Exhaust aftertreatment system

Abstract

An exhaust aftertreatment device (32) comprises a flow unit (33) which is held in a housing (34) of the exhaust aftertreatment device (32). The flow unit (33) comprises at least one wire body (36, 40). The wire body (36, 40) has at least one first region (37, 41) with a first mean density and at least one second region (38, 42) with a second mean density. The second mean density is at least 1.5 times that of the first mean density. The wire body (36, 40) is clamped at the second region (38, 42) between two clamping sections (46, 47) of the housing (34).

Description

[0001] The invention relates to an exhaust aftertreatment device of the type specified in the preamble of claim 1.

[0002] From JP 2017 - 217 641 A, an exhaust aftertreatment device is known which comprises a flow unit made of a wire mesh. The wire body is cylindrical and has a higher density in an outer circumferential region than in an inner region. This is intended to achieve sufficient strength of the connection between the outer region of the wire mesh and the cylindrical housing.

[0003] From JP 2009 - 162 070 A, an exhaust aftertreatment device with a wire mesh body pressed into a housing is known. For positive locking of the wire mesh body, an inwardly projecting projection can be provided on the housing part.

[0004] WO 2024 / 056 780 A1 discloses a working device with an exhaust aftertreatment unit comprising at least one flow-through unit. The flow-through unit may be made of metal wire and be catalytically coated.

[0005] During operation, an exhaust aftertreatment system is subjected to intense heat from the exhaust gases flowing through it. It has been observed that the preload applied when pressing the wire body into the housing, which secures the wire body within the housing, diminishes at the high temperatures generated during operation. Consequently, vibrations produced by the combustion engine on which the exhaust aftertreatment system is mounted can, in known exhaust aftertreatment units, cause the flow-through unit to loosen within the housing and no longer be reliably held in position.

[0006] The invention is based on the objective of creating an exhaust gas aftertreatment device of the generic type in which a secure fixation of the wire body is possible even after a longer operating time.

[0007] This problem is solved with respect to the exhaust aftertreatment device by an exhaust aftertreatment device having the features of claim 1.

[0008] The wire body is designed to have at least one first region with a first average density and at least one second region with a second average density. The second average density should be at least 1.5 times that of the first average density. The wire body is clamped at the second region between at least two clamping sections of the housing.

[0009] Because the second average density is at least 1.5 times that of the first, the wire body exhibits significantly reduced elasticity in the second section. This allows the wire body to be clamped in place in the second section, resulting in a simpler design. Furthermore, because the second average density is at least 1.5 times that of the first, the wire body experiences significantly less exhaust gas flow in the second section compared to the first. Consequently, the second section, where the wire body is clamped, heats up less during operation. This reduced heating prevents the clamp from loosening during operation. Additionally, due to the increased density in the second section, the wire body's elasticity in this area is comparatively low.This allows for a secure fixation of the wire body in a simple way without additional fastening devices.

[0010] The flow unit can have one or more wire bodies. In particular, at least one wire body is a wire mesh. It is possible for at least one wire body to be a wire woven fabric.

[0011] Cavities are formed between the wire segments of the at least one wire body. The exhaust gas flows through these cavities via the flow unit. The cavities extend, in particular, to the outer surfaces of the wire body. Due to these cavities, the at least one wire body does not have a uniform density. The density of a region of the wire body is the average density of that region, which corresponds to the weight of the region divided by the volume of the surrounding material. The volume to which the density is referred includes both the wire segments and the cavities. The fewer cavities the wire body has, the greater its density.

[0012] In particular, the clamping mechanism provides for fixing the wire body between two clamping sections in a second area where the wire thickness is less than the distance between the clamping sections. For a round wire cross-section, the wire thickness corresponds to the wire diameter. The distance between the clamping sections is, in particular, at least twice, and especially at least three times, the wire thickness.

[0013] The wire body can be clamped at one point or at several spaced-apart points in the second region between each pair of clamping sections. The wire body can have several spaced-apart second regions. The wire body can be clamped at one or more of its second regions.

[0014] In particular, all wire bodies of the flow unit are held clamped in the clamping direction at a second area between two clamping sections of the housing.

[0015] The flow unit has, in particular, an inlet surface. The inlet surface is, in particular, an imaginary flat surface that abuts the flow unit.

[0016] In particular, the flow unit has an outflow surface. The outflow surface is, in particular, an imaginary flat surface that abuts the flow unit.

[0017] The outer surfaces of the wire body are uneven due to the presence of at least one wire body. The inlet surface and / or the outlet surface are, in particular, imaginary flat surfaces that abut the flow unit. The flow unit is located, in particular, between the inlet surface and the outlet surface. Specifically, the inlet surface and the outlet surface are opposite sides of an imaginary body that closely encloses the flow unit. The inlet surface and the outlet surface are, in particular, perpendicular to a principal flow direction through the inlet surface and the outlet surface, respectively.

[0018] The clamping direction has at least one directional component that runs perpendicular to the inlet surface. Therefore, the clamping direction is not parallel to the inlet surface, but forms an angle with it greater than 0°. Because the clamping direction has at least one directional component perpendicular to the inlet surface, the exhaust gas flow is not completely directed through the clamping surface. Specifically, the clamping direction runs perpendicular to the inlet surface. This allows the second section to be positioned outside the main flow path through the wire body. As a result, comparatively low heating of the second section during operation can be achieved.

[0019] The clamping direction has at least one directional component that runs parallel to the main flow direction. Therefore, the clamping direction is not perpendicular to the main flow direction, but rather forms an angle with it that is less than 90° or runs parallel to it. Because the clamping direction has at least one directional component parallel to the main flow direction, the exhaust gas flow is not completely directed through the clamping surface. Specifically, the clamping direction runs parallel to the main flow direction. This allows the second area to be positioned outside the main flow path through the wire body. As a result, comparatively low heating of the second area during operation can be achieved.

[0020] Particularly when the inlet surface has an irregular or curved shape, the clamping direction is selected specifically with respect to the main flow direction. Especially when the main flow direction is undefined or curved, the clamping direction is selected specifically with respect to the inlet surface.

[0021] In particular, the second mean density is at least twice, and especially at least three times, the first mean density. The higher the second mean density, the lower the elasticity of the second region and the greater the flow resistance for exhaust gases. Therefore, increasing the second mean density can lead to improved fixation of the wire body.

[0022] In particular, the second area lies outside the flow path of the exhaust aftertreatment system. The flow path is the area of ​​the exhaust aftertreatment system that lies in the direct flow path from an inlet to an outlet. The second area may be fluidically connected to the flow path. However, the second area lies specifically outside the direct flow path of the exhaust gases. In particular, direct inflow into the second area via the inlet is not possible. In particular, direct outflow from the second area through the outlet is not possible. The exhaust gases do not need to flow through the second area to get from the inlet to the outlet.Due to the increased flow resistance of the second area, a flow path through this area exhibits a higher resistance than a direct flow path from the inlet opening through the flow area to the outlet opening. This allows for a simple and effective way to minimize the heating of the second area. Sealing the second area is not required, resulting in a simple design for the flow unit.

[0023] In particular, the area of ​​at least one, and especially each, clamping section is at least 5%, and in particular at least 10%, of the area of ​​the flow-through region measured perpendicular to the inflow surface. In particular, the maximum extent of the second region of at least one wire body, measured perpendicular to the inflow surface, is smaller than the maximum extent of the first region, measured perpendicular to the inflow surface. In particular, the maximum extent of the second region, measured perpendicular to the inflow surface, is smaller for each wire body of the flow-through unit that is clamped between the two clamping sections than the maximum extent of the first region, measured perpendicular to the inflow surface.The increase in density in the second area can be easily achieved during the manufacture of the exhaust aftertreatment device by compressing the second area in a direction perpendicular to the inflow surface between the two clamping surfaces, using a wire body of constant thickness.

[0024] The second region, when viewed perpendicular to the inlet surface, extends around the first region. Specifically, in this viewing direction, the second region completely surrounds the first region. If the first region is cylindrical, the second region extends around the first region in an annular shape.

[0025] A simple design for the flow unit is achieved if the flow unit has an upstream end face to which the inlet surface rests, a downstream end face to which the outlet surface rests, and if the housing rests against at least one of the end faces. By having the housing rest against at least one of the end faces, bypass currents around the flow unit can be easily avoided. In particular, the housing rests against both the upstream and downstream end faces of the flow unit.

[0026] In particular, the housing has at least one inlet opening on the upstream end face and at least one outlet opening on the downstream end face. The housing covers the upstream and / or downstream end face perpendicular to the respective end face in the direction of view, especially at an overlap area that extends along the edge of the end face and whose width is at least 0.5 mm. The overlap area extends, in particular, circumferentially along the entire edge of the respective end face.

[0027] The second section is positioned between the first section and a third section. The housing rests against the third section in such a way that the housing exerts a force from the first section towards the third section. This places the first section under tensile stress. During operation, vibrations act on the wire body, which can compress it when it rests against the housing. The tensile stresses counteract this compression. This at least partially prevents a reduction in the external dimensions of the first section of the wire body. The potential deformation of the wire body during operation can thus be easily counteracted by appropriately shaping the housing.

[0028] The maximum extent of the third region, measured perpendicular to the inlet surface, is in particular greater than the maximum extent of the second region, also measured perpendicular to the inlet surface. A force from the first region towards the third region can be easily generated by the fact that the extent of the housing, measured perpendicular to the inlet surface, increases with increasing distance from the first region in the area adjacent to the third region. For example, the housing in the area adjacent to the third region can have a cross-sectional shape of a slope or ramp. If the first region of the wire body is cylindrical, the housing in the area adjacent to the third region can, for example, have the shape of a conical section.

[0029] In particular, the inlet and outlet surfaces are approximately parallel to each other within the usual manufacturing tolerances. The flow unit has a total thickness. This total thickness is the greatest extent of the flow unit measured perpendicular to the inlet surface, from the inlet surface to the outlet surface. The outlet surface deviates from a path parallel to the inlet surface by no more than 5% of the total thickness at any point. The end faces of the flow unit may be slightly curved. In particular, a slightly concave shape of the inlet and / or outlet surface is provided. Alternatively, the end faces may be flat within the usual manufacturing tolerances. In particular, the upstream end face does not deviate from the inlet surface by more than 5% of the total thickness at any point.Alternatively or additionally, it is specifically stipulated that the downstream end face must not deviate at any point by more than 5% of the total thickness from the outflow surface.

[0030] A different geometry for the flow unit can also be advantageous. In particular, the flow unit can be at least partially curved. It is also possible for the flow unit to have an irregular shape. This can be particularly useful for adapting it to an existing installation space.

[0031] The flow unit may be at least partially coated with a catalytic coating. A catalytic coating is a coating that lowers the activation energy for the chemical reaction. In particular, a catalytic coating is a coating containing a precious metal. The flow unit may also be at least partially coated with a washcoat. In this context, a washcoat is not considered a catalytic coating. A washcoat is defined as a coating that increases the surface area without lowering the activation energy for the chemical reaction. A washcoat coating may serve as a substrate or base for a catalytic coating. However, it may also be the case that at least one wire body, and in particular all wire bodies of the flow unit, are coated only with a washcoat and do not have a catalytic coating.It is also possible for the flow unit to be at least partially uncoated. In particular, it is intended that the flow unit is not completely coated with a catalytic coating. This allows the manufacturing costs of the flow unit to be kept comparatively low.

[0032] For a method of manufacturing an exhaust aftertreatment device, it is particularly provided that the at least one wire body in the second area between the two clamping sections of the housing is compressed to the second density. In particular, all wire bodies of the flow unit between the two clamping sections of the housing are compressed to the second density.

[0033] In particular, a blank of the flow unit, comprising at least one wire body with a uniform average density within the usual manufacturing tolerances, is placed between at least two blank housing parts, and the compression of the flow unit and the shaping of the housing are carried out in a single forming process. Specifically, all wire bodies of the flow unit are compressed in a single forming process along with the shaping of the housing.

[0034] After the housing components have been shaped, they are firmly joined together. This joining can be achieved by welding, soldering, positive locking, or friction locking. Specifically, the housing components are joined in such a way that they cannot be separated without damaging them.

[0035] Exemplary embodiments of the invention are explained below with reference to the drawing. The drawing shows: Fig. 1 a schematic sectional view of a chainsaw with an exhaust silencer and an exhaust aftertreatment device, Fig. 2 a perspective sectional view of the exhaust silencer made of Fig. 1, Fig. 3 a schematic top view of the exhaust aftertreatment system of the exhaust silencer made of Fig. 2, Fig. 4 a partial representation of an exemplary wire body, Fig. 5 a perspective sectional view of an embodiment of an exhaust aftertreatment device on the partition wall of an exhaust silencer, Fig. 6 a cross-section through the exhaust aftertreatment system Fig. 5, Fig. 7 and Fig. 8 schematic representations of a process for manufacturing the exhaust aftertreatment device in different process steps, Fig. 9 a perspective sectional view of another embodiment of an exhaust silencer, Fig. 10 a schematic representation of an embodiment of an exhaust aftertreatment device during manufacturing, wherein the representation shows the state before forming, Fig. 11 to 13 schematic representations of possible alternative forms of flow unit and housing, Fig. 14 a top view of the exhaust silencer, Fig. 15 a perspective view of an exhaust silencer outlet scoop, Fig. 16 a partial sectional view of the exhaust silencer in the area of ​​the outlet scoop.

[0036] Fig. Figure 1 shows a chainsaw 1 as an exemplary embodiment of a hand-held power tool. Instead of the chainsaw 1, another hand-held power tool, for example an angle grinder, a brush cutter, a blower, or a lawnmower, could also be used. The power tool is, in particular, a hand-held tool used during operation.

[0037] The chainsaw 1 has a housing 2 on which a handle 3 is arranged. The handle 3 serves to guide the chainsaw 1 during operation. Control elements, in this exemplary embodiment a throttle lever 4 and a throttle lever lock 5, are arranged on the handle 3. An internal combustion engine 8 is arranged in the housing 2. The internal combustion engine 8 can be controlled by an operator using the control elements. The internal combustion engine 8 drives a tool, namely a saw chain 7 arranged circumferentially on a guide bar 6. The saw chain 7 is in Fig. 1 is shown only schematically.

[0038] The internal combustion engine 8 comprises an air filter 9 and a fuel supply device 10. The internal combustion engine 8 includes an intake duct 11 through which air is drawn in via the air filter 9 during operation. A section of the intake duct 11 is formed within the fuel supply device 10. The fuel supply device 10 can, for example, be a carburetor.

[0039] The internal combustion engine 8 comprises a cylinder 12 in which a combustion chamber 14 is formed. The combustion chamber 14 is bounded by a piston 13 mounted to reciprocate within the cylinder 12. The piston 13 drives a crankshaft 17 via a connecting rod 16. The crankshaft 17 is rotatably mounted in a crankcase 15 about an axis of rotation 18. The crankshaft 17 serves to drive the saw chain 7.

[0040] In the exemplary embodiment, the internal combustion engine 8 is designed as a two-stroke engine, in particular as a single-cylinder engine. The intake port 11 opens into the interior of the crankcase 15. The connection of the intake port 11 to the crankcase 15 is controlled by the piston 13. The internal combustion engine 8 comprises several transfer ports 19 that fluidically connect the interior of the crankcase 15 to the combustion chamber 14 in the region of the piston 13's bottom dead center. An exhaust port 21 leads from the combustion chamber 14 and is connected to an exhaust silencer 23 via an exhaust port 22. The exhaust port 21 is controlled by the piston 13. A spark plug 20, which is controlled by a control device (not shown), protrudes into the combustion chamber 14.

[0041] The exhaust silencer 23 includes an inlet opening 24 through which exhaust gases from the outlet channel 22 enter the exhaust silencer 23. An outlet opening 25 leads from the exhaust silencer 23, through which the exhaust gases escape into the environment. The outlet opening 25 can, for example, be formed on an outlet scoop 76, as shown. Fig. 2 shows.

[0042] In the exemplary embodiment, the exhaust silencer 23 has a silencer housing 27 in which a partition 26 runs. The partition 26 separates a first silencer chamber 30 from a second silencer chamber 31. An exhaust aftertreatment device 32, which will be described in more detail below, is arranged in the partition 26. Exhaust gases flow through the exhaust aftertreatment device 32 in a main flow direction 35. The exhaust aftertreatment device 32 comprises a flow unit 33 through which the exhaust gases flow from the first silencer chamber 30 into the second silencer chamber 31.

[0043] Fig. Figure 2 shows the exhaust silencer 23 in detail in a perspective sectional view. The silencer housing 27 comprises a first partial shell 28 and a second partial shell 29, which are connected to each other at a circumferential rim 53. The partition 26 runs between the partial shells 28 and 29 and, in the exemplary embodiment, is also fixed to the rim 53.

[0044] The exhaust gas aftertreatment device 32 is mounted on the partition wall 26. In the exemplary embodiment according to Fig. 2 The exhaust aftertreatment device 32 has a circumferential rim 54. The partition 26 has an opening 55 through which the exhaust aftertreatment device 32 projects. The rim 54 of the exhaust aftertreatment device 32 overlaps the partition 26 and is fixed to it, for example by a weld.

[0045] The exhaust aftertreatment device 32 has a housing 34. The housing 34 is formed by two housing parts 56 and 57. However, a different design of the housing 34 may also be advantageous. The two housing parts 56 and 57 can, for example, be designed as deep-drawn parts or as stamped parts. The two housing parts 56 and 57 are connected to each other at the edge 54. In the exemplary embodiment, the two housing parts 56 and 57 abut each other at the edge 54 and together form the edge 54.

[0046] The first housing part 56 has an inlet opening 51 for exhaust gases. The inlet opening 51 can be formed by several individual openings in the first housing part 56. The second housing part 57 has an outlet opening 52, which can also be formed by several individual openings. In the exemplary embodiment, the inlet opening 51 and outlet opening 52 are subdivided by several housing struts 70.

[0047] The flow unit 33 is arranged in the housing 34. The flow unit 33 can be formed in one piece or comprise several sub-bodies. In particular, the flow unit 33 consists of one or more dimensionally stable bodies. The flow unit 33 has at least one wire body. In the exemplary embodiment, a first wire body 36 and a second wire body 40 are provided. At least one of the wire bodies 36, 40, in particular both wire bodies 36 and 40, can be a wire mesh. The wire bodies 36 and 40 can be uncoated, coated with washcoat, or provided with washcoat and a catalytic coating. It can be provided that the first wire body 36 and the second wire body 40 have the same coating.Alternatively, the wire bodies 36 and 40 may have different coatings, or one of the wire bodies 36, 40 may have a coating while the other does not. In particular, one of the wire bodies may have a larger amount of catalytic coating per volume of wire body 36, 40 than the other. It may also be provided that the other of the wire bodies 36, 40 does not have a catalytically active coating.

[0048] The first wire body 36 has an upstream end face 49. In the exemplary embodiment, the end face 49 is flat and coincides with an inlet surface 44 in the flow unit 33. The inlet surface 44 is an imaginary plane that abuts the end face 49. The inlet surface 44 is one side of a housing body that closely encloses the wire bodies 36 and 40. The housing 34 has the inlet opening 51 on the end face 49.

[0049] In the exemplary embodiment, the second wire body 40 rests against the first wire body 36. The second wire body 40 is arranged downstream of the first wire body 36 with respect to the main flow direction 35. In the exemplary embodiment, both wire bodies 36 and 40 are identically shaped. However, wire bodies of different shapes, preferably with different thicknesses measured perpendicular to the inlet surface 44, can also be provided. The second wire body 40 has a downstream end face 50, which in the exemplary embodiment is flat. The downstream end face 50 coincides with an imaginary flat outlet surface 45. The housing 34 has the outlet opening 52 on the end face 50.

[0050] During operation, exhaust gases flow from the first silencer chamber through the inlet opening 51 and the end face 49 into the first wire body 36, flow through the first wire body 36, flow from the first wire body 36 into the second wire body 40, and from the second wire body 40 through the end face 50 into the second silencer chamber 31. The exhaust gases leave the exhaust aftertreatment device 32 through the outlet opening 52 of the housing 34. The exhaust gases flow from the inlet opening 51 to the outlet opening 52 in the main flow direction 35. The end faces 49 and 50 are approximately flat. The inlet surface 44 and the outlet surface 45 are, within the limits of manufacturing tolerances, approximately parallel to each other. The inlet area 44 and the outlet area 45 are formed by the planar imaginary surfaces that bear against the individual wire windings of the wire bodies 36 and 40. Fig. For simplicity, wire bodies 36 and 40 are shown as solid bodies. The outlines of the solid bodies correspond to the outer body that forms the inlet surface 44 and the outlet surface 45.

[0051] The flow unit 33 has a total thickness e. The total thickness e is the maximum thickness of the flow unit 33 measured perpendicular to the inlet surface 44 and from the inlet surface 44 to the outlet surface 45.

[0052] The first wire body 36 has a first region 37, which forms the end face 49. The first region 37 of the first wire body 36 is the region of the first wire body 36 through which the exhaust gases flow. The second wire body 40 has a first region 41 through which the exhaust gases flow and which forms the end face 50. The first region 37, 41 of the wire bodies 36, 40 has a first density. The density is the weight of the respective region divided by the total volume. The total volume includes the volume of the wire and any cavities located between the wire loops.

[0053] The wire bodies 36 and 40 each have a second region 38, 42, the density of which is considerably greater than the density of the first region. The density of the second region 38, 42 is at least 1.5 times, in particular at least 2 times, in particular at least 3 times, in particular at least 5 times the first average density of the first region 37 or 41. The second region 38 and 42 of the wire bodies 36 and 40 is arranged outside a flow-through region 48 through which the exhaust gases flow in the main flow direction 35 from the inlet opening 51 to the outlet opening 52. At the second regions 38 and 42, the wire bodies 36 and 40 are clamped between clamping sections 46 and 47 of the housing 34 in a clamping direction 62. Further clamping sections may also be provided.In the exemplary embodiment, the first regions 37 and 40 are approximately cylindrical, and the second regions 38 and 42 surround the first regions 37 and 41 in an annular shape. The clamping sections 46 and 47 are annular recesses in the housing parts 56 and 57. The clamping sections 46 and 47 are positioned opposite each other in a direction perpendicular to the inlet surface 44 with respect to the wire body 36, 40.

[0054] The clamping direction 62 has at least one directional component that runs perpendicular to the inlet surface 44. In the exemplary embodiment, the clamping direction 62 runs perpendicular to the inlet surface 44. In the exemplary embodiment, the clamping direction 62 runs perpendicular to the outlet surface 45.

[0055] The clamping direction 62 has at least one directional component that runs parallel to the main flow direction 35. In the exemplary embodiment, the clamping direction 62 runs parallel to the main flow direction 35.

[0056] The main flow direction 35 runs perpendicular to the inflow surface 44.

[0057] The area of ​​at least one, in particular each, clamping section 46, 47 is at least 5%, in particular at least 10%, of an area of ​​the flow area 48 measured when looking perpendicularly at the inlet area 44.

[0058] The wire bodies 36 and 40 each have a third region 39, 43. The second region 38 and 42 of each wire body 36 and 40 is located between the first region 37, 41 and the third region 39, 43 of that wire body 36, 40. The second region 38, 42, with its comparatively high density, thus separates the first regions 37, 40 from the third regions 39, 43. The third regions 39, 43 also lie outside the flow area 48. Exhaust gases can flow into the second region 38, 42 and through the second region 38, 42 into the third region 39, 43. However, there is no outlet opening from the second area 38, 42 and the third area 39, 43, so the exhaust gases must flow back into the first areas 37, 41 to leave the flow unit 33.

[0059] How Fig. Figure 2 shows that the maximum extent b of each second region 38, 42, measured perpendicular to the inlet surface 44, is smaller than the maximum extent a of each first region 37, 41, measured perpendicular to the inlet surface 44. Fig. 2. The extensions a and b are shown only for the first wire body 36, since the second wire body 40 has identical dimensions in the exemplary embodiment. The second areas 38, 42 can be produced by compressing the wire body 36, 40 in a direction perpendicular to the inflow surface 44.

[0060] As the schematic representation in Fig. Figure 3 shows that the second area 38 runs around the first area 37. The third area 39 runs in a circular ring around the second area 38. Fig. Figure 3 shows a schematic view of the first wire body 36 when viewed perpendicular to the inflow surface 44.

[0061] How Fig. As shown in Figure 2, the housing 34 abuts the flow unit 33 at both the upstream end face 49 and the downstream end face 50. The housing covers the end faces 49 and 50 at their circumferential edge in an overlap area 60. The overlap area 60 extends along the edge of the respective end face 49 or 50, in particular circumferentially. The width h of the overlap area 60 is in particular at least 0.5 mm at at least one point, and in particular at every point of the overlap area 60. Fig. 2 the covering area 60 is only shown for the downstream end face 50.

[0062] How Fig. As also shown in Figure 2, the housing 34 has areas 58 and 59 adjacent to the third area 39, 43. Areas 58 and 59 are inclined to the main flow direction 35. The angle of inclination is greater than 0° and less than 90°. In particular, the angle of inclination is between 20° and 70°. Due to the rotationally symmetrical shape of the flow unit 33, this results in a conical shape of the housing wall in the exemplary embodiment. During the manufacture of the exhaust aftertreatment device 32, a force F is exerted on the third areas 39 and 42 due to the inclined shape of areas 58 and 59. Due to this force F, the second areas 38, 42 and the first areas 37, 41 are under tensile stress.

[0063] The flow unit 33 is clamped in the housing 34. This causes both the clamping sections 46 and 47 and the areas 58 and 59 adjacent to the clamping sections 46 and 47, which are inclined towards the main flow direction 35, to exert a clamping force. The force F exerted by the areas 58 and 59 is radially outwards, as well as in Fig. Figure 3 is shown schematically. The force F exerted by the inclined areas 58 and 59 of the housing 34 on the first areas 37, 41 of the flow unit 33 therefore puts the first areas 37 and 41 under tensile stress and counteracts a reduction in the size of the first areas 37 and 41 due to vibrations and / or heating due to the exhaust gas temperature during operation.

[0064] The third region 39, 43 has a maximum extent c measured perpendicular to the inlet surface 44. In particular, the third region 39, 43 has its maximum extent c at the outer circumference of the flow unit 33. The maximum extent c of the third region 39, 43 is, in particular, greater than the maximum extent b of the second region 38, 42, measured perpendicular to the inlet surface 44. The extent d of the housing 34, measured perpendicular to the inlet surface 44, increases, in particular in the regions 58, 59 adjacent to the third region, with increasing distance from the first region 37, 41. In particular, at least part of the regions 58 and 59 of the housing 34 has a uniform profile inclined to the main flow direction 35.

[0065] Fig. Figure 4 shows an exemplary design of a wire body using the first wire body 36 as an example. The wire body 40 is designed identically. The wire body 36 is constructed of metal wire. In particular, the wire body 36 is a metal mesh. Gaps are formed between the individual wire loops through which the exhaust gas can flow. The lower the average density of the wire body, the greater the proportion of the gaps to the flow cross-section of the wire body 36, 40. The wire of the wire body 36 has a thickness i. In particular, the wire has a round cross-section, and the thickness i corresponds to the diameter of the wire. The clamping sections 46 and 47 have a distance k, as shown. Fig. Figure 2 shows that the distance k is in particular at least 2 times, and in particular at least 3 times, the thickness i.

[0066] Fig. Figure 5 shows an embodiment of an exhaust gas aftertreatment device 32. The same reference numerals denote corresponding elements in all embodiments. In the embodiment shown, the flow unit 33 comprises Fig. 5 a single wire body 36. Alternatively, several wire bodies 36 can be provided in this embodiment as well. The housing 34 of the exhaust aftertreatment device 32 is formed by two housing parts 56 and 57. Housing part 56 forms a circumferential wall 71 on the third region 39 of the wire body 36. Housing part 57 lies within the circumferential wall 71. Housing part 56 has tabs 61 that are bent over and thereby fix housing part 57 to housing part 56. This achieves a positive locking connection.

[0067] How Fig. As also shown in Figure 5, the flow unit 33 in this embodiment has a cross-section in the form of a rounded rectangle. The partition 26 has a bent edge 69 in the area that delimits the opening 55. The flow unit 33 is fixed to the bent edge 69 with its circumferential wall 71. In an alternative embodiment, the partition 26 and the housing part 56 can be formed integrally.

[0068] The connection of the housing parts 56 and 57 of the housing 34 can be achieved by a material-bonded connection, for example by welding or soldering, by a form-fit connection, or by a friction-fit connection. In the exemplary embodiment according to Fig. 5 A positive-locking connection is provided by bending the tabs 61. In the embodiment according to Fig. 2. For example, the housing parts 56, 57 can be welded together.

[0069] How Fig. As shown in Figure 6, the upstream end face 49 and the downstream end face 50 are not flat, but slightly convex. The inlet surface 44 abuts the end face 49. The inlet surface 44 is in Fig. Figure 6 is shown with a dashed line. The inlet area 44 lies against the circumference of the front face 49. The outlet area 45 is also shown in Fig. Figure 6 is shown with a dashed line. The outlet surface 45 rests against the circumference of the end face 50. In the exemplary embodiment, both the end face 49 and the end face 50 are concave. The end faces 49 and 50 deviate by a deviation g from a flat profile defined by the inlet surface 44 and the outlet surface 45. In the exemplary embodiment, the deviation g is greatest in the middle of the end faces 49 and 50. The greatest deviation g is, in particular, less than 5% of the total thickness e of the flow unit 33. The end faces 49 and 50 may also be slightly angled to each other or otherwise irregular. In particular, the outlet surface 45 does not deviate from a profile parallel to the inlet surface 44 by more than 5% of the total thickness e at any point.

[0070] The Fig. 6 and Fig. Figure 7 shows process steps of a method for manufacturing the flow-through unit 33. A wire body 36 is placed between two housing parts 56 and 57. A first housing part 56 is arranged in a die 64, the shape of which corresponds to the outer contour of the finished flow-through unit 33. The housing part 56 can be pre-formed, as shown. In particular, however, the housing part 56 is inserted as a flat sheet metal part. A second housing part 57 is arranged in a punch 65. In particular, the second housing part 57 is also arranged as a blank, in particular as a flat sheet metal part, on the punch 65. However, it can also be provided that the second housing part 57 is pre-formed, as shown. The tool for manufacturing the flow-through unit 33 also has lateral slides 66. The punch 65 is movable in the direction of an arrow 67 towards the die 64.The sliders 66 are movable towards each other in the direction of arrows 68 and perpendicular to arrow 67. How . Fig. Figure 7 shows that the wire body 36 has a uniform total thickness e' before crimping. The total thickness e' is greater than the thickness e ( Fig. 6).

[0071] Fig. Figure 8 shows the arrangement after the punch 65 has been moved into the die 64 and the slides 66 have moved towards each other. The die 64 and the punch 65 have clamped the wire body 36 between the housing parts 56 and 57. In doing so, both the first section 37 was compressed and the second section 38 was compressed to the second density between the clamping sections 46 and 47. The third section 39 of the wire body 36 was also compressed between the housing parts 56 and 57. After compression, the slides 66 bent the tabs 61 over, thus fixing the wire body 36 between the housing parts 56 and 57.

[0072] Fig. Figure 9 shows a variant embodiment of an exhaust silencer 23 with an exhaust aftertreatment device 32. The exhaust aftertreatment device 32 is arranged in an opening 55 of the partition 26. The housing parts 56 and 57 are separately fixed to the bent edge 69 of the partition 26, for example by means of welded connections. In the embodiment shown, the housing parts 56 and 57 are in contact with each other. Fig. 9 are not connected and are only connected to each other via the edge 69 of the partition wall 26. In the embodiment according to Fig. In this embodiment, the wire body 36 comprises only a first section 37 and a second section 38. A third section 39 is not present in this embodiment. The clamping sections 46 and 47 extend to the circumference of the housing parts 56 and 57. In this embodiment, the clamping sections 46 and 47 run approximately parallel to each other. The further design of the exhaust aftertreatment device 32 can be provided as in the preceding embodiments.

[0073] Fig. Figure 10 shows an embodiment of a flow-through unit 33 before the forming of the housing parts 56 and 57 and before the forming of the wire body 36. The wire body 36 is positioned between two housing parts 56 and 57. Both housing parts 56 and 57 are designed as flat sheet metal parts and are formed together with the flow-through unit 33 in a single process step. After forming, the flow-through unit 33 can, for example, Fig. 2 exhibit the depicted form.

[0074] The Fig. Figures 11 to 13 show alternative designs for the shape of first area 37 and housing 34. In the embodiment according to Fig. In the illustrations, housing 34 and first section 37 have different shapes. In the exemplary embodiment, the first section 37 is circular, and housing 34 has the shape of a square or rectangle with rounded corners. The resulting clamping section 46 therefore does not have a uniform width. The clamping section 47, which is shown in the illustrations in Fig. 11 to Fig. 13, which is not visible, is designed to be identical to the respective clamping section 46.

[0075] In the exemplary embodiment, the first region 37 has a circular or elliptical shape, and the housing 34 has a square or rectangular shape, particularly with rounded corners. The first region 37 projects to the edge of the housing 34 at least at one point, in the exemplary embodiment at four points. This results in four separate clamping sections 46 in the corner regions of the housing 34.

[0076] In the exemplary embodiment according to Fig. In the exemplary embodiment, the housing 34 is round or elliptical, and the first area 37 is designed as a rectangle or square, in particular with rounded corners. The first area 37 projects to the edge of the housing 34. In the exemplary embodiment, this results in four separately formed clamping sections 46.

[0077] A design with two opposing clamping areas 46, which may be arranged, for example, on the longitudinal sides of a rectangular first area 37 or housing 34, or with three clamping areas 46, which may be arranged, for example, in the area of ​​the tips of a triangular first area 37 or housing 34, may also be advantageous.

[0078] In the exemplary embodiments according to Fig. In sections 11 to 13, the clamping area 46 is locally designed with a reduced width or is completely interrupted. This allows the housing 34 to be smaller compared to a version with a clamping area 46 of constant width all around. This, in turn, reduces the weight of the flow unit 33.

[0079] The Fig. Figures 14 to 16 show the design of an outlet scoop 76 of the exhaust silencer 23, on which the outlet opening 25 is formed. The internal combustion engine 8 has a reference plane 80 with respect to the exhaust gas temperature to be achieved, which is located in Fig. Figure 14 is shown schematically. The reference plane 80 is an imaginary plane that abuts the internal combustion engine 8 at at least three points. The outlet opening 25 has a distance s to at least one, and in particular to all, reference planes 80 that can be arranged downstream of the outlet opening 25 in the outflow direction 78 on the internal combustion engine 8. The distance s is in particular at least 50 mm. This is particularly advantageous when the exhaust silencer 23 is arranged in a chainsaw 1.

[0080] A projection 77 is arranged on the silencer housing 27. The projection 77 extends at a distance t from the outlet opening 25 in the outflow direction 78. In the exemplary embodiment, the projection 77 is designed as a raised rib. In the exemplary embodiment, the projection 77 is, as Fig. Figure 15 shows the outlet scoop 76 as a single, raised edge of the sheet metal part forming the outlet scoop 76. The projection 77 extends transversely, at least in one section, and in particular approximately perpendicular to the outflow direction 78. The projection 77 runs at least partially parallel to the surface of the outlet opening 25.

[0081] The protrusion 77 has a width m measured perpendicular to the outflow direction 78. The width m is, in particular, larger than the width k of the outlet opening 25. Viewed in the outflow direction 78, the protrusion 77 extends, in particular, beyond the outlet opening 25. In the exemplary embodiment, the protrusion 77 extends with a rounded shape beyond the plane of the outlet opening 25.

[0082] The height o of the elevation is in particular 15% to 20% of a height n of the exit window 25, as Fig. 16 shows.

[0083] The outlet scoop 76 has a length p measured in the outflow direction 78. A shoulder 79 is formed on the silencer housing 27. The shoulder 79 forms, in particular, a separation edge for the exhaust gas flow. In the exemplary embodiment, the shoulder 79 is formed by a kink in the silencer housing, at which the silencer housing 27 dips below the plane of the outflowing exhaust gases.

[0084] Paragraph 79 has a distance r to the outlet opening 25, which in particular corresponds to at least the length p of the outlet cowl 76. A distance t of the protrusion 77 to the outlet opening 25, measured in the outflow direction 78, is in particular less than the length p of the outlet cowl 76.

[0085] Further advantageous embodiments result from any combination of the elements of the embodiments described above.

Claims

[1] Exhaust aftertreatment device (32), wherein the exhaust aftertreatment device (32) comprises a flow unit (33) which is held in a housing (34) of the exhaust aftertreatment device (32), wherein the flow unit (33) comprises at least one wire body (36, 40), wherein the wire body (36, 40) has at least one first region (37, 41) with a first mean density and at least one second region (38, 42) with a second mean density, characterized by , that the second mean density is at least 1.5 times the first mean density and that the wire body (36, 40) is held clamped at the second area (38, 42) between at least two clamping sections (46, 47) of the housing (34). [2] Exhaust aftertreatment device (32) according to claim 1, characterized by, that the wire body (36, 40) is held clamped between the clamping sections (46, 47) in a clamping direction (62), wherein the clamping direction (62) has at least one directional component that is perpendicular to an inflow surface (44) of the flow unit (33) and / or parallel to a main flow direction (35) through the flow unit (33). [3] Exhaust aftertreatment device (32) according to claim 1 or 2, characterized by , that the second mean density is at least twice the first mean density. [4] Exhaust aftertreatment device (32) according to one of claims 1 to 3, characterized by , that the second area (38, 42) lies outside a flow area (48) of the exhaust aftertreatment device (32). [5] Exhaust aftertreatment device (32) according to one of claims 1 to 4, characterized by, that an area of ​​at least one clamping section (46, 47) is at least 5% of an area of ​​the flow area (48) measured when looking perpendicularly at an inflow area (44). [6] Exhaust aftertreatment device (32) according to one of claims 1 to 5, characterized by , that the inflow area (44) of the flow unit (33) is an imaginary flat surface which is adjacent to the flow unit (33). [7] Exhaust aftertreatment device (32) according to claim 6, characterized by , that a maximum extent (b) of the second region (38, 42) measured perpendicular to the inflow surface (44) is smaller than a maximum extent (a) of the first region (37, 41) measured perpendicular to the inflow surface (44). [8] Exhaust aftertreatment device (32) according to claim 6 or 7, characterized by , that the second area (38, 42) runs around the first area (37, 41) when viewed perpendicular to the inflow surface (44). [9] Exhaust aftertreatment device (32) according to one of claims 6 to 8, characterized by , that the flow unit (33) has an outlet surface (45), wherein the outlet surface (45) is an imaginary flat surface, that the flow unit (33) has an upstream end face (49) against which the inlet surface (44) abuts, that the flow unit (33) has a downstream end face (50) against which the outlet surface (45) abuts, and that the housing (34) abuts at least one of the end faces (49, 50). [10] Exhaust aftertreatment device (32) according to claim 9, characterized by, that the housing (34) has at least one inlet opening (51) on the upstream end face (49) and at least one outlet opening (52) on the downstream end face (50), and that the housing (34) covers the upstream end face (49) and / or the downstream end face (50) perpendicularly to the respective end face (49, 50) in the direction of view at an overlap area (60) which extends along the edge of the end face (49, 50) and whose width (h) is at least 0.5 mm.

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