Torque Converter Transient Dynamics Theoretical And Experimental Studies

Torque converters are key components of automatic transmissions. They have critical efects onfuel economy, vehicle performance, and drivability. Transient dynamics are dominant duringvehicle acceleration and deceleration process. The steady state performance of the torqueconverters have been studied for many years. There are few works investigating transientbehavior, especially for experimental studies. This thesis investigates the transient dynamicsof automatic transmissions theoretically and experimentally.The dynamic modeling of torque converters is based on one dimensional concentrated flowtheory. Expressions describing transient state torque ratio and K factor variation with respectto the speed ratio are derived by neglecting transient fluid efects on the flow rate. Transientvariables are defned to indicate the strength of the transient condition. Lab experiments arecarried out on a fully automatic controlled dynamometer that is programmed to follow a pre-defned test procedure. Transient tests regulate the speed to a constant level on either thepump or the turbine side, meanwhile forcing the torque on the other side to step from oneinitial value to another fnal value as fast as possible. Diferent combinations of speed levelsand torque step initial and fnal values capture the transient characteristics. Torque ratio andK factor curves both before and after inertia efects fxed are plotted to investigate the annularfluid efect contribution to the total transient efect. Colormaps and contour plots with thecolors/contour lines representing the value of the transient variables are drawn for the transientefect studies.Analyzing converter phase parts on the torque ratio and K factor plots, it is concluded thatthe transient annular fluid efect is not signifcant compared with the inertia efects. This istrue even when the transient condition is relatively strong. The stator inertia and the transientfluid efect give rise to a coupling point shift phenomenon is observed. The coupling point shift denotes the delay of the phase exchange threshold when the torque converter is under transientoperation. It causes signifcant errors in computer simulations.