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Commercial Vehicle Technology Michael Hilgers Transmissions and Drivetrain Design Second Edition Commercial Vehicle Technology Series Editor Michael Hilgers, Weinstadt, Baden-Württemberg, Germany Michael Hilgers Transmissions and Drivetrain Design Second Edition Michael Hilgers Daimler Truck Stuttgart, Germany ISSN 2747-4046 ISSN 2747-4054 (electronic) Commercial Vehicle Technology ISBN 978-3-662-65859-8 ISBN 978-3-662-65860-4 (eBook) https://doi.org/10.1007/978-3-662-65860-4 © Springer-Verlag GmbH Germany, part of Springer Nature 2021, 2023 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. Responsible Editor: Markus Braun This Springer Vieweg imprint is published by the registered company Springer-Verlag GmbH, DE, part of Springer Nature. The registered company address is: Heidelberger Platz 3, 14197 Berlin, Germany Preface For my children Paul, David and Julia, who derive just as much pleasure from trucks as I do, and for my wife, Simone Hilgers-Bach, who indulges us. I have worked in the commercial vehicle industry for many years. Time and again I am asked, “So you work on the development of trucks?” Or words to that effect. “That’s a young boy’s dream!” Indeed it is! Inspired by this enthusiasm, I have tried to learn as much as I possibly could about the technology of trucks. In the process, I have discovered that one has not really grasped the subject matter until one can explain it convincingly. Or to put it more succinctly, “In order to really learn, you must teach.” Accordingly, as time went on I began to write down as many technical aspects of commercial vehicle technology as I could in my own words. This booklet takes a look at the transmission and the drivetrain. While writing the text, my overriding intention was to describe the technical solutions that are commonly used at the time of printing in a way that can be clearly understood. Readers who are studying this subject (students and technicians) will find this booklet to be a good entry point and as a result, may discover that commercial vehicle technology is also a fasci- nating field of work for them. I further believe that this booklet will also be of value to technical specialists in related disciplines, who are interested in applications beyond their area of expertise, and are looking for a concise, easily comprehensible overview. In this second edition of this booklet some improvements were made to the text and some extensions have been made to make the text even more valuable for the readers. The most important objective of the text is to convey the fascination of truck technology to the reader and to make it an enjoyable exercise. With this in mind, I hope that you, dear readers, have much pleasure reading, skimming and browsing this booklet. Finally, I have a personal favor to ask. It is important to me that this work should continue to be expanded and refined. Dear reader, I would greatly welcome your help in v vi Preface this regard. Please send any technical comments and suggestions for improvements to the following email address: [email protected]. The more specific your comments are, the easier it will be for me to grasp their implications, and possibly incorporate them in future editions. If you discover any inconsistencies in the content or you would like to express your praise, please let me know via the same email address. And now I wish you much enjoyment reading about transmissions. Weinstadt-Beutelsbach Michael Hilgers Beijing Aachen June 2022 Contents 1 Transmissions and Drivetrain Design ................................ 1 1.1 Design of the Drivetrain ........................................ 2 1.1.1 Driving Resistance ...................................... 2 1.1.2 Transmission and Final Drive are Torque—and Rotational Speed Converters .............................. 4 1.1.3 The Real Engine and the Transmission Ratio ................. 4 1.1.4 Traction Limit ......................................... 8 1.1.5 Drivetrain Design for Braking ............................. 8 1.2 Drivetrain Design for Electric Trucks ............................. 9 2 Transmission .................................................... 11 2.1 Main Transmission ............................................ 13 2.1.1 Internal Gearshift System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 2.1.2 Reverse Gear .......................................... 17 2.1.3 The Wheel Diagram ..................................... 17 2.1.4 Design Concept of the Spur Gear System .................... 17 2.1.5 The Gear Ratio ......................................... 19 2.1.6 Losses in the Transmission ............................... 20 2.2 The Split Group .............................................. 21 2.3 Planetary Transmission or Epicyclic Gear System ................... 22 2.4 The Range Group ............................................. 24 2.5 Range-Splitter Gearbox ........................................ 25 2.6 External Gearshift System ...................................... 29 2.6.1 Automated Manual Transmissions .......................... 29 2.7 Automatic Transmission ....................................... 32 2.8 Power Take-Offs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 2.9 The Transfer Case ............................................ 33 vii viii Contents 3 The Clutch ...................................................... 37 3.1 The Friction Clutch ........................................... 37 3.2 Hydrodynamic Clutches and Converters ........................... 39 3.2.1 Clutch Concepts for Heavy Goods Transportation ............. 41 4 Propeller Shaft(s) ................................................ 43 5 Retarders ....................................................... 45 5.1 Secondary and Primary Retarder ................................. 45 5.2 Hydrodynamic Retarders ....................................... 46 5.2.1 Coolant Retarders ....................................... 47 5.3 Inductive Retarders ........................................... 47 5.3.1 Retarders with Permanent Magnets ......................... 47 5.3.2 Retarders with Electromagnets ............................ 48 Comprehension Questions ............................................ 49 Abbreviation and Symbols ............................................ 51 References ......................................................... 53 Index .............................................................. 55 1 Transmissions and Drivetrain Design The task of the transmission, clutch and propeller shaft is to transmit the mechanical motion of the engine to the axle and the wheels. These components also perform other essential functions. The motion of the engine must be converted. The rotating speed of the combustion engine, at any given time is usually not the same as the desired rotating speed of the wheel; and the engine torque must be converted to supply the propulsive force required at the wheel. This task of converting the rotational speed and torque is car- ried out by the transmission. The transmission also makes it possible to reverse the direction of rotation of the wheels, which means the transmission enables the vehicle to travel forwards and backwards. Power take-offs and wear-free continuous brakes—also called retarders—often engage with the transmission as well to receive drive force (in the case of the power take- off) or to deliver brake force to the wheels (in the case of the retarder). The transmission also has a neutral position in which the engine and the drivetrain are mechanically decoupled in the transmission. The clutch is positioned between the engine and the transmission. The clutch discon- nects and connects (couples) the engine from/to the transmission. This disconnection is necessary for starting the engine, the stopping operation and for shifting gears in the transmission. Upon startup, the combustion engine has great difficulty keeping itself running, so the rest of the drivetrain that offers resistance to the rotation of the engine is uncoupled by the clutch. When the vehicle comes to a standstill, the engine continues running at idle speed. So in order to actually bring the vehicle to a standstill, the engine must be disconnected by the clutch. The clutch is also needed for shifting gears in the conventional transmission. Because in order to change gears while driving, there must be no load on the transmission gears. The engine torque must be decoupled so that the gear wheels can be disengaged from each other; for this, the clutch must be opened. © Springer-Verlag GmbH Germany, part of Springer Nature 2023 1 M. Hilgers, Transmissions and Drivetrain Design, Commercial Vehicle Technology, https://doi.org/10.1007/978-3-662-65860-4_1 2 1 Transmissions and Drivetrain Design The propeller shaft is flange-mounted on the transmission output. It transmits the rotating motion to the axle. It also allows the engine-transmission unit to move relative to the axle. The engine, transmission and clutch typically form a permanently bolted block that is suspended within the vehicle frame. Apart from the small amount of play the elastomer mounts for the engine and transmission have, the engine and transmission are fixed on the frame. But the axle moves significantly relative to the vehicle frame as part of the suspension process. This results in a relative motion between the axle and the transmission, which is compensated by the propeller shaft. In the conventional vehicle (without a transfer case), the second flange of the propeller shaft is attached to the final drive input. The purpose of the final drive is to rotate the axis of rotation of the rotating parts by 90°. In trucks, the engine crankshaft, the transmission shafts and propeller shaft rotate about axes that extend approximately in line with the longitudinal direction of the vehicle—the longitudinal axis of the vehicle is usually referred to as the x-axis. On the other hand, the wheels rotate about an axis perpen- dicular to the direction of travel, which is referred to in the industry as the y-axis. The functions of the axle with the final drive and the differential are described in detail in [3]. Depending on the vehicle design, the drivetrain also includes other elements, such as the transfer case, the other drive shafts required by the transfer case, power take-offs and wear-free brake elements. Figure 2.18 illustrates the components of a complex drivetrain in an 8 8 vehicle. × 1.1 D esign of the Drivetrain An immense variety of requirements are considered when configuring the drivetrain such as service life, weight and so on. But above all, the drivetrain must be designed so that it satisfies the basic requirement of enabling the vehicle to overcome driving resistance. 1.1.1 D riving Resistance The force required to overcome total driving resistance: FDriving resistance = FAir + FRoll + FHill (1.1) Driving resistance comprises a weight-dependent component that is required to overcome the gradient, weight-dependent rolling resistance and it comprises the speed-dependent aerodynamic drag. If the corresponding mathematical terms are inserted, the following formula is obtained for motion resistance: