METHOD OF PRODUCING EXHAUST-GAS CARRYING DEVICES, IN PARTICULAR EXHAUST-GAS CLEANING DEVICES

Abstract

A method of producing exhaust-gas carrying devices, in particular exhaust-gas cleaning devices, makes provision that the outer geometry of each substrate is ascertained. An outer housing with an adapted geometry is manufactured dependent on this outer geometry. The substrate, together with a compensation element, are accommodated and clamped in this outer housing.

Description

TECHNICAL FIELD

The invention relates to a method of producing exhaust-gas carrying devices, in particular exhaust-gas cleaning devices, all of which have an outer housing with an insert piece clamped therein, the insert piece comprising a substrate which has exhaust-gas flowing through it, and an elastic compensation element which surrounds the substrate.

BACKGROUND OF THE INVENTION

Exhaust-gas carrying devices representing the subject-matter of the invention are, in particular, exhaust-gas cleaning devices such as catalytic converters and diesel particle filters or a combination thereof. Such devices contain insert pieces that are very sensitive to radial pressure. Traditionally, these insert pieces are predominantly ceramic substrates that have a gas flowing axially through them, and which are wrapped in an elastic compensation element (usually referred to as a lining mat). These insert pieces are retained in an outer housing in axial and lateral directions mainly by radial clamping, while an additional axial support is possible, for instance by a wire mesh ring. The clamping effect has to be large enough so that there is no displacement of the insert piece relative to the outer housing in an axial direction during a driving operation owing to the gas pressure as well as through vibrations. On the other hand, the radial pressure (or in more general terms, the pressure acting laterally inwards) must not be so large as to destroy the insert piece, in particular to destroy the catalytic converter substrate or the diesel particle filter substrate both of which are sensitive to pressure.

The insertion and clamping of the insert piece in the outer housing is usually effected by a so-called wrapping process. Here, a sheet metal envelope is preformed by bending the sheet metal around a roller or mandrel. Subsequently, the insert piece, which includes the substrate and lining mat, is pushed laterally into a prefabricated sheet metal envelope; the latter is firmly wrapped around the insert piece in a force-controlled manner, and finally the envelope is closed by welding. In doing so, the lining mat is compressed.

As the dimensions of the substrate (as well as those of the lining mat) are subject to certain manufacturing tolerances, an optimum clamping of the insert piece in the outer housing is not always ensured by this known method. While a substrate with a particularly small diameter possibly may not be clamped to a sufficient extent, it may happen that a particularly large substrate will be destroyed due to the higher pressure exerted by the compressed lining mat.

In addition, the lining mat, which is provided between the substrate and the outer housing and is intended to provide for pressure compensation and a consistent pretension, is subject to a certain setting process after compression (relaxation), whereby the pressure which is imparted by the lining mat to the substrate diminishes. The spring-back effect of the outer housing after having been inserted and clamped also has the effect that the pressure initially applied on the substrate, and with it the applied clamping force, decreases. Furthermore, the retaining pressure of the lining mat reduces in operation (e.g. by aging).

One theoretical possibility to compensate for the dimensional tolerances of the insert piece during the clamping operation is to close the outer housing in the method described so far in a pressure-controlled or force-controlled manner. In practice, however, it is difficult, even using this measure, to compensate for the large variations in the retaining pressure of the lining mat.

It is the object of the invention to present a method that provides for a sufficiently safe clamping of the insert piece in the outer housing with minimal reject rates.

SUMMARY OF THE INVENTION

This objective is achieved by a method that includes the following steps: a) determining an individual outer geometry of a substrate, b) ascertaining a geometry of an outer housing that is adapted to the individual outer geometry of the substrate, c) producing the outer housing with adapted geometry, and d) mounting and clamping an insert piece in the outer housing.

With the methods known so far, a uniform outer housing has always been used. This uniform outer housing was bent to have a round shape and was closed around the insert piece in a force-controlled or pressure-controlled manner. In the course of the pressure-controlled closure, tolerances in the size of the insert piece were partially counterbalanced in that the outer housing was closed to a somewhat further extent. The invention takes another path by first ascertaining the outer geometry of each individual substrate prior to installation, and subsequently forming, depending on this outer geometry, an outer housing that is exactly adapted to the outer geometry of the respective substrate (including the space for the lining mat). The insert piece, that includes the substrate and compensation element, is then mounted and clamped in its individually fabricated outer housing. In this way, an area-related density of the compressed mat, and with this the retaining pressure exerted by it, is subject to markedly lower fluctuations as is the case in prior art. This means that each insert piece is clamped with a retaining force that is necessary for that insert piece. Thus, it is possible with the method according to the invention to reduce the load on the substrate, which achieves a better durability. “Adapted geometry of the outer housing” means in this context that the shape and the dimensions of the outer housing are specifically tailored. According to the invention, provision is made that the geometry of the outer housing is determined directly from the outer geometry of the substrate. Intermediate steps such as a weight determination or weight calculation are not provided for this purpose.

For improving the accuracy while ascertaining the geometry of the outer housing, the individual weight of the compensation element is determined in addition to determining the outer geometry of the substrate. This is expedient because the pressure, which is to be exerted by the compensation element, depends inter alia on a mass of the insert piece and with this also on a mass of the compensation element.

In order to be able to model even the smallest structures of the substrate, the adapted geometry of the outer housing is produced by incremental deformation. This is particularly advantageous with out-of-round or polygonal substrate cross-sections.

As already mentioned, it is possible to close the outer housing in order to clamp the insert piece. In this case it will be of advantage to ascertain suitable parameters for the closure process prior to closing the housing. The load on the substrate can thereby be kept particularly low.

The process of closing the housing can be effected in a pressure-controlled or distance-controlled manner. A combination of both methods is also possible. A distance-controlled closing method is particularly advantageous, as the geometry of the substrate, and with this the “target geometry” of the outer housing, is already known.

As the outer housing can be adapted to almost any shape of the substrate due to the individual forming process, the method according to the invention can be applied with particular advantage to a substrate that is essentially cylindrical and has a base area that deviates from a circular shape. Thus, in particular, out-of-round contours, for example oval or so-called tri-oval (tri-oval referring to an essentially triangular shape with rounded corners) cross-sections, come into consideration. The method according to the invention allows a defined inhomogeneous or targeted surface pressure that results, especially with such out-of-round contours, in a lower amount of rejection and a better durability. In this way it is possible for a substrate with an oval cross-section to achieve a retaining pressure that is higher in the areas with a larger radius as would be the case with a prefabricated round or preliminarily rounded outer housing which is merely wrapped around an oval substrate. At the same time, local pressure peaks are avoided in the areas with a smaller radius, which occur in the conventional method due to the spring-back effect. In this way a smaller load on the substrate is achieved.

A particularly simple possibility of determining the individual outer geometry is to measure the substrate.

According to one embodiment, data ascertained for the insert piece is fed into a control unit, and in the control unit the individual geometry of the associated outer housing is established. All data is fed into the control unit in a fully automated way by coupling with the measuring devices. The control unit then ascertains the tailored geometry. At the same time the control unit can be coupled with the tool(s) shaping the outer housing so as to have the desired geometry.

The device that is produced by the method according to the invention is, according to one example embodiment, an exhaust-gas catalytic converter, a diesel particle filter or a combination thereof. A pressure-sensitive substrate is provided in each case as a core of the insert piece.

In particular, the housing is configured as a sheet metal housing.

Apart from the already mentioned wrapping process, the method according to the invention can be applied to all methods of producing exhaust-carrying devices and to all methods that rely on a sheet metal housing. Apart from wrapping, in which a prefabricated sheet metal section is wrapped around the insert piece and subsequently fastened and closed at its edges when the predetermined inner dimensions are reached, a so-called “calibration” is possible, too. Here, pressure is exerted from outside against the circumference of a prefabricated closed tube in order to plastically deform the tube and press the tube against the insert piece.

A third method makes provision for a housing that is made up of several shells that are pressed against the insert piece and subsequently fastened to each other.

A fourth embodiment provides for a so-called “tamping” method. Here, a closed cylindrical housing is produced whose inner geometry is already adapted to the outer geometry of the insert piece. After this, the insert piece is inserted into the housing from a front side.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view through a device in the form of an exhaust-gas cleaning device, which is produced by the invention;

FIG. 2 shows schematic views of measuring devices and tools that are used in the method according to the invention;

FIG. 3 is a frontal view of a device produced by the method according to the invention, with a wrapped outer housing;

FIG. 4 is a perspective view, partially in section, of a calibration tool which is used in the method according to the invention;

FIG. 5 is a frontal view of a device produced by the method according to the invention, with an outer housing made up of shells; and

FIG. 6 is a principle sketch showing the process of tamping which is used in the method according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates an exhaust-gas carrying device in the form of a vehicular exhaust-gas cleaning device, and which is accommodated in a motor vehicle. The vehicular exhaust-gas cleaning device is either an exhaust-gas catalytic converter, or a diesel particle filter, or a combination of both.

A core piece of the exhaust-gas cleaning device is an elongated, cylindrical substrate 10, which comprises, for example, of a ceramic substrate or a type of wrapped, corrugated board or other catalytic carrier or filter material with or without a coating. The substrate 10 may have a circularly cylindrical cross-section or a cross-section that is out of round. For the sake of a simplified illustration, a circularly cylindrical cross-section is shown in the Figures. The substrate 10 is surrounded by a lining mat 12, which acts as an elastic compensation element between the substrate 10 and an outer housing 14. The outer housing 14 is designed to have a very small wall thickness; in particular the outer housing 14 is made from sheet metal. At the upstream and downstream positions, an inlet funnel 16 and an outlet funnel 18, respectively, are connected with the outer housing 14.

The substrate 10 forms a prefabricated unit with the lining mat 12.

In operation, exhaust gas flows through the inlet funnel 16 at the end face into the substrate 10 and finally leaves, with a smaller amount of harmful substances, the substrate 10 at the opposite end face in order to leave the cleaning device through the outlet funnel 18.

The manufacturing of the cleaning device will be explained in the following by means of FIGS. 2 and 3. FIG. 2 shows various measuring stations with which properties of each of the insert pieces (i.e. of the substrate 10 and lining mat 12) to be installed are ascertained in view of an individually adapted outer housing for achieving an optimized clamping force of the insert piece in the housing 14.

The measuring stations are coupled via a control unit 20 with tools for producing the outer housing 14 and for mounting and clamping the insert piece in the outer housing 14. The stations, which are explained in detail below, are described in one example order of a production method.

In a first measuring device the outer geometry (form and outer dimensions, in particular circumference) of the substrate 10 is ascertained by using contact-free measuring sensors 22. The measuring sensors 22 are connected with the control unit 20, which stores the measured values obtained for the substrate 10.

Subsequently, the weight of the lining mat 12 is determined on a scale or balance 24, which likewise is coupled with the control unit 20. Here too, the data obtained is stored in the control unit 20.

With the established data of the insert piece (the substrate 10 and lining mat 12) to be installed, the control unit 20 ascertains a geometry of the outer housing (with consideration of a setting factor and compliancy of the fitting mat 12) which is adapted to at least the individual outer geometry of the substrate 10. This can be performed by calculating or by comparison with an association matrix stored in the control unit 20. The individual geometry is targeted to achieve the required clamping force which is to be exerted and is individually adapted to the insert piece.

Apart from the data which has already been mentioned, it would be possible to consider further data of the individual insert piece during the calculation of the outer geometry of the housing, such as the weight of the substrate 10, for example.

In a next step, this ascertained outer housing 14 with adapted geometry is produced by incremental deformation (as indicated at 26). This may be done, for example, by bending around a mandrel or roller. In this process, however, the bending roller must have very small dimensions so that the necessary small deformations can be produced.

Finally, the insert piece prefabricated from substrate 10 and lining mat 12 is assembled together with its tailored outer housing 14 in the so-called “wrapping method” (as indicated at 28). To this purpose, the prefabricated outer housing 14 is slightly opened and the insert piece is laterally inserted into the outer housing 14. The outer housing 14 is closed in a pressure-controlled and/or distance-controlled manner by overlapping edges 30, 32 being superimposed to such an extent that the dimensions of the resulting outer housing 14 are equal to the values as ascertained earlier. The closure process is performed with the aid of suitable parameters (pressure, distance) which earlier were ascertained in the control unit 20 and adapted to the individual substrate 10 or outer housing 14. As a next step, the overlapping edges 30, 32 are welded to each other, or crimped or soldered. The finished product is illustrated in FIG. 3.

Apart from wrapping the outer housing 14, the assembly may also be performed by a so-called calibration. A corresponding calibration device is shown in FIG. 4. This device has numerous radially movable jaws 34 which have the shape of a circle segment and are able to move towards each other so as to define a ring. The circularly cylindrical, tubular outer housing 14 (in which the insert piece is axially inserted) is inserted into the interior of the work space, which is circumscribed by the jaws 34. Subsequently, the jaws 34 are moved radially inwards, while the values with respect to the geometry of the outer housing 14 are used, which were earlier ascertained in the control unit 20. This means that the desired dimensions of the outer housing 14, which before were ascertained by the control unit 20, are achieved by a distance-controlled movement of the jaws 34 with simultaneous plastic deformation of the outer housing 14, which beforehand was circumferentially closed and prefabricated with a correspondingly larger diameter.

Instead of the jaws 34 shown in FIG. 4, it is also possible to perform the calibration with rollers that are laterally pressed against the outer housing 14 (with the insert piece inserted therein) by the predetermined travel distance and then are rotated. In this context, a so-called “spinning process” is also possible, in which the outer housing 14 (with the insert piece arranged therein) is moved by the predetermined travel distance against a single roller. Subsequently, a relative rotation occurs between the roller and the outer housing 14 complete with the insert piece, so that the roller circumferentially presses into the outer housing 14 and plastically deforms the outer housing 14 in an inward direction.

The embodiment shown in FIG. 5 uses two or more shells 36, 38 which are inserted into each other. In this case too, the shells 36, 38 are inserted into each other in a distance-controlled, pressure-controlled, or force-controlled manner so far until the inner dimensions are equal to the ascertained dimensions. The shells 36, 38 are then welded to each other, crimped or soldered, for instance. It is possible, of course, to form the shells 36, 38 preliminarily in such a manner that they have the desired final dimensions, similar to the case described in connection with FIG. 6.

FIG. 6 symbolizes the so-called “tamping” process. In the measuring device the desired dimensions of the outer housing 14 are ascertained. Subsequently, a cylindrical, tubular outer housing 14 is produced with the desired target diameter and the corresponding shaping. This is performed by rolling, for instance. Then the insert piece is axially forced into the selected outer housing 14. Here, corresponding funnel-shaped implements are provided for, of course. As an alternative to producing outer housings with the desired dimensions it is also possible to select from prefabricated outer housings, having different diameters, exactly that one which is suited in terms of the dimensions.

It is to be emphasized that the illustrated method is not intended for experimental purposes in which a single catalytic converter or diesel particle filter is produced. Rather, the method is intended for series production in which each substrate, together with its lining mat, receives its tailored outer housing. The described method results in a better quality of the produced devices with a low investment of capital for the devices.

Claims

1. A method of producing an exhaust-gas carrying devices, in particular an exhaust-gas cleaning device, which has an outer housing with an insert piece clamped therein, the insert piece comprising a substrate, which has exhaust-gas flowing through the substrate, and an elastic compensation element that surrounds the substrate including the following steps:

a) determining an individual outer geometry of the substrate;

b) ascertaining a geometry of the outer housing that is adapted to the individual outer geometry of the substrate to achieve a required clamping force individually adapted to, and to be exerted on, the insert piece;

c) producing the outer housing with adapted geometry; and

d) mounting and clamping the insert piece in the outer housing, with a closure of the outer housing being effected in at least one of a pressure-controlled and force-controlled manner.

2. The method according to claim 1, wherein, in addition to the determination of the individual outer geometry of the substrate, including the step of determining an individual weight of the elastic compensation element.

3. The method according to claim 1, including producing the adapted geometry of the outer housing by incremental deformation.

4. The method according to claim 1, wherein the outer housing is closed in order to clamp the insert piece.

5. The method according to claim 4, wherein suitable parameters for a closure process are ascertained prior to closing the outer housing.

6. The method according to claim 4, including closing the outer housing in at least one of a pressure-controlled and force-controlled manner.

7. The method according to any of the claim 4, including closing the outer housing is effected in at least one of a distance-controlled and geometry-controlled manner.

8. The method according to claim 1, wherein the substrate is essentially cylindrical and has a base area that deviates from a circular shape.

9. The method according to claim 1, including measuring the substrate to determine the individual outer geometry.

10. The method according to claim 1, including feeding data ascertained for the insert piece into a control unit such that the control unit can establish an individual geometry of an associated outer housing.

11. The method according to claim 1, wherein the exhaust-gas carrying device is at least one of an exhaust-gas catalytic converter and a diesel particle filter.

12. The method according to claim 1, including using a sheet metal housing for the outer housing.

13. The method according to claim 1, including producing the outer housing by wrapping the outer housing around the insert piece.

14. The method according to claim, including pressing the outer housing against the insert piece in a calibration process.

15. The method according to claim 1, wherein the outer housing is comprised of several shells that are pressed against the insert piece and fastened to each other.

16. The method according to claim 1, including tamping the insert piece into a prefabricated cylindrical outer housing which has an adapted geometry.