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Hybrid Vehicles Toyota Prius What to expect from the next model year Prius
311 messages, Last post on Apr 26, 2009 at 5:43 AM
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Replying to: wwest (Oct 16, 2007 10:54 am) Turbos are driven by exhaust pressure, not temperature. Keep in mind that a supercharger is mechanically driven and requires energy to run - it boosts power at the cost of economy. To make the net use of SC workable, the engine would have to be smaller or use less fuel.
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Replying to: stevedebi (Oct 16, 2007 12:12 pm) And just what do you think causes all that exhaust (gas) pressure, if not the HEAT of combustion? The Atkinson Cycle allows more EXPANSION, less pressure into the exhaust manifold, of the ignited A/F mixture during the power stroke relative to normal "Otto" engines. "It boosts power at the cost of economy." SURE DOES...!! And that's exactly the point...!! Anytime, ANYTIME, you put that "pedal to the metal" you are asking for POWER in leu of FE. The idea of an SC or TC is to make a small engine act like a BIGGER one when the driver calls for POWER. The Atkinson Cycle makes efficient use of the WASTE energy that might otherwise be used to drive a Turbocharger. An SC configuration as I have suggested would not be a parasitic load on the ICE unless an extraordinary level of POWER was asked for.
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Replying to: wwest (Oct 16, 2007 10:54 am) turbo which would have fit right in the air intake tube on my 2004. It would have given a good pressure boost but was designed for only 30 second operating cycles. The seller (ETurbo) said it would burn up if used for more than a minute at a time. I only needed it on long, straight, steep interstate mountain passes like just west of Denver. Those take 5-10 minutes to climb. Everything else works fine (short, curvy, not too steep). |
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Replying to: wwest (Oct 16, 2007 1:08 pm) Your original statement was about there being insufficient heat from an Atkinson cycle to run a turbo. I gather from your response that you meant that there was insufficient pressure to run the turbo. I can't quite tell if you agree with me vis-a-vis superchargers, but the point is that if you put in a smaller engine to maintain the MPG you don't gain a lot of power. Plus it adds weight and complexity to the engine. Note also that you can't "turn on" the power of a SC when desired; it is always on, boosting power and reducing MPG. Toyota isn't interested in maxing out the performance of the Prius; it is strictly designed for maximizing fuel economy.
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Replying to: stevedebi (Oct 17, 2007 1:02 pm) A slightly smaller, more efficient engine would be fine 95% of the time and on the rare occasions when I do need the boost, it would be there. I think my normal 45-48mpg would go up to over 50mpg except for 5% of the time when the "turbo" was on.
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Replying to: stevedebi (Oct 17, 2007 1:02 pm) If you could make the combustion process fully efficient the exhaust gasses would exit the cyclinder at the exact same temperature at which they initially entered the cyclinder. The Atkinson Cycle gets more efficiency from the fuel BURN by extracting more of the HEAT and converting it to mechanical motion. Less HEAT/(pressure) at BDC equals less pressure into the exhaust manifold once the exhaust valve opens. The SC technique I described allows for continuously variable boost pressure from zero to the maximum allowed by the mechanical limits of the engine and thereby NO LOAD on the ICE until boost is required/called for.
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Replying to: stevegold (Oct 17, 2007 1:45 pm) I was speaking of supercharging, not Turbocharging. |
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Replying to: wwest (Oct 17, 2007 2:23 pm) Don't try and put that statement to an automotive engineer, or a physics professor. I don't understand what kind of "technique" you are describing. Superchargers use the engine power to mechanically enhance the airflow into the engine - the same principle as the turbo charger, except the turbo is driven by exhaust gas, and therefore increases as the engine RPM increases, whereas a supercharger provides constant power - but the energy to power the supercharger has to come from somewhere, and the equipment adds weight to the engine.
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Replying to: stevedebi (Oct 17, 2007 4:45 pm) This is the electric turbo that I thought would work well in the 2004 Prius. It runs at high speed off the 12VDC battery but only when you floor the accelerator. |
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Replying to: stevegold (Oct 17, 2007 6:30 pm) Thanks for the link, interesting stuff. A couple of notes: 1. It is electrically driven, so it would impact the HSD, and the effect would be worse when the vehicle was accelerating - the traction battery would have to run the supercharger AND the electric drive motors. This would deplete the battery faster. 2. ONE PSI boost? 3. I'm not sure if adding boost to an Atkinson cycle engine would increase power. On an Otto cycle engine it works, but the Atkinson cycle is deliberately intended to work with less pressure. I don't know enough to have a definite opinion, just a question.
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