The present invention relates to a power transmission unit for motor vehicles, and more particularly to an improvement of a power transmission unit of the type which comprises an auxiliary transmission for selectively completing low and high speed drive power trains and a primary transmission for selectively completing a plurality of forward drive power trains and a reverse drive power train after one of the low and high speed drive power trains is completed.
In such a power transmission unit as described above, when the primary transmission is shifted to a desired position after completion of a low speed drive power train, a suitable change-speed ratio can be selected to obtain good drivability during travel of the vehicle on town roads or mountain roads. When the primary transmission is shifted to a desired position after completion of a high speed drive power train, a suitable change-speed ratio can be selected to obtain good drivability during travel of the vehicle on a highway. Thus, the power transmission unit of this type is very useful to ensure good drivability without unnecessary fuel consumption under various travelling conditions. In case the power transmission unit is adapted to a small automotive vehicle of front-wheel drive type, it is needed that the transmission unit is designed to be assembled within a limited space of the vehicle.