JD said:
There are electrical losses no matter how you size it up and the
reason they don't generally build electric superchargers is for that
very reason. Power is not free; to make it, requires gas.
I doubt the consumers looking at getting turbos do so for fuel
efficiency. The same logic applies to any supercharger whether
electrical or mechanical.
If you do a bit of math, to get even 10 PSI (to overcome just the
vacuum of the engine) takes a BIG electric motor.
I think you're stuck thinking of motors for your fridge or home heating
furnace. Those aren't efficient motors. What you need is the torque
to supply the air volume needed for the target pressure.
An engine idling at 600 RPM will generate far more boost than a small
electric motor.
From the charts that I've seen for Whipple and turbos, boost doesn't
start until after 1000 RPM.
In addition, the electric supercharger would draw enough power that
even at idle, the car would be a considerable gas hog just to get to
ambient pressure.
But the electrically driven supercharger is NOT running at idle (unless
tolerances for air flow were so tight that the fins have to spin in
order to provide only the amount of air flow needed to run at idle but
unboosted). It doesn't run constantly. It runs only on-demand and for
a very short interval.
That is assuming it has the power to do that; which it won't. A
typical electric motor would lose 10% over direct-drive drive and the
size of the motor would be a limiting factor. A direct-drive
supercharger requires a belt or chain. An electric supercharger of
that size would require a huge motor and monstrous cables to conduct
the electricity. Its all about conservation of energy and you can't
beat the physics yet.
So far no one has even hinted at any physics involved. All claims have
been "you can't do that" without any proof. For rational discussions
on the progress and torque capacity of current electric motor design, I
don't think this is the newsgroup for that. I doubt anyone here is up
on that technology.
Also, there still seems to be confusion that the electric supercharger
is the only supercharger. I never said (and neither did the company)
that it replaces the turbocharger. The electrical system in the VTES
augmented vehicle probably will need redesign but considering it is
used on-demand for a very short interval at only the low-RPM range then
it hardly seems an impossible task. It doesn't sound like something
you just drop into your existing beater. This product is simply giving
the initial push, not supplying all the supercharging needs.
Gor how many cubic feet of air per minute? To charge a 2.5 lire
engine just to ambient, would require a fan to move more than 600
cubic feet per minute of air. That is a lot of air.
Not really. That's only a cube of ~8-1/2 feet on each dimension and
you've got a whole minute to move it. Doesn't seem a difficult task at
all. Even a weak (that you can stop with your finger) 9-inch table fan
can supply 900 CFM (
http://tinyurl.com/yby6q3g). Yes, it has a larger
diameter than the intake for a supercharger but the supercharger is
running at a huge difference in rotational speed for its fins but not
just for volumetric flow.
The volume isn't what's difficult to achieve. It's pressurizing that
volume. What does the turbocharger deliver when it kicks in? Up to
to 14 PSI (I doubt consumer cars are going that high) but I thought the
standard wastegate was calibrated for around 9 PSI for passenger cars.
Does the VTES pre-boost unit have to supply 9 PSI? Hardly. It doesn't
seem like the purpose of the VTES is to supplant the turbo but merely
augment it during its lag period so just 3-5 PSI is more than enough.
So at, say, 4 PSI, how much volume at ambient pressure must be
delivered to pressurize that 1.2 liter capacity? Isn't this a measure
of pressure over ambient? That is, we're not measuring
pounds-per-sq.inch-absolute but pounds-per-sq.inch-guage (which is
relative to the surrounding atmospheric pressure). If we're talking
absolute than 9 PSI would be a vacuum. Going from 14.7 PSI to 18.7 PSI
absolute is the 4 PSI differential (guage). How much more air goes
into the same 1.2 liter space (73 cubic inches) for a 29% increase in
pressure?
For the same volume of 73 cubic inches, how much 1-atmosphere air needs
to be delivered by the supercharger to produce 4 PSI (but without the
restraint that the temperature remain constant since coolers are used
in the turbo/supercharger setup)? Probably around 93 cu. in. I doubt
that an electric motor cannot produce a 4 PSI differential and deliver
a static volume replacement of 100 cubic inches. The VTES doesn't
provide the HP of a supercharger (of which turbocharger is a variety).
It doesn't need to provide the same higher PSI which incurs a much
higher volume of air delivery. It operates at a much lower RPM (so
less volume replacement rate) and under much less pressure.
I haven't found mention of how much PSI (over ambient) that the VTES
supercharger will deliver but it doesn't have to come even close to
what the typical supercharger delivers. Oops, I just reread the
wardsautoworld.com article from my other post that mentions the PSI:
http://wardsautoworld.com/ar/auto_visteon_eyes_electric/
They say about 5 PSI, so I wasn't far off on my guess of 4 PSI. Small
volumetric displacement (1.2 liter, 73 cu. in.), low PSI, short boost
interval. Sure seems doable to me.
"Controlled Power Technologies¢ VTES (Variable Torque Enhancement
System) electric supercharger (earlier post) is being incorporated in a
project by engine developer AVL and will also feature in the Ricardo-led
£3 million (US$5-million) HyBoost program announced by the Technology
Strategy Board on 9 September. Both projects are seeking to maximize
powertrain efficiency at the lowest possible cost."
(
http://www.greencarcongress.com/2009/09/cpt-vtes-20090922.html)
The AVL List GmbH company (
www.avl.com) and the $5M HyBoost program
(
http://www.greencarcongress.com/2009/09/tsb-10mil-20090910.html) don't
seem to be rip-off programs. All-electric cars obviously cannot use the
standard electrical system found in typical gas-powered vehicles of
today or yesteryear. Do hybrids not require a beefed up electrical
system? In one of the other articles I mentioned in my other post, the
VTES motor draws 220A steady state and 350A during acceleration so,
yes, the electrical system will have to be beefed up.