| Due to low cost,convenient operation,steady steering under heavy load and minimal damage to the road surface during driving,heavy trucks with dual front axles are widely utilized nowadays.However,the shimmy phenomenon often occurs in the dual-front axle steering heavy trucks.In some severe cases,the multi-limit cycle self-excited shimmy will be also produced,which will cause the abnormal wear of tires,increase the difficulty of controlling the driving direction of heavy trucks and affect the safety and stability of vehicles.Studies on the dual-front axle heavy trucks are mainly focused on the design and optimization of dual-front axle steering system and the analysis of steering characteristic.However,studies on the self-excited shimmy of the dual-front axle steering heavy trucks,particularly on the multi-limit cycle shimmy are pretty rare.To study the multi-limit cycle shimmy of the dual-front axle heavy trucks,a 8×4heavy truck is taken as the prototype and the method of combing the theoretical and numerical analysis is used to analyze the multi-limit cycle shimmy characteristic.Moreover,a control method that can suppress the multi-limit cycle shimmy is proposed.The main contents of the paper are as follows:(1)A vehicle-road coupled 9-freedom shimmy dynamic model of the dual-front axle steering system is established with consideration of the cornering propertied of tires,nonlinear dry friction of steering system and pavement condition.Hopf bifurcation algebraic criterion is used to analyze the existence of the self-excited shimmy of the dual-front axle steering system.The numerical simulation method is used to study the multi-limit cycle characteristic of the dual-front axle steering system.In addition,the effect of the road adhesion coefficients on the multi-limit cycle shimmy is analyzed.(2)Effects of the steering system stiffness and damping parameters on the multi-limit cycle shimmy characteristic are analyzed to find the stiffness and damping that have great effect on the shimmy characteristic.Moreover,Controlling models of the above stiffness and damping that can suppress the multi-limit cycle shimmy of the dual-front axle steering system are established.(3)On the basis of the dual-front axle steering system,a 11-freedom dynamic model of the full vehicle shimmy system is established with consideration of therolling of the structure above the suspension and the sideslip of vehicle.The numerical simulation method is used to study the multi-limit cycle characteristic of the full vehicle shimmy system.In addition,the effect of the above established stiffness and damping models on the multi-limit cycle shimmy characteristic is studied.Researches show that the multi-limit cycle shimmy occurs not only in the steering system but also in full vehicle and the road driving condition has a great effect on the multi-limit cycle shimmy characteristic.Among the parameters in steering system,the rear longitudinal rod stiffness and the steering tie rod damping of the steering system have great effect on the multi-limit cycle shimmy characteristic.The stiffness and damping models proposed in the paper can greatly restrain the multi-limit cycle shimmy phenomenon. |
