As this is a patent and an invention, it's hard to be sure, of course, you probably need to look at the drawings if any to decide what best to call it.

However, this is one common translation for chariot in many fields (though there are several other possibilities!), and from the context given, it sounds to me as if this might be applicable; it possibly depends just how big this thing is (e.g. how much current is this c/b designed to carry?) as to whether or not 'carriage' would work — I'd have more qualms if this thing were very small (when it might, for example, become a 'slider')

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Note added at 1 jour1 heure (2012-02-14 09:55:33 GMT)
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Now we have seen the image, I can't really think of a better term for this; it does indeed seem to be like a little carriage.

Alternatively, you might consider expanding it to something like 'sliding element', which is perhaps more appropriate for your document.

Here, I don't think my last suggestion of 'slider' would really be applicable.