| 摘要 |
The invention provides an actuator (12) having a piston (18) moveable within a cylinder (20), and a piston rod (22) extending from the piston and providing an actuator ram (14). The piston divides the cylinder into a cylindrical chamber (24) and an annular chamber (26), and a fluid direction control valve (34) controls the supply of fluid between these chambers and a fluid supply line (30) and a fluid return line (32). The actuator is arranged to have first and second modes of operation during extension of the piston rod, the actuator in the first mode having the fluid supply line in communication with the cylindrical chamber and the annular chamber in communication with the fluid return line and in the second mode having the fluid supply line in communication with the cylindrical chamber and the annular chamber connected directly or indirectly to the cylindrical chamber. The actuator system also includes means (36, 38; 102, 104, 106) for automatically switching the actuator from one mode to the other mode. |
