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Old 01-22-2012, 01:32 AM   #101 (permalink)
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Sorry for a bit of a threadjack, but,

In a modern car engine, at optimal load, how much does efficiency change across the RPM band and how much room for improvement is there?

It would make decent sense from a simplicity (and thus cost) standpoint to use a transmission/drive like Old Mechanic has and keep an engine at constant load, varying the RPM when you change driving conditions, if the RPM range of high-efficiency (at high load) is wide enough. I've always thought CVTs were a wonderful idea, with current implementations only falling short in that they're sometimes lossy due to friction, and have limited range of ratio.

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Old 01-22-2012, 02:07 AM   #102 (permalink)
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Originally Posted by Old Mechanic View Post
The key ingredient that has yet to be incorporated is capacitive energy storage at extremely high efficiencies.
I'm not sure I completely follow your use of "capacitive" -- it makes me think "capacitor", as in electric vehicles. They are used (for regen) in some hybrids, but with a lithium battery bank the size used in a 40-mile-range plugin hybrid, the ability of the batteries to absorb braking load is very high. There are electric cars with regen power that can exceed the traction of the tires. I gather you are thinking of ability to store energy very quickly, in the way a capacitor does, but using a hydraulic accumulator.

Very early in my career, I was tech writer for an underground mining equipment company. All the equipment was hydraulically-operated with a big electric motor as the prime mover. I got the job because I could read hydraulic prints, and that ability came mainly from having owned a couple Citroens and fooling with their hydraulic systems, and reading about hydraulics. I've mentioned elsewhere being impressed by a 1960's era hydraulic hybrid powered by an old 1200cc VW beetle engine. The car was basically a huge hydraulic accumulator with wheels. The car would smoke all four tires at the start of what for the day was a very fast 1/4 mile: 10 seconds or so.

So I definitely like your approach.

The appeal, for me, of a plug-in hybrid is that the energy that powers it most of the time can come from a huge list of sources: sun, wind, natural gas, nuclear, hydro, coal, oil, etc. A surprisingly large number of electric car owners also have solar panels, and some of these people are getting very quick paybacks. A second appeal is that electricity is dirt cheap, and will remain so for a long time even if electric vehicles sell at rates higher than the most optimistic projections.

Where I live, a Nissan Leaf costs about 2.5 cents per mile to fuel. A similar sized ICE car at 30 mpg average, costs, today $3.60/30 = 20 cents a mile.

Have you talked with Tom Kasmer? He has the "hydristor" and is a fan of hydraulics: Hydristor - Home Page

I like your comparison of serial hybrids and hypermiling.

I don't think of your post as a hijacking. It's always interesting to see what others are up to.

Thanks Ken.
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Old 01-22-2012, 03:14 AM   #103 (permalink)
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Originally Posted by Ecky View Post
Sorry for a bit of a threadjack, but,

In a modern car engine, at optimal load, how much does efficiency change across the RPM band and how much room for improvement is there?

It would make decent sense from a simplicity (and thus cost) standpoint to use a transmission/drive like Old Mechanic has and keep an engine at constant load, varying the RPM when you change driving conditions, if the RPM range of high-efficiency (at high load) is wide enough. I've always thought CVTs were a wonderful idea, with current implementations only falling short in that they're sometimes lossy due to friction, and have limited range of ratio.
No problem on the threadjack -- it's plenty related enough, I think.

It's a great question. A modern CVT (such as the Nissan unit) provides the full range of useful ratios from a low-enough-low to break traction on a dry road, to a high-enough-high to arrive at a top speed that is HP limited. A lower low would only be useful for lawn mowing, or pushing a snow plow, if one had the traction, and a higher high would reduce top speed and acceleration near top speed.

Neither a CVT nor an IVT keep an engine at either an optimum or constant load. IVT's have, so far, been very lossy. A Cub Cadet has a fan blowing on it's hydrostatic because there are larger losses in an IVT than in a geared transmission (in most systems waste goes off as heat).

About one or two decades ago, Audi offered the same car with CVT*, conventional automatic, and manual. At that time, the conventional automatic was slightly less efficient than the CVT and manual, which were equal. Now, conventional automatics are just as efficient as manuals too. Dual clutch manumatics can be slightly more efficient than the others, especially when coupled to a highly-tuned engine, (that can benefit from the very close gear spacing) but otherwise the difference is slight, because of things like variable valve timing that have provided broader power bands than in the past.

If a car requires 15 HP to travel at 60 mph, it requires 15 HP whether in second, third, fourth, fifth, or sixth gear. A 200 HP engine does not produce 15 hp efficiently, regardless of the rpm. It will produce 15 hp more efficiently if the rpm is low -- in many engines, very low. That means the torque required is relatively high, and the throttle is further open than it would otherwise be, so there are fewer pumping losses. So in general lugging an engine produces better mileage than letting it rev more freely.

This (pumping losses) is the main reason a V6 Honda Accord gets significantly worse mileage than a 4 cylinder version. In both, assuming automatic transmissions, the optimum gear is selected, but in one engine you are operating with the throttle 90% closed, (10% power) and in the other 94% closed (6% power). In the first case, the engine might be 10% efficient, and in the second it might be 8%.

Throw away the big engines, and install a 20 hp engine running at it's torque peak, where it is producing 15 hp. It will run at 30% efficiency. So it will get about three times the mpg of the 4 cylinder. Flat out, the car will have a speed of 65mph, and the 0-60 time will be about 1 minute. To make the car driveable, you'd need a source of burst power, like an electric motor with batteries, or a hydraulic motor and an accumulator.

BSFC maps will tell you the efficiency of an engine at any load and rpm. They have one or more islands (like the colorful chart above for an electric motor). You want the engine to operate in the island with the lowest BSFC. But the driver demands all sorts of HP requirements, so the engine cannot run at the constant torque and rpm define that island.

Thus the idea for a series hybrid (and to a lesser extent a parallel hybrid, and to a lesser extent yet, a light hybrid). In a series hybrid, you can operate at peak efficiency (or very close) all the time. When the batteries (or hydraulic accumulator, or flywheel) are not able to absorb full load power, turn the engine off.

The engine operates at peak efficiency or not at all. The advantage of a plug-in hybrid over a hydraulic or flywheel hybrid is the longer cycles: less time spent warming up, fewer heat shocks, etc -- a big portion of wear is from startups.

On the other hand, a hydraulic hybrid can have other advantages, such as simplicity. So it will be interesting to see what OldMechanic comes up with -- his idea goes beyond just the IVT.

* Now CVTs often have discrete speeds available, because many people find they like the more conventional sound of and engine going through the gears. The difference in efficiency is negligible, because engines are now so flexible.

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Old 01-23-2012, 05:19 AM   #104 (permalink)
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Quote:
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N... At that time, the conventional automatic was slightly less efficient than the CVT and manual, which were equal. Now, conventional automatics are just as efficient as manuals too...
You do need to be careful with this sort of comparison if you are going by EPA ratings as a measure of efficiency. We have demonstrated again and a again that higher primates are perfectly capable of operating a manual transmission vehicle (with a clutch and a neutral, and bump starts) in vastly more efficient modes than CVTs or automatics will allow by staying near bsfc when accelerating, and coasting when not, and taking advantage of the higher peak efficiencies of the manual driveline, and paying lots of attention to their situation (always a good idea).

A lot of manufacturers also play gearing games assuming the manual is for "sport", even though that sport might in actuality be about best efficiency, and not fastest lap times or 1/4 mile
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Old 01-23-2012, 12:27 PM   #105 (permalink)
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You do need to be careful with this sort of comparison if you are going by EPA ratings as a measure of efficiency.
This is something of a sore point for me, because in my world, there are all sorts of misleading measures of fuel efficiency. In my view, the only measure of vehicle efficiency we have is the EPA tests (and careful constructed roads tests or computer models which emulate them, as nearly as possible.)

Driving techniques can change the numbers, but the change is a measure of driving technique, not the vehicular efficiency. (And your point is well taken that some transmissions effectively squelch hypermiling.) EPA survey results show that very few people actually practice hypermiling, so where sample size is large the surveys and EPA numbers match pretty well.

A couple years ago, Aptera was on the cover of Popular Mechanics with a huge 300 mpg headline. But the 300 mpg had absolutely nothing to do with vehicular efficiency -- it related only to driving profile -- they could have claimed 400, 600, 800, etc with exactly the same logic. I've always called the Zing a 100 mpg vehicle, because it gets that when operating on gasoline alone, without any sort of hypermiling, with no change in battery charge level, and with my best approximation of EPA combined testing. Under that condition, Aptera was claiming 120 mpg for the vehicle that was promoted as 300 mpg by Popular Mechanics. The Aptera was, at that time, twice the weight and of greater frontal area than the Zing, and of not-much-lower Cd, so I was already skeptical re the 120 mpg.

I responded to the Aptera 300 mpg with my own equally valid calculation, based, like the Aptera, on a particular driving schedule... except that mine was more realistic, because I have actually done it, and because it represents a realistic average yearly accumulation. Their's was based on a hypothetical daily mileage of something like 100 miles (I'd have to look it up, or think too much, but don't have the time.) That's 36,500 miles per year -- far more than anyone would be likely to drive a two-seater commuter.

In my schedule, I drive 39 miles on electricity, followed by one mile on gasoline. I've gone 40 miles and have consumed 1/100 gallon of gas. 4000 mpg. In their case, they went something like 60 miles on electricity and 40 miles on gas: 1/3 of a gallon of gas, 100 miles: 300 mpg.

I could argue that my figures are more realistic, because 40 miles per day works out to almost the 15,000 miles that the EPA has used, and continues to use, as representative of an average driver's yearly accumulation.

So the Zing is more than 13 times as efficient as the Aptera, given a more realistic daily accumulation. Something is obviously haywire here. That's because in neither case, does the test measure the vehicle's efficiency.

The point being: I can give the Zing any mpg figure I want (and Volt drivers do this, talking about 1200 miles per gallon, etc.) But I am not measuring the vehicle, I'm measuring the driving pattern... or in the case of hypermiling, the driver and his terrain.

Non-commercial interests and individual drivers can measure these things in ways that make sense to them, but vehicle measurements need to be done by the same test to have any meaning, and to remain in the spirit of "truth in advertising."

At least that's my story, and I'm sticking to it.

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Old 01-23-2012, 12:38 PM   #106 (permalink)
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Just curious, what's the current status on the Zing! ? (If I were an investor, what would you report to me?)
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Old 01-23-2012, 12:40 PM   #107 (permalink)
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Ken, when reading how you were going to put the charge termination under control of the driver, I was reminded of some hypermiling techniques where the driver can make a huge difference.

And if you consider the nature of THIS forum, the most cost effective mod is to adjust the nut behind the wheel.

So when someone blanketly says that CVT and Manuals are equal, I will always reserve the right to protest They could not be more unequal IMHO. Especially in the context of ecomodding, where you can (and I have) go get a $300 parts car and install a manual trans and get ~ 50+ mpg TODAY.
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Old 01-23-2012, 12:53 PM   #108 (permalink)
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I guess the point is that maintaining the status quo in driver education while advancing the technology to suit is a sub-optimal proposition. The reason we have this forum is in part to address that situation, and humans can be expected to be better than they are also, and as in your charge termination scheme, they are the ones that know what they want to do and have the ability to predict what will happen, and know when to stop charging the batteries (or get off the gas pedal or ???). And drivers can learn how to manage energy better today, for like zero cost, and with some of the most trivial of modifications.

best efficiency is had from a symbiosis of driver and vehicle, that fact should never be ignored or discarded. Hybrids are at a disadvantage compared to a driver with good technique.
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Old 01-23-2012, 01:57 PM   #109 (permalink)
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"You can't fix stupid".

I've averaged 67 MPG, for over 25k miles, in a CVT equipped Insight without lean burn.
Driving right at or just below the speed limits on the roads I travelled.
615 miles in 10.5 hours driving time at 70 MPG.

I ask repeatedly "What average speed?", when peole post really high mileage claims.
And almost without exception get no answer. I can only guess that means the answer is VERY LOW average speeds.

DCB, we have bumped heads here a few times, that is not the porpose of this post.

If you want to spend your life trying to re-educate drivers, then God help you.
Pop always told me "Blame the system, not the people". What he meant was when you attack people you get nothing, and the ydo percieve it as an attack, but if you change the systems they employ then you have a much greater chance of success.

Maybe that makes me the oddball here, but my method has far greater chances of making the idiots I see on the road every day, more efficient drivers, in spite of their idiocy.

Don't think I have enough heartbeats left on this planet to engage in wholesale behaviour modification. Maybe I am not that much of an idealist.

Thanks Ken for the positive support. My quest has now covered 12 years. In another 12 I will be 73 and probably not driving much, which should make Neil very happy, since my carbon footprint will drop substantially.

I still think Evacuated Tube Transportation Technology is the future, and it will please Neil and the other electric transportation advocates to no end that it is electric.

My solution is a transitional one that bridges the gap between current technology and the point at when we have batteries with the energy density of a NASA flywheel battery.

Until then I have seen no better alternative.

regards
Mech
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Old 01-23-2012, 05:04 PM   #110 (permalink)
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Thanks Ken for the positive support. My quest has now covered 12 years. In another 12 I will be 73 and probably not driving much, which should make Neil very happy, since my carbon footprint will drop substantially.
Mech
I certainly hope you are still driving in 12 years... I'll be 73 then too. My dad just gave his Camry to my daughter, realizing (openly) that he doesn't need it much, and (internally I imagine) that he is potentially dangerous. At 92, He thinks of you and me as young pups.

Funny... right in the middle of this post, my dad called. He'd given his doctor a list of 18 complaints, and was concerned that the doc didn't really do anything. As he read through the list, I thought "Oh no -- he's describing me!" Forgetful... check. Get up in the middle of the night to pee... check.

How did this happen?? Weren't we just in high school?

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