Exhaust system

Abstract

Exhaust system (1) for exhaust gas routing and exhaust gas aftertreatment in a motor vehicle, comprising a first exhaust pipe element (13) having an inlet opening (15) and an outlet opening (17), and a second exhaust pipe element (19) having a longitudinal axis overflow pipe (21) with a shell surface (23) and a first closed end (25), wherein an inlet opening (31) is provided in the shell surface (23) adjacent to the closed end (25), wherein the overflow pipe (21) projects into the outlet opening (17) and is received in the first exhaust pipe element (13) with its closed end (25) and the inlet opening (31),so that exhaust gas flowing in a first direction through the inlet opening (15) can flow through the inlet opening (31) into the overflow pipe (21) and – viewed in the direction of the longitudinal axis of the overflow pipe (21) – can flow out of the first exhaust pipe element (13) through the outlet opening (17) in the overflow pipe (21), and with an injector unit (35) attached to the first exhaust pipe element (13) for introducing a reducing agent into an exhaust gas flow flowing through the first and the second exhaust pipe elements (13, 19), characterized in that the longitudinal axis of the overflow pipe (21) is substantially perpendicular to the first direction, and that the injector unit (35) is arranged and designed in such a way thatthat reducing agent injected by the injector unit (35) can be injected upstream of the inlet opening (31) into the first exhaust pipe element (13) and the first exhaust pipe element (13) has a flow chamber (45) located upstream of the inlet opening (15) and facing away from the overflow pipe (21) of the inlet opening (15) when viewed in the first direction, wherein the injector unit (35) is arranged and oriented such that an injection jet (47, 47') is directed into the flow chamber (45), wherein the injection jet (47, 47') is directed approximately parallel to, at most at an acute angle to, the longitudinal axis of the overflow pipe (21) and away from the inlet opening (31), and in the flow chamber (45) at least one substantially plate-shaped impact element (49, 49', 49") is attached to the overflow pipe (21). and / or is attached to the first exhaust pipe element (13), wherein the impact element (49, 49', 49") has an impact surface (51, 51') facing the injector unit (35).51"), the normal vector of which is substantially parallel to the longitudinal axis of the overflow pipe (21), wherein the baffle element (49, 49', 49") overlaps the inlet opening (31) along a direction oriented transversely to the longitudinal axis.

Description

[0001] The invention relates to an exhaust system for exhaust gas routing and exhaust gas aftertreatment in a motor vehicle according to the preamble of claim 1.

[0002] Exhaust systems of the type discussed here are well-known. They serve two purposes: firstly, to guide exhaust gases within the exhaust stream of an internal combustion engine, and secondly, to treat the exhaust gas, particularly to reduce particle and / or pollutant concentrations. Typically, to reduce nitrogen oxides, liquid reducing agents such as petroleum-based fuel or an aqueous urea solution are injected into the exhaust gas flowing through the system. To achieve efficient pollutant reduction and the most complete chemical reaction possible, it is necessary to vaporize the reducing agent and distribute it as evenly as possible within the exhaust gas stream. In the case of aqueous urea solutions, the urea must be converted to ammonia by hydrolysis and / or thermolysis so that selective catalytic nitrogen oxide reduction can subsequently be carried out.

[0003] European patent application EP 2 128 398 A1 discloses an exhaust system comprising a first exhaust pipe element with an inlet opening and an outlet opening, wherein the first exhaust pipe element is designed as the outlet funnel of a particulate filter. A second exhaust pipe element is provided, which has a transfer pipe with a longitudinal axis and a circumferential surface. This transfer pipe projects into the outlet opening of the first exhaust pipe element and, with its end projecting into the outlet opening, rests tightly against a wall of the first exhaust pipe element, so that the first end is closed. Adjacent to the closed end, a plurality of inlet openings are provided in the circumferential surface, which are designed as rectangular slits and are regularly distributed – viewed in the circumferential direction – over the circumferential surface. Thus, the transfer pipe has inlet openings adjacent to the first, closed end along its entire circumference.It is received with its closed end and inlet openings in the first exhaust pipe element, so that exhaust gas flowing in through the inlet openings in a first direction can flow through the inlet openings into the transfer pipe. The exhaust gas then flows – viewed in the direction of the transfer pipe's longitudinal axis – out of the first exhaust pipe element through the outlet opening. An injector unit for introducing a reducing agent into the exhaust gas stream is provided on the first exhaust pipe element.

[0004] It becomes apparent that the longitudinal axis of the bypass pipe is parallel to the direction in which exhaust gas flows through the inlet opening into the first exhaust pipe element. Therefore, in order to pass from the inlet opening into the bypass pipe and through it to the outlet opening, the exhaust gas must be deflected by approximately 180°. Specifically, the exhaust gas must first be deflected by approximately 90° to be able to flow into the inlet openings, starting from the inlet opening. Within the bypass pipe, a further deflection of approximately 90° occurs. This results in a relatively convoluted flow path for the exhaust gas, which is accompanied by a pressure drop.A swirl of exhaust gas formed in the overflow pipe, which serves to mix the injected reducing agent with the exhaust gas, exhibits a reduced swirl number because the exhaust gas has already lost kinetic energy during the first 90° bend from the inlet opening to the inlet openings. Furthermore, it is evident that the injector unit is arranged such that the reducing agent is injected into the overflow pipe downstream of the inlet openings. For this reason, a mixing section located downstream of the inlet openings for the vaporization and mixing of the reducing agent with the exhaust gas must be comparatively long, which negatively impacts the overall length of the second exhaust pipe element and thus also of the exhaust system as a whole.

[0005] GB 2 381 218 A discloses an exhaust system for exhaust gas routing and aftertreatment in a motor vehicle. A first exhaust pipe element has an inlet opening and an outlet opening. A second exhaust pipe element has a longitudinally oriented transfer pipe with a shell surface and a first, closed end, wherein an inlet opening is provided in the shell surface adjacent to the closed end. The transfer pipe projects into the outlet opening and is received in the first exhaust pipe element with its closed end and the inlet opening, so that exhaust gas flowing in through the inlet opening in a first direction can flow through the inlet opening into the transfer pipe and, viewed in the direction of the longitudinal axis of the transfer pipe, can flow out of the first exhaust pipe element through the outlet opening in the transfer pipe.An injector unit for introducing a reducing agent into the exhaust gas flow passing through the first and second exhaust gas pipe elements is attached to the first exhaust gas pipe element. The longitudinal axis of the transfer pipe is essentially perpendicular to the first direction, and the injector unit is arranged and designed such that the reducing agent injected by the injector unit can be sprayed upstream of the inlet opening into the first exhaust gas pipe element.

[0006] The invention is therefore based on the objective of creating an exhaust system which has an increased swirl number with optimal utilization of the kinetic flow energy of the exhaust gas and a comparatively compact design with the shortest possible mixing distance.

[0007] The problem is solved by creating an exhaust system with the features of claim 1.

[0008] Because the longitudinal axis of the transfer pipe is essentially perpendicular to the direction in which the exhaust gas flows through the inlet opening into the first exhaust pipe element, the incoming exhaust gas can pass from the inlet opening to the inlet opening without deflection, particularly without a 90° deflection. This largely prevents a loss of kinetic energy in the exhaust gas flow, allowing a high swirl to develop as the exhaust gas enters the transfer pipe. Since the reducing agent injected by the injector unit can be injected upstream of the inlet opening into the first exhaust pipe element, injection occurs early in the flow direction, thus optimizing the use of the mixing section, especially in the transfer pipe. At the same time, the reducing agent preferably evaporates at least partially before entering the transfer pipe.Together with the highly efficient swirl with a high swirl number, this results in rapid evaporation and mixing of the reducing agent with the exhaust gas, thereby accelerating the hydrolysis and / or thermolysis of urea. The mixing section itself can therefore be shorter than in the known exhaust system, which has a beneficial effect on the length of the second exhaust pipe element and thus also on the entire exhaust system.

[0009] Preferably, the inlet opening connects directly to the closed end of the overflow pipe, meaning that – viewed longitudinally – it is either not spaced from it or only very slightly. However, it is possible for the inlet opening to have a small distance to the closed end compared to its longitudinal extent.

[0010] The bypass pipe projects into the outlet opening in such a way that the inlet opening is located entirely within the first exhaust pipe element. It is designed to be as short as possible, preferably extending only slightly further into the first exhaust pipe element than the longitudinal extent of the inlet opening. Consequently, the distance – measured longitudinally – between the closed end of the bypass pipe and the inlet opening is minimized to avoid unnecessarily extending the length of the bypass pipe into the first exhaust pipe element and to prevent dead zones for the exhaust flow.

[0011] The overflow pipe is preferably positively engaged in the outlet opening. An edge of the outlet opening thus surrounds the overflow pipe in a contoured or negatively shaped fit, preferably sealing it so that no exhaust gas can escape from the first exhaust pipe element between an edge of the outlet opening and the outer surface of the overflow pipe. Particularly preferably, the overflow pipe is additionally bonded to the first exhaust pipe element in the area of ​​the outlet opening, preferably welded. This results in a particularly tight connection. All the exhaust gas flowing into the first exhaust pipe element through the inlet opening must therefore flow out of the first exhaust pipe element via the inlet opening and through the overflow pipe, as no other flow path leads out of it.

[0012] Using the injector unit, an aqueous urea solution is preferably injected into the exhaust gas stream, the urea being converted to ammonia in the mixing section by hydrolysis and / or thermolysis. Downstream of the mixing section, a catalytically active element, in particular a catalyst for carrying out selective catalytic reduction, is preferably provided, which reacts the nitrogen oxides with the ammonia to form elemental nitrogen and water. However, in one embodiment of the exhaust gas system, it is also possible to inject a different reducing agent, preferably liquid in its initial state, such as a petroleum-based fuel, into the exhaust gas stream using the injector unit.

[0013] The first exhaust pipe element has a flow chamber located upstream of the inlet opening, facing away from the inlet opening's overflow pipe when viewed in the first direction. This means that, viewed in the exhaust gas flow direction from the inlet opening, a flow chamber is located downstream of the overflow pipe. In this chamber, the exhaust gas flowing around the overflow pipe collects upstream of the inlet opening (which faces away from the inlet opening) before entering the overflow pipe. The injector unit is arranged and oriented such that its injection jet is directed into this flow chamber. The term "injection jet" refers both to the reducing agent injected by the injector unit and to the spray pattern of the injector unit, which is essentially conical.The emitted cone of reducing agent opens in a direction away from the injector unit. The injection jet, in particular a longitudinal axis of the emitted cone, is preferably oriented approximately parallel to, or at most at an acute angle to, the longitudinal axis of the overflow pipe and is particularly preferably directed away from the inlet opening. The injector unit is preferably mounted on the first exhaust pipe element in close proximity to the closed end of the overflow pipe, so that the injection jet originates from a region located close to the closed end and propagates away from the inlet opening or the overflow pipe at a preferably small, acute angle along its propagation direction.

[0014] Preferably, the injector unit is designed to inject a plurality of spray cones, particularly preferably two spray cones, into the flow chamber, wherein the spray cones are arranged one behind the other in a direction that is oriented perpendicular to the longitudinal direction of the overflow pipe and parallel to the first direction. Preferably, the longitudinal axis of the spray cone furthest from the overflow pipe (viewed in the first direction) has a larger angle to the longitudinal axis of the overflow pipe than that of a correspondingly front spray cone.

[0015] In any case, the reducing agent is injected upstream of the inlet opening into the flow chamber formed by the first exhaust pipe element, i.e., it is mixed with the exhaust gas stream at a point where the latter has not yet entered the overflow pipe and thus the second exhaust pipe element. This results in a comparatively early mixing of the reducing agent with the hot exhaust gas coming from the oxidation catalyst. This promotes evaporation of the reducing agent, which is also mixed particularly efficiently with the exhaust gas flowing into the overflow pipe, forming a swirl, preferably a double swirl. This allows the mixing distance to be shortened, and a particularly homogeneous mixing occurs, which is further enhanced by the formation of a double vortex.In particular, injecting the gas directly in front of the inlet opening proves advantageous, because this creates an intense, rapid exhaust gas flow into the overflow pipe, which carries away, swirls and evaporates the reducing agent.

[0016] The flow chamber contains at least one substantially plate-shaped baffle element, which is attached to the overflow pipe and / or the first exhaust pipe element. Preferably, the baffle element is welded to the overflow pipe and / or the first exhaust pipe element. It is possible that the baffle element is attached exclusively to the overflow pipe, preferably welded to it. It is also possible that the baffle element is attached exclusively to the first exhaust pipe element, preferably welded to it. Finally, it is possible that the baffle element is attached to both the overflow pipe and the first exhaust pipe element, preferably welded to them. The baffle element has an impact surface facing the injector unit, the normal vector of which is oriented substantially parallel, preferably exactly parallel, to the longitudinal axis of the overflow pipe.The baffle element preferably extends across the inlet opening along a direction that is transverse, preferably perpendicular, to the longitudinal axis of the overflow pipe. The baffle element, preferably designed as a baffle plate, is arranged in the flow chamber such that it is at least partially struck by the at least one injection jet. Reducing agent striking the baffle element preferably rebounds from it, with the rebounding droplets bursting into smaller droplets and thus evaporating more rapidly.

[0017] The baffle element is heated by heat conduction through contact with a wall of the overflow pipe and / or a wall of the exhaust duct element, to which it is preferably attached. It is also heated by the flowing exhaust gas. Thus, the baffle element acts as a vaporizing element, transferring heat of vaporization to the impacting reducing agent. Separate heating of the at least one baffle element is also possible. Furthermore, the baffle element preferably has a temperature above the Leidenfrost temperature of the reducing agent. This ensures efficient vaporization and efficient rebound of reducing agent droplets on the baffle element.

[0018] Preferably, the injection jet also strikes a wall of the first exhaust pipe element. Here, too, droplets preferably bounce off or reducing agent evaporates on the hot wall.

[0019] To promote evaporation on the impact surface of the impact element, this surface can have a textured surface, preferably comprising bumps. Alternatively or additionally, a roughening and / or a coating can be provided. A preferred surface roughness is in the range of at least 5 µm to at most 50 µm. A catalytic coating that promotes the thermolysis and / or hydrolysis of urea is preferably provided as the coating. It is also possible to provide a coating that additionally or alternatively counteracts the formation of deposits, particularly deposits of urea decomposition products. The coating of the impact surface preferably comprises titanium dioxide; it is particularly preferably made of titanium dioxide.

[0020] Because the reducing agent is at least partially evaporated and / or subjected to hydrolysis or thermolysis upon contact with at least one impact element and / or the wall of the first exhaust pipe element before entering the inlet opening of the bypass pipe, the efficiency of the mixing section is significantly increased. This allows the section to be shortened, resulting in a particularly compact exhaust system.

[0021] The at least one impact element and / or the injector unit are preferably arranged relative to each other such that the injection jet strikes the impact surface at an angle of incidence of preferably less than 45° relative to a normal vector. Particularly preferably, the reducing agent is injected such that it strikes the impact surface at least approximately perpendicularly, thereby achieving particularly good wetting of the surface.

[0022] The at least one baffle element is preferably also oriented substantially parallel to the exhaust gas flow flowing around the overflow pipe and into the inlet opening. This ensures that the at least one baffle element forms a minimal flow resistance for the exhaust gas, thus minimizing or preventing pressure loss in the area of ​​the baffle element and thereby intensifying the evaporation, interaction, and mixing of the reducing agent with the exhaust gas in the area of ​​the baffle element.

[0023] A preferred exhaust system is characterized by a cylindrical overflow pipe, at least in the region of the inlet opening. Preferably, the cylindrical geometry includes an oval base, so that the overflow pipe has an oval cross-section. Exhaust gas flowing into the oval overflow pipe through the preferably centrally located inlet opening forms a double vortex, which enables particularly efficient mixing of the reducing agent injected into the exhaust gas stream. The geometry of the overflow pipe is preferably selected to form two counter-rotating exhaust gas flow vortices with an approximately circular cross-section. In this case, the vortices are particularly stable and therefore preferably remain intact over the entire length of the mixing section.

[0024] In another embodiment, the overflow pipe may have a cross-sectional shape corresponding to two adjacent circular segments. In this case as well, particularly if the inlet opening is centrally located, it is possible to form a stable double vortex in the overflow pipe that is maintained along the entire length of the mixing section. The length of the mixing section is preferably at least 200 mm up to 300 mm or even more.

[0025] In yet another embodiment, the overflow pipe can be cylindrical with a circular base. In this case, the inlet opening is preferably off-center and, in particular, arranged so that the exhaust gas flows tangentially into the overflow pipe. This creates a stable single vortex, which also ensures good mixing of the reducing agent with the exhaust gas.

[0026] If the overflow pipe has an oval cross-section, the ratio of the longer cross-sectional axis to the shorter cross-sectional axis is at least 1.5 and at most 2. If the exhaust system is used in conjunction with an internal combustion engine of a motor vehicle with a displacement of approximately 1.6 liters to 3.5 liters, the length of the shorter cross-sectional axis is preferably at least 30 mm and at most 100 mm. Of course, embodiments with different dimensions or ratios are possible.

[0027] A preferred exhaust system is characterized by the fact that the bypass pipe has only one inlet opening. This inlet opening is arranged facing away from the inlet opening of the first exhaust pipe element, so that the exhaust gas flowing in through the inlet opening must first flow around the bypass pipe before it can then flow into the bypass pipe through the inlet opening, as it were, in the opposite direction to the inlet. By flowing around the bypass pipe, the exhaust gas already acquires a swirl and flows into the bypass pipe with a tangential velocity component. Particularly preferred is the bypass pipe being surrounded on both sides by the exhaust gas flow, which is thus divided into two partial flows that – viewed in the direction of flow – flow past the bypass pipe to the right and left and meet behind it in the region of the inlet opening.The partial flows entering the overflow pipe exhibit tangential velocity components pointing in opposite directions, so that a very stable double vortex is formed in a particularly efficient manner and with a high swirl number.

[0028] Preferably, a wall of the first exhaust pipe element is curved inwards in the region of the closed end of the second exhaust pipe element so that it seals tightly against the closed end. This prevents exhaust gas from flowing over the closed end of the bypass pipe and thus reaching the inlet opening. The entire exhaust gas flow must therefore flow around the bypass pipe to the inlet opening, which increases the stability and swirl number of the resulting vortex, particularly the double vortex.

[0029] The inlet opening preferably has a larger dimension along the longitudinal axis of the transfer pipe than transversely to it. Thus, viewed longitudinally, it is elongated, with the ratio of its longitudinal dimension to its transverse dimension preferably being at least 1.5 to at most 4. Particularly preferably, the inlet opening is designed as a slit with a substantially rectangular opening. The ratio of the long side of the rectangle to its short side is preferably at least 1.5 to at most 4. It is possible for the substantially rectangular opening to be rounded at the corners. In particular, the rectangular slit shape of the inlet opening enables a particularly stable formation of a double vortex in the exhaust gas flow within the transfer pipe.

[0030] The inlet opening preferably extends over the entire length of the overflow pipe projecting into the first exhaust pipe element, i.e., from an inner side of the outlet opening to the closed end. The shorter transverse dimension of the inlet opening is preferably smaller than the shorter cross-sectional axis of the oval overflow pipe.

[0031] An exhaust system is also preferred which is characterized in that the first exhaust pipe element is designed as the outlet funnel of an oxidation catalyst. Particularly preferably, the inlet opening effectively covers one outlet side of the oxidation catalyst, so that the first exhaust pipe element is arranged as an exhaust collector element at one outlet of the oxidation catalyst. Thus, the exhaust system as a whole is preferably designed such that the overflow pipe projects into the outlet funnel of the oxidation catalyst. The mixing device formed by the injector unit and the overflow pipe is also arranged directly downstream of the oxidation catalyst, preferably flanged to it.

[0032] In this context, an exhaust system is also preferred in which the first exhaust pipe element is shaped like a cowl. Here, an imaginary plane defined by the inlet opening—namely, an imaginary plane on which the exhaust gas flow through the inlet opening is perpendicular—is oriented essentially, preferably exactly, perpendicular to an imaginary plane defined by the outlet opening—namely, an imaginary plane on which the exhaust gas flow through the outlet opening is perpendicular. Thus, the exhaust gas flow is redirected by essentially, preferably exactly, 90° from the inlet opening to the outlet opening. The first exhaust pipe element covers the overflow pipe projecting into it. Therefore, the arrangement consisting of the first exhaust pipe element and the second exhaust pipe element together has the shape of a cowl.The 90° deflection of the exhaust gas flow occurs essentially when the exhaust gas flows into the overflow pipe, where, starting from the inlet opening, it impacts an opposite wall of the overflow pipe, thereby forming a vortex, in particular a double vortex, and deflecting the exhaust gas flow by 90° because the overflow pipe is closed at its first end, which projects into the first exhaust pipe element.

[0033] A preferred exhaust system is characterized by the inclusion of multiple baffle elements. Particularly preferred are at least three, and preferably up to eight, baffle elements. Preferably, the baffle elements are arranged one behind the other, viewed along the longitudinal axis of the overflow pipe, and preferably parallel to each other with respect to their impact surfaces. The normal vectors of the impact surfaces therefore preferably point at least approximately in the same direction. This makes it possible, in particular, for multiple rebounds of the reducing agent to occur at different baffle elements, with each rebound causing a droplet to break up into smaller droplets, thus significantly accelerating the evaporation of the reducing agent.

[0034] In this context, an exhaust system is also preferred which is characterized by the fact that the baffle elements each have a recess in the baffle surface. This recess is preferably arranged such that the injection jet is directed partially onto the recess. This means that part of the reducing agent emitted by the injector unit passes through the recess, while another part strikes the baffle surface surrounding the recess, so that the injection jet is ultimately deflected by the baffle elements. This results in vortex formation at the edges of the recesses, which further improves the mixing of the reducing agent with the exhaust gas and its vaporization.

[0035] In this context, an exhaust system is preferred which is characterized by the fact that the defined passage areas of the baffle elements decrease along a sequence of baffle elements when viewed in the direction of the injection jet. The passage areas for the reducing agent decrease from baffle element to baffle element, with the passage area of ​​each baffle element decreasing from baffle element to baffle element in the direction of the injection jet. This results in a more pronounced skimming of the injection jet from baffle element to baffle element, which improves vortex formation at the edges, the rebound behavior, the vaporization behavior, and thus the hydrolysis and / or thermolysis, and ultimately the mixing of the reducing agent with the exhaust gas. Preferably, the depth of the passages – measured in a direction perpendicular to a plane defined by the inlet opening – decreases from baffle element to baffle element.Additionally or alternatively, it is preferably provided that the width of the recesses – measured perpendicular to the depth – also decreases from one impact element to the next. In a particularly preferred embodiment, both the depth and the width of the recesses decrease – viewed in the direction of the injection jet – along the sequence of impact elements.

[0036] A preferred exhaust system is characterized by the fact that the injector unit is arranged and aligned such that the injection jet is symmetrically positioned with respect to a plane of symmetry defined by the first direction and the longitudinal direction, which symmetrically divides the inlet opening. The plane of symmetry is thus determined by the fact that it encompasses both the first direction, i.e., the flow direction of the exhaust gas through the inlet opening, and the longitudinal direction of the transfer pipe. The position of the plane of symmetry is further defined by the fact that it symmetrically divides the inlet opening into two equal half-surfaces. The injector unit is then arranged and aligned such that the injection jet is also preferably arranged in a mirror-symmetrical manner with respect to this plane of symmetry.

[0037] In this context, it is also preferred that the at least one baffle element, preferably all baffle elements, are designed and arranged in a mirror-symmetrical manner with respect to the plane of symmetry. This results in an overall mirror-symmetrical arrangement of the geometry of the preferably oval overflow pipe, the injector unit, the injection jet, and the baffle elements. In particular, if the overflow pipe is oval, a double vortex is created that is mirror-symmetrical with respect to the plane of symmetry. Due to the symmetrically arranged injector unit, the symmetrical injection jet, and the symmetrical baffle elements, a particularly homogeneous and uniform distribution of the reducing agent is achieved within the symmetrical double vortex. This ensures that the reducing agent is distributed homogeneously throughout the entire exhaust gas stream, thus minimizing pollutant concentration.

[0038] A preferred exhaust system is also one in which the inlet opening furthest from the inlet opening is designed as the main inlet opening, which preferably has a larger extent in the direction of the longitudinal axis of the transfer pipe than transversely to it, and is particularly preferably designed as a slit-like and substantially rectangular passage surface, and in which at least one secondary inlet opening is further provided in the outer surface of the transfer pipe, which – viewed along the first direction – is preferably arranged laterally to the main inlet opening. The secondary inlet opening preferably has a smaller cross-sectional area than the main inlet opening. It preferably has a larger extent in the direction of the longitudinal axis of the transfer pipe than transversely to it. It is particularly preferably designed as a slit with a rectangular passage surface.Preferably, both the main inlet opening and the at least one secondary inlet opening are designed as rectangular slots, with the secondary inlet opening preferably having a smaller through-area than the main inlet opening. The lateral arrangement of the secondary inlet opening allows exhaust gas flowing laterally past the overflow pipe to enter it. This reduces the pressure loss of the exhaust gas as it flows around the overflow pipe, thereby reducing the overall height (measured longitudinally) and width (measured transversely) of the flow channels surrounding the overflow pipe. This results in a more compact exhaust system. The secondary inlet opening also promotes swirl formation, particularly when the exhaust gas enters the overflow pipe as tangentially as possible.

[0039] A particularly preferred exhaust system features two secondary inlet openings arranged in a mirror-symmetrical fashion with respect to a plane of symmetry defined by the first direction and the longitudinal axis, which divides the main inlet opening symmetrically and corresponds to the previously defined plane of symmetry. Thus, secondary inlet openings are provided on the left and right sides of the transfer pipe's outer surface – viewed in the direction of exhaust gas flow through the inlet opening – allowing exhaust gas flowing around the transfer pipe to enter it. This significantly reduces the pressure loss associated with the flow around the pipe, further enabling a reduction in the height and width of the flow channels surrounding the transfer pipe.

[0040] Preferably, a larger portion of the exhaust gas flow continues to flow completely around the bypass pipe and enters it through the main inlet opening. A preferably smaller portion of the exhaust gas flow enters laterally through the secondary inlet openings, where it contributes to the formation of the vortex, in particular the double vortex.

[0041] Furthermore, all features, including the at least one baffle element preferably provided in this area, previously described for the inlet opening, and in particular for the single inlet opening, are preferably implemented for the main inlet opening. The embodiment described here therefore differs from the previously described embodiments preferably only in that at least one, preferably two, secondary inlet openings are provided.

[0042] A preferred exhaust system comprises an at least one secondary inlet opening with at least one flow guide element through which the exhaust gas can be directed substantially tangentially into the overflow pipe. This particularly favorably promotes the formation of swirl, especially double vortex, because the exhaust gas is guided tangentially into the overflow pipe through the at least one secondary inlet opening and thus acquires a tangential velocity component. The flow guide element is preferably designed as a portion of the overflow pipe's outer surface that is bent outwards and / or inwards when viewed radially, i.e., in a direction perpendicular to the longitudinal direction.Particularly preferred are both an outwardly and an inwardly bent area of ​​the shell surface along the entire longitudinal extent of the secondary inlet opening, resulting in a particularly favorable flow direction in the tangential direction.

[0043] Due to the highly efficient mixing and evaporation of the reducing agent in the area of ​​the inlet opening and the overflow pipe, a separate mixer for distributing the reducing agent injected into the exhaust gas is unnecessary. This also avoids the pressure loss otherwise caused by the mixer, which is advantageous for the exhaust system and especially for downstream exhaust aftertreatment components.

[0044] Preferably, the entire geometric design of the exhaust system, in particular the cross-sectional dimensions of the transfer pipe and the dimensions of the inlet opening, is selected such that a swirl number of at least 0.3 is achieved for the exhaust swirl in the transfer pipe, based on each individual vortex of the double vortex. In particular, the geometry of the exhaust system is designed, depending on the displacement of the internal combustion engine, such that an inlet swirl number of at least 0.3 is achieved.

[0045] The invention will be explained in more detail below with reference to the drawing. The drawing shows: Fig. 1 a schematic longitudinal section view of a first embodiment of an exhaust system; Fig. 2 an enlarged detailed view of the exhaust system according to Fig. 1; Fig. 3 a partially cutaway, three-dimensional representation of an embodiment of an exhaust system according to the Fig. 1 and Fig. 2, and Fig. 4 a partially cut-away, three-dimensional representation of a second embodiment of an exhaust system.

[0046] Fig. Figure 1 shows a schematic longitudinal section of a first embodiment of an exhaust system 1. This system serves for exhaust gas routing and aftertreatment in a motor vehicle. It comprises a first exhaust aftertreatment element 3, a mixing device 5 by means of which a reducing agent is mixed with the exhaust gas stream, the mixing device 5 having a mixing section 7, and a second exhaust aftertreatment element 9.

[0047] Exhaust gas flows in the direction of arrow P from an internal combustion engine into the first exhaust aftertreatment element 3. It flows through this element and thus reaches the mixing device 5, where it is mixed with the reducing agent. The mixing and homogenization is intensified along the mixing section 7 until the exhaust gas finally enters the second exhaust aftertreatment element 9. It then exits this element in the direction of an exhaust pipe (not shown). It is entirely possible that further exhaust aftertreatment elements are connected to the second exhaust aftertreatment element 9. Likewise, it is possible that – viewed in the direction of exhaust gas flow – further exhaust aftertreatment elements are provided upstream of the first exhaust aftertreatment element 3.

[0048] The first exhaust aftertreatment element 3 is designed here as an oxidation catalyst 11, particularly preferably as a diesel oxidation catalyst.

[0049] The exhaust system 1, in particular the mixing device 5, comprises a first exhaust pipe element 13 having an inlet opening 15 and an outlet opening 17. A second exhaust pipe element 19, which is particularly associated with the mixing section 7, comprises a transfer pipe 21, which has a Fig. 1. A longitudinal axis extending in a vertical direction, a lateral surface 23, and a first, closed end 25. A second, open end 27 preferably merges integrally into another end 27, also encompassed by the second exhaust pipe element 19, in which Fig. 1 illustrated embodiment curved exhaust pipe 29, which is part of the mixing section 7, and through which exhaust gas flows to the second exhaust aftertreatment element 9.

[0050] In the outer surface 23, an inlet opening 31 is provided adjacent to the closed end 25, which is arranged facing away from the inlet opening 15 of the first exhaust gas line element 13 - viewed in the direction of exhaust gas flow.

[0051] It is evident that the first exhaust gas duct element 13 is designed here as the outlet funnel 33 of the oxidation catalyst 11. It is also shaped like a cowl, in that an imaginary plane defined by the inlet opening 15, whose normal vector is parallel to the flow direction of the exhaust gas flowing into the first exhaust gas duct element 13, is essentially perpendicular to an imaginary plane defined by the outlet opening, whose normal vector is again oriented parallel to the flow direction of the outgoing exhaust gas. The overflow pipe 21 projects into the cowl-shaped outlet funnel 33 through the outlet opening 17, with the closed end 25 and the inlet opening 31 being accommodated within it.

[0052] In the area of ​​the outlet opening 17, the overflow pipe 21 is positively engaged in the outlet funnel 33, the geometry of the outlet opening 17 preferably being negatively shaped compared to the cross-sectional shape of the overflow pipe 21 at the location of the outlet opening 17. Additionally, the overflow pipe 21 is preferably welded to the outlet funnel 33 in the area of ​​the outlet opening 17, resulting in a positive-locking and material-locking, tight connection. Therefore, it is not possible for exhaust gas from the first exhaust pipe element 13 to escape past the outer surface 23 of the overflow pipe 21 and through the outlet opening 17. Instead, all exhaust gas flowing into the first exhaust pipe element 13 must enter the overflow pipe 21 through the inlet opening 31 and thus into the second exhaust pipe element 19, and from there through the exhaust pipe 29 to the second exhaust aftertreatment element 9.

[0053] The mixing device 5 further comprises an injector unit 35 attached to the first exhaust gas line element 13, through which a reducing agent, preferably liquid in its initial state, preferably an aqueous urea solution, can be injected into the exhaust gas stream.

[0054] It is evident that the exhaust gas flowing in along the direction indicated by arrow P flows through the oxidation catalyst 11 in the same direction and continues along this direction through the inlet opening 15 into the first exhaust pipe element 13, namely the outlet funnel 33. This flow direction is also referred to as the first direction. It is further evident that the longitudinal axis of the transfer pipe 21 is perpendicular to the first direction indicated by arrow P. Thus, the exhaust gas is not deflected by approximately 90° before reaching the transfer pipe 21, as in the known exhaust system, but rather flows towards it along the first direction in which it also passed through the oxidation catalyst 11. This effectively avoids or minimizes pressure loss.

[0055] It is further shown that the injector unit 35 is arranged and designed such that the reducing agent injected into the exhaust gas stream is injected upstream of the inlet opening 31 into the first exhaust gas line element 13. This will be explained in more detail below. In the injection area upstream of the inlet opening 31, in the overflow pipe 21, and in the mixing section 7, the reducing agent mixes with the exhaust gas. If the reducing agent is an aqueous urea solution, the urea is further converted to ammonia by thermolysis and / or hydrolysis.

[0056] The mixture of exhaust gas and reducing agent passes through the exhaust pipe 29 to the second exhaust aftertreatment element 9, which is designed as a filter or catalytic element and preferably comprises first a particulate filter 37, in particular a diesel particulate filter, and – viewed in the direction of exhaust gas flow – immediately downstream of this a catalytic exhaust gas purification unit, in particular a catalyst for a selective catalytic reaction, namely a so-called SCR catalyst 39, a hydrolysis catalyst, an oxidation catalyst and / or a nitrogen oxide storage catalyst. The particulate filter 37 is preferably coated with a material that exhibits catalytic properties in the sense of a selective catalytic reaction, so that a reduction of nitrogen oxides preferably takes place already in the particulate filter 37, which is then intensified and continued in the SCR catalyst 39.

[0057] Fig. Figure 2 shows a detailed enlargement of the embodiment of the exhaust system 1 according to Fig. 1. Identical and functionally equivalent elements are designated with the same reference numerals, so reference is made to the preceding description. The closed end 25 is preferably designed as a cover for the overflow pipe 21, or more preferably as a sealing sheet metal element welded to the outer surface 23. A wall 41 of the first exhaust pipe element 13 is curved inwards in a rear region 43 of the closed end 25 (viewed in the direction of exhaust gas flow) and is preferably tightly fitted to the closed end 25. Exhaust gas flowing into the first exhaust pipe element 13 therefore cannot flow over the overflow pipe 21, and in particular not over its closed end 25, but must instead flow laterally around the overflow pipe 21 to reach the side facing away from the inlet opening 15 and thus to the inlet opening 31.

[0058] In the illustrated embodiment, this is designed as a rectangular gap, the greater extent of which lies along the longitudinal axis of the overflow pipe 21. In the illustrated embodiment, the inlet opening 31 borders – viewed longitudinally – directly on the closed end 25 and extends – again viewed longitudinally – to the outlet opening 17.

[0059] It is possible that the inlet opening 31 does not directly adjoin the closed end 25, but is arranged at a distance from it. However, such a distance is preferably chosen to be significantly smaller than the longitudinal extent of the inlet opening 31 in order to avoid a dead zone in the region of the closed end 25, in which no efficient exhaust gas flow and, in particular, no mixing of the exhaust gas with the reducing agent takes place. It is also possible that the inlet opening 31 does not extend to the outlet opening 17, but is spaced from it – viewed longitudinally. In this case, however, the flow resistance for the exhaust gas formed by the inlet opening 31 is increased, which is why an embodiment in which the inlet opening 31 extends to the outlet opening 17 is preferred.

[0060] Based on Fig. Figure 2 also shows that the first exhaust pipe element 13 has a flow chamber 45 located – viewed in the first direction – away from the overflow pipe 21 of the inlet opening 15, and – viewed in the direction of flow – upstream of the inlet opening 31. Exhaust gas flowing in from the oxidation catalyst 11 through the inlet opening 15 is deflected around the overflow pipe 21, with the partial flows passing to the left and right of the overflow pipe 21 meeting in the flow chamber 45, essentially behind the overflow pipe 21. The exhaust gas then flows from the flow chamber 45 through the inlet opening 31 into the overflow pipe 21.

[0061] The injector unit 35 is oriented such that, in the illustrated embodiment 2, the injection jets 47, 47' sprayed from the injector unit 35 are directed into the flow chamber 45. The injection jets 47, 47' are each cone-shaped and open along an injection direction. It can be seen that one longitudinal axis of the cones of the injection jets 47, 47' is oriented at an acute angle to the longitudinal axis of the overflow pipe 21, with the injection jets 47, 47' being directed away from the inlet opening 31. They are therefore not directed towards the inlet opening 31, but rather towards the wall 41, onto which they also at least partially impinge. The angle that the injection jets 47, 47', in particular their longitudinal axes, form with the longitudinal axis of the overflow pipe 21 is preferably at most 45°.

[0062] In the flow chamber 45, three baffle elements 49, 49', 49" are arranged, which are attached to the overflow pipe 21 and / or to the wall 41 of the first exhaust pipe element 13, preferably welded there. The baffle elements 49, 49', 49" have a baffle surface 51, 51', 51" facing the injector unit 35, the normal vector of which is oriented substantially parallel to the longitudinal axis of the overflow pipe 21. The three baffle elements 49, 49', 49" are arranged one behind the other – viewed in the direction of the longitudinal axis of the overflow pipe 21 – and parallel to each other with respect to their baffle surfaces 51, 51', 51".

[0063] The injection jets 47, 47' now strike at least partially the impact surfaces 51, 51', 51", with reducing agent droplets rebounding from these surfaces. Preferably, the impact elements 49, 49', 49" have at least a Leidenfrost temperature of the reducing agent, thus optimizing the evaporation and rebound of the reducing agent droplets. They are heated either indirectly by the outer surface 23 and / or the wall 41 and the exhaust gas flowing around them, or a direct heating device is provided for heating the impact elements 49, 49', 49". Reducing agent droplets rebounding from the impact surfaces 51, 51', 51" preferably collide with opposing impact elements 49, 49', 49", resulting in multiple rebounds, with each droplet successively breaking up into increasingly smaller droplets. This, along with the heat transfer in the area of ​​the impact surfaces 51, 51', 51", promotes evaporation of the reducing agent.The same applies to the collision of the reducing agent with the wall 41 and a rebound of reducing agent droplets from it.

[0064] Because the evaporation of the reducing agent takes place to a significant extent in the flow chamber 45 before entering the overflow pipe 21, the mixing and, if necessary, also the hydrolysis and / or thermolysis of the reducing agent is significantly improved, which means that the mixing section 7 can be built shorter overall.

[0065] It also shows that the baffle elements 49, 49', 49" overlap the inlet opening 31 along a direction that is transverse, and in the illustrated embodiment, in particular perpendicular to the longitudinal axis of the overflow pipe 21. Exhaust gas flowing around the overflow pipe 21 thus experiences only minimal flow resistance through the baffle elements 49, 49', 49" so that there is an extremely low pressure loss through the baffle elements 49, 49', 49".

[0066] It is possible that probes for exhaust gas measurements are arranged in a region of the first exhaust gas duct element 13 that faces away from the flow chamber 45 and towards the inlet opening 15. Since the flow chamber 45 is virtually shielded from this region by the overflow pipe 21, the probes as well as the oxidation catalyst 11 are protected from reducing agent splashes or droplets.

[0067] It is also evident that the injection jets 47, 47' strike the impact surfaces 51, 51', 51" perpendicularly, or at most at an acute angle. The angle between the injection jets 47, 47' and the normal vectors of the impact surfaces 51, 51', 51" is preferably at most 45°. This efficiently facilitates the rebound of the reducing agent droplets from the impact surfaces 51, 51', 51".

[0068] Fig. Figure 3 shows a partially cutaway, three-dimensional representation of the embodiment of the exhaust system 1 according to the Fig. 1 and Fig. 2. Identical and functionally equivalent elements are marked with the same reference symbols, so reference is made to the preceding description. In Fig. Figure 3 shows that the overflow pipe 21 projecting into the first exhaust pipe element is positively engaged in the outlet opening 17. Preferably, a material connection, in particular by welding, is also provided.

[0069] Furthermore, in Fig. Figure 3 shows that the inlet opening 31 is designed as a rectangular gap which extends – viewed longitudinally – to the outlet opening 17, but not beyond it. Preferably, it extends from the Fig. 3 not shown closed end 25 up to the outlet opening 17. In Fig. 3 It is readily apparent that the inlet opening 31 has a larger extent in the direction of the longitudinal axis of the overflow pipe 21 than transversely to it, so that the rectangular gap formed by the inlet opening 31 extends in the longitudinal direction of the overflow pipe 21.

[0070] Based on Fig. Figure 3 also makes it clear that the first exhaust pipe element 13 essentially caps the overflow pipe 21, whereby exhaust gas flowing from the oxidation catalyst 11 into the outlet funnel 33 flows laterally around the overflow pipe 21 into the flow chamber 45. There, it enters the overflow pipe 21 through the inlet opening 31.

[0071] In the illustrated embodiment, the overflow pipe 21 is cylindrical and oval in cross-section. The inlet opening 31 is located centrally on the side of the overflow pipe 21 furthest from the inlet opening 15 (as viewed along the shorter axis), with respect to the longer axis of the oval cross-sectional area. Exhaust gas flowing through the inlet opening 31 thus forms two counter-rotating, stable exhaust gas vortices in the overflow pipe 21, preferably each with an approximately circular shape when viewed from above.

[0072] Particularly preferably, the ratio between the long axis of the oval cross-section of the transfer pipe 21 and its short axis is approximately two. In this case, a particularly stable double vortex is formed, which is preferably maintained along the entire mixing section 7, and especially also in the exhaust pipe 29 up to an inlet funnel of the second exhaust aftertreatment element 9. The width of the inlet opening 31 – measured perpendicular to the longitudinal axis of the transfer pipe 21 – is preferably smaller than the short axis of the oval cross-sectional shape of the transfer pipe 21.

[0073] In the Fig. In the embodiment shown in Figures 1 to 3, the inlet opening 31 is the only opening provided in the outer surface 23. Therefore, only one inlet opening 31 is provided. The exhaust gas coming from the oxidation catalyst 11 must thus flow completely around the transfer pipe 21 before it can enter it through the inlet opening 31. This imparts a swirl to the exhaust gas as it flows around the transfer pipe 21, which contributes to a high kinetic energy swirl being achieved in the transfer pipe 21, in particular a swirl number of at least 0.3 with respect to each individual vortex of the double vortex, and especially also an inlet swirl number of at least 0.3.

[0074] The following section explains the baffle elements 49, 49', 49" in more detail. These are designed here as baffle plates that overlap the inlet opening 31 perpendicular to the longitudinal axis of the overflow pipe 21 and are thus oriented parallel to the flow of exhaust gas in the flow chamber 45.

[0075] In each of the impact surfaces 51, 51', 51" a recess 53, 53', 53" is provided, which is arranged such that the injection jets 47, 47', which in Fig. 3, which are not shown, are directed in certain areas towards the recesses 53, 53', 53". A portion of the reducing agent encompassed by the injection jets 47, 47' is therefore sprayed through the recesses 53, 53', 53" without contacting the impact surfaces 51, 51', 51", while another portion is essentially peeled off by colliding with the surrounding impact surfaces 51, 51', 51". It can be seen that the recesses 53, 53', 53" define passage areas for the injection jets 47, 47' in the direction of the injection jets 47, 47', - in Fig. 3 also decreases downwards – from impact element to impact element. The proportion of the reducing agent passing through the recesses 53, 53', 53" thus decreases from recess to recess. Consequently, the injection jets 47, 47' are deflected by the recesses 53, 53', 53".

[0076] It is preferably provided that the depth of the recesses 53, 53', 53", measured along the first direction and perpendicular to the longitudinal axis of the overflow tube 21, decreases from impact element to impact element. Alternatively or additionally, it is possible that the width of the recesses 53, 53', 53", measured perpendicular to the first direction and perpendicular to the longitudinal axis of the overflow tube 21, also decreases from impact element to impact element. In the illustrated embodiment, the passage areas decrease by decreasing both the depth and the width of the recesses 53, 53', 53", 53". This results in particularly efficient peeling of the injection jets 47, 47'. Overall, this optimizes the evaporation and, if applicable, also the hydrolysis and / or thermolysis of the reducing agent.This is also due to vortex formation, which occurs when the injection jets 47, 47' peel off at the edges of the impact elements 49, 49', 49".

[0077] Overall, the reducing agent is very efficiently evaporated in the flow chamber 45 by both the baffle elements 49, 49', 49", which act as evaporation elements, and the wall 41, and intensively distributed by the exhaust gas flow entering the inlet opening 31. This distribution is further intensified by the formation of the stable double vortex in the overflow pipe 21. Since the evaporation and mixing occur very efficiently, a separate, additional mixing device is unnecessary. Furthermore, the mixing section 7 can be significantly shorter than in known exhaust gas systems because the reducing agent evaporates and homogenizes early and very rapidly.

[0078] Based on Fig. Figure 3 also shows that the injector unit 35, the baffle elements 49, 49', 49" and finally the injection jets 47, 47' (not shown) are arranged symmetrically with respect to a plane of symmetry that symmetrically divides the inlet opening 31, with both the first direction and the longitudinal direction of the overflow pipe 21 lying in the plane of symmetry. In particular, the baffle elements 49, 49', 49" and the injection jets 47, 47', and preferably also the injector unit 35, are arranged mirror-symmetrically with respect to the plane of symmetry. Since the resulting vortices, and thus the double vortex as a whole, are also mirror-symmetrically formed with respect to the plane of symmetry, the reduction agent is distributed symmetrically into the two vortices, and thus into the symmetrical double swirl, resulting in a particularly intensive homogenization of the reduction agent concentration in the exhaust gas stream.

[0079] Fig. Figure 4 shows a partially cutaway, three-dimensional representation of a second embodiment of an exhaust system 1. Identical and functionally equivalent elements are designated with the same reference numerals, so reference is made to the preceding description. The embodiment according to Fig. 4 differs from the embodiment according to the Fig. 1 to 3 differ in that the inlet opening 31 is not provided as the only inlet opening, but rather is designed as the main inlet opening 55. As in the previously described embodiment, it is arranged facing away from the inlet opening 15 and is designed as a rectangular gap.

[0080] Viewed along the first direction, the following are in Fig. In the embodiment shown in Figure 4, two secondary inlet openings 57, 57' are provided, which have a smaller cross-sectional area than the main inlet opening 55. The secondary inlet openings 57, 57' also have a larger dimension in the direction of the longitudinal axis of the overflow pipe 21 than transversely to it. In particular, they are also designed as a gap with a rectangular cross-sectional area.

[0081] Viewed from the perspective of the exhaust gas flowing from the oxidation catalyst 11, the secondary inlet openings 57, 57' are formed on the left and right sides of the transfer pipe 21, preferably arranged in a mirror-symmetrical manner with respect to the plane of symmetry. Exhaust gas flowing past the transfer pipe 21 enters the interior of the transfer pipe 21 through the secondary inlet openings 57, 57' essentially tangentially, thereby promoting the formation of the double vortex.

[0082] The secondary inlet openings 57, 57' reduce a pressure loss that would otherwise occur because the bypass pipe 21 presents a flow resistance to the incoming exhaust gas, which must first flow completely around the bypass pipe 21 before it can pass through the inlet opening 31. The pressure loss decreases because a portion of the exhaust gas flow enters the bypass pipe 21 laterally through the secondary inlet openings 57, 57', while the remaining portion continues to flow to the main inlet opening 55. It is preferably provided that the larger portion of the exhaust gas flow enters the bypass pipe 21 through the main inlet opening 55, while the smaller portion flows in through the secondary inlet openings 57, 57'. This can be ensured, in particular, by appropriately designing the passage surfaces of the main inlet opening 55 on the one hand and the secondary inlet openings 57, 57' on the other.Due to the reduction in pressure loss and the smaller proportion of exhaust gas that must flow laterally past the overflow pipe 21, the height (measured along the longitudinal axis of the overflow pipe 21) and the width (measured perpendicular to this axis and perpendicular to the first direction) of the flow channels running around the overflow pipe 21, formed by the wall 41 of the first exhaust pipe element 13 on the one hand and the outer surface 23 on the other, can be reduced. Overall, the first exhaust pipe element 13 can therefore be more compact, with a tighter fit around the overflow pipe 21 projecting into it.

[0083] To optimally support, or at least not weaken, the double vortex formed in the overflow pipe 21, it is essential that the exhaust gas flows in tangentially through the secondary inlet openings 57, 57'. This is ensured by at least one flow guide element.

[0084] In the following, this will only be explained in connection with the secondary inlet opening 57. However, the secondary inlet opening 57' is identical or mirror-symmetrical to the secondary inlet opening 57, so that everything that is stated below with regard to the secondary inlet opening 57 also applies to the secondary inlet opening 57'.

[0085] Two flow guide elements 59, 61 are provided, which are arranged and designed in such a way that a tangential flow of the exhaust gas into the overflow pipe 21 through the secondary inlet opening 57 is ensured.

[0086] The flow guide element 59 is designed here as a region of the outer surface 23 that is bent outwards in the radial direction. Similarly, the flow guide element 61 is designed as a region of the outer surface 23 that is bent inwards in the radial direction. Here, a radial direction refers to a direction that is perpendicular to the longitudinal axis of the overflow pipe 21. The flow guide elements 59 and 61 are preferably aligned parallel to each other and ensure a directed, tangential flow of the exhaust gas into the overflow pipe 21.

[0087] The flow of the exhaust gas is in Fig.Figure 4 is symbolized by arrows, with a first set of arrows, one of which is marked here with reference numeral 63, indicating how the exhaust gas from the oxidation catalyst 11 enters the first exhaust gas duct element 13 and flows towards the overflow pipe 21. It is evident that the overflow pipe 21 is arranged with its long cross-sectional axis transversely, in particular perpendicularly, to the first direction of the incoming exhaust gas, while its short cross-sectional axis is aligned parallel to this first direction. A set of curved arrows, one of which is marked here with reference numeral 65, illustrates how a portion of the exhaust gas flow around the overflow pipe 21 enters the overflow pipe 21 tangentially through the secondary inlet opening 57.Not shown is that the larger part of the exhaust gas flow flows laterally around the overflow pipe 21 until it reaches the main inlet opening 55, where it finally enters the interior of the overflow pipe 21, and where a stable, symmetrical double vortex forms.

[0088] A series of arrows, one of which is designated here by reference numeral 67, further indicates how the exhaust gas flows through the second exhaust pipe element 19, in particular through the mixing section 7 and the exhaust pipe 29 (not shown) to the second exhaust aftertreatment element 9 (also not shown). The symmetrical double vortex is preferably maintained up to an inlet funnel of the second exhaust aftertreatment element 9.

[0089] Overall, it is evident that the exhaust system 1 enables a particularly efficient and homogeneous mixing of the exhaust gas with the reducing agent, whereby the reducing agent is evaporated with exceptional efficiency and, if necessary, hydrolyzed or thermolyzed. This allows the exhaust system 1 to be very compact overall and to have a comparatively short mixing section 7. Furthermore, it is shown that the exhaust system 1 depicted in the figures, due to its very compact design, is particularly suitable for use in a motor vehicle whose internal combustion engine is arranged transversely to a longitudinal direction of the vehicle. Reference symbol list 1 Exhaust system 3 first exhaust aftertreatment element 5 Mixing device 7 Mixed section 9 second exhaust aftertreatment element 11 Oxidation catalyst 13 first exhaust pipe element 15 Entrance opening 17 Outlet opening 19 second exhaust pipe element 21 Overflow pipe 23 Surface area 25 first end 27 second end 29 Exhaust pipe 31 Inlet opening 33 outlet funnels 35 injector units 37 particulate filters 39 SCR catalyst 41 wall 43 rear area 45 Flow chamber 47, 47' Injection jets 49, 49', 49" impact elements 51, 51', 51" impact area 53, 53', 53" recess 55 Main inlet opening 57, 57' Secondary air inlets 59 Flow guide element 61 Flow guide element 65 arrows 67 arrows P arrow

Claims

[1] Exhaust system (1) for exhaust gas routing and exhaust gas aftertreatment in a motor vehicle, comprising a first exhaust pipe element (13) having an inlet opening (15) and an outlet opening (17), and a second exhaust pipe element (19) having a longitudinal axis overflow pipe (21) with a shell surface (23) and a first closed end (25), wherein an inlet opening (31) is provided in the shell surface (23) adjacent to the closed end (25), wherein the overflow pipe (21) projects into the outlet opening (17) and is received in the first exhaust pipe element (13) with its closed end (25) and the inlet opening (31),so that exhaust gas flowing in a first direction through the inlet opening (15) can flow through the inlet opening (31) into the overflow pipe (21) and – viewed in the direction of the longitudinal axis of the overflow pipe (21) – can flow out of the first exhaust pipe element (13) through the outlet opening (17) in the overflow pipe (21), and with an injector unit (35) attached to the first exhaust pipe element (13) for introducing a reducing agent into an exhaust gas stream flowing through the first and the second exhaust pipe elements (13, 19), , characterized by, that the longitudinal axis of the overflow pipe (21) is substantially perpendicular to the first direction, and that the injector unit (35) is arranged and designed such that reducing agent injected by the injector unit (35) can be injected upstream of the inlet opening (31) into the first exhaust pipe element (13), and the first exhaust pipe element (13) has a flow chamber (45) located upstream of the inlet opening (15) and facing away from the overflow pipe (21) in the first direction, wherein the injector unit (35) is arranged and oriented such that an injection jet (47, 47') is directed into the flow chamber (45), wherein the injection jet (47, 47') is directed approximately parallel to, at most at an acute angle to, the longitudinal axis of the overflow pipe (21) and away from the inlet opening (31), and in which Flow space (45) at least one substantially plate-shaped impact element (49, 49',49") is attached to the overflow pipe (21) and / or to the first exhaust pipe element (13), wherein the baffle element (49, 49', 49") has a baffle surface (51, 51', 51") facing the injector unit (35), the normal vector of which is oriented substantially parallel to the longitudinal axis of the overflow pipe (21), wherein the baffle element (49, 49', 49") overlaps the inlet opening (31) along a direction oriented transversely to the longitudinal axis. [2] Exhaust system (1) according to claim 1, characterized by , that the overflow pipe (21) is cylindrical at least in the area of ​​the inlet opening (31) and oval in cross-section. [3] Exhaust system (1) according to any one of the preceding claims, characterized by, that the overflow pipe (21) has only one inlet opening (31) which is arranged away from the inlet opening (15) of the first exhaust pipe element (13), wherein the inlet opening (31) has a larger extent in the direction of the longitudinal axis of the overflow pipe (21) than transversely to it, wherein it is designed as a gap with a substantially rectangular passage area. [4] Exhaust system (1) according to any one of the preceding claims, characterized by , that the first exhaust pipe element (13) is designed as an outlet funnel (33) of an oxidation catalyst (11). [5] Exhaust system (1) according to any one of the preceding claims, characterized by, that the first exhaust pipe element (13) is shaped like a cowl, wherein an imaginary plane defined by the inlet opening (15) is essentially perpendicular to an imaginary plane defined by the outlet opening (17), and wherein the first exhaust pipe element (13) virtually caps the overflow pipe (21). [6] Exhaust system (1) according to claim 1, characterized by a plurality of impact elements (49, 49', 49"), which - viewed in the direction of the longitudinal axis of the overflow pipe (21) - are arranged one behind the other and parallel to each other with respect to their impact surfaces (51, 51', 51"). [7] Exhaust system (1) according to claim 6, characterized by , that the impact elements (49, 49', 49") each have a recess (53, 53', 53") in the impact surface (51, 51', 51"), wherein the recess (53, 53', 53") is arranged such that the injection jet (47, 47') is directed in certain areas towards the recess (53, 53', 53"). [8] Exhaust system (1) according to claim 7, characterized by , that the defined penetration surfaces from the recesses (53, 53', 53") of the impact elements (49, 49', 49") decrease along a sequence of the impact elements (49, 49', 49") in the direction of the injection jet (47, 47'). [9] Exhaust system (1) according to any one of the preceding claims, characterized by , that the injector unit (35) is arranged and aligned such that the injection jet (47, 47') is arranged symmetrically with respect to a plane of symmetry defined by the first direction and the longitudinal direction, which symmetrically divides the inlet opening (31). [10] Exhaust system (1) according to claim 9, characterized by , that the at least one impact element (49, 49', 49") is designed and arranged in a mirror-symmetric manner with respect to the plane of symmetry. [11] Exhaust system (1) according to one of claims 1, 2 or 4 to 10, characterized bya main inlet opening (55) arranged facing away from the inlet opening (15) of the first exhaust pipe element (13), which has a larger extent in the direction of the longitudinal axis of the overflow pipe (21) than transversely to it, being designed as a gap with a substantially rectangular passage area, and further characterized by at least one secondary inlet opening (57, 57') in the shell surface (23) of the overflow pipe (21), which - viewed along the first direction - is arranged laterally to the main inlet opening (55), having a smaller cross-sectional area than the main inlet opening (55), and wherein the secondary inlet opening (57, 57') has a larger extent in the direction of the longitudinal axis of the overflow pipe (21) than transversely to it, and is designed as a slot with a rectangular cross-sectional area. [12] Exhaust system (1) according to claim 11, characterized bytwo secondary inlet openings (57, 57') which are arranged in a mirror-symmetrical manner with respect to a plane of symmetry which divides the main inlet opening (55) symmetrically defined by the first direction and the longitudinal axis. [13] Exhaust system (1) according to one of claims 11 and 12, characterized by , that the at least one secondary inlet opening (57, 57') has at least one flow guide element (59, 61) through which exhaust gas can be directed substantially tangentially into the overflow pipe (21), wherein the flow guide element (59, 61) is designed as a region of the shell surface (23) that is bent outwards and / or inwards in the radial direction. [14] Exhaust system (1) according to one of the preceding claims, characterized by the impact element (49, 49', 49") overlaps the inlet opening (31) along a direction that is oriented perpendicular to the longitudinal axis.

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