Patent GB-501978-A (GB)
Title: Improvements in and relating to free chain hoists
IPC: B66D3/16
Filed: 1937-09-08
Abstract: 501,978. Pulley-hoists. COFFING, F. W. Sept. 8, 1937, No. 24506. [Classes 78 (i) and 78 (v)] Relates to free-chain hoists operated in the load-raising direction through an epicyclic train. In the form shown in Figs. 2 to 4, the shaft 16 is rotated clockwise for load elevation by rocking two lever arms 40 alternately and out of phase by pulling on ropes 9, the arms being loose on the shaft and provided with members 44 which frictionally engage annular flanges on discs keyed to the'shaft. A sun gear 79 is keyed to the shaft and engages planet wheels 81 rotatable on a disc 86 keyed to the hub of the sprocket 82 loose on the shaft 16 and over which the load carrying chain 98 passes. The planet wheels also engage an internally toothed ring 77a formed on a disc 77 loosely mounted about the shaft 16 but normally held against rotation in the contraclockwise direction by a pawl 91 engaging one of a number of notches 80 in the disc, whereby clockwise rotation of shaft 16 rotates the sprocket 82 clockwise. A ratchet disc 68 is keyed to the shaft 16 and pawls 72 pivoted on a disc 45 ride over the teeth of the ratchet when the shaft rotates in load raising direction. When the sprocket 82 rotates contraclockwise in load lowering direction, the shaft 16 is also rotated contraclockwise and, through the ratchet and pawls 68, 72, rotates the disc 45. The disc is provided with an overhanging flange 70 around which passes a brake band 46 secured at one end 50 to a fixed point and at the other to a spring 52 adjustably secured to the housing. A sleeve 57 surrounds the spring and bears at its upper end on the end of the brake band. The lower end of the sleeve is engaged by an adjustable stop 62 carried by a lever 60 pivoted at 61 such that' when a rope 66a is pulled, the brake is released more or less and as the disc 45 is driven by the shaft 16 when the latter is rotating in load-lowering direction, load lowering takes place under the control of the brake. The disc with which the levers 40 engage is provided with a centrifugal speed control for the shaft 16 in the lowering direction comprising weights 24, Fig. 5, pivoted at 25 to the disc and at 22 to one end of shoes 20 carrying friction material 21 and pivoted at their other ends 19 to the disc. As the speed increases, the shoes swing outwardly and engage the overhanging rim 18A of the disc. The weights are guided by eyes 34 engaging pins 33 projecting from a boss 26 on the disc and are cushioned against inward movement by bumpers 36. The pawl 91 may be withdrawn to free the ring 77a whereby the load-carrying sprocket 82 may be rotated in either direction without driving the shaft 16 or without having to operate the levers 40, thereby permitting free movement of the load chain as for repositioning. The withdrawal of the pawl may, however, only be effected when no load is on the chain, the spring 94, on pulling the cable 66a, merely being stressed without effecting disengagement of the pawl, when the load is on the chain, owing to the shape of the recesses 80 and the pawl 91. A slight clockwise movement of the ring 77a is necessary to free the recess and this cannot be effected with an unloaded chain. The load chain is cushioned towards the end of its descent by the lever 102 and spring 105, and the operating levers 40 are returned to their elevated positions by springs 120. In another form, the sprocket 1120, Fig. 10, engaging the load chain is secured to a shaft 1121 rotatably mounted in the casing and cover 1110, 1111 and provided with ratchet teeth 1242 about which the boss 1125 of a hand lever 1127 carrying a retractable pawl 1243 is piyotally mounted so that contraclockwise movement of the lever between stops 1206, 1237, Fig. 11, raises the load. A shaft 1159, Fig. 10, is rotatably mounted at one end in the casing 1110 and at the other within the hollow end of the shaft 1121. Sun gear teeth 1189 are formed on the shaft 1159 and a disc 1160 forming part of a brake mechanism and of a speed control device is keyed to the shaft. A disc 1186 carrying planet wheels 1188 is keyed to the shaft 1121, the wheels engaging the sun teeth 1189 and the internal teeth 1191 of a ring 1289 rotatably mounted with respect to the shaft 1121. The ring may always rotate contraclockwise and does so during load elevation, the shaft 1159 then remaining stationary and the brake and speed control inoperative. The ring is normally locked against clockwise rotation so that during load lowering the shaft 1159 is driven through the sun and planet gear by the clockwise rotation of the shaft 1121, the brake and speed control then being inoperative. The pawl holding the ring against clockwise rotation may, however, be withdrawn by actuating a plunger 1203, Fig. 11, but the means for effecting this withdrawal are arranged to be capable of operation only when no load is on the chain so that the chain may then be freely moved in either direction, for example as may be required for positioning it for a new operation, without being subject to the brake and speed control in the lowering direction or having to be actuated by the handle 1127 in the elevating direction. The brake comprises a strap 1164, Fig. 10, encircling an annular flange 1163 on the disc 1160 with a friction lining 1165 interposed. One end of the strap is fixed and the other is secured to an adjustable spring so that the brake is normally "on." A bolt 1227 slidably carried by the lever handle 1127 normally projects therefrom to abut a fixed stop 1237 to limit the downward movement of the handle. The bolt may be retracted by actuating a rod 1231 carried by the handle so that the latter may then be swung slightly further contraclockwise and the bolt then contacts with a lever 1239 to operate a shaft 1144 to release the brake by an amount controlled by the movement of the handle 1127. The pawl 1243 is also retracted by the rod 1231 so that the load now descends under the control of the brake and of the speed control. The latter is generally similar to that shown in Fig. 5 and comprises bands 1167 carrying friction material 1166 and pivoted at one end to the disc 1160. The other ends of the bands are pivoted to weighted arms 1172 which are themselves pivoted on the disc 1160 in such a way that on excessive speed of the latter the arms ride out under centrifugal force and push the bands into engagement with the inner periphery of the cylindrical housing 1110. The housing may be provided with a free sprocket wheel 1138 whereby various arrangements of load chains may be used to vary the mechanical advantage of the system. As shown in Fig. 11, one end of the chain is anchored at 1271 to the housing, the slack passes through a guide 1273 to the driving sprocket 1120, downwardly and around a sprocket in the block carrying the hook which engages the load, upwardly (lap 1273<1>), and over the sprocket 1138 and then downwardly (lap 1273<11>) to be anchored to the hook block whereby the load descends only one-third of the amount of slack taken up. In a modification, the driving sprocket 1420, Fig. 20, is fixed to a shaft 1421 rotatably mounted about a shaft 1424 to which a ratchet disc 1510 is keyed. A wheel 1514 is freely mounted about the shaft 1424 and carries a pawl such that when the wheel is rotated contraclockwise, viewed from the right, as by pulling on a chain 1516 frictionally engaging its grooved periphery the sprocket shaft 1421 is also rotated contraclockwise, but more slowly than the shaft 1424, thereby raising the load, the drive being through the sun and planet gear 1489, 1488, the planet carrier 1486 being keyed to the shaft 1421 and the internally toothed wheel 1481 being held against rotation. Duriiig such rotation of the shaft 1424, the brake 1463 and speed control 1472 are disconnected from the shaft. A ratchet disc 1568 keyed to the shaft slips over pawls pivoted on the disc 1460 corresponding to the disc 1160, Fig. 10, during load elevation, but on rotation of the shaft in the load-lowering direction the disc 1460 is driven therewith to render the brake and speed control operative. These members are similar in construction and action to those shown in Fig. 10. In load lowering the shaft 1424 is driven through the sun and planet gear from the shaft 1421 which is rotated by the weight of the descending load. A free sprocket wheel 1438 is also carried by the housing for providing alternative mechanical advantage. The brake release shaft 1444 is rotated in the brake-releasing direction by clockwise rotation of the chain wheel 1514 when a shoulder on the tail of the pawl which normally operates the ratchet disc 1510 engages a spring-pressed finger 1529 projecting from' an arm 1525 on the shaft 1444 causing the latter to rotate. On the rotation of the wheel 1514 in the driving direction, a cam surface adjacent the pawl shoulder depresses the finger 1529 to permit the pawl to pass. The, pawl holding the internally toothed ring 1481 may be withdrawn to permit free chain movement under the same conditions as in the other form.