Fluid handling – Systems – Multi-way valve unit
Reexamination Certificate
2000-03-09
2001-06-05
Chambers, A. Michael (Department: 3753)
Fluid handling
Systems
Multi-way valve unit
C137S625240, C091S37500R
Reexamination Certificate
active
06240961
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a hydraulic fluid control valve for a power steering gear. In particular, the present invention relates to a control valve that can help to reduce brake shudder, that is, a vibration from a vehicle's brakes into the vehicle steering system.
2. Description of the Prior Art
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 on opposite sides of a piston in a hydraulic motor. When the core and the sleeve are in neutral positions, the hydraulic fluid pressures in the opposed fluid chambers are equal. When the core and the sleeve are rotated from the neutral 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 so as to provide hydraulic power steering assist in the steering gear.
SUMMARY OF THE INVENTION
In accordance with the present invention, an apparatus comprises first and second relatively rotatable valve members which direct hydraulic fluid to flow between the valve members from inlet ports to return ports. The valve members have radially opposed lands and grooves defining orifices that enlarge and orifices that constrict upon relative rotation of the valve members from neutral positions through a range of movement of the valve.
A pair of the constricting orifices are located in parallel between the inlet ports and the return ports. Each of those parallel constricting orifices is defined by a chamfered corner of a corresponding one of the lands. Additionally, the valve members comprise means for providing back pressure at selected orifices between the outlet ports and the inlet ports, the selected orifices including only one of the pair of parallel constricting orifices.
The back pressure is provided by a third land which is spaced from the pair of lands and which defines a third orifice located in series with the one of the pair of parallel constricting orifices. The third orifice has a constant size for all relative positions of the first and second valve members through the range of movement of the valve.
This increase in back pressure helps to limit unwanted piston movement and thereby reduce brake shudder, that is, undesired vibration of the steering wheel when on center.
REFERENCES:
patent: 5244012 (1993-09-01), Tabata et al.
patent: 5263512 (1993-11-01), Emori et al.
patent: 5458153 (1995-10-01), Roeske
patent: 5562124 (1996-10-01), Behrens et al.
patent: 5794507 (1998-08-01), Strong
patent: 5799693 (1998-09-01), Strong
patent: 6082403 (2000-07-01), Strong
Chambers A. Michael
Tarolli, Sundheim, Covell Tummino & Szabo L.L.P.
TRW Inc.
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