Dynamic friction characterization of tripod constant velocity (CV) joints: Experiments, analysis and modeling

Constant Velocity (CV) joints have been favored for automotive applications primarily due to their superiority of constant velocity torque transfer and plunging capability, compared to universal joints. High speed and sport utility vehicles with large joint articulation angles, demand lower plunging friction inside their CV joints to meet noise and vibration requirements, thus requiring more in depth understanding of their internal friction characteristics.;The main goal of this thesis is to develop a physics-based internal friction model of tripod CV joints that can be readily applied during new vehicle development. This model will replace current practices of using empirical fixed friction coefficient values. In order to achieve this goal, a prototype well-instrumented CV joint friction apparatus was designed, built and successfully used to measure the internal friction behavior of actual CV joints. The apparatus is capable of measuring a key performance parameter of friction under different realistic vehicle operating conditions of stroke speeds, CV joint articulation angles and torque variations. The validity of the experimental measurements was confirmed through FE analysis. Also, the validity of Hertzian contact analysis in a CV joint was assessed using the FE method, and found that the Hertzian solutions are practically applicable under low contacting load. These contact results were incorporated in the friction model. Subsequently the friction behavior in CV joints in terms of sliding and rolling friction was investigated by measuring the slip to roll ratio, pure sliding friction coefficient, and also by comparing these results with an elastic-plastic static friction, and rolling friction models. These measurement results and essential friction parameters were subsequently incorporated in the proposed CV joint total friction model, which includes both static and dynamic friction terms. Using the physics-based dynamic friction model, we also developed a model for the Generated-Axial-Force (GAF), which is a practical design variable as is the undesirable force that is seen at a vehicles wheel shaft. The validity of the proposed GAF model was then shown through direct comparison to actual experimental measurements. Finally, using the proposed friction and GAF models, design guidelines in terms of CV joint friction performance were suggested.