【作者】 胡佳；

【导师】 钟志华；

【作者基本信息】 湖南大学 ， 车辆工程， 2008， 博士

【摘要】 儿童乘员安全是汽车碰撞安全领域的重要研究课题之一。国际上关于儿童乘员安全的研究早在上世纪60年代就开始了;美国和欧洲等国分别于70和80年代相继建立了儿童乘员安全法规。随着我国家用汽车保有量的逐年增加,儿童乘员安全问题越来越突出。儿童乘员约束系统(Child Restraint System,CRS)是防止交通事故中儿童乘员伤亡的乘车保护装置,开展这方面的研究工作具有重大的社会意义,尤其在我国实现现有的计划生育政策情况下。本文应用Hybrid III 3岁儿童假人有限元模型和3岁儿童人体有限元模型建立了四种典型的前向式CRS(着衣型、护板型、普通的5点式背带型和ISOFIX CRS)的正面碰撞台车试验的有限元仿真模型。将Hybrid III假人有限元模型仿真的乘员动态响应与试验对照,以校验有限元模型。对比分析了试验和仿真中这四种典型CRS约束下的乘员伤害值及儿童人体有限元模型的应力分布以比较这四种CRS的正面碰撞安全性的优劣。对使用三点式安全带固定的护板型和普通的5点式背带型CRS的安全带有100 mm松弛的误使用情形及普通的5点式背带型CRS和ISOFIX CRS的背带有100 mm松弛的误使用情形进行了有限元仿真分析。结果表明,ISOFIX CRS的正面碰撞安全性最好。ISOFIX CRS是一种国际通用型CRS,实现了与车体简单、牢固和标准化的连接。因此本研究着重对ISOFIX CRS的正面碰撞安全性进行了分析。考虑到对使用前向式CRS的4岁以下儿童乘员,颈部保护非常重要,因此着重对颈部响应进行了深入分析。儿童人体有限元模型的上颈部受力是基于头部的运动力学方程式计算求得的。假人模型与儿童人体有限元模型在仿真中的体幹姿态及下颌与胸部的接触方式有较大差异。假人和儿童人体有限元模型的下颌与胸部的不同的接触力及头部惯性力使得两模型的上颈部受力不同。假人模型的上颈部所受剪力和拉力均较大,而儿童人体有限元模型的上颈部剪力较小,拉力较大。为减小ISOFIX CRS约束下的儿童乘员头部、颈部和胸部受力,考虑给ISOFIX CRS的顶部拉带加限力计。用有限元模型仿真分析了ISOFIX CRS正确使用情形和CRS背带有100 mm松弛的误使用情形下顶部拉带限力计的效果。结果表明限力计有效地降低了头部和胸部加速度及上颈部受力。通过计算假人和儿童人体有限元模型的缓冲能量密度和约束能量密度,及约束能量密度中被CRS背带吸收的能量密度和耗散到CRS安装系统的能量密度,得到了能量密度和效率与胸部加速度之间的关系。结果表明,胸部加速度并不完全由缓冲能量效率决定,而是由被CRS背带吸收的能量效率决定。被CRS背带吸收的能量效率越高,胸部加速度越高。由于关于儿童乘员的侧面碰撞台车试验在国际上还没有统一方案,本研究对侧面碰撞实车试验进行了分析。比较了三种类型CRS(前向式、后向式和婴儿床式CRS)约束下的Q3s 3岁侧面碰撞儿童假人和CRABI 6个月婴儿假人的侧面碰撞实车试验结果,为侧面碰撞台车试验方法的确立提供依据。除前向式CRS中的Q3s假人的胸部压缩量(23.3 mm)略高出指标值(23 mm)外,其余伤害值都低于相应的伤害指标值。虽然在前向式和后向式CRS的试验中,车门腰线通过CRS侧护板间接撞击了假人头部,但头部加速度还是很低。其原因是由于CRS侧护板吸收了撞击能量,且假人头部始终处于CRS侧护板内部。建立了简单的前向式CRS的侧面碰撞有限元模型。将Hybrid III 3岁儿童假人和3岁儿童人体有限元模型的仿真结果与试验结果对比,头部、胸部和髋部的合成加速度峰值大小很接近。本研究以试验和有限元仿真为主要研究手段,对儿童乘员在不同类型CRS约束下的正面和侧面碰撞过程中的乘员动态响应和伤害值进行了深入分析和研究。应用Hybrid III 3岁儿童假人有限元模型和3岁儿童人体有限元模型建立了四种典型的前向式CRS的正面碰撞台车试验的有限元仿真模型。提出了在ISOFIX CRS的顶部拉带加限力计以减轻头颈部和胸部的受力。运用缓冲及约束能量效率理论提出了能量效率与胸部加速度之间的关系。通过对比分析Hybrid III假人和儿童人体有限元模型的动态响应,发现两者在仿真中的体幹姿态及下颌与胸部的接触方式有较大差异。对侧面碰撞实车试验中3种类型CRS约束下的乘员动态响应及伤害值进行了对比分析,同时建立了侧面碰撞有限元模型,为侧面碰撞儿童乘员安全研究工作的开展奠定了基础。希望本研究能为我国儿童乘员安全研究工作的开展和儿童乘员安全法规的建立和实施提供参考。更多还原

【Abstract】 Child occupant safety is one of the important research subject in the field of vehicle crash safety. Child occupant safety research started from 1960s in the world. The US and European countries established regulations for child occupants in 1970s and 1980s. With the number of vehicles increasing every year in China, child occupant safety problem becomes more and more important. As child restraint system (CRS) is shown to be effective on child occupant protection in vehicle crash, the research work in this field has an important social significance, regarding that the policy of one-child in one-family performed in China.In this research, by using a Hybrid III 3YO dummy FE model and a child human FE model, FE simulation of frontal sled tests for four typical types of CRSs (wearable type, impact-shield type, 5-point harness conventional type, ISOFIX CRS) were conducted. Results of the dummy’s kinematics and accelerations in the tests and FE simulations were correlated. A 3-year-old child human FE model was also used in this research. Injury criteria (the head forward excursion, HIC 15, chest 3 ms acceleration and chest deflection) were compared between the four types of CRSs. Stress distribution was analyzed for the child human FE model. Misuse case of seatbelt having 100 mm slack for the impact-shield type and 5-point harness conventional type CRS were analyzed by FE simulation. And misuse case of harness having 100 mm slack for the 5-point harness conventional type and ISOFIX CRS was also analyzed by FE simulations. Results showed that the frontal safety performance of ISOFIX CRS was the best.ISOFIX CRS implements a simple, rigid and standardized connection with vehicle. In this research the child occupant protection in ISOFIX CRS were analyzed in detail. Regarding that it is very important of the neck protection of a child under 4 years old and restrained by a forward-facing CRS, the upper neck response were analyzed in detail. The upper neck force and moment were calculated based on the motion of the head. The torso pose and the contact behavior of the chin and chest were different between the dummy and child human FE model. Different contact behavior caused different contact force. And the upper neck force was affected by the contact force and the head inertial force. For the Hybrid III dummy model, the upper neck shear and tension force were large while for the child human FE model the upper neck shear force was small and the tension force was large.A top-tether force limiter was proposed to reduce the loadings to the head, neck and chest of the child positioned in the ISOFIX CRS. For evaluating the effectiveness of the top-tether force limiter, FE simulations for two conditions, CRS in proper use and CRS harness having slack, were performed. Results showed that the head and chest accelerations and upper neck force and moment were reduced. Ridedown and restraint energy density and the restraint energy density related with the CRS harness and CRS installation system were calculated and analyzed of the relation with the chest acceleration. It was concluded that the chest acceleration was not dependent on the ridedown energy efficiency but dependent on the energy efficiency absorbed by the CRS harness (i.e., the chest acceleration will increase when the energy efficiency absorbed by the CRS harness increases).As there is not an international standard for side impact sled test, in this research full car side impact tests were analyzed. Results of three full car side impact tests of Q3s and CRABI 6MO dummies restrained by three types of CRSs (forward-facing, rear-facing and car-bed type) were analyzed and compared. Except the chest deflection (23.3 mm) of the Q3s restrained by a forward-facing CRS exceeding slightly the threshold (23 mm), all injury criteria were lower than thresholds. Although the door beltline impact the dummy’s head through the CRS side shell indirectly, the HIC 15 was very low. This was because the CRS side shell absorbed lots of impact energy, and the dummy’s head was contained in the CRS shell all along. A simple FE model of side impact was established by using the Hybrid III dummy and child human FE model. The head, chest and pelvis resultant acceleration peaks were comparable between the test and simulations.In this research, based on tests and FE simulations, the behavior, reponses and injury parameters of the child occupant restrained by differet types of CRSs were analyzed. By using a Hybrid III 3YO dummy FE model and a child human FE model, FE simulation of frontal sled tests for four typical types of CRSs were conducted. A top-tether force limiter was proposed to reduce the loads to the child head, neck and chest. By applying the theory of ridedown and restraint energy efficiencies, the relation of the energy efficiencies anad the chest acceleration was proposed. It was found that the torso pose and the contact behavior of the chin and chest were different between the dummy and child human FE model. Results of three full car side impact tests of Q3s and CRABI 6MO dummies restrained by three types of CRSs were analyzed and compared. A simple FE model of side impact was established by using the Hybrid III dummy and child human FE model. Hope that this research can be a good reference for the child occupant safety research work and the establishment and execution of the child occupant safety regulation in our country.更多还原