低质心混凝土搅拌车设计原理与结构

低质心混凝土搅拌车的主要结构和特点。针对市场上大容量混凝土搅拌车质心高的结构特点,介绍了一种能改善整车行驶稳定性的     

高速铁路低矮路堤灰土桩复合地基的动力特性分析

利用有限元软件MIDAS/GTS,分别建立了灰土桩复合地基和未经处理的黄土地基上铁路路基的三维有限元模型,用轨道不平顺法模拟列车荷载,分析计算了在不同速度列车荷载作用下不同路堤高度下地基土中动应力的分布,得出了桩土应力比的变化规律和地基瞬时变形规律。     

不同交联度环氧沥青混合料低温弯曲性能研究

采用交联度分别为75.3%,71.4%,67.3%和58.4%的环氧沥青混合料进行-20℃,-10℃,0℃,10℃温度下小梁三点弯曲性能试验,构建了混合料弯曲强度、弯曲模量、弯曲破坏应变及弯曲应变能密度与温度、交联度的关系方程。结果表明：不同交联度的环氧沥青混合料弯曲强度与模量随着温度的提高而降低,弯曲破坏应变与弯曲应变能密度随着温度的提高而增大;不同交联度的环氧沥青混合料弯曲强度、弯曲模量、弯曲破坏应变及弯曲应变能密度与温度关系基本一致,各弯曲性能参数的温度敏感区间基本相同;温度敏感区间弯曲性能参数变化幅度较大,低于温度敏感区间,则弯曲性能参数变化幅度较小;环氧沥青混合料低温弯曲性能参数与温度、交联度之间具有较好相关性,提出的回归方程可以用于混合料低温弯曲性能预测。     

Dynamic model for the wheel–rail contact friction

Accurately estimating the coefficient of friction (CoF) is essential in modelling railroad dynamics, reducing maintenance costs, and increasing safety in rail operations. The typical assumption of a constant CoF is widely used in theoretical studies; however, it has been noticed that the CoF is not constant, but rather depends on various dynamic parameters and instantaneous conditions. In this paper, we present a newly developed three-dimensional nonlinear CoF model for the dry rail condition and test the CoF variation using this model with estimated dynamic parameters. The wheel–rail is modelled as a mass–spring–damper system to simulate the basic wheel–rail dynamics. Although relatively simple, this model is considered sufficient for the purpose of this study. Simulations are performed at a train speed of 20 m/s using rail roughness as an excitation source. The model captures the CoF extremes and illustrates its nonlinear behaviour and instantaneous dependence on several structural and dynamic parameters.     

A substitute model of two-dimensional dry friction exposed to dither generated by rolling contact of wheel and rail

Dither generated by rolling contact of wheel and rail smoothes dry friction damping provided by the primary suspension dampers of freight wagons and it should be taken into account in numerical simulations. But numerically the problem is non-smooth and this leads to long execution time during simulation, especially when the vehicle with friction dampers is modelled in the environment of an multi-body system simulation program, whose solver has to cope with many strong non-linearities. The other difficulty is the necessity of handling within the code a number of big volume files of recorded dither sampled with high frequency. To avoid these difficulties, a substitute model of two-dimensional dry friction exposed to dither is proposed that does not need application of dither during simulation, but it behaves as if dither were applied. Due to this property of the model, the excitation of the vehicle model by track irregularities may be supplied as low-frequency input, which allows fast execution and, the necessity of handling high-volume files of recorded dither is avoided. The substitute model is numerically effective. To identify parameters of the substitute model, a pre-processing employing a sample of the realistic dither is carried-out on a simple two-degrees-of-freedom system. The substitute model is anisotropic, describing anisotropic properties of the two-dimensional friction arising in the presence of one-dimensional dither. The model may be applied in other branches of engineering, for example, in mechatronics and robotics, where application of dither may improve the accuracy of positioning devices.     

Adhesion estimation at the wheel–rail interface using advanced model-based filtering

The railway industry in the UK is currently expanding the use of condition monitoring of railway vehicles. These systems can be used to improve maintenance procedures or could potentially be used to monitor current vehicle running conditions without the use of cost prohibitive sensors. This paper looks at a novel method for the online detection of areas of low adhesion in the wheel/rail contact that cause significant disruption to the running of a network, particularly in the autumn season. The proposed method uses a Kalman–Bucy filter to estimate the creep forces in the wheel–rail contact area; post-processing is then applied to provide information indicative of the actual adhesion level. The algorithm uses data that, in practice, would be available from a set of modest cost inertial sensors mounted on the vehicle bogie and wheel-sets. The efficacy of the approach is demonstrated using simulation data from a nonlinear dynamic model of the vehicle and its track interface.     

A study on high-speed rolling contact between a wheel and a contaminated rail

A 3-D explicit finite element model is developed to investigate the transient wheel–rail rolling contact in the presence of rail contamination or short low adhesion zones (LAZs). A transient analysis is required because the wheel passes by a short LAZ very quickly, especially at high speeds. A surface-to-surface contact algorithm (by the penalty method) is employed to solve the frictional rolling contact between the wheel and the rail meshed by solid elements. The LAZ is simulated by a varying coefficient of friction along the rail. Different traction efforts and action of the traction control system triggered by the LAZ are simulated by applying a time-dependent driving torque to the wheel axle. Structural flexibilities of the vehicle–track system are considered properly. Analysis focuses on the contact forces, creepage, contact stresses and the derived frictional work and plastic deformation. It is found that the longitudinal contact force and the maximum surface shear stress in the contact patch become obviously lower in the LAZ and much higher as the wheel re-enters the dry rail section. Consequently, a higher wear rate and larger plastic flow are expected at the location where the dry contact starts to be rebuilt. In other words, contact surface damages such as wheel flats and rail burns may come into being because of the LAZ. Length of the LAZ, the traction level, etc. are varied. The results also show that local contact surface damages may still occur as the traction control system acts.     

高掺量橡胶改性沥青性能研究及优选

橡胶沥青的掺量大小对沥青的性能和使用成本都有显著的影响。为了提高橡胶改性沥青掺量的同时兼顾其性能,本研究选择20%、30%、40%、50%4种掺量的橡胶改性沥青,通过温度扫描试验和弯曲梁流变试验评价不同掺量的橡胶改性沥青的高温性能与低温性能,并根据规范要求确定PG分级。通过拟合半对数坐标下车辙因子-温度曲线,对比了老化前后各个沥青的感温性。结果表明：高温流变性能方面,老化前后车辙因子大小均表现为40%RA>30%RA>50%RA>20%RA,当胶粉掺量超过40%以后,高温性能显著下降。随着胶粉掺量的提高,胶粉改性沥青的高温性能先上升后下降,考虑高温性能,则胶粉掺量不宜超过40%。从半对数坐标的拟合结果来看,掺量在20%～40%之间时,胶粉能提高沥青的温度稳定性。低温性能方面,随着胶粉掺量的提高,胶粉改性沥青的低温变形能力和应力松弛能力逐渐增强。综合温度扫描试验和BBR试验的结果,得到4种胶粉改性沥青的PG分级结果：20%RA为PG82-22,30%RA/40%RA为PG88-28,50%RA为PG82-34。综合考虑性能和经济性,在实际工程中较为推荐30%掺量和40%...     

奥迪混合动力车型绝缘电阻故障引起整车无电动模式故障2例

有一辆奥迪Q5 hybrid混合动力汽车和一辆奥迪A6L e-tron混合动力汽车启动时,仪表报警,均显示混合动力系统故障,均无电动模式。初步判断故障范围在高压系统的高压线路连接以及安全控制系统。结合诊断仪读码的分析,故障范围锁定在某个或者多个高电压部件不绝缘,通过对所涉及的元件、电路等进行检测,故障点分别为电驱动装置的功率和控制电子单元内部积水、高电压蓄电池充电器内部不绝缘故障,对其分别进行积水清理、部件更换后,车辆仪表报警灯消失,可正常电动行驶。     

纯电动汽车动力电池系统的低温性能研究

以搭载三元锂电池的纯电动汽车为研究对象,对某纯电动汽车动力电池系统的低温性能进行试验研究,结果表明:续驶里程在-10℃时相比25℃时下降46%,电池荷电量为30%,-10℃时的峰值放电功率比25℃时衰减了51%,电池容量衰减11.6%。为低温环境下纯电动汽车的性能研究提供一定的依据。