Hand held toll and exhaust gas aftertreatment device therefor

Abstract

A hand-held work device comprises an internal combustion engine (8) and an exhaust silencer (23). The exhaust silencer (23) includes a first silencer chamber (47) and a second silencer chamber (48). The exhaust silencer (23) includes an exhaust aftertreatment device (26) comprising at least one flow-through unit (31). The flow-through unit (31) is arranged in a flow path from the first silencer chamber (47) to the second silencer chamber (48). The thickness (b) of the flow-through unit (31), measured from an upstream end face (36) to a downstream end face (37) of the flow-through unit (31) in the area through which exhaust gas flows, is at least 10 mm over at least 70% of the cross-section. The exhaust aftertreatment device (26) does not have a catalytically active coating.

Description

[0001] The invention relates to a hand-held work device of the type specified in the preamble of claim 1 and an exhaust aftertreatment device for a hand-held work device.

[0002] From JP 2009-156158 A, a hand-held work device with an exhaust silencer is known, which incorporates a catalyst. The catalyst can be made of wire and is coated with catalyst material such as platinum.

[0003] US patent 7,293,629 B2 reveals an exhaust silencer with a metal fiber filter to reduce noise and a spark arrestor screen.

[0004] US patent 2005 / 0029039 A1 discloses an exhaust silencer in which a reaction zone is formed inside. The wall bounding the reaction zone may be catalytically coated.

[0005] The JP S48-108026 U reveals an exhaust silencer with several chambers inside.

[0006] The subsequently published EP 4 067 633 A1 discloses an exhaust silencer whose catalyst comprises at least one flow-through element. A first section of the flow-through element is coated with a catalytically active coating. A second section of the flow-through element may only be coated with a washcoat.

[0007] Internal combustion engine-powered handheld power tools, such as chainsaws, angle grinders, brush cutters, blowers, lawnmowers, and the like, are subject to increasingly stringent legal requirements regarding exhaust gas composition. To meet these requirements, it is common practice to use catalytic converters for exhaust aftertreatment, even in such small engines. The parameters for such catalytic converters in handheld power tools differ in many respects from those in the automotive sector, for example. Due to the limited available installation space, exhaust silencers in such handheld power tools must be comparatively small. At the same time, contact between the operator and hot parts of the power tool must be avoided. Therefore, strict requirements also apply with regard to exhaust gas temperatures.The combustion engines used are often premixed-lubricated. Because the fuel in premixed-lubricated engines is at least partially injected into the crankcase, precise fuel metering is not possible. Therefore, the exhaust gas composition of such small engines fluctuates much more than, for example, in automobiles, where the amount of fuel injected directly into the combustion chamber is precisely controlled.

[0008] Therefore, exhaust silencers for such hand-held work equipment must meet different requirements with regard to temperature and weight as well as fluctuating exhaust gas compositions than exhaust silencers used in the automotive sector, for diesel engines or for separately lubricated four-stroke engines, so that solutions from this area cannot simply be transferred to exhaust silencers for hand-held work equipment.

[0009] The invention is based on the objective of creating a hand-held work tool of the generic type that is simple and robust in design. A further objective of the invention is to provide an exhaust silencer for a hand-held work tool.

[0010] This problem is solved with respect to the hand-held work device by a work device having the features of claim 1. With respect to the exhaust silencer, the problem is solved by an exhaust silencer having the features of claim 15.

[0011] According to the invention, the exhaust aftertreatment system does not have a catalytically active coating. In this context, a catalytically active coating is a coating that acts as a catalyst, thus lowering the activation energy for the chemical reaction of the exhaust gases and thereby increasing the reaction rate. A catalytically active coating is, in particular, a coating made of a precious metal. The catalytically active coating is, in particular, a coating that primarily serves to convert hydrocarbons and / or nitrogen oxides.

[0012] Because the exhaust aftertreatment system lacks a catalytic coating, the exhaust gases are heated significantly less in the silencer than in a system with a catalytic coating. This allows for a smaller silencer footprint, as a shorter cooling path for the exhaust gases within the silencer is required. Furthermore, the absence of a catalytic coating saves raw materials, particularly the precious metals used in such coatings, thus reducing manufacturing costs.Surprisingly, it has been shown that in combustion engines of hand-held power tools, sufficient exhaust gas treatment, particularly with regard to particle conversion, is possible even without a catalytically active coating in the exhaust aftertreatment system. Specifically, the flow unit, preferably a wire body of the flow unit, does not have a catalytically active coating.

[0013] The flow unit must have a minimum thickness to ensure sufficient residence time of the exhaust gases within it, thus enabling adequate exhaust gas conversion. A flow unit used for particle conversion must have a thickness of at least 10 mm in the area through which the exhaust gas flows. The flow unit may have a reduced thickness at its edges. For example, the edges of the flow unit may be rounded or chamfered. The specified minimum thickness of 10 mm must be maintained over at least 70% of the largest cross-section, and in particular over at least 80% of the largest cross-section.

[0014] Due to the comparatively large thickness of the flow unit, it exhibits high stability. The cross-sections are oriented perpendicular to the main flow direction through the exhaust aftertreatment system. The largest cross-section is the largest cross-section of the flow unit perpendicular to the main flow direction. The thickness is advantageously measured parallel to the main flow direction. Preferably, the thickness is perpendicular to the first, upstream end face of the flow unit.

[0015] Preferably, the thickness of the flow unit in the area through which exhaust gas flows is at least 15 mm over at least 70% of the largest cross-section, and particularly preferably at least 20 mm. Advantageously, the thickness of the flow unit in the area through which exhaust gas flows over the entire largest cross-section is at least 10 mm, and particularly at least 15 mm.

[0016] Advantageously, all flow units of exhaust aftertreatment units of the exhaust silencer have a thickness of at least 10 mm in the area of ​​the flow units through which exhaust gas flows, over at least 70% of the largest cross-section.

[0017] The at least one flow-through unit is at least partially, and in particular completely, coated with a washcoat. In this context, a washcoat is a coating that increases the surface area without lowering the activation energy for the chemical reaction. For example, the washcoat can be made of aluminum oxide. The washcoat improves the particle-converting effect. Advantageously, the flow-through unit comprises at least one metal wire body. Because the flow-through unit comprises at least one metal wire body, it acts as a particle converter. Oil droplets in the exhaust gas stream are converted in the wire body at sufficiently high temperatures, thereby achieving particle reduction.

[0018] It has been shown that a coating with a washcoat is particularly advantageous for a wire body in order to achieve good results in particle conversion.

[0019] In this context, a wire body is understood to be a dimensionally stable body formed from at least one metal wire. A wire is a thin, elongated, flexible metal part. The wire preferably has a round cross-section. A square cross-section or another suitable cross-sectional shape may also be advantageous. The cross-section of the wire is advantageously constant along its length within the usual manufacturing tolerances. The wire is preferably produced by drawing.

[0020] Alternatively, the flow unit can have a differently constructed flow unit instead of a wire body.

[0021] Advantageously, the wire cross-section of at least one wire body, and in particular of all wire bodies of the exhaust aftertreatment system, is at least 0.07 mm². If the wire has a round cross-section, its diameter is advantageously at least 0.3 mm. This ensures sufficient stability of the wire body. Simultaneously, a large surface area of ​​the wire body is achieved, resulting in effective particle reduction. Advantageously, the wire cross-section of the wire body is no more than 0.8 mm². Advantageously, the wire diameter of a round wire cross-section is no more than 1 mm.

[0022] Advantageously, the wire of the wire body consists at least partially, and in particular entirely, of a nickel alloy or of stainless steel. In this case, stainless steel refers specifically to stainless steel as defined in DIN EN 10088.

[0023] Advantageously, the density of at least one wire element is between 0.6 g / cm³ and 2.0 g / cm³, at least in the area through which the exhaust gas flows. Preferably, the density of all wire elements of the exhaust gas aftertreatment system is between 0.6 g / cm³ and 2.0 g / cm³, at least in the area through which the exhaust gas flows. It has been shown that good particle reduction can be achieved with a wire element density in the specified range. The wire element density is closely related to the proportion of the wire element's cavities to its total volume. The wire element density thus influences the flow resistance and the residence time of the exhaust gases in the wire element. If the density is within the specified range, favorable values ​​for flow resistance and residence time can be achieved.

[0024] It has been shown that the volume of the wire bodies is relevant for effective particle reduction. Advantageously, the sum of the volumes of the flow-through areas of all wire bodies in the flow unit should be at least 0.6 times the displacement of the internal combustion engine.

[0025] The wire body is preferably made of knitted metal. Preferably, the wire body is wound in a spiral shape. Particularly preferably, the wire body is a spirally wound knitted metal mat. In an advantageous embodiment, the wire body is arranged in the exhaust silencer such that the winding axis passes through the upstream and downstream end faces of the wire body. With an approximately cylindrical shape, a constant wire body thickness, within the usual manufacturing tolerances, can thus be easily achieved over a large part of the cross-section, and in particular over the entire cross-section. Advantageously, the winding axis runs perpendicular to the upstream and / or downstream end faces of the wire body.

[0026] The smallest cross-section of the flow unit in the area through which exhaust gas flows is advantageously at least 8 mm², in particular at least 12 mm² per cubic centimeter of displacement of the internal combustion engine.

[0027] Advantageously, the exhaust silencer has an exhaust inlet and an exhaust outlet. Advantageously, at least one flow unit, in particular at least one wire element of the exhaust aftertreatment system, is arranged in each flow path from the exhaust inlet to the exhaust outlet. Therefore, in a preferred design, the exhaust silencer does not have a bypass to the at least one wire element. Exhaust gas must thus be forced to flow through at least one flow unit, in particular through at least one wire element of the exhaust aftertreatment system. This ensures effective particle reduction. Advantageously, there is no flow path from the exhaust inlet to the exhaust outlet that does not pass through at least one flow unit. In this context, a flow path is understood to be a fluidic connection from the exhaust inlet to the exhaust outlet of the exhaust silencer.The exhaust silencer can contain a variety of flow paths from the exhaust inlet to the exhaust outlet.

[0028] To ensure that exhaust gases flowing out of the exhaust aftertreatment system can cool sufficiently in the exhaust silencer, it is advantageously provided that the second silencer chamber has a volume that is at least 80% of the displacement of the internal combustion engine.

[0029] The internal combustion engine is, in particular, a mixed-lubrication engine. A two-stroke engine is especially preferred. In mixed-lubrication engines, the exhaust gas contains oil droplets that can be converted within the wire body. The working device is advantageously designed such that the temperature of the exhaust gas stream at an upstream side of the exhaust aftertreatment device reaches 450 °C to 750 °C after at least two minutes of operation of the internal combustion engine at full load. This temperature can be achieved, for example, by a suitable design of the internal combustion engine and / or a suitable arrangement of the exhaust aftertreatment device. Such temperatures are achieved, in particular, in mixed-lubrication engines in handheld power tools, especially two-stroke engines.It has been shown that at temperatures within this range, sufficient temperatures are present on the upstream side of the exhaust aftertreatment system for effective particle reduction. Therefore, additional heating of the exhaust aftertreatment system, for example by a heating element or by the catalytic reaction of a catalytic coating on parts of the system, is not strictly necessary. This results in a simpler design for the device.

[0030] For an exhaust silencer for a hand-held power tool, it is provided that the silencer includes an exhaust aftertreatment device, and that the exhaust aftertreatment device comprises at least one flow-through unit, in particular at least one flow-through unit with at least one metal wire body. The exhaust aftertreatment device does not have a catalytic coating. Therefore, the metal wire body is not coated with catalytic material. The wire body has no coating, or the coating of the wire body is not catalytic. In particular, any coating of the wire body does not include a precious metal. This results in a simple, cost-effective design, and the exhaust gases exiting the wire body have a comparatively low temperature.

[0031] Exemplary embodiments of the invention are explained below with reference to the drawing. The drawing shows: Fig. 1 a schematic sectional view through a chainsaw, Fig. 2 a schematic sectional view of the exhaust silencer of the chainsaw made of Fig. 1 , Fig. 3 a schematic perspective view of the exhaust aftertreatment device of the exhaust silencer made of Fig. 2 Fig. 4 a schematic representation of a wire body, Fig. 5 a schematic sectional view through the wire of the wire body made of Fig. 4 , Fig. 6 a schematic representation of the manufacture of the wire body.

[0032] Fig. 1 Figure 1 shows a chainsaw 1 as an embodiment of a handheld power tool. Instead of a chainsaw 1, the power tool could also be a brush cutter, angle grinder, blower, lawnmower, or similar tool. The handheld power tool is, in particular, a hand-carried tool. The chainsaw 1 has a housing 2 to which a handle 3 is attached. Operating elements for the chainsaw 1, in this embodiment a throttle lever 4 and a throttle lock 5, are arranged on the handle 3. The chainsaw 1 has a guide bar 6 on which a saw chain 7 is arranged circumferentially. During operation, the saw chain 7 is driven by an internal combustion engine 8 located in the housing 2. The internal combustion engine 8 is advantageously a mixed-lubricated internal combustion engine 8, in this embodiment a two-stroke engine. The internal combustion engine 8 can also be another type of internal combustion engine 8, in particular a mixed-lubricated four-stroke engine.

[0033] The internal combustion engine 8 includes an air filter 9 through which air is drawn in during operation. The air passes through an intake duct 11 to a crankcase 15 of the internal combustion engine 8. A section of the intake duct 11 is formed within a fuel supply device 10, for example, a carburetor. Alternatively, fuel may be supplied via a fuel valve. Fuel may also be introduced at a different location, for example, into the crankcase 15.

[0034] The internal combustion engine 8 comprises a cylinder 12 in which a piston 13 is mounted to move back and forth. The piston 13 defines a combustion chamber 14 formed in the cylinder 12. The combustion chamber 14 is connected to the cylinder via transfer ports 19 in the region of the bottom dead center of the piston 13, which is located in Fig. 1 The piston 13 is connected to the interior of the crankcase 15 via a connecting rod 16. The crankshaft 17 is rotatably mounted in the crankcase 15. The crankshaft 17 is rotatably mounted about a pivot axis 18. A spark plug 20 protrudes into the combustion chamber 14. The chainsaw 1 includes an exhaust silencer 23. An exhaust port 21 leads from the combustion chamber 14 and is connected via an exhaust channel 22 to an exhaust inlet 24 of the exhaust silencer 23.

[0035] During operation, the two-stroke internal combustion engine 8 draws a fuel / air mixture through the intake port 11 into the crankcase 15 during the upward stroke of the piston 13. During the downward stroke of the piston 15, the fuel / air mixture in the crankcase 15 is compressed. As soon as the transfer ports 19 from the piston 13 to the combustion chamber 14 open, the fuel / air mixture flows from the crankcase 15 into the combustion chamber 14. At top dead center, the spark plug 20 ignites the mixture in the combustion chamber. The subsequent combustion accelerates the piston 13 back towards the crankcase 15. Once the piston 13 opens the exhaust port 21, exhaust gases can escape from the combustion chamber 14 and flow towards the exhaust silencer 23. As soon as the transfer channels 19 from the piston 13 to the combustion chamber 14 are opened, fresh fuel / air mixture flows in for the next combustion.

[0036] Alternatively, the internal combustion engine 8 can also operate with a scavenging system and, in addition to the intake port 11, include one or more air channels through which largely fuel-free air is supplied in advance in the transfer ports 19. During the downward stroke of the piston 13, this pre-charged air separates exhaust gases from the preceding combustion from the fresh fuel / air mixture flowing into the combustion chamber 14.

[0037] The exhaust silencer 23 has a silencer housing 32 in which a first silencer chamber 47 and a second silencer chamber 48 are formed. The first silencer chamber 47 is arranged upstream of the second silencer chamber 48. In the exemplary embodiment, the exhaust gas inlet 24 opens into the first silencer chamber 47. However, it can also be provided that further silencer chambers are formed upstream of the first silencer chamber in the silencer housing 32 or in another unit. The exhaust silencer 23 has an exhaust gas outlet 25 from which exhaust gases can flow from the exhaust silencer 23 into the environment. In at least one flow path, in particular in all flow paths between the second silencer chamber 48 and the outlet opening 25, a spark protection screen 33 is arranged in the exemplary embodiment. The spark protection screen 33 can, for example, be a single-layer fabric made of metal wire.In the exemplary embodiment, the exhaust gas outlet 25 leads from the second silencer chamber 48. In an alternative embodiment, further silencer chambers can be provided downstream of the second silencer chamber 48. Alternatively or additionally, it can be provided that further silencer chambers are arranged between the first silencer chamber 47 and the exhaust aftertreatment device 26 and / or between the exhaust aftertreatment device 26 and the second silencer chamber 48.

[0038] In the exemplary embodiment, the first silencer chamber 47 and the second silencer chamber 48 are separated by a partition 28. The exhaust silencer 23 has an exhaust aftertreatment unit 26. In the exemplary embodiment, the exhaust aftertreatment unit 26 is held on the partition 28. Exhaust gases from the first silencer chamber 47 flow through the exhaust aftertreatment unit 26 into the second silencer chamber 48. In the exemplary embodiment, exactly one exhaust aftertreatment unit 26 is provided through which exhaust gases can flow from the first silencer chamber 47 to the second silencer chamber 48. In an alternative advantageous embodiment, several exhaust aftertreatment units 26 can be provided. In an advantageous embodiment variant, several exhaust aftertreatment units 26 are arranged parallel to one another.When two exhaust aftertreatment devices 26 are arranged in parallel, a partial flow of the exhaust gas stream passes through one of the exhaust aftertreatment devices 26 and another partial flow of the exhaust gas stream passes through the other exhaust aftertreatment device 26. Alternatively or additionally, an arrangement of several exhaust aftertreatment devices 26 in series, such that at least a partial flow of the exhaust gas stream passes first through one and then through the other exhaust aftertreatment device 26, can also be advantageous.

[0039] The partition 28 has an opening 34 that establishes a fluidic connection between the silencer chambers 47 and 48. In the exemplary embodiment, the exhaust aftertreatment device 26 projects through the opening 34. A different arrangement of the exhaust aftertreatment device 26 on the partition 28 may also be advantageous.

[0040] The combustion engine 8 and the exhaust silencer 23 are designed such that the temperature of the exhaust gas flow at the upstream side of the exhaust aftertreatment device 26 is between 450°C and 750°C after 2 minutes of operation of the combustion engine 8 at full load. This results in advantageous temperatures for the conversion of the exhaust gas in the exhaust aftertreatment device.

[0041] The exhaust aftertreatment device 26 comprises a flow unit 31, which will be described in more detail below. In the exemplary embodiment, the exhaust aftertreatment device 26 comprises exactly one flow unit 31. In an alternative embodiment, the exhaust aftertreatment device 26 can comprise several flow units 31.

[0042] The flow unit 31 serves for particle reduction, i.e., as a particle converter. Exhaust gases from mixture-lubricated combustion engines contain lubricating oil in droplet form, which is at least partially converted in the flow unit 31.

[0043] The volume of the silencer chambers 47 and / or 48 is advantageously larger than the volume of the flow unit 31. Advantageously, the second silencer chamber 48 has a volume that is at least 80% of the displacement of the internal combustion engine 8. This allows sufficient cooling of the exhaust gases downstream of the exhaust aftertreatment device 26 to occur easily before the exhaust gases leave the exhaust silencer 23 through the exhaust outlet 25. Alternatively or additionally, it is advantageously provided that the first silencer chamber 47 has a volume that is at least 80% of the displacement of the internal combustion engine 8.

[0044] The construction of the exhaust silencer 23 is described below using the following as an example. Fig. 2 described. How Fig. 2 As shown, the silencer housing 32 in the exemplary embodiment is formed from two partial shells 49 and 50, which are connected to each other at a circumferential edge 51. The partial shells 49 and 50 can, for example, be deep-drawn sheet metal parts that are crimped at the edge 51. The partition 28 runs within the silencer housing 32. In the exemplary embodiment, the partition 28 is formed as sheet metal and is also fixed at the edge 51. The exhaust aftertreatment device 26 is arranged in the opening 34 of the partition 28. The first silencer chamber 47 and, downstream of the first silencer chamber 47, the second silencer chamber 48 are formed within the silencer housing 32. The exhaust aftertreatment device 26 is arranged in at least one flow path from the first silencer chamber 47 to the second silencer chamber 48.In the exemplary embodiment, the exhaust aftertreatment device 26 is arranged such that each flow path from the first silencer chamber 47 to the second silencer chamber 48 leads through the exhaust aftertreatment device 26. The exhaust aftertreatment device 26 has a housing 27. In the exemplary embodiment, several inlet openings 29 lead into the housing 27.

[0045] A single inlet opening 29 may also be provided. In the exemplary embodiment, the inlet openings 29 adjoin the first silencer chamber 47. Several outlet openings 30 lead from the housing 27 of the exhaust aftertreatment device 26. A single outlet opening 30 may also be provided.

[0046] The flow unit 31 is arranged in the housing 27 of the exhaust aftertreatment device 26. In the exemplary embodiment, the flow unit 31 is formed by a single wire body 41. How Fig. 2 As shown, the flow unit 31 has a first, upstream end face 36 and a second, downstream end face 37. The exhaust gases flow through the exhaust aftertreatment device 26 in a main flow direction 35. The main flow direction 35 is directed from the first end face 36 to the second end face 37. Due to the structure of the wire body 41, cross flows occur within it. This allows for a multitude of flow paths through the wire body 41.

[0047] In the exemplary embodiment, the entire wire body 41 is permeated by exhaust gas. In an alternative embodiment where not the entire wire body 41 is permeated by exhaust gas, the dimensions specified below refer only to the area permeated by exhaust gas. Areas of the wire body 41 or the flow unit 31 that are not permeated by exhaust gas are not taken into account.

[0048] The thickness b of the flow unit 31 in the area through which exhaust gas flows is advantageously at least 10 mm, particularly at least 15 mm, and preferably at least 20 mm. The thickness b is measured from the upstream end face 36 to the downstream end face 37. The thickness b is advantageously measured parallel to the main flow direction 35. In the exemplary embodiment in which the end faces 36 and 37 are parallel to each other within the manufacturing tolerances, the thickness b is measured perpendicular to the end faces 36 and 37. The flow unit 31 does not need to have the specified thickness b over its entire cross-section. The flow unit 31 has a maximum cross-section E, which is Fig. 2 The flow unit 31 has a section 45, shown with a dashed line. Within section 45, the thickness b is constant in the exemplary embodiment, within the usual manufacturing tolerances. Section 45 is in Fig. 2 The diagram is shown schematically delimited by dashed lines. Advantageously, the flow unit 31 has a thickness b of at least 10 mm over at least 70%, and in particular at least 80%, of its largest cross-section E in the flow-through area. In the exemplary embodiment, the flow unit 31 has a thickness b over the entire area 45. Particularly preferably, the thickness b of the flow unit 31 in the area through which exhaust gas flows is at least 10 mm, and in particular at least 15 mm, over the entire cross-section. The largest cross-section E advantageously extends perpendicular to the main flow direction 35.

[0049] Preferably, the flow unit 31 is formed by a single flow body 41. However, it is also possible for the flow unit 31 to be formed by several flow bodies 41.

[0050] The flow body 41 has a multitude of cavities that allow flow through it. This is in Fig. 4 schematically represented. The flow body 41 has no closed surfaces at least on its end faces 36 and 37, as shown. Fig. 4 The flow unit 31, in the exemplary embodiment, comprises the wire of the associated flow body 41 and the cavities formed between the wire sections. The flow unit 31 designates the casing that surrounds the flow body 41 and against which the flow body 41 rests uniformly, within the limits of manufacturing accuracy and the uniformity of the size and distribution of the cavities.

[0051] As the Figuren 2 und 3 As shown, the housing 27 of the exhaust aftertreatment device 26 is formed by two partial shells 38 and 39. The partial shells 38 and 39 are firmly connected to each other, in particular by a sealing connection. The flow unit 31 is advantageously pressed into the housing 27 of the exhaust aftertreatment device 26.

[0052] How Fig. 3 As shown, the inlet openings 29 and the outlet openings 30 do not overlap in the main flow direction 35. Therefore, exhaust gases must also flow perpendicular to the main flow direction 35 on their way through the exhaust aftertreatment device 26. This increases the residence time of the exhaust gases in the exhaust aftertreatment device 29. A different arrangement of the inlet openings 29 and outlet openings 30 may also be advantageous.

[0053] The flow unit 31 is formed by the at least one wire body 41. Fig. 4 Figure 1 schematically shows a possible design of the wire body 41. In the exemplary embodiment, the wire body 41 is made of knitted metal 42, which has been pressed into a suitable shape. Alternatively, the wire body 41 can also be made of a knitted wire, a wire mesh, or the like. The knitted metal 42 is made of a wire 43.

[0054] Wire 43 is in Fig. 5 The wire 43 is shown schematically in cross-section. In the exemplary embodiment, the wire 43 has a round cross-section with a diameter d. The diameter d is advantageously at least 0.3 mm. The cross-sectional area A of the wire 43 is advantageously at least 0.07 mm². This cross-sectional area is also advantageous for a wire 43 that has a cross-sectional shape other than round. The wire 43 is advantageously made at least partially, and in particular entirely, of a nickel alloy or of stainless steel.

[0055] The wire body 41 is advantageously formed from wound metal knitting 42, as shown schematically in Fig. 6 As illustrated by arrow 44, the metal mesh 42 is wound around a winding axis 46. Before winding, the metal mesh 42 is, for example, in the form of a mat.

[0056] How Fig. 4 As shown, the winding axis 46 advantageously extends from the first end face 36 to the second end face 37 of the flow unit 31. The main flow direction 35 advantageously runs parallel to the winding axis 46. In a preferred embodiment, the wire body 41 has an approximately cylindrical shape. However, another shape for the wire body 41 may also be advantageous. The wire body 41 is advantageously pressed into a suitable shape.

[0057] To achieve sufficient particle reduction, the sum of the volumes of all wire bodies 41 of the flow unit 31 is at least 0.6 times the displacement of the internal combustion engine 8. In the exemplary embodiment, the volume of the wire body 41 of the flow unit 31 is at least 0.6 times the displacement of the internal combustion engine 8. If not all areas of the wire body 41 are flowed through, the sum of the volumes of the flowed-through areas of all wire bodies 41 of the flow unit 31 is at least 0.6 times the displacement of the internal combustion engine 8.

[0058] The density of the wire body 41 is at least 0.6 g / cm³ to 2 g / cm³ in the area through which the exhaust gas flows. This ensures sufficient contact between the exhaust gases and the surface of the wire body 41. Advantageously, the density of all wire bodies 41 of the exhaust silencer 23 lies within the specified range. In the exemplary embodiment, the entire wire body 41 is through which the exhaust gas flows.

[0059] According to the invention, the flow unit 31 does not have a catalytically active coating. In this context, a catalytically active coating is a coating that acts as a catalyst, thus lowering the activation energy for the chemical reaction of the exhaust gases and thereby increasing the reaction rate. A catalytic coating is, in particular, a coating with a precious metal, primarily used for converting hydrocarbons and / or nitrogen oxides. No flow unit 41 of the exhaust aftertreatment system 26 is provided with a catalytically active coating.

[0060] The wire body 41 of the flow unit 31 is coated with a washcoat. In this context, a washcoat is a coating that increases the surface area without lowering the activation energy for the chemical reaction. Therefore, a washcoat is not a catalytically active coating as defined in this document. For example, the washcoat can be made of aluminum oxide.

Claims

1. Handheld work apparatus having a combustion engine (8) and having an exhaust muffler (23) in which are formed a first muffler chamber (47) and a second muffler chamber (48), the exhaust muffler (23) comprising an exhaust gas after-treatment unit (26) which comprises at least one through-flow unit (31), the through-flow unit (31) being disposed in a flow path from the first muffler chamber (47) into the second muffler chamber (48), the thickness (b) of the through-flow unit (31) measured from an upstream end face (36) to a downstream end face (37) of the through-flow unit (31) in the region of the through-flow unit (31) passed through by a flow of exhaust gas being at least 10 mm at least across 70 % of the largest cross section (E), characterized in that the exhaust gas after-treatment unit (26) does not have a catalytically effective coating, and in that the at least one through-flow unit (31) is at least partially coated with a washcoat.

2. Work apparatus according to Claim 1, characterized in that the through-flow unit (31) comprises at least one wire element (41) of metal.

3. Work apparatus according to Claim 2, characterized in that the wire cross section of the at least one wire element (41), in particular of all wire elements (41) of the exhaust gas after-treatment unit (26), is at least 0.07 mm2.

4. Work apparatus according to Claim 2 or 3, characterized in that the wire of the wire element (41) consists at least partially of a nickel alloy or of stainless steel.

5. Work apparatus according to one of Claims 2 to 4, characterized in that the density of at least one, in particular of all, wire elements (41) at least in the region passed through by a flow of exhaust gas is 0.6 g / cm3 to 2 g / cm3.

6. Work apparatus according to one of Claims 2 to 5, characterized in that the sum of the volumes of the regions passed through by a flow of all wire elements (41) of the through-flow unit (31) is at least 0.6 times the cubic capacity of the combustion engine (8).

7. Work apparatus according to one of Claims 2 to 6, characterized in that the wire element (41) is formed from a knitted metal mesh (42).

8. Work apparatus according to one of Claims 2 to 7, characterized in that the wire element (41) is helically wound.

9. Work apparatus according to Claim 8, characterized in that the wire element (41) is disposed in the exhaust muffler (23) in such a way that the winding axis (46) extends through the upstream end face (36) and the downstream end face (47) of the wire element (41).

10. Work apparatus according to one of Claims 1 to 9, characterized in that the smallest cross section of the through-flow unit (31) in the region of the through-flow unit (31) passed through by a flow of exhaust gas is at least 8 mm2 per cubic centimetre of cubic capacity of the combustion engine (8).

11. Work apparatus according to one of Claims 1 to 10, characterized in that the exhaust muffler (23) has an exhaust inlet (24) into the exhaust muffler (23) and an exhaust outlet (25) from the exhaust muffler (23), and in that at least one through-flow unit (31), in particular at least one wire element (41) of the exhaust gas after-treatment unit (26), is disposed in each flow path from the exhaust inlet (24) to the exhaust outlet (25).

12. Work apparatus according to one of Claims 1 to 11, characterized in that the second muffler chamber (48) has a volume which is at least 80 % of the cubic capacity of the combustion engine (8).

13. Work apparatus according to one of Claims 1 to 12, characterized in that the combustion engine (8) is a mixture-lubricated combustion engine (8), in particular a two-stroke engine.

14. Work apparatus according to one of Claims 1 to 13, characterized in that the work apparatus (1) is designed in such a manner that the temperature of an exhaust gas flow on the upstream side of the exhaust gas after-treatment unit (26) after at least 2 minutes of operating time of the combustion engine (8) under full load is 450°C to 750°C.

15. Exhaust muffler for a handheld work apparatus according to one of Claims 1 to 14, wherein a first muffler chamber (47) and a second muffler chamber (48) are formed in the exhaust muffler (23), the exhaust muffler (23) comprising an exhaust gas after-treatment unit (26), the exhaust gas after-treatment unit (26) comprising at least one through-flow unit (31), in particular at least one through-flow unit (31) having at least one wire element (41) of metal, the through-flow unit (31) being disposed in a flow path from the first muffler chamber (47) into the second muffler chamber (48), the thickness (b) of the through-flow unit (31) measured from an upstream end face (36) to a downstream end face (37) of the through-flow unit (31) in the region of the through-flow unit (31) passed through by a flow of exhaust gas being at least 10 mm at least across 70 % of the largest cross section (E), characterized in that the exhaust gas after-treatment unit (26) does not have a catalytic coating, and in that the at least one through-flow unit (31) is at least partially coated with a washcoat.

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