The mechanics of tractor-implement performance: theory and worked examples: a textbook for students and engineers

Abstract

This book, for engineers and engineering students, is about the functional performance of agricultural tractors - how, and how well, they perform the function for which they are designed - pulling loads. It is not about construction, operation or management but about performance and the factors that determine it. Because it treats the tractor in terms of the fundamentals of the subject, it is not limited to any type or size or make. This book is written for professional agricultural engineering courses or equivalent subjects for mechanical engineers. It could also form the basis for short courses for practicing engineers. It assumes a 2nd year level of engineering science. The book develops the subject of tractor performance through the common alternative techniques used in engineering analysis:

- ideal (theoretical, simple mechanics)

- experimental (ideal [firm surface], measurement based)

- theoretical (soft surface)

- empirical (soft surface).

This has an incidental didactic purpose that is lost when authors move from one analytical technique to another without any explanation. The book takes the student/reader through a number of stages from the simple to the more complex, from elementary mechanics of the tractor alone to that for the tractor when attached to an implement. One of the most significant features of the book is that it treats performance in quantitative terms and illustrates this with many associated graphs. These enable the reader to obtain a picture of the relationships that is not possible in a merely descriptive or numerical presentation. The tractor on which the book is based was a typical but actual (30+ kW) tractor (now out of production). It is only used to illustrate the principles being explained and thus follows a well accepted engineering approach. The book is basically analytical but its connection with the ‘practical’ is through the worked examples and the problems with answers given through the text.

Chapter 1 gives an outline of the subject, a justification for its study and an overview of the main systems in the power train of both the conventional and two wheeled tractor. The analysis of performance starts in Chapter 2 with the engine performance as a ‘given’ and extends this, via a simple mechanical analysis, to give the ideal performance of the tractor. The results of tests that are performed by the testing stations following procedures such as those used by the OECD are presented graphically and explained in Chapter 3. This approach is shown to confirm (within appropriate limits) the analysis presented in Chapter 2. Chapters 4 and 5 treat both traction theory (Bekker, Reece etc) and empirical analysis (Wismer, Dwyer etc) in terms of the relevant parameters. Both are required for students to understand the subject and to break into the extensive research literature based on these analyses. Chapter 6 on chassis mechanics covers the fundamentals of the subject appropriate to tractor performance and includes material that has not previously been published in a readily accessible form. In Chapter 7 all of the factors that determine tractor performance are brought together and their relevance to the selection of a tractor to match an implement and their efficient operation, in terms of performance, are illustrated. Chapter 8 (combined with Chapter 7) contains a series of general problems.