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Anti-lock braking system
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PAPER PRESENTATION BY
ROHIT.R.KATTI
IV SEMESTER BE(CS&E)
CELL-9844837159
e-mail:[email protected]
CHINMAY HUNASGI
IV SEMESTER BE(IS&E)
CELL-9844838309
e-mail:[email protected]
AFFILIATION
GOGTE INSTITUTE OF TECHNOLOGY
UDYAMBAG
Anti-lock braking system
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BELGAUM.
CONTENTS PAGE NO.
1. Introduction 1
2. Design 3
3. Working principle 8
4. Types of ABS 12
5. Advantages and disadvantages 14
6. Frequently asked questions 16
7. Conclusion 19
8. References 20
]
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ABSTRACT
In a world where people are craving for high speed bikes and cars so that they get the
thrill out of them, vehicle manufacturers on the other side are in a dilemma as to how to
manage the braking part of the vehicles manufactured .While the basic hydraulic braking
system which is in use now, is not so suitable for high speeds there is a strong need for
an efficient braking system which suffices to the needs of the high speed world.The ABS
revolution brings an end to such a dilemma. ABS which is an acronym for anti-lock
braking system is a very efficient and safe braking system in which the braking is upto a
very high degree,just short of the wheels locking up.It makes use of a central electronic
circuit,four speed sensors (one for each wheel) and two or more hydraulic valves on the
brake circuit.Whenever the speed sensors sense a slip(ie a speed difference) between the
wheels,they move the valves to decrease the pressure on the braking circuit,effectively
reducing the braking force on that wheel,thus allowing the wheel to regain traction.This
paper manifests the various aspects of ABS ,including its advantages and disadvantages.
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1. INTRODUCTION
An antilock braking system (commonly known as ABS, from the German name
”Antiblockiersystem” given to it by its inventors at Bosch) is a system on motor vehicle
which prevents the wheels from locking while braking. The purpose of this twofold: to
allow the driver to maintain steering control and to shorten the braking distances.(by
allowing the driver to fully hit the brake with out fear for skidding or loss of control).
ABS is essentially an enhanced or improved version of ordinary brakes. Simply put, the
ABS is designed to prevent brakes from locking up and skidding when braking hard or
braking on wet or slick surfaces. This adds a significant margin of safety for regular
driving by preventing dangerous skid and allowing the driver to maintain steering control
while trying to stop.
ABS does not necessarily reduce the stopping distance, and in fact it can actually increase
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it slightly on dry pavement. But on wet or slick pavement, it may reduce the stopping
distance up 25% or more-which could be difference between safe stop and an accident.
There are quite a few ABS systems in use today. But one thing they all share in common
is the ability to control wheel lockup during hard braking. A tyre that is just on the verge
of slipping (10 to 20% slippage) produces more friction with respect to the road than on
which is locked and skidding (100%slippage). Once the traction is lost, friction is
reduced, the tyre skids and the vehicle takes longer to stop.
Another point about ABS is that it is essentially an “add-on” to the existing brake
system. It only comes into play when the traction conditions are marginal or during
sudden “panic” stops. The rest of the time, it has no effect on normal driving or braking.
The maximum braking effect is achieved with the wheels on the limit of friction where as
ABS works by releasing the brakes as the wheels break traction, so a skilled driver should
be able exceed the braking performance on an ABS. When activated, the ABS causes the
brake pedal to pulse noticeably. Nevertheless, ABS significantly improves safety and
steering control for drivers during panic braking.
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2. DESIGN
An antilock brake system is designed for a specific vehicle application. A truck which
does not pull a trailer, like a cement mixer, would have a slightly different ABS than a
truck tractor which pulls one or more trailers. Likewise, an antilock brake system for a
trailer would have a different design. ABS for automobiles may be even more specific
and may be designed for a particular brand name and model of car. Since ABS
components must fit and function along with existing vehicle components on each model,
the design and manufacturing process of a new antilock brake system is carried out in
partnership between the automobile manufacturer and the ABS supplier.
Regardless of manufacturer or the type of vehicle, all antilock brake systems operate in a
similar manner. Wheel speed sensors are placed on each wheel that is to be controlled.
Each speed sensor usually has a toothed wheel that rotates at the same speed as the
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vehicle wheel or axle. If the brakes are applied and one or more of the monitored wheels
suddenly begins to reduce speed at a higher rate than the others, the controller activates
the antilock system.
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Fig a. Design of ABS
2.1 Raw Materials
The toothed wheel or gear in the speed sensor is made of soft iron, usually cast. Iron is
chosen because of its high magnetic permeability and low magnetic reluctance. Magnetic
reluctance is roughly equivalent to electrical resistance, and sometimes the toothed wheel
is called the reluctor. The function of the toothed wheel is to allow the permanent
magnet's field to easily pass through each tooth to cause a momentary concentration of
field strength which induces a current in the pick-up coil. The pick-up coil has a
permanent magnet in the core, wrapped with a coil of copper wire.
The controller usually employs transistors known as hot-side drivers which control the
power side of the circuit rather than the ground side. These transistors produce more heat
than usual in an electronic circuit. Rather than being placed in a plastic or stamped steel
housing, they are attached to a cast aluminum housing with a finned heat sink to dissipate
the heat.
The hydraulic brake pressure solenoids used in automobiles have a standard construction
of copper coil elements with steel valves and bodies. They are housed in the same casing
as the brake system master cylinder which is usually cast from aluminum.
The electrical wiring is copper, often with cross-linked polyethylene insulation. To
prevent radio frequency interference (RFI), in which high-power radio signals might be
received through the wiring and cause the system to activate, all wiring is either shielded
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or the wires are run as twisted pairs to cancel out the effects of radio waves. Connectors
are plastic with internal copper contacts.
2.2 The Manufacturing Process
The manufacturing process for antilock brake systems consists of manufacturing the
component parts and then installing those parts on the vehicle. The parts are built in one
plant, then packaged and shipped to a vehicle assembly plant for installation. This is a
typical process for an automobile antilock brake system.
2.2.1 Making the master brake cylinder
1) The master cylinder, including the base for the solenoid body, is cast as a single
unit. The seating and sealing surfaces are machined smooth and the connection ports
are threaded.
2) The individual primary and secondary pistons, solenoid coils, reservoir caps and
seals, pressure accumulator, and any metering and proportioning valves are installed.
The solenoid body has a cover which attaches to the master cylinder with four or
more screws and is sealed with a gasket.
2.2.2 Making the wheel speed sensors
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1) The toothed wheel is cast from iron. Minor machining may be required at the
mounting points.
2) The pick-up coils are wound around the permanent magnet core in a machine
called a coil winder. The entire assembly is encased, or potted, in plastic resin with an
electrical connector attached.
2.2.3 Making the controller
1) The electronic controller components are soldered to a printed circuit board.
2) The board is connected inside a protective housing and mounted to the cast
aluminum heat sink base. External electrical connections are provided for the input
wiring from each speed sensor and the out-put wiring to the solenoids in the master
brake cylinder.
2.3 Installing the ABS
1) In the automobile assembly plant, the steel tubing brake lines are installed in the
framework of the body. They run from the partition between the engine compartment
and the occupant compartment, called the firewall, to the vicinity of each wheel. The
electrical wires for the ABS are also run from the vicinity of each wheel to the
controller location and from the controller to the firewall.
2) The brake master cylinder is bolted to the firewall in the engine compartment near
the brake pedal. The brake lines are attached to the appropriate ports on the solenoid
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body, and the electrical wires are connected.
3) The toothed sensor wheels are pressed onto the outer constant velocity joints or the
ends of the axle spindles so that they ride just inside the wheels. Once the axles are
attached to the frame, the brake lines are attached and the pick-up coils are installed
so that the end of the coils are close to the toothed wheels. The pick-up coils are then
electrically connected to the wires to the controller.
4) The controller is installed either under the instrument panel or in the vehicle's
trunk. The electrical connections are made, including the power connection from the
vehicle battery through the fuse-box.
3.WORKING PRINCIPLE
There are four main components to an ABS system:
1. Speed sensors
2. Pump
3. Valves
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4. Controller
Fig b.Anti-lock brake pump and valves
1) Speed Sensors
The anti-lock braking system needs some way of knowing when a wheel is about to lock
up. The speed sensors, which are located at each wheel, or in some cases in the
differential, provide this information.
2) Valves
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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.
3 ) P u m p
Since the valve is able to release pressure from the brakes, there has to be some way to
put that pressure back. That is what the pump does; when a valve reduces the pressure in
a line, the pump is there to get the pressure back up.
4 ) C o n t r o l l e r
The controller is a computer in the car. It watches the speed sensors and controls the
valves.
3.1 ABS at work
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There are many different variations and control algorithms for ABS systems. We will
discuss how one of the simpler systems works.
The controller monitors the speed sensors at all times. It is looking for decelerations in
the wheel that are out of the ordinary. Right before a wheel locks up, it will experience a
rapid deceleration. If left unchecked, the wheel would stop much more quickly than any
car could. It might take a car five seconds to stop from 60 mph (96.6 kph) under ideal
conditions, but a wheel that locks up could stop spinning in less than a second.
The ABS controller knows that such a rapid deceleration is impossible, so it reduces the
pressure to that brake until it sees an acceleration, then it increases the pressure until it
sees the deceleration again. It can do this very quickly, before the tyre can actually
significantly change speed. The result is that the tire slows down at the same rate as the
car, with the brakes keeping the tires very near the point at which they will start to lock
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up. This gives the system maximum braking power.
When the ABS system is in operation you will feel a pulsing in the brake pedal; this
comes from the rapid opening and closing of the valves. Some ABS systems can cycle up
to 15 times per second.
4.Types of Anti-Lock Brakes
Anti-lock braking systems use different schemes depending on the type of brakes in use.
We will refer to them by the number of channels -- that is, how many valves that are
individually controlled -- and the number of speed sensors.
Four-channel, four-sensor ABS - This is the best scheme. There is a speed
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sensor on all four wheels and a separate valve for all four wheels. With this setup,
the controller monitors each wheel individually to make sure it is achieving
maximum braking force.
Three-channel, three-sensor ABS - This scheme, commonly found on pickup
trucks with four-wheel ABS, has a speed sensor and a valve for each of the front
wheels, with one valve and one sensor for both rear wheels. The speed sensor for
the rear wheels is located in the rear axle.
This system provides individual control of the front wheels, so they can both
achieve maximum braking force. The rear wheels, however, are monitored
together; they both have to start to lock up before the ABS will activate on the
rear. With this system, it is possible that one of the rear wheels will lock during a
stop, reducing brake effectiveness.
One-channel, one-sensor ABS - This system is commonly found on pickup
trucks with rear-wheel ABS. It has one valve, which controls both rear wheels,
and one speed sensor, located in the rear axle.
This system operates the same as the rear end of a three-channel system. The rear
wheels are monitored together and they both have to start to lock up before the
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ABS kicks in. In this system it is also possible that one of the rear wheels will
lock, reducing brake effectiveness.
This system is easy to identify. Usually there will be one brake line going through
a T-fitting to both rear wheels. You can locate the speed sensor by looking for an
electrical connection near the differential on the rear-axle housing.
5.ADVANTAGES AND DISADVANTAGES
5.1Advantages
1.The advantages of ABS brakes (anti-lock braking system), are just as the meaning of
their acronym implies, they eliminate or greatly reduce the possibility of brake lock up .
2.Conventional hydraulic brakes work by using a cylinder (actuator), which squeezes
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brake calipers together around the wheel's rotor when the brake pedal is depressed.
Difficulties arise with these conventional brakes if the road is slick and the driver
executes a panic stop. Under these conditions the wheels may lock up and the tyres run
the risk of losing their grip.
ABS brakes were designed to combat the problem of tire lock up and uncontrolled spins.
Since brakes are most effective at slowing the car at a point just before wheel lock up, a
system that provides for wheel braking while preventing wheel lock up is very desirable.
Anti-lock brakes do just this by using a computer processor to monitor and control the
application of the brakes. At braking, the processor monitors rpm and braking pressure on
each of the vehicle's wheels. With this information, measured amounts of pressure are
sent to each wheel in the form of hydraulic pulses of pressure to the calipers. These pulses
achieve the desired braking pressure without allowing the wheels to lock up.
3.Use of ABS is simple you mash the brake pedal and the computer takes over. No matter
what the surface, ABS adapts to it. Even professional race car drivers can not adapt as
quickly as a computer to changing surfaces. Most of those who live in the snowier regions
know what patchy snow can be like.
4.Steerability of the vehicle is very well maintained.
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5.2 Disadvantages
1) Stopping distance on uniform gravel or snow is somewhat longer. The increase in
stopping distance can be anywhere from 20% to 60%, depending on the particular ABS
and the road conditions. The trade-off, as described above, is that you get to steer. In such
cases ordinary conventional brakes are better since the tyres gather a wedge of snow and
stop early.
2) High cost of the whole system .
6.FREQUENTLY ASKED QUESTIONS
1) What is ABS?
An antilock braking system works with the regular or foundation brakes on your vehicle.
ABS simply keeps your base brakes from locking up. In vehicles not equipped with ABS,
the driver can manually pump the brakes to prevent wheel lockup. In vehicles equipped
with ABS, the driver's foot remains firmly on the brake pedal, allowing the system to
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automatically pump the brakes.
2) What is ABS supposed to do?
ABS mandates changes to heavy duty air brake systems that affect:
Changes to stopping distances
Wheel lock up when the truck is braking
The minimum release time for each brake chamber.
What this means is there must always be full-time electrical for ABS. Therefore, the
electrical assemblies used on trucks must be right sized and must never accidentally
disengage.
3) Does ABS change the way I should use the brakes?
You should not pump your brakes if you have ABS. Just hold your foot firmly on the
brakes pedal and remember that you can still steer.
4)Why is that important?
When your brakes lock up on wet and slippery roads or during a panic stop, you lose
steering control and your vehicle can spin. Rear wheel ABS prevents wheel lockup so that
your car stays in a straight line. If your car has ABS control on all four wheels, you also
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keep steering control. If you have steering control, it is possible to avoid a crash by
steering around hazards if a complete stop cannot be accomplished in time.
5) Does ABS reduce stopping distances?
Not always. In many instances, the stopping distance will still be the same. What ABS
does is offer drivers and extra degree of safety for those unexpected situations out on the
road. Since ABS prevents lock-up, the odds of jack-knifing are greatly reduced.
6) Will I notice anything when the ABS is working?
In many vehicles, drivers may experience a rapid pulsation of the brake pedal--almost as
if the brakes are pushing back at you. Sometimes the pedal could suddenly drop. Also, the
valves in the ABS controller may make a noise that sounds like grinding or buzzing. In
some cars you may feel a slight vibration--this means the ABS is working. It is important
NOT to take your foot off the brake pedal when you hear noise or feel pulsations, but
instead continue to apply firm pressure.
7) Are all antilock systems the same?
They are all very similar in the way they control brake pressure, but some systems are
designed to prevent only the rear wheels from locking up. These rear-wheel-only systems
are found on pickups and sport-utility vehicles. Rear-wheel ABS keeps your vehicle from
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spinning out of control, but you will not have steering control if the front wheels lock up.
All other ABS systems including those for cars and minivans--are designed to keep all
four wheels from locking up. If you own a pickup or sport-utility vehicle, you can check
your owner's manual to see what type of ABS you have.
7.CONCLUSION
The ABS technology has emerged as a new generation braking technology and is set to
revolutionise the automobile industry. The ABS equipped vehicles give greater safety and
steering control during panic braking, and hence give greater confidence to the driver
during braking.
The use of ABS in four wheelers and two wheelers increases the braking power of the
vehicle and considerably reduces the risk of accidents. This technology provides greater
flexibility to the hydraulic braking system. The risk of accidents gets reduced by about
40% as compared to vehicles without ABS.
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Almost all the high speed vehicles that are being manufactured today ,are fitted with
ABS because of the high level of safety and steering control that it provides. Companies
like Diamler Chrysler and Ford have switched to ABS owing to its innumerable
advantages. Companies like Bendix Bosch, Delphi, Nippondenso, Sumitomo and
Toyota are manufacturing high performance ABS and supplying to the vehicle
manufacturers across the world. Though the Antilock braking system is costly and is not
suitable in snowy areas, it is gaining popularity as the people who have used it have
realized its worth..
With more and more development going on in the field of ABS, especially
ESP(electronic stability programme) which incorporates the function of
ABS,TCS(traction control system) and DSP(dynamic stability programme) ,we will
witness vehicles quipped with ESP in the near future.
8.REFERENCES
8.1 Html pages referred.
1.http:\\www.howstuffworks.com
2.http:\\www.technicalpapers.com
3.http\\www.collegetermpapers.com
4.http:\\www.directessays.com
5.http:\\www.edccorp.com
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8.2 Books referred.
1. Popular publishers, "How It Works: Antilock Brakes." Chaikin Don (July 1993, p.88)
2. Home publishers, "Antilock Brake Systems.", Kirk, John (March 1993, pp. 16-18).
3. Road and Track publishers. "Anti-Lock Braking Systems.”, Kott D (February 1994,
p. 110).
4. Popular publishers "Making a Comeback in the Big Rigs (ABS).",Alton john( July
1993, p. 38).
TOTAL WORD COUNT= 3228