A SURVEY ON NEGATIVE CONTROL ARCHITECTURES FOR HYDRAULIC EXCAVATORS

The present survey is one step of a complex research activity, directed toward the conception of innovative solutions for hydraulic directional control valves for excavators of the 20-ton category. In the world scene, as far as the hydraulic circuit present in this type of machines is concerned, a wide diffusion of the Negative Control and Positive Control architectures is observed; in literature it is also possible to find "hybrid" configurations that try to optimize system operation by taking advantage of the peculiarities of the above mentioned architectures. Although the mechanical structure of the excavators is practically standardized among the different manufacturers, interesting solutions and configurations are adopted in the implementation of the directional control valve. The present work aims to analyze and describe the common features observed in some of the commercial devices for the Negative Control architecture, starting from their basic structure (i.e. layout and number of sections), to get to the study of internal regenerations and external confluences (or junctions). In order to understand, in detail, the characteristics of some constructive choices (common and not, between the manufacturers), a full excavator model was implemented in the AMESim simulation environment, that includes a complex directional control valve, actuators and a 3D mechanism with 9 degrees of freedom representing the excavator's kinematics. By means of the simulation model, using the relevant JCMAS standards as a guideline for representative working cycles, a qualitative analysis of system operation is carried out, with a particular focus on multiple actuations (complex movements).