GAS SPRING WITH HYDRAULIC ACCUMULATOR

An industrial gas spring with a hydraulic accumulator includes a piston rod of the received in a hydraulic chamber connected to a gas over hydraulic fluid accumulator chamber in which a compressed gas determines the force required to yieldably move the piston rod from its extended position to its retracted position. On a return stroke of the piston rod as it approaches its fully extended position, a hydraulic damper chamber in the hydraulic cylinder may reduce the velocity of the returning piston rod. The damper chamber may return a hydraulic fluid through an orifice to the hydraulic cylinder chamber. The orifice may provide a varying restriction to vary and control the velocity or rate at which the piston rod returns to its fully extended position.

TECHNICAL FIELD

This invention relates generally to industrial gas springs for forming equipment and more particularly to industrial gas springs with piston rod stroke dampers.

BACKGROUND

Industrial gas springs are well known and have been used in many applications of forming equipment including stamping dies, progressive dies, and racks for progressive dies, for sheet metal stamping, punching, and piercing operations.

A conventional industrial gas spring may include a casing, a piston rod received in part in the casing, a piston rod bearing and seal assembly and a pressure chamber to hold pressurized gas, typically nitrogen, at an operating pressure of, for example, 1,000 to 5,000 psi in some applications. The pressurized gas biases the piston rod to its extended position and yieldingly resists movement of the piston rod from its extended position to its retracted position. In some applications the pressurized gas returns the piston rod from its retracted position to its fully extended position with such a high velocity and force that it produces undesirable vibration and workpiece movement and may even result in dislocation of a workpiece and cause damage to the die or other equipment in which it is used. In some applications this undesirable vibration and workpiece movement has been reduced by use of a separate shock absorber assembly spaced laterally away from the gas spring. But the separate shock absorber assembly adds cost and complexity to the application and introduces a moment arm that is attributed to a distance between the gas spring and the shock absorber assembly and that can lead to stress in such applications. In other applications this undesirable vibration and workpiece movement has been reduced by a cushion chamber in which gas is compressed as the piston rod returns to its fully extended position but this compressed gas cushion chamber may cause the piston rod to momentarily partially retract into the cylinder before it reaches its fully extended position and thus still produce some undesirable vibration and workpiece movement. Such a gas spring is disclosed in U.S. Pat. No. 9,416,840 assigned to Dadco Inc. Therefore, there is still a need for a gas spring which further dampens and significantly reduces this undesirable vibration and workpiece movement.

SUMMARY

In some applications an industrial gas spring may include a self-contained or preferably linked, hydraulic cylinder assembly with a dampener on the return stroke. In some applications a piston rod may be received in a hydraulic chamber connected to a gas over hydraulic fluid accumulator chamber in which a compressed gas such as nitrogen determines the force required to yieldably move the piston rod from its extended position to its retracted position. On a return stroke of the piston rod as it approaches its fully extended position a hydraulic damper chamber in the hydraulic cylinder may reduce the velocity of the returning piston rod. In some applications the damper chamber may return a hydraulic fluid such as an incompressible hydraulic oil through a throttling or restricted orifice to the hydraulic cylinder chamber. In some applications the orifice may provide a varying restriction to vary and control the velocity or rate at which the piston rod returns to its fully extended position. The hydraulic damper chamber when activated counteracts the force on the piston rod created by the nitrogen gas in the accumulator chamber and causes the returning piston rod to slow down at a predetermined rate.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring in more detail to the drawings,FIGS.1-3illustrate an industrial gas spring assembly20including an accumulator cylinder22and a hydraulic cylinder24with a piston rod26and a hydraulic damper28(FIG.3). In use the accumulator cylinder22provides a pressurized hydraulic fluid (sometimes herein after referred to as hydraulic oil) to the hydraulic cylinder24to yieldably urge the piston rod26to its fully extended position and the hydraulic damper28decreases the velocity of the piston rod26as it approaches its fully extended position.

As best shown inFIGS.4&5, the accumulator cylinder22may have a tubular casing30with a closed end32and an open end34with a head36received and removably retained therein by a retaining ring38and with a seal40such as an o-ring received between them. A piston42may be slidably received in an inner cylindrical surface or bore44of the casing30with seals50such as O-rings between them and received in grooves48of the piston42. If desired, guide rings or bearings46may also be received in grooves in the piston42and bear on the casing30. The piston42and casing30may define a gas chamber54on one side of the piston42and on its other side a hydraulic fluid accumulation chamber56.

As best shown inFIG.7, for charging the gas chamber54with a compressed gas such as nitrogen (and/or discharging the compressed gas) a port58may communicate it with a passage60communicating with a fill adapter62which may include a valve (not shown) such as a Schrader valve for opening and closing communication with the passage60. An overpressure relief valve assembly64, a rupture disc, or the like may also be received in the passage60) to communicate the gas chamber54with the atmosphere exteriorly of the casing30in the event of and to relieve an overpressure condition occurring in the gas chamber54.

As shown inFIGS.3-5, the hydraulic fluid accumulation chamber56may continuously communicate with the hydraulic cylinder24via a passage66through the head36communicating with interconnected passages68,70&72in a base plate74. An O-ring seal75(FIG.4) may encircle the passages66&68and be received between the head36and the base plate74. A hydraulic oil fill valve76and a protective plug78may communicate with one end of the passage70which may be closed and sealed at its other end by a plug80threaded therein. The accumulator cylinder22may be received between and attached to the base plate74by cap screws (not shown) threaded into the head36and a top plate82by cap screws84(FIG.2).

Alternatively, as shown inFIG.6, according to another embodiment of a gas spring assembly20′, the accumulator cylinder22and top and bottom plates82′ &74′ may be retained in assembled relationship by tie rods86attached to the plates by cap screws88or the like. Also, a pressure relief valve64′ and a fill adapter62′ may be carried by the top plate82′ along with corresponding passages (not shown).

As shown inFIGS.3,4&5, the hydraulic cylinder24may have a tubular casing90slidably received through a bore92in the top plate82with its closed end94bearing on the base plate74and releasably retained in assembly by a ring96received in part in a groove98in the casing90and complementary recesses in the outboard face of the top plate82and an abutting face of a retainer plate100slidablely received over the casing90and secured to the top plate by cap screws102. The casing90may have an inner cylindrical surface or bore104which defines in part a first or main hydraulic chamber106which communicates through a passage108through its closed end with the passages68,70&72in the base plate74and30) thus the accumulator hydraulic fluid accumulation chamber56. A seal110may be provided by an o-ring encircling the passages108&72and received between the casing closed end94and the base plate74, for example, in a groove112in the closed end94of the casing90.

As best shown inFIG.7the piston rod26may be slidablely received through an annular housing114with one end extending into the first hydraulic chamber106and its other end axially outboard of the casing90at least when the piston rod26is in its fully extended position. The annular housing114may be removably received in the casing90and retained therein by a retaining ring116received in a complimentary groove118in the casing90and against a shoulder119of the housing114adjacent its outboard end. A seal120may be provided between the casing bore92and the housing114such as by an o-ring received between them and in a groove122in the housing114. The piston rod26may be slidably received through guides or bearings124received in grooves126in the housing114and a piston rod seal128may be received in a groove130in the housing114. A piston rod wiper132may also be received in a groove134adjacent the outboard end of the housing114.

As best shown inFIGS.4,5&7, the hydraulic damper28may have an annular collar140carried by the piston rod26for movement in unison therewith and which, as shown inFIGS.4&5, during movement of the piston rod26from its retracted position (shown inFIG.4) toward its fully extended position (FIG.3) enters through a bore142and into a counterbore or pocket144in the annular housing114to provide a second or secondary hydraulic chamber146which decreases the velocity or rate at which the piston rod26moves to its fully extended position. The collar140may be received and retained on a reduced diameter cylindrical portion148of the piston rod26with one end of the collar140bearing on a shoulder150and a retainer ring152received in a groove154in the rod26and bearing on the other end of the collar140. A seal156may be provided between the collar140and the piston rod26such as by an o-ring received in a groove158in the rod.

With reference toFIG.8, a seal162may be provided between an outer cylindrical surface160of the collar140when received in the housing bore142such as by a hard and wear resistant plastic seal received in a groove164in the housing114along with a high temperature o-ring166vieldablely biasing this plastic seal into engagement with this collar140. This plastic seal may be made of a polyacetal, polyamide or polyolefin material which may have a durometer in the range of 70 to 100 on the Rockwell scale, including all ranges, sub-ranges, values, and endpoints of the aforementioned range. A split ring guide or bearing168may be received in an outwardly opening groove170in an exterior flange172of the collar140and slidably bear on the cylindrical bore104of the casing90.

30) With continued reference toFIG.8, to facilitate the rapid flow of hydraulic oil while the piston rod26(FIG.7) is being retracted from its fully extended position and subsequently advanced toward its extended position at least until the collar140engages the seal162, the collar140has at least one and desirably a plurality of circumferentially spaced apart passages176extending generally axially through the collar140, within its annular wall and opening to or communicating with both ends of the collar140. To at least substantially restrict and desirably prevent the flow of hydraulic oil from the secondary hydraulic chamber146through these passages176as the collar140further advances into the secondary hydraulic chamber146(as the piston rod26advances further toward its fully extended position), a check valve assembly178received in each passage176closes. As best shown inFIG.7, each check valve assembly178may have a ball180engageable with a seat182when closed and engageable with a retainer184when open. Both the seat182and the retainer184have through bores186through which hydraulic oil may flow, and/or oil may flow around the retainer184. Upon a retraction of the piston rod26and thus the collar140, each check valve assembly178opens to permit substantially unrestricted flow of hydraulic oil through these passages176and/or around the retainer184. Desirably, to avoid any significant pressure differential between the first hydraulic chamber106and an annular space188between the housing114and the flange172of the collar140they may continuously communicate such as through a port190and open ends of the passages176.

When the piston rod26advances toward its fully extended position sufficiently for the cylindrical surface160of the hydraulic damper28to engage the seal162, the check valves178close due to the increasing pressure of the hydraulic oil in the secondary hydraulic chamber146(as the piston rod26and collar140further advance) which then flows at least essentially only through a restricted orifice192in an outer cylindrical surface of the collar140to thereby decrease the velocity or rate at which the piston rod26further moves to its20) fully extended position. Desirably, as shown inFIGS.9&10, the orifice192extends generally axially from the proximate end toward the distal end of the collar140with a varying cross section which decreases in cross sectional area as the orifice192extends toward the distal or flange172end of the collar140. Desirably, the orifice192may be configured so that it ends at or slightly after the seal162when the proximal end of the collar140engages the housing shoulder150and thus, the piston rod26is in its fully extended position. This variable orifice192decreases the rate of flow of hydraulic oil from the secondary hydraulic chamber146into the first or main hydraulic chamber106as the collar140advances into the secondary hydraulic chamber146to thereby decrease the rate at which the piston rod26advances to its fully extended position.

The size, shape, and varying cross sectional area of the variable orifice192may be determined in any suitable manner such as empirically or by dynamic incompressible fluid flow formulas and calculations as will be apparent to one of ordinary skill in the art. The configuration of the variable orifice192may be formed in the collar140such as by a ball nose end mill used to machine the orifice192therein. The variable orifice192may be at least partially semicircular in cross sectional shape and may be parabolic through at least part of its longitudinal extent.

For use of the gas spring20, the first hydraulic chamber106including the annular space188, secondary hydraulic chamber146, hydraulic fluid accumulation chamber56and interconnecting passages66,68,70,72&108are filled with sufficient hydraulic oil so that when the piston rod26is fully extended, the accumulator piston42is spaced from the head36such as shown inFIGS.3-5. To facilitate knowing when the accumulator piston42is spaced from the head36, as shown inFIG.11, an indicator rod194may be fixed to the accumulator piston42for movement with it and slidably extend through the upper end of the accumulator cylinder22and into a transparent sight glass198mounted on the upper end of the accumulator cylinder22. Suitable seals200such as o-rings may be disposed between the indicator rod194and the upper end of the accumulator cylinder22.

Alternatively, as shown inFIG.12, a sensor202such as a proximity sensor and associated electrical or electronic circuitry may be used to determine and indicate whether the accumulator piston42is spaced from the end or head36of the hydraulic fluid accumulation chamber56. The proximity sensor202may be mounted in this lower end36; or head and responsive to the position of a rod204fixed to and depending from the accumulator piston for movement therewith. A suitable proximity sensor is available from Automation Direct.com as model No. AEI-AP-3F. If desired, the position of this piston relative to the upper end32or head32; of the accumulator gas chamber54may be determined and indicated by a suitable linear position sensor carried206by the upper end of the accumulator cylinder22with a probe208which extends axially and slidably into a tube210fixed to this piston for movement therewith. A suitable linear position sensor is available from Alliancesensors.com as model No. MHPE-7-100-08-01-11-S-08CS.

The accumulator gas chamber54is filled with a compressed inert gas such as nitrogen to the superatmospheric pressure needed to produce the desired magnitude of the force resisting initial movement of the piston rod26from its fully extended position toward a retracted position. Compressed gas may be supplied to the gas chamber54through the adaptor and filler valve62to the desired pressure which may be indicated by a suitable pressure gauge. As shown inFIG.12, if desired an overtravel pressure relief valve212may be provided to limit the maximum pressure of the gas in the chamber54.

In use, typically the gas spring assembly20is repeatedly cycled with each cycle including a retraction stroke of the piston rod26and collar140from a fully extended position as shown inFIG.3to a retracted position where the collar140is disengaged and spaced from the seal162such as shown inFIG.4and a return stroke to the fully extended position. During an initial part of the retraction stroke the check valves178open and hydraulic oil freely flows through the passages176from the main hydraulic chamber106into the expanding volume of the secondary hydraulic chamber146until the collar140disengages from the seal162and may continue to flow through these passages until the piston rod26and collar140reach the desired retracted position. Typically, after at least an initial part of the return stroke from this desired retracted position, the collar140engages the seal162to provide the secondary hydraulic chamber146and the check valves178close such as shown inFIG.5and as the collar140and the piston rod26further advance to their fully extended position hydraulic oil flows from the secondary hydraulic chamber146(as it decreases in volume) through the variable restricted orifice192to decrease the velocity or rate of return to their fully extended position. Since the effective cross sectional area of the variable restriction orifice192decreases as it passes through the seal162, the velocity or rate at which the piston rod26and the collar140move to their fully extended position continues to decrease.

In use of the gas spring assembly20, the force yieldably biasing the piston rod26to its extended position is believed to be substantially constant since it is a function of the pressure of the compressed gas in the accumulator gas chamber54although it may vary somewhat due to heating and thus expansion of the hydraulic oil and/or heating of the compressed gas which may occur due to rapid cycling of the piston rod. But when the piston rod26is retracted and the piston42in the accumulator travels up, the gas chamber decreases and thus the pressure of the gas will increase. The presently disclosed gas spring may eliminate the need for separate shock absorbers spaced laterally away from prior gas springs that do not have one or more of the inventive features disclosed herein.

FIGS.13through17show another illustrative embodiment of a gas spring assembly320. This embodiment is similar in many respects to the embodiment ofFIGS.1—12and like numerals between the embodiments generally designate like or corresponding elements throughout the several views of the drawing figures. Accordingly, the descriptions of the embodiments are hereby incorporated into one another, and description of subject matter common to the embodiments generally may not be repeated.

With reference toFIG.13, the gas spring assembly320includes an accumulator cylinder322including a casing330a,b,c, and a hydraulic cylinder324in fluid communication with the accumulator cylinder322and including a casing390and a piston rod326partly slidably carried in the casing390. The assembly320further includes a base plate374on which lower ends of the cylinders322,324are supported and through which the cylinders322,324fluidically communicate with one another. Although not shown, the hydraulic cylinder324may be coupled to the base plate374via fasteners, welding, threading, or any other suitable coupling. The assembly320additionally includes a top plate382coupled to upper ends of the cylinders322,324, and fastened to the base plate374via suitable fasteners, for instance, cap screws384and tie rods386that may have upper ends threaded to the cap screws384and lower ends threaded into the base plate374. The assembly320also includes a retainer plate400fastened to the top plate382via cap screws402to retain the casing390to the top plate382. Accordingly, the casings330a,b,c,390of the accumulator and hydraulic cylinders322,324are axially trapped between the base and top plates374,382.

The assembly320is structurally and functionally similar to the assembly20illustrated inFIGS.1-12, with some differences that will be described in detail below, with reference toFIGS.13-17.

According to a first difference, the assembly320includes a gas path for charging and/or discharging a gas chamber354. The gas path includes a port358integrated into the top plate382and in communication with the gas chamber354, and with a passage360also integrated into the top plate382and communicating with a fill adapter362for opening and closing communication with the passage360.

According to a second difference, an overpressure relief valve assembly364, a rupture disc, or the like may also be received in a through passage (not shown) through the top plate382to communicate the gas chamber354with the atmosphere exteriorly of the casing330a,b,cin the event of, and to relieve, an overpressure condition occurring in the gas chamber354.

According to a third difference, the accumulator assembly322has a multi-piece casing330a,b,cincluding a first or lower casing330ahaving a lower end514that may be carried in a counterbore516in an upper surface of the base plate374and sealed thereto via one or more seals518. The lower casing330amay be composed of metal, for instance, aluminum or steel tubing and, thus, may be opaque, and facilitates heat dissipation through the cylinder322. The casing330a, b,calso includes a second or upper casing330bhaving an upper end520that may be carried in a counterbore522in a lower surface of the top plate382and sealed thereto via one or more seals524. The upper casing330bmay be composed of a composite, for instance, POLYSIGHT brand composite tubing available from Polygon Composites (www.poblygoncomposites.com) and, thus, may be translucent. Accordingly, one can see various positions of the piston342when filling the gas spring assembly320with hydraulic fluid and/or when charging the gas spring assembly320with gas. The casing330a,b,cfurther includes a third or intermediate casing330ccoupled to the lower and upper casings330a.b. The intermediate casing330cmay include a throughbore that has one or more grooves, reliefs, or the like to carry one or more elements530like seals, wipers, bushings, bearings, and/or the like, and a lower counterbore that receives an upper end526of the lower casing330a, and an upper counterbore that receives a lower end528of the upper casing330b. More specifically, the intermediate casing330cmay be coupled between the lower and upper casings330a,band may carry axially spaced seals530to cooperate with the piston342to further define and separate the hydraulic fluid accumulation chamber536and the gas chamber354.

According to a fourth difference, the piston342is much longer than the previously disclosed piston42ofFIGS.1-14, and has a base wall532at a closed end, a side wall534extending upwardly from the base wall532, and an outwardly flared flange536terminating the side wall534at an open end. The piston342also may include one or more transversely extending holes538proximate the open end, and a guide ring540) carried in a corresponding groove of the flange536. The guide ring540contacts an interior surface of the translucent casing330band, thus, is easy to see externally of the casing330b. In other embodiments, the piston342need not include the flange536or the guide ring540and, instead, the sidewall534could be straight with a slight annular gap between an outer surface of the sidewall534and an interior surface of the translucent casing330bto allow visualization of the positions of the piston342.

According to a fifth difference, the casing330a,b,calso may include a gas vent542through a side thereof. More specifically, the intermediate casing330ccarries the gas vent542in a corresponding vent passage positioned axially between two seals530. The gas vent542permits any gas from the gas chamber354that might be leaking past an upper one of the seals530to vent out the side of the casing330cto atmosphere, instead of leaking into hydraulic fluid in the hydraulic fluid accumulator chamber356, which leakage could cause the hydraulic fluid to lose its incompressibility characteristics.

According to a sixth difference, the hydraulic cylinder324has a collar440with one or more passages476carrying one or more check valves478. With reference toFIGS.15-17, each check valve478includes a ball480, a seat482against which the ball480sealingly seats, and a retainer484coupled to the seat482and against which the ball480may move within but not seal against, such that fluid can flow around the ball480and through external flutes485.

While the forms and embodiments of the invention described herein constitute presently preferred forms and embodiments, many others are possible any may occur to one skilled in the art. It is not intended to mention herein all the possible equivalent forms and embodiments or ramifications of the invention. The terms used herein are merely descriptive, rather than limiting, and various changes may be made without departing from the spirit or scope of the invention.