Power transmission

Abstract

A hydraulic control system comprising a hydraulic actuator having opposed openings adapted to alternately function as inlets and outlets for moving the element of the actuator in opposite directions and a variable displacement pump with loading sensing control for supplying fluid to said actuator. A pair of meter-in valves are provided to which the fluid from the pump is supplied and a pilot controller alternately supplies fluid at pilot pressure to a meter-in valve for controlling the displacement of movement of the meter-in valve and the direction and velocity of the actuator. Alternately pilot pressure from the pilot controller is applied simultaneously to both of the meter-in valves in conjunction with the venting of one of two load drop check valves to provide a regenerative mode. A line extends from the meter-in valve to its respective opening of the actuator and a meter-out valve is associated with each line of the actuator for controlling the flow out of the actuator when that line to the actuator does not have pressure fluid from the pump applied thereto. Each meter-out valve is pilot operated by the pilot pressure from the controller. In a modified form, utilizing a single actuator, the hydraulic control system includes a single meter-in valve associated with one opening of the actuator.