The current and future status of tire monitoring, performance, and recycling technology
We take tires for granted, perhaps too much, but if we learn that tires are at least part and parcel the cause of an accident in which we are involved, we suddenly become very interested. Both from the designer’s point of view and the one servicing them, it is an excellent idea to be aware of recent developments in tire technology.
In this article the following topics are presented:
– Trends and future possibilities of direct tire-pressure monitoring system (TPMS)
– From direct TPMS to the Intelligent Tire
– Electric vehicles: New requirements for tires’ rolling resistance
– Environmentally-friendly or ‘green’ tires
– Requirements for heavy duty vehicle tires (embedded in other sections)
– Test methods for rolling resistance, rolling noise & wet grip
To appreciate how far and fast tire technology (click also here to read more) has been advancing, it is worthwhile to see where tires started and what they looked like even a couple of decades ago. Robert William Thompson invented and patented the pneumatic tire in 1846, but it was not until the 1880s that John Boyd Dunlop literally taped these tires to bicycle wheels. So successful was this that he produced these tires in1888 and patented the product in 1889. Numerous developments in clincher rim technology, cotton reinforcing rods, and rim beads occurred, resulting in the first automobile tire in 1895. In 1904 one could get a mountable tire that included cord reinforcement. By 1924, pneumatic tires had completely replaced the solid ones. Synthetic tires came on line in 1937, followed by radial tires in 1946 for Europe, and rayon belted ones, along with tubeless tires the following year. Through the 1960s, other materials were introduced, such as nylon and fiberglass. Regulations started catching up with these advances, with the U.S. Department of Transportation (DOT) mandating an identification code be stamped on each tire. Since then, information has become quite detailed, showing the load range, type of tire, size, conditions under which it can be used, and so forth . The basic tire was about to under much further change, starting in the mid-1990s, especially with respect to how tires were to be monitored.
Trends and future possibilities of direct tire-pressure monitoring system (TPMS)
Current (2011) state of TPMS
To appreciate what the future holds for tire pressure monitoring system (TPMS), we need to review what exists now. When the first TPMS was developed for Porsche in the mid-1980s, it used a sensor-battery-receiver system, where sensors were mounted some place on the tire, such as the valve stem, rim, or tire cavity. The receiver would be inside the car and be connected to appropriate display equipment. Radio frequency (RF) units received the data created by the sensor and sent it to the receiver, which, in turn, activated a warning light. More modern versions have four to five transmitters (including one for the spare), and the receiver can be integrated with other electronic equipment, such as remote keyless entry units or body control devices. Commercial unlicensed ultrahigh frequency (UHF) normally is used (315 or 434 MHz inEurope). Some receivers get information from tires having a unique serial number, thus avoiding confusion in picking up signals from sensors mounted on surrounding tires. When the warning light is on in a steady state, the tire is under-inflated or not inflated at all. There also could be a fault in the TPMS system, itself, if the tire does have the proper pressure.
Several issues arise in sensor design and location design. First, if the sensors are mounted on the outside of the tire in plain view, such as on the valve stem, thieves can steal them, and they also are the source of unevenly distributed weight, making the tire subject to shimmying, vibration, or other malfunction. Mounting the sensor on the back of the valve stem eliminates the theft problem, and the balancing issue can be reduced with miniaturization, such as in the development of micro mechanical systems and systems using nanotechnology. Sensors also can be incorporated into a band mounted on the inside part of the tire’s rim. However, RF can be blocked or negatively affected by carbon or ferrous content in a tire, making specially manufactured tires necessary. This also limits a car owner’s range of choice in tires, making it more expensive, as is the case with most specialty items.
Alternatives to a TPMS have more than one receiver or antenna that enables the vehicle to discern the particular wheel transmitting data. The vehicle’s computer contains in its database information on the tire’s pressure at the time of manufacture, as well as serial number. Other systems have a radio frequency identification tag (RFID) mounted on each tire that uses 125 KHz to send information at any time to the TPMS. When the ignition switch is turned on, each tire is polled sequentially for information so the driver can identify any tire with problems. This sending of data obviates the signal collision problems associated with the “low-end” systems described above. This “high line” system uses a magnetic field detected by the low frequency (LF) antenna in the TPMS. On-board computers will “re-learn” the data for each tire that may be changed or if there is sensor replacement. While the high line systems tend to be more expensive, they save battery power and give information right at car start-up. Still, other systems use the intensity of the UHF signal (such as the sensor being mounted in the front set of tires or the rear set) as a basis for unique tire identification and other data transmission.
Sensors, themselves, transmit data regarding information not about only the tire’s pressure but also its direction, temperature, tire identification number, and speed of rotation, as well. The pressure, temperature, and tire rotation data are sent as analog signals, which then are converted to digital data for processing. As a note on pressure, it is not reported directly (hence, “direct tire pressure sensors” is somewhat of a misnomer), but as a result of a computation from data obtained about the slow or rapid changes in pressure, indicated by the tire’s state, such as rotation and temperature. Measuring the pressure directly has been deemed too complex and possibly risky, such as issues with the instability of sensor locations.
The environment in which the sensor is placed is one of changing temperature, moisture, and contamination levels, thus placing stress on sensors and batteries. Using batteries presents a number of problems associated with the use of these power storage devices, in general. Battery saving devices, such as improved materials and computer chips that can optimize power usage (commonly about 250μW), have improved, but the problem still remains not only of battery life, which is about 7-10 years, but the disposing of the huge number of batteries produced each year for the TPMS systems. Changing a tire can be traumatic to the sensors and the batteries, as well, so the more times the tire is extracted from the rim, the greater chance the apparatus can be damaged, hence necessitating repair or replacement. Coupled with the usual problems resulting from dead batteries, such as the tire going flat “old style” without the driver being warned, are liability issues. If a driver is dependent upon the system and it fails due to battery problems, the resulting damage can be subject to litigation.
The fact that the sensors and receiver can be made as an independent TPMS system make it amenable to being an after market package that can be installed on older vehicles. This is in line with TPMS being mandatory in the United States for all vehicles manufactured from 2007, onward, as specified by 49 CFR Part 571 Federal Motor Vehicle Safety Standards (FMVSS) . Europe is mandating TPMS in car models from 2012-onward. Starting in 1 January 2013, all South Korean passenger cars will have to have a TPMS, but all existing vehicles will have after 30 June 2014 a TPMS, even if it is retro-fitted. Japan is expected to follow Europe.
In contrast to direct pressure measurement, indirect measurement of tire pressure is accomplished through the characteristics of the tire, itself, such as speed of rotation. An under-inflated tire has to rotate faster than a properly inflated one to maintain vehicular speed, as the covered distance is the same. On a newer TPMS, tire under-inflation can be detected by whether and how the tire vibrates. These systems can be integrated with anti-lock braking systems (ABS) and have the distinct advantage of eliminating sensors in the tires. However, the driver must recalibrate the system by pressing a button on the dashboard. If the tire is under-inflated, the TPMS will not give an accurate report. The regulatory status is mixed, it complying with some laws but not others.
Problems are in store for heavy vehicles, as TPMS doesn’t work well. Not only are there standardization issues, but the very length of trailers raises problems with long-distance transmissions. Battery life is compromised because of the complexity in repairing flats. That the truck loads have to be distributed safely requires more tires, thus raising equipment costs. Retreading is done more on tractor-trailers, another factor limiting sensor life. Truckers will allow for slow leaks, thus affecting accurate tire pressure monitoring. Currently a lot of monitoring is done by pass-through truck stations that report issues to truck drivers.
An issue with TPMS is how accurate it will be with “run-flat” tires, those on which a vehicle can be driven at greatly reduced speeds and distances – enough to get to a repair station. How accurate will the TPMS be in reporting the need for tire repair? Research is ongoing with respect to this question.
Future of TPMS
A primary development will be more countries adopting regulations requiring vehicles have a TPMS system as well as strengthening existing ones . Aside from regulations and standardization, work will proceed in making batteries more efficient, as well as extending the power and range of transmitters so as to guarantee accurate data transmission. As to power requirements, batteries have been a stumbling block, but there is nothing to say that solar power cannot be used. Properly mounted cells can supply that power directly or recharge the batteries. RFID tags are found everywhere and are easily mass produced at low cost. Hence, it can be expected that they will supplant sensors whenever possible, or sensor technology will be further miniaturized and integrated with RFIDs.
To date, the primary emphasis on TPMS has been on passenger vehicles. TPMS will work on heavy vehicles, and systems are marketed, but tire changing complexities and conditions reduce sensor life. Increasing the range of receivers because of the length of the trailers involves more efficient power generation and battery life. Research is progressing on how to make TPMS more amenable to heavy vehicles . However, there does not seem to be a rush for truckers to fit TPMS because of the cost versus benefit .
The primary focus on new development of TPMS is energy efficiency and self-regulating, or “intelligent” tires, covered in the next section.
References (Subject is indicated by URL – accessed 11 June 2011)
 http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&tpl=/ecfrbrowse/Title49/49cfr571_main_02.tpl, http://www.autos.ca/auto-product-reviews/product-review-nvision-tire-pressure-monitoring-system-tpms, http://www.nhtsa.gov/cars/rules/rulings/tpmsfinalrule.6/tpmsfinalrule.6.html
 https://docs.google.com/viewer?url=http://ec.europa.eu/enterprise/sectors/automotive/files/safety/presentation_tyres_en.pdf&embedded=true&chrome=true  https://docs.google.com/viewer?url=http://www-nrd.nhtsa.dot.gov/pdf/esv/esv21/09-0551.pdf&embedded=true&chrome=true http://www.iru.org/cms-filesystem-action?file=en_Resolutions_Technical%20affairs/010_tyre-pressure-monitoring http://www.iru.org/cms-filesystem-action?file=en_Resolutions_Technical%20affairs/010_tyre-pressure-monitoring-systems.E.pdf
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Intelligent Tire Technology
Don’t miss the “7th International Conference Intelligent Tire Technology”,
26-28 September 2011 at the Maritim Rhein-Main Hotel in Darmstadt, Germany.