# [EVDL] How about a CVT and constant speed motor?



## EVDL List (Jul 27, 2007)

Theoretical question:
=

What if you put a constant speed motor mated to a constant velocity transmi=
ssion, not for the typical gear reduction of an ICE, but to change (simplif=
y?) controller requirements? The go pedal would drive the electronics in t=
he CVT, rather than high current PWM circuitry? Not sure if you gain anyth=
ing - just a thought.
=

=

Matt Albertson =

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## EVDL List (Jul 27, 2007)

This would only simplify the control logic, the costly stuff - high power
transistors, DC link capacitors, heat sink, etc. - would remain the same. 
You would shave a few bucks off the controller at most.

Fran




> footer746 wrote:
> >
> >
> > Theoretical question:
> ...


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## EVDL List (Jul 27, 2007)

> Matt Albertson wrote:
> > What if you put a constant speed motor mated to a constant velocity
> > transmission, not for the typical gear reduction of an ICE, but to
> > change (simplify?) controller requirements? The go pedal would drive
> ...


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## EVDL List (Jul 27, 2007)

> footer746 wrote:
> >> What if you put a constant speed motor mated to a constant velocity
> >> transmission...
> 
> ...


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## EVDL List (Jul 27, 2007)

Well, I suppose he was talking about actual/practical CVT.

If you simply have a contactor, the CVT would have to have to have almost an
infinite "gear ratio" range. Imagine driving at a snail's pace in a traffic
jam. Your CVT could not match motor speed to wheel speed. So all of a
sudden you need a clutch. In this situation an electric motor should excel,
but in this case you end up heating the clutch (just like ICE vehicles).

As for high speed, you don't need high voltage. You can simply weaken the
field. In a series field motor this happens automatically as the current
drops (it kind of has a built in transmission). In a shunt field motor you
weaken the field directly. In a AC induction motor with field oriented
control you simply weaken the D component which magnetizes the squirrel
cage.

I doubt you can get away with a contactor and no clutch. Once you have
power transistors the processing power to control them intelligently is
cheap.

Fran




> Lee Hart wrote:
> >
> > footer746 wrote:
> >>> What if you put a constant speed motor mated to a constant velocity
> ...


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## EVDL List (Jul 27, 2007)

> fsabolich <[email protected]> wrote:
> > As for high speed, you don't need high voltage. You can simply weaken the
> > field.
> 
> ...


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## EVDL List (Jul 27, 2007)

> fsabolich wrote:
> > Well, I suppose he was talking about actual/practical CVT.
> 
> I think he said "theoretically"; but I agree that it is more useful to
> ...


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## EVDL List (Jul 27, 2007)

If you look at an ideal motor, reducing field strength won't reduce
horsepower, it'll simply keep it constant. So when you look at the power
curve you have constant torque from 0 rpm to the rpm where counter EMF
equals pack voltage. To go faster you must weaken the field; this puts you
in constant horsepower region where RPM * torque is constant.

My experience is mostly in industry with large DC shunt wound motors, and
they pretty much behave like this.

Of course if you have no transmission, you have to have more power to
compensate. Removing the transmission saves space and weight and allows for
a bigger motor.

Currently I'm working with PM synchronous motors. Compared to induction
motors they are significantly smaller and lighter. So with them you can
simply have lots of power without having big and heavy motors - so it is
possible to work without a transmission. But anyways, I'm drifting off
topic.

Fran

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## EVDL List (Jul 27, 2007)

If you look at an ideal motor, reducing field strength won't reduce
horsepower, it'll simply keep it constant. So when you look at the power
curve you have constant torque from 0 rpm to the rpm where counter EMF
equals pack voltage. To go faster you must weaken the field; this puts you
in constant horsepower region where RPM * torque is constant.

My experience is mostly in industry with large DC shunt wound motors, and
they pretty much behave like this.

Of course if you have no transmission, you have to have more power to
compensate. Removing the transmission saves space and weight and allows for
a bigger motor.

Currently I'm working with PM synchronous motors. Compared to induction
motors they are significantly smaller and lighter. So with them you can
simply have lots of power without having big and heavy motors - so it is
possible to work without a transmission. But anyways, I'm drifting off
topic.

Fran

-- 
View this message in context: http://www.nabble.com/How-about-a-CVT-and-constant-speed-motor--tp15192340p15214957.html
Sent from the Electric Vehicle Discussion List mailing list archive at Nabble.com.

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## EVDL List (Jul 27, 2007)

> --- Morgan LaMoore <[email protected]> wrote:
> .
> > But high speed does require a motor that's designed
> > to handle high
> ...


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## EVDL List (Jul 27, 2007)

> Morgan LaMoore wrote:
> > But high speed does require a motor that's designed to handle high
> > frequencies. Normal industrial AC motors will have excessively high
> > core losses at higher frequencies (leading to excessive heating
> ...


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