Patent GB-510019-A (GB)
Title: Improvements in or relating to lifting and lowering mechanism for the tail gate of avehicle
IPC: B60P1/46
Filed: 1938-01-28
Abstract: 510,019. Guided platform hoists; winding and paying-out apparatus. SHONNARD, H. W. Jan. 28, 1938, No. 2769. Convention date, Jan. 30, 1937. [Classes 78 (iii) and 78 (v)] A loading platform is pivoted at one edge to slides, which travel in vertical guides at the rear of a vehicle, and is provided with means for holding it normal to the guides during the movement of the slides, and for allowing the edge opposite to the pivoted edge to move downwardly after the movement of the slides is arrested by contact with the ground. The platform 100, Fig. 7, is pivoted to slides 94, which move in guides 92, and is, connected by chains 101 to links 96, which are pivoted to the slides and connected to the counterweights by chains 98. Chains 99 connect the counterweights to winding drums 23A. Stops 97 limit the upward movement of the links 96. The winding drums 23A, Fig. 1, are mounted at either end of a shaft 22 which is mounted in bearings in the end of a casing 20 and is driven through gearing by an electric motor 79, Fig. 2, or rotated by a hand crank 24. A friction disc is slidably but non- rotatably mounted on the shaft, and co-operates with a circular plate 31 which is carried by a hub 30 free on the shaft and is attached to a rim 33 provided with gear teeth 34. Another plate 35 secured to the rim forms with it and the plate 31 an oil tight chamber which houses clutch mechanism. A pressure plate 42 supported on the outer ends of radially disposed levers 40 is pressed against the disc 26 by springs 43. The levers are pivoted on the plate 35 and their inner ends bear against a flange on a collar 44 free on the shaft. Another collar 47 free on the shaft has a flange 48 against which bear forked members 50 carried by a shaft 51. Other forked members 54 on this shaft support an internally threaded member 55 which is engaged by a con trol shaft 56. An arm 58 on the shaft 51 is arranged to open a normally closed switch 59 in the motor circuit. The teeth 34 are in mesh with a worm 62, the shaft 60 of which is hollow and receives the motor shaft 78. Complementary clutch members 65, 64 mounted on the shafts 78, 60, respectively, are engaged by a lever 66. Gears 76, 72 on a countershaft 70 mesh with gears 77, 63 on the shafts 78, 60, respectively. The gear 72 is so mounted that it is driven in one direction only by the shaft. The plate 31 is held against reverse movement by pawl- and - ratchet mechanism 80, 81, or by a free wheel clutch. In order to raise a load, the shaft 56 is turned to move the member 55 to the right, Fig. 1. This movement first effects a driving connection between the disc 26 and plate 31, and then removes the arm 58 from the switch 59, thus allowing the switch to close the motor circuit. During hoisting the gear ratio between the motor and worm may be changed by moving the lever 66. When it is desired to lower a load, the shaft 56 is turned' in the opposite direction, and the rate of descent is controlled by allowing the clutch to slip as rapidly or as slowly as desired. A limit switch 102 may be provided in the path of the counterweight to be opened by it to stop the motor if it is desired to arrest the movement of the platform at a predetermined level. The switch 102 cannot be closed until the platform 100 is lowered sufficiently to raise the counterweight out of engagement, thus preventing simultaneous actuation of the hoisting and lowering connections of the mechanism. In a modification the shaft 22 releases a clutch in the driving gear after a predetermined number of rotations, and the clutch cannot be re-engaged until the shaft has been reversed to lower the platform. The Specification as open to inspection under Sect. 91 comprises also a portable crane, an overhead crane, and a lifting jack actuated by similar mechanism. This subject-matter does not appear in the Specification as accepted.