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Atkinson cycle..... - READ ONLY

7 messages,  Last post on Oct 29, 2003 at 6:56 PM

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What is this discussion about? Lexus RX 330, Toyota Highlander, Toyota Sienna, Engine

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#1 of 7 Atkinson cycle..... by wwest Oct 29, 2003 (8:34 am)
I recently read that the way the Prius ICE gets such good, excellent, fuel economy is by derating the engine using the Atkinson Cycle. Apparently this very same engine in normal mode delivers as much as 40 to 50 addition HP.   The Atkinson cycle is the method Mazda uses in the Millenia S but along with a super-charger to maintain a decent power output along with good fuel economy.   The basic idea is to shorten the intake cylinder "volume" while maintaining a higher volume power stroke. The original design concept used a rube goldberg arrangement wherein the piston actually traveled a different, shorter, distance in the intake stroke vs the power stroke.   Mazda, in the Millenia S, and Toyota in the Prius, accomplish virtually the same ends by leaving the intake valve open during a portion of the compression stroke.   So, the question.   Assuming I'm willing to sacrifice say, 30% of the HP and Torque, can I simply retime the intake cam on my RX300, leaving the intake valves open during a portion of the compression cycle, to achieve the same ends?   Would I actually need to mill the heads to achieve the Prius 14:1 compression ratio?   I wouldn't get to the overall efficiency level of the Highlander 4 cylinder due to the frictional lose of the six, but would it result in a substantial improvement in fuel mileage.   Acknowledging that I could no longer accelerate from 0-60 in xx seconds, a statistic that's never impressed me anyway.
#2 of 7 perhaps, assuming input and output cams are on separate shafts by swschrad Oct 29, 2003 (11:27 am)
otherwise, if your camshafts are ground like everything I've ever had, everything on the same shaft, you are Stuck Outta Luck on that idea. it would take a modified camshaft at, as they say, substantial extra expense.
#3 of 7 Vvt-i by wwest Oct 29, 2003 (11:32 am)
Or whatever they, Toyota/Lexus, call it, requires separate intake and exhaust camshafts.
#4 of 7 Miller Cycle by kmeadv2 Oct 29, 2003 (2:47 pm)
I believe the Mazda used the Miller cycle which is a 5 stroke system versus standard 4 stroke.   The Prius ICE is a 4 stroke, it has been derated to optimise economy and torque. In standard form an engine of this type would likely put out 100 or so HP, which would occur at high rpm.   I have never heard of the Atkinson cycle. References please?
#5 of 7 Atkinson cycle.... by wwest Oct 29, 2003 (3:28 pm)
Me neither, found it referenced several places on the internet after reading Toyota stuff that the Prius used it.   5 strokes, how did that compute?   I think....   The atkinson cycle actually uses different piston stroke travel for intake/compression vs power/exhaust, whereas the Miller cycle (Mazda) uses delayed intake valve closing to virtualize the shorter intake/compression stroke.
#6 of 7 The Miller Cycle ICE by kmead Oct 29, 2003 (4:31 pm)
A brief description of the Miller Cycle ICE   http://auto.howstuffworks.com/question132.htm   A more complete description:   http://www.rx7uknet.dircon.co.uk/binhist/miller.html   Way too much info:   http://www.google.com/search?q=miller+cycle+&ie=UTF-8&oe=- UTF-8   I think I am mistaken in stating its a 5 stroke, I recall one description calling the extended compression process as a additional stroke, but cannot lay my hands on it.   I did find a reference to the Atkinson Cycle, which looks more like a theoretical possibility that also adjusts the compression ratio. So far it looks a bit like a great way to lose money:   http://www.mce-5.com/old_site/inside.htm
#7 of 7 Difference is.... by wwest Oct 29, 2003 (6:56 pm)
The miller cycle uses a supercharger and the atkinson does not?

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