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Economy mode for "D"? Running one small motor only, unless exceptional circumstances

Discussion in 'Model S: Battery & Charging' started by AnxietyRanger, Dec 31, 2014.

  1. AnxietyRanger

    AnxietyRanger Active Member

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    In the New Blog: Driving Range for Model S Family.... thread there was talk of how the future "torque sleeping" (resting second motor while coasting) works. This gave me another idea, that I'd like to hear your thoughts on.

    How many of you are familiar with how e.g. Haldex multi-plate clutch operates in some four-wheel drive ICEs like some cars from the Volkswagen group and Volvo. There are some variations of the concept based on generation (later ones are not as limited), but basically the idea has been that it sits on the axle and activates the rear only when front detects slippage - otherwise driving the car as a front-wheel driver.

    I wonder if a similar economy mode for P85D or even 85D (in the latter case they could choose either motor) might be preferable for some people. Of course that would open the driving dynamics to certain inherent weaknesses, the AWD would loose some of its predictability (Haldex cars are not always the most pleasant to drive) and the car would get some of the hallmarks of front drivers like pushing, but the rear motor would activate only when the front is slipping and thus save energy more often than just when cruising.

    Now, of course, the unique feature for such an economy mode in a D Tesla - compared to the average Haldex car - would be loss of power, because the front and back doesn't share an engine, but are run by separate motors. The rear suddenly powering on slippage would have to be regulated so that the car doesn't rocket away unpredictably. Maybe there could be a curve where both slippage and major acceleration would always ask for the rear too, while suitably gentle driving in low-slippage conditions would only run the front.

    Anyway, given that Normal mode probably is the one with "torque sleeping" for coasting only, while Sport and Insane run the fuller gamut of the two motors, there could still be room for an Economy mode that would instead maximize the use of a single, economical motor and rest the rear as much as possible. This would not make for the most compelling driving experience, but it could result in some pretty nice EPA ratings and be a sort of second "range mode".

    Just speculating of course. What do you think - or perhaps has Tesla discussed such an option already?
     
  2. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    There is no mechanical connection between the two motors so having a clutch between them makes no sense. The sleep mode, when implemented, will do what you are suggesting through the electronics.
     
  3. AnxietyRanger

    AnxietyRanger Active Member

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    jerry33: If I was unclear, obviously I didn't mean introducing a physical Haldex or the like into Tesla - just using it as an example of principle that might be replicated/imitated electronically on the Model S D models.

    The sleep mode does not do what Haldex does. Haldex runs FWD always, except when slippery. AFAIK torque sleeping only does FWD when coasting.
     
  4. efusco

    efusco Moderator - Model S & X forums

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    I guess to answer the question you have to know whether the smaller/front motor is actually more efficient than the larger motor. Perhaps it is, I just don't know that for certain. If so, then I think the general idea has validity. Would assume Tesla thought of this and its potential already.
     
  5. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    That wasn't the way I understood it, but we really won't know until the software comes out and people have a chance to try it out. I understood that in normal mode the larger motor would sleep until a certain amount of power was required (or wheel slippage was detected). I'm sure it's not just when the car is coasting.
     
  6. AnxietyRanger

    AnxietyRanger Active Member

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    efusco: I believe Tesla has said the front motor of P85D is more efficient and also that 85D is more efficient when running just one motor.

    jerry33: Fair enough, we don't quite know yet what the Normal mode does exactly. Mind you, I wouldn't personally prefer the Haldex type approach normally - front drivers aren't very dynamic - but might like the option in a range pinch, so a more aggressive Economy mode might make sense in any case?
     
  7. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    I'm pretty happy with the Wh/mi of my S85, and AWD isn't a big motivator for me. I'm not sure how much a really aggressive economy mode would gain over the Normal mode. Tires would likely make more of a difference.
     
  8. AnxietyRanger

    AnxietyRanger Active Member

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    Fair speculation. I, of course, have no numbers on how much more efficient a P85D might be when driven FWD only or with a heavy FWD bias. Might be interesting to have the option, but this is just speculating.
     
  9. Vger

    Vger Active Member

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    Elon indicated that they are themselves at the early end of the learning curve with this technology. Remember, no one has ever done a production road car AWD EV like this before. He indicated that they would continue to refine the torque distribution (vectoring) in multiple upcoming software releases. Based on the last two years with the Model S, I am sure that there will be improvements in handling in all sorts of situations, and perhaps improvements in efficiency as well.
     
  10. The Hellforger

    The Hellforger New Member

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    I dont think you would see any true improvements in economy because you are still gonna have the entirety of the driveline dragging against economy numbers.

    the only way i think you would see an improvement is if they created a way to unlock the hubs of the nondriven wheels similar to the way a 4wd unlocks its hubs from the axle shafts when not needed
     
  11. Johan

    Johan Took a TSLA bear test. Came back negative.

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    I believe the front motor is only more efficient at certain speeds/RPMs so that running solely on the front motor at all speeds does not necessarily make for better efficiency (given one never utilizes more than 20-something horsepowers).
     
  12. AnxietyRanger

    AnxietyRanger Active Member

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    Interesting suggestion - the efficiency of the front motor coming from the "gear effect" (it is effectively running in another gear), not so much from being more economical in itself. That said, I do wonder if it isn't more economical to run just one of the motors in any case. 85D seems to have similar motors front and back (do they have differences in how they are geared?) and it apparently benefits from torque sleeping too? In addition, using just the smaller motor in P85D would also be a limiter of sorts, suggesting energy savings.

    Question would remain, of course, how many P85D drivers would be interested in a heavily FWD biased "economy" mode, in addition to the "normal" mode with coasting torque sleeping?
     
  13. sandpiper

    sandpiper Active Member

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    Same motors, different gearboxes I believe. It effectively has a 2 speed transmission.
     
  14. Johan

    Johan Took a TSLA bear test. Came back negative.

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    #14 Johan, Jan 1, 2015
    Last edited: Jan 1, 2015
    AFAIK there's no info what so ever on the gear ratio of the front motor in the P85D and not on the front or rear motor on the S85D either. Your guess on different gear ratios for front and rear on the S85D is a good one though. The actual gear ratio in the P85D could be the same in front and rear but at a given speed the motors would still be operating at different points of their efficiency curves due to the fact that the front motor is phsically smaller (about half the size of the rear motor?).

    From teslamotors.com forum on this subject:

     
  15. skilly

    skilly Member

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    what we do see in that blog is that at cruising speed the P cars all get the same range rating. Assuming that the Ds are using the new SW to achieve this, it seems reasonable that they are putting the front motor to sleep, no?
     
  16. sandpiper

    sandpiper Active Member

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    #16 sandpiper, Jan 1, 2015
    Last edited: Jan 1, 2015
    Somewhere in the technical blog, it mentions that the rear motor is being shut off - that the smaller front motor is more efficient at cruise. And that's fine. When you're cruising down the highway, there's no reason to need more than a 221 hp front wheel drive car! At 320 watt-hr/mile and 65 mph you're only pushing 28 hp.
     
  17. scottf200

    scottf200 Active Member

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    Driving Range for the Model S Family | Blog | Tesla Motors
     
  18. wycolo

    wycolo Active Member

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    S85D:

    Assume front power unit will be identical to rear unit for interchangeability sake.
    Haldex axle clutches would go in the front to allow superior RWD handling. Highly doubt TM will go the Haldex concept route however.
    Assume front will always get at least 20% torque, increasing to 50%(?) when needed. Thus there is always that AWD 'grip' action going on. 'Sleep' would never be applied to either axle or you would lose that grip on turns.
    Would rear ever want less than 50% torque given equal weight on all 4 wheels??

    I'm sure TM is having lots of fun coming up with initial settings for the early adopters to deal with. We likely will not get an 'insane' mode but still it would be nice to see at least three driving choices.
    --
     
  19. skilly

    skilly Member

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    They explain the response from 'sleep' to 'awake' being undetectable - similar to the concept of ABS. Given that, Im not sure that we would loose any grip in a corner if the system is always monitoring for max balance between efficiency and AWD performance.

    - - - Updated - - -

    how about "spider monkey" mode? :tongue:
     
  20. wycolo

    wycolo Active Member

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    > They explain the response from 'sleep' to 'awake' being undetectable [skilly]

    Ok, so no real need to turn an axle OFF either. Just leave them variable between 20% and 80%, which would also eliminate electrical ON-OFF shock.

    Also, if an axle is OFF it likely lacks REGEN, which is what helps keep the axle on the road! Same concept as having all 4 wheels mechanically connected.

    Lots to play with here. I hope we get to set at least 3 personal driving choices on the s85D.
    --
     

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