| 摘要 |
927,000. Ratchet hoists. DUFF-NORTON CO. June 28, 1960 [May 2, 1960], No. 22653/60. Class 78 (5). A handle-operated ratchet hoist, of which the ratchet 56 (Fig. 3), is engageable by a handle pawl and by a load-sustaining pawl 62, includes a reversing ring 80 rotatable between two positions of which one is occupied for load lowering and the other for load raising. The reversing ring carries cams by which it is ensured that in load lowering the two pawls alternately engage the ratchet with an overlap during which both pawls are in a position to take the load. The ratchet and a load sheave 35 (Fig. 2), supporting the chain 38 are secured to a shaft 30 rotatable in bearings 32, 33 in a housing 3- and the handle, which is rotatable relative to the shaft 30, comprises a lever portion 10 and a portion 12 which forms a cover for the housing 3. A spring-loaded pin 117 fitted in the lever 10 contacts the rim 115 of the housing 3 over one or other of the arcs limited by the pairs of stops 20, 24 and 21, 25 (Fig. 3). The handle pawl 90 (Fig. 5), pivots on a pin 92 secured in the cover 12 and is urged towards the ratchet by a spring 94; the load-sustaining pawl is similarly mounted on a pin 58 in the housing 3. The reversing ring is positioned by the setting of lever 6 (Fig. 1), whose shaft 8 incorporates a stepped portion 84 (Fig. 3), by which a radially protruding limb 121 of the ring may be pushed to rotate the ring against the resistance of spring 150 from the load-lowering position shown to the load-raising position. When lowering with the handle movable between stops 20 and 24, rotation of the handle towards the latter stop causes the pawl 90 to turn the ratchet and force the load-sustaining pawl 62 out of engagement to be held disengaged by the wedging of its corner portion 75 in the angle 140 of the cam 136 of the reversing ring. The load is thus taken by the handle during its downstroke towards stop 20 until a pin 100 (Fig. 5), protruding from the handle pawl engages surface 134 of cam 135. This engagement rotates the ring sufficiently to release the pawl 62 to sustain the load and further handle movement, with the pin 100 following the cam surface 130, disengages the handle pawl. On the succeeding upstroke the ,handle pawl re-engages the ratchet and disengages the load-sustaining pawl. In load raising, the reversing ring takes up a position in which the load-sustaining pawl cannot be held disengaged and in which the pin 100 never reaches the cam 135. The cam 136 is prevented from limiting the stroke during raising by ramping the portion 138 of this cam and by making the pin 100 retractable against spring-loading into the pawl 90. The handle may be positioned for operation between the stops 21 and 25 by temporary retraction of the pin 117 for transfer thereof between stops 20 and 21. When working between stops 21 and 25 the cam 122 performs the functions previously ascribed to cam 135. The lever 16 (Figs. 2, 5 and 12), may be rotated by hand to overcome spring 94 and hold the handle pawl out of engagement to allow for intentional free chaining. |
