POWER STEERING GEAR VALVE

摘要

A rotary valve for a hydraulic power steering gear has a sleeve with slots journalled to an input-shaft with grooves, the co-acting sleeve slots and input-shaft grooves defining axially extending orifices. The orifices are ported as a network such that they form primary (29) and secondary (30) hydraulic Wheatstone bridges arranged in parallel, each bridge comprising two limbs each of which communicates inlet and return orifices to respective inlet and return ports of the valve. The limbs of the primary bridge hydraulically communicate to a respective one of the cylinder ports (4, 5) at an interconnection point of the respective inlet and return orifices in that limb. The secondary bridge limbs do not hydraulically communicate to the cylinder ports. Hydraulic flow from the primary and secondary bridges is hydraulically communicated to the return port via respective primary and secondary return paths. The secondary return path has an annular restriction (71) having a cross section to flow which has a high aspect ratio.