Fluid handling – Systems – Supply and exhaust
Reexamination Certificate
2000-01-19
2001-07-31
Michalsky, Gerald A. (Department: 3753)
Fluid handling
Systems
Supply and exhaust
C091S446000, C091S518000, C137S596130
Reexamination Certificate
active
06267141
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to improvements made to hydraulic directional control valves having a regulating balance designed to sense the highest load pressure, assume an anti-saturation function and provide a function whereby the flow is split independently of the load, this balancing system comprising a plunger that can be displaced in a housing under the action of a differential pressure created by the intake pressure supplied by a hydraulic source applied to a first of its ends and by the highest load pressure applied to its other end, said plunger also being designed to open, in is proportion to the above-mentioned differential pressure, a lateral orifice of the housing connected to a working orifice of the directional control valve in order to apply hydraulic fluid thereto at the intake pressure less said differential pressure.
By way of example,
FIG. 1
of the appended drawings illustrates in cross-section a known mode of operating such a directional control valve as disclosed in
FIG. 1
of document FR-A 2 689 575.
The directional control valve has a body
1
provided with an orifice P for admitting pressurised fluid from a hydraulic source (not illustrated). In the example illustrated, said orifice P is provided in the form of a passage
2
crossing through the body
1
, transversely to the plane of the drawing, and opening at the two main faces of said body, which acts as a support when several directional control valves are stacked side by side and one against the other. At least one orifice T (provided in the form of a passage crossing through the body
1
transversely to the plane of the drawing and opening at the two main faces of said body) is used to return the fluid to a tank (not illustrated). Two working orifices A, B can be connected to a hydraulic device or receiver (not illustrated). A slide valve
4
is designed to slide in a bore
5
which crosses longitudinally through the body
1
and opens at two opposing end faces
6
,
7
thereof. In a conventional manner, the body
1
and the slide valve
4
have passages and/or ducts and/or grooves arranged so as to co-operate, with a view to establishing and/or cutting off the links between the various orifices P, A, B, T of the body of the directional control valve depending on the axial position occupied by the slide valve in the bore. The specific layout of these passages and/or ducts and/or grooves is determined by the person skilled in the art depending on the functions which the is directional control valve is required to perform.
In this specific example, the body
1
also has another transverse passage
8
extending between the main faces of the body and combined with at least one pressure selector, which enables the higher (load sensing pressure or LS pressure) of two pressures, these being the pressure in said passage upstream of the directional control valve and the working pressure of the directional control valve respectively, to be applied to a passage
18
located downstream of the slide valve
4
.
In the bore
5
of the body, the passage
2
connected to the intake orifice P opens into an admission chamber
10
thereof, adjacent to which is another chamber
11
communicating via a passage
12
with a housing
13
in which a freely and tightly sliding plunger
14
is mounted. The passage
12
opens into the housing
13
, at one end thereof, in this case the bottom end (corresponding to an end face of the plunger
14
, in this case its bottom end) whilst at its opposite end (in this case its top end) the housing
13
opens into a cavity
15
in which the head
16
of the plunger
14
may be displaced. The head
16
, which is wider than the body of the plunger, may bear on a shoulder provided at the point where the housing
13
opens into the cavity
15
in order to retain the plunger
14
. A spring
17
is provided in the cavity
15
to push the plunger
14
back against said shoulder in order to fix its position in the absence of pressure. The above-mentioned passage
8
opens into the cavity
15
so that the pressure prevailing in the passage
8
is also present in the cavity
15
and hence applied to the corresponding end of the plunger
14
(in this case its top end).
In addition, the plunger
14
has passing through it an axial passage
18
, opening at one end in its end face facing the passage
12
and at the other end in a diametral passage
19
crossing through the plunger
14
and arranged so that it is closed off by the wall of the housing
13
when the plunger
14
is in the rest position imposed by the spring
17
(illustrated in
FIG. 1
) or in a not fully raised position. A part
28
of the axial passage
18
is provided in the form of a restriction or a nozzle.
The portion of the slide valve
4
which, in the neutral position, extends between the chambers
10
and
11
isolating them from one another is provided with graded notches
20
designed to ensure that the hydraulic fluid flows in a controlled manner in the relevant direction when the slide is displaced in one direction or the other.
Extending from the housing
13
in two approximately diametrically opposed directions are two conduits
21
, in one of which or in each of which a non-return valve
22
is arranged, the two conduits
21
opening, in the bore
5
, into two respective chambers
23
.
Close to the chambers
23
, two respective distribution chambers
24
of the bore
5
are linked by conduits
25
to the respective working orifices or initial orifices A and B of the directional control valve.
Finally, beyond the distribution chambers
24
, two return chambers
26
of the bore
5
are respectively linked by conduits
27
to the return passage
3
opening onto the return orifice T.
The way in which the directional control valve described above works is explained in detail in document FR 2 689 575, mentioned above, to which reference may be made.
Although a directional control valve of the design outlined above is satisfactory in terms its general operating principle, it nevertheless has a disadvantage under certain operating conditions. A directional control valve of this type is not designed to be used alone but to work in co-operation with several directional control valves of the same type to make up a multiple hydraulic directional control system. This being the case, the directional control valves are preferably stacked tightly one against the other by their main faces or large faces so that the respective conduits P, T and LS (passages
8
) all communicate with one another and form continuous passages crossing through the stack from end to end, enabling the multiple directional control device to work.
In a multiple directional control device of this type, if operation of one particular distribution section (i.e. an individual directional control valve) is inhibited due to the action of a pressure LS imposed by another section of the multiple directional control device, it may nevertheless be desirable for that particular distribution section to be allowed to continue in operation so that the hydraulic receiver which it controls can be placed or maintained in operation, albeit at a reduced rate: this might be the case if a machine turret has to be rotated or a machine moved in translation, for example.
In other words, it would seem desirable to be able to impart an operating capability to a specific function, albeit at a lesser or downgraded rate, in spite of the controlled inhibiting action imposed by the general LS circuit of the multiple directional control device, and to do so without having to use a priority circuit for the specific section in question, examples of this being known, given that the use of such, which complicates the overall design and adds to the cost, does not seem to be called for in the context in question.
Accordingly, what is needed is to give the specific distribution section in question a pseudo-priority without substantially modifying the individual directional control valve or the multiple directional control device.
SUMMARY OF THE INVENTION
The objecti
Mannesmann Rexroth S.A.
Marshall O'Toole Gerstein Murray & Borun
Michalsky Gerald A.
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