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 Post subject: Hybrid?
PostPosted: Wed Aug 03, 2011 11:55 am 
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Well, why not? What's the downside to a layout like this? The standard internal combustion engine would power alternators which would power the electric motors, so no heavy battery packs would be needed. The engine isn't driving the car, so no heavy transmission would be needed. Seems to me that it would solve the range issues on electric cars, and even with the heavy motors, still be as light or even lighter than a traditional FR layout. It's an incredibly simple design, so... What am I missing?
Image
Grey=Tires
Green=Standard internal combustion engine
Black=Alternators to power electric motors
Blue=Misc
Red=Electric motors


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 Post subject: Re: Hybrid?
PostPosted: Wed Aug 03, 2011 3:18 pm 
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teejayhoward wrote:
What am I missing?


Errr the Spirit of Driving which is where the heart of a Locost develops from?

I'm sure first model Prius are cheap by now, you know you want to - enjoy.


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 Post subject: Re: Hybrid?
PostPosted: Wed Aug 03, 2011 3:57 pm 
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teejayhoward wrote:
What am I missing?


Electric motors and alternators aren't all that light, and now you're introducing two more energy conversion inefficiencies. It's doable, but not very practical. Jeremy Clarkson did it with his Hammerhead-i Eagle Thrust car, lol.


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 Post subject: Re: Hybrid?
PostPosted: Wed Aug 03, 2011 4:13 pm 
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I would think that the available power to the electric motors would be ~20-50% of the engine power after conversion losses. Without the batteries for storage, peak power for short durations such as accelertion can still be no more than what the engine can power.

Not that this needs to be a primary concern. Just don't think that you'll get the performance the Locost is capable of. It can be done.

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 Post subject: Re: Hybrid?
PostPosted: Wed Aug 03, 2011 6:32 pm 
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And you'd need one hell of an alternator to put out enough amperage to run those and make it worth while. Not to mention running them off the alternator automatically means you are using ac motors vs dc unless you're working in a converter somewhere, which means much higher cost up front...

And what about cornering? With two motors up front, you'd have to develop a system that redistributed torque to the proper wheel to allow for the difference in wheel speed from inside to outside. It could limit voltage output depending on the angle or degree of steering column rotation or tie rod movement bade on a fixed location...

Anyone have a calculator to determine wheel rpm at a given diameter and a given ground speed? The electric motors would have to be capable of a similar rpm to prevent them from being over run...

Or maybe I haven't had enough sleep yet... lol


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 Post subject: Re: Hybrid?
PostPosted: Wed Aug 03, 2011 8:16 pm 
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"Electric drive." It had limited popularity in the 1920s and 1930s for milk trucks and other urban delivery vehicles. The main advantage was that it was "employee proof", which clutches and unsynchronized transmissions were not...

The alternator and motors will weigh more than an automatic transmission, and since the alternators/generators aren't all that big, you'll have to have some batteries to provide acceleration.

If you had a crashed Insight or Prius for a donor it might be an interesting build, but packaging everything within a Seven envelope would be a sizeable project.


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 Post subject: Re: Hybrid?
PostPosted: Wed Aug 03, 2011 9:38 pm 
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The idea isn't totally without merit. .. I was at a local boat show a while back and saw a conversion system for pleasure craft (ie a boat big enough for me to have a real party!) using the classic GM 6.2 to drive a BIG alternator and that drove 2 watercooled AC motors. Also provided the juice for unlimited lights and audio :D

I do't know what your goal is but have you considered a parallel aka "thru the road" setup? IIRC it takes about 25 hp to drag 7 along at 65 or so, use supercaps and an electric booster motor on each front wheel for acceleration. 35 hp ought to be enough to keep the caps charged if its a booster only function and run the car at 75+mph, Jack did it with MAX on less. ..
Fire the Boosters Mr Scott!! :shock: Now that could be a handful of go fast button!

Re; controlling a dual motor drive(assumed to be DC), the overrunning tire loafs and you get dragged thru the corner on the inner tire IF you wire the motors in parallel off of the controller output terminals. Voltage= RPM. .. Motor specs include rpm/volt ratings.
So off you go down the road,the outer tire running at its programmed (typical iirc) 72rpm/volt and oohhh 72 volt so 5184 rpm :ack: as is the inner tire(needs some baby coach wheels with those rpm!).
Then you start a left turn, the outer tire has to cover more territory due to the constraints of the axle/chassis/duct tape but it can't provide additional thrust above its voltage determined rpm so its coasts drawing very little amperage.
Actually you get a teeny tiny bit of extra juice at the inner tire ( parallel wired remember?) when the outer tire begins to function as a generator by being put into overspeed condition (I don't recall exactly the minimum average needed for a usable gain in power provided to the inner tire but it was somewhere ~13% overspeed).

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 Post subject: Re: Hybrid?
PostPosted: Fri Aug 05, 2011 3:18 am 
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Electric drive can be made fairly efficient, where total weight is not a problem.
And that is where you will typically find electric drive, ships, locomotives, and very heavy mining dump trucks.


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 Post subject: Re: Hybrid?
PostPosted: Fri Aug 05, 2011 9:58 am 
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(Many) years ago I did a series of conceptual warship designs where advanced electric propulsion proved effective, but mainly because of the total energy efficiency through being able to share propulsion and hotel loads, thus allowing genset prime movers to run in their optimal load ranges. Ignoring hotel loads (which can be large on ships) a straight mechaical drive is generally lighter and more efficient than an electrical one, although there are exceptions. There are operational requirements though (e.g.: high torque for icebreakers or reduced vulnerability to damage through separation of components) that encourage use of electrical power.

Traditional sets were DC-DC and heavy. Modern ones are generally AC, for reduced mass (and to support hotel loads), but with a requirement for fancy electronics for speed control.

A gas or Diesel electric car would not be my first choice. A hybrid would be much better, but perhaps even heavier. It does beg the question about popularity (?) of hybrids with so much freeeway driving.

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 Post subject: Re: Hybrid?
PostPosted: Fri Aug 05, 2011 10:29 am 
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Quote:
It does beg the question about popularity (?) of hybrids with so much freeeway driving.


There is some sense to this. You just need an engine to cover the normal base load which could be say 25 HP for highway speeds. A battery pack provides extra power for acceleration and gee-wizz but really unless you track the car would rarely be used for more then 10-20 seconds.

It's a huge complexity addition though just so you can step on the fast pedal and go Gee-wizz!

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 Post subject: Re: Hybrid?
PostPosted: Fri Aug 05, 2011 10:43 am 
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KERS! :)

Can we get some DRS while we are at it too? :)


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 Post subject: Re: Hybrid?
PostPosted: Fri Aug 05, 2011 2:12 pm 
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Why not just use one electric motor and hook it to the input on an IRS diff? That would allow you to ignore the issues of different wheel speed in corners. However you still would want to have a battery bank...

EDIT:
At a certain point you are just replacing a drive shaft with a lot of complexity.


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 Post subject: Re: Hybrid?
PostPosted: Fri Aug 05, 2011 4:29 pm 
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Tom17 wrote:
KERS! :)
:cheers:

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 Post subject: Re: Hybrid?
PostPosted: Sat Aug 06, 2011 12:11 pm 
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Hub motors can be fairly inexpensive for the power provided and using them for a booster eliminates the "cogging" issues inherent in low speed motors. .. direct drive would be considered low speed for design values. Still, heavy considering what you get and all unsprung weight at that.
Seems like a single motor would be a simpler choice and there would probably be enough room to fit something in there behind the steering rack, especially if you use an diff configuration with the electric motor running parallel to the axle centerline.
A chain drive diff in the front? hhmmmmmm. ..35# for the chunk, 25# for the motor, 50# for energy storage and control components(see below), 10#(?) for the axles, added complexity. .. percentage wise there's some obvious penalties.
The gross system weight can be reduced by using supercaps but you'll need a much heavier than "normal" alternator to be able to recharge any system in a useful time frame I would think.
This'll give you some numbers for energy storage,
http://www.maxwell.com/products/ultracapacitors/docs/MAXWELL_UC_COMPARISON.PDF

Don't forget to subtract for efficiency losses when calculating available power and the stuff ain't cheap.
You can use driveshaft rpm and engine demand (throttle/engine rpm) to calculate amount of boost needed with the fewest number of variables.

Of course all of the above is rather off topic considering the original question. ..

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 Post subject: Re: Hybrid?
PostPosted: Sat Aug 06, 2011 5:46 pm 
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There is really no escape from the fact that efficient motors and generators require a lot of iron and copper to work well, which is both heavy and expensive.
Ultra light weight high rpm machinery (such as the ubiquitous car alternator) can be made both small and light, but at the expense of efficiency.
Nobody really cares if a 60 Amp automotive alternator takes 1.5Hp or 4Hp to drive it to full output, as long as it does the job producing 60 Amps. But for a hybrid, or electric drive, such gross inefficiency would be difficult to live with.


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