Electric Assisted Turbocharger

[pogba]

I am currently at uni studying Mechanical Engineering. I was wondering what people thought about the idea of introducing an electrical motor or a motor/generator unit ( similar to the system used in the current generation of TC'd F1 cars) at the shaft of a turbocharger for current downsized TC'd petrol driven engines, with the focus on being able to improve the engines transient response with a quicker spool up time.

Would it be possible to introduce such system while still being able to keep the standard 12V battery system, as opposed to switching to a 48V system as some manufacturers are now turning to? I know with a high powered turbo the required power would definitely not be able to run on a 12V system, but if the focus is on a smaller engine (1.0-1.6l) using a small turbo, could this be feasible to use within affordable vehicles?

The work I have currently seen tends to be focused on high powered diesel engines (SQ7) and on high end vehicles (Bentayga), but I cannot find much work revolving around smaller engines. I would like to find out if I am wasting my time, and should maybe focus on bringing such system to slightly larger engines.

Thanks

Edited by pogba on Tuesday 12th April 17:59

[anonymous-user]

Here are some things you might want to google before you start:


1) How fast does a turbo charger spin?
2) How much power does a turbo consume, and how is that power related to it's speed?
3) V=IR and W=VI, so how much power can you pull from a 12v battery, and what limits the power?
4) What limits the rotational speed of an electric motor, and how do losses scale with speed?
5) draw a graph of compressor power vs engine speed under WOT operation for say a 1l engine



Answer those to get an idea for what you are up against!

Here's one i did earlier, which uses a fairly novel architecture to overcome the more limiting factors i've attempted to highlight in those questions above:

SuperGen


and i'd suggest learning about Tigers and Cobra here:

CPT-switched-reluctance-devices


;-)

Edited by anonymous-user on Tuesday 12th April 18:56

[pogba]

Thanks for your reply!

Could you give me some help with 2.) please, I am struggling to figure out how to calculate an approximation for the power a turbo would consume.

As I want to focus on small downsized engines, I will use a max value similar to a ford ecoboost turbo - 250,000 rpm....I know power is dependent on torque and rpm, then I am stuck...

Should I be looking at the power consumed by the turbo in terms of power a turbine will extract from exhaust gasses? or is that over complicating it and I should be looking at how much power is required to simply spin a turbine ?

If it is the latter, could you possibly throw some common turbo turbine dimensions/weights at me in regards to a similar one used in the ford 1.0l ecoboost?
So find the torque first, then find the power value in hp using- rpm*T/5252, then convert this into kW, right?



I realise this is probably really simple, so I apologise for my dopiness

Edited by pogba on Thursday 14th April 03:17

Edited by pogba on Thursday 14th April 04:47

[anonymous-user]

Well, you know where the power in a turbo charger goes! It goes into compressing air. So google "how much power does it take to compress air" and you'll find some basic compressor formulas, based on the compressors pressure ratio, mass flow and efficiency. Google "turbo charger compressor map" to get an idea for typical compressor efficiencies.

Then, work out how much air your engine will swallow at any gioven speed, throttle position and at what pressure. You'll need to estimate Manifold volumetric efficiency, and intercooling effectiveness, but ball park figures will get you close here.

So, now you know what your compressor has to do, and how much power it will absorb, and from the compressor map, how fast it will have to spin to do it.


The next bit is the complex bit, but it you are talking about a electrically driven compressor (ie electric supercharger) it's a lot easier, because you can forget about the turbine! (which is the difficult bit to calculate)



However, above all that is the fundamental issue of matching compressor speed to an electric machine! Work out the electrical commutation frequency of an electric motor at your 250krpm. How long do you have to start the current flowing in each phase winding? Now, based on a sensible phase inductance, how much voltage do you need to do that?


Hence, you'll find really only a couple of architectures have been used:

1) Mechanical transmission - high speed epicyclic (usually friction drive, ie rotrex)
2) Use a much larger compressor than normal to limit peak rpm to around 60krpm, which is juuuuuusst within the reach of a practical electric machine of sufficient power capability.


If you looked at the Supergen link i put in my last post, the "clever" bit of that is the way it combines a high speed mechanical transmission with a pair of electric machines, one of which is driven by the crank! Effectively it uses the electric machines as a CVT, and it takes the required compressor power from the crankshaft!

[pogba]

Hi, using values similar to those of the ecoboost turbo, I got a value of 6.7kw as the power required to compress air. Does that figure seem fine to you?

[chuntington101]

Max_Torque said:

If you looked at the Supergen link i put in my last post, the "clever" bit of that is the way it combines a high speed mechanical transmission with a pair of electric machines, one of which is driven by the crank! Effectively it uses the electric machines as a CVT, and it takes the required compressor power from the crankshaft!

This dose look really interesting. Any reason that OEMs havent started using this? The ability to deliver boost at any rpm and have it totally independent of engine rpm is cleaver. The offset in weight probably isn't that bad either.

[AW111]

Another factor related to power required is accelerating the rotating elements.

Acceletating a compressor to 200,000 rpm in 1/2 second requires a not insignificant amount of power. The inertia of the electric motor and gear train is involved as well.

[Mave]

pogba said:

Hi, using values similar to those of the ecoboost turbo, I got a value of 6.7kw as the power required to compress air. Does that figure seem fine to you?

I haven't done any of the sums or checked your pressure ratio - but my gut feel is that a decent sized turbo making decent boost needs a few 10s of HP so you may be in the right ball park. Can't tell without seeing the workings and assumptions.