Muffler and engine-driven work machine

1. An engine-driven work machine comprising:

an engine including

a piston which is configured to reciprocally move inside a cylinder to which an exhaust port is formed, and

an engine block including the cylinder and a crank case; and

a front end tool configured to be driven by the engine,

wherein an expansion chamber is connected to the exhaust port via a connection duct,

wherein the connection duct includes a first end at a side of the cylinder to which the exhaust port is formed and a second end, and the connection duct extends from the first end in an axial direction of the exhaust port, is bent in a direction away from an axis of the exhaust port, extends in an axial direction of the cylinder and is connected to the expansion chamber at the second end, and

wherein the expansion chamber is disposed between the crank case and an inner side of the connection duct which is bent in the direction away from the axis of the exhaust port.

2. The engine-driven work machine according to claim 1 , wherein the connection duct has a U-shape in which the second end connected to the expansion chamber faces the crank case of the engine.

3. The engine-driven work machine according to claim 1 , wherein the connection duct includes a branching portion, and

wherein a U-shaped branch pipe having a closed end is connected to the branching portion.

4. The engine-driven work machine according to claim 1 , wherein a first flange and a second flange are fixed to both ends of the connection duct, respectively, and the first flange is joined to the exhaust port and the second flange is joined to the expansion chamber.

5. The engine-driven work machine according to claim 2 , wherein the expansion chamber has a wall having a shape following an inner circumference side shape of the connection duct, and

wherein a radius of curvature R 1 of an upper side of the connection duct is larger than a radius of curvature R 2 of a lower side of the connection duct.

6. The engine-driven work machine according to claim 4 , wherein a plate member extending outward is formed at an outer edge of the expansion chamber, and

wherein the expansion chamber is fixed to the engine by inserting the plate member between the cylinder and the first flange.

7. The engine-driven work machine according to claim 6 ,

wherein the plate member includes a second screw part which is for fixing the plate member to the second flange and a third screw hole which is for fixing the plate member to the engine and which is formed in the vicinity of the second screw part.

8. The engine-driven work machine according to claim 1 , wherein the connection duct is configured by two members separated at a cross-section surface parallel to a longitudinal direction thereof, each member being formed by joining a metal press member.

9. The engine-driven work machine according to claim 1 , wherein an exhaust hole is formed at a lateral side of the expansion chamber and an exhaust outlet that discharges the exhaust gas to the front-lower side of the engine is formed to the exhaust hole.

10. A muffler comprising:

an expansion chamber fixed to a cylinder and a crank case of an engine; and

a connection duct connecting an exhaust port of the engine to an opening of the expansion chamber and has a bent shape when viewed from the lateral side,

wherein the expansion chamber is disposed between an inner side of the bent connection duct and the crank case and has a shape following a shape of the crank case and the connection duct adjacent to the expansion chamber.

11. The muffler according to claim 10 ,

wherein a plate member having two openings is formed at an outer edge of the expansion chamber, and

wherein the openings are formed at upper and lower parts of the plate member, respectively, and a first end of the connection duct is connected to the exhaust port via the opening at the upper part of the plate member and a second end of the connection duct is connected to the opening at the lower part of the plate member as an inlet of the expansion chamber.

12. The muffler according to claim 10 , wherein the connection duct includes a branching portion, and

wherein a branch pipe having a closed end is connected to the branching portion.

13. The muffler according to claim 10 , wherein flanges are provided to openings at both ends of the connection duct, and

wherein the flange at the first end of the connection duct is fixed by inserting the plate member between the flange and the engine.

14. The muffler according to claim 10 , wherein the connection duct is formed by caulking, welding or brazing two members which are divided.

15. The muffler according to claim 10 , wherein the connection duct is formed by welding or brazing a passage plate member to an outer wall of the expansion chamber.

16. The muffler according to claim 12 , wherein the branch pipe has a U-shape, and

wherein the branch pipe and the connection duct are arranged such that an axis of the connection duct and an axis of the branch pipe are substantially perpendicular to each other.

17. The engine-driven work machine according to claim 1 , wherein the connection duct is bent in the direction away from the axis of the exhaust port in a plane including the axis of the exhaust port and a cylinder axis.

18. The engine-driven work machine according to claim 1 , wherein the expansion chamber is fixed to the cylinder at the first end side of the connection duct, and the expansion chamber is fixed to the crank case at the second end side of the connection duct.

19. The engine-driven work machine according to claim 1 , wherein a portion of the expansion chamber, which is adjacent to a portion thereof connected to the connection duct, follows a shape of the crank case and protrudes toward a cylinder axis side.