The benefits that a very high torque motor could bring are real but marginal, a few percentage points improvements on the respective metrics. They could instantly be negated by, say, the lower initial reliability of a revolutionary design.
Are there transmissions out there for EVs, and I just haven't been paying attention? And if no, why is it so hard? Is it because of the torque?
In general electric motors have a very wide band of excellent efficiency and an even wider band of great efficiency and they are orders of magnitude more efficient than ICE in any part of their operational torgue/speed range.
Electric motors don't have this particular problem, and they don't need a start gear that is a lot shorter than the other gears (1st to 2nd is usually around a factor two, while from 2nd up to the next higher gear the ratio will change by perhaps 30 % or so) because they can deliver nominal torque at low speeds or from zero speed (so they don't need a clutch, either). An ICE can't do that.
Here are the transmission ratios of a random six speed transmission:
1st 2nd 3rd 4th 5th 6th R
4.2 2.5 1.7 1.3 1 0.8 3.8It isn't that narrow[2]. Engines with fewer gears aren't particularly less efficient, they're just MUCH slower. Look at a map of gears[2]: the top gears are in the efficient range, but the lower gears are only there to allow you to rev the engine high while accelerating. In the ratios you gave, you could cut out 1, 3, 4 and only use gears 2, 5 and 6 and be able to get around fine- you start in second and then shift up as soon as you're rolling. You'd have a much more efficient car but you'd be incredibly slow.
[1]: https://qph.fs.quoracdn.net/main-qimg-0c6c45106b28601fc1aef4...
[2]: http://www.posterus.sk/wp-content/uploads/p12975_02_obr02.pn...
You could get around fine with 2, 4, 6, it's just that it would have very slow and less efficient acceleration (accelerating for longer at low RPM and very high torque is overall less efficient than accelerating for a shorter period of time at a higher RPM, given identical start and end speeds).
And that's exactly the point I made. You need many gears for an ICE because being able to reach a given speed in a given gear says very little on how efficient that is, therefore you need different gears for accelerating versus holding a given speed to get acceptable efficiency.
No, that's the whole point of short shifting.
No. The two types of motor are fundamentally different. Combustion engines need transmissions because they produce relatively constant torque (within 50% of max torque). Electric motors on the other hand produce relatively constant power.
This makes total sense when you think about it. An IC engine is powered by explosions; every explosion produces roughly the same force on the piston regardless of speed. You can't get more power without more explosions because you can't cram more air in the cylinder. You can only speed up the engine.
In an electric motor, you can cram as many electrons into the wires as you want. You are only limited by how much heat is generated. Increasing speed increases heat slower than increasing torque, but you can still basically increase either as much as you want.
Generally speaking, no. P = 2piM*n, while the common types of motor used in electric drives (synchronous and asynchronous three phase machines) will produce nominal torque at (almost) any speed from 0 (not for asynchronous machines) to nominal speed; therefore output power is pretty much proportional to speed.
The only type of motor that comes to mind that has somewhat of a constant-power behaviour to it are series wound motors.
In fact, it's a fundamental property of motors- the power constant. There is a torque constant (rpm/volt), a torque constant (torque/amp) and a motor constant that describes the efficiency of transformation from electrical to mechanical power.
[1]: http://raise.spd.louisville.edu/ECE252/images/L19-18.gif
[2]: http://www.eeeguide.com/speed-control-of-variable-frequency-...
[3]: http://www.motioncomp.com/pdfs/Motor_Constant_Great_Equalize...
If we were to run this motor "constant power" at 300 min^-1 it would provide about 500 N*m of torque and run at a hypothetical current of 300 A -- it's quite clear that that isn't going to go well.
For big stationary motors that are wound for high voltage, the large number of turns means copper losses dominate and limit torque at all but the highest speeds. Nevertheless, those motors can be rewound for lower resistance, which will cause them to have more even tradeoffs at different voltages/currents. Rewinding a squirrel cage rotor is... a bit of a task, obviously, but the torque/voltage constants are always pretty interchangeable.
Electric motors don't stall like an ICE, they produce much of their torque even at 0 rpm and usually operate over a wider rpm range.
A Tesla for instance has an electric motor that goes up to 18,000 rpm with a roughly 10:1 reduction gearbox for 0-155mph speed range without shifting any gears.
First - ICE engines have a minimum running speed, usually between 650-800 rpm. Driving in a gear that runs the engine slower than this can cause the engine to stop running or damage it. The vehicle needs to be able to operate at low speeds, which requires a low gear ratio. Operating at high speeds requires a higher gear ratio so the engine isn't damaged from running at extremely high rpm (efficiency is also an important factor, but secondary).
Second - Motor vehicles with ICE engines (ignoring hybrid assist features) need to be able to move away from a stop with the engine running, and without allowing the engine rpm to drop below idle. This requires a clutch mechanism to disconnnect the running engine from the rest of the drivetrain, and to slip as the vehicle's speed rises to a point where it's safe to lock the engine's rotation speed to the drivetrain's rotation speed. Manual transmissions come with manually operated clutches, newer automatics have automatically operated clutches, and old automatics have a hydraulical coupler that slips at low engine speeds.
Massive vehicles have an extremely low first gear, so they can get going from a stop. Passenger vehicles have a first gear low enough to operate in places like a parking lot. Top fuel drag cars only have one speed; a massive clutch controls engine power transfer to the wheels.
Electric motor vehicles don't have the low speed operation problems that ICE cars have, or anywhere near the level of inertial wear and cacaphony at high rpm, so the transmission can be optional. Transmissions are expensive, and a vehicle in the EV market in its current state doesn't need that level of optimization to be competitive.
I think most people with conversions just drive around in 2nd gear or thereabouts most of the time. Transmissions are a nice-to-have feature though, especially if your motor isn't particularly powerful and isn't made to run at extreme RPMs.