Endless belt power transmission systems or components – Means for adjusting belt tension or for shifting belt,... – Tension adjuster or shifter driven by electrical or fluid motor
Reexamination Certificate
1999-02-02
2001-02-27
Bucci, David A. (Department: 3682)
Endless belt power transmission systems or components
Means for adjusting belt tension or for shifting belt,...
Tension adjuster or shifter driven by electrical or fluid motor
C474S138000
Reexamination Certificate
active
06193623
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates, in general, to a tensioner, and more particularly to a tensioner applied for a chain-type driving member, and being of a type having a piston guided slidably in a bore of a housing and spring-loaded against the driving member, and a damping device for damping movements of the piston by a discharge of hydraulic fluid such as engine oil from a pressure chamber via at least one leak gap of the damping device.
A chain tensioner of this type is disclosed, for example, in German Pat. No. 40 15 708 and includes an annular disk arranged in the cavity of a hollow cylindrical piston which is closed at one end by a bottom. The annular disk has one flat end face which bears against the piston bottom whose inner wall includes radially extending throttling channels which open radially outwards into an annular throttling channel. The annular disk is provided with a through-bore which communicates with these throttling channels. The pressure chamber extends into the interior of the hollow piston. The engine oil which is pressurized by inward movements of the piston flows through the through-bore of the annular disk into the throttling channels and ultimately via an opening in the piston bottom to the outside of the piston i.e., out of the tensioner.
In tensioners of this type, the damping device should be matched very closely to the operational conditions of the tensioner, whereby particular importance is being given to the configuration of the leak gap and the throttling channels because the cross section of flow provided in the throttling channels has a major influence on the damping of the piston. In the case of the referred-to conventional tensioner, the throttling channels are arranged in a crossing pattern which complicates the production. If the throttling channels are made in an extrusion process, excessive variations from specified dimensions can occur in certain cases. A higher precision in shape and size can certainly be obtained by making the throttling channels through a machining process but this involves more work and higher costs. If the piston is of single-piece structure i.e., if the piston skirt and bottom are made as an integral component, it is very difficult, and in the case of very long piston skirts, even impossible to make the leak and throttling channels on the inner wall of the piston bottom.
SUMMARY OF THE INVENTION
It is thus an object of the present invention to provide an improved tensioner, obviating the afore-stated drawbacks.
In particular, it is an object of the present invention to provide an improved tensioner which allows, in particular, a simple manufacture of the damping device while yet enabling a perfect adaptation of the leak and throttling gaps to requirements.
These objects, and others which will become apparent hereinafter, are attained in accordance with the present invention by disposing a rotationally symmetrical body, such as a cylinder, in a receptacle of the damping device such that the leak gap is formed between a wall of the receptacle and a peripheral surface of the rotationally symmetrical body.
The tensioner according to the invention permits the leak gap to be made in a very simple and economic manner with a high degree of precision. A particularly simple solution is realized by configuring the wall of the receptacle with a circular cylindrical contour. Certain deviations of the wall of the receptacle from its circular cylindrical contour are possible but such a configuration is apparently very easy to implement into practice. The leak gap is formed by simply inserting the cylinder in coaxial relationship with the circular cylindrical wall of the receptacle into the receptacle. The peripheral surface and the outer diameter of the cylinder can be fabricated to a high degree of precision. It is also possible, for instance, to use low price cylindrical rolling elements of rolling bearings whose outer diameters, by reason of their intended use, are often very precisely implemented. However, the cylinder may also be replaced by a ball to attain all the advantages of the invention. In the case of the ball, the leak gap would be formed between the equator of the ball and the wall of the receptacle.
As in the afore-described conventional tensioner, the damping device of the tensioner according to the invention is suitably arranged in the hollow piston at the upper end thereof which forms the piston bottom, and the cylinder is disposed, in accordance with the invention, concentric to the piston. In this way, any gas collected in the pressure chamber can be evacuated through the leak gap when the piston bottom is in an overhead position.
The wall of the receptacle is preferably constituted by the inner wall of the hollow piston. However, it is also possible to arrange a bushing inside the hollow piston so that the inner wall of the bushing then forms the wall of the receptacle. This solution is particularly advantageous in the case of hollow pistons with very long skirt portions. A machining of the inner wall of such pistons in the vicinity of the piston bottom is technically very complicated or even impossible because the machining tool has to be inserted very far into the hollow piston. The separate bushing proposed here offers the advantage that the inner wall which is determinative for the leak gap can be made in advance on the bushing. To prevent hydraulic fluid from leaking out between the bushing and the piston, a seal can be arranged so as to seal in the direction of the piston bottom a potential gap forming between the bushing and the piston. The seal is advantageously arranged between the piston bottom and the bushing and comprises a passage for hydraulic fluid discharged from the leak gap.
In similar manner as the conventional tensioner, the damping device and the piston bottom of the tensioner according to the present invention include intercommunicating passages through which hydraulic fluid emanating from the leak gap can be discharged.
To limit an excessively high pressure in the pressure chamber, a pressure relief valve, preferably in the form of a non-return valve, can be provided. The integration of a non-return valve in the tensioner according to the invention is particularly simple if the rotationally symmetrical body is configured as a hollow cylinder. In this case, the hollow cylinder surrounds the non-return valve, and a pressure chamber confronting end face of the hollow cylinder forms a valve seat for the valve ball which is spring-biased in the direction of the valve seat. On build-up of an excessively high pressure in the pressure chamber, the valve ball lifts off the valve seat and pressure medium flows out of the tensioner to the outside, with the above-described through-passages preferably realizing a communication between the non-return valve and the exterior of the tensioner.
REFERENCES:
patent: 4997411 (1991-03-01), Breon et al.
patent: 5366415 (1994-11-01), Church et al.
patent: 5628701 (1997-05-01), Dembosky et al.
patent: 5637047 (1997-06-01), Schulze
patent: 37 41 860 (1989-06-01), None
patent: 40 15 708 (1991-07-01), None
patent: 40 35 823 (1991-12-01), None
patent: 43 40 487 (1994-06-01), None
patent: 43 11 056 (1994-07-01), None
patent: 196 32 383 (1997-02-01), None
patent: 0 483 564 (1992-05-01), None
patent: 0 779 451 (1997-06-01), None
patent: 952375 (1999-10-01), None
patent: 306857 (1998-11-01), None
Koch Reinhard
Schuseil Bolko
Ullein Thomas
Bucci David A.
Charles Marcus
Feiereisen Henry M.
Ina Walzlager Schaeffler OHG
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