Four-axle electric-drive special vehicles are often deployed to execute complex
tasks under extreme operating conditions. Their harsh working environments,
stringent dynamic-response requirements, and high energy demand for mobility
impose higher requirements on both the energy-regeneration efficiency and
braking safety of the braking system. To address these issues, this article
proposes an electro-hydraulic composite braking control strategy for four-axle
electric-drive special vehicles. First, a braking axle-load transfer model for
the four-axle electric-drive special vehicle is established, enabling
axle-to-axle braking force distribution based on axle loads. Second, considering
the motor torque characteristics and battery charging characteristics and by
establishing an anti-lock braking prediction model, an electro-hydraulic
composite braking torque allocation strategy with safety-range constraints on
motor braking torque is designed. Then, to enhance vehicle safety during
emergency braking, an adaptive super-twisting sliding-mode variable-structure
anti-lock braking system (ABS) controller is proposed, and based on this ABS
controller, an emergency braking control strategy is developed in which the
motor braking torque is pre-reduced to within a safe range, with motor-dominant
and hydraulic auxiliary modulation. Finally, simulation and real-vehicle tests
demonstrate that the proposed electro-hydraulic composite braking control
strategy improves the motor braking energy recovery rate under service braking
conditions, reduces the braking distance, and enhances braking safety under
emergency braking conditions.
