Found this, which helps, but I am still not crystal clear on the matter: Electric Cars Are About to Get a Lot Faster and Go a Lot Further on a Charge
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P3D horsepower?
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Found this, which helps, but I am still not crystal clear on the matter: Electric Cars Are About to Get a Lot Faster and Go a Lot Further on a Charge
This too, I got off a Quora post:
"Because of design differences, a gas car with 700 lbs of torque will be able to keep accelerating at high speed while the EV with the same torque production won’t.
The gearing is the reason why, with an EV there isn’t an RPM band the same way a piston engine climbs from 0 to 6000 RPM and has a transmission to multiply the torque. An electric motor spins to a much higher rpm so the lack of gearing doesn’t affect it until higher speeds when it’s at a much higher RPM.
A piston engine with a 5 or 6 or even a 7 speed transmission can lower the RPM at a higher speed by using a transmission that allows for the gear ratio to change as the car is driven. At 80 mph a piston engine can be reduced to just 1500 or 2000 RPM while the EV without a transmission is spinning furiously and thus using more energy than at low speeds.
The faster any motor spins the less torque it will make because it’s a function of inertia. By changing the RPM to be less dependent on the speed of the wheels a piston engine can climb through the smaller RPM band multiple times while the EV doesn’t.
Because the EV needs to make enough torque to continue moving at high RPM it makes more torque at lower RPM because it loses torque from spinning so fast because of the inertia it has to overcome to keep making that much torque.
When EV fans talk about a instant torque they don’t mean a flat torque curve they mean all the torque is at the low end and there aren’t gears to keep the RPMs at the usable low end."
"Because of design differences, a gas car with 700 lbs of torque will be able to keep accelerating at high speed while the EV with the same torque production won’t.
The gearing is the reason why, with an EV there isn’t an RPM band the same way a piston engine climbs from 0 to 6000 RPM and has a transmission to multiply the torque. An electric motor spins to a much higher rpm so the lack of gearing doesn’t affect it until higher speeds when it’s at a much higher RPM.
A piston engine with a 5 or 6 or even a 7 speed transmission can lower the RPM at a higher speed by using a transmission that allows for the gear ratio to change as the car is driven. At 80 mph a piston engine can be reduced to just 1500 or 2000 RPM while the EV without a transmission is spinning furiously and thus using more energy than at low speeds.
The faster any motor spins the less torque it will make because it’s a function of inertia. By changing the RPM to be less dependent on the speed of the wheels a piston engine can climb through the smaller RPM band multiple times while the EV doesn’t.
Because the EV needs to make enough torque to continue moving at high RPM it makes more torque at lower RPM because it loses torque from spinning so fast because of the inertia it has to overcome to keep making that much torque.
When EV fans talk about a instant torque they don’t mean a flat torque curve they mean all the torque is at the low end and there aren’t gears to keep the RPMs at the usable low end."
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Daniel in SD
(supervised)
The M3P rear motor is already extremely efficient at 80mph. A transmission would help give faster acceleration by moving the motor closer to the horsepower peak but would not be worth the additional weight and complexity for a street driven car. I doubt it would improve efficiency for driving at legal speeds.
If transmissions made EVs more efficient then manufacturers would already be using them, they're way cheaper than batteries!
AlanSubie4Life
Efficiency Obsessed Member
I think it's about 200Wh/mi (probably +/-15% error on that) due to drag at 70mph, so using that as a starting point, that's ~100lb-force at that speed. Which is about 18.7HP at 70mph.
TORQUE:
So converted to torque (using 9.04 drive ratio and 13.26in radius of wheel) from 10mph to 100mph:
plot 13.26/12/9.04* 100 * v^2/(70)^2 from 10 to 100 - Wolfram|Alpha
HP:
And HP vs. velocity from 40 to 100mph:
plot 18.7/(7000) * 100*v v^2/(70)^2 from 40 to 100 - Wolfram|Alpha
(So that's 50-55HP at 100mph, as mentioned above).
Yes, though the power is dropping off a bit (after correcting for the drag HP when using the accelerometer method described above - so dropping to a corrected ~380HP at 100mph, from the corrected peak of ~450HP) what I have seen posted elsewhere, the power draw from the battery (has to be read from the CAN bus) is also dropping off a fair amount between 50mph and 100mph. So the efficiency is not that much different at the higher speeds. I don't know whether the battery power draw drops off by a full 15%, but it does drop off.
So whats the frigging horsepower now, does anyone actually have a figure? I have read a lot of (at times interesting) chin stroking and intellectual masturbation over this. Can we just put the number at the first post too, Ive scrolled through bloody pages of this wank.
AlanSubie4Life
Efficiency Obsessed Member
Chill! Or, keep calm and carry on, as the British imperialists would say. Looks like about 450HP peak to the wheels at 50-55mph. HP & Torque to the wheels, not Corrected For Drag
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AlanSubie4Life
Efficiency Obsessed Member
Ah, the Porsche Taycan, a paragon of efficiency.
(Efficiency is not the reason for the transmission.)
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SleeperService
Member
Daniel in SD
(supervised)
It's a little quicker than a Model S at high speeds but way less efficient overall. It's also way more expensive. I'm sure it will be a beast on the track but for a street driven vehicle it doesn't seem worth the extra complexity and cost.
I wish this thread started with “third’s is a drinking game, every time someone says “rollout” or “misinformation” take a sip.
I would not have read all 10 pages because I would have stumbled to bed after about 5 pages...
Can’t wait for the power bump!
I would not have read all 10 pages because I would have stumbled to bed after about 5 pages...
Can’t wait for the power bump!
Don't get more things from Quora. It's like a 3rd-world version of Wikipedia.
You can attach a geartrain to any motor to gear its speed down. All you're doing is reducing the mechanical leverage. That's not a good thing, if what you want is maximum torque where the rubber meets the road.
AlanSubie4Life
Efficiency Obsessed Member
Reducing mechanical advantage can be good. Taking this case as an example, gearing up (more reduction) by a factor of 2 at 100mph would would produce about 2.4 times the torque from the motor turning at half the speed, for the same wheel speed. This would mean 2.4/2 or 20% more torque to the wheels at the same wheel speed (neglecting extra drivetrain losses, which will exist) when using this hypothetical second gear at 100mph. As one would expect...since the motor is making ~450HP at that lower motor rotational speed rather than ~375HP. So even though mechanical advantage has been changed (reduced), the extra torque produced by the motor at lower speed more than compensates.
This is not to first order more efficient, though (likely it is less efficient at all speeds, due to extra drivetrain losses). So you have more losses. In addition the extra power is not free (has nothing to do with efficiency to first order). It is putting out more power, but the battery draw will also be proportionally higher. (Exact details of how it works out depend on the efficiency vs. speed of the motor, which is a different question than power vs. speed)
But anyway, I think this is why the Taycan has a transmission - not for efficiency, but for maintenance of power at high vehicle speeds. Allows them to get that motor back to producing maximum power. The true efficiency of the Taycan has yet to be confirmed, but all signs so far point to it being pretty awful.
Absolutely. If we assume something about the motor in the first place. No motors operate at their optimum at 2000 rpm (like in original example), outside of a municipal bus
SleeperService
Member
Absolutely. If we assume something about the motor in the first place. No motors operate at their optimum at 2000 rpm (like in original example), outside of a municipal bus
The Model 3 has reached its peak [plateau really...] torque at 2000 rpm... I guess it depends on what you count as "optimum" and whether you mean "motor" [aka electric motor] or engine [aka internal combustion engine]. For acceleration, the Model 3 motor(s) seem to leave their optimum [torque plateau] at ~5000 RPM with the horsepower peak at about 6300 rpm.
Daniel in SD
(supervised)
While not optimal the Nissan Leaf drive unit gets 90% efficiency at 2000rpm. You can see from the efficiency map that adding a lower gear would not improve the efficiency in the low load case since it would reduce the required torque. At higher loads it would make a small improvement. A plot versus horsepower would more clearly show the limited benefits of a multispeed transmission.Absolutely. If we assume something about the motor in the first place. No motors operate at their optimum at 2000 rpm (like in original example), outside of a municipal bus
To touch earlier grounds of this thread, a motor may require a transmission to translate its operating range (power band, in revs) into the desired application range (say 0-150, in mph).
Almost all combustion-powered vehicles require it because the motor runs out of revs AND/OR it runs out of torque at high revs... in both cases a change up is required, like alansubie demonstrated. Most n/a petrol engines have a wide'ish power band and simply run out of revs -- redline enforced because piston speed too high, or valvetrain cant catch up. Most diesel engines have a narrow power band and run out of grunt, so you'd shift early before the redline to get more actual torque applied to the wheels. In cases like Mack trucks those things need something like 20 gears
Because Tesla's motor revs really high, and has sufficient output across that entire range, it does not require multiple gear ratios. (Because its torque output is not perfectly flat, having more gears can help, but at the expense of weight and complexity and etc)
So in all, multi-gear transmission is a requirement for some motors, but is not in itself an advantage
Daniel in SD
(supervised)
Having flat torque output would make having multiple gears advantageous for performance. It’s that the electric motors have relatively flat horsepower over a very wide RPM range that makes gearing less beneficial. For maximum performance you want to keep the motor at its horsepower peak.
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