GB2308421A

GB2308421A - Gas spring temperature compensation

Info

Publication number: GB2308421A
Application number: GB9526163A
Authority: GB
Inventors: Etienne Perrin
Original assignee: Draftex Industries Ltd
Current assignee: Laird Holdings Ltd
Priority date: 1995-12-21
Filing date: 1995-12-21
Publication date: 1997-06-25
Also published as: FR2742832A1; GB9526163D0

Abstract

A gas spring comprises a cylinder (10) in which a piston (22) is sealingly slidable, dividing the cylinder into two gas-filled chambers (28,30). The piston carries a piston rod (16) for producing an external operating force in response to the pressure of the gas which tends to drive the piston (22) and its piston rod (16) in a direction outwardly of the cylinder (10). The piston (22) carries a sealing ring (26) which shifts bodily within an annular groove (24) according to the direction of movement of the piston and permits appropriate transfer of gas pressure between the two chambers (28,30). The cylinder includes a second piston (44) defining a chamber (50) containing an heterogenous fluid (52) having the characteristic that a reduction in its volume does not produce any increase in its reactive pressure. If the gas within the two chambers (28,30) expands in response to increased ambient temperature, the second piston (44) reduces the volume of the material (52) so as to compensate for the increased gas volume, and minimising or eliminating any increase in gas pressure resulting from the increased temperature.

Description

FLUID PRESSURE SPRING The invention relates to fluid pressure springs. Such springs embodying the invention and to be described in more detail below by way of example only are in the form of gas springs such as for use in motor vehicle bodies; they may be used in such applications for opening, and maintaining open, hatchback doors and other closure members.

According to the invention, there is provided a fluid pressure spring, comprising a piston-cylinder arrangement containing an operating fluid under pressure which tends to displace the piston from the cylinder to provide an external operating force, and temperature compensation means for compensating for the effect on the operating force of changes in temperature of the fluid, the temperature compensating means including a material the volume of which is variable to at least a predetermined extent without increasing its reactive pressure, and control means responsive to changes in volume of the fluid in response to temperature changes for causing a resultant and corresponding change in volume of the said material whereby to offset any change in the pressure of the fluid.

According to the invention, there is also provided a fluid pressure spring for raising the hatchback door or similar closure member on a vehicle body, comprising a hollow cylinder, a piston slidable within the hollow cylinder and connected to a piston rod sealingly and slidingly extending from a first end of the cylinder and externally pivotally connected to one of the hatchback door on the vehicle body, the cylinder having a second, opposite, end externally pivotally connected to the other of the hatchback door and the vehicle body, the piston dividing the hollow cylinder into a first main chamber between the piston and the second end of the cylinder and a second main chamber through which the piston rod extends, the first and second main chambers being connected by means defining a restricted gas flow passageway, gas under pressure within the first and second main chambers and acting on the piston and the piston rod and tending to drive the piston rod outwardly of the cylinder to produce an external operating force for lifting the hatchback door, means defining a temperature compensation chamber containing material a reduction in volume of which produces no increase in reactive pressure, and a movable member mounted to provide increased volume within the cylinder in response to expansion of the gas due to temperature increase, the movable member producing a corresponding reduction in the volume of the said material.

Gas springs embodying the invention, and for use in motor vehicle bodies, will now be described, by way of example only, with reference to the accompanying diagrammatic drawings in which: Figure 1 is a cross-section through one of the springs; Figure 2 is a cross-section through another of the springs; Figure 3 is a cross-section through a further one of the springs; Figure 4 is a cross-section through another one of the springs; and Figure 5 is a cross-section through yet a further one of the springs.

The gas spring of Figure 1 comprises a hollow cylindrical body 10 having a closed-off end 12 carrying a fixture 14. The opposite end of the cylindrical body 10 has an aperture through which protrudes a slidable piston rod 16. The piston rod is guided by a guide member 18 which is secured at the end of the cylindrical body 10, and a sealing member 20 provides a gas-tight seal around the piston rod 16.

The piston rod 16 carries a piston 22. The piston 22 is provided with an annular groove 24 in which is located a sealing ring 26 in contact with the cylindrical body 10. The piston 22 divides the hollow interior of the cylindrical body 10 into two chambers 28 and 30. Chamber 30 is in this example defined within an inner cylindrical body 32 which is located within the main cylindrical body 10 by an inwardly directed annular shoulder 34.

During manufacture, the chambers 28 and 30 are filled with gas under pressure.

A restricted gas flow passage between chambers 28 and 30 is provided via an axially directed slot 36 in the periphery of the piston 22, a radially directed slot 38 and a plurality of axially directed bores 40. Gas can thus flow between the chambers 28 and 30, under the sealing ring 26, such gas flow passing through the restricted radially directed slot 38.

The width of the groove 24 is greater than the diameter of the sealing ring 26, enabling the sealing ring 26 to be shifted to the other side of the annular groove 24 (that is, shifted to the right as viewed in Figure 1). In this position of the sealing ring 26, the effective cross-sectional size of the gas flow passage is now increased because gas flow is now not restricted by the radial slot 38.

The piston rod 16 carries an end fixture 42.

The fixtures 14 and 42 are used to connect the gas spring between the vehicle body and the closure member which is intended to be control, such as a hatchback door. For example, the fixture 14 can be pivotally secured to the vehicle body and the fixture 42 can be pivotally secured to the hatchback door.

In use, the gas pressure within the cylindrical body 10 produces a force on the piston 22 tending to expel the piston and the piston rod 16 from the cylindrical body, because the gas pressure within the chamber 28 will be exerted over a greater surface area than the gas pressure within the chamber 30, the resultant gas pressure thus effectively being exerted on the cross-sectional area of the piston rod 16. The resultant force thus lifts the hatchback door and holds it in the open position. As the gas pressure drives the piston 22 and the piston rod 16 in the direction outwardly of the cylindrical body 10, frictional force between the interior wall of the cylindrical body 10 and the sealing ring 26 shifts the sealing ring 26 to the left hand side (as viewed in Figure 1) of the annular groove 24.A restricted passageway between chambers 28 and 32 is thus provided, through groove 36, radial groove 38, under the sealing ring 26 and through the bores 40. This allows gas to transfer from chamber 30 to chamber 28 as the piston moves, and controls the speed of movement of the piston.

In order to close the hatchback door, the user applies manual downward pressure on the hatchback door, thus augmenting the weight of the hatchback door and forcing the piston rod inwardly of the cylindrical body 10. The resultant movement of the piston 22 to the left (as viewed in Figure 1) causes the sealing ring 26 to be moved to the right hand end of the annular slot 24 by the frictional force acting on it. Gas can now relatively freely pass under the sealing ring 26 from chamber 28 to 30 as the piston 22 moves to the left (as viewed in Figure 1).

A problem which can arise with gas springs is caused by the effect of ambient temperature on the pressure of the gas within the cylindrical body. If the ambient temperature increases significantly (as in summer), the gas pressure can increase to such an extent as to make it difficult for the hatchback door to be closed. In cold weather, or at night, the gas pressure can be reduced to such an extent that it becomes insufficient to open the hatchback door or to hold it safely in the open position.

The gas spring of Figure 1 incorporates means to compensate for such temperature effects, as will now be described.

As shown in Figure 1, the gas spring incorporates a second piston 44 which is provided with a sealing ring 46. Piston 46 is slidable between the closed end 12 of the cylindrical body 10 and a limit defined by an inwardly directed annular shoulder 48, and thus defines a further chamber 50 within the cylindrical body 10.

Chamber 50 is filled with an heterogeneous material 52 made up of porous matrices indicated at 54 and a liquid 56. This material 52 has the characteristic that its volume can be reduced (to a predetermined maximum extent) without increase in its reactive pressure. In effect, as the material 52 is compressed, a greater proportion of the liquid 56 is accommodated within the porous matrices 54.

In the event of an increase in the ambient temperature surrounding the gas spring, such as in summer for example, the gas within chambers 28 and 30 will tend to expand, thus driving the piston 44 towards the closed end 12 of the cylindrical body.

Because the resultant reduction in the volume of the material 52 does not result in any increase in its reactive pressure (as explained above), the effective volume of the chambers 28 and 30 is increased so as exactly to compensate for the effect of the greater temperature on the gas. Therefore, the higher temperature does not increase the pressure of the gas within the cylindrical body 10.

In this way, therefore, the piston 44 and the material 52 eliminate or minimise any dependence of the gas pressure within the gas spring on temperature.

In order to enable the piston 44 and the material 52 to provide effective temperature compensation over all temperature variations likely to occur, the initial gas pressure within chambers 28 and 30 is selected to be sufficient to open the hatchback door, and to hold it in the open position, at the lowest ambient temperatures likely to be experienced. The piston 44 and the material 52 thus cooperate to maintain the gas pressure at this level in the event of ambient temperature increases.

In the gas spring of Figure 2, items corresponding to those in Figure 1 are correspondingly referenced. As will be apparent, the construction of the piston 22 and its associated parts is the same as in Figure 1. In this case, though, the temperature compensation arrangement is different. The piston 44 in the gas spring of Figure 2 does not now act directly on the temperature compensating material 52. Instead, this material 52 is housed within a chamber 60 in a separate cylindrical body 62, chamber 60 being defined by a further piston 64 having a sealing ring 66.

Movement of piston 44, in response to changes in gas pressure within chambers 28 and 30 is transmitted to, and causes corresponding movement of, piston 64 by means of hydraulic fluid 67. The end 12 of the cylindrical body 10 is not closed off in the gas spring of Figure 2 but is apertured to house a fluid connecting unit 68 with a sealing ring 70. Unit 68 supports the fixture 14 and contains a fluid passageway 72 connected by a pipe 74 to a corresponding fluid connection unit 76 sealed in the end of the cylindrical body 62 by a sealing ring 78.

The operation of the gas spring shown in Figure 2 is the same as the gas spring of Figure 1, the material 52 compensating for the effects of temperature change on the volume of the gas. The arrangement of Figure 2 has the advantage that the volume available for the temperature compensating material 52 can be increased without increasing the size of the gas spring.

Items in the gas spring of Figure 3 corresponding to those in Figure 1 are correspondingly referenced.

The gas spring shown in Figure 3 differs from the gas spring of Figure 1 in that the gas spring of Figure 3 incorporates a compression spring 79 which acts between the head of the piston 22 and a ring 80 secured against movement within the cylindrical body 10. The spring 79 operates to vary the force produced by the gas spring during the opening movement. Thus, it augments the force produced as the opening movement begins, its augmenting force then diminishing.

An aperture 81 in the ring 80 transmits changes in gas pressure within the chambers 28 and 30 to the piston 44, so that the material 52 provides temperature compensation in the manner already explained.

In the gas spring of Figure 4, the piston 22 is constructed in generally the same way as in Figures 1 - 3. However, in the gas spring of Figure 4 it separates the interior of the cylindrical body 10 into two chambers 84 and 86 which are filled with hydraulic fluid instead of gas. Chamber 86 is defined between the piston 22 and a further piston 88 which is slidable on the piston rod 16 and is sealed to the piston 16 by a sealing ring 90 and is sealed against the interior of the cylindrical body 10 by a sealing ring 92. Piston 88 thus produces a chamber 94 which is filled with gas under pressure.

The temperature compensating arrangement comprising the piston 44 and the material 52 is arranged the same way as in Figures 1 and 3.

In operation, the pressure of the hydraulic fluid within chambers 84 and 86 tends to expel the piston 22 and the piston rod 16 in a direction outwardly of the cylindrical body 10. As the piston 22 moves to the right (as viewed in Figure 4), hydraulic fluid can transfer from chamber 86 to chamber 84 through the restricted passageway formed by the slot 36, the radial slot 38, and the axial bores 40 in the manner already explained, and a force is produced which raises the hatchback door. The resultant force tends to move the piston 88 to the right, thus compressing the gas within chamber 94. When the hatchback door is lowered, by means of manual force exerted on it, the piston 22 moves to the left so that the sealing ring 26 is shifted to the right hand side of the annular groove 24 by frictional force.This allows a greater flow of hydraulic fluid through the restricted passageway, which is no longer restricted by the size of the radial groove 38, and hydraulic fluid can thus transfer from chamber 84 to chamber 86.

In the event of ambient temperature changes, tending to expand the volume of the gas (and, to a lesser extent, the volume of the hydraulic fluid), pressure on piston 44 moves it towards the closed-off end 12 of the cylinder. As before, this movement of piston 44 causes no increased pressure to be produced within the material 52 and the effect of temperature on the hydraulic fluid and on the gas is thus eliminated or minimised.

In the gas spring of Figure 5, items corresponding to those in the other Figures are correspondingly referenced.

In the gas spring of Figure 5, the piston rod 16 is replaced by a piston rod 16A which is hollow and incorporates a slidable piston 100 having a sealing ring 102. Piston 100 divides the interior of the piston rod 16A into two chambers 104 and 106.

Chamber 104 is in communication with chamber 30 via a bore 108.

The piston 22 is constructed in the same way as in the other Figures, and divides the hollow interior of the cylindrical body 10 into the chambers 28 and 30.

Chamber 106 within the hollow piston rod 16A is filled with the temperature compensating material 52.

As before, chambers 28 and 30 are filled with gas under pressure.

The gas acts on the piston rod 16, tending to drive it outwardly of the cylindrical body 10 in the manner already explained, thus raising the hatchback door. Lowering of the hatchback door is carried out in the same way as already explained. Gas transfer between chambers 28 and 30 takes place in the same way as in the other Figures.

In the event of an increase in temperature, the volume of the gas within chambers 28, 30 and 104 will tend to increase, thus forcing piston 100 to the right (as viewed in Figure 5), and reducing the volume of the temperature compensating fluid 52.

Because such volume reduction does not result in an increase in pressure, the effect is that any tendency for the increased temperature to increase the gas pressure within the gas spring is thus eliminated or minimised, as before.

In a modification, the heterogeneous material 52 can be replaced by normal hydraulic fluid in which is positioned a flexible sachet containing the heterogeneous material 52; the latter could, for example, be incorporated in a sachet made of flexible polyethylene. This arrangement permits a reduction in the quantity of the heterogeneous material 52 when the required variation in volume is small.

Claims

1. A fluid pressure spring, comprising a piston-cylinder arrangement containing an operating fluid under pressure which tends to displace the piston from the cylinder to provide an external operating force, and temperature compensation means for compensating for the effect on the operating force of changes in temperature of the fluid, the temperature compensating means including a material the volume of which is variable to at least a predetermined extent without increasing its reactive pressure, and control means responsive to changes in volume of the fluid in response to temperature changes for causing a resultant and corresponding change in volume of the said material whereby to offset any change in the pressure of the fluid.

2. A spring according to claim 1, including a piston rod connected to the piston for exerting the operating force.

3. A spring according to claim 2, in which the cylinder has a first end through which the piston rod sealingly and slidably extends, and a second, opposite, end, the piston dividing the interior of the cylinder into a first main chamber positioned between the second end of the cylinder and the piston and a second main chamber through which the piston rod extends, the first and second main chambers containing the fluid under pressure and being interconnected by means defining a restricted fluid-flow passageway for enabling fluid to transfer from the first main chamber to the second main chamber as the said displacement of the piston takes place, and to enable transfer of the fluid from the second main chamber to the first main chamber when the piston is moved inwardly of the cylinder in response to a force applied externally to the piston rod in a direction opposite to the direction of the operating force.

4. A spring according to claim 3, comprising valve means automatically responsive to the direction of movement of the piston within the cylinder to allow increased fluid flow through the passageway when the piston is moving inwardly of the cylinder.

5. A spring according to claim 4, in which the valve means comprises sealing means for providing a seal between the piston and the cylinder, the sealing means being bodily displaceable in response to frictional force exerted on it by movement of the piston, such displacement being between the position in which the sealing means provides partial blockage of the restricted passageway and a position in which it is clear of the restricted passageway.

6. A spring according to any one of claims 3 to 5, in which the control means of the temperature compensating means comprises a compensation chamber including with the said material and the control means comprises a movable member connected to be movable in response to changes in the volume of the fluid in at least one of the first and second main chambers due to temperature changes, the movable member changing the volume of the temperature compensation chamber.

7. A spring according to claim 6, in which the said material is positioned within a flexibly-walled enclosure which is itself positioned in hydraulic fluid in the compensation chamber.

8. A spring according to claim 6 or 7, in which the temperature compensation chamber is defined within the cylinder and is positioned between its said second end and the movable member which is sealingly slidable within the cylinder and itself defines part of the wall of the first main chamber.

9. A spring according to claim 6 or 7, in which the temperature compensation chamber is separate from the cylinder and comprises a hollow body in which the movable member is sealingly slidable, and including pressure transfer means responsive to any increase in volume of the fluid within the said cylinder resulting from temperature increase to cause that volume increase to move the movable member in a direction tending to reduce the volume of the temperature compensation chamber.

10. A spring according to claim 9, in which the fluid pressure transfer means comprises a slide sealingly slidable within the cylinder between the piston and the second end of the cylinder to define a pressure transfer chamber containing hydraulic fluid, and means connecting the hydraulic fluid to move the movable member in the direction tending to reduce the volume of the temperature compensation chamber.

11. A spring according to claim 6 or 7, in which the piston rod is hollow, the movable member being mounted for sealing and sliding movement within the hollow interior of the piston rod and separating the hollow interior of the piston rod into the temperature compensation chamber and a further chamber which is in communication with the second main chamber.

12. A spring according to any preceding claim, in which the operating fluid is gas.

13. A spring according to any one of claims 1 to 11, in which the operating fluid is hydraulic fluid and gas.

14. A spring according to claim 13, in which the operating fluid comprises hydraulic fluid filling the first and second chambers and gas under pressure filling a subsidiary chamber which is defined in the cylinder between the first end thereof and a member slidable on the piston rod and sealed to the piston rod and to the interior of the cylindrical body.

15. A fluid pressure spring for raising the hatchback door or similar closure member on a vehicle body, comprising a hollow cylinder, a piston slidable within the hollow cylinder and connected to a piston rod sealingly and slidingly extending from a first end of the cylinder and externally pivotally connected to one of the hatchback door on the vehicle body, the cylinder having a second, opposite, end externally pivotally connected to the other of the hatchback door and the vehicle body, the piston dividing the hollow cylinder into a first main chamber between the piston and the second end of the cylinder and a second main chamber through which the piston rod extends, the first and second main chambers being connected by means defining a restricted gas flow passageway, gas under pressure within the first and second main chambers and acting on the piston and the piston rod and tending to drive the piston rod outwardly of the cylinder to produce an external operating force for lifting the hatchback door, means defining a temperature compensation chamber containing material a reduction in volume of which produces no increase in reactive pressure, and a movable member mounted to provide increased volume within the cylinder in response to expansion of the gas due to temperature increase, the movable member producing a corresponding reduction in the volume of the said material.

16. A spring according to claim 15, in which the movable member is slidably and sealingly mounted within the cylinder between the piston and the second end of the cylinder, the temperature compensating chamber being defined between the movable member and that end of the cylinder.

17. A spring according to claim 15, in which the piston rod is hollow and the movable member is sealingly slidable within the hollow interior of the piston rod, the movable member dividing the hollow interior of the piston rod into the temperature compensation chamber and a further chamber which is in communication with the second main chamber.

18. A spring according to any one of claims 15 to 17, in which the said material is positioned within a flexibly-walled enclosure which is itself positioned in hydraulic fluid in the compensation chamber.

19. A spring according to any preceding claim, including a mechanical spring for augmenting the operating force, the mechanical spring acting on the piston.

20. A spring according to any preceding claim, in which the material is a heterogeneous material containing porous matrices and a liquid.

21. A fluid spring, substantially as described with reference to Figure 1 of the accompanying drawings.

22. A fluid spring, substantially as described with reference to Figure 2 of the accompanying drawings.

23. A fluid spring, substantially as described with reference to Figure 3 of the accompanying drawings.

24. A fluid spring, substantially as described with reference to Figure 4 of the accompanying drawings.

25. A fluid spring, substantially as described with reference to Figure 5 of the accompanying drawings.