Kunsoo Huh

Active steering control based on the estimated tire forces

Steering of vehicles on a slippery highway is a difficult task for most passenger car drivers. The vehicles tend to slide outward with less lateral forces than on normal roads. When the drivers notice that their vehicles on a slippery highway start to depart from the cornering lane, most of them easily panic and make a sudden steering and/or braking, which in turn may induce spin-out and instability on their vehicles. In the paper, an active steering control method is proposed such that the vehicles on slippery roads are steered as if they are driven by experienced drivers. Those drivers have better perceptive capability of judging the slippery status and they respond faster with smooth compensatory action. In the proposed method, the estimated lateral forces acting on the steering tires are compared with the reference values and the difference is compensated by the active steering method. A fuzzy logic controller is designed and its performance is evaluated on a hardware-in-the-loop simulation system. This method can be realized with a steer-by-wire concept and is promising as an active safety technology.

Development of a Vehicle Stability Control System Using Brake-by-Wire Actuators

The wheel slip control systems are able to control the braking force more accurately and can be adapted to different vehicles more easily than conventional braking control systems. In order to achieve the superior braking performance through the wheel slip control, real-time information such as tire braking force at each wheel is required. In addition, the optimal target slip values need to be determined depending on the braking objectives such as minimum braking distance, stability enhancement, etc. In this paper, a vehicle stability control system is developed based on the braking monitor, wheel slip controller, and optimal target slip assignment algorithm. The braking monitor estimates the tire braking force, lateral tire force, and brake disk-pad friction coefficient utilizing the extended Kalman filter. The wheel slip controller is designed based on the sliding mode control method. The target slip assignment algorithm is proposed to maintain the vehicle stability based on the direct yaw-moment controller and fuzzy logic. A hardware-in-the-loop simulator (HILS) is built including electrohydraulic brake hardware and vehicle dynamics software. The effectiveness of the proposed stability control system is demonstrated through the HILS experiment.

Development of a Multi-body Dynamics Simulation Tool for Tracked Vehicles

In this paper, the nonlinear dynamic modeling methods for the virtual design of tracked vehicle are investigated by using multibody dynamic simulation techniques. The results include high oscillatory signals resulting from the impulsive contact forces and the use of stiff compliant elements to represent the joints between the track links. Each track link is modeled as a body, which has six degrees of freedom, and two compliant bushing elements is used to connect track links. The efficient contact search kinematics and algorithms in the context of the compliance contact model are developed to detect the interactions between track links, rollers, sprockets, and ground for the sake of speedy and robust solutions. In order to validate the developed nonlinear multibody dynamic model against the experimental measurements, several empirical techniques are suggested and applied to the physical proving ground tests of the high mobility tracked vehicle. In this empirical validations, positions, velocities, accelerations and forces of the chassis and the track sub-systems are correlated accordingly.

Vision-based vehicle detection and tracking algorithm design

The vision-based vehicle detection in front of an ego-vehicle is regarded as promising for driver assistance as well as for autonomous vehicle guidance. The feasibility of vehicle detection in a passenger car requires accurate and robust sensing performance. A multivehicle detection system based on stereo vision has been developed for better accuracy and robustness. This system utilizes morphological filter, feature detector, template matching, and epipolar constraint techniques in order to detect the corresponding pairs of vehicles. After the initial detection, the system executes the tracking algorithm for the vehicles. The proposed system can detect front vehicles such as the leading vehicle and side-lane vehicles. The position parameters of the vehicles located in front are obtained based on the detection information. The proposed vehicle detection system is implemented on a passenger car, and its performance is verified experimentally.

Monitoring System Design for Lateral Vehicle Motion

Monitoring of lateral vehicle motion is very useful in many active safety applications such as yaw stability control and rollover prevention. Lateral velocity and sideslip angle are regarded as the most important motion variables. However, it is not feasible during vehicle operation to directly measure them due to the high cost of sensors, limitations to sensor technology, etc. Therefore, the monitoring of lateral vehicle motion can be realized by using either accurate monitoring models or improved estimation algorithms. In this paper, monitoring models are obtained such that they utilize not only the vehicle dynamics but the cornering stiffness and the roll motion as well. Based on these monitoring models, three monitoring systems are constructed to estimate the vehicle velocity and the sideslip angle based on the sliding mode observer, the extended Kalman filter (EKF) including Dugoffs tire model, and the scaled Kalman filter with model error compensator (SKFMEC) methods, respectively. The estimation performance of the monitoring systems is verified in field tests, and the experimental results demonstrate the effectiveness of this approach to provide accurate monitoring of lateral vehicle motion.

Wheel slip control systems utilizing the estimated tire force

The wheel slip control systems are able to control the braking force more accurately and can be adapted to different vehicles more easily than conventional braking control systems. In order to achieve the superior braking performance through the wheel slip control, real-time information such as the tire braking force at each wheel is required. In addition, the optimal target slip values need to be determined depending on the braking objectives such as minimum braking distance, stability enhancement, etc. In this paper, a wheel slip control system is developed for maximizing the braking force and maintaining the vehicle stability based on the braking monitor, wheel slip controller and optimal target slip assignment algorithm. The braking monitor estimates the tire braking force, lateral tire force and brake disk-pad friction coefficient utilizing the extended Kalman filter. The wheel slip controller is designed based on the sliding mode control method. The target slip assignment algorithm is proposed to maximize the braking force and to maintain the vehicle stability, respectively. The performance of the proposed wheel slip control system is verified in simulations and demonstrates the effectiveness of the wheel slip control in various road conditions

IMPLEMENTATION AND VEHICLE TESTS OF A VEHICLE STOP-AND-GO CRUISE CONTROL SYSTEM

Abstract Implementation and vehicle tests of a vehicle longitudinal control algorithm for stop-and-go cruise control have been performed. The vehicle longitudinal control scheme consists of a set-speed control algorithm, a speed control algorithm, and a distance control algorithm. A desired acceleration for the vehicle for the control of vehicle-to-vehicle relative speed and clearance has been designed using linear quadratic optimal control theory. Performance of the control algorithm has been investigated via vehicle tests. Vehicle tests have been conducted using two test vehicles. A 2000 cm3 passenger car equipped with a radar distance sensor, throttle/brake actuators and a controller has been used as a subject vehicle in the vehicle tests. A millimetre wave radar sensor has been used for distance measurement. A step motor and an electronic vacuum booster have been used for throttle/brake actuators. It has been shown that the implemented vehicle longitudinal control system can provide satisfactory performance in vehicle set-speed control and vehicle clearance control at lower speeds.

Optimal Proportional-Integral Adaptive Observer Design for a Class of Uncertain Nonlinear Systems

Proportional adaptive observers, which have only a proportional feedback loop of the output estimation error, may suffer large estimation errors due to disturbances. To improve steady-state estimation performance, this paper presents a proportional-integral adaptive observer for a class of uncertain nonlinear systems, which includes both a proportional feedback loop and an integral feedback loop of the output observation error. The additional integral loop improves steady-state estimation performance and robustness against disturbances. The proportional and the integral observer gains are optimally chosen by solving the L2 gain minimization problem, which leads to the minimal effect of disturbances on the estimation error. The effectiveness of the proposed adaptive observer is demonstrated through a numerical example. This new design approach on a proportional-integral adaptive observer can provide not only better estimation performance, but also a straightforward way to choose optimal observer gains.

Optimal robust adaptive observer design for a class of nonlinear systems via an H-infinity approach

Existing adaptive observers may suffer parameter estimate drift due to disturbances even if state estimation errors remain small. To avoid such drift in the presence of bounded disturbances, several robust adaptive observers have been introduced providing bounds in state and parameter estimates. However, it is not easy for these observers to manipulate the size of the bounds with the selection of the observer gain. To reduce estimation errors, this paper introduces the H-infinity norm minimization problem in the adaptive observer structure, which minimizes the H-infinity norm between disturbances and estimation errors. The stability condition of the adaptive observer is reformulated as a linear matrix inequality, and the observer gain is optimally chosen by solving the resulting convex optimization problem. The estimation performance is demonstrated through a numerical example

Robust Wheel-Slip Control for Brake-by-wire Systems

Wheel-slip control systems are able to control the braking force more accurately and can be adapted to different vehicles more easily than conventional ABS systems. But, in order to achieve the superior braking performance through the wheel-slip control, real-time information such as the tire braking force is required. For example, in the case of EHB (Electro-Hydraulic Brake) systems, the tire braking force cannot be measured directly, but can be approximated based on the characteristics of the brake disk-pad friction. The friction characteristics can change significantly depending on aging of the brake, moisture on the contact area, heat etc. In this paper, a wheel slip The proposed wheel slip control system is composed of two subsystems: braking force monitor and robust slip controller In the brake force monitor subsystem, the tire braking forces as well as the brake disk-pad friction coefficient are estimated considering the friction variation between the brake pad and disk. The robust wheel slip control subsystem is designed based on sliding mode control methods and follows the target wheel-slip using the estimated tire braking forces. The proposed sliding mode controller is robust to the uncertainties in estimating the braking force and brake disk-pad friction. The performance of the proposed wheel-slip control system is evaluated in various simulations.