HANDHELD WORK APPARATUS, AND EXHAUST GAS AFTER-TREATMENT UNIT FOR A HANDHELD WORK APPARATUS, AND EXHAUST MUFFLER

Abstract

A handheld work apparatus includes a combustion engine and an exhaust muffler. A first muffler chamber and a second muffler chamber are formed in the exhaust muffler. The exhaust muffler includes an exhaust gas after-treatment unit which includes at least one through-flow unit. The through-flow unit is disposed in a flow path from the first muffler chamber into the second muffler chamber. The thickness of the through-flow unit measured from an upstream end face to a downstream end face of the through-flow unit in the region of the through-flow unit passed through by a flow of exhaust gas is at least 10 mm across at least 70% of the cross section. The exhaust gas after-treatment unit does not have a catalytically effective coating.

Claims

1. A handheld work apparatus comprising: a combustion engine; an exhaust muffler having a first muffler chamber and a second muffler chamber formed therein; said exhaust muffler including an exhaust gas after-treatment unit which includes at least one through-flow unit; said at least one through-flow unit being disposed in a flow path from said first muffler chamber into said second muffler chamber and having a thickness measured from an upstream end face to a downstream end face of said at least one through-flow unit in a region of said at least one through-flow unit passed through by a flow of exhaust gas of at least 10 mm across at least 70% of a largest cross section; and, wherein said exhaust gas after-treatment unit does not have a catalytically effective coating.

2. The work apparatus of claim 1, wherein said at least one through-flow unit is at least partially coated with a washcoat.

3. The work apparatus of claim 1, wherein said at least one through-flow unit includes at least one wire element of metal.

4. The work apparatus of claim 3, wherein a wire cross section of said at least one wire element of the exhaust gas after-treatment unit is at least 0.07 mm.sup.2.

5. The work apparatus of claim 3, wherein a wire of said at least one wire element is made at least partially of a nickel alloy or of stainless steel.

6. The work apparatus of claim 3, wherein a density of said at least one wire element at least in the region passed through by a flow of exhaust gas is 0.6 g/cm.sup.3 to 2 g/cm.sup.3.

7. The work apparatus of claim 3, wherein a sum of volumes of regions passed through by a flow of all of said at least one wire element of said through-flow unit is at least 0.6 times a cubic capacity of said combustion engine.

8. The work apparatus of claim 3, wherein said at least one wire element is formed from a knitted metal mesh.

9. The work apparatus of claim 3, wherein said at least one wire element is helically wound.

10. The work apparatus of claim 9, wherein said at least one wire element is disposed in said exhaust muffler such that a winding axis extends through an upstream end face and a downstream end face of said at least one wire element.

11. The work apparatus of claim 1, wherein a smallest cross section of said at least one through-flow unit in the region of the at least one through-flow unit passed through by a flow of exhaust gas is at least 8 mm.sup.2 per cubic centimeter of a cubic capacity of said combustion engine.

12. The work apparatus of claim 1, wherein said exhaust muffler has an exhaust inlet into said exhaust muffler and an exhaust outlet from said exhaust muffler; and, at least one of said at least one through-flow unit is disposed in each flow path from said exhaust inlet to said exhaust gas outlet.

13. The work apparatus of claim 1, wherein said exhaust muffler has an exhaust inlet into said exhaust muffler and an exhaust outlet from said exhaust muffler; and, at least one of wire element of the exhaust gas after-treatment unit is disposed in each flow path from said exhaust inlet to said exhaust gas outlet.

14. The work apparatus of claim 1, wherein said second muffler chamber has a volume which is at least 80% of a cubic capacity of said combustion engine.

15. The work apparatus of claim 1, wherein said combustion engine is a mixture-lubricated combustion engine.

16. The work apparatus of claim 1, wherein the work apparatus is configured such that a temperature of an exhaust gas flow on an upstream side of said exhaust gas after-treatment unit after at least 2 minutes of operating time of said combustion engine under full load is 450 C. to 750 C.

17. The work apparatus of claim 1, wherein said combustion engine is a two-stroke engine.

18. An exhaust muffler, in particular for a mixture-lubricated combustion engine in a handheld work apparatus, comprising: an exhaust inlet; an exhaust outlet; a first muffler chamber; a second muffler chamber; a first through-flow unit for exhaust gas after-treatment; a second through-flow unit for exhaust gas after-treatment; said first muffler chamber being disposed upstream of said second muffler chamber; said second through-flow unit having a catalytically effective coating in at least one portion; said first through-flow unit having a smaller quantity of catalytically effective coating in terms of volume than said second through-flow unit or no catalytically effective coating; wherein a first flow path and a second flow path from said first muffler chamber into said second muffler chamber are formed in the exhaust muffler; wherein flow cross sections of said first flow path and said second flow path are structurally predefined and invariable; said first flow path leading through said first through-flow unit and bypassing said second through-flow unit; said second flow path leading through said second through-flow unit and bypassing said first through-flow unit; and, said first through-flow unit and said second through-flow unit being disposed so as to be spatially separated from one another.

19. An exhaust gas after-treatment unit comprising: a housing; a first through-flow unit and a second through-flow unit disposed in said housing; said first through-flow unit having a catalytic coating; said second through-flow unit not having a catalytic coating or having a smaller mass of catalytic coating per volumetric unit than said first through-flow unit; said housing defining at least one first inflow opening into said first through-flow unit, at least one second inflow opening into said second through-flow unit, and at least one transfer opening from said first through-flow unit into said second through-flow unit; said first through-flow unit having an outflow surface and an outflow direction which is oriented perpendicularly to said outflow surface from said first through-flow unit to said second through-flow unit; said second through-flow unit having an inflow surface; and, said inflow surface of said second through-flow unit does not protrude beyond a plane containing said outflow surface.

20. An exhaust gas after-treatment unit comprising: a housing; a first through-flow unit and a second through-flow unit which are disposed in said housing; said second through-flow unit having a catalytic coating; said first through-flow unit not having a catalytic coating or having a smaller mass of catalytic coating per volumetric unit than said second through-flow unit; said first through-flow unit having an outflow surface; said housing having at least one transfer opening through which exhaust gas from said first through-flow unit can flow to said second through-flow unit; and, said housing having at least one outflow opening through which exhaust gas from said first through-flow unit can exit said housing without having previously passed through said second through-flow unit.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0110] The invention will now be described with reference to the drawings wherein:

[0111] FIG. 1 shows a schematic sectional illustration through a chain saw;

[0112] FIG. 2 shows a schematic sectional illustration of the exhaust muffler of the chain saw from FIG. 1;

[0113] FIG. 3 shows a schematic perspective illustration of the exhaust gas after-treatment unit of the exhaust muffler from FIG. 2;

[0114] FIG. 4 shows a schematic illustration of a wire element;

[0115] FIG. 5 shows a schematic sectional illustration through the wire of the wire element from FIG. 4;

[0116] FIG. 6 shows a schematic illustration of the production of the wire element;

[0117] FIG. 7 shows a schematic sectional illustration of a chain saw;

[0118] FIGS. 8 to 15 show schematic sectional illustrations of embodiments of exhaust mufflers of the chain saw from FIG. 7;

[0119] FIG. 16 shows a schematic sectional illustration along the line X-X in FIG. 15;

[0120] FIGS. 17, 18 show a schematic sectional illustration of additional embodiments of exhaust mufflers of the chain saw from FIG. 7;

[0121] FIG. 19 shows a schematic sectional illustration of a through-flow unit;

[0122] FIG. 20 shows a schematic sectional illustration of a handheld work apparatus having an exhaust muffler having an exhaust gas after-treatment unit;

[0123] FIG. 21 shows a sectional illustration through the exhaust gas after-treatment unit of the work apparatus from FIG. 20;

[0124] FIG. 22 shows a schematic lateral view of the exhaust gas after-treatment unit from FIG. 21 when viewed in the direction of the arrow III in FIG. 21;

[0125] FIG. 23 shows a schematic illustration of a potential construction of a through-flow element of a through-flow unit;

[0126] FIG. 24 shows a schematic illustration of an alternative configuration of an exhaust muffler;

[0127] FIG. 25 shows a schematic sectional illustration through a chain saw;

[0128] FIG. 26 shows a sectional illustration of the exhaust gas after-treatment unit of the exhaust muffler of the chain saw from FIG. 25;

[0129] FIG. 27 shows a schematic lateral view when viewed in the direction of the arrow III in FIG. 26; and,

[0130] FIGS. 28, 29 show schematic illustrations of potential configurations of through-flow units.

DETAILED DESCRIPTION

[0131] In FIGS. 1 to 6, the reference signs mentioned hereunder are in each case illustrated without the prefix A.

[0132] FIG. 1 shows as an embodiment for a handheld work apparatus a chain saw A1. Instead of a chain saw A1, the work apparatus can also be a brushcutter, an angle grinder, a blower, a lawnmower or a like work apparatus. The handheld work apparatus is in particular a portable work apparatus. The chain saw A1 has a housing A2 on which a handle A3 is held. Operating elements for the chain saw A1, in the embodiment a throttle lever A4 and a throttle lever lock A5, are disposed on the handle A3. The chain saw A1 has a guide bar A6 on which a revolving saw chain A7 is disposed. During operation, the saw chain A7 is driven by a combustion engine A8 disposed in the housing A2. The combustion engine A8 is advantageously a mixture-lubricated combustion engine A8, in the embodiment a two-stroke engine. The combustion engine A8 may also be a different combustion engine A8, in particular a mixture-lubricated four-stroke engine.

[0133] The combustion engine A8 includes an air filter A9 by way of which air is inducted during operation. The air makes its way to a crankcase A15 of the combustion engine A8 by way of an intake channel A11. A portion of the intake channel A11 is formed in a fuel supply unit A10, for example a carburetor. A different type of supply of fuel, for example by way of a fuel valve, may also be provided. A different location of introducing fuel, for example into the crankcase A15, may also be provided.

[0134] The combustion engine A8 includes a cylinder A12 in which a piston A13 is mounted so as to reciprocate. The piston A13 delimits a combustion chamber A14 formed in the cylinder A12. The combustion chamber A14 is connected to the interior of the crankcase A15 by way of transfer channels A19 in the region of the lower dead center of the piston A13, illustrated in FIG. 1. The piston A13, by way of a connecting rod A16, drives a crankshaft A17 which is rotatably mounted in the crankcase A15. The crankshaft A17 is mounted so as to be rotatable about a rotational axis A18. A spark plug A20 protrudes into the combustion chamber A14. The chain saw A1 includes an exhaust muffler A23. An outlet opening A21, which is connected to an exhaust inlet A24 of the exhaust muffler A23 by way of an outlet channel A22, leads out of the combustion chamber A14.

[0135] During operation, the combustion engine A8, configured as a two-stroke engine, inducts a fuel/air mixture through the intake channel A11 into the interior of the crankcase A15 during the upward stroke of the piston A13. The fuel/air mixture is compressed in the crankcase A15 during the downward stroke of the piston A15. As soon as the transfer channels A19 from the piston A13 to the combustion chamber A14 are opened, the fuel/air mixture flows from the interior of the crankcase A15 into the combustion chamber A14. In the region of the upper dead center, the spark plug A20 ignites the mixture in the combustion chamber. Due to the subsequent combustion, the piston A13 is accelerated back in the direction toward the crankcase A15 again. As soon as the piston A13 opens the outlet opening A21, exhaust gases can flow out of the combustion chamber A14 and flow toward the exhaust muffler A23. As soon as the transfer channels A19 from the piston A13 to the combustion chamber A14 are opened, fresh fuel/air mixture is replenished for the next combustion.

[0136] Alternatively, the combustion engine A8 can also operate with stratified scavenging and, in addition to the intake channel A11, include one or a plurality of air ducts by way of which largely fuel-free air is kept available in the transfer channels A19. During the downward stroke of the piston A13, the pre-stored air separates exhaust gases from the previous combustion from fresh fuel/air mixture flowing into the combustion chamber A14.

[0137] The exhaust muffler A23 has a muffler housing A32 in which a first muffler chamber A47 and a second muffler chamber A48 are formed. The first muffler chamber A47 is disposed upstream of the second muffler chamber A48. In the embodiment, the exhaust inlet A24 opens into the first muffler chamber A47. However, it can also be provided that additional muffler chambers are formed in the muffler housing A32, or in another unit, upstream of the first muffler chamber. The exhaust muffler A23 has an exhaust outlet A25 from which exhaust gases from the exhaust muffler A23 can flow out into the environment. In the embodiment, a spark-protective sleeve A33 is disposed in at least one flow path, in particular in all flow paths, between the second muffler chamber A48 and the exit opening A25. The spark-protective sleeve A33 can be, for example, a single-layer woven mesh of metal wire. In the embodiment, the exhaust outlet A25 leads out of the second muffler chamber A48. In an alternative embodiment, additional muffler chambers can be provided downstream of the second muffler chamber A48. Alternatively or additionally, it can be provided that additional muffler chambers are disposed between the first muffler chamber A47 and the exhaust gas after-treatment unit A26, and/or between the exhaust gas after-treatment unit A26 and the second muffler chamber A48.

[0138] The first muffler chamber A47 and the second muffler chamber A48 in the embodiment are separated by a partition wall A48. The exhaust muffler A23 has an exhaust gas after-treatment unit A26. In the embodiment, the exhaust gas after-treatment unit A26 is held on the partition wall A28. Exhaust gases from the first muffler chamber A47 flow through the exhaust gas after-treatment unit A26 into the second muffler chamber A48. Provided in the embodiment is exactly one exhaust gas after-treatment unit A26 through which exhaust gases can flow from the first muffler chamber A47 to the second muffler chamber A48. In an alternative advantageous embodiment, a plurality of exhaust gas after-treatment units A26 can be provided. In an advantageous variant of embodiment, a plurality of exhaust gas after-treatment units A26 are disposed in parallel. In a parallel arrangement of two exhaust gas after-treatment units A26, one sub-flow of the exhaust gas flow flows through one of the exhaust gas after-treatment units A26, and another sub-flow of the exhaust gas flow flows through the other of the exhaust gas after-treatment units A26. Alternatively or additionally, an arrangement of a plurality of successive exhaust gas after-treatment units A26, so that at least one sub-flow of the exhaust gas flow flows first through the one and then through the other exhaust gas after-treatment unit A26, may also be advantageous.

[0139] The partition wall A28 has an opening A34 which establishes a fluidic connection between the muffler chambers A47 and A48. In the embodiment, the exhaust gas after-treatment unit A26 protrudes through the opening A34. A different arrangement of the exhaust gas after-treatment unit A26 on the partition wall A28 may also be advantageous.

[0140] The combustion engine A8 and the exhaust muffler A23 are configured in such a way that the temperature of the exhaust gas flow on the upstream side of the exhaust gas after-treatment unit A26 after 2 minutes of operating time of the combustion engine A8 at full load is 450 C. to 750 C. This results in advantageous temperatures for converting the exhaust gas in the exhaust gas after-treatment unit.

[0141] The exhaust gas after-treatment unit A26 includes a through-flow unit A31 which will be described in more detail hereunder. In the embodiment, the exhaust gas after-treatment unit A26 includes exactly one through-flow unit A31. In an alternative embodiment, the exhaust gas after-treatment unit A26 can include a plurality of through-flow units A31.

[0142] The through-flow unit A31 serves for reducing particles, thus as a particle converter. Lubricating oil in the form of droplets, which is at least partially converted in the through-flow unit A31, is contained in exhaust gases of mixture-lubricated combustion engines.

[0143] The volume of the muffler chambers A47 and/or A48 is advantageously larger than the volume of the through-flow unit A31. The second muffler chamber A48 advantageously has a volume which is at least 80% of the cubic capacity of the combustion engine A8. Owing to this fact, sufficient cooling of the exhaust gases downstream of the exhaust gas after-treatment unit A26 can easily take place before the exhaust gases leave the exhaust muffler A23 through the exhaust outlet A25. Alternatively or additionally, it is advantageously provided that the first muffler chamber A47 has a volume which is at least 80% of the cubic capacity of the combustion engine A8.

[0144] The construction of the exhaust muffler A23 will be described hereunder with reference to FIG. 2. As shown in FIG. 2, the muffler housing A32 in the embodiment is formed from two component shells A49 and A50 which are connected to one another on a peripheral edge A51. The component shells A49 and A50 can be, for example, deep-drawn parts of sheet metal which are crimped on the edge A51. The partition wall A28 extends in the muffler housing A32. In the embodiment, the partition wall A28 is formed as a sheet-metal panel and likewise fixed on the edge A51. The exhaust gas after-treatment unit A26 is disposed in the opening A34 of the partition wall A28. The first muffler chamber A47 and, downstream of the first muffler chamber A47, the second muffler chamber A48 are formed in the muffler housing A32. The exhaust gas after-treatment unit A26 is disposed in at least one flow path from the first muffler chamber A47 to the second muffler chamber A48. The exhaust gas after-treatment unit A26 in the embodiment is disposed in such a way that each flow path from the first muffler chamber A47 to the second muffler chamber A48 leads through the exhaust gas after-treatment unit A26. The exhaust gas after-treatment unit A26 has a housing A27. In the embodiment, a plurality of inflow openings A29 lead into the housing A27. A single inflow opening A29 may also be provided. In the embodiment, the inflow openings A29 are contiguous to the first muffler chamber A47. A plurality of outflow openings A30 lead out of the housing A27 of the exhaust gas after-treatment unit A26. A single outflow opening A30 may also be provided.

[0145] The through-flow unit A31 is disposed in the housing A27 of the exhaust gas after-treatment unit A26. In the embodiment, the through-flow unit A31 is formed by a single wire element A41. As shown in FIG. 2, the through-flow unit A31 has a first upstream end face A36 and a second downstream end face A37. The exhaust gases flow in a main flow direction A35 through the exhaust gas after-treatment unit A26. The main flow direction A35 is oriented from the first end face A36 to the second end face A37. Due to the structure of the wire element A41, there are cross flows in the wire element A41. As a result, a multiplicity of flow paths through the wire element A41 are possible.

[0146] In the embodiment, the entire wire element A41 is passed through by a flow of exhaust gas. In an alternative embodiment, in which not the entire wire element A41 is passed through by a flow of exhaust gas, the dimensions stated hereunder relate only to the region passed through by a flow of exhaust gas. Regions of the wire element A41, or of the through-flow unit A31, that are not passed through by a flow of exhaust gas, are not taken into account.

[0147] A thickness b of the through-flow unit A31 in the region passed through by a flow of exhaust gas is advantageously at least 10 mm, in particular at least 15 mm, preferably at least 20 mm. The thickness b herein is measured from the upstream end face A36 to the downstream end face A37. The thickness b is advantageously measured parallel to the main flow direction A35. In the embodiment, in which the end faces A36 and A37 extend parallel to one another within the scope of the manufacturing tolerances, the thickness b is measured perpendicularly to the end faces A36 and A37. The through-flow unit A31 does not have to have the stated thickness b across its entire cross section. The through-flow unit A31 has a largest cross section E which is plotted with a dashed line in FIG. 2. The through-flow unit A31 has a region A45. In the embodiment, the thickness b in the region A45 is constant within the scope of the usual manufacturing tolerances. In FIG. 2, the region A45 is schematically illustrated so as to be delimited by dashed lines. Advantageously, the through-flow unit A31 has the thickness b of at least 10 mm across at least 70%, in particular at least 80%, of its largest cross section E in the region passed through by the flow. In the embodiment, the through-flow unit A31 has the thickness b across the entire region A45. Particularly preferably, the thickness b of the through-flow unit A31 in the region of the through-flow unit A31 passed through by a flow of exhaust gas across the entire cross section is at least 10 mm, in particular at least 15 mm. The largest cross section E extends advantageously perpendicularly to the main flow direction A35.

[0148] The through-flow unit A31 is preferably formed by a single through-flow element A41. However, it can also be provided that the through-flow unit A31 is formed by a plurality of through-flow elements A41.

[0149] The through-flow element A41 has a multiplicity of cavities which permit a flow to pass through. This is schematically illustrated in FIG. 4. The through-flow element A41 has no closed surfaces, at least not on the end faces A36 and A37, as shown in FIG. 4. The through-flow unit A31 in the embodiment includes the wire of the assigned through-flow element A41 and the cavities which are formed between the portions of the wire. The through-flow unit A31 defines the envelope element which surrounds the through-flow element A41 and on which the through-flow element A41 rests uniformly within the scope of the manufacturing accuracy and uniformity in terms of size and distribution of the cavities.

[0150] As shown in FIGS. 2 and 3, the housing A27 of the exhaust gas after-treatment unit A26 is formed by two component shells A38 and A39. The component shells A38 and A39 are fixedly connected to one another, in particular in a sealing manner. The through-flow unit A31 is advantageously press-fitted into the housing A27 of the exhaust gas after-treatment unit A26.

[0151] As is shown in FIG. 3, the inflow openings A29 and the outflow openings A30 do not overlap one another in the main flow direction A35. Owing to this fact, exhaust gases on the way through the exhaust gas after-treatment unit A26 must also flow transversely to the main flow direction A35. As a result, the dwell time of the exhaust gases in the exhaust gas after-treatment unit A29 is increased. A different arrangement of the inflow openings A29 and outflow openings A30 may also be advantageous.

[0152] The through-flow unit A31 is formed by the at least one wire element A41. FIG. 4 schematically shows a potential configuration embodiment of the wire element A41. In the embodiment, the wire element A41 is constructed from a knitted metal mesh A42 which has been pressed into a suitable shape. Alternatively, the wire element A41 can also be constructed from a flat-knitted wire structure, a braided wire structure, or the like. The knitted metal mesh A42 is formed from a wire A43.

[0153] The wire A43 is schematically illustrated in the cross section in FIG. 5. In the embodiment, the wire A43 has a round cross section having a diameter d. The diameter d is advantageously at least 0.3 mm. The cross-sectional area A of the wire A43 is advantageously at least 0.07 mm2. This cross-sectional area is also advantageous for a wire A43 that has a cross-sectional shape deviating from the round shape. Advantageously, the wire A43 consists at least partially, in particular completely, of a nickel alloy or of stainless steel.

[0154] The wire element A41 is advantageously formed from a wound knitted metal mesh A42, as is schematically illustrated in FIG. 6. As is highlighted by the arrow A44, the knitted metal mesh A42 is wound about a winding axis A46. Prior to winding, the knitted metal mesh A42 is present in the form of a mat, for example.

[0155] As is shown in FIG. 4, the winding axis A46 advantageously extends from the first end face A36 to the second end face A37 of the through-flow unit A31. The main flow direction A35 advantageously extends parallel to the winding axis A46. The wire element A41 has, in an embodiment, an approximately cylindrical shape. However, a different shape of the wire element A41 may also be advantageous. The wire element A41 here is advantageously pressed into a suitable shape.

[0156] In order to achieve a sufficient particle reduction, it is provided that the sum of the volumes of all wire elements A41 of the through-flow unit A31 is at least 0.6 times the cubic capacity of the combustion engine A8. In the embodiment, the volume of the wire element A41 of the through-flow unit A31 is at least 0.6 times the cubic capacity of the combustion engine A8. If not all regions of the wire element A41 are passed through by a flow, the sum of the volumes of the regions of all wire elements A41 of the through flow unit A31 that are passed through by a flow is at least 0.6 times the cubic capacity of the combustion engine A8.

[0157] The density of the wire element A41, at least in the region passed through by a flow of exhaust gas, is 0.6 g/cm3 to 2 g/cm3. As a result, sufficient contact between the exhaust gases and the surface of the wire element A41 is ensured. Advantageously, the density of all wire elements A41 of the exhaust muffler A23 is in the range stated. In the embodiment, the entire wire element A41 is passed through by a flow of exhaust gas.

[0158] According to the disclosure, the through-flow unit A31 does not have a catalytically effective coating. A catalytically effective coating is presently understood to be a coating which acts as a catalytic converter, thus reducing the activation energy for the chemical conversion of the exhaust gases, and increasing the response rate as a result. A catalytic coating is in particular a coating which includes a precious metal and serves largely for converting hydrocarbons and/or nitrogen oxides. No through-flow unit A41 of the exhaust gas after-treatment unit A26 is provided with a catalytically effective coating.

[0159] The wire element A41 of the through-flow unit A31 in the embodiment is coated with a washcoat. A washcoat is presently understood to be a coating which increases the surface without reducing the activation energy for the chemical conversion. Accordingly, a washcoat is not a catalytically effective coating in the context of the present document. For example, the washcoat can be made of aluminum oxide.

[0160] In FIGS. 7 to 19, the reference signs mentioned hereunder are in each case illustrated without the prefix B.

[0161] FIG. 7 shows a chain saw B1 as an embodiment for a work apparatus. However, an exhaust muffler according to the disclosure can also be used in other work apparatuses, in particular handheld work apparatuses such as brushcutters, angle grinders, lawnmowers or the like. The chain saw B1 has a housing B2 on which a rear handle B3 is fixedly established. The rear handle B3 serves to guide the chain saw B1 during operation. In the embodiment, operating elements, specifically a throttle lever B4 and a throttle lever lock B5, are disposed on the rear handle B3. A guide bar B6, on which a revolving saw chain B7 is guided, is fixedly established on the housing B2. The saw chain B7 is driven by a combustion engine B8 disposed in the housing B2.

[0162] During operation, the combustion engine B8 inducts combustion air through an intake channel B11 by way of an air filter B9. A portion of the intake channel B11 is formed in a fuel supply unit B10, for example a carburetor. The combustion engine B8 has a cylinder B12 in which a piston B13 is guided so as to reciprocate. The piston B13 delimits a combustion chamber B14 formed in the cylinder B12.

[0163] The intake channel B11 opens into a crankcase B15 in which a crankshaft B17 is mounted so as to be rotatable about a rotational axis B18. The crankshaft B17 is rotationally driven by the reciprocating piston B13 by way of a connecting rod B16.

[0164] In the embodiment, the combustion engine B8 is a one-cylinder engine. The combustion engine B8 in the embodiment is a two-stroke engine. However, it can also be provided that the combustion engine B8 is a four-stroke engine. The combustion engine B8 is advantageously a mixture-lubricated combustion engine.

[0165] The combustion engine B8 has a plurality of transfer channels B19 which open into the combustion chamber B14 by way of transfer windows controlled by the piston B13. In the region of the lower dead center of the piston B13 illustrated in FIG. 7, the transfer channels B19 fluidically connect the crankcase B15 to the combustion chamber B14, so that air and fuel can flow from the crankcase B15 into the combustion chamber B14. A spark plug B20 which ignites the fuel/air mixture in the combustion chamber B14 in the region of the upper dead center of the piston B13 protrudes into the combustion chamber B14. During the subsequent downward stroke of the piston B13, an outlet opening B21 from the cylinder B12 is opened by the piston B13, and exhaust gases flow by way of an outlet channel B22 formed in the cylinder B12 into an exhaust muffler B23 connected to the outlet channel B22. Advantageously, the exhaust muffler B23 adjoins the outlet channel B22 of the cylinder B12 directly, optionally with intervening seals, heat shield panels or similar. However, it can also be provided that the exhaust muffler B23 adjoins the outlet channel B22 indirectly, by way of additional intervening components.

[0166] The exhaust muffler B23 has an exhaust inlet B24 into which the exhaust gases flow from the cylinder B12. An exhaust outlet B25 through which the exhaust gases flow into the environment leads out of the exhaust muffler B23. A spark-protective sleeve B26, which is schematically illustrated in FIG. 8, can be disposed on the exhaust outlet B25. A heat protection panel B27, which is disposed between the cylinder B12 and the exhaust muffler B23, is also schematically illustrated in FIG. 8.

[0167] As is shown in FIG. 8, the exhaust gases from the outlet channel B22 flow in an outflow direction B34 out of the cylinder B12 and into the exhaust muffler B23. The exhaust muffler B23 is advantageously formed in the usual way by a plurality of deep-drawn metal sheets which can be connected to one another by crimping their edges together, for example. A plurality of muffler chambers B31 and B32 are formed in the interior of the exhaust muffler B23. The exhaust muffler B23 from FIG. 8 has a partition wall B28 which divides the interior of the exhaust muffler B23 into a first muffler chamber B31 and a second muffler chamber B32. The first muffler chamber B31 and the second muffler chamber B32 are fluidically connected to one another by way of two through-flow units B35 and B36.

[0168] Provided in the embodiment is a first through-flow unit B35 which advantageously does not have a catalytic coating. A second through-flow unit B35 does have a catalytic coating. The first through-flow unit B35 has a smaller quantity of catalytically effective coating in terms of the volume than the second through-flow unit B36. The mass of the catalytically effective coating in terms of the volume is accordingly less in the first through-flow unit B35 than in the second through-flow unit B36. The mass of the catalytically effective coating of the first through-flow unit B35 can be zero. It can be provided that the first through-flow unit B35 and/or the second through-flow unit B36 have/has a washcoat. A washcoat serves to enlarge the surface of the first through-flow unit B35 and/or of the second through-flow unit B36 and does not represent a catalytically effective coating.

[0169] The through-flow units B35 and B36 are in each case preferably formed by one or a plurality of wire elements. The through-flow units B35 and/or B36 are advantageously formed by a knitted metal mesh or a woven metal mesh. It can also be provided here that the through-flow units B35 and B36 have in each case regions with different quantities of catalytic coating. For example, it can be provided that the second through-flow unit B36 does not have a catalytically effective coating in the region of its circumference, so as to avoid any ablation when press-fitting the wire element into a housing B29 of the through-flow unit B36. It can also be provided that at least one through-flow unit B35, B36 has a plurality of wire elements which have different quantities of catalytically effective coating in terms of the volume. The quantity of catalytic effective coating herein is considered for each through-flow unit in terms of the overall volume of this through-flow unit.

[0170] The through-flow units B35 and B36 form two mutually separate flow paths B37 and B38 out of the first muffler chamber B31 into the second muffler chamber B32. Exhaust gas sub-flows flow either through the first through-flow unit B35 or through the second through-flow unit B36. The through-flow units B35 and B36 in the embodiment have a mutual spacing a. In the embodiment according to FIG. 8, the spacing a can be several centimeters. Both through-flow units B35 and B36 are disposed in the partition wall B28. The spacing a is measured on the partition wall B28.

[0171] In the embodiment according to FIG. 8, the through-flow units B35 and B36 have approximately the same shape and size. However, different dimensions of the through-flow units B35 and B36 may be advantageous. The through-flow units B35 and B36 have in each case a thickness e measured in the flow direction. The through-flow units B35 and B36 have in each case a diameter d measured perpendicularly to the flow direction.

[0172] A first flow path B37 extends through the first through-flow unit B35. A second flow path B38 extends through the second through-flow unit B36. Both flow paths B37 and B38 lead from the first muffler chamber B31 into the second muffler chamber B32. In the embodiment according to FIG. 8, splitting exhaust gas flow among the flow paths B37 and B38 takes place due to the positioning of the through-flow units B35 and B36 relative to the exhaust inlet B24 into the exhaust muffler B23.

[0173] Plotted in FIG. 8 is a projection P of the exhaust inlet B24 in the direction of the outflow direction B34 toward the partition wall B28. As is shown in FIG. 8, the first through-flow unit B35 lies partially within the projection P. The second through-flow unit B36 lies completely outside the projection P, specifically at a spacing B from the projection P in the embodiment. In the embodiment, the spacing B is smaller than the spacing a. However, the spacing B can also correspond to the spacing a, or be larger than the spacing a. Owing to the fact that the first through-flow unit B35 lies partially in the extension of the outflow direction B34, more exhaust gas flows through the first through-flow unit B35 than through the second through-flow unit B36. If additional muffler chambers are disposed between the exhaust inlet B24 and the first muffler chamber B31, the projection P-and the flow direction in which the projection P is viewed-advantageously relates to the inflow opening into the first muffler chamber B31.

[0174] FIG. 9 shows an additional embodiment of an exhaust muffler B23. The same reference signs herein refer to equivalent elements in all figures. The exhaust muffler B23 shown in FIG. 9, in addition to the first muffler chamber B31 and the second muffler chamber B32, has a third muffler chamber B33. The third muffler chamber B33 lies in the flow direction between the first muffler chamber B31 and the second muffler chamber B32. The exhaust gases advantageously split into at least two sub-flows. One sub-flow of the exhaust gases flows from the first muffler chamber B31 along a first flow path B37 through a first through-flow unit B35 into the second muffler chamber B32. The first flow path B37 bypasses the third muffler chamber B33. An additional sub-flow of the exhaust gases flows along a second flow path B38 from the first muffler chamber B31 into the third muffler chamber B33 and from there through the second through-flow unit B36 into the second muffler chamber B32. A passage B42 leads from the first muffler chamber B31 into the third muffler chamber B33. The second flow path B38 leads only through the second through-flow unit B36 and bypasses the first through-flow unit B35. Accordingly, exhaust gases on their way into the second muffler chamber B32 flow either through the first through-flow unit B35 or through the second through-flow unit B36.

[0175] In the embodiment according to FIG. 9, the muffler chamber is divided by a first partition wall B40 and a second partition wall B41. The first partition wall B40 separates the first muffler chamber B31 from the second muffler chamber B32. The second partition wall B41 separates the second muffler chamber B32 from the third muffler chamber B33. In the embodiment, the second muffler chamber B32 is disposed between the first muffler chamber B31 and the third muffler chamber B33. The passage B42 extends through both partition walls B30 and B41. However, a different arrangement and configuration embodiment of the partition walls B40 and B41 can also be advantageous.

[0176] By positioning and sizing the passage B42 as well as the third muffler chamber B33, it can be structurally predefined how large the proportions of the entire exhaust gas flow that flow through the first flow path B37 having the first through-flow unit B35 are, and how large the proportion of the exhaust gas flow that flows along the second flow path B38 through the second through-flow unit B36 is. This splitting of the exhaust gas flow is also function of the entire exhaust gas mass flow, and thus a function of the rotating speed and the load of the combustion engine.

[0177] In the embodiment according to FIG. 9, the first through-flow unit B35 lies completely in the projection P of the exhaust inlet B24. The passage B42 in the embodiment lies completely outside the projection P. The passage B42 lies at a spacing f from the projection P. The spacing f is measured on the partition wall B40. As a result, in at least one operative state, preferably at least in the operation under full load, in particular in all operative states, more than 50%, in particular more than 70%, of the entire exhaust gas flow flows through the first flow path B37 and through the first through-flow unit B35.

[0178] As is shown in FIG. 9, the exhaust gas from the first through-flow unit B35 flows out in a first outflow direction B43. The exhaust gas flows out of the second through-flow unit in a second outflow direction B44. As is shown in FIG. 9, the first outflow direction B43 and the second outflow direction B44 are oriented counter to one another. In the embodiment, the outflow directions B43 and B44 are oriented so as to be mutually parallel. The first through-flow unit B35 has a first outflow surface B45. The first outflow surface is the surface of the first through-flow unit B35 through which the exhaust gases from the first through-flow unit B35 exit in the first outflow direction B43. The first outflow surface B45 is contiguous to the second muffler chamber B32. The second through-flow unit B36 has a second outflow surface B46. The second outflow surface B46 is the surface by way of which the exhaust gases from the second through-flow unit B36 flow out in the second outflow direction B44.

[0179] In the embodiment according to FIG. 9, the through-flow units B35 and B36 are of identical size and configured with the same cross-sectional area. In the embodiment, round cross-sectional areas are provided for the through-flow units B35 and B36. However, other cross-sectional areas, for example rectangular, in particular square, cross-sectional areas or irregular cross-sectional areas may also be advantageous. In the embodiment according to FIG. 9, the outflow surfaces B45 and B46 are completely congruent in the outflow direction B43 and correspondingly in the outflow direction B44. The congruence U of the outflow surfaces B45 and B46 is schematically plotted in FIG. 9. The congruence U results when projecting one of the outflow surfaces B45, B46 in the assigned outflow direction B43, or B44, respectively, onto the other of the outflow surfaces B45 and B46.

[0180] Due to the orientation of the outflow directions B43 and B44, and due to the arrangement of the outflow surfaces B45 and B46, the exhaust gas flows flowing in the outflow direction B43 and B44 out of the through-flow units B35 and B36 influence one another during operation. At a low overall exhaust gas mass flow through the exhaust muffler B23, thus at low rotating speeds, the sub-flow flowing in the outflow direction B43 out of the first through-flow unit B35 influences the exhaust gas sub-flow flowing through the second flow path B38 only to a minor extent.

[0181] At a higher overall exhaust gas mass flow, a larger exhaust gas mass flow flows through the first flow path B37. The exhaust gas sub-flow exiting the first through-flow unit B35 influences the exhaust gas sub-flow exiting the second through-flow unit B36 and throttles the latter due to the exhaust gas sub-flow flowing out in the outflow direction B43. As a result, the proportion of the exhaust gas flow flowing through the second flow path B38 is reduced at a higher overall exhaust gas mass flow, in particular when operating under full load with a completely open throttle element in the intake channel B11 of the combustion engine B8. Depending on the basic configuration, the proportion of the exhaust gas sub-flow flowing through the second flow path B38 under full load can be below 70%, in particular below 50%, of the entire exhaust gas mass flow.

[0182] The splitting of the exhaust gas flows can be set by a suitable basic configuration and arrangement of the outflow surfaces B45 and B46, of the spacing a as well as of the position and size of the passage B42. The arrangement of the first through-flow unit B35 relative to the exhaust inlet B24 also influences the splitting of the exhaust gas among the flow paths B37 and B38. Owing to the fact that the proportion of the exhaust gas sub-flow flowing through the second through-flow unit B36 is reduced under full load, the generation of heat in the second through-flow unit B36, which is coated with catalytic material, is reduced so that excessive heating of the exhaust muffler B23 under full load can be avoided. Owing to the fact that during idling, and advantageously also under partial load, a larger proportion of the exhaust gas flow flows through the second through-flow unit B36, an improved exhaust gas after-treatment is achieved in these operative states. At the same time, more rapid heating of the second through-flow unit B36 is achieved when idling, so that the exhaust muffler B23 upon starting reaches the temperature for an optimal catalytic after-treatment of the exhaust gases after starting more rapidly when idling.

[0183] The height c of the passage B42 is plotted in FIG. 9 so as to represent the dimensions of the passage B42. The height c schematically highlights the flow cross section of the passage B42. Adapting the geometry of the passage B42 can be performed by adapting the smallest flow cross section. This is shown in FIG. 10. Here, the passage B42 has a height c which is less than in the embodiment according to FIG. 9. Accordingly, in the embodiment according to FIG. 10, the smallest flow cross section of the passage B42 is smaller than in the embodiment according to FIG. 9. As a result, the sub-flow flowing along the second flow path B38 in the embodiment according to FIG. 10 will be smaller than in the embodiment according to FIG. 9, and the exhaust gas sub-flow flowing through the first flow path B37 will be larger than in the embodiment according to FIG B3. The embodiment according to FIG. 10 corresponds to the embodiment according to FIG. 9, with the exception of the sizing of the passage B42, so that reference is made to the description pertaining to FIG. 9.

[0184] In the embodiments according to FIG. 9 and FIG. 10, the through-flow units B35 and B36 have the same external diameter d. The outflow surfaces B45 and B46 are of identical size. Hereunder, reference is made to the external diameter d, representing the size of the outflow surfaces B45 and B46.

[0185] The through-flow units B35 and B36 have in each case a thickness e measured in the flow direction. In the embodiment according to FIG. 9 and FIG. 10, the thicknesses e of the through-flow units B35 and B36 are of identical size. Different thicknesses e of the through-flow units B35 and B36 can also be advantageous for influencing the splitting of the flow among the flow paths B37 and B38.

[0186] FIG. 11 shows an embodiment in which the first through-flow unit B35 has an external diameter d1, and the second through-flow unit B36 has an external diameter d2. As a result, the cross-sectional area of the first through-flow unit B35 is significantly larger than that of the second through-flow unit B36. The first external diameter d1 is significantly larger than the second external diameter d2. As a result, the second outflow surface B46 is significantly larger than the first outflow surface B45. The first outflow surface B45 is advantageously at least 1.2 times, in particular at least 1.5 times, preferably at least 2 times, the second outflow surface B46. As a result, during operation in at least one operative state, in particular in all operative states, at least 50%, preferably at least 70%, of the entire exhaust gas flow flows through the first flow path B37. In the embodiment according to FIG. 5B, the outflow directions B43 and B44 are directed counter to one another. The second outflow surface B46 is completely congruent U with the first outflow surface B45.

[0187] In the embodiment according to FIG. 12, the through-flow units B35 and B36 are disposed so as to be mutually offset on the partition walls B40 and B41. In the embodiment, both through-flow units B35 and B36 have the same external diameter d and preferably the same cross-sectional area. However, the outflow surfaces B45 and B46 are only partially congruent. The congruence U of the outflow surfaces B45 and B46 is schematically plotted in FIG. 12. The congruence U is derived in a projection of one of the outflow surfaces B45, B46 in the assigned outflow direction B43 or B44, respectively, onto the other of the outflow surfaces B45 and B46. Owing to the reduced congruence U in comparison to the embodiment according to FIG. 9 and FIG. 10, this results in the exhaust gas sub-flow flowing through the first flow path B37 being influenced to a lesser extent by the exhaust gas sub-flow flowing in the second flow path B38.

[0188] FIG. 13 shows an additional embodiment in which the spacing of the partition walls B40 and B41 is significantly reduced in comparison to the embodiments according to FIGS. 9 to 12. The through-flow units B35 and B36 are sized as in FIGS. 9 and 10. However, the through-flow units B35 and B36 have a mutual spacing a which is smaller than the spacing a provided in FIGS. 9 to 12. However, a deviating arrangement and/or dimensioning of the through-flow units B35 and B36 may also be advantageous, for example as in one of the other embodiments. Due to the reduced spacing a, the influence on the exhaust gas sub-flow flowing through the second flow path B38 by the exhaust gas sub-flow flowing through the first flow path B37 is greater than in the preceding embodiments according to FIGS. 9 to 12. In the embodiment according to FIG. 13, as compared with the embodiment according to FIG. 9, this will therefore result in greater reduction of the exhaust gas sub-flow flowing through the second flow path B38 when increasing the overall exhaust gas mass flow.

[0189] FIG. 14 shows an additional embodiment in which the first muffler chamber B31 is significantly smaller than the third muffler chamber B33. The first partition wall B40 is disposed comparatively close to the exhaust inlet B24. The first through-flow unit B35 in the embodiment is disposed completely in the projection P of the exhaust inlet B24, so that a very large proportion of the overall exhaust gas mass flow flows through the first through-flow unit B35. Additionally, in the embodiment according to FIG. 14, the external diameter d2 of the second through-flow unit B36 is configured to be smaller than the external diameter d1 of the first through-flow unit B35. The first through-flow unit B35 has a larger cross-sectional area than the second through-flow unit B36. As a result, the exhaust gas sub-flow that flows through the second flow path B38 is also reduced.

[0190] FIGS. 15 and B16 show an additional embodiment in which the second muffler chamber B32 is separated from the first muffler chamber B31 by way of a divider B47. As is shown in FIG. 16, the first muffler chamber B31 in the embodiment completely surrounds the second muffler chamber B32 on its external circumference. A partial enclosure of the second muffler chamber B32 by the first muffler chamber B31 may also be advantageous. In the embodiment according to FIGS. 15 and 16, the divider B47 is of a tubular configuration. The cross section of the divider B47 here can be suitably adapted to the dimensions of the through-flow units B35 and B36, and to the desired spacing a between the outflow surfaces B45 and B46 of the through-flow units B35 and B36, as well as to the desired flow cross sections. In the embodiment, the divider B47 has an approximately oval shape. A round or polygonal cross-sectional shape may also be advantageous. An irregular cross-sectional shape of the divider B47 is also possible.

[0191] Alternatively, the divider B47 can be formed by one or a plurality of partition walls between housing shells of the exhaust muffler B23.

[0192] In the embodiment, the through-flow units B35 and B36 have the same external diameter d and the same cross-sectional area. Different cross-sectional areas of the through-flow units B35 and B36 may also be provided for influencing the proportions of the exhaust gas flows. In the embodiment according to FIG. 16, the larger proportion of exhaust gas flowing through the first flow path B37 results by virtue of the arrangement of the first through-flow unit B35 in the projection P of the exhaust inlet B24 into the exhaust muffler B24. Additionally or alternatively, the splitting of the exhaust gas flows can also be influenced by way of additional measures, in particular by the additional measures described in the context of the other embodiments.

[0193] FIG. 17 shows an additional embodiment of an exhaust muffler B23, in which both through-flow units B35, B36 are disposed in a partition wall B28. To this extent, the embodiment according to FIG. 17 corresponds to the embodiment according to FIG. 8. In the embodiment according to FIG. 17, a flow directing element B48 is additionally disposed in the exhaust muffler B23, so as to be adjacent to the exhaust inlet B24 into the exhaust muffler B23. The flow directing element B48 is disposed and oriented in such a way that the exhaust gas flow flowing into the exhaust muffler B23 is directed to the first through-flow unit B35. In order to reach the second through-flow unit B36, the exhaust gas flow must flow around the flow directing element B48. As a result, the proportion of the exhaust gas sub-flow flowing through the first through-flow unit B35 in terms of the overall exhaust gas mass flow is larger than 50%, in particular larger than 70%. The splitting of the exhaust gas sub-flows among the through-flow units B35, B36 can be structurally set in the desired manner by a suitable arrangement and basic configuration of the flow directing element B48. In the embodiment according to FIG. 17, the through-flow units B35 and B36 are of identical configuration. However, it can also be provided that the through-flow units B35, B36 have different cross-sectional areas, thicknesses, volumes and/or densities in order to influence the splitting of the exhaust gas flow.

[0194] FIG. 18 shows an additional embodiment of an exhaust muffler B23 in which an additional muffler chamber B49 is disposed in the flow direction between the exhaust inlet B24 and the first muffler chamber B31. In the embodiment, the entire exhaust gas flow flows through the additional muffler chamber B49. The exhaust muffler B23 has a partition wall B28 which separates the first muffler chamber B31 from the second muffler chamber B32, and in which the two through-flow units B35 and B36 are disposed. An additional partition wall B50, which separates the additional muffler chamber B49 from the first muffler chamber B31, is disposed upstream of the first muffler chamber B31. The additional partition wall B50 has a transfer opening B51 through which exhaust gas from the additional muffler chamber B49 can flow into the first muffler chamber B31. In the embodiment, the first through-flow unit B35 is disposed in a projection V toward the transfer opening B51. In the embodiment, the projection V of the transfer opening B51 largely covers the through-flow unit B35 in the flow direction B52 through the transfer opening B51. Complete coverage may also be provided.

[0195] The second through-flow unit B36 lies at a spacing a from the first through-flow unit B35. In the embodiment, the spacing a also corresponds to the spacing of the second through-flow unit B36 from the projection V. The second through-flow unit B36 is disposed completely outside the projection V. Accordingly, the second through-flow unit B36 is not directly subjected to an incident flow of exhaust gas flowing through the transfer opening B51 into the first muffler chamber B31. In order to reach the second through-flow unit B36, the exhaust gas flow first has to be deflected multiple times. As a result, the proportion of the exhaust gas flow flowing through the second through-flow unit B36 is reduced. In the embodiment according to FIG. 18, the through-flow units B35 and B36 are configured to be of approximately identical size. Through-flow units B35 and B36 which are configured to be of different sizes and different densities may also be provided in the embodiment according to FIG. 18.

[0196] FIG. 19 schematically shows the construction of a through-flow unit B35, B36. The through-flow unit B35, B36 includes a wire element B39. The wire element B39 is an inherently stable element. It can also be provided that the through-flow unit B35, B36 includes a plurality of wire elements B39. In the embodiment, the wire element B39 is formed from a metal wire pressed into shape, preferably formed from a knitted metal mesh or a woven metal mesh. The wire element B39 of the first through-flow unit B35 advantageously does not have a catalytic coating. In an alternative embodiment, it can be provided that the wire element B39 of the first through-flow unit B35 is coated with a catalytic coating. The second through-flow unit B36 advantageously has a larger quantity of catalytic coating per volumetric unit than the first through-flow unit B35. Both through-flow units B35 and B36 can have a washcoat.

[0197] In wire elements B39 of this type, there is a turbulent flow within the through-flow unit B35 or B36 during operation. The exhaust gas flow is not laminar as in ceramic honeycomb catalytic converters, for example. Owing to this fact, there are cross flows through the through-flow units B35 and B36 during operation. By virtue of the spatial separation of the through-flow units B35 and B36, cross flows of this type between the through-flow units B35 and B36 can be easily avoided, so that defined through-flow ratios through the regions provided with a catalytic coating, and the regions without a catalytic coating, or with less catalytic coating in terms of the volume, result. As a result, defined flow ratios during operation are achieved in a simple manner.

[0198] The through-flow units B35, B36 have a housing B29. The housing B29 can be tubular, for example. The through-flow unit B35 or B36 can be press-fitted into the housing B29 and be held in the housing B29 as a result.

[0199] The individual embodiments reflect different possibilities for influencing the splitting of the exhaust gas flows among the through-flow units. These different possibilities can be suitably combined with one another in an arbitrary manner, so as to achieve a desired splitting of the exhaust gas flow among the flow paths B37 and B38. Additional advantageous embodiments of the disclosure are derived as a result. Additional advantageous embodiments are derived by the disposal of one or a plurality of additional through-flow units, and/or by the disposal of one or a plurality of additional muffler chambers. In all embodiments, a spark-protective sleeve can additionally be provided, in particular so as to be adjacent to the exhaust outlet. The volumes of the first muffler chamber and of the third muffler chamber, of the first muffler chamber and of the second muffler chamber, as well as of the second muffler chamber and of the third muffler chamber, can in each case be identical or dissimilar in size. The spacing of the through-flow units B35 and B36 in all embodiments in which the outflow directions B34 and B44 are oriented counter to one another is preferably less than 3 cm, in particular less than 2 cm, in order to enable the mutually opposing exhaust gas flows to be influenced. The through-flow units B35 and B36 preferably have different volumes and/or different thicknesses.

[0200] In all embodiments, the quantity of catalytically effective coating relates to the mass of catalytically effective coating.

[0201] In FIGS. 20 to 24, the reference signs mentioned hereunder are in each case illustrated without the prefix C.

[0202] FIG. 20 shows a chain saw C1 as an embodiment for a handheld work apparatus. Instead of a chain saw C1, the work apparatus can also be a brushcutter, an angle grinder, a blower, a lawnmower, or a similar work apparatus. The handheld work apparatus is in particular a portable work apparatus. The chain saw C1 has a housing C2 on which a handle C3 is held. Operating elements for the chain saw C1, in the embodiment a throttle lever C4 and a throttle lever lock C5, are disposed on the handle C3. The chain saw C1 has a guide bar C6 on which a revolving saw chain C7 is disposed. During operation, the saw chain C7 is driven by a combustion engine disposed in the housing C2, in the embodiment by a two-stroke engine C8. The combustion engine can also be a different mixture-lubricated combustion engine, in particular a mixture-lubricated four-stroke engine.

[0203] The two-stroke engine C8 includes an air filter C9 by way of which air is inducted during operation. The air makes its way to a crankcase C15 of the two-stroke engine C8 by way of an intake channel C11. A portion of the intake channel C11 is formed in a fuel supply unit C10, for example a carburetor. A different type of supply of fuel, for example by way of a fuel valve, may also be provided. A different location of introducing fuel, for example into the crankcase C15, may also be provided.

[0204] The two-stroke engine C8 includes a cylinder C12 in which a piston C13 is mounted so as to reciprocate. The piston C13 delimits a combustion chamber C14 formed in the cylinder C12. The combustion chamber C14 is connected to the interior of the crankcase C15 by way of transfer channels C19 in the region of the lower dead center of the piston C13, illustrated in FIG. 20. The piston C13, by way of a connecting rod C16, drives a crankshaft C17 which is rotatably mounted in the crankcase C15. The crankshaft C17 is mounted so as to be rotatable about a rotational axis C18. A spark plug C20 protrudes into the combustion chamber C14. An outlet opening C21, which is connected to an entry opening C24 of an exhaust muffler C23 by way of an outlet channel C22, leads out of the combustion chamber C14.

[0205] During operation, the two-stroke engine C8 inducts a fuel/air mixture through the intake channel C11 into the interior of the crankcase C15 during the upward stroke of the piston C13. The fuel/air mixture is compressed in the crankcase C15 during the downward stroke of the piston C15. As soon as the transfer channels C19 from the piston C13 to the combustion chamber C14 are opened, the fuel/air mixture flows from the interior of the crankcase C15 into the combustion chamber C14. In the region of the upper dead center, the spark plug C20 ignites the mixture in the combustion chamber. Due to the subsequent combustion, the piston C13 is accelerated back in the direction toward the crankcase C15 again. As soon as the piston C13 opens the outlet opening C21, exhaust gases can flow out of the combustion chamber C14 and flow toward the exhaust muffler C23. As soon as the transfer channels C19 from the piston C13 to the combustion chamber C14 are opened, fresh fuel/air mixture is replenished for the next combustion.

[0206] Alternatively, the two-stroke engine C8 can also operate with stratified scavenging and, in addition to the intake channel C11, include one or a plurality of air ducts by way of which largely fuel-free air is kept available in the transfer channels C19. During the downward stroke of the piston C13, the pre-stored air separates exhaust gases from the previous combustion from fuel/air mixture flowing into the combustion chamber C14.

[0207] The exhaust muffler C23 has a housing C27 in which a first muffler chamber C47 and a second muffler chamber C48 are formed. The first muffler chamber C47 is disposed upstream of the second muffler chamber C48. In the embodiment, the entry opening C24 opens into the first muffler chamber C47. However, it can also be provided that additional muffler chambers are formed in the housing C27, or in another unit, upstream of the first muffler chamber. The exhaust muffler C23 has an exit opening C25 from which exhaust gases from the exhaust muffler C23 can flow out into the environment. In the embodiment, the exit opening C25 leads out of the second muffler chamber C48. In an alternative embodiment, additional muffler chambers can be provided downstream of the second muffler chamber C48.

[0208] The first muffler chamber C47 and the second muffler chamber C48 are separated by a partition wall C28. In the embodiment, an exhaust gas after-treatment unit C26, through which exhaust gases can flow from the first muffler chamber C47 into the second muffler chamber C48, is held on the partition wall C28. For this purpose, the partition wall C28 has a connection opening C50 in the region of the exhaust gas after-treatment unit C26. The exhaust gas after-treatment unit C26 includes a first through-flow unit C29 and a second through-flow unit C30 which are to be described in more detail hereunder.

[0209] FIG. 20 schematically shows the arrangement of the entry opening C24 into the exhaust muffler C23 relative to the arrangement of the exhaust gas after-treatment unit C26. The exhaust gases flow in a main flow direction C35 through the exhaust gas after-treatment unit C26. In the embodiment, the main flow direction C35 lies approximately perpendicularly to the partition wall C28. The main flow direction C35 preferably corresponds to an outflow direction C67 from the first through-flow unit C29, to be described in more detail hereunder. Schematically plotted in FIG. 20 is a projection C49 of the entry opening C24 parallel to the main flow direction C35 toward the partition wall C28. As is shown in FIG. 20, the projection C49 lies outside the exhaust gas after-treatment unit C26. The projection C49 and the exhaust gas after-treatment unit C26 are not congruent. Owing to this fact, exhaust gases that flow into the exhaust muffler C23 have to be deflected before they can flow through the exhaust gas after-treatment unit C26. A more uniform distribution of the exhaust gases is achieved as a result, and the exhaust gas after-treatment unit C26 is impinged with exhaust gas in a largely uniform manner.

[0210] The construction of the exhaust gas after-treatment unit C26 will be explained hereunder with reference to FIGS. 21 and 22. As is shown in FIG. 21, the exhaust gas after-treatment unit C26 includes a housing C37. The housing C37 in the embodiment is formed from two component shells C38 and C39. The component shells C38 and C39 are preferably produced from a bent metal sheet, for example as deep-drawn parts. In the embodiment, the component shells C38 and C39 are connected to one another in a sealing manner on a peripheral edge C43 of the exhaust gas after-treatment unit C26.

[0211] The first component shell C38 of the housing C37 is disposed so as to be contiguous to the first muffler chamber C47. The first component shell C38 has all inflow openings of the exhaust gas after-treatment unit C26. The exhaust gas after-treatment unit C26 includes first inflow openings C31 through which exhaust gas flows into the first through-flow unit C29. Moreover, the first component shell C38 has second inflow openings C32 through which the exhaust gas makes its way directly into the second through-flow unit C30.

[0212] The first through-flow unit C29 has an inflow surface C42 through which exhaust gas can flow into the first through-flow unit C29. The inflow surface C42 is formed on an upstream end face C40 of the first through-flow unit C29. The first through-flow unit C29 has a downstream outflow surface C57 through which exhaust gas can exit the first through-flow unit C29. In the embodiment, the inflow surface C42 and the outflow surface C57 lie so as to be mutually parallel. However, a different arrangement of the inflow surface C42 and outflow surface C57 may also be advantageous.

[0213] The second through-flow unit C30 has an inflow surface C58. The inflow surface C58 is formed on an upstream end face C46 of the second through-flow unit C30. The inflow surface C58 in the embodiment is of a flat configuration. The term flat is presently understood to mean flat within the context of the usual manufacturing tolerances. The second inflow openings C32 open out at the end face C46 of the second through-flow unit C30. A transfer opening C34 also opens out at the inflow surface C58. The second through-flow unit C30 has a downstream outflow surface C64. The outflow surface C64 in the embodiment is oriented so as to be parallel to the inflow surface C58. However, a different position may also be advantageous.

[0214] The outflow surface C57 of the first through-flow unit C29 has an outflow direction C67. The outflow direction C67 is oriented perpendicularly to the outflow surface C57 and from the first through-flow unit C29 to the second through-flow unit C30.

[0215] Shown in FIG. 22 is the arrangement of the first inflow openings C31 and of the second inflow openings C32. The first component shell C38 includes a central region C44 which has first inflow openings C31. In the embodiment, five first inflow openings C31 are provided. A different number of first inflow openings C31 may also be advantageous. In the top view illustrated in FIG. 22, thus when viewed in the outflow direction C67 of the first through-flow unit C29, the central region C44 is completely surrounded by a surrounding region C45. In the embodiment, the central region C44 is approximately circular, and the surrounding region C45 forms a ring about the central region C44. The surrounding region C45 has the second inflow openings C32. In the embodiment, eight second inflow openings C32 are provided. A different number of second inflow openings C32 may also be advantageous.

[0216] As is shown in FIG. 22, the exhaust gas after-treatment unit C26 has two portions C51 and C52 which lie behind one another in the outflow direction C67 of the first through-flow unit C29. The first through-flow unit C29 is disposed in the first portion C51, and the second through-flow unit C30 is disposed in the second portion C52. The second through-flow unit C30 does not protrude into the first portion C51. The first through-flow unit C29 does not protrude into the second portion C52. Accordingly, in terms of the main flow direction C35, or in terms of the outflow direction C67 of the first through-flow unit C29, respectively, the second through-flow unit C30 is disposed completely downstream of the first through-flow unit C29.

[0217] The outflow surface C57 of the first through-flow unit C29 lies in an imaginary plane C66 which is illustrated by a dashed line in FIG. 21. The plane C66 is disposed perpendicularly to the main flow direction C35. The second through-flow unit C30 does not protrude beyond the plane C66, in particular counter to the outflow direction C67 of the first through-flow unit C29, but lies completely downstream of the plane C66 or contacts the latter. The plane C66 does not intersect the second through-flow unit C30. The first through-flow unit C29 lies completely upstream of the plane C66 and does not protrude beyond the plane C66 in the outflow direction C67. The through-flow units C29 and C30 extend on opposite sides of the plane C66.

[0218] The first through-flow unit C29 has a largest cross section C69. The second through-flow unit C30 has a largest cross section C70. The largest cross sections C69 and C70 lie perpendicularly to the main flow direction C35 and perpendicularly to the outflow direction C67. In the embodiment, the largest cross section C69 corresponds to the square of half the external diameter f of the first through-flow unit C29 multiplied by . Accordingly, the largest cross section C70 corresponds to the square of half the external diameter g of the second through-flow unit C30 multiplied by .

[0219] The first portion C51 extends from the inflow surface C42 of the first through-flow unit C29 up to the outflow surface C57 of the first through-flow unit C29. The second portion C52 extends from the inflow surface C58 of the second through-flow unit C30 up to the outflow surface C64 of the second through-flow unit C30.

[0220] The first inflow openings C31 open out at the first through-flow unit C29. The first inflow openings C31 lead into the first portion C51. The second inflow openings C32 lead into the second portion C52. In terms of the outflow direction C67 of the first through-flow unit C29, the inflow openings C31 and C32 are mutually offset, specifically by a thickness a of the first portion C51, measured in the direction of the outflow direction C67 of the first through-flow unit C29. The thickness of the first portion C51 corresponds to the thickness a of the first through-flow unit C29 in a central region. The first through-flow unit C29 has radiused corners on its upstream peripheral regions so that this results in a somewhat smaller thickness at that location. The first through-flow unit C29 has the same thickness a across at least 80%, in particular across at least 90%, of its largest cross section C69. The thickness a herein is constant, within the scope of the usual manufacturing tolerances, across at least 80%, in particular across at least 90%, of its largest cross section.

[0221] The second through-flow unit C30 has in its central region a thickness b as measured in the outflow direction C67 of the first through-flow unit C29. The second through-flow unit C30 has chamfers on its downstream peripheral regions, so that this results in a somewhat smaller thickness at that location. The second through-flow unit C30 has the same thickness b across at least 80%, in particular across at least 90%, of its largest cross section C70.

[0222] The first through-flow unit C29 advantageously has a constant thickness a, measured in the outflow direction C67 of the first through-flow unit C29, across at least 80% of its largest cross section C69. The second through-flow unit C30 advantageously has a constant thickness b, measured in the outflow direction C67 of the first through-flow unit C29, across at least 80% of its largest cross section.

[0223] The thicknesses a and b can be approximately of identical size. The thickness a is advantageously half to double the thickness b. The portions C51 and C52 are connected to one another in the housing C37 so that exhaust gases that flow out of the outflow surface C57 of the first through-flow unit C29 can flow into the inflow surface C58 of the second through-flow unit C30. For this purpose, the transfer opening C34 of the housing C37 is provided. In the embodiment, the transfer opening C34 extends across the entire largest cross section C69 of the first through-flow unit C29. However, it can also be provided that one or a plurality of comparatively small transfer openings C34 fluidically connect the two through-flow units C29 and C30 to one another.

[0224] A step C36 which rests on the external circumference of the first through-flow unit C29 by way of a first step portion C53 is formed on the first component shell C38. The second inflow openings C32 are formed in the second step portion C54. The second step portion C54 extends transversely, in particular perpendicularly, to the first step portion C53. The first step portion C53 preferably extends approximately parallel to the outflow direction C67 of the first through-flow unit C39, or to the main flow direction C35, respectively, and the second step portion C54 extends approximately perpendicularly to the main flow direction C35, or to the outflow direction C67 of the first through-flow unit C29, respectively. In the embodiment, the step C36 is formed by a jump in the cross section of the housing C37 of the exhaust gas after-treatment unit C26. In the first portion, the housing C37 has an external diameter d, as is shown in FIG. 22. At the step C36, the external diameter of the housing C37 increases to an external diameter e in the second portion C52. When viewed in the main flow direction C35, the housing C37 in the embodiment is formed with a round cross section. Other cross-sectional shapes may also be advantageous. Accordingly, the step C36 can be formed by an abrupt enlargement of the external dimensions of the housing C37.

[0225] The first portion C51 is formed completely in the first component shell C38. The second portion C52 is formed by the first component shell C38 and the second component shell C39. In the embodiment, the first through-flow unit C29 is disposed completely in the first component shell C38. The second through-flow unit C30 is disposed largely in the second component shell C39. In the embodiment, the second through-flow unit C30 protrudes into the first component shell C38 by way of a portion which is less than 50%, in particular less than 80%, of the thickness b of the second through-flow unit C30. A different arrangement of the through-flow units C29 and C30 in the component shells C38 and C39 may also be advantageous. For example, in an alternative configuration embodiment, it can be provided that the first through-flow unit C29 protrudes into the second component shell C39. A different construction of the housing C37, for example made of a single metal sheet, or from a shell-shaped sheet-metal part and a cover, may also be advantageous.

[0226] In terms of the main flow direction C35, the end face C40 of the first through-flow unit C29 is the upstream side of the first through-flow unit C29. The exhaust gas after-treatment unit C26 has first entry openings C31 only on the end face C40.

[0227] The largest cross section C70 of the second through-flow unit C30 is advantageously larger than the largest cross section C69 of the first through-flow unit C29. The largest cross section C70 of the second through-flow unit C30 is advantageously at least 130%, in particular at least 150%, of the largest cross section C69 of the first through-flow unit C29.

[0228] As is shown in FIG. 21, when viewed in the outflow direction C67 of the first through-flow unit C29, the second through-flow unit C30 projects beyond the first through-flow unit C29. The protrusion c by way of which the second through-flow unit C30 projects beyond the first through-flow unit C29 is advantageously at least 3 mm, in particular at least 5 mm. When viewed in the outflow direction C67 of the first through-flow unit C29, the protrusion C preferably extends across the entire circumference of the first through-flow unit C29. The size of the protrusion C herein can be constant or variable across the circumference. However, the protrusion C is preferably at least 3 mm at each location of the circumference of the first through-flow unit C29.

[0229] In the embodiment, the through-flow units C29 and C30 are in each case of a cylindrical configuration. The cylindrical external contours of the through-flow units C29 and C30 are illustrated by a dashed line in FIG. 22. The first through-flow unit C29 has an external diameter f (FIG. 21). The second through-flow unit C30 has an external diameter g (FIG. 21). The through-flow units C29 and C30 are in each case formed by a through-flow element C41 (FIG. 23). The through-flow elements C41 have a multiplicity of cavities which permit a flow to pass through. This is schematically illustrated in FIG. 23. The through-flow elements C41 do not have closed surfaces, at least not on their inflow surfaces C42 and C58 and on their outflow surfaces C57 and C64 (FIG. 21). In the embodiment, the through-flow units C29 and C30 include in each case the wire of the assigned through-flow element C41 and the cavities that are formed between the portions of the wire. The through-flow units C29 and C30 define the envelope elements which surround the through-flow elements C41 and on which the through-flow elements C41 rest uniformly within the scope of the manufacturing accuracy and the uniformity in terms of size and distribution of the cavities.

[0230] Outflow openings C33 lead out of the exhaust gas after-treatment unit C26. The outflow openings C33 are disposed in such a way that exhaust gas first has to flow through the second through-flow unit C30 in order to make its way to the outflow openings C33. In the embodiment, the outflow openings C33 are formed in the second component shell C39. When viewed counter to the outflow direction C67 of the first through-flow unit C29, the outflow openings C33 can be congruent with the inflow openings C31, C32, or be disposed so as to be offset from the latter.

[0231] In the embodiment, the first through-flow unit C29 and the second through-flow unit C30 are in each case formed by a through-flow element C41. A potential construction for a through-flow element C41 is illustrated in FIG. 23. In the embodiment, the through-flow element C41 is formed from a metal wire. The through-flow element C41 is dimensionally stable. Openings through which exhaust gas can flow through the through-flow element C41 are formed between the loops of the metal wire. The through-flow element C41 is in particular a knitted wire mesh. In the embodiment, each through-flow unit C29, C30 is formed by exactly one through-flow element C41. However, it may also be provided that at least one through-flow unit C29, C30 is formed by more than one through-flow element C41.

[0232] The at least one transfer opening C34 is advantageously the only opening which fluidically connects the first through-flow unit C29 to the second through-flow unit C30. As a result, exhaust gas can flow through the exhaust gas after-treatment unit C26 either by way of the first inflow openings C31 into the first through-flow unit C29, from there by way of the transfer opening C34 into the second through-flow unit C30, and from there through the outflow openings C33 into the second muffler chamber C48. This is highlighted by the arrow C55 in FIG. 22. Alternatively, a sub-flow of the exhaust gas can flow through the second inflow openings C32 directly into the second through-flow unit C30, and from there through the outflow openings C33 into the second muffler chamber C48, as shown by the arrow C56 in FIG. 22. Additional flow paths through the exhaust gas after-treatment unit C26 are not provided.

[0233] The first through-flow unit C29 is coated with a catalytic material. Additionally, a coating with a so-called washcoat can be provided. Accordingly, no catalytic conversion of exhaust gases takes place in the first through-flow unit C29. The second through-flow unit C30 does not have a catalytic coating, or has a smaller mass of catalytic coating per volumetric unit than the first through-flow unit C29. The second through-flow unit C30 therefore acts largely as a particle filter. Owing to the fact that the first through-flow unit C29 is disposed upstream of the second through-flow unit C30, the exhaust gas is intensely heated in the first through-flow unit C29, due to the catalytic conversion. The second through-flow unit C30 preferably serves largely for reducing particles. Lubricating oil in the form of droplets is contained in exhaust gases of mixture-lubricated combustion engines. These droplets form particles in the exhaust gas flow. The lubricating oil in the form of droplets is converted in the second through-flow unit C30. For this purpose, a sufficiently high temperature of the second through-flow unit C30 is required. Moreover, a sufficiently long dwell time of the oil droplets in the second through-flow unit C30 is necessary. The second through-flow unit C30 is preferably rapidly heated by the first through-flow unit C29. The particle-reducing effect of the second through-flow unit C30 is improved as a result. Oil droplets are converted as soon as the temperatures required for this purpose have been reached. In the case of lubricating oils usually used nowadays, the temperature required for the conversion can be in the order of 600 to 700, for example.

[0234] The first through-flow unit C29, which is coated with a catalytically effective coating, in particular with precious metal, preferably serves largely for converting hydrocarbons and/or nitrogen oxides. The second through-flow unit C30 can be configured without a catalytically effective coating, or have a smaller quantity of catalytic coating per volumetric unit than the first through-flow unit C29.

[0235] A catalytically effective coating is presently understood to be a coating which acts as a catalytic converter, thus reducing the activation energy for the chemical conversion of the exhaust gases, and increasing the response time as a result. The second through-flow unit C30 can in particular be coated with a washcoat. A washcoat is presently not considered to be a catalytic coating. A washcoat is understood to be a coating which increases the surface without reducing the activation energy for the chemical conversion.

[0236] Owing to the fact that the second through-flow unit C30 in terms of the outflow direction C67 of the first through-flow unit C29 through the exhaust gas after-treatment unit C26 is disposed completely behind the first through-flow unit C29, a cross flow between the first through-flow unit C29 and the second through-flow unit C30 is not possible. By virtue of the arrangement, exhaust gas that has flowed into the second through-flow unit C30 advantageously does not flow back into the first through-flow unit C29. As a result, the proportion of the exhaust gas flow that flows in through the first through-flow unit C29 can be very positively controlled by way of the configuration embodiment of the largest cross sections C69 and C70, and by way of the configuration embodiment of the inflow openings C31 and C32. The proportion of the exhaust gas flow flowing through the first through-flow unit C29 has a substantial influence on the temperature of the exhaust gas flowing out of the exhaust gas after-treatment unit C26.

[0237] This results in a higher fluidic resistance for the exhaust gas flowing through both through-flow units C29, C30, than for the flow through only the second through-flow unit C30. The splitting of the exhaust gas flow among the first and the second inflow openings C31 and C32 can be easily predefined by way of the thicknesses a and b, and the largest cross sections C69 and C70 of the through-flow units C29 and C30.

[0238] FIG. 24 shows an alternative embodiment for an exhaust muffler C23. The exhaust muffler C23 has a housing C27 in which a first muffler chamber C47 and a second muffler chamber C48 are formed. The muffler chambers C47 and C48 are separated by a partition wall C28. An exhaust gas after-treatment unit C26 is disposed in a connection opening C50 of the partition wall C28. In all embodiments, the same reference signs identify equivalent elements. As is illustrated in FIGS. 20 to 22, the exhaust gas after-treatment unit C26 can be formed by two through-flow units C29 and C30. The exhaust gas after-treatment unit C26 can be configured in such a way that a sub-flow of the exhaust gas flow flows through both through-flow units C29 and C30, and an additional sub-flow of the exhaust gas flow flows only through one through-flow unit C30. Alternatively, the exhaust gas after-treatment unit C26 can be configured in such a way that the entire exhaust gas flow flowing through the exhaust gas after-treatment unit C26 flows through all through-flow units C29, C30 of the exhaust gas after-treatment unit C26. It can be provided here that the exhaust gas after-treatment unit C26 has only a single through-flow unit.

[0239] In an advantageous configuration embodiment, the exhaust gas after-treatment unit C26 has in all regions of the at least one through-flow unit the same quantity of catalytically effective coating per volumetric unit, so that the entire exhaust gas flow flowing through the exhaust gas after-treatment unit C26 flows past a catalytically effective coating.

[0240] In order to prevent excessive heating of the exhaust gas flow, it is provided in the embodiment according to FIG. 24 that a sub-flow of the exhaust gas flow does not flow through the exhaust gas after-treatment unit C26. In the embodiment according to FIG. 24, a bypass channel C61 through which a sub-flow of the exhaust gas flow flows. The exhaust gas sub-flow flowing through the bypass channel C61 is highlighted by arrows C63. This sub-flow does not flow through the exhaust gas after-treatment unit C26.

[0241] The sub-flow of the exhaust gas flow flowing through the exhaust gas after-treatment unit C26 is highlighted by arrows C62. In the embodiment, the bypass channel C61 has a connection opening C59 which connects the first muffler chamber C27 to the bypass channel C61 and through which exhaust gases flow into the bypass channel C61. Moreover, the bypass channel C61 has an exit opening C60 through which exhaust gases from the bypass channel C61 leave the exhaust muffler C23. Accordingly, exhaust gases that flow through the bypass channel C61 in the embodiment do not flow through the interior of the second muffler chamber C48. The bypass channel C61 in the embodiment leads through the second muffler chamber C48 in spatial terms, but is fluidically separated from the latter. Owing to this fact, no mixing takes place between the sub-flow flowing through the bypass channel C61 (arrows C63) and the sub-flow of the exhaust gas flow flowing through the second muffler chamber C48 (arrows C62). The bypass channel C61 is disposed in such a way that it is heated by the exhaust gases disposed in the muffler chamber C48. As a result, a conversion of exhaust gas components in the bypass channel C61 is also possible without a catalytically effective material.

[0242] The bypass channel C61 is preferably routed so as to be adjacent to an external wall of the exhaust muffler C23. The sub-flow flowing through the bypass channel C61 is advantageously smaller than the sub-flow flowing through the exhaust gas after-treatment unit C26. The sub-flow flowing through the bypass channel C61 is advantageously less than 40%, in particular less than 30%, preferably less than 20%, of the entire exhaust gas flow. The quantity of exhaust gas flowing through the bypass channel C61 is preferably set by way of the flow cross sections of the exhaust gas after-treatment unit C26 and of the bypass channel C61.

[0243] In the embodiment, the through-flow units C29, C30 have through-flow elements C41 of metal wire. The metal wire of which the first and/or the second through-flow unit C29, C30 can consist, is in particular made of steel or of a nickel alloy. Other carriers, for example metal fibers, foamed materials or carriers that form elongate, geometrically defined channels, for example carriers of sintered ceramic, may also be advantageous.

[0244] The terms constant and flat in the present context are understood throughout to mean a constant or flat configuration within the scope of the usual manufacturing tolerances.

[0245] In FIGS. 25 to 29, the reference signs mentioned hereunder are in each case illustrated without the prefix D.

[0246] FIG. 25 shows a chain saw D1 as an embodiment for a handheld work apparatus. Instead of a chain saw D1, the work apparatus can also be a brushcutter, an angle grinder, a blower, a lawnmower or a like work apparatus. The handheld work apparatus is in particular a portable work apparatus. The chain saw D1 has a housing D2 on which a handle D3 is held. Operating elements for the chain saw D1, in the embodiment a throttle lever D4 and a throttle lever lock D5, are disposed on the handle D3. The chain saw D1 has a guide bar D6 on which a revolving saw chain D7 is disposed. During operation, the saw chain D7 is driven by a combustion engine disposed in the housing D2, in the embodiment a two-stroke engine D8. The combustion engine may advantageously also be a different mixture-lubricated combustion engine, in particular a mixture-lubricated four-stroke engine.

[0247] The two-stroke engine D8 includes an air filter D9 by way of which air is inducted during operation. The air makes its way to a crankcase D15 of the two-stroke engine D8 by way of an intake channel D11. A portion of the intake channel D11 is formed in a fuel supply unit D10, for example a carburetor. A different type of supply of fuel, for example by way of a fuel valve, may also be provided. A different location of introducing fuel, for example into the crankcase D15, may also be provided.

[0248] The two-stroke engine D8 includes a cylinder D12 in which a piston D13 is mounted so as to reciprocate. The piston D13 delimits a combustion chamber D14 formed in the cylinder D12. The combustion chamber D14 is connected to the interior of the crankcase D15 by way of transfer channels D19 in the region of the lower dead center of the piston D13, illustrated in FIG. 25. The piston D13, by way of a connecting rod D16, drives a crankshaft D17 which is rotatably mounted in the crankcase D15. The crankshaft D17 is mounted so as to be rotatable about a rotational axis D18. A spark plug D20 protrudes into the combustion chamber D14. An outlet opening D21, which is connected to an entry opening D24 of an exhaust muffler D23 by way of an outlet channel D22, leads out of the combustion chamber D14.

[0249] During operation, the two-stroke engine D8 inducts a fuel/air mixture through the intake channel D11 into the interior of the crankcase D15 during the upward stroke of the piston D13. The fuel/air mixture is compressed in the crankcase D15 during the downward stroke of the piston D13. As soon as the transfer channels D19 from the piston D13 to the combustion chamber D14 are opened, the fuel/air mixture flows from the interior of the crankcase D15 into the combustion chamber D14. In the region of the upper dead center, the spark plug D20 ignites the mixture in the combustion chamber. Due to the subsequent combustion, the piston D13 is accelerated back in the direction toward the crankcase D15 again. As soon as the piston D13 opens the outlet opening D21, exhaust gases can flow out of the combustion chamber D14 and flow toward the exhaust muffler D23. As soon as the transfer channels D19 from the piston D13 to the combustion chamber D14 are opened, fresh fuel/air mixture is replenished for the next combustion.

[0250] Alternatively, the two-stroke engine D8 can also operate with stratified scavenging and, in addition to the intake channel D11, include one or a plurality of air ducts by way of which largely fuel-free air is kept available in the transfer channels D19. During the downward stroke of the piston D13, the pre-stored air separates exhaust gases from the previous combustion from fuel/air mixture flowing into the combustion chamber D14.

[0251] The exhaust muffler D23 has a muffler housing D27 in which a first muffler chamber D47 and a second muffler chamber D48 are formed. The first muffler chamber D47 is disposed upstream of the second muffler chamber D48. In the embodiment, the entry opening D24 opens into the first muffler chamber D47. However, it can also be provided that additional muffler chambers are formed in the muffler housing D37, or in another unit, upstream of the first muffler chamber. The exhaust muffler D23 has an exit opening D25 from which exhaust gases from the exhaust muffler D23 flow out into the environment. In the embodiment, the exit opening D25 leads out of the second muffler chamber D48. In an alternative embodiment, additional muffler chambers can be provided downstream of the second muffler chamber D48.

[0252] The first muffler chamber D47 and the second muffler chamber D48 are separated by a partition wall D28. In the embodiment, an exhaust gas after-treatment unit D26 through which exhaust gases can flow from the first muffler chamber D47 into the second muffler chamber D48 is held on the partition wall D28. For this purpose, the partition wall D28 has an opening in the region of the exhaust gas after-treatment unit D26. The exhaust gas after-treatment unit D26 includes a first through-flow unit D29 and a second through-flow unit D30 which will be described in more detail hereunder.

[0253] FIG. 25 schematically shows the arrangement of the entry opening D24 into the exhaust muffler D23 relative to the arrangement of the exhaust gas after-treatment unit D26. The exhaust gases flow in a main flow direction D35 through the exhaust gas after-treatment unit D26. In the embodiment, the main flow direction D35 lies approximately perpendicularly to the partition wall D28. The main flow direction D35 preferably corresponds to an outflow direction D64 from the first through-flow unit D29, which will be described in more detail hereunder. A projection D59 of the entry opening D24 parallel to the main flow direction D35 toward the partition wall D28 is schematically plotted in FIG. 25. As is shown in FIG. 25, the projection D59 lies outside the exhaust gas after-treatment unit D26. The projection D59 and the exhaust gas after-treatment unit D26 are not congruent. Owing to this fact, exhaust gases that flow into the exhaust muffler D23 have to be deflected before they can flow through the exhaust gas after-treatment unit D26. A more uniform distribution of the exhaust gases is achieved as a result, and the exhaust gas after-treatment unit D26 is impinged with exhaust gas in a largely uniform manner.

[0254] The construction of the exhaust gas after-treatment unit D26 will be explained hereunder with reference to FIGS. 26 and 27. FIG. 27 shows a lateral view of the exhaust gas after-treatment unit D26 when viewed counter to an outflow direction D64 of the first through-flow unit D29, which will be explained in more detail hereunder. As is shown in FIG. 26, the exhaust gas after-treatment unit D26 includes a housing D37. In the embodiment, the housing D37 is formed from two component shells D38 and D39. The component shells D38 and D39 can be produced as deep-drawn parts, for example. In the embodiment, the component shells D38 and D39 are connected to one another in a sealing manner on a peripheral edge D50 of the exhaust gas after-treatment unit D26. A different construction of the housing D37, for example from a single metal sheet, or from a shell-shaped sheet-metal part and a cover, may also be advantageous.

[0255] The first component shell D38 of the housing D37 is disposed so as to be contiguous to the first muffler chamber D47, as is shown in FIG. 25. The first component shell D38 has inflow openings D31 of the exhaust gas after-treatment unit D26. Exhaust gas flows through the inflow openings D31 into the first through-flow unit D29. As is shown in FIG. 26, the exhaust gas after-treatment unit D26 has two portions D51 and D52 which lie behind one another in terms of the main flow direction D35. The first through-flow unit D29 is disposed in the first portion D51. The second through-flow unit D30 is disposed in the second portion D52. The second through-flow unit D30 does not protrude into the first portion D51. The first through-flow unit D29 does not protrude into the second portion D52. Accordingly, in terms of the outflow direction D64 of the first through-flow unit D29, in particular in terms of the main flow direction D35, the second through-flow unit D30 is disposed completely downstream of the first through-flow unit D29. The first inflow openings D31 are disposed on an upstream end face D40 of the first through-flow unit D29. No inflow openings D31 are provided on the circumference of the first through-flow unit D29.

[0256] The outflow surface D61 of the first through-flow unit D29 lies in an imaginary plane D66 which is illustrated by a dashed line in FIG. 26. The plane D66 is disposed perpendicularly to the main flow direction D35. The second through-flow unit D30 does not protrude beyond the plane D66, in particular counter to the outflow direction D64, but lies completely downstream of the plane D66 or contacts the latter. The plane D66 does not intersect the second through-flow unit D30. The first through-flow unit D29 lies completely upstream of the plane D66 and does not protrude beyond the plane D66 in the outflow direction D64. The through-flow units D29 and D30 extend on opposite sides of the plane D66. In terms of the outflow direction D64, the second through-flow unit D30 is advantageously disposed completely downstream of the first through-flow unit D29.

[0257] The first through-flow unit D29 has a downstream end face D41 through which the exhaust gases leave the first through-flow unit D29. When viewed in the main flow direction D35, the downstream end face D41 of the first through-flow unit D29, by way of a sub-region, is congruent with the second through-flow unit D30. The exhaust gases can transfer from the first through-flow unit D29 into the second through-flow unit D30 through a transfer opening D34 of the housing D37. The at least one transfer opening D34 is advantageously the only opening that fluidically connects the first through-flow unit D29 to the second through-flow unit D30. Accordingly, exhaust gases that exit the first through-flow unit D29 have to first flow into the second through-flow unit D30.

[0258] The first through-flow unit D29 has the inflow surface D60 through which exhaust gas can flow into the first through-flow unit D29. The inflow surface D60 is formed on an upstream end face D40 of the first through-flow unit D29. The first through-flow unit D29 has a downstream outflow surface D61 through which exhaust gas can exit the first through-flow unit D29. In the embodiment, the inflow surface D60 and the outflow surface D61 lie so as to be mutually parallel. However, a different arrangement of the inflow surface D60 and outflow surface D61 may also be advantageous.

[0259] The second through-flow unit D30 has an inflow surface D62. The inflow surface D62 is formed on an upstream end face D42 of the second through-flow unit D30. The inflow surface D62 in the embodiment is configured to be flat within the scope of the usual manufacturing tolerances. The transfer opening D34 opens out at the inflow surface D62. The second through-flow unit D30 has a downstream outflow surface D63. The outflow surface D63 in the embodiment is oriented parallel to the inflow surface D62. However, a different position may also be advantageous.

[0260] The outflow surface D61 of the first through-flow unit D29 has an outflow direction D64. The outflow direction D64 is oriented perpendicularly to the outflow surface D61 and from the first through-flow unit D29 to the second through-flow unit D30.

[0261] As is shown in FIG. 26, when viewed counter to the outflow direction D64, the first through-flow unit D29 projects beyond the second through-flow unit D30. The protrusion c by which the first through-flow unit D29 projects beyond the second through-flow unit D30 is advantageously at least 3 mm, in particular at least 5 mm. When viewed counter to the outflow direction D64, or counter to the main flow direction D35, respectively, the protrusion c preferably extends across the entire circumference of the second through-flow unit D30. The size of the protrusion c herein can be constant within the scope of the usual manufacturing tolerances, or vary across the circumference. However, the protrusion c is preferably at least 3 mm at each location of the circumference of the second through-flow unit D30.

[0262] In the embodiment, the through-flow units D29 and D30 are in each case of a cylindrical configuration. The cylindrical external contours of the through-flow units D29 and D30 are illustrated by a dashed line in FIG. 27. The first through-flow unit D29 has an external diameter f (FIG. 26). The second through-flow unit D30 has an external diameter g (FIG. 26). The through-flow units D29 and D30 are in each case formed by a through-flow element D46. The through-flow elements D46 have a multiplicity of cavities which permit a flow to pass through. This is schematically illustrated in FIG. 28. The through-flow elements D46 have no closed surfaces, at least not on their inflow surfaces D60 and D62 and on their outflow surfaces D61 and D63 (FIG. 26). In the embodiment, the through-flow units D29 and D30 include in each case the wire of the assigned through-flow element D46 and the cavities that are formed between the portions of the wire. The through-flow units D29 and D30 define the envelope elements which surround the through-flow elements D46 and on which the through-flow elements D46 rest uniformly within the scope of the manufacturing accuracy and the uniformity in terms of size and distribution of the cavities.

[0263] The first through-flow unit D29 has a largest cross section D69. The second through-flow unit D30 has a largest cross section D70. The largest cross sections D69 and D70 lie perpendicularly to the main flow direction D35 and perpendicularly to the outflow direction D64. In the embodiment, the largest cross section D69 corresponds to the square of half the external diameter f of the first through-flow unit D29 multiplied by . Accordingly, the largest cross section D70 corresponds to the square of half the external diameter g of the second through-flow unit D30 multiplied by .

[0264] As is shown in FIG. 26, the housing D37 has outflow openings D32 on the downstream end face D41 of the first through-flow unit D29. A sub-flow D45, which exits the first through-flow unit D29, can flow out of the housing D37 through the outflow openings D32 without first flowing through the second through-flow unit D30. The sub-flow D45 of the exhaust gas flow is schematically illustrated by an arrow in FIG. 26. An additional sub-flow D44 of the exhaust gas flow, which is likewise schematically illustrated by an arrow in FIG. 26, flows into the first through-flow unit D29 at the upstream end face D40 of the first through-flow unit D29, leaves the first through-flow unit D29 at the downstream end face D41, flows into the second through-flow unit D30 through an upstream end face D42 of the second through-flow unit D30, flows through the second through-flow unit D30, and leaves the second through-flow unit D30 at a downstream end face D43 of the second through-flow unit D30. On the downstream end face D43 of the second through-flow unit D30, the housing D37 has at least one outflow opening D33 through which the sub-flow D44 can leave the housing D37. Additional flow paths through the exhaust gas after-treatment unit D26 are not provided. When flowing through the exhaust gas after-treatment unit D26, the entire exhaust gas flow is split into the sub-flows D44 and D45.

[0265] In the embodiment, a plurality of outflow openings D32 and a plurality of outflow openings D33 are provided. However, exactly one outflow opening D32 and/or exactly one outflow opening D33 may also be advantageous.

[0266] In terms of the outflow direction D64, in particular in terms of the main flow direction D35, the outflow openings D32 and D33 are mutually offset, specifically by a thickness b of the second portion D52, measured in the outflow direction. The thickness of the first portion D51 corresponds to a thickness a of the first through-flow unit D29 in a central region. The thickness a is measured in the outflow direction D64, thus perpendicularly to the outflow surface D61. The first through-flow unit D29 has a chamfer on its upstream peripheral regions, so that this results in a somewhat smaller thickness at this location. The first through-flow unit D29 has the same thickness a across at least 80%, in particular across at least 90%, of its largest cross section D69, within the scope of the usual manufacturing tolerances.

[0267] The second through-flow unit D30, in its central region, has a thickness b measured in the outflow direction D64, or in the main flow direction D35, respectively. The second through-flow unit D30 has radiused corners on its downstream peripheral regions, so that this results in a somewhat smaller thickness at this location. The second through-flow unit D30 has the same thickness b across at least 80%, in particular across at least 90%, of its largest cross section D70, within the scope of the usual manufacturing tolerances.

[0268] In the embodiment, the thickness of the first portion D51 corresponds approximately to the thickness a of the first through-flow unit D29. The thickness b can correspond approximately to the thickness of the second portion D52. The thicknesses a and b can be approximately of identical size, in particular within the scope of the usual manufacturing tolerances. The thickness a is advantageously half to double the thickness b.

[0269] The transfer opening D34 of the housing D37 leads from the first portion D51 into the second portion D52. In the embodiment, the transfer opening D34 extends at least across the entire largest cross section D70 of the second through-flow unit D30. However, it can also be provided that one or a plurality of comparatively small transfer openings D36 fluidically connect the two through-flow units D29 and D30 to one another.

[0270] A step D36 which rests on the downstream end face D41 of the first through-flow unit D29 by way of a first step portion D53 is formed on the second component shell D39. The step D36 is in particular formed by a jump in the cross section of the housing D37 of the exhaust gas after-treatment unit D26. In the first portion D51, the housing D37 has an external diameter D, as is shown in FIG. 27. At the step D36, the external diameter of the housing D37 decreases to an external diameter e in the second portion D52. In the embodiment, the housing D37 is configured with a round cross section. Different cross-sectional shapes may also be advantageous. Accordingly, the step D36 can be formed by an abrupt reduction in the external dimensions of the housing D37. The outflow openings D32 are formed in the first step portion D53. A second step portion D54 extends transversely, in particular perpendicularly, to the first step portion D53. The second step portion D54 rests on an external circumference of the second through-flow unit D30. The first step portion D53 preferably extends approximately perpendicularly to the main flow direction D35. The second step portion D54 advantageously extends approximately parallel to the main flow direction D35. No outflow openings are advantageously formed on the second step portion D54. The exhaust gas after-treatment unit D26 has outflow openings D32 and D33 only on the downstream end faces D41 and D43 of the through-flow units D29 and D30, respectively.

[0271] The largest cross section D69 of the first through-flow unit D29 is advantageously larger than the largest cross section D70 of the second through-flow unit D30. The largest cross section D69 of the first through-flow unit D29 is advantageously at least 130%, in particular at least 150%, of the largest cross section D70 of the second through-flow unit D30.

[0272] In the embodiment, the first through-flow unit D29 and the second through-flow unit D30 are in each case formed by a through-flow element D46. Alternatively, it can be provided that one or both through-flow units 29, 30 are formed by two or more through-flow elements D46. Alternatively, it can also be provided that the first through-flow unit D29 and the second through-flow unit D30 are formed by different regions of a single through-flow element D46.

[0273] FIGS. 28 and 29 show potential configuration embodiments for through-flow elements D46. FIG. 28 shows a through-flow element D46 which is formed from a metal wire. The through-flow element D46 is in particular a knitted wire mesh. The construction of the through-flow element D46 illustrated in FIG. 28 is provided in particular for the first through-flow unit D29. However, it can also be provided that the second through-flow unit D30 is formed by a through-flow element D46 corresponding to FIG. 28.

[0274] FIG. 29 shows an alternative configuration embodiment for a through-flow element D46. The through-flow element D46 shown in FIG. 29 includes a carrier D58 in which are formed a multiplicity of channels D57. In the embodiment, the channels D57 extend so as to be mutually parallel, and are preferably formed separately from one another. The carrier D58 is advantageously coated with a catalytically effective material which preferably contains a precious metal. The through-flow element D46 illustrated in FIG. 29 is preferably provided for the second through-flow unit D30. The through-flow element D46 from FIG. 29 can be formed from a ceramic material or from metal, for example. The carrier D58 can preferably be formed from a plurality of metal sheets which are wound. One of the metal sheets is preferably of a corrugated configuration, so as to form the channels D57.

[0275] Other carriers D58, for example metal fibers, foamed materials or other carriers D58 that form elongate, geometrically defined channels, for example carriers D58 of sintered ceramic, may also be advantageous.

[0276] FIG. 27 shows the arrangement of the outflow openings D32 and D33 in the second component shell D38. The second component shell D38 has a central region D55 that has the outflow openings D33. The central region D55 is disposed downstream of the second through-flow unit D30. When viewed counter to the main flow direction D35, the central region D55 is surrounded by a surrounding region D56. The surrounding region D56 forms the first portion D53 of the step D36. The outflow openings D32 are disposed in the surrounding region D56. As is shown in FIG. 27, the outflow openings D32 are disposed so as to be uniformly distributed about the central region D55. Owing to this fact, exhaust gas flowing from the outflow openings D32 flows along a region of the housing D37 in which the second through-flow unit D30 is disposed. The latter is positively cooled as a result.

[0277] The second through-flow unit D30 is coated with a catalytic material. Additionally, a coating with a so-called washcoat can be provided. Accordingly, no catalytic conversion of exhaust gases takes place in the second through-flow unit D30. The first through-flow unit D29 does not have a catalytic coating, or has a smaller quantity of catalytic coating per volumetric unit than the second through-flow unit D30.

[0278] The first through-flow unit D29 preferably serves largely for reducing particles. Lubricating oil in the form of droplets, which is converted in the first through-flow unit D29, is contained in exhaust gases of mixture-lubricated combustion engines.

[0279] The second through-flow unit D30, which is coated with a catalytically effective coating, in particular with precious metal, preferably serves largely for converting hydrocarbons and/or nitrogen oxides. The first through-flow unit D29 can be configured without a catalytically effective coating, or have a smaller mass of catalytic coating per volumetric unit than the second through-flow unit D30.

[0280] A catalytically effective coating is presently understood to be a coating which acts as a catalytic converter, thus reducing the activation energy for the chemical conversion of the exhaust gases, thus increasing the response rate. The first through-flow unit D29 can in particular be coated with a washcoat. A washcoat is presently not understood to be a catalytic coating. A coating which increases the surface of its carrier element without reducing the activation energy for the chemical conversion is understood to be a washcoat.

[0281] Owing to the fact that the second through-flow unit D30 is disposed completely downstream of the first through-flow unit D29 in terms of the main flow direction D35 through the exhaust gas after-treatment unit D26, a cross flow between the first through-flow unit D29 and the second through-flow unit D30 is not possible. As a result, the proportion of the exhaust gas flow that flows through the second through-flow unit D30 can be very positively controlled by way of the configuration embodiment of the cross sections and inflow openings. The proportion of the exhaust gas flow that flows through the second through-flow unit D30 has a substantial influence on the temperature of the exhaust gas flowing out of the exhaust gas after-treatment unit D26.

[0282] This results in a higher fluidic resistance for the exhaust gas flowing through both through-flow units D29, D30 than for the flow through only the first through-flow unit D29. The splitting of the exhaust gas flow among the first and the second outflow openings D32 and D33 can be easily predefined by way of the thicknesses a and b, and the cross sections of the through-flow units D29 and D30.

[0283] The terms constant and flat in the present context are understood throughout to mean a constant or flat configuration within the scope of the usual manufacturing tolerances.

[0284] It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.