Search

EP-4739922-A1 - HYDROPNEUMATIC ACCUMULATOR

EP4739922A1EP 4739922 A1EP4739922 A1EP 4739922A1EP-4739922-A1

Abstract

The invention relates to a hydropneumatic accumulator (1), comprising: - an enclosure (2) formed by a first half-shell (3) and a second half-shell (4) that are screwed to one another by means of a first thread (6) and a second thread (8) arranged on the first half-shell and on the second half-shell, respectively; and - a membrane that is pinched between the first half-shell (3) and the second half-shell (4); the first thread (6) and the second thread (8) have the following characteristics: - a pitch P; - an angle α formed by the engagement flank (22), which is between 15° and 35°; - an angle β formed by the load-bearing flank (23), which is between 5° and 10°; - a radius of curvature R of the root (25), which is between 0.15 P and 0.25 P; - a width L, which is between 0.20 P and 0.40 P; and - a distance D1, which is greater than or equal to the sum of the height H and of the radius of curvature R.

Inventors

  • MITKA, Jérôme
  • DIEUDONNE, Raphaël
  • POREL, François

Assignees

  • Hydro Leduc

Dates

Publication Date
20260513
Application Date
20240703

Claims (11)

  1. Hydropneumatic accumulator (1) comprising: - an enclosure (2) formed by a first half-shell (3) and a second half-shell (4) which are screwed to each other, and - a membrane (9) which is pinched between the first half-shell (3) and the second half-shell (4) and divides the enclosure (2) into a first compartment (12) and a second compartment (13); wherein the first half-shell (3) has an external surface (5) having a first thread (6) and the second half-shell (4) has a skirt (7) which is arranged around the external surface (5) of the first half-shell (3) and which has a second thread (8) cooperating with the first thread (6) to screw the first half-shell (3) and the second half-shell (4) to each other along an axis X; wherein the first half-shell (3) comprises a first abutment surface (18) which is provided at one end of the first half-shell (3) and which is in contact against a second abutment surface (19) which is provided, on the second half-shell (4), radially inside the skirt (7); wherein the first thread (6) and the second thread (8) each comprise a thread defined by a load flank (23), an engagement flank (22) positioned upstream of the load flank (23), an upper face (24) connecting the engagement flank (22) and the load flank (23) to each other and a bottom (25) connecting the engagement flank (22) and the load flank (23) of two adjacent portions of the thread; wherein the first thread (6) and the second thread (8) have the following characteristics: - a P step; - an angle α formed by the engagement flank (22) relative to an axis perpendicular to the X axis which is between 15 and 35°; - an angle β formed by the load-bearing flank (23) relative to an axis perpendicular to the X axis which is between 5 and 10°; - a radius of curvature R of the bottom (25) between 0.15 P and 0.25 P; - a width L corresponding to an axial dimension of the upper face (24) which is between 0.20 P and 0.40 P; - a height H corresponding to the difference between a radial distance between the bottom (25) of one of the first and second threads (6, 8) and the axis X and a radial distance between the upper face (24) of said first or second thread (6, 8) and the axis X; and - a distance D1 corresponding to a radial distance between the bottom (25) of the first thread (6) and the bottom (25) of the second thread (8) which is greater than or equal to the sum of the height H and the radius of curvature R.
  2. Hydropneumatic accumulator (1) according to claim 1, in which the pitch P is between 1.30 and 4 mm.
  3. Hydropneumatic accumulator (1) according to claim 1 or 2, wherein a distance D2 corresponding to the difference between the radial distance between the upper face (24) of the first thread (6) and the X axis and the radial distance between the upper face (24) of the second thread (8) and the X axis is greater than 0.4 P.
  4. Hydropneumatic accumulator (1) according to any one of claims 1 to 3, wherein the second thread (8) has, towards the second abutment surface (19), a truncated end zone (26) in which the thread is truncated so that a radial distance between the upper face (24) of the second thread (8) and the X axis increases in the direction of the second abutment surface (19).
  5. Hydropneumatic accumulator (1) according to claim 4, wherein in the truncated end zone (26), the thread has a truncated helix shape having a half-angle at the apex ε which is between 0.2 and 15°.
  6. Hydropneumatic accumulator (1) according to any one of claims 1 to 5, wherein the first half-shell (3) has a first annular cavity (28) which is positioned axially between the first abutment surface (18) and the first thread (6) and which extends radially towards the X axis beyond the first and second abutment surfaces (18, 19).
  7. Hydropneumatic accumulator (1) according to claim 6, in which the first annular cavity (28) has a radial depth e1, relative to the bottom (25) of the first thread (6), of at least 5 mm.
  8. Hydropneumatic accumulator (1) according to claim 6 or 7, in which the first annular cavity (28) comprises a bottom having several curved zones (34, 35, 36), each of the curved zones (34, 35, 36) joining the adjacent curved zone(s) (34, 35, 36) in a portion projecting towards the first annular cavity (28).
  9. Hydropneumatic accumulator (1) according to any one of claims 1 to 8, in which the second half-shell (4) comprises a second annular cavity (29) which is arranged axially between the second stop surface (19) and the second thread (8) and which extends radially outwards.
  10. Hydropneumatic accumulator (1) according to claim 9, in which the second annular cavity (29) has a radial depth e2 relative to the bottom (25) of the second thread (8) of at least 3 mm.
  11. Hydropneumatic accumulator (1) according to claim 9 or 10, in which the second annular cavity (29) comprises a bottom having several curved zones (30, 31, 32), each of the curved zones (30, 31, 32) joining the adjacent curved zone(s) (30, 31, 32) in a portion projecting towards the second annular cavity (30, 31, 32).

Description

Hydropneumatic accumulator The invention relates to the field of hydropneumatic accumulators. The invention relates more particularly to hydropneumatic membrane accumulators. Technological background Document FR2210725 discloses a hydropneumatic accumulator comprising an enclosure formed by two half-shells that are screwed to each other. An elastomer membrane is pinched between the two half-shells and separates the enclosure into two compartments, one of which is intended to receive a pressurized gas and the other is intended to be connected to a hydraulic circuit. The two half-shells are screwed to each other until the abutment surfaces of the two half-shells come into contact with each other. These abutment surfaces make it possible to create a prestressing force that puts the assembly of the two half-shells under tension. Such hydropneumatic accumulators are not fully satisfactory, in particular because of their insufficient service life. Hydropneumatic accumulators are in fact likely to be subjected, during their service life, to a very large number of cycles, for example in excess of 1,000,000. However, without increasing the thicknesses of the hydropneumatic accumulators of the state of the art, in particular at the level of their threads, they do not have sufficient fatigue resistance to meet such service life requirements. Increasing the thicknesses of hydropneumatic accumulators is also not a fully satisfactory option because, on the one hand, it proves impossible for applications in which space is limited and, on the other hand, leads to an increase in the mass and manufacturing cost of the hydropneumatic accumulator. An idea underlying the invention is therefore to propose a hydropneumatic accumulator of the aforementioned type having excellent resistance to fatigue, without significantly increasing its mass and/or its size. According to a first aspect, the invention provides a hydropneumatic accumulator comprising: - an enclosure formed by a first half-shell and a second half-shell which are screwed to each other, and - a membrane which is pinched between the first half-shell and the second half-shell and divides the enclosure into a first compartment and a second compartment; wherein the first half-shell has an outer surface having a first thread and the second half-shell has a skirt which is disposed around the outer surface of the first half-shell and which has a second thread cooperating with the first thread to screw the first half-shell and the second half-shell to each other along an X axis; wherein the first half-shell comprises a first abutment surface which is provided at one end of the first half-shell and which is in contact against a second abutment surface which is provided, on the second half-shell, radially inside the skirt; wherein the first thread and the second thread each comprise a thread defined by a load flank, an engagement flank positioned upstream of the load flank, an upper face connecting the engagement flank and the load flank to each other and a bottom connecting the engagement flank and the load flank of two adjacent portions of the thread; wherein the first thread and the second thread have the following characteristics: - a P step; - an angle α formed by the engagement flank relative to an axis perpendicular to the X axis which is between 15 and 35°; - an angle β formed by the load-bearing flank relative to an axis perpendicular to the X axis which is between 5 and 10°; - a radius of curvature R of the bottom between 0.15 P and 0.25 P; - a width L corresponding to an axial dimension of the upper face which is between 0.20 P and 0.40 P; - a height H corresponding to the difference between a radial distance between the bottom of one of the first and second threads and the X axis and a radial distance between the upper face of said first or second thread and the X axis; and - a distance D1 corresponding to a radial distance between the bottom of the first thread and the bottom of the second thread which is greater than or equal to the sum of the height H and the radius of curvature R. Thanks to the above-mentioned characteristics of the first and second threads, the fatigue resistance of the hydropneumatic accumulator is significantly improved. Tests have shown in particular that such threads make it possible to improve the fatigue resistance of the hydropneumatic accumulator by more than 60%. In particular, the angle β formed by the load flank makes it possible to optimize the contact surface between the load flanks, the radius of curvature R is sufficiently large to limit stress concentrations in the bottom of the threads and the width L of the threads is sufficiently large to limit the risks of deformation of the threads. Furthermore, since the distance D1 is greater than the sum of the height H and the radius of curvature R, there is a clearance between the upper face and the center of curvature of the bottom, which ensures flat contact between the load-bearing