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We studied the effect of steering dynamics on lateral dynamics for a 1.6 ton 4x4 sport utility vehicle (SUV) on deformable surfaces. The vehicle used for the outdoor tests was equipped with (1) a steering robot to apply repeatable steering wheel excitations and (2) a high-precision differential GPS (DGPS) system to gather physical measures that describe lateral dynamics: lateral acceleration, yaw rate, and vehicle sideslip angle. The vehicle was driven over three different deformable surfaces~a loess and a sandy soil and wet snow~with a constant speed of 10 km/h. The steering robot applied inputs of (1) sine wave excitation at 0.5, 1.0, and 2.5 Hz, and (2) ramp change (or trapezoidal) excitation with steering wheel rate at 100, 500, and 1500 deg/s. Results are presented as frequency paths and time courses to analyze effects of surface and steering dynamics.

The paper contains experimental results of soil stress state under loading of commercial wheeled vehicles. The measurements were performed with the use of SSTs (Stress State Transducers), which enable to determine soil pressures needed for calculations of stress state at a point: principal stresses and their direction cosines as well as octahedral stresses. A detailed description of the measuring method with an introductory theory of operation of the SST together with some methodology aspects of soil pressure measurements are included. The field tests were conducted on three different soil surfaces: loess, sand and turf as well as on snow surface in winter conditions. For the tests, two vehicles were used: a 5,6T 4x4 truck and a 14T 6x6 truck. The vehicles were driven at constant low speed or at different speeds. Moreover, effects of wheel loading, reduced inflation pressure, drive modes (rolling or driving) were also analyzed.

In this paper a model of the wheel-soil system and its identification are presented. The model assumes the interaction between a wheel and soil can be described by the soil stress state under wheel loads. The stress state can be defined by means of the major stresses and their direction cosines, as well as the stresses in the octahedral stress system. Based on the soil stress analysis, traction forces in the wheel-soil system can be obtained by integrating the stresses. Identification of the model was performed using a 5T 4×4military truck, which was driven over three different soil surfaces and over a snow surface. For the identification of the model, values of drawbar pull force as well as soil stresses and deformation were required and they were measured in field experiments.