The primary automatic transmission to implement a torque converter (in lieu of a fluid coupling) was the Buick Dynaflow, which was released to the 1948 product year. In regular driving, the Dynaflow used only the top rated gear, depending on the torque multiplication from the torque convertor at reduce speeds. https://arthuruvsqn.eedblog.com/33890711/the-basic-principles-of-gearbox-auto