Driving force transfer apparatus for four-wheel drive vehicle with fail safe structure

摘要

In a driving force transfer apparatus for a part-time four-wheel drive vehicle with a fail safe structure, a high-speed gear range shift position and a low-speed gear range shift position in a high-speed and low-speed gear range position switching mechanism in a sub transmission are determined without special position sensors. In a case where the special position sensors are installed in the transfer apparatus, a shift position sensor diagnosis operation is effected so that a failure in either of a high-speed gear range position or low-speed gear range position sensor can easily be detected. If the failure in either of the position sensor occurs, a hydraulic (oil) pressure supply for providing a clutch pressure for a frictional clutch is made effective. Furthermore, a failure of either of revolution speed sensor detecting a first output axle revolution speed or detecting a second output axle revolution speed can also be detected. The first output axle is connected to mainly driven road wheels. The second output axle is connected to secondarily driven road wheels.