# Continuously Variable Transmission



## Tedktis (Jan 20, 2012)

Has anyone used a CVT transmission with an EV? A lot of scooters use them, and some cars. Thoughts?


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## Jimdear2 (Oct 12, 2008)

Tedkits,

I'm sure there are more complete and better answers then I'll give, but I'll still put in my two cents worth to see if we can't promote those answers

Normally a ICE powered vehicle uses a transmission to create enough torque from RPM to overcome the inertia of a standing vehicle. A series electric motor has maximum torque at zero rpm and maintains that torque through a significant portion of it's rpm range so a transmission isn't required to get moving and keep it moving.

Where a transmission might be valuable with a series electric motor is with an rpm limited electric motor where you might want to use transmission gearing to use torque to produce rpm to achieve higher speed. Exactly the opposite of an ICE.

There are some high rpm wide range brush-less type motors that might benefit from a transmission because by design they don't start making torque until they get a few rpm. 

Even so vehicles like the Tesla (I believe its motor turns around 11,000 rpm max) still use a single speed transmission and has "brisk" acceleration.

Jim.


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## tomofreno (Mar 3, 2009)

Tedktis said:


> Has anyone used a CVT transmission with an EV? A lot of scooters use them, and some cars. Thoughts?


The Nissan Leaf uses one.


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## gor (Nov 25, 2009)

check max torque rating of cvt - it usually too low ... unless you going to use high speed - low torque e.motor


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## MN Driver (Sep 29, 2009)

tomofreno said:


> The Nissan Leaf uses one.


No, the Leaf uses a single speed reduction gear with a final drive ratio of 7.9377 The max motor speed is 10,390RPM and its max travel speed is 94MPH.

Nissan does use CVT's in a bunch of its cars but not the Leaf. The Prius has always used one and the Honda hybrids that don't have a manual transmission(all of the late models excluding the Accord hybrid) have used a CVT.

I've considered the thought of using a 1st Gen Insight with a CVT because there is a guy who used a turbo with his but the TCM for the CVT is tied to the engine control module and that makes it far less simple than a servo-like attitude of just holding a certain RPM according to throttle demand. ..especially when it factors engine load, HV battery power capability, etc. to make its decision. Another factor is apparently it takes a fair bit of pumping power to keep that output shaft clutch engaged so there is an efficiency detriment, I'm not sure if its significant or not though. I was considering the 220v Kostov run at a higher voltage to stretch the torque max to the 5k to 6k range. Hanging on to a constant 125k+ electrical input from say 30mph+ would be great. Just hope you get to the speed you want to go before you fry the motor. I'm sure for an Insight it could drag out to 112mph tire rating pretty quick though since it is under 2k pounds and aerodynamics like none other .25cD 5sqft DA.


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## GizmoEV (Nov 28, 2009)

MN Driver said:


> Another factor is apparently it takes a fair bit of pumping power to keep that output shaft clutch engaged so there is an efficiency detriment, I'm not sure if its significant or not though.


I just happened to be reading John Wayland's blog where he talked about the difference between the manual and CVT Insight and the fact that the fuel economy difference is not due to the CVT but because the CVT based Insights had the lean burn mode removed to achieve a better emissions rating. Base on that I doubt that the efficiency detriment of the CVT is very much.


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## MN Driver (Sep 29, 2009)

GizmoEV said:


> I just happened to be reading John Wayland's blog where he talked about the difference between the manual and CVT Insight and the fact that the fuel economy difference is not due to the CVT but because the CVT based Insights had the lean burn mode removed to achieve a better emissions rating. Base on that I doubt that the efficiency detriment of the CVT is very much.


The manual is more efficient but most of it actually isn't the lean burn, although lean-burn definitely helps. The CVT gives easy access to the performance by raising the RPM of the engine therefore burning more gas for that acceleration. With the manual transmission you shift at the RPM points for MPG and you get better gas mileage. The lean-burn mostly only works on the flat and has very little extra power for hills or acceleration so it essentially changes your driving style in order to hang on to that 65MPG or better that the driver forces themselves to hold. In essence, that driver is allowing hills to slow them down and essentially hypermiling more. With the CVT the driver might have a solid acceleration at 2500 RPM versus the roughly 1300-1900 efficient RPM acceleration range holding 80-90% load that the CVT doesn't allow. Lean-burn allows the car to operate at 70-90% load while cruising which is great for MPG. All the CVT would need to do to match that is to cut back on RPM but the issue is that it doesn't work that way and most CVT drivers don't try for MPG the same way an MT driver does. If a CVT and MT driver were side by side driving the same course with the MT driver mimicking the CVT driver, the MPG difference would be minimal. Major driving style difference. I'm certain I could get 65+ MPG with a CVT in the summer, I get 70+ MPG with my MT during the summer.

This is a bit off topic since it doesn't tie into electric driving, if you'd like to continue chatting about this I'm willing to discuss in PM.


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## GizmoEV (Nov 28, 2009)

MN Driver said:


> I'm certain I could get 65+ MPG with a CVT in the summer, I get 70+ MPG with my MT during the summer.


I'm responding here only because it relates to CVT efficiency. At http://www.plasmaboyracing.com/blog/?p=124 John Wayland says:



> As a side bar, I was never, ever able to even get close to the same gas mileage as my 5 speed Insight, but I was able to hit 72 mpg on one 200 mile trip. On that same trip where my wife was following me in the 5 speed car, she got 86 mpg.


In any case, I don't think there would be much efficiency difference assuming you could get the CVT to adjust for the optimum RPM of the electric motor for the conditions.


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## mizlplix (May 1, 2011)

It is my understanding that in a CVT system the throttle pedal only tells the computer how fast you want to go and the computer keeps the powerplant at it's optimum torque RPM at nearly all speeds {except for in high gear/higher road speed}.

It is like a "Big Rig" 18 speed Road Ranger transmission- you dont use every gear....it does allow you to nearly match the engine's max. torque RPM with the load you are carrying and the hill you are trying to climb. 

A CVT works like that. Anyone who has owned a snowmobile knows that it takes off rapidly up until a certain RPM where the torque converter{clutch} begins to squeeze the belt and force it to change ratio with the rear spring loaded pulley, keeping the motor at that RPM until it reaches it's physical limit then the motor revs up to it's RPM limit. It automatically gives the most rapid/efficient acceleration

AN electric motor should be no different providing the power rating of the assembly is enough and the torque converter is set to match the motor's max torque RPM.

1-Caveat---you will always have a low gear reverse. 

Miz


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## wguinon (Sep 26, 2010)

I built an electric trike with an ADC 4001 motor, Zilla controller and 134V of LiFePO4. No transmission or clutch just a 4:1 reduction between the motor and rear wheel. It worked out pretty well. Its heavy (1400#) but still delivers stunning acceleration and top speed is 70MPH.
I am considering a CVT because I don't like the noise of direct drive. The motor and entire belt drive train are always turning even when coasting down hill.


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## PhantomPholly (Aug 20, 2008)

CVTs have improved dramatically in the last decade, but I really haven't seen any optimized for use with electric motors and the best ones have all kinds of goofy computers to optimize their workings for a particular ICE.

They really really need a simple generic CVT for electric motors where throttle position directly sets target input RPM. There is no reason for these things to be complicated!


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## Amerjack (Jun 1, 2014)

Hi 
Only one person with answer on question build car with CVT gearbox - NO!! 
If you dont now something you dont write answer. 

I converted Nissan Micra with CVT gearbox - and this gearbox is the best to converted car on electric. Wery easy connect electric motor to gearbox. 
Car drive perfect with this CVT gearbox, smooth and give me moore benefits or i use manual gearbox. 

Why every company now in new cars use now only CVT gearbox, hybrid etc.- and why brand new factory electric cars have CVT gearbox, because is the best to electric motor.

If you have any questions i can help you with this gearbox and send more info and photo.

"electric nissan micra" on Facebook


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## major (Apr 4, 2008)

Amerjack said:


> Hi
> Only one person with answer on question build car with CVT gearbox - NO!!
> If you dont now something you dont write answer.
> 
> ...


That's odd. No production electric car uses a variable ratio transmission of which I am aware. And the hybrids such as the Prius are not using a CVT, those are Synergy drives.

If you've had good success with an electric motor/CVT, good for you. You're about the only one I ever heard of.


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## Amerjack (Jun 1, 2014)

Hi 
Major - trust me i am wery happy with this gearbox in my Nissan Micra - was wery easy connect motor to gearbox, car drive perfect - i now is ECU to CVT but this is no problem - more time i spend connect motor to gearbox - ECU was easy. 
Car drive easy and smooth - always i see when people write this CVT is stupid, is no good to conversion on electric car etc.etc. 
I build electric car with this gearbox and now i start convert next car on electric and again is with CVT gearbox. 

If you interesting i can send you photo - this craisy but this gearbox work perfect trust me.


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## dcb (Dec 5, 2009)

Do you have any technical information about how you control the gear ratio?


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## major (Apr 4, 2008)

Amerjack said:


> Major - trust me i am wery happy with this gearbox in my Nissan Micra - was wery easy connect motor to gearbox, car drive perfect - i now is ECU to CVT but this is no problem
> 
> If you interesting i can send you photo -


Like I said.... good for you. Now I know of 1 success vs 10 to 12 miserable failed attempts at CVT EVs.

And yes, I am (or we are) interested. Please post up photos and description of your project. I encourage you to start a new thread, although you can use this one if you want. And please go to the user CP and fill in your location so it appears when you post. It helps members to relate a bit easier.

Thanks.


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## Amerjack (Jun 1, 2014)

Ok I try fill every think - sorry, and photo. 
My project is very easy and basic - that was my person hobby. 

Nissan Micra CVT:
motor - only 12KW
Gearbox - CVT Nissan
only 48Volt - 4x12V battery 225AH
Controller - Curtis 
If you see is very basic conversion but now i start next car and maybe i upgrade my Micra. 

http://www.evalbum.com/4897

But i am not only one person who converted EV with CVT. 

http://elektroavto.net/sl-SI/8412/el-fiat-punto-2-avtomatik-cvt

http://www.evalbum.com/4792

thanks


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## dcb (Dec 5, 2009)

Ah, so basically the ratio is controlled electronically with a servo (and a microcontroller presumably). That simplifies things a lot over the scooter cvt. Still I wouldn't say it is perfect since cvt has less peak efficiency than gears, and electric motors can have fairly flat efficiency curves (and somewhat flat constant power curves), but it is a readily available transmission and perfectly viable it seems (if you control the ratio).


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## Amerjack (Jun 1, 2014)

https://www.youtube.com/watch?v=CeJi__T-iRg

CVT work:))


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## dcb (Dec 5, 2009)

but not like it should perhaps, if you do figure out how to control the ratio, you will want to be holding the motor at a lower rpm while the ratio changes (to keep it near peak hp longer) for best performance. Otherwise you will fly past peak hp at a low ratio then struggle with acceleration. If you are going to spin a transmission, it'd be good to get the most out of it.

And if you do figure out how to control the ratio, let us know how it's done please 


edit: stepper motor or something (pwm solenoid) perhaps?
https://www.youtube.com/watch?v=bOFGZKwuWfM

Here is a picture of the problem, the xtronic (and all gas cvts AFAIK) allow the revs to go high before it starts changing the gear ratio, you want it to start changing when your series motor power is high at low rpm. Sure the car moves, but it is a long way from optimal. Would you rather do most of your accelerating at 36hp or 18? It might be a good fit for a different kind of (well considered) motor, but not series, not without controlling the ratio.


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