Hydraulic actuator

Abstract

A hydraulic actuator for producing translational movement over a long distance having two jack cylinders with pistons mounted for reciprocal movement and connected to a worm wheel through a worm gear. When a piston is driving, the worm gear acts as a rack to turn the worm wheel and when a piston is being returned to its starting position the worm gear rotates. Means are provided to alternately switch from one cylinder to the other.

We claim:  .[.1. A hydraulic actuator comprising a body structure defining two jack cylinders and ducts for the supply of pressurized hydraulic fluid to, and exhaust of fluid from, said jack cylinders, tow pistons disposed one in each cylinder, each having a helicoidal portion in the form of a screw thread co-acting with a mating portion of an actuator, changeover valve means controlling the admission and exhaust of fluid to and from said cylinders in a manner causing said pistons to reciprocate through power and return strokes with the power stroke of one piston alternating with that of the other and with substantially no time delay between successive power strokes, and means to rotate a selective piston to enable it to move back to its staring position while the other piston drives said mating portion..]. .[.2. An actuator as claimed in claim 1, wherein said jack pistons have a drive connection passing through a seal, said drive connection being rotatable during the return unloaded stroke of said pistons..]. .[.3. An actuator as claimed in claim 1, wherein a plurality of said cylinders is disposed in the available peripheral space around said mating portion..]. .[.4. An actuator as claimed in claim 5, wherein an automatic valve responsive to triggering by path limit detecting means at each end of the stroke of one of said pistons is adapted to pressurize and exhaust said ducts successively with an oscillatory action, whereby no pressure difference exists at one pair of said pistons while one of another pair of said pistons is thrust axially to rotate said mating portion, or to move a linear actuator axially relative to a screwed shaft..]. .[.5. A hydraulic actuator comprising: 
       a. a body structure defining two jack cylinders and ducts for the supply and exhaust of pressurized fluid to and from said cylinders, 
       b. two pistons disposed one in each cylinder, each having a screw threaded portion, 
       c. power transmission means threadingly engaging the screw threaded portion of each piston, 
       d. means to rotate a selective piston to enable it to move back to its starting position while the other piston drives said power transmission means, and 
       e. changeover valve means controlling the admission and exhaust of fluid to and from said cylinders in a manner causing said pistons to reciprocate through power and return strokes with the power stroke of one piston alternating with that of the other and with substantially no time delay between successive power strokes..]. .Iadd. 6. A linear actuator comprising a body structure having a first and a second end and defining a first cylinder and a second cylinder; a first annular piston disposed in said first cylinder and a second annular piston disposed in said second cylinder; a first duct means for continuously communicating a first chamber defined by said first end and said first piston with a relatively high pressure source; a second duct means for continuously communicating a second chamber defined by said second end and second piston with a relatively low pressure source; changeover valve means controlling the admission and exhaust of relatively high pressure fluid to and from a third chamber defined between said first and second pistons in a manner causing said pistons to reciprocate through power and return strokes with the power stroke of one piston alternating with that of the other and with substantially no time delay between successive power strokes; a shaft extending co-axially through said pistons in threaded engagement therewith, means for preventing rotation of the shaft and motor means connected to rotate each piston during its return stroke so that upon admitting high pressure to said third chamber said second piston causes axial movement of the shaft in the direction of the second end and the motor means rotates the first piston such as to cause its movement relative to the shaft and the body structure in the direction of the first end, while upon venting said third chamber, said first piston causes axial movement of the shaft in the direction of the second end and the motor means rotates the second piston such as to cause its movement relative to the shaft and the body structure in the direction of the first end. .Iaddend..Iadd. 7. The actuator of claim 6, including path limit detecting means and an automatic valve responsive to triggering by said path limit detecting means at each end of the stroke of one of said pistons, said valve being adapted to pressurize and exhaust said third duct successively to produce oscillatory motion of said pistons and ensure there is no pressure difference across each piston during its return stroke.