Nondimensional Characterization of the Operational Envelope of a Wet Friction Clutch

Abstract

In recent years, multidisc wet friction clutches are used in demanding powertrains of automatic and dual clutch transmissions targeting high efficiency and smoothness during gearshift. However, the developed flow pattern between the clutch discs is significantly complex and the Computational Fluid Dynamics (CFD) methods employed are quite demanding in terms of computational cost. To deal with this issue semi-analytical solutions were derived, which are limited, however, to specific problems, in order to obtain handy expressions, while also providing insight to the wet clutch physics. Nevertheless, this lack of global validity is counterbalanced by the fact that the governing equations become analytically solvable at specific operational conditions with satisfactory accuracy, provided that the simplifications rendering the truncated terms inactive hold true. In this work, a quantitative way of determining the relative weight of each term of the Navier-Stokes (NS) equations set is presented, based on the post-processing of CFD results using the Buckingham “π-theorem”. The sets of nondimensional numbers created were used to describe and model the physics of the wet clutch.

A comparative study on the effect of disks geometrical features on the drag torque of a wet friction clutch

“…( 9) was derived from the solution of simplified forms of NS equation and thus considerable truncation errors may occur if the neglected terms of Eqs. (3-4) become important [19]. In addition, the presence of grooves in the geometry of the model, indicates another potential cause for the deviation between the results from the Eqs (3,5) and the CFD model.…”