Fluid actuated gear changing system

Abstract

A unique double acting piston and cylinder assembly is disclosed wherein the assembly can be moved to any one of three positively determined positions by application of fluid pressure to any one of three ports. The cylinders include first and second pistons attached to an output shaft for movement therewith, third and fourth pistons slidably mounted on the shaft between the first and second ones, a first stop within the cylinder to limit the movement of the adjacent first and third pistons, a second stop to limit the axial movement of the second and fourth pistons, an extension on the third piston and extending toward the first piston for reaching beyond the first stop to contact and move the first piston, an extension carried by the fourth piston and protruding toward the second piston for reaching beyond the second stop in contacting and moving the second piston, and first, second and third ports on the cylinder for passing fluid under pressure respectively between the two inner, third and fourth, pistons and at the ends of the cylinder whereby any of the three positions can be obtained with pressure supplied to one port with the other two vented. Vents in the cylinder between the first and third pistons and the second and fourth pistons prevent build up of a pressure differential therebetween.