Permanent Preprint library Info. Sf 29 W. 39 St.. F -vi PREPRINT: Subject to revision. Per­ mission to publish this paper, in full or in part, after its presentation and with credit to the author and the Society may be ob­ tained upon request. The Society is nof re­ sponsible for statements or opinions advanced in pa­ pers or discussions at its Meetings. J. ^Nfe Siaojo Planetary Gears For Automatic Transmissions By D. T. SICKIESTEEL Detroit Gear Division-Borg Warner Corp. For presentation at the SAE ANNUAL MEETING Hotel Book-Cadillac, Detroit, Michigan January 8-12, 1951 i SOCIETY of AUTOMOTIVE ENGINEERS, Inc, 29 West 39tfc Street, New York 18, N. Y. Downloaded from SAE International by University of Leeds, Monday, September 24, 2018- 1 - Planetary gearing plays a very important part in automatic and semi­ automatic transmissions for motor vehicle use, In the passenger car field alone, over 7,000,000 units using planetary gearing have been produced and present production runs well over 13,000 per day. Figure 1 gives a general distribution according to passenger car identification. The successful application of torque converter type transmission to commercial and military vehicles indicates very definitely that automatic trans­ missions will become much more popular in bus, trucks, and tracked vehicles in the near future. In fact, research and development engineering groups already have many such designs on actual test. This of course will further the use of planetary gearing even though an auxiliary gear box may be needed to provide adequate overall ratios to give satisfactory performance under most difficult conditions, Planetary gearing basically consists of a sun gear, ring gear, and planet carrier assembly (see Fig. 2 & 3). Any of the three elements can be the input member, reaction member, or output member of the planetary gear train. This offers the transmission designer flexibility in arriving at desired gear ratios and controls for actuating input member and anchoring the reaction member to the case. When any two of the members are locked together a straight through drive results as the gear assembly turns as a solid unit (see Fig. 4)« A great many types of planetary gearsets have been designed and built, however those which have gone into mass production for automobiles are relatively few - probably the first being the Ford Model "T" Transmission (see Fig, 5). This was a so-called all spur planetary transmission having one carrier assembly in­ cluding three sets of stepped pinions driven by the engine and three sun gears acting as reaction and output members. Another type of planetary transmission used in automobiles incorporates the simple planetary gearset. Examples are the Warner Gear overdrive unit (see Fig. 6), General Motors Hydramatic (see Fig, 7 & 8), and the Detroit Gear Studebaker Transmission (see Fig. 9 & 10). Still another type transmission incorporates the double pinion planetary construction. Examples are found in the Packard (see slides 11, 12, & 13), Buick (Fig. 14), Chevrolet (Fig. 15), and Ford-Mercury Transmission (Fig. 16), DESIGN AND CALCULATIONS ' The design of a planetary gearset for an automobile transmission is based upon vehicle type and weight, engine torque and horsepower, tire size, axle ratio, and torque converter or fluid coupling performance (if used). Before the actual design of the gearset is started the number of speeds, approximate ratios, and the number of automatic shifts should be decided, The final selection of the type of gearset to be used will be a com­ promise based on the designer's solutions to some of the following problems: 1. What kind of shifts - crossover, takeaway, etc. 2. Type and number of clutching and holding elements. 3. Methods for supplying oil to clutches, bands, and lubrication. 4. Provision for adequate support for brake drums. Downloaded from SAE International by University of Leeds, Monday, Sep