Image Number 9 for United States Patent #7255662.
An idle rotation speed Nidl of an engine is set to increase with an increase in actual vehicle speed V and with an increase in measured temperature Tb of a battery (step S160). The drive control of the invention controls the engine and two motors to idle the engine at the preset idle rotation speed Nidl and to ensure output of a required power corresponding to a torque demand Tr* to a drive shaft within a range between an input limit Win and an output limit Wout of the battery (steps S190 to S230). Such control enables the engine to have a high following capability and promptly change its output power level in response to a change in power demand P*, which is accompanied by an abrupt variation in torque demand Tr*. The technique of the invention thus desirably reduces the required level of charging or discharging of the battery, which is triggered by a response delay of the engine.