross-sectional area. When the hot exhaust gas passes through these many holes, the temperature of the catalyst is raised. At this time, the longer the residence time of the exhaust gas in the NSR catalyst 460, the more heat exchange is promoted and the temperature of the catalyst rises appropriately. Further, as shown in FIGS. 1 and 2, the engine 1000 side of the catalyst 450 has a smaller pipe cross-sectional area than the catalyst 450, so that the hole in the center portion is the same among the holes provided uniformly in the NSR catalyst 460. However, the flow rate of exhaust gas increases. The temperature rise is promoted in the central part where the flow rate of exhaust gas is large, and the temperature rise is not promoted in the peripheral part.

  The catalyst structure according to the present embodiment is a porous ceramic structure, and has a large number of through holes uniformly in the cross-sectional area of the pipe in the direction in which the exhaust gas flows. Furthermore, as shown in FIG. 3, the NSR catalyst 460 has a shape in which the through hole is bent spirally by a manufacturing method described later. Due to this helical bending, the pipe length in the NSR catalyst 460 becomes longer than the entire length L (2) of the NSR catalyst 460. In particular, the peripheral part is significantly longer than the central part. Thereby, the temperature increase is promoted at the central part where the flow rate of the exhaust gas is large, and the state where the temperature rise is not promoted as the peripheral part is improved. That is, the residence time in the NSR catalyst 460 becomes longer even if the flow rate is smaller in the peripheral portion, and the residence time in the NSR catalyst 460 becomes shorter in the central portion but the flow rate is larger. The relative difference in exchange amount is reduced. As a result, the temperature distribution between the peripheral part and the central part is reduced.

  With reference to FIG. 4, the manufacturing method of the catalyst structure used for the NSR catalyst 460 is demonstrated.

As the material of the catalyst structure, various celluloses and the like are mixed into the ceramic powder slurry to prepare a raw material before molding of desired components. As the material of the ceramic, cordierite, Al ₂ O ₃ , SiC, and various other heat-resistant ceramic powders can be used according to the purpose. Such a material before molding is, for example, extruded and formed into a substantially cylindrical body having a diameter D (1) and a total length L (1) as shown in FIG. At this time, it is molded so that a large number of through holes penetrating the length direction of the substantially cylindrical body are provided.

  Simultaneously with this molding or after this molding, as shown in FIG. 4, a pressing force P is applied so as to shorten the full length direction L (1), and the upper and lower sides of the substantially cylindrical body are gripped in opposite directions. A twisting torsional force is applied. At this time, the center of the point of application of the torsional force is made to coincide with the center of the substantially cylindrical body.

  By such molding. Due to the pressing force P and the torsional force, the total length L (1) is the total length L (2) (L (1)> L (2)), and the diameter D (1) is the diameter D (2) (D (1) <D (2)). Note that the total length L (2) and the diameter D (2) are substantially completed dimensions of the catalyst structure.

  The ceramic structure molded as shown in FIG. 4 is fired under desired conditions. Thus, as shown in FIG. 3, the outer peripheral portion has a unique internal shape in which the spiral length is longer in the catalyst structure body, and the central portion is looser in the spiral shape and the catalyst structure body has a shorter pipe length. The catalyst structure is completed.

  As described above, the catalyst structure according to the present embodiment has a cylindrical shape having a substantially circular cross section, and has a large number of through passages penetrating in the length direction. In addition, with respect to this through-passage, the substantially circular outer periphery is bent in a larger spiral shape and the length of the conduit is longer, and the substantially circular center is bent in a smaller spiral shape and the length of the conduit is shorter. ing. Such a catalyst structure having a substantially circular cross-sectional area and having a conventional catalyst structure in which all the pipes pass through straight and straight, the flow rate of exhaust gas is larger at the center, The part has a lower flow rate of the exhaust gas, and when the temperature is increased by the exhaust gas, the flow rate is different, so the temperature is lower at the outer peripheral part and the time for achieving the catalyst activation temperature is longer. In the catalyst structure according to the present embodiment, the pipe length is longer in the peripheral portion and the pipe length is shorter in the central portion. Therefore, in the peripheral portion, the residence time (that is, the catalyst Since the exothermic time due to chemical reaction is long, the temperature rise can be promoted. Further, in the central portion, the residence time is short even if the flow rate of the exhaust gas is large, so that the temperature difference from the peripheral portion can be suppressed.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a schematic structure figure showing a diesel engine system concerning an embodiment of the invention. It is a figure which shows the detail of the catalyst of FIG. It is a figure which shows the structure of the NSR catalyst of FIG. It is a figure explaining the manufacturing method of the NSR catalyst of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Fuel supply system, 110 Supply pump, 120 Common rail, 130 Fuel injection valve, 140 Shutoff valve, 160 Metering valve, 170 Fuel addition nozzle, 200 Combustion chamber, 300 Intake system, 310 Intercooler, 320 Throttle valve, 400 Exhaust system , 410 exhaust port, 420 exhaust manifold, 430 catalyst upstream passage, 440 catalyst downstream passage, 450 catalyst, 460 NSR catalyst, 470 DPNR catalyst, 480 gap, 490 differential pressure transducer, 500 turbocharger, 510 shaft, 520
Exhaust side turbine wheel, 530 Intake side turbine wheel, 600 EGR passage, 610 EGR valve, 620 EGR cooler, 700 Rail pressure sensor, 710 Fuel pressure sensor, 720 Air flow meter, 730 Air-fuel ratio sensor, 740 Exhaust temperature sensor, 750 Accelerator opening Sensor, 760 crank angle sensor, 800 engine fuel passage, 810 additive fuel passage, 1000 engine, 1100 ECU.

Claims (7)

A catalyst structure in an exhaust gas purification device for an internal combustion engine,
The catalyst structure has a number of communication passages in the flow direction of exhaust gas from the internal combustion engine,
A catalyst structure in which a communication path in a peripheral portion is formed in a spiral shape having a longer communication path than a communication path in a central portion of a flow in a plane perpendicular to the flow direction. A catalyst structure in an exhaust gas purification device for an internal combustion engine,
The catalyst structure has a substantially cylindrical shape,
Provided so that the flow direction of the exhaust gas from the internal combustion engine is the length direction of the substantially cylindrical shape,
The catalyst structure has a large number of communication passages communicating with each other in a substantially cylindrical length direction,
The catalyst structure in which the communication path in the peripheral part is formed in a spiral shape having a longer communication path than the communication path in the central part of the flow in the cross section of the substantially cylindrical shape. A part of the communication path is blocked on the upstream side in the exhaust gas flow direction,
The catalyst structure according to claim 1 or 2, wherein the communication passages other than the part are closed on the downstream side in the exhaust gas flow direction. In a catalyst composed of a plurality of catalyst structures,
A catalyst structure using the catalyst structure according to claim 1 or 2 as a previous catalyst structure. In a catalyst composed of a plurality of catalyst structures,
A catalyst structure in which the catalyst structure according to claim 3 is used as a subsequent catalyst structure. A method for producing a catalyst structure in an exhaust gas purification apparatus for an internal combustion engine, comprising:
Adjusting the ceramic material to a desired material compatible with the catalyst structure;
Extruding the ceramic material into a desired shape having multiple communication paths in the extrusion direction;
The structure molded in the desired shape is molded into a desired final shape by applying a pressing force in the extrusion direction and applying a torsional force in the direction opposite to each other in the forward and backward directions of extrusion. And steps to
Firing the structure molded into the desired final shape. A method for producing a catalyst structure in an exhaust gas purification apparatus for an internal combustion engine, comprising:
Adjusting the ceramic material to a desired material compatible with the catalyst structure;
The ceramic material is extruded into a desired shape having a large number of communication paths in the extrusion direction, a pressing force is applied in the extrusion direction, and a twisting force is applied in the direction of twisting in the forward and backward directions of the extrusion. And forming the desired final shape;
Firing the structure molded into the desired final shape.

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