CA1162955A - Improved pneumatic counterbalance - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A pneumatic spring counterbalance extensible link including a closed end cylinder with an end connector a piston and rod assembly within the cylinder and maintained therein by the crimped over end portion of the cylinder retaining a rod bushing and rod to cylinder seal. The cylinder is pressurized prior to assembly of the complete piston and rod assembly into the cylinder. The piston assembly includes orifice by-pass means either in the piston periphery or in a piston ring, and the piston may include a fail-safe provision in the event the orifice is clogged.
A crimping die assembly is used in assembling and completing final assembly of the counterbalance components while simultaneously maintaining the link in a pressurized environment, utilizing a sealed arrangement between the crimping dies to maintain pressurization of the interior of the dies and the counterbalance components prior to assembly of the components. A dual force embodiment of the counter-balance unit is disclosed and utilizes a floating sealed piston below the main piston and rod assembly. entrapping pre-charged gas in the space between the floating piston and the closed end of the cylinder.

Description

2~ 5 BAC~GROU~D OF TT~E INVENTION
Pneumatic counterbalance units have come into ~idespread use in recent years, being used on various automotive comp~onents such as hoods, trunk lias, hatch backs and on other items such as machine covers, doors and hatchesO
Such pneumatic counterbalances are rather simple pneumatic piston/cylin~er arrangements having a bleed by-pass through or past the piston similar to shock absorbers and oleo struts used on vehicles and aircraft for many years. The well-kno~n principle of operatio~ is based on differential pressure "

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resulting from the differential in cross section areas of the two chambers within the cylinder caused by the piston rod on one side of the pis~on which reduces the area on that side of the pistonO Pneumatic counterbalance units, prior to this invention~ have been pressurized subsequent to assembly, past the shaft seal, or through a fill valve or a fill port which is sealed after pressurization. Prior art units utilize orifice bleed passages through the piston or through the piston rod from one side of the piston to the other side and more sophisticated units have a valving device which varies the bleed rate depending on the direction of movement of the piston.
Other forms of counterbalance devices provide a dual force by using a supplemental compression coil spring which becomes ef~ective at an intermediate position of the piston xod retraction stroke.
Examples of prior art counterbalance units can be seen in the following U.S PatentsO Patent No. 1,994,722 to O. W. Landerslager for Resilient Device; Patent No. 2,774,446 to Bourcier de Carbon for Shock Absorbers; Patent No. 2,788,857 to A~Ro Causse for Shock Absorber, Patent No. 3,207~9~ to E. Wustenhagen et al for Gas Spring, Patent No. 3,222,047 to F. Tuczek for a Pneumatic Suspension Unit; Patent No. 3,589,701 to D~Wo Gee for Vehicl Suspension (Gas 5pring); Patent No.

3,856,287 to Preitag for Piston Rod Seal For Adjustable Pneumatic Spring, Patent No. 3,86~,097 to P.H. Taylor for ~iquid Spring; Patent No. 3,913,g01 to W. Molders for Resilient Supporting Column; Patent No. 3,963,227 to W. Molders for Gas Spring with Dual Damping; Patent No. 4,030,715 to H.O.
Duran for Pneumatic Shock Absorber; Patent No. 4,064,977 to D.F. Taylor for Fluid Amplified Shock Absorber Having De ~aval sd ~ ~ -2-2 9 ~ ~
1 Nozzle; Patent No. 4,09~,302 to Freitag for ~ethod for 2, Charging Pneumatic Suspension Element; and Patent No.
3 d,108, 423 to ~.J. Skubal for Gas Spring~ r~o~k of the

4 foregoing patents disclose various types of piston unit oriflces and of different klnds of seals between the piston 6 rod and cylinder, some being plural O-rings or flat washers 7 or a combination of both kinds and some, e.g., Taylor and 8~ Duran use chevron seals. Duran shows an anti-friction 9l ring on the piston with plural peripheral notches providing 10~ free-flow by-pass of fluid. Some disclose methods of 11, pressuri~ing, e.g., De Carbon shows a valved inlet;
12 , Tuczek shows a multiple inlet svstem with lines and 13, accumulators; Freitag 3,856,287 shows a ball clleck valve;
14i and Freitag 4,098,302 charges gas and liquid past the seals.
15,l' The Taylor Patent No. 3,868,097 teaches a structure and 16 l method of assembl~ for a liquid spring.
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~ 11629~5 SUMMARY OF THE INVENTION
The increase of use of pneumatlc counterbalance units in consumer items has raquired increased production which can result in lac]c of quality control, e.g.~ manufacture requires pressuriza~ion by various techniques of introducing gas into the cylinder following assembly and results in lack of accurate control over the requisite force needed for specific applications. By the present invention a method and tool structure has been developed to make a gas spring counterbalance and includes pressurization within a crimping die assembly, just prior to completely inserting the piston and rod assembly, and maintaining the pressurization during crimping of the cylinder. This results in very accurate quality control of the pressurization of completed unitsO
A unique die assembly was developed to accommodate the method of assembly.
Further developments included a difEerent shaft seal arrangement and providing extruded piston rings with preformed peripheral orifice control grooves and specially .0 constructed piston rings with bi-directional by-pass and metering orifices to control linkage extension and retraction speeds.
To avoid the detrimental aspects of th~ extensible link becoming a fixed length link should the metering orifice become clogged, a fail safe feature has been developed to release the piston seal if the extension force exceeds a certain valueO Also it is desirable in some installations to have a dua~ ~orce capability in the counterbalance unit.
To solve this problem and avoid use of mechanical springs which can break or lose their spring force over a period of extended use, a floating piston COnGept was developed. Such a floating piston is pre-inserted and entraps gas in a lower sd~

~ ~29~5 chamher wikhin the cylinder and its assembly and pressuriza tion can be accommodated by the assembly tools and method of this invention.
A primary feature of this invention resi~es in the provision of a novel pneumatic counterbalance link. The link is pressurized before and during the assembly step.
The piston rod is sealed by a large O-ring or the equivalent which also seals against the c~linder and end bushing.
Unidirectional seal rings, such as a chevron seal, can be used if desired. Several novel embodiments of metering orifices across the piston in the counterbalance combination unit include a preformed radial orifice groove in a piston flange, a preformed peripheral metering groove in an extruded piston ring or providing preformed metering grooves with correlated by-pass grooves in an O-ring held between axially spaced piston flanges. Use of grooves in the piston ring to provide the b~~pass orifices and the metering orifices results in an advantage over the apertured type orifices because the grooves will inherently self clean as the stroke is reversed and the ring moves away from engagement with the piston flange. ~esiliency o-E the O-ring results in flexing of the grooved areas of the O-ring and ; aids in eliminating any contaminants or clogging. The piston flanges enable provision of a fail-safe structure which is accomplished by controlled thickness of all or a portion of one of -the flanges enabling failure by at least a partial destruction of the flange under pre-calculated applied force, resulting in eliminating the orifice controlled bleed pask the p:lston but retaining the basic pneumatic counterbalance action of -the counterbalance link.
A further aspect of this invention resides in the provision of a novel method of assembly of pneumatic counter-sd/fl:~

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balance units wherein the components of the unit are positioned within crimping die tools in a crimping press with a small quantity of oil for lubrication pre-introduced into the cylinder component; the die parts with the components of the unit are moved toward assembly; the die tool parts engage and provide a sealed compartment surround-ing all components of the counterbalance unit. ~t this stage of assembly the die tool compartment is pressurized by gas (e.g., air or nitrogen) under pressure through valve controlled pneumatic pressurizing connections frQm a pressure source. While pressurized the press movement continues, the crimping die parts move closer and the piston assembly parts including the rod seal and the end bushing move into the cylinder entrapping a quantity of pressurized gas within the cylinder. As the press action continues, the open end wall portion of the cylinder is crimped inward by the crimping die tool which retains the bushing, seal, rod and piston in the cylinder and completes the assembly. Via suitable valve control, the sealed die compartment is vented, pre.ssurization is released, the press is reversed, the tools part and the completely assembled counterbalance uni-t is remo~ed.
As further aspects of the invention, the same assembly method can be used to assembly a dual ~orce counter-balance unit, which will include a floating peripherally sealed piston in the cylinder below the rod and primary piston assemblyO The floating piston component can be carried on the bottom of the primary piston, adhered thereto by magnetic force or by use of a sticky substance, such as grease, or the like. As the die parts move toward each other and create the sealed compartment an initial pressuriza-tion of the compartment is ca~sed, and the floating piston is sd/ -6-introduced into the cylinder to a point which accomplishes a sealed relationship with the cylinder, whereupon the die compartment is subjected to higher pressurization, the floating piston sepa.rates from the primary piston and moves into the sd/~ 6A-29~
l' cylinder to an intermediate location of e~uali~ation of 2I pressures on both faces and an addi-tional small quantity 3, oE oil for lubrication is introduced into the cylincler on 4 top of the floating piston. Continued movement of the press and crimping dies completes the asse~bly of the piston and 6 rocl into the cylinder and crimps the cylinder, followed by 7l, removal of pressurization, parting of the die parts and 8' removal of the completed unit.
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'J~; 9 1I Still another ~e~ of the present invention `lO I resides in the provision of novel apparatus to accomplish 11l the combination single stroke assembly and pressurization 12 1l of a pneumatic counterbalance unit. In conjunction with 13 this object is the provision of a novel crimping die tool 14i set for use in a machine press including jig structures to 15',, maintain counterbalance components in pre-assembly positions 16, and having structure to provide a closed sealed cavity 17 , around the counterbalance components together with a system to 18 ll controllably pressuri~e and de-pressurize the cavity durlng l9 il the final stages of assembly of the counterbalance unit. A
20 ll further novel feature resides in provision for pressure injection 21 1l of a predetermined quantity of lubricating oil into the 22 , cylinder after pressurization of the die cavity. This feature 23 l' can be used to introduce oil into the bottom of the cylinder 24 l as well as on top of the floating piston.
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25 1I Further novel features and other ~e~s of this 26 inventlon will hecome apparent from the following detailed 27 1l description, discussion and the appended claims taken in 28 !I conjunction with the accompanying drawings.

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1 BRIEF DESCRIPTION OF I~HE DRAWINGS
2 A preferred structural embodiment of the apparatus 3 and various embodiments of the pneumatic counterbalance 4 of this invention are disclosed i.n the accompanying drawings, in ~ hiCh:
6 Figures 1-4 lllustrate apparatus in accord wi~.h this 7j invention by which the inventive method can be carried out to 8l assemble and pressurize a completed pneumatic counterbalance 9l unit, Figures 1, 2, 3 and 4 showing respective progressive 10~ stages and positions of the press heads, crimping dies and ll, counterbalance components to final assembly of the inventive 12~ counterbalance unit;
13~', Figure 2~ is an enlarged detail section taken on 141 line 2A-2A of Figure 2 through the open end wall of a 15, counterbalance cylinder component prior to assemklyi 16,, E~igure 5 is a partially sectioned elevation view of 17¦ a comPlete pneuma~ic counterbalance link unit according to 18' this invention;
19,. Figure 6 is an enlargea cross section detail of the 20, unit of Figure 5 showing the shaft seal, the shaft, the piston 211 and the piston ring in its metering position when the link 22; is being extended;
23l Flgure 7 is a view simi,lar to Figure 6 hut showing 2d", the piston ring in the by-pass flow position which occurs 25lj when the link is being retracted;
26., Figures 8 and 9, respectively, a plan view and' 27~l a cross section view taken on line 9-9 of Figure 8, show 28,~ the shape and groove details of the piston ring used in the 29,, unit o Figure 5;
30~.¦ Figure lO is a further embodiment o a counter'-31l, balance unit which includes the same components shown in 32'l Figure 5-9 and in addition includes a 10ating piston to 33' provide a dual force counterbalance link;

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-, --8--~ ~2~5 1 ~ Figure 11 is an enlarged de-tail sect.ion of the 2 unit in Figure ]0 showing the primary piston and the floatiny 3 piston positioned in the overload secondary force condition;
4 ~ Figures 12, 13, 13A and 14 are somewhat schematic depictions of stages o:E assemhly of a dual force counter-6 balance link such as shown in Figure 10;
7 , Figure 15 is a schematic depiction of a completely 8 ~ assembled and pressurized dual force unit with the primary 9 ' ~iston spaced from the floating piston in a normal force 10l' condition;
11 , Figure 16 is a schematic depiction like 12 ,~ Figure 15 but illustrates the two pistons engaged and disposed 13, in an overload force condition;
14 jl Figure 17 is a further embodiment with a modified piston assembly with metered orifice extruded in the outer 16' peri~hery of the piston ring;
17~ Figure 18 is a plan view of the cup washer portion 18 ~ of the piston assembly shown in E'igure 17;
19 ¦ Figure 19 is a plan view of the extruded piston 20~, ring of the piston assembly shown in Figure 17;
ii 21 ll Figure 19A is a plan view of a modified piston ring;
22 ¦¦ Figures 20, 21 and 22 are detail section views 23 1i illustrating extansion, retraction and neutral cond.itions of i 24 a still further embodiment of a piston assembly;
25 1I Figure 22A is a plan view of the upper piston 26 1l washer of the Figure 20 device, and 27 ~¦ Figures 23 and 24 are detail views of a further 28 I piston ring molded embodiment with the metering orifice 29 provided as a groove molded 'n the .ing.

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GENEP~AL r)ESCRIPTION
, 2` The various aspects of the invention herein include 3 articles known as ~neumatic or gas springs, which for 4 convenience can be referred to as counterbalance links, as well as an ap aratus and method for making the ar~icles.
6 Representative embodiments of the counterbalance linXs are 7I seen in Figures 5, ]0 and 17 as well as in various other 8 detail views. Figures 5 and 10 of the original Patent Drawings 9~ are full scale of actual units.
10, The first portion of this description will be 11,' directed to the apparatus for making (or assembling) the 12 ll counterbalance links but initially reference is to Figure 5 13 where is shown a rèpresentative embodiment of a counterbalance 14l link 30 having a cylinder 32 whose length will be determined 15,, by the kind of equipment with which the unit is used. I~ithin 16 the cylinder is a piston assembly 34 which separates the 17' cylinder into two compartments which are filled with gas 18 ll (e.g., air, nitro~en or some other inert gas) under pressureO
19, The piston assembly includes a free fitting piston 3G, a piston 20~l ring 38 and the Piston rod or shaft 40 secured at one end 42 21ii to the piston 36 as by swaging over or rlveting the end at 44.
22~l, These pn~umatic counterkalance units, particularly in auto-23,l motive installations are oft`en pressurized up to around 241 2000 psi gas pressure. Pressures can be higher or lower 25''l depending on the instaliation. A counterbalance unit with a piston rod having approximately 0.10 inch~cross-section 27~' area will provide a 5 pound extension force when the cylinder 28il is pre-pressurized at approximately 50 psi, and a 200 pound 29l, force when pressurized at 2000 psi.
30llThe piston shaft 40 pro~ects out through one end 3148 of cylinder 32, the other end 50 of which is closed, as lll l l ~ ~B~9~5 1 by welding a disc 52 thereto. The projected end of shaft 40 has a connector link 54 rigidly secured thereto, as by screw 3 threacls or welding, and a second connector lin]c 56 is secured 4 to the cylincler closed end 50, as by screw threads or ~elding.
Within the cylinder, shaft 40 passes through a large O-ring 6 ' seal 58 and a shaped hushing 60 which has a free close-fit 7 around the shaft ~0 and within cylinder 32~ With the open 8 ' cyllnder end 48 crimped at 62 the bushing 60 provides an g ll end stop abutment for piston movement cushioned by the ll O-ring seal 58. Internal gas pressure keeps the seal 58 ~ and bushing 60 in the end position against the crimped end of 12 , cylinder 32. As shown in Figures 2-4, a pre-determined 13 small quantity of oil 64, e.g., 3-4 cc is placed into 14 i cylinder 32 prior to asse~bly and provides lubrication for I the piston rlng and the large O-ring seal 58. Unit 55 16 represents an attachment clip and is not per se a part of 17 I this invention.

., ~ Suitable materials for the various components can be 19 " mandrel drawn hydraulic steel tubing ~or the cylinder, sheet ii :
~~ steel for the end disc, the piston shaft is hardened, chrome 21 !' plated steel, the bushing can be made from aluminum or steel, 22 !1l the O-ring is elastomeric, e.g. rub~er or plastic, and 23 ' the piston is made from aluminum. As will be described in 2~ 'l detail, the piston and ring components can be and are 2~ ` preferably made from various other materials depending upon ~6 ~ the configuration or modification of desisr.. The piston 27 ~ and its ring, as are true of pneumatic springs, are constructed 28 Ij to provide controlled by-pass flow of gas from one side of 29 l the piston to the other side. There is a relatively free flow l' _ , ~y-pass provided during the retraction or compression stroke 31 1 and an "orifice" metered flow of gas past the piston during the 32 il extension or expansion stroke.
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,1 ASSEMBLY ~PPARATUS
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2 Turning bac] now to Figures 1-4, the appara-tus 3 I for assembliny the counterhalance units as seen in Figures 4 5 and 10 includes a special crimping die tool set fastened to the head 70 and ~ed 72 of a machine press, ~^ihich can 6 be any kno~n kind readily available in machine sho~s. The 7 crimping die tool has upper 74 and lower 16 assemblies which 8 will be a~fixed respectively to the head and bed of the press g l and in working alignment as shown in Figures 1-4. In 10 1 the following description of the tool apparatus and 11 the method of assemhly of a counterbalance link, reference 12 1 will be made to counterbalance link 30 and its re,erenced 13 l components as shown in Figure 5.
14 i ~igure 1 shows the upper and lower crimping die 15 1l assemblies 74 and 76 fastened to the press. The crimping 16 l, ~die set is constructed to enable assembly, pressurization and 17 I crimping of the work piece (counterbalance lin];) in one operation, 18 and the upper and lower die assemblies will seal with 19 '1 one another via a dynamic gas tight seal, such as an O-ring, 20 ~I during an initial ~ressing movement of the press head, to 21 1l enclose the components, during the remainder of the assembly 22 il operation, within a pressurized gas-tight chamber.
23 jl The upper die assembly 74 has a steel base 78 with 24 1 a counterbore 80 sized to receive the shaft 40 of the piston 25 l and shat subassembly. Base 78 also has a lar~e counter-bore 26 l 82 the outer portion 84 of which is threaded and receives 27 ,1l an externally threaded die holder sleeve 86 which has an 28 l~ inner end 88, having an outer circumrerential groove 90 29 il carrying a seallng O-ring 92, which spigots and seals in 30 l the base counterbore 82. Inset into and seated within 31 l the inner end of the die holder sleeve 86 is an upper crimp 32 I die 94 made from tool steel. Carried within the die 94 and .

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1 seated in the upper end is a sleeve insert 96 through 2 which the pre-assembled piston and shaft assembly is 3 inserted with a close sliding flt. The insert sleeve 96 ~: projects downward withill the confines of the die crimping S face 98 a s~tfficient distance to keep the bushing 60 of 6 piston and .shaft assemkly away from the crim~ing surLace to 7; pe.rmit spacing for the crimping operatlon on the cylinder end 48.
8 Note: If a flat end connector link 54 is pre-welded g to the projected end of shaft ~0, then the crimp die 94 will 10, have to have diametral clearance slots 100 and the sleeve 11 insert 96 will also have to be slotted as at 102 to provide 12;~ clearance for the connector link to pass through and up into 13~ the counterbore 80. The latter can be accomplished by 14 ma~ing the sleeve insert in two parts. The pre-assembled piston and rod assemkly is held in the upper die assemkly 16l with a low force which can be accomplished by a permanent 17 magnet 104 fixed at the hase of counterbore 80.
18 The lower die assembly 76 includes a sleeve shaped base 19 part 110 fixed to the press base 72 and upstanding in coaxial 20' alignment with the upper die assembly 74. The upper end 111 2Li of the lower die base is dimensioned to be received within 2?., the upper holder sleeve 86 and during the initial ~ork stroke ~3~ o the press will telescope into the lower end of holder 24l sleeve 86 and be sealed thereto by an 0-ring 112 maintained 25~ ln an outer circumferential ~roove 114, as shown in Figure 3.
26 An intermediate po tion 115 of the base sleeve 76 is 27l~. externally threaded and carries a large stop nut 116 used 28~ to provide a limit stop for the press stroke, as shown in ~9l Figure 4.
30l Interior 118 of sleeve 110 is cylindrical and made to 31ll have a close loose fit with the subassembled counterbalance 32 cylinder 32 which is pre-inserted, base down, into the die 33'~ part 76. When so inserted, c~linder 32 rests against a steel .

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1 plug lnsert 120 situated in the bottom of sleeve ;nterior 118 and 2 seated against the press hed. Plug 120 is exterllally grooved 3 and carries an O-ring seal 122 which seals against the 4 die sleeve interior 118. Just adjacent the top of plu~ 120, the lower die sleeve is radially tapped to receive a pressure ~ line fitting 124 from a gas source 126 under pressure via 7, fluid controls 128 which in a pre-determined sequence will 8 pressurize and depressurize (vent) the crimping die assembly.
9~ An alternate location for the pressurized gas connection can 10'll be in the upper die base 78 as shown in phantom line at 132.
~ Figure 1 shows a modification to the die set where an 12 oil passage 133 is formed in the upper die holder sleeve 86 and 13,~ a unit 134 consisting of an oil pressurizing pump is connected 14,l thereto to introduce a small pre-determined quantity of oil 15, under pressure through a directed orifice 135 into a cylinder 16 component when the upper and lower die assemblies are sealed 17' and pressurized.
18~ Shown in Figure 2, a counterbalance cylinder 32 19" whlch includes a small quantlty, e.g., several cc OL lubricating 20l oil, is placed into the lower die sleeve interior 118 so its 211, closed end is resting on plug 120. If a flat connector lin~ 56 22 li is welded on the end o cylinder 32, a slot 130 in plug 120 231l will receive the connector~ link. The open end of counterbalance il :
24,, cylinder 32 projects above the top end of the lower die sleeve 25l 110 as seen ln Figure 2.
25~ OPE~TION OF APPAP~TUS
27j AND ~7F3THOD OF ASSEME~LING
28 1I COUN~ERBALANC~ LINK
29l Using the crimping apparatus previously described 30~ and with the press in the inoperative open condition (Flgure 1), 31' a cylinder component 32 is placed in the lower crimping 32,i die assembly 76 and a sub-assembled piston assembly 30 with 33'', shaft 40, seal 58 and bushing 60 is placed into the upper 4 die assembly 74 so the components are disposed as shown in `
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1 Figure 2. The press work stro}~e is then initiated, bringing 2 . the upper die assembly 74 do~n toward and into enyagem~nt 3 I with the lower die assembly 76 to the intermediate relationship 4 . shown in Figure 3 where the O-ring seal 112 engages and seals

5 ~ against the inner surface of the upper die holder 86. ~.

6 this precise stage, the interior of the engaged die parts is

7 a sealed cavity, all sub-components of the counterbalance

8 link are inside that sealed cavity, and the cavity is pressurized

9 with a suitable gas under pressure. The pressure will be

10 jl determined by the nature of the intended use of the counter-

11 1 balance link. It will be from several times atmospheric

12 1 pressure up to at least 2000 psi and if desired above 2000 psi.

13 i Most requirements will be satisfled by pressures from 400 to

14 . 2000 psi which can be accommodated by components of gas

15 1 pressurized devices.

16 l At thls stage or instant in the press stroke,

17 i the charge of gas in the cavity is a specific predetermined:

18 ll quantity and pressure and will be the same for every work 'I '

19 , piece being made. As the press continues its stroke, the

20 li projected piston, and the O-ring 58 enter the cylinder 32.

21 Ij Shown in the detail Figure 2A, the internal peripheral

22 1 ed~e of the open end 48 of cylinder 32 is chamfered with a

23 l' duble ent~y chamfer of 15 and 45 to facilitate introduction

24 I' of O-ring 58 into the cylinder. At the press stroke point

25 l where O-ring 58 seals against the inner cylinder surface,

26 . a predeterminecl quantlty of pre-pressurized gas is trappea

27 1 inside the cyllnder and is compressed still further by

28 ll continued operational movement of the press and the ~rimpl~g

29 ii dies. Final movement of the press, as shown in Figure 4,

30 ll causes the inner crimping face 98 of the upper cri~p ~ie 9

31 ~I to abut the cylincler end 48 and pressure crimp the ~*all .en~

32 'll inward to complete the final assembly operation of t~ eumatic 3 3 I counterbalance link.

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1 ~s tlle press starts on its return stroke, the 2 I pressurizin~ line controls will be operated manually or 3 automatically in a krlown manner to shut~off the pressure 4 flow and to vent the die assembly and release pressure from tl~ cavi~y as the press is moving the dle assembl-es to~ard 6 the unsealed condition, so that the cavity is not pressurized 7 when the cavity hecomes unsealed. The completed workpiece 8 is removed and the cycle repeated.

9 1' ~I~THOD APPLT.ED TO ASSET.\IBLE
10 ,, nU~L FORCE COUNTERBALANCE LINK
~ The same apparatus just described relative to 12 I Figures 1-4 can be utilized to assemble a modified version 13 of the single force pneumatic counterbalance link, i.e., 14 1 it can be used to assem~le, pressurize and crimp a dual or 15 !j plural force gas spring, which will be hereinafter described.
16 1 A dual slope output force is employed in some 17 pneumatic springs presently being used to "pop" open an 18 ' automotive trunklid a predetermined amount of about two 19 inches, The lid will then stay at that position until manually 20 Il opened for another amount where the pneumatic spring linkage i 21 1l geometry is such that the lid will open and stay open by 22 ¦l spring force only. Prior to the present invention, dual force 23 ', haa been accomplished by the addition of a small compression !
24 l spring installed into the pneumatic spring cylinder prior 25 ll to insertion of the piston and rod assembly. In normal use 1:
26 when that pneumatic spring is compressed, an additional force 27 ~l must be applied for the final portion of the compressed 28 ~ stroke when and after the piston has contacted the compression 29 ~ spring li .
30 1I This invention accomplishes the dual slope feature 31 pneumatically by incorporating a floating piston in the 32 1I pneumatic spring cylinder. P~hen the piston, which is fixed

33 l to the piston rod, is in en~age~ent with the floating piston 3~ I the output force will increase at a higher rate.

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~ 162~s 1 Figures 10 and 11 show the dual force outp~
2 counter~alance link 136 with a floating piston 170 having an 3 e]as-tomeric sealing O-ring 172. Link 136 and components 4 ' are herelnaEter more specifica].ly described but hasically include similar parts and construction as in the unit 30 o~
6 Figure 5, plus a floating piston. I~ith such a floatiny piston 7 , the cylinder encompasses one sealed compartment 174 behind 8 ' piston 170 and the two compartments, one on each side of the 9 primary by-pass piston as is true in unit 30.
10 l~ Figures 12-16 depict the method of assembly of the dual force counterbalance link 136 in a somewhat schematic manner.
12 ll Figure 12, corresponding to Figure 3, shows the 13 ', initial pressurization mode, where the cylinder contains the 14 l` small amount of lubrication oil 64 previously mentioned with 15 '` neither of the pistons yet inserted into the cylincler.
16 I The floating piston 170 may be tem~orarily attached to the 17 ~, fixed plston assembly 140 by magnetic attraction (e.g., small 18 , magnet 176) or by some other controlled method such as 19 I' sticky grease. The crimp die chamber is initially pressurized 20 I' to a value which is below the final pressure.
21 ll Figures 13 and 13A depict the positions where the 22 li press has moved to accomplish insertion only of the floating 23 I piston to a sealed condition and then (Figure 13A) is backed 24 ¦, off slightly to remove the fixed piston from the floating piston, 25 I~, whereupon the crimp die chamber is immediately subjected to 26 ' the higher final pressure and and predetermined quantity of 27 lli, oil 178 injected via the orifice 135 shown in Figure 1.
28 il Figure 13A depicts the disposition of components after 29 li final pressurization has freed the floating piston fxom the , fixed piston connection (the magnetic holding Eorce being lower 31 il than that holding the fixed piston in the upper die assemhly) , -17-.~

lli 1 and displaces the floating piston 170 into the cylinder 2 compressing the gas ahead of it into compartment 17~ until 3 it equals the flnal pressure and a balance of pressure will 4 exist across the floating piston 170 and the small quantity of oil 178 has been introduced on top of the piston 170.
6, Figure 14 shows the upper dle assembly moved down to introduce 7 I the fixed piston 142, O-ring 162, and bushing 164 into the 8 cylinder 138. Final assembly is accomplished by the same 9 ,I further steps as described with respect to Figures 1-4.
Figure 15 depicts normal operation where the 11 fixed shaft piston 140 moves in and out without contacting the 12 , floating piston 170. The output force is e~ual to the 13 , internal pressure acting on the piston rod area.
14 I Figure 16 depicts the overload force mode where 15 l, the fixed piston 140 contacts the floating piston 170.
16 , Displacing the piston rod 146 into the cylinder 138 displaces 17 the floating piston 170 which is now in contact with the 18 ¦' fixed piston assembly 140 and both pistons move together.
19 ~, The output force on rod 146 is equal to the normal gas 20 ! pressure acting upon the piston rod area and the differential 21 il pressure across the floating piston. Due to the large area 22 1 of the floating piston 170 and the relatively small gas volume 23 1 ahead of it, the output load slope will increase and at a much 2 4 iI higher rate. Another desirable feature of the operation in the overload mode is the elimination of piston orifice dampening 26 l, because there is no flow across the fixed piston. This will 27 1l assist the desired initial "pop" open of an automotive 28 l, trunk lid upon unlatching.

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1 . PNEU~`~TIC
? COUMTERBALANCE LIMKS
.... . . _ 3 ~ This lnvention inclucles a gas spring or 4 pneumatic counterbalance link as has ~een previously descrihed. The link can be a single force outPu-t link 30 6 as described with reference to Figure 5 or a dual output force 7 ; link 136 as hereinbefore described with reference to 8 I Figures 10 and 12-16. In either case the fixed piston 9 , assembly, as illustrated, includes a construction ~hich provides essentially free by-pass flow of gas across the 11 piston during a retraction or compression stroke and a 12 metered orifice flow during the extension or expansion stroke.
13 ~ Several modified versions of -the cooperation piston and ring 14 assemblies are shown herein, any of the emkodiments can be used in the single force link or the dual output force link.
16 I Depending upon the application of use of the counterbalance, 17 l free ~low or metered orifice flow across the piston can be 18 1 in the reverse oE that just described, or free flow, or metered 19 I f~ow, could be provided for ~oth directions of the piston 20 l stroke merely ~y reversing the installation of the piston ring 21 Il or changing its configuration.
22 ! In Figures 5 through 9~ the piston assemhly is a 23 l single piece spool 36 with a thick flange 180 disposed 24 ., toward the cr]mped end 62 of cylinder 32 and a thin flange 25 l 182 disposed toward the cylinder closed end 50. Piston 36 26 is sIipped onto the reduced diameter end 42 of piston shart 27 l~ 40 and the end 42 then swaged over or riveted to securely 28 . fasten the piston. The diameter of thick flange 180 is 29 predetermined to provide sufficient clearance from the cylinder wall to ena~le unrestricted gas flow through the annular.
31 space 184. The diameter of the thin ~lange 182 also has `';

. ' -19-, .1 ., 11 16~9~
1 sufficient clearance to enable unrestricted flow of gas 2 -through ~nnular space 186. Disposed ~lthin the groove oE
3 plston spool 36 is a special mo]ded pis-ton O-ring 38 made of 4 fle~ible elastomeric material, such as synthetic rubber or 5 ~ plastics to permit stretching when the ring is slipped over 6 the flanges. The pis-ton spool can be made of two parts, 7 1 as shown in Figure 11, to permit the piston O-ring 38 to be 8 molded from a synthetlc plastic material which need no~ be g , stretchable, it can be assembled between the two parts of 10 ,I the pis-ton. In either event, the piston O-ring 38 will 11 have an inner diameter sufficiently larger than the base 12 I' diameter 188 of the piston groove, and will be provided 13 with several (4 shown) slots 190 on one side slightly 14 less than 1/2 diameter deep, to enable free flow by-pass 15 ¦l openin~s for gas to flow across the piston 36 when being 16 1I moved in a retraction operation as depicted by arrows in 17 l~ Figure 7. On the other side of the O-ring is a single, 18 'l formed (preferably pre-molded) orifice groove 192 which serves 19 ll to provide orifice metered flow during the expansion stroke 20 ll as shown by arrows in Figure 6. In a typical installatiQn 21 ll such as Figure 5, piston ring 38 is .645 inch diameter with 22 1l a cross-section radius of approximately .100 inch and the 23 li cross-seGtion orifice by-pass is .0006 sq. inch. The rod 24 1~ diameter is 0.314 inch, the cylinder I.D. is 0.620 inch and piston stro~e appro~imately 3.7~ inches.
26 li In Figure 10, the unit 136 is the same and has 27 I~ similar components as those of Figure 5, e.g., cylinder 138, 28 il piston assembly 140 with the ~ail-safe piston 142 made in 29 l, two parts 142a and 142b to enable a synthetic plastic piston 30 ll o-ring 144 to ba pre-assembled with the parts 142a and 142b 31 ll on the end of piston shaft 146. The piston ring 144 has the !l -20-I!
I

1 ~62~
1 same conflguration as ring 3E ancl the piston 142 is staked or 2 1 riveted at 150 on the end 148 of piston shaft 146. Cylinder 3 136 has a closed end 154 with end disc 156 ancl an open end 152.
4 Connector links 158 and 160 are welded to the shaft and cylinder to enable installation as desired. I,arge elastomeric 6 O-riny 162 against the end bushing 164 provides a combination 7 static c~linder seal, dynamic shaft seal and comPliant piston 8 ,, stop. The compliance will provide an additional cushion to g ~ decelerate extension movement and reduce noise at the end of 10 i the stroke. Crimped end 166 of cylinder 138 maintains the ~ components of counterbalance unit 136 in assembly.
12 , Unit 136 of course includes the previously described 13 1Oating piston 170 with its sealing O-riny-172 tra~ping a 14 predetermined quantity of pressurized gas ~etween the piston 170 15 'I and the closed end of cylinder 138.
16 ll Another version of the pneumatlc counterbalance 17 , link, made as afore-described, is shown in Figure 17 with 18 ~ details shown in Figures 18 and 19. The link 200 includes 19 ' the basic cylinder 202 with closed bottom 204 and crimped ~; 20l, end 205 and the piston and rod asse~bly with piston parts 21l' 206 and 208, piston ring 210~ shaft 212, chevron seal 214 1 22 ,l and bushing 216. The piston is made in two parts, a single 23l flanyed spool 206 and a cupped washer 208 Eitted together l!
24~l with piston ring therebetween and staked on the end of the shaft 212. The I.D. of the piston ring 210 and drilled 26'l', orifices 218 in the inner portion of cup washer 208 serve 27 l to provide free flow by-pass of yas in the retraction movement 28'~` of the piston. Piston riny 210 is cut from an extruded tube 29 I made from plastic material such as "HYTREL" and incorporates 30i' an extrusion formed orifice by-pass ~roove 220 on the outer .. I

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~ 11629~5 periphery of the ring. In this embodiment when the cup washer 208 is used~ the shaft and cylinder seal ring 214 can be a chevron seal, with the cup washer flange abutting the mid-section of the chevron seal to avoid damage to the seal lips at the end limit of the stroke. Figure l9a is a modification 210' o:E the extruded piston ring 210 with orifice groove 220', and includes a plurality of internal ribs 222 which serve to coaxially locate the ring 210' on the piston and facilita-te assembly, Figures 20, 21 and 22 illustrate a further embodiment in which a two part piston 224 is used with a plan O-ring piston ring 226 which has its I~Do spaced from ~he inside diameter o-f the piston spool 224O The upper flange part,227 (Figure 22a~ o~ the piston has free flow ~y-pass apertures 228 The lower flange of the piston has a radial metering orifice slot 230 formed therein as by coining, Retraction movement of the piston permits free flow of gas across the piston ring ~., 226 as shown in Figure 21, and extension movement of the piston results in orifice metered flow via orifice groove 230 across the piston as s~oWn .in Figure 20, Figure 22 shows a normal neutral position of the piston at rest, Figures 23 and 24 illustrate an alternate piston ring of molded rubber or plastic which can be used with the - Figures 17 and 20 two part pistons, The piston ring 240 has single meteri.ng ori~ice slots 242 and 244, one on each side of the ring~ This ring can be installed with either face against the downward flange and avoid erroneous upside down installation.

5d/~G ~22-~ 1~2~

FAIL-SAFE PISTON
-2 The counterbalance link has been developed to 3 preclude the problem of orifice contamina-tion by implementation 4 of a feature which increases the orifice size when flow is reversed to Eacilitate the dislodging of any entrapped 6 contaminants. In the event that the orifice remains 7 permanently closed, a catastrophic failure of the counter-8 balance assembly or supporting structure will be precluded 9 ; by a fail-safe piston design which allows a controlled failure of the piston ring supporting surface thereby allowing free 11 flow of gases in both directions. The structural integrity 12 l of the unit, however, is not com~romised and the counter-13 balance will continue to function without the rate controlled 14 i extension feature.
15 ll Contamination of the metering orifice will 16 ~ hydraulically lock the unit and such problems have been 17 encountered particularly in units which incorporate a 18 i drilled orifice. Should an orifice become clogged when the 19 l~ spring is on a vehicle there is a possibility of damage to 20 ~ a door, linkage or failure of the spring if the door is 21 1l forced with the spring hydraulically loc]ced due to a clogged 22 orifice.
23 ; Applicant's fail-safe piston design is shown 2~ 1 in Figures 5-7. The rigllt hand piston flange 182 will i ~e wea~ened by making it thinner or ky addition of a fail-26 safe notch. Mormal operation and load carrying capability 27 ' will not be compromised since the loads with the piston 28 bottomed in the extended condition are carried by the thicker 29 lefthand flange. Should the orifice become clogged and the 30 ' door forceably opened the piston forces will be applied 31 to the right hand flange 182 ~ith the fail-safe feature.

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~~ --23--' ~ ~2g~
1 ~n overload wlll cleform the flange from the piston allo~ing 2 the seal to l'blow out". Deformation of flange 182 uncler such 3 a circum~tance is depicted by phantom line 183 in Figure 6.
4 The pneumatic spring will continue to function after this 5 ~ fail-safe feature has been actuated but operation will be 6 without orifice controlled dampening.
7 1 The invention may be embodied in other specific 8 ' forms without departing from the spirit or essential g ,, characteristics thereof. The present embodiment is therefore 10 ' to be considered in all respects as illustrative and not 11 res-trictive, the scope of the invention being indicated by 12 the appended claims rather than by the foregoing descrlption 13 ~l and all changes which come within the meaning and range of 1~ e~uivalency of the claims are therefore intended to be embraced therein.
16 What is claimed and desired to be secured hy 17 , Letters Patent is~

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Claims (25)

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

1. A pneumatic spring link comprising: a cylinder assembly with a closed end, a piston assembly in said cylinder with a piston shaft extending from the other end of said cylinder, a bushing on said shaft, an annular seal means around said shaft, a piston with piston ring fixed on the end of said shaft; the other end of said cylinder being crimp shaped to retain said bushing; said seal means providing a static seal against said cylinder, and a dynamic seal around said shaft; said piston and piston ring providing means enabling metered orifice by-pass flow of gas across said piston during an extension stroke and a free flow by-pass fluid communication path across said piston during a retraction stroke; a predetermined small quantity of oil being contained in said cylinder; and a predetermined accurate quantity of gas under at least several atmospheres of pressure in said cylinder, having been pre-loaded under pressure into said cylinder before, and maintained under pressure during, the final mechanical assembly steps of forced insertion of the shaft seal and bushing into the cylinder followed by crimping of said other end of the cylinder, whereupon said spring link contains and retains an accurately pressurized and predetermined quantity of gas.

2. A pneumatic spring link as defined in claim 1, wherein said piston assembly further includes a second floating piston with seal ring means disposed between said shaft fixed piston and the closed end of said cylinder assembly with said gas under pressure being equalized on each face of said floating piston; said floating piston adapted to be engaged by said shaft fixed piston during a final portion of the retraction stroke of said shaft to provide a larger force biasing said piston and shaft toward an extended condition.

3. A pneumatic spring link as defined in claim 1, wherein said shaft fixed piston is a dual flange spool shaped piston means rigidly secured on the end of said shaft and the diameter of said spool flanges has a free spaced fit within said cylinder assembly to permit free flow of gas across said piston means; and said piston ring has fluid flow by-pass grooves, is located between the flanges of said spool shaped piston means, and has a close fit with said cylinder; said piston ring being an O-ring with at least one of said by-pass grooves being a metering orifice groove passing metered fluid flow across said piston means when the piston means and shaft move to an extended condition.

4. A pneumatic spring link as defined in claim 3, wherein one of said flanges is made intentionally weak enough to destruct if said orifice by-pass groove becomes inoperative to cause the link to act as a fixed link; said weak flange being the flange closest to the closed end of said cylinder.

5. A pneumatic spring link as defined in claim 4, wherein said weak flange is made thin enough to deflect under a predetermined load tending to extend said shaft when said orifice by-pass groove is inoperative,

6. A pneumatic spring link as defined in claim 3, wherein said spool shaped piston means is made in two axial parts each of which includes a flange and said piston O-ring is a synthetic material.

7. A pneumatic spring link as defined in claim 3, wherein said spool shaped piston means is made in one part and said piston O-ring is made from rubber which can be stretched over the flange.

8. A pneumatic spring link as defined in claim 3, wherein said piston O-ring on one axial side has a plurality of radial by-pass grooves molded therein to enable essentially free flow of gas across the piston and piston ring during retraction movement and the said metering orifice groove is a radial groove molded in the opposite axial side of said O-ring.

9. A pneumatic spring link as defined in claim 1 or 2, wherein said annular seal means around said shaft is a large sealing O-ring which is deformed between said shaft and said cylinder internal wall surface and is maintained against said bushing by gas pressure to provide a static seal to the cylinder, a dynamic seal to the shaft and an end limit cushioning means for the extension limit position of said piston.

10. A pneumatic spring link as defined in claim 1 wherein: said piston has two spaced flanges, the one closest to the crimped end of said cylinder having axially-disposed apertures therethrough; and said piston ring is an extruded synthetic material with a flow metering orifice groove extruded axially at one location on the piston ring outer periphery, the inner diameter of said piston ring being larger than and creating an annular space from said shaft and the ring outer diameter providing a close sliding fit with the inside surface of the cylinder member.

11. A pneumatic spring link as defined in claim 2 wherein: said piston has two spaced flanges, the one closest to the crimped end of said cylinder having axially disposed apertures therethrough; and said piston ring is an extruded synthetic material with a flow metering orifice groove extruded axially at one location on the piston ring outer periphery, the inner diameter of said piston ring being larger than and creating an annular space from said shaft and the ring outer diameter providing a close sliding fit with the inside surface of the cylinder member.

12. A pneumatic spring link as defined in claim 10 or 11, wherein said resilient annular seal is a chevron seal with the chevron flanges directed toward said piston, and said one spaced piston flange being cup shaped with the cup rim directed toward and in axial alignment with the mid-portion of said chevron seal.

13. A pneumatic spring link comprising: a cylinder assembly with a closed end; a piston assembly in said cylinder with a piston shaft extending from the other end of said cylinder, a bushing on said shaft, an annular seal means around said shaft, a piston means with piston ring fixed on the end of said shaft; the other end of said cylinder being crimp shaped to retain said bushing; said seal means providing a static seal against said cylinder, and a dynamic seal around said shaft; said piston means and piston ring providing means enabling metered orifice by-pass flow of gas across said piston in one direction of stroke and a free flow by-pass fluid communication path across said piston means in the other direction of stroke, a predetermined small quantity of oil being contained in said cylinder; said cylinder containing a pre-determined quantity of gas under pressure; said piston means having a spool shaped piston with flanges of less diameter than the I.D. of said cylinder to provide an annular free-flow space between the piston flanges and said cylinder, and at least one of said flanges being deliberately made in a weakened condition as a fail-safe device to deflect and release said piston ring upon contamination clogging of said means providing by-pass flow across said piston, and to thereby permit continued spring function without the metered orifice by-pass flow of gas.

14. A pneumatic spring link as defined in claim 13, wherein the fail-safe weakened piston flange is the flange closest to the closed cylinder end and said means enabling metered orifice by-pass gas flow across said piston is operative during the extension stroke.

15. A pneumatic spring link as defined in claim 13, wherein both flanges are weakened to provide a fail-safe device regardless of direction of stroke when by-pass flow is prohibited by clogging.

16. A pneumatic spring link as defined in claim 1, wherein said means enabling metered orifice by-pass flow of gas across said piston during the extension stroke and a free flow by-pass flow during the retraction stroke comprises a groove in one of the piston for the piston ring, said groove being in the area of abutment between said piston and said piston ring which occurs during the extension stroke; whereby the relative movement of the piston and piston ring into and away from abutting engagement during extension and retraction provides said groove with a self cleaning flow action.

17. A pneumatic spring link as defined in claim 13, 14 or 15, wherein said means enabling metered orifice by-pass flow of gas across said piston during the extension stroke and a free flow by-pass flow during the retraction stroke comprises a groove in one of the piston or the piston ring, said groove being in the area of abutment between said piston and said piston ring which occurs during the extension stroke whereby the relative movement of the piston and piston ring into and away from abutting engagement during extension and retraction provides said groove with a self cleaning flow action.

18. A pneumatic spring link as defined in claim 16, wherein said piston is spool shaped with dual flanges, one of the spool flanges being made intentionally weak enough to destruct if said orifice by-pass groove becomes inoperative to cause the link to act as a fixed link; said weak flange being the flange closest to the closed end of said cylinder.

19. A pneumatic spring link as defined in claim 18, wherein said weak flange is made thick enough to deflect under a predetermined load tending to extend said shaft when said orifice by-pass groove is inoperative.

20. A pneumatic spring link as defined in claim 1, wherein said piston is spool shaped and made in at least two axial parts each of which includes a flange.

21. A pneumatic spring link as defined in claim 1, wherein said piston includes an annular groove in which said piston ring is retained with a loose free fit and said means enabling metered orifice by-pass flow of gas across said piston during the extension stroke and a free flow by-pass flow during the retraction stroke comprises a lateral groove in one of the wall surfaces of the annular groove in said piston, said lateral groove being in the area of abutment between said piston annular groove wall surface and said piston ring which occurs during the extension stroke;
whereby the relative movement of the piston and piston ring into and away from abutting engagement during extension and retraction provides said groove with a self cleaning flow action.

22. A pneumatic spring link comprising: a cylinder assembly with a closed end; a piston assembly in said cylinder with a piston shaft extending from the other end of said cylinder; a bushing on said shaft; an annular seal means around said shaft, said piston assembly including a piston means with flanges and an annular groove therebetween providing a spool shaped piston with piston ring means disposed in the said groove between said flanges on the end of said shaft; the other end of said cylinder being crimp shaped to retain said bushing; said seal means providing a static seal against said cylinder, and a dynamic seal around said shaft; one of said piston flanges having a flat annular surface, with a lateral bleed groove provided therein, on one side surface of said annular piston groove; said piston ring means have a loose free fit in said piston groove, disposed in sliding sealed engagement with the interior surface of said cylinder and adapted to abut said flat annular groove surface to thereby provide in cooperation with said bleed groove a metered orifice by-pass flow of gas across said piston during one direction of piston movement;
a predetermined small quantity of oil being contained in said cylinder; and a predetermined accurate quantity of gas under at least several atmospheres of pressure in said cylinder.

23. A pneumatic spring link comprising: a cylinder assembly with a closed end; a piston assembly in said cylinder with a piston shaft extending from the other end of said cylinder; a bushing on said shaft; an annular seal means around said shaft; said piston assembly including a piston means with flanges and an annular groove therebetween providing a spool shaped piston with piston ring means disposed in the said groove between said flanges on the end of said shaft; the other end of said cylinder being crimp shaped to retain said bushing; said seal means providing a static seal against said cylinder, and a dynamic seal around said shaft; one of said piston flanges having means enabling free gas flow past said one flange; the other of said piston flanges having a flat annular surface, with a lateral bleed groove provided therein, on one side surface of said annular piston groove; said piston ring means have a loose free fit in said piston groove, disposed in sliding sealed engagement with the interior surface of said cylinder and adapted to abut said flat annular groove surface to thereby provide in cooperation with said bleed groove a metered orifice by-pass flow of gas across said piston during its stroke in one direction and a free flow by-pass fluid communication path across said piston during its stroke in the other direction; a predetermined small quantity of oil being contained in said cylinder; and a predetermined accurate quantity of gas under at least several atmospheres of pressure in said cylinder.

24,. A pneumatic spring link comprising: a cylinder assembly with a closed end; a piston assembly in said cylinder with a piston shaft extending from the other end of said cylinder; a bushing on said shaft; an annular seal means around said shaft; said piston assembly including a piston means with flanges and an annular groove therebetween providing a spool shaped piston with piston ring means disposed in the said groove between said flanges on the end of said shaft; the other end of said cylinder being crimp shaped to retain said bushing; said seal means providing a static seal against said cylinder, and a dynamic seal around said shaft; the one of said piston flanges closest to said other end of said cylinder having means enabling free gas flow past said one flange; the other of said piston flanges having a flat annular surface, with a lateral bleed groove provided therein, on one side surface of said annular piston groove; said piston ring means have a loose free fit in said piston groove, disposed in sliding sealed engagement with the interior surface of said cylinder and adapted to abut said flat annular groove surface to thereby provide in cooperation with said bleed groove a metered orifice by-pass flow of gas across said piston during the extension stroke and a free flow by-pass fluid communication path across said piston during the retraction stroke; a predetermined small quantity of oil being contained in said cylinder; and a predetermined accurate quantity of gas under at least several atmospheres of pressure in said cylinder.

25. A pneumatic spring link comprising: a cylinder assembly with a closed end; a piston assembly in said cylinder with a piston shaft extending from the other end of said cylinder; a bushing on said shaft; an annular seal means around said shaft; said piston assembly including a piston means with flanges and an annular groove therebetween providing a spool shaped piston with piston ring means disposed in the said groove between said flanges on the end of said shaft; the other end of said cylinder being crimp shaped to retain said bushing; said seal means providing a static seal against said cylinder, and a dynamic seal around said shaft; the one of said piston flanges closest to said other end of said cylinder having means enabling free gas flow past said one flange; the other of said piston flanges having a flat annular surface, with a lateral bleed groove provided therein, on one side surface of said annular piston groove; said piston ring means have a loose free fit in said piston groove, disposed in sliding sealed engagement with the interior surface of said cylinder and adapted to abut said flat annular groove surface to thereby provide in cooperation with said bleed groove a metered orifice by-pass flow of gas across said piston during the extension stroke and a free flow by-pass fluid communication path across said piston during the retraction stroke; a predetermined small quantity of oil being contained in said cylinder; and a predetermined accurate quantity of gas under at least several atmospheres of pressure in said cylinder, having been pre-loaded under pressure into said cylinder before, and maintained under pressure during, the final mechanical assembly steps of forced insertion of the shaft seal and bushing into the cylinder followed by crimping of said other end of the cylinder, whereupon said spring link contains and retains an accurately pressurized and predetermined quantity of gas.