GB2118272A

GB2118272A - Two-tube hydropneumatic damper with combined seal/valve

Info

Publication number: GB2118272A
Application number: GB08303485A
Authority: GB
Inventors: Rudolf Schmidt; Walter Schalles; Wilfried Kramer
Original assignee: Boge GmbH
Current assignee: ZF Boge GmbH
Priority date: 1982-04-10
Filing date: 1983-02-08
Publication date: 1983-10-26
Also published as: IT8320190A0; GB8303485D0; FR2524952B1; DE3213458A1; IT1160815B; GB2118272B; DE3213458C2; FR2524952A1

Abstract

Hydraulic dampers have a working chamber 16 filled with damping fluid and receiving the working piston and the piston rod 15 and a compensating chamber 14 containing partly hydraulic fluid and partly gas under pressure. Both are connected together at the upper end through a closure unit which contains a piston rod guide 7 and a sealing/valving arrangement 5. The sealing/valving arrangement 5 seals the gas and oil media statically with respect to the outer tube 12, permits filling with gas under pressure from outside, and also allows the transfer of fluid from the working chamber to the gas chamber, whilst preventing gas flowing in the opposite direction, by means of sealing lip 11. The damper is filled with gas round the outside of shoulder 10 before plate 2, carrying the separate piston rod seal, is inserted. <IMAGE>

Description

SPECIFICATION Hydraulic damper of two-tube telescopic construction The invention relates to a hydraulic damper of two-tube telescopic construction, for example for vehicle suspensions, with a gas-filled compensating chamber defined between a cylinder barrel or inner tube and an outer cover, a piston rod extending out of the inner tube through a piston rod guide, with a piston rod seal and a gas seal for sealing off the compensating chamber against loss of gas to atmosphere and an annular space provided above the piston rod guide and communicating with the compensating chamber and with the working chamber.

Such hydraulic dampers are known (e.g.

DE-OS 30 06 174, and DE-OS 27 1 5 826), in which the seal arrangement serves simply as a gas seal for the working chamber and as a static seal for the outer cover. Such a seal arrangement is not suitable for filling the compensating chamber with gas under pressure. Moreover it is a drawback that the radial dimensions of the seal arrangement are dependent on the helical coil spring which is used. However such a helical coil spring is not absolutely essential for operation of the piston rod seal.

Starting from this standpoint, the aim of the invention is to provide a seal arrangement which acts independently of the piston rod seal and takes up little radial space, and which seals off the gas and hydraulic fluid statically with respect to the outer cover and not only permits filling with gas under pressure from outside but also achieves sealing of the gas with respect to the piston rod guide and accordingly with respect to the working chamber, and at the same time permits thepassage of hydraulic fluid from the working chamber to the compensating chamber.

This problem is solved according to the invention in that, between the outer cover and the piston rod guide there is a second annular space communicating with the compensating chamber, and that the gas seal abuts with a first shoulder against the outer cover and with a second shoulder against a disc connected to the piston rod seal, and that the gas seal has an annular sealing lip which engages resili ently against a valve seating disposed in the second annular space.

In this arrangement it is of advantage that not only is the passage of hydraulic fluid from the working chamber to the gas chamber permitted but also a static seal is obtained with respect to the outer cover, the gas seal being independent of the piston rod seal.

The gas seal may have a flange extending in the direction of the piston rod, the flange being provided for forcible location between the disc and the piston rod guide. By means of this location a connection is obtained between the actual piston rod seal and the gas seal. The two seals which are individual before assembly are, after assembly, brought together at this point to form a combined seal arrangement.

According to a further important feature of the invention it is provided that a metallic disc is used as the flange, of which the region facing towards the gas seal extends at an angle into the second annular space and that the gas seal is rigidly bonded to the flange, for example by vulcanisation. The flange is preferably bent back at 45 , this bent-back region having on the inside a vulcanised-on sealing lip and on the outside a vulcanised-on sealing bead. This flange serves for axial loading, the sealing lip and the sealing bead being inserted between the rod guide and the outer cover.

According to a particularly advantageous embodiment of the invention an annular projection or collar is formed, extending axially in the direction of the piston rod seal, by the first and second annular spaces of the piston rod guide, in which collar there is arranged at least one passage disposed circumferentially.

These passages allow the transfer of hydraulic fluid from the working chamber to the gas chamber. The sealing lip of the gas seal lies in sealing engagement with the piston rod guide and only opens for the quantity of hydraulic fluid returning via the bearing annular gap and the passages from the working chamber to the compensating chamber. It prevents flow of gas in the opposite direction from the compensating chamber to the working chamber and thus acts as a non-return valve.

However, before assembly of the piston rod seal, this gas seal allows the compensating chamber to be filled with gas and likewise serves as a gas-blocking non-return valve.

Moreover it is provided that the flange is arranged between the face of the annular web and the disc and that the disc is connected in a force-fitting manner to the outer tube. After the compensating chamber has been filled with gas under pressure, the piston rod seal is brought to its final position and thereby secures the flange of the gas seal so t';at subsequently the disc of the piston rod seal can be connected to the outer cover.

A further embodiment envisages that, for the connection between the outer cover and the disc, the outer cover is flanged over or beaded over.

According to a further important feature of the invention it is provided that the first shoulder of the gas seal has an outside diameter smaller than the inside diameter of the outer cover and that the second shoulder is in the form of an annular bead.

Here it is of advantage that, before the piston rod seal takes up its final position on assembly, a filling with gas under pressure can be undertaken through gaps between the disc of the piston rod seal and the sealing bead and the outer cover of the damper with atmosphere excluded. The gas under pressure can enter the damper without resistance. After the piston rod seal has been pushed into its final position, the disc of tne seal is forcefitted to the flange of the gas seal and simultaneously an axial pressure is exerted on the sealing bead of the gas seal so that the gas seal is deformed radially outwards and the actual sealing between the gas seal and the outer cover tube is obtained.

An embodiment of the invention will now be further described by way of example only with reference to the accompanying drawings, of which: Figure 1 is a longitudinal section through the piston rod guide region of a hydraulic twotube telescopic vibration damper before final closing; and Figure 2 is a longitudinal section through the rod guide region of a hydraulic two-tube telescopic vibration damper after closing.

In Fig. 1 a hydraulic two-tube vibration damper for motor vehicles is shown in a partial view in section in the region of the closure unit. It comprises substantially the outer cover 1 2, the piston rod 1 5 and the cylinder barrel or inner tube 1 3. Between the outer cover 1 2 and the inner tube 1 3 is formed the compensating chamber 1 4, and between the piston rod 1 5 and the inner tube 1 3 is the working chamber 1 6. Above the inner tube 1 3 or cylinder barrel is the piston rod guide 7 of which the outside diameter is received in the outer cover 1 2. Above the rod guide 7 there is a gas seal 5 which has an outside diameter smaller than the inside diameter of the outer cover 12, leaving a gap 4.

The gas seal 5 is vulcanised to a bent-back portion 9 of a flange 8. On that face of it which is away from the rod guide 7 the gas seal 5 has an annular sealing bead 10 which serves for sealing with respect to the disc 2 after assembly. In addition the gas seal 5 has a sealing lip 11 which extends axially into a second annular space 20 and acts as a nonreturn valve.

The compensating chamber 14 is filled with gas through gaps 3 and 4 and through a passage 1 9 of the piston rod guide 7.

In Fig. 2 the damper is shown closed and here a piston rod seal 1 has been brought to its final position so that a disc 2 presses the flange 8 against the annular projection or collar 6, the sealing bead 10 being radially deformed under the axial pressure and -the gas seal 5 acting to seal off the outei cover 1 2 and the disc 2. In this way the static seal is obtained. Finally the free end of the outer cover 1 2 is beaded over.

Through a bearing ring gap 1 7 and passages 1 8 and 19, on operation of the damper, a partial quantity of hydraulic fluid can flow back from the working chamber 16 into the compensating chamber 14, the sealing lip 11 of the gas seal 5 lifting away from the collar 6 on the piston rod guide 7. The sealing lip 11 prevents the return flow of gas in the opposite direction from the compensating chamber 14 to the working chamber 1 6.

Claims

1. An hydraulic damper of two-tube telescopic construction, with a gas-filled compensating chamber defined between a cylinder barrel or inner tube and an outer cover, a piston rod extending out of the cylinder barrel through a piston rod guide with a piston rod seal and a gas seal for sealing the compensating chamber against loss of gas to atmosphere and an annular space provided above the piston rod guide and communicating with the compensating chamber and with the working chamber characterised in that between the outer cover and the piston rod guide there is a second annular space communicating with the compensating chamber, and that the gas seal abuts with a first shoulder against the outer cover and with a second shoulder against a disc connected to the piston rod seal and that the gas seal has an annular sealing lip which engages resiliently against a valve seating disposed in the second annular space.

2. An hydraulic damper according to Claim 1 in which the gas seal has a flange extending in the direction of the piston rod, the flange being provided for forcible location between the disc and the piston rod guide.

3. An hydraulic damper according to Claim 2 in which a metal disc is provided on the flange, of which the region facing towards the gas seal extends at an angle into the second annular space, and that the gas seal is rigidly connected to the flange, for example by vulcanisation.

4. An hydraulic damper according to any preceding claim in which an annular projection or collar is formed on the piston rod guide, extending axially in the direction of the piston rod seal, in which collar there is arranged at least one passage, disposed circumferentially.

5. An hydraulic damper according to any of Claims 2 to 4 in which the flange is arranged between the face of the annular collar and the disc and that the disc is connected in a force-fitting manner to the outer cover.

6. An hydraulic damper according to any preceding claim in which the outer cover is beaded over to form the force-fitting connection between the outer cover and the disc.

7. An hydraulic damper according to any preceding claim in which the first shoulder of the gas seal has an outside diameter smaller than the inside diameter of the outer cover and that the second shoulder is in the form of an annular bead.

8. An hydraulic damper of two-tube telescopic construction having a piston rod sealing arrangement substantially as described with reference to and as illustated in the accompanying drawings.