Vehicle drive system

A vehicle drive system for driving a vehicle using an internal combustion engine, comprising:

• an internal combustion engine configured to generate a drive force for driving a primary drive wheel of the vehicle;
• a stepped variable transmission connected to an output shaft of the internal combustion engine and configured to change a rotational speed of the output shaft of the internal combustion engine and output the changed rotational speed;
• an assist motor provided to apply a drive force to a secondary drive wheel of the vehicle, or apply a drive force to the primary drive wheel without going through the stepped variable transmission;
• and
• a motor control device configured to control a drive force to be output by the assist motor,
• wherein
• the stepped variable transmission is a seamless-shift transmission configured such that a drive force to be transmitted therethrough is interrupted during shifting down, but not substantially interrupted during shifting up, and
• the motor control device is operable, during the shifting down by the stepped variable transmission, to cause the assist motor to generate a drive force to compensate for the interruption of the drive force.