Page 114 - Automotive Engineering

5.1
Chapter 5.1

Transmissions and driveline

Julian Happian-Smith

The aims of this chapter are to: a specific model would also be difficult to justify even for
demonstrate the need for transmission design and a large vehicle manufacturer.
matching; Current developments are extremely interesting as
give examples of common gearboxes and transmis- technology, particularly electronic control, is very much
sions available for vehicle design; blurring the distinction between the conventional classes
indicate the terminology and methods for transmis- of transmission. For example, automatic transmissions
(ATs) are often found now with a manual override
sion design; function to allow the car to be driven using the gears
aid the designer to understand the elements of the selected by the driver. Conversely, manual gearboxes are
analysis of transmission systems.
having automation added to operate the clutch or shift
the gears. These developments not only make the
5.1.1 Introduction transmission interesting from an engineering perspective,
but also create marketing features from an area of the
vehicle often hidden from view and largely ignored by the
This section introduces the transmission systems that can buyer until it causes a problem.
be found in today’s passenger car. Of course, many car-
derived components and systems can also be found in
small commercial vehicles. Also, larger derivatives, which 5.1.1.1 Definitions
have much in common, can be found in heavy goods
and public service vehicles. We have endeavoured to Transmission – This term can be used to describe one
introduce the main transmission types and some areas of unit within the driveline of a vehicle, often the main
technology that can be found within the units. In this gearbox, or as a general term for a number of units.
chapter, however, we can only hope to introduce the Driveline – This includes all ofthe assembly(s) between
subject of transmissions to you. In order to make up for the output of the engine and the road wheel hubs.
this brevity, we include references to other material so you Powertrain – Essentially the driveline and engine to-
are able to follow up any particular subject in greater gether, and may also be taken to include other related
detail. parts of the vehicle such as the exhaust or fuel system.
It is probably worth stating that, in practice, the Automatic transmission – ATs come in various forms
choice of transmission units for a particular vehicle is but have the common ability to change the ratio at
heavily influenced by what is in production and available. which they are operating with no intervention from the
The cost of developing and, more importantly, installing driver.
the equipment to manufacture a new gearbox would be Manual transmission – As the name suggests, drivers
prohibitive for a small specialist vehicle manufacturer. have to change the gear ratio setting rather than the
Equally, producing a special transmission to support transmission doing the job for them.

Introduction to Modern Vehicle Design; ISBN: 9780750650441
Copyright Ó 2001 Julian Happian-Smith. All rights of reproduction, in any form, reserved.