Abstract:
For connection of pipelines which are subject to vibration, for example pipelines in vehicle exhaust systems, a liquid-tight decoupling element is used which includes a, e.g. multi-layer wound, metal hose and a tube accommodated in coaxial relationship inside or outside of the metal hose. A first axial fitting firmly secures one end of the tube. The tube is sized to protrude into a second axial fitting, regardless whether the metal hose is completely compressed or completely stretched, to allow movement of the tube in axial and torsional directions in relation to the second axial fitting.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
   This application claims the benefit of prior filed U.S. provisional Application No. 60/724,413, filed Oct. 7, 2005, pursuant to 35 U.S.C. 119(e), the disclosure of which is hereby incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   The present invention relates to a decoupling element for pipelines subject to vibration. A typical example of an application would be in vehicle exhaust systems. 
   Nothing in the following discussion of the state of the art is to be construed as an admission of prior art. 
   Such devices are intended to connect in a flexible way pipes which are subject to vibration, and to protect them from vibration. In order to meet the requirements of the automotive industry (passenger cars) for gas-tightness, a metal bellows is often a module of such decoupling elements. As the large variations in diameter in the corrugations of the metal bellows may lead to turbulence, a metal hose is usually incorporated into the pipe so as to ensure laminar gas flow. It must be ensured that any noise generated during operation resulting from the metal hose hitting the inside of the bellows is kept to a minimum. This is often achieved by surrounding the hose with braiding. German Offenlegungsschrift DE 198 20 863 A 1 shows a flexible pipe as an example. Instead of using braiding, the metal hose and the metal bellows are connected at defined points so as to prevent the development of the type of noise described above. 
   For commercial vehicles, multi-layer wound metal hoses produced from profiled strip material are frequently used as decoupling element in exhaust systems. Since a low degree of leakage is permissible, it is not necessary to use a gas-tight element such as a metal bellows. A simple example of metal hoses used as decoupling elements is the so-called Agraff hose. Further examples, which have a longer service life and a lower leakage rate than Agraff hoses, have been described in German publications DE 34 41 064 C2 and DE 101 13 180 C2. 
   Wound metal hoses are especially suitable for the exhaust systems of commercial vehicles as they tolerate large offsets in the axial, lateral, and above all the torsional direction without structural tension arising. Their disadvantage, however, is the residual leakage. 
   As legal provisions worldwide will be stipulating a substantially reduced emission of pollutants from commercial vehicles, exhaust systems will increasingly be fitted with exhaust gas treatment modules such as soot filters and SCR systems. SCR systems in particular place new technical requirements on decoupling elements as they reduce nitrogen oxide in exhaust gas by adding AdBlue (=urea). AdBlue is injected into the exhaust gas flow. Depending on the service and ambient conditions, condensate may be formed on the inside walls of the exhaust system. Liquid urea has a good seepage ability and must not emerge from the exhaust system into the environment. For this reason, all pipes used in the exhaust system and in particular decoupling elements must be at least liquid-tight. 
   It would therefore be desirable and advantageous to provide an improved liquid-tight decoupling element to obviate prior art shortcomings and to prevent any penetration of condensate urea into the environment so as to be usable in exhaust systems in connection with SCR systems, while still allowing substantial movements in axial and in particular torsional direction. 
   SUMMARY OF THE INVENTION 
   According to one aspect of the present invention, a liquid-tight decoupling element includes a metal hose, a tube accommodated in coaxial relationship to the metal hose, a first axial fitting for firm connection of one end of the tube, and a second axial fitting for radially securing another end of the tube to allow movement of the tube in axial and torsional directions. 
   According to another feature of the present invention, the tube may be accommodated in coaxial relationship within or outside the metal hose. 
   According to another feature of the present invention, the tube may be sized to protrude in the second axial fitting, regardless whether the metal hose is completely compressed or completely stretched. 
   According to another feature of the present invention, an annular element may be provided for radially securing the tube to the second axial fitting. The tube may hereby be movably mounted in the second axial fitting by the annular element, regardless whether the metal hose is completely compressed or completely stretched. 
   According to another feature of the present invention, the tube may be made of metallic material with a defined mechanical feature and a defined chemical composition. As an alternative, the tube may also be made of elastomer, glass fiber reinforced material, silicate fiber reinforced material, ceramic material, compound material, or composite material. Likewise the annular element may be made of metallic material with a defined mechanical feature and a defined chemical composition, or of elastomer, glass fiber reinforced material, silicate fiber reinforced material, ceramic material, compound material, or composite material. 
   According to another feature of the present invention, the tube may be rigid with a high stiffness. 
   According to another feature of the present invention, the tube may be flexible. 
   According to another feature of the present invention, the tube may have a bellows-type geometry to define corrugations extending in two planes oriented perpendicular to one another in orthogonal relationship to a rotation axis, or with corrugations which extend helically about a perimeter of the tube. 
   According to another feature of the present invention, the tube and the metal hose may demarcate a cylindrical cavity therebetween for receiving a dampening element to effectively prevent metallic contact between the tube and the metal hose and resultant noise generation when vibrating. Suitably, the dampening element is a metal braiding. 
   When using a liquid-tight decoupling element according to the present invention in an exhaust system of a motor vehicle, the second axial fitting may have a circumferential cavity in the form of a bead to collect liquid contained in the exhaust system. The circumferential cavity prevents hereby a migration of liquid past the annular element to an area of the metal hose, especially when the decoupling element is installed horizontally. 
   According to another feature of the present invention, the tube may be a multi-layer wound corrugated tube. 
   According to another feature of the present invention, the tube may be a corrugated tube produced by partial expansion of a tube. 
   According to another feature of the present invention, the tube may be a metal bellows. 
   According to another feature of the present invention, the metal hose may be a multi-layer wound metal hose. 
   According to another feature of the present invention, the metal hose may be connected to the axial fittings. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which: 
       FIG. 1  is a schematic illustration of one embodiment of a decoupling element according to the present invention; 
       FIG. 2  is a schematic illustration of another embodiment of a decoupling element according to the present invention; 
       FIG. 3  is a schematic illustration of a modification of the decoupling element of  FIG. 1 ; 
       FIG. 4  is a schematic illustration of another modification of the decoupling element of  FIG. 1 ; 
       FIG. 5  is a schematic illustration of yet another embodiment of a decoupling element according to the present invention; 
       FIG. 6  is a schematic illustration of still another embodiment of a decoupling element according to the present invention; and 
       FIG. 7  is a schematic illustration of yet another embodiment of a decoupling element according to the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Throughout all the Figures, same or corresponding elements are generally indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the drawings are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted. 
   Turning now to the drawing, and in particular to  FIG. 1 , there is shown a schematic illustration of one embodiment of a decoupling element according to the present invention, generally designated by reference numeral  1 . The decoupling element  1  includes a wound hose  11  which is produced by thread-type multi-layer winding of profiled metallic strip material. Accommodated in the wound hose  11  in coaxial relationship is a flexible metal tube  12  which is firmly connected on a left-hand side with an axial fitting  17  by a material union or in a form-fitting manner. As an alternative, as shown in  FIG. 7 , the tube  12  is accommodated in coaxial relationship outside the metal hose  11 . The metal tube  12  may, e.g. be realized in the form of a multi-layer wound corrugated tube, a corrugated tube  401  shown in  FIG. 6  and produced by partially expanding a tube, or a metal bellows  201 , as shown by way of example in  FIG. 4 . Although the flexible tube  12  is described here as being made of a metal material, it is also possible to make the flexible tube of elastomer, glass fiber reinforced material, silicate fiber reinforced material, ceramic material, compound material, or composite material. 
   A sleeve  15  is fitted between an outside diameter of the flexible metal tube  12  and an inside diameter of the wound hose  11  to define a cylindrical cavity  19  between the flexible metal tube  12  and the wound hose  11 . A dampening element  301 , as shown in  FIG. 5 , such as braiding, may be placed in the annular cavity  19  to effectively prevent metallic contact between the flexible metal tube  12  and the wound hose  11  and thus any noise generation when the decoupling element  1  vibrates. A sleeve  13  is placed over the left-hand end of the wound hose  11  and connected to the hose  11  by a material union or in a form-fitting manner. 
   On the right-hand side, the decoupling element  1  includes an axial fitting  18  by which the wound hose  11  is connected with a second sleeve  14  by a material union or in a form-fitting manner. For reasons of fatigue strength, the flexible tube  12  cannot be firmly connected with the fitting  18 . Rather, an annular element  16  is used to realize an attachment which secures the flexible tube  12  radially in the fitting  18 , while allowing the flexible tube  12  to move in axial and torsional directions. This ensures that the flexible tube  12  needs only to absorb lateral movements during operation. The absence of axial and torsional loads as a consequence of the design has a positive influence on the fatigue strength of the flexible tube  12 . Care must be taken however that the annular element  16  is accommodated inside the right fitting  18 , even when the wound hose  11  is fully stretched or extended. 
   As shown in  FIG. 3 , the fitting  18  may also be provided with a circumferential cavity  101  in the form of a bead to collect any liquid present in the exhaust system and to ensure, particularly when installed horizontally, that no liquid may pass the annular element  16  and migrate to the area of the wound hose  11  against the direction of flow. 
   The decoupling element  1  is liquid-tight when exhaust gas flows from the left fitting  17  to the right fitting  18 . Any residual leakage refers solely to gas and is determined by the sealing effect of the annular element  16  and tightness of the wound hose  11 . As different geometries of the wound hose  11  lead to different leakage rates, any residual leakage can be influenced through suitable construction of the wound hose  11  with lay-on profile, Agraff hoses or hose sections according to the afore-mentioned German publications DE 344 1064 C2 and DE 101 13 180 C2. 
   The decoupling element  1  is designed particularly for decoupling in the axial and torsional directions. Lateral flexibility is determined by the size of the cylindrical cavity  19  and lateral stiffness of the flexible tube  12 . By varying these two elements, different designs are possible. For example, a decoupling element, which is intended exclusively for axial and torsional decoupling, may be provided with a very small cylindrical cavity  19  and a rigid tube  12 . If greater lateral flexibility is required, the cylindrical cavity  19  must be sufficiently large, and the flexible tube  12  should have a low lateral stiffness. 
   Referring now to  FIG. 2 , there is shown an alternative arrangement of a decoupling element, generally designated by reference numeral  10 . Parts corresponding with those in  FIG. 1  are denoted by identical reference numerals and not explained again. The description below will center on the differences between the embodiments. In this embodiment, provision is made for a tube  21  having a staggered diameter. 
   The annular element  16  can be made of pressed metal braiding. As an alternative, the annular element  16  may be made from ceramic, glass fiber reinforced material, silicate fiber reinforced material or composite material. These materials may also be used to fill the cylindrical cavity  19 . 
   To suit a decoupling element according to the invention to a special application, combinations of the above designs are, of course, possible. In addition to its use in vehicle exhaust systems, the liquid-tight decoupling element described is also suitable for industrial applications such as the exhaust systems of stationary turbines. 
   While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. The embodiments were chosen and described in order to best explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. 
   What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims and includes equivalents of the elements recited therein: