Electric vehicles with four individually controlled drivetrains are over-actuated systems and therefore the total wheel torque and yaw moment demands can be realized through an infinite number of feasible wheel torque combinations. Hence, an energyefficient torque distribution among the four drivetrains is crucial for reducing the drivetrain power losses and therefore extending driving range. In this paper, the optimal torque distribution is formulated as the solution of a parametric optimization problem, depending on vehicle speed. An analytical solution is provided for the case of equal drivetrains, under the experimentally confirmed hypothesis that the drivetrain power losses are strictly monotonically increasing with the torque demand. The easily implementable and computationally fast wheel torque distribution algorithm is validated by simulations and experiments on an electric vehicle demonstrator, along driving cycles and cornering maneuvers. The results show considerable energy savings compared to alternative torque distribution strategies.
A significant challenge in electric vehicles with multiple motors is how to control the individual drivetrains in order to achieve measurable benefits in terms of vehicle cornering response, compared to conventional stability control systems actuating the friction brakes. This paper presents a direct yaw moment controller based on the combination of feedforward and feedback contributions for continuous yaw rate control. When the estimated sideslip exceeds a pre-defined threshold, a sideslip-based yaw moment contribution is activated. All yaw moment contributions are entirely tunable through model-based approaches, for reduced vehicle testing time. The purpose of the controller is to continuously modify the vehicle understeer characteristic in quasi-static conditions and increase yaw and sideslip damping during transients. Skid-pad, step-steer and sweep steer tests are carried out with a front-wheel-drive fully electric vehicle demonstrator with two independent drivetrains. The experimental test results of the electric motor-based actuation of the direct yaw moment controller are compared with those deriving from the friction brake-based actuation of the same algorithm, which is a major contribution of this paper. The novel results show that continuous direct yaw moment control allows significant "on-demand" changes of the vehicle response in cornering conditions and to enhance active vehicle safety during extreme driving maneuvers
This paper presents an integral sliding mode (ISM) formulation for the torque-vectoring (TV) control of a fully electric vehicle. The performance of the controller is evaluated in steadystate and transient conditions, including the analysis of the controller performance degradation due to its real-world implementation. This potential issue, which is typical of sliding mode formulations, relates to the actuation delays caused by the drivetrain hardware configuration, signal discretization, and vehicle communication buses, which can provoke chattering and irregular control action. The controller is experimentally assessed on a prototype electric vehicle demonstrator under the worst-case conditions in terms of drivetrain layout and communication delays. The results show a significant enhancement of the controlled vehicle performance during all maneuvers. Index Terms-Actuation delays, experimental tests, integral sliding mode (ISM), torque-vectoring (TV), yaw rate control. NOMENCLATURE a, b Front and rear semi-wheel bases. a x , a y Longitudinal and lateral vehicle accelerations. c F , c R Front and rear track widths. c hs , k hsHalf-shaft torsion damping coefficient and torsional stiffness. f , h, n, k Known functions of the states (x), the contribution due to uncertainties and disturbances, the term multiplied by the control input, and the yaw acceleration contribution due to lateral tire forces and selfaligning torques (SAT), respectively.
The continuous, precise modulation of the driving and braking torque of each wheel is considered to be the ultimate goal for controlling the performance of a vehicle in steady-state and transient conditions. To do so, dedicated torque-vectoring controllers which allow optimal wheel torque distribution under all possible driving conditions have to be developed. Commonly, vehicle torque-vectoring controllers are based on a hierarchical approach, consisting of a high-level supervisory controller which evaluates a corrective yaw moment, and a low-level controller which defines the individual wheel torque reference values. The problem of the optimal individual wheel torque distribution for a particular driving condition can be solved through an optimization-based control allocation algorithm, which must rely on the appropriate selection of the objective function. With a newly developed off-line optimization procedure, this article assesses the performance of alternative objective functions for the optimal wheel torque distribution of a four-wheel-drive fully electric vehicle. Results show that objective functions based on minimum tire slip criterion provide better control performance than functions based on energy efficiency
Fully electric vehicles (FEVs) with individually controlled powertrains can significantly enhance vehicle response to steering-wheel inputs in both steady-state and transient conditions, thereby improving vehicle handling and, thus, active safety and the fun-to-drive element. This paper presents a comparison between different torque-vectoring control structures for the yaw moment control of FEVs. Two second-order sliding-mode controllers are evaluated against a feedforward controller combined with either a conventional or an adaptive proportionalintegral-derivative (PID) controller. Furthermore, the potential performance and robustness benefits arising from the integration of a body sideslip controller with the yaw rate feedback control system are assessed. The results show that all the evaluated controllers are able to significantly change the understeer behavior with respect to the baseline vehicle. The PID-based controllers achieve very good vehicle performance in steady-state and transient conditions, whereas the controllers based on the sliding-mode approach demonstrate a high level of robustness against variations in the vehicle parameters. The integrated sideslip controller effectively maintains the sideslip angle within acceptable limits in the case of an erroneous estimation of the tire-road friction coefficient.
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