French Patent # 406,967 Addition # 12,871

French Patent 406,967 Addition 12,871 - Boizot 2 speed main image

I am not entirely sure what is going on in this patent - but Boizot seems to be proposing a system in which a derailleur with a pulley cage holding two pulleys moves a chain laterally across a multiple freewheel - much as in a modern derailleur.

However there also seems to be some kind of pawl mechanism (items E, F & H on the drawings) that may be designed to temporarily reduce the chain tension at the instant of shifting. The exact operation of this device remains a mystery to me.

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