Power transmission apparatus

A power transmission apparatus comprising:

• a main shaft configured to rotate on a first rotation axis;
• a counter shaft configured to rotate on a second rotation axis parallel to the first rotation axis;
• a shift drum configured to rotate to drive a shifter of at least one of the main shaft or the counter shaft and to make a dowel be extracted or inserted so that a shift gear is relatively non-rotatably joined to the at least one of the main shaft or the counter shaft, thereby selectively establishing a speed stage between the main shaft and the counter shaft;
• a clutch including driving-side first friction plates and driven-side second friction plates, the first friction plates rotatably supported around the main shaft and configured to rotate by power that is transmitted from a crankshaft, the second friction plates disposed alternately with the first friction plates and relatively non-rotatably supported by the main shaft;
• a clutch lifter configured to be displaced between a connection position and a disconnection position, the clutch lifter at the connection position configured to make the first friction plates and the second friction plates be mutually pressed so as to transmit power at the maximum, the clutch lifter at the disconnection position configured to make the first friction plates and the second friction plates be mutually separated so as to disconnect transmission of the power;
• a shift spindle configured to rotate in accordance with a driving force supplied from an electric motor and thereby apply a driving force to the clutch lifter;
• and
• a transmission body configured to transmit a driving force to the shift drum in accordance with rotation of the shift spindle while the clutch lifter moves from the connection position to the disconnection position.