S~20//f LIBRARY REPRINT—Paper was presented at a meeting ^S 5 I of the Metropolitan Section of the Society of Automotive Engineers on Jan. 9, 1958. Subject to revision. Permission to publish the paper, in full or in part, after its pre­ sentation and with credit to the author and the Society, may be obtained upon request. The Society is not responsible for state­ ments or opinions advanced in papers or discussions at its meetings. AUTOMATIC TRANSMISSIONS AND TORQUE CONVERTERS By FOREST McFARLAND Asst. Chief Engr. Buick Motor Div., GMC Society of Automotive Engineers, Inc., 1*85 Lexington Avenue, New York 17, N. Y. Downloaded from SAE International by University of Birmingham, Sunday, September 30, 2018AUTOMATIC TRANSMISSIONS AND TORQUE CONVERTERS In these days of Nuclear Fission, Rockets, and Guided Missiles, we are apt to forget the tremendous amount of effort that has been put into the design of many of our commonplace mechanisms. Our watches are a good example. Just a train of gears, run by a spring with a device we call an escapement, making them run at uniform speed. How many different forms of escapements have been devised? Time and Timekeepers by Professor W. J. Milham says there have been over one hundred different designs of escapements invented for watches. Today we have four or less in use with most of our watches carrying only one or two types. This is a design we now take for granted. The history of automatic transmissions and torque converters is a similar picture, except the "narrowing down" process in design to date has oc­ curred entirely over a period of approximately half a century, and mainly in less than twenty years, rather than over three centuries. Ideas for Automatic Transmissions for automobiles began to appear before automobiles were considered a practical means of transportation. Thomas L. and Thomas J. Sturtevant of Newton Center, Massachusetts, filed a patent application for a motor vehicle January 17, 1901, that disclosed a centrifugal clutch among other devices. Motor car development for many years consisted of making the devices simply operable and improving general function, uppermost being reliability. It is understandable why no automatic transmissions appealed considering the press­ ing problems present. Classification Automatic transmission history can be divided into the following clas­ sifications. 1. Early designs in a variety of forms. 2. Development of the step gear automatic transmission with fluid couplings. 3. Development of the torque converter transmission combined with gearing. Early Designs The early designs are shown in Fig. 1. We se?> they are classified into the following types? Inertia, Variable Crank, Hydrostatic, Pneumatic, Electric and Friction. Early inertia drives were the English Constantinesco arrangement of levers and inertia weights acting on a drive shaft through a ratchet clutch, the Spontan transmission developed by Lungstrom in Sweden, and the Hobbs transmission invented by H. F. Hobbs of Australia, both similar to the Constantinesco unit. Variable crank throw and ratchet devices were developed by DeLavaud in France and others. Hydrostatic drives consisting of a positive displacement pump driven by the engine, pumping fluid to a motor or motors driving the wheels, with means for continuously varying the ratio of flow of the fluid to give continuous­ ly variable change of speed and torque ratio, have been invented and developed since the early days of the automobile. Manley, Hele Shaw, Janney, and Lentz are a few of the many designers. Downloaded from SAE International by University of Birmingham, Sunday, September 30, 2018- 2 - Electric drives, consisting of generators attached to the engine driving electric motors, have been developed in a variety of forms. General Electric, Westinghouse^ and others have developed these drives, some initially for buses but finally mainly for rail cars. An early