Heat Switch for Fuel Filler Flaps

11 July 2008

Researchers at the Fraunhofer Institute for Machine Tools and Forming Technology IWU in Dresden, Germany, have developed a heat switch for fuel filler flaps based on shape-memory material. The new system is smaller, 90% lighter and around 80% less expensive than current systems which rely on a servomotor-based system.

The fuel filler flap is released by a single wire instead of a small servomotor. Click to enlarge.

The prevalent automated mechanism for releasing fuel filler flaps entails a system comprising a small servomotor, several cogwheels and various springs—more than ten separate parts—activated by a button pushed in the cabin.

The Fraunhofer system instead uses a release mechanism made of shape-memory material. If such a material is first deformed and subsequently heated, exposed to a magnetic field or held up to the light, it resumes its original shape. In the case of the filler cap lock, the components contract due to an increase in the temperature.

We pass a current through the wire, and it heats up. The heat causes it to remember its original shape, so it contracts and opens the filler cap. Our release system has several advantages. It is on average 80 percent less expensive than conventional systems. We can also save about 90 percent of the weight, as the special wire only weighs five grams. Even if you opened the filler cap twice a day for ten years, the system would not wear out.

—Dr. Gunther Naumann

The new release system also saves space: While the housing of the usual servo motor takes up a space of 6x4x3 centimeters, the wire can be integrated in the existing tie rod. In other words, it needs no extra space at all.

A prototype of the system has already been built.