Hydrodynamic Split Torque Transmissions Peter Bloch and Raymond C. Schneider Twin Disc Clutch Co. Mathematical Investigation HYDRODYNAMIC SPLIT torque transmissions are power transmissions with two or more parallel paths of power flow and with a hydrodynamic cou- pling or a hydrodynamic torque converter built into one of these power paths. There is already a con- siderable amount of literature about hydrodynamic split torque transmissions, which are sometimes called differential or power-shunt transmissions. This investigation is limited to the discussion of two path systems which consist of a hydrodynamic coupling or converter and a differential or planetary gearset that divides or unites the power flow. Basic Equations Figs. 1-6 show the split torque arrangements for which the following equations are applicable. In Figs. 1-3, the planetary gearset has the func- tion of a torque divider. One of the members of the planetary set is connected to the transmission input shaft, the second one drives the impeller of the hy- drodynamic unit, and the third one is coupled to the transmission output shaft which is also connected to the turbine or the runner of the hydrodynamic unit. This arrangement shall be called "input split," and the ratio of impeller torque to input torque shall be designated a,. Fig. 1 shows true split torque arrangements, with < a, < 0.5 and 0.5 < a, < 1. Part of the input power is going through the hydrodynamic unit, part of it is flowing through the mechanical power path. Fig. 2 shows positive recirculative systems or re- generative systems as they are sometimes called, * Paper presented at SAE National Farm, Construction, and Industrial Ma- chinery Meeting, Milwaukee, Sept. 16, 1959.THISTHIS PAPER deals with hydrodynamic split transmissions. The first part is a mathematical investigation of systems with two parallel power paths of the power-dividing and power-uniting type. The basic equations for split torque transmissions as well as for engine-transmission packages are discussed. General criteria for the usefulness of split torque transmissions are presented. The authors also investigate actual perform- ance characteristics of various split torque transmissions. The overall effect of the engine transmission package on engine speed, output horsepower, output torque, and overall efficiency is analyzed and discussed.* 1 < a, < 2 and 2 < a, < 00. A certain part of the out- put power of the hydrodynamic unit returns to the planetary set. The power circulating through planetary gearset and hydrodynamic unit is, there- fore, larger than the input power of the transmis- sion. The energy flow through the hydrodynamic unit is positive, that is, from impeller to turbine. Fig. 3 shows negative recirculative systems with 0 > a, > –1 and - 1 > a, > – 00. A certain amount of the mechanically transmitted power is flowing in a negative direction through the hydrodynamic unit, VOLUME 68, 1960 257Downloaded from SAE International by University of Birmingham, Monday, October 01, 2018.5 < a, < 1.0 Fig. I — Input split torque arrange- ments — true split We define the following ratios: T,a1= Input split ratio or ratio of impeller torque to input torque for input split. TtOutput split ratio or ratio of turbine a2 = 2 torque to output torque for output split.2 < a, < Fig. 2 — Input split torque arrange- ments — positive recirculative system-1 > > -ce Fig 3 — Input split torque arrange- ments — negative recirculative system from turbine to impeller and back to the planetary gearset. The above classification of input splits is appli- cable to hydraulic couplings and to regular forward converters only. If a reverse converter is used, (that is, a converter whose impeller and turbine have an opposite sense of rotation), the negative recircula- tive system, for example, becomes either a true split or a positive recirculative system. The basic mathe- matical equations for that system, however, do not have to be modified. In Figs. 4-6, th