Mechanism of macroscopic hot spot formation in Cu-based wet clutches considering spline geometry and thermo-mechanical coupling

Temperature variations critically influence the engagement performance of wet clutches, often leading to the failure of friction components. However, conventional thermal models frequently simplify geometric details, resulting in an insufficient understanding of how structural features like splines affect localized thermal stress. To address this gap, a three-dimensional thermo-mechanical coupling model explicitly incorporating spline geometry was developed and solved using the finite element method. The model was validated against full-scale experimental data, achieving high accuracy with relative errors within 3.0%. Simulation results reveal that localized macroscopic hot spots develop, and their locations are systematically correlated with the spline positions. The formation of these hot spots is attributed to the combined effect of (i) mechanical stress induced by elastic deformation due to the spline constraints and (ii) thermal stress arising from thermal expansion under a non-uniform temperature field. Parametric analyses indicate that the rate of change of the temperature gradient with increasing rotational speed is 66.9% higher than that with applied pressure, whereas increasing oil temperature has a minor influence (within 6.1%). This study provides theoretical insights into the spline-induced thermal localization and offers valuable guidance for the design and optimization of friction components.