Independent metering architectures for agricultural tractors auxiliary utilities.

The aim of this paper is to investigate the behaviour of an independent metering circuit architectures equipped with electro-hydraulic controlled multi-spools valves. The analysis is performed with reference to the hydraulic circuit and operating conditions usual of the auxiliary utilities of a mid-size power tractors. The increasing interest to reduce pollutant emissions drives the research to alternative solutions for the hydraulic circuit aimed to decrease power dissipation. From this point of view the independent metering architecture is a potentially energy saving system if compared with the traditional single spool valve architecture. This general feeling has however to be proved in the single application field because the amount of energy saved strongly depends on the kind of duty cycle involved in the analysis. For this work, a typical duty cycle for auxiliary utilities has been used, previously obtained through experimental measurement on a tractor equipped with a front loader. The duty cycle adopted involves two linear actuators, working togetherwith different loads and requiring different flows; this general condition cannot be considered favourable from the point of view of the energy saving potential of the new system but it highlights the fact that if there is an amount of energy saved in this condition, the investment need in time and costs is worth. The modelling is based on a lumped parameter approach and the independent metering valves are created developing a distributor block where any single metering element is modelled on the basis of the commercial EHPV Husco. Different control algorithms have been developed in C++ language to test different control strategy,evidencing the amount of energy saved with respect to the traditional architecture.