EP1508696B1 - Sealing arrangement for a cylinder-piston system - Google Patents

Abstract

The sealing arrangement for a cylinder-and-piston system, in particular, in vacuum pumps comprises circumferential sealing elements (5) with free sections (5b) of which at least the one nearest to the compression space (4) is oriented away from this space.

Description

The invention relates to a sealing arrangement for a cylinder-piston system, in particular in vacuum pumps, for sealing between a cylinder inner wall and a displaceably mounted in the cylinder piston, with at least one cross-sectionally L-shaped annular sealing element, wherein a leg of the L-shaped Sealing element is fixedly mounted on the piston for static sealing and the other, free leg of the sealing element bears dynamically sealingly against the cylinder inner wall.

A generic sealing arrangement for sealing the compression space of a vacuum pump is known, for example, from US Pat. No. 5,921,755. In this known sealing arrangement, two L-shaped sealing elements are mounted on the piston so that the dynamic sealing taking over the free legs of the sealing elements abut each other progressively on the cylinder inner wall.

This known orientation of the free legs of the sealing elements has the disadvantage that increases due to the occurring due to the friction on the cylinder inner wall abrasion of the sealing material in the free leg of the dead space over time, at the top, the compression space facing edge of the piston is formed between the side wall of the piston and the free leg of the sealing element or the cylinder inner wall. As with some vacuum pumps, the piston stroke is very low, for example, only 50 mm, affects already a slight increase in the dead space detrimental to the pump power.

On this basis, the invention is the technical problem of providing a seal assembly of the initially mentioned, which ensures a substantially constant performance of the cylinder-piston system with a long service life.

The solution to this technical problem is characterized in that the dynamic seal causing free leg of at least the upper, a compression space facing edge of the piston arranged sealing member is arranged in the direction away from the compression space direction on the piston.

With the inventive design of the seal assembly is the first time ensures that the material abrasion of the free leg of the seal member by the rubbing contact with the cylinder inner wall has no effect on the size of the dead space, which at the top of the compression chamber facing edge of the piston between the side wall of the piston and the Cylinder inner wall is formed.

In a preferred embodiment of the invention, at least one sealing pair consisting of two L-shaped sealing elements is arranged on the piston.

According to a first embodiment of the invention, the sealing elements of these pairs of seals are arranged on the piston in such a way that the dynamic limbs of the free legs of each pair of L-shaped sealing elements are assigned to one another.

According to a second embodiment of the pairs of seals, it is proposed that the dynamic sealing causing free legs of each pair of L-shaped sealing elements are arranged in the same, by a arranged above the piston compression chamber direction pointing away on the piston.

According to a practical embodiment of the invention, it is proposed that the seal pair consists of a sealing element arranged on the upper edge of the piston facing the compression space and a sealing element arranged on the lower edge of the piston. By using sealing elements on both edges of the piston, on the one hand, the sealing effect of the sealing arrangement is improved and, on the other hand, a tilt-free guidance of the piston in the cylinder is ensured.

The effect of the sealing arrangement can be further improved by arranging in each case a pair of seals consisting of two sealing elements at the upper edge facing the compression space and at the lower edge of the piston.

In order to ensure a constant pressure force of the free leg on the cylinder inner wall, it is further proposed with the invention that at least one free leg of an L-shaped sealing element can be pressed against the cylinder inner wall via a pressure element mounted on the piston, wherein the pressure element advantageously in an annular Groove of the piston mounted, known per se piston ring or spring ring.

As an alternative material for the pressure element, a filled plastic material, in particular an epoxy compound filled with carbon fibers, is proposed according to the invention.

If the sealing arrangement used consists of a plurality of sealing elements, advantageously at least the free leg of the upper, the compression chamber facing edge of the piston nearest sealing element via the pressure element against the cylinder inner wall can be pressed, since the main sealing force is required to prevent an increase in the dead space.

For dimensioning the sealing elements, it is proposed according to the invention that the ratio of the length of the free leg of each L-shaped sealing element to the thickness of the leg mounted fixedly on the piston be 5: 1 to 20: 1 and that of the leg fixed to the piston and causing the static sealing each L-shaped sealing element has a greater thickness than the dynamic sealing causing, applied to the cylinder inner wall free leg of this sealing element. The thickness of the free leg of each L-shaped sealing element is advantageously between 0.3 mm and 1 mm.

A sealing contact of the free legs on the cylinder inner wall with sufficient contact pressure can be further achieved in that the outer diameter of each seal member is greater than the inner diameter of the cylinder.

In order to reduce the frictional resistance between the free leg of the sealing element and the cylinder inner wall and thus to reduce the wear of the sealing material, there is any L-shaped sealing element at least in the area of the dynamic seal causing free leg of a PTFE-containing material.

Since PTFE (polytetrafluoroethylene) is not very abrasion resistant, the invention finally proposes that the PTFE-containing material of the free legs of the L-shaped sealing elements contains at least one mechanical resistance-enhancing additive, this mechanical resistance-enhancing additive advantageously being a metal -, glass, carbon or plastic material, in particular a knitted aramid fiber, such as Kevlar ®, is.

• Fig. 1 einen schematischen Querschnitt durch eine Dichtungsanordnung gemäß dem Stand der Technik;
• Fig. 2 einen ausschnittweisen schematischen Querschnitt durch eine Dichtungsanordnung gemäß einer ersten erfindungsgemäßen Ausführungsform;
• Fig. 3 einen ausschnittweisen schematischen Querschnitt durch eine Dichtungsanordnung gemäß einer zweiten erfindungsgemäßen Ausführungsform;
• Fig. 4 einen ausschnittweisen schematischen Querschnitt durch eine Dichtungsanordnung gemäß einer dritten erfindungsgemäßen Ausführungsform und
• Fig. 5 einen ausschnittweisen schematischen Querschnitt durch eine Dichtungsanordnung gemäß einer vierten erfindungsgemäßen Ausführungsform.

Further features and advantages of the invention will become apparent from the accompanying drawings in which four embodiments of a seal assembly according to the invention are shown by way of example only schematically. In the drawing shows:

• 1 shows a schematic cross section through a sealing arrangement according to the prior art;
• 2 is a fragmentary schematic cross section through a sealing arrangement according to a first embodiment of the invention.
• 3 is a fragmentary schematic cross section through a sealing arrangement according to a second embodiment of the invention;
• Fig. 4 is a fragmentary schematic cross section through a seal assembly according to a third embodiment of the invention and
• Fig. 5 is a fragmentary schematic cross section through a sealing arrangement according to a fourth embodiment of the invention.

Fig. 1 shows schematically the construction of a seal assembly for a cylinder-piston system according to the prior art.

The illustrated cylinder-piston system, which for example forms part of a vacuum pump, consists essentially of a cylinder (1) and a piston (3) mounted longitudinally displaceable in the cylinder (1) by means of a piston rod (2).

To a pressure above the piston (3) arranged compression chamber (4) through which, for example, the extracted from a container to be evacuated air from the cylinder-piston system is sealed against the rest of the cylinder-piston system pressure-tight, is in the illustrated cylinder-piston system, a pair of L-shaped sealing elements (5) are provided. Each sealing element (5) consists of a piston (3) fixedly mounted, statically sealing leg (5a) and a free leg (5b), the dynamic sealingly against a cylinder inner wall (1a) of the cylinder (1).

In this prior art representing sealing arrangement, the L-shaped sealing elements (5) are mounted on the piston (3) that the dynamic seal taking over free leg (5b) of the sealing elements (5) from each other rest against the cylinder inner wall (1a).

Due to the up and down movement of the piston (3) within the cylinder (1) are sealingly on the cylinder inner wall (1 a) abutting free legs (5 b) of the sealing elements (5) of a continuous friction, which over time to an attrition of the cylinder inner wall (1a) along rubbing sealing material leads. Since the free legs (5b) of the sealing elements (5) are designed so that they always abutment against the cylinder inner wall (1 a), one between an upper edge (3a) of the piston (3) and the free leg (5b ) dead space (6) with increasing abrasion of the sealing material, since the free leg (5b) is getting thinner. In particular, in vacuum pumps, in which the piston stroke is often very low, for example, only 50 mm, the dead space (6), which increases in the course of the operating time, has a clearly negative effect on the pumping power of the cylinder-piston system.

The cylinder-piston systems only partially shown in FIGS. 2 to 5 differ from the prior art according to FIG. 1 essentially by the different arrangement of the free leg (5b) of the upper edge (3a) of the piston (FIG. 3) arranged sealing element (5). In all exemplary embodiments illustrated in FIGS. 2 to 5, the free leg (5b) causing the dynamic sealing is at least the sealing element (5) arranged in the upper edge (3a) of the piston (3) facing the compression space (4) the direction away from the compression space (4) on the piston (3).

As can be seen from FIGS. 2 to 5 in comparison to the prior art according to FIG. 1, the embodiments of FIGS. 2 to 5 have the advantage that the material abrasion on the on the cylinder inner wall (1 a) adjacent free leg (5b) of the upper, the compression space (4) facing edge (3a) of the piston (3) arranged sealing element (5) has no effect on the size of the between the upper The edge (3a) of the piston (3) and the cylinder inner wall (1a) formed dead space (6), since the thinning free leg (5b) in these cases, a gap (7) between the side wall of the piston (3) and the cylinder inner wall (1a) below the sealing free leg (5b) increases, but not the volume of the compression chamber (4) with influencing dead space (6).

In the illustrated embodiments, the sealing elements (5) are always arranged in pairs on the piston (3), wherein in the embodiments according to FIGS. 2 and 3, the dynamic sealing causing free legs (5b) of each pair of L-shaped sealing elements (5th ) facing each other on the piston (3) are arranged, while these free legs (5b) in the embodiments according to the figures Fig. 4 and 5 in the same, from above the piston (3) arranged compression space (4) pointing away direction on the piston ( 3) are arranged.

In the first embodiment shown in Fig. 2, the pair of seals consists of one at the upper edge (3a) of the piston (3) and one at the lower edge (3b) of the piston (3) arranged L-shaped sealing element (5). The figure clearly shows the structure of each L-shaped sealing element (5) of a rigidly on the piston (3) fixedly mounted leg (5a) for static sealing, for example, between a piston body (3c) and a piston cover (3d), and a flexible free leg (5b), the piston (3) dynamically against the cylinder (1) sealingly against the cylinder inner wall (1a). The free legs (5b) of the two sealing elements (5) this pair of seals are arranged to each other so that these free legs (5b) assign each other.

The second embodiment of a sealing arrangement shown in FIG. 3 differs from the embodiment described above essentially in that both at the upper, the compression space (4) facing edge (3a) of the piston (3) and at the lower edge (3b) of the Piston (3) each one of two sealing elements (5) existing seal pair is arranged. The free legs (5b) of the two sealing elements (5) of each pair of seals are in turn arranged to each other so that these free legs (5b) assign each other. For fixing in particular of the piston edges (3a, 3b) distant sealing elements (5) of each pair of seals piston inserts (3e) are provided, via which the legs (5a) of the sealing elements (5) are rigidly fixed to the piston (3).

In order to reinforce the contact force of the free legs (5b) on the cylinder inner wall (1 a) and / or ensure that the free legs (5b) abut with sufficient sealing force on the cylinder inner wall (1a) of the cylinder (1) even with progressive material abrasion , In the upper seal pair of this embodiment, additional pressing elements (8), for example, spring rings, provided in the grooves (9) in the piston (3) mounted on the piston side abut the free legs (5b) and against the cylinder inner wall (1a press).

In the illustrated embodiment, the upper pair of seals on two pressing elements (8), while the lower seal pair no pressing element (8) is provided. Of course, it is also possible to equip the lower seal pair with pressure elements (8) or even provide a pressure element (8) in one or both pairs of seals or even form one or both pairs of seals without pressing element. The use of a pressing element (8) is in any case advantageous on the uppermost sealing element (5) next to the compression space (4), since its free leg (5b) has the task of enlarging the dead space (6) by a constant sufficient sealing prevent.

Furthermore, it is also possible in the first embodiment shown in FIG. 2 to provide both or even only one sealing element (5), preferably the upper one, with a pressure element (8).

In the third embodiment shown in Fig. 4, the seal pair again consists of one at the upper edge (3a) of the piston (3) and one at the lower edge (3b) of the piston (3) arranged L-shaped sealing element (5). However, the free legs (5b) of the two sealing elements (5) of this pair of seals are arranged relative to each other such that the free legs (5b) are arranged in the same direction away from the compression space (4) on the piston (3).

The fourth embodiment of a sealing arrangement illustrated in FIG. 5 essentially differs from the embodiment described above in that both at the upper edge (3a) of the piston (3) facing the compression space (4) and at the lower edge (3b) of the Piston (3) each one of two sealing elements (5) existing seal pair is arranged. The free legs (5b) of the two sealing elements (5) of each pair of seals are in turn arranged relative to one another such that these free legs (5b) are aligned in the same direction away from the compression space (4). For fixing in particular the piston edges (3a, 3b) distant sealing elements (5) of each pair of seals in turn piston inserts (3e) are provided, via which the legs (5a) of the sealing elements (5) are rigidly fixed to the piston (3).

Also in this illustrated fourth embodiment are again in grooves (9) in the piston (3) mounted pressure elements (8) provided to reinforce the contact force of the free legs (5 b) on the cylinder inner wall (1 a) and / or ensure that the free Leg (5b) even with progressive abrasion of material with sufficient sealing force against the cylinder inner wall (1a) of the cylinder (1).

In the embodiment shown in FIG. 5, the upper pair of seals on two pressing elements (8), while the lower seal pair, only one pressing element (8) is provided. Of course, it is also possible to equip the lower pair of seals with two pressure elements (8) or even provide a pressure element (8) in one or both pairs of seals or even form one or both pairs of seals without pressure element. The use of a pressing element (8) is in any case advantageous on the uppermost sealing element (5) next to the compression space (4), since its free leg (5b) has the task of enlarging the dead space (6) by a constant sufficient sealing prevent.

Furthermore, it is also possible in the embodiment shown in FIG. 4 to provide both or even only one sealing element (5), preferably the upper one, with a pressure element (8).

In addition to the illustrated and previously described embodiments, embodiments of the seal assemblies can be produced and made quite useful, the combinations and / or modifications of the illustrated Represent examples. For example, it is possible to form the upper sealing element (5) as shown in FIG. 2 or FIG. 4 and to design the lower sealing element (5) as a pair of seals according to FIG. 3 or FIG. 5. Likewise, the entire sealing arrangement also consist only of a sealing element (5) according to FIG. 2 or 4 at the upper edge (3a) of the piston (3), wherein in all the aforementioned sealing arrangements in turn the use of pressing elements (8) is possible and advantageous.

All illustrated and / or only described sealing arrangements are characterized in that the dynamic seal causing free leg (5b) at least of the upper, the compression space (4) facing edge (3a) of the piston (3) arranged sealing element (5) the direction away from the compression space (4) on the piston (3) is arranged, so that no enlargement of the dead space (6) takes place even with progressive abrasion of the material on the cylinder inner wall (1a) adjacent free leg (5b).

In order to reduce the frictional resistance of or on the cylinder inner wall (1a) adjacent free leg or leg (5b), each L-shaped sealing element (5) at least in the region of the dynamic seal causing the free leg (5b) of a PTFE-containing Material. Polytetrafluoroethylene (PTFE) has good sliding properties, especially under mechanical pressure loading, so that high friction losses can be avoided in this way.

On the other hand, PTFE does not have a very high abrasion resistance, it is advantageous if the PTFE-containing material of the free legs (5b) of the L-shaped sealing elements (5) at least one mechanical resistance contains reinforcing additive, which are preferably metal, glass, carbon or plastic materials, in particular knitted aramid fibers, such as Kevlar ®, are suitable.

In addition to the described possibility of forming the pressing elements (8), for example as spring washers, these pressing elements (8) can also be known per se piston rings or rings of a filled plastic material, in particular an epoxy compound filled with carbon fibers.

The sealing effect and contact force of the free legs (5b) of the sealing elements (5) on the cylinder inner wall (1a) of the cylinder (1) is in addition to the material property of the free legs (5b) and / or the pressure elements (8) of the dimensioning of the sealing elements ( 5). A permanent contact of the free legs (5b) on the cylinder inner wall (1a) can be achieved, for example, in that the outer diameter of each sealing element (5) is greater than the inner diameter of the cylinder (1).

Furthermore, the fixed bearing on the piston (3), the static sealing causing leg (5 a) of each L-shaped sealing element (5) advantageously a greater thickness than the dynamic sealing causing, on the cylinder inner wall (1 a) fitting free leg (5 b ) of this sealing element (5), wherein the thickness of the free leg (5b) of each L-shaped sealing element (5) is preferably between 0.3 mm and 1 mm.

Also, the ratio of the length of the free leg (5b) of each L-shaped sealing element (5) to the thickness of the piston (3) fixedly mounted Leg (5a) has an influence on the sealing effect of the seal arrangement. Thus, this length-to-thickness ratio is preferably 5: 1 to 20: 1.

reference numerals

1

cylinder

1a

Cylinder inner wall

2

piston rod

3

piston

3a

upper edge

3b

lower edge

3c

Piston base body

3d

piston Head

3e

spool insert

4

compression chamber

5

sealing element

5a

leg

5b

free thigh

6

dead space

7

gap

8th

pressing element

9

groove

Claims (18)

1. Seal arrangement for a cylinder/piston system, particularly in vacuum pumps, for effecting sealing between a cylinder inner wall (1a) and a piston (3) supported displaceably in the cylinder (1), comprising at least one L-shaped annular sealing element (5), wherein one limb (5a) of the L-shaped sealing element (5) for static sealing is supported in a fixed manner on the piston (3) and the other, free limb (5b) of the sealing element (5) lies in a dynamically sealing manner against the cylinder inner wall (1a), characterized in that the dynamically sealing free limb (5b) at least of the sealing element (5) disposed on the top edge (3a) of the piston (3) facing a compression space (4) is disposed on the piston (3) in the direction pointing away from the compression space (4) .
2. Seal arrangement according to claim 1, characterized in that at least one seal pair comprising in each case two L-shaped sealing elements (5) is disposed on the piston (3).
3. Seal arrangement according to claim 2, characterized in that the dynamically sealing free limbs (5b) of each pair of L-shaped sealing elements (5) are arranged on the piston (3) directed towards one another.
4. Seal arrangement according to claim 2, characterized in that the dynamically sealing free limbs (5b) of each pair of L-shaped sealing elements (5) are arranged on the piston (3) in the same direction pointing away from the compression space (4).
5. Seal arrangement according to at least one of claims 2 to 4, characterized in that the seal pair comprises a sealing element (5), which is disposed on the top edge (3a) of the piston (3) facing the compression space (4), and a sealing element (5), which is disposed on the bottom edge (3b) of the piston (3).
6. Seal arrangement according to at least one of claims 2 to 4, characterized in that on the top edge (3a) of the piston (3) facing the compression space (4) and on the bottom edge (3b) of the piston (3) there is disposed in each case a seal pair comprising two sealing elements (5) .
7. Seal arrangement according to at least one of claims 1 to 6, characterized in that at least a free limb (5b) of an L-shaped sealing element (5) can be pressed against the cylinder inner wall (1a) by means of a pressing element (8) supported on the piston (3).
8. Seal arrangement according to claim 7, characterized in that the pressing element (8) is an as such known piston ring supported in an annular groove (9) of the piston (3).
9. Seal arrangement according to claim 7 or 8, characterized in that the pressing element (8) is made of a filled plastics material, in particular an epoxy compound filled with carbon fibres.
10. Seal arrangement according to claim 7, characterized in that the pressing element (8) is a spring lock washer supported in an annular groove (9) of the piston (3).
11. Seal arrangement according to at least one of claims 7 to 10, characterized in that at least the free limb (5b) of the sealing element (5) situated nearest the top edge (3a) of the piston (3) facing the compression space (4) can be pressed against the cylinder inner wall (1a) by means of the pressing element (8).
12. Seal arrangement according to at least one of claims 1 to 13, characterized in that the statically sealing limb (5a) of each L-shaped sealing element (5) that is supported in a fixed manner on the piston (3) has a greater thickness than the dynamically sealing free limb (5b) of said sealing element (5) that lies against the cylinder inner wall (1a).
13. Seal arrangement according to at least one of claims 1 to 12, characterized in that the ratio of the length of the free limb (5b) of each L-shaped sealing element (5) to the thickness of the limb (5a) supported in a fixed manner on the piston (3) is 5:1 to 20:1.
14. Seal arrangement according to at least one of claims 1 to 13, characterized in that the thickness of the free limb (5b) of each L-shaped sealing element (5) is between 0.3 mm and 1 mm.
15. Seal arrangement according to at least one of claims 1 to 14, characterized in that the outside diameter of each sealing element (5) is greater than the inside diameter of the cylinder (1).
16. Seal arrangement according to at least one of claims 1 to 15, characterized in that each L-shaped sealing element (5) at least in the region of the dynamically sealing free limb (5b) is made of a material containing PTFE (polytetrafluoroethylene).
17. Seal arrangement according to claim 16, characterized in that the PTFE-containing material of the free limbs (5b) of the L-shaped sealing elements (5) contains at least one additive that increases the mechanical stability.
18. Seal arrangement according to claim 17, characterized in that the additive that increases the mechanical stability is a metal-, glass-, carbon- or plastics material, in particular a knitted aramid fibre, such as for example Kevlar ®.

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