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More Voltage in PWR?

Discussion in 'Gen 3 Prius Main Forum' started by Blind Guy, Mar 25, 2010.

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  1. Blind Guy

    Blind Guy New Member

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    I have always felt the electric propulsion from an initial start was more pronounced in PWR mode, and conversely, less in ECO mode.

    I've been convinced that the improved thrust provided in PWR mode was NOT entirely coming from the ICE, or even the increase in throttle sensitivity, but rather an increased power output from MG2.

    In doing some research on the upcoming lexus CT 200h Premium Compact Hybrid, I may have confirmed my suspicions when I ran across one story by one of the Auto Mags (I think), stating that when the CT 200h is in the Normal mode, the MG2 uses 500 Volts, but, when in the Sport mode (PWR in the Prius) the Voltage is upped to 650 Volts, thus accounting for the snappier performance in that mode!

    I'm also conjecturing that since that car will use the Prius's 1.8L engine as well as its ECVT transmissionand a NiMh battery pack, that many, if not all, of their drivetrain features will be/are virtually identical.

    This leads me to believe that much of the Prius's improved performance while in the PWR mode comes from an increase in Voltage to MG2, just like the upcoming Lexus CT 200h's.

    All of you super electrical and mechanical types out there, what do you think, is this a reasonable assumption, and have any of you also felt most of the additional off-the-line and some mid-range power, while in PWR mode, comes from MG2 power improvements?

    David (aka Blind Guy)
     
    #1 Blind Guy, Mar 25, 2010
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  2. silverfog

    silverfog New Member

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    Yes -- it would explain a lot.
     
    #2 silverfog, Mar 25, 2010
  3. jdcollins5

    jdcollins5 Senior Member

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    It seems like a valid explanation to me. People have talked about the ICE kicking in earlier in PWR mode but from what I understand the ICE has very little torque at zero to low speeds due to the lack of gearing reductions for the torque multiplication found in ICE only cars with gear transmissions.

    The added voltage to MG2 would be like a voltage boost in a VF drive and could explain the added acceleration in PWR mode.

    I would also like to hear from the PC experts on this possibility.
     
    #3 jdcollins5, Mar 25, 2010
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  4. patsparks

    patsparks An Aussie perspective

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    I just think the throttle response is greater in the first 50% of accelerator pedal travel.
     
    #4 patsparks, Mar 25, 2010
  5. patsparks

    patsparks An Aussie perspective

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    At low speed high power demand the ICE will run to spin MG1 generating electricity which is channeled via the HSD control unit to MG2 supplementing the energy from the battery. It is a case of all hands on deck when maximum acceleration is requested via the accelerator pedal. When in power mode in the first half of accelerator pedal travel the response is amplified giving a more responsive feel to accelerator pedal inputs.
     
    #5 patsparks, Mar 25, 2010
  6. usbseawolf2000

    usbseawolf2000 HSD PhD

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    My exact thought when I made this comment in the "Lexus CT200h Official Commercial 2010" thread.
     
    #6 usbseawolf2000, Mar 25, 2010
  7. usbseawolf2000

    usbseawolf2000 HSD PhD

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    MG1 voltage has to be boosted to 650v also to generate and supply more power to MG2.
     
    #7 usbseawolf2000, Mar 25, 2010
  8. qbee42

    qbee42 My other car is a boat

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    The Prius Chief Engineer told us in Detroit that the Prius has the same power available in all three modes. The only difference in power is the throttle mapping, which makes the car feel faster or slower in the first half of the accelerator. Once you put your foot into it, it's the same in any mode.

    Tom
     
    #8 qbee42, Mar 25, 2010
  9. Tideland Prius

    Tideland Prius Moderator of the North
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    Yes but could it deliver max power earlier too. IOW, let's say when it gives it its all, it's 650V. Normally, it would be a smooth power delivery up to 650V. In PWR Mode because the throttle is more sensitive, it'll deliver that 650V earlier thus a steeper acceleration curve and the feeling of greater power.

    Does that sound reasonable?



    It does have a reduction gear hence the lower torque output of the MG2 (156lb-ft) in the Gen 3 vs. 295lb-ft in the Gen 2.
     
    #9 Tideland Prius, Mar 26, 2010
  10. jdcollins5

    jdcollins5 Senior Member

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    Could this be a possible explanation of how the throttle mapping may be modified to increase the acceleration rate of the MG's in PWR mode?

    [/QUOTE]It does have a reduction gear hence the lower torque output of the MG2 (156lb-ft) in the Gen 3 vs. 295lb-ft in the Gen 2.[/QUOTE]

    True. Thanks
     
    #10 jdcollins5, Mar 26, 2010
  11. qbee42

    qbee42 My other car is a boat

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    Yes. This is exactly what more aggressive throttle mapping would do.

    This is different than the OP's question, which was inquiring if the Prius used higher maximum voltages in PWR mode, kind of like a turbo feature. The Prius does not do that.

    Tom
     
    #11 qbee42, Mar 26, 2010
  12. Blind Guy

    Blind Guy New Member

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    What prompted me on all this, was how the Prius left from a dead stop, when the engine was warmed up and the engine was shut down when you came to a stop, and then accelerated away when in PWR mode.

    Your initial acceleration (without the ICE even running) is VERY pronounced, thus indicating the ICE plays NO part in the initial acceleration. And, conversely, acceleration from a stop, in Normal is just that, Normal., and acceleration in ECO mode is quite timid.

    I'm unclear on why Lexus would use increased Voltage in their CT 200h's motors, since they use, seemingly, identicle engines and drivetrain units.

    I'm also unsure I understand how throttle mapping would/could affect power delivery from the electric motors. I assumed they were controlled by a rheostat, and I thought they worked in a linear fashon.

    I must admit, my electrical knowledge is fundamental at best, so PLEASE help me understand.

    David (aka Blind Guy)
     
    #12 Blind Guy, Mar 26, 2010
  13. Tideland Prius

    Tideland Prius Moderator of the North
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    Hmm.... but it's the same setup unless what he's saying is that the CTh uses 500V while the Prius uses 650V all the time like HiHy/RXh, GSh, LSh and TCH.

    Yes but if you recall the graph that Ken posted, you'll see how the PWR Mode line curves up and over the normal line (which is taken to be a linear positive relation).

    So instead of slowly ramping up to max torque, max torque is delivered much earlier.

    e.g. Say you want to get to 50mph in a regular car. You could slowly accelerate or you can stomp on the accelerator. The former is like normal mode and the latter is like PWR mode. You're asking the car for more power NOW.

    That is mostly likely how it works if I remember the graph correctly. I think the question is whether or not max voltage is always 650V or whether it's 500V except in PWR mode (or full out acceleration).

    Kinda like how the M5 only puts out 400hp unless you change the setting and tell the car to use all 500hp.
     
    #13 Tideland Prius, Mar 26, 2010
  14. Blind Guy

    Blind Guy New Member

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    ...Yes but if you recall the graph that Ken posted, you'll see how the PWR Mode line curves up and over the normal line (which is taken to be a linear positive relation).

    So instead of slowly ramping up to max torque, max torque is delivered much earlier.

    e.g. Say you want to get to 50mph in a regular car. You could slowly accelerate or you can stomp on the accelerator. The former is like normal mode and the latter is like PWR mode. You're asking the car for more power NOW...

    Does this graph apply to the MG1 & MG2, or is it confined to the ICE only?

    David (aka Blind Guy)
     
    #14 Blind Guy, Mar 26, 2010
  15. Tideland Prius

    Tideland Prius Moderator of the North
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    I have no idea. I assumed it was the combined acceleration. Might wanna ask Ken and see if he has any info on the break-down of power distribution.
     
    #15 Tideland Prius, Mar 26, 2010
  16. Philosophe

    Philosophe 2010 Prius owner

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    Hum...

    To vary power, you vary the motor torque, which varies according to its input voltage.

    So voltage varies continuously depending on the power request (from the ECUs and controlled by the Inverter) that needs to be created by a MG (act as motor) / captured from a MG (act as generator).

    The difference between ECO/Normal/PWR modes is in this context, only a question of mapping between pedal posn and power request to the ECUs.

    If the max system voltage that the Inverter can generate is 650V, you will be able to reach this peak also in ECO mode, simply by pressing the pedal further.

    Confirming this would be quite easy. Do a 0-60 MPH acceleration on both ECO and PWR mode. I'm sure both will achieve the same times, with maybe a very very small difference as ECO mode would make the car react to your initial full power request a bit slower as it averages down the pedal movements to make things more efficient (to address unsteady right foot syndrome...).
     
    #16 Philosophe, Mar 26, 2010
  17. Blind Guy

    Blind Guy New Member

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    THANKS Tideland Prius for your input, perhaps ken is monitoring this Thread and will chime in!

    David (aka Blind Guy)
     
    #17 Blind Guy, Mar 26, 2010
  18. Philosophe

    Philosophe 2010 Prius owner

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    Logically, it needs to apply to the whole user power request, not related to the computer decision on where this power will come from (MG2/ICE). Else you would have a very inconsistent behaviour of the accelerator pedal...

    As an example, when I start my commute each morning, in the cold, while keeping the pedal at the same exact spot:
    1. power will first come from the battery/MG2 (stage 1a), with the ICE at low idle RPM;
    2. then power will come both from the ICE (then revving up with stage 1b) and the battery.
    Hence, acceleration stays exactly the same, even if ICE power output as changed drastically.
     
    #18 Philosophe, Mar 26, 2010
  19. Blind Guy

    Blind Guy New Member

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    By the same token, is it not logical to assume that since the only way for electric motors to produce more horsepower is to receive more voltage, and since switching to PWR mode instantly increases electric motor output, it seems logical to assume it has received more voltage.

    David (aka Blind Guy)
     
    #19 Blind Guy, Mar 26, 2010
  20. qbee42

    qbee42 My other car is a boat

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    Generally modern motor controllers don't increase voltage for more power. Motor controllers don't work like the old rheostat systems. These are modern polyphase inverter systems that vary frequency and pulse width to control speed and torque. Since the rail voltage is generated through an inverter, it is also possible that this could vary with power demand, much like how a class G amplifier works, but I don't know the details with the Prius.

    Tom
     
    #20 qbee42, Mar 26, 2010
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