GB2285670A - Gas spring with charging valve - Google Patents

Abstract

A gas spring includes a pressurised piston and cylinder assembly in which one end of the cylinder 11 is closed by a plug 24 that forms part of a gas charging valve comprising an elongate annular space 36 between the plug and the cylinder wall, a gas charging passage 40 extending from outside the gas spring into the space, and an O-ring which is moved along the space by gas pressure between a sealing position at one end and a gas charging position at the other end, at which a port 42 is opened into the interior of the cylinder. A supplementary flap valve 50 may be provided. <IMAGE>

Description

GAS SPRINGS This invention relates to gas springs, which generally comprise sealed piston and cylinder assemblies charged with gas under pressure on either side of the piston. If a manually operated valve is provided to allow gas to pass from one side of the piston to the other, such gas springs can be used as stepless height adjusters for chairs, tables, computer consoles and the like.

Because of the volume occupied by the piston rod on one side of the piston, retraction of such gas springs reduces their total internal volume and therefore increases their internal gas pressure. If the gas transfer valve is opened and no load is put on the spring, it will naturally extend fully. If the gas spring is used as a height adjustable support, the relation between internal gas pressure and piston rod diameter would normally be chosen so that a pre-determined load on the spring when the valve is opened will be sufficient to retract the spring. The work done is of course stored as increased gas pressure and is available to extend the spring later, against a maximum load that depends on the piston rod area and gas pressure, when the valve is opened.

Gas transfer between the two ends of the cylinder is often accomplished through a surrounding gas jacket, with the transfer valve being located at one end of the cylinder. However, alternative arrangements have been proposed from time to time, and these include the location of the transfer valve in the piston itself. Such a valve can be operated by means of a push rod passing down the centre of the piston rod.

One example of such a proposal is to be found in European patent No 0277298. This patent also illustrates the need for a second valve in the gas spring, this being a charging valve to allow the gas spring to be pressurised after assembly. In this example, a cylinder end plug has a central threaded bore to which a source of pressurised gas can be attached. The bore terminates in a radial passage which opens into a circular groove around a central extension of the plug within the cylinder. The groove is occupied by a rubber 0-ring, which will be locally stretched by the pressure of the applied charging gas to expose the end of the bore, but which seals the bore against the escape of charged gas when the external gas pressure is released.

An alternative charging valve is shown in British patent No 1532001 which discloses a cylinder end plug having a peripheral groove against the internal cylinder wall, and a radial slot in the plug which intersects the groove and communicates with the interior of the cylinder. The groove contains a resiliently deformable sealing ring. A charge of pressurised gas can be introduced through the plug into the groove, and the sealing ring then deforms into the slot to allow the gas into the cylinder, but then reseats in the groove to prevent the subsequent escape of charged gas.

Both these charging valve arrangements require resiliently stretchable sealing rings of a certain elasticity.

The present invention is concerned with means for charging a gas spring with pressurised gas by adopting a different approach, in which a sealing ring is translated, rather than stretched, between distinct sealing and charging positions, under the pressure of the external gas supply when charging the gas spring, and under the pressure of the internal gas charge when the external gas pressure is released.

The present invention concerns aspects of the gas spring described below. The scope of the invention extends to all novel aspects of the gas spring whether individually or in combination with other features as described herein.

More specifically, in one aspect of the invention a gas spring may include a pressurised piston and cylinder assembly in which one end of the cylinder is closed by a plug that forms part of a gas charging valve, said valve comprising an elongate annular space between the plug and the cylinder wall, a gas charging passage extending from outside the gas spring into the said space, and a gas sealing ring retained in the elongate annular space and movable along the said space by gas pressure, between a sealing position towards one end of the said space in which the gas charging passage is closed to the escape of gas from the cylinder, and a charging position towards the other end of the said space in which a gas flow path from the gas charging passage into the cylinder is opened.

The sealing position of the ring may be one in which the ring seals between the plug and the cylinder wall.

The gas sealing ring may be arranged to be more freely movable under gas pressure when it lies towards the said other end of the annular space, ie in the region of the gas charging position, than when it lies towards the said one end of the annular space, ie in the region of the sealing position. To this end, the inner wall of the annular space, defined by the plug, may be tapered over at least part of its length.

In the gas charging position of the sealing ring, the gas flow path may comprise an opening that is uncovered by the ring when it is moved from the sealing position. The opening may extend inwardly through the plug to the interior of the gas spring. One end of the opening may be provided with a further valve, and in particular a flap valve over the inner end of the opening.

Alternatively or in addition, the gas flow path may lie past the ring. This may occur in a region of the annular space where one or more grooves extend along the outside of the plug, or the annular space is deepened by a tapering plug, or in any other suitable way.

Two embodiments of the invention are shown by way of example in the accompanying drawings, in which: Figure 1 is a longitudinal sectional view of a first embodiment of a gas spring in accordance with the invention; Figure 2 is a similar section but enlarged showing only one end of the gas spring, containing a plug and charging valve, the valve being closed; Figure 3 is a view corresponding to Figure 2 but showing the charging valve open; Figure 4 is an elevation of the outer face of the end plug; Figure 5 is a view corresponding to Figure 3 of a second embodiment of the invention; and Figure 6 is an elevation of the outer face of the end plug shown in Figure 5.

The cylinder of the gas spring shown in Figure 1 comprises outer tube 11, which has a honed bore in which a piston 12 slides. The piston is mounted on one end of a hollow piston rod 14 which is sealingly and slidingly supported by bush 16 at one end of the cylinder, from which it protrudes.

At the piston end, the piston rod accommodates a transfer valve housing 18 containing valve spool 20, which can be manually actuated by push rod 22 which passes through the centre of the piston rod.

The other end of the cylinder is closed by end plug 24, which is held in place against the internal gas pressure by spinning over or otherwise forming the end 25 of the tube 11.

If the valve spool 20 is moved into its open position towards the end plug 24, by push rod 22, gas is enabled to flow from one side of the piston to the other through transfer ports 26 and past the exposed waist of spool 20. When the gas spring is pressurised, gas pressure on the end face 27 of spool 20 is sufficient to bias the transfer valve closed, unless push rod 22 is depressed.

Figures 2, 3 and 4 show cylinder end plug 24 and the associated gas charging valve in more detail.

End plug 24 has a flanged base 32 from which a cylindrical skirt 34 extends into the end of cylinder 11, leaving an elongate annular space 36 between the plug and the cylinder wall. The outer end of this space is defined by the peripheral flange 33 of base 32, and the inner end is defined by a retained ring 38.

Two diametrically opposed gas charging passages in the form of grooves 40 around plug flange 33 communicate with one end of annular space 36, and a gas flow path in the form of an opening 42 through skirt 34 communicates with the interior of cylinder 11 from adjacent the inner end of annular space 36.

In the annular space 36, O-ring 44 makes a gas seal between the plug skirt 34 and the cylinder wall 11. It can be translated by gas pressure along the annular space from one end to the other. At the outer end of the annular space (Figure 2), by the end of tube 11, the O-ring seals the inner ends of charging grooves 40 against the egress of pressurised gas from the cylinder. At the inner end of the annular space 36 (Figure 3), the O-ring 44 is the other side of the opening 42 which is accordingly now in direct communication with the charging grooves.

A resilient flap valve 50, in the form of an L-section flexible membrane inside skirt 34, normally lies in a recess 52 and closes the inner end of radial bore 42 to the escape of gas from within the cylinder (Figure 2). However, during charging, the flow of gas into the cylinder from the annular space opens the valve (Figure 3).

After the gas spring is first assembled, it needs to be charged with gas at pressure. First, the piston rod is set at full extension. A gas source is then placed sealingly over the closed end of cylinder 11, so that gas can enter through charging grooves 40, displacing O-ring 44 if necessary to the position shown in Figure 3, and thereby opening the flow path to the interior of the cylinder. When sufficient internal pressure is reached, the gas supply is cut off and external gas pressure rapidly released.

Internal gas pressure past ring 38 then forces O-ring 44 into the gas sealing position shown in Figure 2.

At the same time, the flap valve 50 closes, and presses sealingly over the inner end of skirt opening 42 under the pressure of the gas in the charged cylinder. This minimises gas leakage in the event that O-ring 44 is slow to move along the annular space 36 to a charging passage sealing position.

If it is desired to increase the internal pressure later, more gas can be charged into the spring in the same way. Further, by applying just enough external gas pressure to move the sealing ring to the charging position, a subsequent careful slow reduction of the external pressure can be used to achieve a controlled leakage of gas to reduce the internal pressure to a lower value.

A second embodiment of the invention differs by the substitution of a modified end plug 54 for the end plug 24, as shown in Figures 5 and 6. In other respects the gas springs are the same.

End plug 54 has a flanged base 62 from which a web reinforced cylindrical skirt 64 extends into the end of cylinder 11, leaving an elongate annular space 66 between the plug and the cylinder wall. The outer end of this space is defined by the peripheral flange 63 of base 62, and the inner end is defined by an outturned flange 68 at the end of the skirt.

Two diametrically opposed sets of gas charging grooves 70A, 70B around plug flange 63 communicate with one end of annular space 66, and an opening 72 through skirt 64 communicates with the interior of cylinder 11 from adjacent the opposite inner end of annular space 66. O-ring 44 is located in this annular space and can be translated by gas pressure from one end to the other.

At the outer end of the annular space 66, adjacent charging grooves 70B, O-ring 44 makes a gas seal between the plug skirt 64 and the cylinder wall 11 as in the previous embodiment, and seals the charging grooves against the egress of pressurised gas from the cylinder. Similarly, at the inner end of the annular space 66, the O-ring 44 is the other side of the opening 72.

A significant difference between the end plugs 24 and 54 is that the latter has a taper to the inner end of its skirt 54, from the region of the opening 72 to the flange 68, so that in the portion of the annular space 66 occupied by O-ring 44 when the gas charging valve is open, the O-ring is a looser fit on the skirt 54, and does not press against the inner wall of cylinder 11. This helps to ensure that, when the gas charging pressure is released, O-ring 44 can start its movement along the annular space to the gas sealing position more freely, with less frictional resistance, in order to promote rapid sealing of the valve.

Claims (1)

1. A gas spring including a pressurised piston and cylinder assembly in which one end of the cylinder is closed by a plug that forms part of a gas charging valve, said valve comprising an elongate annular space between the plug and the cylinder wall, a gas charging passage extending from outside the gas spring into the said space, and a gas sealing ring retained in the elongate annular space and movable along the said space by gas pressure, between a sealing position towards one end of the said space in which the gas charging passage is closed to the escape of gas from the cylinder, and a charging position towards the other end of the said space in which a gas flow path from the gas charging passage into the cylinder is opened.

2. A gas spring according to claim 1 wherein the sealing position of the ring is one in which the ring seals between the plug and the cylinder wall.

3. A gas spring according to claim 1 or claim 2 wherein the gas sealing ring is more freely movable along the annular space under gas pressure when it lies towards the said other end of the annular space, than when it lies towards the said one end of the annular space.

4. A gas spring according to claim 3 wherein the inner wall of the annular space, defined by the plug, is tapered over at least part of its length.

5. A gas spring according to any one of the preceding claims wherein the gas flow path that is opened in the charging position of the sealing ring comprises an opening that is uncovered by the ring when it is moved from the sealing position.

7. A gas spring according to claim 6 wherein one end of the opening is provided with a further valve.

8. A gas spring according to claim 7 wherein the said valve is a flap valve over the inner end of the opening.

9. A gas spring according to any one of the preceding claims wherein the gas flow path from the gas charging passage into the cylinder lies, at least in part, past the ring.

10. A gas spring according to claim 1 substantially as herein described with reference to and as illustrated in any of the accompanying drawings.