AMAZING IMPROVEMENTS IN 5KW---200KW MOTOR SIZE—Carl Schwab

When the writer studied AC and DC machinery design at about 1950, the one thing we
did NOT have was the VVVF, (variable voltage, variable frequency) drives. Whether it
was AC or DC the motor fabrication was mainly slot and skein. Whether it was the field
or the armature, they were stacks of laminations with slots stamped into them for the wire skeins.

For power sources we had variable DC or 50-60 cycle AC, probably 3-phase. A variable
frequency source invariably was a DC motor driving an alternator as the generator.
Hardly convenient and frequently more complex to operate. If you really wanted a
variable speed drive, it would be a DC motor with various combinations of series and
parallel field windings used. We spent a LOT of time including lab work, separating iron
loss from copper loss from windage loss etc. to compute efficiency. Much of our design
study was to understand the theory of the motors and in the case of the AC machines
learning the various methods of starting under load etc.

 

The advent of power MOSFET and/or IGBT (insulated gate bipolar transistor) has made
it straightforward to generate multi-phase voltages (usually 2 or 3 phase). For 90 years
the workhorses for AC motors were (are) the induction motor and the synchronous motor.
The new (?) thing is to combine these with a VVVF and apply the package to any manner
of appliance, tools and certainly Ecars and hybrids. The startling improvement is the
efficiency of these packages. The other aspects are fabrication ideas that literally make
these motors assembled by machine and can drive the price way down.

As earlier mentioned the defacto standard method of motor construction had become
slot/skein and the magnet field is radial. In this new iteration the magnetic field is axial.
The upshot of this is now the windings are solenoid type and easily set up for machine
winding. This saves labor and improves quality. An example of this has the windings
with the magnetic field axial but arranged circumferentially say with six coils that are in
fact connected for 2, 3-phase sets. The coils are double-ended driving armature magnet
plates at both ends. The armature plates on either end are sets of 8 neodymium magnets
mounted on rotating armature plates that are mounted on a common shaft. The shaft
passes through the coil set plane. This is the approximate configuration of the YASA
motor.

Yokeless and Segmented Armature, YASA. The performance figure for the YASA
motor, which weighs 23 kg (50.71 lbs) and has a rated peak torque of 700Nm(516 ft-lbs),
is currently 30Nm/kg. Refinement is expected to produce 40Nm/kg. The intention is to
use one motor for each wheel. The YASA motor is what I call a "pancake" type. It is
relatively thin and the diameter much larger. In the case at hand the motor is about 2 ½
inches thick, but the diameter is about 14.5 inches. FWIW another motor, the
NovaTorque, Takes the axial flux flow in a different direction to make a longer smaller
diameter motor. The axial flow idea allows greater flexibility in shaping the motor
package, again an advantage.

Using the 205 65 R15 tire as a reference, its circumference is 80.1 inches. At 30 mph, i.e.
44 fps, the wheel rps is (44 x 12)/80.1=6.59 rps or 396 rpm. If one each for all 4 wheels is driven by the above motor the horsepower available for each wheel at 30mph will be
HP/wheel=(2 x pi x 516 x 396/33,000)=38.9HP. All 4 wheel will become 4 x 38.9=156
HP. For comparison, the IMPACT/EV1 had 135 HP and the acceleration was very good--
--this should be better. And the BER should be fantastic.

As the writer has previously postulated 4WD+4WS for an Ecar, this type of motor is
ideal. Already prototype vehicles using these very motors have been 4WD---and I cannot
believe 4WS isn't shortly to come.

Interesting.

Comments

[Wayne Masters]

Moving on to the Pikes Peak YASA winner with two motor packs.
I'm trying to design a free piston engine with a six phase output to drive a six phase 'YASA" motor.
I have parts on a table and every day I find out why they did it their way at Toyota.
I have an electrical jig to test the magnet coil combos here and I made a round electrical diagram that screamed you're lucky you found this design by accident.
It is 12 coils, ten magnets. Magnets and coils are same size/shape which you don't mention in your article.

I will now retry my mirror and LED spinning arrays with this principle before i move on to fibonacci number combos.