LV04 vehicle construction issue 1

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Student Workbook

LV04 Vehicle Construction (1)

kap all covers 6/9/03 9:48 am Page 7

Student Workbook for Technical Certificates in

Light Vehicle Maintenance and Repair

MODULE LV04 VEHICLE CONSTRUCTION

Contents

Page Page

………

Main categories of materials Weather seals 23

used in automotive construction 3 Progress check 2 24

Metals 3

Ferrous metals 4 Vehicle Chassis Types: 25

High strength steel plate 4 Chassis construction 26

Cast iron 4 Self supporting frame 26

Non–ferrous metals 4 Partly supporting frame (sub-frame) 27

Copper 4 Platform chassis 27 Tin 5 Backbone chassis 28 Lead 5 Composite body 28 Aluminium 5 Ladder frame 29

Other materials (non-metallic) 6 Monocoque body 29

Plastics 6 Space frame 30

Rubber 7 Progress check 3 31

Totally tempered glass 7

Partly tempered glass 8 Chassis Construction Sub-

Laminated glass 8 assemblies: 32

Kevlar 9 Box section 32

Progress check 1 10 Tubular section (space frame) 33

C shaped channel 33

Exercise 1 12 Progress check 4 35

Spoilers and air dams 12

Sub frames 13 Vehicle Safety Construction

Roof panel 13 Features: 36

Scuttle plate 14 Passive systems 36

Side structure 14 Crumple zones 36

Exercise 2 15 Side impact 37

Exercise 3 16 SRS airbag 38

Panel fixing 17

Locking and securing devices 18 (Cont.)

Page ………

Seat belt pre-tensioners 38

Energy absorbing steering column 39

Active systems 40

ABS (Anti-lock Braking System) 40

VSC (Vehicle Stability Control) 40

Materials Used in Vehicle Construction

Main categories of materials used in automotive construction

The modern motor vehicle uses a vast array of differing materials in its

construction, each material adding to the vehicle’s strength, reliability,

resistance to corrosion and low noise vibration and harshness (NVH)

Manufacturers of motor vehicles now have to consider the impact that the use

of such materials will have on the environment

Metals

Metals form the major make up of a vehicle’s construction The properties

that metals possess lend themselves particularly well to use as a constructive

material for vehicles Metals have the following properties:

• ductility – can be drawn into wire

• malleability – can be rolled and hammered into sheets and foil

• large specific gravity (dense)

• high in electrical and thermal conductivity

It should be noted that mercury is a metal but possesses few of the above

properties

Ferrous metals

A ferrous metal is one that is derived from iron Iron is seldom used in its pure form, as it possesses poor strength and durability (it’s quite brittle) To

improve its characteristics, iron is often mixed with carbon The amount of

carbon that is used has a huge effect on the material If we use between

0.035% and 2% carbon, we have just produced steel If we use between 2% and 6.67% we have just produced cast iron

Carbon steel is used for body panels and some suspension components on motor vehicles

High strength steel plate

High strength steel plate can be created by mixing carbon steel with other

materials, or through special heat-treating processes Mixing in silicon,

manganese, phosphorous, titanium, vanadium or chromium can vastly

increase the strength of the steel and allow a manufacturer to reduce the

thickness of the material for a given required strength This reduces cost and saves weight, improving performance all-round Heating steel to specific

temperatures and then cooling them rapidly (known as quenching) can also achieve considerable changes in steels properties

Cast iron

Cast iron (iron containing 2% carbon or more) is often used for engine

components and is hot cast into moulds as a liquid Cast iron has good wear characteristics but is brittle

Tin

Tin is used to a limited degree in vehicle construction, as it is prone to

corrosion It is alloyed with lead to produce solder that is used in the joining of electrical circuits on vehicles An interesting fact is that solder has a lower

melting point than both of its constituent alloy materials (lead and tin)

Lead

Lead is used in the construction of vehicle batteries and is also used in the

alloyed metal of crank shaft bearings

Aluminium

Aluminium, as well as being the most abundant metal (and therefore cheap) is extremely light and has good electrical conductivity It is used extensively on vehicles often making up large proportions of engine components and even

body panels and structural members As can be seen from the table above,

aluminium can be alloyed with many different materials to give it specific

characteristics

Other materials (non-metallic)

Non-metallic materials are used in abundance on modern motor vehicles

They fall into two main categories – organic (natural) and inorganic Organic materials would include leather (seat covers etc.) and plastics (derived from oil) and inorganic would include glass

Plastics

A selection of plastics that are regularly used in the construction of motor

vehicles are shown above

Plastics are classified as either thermoplastics or thermosetting plastics A

thermoplastic is one that becomes pliable again when reheated, a

thermosetting plastic, once initially set, cannot be reheated (they burn rather than melt)

Be aware that ECU casings are often made of ABS and this can be

misleading if you are trying to identify the ABS ECU (Anti-lock Braking

System) as ABS is often stamped on these assemblies to identify the material not the function!

Rubber

Rubber can be either natural or synthetic (man made) Natural rubber is

made from the sap of a rubber tree In its natural state it is of little use, but

once vulcanised – heated with sulphur – it takes on elastic properties (the

ability to readopt original shape once a deflecting force is removed)

Synthetic rubber is an elastic polymer and tends to be far more suited to

vehicle applications Chemical engineers can change its structure to ensure compatibility with highly aggressive oils such as brake fluid

Totally tempered glass

Totally tempered glass is heat-treated in accordance with the diagram above When you heat a given material you change its molecular structure physically Most materials if allowed to cool slowly will readopt their original molecular

condition but if you quench that material (rapidly cool it) it will stick in that

changed state This is often a highly stressed state Glass is no exception Totally tempered glass is cooled rapidly at the end of the process to retain

strength-orientated characteristics Quenching rapidly makes the glass

around four times more shock resistant than conventional glass However, if it does break it often shatters catastrophically because of the quenching

stresses within it depriving the driver of any forward vision For this reason it

is seldom used for front screens

Partly tempered glass

Glass that is partly tempered receives limited quenching to the middle area This process ensures that if breakage occurs the glass that has only been

partly tempered breaks into very large pieces Therefore a limited amount of frontal vision is retained

Laminated glass

To laminate means to layer Laminated glass is two thin sheets of glass

bonded together with a transparent resin film As a safety glass it has huge benefits

The resin layer prevents the glass shards from falling into the vehicle when

the screen breaks It is highly resistant to penetration and frontal view is

maintained upon breakage

Kevlar

Kevlar is a manmade organic fibre introduced in the early 1970’s It combines high tensile strength with low weight and has high chemical resistance It is tough, with high cut resistance and is also flame proof and self-extinguishing Typical applications:

• bullet proof vests

• data transmission cables

• vehicle body panels

Progress check 1

Answer the following questions:

1 What are the minimum and maximum carbon content values for iron to

be classed as steel?

2 In the context of plastics, what does ABS stand for?

3 What does synthetic mean?

4 List five applications for Kelvar on a motor vehicle

5 What does the term laminated refer to when used in conjunction with

vehicle windscreens?

Component Identification

Doors, bonnet and boot lid

It is important to understand that all component parts that go up to make a

vehicle’s body have specific names However, different countries often use different names Typical!

A wing can also be a fender; a doorsill a rocker cover, a bonnet could be

referred to as a hood

Today's vehicles evolved from early forms of transport and as such retain a certain amount of the terminology from these periods For example, a ‘list rail’

is a term used to describe a supporting piece stretching from one side of a

structure to the other (such as the boat lists to port or starboard) A term

derived from our naval heritage

A ‘cant rail’ is a name given to a strengthening structure running from front to rear

A ‘flitch plate’ is a strengthening plate inside a beam

Exercise 1

Label the key components on the diagram below:

Spoilers and air dams

The front air dam and rear spoiler help to stabilise the vehicle and give better fuel economy through improved airflow over the body Some spoilers can

actually create a positive pressure above the assembly, resulting in

considerable down force and vastly improved performance all round

However, this is most unusual for a road car – at best the spoiler reduces lift

at high speed, at worst there are no benefits whatsoever rather than the

enhancement of appeal to some drivers!

Sub-frames

A sub-frame is often used to mount the major assemblies on a vehicle

equipped with a monocoque type chassis configuration

Roof panel

The roof panel is a major structural member, experiencing considerable

compressive forces If the vehicle has a factory fitted sunroof, the roof panel

is often strengthened to accommodate the loss of strength that this item would create

Scuttle plate

The scuttle plate used to form part of the integral structural strength of a

vehicle’s chassis, but designs have altered considerably over the last few

years and the importance of the scuttle has diminished It is now more often a trim panel or at most a mounting for the wiper linkage

Exercise 2

Working directly on the picture below, assign the correct letters to the

component names in the list below:

• chassis leg

• boot floor

• boot floor side extension

Panel fixing

Many different methods are employed to fix panels to a vehicles chassis

Below are a few examples:

Locking and securing devices

Coach bolt

Countersunk screw Self tapping

There are many different types of locking device available, some of which are pictured here They are all designed with one primary task in mind – holding components together, either permanently or temporarily A common

misconception is that a screw has a sharp point and is designed to cut its own thread This is not correct in engineering terms A screw is almost identical to

a bolt with the exception that it is threaded all the way to the bottom of the

head and is seldom used in conjunction with a nut (it screws into threaded

components) A bolt has a thread-less shank Only self-tapping screws (cut their own thread) have sharp points!

Hexagon head bolts and screws are used far less frequently now than was the case only a few years ago You are far more likely to come across multi-

spline types and Torx types where a securing device needs to be

accommodated in a tight space (with hexagon head devices, space needs to

be left around the head to accommodate a socket for the fitting and removal) Tight spaces are now commonplace on light vehicles as manufacturers strive for every gram of weight saving and every centimetre of extra occupancy

space

When ordering a bolt (standard design) from the parts department, they will want to know the following information if the device you want is not specific to task:

• overall length

• diameter

• thread pitch

• strength rating

A typical specification could be:

• 75mm long, M8 coarse thread, strength rating 8

This would give you a bolt that is 75mm in length from its threaded end to the underneath of the head, an 8 mm thread diameter with a thread pitch of

1.5mm with a strength rating that would see it safe up to a torque of 13Nm

Nut Flanged nut Nylock nut

Nuts are also available in several different types When ordering you must

ensure that you ask for a nut that has the same thread as the bolt to which it is

to be fitted – this means both thread diameter and thread pitch Do you want metric fine (1.25mm pitch) or metric coarse (1.5mm pitch)? Some specialist

nuts can be seen above The flanged nut is designed to spread the

compression load a little onto the component surface The Nylock nut (trade name) is designed to grip the bolt thread through means of friction, generated

by the bolts thread cutting through the nylon collar at the top of the nut It

should be noted that these nuts should never be reused Castellated nuts are designed to be used in conjunction with split pins, and wing nuts are used

where regular and easy removal is required (seldom used on modern

vehicles) Shear nuts are often the choice where security is an issue such as with vehicle immobiliser equipment

There are now many different types of chemical compounds available to do anything from locking a thread to prevent vibration loosening, to sealing joints and even temporarily sealing radiators, tyres and cylinder blocks!

Always read the instructions thoroughly before use and if you are unsure of the health and safety risks, always refer to the COSHH data sheet for that

specific product

Some panels are bonded into place and others (like rear masking panels) can

be riveted Masking panels are found under the rear light units and sit on top

of rear bumper Not all parts, like front wings are bolted into place they are also welded Trims are held in place with plastic clips or screws Mouldings that go down the side of vehicles can be held with plastic clips or double sided tape

MIG Welder Spot Welder

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A spot welder is generally used but where space or access is limited or for

welding panels such as chassis legs that need a seam weld a MIG welder is preferred

Riveting: This kind of panel fixing is used on some steel vehicles but only a small amount It is used on a larger scale on aluminium vehicles to fix panels together Bonding of panels is also used on aluminium vehicles and

composite cars and will be used to a greater extent in vehicle production in

the future

Hinges

Hinges are often bolted or pinned to the vehicles chassis Pins are passed

through a locating hole in the hinge, the hinge itself being welded to the body The hinge is in two parts - upper and lower; on the door there is one locating hinge that fixes to the hinge on the body The pin is then inserted into the

hole going through all three parts of the hinge thus fixing the door to vehicle