Centering mechanism for a power steering control valve

Details Centering mechanism for a power steering control valve Centering mechanism for a power steering control valve

1998-01-16

2001-05-29

Lopez, F. Daniel (Department: 3745)

Motors: expansible chamber type

Working member position feedback to motive fluid control

Follower type

C137S625230

Reexamination Certificate

active

06237464

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a hydraulic fluid control valve for a power steering gear.
BACKGROUND OF THE INVENTION
A known hydraulic fluid control valve for a power steering gear includes a valve core rotatable within a valve sleeve. The core and the sleeve control the pressure of hydraulic fluid flowing through the valve between a pump, a reservoir, and a pair of opposed fluid chambers in a hydraulic motor. When the core and the sleeve are in centered positions, the hydraulic fluid pressures in the opposed fluid chambers are equal. When the core and the sleeve are rotated from the centered positions, a plurality of lands and grooves on the core and the sleeve cooperate to increase the hydraulic fluid pressure in one of the opposed fluid chambers, and thereby to provide hydraulic power steering assist in the steering gear.
Such a valve may also include a centering mechanism. The centering mechanism resists rotation of the core and the sleeve from their centered positions, and urges them to return to their centered positions.
SUMMARY OF THE INVENTION
In accordance with the present invention, an apparatus comprises first and second relatively rotatable valve members and a centering mechanism. The valve members are configured to direct hydraulic fluid between the valve members in accordance with their rotational positions. The centering mechanism includes a movable detent member, a spring, and a cam surface. The cam surface is rotatable with one of the valve members so as to cam the detent member against a bias of the spring upon rotation of the valve members from centered positions.
The cam surface has a central portion defining a recess in which the detent member rests when the valve members are in the centered positions. The cam surface further has a pair of side portions on opposite sides of the groove.
A centering mechanism constructed in accordance with the present invention can function in two stages. This feature of the invention is accomplished by the configuration of the cam surface. When the valve members are initially rotated from the centered positions, the central portion of the cam surface engages the detent member so as to cam the detent member outward from the recess against the bias of the spring. The restoring force exerted by the spring increases at a first rate in accordance with the angle at which the central portion of the cam surface opposes the restoring force of the spring. If the valve members are rotated sufficiently for the cam surface to cam the detent member fully out of the recess, one of the side portions of the cam surface will move against the detent member to cam the detent member further against the bias of the spring. The restoring force of the spring will then increase at a second, lower rate in accordance with a greater angle at which the side portion of the cam surface opposes the restoring force. In a hydraulic power steering gear, the centering mechanism can thus function in a first stage in which the restoring force increases at a first rate for relatively low steering angles, and subsequently in a second stage in which the restoring force increases at a second, lower rate for relatively greater steering angles.


REFERENCES:
patent: 2360987 (1944-10-01), Temple
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patent: 4877100 (1989-10-01), Emori et al.
patent: 5230273 (1993-07-01), Fraley, Jr.
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patent: 5562016 (1996-10-01), Schoffel
patent: 5571238 (1996-11-01), Breitweg et al.
patent: 5964315 (1999-10-01), Suzuki et al.
patent: 2044697 (1980-10-01), None

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