Chang-Jun Kim

A study on motion control of 6WD/6WS vehicle using optimum tire force distribution method

This paper presents a motion control method of 6WD/6WS (6-wheel-drive and 6-wheel-steering) vehicle using optimum tire force distribution method. When we make used of independent driving and steering system, the motion control performance of the 6WD/6WS vehicle can be improved. For example, vehicles maneuverability is more improved at low speed and vehicles stability is also improved at high speed. Therefore, it needs to find a control strategy using optimum tire forces. A control strategy must satisfy the drivers command and minimize the energy consumption. When the driver commands vehicle (input steering angle and acceleration/brake pedal stroke), we can obtain the desired yaw moment, the desired lateral force and the desired longitudinal force. Those values are used in the optimum tire force distribution method. The optimum tire force distribution method can find the longitudinal tire force and lateral tire force. That force minimizes the cost function. The cost function is the sum of normalized tire force. The longitudinal tire forces and lateral tire force of each wheel are converted to the reference torque inputs and steering wheel angle inputs. The method was tested on the simulation and effectiveness was verified.

Geometric Path Tracking and Obstacle Avoidance Methods for an Autonomous Navigation of Nonholonomic Mobile Robot

This paper presents a method that integrates the geometric path tracking and the obstacle avoidance for nonholonomic mobile robot. The mobile robot follows the path by moving through the turning radius given from the pure pursuit method which is the one of the geometric path tracking methods. And the obstacle generates the obstacle potential, from this potential, the virtual force is obtained. Therefore, the turning radius for avoiding the obstacle is calculated by proportional to the virtual force. By integrating the turning radius for avoiding the obstacle and the turning radius for following the path, the mobile robot follows the path and avoids the obstacle simultaneously. The effectiveness of the proposed method is verified through the real experiments for path tracking only, static obstacle avoidance, dynamic obstacle avoidance.

Development of adaptive direct yaw-moment control method for electric vehicle based on identification of yaw-rate model

An electric vehicles which is equipped with the in-wheel motors have an advantages in terms of control. For example, by generating different torques at the left and right wheels, the vehicle stability in cornering can be improved. This is called the direct yaw moment control method. In this paper, adaptive direct yaw moment control based on identification of yaw rate model is proposed for electric vehicles. In practical point of view, the incorrect yaw rate model causes the uncertainty to the reference yaw rate. Because the direct yaw moment is determined for tracking that uncertain reference yaw rate, the lateral motion of the vehicle cannot be desirable one. To solve this problem, the identification of the yaw rate model is considered. Therefore, the identified yaw rate model provides the yaw rate for the direct yaw moment method so that the vehicle follows the desired dynamic model. The simulation results show the possibility of the proposed methods.

A study on the improvement of the tire force distribution method for rear wheel drive electric vehicle with in-wheel motor

This paper propose the tire force distribution method for a rear wheel drive electric vehicle. This method is developed to improve the vehicle stability under the high speed cornering condition and save the electric energy. To control the lateral vehicle motion, the desired yaw moment is calculated by yaw rate control using PID theory. And Total desired longitudinal force is also determined by acceleration pedal signal. The tire force distribution method calculates the desired longitudinal tire forces at left and right wheel using the desired yaw moment and total desired longitudinal force and Maximum longitudinal tire force. And Maximum longitudinal tire force is determined by tire friction circle theory. The proposed method is verified by the simulation using CarSim software. And it is found from simulation results that the proposed method provides improvement vehicle stability and saving the electric energy under the high speed cornering condition.

A Study on Independent Steering & Driving Control Algorithm for 6WS/6WD Vehicle

Skid-steered vehicles are favored for military use in off-road operations because of their high maneuverability and mobility on extreme terrains and obstacles. There is a trend towards transforming steered tracked vehicles to skid-steered wheel vehicles for high speed at the expense of reduced mobility. Skid-steered vehicles turn by generating different longitudinal forces at the tires due to the application of different torques to the wheels on the opposite side of the vehicle. Conventional vehicles, however, cannot generate an opposite driving force at each side wheel. Using an independent steering and driving system, six-wheel vehicles can show better performance than conventional vehicles. Hybrid steering is a combination of skid steering in the load velocity and the steered wheel system at high speed. This steering enhances maneuverability under low speed and stability at high speed. This paper describes a 6WS/6WD vehicle for hybrid steering in three parts: the Vehicle Model, the Control Algorithm for Hybrid Steering, and a Simulation. First, the vehicle model is an application of the TruckSim software for 6WS and 6WD. Second, the hybrid steering control algorithm describes the optimum tire force distribution method for energy savings. The last is simulation and verification.

A Study on an Independent 6WD/6WS of Electric Vehicle using Optimum Tire Force Distribution

This paper presents an optimum tire force distribution method for 6WD/6WS(6-Wheel-Drive and 6-Wheel-Steering) electric vehicles. Using an independent steering and driving system, the performance of 6WD/6WS vehicles can be improved, as, for example, with respect to their maneuverability under low speed and their stability at high speed. Therefore, there should be a control strategy for finding the optimum tire forces that satisfy the driver`s command and minimize energy consumption. From the driver`s commands (steering angle and accelerator/brake pedal stroke), the desired yaw moment, the desired lateral force, and the desired longitudinal force were obtained. These three values were distributed to each wheel as the torque and the steering angle, based on the optimum tire force distribution method. The optimum tire force distribution method finds the longitudinal/lateral tire forces of each wheel that minimize the cost function, which is the sum of the normalized tire forces. Next, the longitudinal/lateral tire forces of each wheel are converted into the reference torque inputs and the steering wheel angle inputs. The proposed method was tested through a simulation, and its effectiveness was verified.

Development of Sensor-based Motion Planning Method for an Autonomous Navigation of Robotic Vehicles

This paper presents the motion planning of robotic vehicles for the path tracking and the obstacle avoidance. To follow the given path, the vehicle moves through the turning radius obtained through the pure pursuit method, which is a geometric path tracking method. In this paper, we assume that the vehicle is equipped with a 2D laser scanner, allowing it to avoid obstacles within its sensing range. The turning radius for avoiding the obstacle, which is inversely proportional to the virtual force, is then calculated. Therefore, these two kinds of the turning radius are used to generate the steering angle for the front wheel of the vehicle. And the vehicle reduces the velocity when it meets the obstacle or the large steering angle using the potentials of obstacle points and the steering angle. Thus the motion planning of the vehicle is done by planning the steering angle for the front wheels and the velocity. Finally, the performance of the proposed method is tested through simulation.

Improvement of the Yaw Motion for Electric Vehicle Using Independent Front Wheel Steering and Four Wheel Driving

With the recent advancement of control method and battery technology, the electric vehicle have been researched to replace the conventional vehicle with electric vehicle with the view point of the environmental concerns and energy conservation. An electric vehicle which is equipped with the independent front steering system and in-wheel motors has advantage in terms of control. For example, the different torque which generated by left and right wheels directly can make yaw moment and the independent steering using outer wheel control is able to reduce the sideslip angle. Using of independent steering and driving system, the 4 wheel electric vehicle can improve a performance better than conventional vehicle. In this paper, we consider the method for improving the cornering performance of independent front steering system and in-wheel motor used electric vehicle with the compensated outer wheel angle and direct yaw moment control. Simulation results show that the method can improve the cornering performance of 4 wheel electric vehicle. We also apply the steering motor failure to steer the vehicle turned by the torque difference without steering. This paper describes an independent front steering and driving, consist of three parts; Vehicle Model, Control Algorithm for independent steering and driving and simulation. First, vehicle model is application of TruckSim software for independent front steering and 4 wheel driving. Second, control algorithm describes the reduced sideslip and direct yaw moment method in view of cornering performance. Last is simulation and verification.

Improvement of Hill Climbing Ability for 6WD/6WS Vehicle using Optimum Tire Force Distribution Method

Multi-axle driving vehicle are favored for military use in off road operations because of their high mobility on extreme terrains and obstacles. Especially, Military Vehicle needs an ability to driving on hills of 60% angle slope. This paper presents the improvement of the ability of hill climbing for 6WD/6WS vehicle through the optimal tire force distribution method. From the driver`s commands, the desired longitudinal force, the desired lateral force, and the desired yaw moment were obtained for the hill climbing of vehicle using optimal tire force distribution method. These three values were distributed to each wheel as the torque based on optimal tire force distribution method using friction circle and cost function. To verify the performance of the proposed algorithm, the simulation is executed using TruckSim software. Two vehicles, the one the proposed algorithm is implemented and the another the tire`s forces are equivalently distributed, are compared. At the hill slop, the ability to driving on hills is improved by using the optimum tire force distribution method.