Fundamental performance limitations for a class of electronic two-stage proportional flow valves

This paper examines the dynamics of a popular type of two-stage flow control valve currently seeing increased usage in electrohydraulic systems. This particular component has the trademarked name: 'Valvistor.' While several benefits do exist, there are limitations to the closed loop performance of the valve when it is included in a valve-controlled electrohydraulic system. An attractive feature of this two-stage valve is that the pilot flow can also contribute to the total flow giving higher steady state flow efficiency. However, for dynamic performance this structure results in zeros in the open loop transfer function, which will limit the closed loop bandwidth of a flow control system. This paper presents an analytical model of this particular type of valve and derives the presence of the inherit system zeros. A model simplification is also presented which clearly illustrates the performance-limiting zeros. In addition, identification results on a testbed are presented to give the model and the analysis the necessary experimental validation.