Seung-Jin Heo

Controller design for improving lateral vehicle dynamic stability

A vehicle dynamics control system has been developed in this study for improving vehicle dynamic stability under critical lateral motions. The system consists of a feedforward controller, a state feedback controller, and an estimator for the body sideslip angle. The linear quadratic regulator theory has been exploited for the state feedback gain, and for estimation of the body sideslip angle, a nonlinear observer has been developed. Simulations have been conducted to evaluate the performance of the closed loop system under various driving conditions, and the results will be presented in this paper.

Vehicle Dynamic Analysis and Evaluation of Continuously Controlled Semi-Active Suspensions Using Hardware-in-the-loop Simulation

SUMMARY A semi-active suspension system with continuously variable damper is greatly expected to be used mainly in the future as a high-performance suspension system due to its cost-effectiveness, light weight, and low energy consumption. In this paper, to develop a suitable control logic for the semi-active suspension system, the hardware-in-the-loop simulation is performed for the experimental continuously variable damper combined with a quarter-car model, and the simulation results are compared for passive, on/off controlled, and continuously controlled dampers in the aspects of ride comfort and driving safety, assuming each damper to be installed on the vehicle.

A study on the brake-by-wire system using hardware-in-the-loop simulation

HILS (Hardware-In-the-Loop Simulation) is a scheme that incorporates hardware components of primary concern in the numerical simulation environment. Due to its advantages over actual vehicle test and pure simulation, HILS is being widely accepted in automotive industries as a test bench for designing, evaluating, and benchmarking vehicle control units. Developed in this study is a HILS system for the EHB (Electro-Hydraulic Brake) brake-by-wire system. The system includes a high pressure generator and a valve control system that independently modulates the brake pressures at four wheels. An EHB control logic and a VDC (Vehicle Dynamics Control) logic were tested in the HILS system. Test results under various driving conditions are presented in this paper.

Conservative quadratic RSM combined with incomplete small composite design and conservative least squares fitting

A new quadratic response surface modeling method is presented. In this method, the incomplete small composite design (ISCD) is newly proposed to reduce the number of experimental runs than that of the SCD. Unlike the SCD, the proposed ISCD always gives a unique design assessed on the number of factors, although it may induce the rank-deficiency in the normal equation. Thus, the singular value decomposition (SVD) is employed to solve the normal equation. Then, the duality theory is used to newly develop the conservative least squares fitting (CONFIT) method. This can directly control the over- or the under-estimation behavior of the approximate functions. Finally, the performance of CONFIT is numerically shown by comparing its’ conservativeness with that of conventional fitting method. Also, optimizing one practical design problem numerically shows the effectiveness of the sequential approximate optimization (SAO) combined with the proposed ISCD and CONFIT.

MODELLING OF CONTINUOUSLY VARIABLE DAMPER FOR DESIGN OF SEMI-ACTIVE SUSPENSION SYSTEMS

The continuously variable damper is widely used in the semi-active suspension system since it can yield various damping forces at a given damper velocity. By applying an appropriate control scheme to the damper, satisfaction of both ride comfort and driving safety can be realized. For successful development of the semi-active suspension system, a model that accurately describes the complex and nonlinear behaviour of the continuously variable damper is crucial. In this research, a modelling technique for the continuously variable damper has been studied. Various damper components have been analysed and their effects upon damper characteristics have been closely investigated. The effects of the damper characteristics change upon ride comfort and driving safety have also been investigated via simulations.

New Vehicle Dynamics Model for Yaw Rate Estimation

SUMMARY This paper presents a new vehicle model to estimate vehicle yaw rate. This model is improved from the conventional two-degree-of-freedom vehicle model, so-called bicycle model, taking nonlinear effects into account. This model is still linear, although nonlinear effects are included. Nonlinear effects are expressed as a time variant system. These nonlinear effects are: (i) tyre nonlinearity; (ii) lateral load transfer during cornering; (iii) variable gear ratio with respect to vehicle velocity. Kalman filter equation was derived from the proposed model. Estimation results are validated with the experimental results.

Integrated Chassis Controller Design of Active Steering and Active Braking Systems Using CL Method

Most electronic chassis control systems so far have been designed for optimization of its own performance. This, sometimes, has resulted in performance degradation when two or more control modules were operating together. Recently, great R&D effort is being given to judicious integration of individual chassis control systems in an effort to further enhance the overall vehicle performance. The vehicle system equipped AFS and ESC is a multi-input-multi-output(MIMO) system. In this paper, chassis controller using Characteristic Locus(CL) design method based on frequency-domain techniques was developed for integrating AFS(Active Front Steering) with ESC(Electronic Stability Control) systems. Finally, the proposed controller is varified with CarSim simulation in various driving condition.

Design Optimization of Over-slam Bumper for Moving Part Over-travel

Abstract : A kinematic analysis method has been used as analysis method for dynamic behavior of moving parts of vehicle, especially hood part. Such analysis method, however, has its limitations in terms of design technology, including, over travel of hood that occurs due to lack of considerations of compliance characteristics, such as flexible components of hood’s weather strip and over slam bumper. Therefore, it is necessary to develop a modeling which reflects compliance of flexible components of hood and elastic characteristics of panel for improvement of design process. In this thesis, a finite element method as mentioned earlier, is developed to represent over travel of hood. Also optimization process applying sequential approximate optimization is suggested to prevent over travel. The over travel analysis method and optimization process, which are developed through the research, would make it possible to design with high quality and credibility. Furthermore, it is expected that the time for design would be reduced and the design quality also improved.