CFD Methodology for Torque Converter Clutch Slipping Modeling 2024-01-2150

In torque converters, a lockup clutch is used for direct torque transfer from the engine to the gearbox. Nowadays, earlier lockup engagement is necessary to reduce fuel consumption. It introduces noise and vibration issues in the transmission that are solved by clutch slipping. However, the clutch experiences much heat because of earlier engagement, which needs to be adequately dissipated by ATF oil. To overcome this issue, multi-plate clutches are commonly used for efficient torque transfer and clutch slipping. On the other side, packaging space for torque converters is reducing at the vehicle level, especially in hybrid vehicles, which reduces the efficient cooling of clutches. So, accurate modeling of clutch slipping is necessary to improve the clutch performance and durability of the product. Clutch slipping is a transient phenomenon that involves conjugate heat transfer and rotational flow modeling. There are different ways to model clutch slipping in CFD simulations. One of the modeling methods is applying the power loss as heat flux in clutch facings. However, heat flux is a vector quantity, and its direction is defined. That means the model introduces the approximation in heat transfer direction and reduces calculation accuracy.

In this paper, power loss is applied as an energy source, which is a scalar quantity, and modeling methodology is explained. With this methodology, CFD calculation results are correlated well with test measurement, allowing to match the clutch design with the challenging packaging constraints.