AUTOMATIC TRANSMISSIONS FOR DIESEL ENGINES R. M. SCHAEFER Allison Division General Motors Corp. 1961 SAE Summer Meeting 35 8B Downloaded from SAE International by University of British Columbia, Tuesday, September 25, 2018AUTOMATIC TRANSMISSIONS FOR DIESEL ENGINES by Robert M. Schaefer Allison Division General Motors Corporation APPLICATION TREND Since 1940, there have been many hydrau­ lic transmissions, in one form or another, applied to different types and various kinds of vehicles. These drives maybe a combination of hydraulic couplings or torque converters with friction disconnect clutch and mechanical transmission; or a torque converter and hy- draulically actuated, full-torque-shifting transmission with integral hydraulic retarder optional for certain applications. Their big­ gest penetration has been in the passenger car field where a high percentage of cars are avail­ able with automatic transmissions either as optional or standard equipment. Also the application of the hydraulic transmission to military vehicles has grown to the point where the majority of tactical tracklaying vehicles are now equipped with hydraulic drives. In off-highway equipment the increasing recognition of the advantages of hydraulic drives in the form of torque converter trans­ missions was recently shown by the American Road Builders Association show in Chicago. Back in the 1948 exhibition, there was one ve­ hicle in which a torque converter was offered. However, ten years later a number of builders displayed complete vehicle lines with torque converters. Twenty-three manufacturers ex­ hibited fifty-three vehicles featuring full- tor que-shifting hydraulic transmissions. Automatic transmissions in Highway trucks started out with the application of modi­ fied passenger car transmissions and they have contributed much to the transportation field. Several years ago, the first fully Auto­ matic Transmission was introduced to the commercial truck operator. And it is no secret that practically all major truck manu­ facturers are currently interested and active in adapting or providing this automatic trans­ mission for their line of vehicles (Figure 1). While some of these transmissions which have been applied in these various fields may not be classified as fully automatic, they do indicate the trend of the use of the torque con­ verter and some degree of automaticity. So it is easily seen from this brief re­ view that the concept for the automatic trans­ mission was established some years ago. The engineering approach to its design can be found in many engineering papers and need not be described or explained in this discus­ sion of Automatic Transmissions for Diesels. However, it is important to review some of its basic features. 1 Downloaded from SAE International by University of British Columbia, Tuesday, September 25, 2018AUTOMATIC TRUCK TRANSMISSION This new (Figure 2) concept which was developed by Allison Division, G. M. C. and introduced several years ago to the truck field comprised many new features for the com­ mercial truck or on-highway hauling equip­ ment operator. They are as follows: . Torque Converter . Automatic Lockup Clutch . 6 Speed Planetary Gear Train . Fully Automatic . Hydraulic Retarder This Fully Automatic Truck Transmis­ sion was the first non-automotive type trans­ mission offered to the truck operator. All of the features and characteristics that were de­ sired and achieved in this transmission, in addition to the consideration of the driver's influence on performance, were guided by the truck operator's yardstick - cost per ton mile. A combination of many factors such as stop-and-go operation, saiety, city traffic density, over-the-road hauling and steep grades have placed heavy burdens on both the operator's equipment and driver. Obtaining competitive performance in the face of these traffic conditions taxes life of engines and ve­ hicles, add h