Patent Publication Number: US-2020291837-A1

Title: Exhaust system for an internal combustion engine of a motor vehicle as well as motor vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. non-provisional application claiming the benefit of German Application No. 10 2019 106 159.8, filed on Mar. 11, 2019, which is incorporated herein by its entirety. 
     TECHNICAL FIELD 
     The disclosure relates to an exhaust system for an internal combustion engine of a motor vehicle, with an exhaust-gas line routing exhaust gas and an active silencing device, wherein the active silencing device comprises a sound-generating unit which is acoustically coupled to the exhaust-gas line via a sound line and a sound coupling-in line connected downstream thereto, with the result that sound generated by the sound-generating unit can be introduced into an exhaust gas flow present inside the exhaust-gas line. 
     Furthermore, the disclosure relates to a motor vehicle with such an exhaust system. 
     BACKGROUND 
     Such exhaust systems are known from the state of the art. Via the active silencing device, sound can be generated which is superposed with a sound carried by the exhaust gas flow. Here, the superposition is at least partly destructive in nature, with the result that the sound carried by the exhaust gas flow is muffled or cancelled by the active silencing device. 
     As a rule, loudspeakers which can function only within a specific temperature range are used as sound-generating units of such silencing devices. 
     In exhaust systems, the situation often arises that a temperature of the exhaust gas flow, which carries the sound to be muffled or cancelled, lies outside the temperature window in which loudspeakers or other sound-generating units function reliably. For this reason, such components of active silencing devices must be protected against the high temperatures of the exhaust gas flow. However, thermal protection must not take place at the expense of the acoustic effectiveness of the silencing device. In other words, in exhaust systems with active silencing devices, a compromise between acoustic effectiveness and reliability must always be chosen. 
     An exhaust system is to be provided that has an active silencing device, which is acoustically particularly effective and at the same time functions reliably. In particular, the active silencing device is to be reliably protected against the thermal influences of the exhaust gas flow. 
     SUMMARY 
     An exhaust system has a sound coupling-in line that substantially concentrically surrounds an exhaust-gas line on an outside, and an area of the exhaust-gas line enclosed by the sound coupling-in line has an axial portion facing a sound line and an axial portion connected downstream thereto facing away from the sound line. A first perforation is provided in the axial portion facing away from the sound line and the axial portion facing the sound line is designed perforation-free at least in a portion. A sound generated by the sound-generating unit therefore firstly runs through the sound line and thus passes into the sound coupling-in line, to be more precise into an annular space between the sound coupling-in line and the exhaust-gas line. From here, the sound passes into the inside of the exhaust-gas line via the first perforation and can thus interact with the sound carried by the exhaust gas flow. By a perforation is meant in this connection a group of openings which are arranged with a degree of regularity. An axial portion designed perforation-free at least in a portion is here either designed wholly without perforation or has a perforation merely in one portion. Compared with the axial portion facing away from the sound line, the portion facing the sound line is thus less markedly perforated. This can be effected, for example, in that a total cross section of the perforation openings in the axial portion facing the sound line is lower than a total cross section of the perforation openings in the axial portion facing away from the sound line. Because the axial portion facing the sound line is designed perforation-free at least in a portion, i.e. has no openings at least in a portion, a flow, coming from this axial portion, of a possibly hot exhaust gas flow into the sound line is reduced or wholly prevented. Consequently, a flow of hot exhaust gas to the sound-generating unit is thus also reduced or prevented. A flow of hot exhaust gas in the direction of the sound-generating unit can thus substantially only take place via the axial portion facing away from the sound line and the first perforation provided there. The sound-generating unit is thus protected against a direct inflow by a hot exhaust gas flow because such an inflow is wholly or partly prevented. An exhaust gas flow exiting the exhaust-gas line via the first perforation can reach the sound-generating unit only via several deviations. This means that the exhaust gas flow cools significantly on its way to the sound-generating unit. Thus, the sound-generating unit is effectively protected against the temperature influences of the exhaust gas flow. As a result, it functions reliably and is durable. At the same time, the sound-generating unit can be arranged relatively close to the exhaust-gas line, as a result of which the latter can be operated efficiently and effectively from an acoustic point of view. Moreover, an exhaust system designed in this way can be constructed comparatively compact. In other words, it requires only a comparatively small installation space on a motor vehicle which is fitted with such an exhaust system. It can also be flexibly integrated into available installation spaces. 
     The idea underlying the disclosure is to perforate that area of the exhaust-gas line which is surrounded by the sound coupling-in line but lies in the region of the sound line as little as possible or not at all. The region of the sound line is to be understood as an axial portion of the exhaust-gas line which lies opposite a mouth of the sound line into the sound coupling-in line. The perforation, which is necessary for the acoustic coupling of the sound-generating unit to the inside of the exhaust-gas line, is arranged as far as possible outside the abovementioned region, thus in an axial portion of the exhaust-gas line facing away from the sound line. Here, the axial portion facing away from the sound line can directly adjoin the portion, facing the sound line, that is perforation-free at least in a portion or be arranged at a particular distance from the portion that is perforation-free at least in a portion. 
     Consequently, such an exhaust system is close to ideal in that the sound-generating unit is coupled resistance-free from an acoustic point of view to the inside of the exhaust-gas line, but at the same time exhaust gas cannot flow out of the inside of the exhaust-gas line to the sound-generating unit. 
     A further thermal decoupling of the sound-generating device from the exhaust gas flow can be achieved by lengthening the sound line. The geometric distance of the sound-generating unit from the exhaust-gas line is thereby increased. 
     The first perforation advantageously runs around the whole periphery of the axial portion of the exhaust-gas line facing away from the sound line. This results in an effective coupling of the sound generated by the sound-generating unit into the inside of the exhaust-gas line. 
     The openings comprised by the first perforation preferably each have a substantially round cross section. It has become apparent that such a first perforation is particularly suitable for coupling the active silencing unit to the inside of the exhaust-gas line and at the same time limiting an outflow of exhaust gas via the first perforation. 
     In an embodiment, the exhaust-gas line has a second perforation in the area enclosed by the sound coupling-in line upstream of the first perforation in a peripheral portion facing away from the sound line, wherein a peripheral portion facing the sound line is designed perforation-free. The peripheral portion facing away from the sound line and the peripheral portion facing the sound line are preferably complementary to each other to form the whole periphery of the exhaust-gas line, i.e. there are no further peripheral portions. This second perforation serves to acoustically couple the sound-generating unit to the inside of the exhaust-gas line. A sound generated by the sound-generating unit therefore firstly runs through the sound line and thus passes into the sound coupling-in line, to be more precise into an annular space between the sound coupling-in line and the exhaust-gas line. From here, the sound passes into the inside of the exhaust-gas line via the second perforation and can thus interact with the sound carried by the exhaust gas flow. By a perforation is again meant a group of openings which are arranged with a degree of regularity. Because the peripheral portion facing the sound line is designed perforation-free, thus has no openings, a possibly hot exhaust gas flow coming from the inside of the exhaust-gas line is prevented from flowing directly into the sound line and in this way reaching the sound-generating unit. A flow of hot exhaust gas in the direction of the sound-generating unit is instead possible only via the peripheral portion facing away from the sound line and the second perforation provided there. The sound-generating unit is thus protected against a direct inflow by a hot exhaust gas flow. An exhaust gas flow exiting the exhaust-gas line via the second perforation can reach the sound-generating unit only via several deviations. This means that the exhaust gas flow cools significantly on its way to the sound-generating unit. Thus, the sound-generating unit is particularly effectively protected against the temperature influences of the exhaust gas flow. Moreover, an exhaust system designed in this way can be constructed comparatively compact. 
     For the case where both a first and a second perforation are provided, it can happen that exhaust gases exit the inside of the exhaust-gas line via the second perforation. They can then be returned into the exhaust-gas line again via the first perforation. This is possible due to the downstream arrangement of the first perforation relative to the second perforation. The static pressure prevailing within the exhaust-gas line namely decreases along the flow direction of the exhaust gas. An exhaust gas flow which has exited the exhaust-gas line via the second perforation at comparatively high pressure can thus re-enter the inside of the exhaust-gas line along the pressure gradient via the first perforation. The pressure ratios are reversed in the gap between the exhaust-gas line and the sound coupling-in line. Here, the highest static pressure is reached at the downstream end of the gap, thus in the area of the first perforation. Because of these pressure ratios, hot exhaust gases are consequently prevented from flowing in the direction of the active silencing unit. 
     A radial rib, which preferably extends up to the sound coupling-in line, can be provided on an outer surface of the exhaust-gas line between the peripheral portion facing away from the sound line and the peripheral portion facing the sound line. Such a radial rib represents a flow obstacle for an exhaust gas flow which flows out of the inside of the exhaust-gas line in the direction of the sound-generating unit. Thus, the inflow of hot exhaust gas into the active silencing device is further prevented. In addition, the radial rib can be formed as cooling fin for the exhaust-gas line. Thus, the exhaust gas flow present inside the exhaust-gas line is cooled by via the radial rib. 
     The radial rib can either be attached to the exhaust-gas line on the outside and extend in the direction of the sound coupling-in line or be attached to the sound coupling-in line on the inside and extend in the direction of the exhaust-gas line. It is likewise possible for the radial rib to be connected both to the outside of the exhaust-gas line and to the inside of the sound coupling-in line. For example, the radial rib can be welded to the exhaust-gas line and/or the sound coupling-in line. It is likewise possible to manufacture the radial rib integral with the exhaust-gas line and/or the sound coupling-in line. 
     According to an embodiment, a radial rib is provided in each of the two border areas between the peripheral portion facing away from the sound line and the peripheral portion facing the sound line. Thus, a total of two radial ribs are provided. They each represent a flow obstacle at the transition point between the peripheral portion facing away from the sound line and the peripheral portion facing the sound line, with the result that, as already described above, the inflow of hot exhaust gas into the sound line is impeded or prevented. The two radial ribs are arranged, for example, radially opposite, thus they are offset relative to each other by an angle of 180° on the periphery of the exhaust-gas line. Naturally, it is also possible to choose a different angle here. Thus, for example, the peripheral portion facing away from the sound line can merely cover an angle of 90° and the peripheral portion facing the sound line can cover an angle of 270°. Intermediate values are also possible. As a result of the second radial rib, the protection of the active silencing unit against hot exhaust gases is particularly effective. 
     The radial rib is preferably shorter in axial direction of the exhaust-gas line than the sound coupling-in line. Thus, at an axial end of the annular space formed by the exhaust-gas line and the sound coupling-in line, an acoustic coupling channel results via which sound generated by the sound-generating unit can flow around the radial rib or the radial ribs on the periphery of the exhaust-gas line. Only as it progresses further can the sound pass into the inside of the exhaust-gas line via the second perforation. An effective acoustic coupling of the silencing device to the inside of the exhaust-gas line is thereby guaranteed. 
     An exhaust system in which the radial ribs merely extend to an axial length which corresponds to the axial length of the second perforation is particularly preferred. Thus, no radial ribs are provided in the area of the first perforation. 
     In a variant, the openings comprised by the second perforation each have a substantially rectangular cross section, wherein preferably a short side of the rectangle is oriented in peripheral direction and a long side of the rectangle is oriented in axial direction of the exhaust-gas line. It has become apparent that a second perforation designed in such a way effects a good compromise between a thermal decoupling of the inside of the exhaust-gas line from the active silencing device and an effective acoustic coupling of these components. 
     An alternative design provides that a radial outer end of the radial rib or radial ribs provided on the outer surface of the exhaust-gas line is or are at a radial distance from the sound coupling-in line, wherein each radial rib radiating from the exhaust-gas line is complemented by a radial rib, pointing radially inwards radiating from the sound coupling-in line, which is at only a small peripheral distance from the associated radial rib radiating from the exhaust-gas line or touches the periphery of same, and the radial inside end of which is at a radial distance from the exhaust-gas line. Each radial rib provided on the outer surface of the exhaust-gas line forms a so-called radial rib pair together with the radial rib allocated to it provided on the sound coupling-in line. An alternative term for this is double rib. Such a radial rib pair represents an effective flow obstacle for hot exhaust gases, with the result that the active sound-generating unit is protected against high temperatures. The fact that the radial rib radiating from the outer surface of the exhaust-gas line is not connected to the sound coupling-in line and the radial rib radiating from the sound coupling-in line is not connected to the exhaust-gas line is advantageous in terms of production technology. Namely, the necessity of attaching a radial rib both to the exhaust-gas line and to the sound coupling-in line, which is complex, is avoided. Moreover, the omission of such connections results in a particularly long service life of the exhaust system as the connection points are often exposed to comparatively high stresses. 
     The small peripheral distance between the radial ribs forming the radial rib pair is to be seen in comparison with the line diameter of the exhaust-gas line and means that the distance is at most 10%, preferably at most 5%, of the line diameter. In this way, it is achieved that hot exhaust gas, given a flow in the direction of the active silencing device, is effectively countered by a flow resistance. 
     In an area upstream of the sound coupling-in line, the exhaust-gas line can have an axial bend or an axial kink, in particular wherein an axial bend of substantially 90° is present. The sound coupling-in line is preferably arranged directly adjacent to the axial bend or the axial kink. A compact construction of the exhaust system thus results. As a result of an axial kink or an axial bend, the pressure ratios inside the exhaust-gas line can be influenced in a targeted manner in an area downstream of the axial kink or of the axial bend. In particular, a pressure level is thereby increased in a convex area of the axial bend or of the axial kink. The pressure level decreases correspondingly in a concave area. 
     In this case, the second perforation is preferably arranged downstream of a convex area of the axial bend or of the axial kink. As already explained, the second perforation is arranged in a peripheral portion facing away from the sound line. Because the axial bend or the axial kink causes the pressure in the exhaust gas flow to be higher on the convex side than on the concave side, an exhaust gas flow in the direction of the sound-generating unit is thus effectively prevented. 
     A center axis of the sound line can run substantially along a radial direction of the sound coupling-in line. By this is meant that a predominant proportion of the direction of the center axis of the sound line is oriented in radial direction of the sound coupling-in line. A smaller proportion can also run in axial direction and/or in peripheral direction of the sound coupling-in line. The center axis of the sound line can thus impinge obliquely on the sound coupling-in line, wherein the radial component is always the largest. However, it is preferred that the sound line runs along the radial direction of the sound coupling-in line. This effects a high-quality acoustic coupling of the sound-generating unit to the inside of the exhaust-gas line. Moreover, a compact construction of the exhaust system can thus be achieved. 
     In addition, a motor vehicle of the type mentioned at the beginning is provided which comprises an exhaust system according to the disclosure. Such a motor vehicle emits only little or no sound at all via an exhaust gas flow conducted into the surroundings by the exhaust system. Thus, the motor vehicle can be operated comparatively quietly. At the same time, the motor vehicle is particularly reliable and durable because the temperature-sensitive components of the exhaust system are protected against hot exhaust gas. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure is explained below with reference to various embodiment examples which are shown in the attached drawings. There are shown in: 
         FIG. 1  shows a schematic view of a motor vehicle according to the disclosure with an exhaust system according to the disclosure, 
         FIG. 2  shows the exhaust system according to the disclosure in a view from above, 
         FIG. 3  shows a perspective view of the exhaust system from  FIG. 2 , wherein a sound line and a sound coupling-in line are represented transparent, 
         FIG. 4  shows the exhaust system from  FIG. 2  in a view from above, wherein the sound line and the sound coupling-in line are omitted, 
         FIG. 5  shows a perspective view of the exhaust system from  FIG. 2 , wherein, as in  FIG. 4 , the sound line and the sound coupling-in line are omitted, 
         FIG. 6  shows a schematic detail view of a radial rib of the exhaust system from  FIG. 2 , 
         FIG. 7  shows a schematic detail view of a radial rib of the exhaust system from  FIG. 2  according to an alternative design and 
         FIG. 8  shows a schematic detail view of a radial rib of the exhaust system from  FIG. 2  according to a further alternative design. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a motor vehicle  10  with an internal combustion engine  12  which is coupled to an exhaust system  14 . Thus, the exhaust gas produced by the internal combustion engine  12  is conducted into the surroundings  16  via the exhaust system  14 . 
     The exhaust system comprises an exhaust-gas line  18  routing the exhaust gas and an active silencing device  20 . 
     The active silencing device  20  has a sound-generating unit  22  which comprises, for example, a loudspeaker and a sound line  24 . A sound coupling-in line  26  is connected to the sound line  24  downstream. 
     A center axis of the sound line  24  runs substantially along a radial direction of the sound coupling-in line  26 . The center axes of the sound line  24  and the sound coupling-in line  26  are thus substantially perpendicular to each other. 
     Furthermore, the sound coupling-in line  26  surrounds the exhaust-gas line  18  substantially concentrically on the outside. The center axes of the sound coupling-in line  26  and the exhaust-gas line  18  are thus substantially coincident. 
     The active silencing device  20 , more precisely the sound-generating unit  22 , is acoustically coupled to an exhaust gas flow present inside the exhaust-gas line  18 . Here, sound generated by the sound-generating unit  22  is conducted into the sound coupling-in line  26  via the sound line  24  and thus passes into an annular space which is formed by the sound coupling-in line  26  and the exhaust-gas line  18 . 
     The portion of the exhaust-gas line  18  running inside this annular space can be subdivided into an axial portion facing the sound line  24  and an axial portion, connected downstream thereto, facing away from the sound line  24 . 
     In the embodiment represented, the axial portion facing the sound line  24  and the axial portion facing away from the sound line  24  are directly adjacent to each other. 
     Here, a first perforation  38  is provided in the axial portion facing away from the sound line  24 . The axial portion facing the sound line  24  is designed perforation-free in a portion, as will be explained later. 
     The first perforation  38  runs around the whole periphery of the axial portion facing away from the sound line  24 . 
     Here, the openings of the first perforation  38  have a substantially round cross section. Within the axial portion facing the sound line  24 , the exhaust-gas line  18  furthermore comprises a peripheral portion  28   a  facing the sound line  24  and a peripheral portion  28   b  facing away from the sound line  24 . In the embodiment example represented, the two peripheral portions  28   a,    28   b  are complementary to each other to form the whole periphery of the exhaust-gas line  18 . 
     A second perforation  30  is provided in the peripheral portion  28   b  facing away from the sound line  24 . The peripheral portion  28   a  facing the sound line  24  is designed perforation-free. 
     The sound generated by the sound-generating unit  22  which has already reached the abovementioned annular space, can thus interact with the exhaust gas flow present inside the exhaust-gas line  18  via the first perforation  38  and/or the second perforation  30 . 
     Here, the openings comprised by the second perforation  30  each have a substantially rectangular cross section, wherein the short sides of the rectangle are each oriented in peripheral direction and the long sides of the rectangle are each oriented in axial direction of the exhaust-gas line  18 . 
     Furthermore, the exhaust-gas line  18  has an axial bend  32  in an area upstream of the sound coupling-in line  26  which is designed as a 90° bend in the embodiment example represented. 
     The second perforation  30  and the axial bend  32  are arranged relative to each other such that the second perforation  30  is positioned downstream of a convex area of the axial bend  32 . 
     Moreover, the exhaust system  14  represented comprises a radial rib  34  in each of the border areas between the peripheral portion  28   b  facing away from the sound line  24  and the peripheral portion  28   a  facing the sound line  24 . 
     These can be designed in different ways. 
     In the variant according to  FIG. 6 , the radial rib  34  is attached to an inner surface of the sound coupling-in line  26  and extends in the direction of the exhaust-gas line  18 . Here, a radial distance  36  can be provided between the end of the radial rib  34  lying inside and the exhaust-gas line  18 . Equally, the radial rib  34  can touch the exhaust-gas line  18  or be connected thereto. 
     Alternatively, according to  FIG. 7 , the radial rib  34  can be attached to the exhaust-gas line  18  and extend in the direction of the sound coupling-in line  26 . A radial distance  36  can again be provided which results between the outer end of the radial rib  34  and the sound coupling-in line  26 . It is equally conceivable that the radial rib  34  touches the sound coupling-in line  26  with its outer end or is connected to same. 
     Instead of a single radial rib  34  in each border area between the peripheral portion  28   a  facing the sound line  24  and the peripheral portion  28   b  facing away from the sound line  24 , a radial rib pair can also be provided which comprises radial ribs  34   a,    34   b.  In this connection, the radial rib  34   a  is attached to the sound coupling-in line  26  and extends in the direction of the exhaust-gas line  18 . In contrast, the radial rib  34   b  is attached to the exhaust-gas line  18  and extends in the direction of the sound coupling-in line  26 . 
     In peripheral direction, the radial ribs  34   a,    34   b  are only slightly spaced apart from each other or touch each other. 
     In radial direction, the radial rib  34   a  radiating from the sound coupling-in line  26  has a radial distance  36   a  from the exhaust-gas line  18  at its inner end. The radial rib  34   b  radiating from the exhaust-gas line  18  leaves a radial distance  36   b  free between its outer end and the sound coupling-in line  26 . 
     In all variants, the radial ribs  34 ,  34   a,    34   b  are shorter in an axial direction of the exhaust-gas line  18  and of the sound coupling-in line  26  arranged concentric thereto than the sound coupling-in line  26 . Thus, there is an axial portion of the sound coupling-in line  26  in which there can be flow around the radial ribs  34 ,  34   a,    34   b  in peripheral direction of the exhaust-gas line  18 . To be more precise, the radial ribs  34 ,  34   a,    34   b  extend merely in the area of the second perforation  30 . 
     The mode of operation of the exhaust system  14  is as follows. 
     The sound generated by the sound-generating unit  22  flows via the sound line  24  into the sound coupling-in line  26 . There, it enters into the inside of the exhaust-gas line  18  via the openings of the first perforation  38 . Furthermore, after the sound has flowed around the radial ribs  34 ,  34   a,    34   b  in the area of the first perforation  38 , it also passes into the inside of the exhaust-gas line  18  via the openings of the second perforation  30 . In this way, a sound carried by the exhaust gas flow inside the exhaust-gas line  18  is actively muffled. 
     However, hot exhaust gas can also flow via the openings of the first perforation  38  and the second perforation  30  from the inside of the exhaust-gas line  18  into the annular space formed by the exhaust-gas line  18  and the sound coupling-in line  26 . The active silencing device  20  and in particular the sound-generating unit  22  are to be protected against these hot exhaust gases. 
     Exhaust gas exiting via the openings of the second perforation  30  must first flow around the radial ribs  34 ,  34   a,    34   b  on its path in the direction of the sound-generating unit  22 . Here, the radial ribs  34 ,  34   a,    34   b  represent a flow obstacle on the one hand and cool the exhaust gas on the other. 
     In addition, because of the flow ratios inside the exhaust-gas line  18 , a large part of the exhaust gas which has exited via the openings of the second perforation  30  is conducted back inside the exhaust-gas line  18  via the openings of the first perforation  38 . This is due to the fact that inside the exhaust-gas line  18  a higher pressure prevails in the area of the second perforation  30  than in the area of the first perforation  38 . In the annular space, the pressure ratios are reversed, with the result that a higher static pressure prevails in the area of the first perforation  38 . This also serves to protect the sound-generating unit  22  against high temperatures. 
     A direct flow of hot exhaust gas into the sound-generating unit  22  is also prevented in that the peripheral portion  28   a  facing the sound line  24  is designed perforation-free. 
     Although various embodiments have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this disclosure. For that reason, the following claims should be studied to determine the true scope and content of this disclosure.