Electric forced induction?

[mech5496]

Just stumbled upon a picture of an electric supercharger from the Hercules Racing Team Kassel on Facebook (https://www.facebook.com/photo.php?fbid=10151653308908445&set=a.10150479213213445.377943.158738688444&type=1&relevant_count=1). This reminded me of an old discussion we had on the forums, on the "fantasy engine" thread.




...IMO energy recovery from a turbocompound would be minimal, and most probably dependent on the load/RPM, as it is a mechanical system. What about using it in combination with an alternator? That way you could use exhaust gas energy to produce electricity. Get rid of (mechanical) water and oil pumps and replace them with electric ones should free some power. I know, conversion of mechanical to electric energy would lower the efficiency a bit, but IMO you would have greater control over recovered energy. Alternatively, you can do the above powered by recovered energy from braking (small front hub motors) plus turbocompound.

What about an electric turbo? You could run it entirely on recovered energy, no backpressure, complete control over boost, zero lag etc..



I was re-thinking the latter, i.e. use small electric motors in front hubs to store on-board electric energy, then use that energy to power an electric turbocharger. This would help efficiency a bit plus all benefits from a control point of view, packaging etc. IMO this arrangement should still classify the car as a IC and not a "hybrid". What do you guys think?

[BeunMan]

While we're at it: use thermocouples / thermoelectric generators at the exhaust heat to generate some power. Low efficiency but it 'free'.

[Owen Thomas]

I was re-thinking the latter, i.e. use small electric motors in front hubs to store on-board electric energy, then use that energy to power an electric turbocharger. This would help efficiency a bit plus all benefits from a control point of view, packaging etc. IMO this arrangement should still classify the car as a IC and not a "hybrid". What do you guys think?
I think you would have a hard time selling the vehicle as a non-hybrid, even if the motors are tiny. The easiest way to get some extra energy would probably just be a few extra battery cells. Boring, but effective.

Definitely like the idea, but it follows the same thought process as using an electric instead of shaft/belt driven water pump. Is the power you save/make worth the extra electrical draw and its associated weight? The packaging woes? The nightmares about not restarting at driver change? Personally, I shy away from these type of projects because they're usually someone's bright idea who didn't totally think it through. That's not to say it couldn't be done - and done well - but it just seems like a lot of effort for minimal gain. At least for FSAE ;)

[mech5496]

Owen, I was thinking the front motors (actually generators as they will be used to charge an accumulator and not for propulsion, in order to classify as an IC) producing 1-2kW. Using them in around 20% per lap recuperates significant amount of energy.

Now the best possible (i.e. more efficient) way to use that energy would be converting it directly back to kinetic energy when you need it, using something like "electric turbo-compounding" or using the front motors for propulsion too. It would operate like a KERS system; use the recuperated energy to boost corner exit for instance. I'm quite sure this would classify as a hybrid though...

So to get away from hybrids, just use the recuperated energy to boost the engine! You can also free up some extra engine power by removing auxiliaries like alternator, oil and water pump.


...it follows the same thought process as using an electric instead of shaft/belt driven water pump. Is the power you save/make worth the extra electrical draw and its associated weight?

Well, not really. The idea behind using an electric water pump is that it operates in a certain RPM in which it works efficiently. When using a mechanical pump, losses increase with increased engine RPM. Therefore you use some of the engine power to feed the alternator which converts mechanical to electric energy, then store that very energy on a battery and use it to power the pump. Because neither the alternator nor the pump motor have a 100% efficiency, you dumb away a fair amount of energy in the form of heat throughout the process; and you hope the gains from removing the inefficient in high RPM mechanical pump are more than the losses from the (double) energy conversion, which I doubt. The idea behind my proposed idea is using kinetic energy, otherwise dumped from the brakes in the form of heat every time you press the brake pedal, to power all these systems which would need engine power and fuel in order to work. I will try to quantify these gains in the next few days.

By using small DC motors, the system gets much simpler (no need for a complicated AC/DC converter). DC brushless motors can get really small and light, take a look at ThinGap for instance (http://www.thingap.com/standard-products/). Way less than a kilo per motor and their ring-like design makes them easy to package in the upright/hub assembly, possibly in between the bearings. Also the total accumulator capacity should not be that high, as it is constantly charged when braking, therefore its' weight could be kept relatively low.

Tristan, I like your idea of thermoelectric generators, need to do a bit of research on those to see if you can really gain something. Would you like to give me a hand on that?

[Mbirt]

Did the team from Kassel end up running the electric supercharger on their car or was it relegated to design presentation table adornment?

[TMichaels]

If someone will try to implement the front generators idea than they should definitely check back with the rules committee of the respective competition.
A thing that always baffles me is that there is no voltage limit for the electric system of the combustion cars. A 600V system will probably be rejected at scrutineering, but there is no rule prohibiting that.

[Michael Royce]

Memory says Cal State Poly Pomona won the 2000 Formula Student competition using an electrically driven supercharger.

I think the major key as to whether a car is classed as a hybrid or not is the last phrase of IC1.1.1 which says ".., such as those using electric motors running off stored energy, are prohibited." It is the stored energy provision that counts.

[JWard]

Would an IC car that only recovered energy from the front wheels (or any wheels) be classified a hybrid? I thought the intention of a hybrid was that it used electric power (recovered or on board) to drive the vehicle in parallel or serial (or a combination) with the IC engine? Energy recovery from the front wheels is surely just a more intelligent way of recovering and generating electricity which is and always will be required to power the control and auxiliary systems of the vehicle. It would be a sad day if a vehicle recovering energy from braking the front wheels, instead of an inefficient alternator type system a hybrid (imo).

I'm thinking motors attached to the front wheels, a la delft. Although those ring motors look quite interesting. I doubt anyone would call the system to convert the wheel driven motor voltage (3 phase or DC) into a 12V (or other) voltage for the vehicle does not make it a hybrid, all the other IC car's already have such systems!

ISGs on the other hand would make it a hybrid if used to put energy back into driving the car at any time other than for starting the engine.

Now, this intelligent energy recovery from front wheels and turbo compounding sounds pretty exciting to me. perhaps run all electric auxiliaries because you likely won't be able to spend all the electricity you're able to recover each lap, and you'll find a few free torques all over the range (at the possible cost of some weight - do electric water and oil pumps usually weigh more than their mechanical counterparts? probably, considering the engines already been designed to carry them already)

The electric supercharger (is that rules compliant?). Also brilliant, the advantages of electrically controlled boost have already been mentioned.

I also like the thermoelectric generator idea. Although would this make the exhaust gas energy recovery less efficient? (probably negligible)? or is it harvesting the waste heat energy after the turbo? I just might do some research.

Edit: just seen Michael Royce's reply regarding the running of electric motors from stored energy. This would ban electric superchargers then.

Also... With some work, it might be possible to use the front wheel energy recovery braking to maximise the front two wheels lateral and braking efforts on corner entry. No more locking the inner unloaded wheel (effectiveness probably dependent on the front LLTD?) Some kinematics guys will have to comment on how beneficial if at all this would be, but entirely possible electronically.

[TMichaels]

Memory says Cal State Poly Pomona won the 2000 Formula Student competition using an electrically driven supercharger.

I think the major key as to whether a car is classed as a hybrid or not is the last phrase of IC1.1.1 which says ".., such as those using electric motors running off stored energy, are prohibited." It is the stored energy provision that counts.

At some point in time the energy has to be stored and afterwards the car would be running of stored energy, if it releases the energy back into the front motors for example. Otherwise we would have to insert an energy meter in these cars to make sure that they only draw energy from the front motors, but never supply them.

So am I right that regenerating energy from the front wheels for example would be ok, if it is not stored and later being used to propel the car directly through an electric motor? Because in industry this is considered a "street coupled hybrid".

[DannytheRadomski]

What about using a turbo as a generator instead of as forced induction? I'm not entirely sure how one could go about this, but then you could have similar benefits to the front wheel energy recovery.

[RenM]

how does the hybrid rule prohibit an electric supercharger? The electric motor doesnt provide thrust for the car and is therefore more like an electric water pump.

If you were going to use some thermoelectric generator and a turbocharger you will want to use the generator after the turbine.

All systems you proposed for generating electric power will be rather heavy and complex. I cant really see the advantage compared to using a battery to store the energy, especially as an endurance is finished in a short period of time. You could also run a bigger alternator on your engine, that is only switched on during overrun. Because of the low power requirement the traction of the rear wheels is not really a problem.

[Pete Marsh]

What about electric motors for fans, water and fuel pumps, DRS or gear actuators? All electric motors running off stored energy, and totally allowed. How is a supercharger any different?

Surely the "intent" of that rule is to do with wheel drive or propulsion motors, not any electric motor on the vehicle.

You can do the same thing with hydraulics as well. Efficiency is about the same, power density of the actuators is much better, but worse for the storage. In the case of hydraulics it is not so versatile to use all over, and transmission is more of a hassle, so I would be looking to harvest from the diff rather than the front wheels. There should still be plenty of energy available even at the back I would think.

Pete

[Michael Royce]

Tobias,
Andrew Deakin may be able to confirm this, but my memory says that the Cal State car ran the supercharger directly off their on-board alternator, i.e. they did not store any additional energy beyond a "normal" battery. Apart from the very limited amount stored in the normal 12 volt battery, all the energy used by the car came from the petrol in the fuel tank. In overall terms, the electric supercharger was treated, by the scrutineers, like an electric water pump.

Teams that want to build a hybrid should do so. We would love to see them at the Formula Hybrid competition at New Hampshire International Speedway in May each year. Be aware though, that technically, building a running hybrid is an order of magnitude more difficult that an IC or electric FSAE/FS car! The upside is that GM, FOrd, Chrysler and Toyota are there recruiting as hard as they can. If you want a job in the auto industry and are a member of one of the hybrid teams, your chances of employment are very high!

Michael Royce,
Chief Mechanical Scrutineer,
Formula Hybrid.

[Z]

A thing that always baffles me is that there is no voltage limit for the electric system of the combustion cars. A 600V system will probably be rejected at scrutineering, but there is no rule prohibiting that.
Tobias,

Hmmm, I always thought the spark plugs operate at something like 20,000V (well, that's what it feels like when touching them when the engine is running).

But that would be a good way of giving the Electric cars a bit of an "unfair advantage" - limit the Combustion cars to 600V maximum! :D
~o0o~

Harry,

I reckon the best way of "recovering" braking energy is simply to NOT use the brakes. Good aero, and go around the corners as fast as you go down the straights!

In the production car world the better solution is to have better roads. Minimal sharp corners, and NO traffic lights (especially at the bottom of hills!!!).

The only vehicles that really need regen-braking are inner-city buses that have to stop-start all the time to let the passengers on-off. For these I reckon flywheel energy storage is probably the most efficient (was trialled in the 1970s (?), with a 6 foot diameter steel flywheel under the floor).

Z

[mech5496]

RenM, I do not think that it would be "rather heavy and complex". The total on-board energy that needs to be stored to run all auxiliaries and electric turbocharger would dictate the use of a large capacity (and therefore high weight) battery. Recovering brake energy is a smarter way to charge back your (relatively lightweight) battery than an alternator. Kw-size DC motors are weighting way less than a kilo, so a budget of 2.5-3kg for both motors, controller etc is more than enough. Plus the benefits of brake torque distribution (brake only one motor or both but at different torques to assist steering) and electronic boost control are profound. I don't know if it worth the time/effort (do aero instead :P) but it seems interesting to me!

Oh, and Z you are totally right... ;)

[RenM]

a clever designed electric supercharger wont need a lot of energy during an endurance. Depending on your boost pressure 3-5 kg in batteries will be more than enough.

Your idea sounds nice in theory but application on the track will be a real pain and is not worth the work for a formula student team.
Why not simply use a switchable alternator? Same effect, but a lot less complexity.