Springer Series in Solid and Structural Mechanics 12 Vincenzo Vullo Gears Volume 3: A Concise History Springer Series in Solid and Structural Mechanics Volume 12 Series Editors Michel Frémond, Rome, Italy Franco Maceri, Department of Civil Engineering and Computer Science, University of Rome “Tor Vergata”, Rome, Italy The Springer Series in Solid and Structural Mechanics (SSSSM) publishes new developments and advances dealing with any aspect of mechanics of materials and structures, with a high quality. It features original works dealing with mechanical, mathematical, numerical and experimental analysis of structures and structural materials, both taken in the broadest sense. The series covers multi-scale, multi-field and multiple-media problems, including static and dynamic interaction. It also illustrates advanced and innovative applications to structural problems from science and engineering, including aerospace, civil, materials, mechanical engineering and living materials and structures. Within the scope of the series are monographs, lectures notes, references, textbooks and selected contributions from specialized conferences and workshops. More information about this series at http://www.springer.com/series/10616 Vincenzo Vullo Gears Volume 3: A Concise History 123 Vincenzo Vullo University of Rome “Tor Vergata” Rome, Italy ISSN 2195-3511 ISSN 2195-352X (electronic) Springer Series in Solid and Structural Mechanics ISBN 978-3-030-40163-4 ISBN 978-3-030-40164-1 (eBook) https://doi.org/10.1007/978-3-030-40164-1 © Springer Nature Switzerland AG 2020 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland Aphorism Historia est testis temporum, lux veritatis, vita memoriae, magistra vitae, nuntia vetustatis. (History is the witness of the times, the light of truth, the life of memory, the teacher of life, the messenger of antiquity) Marcus Tullius Cicero, De Oratore, 2.36 v To my wife Maria Giovanna, my sons Luca and Alberto, my nephew Nicolò and my students Preface Gears and gear drives are among the oldest artificial mechanisms invented by man. Rudimentary geared mechanisms, to be considered as the distant predecessors of the current gears, were in fact designed and built after the introduction of the potter’s wheel, and therefore almost certainly in times that blend with the mists of prehistory. Their evolution, from their introduction to today, has not been constant over time. It has been characterized by periods of acquisition of empirical knowledge, through the accumulation of field experiences, and scientific knowl- edge, through scientific theories and scientific methods. The set of acquired knowledge has led to the current gears, which today play an irreplaceable role in power mechanical transmissions with constant transmission ratio as well as in traditional, semi-automatic and automatic geared transmissions for motor vehicles, mechanical and electric industry, wind turbine generators, aerospace industry, especially the helicopter industry, etc. This is due to their extreme versatility and reliability of use. Gears and gear drives in fact allow to solve any practical problem within speed and power ranges that effectively meet the various needs that may arise, even in the most advanced current technology areas, and in those reasonably foreseeable for the future. In the first two volumes of this monothematic treatise on gears, entitled Gears, we discussed the main aspects concerning their design, namely in Vol. 1, the geometric and kinematic design of the various types of gears most commonly used in practical applications, also considering the problems concerning their cutting processes; in Vol. 2, various strengths’ problems of the gears and their load carrying capacity under actual working conditions, also providing the theoretical basis for a better understanding of the calculation relationships of the ISO standards. In order to provide a more complete picture of gears, including their evolution over time, we considered it useful and appropriate to also write a brief history of the same gears, which is the subject of this third volume. As the title of this book indicates, this is a brief history of gears. The historical information provided in this volume is in fact reduced to the essential one, nec- essary to provide the curious reader with news on the main stages of gear devel- opment and related knowledge, from the beginning of the history of the ix x Preface technological man to the present day. Therefore, this volume does not claim to provide a complete picture of the historical development of the gears, for which a specific encyclopedia would be necessary. It is intended only to provide an exhaustive picture of the most significant milestones that determined and continue to determine the current state of knowledge about gears. The first archeological evidences and the first historical documents concerning the beginning of the path of knowledge on gears are certainly to be traced back in the mists of ancient times. The first scientific contributions on gears are to be ascribed to the first two centuries of Hellenism. Further scientific knowledge was acquired, after the long medieval night, starting from the late sixteenth century, with an exponential pro- gression in the twentieth century and at the beginning of this third millennium. Nevertheless, in the current state of knowledge, which is remarkable, the path of knowledge concerning gears cannot be considered concluded. Large dark areas of knowledge still exist on the gears, to be considered as real black holes. The knowledge still to be acquired concerns not only those specificto the numerous disciplines involved in gear design (geometry and kinematics; static and dynamic loads, including those due to impact; friction and efficiency; dynamic response and noise emission; static and fatigue tooth root strength; contact stresses and surface fatigue durability; nucleation of fractures of any kind and their prop- agation until breakage; full film, mixed and boundary lubrication; scuffing and wear; materials and heat treatments; new materials; cutting processes and other manufacturing processes; etc.), but also those arising from their mutual interactions. Other important challenges are those related to the new fields of application (see, e.g., those related to the helicopter and aerospace industry and wind power gen- erators), which require the introduction and design of new types of gear drives that are not reflected in the current technological landscape. Another important chal- lenge is the one concerning the formulation of a unified scientific theory of gears, able to simultaneously consider the geometric–kinematic aspects and those of strength and load carrying capacity. The scholars of vaunted credit, who claim to know everything and to be able to speak or write about any subject, and who boast or attribute themselves knowledge in any field, consider the gears as a synonym of obsolescence, a symbol of the past or, when they are benevolent, a nineteenth-century old stuff. This way of thinking of those we have benevolently referred to as scholars of vaunted credit (no one can therefore accuse this author of not being kindly gentlemen) implies at least the ignorance of the historical evidence that the theory of the gears, considered as mechanisms, is much older, having it characterized the birth of science, in the first Hellenism (see Chap. 3). But the unjustified conviction of these so-called scholars hides a far more serious ignorance. In fact, they prove not to know that the most significant contributions for the calculation of the load carrying capacity of the gears were brought gradually in the entire twentieth century (with the exception of Lewis, 1892—see references in Chap. 3) and that in this beginning of the third millennium, new and equally significant contributions of high scientific value appeared and continue to appear at the horizon (see, e.g., Chaps. 10 and 11 of Vol. 2). Preface xi On the contrary, the true scholars and experts of gear power transmissions are well aware that the gears were yesterday, continue to be today and for a long time yet will continue to be an ongoing scientific and technological challenge. Even today, surely it is worth investing significant financial resources, in terms of manpower, tools and means, in R&S activities on this important area, as all the technologically advanced countries continue to do. This depends on the fact that the gears are a very complex multidisciplinary field, as few in mechanical engineering, and knowledge still be acquired are numerous. We can affirm, without fear of being denied, that gears are the result of ancient knowledge in continuous updating. For the development of new knowledge and new scientific theories concerning any subject, it is necessary to know everything that has been done in the past on the same subject, because who has no past has neither present nor future, because he has no memory.