Abstract:
An exhaust gas cleaning device includes an outer housing, an insert disposed therein, and an elastic compensating element which surrounds the insert. At least before a first operation, an adhesive layer is provided between the insert and the compensating element and/or between the compensating element and the outer housing. Furthermore, there is described a method for manufacturing an exhaust gas cleaning device.

Description:
RELATED APPLICATIONS 
       [0001]    The application is the U.S. National Phase of PCT/EP2007/000200 filed 11 Jan. 2007, which claimed priority to German Application 10 2006 002 688.8 filed 19 Jan. 2006. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention relates to an exhaust gas cleaning device with an outer housing, an insert disposed therein, and an elastic compensating element which surrounds the insert. Furthermore, this invention relates to a method for manufacturing an exhaust gas cleaning device which includes an outer housing with an insert disposed therein, and an elastic compensating element surrounding the insert. 
         [0003]    Exhaust gas cleaning devices in accordance with the invention in particular are catalysts, particulate filters, or combinations thereof. The same usually include an insert in the form of a ceramic substrate, which acts as a mechanical filter (particulate filter) or is coated with a catalytic material for exhaust gas cleaning. The insert is wrapped with an elastic compensating element (usually referred to as bearing mat) and is retained in the outer housing by radial clamping. For this purpose, the elastic compensating element exerts a holding force on the insert, which must be large enough to prevent an axial displacement of the insert relative to the outer housing in driving operation, which can occur for instance as a result of the gas pressure and due to vibrations. 
         [0004]    In exhaust gas cleaning devices known from the prior art it is disadvantageous that the necessary holding force exerted on the insert is only achieved when a bearing mat constituting a so-called “swelling mat” expands (or “swells”) in response to an elevated temperature. For this purpose, however, the swelling mat must once be exposed to a temperature of about 300° C. to 350° C. In a vehicle with a novel exhaust gas cleaning device, in particular in a vehicle driven by a Diesel engine, with an exhaust gas cleaning device disposed in the region of the underbody, only temperatures of about 200° C. initially are achieved in normal driving operation in city traffic. Therefore, it is possible that the bearing mat remains in a non-expanded condition for an extended period, for instance up to the first regeneration of a particulate filter, in which the expansion temperature of the mat is then achieved for the first time. Up to this time there is thus a risk that the insert is axially displaced in the housing due to the insufficient holding force. To prevent this, known bearing mats are made very thick, or an additional axial and possibly radial support is effected, e.g. by wire mesh rings. Another possibility involves using non-swelling bearing mats, with which a sufficient holding force is achieved via a larger gap region. However, these non-swelling bearing mats are clearly more expensive than swelling mats. 
         [0005]    The object of the invention is to create an exhaust gas cleaning device, in which the insert is safely retained from the start (i.e. also before a high temperature was achieved in the exhaust system), and which has little constructive effort and low manufacturing costs. 
       SUMMARY OF THE INVENTION 
       [0006]    In an exhaust gas cleaning device as mentioned above, at least before the first operation, an adhesive layer is provided between an insert and a compensating element, and/or between the compensating element and an outer housing. By using the adhesive layer, an adhesion is achieved between the insert and the compensating element (or between the compensating element and the outer housing), and the insert is safely retained in a mounting position already before the expansion of the compensating element. Even in the case of a non-swelling bearing mat such adhesive layer may be expedient, as the adhesive layer contributes to an increase of the holding force at elevated temperatures, at which the outer housing is slightly expanded. 
         [0007]    Advantageously, the adhesive layer is formed such that its adhesive properties are maintained at elevated temperatures, in particular at temperatures up to 350° C. As mentioned already, the bearing mat expands at a temperature of about 300° C. to 350° C., whereupon the insert is retained in the outer housing safely enough due to the clamping force exerted by the mat. Before the expansion temperature of the mat is achieved, the adhesive layer prevents a displacement of the insert relative to the outer housing. The adhesive layer can be formed such that it melts or burns at elevated temperatures, when it is no longer required for retaining the insert. Advantageously, the adhesive layer is formed of an adhesive which does not secrete any toxic substances during evaporation or combustion. 
         [0008]    In accordance with one example embodiment, the adhesive layer is formed by a double-faced adhesive tape, which has a particularly good processability, a uniform layer thickness, and a short setting time. With an adhesive tape it is also ensured that the adhesive does not penetrate into the bearing mat or the compensating element. 
         [0009]    The double-faced adhesive tape can exclusively consist of an adhesive film, i.e. be completely formed without a carrier layer, for instance in the form of a film. 
         [0010]    Alternatively, the adhesive layer can also be formed by a liquid adhesive or by a spray adhesive. Again, care should be taken that the adhesive does not penetrate into the compensating element. 
         [0011]    The use of an adhesive layer of a thermally activatable adhesive offers a further advantage. It provides for manufacturing the exhaust gas cleaning device by a so-called “stuffing” method, wherein the adhesive layer is applied onto the insert, the elastic compensating element, and/or the outer housing, with the insert and the surrounding compensating element being stuffed into the outer housing. The adhesive will be activated only after stuffing, in particular only during the first operation of the vehicle. In this case, however, the activation temperature of the adhesive should lie distinctly below the temperatures achieved during the first start of the vehicle. 
         [0012]    In principle, any kind of adhesive can be used, and the adhesive layer can for instance be formed by a rubber-based adhesive or by an acrylate-based adhesive. 
         [0013]    In accordance with a second aspect of the invention, a method for manufacturing an exhaust gas cleaning device is provided, which comprises the following steps: The insert, the elastic compensating element, and the outer housing or a sheet metal forming the outer housing are provided. Subsequently, an outer surface of the insert, and/or an inner surface of the compensating element, and/or an outer surface of the compensating element, and/or an inner surface of the outer housing or of the sheet metal are provided with an adhesive layer. Finally, the insert and the compensating element are mounted in the outer housing. By the method of the invention, an exhaust gas cleaning device is created in which the insert is safely retained in the outer housing at any time, i.e. from the time of manufacture. 
         [0014]    These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  shows a longitudinal section through an exhaust gas cleaning device in accordance with a first embodiment of the invention. 
           [0016]      FIG. 2  shows an enlarged detailed view from  FIG. 1 . 
           [0017]      FIG. 3  shows a detailed view similar to  FIG. 2 , but of an exhaust gas cleaning device in accordance with a second embodiment of the invention. 
           [0018]      FIG. 4  shows a schematic representation of the method of the invention for manufacturing an exhaust gas cleaning device. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0019]      FIG. 1  shows an exhaust gas cleaning device  10  for an exhaust system of a motor vehicle. The exhaust gas cleaning device  10  is a particulate filter, an exhaust gas catalyst, or a combination thereof. 
         [0020]    A central part of the exhaust gas cleaning device  10  is an insert  12 , for example an elongated cylindrical substrate, which consists for instance of a ceramic substrate, a wound corrugated board, or some other catalytic carrier or filter material with or without coating. The insert  12  can have a circular cylindrical or non-circular cross-section. A circular cylindrical cross-section is only shown for simplified representation. 
         [0021]    The substrate is surrounded by a bearing mat, which acts as an elastic compensating element  14  between the insert  12  and an outer housing  16 . The outer housing  16  in particular is made of sheet metal and is very thin-walled. Upstream and downstream, an inlet funnel  18  and an outlet funnel  20  are respectively connected with the outer housing  16 . 
         [0022]    Between the insert  12  and the compensating element  14 , an adhesive layer  22  is provided (see also  FIG. 2 ). The same can be formed for instance by a double-faced adhesive tape, a liquid adhesive, or a spray adhesive and prevents a displacement of the insert  12  relative to the compensating element  14  (or to the outer housing  16 ). 
         [0023]      FIGS. 1 and 2  show the exhaust gas cleaning device  10  in the condition before the first operation. In driving operation, exhaust gas flows through the inlet funnel  18  on an end face into the insert  12  and leaves the same with less noxious substances on an opposite end face, in order to leave the exhaust gas cleaning device  10  through the outlet funnel  20 . When the exhaust gas cleaning device  10  reaches a temperature of more than 350° C. in operation of the vehicle, for instance during a regeneration of the particulate filter, the adhesive layer  22  is thermally destroyed, for instance by melting, evaporation or combustion. Since at this time, however, the compensating element  14  is already expanded, a reliable retention of the insert  12  in the outer housing  16  is still ensured. 
         [0024]      FIG. 3  shows an exhaust gas cleaning device in accordance with a second embodiment of the invention, which merely differs from that of  FIGS. 1 and 2  in that between the compensating element  14  and the outer housing  16  a further adhesive layer  22  is provided in addition. The same prevents slipping of the compensating element  14  relative to the outer housing  16 . Of course, an adhesive layer  22  might also be provided only between the compensating element  14  and the outer housing  16 . 
         [0025]    Subsequently, the manufacture of the exhaust gas cleaning device will briefly be explained with reference to  FIG. 4 . First, the insert  12  is provided with an adhesive layer  22  on its outer surface ( FIG. 4   a ), before the compensating element  14  (the bearing mat) is wound about the insert  12  ( FIG. 4   b ). Subsequently, the outer housing  16 , which was prefabricated from a sheet metal for instance by mandrel bending or roller bending ( FIG. 4   c ), is slightly spread and the insert  12  is laterally pushed into the outer housing  16  together with the compensating element  14 . The outer housing  16  is closed, in that the overlapping edges of the outer housing are pushed over each other and welded to each other ( FIG. 4   d ). 
         [0026]    Beside the winding method described above, any other known method for manufacturing an exhaust gas cleaning device can be modified correspondingly. For instance, mounting the insert and the compensating element in the outer housing can be effected by what is called sizing, wherein a plurality of radially movable clamping jaws plastically deform a prefabricated tubular outer housing. In addition, sizing by means of rollers or so-called “spinning” also is possible. The outer housing also can consist of two or more shells, which are pushed into each other and subsequently welded to each other, seamed or soldered. Stuffing the insert along with the compensating element into a prefabricated tubular outer housing also is conceivable. 
         [0027]    Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.