Method for sealing a vibration damper

Abstract

A method for manufacturing a vibration damper, wherein the vibration damper comprises an inner working cylinder and an outer container tube, wherein an end-side piston rod guide and a bottom of the container tube close the vibration damper, wherein in the partially assembled state of the vibration damper an edge of the container tube extends axially over an outer cover side of the piston rod guide and is deformed towards the cover side by a forming tool, wherein the container tube is subjected to heat treatment, wherein at least a longitudinal section of the container tube between the cover side of the piston rod guide and the bottom is heated before the edge is deformed towards the cover side until a defined increase in length of the container tube towards the cover side of the piston rod guide is present.

Description

[0001] The invention relates to a method for closing a vibration damper according to the preamble of claim 1.

[0002] In a vibration damper of the twin-tube design, with an inner working cylinder and an outer reservoir tube, the fundamental problem is that a tension chain between the base of the outer working cylinder, a bottom valve body, the working cylinder, and a piston rod guide must maintain a specific preload force level to prevent internal leakage between working chambers within the working cylinder and an annular compensation chamber between the working cylinder and the outer reservoir tube. Such leakage would cause drops in damping force.

[0003] DE 41 12 946 A1 describes a device and a method for closing a vibration damper. The vibration damper is assembled and filled, and an edge of the outer container tube projecting above the piston rod guide is bent and smoothed onto an outer cover surface of the piston rod guide by means of a tiltable forming roller. During the rolling process, an axially adjustable support bell provides preload on the components within the clamping chain.

[0004] DE 44 07 261 A1 also relates to a device and a method for sealing a vibration damper. In contrast, this device uses a conical device that preforms an edge projecting towards the piston rod guide and creates a defined sealing edge between an outer container tube and the piston rod guide. Subsequently, crimping dies partially deform the edge until it abuts the top surface of the piston rod guide. It is preferably provided that the projecting edge is heated to prevent cracking in the deformation area.

[0005] German patent DE 2 948 391 A1 discloses a method for generating axial preload within a preload chain, in which a pre-assembled vibration damper receives a radial indentation on its outer container tube, thereby reducing the length of the outer container tube relative to the working cylinder. This reduction in length creates an axial preload on the preload chain within the vibration damper.

[0006] The object of the present invention is to provide an alternative method for sealing a vibration damper.

[0007] The problem is solved by heating at least one longitudinal section of the container tube between the top side of the piston rod guide and the bottom before the edge is formed towards the top side, until a defined increase in length of the container tube towards the top side of the piston rod guide is achieved.

[0008] As the outer container tube cools and shortens in length towards the inner working cylinder, an axial preload is built up on the tension chain between the formed edge of the container tube, the piston rod guide to the bottom of the outer container tube.

[0009] Preferably, the outer container tube is heated by means of a surface heating element in order to achieve a uniform and distortion-free longitudinal expansion of the outer container tube.

[0010] According to an advantageous dependent claim, the outer container tube is heated to a maximum of 120°C. This temperature level, in conjunction with the usual length of the outer container tube, is sufficient to achieve the required thermal expansion and thus the necessary prestressing. Additionally, the internal components, some of which are made of plastic, are protected from excessive heat.

[0011] Another measure to protect the internal components is to heat the outer container tube outside of any axial contact area between the piston rod guide and the outer container tube. The piston rod guide contains thermally sensitive components, including the piston rod seal and the container tube seal itself, which are protected by this measure. Furthermore, significantly less heat is transferred to the working cylinder.

[0012] The same goal is achieved by carrying out the forming process with minimal filling of a hydraulic damping medium in a compensation chamber between the working cylinder and the outer container tube. The damping medium in the compensation chamber should not act as a conductor, transferring heat from the container tube to the working cylinder via the damping medium.

[0013] One can provide for the vibration damper to be filled after sealing. Methods are known in which the piston rod guide is partially removed from the piston rod surface.

[0014] A particularly simple solution to this sub-problem is to move a piston rod, which is axially displaceable within the working cylinder, to its maximum extension position. At maximum extension, the fill level in the compensation chamber is at its minimum, and consequently, heat transfer from the outer reservoir tube to the working cylinder is subject to the greatest conductivity, since a partial gas filling in the compensation chamber tends to have an insulating effect.

[0015] Preferably, a piston rod that is axially displaceable within the working cylinder is centered relative to the outer container tube. Due to the minimized axial preload of the components within the clamping chain during the process, centering the piston rod is advantageous for achieving a high-quality product. Because of the reduced or even eliminated axial preload caused by the assembly fixture, its design can be significantly simpler.

[0016] The invention will be explained in more detail using the accompanying description of the figures.

[0017] It shows: Fig. 1 vibration damper with device for carrying out the procedure Fig. 2. Detailed presentation of Fig. 1 before reshaping the container tube

[0018] The Fig. Figure 1 shows a possible device 1 for a method for manufacturing a vibration damper 3. The vibration damper 3 comprises an inner working cylinder 5 and an outer container tube 7. An end piston rod guide 9 and a base 11 of the container tube 7 close the vibration damper 3. The piston rod guide 9 radially positions an axially movable piston rod 13 with a piston 15. The piston 15 can optionally have at least one damping valve and divides the working cylinder 5 into a working chamber 17; 19 on the piston rod side and a working chamber 17; 19 on the remote side. The base 11 of the outer container tube 7 carries a base valve body 21, which can also optionally have damping valves.

[0019] In the fully assembled state of the vibration damper 1, both working chambers 17; 19 are filled with a hydraulic damping medium. An annular compensation chamber 23 between the outer wall of the working cylinder 5 and the inner wall of the outer container tube 5 contains at least a damping medium volume 25 and a gas volume 26, e.g., nitrogen.

[0020] The piston rod guide 9 has at least one piston rod seal 27 and one container tube seal 29. In many cases, a guide bushing 31 is used to guide the piston rod 13.

[0021] The Fig. Figure 1 shows the vibration damper in its fully assembled state.

[0022] In the partially assembled state of the vibration damper, a rim 33 of the container tube 7 extends axially over an outer cover side 35 of the piston rod guide 9, as shown in the Fig. 2 is revealed as a principle representation.

[0023] As the Fig.As shown in Figure 1, the device 1 has a surface heating element 37 that, for example, at least partially encloses the outer container tube 7. Preferably, the surface heating element is designed as an induction heating element, so that there is no open flame with soot formation. The surface heating element 37 selectively heats the outer container tube 7 over a length section 39, specifically between a contact area of ​​the container tube 7 with the piston rod guide 9 and the bottom 11 of the outer container tube 7, until a defined increase in length 41 of the edge 33 of the container tube 7 towards the cover side 35 of the piston rod guide 9 occurs. The piston rod 13, which is axially displaceable in the working cylinder, is centered relative to the outer container tube 7 by a centering sleeve 45 of the device 1. A tiltable, roller-shaped forming tool 43 of the device 1 deforms the edge 33 towards the cover side 35 and thus seals it.The preferred maximum temperature of the outer vessel tube is 120°C. This ensures a sufficiently large increase in length 41, while keeping thermally sensitive components such as the vessel tube seal 29, the piston rod seal, or the guide bushing 31 within a non-critical temperature range.

[0024] Preferably, the forming process is carried out with minimal filling of a hydraulic damping medium in the compensation chamber 23 between the working cylinder 5 and the outer reservoir tube 7. This is intended to achieve minimal heat transfer between the outer reservoir tube 7 and the working cylinder 5. The gas filling 26 in the compensation chamber 23 acts as a thermal insulation element between the outer reservoir tube 7 and the working cylinder 5. One way to implement this principle is to fill the vibration damper only after it has been sealed. Then, only air is present in the entire vibration damper 1, including the compensation chamber 23. Alternatively, the piston rod 13, which is axially displaceable in the working cylinder 5, can be moved to its maximum extension position to achieve the lowest possible fill level of the damping medium in the compensation chamber 23.

[0025] After heating the longitudinal section 39 of the container tube 7 and forming the edge 33, the heated longitudinal section 39 of the outer container tube 7 contracts axially again, thus axially pre-tensioning the working cylinder 5 between the bent edge 33, the piston rod guide 9 on the one hand and the bottom 11 of the outer container tube 7 and the bottom valve body 21 on the other. Reference sign 1 Device 3 vibration dampers 5 working cylinders 7 Outer container pipe 9 Piston rod guide 11 Bottom of the container pipe 13 Piston rod guide 15 pistons 17 piston rod side working space 19 working space far from piston rod 21 Bottom valve body 23 Compensation area 25 Damping medium volume 26 Gas volume 27 Piston rod seal 29 Container pipe seal 31 Guide bushing 33 Edge of the container pipe 35 Cover side of the piston rod guide 37 Surface heating element 39 Longitudinal section 41 Length increase 43 Forming tool 45 Centering sleeve QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 41 12 946 A1

[0003] DE 44 07 261 A1

[0004] DE 2 948 391 A1

[0005]

Claims

[1] Method for manufacturing a vibration damper (3), wherein the vibration damper (3) comprises an inner working cylinder (5) and an outer container tube (7), wherein an end piston rod guide (9) and a bottom (11) of the container tube (7) close the vibration damper (3), wherein in the partially assembled state of the vibration damper (3) an edge (33) of the container tube (7) extends axially over an outer cover (35) of the piston rod guide and is deformed with a forming tool (43) in the direction of the cover (35), wherein the container tube (7) is subjected to a heat treatment, characterized by , that at least a longitudinal section (39) of the container tube (7) between the cover side (35) of the piston rod guide (9) and the bottom (11) is heated before the edge (33) is formed in the direction of the cover side (35) until a defined increase in length (41) of the container tube (7) to the cover side (35) of the piston rod guide (9) is present. [2] Method according to claim 1, characterized by , that the outer container tube (7) is heated by means of a surface heating element (37). [3] Method according to claim 1 or 2, characterized by , that the outer container tube (7) is heated to a maximum of 120°C. [4] Method according to at least one of claims 1 to 3, characterized by , that the outer container tube (7) is heated outside of an axial contact area between the piston rod guide (9) and the outer container tube (7). [5] Method according to at least one of claims 1 to 4, characterized by , that the forming process is carried out with minimal filling with a hydraulic damping medium in a compensation chamber (23) between the working cylinder (5) and the outer container tube (7). [6] Method according to at least one of claims 1 to 4, characterized by , that the vibration damper (3) is filled after closing. [7] Method according to at least one of claims 1 to 4, characterized by , that a piston rod (13) which is axially displaceable in the working cylinder (5) is brought into the maximum extension position. [8] Method according to at least one of claims 1 to 7, characterized by , that a piston rod (13) which is axially displaceable in the working cylinder (5) is centered to the outer container tube (7).

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