Fluid handling – Systems – Supply and exhaust
Reexamination Certificate
2001-09-07
2003-03-18
Michalsky, Gerald A. (Department: 3753)
Fluid handling
Systems
Supply and exhaust
C091S446000, C091S518000, C137S514300, C137S596130
Reexamination Certificate
active
06532989
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns improvements to hydraulic distributors.
2. Prior Art
By way of example,
FIG. 1
of the attached drawings shows, in cross-section, a known embodiment of such a distributor as it appears in
FIG. 1
of the document FR-A-2 689 575 in the name of the common assignee.
The distributor comprises a body
1
provided with an intake orifice P for pressurized fluid supplied by a hydraulic source (not shown). In the example illustrated, said orifice P has the form of a channel
2
passing transversely
1
through body
1
in the plane of the drawing and emerging on the two main faces of said body which serve as contact faces when several distributors are stacked side-by-side and one against the other. At least one orifice T (having the form of a channel passing transversely through the body
1
in the plane of the drawing and emerging on the two main faces of said body) serves to return the fluid to a tank (not shown). Two working orifices A, B are connectable to a hydraulic device or receiver (not shown). A distribution valve slide
4
is able to slide in a bore
5
passing longitudinally through body
1
and emerging on two opposed faces of the ends
6
,
7
of the body. In the conventional manner, the body
1
and the valve slide
4
include passages and/or channels and/or grooves arranged to co-operate in order to establish and/or interrupt the connections between the different orifices P, A, B, T of the distributor body according to the axial position occupied by the valve slide in the bore. The specific arrangements of these passages and/or channels and/or grooves are determined by a person skilled in the art in relation to the desired functions of the distributor.
In addition, in this specific example, the body
1
also includes a further transverse channel
8
extending between the main faces of the body and combined with at least one pressure selector allowing to be transmitted, in a channel
18
situated downstream of the distributor valve slide
4
, the higher (“load sensing” or LS pressure) of the two pressures constituted respectively by the pressure in said channel upstream of the distributor and a working pressure of the distributor.
The channel
2
connected to the intake orifice P emerges in the bore
5
of the body in an intake chamber
10
of said body, close to which another chamber
11
communicates, via a passage
12
, with a housing
13
in which a plunger
14
is mounted freely sliding and forming a fluid-tight seal. Passage
12
emerges into housing
13
at one end of the latter, here the lower end (corresponding to one end face of plunger
14
, here its lower end), while at its opposite end (here its upper end) housing
13
opens into a cavity
15
in which the head
16
of plunger
14
can move. Head
16
, wider in relation to the body of the plunger, can rest on a shoulder formed at the opening of housing
13
into cavity
15
to retain the plunger
14
. A spring
17
is provided in cavity
15
to press plunger
14
against said shoulder so as to fix its position in the absence of pressure. The above-mentioned channel
8
emerges in cavity
15
in such a way that the pressure prevailing in channel
8
is also present in cavity
15
and is therefore exerted on the corresponding end of plunger
14
(here its upper end).
In addition, plunger
14
includes an axial channel
18
emerging, on one side, in its end face opposite passage
12
and, on the other, in a diametrical channel
19
passing through plunger
14
and so arranged as to be closed by the wall of housing
13
when plunger
14
is in the rest position determined by spring
17
(shown in
FIG. 1
) or in a not fully raised position. A part
28
of axial channel
18
is formed as a restriction or nozzle.
The portion of valve slide
4
which extends, in the neutral position, between chambers
10
and
11
, isolating them from each other, is provided with progressive notches
20
intended to ensure a controlled flow of hydraulic fluid in the appropriate direction when the valve slide is displaced in one direction of the other. Two conduits
21
extend from above-mentioned housing
13
in two approximately diametrically opposite directions, in one or both of which conduits a non-return valve
22
is arranged, the two conduits
21
emerging in two respective chambers
23
in bore
5
.
In the proximity of chambers
23
two respective distribution chambers
24
of bore
5
are connected by conduits
25
to the respective working orifices or outlet orifices A and B of the distributor.
Finally, beyond distribution chambers
24
, two return chambers
26
of bore
5
are connected respectively by conduits
27
to return channel
3
emerging into the return orifice T.
The operation of the distributor just described is explained in detail in document FR 2 689 575 already cited, to which reference may be made.
Although a distributor arranged as just described is satisfactory with regard to its general principle of construction, it nevertheless has a disadvantage in certain operating conditions. Such a distributor is intended not to be used alone but in association with several other distributors of the same type to form a multiple hydraulic distribution device. The distributors are then preferably stacked in a fluid-tight manner one against the other by their main or large faces so that the respective conduits P, T and LS (channels
8
) all communicate with each other and form conduits passing from one side of the stack to the other to enable the assembly to operate as a multiple distribution device.
When, in such a multiple distribution device, several sections (single distributors) are actuated simultaneously for large movements of the hydraulic receivers supplied, instabilities due to the inadequate damping of the movements of the balances occur. In other words, because of the simultaneous movements of the balances in the respective distributors, the balances react on each other through the intermediary of channel LS and it is difficult to establish equilibrium in pressure LS.
SUMMARY OF THE INVENTION
The objective of the invention is therefore to provide an improved arrangement of the distributor which avoids this disadvantage and which leads to rapid stabilization of pressure LS in the case of multiple actuation.
To this end, a hydraulic distributor comprises a regulating balance able to perform a function of detecting the highest charge pressure, an anti-saturation function and a delivery-dividing function independent of the charge, this balance including a housing hollowed in the distributor body and in which a plunger is movable, this housing comprising:
a first end able to receive selectively the pressurized hydraulic fluid delivered by a hydraulic source,
a second end in communication with a channel conveying the highest charge pressure, and
a lateral orifice communicating selectively with a working orifice of the distributor, said plunger including a passage provided with a restriction and opening, on one side, towards said first end of the housing and, on the other, opening laterally so as to emerge in the above-mentioned second end of the housing when the plunger occupies a position determined by the excess of said intake pressure reduced by the pressure drop caused by the restriction, as compared to the highest charge pressure prevailing in the above-mentioned second end of the housing, said plunger being arranged to uncover the lateral orifice of the housing and to connect the latter with the first end of the housing in proportion to the pressure differential between the intake pressure and the highest charge pressure prevailing in the second end of the housing.
The hydraulic distributor, arranged in accordance with the invention, is characterized in that the balance comprises:
a fixed central core extending in the housing and coaxially with it;
the tubular plunger interposed sliding freely, coaxially, between the core and the housing, said plunger having a length less than that of the core and being so configured ext
Bianco Paul D.
Fleit Martin
Fleit Kain Gibbons Gutman & Bongini
Mannesmann Rexroth S.A.
Michalsky Gerald A.
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