CA1187681A - Method and apparatus for making pneumatic counterbalances - Google Patents

Abstract

ABSTRACT

The invention relates to a new method of assembly of pneumatic counterbalance units and to apparatus for carrying out that method. Components of the unit are positioned within crimping die tools in a crimping press with a small quantity of lubricating oil pre-introduced into the cylinder component. The die parts holding the components are moved in a direction towards assembly. The die tool parts engage and provide a sealed compartment surrounding all components of the unit. At this stage the compartment is pressurized by gas at several atmospheres and, while pressurized, press movement continues. As the crimping die parts move together the piston assembly parts including the rod seal and the end bushing move into the cylinder and entrap a quantity of pressurized gas within the cylinder. As press action continues, the open end wall portion of the cylinder is crimped inwardly by the crimping die tool, thereby retaining the bushing, seal, rod and piston in the cylinder and completing the assembly. The sealed die compartment is vented, pressurization is released, the press is reversed and the tools move apart to permit removal of the assembled counterbalance unit. The crimping die tools are structured so as to maintain the counterbalance components in their pre-assembly positions and to provide a closed sealed cavity around the components while that compartment is being pressurized and depressurized.

Description

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This is a division o~ copendin~ commonly assigned Canadian Patent Application Serial NoO 370~011 filed February 4, 1981.
BAC~GRO~JD ~F T~E INVENTION
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Pneumatic counterbalance units have come into widespread use in xecent years, being usea on various au~omotive components such as hoods~ txunk lids~ hatch backs a~ld on other i~ems such as machine covers, doors and hatches.
Such pneumat;c counterbalances are rather simple pneumatic pis~on~cyl.inaer arrangemen~s having a bleed by-pass through 10 or pas~ the piston similar to shock absorbers and oleo struts used on vehicles and aircraft for many yearsO The well-~;nown principle of operation is based on differential pressure ~7k 6~
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 piston which reduces the area on that side of the piston. 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 effective at an intermediate position of the piston rod retraction stroke.
Examples of prior art counterbalance units can be seen in the following U.S. Patents: 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. 2,788,867 to A~r Causse for Shock Absorber; Patent No. 3,207,498 to E. ~7ustenhagen 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.W. Gee for Vehicle Suspension (Gas Spring); Patent No.
3,856,287 to Preitag for Piston Rod Seal For Adjustable Pneumatic Spring7 Patent No. 3,868,097 to P.H. Taylor for Liquid Spring; Patent No. 3~913,901 to W. Molders for Resilient Supporting ColumnS Patent No. 3,963,227 to W. Molders for Gas Spring with Dual Damping; Pa-tent No. 4,030,715 to H.O.
Duran for Pneumatic Shock Absorber; Patent No. 4,064j977 to -D.F. Taylor for Fluid Amplified Shock Absorber Having De Laval sd ~ ~ -2-t7 I' 1¦ Nozzle; Paten~ No. 4,098,302 to Freitag for Method for

2 Charging Rneumatic Suspension Element; and Patent No.
31, 4,108,423 to J.J. Skubal for Gas Spring. ~ost of the 4l foregoing patents disclose various types of piston unit 5, orifices and of different kinds of seals be~ween the piston 6 11 rod and cylinder, some being plural O-rings or flat washers 7!1 or a combination of hoth kinds and some, e.g., Taylor and 8l Duran use chevron seals. Duran shows an anti-frictlon 9¦1 ring on the piston with plural peripheral notches providing 10l free-flow by-pass of fluid~ Some disclose methods of 11 I pressurizing, e.g., De Carbon shows a valved inlet;
12 ~ Tuczek shows a multiple inlet SYStem with lines and 13jl accumulators; Freitag 3,856,287 shows a ball check valve;
14 li 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 ~ethod of assembly for a liquid sprin~.

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` SUMMARY OF THE INVENTION
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The increase of use of pneumatic counterbalance units in consumer items has required increased produc-tion which can result in lack of quality control, e.g., manufacture requires pressurization 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. sy the present invention a method and tool structure has been developed to make a gas spring counterbalance and includes pressuri~ation wlthin a crimping die assembly, just prior to completely inserting the piston and rod assembly, and maintaining the pressuri~ation during crimping of the cylinder. This results in very accurate quality control of the pressurization of completed units.
A unique die assembly was developed to accommodate the method of assembly.
Further developments included a different shaft seal arrangement and providing extruded piston rings with preformed peripheral orifice control grooves and specially constructed piston rings with bi-directional by-pass and metering orifices to control linkage extension and retraction speeds.
To avoid ~he detrimental aspects of the extensible link becoming a fixed length link should the metering orifice become clogged, a fail-safe feature has been developed to ~elease the piston seal if the extension force exceeds a certain value. Also it is desirable in some installations to have a dual force 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 concept was developed. Such a floating piston is pre-inserted and entraps gas in a lower sd~

chamber within the cyLinder and its assembly and pressuriæation can be accQmmodated by the assembly tools and method of this invention.
~ primary feature of the invention as described in the parent application resides in the provision of a novel pneumatic counterbalance link.
The link is pr-~essurized be~ore and during the assembly step. The piston rod is sealed by a large 0-ring or the equivalent which also seals against the cylinder and end bushing. Unidirectional seal rings, such as a chevron seal, can be used if ~esired. Several novel embodiments of metering oxifices 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 pre,formed 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 ~y-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. Resiliency of the 0-ring results in flexing of the grooved areas of the 0-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 past the piston but retaining the basic pneumatic counterbalance action of the counterbalance link.
The invention according to this application resides in the provision of a novel method of assembly of pneumatic counter-sd~ -5--

3'7 ti8~1 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. At 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 mo~ement 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, pressurization is released, the press is reversed, the tools part and the completely assembled counterbalance unit is removed.
As further aspects of the invention, the same assembly method can be used to assembly a dual force counter-balance unit, which will include a floating peripherally sealed piston in the cylinder below the rod and prlmary piston assembly. 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 caused, and the ~loating 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 separates from the primary piston and moves into the sd/~-~Y~ -6A-1' cylinder to an intermediate location of e2~ualization of 2 pressures on both faces and an additional small auantity j .
3, of oil for lu~rication is introduced into the cylinder on ~ top o~ the floating piston. Continued movement of the press and crim~ing dies completes ~lle asse~ly of the piston and G rod into the cvlinder and crimps the cylinder, followed by 7j removal o~ press~rization, par~ing of the die parts an.d 8' removal of the completed unit~
~ ¦ Another aspect of the invention according to this application 10 'i resides in the provision of novel apparatus to accor.plish 112, the com~ination single stroke assembly and pressurization 12 1! f a pneumatic counterbalance unit In conjunction with ~ 3 1, this aspect is the provision of a novel crimping die tool 14~ set fQr use in a machine ~ress including jig s~ructures 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 i8',, con~rolla~ly pressurize and de-pressurize the cavity during 19 i~ the ~inal stages of assembly of the counterbalance unit. A
22~2~ ~urther novel feature resides in provision for pressure injection 21 d f a predetermined quantity of lubricating oil into the 22 .. cylinder-after pressurization of the die cavity. This feature 23 i~i can be used to in~roduce oil into the bottom of the cylinder 24 ~2 as well as on top of the floating piston.
25 ~! Further novel features and other ~spects o~ this 26 lnven~io~ will become apparent from the follo~ing detailed 27 i! description~ discussion and the appended claims taken in ~8 !' conjunction ~Jith the accompanying drawings.

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' 1' BRIEF DESCRIPT:I.ON OF T~IÆ D:E~AWINGS
._ _ 2; A preferred structural embodiment of the apparatus 3. and various embodiments of ~he pneumatic counterbalance

4. -of ~hi~ invention are disclosed in the accompanying drawings, S in which:
6 Figures 1-4 illuc:trate apparatus in accord with this 7 invention by which the inventive method can be carried out to 8. assemble and pressurize a completed pneumatic coun~erbalance 9 unit, Figures 1, 2, 3 and 4 showing respective progressive 10~ stages and positions of the press heads, crimping dies and 111I counterbalance components to final assembly of the inventive 12,, counterbalance unit;
13, Figure 2A is an enlarged detail section taken on 14 ll line 2A-2A of Figure 2 through the open end wall of a 15lf counterbalance cylinder component prior to assembly;
16, Figura 5 is a partially sec~ioned elevation view of 17¦. a complete pneumatic counterbalance link unit according to 18 this invention;
19l Figure 6 is an enlarged cross section detail of the 20l unit of Figure 5 showing the shaft seal, the shaft, the piston 21l and the piston ring in its metering position when the link 22, is being extended;
23l Figure 7 is a view similar to E~igure:6 but showing 24 ! the piston ring in the by-pass flow position which occurs 25l' when the link is being retracted;
26. Figures 8 and 9, respectively, a plan view and 27jl a cross section view taken on line 9-9 of Figure 8, show 28l the shape and groove details of the piston ring used in the 29,, unit of Figure 5;
30lj Figure 10 is a further embodiment of a counter-31 li balance unit which includes the same components shown in 32l Figure 5-9 and in addition includes a floating piston to 33,; provide a dual force counterbalance link;

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1 .. !I Figure 11 is an enlarged detail section of the 2 : unit in Figure 10 showing the primary piston and the floating 3 piston posltioned in the overload secondary force condition;
4 Figures 12, 13, 13A and 14 are somewhat schematic S depictions of stages of assembly of a dual force count~r-6 ~lance link such as shown in Figure 10;
7 , Figure 15 is a schematic depiction of a completely 8 l' assembled and pressuri~ed dual force unit with the primary 9 j' piston spaced from the 10ating piston in a normal force 101' condition;
11 ~I Figure 16 is a schematic depiction like 12 li Figure 15 but illustrates the two pistons engaged and disposed 13l~, in an overload force condition;
14l.' Figure 17 is a further embodiment with a ~odified 15, piston assembly with metered orifice extruded in the outer 16l periphery of the piston ring;
17~, Figure 18 is a plan view of the cup washer portion 18 ¦i of the piston assembly shown in Figure 17;
19¦¦ Figure 19 is a plan view of the extruded piston 20,l ring of the piston assembly shown in Figure 17:
21 1I Figure 19A is a Plan view of a modified piston ring;
22 ¦I Figures 20, 21 and 22 are detail section views 23 1 illustrating extension, retraction and neutral conditions of 24 ¦'. a still further embodiment of a piston assemblY;
25 il Figure 22A is a plan view of the upper pistvn 26 ,, washer of the Figure 20 device; and 27 ii Figures 23 and 2~ are detail views of a further 28 " p:iston ring molded embodimenk with the metering orifice 29 il p.rovided as a groove molded in the ring.
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GENERAI. DESC~IPI'ION
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The various aspec-ts of the invention herein include articles ]~nown as pneumatic or gas springs, which for convenience can be referred -to as counterbalance links, as well as an apparatus and me-thod for making the articles~
Representative embodiments of the counterbalance links are seen in Figures 5, lO and 17 as well as in various other detail views. Figures 5 and lO of the original Patent Drawings are full scale of actual units.
The firs-t por-tion of this description will be directed to the apparatus for making (or assem~ling) the counterbalance links bu-t initially reference is to Figure 5 where is shown a representative embodiment of a coun-ter-balance link 30 having a cylinder 32 whose length will be determined by the kind of equipment with which the unit is used. Within the cylinder is a piston assembly 3~ which separates the cylinder into two compartments which are fillea with gas (e.g., air, nitrogen or some other inert gas) under pressure. The piston assembly includes a free fitting piston 36, a-piston ring 38 and the piston rod or sha~t 40 secured at one end 42 to the piston 36 as by swaging ove~
or riveting the end at ~. These pneumatic counterbalance units, particularly in automotive installations are often pressurized up to around 2000 psi gas pressure. Pressures can be higher or lower depending on the installation~ A
counterbalance unit with a piston rod having approximately 0.10 inch2 cross-section area will provide a 5 pound extension force when the cylinder is pre-pressurizea at approximately 50 psi, ana a 200 pound -force when pressurized at 2000 psi.
The piston shaft ~0 projects out through one end ~8 of cylinder 32, the other end 50 of which is closed, as -- 1~) --kh/ ~

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1 , by welding a disc 52 thereto. The projected end of shaft 40 2 ,, has a connector link 54 rigidly secured thereto, as by screw 3 il threads or welding, and a second connector lin]-~ 56 is secured 4 , to the cylinder closed end 50, as by screw threads or welding.
Within the cylinder~ shaft 40 passes through a large O-ring 6 ll seal 58 and a shaped bushing 60 which has a free close-fit 7 1, around the shaft ~0 and within cylinder 32. With the open 8 ! c,ylinder end 48 crimped at 62 the bushing 60 provides an g 1l end stop abutment for piston movement cushioned by the Il, O~ring seal 58. Internal gas pxessure keeps the seal 58 11 1~ and bushing 60 in the end position against the crlmped end of Ii .
12 ll c,ylinder 32. As shown in Figures 2-4, a pre-determined 13 I small ~uantity of oil 64, e.g., 3-4 cc is placed into 14 ¦, cylinder 32 ~rior to assembly and provides lubrication for i~ the piston ring and the large O-ring seal 58. Unit 55 16 represents an attachment clip and is not per se a part of 17 , this invention.

18 il Suitable materials for the various components can be 19 mandrel drawn hydraulic steel tubing for the cylinder, sheet j steel fox the end disc, the piston shaft is hardened, chrome 21 ¦I plated steel, the bushing can be made from aluminum or steel, 22 1' the O-ring is elastomeric, e.g. rubber or plastic, and 23 1' the piston is made from aluminum. As will be described in 24 ~i detail, khe piston and ring components can be and are 1, preferably made from various other materials depending upon 26 the configuxation or modification of design. The piston 27 1', and its ring, as are true of pneumatic springs, are constructed 28 I to provide controlled by-pass flow oE gas from one side of 29 , the piston to the other side. There is a relatively free flow ,~ by-pass provided during the retraction or compression stroke 31 and an "orifice" metered flow of gas past the piston during the 32 jl' extension or expansion stroke.
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1 ASSEM~LY ~PPARATUS
2 Turning bac]c now to Figures 1-4, the apparatus 3 l~ for assembling the counterbalance units as seen in Figures 4 S and 10 includes a special crimping die tool set f~stened to the head 70 and bed 72 of a machine press, which can 6 be any lcnown kind readily available in machine shops. The 7 crimping die tool has upper 74 and lower 76 assemblies which 8 , will be affixed respectively to the head and bed of the press 9 l and in working alignment as shown in Figures 1-4. In 10 j, the following description of ~he tool apparatus and 11 ,' the method of assembly of a counterbalance link, reference 12 1I will be made to counterbalance link 30 and its referenced 13 ¦I components as shown in Figure 5.
14 , Figure 1 shows the upper and lower crimping die 15 l~ assemblies 74 and 76 fastened to the press. The crimping 16 ,i die set is constructed to enable assembl~, pressurization and 17 I crimping of the work piece tcounterbalance lin];) in one operation, 18 il and the upper and lower die assemblies will seal with 19 1 one another via a dynamic gas tighk seal, such as an O-ring, 20 ¦ during an initial pressing movement of the press head, to 21 1l enclose the components, during the remainder of the assembly 22 ,l operation, within a pressurized gas-tight chamber.
23 jl The upper die assembly 74 has a steel base 78 with 24 ! a counterbore 80 sized to receive the shaft 40 of the piston 25 ll and shaft subassembly. Base 78 also has a large counter-bore 26 82 the outer portion 84 of which is threaded and receives 27 1' an externally threaded die holder sleeve 86 which has an 28 i inner end 88, having an outer circumferential groove 90 29 l carrying a sealing O-ring 92, which spigots and seals in 30 i' the base counterbore 82. Inset into and seated within 31 i the inner end of the die holder sleeve 86 is an upper crimp 32 ' die 94 made from tool steel. Carried within the die 94 and , I .

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l seated in the upper end is a sleeve insert 96 through 2 which the pxe~assernbled piston and shaft assembly is 3 inserted with a close sliding fit. The insert sleeve 96 ~ projects downwaxd within the confines of the die crimping S Eace 98 a sufficient distanca to ]ieep the bushing 60 of 6 piston and shaft Assembly a~7ay from the crimping surface to 7 permit spacing for the crimping operation on the cylinder end 4~.
8 Note: If a flat end connector link 54 is pre-welded 9I to the projected end of shaft 40, then the crimp die 94 will 10, have to have diametral clearance slots lO0 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 ~y 14 ma~ing the sleeve insert in two parts. The pre-assembled piston and rod assembly is held in the upper die asser~ly 16l with a low force which can be accomplished by a permanent 17magnet 104 fixed at the base of counterbore 80.
18The lower die assembly 76 includes a sleeve shaped base 19part 110 fixed to the press base 72 and upstanding in coaxial 20; alignment with the upper die assembly 74. ~he upper end 111 I
21ll of the lower die base is dimensioned to be received within 22 the upper holder sleeve 86 and during the initial work stroke 23l of the press will telescope into the lower end of holder 24l sleeve 86 and be sealed thereto by an 0-ring 112 maintained 25ll in an outer circumferential groove 114, as shown in Figure 3.
26 An intermediate portion 115 of the base sleeve 76 is 27l! externally threaded and carries a large stop nut 116 used 2~ to provide a lirnit stop or the press stroke, as shown in 29`l Figure 4.
30, Interiox 118 of sleeve 110 is cylindrical and made to 31~, have a close loose fit with khe subassembled counterbalance 32l cylinder 32 which is pre-inserted, base down, into the die 33 part 76. When so inserted, cylinder 32 rests against a steel ' ,` ~ 6~3~
l plug lnsert 120 situated in the bottom of sleeve in-terior 118 and 2 seate~ against the press ~ed. Plug 120 is exterri,ally grooved 3 and carries an O-ring seal 122 which seals against the 4 clie sleeve interior 118. Just adjacent the top of pluy 120, tlle lower die sleeve is radially tapped to receive a pressure 6; l.ine :Ei.tting 124 from a gas source 126 under pressure via 7 ll flllid controls 12 which in a pre-determined sequence will 8; pressuri~e and depressurize (vent) the crimping die a~sembly.
9 ll An alternate location for the pressuri~ed gas connection can 10ll be .in the upper die base 78 as shown in phantom line at 132.
~ Figure l shows a modification to the die set where an 12l 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 ii under pressure through a directed orifice 135 into a cylirlder 16l component when the upper and lower die assemblies are sealed 17` and pressurizedO
18,~ Shown in Figure 2, a counterbalance cylinder 32 l9l, which includes a small quantity, e.g., several cc of lubricating 20l oil, is placed into the lower die sleeve interior 118 so its 211i closed end is resting on plug 120. If a flat connector link 56 22¦' is weldea on the end of cylinder 32, a slot 130 in plug 120 23 ll will receive the connector link. The open end of counterbalance 24i, cylinder 32 projects above the kop end of the lower die sleeve 25 11 110 as seen in Figure 2.
26OPE~TION OF P~PPARATUS
27 ,AND rlETHbD OF ASSEMiBLING
28 1!COt:lNTERBALANCE LINK
29 !'Using the crimping apparatus previously described 30, and with the press in the inoperative open condition (Figure l),~
!i 31'j a cylinder component 32 is placed :in the lower crimping 32 i die assembly 76 and a sub-a.ssembled pi~ton a,ssembly 30 with 33'' shaft 40, seal 58 and bushing 60 is pl.aced into the upper 34 die assembly 74 60 the components are disposed as shown in i i -14-,j ; ! 11~376Bl 1 Figure ~. The press wor]c stro};e is then initiated, bringing 2 the upper die assembly 74 down toward and into enqagement 3 1~ 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. ~t

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

7 ~ a sealed aavity, all sub components of the counterbalance 3 1 link are inside that sealed cavity, and the cavity is pressurized 9 ll with a suitable gas under pressure. ~he pressure will be l! .
10 jl determined by the nature of the intended use of the counter-~ balance link. It will be from several times atmospheric 12 I pressure up to at least 2000 psi and if desired above 2000 psi.
13 ll Most requirements will be satisfied by pressures from 400 to 14 2000 psi which can be accommodated by components of gas 15 l' pressuriæed devices.
16 ll At this stage or instant in the press stro~e, 17 i the charge of gas in the cavity is a specific predetermined 18 i quantity and pressure and will be the same for every work 19 l, piece being made. As the press continues its stroke, khe 20 ~i projected piston, and the O-ring 58 enter the cylinder 32.
21 1I Shown in the detail Fiyure 2A, the internal peripheral 22 ! edge of the open end 4 3 of cylinder 32 is chamfered with a 23 il duble entry chamfer of 15 and 45 to facilitate introduction 24 1, of O-ring 58 into the cylinder. At the press stroke point 25 'I where O-ring 58 seals against the inner cylinder surface, 2~ a predetermined ~uantity of pre-pressurized gas is trapped 27 i inside the cylinder and is compressed still further by 28 continued operational movement o~ the press and the crimping 29 ll dies. Final movement of the press, as shown in Figure 4, 30 'I causes the inner crimping face 98 of the upper crimp die 94 31 1¦ to abut the cylinder end 48 and pressure crimp the wall end 32 il inward to complete the final assembly operation of the pneumatic !
33 ' counterbalance link.
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1 As the press starts on its return stroke, the 2 pressurizing line controls wlll be operated manually or 3 1l automatically in a known manner to shut-off the pressure 4 flow and to v~nt the die assembly and release pressure from tl~ cavity as the press is moving the die assem~lies toward 6 ! the unsealed condition, so that the cavity is not pressurized 7 ¦I when the cavity becomes unsealed. The completed workpiece

8 l, is removed and the cycle repeated.

9 1! METHOD APPLIED TO ASSEMBLE

10 ¦, ~UAL FORCE couNirERBAL~NcE LIMK

11 ll 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 it can be used to assemble, pressurize and crimp a dual or

15 l' plural forcs 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 l automotive trunklid a predetermine~ amount of about two

19 ll inches. The lid will then stay at that position until manually

20 ¦1 opened for another amount where the pneumatic spriny linkage

21 ll geometry is such that the lid will open and stay open by

22 ¦ spring force only. Prior to the present invention, dual force

23 !I has been accomplished by the addition of a small compression

24 ¦i spring installed into the pneumatic spring cylinder prior

25 ll to insertion of the piston and rod assembly. In normal use

26 ~Ihen that pneumatic spring is compressed, an additional force

27 1, must be applied for the final portion of the compressed

28 li stroke when and after the pi5 ton has contacted the compression

29 spring.

30 ,' This invention accomplishes the dual slope feature

31 I pneumatically by incorporating a floating piston in -~he

32 1I pneumatic spring cylinder. When the piston, which is fixed

33 I to the piston rod, i5 in engagement with the floa~ing piston

34 ,I the output force will increase at a higher rate.

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1 Figures 10 and 11 show the dual force output 2 counterbalance link 136 with a floating piston 170 having an 3 l~ elastomeric sealing O-ring 172. Link 136 and components 4 ' are hereinafter more specifically described but basically include similar parts and construction as in the unit 30 of 6 j Figure 5, plu5 a floating piston. With such a floating piston 7 I the cylinder encompasses one sealed compartment 174 behind 8 I! piston 170 and the two compartments, one on each side of the 9 !~ primary by-pass piston as is true in unit 30.
10 I Figures 12-16 depict the method of assembly of the dual 11 , force counterbalance link 136 in a somewhat schematic manner.
l2 l~ Figure 12, corresponding to Figure 3, shows the 13 I initial pressurization mode, where the cylin~er contains -the 14 li small amount of lubrication oil 64 previously mentioned with 15 I neither of the pistons yet inserted into the cylinder.
16 i~ The floating piston 170 may be temporarily attached to the 17 ii fixed piston assembly 140 by magnetic attraction (e.g., small 18 I~ magnet 176) or by some other controlled method such as 19 1l sticky grease. The crimp die chamber is initially pressurized 20 l' to a value which is below the final pressure.
21 1l Figures 13 and 13~. depict the positions ~.~here the 22 ~, press has moved to accomplish insertion only of the floating ~3 ¦, piston to a sealed condition and then (Figure 13A) is backed 24 ¦, of~ slightly to remove the fixed piston rom the floating piston, 25 lil whereupon the crimp die chamber is immediately subjected to 26 the higher fina~` pressure and and predetermined quantity of 27 ,' oil 178 injected via ~he orifice 135 shown in E~igure 1.
28 ii Figure 13~ depicts the disposition of components after 29 lli final pressurization has freed the floating piston from the ~~, fixed piston connection ~the magnetic holding force being lower 31 ll than that holding the fixed piston in the upper die assemhly) , 17-1i .

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1 and displaces the Eloating piston 170 into the cylinder 2I compressing the gas ahead of it into compartment 174 until 3l it equals the final pressure and a balance of pressure will 4 exist across the ~loating piston 170 and the small quantity of oil 178 has been introduced on top of the piston 170.
6, Figure 14 shows the upper ~ie assembly moved down to introduce 71 the fixed piston 142, O-ring 162, and bushing 164 into the 8 I cylinder 138. Final assembly is accomplished by the same 9 ,I further steps as described with respect to Figures 1-4.
10 ~I Figure 15 depicts normal operation where the ~ Eixed shat piston 140 moves in and out without contacting the 12 ¦ floating piston 170. The output force is equal to the 13 l, internal pressure acting on th piston rod area.
14 I, Figure 16 depicts the overload force mode where 15 i, the fixed piston 140 contacts the floating piston 170.
16 1, Displacing the piston rocd 146 into the cylinder 138 displaces 17 ~,, the floating piston 170 which is now in contac~ with khe 18 ¦' fixed piston assembly 140 and both pistons move together.
19 'i The output force on rod 146 is equal to the normal gas 20 ¦, pressure acting upon the piston rod area and the differential 21 ~I pressure across the floating piston. Due to the large area 22 li of the Eloating piston 170 and the relatively small gas volume ~23 11 ahead of it, the output load slope will increase and at a much 24 ll higher rate. Another desirable :Eeature of the operation in the overload mode is the elimination of piston orifice dampening 26 ,~ because there is no flow across the fixed piston. This will 27 , assist the desirecl initial "pop" open of an automotive 28 I~ trunk lid upon unlatching.
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.1 1 ; PNEU~TIC
2 ~ COUNTEP~BALANCE LIMKS
3 , This invention includes a gas spring or 4 j pneumatic counterbalance linlc as has been ~reviously described~ The link can be a single ~orce out?ut 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 1I Figures 10 and 12-16. In either case the-fixed piston 9 1 assembly, as illustrated, includes a construction ~thich o !~ provides essen~ially free by-pass flow of gas across the 11 .1! piston during a retraction or compression stroke and a 12 ' metered orifice flow during the extension or expansion stroke.
13 ~ Several modified versions o~ the cooperation piston and ring 14 assemblies are shown herein, any of the enbodiments can be 15 ! used in the single force link or the dual output force link.
16 ' Depending upon the application of use of ~he counterbalance, 17 ,I free flow or metered orifice flow across the piston can be 1 18 1 in the reverse of that just describedr or free flow, or metered I
19 l flow, could be provided for ~oth directions of the ?iston 20 1, stroke merely by reversing the installation of the piston ring 21 ~' or changing its coniguration.
22 1,1 In Figures 5 through 9, the piston assembly is a 23 ,l single piece spool 36 with a thick flange 180 disposed 24 ~I toward the crim?ed end 62 of cylinder 32 and a thin flange 25 , 182 disposed toward the cylinder closed end 50. Piston 36 26 is slipped onto the reduced diameter end 42 o~ pistan shaft 27 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 sufficien~ clearance from the cylinder 30 ' ~7all to enable unrestricte~ gas flow through the annular 31 space 18~. The diameter of tlle thin flange 182 also ha~
., -19~

1.
., .

l~b~7681 1 sufficient clearance to enable unrestricted flow of gas 2 1 through annular space 186. Disposed within the groove of 3 , piston spool 36 is a special molded piston O-ring 38 made of 4 ` flexible elastomeric material, such as synthetic rubber or plastics to permit stretching when the ring is slipped over 6 the flan~es. The piston spool can be made o~ two parts, 7 '' as shown in Figure 11, to permit the piston O-ring 38 to be 8 'j molded from a synthetic plastic material which need not be g 1l stretchable, it can be assembled between the two parts of 10 ll the piston. 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 I with several (4 shown) slots 190 on one side slightly 14 ' less than 1/2 diameter deep, to ena~le free flow by-pass 15 1l openings for gas to flow across the piston 36 when being 16 'l moved in a retraction operation as depicted by arrows in Figure 7. On the other side of the O-ring is a single f 18 I' for~ed (preferably pre-molded) orifice groove 192 which serves 19 1I to provide orifice metered flow duriny the expansion stroke 20 ~' as shown by arrows in Figure 6. In a typical installation 21 1I such as Figure 5, piston ring 38 is .645 inch diameter with 22 !1 a cross-sec~ion radius of a~proximately .100 inch and the 23 ¦I cross-section orifice by-pass is .0006 sq. inch. The rod 24 ¦, diameter is 0.314 inch, the cylinder I.D. is 0.620 inch and 25 ' piston stro~e approximately 3.75 inches.
26 i1 In Figure 10, the unit 136 is the same and has 27 ¦~ similar components as those of Figure 5, e.g., cylinder 138, 28 !I piston assembly 140 with the fail-safe piston 142 macle in 29 ll two parts 1~2a and 142b to enable a synthetic plastic p~ston 30 'il O-ring 144 to be pre-assembled with the parts 142a and 142b 31 li on the end of piston shaft 146. ~he piston ring 144 has the .
I!

"`` .1~3~76~
same configuratiorl as ri~g 38 and -the pis-ton 1~2 is staked or rive-ted at 150 on -the end 148 of piston shaft 146 Cylinder 136 has a closed end 154 with end disc 156 and an open end 152. Connec-tor links 158 and 160 are welded io the sha~t and cylinder to enable installation as desired. Large elastomeric O-ring 162 agains-t the end bushing 16~ provides a combination static cylinder seal, dynamic shaft seal and compliant piston stop. The compliance will provide an additional cushion to decelerate extension movement and reduce noise at the end of the stroke. Crimped end 166 of cylinder 138 maintains the components of counterbalance unit 136 in assembly.
Unit 136 of course includes the previously described floating piston 170 with its sealing O-ring 172 trapping a predetermined quantity of pressurized gas between the piston 170 and the closed end of cylinder 138.
Another version of the pneumatic counterbalance link, made as afore-described, is shown in Eigure 17 with details shown in Figures 18 and 19. The link 200 includes the basic cylinder 202 with closed bottom 204 and crimped end 205 and the piston and rod assembly with piston parts 206 and 208, piston ring 210, shaft 212, chevron seal 214 and bushing 216. The piston is made in two parts, a single flanged spool 206 and a cupped washer 208 fitted together with piston ring therebetween and staked on the end of the shaft 212. The I.D. of the piston ring 210 and drilled orifices 218 in the inner portion of cup washer 208 serve to provide free flow by-pass of gas in the retraction movement of the piston. Piston ring 210 is cut from an extruded tube made from plastic material such as "~IYTREL"*
and incorporates an extrusion formed orifice by-pass groo~
220 on the outer * Trademark - 21 -~8~76~31 periphery of the ring. In this embodiment when the cup washer 20~ 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' of the extruded piston ring 210 with orifice groove 220', and includes a plural:ity of internal ribs 222 which serve to coaxially locate the ring 210' on the piston and facilitate 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.D. spaced from the inside diameter of the piston spool 224. The upper flange part 227 (Figure 22a) of the piston has free flow by-pass apertures 228.
The lower flange of the piston has a radial metering orifice slot 230 formed therein as by coining. ~etraction 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 shown 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 2~0 has single metering orifice slots 242 and 24~, 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.

sd/~ 22-, ~8'~681 FAIL-SAFE PISTON
2 !' The counterbalance link has been developed to 3 preclude the problem of orifice contamination by implementation 4 of a feature which increases the oriEice size when flo~ is reversed to facilitate the disloclging of any entrapped 6 contaminants. In the event that the orifice remains 7 permanently closed, a catas~rophic 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 10 ll of the piston ring suppor-ting surface thereby allowing free ll flow of gases in both directions. The struc-tural integrity 12 li of the unit, however, is not compromised and the counter-13 balance will continue to functibn without the ra~e controlled 14 i extension feature.
15 1I Contamination of the metering orifice will 16 l hydraulically lock the unit and such problems have been 17 , encountered particularly in units which incorporate a 18 1 drilled orifice. Should an orifice become clogged when the l9 ,~ 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 il forced with the spring hydraulically locked due to a clogged 22 orifice.
23 , Applicant's fail-safe piston design is sho~n 24 , in Figures 5-7. The right hand piston flange 182 will 25 ', ~e wea~.ened by making it thinner or by addition of a fail-26 safe notch. Normal operation and load carrying capability 27 l' 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 I door forceably opened the piston forces will be applied 31 to the right hand flange 182 with the fail-safe feature.

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An overload will deform the flange from the piston allowing the seal to "blow out". Deformation of flange 182 under such a circumstance is depicted by phantom line 183 in Figure 6.
The pneumatic spring will continue to function after this fail-safe feature has been actuated but operation will be without orifice controlled dampening~
The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within thè meaning and range of equivalency of the claims are therefore intended to be embraced therein.

sd~r,~ -24~

Claims (41)

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

1. A method of assembly of pneumatic counterbalance units and the like which are made at least from a closed end cylinder subassembly and a piston subassembly including a piston means, piston shaft, shaft bushing and shaft to cylinder annular seal means and wherein the assembled counter-balance unit has the piston subassembly with the piston means, shaft bushing and annular seal means assembled within the cylinder subassembly with one end of the shaft projecting from the piston means out of the other end of the cylinder subassembly which is an open end and is crimped to block removal of the piston subassembly comprising: pressurizing the piston subassembly and the cylinder subassembly with gas under pressure of at least several atmospheres; and, in a common sealed environment, inserting the piston means and its seal means and shaft bushing into and within the cylinder subassembly, which includes a predetermined quantity of lubricating oil, with immediate subsequent radially inward crimping of the cylinder subassembly open end, while said piston subassembly and at least the other end portion of the cylinder subassembly are maintained pressurized by said gas, to retain the piston assembly and gas under pressure within said cylinder subassembly.

2. A method as defined in claim 1 wherein said two sub-assemblies are held in upper and lower crimping die assemblies in a press, and said die assemblies with the two subassemblies are moved toward each other by the press; the die assemblies upon initial engagement before the subassemblies come into assembling engagement are sealed and pressurized; the piston subassembly is moved into the pre-pressurized cylinder sub-assembly; and the die assemblies close with each other and crimp the open end of the cylinder subassembly.

3. A method as defined in claim 2, wherein the piston subassembly is located in the upper die assembly and is arranged vertically coaxial with the cylinder subassembly in the lower die assembly and means engaging said one shaft end provides a force to preliminarily maintain the piston subassembly in the upper die assembly.

4. A method as defined in claim 3, wherein said force is a magnetic force.

5. A method as defined in claim 3, wherein said force is the adherence force provided by a small quantity of sticky grease between the shaft end and the upper die assembly.

6. A method of assembly of pneumatic counterbalance units and the like which are made at least from a closed end cylinder subassembly and a piston subassembly including a piston means, piston shaft, a second floating piston with a seal ring, a shaft bushing and shaft to cylinder annular seal means and wherein the assembled counterbalance unit has the piston subassembly with the piston means, the floating piston and seal ring shaft bushing and annular seal means assembled within the cylinder with one end of the shaft projecting from the piston out of the other end of the cylinder which is an open end and is crimped to block removal of the piston assembly comprising: pressurizing the piston subassembly, with the floating piston and its seal ring removably carried on the piston end of the piston subassembly, and the cylinder subassembly in a common sealed environment with gas under pressure of at least several atmospheres;
moving the piston subassembly toward the cylinder sub-assembly until the floating piston, and its seal ring, pass into the cylinder and via its seal ring has a sealed relationship with the cylinder; increasing the pressurization in the common sealed environment and separating the floating piston from the other components of the piston subassembly;

followed by inserting the piston means and its seal means and shaft bushing into the cylinder subassembly, which includes a predetermined quantity of lubricating oil, with immediate subsequent crimping of the cylinder subassembly open end, while said piston subassembly and at least the other end portion of the cylinder subassembly in said common sealed environment are maintained pressurized by said gas, to retain the piston assembly and gas under pressure within said cylinder subassembly.

7. A method as defined in claim 6 wherein after the initial pressurization of the sealed environment and when the floating piston has moved into the cylinder subassembly, a predetermined amount of oil for lubrication is introduced into the cylinder subassembly on top of the floating piston and thereafter the sealed environment pressurization is increased.

8. A method as defined in claim 6 wherein said two sub-assemblies are held in upper and lower crimping die assemblies in a press, and said die assemblies with the two subassemblies are moved toward each other by the press; the die assemblies upon initial engagement before the subassemblies come into assembled engagement are sealed and subjected to the first pressurization; the floating piston is moved into the pre-pressurized cylinder subassembly; said increase in pressure then occurs which forces the floating piston away from the fixed piston into the cylinder subassembly; the die assemblies move closer, the piston subassembly seal means and bushing are fully inserted into the cylinder subassembly; then the die assemblies while still pressurized close with each other and crimp the open end of the cylinder subassembly.

9. A method as defined in claim 8, wherein the piston subassembly is located in the upper die assembly and is arranged vertically coaxial with the cylinder subassembly in the lower die assembly and means engaging said one shaft end provides a force to preliminarily maintain the piston sub assembly in the upper die assembly.

10. A method as defined in claim 9, wherein said force is a magnetic force and a second lower adhering force holds the floating piston on the other end of the shaft.

11. A method as defined in claim 10, wherein said second named force is a magnetic force provided by a small permanent magnet in the top of the floating piston.

12. A method as defined in claim 10, wherein said second named force is the adherence force provided by a small quantity of sticky grease between the other shaft end and the top of the floating piston.

13. A method of assembly of pressurized pneumatic counter-balance units and the like which are made at least from a closed end cylinder subassembly and a piston subassembly including a piston shaft, piston means on one end of the shaft, a shaft bushing and shaft to cylinder annular seal means between the bushing and the piston means and wherein the assembled counterbalance unit has the piston subassembly with the piston means, shaft bushing and annular seal means maintained within the cylinder subassembly with one end of the shaft projecting out of the other end of the cylinder subassembly which is an open end and is crimped to block removal of the piston subassembly comprising: insertion of the piston subassembly into the cylinder subassembly, which includes a predetermined quantity of lubricating oil;
pressurizing of the piston subassembly and cylinder sub-assembly in a sealed common environment with gas under pressure of at least several atmospheres, the insertion into the open end of the cylinder subassembly of at least the seal means and bushing portions of the piston subassembly being accomplished subsequent to said pressurizing step;
and thereafter subsequently radially inwardly crimping the cylinder subassembly open end, while said piston subassembly and at least the open end portion of cylinder subassembly are maintained under said gas environment at a predetermined pressure.

14. A method as defined in claim 13, wherein said two subassemblies are located in upper and lower crimping die assemblies in a press; said die assemblies are moved toward each other by the press; the die assemblies upon initial interengagement, which is prior to the subassemblies being placed into completely assembled engagement, are sealed and pressurized; and the piston subassembly is then completely assembled with its seal and bushing forced into the pre-pressurized cylinder subassembly by further movement of said die assemblies toward each other, whereupon the die assemblies close with each other and crimp the open end of the cylinder subassembly.

15. A method as defined in claim 14, wherein the piston subassembly is located in the upper die assembly and is arranged vertically coaxial with the cylinder subassembly in the lower die assembly and means engaging said one shaft end of the piston subassembly provides a force to preliminarily maintain the piston subassembly in the upper die assembly.

16. An apparatus to make a pneumatic counterbalance spring link or the like from a pre-assembly of a closed end cylinder with the other end open and a second pre-assembled piston assembly which includes a piston shaft with a free end, a piston fixed on the shaft, and an abutment bushing and an annular seal means on the shaft between the free end and said piston, with the seal means between the bushing and the piston, the shaft having a free end which will project from the open end of the cylinder, comprising: a crimping die set with upper and lower hollow telescoping die assemblies adapted to be secured in a press; one die assembly having means to releasably secure the piston assembly by the free end of the shaft and the other die assembly having means to hold the cylinder assembly; means including said press and said die assemblies to move both die assemblies and the counterbalance unit pre-assemblies toward each other with the piston assembly coaxially aligned with the cylinder assembly and moving toward entry into the open end of the cylinder assembly, said die assemblies having means to seal said die assemblies upon initial engagement and during subsequent movement toward each other to provide a sealed cavity within said engaged die assemblies which will contain the counter-balance link pre-assemblies; means to introduce gas under at least several atmospheres of pressure into said sealed cavity prior to further closure movement of the die assembly, which results in insertion of the seal means of the piston pre-assembly into said cylinder; means in said die assemblies adapted to cause inward crimping of the cylinder open end by further movement of the die assemblies after said die assemblies have moved together to a position where the bushing of the piston pre-assembly has been moved into the cylinder by movement of the die assemblies; means enabling separation of said die assemblies; and means operable after crimping to vent pressure from said sealed cavity before reverse movement of said die assemblies opens the sealed cavity.

17. An apparatus as defined in claim 16, wherein said upper die assembly includes an open ended but otherwise pressure tight cavity with space to accommodate and retain the piston sub-assembly within the cavity and the lower die assembly includes a second open ended but otherwise fluid tight cavity including means to accommodate and retain the cylinder sub-assembly in coaxial alignment with the piston subassembly, and one of said die assemblies includes passage means in fluid communication with said means to introduce gas under pressure.

18. An apparatus as defined in claim 17, wherein a portion of said lower die assembly is shaped to pass coaxially into the cavity of said upper die assembly and carries a seal right to effect a gas tight seal between the cavities of each said die assembly.

19. An apparatus as defined in claim 17, wherein said upper die assembly includes a coaxially nested crimping die insert and an inner sleeve bushing insert, the latter being adapted to closely receive the shaft of the piston assembly and to engage and maintain the piston assembly bushing spaced away from said crimping die in a direction toward the lower die assembly.

20. An apparatus as defined in claim 19, wherein the upper die assembly above said nested inserts includes a blind bore which is adapted to receive the shaft of the piston assembly and a magnet is located at the base of said blind bore.

21. An apparatus as defined in claim 19, wherein both of said inserts are radially slotted to enable through passage of a flat connector link fastened to the end of the piston shaft.

22. An apparatus as defined in claim 16, wherein the upper die assembly includes a first sleeve member with an interior passage; said lower die assembly includes a second sleeve member which can coaxially move into the passage of said first sleeve member upon operational movement of said die assemblies;

and adjustable abutment means on the exterior of said lower die assembly providing a positive abutment limit stop for said upper die assembly, at the end limit of the work stroke.

23. An apparatus as defined in claim 22, wherein the upper end of said second sleeve member has an external groove, and an O-ring seal is retained in said groove and will engage and seal the two sleeve members upon and after occurrence of the initial telescoping relationship when the die assemblies are operatively moved toward each other.

24. An apparatus as defined in claim 17, wherein said passage means enabling introduction of gas under pressure into said sealed cavity is located in the lower die assembly.

25. An apparatus as defined in claim 17, wherein said passage means enabling introduction of gas under pressure into said sealed cavity is located in the upper die assembly.

26. A An apparatus as defined in claim 16, wherein means are provided in fluid communication through one of said die assemblies to introduce a predetermined quantity of oil for lubrication into the open end of said cylinder while said die cavity is sealed and prior to final high pressurization.

27. An apparatus as defined in claim 26, wherein said means to introduce oil is in fluid communication through the wall of said upper die assembly into the sealed cavity.

28. An apparatus to make a pneumatic counterbalance spring link or the like from a pre-assembly of a closed end cylinder with the other end open and a second pre-assembled piston assembly which includes a piston shaft with a free end, a piston fixed on the shaft, and an abutment bushing and an annular seal means on the shaft between the free end and said piston, with the seal means between the bushing and the piston, the shaft having a free end which will project from the open end of the cylinder, comprising: a crimping die set with upper and lower hollow telescoping die assemblies adapted to be secured in a press; one die assembly having means to releasably secure the piston assembly by the free end of the shaft and the other die assembly having means to hold the cylinder assembly; means including said press and said die assemblies to move both die assemblies into an initial engagement to provide a sealed cavity within and between said die assemblies which will contain the counterbalance link pre-assemblies; means to introduce gas under at least several atmospheres of pressure into said sealed cavity before the seal means of the piston pre-assembly is forced into the end of the cylinder pre-assembly and prior to the further closure movement of the die assembly, which results in insertion of the abutment bushing and the seal means of the piston pre-assembly into said cylinder; means in said die assemblies adapted to cause inward crimping of the cylinder open end by further movement of the die assemblies after said die assemblies have moved together to a position where the bushing of the piston pre-assembly has been moved into the cylinder; means enabling separation of said die assemblies; and means operable after crimping to vent pressure from said sealed cavity and before reverse movement of said die assemblies opens the sealed cavity.

29. An apparatus as defined in claim 28, wherein said upper die assembly includes an open ended but otherwise pressure tight cavity with space to accommodate at least the shaft end part, bushing and seal means of the piston subassembly within the cavity, and the lower die assembly includes a second open ended but otherwise fluid tight cavity including means to accommodate at least the cylinder subassembly in coaxial alignment with the piston subassembly, and one of said die assemblies includes passage means in fluid communication with said means to introduce gas under pressure.

30. An apparatus as defined in claim 29, wherein a portion of said lower die assembly is shaped to pass coaxially into the cavity of said upper die assembly and carries a seal ring to effect a gas tight seal between the cavities of each said die assembly.

31. An apparatus as defined in claim 29, wherein said crimping means is in said upper die assembly and includes crimping die insert means to closely receive the shaft of the piston assembly and to engage and maintain the piston assembly bushing spaced away from the end portion of the cylinder as that end portion is being crimped by said die assemblies.

32. An apparatus as defined in claim 31, wherein the upper die assembly above said crimping die insert means includes a blind bore which is adapted to receive the shaft of the piston assembly and means are located in said blind bore to engage and retain the piston pre-assembly.

33. An apparatus as defined in claim 29, wherein the upper die assembly includes a first sleeve member with an interior passage; said lower die assembly includes a second sleeve member which can coaxially move into the passage of said first sleeve member upon operational movement of said die assemblies; and work stroke limiting means provide an end limit for the work stroke movement of said die assemblies.

34. An apparatus as defined in claim 33, wherein the upper end of said second sleeve member has an external groove, and an O-ring seal is retained in said groove and will engage and seal the two sleeve members upon and after occurrence of the initial telescoping relationship when the die assemblies are operatively moved toward each other.

35. An apparatus as defined in claim 29, wherein said passage means enabling introduction of gas under pressure into said sealed cavity is located in the lower die assembly.

36. An apparatus as defined in claim 29, wherein.
said passage means enabling introduction of gas under pressure into said sealed cavity is located in the upper die assembly.

37. An apparatus to make a pneumatic counterbalance spring link from a pre-assembly of a closed end cylinder with the other end open and a second pre-assembled piston assembly which includes a piston shaft, having two ends, with a piston fixed on one end of the shaft, and an abutment bushing and an annular seal means on the shaft with the seal means between the bushing and the piston, comprising:
a crimping die set adapted to be secured in a press and having at least one upper die assembly with means to releasably secure the piston assembly by the other end of.
the shaft, said die set also including means to hold the cylinder assembly in said press; means including the press and said die set to enable coaxial alignment and final assembly of the piston assembly and the cylinder assembly with the piston, the seal means and the bushing being inserted in the cylinder; said die set also having means providing a sealed cavity between the cylinder and said upper crimping die assembly with the piston assembly secured therein; means to introduce gas under at least several atmospheres of pressure into said sealed cavity prior to that increment of closure movement of the press which results in insertion of the seal means into said cylinder; means in said upper crimping die assembly adapted to engage and cause inward crimping of the cylinder open end during further, continued movement of said press following that increment of press movement which inserts the bushing into the cylinder.

38. An apparatus as defined in claim 28, wherein means are provided in fluid communication through one of said die assemblies to introduce a predetermined quantity of oil for lubrication into the open end of said cylinder while said die cavity is sealed and prior to final high pressurization.

39. An apparatus as defined in claim 38, wherein said means to introduce oil is in fluid communication through said upper die assembly.

40. An apparatus as defined in claim 37, wherein the means to introduce gas under pressure includes passage means in said die set.

41. An apparatus as defined in claim 40, wherein said passage means enabling introduction of gas under pressure into said sealed cavity is located in the upper die assembly.