"REPRINT.—- Paper was presented at the National Passenger Car, Body, and Materials Meeting of the Society of Automotive Engineers at Detroit, Michigan on March 6, 19f>2. Subject to revision. Permission to publish this paper, in full or in part, after its presentation and with credit to the author and the Society, may be obtained upon request. The Society is not responsible for statements or opinions advanced in papers or dis­ cussions at its meetings* MILITARY TORQUE CONVERTER TRANSMISSIONS FOR TRACK-LAYING VEHICLES By J, E, Storer Allison Division General Motors Corporation The high performance of this country's new series tanks, cargo carriers, and other track-laying Military vehicles now in production is the result of long range planning and development, started before the end of World War U. Under the leadership and control of Detroit Arsenal, Industry was asked to design improved transmissions as part of a new components development program to match the new vehicle developments. It was desired to shape the new hulls around the smallest practicable power package of engine, cooling system, transmission and steering - braking systems, By including in the transmission unit the steering and braking, and by moulding this unit for each vehicle series into an outline arrangement to best match the appropri- - ate engines, much hull space could be saved. The space saved could be used to permit the installation of more powerful engines in the same hull sizes, or could enable smaller, lighter vehicles to be designed. In either case, vehicle power - weight ratios could be improved without sacrifice of other important Military characteristics• It was required that full eapital be made of prior evolutionary develop­ ments in tank transmissions. Torque Converters with power shift gear changes were an already-proved requirement for best performance and handling. A series of trans­ mission design objectives could now be established. Among these objectives were the following: Downloaded from SAE International by University of Leeds, Monday, September 24, 2018- 2 - 1. Maximum power availability and performance coverage. 2. Minimum size and weight. 3. Highest vehicle maneuverability and ease of operation, it. Simplified installation and adjustment. New transmission engineering work was undertaken for Ordnance by General Motors and a series of exploratory designs and models were completed by Product Study #3, now the Transmission Development Section of General Motors Technical Center. This work became the base from which the present production Crossdrive Transmissions evolved. Before discussing the new transmissions, some of the history of earlier transmission systems used in this country's tanks will be reviewed. POWER TRAIN ARRANGEMENTS In World War H, our tanks were built with a number of combinations of manual gear shift, automatic shift and torque converter transmissions, in combina­ tion with the controlled differential. Most of the gear shift transmissions (see Figures 1 and 2) in these tanks had five forward speeds for coverage of the required performance range. With the high horsepower engines needed, heavy duty clutches requiring high manual release forces were used. In operation, it was often difficult to use the most favorable gear ratios available, since in heavy going or on grades, the tank's high rolling resistance would overcome momentum so rapidly that through the time required to shift, speed would drop too far for good operation in the next faster ratio. A natural outcome of difficult shifting was engine abuse, either through low speed lugging on power or overspeeding, particularly in coast. Many tanks were built with twin combinations of Cadillac engines and Hydra­ matic Transmissions. To extend the coverage of this automotive transmission, a 2- speed and reverse gear box was interposed between the transmissions and the controlled differential. The first Army