BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described with reference to the drawings wherein:
FIG. 1 is a schematic section view of a work apparatus according to the invention;
FIG. 2 shows a detail section view taken along line II-II in FIG. 1;
FIG. 3 is a schematic section view of an exhaust-gas muffler which is attached to a cylinder and a crankcase;
FIG. 4 is an enlarged view of the attachment location of the exhaust-gas muffler on the crankcase; and, FIG. 5 shows a variation of the attachment location shown in FIG. 4.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
The work apparatus shown in FIG. 1 is a motor-driven chain saw 1. The motor-driven chain saw 1 has a housing 2 to which a rearward handle 3 is attached. The rearward handle 3 has a throttle lever 4 for the operation of an internal combustion engine 5 mounted in the housing 2. The internal combustion engine 5 is configured as a single-cylinder two-stroke engine and includes an air filter 7 which is connected to the internal combustion engine 5 via a carburetor 6. The intake channel configured in the carburetor 6 opens into a crankcase 13 of the engine 5. The engine 5 has a cylinder 8 wherein a combustion chamber 9 is formed. A piston 10 is mounted for reciprocal movement in the cylinder 8. The piston 10 drives a crankshaft 12 via a connecting rod 11 and the crankshaft 12 is rotatably journalled in the crankcase 13. The crankshaft 12 drives a work tool (not shown in FIG. 1), namely, a saw chain. An exhaust-gas muffler 14 is mounted on the internal combustion engine 5 and has a housing 15. The exhaust-gas muffler 14 has attachment bushings 21 which project through the housing 15 of the exhaust-gas muffler 14.
As shown in the section view of FIG. 2, the cylinder 8 has an outlet 19 from the combustion chamber 9 whereat the exhaust-gas muffler 14 is attached. The attachment bushings 21 end at respective sides of the outlet 19. The heads of attachment screws 20 lie against the base of the attachment sleeves 21, respectively. The attachment screws 20 threadably engage the cylinder 8 on both sides of the outlet 19. The attachment screws 20 define attachment locations 40 and 41 whereat the exhaust-,gas muffler 14 is fixedly connected to the cylinder 8.
As shown in FIG. 3, a reinforcement or stiffening sheet metal part 32 is mounted next to the outlet 19 on the housing 15 of the exhaust-gas muffler 14. The reinforcing sheet metal part reinforces the housing 15 in the region of the attachment locations 40 and 41.
As shown in FIG. 3, the housing 15 of the exhaust-gas muffler 14 is made up of two housing half shells 16 and 17 which are connected to each other at an edge 18. The half shell 17 is bent-over flange connected about the half shell 16 at the edge 18. In this way, a gas-tight connection between the two housing half shells 16 and 17 is provided. A seal can furthermore be mounted on the edge 18. Two partition walls 30 are arranged in the housing 15 of the exhaust-gas muffler 14. These partition walls 30 subdivide the interior space of the exhaust-gas muffler 14 into a chamber 36 disposed at the outlet 19 as well as two chambers 37 and 38. From the chamber 36, the exhaust gas reaches the two chambers 37 and 38 via respective passthrough openings 31 in the partition walls 30.
At the edge 18, an attachment location 42 is configured at the side of the exhaust-gas muffler 14 facing toward the crankcase 13. The exhaust-gas muffler 14 is attached to the crankcase 13 at the attachment location 42. The attachment location 42 is so configured that the exhaust-gas muffler 14 can move at the attachment location 42 relative to the crankcase 13. An attachment screw 22 is provided as an attachment element and the exhaust-gas muffler 14 is attached to the crankcase 13 with this attachment screw. The attachment screw 22 limits the possible relative movement between the exhaust-gas muffler 14 and the crankcase 13. The housing half shells 16 and 17 and the partition walls 30 have a sheet metal thickness (a) which amounts to 0.5 mm or less. Except for the reinforcing sheet metal part 32, no further reinforcement elements are provided on the exhaust-gas muffler 14. Stiffeners such as sheet metal parts or the like are understood as stiffening elements which satisfy no additional function in the exhaust-gas muffler 14 except reinforcement. Reinforcements of this kind are usually mounted on function sheet metal parts of the exhaust-gas muffler 14 in order to reinforce the same.
The attachment location 42 is shown enlarged in FIG. 4. The attachment screw 22 passes through a bushing 23. The bushing 23 lies with a collar 29 on the crankcase 13. Two metal cushion rings 25 are mounted at the outer periphery of the bushing 28 and a section of the edge 18 of the exhaust-gas muffler 14 is arranged therebetween. The edge 18 has an opening 26 through which the bushing 23 and the attachment screw 22 project. The metal cushion rings 25 have respective center openings 28 through which the bushing 23 extends. The diameter of the openings 28 corresponds approximately to the outer diameter of the bushing 23 or is slightly smaller so that a tight seat of the metal cushion rings 25 on the bushing 23 results. The metal cushion ring 25, which is mounted between the edge 18 and the crankcase 13, is enclosed by a sleeve 24 around its periphery. The sleeve 24 is supported on the periphery and a side surface of a metal cushion ring 25 and has a sleeve section 33 which projects into the interior of the opening 26 of the edge 18. The sleeve section 33 is at a spacing to the bushing 23. The edge 18 is supported via the edge 33 of the bushing 24 on the periphery of the metal cushion ring 25. In this way, the exhaust-gas muffler 14 is decoupled from the crankcase 13 in the longitudinal direction (that is, in the effective direction of the attachment screw 22) as well as also perpendicularly to this longitudinal direction.
With one end, the bushing 23 lies against the head of the attachment screw 22 and, with its other end, against the crankcase 13. The bushing 23 is rigidly configured and fixes a defined spacing between the screw head and the crankcase 13. The length of the bushing 23 is so selected that the metal cushion rings 25 are pretensioned by a pregiven distance in the longitudinal direction of the attachment screw 22 when the screw head of the attachment screw 22 lies against the bushing 23. The pretension force then works in an effective direction which extends parallelly to the longitudinal direction of the attachment screw 22.
In the embodiment of the attachment element 42 shown in FIG. 5, the function of the bushing 24 is assumed by the edge 18 itself. The housing half shell 16 is bent over to a collar 27 in the region of the opening 26 of the edge 18. The collar 27 defines an annular section which lies against the outer periphery of a metal cushion ring 25 and so supports the exhaust-gas muffler 14 perpendicular to the effective direction 35 of the pretension force at the metal cushion ring 25.
The metal cushion rings 25 are made of pressed metal wire. Advantageously, stainless steel wire fabric is provided. The metal cushion rings 25 have damping as well as elastic and thermal insulating characteristics. In lieu of the metal cushion rings 25, also other elements can be provided which permit a limited relative movement between the exhaust-gas muffler 14 and the crankcase 13.
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.
Patent Application
20080035098
