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.     

Control of a cable-towed vehicle to minimize slip

Cable-towed vehicles have the potential to reduce the costs of harvesting timber on steep or wet terrain. In many situations, these vehicles would perform best when both the wheels and cable winch are powered. This paper describes a control algorithm which minimizes wheel slip by optimizing the partitioning of power between the winch and tractive drives. Results of tests with an experimental vehicle showed that the algorithm was capable of providing nearly zero average wheel slip.     

基于数据驱动的全线控底盘纵臂式悬架系统研究

汽车在越野类极限路况下行驶,对车身高度有一定范围的调节需求,传统悬架方案与全线控底盘进行技术融合时,存在机构运动干涉、底盘升降过程中车轮外倾程度过大、车轮发生侧向位移等现象,易导致轮胎过度磨损,致使行驶失稳.将车身高度变化对轮胎侧向参数的影响转化为车轮纵向滚动,进而实现稳定的大行程车身高度调节,是解决上述问题的关键.本研究建立整车七自由度动力学模型,对悬架系统导向机构展开力学分析,集两者作为系统研究的输入信息;通过正弦波激振台对弹性元件、减振器进行相关特性参数获取,基于数据驱动开展一体化电动轮的运动学仿真测试,包括对悬架系统关键铰接位置进行力学性能分析、对电动轮整体结构进行运动学特性研究,以此定义系统关键性能指标,结合理论研究与仿真测试,确定双纵臂式主动悬架系统方案.仿真结果与实车验证综合表明,搭载本研究系统方案的全线控平台,进行大行程高度调节过程中,车轮外倾问题得到有效解决,一体化电动轮具备良好的独立运行能力,本研究对提高车辆在极限路况下的通过性具有重要意义.     

A method for predicting the internal motion resistance of rubber-tracked undercarriages,Pt. 2. A research on the motion resistance of road wheels

In spite of an increasing number of rubber-tracked crawlers, the literature provides few guidelines and calculation models suitable for minimizing their internal motion resistance. This article presents a model where the internal resistance of double-flanged road wheels for rubber-tracked vehicles is calculated as a sum of the losses resulting from the indentation of the wheels into the track surface and friction of the wheels against the track guide lugs. The model allows for vertical and lateral load of the wheels, the non-uniform distribution of the wheel pressure on the track, and the relationship between the friction coefficient and normal reaction force in the interface between the wheel and track guide lugs. The model has been verified by experiments. According to the results of model computations and experiments discussed in the article, the internal losses of a given rubber-tracked undercarriage might be reduced if: the road wheels are covered with a material that exhibits low friction coefficient and mechanical hysteresis, the vehicle suspension system features oscillating bogie wheels, the undercarriage is fitted with the largest possible number of road wheels, and the vehicle weight is evenly distributed to all of the road wheels.     

Effect of snow cover on obstacle performance of vehicles

Trafficability of terrain is a function of soft soil, hard or rough ground, geometric obstacles, vegetation, and the riverine environment. All of these terrain aspects are altered by cold temperatures and snow cover. This paper examines the effect of snow cover on obstacle crossing performance of vehicles. The mathematical expressions describing step negotiation, trench crossing, and slope climbing on snow-covered obstacles are given in terms of tracked vehicle, obstacle, and snow parameters.Tests of two tracked vehicles on snow-covered slopes, stream crossings, steps, and trenches were conducted, and some of the results were compared with computed values. Differences between computed and experimental values are attributed to neglecting slip-sinkage and track deflection in the computations.     

Design and development of a new transformable wheel used in amphibious all-terrain vehicles (A-ATV)

Conventional ground-wheeled vehicles usually have poor trafficability, low efficiency, a large amount of energy consumption and possible failure when driving on soft terrain. To solve this problem, this paper presents a new design of transformable wheels for use in an amphibious all-terrain vehicle. The wheel has two extreme working statuses: unfolded walking-wheel and folded rigid wheel. Furthermore, the kinematic characteristics of the transformable wheel were studied using a kinematic method. When the wheel is unfolded at walking-wheel status, the displacement, velocity and acceleration of the wheel with different slip rates were analyzed. The stress condition is studied by using a classic soil mechanics method when the transformable wheel is driven on soft terrain. The relationship among wheel traction, wheel parameters and soil deformation under the stress were obtained. The results show that both the wheel traction and trafficability can be improved by using the proposed transformable wheel. Finally, a finite element model is established based on the vehicle terramechanics, and the interaction result between the transformable wheel and elastic–plastic soil is simulated when the transformable wheel is driven at different unfold angles. The simulation results are consistent with the theoretical analysis, which verifies the applicability and effectiveness of the transformable wheel developed in this paper.     

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.     

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.     

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.     

Study of a driven and braked wheel using maximal monotone differential inclusions: applications to the nonlinear dynamics of wheeled vehicles

A wheel subjected to two friction forces, one exerted by the ground and one exerted by the brake pad, is studied. A formalism using multivalued operators allows us to write the constitutive laws of this wheel in the form of a differential inclusion, for which we have the existence and the uniqueness of the solution, as well as the convergence of the associated numerical scheme. This wheel may be connected by itself to a chassis. The chassis may also be connected to two of these wheels. In these two cases, we again obtain a well-posed differential inclusion, in terms of existence, uniqueness, and convergence of the numerical scheme. In a more general manner, numerous applications can be proposed in the domain of the nonlinear dynamics of wheeled vehicles.     

Determination the ability of military vehicles to override vegetation

Military operations usually include movement over existing roads and also through natural terrain. Wooded terrain is one of the most challenging environments which affect vehicle mobility. The ability of a vehicle to cross a forest area depends on the possibility of determining if the vehicle is able to manoeuvre between tree stems or can override individual trees. Overriding tree obstacles can be more effective if a vehicle needs a shorter time to cross some tree stems rather than manoeuvring around them. Vehicle movement to cross a forest stand depends on vegetation factors as the stem diameter, stem spacing, and also on tree root parameters, which determine the mechanical tree stability, and a vehicle’s ability to override the trees. Also, the technical parameters (width, length, turning radius, weight, traction force) of the selected military vehicle are important to classify the cross-country movement options. This study describes both the theoretical predictions of the movement of vehicles in forest stands and summarizes the results of one of the most extensive testing of vehicles’ ability to cross individual trees.     

Design and development of a variable ground clearance,variable wheel track self-leveling hillside vehicle power chassis (V2-HVPC)

This paper presents a design of hillside vehicle power chassis with the balance rocker suspension mechanism. The objective of design is to achieve a variable ground clearance, variable wheel track and self-leveling chassis adapted to the various types of crop grown ridge section and height. The V2-HVPC design consists of the main body, the balance rocker suspension, two driving axles and the steering system. Those assemblies form an H-type chassis structure where both sides of the driving axle and the main body are connected to power transmission. The ground clearance and wheel track have the adjustable function. The balance rocker suspension is a novel mechanism which ensures full-time four-wheel drive in a complex road environment while maintaining the main body level always in the angle bisector of the two driving axle. According to the hillside terrain and agronomic characteristics of various crops, the ground clearance and the wheel track can be adjusted continuously and smoothly by hydraulic system. The topology diagram and power transmission system diagram are all given correspondingly. Moreover simulation analysis and basic experiments have been carried out to verify the mobility and dynamic performance of the V2-HVPC. The results show that the concept of V2-HVPC is approved reasonable and the design and testing methods are feasible and practical.     

Development of a vehicle to study the tractive performance of integrated steering-drive systems

This paper describes a test-bed vehicle for studying the integration of the steering system of a wheeled vehicle with the drive system. The vehicle was produced in order to determine whether such an integrated system is practical; to investigate tractive performance compared to other steering-drive systems; and to determine under which conditions such a system has better performance. The integrated steering-drive system of the test-bed vehicle uses a computer to co-ordinate the independently driven wheel speeds of the drive system (which is also the primary steering system) with the steer angles of the non-driven steerable wheels to produce a beneficial secondary steering effect. The secondary steering system assists the primary steering system when side forces act on the vehicle, while producing minimal conflict. This concept can be applied to agricultural vehicles such as tractors, harvesters, mowers, sprayers and self-propelled windrowers. The test-bed vehicle is able to be configured for the following steering-drive systems types: open differential drive with steerable wheels, independent drive wheels with castors, locked differential drive with steerable wheels and a computer integrated steering-drive system. The capacity of the test-bed vehicle to be configured as described is a significant advantage when measuring tractive performance, as the results obtained will be more valid due to the vehicle parameters being the same.     

A sea ice terrain model and its application to surface vehicle trafficability

Pressure ridges are the primary obstacle to the movement of amphibious surface vehicles travelling over the Arctic ice pack. Ridge height and spacing data can now be obtained with remote sensing methods and used to construct a realistic three-dimensional ridge model for sea ice terrain. This model can be used to perform trafficability analyses. The results, when combined with vehicle characteristics, can be used to predict vehicle operational performance. There is good agreement between predictions from the model and from simulated routes through sea ice areas selected from aerial photographs.

The terrain model is also useful for mapping regional variations in ridge characteristics throughout the Arctic Basin. The paper also discusses the nature of the rugged shear zone in the offshore region, and the presence of leads caused by dilation of the ice pack in strong weather systems.     

Determining forces required to override obstacles for ground vehicles

The military is constantly expanding the use of unmanned ground vehicles in warfighting applications that often involve complex environments. Part of the focus of military research is to improve or validate existing routing algorithms which are used to predict vehicle mobility. Routing algorithms are based on the time required for vehicle movement through a series of obstacles such as trees or fences, thus requiring an assessment of the ability to override such obstacles as compared to finding an alternate maneuver path. The required overriding force can be computed and compared to a vehicle’s tractive force to determine the best viable option. If overriding the obstacle is an option (tractive force exceeds the required overriding force), the delay in overriding can be assessed as compared to the delay in maneuvering around the obstacle. This study provides a quick and reasonable calculation of the force required to override specific types of vertically embedded obstacles to support the determination of movement capabilities for unmanned ground vehicles on the battlefield.     

Rut depth, soil compaction and rolling resistance when using bogie tracks

There are few studies of rolling resistance for bogie tracks on forestry machines. The aim of this study was to compare the effects of wheels and two types of bogie tracks on rut formation, cone index, and vehicle rolling resistance on some typical forest soils in Sweden. In an experiment, two types of tracks were put on a trailer with a bogie with hydraulic extension on the pulling bar giving the trailer repeatable travelling speed. Loads of 0 and 9.9 Mg were used on the trailer. The main results of this study are: Compared to rather wide and soft tires, tracks on the bogie reduced rut depth by up to 40% and cone index in the ruts by about 10%, although the tracks increased the mass on the trailer by 10–12%. The relative rolling resistance coefficient was not higher for tracks than for wheels. Further studies should be conducted to show the effect of track tension on rolling resistance and flotation and of the effects of tracks on heavy vehicles on subsoil compaction.     

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.     

A method of torque control for independent wheel drive vehicles on rough terrain

Our previous research has revealed that, for vehicles with independently driven wheels, a torque distribution based on the ratio of the vertical load of each wheel to the total vehicle load is efficient for driving on flat ground. In this research, this method of torque distribution was extended to electric off-road vehicles driving on rough ground. In order to examine the driving efficiency of these vehicles, a numerical vehicle model was constructed in the pitch plane. Simulations using the numerical vehicle model on rough ground were conducted with a proposed torque distribution and control method. The numerical results from these simulations were compared with those of a conventional vehicle to evaluate the driving efficiency and trafficability on ground with various profiles. A comparison between the simulations demonstrated that the proposed method of torque distribution to the front and rear wheels based on the ratio of the vertical load is efficient for driving on rough ground.     

Practical method of improving the turnability of terrain vehicles

To improve the trafficability and the turnability of the terrain vehicles, it was already pointed out in a previous report that the control of the ground contact area of the running gear such as tracks and wheels could be highly recommended. The contact area of the running gear must be as large as possible to obtain more traction, however, less contact area would be better to obtain easier turning and steering. In this paper the principle of improving the turnability for the terrain vehicle was theoretically discussed. One of the examples of the practical application of the theory developed here was proposed and applied to the terrain vehicle equipped with eight powered wheels, which was constructed as a test vehicle for this study.