Automotive chassis technology

Module code: AUT203 Assistant lecturer: Pacifique TURABIMANA 2016-2017 Page
MECHANICAL ENGINEERING DEPARTMENT
AUTOMOBILE TECHNOLOGY OPTION
MODULE CODE: AUT 203
MODULE NAME: AUTOMOTIVE CHASSIS TECHNOLOGY
CREDIT: 10
YEAR: II
SEMESTER: II
ACADEMIC YEAR: 2016-2017
ASSISTANT LECTURER: Pacifique TURABIMANA
Gishari, February 2017

Module code: AUT203 Assistant lecturer: Pacifique TURABIMANA 2016-2017 Page i
Cognitive/Intellectual skills/Application of Knowledge
Having successfully completed the module, students should be able to:
1. Explain the difference between unitized vehicles and body-over-frame vehicles.
2. Describe the manufacturing process used in a modern automated automobile assembly
plant.
3. List the basic systems that make up an automobile and name their major components and
functions.
4. Explain the vehicle body repair technology
5. Explain basic operating principle of steering system
6. Explain the operating principle of different steering system
7. Compare the different steering system and explaining advantages and disadvantages.
8. Explain the basic principle of suspension
9. Compare the different types of suspension
10. Describe the basic principle of braking system
11. Differentiate all braking systems

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Table of Contents
List of figures...............................................................................................................................................vi
CHAPTER: 1. CHASSIS FRAME AND BODY .........................................................................................1
Objectives .....................................................................................................................................................1
1.1. Introduction of chassis Frame................................................................................................................1
1.2. Functions of the chassis frame...............................................................................................................2
1.3. Types of chassis frames .........................................................................................................................2
Various loads acting on the frame.................................................................................................................2
1.4. Vehicle body construction .....................................................................................................................3
1.5. Vehicle Body repair...............................................................................................................................5
1.5.1. Introduction to panel beating ..............................................................................................................5
1.5.2. Safe automobile cleaning....................................................................................................................6
1.5.3. Auto body maintenance ......................................................................................................................7
1.5.4. Bumper removal and installation........................................................................................................8
1.5.5. How to repair automotive dent............................................................................................................8
Self- Assessment exercises No 1 ................................................................................................................11
CHAPTER TWO: STEERING SYSTEM..................................................................................................12
Objectives ...................................................................................................................................................12
2.1. Introduction..........................................................................................................................................12
2.2. Requirements of steering system .........................................................................................................13
2.3. Functions of steering system................................................................................................................13
2.4. Steering Components...........................................................................................................................14
2.4.1. Steering wheels.................................................................................................................................14
2.4.2. Steering columns...............................................................................................................................14
Safety steering column................................................................................................................................15
2.4.3. Steering Damper ...............................................................................................................................16
2.4.4. Steering linkage ................................................................................................................................16
2.4.5. Track rod on vehicles with rigid (beam) front axle...........................................................................17
2.4.6. Track rod for independent suspension ..............................................................................................19
2.4.7. Steering box ......................................................................................................................................20
Function of steering gearbox ......................................................................................................................21
Types of steering gearbox...........................................................................................................................21
2.5. Steering Mechanism.............................................................................................................................24
2.6. Power-steering systems........................................................................................................................25
2.6.1. Integral Piston System ......................................................................................................................25
2.6.2. Power-Assisted Rack and Pinion System .........................................................................................26
Components ................................................................................................................................................26
Power-Steering Pump .................................................................................................................................26
Power-Steering Pump Drive Belts..............................................................................................................27
Electric Power Steering...............................................................................................................................27
Flow Control and Pressure Relief Valves...................................................................................................27
Power-Steering Gearbox.............................................................................................................................27
Power-Assisted Rack and Pinion Steering..................................................................................................28
Power-Steering Hoses.................................................................................................................................28

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2.6.3. Electronically Controlled Power steering Systems...........................................................................29
Active Steering............................................................................................................................................30
Steer-by-Wire System.................................................................................................................................31
2.6.4. Four-Wheel Steering Systems...........................................................................................................31
2.7. Work on the steering gear....................................................................................................................32
Adjusting the steering box ..........................................................................................................................32
Measuring wheel alignment........................................................................................................................33
Types of Wheel Alignment.........................................................................................................................33
Factors effects the wheel alignment............................................................................................................34
Caster angle.................................................................................................................................................34
Camber angle ..............................................................................................................................................35
Toe ..............................................................................................................................................................35
King- pin inclination...................................................................................................................................36
Steering system diagnosis...........................................................................................................................36
Self –assessment exercises No 2.................................................................................................................37
CHAPTER 3: SUSPENSION SYSTEM ....................................................................................................39
Objectives ...................................................................................................................................................39
3.1. Introduction..........................................................................................................................................39
3.2. Functions of suspension system...........................................................................................................40
3.3. Requirements of suspension system ....................................................................................................40
3.4. Suspension system components...........................................................................................................40
Springs ........................................................................................................................................................40
Coil Springs ................................................................................................................................................41
Leaf springs.................................................................................................................................................42
Shock Absorbers.........................................................................................................................................45
Macpherson strut suspension components..................................................................................................47
3.5. Electronically controlled suspensions..................................................................................................49
3.6. Servicing electronic suspension components.......................................................................................50
Diagnosis ....................................................................................................................................................50
3.7. Active suspensions/ Active Body Control ...........................................................................................50
Control Procedures......................................................................................................................................52
Basic front-suspension diagnosis (Conventional suspension system) ........................................................53
CHAPTER: 4. TYRE AND WHEEL .........................................................................................................56
Objectives ...................................................................................................................................................56
4.1. Introduction..........................................................................................................................................56
4.2. Acting force .........................................................................................................................................56
4.3. Wheels..................................................................................................................................................57
4.4.Tires ......................................................................................................................................................59
4.4.1. Tube and Tubeless Tires ...................................................................................................................59
4.4.2. Types of Tire Construction ...............................................................................................................61
4.4.3. Basic Components /Tyre Construction .............................................................................................62
4.4.4. Tire ratings and designations ............................................................................................................65
Tire Size......................................................................................................................................................65

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Run flat tyre system ....................................................................................................................................67
4.5. Tire Pressure Monitor (TPM) ..............................................................................................................68
Testing a TPM System................................................................................................................................71
4.6. Tire/Wheel Runout...............................................................................................................................71
Tire replacement .........................................................................................................................................72
Replacing One Tire.....................................................................................................................................73
Replacing Two Tires...................................................................................................................................73
Changing Tire and/or Wheel Size...............................................................................................................73
4.7. Tire repair.............................................................................................................................................74
CHAPTER: 5: BRAKING SYSTEM .........................................................................................................75
Objectives ...................................................................................................................................................75
5.1. Introduction..........................................................................................................................................75
5.1.1. Principle of braking system...............................................................................................................75
5.1.2. Requirements of brake ......................................................................................................................76
5.1.3. Stopping distance and braking efficiency .........................................................................................76
5.1.4. Classification of brakes.....................................................................................................................77
5.2.1. Drum Brakes.....................................................................................................................................78
Drum Brake Systems and Operation...........................................................................................................78
Drum brake components.............................................................................................................................78
Parking Brake System.................................................................................................................................82
Components ................................................................................................................................................82
Operation ....................................................................................................................................................83
Servo brake designs ....................................................................................................................................84
Self-adjustment mechanisms ......................................................................................................................85
5.2.2. Disk brakes........................................................................................................................................86
5.2.2.1. Disc Brake Assembly.....................................................................................................................87
Floating caliper ...........................................................................................................................................88
Fixed caliper................................................................................................................................................88
5.3. Principles of hydraulic brake systems..................................................................................................89
Hydraulic brake system components ..........................................................................................................89
5.4. Hydraulic system safety switches and valves ......................................................................................91
Stoplight Switch..........................................................................................................................................91
Brake Warning Light Switch ......................................................................................................................92
Metering Valve ...........................................................................................................................................92
Proportioning Valve....................................................................................................................................92
Combination Valve.....................................................................................................................................92
5.5. Air brake system ..................................................................................................................................93
Construction and working of Air Brake system..........................................................................................93
Basic components of air brake system........................................................................................................93
Working ......................................................................................................................................................95
Advantages:.................................................................................................................................................95
Disadvantages .............................................................................................................................................96

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5.6. Basics of the electronic chassis control systems..................................................................................96
5.6.1. Anti-lock Braking System ABS........................................................................................................98
ABS systems have the following features: .................................................................................................98
Operating principle .....................................................................................................................................98
ABS with return in a closed circuit.............................................................................................................99
Operating principle with 3/3 solenoid valves ...........................................................................................100
Operating principle with 2/2 solenoid valves ...........................................................................................100
ABS with return in an open circuit and 2/2 solenoid valves.....................................................................100
Structure....................................................................................................................................................101
Electrical circuit of an ABS ......................................................................................................................102
5.6.2. Brake assistant (BAS).....................................................................................................................103
Structure....................................................................................................................................................103
Operating principle ...................................................................................................................................103
5.6.3. Automatic Traction control.............................................................................................................104
Engine Controls ........................................................................................................................................105
5.6.4. Automatic stability control..............................................................................................................105
5.6.5. Sensotronic Brake Control SBC .....................................................................................................107
Advantages of SBC system.......................................................................................................................108
Addtional functions of SBC......................................................................................................................108
5.6.6. DSC (Dynamic Stability Control system）....................................................................................109
Indicative Resources.................................................................................................................................110

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List of figures
Figure 1: Layout of Chassis and its main Components.................................................................................1
Figure 2: Ladder type frame .........................................................................................................................3
Figure 3: Partially self-supporting construction............................................................................................3
Figure 4: Passenger car Floor assembly........................................................................................................4
Figure 5: Main steering components...........................................................................................................14
Figure 6: Steering column...........................................................................................................................15
Figure 7: Safety steering column ................................................................................................................16
Figure 8: Steering linkage/ centrally divided track rod ............................................................................18
Figure 9: Parallelogram steering system mounts (A) behind the front suspension, and (B) ahead of the
front suspension ..........................................................................................................................................19
Figure 10: Track rod divided at one side ....................................................................................................20
Figure 11: Three-piece Track rod ...............................................................................................................20
Figure 12: Worm and sector steering box...................................................................................................21
Figure 13: Recirculating-ball steering box..................................................................................................22
Figure 14: Worm and roller steering box....................................................................................................23
Figure 15: Rack and pinion steering gear ...................................................................................................23
Figure 16: Ackermann steering, toe-difference angle.................................................................................24
Figure 17: A typical hydro-boost system that uses the power-steering pump to power assist brake
applications .................................................................................................................................................25
Figure 18: Power-Assisted Rack and Pinion System..................................................................................26
Figure 19: A variable-assist power-steering system. ..................................................................................29
Figure 20: The main components and circuits of an active steering system...............................................30
Figure 21: The basic layout for a steer-by-wire system..............................................................................31
Figure 22: Three types of caster: (A) zero, (B) positive, and (C) negative.................................................35
Figure 23: (A) Positive and (B) negative camber. ......................................................................................35
Figure 24: Various type of Automotive spring ...........................................................................................41
Figure 25: The different designs of coil springs .........................................................................................41
Figure 26: A rear suspension setup with air springs. ..................................................................................43
Figure 27: The typical location of a stabilizer bar ......................................................................................44
Figure 28: A torsion bar setup. ...................................................................................................................44
Figure 29: Gas-pressure damped shocks operate like conventional oil-filled shocks. Gas is used to keep
oil pressurized, which reduces oil foaming and increases efficiency under seven conditions....................47
Figure 30: A complete MacPherson strut front suspension ........................................................................48
Figure 31: A modified MacPherson suspension has the spring mounted separately from the strut ...........48
Figure 32: The various inputs and outputs for an electronic suspension system. .......................................49
Figure 33: Active Body Control (Layout)...................................................................................................51
Figure 34: ABC hydraulic circuit diagram .................................................................................................52
Figure 35: Force acting on the wheel/tyre combination..............................................................................57
Figure 36: Wheel dimensions are important when replacing tires..............................................................58
Figure 37: A typical tubeless tire................................................................................................................60
Figure 38: The construction of the three basic types of tires......................................................................62
Figure 39: Tyre Thread components...........................................................................................................63

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Figure 40: The tire pressure monitor (TPM) components ..........................................................................70
Figure 41: A TPM tester. ............................................................................................................................71
Figure 42: Checking wheel runout..............................................................................................................72
Figure 43: Drum brake components and bolts to........................................................................................79
Figure 44: Brake shoes................................................................................................................................80
Figure 45: An illustration of typical shoe return springs. Figure 46: Examples of different
types of holddown.......................................................................................................................................81
Figure 47: An inside view of a typical wheel cylinder. ..............................................................................81
Figure 48: Self-adjusters are typically located at the bottom Figure 49: The anchor in a servo brake is
located at the ...............................................................................................................................................82
Figure 50: An illustration of a hand-operated parking brake assembly. .....................................................83
Figure 51: The components of a manually released foot operated parking brake pedal.............................84
Figure 52: Non-servo brakes have leading and trailing ..............................................................................84
Figure 53: An example of a servo brake assembly. ....................................................................................84
Figure 54: An illustration of a typical servo brake self-adjuster and an example of a ratcheting self-
adjuster on a non-servo brake assembly. ....................................................................................................86
Figure 55: Disc brake assembly..................................................................................................................87
Figure 56: Operation of a fixed caliper.......................................................................................................88
Figure 57: A schematic of a basic automotive hydraulic brake system......................................................89
Figure 58: Moisture affects the boiling point of brake fluid.......................................................................90
Figure 59: The basic construction of a dual master cylinder ......................................................................90
Figure 60: Basic components of a brake system, individual units represented by product photos.............94
Figure 61: Basic components of a brake system, individual units represented by graphic symbols ..........95
Figure 62: Slip on the braked wheel ...........................................................................................................97
Figure 63: ABS Closed-loop control circuit ...............................................................................................99
Figure 64: ABS with closed circuit and 2/2 solenoid valves (hydraulic circuit) ......................................100
Figure 65: ABS with open circuit (hydraulic circuit) ...............................................................................102
Figure 66: ABS Electrical circuit..............................................................................................................103
Figure 67: Brake assistant system.............................................................................................................103
Figure 68: A typical system diagram for an ESC system. ........................................................................107

Module code: AUT203 Assistant lecturer: Pacifique TURABIMANA 2016-2017 Page 1
CHAPTER: 1. CHASSIS FRAME AND BODY
Objectives
At the end of this chapter students should be able to:
 Explain the difference between unitized vehicles and body-over-frame vehicles.
 Describe the manufacturing process used in a modern automated automobile assembly
plant.
 List the basic systems that make up an automobile and name their major components and
functions.
 Explain the vehicle body repair technology
1.1. Introduction of chassis Frame
Chassis is a French term and was initially used to denote the frame parts or Basic structure of the
vehicle. It is the backbone of the vehicle. A vehicle without body is called Chassis. The
components of the vehicle like power plant, Transmission system, Axles, Wheels and Tyres,
Suspension, Controlling System like Braking, Steering etc,.. and also electrical system parts are
mounted on the Cassis frame. It is the main mounting for all the components including the body.
So it is also called as Carrying Unit.
Figure 1: Layout of Chassis and its main Components

1.2. Functions of the chassis frame
- To carry load of the passengers or goods carried in body
- To support the load of the body, engine, gearbox etc.
- To withstand the forces caused due to the sudden braking or acceleration
- To withstand the stresses caused due to the bad road condition
- To withstand centrifugal force while cornering
1.3. Types of chassis frames
1. Conventional frame: It has two long side members and 5 to 6 cross members joined
together with the help of rivets and bolts. The frame sections are used generally.
a) Channel section – Good resistance to bending
b) Tabular Section – Good resistance to Torsion
c) Box Section -- Good resistance to both bending and torsion
2. Integral Frame: This frame is used now days in most of the cars. There is no frame and
all the assembly units are attached to body. All the functions of the frame carried out by
the body itself. Due to elimination of long frame it is cheaper and due to less weight most
economical also. Only disadvantage is repairing is difficult.
3. Semi-Integral Frame: In same vehicles half frame is fixed in the front end on which
engine gear box and front suspension is mounted. It has the advantage when the vehicle is
met with accident the front frame can be taken easily to place the damaged chassis frame.
This type of frame is used in FIAT cars and some of the European and American cars.
Various loads acting on the frame
1. Short duration Load- while crossing a broken patch
2. momentary duration Load – While taking a curve
3. Impact loads – due to the collision of the vehicle
4. Inertia load – while applying brakes
5. Static Loads – Loads due to chassis parts
6. Over loads – Beyond Design capacity

1.4. Vehicle body construction
Vehicles have different construction methods according to how it can attach to the vehicle frame.
The different most construction methods used are: separate construction, partially self-supporting
construction and self-supporting construction.
a) Separate construction: This construction, the vehicle body, axles, steering etc are
mounted on the frame. Because of its flexibility, this construction is used almost
exclusively in the manufacture of commercial vehicles, off-road vehicles and trailers. The
main body shape used here is the ladder-type frame, where two side members are
riveted, bolted or welded to several cross-members.
Figure 2: Ladder type frame
b) Partially self-supporting construction: It is generally uses a front and rear frame bolted
into the self-supporting body in the centre section. When compared with the self-
supporting construction, it is possible to implement different body framing variants more
easily.
Figure 3: Partially self-supporting construction

c) Self-supporting construction: This is used in passenger cars and buses/coaches.
In passenger cars the frame is replaced by a floor assembly, which, in addition to the
supporting components such as engine bearings, side members and cross-members, also
contains the luggage-compartment floor and wheel houses.
Figure 4: Passenger car Floor assembly
Apart of body construction, the bodies used in automobiles are divided in two groups, Passenger
body and Commercial body.
According to chassis design, the body can divided into:
- Conventional type
- Integral type
- Semi-Integral type
According to other usage:
- Light vehicle bodies – Cars, Jeeps
- Heavy vehicle bodies – Busses, Larries
- Medium vehicle bodies – Vans, Metadoors
The body of the most vehicles should fulfill the following requirements:
1. The vehicle body should be light
2. It should provide sufficient space for passengers and luggage
3. It should have minimum number of components
4. It should withstand vibrations while in motion

5. It should offer minimum resistance to air
6. It should be cheap and easy in manufacturing
7. It should be attractive in shape and colour
8. It should have uniformly distributed load
9. It should have long fatigue life
10. It should provide good vision and ventilation
1.5. Vehicle Body repair
1.5.1. Introduction to panel beating
Panel beating is the art of shaping the metal back to where it is smooth and level again. Learning
how to be a panel beater is essential. It is the area in auto body work that requires the most skill
and technique. The ability to direct the blows on the damaged area, along with how much force
to exert, separates “the men from the boys,” the amateur from the professional. Practice is the
key to becoming knowledgeable and proficient so do not attempt a large job right away; better to
begin panel beating by practicing on a piece of scrap metal.
It is important to know a little about the dynamics of how the impact on the metal produces
damage in the first place. When force from an accident impacts sheet metal, it produces an area
of direct damage at the point of contact. The impact’s indirect contact affects a wider area,
leaving an array of buckles or “V” channels on the surface of the metal. These ridges appear hard
or rigid. Also observe the direction of the force that caused the damage. This will be important
because you are going to be repairing the damage exactly opposite of how it occurred. In other
words, you will beat out the indirect damage first, then the direct damage.
Body work consists of working with and repairing automobile – car, van and SUV body panels
and other exterior body parts. These include bumpers, hoods, tops, and grilles. Body work is a
very lucrative segment of the automotive repair industry. Hundreds of thousands are employed
world wide in this ever-changing field. The skilled work uses many unique tools, and all kinds of
equipment and techniques to do the job. In addition to welding, there are other basics included in
body work. These basics include panel beating, getting rid of rust, painting, and bodywork
repairs and improvements.
Panel beating is the most basic of all body repair techniques, but it is also one of those that

require the most skill. As a body person you will learn how to expertly get rid of bumps, dents,
and breaks using various panel-beating techniques and tools.
With rust proofing, you will need to know how and why rust occurs so you can effectively
prevent it and get rid of it when it forms on any body part. You also need to learn about the many
products and techniques that are involved with rust removal and rust inhibiting.
Painting is another major skill in body work. As a painter, you will need to know about
preparation not only on the vehicle but in the garage; and about the many kinds of paints,
including undercoats, etch primers, clear-over base coats, enamels, lacquers, metallic paints,
sealers, and low-bake paints. Then you will find out about applicators – the spray guns – that
have various kinds of feeds, and how to use them and clean them.
1.5.2. Safe automobile cleaning
Caring for your vehicle can be a rewarding experience. To make the job of cleaning and
maintaining easier, there are a wide variety of cleaners, for a wide variety of jobs, from which to
choose.
Carburetor/choke cleaner is great for helping to remove varnish, gum and carbon from motor,
exhaust, and ignition parts. Most of these cleaners leave a dry-lubricant film which does not gum
up or harden. But because of this, these cleaners are not recommended for electrical components.
Brake system cleaners should be used to remove grease, brake dust, and brake fluid from the
brake system, where “clean” is absolutely necessary. These cleaners will not leave a residue and
can help eliminate brake squeal often caused by contaminants.
Electrical cleaner will remove corrosion, oxidation, and carbon deposits from electrical
contacts, thus restoring current flow. Use these cleaners to also clean carburetor jets, spark plugs,
voltage regulators, and other component whose surfaces need to be oil-free.
De-moisturants remove moisture and water from electrical components, including voltage
regulators, alternators, fuse blocks and electrical connectors. These cleaners are non-corrosive
and non-conductive.

Degreasers are actually heavy-duty solvents. Use them to eliminate grease from chassis
components and engine parts. Spray or brush them on. Rinse off with either a solvent or water.
Car wash product should be used to wash the exterior of your vehicle. There are many on the
market from which to choose. Just be sure not to choose an abrasive cleaner for the painted and
chromed surfaces of your vehicle because an abrasive cleaner will leave scratches and gouges in
these surfaces. Car wash products are mild detergents that will gently but thoroughly eliminate
grime, dust and dirt from all of your vehicle’s exterior surfaces.
Waxes and polishes help protect painted and plated surfaces from harsh weather conditions
when used appropriately. Different types of paint require different waxes and polishes. Check
with your vehicle’s owner’s manual; usually the manual will recommend a certain type of polish
or wax. Polishes sometimes utilize certain chemicals to remove the top layer of oxidized (dull)
paint from the surfaces of older vehicles. Other polishes contain polymers and silicones for
additional protection. These polishes are often easier to apply and last longer than conventional
products. A good car wax will give your vehicle an extra layer of protection against salt, rust and
heavy-duty dirt. Applying a solid coat of wax before winter weather sets in can help protect your
vehicle.
1.5.3. Auto body maintenance
As technician follow these simple body maintenance suggestions to keep the vehicle looking
good, helping to retain its resale value.
Once every 12,000 miles, or once every six months have the underside of the vehicle steam-
cleaned. This will remove all dirt and oil residue. You can then, if desired, more easily inspect
the area for damaged cables, rust, damaged brake lines, frayed electrical wires, and other
problems. Also once every six months or every 12,000 miles, steam clean and/or degrease the
vehicle’s engine compartment.
The wheel wells deserve your close attention. The undercoating can peel away or the tires can
throw up stones and dirt, causing the paint to flake and chip, and rust to perhaps set in. If you
find any rust, sand the area down to bare metal, then paint with a rust-inhibiting paint.

Wash the entire vehicle body with soap once a week, regular use of detergent is not good for the
vehicle’s paint job. Hose down the exterior with water to loosen the dirt, then use a good car
wash product and a wash mitt to clean the body surfaces, starting with the roof, burnet, and trunk
(boot) areas and working your way down. It is important that you don’t start from the down parts
and then move upwards to avoid dragging sand on your paint and vinyl finishes.
1.5.4. Bumper removal and installation
Almost all cars, trucks, vans and SUVs today are equipped with a supplemental restraint system
(SRS), commonly known as airbags. Warning: Always disarm the airbag system before working
near any airbag component to avoid the possibility of the airbag accidentally deploying. Do not
use a memory-saving device to preserve the system’s memory. Set the parking brake, put the
vehicle in gear or in Park, raise the vehicle and put it on Jackstands. Caution: always use extreme
caution when working underneath or near a raised vehicle.
Remove the pin retainers from the inner fender splash shields, if so equipped. (To release a
retainer, use a panel tool or screwdriver to lift up on the center section, then grab the outer part of
the retainer and pry it up.) From below the bumper, remove the pin retainers from the upper and
lower parts of the bumper’s cover, which may be fastened on a number of areas on the vehicle.
Disconnect any lights, such as fog lights or sidelights. Remove the bumper cover from the
fender. Disconnect the energy absorber from the bumper. To install a replacement bumper,
perform the procedure in reverse.
1.5.5. How to repair automotive dent
Body fillers can have a bad rap, but used correctly it can result in a well done repair. There’s not
a body shop out there that doesn’t use a little body filler. In the old days, body filler was made of
lead, but the resulting loss of brain cells and reproductive acuity sent the use of this material
packing. Aside from a very few holdovers, body filler is a plastic resin that is sandable, adheres
well to metal, and lasts a long time.
What will be needed?
 Sandpaper – 150 grit, 220 grit, 400 grit wet/dry
 Body filler (with hardener, usually included)

 Glazing and spot putty
 Rigid plastic spreader
 Flexible plastic spreader
 Automotive primer
 Patience, patience, patience!
a) Preparing the surface
Be sure you block out a few hours (at least) to do a proper repair. It’s hard to stop in the middle
without risking a screw-up. Before you can fill your dent, you’ll need to remove the paint. Body
filler doesn’t stick well to paint, so you need to sand it down to bare metal. For this job, you can
use a heavier grit sandpaper like a 150-grit. You want to get the paint off fast, and you’ll be
smoothing things out later anyway. Even though your dent may be only a couple of inches long,
you’ll need to remove more paint than that. At least 3 inches beyond the dent is needed (you’ll
see why later). So you’ll be taking at least 6 inches of paint off the car. If you look at the
example pictured, you’ll see some small circles on the surface. Sometimes it’s a good idea,
especially if you are dealing with multiple dents, to mark the location of the damage so you
know where to focus your repair easily. You should also note that the pictured body panel has
evidence of an old repair on it (the beige colored areas are old body filler).
b) Mixing the body-filler
Body filler is a two-part epoxy that you have to mix yourself. You add a creme hardener to the
base filler, which starts a reaction to harden the filler. The filler will harden pretty quickly,
allowing for less than 5 minutes of working time. In the case of Bondo brand filler, the base is
gray and the hardener is red, so you aim for a nice pink tone in the mixture. You can mix the
hardener on pretty much anything clean. Just remember that it’ll be more or less ruined
afterward. This batch was mixed on a cardboard sandpaper package. A nifty reusable filler
batcher is a plastic Frisbee. The filler won’t stick to plastic, so when you’re done you can pop the
old filler right out cleanly. Follow the directions on the filler can to mix the proper amount of
hardener with filler. Mix the two using a rigid plastic spreader. Don’t forget you have a limited
working time once you mix it.

c) Applying the body-filler
Remember, once you’ve mixed the filler, you have less than 5 minutes to get it on the damaged
area. Using flexible plastic spreader, spread filler in an area at least 3 inches outside of the actual
damage. You’ll need the extra space to properly smooth and feather the hardened filler. Don’t
worry about being too neat with it. You’ll be sanding away any ugliness once the filler hardens
d) Sanding the filler
Once the filler has completely hardened the time will vary by temperature, humidity and brand of
filler used, check the box you’re ready to start sanding. With your sandpaper wrapped around a
sanding block (rubber sanding blocks are best and can be purchased in automotive or home
repair stores), start sanding the filler using 150-grit sandpaper. Sand lightly and evenly over the
entire surface of the repair with broad circular strokes. Sand past the edge of the filler to create a
smooth transition. When the filler is pretty close to smooth, switch to the 220-grit paper and
continue until it’s even. It’s not unusual to miss a spot or realize there are some gaps or pits in
your filler. If this is the case, mix a new batch of filler and repeat the process until it’s smooth.
You’ll sand away most of the filler, leaving the dent filled and a smooth transition between metal
and filler.
e) Glazing the repair
Spot putty is another version of filler, but much finer and easier to sand. It doesn’t need to be
mixed and can be applied directly from the tube to the repair. The spot putty fills in any tiny
impressions in the filler. Smooth (or glaze) spot putty across the repair surface with a flexible
plastic spreader. It dries faster than the body filler, but be sure you give it enough time before
you begin to sand it.
f) More sanding
Using 400-grit sandpaper, lightly and evenly sand the spot putty away. Sand it all away flat, and
you’ll be left with only tiny amounts of putty remaining in small scratches and gaps. These may
seem minute, but even the smallest flaw will show up in the paint.
g) Prime the surface

To further prepare and protect your repair, you’ll spray the surface with a primer/sealer. Mask
off an area around the repair to avoid getting paint on any trim or other non-painted areas (don’t
forget, you don’t want paint on your tires, either). Apply the spray primer in light, even coats.
Three light coats are better than one heavy coat.
h) Sanding, one more time
Allow the primer coat to dry, then remove your masking tape and paper. To smooth the repaired
area for painting, you’ll use your 400 grit wet/dry sandpaper, but this time you’re going to wet
sand the repair. Fill a spray bottle with clean water and spray the repair area and the sandpaper. If
you don’t have a spray bottle you can use whatever method you can to keep the paper and repair
area wet. Smoothly sand the primer using a straight back and forth motion. When you begin to
see the old paint show through the primer, you’ve gone far enough. If you sand away too much
primer and you can see metal again, you’ll have to re-prime and re-sand.
Self- Assessment exercises No 1
1. Draw the layout of conventional Chassis with a neat diagram and explain about various
parts on it?
2. What are the functions of chassis frame?
3. What is the frame sections used in automobiles?
4. What are the requirements of bodies for various types of vehicles?
5. What are the different classification of bodies used in automobiles and explain?
6. List 43 steps to paint a car

CHAPTER TWO: STEERING SYSTEM
Objectives
At the end of this chapter, students should be able to:
- Describe the similarities and differences between parallelogram, worm and roller, and
rack and pinion steering linkage systems.
- Identify the typical manual-steering system components and their functions.
- Name the five basic types of steering linkage systems.
- Identify the components in a parallelogram steering linkage arrangement and describe the
function of each.
- Identify the components in a manual rack and pinion steering arrangement and describe
the function of each.
- Describe the function and operation of a manual-steering gearbox and the steering
column.
- Explain the various manual-steering service procedures.
- Describe the service to the various power-steering designs.
- Perform general power-steering system checks.
- Describe the common four-wheel steering systems.
2.1. Introduction
The front wheels of a vehicle are steered so that it moves in the desired direction. The condition
and efficiency of the steering therefore have a major effect on road safely. If any component of
the steering should break or become detached, or if the steering should become blocked, the
vehicle cannot be steered and an accident is then almost inevitable. The steering must therefore
be checked and maintained most carefully and the necessary repair work carried out whenever a
fault is detected.
In 1817, Rudolph Ackermann patented the first stub axle steering system in which each front
wheel was fixed to the front axle by a joint. This made it possible to cover a larger curve radius
with the wheel on the outside of the curve than with the front wheel on the inside of the curve.
Rack and pinion steering was developed at an early age in the history of the car. However, this

became popular when front-wheel drive was used more, since it requires little space and
production costs are lower. The first hydraulic power steering was produced in 1928. However,
since there was no real demand for this until the 1950s, the development of power steering
systems stagnated.
Increasing standards of comfort stimulated the demand for power steering systems. Speed-
sensitive or variable-assistant power steering (VAPS) systems were developed using electronic
controls. The demand for safety and comfort will lead to further improvements in steering
systems.
2.2. Requirements of steering system
Steering system provides the directional change in the movement of an automobile and maintain
in a position as per the driver’s decision without much strain on him and it fulfill the following
requirements:
- It must keep the wheel at all times in to rolling motion without rubbing on the road.
- This system should associate to control the speed.
- It must light and stable.
- It should also absorb the road shocks.
- It must easily be operated with less maintenance.
- It should have self-centering action to some extent.
2.3. Functions of steering system
- It helps in swinging the wheels to the left or right
- It helps in turning the vehicle at the will of the driver
- It provides directional stability
- It is used to minimize the tyre wear and tear
- It helps in achieving self-centering efforts
- It absorbs major part of the road shocks

2.4. Steering Components
The following are the main components of steering system:
1. Steering wheel
2. Steering column or shaft
3. Steering gear
4. Drop arm or pitman arm
5. Drag link
6. Steering arm
7. Track-arm
8. Track rod or tie-rod
9. Adjusting screws.
2.4.1. Steering wheels
The steering wheel, which consists of a rigid rim and a number of spokes connecting the rim to a
center hub, attaches to the top of the steering shaft at its center. Most steering wheel hubs have
internal splines that fit over external splines on the steering shaft. A bolt or nut at the center of
the hub secures the wheel to the shaft. The steering shaft links the steering wheel to the steering
gear while the column jacket, which surrounds part of the shaft, holds support brackets and
switches. This steering shaft has a small intermediate section between the main section and the
steering gear. The steering wheel may also contain controls for the cruise control and audio
controls, as well as the driver’s airbag. An airbag is a device made of nylon cloth that is covered
with neoprene. The airbag is folded and stored in the front center of the steering wheel. In a
front-end collision, the airbag inflates in a fraction of a second to provide a cushion between the
driver and the steering wheel and dashboard.
2.4.2. Steering columns
Typical steering column showing all of the components from the steering wheel to the steering
gear. A flexible coupling is used to isolate road noise and vibration from the steering shaft.
Figure 5: Main steering components

Figure 6: Steering column
Safety steering column
In the event of a head-on collision or similar impact, the driver is often exposed to the risk of
injury from the steering wheel and steering column, if the column is forced back into the car's
interior. This undesirable effect can be minimized by installing a safety steering column. The
column has two universal joints set at opposed angles, or else a telescopic sliding joint. The
safety steering column illustrated has an upper and a lower steering spindle, connected by a tube.
The lower spindle is secured in the tube by a plastic rivet. The outer tube is not solid, but consists
of an expanded metal mesh. In the event of a collision the mesh outer tube deforms, the plastic
rivet is sheared off and the lower spindle is pushed up into the tube. Deformation of the outer
tube absorbs the peak impact force before it can reach the steering wheel, and the spindle sliding
in the tube avoids the risk of injury, The steering column mounting is designed to prevent
impacts from the direction of the floor pan or steering gear from being transmitted to the upper
part of the column.

Figure 7: Safety steering column
2.4.3. Steering Damper
The purpose of a steering damper is simply to reduce the amount of road shock that is
transmitted up through the steering column. Steering dampers are found mostly on 4WD,
especially those fitted with large tires. The damper serves the same function as a shock absorber
but is mounted horizontally to the steering linkage—one end to the center link and the other to
the frame.
2.4.4. Steering linkage
Steering linkage is a connection of various links between the steering gearbox and the front
wheels. The motion of the pitman arm and steering gearbox is transferred so the steering
knuckles of the front wheels through the steering linkages. The swinging movement of the
pitman arm from one side to the side gives angular movement to the front wheel through the
steering linkages.
Types of steering linkage:
1. Conventional steering linkage

2. Direct cross type steering linkage
3. Three piece steering linkage
4. Center arm steering linkage
5. Relay type steering linkage
in steering they are many terms used, Slip angle : “The angle between direction of the motion of
the vehicle and the center plane of the tyre , it ranges from 80
to 100
”, Under steer: “when the
front slip angle is greater than that of rear, the vehicle tends to steer in the direction of side
force”. This provides a greater driving stability, especially when there is a side wind”, Over
steer: “When the rear slip angle is greater than that of front slip angle, the vehicle tends to move
away from the direction of center path”. This is advantageous when the vehicle moving on the
road having many bends curves. Steering gear ratio or reduction ratio: “It has been defined as
the number of turns on the steering wheel required to produce on turn of steering gear cross shaft
to which the pitman arm is attached. General it varies between 14’.1 and 24’.1”. Turning
radius: “it is the radius of the circle on which the outside front wheels moves when the front
wheels are turned to their extreme outer position. This radius is 5 to 7.5m for buses and trucks”.
2.4.5. Track rod on vehicles with rigid (beam) front axle
If they are joined by a rigid axle beam, the wheels cannot perform independent movements as the
suspension compresses. The steering trapeze moves with the front axle beam and is therefore not
obliged to change its shape. A single-piece track rod can accordingly be used between the two
track rod arms.

Figure 8: Steering linkage/ centrally divided track rod
Steering movement is transferred from the pitman arm that is splined to the sector shaft (pitman
shat), through the center link and tie rods, to the steering knuckle at each front wheel. The idler
arm supports the passenger side of the center link and keeps the steering linkage level with the
road. This type of linkage is called a parallelogram-type design.
A disadvantage of this layout is that road bumps can be transmitted directly from the wheels to
the steering wheel, by way of the track rod arms, track rod and steering rod. To avoid this, most
motor vehicles with a beam front axle are fitted with a steering damper resembling a suspension
damper or shock absorber in design.

Figure 9: Parallelogram steering system mounts (A) behind the front suspension, and (B) ahead of the
front suspension
2.4.6. Track rod for independent suspension
If the vehicle has independent front suspension, the steered wheels can move up and down
independently, either to a different extent in the same direction or even in opposed directions. As
a result, the two track rod arms cannot simply be linked by a one-piece track rod. This would
distort and overload the steering linkage as the wheel moves up and down, cause constant
changes to toe-in and lead to severe tyre wear as a result of wheel movement in relation to the
road surface. The safety of the steering gear would be placed at severe risk. For these reasons,
independently-sprung vehicles must be equipped with a split track rod.
Two-piece track rods can be split in the middle or at one side. Steering movements are
transmitted to the linkage either by a steering rod and central arm, or directly from the steering
drop arm on the steering box. Each half of the track rod can be adjusted, to obtain the correct
wheel toe-in angle.

Figure 10: Track rod divided at one side
Three-piece track rods have either an adjustable centre section or adjustable outer sections.
The sections of two- or three-piece track rods are linked together by ball joints. The ball ends can
move in all directions in their sockets as the suspension operates. This enables divided track rods
to accommodate independent wheel movements. Steering dampers are often installed on
steering systems with divided track rods as well.
Figure 11: Three-piece Track rod
2.4.7. Steering box
When the steering wheel is turned, the tubular steering column transmits this movement to the
steering spindle and the steering box. The reduction ratio provided in the steering box slows
down the turning movement and converts it into a pivoting movement of the steering drop arm,
which is connected to the front wheels by the steering linkage (track rods, track rod arms). The

reduction ratio also ensures minimum driver effort at the steering wheel. Passenger cars usually
have a steering reduction ratio of between 10 and 20 to 1; on trucks, the figure is in excess of 20
to 1. Heavy cars and trucks are frequently equipped with power-assisted steering.
Function of steering gearbox
- It converts the Rotary movement of the steering wheel in to the angular turning of the
front wheel
- It also multiplies drives efforts and gives Mechanical advantage.
Types of steering gearbox
- Worm and wheels steering gear
- Worm and roller steering gear
- Re-circulating ball steering gear
- Rack and pinion type steering gear
- Cam and roller gear type steering gear
- Cam and peg steering gear
- Cam and double lever steering gear
- Worm and sector type steering gear.
Worm and Wheel type: this type of steering gear has a square cut screw threads at the end of
the steering column; which forms a warm, at the end of it a worm wheel is fitted and works rigid
with it. Generally covered shaft is used for the worm wheel. The worm wheel can be turned to a
new position the drop arm can be readjusted to the correct working position.
Figure 12: Worm and sector steering box

Re-circulating ball steering gear: in this type of gear box the endless chain of balls are
provided between the worm and nut members. The nut forms a ring of rack having an axial
movement. So that the sector on the rocker shaft racks, the balls roll continuously between the
worm and nut. Being provided with return chambers at the ends of the worm. This method
reduces friction between worm and nut members. This type of steering gear is used for heavy
vehicles.
Figure 13: Recirculating-ball steering box
Worm and roller steering gear: The worm and roller steering box has a steering roller in
place of the sector. The steering worm itself is not cylindrical, but narrows in diameter towards
the centre, so that the steering roller, as it is turned by the worm, also describes an arc round its
pivot point. This turns the steering shaft and moves the steering drop arm as previously
described.

Figure 14: Worm and roller steering box
Rack and pinion steering gear: Rack and pinion is lighter in weight and has fewer components
than parallelogram steering. Tie rods are used in the same fashion on both systems, but the
resemblance stops there. Steering input is received from a pinion gear attached to the steering
column. This gear moves a toothed rack that is attached to the tie-rods.
In the rack and pinion steering
arrangement, there is no pitman arm,
idler arm assembly, or center link.
The rack performs the task of the
center link. Its movement pushes and
pulls the tie-rods to change the
wheel’s direction. The tie-rods are the
only steering linkage parts used in a
rack and pinion system.
Figure 15: Rack and pinion steering gear

Cam and lever type: The cam and lever steering uses one or two lever studs fitted in taper roller
bearing. When the worm in the form of helical groove rotates the stub axle and it also rotates
along with it. This imports a turning motion to the drop arm shaft.
Worm and sector type: In this type the worm on the end of the steering shaft meshes with a
sector mounted on a sector shaft. When the worm is rotated by rotation of the steering wheel, the
sector also turn rotating the sector shaft, its motion is transmitted to the wheel through the
linkage. The sector shaft is attached to the drop arm or pitmen arm.
2.5. Steering Mechanism
There are two types of steering gear mechanisms (1) Davis Steering gear and (2) Ackermann
steering gear.
Davis steering gear: The Davis steering gear has sliding pair, it has more friction than the
turning pair, therefore the Davis steering gear wear out earlier and become inaccurate after
certain time. This type is mathematically accurate.
Ackermann steering system: It has only turning pair. It is not mathematically accurate except
in three positions. The track arms are made inclined so that if the axles are extended they will
meet on the longitudinal axis of the car near rear axle. This system is called Ackermann steering.
Ackermann principle
The wheels must be turned such that the projected centre lines of the steering knuckle of the
wheels on the inside and the outside of the turn meet the projected line of the rear axle. The
circular trajectories covered by the front and rear wheels then have a common centre point.
Figure 16: Ackermann steering, toe-difference angle

2.6. Power-steering systems
The power-steering unit is designed to reduce the amount of effort required to turn the steering
wheel. It also reduces driver fatigue on long drives and makes it easier to steer the vehicle at
slow road speeds, particularly during parking. Power steering can be broken down into two
design arrangements: conventional and nonconventional or electronically controlled. In the
conventional arrangement, hydraulic power is used to assist the driver. In the nonconventional
arrangement, an electric motor and electronic controls provide power assistance in steering.
There are several power-steering systems in use on passenger cars and light-duty trucks. The
most common ones are the integral-piston, and power assisted rack and pinion system.
2.6.1. Integral Piston System
The integral piston system is the most common conventional power-steering systems in use
today. It consists of a power-steering pump and reservoir, power-steering pressure and return
hose, and steering gear. The power cylinder and the control valve are in the same housing as the
steering gear. On some recent model cars and light trucks, instead of the conventional vacuum-
assist brake booster, the hydraulic fluid from the power-steering pump is also used to actuate the
brake booster. This brake system is called the hydro-boost system.
Figure 17: A typical hydro-boost system that uses the power-steering pump to power assist brake
applications

2.6.2. Power-Assisted Rack and Pinion System
The power-assisted rack and pinion system is similar to the integral system because the power
cylinder and the control valve are in the same housing. The rack housing acts as the cylinder and
the power piston is part of the rack. Control valve location is in the pinion housing. Turning the
steering wheel moves the valve, directing pressure to either end of the back piston. The system
utilizes a pressure hose from the pump to the control valve housing and a return line to the pump
reservoir. This type of steering system is common in front-wheel-drive vehicles.
Figure 18: Power-Assisted Rack and Pinion System
Components
Several of the manual-steering parts described earlier in this chapter, such as the steering linkage,
are used in conventional power-steering systems. The components that have been added for
power steering provide the hydraulic power that drives the system. They are the power-steering
pump, flow control and pressure relief valves, reservoir, spool valves and power pistons,
hydraulic hose lines, and gearbox or assist assembly on the linkage.
Power-Steering Pump

The steering pump is used to develop hydraulic flow, which provides the force needed to operate
the steering gear. The pump is belt driven from the engine crankshaft, providing flow any time
the engine is running. It is usually mounted near the front of the engine. The pump assembly
includes a reservoir and an internal flow control valve. The drive pulley is normally pressed onto
the pump’s shaft. There are four general types of power-steering pumps: roller, vane, slipper, and
gear. Functionally, all pumps operate in the same basic manner. Hydraulic fluid for the power-
steering pump is stored in a reservoir. Fluid is routed to and from the pump by hoses and lines.
Excessive pressure is controlled by a relief valve.
Power-Steering Pump Drive Belts
Many power steering pumps are driven by a belt that connects the crankshaft pulley to the
power-steering pump pulley. Nearly all late-model vehicles use a serpentine belt. This belt may
be used to drive all the belt-driven components. Most serpentine belts have a spring-loaded
automatic belt tensioner that eliminates periodic belt tension adjustments.
Electric Power Steering
Many vehicles use a 12- or 42-volt electric motor mounted to or in the steering gear. The motor
replaces the conventional pump and its belts and hoses.
Flow Control and Pressure Relief Valves
A pressure relief valve controls the pressure output from the pump. This valve is necessary
because of the variations in engine rpm and the need for consistent steering ability in all ranges
from idle to highway speeds. It is positioned in a chamber that is exposed to pump outlet
pressure at one end and supply hose pressure at the other. A spring is used at the supply pressure
end to help maintain a balance. As the fluid leaves the pump rotor, it passes the end of the flow
control valve and is forced through an orifice that causes a slight drop in pressure. This reduced
pressure, aided by the springs, holds the flow control valve in the closed position. All pump flow
is sent to the steering gear.
Power-Steering Gearbox

A power-steering gearbox is basically the same as a manual recirculating ball gearbox with the
addition of a hydraulic assist. A power-steering gearbox is filled with hydraulic fluid and uses a
control valve. In a power rack and pinion gear, the movement of the rack is assisted by hydraulic
pressure. When the wheel is turned, the rotary valve changes hydraulic flow to create a pressure
differential on either side of the rack. The unequal pressure causes the rack to move toward the
lower pressure, reducing the effort required to turn the wheels. The integral power steering has
the spool valve and a power piston integrated with the gearbox. The spool valve directs the oil
pressure to the left or right power chamber to steer the vehicle. The spool valve is actuated by a
lever or a small torsion bar.
Power-Assisted Rack and Pinion Steering
Power assisted rack and pinion components are basically the same as for manual rack and pinion
steering, except for the hydraulic control housing. As mentioned earlier, the power rack and
pinion steering unit may be classified as integral. The rack functions as the power piston and the
spool valve is connected to the pinion gear. In a power rack and pinion gear, the piston is
mounted on the rack, inside the rack housing. The rack housing is sealed on either side of the
rack piston to form two separate hydraulic chambers for the left and right turn circuits. When the
wheel is turned to the right, the rotary valve creates a pressure differential on either side of the
rack piston. This causes the rack to move toward the lower pressure and reduces the total effort
required to turn the wheels.
Power-Steering Hoses
The primary purpose of power-steering hoses is to transmit power (fluid under pressure) from the
pump to the steering gearbox, and to return the fluid ultimately to the pump reservoir. Hoses
also, through material and construction, function as additional reservoirs and act as sound and
vibration dampers. Hoses are generally a reinforced synthetic rubber (neoprene) material coupled
to metal tubing at the connecting points. The pressure side must be able to handle pressures up to
1,500 psi (10,342 kPa). For that reason, wherever there is metal tubing to a rubber connection,
the connection is crimped. Pressure hoses are also subject to surges in pressure and pulsations
from the pump. The reinforced construction permits the hose to expand slightly and absorb
changes in pressure.

2.6.3. Electronically Controlled Power steering Systems
The object of power steering is to make steering easier at low speeds, especially while parking.
However, higher steering efforts are desirable at higher speeds in order to provide improved
down-the road feel. The electronically controlled power steering (EPS) systems provide both of
these benefits. The hydraulic boost of these systems is tapered off by electronic control as road
speed increases. Thus, these systems require well under 1 pound (4.4 N) of steering effort at low
road speeds and 3 pounds plus (13.2 N) of steering effort at higher road speeds to enable the
driver to maintain control of the steering wheel for improved high-speed handling.
Figure 19: A variable-assist power-steering system.
A rotary valve electronic power-steering system consists of the power-steering gearbox, power
steering oil pump, pressure hose, and the return hose. The amount of hydraulic fluid flow
(pressure) used to boost steering is controlled by a solenoid valve that is identified as its PCV
(pressure control valve). The electronic power-steering system’s PCV is exposed to spring
tension on the top and plunger force on the bottom. The plunger slips inside an electromagnet.

By varying the electrical current to the electromagnet, the upward force exerted by the plunger
can be varied as it works against the opposing spring. Current flow to the electromagnet is
variable with vehicle road speed and, therefore, provides steering to match the vehicle’s road
speed. General Motors’ variable effort steering (VES) system relies on an input signal from the
vehicle speed sensor to the VES controller to control the amount of power assist. The controller,
in turn, supplies a pulse width modulated voltage to the actuator solenoid in the power-steering
pump. The controller also provides a ground connection for the solenoid. When the vehicle is
operating at low speeds, the controller supplies a signal to cycle the solenoid faster so it allows
high pump pressure. This provides for maximum power assist during cornering and parking. As
the vehicle’s speed increases, the solenoid cycles less and the pump provides a lower amount of
assist. This gives the driver better road feel during high speeds.
Active Steering
Active steering improves vehicle stability by turning the wheels more or less sharply than
commanded by the turn of the steering wheel during some situations. Through inputs and
computer programming, this system can adjust the steering to respond quickly to the threat of
skidding.
Figure 20: The main components and circuits of an active steering system
The system also allows for a variable steering ratio dependent on vehicle speed. Current active
steering systems are not true steer by-wire systems. There is still a mechanical connection
between the steering wheel and vehicle’s wheels.

Steer-by-Wire System
Steer-by-wire systems are not found on any production vehicles today. They are being tested and
have appeared on many concept cars. These systems do not use a steering column or shaft to
connect the steering wheel to the steering gear. The system is totally electronic. The turning of
the steering wheel is monitored by a sensor. The sensor sends an input signal to a controller. The
controller, in turn, sends commands to an electric motor in the steering gear. The commands
from the controller are also based on inputs from a variety of other inputs, such as vehicle speed.
These systems also have a small motor attached to the mount for the steering wheel. This motor
is controlled by a steering controller. This motor provides the correct steering feel for the current
conditions. The driver needs this feel to maintain control of the vehicle. Steer-by-wire systems
allow total customization of steering performance and can provide a constantly variable steering
ratio. The absence of a steering column opens up space in the vehicle’s interior and engine
compartment. The systems are also lighter than conventional steering systems.
Figure 21: The basic layout for a steer-by-wire system
2.6.4. Four-Wheel Steering Systems

A few manufacturers have offered four-wheel steering systems in which the rear wheels also
help to turn the car by electrical, hydraulic, or mechanical means. Although they certainly are not
very common, you should be aware of how they work. Production-built cars tend to under steer
or, in a few instances, over steer. If a car could automatically compensate for an under steer/ over
steer problem, the driver would enjoy nearly neutral steering under varying operating conditions.
Four-wheel steering (4WS) is a serious effort on the part of automotive design engineers to
provide near-neutral steering with the following advantages:
 The vehicle’s cornering behavior becomes more stable and controllable at high speeds as
well as on wet or slippery road surfaces.
 The vehicle’s response to steering input becomes quicker and more precise throughout
the vehicle’s entire speed range.
 The vehicle’s straight-line stability at high speeds is improved. Negative effects of road
irregularities and crosswinds on the vehicle’s stability are minimized.
 Stability in lane changing at high speeds is improved. High-speed slalom-type operations
become easier. The vehicle is less likely to go into a spin even in situations in which the
driver must make a sudden and relatively large change of direction.
 By steering the rear wheels in the direction opposite the front wheels at low speeds, the
vehicle’s turning circle is greatly reduced. Therefore, vehicle maneuvering on narrow
roads and during parking becomes easier.
Because each 4WS system is unique in its construction and repair needs, the vehicle’s service
manual must be followed for proper diagnosis, repair, and alignment of a four-wheel system.
2.7. Work on the steering gear
Adjusting the steering box
The steering box normally has provision for steering shaft and steering spindle axial play and the
backlash between steering spindle and sector or roller to be adjusted. Various methods of
adjustment are provided, depending on the design of the steering box concerned. For this reason,
the manufacturer’s repair instructions should always be compiled with. After adjustment, the
adjusting screws must be secured by tightening the locknuts. The steering wheel should turn
freely.

On the recirculating-ball steering box, the steering spindle bearings are adjusted first, followed
by the position of the steering sector in relation to the steering nut.
On the worm and roller steering box, steering shaft axial play is adjusted first, then steering
spindle axial play and finally backlash between the worm and the roller. The steering worm runs
in an eccentric bushing. This is turned by moving the backlash adjusting lever to move the worm
closer to or farther away from the steering roller. Backlash must also be adjusted with the
steering in its central (straight-ahead) position.
On the rack and pinion steering gear, pinion axial play can be adjusted at the castellated nut.
There is no need for pinion-rack backlash to be adjusted, as the rack teeth are kept pressed
against the pinion all the time by a pressure pad and an anti-shake device. This consists of cup
springs held by a guide pin which also limits their travel.
Measuring wheel alignment
It returns to the positioning of the front wheels and steering mechanism that gives the vehicle
directional stability; reduce the tyre wear to a minimum.
However, there are some measuring rigs which require only a flat surface, which can slope
slightly if local conditions render this necessary. Before taking any measurements, it is essential
to check play in the steering linkage; the tyres must be inflated to the specified pressures. The
front wheels must not have excessive runout, the wheel bearing play must be within the specified
limits and the tyre treads should have worn down by equal amounts at all wheels. Since springs
and dampers can also influence the results, they must be equally effective at all wheels too. After
rectifying any of these shortcomings, front wheel alignment can be checked. According to
German Industrial Standard (DIN 70020), this must take place with the vehicle laden to its gross
weight limit. However, comply with the instructions issued by individual equipment suppliers,
since on many vehicles the alignment measurements are taken with the vehicle unladen (service
weight).
Types of Wheel Alignment
There are two basic types of wheel alignment performed today: two wheels and four wheels. In
a two wheel alignment, only the angles of the front wheels are measured and adjusted. This does

not take into account the relationship between the front and rear axles. Two-wheel alignment was
common before suspension and steering systems became more complex.
Four-wheel alignment measures the angles at the four wheels. On some vehicles, adjustments are
made only to the front wheels. This is primarily due to the fact that there is no way to make
adjustments to the rear wheels. However, by adjusting the front wheels so they are rotating in the
same direction as the rear wheels, the vehicle will tend to move straight. Many vehicles have
provisions for adjusting the rear wheels. When this is the case, the rear wheels are adjusted first
and then the fronts are aligned to the vehicle’s centerline
Factors effects the wheel alignment
1. Factors pertaining to wheel:
a) Balance of wheels (Static and Dynamic)
b) Inflation of tyre
c) Brake adjustments
2. Steering linkages
3. Suspension system
4. Steering Geometry, it refers to the angular relationship between the front wheels and parts
attached to it and car frame. The steering geometry includes: Caster angle, Camber angle,
King pin inclination, Toe-in and Toe-out etc).
Caster angle
Caster is the angle of the steering axis of a wheel from the vertical, as viewed from the side of
the vehicle. The forward or rearward tilt from the vertical line is caster. Caster is most often the
first angle adjusted during an alignment. Tilting the wheel forward is negative caster. Tilting
backward is positive caster. Caster is designed to provide steering stability. The caster angle for
each wheel on an axle should be equal. Unequal caster angles cause the vehicle to steer toward
the side with fewer casters. Too much negative caster can cause the vehicle to have sensitive
steering at high speeds. The vehicle might wander as a result of negative caster. Caster is not
considered to be a tire wearing angle. This about 20
to 40

Figure 22: Three types of caster: (A) zero, (B) positive, and (C) negative
Camber angle
Camber is the angle represented by the tilt of either the front or rear wheels inward or outward
from the vertical as viewed from the front of the car. Camber is designed into the vehicle to
compensate for road crown, passenger weight, and vehicle weight. Camber is usually set equally
for each wheel. Equal camber means each wheel is tilted outward or inward the same amount.
Unequal camber causes tire wear and causes the vehicle to pull toward the side that is more
positive. This about ½ 0
to 20
Camber is adjustable at the control arms on
most vehicles. Some vehicles with a strut
suspension include a camber adjustment at
the spindle assembly. Camber adjustments
are also provided on some strut suspension
systems at the top mounting of the strut. Very
little adjustment of camber (or caster) is
required on strut suspensions if the tower and lower control arm locations are correct.
Figure 23: (A) Positive and (B) negative camber.
Toe
Toe is the distance comparison between the leading edge and trailing edge of the front tires. If
the leading edge distance is less, then there is toe-in. If it is greater, there is toe-out. Actually,
toe is critical as a tire-wearing angle. Wheels that do not track straight ahead have to drag as they
travel forward. Toe adjustments are made at the tie-rod. They must be set equally on both sides
of the car. If the toe settings are not equal, the car may tend to pull due to the steering wheel
being off-center. Toe will change with vehicle speed. As the vehicle moves, friction forces the
tires to move straight ahead or have zero toe. However, aerodynamic forces on the vehicle cause

a change in its riding height. This will also change the toe as well as camber. Therefore, most toe
specifications anticipate these changes and are set to provide zero toe at highway speeds.
King- pin inclination
It is the angle between vertical line to the kingpin axis. The inclination tends to keep wheels
straight ahead and make the wheels to get return to the straight position offer completion of a
turn. The inclination is normally kept 70
to 80
.
Steering system diagnosis
It is important to realize that many steering complaints are caused by problems in areas other
than the steering system. A good diagnosis is one that finds the exact cause of the customer’s
complaint. Although customers may describe the problem in different ways, the most common
complaints, their typical causes, repair and visual inspection of the steering system by inspecting
the tires. Check for correct pressure, construction, size, wear, and damage, and for defects that
include ply separations, sidewall knots, concentricity problems, and force problems are discussed
in Automotive Chassis practice (AUT204).

Self –assessment exercises No 2

1. Describe how a rack and pinion steering, a parallelogram steering, and a worm and roller
system operate.
2. A power-steering hose transmits fluid under pressure from the ………………to
the……………..
3. What is an integral power-steering system?
4. Define the term gearbox ratio.
5. What are the basic features of all four-wheel steering systems?
6. List the four main components in a parallelogram steering linkage and explain the
purpose of each component.
7. What is meant by steering geometry and explain with neat sketches?
8. Explain reversible steering and irreversible steering

CHAPTER 3: SUSPENSION SYSTEM
Objectives
At the end of this chapter, students should be able to:
 Name the different types of springs and how they operate.
 Name the advantages of ball joint suspensions.
 Explain the important differences between sprung and unsprung weight with regard to
suspension control devices.
 Identify the functions of shock absorbers and struts and describe their basic construction.
 Identify the components of a MacPherson strut system and describe their functions.
 Identify the functions of bushings and stabilizers.
 Perform a general front suspension inspection.
 Check chassis height measurements to specifications.
 Identify the three basic types of rear suspensions and know their effects on traction and
tire wear.
 Identify the various types of springs, their functions, and their locations in the rear axle
housing.
 Describe the advantages and operation of the three basic electronically controlled
suspension systems: level control, adaptive, and active.
 Explain the function of electronic suspension components including air compressors,
sensors, control modules, air shocks, electronic shock absorbers, and electronic struts.
 Explain the basic towing, lifting, jacking, and service precautions that must be followed
when servicing air springs and other electronic suspension components.
3.1. Introduction
The automobile frame and body are mounted on the front and rear axle not directly but through
the springs and shock absorbers. The assembly of parts, which perform the isolation of parts
from the road shocks, may be in the forms of bounce, pitch and roll is called suspension system.
If the arrangement connects road wheels to the frame in which raise or fail of the wheel has no
direct effect on the other wheel, it is called independent suspension system.

3.2. Functions of suspension system
1. It prevents the vehicle body and frame from road shocks.
2. It gives stability of the vehicle
3. It safeguards the passengers and goods from road shocks.
4. It gives the good road holding while driving, cornering and braking
5. It gives cushioning effect
6. It provides comfort.
3.3. Requirements of suspension system
- There should be minimum deflection
- It should be of minimum weight
- It should b of low initial cost
- It should have low maintenance and low operating cost
- It should have minimum tyre wear
3.4. Suspension system components
Nearly all automotive suspensions have the same basic components and they operate similarly.
The basic differences between the suspensions found on various vehicles are the construction
and placement of the parts. It consists of springs, shock absorbers, spring shackles, stabilizer, …
Springs
A spring is the core of all suspension systems. Springs carry the weight of the vehicle and absorb
shock forces while maintaining correct riding height. They are compressible links between the
vehicle’s frame and body and the tires. Doing this, they dampen road shock and provide a
comfortable ride. If a spring is worn or damaged, other suspension parts will shift out of their
proper positions and will experience increased wear. Various types of springs are used in
suspension systems are coil, torsion bar, leaf (both mono- and multi-leaf types), and air springs.

Figure 24: Various type of Automotive spring
The springs take care of two fundamental vertical actions: Jounce and Rebound. Jounce, or
compression, occurs when a wheel hits a bump and moves up. When this happens, the
suspension system acts to pull in the top of the wheel, maintaining an equal distance between the
two wheels and preventing a sideways scrubbing action as the wheel moves up and down.
Rebound, or extension, occurs when the wheel hits a dip or hole and moves downward.
Coil Springs
Two basic designs of coil springs are used: linear rate and variable rate. Linear rate springs
characteristically have one basic shape and a consistent wire diameter. All linear springs are
wound from a steel rod into a cylindrical shape with even spacing
between the coils. As the load is increased, the spring is
compressed and the coils twist (deflect). As the load is removed,
the coils flex (unwind) back to the normal position.
Variable rate spring designs are characterized by a combination of
wire sizes and shapes. The most commonly used variable
rate springs have a consistent wire diameter, are wound in a
cylindrical shape, and have unequally spaced coils. This type of spring is called a progressive
rate coil spring. The design of the coil spacing gives the spring three functional ranges of coils:
inactive, transitional, and active. Inactive coils are usually the end coils and introduce force into
Figure 25: The different designs of coil springs

the spring. Transitional coils become inactive as they are compressed to their point of maximum
load-bearing capacity. Active coils work throughout the entire range of spring loading.
Leaf springs
They are formed by bending and made of long strips of steel. Each strip is named as leaf. The
long leaf is called Master leaf, and it consists of eyes at its both ends. One end is fixed to the
chassis frame, the other end is fixed to the shackle spring. The spring will get elongated during
expansion and shortened during compression. This change in length of spring is compensated by
the shackle. The U-bolt and clamps are located at the intermediate position of the spring. The
bronze or rubber is provided on both eyes on master leaf. They are five types of leaf springs such
as full-elliptic type, semi- elliptic type, three quarter-elliptic type, transverse spring type and
helper spring type.
Full elliptic type: the advantage of this type is the elimination of shackle and spring. The
lubrication and wear frequently which are on of the main drawback of this type of springs.
Semi-elliptic: this type is more popular for rear suspensions are used in 75% of cars.
Three-quarter elliptic type: This type is rarely used in now a days. It gives resistance but
occupies more space than other types.
Transverse type: this type of spring is arranged transversely across the car instead of
longitudinal direction.
Helper springs: the helper springs are used in heavy vehicles for rear suspension. When vehicle
fully loaded the main spring as well as helper spring to come in action and absorb the road
shocks. When the load of the vehicle is less the helper spring will not act and the main spring
only absorbs the road shock.

Automotive chassis technology

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