electric supercharger 7

[ed911]

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?

 

[mattsooty]

Warpspeed/Jimwolf,

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.

MS

 

[jimwolf]

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.

 

[Fabrico]

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

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.

 

[globi5]

Not related to electric supercharging but to Twincharging (and thus sort of related to the whole discussion):
Ford and PSA launched a parallel sequential dual turobcharged 4 cylinder diesel engine last year:

http://www.greencarcongress.com/2005/10/ford_and_psa_la.html

http://bioage.typepad.com/photos/uncategorized/twinturbo.jpg

 

[Fabrico]

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!

 

[GunMuse]

"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.

http://www.prnewsnow.com

 

[GregLocock]

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



Cheers

Greg Locock

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

 

[andyv8]

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

http://www.integralp.com/SuperGenArticles.aspx

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.

ttfn,
Andy

 

[Fabrico]

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

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.:-(

 

[andyv8]

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!

 

[turbocohen]

HMMM.. centrifugal loading anybody?

 

[Warpspeed]

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.

 

[Ruaraidh500]

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.

 

[JWaterstreet]

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.

Jeff

 

[Warpspeed]

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.