EP0494049A1 - Catalytic converter and method of manufacturing a catalytic converter - Google Patents

Abstract

The catalyst (1) has a housing (5) with two one-piece shells (7, 9). These each have a curved section (7a, 9a) and flanges (7e, 9e) projecting outward therefrom. The flanges (7e, 9e) are welded to one another in pairs and form an angle with one another at least in a substantial part of their lengths and, for example, over their entire lengths. When producing the catalyst (1), the shells (7, 9) can be produced simply and inexpensively using a forming process. After at least one dimensionally stable core (23) and an elastically deformable intermediate layer (27) enveloping this or each core (23) have been arranged between the two shells (7, 9), these are pressed against one another with a predetermined compressive force and welded to one another. In the series production of catalysts (1), their cores (23) can be installed in the housing (5) well and without damage, even in the event of relatively large deviations from the intended shapes and dimensions. <IMAGE>

Description

The invention relates to a catalyst for the treatment of exhaust gas and a method for producing a catalyst. The catalytic converter is particularly intended for installation in the exhaust pipe of an internal combustion engine - for example the gasoline engine of a road motor vehicle.

A catalyst known from GB-A-2 048 105 has an elongated, metallic housing and two cores arranged therein, each with an approximately oval ceramic body in cross section, which has passages for the exhaust gas and a catalytically active coating. The housing has two shells with curved main sections, which together form a generally cylindrical, approximately cross-sectionally oval jacket and at its two ends adjoining end walls inclined towards the longitudinal axis of the catalytic converter, which are provided with openings in the center. The shells have flanges protruding outward from their curved main sections and welded together. These are essentially parallel to a plane running between the two shells and lie against one another in flat cross-sections at right angles to the weld seams. An intermediate layer is arranged between the inner surface of the housing and each core. This has a sleeve consisting of a wire mesh and a sleeve made of an elastic layer that inflates when heated.

The commercially available ceramic bodies can have shapes that deviate relatively greatly from the intended shapes and can be curved more or less banana-shaped, for example, instead of being cylindrical. Likewise, the actual dimensions can also deviate relatively strongly from the intended nominal dimensions. In the case of the nominal cross-sectional dimensions that are typically approximately 10 cm to 30 cm and the nominal lengths of approximately 30 cm to 60 cm, the deviations from the nominal dimensions are, for example, often more than 1 mm. In addition, the catalysts are typically warmed to approximately 750 ° C to 950 ° C during operation. This heating causes expansion, whereby the metallic housing expands much more than the ceramic body.

Since the ceramic bodies are brittle and fragile, they should be held firmly in the housing both in cold and in warm condition and also in the case of the vibrations that occur during operation, but should not be subjected to excessive pressure forces. The already mentioned intermediate layers of the catalysts are intended to compensate for the deviations in shape and dimensions from the desired shape or the desired dimensions and also the different expansions of the metallic housing and the ceramic body caused by heating. However, if the said deviations are large, they are often insufficiently compensated for by the intermediate layer. If the ceramic body is then subjected to excessive pressure at least in places through the housing, this can cause damage, such as cracks or breaks. If, on the other hand, the ceramic bodies are only held loosely in the housing of a catalytic converter installed, for example, in a motor vehicle, they can be destroyed in a short time by the vibrations and shocks occurring when the motor vehicle is used. Similar problems can possibly also occur with catalysts whose cores are made of a different material instead of ceramic bodies have existing bodies that limit passages for the exhaust gas to be treated. In the case of catalytic converters with housings whose shells have flanges parallel to one plane, there is therefore a risk that a lot of rejects will occur during manufacture and / or that the catalytic converter will be damaged after a short period of use.

Furthermore, from US-A-4 925 634 catalysts with housings are known, the shells of which, when the edge sections are welded together in pairs, abut one another with surfaces which are at least approximately flat and at right angles to a plane running through the different edge sections. The housings contain a core and an intermediate layer arranged between this and the inner surface of the housing. When producing such a catalyst, the core and the intermediate layer are inserted between the two shells. The two shells are then inserted into one another, pressed against one another with a predetermined compressive force and welded at their edge sections. More or less similar catalysts and manufacturing processes are also known from GB-A-2 047 557 and EP-A-0 278 455.

The shells for the housings of such catalysts are usually produced from originally flat sheet metal pieces by deep drawing. However, it is practically impossible to produce shells with edge sections directly adjacent to their edges, which have surfaces parallel to the direction of displacement of the deep-drawing tools, directly during deep-drawing. For the production of such shells, it is therefore necessary, for example, to first form shell-shaped workpieces during deep-drawing which have flanges projecting outwards at right angles to the direction of displacement mentioned. These flanges must then be removed. The removal of the flanges requires at least one additional, relatively complicated cutting process and also causes loss of material. The production of Shells with interlocking edge sections of the type described are therefore relatively expensive.

In the case of catalysts, the shells of which have edge sections which are inserted into one another and welded to one another in the manner described, they cannot be elastically deformed, or at most only very little. This also presents a certain disadvantage because the edge sections cannot contribute to compensating for the different changes in the cross-sectional dimensions of the cores and shells caused by temperature changes.

The invention is therefore based on the object of eliminating disadvantages of the known catalysts and the known processes for producing catalysts. In particular, starting from the catalyst known from GB-A-2 048 105, even with large deviations in the shape and / or the dimensions of the or each core, for example having a ceramic body, from the intended shape or the intended Dimensions are made possible that the or each core is held firmly in the housing without excessive pressure forces acting on it. Furthermore, the catalyst should be simple and economical to manufacture.

This object is achieved by a catalyst according to claim 1 and by a method according to claim 8. Advantageous refinements of the catalyst and of the method emerge from the dependent claims.

The two shells can have jacket sections which together form a generally cylindrical jacket of the housing with an approximately circular or approximately elliptical or approximately oval cross-sectional shape - that is to say apart from the flanges and stiffening beads and / or ribs - parallel to an axis . The Housing may also have an end wall at each of the two ends of its casing, which is formed by end wall sections of the two shells. The two end walls can form an angle with the axis and approach the axis from the ends of the jacket. The end walls can be straight or curved in axial sections or partially straight and partially curved. The housing can furthermore have two openings serving as inlet or outlet for the exhaust gas, located at the centers of the end walls and coaxial to the axis.

The housing can contain at least one core with a generally cylindrical lateral surface, with an approximately circular or elliptical or oval cross-sectional shape and with passages for the exhaust gas. The generally cylindrical casing of the housing can then extend approximately over the length of the core or the entirety of the cores. Furthermore, a deformable intermediate layer can be arranged between the housing inner surfaces formed by the inner shell surfaces and the or each core. If there are two or possibly even more spaced cores, either an intermediate layer extending uninterruptedly over both or all cores or a separate intermediate layer can be provided for each core.

In the catalyst according to the invention, the flanges protruding outwards from the curved sections of the shells and welded to one another in pairs form an angle with one another at least in a substantial part of their length in cuts perpendicular to the weld seams and to their edges. The meaning of the feature "at least in a substantial part of its length" will be explained below. Of the flanges welded together in pairs, at least those parts that form at the angle of the type mentioned should form preferably present, generally cylindrical shell of the housing and are at least generally parallel to the axis. Accordingly, at least those parts of the flanges welded to one another can then form an angle of the type mentioned, which is in the direction running along the general flow direction of the exhaust gas and thus in the direction running from one opening of the housing to its other opening and parallel to the axis of the housing extend the length of the or each core. Furthermore, preferably all of the parts of the flanges welded to one another at the end walls or at least still longitudinal regions of the flanges present at the end walls adjoining the axially parallel flange parts also form an angle of the type mentioned.

The metallic shells are preferably made of a ferritic, stainless or possibly non-stainless steel. A ferritic steel is usually cheaper than an austenitic steel and can also be formed relatively well by non-cutting shaping.

The shells can be produced from originally flat sheet metal pieces by non-cutting shaping, for example by deep drawing or possibly another drawing or pressing process. Here, for example, the outline shapes of the sheet metal pieces intended for shaping can be determined by cutting or in some other way such that they have the intended shapes of the shells after deep-drawing. Such a manufacturing process can thus be used to produce shells by deep drawing, without having to cut off edge sections after the deep drawing or to carry out other shaping operations. The shells for the catalyst according to the invention can be produced inexpensively in this way.

However, if it is desirable for any reason, parts can be cut from the workpieces formed by deep drawing in one cutting operation to thereby form the shells. Since the flanges protrude outwards from the curved sections of the shells, such a cutting process, which may still take place after deep-drawing, is much simpler and cheaper than those of the known and already described shells which have edge sections which can be inserted into one another.

After the shells have been produced, at least one core and an intermediate layer enveloping them can be arranged between the shells. The two shells can then be pressed against one another, the angle formed by the flanges to be welded being reduced by a deformation of the flanges and / or the curved shell sections. The deformation mentioned should be at least partly and for example even completely elastic. By means of a suitable determination of the pressure force exerted on the shells when they are pressed against one another, it can be achieved that the or each core is held in the housing in an optimal manner even if the cross-sectional dimensions of a core differ from the intended cross-sectional dimensions.

The catalyst according to the invention thus enables both cost-effective production and the guarantee of good quality.

When the catalytic converter is finished, the flanges welded together and forming an angle with one another can spring a little. If the dimensions - in particular the cross-sectional dimensions - of the metallic housing and the or each core contained therein are changed differently by temperature changes, the spring action of the flanges may help compensate for these different dimensions.

• die Figur 1 eine Schrägansicht eines Katalysators mit einem aufgebrochenen Gehäuse,
• die Figur 2 einen Querschnitt durch den in der Figur 1 ersichtlichen Katalysator und eine stark schematisierte, teils in Ansicht, teils im Schnitt gezeichnete Presse,
• die Figur 3 einen in der Figur 2 mit III bezeichneten Ausschnitt aus dem Katalysator und den an dessen Gehäuse angreifenden Werkzeugen der Presse und
• die Figur 4 einen der Figur 3 entsprechenden Ausschnitt aus einem andern Katalysator und den an dessen Gehäuse angreifenden Werkzeugen der Presse.

The subject matter of the invention is explained below with reference to exemplary embodiments shown in the drawing. In the drawing shows

• 1 shows an oblique view of a catalytic converter with a broken housing,
• 2 shows a cross section through the catalyst shown in FIG. 1 and a highly schematic press, partly in view and partly in section,
• 3 shows a section designated III in FIG. 2 from the catalytic converter and the tools of the press and
• 4 shows a section corresponding to FIG. 3 from another catalyst and the tools of the press acting on its housing.

The catalyst 1 shown in FIGS. 1 and 2 and partly in FIG. 3 is intended for installation in the exhaust pipe of an internal combustion engine, namely a gasoline engine of a road motor vehicle. The catalytic converter 1 has an elongated shape and an axis 3 running in its longitudinal direction. The catalytic converter has a metallic, gas-tight housing 5, the central longitudinal section of which forms a jacket 5a. This is generally parallel to the axis 3 and cylindrical and, for example, approximately elliptical or oval in cross section. The housing 5 has an end wall 5c at each of the two ends of the jacket 5a, which forms an angle with the axis 3 and approaches the axis 3 away from the ends of the jacket 5a. Each end wall 5c has a collar-shaped and / or neck-shaped extension 5d in the center, for example is circular cylindrical or tapers slightly conically away from the end wall 5c and delimits a circular opening 5e coaxial with the axis 3.

The previously described sections of the housing 5 are formed by two shells, namely a first, lower shell 7 and a second, upper shell 9. Each shell 7, 9 consists of a one-piece, metallic body, namely a piece of sheet metal, and has a jacket section 7a or 9a. The two jacket sections 7a, 9a together form the generally cylindrical jacket 5a of the housing 5 and are provided with beads 7b and 9b, which run in pairs together in a ring around the axis 3, but of course interrupted between the two shells, over the length of the Sheath 5a form distributed channels. In cross section, each jacket section 7a, 9a forms a half ellipse or half an oval, corresponding to the elliptical or oval cross-sectional shape of the jacket 5a. Each shell 7, 9 is connected at both ends of its jacket section 7a or 9a to an end wall section 7c or 9c, which is provided with a shoulder section 7d or 9d. The end wall sections 7c, 9c and the shoulder sections 7d, 9d of the two shells 7 and 9 together form in pairs one of the end walls 5c and one of the shoulders 5d. The part of each shell 7 and 9 formed by the jacket portion 7a, 9a and the two end wall portions 7c, 9c is also referred to below as the curved main portion 7a, 7c, and 9a, 9c of the shell 7 and 9, respectively. Each shell 7, 9 has on both sides of a vertical central plane running through it and the axis 3 at the edges of its main section 7a, 7c or 9a, 9c angled and / or bent outwards away therefrom, and accordingly from the main section 7a, 7c or 9a, 9c and edge sections protruding from the axis 3. The edge sections belonging to the first shell 7 form first flanges 7e. The edge sections belonging to the second shell 9 form second flanges 9e. Each flange 7e, 9e has one with the jacket section 7a or 9a connected flange part 7f or 9f and two flange parts 7g or 9g connected with an end wall section 7c or 9c. Each flange part 7f, 9f is connected at its two ends to one of the flange parts 7g or 9g.

In addition to the two shells 7, 9, the housing 5 also has two connections, each consisting of a separate sleeve 11 inserted in one of the openings 5d.

FIGS. 2 and 3 also show a plane 15 which runs through the axis 3 and between the two shells 7, 9 and therefore in particular also between the curved main sections thereof and which is present parallel to the outside at the edge sections 7e, 9e Edges is. The jacket sections 7a, 9a and the end wall sections 7c, 9c are in pairs at least approximately mirror-symmetrical to the plane 15. The flange parts 7f and 9f associated with the jacket sections 7a, 9a are apart from the angled and / or connecting them to the relevant jacket section. or bent transition or connecting section and at least before the two shells are connected to each other in the manner described, even. As can be seen particularly clearly in FIG. 3, each flange part 7f of the shell 7 is also parallel to the plane 15, while each flange part 9f is inclined away from the jacket section 9a towards the plane 15 and with this one and with the flange 7e forms an angle. This is preferably at least 5 ° and preferably at most 60 ° or better at most 45 ° and for example 10 ° to 25 ° or up to 30 °.

The flange parts 7g connected to the end wall sections 7c are preferably in the relaxed, undeformed state over their entire length the same as the flange parts 7f parallel to the plane 15. The ones with the end wall sections 9c connected flange parts 9g are preferably inclined at least approximately over their entire length and for example exactly at the same angle to the plane 15 as the flange parts 9f. Depending on whether each collar-shaped and / or socket-shaped projection 5d formed by a pair of extension sections 7d, 9d is cylindrical or conical, the flange parts 7g or 9g can, however, in their longitudinal regions which directly adjoin the extension sections 7d, 9d and form transitions possibly have a slightly different position with respect to level 15 than the remaining longitudinal regions of the flange parts 7g or 9g. In this case, the flange parts 7g are then possibly only for the most part parallel to the plane 15 and / or the flange parts 9g are only largely inclined towards the plane 15.

The two shells 7, 9 and the sleeves 11 are made, for example, of ferritic, stainless steel. The flanges 7e, 9e touch each other in pairs along the plane 15 and are firmly and gas-tightly connected to one another by a weld seam 17 only shown in FIG. Each first flange 7e projects beyond the outer edge of the second flange 9e, so that the weld seam 17 is located on that surface of the first flange 7e which faces the second flange 9e. The two sleeves 11 serving as connections are also connected to the two shells by welds.

At least one dimensionally stable core 23 is arranged in the housing 5, there being, for example, two cores 23 spaced apart from one another along the axis 3 and separated from one another by a free space. Each core 23 consists of a relatively short cylinder with an elliptical or oval cross-sectional shape. The cross-sectional shapes of the casing 5a of the housing 5 and the two cores 23 are matched to one another in such a way that the casing 5a and the peripheral or casing surfaces of the cores 23 have a cross section are curved at least approximately parallel to one another. Each core 23 has as its main component a one-piece, dimensionally stable support, namely a ceramic body, which is also referred to as a substrate and is provided with a plurality of passages running parallel to the axis 3. In these, a support layer consisting, for example, of aluminum oxide is applied to the ceramic surface, which is often referred to as a "wash coat" and significantly increases the surface area. The catalytically active layer, which for example consists of at least one noble metal, for example platinum and / or rhodium, is then applied to this carrier layer.

The cross-sectional dimensions, ie the lengths of the two ellipse or oval axes of the inner surface of the casing 5a, are larger than the cross-sectional dimensions, ie lengths of the two ellipse or oval axes of the cores 23, so that there is a space between them and the inner surface of the casing 5a. Arranged in this is a deformable - and namely at least partially elastically deformable - intermediate layer 27 which surrounds the circumferential or lateral surfaces of the two cores 23 and which, according to FIG. 1, also extends over the space between the two cores 23 and, for example, also can extend more or less far beyond the end faces of the two cores 23 facing away from one another, but the regions of the interior of the housing adjoining the end faces of the cores 23 and the openings 5e should remain free. The intermediate layer 27 consists of a layered material which is heat-resistant up to the operating temperatures of the cores 23, for example of a mat which contains inorganic fibers, particles of vermiculite, an inorganic filler and an organic binder, for example. Such mats are available under the trademark INTERAM from 3M Company. Vermiculite is a mica-like, flaky clay mineral that pores when heated by evaporating interlayer water forms and is inflated so that the entire mat swells when heated.

A press 31 used in the manufacture of the catalyst 1 in the manner described above for pressing the two shells 7, 9 against one another, shown schematically in FIG. 2, has a frame 33 which holds a lower support 35 and an upper support 37, preferably at least the upper support and, for example, the lower support are held on the frame in an adjustable manner. The lower support 35 holds a lower pressing tool 43 via a vibrating device 41. A compressive force generating device 45 has at least one hydraulic cylinder 47 attached to the upper support 37 and a piston 49, on the shaft of which the upper pressing tool 53 is attached.

The two pressing tools 43, 53, some of which can also be seen in FIG. 3, each have a trough-shaped recess into which the curved main section of the shell 7 or the shell 9 fits. The two tools 43, 53 are designed such that when the two shells 7, 9 are pressed against one another, at least the free edges of the flanges 7e and 9e of the shells protrude between the tools. The vibrating device 41 is designed to vibrate the lower pressing tool 43 and has, for example, a vibrator which is held on the support 41 and acts on the tool 43 via vibration-damping connecting means and which, for example, has a motor, at least one crank which can be rotated by this, and one of these rotary movements Has vibrating converting crank rod or can be designed as a magnetic vibrator or in any other way. Since the vibrations generated by the vibrating device 41 when the two shells 7, 9 are pressed against one another can be transmitted via this to the upper pressing tool 53, the connecting means connecting the latter to the piston 49 and / or the cylinder 47 with the support 37 connecting connecting means preferably also designed to dampen vibrations.

The hydraulic cylinder 47 is connected to a fluid source 61 via at least one line serving to supply and discharge the hydraulic fluid. This has a reservoir (not shown) for the hydraulic fluid, a manually and / or electrically drivable pump 63 and measuring and control means for the maximum value of the pressure of the hydraulic fluid supplied to the hydraulic cylinder 47 and thus also the maximum value of the pressure force generated by the press when the press is used to be determined. The measuring and control means can have, for example, manually operable switching and / or actuating elements for controlling the pump 63 and a manually adjustable actuating element 65 which serves to set the maximum pressure force value. The measuring and control means furthermore have a measuring and display device 67 in order to display the instantaneous value of the pressure of the hydraulic fluid supplied to the hydraulic cylinder and / or directly the pressure force generated by the pressure force generating device. In a simple embodiment of the press, the actuator 65 can be formed, for example, by an adjustable pressure relief valve. In the case of a press provided for series production, the hydraulic pressure force generating device 47 can, for example, be controlled either manually or automatically. For this purpose, the measuring and control means can have a pressure transducer and a control device, which is provided, for example, with a process computer. In this case, the actuator 65 can be formed by a setpoint generator connected to the control device. The control device can then control the pump 63 and / or at least one electrically or pneumatically controllable valve in such a way that the maximum value of the pressure force exerted by the press on the trays becomes approximately or exactly the same as the setpoint. The press can also be designed to to move the upper process tool 53 at different speeds in different work phases. The tool 53 located at the beginning of a pressing process at a distance from the upper shell above it can, for example, move quickly and with relatively little force over a long distance until it reaches the upper shell 9 and slowly but with relatively large force after reaching the upper shell Caft to be moved down. The tool 53 can then be raised again at a relatively high speed.

When manufacturing a catalyst 1, its cores 23, shells 7, 9 and sleeves 11 are first produced. The two shells 7, 9 are formed by cutting flat pieces of sheet metal and subsequent forming - namely deep drawing of them. To assemble the catalytic converter, the two cores 23 are encased with a flexible mat which serves to form the intermediate layer 27 and are arranged between the two shells 7, 9. These are in turn arranged between the two pressing tools that are still at a distance from one another. The intermediate layer 27 or - more precisely - the vermiculite present in this is still in the unexpanded, not swollen state. The upper pressing tool 53 is now moved downward and presses the shell 9 against the shell 7 with a pressure force generated by the hydraulic pressure force generating device 45. When the two shells are pressed against one another, the vibrating device 41 shakes the lower pressing tool 43 and the other this overlying catalyst, so that the cores 23 and the intermediate layer 27 reach the positions optimally adapted to the shapes of the shells.

The intermediate layer 27 is dimensioned such that it is compressed when the two shells 7, 9 are pressed against one another, for example under an at least partially elastic deformation. In addition, when pressing the two shells 7, 9, the flanges 9e and possibly also the flanges 7e are deformed at least over the greatest part of their lengths and, for example, over their entire lengths a little elastically and possibly also plastically. In addition, the curved main sections of the shells may also be slightly deformed. The deformations of the intermediate layer 27 and the shells when the two shells are pressed against one another produce a counterforce which increases in the course of the pressing process and which must be overcome by the pressing force generated by the press.

As mentioned in the introduction, the ceramic bodies of the cores 23 can have shapes or dimensions that deviate from the intended target shapes and / or target dimensions during series production. In addition, the shapes and dimensions of the shells can also deviate a little from the intended shapes or nominal dimensions in the case of series production, but these deviations in the shells are normally much smaller than in the ceramic bodies. It is now possible to determine an optimum value for the compressive force with which the two shells 7, 9 are pressed against one another at the end of the pressing process and during the welding process by means of a few tests carried out prior to series production. The measuring and control means of the fluid source 61 then make it possible to press the two shells against one another at least approximately or exactly with the same, optimal compressive force in the case of series production of catalysts for all catalysts of the same type. Depending on the shape and dimensions of the catalytic converter, this optimal compressive force can be, for example, at least about 50 N and at most about 500 N.

However, the process computer of the control device could possibly be designed to vary the maximum value of the compressive force depending on at least one measurement variable within a certain, relatively small range. A such a measurement variable could be formed, for example, by the height at which the upper pressing tool 53 reaches the upper shell when it is lowered and begins to press the two shells against one another.

When the two shells 7, 9 are pressed against one another with the intended compressive force, their flanges 7e, 9e are welded together in pairs. The two shells are pressed against each other with a constant pressure during the entire welding process. For welding, an additional material is introduced into the groove formed by the upper surface of the first, lower flange 7e and the free edge of the upper, second flange 9e with a welding wire. A protective gas arc welding is preferably used for the welding process. The plane 15 then runs through the weld seams 17 which are produced during the welding. In order that the openings 5e receive the intended diameters when the shells 7, 9 are pressed against one another, calibration pins can be temporarily arranged in the openings 5e before and during the pressing against one another. If the calibration pins are then removed again, the two sleeves 11 can be inserted into the openings 5e and also welded to the shells before or during or after the welding of the flanges.

After the shells 7, 9 have been welded to one another and to the sleeves 11, the upper pressing tool 53 is pulled upward away from the lower pressing tool 43 and the catalyst 1 is removed from the press 31. The catalyst can then be heated either during a special heating process or when it is used for the first time by the hot exhaust gas flowing through it and the heat generated in the catalyst by chemical reactions of the exhaust gas in such a way that the vermiculite contained in the intermediate layer 27 and thus the entire intermediate layer swells and then swollen and remains elastically deformable even at normal ambient temperature.

In FIGS. 2 and 3, the intermediate layer 27 is drawn with its shape taken in the original, unpressurized state to improve clarity, so that there is a free space between the facing surfaces of two flanges 7e, 9e. In reality, however, the elastically and plastically deformable intermediate layer 27 is pressed into the spaces between the flanges when the shells are pressed against one another and fills them completely at the latest after swelling. In the finished catalytic converter, the intermediate layer 27 therefore seals off the spaces between the flanges in the longitudinal regions of the cores 23. The intermediate layer also closes tightly all the others between the inner surfaces of the casing 5a of the housing 5 and the casing surfaces of the cores 23, so that all of the exhaust gas fed to the catalytic converter flows through the passages of the core 23 when it is used.

Regarding the first flanges 7e, it should also be noted that these are shown in FIGS. 1 to 3 in their original shape, parallel to the plane 15. As already mentioned, the flanges 7e can possibly also be deformed a little when the shells are pressed against one another. Among other things, it depends on the design of the press tools whether such a deformation occurs. If this is the case, at least the outer edge regions of the flanges in FIGS. 1 to 3 can be bent down a little away from the plane 15.

By swelling the intermediate layer 27, the pressure forces exerted by the latter on the inner surfaces of the shells 7, 9 and on the cores 23 are of course greater than when the two shells are pressed against one another, but the pressure exerted on the inner layer after swelling of the intermediate layer pressure forces exerted with the Pressing the shells against one another are linked to this pressure force exerted. The described optimal definition of the compressive force with which the shells are pressed against one another can therefore be achieved that the cores 23 even in the case of relatively large deviations in their shapes and / or dimensions from the intended target shapes or target dimensions Fabrication are still exposed to excessive pressure forces when using the catalytic converter and are held well and a little resiliently in the housing 5 during operation of the catalytic converter in a motor vehicle by the intermediate layer 27. The intermediate layer dampens the vibrations generated by the internal combustion engine and the driving operation of the vehicle when using the catalytic converter and can also compensate for the different dimensional changes of the cores, which are mainly made of ceramic, and the metallic housing, which are caused by the heating and cooling. Possibly the flanges 7e, 9e can also contribute to vibration damping and to compensate for the dimensional changes caused by temperature changes by a certain spring action.

The catalytic converter 101, which is shown in part in FIG. 4, has a housing 105 with a jacket 105a. The housing 105 has a one-piece shell 107 and a one-piece shell 109. Each shell 107, 109 has a curved main section with a jacket section 107a or 109a and two end wall sections which cannot be seen. The two jacket sections 107a, 109a together form the jacket 105a of the housing 105. The end wall sections of the shell 107 and 109, which are not visible in FIG. 4 and correspond to the end wall sections 7c and 9c, form an end wall in pairs. The main sections of the shells are connected at their edges with flanges 107e and 109e. The two shells 107, 109 are symmetrical with respect to a plane 115 running through them. In particular, the flanges 107e, 109e are also symmetrical in pairs to each other and namely at least for the most part - i.e. over their entire length or at most with the exception of those end regions which are connected to the shoulder sections of the shells 107 and 109 corresponding to the shoulder sections 7d and 9d - inclined analogously to the plane 115 like the flanges 9e to the Level 15. The angle formed by the flanges 107e, 109e with the level 115 can possibly be the same as the angle formed by the flange 9e with the level 15 up to a maximum of 60 ° or up to a maximum of 45 °. Since both flanges 107e, 109e are inclined against the plane 115 in the catalytic converter variant shown in FIG. 4, the angle between the two flanges 107e, 109e can then be up to 120 ° or up to 90 °. In most cases, however, it should be sufficient if the angle formed by the two flanges is at most 60 ° or even at most 45 °. The flanges 107e, 109e can then accordingly form an angle of at most 30 ° or even only at most 22.5 ° with the plane 115. The flanges of the two shells 107, 109 touching one another in the finished catalytic converter 101 along the plane 115 are firmly and tightly connected at their edges by weld seams 117, which can be produced either with or without the use of an additional material by inert gas arc welding. The catalytic converter 101 has at least one core 123 encased with an intermediate layer 127 and - unless previously stated otherwise - is of the same or similar design as the catalytic converter 1. The catalytic converter 101 is also produced similarly to the catalytic converter 1. In particular, the shells 107, 109 are pressed against one another for welding with two pressing tools 143, 153.

In the case of catalysts 1 and 101, the flanges which are more or less elastically deformed when the shells 7, 9, 107, 109 are pressed against one another - possibly somewhat depending on how the welding is carried out after removing the catalysts from the press under certain circumstances spring back. This spring back can when the shells are pressed against one another by a corresponding increase in the compressive force and are to a certain extent precompensated so that the shells exert compressive forces of the desired sizes on the cores in the finished catalyst 1, 101.

The catalysts and the processes for their production can be modified in various ways. The casing of the housing can, for example, be generally circular-cylindrical or have two straight sections parallel to one another and two arcs connecting their ends to one another in cross section. Furthermore, instead of the short, circular-cylindrical sleeves 11 serving as connections, any straight or curved pipes of the exhaust pipe can be welded to the two shells of the housing.

The catalytic converter 1 can be modified such that each shell has a flange parallel to the plane 15 on one side of a vertical median plane running through the axis 3 and perpendicular to the plane 15 and on the other side of the vertical ebeme eomem inclined to the median plane 15 .

The end walls may be partially or even completely flat and perpendicular to the axis of the catalyst in the longitudinal sections instead of curved.

Furthermore, if necessary, the catalytic converter can be provided with an inner and an outer housing in order to improve the heat and / or sound insulation. Each of these housings can then each have a jacket and two end walls and are formed by two shells. For example, the four shells can have flanges shaped similarly to shells 7, 9, 107, 109, the flanges of the inner shells projecting outward to about the same extent as those of the outer shells, so that four different shells are provided at each edge belonging flanges welded together could be. However, it would also be possible for the outer housing to enclose the inner housing together with its flanges.

Furthermore, the or each core of the catalyst may have a body made of another, for example metallic material, instead of a ceramic body, which limits passages for the exhaust gas and serves as a carrier for the catalytically active layer.

The intermediate layers present between the metallic shells and the cores can be formed from at least one layer or shell instead of at least one vermiculite-containing mat, which consists of at least one other up to the operating temperatures of the cores and thus up to at least about 750 ° C. and preferably up to at least about 950 ° C heat-resistant material and is deformable - and preferably at least partially elastically deformable. The intermediate layers can be formed, for example, at least in part from metallic material, for example from an alloy known as the main constituent of nickel and also chromium, iron and cobalt, known under the trade name Inconel, or from steel. The metallic intermediate layers can have, for example, at least one wire mesh or knitted fabric or tape or sheet or at least one other part, wherein the metallic material can be porous and foam-like. Furthermore, the intermediate layers may have another mineral, such as fibrous and / or porous mineral, instead of vermiculite.

Instead of temporarily arranging calibration pins in the openings of the housings when the shells are pressed against one another, the sleeves or even connecting pipes used to form connections can be inserted into the openings to be formed before the shells are pressed against one another.

Furthermore, the pressing force generating device 45 of the press may have at least one pneumatic cylinder instead of at least one hydraulic cylinder. In this case, the fluid source 61 would then be designed as a compressed air source. One could perhaps even provide a press whose pressure force generating device has an electric motor and a threaded spindle which can be rotated by it.

Claims (12)

Catalyst for the treatment of exhaust gas, in particular an internal combustion engine, with a housing (5, 105), the two one-piece, metallic shells (7, 9, 107, 109) with curved sections (7a, 7c, 9a, 9c, 107a, 109a ) and flanges (7e, 9e, 107e, 109e) which project outwards and project from one another and are welded together by weld seams (17, 117), characterized in that the flanges (7e, 9e, 107e, 109e) welded together are at least in one form an essential part of their length in cuts at right angles to the weld seams (17, 117) and approach each other outwards towards the relevant weld seam (17, 117). Catalyst according to claim 1, characterized in that of each pair of the welded flanges (7e, 9e) the one, first flange (7e) at least in a substantial part of its length parallel to one between the arched shell sections (7a, 7c, 9a, 9c) extending through plane (15) or at least partially inclined outwards from this and that the other, second flange (9e) forms an angle with said plane (15), the first flange (7e), for example, over the Edge of the second flange (9e) protrudes. Catalyst according to claim 1, characterized in that all flanges (107e, 109e) welded in pairs are inclined at least in a substantial part of their length against a plane (115) running between the shells (107, 109). Catalyst according to one of claims 1 to 3, characterized in that the said angle is at least 5 °, at most 60 ° and for example 10 ° to 45 °. Catalyst according to one of claims 1 to 4, wherein the housing (5, 105) contains at least one core (23, 123) with passages for the exhaust gas and wherein between the inner surfaces of the shells (7, 9, 107, 109) and the or each core (23, 123) is provided with a deformable intermediate layer (27, 129), characterized in that the shells (7, 9, 107, 109) are designed in such a way that the said angle is defined by one of the shells (7, 9 , 107, 109) compressive and deforming compressive force can be reduced. Catalyst according to one of claims 1 to 4, wherein the housing (5, 105) has an axis (3) and the flanges (7e, 9e, 107e, 109e) welded together are generally flange parts (7f, 9f) parallel to this and at their two ends adjoining flange parts (7c, 9c) approaching the axis (3), characterized in that at least the flange parts (7f, 9f) generally parallel to the axis (3) over their entire length Lengths form an angle of the type mentioned, wherein preferably the flange parts (9g) adjoining the two ends of the generally axially parallel flange parts (9f) form an angle of the type mentioned at least in a region of their length. Catalyst according to one of claims 1 to 6, wherein the housing (5, 105) has two openings (5e) for supplying or discharging the exhaust gas and between these openings (5e) at least one core (23, 123) with passages for the exhaust gas contains and wherein between the inner surfaces of the shells (7, 9, 107, 109) and the or each core (23, 123) a deformable intermediate layer (27, 127) is arranged, for example a porous mineral such as vermiculite, or For example, has a metallic material, characterized in that at least those parts of the welded flanges (7e, 9e, 107e, 109e) form an angle with one another of the type mentioned, which are in the extend from one direction to the other opening (5e) over the length of the or each core (23, 123). Method for producing a catalyst according to one of claims 1 to 7, wherein at least one passage for the exhaust gas-containing core (23, 123) with at least one intermediate layer (27, 127) and between the two shells (7, 9, 107, 109 ) is arranged, these are pressed against one another, the at least one intermediate system (27, 127) is compressed when the shells (7, 9, 107, 109) are pressed against one another and the flanges (7e, 9e, 107e, 109e) of the two shells (7 , 9, 107, 109) are welded to one another, characterized in that the flanges (7e, 9e, 107e, 109e) to be welded in pairs at least in a substantial part of their length before the two shells (7, 9, 107, 109) form an angle with each other which is reduced when the two shells (7, 9, 107, 109) are pressed against one another by an at least partially elastic deformation of the shells (7, 9, 107, 109). A method according to claim 8, characterized in that at least one of the two shells (7, 9, 107, 109) is shaken by them when pressed against each other. A method according to claim 8 or 9, characterized in that the two shells (7, 9, 107, 109) are pressed against one another with a compressive force, the maximum value of which is at least approximately equal to a predetermined maximum value, for example at least 50 N and for example, is at most 500 N, and the compression of the or each intermediate layer (27, 127) which takes place when the shells (7, 9, 107, 109) are pressed against one another preferably takes place at least in part under an elastic deformation thereof. Method according to one of claims 8 to 10, characterized in that originally flat sheet metal pieces are formed to form the shells (7, 9, 107, 109), the forming preferably being carried out by deep drawing. A method according to claim 11, characterized in that the sheet metal pieces are cut before the forming such that their edges form the edges of the flanges after the forming, without material having to be separated from the sheet metal pieces after the forming to form the edges of the flanges.

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