Advanced vehicle technology
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- 1. Advanced Vehicle Technology
- 2. To my long-suffering wife, who has provided sup-port and
understanding throughout the preparationof this book.
- 3. AdvancedVehicle TechnologySecond editionHeinz Heisler MSc.,
BSc., F.I.M.I., M.S.O.E., M.I.R.T.E., M.C.I.T., M.I.L.T.Formerly
Principal Lecturer and Head of Transport Studies,College of North
West London, Willesden Centre, London, UKOXFORD AMSTERDAM BOSTON
LONDON NEW YORK PARISSAN DIEGO SAN FRANCISCO SINGAPORE SYDNEY
TOKYO
- 4. Butterworth-HeinemannAn imprint of Elsevier ScienceLinacre
House, Jordan Hill, Oxford OX2 8DP225 Wildwood Avenue, Woburn, MA
01801-2041First published by Edward Arnold 1989Reprinted by Reed
Educational and Professional Publishing Ltd 2001Second edition
2002Copyright # 1989, 2002 Heinz Heisler. All rights reservedThe
right of Heinz Heisler to be identified as the author of this work
has beenasserted in accordance with the Copyright, Designs and
Patents Act 1988No part of this publication may be reproduced in
any material form (includingphotocopying or storing in any medium
by electronic means and whetheror not transiently or incidentally
to some other use of this publication) withoutthe written
permission of the copyright holder except in accordance with
theprovisions of the Copyright, Designs and Patents Act 1988 or
under the terms ofa license issued by the Copyright Licensing
Agency Ltd, 90 Tottenham Court Road,London, England W1T 4LP.
Applications for the copyright holders writtenpermission to
reproduce any part of this publication should be addressedto the
publishersWhilst the advice and information in this book are
believed to be true andaccurate at the date of going to press,
neither the authors nor the publishercan accept any legal
responsibility or liability for anyerrors or omissions that may be
made.Library of Congress Cataloguing in Publication DataA catalogue
record for this book is available from the Library of CongressISBN
0 7506 5131 8 For information on all Butterworth-Heinemann
publications visit our website at www.bh.comTypeset by Integra
Software Services Pvt. Ltd, Pondicherry,
Indiawww.integra-india.comPrinted and bound in Great Britain
- 5. ..........................................1 Vehicle
structure................................................................1.1
Integral body construction1.2 Engine, transmission and body
structures..............................................................................................................................1.3
Fifth wheel coupling
assembly............................................................1.4
Trailer and caravan drawbar
couplings..............................................................1.5
Semi-trailer landing
gear..............................................................
system1.6 Automatic chassis
lubrication...................................... clutch2
Friction........................................................2.1
Clutch fundamentals2.2 Angular driven plate cushioning and
torsional damping
..............................................................................................
2.3 Clutch friction materials2.4 Clutch drive and driven member
inspection
............................................................................................................2.5
Clutch
misalignment.................................................................
clutch2.6 Pull type diaphragm
.....................................................................
clutch2.7 Multiplate diaphragm type
.................................................................
clutch2.8 Lipe rollway twin driven plate2.9 Spicer twin driven
plate angle spring pull type
clutch.................................................................................................
brake2.10 Clutch (upshift)2.11 Multiplate hydraulically operated
automatic transmission clutches
............................................................................
clutch2.12 Semicentrifugal
...................................................................
clutch 2.13 Fully automatic
centrifugal..............................................................2.14
Clutch pedal actuating mechanisms2.15 Composite flywheel and
integral single plate diaphragm
clutch.................................................................................3
Manual gearboxes and
overdrives...................................................................gearbox3.1
The necessity for a3.2 Five speed and reverse synchromesh gearboxes
......................................................................................................3.3
Gear synchronization and engagement3.4 Remote controlled gear
selection and engagement m ....................................
.............................................................. 3.5
Splitter and range change
gearboxes...................................................................
take-off3.6 Transfer box
power...............................................................3.7
Overdrive
considerations....................................................
ratios3.8 Setting gear4 Hydrokinetic fluid couplings and torque
converters..................................................................................................4.1
Hydrokinetic fluid couplings
- 6. 4.2 Hydrokinetic fluid coupling efficiency and torque
capacity
........................................................................................coupling4.3
Fluid friction4.4 Hydrokinetic three element torque converter
...................................................4.5 Torque
converter performance terminology
.......................................................................................................clutches4.6
Overrun
..................................................................4.7
Three stage hydrokinetic converter4.8 Polyphase hydrokinetic torque
converter.........................................................4.9
Torque converter with lock-up and gear change friction clutches
....................5 Semi- and fully automatic transmission
.................................................................................................................5.1
Automatic transmission consideration5.2 Four speed and reverse
longitudinally mounted automatic
transmission.....................................................mechanical
power flow5.3 The fundamentals of a hydraulic control system
..............................................5.4 Basic principle
of a .......................................hydraulically
controlled
gearshift5.5.......................................................
system Basic four speed hydraulic control5.6 Three speed and
reverse transaxle automatic transmission
mechanical..................................power flow5.7 Hydraulic
gear selection control
components..................................................5.8
Hydraulic gear selection control operation
.......................................................5.9 The
continuously variable belt and pulley transmission
...................................5.10 Five speed automatic
transmission with electronic-hydraulic control............ 5.11
Semi-automatic (manual gear change two pedal control)
transmission............................ system6 Transmission
bearings and constant velocity
joints............................................................................................
6.1 Rolling contact bearings
................................................................
joints 6.2 The need for constant
velocity....................................................... 7
Final drive transmission7.1 Crownwheel and pinion axle adjustments
.........................................................................................................
locks7.2
Differential................................................................7.3
Skid reducing
differentials............................................................
axles7.4 Double
reduction..................................................
axles7.5 Two
speed.....................................................................7.6
The third (central) differential
.......................................................................
7.7 Four wheel drive
arrangements.............................................................7.8
Electro-hydralic limited slip differential
- 7. 7.9 Tyre grip when braking and accelerating with good and
poor
road...............................surfaces..............................................................
system7.10 Traction control.......................8 Tyres
........................................................... of
tyres 8.1 Tractive and braking
properties..............................................8.2 Tyre
materials...................................................
design8.3 Tyre
tread.....................................................................
of tyres8.4 Cornering
properties..........................................................
stability8.5 Vehicle steady state
directional.................................................................8.6
Tyre marking
identification..................................................8.7
Wheel balancing............................ 9 Steering
.............................................................
design 9.1 Steering gearbox fundamental
..............................................................
steering 9.2 The need for power assisted
.............................................................
joints 9.3 Steering linkage ball and socket
.......................................................... 9.4
Steering geometry and wheel
alignment......................................................................
pinion9.5 Variable-ratio rack and9.6 Speed sensitive rack and
pinion power assisted steering...............................9.7
Rack and pinion electric power assisted steering
...............................................................................10
Suspension............................................................10.1
Suspension
geometry..............................................................
centres 10.2 Suspension
roll..................................................................analysis10.3
Body roll
stability........................................................................stiffness10.4
Anti-roll bars and roll
..............................................................
stops 10.5 rubber spring bump or
limiting............................................. location 10.6
Axle.....................................................................10.7
Rear suspension arrangements
..................................................................
10.8 Suspension design
consideration............................................................10.9
Hydrogen suspension10.10 Hydropneumatic automatic height correction
suspension ...........................10.11 Commercial vehicle axle
beam
location.......................................................10.12
Variable rate leaf suspension
springs...............................................................................................................................
bogies 10.13 Tandem and
tri-axle.....................................................................10.14
Rubber spring suspension10.15 Air suspensions for commercial
vehicles.....................................................
- 8. 10.16 Lift axle tandem or tri-axle
suspension................................................................................................................10.17
Active suspension 10.18 Electronic controlled pneumatic (air)
suspension for on and off road use
.........................................system11
Brake...........................................11.1 Braking
fun................................................................11.2
Brake shoe and pad fundamentals
............................................................ 11.3
Brake shoe expanders and
adjusters...........................................................11.4
Disc brake pad support arrangements
.................................................................systems
11.5 Dual- or split-line
braking........................................................
braking11.6 Apportional
.....................................................................
(ABS) 11.7 Antilocking brake
system.............................................. servos11.8
Brake 11.9 Pneumatic operated disk brakes (for trucks and
trailers)...............................12 Air operated power brake
equipment and .................vehicle retarders
...............................................................
brakes 12.1 Introductions to air
powered................................................................systems12.2
Air operated power
brake.............................................................12.3
Air operated power brake
equipment....................................................12.4
Vehicle
retarders......................................................................
brakes12.5
Electronic-pneumatic..................................................13
Vehicle
refrigeration.......................................................
terms13.1 Refrigeration 13.2 Principles of a vapour-compression
cycle refrigeration system
......................................................................................13.3
Refrigeration system components13.4 Vapour-compression cycle
refrigeration system with reverse
cycle.................................defrosting...............................................................
14 Vehicle body aerodynamics
.......................................................................14.1
Viscous air flow
fundamentals......................................................14.2
Aerodynamic
drag...................................................14.3
Aerodynamic
lift................................................................14.4
Car body drag
reduction..............................................................
control14.5 Aerodynamic
lift.................................................14.6 Afterbody
drag 14.7 Commercial
...........................................vehicle aeordynamic
fundamentals 14.8 Commercial vehicle drag reducing
devices...................................................
- 9. .................... Index
- 10. 1 Vehicle Structure1.1 Integral body constructionThese box
compartments are constructed in theThe integral or unitary body
structure of a car can form of a framework of ties (tensile) and
strutsbe considered to be made in the form of three box
(compressive), pieces (Fig. 1.1(a & b)) made fromcompartments;
the middle and largest compart- rolled sheet steel pressed into
various shapes suchment stretching between the front and rear road
as rectangular, triangular, trapezium, top-hat or awheel axles
provides the passenger space, the combination of these to form
closed box thin gaugeextended front box built over and ahead of the
frontsections. These sections are designed to resist directroad
wheels enclosing the engine and transmission tensile and
compressive or bending and torsionalunits and the rear box behind
the back axle loads, depending upon the positioning of the
mem-providing boot space for luggage. bers within the
structure.Fig. 1.1 (a and b) Structural tensile and compressive
loading of car body1
- 11. 1.1.1 Description and function of bodyCantrails (Fig.
1.2(4)) Cantrails are the horizon-components (Fig. 1.2) tal members
which interconnect the top ends of theThe major individual
components comprising thevertical A and BC or BC and D door pillars
(posts).body shell will now be described separately under These
rails form the side members which make upthe following
subheadings:the rectangular roof framework and as such aresubjected
to compressive loads. Therefore, they 1 Window and door pillarsare
formed in various box-sections which offer the 2 Windscreen and
rear window railsgreatest compressive resistance with the minimum 3
Cantrailsof weight and blend in with the roofing. A drip rail 4
Roof structure(Fig. 1.2(4)) is positioned in between the overlap- 5
Upper quarter panel or windowping roof panel and the cantrails, the
joins being 6 Floor seat and boot panssecured by spot welds. 7
Central tunnel 8 Sills 9 Bulkhead Roof structure (Fig. 1.2) The
roof is constructed10 Scuttlebasically from four channel sections
which form11 Front longitudinalsthe outer rim of the slightly
dished roof panel.12 Front valanceThe rectangular outer roof frame
acts as the com-13 Rear valance pressive load bearing members.
Torsional rigidity14 Toe boardto resist twist is maximized by
welding the four15 Heel board corners of the channel-sections
together. The slightcurvature of the roof panel stiffens it, thus
prevent-Window and door pillars (Fig. 1.2(3, 5, 6, and 8))ing
winkling and the collapse of the unsupportedWindowscreen and door
pillars are identified by a centre region of the roof panel. With
large cars,letter coding; the front windscreen to door pillars
additional cross-rail members may be used toare referred to as A
post, the centre side door pillars provide more roof support and to
prevent the roofas BC post and the rear door to quarter panel
ascrushing in should the car roll over.D post. These are
illustrated in Fig. 1.2. These pillars form the part of the body
structurewhich supports the roof. The short form A pillar andUpper
quarter panel or window (Fig. 1.2(6)) Thisrear D pillar enclose the
windscreen and quarteris the vertical side panel or window which
occupieswindows and provide the glazing side channels,the space
between the rear side door and the rearwhilst the centre BC pillar
extends the full height ofwindow. Originally the quarter panel
formed anthe passenger compartment from roof to floor andimportant
part of the roof support, but improvedsupports the rear side door
hinges. The front and pillar design and the desire to maximize
visibilityrear pillars act as struts (compressive members)has
either replaced them with quarter windows orwhich transfer a
proportion of the bending effect,reduced their width, and in some
car models theydue to underbody sag of the wheelbase, to each
endhave been completely eliminated.of the cantrails which thereby
become reactivestruts, opposing horizontal bending of the pas-
Floor seat and boot pans (Fig. 1.3) These consti-senger compartment
at floor level. The central BC tute the pressed rolled steel
sheeting shape topillar however acts as ties (tensile members),
trans- enclose the bottom of both the passenger and lug-ferring
some degree of support from the mid-span of gage compartments. The
horizontal spread-outthe cantrails to the floor structure. pressing
between the bulkhead and the heel boardis called the floor pan,
whilst the raised platformWindscreen and rear window rails (Fig.
1.2(2))over the rear suspension and wheel arches is knownThese
box-section rails span the front window as the seat or arch pan.
This in turn joins onto apillars and rear pillars or quarter panels
dependinglower steel pressing which supports luggage and isupon
design, so that they contribute to the resist- referred to as the
boot pan.ance opposing transverse sag between the wheel To increase
the local stiffness of these platformtrack by acting as compressive
members. The panels or pans and their resistance to
transmittedother function is to support the front and rear
vibrations such as drumming and droning, manyends of the roof
panel. The undersides of the rails narrow channels are swaged
(pressed) into the steelalso include the glazing channels.sheet,
because a sectional end-view would show a2
- 12. Fig. 1.2 Load bearing body box-section
memberssemi-corrugated profile (or ribs). These channels by the
semicircular drawn out channel bottoms.provide rows of shallow
walls which are both bent Provided these swages are designed to lay
theand stretched perpendicular to the original flatcorrect way and
are not too long, and the metal issheet. In turn they are spaced
and held togethernot excessively stretched, they will raise the
rigidity3
- 13. Fig. 1.3 (ac) Platform chassis4
- 14. of these panels so that they are equivalent to a sheet
spans between the rear end of the valance, where itwhich may be
several times thicker.meets the bulkhead, and the door pillar and
wing. The lower edge of the scuttle will merge with theCentral
tunnel (Fig. 1.3(a and b)) This is the floor pan so that in some
cases it may form part ofcurved or rectangular hump positioned
longitudin-the toe board on the passenger compartment side.ally
along the middle of the floor pan. Originally itUsually these
panels form inclined sides to the bulk-was a necessary evil to
provide transmission space head, and with the horizontal ledge
which spans thefor the gearbox and propeller shaft for rear wheel
full width of the bulkhead, brace the bulkhead walldrive,
front-mounted engine cars, but since theso that it offers increased
rigidity to the structure.chassis has been replaced by the integral
box- The combined bulkhead dash panel and scuttle willsection
shell, it has been retained with front wheel thereby have both
upright and torsional rigidity.drive, front-mounted engines as it
contributesconsiderably to the bending rigidity of the
floorstructure. Its secondary function is now to houseFront
longitudinals (Figs 1.2(10) and 1.3(a and b))the exhaust pipe
system and the hand brake cable These members are usually upswept
box-sectionassembly.members, extending parallel and forward from
the bulkhead at floor level. Their purpose is to with- stand the
engine mount reaction and to support theSills (Figs 1.2(9) and
1.3(a, b and c)) These membersfront suspension or subframe. A
common featureform the lower horizontal sides of the car bodyof
these members is their ability to support verticalwhich spans
between the front and rear road-wheelloads in conjunction with the
valances. However, inwings or arches. To prevent body sag between
the the event of a head-on collision, they are designedwheelbase of
the car and lateral bending of theto collapse and crumble within
the engine compart-structure, the outer edges of the floor pan are
givenment so that the passenger shell is safeguarded andsupport by
the side sills. These sills are made in the is not pushed rearwards
by any great extent.form of either single or double
box-sections(Fig. 1.2(9)). To resist the heavier vertical
bendingloads they are of relatively deep section. Front valance
(Figs 1.2 and 1.3(a and b)) These Open-top cars, such as
convertibles, which do not panels project upwards from the front
longitudinalreceive structural support from the roof
members,members and at the rear join onto the wall of theusually
have extra deep sills to compensate for thebulkhead. The purpose of
these panels is to transferincreased burden imposed on the
underframe.the upward reaction of the longitudinal members which
support the front suspension to the bulkhead.Bulkhead (Figs 1.2(1)
and 1.3(a and b)) This is theSimultaneously, the longitudinals are
preventedupright partition separating the passenger and from
bending sideways because the valance panelsengine compartments. Its
upper half may form are shaped to slope up and outwards towards
thepart of the dash panel which was originally used totop. The
panelling is usually bent over near thedisplay the drivers
instruments. Some body manu-edges to form a horizontal flanged
upper, thusfacturers refer to the whole partition between
enginepresenting considerable lateral resistance. Further-and
passenger compartments as the dash panel. If more, the valances are
sometimes stepped andthere is a double partition, the panel next to
the wrapped around towards the rear where they meetengine is
generally known as the bulkhead and that and are joined to the
bulkhead so that additionalon the passenger side the dash board or
panel. The lengthwise and transverse stiffness is obtained.scuttle
and valance on each side are usually joined If coil spring
suspension is incorporated, theonto the box-section of the
bulkhead. This bracesvalance forms part of a semi-circular tower
whichthe vertical structure to withstand torsional distor-houses
and provides the load reaction of the springtion and to provide
platform bending resistanceso that the merging of these shapes
compounds thesupport. Sometimes a bulkhead is constructed rigidity
for both horizontal lengthwise and lateralbetween the rear wheel
arches or towers to reinforce bending of the forward engine and
transmissionthe seat pan over the rear axle (Fig. 1.3(c)).
compartment body structure. Where necessary, double layers of sheet
are used in parts of the spring housing and at the rear of the
valance where theyScuttle (Fig. 1.3(a and b)) This can be
considered are attached to the bulkhead to relieve some of theas
the panel formed under the front wings whichconcentrated loads.
5
- 15. Rear valance (Fig. 1.2(7)) This is generally con- Torsional
rigidity of the platform is usuallysidered as part of the
box-section, forming the frontderived at the front by the bulkhead,
dash panhalf of the rear wheel arch frame and the paneland scuttle
(Fig. 1.3(a and b)) at the rear by theimmediately behind which
merges with the heelheel board, seat pan, wheel arches (Fig. 1.3(a,
b andboard and seatpan panels. These side inner-sidec)), and if
independent rear suspension is adopted,panels position the edges of
the seat pan to its by the coil spring towers (Fig. 1.3(a and
c)).designed side profile and thus stiffen the underfloorBetween
the wheelbase, the floor pan is normallystructure above the rear
axle and suspension. When provided with box-section cross-members
to stiffenrear independent coil spring suspension is adopted,and
prevent the platform sagging where thethe valance or wheel arch
extends upwards to formpassenger seats are positioned.a spring
tower housing and, because it forms asemi-vertical structure,
greatly contributes to the1.1.3 Stiffening of platform
chassisstiffness of the underbody shell between the floor (Figs 1.4
and 1.5)and boot pans. To appreciate the stresses imposed on and
the resisting stiffness offered by sheet steel when it is subjected
to bending, a small segment of a beamToe board The toe board is
considered to formgreatly magnified will now be considered (Fig.the
lower regions of the scuttle and dash panel near 1.4(a)). As the
beam deforms, the top fibres con-where they merge with the floor
pan. It is thistract and the bottom fibres elongate. The
neutralpanelling on the passenger compartment sideplane or axis of
the beam is defined as the planewhere occupants can place their
feet when the carwhose length remains unchanged during deforma-is
rapidly retarded. tion and is normally situated in the centre of a
uniform section (Fig. 1.4(a and b)).The stress distribution from
top to bottom withinHeel board (Fig. 1.3(b and c)) The heel board
is the beam varies from zero along the neutral axisthe upright, but
normally shallow, panel spanning(NA), where there is no change in
the length of thebeneath and across the front of the rear seats.
Itsfibres, to a maximum compressive stress on the outerpurpose is
to provide leg height for the passengerstop layer and a maximum
tensile stress on the outerand to form a raised step for the seat
pan so that bottom layer, the distortion of the fibres beingthe
rear axle has sufficient relative movement greatest at their
extremes as shown in Fig. 1.4(b).clearance.It has been found that
bending resistance increases roughly with the cube of its distance
from the neutral axis (Fig. 1.5(a)). Therefore, bend-1.1.2 Platform
chassis (Fig. 1.3(ac)) ing resistance of a given section can be
greatlyMost modern car bodies are designed to obtainimproved for a
given weight of metal by takingtheir rigidity mainly from the
platform chassis andmetal away from the neutral axis where the
metalto rely less on the upper framework of windowfibres do not
contribute very much to resistingand door pillars, quarter panels,
windscreen rails distortion and placing it as far out as
possibleand contrails which are becoming progressively where the
distortion is greatest. Bending resistanceslender as the desire for
better visibility is encouraged. may be improved by using
longitudinal or cross- The majority of the lengthwise (wheelbase)
bend-member deep box-sections (Fig. 1.5(b)) and tunneling stiffness
to resist sagging is derived from both sections (Fig. 1.5(c)) to
restrain the platform chas-the central tunnel and the side sill
box-sectionssis from buckling and to stiffen the flat
horizontal(Fig. 1.3(a and b)). If further strengthening is floor
seat and boot pans. So that vibration andnecessary, longitudinal
box-section members maydrumming may be reduced, many swaged ribs
arebe positioned parallel to, but slightly inwards from,pressed
into these sheets (Fig. 1.5(d)).the sills (Fig. 1.3(c)). These
lengthwise membersmay span only part of the wheelbase, or the full
1.1.4 Body subframes (Fig. 1.6)length, which is greatly influenced
by the design of Front or rear subframes may be provided to
braceroad wheel suspension chosen for the car, the depththe
longitudinal side members so that independentof both central tunnel
and side sills, which are built suspension on each side of the car
receives adequateinto the platform, and if there are
subframessupport for the lower transverse swing arms (wish-attached
fore and aft of the wheelbase (Fig. 1.6 bone members). Subframes
restrain the two halves(a and b)).of the suspension from splaying
outwards or the 6
- 16. Fig. 1.4 Stress and strain imposed on beam when subjected
to bendinglongitudinal side members from lozenging as alter- the
media of rubber mounts is that transmittednative road wheels
experience impacts when travel- vibrations and noise originating
from the tyresling over the irregularities of a normal road
surface. and road are isolated from the main body shell It is usual
to make the top side of the subframeand therefore do not damage the
body structurethe cradle for the engine or engine and transmission
and are not relayed to the occupants sittingmounting points so that
the main body structureinside.itself does not have to be
reinforced. This particu-Cars which have longitudinally
positionedlarly applies where the engine, gearbox and finalengines
mounted in the front driven by the reardrive form an integral unit
because any torque wheels commonly adopt beam cross-memberreaction
at the mounting points will be transferredsubframes at the front to
stiffen and support theto the subframe and will multiply in
proportion to hinged transverse suspension arms (Fig. 1.6(a)).the
overall gear reduction. This may be approxi- Saloon cars employing
independent rear suspen-mately four times as great as that for the
front sion sometimes prefer to use a similar subframe atmounted
engine with rear wheel drive and willthe rear which provides the
pivot points for thebecome prominent in the lower gears.
semi-trailing arms because this type of suspension One advantage
claimed by using separate sub-requires greater support than most
other arrange-frames attached to the body underframe through ments
(Fig. 1.6(a)). 7
- 17. Fig. 1.5 Bending resistance for various sheet sections When
the engine, gearbox and final drive areside members by utilising a
horseshoe shaped framecombined into a single unit, as with the
front longi-(Fig. 1.6(b)). This layout provides a platform
fortudinally positioned engine driving the front wheels the entire
mounting points for both the swing armwhere there is a large weight
concentration, a sub-and anti-roll bar which between them make up
theframe gives extra support to the body longitudinal lower part of
the suspension. 8
- 18. Fig. 1.6 (ac) Body subframe and underfloor structure9
- 19. Front wheel drive transversely positioned modifies the
magnitude of frequencies of theengines with their large mounting
point reactionsvibrations so that they are less audible to theoften
use a rectangular subframe to spread out passengers.both the power
and transmission units weightThe installation of acoustic materials
cannotand their dynamic reaction forces (Fig. 1.6(c)).completely
eliminate boom, drumming, droningThis configuration provides
substantial torsionaland other noises caused by resonance, but
merelyrigidity between both halves of the independent reduces the
overall noise level.suspension without relying too much on the
mainbody structure for support.Insulation Because engines are
generally mountedSoundproofing the interior of the passenger close
to the passenger compartment of cars or thecompartment (Fig.
1.7)cabs of trucks, effective insulation is important. InInterior
noise originating outside the passengerthis case, the function of
the material is to reducecompartment can be greatly reduced by
applyingthe magnitude of vibrations transmitted throughlayers of
materials having suitable acoustic proper-the panel and floor
walls. To reduce the transmis-ties over floor, seat and boot pans,
central tunnel,sion of noise, a thin steel body panel should
bebulkhead, dash panel, toeboard, side panels, inside combined with
a flexible material of large mass,of doors, and the underside of
both roof andbased on PVC, bitumen or mineral wool. If thebonnet
etc. (Fig. 1.7). insulation material is held some distance from the
Acoustic materials are generally designed for onestructural panel,
the transmissibility at frequenciesof three functions: above 400 Hz
is further reduced. For this type ofa) Insulation from noise This
may be created by application the loaded PVC material is bonded to
a forming a non-conducting noise barrier spacing layer of
polyurethane foam or felt, usually between the source of the noises
(which mayabout 7 mm thick. At frequencies below 400 Hz, the come
from the engine, transmission, suspension use of thicker spacing
layers or heavier materials tyres etc.) and the passenger
compartment. can also improve insulation.b) Absorption of
vibrations This is the transfer- ence of excited vibrations in the
body shell toAbsorption For absorption, urethane foam or a media
which will dissipate their resultant lightweight bonded fibre
materials can be used. energies and so eliminate or at least
greatlyIn some cases a vinyl sheet is bonded to the foam reduce the
noise.to form a roof lining. The required thickness of thec)
Damping of vibrations When certain vibra-absorbent material is
determined by the frequencies tions cannot be eliminated, they may
be exposedinvolved. The minimum useful thickness of to some form of
material which in some way polyurethane foam is 13 mm which is
effectivewith vibration frequencies above 1000 Hz.Damping To damp
resonance, pads are bondedto certain panels of many cars and truck
cabs. Theyare particularly suitable for external panels
whoseresonance cannot be eliminated by structuralalterations.
Bituminous sheets designed for thispurpose are fused to the panels
when the paint isbaked on the car. Where extremely high dampingor
light weight is necessary, a PVC base material,which has three
times the damping capacity ofbituminous pads, can be used but this
material israther difficult to attach to the panelling.1.1.5
Collision safety (Fig. 1.8)Car safety may broadly be divided into
two kinds:Firstly the active safety, which is concerned withthe
cars road-holding stability while being driven,Fig. 1.7 Car body
sound generation and its dissipationsteered or braked and secondly
the passive safety, 10
- 20. collision, but overall alignment may also be neces-sary if
the vehicles steering and ride characteristicsdo not respond to the
expected standard of a simi-lar vehicle when being driven.
Structural misalignment may be caused by allsorts of reasons, for
example, if the vehicle hasbeen continuously driven over rough
ground athigh speed, hitting an obstacle in the road, mount-Fig.
1.8 Collision body safetying steep pavements or kerbs, sliding off
the roadinto a ditch or receiving a glancing blow from somewhich
depends upon body style and design struc- other vehicle or obstacle
etc. Suspicion that some-ture to protect the occupants of the car
from serious thing is wrong with the body or chassis alignment
isinjury in the event of a collision. focused if there is
excessively uneven or high tyre Car bodies can be considered to be
made in three wear, the vehicle tends to wander or pull over
toparts (Fig. 1.8); a central cell for the passengers one side and
yet the track and suspension geometryof the welded bodywork
integral with a rigidappears to be correct.platform, acting as a
floor pan, and chassis withAlignment checks should be made on a
level,various box-section cross- and side-members. This clear floor
with the vehicles tyres correctly inflatedtype of structure
provides a reinforced rigid crush-to normal pressure. A plumb bob
is required in theproof construction to resist deformation on
impactform of a stubby cylindrical bar conical shaped atand to give
the interior a high degree of protection. one end, the other end
being attached to a length ofThe extension of the engine and boot
compart- thin cord. Datum reference points are chosen suchments at
the front and rear of the central passengeras the centre of a
spring eye on the chassis mount-cell are designed to form zones
which collapse anding point, transverse wishbone and trailing
armcrumble progressively over the short duration of apivot centres,
which are attachment points to thecollision impact. Therefore, the
kinetic energy due underframe or chassis, and body cross-member
toto the cars initial speed will be absorbed fore andside-member
attachment centres and subframeaft primarily by strain and plastic
energy within the bolt-on points (Fig. 1.9).crumble zones with very
little impact energy actu- Initially the cord with the plumb bob
hangingally being dissipated by the central body cell. from its end
is lowered from the centre of eachreference point to the floor and
the plumb bob con-1.1.6 Body and chassis alignment checks tact
point with the ground is marked with a chalked(Fig. 1.9)cross.
Transverse and diagonal lines between refer-Body and chassis
alignment checks will be neces-ence points can be made by chalking
the full lengthsary if the vehicle has been involved in a majorof a
piece of cord, holding it taut between referencecentres on the
floor and getting somebody to pluckTable 1.1 Summary of function
and application ofthe centre of the line so that it rebounds and
leavessoundproofing materials a chalked line on the floor. A
reference longitudinal centre line may be madeFunctionAcoustic
materials Applicationwith a strip of wood baton of length just
greaterthan the width between adjacent reference
marksInsulationLoaded PVC,Floor, bulkheadbitumen, with or dash
panel on the floor. A nail is punched through one endwithout foam
or and this is placed over one of the reference marks.fibres base,A
piece of chalk is then held at the tip of the freemineral woolend
and the whole wood strip is rotated aboutthe nailed end. The chalk
will then scribe an arcDamping Bitumen or Doors, sidebetween
adjacent reference points. This is repeatedmineralpanels,wool
underside of rooffrom the other side. At the points where these
twoarcs intersect a straight line is made with a
plucked,AbsorptionPolyurethane foam, Side panels, chalked cord
running down the middle of the vehi-mineral wool, or underside of
cle. This procedure should be followed at each endbonded
fibresroof, engine of the vehicle as shown in Fig. 1.9.
compartment,Once all the reference points and transverse and
bonnetdiagonal joining lines have been drawn on the 11
- 21. Fig. 1.9 Body underframe alignment checksfloor, a rule or
tape is used to measure the distances Both the variations of
inertia and gas pressurebetween centres both transversely and
diagonally. forces generate three kinds of vibrations which
areThese values are then chalked along their respectivetransferred
to the cylinder block:lines. Misalignment or error is observed when
apair of transverse or diagonal dimensions differ1 Vertical and/or
horizontal shake and rockand further investigation will thus be
necessary. 2 Fluctuating torque reaction Note that transverse and
longitudinal dimen- 3 Torsional oscillation of the crankshaftsions
are normally available from the manufac-turers manual and
differences between paired1.2.2 Reasons for flexible
mountingsdiagonals indicates lozenging of the frameworkdue to some
form of abnormal impact which has It is the objective of flexible
mounting design tocope with the many requirements, some
havingpreviously occurred.conflicting constraints on each other. A
list of theduties of these mounts is as follows:1.2 Engine,
transmission and body structure 1 To prevent the fatigue failure of
the engine andmountings gearbox support points which would occur
ifthey were rigidly attached to the chassis or1.2.1 Inherent engine
vibrationsbody structure.The vibrations originating within the
engine are2 To reduce the amplitude of any engine vibrationcaused
by both the cyclic acceleration of the reci- which is being
transmitted to the body structure.procating components and the
rapidly changing 3 To reduce noise amplification which would
occurcylinder gas pressure which occurs throughout if engine
vibration were allowed to be transferredeach cycle of
operation.directly to the body structure. 12
- 22. 4 To reduce human discomfort and fatigue bypartially
isolating the engine vibrations fromthe body by means of an elastic
media.5 To accommodate engine block misalignmentand to reduce
residual stresses imposed on theengine block and mounting brackets
due tochassis or body frame distortion.6 To prevent road wheel
shocks when drivingover rough ground imparting excessive
reboundmovement to the engine.7 To prevent large engine to body
relative move-ment due to torque reaction forces, particularlyin
low gear, which would cause excessive mis-alignment and strain on
such components asthe exhaust pipe and silencer system.8 To
restrict engine movement in the fore and aftdirection of the
vehicle due to the inertia of theengine acting in opposition to the
acceleratingand braking forces.1.2.3 Rubber flexible mountings
(Figs 1.10, 1.11and 1.12)A rectangular block bonded between two
metalplates may be loaded in compression by squeezingFig. 1.10 (a
and b) Modes of loading rubber blocksthe plates together or by
applying parallel butopposing forces to each metal plate. On
compres- When two rubber blocks are inclined to each othersion, the
rubber tends to bulge out centrally fromto form a `V mounting, see
Fig. 1.11, the rubber willthe sides and in shear to form a
parallelogrambe loaded in both compression and shear shown by(Fig.
1.10(a)). the triangle of forces. The magnitude of compressive To
increase the compressive stiffness of the force will be given by Wc
and the much smaller shearrubber without greatly altering the shear
stiffness,force by WS. This produces a resultant reaction forcean
interleaf spacer plate may be bonded in betweenWR. The larger the
wedge angle , the greater thethe top and bottom plate (Fig.
1.10(b)). This inter-proportion of compressive load relative to the
shearleaf plate prevents the internal outward collapse ofload the
rubber block absorbs.the rubber, shown by the large bulge around
theThe distorted rubber provides support undersides of the block,
when no support is provided,light vertical static loads
approximately equal inwhereas with the interleaf a pair of much
smaller both compression and shear modes, but withbulges are
observed.heavier loads the proportion of compressive stiffnessFig.
1.11 `V rubber block mounting 13
- 23. These modes of movement may be summarized as follows:
Linear motions Rotational motions 1 Horizontal 4 Roll longitudinal
5 Pitch 2 Horizontal lateral 6 Yaw 3 Vertical 1.2.6 Positioning of
engine and gearbox mountings (Fig. 1.15) If the mountings are
placed underneath the com- bined engine and gearbox unit, the
centre of gravity is well above the supports so that a lateral
(side) force acting through its centre of gravity, such as
experienced when driving round a corner, will cause the mass to
roll (Fig. 1.15(a)). This condition is undesirable and can be
avoided by placing the mounts on brackets so that they are in
theFig. 1.12 Loaddeflection curves for rubber block same plane as
the centre of gravity (Fig. 1.15(b)). Thus the mounts provide
flexible opposition toto that of shear stiffness increases at a
much fasterany side force which might exist without creating arate
(Fig. 1.12). It should also be observed that theroll couple. This
is known as a decoupled condition.combined compressive and shear
loading of the An alternative method of making the naturalrubber
increases in direct proportion to the staticmodes of oscillation
independent or uncoupled isdeflection and hence produces a straight
line graph. achieved by arranging the supports in an inclined `V
position (Fig. 1.15(c)). Ideally the aim is to1.2.4 Axis of
oscillation (Fig. 1.13)make the compressive axes of the mountings
meetThe engine and gearbox must be suspended so that at the centre
of gravity, but due to the weight of theit permits the greatest
degree of freedom when power unit distorting the rubber springing
theoscillating around an imaginary centre of rotation inter-section
lines would meet slightly below thisknown as the principal axis.
This principal axis point. Therefore, the mountings are tilted so
thatproduces the least resistance to engine and gearboxthe
compressive axes converge at some focal pointsway due to their
masses being uniformly distrib-above the centre of gravity so that
the actual linesuted about this axis. The engine can be considered
of action of the mountings, that is, the directionto oscillate
around an axis which passes through of the resultant forces they
exert, converge on thethe centre of gravity of both the engine and
gearbox centre of gravity (Fig. 1.15(d)).(Figs 1.13(a, b and c)).
This normally produces anThe compressive stiffness of the inclined
mountsaxis of oscillation inclined at about 1020 to thecan be
increased by inserting interleafs betweencrankshaft axis. To obtain
the greatest degree ofthe rubber blocks and, as can be seen
infreedom, the mounts must be arranged so that theyFig. 1.15(e),
the line of action of the mounts con-offer the least resistance to
shear within the rubberverges at a lower point than mounts which do
notmounting.have interleaf support.Engine and gearbox mounting
supports are1.2.5 Six modes of freedom of a suspended body normally
of the three or four point configuration.(Fig. 1.14)Petrol engines
generally adopt the three pointIf the movement of a flexible
mounted engine issupport layout which has two forward
mountscompletely unrestricted it may have six modes of (Fig. 1.13(a
and c)), one inclined on either side ofvibration. Any motion may be
resolved into three the engine so that their line of action
converges onlinear movements parallel to the axes which pass the
principal axis, while the rear mount is supportedthrough the centre
of gravity of the engine but at centrally at the rear of the
gearbox in approximatelyright angles to each other and three
rotations about the same plane as the principal axis. Large
dieselthese axes (Fig. 1.14).engines tend to prefer the four point
support14
- 24. Fig. 1.13 Axis of oscillation and the positioning of the
power unit flexible mountsarrangement where there are two mounts
either sidedown at a uniform rate. The amplitude of this cyclicof
the engine (Fig. 1.13(b)). The two front mountsmovement will
progressively decrease and the num-are inclined so that their lines
of action pass through ber of oscillations per minute of the rubber
mountingthe principal axis, but the rear mounts which are is known
as its natural frequency of vibration.located either side of the
clutch bell housing are not There is a relationship between the
static deflec-inclined since they are already at principal axis
level.tion imposed on the rubber mount springing by thesuspended
mass and the rubbers natural frequency1.2.7 Engine and transmission
vibrationsof vibration, which may be given by 30Natural frequency
of vibration (Fig. 1.16) A sprung n0 pbody when deflected and
released will bounce up andx 15
- 25. Fig. 1.14 Six modes of freedom for a suspended blockwheren0
= natural frequency of vibration the engine out of balance forces
and the fluctuating(vib/min)cylinder gas pressure and the natural
frequency of x = static deflection of the rubber (m) oscillation of
the elastic rubber support mounting, i.e. resonance occurs whenThis
relationship between static deflection andnnatural frequency may be
seen in Fig. 1.16. 1 n0Resonance Resonance is the unwanted
synchron-wheren = disturbing frequencyization of the disturbing
force frequency imposed byn0 = natural frequency Transmissibility
(Fig. 1.17) When the designer selects the type of flexible mounting
the Theory of Transmissibility can be used to estimate critical
resonance conditions so that they can be either prevented or at
least avoided.Transmissibility (T) may be defined as the ratio of
the transmitted force or amplitude which passes through the rubber
mount to the chassis to that of the externally imposed force or
amplitude generated by the engine: Ft1T 2 Fdn1n0 where Ft
transmitted force or amplitude Fd imposed disturbing force or
amplitudeThis relationship between transmissibility andFig. 1.16
Relationship of static deflection and naturalthe ratio of
disturbing frequency and naturalfrequencyfrequency may be seen in
Fig. 1.17.16
- 26. Fig. 1.15 (ae) Coupled and uncoupled mounting points17
- 27. The transmissibility to frequency ratio graph rubber
mountings is greater than 112 and the trans-(Fig. 1.17) can be
considered in three parts as follows:missibility is less than one.
Under these conditionsoff-peak partial resonance vibrations passing
to theRange (I) This is the resonance range and should be body
structure will be minimized.avoided. It occurs when the disturbing
frequencyis very near to the natural frequency. If steel
mountsRange (III) This is known as the shock reductionare used, a
critical vibration at resonance would gorange and only occurs when
the disturbingto infinity, but natural rubber limits the trans-
frequency is lower than the natural frequency.missibility to around
10. If Butyl synthetic rubber isGenerally it is only experienced
with very softadopted, its damping properties reduce the peak
rubber mounts and when the engine is initiallytransmissibility to
about 212. Unfortunately, high cranked for starting purposes and so
quickly passesdamping rubber compounds such as Butyl rubber through
this frequency ratio region.are temperature sensitive to both
damping anddynamic stiffness so that during cold weather a Example
An engine oscillates vertically on itsnoticeably harsher suspension
of the engine results.flexible rubber mountings with a frequency of
800 Damping of the engine suspension mounting is vibrations per
minute (vpm). With the informationnecessary to reduce the excessive
movement of a provided answer the following questions:flexible
mounting when passing through resonance,but at speeds above
resonance more vibration is a) From the static deflectionfrequency
graph,transmitted to the chassis or body structure thanFig. 1.16,
or by formula, determine the natural fre-would occur if no damping
was provided.quency of vibration when the static deflection of the
engine is 2 mm and then find the disturbing toRange (II) This is
the recommended working natural frequency ratio. Comment on these
results.range where the ratio of the disturbing frequency b) If the
disturbing to natural frequency ratio isto that of the natural
frequency of vibration of the increased to 2.5 determine the
natural frequency Fig. 1.17 Relationship of transmissibility and
the ratio of disturbing and natural frequencies for natural rubber,
Butyl rubber and steel 18
- 28. of vibration and the new static deflection of the 1.2.9
Subframe to body mountings engine. Comment of these
conditions.(Figs 1.6 and 1.19)3030 One of many problems with
integral body design isa) n0 p pthe prevention of vibrations
induced by the engine, x0:002transmission and road wheels from
being transmitted30 through the structure. Some manufacturers adopt
a 670:84 vib/minsubframe (Fig. 1.6(a, b and c)) attached by
resilient 0:04472 mountings (Fig. 1.19(a and b)) to the body to
which n800the suspension assemblies, and in some instances the ;
1:193 n0 670:84 engine and transmission, are attached. The mass of
the subframes alone helps to damp vibrations. The ratio 1.193 is
very near to the resonance It also simplifies production on the
assembly line,condition and should be avoided by using softerand
facilitates subsequent overhaul or repairs.mounts. In general, the
mountings are positioned so that n800they allow strictly limited
movement of theb) 2:5 n0n0subframe in some directions but provide
greater freedom in others. For instance, too much lateral 800
freedom of a subframe for a front suspension ; n0 320 vib/min 2:5
assembly would introduce a degree of instability 30into the
steering, whereas some freedom in verticalNow n0 p and longitudinal
directions would improve the x quality of a ride. p 30 thus x
n01.2.10 Types of rubber flexible mountings230 30 2 A survey of
typical rubber mountings used for ;xpower units, transmissions,
cabs and subframes n0320 are described and illustrated as follows:
0:008789 m or 8:789 mmA low natural frequency of 320 vib/min is
well Double shear paired sandwich mounting (Fig.within the
insulation range, therefore from either 1.18(a)) Rubber blocks are
bonded between thethe deflectionfrequency graph or by formula jaws
of a `U shaped steel plate and a flat interleafthe corresponding
rubber deflection necessary is plate so that a double shear elastic
reaction takes8.789 mm when the engines static weight bears place
when the mount is subjected to vertical load-down on the
mounts.ing. This type of shear mounting provides a large degree of
flexibility in the upright direction and1.2.8 Engine to
body/chassis mountings thus rotational freedom for the engine unit
aboutEngine mountings are normally arranged toits principal axis.
It has been adopted for bothprovide a degree of flexibility in the
horizontalengine and transmission suspension mountinglongitudinal,
horizontal lateral and vertical axis ofpoints for medium-sized
diesel engines.rotation. At the same time they must have
suffi-cient stiffness to provide stability under shockloads which
may come from the vehicle travelling Double inclined wedge mounting
(Fig. 1.18(b)) Theover rough roads. Rubber sprung mountingsinclined
wedge angle pushes the bonded rubbersuitably positioned fulfil the
following functions:blocks downwards and outwards against the
bent-up sides of the lower steel plate when loaded1 Rotational
flexibility around the horizontal in the vertical plane. The rubber
blocks are subjectedlongitudinal axis which is necessary to allow
theto both shear and compressive loads and the propor-impulsive
inertia and gas pressure componentstion of compressive to shear
load becomes greaterof the engine torque to be absorbed by rolling
ofwith vertical deflection. This form of mounting isthe engine
about the centre of gravity.suitable for single point gearbox
supports.2 Rotational flexibility around both the horizontallateral
and the vertical axis to accommodate anyhorizontal and vertical
shake and rock caused by Inclined interleaf rectangular sandwich
mountingunbalanced reciprocating forces and couples. (Fig. 1.18(c))
These rectangular blocks are19
- 29. Fig. 1.18 (ah) Types of rubber flexible mountings 20
- 30. Fig. 1.18 contd21
- 31. Fig. 1.18 contddesigned to be used with convergent `V
formationon either side of the power units bell housingengine
suspension system where the blocks areat principal axis level may
be used. Longitudinalinclined on either side of the engine. This
configura- movement is restricted by the double `V formedtion
enables the rubber to be loaded in both shear between the inner and
two outer members seen inand compression with the majority of
engine rota-a plan view. This `V and wedge configuration pro-tional
flexibility being carried out in shear. Verticalvides a combined
shear and compressive strain todeflection due to body pitch when
accelerating orthe rubber when there is a relative fore and aft
move-braking is absorbed mostly in compression. Verticalment
between the engine and chassis, in addition toelastic stiffness may
be increased without greatly that created by the vertical loading
of the mount.effecting engine roll flexibility by having metalThis
mountings major application is for the rearspacer interleafs bonded
into the rubber.mountings forming part of a four point suspension
for heavy diesel engines.Double inclined wedge with longitudinal
controlmounting (Fig. 1.18(d)) Where heavy vertical Metaxentric
bush mounting (Fig. 1.18(e)) Whenloads and large rotational
reactions are to be the bush is in the unloaded state, the steel
innerabsorbed, double inclined wedge mounts positionedsleeve is
eccentric relative to the outer one so that22
- 32. there is more rubber on one side of it than on
thedistortion within the rubber. Under small deflec-other.
Precompression is applied to the rubbertion conditions the shear
and compression isexpanding the inner sleeve. The bush is set so
that almost equal, but as the load and thus deflectionthe greatest
thickness of rubber is in compressionincreases, the proportion of
compression over thein the laden condition. A slot is incorporated
in shear loading predominates.the rubber on either side where the
rubber is at its These mounts provide very good lateral
stabilityminimum in such a position as to avoid stressingwithout
impairing vertical deflection flexibility andany part of it in
tension.progressive stiffness control. When used for road When
installed, its stiffness in the fore and aftwheel axle suspension
mountings, they offer gooddirection is greater than in the vertical
direction, theinsulation against road and other noises.ratio being
about 2.5 : 1. This type of bush providesa large amount of vertical
deflection with very littlefore and aft movement which makes it
suitable for Flanged sleeve bobbin mounting with reboundrear
gearbox mounts using three point power unitcontrol (Fig. 1.19(a and
b)) These mountingssuspension and leaf spring eye shackle pin
bushes.have the rubber moulded partially around the outerflange
sleeve and in between this sleeve and an innertube. A central bolt
attaches the inner tube to theMetacone sleeve mountings (Fig.
1.18(f and g))body structure while the outer member is bolted
onThese mounts are formed from male and femaletwo sides to the
subframe.conical sleeves, the inner male member being When loaded
in the vertical downward direction,centrally positioned by rubber
occupying thethe rubber between the sleeve and tube walls will
bespace between both surfaces (Fig. 1.18(f)). Duringin shear and
the rubber on the outside of thevertical vibrational deflection,
the rubber between flanged sleeve will be in compression.the
sleeves is subjected to a combined shear and There is very little
relative sideway movementcompression which progressively increases
the stiff-between the flanged sleeve and inner tube due toness of
the rubber as it moves towards full distor- rubber distortion. An
overload plate limits the down-tion. The exposed rubber at either
end overlaps the ward deflection and rebound is controlled by
theflanged outer sleeve and there is an upper andlower plate and
the amount and shape of rubberlower plate bolted rigidly to the
ends of the inner trapped between it and the underside of the
flangedsleeve. These plates act as both overload (bump)sleeve. A
reduction of rubber between the flangedand rebound stops, so that
when the inner membersleeve and lower plate (Fig. 1.19(a)) reduces
thedeflects up or down towards the end of its move-rebound, but an
increase in depth of rubber increasesment it rapidly stiffens due
to the surplus rubberrebound (Fig. 1.19(b)). The load deflection
charac-being squeezed in between. Mounts of this kind areteristics
are given for both mounts in Fig. 1.19c.used where stiffness is
needed in the horizontalThese mountings are used extensively for
body todirection with comparative freedom of movementsubframe and
cab to chassis mounting points.for vertical deflection. An
alternative version of the Metacone mountuses a solid aluminium
central cone with a flangedHydroelastic engine mountings (Figs
1.20(ac) andpedestal conical outer steel sleeve which can be1.21) A
flanged steel pressing houses and sup-bolted directly onto the
chassis side member, see ports an upper and lower rubber spring
diaphragm.Fig. 1.18(g). An overload plate is clamped betweenThe
space between both diaphragms is filled andthe inner cone and mount
support arm, but nosealed with fluid and is divided in two by a
separatorrebound plate is considered necessary.plate and small
transfer holes interlink the fluid These mountings are used for
suspension appli- occupying these chambers (Fig. 1.20(a and
b)).cations such as engine to chassis, cab to chassis,Under
vertical vibratory conditions the fluid willbus body and tanker
tanks to chassis. be displaced from one chamber to the otherthrough
transfer holes. During downward deflec-Double inclined rectangular
sandwich mounting tion (Fig. 1.20(b)), both rubber diaphragms
are(Fig. 1.18(h)) A pair of rectangular sandwich subjected to a
combined shear and compressiverubber blocks are supported on the
slopes of aaction and some of the fluid in the upper
chambertriangular pedestal. A bridging plate merges thewill be
pushed into the lower and back again byresilience of the inclined
rubber blocks so thatway of the transfer holes when the rubber
reboundsthey provide a combined shear and compressive (Fig.
1.20(a)). For low vertical vibratory frequencies, 23
- 33. the movement of fluid between the chambers is unrestricted,
but as the vibratory frequencies increase, the transfer holes offer
increasing resist- ance to the flow of fluid and so slow down the
up and down motion of the engine support arm. This damps and
reduces the amplitude of mountings vertical vibratory movement over
a number of cycles. A comparison of conventional rubber and
hydroelastic damping resistance over the normal operating frequency
range for engine mountings is shown in Fig. 1.20(c).Instead of
adopting a combined rubber mount with integral hydraulic damping,
separate diagon- ally mounted telescopic dampers may be used in
conjunction with inclined rubber mounts to reduce both vertical and
horizontal vibration (Fig. 1.21). 1.3 Fifth wheel coupling assembly
(Fig. 1.22(a and b)) The fifth wheel coupling attaches the
semi-trailer to the tractor unit. This coupling consists of a semi-
circular table plate with a central hole and a vee section cut-out
towards the rear (Fig. 1.22(b)). Attached underneath this plate are
a pair of pivot- ing coupling jaws (Fig. 1.22(a)). The semi-trailer
has an upper fifth wheel plate welded or bolted to the underside of
its chassis at the front and in the centre of this plate is bolted
a kingpin which faces downwards (Fig. 1.22(a)).When the trailer is
coupled to the tractor unit, this upper plate rests and is
supported on top of theFig. 1.19 (ac) Flanged sleeve bobbin
mounting withtractor fifth wheel table plate with the two halves
ofrebound controlthe coupling jaws engaging the kingpin. To
permit24
- 34. relative swivelling between the kingpin and jaws, the two
interfaces of the tractor fifth wheel tables and trailer upper
plate should be heavily greased. Thus, although the trailer
articulates about the kingpin, its load is carried by the tractor
table.Flexible articulation between the tractor and semi-trailer in
the horizontal plane is achieved by permitting the fifth wheel
table to pivot on hori- zontal trunnion bearings that lie in the
same vertical plane as the kingpin, but with their axes at right
angles to that of the tractors wheel base (Fig. 1.22(b)). Rubber
trunnion rubber bushes normally provide longitudinal oscillations
of about 10 .The fifth wheel table assembly is made from either a
machined cast or forged steel sections, or from heavy section
rolled steel fabrications, and the upper fifth wheel plate is
generally hot rolled steel welded to the trailer chassis. The
coupling locking system consisting of the jaws, pawl, pivot pins
and kingpin is produced from forged high carbon man- ganese steels
and the pressure areas of these com- ponents are induction hardened
to withstand shock loading and wear. 1.3.1 Operation of twin jaw
coupling (Fig. 1.23(ad)) With the trailer kingpin uncoupled, the
jaws will be in their closed position with the plunger withdrawn
from the lock gap between the rear of the jaws, which are
maintained in this position by the pawl contacting the hold-off
stop (Fig. 1.23(a)). WhenFig. 1.20 (ac) Hydroelastic engine
mountcoupling the tractor to the trailer, the jaws of the25
- 35. Fig. 1.21 Diagonally mounted hydraulic dampers suppress
both vertical and horizontal vibrationsfifth wheel strike the
kingpin of the trailer. The spring load notched pawl will then snap
over thejaws are then forced open and the kingpin enters jaw
projection to lock the kingpin in the couplingthe space between the
jaws (Fig. 1.23(b)). The king- position (Fig. 1.24(c)). The
securing pin shouldpin contacts the rear of the jaws which then
then be inserted through the pull lever and tableautomatically
pushes them together. At the sameeye holes. When the tractor is
driving forward, thetime, one of the coupler jaws causes the trip
pin to reaction on the kingpin increases the lockingstrike the
pawl. The pawl turns on its pivot against force between the jaw
projection and the notchedthe force of the spring, releasing the
plunger, allow- pawl.ing it to be forced into the jaws lock gap by
itsTo disconnect the coupling, lift out the securingspring (Fig.
1.23(c)). When the tractor is moving, pin and pull the release hand
lever fully outthe drag of the kingpin increases the lateral force
of (Fig. 1.24(d)). With both the tractor and trailerthe jaws on the
plunger. stationary, the majority of the locking force To
disconnect the coupling, the release handapplied to notched pawl
will be removed so thatlever is pulled fully back (Fig. 1.23(d)).
Thiswith very little effort, the pawl is able to swing cleardraws
the plunger clear of the rear of the jawsof the jaw in readiness
for uncoupling, that is, byand, at the same time, allows the pawl
to swingjust driving the tractor away from the trailer. Thusround
so that it engages a projection hold-off stopthe jaw will simply
swivel allowing the kingpin tosituated at the upper end of the
plunger, thus jam-pull out and away from the jaw.ming the plunger
in the fully out position in readi-ness for uncoupling. 1.4 Trailer
and caravan drawbar couplings 1.4.1 Eye and bolt drawbar coupling
for heavy1.3.2 Operation of single jaw and pawl couplinggoods
trailers (Figs 1.25 and 1.26)(Fig. 1.24(ad)) Drawbar trailers are
normally hitched to the truckWith the trailer kingpin uncoupled,
the jaw will beby means of an `A frame drawbar which is coupledheld
open by the pawl in readiness for couplingby means of a towing eye
formed on the end of the(Fig. 1.24(a)). When coupling the tractor
to the drawbar (Fig. 1.25). When coupled, the towing eyetrailer,
the jaw of the fifth wheel strikes the kingpinhole is aligned with
the vertical holes in the upperof the trailer and swivels the jaw
about its pivot pin and lower jaws of the truck coupling and an
eyeagainst the return spring, slightly pushing out thebolt passes
through both coupling jaws and draw-pawl (Fig. 1.24(b)). Further
rearward movement ofbar eye to complete the attachment (Fig.
1.26).the tractor towards the trailer will swing the jaw Lateral
drawbar swing is permitted owing to theround until it traps and
encloses the kingpin. The eye bolt pivoting action and the slots
between the26
- 36. Fig. 1.22 (a and b) Fifth wheel coupling assemblyjaws on
either side. Aligning the towing eye to the as a damping media
between the towing vehicle andjaws is made easier by the converging
upper and trailer. These rubber blocks also permit additionallower
lips of the jaws which guide the towing eye asdeflection of the
coupling jaw shaft relative to thethe truck is reversed and the
jaws approach the draw beam under rough abnormal operating
con-drawbar. Isolating the coupling jaws from the ditions, thus
preventing over-straining the drawbartruck draw beam are two rubber
blocks which act and chassis system. 27
- 37. Fig. 1.23 (ad) Fifth wheel coupling with twin jaws plunger
and pawl 28
- 38. Fig. 1.24 (ad) Fifth wheel coupling with single jaw and
pawl 29