Theoretical Investigation of the Viscous Damping Coefficient of Hydraulic Actuators

The viscous damping coefficient （VDC） of hydraulic actuators is crucial for system modeling, control and dynamic characteristic analysis. Currently, the resear- ches on hydraulic actuators focus on behavior assessment, promotion of control performance and efficiency. However, the estimation of the VDC is difficult due to a lack of study. Firstly, using two types of hydraulic cylinders, behaviors of the VDC are experimentally examined with velocities and pressure variations. For the tested plunger type hydraulic cylinder, the exponential model B = αν-β （α 〉 0, β 〉 0） or B = α1e-β1ν＋α2e-β2ν（α1, α2 〉 0, β1,β2 〉 0）, fits the relation between the VDC and velocities for a given pressure of chamber with high precision. The magnitude of the VDC decreases almost linearly under certain velocities when increasing the chamber pressure from 0.6 MPa to 6.0 MPa. Furthermore, the effects of the chamber pressures on the VDC of piston and plunge type hydraulic cylinders are different due to different sealing types. In order to investi- gate the VDC of a plunger type hydraulic actuator drasti- cally, a steady-state numerical model has been developed to describe the mechanism incorporating tandem seal lubrica- tion, back-up ring related friction behaviors and shear stress of fluid. It is shown that the simulated results of VDC agreewith the measured results with a good accuracy. The pro- posed method provides an instruction to predict the VDC in system modeling and analysis.