I thought electric cars were 95% efficient.
I must have a very simplistic view of the world if they can get an 18% improvement with a B class car (Focus sized?)

I suppose if you make gearboxes, every problem looks like a gearbox problem.

The lack of transmission is an extremely important maintenance advantage as well.

I suppose if you make gearboxes, every problem looks like a gearbox problem.

Yes, Evolute Drives clearly know little about induction motors or must be reading from 30year old textbooks.

Induction motors can be operated at constant rated torque over their complete speed range providing the inverter voltage is made sufficiently high.

For short time durations induction motors can output a Peak torque of up to 350%, perhaps as high as 420%, before electrical constraints step in. Durations are also limited to avoid rotor meltdowns.

Forget about efficiences quoted at 60Hz since automotive grade 4-pole induction motors don't usually spend much time there (~15mph).

The fact is that induction motors are more efficient the faster they spin, perhaps as high as 99%.

The reason is simple, it takes a certain power to establish the stator field. With the setting up of the magnetic flux needed for rated torque, power output becomes simply proportional to the spin rate.

No more power is needed to maintain that torque. Think of it as a fixed tax that has to be paid following which conversion of power from electrical to mechanical is 100% efficient.

Theoretically, unlimited power lasts for as long as the rotor can survive the rpms but in practice, and it's usually somewhere below 60mph, the motor output has to be constrained electrically by the controller in order to prevent thermal distress to the battery pack. This is the problem faced by the Tesla P85D that has some owners riled up.

To recap, since both efficiency and power increase with rpm it should never be necessary to spin down the motor as you would do with an ICE powered car. This should make the need for a multi-ratio gearbox somewhat moot.

SJC , understand that although my "Vista" browser is said to be all knowing and all powerful but Ph...tt Just not able to find attachments. Would you mind a cut and paste here so that us lesser mortals can see what smug village has produced in Teslamotor land, please and thank you.

By the way in case there is misunderstanding about the P85D. It does entirely achieve the 2.8 sec to 60mph ramp as promised but the 85Kwh battery causes the reigning in above that speed. A larger 90kwh is in the offing(at a price) which will significantly improve subsequent acceleration beyond 60mph.

Well, I agree with Evolute Drives and here is why.
A transmission is not only a speed adapter, it is also a torque converter. With a smaller e-motor and a transmission, you can reach the same torque levels as with a bigger e-motor (excepting high gear where less power and torque is needed for gliding than for acceleration). The bigger the e-motor is, the more current it'll draw under load from the battery. High power density flow is not necessarily of advantage to the battery. On the contrary, the lower the power flow the less strain is exerted on the battery. I could very well imagine that a smaller dimensioned electric motor combined with a 3-gear transmission would suffice general requirements, ease strain on the battery and improve consumption performance.

What is the additional weight of this transmission vs a NISSAN LEAF reduction gear? I would rather not add any more moving/shifting parts. Part of the appeal of EVs is the reduction of moving parts.
I would rather have a battery with more capacity.

mahonj : I'm moving to WIN10 shortly. If that doesn't do it - then I'll try Chrome. In the meantime I was able to reach the thread - thanks SJC much appreciated.

The discussion there runs 3 pages but I didn't see a definitive conclusion. There were comments on data attributed from Tesla being unsubstatiated as far as gear ratios but nothing on whether V/Hz motor characteristics had been changed to suit. It being necessary for the motor design to reflect a change in its V/Hz whenever a gear ratio is changed. You can't change one without changing the other else power peaks will come at the wrong roadspeed, usually too early. That may have been Steve Saleens problem with his P85 enhancement in 2014.

I seem to have a complete earlier post wiped thanking Mahonj for the Chrome suggestion, and then SJC reposting a link I could use. Plus comments on the content of that link. ??
Of course that would be the post that I didn't save, because the system told me it had been posted. I began my response to Yoatman almost directly after.

SJC , I'll give one more kick of the can to this.

electric motors are not always 90% efficient

Not at slow speed and full torque, I'll grant you your point which is exactly as you stated in your first post earlier in this thread.

But these occurences of slow speed operation (<20mph)do not present a significant loss, in total, of battery energy for several reasons.

They are usually of very short duration when accelerating from rest, sub 3 seconds.

They exist during prolonged slow speed operation where the motor demand is bound to be very low so electrical losses are going to be expected to be proportionally low as well.

Finally within this low speed region, the vehicle may actually be slowing down with or without regen braking.
No losses at all.

Aerodynamic losses, which I consider the biggest battery killer, are almost zero in all these scenarios.

If this was an industrial machine then a CVT may be a good idea if considerable high torque while running continuously at low speed was required. BUT for a road vehicle any heavy demand is only transitory as the motor drives the inertia of the vehicle up to cruise speed. I don't see the need for any further mechanical complication to be added here.

If I haven't convinced you by now then at least you are in good company with Evolute Drives they don't see it either.

Alex, no I hadn't heard, but a somewhat less sophisticated alternative to avoid rotor overheat is to cut the rotor in half so to speak and then use the two resulting downsized motors to separately power each axle.

Theoretically the effect is to increase surface to volume ratio by 26%. That opens up the possibilities of more power per motor but with the same motor case temperature as the original single motor drive system.

Splitting the drive unit like this also confers AWD something the Evolute isn't offering I notice.

@SJC,
BTW how do you plan to implement eCVT with electric motors only?
In Toyota eCVT system there are 2 e-motors and ICE attached to the planetary eCVT system.
Did you try on paper to connect 2 or 3 e-motors similar to those currently used and run the numbers from 0 to 100 mph, with calculated all gear ratios in such system?
I'd like to see such a system, its pros and cons , never saw any eCVT with only e-motors.

See if I've got this right. 20,700rpm to 9000rpm in 80mSecs. So you're thinking you can regen a rotor the size of a 1lb coffee can to give up 75% of its rotational energy in less than a tenth of a second. Sorry, not possible, the physics is just not with you.

Do you think is a hypothetical question.

4-pole (2pole-pair/phase) induction motors have twice the torque per unit mass so 2-poles are rarely used except to avoid an inverter. Examine a motor catalog for specs, a 10Hp 2-pole and 4-pole will be seen to have the exact same weight, although the 2-pole will have smaller dia rotor. How do I know ? Compare their rotor inertia constants.

Actually the best way is to run a 230Vac 4-pole on 460Vac @120Hz. The motor will develop twice its nameplate power and run cooler. Has it been done ? Yes.
The Tesla system takes the idea further by winding for @480Hz (~14,000rpm), in this case the stator lams would be made thinner of course and the rotor would be finely balanced to enable it to run with low vibration at that speed.

What you found in catalogs are probably not high performance motors, for cost reasons they may have used the same stator.

Alex, the motors in a Eurotherm catalog are Premium Effcy with copper rotors - aluminum is being phased out as more and more newly installed motors are being inverter fed.

I refer you to the catalog to see first hand that 460Vac 10Hp 2-pole and 4-pole weigh the same even though the former puts out only half the torque of the latter. It gives a more poignant look at the situation. I know I am repeating an earlier post, perhaps I wasn't clear enough, but an intelligent person like yourself may opt for a 230Vac 5Hp 4-pole which makes the exact same torque as a 10 Hp 2-pole (but will naturally weigh and cost a whole lot less) and drive it with a 460Vac inverter at 120Hz to reach ~3600rpm and thus match the performance of the larger 2-pole.

Hopefully these facts and ideas will lessen your enthusiasm for the use of 2-pole motors which today is now a dead end as far as I am concerned.

You are probably already aware that catalog motors are unsuitable anyway since their windings have a V/Hz of 480/60Hz = 8.0V/Hz Automobile inverter motors are more likely to be 0.25V/Hz. Just need 32X more current to reach the same torque. That's where the 1500Amp IGBT's come in. Their use completely changed the picture as they effectively extend the useful voltage range because the adoption of an extra low V/Hz motor winding allows the motor to spin 8X faster before the inverter runs out of voltage headroom.

Tesla was among the first to use them with the legendary 2.8sec to 60 ramp with fixed gear P85D. So I am thinking how much more proof do you need ?

Anway congrats on figuring out what is basically turns out to be the equivalent of the cube root of two, it looks like the generic formula is the cube root of the number of divisions you make of the original motor.
As you discovered, the utility of two motors suggests 26% better cooling/or more power. From that perspective I think you will find that four motor systems begin to look even more interesting.