Patent GB-857233-A (GB)
Title: A hydraulic system for mobile equipment
IPC: B66F9/22
Filed: 1958-07-04
Abstract: 857,233. Lift trucks. SUNDSTRAND CORPORATION, [formerly SUNDSTRAND MACHINE TOOL CO.]. July 4, 1958 [July 23, 1957], No. 21444/58. Class 78 (3). [Also in Groups XXIX and XXXI] An hydraulic system for a fork-lift truck comprises a variable displacement pump supplying liquid to motors for propelling the truck; an adjustable restriction in the pump discharge line controls the supply to the motors, and the pump displacement is automatically adjusted with variations in the pressure drop across the restriction. Summary.-The system comprises a pump 15 supplying liquid to motors 10, 11 for driving the truck, to a motor 13, for extending and retracting the lift fork and to a motor 14 for raising and lowering the fork. The pump 15 and motors 10, 11 are of the axial-piston rotary cylinder block type having adjustable swash-plates, motor 13 is the same type but of constant displacement, and motor 14 is of the jack type. A reversing valve 18 controls operation of the motors 10, 11, and reversing valves 19, 20 control motors 13, 14, respectively. Valves 18, 19, 20 are arranged in series and are biased to a central position in which the lines to the respective motors are blocked and the liquid from the pump is passed to the next succeeding valve. The pump discharge passes through a manuallyadjustable throttle valve 22 upstream of valve 18, 19, 20 and the speed of an engine 17 driving the pump is automatically adjusted with the throttle valve 22. Operation.-The throttle 22 is opened by rotating a hand lever 104 about its axis, which rotates a shaft 102, flexible shaft 103 and an adjustment shaft 86. A crank 96 on shaft 86 adjusts a carburetter 91 to increase the speed of engine 17. The pump then supplies through the throttle 22 and a line 21c to valve 18, and the pressure-drop across the throttle is applied to a valve 23 which when the drop is high is held in a position in which a pump displacement controlcylinder 47 is open to exhaust so that the pump swash-plate is positioned for minimum displacement. With increased flow through the throttle and a reduced pressure drop, the valve 23 rises to open the control cylinder 47 to the supplyline 21c through a line 64 and passages 58, 57 in the valve, thus increasing the pump displacement. A relief valve 24 functions to open the control cylinder to exhaust on the occurrence of an excessive pressure. For forward drive valve 18 is raised by pivotal movement of lever 104 upwardly to move a pilot valve 192 from a position in which a chamber 190 of valve 18 is open to exhaust to a position in which liquid is supplied to this chamber to raise valve 18. Liquid is then supplied through a line 118 to drive motors 10, 11 forwardly. The exhaust from the motors passes through lines 117, 123 and an automatic braking valve 29 to the reach control valve 19. For reverse drive a pilot valve 195 is actuated by lever 104 to supply liquid to a valve chamber 193 to lower valve 18. If the motors tend to overrun, as when the truck is on an incline, the braking valve 29 is actuated by the drop in pressure in the supply and restricts the exhaust from the motors and thus brakes them. When valve 18 is in its central position the motor lines 117, 118 are blocked to brake the motors, and non-return valves 138, 139 are provided to limit the braking effect. The motor swash-plates are normally biased to a minimum displacement position; a torque control valve 31 is provided which opens the motor swash-plate control cylinders to pressure to increase the displacement on the occurrence of high pressure in the supply line 21c. Reach valve 19, which controls motor 13, is operated by solenoids 217, 218 controlled by push-buttons 222, 224 on the control lever 104. Lift valve 20 is operated in a similar manner to valve 18 and is under the control of pilot valve 1921, 1951 operated by horizontal movements of the control lever. Downward movement of valve 20 connects the pressure line from valve 19 to the cylinder of motor 14 to raise the fork, upward movement of valve 20 connects the cylinder to exhaust through an adjustable throttle 180 to lower the fork.