Abstract: Because of the asymmetry characteristics of asymmetric cylinders, more approximate treatments for differential of the pressure in two chambers are needed when deducing its local linear models around working points when adapting the same method with that usually used for symmetrical cylinders, which leads to larger model error. Approximate treatments for two chambers flow are introduced to get the linear equation of load flow, by which a unified model suitable for different piston locations is obtained. Symmetric cylinder model derived by this method is identical with that obtained by traditional method, which further implies that the established model has smaller error. Flow gain and flow-pressure coefficient formulas at center position of servo valves are deduced by regarding the complicated oil flowing state as coexistence of two flowing states responding to two moving directions of cylinders outside the overlap area of servo valves. At different working points with different piston locations and different valve spool positions, the difference between model parameters obtained by simulations and theoretical results calculated by the proposed formulas are much small. Response curves in closed loop control experiments are consistent with those in simulations based on theoretical models at different working points. The above results show that the proposed valve-controlled asymmetric cylinder model has smaller error.

Key words: flow approximation, linear model, load flow equation, valve-controlled asymmetric cylinder