Slashdot Mirror
Inventor Demonstrates Infinitely Variable Transmission
ElectricSteve writes with this excerpt from Gizmag:
"Ready for a bit of a mental mechanical challenge? Try your hand at understanding how the D-Drive works. Steve Durnin's ingenious new gearbox design is infinitely variable — that is, with your motor running at a constant speed, the D-Drive transmission can smoothly transition from top gear all the way through neutral and into reverse. It doesn't need a clutch, it doesn't use any friction drive components, and the power is always transmitted through strong, reliable gear teeth. In fact, it's a potential revolution in transmission technology."
The real icing on the cake is (as mentioned near the end) the secondary drive doesn't require a whole lot of power so it can be run by a flywheel. Infinite torque? Frictionless? This is almost too good to be true, there has to be some catch. Like the primary input drive requires more energy than they expected but I can't see it--although I'm not a mechanical engineer.
... these are the kind of news stories an engineer loves to read about.
This is the kind of thing you like to see -- I hope this man has all the capital he needs and gets that prototype up and running for demonstrations. Plus it's a small time plumber inventor
My work here is dung.
I think the weakness in this design is the need to rotate the "bottom" shaft at a speed equal to the input shaft for neutral. While indeed it doesn't need a lot of power, it's a lot of rotation where, in competing designs, a clutch disengages or the drive motor is idling. I could see a lot of things going wrong if the synchronization was imperfect, or if something went wrong.
How do you start this up from a dead stop? Somehow you have to exactly match the shaft rotation speeds to keep it in neutral before you start moving forward, otherwise there will be a lurch.
I look forward to seeing how this is developed further. It has a lot of potential.
At first blush, I'd say that both Toyota and John Deere have already produced something similar. What he appears to have, however, is a system that can smoothly transition (with power) through neutral and reverse. That indeed could be the cool, patented part, as the rest of his transmission is pretty well understood and actually in production already in many of the applications they list for their invention. I don't see any patent application listed, so I can't tell for sure exactly where his breakthrough is.
Here's the fundamental principle by which his transmission works, though: Basically the idea is you supply driving power to a planetary gear system and then use another variable system such as an electronic motor or, in John Deere's case, a hydraulic motor, to take speed (but not power) away from the output shaft by spinning part of the planetary system. If you understand how a planetary gearbox works, this makes sense. So in John Deere's case, the less-efficient hydraulic motor uses a tiny amount of power to control how the actual, geared, power is transmitted to the wheels. Using this system JD has a completely variable system with a particular gear range (this is a tractor after all) that has a powered neutral stop. In the pictures and video you'll note he has two electric motors that control the ratio.
Toyota does something similar with their hybrids, although it's more of a way to efficiently (and brilliantly, I might add) blend the gasoline motor's power with the electric system in an infinitely variable way.
Another way of implementing an IVT, though I don't think it is as efficient, is to use a differential. Power comes in the normal part of the differential (IE spinning the entire gear assembly), and then power comes out one side, and an electric or hydraulic motor attached to the other side (Where the wheels would normally go). You can then use the motor to change the apparent gear ratio, and even reverse it.
The Thompson coupling was invented not long ago, and I remember being amazed that there was anything new to be done in the area of mechanical power transmission. And now this. Are we all done now, or is there more still?
Fuck the system? Nah, you might catch something.
The new aspect is that this planetary gearset actually has TWO inputs, and the output is determined by the *difference* in speeds between the two. That's how it can go from reverse to forward seamlessly. V1 > V2 is Forward, V1 V2 is Reverse, V1 = V2 is Neutral. Assuming there are no practical limits on the velocity of either input, the possible difference between them is infinite.
Personally I find this really exciting, because i've always been in love with the idea of a variable transmission. Ignoring electric motors for a minute, there are some absolutely INSANE things you can do to a small motor with cams, turbocharging, etc, to extract absolutely massive amounts of power from teeny engines. Like, 1000+hp from sub 2 litre motors. The problem is they end up being extremely peaky (power is only made at a narrow RPM band, or a terribly high one)... but with a variable transmission you can let the engine hunker down in it's sweet spot and let the tranny worry about all the fiddly bits. Hell, you can even do the same thing with a big engine... I wonder if its possible to make five figures of power from a 7 litre? With this we just might find out.
Not to worry about 'infinite' or 'frictionless' - these characterizations are not the intent of the device so we can just evaluate it as a normal continuous transmission being controlled by the ratio of speeds between a control shaft and the drive shaft. Efficiency for low-torque cases can be quite decent as eccentric bearings, gear-qualities and diameters can be controlled well with current techniques.
So... with a real torque, there will definitely be significant forces between the two shafts. Clearly, the full torque will be on the central, driving shaft, while some smaller fraction will be on the upper shaft. As we bring the distance between them down, then the torque between them can decrease, but then there will be more stress on the smaller pinions' teeth. Planetary gears are great for this class of problem and he's throwing decent diameter eccentric bearings in where he can too. The bloke seems honest, and has clearly thrown a fair amount of time and energy into the problem.
There are other approaches to controlling gear ratio via the speed differences between two shafts - he's not trying to do something impossible, he's just trying to do something difficult, successfully. Whether the cost of the bearings and gearing will be favourable when compared to the other approaches is the question. I think his system will work - and decent sealed bearings, high strength pinions, planetary systems - these already exist and are stable tech in current transmissions, even in relatively dirty industrial environments where the transmissions aren't as protected as in cars. In particular, the cost of electronic control for motors has fallen massively over the last years, so if nothing else, the general class of solutions using differential speeds of low-torque motors to control a high-torque transmission is more appealing now.
So, 'genius', no. Hard-working, self-taught engineer? Yes.
The way I understood it (could be wrong), the Prius drive is only one half of what this guy came up with. The clever bit is the other half. The Prius transmission would not work well without significant torque input/output(electric breaking) on the electric side. The way this works, there is almost no load on the ratio selection element, the only input it needs is enough to create a difference in speed.
Mind the frickin' laser...
It's loud. Plus you have to have a heavy hydraulic system (pump, oil reservoir, valving, etc). In practice an electric motor gives you most of the same benefits of a hydrostatic system, but it's a lot lighter and doesn't require an oil system. Of course batteries are heavy, but aren't strictly needed (as in a locomotive).
A few years ago I heard of a design that used small hydraulic motors connected to each car wheel via clutches that would efficiently overcome the propensity of a differential to send power where you don't need it. Basically when slippage was detected, the clutches would engage and the faster wheel would act as a pump, sending fluid to drive the other wheel. The beauty was that if you tied all four wheels into the same system, you could get on-demand four wheel drive as well.
Another prototype I heard of used a hydrostatic system to charge up a nitrogen accumulator in a form of regenerative braking system.
Hydrostatics also has limitations in the amount of power you can transmit. Every large combine harvester we've ever owned has had a hydrostatic transmission, but no tractor ever has had. Combines typically don't pull things; driving power is minimal compared to the power consumed by threshing. Whereas in a tractor, it's all about driving power (outside of PTO applications). You just can't really put 500 HP of pulling power through hydrostatics. Most hydraulic motors are gear motors, which means the oil spins little gears. Under high load, oil slips past the gears without turning them. Compare that to electric where on a daily basis Locomotives pass thousands of horsepower from big diesel engines to the wheels with electric motors.
The largest value of this device is in its "wow, how does that thing work?" design. By baffling the onlooker and also describing the widget very carefully the illusion of a wonderfully useful device can be created.
It has a problem in the real world, though. The reaction torque is equal to the working torque - and the reaction torque path runs through that "secondary control shaft." This will become obvious as soon as he tries to transmit some significant power through his device. What he's showing isn't a new invention at all, it's just a mechanical "summer" that adds the inputs from two input shafts. All that's new here is some fancy handwaving and creative description.
It might be good enough to fool some people but Mother Nature and those who paid attention in school aren't fooled. Maybe if / when he actually tries to transmit some power through his "invention" and the control motor just spins backwards he'll "discover" a source of electrical energy?
Yeah but eliminating clutches removes a common point of failure. So even if the performance benefits aren't that great it may increase the life of the car/machine.