Endless belt power transmission systems or components – Friction drive belt – Including plural interconnected members each having a drive...
Reexamination Certificate
2000-12-15
2002-10-15
Butler, Douglas C. (Department: 3683)
Endless belt power transmission systems or components
Friction drive belt
Including plural interconnected members each having a drive...
C474S237000
Reexamination Certificate
active
06464606
ABSTRACT:
BACKGROUND OF THE INVENTION
This present invention relates to a drive belt for a transmission realizing a continuously variable transmission ratio. The invention further relates to a continuous band for such a drive belt and to a method for producing such a continuous band.
DESCRIPTION OF THE RELATED ART
Drive belts of the present type are generally known through their application in continuously variable transmissions. Currently applied and tested continuous bands have a transverse width ranging from 8 to 35 millimeters, a radial thickness ranging from of 0.10 to 0.30 millimeters and a longitudinal length ranging from 200 to 700 millimeters. These ranges typify the automotive application of the drive belt. The known drive belts are adopted in continuously variable transmissions, where the drive belt runs between the conical sheaves of a pair of adjustable pulleys, whereby the pulley sheaves exert a clamping force on the cross elements. The clamping force on the one hand enables torque transmission through friction between pulleys and drive belt and on the other hand urges the cross elements radially outward with respect to the rotational axle of the pulley. The actual radial movement of the cross elements is limited by the continuous band, so that the clamping force is transmitted by the cross elements to the continuous band via a normal force between the elements and the continuous band. The continuous band is thereby put under tension enabling torque transfer by the cross elements pushing each other from one pulley to the other without buckling of the drive belt. The transmission ratio of the continuously variable transmission is determined by the ratio of the running radii of the drive belt in the pulleys and can be varied from a maximum transmission ratio, wherein the running radius of the drive belt in a first pulley is maximal and that in a second pulley is minimal, via a medium transmission ratio, wherein both said running radii are virtually equal, to a minimum ratio, wherein the running radius in a first pulley is minimal and that in a second pulley is maximal.
Usually, at least the continuous band or bands are of metal to reliably cope with high torque levels that occur in automotive applications. Usually also the separate cross elements of the drive belt are of metal and are dimensioned essentially conforming. Because of its nature of use in continuously variable transmissions, the known drive belt is during operation subjected to extremely high bending and tensile stresses varying in height with the amount of bending in its longitudinal direction and with the torque transmitted by the transmission or the tension in the continuous band resulting therefrom. For this reason avoidance of breakage of a drive belt during the service life of the transmission or the vehicle wherein it is to be applied, e.g. because of fatiguing and/or wear, is a main point of consideration. In the German patent DE-A-2.643.528 it was recognized that abrasive contact between a lateral side of the continuous band and the pulleys or the cross elements, more in particular a neck part of said elements, results in excessive wear and early breakage of the continuous band. To avoid the said contact, a drive belt comprising a continuous band, preferably provided in a set of radially nested continuous bands and a number of cross elements each having a contact face, which is also known as a saddle, intended for interaction with the continuous band and provided with a convex curvature in direction transverse to the longitudinal direction of the belt is disclosed. This transverse curvature of the contact face of the cross elements is intended to obtain a tracking effect, through which the mutual orientation of continuous band and cross elements is promoted and abrasive contact between a side face of the continuous band and the cross elements is avoided.
It appeared in practice that even in cases where the drive belt was constructed according to the know art with a continuous band having a smooth, flat and essentially continuous surface, the problem of additional wear of the continuous band and sometimes of early failure of the belt with respect to what was to be expected could still be observed. Analysis of this problem revealed that it was, at least in some cases, caused by a fatigue crack originating from near the lateral sides of the continuous band. This implied that during operation relatively high Hertze stresses near the lateral sides of the continuous band can still occur, whereby the load is carried to a significant extent by the lateral sides of the continuous band.
SUMMARY OF THE INVENTION
The present invention aims at providing a solution for raising drive belt service life, by preventing said relatively high Hertze stresses near the lateral sides of the continuous band. More in particular, the invention aims at lowering the stress levels occurring during operation in the continuous band, in particular near its lateral sides, by providing it with a suitable transverse curvature, while maintaining the known tracking effect.
The drive belt in accordance with the invention had a continuous band showing a curvature in a direction transverse to its longitudinal direction, which curvature is related to the transverse curvature of the contact face of the cross elements. A drive according to the invention has an improved service life and has continuous band which is shaped in relation to the cross elements of the drive belt such, that contact between band and elements is buildup without unduly high stresses, e.g. Hertze stresses, occurring near the lateral sides of the drive belt.
It is remarked that in the state of the art, such as represented EP-A-0.305.023, drawings are incorporated showing a continuous band having a curvature which is equal to that of the cross element contact face. However, the art does not indicate the circumstances represented in these drawing, e.g. it does not indicate the transmission configuration or the amount of loading of the drive belt. In the absence of such information, it is concluded that these drawings represent a drive belt during operation, where the normal force between continuous band and cross element elastically deforms the band such that it fits the contact face of the cross element. It is further remarked, that the continuous bands of commercially available drive belts of the present type may show a transverse curvature. The curvature known from such belts, however, appears to be irrespective of the curvature of the contact face of the drive belt cross elements and more in particular is not in accordance with the present invention. Therefore it is concluded that the said transverse curvature is a consequence of the manufacturing process of the continuous band.
The solution according to the invention reflects the underlying insight that a continuous band unavoidably shows a transverse curvature, possibly due to characteristics of the manufacturing process, but in any case due to the phenomenon of anti-clastic bending. According to the insight underlying the present invention, the continuous band in the known drive belt is not only subjected to stress due to bending in the longitudinal direction of the drive belt, but also to a significant extent to stresses due to bending in a plane extending transverse to the longitudinal direction of the drive belt, which is virtually in the axial direction. As will be elaborated below, the invention includes and is based on the condition that, when the normal force between cross element and continuous band is buildup to a significant extent, the transverse curvature of the band should be less than that of the contact face. This is particularly important since the analysis of the problem revealed that the said relatively high Hertze stresses near the lateral sides of a continuous band are not only caused by axial contact of continuous band and pulley or the cross element neck part, but also by the nature of the transverse curvature of the band. In particular and surprisingly the said relatively high Hertze stresses were
Brandsma Arjen
Van Der Kamp Johannes Haaije
Van Der Meer Cornelis Johannes Maria
Van Dijnsen Gerardus Petrus Maria
Van Lith Johannes Hendrikus
Butler Douglas C.
Van Doorne's Transmissie B.V.
Young & Thompson
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