Research On Vertical Damping Force Control Based On Dynamic Stiffness Adjustment And Stability Improvement

The quality and the knowledge reserve of nationals are significantly increased and the rational consumption characteristics of automobiles are increasingly significant with the improvement of information level in the current era.Automotive consumers have a clearer understanding and more universal yearning for comfort,stability and safety of automobiles.The suspension system is one of the most important systems in the vehicle.It is related to the vibration isolation of the whole vehicle body and the conduction of various components.Both the ride comfort and the stability of the vehicle are affected by suspension systems as well.However,the potential of suspension assembly is often limited to the field of vertical dynamic control.The vehicle is generally equipped with stability control system nowadays.It seems that the safety and the stability performance of the vehicle has reached a limit.How to further expand the dynamic control potential of the vehicle is the goal and the dream of every research and design personnel.For the suspension assembly,the coupling effect of each direction dynamics can be used to make full use of the vertical dynamics characteristics and the control potential of dynamic stiffness adjustment,so as to further improve the vehicle stability and safety.The goal of this paper is to control the vertical damping force of vehicles with electronic stability control systems by means of real-time control and adjustment of dynamic stiffness,so as to improve the ride comfort,further achieve the purpose of improving rollover prevention ability and vehicle handling stability.The theoretical correctness and the practical feasibility of vertical damping force control based on dynamic stiffness adjustment to improve the dynamic performance of vehicle chassis by means of simulation analysis and vehicle test is verified in this paper.The content of this paper can be divided into the following parts in order to achieve the goal of the paper:Both the theoretical basis of vehicle and the continuous damping control damper model are investigated in Part 1.At first,the 15 degree of freedom vehicle model is expressed by dynamic formula,and the dynamic model of the key assemblies is established by using MATLAB/Simulink software as the simulation platform.Moreover,the working principle of continuous damping control damper is studied and expounded.The radial basis function neural network is used to establish the accurate forward and reverse model of the damper through the performance parameters obtained from the bench test of the damper.The control mechanism of vertical damping force based on dynamic stiffness adjustment is investigated in Part 2.The relationship between continuous damping control and the stability control is investigated creatively from the perspective of dynamic stiffness at first.The coupling effect of the vehicle vertical,the lateral and the longitudinal dynamics is investigated through the analysis of the influence of vertical load on tire sideslip stiffness.The theoretical basis of realizing vehicle dynamic boundary expansion and potential improvement through continuous damping control of vertical dynamics is expounded.Furthermore,the control mechanism of continuous damping control stability is analyzed in detail.The positive correlation between the damping coefficient and the equivalent stiffness is explained by solving the dynamic stiffness of variable damping suspension system.Moreover,the control principle of damping coefficient for rollover safety improvement is investigated by solving the relationship of the equivalent roll angle stiffness and the body roll angle.What's more,the control principle of damping coefficient for the handling and the stability improvement is explained by solving the vertical load redistribution during vehicle roll.Ride comfort control based on the dynamic stiffness adjustment is investigated in Part 3.The relationship between the continuous damping control and the ride comfort control is investigated with the perspective of suppressing the first formant by the dynamic stiffness in the first.The pavement roughness model which can be used for simulation is established and the accuracy of the pavement model is verified through the sine wave superposition method.Furthermore,the formant suppression ride comfort control based on the dynamic stiffness and its evaluation method are described.What's more,the skyhook-acceleration frequency division control strategy and the inter axis preview control strategy are established.The improvement of ride comfort is shown and the ride control principle of dynamic stiffness adjustment is verified by the simulation results.The vehicle rollover prevention control based on the dynamic stiffness adjustment is investigated in Part 4.The instantaneous process of the vehicle rollover is analyzed in detail and the significance of the single-wheel-control for anti-rollover control is explained at first.Moreover,the switch control strategy of continuous damping dynamic stiffness adjustment based on load transfer rate and the anti-rollover control strategy of continuous damping force optimization are established.Through fishhook and crosswind simulation tests,it is verified that two vertical damping force control strategies based on continuous damping dynamic stiffness adjustment have good control effects on safety.The optimal control effect of continuous damping control is better,which shows that the continuous damping control on single wheel makes the whole vehicle realize more accurate and rapid anti-rollover safety control.The increase of roll angle stiffness under dynamic stiffness adjustment can greatly reduce the roll angle in the process of rollover is shown from the dynamic stiffness adjustment of bilateral damping force in rollover condition.Rollover prevention mechanism based on dynamic stiffness adjustment is verified at last.Vehicle handling stability control based on the dynamic stiffness adjustment is investigated in Part 5.At first,the effect of continuous damping control on vertical load distribution is explained from the angle of dynamic stiffness adjustment innovatively.What's more,the control principle of dynamic stiffness adjustment for improving handling stability is explained by the change of steady-state yaw rate gain.The fuzzy control strategy is improved and optimized aiming at the empirical membership function of fuzzy control,and a multi-objective fuzzy control strategy considering the limit performance of both the handling stability and the rollover prevention ability is established.The redistribution effect of continuous damping control on the vertical load of each wheel of the vehicle is shown in the simulation results.Moreover,the load redistribution of front and rear axles is realized by the adjustment of dynamic stiffness.The steady-state yaw rate gain and steering characteristics of the vehicle is changed by the adjustment of dynamic stiffness as well.The handling and stability control theory based on dynamic stiffness adjustment is verified at last.The actual control effects are quantified by the vehicle test in Part 6.The test platform and test conditions are designed and explained at first.Moreover,the hardware used for sensing,control and data acquisition in the whole test link is introduced.What's more,the improvement effects of continuous damping control on the vehicle ride comfort,rollover prevention ability,handling stability performance are verified through the real vehicle test.The quantitative results of the average improvement of vehicle ride comfort by 15%,the improvement of roll stability performance(rollover prevention ability)by 10%,and the further improvement of handling stability by 3% ? 5% on the basis of the original ESP control are obtained through the data comparison at last.The coupling mechanism of isotropic dynamics is considered comprehensively in this paper.The influence of vertical damping force on lateral and longitudinal dynamics through lateral stiffness and vertical load distribution is analyzed in this paper as well.Moreover,the control mechanism of vertical damping force on roll stability and handling stability from the perspective of dynamic stiffness adjustment is put forward,and the theoretical feasibility of roll stability and handling stability control is verified in this paper.Furthermore,the relationship between continuous damping control and ride comfort control is investigated from the perspective of dynamic stiffness suppression of first-order formant,and the dynamic stiffness adjustment control principle of maximum amplitude of formant suppression in frequency domain is verified.Accurate matching research and performance improvement data for higherlevel chassis control systems through the control of vertical damping force without changing the original vehicle stability control systems is provided by this paper.The reference for further research such as in the fields of vehicle chassis integrated control technology,instability and anti-rollover control of commercial vehicles,chassis braking distance and pitch dynamic performance is provided by this paper.On the whole,the paper is of great significance to further improve vehicle ride comfort and stability.