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Could a future version of HSD have a turbocharger?

Discussion in 'Gen 3 Prius Technical Discussion' started by vahrn, Sep 14, 2010.

  1. vahrn

    vahrn New Member

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    I live in a pretty flat area, the largest flat area here in Italy, so I have never had the occasion to try the Prius on some hills... until today. The car of course performed ok, but I could't help not noticing that the ICE has to spin really fast to generate the required torque to overcome uphills.

    So I was wondering, would the Prius be more efficient with a turbocharger?

    Electric motors of course do have lots of torque but only near 0 RPM, this means that they can help you to start from a standstill but as the motor RPM increases generated torque decreases rapidly: at max RPM the generated torque is really low since the max RPM is 12000. So to overcome uphills the HSD has to wait for the ICE to reach it's peak torque point which is 5000 RPM if I am not mistaken. With a turbocharger we could lower that max torque point at something like 2500 RPM and keep it flat up to 5000 RPM. We could also use a smaller engine as the turbocharger also boost horsepower.

    What remains to be ascertained is the impact of the turbocharger on fuel efficiency... and what about using an electric turbine? I'd like to hear your opinions.
     
  2. Skoorbmax

    Skoorbmax Senior Member

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    Aren't turbos better at delivering high-end torque, though? Low-end for this car is delivered via the electric motor, which is ideally suited for low-end. So, a stronger electric motor may be better if you need more low-end torque.
     
  3. GrumpyCabbie

    GrumpyCabbie Senior Member

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    Turbos go pop and are expensive to replace.

    The Prius is great as it is - over ten years and high reliability. If it ain't broke, don't fix it.

    :)
     
  4. qbee42

    qbee42 My other car is a boat

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    The main motor on the Prius, MG2, still has plenty of torque even at cruising speed. It provides a significant boost when passing or hill climbing. Any lag in bringing the ICE up to speed would not be improved by turbocharging. While more torque could be generated at lower engine speeds, you also add turbine lag into the equation. It should be just about a wash. Add to this the fact that a Prius ICE never really goes very fast - 5,000 RPM is pretty tame by today's standards.

    The main advantage of using a turbocharger would be potentially using a smaller, lighter engine. In this case the ICE would be a Miller Cycle instead of the current Atkinson Cycle. Any gains would have to be weighed carefully against the added cost and complexity. So far Toyota has determined that the gains do not offset the liabilities.

    Tom
     
  5. vahrn

    vahrn New Member

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    This seems in favor of my theory...
     
  6. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    "What happens is that the hybrid control system acts in such a way that the peak combined power of the electric motor and the petrol engine is not substantially increased. In other words, total peak power is not much changed over the best it could previously ever be."

    I suspect the computers are shunting his 'extra' HP into charging the HV battery.
     
  7. bwilson4web

    bwilson4web BMW i3 and Model 3

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    This experiment was tried in Australia:
    Turboing-a-Hybrid-Prius

    However, I would like to try and explain the 'WHY' of the results:
    Our 1.8L engine has an electronic redline of 5,200 rpm. More power could be generated but it would be limited by the transmission.

    Unlike an ordinary transmission, ~28% of the engine power flows via an electrical path using MG1 and MG2. It is the electrical limit of MG1/MG2 that prevents any additional engine power from reaching the wheels. However, there is surge energy available in the traction battery.

    Under high power conditions, the traction battery can make up the deficit to the limits of the traction battery capacity, 27 kW. But once that energy draw occurs, there is no further power available for the wheels. In summary, the 28% power by-pass of MG1-MG2 and the 27 kW traction battery limits set how much power can be drawn.

    Now Julian noticed (read the whole series) that he was able to climb hills not faster but with more traction battery power at the top. What is likely to have happened is the higher power from the turbo-boosted engine simply displaced the energy that would have come from the traction battery BUT no more power to the wheels. The total amount of power to the wheels remained the same.

    GOOD LUCK!
    Bob Wilson

    ps. If you could somehow power the rear wheels from another source, you could climb the hills even faster. In the real world, I always recommend going up the hills at a peak efficiency power setting and making up the speed on the downgrade. My measurements suggest ~4,200 rpm is the highest, power rpm because the EGR is at maximum.
     
  8. donee

    donee New Member

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    Hi all,

    Tubos can help in high mountains. Bob is right too. The power is limited due to the electric path. At high altitude however, volumetric efficiency refereced to sea level, is very poor. A turbo helps this allot. No more power, just the same power at all roadable altitudes.

    I am not sure about Italy, but I am not so sure the Alps are that high. The Rockies definately are - from somebody who cruised up the continental divide in at 25 mph in a normally asperated gasoline engine lightly loaded rental truck with the pedal to the metal being dusted by fully loaded 18 wheeler turbo diesel trucks.