文献翻译-多轴车辆的转向特性

Turning characteristics of multi-axle vehiclesAbstract：This paper presents a mathematical model for multi-axle vehicles operating on level ground. Considering possible factors related to turning motion such as vehicle configuration and tire slip velocities, equations of motion were constructed to predict steer ability and driving decency of such vehicles. Turning radius, slip angle at the mass center, and each wheel velocity were obtained by numerically solving the equations with steering angles and average wheel velocity as numerical inputs. To elucidate the turning characteristics faulty-axle vehicles, the eject of fundamental parameters such as vehicle speed, steering angles and type of driving system were examined for a sample of multi-axle vehicles. Additionally, field tests using full-scale vehicles were carried out to evaluate the basic turning char-ataractics on level ground. Keywords: Multi-axle vehicles; Turning maneuverability; Mathematical model1. IntroductionTrack laying running gear has been mainly used in the fields of military and construction for heavy vehicle applications. Recently, running gear with pneumatic tires has been expanding to heavy vehicles in such fields, since tire equipped vehicles excel in speed, silence and energy e?-cogency. Several papers have been published on the subject of tractability and maneuverability of multi-axle vehicles 1,2. A theoretical study to evaluate the turning motion of skid steering vehicles was also developed by Renoir and Cravat 3. More recent army vehicles, such as theMODIX, are designed to be equipped with independent wheel drive and steering, and load control suspensions 4. The MODIX can turn by normal steering, skid steering, or a mixture of both. Additionally, the conversion from mechanical drive to an electric drive unit controlled by each in-hub motor has been examined 57. A hybrid wheel steer system is being developed to complement the independent drive capability of the in-hub wheel motors. However, there has not been a paper or technical publication dealing with the subject comprehensively and in a logical sequence because the phenomenon of dynamic motions of the multi-axle vehicle is complex. This paper describes a computer simulation model to predict turning characteristics of multi-axle vehicles. The equations of motion for the vehicles are constructed for level ground. Tractate and side forces acting under pneumatic tires due to interaction with the ground are of fundamental importance to predict the motion of vehicles. In the numerical simulation, the brush model based on a physical approach was adopted for the tire model 8. The brush model is an idealized representation of tires in the region of contact. In order to determine the turning motion of multi-axle vehicles, the ejects of fundamental parameters such as vehicle speed, steering angles and type of driving system are examined by using specification of an example vehicle. Field tests on multi-axle vehicles were also conducted and compared to the predicted results with the data numerically obtained by the model. The results demonstrated that the proposed mathematical model could accurately assess the turning characteristics of multi-axle vehicles.2. Mathematical model of multi-axle vehicles2.1. Coordinate system and kinematics of the vehicleFig. 1 shows coordinate systems used to describe a multi-axle vehicle with velocity vector V and yaw angular velocity h at the mass center. The coordinate system (X1, X2) is fixed on the level ground with unit base vectors E1, E2. A moving coordinate system (x1, x2) is attached to the vehicle, whose origin is located at the mass center, with unit base vectors e1, e2. 2.2. Equations of motionNewtons second law applied to the vehicle yields:where m and I are the mass and the moment of inertia for the vehicle, respectively. The frictional force Q is defined under the itch wheel, and xi denotes the position vector of the itch wheel. In a steady state turn, the equilibrium equations for the vehicle are obtained by setting V and zero.2.3. Tire slip and frictional forcesModeling of shear force generation for pneumatic tires has been reviewed by Pacifica and Sharp 8 who covers physical and empirical models. The brush model, an analytical model physically derived, has been widely used for vehicle dynamics studies. The relation between deformations of tire treads and shear forces, i.e., side force and tractate force, is simplified and the model idealizes the representation of tires in the region of contact. The horizontal shear forces acting under the tire due to interaction with the ground are assumed to be linearly dependent on the tread displacement from the tread base.In this paper, the brush model has been adopted to the vehicle model. A schematic slip motion of a tire with slip angle is shown in Fig. 2. The slip velocity vector ViS is defined by the relative velocity of tread surface and the ground as follows:Where Vi and ViR denote the traveling velocity vector and the peripheral speed vector, respectively, of the itch wheel. A non-dimensional slip ratio S is defined by the ratio of the norm of slip velocity with the magnitude of the peripheral velocity:Frictional force yields at the limit of the adhesion and the coincident of yielding friction is expressed as a function of slip ratio as follows:where K is a positive constant dependent on the staidness of the tire, and l0 is the maximum coincident of friction. The limit of slip ratio Sm represents the full sliding state of the tire throughout the tread, expressed by Sm =1/K.Fig. 4 shows the lateral force versus the longitudinal force (braking or traction force) plotted at given values of slip angles (rod) for a tire with the property of K= 5.0.As the driving power from the engine is transmitted to the wheel through the deferential, the driving force and the rotational speed of each wheel are influenced by power train types. The general type of driving system for multivalve vehicles is illustrated in Fig. 5. Deferential are mounted in each axle to distribute equal tractate force to both side wheels and the rotational speeds of the wheels depend on the path length of the tires. The property of differential is mathematically expressed as constraint equations:where Qli is the tractate force or the longitudinal shear force on the ith tire, and VR0 is the average peripheral velocity of the tires.3. Experimental evaluationField tests were conducted by using two full-scale vehicles. The low speed turning performance of the vehicles was evaluated on a concrete test ground and on sandy ground. One vehicle was an eight-wheel-vehicle with front-four-wheel-steering, which is identified by vehicle A. The other was a TADANO ALL TERRAIN VEHICLE or vehicle B, which is an eight-wheel-vehicle with all-wheel-steering shown in Fig. 6. The maximum coincident of friction l0 depends on the ground condition. The coercions were measured in the field and l0 =0.6 was obtained with vehicle B on the concrete ground and l0 = 0.8 with vehicle A on the sandy ground. In the field tests, two steering types were examined. One was steering by the front four wheels, and the other by all the wheels.Fig. 7 shows the experimental and predicted results of the turning radius versus steering angles. The parameter indicates the average steering angle of the front wheels and, for all-wheel steering; the angles of the rear four wheels are fixed at a maximum in its steering capability. It is clear that the turning radii of the vehicles A and B decrease as the steering angles increase. The lower line for vehicle B indicates the results of all-wheel steering with rear steering angles, 3=13.7, =23.0, =14.3, =25.0. From Fig. 7 it can be seen that the turning 478radius has been substantially decreased by making use of all the wheels for steering.4. Numerical simulation and results4.1. Vehicle response in four wheel steeringIn order to evaluate the turning characteristics of multivalve vehicles, the numerical simulation was carried out using the specifications of a full-scale vehicle. The mass is m =24,500 kg and the mass center is located at the geometric center. The determination of steering angle of each wheel is shown in Fig. 8 for the case of the first and second axle wheels being steered (4WS: four-wheel steering). Each wheel steering angle d can be obtained geometrically such that all wheels have a steering center C on the middle line between the third and the fourth axles, in a similar way to the Ackerman angle determination. In this simulation, it is assumed that there is an imaginary wheel in the middle of the two wheels on the first axle and the angle of the imaginary wheel d is used to represent the average angle of the front wheels. Fig. 9 shows the steering angles versus time used in the simulations. The vehicle model starts at the origin and accelerates in two seconds up to wheel velocity VR0 = 1.4m/s, (in Figs.9 and 10 the time axis begins at this point) then after 0.5s of straight motion, the vehicle begins steering up to the maximum steering angle =10.Additionally, the lateral force on the third axle is much larger than the forces on the first and second axles. It was found from the numerical results that the sideslip angle of the third axle tires is large and opposite in direction compared to the other tires. 4.2. Effect of rear wheel steering on turning characteristicsThe turning radius of vehicles at low speed is expected to decrease if the rear wheels are steered with opposite angles to the front wheels. Fig. 13 shows the steering radius when the tires on the third and fourth axles are inversely steered to the front wheels. The average steering angle of the rear wheels is defined as the angle of an imaginary wheel in the middle of the wheels on rthe fourth axle as shown in Fig. 13.The change in turning radius versus rear steering angles at l =1.0m is illustrated in Fig. 14 rfor the front steering angles, d =10,20 and 30. It is clear that the turning radius decreases considerably as the rear steering angle increases. In the design of multi-axle vehicles the steer centers of the front wheels do not generally coincide with the center of the rear wheels, as seen previously.作者：K. Watanabe，J. Yamakawa , M. Tanaka, T. Sasaki国籍：American出处：The National Defense Academy, 1-10-20 Hashirimizu, Yokosuka 239-8686, JapanAvailable online 29 March 2006多轴车辆的转向特性摘要： 本文为平地上操作多轴车辆的数学模型，考虑有关的可能因素构建转向车辆配置和轮胎滑移速度，如运动预测的可操作性和这些车辆的驾驶效率。车轮中心转弯半径，滑移角被包含其中，通过车轮角的方程式解决，说明了转折点特征多轴车辆，效果的基本参数，如车速，转向角度和行驶系统类型，多轴车辆的样本。此外，实地测试，使用大型车辆进行了评估水平地面上的基本转折点特征关键词：多轴车辆，可操作性，数学模型1 引言主要运用于军事履带运行车辆和建筑领域的重型车辆，由于轮胎车辆配备擅长在速度，低噪音和高能源效率。最近运行与充气轮胎的齿轮的规模不断扩大至重型车辆的这些领域。已有多份发表的文件关于多轴车辆的通过性和可操作性，Renou 和 Chavan 还进行了一个关于防滑方向盘汽车的评估，更近的军队车辆，如 MODIX，被设计为具有独立配备四轮驱动和转向和负荷控制悬浮,MODIX 能够由正常的车轮，滑移车轮或是两者的混合转动，此外，转换从机械传动电动驱动装置控制每个轮毂电机已审查。混合四轮转向系统正在开发，以补充独立的毂轮马达驱动器的能力。然而，有没有得到全面处理这个问题的论文或技术出版物，并在日志逻辑顺序，因为动态运动的多轴车辆是复杂的现象。本文介绍了一种计算机模拟模型来预测多轴车辆的转向特点，汽车运动的微方程构造为平地，牵引力和侧力的作用下充气轮胎由于与地面交互的基本精神的重要性，来预测车辆的议案，在数值模拟，基于物理的方法刷模型通过轮胎模型，在接触区域里刷模型是理想化的代表轮胎。为了确定多轴转动车辆的运动，如基本参数的影响车辆行驶速度，转向角度和驾驶系统类型检查的一个例子，多轴车辆的实地测试也进行与数字数据的预测结果相比得到的模型。结果表明，提出了数学模型，可以准确地评估多轴车辆的转向特性2 多轴车辆的数学模型2.1 坐标系统和车辆的运动学图 1 所示的坐标系统，用来形容多轴车辆的速度矢量 V 和偏航角速度重心Q。坐标系统（X1，X2）的水平地面上的固定单位基向量E1，E2，连接到一个移动的坐标系统（X1，X2）的车辆，其原产地是在质量中心位于单位基向量E1，E2，车辆 n 个轮子一方独立悬挂弹簧和具有相同属性的支持车身。2.2 运动方程式牛顿第二定律应用于汽车产量：niiQmV21（ ）niiixeI213)(213e其中 m 和