O.T. electric cars - do they have gearboxes?

I've just been for a ride in someone's Nissan Leaf - it was impressive, so quiet and amazing acceleration.
Do electric cars have a gearbox (an automatic one I presume)? Or does the motor just run faster the faster you go? I was told by the owner the optimum speed for economy of battery usage is about 55mph.
It doesn't sound like it's changing gear.
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No gearbox or clutch.
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Well, not like a IC car. They have gearboxes to reduce motor speed to wheel speed.
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Usually. Some do have a two speed gearbox.
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Mainly because an electric motor, when correctly driven, can generate torque from zero speed and don't have such severe upper limits to the speed because there are no reciprocating parts which have to rapidly reverse direction.
Not having a gearbox (automatic or manual) must make it much easier to drive because torque/acceleration is directly dependent on accelerator position and not a combination of that and gear ratio - you don't get gentle acceleration which suddenly becomes kick-in-the-back acceleration as the automatic transmission reacts to your gradually increasing accelerator position by suddenly deciding to change down in a situation where a manual driver would hold onto the present gear. I find this the hardest thing about automatics: I accelerate out of a roundabout and the car suddenly lurches forward so I ease off the throttle slightly and it changes back up - very difficult to hit the happy medium.
It is also easier to build in torque limiting to any value, to prevent the car lurching forwards if you press the accelerator too hard when setting off from rest, or for a cruise control to also accelerate you briskly and yet smoothly from one speed (eg rest) to the another speed speed. The fact that (AFAIK) no cars implement this doesn't mean it's not possible to do.
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Well written software on an auto should make it change rather like a well driven manual.
But it's a pretty poor auto that 'lurches' forward. And where it changes down where there is no need. The now ancient pure mechanical GM auto in my old Rover is pretty well always in the gear I'd choose if it were a manual, and certainly never lurches forward. Of course if you floor it at moderate speeds it will drop to 1st gear and take off like a scalded cat. But not something that happens by accident.
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On 19/04/17 23:03, NY wrote:

The severe upper limit is ion fact the driving voltage, When the motor back EMF hit's that, it wont go faster.

Torque is directly proportionment to current. If you monitor that and pedal position and use the difference top adjust a PWM chopper, then the behaviour will be as you describe. It is not 'given' though. It has to be designed in.
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On Thursday, 20 April 2017 07:20:39 UTC+1, The Natural Philosopher wrote:

Drivel. The motors are three phase synchronous motors with rare earth magnets, not milk float motors.
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On 19/04/17 23:03, NY wrote:

Not only - but motors can be geared virtually - by changing the number of poles.
Say you have a 24 pole motor. By deciding how to drive the windings in phase or antiphase, you can pair off adjacent poles for an effective 12 pole, 8 pole, 6 pole etc setup.
More poles = slower and higher torque, less poles = higher rpm.
I have no idea if this method is used by any car motors but I think some trains do - you can hear the "whirrr... <drop pitch> whirrr" which I can only explain as pole changing as the motor is otherwise directly connected to the axel.
However, I'm pretty sure most traction has at least one set of fixed gears as motor rpms tend to be higher than desired wheel rpms.
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On 20/04/17 08:10, Tim Watts wrote:

What utter bollocks.

Well even there you would be wrong. Its depends on how many poles the motor is built with (as opposed to driven).
I could explain the theory, but you wouldn't understand it would you?
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On 20/04/17 08:13, The Natural Philosopher wrote:

Perhaps you should check your facts before you go slagging people off:
https://en.wikipedia.org/wiki/Dahlander_pole_changing_motor
I'll accept an apology when you've read that.

Perhaps you could try - or is it beneath you?
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On 20/04/17 10:17, Tim Watts wrote:

People would simply say 'too long, didn't bother to read it' and go back to believing simple fairy tales as per usual.
Lets just deal with one aspect. Number of poles. There is a given amount of iron you can cram into a motor, that, plus the magnets you use (unless they are electromagnets) determines the amount of energy *per magnetic reversal* you can get in and out of the system
This leads to a simple rule: the more revs (reversals) the more power. Until other factors limit you, as high frequencies start to impose their own extra losses, as does friction.
Adding more poles allow for more reversals per shaft rotation. It is equivalent to a gearbox. However only using *some* of those poles nets you nothing, because you are simply using less ironwork. Its pointless. No one does it. It is simply like having a smaller motor that weighs more.
Electric motors are UTTERLY different from other motors.They dont really have a 'power rating' re se. Only when fed from a given voltage.
I've run motors designed for 3V, generally used at 6-7v, at 11-12 v and got more than three times the power out of them. The limitation was brush bounce and wear in that case, and the availability of gearboxes to get the insane RPM down to something usable..
In practical terms a multipole motor is bigger and more expensive than a two or three pole motor* BUT if the gearbox you need to use is more expensive and heavier...then the multi-pole wins slightly.
Some of the model motors used to come with kevlar wound rotors, to stop them exploding. More revs, more power.
That's part of the simple story. The more complex story involves understanding copper losses (resistance) iron losses (hysteresis and frictional motor losses) plus issues with the controlling electronics (peak currents, inductance, switching losses and so on). And it it uses permanent magnets, the field strength, weight, and performance versus temperature of those as well.
Each one of which is a book chapters worth.
*two magnetic, three wound poles is the most basic uni-directional motor.
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On 20/04/17 10:51, The Natural Philosopher wrote:

OK - fine. But you haven't explained why it's "bollocks". I've found references to train traction using, at some points in history, pole changing configurations.
Also the type of motor described in the Wiki was an induction motor so no permanent magnets.
Most EMUs these days use induction motors, even on DC lines so the power electronics is there either way.
I'm not sure how having a larger number of lighter stator windings is worse than 2-3 large windings either. Would any large traction motor really use a 3 pole configuration - it seems unlikely - the starting torque would suffer.
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On 20/04/17 11:02, Tim Watts wrote:

sigh. You see. I explain, and it makes no difference.
A 3 pole motor and a 3:1 gear box is EXACTLY equivalent to a 9 pole motor of the same size.
If you found references to pole changing it was almost certainly using all the poles but putting them in series or parallel pairs.
If you only have contactor type switches that's a very crude way to limit starting current. i.e a 6 pole motor can be connected as a 3 pole motor with either twice or half the RPM per volt and twice or half the starting torque or current. Depending whether you series or parallel the windings.,
But that isn't 'switching poles off' .
And all it really does is ensure you can start without burning the motor out. These days an electronic controller does that better.

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On Thursday, 20 April 2017 12:03:28 UTC+1, The Natural Philosopher wrote:

That is a very inaccurate explanation. Verging on bollocks
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On Thursday, 20 April 2017 10:51:23 UTC+1, The Natural Philosopher wrote:

Most of the above is bollocks too.
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On 20/04/2017 10:51, The Natural Philosopher wrote:

I'd take that as the apology Tim :-)
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On Thursday, 20 April 2017 10:17:56 UTC+1, Tim Watts wrote:

This is totally obsolete technology. I remember seeing a few such motors when I was an apprentice fifty odd years ago.
Completely irrelevant for traction.
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On Thursday, 20 April 2017 08:11:00 UTC+1, Tim Watts wrote:

What drivel you write.
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On Thursday, April 20, 2017 at 8:11:00 AM UTC+1, Tim Watts wrote:

I have also noticed that sound and imagined it to be due to exactly what you have described. A neat way of 'changing gear' electrically instead of mechanically. Robert
Robert
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