Patent GB-303007-A (GB)
Title: Improvements in and relating to automatic brake controlling mechanism
IPC: B66D5/04
Filed: 1928-12-12
Abstract: 303,007. Lewis-Shepard Co. Dec. 24. 1927, [Convention date]. Actuated or applied by speed regulators; reverse movement, preventing.-A hoisting machine comprising a rotatable winding drum, an actuating shaft therefor, a brake drum rotatably mounted upon said shaft, a main brake engaging the outer periphery of said brake drum, clutch members on said shaft operable to permit free rotation of said shaft in a direction to raise the load and to engage the inner periphery of said drum when said shaft is rotated in the reverse direction, and manually controlled means for releasing said main brake to permit the descent of the load is characterized bv the provision of a supplemental brake drum rotatably mounted upon said shaft and having means engaging said main brake, and centrifugally movable members connected to said main brake drum operable by the centrifugal force produced by the rotation of the said main brake drum in said reverse direction to engage said supplemental brake drum and cause it to apply said main brake with a force acting to prevent acceleration of the descending movement of the load in excess of a predetermined substantially uniform speed. A brake drum 8 having a cylindrical hub 9 is rotatably mounted on the shafts 6 of a winding drum 7. Pivotally connected brake shoes 10, 11, 12 act on the inner face of the drum 8. The adjacent ends of the shoes 10, 12 are connected by a toggle linkage 13, 14, 16 to an arm 17 extending from the hub 18 which is secured to the shaft 6 by a pin 19. One end of this pin engages a lug 20 on the shoe 11 when the shaft 6 is turned in a clockwise direction, i.e. in the winding direction, to rotate the shoes with the shaft. If the shaft is turned in the opposite direction, the arm 17 will straighten the toggle linkage and the shoes will be forced into engagement with the arm which normally is prevented from rotating by releasable brake mechanism. The outer surface of the drum 8 is engaged by brake bands 23, 24 provided at one end with brackets 26, 27 connected by a bolt 28 and spaced apart by a spring 29. The opposite ends of the bands are connected to bell-crank levers 32, 33 pivoted at 35, 39. A stud 37 extending across the bifurcated arm 36 of the lever 32 is engaged by the slotted end of an arm 38 of the lever 33. A lateral extension 41 of the lever 33 has a head 42 which is slotted to receive a vertically movable guide rod 44. The head 42 rests on a looselymounted collar 46 which is supported by a helical spring 47. A crosshead 48 which rests on a helical spring 50 is fixed to the rod 44 by a pin 49 and supports the spring 47. A pair of links 54 pivoted to the pin 49 are connected by an arm 55 to a shaft 57 having a non- circular head 58 adapted to be engaged by the crank 22 used for actuating the shaft 6. The springs 47, 50 apply the brake bands 23, 24 to the drum 8. If the shaft 57 is rotated slightly in a counterclockwise direction, the arm 55 will depress the crosshead 48, thereby compressing the spring 50 and permitting the expansion of the spring 47, thus reducing the force applied to the arm 41 and gradually releasing the brake bands from the drum to permit descent of the load. If the attendant releases the crank, the spring 50 will expand, and the brakes be reapplied. In order that too rapid a descent of the load shall not take place if the attendant exerts too great a pressure on the crank, automatic means are provided for limiting the speed of rotation of the shaft. This means comprises a brake drum 60 having a hub 61 rotatably mounted on the hub 9. A pair of arms 62, 63 on the drum 60 loosely engage shoulders 30, 31 on the bands 23, 24. Brake shoes 64, 65 within the drum are pivoted at 66, 67 to the web of the drum 8. Links 68, 69 connect the shoes to a stud 70 which is pivotally connected to an extension 72 of a weight 71. When the load descends, the weight 71 will be moved outwards by centrifugal force and the shoes 64, 65 applied. to the drum. As the shoes are rotating with the drum 8, when they engage the drum 60 it will rotate, the arm 63 will engage the shoulder 30 and the brake band 23 will be applied to the drum 8.