Gearbox mechanism

A gear change mechanism is provided which is intended for a gearbox in which changes of the gear ratio in the gearbox are made mechanically in response to actuating signals. The mechanical movements required are as for a conventional gearbox having a H type pattern. A gearbox selector is mounted for movement about an axis and in the direction of the axis. The selector is operable by two actuators (and ), one to move the selector about its axis and the other to move it in the axial direction. Each actuator can be similar having a cylinder and a shaft and annular pistons located about the shaft. For the rotational movement of the selector three positions are required, a neutral, a gear engaged position in one direction and a gear engaged position in the other direction. For movements in the direction of the axis two, three or four positions are required depending upon whether it is a two, three or four rail gearbox. An actuator is proposed which is capable of three, four, or more, positions of movement.