Modelling and performance evaluation of an electromagnetic regenerative shock absorber with mechanical motion rectifier

Abstract

This thesis is mainly concerned with the modelling of an electromagnetic regenerative shock absorber with mechanical motion rectifier (MMR), and its performance evaluation when it is implemented in the suspension of a road vehicle. Unlike a conventional regenerative shock absorber, the inclusion of a sprag-clutch within the MMR module enables the conversion of bi-directional rotational motion into unidirectional rotary input to the coupled electromagnetic generator. Previous studies have shown that the dynamics of a regenerative shock absorber with MMR can be modelled as a piecewise linear system produced by the engagement and disengagement of sprag-clutches within the MMR. It is seen that the MMR based system potentially works as a switchable inerter in parallel with a switchable damper. To characterise the proposed energy harvesting technique, the system is initially discussed when one terminal of the design is blocked, which allows further validations through experiments. In order to comprehensively study dynamics of MMR system, its energy harvesting as well as mechanical power flow performance are evaluated. Additionally, an analogy between the electrical and mechanical active and reactive power flow, using forcecurrent analogy is carried out. This allows better understanding of the power transmission between sub-systems. Moreover, the output of a conventional regenerative shock absorber is generally coupled with an electrical rectifier to convert the AC voltage signal to DC signal for either energy storage or charging electronic devices. In this work, to justify the usage of each rectifier, the electrical rectifier-based regenerative shock absorber is studied in both electrical and mechanical systems. The discussion is further extended to compare performances between electrical rectifiers and MMR in different scenarios. It is shown that MMR is able to offer much superior performance than electrical rectifiers, typically for lower power application. To validate theoretical predictions, the MMR based regenerative shock absorber is tested in a hydraulic Instron machine. A dynamic model of the proposed design is implemented, and its parameters are estimated from the measured data. In order to establish whether MMR allows acceptable energy harvesting performance when incorporated into the suspension of road vehicles, the first step is to investigate the characteristics of the vibration environment. By using the concept of mechanical impedance and mobility, dynamics of the vibration source is studied when the regenerative shock absorber is incorporated into a road vehicle. According to the vibration source characteristic results, the implementation of the MMR based regenerative shock absorber in the suspension system of road vehicles is discussed. The result shows that MMR enables better performance under certain conditions, but it results in a high jerk motion (excessive change of acceleration) as a trade-off. Finally, the procedure for the design of a mechanical motion rectified regenerative shock absorber for a road vehicle suspension system is presented. The proposed design guidelines enable a designer to select desirable parameters for the regenerative shock absorber based on the system constraints and the application environment.

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