GB2101268A

GB2101268A - Gas spring

Info

Publication number: GB2101268A
Application number: GB08217775A
Authority: GB
Inventors: Leo Lauderbach; Jurgen Rossner
Original assignee: Stabilus GmbH
Current assignee: Stabilus GmbH
Priority date: 1981-06-27
Filing date: 1982-06-18
Publication date: 1983-01-12
Also published as: IT8267810A0; ES513457A0; ES8305100A1; BR8203740A; DE3125387A1; FR2508581A1; JPS588838A

Abstract

In a cylinder piston device a cavity defined within the cylinder contains a pressurized fluid. This pressurized fluid comprises at least one component which within a normal range of operational temperature comprises a gaseous phase and a liquid phase. According to the varying partial volume of the piston rod contained within the cavity, at a predetermined temperature the volume of the liquid phase is varied by condensation or evaporation; the pressure acting onto the piston rod remains however constant. The device may be a shock absorber for vehicles, a spring strut, or non-lockable spring or as shown a lockable spring for height adjustable tables chairs. The fluid with the gaseous and liquid phases may be sulphur hexafluoride, difluoromonochloromethane or butene. <IMAGE>

Description

SPECIFICATION Cylinder piston device The present invention is directed to a cylinder piston device. Such a cylinder piston device comprises a cylinder member having an axis and two end walls, a cavity being defined within the cylinder member. A piston rod member extends through at least one of the end walls and is axially movable along said axis of the cylinder member inward and outward of the cavity between a first and a second terminal position. A piston rod sealing and guiding unit is provided adjacent said one end wall for sealingly guiding said piston rod member through said one end wall. A fluid of superatmospheric pressure is enclosed within the cavity. This fluid comprises a gaseous phase. The pressure biases the piston rod member towards one of said terminal positions.

Cylinder piston devices of this type are wellknown in the art and are e.g. described in U.S.

Patent 4 270 635. They may be used e.g. as a shock absorber, as a component of a spring strut for vehicles, as a lockable gas spring, or as a nonlockable gas spring.

In the known type of cylinder piston devices, gases like nitrogen are used which have in the total range of usual operational temperatures only a gaseous phase. The usual range of operational temperatures is e.g. from 70 degrees centrigrade below zero to 100 degrees centrigrade above zero, assuming e.g. a gas spring incorporated into a motor vehicle which is to be used under polar and tropical temperatures. The pressure of such usually employed gases is even at constant tempertures dependent of the varying partial volume of the piston rod member contained within the cavity, which partial volume varies when the piston rod member is moved between said terminal positions.

It is a primary object of this invention to provide a cylinder piston device of the type described above in which the pressure within the cavity is independent from the variable partial volume of the piston rod member contained within the cavity so that the biasing force of the pressurized gas directly or indirectly acting on the piston rod member remains also constant.

A further object is to provide a cylinder piston unit which is highly reliable in operation.

According to this invention, the fluid has at least one component having a gaseous and a liquid phase within a predetermined range of operational temperatures.

The cylinder piston device of this invention is of particular interest for such fields of use in which the normal operational temperatures is substantially constant. Such a field of use is the field of furniture e.g. height-variable chairs and desks which are frequently equipped with gas springs for compensating for the weight of heightadjustable members. In such field of use the temperature is always about 20 degrees centrigrade corresponding to the normal temperature in living rooms, office rooms and the like. Under such conditions, the pressure biasing the piston rod member remains always substantially constant independently of the position of the piston rod member with respect to the cylinder member.This is especially true for designs in which the cross-sectional area of the piston rod is relatively large as compared with the cross-sectional area of the cavity e.g. more than 20% of the cross-sectional area of the cavity. In such devices, when using the usual gases a considerable pressure variation occurs even under constant temperature conditions.

When using a gas according to this invention, a more or less great part of the fluid is condensed or liquefied but the pressure acting onto the piston rod is always the same corresponding to the vapor pressure at the respective temperature.

If fluid escapes out of the cavity the pressure within the cavity remains unchanged at the respective temperature as long as sufficient fluid is contained within the cavity such as to maintain a liquid phase within the cavity. So a correct function of the cylinder piston device is maintained over a long period even if small amounts of fluid can escape. It is further to be observed that the pressure prevailing within the cavity is maintained below a certain maximum pressure which is tolerable in cylinder piston devices of this type.

Unintended temperature increase may occur even if the device is normally located in a room of about 20 degrees centigrade. It is necessary that on such intended temperature increase the mechanical construction of the gas spring and more particularly the cylinder member and the sealing and guiding unit can withstand to the increased pressure.

Most suitable for the cylinder piston device of this invention are gases which have a condensation pressure (corresponding to the vapor pressure) at room temperature of about 20 degrees centigrade which is sufficient for creating a substantial biasing force. These prerequisites are fulfilled by certain hydrocarbons and halogenated hydrocarbons. The gases may be synthetic gases.

It is essential that the applied gases are inert with respect to the mechanical components and sealing components of the cylinder piston device.

Examples for most suitable fluids are sulfurhexafluoride (SFe) and difluoromonochloromethane (CHCLF2).

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.

Brief Description of the Drawing The attached drawing shows an example embodiment of a cylinder piston device of this invention in a longitudinal section along the axis of the cylinder.

Detail Description of the Invention In the Figure, 1 designates the cylinder member, a cavity 1 a being defined within the cylinder member 1. A piston rod 2 extends inwardly and outwardly of the cavity through a piston rod sealing and guiding unit 20. The piston rod 2 is provided with a piston 3 within the cavity 1 a. The cavity is subdivided by the piston 3 into two working chambers 17 and 18. A valve member 4 is provided within the piston 3. The valve member 4 cooperates with annular sealing members 15 and 21 so as to separate the working chambers 1 7 and 1 8 from one another and to separate the space within the piston rod 2 from the working chamber 1 8. The piston 4 is combined with an actuating rod 5 which cooperates with an actuating lever 6 passing through an aperture 7 of the piston rod 2.A passage 1 6 extends through the piston member 3.

In the position as shown, the working chambers 1 7 and 18 are separated from one another by the valve member 4 being maintained in the shown position by internal pressure within the working chamber 18. When the actuating rod 5 is shifted downward the passage 1 6 connects the working chambers 17 and 18 across the piston 3. When the passage 1 6 is closed the piston rod 2 and the piston 3 are stationary with respect to the cylinder 1. When the passage 1 6 is open the piston rod 2 is moved upwards, as seen in the Figure, by the internal pressure within the working chambers 1 7 and 1 8 acting onto piston rod 2.The biasing force acting onto the piston rod 2 is equal to the product of the internal pressure within the cavity 1 a x the cross-sectional area of the piston rod 2 defined by its external diameter.

The cavity 1 a is filled with a pressurized fluid, this fluid having a gaseous phase 22 and a liquid phase 23. The volume of the liquid phase 23 is defined by the position of the piston rod 2 within the cylinder 1. When the piston rod 2 is moved outwardy additional vapor of the liquid phase 23 is evaporated. When the piston rod 2 is moved inwardly additional fluid is condensed.

One recognizes in the Figure a base member 24 fixed to the lower end of the cylinder 1 and being provided with legs 25. One further recognizes a height-adjustable plate 26 fixed to the upper end of the piston rod 2.

EXAMPLE 1 The cavity 1 a is filled with sulfurhexafluoride (SF6). The operational temperature is 20 degrees centigrade. The vapor pressure of the gaseous phase is 21.2 bar. The diameter of the piston rod is 2 centimeters. The cross-sectional area of the piston rod is 3.14 square centimeters. The biasing force acting onto the piston rod is 66.6 kp. This means that the piston rod is biased in outward direction by a force of 66.6 kp and can be pushed inwardly by applying a downwardly directed force of 66.6 kp when the passage 1 6 is open. This force remains constant along the entire stroke of the piston rod 2, as there remains always a liquid phase 23 within the cavity and the pressure corresponds always to the vapor pressure of SF6 at the temperature of 20 degrees centigrade.

EXAMPLE 2 The cylinder piston device has the same design and the same dimensions as described before. The cavity 1 a is filled with CHCLF2. The operational temperature is 20 degrees centigrade. The vapor pressure at this operational temperature is about 9.47 bar. The biasing force acting onto the piston rod is 29.73 kp.

EXAMPLE 3 The fluid is butene-( 1 ) (C4H6). The operational temperature is about 40 degrees centigrade. The vapor pressure acting onto the piston rod is about 5 bar.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

Claims

1. A cylinder piston device comprising a cylinder member having an axis and two end walls, a cavity being defined within said cylinder member; a piston rod member extending through at least one of said end walls and being movable along said axis inward and outward of said cavity between a first terminal position and a second terminal position; a piston rod sealing and guiding unit adjacent said one end wall for sealingly guiding said piston rod member through said one end wall; a fluid under superatmospheric pressure enclosed within said cavity, said fluid comprising a gaseous phase, said pressure biasing said piston rod member towards one of said terminal positions; the improvement comprising said fluid having at least one component having a gaseous and a liquid phase within a predetermined range of operational temperatures.

2. A cylinder piston device as set forth in claim 1, wherein said range of operational temperatures extends between 50 degrees centigrade below zero and 100 degrees centigrade above zero.

3. A cylinder piston device as set forth in claim 1, wherein said range of operational temperatures extends from 20 degrees centigrade below zero to 50 degrees centigrade above zero.

4. A cylinder piston device as set forth in claim 1, wherein said range of operational temperatures extends from 10 degrees centigrade below zero to 30 degrees centigrade above zero.

5. A cylinder piston device as set forth in claim 1, wherein said component has a vapor pressure of at least 1.5 bar within said predetermined range of operational temperatures.

6. A cylinder piston device as set forth in claim 5, wherein said component has a vapor pressure of at least 1.5 bar at 30 degrees centigrade below zero.

7. A cylinder piston device as set forth in claim 5, wherein said component has a vapor pressure of at least 2 bar at 0 degrees centigrade.

8. A cylinder piston device as set forth in claim 5, wherein said component has a vapor pressure of at least 2 bar at 20 degrees centigrade.

9. A cylinder piston device as set forth in claim 5, wherein said component has a vapor pressure of at least 5 bar at 20 degrees centigrade.

10. A cylinder piston device as set forth in claim 5, wherein said component has a vapor pressure of at least 10 bar at 20 degrees centigrade.

1 A cylinder piston device as set forth in claim 5, wherein said component has a vapor pressure of at least 1 5 bar at 20 degrees centigrade.

12. A cylinder piston device as set forth in claim 5, wherein said component has a vapor pressure of less than 1 50 bar at 60 degrees centigrade.

13. A cylinder piston device as set forth in claim 5, wherein said component has a vapor pressure of less than 1 50 bar at 100 degrees centigrade.

14. A cylinder piston device as set forth in claim 5, wherein said component has a vapor pressure of less than 100 bar at 60 degrees centigrade.

1 5. A cylinder piston device as set forth in claim 5, wherein said component has a vapor pressure of less than 100 bar at 100 degrees centigrade.

1 6. A cylinder piston device as set forth in claim 5, wherein said component has a vapor pressure of less than 50 bar at 60 degrees centigrade.

17. A cylinder piston device as set forth in claim 5, wherein said component has a vapor pressure of less than 50 bar at 100 degrees centigrade.

1 8. A cylinder piston device as set forth in claim 1, wherein said component is a synthetic gas.

1 9. A cylinder piston device as set forth in claim 1, wherein said component is a hydrocarbon.

20. A cylinder piston device as set forth in claim 1, wherein said component is a halogenated hydrocarbon.

21. A cylinder piston device as set forth in claim 1, wherein said component is difluoromonochloromethane (CHCLF2).

22. A cylinder piston device as set forth in claim 1, wherein said component is sulfurhexafluoride (SF6).

23. A cylinder piston device as set forth in claim 1, wherein said liquid phase exists in all positions of said piston rod member between said terminal positions, the pressure of said fluid acting onto said piston rod member being constant at a predetermined temperature independently of the respective position of said piston rod member.

^24. A cylinder piston device substantially as described with reference to the accompanying drawing.