Patent GB-929761-A (GB)
Title: Improvements in or relating to torque controlled clutch mechanisms for power transmissions
Inventor: FORSTER DAVID JOHN
IPC: F16D48/06
Filed: 1961-02-01
Abstract: 929,761. Clutch control. S. SMITH & SONS (ENGLAND) Ltd. Feb. 1, 1962 [Feb. 1, 1961], No. 3901/61. Class 80 (2). A torque-controlled clutch mechanism comprises torque responsive means controlling the operation of two clutches which are arranged in series and is such that the first clutch is disengaged at a predetermined torque, and is reengaged, or placed in condition for manually controlled re-engagement, upon subsequent reduction in torque below the predetermined value; and should the first clutch fail to disengage, the second clutch is disengaged at a higher torque, and remains disengaged until re-engaged manually. As shown the first clutch is an electromagnetically engaged friction clutch having a coil 13 in a clutch part 12 fast with an input gear-wheel 10, and a driven armature 15 fixed to the inner periphery of a corrugated annular spring 16 which is clamped at its outer periphery to a carrier 18 and is loaded so as to disengage the clutch. The carrier 18 is rotatably mounted on an output shaft 20 and carries two pins 25 mounting ball bearings 27 constituting follower rollers engageable with cam tracks 30 on a cam member 31. The cam member 31 is shiftable axially against the pressure of a spring 41, the loading of which is adjustable by a nut 44 screwing on to the output shaft, and the cam member 31 forms the input member of the second clutch, an extension 54 of the cam having axial slots 53 receiving ball bearings 52 mounted on radial pins 50 fixed to the output shaft. In operation, under safe torque conditions, the ball bearings 27 are maintained in central recesses 32 in the cam member 31, so that the clutch 54, 50 is engaged, and with the coil 13 energized the clutch 12, 15 is also engaged, and drive is transmitted from the gear 10 to the output shaft 20. On the occurrence of overload, the bearings 27 ride partly out of the recesses 32, thus camming the cam member axially to the right against the loading of the spring 41, and causing an actuating disc 36 carried by the cam member to open a switch 5, 6 to break the circuit to coil 13, thus disengaging the clutch 12, 15. When the torque decreases the switch closes and the clutch re-engages. If desired, a relay operated switch 60 is provided in series with the switch 5, 6, and a relay 59 is deenergized when the switch 5, 6 opens so that the relay switch 60 opens to prevent re-engagement of the clutch until the relay is re-energized by a manually operated switch 61. Should the electromagnetic clutch 12, 15 fail to disengage, upon the torque increasing still further the bearings 27 ride completely out of the recesses 32, allowing the bearings 27 to enter deep recesses, whereupon the spring 41 shifts the cam member 31 to the left, past the initial position shown, to disengage the clutch 54, 50 to interrupt the drive. In order to re-establish drive it is now necessary to reset the mechanism by rotating the output shaft until the bearings 52 are aligned with the slots 53, then to move the cam member to the right against the force of the spring 41, and then align the bearings 27 with the central recesses 32, after which the cam member can be released and drive can be re-established.