Patent GB-641407-A (GB)
Title: Improvements in or relating to elevating mechanism primarily for vehicle tail boards
IPC: B60P1/44
Filed: 1948-09-14
Abstract: 641,407. Vehicle fittings for loading and unloading; load-handling apparatus. JENKINS (CHELTENHAM), Ltd., W. W., PIRIE, R. A., and CHALLIS, A. L. Sept. 14, 1948, No. 24090. [Classes 78 (iii) and 78 (iv)] Mechanism for raising and lowering an overhanging load-carrying platform and employing a parallel link-motion to guide the platform and to control its angular disposition (e.g. to keep it horizontal), comprises a primary link motion having parallel links adapted to swing up and down about pivots carried by a fixed support such as the body of a vehicle and a secondary link motion forming an extension of the primary link motion and comprising parallel links adapted to swing up and down about pivots carried by the primary link motion, the platform being supporting by the secondary link motion and an actuating member such as a hydraulic ram being arranged to act upon part of the secondary link motion to raise and lower the platform. As shown, the tailboard 10 of a vehicle may be lowered to the ground or raised to the level of the vehicle floor 4 and is supported by a hinge bar 9 so that it may be disposed horizontally as shown or turned to a vertical position to close the rear of the vehicle body. The hinge bar 9 is guided by a primary linkage comprising parallel links 6 pivoted to brackets 5 connected to the frame of the vehicle body on each side of the vehicle and supporting a transverse member 7 and by a secondary linkage comprising parallel links 8 pivoted at each side of the vehicle to the members 7, 9. A hydraulic ram 11 on each side of the vehicle is connected between a pivot on the vehicle and a pivot 15 on a member 12 pivoted at 13, 14 to the members 7, 9 respectively, and serves to raise and lower the tailboard 10. During this motion the system takes up a disposition in which the forces due to the load on the tailboard 10, the rams 11 and the reactions in the links 6 are in equilibrium, this disposition being such that during the greater part of the motion the links 8 are substantially horizontal. Stops limit the raising and lowering of the links 8 relatively to the members 7, and buffers may be provided to limit the upward movement of the members 7. The rams 11 are preferably double-acting and may be supplied with pressure fluid from a pump driven by the vehicle engine, and may be provided with means for locking them in the contracted position which is automatically released when pressure fluid is admitted to the ram to extend it. In an alternative construction in which the links 8 are shorter, these links complete their movement relatively to the links 6 before the latter move, the member 7 being provided with ground-engaging feet. The brackets 5 in this construction are secured to the vehicle chassis. Each of the pairs of links 6 may be replaced by two laterally spaced pairs of links, the transverse member 7 being replaced by one such member on each side extending between the laterally spaced pairs of links and the pairs of links 8 being similarly duplicated and engaging a single member 12.