Experimental validation of theoretical and numerical models of a DDV linear force motor

The performances of a Direct Drive Valve (DDV) mainly depend on the characteristics of its Linear Force Motor (LFM) and the availability of accurate models of the LFM plays an important role in the whole actuation system design. The present work deals with the modelling and the experimental characterisation of a LFM. By means of a specifically designed test equipment, the force provided by the LFM of an off-the-shelf DDV is measured as a function of the coil current and of the spool position. The experimental data are compared with the results of two models: a theoretical one, based on the magnetic circuit theory, and a numerical one, based on the FEM analysis of the electromagnetic components of the system. The numerical model provided good results over a wide range of test conditions and it allowed to evaluate correction factors for the theoretical model, related to the presence of secondary paths in the magnetic fluxes and to the distortion of the magnetic flux lines.