Expansible chamber devices – With guide or seal on cylinder end portion for piston or...
Reexamination Certificate
1999-05-04
2001-07-03
Ryznic, John E. (Department: 3745)
Expansible chamber devices
With guide or seal on cylinder end portion for piston or...
Reexamination Certificate
active
06253661
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piston rod guide for axially slidably guiding a piston rod of a piston-cylinder unit.
2. Description of the Related Art
Prior art piston rod guides are known which are made from sintered materials. Replacements for the sintered material in piston rod guides for piston-cylinder units are increasingly being sought after, since the porosity of the sintered material requires that the piston rod guide be sealed over its entire surface with respect to the working chamber. For example, machined aluminum guides are in general use, but these guides are provided with a coating to maintain an acceptable wear performance. However, this coating has an adverse effect on the coefficients of friction.
Slide bushes have been used as a measure to counteract the less satisfactory coefficients of friction of the aluminum guide. There are two main designs of these slide bushes which differ in the position of the slide bush with respect to the piston rod seal. In a first design, the slide bush lies on a side of the piston rod seal away from the working chamber to be sealed. Although the structure of the piston rod guide is relatively simple, it is impossible for any entrained oil to reach the slide bush, and consequently the slide bush becomes worn relatively quickly, particularly in the event of transverse forces. A remedy to this is provided by an entrained oil duct, which guides controlled volumes of oil to the slide bush. However, the entrained oil duct in turn involves increased construction outlay. Reference is made, for example, to German reference DE 44 36 907 A1, which discloses a two-part piston rod guide made from sheet metal.
In principle, the fiction performance is better with a second design of piston rod guides in which the slide bush is arranged between the piston rod seal and the working chamber to be sealed. By way of example, German reference DE 42 07 099 A1 is cited, in which two annular shaped parts form a guide closure. One of the two annular shaped parts, in half section, has a U-shaped profile which forms an entrained oil duct. The second annular shaped part is designed as a multiple stepped cap and is in contact by means of an overlap in the area of the external diameters of the two annular shaped parts. There are two drawbacks associated with this design. Firstly, the guide bush is rather elastic in the transverse direction, and secondly the position of the piston rod seal is not clearly defined, since the cap of the second annular shaped part provides a bearing surface on only one axial side.
A modification to this design is described in German reference DE 42 07 053 A1, but this modification exhibits the same drawbacks described above.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a sheet-metal piston rod seal which is optimized with regard to stability in the axial and transverse directions.
According to the invention, the object is achieved by a sheet-metal piston rod guide for a piston-cylinder unit in which a piston rod is axially movably arrangable, said sheet-metal piston rod guide comprising a casing for centering said piston rod guide in the piston-cylinder unit in which said piston rod guide is to be arranged, said casing having a first axial end connected to an axially extending closure ring and a second axial end, a guide sleeve adjoining a radially inner portion of said closure ring and having a slide bush centered by said guide sleeve, a piston rod seal for sealing a working chamber of the piston-cylinder unit in which said piston rod guide is to be aranged, and a bearing ring radially extending between said guide sleeve and said casing for axially and radially supporting said guide sleeve and bearing said piston rod seal, wherein an interconnection of said bearing ring, said casing, said closure ring, and said guide sleeve comprises a closed force bearing arrangement of said piston rod guide.
Despite the use of sheet metal as the base material for the supporting part of the piston rod guide, a high level of rigidity which is comparable to that of a solid design is achieved while exploiting the cost benefit provided by a sheet-metal solution. The closed force bearing arrangement of the piston rod guide may be used as an entrained oil duct if the piston rod guide is used in a vibration absorber.
Furthermore, according to the invention, or in combination with the inventive idea described, there is provision for one annular shaped part to include the casing and to have an end face which is supported axially on the cylinder and integrally encompassing the closure ring. The integral design makes the component which has to absorb the greatest forces particularly stable. Any weld points or clamped connections are dispensed with and therefore do not present any potential problems.
A particularly sturdy structure is achieved if the end face of the annular component is extended into a radial cover against which the piston rod seal bears.
To optimize the forming outlay on the sheet-metal body, particularly with regard to the sheet-metal forming tools, the piston rod guide may comprise two annular shaped parts.
In a first embodiment, a first annular shaped part comprises the closure ring, the casing, and the guide sleeve and a second annular part comprises the bearing ring. This circumvents the operation of closing the force bearing arrangement by deforming the bearing ring. The operation of deforming the bearing ring to be assessed for each individual case, for small batches, with regard to the tooling cost.
In addition, the bearing ring may be formed by a second annular shaped part. In the simplest design, the bearing ring may be designed as a simple disk.
In a further advantageous configuration, the bearing ring has an axially extending centering ring which bears against the first annular shaped part. The centering ring additionally performs a holding function, to ensure that the bearing ring does not tilt and is not installed in a skew position.
In order to intensify this action further, the centering ring bears against the casing of the first annular shaped part. The casing has the largest radial dimension and thus provides the best holding option.
As an alternative, the second annular shaped part may be U-shaped in cross section with one side of the second annular shaped part forming the bearing ring and one side forming the guide sleeve.
To further improve the positional stability of the bearing ring, the bearing ring may be supported in the axial direction against the closure disk of the first annular shaped part.
In order for pressure to be supplied to the piston rod seal for prestressing the latter, the second annular shaped part has an encircling channel, the boundary surfaces of which assume a centering function with respect to the guide sleeve of the first annular shaped part.
With a view to obtaining a correctly oriented position of the slide bush, the bearing ring projects radially inward beyond the guide sleeve such that the projection forms a bearing surface for the slide bush.
As a further possibility for supporting the bearing ring, there is provision for the casing to have a radially inwardly directed depression for forming a rest plane for the second annular shaped part.
In order to achieve a rest plane which is as large as possible, the inwardly directed depression of the casing are designed as a continuous bead. The continuous bead has a dual function, in that the inwardly directed, continuous bead also accommodates a cylinder seal which seals the working chamber in the area of the piston rod guide.
According to a further advantageous feature, the first annular shaped part has at least one further radially inwardly directed depression, which fixes the second annular shaped part on the rest plane of the first annular shaped part. In this way, the two annular shaped parts are undetachably joined together even before fitting of the piston rod guide has been concluded.
In a further configuration, the further radially inwardly directed
Asadi Hassan
Fenn Gerald
Cohen & Pontani, Lieberman & Pavane
Mannesman Sachs AG
Ryznic John E.
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