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Author Topic: Self-Inflating Tires While You Drive  (Read 2453 times)

Jay Sadie

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Self-Inflating Tires While You Drive
« on: July 19, 2012, 01:20:19 AM »

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.

Not only is underinflation 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 underinflated, the tread wears more quickly, which 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 causes more tire damage.

[float=right][smg id=600 width=400][/float]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.

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.

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 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 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.

[float=right][smg id=601 width=400 caption="Hummer self-inflating tire system: At the wheel"][/float]A Closer Look

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 tires are overinflated, 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 the illustration to the right, 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.)

Early CTIS

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.

Other Systems

  • PressureGuard: The PressureGuard system routes air from the trailer's air supply through the axles, to the hubs and then to the tire valves.
  • TIREMAAX: The TIREMAAX system uses the trailer's air supply to maintain a specific level of tire inflation. When it detects low tire pressure, it signals the operator and then directs air from the trailer air tank to the tire needing inflation.

The Future of Self-inflating Tires

It sounds like something out of a Bond film, but Goodyear has developed a new system which allows tires to automatically inflate themselves.

Called Air Maintenance Technology (AMT), the system features a miniaturized air pump that is fully contained within the tire. Goodyear provided no indication when the technology will start appearing in consumer products, but the company said AMT is powered by the tire's rotational energy.

According to Chief Technical Officer Jean-Claude Kihn, "A tire that can maintain its own inflation is something drivers have wanted for many years. This will become the kind of technological breakthrough that people will wonder how they ever lived without."
« Last Edit: July 19, 2012, 01:42:54 AM by Jay Sadie »
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