| 摘要 |
<p>A power assisted steering gear has an internal valve member 10 capable of restricted rotation in response to a steering input relative to a valve sleeve 11 rotatable with a pinion 4 driving a rack bar 3. The valve sleeve 11 is rotatable in a cylinder 9 of a valve housing 2 and has an annular recess 25 in an external annular face 12. Recess 25 provides a fluid pressure conduit from an input port 26 and fluid flow is controlled by control ports 13, 14 between the valve members 10 and 11 in response to restricted relative rotation between those members. At axially opposite ends of the annular face 12 the valve sleeve 11 forms alternating pressure chambers 35, 36 communicating with ports in the housing 2 for connection to a power assistance ram. Chambers 35 and 36 communicate through passages 39 and 44 with the control ports 13, 14 to control fluid flow to and from the power assistance ram as directed in response to a steering input. By providing the pressure chambers 35 and 36 at the ends of the annular face 12 that face may incorporate a single annular recess 25 and thereby be of relatively short axial length which permits the use of axially short valve members and a corresponding reduction in the axial extent of the valve housing 2 and thereby the space necessary to accommodate the gear. Valve members 10 and 11 are rotationally biased relative to each other and to a neutral condition of the ports 13, 14 by a "C"-shaped spring 21. Exhaust fluid from the control ports and the power assistance ram may return to a reservoir by way of passages 33, 27a, 32a, 32 and outlet port 31.</p> |
