An AWD vehicle can operate in 4WD/2WD either full-time or on-demand by actively controlling the clutch. Active clutch control of AWD vehicles requires an accurate prediction of system-level thermal behavior of the Rear Axle Rear Drive Module (RDM), which generally comprises various components such as bearings, gears, differentials, lube oil and clutches.
A system-level thermal model was developed in a one-dimensional (1D) framework using inputs from empirical, physics-based models and test data. Empirical models were used to obtain heating due to efficiency loss from all rotating and meshing components of the RDM. Three-dimensional computational fluid dynamics (CFD) conjugate heat transfer (CHT) simulations and bench scale testing were used to obtain oil flowrates and heating within the RDM and clutch at various speeds.
At the component-level, the 1D model includes details of the clutch pack to predict clutch interface temperature. At the system-level, details of the RDM were included and both oil and housing temperature were predicted, accounting for oil flow dynamics. The model was generalized to predict real-time thermal dynamics of the clutch and RDM for a given input torque, wheel speed and clutch slip speed.