| Car-trailer combinations(CTCs)are a kind of “tourism and entertainment-oriented”articulated vehicles.When driving on the highway,CTCs are more likely to reach the dynamic critical speed and become unstable because of the dynamic coupling between the towing car and the trailer.And this phenomenon is also called body sway,which brings great hidden trouble to road traffic safety.In the research of vehicle system dynamic,the rearward amplification and influence mechanism of steering system parameters on body sway are studied firstly in this paper.To find out the mechanism of body sway,a 6-DOFs system model of CTCs considering steering system characteristics is established in this paper.The main content of this paper is shown as follows.(1)A theoretical model with 6 DOFs considering steering characteristics of CTCs is established by Lagrange equation.And the corresponding computational model is built in commercial software Trucksim.The steering system stiffness,steering system damping,rotational inertia and dry friction are considered in the theoretical model.And their influence on the yaw motion and sideslip motion of CTCs is investigated.The computional model is used to verify the theoretical model.And the results shows that the dynamic critical speed and yaw rate of these two models have good consistency.(2)The influence of body structure parameters of CTCs on the rearward amplification is analyzed in detail.The critical input angle of steering hand wheel and the critical yaw rate are calculated at different velocities.The effects of vehicle mass,wheelbase and rotation inertia of CTCs on the rearward amplification coefficient and the phase difference of yaw motion between tractor and trailer are studied.The results show that the body structure parameters can lead to the largest rearward amplification coefficient increasing by 80%.The rear wheelbase of the tractor and trailer,the tractor mass and the rotation inertia have great influence on the phase difference of yaw motion.And the yaw motion phase difference can reach 108° at most.(3)The influence of steering system characteristics on the dynamic stability of CTCs is analyzed.Firstly,the influence of different steering system models on the time domain response and critical speed of CTCs is studied.On the basis,the influence of steering system characteristics and the dry friction on dynamic critical,cornering stiffness of tractor front axle and critical yaw rate of CTCs system is analyzed by means of root locus,Jacobian matrix linearization and damping ratio analysis.The results show that the critical speed can increase by 16% under the influence of the steering tie rod stiffness and rack stiffness.And the critical speed can increase by 22% by adjusting the sliding friction factor.Therefore,reasonable selection of steering system characteristics can effectively improve the dynamic stability of CTCs. |
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