Gas spring with overtravel pressure relief

Abstract

To prevent damage to a forming device and / or a workpiece with which a gas spring is used.SOLUTION: An industrial gas spring has: a pressure chamber in a casing with an end wall; a piston rod received at least in part in the casing for reciprocation between extended and retracted positions; and a pressure relief assembly carried by the end wall. The pressure relief assembly may have: a membrane communicating with the pressure chamber; and a plunger configured to breach the membrane when engaged and moved by the piston rod when the piston rod overtravels its design-intended retracted position.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Application No. 62 / 821,073, filed March 20, 2019, which is incorporated by reference in its entirety.

[0002] The present invention relates generally to industrial gas springs for molding equipment, and more particularly to overtravel pressure relief for industrial gas springs. [Background technology]

[0003] Industrial gas springs are well known and are used in many applications in forming equipment including press dies for sheet metal stamping, punching and drilling operations.

[0004] For example, one or more of the gas springs can be used in various embodiments of the molding apparatus to provide a yield or return force to a movable component for supporting the mold or workpiece. For example, in a binder ring embodiment, the gas spring provides a yield force to the binder ring of the mold to hold the metal workpiece, while another part of the mold forms, cuts, stretches, stamps, punches, or bends the workpiece, or is pulled from the workpiece. In a lifter embodiment, the gas spring can provide a yield and return force to lift the workpiece from the mold surface or to maintain control of the workpiece. In a cam tool embodiment, the gas spring can apply a yield force and return the cam actuated tool to its home position. Of course, gas springs may be used in a wide variety of other embodiments. Summary of the Invention

[0005] A conventional industrial gas spring may include a casing, a piston rod received within the casing, a piston rod bearing and seal housing carried by the casing, and a pressure chamber that holds a pressurized gas, typically nitrogen, at an operating pressure of, for example, 1000-5000 psi in some applications. The pressurized gas biases the piston rod to an extended position and yieldably resists movement of the piston rod from the extended position to the retracted position. However, the piston rod may overtravel beyond the intended retracted position of the design, and this overtravel may result in undesirable gas overpressure and other adverse conditions. Rapid return of the piston rod from the overtravel retracted position to the extended position may also damage the molding apparatus and / or workpiece with which the gas spring is used. In the overtravel position of the piston rod, the gas pressure in the chamber may be as much as 50%-100% higher than that pressure in the normal fully extended position of the piston rod.

[0006] In at least some forms, an industrial gas spring having a piston rod and a pressure chamber may have a pressure relief assembly carried by an end wall of a casing. The pressure relief assembly may have a membrane in communication with the pressure chamber and a plunger configured to rupture the membrane when the piston rod is moved into engagement with the piston rod by over-traveling from its designed intended maximum retracted position.

[0007] The membrane may be a homogenous, integral part of the end wall in at least some forms, and may be a separate component in other forms. In at least some forms, the plunger may have a passageway that communicates the pressure chamber with the membrane. In at least some forms, the plunger The jar may have one or more relatively sharp edges for rupturing the membrane.

[0008] In at least some forms, the pressure relief assembly may have a body received within the end wall and carrying a membrane. In at least some forms, the body may also carry a plunger. In at least some forms, the plunger may be slidably received within the body.

[0009] The following detailed description of the preferred embodiments and best mode is set forth with reference to the accompanying drawings. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view of an industrial gas spring with the piston rod in its extended position and having an overtravel pressure relief assembly. [Diagram 2] FIG. 2 is a cross-sectional view of the gas spring of FIG. 1 with the piston rod in an over-travel retracted position actuating the pressure relief assembly. [Diagram 3] FIG. 3 is an enlarged, partial cross-sectional view of the circled portion of FIG. 2. [Figure 4] FIG. 3 is an end view of the plunger of FIG. 2. [Diagram 5] FIG. 11 is a side view of a first variation of the plunger. [Figure 6] FIG. 6 is a cross-sectional view of the plunger of FIG. 5. [Figure 7] FIG. 13 is a side view of a second variation of the plunger. [Figure 8] FIG. 8 is a cross-sectional view of the plunger of FIG. [Figure 9] FIG. 13 is a perspective view of a third variation of the plunger. [Figure 10] FIG. 10 is a side view of the plunger of FIG. [Figure 11] FIG. 10 is an end view of the plunger of FIG. [Figure 12] FIG. 10 is a cross-sectional view of the plunger of FIG. [Figure 13] FIG. 1 is a partial cross-sectional view of a gas spring having a first alternative overtravel pressure relief assembly. [Figure 14] FIG. 14 is a perspective view of a plunger of the release assembly of FIG. 13. [Figure 15] FIG. 13 is a partial cross-sectional view of a gas spring having a second alternative overtravel pressure relief assembly. [Figure 16] FIG. 16 is an enlarged cross-sectional view of the second variant overtravel pressure relief assembly of FIG. 15. [Figure 17] FIG. 17 is an enlarged cross-sectional view taken along line 17-17 of FIG. 16. [Figure 18] FIG. 17 is a fragmentary, enlarged cross-sectional view of the portion of FIG. 16 within circle 18. [Figure 19] FIG. 13 is a semi-schematic, partial cross-sectional view of a gas spring having a third modified overtravel pressure relief assembly. [Figure 20] FIG. 20 is an enlarged perspective view of the overpressure relief assembly of FIG. 19. [Figure 21] FIG. 20 is a side view of the pressure relief assembly of FIG. 19. [Figure 22] 22 is a cross-sectional view taken generally along line 22-22 of FIG. 21. [Figure 23] 23 is an enlarged partial cross-sectional view taken generally along line 23-23 of FIG. 22. [Figure 24] 20 is a semi-schematic, partial cross-sectional view of a modified body of the pressure relief assembly of FIG. 19. [Diagram 25] FIG. 13 is a semi-schematic, partial cross-sectional view of a gas spring having a fourth configuration of an overtravel pressure relief assembly. [Figure 26] FIG. 26 is an end view of the gas spring and pressure relief assembly of FIG. [Figure 27] FIG. 26 is a side view of the pressure relief assembly of FIG. 25. [Figure 28] FIG. 26 is a view of one end of the release assembly of FIG. 25. [Figure 29] FIG. 26 is an end view of the other end of the pressure relief assembly of FIG. 25. [Diagram 30] FIG. 30 is an enlarged cross-sectional view taken along line 30-30 of FIG. 27. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Referring more particularly to the drawings, the drawings show various configurations of pressure relief assemblies of industrial gas springs for molding equipment. In the relief assembly, the piston rod overtravels beyond its intended design maximum retracted position and engages and moves the plunger to pierce, cut or break the metal membrane and vent or release the pressurized gas in the pressure chamber to escape outside the casing of the gas spring. This release of pressurized gas reduces the force with which the piston rod can return from its overtravel position toward its fully extended position and in some applications can prevent the piston rod from returning completely to its fully extended position. This avoids damage to the molding equipment and / or workpiece in which the gas spring is used.

[0012] As shown in FIG. 1, an industrial gas spring 50 for a molding apparatus may include a casing 52 having a rear head or wall 54, a pressure chamber 56, a guide bearing and seal assembly 58 carried by the casing, and a piston rod 60 received through the guide and seal assembly and partially disposed within the pressure chamber. In use, the pressure chamber may be filled with compressed gas, typically nitrogen, in many applications at a pressure typically in the range of, for example, 1,000 to 5,000 psi. The compressed gas in the chamber yieldably biases the piston rod to its fully extended position, with its outer end projecting outwardly of the adjacent end of the casing, as shown in FIG. 1. In use, the outer end of the piston rod 60 may be engageable with or engageable by a mold member or another portion of a press or molding apparatus (not shown) that can reciprocate the piston rod between its fully extended position and its designed and maximum retracted position.

[0013] The gas spring 50 includes an overstroke or overtravel pressure relief assembly 70 that vents the pressure chamber 56 to the outside of the gas spring and relieves or significantly reduces the pressure of the compressed gas therein if the piston rod 60 overtravels back beyond its intended design maximum retracted position (FIG. 2). The pressure relief assembly (hereinafter release assembly) can have a plunger 72 that is moved by the piston rod 60 when the piston rod 60 overtravels on a retraction stroke to cut, shear, pierce or break a membrane 74, opening a path for the pressurized gas in the chamber 56 to vent or escape to the outside of the gas spring. As shown in FIG. 2, the degree of overtravel 76 of the piston rod 60 that results in the breakage of the membrane 74 can be on the order of 0.060 inches (1.52 mm).

[0014] The membrane 74 may be formed as an integral part of the head 54 of the casing as a separating wall between two opposed blind bores 78 and 80, one bore 78 opening into and communicating with the pressure chamber 56 and the other generally opposed bore 80 opening through the exterior face of the head 54 and thereby communicating with the exterior of the gas spring. The membrane 74 is thin enough to be broken by a reasonable amount of force, yet strong enough not to be fatigued under normal operating conditions of the gas spring by the pressure changes experienced with each normal cycle of retraction and extension of the piston rod 60, which cycling is relatively rapid, and may typically occur in the range of 20 to 60 complete cycles per minute when the gas spring is in use.

[0015] The thickness of membrane 74 may depend in part on the maximum operating pressure of the compressed gas in the chamber, the surface area of ​​the membrane exposed to this pressurized gas, and the material from which the membrane is made. For a 1020 carbon steel head having an integral membrane and bore 78, and thus a membrane diameter in the range of about 0.12-0.15 inches (3-4 mm), the nominal thickness of membrane 74 may typically be in the range of 0.010-0.020 inches (0.25-0.50 mm), desirably about 0.010-0.012 inches (0.25-0.30 mm). Desirably, bores 78 and 80 are coaxial, and bore 80 may be somewhat larger than bore 78 to provide some clearance for the cut or pierced portion of membrane 74 when it is ruptured by plunger 72.

[0016] As shown in Figures 3 and 4, the plunger 72 may be a body 82 having a cylindrical outer peripheral surface 84 and a generally flat inner end 86 configured to engage an inner end 88 of the piston rod 60 upon overtravel. Adjacent to its other end, the plunger 72 may have two desirably diametrically opposed, axially extending fingers 90 each having an inclined free end that may be formed with an inclined arcuate or flat surface 92 to provide a relatively sharp edge 94 for advancing a cutting edge 94 to cut, pierce, shear or break the membrane 74 through the membrane by the plunger when moved by the overtraveling piston rod 60. The plunger 72 may also have a preferably coaxial through bore 96 that provides a vent passageway through which compressed gas in the chamber 56 may flow through the membrane 74 to the exterior of the gas spring 50 upon breakage. The plunger 72 may be received in the bore 78 with a press fit or interference fit and retained therein. The degree of this press fit must be small enough to allow the plunger to be easily and rapidly advanced by over-travel of the piston rod 60 without excessive force, such as an ISO interference fit or a snug fit, such as an H7 / f6 fit. This interference fit of the plunger 72 ensures that the plunger does not inadvertently move out of the bore 78 into the pressure chamber 56 during normal use of the gas spring 50. This interference fit can save axial space and area in the release assembly and head, which can be particularly useful for smaller sized gas springs, such as smaller diameter gas springs.

[0017] 5 and 6 show a first modified plunger 100 that may be used in place of plunger 72 of FIGS. 1-4. This modified plunger 100 may have a body 102 having a cylindrical outer circumferential surface 104, a through vent bore 106 that is preferably coaxial with the cylindrical surface, a generally flat first end 108 engageable by the over-traveling piston rod 60, and a second end having an arcuate or curved portion 110 providing a single protrusion 112 having a sharp edge or tip 114 for piercing, cutting, or breaking the membrane 74. This plunger 100 may be press fit into the bore 78 of the head 54 of the gas spring 50.

[0018] 7 and 8 show a second modified plunger 120 that may be used in place of plunger 72. This modified plunger 120 has a body 122 with a cylindrical outer circumferential surface 124, a through bore vent passage 126, a first end 128 that may be generally flat for engagement by the over-traveling piston rod 60, and two generally diametrically opposed, axially extending fingers 130 adjacent its other end, each finger having an angled outer surface 132 that may be arcuate or flat to form a relatively sharp tip or edge 134 that may cut, shear, perforate or break a portion of the membrane 74 radially inward from its periphery, thereby breaking a central portion of the membrane and deflecting it away from the central bore vent passage 126. This modified plunger may be press fit into the bore 78 of the head 54 of the gas spring 50.

[0019] A third modified plunger 140 that may be used in place of plunger 72 is shown in Figures 9-12. This plunger 140 may have a body 142 having an outer cylindrical surface 144 that extends circumferentially around only a portion of the circumferential extent of the body and merges into a recess 146, which may be an axially and laterally extending flat surface 148 having a central portion radially inward of the outer cylindrical surface 144 and cooperates with the bore 78 in the rear head 54 to provide a vent passage. This plunger 140 may have a laterally inner end 150 that may be engaged by the over-traveling piston rod 60, and a pair of diametrically opposed fingers 152 that project axially outward adjacent its other end, each finger having an inclined surface 154, which may be arcuate or flat, adjacent its free end and a pair of diametrically opposed fingers 152 that cut, shear, pierce or otherwise displace the membrane 74 when moved or advanced by the over-traveling piston rod 60 through the membrane. The fingers 152 may be spaced circumferentially from the vent face 148, and desirably each finger may be spaced circumferentially substantially 90 degrees from the vent face. The plunger 140 may be press fit into the bore 78 of the head 54.

[0020] In use, all of these plungers 72, 100, 120, and 140 cut, shear, puncture, or break the membrane when the over-traveling piston rod 60 advances at least partially through the membrane by abutting the membrane 74 and moving the plunger into, through, or at least partially through the membrane.

[0021] FIG. 13 shows another form of overtravel pressure relief assembly 160 received in rear head 54' of casing 52' of gas spring 50' with piston rod 60' slidably received in a bearing and seal assembly. This gas spring 50' may have substantially the same construction and arrangement as gas spring 50 of FIGS. 1 and 2. This relief assembly 160 may have a separate membrane 162 in the form of a disk removably retained by a collar 164 in a bore 166 communicating with the exterior of head 54', and a plunger 168 received in an opposing bore 170 opening into pressure chamber 56'. These bores 166, 170 may be connected by an intermediate bore 172. Collar 164 may have male threads 174 that are matable with complementary female threads 176 in bore 166, and a non-circular recess or socket 178, such as a hexagonal socket, for receiving a tool for installation and removal of the collar from the bore. The collar may have a through vent passage 180 and the other end may have a circumferentially continuous surface 182, which may be flat or slightly arcuate in cross section, for engaging the disk membrane to place the disk membrane 162 into metal-to-metal sealing engagement with a circumferentially continuous shoulder and / or end face 184 of the bore 166 when the collar 164 is tightly threaded into the bore.

[0022] As shown in Figures 13 and 14, the plunger 168 may have a body 186 with a cylindrical outer surface 188, one end 190 of which may be flat for engagement by the over-traveling piston rod 60', and the other end of which may have a pair of diametrically opposed buttresses or narrowed shoulders 192 that merge into a neck 194 having a tip 196 for piercing or breaking the membrane. These shoulders 192 may narrow radially as they extend toward the neck 194, and the neck may narrow radially as it extends toward the tip 196. The tip 196 may be substantially frusto-conical to provide a relatively pointed portion for initially piercing or breaking the membrane 162, and the neck and shoulders may displace a portion of the pierced membrane generally radially outward as it is moved partially into the membrane by the over-traveling piston rod.

[0023] To provide a vent path, a blind axial bore 198 in the plunger 168 may communicate at one end with the pressure chamber 56' and at the other end with a transverse bore 200 through the shoulder portion 192 to release compressed gas from the chamber 56' when the disk membrane 162 is pierced by the plunger. To hold the plunger 168 in the bore 170 during normal operation of the gas spring 50', the plunger may be pressed into the bore with a slight interference fit. On the one hand, this interference fit should generate sufficient frictional forces to hold the plunger 168 in the bore 170, and on the other hand, should not generate sufficient frictional forces to prevent the plunger from moving further into the bore to pierce or break the membrane 162 by overtravel of the piston rod 60'. Typically, this plunger 168 may have a similar ISO snug fit in the bore.

[0024] 15 illustrates an alternative pressure relief assembly 210 that is removably received within a bore 212 through the rear head 54'' of the gas spring 50''. The release assembly 210 may have a collar or body 214 having external threads 216 that are threadably mateable with complementary threads in the bore, and a peripheral flange 218 that is engagable with a shoulder of the counterbore 220 to limit the extent to which the body can be advanced into the bore. The body 214 may have a membrane 222 integrally formed therewith and disposed between a blind bore or passageway 224 that opens into the pressure chamber 56'' and a blind bore or passageway 226 that opens to the exterior of the gas spring 50''. The passageway 226 may include a socket portion 228 having a non-circular configuration, such as a square or hexagonal shape, that is configured to receive a tool for threadably installing and removing the release assembly 210 from the rear head 54'' of the casing 52''. The body 214 may include a circumferentially continuous groove 230 that is configured to receive a seal 232, such as an O-ring, to provide an airtight seal between the body and the rear head 54''.

[0025] As shown in Figures 15 and 16, the plunger 234 may have a body 236 with an exterior cylindrical surface 238 that may be partially received within a bore 240 with a press fit or interference fit in assembly. One end of the plunger may have a generally flat surface 242 configured to be engaged by an over-traveling piston rod 60'', and the other end may include a relatively sharp edge 244 configured to cut, pierce or break the membrane 222 when the sharp edge moves at least partially through the membrane with the over-traveling piston rod, as shown in Figure 18. The relatively sharp edge 244 may be formed adjacent a portion of the circumferential circumference of the plunger by an arcuate surface 246 adjacent the end of the plunger. An air passage between the plunger 234 and the bore 240 in which it is received may be provided by a longitudinally or axially extending recessed surface 248 (FIGS. 17 and 18) which may be flat and disposed radially inward of the radius of the plunger's cylindrical surface 238 to provide a passage between the plunger and the bore through which the compressed gas in the pressure chamber 56″ may flow when the plunger ruptures the membrane 226. Desirably, this recess 248 in the plunger is generally diametrically opposed to the plunger's cutting edge 244. Instead of the plunger 234, any of the plungers 72, 100, 120, 140, and 168 may be used in this release assembly 210.

[0026] When there is no compressed gas in the chamber 56'' of the gas spring 50'', such as during transportation and / or inspection of the gas spring, the membrane 222 of the release assembly 210 may be protected from accidental or inadvertent cutting, puncturing, or rupturing thereof by a tube or sleeve 250 (FIGS. 15 and 16) that is received, such as by a press fit, within the bore 212. The sleeve extends axially to, and preferably slightly beyond, the adjacent end of the plunger and is made of a suitable yieldable material, such as a polymer or thin metal tube, so as to be easily folded, compressed, or crushed by the over-traveling piston rod 60'' that actuates the plunger 234 to rupture the membrane 236 when, in use, the gas spring 50'' has compressed gas within its pressure chamber 56''. This release assembly 210 may be particularly desirable for gas springs having an internal configuration that requires that the release assembly must be installed only from the outside of the rear head.

[0027] FIG. 19 illustrates another form of a pressure relief assembly 260 received within a bore 262 through the rear head 54''' of the gas spring 50''', one end of which communicates with the pressure chamber 56'' and the other end of which communicates with the exterior of the gas spring. The relief assembly 260 can have a body 264 having a cylindrical portion 266 that can be received with a press or interference fit within the bore 262 of the rear head 54'''. The body 264 can have a circumferentially continuous groove 268 configured to receive a seal 270, such as an O-ring, therein to provide an airtight seal between the body and the bore 262 in which it is received. As shown in FIGS. 19, 22, and 23, the body can have a blind bore 272 therein, the open end of which communicates with the pressure chamber 56'' and adjacent its closed end with one face of an integral membrane 274 that extends at least partially in a generally radial direction within the bore. The body may have an internal recess or slot 276 which communicates the other side of the membrane 274 with the exterior of the rear head 54''' through an adjacent portion of the bore 272 and a counterbore 278 in the head. After the blind bore 272 and slot 278 are formed with the thin metal portion therebetween, the membrane 274 may be further formed by pressing at least a portion of this thin metal portion generally radially into the bore 272 to provide a recessed membrane 274 or other form of membrane that provides radial protection within the bore.

[0028] A plunger 280 can have a body 282 with a cylindrical outer surface 284, one end 286 being generally flat and configured to be engaged by the over-traveling piston rod and the other end 288 being relatively sharp and configured to cut, shear or break the membrane 274 as the over-traveling piston rod 60'' advances the plunger 280 further into the bore 272. To provide a vent path to the membrane 274, the plunger body 282 can have an axially extending recess 290, which can be a flat surface located radially inward of the plunger's circumferential outer portion 284. The recess 290 terminates proximate to but spaced from the sharp edge 288. To retain the plunger 280 within the body 264, the plunger may be received in the bore with a slight press or interference fit sufficient to retain it within the bore 272, but not creating sufficient frictional force to prevent the plunger from being advanced into the bore by the piston rod 60'' over-traveling to cut, shear or otherwise break the membrane 274.

[0029] 24 illustrates a modification of the release body 264 by adding an integral thin metal yieldable tubular portion 292 to the end of the body 264 which projects into the pressure chamber 56''. This tubular portion 292 extends axially at least desirably slightly beyond the adjacent end 286 of the plunger 280 to prevent the piston rod 60'' from accidentally displacing the plunger and rupturing the membrane 274 when no compressed gas is present in the pressure chamber 56'' such as during transportation or servicing of the gas spring 50''.

[0030] 25 and 26 show another form of an overtravel pressure relief assembly 300 that is received in a bore 302 having a counterbore 304 through the rear head 54'''' of the gas spring 50'''' and can be installed and completely removed from outside the gas spring. The release assembly 300 can include a body 306 having an externally threaded portion 308 engageable with complementary internal threads in the bore 302 and an enlarged non-circular head 310 having a hexagonal, square, or other non-circular configuration for engagement by a complementary tool to install or remove the release assembly 300 in the head 54''''. The body 306 can include a shoulder 312 that can abut a flat surface of the counterbore to limit the extent to which the body can be threaded into the bore 302 in the head 54''''. A seal 314, such as an O-ring, can be received in a circumferentially continuous groove 316 in the body to provide an airtight seal between the body 306 and the head 54''''. 25 and 30, the body 306 can have an axially extending blind bore 318 which can be coaxial with the threads 308, with an open end communicating with the pressure chamber and adjacent the blind end, at least a portion of one face of a membrane 320 protruding radially into the bore 318. The outer surface of the membrane 320 can communicate with a lateral bore 322 in the body 306 which communicates with the exterior of the gas spring, desirably through a counterbore 304 in the head which opens to the exterior of the gas spring 50''''.

[0031] A plunger 323 can have a body 324 having a cylindrical outer surface 326 with one end 328 configured to be engaged by a piston rod 60'' that overtravels to advance the plunger 322 into the bore 318, and at the other end, an overtravel piston rod 60''. The plunger body 324 may have a relatively sharp edge 330 configured to cut, shear or break the membrane 320 when the plunger rod 60'' advances the sharp edge of the plunger body over at least a portion of the membrane. To provide a passageway for the compressed gas in the chamber 56'' to communicate with the ruptured membrane, the body may be provided by a flat surface extending axially radially inwardly about the circumferential periphery of the plunger body 324 and may have an axially extending recess 332 terminating adjacent and spaced some distance from the cutting edge 330 such that when the plunger 322 ruptures the membrane 320, the passageway 332 communicates with the exterior of the gas spring through the rupture and bores 322 and 304. When the pressure chamber 56'' does not have compressed gas therein, such as during transportation or inspection of the gas spring, a protective tube or sleeve 334 may be received within the bore 318 of the head 54'''' with one end abutting the body 306 and the other end extending at least axially to, and desirably slightly beyond, the adjacent end 328 of the plunger 322 to prevent the piston rod 60'''' from accidentally engaging and displacing the plunger and rupturing the membrane 320. This sleeve 334 may be received within the bore 302 with a slight interference fit. This sleeve may be made of a yieldable material, such as a polymer or thin metal, that can be compressed or crushed when the piston rod 60'' overtravels and displaces the plunger 280 and ruptures the membrane 320 during use of the gas spring 50''''. The basic structure and arrangement of the recessed membrane 320, cutting edge 330, and vent surface 332 of the plunger 322 may be essentially the same as those of the membrane, cutting edge, and vent surface of the plunger of the release assembly 260, and therefore the description thereof will not be repeated here.

[0032] Pressure release assemblies 70 and 160 having a plunger that can be press-fit or interference-fitted into the rear head or wall of the gas spring may be particularly desirable when there is little space or area in the head and / or pressure chamber of a gas spring, such as a small diameter gas spring, or when the gas spring is discarded and not repaired or reused after the first or one occurrence of over-travel of its piston rod breaks the membrane of its release assembly and vents the compressed gas in the chamber. When it is desirable to reuse the gas spring after over-travel of its piston rod breaks the membrane of its release assembly, removable release assemblies 210 and 300 and removable membrane release assembly 160 can be used. This may be particularly desirable with larger diameter gas springs and / or long strokes between the extended and designed retracted positions of their piston rods, since such gas springs are typically significantly more expensive to make than small diameter gas springs.

[0033] All of the disclosed pressure relief assemblies are actuated solely by the piston rod overtravel of the gas spring with which they are assembled, regardless of the gas pressure with which that pressure chamber is initially charged and the maximum pressure that is generated in that chamber when the piston rod is retracted to its maximum design intended position. In other words, these assemblies provide overtravel pressure relief regardless of the pressure of compressed gas in the chamber, and thus gas springs having these release assemblies can be charged to a variety of operating pressures depending on the particular application in which they are used. All of these piston rod overtravel pressure relief assemblies also provide reliable operation because they are directly actuated to provide pressure relief solely by the axial retraction overtravel of the piston rod of the gas spring with which they are utilized.

[0034] While the various forms of the overtravel pressure relief assembly herein constitute presently preferred embodiments, many other forms are possible. It is not intended herein to mention all possible embodiments of the invention or equivalent forms or derivatives. It is understood that the terms used herein are merely descriptive rather than limiting, and that various modifications can be made without departing from the spirit or scope of the invention.

Claims

1. a casing including an axially extending sidewall, an open end, a transversely extending end wall axially spaced from said open end, and a gas pressure chamber defined in part by said sidewall and said end wall; a piston rod at least partially received within said casing for reciprocal movement between an extended position and a retracted position; a pressure relief assembly carried by the end wall; when the piston rod is in the extended position, an inner end of the piston rod communicates with the pressure chamber and an outer end of the piston rod extends generally axially outward from the open end of the casing; The pressure relief assembly includes: a membrane having a first surface communicating with the pressure chamber and a second surface communicating with an exterior of the casing; a plunger having a cylindrical outer periphery, a first end adjacent the membrane, the first end having a protrusion adjacent a portion of the cylindrical outer periphery that includes a sharp edge and configured to rupture the membrane, and a second end axially spaced from the first end; the plunger is disposed within the pressure chamber and configured such that when the piston rod overtravels its designed intended maximum retracted position, the piston rod engages the plunger to move the plunger and break the membrane with the sharp edge of the protrusion.

2. a first blind bore in the end wall forming the first surface of the membrane and in communication with the pressure chamber; 2. The gas spring of claim 1, further comprising a second blind bore in said end wall forming said second surface of said membrane and communicating with said exterior of said casing.

3. the plunger comprises a body having the cylindrical portion of the plunger at least partially between the first end and the second end of the plunger; 3. The gas spring of claim 2, wherein said cylindrical portion of said plunger is partially received within said first blind bore.

4. the projection of the plunger comprises at least two circumferentially spaced, axially extending fingers adjacent the first end of the plunger; Each of the fingers has a relatively sharp edge; 4. The gas spring of claim 3, wherein the relatively sharp edge is configured to break the membrane when advanced at least partially through the membrane by overtravel of the piston rod moving the plunger toward the membrane.

5. The gas spring of claim 4 , wherein the sharp edge is configured adjacent a periphery of the first bore.

6. 5. The gas spring of claim 4, wherein each edge is spaced radially inward of the cylindrical portion of the body of the plunger and radially inward of the periphery of the first bore.

7. the body further comprising only one projection having the sharp edge adjacent the first end of the plunger; 4. The gas spring of claim 3, wherein the sharp edge is configured to break the membrane when moved at least partially through the membrane by the overtravel of the piston rod.

8. The gas spring of claim 3 further comprising an air passage through the plunger body.

9. The cylindrical surface further includes a recess, The gas spring of claim 3 , wherein the recess extends generally axially along the body to provide at least a portion of an air passage between the pressure chamber and the membrane.

10. 2. The gas spring of claim 1, wherein the membrane is a homogeneous, integral part of the end wall.

11. 3. The gas spring of claim 2, wherein the membrane is a homogeneous, integral part of the end wall.

12. 4. The gas spring of claim 3, wherein the membrane is a homogeneous, integral part of the end wall.

13. the membrane is a separate piece from and removable from the end wall; a bore in said end wall communicating with said pressure chamber and a counterbore in said end wall communicating with an exterior of said end wall; The plunger is received within the bore; the separate membrane is received within the counterbore and communicates with the pressure chamber; A collar is removably received within the counterbore; the collar abuts and retains the separate membrane within the counterbore; 2. The gas spring of claim 1, wherein the collar has a through passageway that communicates the membrane with an exterior of the gas spring.

14. 14. The gas spring of claim 13, wherein the collar includes external threads engagable with complementary threads in the counterbore.

15. a passageway through the end wall communicating with the pressure chamber and the exterior of the gas spring; a body received within the passage; a blind bore in the body; the membrane is carried by the body and at least partially within the blind bore of the body; the blind bore communicates with the pressure chamber and the first surface of the membrane; 2. The gas spring of claim 1, wherein the plunger is received in the blind passage with a first end thereof adjacent the membrane.

16. 16. The gas spring of claim 15, wherein the membrane extends generally laterally across at least a portion of the blind bore and is at least a portion of a closed end of the blind bore.

17. 16. The gas spring of claim 15, wherein the membrane is a homogeneous, integral part of the body and protrudes generally radially into the blind passage adjacent a closed end of the blind passage.

18. 18. The gas spring of claim 17, wherein a portion of the plunger is frictionally received and retained within the blind passage of the body.

19. a spring formed of a yieldable material, surrounding at least a portion of the plunger, received within the bore through the end wall, and extending generally axially from at least the second end of the plunger; 20. The gas spring of claim 18, further comprising a sleeve extending in the direction perpendicular to the axis of the gas spring.

20. 16. The gas spring of claim 15, wherein the body includes external threads matable with complementary threads in the passage through the end wall.

21. 16. The gas spring of claim 15, wherein the body is frictionally received within the passage through the end wall by an interference fit.

Images