Analysis on Stability Bar

Abstract

Vehicle anti-roll bars are suspension components used for limiting body roll angle. They have a direct effect on the handling characteristics of the vehicle. Design changes of anti-roll bars are quite common at various steps of vehicle production, and a design analysis must be performed for each change. Finite Element Analysis (FEA) can be effectively used in design analysis of anti-roll bars. However, due to high number of repeated design analyses, the analysis time and cost problems associated with the use of general FEA package programs may create considerable. Disadvantages in using these package programs for performing anti-roll bar design analysis. In this study, an automated design program is developed for performing design analysis of vehicle antiroll bars. The program is composed of two parts, the user interface and the FEA macro. The FEA macro includes the codes for performing deformation, stress, fatigue, and modal analysis of anti-roll bars in ANSYS 10. The user interface, which is composed in Visual Basic 8.0, includes the forms for data input and result output procedures. By the developed software, the FEA of the anti roll bars is simplified to simple data entry via user interface. The flow of the analysis is controlled by the program and the finite element analysis is performed by ANSYS at the background. The developed software can perform design analysis for a wide range of anti-roll bars: The bar centerline can have any 3D shape, the cross section can be solid or hollow circular, the end connections can be of pin or spherical joint type, the bushings can be mounted at any position on the bar with a user defined bushing length. The effects of anti-roll bar design parameters on final anti-roll bar properties are also evaluated by performing sample analyses with the automated design program developed in this study. Ride comfort, handling and road holding are the three aspects that a vehicle suspension system has to provide compromise solutions. Ride comfort requires insulating the vehicle and its occupants from vibrations and shocks caused by the road surface. Handling requires providing safety in maneuvers and in ease in steering. For good road holding, the tires must be kept in contact with the road surface in order to ensure directional control and stability with adequate traction and braking capabilities. The anti-roll bar, as being a suspension component, is used to improve the vehicle performance with respect to these three aspects. The anti-roll bar is a rod or tube that connects the right and left suspension members. It can be used in front suspension, rear suspension or in both suspensions, no matter the suspensions are rigid axle type or independent type. The ends of the anti-roll bar are connected to the suspension links while the center of the bar is connected to the frame of the car such that it is free to rotate. The ends of the arms are attached to the suspension as close to the wheels as possible. If the both ends of the bar move equally, the bar rotates in its bushing and provides no tensional resistance. But it resists relative movement between the bar ends, such as shown in Figure1 Figure 1Antiroll/Sway Bar The bar's tensional stiffness-or resistance to twist-determines its ability to reduce such relative movement and it’s called as “roll stiffness”.