ictionary of
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`Second Edition
`
`UCUVe
`gineering
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`Dictionary of
`Automotive Engineering
`
`Second Edition
`
`Don Goodsell
`CEng, MIMechE, MSAE
`
`Society of Automotive Engineers, Inc.
`Warrendale, Pa.
`
`Oxford
`Singapore
`
`Butterworth-Heinemann
`New Delhi
`London’
`Boston Munich
`Sydney
`Tokyo
`Toronto Wellington
`
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`First published 1989
`Paperback edition 1991
`Second edition 1995
`
`Copyright © 1989, 1995 D.L. Goodsell
`
`Printed and bound in the United States of America.
`
`
`Butterworth-Heinemann Ltd
`Linacre House, Jordan Hill, Oxford OX2 8DP
`
`A memberof the Reed Elsevier plc group
`
`British Library Cataloguing in Publication Data
`A cataloguerecord for this bookis available from the British Library
`
`Butterworth-Heinemann ISBN 0 7506 2795 6
`
`All rights reserved. No part ofthis publication may be reproduced in any material form (including photo-
`copying orstoring in any medium by electronic means and whetheror nottransiently or incidentally to
`some other use of this publication) without the written permission of the copyright holder except in
`accordance with the provisions of the Copyright Designs and Patents Act 1988 or underthe terms of a
`license issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London, England WIP
`QHE.Applications for the copyright holder’s written permission to reproduceany part of this publication
`should be addressed to the publishers.
`
`Society of Automotive Engineers, Inc.
`400 Commonwealth Drive, Warrendale, PA 15096-0001
`Phone: (412) 776-4841
`Fax: (412) 776-5760
`
`Library of Congress Cataloging-in-Publication Data
`
`Goodsell, Don.
`Dictionary of automotive engineering / Don Goodsell. -- 2nd
`ed.
`
`cm.
`p.
`ISBN 1-56091-683-4 (hardcover)
`1. Automobiles--Dictionaries.
`I. Title.
`TL9.G64 1995
`629.2’03--dc20
`
`95-32289
`CIP
`
`SAE ISBN 1-56091-683-4
`
`Permission to photocopyfor internal or personal use,or the internal or personal use of specific
`clients, is granted by SAEforlibraries and otherusers registered with the Copyright Clearance
`Center (CCC), provided that the base fee of $.50 per page is paid directly to CCC, 222 Rose-
`wood Dr., Danvers, MA 01923. Special requests should be addressedto the SAE Publications
`Group. 1-56091-683-4/95 $.50.
`
`Cover photo reproduced with permission of Chrysler Corporation (1995 Dodge Avenger).
`
`SAE Order No. R-159
`
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`U
`
`U-engine Two-stroke engine in which twoparallel pistons are driven by one crank,
`and therefore movein the samedirection for most of the cycle. Sometimescalled
`split-single. A variant ofthis type, the Puch engine, has a Y-shaped connecting
`rod rather than two separately pivoted rods.
`
`unburned hydrocarbons Unburned or incompletely burned products of engine com-
`bustion, particularly as released to the atmosphere as an exhaust emission. Also
`HC; THC.
`
`underbody (1) The bodystructure of the underside of a vehicle including floor,
`wheelwells and stiffening members. (2) The underneath of a vehicleorits effec-
`tive profile, particularly in an aerodynamic context.
`
`underbody flow The flow of air under a moving vehicle, and the aerodynamic
`characteristics thereof.
`
`underbumperapron See apron.
`
`undercarriage The wheels, axles and suspension system of a vehicle, but particu-
`larly of a commercialvehicle.
`
`undercoating (UK: underseal) Heavy protective coating applied to the underside
`of a vehicle to resist corrosion and damage from roadstone impact, and to reduce
`noise transmitted from underthe vehicle.
`
`undercrown Theunderside of a piston crown. See Figures C.6 and P.2.
`
`underhood (1)The engine compartment. (2) (UK: bonnet) The engine and ancil-
`lary equipmentlocated underthe hood.
`
`underrunprotection Transverse structure attached to the rear of a commercial ve-
`hicle chassis to prevent a smaller impacting vehicle from running underthe chas-
`sis.
`
`underscreen See undershield.
`
`underseal See undercoating.
`
`undershield Panelling under an engine compartment, or the whole underside of a
`car. Also underscreen.
`
`underslung worm transmission Worm and worm wheelfinal drive in which the
`worm is set below the worm wheel, giving a low propeller shaft. See alsooverslung
`worm transmission.
`
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`undersquare engine Engine havingalarger stroke than cylinder bore diameter.
`understeer (1) Responseof a vehicleif the ratio of steering wheel angle gradient to
`overallsteeringratio is more than the Ackermannsteer angle gradient. (2) Under-
`responseto steering input, as by generation of excessive slip angle on front wheels.
`(3) Responseof vehicle to steering input characterized by an incrementalincrease
`in yaw rate which necessitates an increasein steer angle to maintain the intended
`radius of turn. See Figure U.1.
`
`ty Direction of
`
`“Fayr& Bleangle
`
`Centrifugal
`
`
`
`
`Figure U.1 Diagrammatic representation of understeer, showing the actual center of turn
`comparedwith the geometric center of turn that would prevail at low speed.
`
`Centre
`of turn
`
`undertread Reinforcing plies laid beneaththetread ofa tire.
`
`uniflow scavenging System of scavengingin two-strokeengines in whichthefresh
`mixture enters the cylinder at one end while the exhaustgases leave through valves
`or ports at the other.
`
`unit fuel injector Assembly which receives fuel at supply pressure andis then actu-
`ated by an engine mechanism to meterandinject the fuel charge into the engine
`combustion chamber.
`
`unit pump Injection pumpcontaining a single pumping element operated by an
`engine cam. Mainly used on marineengines.
`unitary construction (US: unitized construction) (1) Of a vehicle drive system,
`the construction of engine, clutch and gearbox to form onerigid unit, though
`enabling each individual item to be detached.
`(2) Monocoqueorchassis-less
`structure of a vehicle body.
`
`universal joint Rotating shaft coupling that permits angular axial displacement.
`Sometypeswill also operate with linear misalignmentof axes. See also Bendix-
`Tractajoint, Bendix- Weissjoint Cardan shaft; constant-velocityjoint; Hooke’s
`Joint, Layrubjoint; Rzeppajoint.
`
`229
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`Unladen Weight Weightof vehicle (usually a commercial vehicle) normally under-
`stood to include driver and passengerand all service ancillaries, but without pay-
`load.
`
`unleaded gasoline Gasoline which has no added lead alkyls as octane improvers,
`but may nevertheless contain a specified very low maximum amountoflead. See
`also lead-free.
`
`unloader valve Valve that controls or limits air pressure in a pneumatic control
`system such as a commercial vehicle air brake system, usually by exhausting ex-
`cess air to atmosphere. Also governor valve. See also check valve; pressure
`protection valve.
`
`unsprung mass (1) Massof a vehicle undercarriage below the springs. (2) Mass of
`vehicle components not carried by the suspension system.
`In somedefinitions
`half the spring and dampermassis included.
`
`unsprung weight Unsprung massexpressedin gravitational units. Loosely used as
`a synonym for unsprung mass.
`
`updraft carburetor (UK: updraught carburettor) Carburetor in which the in-
`ducted air flows upward pasta jet, usually centrally located in a venturi. See
`Figure C.3.
`
`upper beam The main or driving beam of a headlamp.
`
`upper deadcenter See top dead center.
`
`urban cycle Driving test cycle that simulates driving conditionsin a typical urban
`area.
`
`ute A light commercial or utility vehicle. A pick-up truck. (Australian slang)
`
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