Study On The Movement Behavior Of An Electro-hydraulic Position Control System Under Variable Hydraulic Stiffness

For the three-ways valve controlled hydraulic cylinder the transfer function isusually used to establish the mathematic model. In this method, stability will be limitednear the working point, and it is not suitable for the discussion of the system stabilitywithin the scope of the whole work stroke and the effects of structural parameters onthe system. In order to highlight the effect of the oil volume change in the hydrauliccylinder chamber on the nonlinear of the system, the valve port flow equationexpressed by the differential form, the flow continuity equation and dynamic equationof load were used here, the valve-controlled cylinder system mathematical modelwhich is suitable for the whole working range was established, and thus, the third ordernonlinear differential equation related to the output variables was established also. Theequation was studied with the aid of state space expression method, the Lyapunov’sstability of the equation was discussed, and the limit cycle and initial value sensitivityof the system output was focused on in the discussion. The result shows, the change ofhydraulic cylinder volume with the displacement output leads to the nonlinearity ofvalve control cylinder system, and this nonlinearity lies in each coefficient differentialeuqation. Small changes of the initial value will make the system motion behavior agreat change near the equilibrium point. When equation coefficient value was chosenin certain scope, the system movement behavior presented a limit cycle. Finally, thestable coefficient value area of the equation was determined. Research on theclosed-loop behavior indicates no essential difference between closed-loop andopen-loop behavior.