【正文】 Accepted 18 January 2012)ABSTRACT?Currently, as well as in the past, researchers have shown great interest in developing suspension systems for vehicles and especially in the design and optimization of the suspension parameters, such as the stiffness and the damping coefficient. These parameters are considered to be important factors that have an influence on safety and improve the fort of the passengers in the vehicle. This paper describes a simplified methodology to determine, in a quick manner, the suspension parameters for different types of passenger cars equipped with passive suspension systems. Currently, different types of passenger cars are produced with different types of suspension systems. Finding a simplified methodology to determine these parameters with sufficient accuracy would contribute a simplified and quick method to the inspection of the working conditions of a suspension system. Therefore, a simple system to determine these parameters is needed. An analysis of the suspension parameters is performed using mathematical modeling and numerical analysis conducted using the Working Model software. The result derived from the developed methodology shows small errors when pared with the generic values, and it can be concluded that the design of the suspension parameter measurement device using the developed methodology is useful, simple, and has sufficient accuracy.KEY WORDS : Passenger car, Suspension system, Suspension parameters, Stiffness and damping coefficient1. INTRODUCTION of vehicles. This is a promise between the vertical sprung mass acceleration, the suspension working space, and the dynamic tire load. When the vehicle moves over an uneven road, the vehicle is exposed to various motions and dynamic loads. The vehicle body should be well isolated from the road excitation with minimal suspension motion yet provide good handling performance. The suspension system is the term given to the system of springs, shock absorbers and linkages that connect a vehicle body to its wheels. The design of the vehicle’s front and rear suspension systems may be different. The springs are assumed to have almost linear characteristics while most of the shock absorbers exhibit a nonlinear relationship between the force and the velocity. Generally, a suspension system may be categorized as apassive, a semiactive or an active system. A passive suspension system involves the parallel mounting of the spring and the shock absorber. A passive suspension is linear in nature and is based on the principle of energy dissipation by the damper. The force acting on the vehicle body results from the relative motion and relative velocity of the suspension. A passive system does not have any control elements incorporated in the system toimprove the road vehicle fort or road holding capability and, therefore, is cheaper to manufacture. Even though it does not fulfill all of the required conditions, this type of suspension is used in almost all types of vehicles. The semiactive suspension system also contains a spring and a shockabsorbing device. However, the performance of these devices (stiffness and damping coefficient) can be controlled by supplying an electrical signal or other sources of external power to the system. The active suspension system requires an external power source. Most vehicles that produce this external energy use a hydraulic actuator to generate the desired force. Despite the higher performance than vehicles equipped with an active suspension system, these systems require greater power consumption, are larger and heavier, and have high manufacturing costs, which are serious disadvantages for the use of such systems in conventional vehicles, Bouzara and Richard (2001).2. INFLUENCE OF THE SUSPENSION SYSTEM IN VEHICLE SAFETY A low performing suspension system can directly influence the handling performances of a vehicle, thus increasing the ability for forces from the tire to be transmitted to the vehicle body, which changes the vertical acceleration of the vehicle body, which is the main factor of rider disfort. To design a wellperforming suspension system, tradeoffs in the solution are required and involve the vertical acceleration of the vehicle body, the suspension working space, and the dynamic tire load, which are modulated by introducing the optimal design parameters. There are some reports and investigations that have been performed by CITA (2010) that indicated that defects in the suspension system (mainly caused by worn shock absorbers) affect the braking performance and cornering characteristics (., in lane change maneuvers). Shock absorber wear or defects can lead to a lowered damping efficiency and, hence, to greater wheel load fluctuations. The contact with the ground is, therefore, restricted, and the force transmission between the tires and the surface is limited especially on uneven or bumpy roads. Calvo et al. (2005), in their simulation results, showed that the stopping distance of a vehicle that had worn shock absorbers increased 3% on a smooth road, whereas on an uneven road, the stopping distance increased up to 16% for the same vehicle parameters. These tendencies explain the effect of weak shock absorbers on vehicle brake performance. This is a result of the poor vertical force between the tire and road, which, in turn, dictates the maximum longitudinal force on the tire. Under suchconditions, the driving stability of the vehicle can be limited by the working conditions of the shock absorber. Summarizing this and other driving tests performed by CITA (2010), it was found that low suspension performance affects the following driving situations: Lane change, Cornering (especially on uneven roads)。 2012 KSAE/ 065?10DOI ?012?0059?7 pISSN 1229?9138/eISSN 19763832POSSIBLE EXPERIMENTAL METHOD TO DETERMINETHE SUSPENSION PARAMETERS IN A SIMPLIFIED MODEL OF A PASSENGER CARSH. L