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Motors in series: how do you stop one motor from spinning?

  1. Nov 5, 2016 #1
    Hi All,
    I've been reading up on hybrid vehicles and how the Honda Insight has an electric motor attached directly to the gas engine driveshaft. Their combined output causes the wheels to spin. My question is in regards to when the electric motor is off but the gas engine is on. Why doesn't the gas engine just force the electric motor to spin and the wheel to not move? I know there is some gearing involved, but I don't think the setup is non-backdriveable, and I don't believe there is a physical brake that clutches the electric motor. How about in situations where there is just direct drive? Do they just run the motor at a very low setting to prevent the electric motor rotation? That sounds like a stall scenario to me, and that would use a lot of power. How do you just use one of two motors in a serial configuration?

    Would love to hear your guys' thoughts. Thanks very much!
  2. jcsd
  3. Nov 5, 2016 #2

    Simon Bridge

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    ... With the electric motor switched off, why wouldn't the drive shaft just turn the motor and the wheels? After all the shaft rotates with the engine, and is connected to both.
    Series drivechains are done where both engines are ICE - how does that work if one of the ICEs is not switched on, but not disconnected? Could Honda engineers not use similar solutions?

    How are you supporting this belief?
  4. Nov 6, 2016 #3
    The engine and motor share a common driveshaft. When the motor is 'off', that just means it is spinning and not supplying power or acting as a regenerative brake. This design adds one bearing to the drive train and requires no additional gears or clutches. Very simple and compact.
  5. Nov 6, 2016 #4
    Thanks Simon for taking a look. For your first question, I would expect the switched off motor to rotate (stator rotating with respect to the rotor), sort of acting like a bearing, with no work being done on the wheel itself. With the rotor and stator moving, it is acting like a generator. To lock the rotor and stator together, you would need to always have it on or have a clutch. From what I've read about the car, it doesn't seem to have a clutch in that location.

    I'm mostly thinking about 2 motor cars being used in power saving mode or if one motor is broken.
  6. Nov 6, 2016 #5
    Thanks dschlink. appreciate your thoughts. I should've clarified that the drivetrain setup is when the electric motor stator is attached to the ICE's output shaft. The electric motor's rotor is attached to the wheel. I think i understand the case where the electric motor adds power by a gear. I guess when one motor is off and not acting as a generator (so no back emf), the drag that induces is pretty minimal.
  7. Nov 8, 2016 #6


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    Where have you seen this arrangement used? It sounds like a rather inelegant solution. Your electric motor would need to have a torque output in excess of the ICE output to do any good.

  8. Nov 8, 2016 #7

    Randy Beikmann

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    It's not clear to me what you are describing here. A stator is stationary, and a rotor rotates inside it (on some motors the rotor is outside the stator). But regardless, the rotor and stator are concentric. So having the stator on the ICE output shaft, and the rotor on the wheel, makes no sense.

    Maybe you are talking about two motor/generators?
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