Modelling, testing and analysis of a regenerative hydraulic shock absorber system

Recoverable energy in vehicle suspension systems has attracted intensive attention in recent years for the improvement of vibration suppression performance and the reduction of energy dissipation. Various design concepts and structures of regenerative suspensions have been presented and investigated to recover the energy of linear motion and vibration between the vehicle body and chassis from road disturbances. These studies concentrate on the energy conversion from kinetic energy to electricity. Although a large number of concepts and models have been proposed and evaluated to regenerate power for reuse, the previous simulation works have used significantly simplified models without considering parameter uncertainties and system losses. In addition, experimental works are too simple to support for modelling optimisation.
To advance the technology, a regenerative hydraulic shock absorber is investigated rigorously by examining the system at various developing stages including modelling all hydraulic, mechanical, and electromagnetic processes, simulating its behaviours, identifying its uncertain parameters/variables, fabricating a prototype of a commonly used shock absorber, testing its desirable performance and evaluating its on-road usability, which has given an accurate understanding of dynamic behaviours and power regeneration of a regenerative hydraulic shock absorber system.
Based on the configuration of the prototype, a comprehensive mathematical model is developed for the regenerative hydraulic shock absorber system. The various losses and nonlinearity have been taken into account in modelling hydraulic, mechanical, and electromagnetic processes, which allow more detailed influences and agreeable predictions with the experimental work to be obtained. The introduction of the gas-charged hydraulic accumulator into the system has been explored in both modelling and testing to provide power smoothing in an attempt to give a more stable recoverable power.
Model parameter identifications and refinements based on online data are systemically investigated. It has found that the pressures, rotation speeds and electrical outputs, which are readily available in the system, are sufficient to determine and refine uncertain model parameters such as the voltage constant coefficient, torque constant coefficient, generator internal resistance and rotational friction torque using a common least square method.
The developed experimental rig and measurement systems for the study of regenerative hydraulic shock absorbers are designed and built. The variations in motor pressure and shaft speed under different excitations are evaluated, and also voltage output and recoverable power at different electrical loads are investigated. Additionally, the experimental work is not only used to validate the predicted results comprehensively, but also to offer a practical evaluation method for the system under various operating conditions. In particular, the system using piston-rod dimensions of 50-30mm achieves recoverable power of 260W with an efficiency of around 40% under sinusoidal excitation of 1Hz frequency and 25mm amplitude. Additionally, control strategies and their realisation on a general purpose PC computer are developed based on constant voltage, current and resistance schemes to carry out the investigation of the system performances, which allows it to be fully evaluated upon the compromise between the damping behaviour and power regeneration performance for different road conditions.
Furthermore, the simulation of the entire system and parameter computations are all realised on the Matlab platform, which provides sufficient flexibility to take into account more influence factors for accurate and detailed analysis and thus can be an effective mathematical tool for further development research in this direction such as the optimisation of the structures, control strategies and system integrations.