Three position actuator system

The three position actuator system has an actuating cylinder (1) with a piston which can be acted upon by pressure medium on both sides, can be controlled via control elements (21, 22), such as directional control valves, and is coupled to a selection element (11), such as, for example, a selector fork or selector rod. The piston comprises two oppositely acting double pistons (3, 4) displaceable in a common cylinder housing (2), and assigned to each of the two double pistons (3, 4), there is in the cylinder housing (2) a pressure space (5, 6) with a pressure-medium connection (7, 8). The first piston (9 and 10) of each double piston (3, 4) is connected rigidly in motion to the selection element (11) and the second piston (13, 14) of each double piston (3, 4) is connected in freely displaceable fashion to the first piston (9, 10). In the case of a pressure balance on both sides, the two double pistons (3, 4) are held in the neutral position with their freely displaceable second piston (13, 14) against a stop (15) of the cylinder housing (2) and, when subjected to pressure on one side, can each alternately be displaced out of the neutral position into the selection position, the selecting displacement being imparted to the unpressurised double piston (3 or 4) by both pistons (9 or 10) of the pressurised double piston (3 or 4).