Quote:
Originally Posted by Sprintey
...Also I've noticed Tojo teaming Atkinson cycle motors with its hybrid drive - can anyone explain why these motors are a better choice?...
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The idea us using an "Atkinson" cycle motor is to gain more energy per amount of fuel burned compared to the typical 4 cycle/Otto cycle engine.
This is not the same thing as "make more power".
In the mid-late 1800s James Atkinson came up with a linked connection between what would ordinarily be called a connecting rod and crankshaft.
What this intermediate linking allowed to happen was for all 4 cycles on an internal combustion reciprocating engine to happen in 1 revolution of the crankshaft instead of 2. I have never analyzed one of these so I can not say where the inherent efficiencies are in doing this.
Now let's talk a little bit about what is being called an "Atkinson" cycle engine these days. Anyone dismantling one of Toyota's "Atkinson" cycle engines will be disappointed if they are expecting to see this linked arrangement. It is not there.
What will be found is an engine (I believe in Toyota's case) claimed to be Atkinson is an arrangement the intake valves are held open a significantly longer period of time than usual. This pushes some of the fresh intake charge back into the intake track, which does 2 things from a fuel efficiency standpoint.
1. There is a reduction of pumping losses; power lost to running the internal pump, which an IC engine is.
2. The intake charged push back into the intake track contains residual spent contaminants remaining from the previous combustion. A built in EGR which primarily helps with how fuel is burned in daily driving applications.
For a technical break down of EGR principles I would have to defer to Peter (yearby).
Both methods listed above, original Atkinson cycle and today's "Atkinson" cycle, result in an overall less powerful engine, yet produce more power for amount of fuel consumed.
Unless someone can point me in another direction, what today is called an "Atkinson" cycle engine if really a Miller cycle engine. I know some may have been taught or told contrary, but Ralph Miller patented 2 Miller cycle designs.
One of these principles is at the heart of what Toyota and the world journos call an Atkinson cycle.
The other reduces cylinder pumping losses by closing the intake valve way early prior to the piston reaching bottom dead center (BDC) during the intake cycle. The cylinder never fills up, so it is easier to compress during the compression cycle. It doesn't do anything with EGR.
Again resulting in less total power, yet more power per the amount of fuel consumed.