Under the skin: the tires that make their own electricity

Parent company Sumito Rubber Industries Falken is working with Professor Hiroshi Tani of Kansai University to develop an electronic device to accurately monitor tire wear.

For all the talk about the need for self-driving cars to lower the accident rate, it seems there is still plenty of room to improve the safety of conventional cars as well. Tire condition is vital to safe driving, but it’s fair to say that for many drivers, actively checking tires is very low on the priority list. If tire wear continues unnoticed or ignored, the results can be fatal—especially in wet locations.

Continental once demonstrated under controlled test conditions at the MIRA Proving Ground near Nuneaton that although the legal limit is 1.6 mm across 75% of the tread width, stopping distances in moisture increase dramatically once tire wear drops below 3 mm.

Sumito’s new device, Energy Harvester, requires no batteries. Instead, a small system attached to the inside of the tire generates static electricity to power an equally small tire sensor, which can transmit a data signal to the vehicle’s electronic systems using BLE (Bluetooth Low Energy). Inside the power harvester there are two layers of rubber covered with a film, resulting in a negative and a positive electrode.

When the tire is deformed, the two films rub together, producing static electricity. A group of reapers are arranged in a line across the interior of the frame structure, and as the tire rolls all the way, each one generates a small effort. The changing shape of the voltage waveform between them indicates the variation in tire footprint with tire wear.

The system can be integrated into the tires intended for conventional cars, and talk to the vehicle’s hardware system to warn of excessively worn tires. Working in tandem with vehicle tire pressure monitoring systems (TPMS), it seems logical that combining the two could provide a more effective way to monitor all aspects of tire condition on behalf of the driver. If and when self-driving cars roam freely on the roads, a tire wear monitoring system plus TPMS could be a useful tool for fleet operators and private owners.

The research originally formed part of Sumito’s smart tire concept, which received funding in 2019 from the Japan Science and Technology Agency. The concept aims to turn whole tires into sensors. Other tire manufacturers, notably Continental and Goodyear, have been working on smart tire concepts for a number of years as well.

The Continental’s lateral torsion sensor (SWT) is designed, for the first time a few years ago, to integrate with braking systems to improve stability during braking. Since it could detect vehicle yaw at the source and not after it was in effect, it was also hoped that one day SWT could eliminate the vehicle’s yaw sensor, the most expensive part of the ESP system.

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