Daegun Hong

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.

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

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.

Development of a lane departure monitoring and control system

The lane departure avoidance systems have been considered promising to assist human drivers in AVCS (Advanced Vehicle Control System). In this paper, a lane departure monitoring and control system is developed and evaluated in the hardware-in-the-loop simulations. This system consists of lane sensing, lane departure monitoring and active steering control subsystems. The road image is obtained based on a vision sensor and the lane parameters are estimated using image processing and Kalman Filter technique. The active steering controller for avoiding the lane departure is designed based on the lane departure metric. The proposed lane departure avoidance system is realized in a steering HILS (hardware-in-the-loop simulation) tool and its performance is evaluated with a driver in the loop.

Estimation of Tire Braking Force and Road Friction Coefficient Between Tire and Road Surface For Wheel Slip Control

Recently, wheel slip controllers with controlling the wheel slip directly has been studied using the brake-by-wire actuator. The wheel slip controller is able to control the braking force more accurately and can be adapted to various different vehicles more easily than the conventional ABS systems. The wheel slip controller requires the information about the tire braking force and road condition in order to achieve the control performance. In this paper, the tire braking forces are estimated considering the variation of the friction between brake pad and disk due to aging of the brake, moisture on the contact area or heating. In addition, the road friction coefficient is estimated without using tire models. The estimated performance of tire braking forces and the road friction coefficient is evaluated in simulations.

Estimation of dynamic track tension utilizing a simplified tracked vehicle model

In this paper, track tension estimation methods are developed utilizing a simplified tracked vehicle model so that the track tension can be estimated under various maneuvering tasks such as longitudinal driving on sloping and/or rough roads, turning on flat or sloping roads, etc. The real-time information of the track tension is very important for tracked vehicles because the track tension is closely related to the maneuverability and the durability of tracked vehicles. In the case of longitudinal driving, a modified 3 DOF dynamics model is derived for tracked vehicles and is utilized for estimating the tractive force and track tension. In the case of turning, kinetic models for six road-wheels are utilized for calculating the track tension around the sprocket. The estimation performance of the proposed methods is verified through simulations of the multibody dynamics tool. The simulation results demonstrate the effectiveness of the proposed method under various maneuvering tasks of tracked vehicles.

A performance index for input observer-based monitoring systems

The closed-loop state and input observer (CSIO) is a pole-placement type observer and estimates unknown state and input variables simultaneously. These pole-placement type observers may have poor performance with respect to ill-conditioning factors such as unknown initial estimates, round-off error, modeling error, sensing bias error etc. For the robust monitoring performance, the effects of these ill-conditioning factors must be minimized in designing the observers. In this paper, the transient and steady-state performance of the input observer is investigated quantitatively by considering the error bounds due to ill-conditioning factors. The closed-loop state and input observer with small performance indices are considered as a well-conditioned input observer. By considering both transient and steady-state performance indices, the main performance index is determined as the condition number of the observer eigenvector matrix based on L/sub 2/ norm.