Copyright ® IFAC Automatic Systems for Building the Infrastructure in Developing Countries. Ohrid. Republic of Macedonia. 200 1 TRANSIENT RESPONSE CHARACTERISTICS OF SEMIACTIVE DAMPING WITH FUZZY LOGIC CONTROLLER Darko Babunski, Atanasko Tuneski Faculty of Mechanical Engineering, "Sts. Cyril and Methodius" University, P. D. Box 464,1001 Skopje, Republic of Macedonia. Fax: +3892362298 e-mail: bdarko@ereb1.mfukim.edu.mk Abstract: The designer of damping system for road vehicles is forced to make compromise between the ride comfort and the vehicle safety. For that reason, the new semiactive and active damping policies are invented. The fuzzy logic semi active control policy that is used in this paper is better able to balance the body and axle dynamics than the conventional semi active damping control policies, like sky- or ground-hook semiactive damping policies. The vehicle transient motion is examined for various methods of damping control. The vehicle response was studied for a four- degree-of-freedom, roll-plane model, using passive damping and one method of semiactive damping control, and is compared with other two methods of semiactive damping. Copyright © 2001 IFAC Key words: Fuzzy logic, Vehicle dynamics, Control, Transient responces, Damping 1. INTRODUCTION The semiactive damper control policies include the previously developed on-off skyhook, continuous skyhook, and on-off groundhook control (Ivers and Miller 1994) along with a new method of fuzzy logic semiactive control (Carter 1998). For road inputs, semiactive dampers provide a compromise between the body and axle transient dynamics, compared to passive dampers (Nicholas, et al. 1997). The fuzzy logic control policy that is used in this paper has better body and axle dynamics than the conventional semiactive damping control policies. The designer of vehicle suspension system has to make compromise between ride comfort presented by the body heave displacement and acceleration and safety presented by the body roll and tire heave displacements. The purpose of this research is to examine the effect of fuzzy logic control on the transient response of heave and roll motion of vehicle. Theoretical analysis and simulation of the passive suspension systems, and semi active suspension systems using fuzzy logic controllers have been made with "MATLAB" and "SIMULINK" software. In Paragraph 2 the vehicle 143 model is presented. The fuzzy logic controller model is given in Paragraph 3. The simulation results are presented in Paragraph 5. 2. VEHICLE MODEL The vehicle is presented with four-degree of freedom, roll plane model as shown in Fig. I. The model consists of three masses. The top mass, mb [kg], represents the truck body, while the two lower masses, mt/ [kg], and m tr [kg], represent the left and right tires of the front axle, respectively. The parallel spring and damper combinations located between the truck body and each tire (k sl [N/m], Csl [Ns/m], and ksr [N/m] , C sr [Ns/m)) represent the stiffness and damping of the vehicle suspension system. The respective stiffness of the left and right tires is represented by the lower springs kt/ [N/m] , and k tr [N/m]. On the truck body, a heave force, Fb [N] and a roll force (torque) Tb [Nm], can be exerted. The model has six state variables: Zb, 0 b , Zt/, Ztn Zinl and Zinn where Zb and 0 b represent the heave and roll motions of the truck body, Zt/ and Ztr represent the