A novel cutterhead off-stuck strategy for tunnel boring machine based on electro-hydraulic hybrid driving

The cutterhead driving system of a tunnel boring machine may easily get jammed in fault zones driven by electro-motors of low torque capacity. To improve the geological adaptability, this work presents a novel electro-hydraulic hybrid cutterhead driving system to control high-torque hydro-motors as followers under the torque master–slave strategy together with electro-motors. Specific half closed-type pump–motor system is designed, the work pressure of the hydro-motor is regulated by proportional overflow valve to track the torque of the main electro-motor, and a variable displacement pump is controlled to track the expected speed of the main electro-motor with stable overflow via the proportional overflow valve. Feed-forward control principles are derived via the inner mechanism analyses of the proportional overflow valve and variable displacement pump, and proportional and integral separated feedbacks are also introduced to build compound controllers for the tracking of pressure and pump displacement, respectively. The hybrid driving experiments on a Φ2.5 m tunnel boring machine rig indicate that the hydro-motor could track 1.5 times the main electro-motor torque with error within ±15.2 N m against load change and system oscillation, and the error ratios of hydro-motor and slave electro-motor are similar at normal load and fixed speed. Furthermore, jammed cutterhead could be restarted with each hydro-motor supplying double torque of the main electro-motor, and the required assembly power is only 25% of alternative electro-motors.