Startup commercializing thermo-acoustic Stirling technology for combined heat and power for homes
Mazda showcasing vehicle connectivity application platform at CES

NASA Glenn develops automated flywheel pulse-and-glide system; improving fuel economy up to 40-100%

Innovators at NASA’s Glenn Research Center have developed an automated pulse-and-glide technique using a flywheel energy storage system for on-road vehicles; the technology, which NASA Glenn says can improve fuel economy over existing internal combustion or battery hybrid systems by 40-100%, is available for licensing.

Drivers can use a manual “pulse-and-glide” (PnG) driving technique—accelerating and decelerating an automobile in cycles of approximately 10-30 seconds—as a way to improve fuel economy. A 2009 SAE paper by a team from Virginia Tech and Argonne National Laboratory found that a simulated PnG driving strategy in a Ford Focus delivered 33-77% fuel economy improvement depending on different speed ranges and acceleration times. The fuel economy results of a 2004 Toyota Prius from simulation and testing showed 24-90% fuel economy improvement with PnG drive cycles compared to steady speed results.

The downside of such a technique is that it currently requires sustained attention from the driver. (Further, noted Lee et al. in their 2009 study, a driver in a conventional vehicle must shut off the engine manually to apply this strategy optimally.)

NASA Glenn says that its automated pulse-and-glide flywheel presents an economical, reliable, and long-term solution for a significant improvement in fuel economy performance without requiring driver intervention. Unlike chemical batteries, which also have a short life span and high replacement costs, flywheels provide the power and energy requirements necessary for a robust pulse-and-glide technique, the researchers said.

The flywheel PnG system delivers power and energy between 8-20 kilowatts (kW) and 2-3.5 kilowatt hours (kWh); system lifetime is approximately 10 years.

NASA says that it is seeking a patent on the technology.

NASA is not alone in its current interest in expanding the use of automated PnG capabilities. As one example, in February, Ford Motor Company filed a patent application on technology developed by researchers in the UK for leveraging the pulse-and-glide approach in engine control to maximize fuel economy.

The approach in essence allows small variations in vehicle speed around the threshold speed in order to operate at or close to the optimal BSFC. Using the pulse and glide approach, the vehicle speed will have a mean value around the threshold speed, but the fuel consumption will be reduced in comparison to a constant fueling regime.

As another example, in 2012, Volvo Car Corporation filed its own patent on a new controls-based way to utilize the “pulse and glide” technology not only in coast mode but also in normal driving conditions.


  • US Patent Application Nº 20130226420: Vehicle Speed Control Apparatus And Method

  • EP 2476572 A2 Method for speed control, speed control system and device for use with the speed control system

  • Lee, J., Nelson, D., and Lohse-Busch, H. (2009) “Vehicle Inertia Impact on Fuel Consumption of Conventional and Hybrid Electric Vehicles Using Acceleration and Coast Driving Strategy,” SAE Technical Paper 2009-01-1322, doi: 10.4271/2009-01-1322



This could be very big - it looks like everyone is looking into it.
I wonder will they be able to combine it with regenerative braking so as to have a single KERS for a pulse / regen hybrid?
If you were able to use an ICE at maximum efficiency for nearly all the time, we would see very good mileage from them, without the range/cost problems that we see with batteries.


I had this idea long time ago, one problem is to maintain the catalytic exhaust hot enough to operate properly, but not unsurmountable problem. The main problem is to keep a seamless transition between pulses and glydes so as it doesn't affect the driving experience


Hypermilers have been using PnG for years but as the article points out "it currently requires sustained attention from the driver" and very have mastered the technique. If it can be automated we'll be looking at millions of drivers doubling their MPG.


>> very few have mastered the technique <<


Im interrested to buy but not now as it is not on the market and not in 2 to 3 years as my current car is still good for another 10 years and also i will like to follow this on a long term basis to be sure of his worth. But in 2023 i will buy a used car and a small car year 2017 approx with this gadjet might interess me.

Account Deleted

Many of the techniques used by hypermilers like Wayne Gerdes can be applied much more safely in a hybrid electric vehicle. Thanks to software control of cruise control and other engine system controls it is technically feasible to get very large gains in fuel economy. Regenerative braking and engine shutoff are best handled by automated systems rather than manual techniques.

Also these processes are not limited to the size of vehicle or type of hybrid energy recovery. As pointed out in the article, others like Ford are also exploring these techniques. The Porsche Panamera eHybrid uses a somewhat similar system. Hyundai and Honda are also using an approach like this in their latest hybrids.


Together with 10 and 12 speed automatic transmissions, this is one more mechanical gadget to extend the useful life duration of a dying ICE technology.

Will it be enough to push back the expected 2016-2018 tipping point, i.e. when pure ICEVs will start to lose grounds to electrified vehicles?

On the other hand, large enough units could be a positive asset on most city buses, garbage trucks and urban delivery vehicles?

Roger Pham

PnG has been the technique used by hypermilers to vastly improve on the mpg of even HEV's. Even on conventional ICEV on empty road, mpg can be doubled simply by accelerate the car then turn off the engine and coasting until slow speed and then repeat.

I'm afraid, though, that the flywheel unit may be bulky and heavy to accommodate the high capacity of 2 to 3.5 kWh. With lithium battery having high cycle life like LiFePO4, perhaps an HEV may be more practical.

However, ultimately, a PHEV would be best and would make the PnG issue moot. We now have technology for a PHEV-50 that can be competitive with an ICEV in term purchasing cost, weight, and internal space.


There are?(were)laws regarding coasting considered unsafe in when I sat my licence tests.

This may have changed

Regarded as Lacking control of motor vehicle


Wonder how the electric vehicle freaks will react to this development?


@Mannstein, And I wonder if the anti-EV freaks are getting aroused by this? LOL

Many/most of the "EV Freaks" get into it because they either don't like to see oil being burned because they're "green" or else they don't like oil being burned because we get too much US oil from other sources and give an excuse for the US to spend a fortune on military in the Middle East (my particular pet peeve).

Either way, ANYTHING that cuts down on oil consumption/use is good. If someone hates something that helps that because they "claim to be green" then they're just narrow minded jerkoffs who make things worse. I'm not a hydrogen proponent. But if it actually works and cuts back on oil consumption...then bring it on.
Maybe if you stopped attacking the "EV Freaks" and they stopped attacking people like you...we could actually make some progress.

Or is it more important to you to be "right" in your own mind?


It strikes me that it's nonsensical to store 2 kWh of energy when the kinetic energy of the vehicle is only about 300 Wh and the energy consumption in 30 seconds of cruising is likely to be only 120-170 Wh.  If you size the flywheel so it could absorb the vehicle's complete KE in a braking event even when it was at peak cruising energy you're talking 500 Wh, not 2 kWh or more.


You bring up a good point. If they were using batteries and trying to stay in a sweet spot (say 40% - 60% DoD) to greatly extend battery life, then I'd understand them trying to do 2kWh or more. But I don't think a flywheel has any of those restrictions so why size it so large???

Frankly, if I was doing this, I'd be targeting supercaps with some of the newer ones that could do like 20Wh/kg. Having something that could handle a million or more cycles and approaching 99% efficiency, round trip, would be great.


My previous comment reveals just how long ago I last did a licence test, the papyrus is getting a little dog eared.

I guess this would have to be designed as not to cause road speed variations wich would be inconvenient at best to other road users.

While seamless kers type sustained coasting makes some sense for an ice or hybrid,with most vehicles having an embarresment of processing power, it should be compared to capacitor storage as the efficiency would likely be very similar.
Capacitors would likely would have several advantages in the hybrid including extended storage life, increased effective battery capacity, the usual battery buffering for regenerative storage, so lower parts count.

There is also the matter of universal application across the entire vehicle parc.
An ice only may find flywheel in favour for the same reason, smaller parts count.
I am less certain as to the gyroscopic effect of single rotor Kers but contra rotation would not add too much complexity or system losses if it were negative.

Can I also remind us that appropriate application of technology doesn't lend itself to a one size fits all concept
It has been shown over and over that diversity holds the best opportunity in future proofing by covering as many bases as the local niche markets will support as well as providing a wider test bed and options that have yet to find application.

It is a bit concerning to think that 'all we can muster and more' has such a ready market according to energy use
projections. I believe it is misleading to think in terms of reductions of 30 - 70% etc when the evidence points to the expectation and desirability? of the majority world for development inclusion. Again a dignified option of a lower (national) footprint fits well with the global solution in my mind at least.


I've said it before and I'll say it again: All NASA engineers should be re-tasked into energy research rather than shooting big obects into space.

Good work, keep it coming, NASA.

By the way, it does not have to be a flywheel. Automated PnG works fine with any storage medium that has high energy density, sufficient power density, low loss and high durability (number of cycles, lifetime)


300-500Wh is pretty much how they size capacitors for cars.
I was having a disagreement with someone on here about the needed size of a capacitor pack, so I am glad that you confirm my figures.

william g irwin

Hey guys, don't forget the 4rth dimension! If we can cut half the cylinders in/out w/o jarring the driver, why not extend that to cut the whole engine in and out in single/double crank rotation cycle bursts (very fast cycles!). This seems like a logical next step between start/stop and cylinder cutout, and is consistent w/start stop techniques at intersections too, except the momentum of the existing flywheel (maybe punched up a bit) could keep the engine turning, and the tranny fluidics might absorb the fast pulses. We already have the computer controlling the motor and clutches anyhow! Sounds inexpensive!


Can it be that:

1. Flywheels are best suited for pure ICEVs

2. New higher efficiency supercaps are best suited for electrified vehicles (HEVs, PHEVs, BEVs and FCEVs)?


Is that not just stating the obvious? A car has to possess at least one electric motor/generator before an ultracapacitor can be useful in terms propulsion.

The comments to this entry are closed.