冰面上轮胎摩擦牵引力的实验研究

研制开发了测试冰雪面轮胎力学特性的试验装置,该装置具有可作往复运动的平台冰槽。在不同冰基体温度下,分析了轮胎摩擦引力受侧偏角,载荷和轮胎充气压力的影响,从试验角度论证了轮胎中央充放气系统对改善冬季轮胎牵引性能的作用,该装置的建立将有利于轮胎新结构和新材料的开发,并起到完善现有轮胎力学模型的作用。     

Slip-based experimental studies of a vehicle interacting with natural snowy terrain

As longitudinal slip affects vehicle–pavement interactions on roads and hard surfaces, so too does it play an important role in interactions between vehicles and soft terrains, including snow. Although many slip-based models have been developed recently for tire–snow interactions (e.g., [1] and references cited therein), these models have only been partially validated, due to a lack of relevant experimental data. This paper presents comprehensive data from tests that were performed using a newly-developed test vehicle traversing natural snowy terrain, over a wide range of values for longitudinal slip, vertical load and torque via an effective accelerate/brake maneuver. Drawbar pull, motion resistance, wheel states and tire stiffness were presented as a function of slip; tire sinkage was obtained using a laser profilometer; strength and depth of snow were found using a snow micropenetrometer. The effects of the rear tire going over snow compacted by the front tire were also studied. The maximum traction force normalized by the vertical load is found to be ≈0.47, maximum motion resistance normalized by the vertical load is ≈0.4. Comparison of the trend and order-of-magnitude of test results with those from existing slip-based numerical model [1] shows good comparison in motion resistance, tire sinkage, and longitudinal stiffness, but indicates that a better traction model is needed to improve the comparison.     

Verification and validation of a winter driving simulator

A full vehicle dynamics simulator was constructed in SimCreator^® for the Cold Regions Research and Engineering Laboratory (CRREL) Instrumented Vehicle (CIV) and was used to investigate and validate the newly developed Vehicle Terrain Interaction (VTI) code. The VTI code replaces the tire component of the simulated vehicle, in the Driver and Motion Simulator (DMS), allowing it to report back realistic values while driving on various types of terrain surfaces such as mud, snow, ice, and pavement. The validation effort within this paper is focused on the winter (snow and ice) parts of the VTI code. The outputs from the Engineering Research and Development Center (ERDC) and the DMS VTI codes were validated through field experiments and against the North Atlantic Treaty Organization (NATO) Reference Mobility Model (NRMM). The DMS VTI code can be used with different vehicle models, providing the US. Army with a valuable asset that will allow simulation of existing or conceptual, manned or autonomous, ground vehicle performance for acquisition, planning, or training. This information, along with some basic terrain information, will allow troops to plan the fastest and most effective way of getting to a desired location, while minimizing the possibility of being delayed because of the terrain conditions.     

Lateral slide sinkage tests for a tire and a track shoe

Previous field studies have shown the influence of turning vehicles on rut formation or sinkage. In order to further investigate the relationships, laboratory tests were conduced on a 14.5–20.3 6-PR trailer tire and an Armored Personnel Carrier (APC) track shoe in sand. Lateral displacements, and resulting lateral forces, were applied to the tire and track shoe under constant normal forces. The tire was pulled laterally and the track shoe was pulled back and forth to represent actual movement during vehicle turning. Results show that the lateral force and lateral displacement generated by turning maneuver affect sinkage severely for wheeled and tracked vehicles. The final sinkage caused by the lateral force for the tire is 3–5 times to the static sinkage. For the track shoe, the final sinkage caused by the lateral displacement is about three times to the static sinkage.     

Stochastic modeling of tire–snow interaction using a polynomial chaos approach

Developing accurate models to simulate the interaction between pneumatic tires and unprepared terrain is a demanding task. Such tire–terrain contact models are often used to analyze the mobility of a wheeled vehicle on a given type of soil, or to predict the vehicle performance under specified operational conditions (as related to the vehicle and tires, as well as to the running support). Due to the complex nature of the interaction between a tire and off-road environment, one usually needs to make simplifying assumptions when modeling such an interaction. It is often assumed that the tire–terrain interaction can be captured using a deterministic approach, which means that one assumes fixed values for several vehicle or tire parameters, and expects exact responses from the system. While this is rarely the case in real life, it is nevertheless a necessary step in the modeling process of a deterministic framework. In reality, the external excitations affecting the system, as well as the values of the vehicle and terrain parameters, do not have fixed values, but vary in time or space. Thus, although a deterministic model may capture the response of the system given one set of deterministic values for the system parameters, inputs, etc., this is in fact only one possible realization of the multitude of responses that could occur in reality. The goal of our study is to develop a mathematically sound methodology to improve the prediction of the tire–snow interaction by considering the variability of snow depth and snow density, which will lead to a significantly better understanding and a more realistic representation of tire–snow interaction. We constructed stochastic snow models using a polynomial chaos approach developed at Virginia Tech, to account for the variability of snow depth and of snow density. The stochastic tire–snow models developed are based on the extension of two representative deterministic tire–snow interaction models developed at the University of Alaska, including the pressure–stress deterministic model and the hybrid (on-road extended for off-road) deterministic model. Case studies of a select combination of uncertainties were conducted to quantify the uncertainties of the interfacial forces, sinkage, entry angle, and the friction ellipses as a function of wheel load, longitudinal slip, and slip angle. The simulation results of the stochastic pressure–stress model and the stochastic hybrid model are compared and analyzed to identify the most convenient tire design stage for which they are more suitable. The computational efficiency of the two models is also discussed.     

Modeling and validation of hitch loading effects on tractor yaw dynamics

This paper develops a yaw dynamic model for a farm tractor with a hitched implement, which can be used to understand the effect of tractor handling characteristics for design applications and for new automated steering control systems. Dynamic equations which use a tire-like model to capture the characteristics of the implement are found to adequately describe the tractor implement yaw dynamics. This model is termed the “3-wheeled” Bicycle Model since it uses an additional wheel (from the traditional bicycle model used to capture lateral dynamics of passenger vehicles) to account for the implement forces. The model only includes effects of lateral forces as it neglects differential longitudinal or draft forces between inner and outer sides of the vehicle. Experiments are taken to verify the hitch model using a three-dimensional force dynamometer. This data shows the implement forces are indeed proportional to lateral velocity and that differential draft forces can be neglected as derived in the “3-wheeled” Bicycle Model. Steady state and dynamic steering data are used for implements at varying depths and speeds to quantify the variation in the hitch loading. The dynamic data is used to form empirical transfer function estimates (ETFEs) of the implements and depths in order to determine the coefficients used in the “3-wheeled” Bicycle Model. Changes in a single parameter, called the hitch cornering stiffness, can capture the various implement configurations. Finally, a model that includes front wheel drive forces is derived. Experiments are taken which provide a preliminary look into the effect of four-wheel drive traction forces, and show a difference with two-wheel versus four-wheel drive, on the yaw dynamics of a tractor with the hitched implement.     

On the impact of cargo weight, vehicle parameters, and terrain characteristics on the prediction of traction for off-road vehicles

A realistic prediction of the traction capacity of vehicles operating in off-road conditions must account for stochastic variations in the system itself, as well as in the operational environment. Moreover, for mobility studies of wheeled vehicles on deformable soil, the selection of the tire model used in the simulation influences the degree of confidence in the output. Since the same vehicle may carry various loads at different times, it is also of interest to analyze the impact of cargo weight on the vehicle’s traction.This study focuses on the development of an algorithm to calculate the tractive capacity of an off-road vehicle with stochastic vehicle parameters (such as suspension stiffness, suspension damping coefficient, tire stiffness, and tire inflation pressure), operating on soft soil with an uncertain level of moisture, and on a terrain topology that induces rapidly changing external excitations on the vehicle. The analysis of the vehicle–soil dynamics is performed for light cargo and heavy cargo scenarios. The algorithm relies on the comparison of the ground pressure and the calculated critical pressure to decide if the tire can be approximated as a rigid wheel or if it should be modeled as a flexible wheel. It also involves using previously-developed vehicle and stochastic terrain models, and computing the vehicle sinkage, resistance force, tractive force, drawbar pull, and tractive torque.The vehicle model used as a case study has seven degrees of freedom. Each of the four suspension systems is comprised of a nonlinear spring and a viscous (linear or magneto-rheological) damper. An off-road terrain profile is simulated as a 2-D random process using a polynomial chaos approach [Sandu C, Sandu A, Li L. Stochastic modeling of terrain profiles and soil parameters. SAE 2005 transactions. J Commer Vehicles 2005-01-3559]. The soil modeling is concerned with the efficient treatment of the impact of the moisture content on relationships critical in defining the mobility of an off-road vehicle (such as the pressure–sinkage [Sandu C et al., 2005-01-3559] and the shear stress–shear displacement relations). The uncertainties in vehicle parameters and in the terrain profile are propagated through the vehicle model, and the uncertainty in the output of the vehicle model is analyzed [Sandu A, Sandu C, Ahmadian M. Modeling multibody dynamic systems with uncertainties. Part I: theoretical and computational aspects, Multibody system dynamics. Publisher: Springer Netherlands; June 29, 2006. p. 1–23 (23), ISSN: 1384-5640 (Paper) 1573-272X (Online). doi:10.1007/s11044-006-9007-5; Sandu C, Sandu A, Ahmadian M. Modeling multibody dynamic systems with uncertainties. Part II: numerical applications. Multibody system dynamics, vol. 15, No. 3. Publisher: Springer Netherlands; 2006. p. 241–62 (22). ISSN: 1384-5640 (Paper) 1573-272X (Online). doi:10.1007/s11044-006-9008-4]. Such simulations can provide the basis for the study of ride performance, handling, and mobility of the vehicle in rough off-road conditions.     

Finite element modeling of interfacial forces and contact stresses of pneumatic tire on fresh snow for combined longitudinal and lateral slips

Significant challenges exist in the prediction of interaction forces generated from the interface between pneumatic tires and snow-covered terrains due to the highly non-linear nature of the properties of flexible tires, deformable snow cover and the contact mechanics at the interface of tire and snow. Operational conditions of tire-snow interaction are affected by many factors, especially interfacial slips, including longitudinal slip during braking or driving, lateral slip (slip angle) due to turning, and combined slip (longitudinal and lateral slips) due to brake-and-turn and drive-and-turn maneuvers, normal load applied on the wheel, friction coefficient at the interface and snow depth. This paper presents comprehensive three-dimensional finite element simulations of tire-snow interaction for low-strength snow under the full-range of controlled longitudinal and lateral slips for three vertical loads to gain significant mechanistic insight. The pneumatic tire was modeled using elastic, viscoelastic and hyperelastic material models; the snow was modeled using the modified Drucker-Prager Cap material model (MDPC). The traction, motion resistance, drawbar pull, tire sinkage, tire deflection, snow density, contact pressure and contact shear stresses were obtained as a function of longitudinal slip and lateral slip. Wheel states - braked, towed, driven, self-propelled, and driving - have been identified and serve as key classifiers of discernable patterns in tire-snow interaction such as zones of contact shear stresses. The predicted results can be applied to analytical deterministic and stochastic modeling of tire-snow interaction.     

Analytical model of longitudinal tire traction in snow

An analytical model to estimate longitudinal traction of a tire in snow was developed and verified to have good predictability in comparison with measurements. Snow traction of a tire is composed of four kinds of forces in this model: braking force attributable to snow compression, shear force of snow in void (space between tread blocks), frictional force, and digging force (edge effect generated by sipes and blocks). The mechanical characteristics of snow were considered in the prediction of braking force and shear force, but were not considered in the prediction of other forces. The contribution of shear force of snow in void and the frictional force was large in static traction (traction just before a tire slips). On the other hand, the contributions of digging force and frictional force were large in situations involving high slip ratios.     

Experimental investigation of pneumatic tire performance on ice: Part 1 – Indoor study

Currently, the probability of accident occurrence is much higher when driving on icy roads than on asphalt. Since the tire is the only element of the vehicle that contacts the icy road, it is crucial to thoroughly comprehend the friction mechanism at the tire–ice interface for improved tires and safety systems for icy roads. This study investigates the available friction levels at the tire–ice interface by varying operational parameters through the indoor testing program conducted at the Advanced Vehicle Dynamics Laboratory, Virginia Tech (in part I) and the outdoor testing program conducted at the Keweenaw Research Center (in part II). This two-part article presents the design of experiment, the indoor and outdoor test programs, and friction–slip ratio curves obtained from both test programs for different conditions. The effects of operational parameters and their inter-dependency for the entire slip ratio range during operation on ice is explained, as studied from the two test programs. This article (part I) details the indoor test method consisting of the ice creation procedure, pre-test procedures, the test procedure and analysis of the obtained friction–slip ratio curves. This experimental investigation performs the necessary groundwork and builds a strong foundation towards making driving on ice safe.     

Tire-ice model development for the simulation of rubber compounds effect on tire performance

The material properties of the rubber compounds, which are highly dependent on temperature, have a vital role in the tire behavior. A comprehensive study on the effect of the rubber properties on tire performance, for different temperatures, as well as different road conditions is required to adequately predict the performance of tires on ice.In this study, a theoretical model has been developed for the tire-ice interaction. The temperature changes obtained from the model are used to calculate the height of the water film created by the heat generated due to the friction force. Next, the viscous friction coefficient at the contact patch is obtained. By using the thermal balance equation at the contact patch, the dry friction is obtained. Knowing the friction coefficients for the dry and wet regions, the equivalent friction coefficient is calculated. The model has been validated using experimental results for three similar tires with different rubber compounds properties. The model developed can be used to predict the temperature changes at the contact patch, the tire friction force, the areas of wet and dry regions, the height of the water film for different ice temperatures, different normal load, etc.     

Off-road tire modeling and the multi-pass effect for vehicle dynamics simulation

Off-road operations are critical in many fields and the complexity of the tire-terrain interaction deeply affects vehicle performance. In this paper, a semi-empirical off-road tire model is discussed. The efforts of several researchers are brought together into a single model able to predict the main features of a tire operating in off-road scenarios by computing drawbar pull, driving torque, lateral force, slip-sinkage phenomenon and the multi-pass behavior. The approach is principally based on works by Wong, Reece, Chan, and Sandu and it is extended in order to catch into a single model the fundamental features of a tire running on soft soil. A thorough discussion of the methodology is conducted in order to highlight strengths and weakness of different implementations. The study considers rigid wheels and flexible tires and analyzes the longitudinal and the lateral dynamics. Being computationally inexpensive a semi-empirical model is attractive for real time vehicle dynamics simulations. To the best knowledge of the authors, current vehicle dynamics codes poorly account for off-road operations where tire-terrain interaction dominates vehicle performance. In this paper two soils are considered: a loose sandy terrain and a firmer loam. Results show that the model realistically predicts longitudinal and lateral forces providing at the same time good estimates of the slip-sinkage behavior and tire parameters sensitivity.     

Development of a dynamometric vehicle to assess the drawbar performance of high-powered agricultural tractors

Agricultural tractors are machines originally designed to mechanize agricultural tasks, especially tillage and pulling. A large part of research activities have been interested in optimizing tractor efficiency, in particular in terms of emissions and energy. In this frame, the OECD Tractor Code 2 sets out a drawbar test in specific controlled conditions with the aim of evaluating the power of the tractor available at the drawbar. The principal measurement chain relies on dynamometric vehicles (DV) that are instrumented vehicles specifically engineered to develop horizontal force at the drawbar of agricultural tractors. The CREA Laboratory of Treviglio, Italy, engineered a new dynamometric vehicle to test tractors with up to 200 kW at the drawbar (245 kW at the engine flywheel) and a maximum of 118 kN drawbar force. The chosen basis is a FIAT 6605 N truck (TM 69 6 × 6) which has been transformed into a hydrostatic vehicle driven by a hydraulic system and an auxiliary gearbox. The maximum drawbar force was verified up to 122 kN. The drawbar power verification (200 kW) was successfully carried. The final verification confirmed that the project is valid for the investigation and optimization of the parameters regarding the traction efficiency of agricultural tractors.     

Evaluation of drawbar performance of winter tyres for special purpose vehicles

Driving on ice is still a risky activity. Research has investigated the factors contributing to the friction mechanism and has reported experimental studies of pneumatic tyres on ice in order to develop models that predict tractive and braking performance on ice/snow. Therefore, developing testing methods to obtain relevant experimental data for the validation of models is equally important.There are agricultural and industrial vehicles which are also designed for pulling but there are no specific studies reporting experimental tests on traction force of such machines in snowy conditions. However, this issue is very topical, as demonstrated by the appearance on the market of winter tyres for such vehicles.This study presents a method for testing winter tyres in outdoor test facilities with a focus on traction performance. The conclusions will serve in future investigations as a concise knowledge source to develop improved testing facilities and tyre–ice interaction models, aiding the development of better tyre designs and improved vehicle safety systems.The functional tests hereafter described have been carried out with the aim of evaluating the possibility of measuring the influences of different technique solutions on the performance of certain 17.5 R25 sized industrial tyres.     

Simulation on projectile with high rotating speed penetrating into the moving vehicular door

The numerical program LS-DYNA, is used to simulate the process of the projectile with high rotating speed penetrating into the moving vehicular door. Because of the moving of the vehicular door, the projectile will turn, and the ballistic trajectory will migrate. The paper provides a method to calculate the projectile’s angle of turning’s curve. In the process of the penetration, the projectile’s moving speed is 300 m/s, rotating speed is 0, 3600 n/s and 6370 n/s. The vehicular door’s moving speed is 0, 40 m/s and 80 m/s. The projectile is the semi-sphere nose projectile whose diameter is 7.62 mm; the vehicular door’s thickness is 2 mm. The material model is the JOHN-COOK material model that can characterize strain, strain rate hardening and thermal softening effects. Through comparing with the results by simulation to study the effects of the projectile’s final velocity, the angle of rotation and the ballistic trajectory’s migration with different projectile’s rotating speeds and the vehicular door’s moving speeds.     

Hybrid soft soil tire model (HSSTM). Part III: Model parameterization and validation

Part I describes the tire structure model; part II the contact detection and contact interface models for rigid and deformable terrains; part III the model parameterization and validation. Model parameters are estimated using non-linear least-square optimization to minimize the error between the Hybrid Soft Soil Tire Model (HSSTM) predictions and experimental data. The parameterization routines’ initial conditions are estimated from modal analysis in radial and circumferential directions. The preliminary parameterized model is incorporated in the optimization routine to find tire sidewall and belt parameters in the radial direction using quasi-static cleat loading test data. The vertical force at the spindle and tire contact patch are used to study the model accuracy in the radial direction. FlatTrac tire longitudinal and lateral force test data are employed to estimate the parameters in these directions. The tire shear force and moment at the spindle are validated against experimental data for lateral dynamics performance.     

An instrumented vehicle for offroad dynamics testing

The paper presents an instrumented vehicle that was equipped with measuring systems to perform complete dynamics tests, especially in off-road conditions. The equipment consists of four wheel dynamometers, a steering robot, and a differential GPS system together with an inertial platform, a non-contact vehicle speed sensor, and an on-board computer with software to control the devices and collect experimental data. The four wheel dynamometers measure six elements; based on strain gage force transducers, it measures three orthogonal forces and three moments. The steering robot can control the steering wheel of the vehicle at a variety of excitation modes; it can carry out typical vehicle dynamics tests (ISO 7401, ISO 4138, ISO/TR3888, etc.) as well as custom engineered tests at a wide range of setting parameters (steer angle rate up to 1600 deg/s). The differential GPS system gives true time vehicle kinematics data (velocities, accelerations, angles, etc.) at 10-ns sample rate and 20-mm accuracy. The base vehicle, a Suzuki Vitara 4 × 4, required no special modifications or changes to install the measuring equipment. The paper also describes typical tests performed with the use of the instrumented vehicle together with sample results.     

Total axle load effects on soil compaction

Theoretical and applied research has shown that the pressure at a point in the subsurface soil is a function of both the surface unit pressure and the extent of the area over which it is applied (total load). Thirty years ago, most of the soil compaction from vehicle traffic was in the plow layer and was removed by normal cultural practices. As equipment has increased in size and mass, machine designers have increased tire sizes to keep the soil surface unit pressure relatively constant. However, the increase in total axle loads is believed to have caused an increase in compaction at any given depth in the soil profile, resulting in significant compaction in the subsoil.Two tires of different sizes, a standard agricultural tire and a flotation tire were used to support equal loads. Soil pressures were measured at three depths in the soil profile directly beneath each of the tires. Two soils were used and each was prepared first in a uniform density profile, and then they were prepared with a simulated traffic pan (layer of higher density) at a depth of approximately 30 cm.Results showed that the presence of a traffic pan in the soil profile caused higher soil pressures above the pan and lower pressures below it than was the case for a uniform soil profile. The soil contact surface of the flotation tire was approximately 22% greater than the agricultural tire. The greater contact surface did reduce soil pressures at the soil surface, of course, but the total axle load was still the dominant factor in the 18–50 cm-depth range used in this study.     

Soil compaction and tires for harvesting and transporting sugarcane

Four tire types (A, block-shape tread; B, rib-shape tread; C, low-lug tread; D, high-lug tread) used to harvest and transport sugarcane were compared regarding the compaction induced to the soil. Tires were tested at three inflation pressures (207, 276, 345 kPa) and six loads ranging from 20 to 60 kN/tire. Track impressions were traced, and 576 areas were measured to find equations relating inflation pressure, load, contact surface and pressure. Contact surface increased with increasing load and decreasing inflation pressure; however, the contact pressure presented no defined pattern of variation, with tire types A and B generating lower contact pressure. The vertical stresses under the tires were measured and simulated with sensors and software developed at the Colombian Sugarcane Research Center (Cenicaña). Sensors were placed at 10, 30, 50 and 70 cm depth. Tire types A and B registered vertical stresses below 250 kPa at the surface. These two tires were better options to reduce soil compaction. The equations characterizing the tires were introduced into a program to simulate the vertical stress. Simulated and measured stresses were adjusted in an 87–92% range. Results indicate a good correlation between the tire equations, the vertical stress simulation and the vertical stress measurement.