P610 transaxle

Discussion in 'Gen 4 Prius Technical Discussion' started by bwilson4web, Feb 4, 2016.

  1. bwilson4web

    bwilson4web i3 and Prime

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    In both the Gen-1 and Gen-3, I've seen the MG1 torque change sign to start the engine but immediately go to either negative or zero torque. Even using "B" descending a hill, the engine runs against MG1 and MG2 torque reverses, in effect a mild "R", with the engine generating the reverse power. I've never found a mode beyond the initial cold start and much shorter, hot starts, where the engine is turned by MG1. Even the cold-start, is just a couple of seconds to get the oil pressure up.

    The transaxle, engine driven pump has been constant through all four generations. Both the transaxle and engine oil pumps are the last two that beg being electrically driven.

    Engine drive makes sense because running an oil pump in reverse would pull the lubrication oil the wrong way. The problem is a mechanically driven pump has to be sized for the lowest rpm. At higher shaft speeds a pressure relief valve opens, wasting mechanical energy. Speculation on my part, an electrically driven, engine oil pump might provide another 1-2% gain in engine thermodynamic efficiency, especially at higher power ranges.

    Speculation, tweaking the engine water pump control laws could have reduced the mechanical overhead and added to the 40% thermodynamic efficiency. However, that awaits another day.

    Bob Wilson
     
  2. EZW1

    EZW1 Active Member

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    Excellent! You stated it perfectly, Bob.
     
  3. Trollbait

    Trollbait It's a D&D thing

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    I've made an erroneous assumption in thinking it was the MG1.

    The HSD control laws will allow the transaxle to spin at higher speeds to prevent over revving wear and damage. The ICE can also spin at these times since it can't be decoupled from the transaxle. The valves shut at this time to reduce pumping losses from such spinning. Anytime the crankshaft spins, the oil pumps will be operating also.

    That is my thinking from gleaned info picked up about the system.

    In the non-phev, most of the said spinning is powered by the wheels spinning. Sometimes, and with the PHEV, that over rev protection spin is coming from the MG2.

    The transaxle orientation and layout also needs to be considered when looking at EV mode lubrication. MG2 is the only torque input then, and the transaxle can be positioned where that input is fully fluid bathed. With the PSD further 'up' the chain from that input, splash lubrication can be plenty with the lower stresses at the time.
     
    #23 Trollbait, Feb 17, 2016
    Last edited: Feb 24, 2016
  4. bwilson4web

    bwilson4web i3 and Prime

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    I've not found a mechanism for 'valves shut' in the engine. I see the variable valve angle adjuster for the intake valve but nothing that would keep the valve cam shafts from operating the valve. Would you have an engine diagram or sketch that shows where it is?

    Now I know GM is fond of shutting down cylinders with some sort of valve disabling mechanism:
    [​IMG]

    All I've found in our Prius engines is a hydraulic, back-lash adjuster.

    Bob Wilson
     
  5. Trollbait

    Trollbait It's a D&D thing

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    At some point, someone's reporting or my brain muddled Honda hybrid ICE operation with Toyota's. Honda can close the exhaust valves for when the engine is off but spinning. Is the throttle fully open otherwise during ICE off coasting, or fully closed?
    Graham's Toyota Prius
     
  6. bwilson4web

    bwilson4web i3 and Prime

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    I remember reading something about the Honda engines in the original Insight. But I lost interest when I saw the cone-belt CVT. @chuck is the Honda subject master.

    Bob Wilson
     
  7. Trollbait

    Trollbait It's a D&D thing

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    Where I just the Honda valve operation mentioned in relation to the Civic hybrid. I'm sure the original Insight made use of all of Honda's tricks from that time. In order to cut costs, the Insight2 didn't use the full suite its Civic contemporary had.

    Hypermilers want the manual Insight. In experienced hands, no Prius can beat it.

    Honda's current one motor, and front half of the hybrid AWD-SH, system uses a DCT.
     
  8. ken1784

    ken1784 SuperMID designer

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  9. bwilson4web

    bwilson4web i3 and Prime

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    Source: Test Car List Data Files | Cars and Light Trucks | US EPA

    I trimmed the attached ".txt" file, (CSV format), to the header row and four Prius models. From the description, you may be interested in:
    • AXLE-RATIO - From VI
    • N-V-RATIO - Engine rpm divided by vehicle speed in miles -- from VI

    I'll try to get the New Car Features description and add it too.

    Bob Wilson
     

    Attached Files:

    #29 bwilson4web, Feb 24, 2016
    Last edited: Feb 24, 2016
  10. GasperG

    GasperG Senior Member

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    +1 for this explanation.
     
  11. bwilson4web

    bwilson4web i3 and Prime

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    Corrected:
    If I understand correctly (not sure about this, I admit), you are stating those figures apply to both torque and power - that is, 27.8% of the power would take the electrical path and the rest would go through the mechanical path. I'm afraid this is incorrect though - statically or dinamically. This is only true for the torque due to the PSD geometry, as you said. However, the power being the torque multiplied by the rotational speed of the element the torque is applied on and the part providing the power, the engine shaft rpm [rjw], there is only one special situation in which the above figures also hold true for the power, that is when all the PSD parts - sun/MG1, carrier/ICE, and ring - spin at the very same speed. In the general case though, the power split shares depend on the relative speeds of the components and are therefore vastly different from those figures most of the time. "laevus" above has written the related formula.

    Newton's Third Law:
    When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body.

    In this life, we obey the law.

    Bob Wilson
     
  12. Jeff N

    Jeff N The answer is 0042

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    I've seen people say things similar to that but it doesn't make any sense to me. MG2 has a fixed ratio relationship with the vehicle speed.
     
  13. bwilson4web

    bwilson4web i3 and Prime

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    I suspect they meant to post "MG1" and include a "]" on the initial quote tag.

    Bob Wilson
     
  14. ChapmanF

    ChapmanF Senior Member

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    Hey Bob,

    I'm the last person to fault anybody for the occasional brain glitch, but this one seems to be stuck; I'm 100% confident you know this stuff.

    You have described the fixed, constant-proportion split of torque perfectly. No issue there. It's just that at some points in this thread people have been talking about torque and at other points about power, and these are entirely different things to measure - torque having units of force and length, power dimensioned in force, length, and inverse time, and the power relationship between the shafts being determined not only by the torque split, which is fixed, but their relative rpms, which are not.

    One limiting example, consider a force-charge: the engine is running, producing substantial power; the wheels are stationary, held by the friction brakes, which are experiencing no relative motion, therefore no frictional heating, no power is being dissipated there. 72% of the engine's torque is being applied against MG2, yes, but that sucker isn't moving, and in the Newtonian sense that is zero power mechanically delivered. 28% of the engine's torque is being applied at MG1 which, being the only other thing moving, is the recipient of 100% of the mechanically delivered power.

    Move away from that limiting case (let the wheels start to move) and the power spliit moves away from 0%/100%. But as was posted upthread, the only time it equals the 72%/28% torque split is another special case, namely when the three rpms are all equal.

    -Chap
     
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  15. ken1784

    ken1784 SuperMID designer

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    Thank you, Bob, about the axle ratio (final gear ratio) number.
    What I would like to know is the "reduction gear ratio", something like this ...
    Gen2:295lb-ft(MG2 torque) X1.000(no reduction gear) X 4.113(final gear ratio) = 1213lb-ft(torque at wheels)
    Gen3:153lb-ft(MG2 torque) X 2.636(reduction gear ratio) X 3.267(final gear ratio) = 1318lb-ft(torque at wheels)

    My guess of Gen4 is as follows;
    Gen4:120lb-ft(MG2 torque) X 4.200(guessed reduction gear ratio) X 2.834(final gear ratio) = 1428lb-ft(torque at wheels)

    [email protected]
     
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  16. bwilson4web

    bwilson4web i3 and Prime

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    It took me a couple of years before I realized the 3d law made some of this moot:
    One of the tricks we pay in math (and clever engineering) is to translate the problem into another 'coordinate system.' There are problems found in signals that can only be solved by using "i" the square root of "-1". That is what happened when I realized the Power Split Device (PSD) is splitting the engine power. Suddenly everything made sense.

    Now what folks are trying to figure out is "how many volts and amps" are in the MG1-to-MG2 and MG2-to-MG1 transfers. That way they can apply the 92% rule for the MG1 <=> MG2 transfer. Then your excellent example shows why it does not work:

    Creep to a big wall, resting the front bumper on it, and leave the car in "D" - The engine will remain in idle; MG1 will generate power and send it to MG2, and; MG2 will generate torque that added with the power from MG1 will generate a motive force on the wheels trying to push the bumper through the wall. A sufficiently strong wall will leave the car motionless so no power will flow through the final gears and transmission to the wheels.​

    In reality, the power that takes the electrical path will always be -28% of the engine shaft power. The power that takes the mechanical path can vary from 0 kW to a big number but that path is load dependent. Once you see the problem that way (and it is hard!) understanding the Prius transmission becomes trivial.

    Many years ago, I bought an SAE paper by a Georgia Tech professor that claimed at high-speeds the two-mode transmission was more efficient than the Toyota system. As I read the paper, it slowly dawned that he was trying to model the electrical and mechanical paths over different loads and that was nuts. His conclusion was the Toyota transmission was too inefficient at high speeds yet he never did the dumb thing . . . put the car on a dyno (or in my case, the road.) The had transformed the problem into 'the briar patch' and the whole paper was almost a waste of my $45. What I did learn was his approach was flawed.

    Bob Wilson
     
    #36 bwilson4web, Feb 24, 2016
    Last edited: Feb 24, 2016
  17. Trollbait

    Trollbait It's a D&D thing

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    If the forward momentum of a glide can spin the MG1 for over rev protection, then the motion created by MG2 during EV mode can be allowed to travel up the gear chain to MG/1. With the higher rev limits of gen3, this may not be necessary though.
     
  18. ChapmanF

    ChapmanF Senior Member

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    Assuming we agree in this thought experiment that no mechanical power is passing through the stationary final drive train (counting wheels to MG2, inclusive)—and I think it's safe to say we do—and if we accept your proposition that 28% (in magnitude?) of the engine shaft power is taking the electrical path (which begins with a conversion from mechanical to electrical in MG1), a tiny question presents itself. Where is the rest going?

    Conservation laws are good laws too, right? I obey them literally all the time.

    I assume that's a typo and you meant kW, right? kWhr would be energy, not power.

    -Chap
     
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  19. bwilson4web

    bwilson4web i3 and Prime

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    I have MiniOBD and an earth backed, wall. So I can actually do the first experiment.

    The second is to put the front on jack stands, start the car, and let it run:
    1. Start car and leave in "P"
    2. When engine stops, shift into "D"
    3. Record what happens
    In the second test, there is no drive wheel load beyond the drive friction. So what happens to the power in creep mode on jack stands with no load?

    UPDATE: It will need some way to couple the left and right wheels. If one turns faster than the other, it will trigger the traction control and bugger up the results. It may be easier to rent dynamometer time and a heck of a lot safer.

    Bob Wilson

    Let me know if this addresses your questions.

    Bob Wilson
     
  20. ken1784

    ken1784 SuperMID designer

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    Thank you!
    The "P610 Hybrid_Transaxle.pdf" says as follows;

    MG2 Reduction Gear
    • No. of Drive Gear Teeth : 17
    • No. of Driven Gear Teeth : 53
    So, the gear ratio is 53 / 17 = 3.118

    Let me clarify the #39 post of this thread as follows.
    • Gen2:295lb-ft(MG2 torque) X1.000(no reduction gear) X 4.113(final gear ratio) = 1213lb-ft(torque at wheels)
    • Gen3:153lb-ft(MG2 torque) X 2.636(reduction gear ratio) X 3.267(final gear ratio) = 1318lb-ft(torque at wheels)
    • Gen4:120lb-ft(MG2 torque) X 3.118(reduction gear ratio) X 2.834(final gear ratio) = 1060lb-ft(torque at wheels)
    I guess the torque value at wheels on Gen4 is higher than Gen3, but it isn't.

    [email protected]
     
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