Design And Performance Analysis Of Vibration Isolation System For Ambulance Stretcher

When an ambulances is running,it will encounter road unevenness,braking and turning conditions.The patient on the ambulance will be vibrated in three directions: vertical,pitch and roll due to road excitation.When the road surface excitation is transmitted to the vehicle body,the suspension effectively reduces the high frequency vibration,and the main excitation for the ambulance stretcher vibration is the low frequency vibration of the vehicle body.This paper proposes the new kind of the ambulance stretcher vibration isolation system combining the X-type hydraulic interconnect suspension system and stretcher vibration isolation system based on the air spring.X-type hydraulic interconnect suspension can realize coordinated control of body pitch mode and roll mode,stretcher vibration isolation system based on the air spring can achieve low frequency vibration isolation for patients on ambulance stretcher.This system is beneficial to improve the smooth performance of the ambulance and prevent the patient from getting worse during transportation.At the same time,the nonlinear characteristics of air spring stiffness can be used to select the matching air spring stiffness range for different quality ambulance patients.The main work and conclusions of the paper are as follows:1.According to the thermodynamic theory,the air spring mechanical model is established and the mathematical model of air spring stiffness and damping is obtained.Studying the characteristics of air springs,it is found that the air spring stiffness has nonlinear characteristics and a wide range of variation,meeting the stiffness requirements of ambulance patients under different masses.2.According to the theory of fluid mechanics,the mathematical model of the hydraulic cylinder,damping valve,pipeline,accumulator and other components of the X-type hydraulic interconnect suspension system is established,and by using the hydraulic pressure of hydraulic cylinder as the boundary condition establish mechanical-hydraulic coupling model.According to the multi-body dynamics theory,the ten degree of freedom model of the ambulance stretcher vibration isolation system is established.The smooth performance of the traditional ambulance and the modified ambulance at different speeds and different road surfaces is compared and analyzed.3.According to the human body standard of lying position,the influence of the position of the stretcher on the comfort of the casualty is analyzed.The study found that the distance between the left fulcrum of the stretcher and the ambulance body center of mass should be equal to the distance between the right fulcrum of the stretcher and the ambulance body center of mass.The rear fulcrum of the stretcher should be close to the ambulance body center of mass.In order to balance the good vibration isolation performance and stability performance of the stretcher vibration system,that is,to improve the comfort of the casualty and limit the up and down floating displacement,comfort index for lying position are proposed,and it is found that the stiffness range of the vibration isolation component matched by different quality casualties is different.In summary,this paper establishes the ten-degree-of-freedom ambulance vibration isolation system model,proposes the comfort standard of the positional casualty of the stretcher vibration isolation system and uses the characteristics of air springs to adapt to a variety of load to analyze the ride comfort of different quality casualties.The stiffness range of the vibration isolation component suitable for different quality casualties is obtained.The vibration isolation performance of the ambulance vibration isolation system under different masses is analyzed.