An iterative method to determine clutch clearances in torque converters by integrating the fluid and structure analyses 2020-01-0936
Determining an amount of clutch clearance for the lockup device in a torque converter is important for its being operating precisely in the intended mode. Challenges may exist for these torque converters whose nominal clearances are on purpose very small. Any potential changes in the clutch lockup system (e.g, due to the deformation of components) may make such a small clearance instantaneously diminish during the mode of open-clutch, thus leading to unwanted drags in the clutch and unnecessary loss of energy.
In the open-clutch mode, the actual clutch clearance will be definitely different from the nominal one, because the internal load acting clutch members causes them to be deformed. For instance, the axial deformation of a piston towards the turbine tends to open the clearance more. On the other hand, the deformation on the cover where the piston is axially constrained may pull the piston closer to it and reduce the clutch clearance. All these deformations can be determined by the structural analysis if the fluid pressure around the clutch members is known. However, it has been found that the pressure distribution in a clutch chamber also depends on the very clutch gap through which the fluid flows.
This interdependence between the fluid pressure load and structural deformation entails a two-way disciplinary coupling. In the absence of abundant computation resources, a simple iterative computation method is suggested here to address this problem with some intuitive results.
In particular, a computation fluid dynamics (CFD) is started based on the model with an assumed clutch clearance. If the clearance subsequently determined in the finite element analysis (FEA) due to the CFD pressure is not the same, another CFD is run with a better assumed clearance amount. This iteration process between CFD and FEA will continue until there is only a small difference in the amount of clutch clearance between what is assumed in the CFD and what is solved in FEA based on the pressured mapped from the CFD.The effectiveness of this method will be demonstrated through a typical torque converter, in a step-by-step fashion.