Control Strategy Research On Active Suspension System Of Multi-axle Emergency Rescue Vehicles

In recent years,disaster accidents have occurred frequently in our country.As the main equipment for land rescue,multi-axle emergency rescue vehicles should possess high mobility,ride comfort and handling stability under complex road conditions.The existing multi-axle emergency rescue vehicles mostly adopt passive suspension,whose parameters cannot be adjusted in real time with the road roughness and vehicle vibration states,so it is difficult to guarantee the driving performance of the emergency rescue vehicle on low-grade roads,thereby resulting in reduced rescue efficiency.The active suspension system counteracts the impact of uneven roads by controlling the output energy of the actuators,which can effectively improve the vehicle's mobility,ride comfort and handling stability under different grades of road surface,and meet the performance requirements of emergency rescue vehicles.As the core of active suspension system,active suspension control strategy has become a research hotspot in the field of vehicle control in recent years.In addition,the level of mobility,ride comfort and handling stability of the vehicle not only depends on the suspension system,but also on the coordination of the suspension system and the steering system.At present,the research on integrated control of active suspension system and steering system for multi-axle vehicles is still in the exploratory stage.This study relies on National Key R&D Program “Key Technology Research on Special Chassis and Suspension for High-mobility Emergency Rescue Vehicle(Including Fire Fighting Vehicle)”(Project Number: 2016YFC0802902).In order to improve the mobility,ride comfort and handling stability of multi-axle emergency rescue vehicles under complex road conditions,the active suspension system control strategy,active suspension and steering system integrated control strategy are systematically and in-depth studied in this dissertation.The main work is presented as follows:(1)Using the idea of modularization and block modeling,the nonlinear mathematical model of the whole-vehicle interconnected hydro-pneumatic suspension system is established.In order to provide a comparative benchmark for the active suspension control strategy in the follow-up research,the stiffness and damping characteristics of the interconnected hydro-pneumatic spring and the vehicle's interconnected hydro-pneumatic suspension system are also analyzed.(2)A nonlinear control strategy based on active disturbance rejection technology is studied for active suspension system.Taking full account of the nonlinear and uncertain factors in active suspension system,a nonlinear ESO(Extended State Observer)-based finite-time stabilization output feedback control strategy is proposed according to the idea of active disturbance rejection control and finite time stability control.The controller can drive the vibration state of the vehicle body to converge within a finite time.Using Lyapunov stability theory and geometric homogeneity theory,the stability of finite-time stabilization output feedback controller is systematically proved by taking the vertical motion of the vehicle body as an example.This paper solves the difficult problem of the stability proof for the nonlinear ESO-based controller.By analyzing the zero dynamics of the remaining subsystems,the closed-loop stability and the constraint performance of the vehicle's active suspension system are ensured.The simulation results show that the proposed control strategy can better improve the mobility and ride comfort of the three-axle emergency rescue vehicle while satisfying the constraints of handling stability,when compared with the passive hydro-pneumatic suspension and the active suspension system using linear ESO-based asymptotic stabilization output feedback controller.(3)An active suspension control strategy based on displacement control is studied,and a novel displacement servo control method is proposed for electro-hydraulic servo actuator system.The control idea of active suspension controller based on displacement control is analyzed,and the controller is divided into main loop control and sub-loop control.The main loop controller refers to the invention patent CN 110281727 A of our research group.With the help of vehicle inverse kinematics and displacement-and-attitude deviation compensation idea,the ideal displacement of each actuator that can improve the ride comfort of the vehicle is calculated.An innovative sub-loop output feedback controller based on the NLSDESO(Non-linear Sampled-data ESO)is proposed,which effectively eliminates the adverse effects of the complex nonlinearity,matched and mismatched disturbances in the electro-hydraulic servo actuator system,and the discreteness of the displacement sensor output signals,and can achieve high-performance tracking control for the ideal displacement signal.Using Lyapunov stability theory,the convergence of the NLSDESO and the closed-loop stability of the electro-hydraulic servo(discrete-continuous)hybrid system is proved.Matlab and AMESim co-simulation results indicate that the proposed sub-loop controller considering the discreteness of output signals is feasible,while can improve the transient and steady-state displacement tracking accuracy of the electro-hydraulic servo actuator.(4)A coordinated control strategy for active suspension and all-wheel steering system of multi-axle vevhicle is studied.The coupling mechanism between active suspension system and steering system is analyzed,and an 11-DOF nonlinear dynamic model of the three-axle vehicle and a nonlinear “Dugoff” model of tire are established.Taking into account the nonlinearity and uncertainty of the steering system,based on the super-twisting sliding mode control idea and the finite-time separation principle,a novel all-wheel steering super-twisting sliding mode controller for three-axle vehicle,which overcomes the chattering phenomenon that often occurs in traditional sliding mode control,and makes the steering system states converge to the ideal reference trajectory within a finite time.The simulation results under three typical steering work conditions show that the proposed controller has significant advantages and can better improve the mobility and handling stability of the three-axle emergency rescue vehicle,compared to strategies such as front axle steering,all-wheel steering proportional control,and discontinuous switching sliding mode control.Based on the designed active suspension finite-time stabilization output feedback controller and all-wheel steering super-twisting sliding mode controller,an upper coordinated controller for active suspension and steering coupled system of multi-axle vehicles is further designed.The simulation results verify that the coordinated control strategy for the coupling system can effectively improve the comprehensive driving performance of the vehicle.(5)Experimental research is conducted on the active suspension system of the three-axle emergency rescue vehicle.A suspension unit test platform is built,and multiple sets of electro-hydraulic servo actuator displacement tracking control tests are carried out under different control gains,different sampling periods and different control methods,which verifies the feasibility and high-performance position servo control effect of the sub-loop controller considering the discreteness of the output signals.A three-axle emergency rescue vehicle test platform is established,and real road experiments are conducted under different roadblock conditions.The test results show that,compared with the interconnected hydro-pneumatic suspension system,the active suspension system using the active suspension control strategy based on displacement control can reduce the root mean square values of body's vertical displacement,pitch angle and roll angle by about 30%,effectively improving the vehicle's ride comfort.