Power transmission unit

A power transmission unit with an engine;

• a plurality of speed change gear pairs, each of which has a different gear ratio, and to which a power outputted from the engine is transmitted;
• and an output member for outputting the power transmitted from the speed change gear pair, the power transmission unit comprising:
• a differential mechanism which performs a differential action, the differential mechanism includes a planetary gear mechanism comprising a sun gear as an external gear;
• a ring gear as an internal gear, which is arranged concentrically with the sun gear;
• and a carrier, which holds a pinion gear arranged between the sun gear and the ring gear in a rotatable and revolvable manner, and the carrier is connected with the engine;
• an electric motor, which is connected with the sun gear;
• a first drive shaft connected with the carrier and a second drive shaft connected with the ring gear, the first and second drive shafts being arranged concentrically with each other and coaxially with a rotational center of the planetary gear mechanism, the first drive shaft being longer than the second drive shaft and protruding from the second drive shaft,
• wherein the plurality of speed change gear pairs include a first gear pair and a third gear pair which are adapted to be connected with the carrier and the output member, and a second gear pair and a fourth gear pair which are adapted to be connected with the ring gear and the output member, a drive gear of the first gear pair and a drive gear of the third gear pair are provided on the first drive shaft, a drive gear of the second gear pair and a drive gear of the fourth gear pair are provided on the second drive shaft, and driven gears of the first, second, third, and fourth gear pairs are arranged on the output member and directly mesh with the drive gears of the first, second, third, and fourth gear pairs, respectively, and
• the power transmission unit further comprising:
• a starting means, which connects the second gear pair with the ring gear and the output member when the power is outputted to the output member to start a vehicle while allowing the differential mechanism to perform differential action and allowing the electric motor to establish a reaction force so that the power of the engine is amplified and outputted to the ring gear, and then prevents the differential mechanism from performing differential action, under a condition that the engine is driven and is connected to the carrier, by connecting the carrier and the sun gear with each other to lock the planetary gear mechanism.