multi speed transmissions for EVs

[dcb]

I think this was missed in the other thread, but there is a case for multi speed transmissions on EVs, even if only two speeds. Plus who doesn't want a neutral to coast in option?

Green Car Congress: Antonov study of multi-speed transmission for EVs finds improved efficiency over different drive cycles

[thx712517]

Looks like a decent bump in efficiency for including another gear. I wonder why this isn't a more popular option? Would the reduction in weight and complexity by eliminating the transmission make up for the loss of efficiency?

[johnunit]

I think durability might be a concern also? I know that the Tesla Roadster, at least, has had issues with drivetrain durability.

[bennelson]

Yeah, Tesla loved two-speeds, except that they kept braking them.

The single-speed gear reduction that they finally went with increased their 0-60 time by something like 0.15 seconds!

I've been pretty happy just driving my electric Geo Metro in just Second and Third.

[NeilBlanchard]

I think it depends on the motor used? The SIM-LEI has the one of the lowest Wh/mile of any electric car (~134Wh/mile @ 55MPH) and it has four wheel direct drive. The Edison2 VLCe is ~108Wh/mile @ 45MPH average and it has only one speed with the final drive being chain in a reduction ratio.

The four next most efficient electric cars I know of; the Illuminati Motor Works 7 (160Wh/mile), the FVT eVaro (~165Wh/mile), and Dave Cloud's Dolphin (~165Wh/mile), and the GM EV1 (also ~165Wh/mile) all are one speed. The 7 actually has two speeds, but the taller gear was only ~2% more efficient, and a lot slower acceleration. It is hard to shift an electric car, and it takes a massively strong clutch, as well. The 7 totally ruined their racing grade clutch, and they have to shift it when stopped without it.

None of the production electric cars have a multi-speed transmission. Why is that, I wonder?

[dcb]

multiple speeds is good for 10% -20% efficiency. EVs are new enough that they dont need to be that picky. The tesla makes a lot more heat than it would with a gearbox.

[dcb]

Originally Posted by bennelson

The single-speed gear reduction that they finally went with increased their 0-60 time by something like 0.15 seconds!...

Didn't they dump a lot more current into the motor and add cooling?

[dcb]

Originally Posted by NeilBlanchard

I think it depends on the motor used? The SIM-LEI has the one of the lowest Wh/mile of any electric car (~134Wh/mile @ 55MPH) and it has four wheel direct drive. The Edison2 VLCe is ~108Wh/mile @ 45MPH average and it has only one speed with the final drive being chain in a reduction ratio.

You need to be doing something other than constant speed to see any benefit for multipe gears.

Originally Posted by NeilBlanchard

...It is hard to shift an electric car, and it takes a massively strong clutch, as well. The 7 totally ruined their racing grade clutch, and they have to shift it when stopped without it.

Why mess with a clutch? Who says they have to shift it when stopped without one?!? Who is saying it is hard to shift one?!? You wait till motor rpm is in sync and you shift (or add software to your controller to dial in the motor rpm for your speed for the next gear). The racing clutch was still metro sized on a 3300 lb, ~300hp car, apples and oranges. Why is this such a hard concept?

My one and only two speed EV was trivial to switch gears, just hit the reverse switch
http://ecomodder.com/forum/showthrea...ter-14889.html

[niky]

Hmmm... use a sequential without a clutch? Racing sequentials only need clutches for starts. An EV doesn't have that issue, so can run clutchless, just let the electronics match engine speed to wheel speed to allow the pre-loaded gears to go in.

[Ryland]

Originally Posted by dcb

You wait till motor rpm is in sync and you shift (or add software to your controller to dial in the motor rpm for your speed for the next gear). The racing clutch was still metro sized on a 3300 lb, ~300hp car, apples and oranges. Why is this such a hard concept?

I was just reading about the new NetGain motor speed controller and one of the other motor speed controllers out there can be programmed to work with a motor speed pickup to track RPM so the motor doesn't over speed, it seems like the next step is going to be exactly this, setting up an Arduino or something to drop the motor speed down to match the transmission based off wheel speed at the moment you want to shift, the hard wear is there it's just a program that needs to be written.