Contact Stress Reduction Mechanisms for the CAM-Based Infinitely Variable Transmission

Abstract

The Cam-based Infinitely Variable Transmission (IVT) is a new type of ratcheting IVT based on a three dimensional cam and follower system which provides unique characteristics such as generating specific functional speed ratio outputs including dwells, for a constant velocity input. This paper presents several mechanisms and design approaches used to improve the torque and speed capacity of this unique transmission. A compact, lightweight, and capable differential mechanism based on a cord and pulley system is developed to double the number of followers in contact with the cam at any time, thereby reducing the contact stress between the followers and the cam surface considerably. A kinematic model governing the motion of this differential is developed and a few experimental results from the prototype are presented, showing an overall increase in performance including a smooth output, a wide gear range, and the ability to shift under load. Plans for future improvements to the design, including an inverted external cam mechanism, is also presented along with the expected performance gains.

Design Method of Cam Steering Mechanism Based on Path Fitting

“…To calculate the tangential and normal vectors at the first point, the last row of the calculated theoretical cam vector is removed, and the penultimate row is moved to the first row to form a new vector. Due to the large number of points and the dense distribution of points, according to Lagrange's mean value theorem, the slope of the tangential vector at this point is equal to the vector direction of the line between the two adjacent points, as shown in Formula (15).…”

“…Hua [14] found that the smooth surface of the cam can be reduced by 53% maximum equivalent Von Mises stress. In the experiment, by considering using the constant speed in the staying itinerary, the contact stress was reduced to 41% [15]. Hus [16] adopted a cam with double-concave surface translation from the moving part to reduce the contact stress of the cam's equal pathway.…”

Analytic and numerical results of a disc cam bending with a roller follower

“…6 [32 , 33]. This small region exhibits a very high contact stress during the active region of the cam, when the most significant loading of the followers occurs [6]. As mentioned in earlier section, both the cam and the follower were made of mild carbon steel and the plastic deformation starts when the contact pressure reaches (2.8) of the yield stress.…”

“…Hua et al, found that the smooth surface of cam profile provides a 53% reduction in maximum subsurface Von Mises stress [5]. Contact stress can be reduced to 41% experimentally taking into consideration the dwell stroke for a constant velocity of the cam [6]. SolidWorks, Cosmosmotion and Algor softwares were used by Ghazalli to determine the stress concentration at the point of contact using the finite element analysis [7].…”