Green Car Congress  
Go to GCC Discussions forum About GCC Contact  RSS Subscribe Twitter headlines

« Small modular reactor company Gen4 Energy will not pursue DOE SMR Licensing funding | Main | Neste Oil sells first batch of NExBTL renewable diesel to the US market »

Print this post

Fallbrook Technologies Inc. developing variable speed supercharger drive using its CVP technology

28 April 2012

Nuvinci2
Performance of supercharged Mustang with and without NuVinci CVP; variable ratio vs. 1:1. Source: Fallbrook. Click to enlarge.

Fallbrook Technologies Inc. is developing a variable speed supercharger utilizing its NuVinci continuously variable planetary (CVP) technology. (Earlier post.) Fallbrook has targeted and is soliciting select automotive OEMs for such a variable speed automotive supercharger.

Fallbrook says it has been working closely with a tier one automotive equipment supplier on the development of the device. Test results from that supplier have demonstrated potential fuel-saving, engine down-sizing and/or down-speeding opportunities without adversely affecting performance and drivability.

The NuVinci CVP uses a set of rotating and tilting balls positioned between the input and output components of a transmission that tilt to vary the speed of the transmission. Tilting the balls changes their contact diameters and varies the speed ratio.

Performance gains result from boost optimization over a wider power band, particularly at low engine speeds. NuVinci prototypes designed for use in an OEM application have also passed automotive class durability testing by the tier one supplier.

Nuvinci1
Nuvinci3
Schematic of variable speed supercharger drive. Click to enlarge.   Prototype variable speed supercharger drive. Click to enlarge.

Fallbrook believes, based on testing and independent analysis, that vehicle manufacturers can utilize smaller, more efficient engines with no loss in performance or drivability, thanks to the capability to tailor supercharger boost to driver demand offered by a NuVinci-enabled supercharger.

By controlling supercharger speed independent of engine speed, the NuVinci CVP enables ingestion of only the airflow required by the engine with little to no bypassing, thereby minimizing bypass losses and their associated NVH issues.

In light of the successful test results, Fallbrook and the tier one manufacturer are currently in discussions with potential OEM customers for the NuVinci supercharger drive. Fallbrook believes the drive can be packaged easily, as the current prototype is designed to mate with an existing supercharger line of products.

Fallbrook initially demonstrated its development of a variable speed supercharger drive by designing and building a prototype system coupling a NuVinci CVP with an aftermarket supercharger.

The demonstration car is a 2008 Mustang Bullitt, equipped with a ProCharger supercharger, and a NuVinci DeltaSeries continuously variable speed drive. With assistance in tuning by Lingenfelter Performance Engineering, it demonstrates considerable performance increases at lower engine speeds, when the variable speed drive is activated. The Bullitt prototype has logged more than 3,000 demonstration miles, and remains operational today for regular demonstrations.

Nuvinci4
Simulated performance of downsized 2.0L I4 with Fallbrook supercharger drive. Click to enlarge.

Using an SUV equipped with a 3.6L V6 engine as a baseline, Fallbrook has also simulated the use of a downsized 2.0L I4 engine which has been supercharged in production. In the graph at left, engine torque is depicted on the Y axis, and engine speed on the X axis. The blue dashed curve represents torque from the standard 3.6L V6 engine.

A normally aspirated 2.0L I4 engine would result in the lower curve, producing about 175 N·m peak. By supercharging this engine (grey curve), more than 330 N·m can be produced, approaching the 350 N·m capacity of the larger engine. However, this peak output only comes at the top end of the engine speed range; the vehicle remains underpowered throughout most of the range.

The green area is the chart represents the increased low-end torque generated by a downsized gasoline engine, as compared with the same engine without the supercharger. The red line indicates that the smaller NuVinci supercharger-equipped engine performs on a par with a larger engine.

The NuVinci supercharger drive is part of the NuVinci DeltaSeries line of accessory drive solutions. The NuVinci DeltaSeries line eliminates the compromise of fixed ratio accessory drives by de-coupling accessory RPM from engine RPM. Other DeltaSeries drives in development include applications for HD vehicle cooling fans, high output alternators, AC compressors, and engine crank-mount units, which control the speed of the entire accessory beltline.

April 28, 2012 in Engines, Fuel Efficiency, Vehicle Systems | Permalink | Comments (48) | TrackBack (0)

TrackBack

TrackBack URL for this entry:
http://www.typepad.com/services/trackback/6a00d8341c4fbe53ef0168ead98753970c

Listed below are links to weblogs that reference Fallbrook Technologies Inc. developing variable speed supercharger drive using its CVP technology:

Comments

This could become another way to further downsize ICEs from 2.0 L to 1.2 L or so.

Don't modern variable-pitch turbochargers do the same thing, only more efficiently, since they use some of the exhaust waste heat instead of adding load to the engine? E.g. Ford's Ecoboost engines.

This is cool tech, but I think ICEs are moving more towards electrification of accessories and away from belt drives altogether.

Where were all these ICE gains before EVs hit the market with 100+mpge..

Very good question Kelly. They were in neutral.

Even a variable-geometry turbocharger requires a certain amount of airflow and time to spool up.  A supercharger doesn't have that (though I think electric may be better than mechanical drive).

It's certain that a supercharged engine wastes a lot of energy as exhaust pulses.  A compounding turbine can capture that and feed it back using e.g. BAS-type motors, and I believe we've seen some concepts with all of those elements.

@E-P: I don't think responsiveness is much of a problem with the latest turbo designs, while energy-efficiency has become the overriding concern. This CVT/supercharger enables downsizing, which has efficiency benefits; I just think it's likely to be too little to late. Electric supercharger/turbocharger combos are another way to address any turbo-lag/low RPM issue with turbos. Also, anything relying accessory belt drive is likely to be a short term solution, IMHO--I think belts are on the way out.

@E-P: I don't think responsiveness is much of a problem with the latest turbo designs, while energy-efficiency has become the overriding concern. This CVT/supercharger enables downsizing, which has efficiency benefits; I just think it's likely to be too little to late. Electric supercharger/turbocharger combos are another way to address any turbo-lag/low RPM issue with turbos. Also, anything relying accessory belt drive is likely to be a short term solution, IMHO--I think belts are on the way out.

Where were all these EVs before "EVs hit the market with 100+mpge"?

Nick, I think you're right about belts; the electric bus, whether 13.8 V, 42 V or higher seems to be the target.

The question is what's going to wind up on it, and how.  A battery or ultracap plus BAS can make up for turbo lag, which would allow a supercharger/TIGERS combo to be replaced by a much smaller turbocharger.  VVT implementing the Miller cycle recovers the exhaust energy recycled to supercharging as crankshaft work.  The question is, how much does it cost vs. rolling balls?

The one thing we can know for certain is that the answer changes over time.

Too little too late, Nick?
How about considering this: A NuVinci on one end controlling the supercharger, and another NuVinci on the other end moderating the exhaust compounding turbine, feeding excess exhaust energy back to the engine? No need for energy-wasting "waste gate."

The cost and weight of this set up will be a lot less than an analogous electric setup with electric motor/generator pair, allowing higher market penetration and more fuel saving potential. There may be a modest gain in efficiency as well when electrical losses are avoided with this totally-mechanical setup.

I'm real excited to see this concept demonstrated successfully on a highly-functional, high-performance prototype. I wish the best for their success.

@Roger
I fully agree with your analysis! This would be an interesting concept. The only comment I would like to add is that you may need a two-stage turbine setup. The reason is that with a very high level of turbocharging, the pressure drop over the turbine would be too high to get high efficiency in only one stage. Recall that a conventional turbocompound engine has one turbine in the turbocharger and one “power” turbine, i.e. two turbine stages. The ideal two-stage “power” turbine could be a radial turbine in the first stage and an axial turbine in the second stage.

Agree, Peter.
Two-stage turbocompounding in an Otto-Diesel cycle engine is more efficient at part-load than a Miller cycle engine with a single turbocompounder, while the Otto-Diesel engine has higher power density.

Replace an 3.6 with a 2.0 engine means roughly halve weight and cost of the engine.
It 's amazing the constant torque at 350 Nm in the range between 2000 and 5000 RPM.
Excellent solution as a range extender especially for trucks. The engine designers are playing theirs final trump and is better for them to do so now, before it is too late..

"Where were all these EVs before "EVs hit the market with 100+mpge"?"

Like the enabling NiMH EV battery patent, sitting on a oil/auto shelf.

Face it, as with average auto mpg being in the twenties for a hundred years, big auto/oil, especially US, are happy with the poorest gas mileage the traffic will bear.

Directly, or indirectly, electric vehicles are responsible for the 20% increase in mpg during the last four years.

@Kelly
EVs are not necessarily better than HEVs in a well-to-tank comparison. With US electricity mix, they could even be worse than HEVs. Look at page 116 in the report below. Electricity via plug-in HEVs seems to be the most efficient way to substitute fossil fuels.

http://web.mit.edu/sloan-auto-lab/research/beforeh2/files/kromer_electric_powertrains.pdf

You cannot blame EVs for USA's (any many others) poor energy mix. In our area, we use almost 100% clean hydro and EVs will be much cleaner than any up to date past, current and future ICEVs.

Overnight charging will be almost free (or at reduced rate) because less than 35% of the clean power available is used between 22h and 06h. Many new hydro plants are being built to ensure full energy availability with one or two EVs per home plus increased exports to our good neighbors.

Many local small towns have already installed free public charging stations for short term charges (up to one hour and/or 10 KWh or so) on commercial streets, short term parking lots etc.

Peter XX, whichever report - electricity is always several times more energy efficient than ~30% ICE efficiency - whatever it's source.

Israel/US/Iran seem about to close, perhaps radiate, the Straits of Hormuz and most tanker traded oil.

Then US gas will top $5/gallon, gas-guzzlers will be dumped again(2008), and headlines will read 'electric vehicles are the answer'.

Peter XX keeps citing the Sloan study with the questionable assumptions laid bare on page 120.  How is a PHEV charged by a NGGT going to be more efficient than an EV using the same, given that the ICE in the PHEV is both less efficient and using a more carbon-intensive fuel?  It's impossible.

He's been questioned about this before, and never answered.

Roger, mechanical drives have been a major headache for turbocompounding since it was invented.  Since the world is going electric, it makes more sense to put a generator on the turbine and do it with wires.  A starter motor sized for regenerative braking and capable of doing launch assist can also feed turbine power back to the crankshaft.

The article makes almost only half hearted claims for better efficiency ("demonstrated potential fuel-saving" and "smaller, more efficient engines" one place each).

I think because it would stink.

The reversion to MORE mechanical hardware can be technically gratifying - but just to clean up the small bit of turbo delay?

This does NOT sound like the way to go for fuel efficiency.

They say "with little to no bypassing" I should hope "NONE" - talk about losses!

Variable speed gear driven superchargers provide an easy excellent match for maximum power but modern modeling/analysis tools can provide the same but with much better efficiency, with a turbo.

Don't forget that without Atkinson style over-expansion (or a turbo), a supercharged engine has shockingly high losses out the exhaust pipe.

Turbo componding is way too costly.

@E-P,
True, mechanical drive has been headaches for turbocompounding before NuVinci. There were two issues:
1. torsional fluctuation in the crankshaft wreaking havoc on the tiny high-speed gears of the turbine wheel. Conventional solution for this is the use of fluid coupling, which adds friction.
2. fixed gear ratio, meaning that the turbine wheel got bogged down at engine high load but lower rpm and at lower engine load the turbine wheel can rob power from the crankshaft.

NuVinci can solve both of above problems by
1. allowing some degree of slippage between the ball surface and the outer bell surface. Special fluid layer between the balls and bell surface prevents metal-to-metal contact wear.
2. variable ratio between turbine wheel and crankshaft allowing optimal power transfer between those two without bogging down the turbine wheel when high load is applied to the engine by allowing the turbine wheel to speed up out of proportion to engine's speed.

@TT,
Turbo compounding is way too costly? Perhaps so for ligh-duty engines, but not so for heavy-duty applications that are very sensitive to the cost of fuel.
Fuels are way too costly...

@TT,
Another issue: Supercharged engine has high losses?
That is true if a heavy-duty supercharged engine got boosted all the time.
However, in a sleek sport car with low aerodynamic drag and light weight, the engine can run most of the time with hardly any boost, thanks to the NuVinci variable drive ratio. The engine is way downsized, from 6-cylinder 3.5 liter to 4-cylinder 2 liter, thus operates much more efficiently in ordinary driving.

However, when there suddenly occurs "the need for speed," the boost will come on strong and almost instantaneously thanks to the variable drive ratio, and the engine can come on even stronger than a much larger NA engine. Just look at the chart comparing the torque curves of different engines and boost options.

Since the "need for speed" does not occur often, the net fuel saving can be tremendous! Those with the frequent "need for speed" probably will be swayed by the NuVinci's instantly-gratifying boost and won't mind the extra fuel consumption. For high-speed racing with less frequent pit stop, add a NuVinci-mediated turbocompounder.

@Engineer-Poet & Kelly
Why don’t you read the MIT report? You will find the answers there. I see no reason to explain again what others already have explained a long time ago.

If you do not believe prof. Heywood et al. you should realize that they also published a peer-reviewed paper on from this study. If there was something wrong in the study, why did not the reviewers react to get it corrected? I am convinced that both the MIT researchers and the reviewers know a lot more than both of you. The only problem seems to be that you do not like the results.

The reviewed paper can be bought from SAE. To read this paper, you simply have to pay, so you will of course bring up that issue once again…

http://papers.sae.org/2008-01-0459/

@Roger Pham
Thanks Roger, excellent explanations! I would like to add a couple of comments about the efficiency for the “transmission” to the crankshaft and related issues.

If we assume a turbine speed of 50-60 000 r/min and 2 000 r/min in engine speed for a heavy-duty engine, the ratio of the reduction gear would have to be in the range of 25-30:1. The fluid coupling in conventional turbocompound systems has a slip in the range of 3-5% and some additional losses also occur in the reduction gears. An electric drive system might have somewhat lower total transmission efficiency but this is compensated for by the variable ratio that the electric transmission can provide. The latter advantage can also be achieved by the NuVinci variable speed transmission. The question is if the total losses are smaller than from an electrical drive. To achieve high efficiency, the fluid coupling should be omitted, as you suggest. Other experiences show that the fluid coupling can be omitted for a positive displacement compressor but a compound turbine has much higher inertia, so it will be more difficult to avoid a coupling in this application. If we return to the topic of the article, we can see that NuVinci aim to drive a positive displacement compressor but it is interesting to take the concept one step further by also include compounding in the discussion.

Electrical transmission loss will be considerable. The very high frequency AC current from the turbocompounder generator will have to be rectified at about 10% loss. Loss in the generator will be another 10%. Then this DC current will go to an inverter to drive the engine's starter/motor/generator (BAS) at another 5-10% loss. The BAS motor will have another 10% loss. Adding all the losses of the above will be around 30-40%.

By contrast, from turbine speed to crankshaft reduction can use 2-stage gear, each with 3-5% loss. The NuVinci is expected to contribute to another 3-5% loss. Total losses from mechanical transmission is about 9-15%. This is comparable to the efficiency of a mechanical transmission between the engine and the differential gear housing.

Verify your Comment

Previewing your Comment

This is only a preview. Your comment has not yet been posted.

Working...
Your comment could not be posted. Error type:
Your comment has been posted. Post another comment

The letters and numbers you entered did not match the image. Please try again.

As a final step before posting your comment, enter the letters and numbers you see in the image below. This prevents automated programs from posting comments.

Having trouble reading this image? View an alternate.

Working...

Post a comment

Green Car Congress © 2013 BioAge Group, LLC. All Rights Reserved. | Home | BioAge Group