Optimization of the Lubrication Distribution in Multi Plate Wet-Clutches for HVT Transmissions: An Experimental - Numerical Approach

The paper investigates the lubrication flow within multi plate wet-clutches for hydro-mechanical variable transmissions in order to optimize the oil distribution and to reduce the thermo-mechanical stresses on the plates. Since experimental measurements are very difficult to carry out on a real system, CFD numerical tools are used for predicting the flow distribution in a real geometry under actual operating conditions. A modular approach is adopted for the domain subdivision in order to represent accurately the three dimensional geometrical features, while the volume of fluid approach is used to model the multi-phase flow that characterizes the component. Poor lubrication is predicted where high thermal stresses were observed during tests. Furthermore, the numerical modeling is validated against measurements carried out on an ad-hoc designed test rig, which adopts transparent PMMA and 3D-printed inserts for the flow investigation. Fast imaging techniques are used to capture the multiphase flow pattern within the clutch gear chamber. The testing facility replicates both the geometry of a real clutch and the actual operating conditions. A good agreement between the numerical and the experimental results is found and the analysis highlights the importance of modeling the multi-phase nature of the lubrication process for the accurate prediction of the oil distribution within multi plate wet-clutches. By means of the numerical analysis modifications to the inlet flow configuration and to the leakages' height are developed, leading to a better oil distribution within the clutch and to a more uniform lubrication through the plates clearances.