Patent GB-699249-A (GB)
Title: Improvements relating to braking systems for hoists and the like
Inventor: DOLAN HARRY
IPC: B66B15/00
Filed: 1950-11-22
Abstract: 699,249. Hoists. ENGLISH ELECTRIC CO., Ltd. Nov. 16. 1951. [Nov. 22, 1950 ; Jan. 19, 1951] Nos. 28546/50. and 1498/51 Class 78 (v). In braking systems for hoists of the kind in which the braking torque is determined by the position of a manually-operable controller, direction-responsive means are arranged automatically to vary the effect of the controller so that for any given setting, the torque, as compared with that obtained when the hoist is stationary, is different both when the hoist is being lowered or raised. The brake lever 17, Fig. 1, is connected by links 16, 15, 14, bellcrank lever 13, link 12 and bell-crank lever 11 to the brake engine control valve 10. The link 15 is pivoted at its middle point to a rod 18 which carries a weight 18a and is connected to the core of a solenoid 19. The piston of a hydraulic servo-motor 20 is connected to the link 12, one end of which is engaged in a slot 13a in the lever 13. The servo-motor 20 is controlled by an epicyclic gear 21, the sun wheel 22 of which is driven from the winding drum shaft through gears 24, 23 and the planet carrier 25 of which is coupled to the centrally pivoted member 26. This member is biased to horizontal position by springs 27 and is coupled by links 29, 30 to the piston of the servo-motor and to the slide valve 31 controlling the supply of oil The ring 28 of the gear 21 has appreciable inertia and rotates freely. When the hoist is stationary, the parts are in the position shown. and any movement of the lever 17 will cause a corresponding movement of the valve 10 and the application of a certain braking torque. When the hoist descends, the sun wheel 22 is driven in the direction of the arrow X and the carrier 25 rotates in the same direction thereby tilting the member 26 anticlockwise. This movement tilts the link 30 about the pivot carried by the servo-motor and the slide valve 31 is moved to admit oil to the upper end of the servo-motor through the port 20a to depress the piston and move the link 12 to position B. As the piston moves down, the slide valve returns to the closed position. In position B the effective length of the slotted arm of the lever 13 is greater than in position A, so that for the same movement of the lever 17, a greater movement of the valve 10, and hence a greater braking torque will be obtained. When the hoist is ascending, the member 26 is moved clockwise and the piston raised to move the link 12 to position C in which a less braking torque is obtained. If the supply of current to the solenoid 19 fails, the weight 18a will fall and the brake will be applied, the extent of the application depending as before on the inclination of the link 12. In a modification, Fig. 2, the epicyclic gear is replaced by weightloaded governors 40. 41 driven from the winding drum shaft through bevel gears 42, 43 and gears 23, 24. Ratchet devices 44, 45 are placed between the bevel gears and the governors one of which rotates only when the hoist is rising and the other when it is descending. Links 46, 47 and 30 connect the governors to the servo-motor. The governors may be set to operate at different speeds. In another modification '(not shown) a governor driven from the winding drum shaft through a ratchet device is arranged to maintain an abutment against one end of the member 26 until the speed exceeds a predetermined value. In a further modification (not shown) the carrier 25, Fig. 1, is coupled to a pivoted lever arranged vertically. The lower end of this lever is connected bv a link to the link 29 and abutments are provided on each side of the upper end to limit its angular movement. In this modification, and in the construction shown in Fig. 1. the epicyclic gearing may be replaced by a hydraulic coupling. In a still further modification (not shown) the servo-motor is controlled by the movement of a vertical bar which is suspended by parallel links and is pushed aside by a nut which moves up and down a screw in accordance with the movement of the hoist.