A tire pressure monitoring chipset can help fleet managers improve fuel economy and tell when vehicles are overloaded while also simplifying setup times. The Freescale Semiconductor device is said to be the industry’s smallest sensor, yet it has a broad operating range of 100-1500 kPa, exceeding the levels normally required for heavy commercial trucks.
Though tire pressure sensors are required in passenger cars, those regulations do not apply to trucks. Freescale feels usage in trucking and off-highway applications will grow quickly since properly inflated tires are more economical and safer.
“Demand is driven by economics,” said Ian Chen, Engineering Manager for Freescale’s Sensor Solutions division. “When you’re talking about a major trucking company’s fleet, properly inflated tires can save a couple million dollars per year. Proper inflation also improves safety.”
Freescale’s FXTH8715 integrates a dual-axis accelerometer, motion sensor, RF transmitter, low-frequency receiver, pressure and temperature sensor, and a microcontroller in a 7 x 7 mm package. High integration simplifies installation in all markets, but the turnkey package may be especially attractive in the emerging Chinese marketplace.
“Chinese suppliers do not come from an automotive background,” Chen said. “They want a faster turnaround time, so we need to provide more turnkey solutions. In China, buses and trucks are often overloaded, so the government is encouraging companies to employ tire-pressure monitoring.”
The package has a maximum pressure of 1500 kPa, above the 1300 kPa level normally used in commercial trucking. That is important in off-highway markets as well as buses and trucks.
“In construction and mining, overloading is also very important,” Chen said. “They’re interested in under inflation.”
Using a dual-axis accelerometer simplifies installation while also providing more information for users. The accelerometer provides information that can be used to pinpoint which tire each signal comes from.
“The device sends a signal at the same point in the rotation, which helps the vehicle distinguish between the number of tires on the vehicle,” Chen said. “Also, the dual-axis accelerometer reconstructs where gravity is, so the installer doesn’t have to align the sensor with gravity.”
The technology can be used on trucks that don’t have a dashboard light to display low-pressure alerts. Data can be transmitted to remote sites rather than lighting an in-vehicle alert that may be ignored or forgotten.
“The tire-pressure monitors can be tied to telematic systems that send data to the home office,” Chen said. “If they decide tires are underinflated, they can send a note to the driver, telling him to properly inflate the tires when he pulls in for maintenance.”
The device draws 7 mA, so it lasts 10 years on a coin cell battery, beyond the typical three-year lifetime of a truck tire, Chen noted. Packages will commonly be mounted in the air-pressure valve, but that may change over time.
“There’s a trend to put the chips in the tire, where there’s more information available,” Chen said. “If it’s in the tread, it can count the rotations of the tire, providing a better handle on tread wear, which is especially helpful in fleets where the tires may be moved from vehicle to vehicle. Sensors in the tread can also provide information on road conditions.”
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