Five-position hydraulic actuating apparatus

Hydraulic actuating apparatus with digital input, of the type comprising a movable output member occupying, when at rest, a neutral position towards which it is urged by resilient centring means and capable of moving in opposition to these last to both sides of the said neutral position so as to occupy one or other of two working positions defined by stop means, the displacements of this movable member being caused by opposing hydraulic actuating means each allocated to one direction of displacement and themselves selectively controlled by two two-position control members receiving input commands of a digital nature, characterized by the fact that, to create without resorting to additional control means two additional working positions for the movable output member which are also defined by stop means and to thus obtain five different positions of equilibrium by means of only four binary control words, each of the hydraulic actuating means is composed of two active areas (s.sub.1, s'.sub.1 ;

• s.sub.2, s'.sub.2) acting in the same direction on the movable output member (10) and coming into action one after the other so as to transmit two successive displacement steps to the said member, the putting under pressure of the first (s.sub.1 ;
• s.sub.2) of these areas being caused by one (EV.sub.1 ;
• EV.sub.2) of the two control members, and that of the second area (s'.sub.1 ;
• s'.sub.2) by the other control member (EV.sub.2 ;
• EV.sub.1), this only being made possible, however, when the movable member has already completed a first displacement step in the direction concerned.