Abstract
Light electric vehicles represent one possible outlook of future individual mobility in urban environment without local emission of carbon dioxide. Besides the concept of electric vehicles with one electric motor and a mechanical power transmission to two or four wheels, vehicles with two or more wheel hub motors offer special advantages. This paper describes an approach to a traction control system for four wheel drive (4WD) vehicles with an electric powertrain based on wheel hub motors. Due to fast electronic motor controllers and the usage of brushless DC motors with high power and torque density a high dynamic control of rotational speed and torque in each wheel can be realized. In conclusion with knowledge of driving velocities at each wheel a direct control of the driving force and the slip at each wheel will be possible. In the first step this shall be proofed by building up a simulation model of a vehicle and a powertrain providing a safe and cost effective way in control design. Therefore an enhanced quarter car model and a nonlinear tire model are used [3], [6]. Because of its fast operating frequency compared to the inertial behavior of the vehicle body and wheels, the dynamic of the electronic controlled BLDC motors can be represented by a simplified motor model describing the powertrain. With very fast direct control of driving force and slip at each wheel using the presented electric direct drive powertrain concept, common vehicle control systems like Traction Control System or Electronic Stability Program can be improved due to better performance compared to the usage of hydraulic aggregates or intervention in the engine Electronic Control Unit [5], [7]. In addition to that the energy dissipating during breaking a single wheel can now be recuperated and used for later acceleration or controlling the slip of another wheel by increasing or decreasing the rotational speed. In conclusion the possibility of application and the control design will be discussed via simulation results.
KEYWORDS: Electric vehicle, electrical 4WD, wheel hub motor, slip control, nonlinear vehicle model