# cvt transmission?



## Coley (Jul 26, 2007)

A variable drive like a snowmobile, sorta?


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## shockit (Nov 25, 2007)

I'm thinking of a cvt, like out of a Honda or toyota.


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## Greenflight (Sep 13, 2007)

Pretty close to the same thing... I would imagine it would depend on how they're controlled. While they don't have shift points, they still have a shift "curve" that might not allow the electric motor to rev as high as it should.

It seems like they must have some sort of a kickdown cable or something for acceleration... maybe this could be clamped at high throttle to change the curve. Just speculating here, as I don't really have any experience with these things besides in golf carts...  

Check this out... http://rqriley.com/urba-e.html It uses a cvt... not sure how it's used exactly. Seems like the motor is always run at full the throttle, and the cvt controls speed, or something like that. Might be worth looking into.


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## houseoffubar (Nov 18, 2007)

Shockit, I read an article several years ago about the development of the CVT that Honda built. The constantly variable transmission is actually like a snowmobile , except it pushes the belt, rather than pulls it. The "belt" is also made of steel, and rides in a track so it can be pushed. You may already know this, so on to your question. According to the article the whole reason for this design is increased efficiency. Their claim was that this design approaches the efficiency of a manual transmission. They do use a C.V.T. in the Honda Insight hybrid. This would indicate that it would be suitable for EV use based on efficiency, but there are too many other possible variables that I have no information on. 
This would sure make a nice transmission if it would work out.


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## shockit (Nov 25, 2007)

Thank you both for your inputs
that sounds good. 
Anyone know of an aftermarket cvt? I haven't picked out a donor car yet. If a snowmobile cvt would work, would it need a pump and could it handle ev motor torque?


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## houseoffubar (Nov 18, 2007)

Snowmobile's often exceed 200hp, strength wont be an issue. I don't think they are all that efficient, but they are probably the only thing available after market. Good luck!


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## Greenflight (Sep 13, 2007)

If I understand correctly, snowmobile cvts operate on the basis of centrifugal force- weights inside are pressed against the inside of the drum, causing it to move. So you shouldn't need a pump to make it work like a typical automatic.

Don't take my word for it though- better verify this info before putting any money into it.


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## KiwiEV (Jul 26, 2007)

Like a standard automatic transmission, a CVT is designed to work with the peak torque range of a gas engine. I'd be scared putting it on an electric motor would rob you of a lot of power, not to mention confusing the hell out of the CVT! 

I'm no pro on these things so I'd still be keen to see someone actually use an auto box on an EV. Who wants to be our guinea pig?


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## TheSGC (Nov 15, 2007)

KiwiEV said:


> Like a standard automatic transmission, a CVT is designed to work with the peak torque range of a gas engine. I'd be scared putting it on an electric motor would rob you of a lot of power, not to mention confusing the hell out of the CVT!
> 
> I'm no pro on these things so I'd still be keen to see someone actually use an auto box on an EV. Who wants to be our guinea pig?


I will be the guinea pig! I am using a auto tranny on my EV, which I hope to get going on in the spring. Cold weather and snow is a real slowdown when I don't have a garage....

Here's my site: http://civicity.blogspot.com


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## houseoffubar (Nov 18, 2007)

Greenflight said:


> If I understand correctly, snowmobile cvts operate on the basis of centrifugal force- weights inside are pressed against the inside of the drum, causing it to move. So you shouldn't need a pump to make it work like a typical automatic.
> 
> Don't take my word for it though- better verify this info before putting any money into it.


 Andrew, You have it exactly right. I doubt their efficiency, but one nice feature is that a snowmobile clutch/CVT is almost infinitely adjustable, as far as engagement speed, and ramp up is concerned. You could make on begin to engage at VERY low RPM, with proper centrifugal weights. Probably great for a fast light EV, not so much for commuter.


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## RevDon (Nov 21, 2007)

shockit said:


> Hi all, new here.
> 
> I know that automatic transmissions are not recommended for EV use, however what about using a cvt (continuously variable transmission)?
> 
> ...


Check out this Gizmag article on the Zershift transmission:
http://www.gizmag.com/zeroshift-instant-transmission-for-trucks/8418/


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## arachnyd (Aug 26, 2011)

Not trying to revive the dead, but the lito green motion uses a CVT.

Has the general opinion that CVTs are bad for electric engines still valid 4 years after this thread began? I know a lot of the production cars use cvts so it seems like it should be a legitimate way to go

http://www.litogreenmotion.com/the-sora#/technical-specs


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## mizlplix (May 1, 2011)

By day, I work for the local school district as an Equipment Specialist (tractor mechanic). We have a LOT of 16-31HP stuff with CVT style power transmission.

One is a paint striper to put those lines on the football fields. It uses a manual lever to set the speed. It alters the driving pulley width and lets you set the speed for the best painting.

Another one is a Bunker rake for smoothing baseball infields. It is centrifugal operated by flyweights in the driving pulley. It attempts to keep the RPMs in the motor's torque band for best power while pulling a drag.

The third type is a tractor. It is hydraulic operated. It senses the RPMs and keeps them within the motors torque band except for top speed driving (like going down a road) where it allows the motor to wind up to full RPMs and top road gear.

They are all simple, but share one common trait...They do not have very much speed range. In slow range the driving pulley is about 4" inner diameter and the driven is about 12" diameter (3:1). In top speed range the driving one is about 6" and the driven is about 6" (1:1). 

Rear axle ratio/ tire size will set your top speed. 

The variable set up gives what feels like a 1 to 10 MPH speed step up. 

It will operate in reverse, but stays in low...OK for us to back out of the driveway.

Miz


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## dladd (Jun 1, 2011)

fwiw, the CVT in my Civic GX is nice and smooth. It just works. It's kinda cool, if you're just mellow, the engine will sit at 1500rpm off the line till 30 mph or so. If you romp on it, it'll spin up to ~5k rpm and just sit there while the car (slowly) accelerates. Sort of a weird feeling, the engine isn't increasing revs, but the car is still accelerating. Perfectly suited to a high revving/low power gas engine with a narrow powerband. Not so ideal (I'd think anyway) for an electric motor with a super wide torque curve. Basically the CVT is keeping the gas engine in it's proper rpm range, but that's not so much a concern with an electric motor, right?

I'm an EV rookie still just planning, but based on my experience with the Honda CVT (which works great in my Civic) I would not consider one for use in my EV.


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## zeroexcelcior (Aug 2, 2011)

I've been behind the wheel of a Civic hybrid with a CVT and it's pretty peppy in my opinion.

From what I understand, Toyota used an electrically actuated planetary CVT (an electric motor spins an idler at varying speeds which changes the output ratio) in at least one of their Prius models, maybe something else to look into.

Best of luck.


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## mizlplix (May 1, 2011)

Cvt uses the gear ratio to pull the motor down and keep it in it's torque range.

If used as is, it would cause an electric motor to pull high amps during acceleration by lugging it. You would need to recalibrate it to let the motor spin up to red line, then slowly shift the ratio, keeping the motor hi revving.

Just my educated guess. So, I vote for a manual shifted pulley set, like a John Deere swather mower.

Miz.


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