Metal belt and method for producing such

Details Metal belt and method for producing such Metal belt and method for producing such

1999-04-14

2001-04-17

Fenstermacher, David (Department: 3682)

Endless belt power transmission systems or components

Friction drive belt

Including plural interconnected members each having a drive...

C474S201000

Reexamination Certificate

active

06217471

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a metal belt for a continuously variable transmissions and a method for producing such, where the belt comprises at least one endless metal band, preferably provided in a set of generally conforming nested bands, at least partly being surrounded by transverse elements for at least clamping the belt in between the sheaves of a set of pulleys.
DESCRIPTION OF THE RELATED ART
Such a metal belt is generally known, e.g. from U.S. Pat. Spec. No. 3,949,621. The bands of this known construction have a generally rectangular cross section. Due to its nature of use in continuously variable transmissions, the known belt is during operation subjected to extremely high internal stresses varying in height with the radius of bending and with the moment transmitted or the pull force in a band resulting there from. For this reason avoidance of breakage of the belt during the service life of a belt, i.e. the transmission and vehicle wherein it is to be applied, is a main point of consideration with such belts, in particular with the bands of a belt.
One technical measure intended for prolonging service life is known from European patent publication EP-B-181670. This document teaches to provide permanent compression stresses in the central and edge part of the contact faces of the bands of the belt, thus resulting in a reduction of the level of locally occurring tensile stresses. The publication further teaches the deformation of the edge zones towards a confined shape so as to reduce tensile stresses, particularly occurring from bendings, as a result of which breakage caused by hairline cracks occurring from the edges would be largely avoided.
SUMMARY OF THE INVENTION
The present invention seeks to provide at least a further if not an alternative solution in raising belt service life. According to the invention this may be achieved by accurately defining a particular geometry of a bands cross-section. Bands according to the present invention show extremely small though measurable differences in the thickness along a cross section of a band. It was found in practise however, that the overall shape of a cross section influences the service life time of a belt, to the extend that extremely small deviations from an imaginary rectangular cross section of a band account for significant influence on the expected service life time of a belt.
One factor mentioned to explain the above effect is that a band shaped according to the invention provides a certain amount of precompensation for so called anticlastic deformation occurring during the operation of a belt. However, the local differences in diameter of bending caused by anticlastic deformations hardly effects increase in internal strain as may be expected locally in a band. Moreover, a full precompensation of this effect, for as far as might be achieved, would require a thickness ratios between TA and TC or TB and TC of about 0.5. Nevertheless the minimal amount of deviation from an imaginary cross section, according to the invenvention realises a significant increase in expected life time, and may advantageously be realised by a shaping roller having a relatively easy to produce conformingly shaped roller surface.
It is remarked that anticlastic deformation per se is a generally known phenomenon, e.g. from the article “an optimum study of the anticlastic deformations of strips with tapered edges” as published in the int. Journal of Mechanical Science, 1966, vol. 8. For compensating for anticlastic deformation, this article teaches to concentrate on tapering configuration of the edges. The present invention however differs from these known strip shapes in that the contact face of a band shows a deviation from a flat surface and in that the invention is related to the overall shape of a bands cross section of minimal order. Also, the general art does not take account of the function of taking up extremely high tensile forces as inherent to a bands function, nor of the material a band or strip is made of.
Further, from the article “Hypergeometric Series Solutions of some Anticlastic Deformation Problems”, by Y. C. Pao et.al., published in 1967, a strips cross section is known, the section being defined such that the local thickness is a function of the greatest thickness of the strip and the lateral displacement from a strips centre, such that the thickness of a strip constantly decreases from its greatest thickness in the centre towards zero thickness at a lateral side of the strip. The article is primarily devoted to the mathematical solutions to the problem of anticlastic deformations.
With the present invention the edge zones may comprise ordinary facet rounding or leveling of square edges, as generally known in the art. Measuring of the thickness of a bands edge position should take place beyond such rounding. Normally half a millimeter length away from the edge will provide sufficient distance to such rounding while still being close to the outer edge.
Preferably, a band has a cross section of such shape, that the flat surfaces of contact faces of a band have a smoothly curved surface. In a further development of the geometry according to the invention the thickness in between the two edges of a band is larger than the thickness of any of these. Yet according to a further feature according to the invention, the largest thickness is located substantially centrally in the middle between the edges. In the most preferred embodiment said surface of the band is of elliptical nature. This geometry according to the invention approximates, at least, or is enclosable by circular sections having radii R
1
and R
2
, such that the difference between 1/R
1
and 1/R
2
is smaller than 1.0 m
−1
, where R
1
is the radius for the ellipse of one side face, and wherein R
2
is the ellipse radius of the counter side. Where the sum of 1/R
1
and 1/R
2
should be smaller than 1.0 m
−1
.


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