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Locking MG1

Discussion in 'Gen 2 Prius Technical Discussion' started by Britprius, Mar 12, 2012.

  1. Britprius

    Britprius Senior Member

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    Another hypothetical question. Would it make the Prius more efficient for highway use if MG1 could be locked at speed, making the ICE direct drive to the wheels.
     
    #1 Britprius, Mar 12, 2012
  2. qbee42

    qbee42 My other car is a boat

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    MG1 can be locked at speed. MG1 can be locked at any speed.

    Tom
     
    #2 qbee42, Mar 12, 2012
  3. Britprius

    Britprius Senior Member

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    I do not see any method of locking MG1 and if it could be locked at any speed the ICE would not be able to run with the car below about 20mph since it's minimum RPM is about 950, and at any speed below this with the ICE running MG1 must spin.
    Perhaps you misunderstood my question, I meant MG1 locked stationary with the car at speed.
     
    #3 Britprius, Mar 12, 2012
  4. fuzzy1

    fuzzy1 Senior Member

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    I believe mechanically locking MG1 could make Prius more efficient under certain narrow operating conditions where the ICE RPM is appropriate for the load. But under most highway cruising conditions, this would leave the ICE spinning too fast, departing from its best efficiency. It would end up being throttled into Otto cycle mode, losing a big portion of the gains from its current Atkinson cycle operation.
     
    #4 fuzzy1, Mar 12, 2012
  5. qbee42

    qbee42 My other car is a boat

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    MG1 can be locked by applying stationary field excitation, just like it can be spun in either direction by applying rotating field excitation. Zero RPM is just one point in a continuum from forward to reverse.

    Tom
     
    #5 qbee42, Mar 12, 2012
  6. Britprius

    Britprius Senior Member

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    Yes I can quite see the the requirement for running the ICE at its most efficient speed and one understands that the Toyota techs know what they are doing but MG1 being driven to provide MG2 with electricity does appear under some circumstances a little inefficient. At approximately 60MPH the ICE would be doing 2500RPM with MG1 locked and all it's mechanical power would go direct to the wheels.
    Again this is only hypothetical and I realise putting a mechanical lock into the system would add an extra layer of complexity and give more possible reliability problems.
     
    #6 Britprius, Mar 12, 2012
  7. Britprius

    Britprius Senior Member

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    Tom I am sorry I did not put my point very clearly I admit my mistake. When I said locked I meant mechanically, to lock it electrically would use power that would have to come from the ICE via MG2, and HV battery, and I was trying to avoid electrical conversion inefficiencies where possible.
     
    #7 Britprius, Mar 12, 2012
  8. fuzzy1

    fuzzy1 Senior Member

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    It is a little inefficient, but at this time all the alternatives are worse. To be efficient at 2500 RPM under the light load of normal highway cruising, the intake charge must be reduced even more than is possible with the existing mechanical valve timing control system. Absent better valve controls (e.g. all-electric valves, abolishing the camshaft), this requires partially closing the throttle plate, which brings back the pumping loss inefficiencies of Otto cycle engines.

    There are plenty of opportunities here for inventors to come up with new ideas, or reduce the costs of existing ideas that are not yet cost effective.
     
    #8 fuzzy1, Mar 12, 2012
  9. Britprius

    Britprius Senior Member

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    Fuzzy1 thanks for your input. I believe sometimes ideas come from throwing seemingly outlandish ideas into a discussion can bring about useful innovations and improvement to products.
    I wonder what the losses are turning mechanical power to 3ph/ac to dc to 3ph/ac to mechanical power.
     
    #9 Britprius, Mar 12, 2012
  10. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    I spend a lot of time at 61 MPH on level ground, on a calm day that is about 1700 RPMs in my Gen 2, 2500 RPM is a fairly good grade, 3%?
     
    #10 JimboPalmer, Mar 12, 2012
  11. Britprius

    Britprius Senior Member

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    Thanks for the numbers Jimbo, but I do not understand the 3%. Is that the grade.
     
    #11 Britprius, Mar 12, 2012
  12. qbee42

    qbee42 My other car is a boat

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    Your point was very clear, as were my replies. Electrically locking MG1 takes very little power, so there is little need to add the complexity of mechanical locking. Besides, mechanical locking only works for one special case, where the electrical solution works across a wide range of speeds and loads.

    You seem to be coming from a preconceived notion of efficiency, which doesn't fit with the reality of the situation. I'll state it again: MG1 is lockable, efficiently, through the field excitation. I understand your question, you just insist on dismissing my answer.

    Tom
     
    #12 qbee42, Mar 12, 2012
  13. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    Yes, it is definitely uphill, but not all the way to 'steep'. On steep grades I see 4500 RPM at 61 MPH.
     
    #13 JimboPalmer, Mar 12, 2012
  14. Britprius

    Britprius Senior Member

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    Tom I am not dismissing your answer. I understand your point that you can lock MG1 electrically, but if you go back to my post where I apologized to you for not making it clear in my first post that I was talking about a mechanical lock and it was hypothetical and was asking a reasonable question. There must be a range of speeds where it is more efficient that MG1 does not rotate however narrow that band might be. Any loss is a loss.
    I also said the Toyota techs new what they are doing but any system can be improved not easily not simply but things can always be improved and without enquiring minds we get know where.
     
    #14 Britprius, Mar 12, 2012
  15. Britprius

    Britprius Senior Member

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    Jimbo I was recently on holiday in Cornwall (SW England) it is not unusual to find grades of 33% there, and with four up and luggage for two weeks the Prius coped very well.
     
    #15 Britprius, Mar 12, 2012
  16. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    It does! The computers seem to be able to 'tune' the ICE to 6 RPM steps, and get exactly what they want.
     
    #16 JimboPalmer, Mar 12, 2012
  17. David Beale

    David Beale Senior Member

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    No, sorry, but it is most efficient to lock MG1 electrically. It takes only a small amount of power vs the complexity and potential breakdown of some other mechanical locking mechanism. Not to mention the requirement of actually locking MG1 electrically -before- trying to do it mechanically (ever tried to stop a powerful electric motor?). MG1 doesn't run locked very much as it is often used to generate power while on the road (just watch the MFD and see the constant back and forth drive/generate cycling). That's one of the ways the HSD gets the efficiency it has, preventing the requirement for fuel enrichment on the road when a slight acceleration is required due to a wind gust or slight rise.

    Mechanically locking MG1 would be handcuffing the HSD in its' attempt to be most efficient.
     
    #17 David Beale, Mar 16, 2012
  18. 2009Prius

    2009Prius A Wimpy DIYer

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    One would think Toyota has already spent thousands of man hours to optimize the HSD operation.
     
    #18 2009Prius, Mar 16, 2012
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