All-wheel driving using independent torque control of each wheel

Electric motors offer tremendous potential to create an advanced all-wheel drive system. By driving each wheel with a separate motor, the torque delivered to individual wheels can be precisely controlled. This paper reports control algorithms, simulation results, and initial results of scale model testing of an all-wheel drive system. The control algorithms seek to keep all four wheel speeds within a certain percentage of one another to limit slip, while a torque distribution system sets the torque command for each wheel based on its loading and the need to produce a yaw moment. Torque control algorithms are evaluated using an eight degree-of-freedom vehicle model. A unique road surface simulator is developed to evaluate controller performance on surfaces with realistic transitions between high and low friction patches. A microprocessor-controlled physical model based on a one-eighth scale radio-controlled car driven by four brushless DC motors is constructed as an experimental test platform. The resulting braking, traction, and anti-skid controllers result in a better-handling vehicle with improved safety and performance.