2. Pressed Steel Disc
Most popular and most used types of wheel.
• Strong, light, stiff and resistant to accidental damage.
• Can be manufacture in mass at a very economical low cost.
5. Assembly view 2 Exploded view
Wheel Assembly
A good wheel assembly is one which can sustain such forces over a longer period of time. Thus
it is required to design the wheel assembly considering all these factors. A failure of any
component of the Wheel Assembly means a breakdown of the automobile and in some cases
might also be hazardous for the driver. Thus utmost care must be taken while designing the
Wheel Assembly. The objective of Optimization is always to find the best possible and suitable
dimension. This is because optimization does not always mean reducing dimensions it also
means finding out the dimensions which will just enough to sustain the forces.
Components of Wheel Assembly.
The Wheel Assembly consists of the following Components.
1) Spindle
2) Knuckle
3) Hub
4) Bearings
a. Taper Roller Bearing- Front b. Deep Groove Ball Bearing-Rear
5) Nut
6) Cotter/Split Pin
The wheels assembly generally thought to consist of hub, disc, rim, tyre and tube.
The wheels not only support the weight of the vehicle, but also protect it from road
shocks.
Whereas the rear wheel moves the vehicle, and the front wheel is used to steer it.
All the four wheels must resist the braking stresses and withstand side thrust.
Assembly view 1
6. Wheel Balancing
Tire/wheel assembly balancing is a very basic service, and still a good profit center for tire
dealers who invest in the necessary equipment. Modern cars and light trucks/ SUVs are highly
tuned vehicles, and anticipated performance, driver comfort, fuel economy and tire life all can
be negatively impacted by even the slightest imbalance. Fractions of an ounce truly do matter
today.
Current tire/wheel balancers are much easier to use than earlier machines or the old-school
bubble balancers, with many automatic and computer-generated features designed to deliver
exceptional balance. Many modern tire/wheel bal ancers include features such as direct drive
motors, multiple balancing modes, laser guides, automatic starting with a cycle of seconds,
weight storage bins and automatic static balancing.
There are a number of reasons why you should be checking the balance of the tires/wheels on
your customers’ vehicles. The three basic times when balancing should be done include:
• When a tire is replaced or repaired
• When a balance weight is moved or falls off
• When new tires are purchased
Types of Balancing
In many cases, when a tire is manufactured, it is inspected for static and dynamic balance. Not
every tire, even among the major makers, is directly tested, though. Tires that don’t measure
up in either factor are rejected.
Tire manufacturers measure static balance by the use of a sensor mounted to the spindle
assembly, and measure dynamic balance by mounting a tire on a test wheel, accelerating the
assembly to 300 rpm or higher and then measuring the forces of imbalance as the tire rotates.
In most cases, the old-school bubble balancer is a thing of the past. Dynamic balancers – also
referred to as “spin balancers” or “computer balancers” – are the most prevalent piece of
equipment. Even among dynamic balancers, though, there are vast differences in not only
features but, more importantly, precision.
Dynamic balancers not only determine the location of any imbalance, but also point out the
exact amount of counter weight that must be added to correct the imbalance. Various available
equipment features can make that an even more precise operation.
Road force variation balancing is yet another method that has been in use at the OE level for
many years. While only in limited use in the aftermarket, road force variation equipment is
becoming increasingly popular as vehicle sensitivity to imbalance becomes ever greater.
Steps for Balancing a Tire/Wheel Assembly
1. Turn your machine OFF then ON, which resets the balancer. The machine wakes up using
standard clip-on wheel weight locations.
2. Remove stones/rocks or other debris from tread and any weights already attached to the
wheel. During this process you also should remove any mud, dirt or snow on the inside of the
wheel and make sure that the mounting surface of the wheel is completely
7. 3. Mount a tire/wheel assembly on a balancer that will use standard
clip-on wheel weights. Use the most appropriate mounting method.
Technicians should be careful to avoid back injury and should seek
assistance when lifting a heavy tire/wheel assembly onto a
balancing shaft.
4. There are three main mounting methods. They include:
• Back Cone – Most original equipment and steel wheels can be
mounted properly using this method. The wheel is centered on a
cone from the inner side of the wheel.
• Front Cone – A wheel should be cantered by the outer side of the hub only when the inner
surface will not provide an accurate surface to centre on.
• Pin-Plate – An alternate method of securing and aligning an assembly on a balancing machine
is the pin-plate method. A pin-plate is added instead of a pressure cup.
5. Enter A & D wheel dimensions using offset arm. Before a wheel can be balanced, wheel
dimensions must be entered into the computer on your unit. These include; A = Offset – The
distance measured from the balancer (“0” on offset arm) to inner plane of the wheel rim (inner
weight location). W = Width – The width of the wheel at the rim flanges, measured with
callipers. D = Diameter – The diameter of the wheel as indicated on the tire.
The Back Cone method of mounting
Front Cone mounting is one
The Pin-Plate method is a variation of
the Back Cone method using a
pinplate.
8. 6. For automatic measurement, pull the offset arm out to the wheel, hold it still at clip-on weight
position against the wheel flange and wait for a “beep.” Return the arm to home position.
7. Enter the wheel width dimension. Use plastic callipers to measure wheel width for manual
entry. Press the W key. Use the keypad to enter width value (between 2 and 20 inches.) Lower
the hood for automatic measurement (see above). Note the value entry of the W dimension.
8. Lower the hood. The wheel will spin and unbalances are measured and displayed. The
corrective weight amount appears in the weight display window for inboard and outboard
weight locations.
9. Raise the hood after the tire stops rotating. Make sure that the wheel has stopped before
raising the hood.
10. Inboard centre bar blinks. If an inboard corrective weight is not required, the wheel will
stop at the outboard corrective weight location and you can go to Step 13. 11. Attach inboard
corrective weight. Attach specified weight amount at top-dead-centre on the inside flange of
the wheel. NOTE: Wheel weight suppliers often will supply a rim flange contour gauge to help
technicians select the correct clip-on weight for the wheel. 12. Press NEXT, causing the wheel
to rotate. 13. The outboard centre bar will blink.
TYRE
14. Some tyre designations are prefixed with a letter
P Passenger tyre
LT Light truck tyre
T Temporary tyre
C commercial
1.Width of the tyre
The first number is a three-digit number which refers to the overall width of the tyre in
millimetres.
e.g. 205/55R16 88V
2.Aspect ratio
(Section Height ÷ Section Width = Aspect Ratio )
The second number refers to the aspect ratio, which is the relationship between the tyre's height
and its width. In this example, the sidewall's height is about 55% of the tyre's width.
The letter following the aspect ratio is usually an 'R' which stands for radial.
e.g. 205/55R16 88V
3.Wheel diameter
The next number indicates the diameter of the wheel rim (in inches) on which the tyre will fit.
e.g. 205/55R16 88V
4.Load index
The load index is an assigned number that corresponds with the load-carrying capacity of the
tyre.
e.g. 205/55R16 88V
5.Speed rating
The speed rating is a letter which indicates the range of speeds at which a tyre is certified to
carry a load. Each tyre is assigned a rating from A (lowest) to Z (highest).
e.g. 205/55R16 88V
15. The speed rating of the tyre is given by the letter code, which indicates maximum
recommended speed for that tyre. Common symbols for passenger car tyres include;
S, for up to 180 kilometres per hour.
H, up to 210 kilometres per hour.
V, up to 240 kilometres per hour.
Z for over 240 kilometres per hour.
Tyre Tread Patterns
16. Tyre Valves
A tyre contains the air under pressure, which supports the vehicle load. The tyre valve permits
air under pressure into the tyre chamber (formed between the casing and the rim) when
required, and releases this air for adjustment of pressure or when removal of the tyre is
necessary. The valve stem easily accepts a high-pressure air-line adaptor or a pressure-testing
gauge.
Valve Operation
The valve assembly has a core-pin, which is fixed to a valve seat. This pin passes through an
internally parallel sleeve and the outside of the sleeve is attached to a tapered seal. When the
core assembly is screwed into the core housing, the tapered seal prevents any air leakage
between the core housing and the valve sleeve. The return-spring normally holds the valve in
the closed position, so that compressed air pumped into the tyre is trapped.
For inflation of the tyre, a compressed-air supply pipeline attached to a valve adaptor is fitted
over the valve stem so that the core pin is pushed down. Air from the higher-pressure supply
is then forced through the valve annular core space into the tyre. When desired pressure is
reached, the adaptor is removed, which releases the core-pin so that the valve is closed. When
the tyre pressure is high, the core-pin is depressed slightly to release the excess air from the
tyre. The outer cap keeps the valve out of grit and acts as a secondary seal for the valve
assembly.
17. Tyre Inflation Pressure
Tyre is a flexible structure filled with compressed air.
Inflation pressure plays an important role in carrying the vehicle load.
Inflation pressure is vital to safe use of tyres. Under or over inflation may lead to tyre
failures and / or unsafe performance of tyres or vehicles.
Use of Nitrogen in place of air is also gaining popularity due to its advantages.
The right amount of air for your tires is specified by the vehicle manufacturer and is shown
on the vehicle door edge, door post, glove box door or fuel door. It is also listed in the
owner’s manual.
Air pressure must be measured in a ‘cold’ condition.
There are three likely scenarios for inflation observed in tyres:
1. Under inflation
2. Over inflation
3. Recommended (proper) inflation
i. Under-Inflation: When the tyres are inflated below the recommended inflation pressure, the
condition is said to be under-inflation. Under inflation increases tyre wear, creates excessive heat
and causes the sidewalls to over flex. This leads to tyre’s premature failure.
ii. Over-Inflation: When the tyre is inflated higher than the recommended inflation pressure, the
condition is said to be over-inflation. Over inflated Tyres can cause suboptimal vehicle handling
performance leading to lowering safety levels. Over inflation makes tyres susceptible to impact
damages.
18. iii. Recommended Inflation: It maintains an even ground contact pressure of the tyre tread and
prevents uneven wear. The recommended inflation pressure ensures safe driving, riding comfort
and monetary savings.
Recommended practices for maintaining Inflation Pressure:
Tyre pressure must be checked once in a week with an accurate / reliable tyre pressure
gauge. When the tyres are cold. (Within 2 kms of travel or 3 hours after stoppage).
Don’t forget to check the inflation pressure of spare.
Use of good quality valve core and valve dust caps will ensure proper maintenance of tyre
pressure.
Safety precautions in tyres
Tread depth must be not less than 1.6mm over the central three-quarter of the tyre and
must go all the way round the circumference in an continuous unbroken band with no
bald patches anywhere on the tyre tread.
If radial and cross ply tyres are fitted to the same vehicle, radial ply tyres must be
fitted on the rear.
Cross-ply and radial ply tyres must never be fitted on the same axle.
Tyre pressures must be set to the manufactures recommendations.
The tread and side wall must be free from large cuts, abrasions or bubbles.
It is important to remember that even one trip of the truck, with improper load
distribution may cause irreversible damage to the tyres.
Speed
1. Excessive high speeds results in increased tyre running temperature. As the rubber
gets heated up its modulus, (stiffness) gets reduced.
2. Rubber being a good non-conductor of heat the residual heat is retained causing
increased tyre wear and separation of components.
Wheel Alignment
1. A vehicle is said to be properly align when all the steering and suspension
components and set as per the vehicle manufacturer and when the tyre wheel
assembly are running straight and true.
2. Proper alignment is necessary for perfect vehicle control, uniform and even tyre
wear and safety.
3. Recommended to get the vehicle alignment checked and corrected as per vehicle
owner’s manual as soon as tyre are wearing unevenly or ride handling
problems(vibrations, pulling to one side etc).
Wheel Balancing
1. A wheel which is not properly balanced may setup vibrations which can affect
steering control. Wheels, tyres and tubes are usually checked for balance before
leaving factory.
2. This balance is achieved by positioning weights on the wheel to counterbalance
heavy spots on the tyre wheel assembly.
3. Properly balanced tyres are important for driving comfort and long tyre life.
19. Tyre rotation
1. Rotation of tyre in a vehicle is recommended for a uniform tyre tread wear on all wheel
position to achieve optimum tyre life.
2. It is preferred to rotate tyres as per vehicle manufacturers recommendation or in case
of any uneven tyre wear noticed.
3. It is suggested to check wheel alignment, wheel balance and suspension before the tyres
are rotated. Rotation patterns /pictures to be incorporated.
4. Tyre rotation refers to the periodic shifting of a car's wheels and tyres to ensure
uniform tread wear and longer tread life. Front tyres exert more pressure than the rear
and, hence, it becomes imperative for the tyres to be rotated. Here are some tips on
how and when to get your car tyres rotated
5. The most common problem faced during tyre wear and tear is the wearing out of front
tyres before the rear. In such cases, the two front tyres have to be either replaced with
new ones or with the old, but partly worn out units at the rear. This is where tyre
rotation comes into play. Here are two ways to rotate your car’s tyres.
1. Four Wheel Rotation: This method can be applied only when the running wheels are being
used. Also, it cannot be done with a space-saver tyre (a smaller, limited-use spare tyre) provided
by the manufacturer or if your car has a combination of tube and tubeless tyres. In this method
of rotation, the front tyres go in the corresponding rear hubs and the rear tyres are put on the
opposite front hub. For example, in two wheel drive cars, the rear right tyre will be moved to
the left front and the right rear tyre to the left front. On four-wheel-drive cars, the front tyres
are changed in a criss-cross pattern and the rear tyres shift to the corresponding front hubs.
2. Five Wheel Rotation: This method also uses the spare wheel and can be a bit tricky. The
spare wheel goes to the front right hub and the front tyres go to the corresponding rear hubs.
The right rear tyre will move to the front left hub and the rear left tyre comes out as the spare.
In four-wheel or rear-wheel drive cars, the front tyres are shifted in a criss-cross fashion on to
20. the rear hubs. The rear left tyre is fitted on the right front hub and the rear right tyre becomes
the spare while the original spare moves to the front right hub.
Ideally, rotation of tyres needs to be done every 15,000kms. In the rotation cycle, where the
spare wheel is also included, it's understood that the fifth wheel is also in an equally good
condition as the other four tyres.
Tyre Matching
Mismatching of dual tyres imposes overload on the larger diameter tyre, causing it to over
deflect and so get overheated. The smaller diameter tyre, lacking in equitable road contact,
wears irregularly and faster than normal.
Types of Tyre wear and their causes
1. Camber Wear (One-Sided Wear)
2. Feathered Directional Wear
3. Cupped Wear (Cupping Wear)
4. Centre Wear
5. Shoulder Wear (side Wear)
6. Flat Spot Wear
7. Sidewall Wear
21. 1. Camber Wear (One-Sided Wear)
If one of the shoulders of your tyres has worn down considerably while
the other has changed very little, this is camber wear. It’s characterised
by a gradual slope from one side to the other, and is much easier to
identify than other types of tyre wear which, in turn, means that you get
to the root of the problem quicker and get it sorted
Cause
Considerable wear on the inside and outside edges of the tyre can be
caused variously by suspension misalignment, a bent strut, a dislocated
strut tower, a broken or weak spring, or collapsed or damaged control
arm bushings.
2. Feathered Directional Wear
Feathering is generally caused by the toe of the tyre being too in or
out, which can be fixed with proper wheel alignment. However,
feathering could also be a symptom of aggressive driving, specially
taking corner at high speed.
Cause
Feathered directional wear could be caused by a variety of different
mechanical problems associated with your vehicle. However, these
are arguably the most common: toe misalignment, worn tie rod ends,
bent steering linkage and arms or worn idler arms.
3. Cupped Wear (Cupping Wear)
Cupped wear is signified by cups and dips appearing around the
edge of the tread. Unlike the other types of tyre wear, cupped wear
doesn’t follow a specific pattern, which makes the wear itself look
much less uniform than, say, camber wear. So, if you notice dips
and cups appearing sporadically over the surface of your tyres,
you’ll know that this is cupped wear.
Cause
Causing by a worn suspension system or shock absorber, cupping occurs
from repeated up and down motions, almost like hopping.
22. 4. Centre Wear
Like feathered wear, it’s not always easy to spot when your tyres are
showing signs of centre wear, given that the centre of your tyres tend
to be out of sight underneath the wheel arches. However, if you do
peek under and take a look, you will notice a strip around the centre
your tyres where the tread has worn down.
Cause
Centre wear can happen on your tyre when it has been over inflated.
Your owner’s manual should contain all information regarding the needed
pressure of tyres, be sure to follow it. This will wear out your tyres along
the centre and leave the edges untouched, as the bulge from over
inflation keeps the edges off the ground.
5. Shoulder Wear (Side Wear)
Unlike centre wear, shoulder wear should be pretty easy to spot
because, of course, the shoulders will be more worn than the centre.
While the shoulders and edges of tyres will always round off
(although perhaps to different extents), tyres with significant shoulder
wear will look almost tubular by comparison
Cause
1. Under inflation and / or overload
2. Repeated sharp turns at a high speed in cornering
3. Improper matching of tires and rims
4. Tires are not rotates timely
6. Flat Spot Wear
As the main surface area is turning flat and smooth, always remember to use
brakes lightly, continued aggressive use will cause your tyre to rupture.
Cause
Flat spot wear is often caused by aggressive or emergency braking,
although it may also be an indication of a larger brake issue. If you spot
this type of wear — and don’t remember making any sudden or hard
stops — have your brake system checked for a foundation issue.
23. 7.Sidewall Wear
look for cuts or cracks in the sidewall; both of which could indicate a leak in your tyre. If the
sidewalls on your tyres are not in good shape
Cause
Sidewall wear is usually caused by a driver who parks too close to the curb. Additionally, this
type of wear is often seen in urban settings with street parking. And, in excessive cases,
sidewall wear can weaken the tire’s core and cause a tire to buckle.
Selection of Tyre under different applications
24. Retreading Cold or Hot explained
Why retreading:
Retreading is a safe, efficient and environmentally friendly way to breathe new life into worn
tyres: The "worn-out" tread of the tyre is replaced with a brand-new one and this means that the
tyre can be used again!
Unfortunately, however, not every tyre can be retreaded. The requirements are:
The tyre was used correctly in its "first life", driven with the right air pressure and treated with
care.
The tyre's frame, the carcass, is not seriously damaged.
In addition, whether a retreadable carcass can be reused depends on the type of tyre. The
following retreading limits apply:
Car tyres: 1 time
Light truck tyres: Generally 1 time
Truck tyres: 1 to 3 times
Aircraft tyres: Up to 12 times
There are two techniques for retreading:
Hot retreading or Precure "cold" retreading.
The benefits of retreading are that it is both environmentally friendly and cost-efficient!
When the tread has worn off, only about 20% of the tyre is used up. The carcass, which
represents about 80% of the tyre's value, can be re-rubberised for a "new tyre life".
To produce a truck or bus tyre requires about 60-80 kg of rubber mixture. Retreading the tyre
takes only about 15 kg of rubber. A considerable amount of raw materials can therefore be saved.
In the EU, this equates to more than 300,000 tonnes per year!
To produce a car tyre requires about 28 litres of crude oil. To retread a car tyre, on the other hand,
only 5.5 litres of oil are needed.
Retreading saves over 500,000 tonnes of crude oil in the EU every year.
Retreads save the user a great deal of money, since they will do about the same mileage as new
tyres, but cost only 45-60% of the price of a comparable new tyre.
While retreading does not eliminate the need to dispose of old tyres, it does delay it considerably.
This helps keep down the fast-growing cost of disposal and takes the pressure off landfills.
Retreads and their place on the market
The proportion of retreads on the replacement car and truck tyre market in Europe still varies
widely.
25. For car tyres, retreads make up only 1-2% of the market in Switzerland and the Netherlands,
but this figure rises to over 20% in Scandinavia. In Germany, retreads account for around 10%
of car tyres, a proportion which rises to 20% for winter tyres.
For truck tyres, the proportion of retreads is much higher, ranging from around 40% in Spain
to over 70% in Finland. In Germany and France, retreads make up around half of the
replacement tyre market for trucks. Over 15 million truck and bus tyres are used every year
across the EU. Of these, around 8 million are new tyres, and over 6 million are retreads.
Retreading plays a particularly important role in aircraft tyres, which are subjected to extreme
stresses. Aircraft tyres have to withstand huge strain at speeds of over 250 km/h, and undergo
retreading after around 150 take-off and landing manoeuvres. Retreading can take place up to
twelve times. The testing procedures are naturally very stringent here, and safety takes top
priority.
High-quality retreading is the alternative to new tyres for commercial vehicles, since it offers
safety, top running performance and an excellent cost-benefit ratio. More and more consumers
are recognising and coming to appreciate the positive image of high-quality retreads.
HOT Retreading:
Hot retreading involves the vulcanisation of a tyre in a mould at a temperature of around 150
°C. The tread and the sidewall veneer of the tyre are made up of non-vulcanised rubber
compounds. The shape and tread of the tyre are created in the heating press.
Arguments in favour of hot retreading:
Suitable for all tyre applications, including car and aircraft tyres.
Material costs are lower than the more complex products required for precure retreading.
Hot retreading also allows extensive repairs to be carried out on the tyre carcass (e.g. belt
replacement).
Even bias-ply carcasses can undergo hot retreading without any problems. Points to note:
A separate mould is required for each tread and size. This requires a high level of investment
in a range of moulds, which will be need to be regularly updated.
The production process needs to be designed for large numbers of tyres. This calls for a central
production workshop, an extended customer area and therefore brings with it relatively high
logistics costs.
26. Cold Retreading:
Precure or "cold" retreading involves vulcanisation without a mould at a temperature of
between 95 °C and 110 °C. The tyre is put together using a pre-vulcanised tread liner (= new
tread) and a non-vulcanised bonding gum layer. The bond between the carcass, the bondung
gum and the precured tread is created in an autoclave. Precure retreading has become fully
established in the truck tyres sector since the introduction of radial tyres in the mid-1960s.
Arguments in favour of Cold/precure retreading:
Less investment is required on the part of the retreading plant (no expensive moulds) and lower
follow-up costs, since it is the material supplier who updates the range of moulds.
A wide range of tread types are available, allowing the optimum tread to be selected for the
tyre application.
The comparatively low investment costs involved mean that decentralised, smaller production
units can be operated. This means lower logistics costs and makes the operator more flexible
and closer to his customers.
The precure retreading process is kind to the carcass, since vulcanisation temperatures are
lower and put less strain on the rubber-metal bonds in the carcass. Heat build-up in the tyre,
rolling resistance and other tyre properties are often easier to assess than with hot retreading.
With comparable tread geometries, the running performance of a precured retread is often
better than a hot retread and the same as an equivalent new tyre.
Factors Affecting Tyre Performance
1. Matching and installation of tires
Tires installed correctly or not directly related to the life of the tire, especially when the
replacement tires. Different tire types and patterns, due to different actual size and load
capacity of the tires, must not in any mix. Also, if you yourself cannot fully grasp the skills of
replacement tires, we recommend that you go to a professional tire shop or vehicle
replacement at an authorized service provider.
27. 2. Working pressure
Tire pressure is too low or too high, will affect the life of the tire. If the tire pressure is too
low, the radial deformation increases, excessive deformation of the tire wall on both sides,
resulting in the tread shoulders and wear phenomena, the tire temperature rises, it will
seriously reduce the life of the tire.
If the tire pressure is too high, increasing the rigidity of the tire deformation and contact area
is reduced, so that the central unit pressure increases tread wear Caroline drama. Produce
central tread wear phenomenon that affects comfort and reduce tire life. Tests show that if we
raise the pressure by 25%. Tire life will be shortened by about 30%.
3. Tire load
The larger the load of the vehicle, the shorter the life of the tire, this is not to question the
contents. Especially in the case of overload more prominent. Regular tire manufacturers to
produce tires are marked with load index.
4. Driving speed
Regular tire manufacturers to produce tires are marked with speed level index. Tires should
be used within a specified speed level index corresponding to the maximum speed.
5. Tire temperature
Vehicles in the process, the tire due to stretching, compression and friction, causing the tire
temperature rises. High temperatures easily exacerbate or even puncture the tire wear occurs.
6. Chassis status
Front, the rear axle parallelism, wheel alignment, brakes and chassis other parts working
conditions will be different degrees of technical conditions affecting the life of the vehicle
tires. Once a serious traffic crash, vehicle owners are sure to open the chassis to a
professional repair station status checks and adjustments.
7. Road conditions
If the vehicle is a long gravel road or in the harsh road conditions, tire life will certainly be
reduced. This is no exception for off-road tires.
8. Driving habits
This is a factor related directly with the owners. Start too fast, sharp steering, emergency
braking, high-speed driving on poor road conditions of the lot, often when the tire rubs up
and down curbs and parking barriers, etc., can lead to severe tire wear, thereby reducing tire
life.
9. Tire maintenance
Tire timely transposition, the appropriate choice of tread, ground maintenance routine, check
the tire pressure regularly and timely repair and are an important factor in the ground dug
extend the life of the tire tread in the gravel, and other foreign matter.
10. Vehicle maintenance
Many car repair experts say a vehicle to "30% repair, 70% maintenance"; do not wait until a
failure occurs before opening to the repair station maintenance. Periodic maintenance and
extend tire life are also closely related to the vehicle. Wheel alignment, steering knuckles,
wheel bearings and suspension systems checked regularly to maintain one less.
28. SECTION II : BRAKING SYSSTEM
Function
1. Deceleration
The main function of the brake system is to decelerate or decrease the speed of a vehicle. By
stepping on the brake pedal, the brake pads compress against the rotor attached to the wheel,
which then forces the vehicle to slow down due to friction.
2. Absorption
A brake system absorbs the kinetic energy of the vehicle mechanically or electrically in order
to decrease its speed. In mechanical brakes, friction converts the kinetic energy into heat. In
electric brakes, an electric current forces a magnet to apply the brakes.
Requirements:
The brake must be strong enough to stop the vehicle within minimum distance. It is
inversely proportional to brake efficiency and proportional to square of speed.
Provide good control over vehicle during emergency braking and vehicle must not skid
After prolonged period of application of brakes, the coefficient of friction drops and
property of brake material changes which leads to less braking effect. This is called
Brake Fade and hence brakes must have antifade characteristics.
Cooling of the brakes must be very efficient
The maximum retarding force F applied by the brakes at the wheels must be close to
F=μN
The brake torque depends upon effective axle height and braking force between road
surface and tyre. Hence anchor pin supporting brake shoes must have enough strength
to withstand high braking load.
Principle of operation:
Brake works on the principle of friction. When a moving clement is brought into contact with
a stationary element, the motion of the moving element is affected. This is due to frictional
force, which acts in opposite direction of the motion and converts the kinetic energy into heat
energy.
TYPES OF BRAKES
1. Mechanical Brakes
I. Drum Brakes (a) Internal expanding shoe type
(b) External contracting shoe type
II. Disc Brakes
2. Hydraulic Brakes
3. Power Brakes
I. Air Brakes
II. Air Hydraulic Brakes
III. Vacuum Brakes
IV. Electric Brakes
29. Mechanical Brakes
Elementary theory of Shoe (block) brake
A single block or shoe brake is shown below. It consists of a block or shoe which is pressed
against the rim of a revolving brake wheel drum. The block is made of a softer material than the
rim of the wheel. This type of a brake is commonly used on railway trains and tram cars. The
friction between the block and the wheel causes a tangential braking force to act on the wheel,
which retard the rotation of the wheel. The block is pressed against the wheel by a force applied
to one end of a lever to which the block is rigidly fixed. The other end of the lever is pivoted
on a fixed fulcrum O.
Single block brake. Line of action of tangential force passes through the fulcrum of the lever.
Let
P = Force applied at the end of the lever,
RN = Normal force pressing the brake block on the wheel,
r = Radius of the wheel,
2θ = Angle of contact surface of the block,
µ = Coefficient of friction, and
Ft = Tangential braking force or the frictional force acting at the contact surface of the block
and the wheel.
If the angle of contact is less than 60°, then it may be assumed that the normal pressure
between the block and the wheel is uniform. In such cases, tangential braking force on the
wheel,
Ft= µ.RN
and the braking torque,TB = Ft.r = µ RN. r
Let us now consider the following three cases :
CASE I : When the line of action of tangential braking force (F) passes through the fulcrum
O ofthe lever, and the brake wheel rotates clockwise as shown in Fig. 25.1 (a), then for
equilibrium, taking moments about the fulcrum O, we have,
∴ Braking torque,
It may be noted that when the brake wheel rotates anticlockwise, then the braking
torque is same, i.e.
30. I. Drum Brake
a) Internal expanding shoe brake
Construction
An internal expanding shoe brake consists of two
shoes S1 and S2 .
The outer surface of the shoes are lined with some
friction material (usually with Ferodo) to increase the
coefficient of friction and to prevent wearing away of
the metal.
Each shoe is pivoted at one end about a fixed fulcrum
O1 and O2 and made to contact a cam at the other end.
Working
When the cam rotates, the shoes are pushed outwards
against the rim of the drum.
The friction between the shoes and the drum produces the braking torque and hence reduces
the speed of the drum.
The shoes are normally held in off position by a spring .
The drum encloses the entire mechanism to keep out dust and moisture.
b) External contracting shoe brake
An external contracting brake is tightened around the rotating drum by moving the brake
lever. The brake band is made of comparatively thin, flexible steel, shaped to fit the drum,
with a frictional lining riveted to the inner
surface his flexible band cannot withstand the high pressure required to produce the
friction needed to stop a heavily loaded or fast-moving vehicle, but it works well as a
parking brake or hold brake.
The brake band is anchored opposite the point where
the pressure is applied. In addition to supporting the band,
the anchor allows adjustment of the brake lining clearance. Other adjusting screws and
bolts are provided at the ends of the band.
31. II. Disc Brake
Disc brakes are fairly simple to work with, once
you know the parts and their functions.
The main components of a disc brake are:
Rotor
Caliper, which contains a piston
Brake pads In a disc brake,
The brake pads squeeze the rotor instead of the
wheel, and the force is transmitted
hydraulically instead of through a cable.
Friction between the pads and disc slows the
disc down.
Working
When a brake lever or pedal is pressed, the push rod which is connected to lever or pedal and
master cylinder piston pushes the master cylinder piston. This movement allows the master
cylinder piston to slide and push the return spring inside the bore of master cylinder, which
generates pressure in reservoir tank. At this moment a primary seal allows the brake fluid of
reservoir tank to flow over it into the brake hosepipes. A secondary seal ensures that the brake
fluid does not go other side.
Then the fluid enters in to cylinder bore of caliper assembly via brake hosepipes and pushes
the caliper piston or pistons. At this time the piston ring moves in rolling shape with piston.
Then the caliper piston pushes brake pad. This movement causes brake pads to stick with brake
disc which creates friction and stops the brake disc/rotor to rotate. This way disk brake system
stops or slows down the vehicle.
Advantages of Disk Brake:
1. Disk brake requires less effort (brake torque) to stop the vehicle compare to drum
brake.
2. It generates less heat compare to drum brake for the same brake torque.
3. Ease of maintenance as disk brake is outside the wheel rim.
4. It cools down faster compare to drum brake.
5. If worn out brake shoes are not changed at proper time it can cut the brake drum in
drum brake. Disk brake does not have such problem.
6. It is less likely to skid compare to drum brake in wet condition.
7. It is much safer than drum brake in hard braking condition. Under such condition
drum brake can lock up the rear wheel.
8. It has brake pad wear indicator which is not there in drum brake.
32. Disadvantages of Disk Brake:
1. It is expensive compare to drum brake.
2. More skills require to operate disk brake compare to drum brake that’s the reason
why some people are not comfortable with disk brake
3. If any air remains in disk brake system, it can cause accident as the brake will not
work effectively.
4. Disk brake assembly has more moving parts and much complex than drum brake.
5. It requires lot of effort at maintenance front like brake fluid (bleeding), change of
brake pads etc. compare to drum brake.
SELF-ENERGIZING BRAKES
33. working
All modern hydraulic wheel brakes of the drum type have a 'self-energizing" or 'servo'
feature in which the force of the rotating drum is utilized to increase the brake
pressure.
In Figure when the vehicle is traveling forward, the drum is rotating in a counter
clockwise direction.
When the brakes are applied, the primary shoe at the left tends to move in the
direction of the drum rotation, because of the friction of the rotating drum.
Since the primary shoe is linked to the secondary shoe at the bottom the secondary
shoe is forced around against the anchor pin at the top.
The result of this wrapping action is that both shoes are forced into tighter contact
with the drum and the braking pressure is more uniformly applied.
When the brakes are applied while the car is in reverse, the secondary shoe tends to
move in a clockwise direction against the primary shoe, forcing the latter against the
anchor pin.
BRAKE FRICTION:
During braking the heat energy is first borne by the two contact surfaces of the brake namely
the brake disc and the brake pad (or drum and shoe in the case of drum brakes) and is then
transferred to the contacting components of the brake such as the calipers of the brake as well
as surroundings.
The demand on brake pad are Maintain a sufficiently high friction co-efficient with the brake
disc and no decompose with the brake disc is compromised, at high temperatures as well as
exhibit a stable and consistent friction co -efficient with a disc brake. Brake pad comprise the
following subcomponents are;
A. Friction additives – which determine the frictional properties of brake pads and
comprise a mixture of abrasives.
B. Fillers – which reduce the cost and improve the manufacturability of brake pads.
C. A binder – which holds components of a brake pad together.
D. Reinforcing fibres which provide mechanical strength.
Properties of good material for brake lining High frictional coefficient, Super thermal
conductivity, High thermal diffusivity, Low mass, High wear resistance, Low noise
susceptibility, No expensive, Easily available, Avoids damage to the braking surface,
Eliminates cosmetic issues and Eliminates corrosion related judder.
FRICTION MATERIALS
A. Asbestos
Asbestos become the major material for friction material composition over eight decade and
become more wide spread during the industrial revolution in1866. Asbestos were from Greek
word which mean "unquenchable" or "inextinguishable” is a set of six naturally occurring
silicate minerals exploited commercially for their desirable physical properties.
34. B. Kevlar or Aramid T
he use of non-metallic friction material seems to become the solution forth asbestos friction
material. Friction material made from Kevlar or aramid fiber. Aramid fiber (a generic
expression denoting fiber made from the condensation product of isophthalic orterephthalic
acids and morphenylene diamine such as Kelvar fibre sareal so widely used as reinforcing fiber
,but they are a deferent class of fiber in that the relatively so fiber. They are very light an
excellent thermal stability, with a very good stiffness to weight ratio.
C. Fibertuff
Fibertuff is a product designed to give the wear of a ceramic facing, yet have the engagement
and disengagement qualities of an organic material. Fibertuff intended to wear against its
mating surfaces like organic material. Used primarily in the stamped steel and cast units, this
product offers greater life than organic material with many of the same qualities that organic
friction has traditionally offered. Around -town delivery trucks and mid-range applications find
that this product works best.
HYDRAULIC BRAKES
Hydraulics is the use of a liquid under pressure to transfer force or motion, or to
increase an applied force.
The pressure on a liquid is called HYRAULIC PRESSURE.
And the brakes which are operated by means of hydraulic pressure are called
HYDRAULIC BRAKES.
These brakes are based on the principle of Pascal’s law.
35. Components
components and their functions in a hydraulic braking system are as follows.
1. Brake Pipes.
These are steel pipes which form part of the fluid circuit between the master-cylinder and the
wheel-cylinders. These pipes transfer the fluid along the body structure and rigid axle members.
Flexible hoses connect the sprung body pipes to the unsprung axle wheel-brake units, to allow
for movement
2.Master-cylinder.
This converts foot-pedal force to hydraulic pressure within the fluid system by means of the
cylinder and piston
3.Disc-brake.
This comprises of a disc bolted to the wheel hub. This is sandwiched between two pistons and
friction pads. The friction pads are supported in a caliper fixed to the stub-axle (Fig. 28.36).
When the brakes are applied, the pistons clamp the friction pads against the two side faces to
the disc.
4.Drum-brake.
This uses two brake-shoes and linings supported on a back-plate. The back-plate is bolted to
the axle-casing. These shoes pivot at one end on anchor pins or abutments attached to the back-
plate (Fig. 28.36). The other free ends of the both shoes are forced apart when the brakes are
applied. The shoes expand radially against a brake-drum positioned concentrically on the wheel
hub.
5.Wheel-cylinders.
As the hydraulic line pressure acts on the cross-sectional area of the disc and drum cylinder
pistons (Fig. 28.36) in wheel cylinders, the hydraulic pressure is converted into braking effort.
This braking effort either presses the friction pads against the side faces of the disc or forces
the shoe friction linings against the inside of the drum.
Working
A hydraulic braking system transmits brake-pedal force to the wheel brakes through
pressurized fluid, converting the fluid pressure into useful work of braking at the wheels. A
simple, single-line hydraulic layout used to operate a drum and disc brake system is illustrated
in Fig. The brake pedal relays the driver’s foot effort to the master-cylinder piston, which
compresses the brake fluid. This fluid pressure is equally transmitted throughout the fluid to
the front disc-caliper pistons and to the rear wheel-cylinder pistons. As per the regulations a
separate mechanical parking brake must be incorporated with at least two wheels. This
provision also allows the driver to stop the vehicle in the event of failure of the hydraulic brake
system.
In a hydraulic braking system the braking force is directly proportional to the ratio of the
master-cylinder cross-sectional area to the disc or drum-brake wheel-cylinder cross-sectional
areas. Therefore these cylinder diameters are appropriately chosen to produce the desired
braking effect. The wheel-cylinder cross-sectional areas of the front and rear disc-and drum-
36. brakes respectively may be chosen to produce the best front-to-rear braking ratio. Hydraulic
fluid is incompressible provided there is no trapped air in the system. If air is present in the
braking circuit, the foot-brake movement becomes spongy. In a hydraulic system the internal
friction exists only between the cylinder pistons and seals. The friction is caused by the fluid
pressure squeezing the seal lips against the cylinder walls as the piston moves along its stroke.
A hydraulic braking system is suitable only for intermittent braking applications, and a separate
mechanical linkage must be incorporated for parking brakes.
Advantages over the mechanical
This provides equal braking effort on all wheels.
This requires relatively less braking effort to deliver the same output.
This is a fully compensated system so that each brake receives its full share of the pedal
effort.
The efficiency of the hydraulic system is greater than that of the mechanical layout.
This system is suitable for vehicles having independent suspension.
It is easy to alter thrust on shoe because the force exerted on a piston depends on the
piston area. The larger the area, the greater the thrust on the trailing shoe, so a larger
piston can be used.
BRAKE FLUID
Properties
Does not thicken or then with changing heat
Must not boil
Must be compatible with brake parts material
Must lubricate internal parts
Must not evaporate easily
FLUIDS
GLYCOL BASED
(ABSORB
WATER)
DOT 3
DOT 4
SILICON BASED
(DOESN’T
ABSORB WATER)
DOT 5
37. Brake Fluid types
DOT= Department of Transportation
DOT 3 and 4 DOT 5
Polyglycol based
Most common
Compatible with one another
Inexpensive
Destroys paint
Ruined by moister
• Silicone Based
• Used only for heavy duty applications
• Not Compatible with 4&5
• Very Expensive
• Does not damage paint
Fluid Contaminates
Moister- Lowers boiling point
water boils @ 212*F DOT 3 boils @ 401*F
Petroleum Based Product-
soften rubber parts causing swelling
Dirt & Debris-
causes corrosion and clogs
Air and Vapours
Compressible prevents pressure from reaching brakes
AIR BRAKES
A pneumatic brake or compressed air brake system is the type of brake system in which the
compressed liquid fluid from the hydraulic system is replaced with the compressed air for
applying pressure to the master cylinder’s piston which in turn presses the brake pads in order
to stop or decelerate the vehicle.
38. 1. Air compressor- It is the compressor that pumps air from atmosphere to the air storage tank
and is driven by the engine through belt drive.
2. Air compressor governor- It is the governing device used in air brake system that controls
the compression pressure of the air that is pumped to the air storage tank through air
compressor.
3. Air dryer- It is the device used to remove moisture content from the air coming from the
atmosphere to prevent the lines and air storage from water condensation that can cause brake
failure such as during winters due to the freezing of that condensed water.
4. Air storage (reservoir)- It is the tank that is used to store the compressed air sent by the
compressor, this storage always has enough amount of compressed air so that the brakes can
be applied several time and also prevents the brake failure when the air compressor shows
malfunctioning.
5. Brake pedal- It is the mechanism that is operated by the driver and is used to actuate the
brakes in order to stop or decelerate the vehicle. Brakes when pressed pushed the compressed
air which in turn applies brakes to the moving tyre.
6. Dirt collector- It is the device that is placed inside a brake pipe line at place where a branch
is separated and taken off to the triple valve which removes dirt from the air before sending it
to the triple valve
7. Brake cylinder or Brake chamber- It is the device that consists of a cylinder and piston over
which the compressed air pressure is applied in order to push brake pads which in turn makes
frictional contact with the disc or drum in order to stop or decelerate the vehicle.
8. Brake valve or Triple valve- The actuation and release of brake requires continuous release
and building of pressure inside the brake lines and brake cylinder according to the motion of
the brake pedal this is done by the triple valve used in air brake system.
9. Brake drums – Brake drum is the component through which the brake force due to frictional
contact between brake pads and drum lining is transferred to the wheel in order to stop or
decelerate the vehicle, Outer surface of the brake drum consisting of drum lining rotates with
the wheel and the inner part consisting of brake shoes stays in its state of rest when the brake
pedal is not pressed.
Working of Air Brake System
When the driver of a vehicle presses the brake pedal in order to stop or decelerate the
vehicle the following processes takes place-
When the driver starts the engine the brake compressor starts as it is driven by the
engine which in turn starts compressing the atmospheric air and through the compressor
governor this compressed air with optimum pressure is sent to the compressed air
reservoir which always has some amount of air stored from the previous cycle.
When the driver presses the brake pedal the outlet valve of the triple valve closes and
inlet valve opens up which in turn gives passage to the compressed air from the
reservoir to pass through the brake lines of the system.
This compressed air flowing through the brake lines is then transferred to the brake
cylinder which has piston inside it.
When the compressed air applies pressure over the piston inside the brake chamber,
piston moves away from its original position which converts this pneumatic energy into
the mechanical energy.
On the wheel end of the brake cylinder, brake drums are placed inside which there is a
housing of the mechanical actuator like springs or slacks having brake pads at its outer
end.
39. Due to the movement of piston because of the pressure applied by the compressed air,
The mechanical actuator inside the brake drum expands which in turn pushes the brake
pads in outward direction in order to make frictional contact with the rotating drum
lines.
With this frictional contact between brake pads and rotating drum lines brakes are
applied to the wheels in order to stop or decelerate the vehicle.
Application
Due to its property of preventing brake failure, air brakes systems are widely used in
various vehicles but in heavy vehicles like trucks and buses due to the government
vehicle regulations air brake system is mandatory.
It is used in railways
All the trucks and busses on the road today use air brake systems, few from them are.
1. Volvo 9400PX buses.
2. Bharat Benz 3123R truck.
40. A vacuum servo is a component used on motor vehicles in their braking system, to
provide assistance to the driver by decreasing the braking effort.
The two types of vacuum boosters used on modern vehicles are the single-diaphragm
and the tandem-diaphragm (or dual-diaphragm) booster.
Both booster types operate similarly but the tandem-diaphragm booster is smaller in
diameter and is used on vehicles where space is critical.
Construction:
The vacuum booster is a metal canister that contains a valve and a diaphragm.
A rod going through the centre of the canister connects to the master cylinder's piston
on one side and to the pedal linkage on the other.
Another key part of the power brakes is the check valve.
The figure above shows a check valve, which is a one-way valve that only allows air to
be sucked out of the vacuum booster. If the engine is turned off, or if a leak forms in a
vacuum hose, the check valve makes sure that air does not enter the vacuum booster.
This is important because the vacuum booster has to be able to provide enough boost
for a driver to make several stops in the event that the engine stops running.
The diaphragm is connected to a port which opens and lets atmospheric air to the other
side of the diaphragm.
The diaphragm is retained in the back position when not in operation by a spring.
41. Working:
When the brake pedal is released, an internal vacuum port is open which allows engine
vacuum to flow from the check valve to both sides of the diaphragm. With equal
pressure (vacuum) on both sides, the diaphragm is held to the rear by spring pressure.
As the brakes are applied, the brake pedal pushrod moves forward, which closes the
vacuum port and opens the air inlet valve. This action seals off the backside of the
diaphragm from the vacuum source and at the same time allows filtered atmospheric
air pressure to pass through the air inlet valve to the diaphragm backside. The
combination of atmospheric pressure on the backside and vacuum on the front side then
moves the diaphragm and master cylinder pushrod forward to apply the brakes.
ENGINE EXHAUST BRAKE
This type of brake is used as an Auxiliary brake.
It is meant for use while travelling on a lengthy downhill gradient and also in heavy
traffic.
When it becomes necessary to slow down continuously over a large distance.
Construction
The main components of this brake are
1. PRESSURE REGULATOR-to regulate Compressed air.
2. FOOT CONTROL VALVE-for actuating the Exhaust brake.
3. AIR CYLINDER-operates the linkage to actuate the butterfly vale in Exhaust manifold.
4. LINKAGE-to actuate the control lever of the Valve.
42. Working
The brake comes into operation.
When the foot control valve is pressed, the compressed air from the air tank enters the
air cylinder.
Where it operates a linkage to close the butterfly valve at the Exhaust manifold, which
also cut-off the fuel supply through linkage.
The moment the foot is taken off the valve, the brake gets released.
In this way, this type of brakes effect fuel economy also.
This brake is very effective below vehicle speed 40 kmph.
PARKING BRAKE
Not an “Emergency” Brake
Used specifically to keep a parked vehicle from moving
Usually on rear wheels only
Mechanically operated
a. Static Friction: at rest friction- More friction
b. Kinetic Friction: in motion friction- less friction
Once upon a time, almost every car had drum brakes installed on the rear wheels, which
made it possible for automakers to include a cable-activated mechanism that
would hold the brake shoes in place inside the drum without using the hydraulic system.
This cable was controlled via either a pedal on the driver’s left or a handle in the center
console. Both were directly linked to the cable itself.
Once disc brakes began to proliferate, car companies adopted a different parking-brake
design strategy. Some continued to include a small drum brake inside the disc that
43. functioned much like the original drum system once the cable was pulled, while others
introduced a cable that forces the rear brake calipers to clamp down on the rotor.
On modern cars, the pedal or hand brake is often replaced by a button that electronically
activates the cable. This is done primarily to free up more space in the center console,
where most hand brake levers are traditionally located.
REGENERATIVE BRAKING SYSTEM
Regenerative braking is an energy recovery mechanism which slows a vehicle or object by
converting its kinetic energy into a form which can be either used immediately or stored until
needed. In this mechanism the electric motor uses the vehicle's momentum to recover energy
that would be otherwise lost to the brake discs as heat. This contrasts with conventional braking
systems, where the excess kinetic energy is converted to unwanted and wasted heat by friction
in the brakes, or with dynamic brakes, where energy is recovered by using electric motors as
generators but is immediately dissipated as heat in resistors. In addition to improving the
overall efficiency of the vehicle, regeneration can greatly extend the life of the braking system
as its parts do not wear as quickly.
44. Driving conditions have a large impact. You’ll see much better effectiveness for regenerative
braking in stop-and-go city traffic than in highway commuting. This should make sense, as if
you’re repeatedly braking, you’ll recapture a lot more energy than if you simply drive for hours
without touching the brake pedal. Terrain also plays a large role here too, as uphill driving
doesn’t give you much chance for braking, but downhill driving will regenerate a much larger
amount of energy due to the long braking periods. On long downhills, regenerative braking can
be used nearly constantly to regulate speed while continuously charging the battery.
FAIL-SAFE BRAKE
The term fail-safe brake refers to a type of brake that engages to prevent shaft rotation
when electrical power is removed for any reason. When power is restored, the brake
releases and stays in the off position.
Like all friction clutches and brakes, fail-safe brakes generate torque through friction
surfaces that are clamped together. The source of the clamping force distinguishes the
two basic types — permanent magnet and spring-set.
In general, permanent-magnet brakes are used in applications that require frequent on-
off cycling and consistent performance, whereas spring-set brakes are better suited for
static holding applications and low-cycle dynamic operation.
ANTILOCK-BRAKING SYSTEMS (ABS)
Principles
The reason for the development of antilock brakes is in essence very simple. Under braking, if
one or more of a vehicle’s wheels lock (begins to skid) then this has a number of consequences:
a. braking distance increases,
b. steering control is lost, and
c. tire wear will be abnormal.
The obvious consequence is that an accident is far more likely to occur. The application of
brakes generates a force that impedes a vehicles motion by applying a force in the opposite
direction. During severe braking scenarios, a point is obtained in which the tangential velocity
of the tire surface and the velocity on road surface are not the same such that an optimal slip
which corresponds to the maximum friction is obtained. The ABS controller must deal with
the brake dynamics and the wheel dynamics as a whole plant.
45. Components:
Speed sensors
A speed sensor is used to determine the acceleration or deceleration of the wheel. These
sensors use a magnet and a Hall effect sensor, or a toothed wheel and
an electromagnetic coil to generate a signal. The rotation of the wheel or differential
induces a magnetic field around the sensor. The fluctuations of this magnetic field
generate a voltage in the sensor. Since the voltage induced in the sensor is a result of
the rotating wheel, this sensor can become inaccurate at slow speeds. The slower
rotation of the wheel can cause inaccurate fluctuations in the magnetic field and thus
cause inaccurate readings to the controller.
Valves
There is a valve in the brake line of each brake controlled by the ABS. On some systems, the
valve has three positions:
In position one, the valve is open; pressure from the master cylinder is passed right
through to the brake.
In position two, the valve blocks the line, isolating that brake from the master
cylinder. This prevents the pressure from rising further should the driver push the
brake pedal harder.
In position three, the valve releases some of the pressure from the brake.
Pump
The pump in the ABS is used to restore the pressure to the hydraulic brakes after the valves
have released it. A signal from the controller will release the valve at the detection of wheel
slip. After a valve releases the pressure supplied from the user, the pump is used to restore a
desired amount of pressure to the braking system. The controller will modulate the pump's
status in order to provide the desired amount of pressure and reduce slipping.
Controller
The controller is an ECU type unit in the car which receives information from each individual
wheel speed sensor. If a wheel loses traction, the signal is sent to the controller. The controller
46. will then limit the brake force (EBD) and activate the ABS modulator which actuates the
braking valves on and off.
Electronic Control Unit (ECU)
The work of ECU is to receive, amplifies and filter the sensor signals for calculating the speed
rotation and acceleration of the vehicle. ECU also uses the speeds of two diagonally opposite
wheels to calculate an estimate for the speed of the vehicle. The slip of each wheel is obtain by
comparing the reference speed with the individual wheel. During wheel slip or wheel
acceleration condition signal server to alert the ECU. The microcomputer alert by sending the
trigger the pressure control valve of the solenoids of the pressure modulator to modulate the
brake pressure in the individual wheel brake cylinders.
The ECU reacts to a recognized defect or error by switching off the malfunctioning part of the
system or shutting down the entire ABS.
Working
A locked-up wheel provides low road handling force and minimal steering force.
Consequently the main benefit from ABS operation is to maintain directional control
of the vehicle during heavy braking. In rare circumstances the stopping distance may
be increased however, the directional control of the vehicle is substantially greater
than if the wheels are locked up.
The main difficulty in the design of ABS control arises from the strong nonlinearity
and uncertainty of the problem. It is difficult and in many cases impossible to solve
this problem by using classical linear, frequency domain methods. ABS systems are
designed around system hydraulics, sensors and control electronics. These systems
are dependent on each other and the different system components are interchangeable
with minor changes in the controller software .
The wheel sensor feeds the wheel spin velocity to the electronic control unit, which
based on some underlying control approach would give an output signal to the brake
actuator control unit. The brake actuator control unit then controls the brake actuator
based on the output from the electronic control unit. The control logic is based on the
objective to keep the wheels from getting locked up and to maintain the traction
between the tire and road surface at an optimal maximum.
Wheel Velocity
Sensor
Vehicle Velocity
Sensor
Tire Road
Interaction
Control Algorithm Brake Actuator
Valve
Brake Actuator
47. ANTISKID SYSTEM OPERATION
Components
1. Wheel Speed Sensors
An antiskid system consists basically of three components: The wheel speed
sensors, the control box, and the control valves. There are two types of systems in
use, an AC system and a DC system. They are essentially alike except for the wheel
speed sensors, and one circuit in the control box.
2. Control Valves
A three-port antiskid control valve is located in the pressure line between the brake
valve and the brake cylinder, with a third line connecting the control valve to the
system return manifold. For normal operation of the brakes, when no skid is being
indicated, the valve allows the brake fluid to flow into and out of the brake, with
the valve serving only as a passage. But, if the wheel speed sensor determines that
one of the wheels is beginning to decelerate fast enough to cause a skid, its
changingoutput voltage is measured in the control box, and a direct current signal
is sent to the control valve to close off the pressure port and open the passage
between the brake and the system return.
3. Control Unit
The work of ECU is to receive, amplifies and filter the sensor signals for calculating
the speed rotation and acceleration of the vehicle. ECU also uses the speeds of two
diagonally opposite wheels to calculate an estimate for the speed of the vehicle.
Working
When brake force is applied to a vehicle wheel that is in normal contact with the
pavement, the rubber of the tire begins to stretch in response to friction heating and the
force applied to the tire-pavement interface. This has the effect of making the tire
circumference significantly larger than it is without the brakes applied.
When brake force is applied, the angular velocity of the braked wheel drops by several
percent. Early researchers thought that this slowing down was the result of the tire
48. slipping against the pavement and coined the term "slip velocity" to express the
difference between the circumferential speed of the braked and un-braked wheels. If
the level of braking is increased until the co-efficient of friction, mu, can no longer
support the force being applied to the rubber, then true slip begins and the available
stopping force begins to diminish.
Operation at the peak of the mu-slip curve gives the highest braking efficiency.
Research suggests that a small level of true slip may increase mu and that the peak of
the curve actually occurs after true slip has begun. Operation just beyond the peak of
the curve results in increased tire wear and if the brake force is further increased, a skid
develops that may lock the wheel and blow the tire if unchecked. Aircraft tires can blow
in as little as 300 milliseconds at high speeds if the wheel is locked.
Modern Hydro-Aire brake control systems work by measuring the speed of the wheel
to determine slip and developing a correction signal to adjust brake pressure to keep the
tire operating at the peak of the mu-slip curve. A rotary transducer, which is usually
mounted in the aircraft axle, measures wheelspeed and provides a signal to an electronic
brake system control unit (BSCU). The control unit derives where the tire is operating
on the mu-slip curve for the prevailing runway conditions and sends a correction signal
to the antiskid valve to reduce applied brake pressure.
Braking Efficiency:
High braking efficiency is required as on many occasions the brakes are required to
stop the vehicle in emergency. However higher brake efficiency not only leads to
stopping in a shorter time, may also cause injury to the driver operator due to high
decelerating forces and dislodging of loads in the trolley. Higher braking efficiency also
causes rapid wear of the brakes and there is more risk of losing control of the vehicle.
Braking efficiencies of the order of 50-80% enable to stop within reasonable distance.
However the stopping distance varies with the type of road conditions and condition of
the tyres.
Braking distance generally refers to the distance a vehicle will travel from the point
when the brakes are fully applied to when it comes to a complete stop. It is primarily
affected by the original speed of the vehicle and the coefficient of friction between
the tires and the road surface. Braking distance also includes the reaction time to when
the driver feels the need to stop the vehicle and the response time
50. 1. Loading conditions
The mass of the test vehicle shall be recorded under the condition where two persons are sitting
in the front seats of the vehicle at the time of delivery, provided that the test vehicle mass shall
be the mass at the time of delivery +110 +20/-0 kg with one driver including measuring
equipment.
2. Tires
The tires that are fitted at the time of purchasing the test vehicle shall be used. The operation
for running in the tires shall be conducted at the same time as the test vehicle is driven so that
the bedding of the braking system may be conducted, as described in Paragraph 3.1 (3).
Furthermore, prior to running (at normal temperature), the air inflation pressure of the tires
shall be adjusted on a horizontal level to the value for normal operation, as described in the
Specification Table provided by the manufacturer.
3. Brake system
The discs, drums and friction materials that were installed when the test vehicle was purchased
shall be used after bedding them in according to the procedure prescribed in Paragraph 4.1. The
braking system shall be adjusted normally as specified. Furthermore, the braking system shall
be free from adverse effects such as abnormal heat gain or wetting.
4. Drive axle
For motor vehicles where it is possible to select the drive axle, drive axle that is normally used
shall be selected.
Meteorological Conditions
(1) The mean wind velocity during the test shall be 5 m/s or less.
(2) The temperature of the road surface of the proving ground shall be within the range given
below. Ideally, this condition shall be maintained, however, if the temperature is lower than
the requirement but the schedule cannot be changed because subsequent test schedules are
fixed, the brake test may be performed provided that the published
results are accompanied by a note explaining that the braking distance may be slightly shorter
than the required condition.
Measurement Items
The following items shall be measured and confirmed in the test:
Road surface temperature of the proving
ground under dry conditions
35.0 ± 10.0°C
Road surface temperature of the proving
ground under wet conditions
27.0 ± 5.0°C
51. (1) Brake temperature prior to braking
(2) Initial braking speed
(3) Pedal application force
(4) Stopping distance
(5) Deviation from the lane
Measuring equipment
The following measuring equipment to be used in the test shall be capable of smoothly handling
the data of the measurement items prescribed in Paragraph 3.4:
(1) The vehicle speed measurement device shall measure the test speed with a margin of error
of ±1%.
(2) The stopping distance measurement device shall measure the stopping distance with a
margin of error of ±1%.
(3) The brake temperature confirmation device shall measure the temperature with a margin
of error of ±3%.
(4) The pedal pressure measurement device shall measure the pedal application force with a
margin of error of ±1%.
Testing Method
Burnish Running
Burnish the brakes (disk brakes or drum brakes) by making 200 stops from 64 km/h at
deceleration of 3.7 m/s2. The interval from the start of one service brake application to the start
of the next shall be either the time necessary to reduce the initial brake temperature to 110–
132°C, or the distance of 1.6 km, whichever occurs first. Accelerate to 64 km/h after each stop
and maintain that speed until making the next stop (same as FMVSS105, S7.4.1.1).
Weight transfer
Weight transfer and load transfer are two expressions used somewhat confusingly to
describe two distinct effects:[1]
the change in load borne by different wheels of even perfectly
rigid vehicles during acceleration, and the change in center of mass (CoM) location relative to
the wheels because of suspension compliance or cargoshifting or sloshing. In
the automobile industry, weight transfer customarily refers to the change in load borne by
different wheels during acceleration.
Braking Ratio
Braking power of vehicles in relation to their weight, and the gradient of the slope over which
they are operating. The braking distance is the distance a train needs in which to stop or reduce
speed, from travelling at a given speed.
