DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0065] First Embodiment

[0066] A method of manufacturing the hollow ceramic monolithic support and a molding die according to the first embodiment of the present invention will be described below with reference to FIGS. 1 ( a ) through 6 .

[0067] The molding die 1 used in this embodiment has a die 2 , an outer periphery guide ring 3 and an inner periphery guide ring 4 as shown in FIGS. 1 ( a ) and 1 ( b ).

[0068] The molding die 2 has an introduction hole section 21 provided with introduction holes 210 through which a material is introduced, and a slit section 22 provided with slits 220 that communicate with the introduction holes 210 for forming the material into honeycomb shape. The slit section 22 protrudes from the surrounding thereof and has slits 220 formed in rectangular grid configuration. Provided on the opposite side of the slit section 22 is the introduction hole section 21 having a multitude of the introduction holes 210 formed so as to communicate with the crossing portions of the slits 220 .

[0069] Provided at the center of the die 2 is a through hole 29 through which a bolt 51 is inserted for fastening an inner periphery guide ring 4 to be described later. Pin holes 28 are provided at two positions outside the slit section 22 for fastening an outer periphery guide ring 3 to be described later.

[0070] The outer periphery guide ring 3 has an outer periphery erected portion 31 formed to extend from the outer peripheral end of the slit section in the direction of extrusion, and an outer periphery protruding portion 32 that protrudes from the outer periphery erected portion 31 inward and is separated from the slit section 22 by a gap C 1 ( FIG. 1 ( b )), as shown in FIGS. 3 ( a ) and 3 ( b ).

[0071] The outer periphery erected portion 31 has a ring shape, with an inner peripheral surface 310 thereof being formed so as to abut the outer peripheral surface of the slit section 22 of the die 2 . The gap C 1 is secured by making the height of the outer periphery erected portion 31 greater than the height of the slit section 22 . The gap C 1 is set to 0.2 mm in this example.

[0072] The outer periphery protruding portion 32 is formed so that an outer periphery opposing surface 321 that opposes the slit section 22 protrudes inwardly so as to secure the gap C 1 from the slit section 22 as shown in FIGS. 1 ( a ), 1 ( b ), 3 ( a ) and 3 ( b ). The outer periphery protruding portion 32 has a tapered surface 322 formed on the inside thereof so as to expand gradually along the extruding direction. Distal end of the outer periphery protruding portion 32 is formed in circular shape of a size that matches the outer dimension of the hollow ceramic monolithic support 8 to be manufactured.

[0073] The outer periphery guide ring 32 has a pin hole 38 for fastening the outer periphery guide ring onto the die 2 .

[0074] The inner periphery guide ring 4 has an inner periphery erected portion 41 formed to extend from the center of the slit section 22 in the direction of extrusion, and an inner periphery protruding portion 42 that protrudes from the inner periphery erected portion 41 outward and is separated from the slit section 22 by a gap C 2 ( FIG. 1 ( b )), as shown in FIGS. 4 ( a ) and 4 ( b ).

[0075] The inner periphery erected portion 41 has a cylindrical shape having a through hole 419 at the center thereof and an outer peripheral surface 410 . The gap C 2 is secured by means of the height of the inner periphery erected portion 41 . The gap C 2 is set to 0.2 mm in this example.

[0076] The inner periphery protruding portion 42 is formed so that an inner periphery opposing surface 421 that opposes the slit section 22 protrudes outwardly so as to secure the gap C 2 from the slit section 22 as shown in FIGS. 1 ( a ), 1 ( b ), 4 ( a ) and 4 ( b ). The inner periphery protruding portion 42 has a tapered surface 422 formed on the outside thereof so as to contract gradually along the extruding direction. The distal end of the inner periphery protruding portion 42 is formed in circular shape of a size that matches the inner dimension of the hollow ceramic monolithic support 8 to be manufactured.

[0077] The molding die 1 of this example is made by assembling the outer periphery guide ring 3 and the inner periphery guide ring 4 on the die 2 .

[0078] When assembling the outer periphery guide ring on the die 2 , the outer periphery guide ring 3 is placed on the outer periphery of the slit section 22 of the die 2 , and the pins 55 are inserted into the pin holes 28 , 38 for securing.

[0079] When fastening the inner periphery guide ring 4 onto the die 2 , a disk-shaped adjustment plate 45 that has a through hole 450 is prepared, and the adjustment plate 45 , the die 2 and the inner periphery guide ring 4 are assembled so that the through holes 450 , 29 and 419 are aligned concentrically. The bolt 51 is passed through the through holes 450 , 29 and 419 and is secured with a nut 52 . Thus the inner periphery guide ring 4 is secured onto the die 2 .

[0080] Now a method of manufacturing the hollow ceramic monolithic support 8 using the molding die 1 having the constitution described above will be described below.

[0081] First, the molding die 1 is set at the distal end of a screw extrusion molding apparatus that is not shown in the drawing. A kneaded green ceramic material is charged into the screw extrusion molding apparatus to carry out extrusion molding.

[0082] In this example, a powdery material prepared in such a proportion that constitutes cordierite as the final product with a binder and other components added thereto was used as the ceramic material.

[0083] The ceramic material that is extruded continuously by the screw extrusion molding apparatus passes through the molding die 1 thereby to be molded into the hollow ceramic monolithic support 8 .

[0084] As shown in FIG. 5 , an outer periphery skin portion 81 is formed from the ceramic material 88 that passes through the gap C 1 provided between the outer periphery protruding portion 32 and the slit section 22 of the outer periphery guide ring 3 . The ceramic material 88 that is extruded to pass through the slit section 22 that opposes the outer periphery opposing surface 321 of the outer periphery protruding portion 32 flows into the gap C 1 surrounded by the slit section 22 , the outer periphery opposing surface 321 and the inner surface 310 of the outer periphery guide ring 3 , so as to flow toward the center, and changes direction at the end of the outer periphery protruding portion 32 so as to flow in the direction of extrusion thereby to form the outer periphery skin portion 81 .

[0085] Also, as shown in the drawing, an inner periphery skin portion 83 is formed from the ceramic material 88 that passes between the inner periphery protruding portion 42 and the slit section 22 of the inner periphery guide ring 4 . The ceramic material 88 that is extruded to pass through the slit section 22 that opposes the inner periphery opposing surface 421 of the inner periphery protruding portion 42 flows into the gap C 2 surrounded by the slit section 22 , the inner periphery opposing surface 421 and the inner surface 410 of the inner periphery guide ring 4 , so as to flow toward the outer periphery, and changes direction at the end of the inner periphery protruding portion 42 to flow in the direction of extrusion thereby to form the inner periphery skin portion 83 .

[0086] It is also effective to form the outer periphery protruding portion 32 and the inner periphery protruding portion 42 to have cross sections at the distal end thereof as shown in FIG. 13 . In this case, the ceramic material 88 , that has been introduced into the gap C 1 surrounded by the outer periphery opposing surface 321 and the inner surface 310 or into the gap C 2 surrounded by the inner periphery opposing surface 421 and the inner surface 410 , can flow smoothly along a path of an arc shape toward the distal end of the outer periphery protruding portion 32 or the inner periphery protruding portion 42 .

[0087] As shown in the drawing, the ceramic material 88 that is extruded through the slit section 22 surrounded by the inner periphery skin portion 83 and the outer periphery skin portion 81 is formed into the main body 82 of honeycomb shape having the rectangular grid.

[0088] As the outer periphery skin portion 81 , the main body 82 and the inner periphery skin portion 83 are formed integrally and at the same time, the hollow ceramic monolithic support 8 ( FIG. 6 ) that has a hollow space 80 formed in the inner periphery skin portion 83 can be manufactured continuously.

[0089] The hollow ceramic monolithic support 8 thus manufactured has the hollow space 80 and the inner periphery opposing surface 83 that surrounds the hollow space 80 is formed integrally on the inner surface of the main body 82 . As a result, the hollow ceramic monolithic support 8 has a very high isostatic strength.

[0090] Since the hollow ceramic monolithic support 8 of the constitution described above can be manufactured simply by extrusion molding as described above, waste of material and the need for the additional processes of the prior art are eliminated, thus reducing the manufacturing cost.

[0091] While the main body 82 of rectangular honeycomb is described in the example described above, the shape may be changed to a hexagon or another shape.

[0092] The slit section 22 , the outer periphery guide ring 3 and the inner periphery guide ring 4 are assumed to have circular shapes in the example described above, they may also be made in an oval, a race track or another shape.

[0093] Dimensions of the adjustment plate 45 , the outer periphery guide ring 3 and the inner periphery guide ring 4 , dimension of the slit 220 of the slit section 22 , and the dimension and location of the introduction holes of the introduction hole section 21 may also be altered so as to match the dimension and shape of the hollow ceramic monolithic support 8 to be manufactured.

[0094] The means for fastening the die 2 , the outer periphery guide ring 3 and the inner periphery guide ring 4 together may also be changed to other binding means such as the use of other fixtures, brazing or thermal diffusion.

[0095] Moreover, shape of the hollow ceramic monolithic support 8 is not limited to the substantially circular cross section as described above, and may be substantially rectangular section as shown in FIG. 14 or substantially oval section as shown in FIG. 15 . The shape of the hollow ceramic monolithic support 8 should be determined in consideration of the installing position and available space for installation.

[0096] Second Embodiment

[0097] In the hollow ceramic monolithic support 8 manufactured in this example, as shown in FIGS. 7 , 8 ( a ) and 8 ( b ), the ribs 84 located near the inner periphery skin portion 83 and the outer periphery skin portion 81 have higher strength than other ribs, in contrast to the hollow ceramic monolithic support 8 manufactured in the first embodiment.

[0098] In the hollow ceramic monolithic support 8 described above, the ribs 84 located in a layer about one cell (one or more cells) from the inner periphery skin portion 83 are made with a high-strength portion S 2 having higher strength than an ordinary portion P consisting of the ribs located outside thereof. Also the ribs 84 located in a layer about one cell from the outer periphery skin portion 81 are made in a high strength portion S 1 having higher strength than the ordinary portion P consisting of the ribs located inside thereof.

[0099] The molding die 1 used in this example is a variation of the molding die 1 of the first embodiment wherein the die 2 is modified as shown in FIGS. 9 ( a ) to 10 ( c ). In the die 2 , width of the slit 220 located in the region S 1 near the periphery of the slit section 22 and in the central region S 2 is made larger than the width of the slits 220 located in the ordinary region P located between S 1 and S 2 . Specifically, width of the slits 220 located in the region P is set to 80 μm, and width of the slits 220 located in the regions S 1 and S 2 is set to 107 μm.

[0100] When the molding die 1 having the constitution described above is used, the high strength regions S 1 and S 2 of the ribs 84 can be made stronger by making the thickness thereof larger than that in the ordinary portion P. Specifically, thickness of the ribs 84 was about 100 μm in the high strength regions S 1 and S 2 and about 75 μm in the ordinary region P.

[0101] Thickness of the ribs 84 can be set within a range from about 50 to about 150 μm depending on the application. When the high strength regions S 1 and S 2 are formed with thick ribs, it is desired to make the thickness 1.1 to 3 times that of the ordinary portion P. When the thickness ratio is below 1.1, the strength cannot be increased sufficiently and, when the thickness ratio is larger than 3, the pressure loss becomes too large.

[0102] The high strength regions S 1 and S 2 of the hollow ceramic monolithic support 8 can be extended to up to 10 cells.

[0103] This embodiment is similar to the first embodiment in other aspects of constitution, operation and effect.

[0104] Third Embodiment

[0105] This embodiment is an example of applying the hollow ceramic monolithic support 8 of the second embodiment to a catalytic converter system as shown in FIG. 11 .

[0106] The catalytic converter system 7 of this example is an exhaust gas purifying system for automobile having two catalytic converters 71 , 72 installed in series as shown in the drawing. The catalytic converter 71 is a CC catalyst and the catalytic converter 72 is an UF catalyst.

[0107] The CC catalyst 71 is constituted by installing the hollow ceramic monolithic support 8 , a butterfly valve 711 , an actuator 712 and a bypass passageway 713 in a casing 710 . The actuator 712 may be driven either by an electromagnetic motor or by negative pressure. In this example, the hollow ceramic monolithic support 8 carries a very low temperature activating catalyst, of which the activation initiating temperature is 300° C., supported thereon. Specifically, Pd (palladium) having a mean particle size of 1 nm or less is supported.

[0108] The UF catalyst 72 uses a conventional monolithic support 720 of cylindrical shape, with Pt (platinum) and Rh (rhodium) supported on the monolithic support 720 . The catalyst can be supported by various methods that have been reported and any of which can be applied to this case, it is preferable to fire active alumina and the noble metal together.

[0109] The CC catalyst 71 is made by inserting the hollow ceramic monolithic support 8 wrapped by a mat made of alumina fibers into a converter casing 710 under pressure. The hollow ceramic monolithic support 8 must have isostatic strength to endure the pressure of insertion, specifically 1 MPa or higher pressure. It has been difficult to ensure this strength in the case of the conventional hollow ceramic monolithic support. In the case of the hollow ceramic monolithic support 8 described above, an isostatic strength of 1 MPa or higher can be easily ensured as the high strength regions S 1 and S 2 having thick ribs are provided along with the outer periphery skin portion 81 and the inner periphery skin portion 83 as shown in FIGS. 7 , 8 ( a ) and 8 ( b ). Therefore, the hollow ceramic monolithic support 8 will not be destroyed when inserted into the converter casing 710 under pressure.

[0110] While the hollow ceramic monolithic support 8 is provided with a tubular member installed as the bypass passageway 713 in the hollow space 80 thereof, a mat made of alumina fibers is installed also in the gap between the hollow ceramic monolithic support 8 and the bypass passageway 713 for the purpose of sealing against exhaust gas and prevention of vibration.

[0111] Specifically, while the bypass passageway 713 wrapped by the mat is inserted into the hollow space 80 of the hollow ceramic monolithic support 8 by applying pressure, breakage from the inside can also be prevented at this time. This is because the high strength regions S 1 and S 2 having the thick ribs are provided along with provision of the outer periphery skin portion 81 and the inner periphery skin portion 83 .

[0112] Now the operation of the catalytic converter system 7 will be described with reference to FIG. 11 . When the internal combustion engine 79 is started in a cold state, namely when a signal from a cooling water temperature sensor, that is not shown in the drawing, indicates a temperature lower than a certain level, the ECU 77 directs the actuator 712 to close the butterfly valve 711 . Accordingly, all the exhaust gas discharged from the internal combustion engine 79 passes through the main body 82 of the hollow ceramic monolithic support 8 .

[0113] As the very low temperature activating catalyst is supported on the ribs 84 of the hollow ceramic monolithic support 8 as described above, a better low temperature activity, than in the conventional CC catalyst, is provided, so as to purify the exhaust gas efficiently when the temperature is low.

[0114] Then as the temperature rises, the UF catalyst 72 becomes activated. During the operation of the internal combustion engine, while the butterfly valve 711 remains closed until the load increases to a medium level, the ECU 77 directs the actuator 712 to open the butterfly valve 711 when the load increases to a high level, specifically when the ECC 77 determines that the exhaust gas temperature has reached 80° C. or higher. This causes the exhaust gas to flow into the bypass passageway 713 , so that coagulation of the very low temperature activating catalyst due to the heat can be suppressed resulting in higher durability.

[0115] At this time, the UF catalyst 72 has already been activated by the heat received from the exhaust gas that has been purified while passing through the CC catalyst. Therefore, toxic component of the exhaust gas, of which the path has been switched by the butterfly valve 711 , is purified by the UF catalyst 72 and hardly pollutes the atmosphere. When the load decreases below the medium level, the ECU 77 controls the actuator 712 again to operate the butterfly valve 711 so as to pass the exhaust gas through the main body 82 of the hollow ceramic monolithic support 8 .

[0116] In this system, as described above, low-temperature activity and heat resistance can be improved and, moreover, the pressure loss can be decreased by the combined use of the hollow ceramic monolithic support 8 and the bypass passageway 713 .

[0117] Fourth Embodiment

[0118] This embodiment is an example of controlling the catalytic converter system 7 of the third embodiment in accordance to the load on the internal combustion engine.

[0119] The control process in this example comprises steps S 110 (hereinafter referred to simple as S 110 ) through S 130 as shown in the control flow chart of FIG. 16 .

[0120] S 110 is a step for determining whether the load on the internal combustion engine is W or higher.

[0121] S 121 is a step of opening the butterfly valve 711 of the CC catalyst 71 so that the exhaust gas flows through the bypass passageway 713 of the hollow ceramic monolithic support 8 .

[0122] S 122 is a step of closing the butterfly valve 711 so that the exhaust gas flows through the main body 82 of the hollow ceramic monolithic support 8 .

[0123] In this example, the load on the internal combustion engine was estimated by using the degree of throttle opening and the amount of air intake of the internal combustion engine. A preparatory experiment was conducted before implementing this example. It was found in the experiment that there may be a case that the very low temperature activating catalyst coagulates due to heat when the operation of the internal combustion engine exceeds a medium load. Accordingly, the value W was set equal to medium load for the threshold in S 110 .

[0124] The catalytic converter system 7 was controlled according to the control flow chart organized as described above.

[0125] In this control process, when the load on the internal combustion engine is below W, the butterfly valve 711 is closed. This causes all the exhaust gas of which the temperature is relatively low to pass through the main body 82 of the hollow ceramic monolithic support 8 . When the load on the internal combustion engine is higher than W, on the other hand, the butterfly valve 711 is opened. This causes all the exhaust gas of high temperature to pass through the bypass passageway 713 . As a result, according to this example, an exhaust gas of a wide temperature range, from a low to a high temperature, can be efficiently purified similarly to the third embodiment.

[0126] Particularly, in this example, the load on the internal combustion engine is estimated according to the degree of throttle opening and the amount of air intake of the internal combustion engine. As a result, stable control can be carried out while simplifying the constitution of the catalytic converter system 7 .

[0127] The load on the internal combustion engine can also be estimated by using such parameters as the vehicle speed or acceleration besides the degree of throttle opening and the amount of air intake described above.

[0128] This embodiment is similar to the third embodiment in other aspects of constitution, operation and effect.

[0129] Fifth Embodiment

[0130] This embodiment is an example of controlling the catalytic converter system 7 of the third embodiment in accordance to the cooling water temperature of the internal combustion engine.

[0131] Control process in this example comprises steps S 210 through S 230 as shown in the control flow chart of FIG. 17 .

[0132] S 210 is a step of determining whether the cooling water temperature is 80° C. or higher or not.

[0133] S 221 is a step of opening the butterfly valve 711 of the CC catalyst 71 so that the exhaust gas flows through the bypass passageway 713 of the hollow ceramic monolithic support 8 .

[0134] S 222 is a step of closing the butterfly valve 711 so that the exhaust gas flows through the main body 82 of the hollow ceramic monolithic support 8 .

[0135] The catalytic converter system 7 was controlled according to the control flow chart organized as described above.

[0136] In this control process, when the cooling water temperature is below 80° C., the butterfly valve 711 is closed. This causes all the exhaust gas of which temperature is relatively low to pass through the main body 82 of the hollow ceramic monolithic support 8 . When the cooling water temperature reaches 80° C. or higher, on the other hand, the butterfly valve 711 is opened. This causes the exhaust gas at high temperature to pass through the bypass passageway 713 . As a result, according to this example, an exhaust gas of a wide temperature range, from a low to a high temperature, can be efficiently purified similarly to the third embodiment.

[0137] Particularly, in this example, the catalytic converter system 7 is controlled in accordance to the cooling water temperature. As a result, stable control can be carried out while simplifying the constitution and at low cost.

[0138] This embodiment is similar to the third embodiment in other aspects of constitution, operation and effect.

[0139] Six Embodiment

[0140] This embodiment is an example of manufacturing the hollow ceramic monolithic support 8 of the same shape as that of the second embodiment by another manufacturing method, as shown in FIGS. 12 ( a ) through 12 ( c ).

[0141] Specifically, in this example, a ceramic monolithic support is manufactured as an intermediate product by using a molding die that is made by assembling only the outer periphery guide ring 3 on the die 2 without providing the inner periphery guide ring 4 , instead of the molding die 1 of the second embodiment. Accordingly, the ceramic monolithic support does not have a hollow space in the main body 82 thereof, but has the outer periphery skin portion 81 instead, as shown in FIG. 12 ( a ). The ribs 84 in the central portion and in the peripheral portion of the main body 82 are made thicker to form the high strength regions S 1 , S 2 . There is the ordinary portion P between the high strength regions S 1 and S 2 .

[0142] Then the hollow space 80 is made in a boring process in which only the peripheral portion of the high strength region S 1 at the center remains, as shown in FIG. 12 ( b ).

[0143] Then as shown in FIG. 12 ( c ), the inner periphery skin portion 83 is formed by attaching the ceramic material, that makes cordierite, to the inner peripheral surface of the main body 82 .

[0144] Then the final product is obtained through processes such as drying and firing.

[0145] In this example, unlike the second embodiment, the hollow ceramic monolithic support 8 that has the high strength regions S 1 and S 2 along with the outer periphery skin portion 81 and the inner periphery skin portion 83 as shown in FIG. 12 ( c ) can be manufactured if a boring process is employed, rather than molding the hollow ceramic monolithic support in a single run in the extrusion molding process.

[0146] An operation and an effect, similar to those of the first embodiment, can be achieved in this case.