In recent years, vehicles driven by an internal combustion engine such as ATVs (All Terrain Vehicles), tractors, or recreation vehicles that are driven vehicles intended mainly for driving on rough ground have been incorporating a power supply unit that uses a generator driven by an internal combustion engine for driving a vehicle as a power supply to generate a commercial AC output of AC 100 V, AC 200 V (50 Hz or 60 Hz), or the like when the vehicle is stopped, in order to allow electric tools or home appliances to be used outdoors. Such a vehicle often uses a power transmission device that is provided between an internal combustion engine and drive wheels, includes a continuously variable transmission (CVT) having a gear position for cutting power transmission, and an automatic clutch mechanism such as a centrifugal clutch, and starts the power transmission when a rotational speed of the engine reaches a predetermined power transmission start rotational speed (a rotational speed at which the automatic clutch mechanism starts the power transmission) or higher.
When the vehicle driven by the internal combustion engine incorporating the power supply unit uses the power transmission device as described above, the gear position of the power transmission device is in a position other than a neutral position or a parking position at the time of generation. If the rotational speed of the engine is increased to a rotational speed at which a generator generates a predetermined output, with power transmission being performed via the power transmission device, the clutch may be connected to start the vehicle.
In order to prevent this, as disclosed in, for example, Japanese Patent Application Laid-Open No. 2001-231106, such a vehicle driven by an internal combustion engine has a gear position sensor that detects a gear position of a power transmission device, and only when the gear position sensor detects that the gear position is in a position for cutting power transmission, speed control means which controls a rotational speed for generating electric power.
However, even with such a construction, if a failure of the gear position sensor, or a failure of the power transmission device causes the gear position sensor to detect by mistake that the power transmission is cut in spite that the power transmission device is in a state of performing the power transmission, the speed control means controls the speed, and thus a possibility of runaway of the vehicle at the time of generation cannot be completely eliminated.
In order to solve this problem, it is preferable to determine whether the power transmission device is in the state of cutting the power transmission, or the state of performing the power transmission (determine on/off of the power transmission) independently of the gear position sensor.