Design procedures for hybrid hydromechanical transmissions

Hybrid hydromechanical transmissions are particularly suitable for heavy vehicle and have the potential to provide better efficiencies than other hybrid architectures. However, their study must be carried out with care, since there are many possible transmission configurations and there is not one superior to the others for all applications. The particular complexity of these transmissions requires that design be treated as an optimization problem. In this paper, the optimization procedures of the "non-optimal" type are compared with the "optimal" ones, which are more precise than the former, but much heavier in terms of calculation time. The former consist of two sections. The first one is dedicated to the simultaneous optimization of the layout and components of the non-hybrid hydromechanical transmission; the second one is dedicated to the accumulator only, which can be optimized by means of simple physical laws or by means of a "Design of Experiments "procedure. The "optimal" procedures, on the other hand, proceed with the sizing of the entire hybrid transmission through a mathematical programming problem that can be single or multi-objective. It will be demonstrated that the DOE "non-optimal" procedure provides results very close to those derived from the "optimal" procedures, with considerable savings in calculation times.