Manual Gearbox Design Part 1 pot

Alternative types of crown wheel and pinion designs to the widely used Gleason system are covered, that is, Klingelnberg and Oerlikon.. Various types of differential are described along

Manual Gearbox Design

Alec Stokes

Society of Automotive Engineers

Butterworth-Heinemann Ltd

Linacre House, Jordan Hill, Oxford OX2 8DP

C) PART OF REED INTERNATIONAL BOOKS

OXFORD LONDON BOSTON

MUNICH NEW DELHI SINGAPORE SYDNEY

TOKYO TORONTO WELLINGTON

First published 1992

0 Butterworth-Heinemann Ltd 1992

All rights reserved No part of this publication

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Designs and Patents Act 1988 or under the terms of a

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Applications for the copyright holder’s written permission

to reproduce any part of this publication should be addressed

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British Library Cataloguing in Publication Data

Stokes, Alec

Manual gearbox design

I Title

629.244

ISBN 0 7506 0417 4

Library of Congress Cataloguing in Publication Data

Stokes, Alec

Manual gearbox design/Alec Stokes

p cm

Includes index

ISBN 1 56091 256 1

1 Automobiles - Transmission devices - Design and construction

1 Title

TL262.S76 1992

CIP

Typeset by Vision Typesetting, Manchester

Printed and bound in Great Britain

Acknowledgements

The author would like to acknowledge the assistance and back-up given by the following during the preparation of this manuscript:

(a) The Gleason Gear Co., the Oerlikon Co of Switzerland and Klingelnberg of Germany whose representatives have always been willing to supply information and help with any problems that have arisen

(b) Colleagues in the gear and transmission design field and the personnel involved

in research work connected with the gearing industry These include the oil companies, gear machine tool manufacturers and the many universities and research establishments involved The help given by the various metallurgists with whom I have been privileged to work is remembered with gratitude (c) Mrs G Kell, who provided the facility for me to do the writing during my stay with her while working at Lotus

(d) Mr A.C Rudd and Lotus Engineering, who revitalized my interest in gear design by employing me at the ripe old age of 60

(e) The transmission section at Lotus Engineering and the Power Train Director,

Mr H.F Kemp, who have had the faith to back my judgement over the past four and a half years

(f) Finally my family, who have put up with the various pieces of paper left around, which have always been carefully collected and saved Also for the encourage- ment given to keep pushing on and try to achieve the objective that I set myself

VI11

Preface

This book has been written in an effort to put down on paper some of the experience

I have gained during my forty-five years in the transmission design field, thirty-one years of which was designing Formula One gearboxes, and the last five years before retirement with Lotus Engineering as Chief Designer - Transmissions Knowing of

no other book that covered this subject made me more determined to proceed with

it

I have attempted to work through the design procedure in the same order used on the many gearbox designs I have been involved with Alternative types of crown wheel and pinion designs to the widely used Gleason system are covered, that is, Klingelnberg and Oerlikon Various types of differential are described along with interlock systems which prevent the selection of more than one gear at a time It contains a wide coverage of gear failures, their causes and requirements to prevent further failures, together with an engineering understanding of lubrication and its application The book also includes a list of materials along with the heat treatment applied and race-proven in the B.R.M Formula One Racing Transmissions as a guide to the designer

A Stokes

vii

Introduction

The purpose of this book is to provide both the student and young professional design engineer with an overall guide to the amount of work involved in the design of

a manually operated automotive gearbox, and the problems that can be encoun- tered both during the design stages and in operation

I am unaware of any other book which gives such information and at the same time attempts to provide a methodical system of solving what appears to be a fairly straightforward engineering design problem to the majority of people, but often turns into one requiring great care and dedication Otherwise the design can develop into a very complex piece of machinery which is both difficult and expensive to produce and proves incapable of achieving the original objectives that were laid down for the transmission

The purpose of any gearbox or transmission is to provide a drive, which often includes a range of selected intermediate gear ratios, between the power unit and the final source of the drive, whether it is to be used in an industrial, marine or automotive application

In the automotive industry this means the provision of a drive between the engine and the road wheels This drive must be smooth, quiet and efficient and capable of being produced to a strict budget price while proving extremely reliable With the exception of a transversely mounted engine and gearbox unit, the drive will at some point have to change direction through a 90" angle

Starting with the 90" angle drive, this being one of the following types of gear: (a) a pair of straight bevel gears

(b) a pair of spiral bevel gears

(c) a pair of hypoid bevel gears and commonly known as the crown wheel and

this book will attempt to follow the design sequence used by the author during the design of a manually operated automotive gearbox Each of the chapters will deal with a-specific problem which is encountered during the design phases and during operation

pinion

Chapter 1 This chapter begins with a comparison of the merits of spiral bevel gears and hypoid gears when employed as the final drive in the automotive gearbox,

i x

x Introduction

i.e the crown wheel and pinion Then the identification of the hand of spiral of both the spiral and hypoid bevel gears is explained, followed by the recommended hand

of spiral The major portion of the remainder of the chapter gives the details of the

‘Empirical formulae and calculation procedures’ produced by the American Gleason Gear Co for rear axle or final drive units These formulae give the following details:

(a) torque at rear axles, and vehicle performance torque

(b) axle torque, and axle torque from wheel slip

(c) drive pinion torque

(d) stress determination and scoring resistance

The final pages cover the calculation of the crown wheel and pinion ratio and the layout of the initial lines for the gearbox design

These foregoing calculations provide a means of ensuring that the crown wheel and pinion operates satisfactorily relative to its specific environment and is designed with adequate strength to cope with the range of torques involved

Chapter 2 This chapter attempts to describe the process of designing the internal running gear, starting with the range o f internal ratios, the input shaft, the intermediate shaft and the output shaft The formulae for stressing these shafts are given, to enable the size of the shafts to be finalized This is followed by the calculation of the road speed in the various internal ratios, and the selection of the ratios most suited for the particular application The next pages describe various types of gear engagement systems and the need for an interlock system which prevents more than one internal gear being selected at any given time

The final pages cover the various types of differential that can be used, the choice

of bearings and oil seals and finally the type of lubrication system required to suit the application The closing pages also describe the layout of the gearbox internal running gear and the gearbox casing; the situations that the casing must be able to cope with are also described in some detail

Chapter 3 This chapter is totally dedicated to a complete description of the lubrication of gears Starting with a brief history of the many dramatic changes that have been made in the lubrication of gears and lubrication in general engineering in the past few years, the various methods used to apply lubricant to gears are listed and explained The problems of applying lubricant to the various types of gear, with the varying characteristics in the way in which the teeth of the mating gears move relative to each other, are also covered in some detail This is followed by some advice on the type of lubrication to be chosen from the varying applications relative

to the type of gear form and the pitch line speed Then the loss in efficiency due to excess or inadequate lubrication is analysed The final pages look at different types

of lubricant used in gear drives

Chapter 4 This chapter is dedicated to all the various forms of gear failure that can

be encountered by the engineer where gear trains are concerned In the examination

of the failures, the varying reasons or causes of failure, along with suggested remedies, are listed

(a) complete fracture of the gear tooth, usually occurring at the root of the tooth The failures in any gear train fall into one of two forms, as follows:

which breaks away in one whole section

Introduction xi

(b) damage or destruction of the working or mating faces of the gear teeth The factors which either individually or as a combination result in the above failures are listed, before the identification of the failures and their respective remedies

Chapter 5 The different forms of crown wheel and pinion that are available to the designer are discussed in this chapter The three forms are:

(a) the Gleason system, produced by the Gleason Gear Co of America

(b) the Oerlikon system, from the Oerlikon Co of Switzerland

(c) the Klingelnberg system, introduced by the German company, Klingelnberg The differences between the three methods are discussed, together with a general description of the forces created when a pair of spiral bevel gears run together The movement of the tooth contact pattern as the load applied to the gear increases is also discussed The final pages of the chapter give a brief description of, and the calculations for, the manufacturing and inspection dimensions for a pair of Klingelnberg palloid spiral bevel gears

Chapter 6 The design features, the production features and the calculation of the manufacturing and inspection dimensions for a pair of Oerlikon cycloid spiral bevel gears are given in the early part of this chapter The latter part advises the designer of the varying stages which are usually covered by the design, production and development departments prior to the introduction of a new transmission onto the market, and emphasizes the co-operation necessary between these departments if the product is to be successful

Chapter 7 This final chapter covers the design of a racing-type rear engine mounted gearbox The opening pages deal with the aims of the gearbox and the reasons for each of the aims Following this, the design procedures for the internal gear pack are discussed, along with the arrangements of the various shafts This covers the location of the shafts, together with their supporting bearings Different layouts and bearing location methods for the crown wheel and differential are covered, as are the methods used to locate these assemblies and some of the problems that can be encountered with them This is followed by a listing and brief description of the varying types of differential units that are used in racing gearboxes

Having discussed the ‘in-line’ layout for the internal gear pack, the next few pages describe a transverse gearbox layout where the internal gear pack lies across the car chassis The problems of internal ratio changing with the transverse gearbox layout are discussed, along with the major problem which can affect the overall car performance, namely a simple and positive gear change system that can be fitted and adjusted so that the driver is able to make quick and totally reliable gear change movements

Following the section giving details of these problems, the advantages of using a

transverse gearbox are listed, together with the practical reasons for these advantages This is followed by a description of the gear change systems t h a t have been utilized in the past, along with the arrangements of the selector forks that give the quickest gear change movements An interlock system that prevents the

selection of more than one gear at a time is an essential part o f the gear cl~anpc

xii Introduction

system As well as covering the positive location of the selector dog rings, various

systems that have been used are listed

The later part of this chapter, having arrived at a preliminary design and layout for the gearbox internals, deals with the problems that can be encountered with the lubrication system and various methods that are used to cope with the high speeds and heavy tooth loads involved The design of the gearbox casings and the detailing

of each component part ready for manufacture are given in the final pages, along with a guiding list of materials that the author used for the various components during his thirty or so years’ involvement in the design of Formula One racing gearboxes

Contents

Preface

Acknowledgements

Introduction

1 Crown wheel and pinion

Torque at rear axles

Vehicle performance torque

Axle torque (from maximum engine torque through the lowest

Axle torque - from wheel slip

Drive pinion torque

Stress determination and scoring resistance

Bending stress

Contact stress

gear ratios)

2 Internal running gear

Shaft stressing for size

Input shaft

Intermediate shaft

Output shaft

Internal gears

Lubrication system

Gear engagement

Interlock system

Reverse gear

Differential

Bearing arrangement and casing

3 Lubrication of gears

Principles of gear lubrication

Group A

Spur gears

Helical gears

vii

ix

V l l l

1

4

5

16

16

19

19

19

20

22

22

26

27

27

30

33

36

36

36

37

vi Contents

Bevel gears

Crossed helical gears

Worm gears

Hypoid gears

Tests for lubricating oils

Group B

4 Gear tooth failures

Gear tooth failure

Tooth fracture

Tooth surface failures

5 Crowa wheel and pinion designs

Klingelnberg palloid spiral bevel gear calculations

Basic conception

Terminology

Bevel gear calculations

‘0’-bevel gears

Bevel gear V drives

Tooth profiles

Gear blank dimensions

Formulae for the determination of the external forces

Strength of teeth

Rules for the examination of the tooth profile by the

graphic method

Example of spiral bevel gear design

6 Oerlikon cycloid spiral bevel gear calculations

Design features

Production features

Gear calculation with standard En cutters

Strength calculation

7 Gearbox design - rear-engined racing cars

Basic aims

In-line shaft arrangement

Internal gear arrangement

Face-dog selectors

Bearhg arrangement

Crown wheel and pinion layout

Differential location and type

Transverse-shaft arrangement

Selector system

Selector interlock system

Lubrication method

Gearbox casing

Materials guide

38

38

39

39

40

46

50

52

53

54

61

66

66

67

67

80

82

83

84

88

96

100

106

113

113

113

117

1 30

134

134

135

137

137

139

141

143

148

150

152

155

157

158

Index 161