Patent GB-1322101-A (GB)
Title: Device for transmitting in a bi-directional and non-reversible way a limited torque
IPC: F16H35/10
Filed: 1971-04-19
Abstract: 1322101 Brakes applied to limit torque; automatic brakes; one-way acting band brakes MICROTECNICA SpA 19 April 1971 [7 March 1970] 22268/71 Heading F2E A bi-directional brake connected to a member capable of being driven maintains the member braked relative to each direction of rotation when the member is at rest; means inserted between the brake and a shaft capable of driving suppress the braking action of the brake when the shaft is actually driving; and means also inserted between the brake and the shaft reinstate the braking action when the torque being transmitted exceeds a predetermined value. As shown in Figs. 1 and 2, a driven toothed wheel 1 rotatable on a driving shaft 2 is connected by flexible torsion blades 8 to two sleeves 4, 5, keyed at 6, 7 to the driving shaft 2. Surrounding each half of the driving shaft is a brake in the form of a helical spring 11 or 12, pre-stressed before insertion so as to make contact with the interior of a fixed tubular shell 9 or 10. Each brake is adapted to act upon both the driven wheel 1 and the driving shaft 2 by down-turned inner end 13 or 14 having a connection, fixed or optionally with a certain amount of play, with the wheel 1, and downturned outer end 15 or 16 located in a peripheral slot in sleeve 4 or 5. Both springs are coiled in the same direction. When the driven wheel 1 is at rest, and an attempt is made to rotate it independently of the driving shaft 2, in one direction, the wheel's connection with the springs will cause one spring to be wound up (and thus freed from the fixed shell) and the other to be unwound and thus exert a braking effect. Attempted rotation in the other direction will produce an analogous effect. The unbracketed numerals in Fig. 2 represent the components seen from the direction II of Fig. 1, and vice versa. When shaft 2 drives in the counterclockwise sense of Fig. 2 (top of shaft receding in Fig. 1), the blades 8 on the left of wheel 1 twist until sleeve 4 has rotated through an angle a, Fig. 2, relative to wheel 1, corresponding to a minimum torque, e.g. Ca. Engagement surface 17 on sleeve 4 thereupon engages end 15 of spring 11 and tends to wind it, thus releasing the braking action and entraining wheel 1. Wheel 1 in turn entrains end 14 of spring 12, tending to wind it. At the end where sleeve 5 is situated, engagement surface 20 thereon does not normally contact end 16 of spring 12 because angle b exceeds angle a. But when the torque is excessive, e.g. Cb, due to abnormal resistance to, or stopping of, wheel 1, surface 20 engages end 16 of spring 12 and tends to unwind it, so spring 12 transfers the excess torque to shell 10: shaft 2 may even be stopped. Analogous actions occur when shaft 2 drives in the opposite direction. Fig. 3 shows an embodiment wherein once the drive has been stopped for excess of torque it remains stopped until the driving shaft is rotated in the opposite direction. Torsion blades between sleeve 5 and wheel 1 are omitted, and between sleeve 4 and wheel 1 they are replaced by a ring 24 splined on shaft 2 and urged rightwards by spring 26 so that inclined surfaces 27, 28 engage with corresponding surfaces 27, 28 on hub 3 of wheel 1 during normal rotation. At excessive torque, mutual angular displacement brings steps 2 together, after which reverse rotation is necessary to separate them. For equivalent action in the opposite direction, the surfaces 27, 28 are inclined in the opposite direction.