Locking device for securing objects which are movable relatively to one

Abstract

A locking device for selectively securing two movable objects in desired positions relative to each other includes a cylinder and a piston movable within the cylinder and defining first and second working chambers of variable volumes. A fluid exchange connection provided on the piston includes a flow chamber having openings that communicate with the working chambers. A valve body slidably received on the piston in sealed relation is biased by a spring into a position closing the opening from the flow chamber to first working chamber. When the fluid pressure in the second working chamber exceeds a predetermined amount and acts on the valve body, the valve body is moved against the spring bias and opens to allow fluid to flow through the fluid exchange connection. In the open position, a larger area of the valve body is exposed to the pressure in the second chamber. A restriction in the flow path between the flow chamber and the first chamber produces a pressure drop between the flow chamber and the first chamber and allows the fluid exchange connection to remain open with a reduced pressure in the second chamber. The device thus provides for a large holding force when the valve body closes the opening and a small resistance to movement after the valve body is moved from closed. By providing two spring-biassed valve bodies acting in opposed directions, control of movements of objects in opposite directions is obtained.