F2014-Special Session 'Vehicle Dynamics Control for Fully Electric Vehicles - Outcomes of the European Project E-VECTOORC' ELECTRIC AND FRICTION BRAKING CONTROL SYSTEMS FOR AWD ELECTRIC VEHICLES

ABSTRACT Research and/or Engineering Questions/Objective: Design of brake system for electric vehicles includes development of a number of functions as (i) brake torque blending between the friction brakes and electric motors, (ii) regenerative braking mode, and (iii) anti-lock brake system (ABS) operating with electric motors. The presented study has investigated these functions in relation to the vehicle with four individual electric motors and decoupled electro-hydraulic brake system. Methodology: The proposed blending and regenerative braking control algorithms use the strategy of brake force distribution with maximization of energy that could be recuperated during the braking manoeuvres. The realization of anti-lock brake system is based on the direct individual wheel slip control. The corresponding controller includes also several accompanying functions like slip target adaptation and switching in ABS mode between operation of electric motors and hydraulic brake system. Experimental investigations of the developed brake system has been performed using model- and hardware-in-the-loop tests with IPG CarMaker software environment and brake test rig based on dSPACE components and equipped with the hydraulic brake robot. Results: The study has pointed out to the impact of blended brake operation on the brake pedal feel. The subsequent adaptation of the decoupled electro-hydraulic brake system to all-wheel drive electric vehicle allowed to improve the system response time and to achieve the brake pedal dynamics close to conventional coupled brake systems. Regarding the ABS, the results obtained for different road conditions and reference slip values confirmed (i) achievement of sufficiently smooth tracking of the reference slip ratio for powertrain configurations with half-shafts of low (9000 Nm/rad) and high (21000 Nm/rad) torsional stiffness (ii) and considerable improvement of the brake performance. Limitations of this study: The brake performance achieved by developed control functions implementation is investigated and their functionality is confirmed through hardware-in-the-loop experiments. The validation of the developed brake system functionality on the vehicle demonstrator is planned as the next step of represented research. What does the paper offer that is new in the field including in comparison to other work by the authors: The most of known research results in the field of brake control for full electric vehicles relate to the vehicle configurations with in-wheel motors. The presented study considers novel powertrain architecture integrating individually-controlled wheel-near motors, gearboxes and half-shafts. Conclusion: The methodology for calculation and analysis of the brake torque distribution and electric / friction brake blending has been developed. The direct slip controller of ABS operating with friction brakes and electric motors is proposed. All developed components of the brake system are tested for all-wheel drive electric vehicle configuration.