# CVT - hopless conversion?



## dougingraham (Jul 26, 2011)

Maury Markowitz said:


> But what about my Civic Hybrid? I've only got 100k on it so I'm in no hurry to do anything, but that CVT... is there any way to use that on an AC-50?


It would seem like it could be made to work. At rest the CVT is set to its greatest reduction ratio to amplify the torque. If you command a rapid acceleration you would run the motor current up to maximum (650A I believe) and when you reach the RPM point where the current starts to back off you continue by changing the CVT drive ratio so as to hold that 650A maximum load. Once you reach the desired speed you would drop the motor RPM and maintain speed with the CVT to reduce wear on the motor side of things.

A CVT is really good for pairing with ICE that have a torque peak at a particular RPM. That way you can operate the ICE at its maximum torque point when accelerating and at its maximum efficiency point when holding speed. It is not needed with electric because there isn't really a torque peak or much of a max efficiency point.

I wouldn't use a CVT as it will be heavy for the amount of power it can deal with and probably somewhat fragile and finicky. You need to use it in a completely different way than what was intended when they designed it. You will need to come up with your own ECU to control the AC50 drive system and the CVT based on throttle position and drive system loading. It is possible you could take advantage of the CVT when doing regen braking in some way. You might want to see how much torque it can handle. It might be that an AC50 could turn it into a box of debris too easily.


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## mizlplix (May 1, 2011)

I have been using CVT's of different types for many years. What Doug said is very true.

Now, how does the HP and TQ of the ICE set up compare to the AC50?

That will give you a clue.

ALSO: Your biggest problems would be the final hook up. 

You would have to make a shaft/plate unit that duplicated the rear of the Ford engine where it goes into the transmission housing. 

It must have an input shaft to mount the torque converter plus extend out to couple the AC50. 

It all needs an adapter plate to hold the drive bearing plus seal in the transmission fluid. 

After all that trauma you would need to spoof the ECU to tell it the ICE was still running and give it all of the inputs it expects to see.

After all of these conditions are met, the real fun starts. You need to somehow force it to match the AC50 torque curve. 

Run in low ratio up to the RPM where the AC50 is strong, then start slowly changing the bias while the car is accelerating but keeping the AC50 at that fixed RPM.

Not impossible, but very demanding. 

When it is all said and done, you will still have that old car with creaky doors.

I personally prefer to sell and buy a nicer car to convert. You will be keeping it a long time...?

My $.02, Miz


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## Maury Markowitz (Jul 6, 2012)

mizlplix said:


> I personally prefer to sell and buy a nicer car to convert. You will be keeping it a long time...?


Given everything you've said here, I'll just sell it 

It seems it would be much easier to convert the Echo, which lacks most of the fancy communications between the engine and transmission.

Out of curiosity, is the "gearing ratio" of a traditional transmission wider than what is needed for a motor? IE, would a perfect transmission for an electric car have more gears with a wider ratio range? Less gears with a smaller range? More gears with less range?

I *suspect* that the flatter torque curves implies less gears are needed, but I can't guess as to to the range issue.


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## mizlplix (May 1, 2011)

The *torque curve* on any power plant deals to it's ability to accelerate. 

The* flatness* of the curve is the useful part. A perfect curve is one that starts out at peak and stays there to the RPM limit. (not going to happen)

AN *electric motor* usually has the useful part nearest the bottom end and extends to the upper mid range.

An *ICE *usually starts out weak and gradually builds up to a peak and then decays making the useful part, mid range to upper range. (_GENERALLY_)

So, an EV can be _said to be_ more like a Diesel engine than a gasoline one.

The local terrain(hills), your top speed needed,the tire diameter and the weight of the vehicle- will give you your final drive ratio (differential gearing).

The power plant's useful torque-RPM range (the flat part) will dictate the gear split (useful RPM width in each gear)

The number of transmission gears required, is the split (RPM width) divided into the final drive RPM's.

EXAMPLE:With a 3.55 rear axle and a 28" O.D. tire. 

1st gear= 0 mph to 15 mph.
2nd gear= 12 mph to 35 mph.
3rd gear= 28 mph to 65 mph.
4th gear= 55 mph to 72 mph.
5th gear= 70 MPH to 110 MPH.

With a wide/flat torque Electric motor, You can drive in 1st and 3rd gears all day long and never need the others. (Providing it stays within it's RPM range)

But, if you have a decent hill, 2nd gear will be really welcome, just like any other vehicle. 

Truth is that most all drivers are oblivious to their car, just like they treat their shoes. We EV'ers are more aware of what our vehicle is doing, although some of us tend to obsess about it and make it seem complicated when it is not.

Now, having said all of the above: The perfectly geared car is extremely rare because there are *always* compromises. 

AC or DC- (Generally speaking), the smaller diameter motors give less torque but have higher RPMs. The larger the motor diameter gets, the lower the top RPMs become but the trade off is a torque increase.

AC usually has higher RPMs than a similar DC motor simply because of brush issues (arcing-timing lag and commutator RPM limits). 

A DC motor usually has greater torque and in a lower RPM than a similar AC motor.

The above mentioned motor type operational differences will also affect the gear selection to a minor degree.

1-Decide the top speed you will drive.
2-Measure your tire diameter.
3-Figure the motor RPM that you want to cruise at.
4-Using your motor torque curve, decide how many gears you need.

Your motor can surprise you. It can not read a torque chart and so will drive above and below the band you have chosen to cover up any minor gearing issues.

Miz

NOTE: All of the above is my opinion based on my life experiences. If I have mis-stated anything, let me know and I will edit it. TYVM


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## rmay635703 (Oct 23, 2008)

One old 48v 55mph car had a belt drive CVT for speed control and it was actually very efficient, emualte that and you have something.


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## Maury Markowitz (Jul 6, 2012)

Great summary M!


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## iti_uk (Oct 24, 2011)

Judging by the following dyno plot;










The AC50 certainly does have a "peak". It's true that (in this example) the torque curve is flat from 0 to about 3000RPM, but surely the power peak is more useful with a CVT than the torque peak, since power is independent of gearing. This would mean holding the motor at ~3100RPM in the example given and having the CVT alter the wheel speed accordingly, meaning that this motor absolutely could be treated as if it were an ICE.

What's not shown on the graph is efficiency. For cruising, hold the motor at the maximum efficiency RPM, whereas acceleration would be handled as described above.

Chris


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## Maury Markowitz (Jul 6, 2012)

There's something that piques my interest in that graph...

On my Civic Hybrid I notice that acceleration a few hundred meters onto the highway can use as a much fuel as driving steady for several kilometers. More to the point, the rate of acceleration is important - pressing harder on the gas pedal uses *much* more gas.

If you think about it for a moment, this should not actually be the case. The amount of *energy* needed to change speed is defined simply by the start and end speeds. That is, accelerating 0-100 km/h in 30 seconds should, in theory, use the same amount of energy as doing the same in 15 seconds. But it doesn't.

I have yet to hear a clear explanation of what, exactly, is the root cause. However, one key issue appears to be this - a ICE running at 2x the RPM will require 2x the fuel just to keep the flames burning right. This is independent of the actual amount of power being produced. I suspect this is the primary cause for the effect above - in order to generate the required torque to accelerate more quickly, the engine has to run at higher RPM, and thus the fuel need is both the extra energy for acceleration PLUS the amount needed just to run the engine.

So... looking at the graph you posted iti, it seems that this is not the case for an electric motor. The torque curve for this motor remains basically flat up to 3000 RPM, as does the current and a slight *reduction* in voltage. This *implies* that the amount of energy needed to keep the motor turning is constant through this range - which kinda makes sense.

So I *suspect* that as long as I accelerate within that range, the "speed of acceleration" will not have much, if any, effect on the "milage". Is this the case?


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## major (Apr 4, 2008)

Maury Markowitz said:


> So... looking at the graph you posted iti, it seems that this is not the case for an electric motor. The torque curve for this motor remains basically flat up to 3000 RPM, as does the current and a slight *reduction* in voltage. This *implies* that the amount of energy needed to keep the motor turning is constant through this range - which kinda makes sense.


Hi Maury,

The current shown on that graph is phase current in the motor. It is not battery current. The battery current will more closely follow the shape of the power.

The voltage shown is battery voltage. The motor voltage starts low at low speed and increases up to about 3000 RPM. 

The *power* produced by the motor is shown with its own trace. In no way does this *imply* any constant *energy* range.

major


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## major (Apr 4, 2008)

Maury Markowitz said:


> The amount of *energy* needed to change speed is defined simply by the start and end speeds. That is, accelerating 0-100 km/h in 30 seconds should, in theory, use the same amount of energy as doing the same in 15 seconds. But it doesn't.


The Kinetic Energy (KE) is solely dependent on the speed for a given mass. However the total energy for the change of speed related to a vehicle must include the work done over the distance traveled while changing speed and also the change in potential energy associated with a difference in altitude. So it is not as simple as you imply.

When you accelerate faster, the change in KE is done in a shorter time, therefore at a faster rate. The rate of energy change (or the rate at which work is done) is power. So the faster acceleration uses higher power. Many devices such as engines are less efficient at higher power.

Even with equal distance covered at equal altitude, a faster acceleration will involve more work if a greater portion of that distance is traveled at higher speed. Higher speed requires more power to overcome road loss (aero and friction). So this is an additional energy requirement over the change in KE. The good news is that you get to your destination sooner, so are more productive


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## Maury Markowitz (Jul 6, 2012)

major said:


> The Kinetic Energy (KE) is solely dependent on the speed for a given mass. However the total energy for the change of speed related to a vehicle must include the work done over the distance traveled while changing speed and also the change in potential energy associated with a difference in altitude. So it is not as simple as you imply.


From a strict physics perspective if it just that simple. The issue is here...



major said:


> When you accelerate faster, the change in KE is done in a shorter time, therefore at a faster rate. The rate of energy change (or the rate at which work is done) is power. So the faster acceleration uses higher power. Many devices such as engines are less efficient at higher power.


Right, which is precisely why I'm interested in that graph.



major said:


> Even with equal distance covered at equal altitude, a faster acceleration will involve more work if a greater portion of that distance is traveled at higher speed.


That will be a *tiny* effect. My daily commute is about 95km one way. I spend maybe 250m of that accelerating up to hiway speed. The overall effect will be way below the measurement accuracy of the instruments.

Yet in fact, the effect of acceleration appears to be very measurable indeed. In some cases, when the meter is reset, it can account for 0.1 to 0.2 l/100km. To put that in perspective, to get that back I normally have to drive about 25 km at best performance.

I suspect my performance is in fact much better than what most people get. Without a gauge, most people just mash the accelerator until they reach speed, and if my case can be applied, they are getting truly horrible milage during that period.

But if the effect is not as pronounced with an electric motor (which I can't say yet) then perhaps the fleet milage goes up for this reason alone. I know I would like to be able to accelerate faster without ruining my milage - the Civic Hybrid is very pokey!


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## Maury Markowitz (Jul 6, 2012)

major said:


> The current shown on that graph is phase current in the motor. It is not battery current. The battery current will more closely follow the shape of the power.


Bummer. So we need another graph, one with efficiency would be excellent.


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## McRat (Jul 10, 2012)

Maury Markowitz said:


> There's something that piques my interest in that graph...
> 
> On my Civic Hybrid I notice that acceleration a few hundred meters onto the highway can use as a much fuel as driving steady for several kilometers. More to the point, the rate of acceleration is important - pressing harder on the gas pedal uses *much* more gas.
> 
> ...


Here's how I understand it:

BSFC - Brake Specific Fuel Consumption is how much HP a pound of fuel generates.

ICE engines have a "sweet spot" usually at their torque peak, where the BSFC is highest. This varies wildly from engine to engine. Ever wonder how a 505HP Corvette that weighs 3200lb empty doesn't get a fuel-guzzler tax? At freeway speeds in top gear, it's at the sweet spot.

One engine could be 8000 rpm and another could be 50 rpm.

A digitally controlled CVT is used to keep the engine at it's BSFC rpm for the throttle opening and other conditions. Climbing a hill at 60mph might get better economy at 2000 rpm, while cruising on a freeway at 60mph might be 1500. It adjusts based on it's programming. It's load, temp, fuel quality, throttle opening, baro pressure, etc, dependent as well.

If an electric motor is has an area of operation that show a big gain in efficiency, then a CVT would help range. But I doubt it has near the variation in BSFC that ICE engines do. Some are tragically inefficient at certain loads and RPMs.

BTW, this is why diesels get better mileage at the same HP. The fuel has the same calories per pound as gas, but the BSFC is far better with the diesel.


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## McRat (Jul 10, 2012)

To make the acceleration thing clearer:

If I stay at a .33 BSFC to accelerate 1 mph/sec, but it drops to .10 for the conditions that go 2mph/sec, it isn't necessarily RPM. 

Perhaps I'm in second gear on the 1mph test, and my engine is most efficient at 3000-3500 rpm.

But I'm in 3rd gear for the second test, and my RPM is only 2000-2500 for the test. But my BSFC for open throttle at low RPM is lousy.

When I tow very heavy (23,000lb), my mileage is better at 2100 rpm than at 1600 rpm. When I'm unladen, my mileage is better at 1600 than 2100. (4th gear vs. 5th gear).


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## McRat (Jul 10, 2012)

Sidebar, I'm converting a Honda Insight into an electric sportscar. It has a CVT. They cost about $3000 to rebuild, are heavy, and can't handle large amounts of torque.


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## santossrg (Jan 6, 2016)

McRat said:


> Sidebar, I'm converting a Honda Insight into an electric sportscar. It has a CVT. They cost about $3000 to rebuild, are heavy, and can't handle large amounts of torque.


Did you completed the conversion? Did you kept the CVT?

Best regards.


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## ferd (Dec 1, 2015)

"The amount of *energy* needed to change speed is defined simply by the start and end speeds." No - the necessary energy is a combination of not only the those speeds, but also vehicle loading during that time (due to road grade and conditions, momentum, and vehicle weight, etc.) and the motor's efficiencies at different operating points throughout that time period (including fuel to power conversion, and friction, etc.). 

“a ICE running at 2x the RPM will require 2x the fuel just to keep the flames burning right. This is independent of the actual amount of power being produced. I suspect this is the primary cause for the effect above - in order to generate the required torque to accelerate more quickly, the engine has to run at higher RPM, and thus the fuel need is both the extra energy for acceleration PLUS the amount needed just to run the engine.” I’m sorry, but that explanation is too over-simplified (which could be why it seems baffling). “Keeping the flames burning right” creates the power produced – it’s not independent of it. I hate to sound like a grumpy old man lecturing you, so please take some time to research how an ICE works. Then expand that understanding to the whole system: the ICE operating in a real world vehicle under real world conditions. It can be complicated, but better to learn to understand it than to fool yourself with over-simplified theories.

A CVT is more advantageous to an ICE vehicle than an EV because the ICE outputs a relatively narrow useful torque band compared to an electric motor, and also because the ICE’s torque output is less stable than an electric motor’s. However you can extend your battery pack range if you employ a transmission (CVT designs included).

We built a custom-designed CVT for an EV project to see what it might do. We used industrial components instead of automotive components because of concerns (already posted by others) of trying to force a CVT designed for an ICE to work with an electric motor (which had totally different needs). We found that yes, the CVT did improve our EV’s performance somewhat, but not enough to justify its weight or cost. However, the project was terminated way before I was satisfied with our experiments (due to a flighty project manager) so there could be unrealized potential here. If you should pursue this route I’d love to know what you find (as well as how you do it).

Again, sorry for the harsh – don’t let me scare you from thinking or experimenting. Just trying to save you some hardship and money by suggesting more research before spouting theories.


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