Inventor Demonstrates Infinitely Variable Transmission 609
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."
Um, Prius anyone? (Score:2, Informative)
The "transmission ratio is controlled by the relative speed of the motor driven shaft" technique is exactly what's used by the transmission in the Prius (and every other Toyota, Nissan, and Ford hybrid).
Today's CVTs are No Match (Score:3, Informative)
The greatest limitation on today's CVTs is the lack of sufficiently strong materials for the belts. While research and development has already yielded marketable CVTs, they are limited to being paired with relatively low displacement, low horsepower, low torque engines for durability purposes. Your father's Oldsmobile's honkin' huge Rocket V-8 or your cousin Bubba's new pickup truck's V-10 would likely tear any of those CVT belts to shreds. Supposing that this new design is strong enough, those engine pairing limitations could be done away with once and for all.
Hydrostatics... (Score:3, Informative)
Re:Electric motors (Score:4, Informative)
Re:Brilliant. Go Steve! (Score:4, Informative)
Re:Electric motors (Score:4, Informative)
As a mechanical engineer... (Score:2, Informative)
Re:Brilliant. Go Steve! (Score:3, Informative)
watch the video half way down TFA- it shows in pretty fair detail how the d-drive transmission works.
Re:Um, Prius anyone? (Score:1, Informative)
No, it's not, at all. if you take that one random sentence fragment then yes you could apply it to both, or pretty much any automatic transmission for that matter. however, this idea is brand new, and not used anywhere. WTFV, since RTFA won't get you all that far.
Re:Fuel economy (Score:3, Informative)
Your Prius's CVT has limited torque because your CVT uses power transfer mechanisms other than toothed gears alone. The D-drive uses toothed gears only, not belts, not friction plates, etc. This allows for more torque than other CVT designs.
Re:What concerns me (Score:2, Informative)
I think you're exactly right. The invention seems to take a fixed-speed motor and a variable-speed motor of identical power and combine them into a variable-speed motor of identical power.
Re:Brilliant. Go Steve! (Score:2, Informative)
I think Toyota already invented this with their Prius hybrid car. It uses a traditional planetary gear, but in addition to the gasoline engine and the wheels, it's also tied to an electric motor. The electric motor spins as different rates (or not at all), thereby choosing an infinite number of engine-to-wheel ratios.
Meanwhile:
I have a VW Beetle with 6 gears automatic. Obviously that's not a CVT, but the huge number of gears keeps my engine hovering at 2000 rpm consistently (between 10 and 60 mph), so it has the same effect as a CVT (keeps the engine at the most efficient spot).
Re:How a planetary-based IVT system works in gener (Score:5, Informative)
Hate to reply to my own post, but here is a fairly detailed explanation of John Deere's IVT: http://salesmanual.deere.com/sales/salesmanual/en_NA/tractors/2006/feature/transmissions/8030_option_code_1127_1137_ivt_trans.html [deere.com] . The relevant part is "The John Deere IVT uses a hydromechanical, power-splitting design where a portion of the power is transmitted mechanically and a portion hydrostatically. A hydromechanical transmission is more efficient than a purely hydrostatic transmission because gears carry power more efficiently than a hydraulic pump and motor. By careful selection of the gearing, the John Deere IVT carries a maximum of the power mechanically both at normal field working speeds and at transport speeds, taking maximum advantage of the higher mechanical efficiency while providing the control and versatility of a hydrostatic." And of course this power-splitting is done via a planetary gear system.
I say this not to take away from the D-Drive's awesomeness (John Deere doesn't do reverse without shifting a gear), but to help offer explanations of how it actually works.
Re:Hydrostatics... (Score:5, Informative)
Fluid friction losses. Recirculating a fluid via a pump in a closed system actually makes a bit of heat, especially when there's a bit of load on it. Works great when something can be built big and doesn't need to go very fast (like the tractor application you mentioned, also used a lot in earth moving equipment and fork-lifts), but when having something that goes fast - not so much. Also if you go too fast, you're either going to have some kind of undesirable hammering or cavitation at a certain point depending on what kind of pump you use to provide hydraulic power.
Some air motors use a tilt-block that does something similar as well in regards to infinite variable speeds, but they're not so much about efficiency as about being able to control speed in industrial environments where electric motors aren't always desired. (Like working around water or in a no-spark environment.)
Re:Uh... (Score:3, Informative)
The control system has the smaller central gear, so there will be some mechanical advantage that will "step up" the torque the control system can provide, allowing for a smaller control powerplant.
He mentions a kinetic recovery system to power it, which to me indicates an intention for intermittent use. I'm thinking its target purpose is as a no-wear mechanical clutch. Without power input, it sends full power through, which is bad for a failure mode... but good as a clutch. I interpret that the control is least power hungry at ratios close to 1:1 and demands the most power at low ratios; however, I think the "powered zero" requires little power, since there is no torque output.
You could attach smaller version of this device to a PTO to drive the control system variably from the drive motors own power, and control it with an even less powerful electric motor. Stacking the control system(s) like this could allow large scale versions.
Some linkies from the gizmag comments: A Prius drivetrain simulator [sannet.ne.jp], A John Deere CVT animation [youtube.com]
Re:Differential, anyone? (Score:3, Informative)
Yes, the behavior of this "transmission" should look familiar to anyone who has ever played with a differential while experimenting with Lego gears.
With a classic differential (the piece pictured here: http://en.wikipedia.org/wiki/Differential_(mechanics) [wikipedia.org] ), there are four different things rotating, and their speeds are related. The equation is something like (A-B) = (C-D). The problem is that one of these rotating things is very hard to access mechanically - the inner bevel gear, whose axis of rotation moves as the casing of the differential rotates.
It seems like this device is equivalent to a single differential, with one small bonus which explains the additional mechanical complexity: all four rotating parts are easily accessible. There is a shaft coming out of each end, and two shafts exposed in the middle, whose axes of rotation are not moving and therefore motors can easily be attached.
This is a clever re-arrangement of a differential, but I don't really think it will lead to a super-efficient transmission because you still need a secondary motor which needs to be variable speed, and which will be subjected to a potentially wide range of torques. So it just introduces a new problem.
Re:Brilliant. Go Steve! (Score:5, Informative)
BTW, couldn't you do this sort of thing with a differential?
Yes. That's basically what the Prius does: it uses a differential (actually an epicyclic, which is a flattened differential) as a mixer, and drives one input with a gas engine and the other with an electric motor, giving not only an infinite number of speeds but also a way to use the engine to charge the motor with excess power, or use the motor for braking. But then you need both an engine and a motor. Managing an infinite drive from a single input is pretty cool.
Video of D-Drive (Score:3, Informative)
Re:Brilliant. Go Steve! (Score:5, Informative)
And FYI, an OTTO cycle engine is not most efficient at 2000 rpm. It's most efficient at its horse power peak RPM, and at full throttle. Anything less than that (RPM or throttle), and you lose volumetric efficiency. And when I say efficient, I'm saying the power/fuel use is the maximum. It's all about the intake and exhaust design (you can tune them for maximum efficiency at a particular RPM for a particular engine design). That's why hybrids typically use smaller engines. So that you can run it closer to its peak power for longer (40hp at full throttle would be plenty to cruise on the highway and still be able to charge the batteries without needing to be throttled back).
Re:Electric motors (Score:3, Informative)
Re:Automatic transmissions fail before engines, no (Score:3, Informative)
Yeah, but maintenance on a manual transmission is a fair bit cheaper. Moreover, an automatic requires far more regular maintenance that, if not properly performed, can lead to much faster breakdown.
Re:Automatic transmissions fail before engines, no (Score:2, Informative)
The difference is that when an automatic does go, the parts are more expensive and the job is more complex because there is no convenient place to put a point of failure. In a manual, the designed point of failure is the clutch pads. it is relatively simple to pull it apart and replace the pads. At most, in a well designed car like a Subaru, it is a 2 or 3 hour job. I've seen automatics take 2 days. At $90/hour for shop time the repair of an automatic means you eat ramen for a month, while the servicing of a clutch means you can have some steak.
Re:Differential, anyone? (Score:3, Informative)
Not a differential, but two: an adder-subtractor.
Found here:
http://staff.science.uva.nl/~leo/lego/diff.html [science.uva.nl], apllied here: http://technicbricks.blogspot.com/2008/09/tbs-techtips-17-adder-substractor.html [blogspot.com]
Re:Hydrostatics... (Score:3, Informative)
They were used in cars, back in the '60's. The actual name of the transmission escapes me right now, but they came in both mechanical and hydraulic flavors. One gave you more torque, the other more power. Bah, and I'm sure they weren't called hydrostatic, but they could do exactly the same things. GM put them on their super-blocks.
Re:Brilliant. Go Steve! (Score:3, Informative)
It has two - he just renamed one of them as the "control shaft".
NTSHF,MAN.
Re:Differential, anyone? (Score:3, Informative)
I agree, the motors are not torquing against each other, that would be very inefficient.
But the control motor will be be subjected to torques related to propelling the vehicle. It doesn't just "turn the gear".
Example: Let's say the control shaft is rotating at a rate r. When the control shaft rotates faster, at rate 2r, that would be a higher gear (in other words, the output shaft would have higher speed and lower torque than the input shaft). If it's rotating at rate r/2, that would be an easier gear.
Now, with the control shaft rotating at r, let's say the vehicle experiences a reaction force (e.g. friction, or going up a hill). This torque against the output shaft will be transmitted back to the engine, obviously trying to make it go slower. But the control shaft is equally linked to the drive train. The reactive torque at the output shaft will try to slow down the control shaft (because slower rates, like r/2, are easier gears, and the system is continuous - there's nothing locking it into a gear). So in the same way an outside reactive torque places a load on the main engine, it will also place a load on the control motor.
Re:something to hide? (Score:5, Informative)
Then finally at the end they showed the back and surprise, there's another motor there
They mention the electric motor 2 minutes in, and they constantly talk about driving the bottom shaft, implying you are providing some sort of power input. They didn't show the back of the device for a while because looking at an electric motor is less helpful than seeing the output when trying to understand how the thing works.
As they wrapped up the video they did admit that this little kink is going to be the determining factor in whether or not it's a useful design
They spent most of the video trying to explain how the device works, so understandably they get to the application stuff only at the end. He just showed the device working perfectly fine with an electric motor- you don't need to work out a continuously variable input from the main motor unless you really want to. As for the efficiency, the input power is exactly the main concern, but it sounds perfectly plausible for this input to require minimal power. As they mention, the electric motor isn't seeing any of the main motor's power, so the required power for it can be very small.
I agree vibration issues and robustness have yet to be seen, but the device is simple enough it should be feasible. Engineering this from a demo to a working transmission for a full-size motor can be as much work as developing it in the first place, so it may be a while before we see where this goes.
Re:Brilliant. Go Steve! (Score:4, Informative)
No, the most efficient point is at peak torque. That's where the engine is able to produce the most energy for a given amount of gas. The horsepower peak is where the engine is producing the most power (energy/time). It is not necessarily it's most efficient point unless they coincide which is rare.
Re:Automatic transmissions fail before engines, no (Score:3, Informative)
> Show me a dry clutch as used on most cars that outlasts an automatic
> transmission.
any that is being operated by someone who knows what the hell he is doing.
Tractors don't use torque converters. There's a reason for that.
Re:Brilliant. Go Steve! (Score:3, Informative)
I hope you're not saying what I think you're saying. Transmissions CAN'T increase horsepower. All they do is keep the engine from stalling by trading speed for torque. Horsepower is rotational speed X torque so the total horsepower doesn't change just the ratio of torque to rotational speed.
I think the transmission design is very cool and I'm amazed that someone can still come up with new ways to combine gears that haven't been done before. In fact, there was a post claiming someone had come up with a substantially similar design so maybe it isn't really new after all. For safety reasons the D-Drive will probably still require some sort of clutch since a sudden failure of one of the inputs could do really bad things to the driver and the vehicle.
Re:Brilliant. Go Steve! (Score:3, Informative)
You've got the volumetric efficiency relative to rpm part backwards. Volumetric efficiency goes down with rpm. Thermal losses go up as surface area of cylinder goes up. However, pumping losses etc go up with rpm. So, the most efficient engine is one that is able to produce the most torque out of the smallest displacement. Or in other words, run at the lowest rpm to meet application's power needs. This is what lies at the heart of why you see in countries where fuel is more expensive than in the US the majority of cars sold are turbocharged diesel engines even though these engines are much more expensive to make than gasoline engines -- they get high power at low rpm the way large engines do but have lower surface area in cylinders). In other words, they are large engines stuffed into small displacement using positive pressure induction and high compression ratio. Another example would be how, if you have a manual transmission car, you'll notice that operating at higher rpms exponentially decreases mpg. A corvette with almost twice the power of a car like a Honda S2000 will actually get better gas mileage in any conditions where the drivers are using the full power of the vehicles (eg racing of course but even just driving them like sports cars are designed to be driven on mountain roads or whatever).
Re:Brilliant. Go Steve! (Score:3, Informative)
Re:Fuel economy (Score:3, Informative)
This is wrong; the Prius uses only toothed gears as well. The previous generation used a chain drive in addition to gears, but the current generation uses just gears.
The Prius "CVT" is very unlike any other CVT, so people often differentiate it by calling it an eCVT (for electric), since there are no friction components.
Re:Brilliant. Go Steve! (Score:5, Informative)
Not true. Volumetric efficiency is measured as the the volume of air taken in on each stroke vs the displacement of the cylinder. So if 1 liter of STP (Standard Temperature and Pressure) gets drawn into the cylinder, and the dispacement of that cylinder is 1.2 liters, the total efficiency is 1/1.2 (or about 83%). At 0 RPM and 100% throttle (well, any throttle position that isn't completely closed), volumetric efficiency is always 100%. But as the engine starts turning (at full throttle, otherwise the vacuum drawn by the throttle restriction will reduce efficiency), the actual efficiency will depend on intake design. Considering that OTTO cycle engines use valves, air is only drawn in 25% (about) of the time. So the vacuum drawn trying to draw that air in will cause the efficiency to drop. However, intake runners are designed for this. So basically, when the valve closes, the momentum of the air causes a pressure build up behind the valve. That pressure will cause the air to reverse direction. This leads to a harmonic wave in the intake runner. The frequency of the wave is dependent on the design of the intake runner (cross-sectional area, cylinder volume and length mainly, but curves and other obstructions do play a part). If the valve opening is timed properly with this frequency, the incoming pressure wave from the harmonic will actually force air into the cylinder. That's how some racing engines can actually achieve a higher than unity volumetric efficiency at a specific RPM. It's all relative to the design of the engine. Some engines may be designed for 2000 rpm. And increasing the RPM over that WILL decrease VE. But you cannot say as a general rule that VE is inversely proportional to RPM, because it isn't. And pumping losses are directly proportional to VE (in fact, the pumping losses are DUE to VE below 100%).
You do have a point that thermal and mechanical losses do increase with RPM (Mechanical due to friction, thermal due to the increased movement of air around the parts). However, your reasoning behind diesels being more previlent is flawed. It's not because they operate at a lower RPM. It's because of a few reasons. First off, diesel is denser (energy/volume) than Gasoline while still having a similar stoichiometric ratio with air. Secondly, diesels are typically built without a throttle blade. That means that even at idle or lower power settings, there is no restrictive plate to draw a vacuum (and hence harm VE). Since diesel doesn't behave as bad as gasoline when run lean, they typically control power output by controlling the fuel flow. Third, diesel engines tend to burn much hotter than gas engines (the flame front is significantly hotter), so there is a more complete burn. You combine these effects, and you can see why they are more efficient (and it's not because they run slower). The reason that diesel engines typically run "slower" is two fold. First, since diesel engines don't use spark plugs, timing is controlled by the mechanical fuel injectors (direct injection). They were simply not fast and accurate enough to time at high rpm. The second reason, is that diesel is slower burning than gasoline. So at higher RPMs, there's a large chance that combustion won't be complete when the exhaust stroke starts (resulting is a large drop in efficiency and a large increase in mechanical stress).
Re:Brilliant. Go Steve! (Score:5, Informative)
It's quite different from the HSD in that it has three inputs, contrary to what GP said - one power input, and two control inputs, both of which ought to require just a fraction of the input power to control the input/output gear ratio.
Real engineers disagree on the "inventor's" website:
http://infinitelyvariabletransmission.com.au/wp-content/uploads/2010/05/dDrive-Transmission-Report.pdf [infinitely...ion.com.au]
"The torque provided by the Control shaft will typically be of the same magnitude as the torque provided by the Input shaft."
"The Control shaft (and associated mechanical elements) should be sized to this torque requirement
accordingly – the Input and Control should be considered as parallel power paths rather than as ‘power’
and a ‘control’ elements respectively."
So this whole thing isn't very useful. To add this as a transmission to a power motor, you need
one ore two additional motors of same power with variable speed and enough torque at any speed.
Re:Brilliant. Go Steve! (Score:4, Informative)
Re:Fuel economy (Score:3, Informative)
All mileage is from fueleconomy.gov, highway mpg. City is lower, of course, but these all looked like they could average 30mpg across the board if a good chunk of your driving was highway.
Toyota Camry (four door family sedan) - 33mpg
Saturn Aura (four door family sedan) - 33mpg
Chevy Malibu (four door family sedan) - 33mpg
Nissan Altima (four door family sedan) - 32mpg
VW Jetta (smaller four door sedan) - 42mpg
VW Golf (smaller three door hatchback) - 42mpg
Audi A3 (five door hatchback) - 42mpg
I actually drove an Altima for a year and a half in 2005, it was nice enough for a professional and big enough to fit four adults in relative comfort and carry luggage in the trunk. It averaged about 27-28mpg across the board. Any 4 cylinder petrol ICE with 2.0L or less displacement can get close to 30mpg, if the car manufacturer is trying. Anything bigger than that (engine size) - you have to resort to fancy tricks like hybrid or what have you.
You touched on where it doesn't make sense - and I'm right there with you : my SUV averages about 16mpg and when my daily drive was less than 10 miles per day it didn't matter. When I got a temporary reassignment and was driving 60 miles per day, and gas was $4 a gallon, on paper it looked like I'd save more each month in gas than the payment on a new hybrid. I considered it, but ultimately kept my SUV (makes more sense during the winter - clearance and 4wd are more important to me during the snow season.)
Re:Brilliant. Go Steve! (Score:3, Informative)
Re:Brilliant. Go Steve! (Score:4, Informative)
manuals [...] are a small percentage of cars
Nitpicking: that applies in the US. In a great part of the world it is the contrary. As an example, in France, driving school and driving tests are by default on manuals. If you take the test on an automatic, you get a license saying it is limited to automatics. The times I've bought cars, the dealers never even asked if I'd prefer automatics.
In other news, automatics have reputation of being less fuel-efficient and slow to kick in when you quick acceleration. Maybe that is no longer true, but the reputation sticks.
Re:Brilliant. Go Steve! (Score:4, Informative)
it may increase the life of the car/machine.
Sadly, this may kill the project.
It seems that manufacturers don't want to build things that last forever. Planned obsolescence is the current fashion.
Planned obsolescence because of new safety measures, new gadgets on-board and new designs yes. Because of breakdowns, no. Perception in the eyes of buyers about how reliable your brand of cars is, can kill the sales of any car if people think your car breaks down faster than other cars. Toyota sells so many cars precisely because they don't break down (or are perceived as more robust) as US cars. In fact, it's incredibly difficult to sell US made cars in Europe because of exactly this problem. So any car manufacturer who can make his cars more reliable, in whatever way, *while not heavily impacting the manufacturing cost*, will do so.
Re:Brilliant. Go Steve! (Score:4, Informative)
Not for windmills, generators and the like, keeping those at a constant RPM can be more useful independant of input power. It may also prove useful in electric cars, as if you can keep everything always working at it's peak efficiency you can go further on less power. There are many situations where it would be better to have a constant RPM in and a variable out (or vice versa), the question then becomes are these as easy to work with and reliable as existing gearboxes. Planetary gears, work at approximately the maximum efficiency most of the time, these theoretically can work at maximum efficiency ALL of the time.
If they can be a drop in replacement for existing tech, then I can see this taking off, if not or they require complex setups/electronics it might be a more niche product. Also how efficient this tech is, in comparison with existing systems, as if the gearbox itself is only 75% efficient, this would rule out the benefit of having an infinietly variable ratio. Pulling some numbers out of my ass I believe gearboxes are some where in the 95-99% efficient
Re:Transmission innovation (Score:3, Informative)
Well this D-Drive resembles the Thompson coupling in that they both seem new but they're really not. The Thomson coupling is a (admittedly nicely packaged) double cardan joint, while the D-Drive is a powered-planetary, already used in infinitely variable transmissions before. I'm not sure if that particular arrangement existed before, and it's nice to see that novelty is still possible in basic mechanics, but similar devices with powered neutral already exist (for example in tractors).