Advances - in - Vehicle - Design

Advances - in - Vehicle - Design

(Parte 1 de 7)

Advances in Vehicle Design Advances in Vehicle Design

To Ruth To Ruth

Advances in Vehicle Design by John Fenton

Professional Engineering

Publishing

Professional Engineering Publishing Limited London and Bury St Edmunds, UK

First published 1999

This publication is copyright under the Berne Convention and the International Copyright Convention. All rights reserved. Apart from any fair dealing for the purpose of private study, research, criticism, or review, as permitted under the Copyright Designs and Patents Act 1988, no part may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, electrical, chemical, mechanical, photocopying, recording or otherwise, without the prior permission of the copyright owners. Unlicensed multiple copying of this publication is illegal. Inquiries should be addressed to: The Publishing Editor, Mechanical Engineering Publications Limited, Northgate Avenue, Bury St Edmunds, Suffolk, IP32 6B W, UK.

© John Fenton ISBN 1 86058 181 1

A CIP catalogue record for this book is available from the British Library.

The publishers are not responsible for any statement made in this publication. Data, discussion, and conclusions developed by the Author are for information only and are not intended for use without independent substantiating investigation on the part of the potential users. Opinions expressed are those of the Author and are not necessarily those of the Institution of Mechanical Engineers or its publishers.

Printed and bound in Great Britain by St Edmundsbury Press Limted, Suffolk, UK vii Preface

Chapter 1: Materials and construction advances

2 Steel durability and structural efficiency 3 Vigorous development of light alloys

4 Hybrid metal/plastic systems 7 Recycled PET, and prime PBT, for sun-roof parts 10 Material property charts and performance indices 13 Design for self-pierce riveting

Chapter 2: Structure and safety

20 Structure analysis for interior noise 24 Preparing for statutory pedestrian protection 27 Design for the disabled 31 Adaptive restraint technologies

Chapter 3: Powertrain/chassis systems

36 Powertrains: the next stage? 45 Constant-pressure cycle: the future for diesels? 47 Valve arrangements for enhanced engine efficiency

52 Trends in transmission design 58 The mechanics of roll-over 62 Suspension and steering linkage analysis

Chapter 4: Electrical and electronic systems

70 Automotive electronics maturity 76 Navigation system advances 79 Digital circuits for computation 81 Proprietary control system advances

84 Hybrid drive prospects 90 Automation of handling tests

Chapter 5: Vehicle development

102 Ford Focus 108 Land Rover Freelander

112 Project Thrust SSC

Chapter 6: Systems development: powertrain/chassis

118 Engine developments 122 Engine induction systems 124 Refinement and reduced emissions

128 Drive and steer systems 133 Suspension development 139 Braking systems

Chapter 7: System developments: body structure/systems

145 Body shell integrity 147 Chassis/body shell elements

151 Car body systems 151 Occupant restraint

155 Doors, windows and panels 159 Trim and fittings 161 Aerodynamics and weight saving 163 CV systems 163 CV chassis-cab configuration 164 Cab/body fittings

168 Advanced bus/ambulance design

Preface

This lite'rature survey is aimed at providing the vehicle design engineer with an update in vehicle and body systems. The author has scanned the considerable output of technical presentations during 1997- 9 to extract and distil developing technologies of particular import to the working designer. The easily digestible presentation, with unusually high dependence on diagrammatic presentation, continues the popular style used for the original handbooks that were compiled by the author, and published by Professional Engineering Publishing. These are listed on the Related Titles page overleaf. Advances in Vehicle Design serves both as an update to the earlier volumes and as a stand-alone volume. The referenced leads provided in the text are intended to help designers and engineers from whatever background discipline. Widespread availability of computing power to designers and engineers has created the possibility of considerably shortening the lead-times between design conception and prototype manufacture. Much of the material covered here will assist in establishing predictive techniques.

Advances in Vehicle Design is an update of vehicle and body systems design in that it provides readers with an insight into analytical methods given in a wide variety of published sources such as; technical journals, conference papers, and proceedings of engineering institutions, for which a comprehensive list of references is provided. The analyses are therefore not necessarily fully developed or rigorously evaluated. Recourse to the original references is necessary particularly in order to understand the limiting assumptions on which the analyses are based.

Much of the analytical work is centred around impending legislation and, where this is quoted in the text, it is for illustration only and it is, of course, important to examine the latest statutes in the locality concerned. The list of references given at the end of the volume is a key element of the publication, providing where possible a link to the original publication source. Where the original publication is not available in bookshops, many of the sources can be found in libraries such as those of the Institution of Mechanical Engineers, London, or the Motor Industry Research Association, in Nuneaton, UK,as well as the BritishLibrary.Othersimilar respositories of techincal information should be able to provide a selection of original source material. Where the source is a company announcement of techniques and systems, names, but not addresses, of the companies/consultancies are given. Most operate internationally and have different national locations, best found by enquiry in the country concerned. For the patent reviews in chapters six and seven, full specifications can be purchased from The Patent Office, Cardiff Road, Newport, NP91RH, UK.

Related Titles

Title Editor/Author ISBN/ISS N

Multi-Body Dynamics HRahnejat Gasoline Engine Analysis J Fenton

Handbook of Automotive Body Construction J Fenton and Design Analysis

Cranes - Design, Practice and Maintenance J Verschoof Handbook of Automotive Body Systems Design J Fenton Handbook of Automotive Powertrain and J Fenton Chassis Design Vehicle Handling Dynamics J Ellis Handbook of Vehicle Design Analysis J Fenton Automotive Braking: - Recent Developments D Barton Brakes and Friction Materials G A Harper Automotive Engineer Monthly Magazine W Kimberley Journal of Automotive Engineering (IMechE Proceedings Part D)

For full details of all Professional Engineering Publications please contact:

Sales Department Professional Engineering Publishing Nothgate Avenue

Bury St Edmunds IP326BW

Fax: +4(0)128471869 3 E-mail: sales@imeche.org.u k

Chapter 1: Materials and construction advances

The considerable comeback made by the steel industry in restating its case for structural superiority over the light alloys, and the ever moving goalposts of developing aluminium and polymer composites, open this chapter. The re-emergence of hybrid metal/plastic structures is also discussed as well as the creation of reinforced plastics with recycled-polymer matrices. The move to material property charts which lead to the creation of performance indices is next examined and the chapter concludes with the efforts to make self-pierce riveting a viable alternative to conventional welded joints in body construction.

Steel durability and structural efficiency

According to researchers at Lotus Engineering1, market expectations for durability of vehicle body panels is typically seven years or 100 0 miles, with an expectation of 10 years corrosion-free life. British

Steel engineers2 have shown the main influences on durability with the corrosion triangle of Fig 1. In product design the traditional approach has been to remove moisture traps, allow better penetration of paint and evolve design with greater resistance to stone chipping. There had also been gradual adoption of one-side zinc-coated steel panels, offering protection on the inside and good paintability on the outside. More recently there had been a move from hot dip galvanized to electrozinc panels, spurred by Japanese manufacturers; these offer a range of ductilities, increased weldability and the ability to alloy the coating to provide various coating thicknesses and corrosion resistance levels. Now double- sided coated steels are favoured with differential coating weights: typical thicknesses are now 45-60 g/m2. Future quality improvements are promised by development work in surface treatment and formability. Permanent organic based topcoats or

phosphate coatings are providing improved performance in both weldability and corrosion prevention.

Another new initiative is a drive by the OEMs to replace electroplated products by 'galvanneal' ones for outside parts, in the interests of production economy. These have the ability to provide good paintability.

In a joint venture between British Steel Strip

Products and Rover Group, trial parts were prepared for the Rover 600, including front fender, front door skin, rear door skin and bonnet. In 1997 all new models were produced with two-sided galvanneal full-finished panels. In the longer term, the authors see the development of non-bake hardening, higher strength steel substrates with enhanced formability for use with galvanneal coatings, and the introduction of extra high strength transformation induced plasticity (TRIP) steels as substrates for zinc type coating which will offer yield strength approaching 1500 MPa, alongside high ductility. Prepainted body finished sheet steel, which obviate the electropheritic primer coat are also expected, as is a possible new coating process based on vapour deposition of zinc in

Car body weight reduction of 25%, without cost penalty, plus a 20% reduction in part count, has been the result of the final phase of the USLAB project for light-weighting steel automotive structures carried out by an international consortium of steel companies supervised by Porsche Engineering Services. The objective of a feasible design, using commercially available materials and manufacturing processes, has also been met. An 80% gain in torsional rigidity, and 52% in bending, has also been recorded and estimated body-shell cost of $947 compares with $980 for a year 2000 comparison figure for

Environmen t (including micro environment)

Autobody

Materials of Construction

Design

Fig 1: Triangle of factors affecting corrosion

Fig 2: ULSAB body shell

Fig 3: Monoside panel Fig 4 : Side roof rail

a conventionally constructed body to a similar specification. The 203 kg body shell (Fig 2), of 2.7 metres wheelbase, has a torsional rigidity of 20,800 Nm/deg and a first torsional vibration mode of 60 Hz, using the well-documented construction techniques.

A supercomputer analysis of crashworthiness has shown that frontal NCAP and rear movingbarrier levels have been achieved at 17% higher than the required speed. The body has also satisfied 5 kph/50% offset AMS, European side impact and roof crush requirements. The 35 mph frontal NCAP showed a peak deceleration of 31 g, considered satisfactory in that stiffer body sides are required to meet 50% AMS offset requirements. The offset AMS frontal impact deceleration showed a peak at 35g, considered a good result in relation to the severity of the test. The simulation was carried out at 1350 kg kerb weight, plus 113 kg luggage and 149 kg for two occupants. At the final count, high strength steel was used for 90% of the structure, ranging from 210 to 550 MPa yield, in gauges from 0.65 to 2 m. Around 45% of the structure involved laser-welded tailored blanks, including the monoside panels, Fig 3, which ranged in gauge from 0.7 to 1.7 m and was made up of steel elements having yield strengths from 210 to 350 MPa. Fig 4 shows the hydroformed side roof rail.

To the casual observer the elements of the complete body shell 'look' more structurally efficient but they still seem a far cry from a fully optimized shape for the steel 'backbone', as much of the material seems to be still used in relatively low stress areas where its function is as a 'cover' rather than a fully working structural element. Perhaps the next stage in weight reduction should be in designing a highly efficient steel monocoque, then moulding over plastic elements for the non-structural covering and closure shaping details, using the hybrid metal/ plastics techniques discussed later in this chapter.

Vigorous development of light alloys

Phase 2 of Audi's aluminium alloy body construction programme was unveiled at a recent Motor Show in the form of the A12 concept car, Fig 5. The 3.76 metre long times 1.56 metre high car weighs just 750 kg in

1.2 litre engined form, some 250 kg less than a conventional steel body vehicle, it was argued. The number of cast nodes has been reduced compared with the Phase-one aluminium alloy structure of the Audi A8. Most of the nodes are now produced by butt-welding the extruded sections. High level seating is provided over a sandwich-construction floor.

Use of internal high pressure reshaping techniques has reduced the number of shaping and cutting operations required

The 1997 International Magnesium Association Design Award for applications went to the diecast instrument panel support beam, Fig 6, on the GM G-van. It is a one-piece design weighing, at 12.2 kg, 5.9 kg less than the welded steel tubular structure it replaced. Proponents of magnesium alloy are pointing out that as die-castings in the material solidify from the outside in, they enjoy a dense chilled skin together with a relatively course-grained interior. Skin thickness is said to be relatively constant regardless of total wall thickness so that reductions in section size can often be made when the material is used as a substitute. The AZ91D (9% aluminium, 1% zinc) alloy is now finding application in removable rear seats for minivans. In the seat systems shown in Fig 7, Delphi Automotive have achieved 60% weight reduction over conventional construction by adopting a cast magnesium cushion frame and an extruded

Fig 5 A12 concept car and structure aluminium back frame. Other magnesium grades are being used in combination with engineering plastics for composite instrument panels. VW have also demonstrated a Polo door in pressure die-cast magnesium with a carbon fibre reinforced outer panel, which offers over 40% weight reduction over conventional steel construction.

Hybrid metal/plastic systems

Metal/plastic composites have been promoted again by Bayer in a recent presentation to body engineers3 .

A compelling argument is made for using simplified thin-wall structures in high strength metals which are stabilized by plastic composites which can also cut down on welding operations when combined as an inmould assembly. The complexity of CV-cab and car bodies has often ruled against the effective use of lightweight metal systems on their own.

(Parte 1 de 7)

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