How much power is used to spin ICE at 42 mph plus?

Discussion in 'Gen 2 Prius Technical Discussion' started by Lain, Mar 27, 2021.

  1. Lain

    Lain Junior Member

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    Please disregard this page. Sorry for the two-part comment! I'm inept at posting.
     
    #21 Lain, May 12, 2021
    Last edited: May 12, 2021
  2. fuzzy1

    fuzzy1 Senior Member

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    Chapman can answer this much better than I. But from both ancient and very recent posting to other threads here, the answer seems to be "yes".

    Though this is a secondary reason for EGR. The primary reason is to reduce NOx pollution.
     
  3. ChapmanF

    ChapmanF Senior Member

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    I guess the question here might have been "specifically during EV operation at 42+MPH, when the engine is being turned without fuel in order to manage MG1 rpm, is the ECM doing anything clever with the EGR valve to reduce manifold vacuum and pumping loss?"

    My answer is I'm sure I don't know. The answer wouldn't come from the usual theory on how EGR is used in an operating engine; it will just boil down to whether the Toyota engineers thought of doing that, and whether that ends up being a better way to reduce manifold vacuum in those conditions. I'm not sure it would be; I mean, in those conditions, just opening the throttle valve wider would let them lower the manifold vacuum as much as they'd want.

    I guess they might have to weigh that against how much heat they lose from the engine that way, and the need to warm it up again next time fueled operation is needed.
     
  4. fuzzy1

    fuzzy1 Senior Member

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    When read that way, I must also say that I don't know or even have a clue. Between not rechecking the thread, and also in seeing the phrase "inert gas", my quick answer assumed normal operation, not fuel cut-off mode.
     
  5. Lain

    Lain Junior Member

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    My apologies! (I hijacked my own topic.) Yes, I meant to ask about the function of high-volume cooled EGR under normal operation.
    In any case, it would be interesting to compare Gen 3&4 manifold pressure and EGR valve-position data with throttle angle, and other engine operating values under normal operation.
    Thanks again!
     
  6. pasadena_commut

    pasadena_commut Active Member

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    This brings back memories of Thermodynamics class. If the compression and expansion are adiabatic that description is correct, neglecting friction in the mechanism. (Physicists "always" neglect friction when describing mechanical systems, and cows are spherical!) Adiabatic is just a fancy word meaning heat does not move in or out of the system. It does not apply exactly to a car engine, which is metal and has coolant circulating in it. However, if the engine is spinning at a normal rate that part of the cycle is a very close approximation to adiabatic because there is not enough time for the system to move very far towards thermal equilibrium at any time point.

    The compression and expansion (power with no fuel) phases cover half of the four in the engine cycle. The intake phase accounts for most of the drag in engine braking in normal cars as the piston sucks air through the resistance in the intake. In theory the exhaust phase could also be used for braking if the car had a way to increase the flow resistance in the exhaust. Any blockage in the exhaust path which resulted in compression (and heating) with the hot air still eventually exiting through the exhaust would brake. For instance, the exhaust valves might be adjusted to only open slightly. That would compress the air, but by allowing it to leak out, the energy would be lost from the engine through the exhaust. However, I am not aware of any vehicle that actually modulates the exhaust pathway to provide braking. It would probably be pretty easy to vent a turbocharger output to the atmosphere instead of feeding it back into the intake, which would provide some braking, but perhaps not enough to be worth the bother.
     
  7. mr_guy_mann

    mr_guy_mann Active Member

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    What you describe actually sounds like two different engine braking systems used in heavy diesel trucks. One is the exhaust brake- a butterfly valve in the exhaust manifold (or vanes of a VGT turbo) that closes so that the engine (compression and exhaust stroke) has to push air against the back pressure. The second is the "Jake brake". Here a special part of the valve train is activated on deceleration- opening the exhaust valve just at/after the peak of the compression stroke.
     
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