Constant speed actuator

Claim 1

A fluid actuated and hydraulically damped actuator for ensuring a constant speed of actuation over the working length of a load piston, regardless of external piston loading or fluid supply pressure, comprising, in combination: (A) a cylindrical housing comprising a constant diameter cylinder having a first end wall and a second end wall, respectively closing each end of said cylinder, with a fluid pressure supply port at said first end wall; and (B) a centrally disposed load shaft extending through said second end wall and inwardly into said cylinder, a load piston secured onto the inward extension of said load shaft to thereby define a hydraulic damping chamber in an annular space between said second end wall and said load piston, said load piston being sealingly engaged for longitudinal travel within said cylinder; and (C) a drive piston, comprising a free piston sealingly engaged for longitudinal travel within said cylinder, and spaced from said first end wall to define an actuation chamber, and spaced from said load piston to define a hydraulic working chamber; and (D) a first hydraulic passage, communicating with said hydraulic damping chamber and a second hydraulic passage communicating with said hydraulic working chamber; and (E) a first hydraulic line means fluidly interconnecting said first hydraulic passage, comprising at least one orifice on said load shaft, and a first port of a bypass valve, and a second hydraulic line means fluidly interconnecting said second hydraulic passage and a second port of said bypass valve, wherein said both hydraulic chambers, said first and second hydraulic line means and said bypass valve are filled with, and define, a closed volume of hydraulic fluid, wherein further; (F) said bypass valve partially extends inwardly from said load piston and is disposed at least partially within the inward extension of said load shaft, and said free piston includes a recess in a first surface thereof which is adapted to accept the extension of said bypass valve when the volume of said hydraulic working chamber approaches a minimum; wherein said bypass valve is operable to automatically allow only a constant volumetric flow rate of fluid to pass between said first and second ports regardless of variable hydraulic pressures in said first and second hydraulic line means whereby speed of actuation of said load shaft will remain substantially constant, whenever fluid pressure supplied to said supply port is equal to, or above, a threshold value.