GB2170574A

GB2170574A - A pneumatic spring

Info

Publication number: GB2170574A
Application number: GB08601156A
Authority: GB
Inventors: Peter Schlottermuller
Original assignee: Stabilus GmbH
Current assignee: Stabilus GmbH
Priority date: 1985-02-02
Filing date: 1986-01-17
Publication date: 1986-08-06
Also published as: FR2576995A1; GB8601156D0; DE3503537A1; GB2170574B; JPS61184241A

Abstract

In a gas spring the piston rod 3 is introduced through one end wall of the cylinder 2 by means of a guiding and sealing device 5,6. An annular separating piston 7 sealingly engages the piston rod 3 and the internal surface of the cylinder 2. A sealing liquid is contained within an annular sealing chamber 11 located axially between the sealing and guiding device 5,6 and the annular separating piston 7. A body of pressurized gas 10 is provided on the other side of the separating piston. The pressurized gas acts onto the separating piston 7 such as to create pressure of the sealing liquid within the sealing chamber 11, but additionally a separate spring 12 is provided which acts on the separating piston 7 in parallel with the pressurized gas such as to increase the pressure of the sealing liquid beyond the pressure of the pressurized gas. Spring 12 could be replaced spring elements of other type, eg. a secondary annular gas chamber. <IMAGE>

Description

SPECIFICATION A pneumatic device In gas springs it is known to provide a sealing liquid within the cylinder adjacent a piston rod guiding and sealing unit in order to improve the sealing properties of the piston rod guiding and sealing unit.

For sealing the piston rod of a pneumatic spring it is known from Fed. German Utility Model 1,971,284 to seal off the gas chamber, which is under high pressure and arranged in a container, by means of a sealing liquid. For this purpose a liquid-filled chamber is provided adjoining a piston rod seal, so that the piston rod seal is effective essentially as liquid seal.

Any slight liquid loss in this chamber has the effect that a gas cushion forms in this liquidfilled chamber and escapes through the piston rod seal substantially more quickly than the liquid. An increased gas concentration in the liquid-filled chamber not only is detrimental to the lubrication between piston rod and piston rod seal and leads to increased friction and wear of the piston rod seal, but also effects a gradual pressure reduction within the container, so that after lengthy use the spring force diminishes. It is further proposed by Fed. German Pat. Appl. No. P 34 13 698.3 to seal off the liquid-filled chamber from the pneumatic spring gas chamber, which is under high pressure, by means of a separator piston.This separator piston is provided with seal elements which engage in sealing manner on the one hand on the piston rod and on the other hand the inner surface of the container.

Thus friction forces occur between the separator piston and the inner surface of the container and the outer surface of the piston rod so that-caused by the actuation of the gas spring and/or fluctuations of the ambient temperature-a pressure drop can occur from the gas chamber to the liquid-filled chamber. On account of different diffusion effects such as permeation and the dependence upon temperature, pressure and time thereof, under the ordinary working conditions it is not possible to prevent the formation of small gas quantities in the liquid-fiiled chamber, so that the disadvantages described already can occur, even though in reduced form.

corresponding to British Appln. Ser. No. 84 09 158 French Appln. Ser. No. 84 06 009 Japanese Appln. Ser. No. 75 197/84 U.S. Appln. Ser. No. 533 202 The arrangement of a spring as shown in one form of embodiment of Federal German Pat.

Appln. No. P 34 13 698.3 produces a greater pressure drop between the gas chamber under higher pressure and the liquid-filled chamber under lower pressure, so that thus the abovedescribed disadvantages are not eliminated but reinforced.

It is an object of the present invention to provide a pneumatic device which avoids the disadvantages of the known designs and guarantees satisfactory sealing over a long period of time without-at least without appreciable-loss of gaseous working medium.

A pneumatic device comprises means defining a container, said container having an internal surface. A piston rod member enters into this container through a piston rod guiding and sealing unit. This piston rod member has an axis and an external surface and is movable in the direction of the axis inward and outward of the container. An annular separating wall unit is in sealing engagement with both the external surface of the piston rod member and the internal surface of the container. This annular separating wall unit is capable of axial movement with respect to both the external surface of the piston rod member and the internal surface of the container. An annular sealing chamber is defined by the external surface of the piston rod member and the internal surface of the container axially between the piston rod guiding and sealing unit and the annular separating wall unit.A body of sealing liquid is contained within the annular sealing chamber. A working cavity is defined within the container on the side of the annular separating wall unit which is remote from the piston rod guiding and sealing unit. A volume of gas under pressure is contained within the working cavity. Spring means distinct from the volume of gas under pressure act in axial direction onto the annular separating wall unit such as to increase the pressure of the sealing liquid within the annular sealing chamber beyond a pressure resulting from the volume of gas under pressure.

The above-defined object is achieved in that in no operating condition there is a pressure in the annular sealing chamber, filled with liquid sealing medium, less than the pressure within the working cavity, so that the undesired diffusion effects between the working cavity and the annular sealing chamber filled with liquid sealing medium are minimised. Furthermore, the percentage pressure fluctuation on the piston rod seal for a given internal pressure fluctuation is reduced, which facilitates the design of the seal of the piston rod guiding and sealing unit which mostly is optimalised only for a specific pressure drop in which it can be operated with favourable sealing effects.

The design of this invention is also advantageous for those cases of use where, at least temporarily, a nagative pressure can occur in the working cavity adjacent the annular separating wall unit.

In view of a most simple design compressive spring means can be used. These compressive spring means can be supported by a support face which is provided within the working cavity by the means defining the container. A helical compression spring is preferred. It is however also possible to use tension springs or secondary gas cushions for obtaining the increased pressure in the annular sealing chamber.

The additional spring means are preferably arranged such that they act onto the annular separating wall unit in parallel with the action of the volume of gas under pressure. The spring means should be subject to such a prestress that the pressure of the sealing liquid within the annular sealing chamber exceeds the pressure of the volume of gas under pressure under substantially all working conditions, preferably under all working conditions. So, the migration of gas from the working cavity to the annular sealing chamber is farly reduced.

In use of a gas spring it may occur that the pressure of the gas adjacent the separating wall unit is reduced below the ambient atmospheric pressure. This may lead to an inversion of the pressure drop at the seal of the piston rod guiding and sealing unit.

In accordance with a further feature of the present invention the spring means are subject to such a prestress that the pressure of the sealing liquid within the annular sealing chamber is greater than atmospheric pressure surrounding the pneumatic device under substantially all working conditions and preferably under all working conditions. So, the pressure drop at the seal of the piston rod guiding and sealing unit is always of the same direction, which allows the use of a simplified seal design and particularly the use of a seal design with reduced friction.

As certain frictional forces always act onto the separating wall unit in axial direction as a result of sealing engagement with the external surface of the piston rod member and the internal surface of the container the prestress exerted by the spring means should be such as to overcome these frictional forces.

A very simple construction of the annular separating wall unit is obtained if an annular separating piston member is integral with annular sealing elements.

The pneumatic device may further comprise a working piston unit connected to the piston rod member within the working cavity which divides the working cavity into two chambers, in which case the two working chambers are interconnected by passage means. These passage means may be throttled. In such case it is likely that a reduced pressure in the wórk- ing chamber adjacent the annular separating wall unit can occur and therefore the concept of the present invention is particularly interesting for this widely distributed type of pneumatic springs.

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 drawings and descriptive matter in which there are illustrated and described preferred embodiments of the invention.

The invention will be explained in greater detail below by reference to the examples of embodiment as represented in the drawing, wherein: Figure 1 shows a pneumatic device according to the invention, in longitudinal section; and Figure 2 shows a modified embodiment.

The pneumatic spring 1 as shown in Fig. 1 possesses a cylindrical container 2, one end of this container 2 being closed by a container bottom which is provided with a joint eye for attachment to a component. A working piston 4 connected with a piston rod 3 slides on the internal surface of the container 2, while the piston rod 3 is guided by means of a piston rod guide 5 and sealed to the exterior by a piston rod seal 6. A liquid-filled annular sealing chamber 11 is separated from a pressurised gas cavity 10 by a separating piston 7 formed by a support ring 8 and a separating piston seal 9. This separating piston 7 is loaded by a spring 12 which bears on a support face 13 situated in the gas cavity 10, which support face is preferably formed by a corrugation arranged in the container 2.The spring 12 formed as a compression spring has a spring force which is greater than the friction force acting onto the separating piston seal 9 as a result of friction on the internal surface of the cylinder 2 and on the external surface of the piston rod 3. Thus the object is achieved that the pressure in the liquid-filled annular chamber 11 is greater than the pressure in the gas cavity 10 in every operating condition of the gas spring. This also has the consequence that the gas diffusion out of the gas cavity 10 into the liquid-filled annular chamber 11 is minimised. Re-setting of the separating piston seal 9 is guaranteed under all operating conditions, so that changing temperatures or changing pressure, caused by the actuation of the gas spring, effect no transition of even slight gas quantities out into the liquid-filled annular chamber 11. The additional pressure force exerted by the spring 12 upon the separating piston 7 can be made so great that, even in unfavourable cases, a higher pressure always prevails in the liquid-filled annular chamber 11 than on the other side of the piston rod seal 6. Accordingly even in such cases of utilisation the piston rod seal 6 can be made as a simple seal, since it is loaded only in one pressure drop direction.

The form of embodiment according to Fig.

2 differs from that according to Fig. 1 essentially in that the separating piston 7 is formed by a gasket 14. This gasket 14 separates the liquid-filled annular chamber 11 from the pressurised gas cavity. The spring 12 supported on the support face 13 and situated in the gas cavity 10 acts through a support washer 15 upon the gasket 14 and acts in parallel to the force exerted by the gas pressure of the gas cavity 10 upon the separating piston 7.

In place of the spring 12 formed as a helical compression spring it is of course possible to use mechanical or pneumatic spring elements of any desired configuration, which exert upon the separating piston 7 a spring force acting in parallel to the pressure of the gas cavity 10. It is even possible that the helical compression spring is replaced by a secondary annular gas chamber which is defined by the separating piston 7 on the one hand and a further separating piston adjacent the support face 13 on the other hand.

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.

It is to be noted that the reference numbers in the claims are only provided in view of facilitating the udnerstanding of the claims.

These reference numbers are by no means to be understood as restrictive.

Claims

1. A pneumatic device comprising: means defining a container (2), said container (2) having an internal surface; a piston rod member (3) entering into said container (2) through a piston rod guiding and sealing unit (5, 6), said piston rod member (3) having an axis and an external surface and being movable in the direction of said axis inward and outward of said container (2); an annular separating wall unit (7) in sealing engagement with both the external surface of said piston rod member (3) and the internal surface of said container (2), said annular separating wall unit (7) being capable of axial movement with respect to both said external surface of said piston rod member (3) and said internal surface of said container (2);; an annular sealing chamber (11) being de-fined by said external surface of said piston rod member (3) and said internal surface of said container (2) axially between said piston rod guiding and sealing unit (5, 6) and said annular separating wall unit (7); a body of sealing liquid within said annular sealing chamber (11); a working cavity (10) within said container (2) on the side of said annular separating wall unit (7) which is remote from said piston rod guiding and sealing unit (5, 6); a volume of gas under pressure within said working cavity (10);; spring means (12) distinct from said volume of gas under pressure and acting in axial direction onto said annular separating wall unit (7), characterized in that said spring means are arranged such as to increase the pressure of said sealing liquid within said annular sealing chamber (11) beyond a pressure resulting from said volume of gas under pressure.

2. A pneumatic device as set forth in claim 1, said spring means (12) being compressive spring means (12) and being supported by a support face (13), said support face (13) being provided within said working cavity (10) by said means defining said container (2).

3. A pneumatic device as set forth in claim 1 or 2, said spring means (12) comprising a helical compression spring (12).

4. A pneumatic device as set forth in one of claims 1 to 3, said spring means (12) acting onto said annular separating wall unit (7) in parallel with the action of said volume of gas under pressure.

5. A pneumatic device as set forth in one of claims 1 to 4, said spring means (12) being subject to such a prestress that the pressure of said sealing liquid within said annular seaiing chamber (11) exceeds the pressure of said volume of gas under pressure under substantially all working conditions.

6. A pneumatic device as set forth in claim 5, said spring means (12) being subject to such a prestress that the pressure of said sealing liquid within said annular sealing chamber (11) exceeds the pressure of said volume of gas under pressure under all working conditions.

7. A pneumatic device as set forth in one of claims 1 to 6, said spring means (12) being subject to such a prestress that the pressure of said sealing liquid within said annular sealing chamber (11) is greater than atmospheric pressure surrounding said pneumatic device (1) under substantially all working conditions.

8. A pneumatic device as set forth in claim 7, said spring means (12) being subject to such a prestress that the pressure of said sealing liquid within said annular sealing chamber (ii) is greater than atmospheric pressure surrounding said pneumatic device (1) under all working conditions.

9. A pneumatic device as set forth in one of claims 1 to 8, said spring means (12) being subject to such a prestress as to overcome frictional forces acting onto said annular separating wall unit (7) in axial direction as result of sealing engagment with said external surface of said piston rod member (3) and said internal surface of said container (2).

10. A pneumatic devive as set forth in one of claims 1 to 9, said annular separating wall unit (7) comprising an annular separating piston member (8) and annular sealing elements (9) provided on said annular separating piston member (8) for engagement with said external surface of said piston rod member (3) and with said internal surface of said container (2).

11. A pneumatic device as set forth in claim 10, said annular separating piston member (14) being integral with said annular sealing elements.

12. A pneumatic device as set forth in one of claims 1 to 11, said piston rod member (3) being connected to a working piston unit (4) within said working cavity (10) said working piston unit (4) dividing said working cavity (10) into two working chambers, passage means being provided for connecting said working chambers.

13. A pneumatic device as set forth in claim 12, said passage means comprising throttling means.

14. A pneumatic device as claimed in claim 1, substantially as described herein with reference to and as illustrated by any one of the examples shown in the accompanying drawing.