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Old 12-24-2010, 12:58 AM   #21 (permalink)
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I think both Frank AND some of the others are right.

If an ICE is "specked" to provide acceleration hp as well as cruise hp, cruise mode will, by design be quite restrictive and lower bsfc.

Also, HP for HP The hybrids available are weighted more toward the ICE side of the equation, going back to the needing to be "specked" for the ICE to both accelerate and provide cruise power.

Theres one thing I'm sure of, Electric motors shine at providing low end torque and suck at providing torque at the top of their curves.

The tweak Im kind of excited about is in the way that someone suggested I set mine up, avoiding a LOT of inneficiencies:

Use 2 drive sprockets on the electric motor, one leading to the wheel, one leading to a centrifigual clutch on the diesel.

for low speed (45 and under) its an electric car.
above 45, the deisel comes on and stays on at WOT. Actually about 80% of full output, its best bsfc sweet spot.

Here is the fun part, because the diesel is specked at 125% of the highway requirement, when the car is being "pushed' by the diesel which is running at a constant speed and output, one can modulate regen on the controller to controll speed.

so rough numbers:

50mph flat ground hp requirement to move car 4hp , about 5hp goes into pack via regen.

70mph flat ground hp requirement to move car 5.5 hp about 3.5 hp goes into pack via regen,

60 going up a steep hill requirement to move car 9hp. All engine power (and all electric power for that matter) goes to moving car, no regen.

Naturally, one could use electric power to cruise on highway as well and I know I would till the batteries were sufficiently discharged, say a nice battery preserving 70% soc.

No this is essentially dialing in regen to control speed. it would be super cool if someone could help figure out how to use a gps's signal for example to talk to a cycle analyst or other multi gauge to basically take over the regen dialing upping and downing as a sort of cruise control :-)

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Old 12-24-2010, 01:28 AM   #22 (permalink)
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Specked, like eggs?

No no no no no... you do NOT want to govern speed with "regen"! It is not efficient.
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Old 12-24-2010, 01:35 AM   #23 (permalink)
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specked, perhaps im not spelling it right, as in specifications meant for.

Id love to learn more on your opinions of regens efficiency, I am aware of the regens function of putting amps into a pack based on occasional braking, not too much upside there.

But I have the Sevcon people telling me that their brushless motor controller is as efficient on the regen side as it is on the drive side (High 90s)
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Old 12-24-2010, 01:52 AM   #24 (permalink)
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That the Sevcon has 90% eff for regen may be, but that is not the efficiency of the whole system. Brake regen is reclaiming some portion of energy already expended in getting up to speed that would otherwise be completely wasted- a good thing generally, but some of us have habits and conditions that allow such gentle braking that the penalty for paying for and carrying around the regen equipment is greater than the payback.

I think it is safe to say that your best bet to keep the batt pack charged is via plugging it into a wall outlet- money-wise, fuel efficiency-wise, emissions-wise, all that.

Oh- "spec'd" is short for "specified".
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Old 12-24-2010, 09:54 AM   #25 (permalink)
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Agreed on Regen, and how to best keep the pack charged.
The ICE is for when I need to go further then that ;-)
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Old 12-24-2010, 09:56 AM   #26 (permalink)
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Quote:
Originally Posted by Frank Lee View Post
You haven't picked up what I'm putting down....

ICEs are most efficiently converting fuel to work during acceleration EVEN THOUGH that is when MILES per gallon are the worst.
I know a loaded ICE gets more efficient when you look at the specific power output.
But as it is, it's the mpg - the fuel used - that really counts.

Look at the EPA car guide.
Highway mpg are about 50% higher than city mpg (except for hybrids).
So it makes sense not to use a big ICE for the most fuel consuming phase of the ride.

Surely the acceleration phase is also a real drain on a battery in an EV.

Quote:
Shouldn't those power values be reversed?
Yes, though I doubt Toyota or Honda dared to do that when they launched their hybrids.
Instead they opted for a concept with rather minimal changes to normal car designs.

If they had dared, then essentially they'd have been building an EV with a tiny ICE cruise engine / range extender that never powers the car directly.
Buyers may not have been ready for that.
Probably still aren't.


"What about the engine ?"
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Old 12-24-2010, 09:59 AM   #27 (permalink)
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Originally Posted by Frank Lee View Post
Insight I has a 67 hp ICE and a 6-13 hp electric. Shouldn't those power values be reversed?
Yes, but the Insight's battery is too small to get it over a mountain. That being the case, the ICE has to be sized to handle a continuous hill climb, which requires around 50HP.

Honda's proposing to put a 160HP electric motor and a 2.0L Atkinson engine in the Accord PHEV. I'm sure it'll sell about as well as the first Accord Hybrid, because its design philosophy appears to be the same: add electric drive, go faster than before. Too bad go-fast enthusiasts don't care about fuel economy, and vice versa.

Should have been a 60HP electric motor and a 1.0L Atkinson engine in a Fit or second-gen Insight.
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Old 12-24-2010, 10:04 AM   #28 (permalink)
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Quote:
Originally Posted by euromodder View Post
I know a loaded ICE gets more efficient when you look at the specific power output.
But as it is, it's the mpg - the fuel used - that really counts.
No, the specific power output is what counts. Specific power output times road load equals fuel consumption, and road load isn't going to change unless you change tires, vehicle mass, or aero.
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Old 12-24-2010, 03:53 PM   #29 (permalink)
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Quote:
Originally Posted by euromodder View Post
I know a loaded ICE gets more efficient when you look at the specific power output.
But as it is, it's the mpg - the fuel used - that really counts.

Look at the EPA car guide.
Highway mpg are about 50% higher than city mpg (except for hybrids).
So it makes sense not to use a big ICE for the most fuel consuming phase of the ride.
I'm at a loss as to how to rephrase it again so we can cross this gulch. I know what you are saying but I don't think you're hearing me.
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Old 12-24-2010, 05:35 PM   #30 (permalink)
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Acceleration requires multiple times more energy than cruising, we can agree on that.

What Frank is trying to say is the IC engine is operating at higher BSFC when accelerating.

It may be better understood by adjusting the road conditions to the ideal state.
You climb a grade using the highest gear and then coast downhill with the engine off.

This is essentially pulse&glide (engine off glide). You can see this when you have an instant fuel economy reading. Slight grades reduce instant mileage fractionally, while the potential energy state is increased by elevating the vehicle. Then that same energy is used to coast downhill with no fuel consumed.

In climbing a grade, your ideal would be at best BSFC in highest gear. The increased efficiency translates into increased elevation, which is stored energy. Like the roller coaster which travels most of its track without power the benefit is distance travelled without any additional energy requirements.

Understanding this, it should be easy to understand that constant speeds where lower power requirements are normal, is precisely where the throttled IC engine is least efficient, even though the mileage may seem to be better (and it is) the load on the engine is so low that efficiency is terrible.

Build a vehicle with 4 separate engines that are each 25% of the size of the original engine. Use all 4 for acceleration and only one for cruising and you mileage would be much better, because you could optimize the BSFC for the conditions by using 1,2,3 or 4 depending on the loads applied.

If your 60 MPH sustained load is 15 HP, you need a max 25 HP engine for best BSFC, but then you would not have any reserve power for sustained grades or strong acceleration.

Car engines are designed for the worst case scenario so they have the power reserves to provide acceleration or grade climbing capabilities, but that same over sized engine operates at less than half its maximum efficiency when it only needs to produce 10% of its maximum power, because the air intake is restricted and the actual compression before combustion is less than half of the same compression when there is no manifold vacuum.

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