CA1176951A

CA1176951A - Hydropneumatic damper

Info

Publication number: CA1176951A
Application number: CA000413969A
Authority: CA
Inventors: Max Malizard
Original assignee: Dosapro Milton Roy SA
Current assignee: Dosapro Milton Roy SA
Priority date: 1981-10-30
Filing date: 1982-10-20
Publication date: 1984-10-30
Also published as: EP0078721A1; FR2515761B1; DE3263148D1; ATE12816T1; EP0078721B1; FR2515761A1

Abstract

ABSTRACT OF THE DISCLOSURE

The invention relates to an enclosure divided into two chambers, sealed one from the other by a deformable diaphragm, one of said chambers being provided with a conduit connecting it with a hydraulic installation, whereas the other chamber is provided with a conduit connecting it with an auxiliary capacity of gas.
According to the invention, the dividing diaphragm is equipped in its center with a built-in element consisting of two parts symmetrical with respect to the diaphragm, of substantially truncated shape, whereas the two aforesaid conduits issue into their respective chamber through a widening-out substantially truncated portion, having the same conicity as said two parts, said truncated portions and parts being in axial alignment.

Description

- 117~951 The principle of hydropneumatic dampers, designed to absorb pressure and flow variations in a hydraulic installation, essentially consists in pressure-balancing a compressible gas with a hydraulic fluid inside a close-volume capacity.-It is known that to prevent the gas fromdissolving into the liquid and to allow a pre-compression of the gas without any hydraulic pressure, it is neces-sary to place between the gas and the liquid a supple - 10 deformable dividing wall to restrain the gas.
Two main embodiments of ~uch a supple wall are known, these are the ~bladder~ type and the ~'diaphragm"
type. In the bladder type, the damper is made up by cylinder-shaped metallic reservoir ending in two substantially spherical caps in which is introduced a bladder which, in the free state, adopts the shape ~ of the reservoir. The upper cap comprises a connecting means for the neck of the bladder permitting to inflate it by way of a valve; the lower part comprises a connection permitting the communication with the liquid of the circuit a~ well as a grid or a valve ~y~tem limiting the downwards course of the bladder whenever its inflating pressure exceeds that of the circuit.
The di~advantage with this device, which can be pre-inflated to a suitable pre~sure before being connect-ed to the circuit, is that it iR unsuitable for thick liquids which risk to obstruct the system connecting it to the circuit and to damage the bladder. In addition, in case of insufficient inflating or of a gas leak, the bladder is pressed back towards the top where there is no abutment system, so that it suffers e~cessive deformation which can ruin the blad~er. Finally, even in normal conditions of operation the deformations necessary for the device to work, demand a ~upple ~k ~ 117~951 diaphragm with a good bending Ytrength, this implying the use of ela~tomer-type materials, the chemical behaviour of which is unsuitable for certain applications.
In the diaFhragm type, the reservoir is made up by two symmetrical metallic shells and the dividing diaphragm substantially adopts, in the free state~ the inside shape of the shells; said diaphragm i~ tightly qecured by its periphery in the shell-joining plane.
The upper shell contains the inflating device and the lower shell contains the connection to the circuit and a grid or equivalent valve device preventing the extrusion of the diaphragm. This device presents one advantage over the preceding one in that the diaphragm suffers less mechanical fatigue and in that it is better protected against damages in case of gas leaks or of excessive pressure. It has nonetheless the same disadvantage of the abutment system beccming obstructed ~ by a thick liquid.
It should also be noted that it i~ often advan-tageous in order to obtain the best possible damping results, to have a volume of gas which is clearly greater than the volume corresponding to the maximum deflection of the diaphragm~which latter is less than the inner volume of the shells. It is then necessary to use the known dampers associated with auxiliary gas capacities, using a system of pipes and fittings, which increases the risks of leaks, the overall size of the instal-lation and the cost of the equipments.
It is the object of the present invention to overcome these disadvantages by proposing an easy-to-produce hydropneumatic damper, which uses a diaphragm-type separation, and is equipped with mean~ permitting to limit the possible deformations of the diaphragm due to a gas leak or to excessive pressure, or due to in~lating under a nil hydraulic pressure, these means - --` il7~951 permitting to as~ociate, in simple manrier, an auxiliary capacity of gas which communicateq directly with the air chamber of the damper, the volume of which capacity i~ adjustable a~ required.
The invention proposes to this effect a hydro-pneumatic damper constituted by an.enclosure divided into two chambers, sealed one from the other by way of a deformable diaphragm, one of said chambers being provided with a conduit connecting it with a hydraulic instal-lation, whereas.the other chamber is provided with a conduit connecting it with an auxiliary capacity of gas.
According to one characteristic of the invention, the aforesaid dividing diaphragm is equipped in its cen-ter with a built-in element consisting of two parts symmetrical with respect to the diaphragm, of substantial-ly truncated shape, whereas the two aforesaid conduits issue into their reapective chamber through a widening-out sub~tantially truncated portion, having the same conicity a~ said two parts, said truncated portions and parts being in axial alignment.
Preferably, each truncated part of said element is axially extended by a centering projection.
According to one advantageou~ embodiment of the invention, said diaphragm is provided in its center with an orifice of which the annular edge is substantial-ly flat, and comprises on each face a substantially semi-annular bead wherea~ the two parts of said element comprise two plane faces one opposite the other, each one of which is provided with a semi-annular groove to receive the said bead, and one of ~aid part~ forming ~crew to be joined to the other part through the orifice of the diaphragm, said two parts gripping the said bead between them.
Tn addition, one of said parts is provided with a radial shoulder member on which abuts the other part, and which is at a di~tance from its plane face substant-ially equal to the thickness of the flat edge of the diaphragm.
Moreover, the said diaphragm is made of rubber and coated on its face directed towards the hydraulic chamber with a layer of plastic material, and it comprises an external annular edge whicll is substantially flat and provided with semi-annular beads fastening it to the enclosure.
The central part of the membrane which extends between the two aforesaid flat edges, take on, in the free state, a substantially annular shape.
Finally, the damper according to the invention will be advantageously constituted by two half-shells, between which are gripped the external beads of the diaphragm, the conduit of communication with the auxiliary capacity being constituted by an orifice traversing one of the half-shells, and the said capacity being constituted by a sleeve surrounding the said orifice and cooperating tightly by one of its ends with a base member and by its other end, with the ~aid half-shell, the said ba4e member and the other half-~hell comprising means for fastening together the stacked up assembly.
The invention will be more readily understood on reading the following description with reference to the accompanying drawings, in which :
- Figure 1 is a diagrammatical cross-section of the apparatus according to the invention;
- Figure 2 illustrates a cross-section of a preferred embodiment of the center of the diaphragm in the damper according to the invention.
Referring first to Figure 1, this shows an enclosure 1 made up by two half-shells la and lb defining an internal volume. A dividing diaphragm 2 ` 1176951 divides this internal volume into two chambers A and B, chamber A being the hydraulic chamber and ~hamber B being the air chamber of the damper. The lower shell la is provided at it~ lower part with a threaded orifice 3a by which it is connected with a hydraulic installation (not shown). The conduit 3a issues into chamber A via a widening out portion forming a conical bearing 4a which connects up with the inner wall of the half-shell la. Said half-shell comprises, in one piece therewith, an external flange 5 provided with holes to allow the passage of assembling bars 7. The half-shell la is also pro~ided on its face resting against the half-shell lb, with a semi-annular groove 8a.
The inside shape of the upper half-shell lb is symmetrical to the inside shape of the half-shell la. Said upper half-shell lb is also provided with an orifice 3b issuing into chamber B through a bearing ~ part 4b, said orifice forming the end of a conduit connecting the chamber B with an au~iliary capacity of gas to be described in more detail hereinafter. And its face resting on the half-shell la also comprises a semi-annular groove 8b.
The half-shell lb is topped by a sleeve 9, a tight connection between these two elements being ensured by an 0-ring 10. Said qleeve is closed at its other end by a base member 11 which is also provided with an 0-ring 12. Said base member, which is edged with a flange 13, is held in position against the sleeve 9, which acts as a tie -piece, resting on the half-shell 30 lb and applying it against the half-shell la by means of assembly bars 7.
The internal volume 14 of the sleeve constitutes the auxiliary capacity of gas, which communicates with - the chamber B via the orifice 3b and is adapted to be inflated through a valve 15. A conduit 16 can be used .

1~769Sl to inse~ in a pre~sure gauge.
The dividing diaphragm 2 is, in the illu~trated example, a composite diaphragm, constituted by a layer 2b ~the thickest) on the side of chamber B, in synthetic or natural rubber, and by a layer 2a (the thinnest) on the side of chamber A, in plaqtic material such as for example tetrafltloroethylene, The thickne~
proportion of the two constituents is around 4/5, 1/5.
Said diaphragm comprises a substantially flat peripheral annular portion 17. Each face of thi~ periph-eral portion comprises a bead 17a, 17b constituted by half a torus, the radius of which is about equal to the thickness of the diaphragm. It will be noted on the figure that one at least of~ the mutual bearing faces i5 f the half-shells la lb comprises a kind of spot-facing over a depth substantially equal to the thic~ess of the diaphragm. And the grooves 8a and 8b have dimensions such that when two shells are applied one against the other, the crushing of the beads 17a, 17b does not exceed 20% of the thickness of the diaphragm in that point. Said diaphragm is thus in~erted between the half-shells la, lb solely at the level of the beads 17a, 17b which cooperate with the grooves 8a, 8b in the same way as 0-rings, to ensure tightness between chambers A and B. As a result, the life of the diaphragm which is spared excessive strains at the level of its anchoring, is lengthened.
Towards the center, the said diaphragm compriseg a part 18 which is substantially annular shaped when in the free state. The radius of said annular part is such that the total length of the meridian section of the diaphragm is equal to the total length of the inner meridian section of one of the half-shells la, lb. It will also be noted that the shape (like spherical caps for example) of the inner walls of the ~-~ li7~951 enclosure 1 is such that the deflection of the diaphragm does not exceed 10 to 15% of its ~erviceable diameter.
Finally, as shown more clearly in Figure 2, the said part 18 i~ extended by a flat annular ring 19 which is also provided with bead~ 19a, 19b identical to beads 17a, 17b, said ring surrounding a central orifice 20.
A metal part 21 is ~ecured by its centre to the diaphragm 2, It is composed of two symmetrical parts 21a, 21b, one of which carries a screw 22 and the other is shaped into a nut 23. The nut and screw cooperation is achieved through orifice 20. The part 21b presents a radial bearing face 24 which cooperates with a radial shoulder 25 of the part 21a. A kind of spotfacing f radial face 26 is provided in the part 21a so that the distance between the said face 26 and said shoulder is equal to the thickness of the diaphragm.
S~mi-annular grooves 27a and 27b are provided in ~aid face4 24 and 26 and cooperate with the beads 19a and 19b in the aame way as grooves 8a and 8b cooperate with the beads 17a, 17b when the two parts 21a, 21b are screwed one into the other.
Each of said parts comprise~ a truncated external surface 28a, 28b, the angle at the top of which is about 120, extended by an external surface 29a, 29b which is also truncated, the angle at the top of which is about 90, and which surrounds a projection provided for centering the part 210 Thus, the bearing faces 4a and 4b having the same conicity as the surfaces 28a, 28b, when the diaphragm is applied against the inner walls of the enclosure 1, the said surfaces rest against the said parts. In this case, tle diaphragm rests entirely again~t the wall, working solely in flexion, without any risk of elongation or extrusion whatever the differential pr~ssure which urge~ it out-i:~7695:1 wardly of the enclosure.
Finally, another faet to be noted is the presence of slots 30a, 30b at the tops of part 21 provided for assembling and dismantling purposes.
The way in which this deviee works is well known and can be ~ummed up as a sueeessionofpartial filling and emptying of the upper part of the capacity with deformation of the diaphragm : as a result, variations in the pressure of the gas oecur whieh are dependent on the ratio between the corresponding maximum and minimum volumes~
Without going into detail, it will be simply recalled that in normal operation, the cubic capacity to be absorbed should be le~s than the deflection i5 of the diaphragm between its abutmentq and that the average position of saiddiaphragm depends on the pre-inflatins pres~ure nlld on tl-e total volume, including that of the auxiliary capaeity. Generally, the greater the volume of gaA, the better the abqorbing eapacity; on the other hand, the aeceptable variations of the meAn pressure are that more reduced. Therefore, it is poqsible in every ease of eirc~it and of operation~
to find a compromise between these different faetors.
Calculations and experience have shown that, in most ca~es, the bladder type or diaphragm type dampers in their conventionally-known form do not permit to find this compromise without considerably larger dimensions, leading to higher costs and more room-Apace. An auxili-ary eapaeity eovering the total deflection of the diaphragm, represents on the eontrary a satiA~`actory eompromise for many applieations.
The volume of the auxiliary capacity 14 accord-ing to the invention can easily be altered. Indeed, the sleeve 9 can be replaeed by a longer or shorter sleeve. As a variant, a capacitycan be provided which is integral with the half-shell lb, this being obtained by welding the sleeve 9 to the base ~ember 11 and to the ~aid ~hell. Another possibility, is to design the damper according to the invention with two half-4hells identical to that la, with their fIange 5, the air capacity being then connected by screwing in the same way a~ the hydraulic circuit.
The ~pecial shape of the abutment, integral with the diapbragm, which completely clears a wide orifice in the working position and completely ~eals it off at end-of-ctroke, permits to use the apparatus with thick liquid~ without the risks of blockage and of internal depo~its found with the known device~. Pre-inflating in the open or on a non-pressurized circuit is al~o pos~ible. The insulation, achieved on the ~ide of the air chamber by the valve`21 on the bearing face 4b, protect~ the diaphragm again~t any gas leaks or excesRive pressures from the hydraulic circuit which would damage a bladdcr-type damper. It enable~ to utilize the whole deflection #troke, leaving a re~idual volume which will help the damping, which i~ impo~sible with the conventionally known bladder or diaphragm damper~, and thi~ without any ri~k.for the diaphragm in all cases of operation, even outside the normally prescribed limit~. .

... .

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A hydropneumatic damper comprising an enclosure, a deformable diaphragm dividing said enclosure into two cham-bers, one of said chambers being provided with a conduit for connection to a hydraulic installation and the other chamber being provided with a conduit establishing communication with an axiliary gas chamber, a profiled element mounted in the central region of said diaphragm having parts on either side thereof facing said conduits, and said conduits having surfaces matching said parts such that in extreme positions of said diaphragm said parts seat in said conduits to pre-vent excessive distortion of the diaphragm.

2. A hydropneumatic damper according to claim l, wherein said parts are symmetrical with respect to the diaphragm,

3. A hydropneumatic damper according to claim 1, where-in said parts comprise truncated cones and said matching surfaces define outwardly flared entrances to said conduits for receiving said cones.

4. A hydropneumatic damper according to claim 3, where-in said conduits and said parts of the profiled element are in axial alignment.

5. A hydropneumatic damper according to claim 3, where-in said truncated cones are axially extended by a central protruberance.

6. A damper as claimed in claim 1, wherein said dia-phragm has at its center an orifice of which the annular edge is substantially flat, a substantially semi-annular bead is located on each face, the two parts of said element have opposed plane faces, each of which is provided with a semi-annular groove to accommodate said bead, and said parts are screwed together through the orifice so as to gripp the bead between them.

7. A damper as claimed in claim 6, wherein one of said parts is provided with a radial shoulder member on which abuts the other part, and which is at a distance from its plane face substantially equal to the thickness of the flat edge of the diaphragm.

8. A damper as claimed in claim 6, wherein said dia-phragm comprises an external annular edge which is substan-tially flat and provided with semi-annular beads fastening it to the enclosure.

9. A damper as claimed in claim 8, wherein the said diaphragm is made of rubber and coated on its face directed towards the hydraulic chamber with a layer of plastic material.

10. A damper as claimed in claim 8 or 9, wherein the two internal and external flat portions of the diaphragm are joined together by a portion of diaphragm which is substan-tially annular shaped in the free state.

11. A damper as claimed in any one of claims 1 to 3, wherein the enclosure is constituted by two half-shells between which are gripped external beads of the diaphragm, the conduit of communication with the auxiliary chamber being constituted by an orifice traversing one of the half-shells, and the said chamber being constituted by a sleeve surround-ing the said orifice and cooperating tightly by one of its ends, with a base member and by its other end, with the said half-shell, the said base member and the other half-shell comprising means for fastening together the stacked assembly.