BACKGROUND OF THE INVENTION AND PRIOR ART The present invention refers to a spring element including a longitudinal centre axis and a bellow-shaped wall member, which extends around the longitudinal centre axis and is arranged to provide a spring force in the direction of the longitudinal centre axis.

The invention also refers to a sealing device including : a first sealing element having a sealing surface, a second sealing element having a sealing surface, and a spring element, which is arranged to press the sealing surfaces to sealing abutment against each other.

There is a plurality of various types of spring elements, which during elastic shape change may absorb and exert a spring force.

Spring elements may thus be used for various purposes, for instance absorbing chocks, generating a movement or exert a pressure in, for instance, a valve or a sealing. All spring elements have a theoretical spring constant and in reality a damping.

Normally, spring elements manufactured of steel have a relatively low inner damping whereas spring elements manufactured of for instance rubber may have a high inner damping. Helical spring elements are typically manufactured of steel or any other metal and thus have a low inner damping. When such spring elements are used in various connections, for instance for chock absorption, a damping member is normally provided in parallel with the spring element.

The present invention refers to a spring element which includes or consists of a bellow. Such bellow springs are used in various

connections, for instance in sealing devices for pressing, by a spring force, a sealing element against another sealing element.

The bellow-shaped wall member encloses an inner space through which, for instance, a rotating shaft may extend. Examples of such spring elements for shaft sealing devices are disclosed in EP-B-312 184, EP-A-882 915 and GB-A-2,111, 139.

When such rotating shafts are rotating with a high speed, vibrations and oscillations occur. It is therefor important that the spring element may absorb these oscillations in a satisfactory manner so that the two sealing elements abut each other with a substantially constant contact pressure. Furthermore, it is important that the spring element has a long lifetime. One problem with such spring elements is the difficulty to achieve a suitable and sufficient damping for ensuring constant contact pressure between the sealing elements and for ensuring that the sealing device does not start self-oscillating.

SUMMARY OF THE INVENTION The object of the present invention is to provide a spring element, which is of the initially defined type and which has a high inner damping.

This object is achieved by the initially defined spring element, which is characterized in that the wall member includes an outer bellow- shaped sheet, an inner bellow-shaped sheet and an interspace between the outer and inner sheets, which has a substantially uniform thickness and houses a viscous material.

Such a spring element, which includes or consists of a bellow- shaped wall member, has a very high damping and may therefore in a sufficient manner resist vibrations. The spring element according to the invention may thus be used in all applications where a spring force is required and where vibrations are present. The bellow- shaped wall member encloses a space inside the inner sheet, which space may receive a rotating shaft, for instance. The bellow-shaped

wall member of the spring element may for instance have a substantially cylindrical or substantially conical extension along the centre axis. The extension along the centre axis may vary depending on which spring and damping properties are desired in individual applications.

According to an embodiment of the invention, the bellow-shaped wall member has an extension along the centre axis and a wave- shape with subsequently positioned valleys, which are located at a relatively short radial distance from the centre axis, and peaks, which are located at a relatively long radial distance from the centre axis. Furthermore, the bellow-shaped wall member advantageously has a continuous extension, i. e. it lacks substantially sharp edges or bendings. In particular, said valleys and peaks may have a soft curvature. By such a continuous soft shape of the bellow-shaped wall member, a long lifetime of the spring element is ensured.

According to a further embodiment of the invention, said interspaces have a substantially uniform thickness along substantially the whole wall member, i. e. the two sheets extend substantially in parallel with each other. In such a way a uniformly distributed damping characteristic is achieved along the whole bellow-shaped wall member.

According to a further embodiment of the invention, said sheets include a respective metal sheet, preferably of stainless steel. By such metal sheets excellent spring properties of the spring element are achieved.

According to a further embodiment of the invention, said viscous material is plastically or elastically extensible. The viscous material may be selected among a plurality of various materials depending on which damping properties are desired. The viscous material may thus be a fluid, in the form of a gas or a liquid, or a solid material for instance natural or synthetic rubber, any polymer material, etc. A viscous material in the form of a fluid may be compressible or incompressible. Advantageously, said viscous material has,

however, a relatively high inner damping, i. e. a substantially higher inner damping than the material of the two sheets. The viscous material is selected depending on which vibration frequencies are to be damped.

The object is also achieved by the initially defined sealing device, characterized in that the wall member includes an outer bellow- shaped sheet, an inner bellow-shaped sheet and an interspace between the outer and inner sheets, which has a substantially uniform thickness and houses a viscous material.

Such a sealing device ensures a tight abutment of the sealing elements against each other at a substantially constant contact pressure even if the device is subjected to strong vibrations of arbitrarily frequencies, since the spring element in an efficient manner is capable of damping such vibrations.

According to an embodiment of the invention, the sealing device is arranged to seal a passage through a wall between a first space and a second space, wherein a rotatable shaft is arranged to extend in the passage through the wall in such a way that a gap is formed, which extends around the shaft between the shaft and the wall, wherein the first sealing element is annular and connected to the shaft and the second sealing element is annular and connected to the wall. Advantageously, the spring element, i. e. the bellow- shaped wall member of the spring element, is provided around the shaft, wherein the shaft extends through the space formed inside the inner bellow-shaped sheet. Advantageously, the centre axis of the spring element is substantially concentric with the shaft.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is now to be explained more closely through a description of various embodiments and with reference to the drawings attached.

Fig 1 discloses a sectional side view of a spring element according to an embodiment of the invention.

Fig 2 discloses a part of the spring element in Fig 1.

Fig 3 discloses a part of a spring element according to a second embodiment.

Fig 4 discloses a sectional view of a sealing device according to the invention.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS OF THE INVENTION Figs 1 and 2 disclose a spring element E which includes a bellow- shaped wall member 1. The wall member 1 extends substantially concentrically around a longitudinal centre axis x of the spring element E. The spring element E may be arranged to provide a compression spring force in the direction of the longitudinal centre axis x after a compression, or to provide a tension spring force in the direction of the longitudinal centre axis x after an extension.

The wall member 1 has a first open end 2 and a second open end 3. Between the two open ends 2,3, the wall member 1 is substantially complete or closed, and includes an inner space 4. As appears more closely from Fig 2, the wall member 1 includes an outer bellow-shaped sheet 6 and an inner bellow-shaped sheet 7.

The outer sheet 6 adjoins the surrounding environment and the inner sheet 7 adjoins the inner space 4. Between the sheets 6 and 7, there is an interspace housing a viscous material 8. The interspace and the viscous material 8 have a substantially uniform thickness along substantially the whole wall member 1, i. e. the sheets 6 and 7 extend substantially in parallel to each other.

The bellow-shaped wall member 1 thus has an extension along the centre axis x and a wave shape with subsequently positioned valleys located at a relatively short radial distance a from the centre axis x, and peaks located located at a relatively long radial distance b from the centre axis x.

The bellow-shaped wall member 1 has a substantially continuous extension, i. e. the wall member 1 lacks substantially all sharp edges or bendings. Instead, the wall member 1 and said valleys and peaks substantially all have a soft curvature, which appears from Figs 1 and 2. In the embodiment disclosed, the wall member 1 has a generally cylindrical shape. It is to be noted, however, that the wall member 1 also may have a general shape deviating from the one disclosed, for instance a generally conical shape where one end 2, 3 of the wall member 1 has a smaller radius than the other end 2,3.

It is also possible to let the wall member 1, for instance, have a relatively small radius at the ends 2,3 and a larger radius between the two ends 2,3. The general shape of the wall member 1 may be selected depending on which spring and damping properties are desired in the particular application.

The sheets 6,7 are preferably manufactured of a metal materiel having good spring properties. For instance, the sheets may be manufactured of a steel, advantageously a corrosion resistant or stainless steel. The viscous material 8 has a relatively high inner damping which is significantly higher than the damping of said sheets 6,7. The viscous material 8 is plastically or elastically extensible. Advantageously, the viscous material 8 may include a natural or synthetical rubber material or any other polymer material.

The viscous material 8 may be a solid material or possibly a liquid.

The viscous material 8 may be compressible or incompressible.

Consequently, there are many alternatives for the viscous material 8. The selection depends in the first place on which damping properties are desired in the individual application.

In the embodiment disclosed in Fig 2, the thickness of each of the sheets 6,7 is thicker than the thickness of the viscous material 8. In Fig 3, another embodiment is disclosed, which differs from the first embodiment merely in that the thickness of each of the sheets 6,7 is smaller than the thickness of the viscous material 8. It is to be noted that the difference in the thickness of the outer sheet 6, the inner sheet 7 and the intermediate viscous material 8 may be varied

depending on the desired spring and damping properties. The sheets 6 and 7 may also have different thickness.

Fig 4 discloses the spring element E in an advantageous application in a sealing device. The sealing device includes a first annular sealing element 21 and a second annular sealing element 22. The first sealing element 21 is rigidly mounted to a rotating shaft 23 and the second sealing element 22 is connected to a stationary wall 24 via the spring element E. The wall 24 separates a first space 25 from a second space 26. The wall 24 includes a passage 27 between the spaces 25 and 26, wherein the rotatable shaft 23 extends through the passage 27 in such a way that a gap is formed between the shaft 23 and the wall 24. The purpose of the sealing device is to close this annular gap.

Such a sealing device may advantageously be used together with any rotating equipment.

The first sealing element 21 includes an annular body 31 of a suitable sealing material, which forms an annular sealing surface 41, and the second sealing element 22 includes an annular body 32 of a suitable sealing material, which forms an annular sealing surface 42. The spring element E will press the substantially stationary sealing surface 42 with a spring force F against the rotating sealing surface 41 to sealing contact with each other. At the same time the substantially closed wall member 1 ensures that no fluid may pass the passage 27 between the shaft 23, the wall 24 and the second sealing element 22. It is to be noted that the spring element E, as an alternative, may be rigidly connected to the rotating shaft 23 and thus press the sealing surface 41 of the rotating sealing element 21 against the sealing surface 42 of the substantial stationary sealing element 22, wherein the second sealing element 22 is rigidly connected to the wall 24.

The invention is not limited to the embodiment disclosed and the application disclosed in a sealing device. The spring element E may be used in a plurality of various connections in order to provide a spring force with a high damping.