Endless belt power transmission systems or components – Friction drive belt – Including plural interconnected members each having a drive...
Reexamination Certificate
1999-09-24
2001-08-14
Bucci, David A. (Department: 3682)
Endless belt power transmission systems or components
Friction drive belt
Including plural interconnected members each having a drive...
C474S201000
Reexamination Certificate
active
06273837
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to belts for a continuously variable transmission. The belts are formed by supporting a large number of metal elements on a metal ring assembly wherein multiple sheets of endless metal rings are layered.
2. Description of the Prior Art
When a metal belt of a continuously variable transmission is gripped by V-faces of its drive pulley and driven pulley, tension is generated in the metal belt. Since the tension varies depending on the drive power and the braking power produced by the two pulleys, the tensile stress applied to each metal ring changes periodically with the circulation of the metal belt. Moreover, since the circulating metal belt is bent where it wraps around the pulleys and is stretched in the chord parts between the pulleys, the flexural stress applied to each metal ring also varies periodically. As a result, the total stress (the sum of the above-mentioned tensile stress and the above-mentioned flexural stress) applied to each metal ring varies periodically during one revolution of the metal belt.
Japanese Patent Application Laid-Open No. 57-57938 has therefore proposed that by applying a) a residual compressive stress to the radially outer surface of each metal ring of the metal ring assembly and b) a residual stretching stress to the radially inner surface, the median of the stress amplitude (stress median) applied to each metal ring, which varies periodically, is made as close to 0 as possible thereby attempting to extend the wear life of the metal belt.
The above-mentioned conventional arrangement does not differentiate between the metal ring of the innermost layer from the other metal rings. A residual compressive stress is applied to the radially outer surfaces of all the metal rings, and a residual stretching stress is applied to the radially inner surfaces. Therefore, the durability of the entire metal belt is restricted by the durability of the metal ring of the innermost layer which is used under severe conditions such as those resulting from large changes in tension. Moreover, the processing needed in order to apply the residual compressive stress and the residual stretching stress to the radially outer and inner surfaces of each metal ring becomes a principal cause for increased cost.
SUMMARY OF THE INVENTION
The present invention has been conducted in view of the above-mentioned circumstances, and it is an objective of the present invention to increase the durability of the entire metal ring assembly by prolonging the wear life of the metal ring of the innermost layer which is the one which is most easily fractured.
The metal ring of the innermost layer of such a metal ring assembly is in direct contact with the saddle surfaces of the metal elements, whereas the radially inner surfaces of the other metal rings are in direct contact with the radially outer surfaces of the other metal rings. Therefore, the coefficients of friction of the two contact areas are different from each other. More specifically, the coefficient of friction of the radially inner surface of the metal ring of the innermost layer, which is in direct contact with the saddle surfaces of the metal elements, has actually been measured and found to be larger than the coefficient of friction of the radially inner surfaces of the other metal rings. As a result, as is described in detail in the embodiment below, the change in tension applied to the metal ring of the innermost layer (the difference between the maximum tension and the minimum tension in one cycle) becomes larger than the changes in tension applied to the other metal rings.
In order to achieve the above-mentioned objective, the present invention is a belt for a continuously variable transmission formed by supporting a large number of metal elements on a metal ring assembly wherein multiple sheets of endless metal rings are layered. The thickness of the metal ring of the innermost layer is different from the thickness of the metal rings of layers other than the innermost layer. The thickness of the metal ring of the innermost layer is set so that the stress amplitude applied to the metal ring of the innermost layer is not more than the stress amplitude applied to the metal rings of layers other than the innermost layer.
The invention is further characterized in that the thickness of the metal ring of the innermost layer is set so that the stress amplitude applied to the metal ring of the innermost layer is not more than the stress amplitude applied to the metal rings of layers other than the innermost layer provided that the difference between the tension applied to the chord part on the stretched side and the tension applied to the chord part on the relaxed side of the metal ring of the innermost layer is different from a difference between tension of the chord part on the stretched side and the tension of the chord part on the relaxed side of the metal rings of layers other than the innermost layer. The sum of the tension of the chord part on the stretched side and the tension of the chord part on the relaxed side of the metal ring assembly is distributed evenly in the radial direction of the metal ring assembly.
The invention is further characterized in that the thickness of the metal ring of the innermost layer is set so that at a maximum horsepower operating state, the stress amplitude applied to the metal ring of the innermost layer coincides with the stress amplitude applied to the metal rings of layers other than the innermost layer.
Since the coefficient of friction of the radially inner surface of the metal ring of the innermost layer, which is in contact with the saddle surfaces of the metal elements, is larger than the coefficient of friction between the metal rings which are in contact with each other, the change in tension applied to the metal ring of the innermost layer (i.e., a difference in tension between the chord part on the stretched side and the chord part on the relaxed side) becomes larger than the change in tension applied to the other metal rings, and the stress amplitude applied to the metal ring of the innermost layer accompanying the change in tension becomes larger than the stress amplitude applied to the other metal rings. As a result, if the thickness of the metal ring of the innermost layer is set at a value equal to the thickness of the other metal rings, when considering the total stress which comprises the tensile stress applied to the metal rings and the flexural stress applied to the metal rings , the total stress amplitude applied to the metal ring of the innermost layer becomes larger than the total stress amplitude applied to the other metal rings. Thus the durability of the metal ring of the innermost layer is restricted.
By differentiating the thickness of the metal ring of the innermost layer, which is used under the most severe conditions, from the thickness of the other metal rings so as to differentiate the flexural stress applied to the metal ring of the innermost layer from the flexural stress applied to the other metal rings, the total stress amplitude applied to the metal ring of the innermost layer can therefore be reduced so as to be not more than the total stress amplitude applied to the other metal rings. That is to say, if the thickness of the metal ring of the innermost layer is set so that the total stress amplitude applied to the metal ring of the innermost layer is not more than the total stress amplitude applied to the other metal rings, the durability of the metal ring of the innermost layer, which is used under the most severe conditions, can be made higher than the durability of the other metal rings to increase the life span of the entire metal ring assembly.
In particular, if the difference between the tension applied to the chord part on the stretched side and the tension applied to the chord part on the relaxed side of the metal ring of the innermost layer is assumed to be different from a difference between the tension of the chord part on the stretched side and the tension
Akagi Hirofumi
Shimada Takamichi
Yoshida Hideaki
Arent Fox Kintner Plotkin & Kahn
Bucci David A.
Charles Marcus
Honda Giken Kogyo Kabushiki Kaisha
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