Four wheel torque blending for slip control in a hybrid electric vehicle with a single electric machine

Vehicle electrification aims at improving energy efficiency and reducing pollutant emissions. It also creates opportunities to enhance active safety systems with the use of electric machines (EM) as regenerative braking actuators to support the friction brake system. Vehicle energy efficiency can be improved by integrating regenerative braking (RBS) and friction brakes to enable more frequent energy recuperation activations especially during high deceleration demands. This study aims at designing and implementing a new torque allocation strategy for wheel slip control in a four-wheel-drive (4WD) hybrid electric vehicle (HEV) with a single EM. The antilock braking system (ABS) is designed using sliding mode control, which offers robustness against tyre force nonlinearity. A brake torque blending algorithm is developed to distribute torques between electric and friction brake actuators based on a pre-defined energy recuperation priority. The challenge of allocating brake torques at each of the four wheels with brake-by-wire (BBW) and a centralized EM is particularly addressed in this study. Simulation analyses using a hardware-in-the-loop (HIL) test rig are conducted to verify the proposed control algorithms.