Atkinson vs. Otto Cycle

This sounds like a good idea for when electric valves become reality. But with Toyota's mechanical variable intake valve, aren't they already applying the full practical range of their system?

 

You must mean significantly steeper than the maximum legal slope of Interstate Highways, 7%.

Being accustomed to 1980's era four-bangers, one of which did struggle, I'm quite happy with the power of a Prius.

 

Oh I didn't mean slopes on highways, I meant climbing (literally) hills, as in scenic provincial, federal parks like the Rockies. I just went to a provincial park here in Ontario in the last 2 weeks to enjoy the fall colours and I encountered a LOT of really STEEP and long hill climbs. Those hills made me felt I was on a roller coaster. When I was climbing the hill I could only see the sky and at the summit of the hill I felt like the car was going air-born and going to plunge down a cliff. It was THAT scary STEEP.

 

If the SAAB example can tilt the whole cylinder to alter the compression ratio, it's hard to believe Toyota can't figure out a way to make a bigger range of opening/closing timing for the intake valve?

 

I think I'll just stick with mild hills that the Prius handles fairly well, such the high parks, 12000 foot passes, and 14000 foot summit climbs of the Colorado Rockies.

 

1st A. There are Prius Valve Timing Diagrams showing that this is done! but a few more ccs of displacement should help as in the Prius 2010 model.

2nd A. The Ford EcoBoost 3.5L V6 does this and adds Twin Turbos to bring the torque of an Atkinsonized VVT direct injected engine power back up to 350HP.... yikes V8 territory.
The 'new'2.0L I4 version should bring the power level into the range to replace the 2.5L N/A Atkinsonized engine used in the Fusion Hybrid and may be deployed in the new Focus C Platform, who knows? certainly not me.

 

Toyota has variable valve timing on the Prius now. If you close the intake valve at Bottom Dead Center without some means of altering the 13 to 1 compression ratio, even premium gas will not have enough Octane to prevent detonation. As you use Otto cycle valve timing, you need Otto cycle compression ratios. The Saab system is not the only way, but it is a good way.

 

Sorry to resurrect an old thread, but I have a question that has been brought up recently regarding valve timing. We understand that the intake closes after the piston leaves BDC, reducing the compression stroke, but the question we have is, once the engine is running at cruising RPMS, does the valve close earlier, increasing compression now that it is running? How does it prevent blowback if the piston starts to force the air/fuel mixture back out of the intake valve, and doesn't it create a pulse in the intake then?

 

It doesn't prevent blowback through the intake valve. This blowback is its standard operating mode. It allows the engine to operate with much less intake manifold vacuum, thereby reducing the power wasted as 'pumping loss'.

 

Interesting, thats what we thought, but wasnt sure. I guess with electronic injection, it would be less likely to cause a saturation issue with too much fuel in the intake. I can see it being even more efficient if it were direct injection, but the blow back would cause gumming issues on the back of the valves even more so than they do on Otto cycle GDI. I can't see how it would work at all with a Carb.

 

One PC discussion was an individual trying to fix his Gen1 Prius. The root cause of his problem was gunk building up in the intake manifold. When he cleaned the intake manifold tubes out the problem was resolved. This was likely caused by the "blowback" that you are discussing.

JeffD

 

Curious, is this also why the idle RPM is around 1500 and not the usual 700-800?

 

Why would they need a larger range for valve actuation?

 

For much of the engine warmup cycle, my nonhybrids also idled somewhere in the 1500 RPM range, while this Prius idles right at 1280.

Once everything is warm, my nonhybrids did drop to 700-800, but this Prius drops to 0.

 

Maybe a bit off topic - but can you clarify what you mean? 91 premium will still cause detonation I'm looking into swapping my Cams and Cam Gear with the 1NZ-FE but keeping the Prius pistons. Can't find anyone in the US that has done a 'Prius Piston Swap' on the 1NZ-FE but it has been done over at YarisWorld.com - there are those in Indonesia have done this swap successfully. Not only do you get a HP boost from the Otto Cycle 15-20HP but the additional boost from the higher compression Prius Pistons.

 

Wish i had my Prius still - someone finally did the cam swap. Wish there was a way to merge these threads...

1nz-fe Cam Swap | PriusChat

 

Sick, just sick! I would love to know things like acceleration, HP and gas mileage..... Another Priuschat person proving to the world.........it can be done!