Numerical and Experimental Study of a Novel Concept for Hydraulically Controlled Negative Loads

This paper presents a numerical and experimental investigation of a novel concept that eliminates oscillations in hydraulic systems containing a counterbalance valve in series with a pressure compensated flow supply. The concept utilizes a secondary circuit where a low-pass filtered value of the load pressure is generated and fed back to the compensator of the flow supply valve. The novel concept has been implemented on a single boom actuated by a cylinder. A nonlinear model of the system has been developed and an experimental verification shows good correspondence between the model and the real system. The model is used for a parameter study on the novel concept. From the study it is found that the system is stable for large directional valve openings and that for small openings a reduction of the oscillatory behaviour of the system can be obtained by either lowering the eigenfrequency of the mechanical-hydraulic system or by lowering the pilot area ratio of the counterbalance valve.