Study On Rollover Instability Mechanism And Active Anti-rollover Control Method For Articulated Steer Vehicles

Traveling on complex road as well as working in poor conditions, the gravity center ofarticulated steer vehicles (ASV) will severely offset laterally when steering, leading a highprobability of rollover accident. The rollover instability mechanism and active anti-rollovercontrol method of the ASV was studied under the support of National Natural ScienceFoundation of China (NO.51175216) and Ministry of Education Fund for the Doctoral(NO.20100061110014). Firstly, a7-DOFs nonlinear dynamics model was built, it includedarticulated steering movement, swinging bridge movement and ground environmentalparameters. Then the instability mechanism and dynamic rollover stability index for the ASVwere obtained. On the basis above, we proposed active anti-rollover control method combinedwith active braking, active steering and swing bridge adjustment. The specific work is asfollows:According to the structural features of the ASV, it was divided into three parts: a frontbody, a rear body and a rear axle. By analyzing the connections and relationships among thethree parts, we obtained the vehicle DOFs which contains the translational movements(longitudinal, lateral and vertical) and the rotational movements (pitch and yaw of the wholevehicle, roll of the front body and the rear body). On this basis, a7DOFs nonlinear dynamicsmodel of the ASV was built. A physical prototype model of the ASV was designed andmanufactured to validate the dynamic model under three conditions (turning on level ground,passing over obstacles and turning on uneven road). The test results agreed well with thesimulation ones. Thus, the proposed dynamic model was convinced to be reasonable and couldbe served as a tool for analyzing the stability of the ASV.Based on the established dynamics model, detailed analysis of a wheel loader’s dynamicrollover stability was carried out in the conditions of turning/passing over obstacles andtraveling on slopes. The analysis results showed that the stability of the ASV largely dependedon the roll angular velocity. Rollover will occur when the roll angular velocity exceeds acritical threshold which affected by vehicle structure, lateral acceleration and slope angle. Onthis basis, a dynamic stability index (DSI) applicable to ASV was defined. The DSI containsthe information of roll rate, lateral acceleration and slope angle.After obtaining the rollover mechanism of ASV, the effect of active braking, activesteering and swing bridge adjustment on rollover stability was studied. The results showedthat (1) Active braking will be propitious to improve vehicle stability when cornering;(2)Active Steering will help to improve the roll stability of the vehicle when cornering andpassing over obstacles under the premise of no secondary accident occurring;(3) Swing bridge adjustment will improve vehicle stability in any instability conditions by changing the positionof the vehicle’s center of gravity. Considering the characteristics of the anti-rollover controlmethod of the active braking, active steering and swing bridge adjustment, respectively, weproposed an active anti-rollover control method combined with active braking, active steeringand swing bridge adjustment, which is verified by using the physical prototype.In order to achieve the active anti-rollover control method mentioned above, the existingpassive swing bridge had been improved by adding an electro-hydraulic proportional controlsystem. This control system could achieve the following functions:(1) The swing bridge canbe free to swing with the terrain when the vehicle is traveling normally, it is the basic functionof the swing bridge;(2) Control the swing bridge to roll in the opposite direction to achieveactive anti-rollover control by adjusting the position of the vehicle’s center of gravity when therollover occurring. Finally, based on multi-body dynamics software RecurDyn and controlsoftware Matlab/Simulink, a virtual prototype model of one wheel loader which contains theimproved swing bridge was built to verify the reasonableness of the control system. The resultsshowed that the improved swing bridge could achieve active anti-rollover control of ASV aswell as guarantee its basic function.In summary, this paper established a rollover dynamics model and designed physicalprototype model of the ASV. The rollover instability mechanism and the active anti-rollovercontrol method for the ASV were analyzed by both dynamic simulation and experimentalvalidation. The research provides a basis for the safety design and the development of activesafety technology of the ASV, and it is of significance for protecting the life of the driver ofthe ASV.