Drive force control system for hybrid vehicles

A drive force control system for a hybrid vehicle, comprising:

• an engine;
• a first rotary machine;
• a transmission mechanism in which a first rotary element connected to the engine, a second rotary element connected to the first rotary machine, and a third rotary element connected to an output member are connected to one another to perform a differential action, in which a torque delivered from the engine is transmitted therethrough to the output member by establishing a reaction torque by the first rotary machine, and in which an operating mode can be selected from a first mode in which the output torque of the engine is delivered to the output member side at a first predetermined ratio and a second mode in which the output torque of the engine is delivered to the output member side at a second predetermined ratio that is smaller than the first predetermined ratio;
• and
• a second rotary machine that is connected to the output member to transmit a torque to the output member,
• wherein the hybrid vehicle is propelled in a reverse direction by a reverse torque generated by the second rotary machine,
• wherein a torque delivered from the engine to the output member through the transmission mechanism during operation of the engine is applied in a direction opposing the reverse torque, and
• wherein the drive force control system comprises a controller to control the transmission mechanism, that is configured to prevent selection of the first mode when the engine is in load operation where the engine is driven at a speed higher than an idling speed during propulsion of the hybrid vehicle in the reverse direction.