Patent GB-771507-A (GB)
Title: Improvements in or relating to hydraulic systems for tractor power-lift mechanisms
IPC: A01B63/10
Filed: 1955-03-18
Abstract: 771,507. Tractor power-lift mechanisms. FORD MOTOR CO., Ltd. March 18, 1955 [March 19, 1954], No. 8006/55. Class 79(1). In a tractor power-lift hydraulic system a ram 14 is connectable by a control valve 18 to a pump 10 and a sump 11 whereby in " neutral " and " lower " positions of the valve the pump output is connected to the sump and in a " raise " position of the valve the output is connected to the ram, a double-acting ram 15 is connectable by a second control valve 17 to the pump 10 and sump 11 whereby in " neutral " and " lower " positions of the valve 17 the pump output by-passes the ram 15 to the sump and in a " raise " position of the valve 17 the putput is connected to the ram 15, the rams 14, 15 being connected to the sump 11 when the valves are in the lower positions, and the latter connnections include a two-position valve 23 having a shiftable element 23b resiliently urged to block one connection, whereby concurrent movement of the valves to their " lower " positions produces sequential " lowering " of the rams. As shown the mechanism comprises a second double-acting ram 16. The ram 14 may be provided at the rear of the tractor and the rams 15, 16 control a forwardly-mounted implement. The valves are controllable from the tractor driver's station. The pump 10 discharges through a pipe 13 having branches 13a, 13b, 13c, flow to the branches 13b, 13c being controlled by a flow equalizer member 21 to give an equal flow to each ram 15, 16. The member 21 can be by-passed by a valve 22 in the position shown in Fig. 1, movement of the valve 22 to the right bringing the flow equaliser member 21 into action. The branches 13b, 13c are connected by pipes 1361, 13c<SP>1</SP> to ports 17k in the valves 17 and the branch 13a is connected by a pipe 13a to a port 17d in one of the valves 17. With both the valves 17 in their " neutral " positions as shown, the port 17d is connected to a port 17g which is connected by a pipe 13d to the port 17d in the other valve 17, the latter port 17d being connected by the port 17g to a pipe 13e leading to the ram 14. Thus if either the valves 17 are moved to the " raise " or " lower " position, liquid from the pump 10 is cut off from the ram 14. Movement of the valve spindle 17b to the right or left admits liquid from the port 17k to either of ports 17m, 17n. Flow through the port 17m, for example, of the valve 17 associated with the ram 15 moves a shuttle 24b in a checkvalve 24 to the right, thereby opening a valve 24e and connecting one side of the ram 15 to exhaust and the liquid flow opening a check valve at the left hand end of the check valve 24 and admitting liquid through a pipe 15b to the other side of the piston 15a. Opening of the valve 24e connects a pipe 15c through the port 17n to an axial bore 17b in the valve spindle 17b the bore 17b communicating through a port 17n with an exhaust pipe 26. The pipe 13e supplying liquid from the pump 10 to the primary ram 14 leads to a low pressure relief valve 19 and a check valve 25, the valves being connected by a valve seat 28, the valve 19 being normally unseated permitting liquid to discharge to the sump 11 from the pipe 13e through a conduit 30, space 20e of a valve 20, and pipe 31. Liquid pressure in the pipe 13e normally passes through a conduit 13f to act on the right hand face of a piston portion 20c of the valve 20, thereby maintaining the valve 20 in its extreme lefthand position, the left hand face of the portion 20c being acted on the liquid pressure in the sump 11 through a space 18e in the bore 18d of the valve 18, and a port 18c. Movement of the spindle 18b of the valve 18 to the left to its raise position permits liquid in the conduit 13f to pass through ports 18m, 18c to the left hand side of the piston portion 20c thereby moving valve 20 to the right and causing a piston portion 20h of valve 20 to close port 20g leading to exhaust pipe 31. The resultant build-up in pressure on the ouput side of the pump 10 causes check valve 25 to open, thereby connecting pipe 13e to a pipe 29 leading to ram 14. Movement of the spindle 18b to the right of the position shown in Figs. 1 and 4 opens a port 18j thereby connecting an exhaust pipe 32 from the ram 14 through ports 18n, 20g to the exhaust pipe 31. The exhaust pipes 26, 31 are connected to a pipe 33 leading to the sump 11 by the valve 23. Normally the connection between pipes 26, 33 is obstructed by the valve 23, but the valve is moved by liquid pressure in the pipe 26 to open the connection and close the connection between the pipes 31, 33, whereby the rams cannot be exhausted simultaneously.