Transmission mechanism including shift drum and actuator unit which are coaxially disposed

1. A straddle vehicle comprising:

a shift drum that makes a shift change of a transmission including a plurality of gear trains;

a transmission case enclosing the shift drum, the transmission case comprising a side wall portion provided with an insertion hole into which an end portion of the shift drum is inserted;

an actuator unit secured to an outer surface of the side wall portion, the actuator unit comprising a drive shaft that outputs drive power to rotate the shift drum, the drive shaft having the same rotational axis as the shift drum and being connected to the shift drum on the rotational axis; and

a gear position sensor that detects a rotational angle of the shift drum, wherein

the gear position sensor is provided at the outer surface of the side wall portion of the transmission case in a vehicle width direction, and

the actuator unit overlaps the gear position sensor such that the gear position sensor is hidden by the actuator unit as viewed from outside in the vehicle width direction.

2. The straddle vehicle according to claim 1 , wherein the gear position sensor is disposed away from the rotational axis of the shift drum.

3. The straddle vehicle according to claim 2 , further comprising a power transmission mechanism linked to the shift drum, wherein

the gear position sensor comprises a detection shaft to which the rotation of the shift drum is transmitted through the power transmission mechanism, and

the gear position sensor is disposed in such a manner that a detection axis of the detection shaft is parallel to the rotational axis of the shift drum.

4. The straddle vehicle according to claim 3 , wherein

the side wall portion is provided with a passage hole through which passes a power transmission route including the power transmission mechanism and the detection shaft,

the gear position sensor is disposed outside the transmission case, and

the power transmission mechanism is disposed inside the transmission case.

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

a power transmission loop that transmits rotational power from an output shaft of the transmission to a rear wheel of the straddle vehicle; and

an annular member that is disposed at an end of the output shaft and around which the power transmission loop is wound, wherein

the actuator unit is disposed beneath the annular member, and

the actuator unit is inclined to extend downwardly and forwardly.

6. The straddle vehicle according to claim 1 , wherein the actuator unit is disposed further inward than an outer end of the transmission case in the vehicle width direction.

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

a cam member rotatable together with the shift drum, the cam member having an outer circumferential surface provided with a plurality of recesses arranged circumferentially at intervals, the plurality of recesses being in one-to-one correspondence with a plurality of shift positions of the transmission;

a swinging member comprising a projection contacting the outer circumferential surface of the cam member, the projection being fittable into the recesses; and

a spring member biasing the projection of the swinging member toward the outer circumferential surface of the cam member, wherein

a biasing force of the spring member is greater than a rotational resistance force of the actuator unit in a power-off state and smaller than the drive power of the actuator unit.

8. The straddle vehicle according to claim 7 , wherein the cam member, the swinging member, and the spring member are opposed to the actuator unit across the transmission case in a direction of the rotational axis.

9. The straddle vehicle according to claim 1 , wherein the gear position sensor is disposed further inward than an electricity generator cover of the transmission case in the vehicle width direction.