Adaptive Coordinated Path Tracking Control Strategy for Autonomous Vehicles with Direct Yaw Moment Control

It is a striking fact that the path tracking accuracy of autonomous vehicles based on active front wheel steering is poor under high-speed and large-curvature conditions. In this study, an adaptive path tracking control strategy that coordinates active front wheel steering and direct yaw moment is proposed based on model predictive control algorithm. The recursive least square method with a forgetting factor is used to identify the rear tire cornering stiffness and update the path tracking system prediction model. To adaptively adjust the priorities of path tracking accuracy and vehicle stability, an adaptive strategy based on fuzzy rules is applied to change the weight coefficients in the cost function. An adaptive control strategy for coordinating active front steering and direct yaw moment is proposed to improve the path tracking accuracy under high-speed and large-curvature conditions. To ensure vehicle stability, the sideslip angle, yaw rate and zero moment methods are used to construct optimization constraints based on the model predictive control frame. It is verified through simulation experiments that the proposed adaptive coordinated control strategy can improve the path tracking accuracy and ensure vehicle stability under high-speed and large-curvature conditions.

Torque allocation strategy for four in-wheel-motor drive electric vehicle based on layered control

The differential torque of four in-wheel-motor drive electric automotive will affect vehicle stability, and applications of the differential driven assisting steering (DDAS) will be limited consequentially. To solve this problem, stability analysis and control system design is essential, therefore a DDAS stability control system is designed based on the layered control of yaw moment. Correlation functions are used to reflect the shifts of vehicle characteristic state between stable and unstable states, and help to determine the control weight of each subsystem in the lower-layer controller. In the lower-layer controller, the strategy of direct steering-wheel torque control is used to build a DDAS controller. Under different vehicle moving states, differential driving torque and yaw moment vary with the change of the control weights; and according to the theory of quadratic programming, optimal allocation of four-wheel driving torques will be made according to the total driving torque. The effectiveness of the proposed control system is verified by numerical simulation and hardware-in-the-loop experiment. The results show that the proposed control method can improve vehicle stability and ensure driving safety.

An Energy Efficient Control Strategy for Electric Vehicle Driven by In-Wheel-Motors Based on Discrete Adaptive Sliding Mode Control

This paper presents an energy efficient control strategy for electric vehicle (EV) driven by in-wheel-motors (IWMs) based on discrete adaptive sliding mode control (DASMC). The nonlinear vehicle model, tire model and the IWM model are established at first to represent the operation mechanism of the whole system. Based on the modeling, two virtual control variables are used to represent the longitudinal and yaw control efforts to coordinate the vehicle motion control. Then DASMC method is applied to calculate the required total driving torque and yaw moment, which can improve the tracking performance as well as the system robustness. According to the vehicle nonlinear model, the additional yaw moment can be expressed as a function of longitudinal and lateral tire forces. For further control scheme development, a tire force estimator using unscented Kalman filter is designed to estimate real-time tire forces. On these bases, energy efficient torque allocation method is developed to distribute the total driving torque and differential torque to each IWM, considering the motor energy consumption, the tire slip energy consumption and the brake energy recovery. Simulation results of the proposed control strategy using co-platform of Matlab/Simulink and CarSim® demonstrate that it can accomplish the vehicle motion control in a coordinated and economic way.

VERTICAL AND SLOPED BANK EFFECTS ON DIFFERENT SHIP TYPES

This study employed computer design software to completely draft 3D ship models; then, computational fluid dynamics were used to establish numeric navigation channels and simulate fluid hydrodynamic analysis of ships navigating along shore banks. The parameters considered comprised bank type (vertical and sloped), ship model (two types), velocity, ship-to-bank distance, and navigation time. Figures and tables were used to present the distribution of ship stern eddy current, flow field pressure, and velocity, and the comparison of center of mass deviation, sway force, and yaw moment. Results showed that ships navigating along embankments and channels produced asymmetric flows, which draw the bow away from the shore. Larger ships are substantially more influenced by bank effects than smaller ships. Large sway forces and yaw moments are produced in large ships, drifting the bow away from the bank and the stern towards the bank, increasing the risk of collision with the embankment. From the study results, the characteristics of bank effects are understood and can be used for assisting the safe navigation of ships in restricted waters.

Fractional Calculus Control of Road Vehicle Lateral Stability after a Tire Blowout

The lateral stability control of the vehicle can avoid serious traffic accidents when it had a tire blowout during the operation. This article proposes a robust nonlinear control method for controlling vehicle lateral stability after a tire blowout. To be exact, a seven degree of freedom dynamic model of vehicle with modified Dugoff tire model is established. The yaw moment of vehicle is performed by differential braking once the tire blowout occurring. As for control strategy, taking the linear two degree of freedom vehicle model as the reference, using the deviation of yaw rate and the vehicle side angle between the actual value and the reference value as the controller input parameters, the fractional calculus theory is utilized for yaw moment controller which was investigated by regulating the brake moment of blowout vehicle for improving its stability. The results of computer simulation show that the design controller of fractional PID can more effectively enhance the blowout vehicle performance stability compared with the vehicle with the non control, PID control, no matter in straight road or curve road.

Extension Coordinated Multi-Objective Adaptive Cruise Control Integrated with Direct Yaw Moment Control

An adaptive cruise control (ACC) system can reduce driver workload and improve safety by taking over the longitudinal control of vehicles. Nowadays, with the development of range sensors and V2X technology, the ACC system has been applied to curved conditions. Therefore, in the curving car-following process, it is necessary to simultaneously consider the car-following performance, longitudinal ride comfort, fuel economy and lateral stability of ACC vehicle. The direct yaw moment control (DYC) system can effectively improve the vehicle lateral stability by applying different longitudinal forces to different wheels. However, the various control objectives above will conflict with each other in some cases. To improve the overall performance of ACC vehicle and realize the coordination between these control objectives, the extension control is introduced to design the real-time weight matrix under a multi-objective model predictive control (MPC) framework. The driver-in-the-loop (DIL) tests on a driving simulator are conducted and the results show that the proposed method can effectively improve the overall performance of vehicle control system and realize the coordination of various control objectives.

Effects of Aerodynamic downforce on Vehicle Control and Stability

This paper deals with the analysis of vehicle handling with the variation of downforce. A vehicle with aero package were taken and the values of aerodynamic downforce and front downforce distribution for different front and rear ride heights were taken. This was followed by the generation of yaw moment diagram at original ground clearance of 30mm. Aero map data were collected and individual yaw moment diagrams were collected from which vehicle handling parameters are noted. Different contour plots were made to understand the variation of vehicle handling with different ride heights (aerodynamics downforce and downforce distribution). The paper concludes with the sensitivity study where effects of aerodynamic downforce were recorded on vehicle control and stability.