| Ambulances,special vehicles oriented to "Chase Lifetime," are frequently operating in emergency conditions such as rapid acceleration,emergency braking,and collision avoidance steering,which could easily cause patients(especially cardiovascular and critically ill patients)to have adverse reactions,such as,nausea,dizziness,and increase of intracranial blood pressure.This could cause secondary injuries or even death to patients.In addition,the unstable environment in the ambulances obstructs medical staff from implementing emergency rescue.Furthermore,Modern intensive care ambulance vehicles are equipped with a variety of emergency treatment equipment,which increases the vehicle’s weight and the height of the center of gravity,which further deteriorates the ambulances riding environment.The suspension system is a critical component that determines the ride comfort and handling stability of the vehicle.However,the current ambulance is directly modified from a light truck or an off-road vehicle.The traditional suspension that it uses has the inherent defect of suspension mode coupling and cannot simultaneously achieve multiple contradictory performance targets.Thus,it cannot meet the highperformance requirements of modern ambulances.To this end,this dissertation develops an X-type Pitch-and Roll-resistant Hydraulically Interconnected Suspension(XPR-HIS)system with a mode decoupling function to conduct the research on coordinated control of ride comfort and vehicle-body posture for intensive care ambulances under the support of the National Natural Science Foundation of China(Grant No.51675152)and School-Enterprise Cooperation Project.The research contents and innovative contributions are as follows:(1)A "mechanical-hydraulic-pneumatic" coupling dynamic modeling method for hydraulic interconnected suspension is proposed.This method considers the timevarying characteristics of the gas-liquid mixed fluid in the hydraulic interconnection system and derives the time-varying equation of the mixed fluid with pressure.In addition,based on the bending deformation theory of the thin circular plate,the deformation equation for the damping valve plate is derived.The nonlinear correction function corrects the deformation error of the valve plate,uses the finite element method to identify the deformation nonlinear correction function,and then derives the damping valve’s variable opening throttling characteristics caused by the deformation of the valve plate.Combined with pipeline and accumulator fluid dynamics equations,a set of coupled dynamic modeling methods for hydraulically interconnected suspension systems is summarized.The correctness of the proposed method is verified through a bench test of the single-cylinder interconnected suspension system.Compared with the traditional method,it shows that the proposed method has a unique advantage of describing the hysteresis phenomenon.(2)An XPR-HIS system is proposed for the ambulance dynamic performance requirements.Combining the coupling dynamic modeling method and the interconnection configuration,the frequency domain and time-domain dynamic models of the entire ambulance vehicle is established.The additional stiffness and damping characteristics display the expression of the hydraulic interconnection suspension is derived.On this basis,analyze the dynamic characteristics of the XPR-HIS system to study the stiffness and damping characteristics of different suspension motion modes.Secondly,analyze the system modal and frequency response characteristics based on the frequency domain dynamic model of the whole vehicle,and study the inherent characteristics of the suspension Finally,the time domain dynamic analysis is carried out according to the speed bump,emergency steering,and braking conditions of the ambulance to comprehensively evaluate the ride comfort and operational stability of the vehicle.The analysis results show that the proposed XPR-HIS system can significantly improve the ambulance’s dynamic performance,providing a new solution for improving the ambulance’s dynamic performance.It also provides the model foundation for the subsequent parameter optimization design and semi-active control reference.(3)A hierarchical multi-objective optimization method for the parameter design of two-stage suspension system is proposed considering the complex model of the prone human body.Given the decoupling advantages of XPR-HIS,the calculation method of modal energy spectral density in the frequency domain is introduced to study the impact of XPR-HIS system parameters on the performance of the vehicle and to determine the critical parameters of the system;in addition,establish the head,body trunk,pelvis and the three-part human body model of a patient with 6 degrees of freedom in a prone posture connected with joints,and together with the vehicle model equipped with XPR-HIS system to construct a coupling model of the ambulance secondary suspension system;further,the complex model is multi-variable and multiobjective.A multi-objective hierarchical optimization method is proposed for the optimal solution convergence.Compared with traditional single optimization,this method reduces the number of design variables and optimization objectives of singlelevel optimization through the comprehensive sensitivity ratio.The analysis results show that using the proposed method,without sacrificing the calculation efficiency,the optimization quality and the convergence speed of the optimal solution could be significantly improved,and the optimal matching of the hydraulic interconnection suspension and the stretcher suspension parameters could be achieved.(4)An nonlinear controller of a semi-active hydraulically interconnected suspension is designed based the adaptive model predictive control method.According to the above parametric analysis and optimization results,a hydraulic interconnected suspension system with independently controllable compression and return stroke damping was designed,and then the damping force adjustment range and feasibility were analyzed.For this suspension system’s nonlinear strong coupling characteristics,the adaptive model predictive control method is used for nonlinear controller design.In the control process,the time-varying Kalman filter observer is used to estimate the vehicle state information in real-time,and the dynamic performance and control effect of the semi-active suspension is verified through simulation analysis.The comparative analysis with the passive hydraulic interconnected suspension shows that the proposed semi-active system significantly reduces body acceleration and tire dynamic load and improves vehicle comfort and operational stability.(5)Bench test and prototype vehicle test is carried out.Based on the XPR-HIS system proposed in this paper,a two-cylinder hydraulic interconnected suspension test bench was built.The stiffness and damping characteristics are studied using quasistatic and dynamic loading methods.In addition,modified from a vehicle commonly used as an ambulance,the suspension system has been restructured.The ride comfort and handling stability tests of the vehicle through speed bumps,serpentine winding piles,and double line shifting have been performed.The test results show that the XPRHIS system proposed in this paper can significantly improve the ambulance’s pitch-roll stability without sacrificing the ride comfort of the vehicle,and the theoretical model is systematically verified from the perspectives of the test bench to the vehicle.This paper focuses on the new XPR-HIS system to carry out the theoretical and experimental studies on coupling dynamics modeling method,vehicle dynamics analysis,two-stage suspension system parameter optimization strategy and semi-active control method.The results show that the ride comfort and vehicle-body posture sability are improved comprehensively,which provides a stable and safe environment for medical staff to implement emergency rescue measures,and also provides a practical and feasible solution with controllable cost and superior performance for the ambulance industry’s innovation and upgrading. |
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