Fail safe redundant drive shaft apparatus including electrically operative failure detection means

Claim 1

Drive shaft apparatus, comprising: a drive shaft having driving and driven members; primary torque transmitting means coupling the driving and driven members; redundant torque transmitting means coupled to the primary torque transmitting means and rendered operative upon a failure of the primary torque transmitting means for coupling the driving and driven members, the redundant torque transmitting means including a first spline member coupled to the primary torque transmitting means and coupled to one of the driving and driven shafts, a second spline member coupled to the primary torque transmitting means and coupled to the other of the driving and driven shafts, the first and second spline members being in mating relation, with the respective splines thereof being disengaged so that the redundant torque transmitting means is inoperative when the primary torque transmitting means is operative, and one of the first and second spline members being displaced upon a failure of the primary torque transmitting means, whereupon said means is rendered inoperative so that the respective splines of the first and second spline members are engaged and the redundant torque transmitting means is rendered operative; the one spline member having a first main torque transmitting section and a second relatively thin section secured to the first section, and an insulating member separating the first and second sections so that an open electrical circuit through the one and the other of the first and second spline members and the primary torque transmitting means is provided when the redundant torque transmitting means is inoperative, with said circuit being closed through the engagement of the respective splines of the first and second spline members when the redundant torque transmitting means is operative; a transformer circuit arranged with the redundant torque transmitting means and including a stationary winding, means for exciting the stationary winding and a winding inductively coupled to the stationary winding and rotating with the drive shaft; the operative redundant torques transmitting means affecting the transformer circuit for short circuiting the rotating winding; and means connected to the transformer circuit for sensing the short circuit which is indicative of a failure of the primary torque transmitting means.