ENHANCING HYDROSTATIC GEAR EFFICIENCY THROUGH NONLINEAR OPTIMAL-CONTROL STRATEGIES

Energy efficiency and short response times are usually conflicting goa ls. In the case of hydrostatic gears, two basic system configurations are commonly used, which allow to obtain better efficiency - the prima ry control setup - or faster responses - the secondary control. In thi s paper, (1) a different control setup is proposed, combining both pri mary and secondary control, and this new setup is shown to allow even faster responses than the secondary control having, in general, much l ower energy requirements. We also address (2) the question of the desi gn of a multiobjective optimal control for the proposed nonlinear stru cture, 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 o f pump and motor swash plate displacement yields a better trade-off be tween response speed and efficiency, and that solving approximately th e nonlinear optimization problem delivers better efficiency than optim izing a system consisting of the original plant and a linearizing feed back.