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Motor Noise - Possible Cause and Potential Solution

Discussion in 'Model S' started by gavine, Feb 3, 2016.

  1. gavine

    gavine Petrol Head turned EV Enthusiast

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    I'm pretty sure it is known that the cause of the milling noise is a worn bearing. I have always thought that regen was the culprit and I'm thinking Tesla knows this too which is why I have speculated that Tesla keeps "lightening" the regen in order to minimize the forces on the bearings during regen.

    I bought a BMW i3 as our second car a few weeks ago and I noticed that the regen disables when going over bumps in the road. I wonder if BMW engineers realized in advance that regen over bumps is bad for the bearings so they put this protective measure in place.

    If this is true, perhaps Tesla can do the same and bring back full regen again!
     
  2. MP3Mike

    MP3Mike Active Member

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    That sounds horrible; bumps in the road cause your deceleration to change? Yuck.
     
  3. gavine

    gavine Petrol Head turned EV Enthusiast

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    Yeah, it's not great. It forces you to use the brakes, or at least get ready to. Kind of scary sometimes. It also suspends regen when cornering. I don't like that either. The i3 is a great little car, but it makes me appreciate how much Tesla nailed it on their first try. The i3 is still better than most ICE cars, but a Tesla it is not. So many little things that just aren't as good and it's surprising coming from such a well-regarded and established company.
     
  4. jerry33

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

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    All cars that have most of the regen on the brakes do this. Tesla avoided the problem by having all the regen on the accelerator pedal where it belongs. It's also makes the braking system much simpler and robust.
     
  5. R3D-83

    R3D-83 Member

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    The i3 has all regen on the accelerator pedal ("where it belongs") too. This story is about something else.

    How does it work? Because i3 is RWD, it regenerates with the rear wheels. Does it release the regen in the moment when the front wheels hit the bump? If yes, this method wouldn't work with an AWD car (like a D Tesla) because it was already too late for the front motor.
     
  6. gavine

    gavine Petrol Head turned EV Enthusiast

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    Correct...the regen is on the go-pedal, just like Tesla

    I'm not sure how it works. I'll have to pay closer attention. I just know that the regen cuts-out if there are bumps when I'm slowing down. I'm thinking it has some kind of "bump sensor" that turns regen off when it senses a certain level of "bumpiness". They obviously did it for a reason and it's definitely not to make the driving experience better so I presume the reason is to protect the drive train.

    One other thing, speaking of the accelerator on the i3, is they seem to have tuned the pedal to allow coasting on a longer range of pedal so you don't need to be very accurate to coast in neutral. Sounds good on paper, but it brings a small "hesitation" to the pedal when you are coasting and want to accelerate again. Another win for Tesla's implementation. The power meter on the i3 is also not as accurate as Tesla. It's very "cartoony". Score another for Tesla.
     
  7. Bangor Bob

    Bangor Bob Member

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    It's the ABS/stability control system. When the rear wheels go over a bump during regen it can cause the wheels to slip, the ABS system detects the speed difference between the front and rear wheels, and reduces regen until the speeds match again.

    Normal, but annoying.

    Regen forces on the bearings should be no different in character than drive forces, other than being smaller.
     
  8. TurboFroggy

    TurboFroggy Member

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    This is 100% correct. ABS is has full override of regen. Every EV I have had dating back to my 2000 Ford Ranger EV had this ABS - Regen connection.
     
  9. mechapreneur

    mechapreneur Member

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    Cutting out braking/regen over bumps is probably traction control kicking in.
     
  10. gavine

    gavine Petrol Head turned EV Enthusiast

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    That's all great, but why is Tesla not doing it then? Do our cars engage the brakes to mimic regen?

    And now I know how the i3 does it, but I still wonder why.
     
  11. Dithermaster

    Dithermaster Member

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    Our Prius would cut over from regen to friction braking when it went over a bump. The only problem was the cutover wasn't instant -- it would release regen instantly and then it took a moment for the friction to start, so the car felt like it was accelerating (it wasn't, but the lack of deceleration feels like acceleration <g>) which was unnerving. There was a certain offramp in town where it happened every time. My Volt did something similar, but far less frequently. I've never had the Model S do it yet. It does take some getting used to the fact that you get different amount of regen depending on temperature. I wish they could vector the regen into the heater when it's cold instead of giving you nothing (yes, it's cold here).
     
  12. murphyS85

    murphyS85 Member

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    I have never driven an AWD car so I will limit this to a RWD or a FWD car. Regen is applied to the wheels by the motor acting as a generator. The force is transmitted to the wheels through the differential. If either wheel loses traction, for whatever reason, regen force is no longer possible because of the way a differential works. A limited slip differential would help with this. The other option would be for the braking system to apply the friction brake to the wheel that has no traction but the duration of the wheel bounce appears to be too short for this to happen. I have not yet experienced the problem in my model S but it happens all of the time in my FWD 2013 Ford Fusion Energi during regen braking. It does feel like acceleration but it is actually the instantaneous loss of all braking that makes it feel like acceleration. If you want to experiment with this situation, find a manhole cover that is significantly lower than the surface of the road. Drive over the manhole cover using regen braking. While the wheel is in the air, over the manhole cover, there will be no regen braking at all until it drops down and makes contact with the manhole cover.
     

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