Abstract
Keywords
Continuously Variable Transmission, Metal V-belt, Stress simulation, Pulley stiffness, Fatigue
Abstract
The metal pushing V-belt is a key part of the continuously variable transmission (CVT), and it is essential to know the fatigue strength of the belt in order to be able to guarantee its durability for a long operating life. Fatigue testing, however, not only requires an enormous amount of time for each variable operating condition, but it also includes the influence of the pulley on belt strength. Consequently, it is not necessarily possible to adequately know the fatigue strength of the belt itself in quantitative terms.
This paper describes how the problem was resolved by the development of a new simulation technique that simultaneously estimates the behavior and stress of a metal belt under high rotational speeds. A finite element method used in crash analysis has been adopted as the solver for the newly developed simulation. The analysis model completely represents the layered rings and many blocks that are the component parts of the metal belt, and it shifts and transmits the driving torque from the driving pulley to the driven pulley by means of frictional force on the contact surface. The flexural stiffness of the pulley in an axial direction is also taken into consideration, and that stiffness value was obtained by stand-alone static analysis of the pulley. The results showed clearly that the two edges of the innermost ring, which was estimated to be the location where damage would first appear in endurance testing, was where the greatest tensile stress was generated. Tests under different operating conditions also showed that a correlation exists between the belt fatigue life and the stress on the innermost ring. This made it possible for the first time to use an S-N diagram to judge belt durability. Meanwhile, the influence of the pulley revealed that the belt impact stress becomes greater as the flexural stiffness increases. In addition, the difference between left and right pulley rigidity causes the belt alignment to change during operation, and it was found that when a relative speed differential exists between the ring edge and the pulley or the block neck, ring edge contact may occur. The damage resulting from such ring edge contact can contribute to the deterioration of ring fatigue life. This indicates the importance of designing the pulley with the proper rigidity so that it will not cause such contact damage. The simulation technique was also applied to a belt that had been newly developed by Honda. This belt features a longer ear and a shorter block V-surface in order to enable a wider ratio range. The results showed that differences in block shape cause changes in pitching behavior under high rotational speed, and the above-mentioned S-N diagram supported the conclusion that the belt strength had changed in an advantageous direction.