Change-speed transmission for wheeled vehicles

A power transmission unit having a change-speed gearing including a front output shaft and a countershaft arranged in parallel with an input shaft, and a plurality of change-speed gears on said front output shaft and in meshing engagement with respective counter gears on said countershaft to provide a selected speed-ratio drive power train, said countershaft being drivingly connected to said input shaft to receive an input torque thereon, comprising:

• a rear output shaft coaxially arranged with said front output shaft, said rear output shaft having a front end portion provided at its outer periphery with a spline and rotatably coupled with the rear end of said front output shaft;
• a clutch hub fixedly mounted on said front output shaft and located at one side thereof adjacent to the front end portion of said rear output shaft, said clutch hub being provided at its outer periphery with a spline corresponding with the outer spline of said rear output shaft;
• a first hub sleeve axially slidably coupled over said clutch hub and being provided at its inner periphery with a spline in engagement with the outer spline of said clutch hub, said first hub sleeve capable of being brought into engagement with the outer spline of said rear output shaft during the shifting operation thereof toward said rear output shaft, to thereby provide a torque transmission between said front and rear output shafts;
• a speed-reduction driven gear rotatably mounted on said front output shaft and located adjacent to the other side of said clutch hub, said driven gear being provided with a hub portion confronting with said clutch hub and being in meshing engagement with an additional counter gear on said countershaft to thereby provide a high power torque transmission from said countershaft to both said front and rear output shafts at a lower speed than that of the selected speed-ratio drive power train;
• and
• a second hub sleeve axially slidably coupled over the hub portion of said driven gear by means of a spline connection, said second hub sleeve being provided at its inner periphery with a spline corresponding with the inner spline of said first hub sleeve and capable of being brought into engagement with the outer spline of said clutch hub during the shifting operation thereof toward said clutch hub to effect the high power torque transmission when said first hub sleeve is engaged with the outer spline of said rear output shaft.