Enhancing hydrostatic gear efficiency through nonlinear optimal control strategies

Energy efficiency and short response times are usually conflicting goals. In the case of hydrostatic gears, two basic system configurations are commonly used, which allow to obtain 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. We also address (2) the question of the design of a 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. It is shown that combined use of pump and motor swash plate displacement yields a better trade-off between response speed and efficiency, and that solving approximately the nonlinear optimization problem delivers better efficiency than optimizing a system consisting of the original plant and a linearizing feedback.