In recent years, the interest in the design, construction and utilization of rubber tracks for agriculture and earth moving machinery has increased considerably. The development of such types of tracks was initiated by the efforts to invent a more environmentally friendly vehicle-terrain system. These tracks are also the result of the continuous effort to develop more cost-effective traction systems. A rubber-surfaced and friction-based prototype track was developed and mounted on the patented modification of a new Allis Chalmers four wheel drive tractor. The track is propelled by smooth pneumatic tyres by means of rubber-rubber friction and the tractive effort of the track is mainly generated by soil-rubber friction between the rubber surface of the track elements and terrain. The experimental track layer tractor, based on an Allis Chalmers 8070 tractor (141 kW) was tested on concrete and on cultivated sandy loam soil at 7.8%; 13% and 21% soil water content. The contact pressure and the tangential force on an instrumented track element, as well as the total torque input to one track, was simultaneously recorded during the drawbar pull-slip tests. Soil characteristics for pressure-sinkage and friction-displacement were obtained from the field tests by using an instrumented linear shear and soil sinkage device. By applying the approach based on the classical bevameter technique, analytical methods were implemented for modelling the traction performance of the prototype track system. Different possible pressure distribution profiles under the tracks were considered and compared to the recorded data. Two possible traction models were proposed, one constant pressure model, for minimal inward track deflection and the other a flexible track model with inward deflection and a higher contact pressure at both the front free-wheeling and rear driving tyres. For both models, the traction force was mainly generated by rubber-soil friction and adhesion with limited influence by soil shear. For individual track elements, close agreement between the measured and predicted contact pressure and traction force was observed based on the flexible track model. The recorded and calculated values of the coefficient of traction based on the summation of the traction force for the series of track elements were comparable to the values predicted from modelling. However, the measured values of drawbar pull coefficient were considerably lower than the predicted values, largely caused by internal track friction in addition to energy dissipated by soil compaction. The tractive efficiency for soft surface was also unacceptably low, probably due to the high internal track friction and the low travel speeds applied for the tests. The research undertaken identified and confirmed a model to be used to predict contact pressure and tangential stresses for a single track element. It was capable of predicting the tractive performance for different possible contact pressure values. / Thesis (PhD (Argricultural Engineering))--University of Pretoria, 2007. / Civil Engineering / Unrestricted

京都大学 / 0048 / 新制・論文博士 / 博士(農学) / 乙第13294号 / 論農博第2877号 / 新制||農||1073(附属図書館) / 学位論文||R1||N5239(農学部図書室) / (主査)教授 清水 浩, 准教授 中嶋 洋, 教授 飯田 訓久 / 学位規則第4条第2項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

The tire-ice interaction is a highly complex phenomenon, which has a direct influence on the overall performance of the pneumatic tire. From tire-terrain interaction dynamics, it is evident that icy road conditions and tire operational parameters play a vital role in determining the overall performance of the vehicle. With the reduction of traction available at the surface in icy conditions, the dynamics of the vehicle becomes more unpredictable, as the system can become unstable. In order to design an appropriate safety system, the tire-ice interaction must be closely investigated. Since the tire is the part of the vehicle that is in direct contact with the terrain during operation, it is critical to have an in-depth understanding of the contact mechanics at the contact patch. This study has led to the development and validation of an existing tire-ice model to further improve the understanding of the contact phenomena at the tire-ice interface. Experimental investigations led to a novel measurement technique in order to validate the semi-empirical based tire-ice contact model. The Advanced Tire-Ice Interface Model serves to simulate the temperature rise at the contact patch based on the pressure distribution in the contact patch, thermal properties of the tread compound and of the ice surface. Since its initial development, the advanced model is now capable of simulating the thin water film created from the melted ice, the prediction of tractive performance, the estimation of the viscous friction due to the water layer, and the influence of braking operations including the locked wheel condition. Experimental studies, carried out at the Terramechanics, Multibody, and Vehicle Systems (TMVS) Laboratory, were performed on the Terramechanics Rig. The investigation included measuring the bulk temperature distribution at the contact patch in order to validate the temperature rise simulations of the original Tire-Ice Model. The tractive performance of a P225/60R16 97S Standard Reference Test Tire and a 235/55R-19 Pirelli Scorpion Verde All-Season Plus XL were also investigated during this study. A design of experiment was prepared to capture the tire tractive performance under various controlled operating conditions. / Ph. D. / Icy road conditions and tire performance play a vital role in determining the overall performance of a vehicle. With the reduction of traction available at the surface in icy conditions, the vehicle becomes more unpredictable and can become uncontrollable. In order to design an appropriate safety system, the tire-ice interaction must be closely investigated. This research aims at enhancing the understanding of the tire-ice contact interaction at the contact patch through modeling and experimental studies for a pneumatic tire traversing over solid ice. Prior work in the laboratory produced a Tire-Ice Model (TIM) with the purpose of estimating the friction at the tire-ice interface. The current work builds on that study, resulting in the Advanced Tire-Ice Interface Model (ATIIM). This model predicts the temperature rise at the tire-ice interface based on the measured pressure distribution and the thermal properties of the tire and of the ice surface. This model allows a more thorough investigation of the tire-ice interface, being capable of predicting the height of the thin water film created from the melted ice, the prediction of tractive performance of the tire, the estimation of the viscous friction due to the water layer at the contact interface, and the influence of braking operations, including the locked wheel (skid) condition. Experimental studies were carried out at Terramechanics, Multibody, and Vehicle Systems (TMVS) Laboratory on the Terramechanics Rig. The experimental investigation included measuring the temperature at various points at the tire-ice interface in order to compare the temperature rise predicted using the ATIIM. Furthermore, the tractive performance of the tire was also investigated by examining different conditions of vertical tire load, tire inflation pressure, and ice surface temperatures as well as various steering configurations set by the user. In addition to investigating the performance at the tire-ice interface, a vehicle model in which the front wheels are considered as one (and the same for the rear wheels), often referred to as the bicycle model, is studied while traveling over smooth ice. To ensure the accuracy of the vehicle simulation, the tire model chosen must account for the actual conditions in which the model will operate. In this study, the ATIIM is incorporated in empirical tire models commonly used in industry and used in conjunction with a vehicle model to accurately predict the behavior of the vehicle when operating on smooth ice.

Tire performance over soft soil influences the performance of off-road vehicles on soft soil, as the tire is the only force transmitting element between the off-road vehicles and soil during the vehicle operation. One aspect of the tire performance over soft soil is the tire tractive performance on soft soil, and it attracts the attention of vehicle and geotechnical engineers. The vehicle engineer is interested in the tire tractive performance on soft soil because it is related to vehicle mobility and energy efficiency; the geotechnical engineer is concerned about the soil compaction, brought about by the tire traffic, which accompanies the tire tractive performance on soft soil. In order to improve the vehicle mobility and energy efficiency over soft soil and mitigate the soil compaction, it's essential to develop an in-depth understanding of tire tractive performance on soft soil. This study has enhanced the understanding of tire tractive performance on soft soil and promoted the development of terramechanics and tire model parameterization method through experimental tests. The experimental tests consisted of static tire deflection tests, static tire-soil tests, soil properties tests, and dynamic tire-soil tests. The series of tests (test program) presented herein produced parameterization and validation data that can be used in tire off-road traction dynamics modeling and terramechanics modeling. The 225/60R16 97S Uniroyal (Michelin) Standard Reference Test Tire (SRTT) and loamy sand were chosen to be studied in the test program. The tests included the quantification or/and measurement of soil properties of the test soil, pre-traffic soil condition, the pressure distribution in the tire contact patch, tire off-road tractive performance, and post-traffic soil compaction. The influence of operational parameters, e.g., tire inflation pressure, tire normal load, tire slip ratio, initial soil compaction, or the number of passes, on the measurement data of tire performance parameters or soil response parameters was also analyzed. New methods of the rolling radius estimation for a tire on soft soil and of the 3-D rut reconstruction were developed. A multi-pass effect phenomenon, different from any previously observed phenomenon in the available existing literature, was discovered. The test data was fed into optimization programs for the parameterization of the Bekker's model, a modified Bekker's model, the Magic Formula tire model, and a bulk density estimation model. The modified Bekker's model accounts for the slip sinkage effect which the original Bekker's pressure-sinkage model doesn't. The Magic Formula tire model was adapted to account for the combined influence of tire inflation pressure and initial soil compaction on the tire tractive performance and validated by the test data. The parameterization methods presented herein are new effective terramechanics model parameterization methods, can capture tire-soil interaction which the conventional parameterization methods such as the plate-sinkage test and shear test (not using a tire as the shear tool) cannot sufficiently, and hence can be used to develop tire off-road dynamics models that are heavily based on terramechanics models. This study has been partially supported by the U.S. Army Engineer Research and Development Center (ERDC) and by the Terramechanics, Multibody, and Vehicle (TMVS) Laboratory at Virginia Tech. / Doctor of Philosophy / Big differences exist between a tire moving in on-road conditions, such as asphalt lanes, and a tire moving in off-road conditions, such as soft soil. For example, for passenger cars commonly driven on asphalt lanes, normally, the tire inflation pressure is suggested to be between 30 and 35 psi; very low inflation pressure is also not suggested. By contrast, for off-road vehicles operated on soft soil, low inflation pressure is recommended for their tires; the inflation pressure of a tractor tire can be as low as 12 psi, for the sake of low post-traffic soil compaction and better tire traction. Besides, unlike the research on tire on-road dynamics, the research on off-road dynamics is still immature, while the physics behind the off-road dynamics could be more complex than the on-road dynamics. In this dissertation, experimental tests were completed to study the factors influencing tire tractive performance and soil behavior, and model parameterization methods were developed for a better prediction of tire off-road dynamics models. Tire or vehicle manufacturers can use the research results or methods presented in this dissertation to offer suggestions for the tire or vehicle operation on soft soil in order to maximize the tractive performance and minimize the post-traffic soil compaction.