Gear walk instability caused by brake-disc friction characteristics

A multi-body dynamic rigid-flexible coupling model of landing gear is established to study the gear walk instability caused by the friction characteristics of the brake disc.After validating the model with the experimental results,the influence of the landing gear structure and braking system parameters on gear walk is further investigated.Among the above factors,the slope of the graph for the friction coefficient of the brake disc and the relative velocity of brake stators and rotors is the most influential factor on gear walk instability.Phase trajectory analysis verifies that gear walk occurs when the coupling of multiple factors causes the system to exhibit an equivalent negative damping trend.To consider a more realistic braking case,a back propagation neural network method is employed to describe the nonlinear behavior of the friction coefficient of the brake disc.With the realistic nonlinear model of the friction coefficient,the maximum error in predicting the braking torque is less than 10%and the effect of the brake disc temperature on gear walk is performed.The results reveal that a more negative friction slope may contribute to a more severe unstable gear walk,and reducing the braking pressure is an effective approach to avoid gear walk,which provides help for future braking system design.

Squeeze-Strengthening Effect of Silicone Oil-based Magnetorheological Fluid

In order to study the squeeze-strengthening effect of silicone oil-based magnetorheological fluid （MRF）, theoretical basis of disc squeezing brake was presented and a squeezing braking characteristics test-bed for MRF was designed. Moreover, relevant experiments were carded out and the relationship between squeezing pressure and braking torque was proposed. Experiments results showed that the yield stress of MRF improved linearly with the increasing of external squeezing pressure and the braking torque increased three times when external squeezing pressure achieved 2 MPa.

Study on a segmented electro-pneumatic braking system for heavy-haul trains

The large longitudinal impact of heavy-haul trains is the main factor limiting their development,and the asynchronous nature of train-braking systems is the main cause of this longitudinal impact.In this paper,a segmented electro-pneumatic braking solution fully compatible with the existing freight-train braking system in China is proposed to improve the synchrony of train-braking systems.A simulation model for this braking system is developed based on air-flow theory,the 120 distribution valve and electronic control devices.The braking characteristics obtained from simulations are compared to those from the train-brake testing platform,and show high fidelity.On this basis,the effects of the new braking system on the braking capacity and longitudinal impact of a 20000 t heavy-haul train are analysed by further simulation.The results show that during service brakes,the segmented electro-pneumatic braking system can increase the braking capacity by 4.2–24.7%and reduce the coupler force by 21.6–68.0%.Therefore,it can be seen that the segmented electro-pneumatic braking system is a new type of electro-pneumatic brake that meets the needs of the Chinese railway network.It solves the problem of the longitudinal impact of heavy-haul trains satisfactorily,and its compatibility with the existing braking system(resulting in a reduced modification workload)makes it possible to maintain normal operations on heavy-haul lines while trains undergo modification.