Multistage gear transmission system

A multistage gear transmission system comprising:

• a speed-change gear unit having
• a countershaft configured to receive rotation transmitted from an engine inside a gearbox,
• a plurality of driving gears configured to receive rotation from the countershaft,
• a plurality of driven gears meshing with the driving gears to receive the rotation,
• a driveshaft configured to externally transmit the rotation of the driven gears,
• a transmission member slidably provided in the countershaft and/or the driveshaft to transmit the rotation by meshing with the countershaft and a predetermined one of the driving gears and/or meshing with a predetermined one of the driven gears and the driveshaft,
• a shift fork shaft configured to hold, slidably in an axial direction, the shift fork provided to move the transmission member, and
• a gear shift cam configured to move the shift fork;
• a control unit configured to issue a gearshift execution command when a gearshift manipulation is received, and/or a predetermined condition set in advance is satisfied;
• a gearshift actuator having
• a motor actuated in response to the gearshift execution command from the control unit to rotate the gear shift cam by a predetermined angle, and
• a gearshift actuation transmission mechanism configured to transmit actuation generated from the motor to the gear shift cam,
• wherein the motor is provided with a motor gear installed to rotate in synchronization with a motor output shaft,
• the gearshift actuation transmission mechanism is provided with a gear shift cam-side actuator gear directly engaged with the gear shift cam to transmit rotation,
• the gear shift cam-side actuator gear meshes with the motor gear directly or indirectly by interposing another actuator gear to transmit the rotation from the motor to the gear shift cam;
• a propulsion transmission component installed in an end of the driveshaft outside of the gearbox to rotate in synchronization and transmit rotation to a propulsion wheel;
• and
• a protection member installed outside of the gearbox to externally cover a part of the propulsion transmission component,
• wherein the gearshift actuation transmission mechanism is positioned inward in an axial direction of the driveshaft with respect to the protection member.