Electronically controlled hydraulic system for lowering a boom in an emergency

An industrial lift truck has a boom that is raised and lowered by a first hydraulic actuator and a load carrier that is pivoted with respect to the boom by a second hydraulic actuator. In the event that the supply of hydraulic fluid for powering the actuators fails, the boom may be lowered by gravit...

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Bibliographische Detailangaben
1. Verfasser:	STEPHENSON DWIGHT B
Format:	Patent
Sprache:	eng
Schlagworte:	BLASTING CRANES DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR DREDGING FIXED CONSTRUCTIONS FLUID-PRESSURE ACTUATORS FLUID-PRESSURE ACTUATORS, e.g. SERVO-MOTORS FOUNDATIONS HAULING HEATING HOISTING HOISTING, LIFTING, HAULING OR PUSHING, NOT OTHERWISE PROVIDEDFOR, e.g. DEVICES WHICH APPLY A LIFTING OR PUSHING FORCEDIRECTLY TO THE SURFACE OF A LOAD HYDRAULIC ENGINEERING HYDRAULICS OR PNEUMATICS IN GENERAL LIFTING LIGHTING LOAD-ENGAGING ELEMENTS OR DEVICES FOR CRANES, CAPSTANS,WINCHES, OR TACKLES MECHANICAL ENGINEERING PERFORMING OPERATIONS SOIL SHIFTING SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL TRANSPORTING WEAPONS
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Beschreibung
Zusammenfassung:	An industrial lift truck has a boom that is raised and lowered by a first hydraulic actuator and a load carrier that is pivoted with respect to the boom by a second hydraulic actuator. In the event that the supply of hydraulic fluid for powering the actuators fails, the boom may be lowered by gravity by draining fluid from the first hydraulic actuator. To prevent a load from sliding off the load carrier as the boom descends, the load carrier is pivoted to maintain a substantially constant angular relationship to the ground. This is accomplished by selectively conveying fluid drained under pressure from the first hydraulic actuator into the second hydraulic actuator. Changes in the position of the boom are sensed and, in response, the flow of fluid into the second hydraulic actuator is controlled to produce corresponding changes in the load carrier position.