Straddle vehicle

1. A straddle vehicle comprising:

a shift drum which changes a gear position of a transmission including a plurality of gear trains and is formed with an engaged part in an end surface thereof;

a transmission case which accommodates the shift drum therein, and is formed with a circular insertion hole coaxial with the shift drum, the end surface of the shift drum being accommodated in the insertion hole;

a gear position sensor having a circular outer peripheral surface and including an engagement part engageable with the engaged part of the shift drum in a state in which the gear position sensor is inserted into the insertion hole, the gear position sensor being configured to detect a rotation angle of the shift drum; and

a seal ring fitted to the outer peripheral surface of the gear position sensor,

wherein the insertion hole includes a first inner peripheral surface with which the seal ring is in tight contact in a state in which the engagement part is engaged with the engaged part of the shift drum, and a second inner peripheral surface located closer to an entrance of the insertion hole than the first inner peripheral surface and having a diameter larger than a diameter of the first inner peripheral surface,

wherein in a state in which the seal ring has passed through the second inner peripheral surface and has reached an entrance of the first inner peripheral surface, at least a portion of the engagement part of the gear position sensor is fitted to the engaged part of the shift drum,

wherein the insertion hole further includes a third inner peripheral surface formed between the first inner peripheral surface and the second inner peripheral surface and facing the entrance of the insertion hole, and

wherein the third inner peripheral surface is provided at a location where at least a portion of the engagement part is fitted to an entrance portion of the engaged part in a state in which the seal ring is in contact with the third inner peripheral surface.

2. The straddle vehicle according to claim 1 ,

wherein the third inner peripheral surface is an inclined surface with a diameter reduced in a direction from the second inner peripheral surface toward the first inner peripheral surface.

3. The straddle vehicle according to claim 1 ,

wherein the second inner peripheral surface has an inner diameter which is equal to or larger than an outer diameter of the seal ring.

4. The straddle vehicle according to claim 1 ,

wherein a clearance in a circumferential direction around an axis line which is formed between the engagement part of the gear position sensor and the engaged part of the shift drum is increased as the gear position sensor approaches the entrance of the insertion hole.

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

a vehicle body frame supporting the transmission case; and

a side stand provided so that the vehicle body frame is tilted to a first side in a vehicle width direction during use of the side stand,

wherein the shift drum extends in the vehicle width direction, and

wherein the insertion hole opens outward of the transmission case, on the first side in the vehicle with direction.

6. A straddle vehicle comprising:

a shift drum which changes a gear position of a transmission including a plurality of gear trains and is formed with an engaged part in an end surface thereof;

a transmission case which accommodates the shift drum therein, and is formed with a circular insertion hole coaxial with the shift drum, the end surface of the shift drum being accommodated in the insertion hole;

a gear position sensor having a circular outer peripheral surface and including an engagement part engageable with the engaged part of the shift drum in a state in which the gear position sensor is inserted into the insertion hole, the gear position sensor being configured to detect a rotation angle of the shift drum; and

a seal ring fitted to the outer peripheral surface of the gear position sensor,

wherein the insertion hole includes a first inner peripheral surface with which the seal ring is in tight contact in a state in which the engagement part is engaged with the engaged part of the shift drum, and a second inner peripheral surface located closer to an entrance of the insertion hole than the first inner peripheral surface and having a diameter larger than a diameter of the first inner peripheral surface,

wherein in a state in which the seal ring has passed through the second inner peripheral surface and has reached an entrance of the first inner peripheral surface, at least a portion of the engagement part of the gear position sensor is fitted to the engaged part of the shift drum, and

wherein the second inner peripheral surface has a constant diameter.

7. A straddle vehicle comprising:

a shift drum which changes a gear position of a transmission including a plurality of gear trains and is formed with an engaged part in an end surface thereof;

a transmission case which accommodates the shift drum therein, and is formed with a circular insertion hole coaxial with the shift drum, the end surface of the shift drum being accommodated in the insertion hole;

a gear position sensor having a circular outer peripheral surface and including an engagement part engageable with the engaged part of the shift drum in a state in which the gear position sensor is inserted into the insertion hole, the gear position sensor being configured to detect a rotation angle of the shift drum; and

a seal ring fitted to the outer peripheral surface of the gear position sensor,

wherein the insertion hole includes a first inner peripheral surface with which the seal ring is in tight contact in a state in which the engagement part is engaged with the engaged part of the shift drum, and a second inner peripheral surface located closer to an entrance of the insertion hole than the first inner peripheral surface and having a diameter larger than a diameter of the first inner peripheral surface,

wherein in a state in which the seal ring has passed through the second inner peripheral surface and has reached an entrance of the first inner peripheral surface, at least a portion of the engagement part of the gear position sensor is fitted to the engaged part of the shift drum, and

wherein a first distance from an end edge of the seal ring on an inner side in a vehicle width direction, to an end edge of the engagement part on the inner side in the vehicle width direction, is longer than a second distance from the end surface of the shift drum on an outer side in the vehicle width direction to an end edge of the first inner peripheral surface on the outer side in the vehicle width direction.

8. The straddle vehicle according to claim 7 , wherein the first distance is shorter than a third distance from the end surface of the shift drum on the outer side in the vehicle width direction to an end edge of the second inner peripheral surface on the inner side in the vehicle width direction.