F1technical.net

NTS wrote:Could anybody explain to me what the main reasons are that a normal gearbox is not suitable for an EV? Gearboxes that can handle high torque exist for heavy diesel vehicles so that's presumably not the main issue?

Plenty of EVs use "normal gearboxes". Auutogyro is just constantly pushing his own transmission design.

Pierce89 wrote:Plenty of EVs use "normal gearboxes". Auutogyro is just constantly pushing his own transmission design.

Only hybrids so far right? The production full-electric cars from Nissan (Leaf), Tesla (Roadster, Model S) and BMW (i3) all have a direct drive from the electromotor and no gearbox.

I don't know of any production electric cars with a direct drive. The most common solution is a single speed box, usually with a ratio in the neighborhood of 10:1. A gearbox is still often necessary but with no clutch/torque converter and a fixed ratio, it's different from a "normal" car's gearbox.

Sorry, that's what I meant but couldn't find the right word. "Single gear gearbox" sounded weird when I wrote it.

NTS wrote:Sorry, that's what I meant but couldn't find the right word. "Single gear gearbox" sounded weird when I wrote it.

Depends on the motor as to the reduction gearing but it still means there are no 'gear changes'.
When they try changing gear with electric drive two things happen.
First the transmission tries to jerk the driver out of the car.
Second the mechanical impact of the shift mechanism is so high it reduces the life of the gearbox.
In the case of the Tesla two speed this was 2000 miles.
Simple fact not a scratched record.

The only fact is maybe the Tesla reliability. But could you please explain why you think that your points are fact?

It should easily be possible to revmatch the motor to the speed of the car to reduce any impact and be easily able to keep the stresses at a reasonable level.

autogyro wrote:

NTS wrote:Sorry, that's what I meant but couldn't find the right word. "Single gear gearbox" sounded weird when I wrote it.

Depends on the motor as to the reduction gearing but it still means there are no 'gear changes'.
When they try changing gear with electric drive two things happen.
First the transmission tries to jerk the driver out of the car.
Second the mechanical impact of the shift mechanism is so high it reduces the life of the gearbox.
In the case of the Tesla two speed this was 2000 miles.
Simple fact not a scratched record.

Jerk coming from a shift is obviously a motor control problem, nothing to do with the gearbox...

Does anyone know who made the Tesla gearbox?

NTS wrote:

Pierce89 wrote:Plenty of EVs use "normal gearboxes". Auutogyro is just constantly pushing his own transmission design.

Only hybrids so far right? The production full-electric cars from Nissan (Leaf), Tesla (Roadster, Model S) and BMW (i3) all have a direct drive from the electromotor and no gearbox.

I was speaking of electric race cars. There a big electric drag racing scene in the US and the fast cars all use gearboxes.

Wonder why BMW is not fielding a team considering how big they are for new tech

autogyro wrote:When they try changing gear with electric drive two things happen.
First the transmission tries to jerk the driver out of the car.
Second the mechanical impact of the shift mechanism is so high it reduces the life of the gearbox.

Ok, but I'm genuinely trying to figure out what causes that. As a complete outsider to gearbox design and EVs I would assume it is just:

1. Move the "thingy" that disengages the current gear
2. Instruct motor controller to match the calculated revs for the next gear
3. Move the "thingy" further to engage the next gear

The gap for step 2 can be very small since a motor controller should be able to handle this rev-match phase very precisely and very quick with an electric motor right? What is the main thing that makes this not work?

Pierce89 wrote:I was speaking of electric race cars. There a big electric drag racing scene in the US and the fast cars all use gearboxes.

Thanks, I didn't know that. What type of gearboxes do they use? Is it possible to drive those "smooth" with some effort? And how "lastig" are they? Single race? Or much longer?

autogyro wrote: First the transmission tries to jerk the driver out of the car.

Gearboxes for EVs don´t use a clutch?

I´ve never thought about this, but I guess they don´t use it, since it´s not needed to start from still

Is that the problem of gearboxes for EVs?

I'm a bit late here, sorry... why gooved tyres?

Jerk coming from a shift is obviously a motor control problem, nothing to do with the gearbox...

It has everything to do with the gearbox.
Lay shaft gearboxes or even hydraulic clutched epicyclic auto boxes are totally unsuitable for stepped gearing on an electric power train.
Its a bit like trying to hit a rotating flywheel with a sledge hammer.

If you follow the current trend (which is wrong) you would use two or at most three gears.
This results in a wide rpm change at the shift points, you either get a huge bang (sledgehammer shift), or if you time the shift overlap (with your wonderful all singing computer control) and wait for things to slow down and match up the shifts become too long and your efficiency gain is lost.
You could reverse the motor polarity during the shift but that would probably blow the gearbox in half.
It would definitely waste energy.
If you use more gears to reduce the rpm drops you negate the benefits of using a gearbox in an electric power train anyway.
So you use one gear, as they all do accept on racing cars where the drivers teeth are not so important.

I know the answer but nobody cares.

autogyro wrote:Jerk coming from a shift is obviously a motor control problem, nothing to do with the gearbox...

It has everything to do with the gearbox.
Lay shaft gearboxes or even hydraulic clutched auto boxes are totally unsuitable for stepped gearing on an electric power train.
Its a bit like trying to hit a rotating flywheel with a sledge hammer.

You are going to have to explain it using newtonian mechanics auto. Poetic analogies don't quite get the job done...

I believe Newtonian physics was a bit before electric traction last time I read up on him.