Abstract: A three element, three phase hydrodynamic torque converter having improved structural and hydrodynamic characteristics, and automatic transmissions that use a plurality of such hydrodynamic torque converters as replacements for multiple disc wet clutches or the like to effect transmission ratio changes. The hydrodynamic torque converters use a centrifugal impeller and a centrifugal turbine on the forward axial side of the torque converter, and a centripetal stator mounted to the converter shell on the rearward axial side. Three phase operation results when using the specified geometries: [1] torque multiplication, where the speed ratio i=n.sub.t /n.sub.p is greater than one; [2] coupling phase, where the speed ratio approaches one; [3] extension phase, where the speed ratio equals one and then exceeds one. For operation with speed ratio i=n.sub.t /n.sub.p in the range 0.6 .ltoreq.i .ltoreq.1.3, operational efficiency .eta. is found to be between 82 and 88 percent.