A three-dimensional vehicle-track coupled dynamics model, with the inclusion of the axle-box bearings, has been developed, which considers the coupling effects between the bearing and the vehicle components. Some non-linear factors, such as time-varying bearing stiffness, bearing clearance, wheel-polygonal wear and the non-linear wheel-rail contact forces, are also considered. Dynamic analysis has been implemented through numerical simulations that consider different amplitudes and harmonic orders of measured and idealised polygonal wheel wear. Both model analysis and validation were supported by field tests. Results show that the roller-raceway contact forces increases with vehicle speed and the amplitude of polygonal wear. However, the influence of wear upon the axle-box bearing is found to be small in the low-speed range, but at higher operating speeds, polygonal wear leads to a rapid increase in bearing contact forces and the potential for degradation. During vehicle operations, both high order (17th to 20th order) and lower order (1st to 4th order) wheel-polygonal wear patterns are generated. The former's influence on axle-box bearing forces is more significant. Hence, the identification and rectification of this order of wear should form part of maintenance practice and potentially also be considered in the design of axle-box bearings for high-speed trains.

The Axle-box bearing (ABB) is a key component in the high-speed train which suffers multiple stochastic excitations in realistic working conditions. The ABB's health status is crucial for the reliable and safe operation of the rolling stock. This paper proposes a novel stochastic vehicle–track coupled model to evaluate the dynamic performance of ABBs in a high-speed train with unsteady wind load and random track irregularities. The nonlinear bearing stiffness and unsmooth nonlinearities of the bearing clearances are properly considered based on the Hertzian contact theory. The von Karman power spectral density is adopted to generate the time-history of the fluctuating wind speed on a moving vehicle. The unsteady wind loads acting on the carbody are derived based on the fluid-induced vibration theory. The empirical PSD of track irregularity is adopted to generate the time-history of track irregularities. The Monte Carlo method is employed to analyse the roller–raceway contact stress with random excitations of unsteady wind and track irregularities. The results indicate that the track irregularities and unsteady wind have a non-negligible effect on the dynamic performance of ABBs. The crosswind may cause the partial loading phenomenon of the ABBs. The increase of crosswind speed significantly increases the probability of the contact stress exceeding the safety threshold, which challenges the service safety of the key components inside the train.

To improve vehicle fuel economy whilst enhancing road handling and ride comfort, power generating suspension systems have recently attracted increased attention in automotive engineering. This paper presents our study of a regenerative hydraulic shock absorber system which converts the oscillatory motion of a vehicle suspension into unidirectional rotary motion of a generator. Firstly a model which takes into account the influences of the dynamics of hydraulic flow, rotational motion and power regeneration is developed. Thereafter the model parameters of fluid bulk modulus, motor efficiencies, viscous friction torque, and voltage and torque constant coefficients are determined based on modelling and experimental studies of a prototype system. The model is then validated under different input excitations and load resistances, obtaining results which show good agreement between prediction and measurement. In particular, the system using piston-rod dimensions of 50–30 mm achieves recoverable power of 260 W with an efficiency of around 40% under sinusoidal excitation of 1 Hz frequency and 25 mm amplitude when the accumulator capacity is set to 0.32 L with the load resistance 20 Ω. It is then shown that the appropriate damping characteristics required from a shock absorber in a heavy-haulage vehicle can be met by using variable load resistances and accumulator capacities in a device akin to the prototype. The validated model paves the way for further system optimisation towards maximising the performance of regeneration, ride comfort and handling.