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In this paper, an optimal path-planning method is proposed for autonomous ground vehicles in case of overtaking a moving obstacle by the application of a two-phase optimal-control problem. When the autonomous vehicle detects a moving vehicle in a proper speed and distance ahead, it decides to overtake the obstacle by executing a double-lane change manoeuvre. The path for the overtaking manoeuvre is generated by a two-phase optimal path-planning problem. The cost function of the first phase is defined in such a way that the vehicle approaches the obstacle as close as possible.In the second phase, the cost function is defined as sum of the vehicle lateral deviation from the reference path and the rate of steering angle. At the same time, the lateral acceleration of the vehicle must not exceed a specified limit. The radio pseudo-spectral method, which is a method for direct trajectory optimization using global collocation at Legendre-Gauss-Radau points, is applied for solving the two-phase nonlinear optimal-control problem. A full nonlinear vehicle model in CarSim software is used for path-tracking simulation by importing path data from a MATLAB code. The simulation results show that the generated path for the autonomous vehicle satisfies all vehicle-dynamics constraints and hence is applicable for a real autonomous vehicle.

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A yaw moment control system is developed for a front-wheel-drive vehicle utilizing two brushless d.c. electric motors embedded in the rear wheels. An optimal linear quadratic regulator (LQR) controller is employed by using a four-degrees-of-freedom (4DOF) linear vehicle model. The objective is to include important effects of roll and steering into the controller design. A two-degrees-of-freedom (2DOF) optimal LQR model is also used for comparison purposes. For the simulation of system at different conditions, a non-linear eightdegrees-of-freedom vehicle model is used. The performances of the controlled vehicle have been compared with those of the uncontrolled vehicle in order to investigate the effectiveness of the proposed controllers. Simulation results indicate that, in normal situations where the uncontrolled vehicle becomes unstable, the controlled vehicles with both 2DOF and 4DOF controllers show stable responses. In severe conditions, however, even the 2DOF controller fails to stabilize the vehicle, whereas the 4DOF controller is successful in maintaining the stability of vehicle.

The paper investigates the improvement of vehicle dynamic performance by the use of a rear, electronically controlled, limited slip differential. This control is based on the vehicle yaw rate, rear wheel slip values, and braking subsystem on the front wheels. An optimal linear quadratic regulator (LQR) controller is employed together with an elaborate six-degree-offreedom linear vehicle model. The objective is to include the important effects of roll and steering dynamics into the controller design. For simulation purposes, the optimal controller is included in a nine-degree-of-freedom, non-linear vehicle-handling model developed for the study. Simulation results are obtained using MATLAB/Simulink for different vehicle manoeuvres. Results indicate that use of the active differential improves the handling qualities and driver perception especially at cornering situations while accelerating, at which other control methods based on braking decelerate the vehicle not in favour of the driver's desires.