Variable assist power steering control valve

摘要

A variable assist power steering system for an automotive vehicle, the system having a source of hydraulic fluid (10), a power steering assembly (30) having a low speed inlet (32) and a high speed inlet (34), and a control valve (50) for continuously delivering hydraulic fluid to the low speed inlet and for delivering fluid to the high speed inlet only at vehicle speeds above a predetermined level. The control valve has an annular spool (64) which moves freely within a cylindrical housing (52), and it has a second spool (74) which is caused to move linearly by a solenoid (86) which acts on the one end thereof and a spring (88) which acts on the other end thereof. The second spool has a central portion (76) which is positioned within the annular spool and which defines an annular passage (68) therewith. The second spool further has enlarged end portions (78, 80) positioned outside of the ends of the annular spool to permit fluid to flow into the annular passage from each end. Energization of the second spool by the solenoid, which is accomplished in response to vehicle speed by speed responsive control devices (120, 130), will cause the annular spool to move with the second spool to maintain substantially balanced hydraulic flow into the annular passage from each of its ends. The annular spool has a flow path (66, 70) which communicates with the low speed inlet in both the solenoid energized and solenoid de-energized positions of the second spool, and a flow path (72) which communicates with the high speed inlet only in the solenoid de-energized position of the second spool.