GB543584A - Improvements in or relating to levelling devices - Google Patents

Abstract

543,584. Automatic control systems for mobile platforms. RUSTON-BUCYRUS, Ltd. Aug. 15, 1940, No. 13065. Convention date, Aug. 17, 1939. [Class 38 (iv) ] Altitude.-A level-responsive control for four power-operated jacks supporting four separate caterpillar tractors the base of a heavy excavator or other machine comprises a single motor-driven pump P and double-acting valves V1 ... V4 selectively controlling the supply of pressure oil to jacks 1 ... 4 and the release of oil to a common suction pipe 11. Electro-magnets 20 (E Fig. 3) are controlled by pairs of switches F on each diagonal of the base through relays A associated with relays B, G operated by switches closed by each jack when fully contracted and expanded respectively. The relays comprise interlock contacts so that no jack can be expanded (or contracted) when the opposite one is fully contracted (or expanded) and one or both of the other jacks is fully expanded (or contracted) but causing automatic levelling to proceed beyond the point when a given jack has been fully expanded (or contracted) by simultaneous contraction (or expansion) of the jacks on the other diagonal. Simultaneous contraction is obtained by automatically energizing an electro-magnet 18 which opens a valve connecting a sump S to the suction pipe 11 and simultaneous expansion by relays D associated with the respective diagonals which cause actuation of valves V, V3 or V2, V4. An adjustable constriction 9 controls the speed of contraction. The coil 18 may be manually controlled by a switch 81. Firm contact with the ground is ensured at each corner by switches 27 (H, Fig. 3) which close when the pressure in any jack falls below a given value; these energize the appropriate electro-magnet 20. Manual control of each electro-magnet 20 (E), is obtained by push-button switches G, but the pump motor starting circuit is opened by relays C if the jack is fully expanded. When the tractors are in motion the control circuits described are disabled by a relay 91 and the equivalent of a three point support for the base is obtained by a coil 31 opening a valve 30 connecting the oil pipes of two adjacent jacks. The valves V1 ... V4 may each be replaced by two single acting valves. No automatic system may be applied to a system using any kind of power acuated means for raising and lowering the corners of the base. Specification 503,932 and U.S.A. Specification 2,202,009 are referred to.