Yesterday we met the Cotal semi automatic and electromagnetically operated gearbox and learned that it had both a normal and an overdriven (or surmultipliée as its makers would have it) version.
Let’s explore la version surmultipliée. As we see Peugeot offered (and made it under licence) for the 402 and promised stupefying economy of consumption. Also, fast. Don’t try and pass it, the ad says.
The normal Cotal had two epicyclic gearsets working in series. The planet carrier of the first drove the ring gear of the second which in turn turned its own planet carrier in the same direction but more slowly. The carrier turned slower than the ring gear and therefore the ring gear turned faster than the carrier. Swap around the input and output then and we can create an overdriven gear. The overdrive Cotal did just that. The planet carrier of the first epicyclic was connected to the carrier of the second epicyclic which turned its ring gear faster and so now the highest gear is even higher.
Except that it wasn’t that simple. Each of the four speeds used both of the epicyclics so each speed was affected by the new arrangement. We can do a little table explaining how and describing the various possibilities as low (a reduction gear), direct (no change) and high (overdrive).
So the old first is gone, second is the new first, there’s a new second, fourth is the new third and we have a new and overdriven fourth. All of which means the various gear ratios and probably the final drive have to be changed so that first is now low enough to be usable and the gaps between the remaining ones are manageable.
It’s an idea which has had several outings. In the 1980s VW sold “Formel E” versions of their cars which for the cheaper ones included a 3+E gearbox, where third was top and fourth became an overdrive marked as E.
There’s not that much new in the world.