|
Tire Pressure Sensing Technology
Measuring the pressure and other parameters of tires at operating speeds is necessary for a new generation of safe, efficient tires supported by developing technologies. As the world’s largest tire manufacturer and the only American tire manufacturer, Goodyear Tire and Rubber Company wondered if it would be possible to mount wireless, robust transient sensors in its tires to monitor tire pressure and other parameters. While current technologies allowed tire pressure to be monitored, these systems used individual batteries, required considerable maintenance, and were also fairly expensive. Goodyear had a better idea, but it needed help from Sandia National Laboratories, which had the background in sensor development and micromechanical devices required to bring it to fruition.
Goodyear’s previous work with Sandia on tread modeling had revolutionized tire design, increased revenue on the sales of the tires by 18%, and resulted in safe and superior tread designs for the consumer, so Goodyear knew the value of having Sandia as technical partner. As it has on more than twenty technically complex projects since the 1990s, Goodyear approached Sandia with another technical challenge, this time to evaluate the feasibility of producing a wireless, passive sensor system with a pressure sensor that could be embedded in tires. There were also many benefits to the Department of Energy in terms of energy use and safety as well as to Department of Homeland Defense applications.
The tire pressure sensing technology investigated involves measuring the delay of radio frequency (RF) pulses absorbed and then re-radiated from a surface acoustic wave (SAW) device and has been demonstrated in rolling tires at speeds up to 80 miles per hour. Sandia and Goodyear designed an inexpensive SAW-based pressure sensor employing multiple SAW transducers on a single substrate that, when coupled with a pressure-sensitive conducting membrane, produced a reflected RF pulse at a specific time and correlated to a specific pressure. The system consists of an active RF transceiver that would be mounted on the car as well as four totally passive pressure sensors mounted in each of the tires.
 |
|
Tire pressure sensor mounted on the sidewall of a Goodyear Eagle in preparation for
rolling testsa |
|
The sensors were placed in a cavity machined into the material and sealed with a flexible conductive membrane that had a standard pressure in the cavity. When an overpressure was applied to the membrane, it deflected and made contact with conducting levels produced on the interior of the cavity. The ridges were electrically connected to the conductive fingers of the SAW device. When the pressure was high enough to deflect the membrane into one of the conducting levels, selected fingers on the SAW device were grounded, producing patterned acoustic reflections to an impulse RF signal. The timing of the pattern allowed determination of the deflection of the membrane, which in turn was a function of the pressure in the tire.
|
