基于ABS的车辆弯道稳定性控制仿真研究

车辆在低附着弯道路面上制动是一种非常危险的工况.本文从车辆在低附着弯道路面上制动整车受力的角度出发,分析了车辆弯道制动时ABS控制的不足,提出了车辆ABS与横摆力矩控制协调控制的制动力控制策略.利用模糊控制原理设计了横摆力矩控制器,在制动车辆ABS的基础上,通过对车辆的横摆力矩控制和车轮滑移率的调节,实现了制动过程中对附加横摆力矩的动态调整,从而可以在不增加硬件成本的条件下实现车辆在低附着弯道路面上制动的稳定控制.最后进行仿真试验验证了该控制方法的有效性.     

Internal stresses during rolling friction and their evaluation

The estimation of wear of materials intended for practical use demands a detailed knowledge of applied forces and internal stresses in materials. For a dry friction rolling-body model the relationship between the internal stresses and the normal force, slip and rolling length was determined. The evaluation of the internal stresses was carried out on the basis of a practical (wheel/rail) frictional system. X-ray determination of forces proved to be an efficient method of measuring forces in the surface of metallic rolling bodies. The purpose of internal stress measurements is to follow plastic deformation at frictional surfaces and consequently to establish new criteria for the deformation and resistance of materials and their application to frictional systems.     

轮胎稳态运动学与六分力预报Ⅰ:理论与方法

提出一种新的轮胎运动学描述和六分力预报理论。滚动接触是汽车轮胎力学、轮轨动力学的核心问题,由于涉及刚体转动与有限变形,滚动接触运动学与动力学的描述与求解非常困难。用拉格朗日—欧拉混合描述法分析大变形滚动接触结构的速度场、加速度场和接触变形。以车轮定位角为卡尔丹角,用拉格朗日描述,得到了包含刚体转动和弹性变形的轮胎速度场。而接触区域的变形和受力用欧拉描述,通过欧拉网格和拉格朗日网格的信息传递,完成滚动结构动力学分析。所提出的理论可以退化到Fiala模型,并可以从理论上解释子午线轮胎的伪侧偏和伪侧倾现象。基于所建立的运动学理论和非线性有限元,建立轮胎六分力预报方法。针对某轿车子午线轮胎,分析轮胎接地面滑移速度、接地面积、接地压力、侧向剪力分布等随着侧偏角的变化规律,并研究该轮胎侧偏力和回正力矩随着胎面刚度和摩擦因数的参数敏感性。结果表明轮胎侧偏刚度和回正刚度主要受结构刚度控制,而峰值侧偏力和峰值回正力矩主要受摩擦因数控制。将利用所建立的方法和试验,探讨带束层结构对大规格子午线轮胎侧偏特性的影响规律,进一步验证所提出的理论和方法的正确性。所提出的理论和方法开辟了直接从轮胎设计预报轮胎六分力的新途径。     

二维库伦摩擦力系统的精确解及新数值算法研究*

在路径坐标系下,引入了恒定外部激励力二维库伦摩擦力系统滑移轨迹的精确解。当量纲一的外部激励力F>1时,系统会最终进入黏滞状态,给出了对应的黏滞的位置和黏滞发生的时刻;当F<1时,系统会保持滑移状态。当初始时刻外部激励力的方向与初始速度方向之间的夹角值较大时(接近于反向),则在轨迹中存在一个滑移方向发生剧烈变化的拐点,特别的,当F>1时,拐点接近于黏滞位置。传统积分算法不易求解含有转换及捌点的二维库伦摩擦力系统。假设在足够小的时间步长内,时变外载荷激励可以近似认为保持恒定不变,则利用上述解析解能够建立一种新的库伦摩擦力系统数值求解算法,进而分析粗糙接触表面多结点模型的微滑移以及微滑移诱发的磨损与能量损耗等。     

一种用于高旋稳定弹药的超声电机调速系统

针对高旋转制导弹药平台的固定式鸭舵控制,提出了一种旋转型行波超声电机驱动进给机构的制动方式和舵机调速系统,搭建了舵机性能测试试验平台并获得了良好的速度控制性能。首先,采用库伦加黏性摩擦理论建立了超声电机驱动的制动盘和旋转盘之间的摩擦制动模型,综合考虑超声电机的机械负载特性,计算了制动盘对旋转盘产生的摩擦力矩,得到了旋转盘(外壁设计有舵翼)的转速输出方程;其次,结合试验与仿真分析,测定了结构的阻尼系数;最后,通过试验验证了基于超声电机作动制动模型的正确性,测量了舵机的速度控制曲线,引入速度波动率来衡量速度控制效果。试验表明,舵机速度调控响应时间小于150ms,速度波动率能够控制在10%以内。     

基于LuGre模型的转子压缩机滑片-滑槽运动副摩擦力测试

为研究转子压缩机滑片-滑槽运动副的摩擦特性,根据LuGre摩擦模型的建模方法和该运动副的运行特点及工况特点,设计并搭建了滑片-滑槽等效摩擦力测试系统,分析了该系统的摩擦力跃动现象、数据采集区域和摩擦力测量的重复性问题,并进行了摩擦力测试实验。结果表明：该摩擦力测试系统可以根据压缩机的实际工况,对滑片均匀加载相应的正压力FH,并能实现不同匀速直线运动下的摩擦力测量;可以有效消除低速润滑不均匀导致的摩擦力跃动现象;通过润滑初始化可以较准确地获得基于滑片速度变化的摩擦力表达曲线。实验结果与数值计算结果吻合,从而为正确辨识LuGre摩擦模型的参数提供了实验依据。     

Drive control algorithm for an independent 8 in-wheel motor drive vehicle

This paper describes a drive control algorithm based on optimal coordination of drive torque for an independent 8 in-wheel motor drive vehicle. The drive controller improves lateral stability and maneuverability. The drive controller consists of upper level controller and lower level controller. The upper level controller determines front, middle steering angle, additional net yaw moment and longitudinal net force according to the reference velocity and steering commands. The lower level controller coordinates additional tractive and braking forces to guarantee desired longitudinal net force and yaw moment. This controller is based on optimal control theory and takes into consideration the friction circle related to the vertical tire force and friction coefficient acting on the road and tire. Distributed tractive and braking forces are determined as proportional to the size of the friction circle according to the changes at driving conditions. The response of the 8 in-wheel drive vehicle implemented with this drive controller has been evaluated via computer simulations conducted using Matlab/Simulink dynamic model. Computer simulations of an open-loop J-turn maneuver and a closed-loop driver model subjected to double lane change have been conducted to demonstrate improved performance and stability of the proposed drive controller.     

二氧化碳制冷系统内啮合转子压缩机齿间受力特性

齿间受力特性直接影响到内啮合转子压缩机的可靠性和寿命,但目前还缺乏相关研究报道。在忽略齿间间隙和摩擦力后,建立合适的内外转子受力模型,引入线弹性理论,通过采用变形量的大小来关联各啮合点之间接触力的相对大小,从而可简化接触力的计算。模型着重对齿间接触力、接触力矩以及它们与气体力、支撑力和驱动力矩之间的关系进行分析。并以一1匹二氧化碳超临界制冷循环压缩机为例,对模型进行求解。计算结果表明,与气体力相比,该压缩机齿间接触力比较小,外转子受到的气体力矩完全由接触力矩平衡,而且该压缩机驱动力矩平稳,周期呈2/Z2变化。研究的结果对内啮合压缩机的设计有一定指导意义。     

An analytical model to investigate skidding in rolling element bearings during acceleration

Skidding, which occurs in rolling element bearings during shaft rotational acceleration, causes wear and incipient failure. This paper presents an analytical model to investigate skidding during rolling element bearing acceleration, taking account of the contact force and friction force between the rolling elements and the races and the cage, gravity, and the centrifugal force of the rolling elements. The Hertzian contact theory is applied to calculate the non-linear contact force. The Coulomb friction law is used to calculate the friction force. All forces above are included in force equilibrium equations to derive the non-linear governing equations of the bearing during acceleration, and are solved using a fourth-order Runge-Kutta algorithm with fixed time step. The proposed model is verified by comparison to other published results and with experimental results. The proposed model can be used to investigate skidding in rolling element bearings during acceleration and the transient motion behavior of rolling elements, and it will lay the theoretical foundations for eliminating skidding in rolling element bearings.     

Analytical and experimental study on asymmetrical sheet rolling

An analytical model assuming constant shear friction between the rolls and sheet is proposed to explore the characteristics of asymmetrical cold and hot sheet rolling. In the hot sheet rolling process, the surface friction stress is assumed to be equal to the yield shear strength (i.e. τ = k). As the friction factor m is less than 1, the simulation for the cold rolling process can be conducted. To verify the validity of the proposed analytical model, a series of experiments on asymmetrical cold sheet rolling of aluminium are carried out. The total rolling force and the forward slip are measured. The proposed model is also used to estimate friction factor (m) with the measured forward slip. With the estimated friction factors, the analytical rolling forces are calculated to compare with experimental data. Reasonable agreement is found. By this proposed analytical model, it is noted that a large amount of calculation time and computer expense are saved, and the characteristics of asymmetrical cold and hot sheet rolling are obtained easily and rapidly.     

Synthetic lubricants in cold strip rolling

The embedded-pin technique is used to monitor the variation of the interfacial forces during cold rolling of aluminium slabs. The results confirm earlier conclusions, indicating that the frictional coefficient is a strong function of the process and material parameters. Coefficient of friction values deduced from forward slip measurements are close to the present data, confirming that in spite of several drawbacks of the experimental technique, it can yield very useful results. Lubricants are shown to reduce the loads on the rolling mills in a significant manner.     

盘式制动器的原理与应用

桥式起重机起升机构制动器的摩擦零部件,以一定的作用力压紧机构中某一根轴上的制动轮,产生制动力矩,利用这个制动力矩使物体质量和惯性力等所产生的力矩减小,直至两个力矩平衡,达到调速或制动的要求。盘式制动器由于制动转矩大,性能稳定可靠,外形尺寸小,磨损小,正广泛应用在起重机械设备上。     

轧制塑性加工中的摩擦力

本文依据轧制塑性加工中的滚一滑摩擦机理建立一个新的摩擦力概念,并在此基础上给出一个相应的摩擦力计算公式。文中用该公式对轧制咬入过程中的摩擦力进行了计算。并以实验对其计算结果进行了验证。同时还对计算结果进行了分析。文中的结论可供有关研究人员参考。     

考虑运动副摩擦时平面闭链五杆机构逆动力学分析

提出一种修正的指数摩擦模型,给出了摩擦系数与速度的关系式,避免了速度零点的多值问题,建立了机构运动副摩擦的数学模型。建立了包含运动副摩擦的平面闭链五杆机构的逆动力学模型,并给出了一种迭代求解方法,可得到运动副的约束力、驱动力和运动副摩擦力矩。在相同运动规律下,对计入和不计入运动副摩擦两种情形进行驱动力矩的比较。仿真结果表明:两种情形下的驱动力矩有较明显的差异,在速度反向区,运动副摩擦力矩的变化剧烈,对机构驱动力矩的影响最大,在机构运行速度较低时,这种现象更为明显。     

Identification of the nonlinear excitation force acting on a bowed string using the dynamical responses at remote locations

For achieving realistic numerical simulations of bowed string instruments, based on physical modeling, a good understanding of the actual friction interaction phenomena is of great importance. Most work published in the field including our own has assumed that bow/string frictional forces behave according to the classical Coulomb stick-slip model, with an empirical velocity-dependent sliding friction coefficient. Indeed, the basic self-excited string motions (such as the Helmholtz regime) are well captured using such friction model. However, recent work has shown that the tribological behavior of the bow/string rosin interface is rather complex, therefore the basic velocity-dependent Coulomb model may be an over-simplistic representation of the friction force. More specifically, it was suggested that a more accurate model of the interaction force can be achieved by coupling the system dynamical equations with a thermal model which encapsulates the complex interface phenomena. In spite of the interesting work performed by Askenfelt [32], a direct measurement of the actual dynamical friction forces without disturbing the string motion is quite difficult. Therefore, in this work we develop a modal-based identification technique making use of inverse methods and optimization techniques, which enables the identification of the interface force, as well as the string self-excited motion, from the dynamical reactions measured at the string end supports. The method gives convincing results using simulated data originated from nonlinear computations of a bowed string. Furthermore, in cases where the force identifications are very sensitive to errors in the transfer function modal parameters, we suggest a method to improve the modal frequencies used for the identifications. Preliminary experimental results obtained using a basic bowing device, by which the string is excited with the stick of the bow, are then presented. Our identifications, from the two dynamical string reactions, are consistent as attested by the comparison of the two available versions of the string dynamical motion and of the friction force. Furthermore, the method seems adequate to investigate the interface force for the bowed string.     

盘式制动器的原理与应用

桥式起重机起升机构制动器的摩擦零部件,以一定的作用力压紧机构中某一根轴上的制动轮,产生制动力矩,利用这个制动力矩使物体质量和惯性力等所产生的力矩减小,直至两个力矩平衡,达到调速或制动的要求.盘式制动器由于制动转矩大,性能稳定可靠,外形尺寸小,磨损小,正广泛应用在起重机械设备上.     

Fundamental studies on the brake friction of resin-based friction materials

The effects of various factors on brake friction were studied on the braking of a cast iron disk by small brake specimens made of resin, resin-asbestos composites and three-component composites. When the disk temperature rises, the resin-based composites containing asbestos and high melting point additive exhibit considerably lower friction during braking following high friction in the initial braking stage. The initial high friction is attributed to the deformation resistance of the resin in the composite. Low friction is attributed to the lubricating action of resin decomposition products in the neighbourhood of the filler raised to a high temperature by frictional heating. Increase of friction toward the end of braking is mainly due to increase of the true contact area as the frictional speed decreases. Variation of the average frictional coefficient during braking with load and the initial speed is generally small. There is no correlation between the mechanical properties and the brake frictional behaviour of resin-based composites.     

车辆动力学稳定性系统变结构滑模控制研究

探讨了转弯车辆行驶在极限运动工况下时，依靠施加各车轮不同纵向制动力从而产生辅助横摆力矩来提高车辆动力学稳定性的基本原理，推导了两自由度车辆横向动力学方程，提出了车辆侧滑速度的3种实时估计方案（积分法，代数法和Luenberger观察器法），视实际车辆前后轮胎侧偏刚度为有界不确定性参数，为跟踪线性两自由度理想车辆模型的稳态输出响应，设计了车辆动力学稳定性变结构控制策略，通过仿真验证了该方案可行性。     

汽车风冷盘式制动器摩擦学特性试验研究

为得出制动参数对汽车风冷盘式制动器摩擦学特性的影响机理,考虑空气流动和车辆惯性因素,基于噪声、振动与声振粗糙度（NVH,Noise Vibration and Harshness）台架试验机精确模拟制动工况,研究摩擦副表面在不同制动压力（1.0~3.0 MPa）、行驶速度（5~30 m/s）以及温度（100~350  ℃）条件下平均摩擦系数与摩擦稳定系数的变化规律。试验结果表明：制动压力增大时,摩擦力矩并非一定随之增大,尤其是较高行驶速度条件;当制动盘表面温度超过300 ℃时,低速条件下的平均摩擦系数和摩擦稳定系数急剧减小。     

Study of the Falling Friction Effect on Rolling Contact Parameters

The existence of a wheel–rail friction coefficient that depends on the slip velocity has been associated in the literature with important railway problems like the curving squeal and certain corrugation problems in rails. Rolling contact models that take into account this effect were carried out through the so-called Exact Theories adopting an exact elastic model of the solids in contact, and Simplified Theories which assume simplified elastic models such as Winkler. The former ones, based on Kalker’s Variational Theory, give rise to numerical problems; the latter ones need to adopt hypotheses that significantly deviate from actual conditions, leading to unrealistic solutions of the contact problem. In this paper, a methodology based on Kalker’s Variational Theory is presented, in which a local slip velocity-dependent friction law is considered. A formulation to get steady-state conditions of rolling contact by means of regularisation of the Coulomb’s law is proposed. The model allows establishing relationships in order to estimate the global properties (creepage velocities vs. total longitudinal forces) through local properties (local slip velocity vs. coefficient of friction) or vice versa. The proposed model shows a good agreement with experimental tests while solving the numerical problems previously mentioned.