Piston cylinder device with protection arrangement and method of protecting a piston cylinder device against overload or failure of the piston cylinder device

Abstract

A piston cylinder device (1) comprising a cylinder (2) with a first and a second end and a guide (6), such that a pressure chamber (8) is formed in the cylinder. A piston (12) is moveable in the pressure chamber (8). The guide (6) is fixedly secured to the cylinder (2) by a lock ring (7). A sealing means (9) is arranged to seal between the guide (6) and an inner wall of a tubular wall (3) of the cylinder (2) to prevent fluid leakage from the pressure chamber (8) to the surroundings. The piston cylinder device (1) is provided with a material weakening zone (13) arranged in the inner wall of the tubular wall (3) of the cylinder (2) axially between the lock ring (7) and the second end (20) of the cylinder (2), the material weakening zone (13) being arranged to be deformed or sheared against the lock ring (7) at a predetermined level of impact of the piston (12) against the guide (6). A leakage gap (14) is arranged to interrupt the sealing means (9) upon deformation or shearing of the material weakening zone (13) such that gas from the pressure chamber (8) is allowed to leave the pressure chamber (8) through said leakage gap (14) to the surroundings.

Claims

1. A piston cylinder device, comprising: a cylinder having a wall, an end wall at a first end of the wall, an opening at a second end of the wall, and a guide that is positioned at or adjacent to said second end of the wall; said wall, said end wall and said guide forming a pressure chamber there between; a piston disposed within the pressure chamber and connected to a piston rod; a portion of said piston rod extending through said guide and into said pressure chamber and a portion of said piston rod positioned outside said guide and said pressure chamber; at least a portion of said piston rod being slidable relative to said guide; said guide being fixedly secured to said cylinder by a lock ring; a sealing arrangement arranged that forms a seal between said guide and an inner wall surface of said wall to inhibit fluid leakage from said pressure chamber between said inner wall of said wall and said guide; a material weakening zone positioned in a portion of said inner wall of said wall; said material weakening zone is positioned a) above said locking ring and extends to said second end of said wall or b) above said locking ring and below said second end of said wall, and wherein said material weakening zone is spaced from said second end of said wall; said sealing arrangement positioned below said locking ring; at least a portion of said material weaken zone is configured to deform or shear in a direction toward said second end of said cylinder at a predetermined level of impact of said piston against said guide when said piston is moving axially upward in said cylinder thereby causing said locking ring to push upwardly on a lower portion of said material weakening zone to cause said material weakening zone to deform or shear; and a leakage gap configured to interrupt said sealing arrangement upon deformation or shearing of said material weakening zone such that gas from said pressure chamber is allowed to leave said pressure chamber through said leakage gap.

2. The piston cylinder device as defined in claim 1, wherein said material weakening zone is located between said lock ring and said second end of said wall; and said material weakening zone is spaced below said second end of said wall.

3. The piston cylinder device as defined in claim 1, wherein said material weakening zone includes a continuous or discontinuous circumferential groove in the said inner wall of said wall.

4. The piston cylinder device as defined in claim 1, wherein said sealing arrangement is positioned between said lock ring and said first end of said wall.

5. The piston cylinder device as defined in claim 4, wherein said leakage gap is at least partially located between said lock ring and said sealing arrangement.

6. The piston cylinder device as defined in claim 5, wherein said leakage gap is at least partially located in said inner wall of said wall.

7. The piston cylinder device as defined in claim 6, wherein said leakage gap includes a continuous or discontinuous circumferential groove in said inner wall of said wall.

8. The piston cylinder device as defined in claim 6, wherein said leakage gap is at least partially integrated with a lock ring groove at least when said material weakening zone is deformed or sheared; said lock ring groove at least partially includes said lock ring.

9. The piston cylinder device as defined in claim 1, wherein said material weakening zone is configured to inhibit or prevent fracturing apart of an outer wall of said wall.

10. A method of protecting a piston cylinder device against overload comprising: providing said piston cylinder device, said piston cylinder device comprising: a cylinder having a wall, an end wall at a first end of the wall, an opening at a second end of the wall, and a guide that is positioned at or adjacent to said second end of the wall; said wall, said end wall and said guide forming a pressure chamber there between; a piston disposed within the pressure chamber and connected to a piston rod; a portion of said piston rod extending through said guide and into said pressure chamber and a portion of said piston rod positioned outside said guide and said pressure chamber; at least a portion of said piston rod being slidable relative to said guide; said guide being fixedly secured to said cylinder by a lock ring; a sealing arrangement arranged that forms a seal between said guide and an inner wall surface of said wall to inhibit fluid leakage from said pressure chamber between said inner wall of said wall and said guide; a material weakening zone positioned in a portion of said inner wall of said wall; said material weakening zone is positioned a) above said locking ring and extends to said second end of said wall or b) above said locking ring and below said second end of said wall, and wherein said material weakening zone is spaced from said second end of said wall; said sealing arrangement positioned below said locking ring; at least a portion of said material weaken zone is configured to deform or shear in a direction toward said second end of said cylinder at a predetermined level of impact of said piston against said guide when said piston is moving axially upward in said cylinder thereby causing said locking ring to push upwardly on a lower portion of said material weakening zone to cause said material weakening zone to deform or shear; and a leakage gap configured to interrupt said sealing arrangement upon deformation or shearing of said material weakening zone such that gas from said pressure chamber is allowed to leave said pressure chamber through said leakage gap; and causing said piston to impact against said guide at a predetermined level of impact thereby causing said locking rick to apply a force to an underside of said material weakening zone there causing said material weakening zone to deform or shear, and thereby cause fluid to flow into said leakage gap and to bypass said sealing arrangement to reduce pressure in said pressure chamber.

11. The method as defined in claim 10, wherein said material weakening zone is located between said lock ring and said second end of said wall; and said material weakening zone is spaced below said second end of said wall.

12. The method as defined in claim 10, wherein said material weakening zone includes a continuous or discontinuous circumferential groove in the said inner wall of said wall.

13. The method as defined in claim 10, wherein said sealing arrangement is positioned between said lock ring and said first end of said wall.

14. The method as defined in claim 13, wherein said leakage gap is at least partially located between said lock ring and said sealing arrangement.

15. The method as defined in claim 14, wherein said leakage gap is at least partially located in said inner wall of said wall.

16. The method as defined in claim 15, wherein said leakage gap includes a continuous or discontinuous circumferential groove in said inner wall of said wall.

17. The method as defined in claim 15, wherein said leakage gap is at least partially integrated with a lock ring groove at least when said material weakening zone is deformed or sheared; said lock ring groove at least partially includes said lock ring.

18. The method as defined in claim 10, wherein said material weakening zone is configured to inhibit or prevent fracturing apart of an outer wall of said wall.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a longitudinal cross-sectional view of a piston cylinder device with a material weakening zone arranged in the inner wall of the cylinder.

(2) FIGS. 2-5 are magnifications of a portion of the piston cylinder device of FIG. 1.

(3) In FIG. 3 the piston rod of the piston cylinder device is shown freely accelerating in the cylinder in a direction X out of the cylinder.

(4) In FIG. 4 the moment of contact between a travelling piston and the guide is shown.

(5) In FIG. 5 deformation/shearing of the material weakening zone against the lock ring is shown.

(6) FIG. 6 is a magnification of an alternative embodiment of the piston cylinder device of FIG. 1 with a leakage gap arranged at an axial distance from the lock ring groove.

(7) FIG. 7 is a magnification of yet an alternative embodiment of the piston cylinder device of FIG. 1 with a leakage gap integrated with the lock ring groove.

(8) FIG. 8 shows a discontinuous circumferential groove in the inner wall of the tubular wall of the cylinder of the piston cylinder device.

DETAILED DESCRIPTION

(9) In FIG. 1 a piston cylinder device 1 is shown. The piston cylinder device comprises a cylinder 2 having a tubular wall 3 with an end wall 4 closing off one end of the tubular wall. The opposite, second end 20 of the tubular wall 3 includes an opening 5, and a piston rod guide 6 is fixedly secured within the opening 5 by a lock ring 7 so as to form a pressure chamber 8 in the cylinder 2. The lock ring 7 is arranged to protrude in a circumferential lock ring groove 40 of the inner wall of the tubular wall 3 of the cylinder 2 and an opposing lock ring groove 41 of an outer wall of the guide 6, see FIG. 2.

(10) The pressure chamber 8 is normally pre-loaded with gas under high pressure, typically in the order of 50-200 bar, normally 150 bar.

(11) Sealing means 9, FIGS. 1-7, is disposed between the inner wall of the tubular wall 2 and the piston rod guide 6 to prevent fluid leakage from the pressure chamber 8 between the outer surface of the guide 6 and the inner wall of the tubular wall to the surroundings. The sealing means 9 may be axially arranged between the lock ring 7 and the first end 4 of the cylinder 2, see FIG. 1. The sealing means 9 may be arranged in a circumferential groove in the outer wall of the guide, FIGS. 1-7. Alternatively, the sealing means 9 may be arranged in a circumferential groove in the inner wall of the tubular wall 3 of the cylinder 2 (not shown).

(12) The guide 6 includes a central opening 10 therethrough, and a piston rod 11 is slidingly received in the opening 10 and extends into the pressure chamber 8. A piston 12 is secured to the end of the piston rod 11 in the pressure chamber 8.

(13) A seal 21 surrounds the piston rod 11 in order to prevent fluid leakage between the piston rod 11 and the guide 6.

(14) The piston cylinder device 1 is provided with a material weakening zone 13 arranged in the inner wall of the tubular wall 3 of the cylinder 2 axially between the lock ring 7 and the second end 4 of the cylinder 2. The material weakening zone 13 is arranged to be deformed or sheared against the lock ring 7, FIG. 5, at a predetermined level of impact of the piston 11 against the guide 6.

(15) A leakage gap 14 is arranged to interrupt the sealing means 9 upon deformation or shearing of the material weakening zone 13 such that gas from the pressure chamber 8 is allowed to leave the pressure chamber 8 through the leakage gap 14 to the surroundings.

(16) Due to the presence of the material weakening zone 13 in the inner wall of the tubular wall 3 of the cylinder 2 axially between the lock ring groove and the second end of the cylinder 2, the piston cylinder device 1 is designed to stop, in a controlled manner, a piston rod 11 moving with high velocity in a direction out of the cylinder, along arrow X shown in FIGS. 1 and 3, caused by failure of the piston cylinder device 1.

(17) In FIG. 3 the piston rod 11 is shown freely accelerating in the cylinder 2 in a direction X out of the cylinder 2. In FIG. 4 the moment of contact between a travelling piston 12 and the guide 6 is shown. Through the contact between the parts of the piston cylinder device 1 during release of the piston rod 11 from a compressed state due to failure or overload of the piston device the lock ring 7 is pressed into the lock ring groove 40 of the cylinder 2 and the material of the material weakening zone is deformed or sheared, FIG. 5. Thereby the axial position of the guide 6 is displaced towards the second end of the cylinder 2. Upon the axial movement of the guide 6, the sealing means 9 becomes interrupted by the leakage gap 14 such that gas from the pressure chamber 8 is allowed to leave the pressure chamber 8 through the leakage gap 14 to the surroundings. Thereby, the speed of the piston 11 is reduced to zero without any of the piston cylinder device parts being separated from each other and leaving the piston cylinder device. Through the material deformation/shearing of the material of the material weakening zone against the lock ring 7 energy from the released piston rod 11 is absorbed by the material weakening zone 13.

(18) The material weakening zone 13 may be formed between the lock ring groove and a continuous or discontinuous circumferential groove 30 (see FIG. 8) in the inner wall of the tubular wall of the cylinder. In FIG. 8 a discontinuous such groove is shown. A discontinuous circumferential groove may be a milled or bored undercut along the circumference.

(19) The leakage gap 14 may be axially arranged between the lock ring 7 and the sealing means 9 as shown in FIGS. 1-7. Alternatively, the leakage gap may be arranged between the sealing means 9 and the first end 4 of the cylinder 2 (not shown). The leakage gap 14 may be arranged in the inner wall of the tubular wall 3 of the cylinder 2, see FIGS. 2-7. The leakage gap 14 may alternatively be arranged in the outer wall of the guide 6 (not shown).

(20) The leakage gap 14 may be a continuous or discontinuous circumferential groove in the inner wall of the tubular wall 3 of the cylinder 2.

(21) The discontinuous circumferential groove may be a milled or bored undercut along the circumference of the inner wall of the tubular wall.

(22) The leakage gap 14 may be integrated with the lock ring groove, see FIGS. 1-5 and FIG. 7. In the embodiment in FIG. 7 the leakage gap extends longer in the longitudinal direction along the inner wall of the tubular wall than the leakage gap in the embodiments of FIGS. 1-5.

(23) The leakage gap 14 may alternatively be arranged at an axial distance from the lock ring groove, see FIG. 6.