Patent Application
20060079360
The invention relates to a belt tensioning device having a substantially cylindrical receiving housing and a hub coaxially arranged therein. The receiving housing and the hub are supported so as to be rotatable relative to one another as well as supported by a helical torsion spring so as to be pretensioned relative to one another, and having a damping device which comprises a circumferentially slotted damping bush and a strip spring adapted to the damping bush.
A belt tensioning device of this type is known from the German Patent Publication DE 101 31 916 A1. Here the strip spring encloses the damping bush, with both being arranged at a distance from the helical torsion spring which is positioned on a larger radius and is connected in a rotationally fast way to the receiving housing on the one hand and the hub on the other hand. The spring force of the torsion spring is transmitted via a roller carrier and a roller in the form of a pretensioning force to a tensioning belt, with the damping mechanism having the task of claming the spring/mass system and of avoiding undesirable belt vibrations. The damping effect in this case is clearly asymmetric, and with a tightening strip spring there occurs a higher damping rate and with an opening strip spring there occurs a lower damping rate. In many cases, the belt tensioning device of this type can achieve satisfactory damping rates.
The object of the present invention is to propose a belt tensioning device which, while comprising an extremely compact design, ensures a particularly high damping rate which is urgently required. In view of the present trend of having charged engines with a small piston displacement in connection with a very high performance rate and a highly non-uniform crankshaft rotation.
The objective is achieved by providing a belt tensioning device of the initially mentioned type which is characterized in that the damping bush rests against the inside of the receiving housing. The strip spring is arranged between the damping bush and the torsion spring and the strip spring and the torsion spring are connected in series, wherein one of the two is supported on the receiving housing and the other one of the two on the hub.
The means described here ensure a compact shape with a very small housing diameter. As compared to prior art solutions, the invention requires only a small number of components, so that the production costs are highly advantageous. The axial position of the damping device can vary, so that heat dissipation can be effected either via the housing base or via a cover at the hub. As will be described in detail in connection with the drawings, a free end of the helical torsion spring is supported in a play-free way on an angled free end of the strip spring, thus effecting a transmission of force in a tangential direction with reference to the housing axis in order to increase the radial contact pressure force of the strip spring relative to the damping bush. The latter preferably is made of plastic. The strip spring itself is designed in such a way that it is used with a predetermined calculated pretension, thus applying a largely constant radial force radially outwardly to the damping bush. The pretensioned torsion spring, too, is tightened radially and applies radial forces to the damping sleeve. The total friction decisive for the damping effect thus consists of two separately settable and definable factors:
In view of the selected arrangement of movable and stationary components, there occurs a damping effect which is asymmetric relative to the direction of rotation, such as it is known from prior art belt tensioning devices.
In the preferred embodiment, the receiving housing comprises screwing means for being fixed to a machine component, and the roller carrier which is movable around the axis of rotation is connected to the hub.
The hub is preferably integrally connected to a housing cover which closes the receiving housing. At one spring end, the strip spring can engage the housing cover by means of an engaging lug formed on to the strip spring. As already mentioned, the strip spring, at its free end, is supported on the free end of the torsion spring which, in turn, by means of its free end, is supported in a form-fitting and positive way on the receiving housing. The two springs are built in under pretension, with the relative rotational movement between the hub on the one hand and the receiving housing on the other hand, being limited by mutual abutment means. This abutment means, more particularly, is provided directly at the receiving housing on the one hand and at the housing cover connected to the hub on the other hand. Between the hub and the respective bearing journal at the receiving housing, there is preferably arranged a friction-reducing bearing bush.
A belt tensioning device of the type described makes it possible to achieve damping values greater than 50%, i.e. the amplitude value of damping (Nm)—with reference to the spring pretension in the nominal position (Nm)—is to be greater than 50%.
A preferred embodiment of an inventive belt tensioning device is illustrated in the drawings and will be described below.
The other free end 15 of the strip spring 14 is bent inwardly. This free end 15 of the strip spring 14 supports the torsion spring 13 on its free end. The second end 27 of the torsion spring 13 rests against the inside of the receiving housing 11 in a rotationally fast way.
The outside of the strip spring 14 is surrounded by the damping sleeve 16 which can be seen to be provided with a circumferential slot 29 dividing the circumference of the sleeve.
In
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2004 047422.2 | Sep 2004 | DE | national |
