Druckverteilung auf Kontaktflächen unter Forstreifen

Abstract

Technical and ecological effects of automated forestry machines is influenced in part by the distribution of pressure on the surface beneath the wheel. However, it is precisely under typical forest conditions that these effects have not yet been examined. This research project Druckverteilung auf Kontaktflächen unter Forstreifen or Pressure Allocation on Contact Areas under Forest Tires (PrAllCon) was designed to supply this missing information.A market analysis provided a detailed report of the composition of the tires found on automated machines used in Germany s forests. Parallel to this, a technique was developed by which the pressure allocation on the contact surface could be measured while also taking into account the degree of support between the lugs of the tire profile (measured with sand of defined composition). In order to prepare the new tires for this test they had to be driven several times using a rolling machine. The desired data were then obtained by means of a hydraulic simulation of wheel load with analog calculation of surface area pressure distribution and it s subsequent digital visualisation.In general it could be ascertained that the focus of the pressure load was concentrated in the middle of the contact area and decreased steadily towards the periphery. This became more pronounced as wheel load and tire pressure increased. Further processing and analysis of these pressure distributions as a function of wheel load and tire pressure was done by using programs developed by the IFA together with software for statistical analysis. The results demonstrated that the pressure did indeed have a bell-shaped distribution with an elliptical cross-section. The maximum pressure values were calculated using width and length measurements from vertical cross sections of the respective distribution curves. These bell-shaped pressure progressions could be represented in a function of determination. An average coefficient of determination of 92% enabled the determination of every measured contact area pressure distribution as well as the prediction of pressure distribution for the entire tire collective. Analysis of regression curves showed that not only wheel load and tire pressure but also the distribution of pressure over the contact area are influenced by the tire parameters: width and diameter. The creation of a prognosis model makes it also possible to predict the pressure distribution as dependent on the variables tire width and length. The validity of this method extends only to tires whose parameters lay within those of the collective measured in this study.In addition to maximum pressures mean pressures were also examined. Between the maximum pressures and the maxima of the mean pressure distributions there existed a plausible correlation that could be derived using simple regression. The factor was calculated to be 2.74. Thus, given a maximum pressure, the corresponding mean pressure can be inferred.