大侧倾角下UniTire稳态侧倾侧偏工况侧向力模型

大侧倾角下,轮胎侧偏力学特性仅仅采用等效侧偏角的方法不能进行准确描述,还需要考虑侧倾对其他关键参数的影响。基于简单刷子模型,建立轮胎稳态侧倾侧偏工况侧向力物理模型,导出用于半经验建模的理论边界条件。采用定性分析及试验观察相结合的方法分析侧倾对侧偏刚度和摩擦因数的影响,并建立相应的半经验模型。根据理论边界条件,分析侧倾对UniTire稳态侧向力模型中曲率因子的影响,并提出新的曲率因子表达式。通过轮胎试验数据进行参数辨识,结果表明所建立的UniTire稳态侧向力模型具有很高的精度,并且能够表达大侧倾角下轮胎的力学特性。     

磨损对轮胎侧偏刚度和回正刚度影响的研究

基于轮胎六分力测试结果,研究不同磨损状态下轮胎的侧偏力学特性,得出轮胎侧偏特征参数随着轮胎磨损量的变化规律。通过建立胎面磨损模型阐明轮胎磨损特性变化的机理,得到胎面刚度与磨损量的表达式,之后根据该表达式和考虑轮胎磨损状态的轮胎刷子模型,建立考虑胎面磨损的轮胎复杂刷子模型。通过模型推导得到磨损量与轮胎侧偏刚度、回正刚度的关系,以该关系为UniTire轮胎模型的建模基础表达公式,建立考虑磨损的UniTire侧偏模型。为验证模型的正确性,采用3种磨损状态的侧偏数据进行参数拟合,得到考虑磨损的UniTire侧偏模型,并预测其他2种磨损状态下的轮胎侧偏特性。预测模型的仿真结果与试验结果之间的误差较小,有效证明了考虑磨损的UniTire侧偏模型的预测能力。本研究有助于完善UniTire轮胎模型,为UniTire模型室内外扩展应用提供理论和技术支持。     

复合工况下四轮驱动电动汽车操纵稳定性控制

设计一个考虑车辆侧纵向耦合的模型预测控制器(Model predictive control,MPC)用于提升四轮驱动电动汽车在复合工况下的操纵性和稳定性.基于传统UniTire轮胎模型,推导面向控制器设计的复合工况UniTire轮胎模型解析表达式;基于前后轮侧偏角相平面提出一种新的车辆稳定性评价标准,通过前后轮侧偏角的位置到坐标原点的距离判断车辆的稳定性,给出定量的稳定性指标;采用MPC控制器结构将车辆操纵性控制、稳定性控制以及四轮滑移率约束作为目标函数,采用复合工况UniTire轮胎模型表达式和双轨车辆模型构建预测模型,并且通过稳定指标和轮胎滑移率实时调整各个目标的权重以达到最优的控制效果;通过Simulink-CarSim联合仿真和硬件在环(HiL)测试对算法进行验证,结果表明,该控制器能够根据车辆稳定性指标动态调节跟踪权重,有效提升车辆的操纵性和稳定性.并且由于复合UniTire轮胎模型的使用,极限工况下控制器决策的四轮力矩更小,有效地抑制轮胎滑移率的增加.     

轮胎非稳态侧偏特性非线型仿真模型

在稳态指数统一模型的基础上,根据动态过程有效滑移率的微分表达,建立轮胎非稳态侧偏特性非线性仿真模型。在实验中发现当用有效滑移率和准稳态要领来计算回正力Ｄｘ时,有滑移超前而加正力滞后现象,该现象可以通过一个一阶滤波器来表达。模型的计算结果与实验结果对比,表明该模型可以反遇轮胎非线笥侧偏特性,可以用于汽车操纵动力学研究。     

轮胎非稳态侧偏特性非线性仿真模型

在稳态指数统一模型的基础上,根据动态过程有效滑移率的微分表达,建立轮胎非稳态侧偏特性非线性仿真模型。在实验中发现当用有效滑移率和准稳态概念来计算回正力臂 Ｄｘ 时,有滑移率超前而回正力臂滞后现象,该现象可以通过一个一阶滤波器来表达。模型的计算结果与实验结果对比,表明该模型可以反映轮胎非线性侧偏特性,可以用于汽车操纵动力学研究。     

车辆纵-侧-垂向动力学统一建模及实车验证

目前车辆动力学模型多从各运动方向或关注的运动姿态来分别建立,缺乏纵-侧-垂向动力学统一建模思路。为全面描述车辆多系统耦合下的复杂系统非线性动力学行为,研究一种车辆纵-侧-垂向动力学统一建模方法。建立包含发动机动态特性、传动系统和车轮的动力传动系统模型,在分析车体运动学特性的基础上,采用拉格朗日分析力学方法建立同时反映车辆纵向、侧向和垂向运动特性的强非线性统一动力学模型,并建立悬架和轮胎模型求得作用于车体的广义力。利用某车型的标准数据和实测数据,进行车辆纵-侧-垂向动力学统一模型的多工况仿真验证和实车验证,所建立的车辆动力学模型能够精确模拟实际车辆的复杂动力学行为特性,验证了车辆纵-侧-垂向动力学统一建模方法的有效性和可行性。可为智能车辆控制系统设计和功能验证提供高保真度的仿真载体,缩短控制算法开发时间。     

矿用汽车整车稳态转向特性建模分析

准确的整车模型对车辆稳态转向特性研究具有重要影响,综合考虑具体研究的内容和计算分析的复杂程度,以四自由度的车辆模型为基础对矿用汽车的稳态转向特性进行分析。建立矿用汽车所采用的18.00-25工程轮胎的侧偏特性模型,用于车辆操纵稳定性分析;在前后悬架侧倾特性分析的基础上,建立了整车稳态转向工况的分析模型,以车身侧倾时各轮垂向载荷重新分配的情况为依据,研究车辆悬架对稳态转向特性的影响;通过几何图解方法分析车架扭转对整车侧倾的影响;对车辆的稳态转向特性进行评价。结果表明:车架对操纵稳定性的影响程度随车辆侧向加速度的增大而增大,且适当提高车架刚度有利于改善操控稳定性;该车中性转向点侧向加速度和不足转向度基本能够满足要求,车身侧倾度与普通车辆相比较小。     

轮胎非稳态侧偏特性对汽车操纵性的影响

以考虑胎体复杂变形的轮胎非稳态侧偏特性理论模型为基础,建立考虑轮胎非稳态侧偏特性的角输入汽车模型,分析轮胎非稳态侧偏特性对汽车操纵性的影响。     

考虑迟滞特性的轮胎纵向动力学模型

轮胎是汽车唯一接地部件，提供汽车运动需要的所有驱动、转向和制动力。轮胎模型是汽车动力学的基础，汽车动力学及其控制技术的进一步发展有赖于精确的轮胎模型技术。为此提出一种考虑轮胎变形迟滞特性的轮胎简化物理模型，结合电容-电阻(Resistor-Capacitor,RC)迟滞算子，分析轮胎胎体压缩回弹和制动力加载卸载两个层面的迟滞特性，并分别建立纵滑工况下的轮胎稳态模型HysTire和动态模型Dyn-HysTire。为了验证HysTire模型和Dyn-HysTire模型的准确性，对某型号Pirelli轮胎纵滑工况下的试验数据进行建模。结果显示，稳态模型HysTire提供了与魔术公式相似的拟合精度，而引入滑移率变化率的动态Dyn-HysTire模型的拟合结果的均方差(Mean square error,MSE)值相比于魔术公式降低了约30%，显著提高了轮胎的仿真精度。另外Dyn-HysTire模型同样提供了堪比LuGre模型和PAC2002模型对轮胎动态特性的表达能力。最后在1/4车辆ABS仿真中进一步验证，相比于魔术公式，考虑迟滞特性的Dyn-HysTire模型更能反映出轮胎的真实力学特性，...     

考虑轮胎侧偏特性的赛车转向几何研究

为了提高赛车轮胎侧向附着合力及转向极限侧向加速度,提出了一种考虑轮胎侧偏特性的转向几何。通过分析轮胎侧偏角的影响,确定了整车转向瞬心位置,并建立了三自由度整车模型。结合轮胎力学模型,以最大化整车轮胎侧向附着合力为目标,采用隔代映射遗传算法对考虑轮胎侧偏特性的转向几何进行求解。整车仿真和试验结果表明,相比阿克曼转向几何,考虑轮胎侧偏特性的转向几何可以更有效地增大整车轮胎的侧向附着合力,提高赛车在极限工况下的转弯性能。     

湿滑状态下轮胎路面摩擦特性的数值分析方法

为研究湿滑状态下轮胎路面的摩擦特性,以胎面橡胶和沥青路面作为研究对象,利用谐波叠加法建立三维粗糙路面模型,采用“伪”流体动力轴承作用等效反映路面水膜“密封”作用,综合使用有限元软件ABAQUS和计算流体动力学软件Fluent得到湿滑状态下橡胶与路面滑动接触时的橡胶接触压力、滞后摩擦力及路面水膜承载力,由此形成了综合兼顾橡胶材料、接触压力、滑动速度、路面形貌和路面水膜等多因素的轮胎与湿路面摩擦特性的仿真方法。通过橡胶与干-湿路面摩擦特性的变化与公开的试验对比,证明本方法的合理性和可行性,并进一步分析滑动速度、接触压力和路面特征对湿滑状态下轮胎路面摩擦特性的影响规律。研究结果为轮胎和路面的抗湿滑性设计及优化提供理论依据。     

实心橡胶轮胎非线性有限元分析

根据高速履带车辆实心橡胶轮胎的工作条件,在合理假设基础上建立了滚动工况轮胎三维有限元分析模型.借助大型有限元分析软件ANSYS 11.0,充分考虑非线性(材料、几何、状态非线性)的情况下,计算了不同载荷、速度条件下负重轮的应力一应变场.结果表明,稳态滚动负重轮橡胶轮胎车速对拉伸应力应变的影响较大,而对压缩应力应变影响很小;负载对压缩应力应变的影响较大,呈近似直线关系,而对拉伸应力应变的影响很小,为负重轮实心轮胎的设计及其温度场的计算提供重要的理论依据.     

麦弗逊悬架仿真试验与优化研究

建立某电动汽车麦弗逊悬架系统的虚拟模型,对轮胎横向滑移量进行仿真。对该悬架系统进行试验研究,测量轮胎的实际横向滑移量。仿真结果和试验结果之间的误差小于7%,说明该虚拟模型是精确的。以轮胎横向滑移量为目标函数,利用虚拟模型对该悬架系统的结构参数进行优化研究,结果表明在设计变量的取值范围内和约束条件下,目标函数存在着多个极值点,需要选择多个初始点进行优化,才能得到更好的结果。     

基于三维接触的滑环式旋转组合密封性能主控因素分析

密封圈二维有限元分析中,常将密封圈接触面上最大接触压力推广到整个接触面上,针对这种不够精确的方法,提出了一种基于三维仿真模型的有效接触压力高精度计算方法。建立组合密封圈的三维模型,模拟实际工况,对影响其动密封特性的轴往复运动速度、轴转速、介质压力、O形圈压缩量、滑环厚度、滑环动接触面开槽进行了研究,并利用有效接触压力计算方法分析了动接触面上有效接触压力的分布情况。结果表明：滑环开槽、滑环厚度、O形圈压缩量以及介质压力对组合密封圈有效接触压力影响较大,内轴往复速度以及转速达到一定值后对有效接触压力影响较大。研究结果为滑环式组合密封圈的优化设计提供了参考。     

The Frictional Properties of Newtonian Fluids in Rolling–Sliding soft-EHL Contact

A combined experimental and numerical study has been carried out to explore friction in rolling–sliding, soft-EHL contact. Experimental work has employed corn syrup solutions of different concentrations in water to provide a range of lubricant viscosities and has measured Couette friction in mixed rolling–sliding conditions over a wide range of entrainment speeds. A Stribeck curve has been generated, ranging from the boundary to full film, isoviscous-elastic lubrication regime. In the latter regime, friction coefficient is approximately proportional to the product of (entrainment speed × viscosity) raised to the power 0.55. Numerical solution of the isoviscous-elastic lubrication regime has been used to derive predictive equations for both Couette and Poiseuille friction in circular, soft-EHL contacts. This shows that in soft-EHL the Poiseuille or “rolling” friction can have magnitude comparable to the Couette friction. The calculated Poiseuille friction coefficient can be predicted from non-dimensional load and speed using a simple power law expression similar to that used for film thickness. However accurate prediction of calculated Couette friction coefficient requires a two-term power law expression. Comparison of experimental and numerical Couette friction coefficients shows quite good agreement between the two, with a similar non-dimensional speed dependence, but slightly lower predicted than measured values.     

汽车轮胎橡胶摩擦试验研究

介绍了所开发的轮胎橡胶摩擦试验台,提出了轮胎橡胶摩擦试验方法。在该试验台上进行了干水泥路面、冰面等工况下的轮胎橡胶块摩擦试验,对所得试验结果进行了分析、处理。初步掌握了路面、温度、垂直压力和滑移速度等因素对摩擦因数的影响。在此基础上把动摩擦的概念引入轮胎半经验模型,对现有模型进行了改进。提出了应用轮胎低速试验数据预测高速下轮胎特性的方法。     

Experimental Research on Friction of Vehicle Tire Rubber

A newly developed tire rubber friction test machine is introduced. Friction test method of tire rubber is provided. Test data of tire rubber friction on concrete and icy road surfaces are obtained and analyzed. The effect of different road surface, ambient temperature, contact pressure, and slip velocity on friction coefficient is apprehended. The dynamic friction is introduced to tire semi-empirical modeling, and the accuracy of the model is improved. A way of forecasting tire property on high-rolling speed using data from low-rolling speed tire test is illustrated.     

Prediction of the Dynamic Properties of Temperature Sensors in Arbitrary Gases

Abstract

This paper presents a theoretical investigation with experimental model verification of the dynamic properties identification of contact temperature sensors in arbitrary gases. For prediction of dynamic behaviour of temperature sensors in mainly uncommon atmospheres and under conditions where standard experimental work could not be carried out, a mathematical model was built for calculating the dynamic parameters of temperature sensors in various gases at different thermodynamic conditions on the basis of experimental work. Frequently, a sensor's dynamic properties and sensitivity to different or changed thermodynamic conditions such as temperature, pressure, velocity, or even composition of gases in operation conditions can be a crucial factor in the regulation and control of the system. The main part of the contribution describes the mathematical model, its connection with the experimental results and limits within which the discussed relation are valid. The contribution also introduces, on the based of non-dimensional correlation and supposition that the time behaviour, is a function of pressure and velocity; a simplified expression is offered for the calculation the heat transfer coefficient as one of the most significant factor in determining the dynamic properties and behaviour of temperature sensor. The presented investigation has shown applicability of an elaborated mathematical model in connection with experimental results, as well as the employability of a simplified calculated expression which was verified with a standard iterative method. The built model and results of calculations show high applicability of the model, especially in investigations and analyses where different arbitrary gases under different thermodynamic conditions are used.     

Effects of Interfacial Strength and Roughness on the Static Friction Coefficient

A finite element model is used to simulate sliding inception of a rigid flat on a deformable sphere under combined normal and tangential loading. Sliding inception is treated as the loss of tangential contact stiffness under combined effects of plasticity, crack propagation and interfacial slip. Energy dissipation distribution is used to quantify the relative contribution of these mechanisms on the increased compliance during tangential loading. Materials with different strength and toughness properties, and varying local interface conditions ranging from fully adhered to finite friction, are studied to relate variations in plastic deformations, crack and slip to the sliding inception. For fully adhered contact condition, crack and fracture toughness have no effect on sliding inception, with plasticity, the dominant failure mechanism. A measure of recoverable strain (yield strength to Young’s modulus ratio) is found to be the most influential parameter in sliding inception. Interfacial slip is expectedly the dominant mechanism for sliding inception for lower coefficient of friction, modeling lubricated contacts. Interplay of plasticity and interfacial slip is found to govern the onset of sliding for higher local friction coefficients. Furthermore, the single asperity results are incorporated in a statistical model for nominally flat contacting rough surfaces under combined normal and tangential loading to investigate the stochastic effects due to surface roughness and material property uncertainties. The results show that the static coefficient of friction strongly depends on the normal load, material properties, local interfacial strength and roughness parameters.