Conventionally, a known hybrid vehicle includes: an engine, which is a power source; a first motor/generator (MG1) operated as a generator; a second motor/generator (MG2), which is another power source operated as a motor; a power transmitting means having a planetary gear mechanism to which the engine and the first motor/generator are connected; and a means (MG1 locking means) for stopping rotation of the first motor/generator. The power transmitting means also functions as a transmission mechanism for engine output, and is configured so as to allow switching between continuously variable transmission ratio mode, in which transmission ratio is varied continuously, and fixed transmission ratio mode, in which transmission ratio is fixed. To exert control in continuously variable transmission ratio mode, the MG1 locking means allows the first motor/generator to rotate freely, and the rotation number of the first motor/generator is controlled, thereby changing the rotation number of the engine. Conversely, to exert control in fixed transmission ratio mode, rotation of the first motor/generator is stopped by the MG1 locking means. That is, the MG1 locking means has the function of a transmission mode changing means. For example, a hybrid vehicle of this type is described in the Patent Literature 1 given below. In the hybrid vehicle in the Patent Literature 1, when the rotation number of a first motor/generator falls within a predetermined range (when the rotation number falls below a permissible rotation number value), a brake or clutch, serving as an MG1 locking means, is engaged to stop the rotation of the first motor/generator.
The Patent Literature 2 given below describes a driving device that drives the front wheels using engine output, and drives the rear wheels using from electric motor output via an electromagnetic clutch. The electromagnetic clutch has a cam mechanism. Therefore, this driving device is configured such that, in order to prevent noise emission as a result of reversed rotation of both cam members of a cam mechanism when a vehicle changes running direction forward or backward, the electromagnetic clutch is temporarily disconnected when each cam member of the cam mechanism rotates in reverse; after reverse rotation of each cam member has been unlocked, the electromagnetic clutch is connected again.