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Unusual ways to change gear, cont'd

Time to go to France and things French, like the very French Cotal semi automatic electromagnetically operated gearbox.

Illustration for article titled Unusual ways to change gear, contd

Yes, it’s a bit of a mouthful. It was de rigueur on luxury (and some not so luxury) French cars between the wars and on to the 1950s. Designed to spare the driver the considerable inconvenience of learning to change gear quietly and smoothly in the pre synchromesh era, it used instead a pair of epicyclic gear sets and four electromagnets. The epicyclics provided the ratios and the electromagnets were an alternative to other means of engaging friction materials.

To begin, here’s an epicyclic about its business.


The central gear is the sun wheel, the smaller silver ones orbiting about it are planet wheels which are attached to a red planet carrier and around all these we have an annulus or ring gear (or as Cotal called it, a couronne or crown). If you hold one of these elements (sun, ring or planet carrier) still, apply power to a second and take power from a third you can in principle obtain two overdrive speeds, two reduction speeds and two reverses. Join any two elements and you obtain direct drive with no reduction or multiplication. In the gif, the ring gear is blocked and the planet carrier is turning more slowly than the sun gear. If you drive the sun and take power from the planet carrier you’ve got a reduction gear.

The Cotal had a pair of these, each equipped with two magnets and each providing a different reduction gear (which is crucial).


For the first of its four speeds, the first gearset is just as above. The engine drives the sun, one of the magnets blocks the ring gear and drive is taken at a reduced speed from the planet carrier.

Now the tricky bit. The planet carrier drives the ring gear of the next gear set. The sun is blocked by another magnet so the planet carrier turns in the same direction as the ring gear, but slower. We’ve now succeeded in reducing the rotational speed in two stages.


Next up is second gear. The first epicyclic stays as it is but the second is locked by another magnet and doesn’t provide any reduction so the output shaft is now turning faster.

Third comes next as you would expect. Remember how the two epicyclics are different? That’s important because there’s now a swap. The first epicyclic is locked (no reduction), the second has its sun blocked (another magnet) and provides a reduction but less so than the first gear set. That’s a higher gear.


To finish off we lock both epicyclics so no reduction and direct drive.

There was also an overdrive version which arranged the second epicyclic differently.


So overall, power going left to right:

Ist low-low

2nd low-high

3rd high-low

4th high-high

To control all this, a little lever in a little gate, like so:

Illustration for article titled Unusual ways to change gear, contd

It was called a moutardier, a mustard pot, because it looked like a spoon stuck in an old fashioned mustard pot.

You’ll notice we haven’t mentioned going astern. The epicyclics didn’t lower themselves to that so there was a separate reverser built into the front of the box, resulting in principle in four gears in each direction. In practice you were supposed to use third in reverse because the latter was much lower than forward and first reverse was therefore so low that the torque would do the rest of the transmission an expensive mischief.


Also unmentioned is stopping and starting, handled by a traditional clutch and pedal. You can see the lever in the first image.

So now you know how to deal with driving your first Delahaye. They nearly all had Cotals.

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