GB866833A - Improvements in or relating to control-gear for hydraulic circuits - Google Patents

Abstract

866,833. Hydraulic control systems. LANSING BAGNALL Ltd., and ARNOT, A.E.R. June 22, 1959 [June 27, 1958], No. 20767/58. Class 69 (2). [Also in Group XXX] An hydraulic control system for a fork-lift truck comprises electromagnetic means for controlling the speed of a motor so that a pump driven by the motor has more than one rate of delivery, a control valve 106, 136, 109 between the pump and devices 28, 31, 34 utilizing the delivery, and connections 45, 46 between the electromagnetic means for controlling the motor and the control valve operative to actuate the means in accordance with the rate of utilization selected by the control valve. The truck has fork arms 33 which are movable horizontally by a piston-arid-cylinder device 28, vertically by a piston-and-cylinder device 34, and tiltable by a piston-and-cylinder device 31. The delivery from the pump is selectively directed to the devices 28, 31, 34 by levers 37, 36, 35, respectively, operating the valves 106, 136, 109 in a casing 44. The pump is driven by the motor which has resistances connected either in series or shunt under the control of microswitches 45, 46 so that the motor has two speeds and the pump a high and low rate of delivery, one or both of the micro-switches being operated by plates which are rotatably supported on bars 80, 81 and rocked by the movement of the levers 36, 35, 37 about a bar 40. In operation, when the fork arms are to be moved horizontally forward, the lever 36 is rocked forwardly to operate its valve 136 and actuate the micro-switch 46 to start the motor, further movement of the lever actuating the switch 45 so that the motor runs at its highest speed and maximum delivery is obtained from the pump. When the arms are to be retracted, the lever 36 is rocked rearwardly to move the valve 136 to its appropriate position and only the micro-switch 46 is actuated so that the motor runs at its slower speed which is necessary because of the smaller effective area of the piston caused by its rod 29. The lever 37 when moved in one direction for raising the arms 33 operates both switches to provide maximum delivery from the pump to the device 34, and when moved in opposite direction operates neither of the switches, the arms being lowered by gravity. Only the micro-switch 46 is actuated when the lever 35 is moved forward or rearward sothat tilting is always at slow speed. The rates of delivery of the pump are arranged to be slightly above that to be utilized, the excess being conducted away by a relief valve. In other embodiments, the pump delivery may be varied by controlling an accelerator on the motor or a control lever on the pump.