Tire Pressure Monitoring Systems

Basic Description

Tire Pressure Monitoring Systems (TPMS) are mandatory on all new cars sold in the United States since September 1, 2007. Tire pressure monitoring systems monitor the internal temperature and pressure of an automobile's tire. These systems warn drivers of under inflation, leaks, and the loss of air pressure that occurs naturally. Tires typically lose about 1 psi (pounds per square inch) each month due to natural permeation. This loss can be greater in warm weather.

In an under-inflated tire the sidewalls will flex excessively creating high temperatures that degrade the tire and make failure more likely. The chief challenge to measuring tire pressure is the simple fact that the tire is rotating at high speeds and making a direct electrical connection to a rotating tire is difficult. The tire is also exposed to unexpected hazards, water, and road chemicals and subjected to severe centrifugal forces. TPMS systems must be designed to endure these harsh conditions and meet four key requirements: They must secure the sensor in the tire or wheel, provide power to the sensor, extract data from the sensor, and display the information to the driver.

Direct Systems attach a pressure sensor/transmitter to the vehicle's wheel inside the tire's air chamber. An in-car receiver warns the driver instantly if the pressure in any one tire falls below a pre-determined level.

Indirect Systems use the vehicle's antilock braking system's wheel speed sensors to compare the rotational speed of one tire vs. the others. If one tire is low on pressure, it will turn a different number of revolutions per mile than the other three tires.

Sensors

Air pressure sensor, temperature sensor

Actuators

Low-tire-pressure display (usually in dashboard).

Data Communications

Data communication between tires and control unit: typically 315 MHz RF link.
Wake-up signal to tire mounted sensors: typically a low-frequency EM signal.
Control unit communications: typically CAN bus

Manufacturers

Atmel, Beru, Continental, Doran, IQ mobile, Lear, Lionax, Orange Electronic, Pacific, Pressure Pro, Schrader, SmarTire, STE Engineering, STEMCO, TRW, VisiTyre

For More Information

[1] Transportation Recall Enhancement, Accountability, and Documentation (TREAD) Act, Section 12, "Tire pressure warning."

[2] Tire Pressure Monitoring (TPM) System, Microchip Technology Application Note, AN238 (pdf file)

[3] Tire Pressure Monitoring System, U.S. Patent #7224267, May 29, 2007.

[4] A. Chait, Powering Tire Pressure Sensors, Sensors Magazine, Jul. 1, 2007.

[5] K. Mnif, A Smart Tire Pressure Monitoring System, Sensors Magazine, Nov. 1, 2007.

[6] Tire Pressure Monitor Systems (TPMS), AA1car.com

[7] Toyota Prius TPMS Tire Pressure Monitoring System, YouTube, 2008.

[8] Tire Pressure Monitoring System (TPMS) at Freescale Ford Road Show, YouTube, 2009.