Fluid handling – Self-proportioning or correlating systems – Self-controlled branched flow systems
Reexamination Certificate
1998-11-06
2001-01-16
Michalsky, Gerald A. (Department: 3753)
Fluid handling
Self-proportioning or correlating systems
Self-controlled branched flow systems
C060S405000, C180S406000
Reexamination Certificate
active
06173728
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a valve for use in a hydraulic power steering system.
BACKGROUND OF THE INVENTION
A hydraulic power steering system for a vehicle includes a steering control valve. The control valve controls the pressure of hydraulic fluid flowing between a pump, a reservoir, and a hydraulic power steering actuator. A steering linkage connects the actuator to a pair of steerable vehicle wheels. When the driver of the vehicle rotates the steering wheel, the control valve responds by varying hydraulic fluid pressures in the actuator. The system thus provides hydraulic power steering assistance to the steerable wheels that are linked to the actuator.
The pump is driven by the vehicle engine. If the engine fails, the pump may fail to provide a flow of hydraulic fluid that is sufficient to operate the actuator. Therefore, a hydraulic power steering system may include an auxiliary pump which is driven by a ground-engaging vehicle wheel or other driving means. If the engine should fail while the vehicle is in motion, the auxiliary pump can provide a flow of hydraulic fluid sufficient for operating the actuator. Such a steering system further includes a switching valve between the control valve and the two pumps. The switching valve directs hydraulic fluid to the control valve selectively from the two pumps.
SUMMARY OF THE INVENTION
The present invention comprises a switching valve for use in a hydraulic power steering system with a primary pump, an auxiliary pump, and a steering control valve.
The switching valve includes a longitudinally movable valve spool. A spring biases the spool to a neutral position. The switching valve is configured to direct hydraulic fluid from the primary pump to the control valve when the spool is in a primary position, and to direct hydraulic fluid from the auxiliary pump to the control valve when the spool is in an auxiliary position. The spool is movable against a bias of the spring from the neutral position to the primary position under the influence of a hydraulic fluid pressure differential between the opposite ends of the spool.
In accordance with a principal feature of the present invention, the switching valve defines a pair of flow paths for directing fluid from the primary pump to the opposite ends of the spool when the spool is in the neutral position. One of the flow paths is constricted relative to the other. As a result, the hydraulic fluid pressure differential develops more rapidly than if one of the flow paths were not relatively constricted.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other features of the present invention will become apparent to one skilled in the art to which the present invention relates upon reading the following description of the invention with reference to the accompanying drawings, wherein:
FIG. 1
is a view of an apparatus including a switching valve comprising a preferred embodiment of the present invention;
FIG. 2
is a view similar to
FIG. 1
showing certain parts of the switching valve in shifted positions;
FIG. 3
also is a view similar to
FIG. 1
, with certain parts of the switching valve being shown in differently shifted positions; and
FIG. 4
is a view taken on line
4
—
4
of FIG.
1
.
REFERENCES:
patent: Re. 25036 (1961-09-01), Donner et al.
patent: 3279558 (1966-10-01), Allen et al.
patent: 3280557 (1966-10-01), Sattavara
patent: 3747725 (1973-07-01), Feustel et al.
patent: 4237993 (1980-12-01), Jablonsky
patent: 5257670 (1993-11-01), Miller et al.
patent: 1555906 (1970-01-01), None
patent: 926831 (1963-05-01), None
patent: 2001287 (1979-01-01), None
patent: 2049585 (1980-12-01), None
patent: 1593974 (1981-07-01), None
patent: 2151996 (1985-07-01), None
patent: 2154188 (1985-09-01), None
A copy of European Search Report dated Feb. 2, 2000.
Hudgens Bernard C.
Stingley Lowell D.
VanderMolen Gary L.
Venable Frederick D.
Michalsky Gerald A.
Tarolli, Sundheim, Covell Tummino & Szabo L.L.P.
TRW Inc.
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