Exhaust device for combustion engine

1. An exhaust device, for a multi-cylinder engine, comprising: a plurality of exhaust pipes disposed such that downstream end portions thereof are aligned in a lateral direction perpendicular to an axial direction thereof; and a collecting pipe connected to the downstream end portions of the exhaust pipes, wherein:

the downstream end portions of the exhaust pipes have insertion sections that are inserted into an upstream end portion of the collecting pipe,

the upstream end portion of the collecting pipe has a cover section that covers the entirety of circumferences of the insertion sections;

outer circumferential surfaces of the insertion sections of the exhaust pipes and an inner circumferential surface of the cover section of the collecting pipe are joined over the entirety of circumferences thereof at a collecting pipe joining region,

the collecting pipe joining region has a displacement portion having its position shifted in the axial direction toward the lateral direction relative to the remaining portion thereof, and

the displacement portion is formed as a recess that is recessed toward the downstream side in the axial direction.

2. The exhaust device as claimed in claim 1 , wherein:

the collecting pipe has paired divisional parts that are separable into two in a direction perpendicular to the lateral direction, and the collecting pipe is formed by the paired divisional parts being joined to each other; and

the displacement portion is formed in each of the paired divisional parts.

3. The exhaust device as claimed in claim 1 , wherein:

the two adjacent downstream end portions of the plurality of exhaust pipes are joined at an exhaust pipe joining region;

the exhaust pipe joining region is joined to the collecting pipe joining region; and

a bottom portion of the recess is positioned between the two downstream end portions of the exhaust pipes.

4. The exhaust device as claimed in claim 1 , wherein an axial dimension of the displacement portion is set so as to be greater than or equal to a radius of each exhaust pipe.

5. The exhaust device as claimed in claim 1 , wherein:

the two adjacent downstream end portions of the plurality of exhaust pipes are joined at an exhaust pipe joining region; and

a portion of the displacement portion which extends across the exhaust pipe joining region extends along a plane perpendicular to the axial direction.

6. The exhaust device as claimed in claim 2 , wherein:

each of the paired divisional parts has the displacement portion; and

the respective displacement portions are connected at a bottom portion that extends over the paired divisional parts so as to form a U-shaped recess.

7. The exhaust device as claimed in claim 2 , wherein the collecting pipe has a cross-sectional area in which a downstream side portion of the collecting pipe is enlarged as compared to an upstream end portion thereof where the exhaust pipes are inserted.

8. The exhaust device as claimed in claim 1 , wherein a tilt angle θ of the displacement portion relative to the axial direction is set to be less than 45°.

9. The exhaust device as claimed in claim 1 , wherein:

the exhaust pipe is formed as a circular pipe;

the downstream end portion of the exhaust pipe has an insertion section that are inserted into the upstream end portion of the collecting pipe; and

an axial length L of the insertion section is greater than an outer diameter d1 of the exhaust pipe.

10. The exhaust device as claimed in claim 1 , wherein the displacement portions are provided at plural locations in the lateral direction.

11. A saddle-riding vehicle comprising the exhaust device as claimed in claim 1 , wherein

the engine is disposed rearwardly of a front wheel;

the exhaust pipes are connected to an exhaust port defined at a front surface of the engine;

the two downstream end portions of the exhaust pipes are adjacent to each other;

the collecting pipe is disposed below the engine: and

the collecting pipe has an upper portion provided with a mounting seat, to which a sensor for detecting a content of oxygen in exhaust gas is mounted, the mounting seat being disposed downstream of the two downstream end portions of the exhaust pipes.

12. The exhaust device as claimed in claim 1 , wherein the exhaust pipes are welded to the collecting pipe along the collecting pipe joining region including the displacement portion.

13. The exhaust device as claimed in claim 12 , wherein welding lines are formed along the collecting pipe joining region, and

wherein the welding lines are not aligned in the lateral direction.

14. The exhaust device as claimed in claim 1 , wherein the displacement portion forms a zigzag shape in the axial direction around the collecting pipe joining region.

15. The exhaust device as claimed in claim 1 , wherein a distance d2 of the recess is greater than or equal to half of the outer diameter d1 of the exhaust pipe.

16. An exhaust device, for a multi-cylinder engine, comprising:

a plurality of exhaust pipes disposed such that downstream end portions thereof are aligned in a lateral direction perpendicular to an axial direction thereof; and

a collecting pipe connected to the downstream end portions of the exhaust pipes, the collecting pipe including a mounting seat, to which a sensor for detecting a content of oxygen in exhaust gas is mounted, wherein:

the downstream end portions of the exhaust pipes are joined together and have insertion sections that are inserted into an upstream end portion of the collecting pipe,

the upstream end portion of the collecting pipe has a cover section that covers the entirety of circumferences of the insertion sections,

outer circumferential surfaces of the insertion sections of the exhaust pipes and an inner circumferential surface of the cover section of the collecting pipe are joined over the entirety of circumferences thereof at a collecting pipe joining region, and

the collecting pipe joining region has a displacement portion shifted in the axial direction and formed as a recess that is recessed toward the downstream side in the axial direction.