Steve Durnin’s D-Drive may be the holy grail of infinitely variable transmissions.  The video below will illustrate, at least in part.  The thrill of the D-Drive is it lacks a friction connection for neutral, hydraulic power flow or hydraulic actuation, a torque converter or any other device that bleeds off energy – it seems, but not entirely that the whole of the power in can be converted to work with a minimum amount of loss.

To grasp what’s happening one has to understand planetary and orbital gear sets. In planetary sets there is a large outer (ring) gear with teeth on the inside.  The inside teeth mate to a set of 2, 3, 4 or more little ‘planet’ gears (planet set) whose axles are tied together (by a carrier frame) such that they as a set mesh with the large outer gears inside teeth – and – with an inner gear’s (sun gear) outside teeth.

In an orbital gear set the inner gear drives an eccentric orbiting gear from the inside while the outside eccentric gear’s teeth drives to an outer ring.

Keep in mind that the large outer ring gear can turn or be locked, the planet gears must rotate on the carrier frame and the carrier that holds them can rotate or be locked.  The inner sun gear too can rotate or be locked as well.  The combinations make for some interesting speed ratios across the possible lock or rotate choices.  Torque multiplication and over drive ratios can be made available.  Planetary gear sets can be made extremely strong and simple and are relatively lightweight and robust.

What Durnin has done is stack two doubled planetary sets in a row behind an eccentric orbital set with the innovation of not locking one of the three axles, but to control the speed of rotation. Well, its not exactly that simple . . .

This is where the mind bending comes in.  Gizmag took a publicity shot and missed so you’re humble writer will take a shot at describing the power path which should enable the engineers out there to calculate the energy needed to make the D-Drive function. Correct me if I’m wrong with a comment, but here goes . . .

Power comes in to the inner gear of orbital set, which turns the eccentric ring and idles the outer gear.  The ring gear is connected to planetary set #1 at the planet set.  Stop.  This planetary set isn’t your usual planetary set.

The second and third planetary sets have a double wide outer ring with the carrier planet and the sun – this is the D-Drive innovation.

The incoming power on the planet carrier is split to the front planet set sun gear heading out to the sun gear of the back of the third planetary set, and to the front and back of the ring that is free to rotate and then on to the back planet gear that’s connected to the front of the third planetary set using a shaft locked planet gear on a shaft.  The output is the back planet carrier axle.  Simple, much simpler than the video.  Here’s why.

First, the front eccentric is really just s a speed reduction that isn’t part of the invention, but is to slow things down enough to see.

There are issues; the torque needed to control the two shafts will be substantial, essentially matching up to the input energy. Two controlling shafts aren’t required – the effect could be achieved with just one.  Then there is the matter of the split power out.  The inventor has thought that the power direction would be the way he envisioned it, yet it could very well be reversed, and if thought through the relationships could be exploited such that one power out could be primary and another secondary as in a generator and drive wheels.

As this was written Gizmag has updated their site with some of the matters I raise. The folks at Gizmag have gone from press release enthusiasm to corrected doom.  But Toyota’s Prius uses a sort of similar power path, thus the D-Drive has a future, if already tortured.

But thought through a realization sinks in.  As Mr. Durnin pointed out fueled engines have and can have even tighter efficiency operating zones.  The D-Drive used in a reversed power path could be controlled to deliver power to a generator and/or the drive wheels with the demand for drive power leaving high efficiency power excess for generation.

For all the media fluffing let’s not let go of a major innovation – those double ring gears and Durnin’s first round of application are significant.  Mr. Durnin is going to need a top-flight patent lawyer, because the D-Drive is very efficient and this writer suspects, the control energy Durnin’s design requires should be a part of the load.  A controlled generator could not just use the energy, but direct it as well.

It’s also just round one.  Someone, Durnin one hopes, will double the carrier gears and the sun gears to other applications.  Actually one could go triple either at the sun or ring, double at the carrier and single opposite to the tripled gear.

There is also an engineering report paid for by Durnin available for download.

Mind bending?   A little while for sure, both in how it works and how it can be used.  Planetary sets have been studied for decades, its great to see a new means of utilizing them with a split power path as well.

Lets wish Durnin well and hope the world’s engineers realize the potential Durnin’s innovation offers.


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