Search Results

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.

The paper describes a field experiment on the lateral dynamics of a light sport utility vehicle (SUV), driven over two different deformable surfaces (sand and loess). The vehicle was equipped with a steering robot, four wheel dynamometers, and a differential global positioning system (DGPS). The main purpose of this study was to determine (1) tire lateral forces on steered wheels of the vehicle and (2) vehicle response to two different methods for the steering angle excitation: a sine wave and a ramp change. The steering robot installed in the vehicle allowed us to perform tests with various parameters (sine wave at 0.5, 1.0 and 2.5 Hz, ramp change at 100, 500 and 1500 deg/s) and to repeat the tests as needed for further analysis of the data (the so called “open loop”).

The paper includes a description of a rotating wheel dynamometer developed for off-road testing of military vehicles. The purpose of the dynamometer is to measure all three forces and moments acting on a wheel at the same time. The dynamometer was designed as an autonomous measuring device, with on-board data acquisition system and power supply. Application of the dynamometer for testing of a vehicle requires only minor modifications of the wheel rim and the use of a wheel hub adapter. The device was designed for wheeled vehicles of weights ranging from 1.5 to 6 tonne. The dynamometer was installed on two different vehicles: a 1.6-tone SUV and a 5-tonne armored personal carrier. The paper contains detailed descriptions of the design and development as well as sample results from early road and off-road tests. Two of the advantages of the dynamometer over the existing, commercially available solutions are its low cost and versatility.

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.

This paper presents a new method for off-road traction and mobility research. This is an experimental method, in which traction measures (drawbar pull, rolling resistance, and vertical load) are correlated with respective stresses in soil, generated under a vehicle's load: major stress S1, shear, and normal stresses in the octahedral stress system. A theoretical background for the proposed method lies in Bekker's traction equations, where tractive forces are correlated with stresses on a contact surface between a wheel and terrain. Substituting surface stresses with volume stresses is expected to result in a more precise description of wheel-soil interactions. The soil stress - tractive forces relationships were obtained in real-size field tests using wheeled and tracked vehicles, driven on sand, loess, and turf. Traction and soil stresses were measured simultaneously with the use of original measuring methods, which are described in the paper.