Patent GB-634781-A (GB)
Title: Improvements in or relating to overload release clutch mechanisms
IPC: F16D43/202
Filed: 1946-09-27
Abstract: 634,781. Overload release ratchet clutches. NAAMLOOZE VENNOOTSCHAP PHILIPS' GLOEILAMPENFABRIEKEN. Sept. 27, 1946, No. 28908. Convention date, March 29, 1943. [Class 80 (ii)] In an overload release clutch of the kind having an intermediate member connected to the driven member by a spring and to the driving member by clutch means governed by relative displacement of the intermediate and driven members, and in which when the clutch means is disengaged the intermediate member is checked against movement effective to diminish the relative displacement, the spring is so arranged that its equivalent lever arm decreases with increase in the relative displacement so that the torque exerted by the spring remains substantially constant. As shown, a stationary member 5, Fig. 1a, surrounds a driven member 3, about the shaft 9 of which are rotatably mounted a driving member 24 and an auxiliary member 4. Pins 1 on the member 4 project into peripheral cut-outs in the member 3 and are normally held to one side of these cut-outs by springs 2, Fig. 1b, which transmit the drive to the members 3 via pins 19. Spring- loaded interacting pawls 12, 15, Fig. 1c pivoted on the member 4, are alternately engageable with ratchet toothed wheels 11, 13 on the members 24, 5 respectively. Pins 16, 22 on the driven member 3 project through circumferential slots 25, 26 in the member 4, the pawls being normally held by the action of the springs 2 in the position shown in which the pin 16 holds the pawl 15 inoperative and maintains the pawl 12 engaged to transmit drive to the member 4. Upon overload, the springs 2 yield and the pin 16 releases the pawl 15, which is biased towards engagement by the differential pressure of the pawl springs, but which, owing to the tooth pressure between the pawl 12 and wheel 11, does not engage until the pin 22 constrains the pawl 12 to disengage and break the drive. When overload passes, the springs 2 contract and restore the clutch to its original condition. The wheel 11 and pawl 12 may have hooked teeth to necessitate reverse relative rotation before they disengage. The springs 2 are so arranged relative to the drive axis that the torque exerted by them remains substantially constant as they stretch. They may be replaced by a spring 49, Fig. 2, whose point of attachment to a rod 45 pivoted on the driven member 42 is movable in an axial plane at right angles to the axial plane through its point of attachment to the auxiliary member 40 upon operation of a lever 44 actuating a sliding sleeve 43 linked to the rod 45. The torque exerted by the spring 49 may thus be varied whilst its average tension remains unaltered. Two clutches driving in opposite directions may be arranged in series giving a bidirectional drive with overload release in both senses, or the wheel 11 and pawl 12 may be formed with straight-sided teeth giving a bidirectional drive with overload release in one sense only. The invention is applicable to the adjustment of a rotary shaft into predetermined angular positions, the shaft being driven through a clutch according to the invention and carrying ratchet discs which co-act with stationary pawls to lock the shaft in the various positions. The Specification as open to inspection under Sect. 91 describes an arrangement in which the pawls 12 and 15 are replaced by a single double-acting pawl actuated in both directions by a single pin and a throw-over spring, the disposition of the parts being such that the pawl can complete its engagement with the wheel 13 even if slight backward movement of the pin in its slot under the influence of the spring 2 occurs during the appropriate pawl movement. The Specification as open also states that the springs 2 may be replaced by a multi-turn spiral spring of adjustable tension, or that more than two springs may be used, and also that the pawl and ratchet devices may be replaced by friction or electromagnetic couplings or claw clutches. This subject-matter does not appear in the Specification as accepted.