Patent ID: 8091584

Claim:
An actuator position control device comprising: an electrically controlled servo-valve including a hydraulic distributor having at least one high pressure (HP) supply hole, at least one low pressure (LP) outlet and at least two use holes, each use hole being connectable to high pressure or low pressure, depending on the controlled position of a slide of the hydraulic distributor; and an actuator including a slide carrying at least two stages and being slidable in a cylinder, the actuator having two control chambers connected to respective use holes of the servo-valve distributor and each situated on one side of a respective stage and an intermediate chamber connected to high or low pressure and situated between another side of each of the said stages, the hydraulic distributor slide being taken, in the event of electrical control failure, to a safety position in which it causes the immobilization of the actuator slide substantially in its position at the moment of the failure, wherein in the safety position of the hydraulic distributor slide, the actuator control chambers are taken, via their connection with the distributor use holes, to a same low or high pressure opposed to a pressure applied in the intermediate chamber so that each actuator slide stage is then subjected to high pressure on one of the sides and to low pressure on the other side, and sealing between each of the said stages of the actuator slide and the actuator cylinder is carried out by a dynamic seal which is elastically deformable under an effect of a pressure difference between the sides of each of the said stages to produce a frictional force between each of the said stages and the cylinder, which increases as a function of the difference between the pressures exerted on the two sides of the stage.