Abstract:
An exhaust system composed of a plurality of components for an internal combustion engine for connecting to a manifold, the exhaust system includes at least one first section, which is provided indirectly or directly after the manifold in the flow direction, and a second section, which is directly adjacent thereto in the flow direction, wherein the two sections are connected to each other by a mechanical decoupling element. The resonant oscillations in the range above 600 Hz are to be attenuated in the exhaust system by more than 15 dB and, at the same time, the exhaust system is to be sufficiently rigid and self-supporting and designed to be lastingly gas-tight. For this purpose, a single-walled arid self-supporting acoustic insulating element is integrated in the exhaust system in the flow direction upstream of, or in, the first section.

Description:
FIELD OF THE INVENTION 
     The invention relates to an exhaust gas system for an internal combustion engine to be connected to a manifold. The exhaust gas system consists of at least one first section provided in the direction of flow directly or indirectly downstream of the manifold, and of a second section following it in the direction of flow with the two sections being interconnected via a mechanical de-coupling element. 
     BACKGROUND OF THE INVENTION 
     The exhaust gas system Is mechanically de-coupled by means of the de-coupling element for providing a certain degree of flexibility over the length of the vehicle. As mechanical de-coupling elements non-self-supporting, flexible connecting elements, such as corrugated tubes or flexible, tubes are, inserted between two sections of the exhaust gas system. Due to the fact that the corrugated tubes or flexible tubes are hot self-supporting, they must be supported. Owing to their small degree of stiffness and flexibility, they have also the inherent property of absorbing to a certain extent vibrations in certain frequency ranges. Such flexible sound-absorbing insulating elements are described for instance in U.S. Pat. No. 5,456,291 A and in EP 1 431 538 B1. 
     For a mechanical articulated de-coupling of two pipe flanges or casing flanges of an exhaust gas system which permits a relative bending of the exhaust gas system, also jolted connecting elements which have a joint-like flexibility are inserted between two sections. These de-coupling elements which are described in DE 198 12 611 C2 or in JP 199789173 A (Hei9-89173) are shaped as a jolted pipe length which forms in the longitudinal section an S-shaped spring. Owing to the reduced wave shape the said connecting elements are stiff when compared to the corrugated tubes; they are, however, self-supporting. In order to increase their flexibility they can be provided with a longitudinal slot according to DE 198 12 611 C2. 
     It is known that due to most different modern construction methods for exhaust gas systems and internal combustion engines, an increasing number of vibrations in the audible range are caused, in spite of a mechanical de-coupling, by resonance in different components. Flatter forms of mufflers, the use of thin-wall, ventilation-slot-insulated sheet metal manifolds and turbochargers in diesel engines as well as changes in the combustion process result in additional vibrations in the structures and thus in additional solid-borne vibrations. 
     This kind of solid-borne vibration may be reduced directly in the structures by means of sound-absorbing insulating elements in the exhaust gas system or also by great impedance leaps in components of an exhaust gas system. 
     According to DE 10 2006 040 980 A1 impedance leaps are achieved with a sound-absorbing insulating element provided with radial widenings of the cross-section which are attached onto the pipe like a pipe clamp. 
     In DE 20 2004 005 526 U1 a rigid flanged joint is described for the reduction of solid-born vibrations which muffles the transmission of vibrations by means of a line-shaped structure in the circumferential direction around the pipe axis or flange axis. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to muffle resonance vibrations within the range above 600 Hz in an exhaust gas system by more than 15 dB and to provide at the same time ah exhaust gas system which is sufficiently rigid and self-supporting as well as permanently gas-proof. 
     The object is accomplished by the integration, in combination with a mechanical de-coupling elements of a single-wall and self-supporting sound-absorbing insulating element into the exhaust gas system in flow direction upstream of or within the first section, with the sound-absorbing insulating element being provided with at least an internal connecting sleeve and with at least one external connecting sleeve offset to the outside in a direction radial to a central axis, with a central section longitudinally shortened in the direction of the central axis being provided that is arranged between the two connecting sleeves and connects the two connecting sleeves, with the cross-section of the said central section forming a U or S eccentricity. 
     It was found out through sound measurements that the known flexible and self-supporting mechanical de-coupling elements in the form of a shortened pipe length with an S eccentricity in the frequency range above 600 Hz, in particular from 3,000 Hz to 6,000 Hz, have sound-absorbing insulating properties which were not to be expected that reduce to a considerable extent the interactions in the other sections of the exhaust gas system and the generation of solid-borne vibrations. The geometric and constructive measures taken with a view to achieving a greatest possible damping resulted in the finding that very good damping properties can be achieved even with a comparatively rigid and self-supporting configuration of the S shaped de-coupling element. 
     In this context it is advantageous to configure the tube-shaped sound-absorbing insulating element in the direction of the central axis as short as possible thereby accomplishing a flexural rigidity adequate for its use as a self-supporting sound-absorbing insulating element. In the region where the sound-absorbing insulating element is integrated into the exhaust gas system it need not function as a mechanical de-coupling element and may have a relative flexural rigidity. 
     Here, it may also be of importance that the push-in depth is in the range from 5 mm to 16 mm, maximally 30 mm. 
     In accordance with the invention the insulating property can be further improved when the sound-absorbing insulating element is connected directly upstream of or to the component which in the last analysis generates the resonance in the transmitting components. The internal radius and the external radius have advantageously a size from 6 mm to 30 mm with both radii having, however, a different size in relation to each other. 
     In this connection it may also be advantageous when the internal connecting sleeve in the direction of the central axis is positioned offset to the external connecting sleeve and/or when the two connecting sleeves overlap each other by the size of a push-in depth e from 5 mm to 30 mm. The length of the push-in depth e is the measure by which the external connecting sleeve in the direction of the central axis projects beyond the internal connecting sleeve. For the said length, both the pipe length that is provided between the internal radius and the external radius and the two radii themselves are to be taken into account for the size of the push-in depth e. The shorter the push-in depth e, the greater the sound-absorbing insulation which is accomplished with the element. 
     Moreover, it is advantageous that the basic diameter of the internal connecting sleeve is smaller by at least 20% to maximally 40% than the diameter of the external connecting sleeve. The sound-absorbing insulation can be essentially influenced by the two end geometries of the two connecting sleeves since the vibration behaviour distinctly deviates in the event of transmission from a small to a larger connecting sleeve from the vibration behaviour which would be attained when the internal connecting sleeve as intake connecting sleeve would have the same size as the external connecting sleeve as exhaust connecting sleeve. 
     As far as the insulating properties are concerned, it may also be advantageous when a central section which connects the two tube-shaped connecting sleeves is provided with at least one external radius connected at the external connecting sleeve and one internal radius connected at the internal connecting sleeve as well as a pipe length connecting the two radii, with the pipe wall of the pipe length being arranged in parallel to or in an angle a between 2.5° and 15° to the central axis. This additional possibility of influencing the insulating effect offers also the advantage that in the presence of a connecting geometry for the internal connecting sleeve or for the external connecting sleeve the size of the two radii can be varied, i.e. that with very small radii this pipe length includes an increasingly larger angle a to the central axis. Another advantage is that the connecting geometry can be enlarged or reduced by the variation of angle a both for the internal connecting sleeve and for the external connecting sleeve. 
     In this connection it can also be advantageous when the single-wall sound-absorbing insulating element is made of sheet metal or cast metal and the insulating element is provided in a direction along the work piece with continuously or discontinuous increasing wall thicknesses ranging from 1 mm to 2.8 mm, in particular ranging from 1.2 mm to 1.9 mm. The insulating effect which is achieved by means of a decreasing Wall thickness has an advantageous effect in particular in the frequency range over and above 2,000 to 6,000 Hz. This is advantageous in particular insofar as when the diameter of the external connecting sleeve is adjusted from a smaller to a larger size the wall thickness does anyhow become thinner. Consequently, a cylindrical pipe with a basic diameter matching the internal connecting sleeve on the exhaust side would be adjusted up to the size of the diameter for the external connecting sleeve. 
     In addition it may be advantageous when the sound-absorbing insulating element has in the flow direction S downstream of the internal connecting sleeve a reduced internal diameter when compared to the basic diameter. By means of this measure, a kind of taper in the passage from the internal connecting sleeve to the central section is formed, by which in particular the vibrations which exist in the exhaust gas pipe are influenced in respect of the insulation. 
     It may be of particular importance for the present invention When the sound-absorbing insulating element is made of an adjusted pipe length with a basic diameter on the intake side from 45 mm to 85 mm and a diameter on the exhaust side from 55 mm to 115 mm as well as with an absolute length in the direction of the central axis from 230 mm to 420 mm. The ratio of basic diameter to diameter sub-stantially influences the insulating property of the element. 
     In connection with the inventive configuration and arrangement it may be advantageous when the sound-absorbing insulating element is integrated into an end wall of a sheet metal housing for a filter or a converter or a muffler with at least a part of the end wall connecting in a radial direction to the central axis to the internal connecting sleeve, and/or to the external connecting sleeve. This facilitates the integration of the insulating element, into a component that is present in the exhaust gas systems and to which an exhaust gas pipe would anyhow be connected. Moreover, the integration into an end wall offers the advantage that the overall length and thus also the rigidity of the element can be increased which has an essential impact on the insulating property. 
     Furthermore, it can be advantageous when the sound-absorbing insulating element, is positioned at an outlet of a housing for a turbocharger. Since turbo-chargers make, a comparatively great contribution to the solid-borne vibration which is generated in the exhaust gas system within the range from 600 Hz to 6 kHz, a positioning of such ah insulating element directly downstream of the turbocharger is of great importance, and by means of such a positioning the greater diameter adjusted in the area of the external connecting sleeve can be more easily integrated into the geometry of ah exhaust gas system because this external connecting sleeve is connected directly to the housing, and a possibly required reduction of the diameter again down to the size of the diameter that is provided for the other exhaust gas pipes which corresponds to the internal connecting sleeve is not necessary. 
     Furthermore, the use of a mechanical de-coupling element for an exhaust gas system for the sound-absorbing insulation of an exhaust gas system within the frequency range from 600 Hz to 6 kHz can be advantageous when the sound-absorbing insulating element is provided with at least one internal connecting sleeve and at least one external connecting sleeve offset to the outside in a direction radial to a central axis, with a shortened central section being provided that is arranged between the two connecting, sleeves and connects the two connecting sleeves, with the cross-section of the said central section forming a U or S eccentricity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages and details of the invention are explained in the patent claims and in the description and are shown in the figures in which 
         FIG. 1  shows an exhaust gas system connected to ah engine; 
         FIG. 2  shows a cross-section of an insulating element which is integrated between two components of an exhaust gas system; 
         FIG. 3  shows an upper section of a cross-section of an insulating element with an internal diameter that is reduced when compared to the basic diameter; 
         FIG. 4  shows a cross-section of an insulating element with a pipe section positioned opposite the central axis; 
         FIG. 5  shows the integration of an insulating element into an end wall of a housing; 
         FIG. 6  shows, a configuration according to  FIG. 5  where the insulating element is positioned in a radial direction centrally to the end wall; 
         FIG. 7  shows a configuration according to  FIG. 6  where the insulating element has a U eccentricity; 
         FIG. 8  shows the integration of an insulating element into a cone-shaped end wall of a sheet metal housing. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows an exhaust gas system  4  consisting of a first section  41  and a second section  42 . The first section  41  is formed by a converter  45  and exhaust gas pipes  47  connected on both sides of converter  45 . The second section  42  consists of a particulate filter  44  and a muffler  46 , with the particulate filter  44  and the muffler  46  being interconnected via an exhaust gas pipe  47 . Upstream of the particulate filter  44  there is also provided an exhaust gas pipe  47  to which a mechanical de-coupling element  40  is connected which interconnects the two sections  41 ,  42 . The purpose of the mechanical de-coupling element  40  is essentially to guarantee a certain freedom of movement of the exhaust gas system  4  over its entire length. 
     The entire exhaust gas system  4  is connected via a sound-absorbing insulating element  1  to an outlet opening of a turbocharger  5  which connects the exhaust gas system  4  via the manifolds  3  with the internal combustion engine  2 . The vibrations which are supplied into the exhaust gas system  4  via the exhaust gas flow and the turbocharger  5  are substantially damped via the sound-absorbing insulating element  1  within the range from 600 Hz to 6 kHz so that the solid-borne emissions of converter  45 , of particulate filter  44  and of muffler  46  are reduced. At the same time, the vibrations that are still present in the first section  41  of the exhaust gas, system  4  are also influenced and also partially damped by the mechanical de-coupling element  40  so that the combination of the sound-absorbing insulation with the insulating element  1  and the damping of vibration with the mechanical de-coupling element  40  brings about a reduction of the solid-borne vibration within the second section  42  of exhaust gas system  4 . 
       FIG. 2  shows a schematic cross-section of a sound-absorbing insulating element  1  with an S eccentricity  120 . The sound-absorbing insulating element  1  is provided with an internal connecting sleeve  10  and an external connecting sleeve  15  in a radial direction to the central axis  13 . The external connecting sleeve  15  projects in the axial direction to the central axis  13  beyond the internal connecting sleeve  10 , The connection of the external connecting sleeve  15  with the internal connecting sleeve  10  forms a central section  12  with an S eccentricity  120  in the cross-section. The central section  12  is formed by the external radius  152  connected to the external connecting sleeve  15  and the internal radius  102  connected to the internal connecting sleeve,  10  as well as by a pipe length  14  which connects the two radii  102 ,  152 . 
     The projection of the external connecting sleeve  15  beyond the internal connecting sleeve  10  is termed push-in depth e the total of which is made up by the size of the pipe length  14  and the two radii  102 ,  152 . The length L of the insulating element  1  in the direction of the central axis  13  is measured from the intake opening at the internal connecting sleeve  10  up to the exhaust opening at the external connecting sleeve  15 . 
     As is shown in  FIG. 2 , an exhaust gas pipe  47  connects to the internal connecting sleeve  10  in the flow direction S upstream of the insulating element  1 . In the flow direction S downstream of the insulating element  1  a schematically shown exhaust gas element  48  is connected to the insulating element  1 . In  FIGS. 5 to 8 , examples of such exhaust gas elements  48  are shown by sheet metal housings  43 . 
     The S eccentricity  120  can have, in different embodiments which are not shown, a basic diameter  101  at the intake side ranging from 45 mm to 85 mm and a diameter  151  at the exhaust side ranging from 55 mm to 115 mm as well as an absolute length L in the direction of the central axis  13  ranging from 230 mm to 420 mm, where the ratio of the diameters  101 ,  151  and of the length L can be selected in such a manner that the natural frequency at a medium input frequency
     a) of 350 Hz amounts to a medium axial transmission loss of at least −18 dB and   b) of 600 Hz amounts to a medium axial transmission loss of at least 0 dB and   c) of 1,000 Hz amounts to a medium, axial transmission loss of at least 8 dB and   d) of 3,000 Hz amounts to a medium axial transmission loss of at least 20 dB.   

     With these parameters of the geometry the natural frequency can be shifted when compared to a cylindrical exhaust gas pipe within the range from 400 Hz to 700 Hz, with a positive damping being achievable as from 600, Hz or as from 900 Hz. Moreover, a maximum damping of 30 dB can be achieved in the range from 600 Hz to 6 kHz. 
       FIG. 3  shows a special embodiment of the S eccentricity  120  where the pipe length  14  which is provided between the two radii  102 ,  152  is positioned opposite the central axis  13  by an angle a. It can be seen that the pipe length  14  is thus not positioned in parallel to the central axis  13  as is shown for instance in  FIG. 3 . Through the variation of the angle a both the basic diameter  101  of the internal connecting sleeve  10  and the diameter  151  of the external connecting sleeve  15  can be varied in relation to each other. In particular in the event, when the sound-absorbing insulating element  1  is made from a cylindrical pipe and adjusted which has essentially a pipe diameter that Corresponds to the basic diameter  101  of the internal connecting sleeve  10 , the external connecting sleeve  15  is adjusted by a specific size. In accordance with the required geometrical sizes and with a view to the wall thickness which is essential for the external connecting sleeve  15 , the diameter  151  of the external connecting sleeve  15  can be varied by means of the variation of angle a, in particular when the internal and the external radius  102 ,  152  are to have, a fixed size. Also in this embodiment the push-in depth e is decisive through the size of the two radii  102 ,  152  and the length L of the pipe length a in the direction of the central axis  13 . 
     When compared to  FIG. 3 ,  FIG. 4  shows a modified embodiment in which Within the area of the internal radius  102  the internal diameter  103  is reduced when compared to the basic diameter  101  of the internal connecting sleeve  10 . In flow direction S a compression of the exhaust gas flow is thus achieved, and, at the same time, influence is exerted on the acoustic waves inside the internal connecting sleeve  10 . 
       FIG. 5  shows a preferred embodiment where the sound-absorbing insulating element  1  is integrated into an end wall  430  of a sheet metal housing  43  of an exhaust gas system  4 . In particular in spun mufflers the end wall  430  is inserted in the direction of the central axis  13  into the sheet metal housing  43  so that the mounting of the insulating element  1  into the end wall  430  is possible prior to the winding of the housing. For this purpose, the sound-absorbing insulating element  1  with the external connecting sleeve  15  is welded into a corresponding opening of the end wall  430 . The diameter  151  of the external connecting sleeve  15  which is considerably larger than that of the internal connecting sleeve  10  practically forms the exhaust side for the exhaust gas that is flowing in the flow direction S so that the exhaust gas and/or the exhaust gas flow further propagate downstream of the sound-absorbing insulating element  1  in the sheet metal housing  43  in radial direction. This offers also the advantage that by means of a reduction of the diameter  151  of the external connecting sleeve  15  in the event of a continuation within the exhaust gas pipe which has approximately the same diameter as the internal connecting sleeve  10 , a decrease of the cross-sectional area can be avoided. 
       FIG. 6  shows an embodiment similar to that in  FIG. 5  as far as the positioning within ah end wall  430  of a sheet metal housing  43  is concerned. In this ease, the S shaped sound-absorbing insulating element  1  is, however, positioned in a radial direction to the central axis  13  approximately in the centre of the end wall  430  so that, starting from the exhaust gas pipe  47  that is mounted in the end wall  430 , at first a first section of the end wall  430  in the radial direction forms a connection to the sound-absorbing insulating element  1  and, following the sound-absorbing insulating element  1  in the radial direction, a second section of the end wall  430  forms the joint and the connection to the circumferentially arranged sheet metal housing  43 . In this embodiment the internal connecting Sleeve  10  and the external connecting sleeve  15  are extremely short and the adjoining components are hot arranged, as in the preceding embodiments, in an axial direction to the central axis  13  adjoining the sound-absorbing insulating element  1  but in radial direction. 
       FIG. 7  shows an embodiment similar to that in  FIG. 6  where the sound-absorbing insulating element  1  does not have an S shaped cross-section but a U shaped cross-section  120 . The U shaped sound-absorbing insulating element  1  is provided with one radius only that is termed internal radius  102  and can, due to the existing geometry, be used exclusively in those regions where the other components follow the, sound-absorbing insulating element  1  in the radial direction to the central axis  13 . 
       FIG. 8  shows an embodiment where the sound-absorbing insulating element  1  forms a connection between an exhaust gas pipe  47  and a sheet metal housing  43  with the sheet metal housing  43  having a cone-shaped end wall. Here, too, the larger diameter  151  of the external connecting sleeve  15  when compared to the diameter of the internal connecting sleeve  10  is advantageously accomplished through the connection to the sheet metal housing  43  so that a decrease of the cross-sectional area, of the diameter  152  of the external connecting sleeve  15  to a smaller size is not required.