Abstract—This paper focuses on a semi-active suspension control applied to the secondary vertical suspension system of railway vehicle. The dynamics of nine degrees-of-freedom (9-DOF) railway vehicle model are governed which includes a vehicle body, two bogies and four wheel-set. The disturbance considered is track irregularity which is modeled as a sine wave. The control algorithm for the semi-active suspension system is developed based on PID controller and Stability Augmentation System (SAS) which is consists of inner and outer loops controller to reduce the effect of track disturbance and stabilize the pitch and roll response. The performances of passive and semi-active suspension are compared by simulation using MATLAB-SIMULINK software. The results of the study show that the PID and SAS controllers are able to significantly improve the ride quality of railway vehicle body. It can be noted that the an inner loop control (ride control loop) is able to further improve the performance of SAS controller for the system. Keywords—railway suspension, stability augmentation system, magneto-rheological damper, vertical response. I. INTRODUCTION AILWAY vehicle has become one of the important public transport systems in recent years due to economical transportation as well as minimizing air pollution. Under competition from other modes of transport, the train passenger has come to expect shorter journey times with better ride comfort. Due to this, development of high- speed railway vehicle has become a great interest in many countries because it has been proven as an efficient This work was supported by the Ministry of Education of Malaysia, Universiti Teknologi Malaysia (UTM) through Research Grant University entitle "Development of Magnetorheological Damper for Improving Ride Comfort of Railway Vehicle” Sub Project No: 08J47, and Universiti Teknikal Malaysia Melaka (UTeM)through laboratory facilities. M. H. Harun is with the Faculty of Mechanical Engineering, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, MALAYSIA (phone: +606-234 6918; fax: +606-2346898; e-mail: hanif@ utem.edu.my). H. Jamaluddin and R. A. Rahman are the Professors at the Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor, MALAYSIA (e-mail: hishamj@fkm.utm.my and roslan@fkm.utm.my). K. Hudha is with the Faculty of Engineering, Universiti Pertahanan Nasional Malaysia, Kem Sungai Besi, 57000 Kuala Lumpur, MALAYSIA (e-mail: k.hudha@upnm.edu.my). W. M. Zailimi is with the Faculty of Mechanical Engineering, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, MALAYSIA (e-mail: zailimi@ utem.edu.my). transportation system. With increasing the speed of the vehicle on a railway vehicle track, the vehicle tends to be unstable due to the increased magnitude motions in various directions such as vertical and lateral. These motions will cause the vehicle passenger to be uncomfortable. In order to deal with this issue, several researches, developers, and engineers from academia and industry have been studied on this matter successfully [1-8], and they reveals that passive suspension system has reached its limit when speed is increasing. Therefore, semi-active suspension technology in railway vehicle can be considered as an alternative solution for this issue, since it offers better possibilities of improving vehicle’s dynamic performance compared to the conventional passive solution [9]. Early work on the semi-active suspension systems has been achieved in the early of 1990s by a group of researchers from ALSTHOM. This study was carried out by O'Neill and Wale [10] on a secondary suspension system of railway vehicle fitted with controllable dampers and the results showing an improvement in ride comfort of 25%. Recent effort on improving the dynamic performance of railway vehicle has been successfully done by Shin, et al. [4]. They was performed a series of simulations and tests on a roller rig with application of MR damper on a secondary suspension system. The development of semi-active secondary vertical suspension of railway vehicle system also has been successfully done through simulation study by Liao and Wang [11] which focusing on improving the ride quality of railway vehicle. The results of the study showed the proposed control was feasible and effective in suppressing the vibration of railway vehicle body. In recent years, advanced control technology has a major impact to the railway vehicle dynamic development since 1975. The vehicle dynamicists have been aware with the use of actuators, sensors and electronic controllers in vehicle suspension. The general benefits can be achieved is better ride quality and running stability of railway vehicle. In this study, a semi-active hybrid skyhook-stability augmentation (Skyhook-SAS) suspension system is proposed for reducing unwanted railway vehicle body motion in lateral direction. Much successful theoretical work on semi-active[6, 12-14] and active [15-17] control for body vibration of railway vehicle has been carried out in China [12, 13] and Japan [16]. But in contrast, there are many challenges must be taken into account especially in research and development of semi-active Application of Stability Augmentation System for Semi-active Railway Vehicle Secondary Vertical Suspension M. Hanif Harun, H. Jamaluddin, K. Hudha, R. Abd Rahman, W. Mohd Zailimi R INTERNATIONAL JOURNAL OF MATHEMATICAL MODELS AND METHODS IN APPLIED SCIENCES Volume 8, 2014 ISSN: 1998-0140 294