Patent GB-851423-A (GB)
Title: Ratchet device
IPC: F16D41/16
Filed: 1958-04-28
Abstract: 851,423. Locking movable members. AMERICAN MACHINE & METALS Inc. April 28, 1958 [April 29, 1957], No. 13433/58. Classes 80 (3) and 80 (4). [Also in Group XXV] A pawl and ratchet locking device for retaining a rotatable or linearly-movable member in a desired position against the action of a spring or gravity is released by a small forward movement of the movable member itself. As shown a spring-wound cable drum 4, Fig. 2, is rotatable on an arbor carrying a fixed ratchet wheel 36 engaged by a slotted pawl 48, Fig. 4, slidably and rockably mounted on a pin 44 carried by a bracket 42, Fig. 2, on the drum. A torsion spring 56 which has its ends freely mounted in openings in the pawl and in the bracket 42 on the drum, biases one or other end of the pawl downwardly, according to the direction of offcentre of the pawl on its pin 44. Similarly the spring 56 urges the appropriate end of the pawl slot 50 against the pin 44. Thus the pawl 48 has two stable positions in which the spring 56 holds either the end face 72 thereof (Fig. 4) or the nose 68 thereof (Fig. 9) in engagement with the fixed ratchet wheel 36, so allowing respectively anti-clockwise or clockwise movement of the drum carrying the pin 44. Operation.-In Fig. 3 the pawl nose 68 engages the undercut portion 70 of a fixed ratchet tooth, thus preventing anti-clockwise movement of pin 44, i.e. preventing the cable drum from being rewound by its spring motor 22, Fig. 2. Spring 56, Fig. 3, is trying to pivot the pawl 48 clockwise. If the cable is pulled to unreel, the drum and pin 44 move clockwise, so withdrawing nose 68 and permitting spring 56 to pivot the pawl clockwise to the Fig. 4 position so that the next tooth face 74 is engaged by the pawl end 72, and the pawl is temporarily arrested. The pin 44 continues to move clockwise along the pawl slot 50 until it passes beyond the centre line, Figs. 7, 8 (not shown), whereupon spring 56 pivotally disengages the pawl from the tooth face 74 and moves it to bring the other end of slot 50 against the pin 44. In this position unreeling (clockwise) is freely permitted, the nose 68, Fig. 9, riding over the contour of the ratchet wheel. When sufficient cable has been unreeled and it is released, the drum spring commences to rewind the cable, the pin 44 and pawl 48 being thus moved anti-clockwise. After a small movement the nose 68 engages under the tooth portion 70 and is arrested, and the pin 44 then moves along the slot 50 until it too is arrested, the parts then being again in the Fig. 3 position. In order to allow rewinding a small length of cable is unreeled, sufficient to withdraw the nose 68, as in Fig. 4, but insufficient to bring the end 72 into engagement with the next tooth face 74. The spring 56 then holds the nose 68 clear of the ratchet teeth so that rewinding by the drum spring, i.e. anti-clockwise movement of pin 44 and pawl 48, is freely permitted. The bracket 42 may carry in addition to the pin 44 a camming pin, Figs. 15-17 (not shown), which in the event of spring 56 being or becoming too weak to rock the pawl, engages the upper surface of the pawl to rock it towards the Fig. 9 position. In a construction for controlling the linear movement of a window sash 139, Fig. 20, a spring-loaded slotted pawl 140 is mounted on the sash and co-operates with fixed ratchet teeth 132 on the window frame in a manner similar to that described above. The teeth 132 have camming portions 135 and deeply undercut portions 134 which ensure that a considerable back travel is necessary to effect release of the device. Alternatively the pawl and ratchet teeth may have shapes similar to those shown in Fig. 3, with or without the undercut tooth portions.