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Need your input please!

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by bear4, Jan 18, 2012.

  1. bear4

    bear4 Junior Member

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    I am visiting from Gen III forums here, and I am asking for your input regarding potential design issue with MG2 that I recently discovered. Apparently this issue appears to be common to both Gen II and III, however, was not noticed/documented before. I am working with Toyota and hopefully with more statistical data about the issue we can get Toyota to issue a TSB to correct it. The issue with MG2 Rumble is described here:
    http://priuschat.com/forums/gen-iii...ubleshooting/101818-mg2-rumble-vibration.html

    Please post in this thread and let us know if your Gen II Prius exhibits the same issue or not
    Thank you!​
     
  2. uart

    uart Senior Member

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    Qbee42 nailed it in the first reply (#2) of that thread, and then explained it again in #13, that was as far as I read. A small amount of cogging in the electric motors at low excitation frequencies.

    It's a "design issue" in exactly the same sense as an idling engine in a normal car making a small amount of vibration as cylinders fire and pistons stroke. It's not practical to build a gasoline engine that has zero amount of vibration at idle. It's not practical to build an inverter+AC motor drive that has zero amount of torque pulsations at very low speed (though you can get close).

    As the speed increases, and the inverter output frequency increases correspondingly, then the torque pulsations get smaller and the higher frequencies are more effectively filtered by the drive train.

    I feel the same thing in my gen2 at very low speed when I'm creeping up my driveway waiting for the automatic garage door to open. It's the same (non-)issue.
     
  3. qbee42

    qbee42 My other car is a boat

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    Just to be clear, this thread was started by a Prius owner collecting information which he intends to give to Toyota. "Working with Toyota" does not imply that he is a Toyota engineer or contractor.

    That said, there is nothing wrong with passing along information. If you notice a low speed cogging sensation, feel free to tell him about it.

    Tom
     
  4. uart

    uart Senior Member

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    Tom I saw in the other thread that you don't notice the "issue" in the Gen2. Try doing it not quite as the OP describes but instead do it on an incline like a mild/steep driveway, again just creeping at very low speed, but with MG2 under a little bit of load so that perhaps you'll need a small amount of "go pedal" input. Under load like this, and at about half walking speed, you might feel a small amount of torque pulsation (cogging) from the motor.
     
  5. Britprius

    Britprius Senior Member

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    Yes I feel this pulsing at low speed in reverse and forwards but I to put it down to cogging of the electric motor as did Uart. I used to work with digital servo motor control systems and this sometimes caused problems when systems were required to run very slowly, unless the motor and gearing was chosen with great care.
     
  6. seilerts

    seilerts Battery Curmudgeon

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    You should sell the car. It will only make you crazy. Toyota will never fix an issue like this. These transmissions will run a million miles if you change the fluid regularly.
     
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  7. uart

    uart Senior Member

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    +1

    Seriously this is as silly as trying to get Toyota (or any manufacturer) to put out a TSB like :

    TSB: Gasoline engine makes a small amount of vibration and noise when running. :p
     
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  8. kohnen

    kohnen Grumpy, Cranky Senior Member

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  9. bisco

    bisco cookie crumbler

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    havn't felt anything like that in 9 years in an 04 and 08.
     
  10. bear4

    bear4 Junior Member

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    With Prius being so quiet compared to conventional vehicles, every small noise/vibration is noticable. I do not feel that this is unreasonable to ask Toyota to address this issue. Many people do not notice it, however, attention to small details like this is what makes it different when you decide what make to purchase, and I believe Toyota at least should take this issue into consideration. My dealer seems to be willing to work with me on this problem. I am waiting for a toyota engineer to come down and look at the problem, this should happen within next few weeks.

    In the meantime I am trying to collect more data and also check other hybrid makes to see if they experience the same issue. I am going to test-drive chevy volt today and will report here. Thanks for all the input, please keep it coming!
     
  11. uart

    uart Senior Member

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    I looked at the other thread and it seems a few people have noticed it in the G3, though most aren't seeing it as a problem. I thought the following post also explained it pretty well.
    So various people have come to the same conclusion, low speed "cogging" of the electric motor MG2 at about 1 MPH.

    I don't know if it's worse on the G3, but on my G2 I need to be going about 1MPH (sustained) up hill on super smooth pavement to even notice it, and even then it's very minor. Also, to be honest, I hardly ever drive at a sustained speed of 1 MPH anyway.
     
  12. bear4

    bear4 Junior Member

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    Well, I went out and test drove Chevy Volt today. I was quite impressed - the car is very refined and super-smooth and quiet compared to Prius. Obviously the gas engine never came on during my 20-min test drive, but also the road noise was a lot less than in Prius. Interior appears to be of a very good quality, no rattles and noises. I did check for cogging I am researching in the thread, and there was none! I could not make the electric motor vibrate, even at very low speeds. Overall Volt appears to be a step up from Prius, I was impressed with this Chevy product. And, as discussed previously, it is indeed possible to make a motor with zero cogging. I don't know why Toyota did not do it with Prius, but chevy did with Volt.
    Please keep the data coming, I believe we should stay on this and see if Toyota will eventually come out with a TSB...
     
  13. uart

    uart Senior Member

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    Not actually zero, but yes I think it can be made small enough to be imperceptible. I think the low speed torque pulsations in the Prius are very small but perhaps there is a resonance with the suspension or something at this one particular speed (about 1 MPH) that makes it just noticeable. Again it comes back to the minor nature of these pulsations and the fact that they can only be felt at extremely low sustained speed. So few people spend any significant time driving under those conditions (a sustained 1 MPH) that I doubt you'll find too many people that are bothered by it.

    Torque pulsations (or cogging) can be due to either the motor (torque variations with angular position inherent within the motor) or the inverter (presence of harmonics in the synthesized waveform).

    If the main source of the cogging was the inverter then perhaps it could be *relatively* easily addressed, but if it's inherent in the motors then it's completely impractical.

    The point is that even if there was a simple fix the cost of the TSB would be huge. And it's just not that bigger deal.