A drivetrain in a vehicle includes a number of elements, and some of them are comprised of clutches. One example thereof is a free-running differential. A free-running differential is a kind of differential that allows differential motion between right and left axles, and is comprised of a clutch that controls transmission and interruption of torque. When the clutch gets disconnected, one set of axles is capable of freely rotating and then the torque is transmitted only to another set of axles so that the vehicle runs in the 2WD (two-wheel-drive) mode. When the clutch gets connected, as the free-running differential transmits the torque also to the axles at issue, the vehicle runs in the 4WD (four-wheel-drive) mode. Specifically, the free-running differential is one of options for realizing a part-time 4WD vehicle.
Whether the clutch is connected or disconnected is often determined depending on whether the power is input to an actuator for the clutch. Connection of the clutch may sometimes fail even though the actuator is powered on, however. Because even in such instances the vehicle may keep running without causing considerable problems, this method of determination remains somewhat uncertain. There had been a proposal of an art for using a contactless sensor for example to detect positions of a clutch.
Japanese Patent Application Laid-open No. 2006-46594 discloses a related art.