Straddle-type vehicle

1. A straddle vehicle comprising:

an engine which generates driving power for allowing the straddle vehicle to travel and emits an exhaust gas;

an exhaust device including:

a catalyst which contacts the exhaust gas to clean the exhaust gas,

an inner tube in which the catalyst is disposed in an inner passage thereof through which the exhaust gas flows, the inner tube extending to a location that is downstream of the catalyst, in a flow direction of the exhaust gas; and

an outer tube which covers an outer peripheral surface of at least a region of the inner tube in an axial direction of the inner tube, and has a muffling space through which the exhaust gas discharged from an exit of the inner tube is flowed to reduce an exhaust noise radiated from the engine;

at least one exhaust pipe through which the exhaust gas emitted from the engine is led to the catalyst; and

a downstream oxygen sensor which is disposed to detect an oxygen concentration of the exhaust gas flowing through the inner passage of the inner tube after flowing through the catalyst, at a location that is downstream of the catalyst in the inner passage of the inner tube,

wherein the downstream oxygen sensor includes an oxygen detecting section which detects the oxygen concentration of the exhaust gas,

wherein the outer tube is provided with a first insertion hole into which the downstream oxygen sensor is insertable,

wherein the inner tube is provided with a second insertion hole into which the downstream oxygen sensor is insertable,

wherein in a state in which the downstream oxygen sensor is inserted into the first insertion hole, the oxygen detecting section is exposed in the inner passage of the inner tube,

wherein a pipe member having an insertion space into which the downstream oxygen sensor is insertable, is joined to a peripheral edge of the second insertion hole of the inner tube and a peripheral edge of the first insertion hole of the outer tube,

wherein the exhaust device has a structure in which a displacement of each of a first joining portion of the outer tube and a second joining portion of the inner tube, from a reference position, is permissible, the first joining portion and the second joining portion being joined to the pipe member, and

wherein an amount of the permissible displacement from the reference position in the axial direction of the inner tube, of at least one of the first joining portion and the second joining portion, is set to be greater than that in a radial direction of the inner tube, of at least one of the first joining portion and the second joining portion.

2. The straddle vehicle according to claim 1 ,

wherein the outer tube is provided with a recess which is recessed toward the inner tube,

wherein the recess is provided with the first insertion hole, and

wherein in a state in which the downstream oxygen sensor is inserted into the first insertion hole, the downstream oxygen sensor is mounted on the outer tube.

3. The straddle vehicle according to claim 1 ,

wherein the downstream oxygen sensor includes a protruding portion protruding outward from the outer tube, and

wherein when a vehicle body is viewed from a front, the protruding portion extends upward from the outer tube in such a manner that the protruding portion is tilted with respect to a horizontal direction as the protruding portion extends outward in a vehicle width direction.

4. The straddle vehicle according to claim 1 , further comprising:

an electronic control unit which monitors an output signal of the downstream oxygen sensor,

wherein the downstream oxygen sensor includes a wire connected to the electronic control unit, and

wherein the wire is disposed in an outside region of the outer tube.

5. The straddle vehicle according to claim 1 ,

wherein the engine is disposed at a center of a vehicle body extending in a forward and rearward direction, the vehicle body being provided with the engine, the exhaust device, and the exhaust pipe, and

wherein when the vehicle body is viewed from a side, the catalyst is disposed below the engine.

6. The straddle vehicle according to claim 1 ,

wherein the outer tube includes a first member and a second member which are joined to each other.

7. The straddle vehicle according to claim 6 ,

wherein the downstream oxygen sensor is mounted on the outer tube at a location that is apart from a joining portion of the first member and a joining portion of the second member which are joined to each other.

8. The straddle vehicle according to claim 6 ,

wherein the first member includes a non-joining portion disposed at an intermediate portion of the joining portion of the first member in such a manner that the non-joining portion of the first member is apart from the second member, and the second member includes a non-joining portion disposed at an intermediate portion of the joining portion of the second member in such a manner that the non-joining portion of the second member is apart from the first member, and

wherein in a state in which the non-joining portion of the first member and the non-joining portion of the second member are disposed to face each other, and the first member and the second member are joined to each other, a space is formed between the non-joining portion of the first member and the non-joining portion of the second member, and the downstream oxygen sensor is inserted into the space formed between the non-joining portion of the first member and the non-joining portion of the second member.

9. The straddle vehicle according to claim 1 , further comprising:

an upstream oxygen sensor,

wherein the inner tube extends to a location that is upstream of the catalyst in the flow direction of the exhaust gas, and the upstream oxygen sensor is disposed to detect the oxygen concentration of the exhaust gas flowing through the inner passage of the inner tube, at a location that is upstream of the catalyst, and

wherein a passage cross-section of the inner tube from a location of the inner tube at which the downstream oxygen sensor is mounted to a location of the inner tube at which the upstream oxygen sensor is mounted has the same shape.

10. The straddle vehicle according to claim 9 ,

wherein a passage cross-sectional area of the inner tube at a location of the inner tube at which the downstream oxygen sensor is mounted is equal to a passage cross-sectional area of inner tube at a location of the inner tube at which the upstream oxygen sensor is mounted.

11. The straddle vehicle according to claim 9 ,

wherein in the inner passage of the inner tube, a detection region of the downstream oxygen sensor, a region at which the catalyst is disposed, and a detection region of the upstream oxygen sensor are located on a common axis line.

12. A straddle vehicle comprising:

an engine which generates driving power for allowing the straddle vehicle to travel and emits an exhaust gas;

an exhaust device including:

a catalyst which contacts the exhaust gas to clean the exhaust gas,

an inner tube in which the catalyst is disposed in an inner passage thereof through which the exhaust gas flows, the inner tube extending to a location that is upstream of the catalyst in a flow direction of the exhaust gas; and

an outer tube which covers an outer peripheral surface of at least a region of the inner tube in an axial direction of the inner tube, and has a muffling space through which the exhaust gas discharged from an exit of the inner tube is flowed to reduce an exhaust noise radiated from the engine;

at least one exhaust pipe through which the exhaust gas emitted from the engine is led to the catalyst; and

an oxygen sensor which is disposed to detect an oxygen concentration of the exhaust gas flowing through the inner passage of the inner tube, at a location that is upstream of the catalyst in the inner passage of the inner tube,

wherein the oxygen sensor includes an oxygen detecting section which detects the oxygen concentration of the exhaust gas,

wherein the outer tube is provided with a first insertion hole into which the oxygen sensor is insertable,

wherein the inner tube is provided with a second insertion hole into which the oxygen sensor is insertable,

wherein in a state in which the oxygen sensor is inserted into the first insertion hole, the oxygen detecting section is exposed in the inner passage of the inner tube,

wherein a pipe member extending from the inner tube toward the outer tube and having an insertion space into which the oxygen sensor is insertable, is joined to a peripheral edge of the second insertion hole of the inner tube and a peripheral edge of the first insertion hole of the outer tube,

wherein the exhaust device has a structure in which a displacement of each of a first joining portion of the outer tube and a second joining portion of the inner tube, from a reference position, is permissible, the first joining portion and the second joining portion being joined to the pipe member, and

wherein an amount of the permissible displacement from the reference position in the axial direction of the inner tube, of at least one of the first joining portion and the second joining portion, is set to be greater than that in a radial direction of the inner tube, of at least one of the first joining portion and the second joining portion.

13. The straddle vehicle according to claim 12 ,

wherein the engine is disposed at a center of a vehicle body extending in a forward and rearward direction, the vehicle body being provided with the engine, the exhaust device, and the exhaust pipe, and

wherein when the vehicle body is viewed from a side, the catalyst is disposed below the engine.