The presented work illustrates an investigation on the observer synthesis for a highly nonlinear railway running gear system. The specific focus is on the longitudinal dynamics and the associated adhesion effects, i.e. the friction conditions between wheel and rail. This interface strongly influences the brake and the traction performance of trains and, thus, its detailed consideration is of crucial importance in terms of safety and comfort.
The observer design is accomplished for the experimental running gear developed at the German Aerospace Center (DLR). The article focuses on the first steps of the observer synthesis: (i) the set-up of the observer model, (ii) the selection of an appropriate observer method, (iii) and the validation of the observer in a simulation environment. The determining aspect of the model implementation is the consideration of the nonlinear wheel-rail contact. To cover this nonlinear behavior an Extended Kalman Filter (EKF) is used in combination with a parameter estimator for the friction characteristics in the wheel-rail interfaces. In the end, the received results prove that the observer accurately estimates the system behavior and provides reliable information on the adhesion characteristics and related longitudinal dynamics.
Based on this findings one of the upcoming steps at the DLR is to validate the observer in the real-time environment of the test rig. Regarding the use of the presented approach in a train some significant improvements of traction control systems are enabled. A first application could be an enhanced brake control to narrow down the variance of brake distances in daily operation. Furthermore, an advanced usability of the condition based monitoring of traction and brake systems is facilitated with the additional information on the friction conditions.
