Wireless Tyre Pressure Monitoring （2）

Published:2011/8/1 1:03:00 Author:Amy From:SeekIC

By Helmuth Lemme

Batteryiess systems

The Lithium battery is a source of problems with all systems. Exchanging the battery is time-consuming. The battery is also heavier than the entyre electronic cir­cuit and it obviously requires a very stable mounting method in view of the cen­trifugal acceleration. When braking hard, the tempera­ture inside the tyre can reach up to 100 degrees C which may easily damage the battery. Finally, flat Lithium bat­teries are toxic waste hence have to be disposed of using the proper channels.

A solution to the above prob­lems was found in the use of passive sensor responders that are interrogated over radio. The RF energy allows the transponder to return the instantaneous tyre pressure ’over the air’. The sensor goes inactive again until the next RF trigger arrives. The princi­ple is well established in RFID (’radio tagging’) systems that have been around for years.



The technology offers several options. One very elegant solution is called ’surface-wave elements’. A system using these devices was developed by the Siemens research labs but never made it to volume production. Instead, Siemens in co-opera­tion with Goodyear are now working on a different system which reportedly is cheaper as well as less complex. Here, the transmission is inductive: inductors are fitted on the wheel and the wheel holder, the assembly producing a transformer effect (Figure 3). A short RF pulse at a carrier frequency of 125 kHz supplies the energy for the measure­ment and returning of a data packet containing the current tyre pressure. The system is to be perfected for launching in 2006.

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