On 19/04/17 23:03, NY wrote:
"DerbyBorn" wrote in message
2.236...
Murmansk wrote in
:

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.


No gearbox or clutch.

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.

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

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.

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.


--
"When a true genius appears in the world, you may know him by this sign,
that the dunces are all in confederacy against him."

Jonathan Swift.