Fluid handling – Line condition change responsive valves – Pilot or servo controlled
Reexamination Certificate
2002-08-05
2004-06-08
Krishnamurthy, Ramesh (Department: 3753)
Fluid handling
Line condition change responsive valves
Pilot or servo controlled
C137S614200
Reexamination Certificate
active
06745792
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a hydraulic relief valve capable of preventing mutual interferences due to the direct collisions of feedback fluid when draining a high-pressure hydraulic fluid into a pressure-oil tank in order to protect a hydraulic circuit in case that the hydraulic fluid discharged from a hydraulic pump mounted in construction equipment and the like reaches a pressure value set in the hydraulic circuit.
2. Description of Prior Art
In general, the heavy construction equipment such as an excavator drives an actuator such as a hydraulic cylinder mounted to the excavator by means of a hydraulic fluid discharged from a hydraulic pump for work, the hydraulic fluid from the hydraulic pump is supplied to various actuators via a control valve controlling flow directions thereof, so that, in case that a high pressure excessive of a working pressure set in the hydraulic circuit occurs, a relief valve is mounted in the control valve to constantly maintain the working pressure by draining the working fluid into the pressure-oil tank.
Accordingly, if the performance of the relief valve is deteriorated, the working performance of a corresponding actuator is deteriorated as well as high-frequency coupling and chattering phenomena occur during the drain of the high-pressure fluid, to thereby make worse the workability and reliability on the equipment due to noisy sounds tormenting drivers.
FIG. 1
is a cross-sectioned view of a conventional hydraulic relief value.
As shown in
FIG. 1
, the hydraulic relief valve comprises a sleeve
5
, a main poppet
1
controlling a feedback fluid v on the side of the main poppet which is drained into a pressure-oil tank T by opening and closing a throttle d of the sleeve
5
, and a feedback fluid path c on the side of a pilot poppet which drains a high-pressure working fluid in case that a high pressure over a set value in a back-pressure chamber b formed in the sleeve
5
occurs.
Further, comprised is a valve seat
7
centered with a through-hole
7
a
and supported at the outlet of the sleeve
5
, and a pilot poppet
2
supported to open and close the through-hole
7
a
of the valve seat
7
and for opening the through-hole
7
a
when a high pressure over a set value in the back-pressure chamber b occurs and draining into the pressure-oil tank T a feedback fluid w on the side of the pilot poppet via the feedback fluid path c.
A reference numeral
3
not described in the drawing denotes an elastic member pressure-supporting the pilot poppet
2
and elastically biasing the closed through-hole
7
a
in an initial state, and
8
an elastic member pressure-supporting the main poppet
1
and elastically biasing the closed throttle d in an initial state.
Accordingly, a working fluid discharged from a hydraulic pump P have the same pressure as an internal pressure of the back-pressure chamber b past the throttle a of the main poppet
1
, and the main poppet
1
maintains the closed throttle d of the sleeve
5
in an initial state by a pressure difference at both ends thereof due to a difference of diameters D1 and D2(D1<D2) thereof, so the feedback fluid v on the main poppet side is not drained into the oil tank T.
If the pressure of the working fluid flowing into the back-pressure chamber b discharged from the hydraulic pump P becomes excessive of the elastic coefficient of the elastic member
3
pressure-supporting the pilot poppet
2
, and the pilot poppet
2
overcomes an elastic force of the elastic member
3
and is shifted to the right direction of the drawing, so the high-pressure hydraulic fluid in the back-pressure chamber b passes the throttle e of the valve seat
7
and the feedback fluid path c on the pilot poppet side in order and drains into the oil tank T and the working pressure in the back-pressure chamber b becomes less than that of the hydraulic fluid discharged from the hydraulic pump P.
As such, upon shifting the main poppet
1
to the right direction of the drawing, the feedback fluid v on the main poppet side, which is discharged from the hydraulic pump P, is drained to the oil tank T through the throttle d of the sleeve
5
and a drain hole
5
d
of the sleeve
5
which are opened, so the pressure of hydraulic fluid discharged from the hydraulic pump P does not increase any further.
In the meantime, upon shifting the pilot poppet
2
to the left direction of the drawing by a restoration force of the elastic member
3
pressure-supporting the pilot poppet
2
with a fallen pressure inside the back-pressure chamber b, the through-hole
7
a
of the valve seat
7
is closed and the pressure inside the back-pressure chamber c increases again, so the main poppet
1
shifts to the left direction of the drawing due to a pressure difference of both ends caused by a difference of the diameters D1 and D2 thereof and then the pressure set in the hydraulic circuit can be maintained.
However, if the hydraulic fluid discharged from the hydraulic pump P reaches a set pressure value, for the hydraulic fluid of the back-pressure fluid chamber b, the feedback fluid w on the pilot poppet side which is drained into the hydraulic tank T through the throttle e and the feedback fluid path c on the pilot poppet side, and the feedback fluid v on the main poppet which is discharged from the hydraulic pump P and drained into the hydraulic tank T through the throttle d of the sleeve
5
and a drain hole
5
d
are collided to each other and collected into the hydraulic tank T, so a noise problem producing fluid-current sounds in the collisions occurs as well as another problem rises in which the inherent working performance of the hydraulic relief valve is deteriorated due to hydraulic mutual interferences.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a hydraulic relief valve capable of preventing a feedback fluid on a pilot poppet side and a feedback fluid on a main poppet side from collisions when drained into a hydraulic tank by relief valve operations to minimize the occurrence of fluid-current sounds and of securing a smooth operation performance of the relief valve due to hydraulic interferences.
In order to achieve the above object, in a hydraulic relief valve having a sleeve, a main poppet shiftably coupled inside the sleeve and for opening and closing a throttle of the sleeve, a feedback fluid paths formed inside the sleeve for draining hydraulic fluid into a pressure-oil tank upon occurrence of a high pressure over a pressure value set in a back-pressure chamber formed inside the sleeve, a valve seat supported at an outlet of the sleeve and having through-holes, and a pilot poppet supported to open and close the through-holes and for draining the hydraulic fluid into the oil tank through the feedback fluid paths upon the occurrence of the high pressure of the back-pressure chamber, a preferred embodiment of the present invention provides an annular interference-preventing projection formed on an outer periphery of the sleeve and placed at boundary portions of the feedback paths of the feedback fluid on the main poppet side through the throttle of the sleeve and the feedback fluid on the pilot poppet side which passes a feedback fluid path formed inside the sleeve, to thereby prevent the feedback fluid on the main poppet side and the feedback fluid on the pilot poppet side from direct collisions when the feedback fluids are respectively drained into the oil tank.
Preferably, according to a preferred embodiment of the present invention, the annular interference-preventing projection is formed in one body on the outer periphery of the sleeve.
Further, the annular interference-preventing projection is machined as a part separated from the sleeve and fixedly coupled to the outer periphery of the sleeve.
Yet further, the annular interference-preventing projection is screw-coupled to a screw part formed in the outer periphery of the sleeve.
Furthermore, the annular interference-preventing projection is fixedly welded to the outer periphery of the sleeve.
R
Harness & Dickey & Pierce P.L.C.
Krishnamurthy Ramesh
Volvo Construction Equipment + Holding Sweden AB
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