Thesis (Ph. D.)--North Carolina State University. / Cover title. Includes vita. Includes bibliographical references (p. 35-36). Also available online via the NCSU Libraries website (http://www.lib.ncsu.edu/).

Thesis (PhD) -- University of Alabama, 1997

Call number: LD2668 .T4 1959 R44

The agricultural tractor is designed as a general purpose machine and consequently, does not perform all its tasks at maximum efficiency. Various methods of increasing the field performance of these vehicles have been studied. Traction is one of the main factors limiting the field performance of the modern tractor. The process of developing traction has therefore been investigated by many researchers and although this study has resulted in a better understanding of the mechanics, it has not to any great extent assisted the operator to optimize performance in the field. It was concluded that in order to solve the problem the operator required a control system to maintain the dynamic load and inflation pressure at optimum levels. Work was carried out to develop and evaluate such a system using the Single Wheel Traction Research Vehicle at the USDA's National Soil Dynamics Laboratory in Auburn, Alabama, USA. A computer management system was developed to control the dynamic load, net traction and inflation pressure of the test tyre. During a simulated field operation the system was programmed to cycle the tyre over its operating range of dynamic load and inflation pressure while monitoring tractive efficiency. A tractive efficiency response surface was computed for the particular condition and the surface searched for the dynamic load and inflation pressure levels which resulted in maximum tractive efficiency. The tyre was then controlled and operated at maximum tractive efficiency. Evaluation showed that within the operating range of the tyre, tractive efficiency varied considerably with dynamic load, inflation pressure, net traction and soil condition. The results indicated that a considerable advantage could be obtained by using such an arrangement on a tractor. The system would automatically maximize the tractive efficiency of the tractor under the particular field conditions and with the particular implement being used. Implements could be ballasted and the hitch system used to control the weight transfer to ensure maximum tractive efficiency. Systems such as these would result in a significant improvement in the field performance of the machine and a reduction in management time required to optimize the performance of the tractor implement combination. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1991.

Thesis (M.S.)--Auburn University, 2007. / Abstract. Includes bibliographic references (ℓ. 88-89)

Thesis (M.S.)--Auburn University, 2008. / Abstract. Vita. Includes bibliographical references (p. 83-85).

M.Tech. (Mechanical Engineering) / The dissertation documents the design project of a low cost tractor prototype to be manufactured locally. The design and manufacturing of a South African tractor is part of a larger project namely “Roads for Africa” initiated by the local company Terragrader (Pty) Ltd. The design parameters of the tractor were established based on the power needs of a dirt roads refurbishing machine the “Terragrader” manufactured by the same company. Although the tractor was designed to power the Terragrader machine, it can successfully be used to power different agricultural machines or transport. The designed South African tractor has to be versatile, easy to adapt to different working conditions. The design aim is to produce a tractor able to provide adequate power at a cost of about R500 000, whereas the market offers similar machine at a much higher price starting from about R800 000. The concept of a South African tractor is not new but due to import options, there was never a known / well established South African brand. Due to the shrinkage of the South African mechanical manufacturing industry by nearly 40 % in the last years, a successful tractor design and manufacturing will contribute toward the much needed job creation. Due to its complexity the project is a combination of newly designed parts and outsourced components. The integration of design establishes the layout of the tractor with the aid of virtual 3D solid modeling.

No description available.

Thesis (Ph.D.)(Civil and Biosystems Engineering)--University of Pretoria, 2005. / Includes bibliographical references. Includes bibliographical references. Available on the Internet via the World Wide Web.

Farm equipment is becoming an increasingly important financial asset for many farmers. Tractors probably represent the single largest component of equipment asset value. As such, changes in tractor values can have a dramatic effect on a farmer's financial situation. Changes in equipment value can be attributed to depreciation and the value of output produced. The general objective of this study was to identify a specific set of variables explaining changes in equipment value and to determine the relative importance of these variables. The Box-Cox power transformation technique was employed in estimating the depreciation patterns. The method was applied to two different sources of used tractor prices--auction and advertised. Remaining value (RV), defined as the real market price in time t divided by real purchase price, was regressed against several independent variables. These independent variables were age, usage per year, condition, horsepower, manufacturer, regions of the U.S., auction types, and net farm income. A number of these variables were found to have some important impact on RV. Depreciation patterns were found to differ between manufacturers. Significant differences in remaining values (RV) were found to exist for different regions of the U.S. and different auction types. For both auction and advertised data, an increase in usage produces a noticeable decrease in RV. For auction data, however, the level of usage tends to have greater influence on RV when the tractor is newer. The results did not closely approximate any clear depreciation pattern. The depreciation patterns are accelerated relative to straight-line method and are a combination of the geometric and sum-of-the-year's digits functions. The RV model was used to examine optimal replacement ages for farm tractors. Annual usage levels had the most influence on the age at which tractors were replaced. Expensing and some tax law changes had a less significant impact. / Graduation date: 1989