基于ADAMS的急救车担架支架减振特性仿真分析与优化研究

【作者】 王猛；

【导师】 徐新喜；

【作者基本信息】 中国人民解放军军事医学科学院 ， 卫生防护防疫技术与装备， 2009， 博士

【摘要】 车载担架支架的乘卧舒适性是伤病员运送车辆的重要评价指标之一。本文以某型急救车为研究对象,以降低卧姿伤病员的振动能量、提高乘卧舒适性为目标,对担架支架减振系统进行了仿真分析与优化设计研究。围绕车载担架支架乘卧舒适性研究所涉及的关键技术,对多体系统动力学理论、汽车平顺性研究方法、担架支架减振技术(包括钢丝绳弹簧、阻尼减振等技术)的研究现状与发展趋势进行了归纳和总结。根据急救车的振动特点,基于多体系统动力学理论,建立了包括简化悬架、车身、担架支架系统、卧姿人体质量块在内的9自由度振动微分方程,模型中考虑了刚性限位器的碰撞作用,钢丝绳弹簧简化为三向弹簧。运用多体系统动力学仿真分析软件ADAMS进行了模型的求解计算。依据GB4970-1996《汽车平顺性随机输入行驶试验方法》、QC/T677-2001《卧铺客车平顺性随机输入行驶试验方法》和GB/T18368-2001《卧姿人体全身振动舒适性的评价》的相关规定,在机械工业部工程机械军用改装车试验场(北京延庆)进行了两种代表性路面(砂石路和沥青路)激励下常用车速的道路试验,测量了卧姿、坐姿人体相应部位的振动加速度信号。通过对乘员相应测试部位加速度采样信号的1/3倍频程进行两次计权计算,对卧姿、坐姿人体的舒适性进行了评价。试验数据的分析结果表明,两种路面下担架支架的减振效果均没有达到工程设计的要求(减振效率(?)30%),砂石路激励下甚至还会引起乘员的不舒适。因此,本文针对砂石路激励下担架支架的减振效果进行了优化设计研究。在ADAMS软件中建立了与样车模型相一致的车辆振动系统仿真分析模型,模型包括车轮(4个)、车身、等效悬架系统、担架支架、卧姿人体质量块,其中,悬架参数通过基于遗传算法的参数识别方法获得,钢丝绳弹簧用轴套力Bushing模拟,刚性限位器发生作用时的反作用力用Impact函数计算。用汽车试验场道路试验测得的车辆轴头信号在时间域内对系统进行激励,真实模拟了车载担架支架系统的振动情况,仿真与试验结果对比表明,两种路面激励下模型的误差仅为8.267%和7.611%,说明模型具有较高的计算精度;在此基础上对模型进行了减振特性的优化研究,考虑的因素主要有钢丝绳弹簧的数量、刚度、位置、方向,各种分析结果表明担架支架系统的振动响应特性得到了有效改善。但是在随机振动的隔离中,单一由钢丝绳弹簧组成的减振系统,很难满足减振效率的设计要求。针对钢丝绳弹簧阻尼比偏小的问题,提出了采用小刚度弹簧并附加液压阻尼器的阻尼减振方案。对该方案的刚度、阻尼匹配关系进行了仿真分析与优化设计研究,优化结果为:钢丝绳弹簧垂向刚度K_y=2737N/m,阻尼器阻尼系数C=2605Ns/m,砂石路激励下垂向减振效率为32.53%,沥青路激励下的减振效率为34.26%。这一分析结果理论上满足了工程设计要求,但在工程实际中,由于钢丝绳弹簧的刚度过小,维持系统静平衡所需的初始变形量较大,因而工程应用实现起来困难较大。为解决钢丝绳弹簧渐软特性的不足,在担架支架阻尼减振研究的基础上,设计了四种两级钢丝绳组合式减振方案,经仿真分析与优化研究,优选出最佳减振方案,不仅其对应的砂石路激励下的减振效率可达到31.29%,沥青路激励下的减振效率可达到32.51%,而且两级钢丝绳弹簧的垂向刚度(分别为11545.6 N/m和30101.4 N/m)相对阻尼减振的优化结果(2737N/m)有了显著的提高,有利于工程应用的实现。急救车主要行驶在平稳随机路面上,但有时也会遇到凸起或凹坑,这时就表现为冲击激励。为了估算各种方案是否满足冲击情况下的安全性要求,针对原车加装阻尼器前后和采用两级钢丝绳组合式减振方案的优化结果,在Simulink模块中搭建仿真分析模型,分别进行了各方案抗冲击减振效果的简化分析。分析结果表明:原车减振方案的优化结果中,系统最大响应加速度较小,但振动衰减缓慢,且最大响应位移较大,系统稳定性较差;加装阻尼器的后两种方案中,系统的最大响应加速度降低较小,但振动衰减迅速,且最大响应位移也较小,合理兼顾了稳定性与减振效率这一对矛盾,特别是优选出的最佳两级钢丝绳组合式减振方案,用最大响应加速度评价的冲击减振效率达到了68.69%,而最大相对位移仅为3.4mm,有效改善了担架支架减振系统的稳定性。更多还原

【Abstract】 The ride comfort of the stretcher-support on vehicle is one of the important evaluation indices of wounded transportation vehicle.In order to reduce the vibration energy and improve the ride comfort of the supine wounded,the vibration absorption property of stretcher-support is simulated and optimized in this dissertation.The present situation and developing trend of the key technology related to the study of the comfortable characteristic of the stretcher-support on vehicle is summarized,including the theory of multi-body system dynamics,the study methods of vehicle ride comfort,the related technology of stretcher-support vibration absorption about wire rope spring and vibration damping.According to the vibration characteristics of the emergency ambulance,the vibration differential equation of nine DOFs(Degrees of Freedom) is founded based on the theory of multi-body system dynamics,including simple suspension system,vehicle body,vehicle stretcher-support system and the body mass of recumbent position crew.In this model,the collision of rigid limiters is also considered,and the wire rope springs are simplified to three direction springs.The model is analyzed in ADAMS,the automatic analysis software of multi-body system dynamics.In accordance with the relevant provisions of GB4970-1996 " Method of random input running test--Automotive ride comfort",QC/T677-2001 "Method of random input running test-ride comfort of sleeper bus" and GB/T18368-2001 "Comfort evaluation of human exposure to whole-body vibration in recumbent position",the road test of common speed under the excitation of two representative roads(graveled road and bituminous road ) is carried out at the test ground of reequipped military vehicle of the Mechanical Industry Department(located in Yanqing,Beijing),the acceleration signal transferred to the occupants in the recumbent position and seated position is sampled.Through two terms’ weighting of 1/3 OCT of sample acceleration signals on the occupants’ corresponding parts,the ride comfort in the recumbent position and seated position is evaluated.The analysis results of test data shows that the vibration absorbing efficiency of stretcher-support under the two types of road can’t meet the requirement of engineering design(vibration absorbing efficiency≮30%), and the vibration even causes the occupants’ uncomfortableness under the exciting of the gravel,road,therefore,the numerical simulation and optimization for the vibration absorbing efficiency of stretcher-support is carried out under this case.The virtual prototype model of vehicle vibration system according with the prototype, including four wheels,vehicle body,equivalent suspension system,stretcher-support system and the body mass of recumbent position,is built in the simulation analysis software ADAMS based on mechanical system dynamics,in which,the suspension parameters are obtained through the parameters identification method based on genetic algorithm,the wire rope springs are simulated by bushing model,and the collision force of rigid limiter is calculated through the function of impact.The simulation model is excited in the time domain by the four channels acceleration signals on the end of axletree from the road test and the real vibration condition is fully simulated.From the results comparison between the test and simulation,the calculation error under the exciting of the two roads is only 8.267%and 7.611%,which shows that this model has a higher precision.Through the optimization study of this virtual model,considered such factors as the number,stiffness,position and direction of the wire rope springs,the reasonable absorbing vibration scheme is founded.From the analysis results,the vibration absorption system only made up of wire rope springs can’t match the industry design targets,although the vibration response characteristics of stretchers has been largely improved.To deal with the problem that the damping ratio of wire rope spring is comparatively small,a new kind of vibration absorption scheme is set up using less stiff springs with vibration damping device.And the matching relation of stiffness and damping is simulated and optimized.As a result,the vertical stiffness of wire rope spring K_y is 2737N/m,damping coefficient C is 2605Ns/m and the vibration absorbing efficiency under the gravel road excitation is 32.53%and 34.26%under the excitation of bituminous road.The result of this analysis can meet the design requirements of the project in theory,but in the engineering application,it is comparatively difficult to achieve because the stiffness of wire rope spring is too little and the initial deformation to maintain the system static equilibrium is larger.Based on the study of vibration damping,four types of two-stage combined vibration absorbing schemes are designed in order to get over the shortcoming of wire rope spring’s soften characteristic.The best scheme is selected after simulation and optimization study.Not only the vibration absorbing efficiency in this scheme can reach to 31.29%and 32.51% corresponding to the exciting of gravel road and bituminous road,but also the stiffness of the two-stage wire rope spring(11545.6 N/m and 30141.4 N/m respectively) has been largely improved compared to the optimization results of damping vibration(2737N/m),which is conducive to realize in the engineering application.The emergency ambulance mainly runs on the stationary random road but sometimes it will pass the convex surface or pits on the road,the vibration presents shock excitation in this case.In order to evaluate whether the design schemes can match the security requirements under shocking excitation,the shock vibration isolation efficiency is simply analyzed in the Simulink module for the optimized results on the vibration isolation scheme of pre/post adding;dampers as well as the best scheme of the two-stage combined.The analysis results show that in the optimized results of original scheme,the maximal response acceleration is comparatively little,but the attenuation is very slow,and the maximal response displacement is too large,the system stability is comparatively weak;In comparison,in the two schemes of adding vibration damping device,the decrease of the maximal response acceleration became little,but the attenuation is fast,and the maximal response displacement is also little,therefore the system stability and vibration absorption efficiency are balanced reasonably.In the selected scheme of the two-stage combined vibration absorbing,the vibration absorbing efficiency reaches to 68.69%using the maximal response acceleration as evaluation indicator and the maximal response displacement is only 3.4mm,the stability of stretcher-support system is improved largely.更多还原