OT: Tesla Road Test

But you could, theoretically, buy it and drive it back. That's one thing the Volt has in spades over the alternatives. It's heavy and expensive, but the range is decent.

I'd be interested in a serial hybrid with, say, a 20kW traction motor, a 10kW generator, and minimal battery. That could be light, minimal moving parts, and, running the genset at peak efficiency, it'd be easy on the gas.

Cheers, James Arthur

On Monday, June 26, 2017 at 6:33:16 PM UTC-7, snipped-for-privacy@yahoo.com wrote: ..

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You've mentioned that before and I explained that it wouldn't be as efficient as current offerings and unacceptable performance for 99% of people.

kevin

Sorry about that, but I didn't see your name on them. They said something about a Federal Reserve and had the signature of some other guy on them

There isn't any maximum "theoretical efficiency" of a generalized ideal Otto cycle ICE, you could "theoretically" make it as arbitrarily close to 100% as you like if you could somehow raise the hot reservoir temperature arbitrarily high.

In the real world where you have to use real gases, fuels, and temperatures and compression ratios much less than infinity the limits imposed just from the first step in imposing real-world physics is considered to be around 45%, the most efficient Otto cycle gas engine ever designed has a thermal efficiency of probably around 35%, add the constraints imposed on a gas engine for a production vehicle and it'll have a thermal efficiency of barely 20%, and then you lose another 5% in the drivetrain, you lose another 5% every time you brake and the energy you used accelerating to overcome inertia is lost as heat, and you're finally left with maybe 8-10% of what you stared with being dissipated to overcome wind and rolling resistance, which is what you actually want to use it for.

On Monday, June 26, 2017 at 7:59:43 PM UTC-7, bitrex wrote: ...

The current model Prius reaches 40%. The previous one 38.5%.

The VW diesels can be up to 45%.

kevin

On Monday, June 26, 2017 at 7:59:43 PM UTC-7, bitrex wrote: ..

Your points are valid although with conventional vehicles one additional pr oblem is that the engine rarely operates at anywhere near its peak efficien cy (and it isn't efficient to keep them at constant RPM as many people advo cate).

Hybrid vehicles try to only operate the engine at its optimum and if the po wer required for propulsion is below what the engine can deliver efficientl y it is turned-off and the vehicle runs off the battery until the battery n eeds recharging by the engine. The engine then propels the vehicle and rech arges the battery. (This is a normal hybrid not a plug-in).

The optimum operating point for an internal combustion engine is usually ne ar full load at a speed that provides the power needed.

kevin

I don't see any reason the auto industry couldn't build that car today, if there was enough demand in the market for it. In fact it might be possible to DIY a serial hybrid like that with parts available online right now for maybe 10 grand - there's a small community of DIY electric conversion/hybrid builders, and shops that sell all the required parts including gensets, batteries, traction motors, charge controllers, CANBUS controllers, supercapacitors, etc.

Someday a fun project might be to build a plug-in hybrid like that. How about using something like a early 2000s manual transmission New Beetle hulk as the starting point? Could probably get one of those with a bad ICE for $500 that's otherwise in good shape for $500. And instead of the

4 banger maybe stick in one of these cute UAV rotary engines

On Monday, June 26, 2017 at 8:35:44 PM UTC-7, bitrex wrote: ...

The efficiency is pretty bad at 0.61lb/BHP/Hr

A good gasoline engine would be around 0.3 lb/BHP/Hr

kevin

I remember the conversation, of course.

I know most people would prefer a battle tank with blazing acceleration. My Acura needs ~10kW to maintain 70mph on the flat; a lighter, smaller, more streamlined car would need less.

Direct electric drive eliminates the clutch, transmission, & drive shaft, saving moving parts, weight, loss, etc.

So, 20kW motive seems about right--10kW for the flat, and 10kW extra for hills. But then I grew up going on family camping trips in a ~40kW VW van, climbing mountains in a bus loaded with six bodies, boat on the top, and half a ton of gear.

Efficiency-wise, an ICE at optimum torque and RPM into a generator has to beat a parallel hybrid's ICE run over the full range of torque and RPM handily, right? The difference can be 2:1, IIRC. The combination should be /more/ efficient than current offerings, not less.

Cheers, James Arthur

A plug-in implies a big, heavy battery, which I'd rather not lug around. Remember, for economy, the lighter the better. Just big enough to get a "boost" up a hill would be a great size.

But I've already solved the problem with a different sort of hybrid--I walk or bicycle most places, and drive a fuel-efficient car for the rest.

(It's down to 34mpg though--I might have a sticky caliper, dragging a brake shoe.)

Cheers, James Arthur

On Monday, June 26, 2017 at 11:39:30 PM UTC-7, snipped-for-privacy@yahoo.com wrote: ...

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Unlikely - what you're suggesting would be similar to a BMW i3 Rex with a s maller battery.

The i3 has a 650cc 34HP 2-cylinder range extender with an alternator that p rovides power to the main HV system. There is no mechanical connection to the wheels. The whole car weighs less than 2,900lb. So it is light by mode rn standards.

When running on gasoline The BMW only gets ~34mpg. The Prius with its serie s/parallel system, in a larger car with an engine that is 250% larger gets in the high 50's.

Admittedly the aerodynamics of the BMW i3 are not very good but they could only be improved by 15-20%.

There are a few factors to take into consideration:

1) As soon as you have a series hybrid you get a ~15% disadvantage compared to a parallel hybrid because of the ~20% loss in the dual conversion from mechanical to electrical and back again. A parallel hybrid avoids this.

2) With a gasoline engine the most efficient speed to produce power is in t he range 1500-2000RPM. If you want to get 10-20kW efficiently you actually need an Atkinson style engine in the 1-1.8L range. If you run the engine f aster it reduces its efficiency. As examples of this the Prius has a 1.8L engine in its current form, it used to be 1.5L. The Volt has a 1.4/1.5L en gine.

3) A hybrid does not run the engine over the "full-range of torque and rpm" . They actually constrain it to only run at the efficient part of the engi ne curve - which basically means run it at close to maximum torque all the time.

At the low end if the driver power requirement doesn't fit the curve the en gine is not run and the power comes from the battery. At he high-end the d river can run the engine into more inefficient regime at his discretion. (h ttp://techno-fandom.org/~hobbit/cars/SAE-bsfc.gif)

4) I expect that 10kW to maintain 70mph in the Acura is a bit lower than it actually requires.

This article

indicates that a Prius with a Cd of 0.26 takes 14HP @70. This is about 10.5kW. You are unlikely to get better tha n that. Add in transmission losses and you will need more. You will also n eed power to operate lights, heating etc. Maybe not much but adds up to a couple of hundred Watts even without A/C.

Overall even a very trimmed down car with your specification is not likely to beat current vehicle offerings and would have many compromises.

kevin

How big is the hill? San Francisco to Truckee? That's over two miles straight up!

Many of us don't have the option of walking so much. I walk a mile round trip to my mailbox. Anything else I have to drive.

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Rick C

Both the first and second generation Volt have a mode called "Mountain" which allows you to charge up the battery while driving to some fixed percentage of full capacity, around 35% IIRC. Like say if your battery is flat and you want to charge up driving into the city so you can glide around on electric in traffic, or I guess need extra torque in terrain with a lot of steep grades.

You can engage it any time you like, even cruising on the highway at 70. In my first gen when I did that it would work fine, but you could often hear that little 1.5L absolutely screaming away under the hood wide open at some ridiculous RPM; it was so loud that it was distracting and I don't think you'd want to run it in that mode on the highway in that mode with a first gen for any length of time.

I assume the engine/drivetrain wasn't being driven out of tolerances but it certainly didn't sound like it would be great for longevity to run it like that too often.

The second gen doesn't seem to have his problem, but I don't believe the battery charges as fast in that mode on the highway, maybe limiting the charging speed off the ICE in "Mountain" was one of the compromises they made to reduce the displacement a little and allow owners to use 87 octane instead of premium.

On Tuesday, June 27, 2017 at 5:11:49 AM UTC-7, rickman wrote: ...

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Hardly - Truckee is at 5,800 feet elevation. That's just over a mile.

kevin

Sorry, my bad. I did the conversion quickly and messed up my numbers. Sometimes I do math like that where I just "feel" the answer. This time I flubbed it. Still, that's a full mile vertical which is 7.8 kWhr or almost half the Volt full battery capacity.

In the Tesla Model S the vertical climb energy would be either 13% or 10% of the total range (depending on battery pack). Model 3 performance has to be estimated, but with 3,600 lbs weight and 60 kWHr capacity, the vertical climb would use about 13%. So once again the issue of range anxiety is vastly overrated.

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Rick C

:

smaller battery.

provides power to the main HV system. There is no mechanical connection t o the wheels. The whole car weighs less than 2,900lb. So it is light by mo dern standards.

2,900 lbs is light? For what, an armored personnel carrier? My four-door Acura hatchback specs at 2,350 lbs, and I've always thought of *that* as overly heavy.

The i3 has a large battery pack for plug-in use--that accounts for part of the weight--and a 130kW electric motor. Geeez.

This is closer to what I'd want--0.8L diesel, 20kW electric, 800kg,

120mpg on diesel.

The two-seater tandem version weighs 380kg--that would be fine for errands around town.

What a pig. Because it's heavy, no doubt, and boxy.

e that is 250% larger gets in the high 50's.

If real, that makes the Prius a lot more attractive. 50 or 60mpg is fine with me, provided it doesn't cost more than the gas it saves.

The Prius doesn't look that streamlined to my eye, but then neither does my Acura (drag coefficient = 0.34).

d only be improved by 15-20%.

Why? cd = 0.30

)

0.186 was possible in the 1930's.

ed to a parallel hybrid because of the ~20% loss in the dual conversion fro m mechanical to electrical and back again. A parallel hybrid avoids this.

But then you need a mechanical drivetrain, adding weight and moving parts.

the range 1500-2000RPM. If you want to get 10-20kW efficiently you actual ly need an Atkinson style engine in the 1-1.8L range. If you run the engine faster it reduces its efficiency. As examples of this the Prius has a 1.8 L engine in its current form, it used to be 1.5L. The Volt has a 1.4/1.5L engine.

m". They actually constrain it to only run at the efficient part of the en gine curve - which basically means run it at close to maximum torque all th e time.

That's smart, better than I thought. Thanks.

engine is not run and the power comes from the battery. At he high-end the driver can run the engine into more inefficient regime at his discretion.

it actually requires.

26 takes 14HP @70. This is about 10.5kW. You are unlikely to get better t han that. Add in transmission losses and you will need more. You will also need power to operate lights, heating etc. Maybe not much but adds up to a couple of hundred Watts even without A/C.

I checked my notes from 2005, and you're right. I derived the Integra's rolling losses as 13.7hp at 60mph not 70mph. I measured the deceleration time, coasting from 60 to 55mph on a flat strip. With mass known, calculati ng dissipation in MJ/s and converting to hp is straightforward.

That 13.7hp figure did not include the power an engine would need to overcome transmission losses, so, add an appropriate percentage.

y to beat current vehicle offerings and would have many compromises.

Something like the VW concept car I linked above would be great with me. Ju st get it under $20k, first. There's no reason it should be ?111,000, that's nuts.

Cheers, James Arthur

I did a search and the only Acura I can find that's not well above that weight is an Integra from the 80's. Clearly 2,350 is a vary light weight for a car.

$150,000, yes, that would make for a nice errand vehicle.

Streamlining is only important at speed. This wouldn't be your "around town" car?

They use exactly this dual conversion in locomotives to provide better control and efficiency. They have the diesel engines running generators and traction motors by the axles if not on the axles.

When a car is driven by electric motor(s), why is a transmission needed? I saw the Tesla has a transmission with 1 speed. Certainly they don't need it for reverse do they?

It's also not very practical as a car. But once the MPG gets above 50, how much further does it need to go?

Typical cars are roughly 3 to 5 gal per 100 miles. 50 MPG is 2 gal/100 miles, saving 1 to 3 gal/100 miles. To cut that in half would require 100 MPG only saving 1 more gal. There is a point of diminishing returns for the lengths we have to go and the sacrifices needed to achieve the extreme savings.

I would prefer a crossover/suv type vehicle myself. There are hybrids, but they only get in the 30's of MPG rather than 50's. At least I haven't found any that come close to 50 yet. Clearly it isn't all body shape as the Tesla model X seems to do pretty well nearly matching the model S in range from the same batteries.

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Rick C

The Model X is like, the least practical car ever! For 100k I could have a Volt for commuting, a Maserati Ghibli for weekends and trips, and probably enough left over for 5 years worth of electricity and gas to put in 'em!

You have a very strange idea of practicality. People don't normally use the term practicality to refer to price. The Model X is very practical doing nearly all functions of what a car is called on to do including pulling a trailer. The shape of the two seater car requires driver and passenger to sit tandem. There is little room for cargo. It is just one step above a motorcycle in terms of practicality.

If you want a Maserati, go for it. I think you will find it is the least practical car you would ever want to own. It also sucks as a fun car. The acceleration is far below the Tesla cranking out 0 to 60 times that are twice the best Tesla times.

Carbon on the valves! I'm pretty sure that's one problem a Tesla will never have, "Carbon on the valves!" I must have seen that movie 40 years ago and I still remember that line.

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Rick C