Electrical Supercharger

[Stephen Dubovsky]

...
>allowing higher operating temps.  There's not much improvement
>that's to be expected from something that's already the
>most efficient mechanical devices known to man -- on the
>order of 70 - 85 %  when you reach 100% you have the long
>sought after perpetual motion machine!
...
   Working on EVs for a living, I must tell you motors have come a long
way.  First, the very good ones are designed using FEA software and not
trial and error so you get the maximum efficiency and use of the iron.
Some induction machines today get 92-95% near full load and PMSMs can get
to 98% (go visit the solectria web sight and look up their 8-10hp PMSM for
solar cars - We've used it and it has a broad eff range too).  Another
small advance is that you aren't limited to 60Hz machines anymore.  Torque
is a function of rotor mass and you simply turn the motor 20krpm for
lots-o-hp and gear it down (if reqd) to get more torque (this is the trend
in motor design - eventually thermal problems limit the minimum size).  The
biggest advancement is inverters.  It makes the PMSM practical and the
induction machine better.  For an induction motor, the starting torque is a
function of rotor resistance, so to start one off the 60Hz line, you have
to add rotor resistance to get enough starting torque.  W/ a field oriented
control, you don't need that R (causes lots of loss) so you try to make the
rotor R = 0 (NO starting torque at 60Hz) and use a DSP to control the field
in the machine to get max T at 0 speed some other way.  An AC machine w/
vector control can be MUCH smaller and lighter than a DC machine due to all
of this.  (BTW, most inverter effs run 92-98% if the system was designed
correctly - leading to a composite eff of 82-96%.  Also, the higher the
eff, less heat lost in the motor/inverter, the smaller and lighter you can
make them both (often raising the eff a LITTLE farther in the process))
  If you look at the Saturn EV1 (was the GM impact) it does 0-60 in 7-8s?
and has only 120hp w/ direct drive (no shifting).  The motor makes monster
torque everywhere (actually its flat from 0 to almost max speed) and turns
fast enough to make the thing go 80-100 w/o a gear shift.  It also weighs
alot w/ all the batteries.  Take a 3000+lb vehicle w/ 120hp and try 0-60 in
3rd gear (so it can get to 100 w/o shifting).  Dont think you'll see
anything short of 20 secs;)
SMD