Abstract: A drivetrain for transmitting driving force from an engine to a drive shaft of a vehicle, includes a planetary gear mechanism including first to five rotational elements arrayed on an alignment chart, the first rotational element being connected to an output shaft of the engine and the second rotational element being connected to the drive shaft, a first motor-generator connected to the third rotational element, and a second motor-generator connected to the fourth rotational element.

Abstract: A four-element, two-freedom-degree planetary gear mechanism is constructed by arraying four input/output elements of a sun gear S1, a ring gear R, a carrier C and a sun gear S2 in a alignment chart. One of the two elements R and C arrayed on the inner side is assigned to the input In from an engine whereas the other is assigned to the output Out to the drive shaft, and the two outer elements S1 and S2 are connected to motor-generators MGi and MGo, respectively. As a result, the torque for the motor-generators to bear can be made lower than the engine output, and the energy to pass through the motor-generators is made lower to improve the transmission efficiency of the drivetrain.

Abstract: The drivetrain includes a differential mechanism having four or more input/output elements and having two degrees of freedom. The input In from an engine, the output Out to a drive shaft, and two motor-generators MGi and MGo are assigned to the elements, and one of the elements other than the element to which the output assigned is provided with brakes B. By braking the element other than the output with the brakes, a large reduction ratio can be achieved, so startability can be improved without enlarging the capacities of the motor-generators.