US Patent 7552003 Control apparatus and control method for hybrid vehicle

A control method for a hybrid vehicle which includes an engine, a first motor/generator, a second motor/generator, and a manual changing device that changes a driven state of an output member of the engine that depends on a driving state of the engine and a driving state of the second motor/generator, includes the steps of detecting required driving force of the vehicle; detecting required output torque of the second motor/generator based on the required driving force when a change in a rotational speed of the engine is detected; comparing the detected required torque to the maximum permissible torque of the second motor/generator, and increasing a gear ratio when it is determined that the required output torque is greater than the maximum permissible torque.