| 摘要 |
PCT No. PCT/AU96/00267 Sec. 371 Date Oct. 30, 1997 Sec. 102(e) Date Oct. 30, 1997 PCT Filed May 3, 1996 PCT Pub. No. WO96/34789 PCT Pub. Date Nov. 7, 1996A low noise rotary valve for a hydraulic power steering gear offering flexibility in the design of the boost characteristic has inlet ports to receive hydraulic fluid from a pump, return ports to return hydraulic fluid to the pump, and cylinder ports to communicate the hydraulic fluid to left and right-hand cylinder chambers of the hydraulic power steering gear. The valve has an input-shaft with a plurality of axially extending grooves separated by lands. A sleeve that has in its bore an array of axially extending slots that circumferentially align with the lands on the input-shaft is journalled on the input-shaft. A torsion bar residing in a bore of the input-shaft compliantly connects the input-shaft to a driven member. The interfaces between the co-acting input-shaft grooves and sleeve slots define axially extending orifices which open and close when relative rotation occurs between the input shaft and the sleeve. These orifices are ported as a network such that they form primary and secondary hydraulic Wheatstone bridges each having right and left-hand inlet orifices and return orifices. Hydraulic flow from the primary bridge is hydraulically communicated to the return port via a primary return path and the hydraulic flow from the secondary return path is hydraulically communicated to the return port via a secondary return path. The secondary return path contains an annular restriction having a cross-section to flow which has a high aspect ratio. Thus, the return path of each secondary bridge provides a restriction in hydraulic flow to the upstream orifices that causes a back pressure to be applied to the secondary upstream orifices. This back pressure significantly suppresses the generation of cavitation noise in the upstream secondary orifices.
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