Compliance and Friction in Elastic and Mechanical Joints of Race Car Suspensions

The goal of this project was to improve the understanding of various joints available for use in high performance small-scale automotive suspensions. The data and conclusions from this effort can be more widely applied to any instance where positive motion control is required with minimal or controlled levels of friction and compliance. This project involved testing and analysis of a series of mechanical joint samples obtained from the Aurora Bearing Company. The particular joint focused on for the majority of the testing is commonly known as a rod end. Ten different samples of varying materials and construction styles were tested and compared. They were evaluated for both compliance and friction over a range of loads to approximate their behavior under normal use. This data was obtained using an Instron tension-compression machine and a selection of appropriately designed and constructed fixtures. Discrete curves for the compliance of ten different samples of 5/16” rods are presented, as well as curves for the friction under load in both directions of motion (pivotal and rotational). In addition, preliminary compliance testing involving two sizes of rod ends and a similarly sized spherical bearing indicate scale and construction dependencies.

A kinematic model was developed to better understand how the measured characteristics of these joints affect their application for a Formula SAE race car suspension. Based on the model and the experimental data, incremental but significant improvements in overall suspension compliance and frictional characteristics are shown for this specific application. Conclusions based on this work indicate similar optimizations for virtually any jointed mechanical linkage where these issues are relevant.