Flow Control Systems for Mobile Applications

The contribution reports about some simulation studies carried out on three flow control systems used in mobile applications: a standard open centre system with 613 directional valves and fixed displacement pump (OC), a load sensing system with pressure compensated pump (LS), a closed centre system with variable setting pressure compensated pump (PC). The aim is to compare the relatively new PC system with the well established OC and LS systems. All systems have two parallel actuators (rotational) and are considered from three points of view: a) overall efficiency, which involves two different criteria: the power efficiency in a local sense (as ratio of steady state power terms), and the energy efficiency in a cyclic sense (as ratio of energy terms during a given time history); b) controllability and sensitivity, which involves the effect on the metered flow due to changes in actuator load (both resistive and overrunning) and directional valve displacement. When both actuators work, the cross effects are also considered; c) dynamic response, which involves the system behaviour when step inputs (both positive and negative) are applied to actuator load and directional valve position. The relevant response is qualified by means of the standard titles of merit (response time, rising time, overshoot, . ..). As to point a) the PC scheme is sometimes the best in the local sense, but the LS scheme seems always the best in the cyclic sense. As to point b) the PC scheme is about halfway between OC and LS; from the first it gets some large dead bands and high load sensitivities, from the second some large control ranges and favourable flow gains. As to point c) the PC scheme reacts smoothly, though with higher response times