9/1/2003 | 6 MINUTE READ

Wiring The Tires

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Siemens VDO Automotive and Goodyear have developed a tire monitoring system that goes beyond government mandates and makes tires an integral part of a vehicle's electronic network. Will it be the technology of choice in the future?


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 Tires are dumb. Though the four tire contact patches transmit all of the forces that make up ride and handling performance, tires themselves have been left out of the rapid vehicle electronification that’s taken place in the past few years–until now. The U.S. TREAD Act, which requires the installation of tire pressure monitoring (TPM) systems on new cars beginning this year, has focused attention on gathering accurate data from tires. But automakers seem chiefly interested in finding the cheapest way to stay within the letter of the law rather than exploring the full wealth of information that can be gleaned about tire performance.

OEMs at first thought they could get TPM on the cheap by using existing anti-lock braking systems (ABS) to gauge pressure loss by measuring changes in the effective rolling radius of tires brought on by deflation. But this indirect sensing method has proven to be highly inaccurate since tires can lose up to a third of their pressure and still be within the margin of tire to tire variation. Also, rotational differences caused by tires slipping on slick or gravelly roads can generate false readings, and since ABS sensors need time to accumulate data, a driver could go quite a distance on perilously low tires before the system recognized the situation.

Direct TPM systems, which use self-contained rim- or stem-mounted sensing units that communicate via a radio frequency (RF) link, are far more accurate than ABS-based solutions and are becoming the hardware of choice for automakers anxious to quickly get a system on their vehicles. But they have their own drawbacks: limited battery life forces these “active” systems to strike a balance between transmitting data and conserving power, and when the battery goes dead the entire unit must be replaced.

Tire IQ. Goodyear and Siemens VDO Automotive have developed a third kind of TPM system that provides data accuracy equal to active units but solves the battery life problem by taking the unusual approach of building a battery-less passive sensor into the tire itself. Called “Tire IQ”, the system relies on a tiny six gram pellet that contains a computer chip and sensor, and is built into the tire sidewall just above the rim. The system uses RF transceivers mounted on the suspension to energize the pellets at regular intervals and take readings on each tire’s condition. (This method is the same one used in vehicle ignition immobilizers and RF ID badges.) Because this approach obviates the need for a battery, the tire sensors can be queried far more often than an active system, providing a more immediate and complete record. To ensure that the pellet can always receive the energizing “ping” from the transceiver regardless of its position, the system also includes a wire antenna that encircles the inside of the tire and is always within signaling proximity. The transceivers send the data back to a central electronic control unit which transmits it to an instrument panel display or to other vehicle control systems.

Because the sensor is integrated into the tire itself it is able to gather far more data than just air pressure and temperature. “It can provide a full range of data including tire stiffness and strain in the tire wall as a vehicle is undergoing a turning or braking maneuver,” says Ken Chance, business development senior engineer at Siemens VDO Automotive. And that opens up a lot of possibilities for improving ride and handling. Chance notes that current ride control systems (like vehicle stability control) base their calculations on general tire parameters since they have no access to real-time data. But with Tire IQ, “You would have millisecond-by-millisecond information coming back from the tire on its state,” he says. Ride control systems could then be programmed to precisely compensate for factors like the reduction in stiffness that occurs when a tire gets warmer during a drive, resulting in improved handling dynamics.


To encourage other tire makers to adopt systems based on the principles of Tire IQ, Goodyear and Siemens VDO Automotive have created an open standard for development. Specifications include:

  • Command and response message structure between the tire sensor and the transceiver.
  • Frequency of messages: 134.5 kHz.
  • Location and orientation of ferrite rod antenna and bounds on antenna material impedance.
  • Durability requirements on cyclic tension, compression and bending.

Building sensors into every tire has the additional benefit of allowing a vehicle’s electronic systems to identify individual tire information and adjust accordingly. Tire load and speed ratings, type (warm weather, winter, spare) and performance characteristics like stiffness can be downloaded to the vehicle as soon as a tire is installed. Tire IQ also tracks service history data, and breaks it down into segments such as mileage traveled at high speed or at low pressure. It can signal when tires are worn or when rotation is necessary. Its leak rate monitoring function repeatedly queries any tire that it suspects of leaking, calculates the leakage rate, and then determines and displays an estimate of the amount of time it will take to reach a critically low pressure. It even has a “signal when filled” function that lets the driver know when a tire has been filled to its optimum pressure.

Once and Future Challenges. Though Siemens VDO’s engineers are used to designing durable automotive electronics, making components that can withstand the strain and vibration associated with the unsprung mass of a tire directly in contact with the road was a new challenge. “We had to invent the technology that would let the electronics live inside of the tire,” says Chance. That translated into giving components the free play necessary to absorb events like hitting a pothole at 65 mph; the 360° wire antenna has a wavy pattern that allows it to move with the sidewall. Thus it can take more strain than a simple circle. Also, the sensor pellet is not rigidly attached to the antenna with a solder joint that could crack under stress, but is concentric to the wire without being physically connected to it. The close proximity allows it to receive and transmit messages via an electromagnetic field while giving it the freedom to flex. Chance says that the difficulty of developing these components is one of the chief reasons why other companies have not taken this approach. “The physical challenge of overcoming strain is a pretty big achievement,” he says.

But now that the technological hurdles have been surmounted, Tire IQ faces an arguably bigger problem–market acceptance. Active TPM systems may have battery life constraints and fewer features but the units are easily installed and interchangeable between various brands of tires. And they are already being manufactured by competing suppliers, so costs should fall as volume increases and competition heats up. (Siemens VDO Automotive is actually one of the biggest players in the active TPM market.) Tire IQ, on the other hand, is currently only being championed by Goodyear, and though the company is offering an open standard to any other tire maker interested in developing Tire IQ-based systems, until that happens potential customers would have to spec Goodyear tires exclusively. Given automakers’ dual sourcing policies that seems unlikely on a large scale, but an unnamed OEM has signed on for some of the first production units which will be made in early 2006.

As for cost, Robert Benedict, senior research and development associate at Goodyear, offers the shopworn phrase, “It is very competitive when you look at price versus features.” Translation: it’s expensive but high-end makers will pay to get all of the neat features. He is more definitive when he says, “At some of the OEMs we talk to this system costs less than what they are paying today.”

Still, as safety regulations continue to expand and ride control systems proliferate the immense amount of valuable data generated by tires cannot be ignored. Tires will be wired. The only question is whether the Tire IQ approach will become the standard.



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