Study on the Non-linear Parametric Model of Hydraulic Dampers Before Relieving for Railway Vehicles

The objective of this work is to establish an accurate non-linear parametric model which relates the physical parameters with the damping characteristics of the hydraulic damper before relieving. A new non-linear parametric model including the sub-models of the orifice, hydraulic fluid, pressure chambers, reservoir chamber, etc. is established based on the theory of the fluid mechanics. Subsequently, a new force element of the hydraulic damper based on the new non-linear model is developed with Fortran language in the secondary development environment of the multi-body dynamics software SIMPACK. Used the force element, the force-displacement and force-velocity characteristics of the modified yaw damper with the base diameter of 0.4 and 0.6 mm are calculated under different amplitudes and frequencies of the sinusoidal excitation. Comparing with the experimental results obtained under the same condition, it shows that the new model can accurately model the nonlinear static and dynamic characteristics. Furthermore, the leakages for the high frequency, the air release and cavitation for the modelling of the fluid shortage, the non-constant flow coefficient of the orifice and the dynamic states of the fluid should be included in the modelling of the hydraulic damper before relieving. The non-linear parametric model proposed in this paper is more applicable to the railway vehicle system dynamics simulation and individual system description of the hydraulic damper.