# [EVDL] CVT, constant speed.



## EVDL List (Jul 27, 2007)

Ever since seeing the post asking about shaft speed and maintaining 5000 rpm
I can't get it off my mind. What would be the down side? At start up the
transmission is at maximum ratio. By monitoring motor speed and having a
preset running rpm the transmission becomes variable to maintain the
selected maximum rpm. All it will take is a simple feedback from the rpm
sensor to the PWM circuit that controls the pulley pressure within the
transmission.

Good idea?

Mark Grasser



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## EVDL List (Jul 27, 2007)

Mark, it seems to me it makes sense for an industrial
AC induction motor which isn't designed for a wide RPM
range, e.g. a 3600 RPM motor can just be run at
3000-4000 RPM and have the CVT do most of the work.
Similiarly, using an automatic trans with a torque
converter would work as well, keep the motor running
at 2000-3000 rpm with lockup at cruising speed.
Jack



> --- Mark Grasser <[email protected]> wrote:
> 
> > Ever since seeing the post asking about shaft speed
> > and maintaining 5000 rpm
> ...


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## EVDL List (Jul 27, 2007)

> --- Mark Grasser <[email protected]> wrote:
> 
> > Ever since seeing the post asking about shaft speed
> > and maintaining 5000 rpm
> ...


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## EVDL List (Jul 27, 2007)

> --- Mark Grasser <[email protected]> wrote:
> 
> > Ever since seeing the post asking about shaft speed
> > and maintaining 5000 rpm
> ...


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## EVDL List (Jul 27, 2007)

On Thu, Mar 13, 2008 at 1:30 PM, Mark Grasser <[email protected]>


> wrote:
> 
> > This setup would get you low current start-ups because of the high ratio
> > and
> ...


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## EVDL List (Jul 27, 2007)

> Mark Grasser wrote:
> 
> > It has always been
> > my understanding that the higher the motor speed the lower
> ...


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## EVDL List (Jul 27, 2007)

Another option would be to use a shunt motor. Shunt motors work hard to maintain the same RPM. If you load them down, they draw more current, and make more power and torque trying to speed up. If you push them, like going downhill, they resist by making negative torque and pumping current back into the batteries.

So with a shunt motor on a CVT, you could do away with the expensive silicon controller.

Control with a modern CVT would still be tricky, though. The Honda CVT revs up the motor when you need more power (opposite of what a shunt motor would tend to do). I'm not sure how it would react if you just fed the tranny a constant RPM.

A shunt motor with a CVT might be the cheapest EV you could make, if you could figure out the transmission control. A more conventional approach, with a manual transmission and a motor controller, would be more efficient.



> --- Mark Grasser <[email protected]> wrote:
> > Ever since seeing the post asking about shaft speed
> > and maintaining 5000 rpm
> > I can't get it off my mind. What would be the down
> ...


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## EVDL List (Jul 27, 2007)

> > Mark Grasser wrote:
> >
> >> It has always been
> >> my understanding that the higher the motor speed the lower
> ...


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## EVDL List (Jul 27, 2007)

From: David Dymaxion
> Another option would be to use a shunt motor.

A shunt motor works fine for constant speed operation. If the transmission has a fixed ratio, it would drive like you have cruise control engaged.

However, this may not be what you want. If you have a motor with a field winding, I think you'd be better off adjusting the field current instead of the transmission ratio to control speed, regen, and efficiency.

For example, running at constant speed implies constant losses. At full load, a 10kw motor might have 1kw of friction and windage losses, so it's 90% efficient. At 1/10th load, it still has 1kw loss (since speed is the same), but is only producing 1kw of power, so it is only 50% efficient. It would be better to slow it down 10:1 so the losses go down 10:1, so you maintain efficiency. Use the transmission to change the speed instead.

But if you have a PM motor and no controller, you're stuck with constant speed. You can't adjust field strength, and can't adjust armature voltage with it switched straight across the pack. Now you *have* to change the ratio with your CVT to change speed. This isn't particularly efficient, but it is easy. This is how a lot of earthmovers and lawnmowers work -- the engine (usually ICE) runs at a constant RPM, and the CVT (usually hydraulic) changes ratio to control speed.

The only thing new is the history you don't know yet. -- Harry Truman
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart-at-earthlink.net

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## EVDL List (Jul 27, 2007)

> Lee Hart <[email protected]> wrote:
> 
> > This is how a lot of earthmovers and lawnmowers work -- the engine
> > (usually ICE) runs at a constant RPM, and the CVT (usually hydraulic)
> ...


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## EVDL List (Jul 27, 2007)

My gasser car is a 2005 Ford Fivehundred with a CVT transmission. I find the 
transmission is better for a gasser then an EV for a couple of reasons. The 
CVT is still an automatic transmission that has a lot of moving parts to 
move. This takes energy that would be better used by go to the wheels in a 
manual transmission. Second is that when I drive my EV I accelerate up to 
speed, then coast a bit, and then accelerate to maintain a constant speed 
down the road. Keeping constant current flowing to the motor to maintain 
5000rpm is not an efficient way to drive an EV in my opinion.

I do have to say I enjoy the CVT. It actually drives kind of like and EV in 
the sense that you never feel it shift. The CVT always keeps my RPMs as low 
as possible for my driving conditions. Normal 60mph highway cursing speed 
keeps the engine at about 1500 to 1700rpm. When I put the petal to the metal 
the RPMs shoot up to 5000rpm and stay there as the car accelerates. I find 
the best gas mileage I get is when I'm on the freeway with it on cruse 
control. It keeps the RPMs as low as possible to get me down the road.

Ted
Olympia, WA
N47 03.442 W122 49.108
http://www.evalbum.com/915
"THE Stone Age did not end for lack of stone, and the Oil Age will end long 
before the world runs out of oil."
Quotation is from Sheikh Zaki Yamani, a Saudi Arabian who served as his 
country's oil minister three decades ago.

----- Original Message ----- 
From: "Mark Grasser" <[email protected]>
To: <[email protected]>
Sent: Wednesday, March 12, 2008 5:28 PM
Subject: [EVDL] CVT, constant speed.


> Ever since seeing the post asking about shaft speed and maintaining 5000 
> rpm
> I can't get it off my mind. What would be the down side? At start up the
> transmission is at maximum ratio. By monitoring motor speed and having a
> preset running rpm the transmission becomes variable to maintain the
> selected maximum rpm. All it will take is a simple feedback from the rpm
> sensor to the PWM circuit that controls the pulley pressure within the
> transmission.
>
> Good idea?
>
> Mark Grasser
>
>
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>
> 


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## EVDL List (Jul 27, 2007)

> --- David Dymaxion <[email protected]> wrote:
> 
> <snip>
> > So with a shunt motor on a CVT, you could do away
> ...


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## EVDL List (Jul 27, 2007)

> David Dymaxion wrote:
> >> So with a shunt motor on a CVT, you could do away
> >> with the expensive silicon controller.
> 
> ...


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## EVDL List (Jul 27, 2007)

My understanding is that old CVT's used a belt, like the variable speed
bridgeport. This was wastefull, the belt slideing off the pully and
wedging into it took up some energy and wore out the belt.

But the two CVT designs I have seen are different, they use a metal on
metal contact with a special oil to create traction.

I wonder what the effiency of the newer CVT's is?

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## EVDL List (Jul 27, 2007)

In one of my earlier post I said that a CVT has to many moving parts to make 
it an energy efficient alternative to a manual transmission. I just might 
have to stand corrected on this one after viewing this YouTube video on a 
new type of CVT.

http://www.youtube.com/watch?v=kVPjhmTThPo

There was another good video of what I consider a traditional belt driven 
CVT too. The metal belts are great upgrade from the rubber belt of 
yesteryears. But I still feel it would have to much energy loss in a EV 
application.

http://www.youtube.com/watch?v=ABaJidk9SJA

Ted
Olympia, WA
N47 03.442 W122 49.108
Thank GOD for Thomas Edison. Without him we would all be watching TV by 
candle light.


----- Original Message ----- 
From: "Jeff Shanab" <[email protected]>
To: <[email protected]>
Sent: Friday, March 14, 2008 10:52 PM
Subject: Re: [EVDL] CVT, constant speed.


> My understanding is that old CVT's used a belt, like the variable speed
> bridgeport. This was wastefull, the belt slideing off the pully and
> wedging into it took up some energy and wore out the belt.
>
> But the two CVT designs I have seen are different, they use a metal on
> metal contact with a special oil to create traction.
>
> I wonder what the effiency of the newer CVT's is?
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>
> 


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## EVDL List (Jul 27, 2007)

That first one is very interesting in the way that it was turned into a
bike hub transmission.

Nissan put a different prototype on a 300zx twin turbo limited edition
that handled 600 hp. It was made of two polished hollow half spheres one
driven by an input shaft and one driven by an output shaft. The dumbell
shaped roller between them could be angled by a rod that came in from
the gap between the two spheres.

They later Changed the design :"Toroidal"

http://auto.howstuffworks.com/cvt3.htm
http://www.carbibles.com/images/cvttoroidalnissan.jpg

These are the ones that are metal on metal and i was lead to believe
depend on a special oil that increases friction under high load to
increase the capacity for the tiny contact area. Putting two in series
was a great improvement, Nissan seems to lead this area in practical
implemented applications.


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