Issue



MEMS, MCU, and RF integrate for better tire-pressure monitoring


11/01/2007







By Eric Caron, Freescale Semiconductor

Freescale (www.freescale.com) has combined advanced MEMS technology with a microcontroller and RF transmitter to create a versatile, system-in-package (SiP) tire pressure monitoring system (TPMS) that differs from most others. The Freescale MPXY8300 “smart sensor” takes advantage of MEMS capacitive technology, and we believe it to be the first single-package TPMS solution to use capacitive technology for sensing both air pressure and dual-axis (XZ) acceleration to measure wheel rotational speed and direction. Capacitive technology is more power-efficient than traditional piezoresistive techniques, and the capacitive accelerometer is also more cost-effective to manufacture because both axes can be fabricated on a single die.

By incorporating an RF transmitter with the TPMS module, measurements for each tire, including the spare, can be transmitted in real-time to the cockpit instrument cluster. This system continually monitors tire inflation and can, depending on the car model, produce a visual verification for the driver from his or her seat.

Properly inflated tires enable greater fuel efficiency, which is particularly critical for large trucking firms that deploy hundreds of large vehicles. On a heavy truck that has 18 or more wheels, the TPMS modules’ ability to extend tire lifetimes and keep fuel costs low can translate into significant savings.

The Freescale TPMS is a simple, highly integrated, flexible, and intelligent single-package solution designed to support both cars and medium/heavy duty trucks. The technology is adaptable, however, for other applications. In the future, a similar integrated system could monitor critical material transportation and storage conditions, including temperature, impacts, external and internal pressure, container fill level, and orientation (making sure “this side up” is still “up”). Other applications include air-flow measurement and air/fluid leak monitoring for HVAC systems; air-speed indicator for airplanes, boats, etc.; fluid-level indicator for fuel tanks and water storage reservoirs; and wireless fluid/gas pressure gauge for such applications as sump pumps and pressure cookers.

Eric Caron is MEMS-based sensors (auto) product marketing manager at Freescale Semiconductor. He can be reached at eric.caron@freescale.com.