Self Inflecting Tyers Details

Self Inflecting Tyers
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 applications. In this article, we're going to learn about some of the tire-inflation systems out there and see when there might be one on the market for us regular people who drive regular vehicles.

The system is simple but very clever, and involves fitting a tube chamber to the tyre wall. When the car is moving, the tube acts as what is known as a peristaltic pump and pushes air into the tyre. When the tyre reaches its desired pressure, a valve prevents any more air being pumped in.

This means that the tyre pressure - which we should all check regularly, though most of us don't - no longer has to be checked at all. If air is lost, the SIT system provides more, so the tyre is always at its correct pressure, which in turn means increased tyre life and better fuel economy.
About 80 percent of the vehicles on the road are driving with two or more tyres under inflated. 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 tire pressure gauge. Not only is under inflation bad for your tyres, but it's also bad for your fuel mileage, efficiency affects the way your car handles and it may lead to accidents which causes vehicle damage, some times it may take life of the people. Hence as and when required the tyres has to be inflated,

As we move on to remote areas such as war fields, forest areas, ghat sections, small villages etc, air compressors from which tyres are generally inflated may not be available so it affects the journey. Hence self inflating tyres are helpful in such conditions.

Self inflating tyres indirectly increase mileage, efficiency. It reduces accidents, vehicle damage and save life. Also it allows a vehicle to adjust to the current terrain for ideal performance and safety in those conditions.

Tyres:
Tire, device made of rubber and fabric and attached to the outer rim of a vehicle wheel. Solid rubber tyres were in limited use before 1850; they are still used in some special applications, e.g., for industrial trucks in factories. The pneumatic rubber tire uses rubber and enclosed air to reduce vibration and improve traction. It was first patented by Robert W. Thomson, a Scottish civil engineer; however, it was not a commercial success until the Scottish inventor John Dunlop patented a pneumatic bicycle tire in 1888 and started a tire company.

The main parts of a modern pneumatic tire are its body, tread and sidewalls, and beads. The body is made of layers of rubberized fabric, called plies that give the tire strength and flexibility. The fabric is made of rayon, nylon, or polyester cord. Covering the plies are sidewalls and tread of chemically treated rubber. The sidewalls form the outer walls of the tire. The tread is a thick hoop of rubber that comes into direct contact with road surfaces. To improve its traction, the tread has patterns of deep and shallow grooves and channels, depending on the intended use, and also may have protruding metal studs for icy or snowy conditions. High-performance tyres have treads optimized for warm weather, and winter (or snow) tyres are optimized for cold and snow; all-season tyres are general-purpose tyres. Imbedded in the two inner edges of the tire are steel hoops, called beads that hold the tire to the wheel rim.

In the older type of pneumatic tire, air is sealed in an inner tube of butyl rubber beneath the body. In a tubeless tire the seal between the beads and the wheel rim is airtight and the underside of the tire body is coated with butyl rubber to keep the air from escaping. A puncture in a tire leads to loss of air and a so-called flat tire. Self-sealing tyres are lined with a rubber or rubber like compound that when the tire is punctured by a slim object, such as a nail, coats the object and seals the hole to prevent air from escaping. A recent innovation is the run-flat tire. In the most common version, the sidewall is reinforced so that, in case of a large puncture and a total loss of air pressure, the tire is self-supporting; the vehicle can continue operating as if there were no tire problem for up to 125 mi (200 km). An innovative bead design keeps the tire securely on the rim. Such tyres are often linked to a pressure monitoring system that alerts the vehicle operator to the puncture.

The most important feature of tire design is the arrangement of the cord, or ply. The three main types are bias ply, radial-ply belted, and bias-ply belted. In a bias-ply tire the cords in a single ply run diagonally from the beads on one inner rim to the beads on the other. However, the orientation of the cords is reversed from ply to ply so that the cords crisscross each other. In a radial-ply (also called radial-ply belted) tire the cords in every ply run perpendicularly from the beads on one inner rim to the beads on the other, and there is a rigid belt, usually of fine steel wire, between the tread and the plies. This construction provides longer tread wear but a rougher ride. In a bias-ply belted tire the cords in the plies are aligned as in a bias-ply tire, but a rigid belt, usually of synthetic fabric, is added. This tire has longer tread life than a bias-ply tire and provides a more comfortable ride than does a radial-ply tire.

Pneumatic tyres are made in a variety of sizes to accommodate a variety of vehicles. The size is usually expressed by a standardized code of the form Axxx/yyBzz, where A designates the type of vehicle the tire is made for, such as P (passenger) or LT (light truck); xxx denotes the tire width in millimeters; yy denotes the aspect ratio (the ratio of the tire's height to its width); B is an R if the tire is of radial-ply construction; and zz is the wheel-rim diameter in inches. In addition, an alphabetic speed rating and a numeric tread-wear rating are embossed on the outer wall of the tire. Most tyres are of the balloon type, with a large cross section and thin sidewalls. The large size permits a low inflation pressure, and the increased tread area gives better traction and braking qualities. Excessive tire wear is caused by incorrect inflation, wheel misalignment, sudden braking, and high speeds.

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 applications. In this article, we're going to learn about some of the tire-inflation systems out there and see when there might be one on the market for us regular people who drive regular vehicles.

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 under inflated. Under inflated tyres also overheat more quickly than properly inflated tyres, which cause more tire damage. The figure below indicates areas of under inflated, properly inflated and over inflated tyres.

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 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 tire fails.
Because of the extra resistance an under inflated tire has when it rolls, your car's engine has to work harder. AAA statistics show that tyres that are under inflated 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.

Difference Between Run Flat Tyres and Self Inflated Tyres:
Our tyres aren't what carry the weight of our cars and trucks -- it's the air inside the tyres. Run-flat tyres use a strong sidewall 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 you're going even if a tire 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 tire pressure at the proper level. Self-inflating systems are designed more for slow leaks and for optimizing performance and safety than for keeping a vehicle moving on a tire that will no longer hold air.

Self Inflating System:
The system is simple but very clever, and involves fitting a tube chamber to the tyre wall. When the car is moving, the tube acts as what is known as a peristaltic pump and pushes air into the tyre. When the tyre reaches its desired pressure, a valve prevents any more air being pumped in.

This means that the tyre pressure - which we should all check regularly, though most of us don't - no longer has to be checked at all. If air is lost, the SIT system provides more, so the tyre is always at its correct pressure, which in turn means increased tyre life and better fuel economy.

Objective of Self Inflating System:
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. The problem has to be intimated to the driver. 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 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 tyres to prevent airflow from all tyres 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 tyres, 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.

Type of Self Inflating System:
We have different types of self inflating system. They are
Central tire inflating system
Airgo system
Tire Maintenance System (TMS)
Meritor Tire Inflation System (MTIS)

Central Tyre Inflation System (CTIS):
History of Central Tyre Inflating System:
As early as 1984, GM offered the CTIS on CUCV Blazers and pickups. CUCV stands for Commercial Utility Cargo Vehicle, and these trucks have been used by the U.S. military since the mid-1980s. They are essentially full-size Chevrolet Blazers and pick-ups that have special equipment added for military applications.

Parts of central tyre inflating system:
The idea behind the CTIS is to provide control over the air pressure in each tire 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 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 Tire Pressure Control System (TPCS) for commercial, heavy machinery use. 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 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 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 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 tire-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 tire 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.

Working of Central Tyre Inflation System:
Here is what happens 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.

In this illustration, you can see 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 tire to continue supporting the vehicle even when it will not hold any air.)

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.

Tyre Maintenance System (TMS):
Dana Corporation's Tire Maintenance System is a "smart" system for tractor trailers that monitors tire 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 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 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 tire pressures and solenoids that control airflow to the tyres.

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 tire'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 tyres 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 tire(s) until the correct pressure is reached.

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 tire; this ensures that while one tire is being inflated, the other tyres don't lose air pressure.

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.

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:
Michelin is working with several other companies to develop an active pressure-management system called TIPM (Tire Intelligent Pressure Management), due to be available sometime in 2005. 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 AirPump system.
The EnTire Self-Inflating Tire 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 AutoPump 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. AutoPump has a warning system that is activated when there is a puncture. Check out Cycloid Videos to watch the AutoPump system in action.

Self-inflating Tyres for Bicycles and Motorcycles:
Now cyclists can also motor with the peace of mind that a flat tire 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 tire as you pedal. Like the EnTire 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 tire's air valve to maintain the pressure. When the air pressure in the tire 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 tire 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 tire. When the tire deflates naturally, the valve opens and pumps air into the tire until it reaches the correct pressure. If there is a puncture, the system warns the rider as it allows air to move into the tire.