Heretical mode on third gen Prius, what do we know?

Discussion in 'Gen 3 Prius Technical Discussion' started by vahrn, Jan 21, 2010.

  1. usbseawolf2000

    usbseawolf2000 HSD PhD

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    1) eCVT (Power Split Device) is geared to split 72% of the torque to the wheels. It then goes through the final gear (3.4 if I recall). You can't change it but the ICE torque can change which depends on the load and RPM. We have indirect control with the foot with the amount of power request. HSD decides the optimum ICE torque and RPM based on the BSFC operating line.

    2010 Prius 2ZR-FXE engine efficiency map | PriusChat

    2) There is PID for requested ICE torque but I think it is read only. Even if we can adjust it, we may be messing up the efficiency. You'll need to calculate and adjust it hundreds of time a sec, something a computer was already programmed to do.

    In summary, from a driver's point of view, the only plausable way to control is with the right foot. It works simple enough.
     
  2. briank101

    briank101 Member

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    @usbseawolf2000 Has anyone quantified the if the power losses via the electrical path in heretical mode are equivalent to the power losses in the other direction - so for example is MG1 at -4kW have just as much electrical path losses as MG1 at +4kW (in heretical mode)? I understand keeping MG1 at 0kW almost eliminates the electrical path losses where the PSD power split (not torque split) is then ~100% mechanical path. But unless I'm going up a specific incline at specific speed, the car will try to keep accelerating (albeit gradually) to a very high speed if trying to maintain MG1 at 0kW. There is possibly some speed on the flat at 80 mph or so where MG1 can be kept at 0 kW and the car will no longer accelerate.

    PS: In the 40 to 65 mph range it's nice to have that MG1 = 0kW (+ or - a few kW) goal to aim for when trying to determine an efficient acceleration rate that has a high transmission efficiency. I just wish Toyota put in some kind of automatic clutch that would lock MG1 when certain criteria are met.
     
  3. usbseawolf2000

    usbseawolf2000 HSD PhD

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    I tried driving with the goal of MG1 power zero. The result does not increase MPG. Either ICE rpm was too high or vehicle speed was high, resulting in other losses.

    It is better to let MG1 do it's job, eCVT, by varying both electrical and mechanical paths.
     
  4. briank101

    briank101 Member

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    I suspect when accelerating faster with MG1 at say -20 kW is overall just about as efficient as accelerating slowly with MG1 at -10 kW, for example. Reason being, one accelerating with MG1 at -10 kW will take about twice as long to accelerate to their final speed, so the overall electrical energy loss comes out about the same, that is -20 kW for 5 sec, give the same energy loss as -10 kw for 10 sec. So another reason why accelerating faster to your desired speed doesn't significantly affect your mpg. Also with a cold engine, extra electrical heat losses in the inverter may be of benefit because it gets the engine coolant warmed up faster (if indeed inverter heat is transferred to engine coolant), and the engine warms to the more efficient operating range sooner, at least that's my unverified theory.
     
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