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electric supercharger

electric supercharger

electric supercharger

I am familiar with turbo chargers and belt driven superchargers, but recently read a little about electric-driven superchargers.  They can run off batteries or an alterator.  Anyone else know anything about them, or have experience with them?

RE: electric supercharger

We tried a powerful short-burst electric "turbo-charger" of sorts, on buses in Los Angeles. The intented purpose was to eliminate the puff associated with older Diesel engines. It worked, but for stop and go driving it ended up requiring more electrical power than even a modified charging system could provide.

RE: electric supercharger

They're all over eBay at the mo........

With varying degrees of claims.......



"It's not always a case of learning more, but often of forgetting less"

RE: electric supercharger

We measured the power consumption of a supercharger on a 4 litre V6. It was around 40 hp.

Have you seen a 40 hp electric motor? Can you imagine running one on 12 V?

Even if we assme that the blower was only half as efficient as a modern design, and you only needed half the airflow, that is still 10 hp, or several hundred amps.


Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: electric supercharger

The use of electric superchargers has only started to become interesting and viable with the advent of the 42v electrical system - I doubt there is anything particularly useful running on 12v, especially some of these things you see on e-bay!

The use of an electrical supercharger is attractive in a number of ways, not least the fact that boost ceases to be a function of engine speed. Without the need to worry about wasted energy through the compression of air that is simply going to be sent through a bypass valve.


RE: electric supercharger

Electrically assisted turbochargers are starting to break ground as engine downsizing catches on.  But I've yet to hear of a car in production with one.  A google search on "electrically assisted turbocharger" score many good hits.

RE: electric supercharger

Thanks for the responses.  If you can, take a look at boosthead.com, let me know what you think of this guy's setups.  Thanks.

RE: electric supercharger

How is boost not a function of engine speed.


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RE: electric supercharger

Boost is a function of the on-off switch.


RE: electric supercharger

Pat ?!?

Surely the whole point of the 'electric' part of the supercharger is that an electric motor drives a compressor which then produces boost pressure. Making boost a function of electrical supply to the motor.

A 'normal' supercharger however is a compressor driven by a pulley that is in turn driven by the crankshaft of the engine, with boost a function of the cranksspeed (engine speed?!?)

In the electrical system there is no compressor/crank coupling - so boost is not a functino of crank speed. You could, in therory provide full boost pressure with the engine not running.

Perhaps you are talking about massflow, which IS a function of engine speed, boost and also VE...In which case we are talking at cross purposes.


RE: electric supercharger


Even though the electric "turbo" we used was probably a different design, it was incredibly powerful. The REP fired it up in the main office. Though aimed at an open door 10 feet away, it still cleared all the papers off several desks. The thing I would question most is electrical reserves vs desired duty cycle.

BTW, the one we tried worked in parallel with the OEM turbo. It used a simple flapper valve on the output side of the OEM turbo. The electric unit came on as soon at the throttle was pushed, moved the flapper, and simply out blew the OEM turbo until OEM boost came up. When this happened the flapper would move back and the electric unit would shut off till next time. Worked great, but even with an automatic transmission it used too much electricity for commercial city driving.

RE: electric supercharger

250cfm... but at what pressure?  They will do zip for you if they can't create a pressure differential beyond 0 psi...

Dan - Owner

RE: electric supercharger

The last I understood these units to do is apply boost in the lower RPM torque curve area of a gas engine then taper off as engine HP/rpm builds up (using a controller).
Using this type application, the blower becomes a helper and does not run all the time but makes the overall torque curve quite high and flat where it is most needed.
I feel the smaller displcment engines benifit more for having the additional low end torque than trying to use this on large displacments that should already have enough reasonable torque.

I run a Kenne Bell positive displacment 1500 cc blower on a 5L v8.  It 'do make' the motor feel like a big displacment for throttle response from about 1800 rpm upward and is even better off idle before boost actually begins.

RE: electric supercharger

Boost is a function of airflow supplied over airflow used.

Airflow used is fairly well directly related to engine speed. A crank driven positive displacement supercharger also supplies air fairly well relative to engine speed. An engine with a crank driven properly sized roots blower will have an almost flat boost curve relative to engine speed over the normal operating speed.

I would expect an electric driven supercharger will only give constant boost if it is well regulated with pressure switches and controllers to control the electric motor well enough to overcome reaction times, relative friction and inertia and if the electric motor can provide enough power to keep up with engine requirements.

As mentioned earlier by Greg, this can be a very large electric motor, needing a very powerful electrical system to support it.

Crank driven simply requires a belt and two pulleys.

I guess, the question, or the quest will be, is the total package for the smaller engine and electric supercharger, smaller or larger than the larger engine with NA, turbo or belt driven or compounded belt driven positive displacement and turbo.


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RE: electric supercharger

I just followed the link.

So what is it supposed to tell me that explains away with any supporting data, any of the objections above.


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RE: electric supercharger

Just to add to the confusion, that is an electrically controlled mechanical CV transmission for a fairly conventional compressor. Not a bad way of doing it, but not really what this thread is talking about.

I like the idea of the all electric system. It would only activate at full throttle and it would run out of puff gracefully. But, on a 12V car I really don't see how to power it. Maybe an additional pair of deep discharge batteries in series, then switch them back to parallel for charging.


Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: electric supercharger

The link was for general interest rather being a direct response to the posting that came before it (yours). Some of the criticism of electrically driven supercharging was the electric power needed to drive the compressor.

If you drive the compressor electrically then its speed is not directly linked to engine speeds and you have a CVT of sorts. The problem raised by the criticism of the electric power required for electric supercharging can then be rephrased: how can you electrically control the continuously varying ratio between engine speed and supercharger speed, without all the supercharger power being electrically sourced?

Powersplitting the engine power to the supercharger and just using an electric motor/generator for controlling the ratio is one way to drop the electric power figures, and that is what the nexxtdrive supercharger does. It seems to have two motors, so that one can generate and one consume power, in a way similar to the Prius CVT.

So - without any supporting data, sorry - I think it explains away the need for large external electric power. I think electrical power would be reduced due to a power split mechanism, and that electrical power would be circulting internally between a generator and a motor.

RE: electric supercharger

$179. eBay electric supercharger = $ 12. boat bilge blower = free lunch.

RE: electric supercharger

This may be a miles off topic, but the best solution to all these turbo problems with todays technology, seems to be to combine a turbo with a positive displacement supercharger, (with the compressors simply run in series). This has now been succesfully done on three mass produced production engines.

Nissan did it with the March, a small hatchback not sold outside Japan, it combined a Garret turbo with a roots blower.

Lancia did it with the Delta S4, again a KKK turbo with a roots blower, and two intercoolers.

VW are doing it right now with the Golf GTI hatchback just released in Europe this year.

I built an experimental system like this myself over fifteen years ago, the results were exceptionally good in all respects.  The corporate bean counters are probably the only real obstacle to overcome, otherwise I am sure many more forced induction production engines would now be using this system.

It combines lag free low end torque, with high top end airflow.  The advantages of being able to keep boost pressure just above exaust back pressure should not be overlooked. The torque curve can be made any shape you wish to make it, and it is relatively simple. Initial cost is the only real disadvantage.

I very much doubt if an electric supercharger could beat it, if you also take into account the extra charging and battery capacity that would be required. If used constantly, the extra alternator load must rival the power requited to drive a supercharger. And a small supercharger would probably have less weight and volume than an extra lead acid battery or three.  

RE: electric supercharger


The following is from my post 20/06/06


I guess, the question, or the quest will be, is the total package for the smaller engine and electric supercharger, smaller or larger than the larger engine with NA, turbo or belt driven or compounded belt driven positive displacement and turbo


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RE: electric supercharger

I just though I would emphasize and expand on that idea a bit Pat.

Compounding still remains relatively unknown, even though the idea has been around for a very long time.

Many if not all long distance road diesels typically run a turbocharger compounded with a roots scavenge blower. They not only have plenty of torque !!!  but the specific power is not too bad either.

The same idea works wonderfully well on a four stroke  gasoline engine.

RE: electric supercharger

This has been one of the most entertaining technology to watch progress and squirm over the years. The obvious (or should be) issue of power vs. required work of electric air chargers has been bent, distorted, manipulated and flat out ignored to push allot of agenda depending on the number of investors and or customers needing to be fleeced. The near critical mass of 42V standards and implementation and then collapse, left allot of people in holding patterns with some reasonable systems that started to look good at 42V, but no way at 12V. Hybrid is the only daylight most of those systems will see in the near future until 42V is back on (Betamax = better technology without critical mass). The real goods in elec superchargers is the fact that it isn't bound by exhaust volume or RPM and can harmonize with critical control strategies not available to turbo/supercharger devices (VNT is closest). Vehicles that operate one day with a full payload and then dead head the next are difficult to resolve for emissions and power in both modes, and is one example of what makes the E charger so sought after. Since you can plan on 20 to 30 hp to drive any of today's best compressors to the mass flow requirements to replace a turbo or s/charger, you will still have  the same parasitic lose or more, so in the long run the real upside to E-charging is its on command mode of operation. If this on command - as needed attribute was not inherent to the E charger, it would not be continually reinvented. My company spent about five years working with Dave Kapich, a brilliant guy (Kapich Engineering) that holds the patents for a hydraulically driven supercharger (HydraCharger) for use in the automotive aftermarket and learned just how important the on demand attribute is and will be from here on. The Hydracharger is an on demand device much like a E charger except it is a centrifugal compressor drive by a hydraulic turbine at 2000 to 3000 psi that is controlled via an electro-proportional valve from the ECU. What we learned was we probably would never make more peak power than turbo or supercharger but we could control throttle response, drivability, and emissions with much greater accuracy and with a much smaller engine. Throttle rate and jerk can be interpreted more closely as "driver intent" instead of "engine requirement" as the engine torque can now be slaved more accurately to the driver intent based on throttle rate change nuances. Many more boost control strategies are possible for on demand boosting like maintaining a mapped delta P across the throttle, based on, rpm and throttle rate where say a .5psi delta is maintained at the throttle during cruise and varied based on throttle opening rate up to the peak boost limit for example. The Hydracharger is now being used as an alternative to E charging in diesel turbo assist. Until motor armatures are developed that can spin 50K RPM, develop 20+HP on 12 to 24V, and operate  day to day at -40C to 180C E charging will not be a big player. Looking forward to a few more years of entertainment on this one!

RE: electric supercharger

Interesting jimwolf!
That again mentions something that is cris-crossed in this thread, which is duty cycle. "On-demand" means just that; short periods of boost for acceleration, not prolonged or continuous operation to make up for cubic inches. Construction and consumption wise, they really are apples and oranges. Nothing determines parameters or feasability more than duty cycle and defining the purpose.  

Using hydraulics was a bit crazy years ago but not any more. It makes sense for intermittant or continuous operation. Good thing we invented accumulators, otherwise we would have to deal with hydro-lag.:)

RE: electric supercharger

If VW would electrically drive a supercharger to charge its 1.4 l engine Twincharger below 2500 rpm it would not require more than 4kW at 1 bar (P = approx. p*V/t). It might not even be considerably heavier than the mechanical version since it can use a lighter, more efficient centrifugal supercharger without parasitic loss, which since it doesn't need a mechanical connection to the engine, can be placed just next to the batteries (short thick copper cables). To take care of the short current bursts, this car could run with two 12V batteries. One 12V battery would still be parallel to the entire system and the second 12V battery would be in series to the first and run the supercharger on demand. The alternator would be larger (24V), charge both batteries and be turned off at full throttle (no parasitic loss) and run at full load when decelerating (and even regenerate some of the braking energy). With this system it is not possible to run full throttle for more than a few seconds, simply because the larger turbo is eventually up and running. And therefore the electric energy needed to run the system is relatively low (no need for a big and heavy battery pack).

Besides the Prius has a 50kW electric motor and a 12V system. Granted it also has some more powerful NiMH batteries as well, but obviously providing 50kW even in a relatively small car of electric power is not an issue. And running over 200V in a car with a 12V system is apparently not a big problem either. Otherwise we should occasionally see a Prius on an emergency lane.

Also BMW showed that turbosteamer concept not too long ago. If the turbosteamer would run an electric generator it could provide sufficient electric energy to run an electric supercharger. Besides, power requirements of electric supercharger are high, but energy requirements aren't really that high - at least not in countries with speed limits, curves and traffic jams (which I believe most have). So there's not necessarily a need to carry a lot of batteries to provide enough electric power for constant full throttle operation.

I believe an electric supercharger has some merits and it might be an alternative to hybrids. Of course, not quite as efficient but it wouldn't come with the mass penalty of a hybrid and therefore make an option for a more efficient sportscar.

Last but not least: Superchargers and regenerative braking systems are prohibited in F1.

RE: electric supercharger

One thing that has not been mentioned is the extra power required to accelerate an electrically driven centrifugal supercharger up to boost producing Rpm.  

If it takes many horsepower to run it continuously at final boost pressure, it is going to take considerably more power to accelerate both the motor itself, and the blower rotor from stationary up to perhaps 100,000 Rpm+ in a sufficiently short time to be effective.

Fair enough your rotor can be aluminum, but your motor still needs to be a copper and iron rotor of some sort, and reducing motor mass and inertia is not going to be so easy. To get the rotor acceleration, raw Kw are going to be required.

That may impose a huge extra electrical power penalty for lag free on/off driving.

But there is another quite different problem....

At least with engines that have few cylinders, there will be an engine Rpm below which very high boost pressures are going to cause unacceptable crankshaft speed fluctuations that the flywheel is not going to be able to cope with. This may cause some small drama in the following transmission.  The idea of massive low Rpm boost sounds attractive, but it can create problems elsewhere.

A properly sized screw supercharger can readily produce full rated boost pressure at or even below 2,000 engine Rpm. That may be about as low as you would really want to go for the reasons stated above. Adding electric drive to the supercharger to get even more low Rpm boost may just not be practical.

I read somewhere that Jaguar had to increase flywheel weight on their V8 when they added the Eaton supercharger. Apparently there were low speed torque fluctuations not present in the normally aspirated version of that engine. And that was with an eight cylinder engine and a roots blower.

The problem is likely to be far worse on a four cylinder engine with a screw blower, (or an electric centrifugal).


RE: electric supercharger

To overcome the supercharger's inertia one can use capacitors.

Small diesel engines have probably high crankshaft fluctuations as well (low rpm and high cylinder pressure). This just means that engines need to be designed accordingly. As far as I know the VW 1.4l engine with its Twincharger is quite different to the 1.4l NA engine as well.

I do see that there's still development work to be done. And it is not free, but it is feasible with the technology available today. If gas prices continue to rise, this option will become more attractive since it is one way apart from many others to make engines more efficient.

Btw here's article about eBooster an electric supercharger from BorgWarner Turbosystem: http://www.3k-warner.de/files/library/bwts_library_139_326.pdf

RE: electric supercharger

I'm with Warpspeed.

Unless the centrifugal blower is kept wound up to maintain boost, there will still be lag as the electric motor and blower accelerate from rest.

If it is kept wound up to maintain pressure until the turbo takes over, there will be considerable time when it is running against a part open or closed throttle, so it is in a ready state to overcome lag.

If I where to do this tomorrow, I would be looking at smallish belt driven screw blowers fed from a biggish turbo, maybe with a bypass valve around the blower, depending on whether it became a choke point at higher speeds.


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RE: electric supercharger

In my system I used a roots blower with an air bypass system fitted fitted around it. The bypass was held fully open at idle and light throttle, and progressively closed with increasing throttle opening. Flat out, the bypass was shut tight.

The goal was to completely unload the supercharger at idle and light throttle. With a fully open air bypass, it is like having the rotors spinning in free air with no outer casing. There is almost no parasitic power loss, very little noise and almost no heat generated that way.  It will considerably improve fuel consumption, and the supercharger runs much cooler.

The pneumatically controlled bypass consisted of a modified external turbocharger wastegate. The control diaphragm was connected with two hoses directly across the throttle body. It will be appreciated that the differential pressure drop across the throttle holds the wastegate open against it's spring.

This is really the same as manifold vacuum (in the unboosted condition).  But because it is the differential pressure directly across the throttle, the control pressure drops to zero with a wide open throttle, no matter how high the boost pressure rises.

Choice of spring rate and free length in the wastegate enables you to tailor how the bypass closes with increased throttle opening. This is a wonderful tool for adjusting drivability because it is load sensitive. Where and how rapidly boost rises with increasing throttle opening can be very smooth and precise indeed.

The final step is as Pat says, add a very large turbocharger to the whole system. That will do wonders for the top end airflow.

In order for a positive displacement supercharger to create boost pressure, the swept volume of the supercharger must be significantly higher than that of the engine. At higher Rpm it can never really become a restriction. The Ve of both supercharger and engine will fall with Rpm, but the turbo will more than make up for that.

As I said earlier I developed this fairly unique bypass system myself a very long time ago, and was absolutely delighted with the results. The blower bypass system is the key to reducing light throttle parasitic blower drive loss, and is a powerful tool for adjusting throttle feel and drivability. It also eliminates the need for a supercharger drive clutch, (which can add a whole lot of other problems).

I would be very surprised if an electric supercharger could beat it when all aspects are taken into account.

RE: electric supercharger

The 92 Series Detroit Diesels have used blower bypass valves for many years on their Roots type blowers. They work just the opposite. Closed at idle and light throttle and opened up with more turbo boost. Fully open at full turbo boost. Seems more sensible as it eliminates parasitic drive losses at high speeds and does not require an oversized turbo. Throttle response, driveability, and mileage are always maximized.

This setup could work well with a non-centrifugal electric blower.  

RE: electric supercharger

As I said before, the lag issue can be solved with capacitors. Acceleration is a question of power and as long as power is only needed for a very short time (less than a second) it can be provided with capacitors mounted close to the supercharger (short cables).
In this particular case if you go on page 16 of this paper, it only takes 0.4s to reach 60,000rpm (without capacitors).
So it is an issue that can be solved.

An electric powered roots supercharger would work as well. But centrifugal superchargers have the advantage of being lighter and more efficient and unfortunately the disadvantage they don't produce boost at low rpms. If the supercharger is independent of engine rpm this is not an issue anymore.

Btw capacitor technology is also evolving:

RE: electric supercharger

An electric supercharger has the advantage of no parasitic loss and re-use decelerating energy (regenerative braking).

If maximum efficiency is the goal, an electric supercharger has definitely an edge over a mechanical system.
If maximum power is the goal, possibly not.

RE: electric supercharger

An electric supercharger per se doesnt have any means of "re-use decelerating energy (regenerative braking)."

In order for that you need to have some sort of ISG and the 42v system to match it...


RE: electric supercharger

Fabrico, I am not at all familiar with the scavenge blower system fitted to Detroit two stroke diesels, but they are rather different to gasoline engines.

The main difference as you know, is that gasoline engines are throttled, and diesels are not.

With a gasoline engine equipped with a positive displacement supercharger, you quite obviously cannot just throttle the air at the supercharger outlet. When you close the throttle the pressure spike would almost certainly burst or break something. Airflow is just not controllable after the blower.

Throttling the air at the blower intake has one very serious disadvantage.  At small throttle openings the supercharger behaves like a massive vacuum pump. It sucks furiously against the closed throttle. The supercharger will consume a surprisingly high drive power in that mode of operation, it will also run very hot and be objectionably noisy.

Every supercharged production car that I am aware of has a bypass system of some type fitted, and it is always kept open at idle and light throttle highway. Interestingly almost none of the homemade hot rod engines bother fitting a bypass, but usually they are not the least bit interested in fuel economy or light throttle blower noise.

If a remote air/air intercooler is being used with long pipework, fitting the throttle to the blower intake is just not going to work. Throttle response will be horrible to the point of the vehicle being undrivable. With a modern EFI vehicle, the throttle CAN be placed after a positive displacement supercharger if a suitable bypass system is used. But without a bypass it is just not possible.

For the very best results, run EFI, a supercharger bypass, an intercooler, and individual throttle bodies mounted as close to the cylinder head as possible. (With or without a turbo as well).

Diesel engines, especially two stroke diesel engines are a whole different ball game.

RE: electric supercharger

Again the Prius has regenerative braking but it does not have a 42V system. It has 12V battery and a 12V system like every other car.

And again as posted before a powerful alternator can partially recycle decelerating energy as well.

RE: electric supercharger

Your compassion for your invention is understandable, however, the arrangement you envision for the system I mention is not. All production, non-production, bypass, or non-bypass supercharged gasoline engines are throttled without significant problem. To my knowledge, none of them are throttled at the supercharger output. For some reason yours and everyone else’s blowers are throttleable at the intake, but mine is not. I assure you, the system I mentioned does not turn into a massive, furiously sucking, power draining, overheating, noisy, breaking or bursting monster, as you suggest. This is especially true at idle and low to moderate speeds, which is where the blower mainly operates.  

Supercharged engines are famous for excellent throttle response, with or without a turbocharger. Of course this can only happen with any bypass closed.  

You have suggested how well “compounding” would work on various occasions. Would your compounded system include the use of long piping, a remote air/air intercooler, and the other calamities you mentioned above? How would you handle throttling of the compounded system you promote?

Reliance on a Roots type blower for medium to high speed engine output is favorable to power but not significant efficiency. The system I mention not only bypasses at cruise but accepts a fairly well matched volume of air from the turbo, thus letting the blower virtually coast. At cruise, there is very little heat generated or mechanical power consumed, by the blower. Air from the turbo suffers little impedance by the blower. Closing the bypass at higher speeds compounds boost and makes significantly more power available in that range as well. Inter-cooling is done directly under the blower and has no air piping.     

Please note, my post above meant to say “small centrifugal” blower instead of “non-centrifugal” blower. This is roughly one half of a turbo charger and can spool up immediately. An electric Roots type blower or geared Mcculloch centrifigual type are not on the menu. I would also question the practicality of any continuous electric blower.  

In favor of your mentions of compounding, the electric "turbo" system I experimented with was on this same type of engine. This means an electric powered air pump pushing into a compounded system. It was not overly complicated, and except for electrical demand, worked flawlesly. The electrical demand was not way off, but just past practical. Another hurdle is that a 2-stroke needs more air than a similar size/speed 4-stroke. This alone could put electrial demand back in the practical range.     

globi5, you are probably right about capacitors doing a great job of powering or helping to power an on-demand blower. Capacitors charge differently than batteries which might open new doors to regenerative or alternate sources of electircal power.

RE: electric supercharger

Well, all I can say then is Jaguar, Mercedes Benz, Toyota, and GM must have all got it totally wrong. Even Eaton must be wasting their time when they build a bypass butterfly right into the blower casing in some models, and a rear bolt on bypass butterfly assembly in other models.

As I said EVERY production supercharged car I am aware of uses an effective bypass system, and it works exactly as I described, usually controlled by the ECU. It is certainly not my invention, but a standard requirement for any properly designed production road supercharger system.

I am well aware that hot rodders and drag racers have been bolting GM blowers onto the tops of Chev (and other)engines for around sixty years, with massive carbies mounted on top. They work fine for what they are required to do. Not a bypass system in sight there anywhere either.

But you have never, and will never see anything like that on a 2006 model standard factory production car that has to meet acceptable small throttle fuel economy and NVH requirements.

And trust me, a downstream butterfly on a positive displacement supercharger WILL break something when you snap the throttle shut to change gear at 6,500 Rpm.

The very small mass airflow at light throttle, passing through a remote intercooler and long interconnecting pipework offers almost unmeasurable pressure drop and is not a problem. But the throttle absolutely must be located reasonably close to the engine. It can be located before or after the blower, as long as there is a bypass system fitted.

Study any supercharged production car and see how it is done. There are plenty of wide design variations, but they all have a blower bypass system fitted, every single one.

RE: electric supercharger

globi5 (Mechanical) 7 Jul 06 11:44  
Again the Prius has regenerative braking but it does not have a 42V system. It has 12V battery and a 12V system like every other car.  "

It has a 200 V (ish) battery to handle the regen. I find your statement disingenuous at best.


Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: electric supercharger

Warpspeed, what is your point? Do you really read other's posts? Is no one allowed to talk about different methods or ideas?

The only one who ever mentioned anything about using a downstream throttle is you.

The only one saying anything about popularity, necessity, or location of bypass valves is you.

The only one arguing their system is better is you.

You deny it is at all your invention yet before:


In my system I used...The goal was to...As I said earlier I developed this fairly unique bypass system myself a very long time ago, and was absolutely delighted with the results....I would be very surprised if an electric supercharger could beat it when all aspects are taken into account.

Again, compassion for something you believe in is understandable, but it should not get in the way of letting others discuss alternative ideas and taking the time to hear what they are saying.

RE: electric supercharger

Greg Locock, the point was that you don't need a 42V system to provide more electric power. The 12V light bulb doesn't care if there's an electric motor running seperately on a higher voltage. Actually I already posted before that the Prius has a seperate battery to provide electric power for its 50kW electric motor. However, and this is the crucial point, the entire rest of the car still runs on a 12V system.

The question I answered was whether electric powered superchargers are feasible and whether they have merits. The Prius shows that it is possible to provide a lot of electric power reliably without switching to a general 42V system.  
And again electric superchargers have merits because:
* no parasitic loss.
* be able to take advantage of a centrifugal supercharger (lighter and higher efficiency).
* no frictional losses when cruising.
* more freedom about where to place supercharger.
* operate supercharger at any speed independent from engine speed.
* can take advantage of regenerative braking.

Nobody claims that electric driven supercharger don't have disadvantages as well. But again that it is technically feasible and that it has advantages compared to a mechanical system, especially when it comes down to fuel saving measures, is obvious. And I also believe if Turbo system companies like BorgWarner are working on it, it can't be such a ridiculous concept after all.

RE: electric supercharger

The 200V battery is used for regen. The bus voltage of the low voltage circuit is irrelevant.


Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: electric supercharger

Fabrico, the whole point of this thread is to discuss electric supercharging, and to my way of thinking that includes comparing it to normal direct mechanically driven superchargers.

An air bypass system is used in order to obtain far lower parasitic drive losses when boost is not required. That is a very important point in the the whole comparison between electric drive, and direct mechanical drive. It eliminates the single biggest disadvantage of direct mechanical drive.

My whole point raising all this, is that a properly controlled mechanically driven positive displacement supercharger would be extremely difficult to beat when all aspects are taken into consideration.

Throttle response, or lack of the dreaded lag is another aspect of electric supercharging. Power to the electric drive motor will need to be very accurately modulated, with PWM, many Kw of it. Nobody here has mentioned that little problem so far. You cannot just switch it on and off. Location of the throttle is also very important for throttle response. Downstream is always better. Incidentally Toyota use a downstream throttle with a roots blower, so it is relevant to understanding what is already out there.
Lastly, by far, the majority of air bypass systems used today use the ECU to fully map the bypass valve electronically.  When I built my bypass it was totally pneumatic. Toyota also use full pneumatic control, but they are still the only OEM to do so.

I only mentioned it because to anyone deeply interested in supercharging it is a very simple and practical alternative to software mapping. The adaption of an ordinary external wastegate to do the job is a very effective solution, which is my only contribution.

Electric supercharging has a very big job ahead of it to beat direct mechanical drive, and there is a lot more to it than just hooking up a very powerful electric motor to a centrifugal compressor and calling the job done.


RE: electric supercharger

Come on guys play nice.

This thread contains a lot of VERY interesting stuff, and at least probes into new developments and I for one do not want to see it disappear because of inappropriate argument.

Questioning where problems might lay, or where one seems to be intently following one path to the extent of becoming blind to other possibilities is healthy, but arguing the point to save face when evidence is presented to question your previous comments is pointless and damaging to creative thought.


Did you read my post of 20/06/06


I would expect an electric driven supercharger will only give constant boost if it is well regulated with pressure switches and controllers to control the electric motor well enough to overcome reaction times, relative friction and inertia and if the electric motor can provide enough power to keep up with engine requirements.

I appreciate it was a bit brief, but believe it implied these areas might contain problems still to be overcome, or to at least beg the question.

I was sure many people here with special knowledge in some aspects would each add their 2 cents worth.

Passion can be good, but it should not overpower reason.


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RE: electric supercharger

Additional papers on electrically assisted supercharging:

I believe, the reason we don't see them in cars yet is less technically based but rather because of the higher costs of a supercharged engine (electric or not) in general and these extra costs simply don't justify a supercharger in the first place even if fuel consumption is reduced by 15% due to the higher efficiency at cruising. A 1.2l engine with supercharger is still more expensive than a 1.6l n.a. engine.

RE: electric supercharger

Well said, patprimmer.

Although some regulation of the electric motor would likely be needed to control air flow, it would seem that perhaps half that function could be done working with the air itself. Of course another viable alternative is to have more than one air pump.winky smile  

As far as electrical demands and my very limited experience, most of the testing was done on a 426 cubic inch 2-stroke engine AND the entire system was 12 volt! It does not get much worse than that, yet it was close to being pratical for an on-demand duty cycle. Using higher voltage DC, 3-phase AC, capacitors, or a combination of these, would be nothing but better.

It may or may not be considered parasistic, but the power required to spool up an electric blower for on-demand type system is substantial, almost colasal. This might be a good place for capacitors. Though lag and amperage are one, there is no question that electric motors can spool up fast enough. A well thought out system would not have to be expensive.

RE: electric supercharger

I would consider the power used to charge up batteries or capacitors to be parasitic, unless they are produced entirely from required braking. This seems unlikely to me.

I would think there might be a substantial difference in the spool up time for the unloaded motor vs the spool up time to full boost.

0.4 seconds can be quite a long time when waiting for throttle response in a sporty car. Probably quite OK in a truck, limo, aircraft or most boats.


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RE: electric supercharger

Pat, now that you mention it, I have put my electronic engineers hat on, and been giving this some serious thought from the control aspect. I see the control of an independent electric assist of a turbo as being rather problematic, quite apart from everything else.

For a start, there will be a reasonably complex (approximately) square law relationship between the boost produced and motor Rpm of the assisting compressor, and meanwhile the turbo is spooling up all by itself fairly independently of anything else with it's own dynamics.

That rush of acceleration common to turbo engines may become difficult to control, because as the turbo spools up, the assisting booster compressor must somehow be smoothly reduced in effect.

My only experience is with positive displacement (roots blower) turbo assist, and that has none of the flow control problems, because of the fixed displacement and solid mechanical coupling to the engine.

I believe inertia, and the grossly nonlinear characteristics and response of a centrifugal electric booster my be extremely difficult if not impossible to control satisfactorily in any feedback loop. The sort of fast stable response that will be required may just not be possible.

I am fairly sure a proper feed forward control system is the only way it could be made to work at all.

While a nice rush of acceleration might feel pretty good, something where boost pressure fluctuates up and down unpredictably, with two systems fighting each other, might feel rather odd. When the centrifugal booster backs off, exhaust gas volume falls...

I believe a feed forward system, (possibly modified with some self learning ability) may work, but the control system, and all the required sensors to do it would significantly add to cost and complexity.

RE: electric supercharger

Looking positively at the basics of a simple electric boost system...Control of motor speed is not a problem elsewhere and should not be a huge problem here. Motors can be controlled by PWM, frequency, voltage, amperage, or electro/mechanical configuration. That the motor(s) even need minute control is far from proven. Operation independent of engine RPM would offer significant advantage.  

Taking the .4 second spool-up time and RPM at face value, it needs to be considered that the time between 0.0 and .4 is not lost. The time of .2 seconds would have the motor spinning at 25 to 35K. At any rate, the boost from an electric air pump can out accelerate the engine or driver’s needs. A significant amount of energy can be saved by limiting the motor/pump performance to the level of other components.   

The mention of more than one air pump in my last post, in the context it was presented, was intended to lead those with imagination to the possibility of having more than one electric air pump. There is no reason that pumping of air can’t or shouldn’t be progressive. A motor/half-turbo setup is very compact. Having two or even more is not impractical. Using a smaller unit for each pair of cylinders or even a unit per cylinder, is not out of the question.

RE: electric supercharger

Yes I agree Fabrico, I doubt if most average drivers could actually move the throttle to fully open in 0.2 seconds anyway. Acceleratin time of the electric motor is really just a case of throwing more electrical power (and cooling) at the problem. But a viable control strategy still remains the biggest hurdle in my mind.

I have heard many people suggest that when a mechanical (electric?) supercharger is combined with a turbo, the supercharger can be switched off once the turbo has reached full boost. But can it?

If the heavily loaded engine is accelerating under boost conditions, and the supercharger is providing an appreciable proportion of that boost, a moments thought will tell you that you cannot simply suddenly just switch the supercharger off.  The very sudden drop off in boost, and engine torque would be quite disconcerting.

I see the control problem not during the initial acceleration phase of an electric supercharger, but how the heck do you control it in such a way that it does not have to run continuously while the engine is in boost? If that is true, then the exhaust driven turbo really becomes redundant.

The whole concept of electric supercharging is really to improve transient response and drivability. But I see it as becoming more of a giant liability to drivability. No doubt it could be made to taper off gradually so the turbo and wastegate could catch up. But that can only really be done smoothly when the whole system is running near steady state.

Accelerating up through the gears will not present much of an opportunity to turn off the electric assist. Running it almost continuously for repeated long bursts will present a fearsome electrical load. That power must come from somewhere, and we are right back where we started with high parasitic drive losses into the electrical charging system.

I still have very serious doubts that this electric centrifugal idea can beat a direct driven positive displacement turbo assist.

The roots blower will already be up to speed when you open the throttle. The bypass system closes proportionally as the throttle moves, and the whole induction system pressurises within a few turns of the blower. With the bypass fully open parasitic drive losses are almost zero. Power to run the supercharger is only absorbed during actual open throttle acceleration. There are no transient or flow control problems either. And it is simple.

Funnily enough a roots blower is preferred in this application to a screw blower. Required supercharger pressure ratio will be quite low, and it will be resonably efficient. But the big advantage of the roots blower is that it can be completely unloaded by reducing the pressure differential across it to effectively zero. A screw blower has some internal compression. It therefor always absorbs power crushing the air between the rotors, even when differential pressure across the blower is zero. A screw blower will be much better in every other respect, but the much lower fully unloaded drive losses make a roots blower more desirable where fuel economy is extremely important.

I know I am heavily biased with this, but I still cannot see an electric assist being able to beat it, either for transient response, energy efficiency, or cost.

Just a final word on the functioning of the bypass system. It will be appreciated that the rotors of a roots blower do not directly compress the air. If inlet pressure and outlet pressure are identical, the rotors just spin freely around inside the casing, and no work is done.

It will also be appreciated that as soon as the air is throttled, either at inlet or outlet, a pressure differential will be created. The blower will then consume additional drive torque. It will be working against the resistance of the closed throttle and will consume significant drive power in doing so.

That is exactly the situation that exists during idle or small throttle highway operation. The supercharger is working against an almost fully closed throttle. Opening an air bypass path directly around the supercharger is just as effective as de-clutching, but it has the very great advantage of being ready for instant action by already having the rotors running at full operating speed.

I very much doubt if any electric motor could beat that instant state of readiness of an already up to speed roots blower !!

And one final point. I have heard it claimed that a supercharger will become restrictive once the turbo is boosting. That is never true in practice. If supercharger discharge pressure is higher than supercharger intake pressure, it is certainly cannot be acting as a restriction!   

RE: electric supercharger

A lot of the control instability predicted here would be self imposed, if the control designer chooses to assign boost or MAP to the primary loop. MAF is a better choice for P and assign MAP to any required sub-loops needed for system constraints. As stated previously, boost is nonlinear to engine V.E. as well as compressor power requirements. MAF along with compressor speed, engine speed, and throttle rate ( emphasis on rate) are probably better elements of choice in the prime control loop.
Again, the E charger is only of interest if it can more effectively achieve driver intent while adhering to system constraints, either in conjunction with or in lieu of a turbocharger. It's important not to get to myopic about the E charger as the only indepentant boosting device solution. If a centrifical compressor is driven with an efficiant continously variable drive unit, the E chargers attributes are easily halfed. If this variable drive unit is hydraulically coupled to the compressor, it might also be possable to divert crank power to a hydraulic accumulator on braking. This has it's own ineffeciencies to deal with, but probably on par with the crank to alternator to motor to compressor power path of most proposed E charger systems.

RE: electric supercharger

Good points Jim.

I still think any feedback system would fall far short of what would be required.  

As an example, it would be like trying to control engine fuel flow purely from the output of an oxygen sensor and nothing else. No matter what you do, any feedback system can only respond once the system output has changed. Getting both speed and stability with something like that except under ideal, completely steady state conditions would be all but impossible.

A normal engine management system is a feedforward system. It looks at all the inputs, and engine fuel requirements are predicted and then applied. Tuning the ECU is about getting that prediction right, over a very wide combination of inputs. And, feedforward is never a closed loop system, so it cannot become unstable. The output may be wrong, but it never goes totally nuts with cyclic instability.

I use this example only to illustrate the difference between feedback, and feedforward, for those here not familiar with the terms.

Something similar would be needed to control this electric supercharger. Characteristics of supercharger, turbo, and engine would need to be modeled in software. Not just static values, but the dynamic ones too. Power to the supercharger would need to be controlled in a predictive manner.

Waiting for boost to fluctuate, and then attempting to correct it somehow is just not going to work. If it over corrects, the system could easily become unstable. How much, and how fast to correct are the two basic rules of feedback loop design and tuning. Nested control loops, with extreme non linearities and significant time delays, are an absolute nightmare.

RE: electric supercharger

I dont see it as a problem,

After all, closed loop boost control can, has and is quite easily done elsewhere with an ECU controlled PWM actuator, so why not here?

Even with a turbocompounded system I dont see how there would be a problem?

Warpspeed, you seem to be implying that there are precious few closed loop control systems in a modern engine management system - is that a statement you have thought thorough?

What is the worry about the 'characteristics of the supercharger?' Surely the amount of air that enters the engine is what matters? Which is easily and effectively calculated without ever needing to know what the supercharger is doing.

A properly calibrated torque based control system would be more than adequate to control this system - gone are the days of simple speed/density or alpha/n control systems.


RE: electric supercharger

Ahh, fresh air!
Specific comparisons are useful, but constant, boundless, inaccurate, repetitive, negativity is not. It also does not help for one to make up unresonable scenarios then talk about how impossible they are to solve.

I also don't see much of a problem with motor control. Simple matching of the motor/turbine to engine breating needs would eliminate extremes. And, dare I mention it, there is no reason the air pump can't be fitted with a re-circulating bypass valve.  

Electric boost is perhaps at it's very best and simplest when piggy-backed onto a turbo charger. Using the flap valve method I described earlier, all airflow transistions are perfectly seamless and the electric motor can simply be turned off with no ill effects.

Upon takeoff and until it runs out of steam, an electric air pump can certainly keep pace with a typical direct drive blower setup, with or without turbo assist.

RE: electric supercharger

Regarding parasitic loss:
I guess I should have said: There's no need for parasitic loss at full throttle, which is the point I tried to make, since you can get the same amount of power with less boost or you can get the same amount of power with same boost and a smaller engine.
Also, if an engine has lots of low end torque (which an electrically assisted supercharger can have), one can also drive lower geared = reduced fuel consumption.

If engine downsizing is the future, electrically assisted supercharging or electrically assisted turbocharging or a combination of both could be part of this future:
http://www.energy.ca.gov/fuels/petroleum_dependence/documents/2003-06-06_hearing/public_comments/HONEYWELL_COMMENTS.PPT#285,16, Fuel Economy, CO2 and Cost  Benefits

RE: electric supercharger

...and if the battery is charged while cruising, pumping losses are also reduced.

Also, engines can deal with more boost at low rpms and/or higher compression ratio since heat production is lower at low rpms and so is detonation-risk. (Assuming torque fluctuations are as in a Diesel engine taken care of).

RE: electric supercharger

Feedforward or preact can be used to describe an attribute of a closed loop systems and does not necessarily need to describe an alternative to a closed loop system. Set points and Kp, Ki,Kd can be static or dynamic in a PID loop. Feedforward (preact) can be added to the loop either by dynamically trimming on the Kpid coefficients or by trimming set points to Best Possible during transient conditions for example. Electronic boost controllers for example have used every possible combination of control strategies ever thunk up, with good, to disastrous results. Adding feedforward to a boost controller loop is normally helpful but tricky, in that you are giving the loop information that it is not capable of anticipating on it's on and commanding it to act on it in a specific way. Once you incorporate this expert system, you are responsible for all unpredicted scenarios that the end user will get into. If not well thought out, it is possible to cause dangerous boost spikes by upsetting the underlying loop. Typically the designer sets up a learning session the installer runs the car through to learn the rate boost climbs at full throttle and uses this information in various ways during future operation. Unless this is done under all conditions (IE each gear, up hill, down hill, etc) you may have added information the system is expected to assume correct under ALL conditions, building a land mine into the soup. Feedforward, fussy logic, expert syst., PID, cascading PID are tools in the box to be mixed as needed normally never the eloquent solution alone.

Fabrico, the bypass your describing does work, I have one from a Penta/Volvo somethingorother we used during testing of the Hydracharger. I dug it out this morning and took a picture of it, I think being a Penta it is from a marine application, maybe someone else would know if they saw it. It has a 3.25" inlet checked by a flopper door, a 3.25" outlet, and a 3" y'd inlet for the compressed feed. Here is the picture. http://www.jimwolftechnology.com/images/diverter_valve.jpg

RE: electric supercharger

O/k fair enough guys, you all make it sound so very simple. I have been struggling with power electronics, control systems and feedback loops for most of my working life.

Anyhow, back on topic. Does anyone know if these electric superchargers have been successfully installed on a vehicle yet ?

If it is all so very simple to apply, where are the road test results ?

RE: electric supercharger

No need to struggle Warp. And none of us knows how simple or complicated it really has to be. Components have been around, but as far as I know, a comprehensive system is new technology.
I hope you don't mind posting your picture jimwolf, but that's just the kind of low tech, reliable components I've been talking about. The unit I worked with was a little more streamlined and had a position sensor for the door. The sensor told the controller that the turbocharger was taking over and to unplug the electric. Failsafe really.
There may be other things worthy of consideration. While turbochargers are a reliable way to more power, the only time they have low parasitic loss is when they are providing little or no boost. This is not helped by the fact that their design is compromised in having to satisfy a broad RPM range. An electric air boost system could allow for a more efficient turbo design.

RE: electric supercharger

Yes, all the electric boost systems I have seen so far are just a complete joke, like this one for instance:


But a high powered electric booster with real balls is quite  a different matter altogether. I will watch this with growing interest.

I hate to be a wet blanket Fabrico, but I play it as I see it, based on my own knowledge and practical experience.

Anyhow, beware of using flaps and control valves with any centrifugal compressor. There is a belief that you can spin up a centrifugal compressor and use it to open a flap when developed pressure has become sufficient. It can certainly be done, but only with a bit of thought and some additional complication.

The problem is compressor surge. A centrifugal absolutely must have some minimum flow in order to work at all. It cannot develop pressure into a dead end against a flap. It will definitely need some sort of fairly generous air bleed system (which can later be closed).

It is always vastly easier to place a centrifugal in series with something else, rather than in parallel.

I really hope this is going to be taken as intended, as constructive advice, not as criticism.


RE: electric supercharger

Whilst it is not an electric supercharger by any means, the current Mannic hillclimb cars uses a system that I find ingenious. It uses a large turbocharger with its own fuel supply to burn, much like a gas turbine. This produces 23-30psi at idle to full rpm, with minimal engine lag.
Mind you it is a competiton car in hillclimbs, so durability and emissions are not a concern. It can be seen in the current racetech magazine, though it has been around for the past 5-6 years.

RE: electric supercharger


I think that maybe there is a general lack of understanding of the architecture of a modern ECU strategy - that is why the notion of how to control an electric supercharger seems difficult.

If a torque based controller were used then there is less of a problem (although the system become more complex). Instead of having the throttle plate & throttle pedal connected, the ECU controls the throttle & the pedal is just a 'torque request' the actual realisation of that torque is commanded by the ECU controlling boost, throttle angle, fuelling, spark advance, cam position etc

Using this sort of set up would mean that the amount of torque & the rate of delivery is not a simply function of the throttle position & the amount of boost.  It is about the amout of air 'commanded' into the cylinder (slow path) and the spark advance (fast path).

There is obviously a lot of clever control engineering between the demand & realisation but the raison d'etre is the fact that things such as VVT, electronic boost actuators, intake tuning valves etc etc are totally transparent to the driver who is moving the pedal. It also means that the engine can be performing at its optimum at all times.


RE: electric supercharger

Good call Mattsooty. I don't know your area of work, but you are right that this whole discussion of E charging and other independent boost devices derives it's ultimate importance in the fact that along with "drive by wire" it allows control strategies to interpret throttle movements purely as driver intent. Most late model cars already have drive by wire throttles which was the first step to isolating throttle pedal movement exclusively to driver intent. Without an independent on demand device to fill in torque at lower rpm, Swelling the throttle plate ahead of the pedal (based on pedal RATE not position) has so far produced only small improvements as perceived by the driver. Remember this isn't as much about making additional power as that is already a done deal with SC/turbos, this is about making a practical device that the engine management designer can use to ultimately give the driver a perception of linier torque to accelerator pedal movement within the constrains of the system. The complexity of satisfying emissions, driver satisfaction, mileage and the like needs independent boost devices to move forward, and even more so with CO2 requirements moving front and center. I tend to migrate back to the control side of this topic more than the machine side for one reason, "it's not about the device, it's about what your trying to do with it"! Remember when CVT transmissions became practical, it was like Christmas morning for the control engineers. For the first time TPS and vehicle speed could be used to close a loop on engine RPM during cruise mode. This is an example of a slave device that is now on board production vehicles and performing reliably, but will evolve more by the control strategies ahead than by changes to the device itself. My company occasionally does feasibility studies of the Hydracharger for OE automakers and it is always the on demand thing they ask for. Reliable independent boost devices will be big bucks ahead and that is why big companies like Garrett, Borg Warner, Visteon etc. continue to beat the bushes on this.

RE: electric supercharger


I really hope this is going to be taken as intended, as constructive advice, not as criticism.

Warp, I'm glad you threw that in there. Believe me, we can see your interest and related knowledge in this crazy stuff. What would be most helpful is if you would question things rather than condemn them. I took a look back and did not see many question marks in your posts. If something sounds ridiculous or confusing, question it instead of attacking it. Maybe someone can give you an answer or maybe they will take your question and make it even worse. Who knows, give it a chance.

The system I worked with used a flap valve, was plumbed in parallel, and had no surge whatsoever at any time. The flap valve was a simple device, did not slam or interfere with pumping or flow in any way. It was extremely simple and worked flawlessly. And, yes, it could work that way on a gas engine. And no, it was not the catch-all, do-all ultimate system. If you want to know how that was accomplished, all you need to do is ask smile

jimwolf, you bring up several good points.  

This is obviously expanding in several directions. Some topics presented here are pretty meaty in themselves and would be discussed best by themselves. I will be starting a thread on at least one directly related but specialized topic.

RE: electric supercharger

Goodness!  That package almost sounds like it's alive. I hope they programmed a little apathy into the ECU so it doesn't get too smart and decide to commit suicide!

RE: electric supercharger

"Have you seen a 40 hp electric motor? Can you imagine running one on 12 V?"

T x RPM/ 5252 = HP

DC motors don't suffer from the RPM limit that the mechanical blower suffers from meaning the mechanical needs More surface area in its pump to achieve the desired CFM of air at the given pressure.

At 30,000 RPM both the voltage requirment and the blade size decrease.  So the Electric adapter to the mech style blower(bad idea probably suggested by the marketing department and not the engineering dept.) All electric is feasible and whether its a "good one" will really be in the thinking of the elctric to mechanical conversion rate of the product itself.  Yes 42 volt is easier to get more power from at lower rpms.  So Lower voltage the system the more RPM needed to compete and that should be taken into account.


RE: electric supercharger

So from that I can't understand whether you know how big a 40 hp electric motor is. Do you ?


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RE: electric supercharger

Have a look at a hybrid approach (albeit still in the concept stage)


A supercharger using a turbo compressor wheel, 10:1 ratio drive (CVT) and electrical assist to improve the transient response of the compressor.

Technically looks quite interesting, but I don't think costs have been fully investigated yet.


RE: electric supercharger

Good grief, that motor is huge! Could it be the fabled 40hp monster? smile

I hope the armatures are light, otherwise it will consume a good bit of electro/mechanical power just getting out of its own way.

Imagine diagnosing a complaint of poor throttle response.sad

RE: electric supercharger

It's a prototype - only 1 of 3 in existance, hence the size.
(please note I'm not related to the company in any way....)
Also many 100's of volts internally.....

Definately wouldn't fancy the diagnostics/control strategy job myself!

RE: electric supercharger

HMMM..  centrifugal loading anybody?

RE: electric supercharger

The only really sane way to do it may be to use at least one stage of epicyclic gearing to step up the motor Rpm to something more usable. I doubt very much if a motor that large could ever be direct coupled to such a small centrifugal rotor. The proportions just look plain wrong.

The now ancient Paxton supercharger had an internal speed step up ratio of x4.4 using steel balls in a spring loaded planetary drive. That could produce the 35,000 maximum rated rotor Rpm, when driven from a vee belt.

RE: electric supercharger

The SuperGen concept has TWO motors:

One that you have noticed (the large one) this is driven at engine speed and provides the following functions:

1) Engine starting to allow start/stop

2) Alternator replacement to generate power for the vehicle

3) Generator to source/sink power for the second motor.

It is this much smaller motor (it doesn't have to start the engine and DOES have to be responsive) that controls the speed of the compressor wheel.  There is still a large ratio between the control motor speed and the comp wheel speed (which is driven by the sun shaft of the epicyclic).

The key point is that the motor controls the speed so at low speed where the natural speed of the compressor on a fixed epicyclic would be low, we can apply a large speed to the control motor to get full comp wheel speed even at low engine speeds.  At higher engine speeds, the epicyclic natural ratio results in a large compressor speed so the control motor is stationary.

It is important to note that all the power for the device when operated like this comes from the belt.  The power for the control motor comes from the large motor acting as a generator.

The large motor can also apply a torque down the belt to act as a mechanical assist as well. During this mode, where both boost and torque are being generated for maximum lauch effect, power can be supplied externally from supercaps etc.  

The device is indeed in development and testing is ongoing.

Turbocohen, centrifugal forces were calculated during the design process.

And Clsshore is also right while the motor controller terminals are at 12V, the device operates internally at a voltage much higher than that.  Otherwise the efficiencies would be poor.

RE: electric supercharger

I've been away from this forum for awhile, and this thread was good reading!  

Just wanted to point out an error from Warpspeed posted awhile back, to wit:

" Many if not all long distance road diesels typically run a turbocharger compounded with a roots scavenge blower. They not only have plenty of torque !!!  but the specific power is not too bad either."

No over the road diesels use roots blowers anymore, & haven't since the early 90's when the 2 cycle V92 diesels were outlawed for road use.  All modern diesels use turbos these days, and variable geometry ones at that.


RE: electric supercharger

Interesting Jeff, thanks for pointing that out. It may be a bit behind the times now then on heavy road diesels, but the point I really wished to make was that compounding a roots blower and a turbo is nothing new.

The current model Golf GTI (sold in Europe) uses  both a roots blower and a turbo, so the concept is still quite practical and up to date in other areas.     

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