Exhaust+Electric hybrid turbo

[nightfire]

I've got a massive electric motor I use for flying large-scale R/C aircraft. It'll run 4kW for 30 seconds (100A @ 40V) and 3kW continuously.

I've decided I'm doing a turbo this spring, but I've been really torn between that and a SC, because honestly, call me typical American (even though I'm Canadian).. I'm looking for low-end torque, not peak HP. I drive downtown mostly, so I like to keep my revs below 5000 so as to not attract attention.

So I had an idea.

I've never even held a turbo before, so I don't know what the shaftage is like. But, in theory, it would be possible to bolt up an electric motor to the turbo, whose sole duty is to get the turbo moving at low revs as soon as the TPS reads >0. It could spin up the turbo to 6PSI @ 1000rpm easily, and gradually back off as the exhaust pressure builds.

Yes I know electric turbos have been done.. but this is a hybrid. Electric power from 1000-2500rpm, exhaust pressure from 2000-7000rpm.

In fact at a low CFM rate (<2500rpm), the motor would probably only draw 1kW-2kW. I'd need two small lead-acid batteries in series with a charge controller (like Thomas Knight's setup), but the stock alternator could easily handle the extra load. As a bonus, the spinning exhaust blades would create a scavenging effect on the exhaust, clearing the cylinders better at low revs.

The problem would be gearing the electric motor (max RPM of 15k) and keeping it cool. The magnets demagnetize above 150C.

Has anyone tried this or heard of such a thing?

[onlytrueromeo]

This actually seems like a cool idea - its almost like a supercharger in the lower rpms...but there are some obvious problems.

For 1, how would you possibly attach the motor to the turbo? You'd either have to make your own custom housing or try to modify it on the inlet side, restricting airflow to the turbo...you could minimize this by having a long shaft, but then you wouldnt be able to have a filter on it, and a long shaft would cause problems w/ torque transfer as electric motors usually have a ton of torque.

Possible? Sure. Feasible? Prob not unless you have alot of money, in which case a super-turbo or TT combo will prob be better.

[nightfire]

This actually seems like a cool idea - its almost like a supercharger in the lower rpms...but there are some obvious problems.

For 1, how would you possibly attach the motor to the turbo? You'd either have to make your own custom housing or try to modify it on the inlet side, restricting airflow to the turbo...you could minimize this by having a long shaft, but then you wouldnt be able to have a filter on it, and a long shaft would cause problems w/ torque transfer as electric motors usually have a ton of torque.

Possible? Sure. Feasible? Prob not unless you have alot of money, in which case a super-turbo or TT combo will prob be better.

Well, I was thinking of mounting the motor it in a hugely oversized intake (like, say 5"). It would help keep it cool, which would be a huge problem when the motor is spinning at 50,000 or whatever the turbo spins up to.

Actually, that could be another problem. The motor itself might explode at that speed. So I'd need a clutch. :/

Hmm.

[nightfire]

Actually my brother had an interesting idea just now. Why not simply do a 2-stage system, with the electric turbo using a dedicated (small) compressor, that joins in the intake through a 1-way valve. So the electric motor fires up and blows air through the turbo. Then, once a negative pressure develops in front of the electric turbo, shut it down (the main turbo has taken over).

[onlytrueromeo]

Its not feasible to hook a motor to a turbo...you'd be better off hooking the motor to a vacuum pump and actually pushing air into the intake - like an electric turbo, for the first 1000rpms or whatever you're thinking. It wouldn't have the juice for upper rpms, but you wouldnt be needing it for that. With this setup youd need an EMS for a TT setup, and do lots of custom work tryin to regulate an electric motor...if it pushed out enough air, it could work, but without a BOV for that it would prob blow up your motor...lol

You want low end torque for driving around town...WHY? You want to peel out everywhere? Its annoying to drive the ZE in traffic, I feel like Im going to rear-end everyone (but I also hate driving in traffic).

EDIT: I was thisssss close to posting this before you!

[nightfire]

Hahaha... great minds think alike I suppose (guess I can't count myself in that one though. )

Well, my biggest pet peave is taking a corner in 2nd. I hate shifting down to 1st. So I'll often exit a corner at 1500RPM, and have absolutely no power.

I'm a very civilized and quiet driver; I have an LSD and very rarely spin my tires (except in the winter). But I want power on-tap when it's time.

And yeah, still retain a BOV after the turbo. Everything else should function like normal, no?

*EDIT* Actually I was just thinking. There's no need to have a 1-way valve to protect the electric motor. Just a vacuum sensor that shuts it off. Since it's a Y pipe with one half going to a large air filter, the negative pressure will never build up enough to spin the motor to its destruction. um.. i think.

[RS_OBD'oh_2]

you have to check out dyno graphs for various turbo setups. It's all about picking the correct turbo for your driving style/needs. If you look at the graphs for a time attack car, they need to generate plenty of low-end torque and develop most of their power by 5000rpms. If you don't go too large, you don't have much, if any turbo lag. You won't need to bother with crappy electronic crutches if you simply buy the right turbo. Call around to a few companies and see what they would recommend.

[nightfire]

I'm still in my research phase right now (all of this new to me) but I see what you mean. With the right A/R ratio, does 2-3psi @ 1800rpm sound feasable? At the same time delivering 10psi at, say 5000?

[fowljesse]

Once I'm done (if EVER) with the stuff I'm working on, I'm going to start to work on hooking a 2-stroke engine to either a super, or turbocharger. Kind of the same issues as you'd run into. I know that I can make it work, since I have MegaSquirt now. I just don't know if I'll get sick of tuning it, and give up before it's perfected.
Let us know if you go for it!

[nightfire]

Well even a small RC rotary will top out at 20k rpm, which probably isn't enough for a turbo. Though you might be able to make it work with a supercharger. Except then you have a problem with gearing because they expect 2-5000rpm and producing enough torque to spin one would require quite a large 2-stroke.

[hgallegos915]

I dont get you.. why do you want to do this?

My t3t4 at idle is spinning around already.. its never stopped.. always moving when the engine is on.. what would be the point of this? the electric one would just become a restriction for the turbo itself. If you want to do a real good project, do twin turbo, a small one for quick spool and a large one for top end.


Or like the probetalk guy, he did supercharger and turbo at the same time.. he spools like crazy.

[nos92mx3]

THe biggest problem i see with you electric motor attached to a turbo is, you are going to destroy the turbo. with something attached to the end of the compressor wheel or turbine wheel you will be throwing it out of balance, you would need to get both the electric motor and turbo balanced at the same time while connected to each other.

not to mention way over thought, if you really only want low end power, just get a decent sized garrett with a small turbine side (exhaust side) it will choke out up top but give you the low end balls that you want.

[RS_OBD'oh_2]

there's a butt-load of turbo charged cars out there ~400 hp that hit peak hp and tq in and around 5000rpm. Search. the right turbo for the right app'
search

[nightfire]

THe biggest problem i see with you electric motor attached to a turbo is, you are going to destroy the turbo. with something attached to the end of the compressor wheel or turbine wheel you will be throwing it out of balance, you would need to get both the electric motor and turbo balanced at the same time while connected to each other.

not to mention way over thought, if you really only want low end power, just get a decent sized garrett with a small turbine side (exhaust side) it will choke out up top but give you the low end balls that you want.

Yeah, I'm starting to understand that now. I'm looking at a T3 with a .42 compressor / .48 turbine AR and according to the turbo calculator I've been playing with, the map seems optimal for minimum boost @ 1500rpm (1psi), max at 3000rpm (10psi), safely away from the surge limit. And it seems like it might be able to flow enough exhaust to not heavily restrict at 7000rpm.

[nightfire]

I dont get you.. why do you want to do this?

My t3t4 at idle is spinning around already.. its never stopped.. always moving when the engine is on.. what would be the point of this? the electric one would just become a restriction for the turbo itself. If you want to do a real good project, do twin turbo, a small one for quick spool and a large one for top end.


Or like the probetalk guy, he did supercharger and turbo at the same time.. he spools like crazy.

I was thinking about using an electric turbo to maintain pressure in the intake (prior to the gas turbo), similar to a twin turbo setup. At <100CFM, a 2kW electric turbo could easily maintain 5-6psi until the turbo has enough exhaust pressure to take over.

But anyway, for my goals it looks like a single small turbo will be fine.