Hydraulic tensioning device for a flexible drive means

The invention relates to a hydraulic tensioning device for a flexible drive element, in particular, for a chain or a belt, wherein this device comprises a housing with a cylindrical inner surface at least in some sections, wherein a piston is arranged so that it can move in the axial direction in the housing, and wherein an inner space formed by the housing and the piston for holding hydraulic fluid is in connection with the surroundings via at least one ventilation drill hole machined into the housing and/or into the piston.

Hydraulic tensioning devices for chain or belt drives are known in the prior art. A tensioning device according to the class is described in DE 198 28 309 A1. In that document, a piston is arranged so that it can move in the axial direction in an element functioning as a hydraulic cylinder, wherein hydraulic fluid is located in the resulting inner space. The problem-free functioning of the desired hydraulic damping effect requires the ventilation of the system. To this end, the housing of the known tensioner carrying the cylinder has a ventilation opening.

DE 20 2007 002 456 U1 exhibits a similar solution. Also here, in a piston-cylinder system, a ventilation device is arranged that is sealed here with a valve body in the form of a ball.

The production of the ventilation possibility requires relatively high production-related expenses in the known solutions. This results in corresponding costs, not only costs concerning the production of the required parts, but also with respect to the assembly of the tensioner.

The present invention is based on the objective of refining a tensioning device of the type noted above so that it is possible to disclose a reliably vented system that distinguishes itself through a simple configuration and that can thus be realized in an economical way.

The solution by the invention for meeting this objective is characterized in that, in the region of the ventilation drill hole, a sealing element is arranged that is permeable for gas and is impermeable for hydraulic fluid.

As the material for such a sealing element, various solutions could be considered, as will be discussed farther below. It is essential that a problem-free ventilation of the inner space of the piston-cylinder system can take place without hydraulic fluid being discharged.

The sealing element could be arranged on the inner wall of the housing and/or on the inner wall of the piston. It could have a plate-shaped or disk-shaped construction.

A tensioning spring that can generate a spring force between the housing and the piston is usually arranged in the inner space. In this case, it is advantageously provided, preferably with respect to production and assembly, that the tensioning spring presses the plate-shaped or disk-shaped sealing element against the inner wall of the housing and/or the piston.

According to another solution, the sealing element can comprise a carrier element that holds at least one gas-permeable membrane. Here, the carrier element preferably has a rotationally symmetric construction. It is advantageous when the carrier element holds two gas-permeable membranes with a defined spacing. Advantageously, a filler can then be arranged between the membranes. This could involve sand, for example.

The sealing element advantageously is formed of porous material or has such material. It could be made from plastic, ceramic material, or sintered metal.

In accordance with the invention, it is possible to guarantee a reliable ventilation of the hydraulic pressure space and thus an optimization of the desired hydraulic damping effect of the tensioning system. This can be achieved in a simple and economical way. The required parts for the tensioning element and especially for the ventilation are few in terms of number and economical in terms of production. The assembly also has a simple and thus economical configuration.

Embodiments of the invention are shown in the drawings. Shown are:

FIG. 1 , schematically, in a front view shown in section, a tensioning device of a belt or chain tensioner, and

FIG. 2 , schematically, in a sectioned front view, a sealing element of the tensioning device in an alternative construction.

In FIG. 1 , a tensioning device 1 of a chain tensioner is shown schematically whose functioning has been known for a long time. Reference is made explicitly here to DE 198 28 309 A1 and DE 20 2007 002 456 U1 in which such tensioning devices are described.

The central element of the tensioning device 1 is a housing 2 that acts as a hydraulic cylinder and has a cylindrical inner surface 3 . This is used for guiding a piston 4 that is arranged so that it can move in the axial direction in the housing 2 . Because the piston 4 is constructed as a hollow cylinder-housing 2 and piston 4 form an inner space 5 that can be filled with hydraulic fluid.

For ensuring a problem-free hydraulic damping of the system, it is required that the inner space 5 can be vented. For this purpose, the piston 4 has a ventilation drill hole 6 . Naturally, the passage between inner space 5 and surroundings U is not allowed to be open, in order not to allow the hydraulic fluid to escape. Therefore, a sealing element 7 is arranged in front of the ventilation drill hole 6 . More precisely, the sealing element 7 is positioned on the inner wall of the piston 4 in front of the ventilation opening 6 .

The piston-cylinder system is loaded elastically—as in the solutions noted above—by a tensioning spring 8 acting in the axial direction. The tensioning spring is here mounted so that it holds the sealing element 7 in position, i.e., presses against the inner wall of the piston 4 .

In the solution according to FIG. 1 , the sealing element comprises a disk made from porous material, for example, made from sintered metal that is indeed permeable for gas (air) due to the existing micro-pores, but is impermeable for hydraulic fluid.

Due to the gas permeability of the sealing element 7 , a gas exchange is possible between inner space 5 and surroundings U, i.e., a ventilation of the inner space 5 can take place.

In the lower region, the housing 2 has a drill hole 13 , with a non-return valve 12 bordering this hole, as is typical in constructions according to the class.

The solution according to FIG. 2 does not have—as in FIG. 1 —a plate or disk made from gas-permeable material as the sealing element, but instead the sealing element 7 is a multi-part component.

This comprises carrier element 9 that has a rotationally symmetric construction, so that it likewise has a disk shape. The carrier element 9 holds two gas-permeable membranes 10 with a spacing a. A filler 11 is arranged between the membranes 10 —somewhat as a support element—with the filler involving sand in the embodiment. Consequently, the sealing element 7 according to FIG. 2 also fulfills the stipulated problem, i.e., it is permeable for gas (air), but is not for hydraulic fluid.

1 Tensioning device

2 Housing

3 Cylindrical inner surface

4 Piston

5 Inner space

6 Ventilation drill hole

7 Sealing element

8 Tensioning spring

9 Carrier element

10 Gas-permeable membrane

11 Filler

12 Non-return valve

13 Drill hole

U Surroundings

a Spacing