EP0121175B1 - Helically wound conical shape metal strip catalyst supporting matrix for internal-combustion engines - Google Patents

Abstract

1. A catalyst support body for internal combustion engines consisting of a supporting matrix with flat (8) and/or corrugated (7) sheet-metal strips which are spirally and, at least in sub-regions, helically wound and are connected to one another and to the inner side of a casing (20) by welding, soldering or sticking, characterized in that the ratio of the width (b) of the sheet-metal strips (7, 8) to the slope(s) of the helix or the diameter of the supporting matrix is so selected that no cross-section through the winding cuts all the sheet-metal strip layers, i.e. the axial spread (h) of the supporting matrix, which is in the form of a hollow cone, is greater than twice the width (b) of the sheet-metal strips (7, 8).

Description

The present invention relates to a metallic carrier body for coatings of catalytically active substances for cleaning exhaust gases, in particular for internal combustion engines. These metallic catalyst carrier bodies consist of a carrier matrix with spirally wound, very thin-walled, smooth and / or corrugated metal strips, which are in a circular cylindrical or oval cylinder. the casing pipe are technically connected by welding, soldering or gluing.

In DE-A-29 24 592 numerous soldering methods for the production of such catalyst carrier bodies are indicated and in Fig. 7 of the corresponding description a catalyst carrier body is also shown, which forms a particularly firm solder connection between its outer layer and the jacket tube. These catalyst carrier bodies are exposed to considerable and changing thermal and mechanical loads during the operation of internal combustion engines, in particular motor vehicle engines. The thin-walled sheets of the carrier matrix are heated at high engine power in a very short time by the catalytic conversion of the exhaust gas from an operating temperature of approx. 500 ° C locally over more or less large areas to temperatures above 900 ° C, while the surrounding thick-walled jacket pipe is cooled by external air cooling maintains a relatively low operating temperature of approx. 300 ° C for a long time and thus prevents the carrier matrix from stress-free thermal expansion of its volume. The resulting plastic pressure deformations of the carrier matrix cells at high temperature cause high tensile loads on the cell walls and their connection points in the cooling phase due to inertia-related temperature gradients between the matrix and the casing tube Can lead sections of the carrier matrix body.

In trials with high-performance catalysts, it was clearly determined that not only the axial and radial forces generated by gas pressure, pulsation and vibrations have to be taken into account with regard to the stability and a functional lifetime of metallic catalyst carrier bodies, but also those caused by an expansion hindrance in the Heating and cooling the radial alternating loads caused by the carrier matrix are of far greater importance.

DE-A-29 05 241 describes a catalyst carrier body made of a conical winding which is intended to improve the known cylindrical windings with regard to the flow, the heat load, the light-off behavior and the ability to be installed. This document relates to winding bodies in the normal and widely used dimensions and at no point attaches the necessary evaluation to the solution of the pending, however not considered thermal expansion problems in the radial direction, the diameter-length ratio. Accordingly, the solution proposed there, as will be explained in more detail below, does not eliminate the aforementioned risk of alternating load breakage.

The object of the present invention is a catalyst carrier body made of smooth and / or corrugated, spirally wound sheet metal strips which are fastened by joining technology in a jacket tube, which avoids the disadvantages mentioned above.

From US-A-2 552 615 a muffler is also known which has smooth and corrugated sheet metal strips wound spirally and helically into hollow cone-shaped structures in its interior, which are intended to even out the exhaust gas flow of a motor vehicle, whereby sound absorption is effected. Problems of alternating thermal loads and vibrations are not considered in this document. Likewise, no suitable connection techniques are specified which would enable the ideas contained therein to be transferred to the catalyst carrier body.

The object of the present invention is to provide a catalyst carrier body according to the preamble of claim 1, which avoids the disadvantages mentioned above.

To achieve this object, a catalyst body according to the first claim is proposed. Thereafter, the ratio of the width of the sheet metal strips to the pitch or the outer radius of the helical winding should be selected so that no cross section through the winding cuts all layers of sheet metal strips, i.e. the axial dimension of the hollow-cone-like carrier matrix is greater than twice the width of the sheet metal strips . A catalyst carrier body designed in this way has the advantage that each cross section perpendicular to the longitudinal axis has only relatively narrow ring zones made of carrier matrix cells, which in the radial direction are not hampered by neighboring cells in terms of their freedom of expansion both outwards and inwards and are therefore not subject to any alternating plastic deformations with the previous carrier bodies. Since the expansion stresses of the matrix cells increase disproportionately with increasing ring zone width in relation to the temperature gradients distributed differently over the inflow surface, support body pieces with a small sheet metal strip width are particularly advantageous. On the other hand, the advantage according to the invention of unimpeded radial freedom from expansion of the matrix cells in the case of catalyst carrier bodies is eliminated Winding band width is greater than half the axial extent of the helical winding. The same applies to the winding tape width in relation to the outer radius of the winding, because the high section modulus of the corrugated tape transversely to the corrugation direction allows only a slight conical shape of the winding body in its longitudinal axis due to the required helical curvature of the shaft axis. If the winding bandwidth is too large, a large part of the length of the carrier body remains completely filled with cell structures over the entire area of the cross section perpendicular to the longitudinal axis, so that the aforementioned problems occur unchanged in this part of the matrix. This also applies to the above-mentioned catalyst body in accordance with DE-A-29 05 241.

In a further embodiment of the invention it is proposed that the support matrix should have a truncated cone shape. If the height of the hollow truncated cone is still greater than twice the width of the winding tape, the advantages described so far are retained, so that the inner part can expand without being obstructed by the casing tube.

In a further embodiment of the invention it is proposed in claim 3 that the catalyst carrier body is W-shaped in longitudinal section. This shape results when the slope changes its sign at one point during the winding of the helical winding. If, in this case as well, the total axial extent of the helical winding exceeds twice the width of the winding tapes, the advantages described are retained. With this arrangement, which is particularly suitable for catalyst bodies of larger diameter, the installation dimensions are considerably reduced compared to the normal-conical shape, without restricting the flexibility of the matrix with regard to the freedom from expansion. The shapes of the carrier matrix described so far can be produced by initially winding them and then pressing them into the desired shape.

In claim 4 it is proposed that the carrier body should consist of a plurality of matrix sections arranged axially one behind the other with a clearance. Because of the narrower width of the winding tapes in accordance with the present invention, it may be that several matrix sections are necessary for adequate catalysis. The division of the total catalyst length into several narrow sections with free spaces in between leads to a further advantage in other respects. Calculations and tests have shown that with the usual dimensions and the gas velocities in the parallel channels of the previous catalytic converters, the flow changes to the laminar state after about 20-30 mm, which is necessary for the chemical processes taking place in a catalytic converter because of the lack of surface contacting of the exhaust gas is less favorable than a turbulent flow. Due to the division into a plurality of partial catalyst bodies arranged one behind the other in the direction of flow, the flow to each catalyst portion is only in the turbulent state. which significantly improves the catalytic effectiveness. When the exhaust gas emerges from the previous catalyst section into the intermediate space to the next section, the exhaust gas mixes very well, which also contributes to improving the catalytic efficiency in terms of heat distribution, light-off behavior and conversion rate.

It appears expedient that the cone-like shape of the catalyst body proposed in the first claim is opposite to the direction of flow of the hot exhaust gas. In this arrangement, which can also be improved by a corresponding conical shape of the housing, the hot exhaust gases are diverted from the center a little more than before to the peripheral areas of the catalyst body, so that the hot gases are distributed more uniformly than previously over the cross section of the catalyst body will.

• Figur 1 zeigt einen Längsschnitt durch einen rotationssymmetrischen Abgaskatalysator, bestehend aus drei Katalysator-Teilkörpern von hohlkegeliger Form in einem zylindrischen Mantelrohr.
• Fig. 2 zeigt einen Querschnitt A-A durch Fig. 1.
• Fig. 3 zeigt die Schnittkontur eines einzelnen Katalysatorkörpers von kegelstumpfartiger Form.
• Fig. 4 zeigt ebenfalls die Schnittkontur eines einzelnen Katalysatorkörpers mit einem W-förmigen Längsschnitt.

The figures show exemplary embodiments of the invention.

• Figure 1 shows a longitudinal section through a rotationally symmetrical exhaust gas catalytic converter, consisting of three catalytic converter bodies of hollow conical shape in a cylindrical jacket tube.
• FIG. 2 shows a cross section AA through FIG. 1.
• Fig. 3 shows the sectional contour of a single catalyst body of the shape of a truncated cone.
• Fig. 4 also shows the sectional contour of a single catalyst body with a W-shaped longitudinal section.

In Fig. 1, the conical catalyst carrier body 1 are attached in triplicate in the cylindrical jacket tube 2, which is connected via conical transition pieces 3 and 5 to the cylindrical pipe socket 4 and 6. The arrow on the pipe socket 4 shows the direction of flow of the incoming exhaust gas. It can be seen that the flow is distributed over the entire cross section of the catalyst body due to the conical shape and due to the resistance in the catalyst body. The catalyst bodies are, as can be seen from Fig. 2, wound in a conventional manner from a smooth 8 and a corrugated 7 sheet metal strip, z. B. the outer layer of a corrugated metal strip rests on the inner surface of the casing tube 2. According to the present invention, the sheet metal strips are wound comparatively narrow and helically. The width b of the metal strips and the slope s of the helical winding, and the overall axial extent h of the helical windings are shown in FIG. 1. It can be seen that a cut perpendicular to the longitudinal axis of the catalyst carrier body can only cut all winding layers only if if the axial extent h is more than twice the width of the winding tapes b.

3 and 4 show further embodiments for the exhaust gas catalyst carrier body. 3 shows a frustoconical support matrix 9 and FIG. 4 shows a W-shaped shape 10. Viewed axially, these designs look as shown in FIG. 2.

Claims (4)

1. A catalyst support body for internal combustion engines consisting of a supporting matrix with flat (8) and/or corrugated (7) sheet-metal strips which are spirally and, at least in subregions, helically wound and are connected to one another and to the inner side of a casing (20) by welding, soldering or sticking, characterised in that the ratio of the width (b) of the sheet-metal strips (7, 8) to the slope(s) of the helix or the diameter of the supporting matrix is so selected that no cross-section through the winding cuts all the sheet-metal strip layers, i. e. the axial spread (h) of the supporting matrix, which is in the form of a hollow cone, is greater than twice the width (b) of the sheet-metal strips (7, 8).

2. A catalyst support body as claimed in Claim 1, characterised in that the supporting matrix is in the form of a truncated hollow cone (9).

3. A catalyst support body as claimed in Claim 1, characterised in that in longitudinal section, the supporting matrix is W-shaped (10).

4. A catalyst support body as claimed in Claim 1, 2 or 3, characterised in that the support body consists of a plurality of partial matrix components which are axially arranged one behind another at spaced intervals.

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