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 39. 1.4.2 Ball and socket towing bar coupling forlight caravan/trailers (Fig. 1.27)Light trailers or caravans are usually attached tothe rear of the towing car by means of a ball andsocket type coupling. The ball part of the attach-ment is bolted onto a bracing bracket fitted directlyto the boot pan or the towing load may be sharedout between two side brackets attached to the rearlongitudinal box-section members of the body. A single channel section or pair of triangularlyarranged angle-section arms may be used to formthe towbar which both supports and draws thetrailer. Attached to the end of the towbar is the sockethousing with an internally formed spherical cavity.This fits over the ball member of the coupling sothat it forms a pivot joint which can operate in boththe horizontal and vertical plane (Fig. 1.27). To secure the socket over the ball, a lock devicemust be incorporated which enables the coupling toFig. 1.25 Drawbar trailerbe readily connected or disconnected. This lockmay take the form of a spring-loaded horizontallypositioned wedge with a groove formed across itsThe coupling jaws, eye bolt and towing eye aretop face which slips underneath and against thegenerally made from forged manganese steel with ball. The wedge is held in the closed engaged pos-induction hardened pressure areas to increase the ition by a spring-loaded vertical plunger which haswear resistance.a horizontal groove cut on one side. An uncouplinglever engages the plungers groove so that when thecoupling is disconnected the lever is squeezed to liftOperation of the automatic drawbar coupling and release the plunger from the wedge. At the(Fig. 1.26) In the uncoupled position the eyebolt same time the whole towbar is raised by the handleis held in the open position ready for coupling to clear the socket and from the ball member.(Fig. 1.26(a)). When the truck is reversed, the jaws Coupling the tow bar to the car simply reversesof the coupling slip over the towing eye and in the the process, the uncoupling lever is again squeezedprocess strike the conical lower end of the eye boltagainst the handle to withdraw the plunger and the(Fig. 1.26(b)). Subsequently, the eye bolt will lift. Thissocket housing is pushed down over the ball mem-trips the spring-loaded wedge lever which now rotates ber. The wedge moves outwards and allows the ballclockwise so that it bears down on the eye bolt.to enter the socket and immediately the wedgeFurther inward movement of the eye bolt between springs back into the engaged position. Releasingthe coupling jaws aligns the towing eye with the eyethe lever and handle completes the coupling bybolt. The spring pressure now acts through the wedgepermitting the plunger to enter the wedge locklever to push the eye bolt through the towing eye and groove.the lower coupling jaw (Fig. 1.26(c)). When the eyeSometimes a strong compression spring is inter-bolt stop-plate has been fully lowered by the springposed between the socket housing member and thetension, the wedge lever will slot into its groovetowing (draw) bar to cushion the shock load whenformed in the centre of the eye bolt so that it locks the car/trailer combination is initially driven awaythe eye bolt in the coupled position. from a standstill. To uncouple the drawbar, the handle is pulledupwards against the tension of the coil springmounted on the wedge level operating shaft1.5 Semi-trailer landing gear (Fig. 1.28)(Fig. 1.26(d)). This unlocks the wedge, freeing the Landing legs are used to support the front of theeyebolt and then raises the eye bolt to the semi-trailer when the tractor unit is uncoupled.uncoupled position where the wedge lever jams itExtendable landing legs are bolted vertically toin the open position (Fig. 1.26(a)).each chassis side-member behind the rear wheels of 30 40. Fig. 1.26 (ae) Automatic drawbar coupling 31 41. 1.6 Automatic chassis lubrication system 1.6.1 The need for automatic lubrication system (Fig. 1.29) Owing to the heavy loads they carry commercial vehicles still prefer to use metal to metal joints which are externally lubricated. Such joints are kingpins and bushes, shackle pins and bushes, steering ball joints, fifth wheel coupling, parking brake linkage etc. (Fig. 1.29). These joints require lubricating in proportion to the amount of relative movement and the loads exerted. If lubrication is to be effective in reducing wear between the moving parts, fresh oil must be pumped between the joints frequently. This can best be achieved by incorporating an automatic lubrication system which pumps oil to the bearingsFig. 1.27 Ball and socket caravan/trailer towing surfaces in accordance to the distance travelled byattachment the vehicle.the tractor unit, just sufficiently back to clear the1.6.2 Description of airdromic automatic chassisrear tractor road wheels when the trailer is coupled lubrication system (Fig. 1.30)and the combination is being manoeuvredThis lubrication system comprises four major com-(Fig. 1.28(a)). To provide additional support forponents; a combined pump assembly, a power unit,the legs, bracing stays are attached between the legsan oil unloader valve and an air control unit.and from the legs diagonally to the chassis cross-member (Fig. 1.28(b)). The legs consist of inner and outer high tensile Pump assembly (Fig. 1.30) The pump assemblysteel tubes of square section. A jackscrew with a consists of a circular housing containing a ratchetbevel wheel attached at its top end supported by the operated drive (cam) shaft upon which areouter leg horizontal plate in a bronze bush bearing. mounted one, two or three single lobe cams (onlyThe jawscrew fits into a nut which is mounted at one cam shown). Each cam operates a row of 20the top of the inner leg and a taper roller bearing pumping units disposed radially around the pumprace is placed underneath the outer leg horizontal casing, the units being connected to the chassissupport plate and the upper part of the jackscrew bearings by nylon tubing.to minimize friction when the screw is rotated (Fig.1.28(b)). The bottom ends of the inner legs maysupport either twin wheels, which enable the trailerto be manoeuvred, or simply flat feet. The latter arePower unit (Fig. 1.30) This unit comprises aable to spread the load and so permit greater load cylinder and spring-loaded air operated pistoncapacity.which is mounted on the front face of the pump To extend or retract the inner legs, a windingassembly housing, the piston rod being connectedhandle is attached to either the low or high speed indirectly to the drive shaft ratchet wheel by way ofshaft protruding from the side of the gearbox. The a ratchet housing and pawl.upper high speed shaft supports a bevel pinionwhich meshes with a vertically mounted bevelwheel forming part of the jackscrew. Oil unloader valve (Fig. 1.30) This consists of a Rotating the upper shaft imparts motion directlyshuttle valve mounted on the front of the pumpto the jackscrew through the bevel gears. If greater assembly housing. The oil unloader valve allows airleverage is required to raise or lower the front of thepressure to flow to the power unit for the powertrailer, the lower shaft is engaged and rotated. stroke. During the exhaust stroke, however, whenThis provides a gear reduction through a com-air flow is reversed and the shuttle valve is liftedpound gear train to the upper shaft which then from its seat, any oil in the line between the powerdrives the bevel pinion and wheel and hence theunit and the oil unloader valve is then discharged tojackscrew. atmosphere.32 42. Fig. 1.28 (a and b) Semi-trailer landing gear33 43. Fig. 1.29 Tractor unit automatic lubrication systemAir control unit (Fig. 1.30) This unit is mountedhousing. Because the pawl meshes with one of theon the gearbox and is driven via the speedometer ratchet teeth and the ratchet wheel forms part oftake-off point. It consists of a worm and wheel drivethe camshaft, air pressure in the power cylinder willwhich operates an air proportioning controlpartially rotate both the ratchet and pawl housingunit. This air proportioning unit is operated by a and the camshaft clockwise. The cam (or cams) aresingle lift face cam which actuates two poppet in contact with one or more pump unit, and so eachvalves, one controlling air supply to the powerpartial rotation contributes to a proportion of theunit, the other controlling the exhaust air from the jerk plunger and barrel pumping cycle of each unitpower unit.(Fig. 1.30).As the control unit face cam continues to rotate, the inlet poppet inlet valve is closed and the exhaust1.6.3 Operation of airdromic automatic chassis poppet valve opens. Compressed air in the air con-lubrication system (Fig. 1.30) trol unit and above the oil control shuttle valve willAir from the air brake auxiliary reservoir passes by now escape through the air control unit exhaustway of the safety valve to the air control (propor-port to the atmosphere. Consequently the com-tioning) unit inlet valve. Whilst the inlet valve is pressed air underneath the oil unloader shuttleheld open by the continuously rotating face camvalve will be able to lift it and any trapped air andlobe, air pressure is supplied via the oil unloaderoil in the power cylinder will now be released viavalve to the power unit attached to the multipumpthe hole under the exhaust port. The power unitassembly housing. The power unit cylinder is sup-piston will be returned to its innermost position byported by a pivot to the pump assembly casing, the spring and in doing so will rotate the ratchetwhilst the piston is linked to the ratchet and pawland pawl housing anti-clockwise. The pawl is thus34 44. Fig. 1.30 Airdromic automatic chassis lubrication system 35 45. able to slip over one or more of the ratchet teeth to When the individual lubrication pump unitstake up a new position. The net result of the powerprimary plunger is in its outermost position, oilcylinder being charged and discharged with com-surrounding the barrel will enter the inlet port,pressed air is a slow but progressive rotation of thefilling the space between the two plungers. As thecamshaft (Fig. 1.30).cam rotates and the lobe lifts the primary plunger, A typical worm drive shaft to distance travelledit cuts off the inlet port. Further plunger rise willrelationship is 500 revolutions per 1 km. For 900partially push out the secondary plunger and soworm drive shaft revolutions the pumping cam open the check valve. Pressurised oil will thenrevolves once. Therefore, every chassis lubricationpass between the loose fitting secondary plungerpoint will receive one shot of lubricant in this and barrel to lubricate the chassis moving part itdistance.services (Fig. 1.30).36 46. 2Friction clutch2.1 Clutch fundamentals2.1.3 Multi-pairs of rubbing surfaces (Fig. 2.1)Clutches are designed to engage and disengage theAn alternative approach to raising the transmittedtransmission system from the engine when a vehicle torque capacity of the clutch is to increase theis being driven away from a standstill and when thenumber of pairs of rubbing surfaces. Theoreticallygearbox gear changes are necessary. The gradualthe torque capacity of a clutch is directly propor-increase in the transfer of engine torque to the tional to the number of pairs of surfaces for a giventransmission must be smooth. Once the vehicle is clamping load. Thus the conventional single drivenin motion, separation and take-up of the drive for plate has two pairs of friction faces so that a twingear selection must be carried out rapidly without or triple driven plate clutch for the same springany fierceness, snatch or shock. thrust would ideally have twice or three times the torque transmitting capacity respectively of that of2.1.1 Driven plate inertia the single driven plate unit (Fig. 2.1). However,To enable the clutch to be operated effectively, the because it is very difficult to dissipate the extradriven plate must be as light as possible so thatheat generated in a clutch unit, a larger safety factorwhen the clutch is disengaged, it will have the mini-is necessary per driven plate so that the torquemum of spin, i.e. very little flywheel effect. Spincapacity is generally only of the order 80% per pairprevention is of the utmost importance if the vari-of surfaces relative to the single driven plate clutch.ous pairs of dog teeth of the gearbox gears, be theyconstant mesh or synchromesh, are to align in the2.1.4 Driven plate wear (Fig. 2.1)shortest time without causing excessive pressure,Lining life is also improved by increasing thewear and noise between the initial chamfer of thenumber of pairs of rubbing surfaces because weardog teeth during the engagement phase. is directly related to the energy dissipation per unit Smoothness of clutch engagement may bearea of contact surface. Ideally, by doubling theachieved by building into the driven plate somesurface area as in a twin plate clutch, the energysort of cushioning device, which will be discussed input per unit lining area will be halved for a givenlater in the chapter, whilst rapid slowing down of slip time which would result in a 50% decrease inthe driven plate is obtained by keeping the diameter,facing wear. In practice, however, this rarely occurscentre of gravity and weight of the driven plate to(Fig. 2.1) as the wear rate is also greatly influencedthe minimum for a given torque carrying capacity.by the peak surface rubbing temperature and the intermediate plate of a twin plate clutch operates at2.1.2 Driven plate transmitted torque capacity a higher working temperature than either the fly-The torque capacity of a friction clutch can bewheel or pressure plate which can be more effect-raised by increasing the coefficient of friction ofively cooled. Thus in a twin plate clutch, half thethe rubbing materials, the diameter and/or the energy generated whilst slipping must be absorbedspring thrust sandwiching the driven plate. Theby the intermediate plate and only a quarter eachfriction lining materials now available limit theby the flywheel and pressure plate. This is usuallycoefficient of friction to something of the order of borne out by the appearance of the intermediate0.35. There are materials which have higher coeffi-plate and its corresponding lining faces showingcient of friction values, but these tend to be evidence of high temperatures and increased wearunstable and to snatch during take-up. Increasingcompared to the linings facing the flywheel andthe diameter of the driven plate unfortunately pressure plate. Nevertheless, multiplate clutchesraises its inertia, its tendency to continue spinningdo have a life expectancy which is more or lesswhen the driven plate is freed while the clutch is inrelated to the number of pairs of friction faces forthe disengaged position, and there is also a limit toa given diameter of clutch.the clamping pressure to which the friction liningFor heavy duty applications such as thosematerial may be subjected if it is to maintain its required for large trucks, twin driven plates arefriction properties over a long period of time.used, while for high performance cars where very37 47. Fig. 2.1 Relationship of torque capacity wear rate and pairs of rubbing faces for multiplate clutchrapid gear changes are necessary and largeamounts of power are to be developed, smalldiameter multiplate clutches are preferred.2.2 Angular driven plate cushioning and torsionaldamping (Figs 2.22.8)2.2.1 Axial driven plate friction lining cushioning(Figs 2.2, 2.3 and 2.4)In its simplest form the driven plate consists ofa central splined hub. Mounted on this hub is athin steel disc which in turn supports, by means ofa ring of rivets, both halves of the annular frictionlinings (Figs 2.2 and 2.3). Axial cushioning between the friction liningfaces may be achieved by forming a series of evenlyspaced `T slots around the outer rim of the disc.This then divides the rim into a number of seg-ments (Arcuate) (Fig. 2.4(a)). A horseshoe shapeis further punched out of each segment. The centralportion or blade of each horseshoe is given a per-manent set to one side and consecutive segmentshave opposite sets so that every second segment isriveted to the same friction lining. The alternativeset of these central blades formed by the horseshoepunch-out spreads the two half friction linings apart. An improved version uses separately attached, verythin spring steel segments (borglite) (Fig. 2.4(b)), pos-itioned end-on around a slightly thicker disc plate.These segments are provided with a wavy `set so asto distance the two half annular friction linings. Both forms of crimped spring steel segmentssituated between the friction linings provideFig. 2.2 Clutch driven centre plate (pictorial view)38 48. Fig. 2.3 Clutch driven centre plate (sectional view) Fig. 2.4 (a and b) Driven plate cushion take-upprogressive take-up over a greater pedal travel andThe spring take-up characteristics of the drivenprevent snatch. The separately attached spring plate are such that when the clutch is initiallysegments are thinner than the segments formed out engaged, the segments are progressively flattened soof the single piece driven plate, so that the squeeze that the rate of increase in clamping load is providedtake-up is generally softer and the spin inertia of the by the rate of reaction offered by the springthinner segments is noticeably reduced. segments (Fig. 2.5). This first low rate take-up A further benefit created by the spring segments period is followed by a second high rate engage-ensures satisfactory bedding of the facing material ment, caused by the effects of the pressure plateand a more even distribution of the work load. In springs exerting their clamping thrust as they areaddition, cooling between the friction linings occurs allowed to expand against the pressure plate andwhen the clutch is disengaged which helps to sta- so sandwich the friction lining between the flywheelbilise the frictional properties of the face material. and pressure plate faces. The advantages of axial cushioning of the facelinings provide the following: 2.2.2 Torsional damping of driven platea) Better clutch engagement control, allowing lower engine speeds to be used at take-up thusCrankshaft torsional vibration (Fig. 2.6) Engine prolonging the life of the friction faces.crankshafts are subjected to torsional wind-upb) Improved distribution of the friction work over and vibration at certain speeds due to the power the lining faces reduces peak operating tempera-impulses. Superimposed onto some steady mean tures and prevents lining fade, with the resultingrotational speed of the crankshaft will be additional reduction in coefficient of friction and subse- fluctuating torques which will accelerate and decel- quent clutch slip.erate the crankshaft, particularly at the front pulley39 49. the gear teeth, wear, and noise in the form of gear clatter. To overcome the effects of crankshaft torsional vibrations a torsion damping device is normally incorporated within the driven plate hub assembly which will now be described and explained. Construction and operation of torsional damper springs (Figs 2.2, 2.3 and 2.7) To transmit torque more smoothly and progressively during take-up of normal driving and to reduce torsional oscillations being transmitted from the crankshaft to the trans- mission, compressed springs are generally arranged circumferentially around the hub of the driven plate (Figs 2.2 and 2.3). These springs are inserted in elongated slots formed in both the flange of the splined hub and the side plates which enclose the hubs flange (Fig. 2.3). These side plates are riveted together by either three or six rivet posts which pass through the flanged hub limit slots. This thusFig. 2.5 Characteristics of driven plate axial clampingload to deflection take-up provides a degree of relative angular movement between hub and side plates. The ends of the helical coil springs bear against both central hub flange and the side plates. Engine torque is therefore transmitted from the friction face linings and side plates through the springs to the hub flange, so that any fluctuation of torque will cause the springs to compress and rebound accordingly.Multistage driven plate torsional spring dampers may be incorporated by using a range of different springs having various stiffnesses and spring loca- tion slots of different lengths to produce a variety of parabolic torsional loaddeflection characteris- tics (Fig. 2.7) to suit specific vehicle applications.The amount of torsional deflection necessary varies for each particular application. For example, with a front mounted engine and rear wheel drive vehicle, a moderate driven plate angular movement is necessary, say six degrees, since the normal trans- mission elastic wind-up is almost adequate, but with an integral engine, gearbox and final drive arrange- ment, the short transmission drive length necessit-Fig. 2.6 Characteristics of crankshaft torsional ates considerably more relative angular deflection,vibrations undamped and damped say twelve degrees, within t