A hybrid transient/quasi-static model for wet clutch engagement

This work presents a comprehensive formulation of the equations governing the lubrication and the lock-up phases of an engaging wet clutch. A finite element model is established through the coupling of the Reynolds equation of the fluid film model with the dynamic force and torque equilibrium equations of the two-disc system. To solve the problem, an efficient hybrid simulation technique is introduced, capable of capturing the rapidly evolving transient phenomena at the start of the engagement phase, which later settles into a quasi-static one as the film thickness asymptotically decreases. The simulation tool is benchmarked against previously published results and is later used to investigate the effect of a newly introduced groove configuration utilising variablewidth grooves. The proposed geometry is compared against the well-known radial groove configuration on the engagement characteristics, resulting into decreased hydrodynamic peak force by approximately 20%. The supremacy of the proposed groove design over the standard radial geometry is further verified through a newly introduced groove design criterion that takes into consideration the relative effect of squeeze and torsional Couette flows during the hydrodynamic phase of the engagement. Finally, a comprehensive parametric study is conducted to capture the effect of the groove width and depth on the engagement variables.