Hydraulic locking device

Claim 1

In a locking device of the character described to control relative movement between two members, comprising a hydraulic cylinder connected to one of the two members, a tubular piston rod extending through at least one end of said cylinder and connected to the other of the two members, a piston united with the piston rod, the piston dividing the interior of the cylinder into two locking chambers, and a locking valve controlling fluid flow between the two chambers to control the freedom of movement of the piston, the improvement comprising: a reservoir for hydraulic fluid to replenish the fluid in the two chambers, a portion of said tubular piston rod forming a wall of the reservoir, said reservoir having a movable wall; means including a radial port in said portion of the tubular piston rod to permit flow of hydraulic fluid from the reservoir to one of said two locking chambers when the piston is at one of its two opposite limit positions, spring means acting against said movable wall of the reservoir to place the fluid in the reservoir under pressure for effecting flow to one of said locking chambers; and sealing means embracing the tubular piston rod adjacent one end of the reservoir, said radial port being positioned along the length of the tubular piston rod to move out of communication with the reservoir into the region of said sealing means and past the sealing means when the piston moves out of one of its limit positions towards its other limit position whereby the reservoir is cut off from both of said locking chambers whenever the piston moves out of said limit position.