Design of manned lunar rover wheels and improvement in soil mechanics formulas for elastic wheels in consideration of deformation

Most of the current lunar rover vehicle wheels are inconvenient for changing broken wheels and have poor shock absorbing in driving, so they cannot be used to carry people on the moon. To meet the demands for manned lunar transportation, a new wheel possessing a woven metal wire mesh tire and using hub-rim combination slide mechanism is designed in this article. The characteristics of the new wheel is analyzed by comparing with the same-size conventional rover wheels after demonstrating the validity of FEM simulation. The new wheel possesses lighter structure and superior shock absorbing. It also provides stronger traction because the deformation of the designed wheel increases the contact area between the tire and lunar terrain. In order to establish an on-line soil parameter estimation algorithm for low cohesion soil, the stress distribution along a driven deformable wheel on off-road terrain is simplified. The basic mechanics equations of the interaction between the wheel and the lunar soil can be used for analytical analysis. Simulation results show that the soil estimation algorithm can accurately and efficiently identify key soil parameters for loose sand.     

Some further studies on the mechanical properties of muskeg in relation to vehicle mobility

An experimental study of the mechanical properties of two types of muskeg was carried out. The results have further verified the basic features of a mathematical model for the pressure-sinkage characteristics of muskeg proposed previously. The procedure for deriving the value of the stiffness of the underlying peat from load-sinkage tests has been validated. The response of the muskeg to repetitive loading was measured. It has been found that these muskeg types exhibit noticeable elastic rebound and hysteresis during the unloading-reloading cycle. The average slope of the unloading and reloading line appears to increase with the load level at which the unloading-reloading cycle begins. The experimental results further confirm that from thw vehicle mobility as well as environmental protection standpoints, the tearing-off of the muskeg surface mat by vehicle running gear is to be avoided. When the mat is torn, the vehicle running gear will be in contact with the underlying peat which has lower bearing capacity and shear strength. This results in higher sinkage and lower traction.     

Analysis of the vibration-excitation effect caused by deformable soil surfaces

Terrain roughness induces vibrations in the chassis of vehicles moving cross-country. These vibrations affect the comfort of the occupants detrimentally and, when a certain rough ride condition is exceeded, the vehicle can no longer be controlled by the driver. This study deals with the relationship between terrain roughness and the vehicle traveling over it. In the case of deforming soil, the so called original soil profile is altered significantly by the vehicle. This study determines the original as well as the modified profiles, the latter being caused by the vehicle traveling over the former. The vehicle's transfer function is used to compute the effective profile, which generates the actual vibrations of the vehicle. These investigations are presented for several soil types and for a number of vehicles whose mass and running gear design are known.     

化学跑合剂对跑合效果的影响

在ＢＪ５２Ａ胶合试验机、ＪＰ－ＢＤ１５００型接触疲劳试验机和ＣＬ－１００齿轮试验机上考察了化学跑合剂的作用，并就其机理进行了探讨。结果表明：采用化学跑合剂跑合后，表面粗糙度明显降低；表面接触面积增大，可以实现１次满载快速跑合；与采用含磨料的跑合方法比较，化学跑合剂可以明显提高表面接触精度，减少裂纹源的发生和发展，使表面承载能力明显提高。当齿轮加工精度较低或高速、重载齿轮的硬齿面精加工存在困难时，可     

Comparison of the traffic performance of a two-axle four wheel drive (4WD), rear wheel drive (RWD), and front wheel drive (FWD) vehicle on loose sandy sloped terrain

The traffic performances during driving and braking of a 5.88 kN weight wheeled vehicle with two-axle four wheel drive, rear wheel drive, and front wheel drive running up and down a loose sandy sloped terrain were compared by means of a simulation. For the given dimensions of the vehicle and the given terrain-wheel system constants, the relationship between the effective tractive and braking effort of the vehicle, the amount of sinkage of the front and rear wheels, the total amount of sinkage of the vehicle, and the slip ratio were calculated to estimate the optimum height of force of application and the optimum eccentricity of the center of gravity of the vehicle. It was observed that, during driving action, the maximum effective tractive effort of the four wheel drive vehicle (4WD) was larger than that of the rear wheel drive vehicle (RWD), which in turn was greater than that of the front wheel drive vehicle (FWD). During the braking action, the effective braking effort at skid -20% of the four wheel vehicle (4WB) was larger than that of the front wheel brake vehicle (FWB), in turn greater than that of the rear wheel brake vehicle (RWB), when the two-axle four wheel vehicle is moving up or down the loose sandy sloped terrain. The maximum terrain slope angle up which the two-axle wheeled vehicle is able to move during driving action was found to be about 0.067π rad for the 4WD vehicle, about 0.031π rad for the RWD vehicle, and about 0.017π rad for the FWD vehicle. The effective braking effort at skid-20% of 4WB, FWB and RWB was found to decrease with slope angle.     

Active bogies and chassis levelling for a vehicle operating in rough terrain

Four axle vehicles with bogies can adapt the position of the wheels to follow irregularities in the terrain, having an obstacle surpassing ability far greater than conventional 2-axle vehicles. Still, the ability to overcome discrete obstacles on a steep slope is very different depending on the wheel that is facing the obstacle. A possible solution to diminish this variation can be found if the vehicle is able to actively redistribute the load on each wheel. One strategy is to design the suspension mechanism so it can regulate its height, being able to level the chassis. Also, an active torque on the pin join between the bogie and the chassis can be applied with the same goal, adopting a system of active bogies. Both solutions have been parametrically studied in a bi-dimensional multibody model of a 4-axle vehicle with double bogies. The results show an improvement independent of obstacle position and terrain angle when using active bogies. With height regulation, this improvement is limited to the rear bogie wheels, but the obstacle surmounting capacity of the vehicle as a whole can be considerably increased if the optimal regulation point is found. Possible applications for such enhanced vehicles with bogies are performing different tasks in forest areas with obstacles on steep slopes or unstructured terrain exploration.     

Integration of uniform design and quantum-behaved particle swarm optimization to the robust design for a railway vehicle suspension system under different wheel conicities and wheel rolling radii

This paper proposes a systematic method, inte-grating the uniform design(UD)of experiments and quantum-behaved particle swarm optimization(QPSO),to solve the problem of a robust design for a railway vehicle suspension system. Based on the new nonlinear creep model derived from combining Hertz contact theory, Kalker's linear the-ory and a heuristic nonlinear creep model,the modeling and dynamic analysis of a 24 degree-of-freedom railway vehi-cle system were investigated.The Lyapunov indirect method was used to examine the effects of suspension parameters, wheel conicities and wheel rolling radii on critical hunting speeds.Generally,the critical hunting speeds of a vehicle sys-tem resulting from worn wheels with different wheel rolling radii are lower than those of a vehicle system having origi-nal wheels without different wheel rolling radii.Because of worn wheels, the critical hunting speed of a running rail-way vehicle substantially declines over the long term. For safety reasons,it is necessary to design the suspension sys-tem parameters to increase the robustness of the system and decrease the sensitive of wheel noises.By applying UD and QPSO,the nominal-the-best signal-to-noise ratio of the sys-tem was increased from?48.17 to?34.05 dB.The rate of improvement was 29.31%.This study has demonstrated that the integration of UD and QPSO can successfully reveal the optimal solution of suspension parameters for solving the robust design problem of a railway vehicle suspension sys-tem.     

Prediction of ground pressure distribution under tracked vehicles—II. Effects of design parameters of the track-suspension system on ground pressure distribution

The effects of vehicle design parameters on ground pressure distribution and track tension are evaluated quantitatively using the analytical method described in Part I of this paper. The ground pressure distribution of a vehicle is closely related to vehicle sinkage and external motion resistance, while the track tension affects the internal resistance of the track-suspension system. It is found that the number of road wheels on the track has a significant effect on both ground pressure distribution and track tension. On the other hand, the diameter of the road wheels has only a moderate influence on track tension and a rather insignificant effect on ground pressure distribution. The stiffnesses of the suspension and the track tensioning springs have varying degrees of influence on ground pressure distribution and track tension dependent upon terrain stiffness. It is also found that the initial track tension has a significant effect on the actual track tension over a wide range of terrain and a slight to moderate influence on ground pressure distribution, dependent upon terrain stiffness.It should be noted that although individually some of the design parameters have only a slight or moderate effect on ground pressure distribution and track tension, their combined effects may be significant. Therefore, in the selection of design parameters of the track-suspension system, their combined influence must be carefully examined.     

车轮多边形激励下高速列车制动界面摩擦学行为分析

高速列车车轮多边形磨耗是一种沿车轮周向的不均匀磨耗,是列车服役过程中常见的车轮失效现象,其产生的剧烈轮轨激励严重威胁车辆系统服役可靠性. 制动系统作为保障高速列车服役安全的核心部件,其界面摩擦学行为直接受到轮轨激励的影响. 为探究车轮多边形激励下的制动界面摩擦学行为,建立了刚柔耦合车辆动力学模型和制动系统热机耦合有限元模型,并分别通过线路试验和台架试验验证了模型的正确性. 然后,提出一种考虑车轮多边形激励的制动界面摩擦学行为分析方法,能够真实地反映服役过程中制动界面摩擦学行为. 基于此,研究了不同车辆运行速度下车轮多边形激励对制动系统动态接触、温度以及振动特性的影响规律. 结果表明:车轮多边形磨耗导致系统接触面积、摩擦热、接触应力和振动等摩擦学行为更为复杂且剧烈. 此外,系统接触面积标准差和振动加速度均方根值随速度的增加而增大. 因此,车轮多边形磨耗对制动界面摩擦学行为具有不可忽略的影响. 该研究成果可为制动系统界面摩擦学行为研究及结构优化设计提供有效方法与工程指导.      

Prévision de la répartition de la pression sous des véhicules à chenilles Ilème partie - effects des paramètres de conception du système de suspension des chenilles sur la répartition de la pression sur le sol

The effects of vehicle design parameters on ground pressure distribution and track tension are evaluated quantitatively using the analytical method described in Part I of this paper. The ground pressure distribution of a vehicle is closely related to vehicle sinkage and external motion resistance, while the track tension affects the internal resistance of the track-suspension system. It is found that the number of road wheels on the track has a significant effect on both ground pressure distribution and track tension. On the other hand, the diameter of the road wheels has only a moderate influence on track tension and a rather insignificant effect on ground pressure distribution. The stiffnesses of the suspension and the track tensioning springs have varying degrees of influence on ground pressure distribution and track tension dependent upon terrain stiffness. It is also found that the initial track tension has a significant effect on the actual track tension over a wide range of terrain and a slight to moderate influence on ground pressure distribution, dependent upon terrain stiffness.It should be noted that although individually some of the design parameters have only a slight or moderate effect on ground pressure distribution and track tension, their combined effects may be significant. Therefore, in the selection of design parameters of the track-suspension system, their combined influence must be carefully examined.     

Comparison of different bogie configurations for a vehicle operating in rough terrain

Conventional wheeled vehicles have serious mobility limitations in rough terrain while walking vehicles have inherent drawbacks such as a high number of DOF and actuators, control complexity and low energy efficiency. Vehicles that passively fit the position of multiple wheels to maintain contact with the ground can be a good solution to this problem. The present work aims to comparatively quantify the ability of overcoming obstacles that is achieved by using different configurations of vehicles with bogies. Different configurations of vehicles facing obstacles when climbing along ramps of different longitudinal slope have been modeled. Further analyses have been done in order to investigate the influence of the position of the center of gravity and obstacle traversing speed. Different asymmetrical bogie configurations have also been proposed to further improve the obstacle surmounting capacity of the 4-axle vehicle. The results show a clear improvement in the ability to overcome obstacles when using bogies. Compromise solutions can be found for the obstacle traversing speed and position of the center of gravity. Asymmetrical bogie geometry can provide an improvement in the obstacle surmounting ability, although vehicle application has to be taken into account to find the best solution.     

The optimum height of application of force and eccentricity of a wheeled vehicle running on a loose sandy soil

In earthmoving sites, multi-wheeled vehicles are used to excavate a sandy soil or to pull other construction machinery. In this paper, the mechanism of a 5.88 kN weight, two-axle, four-wheel vehicle running on a loose sandy soil is theoretically analysed. For given terrain-wheel system constants, the combination of the effective braking force of the front wheel during pure rolling state and the effective driving force of the rear wheel during driving action will clarify the relation between effective effort of the vehicle and slip ratio and the relation between amounts of sinkage the front and rear wheels and slip ratio, etc. The maximum effective tractive effort of the vehicle varies with the height of application force and the position of the center of gravity of the vehicle. The optimum height of application of force and the eccentricity of the center of gravity to obtain the largest value of the maximum effective tractive effort can be explained with an analytical simulation program. Results of this study showed that the optimum height of application force should be 30 cm and the optimum eccentricity of the center of gravity is 0.05 for a vehicle considered for this study.     

车辆纵向非光滑多体动力学建模与数值算法研究

在建立车辆纵向多体系统的动力学模型中, 将车身与车轮视为刚体, 两者通过减振器链接; 将传动系统视为一个圆盘通过扭簧和阻尼器与驱动轮连接; 将车轮与路面间的接触力简化为法向约束力、摩擦力和滚阻力偶,其中摩擦力的模型采用库仑干摩擦模型. 采用笛卡尔坐标作为该系统的广义坐标用于描述该系统的位形, 给出系统单双边的约束方程, 应用第一类拉格朗日方法建立了系统的动力学方程. 由于摩擦与滚阻的非光滑性, 使得该系统动力学方程不连续. 为便于计算, 建立了车轮与路面接触点的相对切向加速度与摩擦力余量的互补条件、车轮角加速度与滚阻力偶余量的互补条件, 以及车轮轮心法向加速度与路面法向约束力的互补条件. 将接触—分离、黏滞—滑移的判断问题转化成线性互补问题的求解, 并给出了具有约束稳定化的基于事件驱动法的数值计算方法. 最后, 应用该方法对车辆纵向多体系统进行了仿真, 分析了输出扭矩、摩擦及滚阻系数对其动力学行为的影响.      

Modeling and Simulation of a Three-Wheeled Mobile Robot on Uneven Terrains with Two-Degree-of-Freedom Suspension Mechanisms

A wheeled mobile robot (WMR) will move on an uneven terrain without slip if its torus-shaped wheels tilt in a lateral direction. An independent two degree-of-freedom (DOF) suspension is required to maintain contact with uneven terrain and for lateral tilting. This article deals with the modeling and simulation of a three-wheeled mobile robot with torus-shaped wheels and four novel two-DOF suspension mechanism concepts. Simulations are performed on an uneven terrain for three representative paths—a straight line, a circular, and an ‘S’-shaped path. Simulations show that a novel concept using double four-bar mechanism performs better than the other three concepts.     

Interaction of subway LIM vehicle with ballasted track in polygonal wheel wear development

This paper develops a coupled dynamics model for a linear induction motor (LIM) vehicle and a subway track to investigate the influence of polygonal wheels of the vehicle on the dynamic behavior of the system. In the model, the vehicle is modeled as a multi-body system with 35 degrees of freedom. A Timoshenko beam is used to model the rails which are discretely supported by sleepers. The sleepers are modeled as rigid bodies with their vertical, lateral, and rolling motions being considered. In order to simulate the vehicle running along the track, a moving sleeper support model is introduced to simulate the excitation by the discrete sleeper supporters, in which the sleepers are assumed to move backward at a constant speed that is the same as the train speed. The Hertzian contact theory and the Shen- Hedrick-Elkins’ model are utilized to deal with the normal dynamic forces and the tangential forces between wheels and rails, respectively. In order to better characterize the linear metro system (LMS), Euler beam theory based on modal superposition method is used to model LIM and RP. The vertical electric magnetic force and the lateral restoring force between the LIM and RP are also taken into consideration. The former has gap-varying nonlinear characteristics, whilst the latter is considered as a constant restoring force of 1 kN. The numerical analysis considers the effect of the excitation due to polygonal wheels on the dynamic behavior of the system at different wear stages, in which the used data regarding the polygonal wear on the wheel tread are directly measured at the subway site.     

Design and characterization of GRC-1: A soil for lunar terramechanics testing in Earth-ambient conditions

Earth experiments must be carried out on terrain that deforms similarly to the lunar terrain to assess the tractive performances of lunar vehicles. Most notably, terrain compaction and shear response underneath the lunar vehicle wheels must represent that of the Moon. This paper discusses the development of a new lunar soil simulant, Glenn Research Center lunar soil simulant #1 (GRC-1), which meets this need. A semi-empirical design approach was followed in which the soil was created by mixing readily available manufactured sands to a particle size distribution similar to the coarse fraction of lunar soil. By varying terrain density, a broad range of in situ cone penetration measurements collected by the Apollo mission astronauts can be replicated. An extensive set of characterization data is provided in this article to facilitate the use of this material. For reference, the index and geotechnical properties of GRC-1 are compared to the lunar soil and existing lunar soil simulants.     

A spatial motion analysis model of tracked vehicles with torsion bar type suspension

A spatial motion analysis model for high-mobility tracked vehicles was constructed for evaluation of ride performance, steerability, and stability on rough terrain. Ordinary high-mobility tracked vehicles are equipped with independent torsion bar type suspension system, which consists of road arms and road wheels. The road arm rotates about the axis of torsion bar, and rigidity of the torsion bar and cohesion of damper absorb sudden force change exerted by interaction with the ground. The motion of the road arms should be considered for the evaluation of off-road vehicle performance in numerical analysis model. In order to obtain equations of motion for the tracked vehicles, the equations of motion for the vehicle body and for the assembly of a road wheel and a road arm were constructed separately at first. Two sets of equations were reduced with the constraint equations, which the road arms are mechanically connected to the vehicle body. The equations of motion for the vehicle have been expressed with minimal set of variables of the same number as the degrees of freedom for the vehicle motion. We also included the effect of track tension in the equations without constructing equations of motion for the tracks. Numerical simulation based on the vehicle model and experiment of a scale model passing over a trapezoidal speed bump were performed in order to examine the numerical model. It was found that the numerical results reasonably predict the vehicle motion.     

Interaction of railway vehicles with track in cross-winds

This paper presents a framework for simulating railway vehicle and track interaction in cross-wind. Each 4-axle vehicle in a train is modeled by a 27-degree-of-freedom dynamic system. Two parallel rails of a track are modeled as two continuous beams supported by a discrete-elastic foundation of three layers with sleepers and ballasts included. The vehicle subsystem and the track subsystem are coupled through contacts between wheels and rails based on contact theory. Vertical and lateral rail irregularities simulated using an inverse Fourier transform are also taken into consideration. The simulation of steady and unsteady aerodynamic forces on a moving railway vehicle in cross-wind is then discussed in the time domain. The Hilber–Hughes–Taylor α-method is employed to solve the nonlinear equations of motion of coupled vehicle and track systems in cross-wind. The proposed framework is finally applied to a railway vehicle running on a straight track substructure in cross-wind. The safety and comfort performance of the moving vehicle in cross-wind are discussed. The results demonstrate that the proposed framework and the associated computer program can be used to investigate interaction problems of railway vehicles with track in cross-wind.     

Structure design and traction trafficability analysis of multi-posture wheel-legs bionic walking wheels for sand terrain

Nowadays, the existing walking wheels still have problems with the wheel-legs structure and the traction trafficability on the loose sand. It is commonly believed that African ostrich (Struthio camelus) is a kind of bipedal species with superior running performance on the sandy environment. Being enlightened by this, four bionic walking wheels (herringbone wheel, in-line wheel, V-shaped wheel and combination wheel) were designed and tested by imitating the structure and posture of ostrich’s feet travelling on sand. The results showed that when the wheel load was 20, 30 and 50N respectively and the slip ratio was less than 35%, the herringbone wheel had better traction trafficability than that of other wheels. When the wheel load was 30, 50 and 70N and the slip ratio was more than 35%, the in-line wheel had better performance than that of other wheels. It was shown in this thesis that the bionic walking wheels designed with the multi-posture wheel-legs and the simple structure could reduce the soil resistance and the disturbance to sand, thereby achieving a superior performance of traveling on sand. In addition, a new idea and research method for designing of walking mechanism on soft terrain has been provided in this thesis.