Torque Converter CFD Engineering Part II: Performance Improvement through Core Leakage Flow and Cavitation Control

The performance of a large-volume production torque converter is slightly different from those of development prototype due to the core leakage flow. The sealing gap between the stator crown and pump or turbine core of the production converter is usually larger than that of prototypes because of fabrication method and tolerances. In this work, the core leakage flow of torque converter was investigated using CFD. The core region was modeled and coupled together with other three major components of a converter. Studies show that for a particular converter the core leakage flow could result in a 3.6% stall torque ratio reduction and a 2% peak efficiency decrease. The effects of sealing gap dimensions were also studied.

Computational investigations in this work indicated that the variation of input K factor with input torque level observed in dyno tests is due to the cavitation in the torque converter. Cavitation occurs at high input torque and low speed ratio conditions because of the high volume flow rate and large incidence angle at the stator inlet. The torque converter performances at different input torque levels were predicted by CFD simulations with a cavitation model. A new concept of the maximum input torque of a torque converter, which is limited by cavitation, is presented. The engineering solutions to reduce converter cavitation are also discussed in this paper.