| 摘要 |
<p>A rotary valve for a hydraulic power steering gear, has a sleeve (11) with slots (19a-b) journalled to an input-shaft (10) with grooves ( 18a-c), the co-acting sleeve slots and input-shaft grooves defining axiall y extending orifices. The orifices are ported as a network such that they form primary and secondary hydraulic Wheatstone bridges arranged i n parallel, each bridge comprising two limbs each of which incorporate inlet and return orifices communicating to respective inlet and return ports of the valve. The limbs of the primary bridge incorporate means providing hydraulic communication to one of the cylinder port, whereas the limbs of the secondary bridge do not incorporate such means. The return orifice (34a, 34b) in each secondary brid ge limb is formed by a metering edge contour on the edge of a secondary return groove (18c) and circumferentially overlapping an adjacen t sleeve bore land when the valve is in its neutral position to such an extent such that the return orifice provides a restriction to hydraulic flow for all valve operating angles thereby applying a back pressure to the upstream inlet orifice. The back pressure being sufficient t o significantly suppress the generation of cavitation noise in the inlet orifice.</p> |
