Fluid handling – Processes – With control of flow by a condition or characteristic of a...
Reexamination Certificate
1999-05-19
2001-03-06
Michalsky, Gerald A. (Department: 3753)
Fluid handling
Processes
With control of flow by a condition or characteristic of a...
C091S446000, C091S447000, C091S455000, C137S596150, C137S596160, C137S596200, C137S625680
Reexamination Certificate
active
06196247
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a valve assembly for actuation of a user, and a method for actuating such a valve assembly.
The like valve assemblies are employed in mobile hydraulics for actuating single and double-action users such as, for example, hydraulic motors or power lifters. Herein a throttle device whereby the supplied or drained volumetric flow of hydraulic oil may be throttled is arranged in each of the work conduits leading to the user, i.e., in the supply conduit and in the drain conduit.
In
FIGS. 1
to
3
, which shall even now be referred to, several exemplary applications of such known throttle devices are represented.
FIG. 1
shows a valve assembly for actuating a double-action user which may, for example, be a lifting cylinder
200
. To the cylinder chamber and to the annular chamber of the lifting cylinder
200
a work conduit
206
or
208
is connected. For outward movement of the lifting cylinder
200
, the hydraulic oil is supplied via work conduit
206
to the lifting cylinder
200
, with the hydraulic oil displaced from the annular chamber being returned to the tank through the work conduit
208
which acts as a drain conduit.
For the purpose of throttling the hydraulic oil supply and drain, two valve throttles
210
,
212
are arranged in the two work conduits
206
and
208
, the valve members of which are coupled mechanically. The ratio of supply and drain opening of the valve throttles is determined by the mechanical coupling of the opening lands of the common spool, so that at a particular setting of the valve throttle
210
, a pressure loss &Dgr;p
2
will ensue in the drain conduit (work conduit
208
). This pressure loss is undesirable in particular in where single-action users are connected as it does not fulfil a meaningful function. The pressure loss results in energy losses, in heating of the hydraulic oil, and eventually in premature wear of the valve throttle.
In
FIG. 2
a valve assembly for actuating a blower motor
214
is represented. In this alternative, two independently apportionable valve throttles
210
,
212
are used which may each be employed in a motor having two directions of rotation for throttling of the volumetric flow of hydraulic oil in the supply conduit. In a case where a motor having one direction of rotation is used, drain throttling—in this case the valve throttle
212
in the drain conduit
208
—causes unnecessary pressure losses, so that the above specified drawbacks also exist in this type of valve assembly.
FIG. 3
shows an application wherein a lifting cylinder
200
is used for lifting or lowering an extension arm
215
of lifting gear
216
. In order to lift the load m, the cylinder chamber of the lifting cylinder
200
is supplied with hydraulic oil, so that the cylinder moves outward and the extension arm
215
is moved upward in the representation of FIG.
3
. The hydraulic oil present in the annular chamber is displaced as a result of the outward movement and returned to the tank. As a result of the load m exerting a tensile force on the extension arm
215
, a resulting force acts on the lifting cylinder
200
which is maximum when the extension arm
215
extends horizontally and diminishes concurrently with a rotation of the extension arm
215
from this horizontal position. The further the extension arm
215
is lowered into the horizontal position, the higher becomes the weight on the drain side of the lifting cylinder
200
, so that the latter is pressed downward in the representation of FIG.
3
. Due to the rising volumetric drain flow Q
2
, cavitation may occur in the supply conduit which continues to receive a volumetric supply flow Q
1
, whereby the components of the valve assembly are strained in a maximum degree, which may also bring about control instability. For this reason it is also necessary to adapt drain throttling to the lifting conditions of the lifting gear. Under particular operating conditions, such drain throttling generates pressure losses which are not acceptable for the above named reasons.
In order to avoid such unnecessary pressure losses, so-called “non-pressurised tank returns” have, for example, been provided in motor applications for farming tractors, which may be connected to the drain side of the motor by means of a quick coupling and whereby the drain throttle may be bypassed. It is a drawback in such an auxiliary construction that the vehicle must be provided with a separate tank connection piece including a quick coupling, and that the operator must manually connect the non-pressurised tank return. Such an auxiliary construction can be sensibly employed only if it is intended to maintain the respective operating condition over a prolonged period of time. In the case of a change of user actuation, for example a reversal of direction of rotation of the motor etc., ports must be reconnected, so that the requirements in terms of operation are considerably high.
SUMMARY OF THE INVENTION
An object of the present invention is furnishing a valve assembly and a method for controlling a valve assembly, wherein the energy losses in the drain of a user may be reduced to minimum at minimised expense in terms of device technology.
This object is attained by a valve assembly for actuation of a user, comprising a continuously adjustable directional control valve acting as a supply throttle whereby a pump port may be connected to user ports. In the assembly, the user is connected through work conduits to the directional control valve, and in each work conduit a throttle device is arranged such that the drain volumetric flow of hydraulic oil from the user may be adjusted. In addition, each throttle device may be controlled to be open entirely independent of a spool position of the directional control valve.
The present invention is also directed to a method for actuation of such a valve assembly comprising adjusting the volumetric supply flow to the user by actuating the directional control valve and controlling the drain-side throttle device to be entirely open.
By the measure of designing the valve assembly to include throttle devices in the supply and drain conduits and designing them such as to be actuatable independently of a supply throttle, the respective throttle device acting as a drain throttle may at the port of single-action users etc. be set to a maximum cross section of flow, so that the pressure losses in the drain are minimised. The hydraulic oil volume flow is adjusted by means of a directional control valve acting as a supply throttle.
It is preferred to provide the throttle device with two functions, so that it will act as a releasable non-return valve in its one function and may be used for throttling the volumetric supply or drain flow by means of an additional metering land in its other function.
Particularly simple actuation of the throttle device and of the directional control valve acting as a throttle is obtained if a control side of the directional control valve and one of the throttle devices receive an equivalent control signal.
The throttle device may be designed as a directional control valve including a non-return position and several continuously adjustable flow positions or as a throttle device with separate function elements such as, for example, a main poppet and a push-open piston which are mechanically coupled to each other.
For actuation of the valve assembly according to the invention, three variants were found to be particularly advantageous.
In the first variant, initially only the control pressure for the drain-side throttle device is increased while the other control pressure for the supply-side throttle device is maintained constant—preferably at Zero. The first control pressure is increased until a predetermined control pressure difference is established, whereby the directional control valve acting as a supply throttle may be moved into a predetermined position for adjusting the hydraulic volumetric flow. Subsequently, while retaining the control pressure difference, both control pressures are increased until the co
Knoell Burkhard
Rueb Winfried
Mannesmann Rexroth AG
Michalsky Gerald A.
Oliff & Berridg,e PLC
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