In the past several months I have gotten a lot of inquiries about various types of devices that, in some manner, monitor or address truck tire pressure.
It seems the Transportation Recall Efficiency, Accountability and Documentation (TREAD) Act has piqued the interest of many people who fear or anticipate that the National Highway Traffic Safety Administration (NHTSA) will mandate monitor usage on commercial trucks in the very near future. After all, this agency already has mandated their installation on passenger cars and light trucks, so it's not surprising that it would now turn its attention to the heavy vehicle sector.
What amazes me the most, however, is how many people in the truck tire and trucking industries have no clue about the products that are available today to monitor truck tire inflation.
A Newport Communications fleet survey done in 1998 of trucking companies found that 26.1 percent of the respondents were not familiar with this technology. Even more amazing, 48.4 percent said they were not likely to use it. That left only 25.5 percent who might see value in these types of products.
But that was 1998. In 2002, perspectives and attitudes may be changing-or it's possible they will be forced to change if NHTSA decides to mandate the use of tire pressure monitoring devices for commercial vehicles.
``What are these devices?'' you ask. Well, there are several types-and myriad numbers of products on the market that address tire inflation pressure in some manner. The majority is for the passenger/light truck market, but there are close to 30 that are engineered specifically for the heavy, commercial truck market. These products are either available on the market today or are in advanced stages of development.
The products specifically designed for the trucking industry can be broken down into these major types:
* Dual tire pressure equalizers;
* Tire pressure monitors;
* Tire inflation systems; and
* Other technologies.
Dual tire pressure equalizers
Tire pressure equalizers are designed to make tire pressure maintenance a bit easier and equalize the pressure between two tires of a dual assembly. By equalizing tire pressure, irregular tire wear is reduced and rolling resistance is decreased, which improves fuel economy.
In the Technology and Maintenance Council's (TMC's) ``Tire Air Pressure Study,'' which I mentioned in my column last month, mismatched air pressure between duals is a major problem in tires traversing the highways today. This study found that 19.7 percent of all tractor dual tires and 24.9 percent of all trailer dual tires had mismatched inflation pressures that exceeded 5 psi.
Tire pressure equalizer systems equalize dual tire pressure by allowing air to transfer from one tire to another as they run down the road. This is accomplished by the use of two hoses that are plumbed to a check valve, and each attaches to the valve stem of a dual tire.
The check valve is attached to the hub. The valve opens to allow airflow between the tires but closes and shuts the air off in case of an instantaneous air loss, preventing both tires from going flat. In a slow leak situation, the valve isolates both tires after a pressure drop of approximately 10 psi. Since a central valve is located in these devices, a single airing point is provided that eliminates the need to remove the hoses to add air to the tires and makes airing the tires easier since both tires in the assembly are aired at the same time.
These systems also provide a visual indicator of air pressure conditions in the tires that can be seen from about 20 feet away. They do not provide actual inflation pressures but provide different types of so-called ``go-no-go'' gauges that easily can display whether the tires are underinflated, overinflated or at the correct pressure. This display feature is the primary difference between these systems. They cost between $60 and $75 an axle end in low volume quantities.
Tire pressure monitors
There are several types of tire pressure monitors. These systems can be categorized as follows:
* Valve-stem-mounted tire pressure monitors;
* Wheel-mounted tire pressure monitors; and
* Tire-mounted tire pressure monitors.
All of these systems monitor tire pressure through a device that senses the pressure and then forwards a radio frequency signal to a display of some kind that is located in the tractor cab or in a more remote location. Many systems also monitor temperature and convert the actual hot tire pressure to cold pressure so that meaningful data are related to the user.
Valve-stem-mounted tire pressure monitors-There are about six manufacturers of valve-stem-mounted tire pressure monitors. The sensors of these devices screw onto the end of valve stems like valve caps or use special valve stems with sensors that are held inside the wheel to detect tire pressure.
Most of them send a signal to the cab where a display indicates current tire pressures and alerts the driver when the tire pressure drops below a preset level. The alert may be indicated with a warning light, audible signal or both. Some systems come with software that maintains tire pressure history files while others can be coupled to a satellite transmitter to relay information to a central control facility. The cost of these systems range from $500 to $1,200 for an 18-wheeled tractor-trailer unit.
Wheel-mounted tire pressure monitors-Two products monitor tire pressures from sensors attached to the wheels. One is strapped in the wheel well and collects pressure and temperature data that are transmitted via radio frequency to a receiver display located inside the vehicle. The other attaches a module to the outside of the wheel rim and is connected to the tire valves with hoses. It monitors pressure only.
When tire pressure drops below a pre-set level, both of these products use a warning light and audible alarm to warn the driver of the pressure loss. Neither of these products is marketed currently in the U.S., but pricing for one is expected to be in the $650 range for a tractor-trailer combination.
Tire-mounted tire pressure monitors-Several large tire companies have been developing tire pressure sensors that are installed inside the tire on the innerliner with the use of a repair-type patch on which the sensor is attached. (Eventually they hope to develop a version that's small and light enough to be built into the tire itself.)
To date, they have concentrated their efforts in the off-the-road market due to the complexity of developing these systems, the high costs of technology and the size flexibility and cost effectiveness that these large, $25,000 off-road tires offer. These sensors are read with handheld and on-board and/or stationary readers that can inform drivers of tire conditions as well as send this information to a central location.
The companies eventually intend to bring this technology to the commercial truck tire market. Currently, the sensors that have been developed for this market are about the size of a pack of cigarettes-which is too large to work in the smaller truck tire sizes. Some smaller prototypes have been running in the commercial truck market, but the cost of this technology is nowhere near the under $10 limit for sensors that fleets have been requesting. None of these systems is available yet for the commercial truck and bus market.
Tire inflation systems
Basically, there are two types of tire inflation systems that are manufactured by about nine companies. The first type-central tire inflation systems-uses air from the vehicle's air brake system to inflate the vehicle's tires. The second type uses some kind of pump-separate from the vehicle's air system-to generate air. These systems are referred to as continuous tire pressure pumps.
Central tire inflation systems take the air that is stored in a vehicle's air brake wet tanks and uses it to supply air to the tires. This can be done on demand or automatically triggered through sensors that monitor tire pressure. All of these systems have pressure protection valves that allow air to flow to the tires only when the brakes have sufficient pressure to operate correctly.
These systems can be broken down into two types: constant and variable.
Constant tire inflation systems maintain tire pressure at a single preset level. They eliminate the need to check tire pressure manually and allow a vehicle to remain in-service despite small air leaks in one or more of its tires.
Constant systems have no involvement from the driver. They automatically sense the pressure in the tires and inflate as necessary when they lose air. Some systems address only tractor tires, others only trailer tires, and some systems provide pressure to both the tractor and trailer. The cost for these systems ranges from $700 to $3,200.
Variable central tire inflation systems can raise or lower tire pressures during vehicle operation to compensate for varying load and road conditions in addition to maintaining tire pressure. These systems allow the driver to interact with the system and change tire pressure on demand.
They are expensive and usually used for on-off road operations such as logging, construction, mining, gravel hauling, concrete, exploration and military and allow these vehicles to operate better in sand, mud, on forest roads, etc. Variable systems are extremely complex and range in price from $1,200 to $13,000.
There is one manufacturer of a continuous tire pressure pump. This device is mounted on the axle end of dual tire assemblies and is attached to the valve stems with hoses.
The rolling motion of the wheel (centrifugal force) continuously powers the self-contained pump compressor, which generates compressed air as the vehicle runs down the road. Both inner and outer tire pressures can be easily checked from a hub-mounted valve stem. (A visible pressure gauge is an option.) The pump is set at the factory with the maximum pressure that the tires would be inflated to so it will not overinflate or deflate the tires.
When a tire experiences an air leak, the pump supplies air independently to that tire at a steady rate of 6 psi an hour. It does not equalize pressure between the dual tires. Due to overall width limitations on commercial vehicles, the pump cannot be installed on steer axle ends. The cost of this product ranges from $200-$250 an axle end, depending upon the accessories chosen.
Other types of systems
With the advent of the TREAD Act, engineers in all types of technologies have come out of the woodwork to address the problem of tire failures. Coming to market are technologies that do not fit the general category of tire pressure monitors but do address the detection of tire failures.
One such technology is thermal imaging inspection. This system detects tire faults that lead to tire failures as a result of heat buildup inside a tire. The pattern of heat that builds up can be viewed with a thermal imager (camera) that takes temperature-sensitive snapshots of tires. This product can be programmed to recognize separations and give advanced warning of an impending failure. The camera is mounted at a stationary location and vehicles are driven by it after running at highway speeds to build up heat.
The cost for this system is currently about $90,000-$100,000, but the developing company has a target price of around $20,000 for a smaller hand-held version.
I'm sure that there also will be other new entrants into this market, as the TREAD Act has invigorated interest and development in tire pressure monitoring devices. With the federal government's interest in tire pressure and highway safety, it's safe to assume that truckers will be feeling more pressure to use these technologies.