MUFFLER AND OUTLET STUB FOR A MUFFLER

Abstract

A muffler having a muffler housing with a muffler chamber formed therein includes an outlet stub. In the stub, a channel is formed through which exhaust gases escape. The channel has a throttle location with a smallest flow cross-section and a discharge opening with a discharge flow cross-section. The channel is bounded by a wall. The flow cross-section increases substantially continuously from the smallest flow cross-section to the discharge flow cross-section at least in a section in the direction from the throttle location to the discharge opening. The stub has a fastening location at which it is held in an outlet opening of the muffler housing. The wall is closed continuously over its circumference from the throttle location to the discharge opening. The section of the channel extends in a sectional plane containing a center axis of the channel into a longitudinal section of the stub having the fastening location.

Claims

1. A muffler comprising: a muffler housing having at least one muffler chamber formed therein; an outlet stub, in which an outlet channel is formed, through which exhaust gases escape from the muffler housing into an environment; said outlet channel defining a center axis, a throttle location with a smallest flow cross-section, and a discharge opening with a discharge flow cross-section; said outlet channel being bounded by an inner wall of said outlet stub; said outlet channel having a flow cross-section which increases continuously from said smallest flow cross-section to said discharge flow cross-section at least in a section in a direction from said throttle location to said discharge opening; said outlet stub having a fastening location at which said outlet stub is held in a housing discharge opening of said muffler housing; said inner wall of the outlet stub being closed continuously over its entire circumference from said throttle location to said discharge opening; and, said section of the outlet channel extending in a sectional plane containing said center axis into a longitudinal section of said outlet stub having said fastening location.

2. The muffler of claim 1, wherein said outlet stub is held sealingly in said housing discharge opening at said fastening location.

3. The muffler of claim 1, wherein said outlet stub has an outer thread with which said outlet stub is screwed into said muffler housing and which forms said fastening location.

4. The muffler of claim 1, wherein said section of said outlet channel in which said flow cross-section of said outlet channel increases continuously in the direction from said throttle location to said discharge opening extends into the longitudinal section of said outlet stub; and, said longitudinal section is arranged upstream of said fastening location.

5. The muffler of claim 1, wherein said inner wall of said outlet stub has a curved profile at least in one section from said fastening location to said discharge opening in a sectional plane containing said center axis.

6. The muffler of claim 1, wherein said inner wall of said outlet stub has a continuously curved profile at least in one section from said fastening location to said discharge opening in a sectional plane containing said center axis.

7. The muffler of claim 1, wherein a ratio of said discharge flow cross-section to said smallest flow cross-section is at least 3.

8. The muffler of claim 1, wherein a ratio of said discharge flow cross-section to said smallest flow cross-section is at least 4, at least 5, or at least 6.

9. The muffler of claim 1, wherein said outlet channel has a channel length, measured along said center axis, from a downstream end of said throttle location to said discharge opening; a ratio of said channel length to a channel diameter of said outlet channel at said discharge opening is at least 1; and, in a flow cross-section which is not circular, said channel diameter is a calculated diameter of a circular cross-section of identical area.

10. The muffler of claim 1, wherein said outlet channel has a channel length, measured along said center axis, from a downstream end of said throttle location to said discharge opening; a ratio of said channel length to a channel diameter of said outlet channel at said discharge opening is at least 1.5; and, in a flow cross-section which is not circular, said channel diameter is a calculated diameter of a circular cross-section of identical area.

11. The muffler of claim 1, wherein said outlet channel has a circular flow cross-section at least from a downstream end of said throttle location to said discharge opening.

12. The muffler of claim 1, wherein said inner wall of said outlet stub encloses an angle (a) of not more than 30 with said center axis at said discharge opening in a sectional plane containing said center axis.

13. The muffler of claim 12, wherein said angle () is not more than 30 from said throttle location to said discharge opening at each point of said inner wall.

14. The muffler of claim 1, wherein said outlet stub includes a spark protection screen, which forms an inlet opening in said outlet stub; and, said outlet stub is formed by a one-piece base body and said spark protection screen.

15. An outlet stub for a muffler, the outlet stub comprising: an outlet stub body defining an outlet channel through which exhaust gases can escape from a muffler housing into an environment; said outlet channel defining a center axis, a throttle location with a smallest flow cross-section, and a discharge opening with a discharge flow cross-section; said outlet channel being bounded by an inner wall of said outlet stub; said outlet channel defining a flow cross-section which increases continuously from said smallest flow cross-section to said discharge flow cross-section at least in a section of said outlet channel in a direction from said throttle location to said discharge opening; said outlet stub body having a fastening location at which the outlet stub is configured to be held in a housing discharge opening of the muffler housing; said inner wall being closed continuously over an entire circumference of said inner wall from said throttle location to said discharge opening; and, said section extending in a sectional plane containing said center axis into a longitudinal section of said outlet stub having said fastening location.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0038] The invention will now be described with reference to the drawings wherein:

[0039] FIG. 1 shows a schematic cross-sectional view of a work apparatus;

[0040] FIG. 2 shows a side view of the muffler of the chain saw from FIG. 1;

[0041] FIG. 3 shows a sectional illustration of the muffler from FIG. 2;

[0042] FIG. 4 shows a perspective illustration of the outlet stub of the muffler from FIGS. 2 and 3;

[0043] FIG. 5 shows a top view of the outlet stub from FIG. 4;

[0044] FIG. 6 shows a top view of the outlet stub in the direction of the arrow VI in FIG. 5;

[0045] FIG. 7 shows a side view of the outlet stub in the direction of the arrow VII in FIG. 5;

[0046] FIG. 8 shows a side view of the outlet stub in the direction of the arrow VIII in FIG. 5;

[0047] FIG. 9 shows a section along the line IX-IX in FIG. 6; and,

[0048] FIG. 10 shows an embodiment of an outlet stub in a sectional illustration according to FIG. 9.

DETAILED DESCRIPTION

[0049] FIG. 1 shows a chain saw 1 as an embodiment for a handheld work apparatus. The handheld work apparatus may also be another handheld work apparatus, preferably a work apparatus carried by hand during operation. For example, the work apparatus may be an angle grinder, a brush cutter or a blower.

[0050] The chain saw 1 has a housing 2. A handle 3 is held on the housing 2, preferably via anti-vibration elements. Operator control elements, in the embodiment a throttle lever 4 and a throttle lever lock 5, are arranged on the handle 3. A combustion engine 8 is arranged in the housing 2. The combustion engine 8 is used to drive a tool. The tool of the chain saw 1 is a saw chain 7, which is arranged circumferentially on a guide bar 6. The saw chain 7 is merely illustrated schematically in FIG. 1.

[0051] The combustion engine 8 is in particular a two-stroke engine. The combustion engine 8 is in particular a single-cylinder engine. The combustion engine 8 draws in air via an air filter 9. The air is drawn into a crankcase 15 of the combustion engine 8 via an intake channel 11. The combustion engine 8 includes a fuel supply unit 10, which may be, for example, a carburetor. The fuel supply unit 10 may include a valve, preferably an electromagnetic valve, which supplies the fuel to the intake channel 11 or the crankcase 15.

[0052] The combustion engine 8 has a cylinder 12 in which a combustion chamber 14 is formed. A piston 13 is mounted reciprocally in the cylinder 12. The piston 13 delimits the combustion chamber 14. The piston 13 drives a crankshaft 17, which is mounted rotatably in the crankcase 15 about a rotational axis 18, via a connecting rod 16. The interior space of the crankcase 15 is fluidically connected to the combustion chamber 14 in predetermined positions of the piston 13, preferably in the region of the bottom dead center of the piston 13, via transfer channels 19. A spark plug 20 protrudes into the combustion chamber 14. An outlet opening 21 leads from the combustion chamber 14 and is connected via an outlet channel 22 of the cylinder 12 to a muffler 23.

[0053] During operation, combustion air is drawn into the interior space of the crankcase 15 during the upward stroke of the piston 13, that is, during a movement of the piston 13 reducing the volume of the combustion chamber 14, as soon as the intake channel 11 is opened to the interior space of the crankcase 15. During the counter-movement of the piston 13, that is, during the downward stroke of the piston 13, the fuel/air mixture in the interior space of the crankcase 15 is compressed. As soon as the downwardly moving piston 13 opens the transfer channels 19 to the combustion chamber 14, the fuel/air mixture flows from the interior space of the crankcase 15 into the combustion chamber 14. During the subsequent upward stroke of the piston 13, the fuel/air mixture in the combustion chamber 14 is compressed and ignited by the spark plug 20 in the region of the top dead center of the piston 13. The resultantly initiated combustion of the fuel/air mixture accelerates the piston 13 to the crankcase 15. As soon as the outlet opening 21 is opened by the piston 13, the exhaust gases flow from the combustion chamber 14 through the outlet channel 22 into the muffler 23.

[0054] The muffler 23 has a muffler housing 27. The muffler housing 27 has an exhaust inlet 24 via which the exhaust gases enter a first muffler chamber 29 of the exhaust muffler 23. In the embodiment according to FIG. 1, the muffler 23 has a further, second muffler chamber 30, which is separated from the first muffler chamber 29 by a partition wall 28. An exhaust gas aftertreatment unit 26 may be arranged in the partition wall 28. The exhaust gas aftertreatment unit 26 may include a catalytic converter. An exhaust outlet 25 leads out of the muffler housing 27.

[0055] FIGS. 2 and 3 show the muffler 23 in detail, the partition wall 28 not being illustrated. It may also be provided that the muffler 23 does not have a partition wall 28. As shown in FIGS. 2 and 3, the muffler housing 27 is formed from a first housing shell 32 and a second housing shell 33, which are connected to each other at an edge 34. Another structure of the muffler housing 27, for example consisting of other housing parts, may also be advantageous. The exhaust outlet 25 is formed at an outlet stub 35. The exhaust outlet 25 is formed on the same housing shell 32 as the exhaust inlet 24. Another arrangement of exhaust inlet 24 and exhaust outlet 25 may also be advantageous.

[0056] As shown in FIG. 3, the muffler housing 27 has a housing discharge opening 31, which is formed on a threaded sleeve 49. The threaded sleeve 49 is fixed in the first housing shell 32. The outlet stub 35 is held sealingly in the threaded sleeve 49. In the embodiment, the outlet stub 35 is screwed into the threaded sleeve 49. The outlet stub 35 has a spark protection screen 41 which protrudes into the interior space of the muffler housing 27.

[0057] The outlet stub 35 has a discharge opening 38. The discharge opening 38 forms the exhaust outlet 25 from the muffler 23. An outlet channel 40 opens at the discharge opening 38. The outlet channel 40 is bounded by an inner wall 39 of the outlet stub 35. For screwing into the threaded sleeve 49, the outlet stub 35 has an outer thread 46. The outer thread 46 forms a fastening location at which the outlet stub 35 is held in the housing discharge opening 31 of the muffler housing 27. The outlet stub 35 also has an engagement contour 47. In the embodiment, the engagement contour 47 is configured as a hexagon stub. The engagement contour 47 is arranged in the section of the outlet stub 35 which protrudes from the muffler housing 27, as also shown in FIG. 3. By way of the engagement contour 47, the outlet stub 35 can be held for screwing in or unscrewing. As shown in FIG. 3, the engagement contour 47 is located between the outer thread 46 and the discharge opening 38.

[0058] The spark protection screen 41 is configured in the manner of a bag and surrounds an interior space 42. The spark protection screen 41 forms an inlet opening into the interior space 42 of the spark protection screen 41. As shown in FIG. 4, the spark protection screen 41 includes a first section 43 with a round cross-section which, in the embodiment, adjoins the outer thread 46. The end region of the spark protection screen 41 is formed by a second section 44 which has a flat cross-section.

[0059] As the top view in FIG. 5 shows, the first section 43 has a diameter g with a round cross-section. The second section 44 with a flat cross-section has a width i which corresponds in particular to the diameter g. As shown in FIG. 6, the second section 44 has a thickness h, which is significantly smaller than the width i. The configuration of the spark protection screen 41 is also visible in FIG. 8.

[0060] As shown in FIG. 9, the outlet stub 35 is formed by a base body 45 and the spark protection screen 41. In the embodiment, the outlet stub 35 does not have any further components. The spark protection screen 41 is attached to an end section 48 with a round outer cross-section of the base body 45. The end section 48 adjoins the section of the base body 45 which bears the outer thread 46. The outlet channel 40 is formed in the base body 45. The end portion 48 has an inlet opening 50, through which exhaust gases can flow from the interior space 42 of the spark protection screen 41 into the outlet channel 40.

[0061] The configuration of the outlet channel 40 of the outlet stub 35 is shown in FIGS. 7 and 9. The outlet channel 40 has a throttle location 37. The throttle location 37 indicates the region of the outlet channel 40 which has the smallest flow cross-section. The flow cross-section A1 at the throttle location 37 is shown in FIG. 7. FIG. 9 shows the diameter d1 of the outlet channel 40 at the throttle location 37. The inner wall 39 of the outlet channel 40 extends continuously and closed over the entire circumference of the outlet channel 40 from the throttle location 37 to the discharge opening 38. An air inlet at the throttle location 37 between the throttle location 37 and the discharge opening 38 is not provided. The base body 45 is configured to be continuously closed over its entire circumference between the inlet opening 50 and the discharge opening 38.

[0062] At the discharge opening 38, the outlet stub 35 has a discharge flow cross-section A2. The ratio of the discharge flow cross-section A2 to the smallest flow cross-section A1 is at least 3, in particular at least 4, preferably at least 5.

[0063] The outlet stub 35 has a center axis 36. The center axis 36 is the longitudinal center axis of the outlet channel 40. In the outlet channel 40, exhaust gases flow in a main flow direction 54. The center axis 36 connects the centers of gravity of all the flow cross-sections lying perpendicularly to the main flow direction 54.

[0064] In the sectional plane which is illustrated in FIG. 9 and contains the center axis 36 of the outlet stub 35, the inner wall 39 encloses an angle with the center axis 36 at the discharge opening 38. The angle is not more than 30. Particularly preferably, the angle is between 20 and 25. At the discharge opening 38, the inner wall 39 is in particular configured to be sharp-edged within the scope of the manufacturing accuracy. No chamfer or rounding is provided at the discharge opening 38.

[0065] In order to avoid a flow separation of the exhaust gases from the inner wall 39, the angle which the inner wall 39 of the outlet stub 35 encloses with the center axis 36 at the discharge opening 38, in particular in each sectional plane containing the center axis 36, is not more than 30. Especially in particular, the angle in at least one sectional plane, preferably in each sectional plane containing the center axis, from the throttle location 37 to the discharge opening 38 at any point of the inner wall is not more than 30. In the embodiment, the angle , which the inner wall 39 of the outlet channel 40 encloses with the center axis 36, in a sectional plane containing the center axis 36, is the greatest at the discharge opening 38. In the embodiment, the angle , which the inner wall 39 of the outlet channel 40 encloses with the center axis 36, in all the sectional planes containing the center axis 36, is the greatest at the discharge opening 38. In the embodiment, the angle increases continuously from the throttle location 37 to the discharge opening 38.

[0066] In the embodiment, the inner wall 39 is configured to be rotationally symmetrical to the center axis 36. This makes it easy to produce the outlet channel 40. In a rotationally symmetrical configuration of the inner wall 39, the center axis 36 is the axis of symmetry of the outlet channel 40. The inner wall 39 of the outlet stub 35 has a continuously curved profile in particular in at least one sectional plane containing the center axis 36, in the embodiment in all the sectional planes containing the center axis 36, from the throttle location 37 to the discharge opening 38.

[0067] The throttle location 37 has an upstream end 51 and a downstream end 52. The outlet channel 40 has a length e, measured parallel to the center axis 36, from the downstream end 52 of the throttle location 37 to the discharge opening 38.

[0068] In the embodiment, the throttle location 37 has a length b, measured parallel to the center axis 36. The length b is measured from the upstream end 51 to the downstream end 52 of the throttle location 37. The length b of the throttle location 37 is in particular at least 1 mm. The throttle location 37 has the same diameter d1 over its entire length b. The throttle location 37 is formed by a section of the outlet channel 40 with a constant cross-section. In one embodiment variant, the throttle location 37 is formed by the narrowest cross-section of an outlet channel 40 with a continuously curved profile. In this embodiment variant, the upstream end 51 coincides with the downstream end 52 of the throttle location 37.

[0069] At the discharge opening 38, the outlet channel 40 has a diameter d2. The diameter d2 is significantly larger than the diameter d1 at the throttle location 37.

[0070] The ratio of the length e of the outlet channel 40 to the diameter d2 of the outlet channel 40 at the discharge opening 38 is in particular at least 1, in particular at least 1.5. The outlet channel 40 is accordingly configured to be comparatively long.

[0071] As shown in FIG. 9, the outer thread 46, which forms the fastening location of the outlet stub 35 in the muffler housing 27, is arranged in a length section 53 of the outlet stub 35, which is arranged downstream of the downstream end 52 of the throttle location 37. A length section 55 of the outlet stub 35 extends upstream of the length section 53. The throttle location 37 is arranged in the length section 55. A length section 57 of the outlet stub 35 extends downstream of the length section 53. In particular, the length sections 53, 55 and 57 adjoin one another, as illustrated in the embodiment. The outlet stub 35 has in particular no further length sections. Alternatively, it can be provided that the outlet stub 35 has further length sections.

[0072] The outer thread 46 is arranged in a length section 53 which extends between the length section 55 of the outlet stub 35 having the throttle location 37 and the discharge opening 38. The inner wall 39 of the outlet stub 35, as shown in FIG. 9, has a curved profile in the length section 53 in the illustrated sectional plane containing the center axis 36. In the length section 53, the outlet channel 40 widens in the main flow direction 54.

[0073] The outlet channel 40 has a section 56 in which the flow cross-section continuously increases in the direction from the throttle location 37 to the discharge opening 38. In the figures, the longitudinal extent of the section 56 is shown outside the outlet channel 40 for the sake of a better overview, although the section 56 is a section of the outlet channel 40. The section 56 extends in particular from the throttle location 37 to the discharge opening 38, as illustrated in the embodiment. The section 56 extends into the length section 55 arranged upstream of the length section 53. The section 56 extends through the housing discharge opening 31 into an interior space of the muffler 23.

[0074] It may be provided that the flow cross-section of the outlet channel 40 in the section 56 increases continuously in the direction from the throttle location 37 to the discharge opening 38.

[0075] In an alternative embodiment, the section 56 of the outlet channel 40 may increase substantially continuously. In particular, the section 56 has a partial region in which the flow cross-section of the outlet channel 40 is constant and/or decreases. A substantially continuously increasing flow cross-section is present whenever the partial region, in which the flow cross-section of the outlet channel 40 does not increase, and in which the flow cross-section is in particular constant, extends in particular over no more than 20%, in particular over no more than 10%, in particular over no more than 5%, of the length of the section. A reduction in the flow cross-section in the specified direction in the partial region may be provided. In particular, no reduction in the flow cross-section in the specified direction is provided in the partial region.

[0076] In the embodiment, the fastening location of the outlet stub 35 is formed on a thread. Alternatively, the outlet stub 35 may also be fixed to the muffler housing 27 in other ways, for example via a welded connection or a separate fastening element. The fastening location is then formed at the welded connection or at the separate fastening element. A different type of fastening of the outlet stub 35 to the muffler housing 27 may also be provided.

[0077] The spark protection screen 41 has a length f, measured parallel to the center axis 36.

[0078] As shown in FIG. 9, both the engagement contour 47 and the outer thread 46 are formed in a length section of the base body 45, which extends between the throttle location 37 and the discharge opening 38. Owing to the fact that the engagement contour 47 and the outer thread 46 are arranged downstream of the throttle location 37, a short construction length of the base body 45 can be achieved. The section of the outlet stub 35 protruding from the muffler housing 27 is comparatively short, although the curved region of the inner wall 39 has a comparatively large length e.

[0079] An alternative embodiment of an outlet stub 35 is shown in FIG. 10. The same reference symbols refer to corresponding elements as in the preceding figures, to the description of which reference is made. The embodiment according to FIG. 10 differs from the embodiment according to FIG. 9 in the configuration of the inner wall 39 of the outlet stub 35. In the embodiment according to FIG. 10, the inner wall 39 is assembled by sections 56a, 56b, 56c, which form the section 56. In a section 56a adjoining the throttle location 37 downstream of the throttle location 37, the inner wall 39 runs in the illustrated sectional plane containing the center axis 36, inclined to the center axis 36 about an angle 1. In the section 56b adjoining the section 56a downstream, the inner wall 39 runs in the illustrated sectional plane containing the center axis 36, inclined to the center axis 36 about an angle 2, which is greater than the angle 1. In the section 56c adjoining the section 56b downstream, the inner wall 39 runs in the illustrated sectional plane containing the center axis 36, inclined to the center axis 36 about an angle 3, which is greater than the angle 1 and greater than the angle 2.

[0080] The inner wall 39 is assembled from a plurality of sections 56a, 56b, 56c each having a frustoconical contour of the inner wall 39. In particular, at least two sections 56a, 56b, 56c are provided with a different cone angle. Also in the embodiment according to FIG. 10, the flow cross-section widens continuously in the main flow direction 54. There is no length section between the throttle location 37 and the discharge opening 38 in which the flow cross-section in the main flow direction 54 remains the same or decreases. Alternatively, a partial region between the sections 56a, 56b and/or 56c may be provided in which the flow cross-section of the outlet channel 40 is constant or decreases. The length of the partial region is comparatively small here, and therefore a substantially continuous increase in the flow cross-section results.

[0081] Further embodiments emerge by any combination of the embodiments with one another.

[0082] In the illustrated embodiments, the outlet channel 40 has a circular flow cross-section. However, another cross-sectional shape may also be advantageous.

[0083] 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.