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Manual Gearbox Design Manual

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Manual Gearbox Design
A. Stokes
172 pages

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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 encountered 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 pinion.

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.


1 Crown wheel and pinion
Torque at rear axles
Vehicle performance torque
Axle torque (from maximum engine torque through the lowest gear ratios)
Axle torque - from wheel slip
Drive pinion torque
Stress determination and scoring resistance
Bending stress
Contact stress

2 Internal running gear
Shaft stressing for size
Input shaft
Intermediate shaft
Output shaft
Internal gears
Lubrication system
Gear engagement
Interlock system
Reverse gear
Bearing arrangement and casing

3 Lubrication of gears
Principles of gear lubrication
Group A
Spur gears
Helical gears
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 Crown wheel and pinion designs
Klingelnberg palloid spiral bevel gear calculations
Basic conception
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
Bearing arrangement
Crown wheel and pinion layout
Differential location and type
Transverse-shaft arrangement
Selector system
Selector interlock system
Lubrication method
Gearbox casing
Materials guide