Pritchard, E., Gould, R., and Johnson, R., "A Fluid Model Extension of the Torque Converter into the Overrunning Regime," SAE Technical Paper 2014-01-1752, 2014, doi:10.4271/2014-01-1752.
The introduction of parallel post transmission hybrid electric vehicles has demonstrated a limitation of previous mathematical models of the hydraulic torque converter. Earlier models developed by Hrovat and Tobler (2) and Kotwicki (4) in the 1980's only covered the cases of the below coupled and coupled states without anticipating the need to analyze the converter in the overrunning case. This study develops the relations for the overrunning case, allowing the reader to establish accurate predictions or computer simulations of the flow, torque, and speeds that will be result in the case of a post transmission hybrid system. Without additional measures, these post transmission hybrid systems will generate large fluid losses in the torque converter.