GB746148A - Improvements in or relating to hoists - Google Patents

Abstract

746,148. Disc brakes. TRIGGS, W. W. (Yale & Towne Manufacturing Co.). July 5, 1954, No. 19631/54. Class 103 (1). [Also in Groups XXIV and XXX] In a hoist of the type in which a combined clutch and brake mechanism, i.e. a Weston brake, is provided to hold and control a load applied to the hoist, a ratchet disc, mounted for free rotation in the axis of the drive shaft and forming part of the clutch and brake mechanism, is formed with a series of ratchet teeth at one side thereof and projecting parallel to the axis of rotation and a pawl having a series of teeth is mounted in a direction parallel to the axis of rotation towards and away from the ratchet disc; spring means being provided through which the pawl is pressed bodily on its mounting means towards the ratchet disc to oppose rotation of the drive shaft in a load lowering direction by engagement of the pawl teeth with the ratchet teeth. In the embodiment illustrated in Fig. 1, the hoist chain 15 is reeved over the load sheave 13 which is driven by a drive shaft 14 fitted with a pinion 17 which meshes with a gear 16 splined on to the load sheave. The drive shaft 14 is operated by a hand wheel 18 rotatably engaged upon a screw threaded portion 19 of the drive shaft so as to control the latter through a combined clutch and brake mechanism 20. The combined clutch and brake mechanism 20 comprises a friction disc 21 mounted upon the threaded shaft portion 19, and a ratchet disc 22, provided with a friction ring 22a, confined between the handwheel 18 and the friction disc 21. When the handwheel 18 is shifted inwardly, by its rotation relatively to the threaded portion 19, the ratchet disc 22, friction disc 21, the handwheel 18 and the drive shaft 14 are secured for rotation as a unit, thus permitting a load upon the hoist chain 15 to be raised by clockwise rotation of the hand wheel 18. If the driving force of the hand wheel 18 is discontinued, the weight of the load on the chain 15 will tend to rotate the drive shaft 14 and the brake in a reverse direction to lower the load. This tendency is prevented by a pawl 25 provided with inclined teeth 27 being spring urged by coil springs 28 into engagement with a series of ratchet teeth 24 formed on a continuous cylindrical flange 23 of the ratchet disc 22. A cushioned pressure ring 31 is provided between the handwheel 18 and the ratchet disc 22 to contribute also to uniform control and operation in order that there will be no eccentric forces upon the friction disc 21. The load is permitted to descend by a slipping action of the combined brake and clutch mechanism to an extent corresponding to the rotation of the hand wheel 18.