| 摘要 |
A power assisted gear assembly in which a piston 3 forms with its cylinder opposed chambers 4, 5. Displacement of the piston provides a steering output and such displacement is effected by rotation of an input component 6 which screw threadedly engages the piston 3. Two fluid systems are provided with respective inlets 18, 20 and with the chambers 4, 5 being located one in each fluid system. A valve 10, 15, 16 adjusted by the input component 6 when displacing the piston 3 controls fluid flow through the two fluid systems to an outlet 29 and such valve has a neutral condition to which it is biased by springs 25, 26 or by fluid pressure in the fluid systems in which both fluid systems communicate with the outlet 29 for an open center system. The adjustable part 10 of the valve is in the form of an axially displaceable bearing for the component 6 or a circumferentially displaceable nut through which the piston 3 is driven from the component 6 and this adjustable part is adjusted from the neutral condition of the valve by rotation of the input component 6 and in response to the reaction from the force applied to displace the piston 3 so that such adjustment closes one or the other of the fluid systems, the fluid system which is closed being that in which is located the chamber 4, 5 which under fluid pressure provides assistance to displacement of the piston 3 in the same axial direction as that in which it is driven by rotation of the component 6. There is also disclosed a steering system in which fluid pressure to the inlet ports 18, 20 is derived from the outlets 31, 34 of a flow divider 32.
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