Wongun Kim

Development of a path-tracking control system based on model predictive control using infrastructure sensors

This paper describes the development of an infrastructure-based path-tracking control system. The control system consists of an infrastructure sensor module, a vehicle controller and actuator modules. A reference path is defined from a start point to a destination and a modified reference path is generated to obtain a safe vehicle trajectory for collision avoidance in the case where obstacles and other vehicles exist. Receiving information about vehicle position, heading angle and obstacles surrounding the vehicle from an infrastructure sensor module, the vehicle controller calculates control inputs such as steering wheel angle, throttle angle and brake torque to track the modified reference path which guarantees minimum clearance to obstacles. The vehicle controller comprises three parts: a path-generation algorithm, a path-following controller and a speed controller. The path-generation algorithm generates the modified reference path using the model predictive control method. The path-following controller calculates steering angle in order to track the modified reference path. From the speed controller, throttle and brake control inputs are generated to follow the reference velocity. The path-tracking control system was implemented using a test vehicle and an infrastructure sensor module.

Skid Steering-Based Control of a Robotic Vehicle with Six in-Wheel Drives

This paper describes a driving control algorithm based on a skid steering for a robotic vehicle with articulated suspension (RVAS). The RVAS is a kind of unmanned ground vehicle based on a skid steering using an independent in-wheel drive at each wheel. The driving control algorithm consists of four parts: a speed controller for following a desired speed, a lateral motion controller that computes a yaw moment input to track a desired yaw rate or a desired trajectory according to the control mode, a longitudinal tyre force distribution algorithm that determines an optimal desired longitudinal tyre force, and a wheel torque controller that determines a wheel torque command at each wheel in order to keep the slip ratio at each wheel below a limit value as well as to track the desired tyre force. Longitudinal and vertical tyre force estimators are required for the optimal tyre force distribution and wheel slip control. A dynamic model of the RVAS for simulation study is developed and validated using the vehicle test data. Simulation and vehicle tests are conducted in order to evaluate the proposed driving controller. It is found from simulation and vehicle test results that the proposed driving controller provides a satisfactory motion control performance according to the control mode.

Fault-tolerant driving control of a steer-by-wire system for six-wheel-driving–six-wheel-steering vehicles

This paper describes a fault-tolerant driving control strategy for steer-by-wire system failures in six-wheel-driving–six-wheel-steering vehicles. The fault-tolerant driving control algorithm was designed to obtain vehicle manoeuvrability as close as possible to that of non-faulty vehicles by redistributing the tractive forces of the non-faulty wheels. Since a faulty steer-by-wire system induces a high lateral tyre force, which is the resistance to the yaw motion of the vehicle, a high-wheel slip control strategy is used to minimize the resistive lateral tyre force of the faulty steer-by-wire system. The fault-tolerant driving performance of a faulty six-wheel-driving–six-wheel-steering vehicle was investigated via computer simulations. To investigate the effectiveness of the proposed fault-tolerant driving control algorithm, the fault recovery rate was defined and calculated in terms of the vehicle manoeuvrability. Simulation studies show that the proposed fault-tolerant driving control algorithm can significantly improve the vehicle manoeuvrability, compared with the optimal traction redistribution method.

An optimal traction, braking, and steering coordination strategy for stability and manoeuvrability of a six-wheel drive and six-wheel steer vehicle

This paper describes an optimal traction, braking and steering coordination to improve vehicle lateral stability and manoeuvrability of a six-wheel driving/six-wheel steering (6WD/6WS) vehicle. The optimal coordination controller consists of an upper and lower level controller. The upper level controller determines front, middle steering angle, desired net yaw moment, and longitudinal net force according to the reference velocity and steering angle corresponding to a manual driver. The desired yaw moment is calculated by sliding-mode control theory. Based on the desired longitudinal net force, yaw moment, and tyre force information as inputs from the upper level controller, the lower level controller determines distributed lateral tyre forces and longitudinal tyre force on each wheel in proportion to the size of the friction circle of each wheel. The size of a friction circle is estimated using longitudinal/lateral velocity, yaw rate, wheel torque, and wheel angular velocity. Vehicle–driver–controller closed-loop simulations have been conducted to investigate the improved performance of the proposed optimal coordination controller over a conventional direct yaw moment controller (DYC) of the vehicle equipped with a mechanical drive system.

Friction circle estimation-based torque distribution control of six-wheeled independent driving vehicles for terrain-driving performance

This paper describes torque distribution control of six-wheeled in-wheel motor vehicles by considering the friction circle of each wheel for enhanced terrain-driving performance. Using control allocation, the proposed torque distribution algorithm determines the torque command to each wheel, by considering the size of the friction circle. The friction circle of each wheel is estimated using a linear parameterized tyre model with two threshold values. The parameters and the threshold values are computed from measurements of the wheel speed, the yaw rate, the acceleration and the torque command signals using a recursive least-squares method. Simulation studies were conducted using TruckSim and MATLAB/Simulink co-simulations. It was confirmed that the proposed friction circle estimation algorithm can be successfully used for torque distribution to enhance the terrain-driving and hill-climbing performance.

Coordinated Control of Tractive and Braking Forces Using High Slip for Improved Turning Performance of an Electric Vehicle Equipped with In-Wheel Motors

This paper describes development of coordinated control of tractive and braking forces using high wheel slip in order to enhance turning performance of electric vehicle equipped with in-wheel motors. In the case of conventional vehicle, turning radius is definitely limited by kinematic features with respect to wheel base, maximum steering angle and track width of the vehicle. Military and special purpose vehicles are required to overcome turning radius limitation in order to conduct urgent and emergency tasks and avoid enemies rapidly. The control purpose is achieved by minimizing lateral tire force of rear wheels using excessive wheel slip condition. It is possible for the vehicle to turn around central turning point using the proposed algorithm. The center turning point is defined based on the drivers intention. The coordinated control algorithm consists of three parts: an upper level controller that computes the desired net force and moment in order to make one point turning motion, a lower level controller distributes tractive and brake input torques of each wheel for excessive slip control and sensor/estimator provides vehicle information to controllers. Computer simulations have been conducted to evaluate performance of the proposed control algorithm. It has been shown from simulation results that turning performance can be significantly improved.

Driving control architecture for six-in-wheel-driving and skid-steered series hybrid vehicles

This paper presents a driving control method including torque distribution, slip control and regenerative-hydraulic brake control to maximize maneuverability for six-in-wheel-drive and skid-steered series hybrid vehicles. Wheel torque command to each wheel, to track both net longitudinal force and net yaw moment, is distributed based on control allocation method. Because regenerative brake torque does not satisfy desired deceleration under certain speed condition, hydraulic brake system is controlled to obtain suitable brake force rapidly. The maneuvering performance of the six-wheeled and skid-steered vehicle with the proposed driving controller has been compared to that of an Ackerman-steered vehicle with even-distribution controller via TruckSim & Matlab-Simulink co-simulations.