DE9421061U1 - Catalytic converter - Google Patents

Description

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Description:

The invention relates to devices for catalytic cleaning of exhaust gases from internal combustion engines according to the preamble of claim 1.

State-of-the-art exhaust gas catalysts for motor vehicles usually have a housing made up of two deep-drawn sheet metal shells. First, the catalytically active body, usually a ceramic block with honeycomb-like channels, is wrapped in a compressible and expandable bearing mat. This package is then placed in the lower sheet metal shell. The upper sheet metal shell is then placed on top and brought together using a hydraulic press. Finally, both sheet metal shells are welded together gas-tight.

However, this manufacturing method has some significant disadvantages. When deep-drawing the sheet metal shells, a relatively large amount of sheet metal waste is produced, particularly in the area of the cones. The sheet metal thickness must be calculated based on the point with the maximum deepening ratio, so that the other points are usually over-dimensioned, which means that the weight and price are high. The main disadvantage of the conventional manufacturing method is that there is no way of checking whether the package of the cat body and insulation mat is positioned precisely in relation to the lower and upper sheet metal shells. If an oval cat body is twisted by even a few degrees, high pressure peaks occur on one side when the two housing shells are brought together, which lead to the cat body breaking. After the housing has been welded shut, there is no way of repairing this.

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Attempts have also been made to manufacture the catalyst housing from prefabricated pipes. In this case, the package of the catalyst body and bearing mat must be pushed axially into the housing. Attempts have already been made to achieve this using a funnel. However, this requires high pushing forces due to the friction of the insulation mat on the funnel and housing walls, which often leads to the bearing mat being displaced or even destroyed.

The present invention is based on the object of specifying exhaust gas catalysts with tubular housings, which allow the package consisting of the catalyst body and bearing mat to be inserted into the housing without force and which can be manufactured particularly quickly.

This object is achieved by a device having the features of claim 1.

The present invention is based on the principle of using a piece of pipe as the catalyst housing, which initially has a certain excess so that the package of catalytically active body and bearing mat can be inserted without force. The cross-section of the pipe is then mechanically reduced using a press known per se, which is equipped with at least two, but preferably a large number of radially acting pressure pieces, so that the bearing mat clamps the catalyst body sufficiently. The catalyst body is automatically centered in the housing due to the radial direction of the force. Tests have shown that when the housing cross-section is reduced, the catalyst body is not damaged, even if it is a ceramic honeycomb body.

This production is fast, technically safe and inexpensive.

Like conventional exhaust gas catalysts, the catalyst manufactured according to the invention also requires inlet and outlet cones that establish the connection to the exhaust gas pipes. The process of pulling in the ends of pipes using axially acting stamps designed as conical sleeves is an old technique, but has not been used to manufacture catalyst housings until now because there was a fear that the pressure-sensitive catalyst body would be damaged in the process, or because there was a fear that the housing would expand again due to the axial forces, so that the catalyst body would lose its firm fit. However, these concerns have been overcome.

According to an advantageous development of the invention, the ends of the pipe housing are pressed onto the gas-carrying pipe during insertion. As a result, the gas-carrying pipe is already connected to the cat housing to such an extent that the subsequent manipulations until the gas-tight weld seam is completed can be carried out without special precautions.

According to an advantageous development of the invention, not only are the ends of the pipe housing drawn in, but the ends of the exhaust gas pipes are also widened. This process variant is particularly advantageous if there are large diameter differences between the pipe and the housing.

The invention will be explained in more detail in the form of an embodiment with reference to the drawing.

Fig. 1 purely schematically as a longitudinal section of an exhaust gas catalyst and some of the steps for its manufacture

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needed tools,

Fig. 2 a plan view in direction II of the front side of the finished exhaust gas catalyst according to Fig. 1 and

Fig. 3 is a section along the line III-III in Fig. 1.

Fig. 1 shows a longitudinal section of an exhaust gas catalyst, the housing 1 of which consists of a piece of pipe with, for example, a circular, oval or other cross-section. A catalyst body 4 wrapped in a bearing mat 5, here a ceramic monolith provided with honeycomb-shaped channels, was inserted into the pipe 1. The cross-section of the pipe housing 1 has a sufficient oversize compared to the cross-section of the package made up of the catalyst body 4 and bearing mat 5, so that force-free positioning is possible.

The cross-section of the tubular housing 1 is then reduced to such an extent by means of a plurality of pressure pieces 10, which are moved radially together using a hydraulic press (not shown), that the catalytic converter body 4 is correctly positioned in the housing 1. The bearing mat 5 fixes the catalytic converter body 4 in place with a spring, insulates the housing 1 from the catalytic converter body 4 and compensates for the thermal expansion differences between the catalytic converter body 4 and the housing 1.

The ends 7 of the pipe 1 are then deformed into an inlet or outlet cone 2. This is done with the help of an axially movable stamp 11 designed as a conical sleeve, which is also moved by a hydraulic press (not shown). The stamp 11 has a central opening through which an exhaust gas-carrying pipe 3 can be passed.

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When the piston 11 is closed, the pressure pieces 10 remain pressed against the housing 1. In this way, the housing 1 is fixed in position precisely; it also prevents the axial forces from deforming the housing 1 in the area of the catalytic converter body 4.

As shown in Fig. 1 and 2, the end 7 of the pipe housing 1 is deformed to such an extent that it clamps the exhaust gas pipe 3. This creates a unit that is easy to handle.

Finally, cone 2 and tube 3 are welded gas-tight with a circumferential weld seam 6.

As the top view of the front side of the catalyst housing 1 according to Fig. 2 or the cross section according to Fig. 3 show, wrinkles occur when there are large diameter changes. There are several ways to prevent this wrinkling.

A first possibility is to widen the end of the exhaust pipe 3 in a funnel shape. Increases in diameter by 30% are possible without cracking. Larger diameter changes are possible if the pipe ends 3, 7 to be deformed are deformed in the heated state.

In practice, inner cones are often used to insulate the outer cones against the hot exhaust gases, fix the catalytic converter body 4 axially and/or protect the end faces of the bearing mat 5 from exhaust gas pulsations. Such prefabricated inner cones do not interfere with the method according to the invention. Rather, they can be clamped between the cone 2 and the pipe 3 in the same operation when the pipe housing 1 is pulled in and finally fixed with the weld seam 6.

Claims (4)

&mdash; 6 ~ Protection claims: 1. Device for catalytically cleaning the exhaust gases of combustion engines, comprising a tubular housing (1) with inlet and outlet cones (2), a catalytically active body (4) and a compressible bearing mat (5) between the catalytic body (4) and the housing (1), characterized by the features: - the cross-section of the initially oversized tubular housing (1) is mechanically reduced, - the ends (7) of the tubular housing <1) are drawn into an input or output cone (2) by means of an axially movable stamp (11) designed as a conical sleeve. 2. Device according to claim 1, characterized by the Herkma I: - the retracted end (7) is pressed onto a gas-carrying pipe (3). 3. Device according to claim 2, characterized by the HerkmaI: - the cross-section of the pipe (3) is expanded at the connection point. 4. Device according to one of claims 1, 2 or 3, characterized by the feature: - Pipe (3) and cone (2) are welded.