The ultimate efficiency 4-passenger car
 

Hello, folks,

I wrote a nine-page analysis for the Sierra Club on what they should expect for the likely efficiency of a personal automobile at some time in future, say 10 or 20 years from now. (Or, maybe sooner.) I think you can access it here:

http://ecomodder.com/AutomobileEfficiency.doc

This is a Word file. If you have trouble, let me know, and it will get fixed.

The final conclusion is that this future car will get 150+ miles per gallon at 60 mph on the highway. The EV folks of course will want to know how much electricity it would take as an EV, and I didn't include that in the paper. But I can convert to an EV, given the plug-to-wheels efficiency.

For EV efficiency of 70% (plug to wheels), the future car would use 123 watt-hours per mile at 60 miles an hour.

Ernie Rogers

:thumbup: Good work, Ernie.

What exactly is your relationship to the sierra club?

What do we lack now that we will have in 2030? Why can't you build this 150mpg cruiser in 2009?

I hope lightweight alloys and composites will become more affordable. I'm sure rolling resistance will continue to improve, and I look forward to rolling on future LRR tires. Just be aware that current solar car LRR tires may be too low traction for anything besides solar cars.

Aerodynamics is a mature field. The existence of concept cars from the 1950s with Cd as low as .14 indicates we have been capable of excellent aerodynamics since at least then. The development of computational fluid dynamics may have been the final advancement in aerodynamics research. If automotive Cds continue to decrease, it will not be due to emerging technologies, but to making aero a higher priority during the design process.

A four seat, probably four wheeled, "stretch-Aptera" concept would come close to the pinnacle of fuel efficiency achievable with current technology. Punching the numbers for an Aptera that put on 300lbs into the simulator at Aerodynamic & rolling resistance, power & MPG calculator - EcoModder.com , we get an amazing 158mpg at 60mph steady-state cruise. EPA fuel economy would be much less, maybe 100mpg? If there were enough demand for it, it could sell for $30-40k.

Perhaps the constraints of "consumer acceptability"?

That's the limiting factor the automakers routinely march out as a reason to shoot down ideas that stray from where they really want us to be.

One big question: why on earth should a PERSONAL automobile carry four passengers? Get past that mental block, and you have room to cut weight & improve efficiency even further.

Of course there's also a market for family cars, that can carry four or more, but there's a large percentage of the population that doesn't need cars this size.

Member, transportation expert /chair in Provo, Utah

I agree, Robert,

Mostly we are waiting for industry inertia. Uhh, the Aptera is an EV?

If you are talking about mpg equivalent, I wasn't for the new car. You can check my calculations--punch my design parameters into the program. Present engines can't deliver 150 mpg until you get about 40% efficiency, which isn't available yet.

James, your problem is simple-- you are smarter than the average U.S. car buyer, who thinks he needs to cover all possible uses in just one car size and shape.

Ernie

So, the Sierra Club thinks that climate change and current trends allow economic predictions more than a decade distant? I wish I found this reassuring.

Consider for the moment that this same question was asked during the 1973 oil embargo, when, interestingly, the price of gasoline quadrupled (Sound familiar?) Cars back then didn't have as standard equipment: Air conditioning, electric windows, cruise control, automatic transmissions, etc.

If vehicles had stayed the same during this entire time, the technological improvments would have resulted in improvements in fuel economy as suggested. However, vehicles that sell today have higher acceleration rates, better crash survivability, less harmful emmissions, more luxurious features, better sound insulation - but they are also heavier. As Ernie pointed out in his article, weight = fuel consumption.

Nope, The problem is you and me and what we are willing to accept.

What is your guess?
 

Hello, Bob,

What is your guess for 10 years hence?

Ernie

Some real truth here
 

Hello, Racer,

You have a very good point here. While some of us want a small, simple car, what we are offered is determined by the majority. (My brother-in-law lusts for a Chrysler 300, though he knows the planet is in peril.)

It was about a month ago that Volkswagen announced that they would not be bringing the 2010 Polo Bluemotion to the U.S. because "it isn't big enough for Americans."

Fuel economy claimed for the 2010 Polo is 80 mpg.

Ernie Rogers

Comments from the Grinch:

1. I do agree that the minimum aspect ratio for an efficient tire is 55% and that might be pushing it.
2. Empirical experience about tire diameter is at variance to the assertion that bigger tires are more efficient. Wheel-tire assemblies are big flywheels that the engine must accelerate along with the vehicle every time the vehicle speeds up. Rotational moment of inertia goes up with the square of diameter. If a vehicle were operated like Class 8 trucks with long periods of operating at more or less constant road speed, this is not much of an issue. Lighter-duty vehicles have to operate in an environment of stop-and-go or at least one of deeper variations in speed. Hence there such vehicles have more scope for having to speed up these “flywheels.” Pickup trucks operate with very large wheel-tire diameters and invariably the bigger the outside diameter, the worse the MPG. I’ve never seen any real world variation in that generalization.
3. The air resistance of bigger diameter tires is subject to debate. With lifted pickups, the air resistance goes up greatly. Maybe, as with the Aptera, sitting taller may get a very streamlined body out of what aeronautical engineers call “ground effect.” Ground effect is the high lift/high drag regime of a wing flying close to the ground. When the plane climbs out of ground effect the rate of climb decreases as lift is lost but air speed increases as drag drops away.
4. High diameter, narrow width “pizza cutter” wheel-tire assemblies have some definite non-efficiency problems. They make the vehicle more top-heavy, therefore for safety’s sake, the designer has to increase track width. “Pizza cutters” are murder on wheel bearings.
5. Moving on to engines, the best way to increase engine efficiency without major expense is to eliminate throttling. Throttling imposes high pumping loads on the engine which reduces thermodynamic efficiency. Two ways around the throttling problem. The first is the diesel engine. It modulates power with the fuel injection and always operates at maximum volumetric efficiency. The EPA despises the diesel engine so using one may be problematic in the US. The second way is to use a true series hybrid. The tramming motors operate off the propulsion battery, and the engine only acts to charge the battery. Thus the engine can be an “on-off” engine that runs at full throttle when it is operating. The efficiency of this setup will approach that of the diesel but will require extra weight, complexity, and expense.
6. To make a high-MPG car, maybe the best approach is to simply lengthen out a 2F1R tricycle like the HyperRocket. Have four tandem seats rather than two. You wind up with a long, but narrow vehicle. It may be necessary to widen out the track and maybe go to a narrow two-wheel rear axle. This longer vehicle will be easier to achieve a very low Cd with. A tandem arrangement vehicle will probably encounter stiff sales resistance from families with small children. You would have to stop the car to tend to the kids. Myself, I’d see that as a feature rather than a bug. (I nearly met my Maker one night when some tom-fool woman reached over to mess with the brat and swerved in front of me) People with kids probably will not see it that way.
7. The four-seat car is a necessity and may become more so. If people cannot afford but one car, it has to meet the family mission. As cars become more complex and made of exotic materials, they will become more costly. Higher price means lower volume. So the four-seat car is not going to go away.
8. As I stated before, you can mandate all you like, but the car has to be designed to meet the needs of the customer at a reasonable price or they simply will not buy it and view whatever agency that foisted an unacceptable car on them as a latter-day version of Jimmy Carter’s sweater.

Misconceptions
 

[QUOTE=Big Dave;104375]Comments from the Grinch:

2. Empirical experience about tire diameter is at variance to the assertion that bigger tires are more efficient. Wheel-tire assemblies are big flywheels that the engine must accelerate along with the vehicle every time the vehicle speeds up. Rotational moment of inertia goes up with the square of diameter.

Aye, but wheel RPM for a given speed decreases with greater diameter. The tread moves at the same speed, there's just more of it.

3. The air resistance of bigger diameter tires is subject to debate. With lifted pickups, the air resistance goes up greatly. Maybe, as with the Aptera, sitting taller may get a very streamlined body out of what aeronautical engineers call “ground effect.” Ground effect is the high lift/high drag regime of a wing flying close to the ground. When the plane climbs out of ground effect the rate of climb decreases as lift is lost but air speed increases as drag drops away.

Aircraft in ground effect have less induced drag. The ground makes the wing more efficient; it does not affect form or skin drag substantially.

4. High diameter, narrow width “pizza cutter” wheel-tire assemblies have some definite non-efficiency problems. They make the vehicle more top-heavy, therefore for safety’s sake, the designer has to increase track width. “Pizza cutters” are murder on wheel bearings.

Or the designer can adjust the suspension and bearing sizes to suit. Given the wheel offsets that don't seem to demand bearing changes, and the more constant loading they induce, I'd not worry about that.

S.w.a.g.
 

If any of the company names seem familiar, it will because the new operators are leaving them as local landmarks and history. International trade will be much reduced, and there will be either far fewer domestic animals, or people. Most technology will be makeshift, locally adapted and recycled. Unless a world government is collecting taxes for effective carbon sequestration, agriculture will be failing. We might also be recovering from nuclear war, loss of the grid to a solar storm, or other earth changes.

Doh! ya went the wrong way with the number of wheels and at the wrong end too :) You are absolutely right though that narrower is better efficiency wise.

It isn't much of a stretch to envision a drive by wire two wheeler that is as easy to drive as a 4 wheeler, with auto outriggers or some other stabilization scheme thing you and I arent yet clever enough to describe.

Do like the commuter trains and have the seat backs be moveable so you can have people facing each other. Heck drive by wire from any (preferrably forward facing) seat for that matter. Just don't get so attached to the crutches of extra wheels, or worse yet, mandate them.

And of course being narrower it will collide with less stuff besides air.

The pizza cutters on my 10 speed never had a problem with the bearings :)

I guess I was thinking about the Aptera 2h.

That's because you incline the vehicle when you turn, so there's little axial load on the bearings.

If your design leads to bearing problems, there are solutions, such as bearings wider than the wheels, or a 30kmi wheel bearing replacement interval. Or by inclining the vehicle when you turn: General Motors (GM)

Of course, "real" vehicles lean into corners, better visibility when upright, better handling in the corners, less scrubbing. not like all those ox-carts you see on the roads these days ;)

You know, Ernie, most of the time I don't actually regard this as a problem :-)

Which can make life rather... um, interesting, shall we say? in the winter, when there's a bit of snow & ice around. Or loose gravel, any time of year.

extra smart drive by wire, auto outriggers, whatever.

or just poo poo it due to lack of imagination.

Note, if it has more than two wheels, it aint "ultimate" in my book. Not for efficiencies sake anyway.

Hi,

I think that if the wheels and tires were not inflated, but rather were steel hoops, and solid rubber tread -- the suspension could be tuned to provide the dampening AND the hydraulic pressure from the shocks could drive the alternator. This would:

1) Extremely low rolling resistance
2) regenerative energy from the suspension motion
3) greatly lowered parasitic drains on the engine because the alternator is driven by the suspension -- and the other things like A/C, oil pump, fuel pump, etc can be electrically driven

Also, I think a serial hybrid that had a cam-driven engine (which are about 40% efficient!), which has counter-rotating output shafts, could be used to directly spin the armature and the stator in opposite directions. This allows the engine to run at one constant RPM, and the torque required to do this is virtually constant, so the engine's combustion chambers and valve train can be optimized for this.

harping
 

I would recommend all members pick up a copy of the World Almanac.Not only is is handy for terrorist organs to plan the end of America,it also contains the statistics which support the notion,that America is doing a pretty good job of destroying itself without any outside intervention.------- Ernie,with respect to your thesis,I would call attention to the fact that in spite of CAFE,the American fleet is attaining less than 17-mpg.-------- One of the greatest sources of stress I've encountered,is the fact that fuel economy is not determined by the automobile,as it is by the environment in which it is operated within,which is completely beyond the control of automakers.-------- The tapestry of economic entanglements between producing/consuming/taxation/planning/permits/development/zoning/budgets/codes/advertising/credit/investment/pensions/employment/incorporation/growth/stability/regulation/legislation/politics/media/accounting/actuarials/public education/church/methodology/markets/resources/access/etc.,has grown to be such an incestuous and symbiotic organism,any attempt to alter any tentacle is met with harsh resistance from the rest.--------- I firmly do not believe that solutions to environmental challenges can be relied upon soley from technological innovation or full exploitation of known technology.------------ The entire public mind of America would require a complete shift,within the public,business,and elected/appointed/hired -goverment officials/employees arena.

Weren't we asked to keep it about the cars?

Wow, Neil,

That was terrific creative thinking.

One day I tried to calculate the energy available from the shocks. It was just a wild guess of course--I got about 200 watts, decided that would be nice but couldn't replace the alternator without some big efficiency improvements in the accessory loads.

Ernie Rogers

Hi Ernie,

If our current inflated tires are (at least?) half of the suspension, and if the tires/wheels are made to be very low RR, then that means even more power is available from the suspension?

Also, if you build a serial hybrid, then the requirements for electrical power is reduced, and the whole thing is made to generate power, so an alternator is moot.

Have you guys seen the cam driven engine concept? This allows the engine to have it's torque maximized -- with a crankshaft and connecting rods, you are locked into the sinusoidal motion, which is poorly matched to the timing of peak power being produced in the combustion chamber.

The other huge advantage of a serial hybrid is that you can run the engine at a set RPM at it's peak efficiency, and there is no clutch or transmission losses.