BMW Vision EfficientDynamics Concept 0.22Cd

[Frank Lee]

All that external layering and ducting throws me off a bit as far as low drag aero goes. They must have found ways of making the advantages of the ducts more than counteract the disadvantages. I'm kinda skeptical of ducting/layering being the best way to go though.

[jamesqf]

Originally Posted by lunarhighway

...somehow cars like the aptera do not convey a muscle car feel or sence of great "power"...

Which for me is a major selling point. I don't want/need a car to project an impression of power or muscle, since I can do all of that that's needed without mechanical help :-)

[RobertSmalls]

Originally Posted by winkosmosis

Why cut those numbers to 1/3? What would be gained by having weaker electric motors and diesel?

A 0.5L, 55HP diesel delivers better MPG than a 1.5L, 160HP diesel because it tends to operate closer to its limits, where engines are more efficient. (This car will probably require ~20HP for highway cruising.) Because it and the electric motors are smaller, they have less internal friction, and they weigh less. They can also have smaller driveshafts, fuel pumps, etc. which save weight and money throughout the car. That, plus tires, spells out the difference between a high tech, high MPG car that I would buy, and a high tech, high performance car that I wouldn't.

[winkosmosis]

Originally Posted by RobertSmalls

A 0.5L, 55HP diesel delivers better MPG than a 1.5L, 160HP diesel because it tends to operate closer to its limits, where engines are more efficient. (This car will probably require ~20HP for highway cruising.) Because it and the electric motors are smaller, they have less internal friction, and they weigh less. They can also have smaller driveshafts, fuel pumps, etc. which save weight and money throughout the car. That, plus tires, spells out the difference between a high tech, high MPG car that I would buy, and a high tech, high performance car that I wouldn't.

Are engines really more efficient at their limits, or does it just happen that engines are tuned in such a way that a small engine is more efficient than a big engine, aside from the reciprocating mass difference?

I think a 1.5L diesel could be almost as efficient if it's tuned and set up to take advantage of the hybrid electric motor assistance. For example, instead of spinning at 2000rpm on the highway, spinning at 1000rpm, since accelerating can be handled by the electrics.

[lunarhighway]

Are engines really more efficient at their limits,

not really. autospeed did a pretty good article about break speciffic fuel consumption.
every engine has a sweet spot, where it extracts the most power from the fuel it uses, usually this is at about 50% or more throttle and at low revs.
you can mostely make use from this while accelerating. because smaller engines will need more throttle for a given ammount of power they'll often opperate more within this optimal spot them bigger engines.

an engine wich can run at a constant rmp and at a constant load could be dimentioned and tuned exactly for this... and would be much more efficient them
the valve timing would be set for this exact spot, and it wouldn't even need a throttle

[lunarhighway]

i found some more images about the concepts developement, with 3 images of how the air flows over the body. these are more artistic renderings but nevertheless quite interesting. theres also some picutres wich reveal the ubcerlaying structure of the car
BMW Vision EfficientDynamics: the design

[RobertSmalls]

Originally Posted by winkosmosis

Are engines really more efficient at their limits, or does it just happen that engines are tuned in such a way that a small engine is more efficient than a big engine, aside from the reciprocating mass difference?

Engines tend to be more efficient near their limits.

Brake Specific Fuel Consumption (BSFC) Maps - EcoModder

Pumping losses, friction, and reciprocating mass waste more energy in a larger engine, too. Downsizing the engine will improve MPG, unless it causes you to drive around at redline with your foot to the floor. See the above-linked plots. If your engine and gearbox are set up so you cruise at 2500RPM and 80% throttle, you'll do well. Though that would mean you'd have to downshift to pass, but that's worth it if it means a few more MPG.

[cfg83]

Hello -

They'll be offering a BMW 320d in Europe that sports "EfficientDynamics" concepts :

BMW 320d EfficientDynamics Edition announced

... Force comes from the 2.0-litre four-cylinder turbo diesel motor with an aluminium crankcase, a diesel particulate filter, common rail direct fuel injection with piezo-injectors and variable intake geometry.
...
The gearbox features a longer final drive ratio. Performance is good with a 0 - 100km/h time of 8.2 seconds and a top speed of 225km/h.
...
These and other improvements give the 320d EfficientDynamics Edition an average fuel consumption of 4.1 litres per 100km (68.9mpg/UK) and a C02 rating of 109g/km

That's 57.37 MPG/US.

CarloSW2

[Old Mechanic]

Efficiency is best at lower RPM and higher loads, for normal passenger car designs.

When the effective compression (actual compression in the cylinder when combustion occurs) is highest you get the most power (without full load enrichment). Higher RPM reduces the efficiency due to reciprocation and friction losses.

Mileage would be fantastic if you could use a 20 HP engine to produce 10 HP to maintain a certain speed, but your performance would be pitiful.

The current trend is towards smaller engines that still have enough power reserve for decent performance. This is one reason forced induction may be the best solution, because it provides a reserve of power in a smaller engine.

Alfa Romeo built a Grand Prix engine in 1950 that produced 390 HP from 90 cubic inches, but it only got 2 MPG in racing trim. Modern technology allows the best of both worlds with variable valve timing and precision fuel and ignition controls and ultra high pressure fuel injection.

regards
Mech

[lunarhighway]

bmw already offers "EfficientDynamics" models over here.

last weekend i saw a 1 series hatchback up close (my brother in law swapped his mpv company car with a coworker who went on holliday with it)

the underside is completely smoothly panneled as far a i could see from the front, and both grills have active grillblocks that close the grill off from behind these features are standard across the bmw line... i think some models also come with start-stop tech, wich basically shuts down the engine when you shift to neutral and let of the clutch, and restarts when you depres the clutch again

BMW EfficientDynamics : Air vent control