• Title, Summary, Keyword: 4WS(Four Wheel Steer)

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Effect of four-wheel steering system on vehicle handling characterisitcs (4륜 조향시스템이 차량의 주행역학적 특성에 미치는 영향)

  • 심정수;허승진;유영면
    • Journal of the korean Society of Automotive Engineers
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    • v.12 no.3
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    • pp.21-29
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    • 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.

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Design of a Robust Controller to Enhance Lateral Stability of a Four Wheel Steer Vehicle with a Nonlinear Observer (비선형 관측기를 이용한 사륜조향 차량의 횡방향 안정성 강화를 위한 강인 제어기 설계)

  • Song, Jeong-Hoon
    • Transactions of the Korean Society of Automotive Engineers
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    • v.15 no.6
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    • pp.120-127
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    • 2007
  • This paper describes the development of a nonlinear observer for four wheel steer (4WS) vehicle. An observer is designed to estimate the vehicle variables difficult to measure directly. A brake yaw motion controller (BYMC), which uses a PID control method, is also proposed for controlling the brake pressure of the rear and inner wheels to enhance lateral stability. It induces the yaw rate to track the reference yaw rate, and it reduces a slip angle on a slippery road. The braking and steering performances of the anti-lock brake system (ABS) and BYMC are evaluated for various driving conditions, including straight, J-turn, and sinusoidal maneuvers. The simulation results show that developed ABS reduces the stopping distance and increases the longitudinal stability. The observer estimates velocity, slip angle, and yaw rate of 4WS vehicle very well. The results also reveal that the BYMC improves vehicle lateral stability and controllability when various steering inputs are applied.

A Study on Lateral Stability Enhancement of 4WS Vehicle with Active Front Wheel Steer System (능동전륜조향장치를 채택한 사륜조향차량의 횡방향 안정성 강화에 대한 연구)

  • Song, Jeong-Hoon
    • Transactions of the Korean Society of Automotive Engineers
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    • v.20 no.2
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    • pp.15-20
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    • 2012
  • This study is to propose and develop an integrated dynamics control system to improve and enhance the lateral stability and handling performance. To achieve this target, we integrate an AFS and a 4WS systems with a fuzzy logic controller. The IDCS determines active additional steering angle of front wheel and controls the steering angle of rear wheel. The results show that the IDCS improves the lateral stability and controllability on dry asphalt and snow paved road when double lane change and step steering inputs are applied. Yaw rate of the IDCS vehicle tracks reference yaw rate very well and body slip angle is reduced about by 50%. Response time of the IDCS vehicle is also decreased.

A Study on Controller Design to Improve the Driving Performance of the Four Wheel Steering Vehicle (4륜 조향 차량의 주행성능 개선을 위한 제어기 설계에 관한 연구)

  • Sohn, Ju-Han;Choi, Sung-Uk;Lee, Young-Jin;Lee, Jin-Woo;Lee, Kwon-Soon
    • Proceedings of the KIEE Conference
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    • pp.2569-2571
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    • 2000
  • In the vehicle steering system, we can consider two methods to steer the vehicle. One is a front wheel steering(FWS), the other is a four wheel steering(4WS). The four wheel steering method has been recently introduced to improve the steering performance. In this paper, we present a design of the four wheel steering controller. First, we constructed the neural network two degree of freedom PID controller to control the 4WS system. Then we compared the performance of conventional PID controller with our proposed controller in terms of yaw rate and side slip velocity. The computer simulation results show that 4WS system controlled by the proposed controller has well driving performances than the other.

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Using an ABS Controller and Rear Wheel Controller for Stability Improvement of a Vehicle (ABS 제어 및 후륜조향 제어기를 이용한 차량 안정성 개선에 관한 연구)

  • Song, Jeong-Hoon;Boo, Kwang-Suck;Lee, Jong-Il
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.28 no.8
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    • pp.1125-1134
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    • 2004
  • This paper presents a mathematical model which is about the dynamics of not only a two wheel steering vehicle but a four wheel steering vehicle. A sliding mode ABS control strategy and PID rear wheel control logic are developed to improve the brake and cornering performances, and enhance the stability during emergency maneuvers. The performances of the controllers are evaluated under the various driving road conditions and driving situations. The numerical study shows that the proposed full car model is sufficient to accurately predict the vehicle response. The proposed ABS controller reduces the stopping distance and increases the vehicle stability. The results also prove that the ABS controller can be employed to a four wheel steering vehicle and improves its performance. The four wheel steering vehicle with PID rear wheel controller shows increase of stability when a vehicle speed is high and sharp cornering maneuver when a vehicle speed is low compared to that of a two wheel steer vehicle.

Development of the Dynamic Model and Control Logic for the Rear Wheel Steering in 4WS Vehicle (후륜 조향 동력학 모델 및 제어 로직 개발)

  • 장진희;김상현;한창수
    • Transactions of the Korean Society of Automotive Engineers
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    • v.4 no.6
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    • pp.39-51
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    • 1996
  • In the turning maneuver of the vehicle, its motion is mainly dependent on the genuine steering characteristics in view of the directional stability for stable turning ability. The under steer vehicle has an ability to maintain its own directonal performance for unknown external disturbances to some extent. From a few years ago, in order to acquire the more enhanced handling performance, some types of four wheel steering vehicle were considered and constructed. And, various rear wheel control logics for external disturbances has not been suggested. For this reason, in this posed rear wheel control logic is based on the yaw rate feed back type and is slightly modified by an yaw rate tuning factor for more stable turning performance. And an external disturbance is defined as a motivation of the additional yaw rate in the center of gravity by an uncertain input. In this study, an external disturbance is applied to the vehicle as a form of the additional yawing moment. Finally, the proposed rear wheel control logic is tested on the multi-body analysis software(ADAMS). J-turn and double lane change test are performed for the validation of the control logic.

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Development and Evaluation of ESP Systems for Enhancement of Vehicle Stability during Cornering (II) (차량의 선회시 주행 안정성 강화를 위한 ESP 시스템 개발 및 성능 평가 (II))

  • Song, Jeong-Hoon
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.30 no.12
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    • pp.1551-1556
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    • 2006
  • Two yaw motion control systems that improve a vehicle lateral stability are proposed in this study: a rear wheel steering yaw motion controller (SESP) and an enhanced rear wheel steering yaw motion controller (ESESP). A SESP controls the rear wheels, while an ESESP steers the rear wheels and front outer wheel to allow the yaw rate to track the reference yaw rate. A 15 degree-of-freedom vehicle model, simplified steering system model, and driver model are used to evaluate the proposed SESP and ESESP. A robust anti-lock braking system (ABS) controller is also designed and developed. The performance of the SESP and ESESP are evaluated under various road conditions and driving inputs. They reduce the slip angle when braking and steering inputs are applied simultaneously, thereby increasing the controllability and stability of the vehicle on slippery roads.