Gas spring

Abstract: A gas compression spring comprises a gas-filled cylinder (10) in which a piston (26) carrying a hollow piston rod (18) is slidable and divides the interior of the cylinder (10) into two chambers (32,34). Over part of the length of the cylinder, a groove (56) is provided in the cylinder wall. Gas pressure within the cylinder (10) causes the piston (26) to drive the piston rod (18) outwards of the cylinder (10), this being permitted by the groove (56) which allows transfer of gas pressure between the chambers (34 and 32). When the piston (26) reaches the end of the groove (56), such gas pressure transfer ceases and movement of the piston rod (18) stops. External manual force applied to a control rod (44), extending through the hollow interior of the piston rod (18), unseals an opening (40) at the end of the piston rod (18) which communicates with the first chamber (32). Gas pressure transfer can now take place between the two chambers via an opening (42) and the interior (43) of the piston rod (18). Movement of the piston rod (18) outwardly of the cylinder under the pressure exerted by the gas now re-commences, but can be halted at any desired position by release of the force manually exerted on the control rod (44).

Description: The invention relates to a gas compression spring for moving a member on a body from a first position corresponding to compression of the spring to a second position, comprising an arrangement of a piston movable within cylinder means, the piston carrying a piston rod slidingly and sealingly extending outwardly of one end of the cylinder means; the opposite end of the cylinder means and a point on the piston rod where it extends from the cylinder means being adapted for connection between the body and the said member; the interior of the cylinder means being filled with gas under pressure and the piston dividing the interior of the cylinder means into a first chamber defined at least in part by the head of the piston and a second chamber through which the piston rod extends; the first and second chambers being interconnected by first gas flow means providing a first restricted gas flow path between points which are respectively situated in the first and second chambers and which are separated by respective predetermined parts, only, of the stroke of the piston, the restricted gas flow path permitting limited flow of gas from the second chamber to the first chamber as the gas pressure moves the piston over the said predetermined parts of the stroke and correspondingly moves the piston rod from an inner piston rod position towards an outer piston rod position more outwardly of the cylinder means, whereby to move the member towards the second position, the said limited flow of gas not being permitted when the piston is outside the said predetermined parts of its stroke so that movement of the piston rod towards the outer piston rod position due to such flow of gas is prevented; and reverse flow means permitting gas pressure transfer between the first and second chambers when the piston rod is moved towards the inner piston rod position by an externally applied force. Such a gas spring is known from GB-A-1 528 820. In this gas spring, the first gas flow means comprises two grooves in the interior wall of the cylinder means which extends longitudinally along the cylinder means and are separated by an ungrooved portion. As the piston rod travels towards the outer piston rod position, the piston travels over the first groove permitting limited flow of gas from the second chamber to the first chamber. When the piston reaches the ungrooved portion, piston rod movement stops. The piston rod can only be moved beyond this position, so that the piston then reaches the second groove which again permits restricted gas transfer, by the application of an externally applied force which has to be sufficient to overcome the gas pressure within the cylinder means. The invention aims to deal with this problem. Therefore, in accordance with the invention, the known gas spring is characterised by second gas flow means providing a second restricted gas flow path for controllably by-passing the piston when the piston is outside the predetermined parts of its stroke and thus providing a by-pass path connecting the first and second chambers; and control means operable from outside the cylinder means for switching the second gas flow means between a blocked condition in which gas flow through the second gas flow path is blocked and an unblocked position in which gas flow is permitted through the second gas flow path and allows the gas pressure to move the piston rod towards the outer piston rod position when the piston is outside the predetermined parts of its stroke. Gas springs embodying the invention and to be described below by way of example can be used in motor vehicles for easing the opening of closure members such as luggage and engine compartment lids and hatchbacks. However, they can be used for other purposes. Gas springs embodying the invention, and for use in controllably opening hatchbacks in motor vehicles, will now be described, by way of example only, with reference to the accompanying diagrammatic drawings in which: Figure 1 is a longitudinal section through one of the gas springs; Figure 2 is a longitudinal section through a modified form of the gas spring of Figure 1; Figure 3 is a longitudinal section through another modified form of the gas spring of Figure 1; Figure 4 is a longitudinal section through another one of the gas springs; and Figure 5 shows, to an enlarged scale, parts of the gas spring of Figure 4 in the region indicated by the arrow V in Figure 4. Referring to Figure 1, the gas spring comprises a cylindrical body 10 having a closed end 12 on which is mounted a fixture 14. The opposite end of the cylinder 10 is closed off by an integral wall 16 which is apertured to allow passage of a hollow piston rod 18. The piston rod 18 slides in a guide 20 and through an air-tight seal 22. The piston rod 18 is attached to a further fixture (not shown) . In use, the gas spring is mounted on a vehicle body so as to control the pivotting movement of a horizontally pivotted closure member such as the hatchback, the lid of a luggage compartment, or the lid of the engine compartment. One of the fixtures (the fixture 14 or the fixture carried by the distal end of the piston rod 18) is attached to the body of a vehicle and the other is attached to the hatchback (or other movable member). The gas spring may, however, be used in many other applications. Within the cylinder 10, the piston rod 18 is attached to a piston 26 which is provided with a circular groove 28 in which is located a sealing ring 30, the groove 28 being wider than the sealing ring 30. The piston 26 and the sealing ring 30 separate first and second chambers 32 and 34 within the cylinder 10. The piston rod 18 is hollow and extends through the piston 26 to define an open end 40. A hole 42 in the piston rod 18 communicates with the chamber 34. A control rod 44 extends slidably through the hollow interior of the piston rod 18 and protrudes into the chamber 32 through the aperture 40 in the piston rod, the control rod 44 terminating in a cap 46 which carries a sealing ring 48. A reduced-diameter portion 50 of the control rod 44 extends between the cap 46 and an enlarged region 52 which carries a sealing ring 54. A passage-way 55 is defined between the outside of the enlarged region 52 of the control rod 44 and the inside wall of the piston rod 18. Sealing ring 54 makes an airtight seal with the interior wall of the hollow piston rod 18. Along a portion of its interior wall, the cylinder 10 is provided with a groove 56. Along another portion 58, however, of the interior wall of the cylinder, there is no such groove. The airtight seal 22 is held in position by a ring 60 which is itself locked into the cylinder 10 by a circumferential shoulder 62. The whole of the hollow interior of the cylinder 10 is filled with gas under pressure. When the hatchback (or other closure member) is unlatched and lifted slightly, the gas pressure within the gas spring acts on the cross-section of the piston rod 18 and drives it and the piston 26 in a direction outwardly of the cylinder 10, thus raising the hatchback. During the consequential initial movement to the right (as viewed in Figure 1) of the piston 26, gas can transfer from chamber 34 to chamber 32 through the groove 56, the cross-sectional size of the groove controlling the speed of movement of the piston. During this movement of the piston, the frictional force between the sealing rings 30 and the wall of the cylinder holds the sealing ring in the position shown in Figure 1, and gas entering a groove 64 from chamber 34 is blocked against further travel. The gas pressure in chamber 32, acting on cap 46, causes the sealing ring 48 to make a gas-tight seal around the open end 40 of the hollow interior of the piston rod 18. When the piston 26 has travelled sufficiently far to the right (as viewed in Figure 1), the sealing ring 30 will be brought into contact with the un-grooved wall portion 58. Gas transfer between chamber 34 and chamber 32 is thus now blocked. The force exerted by the gas pressure on the piston 26 can no longer overcome the weight of the hatchback. Further movement of the piston and the piston rod therefore now stops. A pressure difference thus exists between chambers 32 and 34 which holds the hatchback or other closure member in a partially open position against its weight. However, if a manual force is exerted (by the user) on the control rod 44, so as to move it slightly to the left (as viewed in Figure 1), the sealing ring 48 is moved away from the end 40 of the piston rod. Chamber 34 is thus placed in communication with chamber 32 via the aperture 42 and the annular passageway 55. Gas pressure transfer between chambers 34 and 32 now resumes. The spring therefore now exerts a force capable of lifting the hatchback. The piston 26 now continues its movement to the right (as viewed in Figure 1), and the hatchback is lifted towards its open position. If the user removes the force exerted on the control rod 44, the gas pressure within chamber 32 will cause the cap 46 and the sealing ring 48 to move back towards the end 40 of the piston rod so as to close off that end. Pressure transfer between chambers 34 and 32 thus stops again, and further movement of the piston rod, and thus the hatchback, stops. In this way, unlatching of the hatchback causes the gas spring to open the hatchback to a predetermined intermediate position at which it stops. However, the user can cause the gas spring to re-start its opening movement, to lift the hatchback further, by applying a force to a control rod 44 as explained. The hatchback can then be caused to stop again, at any desired position, by removal of the force on the control rod. In order to close the hatchback, the user applies a downward force on the hatchback. This increases the effective weight of the hatchback, thus overcoming the gas pressure acting on the piston 26. As the piston begins to move to the left, as viewed in Figure 1, friction acting on the sealing ring 30 moves the sealing ring relatively to the right of the groove 28 as viewed in the Figure. Communication between chambers 32 and 34 is now established through passages 64, under the sealing ring 28 and thence through gap 65. Gas pressure can now transfer from chamber 32 to chamber 34 to facilitate lowering of the hatchback and movement of the piston 26 to the left as viewed in Figure 1. Such gas transfer will of course take place even if the sealing ring 30 is in contact with the un-grooved wall portion 58: if the sealing ring 30 is overlying the groove 56, the latter no longer controls the gas flow. Items in Figure 2 correspond to those in Figure 1 are similarly referenced. The arrangement of Figure 2 differs from the arrangement of Figure 1 in that the interior wall of the cylinder 10 has a first groove 56A and a second, axially spaced, groove 56B. A first un-grooved portion 58A is positioned between the groove 56A and the groove 56B, and a second un-grooved portion 58B is positioned between the groove 56B and the exit end of the cylinder 10. The operation of the gas spring of Figure 2 is generally the same as for the gas spring of Figure 1. Thus, after the hatchback has been unlatched and lifted slightly, the gas pressure within the cylinder acts on the cap 46 of the piston rod to move the piston 26 along the groove 56A, the groove 56A allowing gas pressure transfer between chamber 34 and chamber 32. Movement of the piston, and thus the hatchback, stops when the sealing ring 30 comes into contact with the first un-grooved portion 58A. Movement of the piston (to the right as viewed in Figure 2), and thus raising of the hatchback, can be re-started in the manner explained in conjunction with Figure 1 by manual force on the control rod 44. This manual force moves the cap 46 and the sealing ring 48 away from the end 40 of the piston rod 18, allowing gas pressure transfer between chamber 34 and chamber 32 through aperture 42 and passage 55. This movement can be stopped by removing the force on the control rod 44, so as to allow the control rod to revert to the position illustrated. The hatchback can thus be stopped at any desired position while the sealing ring 30 is in contact with the un-grooved wall portion 58A. When the piston has moved sufficiently far to the right (as viewed in Figure 2) so that the sealing ring 30 comes into contact with the portion of the cylinder provided with the second groove 56B, uninterrupted movement of the piston to the right (as viewed in the Figure) continues, because gas pressure can now transfer from chamber 34 to chamber 32 via groove 56B. Again, the cross-sectional side of the groove 56B controls the speed of movement of the piston. When the piston has moved sufficiently far to the right so that the sealing ring 30 comes into contact with the second un-grooved portion 58B, gas pressure transfer between chambers 34 and 32 is once more stopped. The force exerted by the spring is therefore reduced and can no longer lift the hatchback. Movement of the piston, and thus of the hatchback, again stops. As before, however, movement of the piston to the right (as viewed in Figure 2) can be re-started by the application of manual force on the control rod 44, in the manner explained. In this way, the piston can be arranged to stop at any desired position within the un-grooved portion 58B of the wall of the cylinder 10. The hatchback is lowered by the application of a lowering force, the resultant movement to the left of the piston 26 causing the sealing ring 30 to shift to the right (as viewed in the Figure) of the groove 28, and gas pressure can then transfer between chamber 32 and chamber 34 via the bores 64 and gap 65, thereby facilitating lowering of the hatchback under its weight even if the sealing ring 30 is in contact with an ungrooved portion of the cylinder wall. In addition, of course, such gas pressure transfer takes place freely through groove 56B and 56A as the piston 26 passes over the grooved portions. Items in Figure 3 corresponding to those in Figures 1 and 2 are similarly referenced. In the arrangement of Figure 3, the positions of the groove 56 and the un-grooved portion 58 of the interior wall of the cylinder 10 are reversed. The un-grooved portion 58 is now adjacent the end 12 of the cylinder. Therefore, the piston 26 and the piston rod 18 are effectively locked at the innermost position within the cylinder 10. The sealing ring 30, acting on the un-grooved portion 58, prevents gas pressure transfer between chambers 34 and 32. Therefore, when the hatchback is unlatched, the gas spring cannot act to raise it. In order to raise the hatchback, the user has to apply manual force to the control rod 44, so as to move it slightly to the left (as viewed in the Figure). Sealing ring 48 therefore no longer seals the open end 40 of the piston rod 18. Gas pressure transfer can now take place between chamber 34 and chamber 32 through the aperture 42 and passageway 55. The piston 26 can thus start to move to the right, and the piston rod 18 thus starts to lift the hatchback. As before, the user can cause the raising movement of the hatchback to stop at any desired position, by releasing the manual force on control rod 44. When the piston 26 reaches the groove 56, gas pressure transfer between chamber 34 and chamber 32 can freely take place through the groove 56 and movement continues until the hatchback is fully raised. Lowering of the hatchback takes place in the manner already explained. It will be appreciated that the arrangements of the grooved and un-grooved portions of the cylinder, as shown in Figures 1,2 and 3, are merely examples of many different possible arrangements. For example, the arrangement shown in Figure 3 could be further modified by arranging for an additional un-grooved portion of the cylinder wall to be provided Items in Figures 4 and 5 corresponding to those in Figures 1,2 and 3 are similarly referenced. In the gas spring of Figures 4 and 5, the interior wall of the cylinder 10 not only has a groove 56 but it also has a concentric passageway 80 which extends over a substantial part of the length of the cylinder. The concentric passageway 80 is connected to the chamber 34 via a groove 82 in the fixing ring 60. At its opposite end, the passageway 80 is connected to a valve arrangement indicated generally by the reference 84. The valve arrangement 84 comprises a body 86 which is sealingly mounted within the interior of the cylinder by means of a sealing ring 88. The end of the cylinder 10 is closed off by a boss 90 carrying the fixture 14. Intermediate members 92 and 94 together define an intermediate chamber 96 which is connected to the concentric passageway 80 via a radial bore 98. Body portion 92 is sealed against the wall of the cylinder 10 by a sealing ring 100. A control rod 102 extends slidingly through the body 90 and into and through the intermediate chamber 96. The control rod 102 passes through an opening 104 and has an enlarged portion 106 which is terminated by a nut 108 in a recess 110 which is in communication with the chamber 32. A sealing ring 111 seals around the stem of the control rod 102, and a further sealing ring 112 seals around the enlarged portion 106 of the control rod. When the hatchback is unlatched and lifted slightly, the gas pressure within the gas spring causes the piston 26 and the piston rod 18 to move to the right as viewed in Figure 4, thus lifting the hatchback. This movement takes place because gas pressure can transfer between chambers 34 and 32 via the groove 56 in the manner already explained with reference to the previous Figures. However, when the piston reaches the un-grooved portion 58 of the cylinder, gas pressure transfer between chambers 34 and 32 stops. The hatchback is therefore arrested. In order to enable the gas spring to raise the hatchback further, the user presses on the end of the control rod 102 so as to move the control rod to the right as viewed in Figure 4. The enlarged portion 110 of the control rod 102 moves away from the sealing ring 112. Chamber 34 is now placed in communication with chamber 32 via groove 82, concentric passageway 80, radial bore 98, intermediate chamber 96, opening 104 and recess 110. The hatchback therefore starts to rise further. However, the operator can stop such further movement of the hatchback by releasing the force exerted on control rod 102. The control rod thus moves to the left again (as viewed in Figure 4) under the action of the pressure within chamber 32, and further movement of the hatchback stops. The hatchback can be lowered by applying a lowering force to it. The resultant movement of the piston 26 shifts the sealing ring 30 to the right hand side (as viewed in the Figure) of groove 28. Gas pressure transfer can take place between chambers 32 and 34 via the bores 64 and the gap 65. In the valve arrangement 84 of Figure 4 the enlarged portion 106 of the rod 102 produces a chamfer 114. Therefore, the pressure in the chamber 96 (acting through passageway 80 from chamber 34) produces a force acting on chamfer 114 tending to move the enlarged portion 106 out of the chamber 96. This force thus reduces the force which the user has to exert on the rod 102 to connect chamber 96 to chamber 32. In addition, if the user should attempt to lift the hatchback without moving the rod 102 to the released position, the resultant increased pressure in chamber 34 is able itself to move the enlarged diameter portion 106 out of the chamber 96, thus connecting chamber 34 to chamber 32. This reduces the pressure in chamber 34 which might otherwise damage the sealing ring 30. In Figures 1,2 and 3, the same advantage can be obtained by increasing the area of the left hand end (as viewed in these Figures) of the passageway 55 relative to the area at its opposite end. The pressure in passageway 55 (from chamber 34) thus tends to push the cap 46 of the control rod 44 away from the sealing ring 48.

Claims: A gas compression spring for moving a member on a body from a first position corresponding to compression of the spring to a second position, comprising an arrangement of a piston (26) movable within cylinder means (10), the piston (26) carrying a piston rod (18) slidingly and sealingly extending outwardly of one end (16) of the cylinder means (10); the opposite end (14) of the cylinder means (10) and a point on the piston rod (18) where it extends from the cylinder means (10) being adapted for connection between the body and the said member; the interior (32,34) of the cylinder means (10) being filled with gas under pressure and the piston (26) dividing the interior of the cylinder means (10) into a first chamber (32) defined at least in part by the head of the piston (26) and a second chamber (34) through which the piston rod (18) extends; the first and second chambers (32,34) being interconnected by first gas flow means (56;56A,56B) providing a first restricted gas flow path between points which are respectively situated in the first and second chambers (32,34) and which are separated by respective predetermined parts, only, of the stroke of the piston (26), the restricted gas flow path permitting limited flow of gas from the second chamber (34) to the first chamber (32) as the gas pressure moves the piston (26) over the said predetermined parts of the stroke and correspondingly moves the piston rod (18) from an inner piston rod position towards an outer piston rod position more outwardly of the cylinder means (10), whereby to move the member towards the second position, the said limited flow of gas not being permitted when the piston (26) is outside the said predetermined parts of its stroke so that movement of the piston rod (18) towards the outer piston rod position due to such flow of gas is prevented; and reverse flow means (28,30,64) permitting gas pressure transfer between the first and second chambers (32,34) when the piston rod (18) is moved towards the inner piston rod position by an externally applied force; characterised by second gas flow means (46;106) providing a second restricted gas flow path (42,50;80,82,96) for controllably by-passing the piston (26) when the piston (26) is outside the predetermined parts of its stroke and thus providing a by-pass path connecting the first and second chambers (32,34); and control means (44;102) operable from outside the cylinder means (10) for switching the second gas flow means (46;106) between a blocked condition in which gas flow through the second gas flow path (42,44,55;80,96) is blocked and an unblocked position in which gas flow is permitted through the second gas flow path (42,55;80,96) and allows the gas pressure to move the piston rod (18) towards the outer piston rod position when the piston (26) is outside the predetermined parts of its stroke. A gas spring according to claim 1, characterised in that the first gas flow means comprises a groove (56) in the interior wall (58) of the cylinder means (10) and extending along a predetermined part, only, of its length. A gas spring according to claim 1, characterised in that the first gas flow means comprises two grooves (56A,56B) in the interior wall (58) of the cylinder means (10), each groove (56A,56B) extending along a respective predetermined part, only, of the length of the cylinder means (10) and being separated along the length of the cylinder means (10) by an ungrooved portion (58A) of the interior wall (58) of the cylinder means (10). A gas spring according to any preceding claim, characterised in that the second gas flow means comprises means (42,55) defining a gas flow passage extending through the piston (26) and in that the control means comprises valve means (46) for blocking and unblocking this passage. A gas spring according to claim 4, characterised in that the piston rod (18) is hollow and the gas flow passage (42,55) extends through the piston rod (18) and through the piston (26) and is open to one of the first and second chambers (32,34), the valve means (46) comprising means for controlling communication between the gas flow passage (42,55) and the other of the first and second chambers (32,34). A gas spring according to claim 5, characterised in that the control means comprises a control rod (44) extending through the piston rod (18) from outside the cylinder means (10) and connected to the valve means (46). A gas spring according to claim 1 or 2, characterised in that the second gas flow means comprises a passageway (80,82,96) connecting the second chamber (34) to the first chamber (32), and the control means comprises valve means (106) for blocking and unblocking this passageway (80,82,96). A gas spring according to claim 7, characterised in that the passageway (80,8,96) is partially formed within the wall of the cylinder means (10) and extends between ends axially displaced with reference to the cylinder means (10), one of the ends (82) being open to one of the first and second chambers (32,34) and the other end (96) being controllably connectable to the other of the chambers (32,34) by the valve means (106). A gas spring according to claim 8, characterised in that the said one end of the passageway (80) is open to the second chamber (34), and in that the passageway comprises an intermediate chamber (96) positioned within the cylinder means (10) adjacent its said opposite end, the intermediate chamber (106) being connected to the other end of the passageway (80), the valve means comprising means (106) for controllably connecting the intermediate chamber (96) to the first chamber (32). A gas spring according to any one of claims 7 to 9, characterised in that the passageway (80) includes a passageway concentric with the interior of the cylinder means (10). A gas spring according to any preceding claim, characterised in that the reverse flow means is one-way valve means (28,30,64) comprising sealing means (30) carried by the piston (26) and acting between the piston (26) and the cylinder means (10) and operative to provide a gas seal therebetween when the piston rod (18) is moving outwardly of the cylinder means (10) towards the outer piston rod position and to allow the passage of gas between the piston (26) and the cylinder means (10) when the piston rod (18) is moving in the opposite direction.

Inventors: PERRIN ETIENNE, PERRIN, ETIENNE
Applicants: TRELLEBORG AB
Application year: 1996
Main classification: F16F9
IPC codes: F16F9