Coil spring booster: A single-channel regenerative braking system for tram in a sustainable city

•A coil spring booster (CSB) was proposed for regenerative braking in sustainable city trams.•CSB stores and releases braking energy with single-channel transmission characteristics.•Simulations and tests confirm the feasibility of the proposed CSB.•The CSB shows potential as a Nexus for smart trams & sustainable cities. This paper presents a single-channel regenerative braking system (SC-RBS) for trams in sustainable cities. The system consists of three components: the mechanical subsystem, the electrical subsystem, and the control subsystem. The mechanical subsystem, utilising a coil spring booster (CSB), effectively stores braking energy as elastic potential energy, enhancing the flexibility of the braking system. The electrical subsystem converts braking energy into electrical energy. The control subsystem ensures cooperative operation among the mechanical subsystem, the electrical subsystem, and traditional friction braking methods. The study focuses on the characteristics and design process of coil springs, showing that braking force significantly impacts braking efficiency and energy recovery. Finite element analysis demonstrates the working mode of the coil spring in auxiliary braking. Furthermore, the tests conducted on a prototype analysed the energy storage characteristics of the coil spring, revealing the influence of mechanical properties, supporting connection strength, and the number of coil springs. Overall, the proposed SC-RBS utilising the CSB enables efficient utilisation of tram regenerative braking energy, contributing to the development of sustainable cities.