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The nonlinear flow characteristics induced by the geometrical features in various flow areas are often ignored. The strictly dynamical symmetry assumption is not sufficient to design the hydraulic control system by adopting the proportional valve, and the research about the proportional valve model can be used in all moving areas and all covered types of spool is deficient. To overcome this problem, the uniform nonlinear flow mathematical model for the electrohydraulic proportional valve is constructed. The relational expression between the orifice flow of the proportional valve and the geometrical future and physical characteristics of spool is constructed to obtain a series continuous nonlinear flow equations of median positive overlap, negative overlap and zero overlap proportional valve. The experiment validates that, for positive overlap, the flow input into the hydraulic tank is proportional to the displacement of the spool in the dead zone. For negative overlap, even though the spool located at the median, the flow output also exists, and induces the piston movement of hydraulic tank. This situation is consistent with the non-matching overlap response of actual negative proportional valve. KeywordsProportional valve; median overlap; flow control; nonlinear flow; nonmatching response

Analysis and Experimental Study of Median-Nonlinear Flow Characteristics in Hydraulic Proportional Valve