| Rear wheel steering technology is one of the methods to improve vehicle handling stability.However,the traditional rear wheel steering system has its limitations due to the fixed structure and material parameters.It can only improve vehicle handling within a certain speed range.With the continuous emergence and development of new intelligent materials,many new technologies have emerged in machinery,aviation,civil and other fields.This paper will explore the application of intelligent materials in compliant rear wheel steering vehicle,and put forward semi-active control regulation law and the research of intelligent compliant system for rear wheel steering vehicle.Considering that intelligent materials generally have viscoelastic mechanical properties,the constitutive relationship of intelligent materials is described by fractional calculus.Taking the nonlinear characteristics of tires and the influence of rear wheel steering system into consideration,a three-degree-of-freedom non-linear fractional-order dynamic model of vehicles is established.Through a lot of numerical simulation,the results show that the vehicle occurred the self-excited shimmy phenomenon and this shimmy phenomenon can be improved by changing the parameters of intelligent materials and the structural parameters of CRS system.In addition,this paper mainly studies on some hopf bifurcation figures of parameters of CRS system,which can also provide the reasonable scope of some parameters of CRS system for designing the CRS mechanisms.A semi-active control strategy is proposed based on the characteristics of new intelligent materials.This method can adjust the material parameters of the CRS system in a certain range,realize the adjustable compliant stiffness,and then connect an intelligent damper in parallel to realize the adjustable damping of the CRS system,so as to improve the stability of the compliant steering vehicle.In this paper,the transfer function of front wheel angle and sideslip angle of the rear wheel steering vehicle model is obtained,and the stiffness regulation law and the damping regulation law of the compliant steering system are figured out due to this transfer function.Based on this regulation law,the handling stability of the linear vehicle model and the non-linear vehicle model are studied respectively.The simulation results show that the sideslip angle of the center of mass and the yaw rate of CRS vehicle with semi-active control of linear model decrease obviously compared with CRS vehicle which have no control strategy and the vehicle stability is improved especially at high speed.Under the semi-active control of non-linear model,the sideslip angle of the vehicle center of mass was more connected to zero value.Besides,the semi-active control strategy of non-linear model had a good effective both in low and high speed driving state.The results show that the semi-active control strategy is feasible and practical as well,and more suitable for the non-linear CRS vehicle.In order to combine intelligent material with compliant steering technology,an intelligent compliant steering system is designed in this paper.The system is composed of four-bar motion mechanism and control maneuvering part.Under the action of organic silicon molecular intelligent material and intelligent compliant steering mechanism,the rear wheel steering angle is controlled by changing the compliant stiffness.The intelligent compliant steering mechanism is modeled by CATIA and assembled and simulated by ADAMS.The simulation results show that the intelligent CRS mechanism has displacement amplification effect,and it also verify the feasibility of the intelligent rear-wheel steering mechanism.And when the vehicle steers at a certain speed,only releasing a certain amount of current is needed to realize rear wheel steering.On the other hand,the rationality and applicability of intelligent steering mechanism are demonstrated by comparing the relationship between electric current and steering angle under different lateral forces. |
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