| 摘要 |
<p>1. Annular hydraulic jack device, in particular for operating a chuck for clamping parts on a machine tool, comprising a coaxial rotating hydraulic seal, the shaft of which is formed by a tubular extension (3) of an end of the cylinder of the hydraulic jack, received coaxially in rotation in a fixed part (9) in the form of a ring, two main ducts (22a -22b ), each of which comprises at least one annular groove (a, b) provided in the cylindrical middle part of one of the two coaxial and opposite walls which are formed by the external wall of the tubular extension (3) and the internal wall of the fixed part (9), the annular grooves (a and b) of the main ducts of which are provided between two annular collecting grooves (c and d) - themselves provided in the cylindrical middle part of the internal wall of the fixed ring (9) - and the said main ducts leading, respectively, into two compartments defined by an annular piston inside the cylinder of the jack, and inside each of which there is provided a non-return valve which an auxiliary duct, serving to actuate opening of the said valve, joins to the other main duct (22a -22b ) upstream of its own valve, as well as means for alternately connecting one of the inlets of the two main ducts to a source of pressurised hydraulic fluid and the other one to a reservoir storing this fluid at atmospheric pressure, the two non-return valves being accommodated in suitable bores provided on either side of the central opening of the annular jack, in the end of the jack cylinder which is integral with the tubular extension, characterized in that the fixed ring (9) is made of a material having a heat expansion coefficient greater than that of the material from which the tubular extension (3) is made, so that heating of the hydraulic fluid is reduced by the axial distance separating the annular collecting grooves (c and d) and so that the value of the radial operational play between the fixed ring (9) and the tubular extension (3) remains substantially constant at all rotational speeds.</p> |
