The invention relates to an electromechanical-hydraulic
piston actuator (2) for providing pressurized pressure medium for a
brake system of a vehicle, comprising an
electric motor (6) having a statorand a rotor (10), a rotation-translation gearing (32) which is driven in rotation by the
electric motor (6) and which has a rotatable nut (40) and a
threaded rod (48) that is prevented from rotating and mounted so as to be able to slide in its axial direction, a
piston (50) coupled to the
threaded rod (48) in the axial direction thereof, a
hydraulic cylinder (58) with a hydraulic chamber (56) which is filled with pressure medium and into which the
piston (50) can be displaced, by a translatory movement of the
threaded rod (48), from a retracted piston position in the direction of an advanced piston position in order to pressurize the pressure medium and / or expel same from the chamber (56), and a
hydraulic connection (60) which is connected to the chamber (56) and via which pressure mediumcan be expelled from the chamber (56), and a supporting structure (3) to which the
electric motor (6), the rotation-translation gearing (32) and the
hydraulic cylinder (58) are attached, there being provided, between the rotor (10) of the electric motor (6) and the nut (40), an isolation device (70) for piston-travel-controlled isolation of the rotary
coupling.