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# Series Epicyclic Transmission

Four clutches/bands gives 16 ratios to pick from!
 (+3) [vote for, against]

I'd be surprised if this hasn't been baked, but wouldn't know where to start looking. This idea is based on a modular gear ratio system.

Imagine an epicyclic gear ratio (see link), taking either direct drive (ring and planet carrier locked) form or reduction (ring locked to housing, drive from planet carrier) form. This would be implemented by having the unit naturally locked in direct drive mode by a sprung system, effectively pegging the planet carrier to the ring gear. The 'reduction' mode would be accessed by having a band around the ring gear that, as it clamps down, releases the planet lockers and then takes hold of the ring gear, fixing it to the gearbox casing.

Now imagine two of these running in series, but with subtle changes in the tooth counts to give different ratios when in reduction mode. This gives four distinct overall ratios... D-D=1 0.9->D = 0.9 D->0.8 = 0.8 0.9->0.8 = 0.72

Using more ratios would lead to 2^n possible overall combinations (ie. 3->8, 4->16, 5->32). Since the most basic implementation if this could be implemented using n digital outputs feeding relays, valves or other actuation equipment. If you were feeling particularly clever, you could have the switches for each stage on the dashboard and flip them manually (assuming you spend too much time around computers, and therefore count instinctively in binary).

Note that you would only get n+1 ratios if using the same ratio for each stage.

A normal gearbox uses an approach like this...

Engine -> 1:1 or 1.5:1 or 2:1 or 3:1 or 4:1 or... -> Final Drive

Because each ratio is defined by a single pair of gears.

My proposition is this...

Engine -> 1:1 or 1.2:1 -> 1:1 or 1.5:1 -> 1:1 or 2:1 -> Final Drive

giving ratios of: 3.6:1, 3:1, 2.4:1, 2:1, 1.8:1, 1.5:1, 1.2:1, 1:1

The increased number of ratios available is because each ratio can interact with the other two.

I think the number of ratios offered would be more useful in a commercial vehicle (truck, tractor etc.) than a car. It could be implemented in a 'tiptronic' or auto mode, rather than manual. Hydraulics, or possibly pneumatics would probably be the most appropriate for activating the bands.

 — Skrewloose, Feb 25 2009

Wiki's Epicyclic Gearing Explanation http://en.wikipedia...i/Epicyclic_gearing
Gives an explanation of the gearing principle I'm making use of. [Skrewloose, Mar 08 2009]

KerTrain http://www.kertrain.com/incremental.htm
Complicated machining for its own sake. [eight_nine_tortoise, Mar 10 2009]

2 buns but no comments (thanks)... I feel lonely :(
 — Skrewloose, Mar 05 2009

using multiple and compound planetary gearsets really isn't a new idea. I admit that the idea of multiple planetary sets stacked together really appeals to me too. Maybe you could make a diagram and change the title to something less confusing .
 — WcW, Mar 05 2009

 Clutches need to be engaged at a rate controlled by the vehicle operator. I like the idea, but the human-machine interface needs usability work.

Perhaps this could map to a single clutch pedal and an 8-gate shifter with high/low selector? Some articulated lorries use separate pedals for a high and low clutch, but this interface is awkward.
 — ed, Mar 05 2009

There was a system for buses demonstrated (Tomorrow's World, c.1982) that had a clutch-per-ratio, but I don't know how it worked. I guess it wasn't very successful.
 — AbsintheWithoutLeave, Mar 05 2009

 //I'd be surprised if this hasn't been baked, but wouldn't know where to start looking.//

You can go to www.uspto.gov and click on "Search patents" on the patent drop-down menu.
 — ldischler, Mar 08 2009

I've updated the post, and couldn't find anything on the patents office doing what I'm after here. Looks like I'm in the clear!
 — Skrewloose, Mar 08 2009

planetary. Really this is exactly how a 4+ speed automatic transmission works right now. Generally we have as many speeds as can stack efficiently and reliably. More bands means more valves, regulators, friction, weaknesses (torque load) and weight. For trucks and buses the problem of friction (fuel economy) and weakness (profound impact stress and high sustained loading) basically kept the number of gears to a minimum.
 — WcW, Mar 09 2009

Speak to the guys at KerTrain [link] if they can't make it work no one can.
 — eight_nine_tortoise, Mar 10 2009

Looks like they have - just what I was thinking, but taken to the extreme.
 — Skrewloose, Mar 31 2010

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