Tire malfunction while car traveling at high speed is what the drivers most worry about and difficult to prevent as well as one of the major causes of sudden traffic accidents. No matter domestic or abroad traffic accidents occurred especially in highway due to puncture. Experts emphasize that the best preventive measure is to be aware of the insufficient tire pressure in advance and take timely precaution. Tire Pressure Monitoring System(TPMS) is born of the above reasons. It is mainly used to monitor tire pressure automatically and alarm to warn the driver to take measures in time when the tire is in unsafe state so that to achieve pre-protection.

The importance of correct tire inflation pressure is well known. Vehicle handling is decided upon the tire-road contact patch. Furthermore fuel consumption increases and tire lifetime decreases with 20 % for every 0.2 bar under-inflation. It is also known that tire problems are the third most common breakdown for vehicles. 75% of all tire flats are preceded by under-inflation or slow leakage. With a tire pressure monitoring system severe accidents can be avoided and both economical and environmental benefits can be made.

There are two ways of monitoring the tire pressure:

Direct TPMS

One way is to mount a pressure sensor at the rim on each tire and via a communication-link (usually a radio-link) transfer the sensor value to a central unit. This is called direct tire pressure monitoring. Direct TPMS employ pressure sensors on each tire, either internal or external. The sensors physically measure the tire pressure in each tire and report it to the vehicle's instrument cluster or a corresponding monitor. Some units also measure and alert temperatures of the tire as well. Due to the extra hardware needed this method is very expensive.

Indirect TPMS

The other alternative, called indirect tire pressure monitoring uses existing sensors and software algorithms. Indirect TPMS do not use physical pressure sensors but measure air pressures by monitoring individual wheel rotational speeds and other signals available outside of the tire itself. First generation iTPMS systems are based on the principle that under-inflated tires have a slightly smaller diameter (and hence higher angular velocity) than a correctly inflated one. These differences are measurable through the wheel speed sensors of ABS/ESC systems. Second generation iTPMS can also detect simultaneous under-inflation in up to all four tires using spectrum analysis of individual wheels, which can be realized in software using advanced signal processing techniques.The indirect systems are very cost-effective (no extra hardware).

Benefits of TPMS

• Fuel savings
• Extended tire life
• Decreased downtime and maintenance
• Improved safety
• Environmental efficiency
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