Does anyone know if the upcoming 3.3L V6 used in the Highlander Hybrid/RX 400H will be an Atkinson cycle version or the same as is in the non-hybrid versions? Jay
Probably on the Atkinson cycle, given that, according to the Toyota Web site, the Hylander will be able to run on 87 octane gasoline, whereas the existing V6-equipped models require premium.
It would make no sense for them not to use the Miller Cycle engine like they have in the Prius. The extra expansion in the power stroke is the main contributor to lower emissions and higher mileage. Although Toyota advertises the Pruis as using the Atkinson Cycle, it is technically a Miller Cycle Engine. The Atkinson Cycle uses a compound crankshaft which mades the power stroke longer than the intake stroke. While elegant in it's design, it is not as durable as the conventional internal combustion engine (Otto Cycle). The Miller Cycle delays the closing of the intake valve, which reduces the volume of the air being compressed. This allows the engine to have different compression and expansion displacements, but with a simpler crankshaft.
Could you explain why you think it would "make no sense to use the Miller cycle engine"? It seems to make perfect sense if a key goal is to reduce emissions. If they can obtain high MPG, lower emissions, and still maintain good power and acceleration it seems to make perfect sense to use the Miller cycle. BTW, thanks for the explaination of the difference b/w Miller & Adkins cycle.
One word makes a big difference, huh? I think vapor_pearl said it would make no sense NOT to use the Miller Cycle. In other words, they should use it!
Thank you delrey (one point for you for the assist), and sorry efusco for the double negative, I should have said that it makes all the sense in the world to use the Miller Cycle. Keep in mind that the only reason the Miller Cycle is practical, is because it is coupled with a high torque electric motor. Miller Cycle Engines have poor low end torque, which is why they are not practical for conventional cars.
Toyota is probably not far from the mark on this. Miller's contribution was a simple and elegant modification to the Otto engine design to achive the Atkinson cycle. While a true Atkinson engine uses a mechanically complex system to get two different stroke lengths, Miller effectively shortened the compression stroke by simply keeping the intake valves open during the first part of the compression stroke. (On the Prius, with variable timing, the intake valves appear to be open during the first 1/3 to 1/2 of the compression stroke.)
I was under the impression that the difference between the Atkinson and the Miller cycle was that Miller also introduced forced induction (via supercharging) to offset the low end torque losses seen with the modified stroke. Because the Prius doesn't utilize forced induction, they still refer to it as the Atkinson cycle.
I think that htmlspinnr is absolutely right (one point for you). I knew this site was a plethora of information and knowledge. After some online research it appears that forced induction is a key part of the Miller Cycle. And in order for it to work at low RPMs, it has to be through a supercharger and not a turbocharger. While I stand corrected and acknowledge that the cycle used in the Prius should be credited to Atkinson, lets be thankful that Toyota decided not to use his compound crankshaft.
