• Transactions of the Korean Society of Automotive Engineers
• /
• v.2 no.5
• /
• pp.101-109
• /
• 1994

Recently, four-wheel steering systems have been developed and studied as one of the latest automotive technologies for improving the handling characteristics of a vehicle. In much of the proposed four-wheel steering systems, the side slip angle at the vehicle's center of gravity is maintained at zero. This approach allows the greater maneuverability at low speed by means of counter-phase rear steering and the improved stability at high speed through same-phase rear steering. In this paper, the effects of several four-wheel steering systems are studied and discussed on the responsiveness and stability of the vehicle by using the linear analysis. Especially, the effects of the cornering stiffnesses of both front and rear wheels are investigated on the yaw velocity gain and critical speed of the vehicle.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.3 no.3
• /
• pp.119-128
• /
• 1995

A driver-vehicle model means the integrated dynamic model that is able to estimate the steering wheel angle from the driver's desired path based on the dynamic characteristics of the driver and vehicle. In this paper, the dynamic characteristics of several four-wheel steering systems with the simultaneously steerable front and rear wheels are investigated and compared by means of the driver-vehicle model. Especially, the presented analysis results are obtained by using the ISO test codes such as lane change, double lane change and slalom, and the effects of the driver's steering response time and vehicle speed are examined on the responsiveness and stability of vehicle.

• Journal of the Korean Institute of Intelligent Systems
• /
• v.7 no.4
• /
• pp.29-39
• /
• 1997

A discrete model reference control scheme for a vehicle four wheel steering system(4WS) is proposed and evaluated for a class of discrete time nonlinar dynamics. The schmen employs a neural network to identify the plan systems, wher the neural network estimates the nonlinear dynamics of the plant. The algorithm is proven to be globally stable, with tracking errors converging to the neighborhood of zero. The merits of this scheme is that the global system stability is guaranteed. Whith thd resulting identification model which contains the neural networks, the parameters of controller are adjusted. The proposed scheme is applied to the vehicle active four wheel system and shows the validity and effectiveness through simulation. The three-degree-of freedom vehicle handling model is used to investigate vehicle handing performances. In simulation of the J-turn maneuver, the yaw rate overshoot reduction of a typical mid-size car is improved by 30% compared to a two wheel steering system(2WS) case, resulting that the proposed scheme gives faster yaw rate response andl smaller side slip angle than the 2WS case.

• Journal of the korean Society of Automotive Engineers
• /
• v.12 no.3
• /
• pp.21-29
• /
• 1990

Equipments of passenger cars with modern technologies are gaining their importance. Related with such developments, the four-wheel steering system (4WS) was introduced recently to a few passenger cars in the market. The most important research goal on this new steering system is improvement of active safety, in other words, improvement of handling characteristics of vehicle stability and maneuverability. This paper presents a computer-based study about the effects of 4WS system on the vehicle handling characteristics. A simple bicycle model of 2 d.o.f. is used for the development of four wheel control algorithms of 4WS system, and the rear wheel control strategies are applied to a complex vehicle model of 16 d.o.f. for simulation of selected ISO-driving tests. The 4WS systems, which reduce the sideslip angle at the mass center of vehicle to almost zero, show much improved handling characteristics compared to that of the conventional 2WS system. These 4WS systems, however, result in vehicles with eigen-steer characteristics of extreme understeer behaviour.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.4 no.4
• /
• pp.87-96
• /
• 1996

The proportional pressure control valve(PCV) is an essential component in the open loop controlled rear wheel steering gear of the four wheel steering(4WS) system on the passenger car. The valve should have versatile functions and higher performance. But, it is hard to find the proportional pressure control valve suitable for the 4WS system. In this paper, the determination of the valve parameters was studied by the stability discrimination and the characteristic analysis for the purpose of the development of a new PCV for the 4WS. The mathematical model of the valve was derived from the valve-cylinder system and the programme for numerical computation was developed. The transfer function of the system was obtained from the mathematical model. The characteristics of the valve were inspected through the experiment and compared to those obtained by numerical method. And then the stability discrimination of the system was done by root locus and the analysis of characteristics was done by the developed programme. From the experiment and the analysis of characteristics was done by the developed programme. From the experiment and the inspection, the appropriation of mathematical model and the usefulness of the programme were confirmed. And the parameters which might affect the performance of the valve can be determined by considering the stability discrimination, the characteristics analysis and required functions.

• Journal of the Korean Institute of Intelligent Systems
• /
• v.9 no.5
• /
• pp.480-489
• /
• 1999

Design and experimental results of yaw rate controller is described for electricallydriven four wheel vehicle without steering mechanism. Yaw rate controller has been known to be necessary to cope with nonlinear char-acteristics of the wheel/road conditions with respect to different road condition and steering angle. For an effective yaw rate control, a fuzzy PID gain scheduler is considered with changing control parameters. In order to apply proposed algorithm to the system a downsized four wheel drive electrically driven vehicle without steering mechanism was manufactured. With these techniques the proposed yaw rate controller is shown by experiment results to be obtained suficient performance in the whole steering regions.

• Journal of Auto-vehicle Safety Association
• /
• v.15 no.2
• /
• pp.13-20
• /
• 2023

This paper presents a fault tolerant control strategy for Steer-by-Wire (SbW) systems. Among many problems to be solved before commercialization of SbW systems, maintaining reliability and fault tolerance in such systems are the most pressing issues. In most previous studies, dual steering motors are used to achieve actuation redundancy. However, relatively few studies have been conducted to introduce fault tolerant control strategies using rear wheel steering system. In this work, an actuator fault in front wheel steering is compensated by active rear wheel steering. The proposed fault tolerant control algorithm consists of disturbance observer and sliding mode control. The fault tolerant control performance of the proposed approach is validated via computer simulation studies with Carsim vehicle dynamics software and MATLAB/Simulink.

• Journal of Institute of Control, Robotics and Systems
• /
• v.19 no.1
• /
• pp.45-55
• /
• 2013

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.

• International Journal of Automotive Technology
• /
• v.8 no.3
• /
• pp.299-308
• /
• 2007

This study proposes a two-layer hierarchical control system that integrates active front wheel steering and four wheel braking torque control to improve vehicle handling performance and stability. The first layer is a robust model matching controller (R-MMC) based on linear matrix inequalities (LMIs), which optimizes an active front steering angle compensation and a desired yaw moment control, and calculates reference wheel slip for the target wheel according to the desired yaw moment. The second layer is a moving sliding mode controller (MSMC) that can track the reference wheel slip in a predetermined time by commanding proper braking torque on the target wheel to achieve the desired yaw moment. Since vehicle sideslip angle measurement is difficult to achieve in practice, a sliding mode observer (SMO) that requires only vehicle yaw rate as the measured input is also developed in this study. The performance and robustness of the SMO and the integrated control system are demonstrated through comprehensive computer simulations. Simulation results reveal the satisfactory tracking ability of the SMO, and the superior improved vehicle handling performance, stability and robustness of the integrated control vehicle.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.10 no.1
• /
• pp.209-215
• /
• 2002

A study of the guideway vehicle was made for a comparison of ride stabilities between its two primary steering types; one is the front wheel steering and the other the front-rear wheel. A numerical model as a closed loop system was built for an investigation of various factors to have an influence on the vehicular critical speed which is closely associated with ridabilities. It was shown that dynamics stabilities of the front steering type was much better over a large value of steering gain and the longer distance between front axle and guide link for both types provided better stabilities as well. A large steering gain ratio of the front to the rear significantly plays an important role in an improvement of stability in the front-rear steering. To observe a qualitative trend on stability behaviors, the root locus was obtained by considering a time lag which may be frequently caused by the complicated steering mechanism. In performing so, the appropriate selection of steering gain had a greater effect on the front-rear steering vehicle far more ride comfort. In addition, the dynamics model proposed here can be utilized for a more accurate evaluation on the vehicle design in lateral or yawing absorber and moreover expanded for the analysis of independent four-wheel steering vehicle.