Overland transport without roads

The need for off-road vehicles as applied to commerce, warfare, and recreation is examined. Most of the developments in the mobility of off-road vehicles have had a primarily military background. The main impediments to off-road mobility are defined as major obstacles, soft ground, and rough ground. Optimization of track design for accommodating these impediments in military vehicles reveals the importance of the ratio of Mean Maximum Pressure to Mean Pressure of a traced vehicle. It appears that contemporary commercial cross-country vehicles contain limitations in their designs which culd be overcome with available knowledge. These limitations include soft ground mobility, and speed over rough ground.The role of hovercraft in providing off-road mobility is reviewed, and special attention is given to the most recent requirements for avoiding environmental disturbance when using off-road vehicles in the Canadian North.     

Prediction of impacts of wheeled vehicles on terrain

Traffic of off-road vehicles can disturb soil, decrease vegetation development, and increase soil erosion. Terrain impacts caused by wheeled off-road vehicles were studied in this paper. Models were developed to predict terrain impacts caused by wheeled vehicles in terms of disturbed width and impact severity. Disturbed width and impact severity are not only controlled by vehicle types and vehicle dimensions, but also influenced by soil conditions and vehicle dynamic properties (turning radius, velocity). Field tests of an eight-wheeled vehicle and a four-wheeled vehicle were conducted to test these models. Field data of terrain–vehicle interactions in different vehicle dynamic conditions were collected. Vehicle dynamic properties were derived from a global position system (GPS) based tracking system. The average prediction percentage error of the theoretical disturbed width model is less than 20%. The average absolute error between the predicted impact severity and the measured value is less than an impact severity value of 12%. These models can be used to predict terrain impacts caused by off-road wheeled vehicles.     

Improving off-road vehicle handling using an active anti-roll bar

To design a vehicle’s suspension system for a specific, well defined road type or manoeuvre is not a challenge any more. As the application profile of the vehicle becomes wider, it becomes more difficult to find spring and damper characteristics to achieve an acceptable compromise between ride comfort and handling. For vehicles that require both good on- and off-road capabilities, suspension design poses a significant challenge. Vehicles with good off-road capabilities usually suffer from poor on-road handling. These vehicles are designed with a high centre of gravity due to the increased ground clearance, soft suspension systems and large wheel travel to increase ride comfort and ensure traction on all the wheels. All of these characteristics contribute to bad handling and increased rollover propensity even on good level roads. It is expect from these vehicles to have the same handling characteristics as a normal on-road vehicle. This paper analyses the use of an active anti-roll bar as a means of improving the handling of an off-road vehicle without sacrificing ride comfort. The proposed solution is simulated, designed, manufactured, implemented and tested to quantify the effect of the active anti-roll bar on both the handling and ride comfort of an off-road vehicle.     

The ride comfort vs. handling compromise for off-road vehicles

When designing vehicle suspension systems, it is well-known that spring and damper characteristics required for good handling on a vehicle are not the same as those required for good ride comfort. Any choice of spring and damper characteristic is therefore necessarily a compromise between ride comfort and handling. The compromise is more pronounced on off-road vehicles, as they require good ride comfort over rough off-road terrain, as well as acceptable on-road handling. In this paper, the ride comfort vs. handling compromise for off-road vehicles is investigated by means of three case studies. All three case studies indicate that the spring and damper charcteristics required for ride comfort and handling lie on opposite extremes of the design space. Design criteria for a semi-active suspension system, that could significantly reduce, or even eliminate the ride comfort vs. handling compromise, are proposed. The system should be capable of switching safely and predictably between a stiff spring and high damping mode (for handling) as well as a soft spring and low damping mode (for ride comfort). A possible solution to the compromise, in the form of a four state, semi-active hydropneumatic spring-damper system, is proposed.     

A roll stability performance measure for off-road vehicles

The roll stability is significant for both road and off-road commercial vehicles, while the majority of reported studies focus on road vehicles neglecting the contributions of uneven off-road terrains. The limited studies on roll stability of off-road vehicles have assessed the stability limits using performance measures derived for road vehicles. This study proposes an alternative performance measure for assessing roll stability limits of off-road vehicles. The roll dynamics of an off-road mining vehicle operating on random rough terrains are investigated, where the two terrain-track profiles are synthesized considering coherency between them. It is shown that a measure based on steady-turning root-mean-square lateral acceleration corresponding to the sustained period of unity lateral-load-transfer-ratio prior to the absolute-rollover, could serve as a reliable measure of roll stability of the vehicle operating on random rough terrains. The robustness of proposed performance measure is demonstrated considering sprung mass center height variations and different terrain excitations. The simulation results revealed adverse effects of terrain elevation magnitude on the roll stability, while a relatively higher coherency resulted in lower terrain roll-excitation and thereby enhanced vehicle roll stability. Terrains with relatively higher waviness increased the magnitude of lower spatial frequency components, which resulted in reduced roll stability limits.     

Vehicle movement patterns and vegetative impacts during military training exercises

The operation of off-road vehicles during military training exercises can affect the environmental conditions of training lands by removing or disturbing vegetation. The use of global positioning systems (GPS)-based vehicle tracking systems can help to characterize the movement of vehicles during training exercises for the purpose of quantifying vegetative impacts. The combination of GPS positions of vehicles in the field during a training exercise, and geographic information system (GIS) maps of the training installation can provide information about vehicle-specific vegetation impacts of a training exercise, as related to vehicle locations, turning radius and velocity. Such relationships can be used to estimate off-road vegetation impacts. Twenty GPS-based vehicle tracking systems were installed on vehicles of the US Army 3rd Brigade 1/14 Cavalry to evaluate vegetation impacts during a 10 day reconnaissance training exercise at Yakima Training Center in Yakima, WA. The vehicle tracking systems were programmed to record the position of the vehicles every second. The resulting vehicle tracking data were analyzed for quantity of travel per day of the training activity, quantity of travel on and off roads, off-road vehicle dynamic properties turning radius and velocity, and off-road vegetation removed. The vehicles were in motion an average of 8.4% (approximately 2 h per day) of the training exercise time. The average distance traveled per day on roads was 33.5 km, and the average distance traveled per day off-roads was 7.7 km. On average, the vehicles spent 16% of their off-road traveling time at turning radii less than 20 m. Vegetation impacts were compared for different missions. The zone reconnaissance mission produced the highest vegetation impact per distance traveled.     

Motion resistance measurements on large lug tyres

Motion resistance of tyres directly contribute to the operational costs of all vehicles. Advances in the design and simulation of large off-road vehicles (construction, mining, agriculture etc.) have increased the need for accurate models of large off-road tyres. Vehicle OEMs use coast down and drawbar pull tests to determine the motion resistance of tyres used. Drum test rigs and motion resistance test trailers can also be used to determine motion resistance. Most research on motion resistance to date have been conducted on passenger car tyres with on-road truck tyres coming into focus. Motion resistance studies on agricultural tyres traversing over deformable terrain have been conducted in the past. However as more off-road vehicle are being used on-road OEMs of off-road vehicle are infesting in motion resistance measurements on non-deformable terrain. This paper compares different methods used to measure the motion resistance of a large lug tyre, as used in agricultural applications, on non-deformable terrain. Some basic considerations that need to be taken into account are the very low longitudinal forces that need to be measured compared to the large vertical load carried by the tyre and tyre operating conditions.     

A comparison of ground vehicle mobility analysis based on soil moisture time series datasets from WindSat,LIS, and in situ sensors

Soil moisture is a key terrain variable in ground vehicle off-road mobility. Historically, models of the land water balance have been used to estimate soil moisture. Recently, satellites have provided another source of soil moisture estimates that can be used to estimate soil-limited vehicle mobility. In this study, we compared the off-road vehicle mobility estimates based on three soil moisture sources: WindSat (a satellite source), LIS (a computer model source), and in situ ground sensors (to represent ground truth). Mobility of six vehicles, each with different ranges of sensitivity to soil moisture, was examined in three test sites. The results demonstrated that the effect of the soil moisture error on mobility predictions is complex and may produce very significant errors in off-road mobility analysis for certain combinations of vehicles, seasons, and climates. This is because soil moisture biases vary in both direction and magnitude with season and location. Furthermore, vehicles are sensitive to different ranges of soil moistures. Modeled vehicle speeds in the dry time periods were limited by the interaction between soil traction and the vehicles’ powertrain characteristics. In the wet season, differences in soil strength resulted in more significant differences in mobility predictions.     

Design and testing of lateral seat suspension for off-road vehicles

Operators of off-road vehicles such as construction, forestry, agricultural vehicles and mining vehicles are exposed to excessively high levels of vertical and lateral vibrations which can pose health risks to the drivers. Ride improvement through seat suspensions has been successful in the vertical mode, however, seat suspensions have been virtually ineffective in the lateral mode. Computer simulation studies have shown that a seat suspension with a dynamic absorber can significantly improve lateral ride. In this investigation, the lateral ride performance of an off-road vehicle with a seat suspension having a dynamic vibration absorber is studied. Based on parametric sensitivity and optimization analyses in establishing optimal parameters, a prototype suspension is designed and fabricated, and then tested in the laboratory as well as on the field. Analytical results are compared to those derived from the test data in order to illustrate the validity of the computer model. The investigations through laboratory and field testing of the lateral seat suspension system have demonstrated potential in improving ride.     

Parameterization and modelling of large off-road tyres for ride analyses: Part 2 – Parameterization and validation of tyre models

Every mathematical model used in a simulation is an idealization and simplification of reality. Vehicle dynamic simulations that go beyond the fundamental investigations require complex multi-body simulation models. The tyre–road interaction presents one of the biggest challenges in creating an accurate vehicle model. Many tyre models have been proposed and developed but proper validation studies are less accessible. These models were mostly developed and validated for passenger car tyres for application on relatively smooth roads. The improvement of ride comfort, safety and structural integrity of large off-road vehicles, over rough terrain, has become more significant in the development process of heavy vehicles. This paper investigates whether existing tyre models can be used to accurately describe the vertical behaviour of large off road tyres while driving over uneven terrain. [1] Presented an extensive set of experimentally determined parameterization and validation data for a large off-road tyre. Both laboratory and field test are performed for various loads, inflation pressures and terrain inputs. The parameterization process of four tyre models or contact models are discussed in detail. The parameterized models are then validated against test results on various hard but rough off-road terrain and the results are discussed.     

Non-conventional land transport systems

Locomotion in saturated terrain and some special vehicle solutions for saturated agricultural terrain were discussed, as well as arrangements that increase the mobility of off-road vehicles for military purposes, component and motor alternatives for off-road vehicles, and the new Maglev and Eurotren Monoviga guided transport systems .     

Analysis of vehicle platoon movement and speed-spacing relationships during military exercises

In this study a method that identifies off-road vehicle column movement was developed and evaluated. Previous studies have revealed that multiple vehicle passes produce detrimental soil and terrain impacts. Identifying the frequency and location of this type of multi-pass impact during military maneuvers is difficult. This method will aid in the assessment of environmental impacts of off-road military vehicles by allowing land managers to characterize vehicle movement patterns, especially column movement, at military training installations during maneuvers. GPS units mounted on military vehicles collected on and off-road tracking data during a reconnaissance maneuver at Fort Lewis Military Installation, Washington. A set of data utilizing a Stryker platoon of four vehicles was used to evaluate this method. The GPS coordinates, speed, and direction of travel of each vehicle was collected at each second. A criteria to identify platoon column movement was developed based on vehicle proximity, speed and direction of travel. The results of this study show that the method can correctly identify off-road column movement for the purpose of evaluating the multi-pass impacts on the terrain. In addition, using this approach the vehicle movement patterns associated with on- and off-road platoon movement (i.e. vehicle speeds and spacing) were evaluated.     

Semi-active hydropneumatic spring and damper system

This paper is concerned with the development of a semi-active hydropneumatic spring and damper system, comprising of a two state hydropneumatic spring and a two state hydraulic damper. The system was specifically developed to improve the ride comfort and handling of large off-road vehicles. The suspension requirements for good ride comfort and handling for heavy off-road vehicles are discussed with special reference to the advantages of semi-active hydropneumatic springs and semi-active dampers. The layout and functioning of an experimental spring and damper unit used for laboratory tests are discussed. Spring and damper characteristics, as well as valve response times for both the semi-active spring and semi-active damper were determined. A single degree of freedom test rig with a sprung mass of 3 tons was used to perform first order ride comfort tests. Tests include step response and random input response. The test rig was also used to evaluate semi-active control strategies for both spring and damper as well as a control strategy for implementing ride height adjustment without using an external hydraulic pump.     

Technology showcase active ride control system

In totally passive suspension systems, soft springs used to obtain a comfortable ride result in poor handling during cornering manoeuvres. If hard springs are used for good handling, ride quality surfers. This article describes the use of controlled hydraulic suspension systems to improve both ride and handling of on-and off-road vehicles. By incorporating inertial valve controls, multiple interconnected valves, and pressurized gas springs in the suspension system, a combination of good ride and handling is achieved without the large power consumption of a fully active suspension system. The mechanical features and operation of these recently developed suspension systems, and their application in a number of commercial, military, and agricultural vehicles are discussed.     

Application of similitude to soil-machine systems

Model tests can be used to predict the performance of full-scale off-road vehicles and earth-moving and agricultural machines as an aid to their design and development. The principles of similitude as applied to soil-machine system modeling are discussed, and some past studies and examples of these applications are examined. The opportunities for future research to improve these techniques are identified.     

Analysis of a hydrostatic transmission driveline for its use in off-road multiple axle vehicles

There is a vast range of off-road multi-axle wheeled vehicle configurations. Some of the most common are the three axle rigid vehicles or the four axle articulated vehicles. However, these types of vehicles have the problem of using very complex transmission configurations. In addition, the requirements in terms of torque in each of the wheels are quite variable and non uniform. This work aims to model and study, from the standpoint of performance and energy efficiency, the driveline of such vehicles. The modelling process for the design and analysis of a hydrostatic transmission aimed at off-road multiple axle vehicles has been conceptually described. Mathematical models for the main components of the transmission and a global model of the driveline have been defined. A specific example study is presented, applying the described procedure. Results show that the overall performance of the transmission is highly dependent on the operating conditions, on the selected configuration and on the used components. The results also show that the actual instantaneous efficiency of each of the components is usually far below their maximum catalogue value. In the case study efficiencies up to 64% have been reached for the overall transmission.     

Development of a new type of electric off-road vehicle powered by microwaves transmitted through air

Needless to say, we are now facing a critical state in the global environment, i.e. global warming. We have to change our way of thinking and our economic systems from those dependent on fossil resources to those dependent on renewable energy resources, such as solar energy. In our field of research, electric vehicles are considered the best choice for reducing carbon dioxide emissions. A battery is not an adequate energy source for electric vehicles, because batteries quickly get depleted because of its low energy and power density. A fuel cell is a more favorable alternative to the battery; however, it has large mass and can only replace the internal combustion engine, but the power transmission mechanisms are still necessary. The new concept of an electric off-road vehicle proposed here is entirely different from those mentioned above. The vehicle has neither a combustion engine nor a battery but only electric motors. Energy to drive the motors is transmitted through air as microwaves at 2.45 GHz. This technology was developed at the Research Institute for Sustainable Humanosphere, Kyoto University, as a method for transmitting electricity from a large-scale solar power station (SPS) orbiting in space to the Earth. We have constructed some models of electric off-road vehicles and investigated their adoptability to microwave power transmission. In this paper, some experimental results on the use of microwave power transmission for powering the vehicles are presented, and some problems such as low energy transmission efficiency are also discussed.     

Tire compaction capacity rating on non-standard soil

Tire Compaction Capacity rating system with its CC index was evolved to support the choice of proper tires for off-road vehicles or machines operating on crop producing land with aim to prevent harmful compaction of the ground. This system, fundamentally presented in the Journal of Terramechanics, Vol. 52/2014, is based on a great number of laboratory compaction tests in common clay–loam soil (here marked as standard soil). The presented article deals especially with more accurate application of numerical rating to sandy and clay soils (very different grain size) under the designation equivalent Compaction Capacity (eCC) index, however, is applicable to an arbitrary soil type. The features and practical use of eCC rating are explained and discussed in this technical note.     

“Wheels vs. tracks” – A fundamental evaluation from the traction perspective

The issue of wheeled vehicles vs. tracked vehicles for off-road operations has been a subject of debate for a long period of time. Recent interest in the development of vehicles for the rapid deployment of armed forces has given a new impetus to this debate. While a number of experimental studies in comparing the performances of specific wheeled vehicles with those of tracked vehicles under selected operating environments have been performed, it appears that relatively little fundamental analysis on this subject has been published in the open literature, including the Journal of Terramechanics. This paper is aimed at evaluating the tractive performance of wheeled and tracked vehicles from the standpoint of the mechanics of vehicle–terrain interaction. The differences between a tire and a track in generating thrust are elucidated. The basic factors that affect the gross traction of wheeled and tracked vehicles are identified. A general comparison of the thrust developed by a multi-axle wheeled vehicle with that of a tracked vehicle is made, based on certain simplifying assumptions. As the interaction between an off-road vehicle and unprepared terrain is very complex, to compare the performance of a wheeled vehicle with that of a tracked vehicle realistically, comprehensive computer simulation models are required. Two computer simulation models, one for wheeled vehicles, known as NWVPM, and the other for tracked vehicles, known as NTVPM, are described. As an example of the applications of these two computer simulation models, the mobility of an 8 × 8 wheeled vehicle, similar to a light armoured vehicle (LAV), is compared with that of a tracked vehicle, similar to an armoured personnel carrier (APC). It is hoped that this study will illustrate the fundamental factors that limit the traction of wheeled vehicles in comparison with that of tracked vehicles, hence contributing to a better understanding of the issue of wheels vs. tracks.