Image Number 2 for United States Patent #4643039.
The two endless screws (202, 203) and the four gear wheels (207, 209-307, 309) which mesh with the endless screws and with each other in pairs, have inclined teeth in opposite directions at an angle a, while the secondary gear wheels (210, 310) fixed in rotation with two respective ones of the gear wheels (209, 309) have teeth inclined at an angle b such that tan a/tan b=D1/D2, where D1 is the pitch diameter of the gear wheels and D2 is the pitch diameter of the secondary gear wheels. The secondary gear wheels (210, 310) mesh with tertiary gear wheels (213, 313) which are fixed on an intermediate shaft (315) which bears a gear wheel having straight teeth and forming part of an outlet reduction stage.
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