In a power transmission apparatus, a second clutch includes a divider dividing driving clutch plates and driven clutch plates in an axial direction such that a first region adjacent to a clutch pressure plate and a second region adjacent to a centrifugal clutch are defined. The second clutch presses the driving clutch plates and the driven clutch plates in the first region and the second region against each other during operation of the centrifugal clutch, and presses the driving clutch plates and the driven clutch plates in the first region against each other during operation of a back torque transmission cam.

In a power transmission apparatus a second clutch includes a divider dividing driving clutch plates and driven clutch plates in an axial direction such that a first region adjacent to a clutch pressure plate and a second region adjacent to a centrifugal clutch are defined. The second clutch presses the driving clutch plates and the driven clutch plates in the first region and the second region against each other during operation of the centrifugal clutch, and presses the driving clutch plates and the driven clutch plates in the first region against each other during operation of a back torque transmission cam.

In a power transmission apparatus a second clutch includes a divider dividing driving clutch plates and driven clutch plates in an axial direction such that a first region adjacent to a clutch pressure plate and a second region adjacent to a centrifugal clutch are defined. The second clutch presses the driving clutch plates and the driven clutch plates in the first region and the second region against each other during operation of the centrifugal clutch, and presses the driving clutch plates and the driven clutch plates in the first region against each other during operation of a back torque transmission cam.

A power transmission apparatus a centrifugal clutch including a holder and a press. The holder and the press are each circumferentially provided with protrusions fitted and attached to cut-outs of a clutch housing. The holder is an integrated assembly into which a mass that is being held is integrated. The integrated assembly and the press are non-connected separate components and are independently movable toward or away from each other.

A power transmission apparatus a centrifugal clutch including a holder and a press. The holder and the press are each circumferentially provided with protrusions fitted and attached to cut-outs of a clutch housing. The holder is an integrated assembly into which a mass that is being held is integrated. The integrated assembly and the press are non-connected separate components and are independently movable toward or away from each other.

In a power transmission apparatus, a centrifugal clutch includes a holder, a press, a first spherical 14bodv that is partially protruded from a first opening and in contact with a rolling contact surface of the press so as to be rollable thereon, and a second spherical body that is partially protruded from a second opening and in contact with a rolling contact surface of the holder so as to be rollable thereon. A through hole has a tapered shape from the first opening to the second opening. Disconnection of the first spherical body is prevented by an outer peripheral edge of one of the first opening and the second opening that has a smaller diameter.

In a power transmission apparatus, a centrifugal clutch includes a holder, a press, a first spherical 14bodv that is partially protruded from a first opening and in contact with a rolling contact surface of the press so as to be rollable thereon, and a second spherical body that is partially protruded from a second opening and in contact with a rolling contact surface of the holder so as to be rollable thereon. A through hole has a tapered shape from the first opening to the second opening. Disconnection of the first spherical body is prevented by an outer peripheral edge of one of the first opening and the second opening that has a smaller diameter.

During movement of a mass of a centrifugal clutch a radially inner position to a radially outer position and a resulting increase in torque transmitted from an input gear to an output shaft, a power transmission apparatus includes a first torque region where the apparatus restricts operation of a pressing assist cam and a second torque region where the apparatus allows operation of the pressing assist cam.

During movement of a mass of a centrifugal clutch a radially inner position to a radially outer position and a resulting increase in torque transmitted from an input gear to an output shaft, a power transmission apparatus includes a first torque region where the apparatus restricts operation of a pressing assist cam and a second torque region where the apparatus allows operation of the pressing assist cam.

Friction clutch pressure plate device 11 which is provided between spring device 12 and clutch disc unit 4 of friction clutch 1 comprises primary pressure plate 19, secondary pressure plate 22 which is capable of approaching and receding from primary pressure plate 19, and a plurality of weight plates 23 which are slidably arranged between mutually opposed side faces 19a, 22a of primary pressure plate 19 and secondary pressure plate 22. Primary pressure plate 19 comprises first outer circumferential wall 25 having inclined inner wall face 24, secondary pressure plate 22 comprises second outer circumferential wall 28 having perpendicular inner wall face 27, and weight plate 23 comprises tip portion engaging surface that engages with perpendicular inner wall face 27 and a tip portion inclined surface 32 that engages with inclined inner wall face 24.