DYNAMICAL ANALYSIS OF AN OFF-ROAD VEHICLE SUSPENSION Fernando Nunes Buarque Pedro Manuel Calas Lopes Pacheco Leydervan de Souza Xavier Paulo Pedro Kenedi CEFET/RJ - Department of Mechanical Engineering 20.271.110 - Rio de Janeiro - RJ - Brazil E-Mail: fbuarque@pl.microlink.com.br,calas@cefet-rj.br, xavierls@cefet-rj.br, pkenedi@cefet-rj.br Abstract. The suspension behavior affects significantly the performance of a vehicle. An optimal condition must guarantee the best compromise among conflicting performance indices pertaining to the vehicle suspension system, that is, comfort, road holding and working space. Therefore, in the development phase of a vehicle design a complete study should be done to verify the actual improvement of optimal suspension characteristics and adjustments in the vehicle overall performance. This work presents a dynamic analysis of an off-road conventional automotive suspension, which was developed for an off-road vehicle type Mini-Baja. A four-degree of freedom dynamic model was developed to study the behavior of the suspension and the influence of the main parameters in the transmissibility of accelerations to the passengers. The model considers the coupling between the front and rear suspension system. Numerical simulations were developed to study the behavior of the suspension submitted to a sequential disturbance, just as it happens when a vehicle in movement comes across a road obstacle like a hole or an elevation. The results obtained with this methodology were analyzed in agreement with the procedures and limits supplied by the ISO 2631-1/97 standard, Evaluation of Human Exposure to Whole-Body Vibration, regarding the aspects related to the passengers health and comfort. The study developed indicates that this methodology can be used as an effective tool for the design and improvement of vehicle suspensions. Keywords. Vehicle Suspension, Modeling, Numerical Analysis, Dynamical Analysis 1. Introduction The Mini-Baja vehicle is completely developed and built by undergraduate engineering students with the orientation of a professor board. During the development, the students are exposed to a real engineering problem involving several areas of knowledge. CEFET/RJ participates on the SAE-Brasil competition since 1997. In the competition these vehicles, which should respect technical and safety SAE standards, are submitted to several tests that expose it to severe conditions. Mini-Baja vehicles are highly competitive which demands an optimized project using advanced technologies. Figure (1) shows the CEFET/RJ vehicle that participated on the VI Baja Cross São Carlos 2002 SAE-Brasil event. During the design process of the Mini-Baja structure it is necessary to quantify the maximum loads in the suspension and the accelerations and loads transmitted to the structure by the suspension. Usually, in the design of a vehicle, a static analysis is developed considering a static load that is equivalent to the maximum dynamic load. The equivalent static load is estimated using factors obtained in literature. These factors are generally quite conservative and they strongly depend on the suspension type. It is well know that the use of these factors can lead to a heavy vehicle. In that way, this work presents results from a project that is under development at CEFET/RJ that contemplates the use of experimental and numerical analysis to gain insight and improve an off-road vehicle, which is developed every year in CEFET/RJ to the Mini-Baja / SAE-Brazil competition. (a) (b) Figure 1 - Mini-Baja CEFET/RJ vehicle (2002 B12C team). (a) Overall view and (b) front suspension detail.