Patent ID: 6892598

Claim:
A gear change mechanism for a gearbox in which changes of gear ratio in the gearbox are made mechanically in response to actuating signals, the mechanism including first and second actuator assemblies each connected to a gearbox gear change selector, the selector being movable about an axis and in the direction of said axis to a plurality of positions for effecting changes of gear in the gearbox, the first actuator assembly being arranged to move the selector in said axial direction between a plurality of axial positions, the selector having a radially outwardly directed arm, the second actuator assembly being directly drivingly connected to said arm to transmit reciprocal movement of the actuator to provide rotational movement of the selector about said axis between a plurality of rotational positions, each of the first and second actuator assemblies including a cylinder, a shaft located in the cylinder and drivingly connected to the selector, and a piston located about said shaft for movement axially of said shaft, and in each case the cylinder shaft and piston together define chambers into which pressure fluid is selectively introduced so that the shaft is movable to at least three different axial positions, wherein the shaft of the first actuator is substantially perpendicular to the shaft of the second actuator, and the gear change mechanism comprises two fluid control valves being selectively operable to admit fluid to the chambers and thereby move the shaft, and wherein the cylinder shaft and piston provide four chambers within the cylinder, and each chamber is connectable to a source of pressure fluid, connection being selectable to effect movement of the shaft to any one of said positions.