Patent Publication Number: US-11377989-B2

Title: Muffler

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority under 35 U.S.C. § 119 of German Application 10 2018 101 254.3, filed Jan. 22, 2018, and 10 2018 104 239.6 filed Feb. 26, 2018, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention pertains to a muffler for an exhaust system of an internal combustion engine, for example, in a vehicle. 
     BACKGROUND 
     A muffler, in which an exhaust gas pipe group sending exhaust gas into a muffler housing and out of the muffler housing is provided, is known from DE 10 2015 222 088 A1. The exhaust gas pipe group of this prior-art muffler comprises an inlet pipe, which is open at a downstream inlet pipe end to an expansion chamber formed in the housing. A first outlet pipe is inserted with an upstream outlet pipe end area into the inlet pipe through an inlet pipe opening formed at the inlet pipe end and extends with its outlet pipe end area in the inlet pipe, so that the inlet pipe is open to the expansion chamber in the area of the inlet pipe opening via an intermediate space formed between the inlet pipe and the first outlet pipe. A second outlet pipe is open towards the expansion chamber at its upstream end located in the interior of the muffler housing. Exhaust gas introduced into the muffler housing via the inlet pipe leaves the muffler housing via the first outlet pipe and the second outlet pipe. 
     SUMMARY 
     An object of the present invention is to provide a muffler for an exhaust system of an internal combustion engine, especially for a vehicle, which has a low pressure loss and faint flow noises and can be adapted to the acoustic profile to be provided for an internal combustion engine in a simple manner. 
     This object is accomplished according to the present invention by a muffler for an exhaust system of an internal combustion engine, comprising a muffler housing and at least one exhaust gas pipe group, the at least one exhaust gas pipe group comprising:
         an outlet pipe, which is open to an expansion chamber formed in the muffler housing, wherein exhaust gas sent via the at least one exhaust gas pipe group leaves the muffler housing via the outlet pipe,   a first inlet pipe, wherein the first inlet pipe has an inlet pipe end area, which is inserted into the outlet pipe and extends in the outlet pipe, and   a second inlet pipe, wherein the second inlet pipe is open towards the expansion chamber.       

     Due to the adaptation of the length of the end area of the first inlet pipe, which said end area is inserted into the outlet pipe, efficient adaptation to a desired acoustic characteristic of such a muffler is possible in case of superimposition of the exhaust gas flows provided through the two inlet pipes. As an enlargement of the flow cross section does, in principle, take place in the transition from the first inlet pipe to the outlet pipe, an increase in flow resistance leading to flow noises and also to loss of output is avoided to the greatest extent possible. 
     To couple the outlet pipe to the expansion chamber, it is proposed that the outlet pipe have an outlet opening receiving the first inlet pipe at an upstream end of the outlet pipe and that the outlet pipe be open to the expansion chamber via an intermediate space formed between the outlet pipe and the first inlet pipe in the area of the outlet pipe opening. 
     As an alternative or in addition, provisions may be made
         for the outlet pipe to be open to the expansion chamber via at least one passage opening provided in a pipe wall of the outlet pipe, or/and   for the first inlet pipe to be open to the expansion chamber via at least one passage opening provided in a pipe wall of the first inlet pipe, or/and   for the first inlet pipe to be open to an intermediate space formed between the outlet pipe and the first inlet pipe via at least one passage opening provided in a pipe wall of the first inlet pipe.       

     To now prevent the discharge of exhaust gas fed via the first inlet pipe into the expansion chamber, but to guarantee, on the other hand, an efficient introduction of exhaust gas sent via the second inlet pipe into the expansion chamber into the outlet pipe, it is proposed that a plurality of passage openings be provided in the pipe wall, or/and that at least one passage opening and preferably each passage opening be provided in the area in which the inlet pipe end area extends. 
     For further influencing the acoustic characteristic, at least one additional chamber separated from the expansion chamber by a wall may be provided in the muffler housing. At least one opening establishing a connection between the expansion chamber and the additional chamber separated from this by the wall may now be provided in the wall. Further, the outlet pipe may be open to the additional chamber via at least one passage opening provided in a pipe wall of the outlet pipe. 
     The outlet pipe may comprise at least one and preferably two outlet pipe end pipes for the discharge of exhaust gas from the muffler housing. Such outlet pipe end pipes may also form at the same time the tail pipes of an entire exhaust system, via which the exhaust gas, optionally treated in one or more catalytic converter devices to reduce the pollutant emission, is discharged to the outside. However, a connection to an area of an exhaust system, which area is arranged downstream, for example, to another muffler, may, in principle, also be brought about via such outlet pipe end pipes. 
     For a stable connection, the first inlet pipe may be connected to the outlet pipe by
         at least one welded area, preferably slot weld area, or/and   at least one disk-shaped connection element with at least one passage opening and preferably with a plurality of passage openings.       

     Further, a preferably exhaust gas-actuated exhaust flap may be provided in the first inlet pipe to influence the exhaust gas flow characteristics and hence also the acoustic characteristic. 
     The first inlet pipe and the outlet pipe may have a round cross-sectional geometry at least in their length areas in which they are inserted one into the other, at least one pipe of the inlet pipe and the outlet pipe having a circular cross-sectional geometry or/and at least one pipe of the first inlet pipe and the outlet pipe having a flattened round, preferably elliptical or oval cross-sectional geometry. 
     For an efficient guiding of exhaust gas and for avoiding losses of output in the internal combustion engine to the extent possible, two exhaust gas pipe groups may be provided especially for exhaust systems that are to be used in cooperation with larger internal combustion engines, in which case the outlet pipe and the second inlet pipe of a first of the exhaust gas pipe groups are open towards a first expansion chamber and the outlet pipe and the second inlet pipe of a second of the exhaust gas pipe groups are open towards a second expansion chamber. For example, the cylinders of an internal combustion engine may be divided into two groups, and one of the exhaust gas pipe groups may be assigned to each of these two groups of cylinders. 
     To make it possible to maintain a separation of the exhaust gas flows in the interior of the muffler housing as well, it is proposed that there be no exhaust gas exchange connection between the first expansion chamber and the second expansion chamber. 
     To set the acoustic profile of a muffler comprising two exhaust gas pipe groups, the first exhaust gas pipe group and the second exhaust gas pipe group may differ, for example, in
         the shape of the cross section or/and the size of the cross section of the outlet pipe or/and of the first inlet pipe,       

     or/and
         the shape of the cross section or/and the size of the cross section of an intermediate space formed between the outlet pipe and the inlet pipe end area of the first inlet pipe,       

     or/and
         the length of the inlet pipe end area extending in the outlet pipe,       

     or/and
         the shape of the cross section or/and the size of the cross section of the second inlet pipe,       

     or/and
         the number of outlet pipe end pipes,       

     or/and
         the number or/and positioning or/and the size of passage openings provided in a pipe wall of the outlet pipe or/and in a pipe wall of the first inlet pipe.       

     The present invention further pertains to an exhaust system for an internal combustion engine, comprising a muffler having a configuration according to the present invention and, associated with the at least one exhaust gas pipe group, an exhaust gas duct system sending exhaust gas to the first inlet pipe and to the second inlet pipe. The exhaust gas discharged by an internal combustion engine is sent, optionally after flowing through one or more exhaust gas treatment devices to reduce the percentage of pollutants in the exhaust gas, to the muffler via the exhaust gas duct system. 
     It may also be made possible to additionally influence the acoustic characteristic during the operation of an internal combustion engine by the exhaust gas duct system comprising an exhaust flap in association with the first inlet pipe in at least one and preferably each exhaust gas pipe group. Such an exhaust flap comprises a flap diaphragm, which is adjustable, in general, by an electric motor-powered actuating drive, and which is adjustable, for changing the exhaust gas flow to the respective first inlet pipe, between a released position maximally releasing the exhaust gas flow and a closed position maximally throttling or preventing the exhaust gas flow and which may also have intermediate positions between the released position and the closed position for changing the acoustic characteristic essentially continuously. 
     To send exhaust gas to the two inlet pipes of a respective exhaust gas pipe group, it is proposed that in at least one and preferably in each exhaust gas pipe group, the exhaust gas duct system has an exhaust gas main line and a first exhaust gas branch line leading at a branching point from the exhaust gas main line to the first inlet pipe as well as second exhaust gas branch line leading from the exhaust gas main line to the second inlet pipe. 
     If the branching point has an exhaust gas flow regulating device and the exhaust gas flow into the first exhaust gas branch line and the exhaust gas flow into the second exhaust gas branch line are variable due to the exhaust gas flow regulating device, the acoustic characteristic can be influenced over a broader range by influencing the exhaust gas flow, i.e., the respective percentages of the total exhaust gas flow being sent through the two inlet pipes. 
     In case of such a configuration, the exhaust flap may be provided in the first exhaust gas branch line in at least one exhaust gas pipe group and preferably in each exhaust gas pipe group. The distribution of the partial exhaust gas flows sent through the respective inlet pipes and hence also the acoustic characteristic of the muffler can thus be influenced by the exhaust flap, on the one hand, and by the exhaust gas flow regulating device, on the other hand. 
     In another type of configuration, an exhaust flap may be provided in the first inlet pipe in at least one exhaust gas pipe group and preferably in each exhaust gas pipe group. 
     The present invention will be described below with reference to the attached figures. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  is a schematic view of an exhaust system of an internal combustion engine with a muffler and with an exhaust gas duct system sending exhaust gas to the muffler; 
         FIG. 2  is a schematic view, corresponding to that in  FIG. 1 , of an alternative type of configuration of an exhaust system and of a muffler provided therefor; 
         FIG. 3  is a view showing different cross-sectional shapes a), b), c), and e) of a first inlet pipe of a muffler according to  FIG. 1  or  FIG. 2 , which said inlet pipe is inserted into an outlet pipe; 
         FIG. 4  is a view showing different connection types a), b) and c) of an outlet pipe to a first inlet pipe; and 
         FIG. 5  is a schematic detail view showing the muffler of  FIG. 1  with alternative configuration aspects. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to the drawings, in a schematic view,  FIG. 1  shows an exhaust system, generally designated by  10 , for an internal combustion engine in a vehicle. The exhaust system  10  comprises as its essential component a muffler  12 , which may be arranged, for example, as a rear muffler at an end area of an exhaust system generally in the rear area of a vehicle. The muffler  12  comprises an essentially cylindrically shaped muffler housing  14  with a, for example, circular cross section with a circumferential wall  16  and with a respective front wall  18 ,  21  each at the two longitudinal end areas thereof. To introduce and remove exhaust gas discharged from an internal combustion engine, the muffler  12  further has an exhaust gas pipe group generally designated by  19 . The exhaust gas pipe group  19  comprises an outlet pipe  20 , which may be carried at the front wall  18 , on the one hand, and, for example, at an intermediate wall  22  arranged in the interior of the muffler housing  16 , on the other hand. An upstream end  24  of the outlet pipe  20  is located in an expansion chamber  26  formed essentially between the front wall  21  and the intermediate wall  22 . At a downstream end area  28 , the outlet pipe  20  has two outlet pipe end pipes  30 ,  32 , which pass through the front wall  18  and which may also be, for example, the tail pipes of the entire exhaust system  10 , via which tail pipes  30 ,  32  the exhaust gas discharged from an internal combustion engine is released to the surrounding area. With its length area extending between the intermediate wall  22  and the front wall  18 , the outlet pipe  20  extends essentially in another chamber  34 , in which the branching of the outlet pipe  20  into the two outlet pipe end pipes  30 ,  32  may be provided as well. This branching could, in principle, also be arranged outside the chamber  34  or the muffler housing  14 . The intermediate wall  22  separating the expansion chamber  26  from the other chamber  34  may be provided, as is shown, with a plurality of openings  36  in order to establish a connection between the two chambers  26 ,  34 . The essential function of the intermediate wall  22  may be to provide a support for the outlet pipe  20 . 
     The exhaust gas pipe group  19  further comprises a first inlet pipe  38 . The first inlet pipe  38  is led through the front wall  21  into the interior of the muffler housing  14  and it passes through the expansion chamber  26 . The first inlet pipe  38  is arranged such that it extends with an inlet pipe end area  40  through an outlet pipe opening  42  at the upstream outlet pipe end  24  and into the outlet pipe  20 . The inlet pipe end area  40  thus forms the length area of the first inlet pipe  38 , which said length area extends in the interior of the outlet pipe  20 . The first inlet pipe  38  is open into the outlet pipe  20  at a downstream end  44 . The outlet pipe  20  is, in turn, open to the expansion chamber  26  via an intermediate space  46  formed between the inlet pipe end area  40  and the outlet pipe  20 . 
     A second inlet pipe  48  passes through the front wall  21  into the expansion chamber  26  and is open towards the expansion chamber  26 . Thus, there also is, in principle, a flow connection between the second inlet pipe  48  and the outlet pipe  20  via the intermediate space  46 . 
     To feed exhaust gas to the muffler  12  or to the two inlet pipes  38 ,  48 , an exhaust gas duct system  50  shown only schematically in  FIG. 1  is provided. This system comprises an exhaust gas main line  52 , which is configured, for example, as a pipe and which is branched at a branching point  54  into a first exhaust gas branch line  56 , which leads to the first inlet pipe  38  and is likewise configured, for example, as a pipe, and into a second exhaust gas branch line, which leads to the second inlet pipe  48  and which is likewise configured, for example, as a pipe. While the second exhaust gas branch line  58  may lead, for example, directly to the second inlet pipe  48 , the first exhaust gas branch line  56  may lead via an exhaust flap  60  to the first inlet pipe  38 . The percentage of the exhaust gas arriving via the exhaust gas main line  52 , which percentage is fed to the first inlet pipe  38 , may be changed by an adjustable flap diaphragm  62  of the exhaust flap  60 . The flap diaphragm  62  may be able to be adjusted, for example, by an electric motor-powered actuator between an open position and a closed position, or it may be prestressed in the direction of the closed position and adjusted by the exhaust gas pressure from the closed position in the direction of the open position. The two exhaust gas partial flows being sent to the two inlet pipes  38 ,  48  may be additionally influenced by an exhaust gas regulating device  64  provided, e.g., at the branching point  54 . This device can set, for example, the quantities of exhaust gas being sent to the respective exhaust gas branch lines  56 ,  58  by means of an adjustable flap, so that, for example, the entire exhaust gas flow may be sent over the second exhaust gas branch line  58  or the entire exhaust gas flow may be sent over the first exhaust gas branch line  56 , or a percentage of the exhaust gas flow, whose quantity is adjustable, may be sent via each of these branch lines  56 ,  58 . Due to the assembly units exhaust flap  60  and exhaust gas flow regulating device  64 , which can also be actuated and hence adjusted during the operation of an internal combustion engine, it is possible to influence the acoustic characteristic of the muffler  12  during the operation based on the fact that the exhaust gas flows can be varied thereby. 
     Another influence on the acoustic characteristic of a muffler, which influence is to be specified in the design of the muffler  12 , can be achieved by the interaction of the first inlet pipe  38  with the outlet pipe  20 . The depth of insertion of this inlet pipe into the outlet pipe  20  and also the shape of the cross section and the dimension of the cross section of the intermediate space  46  formed between the inlet pipe end area  40  and the outlet pipe  20  have a substantial influence on the acoustic characteristic of the muffler  12 . Since there is an expansion of the flow cross section in the area in which the exhaust gas being sent via the first exhaust gas branch line  56  leaves the first inlet pipe  38  and enters the outlet pipe  20 , throttling, which could compromise the output of an internal combustion engine, also fails to occur in this area. 
     The depth of insertion of the first inlet pipe  38  into the outlet pipe  20  could also be selected, for example, such that the first inlet pipe  38  ends in the area in which the expansion chamber extends. A flow connection could also be achieved or additionally achieved between the outlet pipe  20  and the expansion chamber  26  by a plurality of passage openings, through which the percentage of exhaust gas flow being sent via the second inlet pipe  48  into the expansion chamber  26  can flow into the outlet pipe  20 , being provided in a pipe wall of the outlet pipe  20 . To now prevent exhaust gas being introduced via the first inlet pipe  38  from flowing through such passage openings into the expansion chamber  26 , such passage openings are preferably positioned in the length area of the outlet pipe  20  in which the inlet pipe end area  40  extends, so that exhaust gas leaving the inlet pipe  38  enters into the area of the outlet pipe  20  in which no such passage openings are provided. Since it shall further be ensured that the exhaust gas being fed via the first inlet pipe  48  is not discharged, in principle, to the expansion chamber  26 , the first inlet pipe  38  has no passage openings establishing a direct flow connection to the expansion chamber  26  in its pipe wall in its length area passing through the expansion chamber  26 , especially also in its length area extending outside the outlet pipe  20 , so that the first inlet pipe acts as a simple through pipe. 
     It should further be noted that more partitions may, of course, also be provided to influence the acoustic characteristic of the muffler  12  and these may be positioned at a different location or/and the muffler housing  16  may be lined with sound-insulating material, for example, fiber material, at least in some areas. 
     An alternative type of configuration is shown in  FIG. 2 . This utilizes, in principle, the configuration principles that were explained above with reference to  FIG. 1  and to the exhaust gas pipe group  19  shown there, but it has, contrary to the type of configuration according to  FIG. 1 , two such exhaust gas pipe groups  19 ,  19 ′. The exhaust gas pipe group  19  of the type of configuration shown in  FIG. 2  may correspond in terms of its design and function essentially to the exhaust gas pipe group  19  of the type of configuration shown in  FIG. 1 . This also applies to the exhaust gas duct system  50  with its two exhaust gas branch lines  56 ,  58  and with the exhaust flap  60  provided in the first exhaust gas branch line, which system  50  is shown only partially in  FIG. 2  and is assigned to the first exhaust gas pipe group  19 . 
     The second exhaust gas pipe group  19 ′ shown in  FIG. 2  also comprises an outlet pipe  20 ′, which is carried on the partition  22 , on the one hand, and on the front wall  21 , on the other hand. Unlike the outlet pipe  20  of the first exhaust gas pipe group  19 , the outlet pipe  20  of the second exhaust gas pipe group  19 ′ has only one exhaust gas pipe end pipe  30 ′, which is provided essentially by the downstream end area  28 ′ thereof and which is passed, for example, through the front wall  21 . The first inlet pipe  38 ′ of the second exhaust gas pipe group  19 ′ extends through the front wall  18  and extends with its inlet pipe end area  40 ′ in the upstream part of the outlet pipe  20 ′ of the second exhaust gas pipe group  19 ′. 
     An exhaust gas duct system  50 ′, which may be configured, in principle, like the exhaust gas duct system  50  provided in association with the first exhaust gas pipe group  19  and may have a first exhaust gas branch line  56 ′ as well as a second exhaust gas branch line  58 ′, is associated with the second exhaust gas pipe group  19 ′. For example, the exhaust gas duct systems  50 ,  50 ′ associated with the two exhaust gas pipe groups  19 ,  19 ′ may cooperate with respective different groups of cylinders of an internal combustion engine or send the exhaust gas discharged by these cylinders to the respective exhaust gas pipe groups  19 ,  19 ′ of the muffler  12 . 
     To functionally uncouple the two exhaust gas pipe groups  19 ,  19 ′ from one another, the partition  22  is preferably configured without openings in the exemplary embodiment shown in  FIG. 2 , so that a separate expansion chamber  26  or  26 ′ is formed in association with each exhaust gas pipe group  19 ,  19 ′ in the muffler housing  14 , and there is no exhaust gas exchange connection between the two expansion chambers  26 ,  26 ′. 
     In the configuration shown in  FIG. 2 , the two exhaust gas pipe groups  19 ,  19 ′ can also cooperate in different manners concerning the acoustic characteristic especially in the interaction of the respective first inlet pipe  38 ,  38 ′ with the outlet pipe  20 ,  20 ′. Thus, as is shown in  FIG. 2 , the depth of insertion of the respective first inlet pipe  38 ,  38 ′ into the outlet pipe  20 ,  20 ′ may be different. The relative positioning at right angles to the direction of the longitudinal extension may also be selected differently. In addition, it is possible to select the shape of the cross section or/and the dimension of the cross section of the first inlet pipes  38 ,  38 ′ differently, just as the shape of the cross section or/and the dimension of the cross section of the respective outlet pipes  20 ,  20 ′. The second inlet pipes  48 ,  48 ′ may also be selected differently in terms of the shape of the cross section or/and the dimension of the cross section. It should be noted here that if the dimension of the cross section is referred to, this may designate, for example, the cross-sectional area through which flow can take place or, in case of a circular configuration, the internal diameter or the inner radius of the respective pipes involved. 
     In its views a)-e),  FIG. 3  shows different possibilities of how the interaction of the first inlet pipe  38  with the outlet pipe  20  can be varied. It should be noted that this also pertains, of course, to the interaction of the first inlet pipe  38 ′ with the outlet pipe  20 ′ of the second exhaust gas pipe group  19 ′ in the configuration according to  FIG. 2 . 
       FIG. 3 a   ) shows that the two pipes  20 ,  38  pushed one into the other may be provided each with a circular cross-sectional shape and the first inlet pipe  38  with its inlet pipe end area  40  may be arranged eccentrically in relation to a central longitudinal axis of the outlet pipe  20 , for example, it may touch the circumferential wall of the outlet pipe  20  with its circumferential wall and can be fixed to same, for example, by connection in substance, e.g., welding or soldering. The intermediate space  46  formed between these two pipes  38 ,  20  thus has an essentially sickle-shaped form. 
     The two pipes  20 ,  38  configured with round, especially circular cross-sectional geometry in the type of configuration shown in  FIG. 3 b   ) are arranged concentrically to one another, so that the intermediate space  46  has an essentially circular ring-shaped configuration. Such a concentric arrangement of pipes configured, for example, with an elliptical cross-sectional geometry is possible as well. 
       FIG. 3 c   ) shows an exemplary embodiment, in which the outlet pipe  20  is configured with a circular cross-sectional shape at least in its length section receiving the first inlet pipe  38  or the inlet pipe end area  40  thereof or in a part of said length section, while the inlet pipe end area  40  may be configured with a cross-sectional shape differing from a circular cross-sectional shape, for example, with an elliptical or oval cross-sectional shape. The configuration could, of course, also be such here that the outlet pipe  20  has a geometry different from a circular cross-sectional shape, while the inlet pipe end area  40  is provided with a circular or, for example, likewise non-circular cross-sectional shape. The two pipes  20 ,  38  touch each other in a circumferential area, so that they may be connected to one another, as will be explained below, in this area of mutual contact. 
     In the exemplary embodiment shown in  FIG. 3 d   ), the outlet pipe  20  has, at least in its length area receiving the end area  40  of the first inlet pipe  38 , a round, elliptical cross-sectional geometry, while the first inlet pipe  38  has a circular cross-sectional geometry in its end area  40  extending in the outlet pipe  20 . The two pipes  20 ,  38  touch each other in a circumferential area in this exemplary embodiment as well, but they may also be arranged such that the first inlet pipe  38  is also arranged centered in the vertical direction in the outlet pipe  20 . 
       FIG. 3 e   ) shows an embodiment of the two pipes  38 ,  20  with a respective flattened round, for example, elliptical cross-sectional geometry, and the two pipes  20 ,  38  touch each other mutually in a circumferential area here as well, especially in areas with the respective greatest radius of curvature. 
       FIG. 4  shows different possibilities of the mutual connection of the pipes  20 ,  38 . Thus,  FIG. 4 a   ) shows the connection of the pipes  20 ,  38  configured with the cross-sectional geometry shown in  FIG. 3 d   ). In their areas in which they are mutually in contact with one another, the pipes  20 ,  38  are connected to one another in a plurality of slot weld areas  68  following one another, for example, in the longitudinal direction of the pipe. A plurality of slots, which follow each other, e.g., in the longitudinal direction of the pipe, may be provided for this in the pipe wall of the outlet pipe  20 . They may be welded to one another through these slots or along the contact line of the two pipes  20 ,  38 . 
     In the type of connection shown in  FIG. 4 b   ), the two pipes  20 ,  38  may be connected to one another by one or more ring-shaped disks  70  arranged in the intermediate space  46 . In particular, such a disk  70  may be provided at the upstream end of the outlet pipe  20 , at the location at which the first inlet pipe  38  enters this end and may be fixed by welding at both the outlet pipe  20  and the first inlet pipe  38 . As is indicated by a dash-dotted line, a plurality of passage openings, which follow each other in the circumferential direction and which provide a connection between the intermediate space  46  and the expansion chamber  26 , are provided in the disk  70 . 
       FIG. 4 c   ) shows the connection of the two pipes  20 ,  38  with the use of connection elements  74  in the form of rods or bolts. These may be fixed on the outer circumference of the first inlet pipe  38  and on the inner circumference of the outlet pipe  20  by, for example, welding. It should be noted that more than two connection elements  74  in the form of rods or bolts may be provided distributed over the circumference and in the longitudinal direction of the pipe. These may also be elongated in a plate-like manner especially in the longitudinal direction of the pipe and hence also in the exhaust gas flow direction and may have, for example, a profiling in the form of a drop or bearing surface. 
       FIG. 5  shows design variants of the outlet pipe  20  and of the first inlet pipe  38  inserted into same. It should be noted that the design variants explained below may be embodied in themselves or in any combination in the muffler shown in  FIG. 1  as well and also in one or both of the exhaust gas pipe groups  19 ,  19 ′ shown in  FIG. 2 . 
       FIG. 5  shows that passage openings  66  may be provided in different positions in the respective pipe wall in the outlet pipe  20  or/and in the first inlet pipe  38 . Thus, such passage openings  66 , via which the first inlet pipe  38  is open towards the expansion chamber  26 , may be provided in the first inlet pipe  38  in the length area thereof, which extends outside the outlet pipe  20  but in the expansion chamber  26 . Passage openings, via which the intermediate space  46  is open towards the expansion chamber  26 , may also be provided in the outlet pipe  20  in the area thereof that extends in the expansion chamber  26 . The outlet pipe  20  may also be provided with passage openings  66  in its length area extending in the additional chamber  34 . These passage openings may be provided, for example, in the length area of the outlet pipe  20 , in which the end area  40  of the first inlet pipe  38  extends, so that the intermediate space  46  is open towards the additional chamber  34  via such passage openings  66 . Such passage openings may also be provided in other length areas of the outlet pipe  20 , which extend in the area of the additional chamber  34 . Thus,  FIG. 5  shows passage openings  66  in the downstream end area  28  of the outlet pipe  20  at a location where this has an approximately Y-shaped form and passes over into the two tail pipes  30 ,  32 . 
     It should be stressed that such passage openings  66  provided in different areas of the pipes  20 ,  38  may differ in terms of their grouping density or/and their cross-sectional geometry or/and their size. Such passage openings may be provided in respective identical positions and with the same shape or size in the two exhaust gas pipe groups  19 ,  19 ′ in the exemplary embodiment shown in  FIG. 2  as well. As an alternative, the two exhaust gas pipe groups  19 ,  19 ′ may differ in terms of the number or/and size or/and shape or/and positioning of such passage openings  66 . 
     Another configuration aspect shown in  FIG. 5  is the provision of an exhaust flap  60  or of an adjustable flap diaphragm  62  thereof in the first inlet pipe  38 , preferably in the length area of said inlet pipe extending in the muffler housing  14 . Since this area is accessible only poorly for a motor actuation of the flap diaphragm  62 , such a configuration of the exhaust flap  60 , in which the flap diaphragm  62  is prestressed, for example, by a spring into a closed position and can be adjusted by the exhaust gas pressure in the first inlet pipe  38  in the direction of an open position, is suitable here. 
     It should also be noted concerning the provision of such an exhaust flap  60  in the interior of the muffler  12  that such a configuration can be embodied in one or both exhaust gas pipe groups  19 ,  19 ′ of the configurations shown in  FIG. 2 . Such a passive exhaust flap  60  could also be provided in the first inlet pipe  38  in the interior of the muffler  12  in one of the two exhaust gas pipe groups  19 ,  19 ′, while an exhaust flap  60  shown in  FIG. 2  could be provided outside the muffler in the exhaust gas duct system and could be actuated, for example, by an electric motor in the other of the two exhaust gas pipe groups  19 ,  19 ′. 
     It becomes possible due to the configuration according to the present invention of a muffler especially in the interaction of an inlet pipe with an outlet pipe receiving same to vary the acoustic characteristic or the acoustic profile of a muffler in a broad range and thus to provide a desired acoustic profile for an internal combustion engine. This can be supported by the fact that the respective partial flows of the exhaust gas released by an internal combustion engine, which flows are fed in a first inlet pipe and in a second inlet pipe, can already be influenced in the exhaust gas feed, so that a basic acoustic profile can be predefined by the design configuration of the muffler, on the one hand, and, on the other hand, this basic acoustic profile can be varied by acting on an exhaust flap or/and an exhaust gas flow regulating device depending on the operation. 
     While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.