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MG1/MG2 RPM's (Scangauge)

Discussion in 'Gen III 2010+ Prius Technical Discussion' started by Canard, May 18, 2012.

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  1. Canard

    Canard Member

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    Hi all,

    I’ve set up my Scangauge II with my Prius and have entered the codes for the two XGauges that correspond to MG1 and MG2 rpm.

    However, while crusing at steady speed with ICE off (0 rpm), the speed of MG1 and MG2 do not seem correct to me. I am noticing that they are both almost the same number. For example, at 55 km/h with ICE off, MG1 reads -4120 rpm and MG2 reads 4190 rpm.

    photo.JPG

    I would have expected that MG2 (the small motor driving the sun gear) would be running about 3 times faster than MG2 (driving the annulus). I don’t know the exact ratio between the sun and annulus but it should be directly proportional to the motor speeds reported by the SGII.

    I’ve double-checked the codes and I have entered them all in correctly.

    Any ideas?

    Thanks in advance,

    -Iain
  2. jdcollins5

    jdcollins5 Senior Member

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    Your MG2 speed is correct. MG2 speed will be based on your wheel speed. With the MG2 speed reduction unit gear ratios the max motor speed, 13500 RPM, is reached at 180 km/h. So at 55 km/h the motor speed calculates out to 4125 RPM which is close to the 4190 you are seeing.

    The MG1 speed, with ICE off, will be based on MG2 speed, the MG2 speed reduction gear ratios and the ICE planetary gear ratios. The -4120 RPM seems reasonable from what I remember seeing at your speed.
  3. Canard

    Canard Member

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    Out of curiousity, what are the ratios? (I've been unable to find them) - better yet, the number of teeth on all 3 gears.

    I would have thought the MG1 (sun) to MG2 (annulus) would be something ilke 3:1... which is why I questioned the almost 1:1 I was seeing reported by the ScanGauge.

    The physical nature of a planetary gearset cannot do 1:1 inherently between sun and annulus... there would be no room for the planets (ICE).

    -Iain
  4. Judgeless

    Judgeless Senior Member

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    I use an OBD2 Bluetooth device that sends that info to my cell phone or tablet. Here is MG1, MG2, ICE and the current temperature for each of those.

    [​IMG]
  5. Canard

    Canard Member

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    Thanks, Judgeless - but what would MG1 and MG2 report if ICE is 0?

    I see that the sun (MG1) has 30 teeth and annulus (MG2) has 78; with ICE (planet carrier) at 0 rpm, if MG2 is correct at 4190 I would expect MG2 to see -10 894 rpm.

    -Iain
  6. Judgeless

    Judgeless Senior Member

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    It depends how fast you are going. This is a great site that shows what happens with MG1, MG2 and the ICE as you drive.

    Toyota Prius - Power Split Device
  7. jdcollins5

    jdcollins5 Senior Member

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    There is a speed reduction unit, or another planetary gearset between MG2 and the main ICE planetary gearset. Find attached a copy of the gear ratios along with gear tooth counts that I found on here and then did the calculations for the MG2 RPM versus wheel speed.

    Attached Files:

  8. Canard

    Canard Member

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    I thought MG1 directly drives the sun, ICE drives the planet carrier (through a tortion damper), and MG2 is integrated directly into the ring gear - which then is coupled to the diff housing through a two-stage reduction.

    Is that not the case?

    -Iain
  9. Judgeless

    Judgeless Senior Member

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    Canard. MG1 drives the sun gear.

    Go to the web site I posted above. Scroll down to the middle of the page. It has an animate illustration of how everything works. When you scroll your mouse over each gear it gives a lot of details.

    Toyota Prius - Power Split Device

    [​IMG]
    1 person likes this.
  10. Canard

    Canard Member

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    Yes, thanks - I've played with that many times. However, go punch in the numbers you see on my Scangauge. You can't. :)

    What I'm getting at: There should be a 2.6:1 ratio between MG1 and 2 if ICE is off. The animation supports this. The numbers on my scangauge do not support this. So: Where's the problem? Why is my scangauge incorrectly reporting MG1 (or 2)?

    -Iain
  11. jdcollins5

    jdcollins5 Senior Member

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    That was the Gen II. The Gen III is different. Search on here for the Gen III hybrid system. I know there is one that shows the Gen II next to the Gen III so you can really see the difference.
  12. vincent1449p

    vincent1449p Active Member

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    jdcollins5 is right, that is for the Gen2. Gen3 has an additional Speed Reduction Gear (see attachments).

    I 've derived the relationship of MG1, MG2 and ICE in this link:

    MG1 = ( 18 / 5 ) * Engine - ( 143 / 145 ) * MG2

    MG2 = ( 145 / 143 ) * ( ( 18 / 5 ) * Engine - MG1 )

    Engine = ( 5 / 18 ) * ( MG1 + ( 143 / 145 ) * MG2 )

    If you plugin your numbers, everything will make sense.

    Vincent

    Attached Files:

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  13. Canard

    Canard Member

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    I'm a mechanical/visual person, so the picture worth a thousand words. Thank you very much! I did not realize there was a secondary reduction unit.

    Reading back through the other forum posts (took me a while to find), the extra reduction unit is 1:2.6363..., which gets the MG2 rpm right around the same as MG1 (which is what I was seeing on the SGII).

    So at some point Toyota made the design tradeoff of adding an extra reduction unit in order to use a smaller, higher speed motor for MG2. We do this all the time in automation design, trading off gearing for motor size. It's sort of a "black art" to optimize... playing around with the motor sizing software. You can use less of a reduction with a motor that has more torque at a lower speed (as in Gen2), or put a bigger reduction gear on and have a smaller motor with lower inertia that runs at a higher rpm (Gen3).

    This forum is great.

    -Iain
  14. spiderman

    spiderman wretched

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    Well now that you got that all down, perhaps you can update that animation with the GenIII gearing. :)
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