Gas spring

Abstract

A gas spring (1) comprising: an outer casing (2) having, on the inside, a first (3) and a second cavity (4) adjacent to one another and separated from one another by a dividing wall; a first oblong-shaped piston-rod (5), which engages said dividing wall in an axially slidable and fluid-tight manner, so as to project cantilevered inside both cavities (3, 4) and form / delimit, inside said first cavity (3), a variable-volume closed chamber (6) containing pressurized gas; and a second oblong-shaped piston-rod (7), which is fitted in the outer casing (2) in an axially slidable and fluid-tight manner, so as to project cantilevered outside the casing (2) and, at the same time, also project cantilevered inside the second cavity (4) so as to form / delimit, inside said second cavity (4) and together with the first piston-rod (5), a variable-geometry closed chamber (8) containing incompressible liquid.

Description

[0001] "GAS SPRING"

[0002] Cross-Reference to Related Applications

[0003] This Patent Application claims priority from Italian Patent Application No . 102023000012459 filed on June 16 , 2023 , the entire disclosure of which is incorporated herein by reference .

[0004] Technical Field

[0005] The present invention relates to a gas spring .

[0006] In more detail , the present invention relates to a gas spring adapted to be used in the field of sheet metal pressing . Use to which the following disclosure will make explicit reference without thereby losing generality .

[0007] Background of the Invention

[0008] As is known, the gas springs used in dies for sheet metal pressing generally comprise : a cup-shaped body substantially cylindrical in shape ; a guide bushing, separate and distinct from the cup-shaped body, which f luid-tightly seals the mouth of the cup-shaped body by means of the interposition of a series of annular sealing gaskets ; and a substantially cylindrical-shaped, piston-rod which is fitted in a pass- through and axial ly slidable manner into the hole at centre of the guide bushing, so that it can move axially with respect to the cup-shaped body between a retracted position and an extracted or extended position .

[0009] In more detail , the piston-rod is inserted in the guide bushing in a fluid-tight manner by the interposition of a series of annular sealing gaskets , so as to form / delimit , together with the cup-shaped body and the guide bushing, a variable-volume closed chamber, which is filled with a high- pressure gas .

[0010] The high-pressure gas keeps the piston-rod in the extracted or extended position, i . e . with the flanged inner end of the piston-rod in abutment against the guide bushing, until the piston-rod does not undergo an axial force capable of overcoming the thrust of the gas .

[0011] Clearly, the elastic thrust exerted by the gas spring depends on the dimensions of the gas spring and on the nominal pressure of the gas present inside the gas spring, i . e . the pressure of the gas when the piston-rod is in the extracted or extended position .

[0012] Generally, the bottom of the cup-shaped body moreover accommodates a one-way valve ( also called a non-return valve ) and a safety plug .

[0013] The one-way valve is used to introduce pressurised gas into the gas spring . The safety plug, in turn, is structured so as to automatically discharge the pressurised gas outside of the gas spring when the pressure of the gas exceeds a predetermined upper limit and / or when the piston-rod performs an "overtravel" , i . e . when the piston-rod retracts inside the cup-shaped body exceeding the maximum travel allowed by the dimensions of the gas spring .

[0014] Unfortunately, the gas springs described above have certain structural limitations that make the use thereof problematic in some industrial applications .

[0015] In cold sheet metal pressing, for example , there may be required very high elastic thrusts , demanding large-diameter gas springs . Unfortunately, however, the dimensions of these gas springs are o ften incompatible with the space available in the die , with all the problems that this entails .

[0016] Summary of the Invention

[0017] Aim of the present invention is to reali ze a gas spring, which is capable of providing, for the same outer diameter of the casing, elastic thrusts of a signi ficantly higher value than those provided by conventional gas springs .

[0018] In accordance with these aims , according to the present invention there i s provided a gas spring as defined in claim 1 and preferably, though not neces sarily, in any one of the claims dependent thereon . Brief Description of the Drawings

[0019] The present invention will now be described with reference to the accompanying drawings , which show a nonlimiting embodiment thereof , wherein :

[0020] - Figure 1 is a perspective view o f a gas spring reali zed according to the teachings of the present invention;

[0021] - Figure 2 is a side view of the gas spring illustrated in Figure 1 , sectioned along the mid-plane and with parts removed for clarity' s sake ;

[0022] - Figure 3 is an enlargement of the upper part of the gas spring illustrated in Figure 2 , with parts removed for clarity' s sake ; whereas

[0023] - Figure 4 shows the gas spring of Figure 2 during operation .

[0024] Detailed Description of the Embodiments

[0025] With reference to figures 1 , 2 , 3 and 4 , number 1 denotes as a whole a gas spring that can be advantageously used in the presses or dies for cold sheet metal pressing and the like .

[0026] The gas spring 1 firstly comprises : an outer casing 2 with a rigid, sel f-supporting structure , which is preferably oblong in shape and is internally provided with two large , closed cavities 3 and 4 , that are arranged one adj acent the other preferably aligned along a longitudinal axis A of the casing 2 , and are separated and isolated from one another by an inner dividing wall ; and a first oblong-shaped piston-rod 5 , which extends parallel to the longitudinal axis A and engages , in pass-through and axially slidable manner, the dividing wall of casing 2 separating the cavities 3 and 4 from each other, so as to proj ect cantilevered inside both cavities 3 and 4 .

[0027] The piston-rod 5 , in addition, engages the inner dividing wall of the casing 2 substantial ly fluid-tight , so as to keep the cavities 3 and 4 isolated from one another and at the same time to form / delimit , inside the lower cavity 3 of casing 2 , a variable-volume closed chamber 6 that contains / is adapted to contain nitrogen or other pressurised gas .

[0028] In other words , the piston-rod 5 i s preferably fitted in axially slidable manner into a substantially complementary- shaped, straight through hole which is made in the dividing wall of casing 2 . Preferably, an annular sealing gasket is moreover located inside the straight through hole , between the piston-rod 5 and the casing 2 , so as to isolate the cavities 3 and 4 from one another in a fluid-tight manner .

[0029] The pressurised gas present inside the lower cavity 3 , or rather inside the variable-volume closed chamber 6 , moreover has a pressure higher than the external one so as to maximise the volume of the same closed chamber .

[0030] In addition, the segment of piston-rod 5 that remains stably inside the lower cavity 3 of casing 2 is preferably provided with an anti-extraction structure , which is adapted to prevent the complete coming out of the piston-rod 5 from the lower cavity 3 due to the thrust exerted by the pressurised gas .

[0031] The pressurised gas present inside the lower cavity 3 , or rather inside the variable-volume closed chamber 6 , is therefore adapted to bring and keep the piston-rod 5 in a fully extracted or extended position ( see figure 2 ) , wherein the anti-extraction structure of the piston-rod 5 i s arranged in abutment against the dividing wall of casing 2 separating the inner cavities 3 and 4 from one another .

[0032] In the example shown, in particular, the nominal / minimum pressure of the gas contained in lower cavity 3 , or rather in the variable-volume closed chamber 6 , ( i . e . the gas pressure with the piston-rod 5 in the fully extracted or extended position) preferably ranges between 20 and 350 bar .

[0033] With reference to Figures 1 , 2 , 3 and 4 , in addition the gas spring 1 comprises also a second oblong-shaped piston- rod 7 , which preferably extends parallel to the longitudinal axis A, is fitted in the outer cas ing 2 in axially slidable and fluid-tight manner, so as to proj ect cantilevered outside of the outer casing 2 and at the same time also proj ect cantilevered inside the upper cavity 4 of casing 2 , so as to form / delimit , inside the upper cavity 4 and together with the piston-rod 5 , a variable-geometry closed chamber 8 that contains / is adapted to contain oil or other incompressible liquid .

[0034] Clearly, being filled with the incompressible liquid, the variable-geometry closed chamber 8 is capable of varying its shape , while however keeping its overall volume constant .

[0035] In more detail , the piston-rod 7 i s preferably fitted in axially slidable manner in a substantially complementary- shaped, straight hole which is made in the outer casing 2 so as to connect the upper cavity 4 of casing 2 directly with the outside .

[0036] The segment of piston-rod 7 that stably remains inside the upper cavity 4 of casing 2 , moreover, is preferably provided with an anti-extraction structure , which is adapted to prevent the pi ston-rod 7 from completely coming out from the upper cavity 4 due to the thrust exerted by the incompressible liquid .

[0037] With particular reference to Figures 2 , 3 and 4 , in addition the piston-rod 7 is preferably substantially aligned, or rather substantially coaxial , to the pi ston-rod 5 beneath, and is preferably also provided with an oblongshaped blind cavity 9 , which directly faces the piston-rod 5 so as to form a part of the variable-geometry closed chamber 8 , and is moreover stably engaged in axially slidable manner and with mechanical clearance by the segment of piston-rod 5 that is located ins ide the upper cavity 4 of outer casing 2 .

[0038] In more detail , the blind cavity 9 of piston-rod 7 preferably has a shape substantially complementary to that of the corresponding portion of piston-rod 5 . The piston- rod 7 , in addition, is preferably also provided with one or more auxiliary grooves 10 extending more or less longitudinally along the inner lateral surface of the blind cavity 9 so to facilitate the passage of the incompressible liquid in the interstitial space between the piston-rods 5 and 7 , to and from the ceiling of the blind cavity 9 .

[0039] In even more detail , the segment of piston-rod 5 that engages the blind cavity 9 of piston-rod 7 preferably has an substantially constant cross-section roughly along its entire length . The blind cavity 9 of the piston-rod 7 , in turn, preferably has a substantially constant cross-section complementary to that of the piston-rod 5 .

[0040] Preferably, the ceiling of the blind cavity 9 of piston- rod 7 furthermore communicates with the outside of gas spring 1 via a through duct , which is selectively closable in fluid- tight manner by means of a plug, and advantageously also has a profile converging towards the mouth of the same through duct .

[0041] With reference to Figures 2 , 3 and 4 , preferably the segment of piston-rod 7 that remains stably inside the upper cavity 4 of casing 2 , is moreover shaped / structured so as to cooperate in fluid-tight manner with the inner lateral surface of the upper cavity 4 , so as to longitudinally divide the same upper cavity 4 into two parts of complementary shape .

[0042] In more detail , the piston-rod 7 is preferably provided with an annular sealing gasket , which is fitted on the segment of piston-rod 7 that remains stably inside the upper cavity 4 of casing 2 , so as to interpose itsel f between the piston-rod 7 and the fluid-tight casing 2 .

[0043] The part of the upper cavity 4 that is adj acent to the lower cavity 3 of casing 2 and is engaged by the pi ston-rod 5 , contains the incompressible liquid and thus forms the variable-geometry closed chamber 8 .

[0044] Preferably the other part of the upper cavity 4 instead communicates with the outside .

[0045] With particular reference to Figures 2 and 4 , similarly, the segment of piston-rod 5 that remains stably inside the lower cavity 3 of casing 2 is preferably shaped / structured so as to cooperate in fluid-tight manner with the inner lateral surface of lower cavity 3 , so as to longitudinally divide the same lower cavity 3 into two parts of complementary shape .

[0046] In more detail , the piston-rod 5 is preferably provided with an annular sealing gasket , which is fitted on the segment of piston-rod 5 that remains stably inside the lower cavity 3 of casing 2 , so as to interpose itsel f between the piston-rod 5 and the fluid-tight casing 2 .

[0047] The part of lower cavity 3 that is delimited by the bottom of the lower cavity 3 and the piston-rod 5 ( and thus does not surround the piston-rod 5 ) , contains the pressurised gas and forms the variable-volume closed chamber 6 . Preferably, the other part of lower cavity 3 , i . e the part of lower cavity 3 adj acent to the upper cavity 4 of casing 2 , instead communicates with the outside .

[0048] With reference to Figures 1 , 2 and 4 , in particular, the outer casing 2 is preferably substantially cylindrical in shape and is preferably made mainly of metal material .

[0049] The lower cavity 3 and / or the upper cavity 4 , in addition, preferably is / are substantially cylindrical in shape and preferably extend inside the casing 2 while remaining locally coaxial to the longitudinal / central axis A of casing 2 . Preferably, the cavities 3 and 4 of casing 2 are therefore substantially coaxial with each other .

[0050] Similarly, the piston-rod 5 and / or the piston-rod 7 preferably is / are substantially cylindrical in shape , are preferably made of metal material , and preferably extend substantially coaxial to the longitudinal / central axis A of casing 2 .

[0051] Preferably, the piston-rods 5 and 7 are therefore substantially coaxial with each other and are telescopically inserted into one another . With reference to Figures 1 , 2 , 3 and 4 , in particular the outer casing 2 preferably comprises : an outer cup-shaped body 12 advantageously substantially cylindrical in shape , which preferably has a one-piece structure and preferably extends substantially coaxial to the longitudinal / central axis A; an inner cup-shaped body 13 advantageously substantially cylindrical in shape , which has a one-piece structure , and is inserted in the initial segment of the central cavity of the outer cup-shaped body 12 , such that its bottom wall is arranged at a predetermined distance from the bottom wall of the outer cup-shaped body 12 ; and a guide bushing 14 advantageously substantially cylindrical in shape , distinct and separate from the cup-shaped bodies 12 and 13 , which has a one-piece structure and is arranged to close the mouth of the outer cup-shaped body 12 and / or of the inner cup-shaped body 13 .

[0052] Preferably, the outer cup-shaped body 12 and / or the inner cup-shaped body 13 and / or the guide bushing 14 is / are also made of metal .

[0053] The piston rod 5 engages the bottom wall of the inner cup-shaped body 13 in a pass-through and axially slidable manner, while the piston-rod 7 engages the guide bushing 14 in a pass-through and axially slidable manner .

[0054] In more detail , the inner cup-shaped body 13 is preferably entirely housed in the initial segment of the central cavity of the outer cup-shaped body 12 .

[0055] Preferably, the inner cup-shaped body 13 is moreover structured so as to engage said initial segment of the central cavity of the outer cup-shaped body 12 in an axially slidable manner .

[0056] In addition, the cup-shaped body 13 preferably has , in its bottom wall , a straight through hole that extends coaxial to the longitudinal / central axis A, has a cross-section substantially complementary to that of the piston-rod 5 and is engaged in a pass-through and axially slidable manner by a corresponding segment of the same piston-rod 5 .

[0057] With reference to Figures 2 and 4 , the casing 2 of gas spring 1 preferably also includes at least one annular gasket 15 , which is advantageously made o f polymeric material , and is located inside the straight through hole present in the bottom wall of the inner cup-shaped body 13 , between the piston-rod 5 and the same inner cup-shaped body 13 , so as to prevent the passage of pressurised gas and / or incompressible liquid inside the interstitial space between the cup-shaped body 13 and the piston-rod 5 .

[0058] Preferably, the lower cavity 3 of casing 2 is therefore delimited by the outer cup-shaped body 12 and the inner cupshaped body 13 .

[0059] In other words , the lower cavity 3 of casing 2 is preferably delimited longitudinally by the bottom wall of the inner cup-shaped body 13 and by the bottom wall of the outer cup-shaped body 12 .

[0060] With particular reference to Figures 2 and 3 , the central hole of the guide bushing 14 , on the other hand, preferably has a circular cross-section substantially complementary to the local cross-section of piston-rod 7 , and is engaged in a pass-through and axially slidable manner by the piston-rod 7 advantageously by the interposition of at least one centring ring 16 and / or at least one oil-wiper annular gasket 17 , both of known type and preferably made of polymeric material .

[0061] In addition, the guide bushing 14 preferably engages the mouth of the central cavity of the outer cup-shaped body 12 up to the rim delimiting the mouth of the inner cup-shaped body 13 , and is adapted to retain the inner cup-shaped body 13 inside the outer cup-shaped body 12 .

[0062] Preferably the upper cavity 4 of casing 2 is therefore delimited by the inner cup-shaped body 13 and the guide bushing 14 .

[0063] In other words , the upper cavity 4 of casing 2 is preferably delimited longitudinally by the guide bushing 14 and by the bottom wall of cup-shaped body 13 .

[0064] In more detail , the guide bushing 14 is preferably screwed into the mouth of the central cavity of outer cupshaped body 12 , and is preferably adapted to retain the inner cup-shaped body 13 stably in abutment against a protruding annular shoulder, which is made inside the central cavity of outer cup-shaped body 12 , at a predetermined distance from the bottom of the same central cavity .

[0065] Preferably, the outer cup-shaped body 12 moreover has , inside the central cavity and at said annular shoulder, an annular groove communicating with the outside via a connecting duct 18 that preferably extends radially through the side wall of the same outer cup-shaped body 12 .

[0066] With reference to Figures 2 , 3 and 4 , in turn the piston- rod 5 preferably comprises a cup-shaped body 20 advantageously substantially cylindrical in shape , which is preferably made of metal material and is fitted in a pass- through and axial ly slidable manner in the dividing wall of casing 2 separating the cavities 3 and 4 from one another, or rather in the straight through hole present in the bottom wall of inner cup-shaped body 13 , with the concavity turned towards the lower cavity 3 , or rather towards the bottom of the central cavity of outer cup-shaped body 12 . In other words , the cup-shaped body 20 is preferably substantially coaxial to the longitudinal / central axis A.

[0067] Preferably, the mouth of cup-shaped body 20 is furthermore provided with a protruding annular flange , which is adapted to prevent the cup-shaped body 20 from being completely extracted from the lower cavity 3 .

[0068] In addition, the shape of the annular flange of cupshaped body 20 is preferably substantially complementary to that of the cross-section of the lower cavity 3 of casing 2 , or rather to that of the cross-section of the final segment of the central cavity of the outer cup-shaped body 12 . With reference to Figures 2 and 4 , preferably the piston- rod 5 also comprises : at least one annular sealing gasket 21 , which is advantageously made of polymeric material and is fitted on the annular flange of the cup-shaped body 20 so as to prevent the passage of pressurised gas into the interstitial space between the same flange and the side wall of the outer casing 2 , or rather of the outer cup-shaped body 12 ; and optionally also a centring ring 22 , which is preferably made of polymeric material and is fitted on the annular flange of cup-shaped body 20 so as to rest and slide on the inner surface of the lower cavity 3 .

[0069] With reference to Figures 1 , 2 , 3 and 4 , in turn, the piston-rod 7 preferably comprises a cup-shaped body 25 advantageously substantially cylindrical in shape , which is preferably made of metal material and is fitted in a pass- through and axial ly slidable manner in the guide bushing 14 that closes the mouth of the outer cup-shaped body 13 , with the concavity turned towards the upper cavity 4 , or rather towards the bottom of the central cavity of the inner cupshaped body 13 . In other words , the cup-shaped body 25 is preferably substantially coaxial to the longitudinal / central axis A of casing 2 .

[0070] Clearly, the central blind cavity of cup-shaped body 25 is preferably engaged in axially slidable manner by the upper part of cup-shaped body 20 and forms the blind cavity 9 of piston-rod 7 .

[0071] In more detail , the central cavity of cup-shaped body 25 preferably has a shape substantially complementary to the upper part of cup-shaped body 20 .

[0072] Preferably, the cup-shaped body 25 moreover has , inside the central blind cavity, a series of straight grooves which extend along its side wall parallel to the longitudinal axis of the body, i . e . parallel to the longitudinal / central axis A of casing 2 , and are advantageously also spaced substantially regularly around the same longitudinal axis . Preferably, the mouth of cup-shaped body 25 is further more provided with a protruding annular flange that is adapted to prevent the cup-shaped body 25 from being completely extracted from the upper cavity 4 .

[0073] In addition, the shape of the annular flange of cupshaped body 25 is preferably substantially complementary to that of the cross-section of the lower cavity 4 of casing 2 , or rather to that of the cross-section of the central cavity of the inner cup-shaped body 13 .

[0074] With particular reference to Figure 3 , preferably the piston-rod 7 moreover comprises : at least one annular sealing gasket 26 , which is advantageously made of polymeric material and is fitted on the annular flange of the cup-shaped body 25 , so as to prevent the passage of pressurised oil into the interstitial space between the same flange and the side wall of the outer casing 2 , or rather of the inner cup-shaped body 13 ; and optionally also a centring ring 27 , which is preferably made o f polymeric material and is located on the mouth of cup-shaped body 25 so as to rest and sl ide on the outer surface of piston-rod 5 , or rather of the cup-shaped body 20 .

[0075] Clearly, the centring ring 27 is structured so as to not obstruct the passage of the incompressible liquid that fills the variable-geometry closed chamber 8 , in the interstitial space between the piston-rods 5 and 7 .

[0076] Preferably, the cup-shaped body 25 is moreover provided with a through hole 28 advantageously straight and / or substantially coaxial to the longitudinal / central axis A, which passes through the bottom wall of the same cup-shaped body 25 and ends inside the central blind cavity .

[0077] In addition, the piston-rod 7 preferably also comprises a closing plug 29 advantageously with a mushroom structure , which is inserted in the through hole 28 advantageously in removable manner, and is adapted to fluid-tight close the same through hole 28 . Preferably, the bottom of the central cavity of cupshaped body 25 furthermore has a substantially f rustoconical profile , converging towards the mouth of the through hole 28 .

[0078] In addition, the final segment of through hole 28 connecting to the bottom of the central cavity of cup-shaped body 25 , has a profile converging towards the same central cavity .

[0079] Clearly, the bottom of the central cavity of the cupshaped body 25 corresponds to the ceiling of the bl ind cavity 9 of piston-rod 7 .

[0080] With reference to Figures 1 , 2 and 4 , preferably the gas spring 1 is finally provided with a one-way valve 30 , via which it is possible to introduce the pressurised gas into the lower cavity 3 of casing 2 , or rather into the variablevolume closed chamber 6 ; and / or of a safety plug 31 , which is structured so as to automatical ly discharge , outside the gas spring 1 , the pressurised gas present in the lower cavity 3 , or rather in the variable-volume closed chamber 6 , when the pressure of the gas present in the same lower cavity 3 exceeds a predetermined maximum limit and / or when the piston- rod 5 makes an "overtravel" , i . e . when the piston-rod 5 reenters the lower chamber 3 exceeding the maximum travel allowed by the dimensions of the gas spring 1 .

[0081] In more detail , the bottom wall of casing 2 , or rather of the outer cup-shaped body 12 , that contributes to delimiting the variable-volume closed chamber 6 , is preferably provided with two through ducts that connect the variable-volume closed chamber 6 with the outside .

[0082] A first through duct is closed in fluid-tight manner by the safety plug 31 .

[0083] The second through duct , in turn, accommodates the oneway valve 30 and, preferably, ends inside the lower cavity 3 of casing 2 , at the top of a protuberance 32 rising from the bottom of the same cavity . Preferably the mouth of the second through duct is furthermore closed in fluid-tight manner by an additional closing plug 33 , preferably with a mushroom structure .

[0084] In the example shown, in particular, the first through duct is preferably substantially straight and advantageously also parallel to the casing longitudinal / central axis A.

[0085] The safety plug 31 , in turn, is preferably structured so as to protrude cantilevered inside the lower cavity 3 , in order to be hit by the piston-rod 5 making an "overtravel" , i . e . when the piston-rod 5 re-enters inside the lower cavity 3 exceeding the maximum travel allowed by the dimensions of the gas spring 1 .

[0086] The second through duct , on the other hand, is preferably L-shaped and advantageously ends inside the lower cavity 3 , at the top of a protuberance 32 which is substantially coaxial to the longitudinal / central axis A of casing 2 .

[0087] The protuberance 32 allows the incompressible liquid reaching the closed chamber 6 to accumulate on the bottom of the chamber without reaching and / or damaging the one-way valve 30 .

[0088] The one-way valve 30 and the safety plug 31 are components already known and readi ly available on the market , so they will not be further described .

[0089] Operation of gas spring 1 di f fers from that of a traditional gas spring in that the incompressible l iquid in the upper cavity 4 of casing 2 , or rather in the closed chamber 8 , transmits any axial displacement of the piston- rod 7 to the piston-rod 5 , ampli fying the value thereof with a multiplication coef ficient that is a function of the dimensional ratio between the piston-rods 5 and 7 .

[0090] Clearly, the ampli fication of the axial displacements of the piston-rod 5 results into a greater variation of the volume of the closed chamber 6 and, consequently, in a greater variation of the pressure of the gas present in the closed chamber 6 . In more detail , the re-entry of the piston-rod 7 inside the upper cavity 4 of casing 2 forces the incompressible liquid to move inside the blind cavity 9 of piston-rod 7 , passing through the interstitial space between the piston- rods 5 and 7 .

[0091] The accumulation of the incompress ible liquid inside the blind cavity 9 of piston-rod 7 , in turn, forces the piston- rod 5 to retract inside the lower cavity 3 of casing 2 , compressing the pressurised gas present inside the closed chamber 6 .

[0092] The di f ference between the outer diameter DI of the piston-rod 5 and the inner diameter D2 of the upper cavity

[0093] 4 determines the amount of incompressible liquid that moves to and from the blind cavity 9 o f piston-rod 7 per unit of length of the axial movement of piston-rod 7 , and thus the multiplication coefficient of the travel of the piston-rods

[0094] 5 and 7 .

[0095] For example , with an outer diameter DI of pi ston-rod 5 equal to approximately 32 mm and an inner diameter D2 of the upper cavity 4 equal to approximately 48 mm, a multiplication coef ficient of more than 2 is obtained .

[0096] Considering the multiplication ef fect due to the incompressible liquid present in the closed chamber 8 , with an inner diameter of the lower cavity 3 of casing 2 equal to only 50 mm and a nominal gas pressure equal to approximately 130 bar, the gas spring 1 is capable of generating, in response to a travel of the piston-rod 7 equal to only 50 mm, an elastic thrust of over 6000 daN ( decanewton) .

[0097] The advantages connected to the particular structure of gas spring 1 are remarkable .

[0098] With the same outer diameter, the gas spring 1 is capable of producing a much higher elastic thrust than that of conventional gas springs .

[0099] The presence of the auxiliary grooves 10 inside the blind cavity 9 of piston-rod 7 facilitates the passage of the incompressible liquid to and from the area of closed chamber 8 that is located at the top of piston-rod 7 , considerably improving the dynamic behaviour of the gas spring 1 .

[0100] The presence of closing plug 29 and the converging shape of the blind cavity 9 of piston-rod 7 facilitate the filling of the closed chamber 8 and prevent formation and stagnation of bubbles inside the same closed chamber 8 .

[0101] It is finally clear that modi fications and variations may be made to the gas spring 1 without thereby departing from the scope of the present invention .

[0102] For example , in a less sophisticated variation, the piston-rod 7 may fluid-tight engage the central hole of the guide bushing 14 .

[0103] In other words , the casing 2 of gas spring 1 may also include a second annular sealing gasket , which is advantageously made of polymeric material , and is located inside the guide bushing 14 , between the piston-rod 7 and the same bushing, so as to prevent the leakage of incompressible liquid in the interstitial space between the guide bushing 14 and the piston-rod 7 .

[0104] Clearly, in this variation the piston-rod 7 may advantageously lack the annular gasket 26 .

Claims

CLAIMS1. A gas spring (1) characterized by comprising: an outer casing (2) having, on the inside, a first (3) and a second cavity (4) adjacent to one another and separated from one another by a dividing wall; a first oblong-shaped piston-rod (5) , which engages said dividing wall in axially slidable and fluid-tight manner, so as to project into both cavities (3, 4) and form / delimit , inside said first cavity (3) , a variable-volume closed chamber (6) containing pressurized gas; and a second oblong-shaped piston-rod (7) , which is fitted in the outer casing (2) in axially slidable and fluid- tight manner, so as to project out of the casing (2) and, at the same time, also project into the second cavity (4) in order to form / delimit, inside said second cavity (4) and together with the first piston-rod (5) , a variable-geometry closed chamber (8) containing incompressible liquid.

2. The gas spring according to Claim 1, wherein said second piston-rod (7) is aligned with said first piston-rod (5) and is provided with an oblong-shape blind cavity (9) , which directly faces the first piston-rod (5) so as to form part of the variable-volume closed chamber (8) and which is moreover permanently engaged, in axially slidable manner and with a mechanical clearance, by the segment of the first piston-rod (5) that is located inside the second cavity (4) of the outer casing (2) .

3. The gas spring according to Claim 2, wherein the blind cavity (9) of the second piston-rod (7) has a shape that is substantially complementary to the one of the corresponding portion of the first piston-rod (5) ; the second piston-rod (7) being moreover provided with one or more auxiliary grooves (10) that extend, more or less longitudinally, along the inner lateral surface of the blind cavity (9) so as to facilitate the passage of the incompressible liquid in the interstitial space between the piston-rods (5, 7) .

4. The gas spring according to Claim 3, wherein thesegment of the first piston-rod (5) engaging the blind cavity (9) of the second piston-rod (7) in slidable manner has a substantially constant cross-section and the blind cavity (9) of the second piston-rod (7) has a cross-section substantially constant and complementary to the one of the first piston-rod (5) .

5. The gas spring according to Claim 3 or 4, wherein the ceiling / bottom of the blind cavity (9) of the second piston- rod (7) communicates with the outside via a through duct (28) , which is selectively closable in fluid-tight manner and moreover has a profile converging towards the mouth of the same through duct (28) .

6. The gas spring according to any one of the preceding claims, wherein the segment of the second piston-rod (7) permanently remaining inside the second cavity (4) of the outer casing (2) is shaped / structured so as to cooperate, in a fluid-tight manner, with the inner lateral surface of the same second cavity (4) .

7. The gas spring according to any one of the preceding claims, wherein the segment of the first piston-rod (5) permanently remaining inside the first cavity (3) of the outer casing (2) is shaped / structured so as to cooperate, in a fluid-tight manner, with the inner lateral surface of the same first cavity (3) .

8. The gas spring according to any one of the preceding claims, wherein the outer casing (2) comprises: an outer cup-shaped body (12) with a one-piece structure; an inner cup-shaped body (13) with a one-piece structure, which is inserted in the initial segment of the central cavity of the outer cup-shaped body (12) , so that its bottom wall is arranged at a predetermined distance from the bottom wall of the outer cup-shaped body (12) ; and a guide bushing (14) , which is separate and distinct from the outer (12) and inner (13) cup-shaped bodies and closes the mouth of the outer cup-shaped body (12) and / or of the inner cup-shaped body9. The gas spring according to Claim 8, wherein the outer cup-shaped body (12) , the inner cup-shaped body (13) and the guide bushing (14) are substantially cylindrical in shape.

10. The gas spring according to Claim 8 or 9, wherein the first piston-rod (5) engages the bottom wall of the inner cup-shaped body (13) in a pass-through and axially slidable manner, and the second piston-rod (7) engages the guide bushing (14) in a pass-through and axially slidable manner.

11. The gas spring according to Claim 8, 9 or 10, wherein the inner cup-shaped body (13) is entirely housed in the initial segment of the central cavity of the outer cup-shaped body (12) , and the guide bushing (14) engages the mouth of the outer cup-shaped body (12) so as to hold said inner cupshaped body (13) inside said outer cup-shaped body (12) .

12. The gas spring according to Claim 11, wherein the inner cup-shaped body (13) engages the initial segment of the central cavity of the outer cup-shaped body (12) in axially slidable manner.

13. The gas spring according to any one of the preceding claims, characterized by additionally comprising a one-way valve (30) through which the pressurized gas can be introduced into the variable-volume closed chamber (6) , and / or a safety plug (31) which is structured so as to automatically release, out of the gas spring (1) , the pressurized gas present in said variable-volume closed chamber (6) , when the pressure of the gas present in said variable-volume closed chamber (6) exceeds a predetermined maximum limit and / or when the first piston-rod (5) makes an overtravel .

14. The gas spring according to Claim 13, wherein the oneway valve (30) is accommodated inside a second through duct, which ends inside the first cavity (3) of the outer casing (2) , at the top of a protuberance (32) projecting from the bottom of the same first cavity.

15. The gas spring according to any one of the preceding claims, wherein the outer casing (2) is substantially cylindrical in shape, and wherein said first and second cavities (3, 4) are substantially cylindrical and are arranged inside the outer casing (2) substantially coaxial to the casing central / longitudinal axis (A) .

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