Patent ID: 8833067
Filing Date: 2014-09-16
Classification: F15B

Abstract:
1. A hydraulic system comprising: an actuator having a piston disposed within a cylinder, and a rod extending from the piston and extending out of the cylinder, the piston defining a rod chamber and a cap side chamber within the cylinder, a pump adapted to operate as a pump or as a motor, the pump being adapted to selectively provide varied flow rates, the pump being adapted to deliver pressurized hydraulic fluid to and receive pressurized hydraulic fluid from the chambers of the actuator, movement of the piston relative to the cylinder being dependent upon the selectively varied flow rates, a controller configured to control the displacement of the pump in response to a commanded motion and relative positions of the piston and cylinder, a rod side fluid connection between the pump and the rod chamber, a cap side fluid connection between the pump and the cap side chamber, a first mechanical hydraulic valve disposed in the cap side fluid connection, the first mechanical hydraulic valve having at least a first position preventing flow through the cap side fluid connection, and a second position permitting flow through the cap side fluid connection, the first mechanical hydraulic valve being adapted to be disposed in at least one of its first or second positions as a result of a first hydraulic pressure differential applied across the first mechanical hydraulic valve, and a second mechanical hydraulic valve disposed in the rod side fluid connection, the second mechanical hydraulic valve having at least a first position preventing flow through the rod side fluid connection, and a second position permitting flow through the rod side fluid connection, the second mechanical hydraulic valve being adapted to be disposed in at least one of its first or second positions as a result of a second hydraulic pressure differential applied across the second mechanical hydraulic valve, wherein the first and second mechanical hydraulic valves are maintained in the respective first positions when the pump is not operative.