Recently, attention has been focused on a Hybrid Vehicle as an environment-friendly motor vehicle. Hybrid vehicles are identified as a motor vehicle that uses a power transmission mechanism driven by a direct-current power supply via an inverter in a power control unit, as well as the conventional engine, as mechanical power sources. Stated differently, a hybrid vehicle obtains a mechanical power source by driving the engine, and additionally, obtains a mechanical power source by converting a direct-current voltage from the direct-current power supply into an alternating-current voltage by means of the inverter, and using the alternating-current voltage obtained by conversion to rotate a motor in the power transmission mechanism.
The power transmission mechanism splits a power output from the engine at a gear mechanism such as a planetary gear, for providing the same to a rotary electric motor for control and an output side for running, controls the rotary electric motor for control such that it mainly serves as a generator to steplessly control output torque of the planetary gear described above, and furthermore, combines torque of another electrical motor for driving (assisting) with the output torque of the planetary gear described above, as needed, to output the same to the output shaft. For example, Japanese Patent Laying-Open No. 2004-66898 describes a vehicle drive mechanism of an FR hybrid vehicle. A power control unit that includes an inverter, a converter, a reactor, and a capacitor is generally accommodated in a PCU casing, and disposed in an engine room.
In recent years, as described in Japanese Patent Laying-Open No. 2004-297846, there has been proposed a vehicle drive mechanism in which a plurality of coolers are disposed radially by setting a motor shaft or a driving shaft as the center, and allowing cooling surfaces of the coolers to be parallel with the drive shaft or the driving shaft, and one or both of the cooling surfaces of each of the coolers is equipped with a semiconductor module for supplying electric power to a rotary electric motor, so that a power transmission mechanism and a power control unit are integrated without causing excessive increase in size.
Generally, in the power transmission mechanism, a radius of a gear mechanism such as a planetary gear measured from the drive shaft, and a radius of a rotary electric motor measured from the drive shaft are not the same, and different from each other. Therefore, a space identified as a dead space is left in an enclosure of the power transmission mechanism, on an outer peripheral side of the planetary gear and an outer peripheral side of the rotary electric motor. In the conventional vehicle drive mechanism described above, effective use of a space in the power transmission mechanism has not yet been achieved sufficiently.
In contrast, the PCU casing disposed in the engine room accommodates various electrical apparatuses such as a capacitor, a boost inverter, and a converter. The PCU casing has a large volume, and hence a ratio at which the PCU casing occupies the engine room is high.
The vehicle drive mechanism, which is described in Japanese Patent Laying-Open No. 2004-297846 described above, does not aim to effectively utilize a dead space in the power transmission mechanism, and merely modifies the positions of the semiconductor modules, which have been accommodated in the PCU casing. Therefore, the vehicle drive mechanism having the semiconductor module and the power transmission mechanism integrated therein has increased in volume, and disadvantageously, a volume of the engine room is even more decreased accordingly.