According to AAA, about 80 percent of the cars on the road are driving with one or more tires under-inflated. Tires 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 each month in the winter and even more in the summer. And, it is not possible to 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 tires, but it's also bad for your gas mileage, affects the way your car handles and is generally unsafe.
When tires 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 tires also overheat more quickly than properly inflated tires which cause more tire damage. The faded areas below indicate areas of excessive tread wear.
Because tires 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 underinflated tire has when it rolls, your car's engine has to work harder. AAA statistics show that tires 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.
Self-inflating tires, 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.
Tire inflation systems in general follow three steps in achieving the goal of inflating the tires. These are:
While the available tire inflation systems vary in design, they share some common elements:
There are various types of self-inflating tire systems used in the market depending upon the type of vehicle, speed and terrain. The important ones are as follows:
3.1.?? Central Tire Inflation 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 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.
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 tire-pressure setting, signals from the control panel travel to the electronic control unit, to the pneumatic control unit and finally 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 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.
Tire Maintenance System (TMS) 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 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 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 tire until the correct pressure is reached.
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, the system draws air from the vehicle's pneumatic system and sends it by way of the vehicle's axle, through the axles themselves if they're pressurized or by way of tubing if they're not, through the hubcap assembly 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.
The Meritor Tire Inflation System (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.
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 tires 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.
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.
Download your Full Reports for Self Inflating Tyres
The first concept generated consists of a tire containing a thermoelectric heating device. In this arrangement, an automatic, speed-based sensor would alert the tire inflation system of a necessary pressure increase due to a significant increase in vehicle speed (such as in highway driving). This wouldthen permit the DC-operated heat pump to increase the temperature of the wheel rim along the perimeter, which would in turn increase the temperature of the air in the tires due to convection. The tire pressure would then be increased in accordance to the ideal gas law:
P = (nRT)/V
where, P = pressure inside the tire
T = temperature of tire
V = volume of gas inside the tire
The second concept generated consists of a magnetically-actuated tire profile. For this setup, an electromagnet would be situated in the wheel hub while a metal strip would be embedded inside the circumference of the tire. A sensor would then detect excessive vehicle rolling resistance and direct the system to send a current to the electromagnet. This would create a magnetic field within the tire, which would in turn create a repulsion force on the metal strip in the tire. This would change the tire shape by expanding the profile along the circumference of the tire. Additionally, this would provide the tire with greater stiffness. Ultimately, these two factors would reduce rolling resistance in the tire and henceimprove vehicle fuel economy, tire wear, and safety.
The third concept generated consists of a self-actuated air pump for each tire on a passenger vehicle. In this arrangement, four air pumps (one for each tire) would be situated at the center of the wheel hubs. The system would then be activated as the vehicle was in motion through the rotation of the wheels. This rotation would generate a suction force proportional to the speed (revolutions per minute) of the vehicle, pulling fresh air into the air pump. From here, a single air passageway connecting the pump to the tire would enable the tire to be filled with air as necessary. It should be observed, therefore, that this tire inflation system would be primarily dependent on vehicle speed.
The fourth concept generated involves an expandable wheel rim. For this design, a wheel rim with hollowed-out spokes containing ejector pins would be used. Surrounding this rim would be a durable, elastic band covering the perimeter of the wheel. This band would be the only barrier between the wheel rim and the inside of the tire. A pressure sensor would then detect insufficient pressure within the tires and direct the system to adjust the tire pressures accordingly. When activated, a DC-current would power motors in the wheel hubs that would radially extend the ejector pins and the surrounding elastic band on the wheel rims. This would result in a volume reduction of air in the tires. The tire pressures would then be increased as given in the ideal gas law.
The final concept documented in this section involves a high-pressure reservoir system. In this setup, a high pressure reservoir would be placed directly on each wheel rim with air passageways linking the reservoirs with the tires. Actuator-controlled valves would then maintain the tire pressures as specified by the consumer. It should be noted that the actuator-controlled valve would be nominally set to the cold tire pressure and that a pressure relief valve would be placed on each tire to reduce pressure as necessary.
The advantages of self-inflating tire systems to drivers are:
It also has several benefits for the manufacturer:
- Peristaltic tube chamber integrated into the tire wall.
- Automatic pressure regulator with interface connecting the tire interior with outside environment.
?????????????????????????
The disadvantages of self-inflating tire systems are:
Download your Full Reports for Self Inflating Tyres
Advertisement