Hybrid drive system

A hybrid drive system, comprising:

• an internal engine;
• a motor/generator which is rotated and generates electric energy;
• and
• an infinitely variable transmission, which comprises a continuously variable transmission arranged between a primary shaft and a secondary shaft and shifts a torque ratio between these shafts continuously, a planetary gear unit comprising a first rotational element interlocking with a primary side of the continuously variable transmission mounted on the primary shaft, a second rotational element interlocking with a secondary side of the continuously variable transmission mounted on the secondary shaft, and a third rotational element combining rotations of the first rotational element and the second rotational element in a state where torque circulation occurs and the combined rotation is output to driving wheels, the infinitely variable transmission performing a neutral control self-converging in order that the third rotational element is in a neutral position and a shift control shifting continuously from the neutral position to the continuously variable transmission, wherein outputs from at least one of the motor/generator and the internal engine is transmitted to the drive wheels via the infinitely variable transmission.