【作者】 齐海政；

【导师】 管欣；

【作者基本信息】 吉林大学 ， 车辆工程， 2011， 博士

【摘要】 随着高速公路网络和公路物流业的蓬勃发展,商用车用户要求车辆在实现大载重量的同时要尽可能提升日常行驶速度,以便提高日均运输效率。目前,商用车的载重量已经接近法规极限,提升空间有限,然而日常行驶速度却相对较低,具有较大的提升空间。因此,国内外商用车制造商都在不遗余力的提升车辆的日常行驶速度。国外高端重型商用车的日常行驶速度已经超过100km/h,而国内商用车的日常行驶速度距此尚有较大的差距。日常行驶速度的提高一方面需要有大功率发动机作为保证,另一方面需要高品质的整车平台作为支持。随着商用车行驶速度的提升,阻碍行驶速度提升的不良动态过程现象,诸如：行驶稳定性下降、整车振动加剧等,开始显现。这些现象产生的原因主要是高速情况下,商用车总成响应不再像低速情况下那样相互影响较小,而是在中、高频响应上产生耦合。这一方面是由于商用车行驶速度的提升所带来的外界和自身激励频率的提升；另一方面是由于商用车自身结构特点所带来的。因此,继续采取适用于低速稳态情况下的方法,针对单一动力学性能进行总成特性匹配,不能实现对制约行驶速度提升的不良动态过程的有效控制,而应当在整车动力学性能的综合考虑下进行总成特性的优化匹配。基于总成特性的汽车动力学模型是商用车预开发阶段进行总成特性匹配和整车性能验证的有力工具。现有的商用车基于总成特性模型以稳态性能仿真为主,计算结果与实车的稳态性能可以达到较高的一致性,但是尚不能对中、高频的不良动态过程现象做出准确的模拟。因此,想要进一步提升基于总成特性模型在产品开发中的应用价值,实现整车开发的全数字化仿真,需要模型不仅能够进行稳态性能的准确预测,而且能够对动态过程现象进行仿真研究,这正是本文的研究初衷和学术价值所在。本文在调研国内外商用车动力学研究和模型发展状况的基础上,针对现有商用车主要以整车稳态性能仿真为主,缺乏总成中、高频响应耦合描述的不足,探索具备动态过程仿真能力的商用车基于总成特性动力学模型建模中的关键问题。探索的重点和难点集中在,与提升基于总成特性模型仿真分析频率相关的,关键总成特性建模方面。围绕研究的重点和难点主要从以下四个方面展开论文的研究工作：首先,基于总成特性的商用车动力学性能建模研究。介绍基于总成特性商用车动力学性能模型的建模动机以及目前广泛使用的基于总成特性的商用车动力学性能模型的总体建模思想和主要自由度的建模方法,并以此建立基于总成特性的商用车性能模型。通过整车试验数据验证所建立的整车性能模型正确性的同时,也表明了模型能够较好的反映商用车的稳态性能。为后文在这一稳态模型的基础上,研究关键总成特性细致建模方法及对整车模型仿真频率提升的影响奠定基础。其次,商用车底盘扭转刚度特性建模研究。商用车相对于乘用车而言底盘扭转刚度较小。受到激励力的作用,会造成底盘上关键总成装配硬点的相对位置发生变化,同时,会形成总成中、高频响应间的耦合。现有模型使用多质量块离散底盘结构并在其间加入扭簧来描述底盘扭转弹性。扭簧刚度采用静力试验方法获得,质量和转动惯量采用静态下的轴荷确定。这种方式虽然能够描述稳态下底盘扭转特性,但不能准确反映底盘扭转特性的中、高频动态效果。本文根据商用车底盘的扭转模态特点选择边梁形式的集中质量扭转弹簧模型,并采用传递函数等效的方法,确定集中质量块的转动惯量、扭簧刚度特性以及扭转脊线位置等总成特性,从而实现在一定频率范围内描述底盘扭转特性的动态效果。再次,钢板弹簧非独立悬架总成特性建模研究。悬架总成的导向和承载特性直接影响整车操纵稳定性和乘坐舒适性,是商用车预开发阶段重点关注的总成特性。目前,悬架导向特性主要通过K&C特性试验获得,但国内缺乏相关的商用车悬架试验设备；悬架承载特性主要使用SAE三连杆模型和Fancher模型描述,SAE三连杆模型能够实现非线性名义刚度特性描述,但不能模拟迟滞现象；Fancher模型虽然能够模拟迟滞现象,但不能较好反映承载特性边界的移动和延迟系数的变化。本文采用多体系统动力学方法建立悬架结构模型。使用离散质量钢片和Beam梁建立簧片模型,通过簧片间加入静、动摩擦环节反映簧片间的干摩擦,从而实现悬架K&C特性的仿真获取；通过在现有SAE三连杆模型的铰接点处加入描述静、动摩擦效果的力元,使用优化方法确定力元参数,从而实现迟滞现象的模拟；通过使用悬架变形量修正现有Fancher模型中的参数,实现承载特性边界移动和延迟系数变化的模拟。最后,动力传动系统非稳态总成特性的建模研究。动力传动系统是商用车中重要的激励源,对其非稳态工作特性的建模可以有效提升整车模型的分析频率。现有模型中发动机采用稳态万有特性描述发动机的力矩特性,同时,孤立的考虑传动系统的动力传递特性。缺乏传动系统中部件非稳态工作特性和对底盘激励环节的描述,不能反映动力传动系统中的真实扭矩波动和对底盘的激励现象。本文使用仿真计算方法,获得典型工况下发动机气缸内燃烧压力特性,通过三维插值方法得到瞬时缸内燃烧压力,实现发动机扭矩波动和机体振动现象的仿真,同时,建立传动系统中的万向节激励模型和传动轴中间支撑模型,实现传动系统对底盘的激励效果的模拟。综上所述,本文重点探索了影响基于总成特性商用车动力学模型仿真分析频提升和动态过程现象描述的关键问题,并在以下四个方面有所进展：第一、针对现有底盘扭转特性模型参数获取方法的不足,提出了基于传递函数等效原理辨识扭转弹簧模型转动惯量参数和刚度特性的方法,实现了底盘扭转刚度特性动态效果的仿真；第二、针对现有悬架承载特性Fancher模型在边界移动和延迟系数变化描述方面的不足,提出采用悬架变形量修正修正边界移动和延迟系数变化的方法,实现悬架承载特性的精细仿真；第三、针对现有悬架承载特性SAE三连杆模型在迟滞特性仿真方面的不足,提出在铰接点处加入描述动静摩擦效果的力元,采用优化方法确定力元参数,实现悬架承载特性迟滞现象的仿真。第四、针对发动机采用稳态力矩特性的不足,提出采用基于气缸内燃烧压力特性建立发动机非稳态动力学模型,实现发动机非稳态工作特性的仿真。更多还原

【Abstract】 Since there is a vigorous development of high-way network and goods communication by road, the commercial vehicles are required to transfer goods as much as possible and enhance the transfer speed as well in order to prompt the efficiency per day. So far, the load is close to legislation limits and difficult to improve. Whereas the speed is relatively low and could be prompted. So, commercial vehicle manufactures in the world spare no effort to enhance the vehicle speed. The top foreign heavy commercial vehicle speed has been over 100 km/h, while domestic commercial vehicle speed is far less than that. There are 2 ways to enhance the speed, one is a equipting powerful engine and another one is improving quality of the vehicle platform.When the commercial vehicle speeds up, there are some negative phenomenons during the dynamic process, such as the decrease of driving stability, the increase of vehicle vibration, et al, appear to counteract the promotion of driving speed. The main reason is that under middle and high frequency the response of assemblies are coupled and influenced by others, whereas under low frequency the influence could be neglected. High speed and the structure of the vehicle itself could result in the increase of both vehicle and environment excitation frequency. The approach aiming to improve single performance of vehicle dynamics which suitable for the low speed could not impede the influence of the transient factors mentioned above. The total vehicle dynamics performance should be considered in order to get optimum subsystem characteristics.During pre-development stage, the vehicle dynamics model based on assembly characteristic is a powerful tool for assembly characteristic matching and full vehicle performance evaluation. Current commercial vehicle model based on assembly characteristic depends on the simulation of steady state performance, and the results are in high coherence with the tests at steady state. But it can’t simulate the exact state when there is negative dynamic phenomenon mentioned above.Then if we want to further explore the potential of vehicle model based on assembly characteristic during pre-development stage and make the digital simulation accuraty, we need a model that not only can predict exact steady-state performance, but also can simulate the dynamic process phenomenon.After a detail review on domestic and foreign commercial vehicle dynamics and vehicle model development, considering current commercial vehicle models that are mainly focused on steady-state simulation and lack of description of medium and high frequency coupling, some key issues on the commercial vehicle model based on assembly characteristic which could be capable of dynamic process simulation are addressed. From the view of difficult points of this research, we have done the following work:First, a primary commercial vehicle dynamics model based on assembly characteristic is set up. Based on analysis of the key points of vehicle stability and simulation of dynamic process, the motivation and the key issues of modeling the assembly characteristic are introduced and analyzed. The vehicle model is validated by proving ground data.Second, chassis torsion characteristic of commercial vehicle is modeled and simulated. Compared to passenger cars, commercial vehicle chassis torsional stiffness is smaller. The excitation force would result in relative position changes of key assembling hard points and coupling response at medium and high frequency as well. The current model based on discrete multi-chassis structure mass includes torsion spring as analogue of the chassis torsion characteristic. Torsional stiffness is from static test, which can show the steady-state torsion characteristic, but can’t show the dynamic phenomenon. A transfer function which is an equivalent method is introduced in this paper to identify the mass moment of inertia and torsional stiffness. This method could be used to describe dynamic chassis torsion characteristic in a specified frequency range.Furthermore, leaf spring solid axle suspension is modeled and simulated. The K&C and load supporting characteristic of suspension assembly play an important role on vehicle handling and ride preformance directly and thus are an important characteristic at commercial vehicle pre-development stage. At present, suspension K&C characteristic is mainly from K&C rig test, but the relevant equipments are not available in China. Suspension load supporting characteristic are mainly described by SAE 3-link model and Fancher model. The 3-link model can describe the non-linear nominal stiffness characteristic of suspension, but couldn’t simulate hysteresis phenomenon. Fancher model can simulate hysteresis phenomenon, but it couldn’t describe the movement of envelope curve and the change of transition curve. In this paper, a multibody dynamics suspension model based on structure is established by adding stick-slip friction force element to get suspension K & C characteristics; through adding static and dynamic friction effect of the force element to the existing SAE three-link model of the hinge point to achieve hysteresis simulation; by virtue of suspension deformation correction to improve Fancher suspension and achieve load supporting character boundary move and delay coefficient simulation.Finally, powertrain system is modeled and simulated. Powertrain is an important excitation source of the commercial vehicle, non-steady-state characteristic model could efficiently enlarge the analysis frequency range of the vehicle model. Engine torque is expressed by engine steady-state universal characteristic in the existing model, because of the lack of non-steady-state characteristic and excitation of chassis part, could not be simulated the torsion fluctuation and phenomenon of excitation. Combustion pressure characteristic of engine cylinders at typical condition is acquired by simulating, then the instantaneous pressure is obtained by three-dimensional interpolation, and the engine torsion fluctuation and vibration phenomenon can be simulated finally. The secondary torque excitation model of universal joint is also established and used in the chassis system, so that the excitation effect of powertrain to the chassis can be simulated.Above all, several key issues of commercial vehicle dynamics model based on assembly characteristic are researched in this paper. They are mainly about factors affecting the promotion of analysis frequency and dynamic process description. Five main innovation are as follows:Firstly, according to the deficiency of present method to get the chassis torsion characteristic, a method based on transfer function equivalence theory is brought out to identify the torsion spring moment of inertia and stiffness characteristic, so that the dynamic effect of chassis torsion stiffness characteristic can be simulated.Secondly, to solve the problem that the present Fancher model could not describe envelopes movement and transition curves changes, a method is brought out to revise them by suspension displacement, so the suspension load hysteresis characteristic is simulated exactly.Thirdly, since the SAE3-link model could not describe the hysteresis characteristic of suspension, a method of building stick-slip friction force element in the joints is used to resolve this problem.Finally, because it is kind of shortcoming to use the steady-state torque characteristic in the present engine model, a non-steady-state engine dynamics model based on cylinder combustion pressure characteristic is brought out. This model can simulate engine torque fluctuation and engine vibration.更多还原