Patent ID: 8490391

Claim:
A hydrostatic actuator comprising: a master cylinder, including a housing and a piston, wherein the piston is axially displaceable in the housing and applies pressure to a pressure chamber filled with a pressure fluid; a planetary rolling-contact gear system converting a rotary drive into an axial movement, wherein the planetary rolling-contact gear system comprises a sleeve, a gear spindle, and at least one planetary rolling body rolling off therebetween; and, an electric motor driving the planetary rolling-contact gear system, wherein the electric motor comprises a stator fixed to the housing and a rotor rotatable relative to the stator, wherein: the pressure chamber is annularly shaped and the planetary rolling-contact gear system is arranged radially inside the pressure chamber; the at least one planetary rolling body includes first toothing; the sleeve includes first and second radially inwardly extending protrusions; each of the first and second protrusions include second toothing engaged with the first toothing; and, the first and second protrusions are separated, in an axial direction, by a portion of the sleeve free of the second toothing.