self inflating tyres full report
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SELF LUBRICATING TYRES

ABSTRACT

SELF INFLATING TYRES
Development in automobile engineering is the sign of rise in civilization. Along with comfort and facitilities it has revolutionized the living habits of the people to a great extent. Large scale use of power window, steering system, anti locking brakes, electronic control of car, self inflating tyres etc, will not only reduce the operating cost but also add standards in comfort. Self-inflating tyres are one of them.
Tyres are not carrying the weight of cars and trucks but it is the air inside the tyres which carries it. Run flat tyres use a strong side wall material that supports the car even if there is no air in one or more of the tyres. This makes it possible to get where we are going even if a tyre is punctured and deflated. Run flat tyres are constructed using alternating layers of heat resistant cord and rubber and usually crescent “shaped wedges of weight- supporting material, strengthening the sidewalls to prevent them from folding over when there is no air pressure.
Self-inflating tyres, on the other hand, are designed to constantly maintain tyre pressure at the proper level. Self-inflating systems are designed more for the slow leaks and for optimizing performance and safety than for keeping a vehicle moving on a tyre that will no longer hold air. Self-inflating tyres allow a vehicle to adjust to the current terrain for ideal performance and safety in those conditions
Currently, lots of consumer vehicles are equipped with pressure-monitoring systems, but there's no way for the driver to do anything about it without an external air source. There are lots of self-inflating-tire systems on the market, but most of them are only available for commercial and military application

Submitted by:

JAYDEEP SINH VAGHELA & SNEHAL PARMAR
PERMANENT ADD:-
MATRUCHHAYA D/118, SUBODHNAGAR,
BHD. DIGJAM MILL, NEAR GANESH HALL,
AIR FORCE ROAD, MANJALPUR,
BHAKTINAGAR, BARODA- 390011
JAMNAGAR.



TIRE-INFLATION BASICS

About 80 percent of the cars on the road are driving with one or more tyres under inflated (as per AAA). Tires lose air through normal driving (especially after hitting pot holes or curbs), permeation and seasonal changes in temperature. Tyres lose one or two psi (pounds per square inch) each month in the winter and even more in the summer. It cannot be told that tyres are properly inflated or not by looking at them. Tyre pressure gauge is used for this. Not only is under inflation bad for tyres, but it's also bad for gas mileage, also affects the way car handles and is generally unsafe.
When tyres are under inflated, the tread wears more quickly. This equates to 15 percent fewer miles which can be drived on them for every 20 percent that they're under inflated. Under inflated tires also overheat more quickly than properly inflated tires, which cause more tire damage.


As tyres are flexible, they flatten at the bottom when they roll. This contact patch rebounds to its original shape once it is no longer in contact with the ground. This rebound creates a wave of motion along with some friction. When there is less air in the tire, that wave is larger and the friction created is greater -- and friction creates heat. If enough heat is generated, the rubber that holds the tire's cords together begin to melt and the tyre fails. Extra resistance of an under inflated tire while rolling makes carâ„¢s engine to work harder. .AAA statistics show that tires that are under inflated by as little as 2 psi reduce fuel efficiency by 10 percent
SELF-INFLATING SYSTEMS
Tire-inflation systems have three general goals:
¢ Detect when the air pressure in a particular tire has dropped - This means they have to constantly (or intermittently) monitor the air pressure in each tire.
¢ Notify the driver of the problem
¢ Inflate that tire back to the proper level - This means there has to be an air supply as well as a check valve that opens only when needed.
PARTS OF ANY SELF-INFLATING SYSTEM

While the available tire inflation systems vary in design, they share some common elements.
¢ They all use some type of valve to isolate individual tires to prevent airflow from all tires when one is being checked or inflated.
¢ They have a method for sensing the tire pressures. This is addressed in most cases with central sensors that relay information to an electronic control unit and then to the driver.
¢ They have an air source, which is usually an existing onboard source such as braking or pneumatic systems. When using an existing system, however, they have to ensure that they don't jeopardize its original function. For this reason, there are safety checks to ensure that there is enough air pressure for the source's primary use before pulling air for tire inflation.
¢ There has to be a way to get the air from the air source to the tires, which is usually through the axle. Systems either use a sealed-hub axle with a hose from the hub to the tire valve or else they run tubes through the axle with the axle acting as a conduit.
¢ There has to be a pressure relief vent to vent air from the tire without risking damage to the hub or rear-axle seals.
CENTRAL TIRE INFLATION SYSTEM (CTIS)
CTIS is provided to control the air pressure in each tyre as a way to improve performance on different surfaces. For example, lowering the air pressure in a tire creates a larger area of contact between the tire and the ground and makes driving on softer ground much easier. It also does less damage to the surface. This is important on work sites and in agricultural fields. By giving the driver direct control over the air pressure in each tire, maneuverability is greatly improved.
Another function of the CTIS is to maintain pressure in the tires if there is a slow leak or puncture. In this case, the system controls inflation automatically based on the selected pressure the driver has set.
CTIS: INSIDE
Here is a look at the overall system:


A wheel valve is located at each wheel end. For dual wheels, the valves are typically connected only to the outer wheel so the pressure between the two tires can be balanced. Part of the wheel valve's job is to isolate the tire from the system when it's not in use in order to let the pressure off of the seal and extend its life. The wheel valve also enables on-demand inflation and deflation of the tires.
An electronic control unit (ECU) mounted behind the passenger seat is the brain of the system. It processes driver commands, monitors all signals throughout the system and tells the system to check tire pressures every 10 minutes to make sure the selected pressure is being maintained. The ECU sends commands to the pneumatic control unit, which directly controls the wheel valves and air system. The pneumatic control unit also contains a sensor that transmits tire-pressure readings to the ECU.
An operator control panel allows the driver to select tire-pressure modes to match current conditions. This dash-mounted panel displays current tire pressures, selected modes and system status. When the driver selects a tyre-pressure setting, signals from the control panel travel to the electronic control unit to the pneumatic control unit to the wheel valves.
When vehicles are moving faster (like on a highway), tire pressure should be higher to prevent tyre damage. The CTIS includes a speed sensor that sends vehicle speed information to the electronic control unit. If the vehicle continues moving at a higher speed for a set period of time, the system automatically inflates the tires to an appropriate pressure for that speed.
This type of system uses air from the same compressor that supplies air to the brakes. A pressure switch makes sure the brake system gets priority, preventing the CTIS from taking air from the supply tank until the brake system is fully charged.
A CLOSER LOOK
On the road: The electronic control unit tells the pneumatic control unit to check current pressure and either inflate or deflate the tire to the pressure selected by the driver. If the system determines that inflation is needed, it first checks to make sure that brake pressure reserves are where they should be; if they are, it applies a slight pressure to the wheel valve to allow inflation. If the tyres are over inflated, the system applies a slight vacuum to the wheel valve. When the pneumatic control unit reads that the appropriate pressure is reached, the valve closes


Hummer self-inflating tire system: At the wheel
The pathway that the air travels for inflation or deflation once it gets to the wheel. The tubing runs from the vehicle's air compressor through the wheel hub and then to the tire valve. The "quick disconnect fitting" allows the tire to be separated from the CTIS system for removal or
servicing. (This diagram also shows the Hummer's run-flat feature, which allows the tyre to continue supporting the vehicle even when it will not hold any air.)
Tire Maintenance System (TMS)

Tire Maintenance System is a "smart" system for tractor trailers that monitors tire pressure and inflates tires as necessary to keep pressure at the right level. It uses air from the trailer's brake supply tank to inflate the tires.


The system has three main components:
¢ The tire hose assembly provides the air route to inflate the tire and has check valves so that the air lines and seals do not have to be pressurized when the system is not checking or inflating the tires. This cuts down on wear and tear on the seals.
¢ The rotary joint is comprised of air and oil seals and bearings and connects the air hose from the non-rotating axle to the rotating hubcap. Its air seals prevent leakage,
and the oil seal prevents contamination. The rotary hub also has a vent to release air pressure in the hubcap.
¢ The manifold houses the pressure protection valve, which makes sure the system doesn't pull air if the brakes' air supply is below 80 psi. It also houses an inlet filter to keep the air clean, a pressure sensor to measure tire pressures and solenoids that control airflow to the tires.
Like the CTIS, this system also has an electronic control unit that runs the entire system. It performs checks to make sure the system is operational, notifies the driver via a warning light on the trailer (visible through the rear-view mirror) if a tyre's pressure drops more than 10 percent below its normal pressure and performs system diagnostics.
The system performs an initial pressure check and adds air to any tire that needs it. The check valves in each tire hose ensure that the other tires don't lose pressure while one tire is being inflated. After an initial pressure check, the system depressurizes to relieve pressure from the seals. Every 10 minutes, the system pressurizes the lines and rechecks tire pressures.
The system measures tire pressure using a series of air pulses in the air lines. If the target pressure in the line is not reached after a certain amount of time, the system begins inflating the tyre(s) until the correct pressure is reached.
AIRGO SYSTEM

The AIRGO system is a constant monitoring system that uses a series of check valves to detect a loss in air pressure.


Unlike some of the other systems, AIRGO doesn't use air from the vehicle's braking system. When air seepage has occurred at any of various points in the system (1), the system draws air (2) from the vehicle's pneumatic system (not shown) and sends it by way of the vehicle's axles (3) -- through the axles themselves if they're pressurized or by way of tubing if they're not -- through the hubcap assembly (4) and into the tire requiring inflation.
A warning light, located on the trailer but visible through the driver's rearview mirror, illuminates when the system has inflated a tire.
Since this is a constant monitoring system, which puts a lot of wear and tear on the seals, AIRGO uses carbon-graphite and case-hardened steel for its seals rather than rubber.
Meritor Tire Inflation System (MTIS)
The MTIS is designed for use on tractor trailers. It uses compressed air from the trailer to inflate any tire that falls below its appropriate pressure. Air from the existing trailer air supply is routed to a control box and then into each axle.
The air lines run through the axles to carry air through a rotary union assembly at the spindle end in order to distribute air to each tire. If there is significant air-pressure loss, an indicator light informs the driver.

The overall system is made up of a wheel-end assembly and a control module.
Wheel-end assembly
The wheel-end assembly includes a flexible hose with check valves. The check valves only allow air to flow into each tyre; this ensures that while one tire is being inflated, the other tyres don't lose air pressure.

Wheel-end assembly
This assembly also incorporates a stator (a non-rotating part) inside the axle spindle and a flow-through tee that is attached to the hubcap. The flow-through tee has a dynamic seal to allow rotation while preventing pressure loss when pressurized air passes from the axle to the hub, which occurs through a tube that runs from the stator into the tee.
In the hubcap assembly, there is a vent to make sure pressure does not build up in the wheel end. A deflector shield keeps contaminants such as dirt and water from entering the wheel end.
For axles with hollow spindles, a press plug seals the pressurized axle interior from the wheel end in order to secure the stator.
Controls
The system control module has a shut-off valve to stop air from being sent to the system, as well as a filter to remove moisture and contaminants. The petcock releases system pressure so maintenance can be performed. Like some of the other systems that use onboard air supplies, this system has a pressure protection valve so that it won't pull air if the air supply is below 80 psi.


Control system
A system pressure adjustment knob allows for adjustments to the overall system air pressure. A flow-sensing switch activates the indicator light to let the driver knows if a significant amount of air is being pumped into a tire, which would indicate a potential puncture.
THE FUTURE OF SELF-INFLATING TYRES
There is a development of an active pressure-management system called TIPM (Tyre Intelligent Pressure Management), due to be available sometime. This system has a compressor that automatically adjusts the pressure in each tire while the vehicle is in operation to compensate for leaks and slow-leak punctures. The driver will be able to adjust the pressure depending on the desired driving mode: comfort, sporty, all-terrain or over-obstacle.
There are at least two other systems in the early development stages that are oriented toward the consumer market -- the Entire system and the Cycloid Air Pump system.
The Entire Self-inflating Tyre system uses a valve that pulls in air from the atmosphere. It then pumps the air into the under-inflated tire using a peristaltic-pump action. The goal is to constantly maintain a specific pressure.

The Entire system is based on this type of peristaltic pump mechanism.

The Auto Pump tire-inflator system by Cycloid has a small, wheel-hub-mounted pump that is powered by the turning of the wheels. When the system's monitor detects a drop in pressure of 2 to 3 psi, it pumps air into the under inflated tire. Auto Pump has a warning system that is activated when there is a puncture.
The computer senses rotation using a rotation sensor on each wheel. If the computer were programmed correctly and if there were a light on the dashboard, then the computer could detect a flat tire. What the computer could do is look at different rotational speeds for one out of the four wheels. A flat tire would spin faster than a properly inflated tire, so the computer would look for one tire spinning faster than the other three, on average, over the course of a period of time. Then it could warn the driver by activating the light on the dash.
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Abstract
Self inflating tyre system is an automatic mechanishm for maintaining proper level of pressure inside the vehicle tyres.Or in other words it is an automatic infalation or deflation system used in tyres.This system reduces the wear of the tread of the tyre and increases driving comfort. It also increases fuel efficiency and ensures safe driving.The main self inflating systems used are CTIS and TMS systems.
1. INTRODUCTION
The mode of transport is one of the most important criterions these days. The vehicles safety is thus essential. Accidents are also increasing at a quick pace. There are several factors which causes these accidents. The improper inflation of tyres is one among them. Tyres lose air through normal driving (especially after hitting pot holes or curbs), permeation and seasonal changes in temperature. When tyres are under inflated, the tread wears more quickly. Under inflated tyres get damaged quickly due to overheating as compared to properly inflated tyres. The under inflation also causes a small depreciation in the mileage as well. Above all the vehicles running with under inflated tyres can cause accidents.
Thus to rectify all these defects we are using self inflating systems. The pressure monitoring systems in such systems helps in monitoring the tyre pressure constantly. The system which contains sensors feed the information to a display panel which the driver can operate manually. The electronic unit controls all the information. The source of air is taken from the vehicles air braking system or from the pneumatic systems. Thus it helps in re-inflation of the tyres to proper pressure conditions.
2. HOW TYRES WORK
If you're in the market for new tyres, all of the variables in tyre specifications and the confusing jargon you might hear from tyre salesmen or "experts" might make your purchase rather stressful. Or maybe you just want to fully understand the tyres you already have, the concepts at work, the significance of all of those sidewall markings. What does all this stuff mean in regular terms
In this article, we will explore how tyres are built and see what's in a tyre. We'll find out what all the numbers and markings on the sidewall of a tyre mean, and we'll decipher some of that tyre jargon. By the end of this article, you'll understand how a tyre supports your car, and you'll know why heat can build up in your tyres, especially if the pressure is low. You'll also be able to adjust your tyre pressure correctly and diagnose some common tyre problems!
How Tyres are Made
As illustrated below, a tyre is made up of several different components.
The Bead Bundle
The bead is a loop of high-strength steel cable coated with rubber. It gives the tyre the strength it needs to stay seated on the wheel rim and to handle the forces applied by tyre mounting machines when the tyres are installed on rims.
The Body
The body is made up of several layers of different fabrics, called plies. The most common ply fabric is polyester cord. The cords in a radial tyre run perpendicular to the tread. Some older tyres used diagonal bias tyres, tyres in which the fabric ran at an angle to the tread. The plies are coated with rubber to help them bond with the other components and to seal in the air. A tyre's strength is often described by the number of plies it has. Most car tyres have two body plies. By comparison, large commercial jetliners often have tyres with 30 or more plies.
The Belts
In steel-belted radial tyres, belts made from steel are used to reinforce the area under the tread. These belts provide puncture resistance and help the tyre stay flat so that it makes the best contact with the road.
Cap Plies
Some tyres have cap plies, an extra layer or two of polyester fabric to help hold everything in place. These cap plies are not found on all tyres; they are mostly used on tyres with higher speed ratings to help all the components stay in place at high speeds.
The Sidewall
The sidewall provides lateral stability for the tyre, protects the body plies and helps keep the air from escaping. It may contain additional components to help increase the lateral stability.
The Tread
The tread is made from a mixture of many different kinds of natural and synthetic rubbers. The tread and the sidewalls are extruded and cut to length. The tread is just smooth rubber at this point; it does not have the tread patterns that give the tyre traction.
Assembly
All of these components are assembled in the tyre-building machine. This machine ensures that all of the components are in the correct location and then forms the tyre into a shape and size fairly close to its finished dimensions.
3. HOW TYRES SUPPORT A CAR
You may have wondered how a car tyre with 30 pounds per square inch ( psi ) of pressure can support a car. This is an interesting question, and it is related to several other issues, such as how much force it takes to push a tyre down the road and why tyres get hot when you drive (and how this can lead to problems).

The next time you get in your car, take a close look at the tyres. You will notice that they are not really round. There is a flat spot on the bottom where the tyre meets the road. This flat spot is called the contact patch.
If you were looking up at a car through a glass road, you could measure the size of the contact patch. You could also make a pretty good estimate of the weight of your car, if you measured the area of the contact patches of each tyre, added them together and then multiplied the sum by the tyre pressure. Since there is a certain amount of pressure per square inch in the tyre, say 30 psi, then you need quite a few square inches of contact patch to carry the weight of the car. If you add more weight or decrease the pressure, then you need even more square inches of contact patch, so the flat spot gets bigger.
A properly inflated tyre and an under inflated or overloaded tyre
You can see that the under inflated/overloaded tyre is less round than the properly inflated, properly loaded tyre. When the tyre is spinning, the contact patch must move around the tyre to stay in contact with the road. At the spot where the tyre meets the road, the rubber is bent out. It takes force to bend that tyre, and the more it has to bend, the more force it takes. The tyre is not perfectly elastic, so when it returns to its original shape, it does not return all of the force that it took to bend it. Some of that force is converted to heat in the tyre by the friction and work of bending all of the rubber and steel in the tyre. Since an under inflated or overloaded tyre needs to bend more, it takes more force to push it down the road, so it generates more heat.
Tyre manufacturers sometimes publish a coefficient of rolling friction (CRF) for their tyres. You can use this number to calculate how much force it takes to push a tyre down the road. The CRF has nothing to do with how much traction the tyre has; it is used to calculate the amount of drag or rolling resistance caused by the tyres. The CRF is just like any other coefficient of rolling friction: The force required to overcome the friction is equal to the CRF multiplied by the weight on the tyre. This table lists typical CRF for several different types of wheels.
Tyre Type Coefficient of Rolling Friction
Low rolling resistance car tyre 0.006 - 0.01
Ordinary car tyre 0.015
Truck tyre 0.006 - 0.01
Train wheel 0.001
Let's figure out how much force a typical car might use to push its tyres down the road. Let's say our car weighs 4,000 pounds (1814.369 kg), and the tyres have a CRF of 0.015. The force is equal to 4,000 x 0.015, which equals 60 pounds (27.215 kg). Now let's figure out how much power that is. We know that power is equal to force times speed. So the amount of power used by the tyres depends on how fast the car is going. At 75 mph (120.7 kph), the tyres are using 12hp, and at 55 mph (88.513 kph) they use 8.8 horsepower. All of that power is turning into heat. Most of it goes into the tyres, but some of it goes into the road (the road actually bends a little when the car drives over it).
From these calculations you can see that the three things that affect how much force it takes to push the tyre down the road (and therefore how much heat builds up in the tyres) are the weight on the tyres, the speed you drive and the CRF (which increases if pressure is decreased). If you drive on softer surfaces, such as sand, more of the heat goes into the ground, and less goes into the tyres, but the CRF goes way up.

4. TYRE-INFLATION BASICS
About 80 percent of the cars on the road are driving with one or more tyres underinflated. Tyres lose air through normal driving (especially after hitting pot holes or curbs), permeation and seasonal changes in temperature. They can lose one or two psi (pounds per square inch) each month in the winter and even more in the summer. And, you can't tell if they're properly inflated just by looking at them. You have to use a tyre-pressure guage. Not only is underinflation bad for your tyres, but it's also bad for your gas mileage, affects the way your car handles and is generally unsafe.
PROBLEMS WITH TYRES
When tyres are under-inflated, the tread wears more quickly. According to Goodyear, this equates to 15 percent fewer miles you can drive on them for every 20 percent that they're underinflated. Underinflated tyres also overheat more quickly than properly inflated tyres, which cause more tyre damage. The faded areas below indicate areas of excessive tread wear.

Because tyres are flexible, they flatten at the bottom when they roll. This contact patch rebounds to its original shape once it is no longer in contact with the ground. This rebound creates a wave of motion along with some friction. When there is less air in the tyre, that wave is larger and the friction created is greater and friction creates heat. If enough heat is generated, the rubber that holds the tyre's cords together begin to melt and the tyre fails. Because of the extra resistance an underinflated tyre has when it rolls, your car's engine has to work harder. A statistics show that tyres that are underinflated by as little as 2 psi reduce fuel efficiency by 10 percent. Over a year of driving, that can amount to several hundred dollars in extra gas purchases.
5. HOW TYRE PRESSURE GAUGES WORK
Underinflation can cause tyres to wear more on the outside than the inside. It also causes reduced fuel efficiency and increased heat buildup in the tyres. It is important to check the tyre pressure with a guage at least once a month. so it is essential to have a tyre pressure monitoring system in our vehicles.
Inside the Pressure Gauge the parts of a typical pressure gauge look like this:

There are three simple steps involved in measuring a tyre's pressure with a pressure gauge: Get in a steady position to apply the pressure gauge to the valve stem.
¢ Apply the gauge, forming a good seal between the gauge and the stem and releasing air from the tyre into the gauge. Note how the pin inside the gauge presses against the valve pin inside the valve stem to release air from the tyre.
¢ Read the pressure from the gauge.

Inside the tube that makes up the body of the pressure gauge, there is a small, tight-sealing piston much like the piston inside a bicycle pump. The inside of the tube is polished smooth. The piston is made of soft rubber so it seals nicely against the tube, and the inside of the tube is lubricated with a light oil to improve the seal. In the picture below, you can see that the piston is at one end of the tube and the stop is at the other. A spring runs the length of the tube between the piston and the stop, and this compressed spring pushes the piston toward the left-hand side of the tube.


The funny spherical thing on the left end of the gauge is hollow. The opening in the sphere is designed to engage a tyre's valve stem. If you look in the opening, you will be able to see a rubber seal and a small fixed pin. The rubber seal presses against the lip of the valve stem to prevent air from leaking during the measurement, and the pin depresses the valve pin in the valve stem to let air flow into the gauge. The air will flow around the pin, through the hollow passage inside the sphere and into the piston chamber. When the pressure gauge is applied to the valve stem of a tyre, the pressurized air from the tyre rushes in and pushes the piston toward the right. The distance the piston travels is relative to the pressure in the tyre. The pressurized air is pushing the piston to the right, and the spring is pushing
back. The gauge is designed to have some maximum pressure, and for the sake of example let's say it is 60 psi. The spring has been calibrated so that 60-psi air will move the piston to the far-right of the tube, while 30 psi moves the piston half-way along the tube, and so on. When you release the gauge from the valve stem, the flow of pressurized air stops and the spring immediately pushes the piston back to the left. To allow you to read the pressure, there is a calibrated rod inside the tube:


The spring is not shown in this figure, but the calibrated rod fits inside the spring. The calibrated rod rides on top of the piston, but the rod and the piston are not connected and there is a fairly tight fit between the rod and the stop. When the piston moves to the right, it pushes the calibrated rod. When the pressure is released, the piston moves back to the left but the rod stays in its maximum position to allow you to read the pressure.
6. SELF-INFLATING SYSTEMS
Tyre-inflation systems have three general goals:
¢ Detect when the air pressure in a particular tyre has dropped - This means they have to constantly (or intermittently) monitor the air pressure in each tyre.
¢ Notify the driver of the problem
¢ Inflate that tyre back to the proper level - This means there has to be an air supply as well as a check valve that opens only when needed.
Parts of Any Self-inflating System
While the available tyre inflation systems vary in design, they share some common elements.
¢ They all use some type of valve to isolate individual tyres to prevent airflow from all tyres when one is being checked or inflated.
¢ They have a method for sensing the tyre pressures. This is addressed in most cases with central sensors that relay information to an electronic control unit and then to the driver.
¢ They have an air source, which is usually an existing onboard source such as braking or pneumatic systems. When using an existing system, however, they have to ensure that they don't jeopardize its original function. For this reason, there are safety checks to ensure that there is enough air pressure for the source's primary use before pulling air for tyre inflation.
¢ There has to be a way to get the air from the air source to the tyres, which is usually through the axle. Systems either use a sealed-hub axle with a hose from the hub to the tyre valve or else they run tubes through the axle with the axle acting as a conduit.
¢ There has to be a pressure relief vent to vent air from the tyre without risking damage to the hub or rear-axle seals.
7. CENTRAL TYRE INFLATION SYSTEM (CTIS)
The idea behind the CTIS is to provide control over the air pressure in each tyre as a way to improve performance on different surfaces. For example, lowering the air pressure in a tyre creates a larger area of contact between the tyre and the ground and makes driving on softer ground much easier. It also does less damage to the surface. This is important on work sites and in agricultural fields. By giving the driver direct control over the air pressure in each tyre, maneuverability is greatly improved.
Another function of the CTIS is to maintain pressure in the tyres if there is a slow leak or puncture. In this case, the system controls inflation automatically based on the selected pressure the driver has set.
There are two main manufacturers of the CTIS: U.S.-based Dana Corporation and France-based Syegon (a division of GIAT). Dana Corporation has two versions, the CTIS for military use (developed by PSI) and the Tyre Pressure Control System (TPCS) for commercial, heavy machinery use. In the next section, we'll take a look at the inner workings of a basic CTIS setup.
CTIS: Inside
Here is a look at the overall system:
A wheel valve is located at each wheel end. For dual wheels, the valves are typically connected only to the outer wheel so the pressure between the two tyres can be balanced. Part of the wheel valve's job is to isolate the tyre from the system when it's not in use in order to let the pressure off of the seal and extend its life. The wheel valve also enables on-demand inflation and deflation of the tyres.
An electronic control unit (ECU) mounted behind the passenger seat is the brain of the system. It processes driver commands, monitors all signals throughout the system and tells the system to check tyre pressures every 10 minutes to make sure the selected pressure is being maintained.
The ECU sends commands to the pneumatic control unit, which directly controls the wheel valves and air system. The pneumatic control unit also contains a sensor that transmits tyre-pressure readings to the ECU.
An operator control panel allows the driver to select tyre-pressure modes to match current conditions. This dash-mounted panel displays current tyre pressures, selected modes and system status. When the driver selects a tyre-pressure setting, signals from the control panel travel to the electronic control unit to the pneumatic control unit to the wheel valves. When vehicles are moving faster (like on a highway), tyre pressure should be higher to prevent tyre damage. The CTIS includes a speed sensor that sends vehicle speed information to the electronic control unit. If the vehicle continues moving at a higher speed for a set period of time, the system automatically inflates the tyres to an appropriate pressure for that speed.
This type of system uses air from the same compressor that supplies air to the brakes. A pressure switch makes sure the brake system gets priority, preventing the CTIS from taking air from the supply tank until the brake system is fully charged.

8. TYRE MAINTENANCE SYSTEM (TMS)
Dana Corporation's Tyre Maintenance System is a "smart" system for tractor trailers that monitors tyre pressure and inflates tyres as necessary to keep pressure at the right level. It uses air from the trailer's brake supply tank to inflate the tyres.

The system has three main components:
¢ The tyre hose assembly provides the air route to inflate the tyre and has check valves so that the air lines and seals do not have to be pressurized when the system is not checking or inflating the tyres. This cuts down on wear and tear on the seals.
¢ The rotary joint is comprised of air and oil seals and bearings and connects the air hose from the non-rotating axle to the rotating hubcap. Its air seals prevent leakage, and the oil seal prevents contamination. The rotary hub also has a vent to release air pressure in the hubcap.
¢ The manifold houses the pressure protection valve, which makes sure the system doesn't pull air if the brakes' air supply is below 80 psi. It also houses an inlet filter to keep the air clean, a pressure sensor to measure tyre pressures and solenoids that control airflow to the tyres.
Like the CTIS, this system also has an electronic control unit that runs the entyre system. It performs checks to make sure the system is operational, notifies the driver via a warning light on the trailer (visible through the rear-view mirror) if a tyre's pressure drops more than 10 percent below its normal pressure and performs system diagnostics.
The system performs an initial pressure check and adds air to any tyre that needs it. The check valves in each tyre hose ensure that the other tyres don't lose pressure while one tyre is being inflated. After an initial pressure check, the system depressurizes to relieve pressure from the seals. Every 10 minutes, the system pressurizes the lines and rechecks tyre pressures.

The system measures tyre pressure using a series of air pulses in the air lines. If the target pressure in the line is not reached after a certain amount of time, the system begins inflating the tyres until the correct pressure is reached.
9. THE FUTURE OF SELF-INFLATING TYRES
Michelin is working with several other companies to develop an active pressure-management system called TIPM (Tyre Intelligent Pressure Management), due to be available sometime in 2005. This system has a compressor that automatically adjusts the pressure in each tyre while the vehicle is in operation to compensate for leaks and slow-leak punctures. The driver will be able to adjust the pressure depending on the desired driving mode: comfort, sporty, all-terrain or over-obstacle.
There are at least two other systems in the early development stages that are oriented toward the consumer market the En-tyre system and the Cycloid Air Pump system.
The entire self inflating system uses a valve that pulls in air from the atmosphere. It then pumps the air into the under-inflated tyre using a peristaltic-pump action. The goal is to constantly maintain a specific pressure.
The En-tyre system is based on this type of peristaltic pump mechanism.
The Auto Pump tyre-inflator system has a small, wheel-hub-mounted pump that is powered by the turning of the wheels. When the system's monitor detects a drop in pressure of 2 to 3 psi, it pumps air into the underinflated tyre. Auto Pump has a warning system that is activated when there is a puncture.
Self-inflating Tyres for Bicycles and Motorcycles
Now cyclists can also motor with the peace of mind that a flat tyre isn't going to ruin their ride. Bridgestone Cycle of Japan has developed the Air Hub, which uses a rotating air pump that replenishes air in the tyre as you pedal. Like the En-tyre method, it keeps the air in the tyres at a constant pressure level. The air pump is in the hub and is run by the rotation of the wheel. A small tube runs compressed air to the tyre's air valve to maintain the pressure. When the air pressure in the tyre is where it should be, excess air is exhausted through a device in the middle of the hose.
Pirelli has also come up with a self-inflating tyre system for motorcycles and scooters. The Pirelli Safety Wheel System uses a monitoring system along with a special rim and an internal tube containing compressed air. It also has a valve to regulate the pressure between the tube and the tyre. When the tyre deflates naturally, the valve opens and pumps air into the tyre until it reaches the correct pressure. If there is a puncture, the system warns the rider as it allows air to move into the tyre.
10. CONCLUSION
Thus self inflating tyres help us in attaining certain helpful criterions.
1. It helps in the monitoring of tyre pressure constantly
2. Thus it provides inflation or deflation of the tyre
3. It helps in attaining better mileage
4. It also helps in providing comfortable driving.
11. REFERENCES
1. Crouse.Anglin, Automotive Mechanics, Tata McGraw Hills.
2. howstuffswork.com
3. cycloid.com
4. goodyeartyres.com
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