AN IMPROVED TORQUE LIMITER

1,246,180. Torque-limiting devices. H. M. HOBSON Ltd. 28 May, 1970 [24 March, 1969], No. 15330/69. Heading F2E. A torque limiter includes a cam 10 constituting the input member, a plurality of rollers 11, a roller cage 12 constituting the output member, a torsion spring 14 connected between the input member 10 and the output member 12, and a fixed outer race 13. The torsion spring 14 may be a torsion bar, as shown, or a coil spring. Under normal conditions, when driving torque is applied, e.g. by an input shaft, to the input member, the output member is driven both by co-operation between cam 10, rollers 11 and the cage and by the torsion spring 14. In this phase the rollers are clear of the fixed outer race 13 (Fig. 2, not shown). When the driven mechanism (including an output shaft connected to the output member) develops excessive torque, the torsion spring 14 twists, thereby causing relative rotation of cam 10 and cage 12 to the positions shown in Fig. 3 in which the balls 10 are forced outwardly to lock in the wedge angles between cam 10 and fixed outer race 13, the input torque being thereby stalled. The device operates for both directions of rotation of the input member. The device is re-setting in the sense that if, after the input has been stalled, the torque of the output member falls to a predetermined level, it will revert to a straight-through drive. The device may be an independent unit, or incorporated in a driving unit or a driven unit. The torsion spring may be pre-loaded, so that all values of torque lower than the pre-load will be transmitted without twisting the spring.