A peristaltic pump built into the rim of a vehicle tyre has been shown to keep it correctly inflated at all times. This not only extends the life of the tyre but also improves fuel economy and safety.

The Self Inflating Tire (SIT) is the patented invention of Coda Development, which is based in Prague in the Czech Republic. The pumping tube could be created as a crevice within the tyre sidewall. As the tyre comes into contact with the road, the tyre compresses and creates a restriction in the tube, which is moved along the tube as the wheel rotates. This creates a pumping action.

When the tyre and rim are assembled, the crevice is sealed by the pressure between them. The company says that it is also possible to have the tubing as a separate unit between the rim and the tyre, in which case the tyre presses on the tube and creates the restriction that is moved along it. It was this form that was used for testing the prototype.

It is expected that sufficient air would be pumped to keep the average tyre inflated by only one rotation in 3,000. It therefore needs to have a management system in the form of a valve, to ensure that the tyre is not quickly over inflated.

When no pumping is required, the managing system connects both the inlet and outlet of the pumping tube with the inside space of the tyre. When the tyre pressure falls below optimal, the management system closes the valve on the inlet end of the pumping tube where it connects to the inside of the tyre. This results in suction in this part of the tube, so that it draws air in through a check valve, which is normally kept closed by the positive pressure within the pumping tube and the tyre.

Once the correct pressure has been reached, the pressure management system opens the valve on the inlet end of the tube, and the pressure from the tyre rushes into the entrance of the pumping tube, closing the check valve.

The pressure management system need not be electronic. It could, for example, take the form of a container of compressed air equipped with a membrane. The membrane would be placed against the intake valve at the inlet end of the pumping tube. As the tyre pressure falls below its desired level, the air inside the container would expand and push the valve shut.

Alternatively, it could be replaced by a calibrated spring. However, if the system was electronically managed, it could form part of the tyre pressure monitoring that is now required on all new cars and light vans sold in the USA. As the pressure management device is normally surrounded by the tyre, it need not be made very robust.

Alternatively, the pumping tube could be connected to the outside air. In such an embodiment, a valve on the outlet end of the pumping connecting it to the outside air would be closed when the tyre needed to be inflated.

Currently, 38% of cars in the European Union are running on under inflated tyres. It is estimated that this results in 5.3billion litres of wasted fuel costing an estimated €7billion and 12.3million tonnes of CO2 into the atmosphere annually.

The idea received the Tire Technology of the Year award at the Tire Technology Expo in Hamburg earlier in the year.

Pointers

* Tyres are kept inflated by a peristaltic pumping tube either built into the tyre wall or between the tyre and the rim

* Control is by opening and closing a single valve. This could be effected either manually or electronically