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A gas spring for forming equipment, including a piston received at least partially in a cylinder for reciprocation between extended and retracted positions, and including a throttling passage disposed between the piston and the cylinder in fluid communication between first and second pressure chambe

A gas spring for forming equipment, including a piston received at least partially in a cylinder for reciprocation between extended and retracted positions, and including a throttling passage disposed between the piston and the cylinder in fluid communication between first and second pressure chambers during at least a portion of the reciprocation of the piston. The throttling passage is of variable cross-sectional area, which varies with a length of the passage to at least partially restrict gas flow therethrough in a manner varying with return of the piston toward its extended position to decelerate the piston at a predetermined rate.

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1. A gas spring for forming equipment, comprising: a cylinder having an inner cylindrical surface at least in part defining a first pressure chamber constructed to receive a pressurized gas in the first pressure chamber;a piston at least partially received in the first pressure chamber of the cylind

1. A gas spring for forming equipment, comprising: a cylinder having an inner cylindrical surface at least in part defining a first pressure chamber constructed to receive a pressurized gas in the first pressure chamber;a piston at least partially received in the first pressure chamber of the cylinder for reciprocation between extended and retracted positions over a cycle including a retraction stroke and a return stroke and yieldably biased to the extended position by pressurized gas in the first chamber;a cushion seal disposed between the cylinder and the piston, not carried by the piston, and, during at least a portion of the movement of the piston to the extended position the piston moves relative to the cushion seal to separate and seal the first pressure chamber on one side of the cushion seal from a second pressure chamber defined by the cylinder and the piston on another side of the cushion seal;at least one check passage having a bore carried by the piston and while the piston engages the cushion seal the check passage communicates at one end with the second pressure chamber and at another end with the first pressure chamber;at least one check valve in the bore of the check passage which closes when the piston engages the cushion seal as the piston moves toward its extended position to inhibit gas flow through the check passage from the second pressure chamber to the first pressure chamber; andat least one throttling passage separate from the check passage and check valve, carried by the piston, disposed between the piston and the cylinder, not in the inner cylindrical surface of the cylinder, and while the piston engages the cushion seal the at least one throttling passage communicates at one end with the second pressure chamber and at an other end with the first pressure chamber;the at least one throttling passage is configured to at least partially restrict gas flow therethrough from the second pressure chamber to the first pressure chamber by its cross-sectional area over at least a part of its longitudinal extent varying and decreasing toward its end communicating with the first pressure chamber so as to reduce velocity of the piston at a predetermined rate during the return stroke as the piston returns to its fully extended position. 2. The gas spring of claim 1, wherein the at least one throttling passage varies in cross-sectional area at the cushion seal with displacement of the piston. 3. The gas spring of claim 1, wherein the at least one throttling passage is a groove open to an external surface of the piston, wherein the cushion seal bounds the groove. 4. The gas spring of claim 3, wherein the cylinder includes a housing having an inner surface defining at least part of the first pressure chamber, and a piston guide received at least partly in the housing and having a through bore and also having an outer surface with a portion disposed generally adjacent to the inner surface of the housing. 5. The gas spring of claim 4 wherein the piston includes a piston rod and a piston collar carried by the piston rod, wherein the piston rod is at least partially disposed in the through bore of the piston guide for reciprocation between the extended and retracted positions, and wherein at least part of the second pressure chamber is defined between the piston and the piston guide during at least a portion of the reciprocation of the piston. 6. The gas spring of claim 5 wherein the piston further comprises: at least one bearing carried in at least one corresponding groove in an inner surface of the piston guide for cooperation with an external surface of the piston rod; andat least one bearing carried in a corresponding groove in an external surface of the piston collar;so as to facilitate guiding the piston within the cylinder during at least a portion of the reciprocation of the piston. 7. The gas spring of claim 5 wherein the piston guide includes a guide body, and a skirt axially depending from the guide body and the piston is at least partially disposed in the skirt when the piston is in its extended position. 8. The gas spring of claim 7 further comprising a piston rod seal disposed between the piston rod and the guide body, and wherein the piston further includes a cushion collar carried by the piston rod between the piston collar and the guide body, wherein the first pressure chamber is defined by the housing and a portion of the piston on one side of the cushion seal when the cushion seal is in contact with the cushion collar, and the second pressure chamber is defined by another portion of the piston and the piston guide between the piston rod seal and the cushion seal when the cushion seal is in contact with the cushion collar. 9. The gas spring of claim 1 wherein the piston disengages from the cushion seal during the retraction stroke of the piston. 10. The gas spring of claim 9 wherein the piston re-engages the cushion seal during a return stroke of the piston, at which point the pressure chambers are in fluid communication only through the throttling passage. 11. The gas spring of claim 1, wherein each of the at least one throttling passage is of variable cross-sectional area, which varies with a length of the passage. 12. A gas spring for forming equipment, comprising: a cylinder having an inner cylindrical surface at least in part defining a first pressure chamber constructed to receive a pressurized gas therein;a piston received at least partially in the first pressure chamber of the cylinder for reciprocation between extended and retracted positions and to partially define the first pressure chamber between one side of the piston and the cylinder and to partially define a second pressure chamber on another side of the piston, and the piston yieldably biased to a fully extended position by pressurized gas in the first pressure chamber;a collar carried by the piston for reciprocation with the piston;a cushion seal carried by the cylinder and engaging the collar during a portion of the movement of the piston to the extended position of the piston to separate the first pressure chamber on one side of the cushion seal from a second pressure chamber on the other side of the cushion seal,a passageway wholly within the collar and while the collar engages the cushion seal the passageway communicates adjacent one end with the second pressure chamber and adjacent another end with the first pressure chamber;a check valve which communicates with the passageway and closes when the collar engages the cushion seal as the piston moves toward its extended position to inhibit gas flow through the passageway from the second pressure chamber to the first pressure chamber;a throttling passage separate from the passageway and check valve, not in the inner cylindrical surface, and disposed between the collar and the cylinder in fluid communication between the first and second pressure chambers during at least a portion of movement of the piston from its retracted position to its fully extended position; anda cross-sectional area of the throttling passage is constructed to at least partially restrict gas flow therethrough from the second pressure chamber to the first pressure chamber with its cross-sectional area over at least a part of its longitudinal extent varying and decreasing toward its end communicating with the first pressure chamber to decelerate the return of the piston to its fully extended position. 13. The gas spring of claim 12, wherein the at least one throttling passage is a groove open to an external surface of the piston, and a cushion seal bounds the groove. 14. The gas spring of claim 13, wherein the cylinder includes a housing having the inner cylindrical surface defining at least part of the first pressure chamber, and a piston guide received at least partly in the housing and having a through bore and also having an outer surface with a portion disposed generally adjacent to the inner cylindrical surface of the housing. 15. The gas spring of claim 14 wherein the piston includes a piston rod and the collar is carried by the piston rod, wherein the piston rod is at least partially disposed in the through bore of the piston guide for reciprocation between the extended and retracted positions, and wherein at least part of the second pressure chamber is defined between the piston and the piston guide during at least a portion of the movement of the piston to its fully extended position. 16. The gas spring of claim 15 wherein the piston further comprises: at least one bearing carried in at least one corresponding groove in an inner surface of the piston guide for cooperation with an external surface of the piston rod; andat least one bearing carried in a corresponding groove in an external surface of the piston collar;so as to facilitate guiding the piston within the cylinder during at least a portion of the reciprocation of the piston. 17. The gas spring of claim 16, wherein the piston guide includes a guide body, and a skirt axially depending from the guide body and within which the collar is at least partially disposed in the extended position of the piston, and wherein the first pressure chamber is defined by the housing and a portion of the piston on one side of the cushion seal when the cushion seal is in contact with the cushion collar, and the second pressure chamber is defined by a portion of the collar and the piston guide between the piston rod seal and the cushion seal when the cushion seal is in contact with the collar. 18. The gas spring of claim 12 wherein the collar disengages from the cushion seal during the retraction stroke of the piston, and the collar re-engages the cushion seal during a portion of the return stroke of the piston, at which point the pressure chambers are in fluid communication only through the throttling passage.