Actuator

Claim 1

An actuator, operable by hydraulic fluid under pressure, comprising, in combination, an axially elongated cylinder having a non-circular cross-section throughout its length and having a central axis; end walls closing the opposite ends of said cylinder; first and second non-circular and non-rotatable axially spaced pistons in said cylinder in direct engagement with the interior surface thereof and dividing said cylinder into first and second end chambers and an intermediate chamber; a piston rod extending through said pistons and said end walls, to project beyond said end walls, coaxially with said center axis, said piston rod being rotatable relative to said pistons; means restraining relative axial displacement of said piston rod and said first piston; said piston rod being formed with at least one male spiral thread and said second piston being formed with at least one female spiral thread engaged with a respective said male spiral thread; first and second relief pressure valves in said first piston communicating with said first chamber and said intermediate chamber, and opening in respective opposite axial directions; said first relief pressure valve opening toward said first chamber and said second relief pressure valve opening toward said intermediate chamber; and first and second port means in respective end walls for selectively supplying hydraulic fluid to said chambers and exhausting hydraulic fluid therefrom, said first port means communicating with said first chamber and said second port means communicating with said second chamber; whereby, when said first port means is connected to exhaust and said second port means is connected to a source of hydraulic fluid under pressure, said first and second pistons will advance said piston rod, without rotation thereof, toward the end wall having said first port means with said first relief pressure valve blocking communication between said first chamber and said intermediate chamber until said first piston is blocked from further movement toward the end wall having said first port means; said second piston then advancing toward said first piston with the pressure in said intermediate chamber opening said first relief pressure valve to exhaust fluid from said intermediate chamber into said first chamber and out through said first port means, said second piston, due to its threaded engagement with said piston rod, rotating said piston rod; said first and second pistons, upon connection of said first port means to a supply of hydraulic fluid under pressure and said second port means to exhaust, initially moving said piston rod without rotation in a direction toward the end wall having said second port means with said second relief pressure valve blocking communication between said first chamber and said intermediate chamber; upon blockage of movement of said piston rod toward said end wall having said second port means and continued supply of hydraulic fluid to said first port means, said second relief pressure valve connecting said first chamber to said intermediate chamber opens to increase the pressure in said intermediate chamber to advance said second piston toward the end wall having said second port means to effect reverse rotation of said piston rod.