RE: EVLN(1-O-X revolutionary digital EV motor)

["Roger Stockton" <rstockton@delta-q.com>]

> -----Original Message-----
> From: owner-ev@listproc.sjsu.edu
> [mailto:owner-ev@listproc.sjsu.edu] On Behalf Of Peter VanDerWal
> Sent: October 30, 2001 11:32 PM
> To: ev@listproc.sjsu.edu
> Subject: Re: EVLN(1-O-X revolutionary digital EV motor)
> 

[snip]

> Actually you could also say that efficiency is at infinitee 
> at zero rpm. Efficiency is power out divided by power in.  
> 0/0 is technically zero but the result of any number divided 
> by zero can also be said to be infinite.
> 
> It's a moot point.

Agreed... sort of ;^>

It's probably more accurate to observe that efficiency is undefined (or
at least meaningless) with 0 input power.  I guarantee that you can
apply a small (but still non-zero) input power to any EV traction motor
and still observe 0RPM, which by definition is 0% efficiency.

>  The only time the motor is running at 
> such low efficiency is when it's drawing very little power.  

Not necessarily.  Cruising along at 1-2mph on the flat and level
may require very little power, but repeatedly accelerating 3000lbs
or more of EV between 0 and 5mph will require a more significant
amount (and at these low speeds, regen is very ineffective at
recovering any of this energy at each stop).  Likewise, creeping
up any sort of grade at these low speeds will consume more
significant amounts of energy.

[snip]

> you 
> have to consider how much power is spent at each unit of time 
> (pick small units) add it all up and you'll find that getting 
> better efficiency at super low power levels (relatively 
> speaking) isn't going to amount to a hill of beans.

True enough, but your assumption is that accelerating a heavy EV
from a stop repeatedly represents operation at "super low power
levels".  Watch your ammeter and I believe you will find that
acceleration from a stop will result in higher current draws than
steady state operation at highway speeds (for modestly aerodynamic
vehicles and "keeping up with traffic" type acceleration).  When
you're bored sometime, go out with a full charge and just do
repeated accelerations from 0-10 or 20mph until the pack is dead
and notice how little total distance you travelled on that charge
(especially if you do it only using a gear ratio that would let
you hit a top speed in the 80-90mph ballpark) compared to what
you can do at a constant speed of 40-50mph.

Inefficiency at these sorts of stop-and-go speeds is not a big
concern if you don't spend a lot of time there, so the 1-0-X
device may provide very little benefit in the real world.

Do bear in mind that my comments were intended to illustrate why
it would not surprise me that the EV1 takes a big range hit in
urban stop and go traffic vs highway cruising, not necessarily
to endorse the 1-0-X claims.  I think the person who made the
observation about parasitic loads representing more significant losses
when long periods of time are spent traversing relatively small
distances at low speeds has a very good point (quite possibly closer to
the heart of the range hit issue than drivetrain efficiency).

[snip]

> > Also, one should expect an EV with a fixed drivetrain
> > ratio to exhibit a greater difference between steady-
> > state operation and urban traffic conditions than would
> > an identical vehicle with a multi-speed transmission.
> >
> 
> Why?  Realistically it all depends on the torque map of the 
> motor.  Many AC motor/controllers have nearly flat efficiency 
> over a wide range of torque/rpm, for these motors a 
> multi-speed transmission might actually decrease efficiency 
> (due to their higher friction).

Remember, the comment was made in the context of explaining
why I would not be suprised at the efficiency hit reported for
the EV1 in stop and go traffic vs highway operation; my point
is that because it has a fixed drive ratio it will take a bigger
efficiency hit at very low speeds than it would with a
multi-speed tranny.

Quite simply, no matter how broad the efficiency map it still
drops to 0% efficiency near 0RPM and from the examples we've
seen, remains at least 20% lower than peak efficiency until
1000RPM or more.  With a fixed drive ratio, a highway-capable
vehicle will spend more time operating in these inefficient
low RPM ranges in stop and go traffic than would the same
vehicle with the ability to select a gear ratio that let the
motor RPM build through this range more rapidly so that more
time in stop and go is spent in the broad high efficiency
range.  The addition of a multi-speed transmission might well
reduce drivetrain efficiency slightly vs the fixed ratio
transmission, but it will very likely allow the *difference*
in efficiency between steady-state operation at speed and
stop-and-go traffic to be reduced.  (The multi-speed tranny
also allows the effectiveness of regen to be improved at the
low speeds characteristic of urban stop-and-go operation.)

> 
> > It will be interesting to see if the 1-O-X folks come up
> > with anything of practical application

[snip]

> It would be interesting, but given the fact that the best 
> thing they have to brag about so far is an obscure 
> plug-n-play Mr. Microphone, I'm not holding my breath.

Amen.

Cheers,

Roger.