Michelin Uses RFID to Track Tire Pressure and Tread for London Bus Company

By Claire Swedberg

The tires on Stagecoach London's double-decker buses are equipped with passive EPC RFID tags and wireless air-pressure sensors that record a tire's pressure and tread depth within a matter of seconds.

Tire manufacturer Michelin is supplying an RFID-enabled version of its X InCity tires to some of London's buses, with a goal of making it simpler for bus-fleet managers to monitor tire pressure, and thereby improve safety and efficiency. Some of these RFID-enabled tires are currently being utilized by bus-service provider Stagecoach London, and are expected to be in service during the 2012 Olympic Games, to be held from July 27 to Aug. 12.

Michelin embeds EPC Gen 2 passive ultrahigh-frequency (UHF) radio frequency identification tags into tire sidewalls during the manufacturing process. This allows the city's bus-fleet operators or Michelin's staff to use RFID to automatically identify each tire at the time that its pressure is being measured. The tags are used in conjunction with embedded wireless pressure sensors that measure a tire's air pressure and then transmit that data at 433 MHz. The wireless sensor solution is known as the Tire Pressure Monitoring System (TPMS). To date, the company has been providing the RFID- and sensor-equipped tires for use on double-decker buses at Stagecoach London, according to Darren Roe, Stagecoach London's engineering director. The firm expects to have 100 of its buses fitted with the RFID-enabled tires by the end of 2012.

Translogik's iProbe+ device is being used to wirelessly read each tire's pressure sensor and EPC RFID tag, and to measure tread depth.

At present, Michelin's staff uses Translogik's iProbe+ handheld device, designed specifically for this application, to capture RFID tag and pressure-sensor data regarding Stagecoach London's buses. Eventually, though, the bus company expects to take on that task itself. Michelin's workers currently record tire pressures every three months on all RFID-enabled Michelin tires used by Stagecoach London, Roe says. However, he adds, "with this new initiative, there is no reason why we cannot record them every time the vehicle safety is checked," which occurs every 21 days.

Michelin has already manufactured 50,000 such RFID-enabled tires as part of its development and testing, and has logged a total of 6 billion driving hours during that testing period.

During a tire inspection, the iProbe+ device reads the unique ID number encoded to the RFID tag, within a range of up to 50 centimeters (19.7 inches), in order to identify which tire is being tested. The iProbe+ also reads the pressure sensor, by exciting the tire's surface acoustic wave (SAW) pressure sensor via a low-frequency (LF) 125 kHz transmission. In response, the passive sensor uses the power from the reader's signal to transmit its own signal along the 433 MHz RF band, with the exact frequency dependant on the tire pressure. Based on the specific frequency of the sensor's signal, the iProbe+ then calculates the tire's pressure. Finally, the operator utilizes the handheld device to determine tread depth. The pressure and tread-depth data is linked with the tire's unique ID on the handheld unit, and can be forwarded to a back-end server, either via a Bluetooth connection or by docking the handheld.

The RFID tags—including the chip and antenna—have been seven years in development, Michelin reports, and the company currently has 20 patents pending. The technology is intended not only to be built into Michelin's tires, but also to be made available to other tire manufacturers, for use on buses and trucks for which storing data regarding tire quality is important. The tags, which measure 5 centimeters (2 inches) in length, come with 512 bytes of data storage capacity.

Many buses operated by Stagecoach London have been fitted with Michelin’s X InCity tires that have integrated EPC Gen 2 passive RFID tags and wireless air-pressure sensors.

Without the TPMS system, Michelin reports, it typically takes operators a total of 15 minutes to check the pressure and condition of every tire on a bus or truck, and to then record that information.

In the absence of an RFID solution, the staff must remove the cap from each tire's valve and attach a pressure gauge in order to measure the pressure. The workers must then manually write down or input the resulting measurements, as well as the serial number printed on each tire's outer sidewall. The serial number can sometimes be difficult to read if the tire has been rubbed or scraped against curbs or other obstacles, says Jean-Claude Pats, the head of Michelin Europe's trucks division.

"The idea is not to do it more frequently," Pats explains, "but to do it faster, more reliably, and to automatically generate data that can be used to issue a report to the customer, and can be stored in a database that will be used to follow the tire performance."

The installation of RFID-enabled tires on the buses began at Stagecoach London in May 2012, says Pats, who expects that 1,200 RFID tires with TPMS sensors and RFID tags will be mounted by the end of this year. He notes that "85 percent of London buses are fitted with Michelin tires, but not all of them will receive the RFID technology in the immediate future."

Michelin Europe's Jean-Claude Pats

Michelin is not employing a specific brand of RFID chip to create its tire tag. Rather, the company reports that it utilizes only chips with a user-memory bank, in order to offer a space for customer data.

"RFID is considered as a 'service enabler' that will allow service providers to reliably link their services to an individual tire," Pats states.

With the TPMS system in place, all of a vehicle's tires can be fully inspected in less than five minutes. The data accumulated by the inspection tool can then be stored either on the customer's or tire service provider's back-end database. Since Stagecoach London has appointed Michelin as its sole tire supplier, Pats says, Michelin's server is currently hosting the Stagecoach data.

By using RFID technology, Roe says, he anticipates that Stagecoach London will not only trim the amount of time it takes to check tire pressure, but also see a reduction in damage to the tires' valve caps, or the valve's extension seals, that can result from utilizing a conventional pressure gauge. Such damage, he notes, can lead to slow pressure leaks. Roes expects the improved tire pressure management to result in greater tire longevity, due to better load and less wear conditions. "And the biggie: improved fuel consumption," he says. "Tons of information is available on how much even a slightly deflated tire contributes to poor fuel consumption."