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BMW i3 drive unit vs Tesla drive unit

jborak

Member
Oct 8, 2015
46
0
NJ
Does anyone know if BMW and Tesla use very difficult electric motor technology for their drive units? I've been reading about some Tesla drive units and trying to learn the differences between the large drive unit and the small drive unit. They seem to be identical except for output and weight. But how do they differ from the drive unit BMW uses in their i3? Or the Nissan Leaf, Volt, etc.. for that matter.

Thanks!
 

Doug_G

Lead Moderator
Apr 2, 2010
17,881
3,351
Ottawa, Canada
Haven't seen much information on the BMW unit. Most electric cars use a permanent magnet DC motor, using rare earth magnets. One article I found indicated that it is a synchronous AC motor.

Tesla uses three phase asynchronous AC motor (invented by Nicola Tesla).

I doubt there is much similarity internally. Electric motors tend to be cylinders so they all "look the same" on some level.
 

TEG

Teslafanatic
Aug 20, 2006
21,819
8,833
Yes, Nissan LEAF uses a permanent magnet system, whereas Tesla is full induction motor.

Electric vehicle traction motors without rare earth magnets

Apparently BMW created something novel, with a 'hybrid' motor design:
Green Car Congress: BMW’s hybrid motor design seeks to deliver high efficiency and power density with lower rare earth use
...With its introduction of the eDrive motor—a proprietary hybrid synchronous motor designed to exploit both permanent magnets and the reluctance effect—in both the BMW i3 (earlier) and i8 (earlier post), BMW is advancing what it sees as an answer to achieving the highest possible power density and efficiency coupled with minimum possible use of magnets containing rare earth materials...


 

MacroP

Member
Jan 12, 2013
120
6
West Oz
I doubt there is much similarity internally. Electric motors tend to be cylinders so they all "look the same" on some level.

Actually the stator and it's windings would be very similar for all three types. Obviously the AC induction (Asynchronous) rotor is quite different to a DC brushless rotor. However the rotor for a DC brushless motor and an AC (permanent magnet) Synchronous motor would be quite similar in that they have permanent magnets on the rotor. The DC motor rotor may have more magnet poles though.

The 'drive' for a modern AC or DC motor used here would look similar too but operate differently and the power semi's would be slightly different. A modern inverter would use IGBTs and a DC controller may use MOSFETs. Both a transistor nonetheless though.

PS. Sorry can't comment on these other types (like switched reluctance) as you just don't see them in heavy industry (mostly mining) which is my background. I remember being taught about them 25 years ago and that was it. I don't remember the axial flux design though. Most of the modern AC or DC motors already are quite efficient. All have their pros and cons. IMO, for the motor, we don't really need to re-invent the wheel here (just the battery).
 
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TEG

Teslafanatic
Aug 20, 2006
21,819
8,833

Man, that reminds me how much better looking the concept was compared to what went into production...

concepti3.png


( They mangled the rear doors and window... )
 

ecarfan

Well-Known Member
Sep 21, 2013
19,224
13,875
West Vancouver, British Columbia
Wow, that i3 concept looks far better than the production i3! It continues to astonish me that car companies create beautiful concept cars and then far less attractive, or even ugly, production versions. It's great that Tesla doesn't do that.
Man, that reminds me how much better looking the concept was compared to what went into production...
View attachment 99297
( They mangled the rear doors and window... )
 

electracity

Active Member
Jun 8, 2015
4,028
2,531
60606
Wow, that i3 concept looks far better than the production i3! It continues to astonish me that car companies create beautiful concept cars and then far less attractive, or even ugly, production versions. It's great that Tesla doesn't do that.

Like the Bolt, BMW chose the most economic shape(cost and weight) for their lower end but mainstream EV. The functional shape of an EV is naturally a blunt nose, which Tesla knows doesn't work with their S3XY strategy. The future mid range EVs from the major will be better and more conventional looking: i5, Volvo, and possibly a new Nissan. Plus some unannounced cars from Mercedes and others.


Back to motors: Why was Tesla not able to buy the motor they wanted? Did perhaps the motor manufacturers want a more conservative design that didn't break?
 
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Vger

Active Member
Apr 10, 2009
1,781
210
Salt Spring Island, BC, Canada
AFAIK one of the most challenging aspects of the Tesla motors is the liquid cooling of the rotor. That requires intricate plumbing into the moving core of the motor.

It is also interesting to note that apparently the Model 3 will have a new motor, which will hence be at lest a fourth-generation design (Roadster->MS rear->MS front->Model3).
 
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Reactions: TEG

scaesare

Well-Known Member
Mar 14, 2013
8,373
13,927
NoVA
Thanks for that PDF for the BMW stuff, Jeff N.

TEG, the excerpt you provided refers to the "reluctance" aspect of the motor... but I've yet to see if they are doing anything special there. New variable-reluctance motors have been developed that promise to be significantly more powerful for a given size, but they have very significant inverter implications. I'm not sure BMW is really exploiting that... and the PDF doesn't seem to speak to that either.

I wish I could find some more on this.
 

stopcrazypp

Well-Known Member
Dec 8, 2007
10,246
5,156
Back to motors: Why was Tesla not able to buy the motor they wanted? Did perhaps the motor manufacturers want a more conservative design that didn't break?
Tesla used an induction motor to keep with the name (Tesla invented it). Also the Roadster was descended from a lot of work by AC propulsion which also uses induction motors, and that lineage continues. Tesla squeezes a lot of peak power out of a small and lightweight package while using no rare-earth metals (a cost driver in recent years). A large majority of the industry has gone with permanent magnet motors instead (they have higher peak efficiency and the rotors don't heat up as much).
 

stopcrazypp

Well-Known Member
Dec 8, 2007
10,246
5,156
I do not think the founders said "We want to start an EV company named Tesla so because that is the name we have to use an AC induction motor."
That may not be the main cause of it (the AC Propulsion lineage has much more to do with it), but I would say definitely plays a factor in Tesla sticking with an induction motor when practically all of the others gone with something else.
 

TEG

Teslafanatic
Aug 20, 2006
21,819
8,833
I don't know how true, but some have said Tesla does inductance motors because they have the engineering skill to make a performance inverter than can do it well, and others lack that capability. Others 'resort' to permanent magnet motors because they are easier to engineer, but at a higher materials cost.

The BMW PDF makes me think more that BMW chose their approach because they thought it was the best technology, not because they were incapable of making a great induction motor.
 

jborak

Member
Oct 8, 2015
46
0
NJ
Thanks for sharing all of this information on electric motors. It's interesting to know more about the differences and the reasons for them.
 

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