Development Of Integrated Stability Control Algorithm For Four-axle Commercial Vehicle Based On Active Steering And Differential Braking

Commercial vehicles have large loading capacity,which plays an irreplaceable role in highway logistics and mining transportation.However,its disadvantages,such as large load,high center of mass,narrow wheel track and long wheelbase,make it easy for commercial vehicles to have rollover and yaw instability accidents.Among all of these heavy commercial vehicles,the multi-axle commercial vehicles are mostly used to transport high quality goods,and their working environment is the worst.They need researchers pay more attention on their stability control.However,there are few stability control systems developed specifically for multi-axle commercial vehicles.Furthermore,many researches have simplified multi-axle vehicles into two-axle vehicles.This paper originates from the Science and Technology Development Project of Jilin Province(No.20170414045 GH,Stability control of heavy commercial vehicle based on electronic brake system)and the project(No.51575224,Study on liquid-solid coupling mechanism and anti-rollover control of highway liquid tank truck)funded by National Natural Science Foundation of China.On the basis of summarizing and analyzing the previous work,an integrated stability control algorithm for multi-axle commercial vehicles is proposed in this paper.The control algorithm integrates the differential braking and active steering according to the new rules.This paper tries to provide theoretical support for the national independent research,development and design of the national multi-axle vehicle stability integrated controller.This paper mainly carries out the following aspects of research work:1.In this paper,a novel method of modeling the vertical loads of multi-axle vehicle is presented,according to which two vertical load models for three-axle vehicle and four-axle vehicle are established.Based on the four-axle vehicle veritical load model,a four-axle commercial vehicle model is proposed.The major difference between multi-axle vehicles and two-axle vehicles is that the distribution of vertical loads between the wheels is more complex.In order to solve the over-constraint problem in calculating the vertical load of multi-axle vehicles,the multi-axle vehicles are divided into several parts and the virtual forces are applied at the disconnection position.According to this modeling method,the vertical load models of three-axle vehicle and four-axle vehicle are established.Combined with the simplified tire Magic Formula(MF)model and 3 DOF vehicle model,the vehicle model of four-axle vehicle is established.2.In this paper,Adaptive Treble Extended Kalman Filter(ATEKF)estimation algorithm is proposed to estimate and identify the tire vertical loads,vehicle state and parameters of each wheel of four-axle commercial vehicle.In the real situation,many parameters and states of vehicles are not easy to obtain directly.Therefore,it is necessary to identify and estimate them.The parameters of multi-axle vehicle tire vertical loads model and tire vertical loads acquisition also face the same problem.Based on Extended Kalman Filter(EKF),this paper improves it by adding sliding mode approach unit to improve the computing speed.After studying the rough calculation method of four-axis vehicle parameters,a new algorithm of initial value adaptive updating of filtering estimation algorithm is proposed.On this basis,Adaptive Treble Extended Kalman Filter(ATEKF)is established to estimate and identify the tire vertical loads,parameters and state of four-axle vehicle.Finally,according to the law of rear magnifying effect,the adaptive adjustment method of vertical load of the third and fourth axes is put forward.3.This paper presents a control capability comparison method between differential braking and active steering.By calculating the maximum yaw moment generated by the two control modes under the current vehicle states,the method judges the control ability at the current moment.Differential braking and active steering have their own advantages and disadvantages.If the maximum influence of differential braking and active steering on the vehicle under the current states can be known,it is of great significance for the integration.In order to understand the vehicle state variation caused by the two control modes at a certain time,this paper calculates the yaw moment and lateral force generated by the differential braking and active steering of each wheel and axle respectively,and analyzes the control effect under different states and position parameters.On this basis,the calculation method of maximum yaw moment is summarized.Based on its maximum yaw moment,the capability comparison method of differential braking and active steering system under a certain working condition is proposed.4.In this paper,a multi-axle commercial vehicle integrated stability control system with track offset suppression function is established.In order to improve the stability of multi-axle vehicles,an integrated stability control algorithm is proposed in this paper.The linchpin of the stability integrated control algorithm is the calculation of the total control quantity and the control quantity distribution to the integrated subsystem(differential braking and active steering).The stability integrated control system algorithm proposed in this paper consists of three layers: decision layer,distribution layer and execution layer.After the decision layer determines the vehicle needs to be controlled,the system uses the sliding mode control algorithm to calculate the total control quantity required by the system.Then,based on the vehicle status at the moment,the possible range of vehicle travel trajectory in the future is predicted.Based on the predicted results,the possible road exit direction of the vehicle in the future is determined.Then,the total control amount is distributed according to the ability of active steering and differential braking and the trajectory deviation situation.The distribution layer calculates the required slip rate and active rotation Angle by optimizing or simplifying the algorithm.Finally,the execution layer controls the wheel slip ratio through the sliding mode control algorithm,and the active steering system uses the control method of constant speed steering to achieve the target active steer angle.5.A hardware-in-loop test bench is built and the integrated stability control algorithm proposed in this paper is verified on the test bench.In order to verify the real-time performance and control effect of the integrated stability control method,this paper establishes the multi-axis vehicle stability control system hardware in the ring test bench.The test bench contains three axles of complete braking system hardware,driver brake pedal and steering wheel hardware system.The target vehicle in this paper is a four-axle vehicle,and the fourth axle is simulated with the models in Truck Sim,for it has both active steering and differential braking systems.After verification,the stability integrated control system proposed in this paper has good real-time performance and control effect,and the algorithm can effectively alleviate the deviation caused by stability control.The innovative achievements of this paper are as follows:1.A modeling method of multi-axle vehicle wheels vertical load is proposed in this paper.In order to better analyze the characteristics of multi-axle vehicles,this paper proposes a method of building a multi-axle vehicle wheel vertical load model,based on which the three-axle and four-axle vehicle wheel vertical load models are built.On the basis of the four-axle vehicle wheel vertical load model,a four-axle commercial vehicle model is built.2.An Adaptive Treble Extended Kalman Filter(ATEKF)estimation algorithm is proposed.In order to obtain more accurate data and state of each wheel’s vertical load in the control,this paper proposes An Adaptive Treble Extended Kalman Filter(ATEKF)estimation algorithm on the basis of the extended kalman filter(EKF)estimation algorithm to estimate and identify the states and parameters of four-axis vehicles.3.This paper proposes a method to compare the control ability of differential braking and active steering.The method calculates the maximum yaw moment of the two control modes under the current condition to judge the capacity of the two control modes at the moment.This paper also gives the calculation method of maximum yaw moment which can be generated by differential braking and active steering.4.This paper proposes a stability integrated control algorithm for four-axle commercial vehicles,which integrates differential braking and active steering by adopting a novel coordination strategy.This coordination strategy is simple and flexible.Only by increasing the deviation mitigation factor,the trajectory deviation generated in the control can be suppressed,and the integrated sub-control mode can be easily isolated by changing the coefficient.In view of the disadvantages of the control algorithm,such as slow computation speed,this paper proposes a simplified calculation method for the target brake force of the wheel and the target angle of the active steering based on the analysis above.