| 摘要 |
A hydraulic power assisted vehicle steering system includes a steering input shaft which is journalled for rotation in a housing and fixed axially in the housing; an inner valve sleeve pinned to the input shaft and rotating therewith; and an outer valve sleeve fixed axially in the housing and rotatable about the inner valve sleeve. Turning the steering input shaft causes relative rotation between the inner and outer valve sleeves, directing fluid flow to control directional assist. The inner valve sleeve slides axially between the input shaft and the outer valve sleeve. Axial sliding movement of the inner valve sleeve progressively covers and uncovers wide end portions of fluid control grooves in one of the valve sleeves. When the wide end portions are uncovered, greater relative rotation between the inner and outer valve sleeves is required before assist is generated. The inner valve sleeve is moved axially as a function of vehicle speed, to provide more assist at lower speeds and progressively less assist as vehicle speed increases.
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