Composite brake system based on sliding-mode freestanding triboelectric nanogenerator

Triboelectric nanogenerators (TENG) based on contact electrification can efficiently harvest irregular and random mechanical energy, aligning with the design principles of green cars. This paper introduces a composite brake system that incorporates a sliding-mode freestanding TENG (SF-TENG) for collecting braking energy. This electro-hydraulic composite brake system consists of disc brake, SF-TENG brake, and hydraulic circuits. The grid-like PTFE film and Al film are the rotor and stator of the SF-TENG. The input oil pressures of disc brake and SF-TENG brake are controlled by the electro-hydraulic brake system. In order to ensure the service life of the triboelectric pair, a hydraulic circuit for SF-TENG-brake, equipped with a unidirectional pressure relief valve, has been designed to set the upper limit of the contact pressure for the triboelectric pair. Based on the single-track model and the composite braking system model, a sliding mode control strategy is proposed for emergency braking scenarios. In this strategy, the braking torque of the SF-TENG brake is considered as a disturbance in the control input to enhance the robustness of optimal slip ratio tracking. A key feature of this system is the use of a dedicated hydraulic circuit to decouple the energy harvesting function from the critical safety braking function, thereby maintaining unimpaired braking performance and enabling efficient recovery of braking energy. The SF-TENG brake can harvest 0.99 mJ of kinetic energy during an emergency braking event.