Device for catalytic conversion of exhaust gases in an exhaust system and process for manufacturing such a device

In a device for the catalytic conversion of exhaust gases in an exhaust system, in particular an exhaust system of a combustion engine, and a process for manufacturing the same, a catalyst carrier body is provided with a multiplicity of channels through which an exhaust gas can flow. At least a part of a free flow cross-section of the channels is closed in an exhaust gas flow direction by plastic deformation of channel walls in an outer annular region of the catalyst carrier body. The plastic deformation can be carried out with a tool. The tool has a disk rotatable about an axle. The disk is pressed with force against the catalyst carrier body and the jacket so that a plastic deformation of the jacket tube and the channel walls occurs. A circumferential bead directed towards the carrier body is produced. Other techniques for plastic deformation are possible. The thus closed outer channels form a heat insulation with respect to the jacket tube, so that the catalyst carrier body heats up more quickly in a cold-starting phase.

BACKGROUND OF THE INVENTION
 Field of the Invention
 The invention relates to a device for the catalytic conversion of exhaust
 gases in an exhaust system, in particular in an exhaust system of a
 combustion engine, including a catalyst carrier body having a multiplicity
 of channels through which an exhaust gas can flow. The invention also
 relates to a process for manufacturing such a device.
 In order to attain conversion of hydrocarbons and carbon monoxide contained
 in a combustion engine which is as complete as possible, the catalytic
 converter must be at a minimum temperature at which the catalytic
 conversion of components of the exhaust gas can take place. In general,
 that temperature is described as a so-called initiation temperature. The
 catalyst is heated during a cold starting phase by hot exhaust gas. It is
 also known to at least partially electrically heat the catalyst carrier
 body. In order to ensure that the output of pollutants is as low as
 possible during the cold starting phase, and for mechanical reasons, it
 has been proposed that the catalyst carrier body be constructed with an
 internal insulation in order to reduce heat loss to a housing and into the
 surroundings.
 A device for catalytic conversion of exhaust gases in an exhaust system, in
 particular in an exhaust system of combustion engines, is known from
 German Published, Non-Prosecuted Patent Application DE 36 02 134 A1. That
 device is provided with a metallic catalyst carrier body disposed in a
 housing. The carrier body is provided with a large number of channels
 through which an exhaust gas can flow. The internal insulation of the
 catalyst carrier body is created according to German Published,
 Non-Prosecuted Patent Application DE 36 02 134 A1 in such a way that a
 radially inward facing collar is disposed in front of the catalyst carrier
 body. The height of the collar is 3-15% of the diameter of the catalytic
 converter, but at least 1 mm. A zone of eddy current is produced in the
 exhaust gas flow through the use of that collar and in that way direct
 contact of the hot exhaust gas with an outer annular region is avoided.
 A device for the catalytic conversion of exhaust gases in an exhaust system
 is known from German Utility Model DE G 87 12 267.7 U1. The device
 includes a catalyst carrier body which is provided with a large number of
 flow channels for an exhaust gas and which is fitted into a sleeve-like
 housing. The housing is thermally insulated with respect to the catalyst
 carrier body. The insulation is obtained by placing the catalyst carrier
 body between end rings which close at least an outer layer of a metallic
 matrix body and thereby the outer flow channels in the matrix. In that way
 the outer region of the catalyst carrier body is provided with a closed
 air gap, through which exhaust gas does not flow and which serves as heat
 insulation.
 SUMMARY OF THE INVENTION
 It is accordingly an object of the invention to provide a device for
 catalytic conversion of exhaust gases in an exhaust system and a process
 for manufacturing such a device, which overcome the hereinafore-mentioned
 disadvantages of the heretofore-known devices and processes of this
 general type and in which the manufacture of a catalyst carrier body with
 an internal insulation is simplified.
 With the foregoing and other objects in view there is provided, in
 accordance with the invention, a device for catalytic conversion of
 exhaust gases in an exhaust system, in particular in an exhaust system of
 combustion engines, comprising a catalyst carrier body having an outer
 annular region and having channel walls defining a multiplicity of
 channels with free flow cross-sections through which an exhaust gas can
 flow in a given direction, at least a part of the free flow cross-sections
 of the channels being closed in the given direction in the outer annular
 region by plastic deformation of the channel walls.
 In contrast to the known devices for catalytic conversion of exhaust gases,
 an air gap enclosed in an outer region of the catalyst carrier body is not
 created by additional rings or the like, but instead the free flow
 cross-section of the channels is closed in part, that is to say in at
 least an axial part, by plastic deformation of the channel walls in the
 direction of flow of the exhaust gas. In this way the manufacture of the
 device is simplified, since a collar or end ring no longer has to be
 fitted in the housing. If the catalyst carrier body is composed of several
 wound layers of sheet metal, the plastic deformation can already be
 carried out during winding. This simplifies the manufacturing process for
 wound catalytic converters, since the winding procedure and the plastic
 deformation can take place at the same time.
 In accordance with another feature of the invention, the channels are
 closed in the vicinity of a waste gas inlet. The plastic deformation of
 the channels is advantageously carried out prior to the application of a
 catalytically active layer on the catalyst carrier body. The coating (wash
 coat) is usually applied through the use of a suspension flowing through
 the catalyst carrier body. The catalyst carrier body can be disposed in
 such a way that the suspension flows into the channels which are closed on
 one side. The wash coat then fills up the channels. It forms a thermal
 insulation. If the catalyst carrier body is disposed in such a way that
 the closed channels are in the region where the suspension enters the
 catalyst body, the channels cannot be filled with the suspension. This
 improves the insulation since the heat conductivity of the catalyst
 carrier layer which completely fills up the channel is better than that of
 the atmosphere in the channels.
 In accordance with a further feature of the invention, the channels are
 closed in the vicinity of the exhaust gas intake and outlet. If the
 plastic deformation does not completely close individual channels, this is
 compensated for by the subsequent coating, which closes small gaps.
 In accordance with an added feature of the invention, the channels in the
 catalyst carrier body are configured in layers on top of one another, and
 up to five layers of the channels, preferably two, are closed. In this way
 an advantageous compromise between the necessity of having catalytically
 active surfaces and of heat insulation is obtained, without the external
 dimensions of the catalyst carrier body having to be substantially
 enlarged.
 With the objects of the invention in view there is also provided a process
 for manufacturing a device for catalytic conversion of exhaust gases in an
 exhaust system, in particular in an exhaust system of combustion engines,
 which comprises dividing a catalyst carrier body into a multiplicity of
 channels having free flow cross-sections through which an exhaust gas can
 flow in a given flow direction; and plastically deforming the channels in
 an outer annular region of the catalyst carrier body for closing at least
 a part of the free flow cross-sections in the given direction.
 In accordance with another mode of the invention, the plastic deformation
 is carried out in such a way that the catalyst carrier body is compressed
 in a die. When the catalytic converter carrier body is compressed, the
 outer region of the carrier body is deformed, so that the channels are
 closed.
 In accordance with a further mode of the invention, the compression die is
 provided with a conical or annular wall.
 In accordance with an added mode of the invention, instead of compressing
 the catalyst carrier body in a die, the plastic deformation of the channel
 walls is carried out in such a way that a force is exerted upon an outer
 annular region through the use of a stamp, which results in plastic
 deformation of the channel walls.
 In accordance with an additional mode of the invention, the tamp is annular
 or has a wall sloping from the inside to the outside. If the stamp is
 provided with a wall sloping from the inside to the outside, the free flow
 cross-section of the channels can be closed by bending the channel walls.
 With an annular stamp, the channel walls are crushed.
 In accordance with yet another mode of the invention, during the plastic
 deformation the catalyst carrier body is restrained by its end opposite to
 where the force is being applied. This has the advantage that the
 individual layers of the catalytic converter carrier body are not
 displaced with respect to one another.
 Catalytic converter carrier bodies are known which are composed of a
 multiplicity of alternately structured and preferably smooth layers of
 sheet metal. Such metallic catalytic converter carrier bodies are
 surrounded by a jacket tube.
 With the objects of the invention in view there is additionally provided a
 process for manufacturing a device for catalytic conversion of exhaust
 gases in an exhaust system, in particular in an exhaust system of a
 combustion engine, which comprises dividing a catalyst carrier body into a
 multiplicity of channels having free flow cross-sections through which an
 exhaust gas can flow in a given direction; surrounding the catalyst
 carrier body with a jacket tube; and plastically deforming the jacket tube
 and the channels in an outer annular region of the catalyst carrier body
 for closing at least a part of the free flow cross-sections in the given
 direction.
 In accordance with another mode of the invention, the plastic deformation
 of the jacket tube and of the channels is carried out in such a way that
 at least one circumferential bead, directed towards the interior, is
 formed in the jacket tube. The bead can also be used for joining the
 catalyst carrier body to a housing.
 In accordance with a concomitant mode of the invention, the plastic
 deformation is carried out through the use of free forming, rolling or
 working.
 Other features which are considered as characteristic for the invention are
 set forth in the appended claims.
 Although the invention is illustrated and described herein as embodied in a
 device for catalytic conversion of exhaust gases in an exhaust system and
 a process for manufacturing such a device, it is nevertheless not intended
 to be limited to the details shown, since various modifications and
 structural changes may be made therein without departing from the spirit
 of the invention and within the scope and range of equivalents of the
 claims.
 The construction and method of operation of the invention, however,
 together with additional objects and advantages thereof will be best
 understood from the following description of specific embodiments when
 read in connection with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 Referring now to the figures of the drawings in detail and first,
 particularly, to FIG. 1 thereof, there is seen a catalyst carrier body 1
 that is provided with a multiplicity of channels 2 through which an
 exhaust gas can flow from a waste gas inlet to a waste gas outlet defined
 by ends of the body. The channels 2 are constructed through the use of an
 alternating configuration of structured sheet metal layers 12 and smooth
 sheet metal layers 13. Each channel is provided with a free flow
 cross-section 4, which is delimited by channel walls 11. The channel walls
 are formed by the layers 12, 13 of sheet metal. In order to provide
 plastic deformation in an outer annular region 3 of the catalytic
 converter carrier body 1, the carrier body is compressed in a die 7 shown
 in FIG. 1. For this purpose, the catalyst carrier body 1 can be held, for
 example through the use of clamps which are not shown, and correspondingly
 compressed in the die 7. In the illustration according to FIG. 1, the
 honeycomb body 1 is compressed in the die 7 through the use of a tool 14.
 An annular wall 8 is configured in the first embodiment of the die 7 shown
 in FIG. 1. The width of the annular wall 8 corresponds to the width of
 channels to be closed in the honeycomb body 1. A jacket 15 which has inner
 contours that correspond to outer contours of the catalyst carrier body 1,
 is connected to the wall 8.
 FIG. 2 shows a second embodiment of a die 7. The die 7 has a wall 8 which
 is conically configured.
 FIG. 3 shows a honeycomb body 1, which is compressed in a corresponding die
 7 according to FIG. 2. The channels 2 are closed in the annular region 3.
 An edge region of the carrier body is correspondingly configured at an
 angle.
 Instead of compressing the carrier body 1 in a die 7, the channels 2 may be
 closed by plastic deformation through the use of a stamp 9 or 9' shown in
 FIGS. 4 and 5. The stamp 9 or 9' can be moved backwards and forwards and
 is provided with an annular projection 16.
 The stamp 9' differs from the stamp 9 in that it is provided with a wall 21
 sloping from the inside to the outside.
 Carrier bodies 1 are shown in FIGS. 6 and 7. In the carrier body which is
 shown in cross-section in FIG. 6, the channels 2 have been closed in the
 outer annular region through the use of the stamp 9. FIG. 7 shows a
 carrier body in which the stamp 9' according to FIG. 5 has been used.
 FIG. 8 illustrates the manufacture of a device for catalytic conversion of
 exhaust gases in an exhaust system, in particular in an exhaust system for
 combustion engines. In this configuration, a catalyst carrier body 1 is
 surrounded by a jacket tube 10 and is provided with a large number of
 channels 2. The catalyst carrier body can be manufactured in such a way
 that a plastic deformation of the jacket tube 10 and of the channels 2 is
 carried out in an outer annular region 3, so that a free flow
 cross-section 4 of the channels 2 is partially closed in the direction of
 flow of the exhaust gas. The plastic deformation can take place through
 the use of a tool 17. The tool 17 is provided with a disk 18, which has a
 substantially triangular cross-section on its outer edge area and is
 rotatable about an axle 19. The disk 18 is pressed with force against the
 catalyst carrier body 1 and the jacket 10, so that a plastic deformation
 of the jacket tube 10 and the channel walls occurs. A bead 20 is produced
 circumferentially with respect to the carrier body 1.
 The tool 17 can rotate about the catalyst carrier body 1. It is also
 possible to dispose the tool 17 in a stationary manner and to allow the
 catalyst carrier body 1 to rotate about its axis.
 The configuration of the bead 20 can be in steps, in which case the tool 17
 is advanced correspondingly.