Endless belt power transmission systems or components – Means for adjusting belt tension or for shifting belt,... – Guide roll mounted for movement of its axis along arcuate...
Patent
1994-12-15
1995-10-17
Buiz, Michael Powell
Endless belt power transmission systems or components
Means for adjusting belt tension or for shifting belt,...
Guide roll mounted for movement of its axis along arcuate...
F16H 708
Patent
active
054585414
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a friction-damped tensioning system for belt or chain drives which is preferably used in internal combustion engines according to the features of the preamble of claim 1.
An arrangement of this type can be found in DE-A-32 25 411. According to it a housing is provided on which is disposed a tensioning part swivellable unilaterally for receiving a tension roller. By means of a screw carried centrally through the housing the arrangement is fastened for example on the crankcase of an internal combustion engine. The shaft of the screw is encompassed in the housing by a bearing part on whose surface area a torsion spring, implemented as helical spring, is carried which is braced at one end on the flange of the bearing part and on the opposing end on the swivellable tensioning part. Between the flange of the bearing part and a carrier plate of the arrangement is inserted a damping device. When installed, the torsion spring causes a displacement of the tensioning roller in order to maintain a given belt tension force by horizontally swinging the tensioning part. This leads to a damped setting movement through the damping device. As the damping device serves an elastomer friction disk in which the coefficient of friction is negatively influenced by the temperature. To attain a high service life of the friction coating, which means avoidance of impermissible heating and high wear-and-tear, an enlargement of the friction surface or a reduced spring force are necessary. Both measures negatively affect the function or the required construction space of the arrangement.
It is therefore the task of the invention to provide a tensioning arrangement which ensures a nearly constant moment of friction independently of the temperature over the lifetime of the tensioning system, and which has a low degree of wear-and-tear and requires a relatively small friction surface.
This task is solved according to the invention through the features listed in the characterizing part of claim 1.
According to the invention a friction coating comprising an organic material is provided. The advantageously used asbestos-free material exhibits material properties whose maximum surface pressure reaches 2 N/mm.sup.2 and thus markedly exceeds the value of 0.5 N/mm.sup.2, common for synthetic materials (for example elastomers or thermoplastics). The coefficient of friction of the material according to the invention has temperature-dependent changes which are negligible compared to synthetic materials. Due to the higher permissible surface pressure it is possible to use a friction coating with smaller radial dimensions, which, consequently, permits the implementation of the entire tensioning arrangement requiring a smaller constructional space. This results in significant cost advantages.
The constructional design of the tensioning arrangement provides the division of the spring force of the loaded torsion spring through which, in the direction of the circumference, prestress is exerted onto the belt or the chain and the friction coating used for damping is exclusively acted upon by an axial force. Independently of the position of the tensioning part relative to the basic part, no dependence on the moment of friction occurs according to the invention since the friction element and, consequently, the friction coating is acted upon by an axial force which remains constant.
The friction coating is advantageously also not exposed to deformation work of any kind which, in the case of prior tensioning systems, has prevented maintaining a constant coefficient of friction and therefore has decreased the service life of the friction coating.
As a suitable material for the friction coating is used according to the invention an asbestos-free friction material based on graphite-duroplastic-unvulcanized rubber with a synthetic fiber reinforcement which a very high wear-and-tear resistance can be attained.
In one constructional embodiment the friction disk frictionally engages the friction coating fastened on the basic part. The friction
REFERENCES:
patent: 5030172 (1991-07-01), Green et al.
patent: 5250009 (1993-10-01), Sidwell et al.
patent: 5348514 (1994-09-01), Sidwell et al.
International Search Report No. PCT/EP93/01809 29 Oct. 1993.
Adler Hellmut
Polster Rudolf
Schmid Michael
Buiz Michael Powell
INA Walzlager Schaeffler KG
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