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Crissa

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Variable gears reduce the available torque for electric motors can produce, because electric motors can produce more torque than transmissions can handle.

-Crissa
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Variable gears reduce the available torque for electric motors can produce, because electric motors can produce more torque than transmissions can handle.

-Crissa
Not sure who that was directed at, but all Teslas have transmissions that handle the torque just fine. Even the "variable" ones or stepped ones (like Taycan) work too with electric motors and the torque they can deliver.

The Prius CVT was not a rubber band model (like in a moped), it was just a planetary gear with two electric motors driving it.
 

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...are not variable, which is why I used that word first.

-Crissa
That still confuses me a bit, as all the transmissions I know of in vehicles, typically are used to increase the torque and not reduce it. Be that torque from electric motors or ICE, through variable, stepped or fixed ratio transmissions.

Just like a lever gives you the ability to move something, you couldn't without a lever.
 

Crissa

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Alas, electric motors can have lots of torque. That's based on their wattage. It's speed they run out of. Even my dinky electric bike with its artificially lowered bottom-end torque can break the tire loose given the least opportunity.

Electric has different torque curve, different tradeoffs from what you're used to, that's all.

-Crissa
 


JBee

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Alas, electric motors can have lots of torque. That's based on their wattage. It's speed they run out of. Even my dinky electric bike with its artificially lowered bottom-end torque can break the tire loose given the least opportunity.

Electric has different torque curve, different tradeoffs from what you're used to, that's all.

-Crissa
I'm very familiar with electric motor torque curve and those of ICE too. But:

The primary purpose of a transmission in any vehicle is to increase available torque at any given vehicle velocity. Put simply transmissions are designed to increase torque and don't reduce it as you claim. Be they variable, stepped or fixed ratio transmissions.

Further gearbox failure has nothing to do with electric motors or ICE motors, and is just simply because of poor engineering of the transmission. There are many ICE engines with more torque than Plaid that run through decently engineered gearboxes just fine.

Which makes this statement nonsensical:

Variable gears reduce the available torque for electric motors can produce, because electric motors can produce more torque than transmissions can handle.
Maybe a refresh of what torque actually is would help:
https://en.m.wikipedia.org/wiki/Torque
 
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Crissa

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The primary purpose of a transmission in any vehicle is to increase available torque at any given vehicle velocity. Put simply transmissions are designed to increase torque and don't reduce it as you claim. Be they variable, stepped or fixed ratio transmissions.
Sorry, but you're wrong. But just in this one case.

Transmissions in EVs are primarily to increase operational speed, not torque.

And all transmissions - because they have internal resistance - lose some amount of torque. Yes, they may give you more mechanical advantage and increase torque at the wheel, but they're losing it from the parts grinding together all the same.

This is why EV torque can't be measured at the motor. Because it's going to be highest there. What matters is what you can get to the tires.

If I and @ajdelange agree on something, it's probably true.

-Crissa
 

JBee

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Sorry, but you're wrong. But just in this one case.

Transmissions in EVs are primarily to increase operational speed, not torque.
Um no. Many Ev's do not have enough torque for direct drive of the wheels for high acceleration performance, except hub motors and the like, including Teslas. They do have ample speed though.

For example the Model S Plaid, one of the most powerful Ev's out there, with one of the fastest spinning motor rotors (that's why its CF wrapped), has a gear ratio of 8.47:1. That means there is some 8 times more torque at the wheels than what the motor can produce.

And all transmissions - because they have internal resistance - lose some amount of torque. Yes, they may give you more mechanical advantage and increase torque at the wheel, but they're losing it from the parts grinding together all the same.

This is why EV torque can't be measured at the motor. Because it's going to be highest there. What matters is what you can get to the tires.

If I and @ajdelange agree on something, it's probably true.

-Crissa
As before torque is higher at the wheel after the transmission, and not at the motor as you say. This is because "RPM is being traded for torque". Think of a transmission ratio as the length of a simple lever on a fulcrum.



Lets do another calculation to demonstrate:
- Plaid wheel is a 265/35 ZR21 with 719mm diameter and 2.258m circumference
- if it were true that a transmission on the Plaid MS would reduce torque to "increase operational speed" as you say then if they would leave the ratio as 1:1 you would get;
-30,000RPM CRIM motor from Plaid x 2.258m wheel circumference x 60minutes in an hour = 4064kmh or 2540MPH!!

It should be clear that you statement
"Transmissions in EVs are primarily to increase operational speed, not torque"
is in fact exactly opposite to the truth.

As for the torque losses due to "grinding" resistance these are trivial for the torque component, and even for the power transfer are not significant in the grand scheme of things. They're less than the rolling resistance and the deformation of the tyre on the road by far.
 

Bill906

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The primary purpose of a transmission in any vehicle is to increase available torque at any given vehicle velocity.
In modern ICE transmissions they increase OR decrease available torque depending on what gear. Although the term "overdrive" is somewhat ambiguous, most mechanical discussions use the term to mean a gear ratio where the input speed is slower than the output speed. In that case torque is sacrificed for speed.

My Jeep Grand Cherokee has 8 forward gears. Gears 1-5 are "Underdrive" (input faster than output). Gears 7-8 are "Overdrive" (input slower than output) and 6th gear is 1:1.

First Gear Ratio 4.71:1
Second Gear Ratio 3.14:1
Third Gear Ratio 2.11:1
Fourth Gear Ratio 1.67:1
Fifth Gear Ratio 1.29:1
Sixth Gear Ratio 1.00:1
Seventh Gear Ratio 0.84:1
Eighth Gear Ratio 0.67:1
 

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In modern ICE transmissions they increase OR decrease available torque depending on what gear. Although the term "overdrive" is somewhat ambiguous, most mechanical discussions use the term to mean a gear ratio where the input speed is slower than the output speed. In that case torque is sacrificed for speed.

My Jeep Grand Cherokee has 8 forward gears. Gears 1-5 are "Underdrive" (input faster than output). Gears 7-8 are "Overdrive" (input slower than output) and 6th gear is 1:1.

First Gear Ratio 4.71:1
Second Gear Ratio 3.14:1
Third Gear Ratio 2.11:1
Fourth Gear Ratio 1.67:1
Fifth Gear Ratio 1.29:1
Sixth Gear Ratio 1.00:1
Seventh Gear Ratio 0.84:1
Eighth Gear Ratio 0.67:1
Sure I could say "optimise" instead, but the point is that without a high ratio to increase the torque none of them would be able to start to drive.

Otherwise feel free to try to drive your ICE car only in sixth gear and see how you go. ;-)

But seriously you still have a differential gear as well which means you still have a ratio between the motor/ICE and wheels.
 


Bill906

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ICE's REQUIRE a variable transmission
Electric motors do not require variable transmission, but could be used optionally.

Cons of using variable transmission include added weight, cost, complexity and loss of power do to added friction.

I'm not sure what the benefits are. To run the electric motor in a slightly better area of it's torque curve?

When you say planetary gear system, are you talking one planetary gearset or cascading gearsets like a typical automatic transmission. How many discrete gear ratios are you suggesting? Or are you talking some complex system that creates a continuously variable ratio?
 

JBee

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ICE's REQUIRE a variable transmission
Electric motors do not require variable transmission, but could be used optionally.

Cons of using variable transmission include added weight, cost, complexity and loss of power do to added friction.

I'm not sure what the benefits are. To run the electric motor in a slightly better area of it's torque curve?

When you say planetary gear system, are you talking one planetary gearset or cascading gearsets like a typical automatic transmission. How many discrete gear ratios are you suggesting? Or are you talking some complex system that creates a continuously variable ratio?
Neither, I'm arguing against more complex gear arrangements including the planetary gear of this thread. I understand the torque curve comparison between ICE and EV and that a electric motor can get away with a single ratio gear.

My conversation was with Crissa, as those comments weren't correct. You might have to read the thread from further up. :cool:
 

Bill906

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Neither, I'm arguing against more complex gear arrangements including the planetary gear of this thread. I understand the torque curve comparison between ICE and EV and that a electric motor can get away with a single ratio gear.

My conversation was with Crissa, as those comments weren't correct. You might have to read the thread from further up. :cool:
Sorry, I had you confused with the original poster.
 

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Increased efficiency, because the motor speed is not tied to tire speed, the motors may operate near their most efficient.
The difference between most efficient speed and least efficient speed is not very significant.

Much greater low end torque, the motors can deliver full speed power to shaft at 0 RPM's.
Electric motors already produce lots of torque at low end.
At zero speed power is also zero. Power is the product of torque and speed.

Effective and efficient regeneration all the way down to 0 RPM.
At low speed there isn’t that much regen power to recoup.

You can run the induction motor at low RPM's and high torque for some limited amount of time.
Depending on what “high torque” means. You can run a motor at high rpm and high torque for some limited amount of time also.
You can run a motor at rated current continuously. The only caveat I know of to that is with a typical industrial 3 phase motor that is cooled by a fan driven by the motors shaft. At low speeds the fan is not turning fast enough to cool the motor. So yes, THAT type of motor can overheat at high load (high current) at low speeds. I feel very confident in assuming EV motors do not use the motor shaft powered fan cooling system.

As any motor slows down it becomes a less efficient generator.
The slower the speed, the less power there is to recoup.

tire at 0 rpm, first motor at +10,000 rpm, second motor at -10,000
Not sure how spinning two motors at 10,000RPM yet the wheels are not turning is efficient.
 

Crissa

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Your own chart shows a static power with a variable interval.

Nearly all highway-capable EVs use multi-phase variable pulse power to control the motor, which gives them a very long, flat torque curve.

As I pointed out, even the motor in my Zero has to be artificially limited in power not to spin the tire at low speed. Torque is not a problem.
https://www.motorcycle.com/manufacturer/zero/living-with-a-zero-sr.html

There's no need for additional transfers that lower efficiency.

Tesla solves any problem here by having multiple motors set to different, overlapping curves. That gives us cheap all wheel drive on top of a more efficient drive system.

-Crissa
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