Model S All Wheel Drive - How Does It Work?

ArtInCT · Oct 13, 2014

I have tried to read as much as I can about the new Model S All Wheel Drive (Dual Electric Motor) system. Sadly that is not too much as I cannot find much data.
I am yet to find out how Tesla has implemented the AWD system.
Are both motors "always" working all the time at the same rate?
Has Tesla engineering come up with some way to "idle" or "free wheel" a motor if the car's speed and terrain on which it is traveling does not demand power from both motors?

In the case of the P85D I could see how the larger motor could be put to sleep if you were cruising along at 40-60 on flat terrain with no headwinds... but maybe I am expecting too much?

I have heard there are up to three "modes" or performance profile characteristics, do any of you have any details on these modes?

I wonder if there will be future enhancemnts coming?

Thanks,
Art

Olle · Oct 13, 2014

You are right, the motor not in use will be put to sleep, simply by its inverter not applying power to it. You probably already noticed that your motor doesn't create friction when you coast. Whichever motor is in a more efficient spot at any given moment will do the job, provided it has enough traction and power

mgboyes · Oct 13, 2014

The great thing about using an electric motor (and especially an induction motor) is that as well as simulating forward and reverse gears just by running the motor in the opposite direction, you can also simulate neutral just by not allowing any current to flow (i.e. disconnecting it). There's no clutch in a Model S - the motor shaft is always connected to the rear wheels so when they turn, it turns. So arranging it so that at different speeds one or other motor is inactive (or contributing less power) is trivially easy.

TEG · Oct 13, 2014

Having a clutch to disengage the non powered motor would probably help efficiency a bit, but probably not worth it in terms of complexity, reliability concerns, weight and cost.
Also, you don't want any delay when you want to start applying power again.

Cottonwood · Oct 13, 2014

TEG said:
Having a clutch to disengage the non powered motor would probably help efficiency a bit, but probably not worth it in terms of complexity, reliability concerns, weight and cost.
Also, you don't want any delay when you want to start applying power again.

I'm sure that efficiency gains are very small. Electric motors do not have pumping losses like an ICE. When current is not applied to the induction motor, the rotor is just a flywheel. The only losses are bearing losses air drag on the spinning rotor, and those are most likely tiny.

bigmaple1 · Oct 13, 2014

If you have ever checked out the motor display in a showroom, you can spin the shaft and the motor keeps spinning when you let go. I think the internal friction losses in the motor are very small. If you live in a cold climate and haven't preheated your battery in the winter, you can see what having no regen is like -- the car will coast effortlessly (this is of course, a 2wd experience, I would expect the AWD version to essentially be the same though)

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Model S All Wheel Drive - How Does It Work?

ArtInCT

Always Learning

Olle

Active Member

mgboyes

Member

TEG

Teslafanatic

Cottonwood

Roadster#433, Model S#S37

bigmaple1

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