Composite brake system based on sliding-mode freestanding triboelectric nanogenerator

Abstract

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.