Going from 4WD to 2WD with the touch of a button, what is the correct approach

[ardillolambo]

Folks,

My project is a dual motor set up, for the moment I'm thinking to do an AWD application, but what about having the option for ECO (2WD) which I configure with my control set up, with the push of a button for extended range and cruising.

So what would be the correct approach to dis-able the motor that won't run....
I'm assuming the car should be in a complete stop...then what?

Turn OFF the ignition signal on the desired motor?
Keep Ignition on, but motor in neutral?
when doing 2WD....Which is preferred FWD or RWD or may be it don't matter? I guess it don't matter

Regards,

[johu]

Yes just cut the direction signal. Works even mid-drive

[uhi22]

extended range and cruising

Does it make a difference in consumption to run in the one motor in neutral? I understand, some cars have a mechanical clutch to decouple the motor if not used.

[m.art.y]

Looked into this with another customer. If there is no way to physically disconnect the motor from the drivetrain for cruising when not used then preferably it has to be the induction type of motor. PMSM will draw a little bit of current even when freewheeling.

[ardillolambo]

@ Johu
ok, pardon my ignorance but if I cut the motion direction (will be in neutral) on the run to go from AWD to 2WD or vise versa the OI board will not regen? Do I need to change a parameter on the controller board?

[ardillolambo]

Does it make a difference in consumption to run in the one motor in neutral? I understand, some cars have a mechanical clutch to decouple the motor if not used.

I believe so, I won't be "0" if I followed what Johu suggested, basically the inverter board will be consuming from the 12 volt system but definitely range will be increase since the motor isn't pulling juice from the HV battery

[ardillolambo]

Looked into this with another customer. If there is no way to physically disconnect the motor from the drivetrain for cruising when not used then preferably it has to be the induction type of motor. PMSM will draw a little bit of current even when freewheeling.

No, I do not have a mechanism to disconnect the motor from the drive train. Yes, I was expecting to draw something, if the inverter board still energized in "neutral" as Johu suggested.

[m.art.y]

No, I do not have a mechanism to disconnect the motor from the drive train. Yes, I was expecting to draw something, if the inverter board still energized in "neutral" as Johu suggested.

What type is your motor that you plan to freewheel like that? If it is a permanent magnet type of motor if won't be just the inverter drawing from 12v. Motor will be drawing couple amps from HV battery also.

[ardillolambo]

What type is your motor that you plan to freewheel like that? If it is a permanent magnet type of motor if won't be just the inverter drawing from 12v. Motor will be drawing couple amps from HV battery also.

It is a Tesla SDU, If it draws some current from the HV battery that will be fine, but still less than if I'm running the motor.

[barracuda816]

Will this really make much of a difference in terms of efficiency? I would assume, all things being equal, it would take x amount of force to keep the vehicle at a constant velocity. If you have 2 motors then each will be providing a proportion of x if you dissconect one now the other will be supplying the entire amount of x. Of course there are losses but I would have thought they are quite small and the drag will remain the same if there is no mechanical disconnect.

[johu]

The 2WD version of the the vehicle is always more efficient than the 4WD. Partly explained by the weight difference but not just that.
Also most 4WD vehicles use a PM motor in the rear and async motor in front. It only steps into action on high torque requests.

For fine grained control I'd suggest a VCU and separate CAN throttle control for each DU. But cutting the forward signal is a workable low tech approach. And no it doesn't regen in neutral, the sine variant even shuts down PWM

[ardillolambo]

The 2WD version of the the vehicle is always more efficient than the 4WD. Partly explained by the weight difference but not just that.
Also most 4WD vehicles use a PM motor in the rear and async motor in front. It only steps into action on high torque requests.

For fine grained control I'd suggest a VCU and separate CAN throttle control for each DU. But cutting the forward signal is a workable low tech approach. And no it doesn't regen in neutral, the sine variant even shuts down PWM

Johu,

I'm using a Model S throttle pedal that have two sets pedal positions sensors, that was my original design thinking about the 2WD & AWD modes.
Sorry about my ignorance, when you say VCU what is it? besides the low tech option of cutting the forward/reverse direction what you will suggest to be a more elaborate approach

Regards,

[ardillolambo]

Will this really make much of a difference in terms of efficiency? I would assume, all things being equal, it would take x amount of force to keep the vehicle at a constant velocity. If you have 2 motors then each will be providing a proportion of x if you disconnect one now the other will be supplying the entire amount of x. Of course there are losses but I would have thought they are quite small and the drag will remain the same if there is no mechanical disconnect.

Applying your approach and.....all things being equal....then a V8 should be as efficient as a Inline 4 when cruising? Any body that owns a V8 knows that's not the case. That's why some high tech V8's have a cylinder deactivation when cruising as fuel saver mechanism. Even thou electric motors behave different, that's why I think a motor deactivation will be more efficient when cruising, also I'm not saying that I'll do it, just exploring what needs to be done in order make motor deactivation possible and if its worth it.
Regards,

[barracuda816]

A really interesting experiment. I would love to see the difference in efficiency on the car before and after the mod.

I agree about ICE motors. But they are a different beast entirely, combustion is a really inefficient way of creating torque, not to mention the pumping losses. With electric motors I would think the gains would be really insignificant.

I am by no means an expert and would love to see the outcome either way.

[ardillolambo]

It may happen... I just have to add two more relays to separate the Reverse & Forward motion signals to each SDU, activate/deactivate those relays depending on the mode selected, then a lot of road testing which I'm far away from it.

Another thing I was thinking....instead of doing 2WD/AWD modes....what about an ECO mode button (which I have already) and change the configuration for the 2 SDU's and give a mild acceleration profile, if not in ECO mode (Sports Mode) give an aggressive acceleration profile.

But the question here is, can this be done? the OI inverter board have this capability?