Establishment of a Method for Predicting Cam Follower Wear in the Material Development Process 902087

Many studies have been reported concerning fundamental tribological research aimed at reducing the severe valve train wear that occurs in internal combustion engines. In this paper, cam follower wear was theoretically and experimentally analyzed at the material development stage. Statistical methods have been applied to practical use in determining the material properties quantitatively. Based on the results, a method for predicting cam follower wear has been derived which has made it possible to develop new valve train systems more efficiently. Further, a guideline for developing new wear resistant materials was also clarified. Finally, the precision high chrominum cast iron rocker arm is described, along with its application to a new NISSAN high-performance 4-cylinder DOHC engine, as an example of the use of this method to develop new wear-resistant materials.

THE DEVELOPMENT requirements for automotive engines in recent years have included high power output, compact size, light weight, drive ability and good fuel economy. Quality levels in each of these areas have shown noticeable advancement year after year along with the technological progress seen in many related disciplines. In add it ion to the improvements demanded in quality, it has also become increasingly important to shorten development lead times and to carry out development work with maximum efficiency.

Therefore a great deal of effort has been exerted at the R&D stage toward improving the wear resistance of the cam follower, as the performance of this component has a major effect on the overall quality of an automotive engine.^(1)(2)(3) Basic research activities are also being vigorously conducted in numerous fields toward the same end.

The wear phenomena of the cam follower have been the object of various R&D efforts, particularly in the field of tribology. However, an optimum solution has yet to be found for improving the wear performance of the cam follower. For this reason, it is usually necessary to rely on the experience engineers have accumulated over the years and on repeated durability tests carried out over an extended period of time.

This paper presents a new method for predicting the wear performance of wear-resistant materials which has been developed on the basis of experimental analyses and previous knowledge. The aim of this method is to improve the wear performance of the cam follower. Specifically, this work focused on scuffing as one of the most fundamental types of wear. Wear evaluation tests were conducted to determine the wear performance of various types of materials and also to investigate the wear mechanism. Then, a multiple regression analysis was performed on the test results to find the correlation between the properties of the materials and their wear performance. In the course of conducting this statistical analysis, a method was devised for predicting the effect of differences in material properties on wear performance. This technique is intended to support the development of optimum materials and to make it possible to develop materials efficiently that will contribute to improved wear performance of the cam follower. Finally, an example will be presented of the application of this wear prediction method to the development of a compact rocker arm for use in a new engine.