Enhancing hydrostatic gear efficiency through nonlinear optimal control strategies

Energy efficiency is a common control goal for many applications, especially in vehicles or ships. This goal stands usually in contradiction with another common goal, fast response. In the case of hydrostatic gears, two basic system configurations are used, which allow better efficiency-the primary control setup-or faster responses-the secondary control. In this paper, (1) a different control setup is proposed, combining both primary and secondary control, and this new setup is shown to allow even faster responses than the secondary control having, in general, much lower energy requirements. The authors also address (2) the question of the design of the multiobjective optimal control for the proposed nonlinear structure, showing that the noninferior set, i.e. the set of points where the reduction of one cost function needs the increase of the others, depends on the control algorithm used. Comparing model reference linearization and the approximate solution of the nonlinear Hamilton-Jacobi-Bellman (HJB) equation, it is shown by simulations that the second approach is more efficient, but less robust than the first one