Patent ID: 7534191

Claim:
A power output apparatus that outputs power to a drive shaft, comprising: an internal combustion engine; a storage portion; a first electric motor that receives and outputs power, and that exchanges electric power with the storage portion; a power split device that is connected to an output shaft of the internal combustion engine and the drive shaft, and that receives power from the output shaft and outputs the power to the drive shaft or receives power from the drive shaft and outputs the power to the output shaft while exchanging electric power with the storage portion and exchanging power with the internal combustion engine; a shifting portion that transfers power between a rotating shaft of the first electric motor and the drive shaft while changing a speed ratio based on a rotational speed of the rotating shaft of the first electric motor and a rotational speed of the drive shaft; an engine speed detection portion that detects an engine speed that is a rotational speed of the output shaft of the internal combustion engine; a drive shaft rotational speed detection portion that detects the rotational speed of the drive shaft; a rotating shaft rotational speed detection portion that detects the rotational speed of the rotating shaft of the first electric motor; a drive shaft rotational speed estimation portion that estimates the rotational speed of the drive shaft based on the engine speed detected by the engine speed detection portion and a driving state of the power split device; a required drive power setting portion that sets a required drive power required for the drive shaft; and a control portion that controls the internal combustion engine, the power split device, the first electric motor, and the shifting portion to output the required drive power to the drive shaft, wherein the speed ratio in the shifting portion is changed, based on the rotational speed of the drive shaft detected by the drive shaft rotational speed detection portion or the rotational speed of the drive shaft estimated by the drive shaft rotational speed estimation portion, and the rotational speed of the rotating shaft detected by the rotating shaft rotational speed detection portion, when an estimation function of the drive shaft rotational speed; and is performed properly, that is when the drive shaft rotational speed estimation portion can estimate the rotational speed of the drive shaft; and the speed ratio in the shifting portion is maintained, when a malfunction has occurred in the estimation function, that is when the drive shaft rotational speed estimation portion cannot estimate the rotational speed of the drive shaft.