Distribution device for a hydraulic servo-mechanism operating silently.
1. Distribution device for a hydraulic servo mechanism operating silently, particularly for a power steering mechanism, comprising two cylindrical fluid distributing elements arranged in coaxial relationship and adapted for limited relative rotation around their common axis in either sense with respect to a relative neutral position overcoming the force of biassing means (18), the distributing elements having orifices and cavities defining a fluid path (26) between a pressure fluid source (27) and a fluid reservoir (28), the fluid path including two parallel branches (56, 57) having variable section passage means operating via overlap of the contacting cylindrical surfaces of the distributing elements and having in first line, in each of the branches, two types (a, b) of passages showing opposite sense of cross-sectional variation when rotated out of the relative neutral position in either direction, the two passage means of said two types being connected in series between the pressure fluid source and the reservoir, the portion of the fluid path defined between the passage means of said two types communicating with a working pressure fluid tap (37, 39) of the respective branch ; characterized in that two passages of the same type (61a-61b, 62a-62b) are arranged in each branch between said pressure fluid tap and the fluid reservoir, i.e. principal passage means (61a, 61b) having priority closing characteristics viz. secondary passage means (62a, 62b) having posterior closing characteristics ; and in that said secondary passage means and a flow restricting element (63) are connected in series, said series connection formed by the secondary passage means and the flow restricting element being in turn shunted in parallel across the principal passage means.