| In the vehicle suspension system and steering system design process,the positional parameters of kingpin is an important factor that has to be considered.Usually it is closely related to the positional parameters of wheel,both of them affect the handling stability of the vehicle,However,due to various factors,the research on the position parameters of kingpin is uneven,and the research on the kingpin inclination angle,the caster angle,the caster offset and the scrub radius is deep and comprehensive,but the attention and research on the castor offset at wheel centre and the kingpin offset at wheel centre are limited.Therefore,this paper takes the positional parameters of kingpin as the research object,the contribution of the kingpin inclination angle,the caster angle and the castor offset at wheel centre on the body lift are studied,and the influence of the castor offset at wheel centre on the vehicle handling stability is mainly studied.Firstly,according to the reality that there is no intersection between the center line of the wheel and the steering axis in some vehicles,through describe the relative positional relationship between the center line of the wheel and the kingpin axis,the physical model of the body lift is established.Then based on the physical model of the body lift and uses the method of graphic transformation to establish the mathematical model of the body lift.The mathematical model analysis results show that the castor offset at wheel centre have a significant influence on the body lift.Then the improved Sobol method is used to analyze the global sensitivity of the body lift mathematical model in MATLAB.The contribution of caster angle,camber angle,toe angle and castor offset at wheel centre are compared and analyzed,the result shows that the kingpin inclination angle,the caster angle and the castor offset at wheel centre have a great influence on the body lift,and the total effect index in the sensitivity index reaches 0.162,0.078 and 0.072 respectively.Secondly,the double wishbone front suspension model is built based on Adams/View and Adams/Car,and the model is simulated by steering and parallel wheel travel to analyze the motion characteristics of suspension,then conducts sensitivity analysis on the body lift base on Adams/Insight,and the results of suspension motion simulation test and theoretical analysis are compared and verified.The results show that the theoretical analysis is feasible and effective.Then,for the problems found in the parallel wheel travel simulation test,the hard point optimization of the suspension is carried out,and the global optimization idea of the front suspension is proposed.The suspension optimization results show that the optimized suspension motion characteristics meet the optimization expectations.Finally,the vehicle model was assembled based on Adams/Car,the steady-state rotation test,the steering returnability test,and the steering portability test are carried out according to the national standard of the vehicle controllability and stability test method.The test results show that the castor offset at wheel centre not only affects the steady-state response,but also has a significant impact on the return-to-back performance and steering portability.After comprehensive consideration,the negative castor offset at wheel centre with a smaller absolute value is beneficial to improve the vehicle handling stability.In addition,the comparative simulation results of the Vorlauf geometry show that even if the caster offset is consistent,the difference of castor offset at wheel centre will still lead to changes in the handling stability of the vehicle. |
